Power Transmission Reference Guide February 2017

designworldonline.com

motioncontroltips.com

February 2017

Power Transmission REFERENCE GUIDE

pt guide 2-17 final cover.indd 1

2/24/17 10:53 AM

PURCHASE

PRODUCTS

ONLINE

www.thkstore.com Large Inventory

Easy Access

Major Credit Cards Accepted

Grease MSDS

2D/3D CAD & Product Configurator

Available for USA/Canada/ Mexico Customers

Collect Shipping Available

Quotation File

Clear lead times and prices are listed in the store (no RFQ required)

Contributes to quick delivery

Grease MSDS (Material Safety Data Sheets) can be downloaded

Visa, Mastercard, and American Express

We ship to the USA (mainland), Canada, and Mexico

2D/3D models and product configurator available for download in most file formats

Cart contents can be downloaded as quotation

Shipping via customer’s carrier account

Contact Us • If you have any questions, please contact TOSsales@thk.com.

• In addition to items in the store, we accept CUSTOM ORDERS.

Technical Support Available • technicalsupport@thk.com • https://tech.thk.com/

THK America, Inc. 200 E. Commerce Dr. Schaumburg, IL 60173

THK PTGuide 2-17.indd 1

2/9/17 1:54 PM

Your Custom Gearbox Solutions are CGI Standard Products.

Advanced Products for Robotics and Automation CGI Motion standard products are designed with customization in mind. We understand most off-the-shelf products or a complete in-house design may not fit your application, so our standard products are designed for functional flexibility. Our team of experts will work with you on selecting the optimal base product and craft a unique solution to help differentiate your product or application. So when you think customization, think standard CGI gearbox assemblies. Connect with us today to explore what CGI Motion can do for you.

copyrightŠ2015 cgi inc. all rights reserved. 0804stdp

CGI 1-17.indd 1

800.568.GEAR (4327) • www.cgimotion.com

2/10/17 9:06 AM

LISA EITEL SENIOR EDITOR @DW_LISAEITEL

updated information on evolving power-transmission designs POWER-TRANSMISSION COMPONENTS are core to the operation of innumerable motion designs wherever electric motors engage loads to execute machine tasks. That’s thanks to their enduring performance and cost effectiveness. But as detailed in the updated sections of this 2017 Power Transmission Reference Guide, applications for power-transmission designs continue to proliferate with technical innovations based on new geometries, materials, and kinematics.

Advances in electronics for motion control have made leveraging these mechanical devices easier than ever — yielding levels of precision output once impossible.

In fact, today’s motion designs use an increasingly diverse array of actuators, bearings, brakes, collars, couplings, gearing, and rotary-to-linear devices with ever-increasing performance. Longtime readers of this Power Transmission Reference Guide will notice that we’ve begun to address frequently asked questions related to these specific technologies.

What if a nanopositioning application needs higher forces from its actuator? How is ballscrew accuracy defined? What’s the difference between traditional chain drives and rigid-chain actuators?

How to specify retaining rings? How do you specify industrial shock absorbers? Where do electromechanical actuators make more sense than those based on fluid power?

That’s just a sampling of new territory we’ve begun to cover.

So please use this Reference Guide as a primer on component functions or as a basis for smart application of evolving motion engineering.

In addition, as the world of power-transmission design evolves, count on us on Design World for technology updates that help make specification and integration of components more informed.

2

Editorial — PT Ref Guide 02.17 V2.LE.indd 2

DESIGN WORLD — MOTION

Give us feedback or make requests for future editorial by emailing or tweeting to me at leitel@wtwhmedia.com and @ DW_LisaEitel, @Linear_Motion and @Motion_Control.

Connect with the Design World Facebook page at facebook. com/DesignWorldNetwork, and let us know about your design challenges and successes.

One last note: This Reference Guide is part of a four-installment series that Design World publishes. April brings the Motion Trends issue; August brings the 2017 Motion Systems Handbook; and November brings the beautifully illustrated Motion Casebook.

These issues will detail the latest in electronic and programming technologies for motion controls, and they will showcase applications stories on how some OEM and plant engineers are tackling modern motiondesign challenges.

Also get breaking motionindustry announcements (not to mention the newest technical features) on our motion tips sites— motioncontroltips.com, linearmotiontips.com, bearingtips.com, couplingtips.com, and robotictips.com.

Thank you for reading.

2 • 2017

2/8/17 4:30 PM

Affordable Power Transmission

high-quality components at low prices!

NEW Wider Range of Sizes

Synchronous Drives AutomationDirect’s line of synchronous drive components provides the same positive timing action of gears or chains, but with the flexibility and quiet operation of belts.

• Timing pulleys (sprockets) in both aluminum and steel are available in plain bore or tapered bushing mounting styles in L, XL and NEW MXL sizes.

• Timing (toothed) belt options include several popular pitches and widths and are available in fiberglass reinforced neoprene, or polyester reinforced polyurethane (in limited sizes).

• Tapered bushings in both QD® and Taper-lock styles are available in most popular shaft sizes for mounting a variety of pulleys or sprockets to shafts.

Get dependable power transmission at low, low prices with SureMotion® synchronous drives!

Drive Pulleys starting at:

$5.25

Belt and Pulley Selector Tool: http://go2adc.com/beltandpulley

Drive Belts starting at:

$2.00

Worm Gearboxes

Precision Gearboxes

IronHorse® worm gearboxes are available in both aluminum and cast iron with a variety of frame sizes and ratios. Dual shaft, right hand shaft, and hollow shaft options are offered and come with a one year warranty.

The SureGear® PGCN, PGA and PGB series of high-precision servo gear reducers are excellent choices for applications that require accuracy and reliability at an exceptional value.

•

SureGear small NEMA motor gearboxes start at $209.00

•

Aluminum gearboxes start at $88.00

•

SureGear servomotor gearboxes start at $398.00

•

Cast Iron gearboxes start at $147.00

Research, price, buy at: www.automationdirect.com/power-transmission

Order Today, Ships Today! * See our Web site for details and restrictions. © Copyright 2016 AutomationDirect, Cumming, GA USA. All rights reserved.

Automation Direct PTGuide 2-17.indd 3

1-800-633-0405

the #1 value in automation

2/9/17 1:55 PM

M O T I O N C O N T R O LT I P S. C O M

POWER TRANSMISSION REFERENCE GUIDE EDITORIAL

DESIGN & PRODUCTION SERVICES

Editorial Director Paul J. Heney pheney@wtwhmedia.com @dw_Editor

VP Creative Services Mark Rook mrook@wtwhmedia.com @wtwh_graphics

Managing Editor Leslie Langnau llangnau@wtwhmedia.com @dw_3Dprinting

Art Director Matthew Claney mclaney@wtwhmedia.com

Executive Editor Leland Teschler lteschler@wtwhmedia.com @dw_LeeTeschler

Graphic Designer Allison Washko awashko@wtwhmedia.com

Senior Editor Miles Budimir mbudimir@wtwhmedia.com @dw_Motion Senior Editor Mary Gannon mgannon@wtwhmedia.com @dw_MaryGannon Senior Editor Lisa Eitel leitel@wtwhmedia.com @dw_LisaEitel Associate Editor Mike Santora msantora@wtwhmedia.com @dw_MikeSantora

@wtwh_designer

Traffic Manager Mary Heideloff mheideloff@wtwhmedia.com Production Associate Tracy Powers tpowers@wtwhmedia.com Director, Audience Development Bruce Sprague bsprague@wtwhmedia.com

Digital Media Manager Patrick Curran pcurran@wtwhmedia.com @wtwhseopatrick

Marketing Coordinator Lexi Korsok lkorsok@wtwhmedia.com @wtwh_Lexi

Senior Web Developer Patrick Amigo pamigo@wtwhmedia.com @amigo_patrick

Digital Marketing Specialist Josh Breuler jbreuler@wtwhmedia.com @wtwh_Joshb

Web Production Associate Skylar Aubuchon saubuchon@wtwhmedia.com @skylar_aubuchon

Marketing Associate Aly Ryan aryan@wtwhmedia.com @wtwh_Aly

Web Production & Reporting Associate Jennifer Calhoon jcalhoon@wtwhmedia.com @wtwh_Jennifer

Digital Marketing Director Virginia Goulding vgoulding@wtwhmedia.com @wtwh_virginia Manager Webinars Stacy Combest scombest@wtwhmedia.com @wtwh_Stacy

VIDEO SERVICES Videographer Manager John Hansel jhansel@wtwhmedia.com @wtwh_Jhansel Videographer Bradley Voyten bvoyten@wtwhmedia.com @bv10wtwh Videographer Derek Little dlittle@wtwhmedia.com

DIGITAL MEDIA/MARKETING Web Development Manager B. David Miyares dmiyares@wtwhmedia.com @wtwh_WebDave

Marketing Manager, Social Media & Events Jen Kolasky jkolasky@wtwhmedia.com @wtwh_Jen

FINANCE Controller Brian Korsberg bkorsberg@wtwhmedia.com Accounts Receivable Specialist Jamila Milton jmilton@wtwhmedia.com

WTWH Media, LLC 6555 Carnegie Ave., Suite 300 Cleveland, OH 44103 Ph: 888.543.2447 FAX: 888.543.2447

DESIGN WORLD does not pass judgment on subjects of controversy nor enter into dispute with or between any individuals or organizations. DESIGN WORLD is also an independent forum for the expression of opinions relevant to industry issues. Letters to the editor and by-lined articles express the views of the author and not necessarily of the publisher or the publication. Every effort is made to provide accurate information; however, publisher assumes no responsibility for accuracy of submitted advertising and editorial information.

Non-commissioned articles and news releases cannot be acknowledged. Unsolicited materials cannot be returned nor will this organization assume responsibility for their care.

DESIGN WORLD does not endorse any products, programs or services of advertisers or editorial contributors. Copyright© 2017 by WTWH Media, LLC. No part of this publication may be reproduced in any form or by any means, electronic or mechanical, or by recording, or by any information storage or retrieval system, without written permission from the publisher.

Subscription Rates: Free and controlled circulation to qualified subscribers. Non-qualified persons may subscribe at the following rates: U.S. and possessions: 1 year: $125; 2 years: $200; 3 years: $275; Canadian and foreign, 1 year: $195; only US funds are accepted. Single copies $15 each. Subscriptions are prepaid, and check or money orders only.

2014 Winner

2011 - 2016

Subscriber Services: To order a subscription or change your address, please email: designworld@halldata.com, or visit our web site at www.designworldonline.com POSTMASTER: Send address changes to: Design World, 6555 Carnegie Ave., Suite 300, Cleveland, OH 44103

4

PTGUIDE Staff Page.indd 4

DESIGN WORLD — MOTION

2 • 2017

motioncontroltips.com | designworldonline.com

2/24/17 11:16 AM

Your ball screw Your servomotor Our coupling

Together a winning combination for today’s servomotor applications.

Our ServoClass® couplings have been recently redesigned to enable your actuator to go even faster and achieve the positional accuracy that will take your designs to the next level. Our couplings will do all this with low bearing loads.

3 New sizes now available.

Now, size, select and see the right ServoClass® coupling solution for your application with Zero-Max 3D CAD files.

Check our FAST deliveries.

www.zero-max.com 800.533.1731

Zero-Max PTGuide 2-17.indd ServoClass Coupling5Design World Feb 2017.indd 1

2/9/17 11:54 1:57 PM 1/10/17 AM

MOTIONCONTROLTIPS.COM

INSIDE THE POWER TRANSMISSION REFERENCE GUIDE VOLUME 3 NUMBER 1

29

64

50

P2 P8 2017 PTDA Update

Updated information on evolving power-transmission designs

Actuators Electrical .....................................................10 Pneumatic ...................................................13 Rigid Chain .................................................15 Ballscrews .........................................................16 Bearings ............................................................19 Belts & Pulleys ..................................................23 Brakes & Clutches .............................................27 Couplings .........................................................29 Drives ................................................................35 Encoders ...........................................................37 Gearing .............................................................39 Gearmotors ......................................................47 Leadscrews........................................................48 Linear Guides Rails, Slides & Systems ..............50 Locking Devices & Shaft Collars .......................53 Motors ..............................................................56 Positioning Stages ............................................60 Rack & Pinion Sets ............................................62 Retaining Rings .................................................63 Shock, Vibration Damping ................................64 Wave Springs ....................................................69

Cover photography by Miles Budimir

6

DESIGN WORLD — MOTION

contents — PT Guide 2-17 v1.indd 6

2 • 2017

motioncontroltips.com | designworldonline.com

2/24/17 11:14 AM

Now available in Spanish and as the Power Transmission HandbookÂŽ ebook.

Visit ptda.org/Handbook for more information

PTDA UPDATED AD - PTGuide 2-17.indd 7

2/9/17 1:59 PM

2017 PTDA Update

EDITED BY MIKE SANTORA

NORTH AMERICAN POWER TRANSMISSION/ MOTION CONTROL MARKET RE-STATED

The PTDA Power Transmission & Motion Control Market Size Report recently re-stated that the North American power transmission and motion control market is estimated at $70.4 billion, including the U.S., Canadian and Mexican markets.

The PTDA Power Transmission & Motion Control Market Size Report recently re-stated that the North American power transmission and motion control market is estimated at $70.4 billion, including the U.S., Canadian and Mexican markets.

The report also updates a 2013 PTDA market size research study

to include a U.S. market size update for calendar year 2015 and restates the assumptions used to define the U.S. Distributor Available Market (DAM) size, which is lower than previously reported in 2013.

This report is an important tool to analyze markets for growth opportunities that are segmented by customer type and geographic territory in 14 product categories: • • • • • • • • • • • • • •

Accessories Adjustable/variable speed drives Bearings Belts & chain drives Clutches & brakes Controls Conveyors & material handling components Gearing Hydraulics & pneumatics Industrial specialty chemicals Linear motion products Motors Pumps Shaft couplings & u-joints

2017 LEADERSHIP DEVELOPMENT CONFERENCE Registration is now open for the 2017 Leadership Development Conference to be held on March 23-24, 2017, at the Hyatt Centric French Quarter New Orleans, New Orleans, La. PTDA members continuously seek ways to educate their future management teams so they can step into a 8

DESIGN WORLD — MOTION

PTDA Update — PT Ref Guide 02.17 V1.indd 8

2 • 2017

motioncontroltips.com | designworldonline.com

2/10/17 8:36 AM

PTDA UPDATE

Designed for emerging power transmission/motion control (PT/MC) industry leaders who want to enhance their management skills, network in small group settings and learn best practices that support business results.

supervisory role ready to excel. Designed for emerging power transmission/motion control (PT/MC) industry leaders who want to enhance their management skills, network in small group settings and learn best practices that support business results.

Features: • March 23 dinner along with industry leaders providing an opportunity for networking and shared experiences to build relationships • The day-long Leadership Development Conference on March 24 for emerging industry leaders with a program designed to teach collaboration techniques in a fun and interactive way by combining music with behavioral science The chair for the PTDA 2017 Leadership Development Conference task force, Chris Gumas, director of marketing, Ruland Manufacturing Co. said, “Collaboration is the ultimate disruptor. In an era of dynamic change and the push towards individualism, the most successful organizations value collaboration above all else.”

Registration is open to all employees of any PTDA member company and is limited to 42 participants.

The day-long Leadership Development Conference on March 24 for emerging industry leaders with a program designed to teach collaboration techniques in a fun and interactive way by combining music with behavioral science

motioncontroltips.com | designworldonline.com

PTDA Update — PT Ref Guide 02.17 V1.indd 9

MEMBERSHIP CRITERIA FOR A MORE INCLUSIVE PTDA Newly revised Distributor Membership criteria will now be more inclusive and ensure the Association is fully representative of distributors in the power transmission/motion control industry. Distributor member criteria now lets distributor companies join that may not have met the previous criteria because of their business model, the customers they serve or the products they distribute.

Criteria changes: • A distributor company must stock and distribute products from one or more of the following product categories: adjustable/variable speed drives, bearings, belt and chain drives, clutches and brakes, motor/motion control products, conveyors & material handling components, shaft couplings & u-joints, hydraulics & pneumatics, gearing, linear motion, industrial specialty chemicals, motors, and pumps. This replaces the previous language which stated “from some of the product categories” • A distributor company must be an authorized stocking distributor for at least one PTDA manufacturer member, versus the previous language which stated “two PTDA manufacturer members” In addition, air compressors have been added to the Pumps category and generators added to the Motors category.

“Power transmission/motion control distributors know the value of PTDA membership, but several were ineligible under the previous criteria. The vision of PTDA’s Board of Directors and Manufacturer Council just created new opportunities for all of us, while being faithful to our core purpose,” said PTDA President, Tom Clawser, director reliability services, Brown Transmission & Bearing Co., Delta Reliability Div. These changes are effective immediately.

“The vision of PTDA's Board of Directors and Manufacturer Council just created new opportunities for all of us, while being faithful to our core purpose,” said PTDA President, Tom Clawser, director reliability services, Brown Transmission & Bearing Co. Delta Reliability Div.

PTDA www.ptda.org 2 • 2017

DESIGN WORLD — MOTION

9

2/10/17 10:56 AM

Now there’s a second frame size of Exlar brand FTX Series actuators (using planetary roller screw technology) from the Curtiss-Wright Sensors & Controls Division. These rod-style actuators offer higher performance and ease of maintenance than previously available — suitable as an alternative to hydraulic cylinders in some cases. Continuous force to 10,000 lbf, speed to 46 in./sec, and strokes from 6 in. to 3 ft allow their use in myriad applications.

Electric Actuators SELECTING STANDARD & SPECIALTY OFFERINGS ELECTROMECHANICAL ACTUATORS are integrated units that deliver straight-stroke motion. Today’s actuators are so efficient that types for different design needs have proliferated, with designs that are easier and more cost-effective than ever to integrate into machinery.

Belt-drive actuators are cost-effective designs that move loads at high linear speeds. The motor is separate from the drive, so the mechanical advantage can increase thrust speed. Caveat: Belt drives wear over time and require maintenance. In contrast, screw drives (using roller, ball, or leadscrews) have longer life. The motor transmits power through a coupler or pulley arrangement to rotate the screw and translate a nut along the screw axis. Attached to this nut is either the rod or saddle of the actuator.

Taking ruggedness further are actuators based on linear motors. Motor power directly drives actuator motion. The rotor travels in a linear fashion along the stator.

There have been significant innovations over the last decade in electricactuator control systems. Faster bus systems such as industrial Ethernet and real-time communication make using electric actuators simpler than ever.

So stepper and servo drive options with Ethernet protocols (Ethernet IP, Modbus, TCP) are now turning single-axis actuators into simple, low-cost motion devices with infinite positioning, precise control. and longer life.

The most common solution for nanopositioning applications are piezo motors (also called piezo actuators) that use no mechanical bearings or transmission components. Piezo motors operate on the reverse piezoelectric effect that induces a mechanical stress on a piezo material when an electrical charge is applied. Piezo actuators leverage this effect to produce motion (expansion or contraction) and force.

But while their speed and force capabilities are relatively high for their small size, piezo actuators don’t fit all nanopositioning applications. In some cases, a linear-motor stage or voice-coil actuator is a better choice, depending on the performance criteria.

ELECTRIC-ACTUATOR VARIATIONS FOR NANOPOSITIONING

Linear motors are direct-drive noncontact devices that don’t suffer from the effects of friction, compliance, or backlash. This lets them produce nanometer-level motion. Linear motor

Nanopositioning — positioning on the scale of one-billionth of a meter — is a common requirement in semiconductor and medical applications, such as metrology, scanning, dispensing, and pumping. But consistently getting nanometer-level resolution is beyond the scope of most devices that use mechanical rolling or recirculating elements.

10

DESIGN WORLD — MOTION

Electric Actuators — PT Ref Guide 02.17 V4.indd 10

2 • 2017

WHEN NANOPOSITIONING NEEDS HIGHER FORCES

motioncontroltips.com | designworldonline.com

2/9/17 9:45 AM

Power Transmission and Motion Control Solutions for Industrial Applications

The Power Brands in Power Transmission Ameridrives Couplings

Guardian Couplings

Marland Clutch

TB Wood’s

Bauer Gear Motor

Huco

Matrix

Twiflex Limited

Bibby Turboflex

Industrial Clutch

Nuttall Gear

Warner Electric

Boston Gear

Inertia Dynamics

Stieber Clutch

Warner Linear

Delroyd Worm Gear

Kilian

Stromag

Wichita Clutch

Formsprag Clutch

Lamiflex Couplings

Svendborg Brakes

Altra PTGuide 2-17.indd 11

www.AltraMotion.com 2/10/17 1:51 PM

for higher forces. When used in nanopositioning applications, linear-motor stages are typically integrated with either air bearings or crossed roller slides for support and guidance.

However, air bearings have a significant benefit over mechanical bearing guideways in nanopositioning applications, in that they’re completely non-contact and virtually frictionless, whereas mechanical bearings suffer from wear and startup friction.

Linear-motor stages offer two primary benefits over piezo actuators — higher stroke and force capability. In general, piezo actuators are when the application calls for strokes of a few inches or less, for rapid, oscillating motion, or for high holding force when powered off. Linear motors, on the other hand, are typically used for strokes greater than a few inches and can be built in lengths up to several meters. This is beneficial, for example, in medical imaging equipment, where the overall stroke is quite long, but the positioning resolution required is in the nanometer range. Linear motors can also achieve high acceleration and simultaneously produce thrust forces in the thousands of Newtons. However, linear motor stages have a much larger footprint than piezo actuators, making them a challenge to integrate into small devices Voice-coil actuators are like piezo actuators in size and footprint, but their operating principle is more like that of linear motors, consisting of a coil and a permanent magnet field. When current is applied to the coil, the motor moves in one direction, generating a force that is proportional to the current. When the direction of the current is reversed, the actuator moves in the opposite direction.

Like linear motors, voice coils can be integrated with crossed roller slides or, more commonly, with air bearings for guidance and load support. Unlike ironcore linear motors, voicecoil actuators don’t suffer from the effects of cogging, giving them extremely smooth motion. Although they can achieve longer stokes than piezo actuators, voice-coil actuators are still somewhat limited in stroke length. Maximum stroke for a voicecoil actuator is typically 5 to 6 in. Longer strokes are possible, but efficiency decreases in proportion to the actuator’s length.

Voice-coil actuators (like piezo actuators) can be configured to provide either linear or rotary motion. In linear motion applications, they’re commonly used to supply force or pressure control, whereas in rotary applications they supply torque. Although voice coils supply high force (or torque) for

This Tolomatic RSA-HT rod-style actuator handles high duty-cycle needs in demanding applications. It can be a replacement for hydraulic designs. Force output is 4,038 to 12,900 lbf.

12

DESIGN WORLD — MOTION

Electric Actuators — PT Ref Guide 02.17 V4.LE.LL.indd 12

2 • 2017

their size, piezo actuators generally provide higher continuous, intermittent, and holding forces. Like piezo actuators, the low moving mass and inertia of voice coil actuators makes them suitable for high frequency, oscillating movements.

HOW TO SELECT AN ELECTRIC ACTUATOR FOR GENERAL-PURPOSE APPLICATIONS? Start with the motion profile. This establishes demands for velocity and time as well as force (or torque) and the required travel distance. This is also the place to determine the maximum stroke needed as well as maximum and minimum speed requirements.

Then calculate the load. This can have many different components including inertial load, friction load, the external applied load, as well as the gravitational load. Load calculations also depend on the orientation of the actuator itself, whether it’s horizontal or vertical.

Duty cycle (the ratio of operating time to resting time expressed as a percentage) is next.

The cycling rate may be in seconds, minutes, hours or even days, and knowing the operating hours per day may also be necessary. Knowing the duty cycle helps engineers estimate system-life requirements and can help them avoid problems such as overheating, wear and premature component failure due to incorrectly sized actuators.

Actuator specifications should meet or exceed application requirements for accuracy, backlash, and straightness and flatness of linear motion. This directly impacts system cost — so if the application doesn’t demand high accuracy or precision, don’t buy a more expensive actuator when a less expensive one will do.

Engineers must also pick the proper configuration for the actuator in the final design.

This includes mounting and other external components such as holding brakes and communication and power cables. Also consider the operating environment for the actuator.

What are the temperature requirements?

Will there be water, oil or abrasive chemicals present? Contaminants can affect seals and impact actuator working life, so pick actuators with sufficient IP ratings.

motioncontroltips.com | designworldonline.com

5/2/17 12:36 PM

PNEUMATIC ACTUATORS

Actuators:

PNEUMATICALLY OPERATED CYLINDERS

TO SOME PLANT ENGINEERS, compressed air is considered the fourth utility, after electricity, gas and water. Driving linearmotion applications with pneumatic actuators (or air cylinders) is a relatively easy and inexpensive approach. Today’s actuator technology includes better piston seals and rod wiper seals, which make pneumatic actuators more resilient and efficient than ever.

These seals reduce leakage and withstand extreme temperatures for use in more environments. Surfaces with permanent lubrication, servo-pneumatic controls, improved corrosion resistance and aircushioning features make pneumatic actuators more useful.

With pneumatics, pressurized gas—generally air that may be either of the dry or lubricated type—is used to actuate an end effector and do work. End effectors can range from the common cylinder to more application-specific devices such as grippers or air springs. Vacuum systems, also in the pneumatic realm, use vacuum generators and cups to handle delicate operations, such as lifting and moving large sheets of glass or delicate objects. Pneumatics is commonly used in medical, packaging, material handling, entertainment and robotics industries.

By its nature, air is easily compressible, and so pneumatic systems tend to absorb excessive shock. Most pneumatic systems operate at a pressure of about 100 psi, a small fraction of the 3,000 to 5,000 psi that some hydraulic systems see. As such, pneumatics are generally used when much smaller loads are involved.

An air compressor is used to reduce the volume of the air, increasing the pressure of the gas. The pressurized gas travels through pipe and pneumatic hoses and is controlled by valves on the way to the actuator. The air supply itself must be filtered and monitored constantly to keep the system operating efficiently and the various components working properly. This also helps to ensure long system life.

In recent years, the control available within pneumatic systems (thanks to advanced electronics and componentry) has increased a great deal. Where once pneumatic systems could not compete with

motioncontroltips.com | designworldonline.com

Pneumatic Actuators — PT Ref Guide 02.17 V3.indd 13

many comparable electronic automation systems, the technology today is seeing a renaissance of sorts.

PNEUMATIC ACTUATOR OPERATION One of the simplest and most cost effective ways to accomplish linear motion is with a pneumatic actuator, sometimes referred to as an air cylinder. An actuator is a device that translates a source of static power into useful output motion. It can also be used to apply a force.

Pneumatic actuators are mechanical devices that use compressed air acting on a piston inside a cylinder to move a load along a linear path. Because the operating fluid in a pneumatic actuator is simply air, “leakage” doesn’t drip and contaminate surrounding areas.

There are many styles of pneumatic actuators, including standard piston rod cylinders, rodless cylinders, telescopic cylinders, diaphragm cylinders and through-rod cylinders. The most popular style consists of a piston and rod moving inside a closed cylinder. This style can be sub-divided into two types based on the operating principle: single acting and double acting.

Single-acting cylinders use one air port to let compressed air enter the cylinder to move the piston to the desired position, as well as an internal spring to return the piston to the “home” position when the air pressure is removed.

Double-acting cylinders have an air port at each end and move the piston forward and back by alternating the port that receives the high pressure air. (Air on the opposite side of the piston is vented to atmosphere normally.)

2 • 2017

DESIGN WORLD — MOTION

13

2/10/17 1:53 PM

Closed Loop Drives and Motors for EtherCAT® Networks

StepSERVOTM Drives and Motors Greater torque, higher acceleration Better throughput in point-to-point motion Higher efficiency, quieter operation EtherCAT networking with CANopen CiA 402 operating modes

StepSERVOTM

Connected. Customized. Closed Loop.

StepSERVOTM technology from Applied Motion Products combines the high torque capabilities of step motors with the closed loop dynamic control of servo systems. The result is a motor and drive solution that operates more quietly and efficiently, while providing greater torque and higher acceleration rates than traditional step motor systems.

SS-EC StepSERVO Drives and Motors support CANopen over EtherCAT (CoE) control, allowing them to be integrated into new and existing EtherCAT networks. By combining the high-speed networking capabilities of EtherCAT with the motion control performance of StepSERVO, Applied Motion offers yet another feature-packed series of motors and drives designed to help you Make it Move.

In a typical application, the actuator body is connected to a support frame and the end of the rod is connected to a machine element to be moved. An on/off control valve directs compressed air into the extend port while opening the retract port to atmosphere. The difference in pressure on the two sides of the piston results in a force equal to the pressure differential multiplied by the surface area of the piston (less any friction in the actuator itself).

If the load connected to the rod is less than the resultant force, the piston and rod will extend and move the machine element. Reversing the valving and the compressed air flow will cause the assembly to retract back to the “home” position. Pneumatic actuators are at the working end of a fluid power system. Upstream of these units, which produce the visible work of moving a load, are compressors, filters, pressure regulators, lubricators, on/off control valves and flow controls. Connecting all of these components together is a network of piping or tubing (either rigid or flexible) and fittings.

Pressure and flow requirements of the actuators in a system must be taken into account when selecting these upstream system components to ensure desired performance.

Undersized upstream components can cause a pneumatic actuator to perform poorly, or even make it unable to move its load at all.

800-525-1609 www.Applied-Motion.com Email: sales@applied-motion.com EtherCAT® is a registered trademark and patented technology, licensed by Beckhoff Automation GmbH, Germany

14

Pneumatic Actuators — PT Ref Guide 02.17 V3.indd 14

DESIGN WORLD — MOTION

2 • 2017

2/9/17 10:30 AM

RIGID CHAIN ACTUATORS

WHAT’S THE DIFFERENCE BETWEEN TRADITIONAL

chain drives & rigid actuators?

RIGID-CHAIN ACTUATORS have the mechanical benefits of conventional chain but can act in horizontal push setups or vertically as jacks. Plus they’re compact.

In contrast, traditional chain can only pull, so needs two drives for bidirectional motion. Traditional screw jacks for vertical power transmission need space for retraction that’s as long as the working stroke itself.

In short, rigid-chain actuators pair an electric motor with chain having shoulders on each link. The motor output shaft applies tangential force to the chain. Then the chain comes out and straightens, and its links’ shoulders lock to form a rigid series. When the motor runs in the opposite direction, the chain shoulders disengage to allow for coiling.

Within the actuator body, reaction plates and guides counter thrust resistance and keep the chain

on track. Links travel around the pinion to exit the actuator body along the stroke path. Here, the motor’s torque comes to act as forward thrust via the link shoulder to the rest of the links’ shoulders. The last link in the chain before the load has geometry that puts the thrust higher than the articulation axis. This makes a moment that effectively locks the link shoulders. In reverse, pulling force acts along the links’ cross axes.

Before specifying a rigid-chain actuator, determine total application load, including transported load, acceleration forces, external environmental forces, and that due to friction (with a coefficient between 0.05 and 0.5 for typical rigid-chain actuator setups). Next, determine what type of actuator body and chainstorage magazine the application can accommodate. Determine whether the chain will need to change direction on its way from the magazine to actuator body. Actuators usually feed chain around 90° or 180° turns.

SOLUTIONS FOR PRECISION MOVEMENT OF VERY HEAVY LOADS

QUICK DIE CHANGEപͳപSTAGE AND ORCHESTRA LIFTSപͳപCUSTOM ENGINEERED SYSTEMSപͳപINDUSTRIAL LIFTS LinkLiŌ liŌ columns

RollBeam Telescopic push-pull

LinearBeam guided push-pull Press-mounted dual push-pulls

SERAPID Inc. | 34100 Mound Rd. | Sterling Heights, MI | Tel +1 586-274-0774 | info-us@serapid.com | www.serapid.com motioncontroltips.com | designworldonline.com

DW half page rv.indd 1 Rigid Chain Actuators — PT Ref Guide 02.17 V2.LE.indd 15

2 • 2017

DESIGN WORLD — MOTION

15

4/12/2016 2:17:33 PM 2/10/17 8:44 AM

This illustration of a ballscrew from Dynatect shows a cutaway view of the nut, showing the ball grooves and the balls that recirculate within the nut.

Ballscrews: THE BASICS

A TRIED AND TRUE METHOD of linear actuation is the ballscrew.

Compared to other actuation methods such as leadscrews, they typically cost a bit more but are generally more accurate. They also boast higher efficiencies, even though they demand more lubrication because of the use of recirculating balls.

The basic components of a ballscrew are a nut, a screw with helical grooves, and balls (often made from steel, ceramic, or hard plastic material) that roll between the nut, the screw and the grooves when either the screw or nut rotates. Balls are routed into a ball return system of the nut and travel in a continuous path to the ball nut’s opposite end. Seals are often used on either side of the nut to prevent debris from compromising smooth motion.

Ballscrews are typically classified according to factors such as lead accuracy, axial play and preload, and life/load relationship.

Lead accuracy refers to the degree to which the shaft’s rotational movements are translated into linear movement. (See sidebar.)

With lead accuracy and axial play determined by the manufacturing method of the ballscrew shaft and the assembly of the nut, high lead accuracy and zero axial play is usually associated with relatively higher-cost precision ground ballscrews, while lower lead accuracy and some axial play is associated with lower cost rolled ballscrews.

Another important ballscrew parameter is axial play. This is the degree to which a ball nut can be moved in the screw axis direction without any rotation of either nut or screw. Preload is typically applied to eliminate axial play, which also has the effect of removing backlash and increasing stiffness.

Ball recirculation inside the ball nut can affect precision and repeatability. Thus, ball nuts are available with a range of preload options to reduce or remove the axial play as they rotate around the screw. Minimal axial play allows better accuracy because no motion is lost from the clearance in the balls as they reengage.

Several techniques for preloading are common. Some of these methods include oversizing the balls inside the nut housing; using the so-called “double-nut” or “tension nut” method; or by using

16

DESIGN WORLD — MOTION

Ballscrews — PT Ref Guide 02.17 V1.indd 16

2 • 2017

a manufactured offset in the raceway spiral to change the angle of ball engagement (the “lead shift” method) and deliberately force the balls into a preload condition. Each method has its advantages and disadvantages, but all serve to minimize or eliminate backlash between the nut and screw.

Perhaps the biggest overall benefit of a ballscrew is the high efficiency that can be well over 90%. By contrast, Acme leadscrews average about 50% efficiency or less. There are also minimal thermal effects. Ballscrews also offer smooth movement over the full travel range. The higher cost of ballscrews can be offset by decreased power requirements for similar net performance.

One drawback to ballscrews is that they require high levels of lubrication. Ballscrews should always be properly lubricated, with the correct type of lubricant, to prevent corrosion, reduce friction, extend operating life, and ensure efficient operation.

Ballscrews are a bearing system, so they need some type of lubrication to avoid metalto-metal contact of the balls in the raceway.

While the lubrication choice can be either oil or grease, it’s advisable to avoid solid additives (such as graphite) as they will clog the recirculation system. An NLGI no. 2 type grease is recommended but it should also depend on the application, whether foodgrade or another special type of lubrication is

motioncontroltips.com | designworldonline.com

2/10/17 10:57 AM

HIGH SPEED, LOW NOISE AND ADVANCED PERFORMANCE. COMPACT FA SERIES BALL SCREW NSK’s Compact FA Series ball screw delivers smooth, quiet motion at exceptionally high speeds. This space-saving design can also be equipped with K1™ Lubrication Units to extend product life and provide a maintenance free solution. Standard sizes available within Quick Ship program for 4 week delivery. Choose to work with the best in innovation: NSK.

www.nskamericas.com

NSK Precision 1-17.indd 17

2/10/17 9:07 AM

PRECISION GROUND BALL SCREWS

 required. Ballscrews, especially those used in machine tools, generally require lubricants with EP additives to prevent excessive wear.

Lubrication amount will usually be fixed, but the frequency of lubrication will vary depending on factors such as the move cycle characteristics or the level of contamination in the environment. Contaminated lubrication can increase friction. In addition, ballscrews can fail if the balls travel over metal chips or dirt in the ball thread raceway. Using lubricants recommended by machine tool manufacturers can help prevent this effect. Using telescopic covers or bellows can help keep ballscrews clean when used in environments with many contaminants.

Manufactured based on your needs, not around predetermined catalog sizes.

• Quickly Engineered in Real-Time with Automated CAD Systems • Manufactured from Existing Part, Print, or Your Specifications • “Zero Lost Motion” Solutions to Eliminate Deadband and Minimize Backlash • High Precision up to ANSI Class 2 or DIN/JIS Class 1 Spec.

• Optimized Performance & Longer Life – Ball Screw Characteristics Based on ANSI & ISO Standard Calculations • Large Diameters up to 6” and Long Lengths (Longest to date: 54 feet) • Additional Capabilities: • Full Service Repair with Rebuild Options and Reverse-Engineering • Economical Whirled Ball Screws For Non-Precision Applications

How is ballscrew accuracy defined?

Accuracy is an important criteria in ballscrew selection. But with two production methods and four different standards governing ballscrew accuracy, making the best selection for an application can be challenging. Understanding these standards and terminology, as well as the differences between the two manufacturing methods, will help you choose a ballscrew that meets specifications, without paying for higher accuracy than the application requires.

There are four standards that specify ballscrew lead accuracy; JIS B1192, DIN 69051, ISO 3408, and ANSI-B5.48. The DIN and ISO standards are nearly identical and are sometimes referenced together (DIN 69051/ISO 3408 or simply DIN/ISO), while the ANSI standard is used less often than the others. Regardless of which standard(s) a ballscrew manufacturer follows, they’re all supported by the same underlying principle — how closely does the ballscrew reach the intended position? To answer this question, the standards define four criteria for specifying ballscrew accuracy: •

ep: Average lead deviation. The difference between the specified travel and the mean travel, where the mean travel is the best-fit line of the deviation curve over the useful length of the ballscrew.

•

νu: Maximum deviation range. The maximum range of travel deviations (peak-to-valley) over the useful length of the ballscrew. This is shown by two parallel lines which “enclose” the full lead deviation curve. (This specification is applicable only to positioning ballscrews.)

•

ν300: Maximum deviation range over 300 mm. This is similar to νu, but measured over any 300 mm section of the useful length. The ν300 criteria is the most commonly used definition of lead accuracy.

•

ν2π: Maximum deviation range over one revolution (2πr), also known as “lead wobble.” (This specification is applicable only

LEARN MORE AT DYNATECT.COM/LSI

to positioning ballscrews.)

(800) 298-2066 / SALES@DYNATECT.COM

Ballscrews — PT Ref Guide 02.17 V1.indd 18

18

DESIGN WORLD — MOTION

2 • 2017

2/10/17 10:59 AM

BEARINGS

Bearing basics REVIEW:

BEARINGS reduce frictional forces in moving machine sections by giving a surfaces something on which to roll, rather than slide over. There are some fundamental elements that all bearings share, but specific application needs call for numerous variations of this universal motion component. Engineers incorporate different bearings in a motion system depending on the speeds, loads, and operating conditions a bearing with encounter.

BALL BEARING FAQS ABOUT PRELOAD AND MORE

The most common form of bearing is the ball bearing. As the name implies, ball bearings use balls for low-friction motion between bearing races. Because the contact area between the balls and races is so small, ball bearings cannot support loads as other bearings can and are best suited for light to moderate loads. However, their small surface contact also limits heat from friction, so ball bearings are suitable in high-speed applications.

Preload is crucial in nearly all highprecision and high-speed applications,

motioncontroltips.com | designworldonline.com

Bearings — PT Ref Guide 02.17 V2.indd 19

especially when positional and rotational accuracy are concerns. Radial play under operating conditions means that a bearing race can be moved radially and axially relative to the other. Looseness such as this leads to non-repetitive runout which is detrimental in applications like electric motors machine tool spindles, high-speed hand tools and optical encoders The introduction of axial preload forces the balls into raceway contact. The resulting contact angle sets the balls to rotate in a uniform circumferential plane. There are many methods to preload ball bearings but one of the most common is spring preloading. Spring preloading is cheap, simpler and usually the first option considered. Coil springs or wave spring washers are most commonly used, but a variety of spring types are available. The spring is used to press the races together, or apart.

BENEFITS OF PRELOADING BALL BEARINGS INCLUDE: • • • • •

Rotational accuracy and precise shaft positioning Elimination or reduction of ball skidding Control and reduction of axial and radial deflection under applied load Noise reduction Load sharing between bearings

2 • 2017

Plain bearings, like these from igus, are the simplest form of bearing. They have no moving parts and are often cylindrical.

The design of the bearing differs depending on the intended motion.

DESIGN WORLD — MOTION

19

2/10/17 8:25 AM

Replace your metal bearings and reduce costs by 40%

COMMON QUESTIONS ABOUT THRUST BALL BEARINGS

Thrust ball bearings are for applications with primarily axial loads and shaft misalignment. These bearings also work in high-speed applications, such as in the aerospace and automotive industries.

Consider some of the concerns when such bearings run in very hot environments.

In general, grease life is cut in half for every 15°C rise above 70°C. In addition, lubricant viscosity plummets, leading to reduced fatigue life. Raceway hardness is reduced, which cuts fatigue life. Seals dry and crack and that leads to loss of lubricant and entrance of contamination. Cages and retainers weaken, which in turn increases the risk of catastrophic failure. In addition, the rings experience permanent growth, leading to changes in fits, wear of shaft, inability for bearing to float in housing, loss of bearing internal clearance.

Low temperatures pose different challenges to bearings.

Lubricant viscosity becomes too high, leading to increased torque, skidding. Seals lose pliability, leading to seal failure, loss of lubricant, entrance of contamination. Cages and retainers becomes brittle, which can ultimately cause to catastrophic failure.

SELF-ALIGNING BEARING TIP:

A self-aligning bearing is recommended when the alignment of the shaft and housing is difficult or when the shaft may bend during operation. Similar to deep groove ball bearings, most self-aligning ball are for general use.

Reduce cost and increase technology with iglide® iglide® plastic bearings are 100% self-lubricating, maintenancefree, and available in a range of 40+ materials to suit even the most demanding applications.

With product selection tools, reliable lifetime calculation, CAD downloads, and more available online. Thousands of dimensions in stock and ready to ship as early as same-day.

This is a preloaded bearing.

Image courtesy of AST.

Free samples available at www.igus.com/drytechbox sales@igus.com 1.800.521.2747

This is a cutaway of a spring preload bearing system.

Image courtesy of AST.

20

Bearings — PT Ref Guide 02.17 V2.indd 20

DESIGN WORLD — MOTION

2 • 2017

2/10/17 11:05 AM

iglide® plastic bearings are 100% self-lubricating, maintenancefree, and available in a range of 40+ materials to suit even the most demanding applications.

With product selection tools, reliable lifetime calculation, CAD downloads, and more available online. Thousands of dimensions in stock and ready to ship as early as same-day. ® ® iglide iglide plastic plastic bearings bearings are are 100% 100% self-lubricating, self-lubricating,maintenancemaintenancefree, free, andand available available in ainrange a range of of 40+40+ materials materials to suit to suit even even the the most most demanding demanding applications. applications.

With With product product selection selection tools, tools, reliable reliable lifetime lifetime calculation, calculation, CAD CAD downloads, downloads, andand more more available available online. online.

Thousands Thousands of dimensions of dimensions in stock in stock andand ready ready to ship to ship as as early early as same-day. as same-day.

iglide® plastic bearings are 100% iglide® plastic bearings are 100% self-lubricating, maintenanceself-lubricating, maintenancefree, and available in a range free, of and available in a range of 40+ materials to suit even the 40+ materials to suit even the most demanding applications. most demanding applications.

With product selection tools, With product selection tools, reliable lifetime calculation, CAD reliable lifetime calculation, CAD downloads, and more available downloads, and more available online. Thousands of dimensions online. Thousands of dimensions in stock and ready to ship in as stock and ready to ship as early as same-day. early as same-day.

Reduce cost and increase Reduce cost and increase Reduce cost and increase ® ® technology with iglide technology with iglide technology with iglide® Reduce Reduce cost cost and and increase increase ® ® technology technology with with iglide iglide

sales@igus.com 1.800.521.2747

Free samples available at www.igus.com/drytechbox

sales@igus.com 1.800.521.2747

Free samples available at www.igus.com/drytechbox Free samples available at www.igus.com/drytechbox

sales@igus.com 1.800.521.2747

Free Free samples samples available available at at www.igus.com/drytechbox www.igus.com/drytechbox

sales@igus.com sales@igus.com 1.800.521.2747 1.800.521.2747

and reduce costs by 40%and reduce costs by 40%

and reduce costs by 40%

andand reduce reduce costs costs by by 40% 40%

21

Unmatched testing, widest selection, and a full guarantee for up to 36 months make Chainflex a world leader in continuousflex cable performance. More than 1,200 cables in a range of types available from stock and ready to ship in as little as 24 hours. Never any cutting costs or minimum orders.

Free samples available at www.igus.com/cf-sample sales@igus.com 1.800.521.2747

Replace your metal bearings

Bearings — PT Ref Guide 02.17 V2.indd 21

DESIGN WORLD — MOTION

Reduce downtime and increase service life with Chainflex® cables

and reduce costs by 40%

2 • 2017

Reduce cost and increase technology with iglide®

Possibly the oldest form of bearing, roller bearings can be spherically or cylindrically shaped and are common in applications such as conveyor belt rollers. Because of their shape, roller bearings have greater surface contact than ball bearings, and are thus able to handle larger loads without deforming. Their shape also allows for a moderate amount of thrust load since the weight is distributed across cylinders instead of spheres.

When a design needs reduced friction but has limited space, a needle roller bearing maybe suitable. A needle roller bearing is a roller bearing for which the length is at least four times the diameter.

Despite a low cross section, the large surface area of needle roller bearing let them support high radial loads.

They usually consist of a cage, which orients and contains the needle rollers and an outer race, which is sometimes the housing itself. The bearings can often be found in two different arrangements. The first is a radial arrangement, in which the rollers run parallel to the shaft. The second is a thrust arrangement, in which the rollers are placed flat in a radial pattern and run perpendicular to the shaft.

These bearings are often used in automotive applications, such as rocker arm pivots, pumps, compressors and transmissions. The drive shaft of a rearwheel drive vehicle typically has at least eight needle bearings (four in each U joint) and often more if it is particularly long, or operates on steep slopes.

Tapered roller bearings feature tapered inner and outer ring raceways with tapered rollers arranged between them, angled so the surface of the rollers converge at the axis of the bearing. These bearings are unique in that, unlike most bearings that can handle either axial or radial loads, they can handle large amounts of load in both directions.

A single row taper bearing is limited in that it can only take high axial loads from one direction, but if adjusted against a second tapered roller bearing, that axial load is counteracted. This allows the bearings to accept high radial and axial loads from multiple directions.

The ability of a tapered roller bearing to accommodate angular misalignment of the inner ring in relation to the outer

iglide® plastic bearings are 100% self-lubricating, maintenancefree, and available in a range of 40+ materials to suit even the most demanding applications.

With product selection tools, reliable lifetime calculation, CAD downloads, and more available online. Thousands of dimensions in stock and ready to ship as early as same-day.

ROLLER BEARINGS- NEEDLE AND OTHER TYPES

Guaranteed for 36 months Free samples available at www.igus.com/drytechbox

Depending on the series, most selfaligning bearings can be interchanged with standard ball bearing assemblies. (6200 and 6300 have direct interchanges with the 1200 and 1300 series).

Normal mounting and handling procedures for a cylindrical bore bearing should be followed. For the tapered bore, special care must be taken to ensure the bearing is driven up the taper the appropriate amount. Because matching the bearing to the specific application is critical, it is important to verify your application need with your selected vendor.

Continuousflex cables sales@igus.com 1.800.521.2747

This NSK SJ design high-temperature ball bearing has solid lubricant. It’s an example of NSK’s SPACEA Series bearings for extreme environments.

Applications include vacuum vapor deposition equipment, kilns, kiln cars, steel plants, high-temperature conveyance equipment.

BEARINGS

2/10/17 11:05 AM

Unlike plastic, metal bearings, such as this PTFE-lined metal option, corrode quickly when exposed to moisture.

ring is limited to a few minutes of arc. As with other roller bearings, tapered roller bearings must be given a minimum load, especially in high speed applications where the inertial forces and friction can have a damaging effect between the rollers and raceway.

PLAIN BEARINGS FOR COST-EFFECTIVE OR RUGGED DESIGNS

Plain bearings are the simplest form of bearing available, as they have no moving parts. They are often cylindrical, though the design of the bearing differs depending on the intended motion. Plain bearings are available in journal, linear and thrust versions.

Journal style bearings support radial motion where a shaft rotates within the bearing. Linear bearings are often used in applications requiring slide plates, as these bearings are designed to permit motion in a linear motion. Finally, a plain thrust bearing can do the same job as its roller bearing counterpart, but instead of using cone shaped rolling elements, the bearing uses pads arranged in a circle around the cylinder.

These pads create wedge-shaped regions of oil inside the bearing between the pads and a rotating disk, which supports applied thrust and eliminates metal-on-metal contact.

Out of all the bearing types available, plain bearings tend to be the least expensive. They can be made from materials including bronze, graphite, plastics or a combination of these materials. Plastics such as Nylon, PTFE and polyacetal are common. Improvements in material characteristics have made plastic plain bearings increasingly popular in recent years. Plain bearings of all types, however, are lightweight, compact and can carry a substantial load.

As far as lubrication is concerned, some plain bearings require outside lubrication while others are self-lubricating.

Plain bearings made of bronze or polyacetal, for example, contain lubricant within the walls of the bearing, but require some outside lubrication to maximize performance. For other plain bearings, the material itself acts as the lubricant. Such is the case with bearings made from PTFE or metalized graphite.

The growing popularity of plain plastic bearings and increasingly stringent industry standards has resulted in more consumers requiring the bearings to meet FDA and RoHS standards. There has even been a call for the bearings to meet the standards of EU directive 10/2011/EC, which takes the material-manufacturing process into account.

22

Bearings — PT Ref Guide 02.17 V2.indd 22

DESIGN WORLD — MOTION

2 • 2017

3/7/17 11:51 AM

BELTS & PULLEYS

Linear positioning actuators of extremely long stroke lengths — such as this LoPro linear actuator from Bishop-Wisecarver Corp. — typically use belt drives.

Polyurethane belting is quiet and delivers long mechanical actuation with good accuracy and high speeds. LoPro actuators are three to 8 m long, but units to 15 m are possible.

Belt & Pulley OPTIONS IN

DESIGN

INDUSTRIAL BELT DRIVES consist of rubber belts that wrap around drive pulleys, in turn driven by electric motors. In a typical setup, the belt also wraps around one or more idler pulleys that keep the belt taut and on track. The main reasons that engineers pick belt drives over other options is that modern varieties require little if no maintenance; they’re less expensive than chain drives; and they’re quiet and efficient, even up to 95% or more. In addition, the tensile members of today’s belts— cords embedded into the belt rubber that carry most the belt load—are stronger than ever. Made of polyester, aramid, fiberglass or carbon fiber, these tensile cords make today’s belt drives thoroughly modern power-transmission devices. motioncontroltips.com | designworldonline.com

Belts & Pulleys — PT Ref Guide 02.17 V2.LE.indd 23

Manufacturers generally describe belts and pulleys with five main geometries. Pitch diameter is the drive-pulley diameter.

Center distance is the distance between the two pulleys’ centers.

Minimum wrap angle is a measure of how much the belt wraps around the smallest pulley. Belt length is how long the belt would be if cut and laid flat. Finally, in the case of toothed belts (also called synchronous belts) the pitch is the number of teeth per some length—so a 3-mm pitch means that the belt has one tooth every 3 mm.

Some general guidelines are applicable to all timing belts, including miniature and double-sided belts. First, engineers should always design these belt drives with a sufficient safety factor—in other words, with ample reserve horsepower capacity. Tip: Take note of overload service factors. Belt ratings are generally only 1/15 of the belt’s ultimate strength. These ratings are set so the belt will 2 • 2017

DESIGN WORLD — MOTION

23

2/9/17 10:56 AM

Manufacturers of Power Transmission and Motion Control Components deliver at least 3,000 hours of useful life if the end user properly installs and maintains it. The pulley diameter should never be smaller than the width of the belt.

As mentioned, belts are quieter than other powertransmission drive options … but they’re not silent. Noise frequency increases proportionally with belt speed, and noise amplitude increases with belt tension. Most belt noise arises from the way in which belt teeth entering the pulleys at high speed repeatedly compresses the trapped pockets of air. Other noise arises from belt rubbing against the flange; in some cases, this happens when the shafts aren’t parallel.

Pulleys are metal or plastic, and the most suitable depends on required precision, price, inertia, color, magnetic properties and the engineer’s preference based on experience. Plastic pulleys with metal inserts or metal hubs are a good compromise.

Tip: Make at least one pulley in the belt drive adjustable to allow for belt installation and tensioning. Also note that in a properly designed belt drive, there should be a minimum of six teeth in mesh and at least 60° of belt wrap around the drive pulley. Other tips:

Concentric Maxi Torque

Stock and Custom Keyless Hub-to-Shaft Connection System Email or call to get your CMT Stock Products Catalog Order today. Ships today!

•

•

Pretension belts with the proper recommended tension.

This extends life and prevents belt ratcheting or tooth jumping.

Align shafts and pulleys to prevent belt-tracking forces and belt edge wear. Don’t crimp belts beyond the smallest recommended pulley radius for that belt section.

Custom Synchronous Drives

Precise. Reliable. Cost Effective.

Timing Pulley Stock

Guaranteed When You Need It. Custom Machine & Tool Co., Inc. (800)355-5949•sales@ cmtco.com www.cmtco.com Precise. Reliable. Trusted.

Continental Select ContiCleat is conveyor belting for taking goods along steep inclines of up to 45° — and 17 different profile options convey myriad materials and shapes.

American Engineering • American Made © 2017 Custom Machine & Tool Co., Inc.

Belts & Pulleys — PT Ref Guide 02.17 V2.LE.indd 24

24

DESIGN WORLD — MOTION

2 • 2017

2/9/17 11:07 AM

Stock and Custom Mechanical Components One Convenient Source

ISO 9001

9100

AS

REGISTERED

Custom Design, Engineering & Manufacturing • Timing Belts and Pulleys Precision Gears & Gearboxes • Precision Machined Components Molded Components • Mechanical Assemblies

U SA

Manufacturer • Est. 1950

We Provide Total Motion Control Solution Design ► Engineer ► Manufacture ► Assemble SETTING IDEAS INTO MOTION

Ship Complete Subassemblies for a Wide Variety of Product Applications.

Call our Engineers for a Design Consultation and Place Your Order Today.

Phone: (800) 819-8900 Fax: (516) 326-8827 www.sdp-si.com

D

SDP/SI PTGuide 2-17.indd 25 DW-Supplement-2-2017.indd 1

2/9/17 2:01 PM 12/15/16 5:58 AM

• •

Select the appropriate belt for the design torque.

Select the appropriate belt material for the environment (temperature, chemical, cleaning agents, oils and weather). Beltand-pulley systems are suitable for myriad environments, but some applications need special consideration. Topping this list are environmental factors.

Dusty environments don’t generally present serious problems as long as particles are fine and dry. But particulate matter can act as an abrasive and accelerates belt and pulley wear.

Debris should be prevented from falling into belt drives. Debris caught in the drive is generally either forced through the belt or makes the system stall. In either case, serious damage occurs to the belt and related drive hardware.

ADHESIVE KEEPS OUT UV LIGHT & LETS THE LIGHT IN TWO PART EPOXY EP30-2LB

Blocks UV Light Transmission BLOCKS UV LIGHT 200-400 nm

TRANSMITS VISIBLE LIGHT 450-900 nm and above

OPTICALLY CLEAR Refractive Index: 1.55

154 Hobart St., Hackensack NJ, 07601 USA ∙ +1.201.343.8983 ∙ main@masterbond.com

www.masterbond.com

Light and occasional contact with water—during occasional washdowns, for example—has little serious effect. However, prolonged contact with constant spray or submersion can significantly reduce tensile strength in fiberglass belts and make aramid belts break down and stretch out. In the same way, occasional contact with oils doesn’t damage synchronous belts. But prolonged contact with oil or lubricants, either directly or airborne, significantly reduces belt service life. Lubricants cause the rubber compound to swell, break down internal adhesion systems and reduce felt tensile strength. While alternate rubber compounds may provide some marginal improvement in durability, it’s best to prevent oil from contacting synchronous belts.

Ozone can be detrimental to the compounds used in rubber synchronous belts. Ozone degrades belt materials in much the same way as excessive temperatures.

Although the bumper materials used in belts are compounded to resist the effects of ozone, eventually chemical breakdown occurs and they become hard and brittle and begin cracking. The amount of degradation depends on the ozone concentration and generation of exposure.

Rubber belts aren’t suitable for cleanrooms, as they risk shedding particles. Instead, use urethane timing belts here … keeping in mind that while urethane belts make significantly less debris, most can carry only light loads.

Also, none have static conductive construction to dissipate electrical charges.

26

Belts & Pulleys — PT Ref Guide 02.17 V2.LE.indd 26

These are timing belts, timing-belt pulleys, and Fairloc hubs from Stock Drive Instruments/Sterling Instrument (SDP/SI). The company specializes in these power-transmission components. Its Fairloc hub centers shafts and keeps mounted pulleys aligned.

DESIGN WORLD — MOTION

2 • 2017

2/10/17 1:59 PM

BRAKES & CLUTCHES

Nexen Group’s Eclipse servomotor brakes offer 50% more torque than competitive models — from 2 to 125 Nm. An advantage over some spring-engaged electrically-released brakes is that no energy is consumed when the brake is disengaged.

brakes and clutches ESSENTIAL FUNCTIONS OF

POWER-TRANSMISSION AND MOTION DESIGNS rely on stopping loads predictably, especially to ensure machinery and operator safety. To that end, torque limiters, clutches, and brakes stop, hold or index loads. Migration towards applicationspecific designs has quickened as several industries are pushing the performance envelope of stock components.

Brakes stop loads (typically rotating loads) and go in applications that need accurate stopping of the load with motors that stop as well. Clutches transfer torque and go in applications where the machinery must engage or disengage a load and motor while letting the motor continuously run. With a clutch, the design usually lets the load coast to a stop. Clutch and brake combinations go where a machine stops and starts a load while the motor continues to rotate. In fact, both clutches and clutch-brake combinations can mount to a motor shaft or mount to a base and engage the drive shaft with a belt drive, chain drive or coupling.

motioncontroltips.com | designworldonline.com

Brakes & Clutches — PT Ref Guide 02.17 V3.indd 27

A machine’s motor frame size and horsepower dictate brake and clutch types suitable for a given design. The general steps to pick a given unit are to categorize the axis orientation; determine total axis load and kinetic energy to stop it; calculate allowable travel before stopping or slowing and time of engagement; maximum load velocity and required clutch or brake force; driving and backdriving torque; and required brake or clutch geometry.

Manufacturers provide quick-selection charts that list clutch and brake sizes for given motor horsepower ranges and shaft speed. Most of these charts are based on the dynamic torque capacity of the clutch or brake and the motor’s torque capacity plus an overload factor of some value. This presumes that the motor is appropriately sized to the application. Tip: Designs with aggressive cycle rates need special consultation with the manufacturer on heat-dissipation capacities.

Note that harmonization of international safety standards is a factor in brake and clutch selection even as controls have come to integrate more safety features. Those include ANSI B11 Series and OSHA rules in the U.S. and EN ISO 13849 as a global standard on safety to sufficiently mitigate risk — with EN ISO 13849 and EN IEC 62061 possibly merging (as IEC/ISO This is a Mach III slip clutch adapted 17305 should it go forward) requiring to diameter restriction. In fact, brakes compliance of machines that go through and clutches from Mach III Clutch Inc. come in torque capacities to 62,000 the E.U. Many machine builders adhere lb-in. and with mounting configurations to these standards for competitive global for through-shaft, end-of-shaft, flange, NEMA frame, IEC frame, and cusadvantage. tom-motor frame mounting.

2 • 2017

DESIGN WORLD — MOTION

27

2/9/17 11:30 AM

Bluegrass, Bourbon &

Brakes

FAQ: WHERE ARE MECHANICAL SLIP CLUTCHES STILL MORE APPROPRIATE THAN USING ELECTRIC MOTORS FOR THROTTLING POWER?

Slip clutches (including those based on friction plates, shear pins, or ball detents) are most associated The FEB0590 by Carlyle Johnwith overload protection, but son is a spring-set brake used for medical applications such they can also let axes get variable as surgical robotic arms. Highmotion off motors running at ly accurate, the brake allows for precision movement and constant speed. That allows for position control. simple and cost-effective drives — and lets some axes run faster when tensioning webs, capping bottles, or indexing conveyors.

In fact, even continuous-slip clutches usually last for the life of the design. Capacity is limited by heat buildup, sometimes calculated as Watts = Torque (lb-in.) x rpm multiplied by an adjustment factor. Exceeding this value shortens life, but many designs last 30 million cycles or longer.

Slip clutches for tension control can transmit torque that increases with rotational speed to cut stiction and smooth out starts. In contrast, such clutches on machine tools can help extend tool life with cushioning — or on capping axes, they can eliminate tool slipping. Here, adjustable torque settings simplify setup and changeovers. Clutches on index tables and conveyors can slip until a solenoid engages to allow turning — on designs needing force control, slip clutches can push against kinematic linkages to engage arms or gates.

Yes, Brakes

For 45 years, Mach III has produced made-to-order friction brakes, clutches and torque limiters that meet the exact requirements of our client’s applications.

SEPAC Stationary Field Tooth clutches (of the SFTC Series) have a high torque-to-size ratio and can operate dry or in oil. Static torque is 40 to 5,200 lb-ft and maximum speed is 1,400 to 3,500 rpm; there are eight standard sizes.

• 2,000+ models • Torque to 60,000 in-lbs.

• Quick & reliable lead times • Expert engineering assistance

Get to know another fine product from Kentucky.

859-291-0849 machiii.com

Brakes & Clutches — PT Ref Guide 02.17 V3.indd 28

28

DESIGN WORLD — MOTION

2 • 2017

2/9/17 11:31 AM

COUPLINGS

Couplings REVIEW OF

FOR MOTION TRANSMISSION

COUPLINGS ARE MECHANICAL DEVICES that connect shafts together. Couplings join rotating equipment such as motors to transmit several motion parameters— including the precise transmission of velocity, angular positioning and torque. The simplicity of these devices often obscurea their importance.

Couplings should allow some end movement. There are two types: flexible and rigid. Engineers use rigid couplings when dealing with colinear shafts and flexible couplings for applications expecting misalignment.

There are also many coupling styles. Rigid couplings include sleeve-style and clamped, or compression style, and require precise alignment. Flexible couplings include bellows, jaw, Oldham, disc and beam styles.

Rigid couplings are torsionally stiff and excel where shafts are already in proper alignment; parallel shaft misalignment ideally should be well below one thousandth of an inch. One drawback is that they are susceptible to vibration and therefore not suitable at high speeds.

Sleeve-style rigid couplings work in light- to medium-duty applications. The one-piece sleeve—essentially a tube with an inner diameter that is the same as the shafts it is joining—has two setscrews to fasten it to the shaft. They offer ease of use, high torque capacity, zero backlash and stiffness.

The beam coupling is compact, cost effective and has a proven track record for reliability,. Additionally, beam style rigid couplings are usually machined from a single-piece of material which simplifies assembly.

FLEXIBLE COUPLINGS Engineers specify flexible couplings when there is misalignment between shafts. These couplings handle misalignment while still transmitting torque. Misalignment may consist of one or several types simultaneously including axial, lateral, skewed or angular. Motors lose efficiency in speed and torque generation as misalignment increases. Premature wear is also a concern as it can lead to failed bearings, broken shafts and excessive vibration.

Typically, flexible couplings are the most compliant components in motion systems. Torsional stiffness is a critical factor regarding maintaining positional control over a load. Servomotors often

FAQS ABOUT RIGID COUPLINGS Incorporating the features of a rigid coupling can help an engineering department minimize the management of drawings for integrated components. Also, the purchasing department only needs to order, receive, and inventory one full featured coupling rather than numerous parts.

Conversely, clamped or compression-style couplings have a two-part design. They wrap completely around the shaft. This configuration protects the shaft and provides increased torsional holding power. The two-piece design also allows quick removal in maintenance situations.

motioncontroltips.com | designworldonline.com

Couplings — PT Ref Guide 02.17 V4.indd 29

This safety coupling uses elastomer inserts which can be replaced in the field. The coupling provides some vibration damping and compensation for misalignment as well.

Image courtesy R+W.

2 • 2017

DESIGN WORLD — MOTION

29

2/10/17 2:00 PM

undergo many start and stops.

Start and stop applications like this demand torsionally stiff couplings. Torsionally flexible couplings are better suited for vibration damping-dependent applications.

Types of motion differ in applications as well. For example, in manufacturing lines, motion can be start and stop or continuous. With start and stops scenarios, couplings can dampen vibration, diminish the settling time and improve throughput. Conversely, continuous motion applications emphasize torsional strength over vibration damping. Applications requiring motion control precision, say, a packaging and scanning and inspection, call for zero-backlash couplings.

Backlash comes from free-play between the mating components that make up a multi-piece coupling. Most flexible couplings are multi-piece assemblies. Although advances in manufacturing techniques have improved, backlash can still occur.

With a new part, consider the coupling’s fit and if the mating parts will hold up over time; the purpose of flexible couplings is to flex, which stresses the assembly points.

Note: There is a difference between backlash—true mechanical clearance, as in the type found between gear teeth—and torsional deflection, or wind-up. To eliminate backlash, most couplings are preloaded or are inherently backlash free, like the bellows coupling. But they all have different levels of torsional stiffness, which is often traded off for lateral flexibility during the coupling selection process. Bellows couplings often have the highest torsional stiffness of any servomotor coupling, do not handle as much misalignment, but also do not impose heavy reaction loads onto the shafts and bearings as they flex.

Bellows couplings are common in motion systems requiring precision control and misalignment compensation. In precision applications, it is important to address performance factors necessary for the task.

30

DESIGN WORLD — MOTION

Couplings — PT Ref Guide 02.17 V4.indd 30

2 • 2017

Many manufacturers combine coupling features for specific needs. This is a safety coupling from R+W featuring a symmetrically formed, stainless-steel bellows (that’s also torsionally rigid) for the inline flexible element.

Bellows couplings are typically made of a stainlesssteel tube hydroformed to create deep corrugations making them flexible across axial, angular and parallel misalignments. Bellows couplings absorb slight misalignments from perpendicularity and concentricity tolerances between the mounting surfaces of the connected components.

Benefits of bellows couplings also include precise transmission of velocity, positioning and torque.

Bellows couplings are known for high torsional rigidity, and flexibility with axial, angular and parallel shaft misalignment.

When specifying a bellows coupling, the first parameters to address are the torque and connecting shaft sizes. The nominal torque rating (continuous torque transmission) of the coupling should be greater than the peak torque of the application to ensure a secure connection. Connecting shaft sizes must also be within the acceptable range of the coupling. If the shaft diameter is smaller than the specified range on the coupling, the torque transmission value of the coupling can decrease due to inadequate clamping force between the hub and shaft.

Misaligment is the next consideration. Each form of misalignment creates stress in the bellows which can lead to distortion and failure. However, if the misalignment values are not exceeded and the operating torque is

motioncontroltips.com | designworldonline.com

2/10/17 11:09 AM

It’s not a web page, it’s an industry information site So much happens between issues of Design World that even another issue would not be enough to keep up. That’s why it makes sense to visit designworldonline.com and stay on Twitter, Google plus, Facebook and Linkedin. It’s updated regularly with relevant technical information and other significant news to the design engineering community.

designworldonline.com

DW house ad 2017.Vers2.LL.indd 31

2/10/17 12:32 PM

below the rated torque of the This is a solid coupling for use when one shaft is floating.

However, this coupling will cause high bearing loads if used coupling, there can be an infinite between two fixed shafts. Image courtesy Helical Products number of cycles without failure.

Other application-specific parameters are speed and temperature. Depending on the manufacturer, most metal bellows couplings are suitable at speeds up to 20,000 RPM without additional balancing. Couplings with balanced conical hubs can be operated with speeds over 25,000 RPM. In general, bellows couplings are not sensitive to temperature like elastomer style couplings, and can be used temperatures up to 300° C. Jaw couplings feature two metal hubs and a spider insert, usually made of elastomer, which are fitted together to absorb vibration and shock. The elastomer can vary in hardness and temperature ratings, so spiders can be chosen for specific applications. Because they are not as torsionally stiff as other couplings, they are better suited to constant motion applications.

There are two types: straight jaw and curved jaw with zero backlash. Because accuracy of torque transmission can be an issue, straight jaw couplings are not used in most servo applications. Curved jaw couplings reduce deformation on the spider and the effects of centrifugal forces at high-speed (to 40,000+ rpm and beyond). Both types easily handle axial motion. If a spider breaks, the driving jaws can still contact the driven jaws directly, maintaining operation, making jaw couplings fails-safe designs.

Oldham couplings can be preloaded to eliminate backlash and can handle misalignment of all types depending on the disc material. They are often an alternative to straight jaw couplings on general industrial equipment such as pumps, valves, gearboxes and conveyor systems. They are versatile and offer long lives when misalignment is an issue. Their three-piece design—two hubs and a torque-transmitting center—makes them easy to install and disassemble.

Oldham couplings can be made from a variety of materials for different applications. For example, if zero backlash is required versus vibration reduction. They are best suited when parallel misalignment may be high. And because of their three-piece design, axial motion is limited.

Disc couplings are a logical choice for servomotor applications because they transmit high torque, operate at high or changing speeds, and handle misalignment and system loads.

While a coupling’s torque, misalignment and speed This is the cross section of a bellows coupling from GAM. capacities need to be evaluated against a system’s

32

DESIGN WORLD — MOTION

Couplings — PT Ref Guide 02.17 V4.indd 32

2 • 2017

motioncontroltips.com | designworldonline.com

2/10/17 11:09 AM

Metal Bellows Transfer Transfer Pressure Pressure or or Temperature Temperature into into Linear Linear Movement Movement

Electrodeposited Bellows

Features: • Zero backlash • Thinnest high strength walls • Seamless construction • Minimal side loading • Diameters as small as 0.020 in (5mm) • Highest cycle life • Design assistance for Customization

buy.servometer.com

Edge Welded Bellows

Features: • Highest stroke length (90%) • Highest cycle life • Customization • Repeatability • Media compatibility • High temperature • SS, Titanium, alloys, etc.

buy.bellowstech.com

Making the Impossible… Possible!

Servometer PT Guide .indd 33

2/10/17 8:45 AM

WHEN SAFETY IS A REQUIREMENT 0.1-2,800 NM.

requirements, the disc-pack usually is the most important aspect of the coupling’s construction because it will affect all critical performance aspects of the coupling and the system.

The most common type of discpack is made of metal and is found in different shapes (straight-sided, scalloped edges, square). In the case of metal disc couplings, double-flex designs are needed in case of parallel shaft misalignment. The single-flex variety of metal disc coupling is good for angular misalignment but not parallel. This is an advantage if a user needs to suspend a load between two single-flex couplings, because their lateral stiffness can support the weight of the intermediate component.

Beam, or helical couplings are usually made of aluminum, but stainlesssteel versions are available for corrosive environments and increased torque and stiffness. Their one-piece design makes them easy to maintain. Offering zero backlash, they feature spiral cuts that transmit torque and can handle all types of misalignment and angular, parallel or axial motion. Parallel motion is more of a challenge for the single beam design because it must bend in two directions, which causes stress and possible failure.

Two designs exist under this style—single and multiple beams.

Single beams are best suited to lowtorque applications where no parallel misalignment is present, while multiplebeam designs are stiffer, for higher maximum torque capabilities.

WWW.RW-AMERICA.COM

34

Couplings — PT Ref Guide 02.17 V4.indd 34

DESIGN WORLD — MOTION

2 • 2017

2/10/17 2:03 PM

DRIVES

Servo drives, such as these AKD 32-kW drives from Kollmorgen, pack a lot of power in a small space. They feature a fast a 0.67µsec current loop and support network options including Ethernet /IP, Profinet, EtherCAT, Modbus TCP, CANopen, and SERCOS III, among others.

Motor drives: WHEN TO USE A DC DRIVE VS. AN AC FLUX-VECTOR DRIVE

SIMPLICITY First, there’s the issue of available power required for the drive. VFDs typically use 3-phase ac supply voltage, which isn’t always available. If the application only has access to single-phase power, then a dc drive is a better option, because the VFD would have to be de-rated in order to ensure that its components could handle the higher current associated with the single-phase input.

Also, an ac vector drive requires an encoder or feedback device in order to operate in true closed-loop mode, which adds cost and complexity to the system. A dc drive, on the other hand, can operate via internal armature feedback, foregoing the need for an external encoder.

The need for commissioning and tuning, according to the motor parameters and application, are additional examples of the complexity of ac vector drives.

Conversely, dc drives are simple to start up, troubleshoot and maintain. Even dc motor

motioncontroltips.com | designworldonline.com

Drives — PT Ref Guide 02.17 V2.indd 35

brushes have become more robust and are less likely to require maintenance or replacement than they once were.

In general, when faced with a choice between two solutions that both meet the application requirements, the more desirable option will be the one that is less complex, which, in this case, is the DC motor-drive system.

STARTUP TORQUE Traditional AC motors cannot produce torque at low or zero speed due to slip, which is the difference between the speed of the rotating magnetic field and the speed of the rotor. Slip is essentially energy loss, which is converted to heat that can damage motor and cable insulation. Because of this heat, the motor cannot produce full torque at low (or zero) speed in continuous operation. However, closed-loop vector control of VFDs solves this problem, by allowing the controller to adjust the torque through control of the flux (magnetizing) current. This enables the drive to provide good torque control regardless of speed, including down to zero speed.

So why wouldn’t ac vector drives be preferred over dc motor-drive systems for applications that require high startup torque or holding torque? The primary reason is simple: cost. Vector drives are complex, and thus, more expensive than DC drives.

And for true, closed-loop operation of an ac vector drive, the need for an additional encoder further drives up the cost.

With simple startup, good torque and speed regulation, and an overall lower cost, dc motor-drive combinations are, in many cases, the preferred choice for applications requiring high startup torque or zero- or low-speed holding torque.

2 • 2017

DESIGN WORLD — MOTION

35

2/9/17 10:26 AM

+

=

0C/

Makes no cents!

Adding an inefficient worm gearbox to a premium efficient motor doesn’t make sense if you are trying to save money.

Why gain 2-3% energy savings with a more efficient motor and then lose 50% or more through the worm gear?

Solution: Use a helical-bevel gearmotor from SEW-EURODRIVE and obtain 96% efficiency. Now that makes a lot of cents!

seweurodrive.com | 864-439-7537

SEW Eurodrive PTGuide 2-17.indd 36

2/9/17 2:10 PM

ENCODERS

encoders HOW ARE

WIRED INTO MOTION DESIGNS?

THERE ARE TWO MAIN WAYS to wire incremental encoders and three common ways to wire absolute encoders into systems.

In single-ended wiring for incremental encoders, each channel needs only one wire. Remember that channels are any data streams that the encoder produces. For example, a common quadrature encoder has two channels (A and B) to track speed as well as rotational direction … so it needs two wires in single-ended wiring.

Differential wiring for incremental encoders needs two wires per channel that reference each other — so the wires carry signals that are 180° out of phase. To illustrate, other incremental encoders have three channels of data transmission — A, B and Z for indexing to a setpoint.

Such an encoder with differential wiring has six wires total, and each channels’ wire pairs feed twin signals to a controller that discards errors to clean the input.

Single-ended wiring is usually the cheaper option, because it uses one wire per channel, with one end connected to the encoder and the other connected to the controller’s I/O system. However, it is only suitable for short runs of wire because it’s more susceptible to interference. That said, single-ended wiring is easy to implement, as there is only one wire per channel and a common ground.

Differential wiring is more immune to common-mode interference because its wiring consists of a twisted pair of shielded wires with complementary signals. So differential wiring is better for longer cable runs.

As mentioned, absolute encoders can be wired in one of three ways. Serial and bus interfaces have multiple protocols or standards, some of which are open-source, while others are proprietary to specific manufacturers. When considering how to wire an absolute encoder, the required resolution, level of application control, flexibility, and ease of implementation all factor into the decision.

Wiring an encoder in parallel is the most straightforward method and is the standard for single-turn encoders. In parallel wiring, the encoder is connected directly to the receiving device. Each wire handles just one data bit, which means that the more bits of resolution an encoder has, the more wires are required. For high-resolution devices, this can become burdensome and costly—particularly for multi-turn encoders, which have higher bits per turn and multiple turns.

Parallel wiring often provides output in a modified version of binary code, known as reflected binary code, or Gray code (named for

motioncontroltips.com | designworldonline.com

Encoders — PT Ref Guide 02.17 V3.indd 37

Frank Gray, the researcher who developed it). Standards binary code presents a problem for data transmission, because some steps involve changes in more than one bit (digit). Gray code avoids this problem by changing only one bit at each step. Because it uses one wire per bit, parallel wiring is best for simple implementations. Distance is also limited to less than 10 meters due to the potential for noise interference. It is, however, a very fast communication method, with all the data available in real time, all the time.

Serial wiring provides pointto-point communication from a master PLC or microcontroller to a slave encoder. There are several serial interfaces, with SSI (Synchronous Serial Interface) being the most common, particularly in Europe, while BiSS (Bidirectional Synchronous Serial Interface) is relatively new. EnDat is a proprietary interface developed by Heidenhain. The main benefit of EnDat is that it provides for internal memory in the encoder and can carry more information than SSI. Similarly, HIPERFACE is a proprietary interface developed

by Max Stegmann GmbH, which provides absolute position information at start-up, and then provides incremental encoder data after that. Both BiSS and HIPERFACE can be connected either

2 • 2017

DESIGN WORLD — MOTION

37

2/10/17 11:33 AM

point to point or via bus. Each of these interfaces except HIPERFACE uses synchronous data transmission, in which the transfer of data is managed by synchronized clocks in the transmitting and receiving devices.

Serial communication works for applications with too many outputs for parallel wiring to be practical, but too few to justify a bus communication. As a benefit, serial communication works over longer distances than parallel or bus wiring schemes, sometimes over 1000 meters. However, because serial wiring schemes are pointto-point, there are limits to the number of nodes (devices) that can be included in a network.

A bus interface lets the encoder communicate with other devices on the network on a peer-to-peer basis, and is also known as a ring topology. Two common bus protocols are DeviceNet and Profibus. Profibus was developed by the European Community and is, in general, more popular in Europe, while DeviceNet was developed

by Allen Bradley (now part of Rockwell Automation), and is generally more common in the U.S. Because more than one device can be connected to a single controller, bus interfaces use fewer cables than other wiring types in most applications. They also perform well over longer distances to 100 meters. The network topology is generally more complex and individual components more expensive than those of other options.

However, total system cost can be less than other wiring methods due to less cabling and setup complexity.

The PROGRAMMABLE Size 25 shaft encoder that goes ANYWHERE

SAME DAY SHIPPING

on select configurations!

Program your CPR, output, and waveform!

EPC’s new PROGRAMMABLE Model 25SP Accu-CoderPro™ is the only Size 25 Shaft Encoder you’ll need. You’ll save time and money, and reduce your inventory, by keeping these on your shelf.

With the easy-to-use interface, you can program these specs: CPR – any resolution from 1 to 65,536 Waveform – choose from 32 options Output type – 6 different outputs Designed for an industrial environment, the Model 25SP can operate in temperatures from -40º to 100º C, comes standard with dual bearings rated 80lbs axial or radial, and offers sealing up to IP67.

Call EPC today to learn how the Model 25SP can be your encoder solution.

1-800-366-5412 • www.encoder.com

Encoders — PT Ref Guide 02.17 V3.indd 38

WATCH ONLINE!

Product demos and more at youtube.com/user/EncoderProducts

2/9/17 12:01 PM

GEARING

Gearing:

WHAT ARE SOME INNOVATIONS ON THE HORIZON?

MATERIALS could soon spur a new class of planetary and strainwave gears used in robotics.

Gears let robotic limbs move smoothly and stop on command — or make moves shaky and jerky if of insufficient quality. So a team led by technologist Douglas Hofmann at NASA’s Pasadena Jet Propulsion Laboratory recently developed gears made of an alloy called bulk metallic glass (BMG) to give engineers another option for robotics. In fact, gears made of BMGs could find use on NASA spacecraft headed for Jupiter’s moon Europa and other harsh environments.

Both a metal and glass in its atomic structure, BMGs are rapidly cooled to trap a noncrystalline amorphous-metal form.

Manufacturers can cast BMGs using injection molding, but the Shown here are an SM miter gear and a PM process yields components with much higher strength and wear plastic miter gear from KHK USA Inc. in an electric-component assembly machine. resistance than cast plastics. BMGs also don’t get brittle in extreme cold, which prevents gear-tooth fractures in sets made of BMG ... even down to -328° F. BMGs may soon lower the cost of manufacturing strain-wave gears, in the joints can be very expensive but are too. This gear type includes a metal ring that flexes as the gear spins. That required to prevent shaking,” Hofmann said. ring is tricky to mass produce and ubiquitous in expensive robots. BMGs “Performance at low temperatures is an let strain-wave gears perform at low temperatures and allow for strainadded benefit.” In a similar way, BMGs could wave manufacture at a fraction of the cost of their steel versions without improve planetary gearsets, too. sacrificing performance. This could one day reduce the cost of robots using Curiosity is currently equipped with steel strain-wave gears, as gearing is often their most expensive part. gears, which must be lubricated to avoid wear.

“Mass producing strain-wave gears using BMGs may impact the What’s worse, gear lubricant must be heated consumer-robotics market — especially for humanoid robots where gears to operate at Mars’ low temperature. This is a problem because Curiosity spends 30% of its discretionary power to heat gear lubricant — Gears for spacecraft must be made of materials that don’t wear out in extreme space conditions that include vacuum and cryogenic temperatures. Bulk metallic glass (BMG) doesn’t get brittle in and the heaters weigh 100 kg, further sapping extreme cold, which makes BMG-cast gears excel in robotics working on icy planets.

Curiosity’s power underway. Every morning Image courtesy NASA/JPL-Caltech when scientists turn on the rover, they must let the gears warm up — losing time and energy.

Right now, BMGs are only common in cosmetic parts such as electronics cases (as engineers assume they’re all too brittle for structural parts). But BMGs are a diverse class of materials with drastically different properties depending on atomic makeup.

Testing shows a BMG variety of copper and zirconium is most suitable for spacecraft gears thanks in part to wear resistance 60% better than that of the steel gears in the Curiosity rover now.

motioncontroltips.com | designworldonline.com

Gears — PT Ref Guide 02.17 V6.indd 39

2 • 2017

DESIGN WORLD — MOTION

39

2/10/17 11:11 AM

Gearing Basics:

GENERAL DESIGN

GEARS mesh with other gears to transmit altered torque and rotation. In fact, gearing can change the speed, torque and direction of motion from a drive source. When two gears with an unequal number of teeth engage, the mechanical advantage makes their rotational speeds and torques different.

In simple setups, gears are flat with spur teeth (with edges parallel to the shaft) and the input gear’s shaft is parallel to that of the output. Spur gears mostly roll through meshing, so can be 98% or more efficient per reduction stage. However, there is some sliding between tooth surfaces, and initial tooth-to-tooth contact occurs along the whole tooth width at once, causing small shock loads that induce noise and wear.

Sometimes lubrication helps mitigate these issues.

In more complex setups, parallel-axis gearsets have helical gears that engage at an angle between

90° and 180° for more tooth contact and higher torque capacity. Helical reducers are suitable for higherhorsepower applications where long-term operational efficiency is more important than initial cost. Helical gear teeth engage gradually over the tooth faces for quieter and smoother operation than spur gearsets.

They also tend to have higher load capacities. One caveat: Angled tooth contact generates thrust that the machine frame must resolve.

No matter the subtype, most parallel-axis gearsets have gear teeth with tailored involute profiles— customized versions of the rolled trace off a circle with an imaginary string. Here, mating gears have tangent pitch circles for smooth rolling engagement that minimizes slipping. A related value, the pitch point, is where one gear initially contacts its mate’s pitch point. Involute gearsets also have an action path that passes through the pitch point tangent to a base circle.

Variations abound for gear geometries Besides parallel-axis gearsets, there are nonSpur gearsets are simple ...

Zerol bevel gearsets are parallel and right-angle a special veriation of straight right-angle gearsets. These have input and bevel sets. output shafts that protrude in different directions to give engineers more mounting Pitch circle and design options. The gear teeth of such gearsets are Planetary gearsets are compact and either bevel (straight, spiral run to 10,000 rpm. or zerol), worm, hypoid, skew Here, a lightweight Schaeffler differential Reaction force or crossed-axis helical gears. for a hybrid vehicle has an ... but helical gearsets are The most common are bevel axial spline to boost efficiency. more efficient. Cross-axis sets are another option. gearsets with teeth cut on Worm gearsets are rugged an angular or conical shape. and don’t let designs backdrive ...

Hypoid gears are much like which can eliminate the need for brakes. spiral-bevel gearsets, but the input and output shaft axes Note there’s some overlap between bevel The ratio of a helical or and worm applications. Case in point: The don’t intersect, so it’s easier to bevel gearset is simply MS-Graessner DynaGear here is a the number of teeth in the integrate supports. In contrast, single-stage bevel gear with a 30:1 ratio. larger gear divided by zerol gearsets have curved the number of teeth in the smaller gear. Other gear teeth that align with the shaft types such as planetary to minimize thrust loads. gears have more complex ratio relationships.

40

DESIGN WORLD — MOTION

Gears — PT Ref Guide 02.17 V6.indd 40

2 • 2017

motioncontroltips.com | designworldonline.com

2/9/17 10:14 AM

Motion control challenge? can help

Gear Reducers

Servo Couplings

Linear Mount Products

Whether it’s Gear Reducers, Servo Couplings, or Linear Mount Products, GAM is the complete source for your Motion Control Needs.

With one of the largest product offerings in the motion control industry as well as the engineering expertise and manufacturing capabilities to develop customized solutions, GAM can help with your application. Being flexible to meet the needs of customer requests and great service are what set GAM apart from the rest. GAM Can.

Toll Free 888.GAM.7117 | www.gamweb.com | info@gamweb.com

901 E. Business Center Drive, Mount Prospect, IL 60056

Gam PTGuide 2-17.indd 41 13_GAM_022_Ad_F.indd 1

Š 2013 GAM. ALL RIGHTS RESERVED

2/9/17 2:12 PM 7/29/13 1:01 PM

Gearing Basics

GENERAL SPEED REDUCERS, SHAFT-MOUNT SETS, WORM DRIVES GEAR REDUCERS, also known as speed reducers, are a component of many mechanical, electrical, and hydraulic motors. Essentially it is a gear or series of gears combined in such a manner as to alter the torque of a motor. Typically, the torque increases in direct proportion to the reduction of rotations per unit of time.

Speed reducers come in two varieties; base mounted and shaft mounted. Shaft-mounted types come in two versions. One is truly shaft mounted in that the input shaft of the drive motor supports it … with a special coupling to address torque reactions.

The other mounts to the machine housing so the input shaft doesn’t support the reducer’s weight or address torque reactions.

42

DESIGN WORLD — MOTION

Gears — PT Ref Guide 02.17 V6.indd 42

2 • 2017

By the American Gear Manufacturers Association (AGMA) definition, engineers apply the term “speed reducer” to units operating at pinion speeds below 3,600 rpm or pitch-line velocities below 5,000 fpm. (The AGMA is an international group of gear manufacturers, gear consultants, academics, and gear users and suppliers.) Reducers operating at speeds higher than these are called high-speed units.

Manufacturers base catalog ratings and engineering specifications for speed reducers on these AGMA standards.

There are as many types of speed reducers as there are gear types. Consider reducers in which the input and output shafts are at different angles. The most common of these are worm-gear reducers.

motioncontroltips.com | designworldonline.com

2/9/17 10:15 AM

GEARING

Rexnord offers their large Falk V-Class gear drives (in sizes 107 to 167) with lead times of just a few weeks or shorter. That helps plants minimize unplanned downtime and shutdowns.

V-Class drives with short lead times include those with standard TA taper bushings, single and double-ended shafts, shaft fans, couplings, guards, and alignment-free options.

Worm gear reducers are used in low to moderate-horsepower applications. They offer low initial cost, high ratios, and high output torque in a small package, along with a higher tolerance for shock loading then helical gear reducers. In a traditional setup, a cylindrical toothed worm engages a disk-shaped wheel gear with teeth on its circumference or face.

Most worm gears are cylindrical with teeth of consistent size (for one pitch diameter for the length). Some worm-gear reducers use a double-enveloping tooth geometry, though—with a pitch diameter that goes from deep into short and back to deep—so more teeth engage. No matter the version, most wheel gears in worm-based reducers sport cupped teeth edges that wrap around the worm shaft during engagement. In many cases, the sliding engagement lowers efficiency but extends life, as worm-gear mating holds a film of lubricant during operation. The ratio of a worm-gear ratio is the number of wheel teeth to the number of threads (starts or leads) on the worm.

A FEW WORDS ON GEARHEADS A gearhead is like a gear reducer — except a gearhead doesn’t just reduce speed. Engineers use them wherever an application calls for high torque at low speed. It reduces a load’s reflected mass inertia, which makes accelerating heavy loads easier, enabling designs to run off smaller motors. Gearheads come in a variety of styles from basic spur gearheads to more complex planetary gearheads and harmonic type gearheads, each with their own characteristics and suitable applications. One caveat: In some applications, gearhead backlash may become an issue. In this case, consider using a gearhead with low or zero backlash.

2 • 2017

Gears — PT Ref Guide 02.17 V6.indd 43

DESIGN WORLD — MOTION

43

2/9/17 10:15 AM

Gearing Basics:

GEARBOXES, SPECIALTY GEARHEADS, AND SERVOGEAR SETS

SERVO SYSTEMS are precision-motion setups that demand servogear reducers with good torsional stiffness, reliable output torque and minimal backlash. OEMs tasked with integrating servo systems should look for quiet reducers that easily mount to the motor and require little or (if possible) no maintenance.

In fact, a lot of advanced machinery integrates servogears into application-specific electromechanical arrangements, and several of these arrangements are common enough to have specific labels. Here is a look at some of the most widespread.

Gearmotor: This complete motion component is a gear reducer integrated with an ac or dc electric motor. Usually the motor includes the gears on its output (typically in the form of an assembled gearbox) to reduce speed and boost available output torque.

Engineers use gearmotors in machines that must move heavy objects. Speed specifications for gearmotors are normal speed and stallspeed torque.

Gearbox: This is a contained gear train … a mechanical unit or component consisting

Spiroid® gear

Worm gear

Spiroid® or Helicon® gear Helicon® gear Hypoid gear

Spiral bevel gear

of a series of integrated gears. Planetary gears are common in integrated gearboxes.

Planetary gears: Particularly common in servo systems, these gearsets consist of one or more outer planet gears that revolve about a central, or sun, gear. Typically, the planet gears mount on a movable arm or carrier that rotates relative to the sun gear. The sets often use an outer ring gear, or annulus, that meshes with the planet gears.

The gear ratio of a planetary set requires calculation, because there are several ways they can convert an input rotation to an output rotation. Typically, one of these three gear wheels stays stationary; another is an input that provides power to the system, and the last acts as an output that receives power from the driving motor. The ratio of input rotation to output rotation depends on the number of teeth in each gear and on which component is held stationary.

Planetary gearsets offer several advantages over other gearsets. These include high power density, the ability to get large reductions from a small volume, multiple kinematic combinations, pure torsional reactions and coaxial shafting.

Another advantage to planetary gearbox arrangements is power-transmission efficiency. Losses are typically less than 3% per stage, so rather than waste energy on mechanical losses inside the gearbox, these gearboxes transmit a high proportion of the energy for productive motion output. Planetary gearbox arrangements distribute load efficiently, too. Multiple planets share transmitted load between them, which greatly increases torque density. The more planets in the system, the greater load ability and the higher the torque density. This arrangement is also very stable due to the even distribution of mass and increased rotational stiffness. Disadvantages include high bearing loads, inaccessibility and design complexity.

In servo systems, besides boosting output torque, gearboxes impart another benefit—reducing settling time. Settling time is a problem when motor inertia is low compared to load inertia … an issue that’s the source of constant debate (and regular improvement) in the industry. Gearboxes reduce the reflected inertia at the controls by a factor equal to the gear reduction squared.

Shown here are Spiroid and Helicon brand gearing. Suitable for right-angle power transmission in applications with high power density requirements, these skew-axis gear forms operate on nonintersecting and non-parallel axes. Compared to traditional right-angel bevel and worm gearing, the gear-centerline offset of Spiroid and Helicon branded gearing allows for more tooth-surface contact and results in higher contact ratios. This boosts torque capacity and smooths motion transmission. Spiroid brand gears use advanced software and tooling to make the proprietary gearing fit specific application requirements. The gearsets are quiet, stiff, and compact, delivering ratios from 3:1 to 300:1 and beyond.

44

DESIGN WORLD — MOTION

Gears — PT Ref Guide 02.17 V6.indd 44

2 • 2017

motioncontroltips.com | designworldonline.com

2/9/17 10:16 AM

GEARING

Gearing Basics: CONSULTATION,

CUSTOM DESIGN, AND ANALYSIS

CUSTOM GEARBOXES are increasingly common, mainly because they’re easier than ever to manufacture to specification. Modern manufacturing lets some suppliers make gearboxes and components to meet specific application requirements. New supplier approaches to giving engineering support as well as new machine tools, automation and design software now let OEMs and end users get reasonably priced gearing even in modest volumes.

When enlisting help from a consultant or manufacturer, review the following and answer as many of these questions as possible:

• •

• • •

•

•

What’s the input speed and horsepower?

What’s the gearbox target output speed or output torque? This partially defines the required gear ratio.

What are the characteristics of use? How many hours per day will the gearbox run? Will it need to withstand shock and vibration?

How overhung is the load? Is there internal

overhung load? Remember that bevel gears usually can’t accommodate multiple supports, as their shafts intersect … so one or more gears often overhang.

This load can deflect the shaft which misaligns the gears, in turn degrading tooth contact and life. One potential fix here is straddle bearings on each side of the gear.

Does the machine need a shaft or hollow-bore input ... or a shaft or hollow-bore output?

How will the gearing be oriented? For instance, if specifying a right-angle worm gearbox, does the machine need the worm over or under the wheel? Will the shafts protrude from the machine horizontally or vertically?

Does the environment necessitate corrosion-resistant paints or stainless-steel housing and shafts?

Service factor: The starting point for most gearbox manufacturers is to define a service factor. This adjusts for such concerns as type of input, hours of use per day, and any shock or vibration associated with the application. An application with an irregular shock (a grinding application, for example) needs a higher

KHK USA Inc. manufactures gearing to operate in ratchets and pawls, which is mechanical gearing that transmits intermittent rotary motion. They only let shafts rotate in one direction.

motioncontroltips.com | designworldonline.com

Gears — PT Ref Guide 02.17 V6.indd 45

2 • 2017

DESIGN WORLD — MOTION

45

2/10/17 2:08 PM

service factor than one that’s uniformly loaded. Likewise, a gearbox that runs intermittently needs a lower factor than one used 24 hours a day.

Class of service: Next, define a class of service. A gearbox paired to a plain ac motor driving an evenly loaded, constantspeed conveyor 20 hours per day may have a service class 2, for example.

This information comes from charts from gearbox manufacturers that list classes of service.

Overhung load: The gearbox manufacturer’s catalog or website lists values for the maximum overhung load that is permissible for that sized unit. Tip: If the load in an application exceeds the allowed value, increase the gearbox size to withstand the overhung load.

Mounting: Next, pick the mounting. Common mounting configurations abound, and gearbox manufacturers offer myriad options for each unit size. A flanged input with hollow bore for a C-frame motor combined with an output shaft projecting to the left may be the most common mounting, but there are many other choices.

Options such as mounting feet for either above or below the body of the gearbox, hollow outputs, and input and output configuration are all possible. All gearbox manufacturers list their mounting options as well as dimensional information in catalogs and websites.

Remember that today’s custom and standard gearing aren’t mutually exclusive. Where fullycustom gearboxes aren’t feasible (if quantities aren’t high enough, for example) consider working with manufacturers that sell gearboxes built to order from standard modular subcomponents. Otherwise, for small quantities of true custom gearboxes, look for manufacturers that leverage the latest CAD software, CAM software and machine tools to streamline postprocessing work and reduce the cost of one-offs.

DieQua has more Gearhead Solutions Different Technologies Provide Different Benefits

Are You Selecting The Correct Technology For Your Motion Profile?

Whether your application requires dynamic acceleration, precise positioning or simple motion control, several gear technologies can do the job. But which one does it best?

Planetary Designs

Precision Worm

Spiral Bevel

High Torque Helical

Precision Hypoid

Precision Cycloidal

Only DieQua offers you the widest range of servo motor gearhead designs, along with the experience and expertise to help select the optimal solution to satisfy your needs.

If you are specifying servo gearheads, you should be talking to DieQua!

www.diequa.com half page horizontal ad new.indd 1

46

DESIGN WORLD — MOTION

Gears — PT Ref Guide 02.17 V6.indd 46

630-980-1133 11/15/16 3:22 PM

2 • 2017

motioncontroltips.com | designworldonline.com

2/9/17 10:18 AM

GEARMOTORS

Gearmotor BASICS

THE TREND IN INTEGRATED SYSTEMS is bringing with it a renewed interest in gearmotors. Specifically, the focus on cutting energy costs represents an opportunity for gearmotors as they can fit into many diverse applications and can help in containing global energy costs.

Gearmotors are essentially an electrical motor, either ac or dc, combined with a gear reducer. They can deliver high torque at low horsepower or low speed. The way they operate is to use gears, typically assembled as a gearbox, to reduce speed, which makes more torque available.

Gearmotors have several advantages over other kinds of motor/gear combinations. Most importantly, they can simplify design and implementation by eliminating the step of separately designing and integrating the motors with the gears, thus reducing engineering costs.

Also, if sized properly, the right combination of motor and gearing can prolong gearmotor life, leading to optimum power management.

Another advantage is that gearmotors, being integrated units, eliminate the need for couplings and also any potential issues with alignment. These problems are more common when a separate motor and gear reducer are connected together. Often this leads to more engineering time and cost as well as the potential for misalignment, causing bearing failure and ultimately reduced useful life.

Motors and gear reducers can be mixed and matched as needed to best fit the application, but in the end, the complete gearmotor is the driving factor.

There are a number of motors and gearbox types that can be combined; for example, a right angle worm, planetary and parallel shaft gearbox can be combined with permanent magnet dc, ac induction, or brushless dc motors.

Even though there are a range of gearmotor types (i.e. different motor and gearing combinations) not just any one will work for any application. Certain combinations will be more efficient and cost-effective than others, depending on the application requirements.

Knowing the application and having accurate ratings for the gearmotor is the foundation for successfully integrating a gearmotor into a system.

motioncontroltips.com | designworldonline.com

Gearmotors — PT Ref Guide 02.17 V1.indd 47

A good example of three of the most common types of gearmotor configurations, from Brother Gearmotors. From left to right, a right-angle hollow-shaft gearmotor, right-angle shafted gearmotor, and an inline shaft gearmotor.

When to pick a preengineered gearmotor and when to design your own?

There are two ways of selecting a gearmotor. One is simply choosing a pre-engineered unit and the other is picking a motor and gearbox separately and then assembling them into one finished unit.

So, which method is best? The answer is partly application specific, partly a matter of resources.

Regardless of the method, there are some things common to both approaches. In either case, it helps to know as much about the specific application needs as possible. For example, speed and torque requirements as well as mechanical issues like mounting configuration and orientation, as well as any thermal and environmental considerations.

Perhaps the biggest factor in deciding which route to go involves available resources. So, going the pre-engineered route will likely be the best choice when time is a premium and when a quick selection process is best, not a long one involving a lot of engineering resources.

One of the biggest advantages of selecting a pre-engineered gearmotor is that the manufacturer has done most of the work already.

A lot of the uncertainty has been dealt with. So there’s no need to pick a motor and gearbox separately and assemble them together and hope for the best. Going the pre-engineered route saves engineering time and resources, eliminates complexity, and reduces design risk.

So what about the alternative, selecting a separate motor and gearing and assembling them together? There are a number of reasons to consider this route. One may be cost. That is, it may be less expensive than choosing a pre-engineered gearmotor from a manufacturer. Another reason may be that the application is unique and the belief is that one’s own engineers can design the best solution and also have more control over the final design.

2 • 2017

DESIGN WORLD — MOTION

47

2/9/17 11:42 AM

Leadscrew BASICS

A LEADSCREW, or power screw, is a threaded rod or bar that translates rotational motion into linear motion. The operating principle of a leadscrew is to generate sliding rather than rolling friction between a nut and the screw. This generates more friction, which means a lower overall efficiency. And efficiency, when talking about leadscrews, is simply the ability to convert torque to thrust while minimizing mechanical losses.

Leadscrews drive axes on a wide range of machines, both large and small. They usually sport higher ratings than comparable ballscrews thanks to more contact between the nut and screw load surfaces.

How a leadscrew is manufactured can determine the performance and cost of the leadscrew. For instance, there are three ways leadscrews can be manufactured; by machining, rolling, or grinding. Ground leadscrews are the most expensive and are generally considered to be the highest performing as well.

The thread type also determines efficiency. Acme threads are the simplest to produce, the most inexpensive, but also among the least efficient.

48

DESIGN WORLD — MOTION

Leadscrews — PT Ref Guide 02.17 V1.indd 48

2 • 2017

Other types include buttress threads and square threads, which generally have the least amount of friction and higher efficiencies.

Leadscrews have a number of advantages including a relatively high load-carrying capacity.

They are also compact and simple to design into a system with a minimal number of parts.

The motion is also generally smooth and quiet and requires little maintenance. Leadscrews also work well in wash-down environments because the materials used and the lubricantfree operation allows total immersion in water or other fluids.

On the downside, leadscrews generally don’t have high efficiencies. Because of lower efficiency ratings they ’re not used in applications requiring continuous power transmission.

There’s also a high degree of friction on the threads meaning that the threads can wear quickly.

Because a leadscrew nut and screw mate with rubbing surfaces

motioncontroltips.com | designworldonline.com

2/9/17 12:09 PM

LEADSCREWS

they have relatively higher friction and stiction compared to mechanical parts that mate with rolling surfaces and bearings.

There are several parameters that help determine leadscrew performance. These include thrust, speed, accuracy and repeatability.

Two of the most important factors in determining the performance of a leadscrew are the screw pitch and lead. The pitch is the linear distance between the threads while the lead is the linear distance the nut travels.

Speed is another critical parameter. Leadscrews have a critical velocity, which is the rotational velocity limit of the screw. Reaching this limit induces vibrations in the leadscrew.

Accuracy and repeatability are also important factors. The accuracy of a leadscrew is a measure of how close to a desired end point the assembly can move a load to within a given tolerance. The accuracy of the leadscrew will mostly determine the system’s accuracy. On the other hand, repeatability is a measure of how well a leadscrew assembly can repeatedly move a load to the same position.

A range of industries is adopting new leadscrew components and linear systems. Designers are looking for ways to simplify machines, reduce design weight and simplify assembly and maintenance. Similarly, both additive manufacturing (i.e. 3D printing) and traditional subtractive processes such as plasma cutting, laser and waterjet manufacturing, as well as factory automation, are driving new leadscrew uses.

WHICH IS BETTER; A LEADSCREW OR BALLSCREW? Leadscrews are often regarded as the less expensive alternative to ballscrews – suitable only for light-duty applications with low precision requirements. While it’s true that ballscrews often have the advantage over leadscrews when it comes to load capacity and rigidity, leadscrews’ reliance on sliding, rather than rolling, motion makes them the better choice for some applications. Here are five applications where leadscrews can be a better fit than ballscrews.

Vertical operation Leadscrews are based on sliding contact between the nut and the screw, which makes them less efficient than ballscrews. But in a vertical application, this inefficiency has a benefit; it can prevent the load from backdriving when the motor is powered off. This ability to maintain a vertical load without backdriving is important in applications where the load needs to wait at the top of its stroke while other processes take place, such as tray stacking and parts sorting. In order to use a ballscrew in these applications, a brake or holding device would be needed, whereas a leadscrew can typically (depending on its efficiency) hold a vertical load without the use of a brake.

Cleanroom environments Lubrication is a liability in cleanroom environments, as oils and greases are major sources of contamination. And while a ballscrew (or any metalto-metal contact bearing) requires lubrication, a leadscrew made of stainless steel with a self-lubricating polymer nut does not, making it the more cleanroom-friendly option. This is especially important in medical, laboratory, and electronics applications, where not only is it essential to

motioncontroltips.com | designworldonline.com

Leadscrews — PT Ref Guide 02.17 V1.indd 49

maintain the integrity of the cleanroom, but where airborne lubrication particles would cause damage to delicate parts or processes.

Highly contaminated environments Because their motion relies on sliding friction rather than rolling elements, leadscrews are much more tolerant than ballscrews of dust, chips, and debris. And despite harsh environmental conditions, leadscrews don’t require seals – which add friction and can need frequent replacement – because there’s no lubrication to keep in, and keeping contamination out is not as critical as it is for ballscrews. Applications such as woodworking and paper processing, which produce a considerable amount of dust and chips, can shorten ballscrew life significantly, while leadscrews can withstand these environments with little effect on performance or life.

Washdown applications With no lubrication to be flushed out, and a wide variety of materials and coatings for both the screw and nut, leadscrews are a natural choice for washdown environments. This is especially beneficial in food and beverage processing and packaging applications, where equipment must be regularly washed and sanitized.

Some leadscrews can even operate when completely submerged in water, making them suitable for water-jet applications.

Low noise applications The steel-on-steel rolling elements and recirculation inherent in ballscrews cause them to generate significant noise.

Leadscrews, on the other hand, produce relatively little noise, relying on sliding motion rather than rolling elements. Because of their low noise level, leadscrews are often used in laboratory automation and medical imaging equipment, where the environment is inherently quiet, and users or patients could be disturbed by excessive noise. Consumer devices, such as printers, scanners, and appliances also require lownoise components, where leadscrews are the preferred choice over ballscrews.

2 • 2017

DESIGN WORLD — MOTION

49

2/9/17 12:10 PM

Heavy Duty Slides from HepcoMotion work for long-length transport applications such as pick-and-place or robot-translation stages. V slide rails are made from bearing-grade steel in sections to four meters long. The V slides typically bolt to aluminum extrusions or supporting back plates. A guide wheel bearing with matching V geometry rolls on the V slide raceway.

Image courtesy Bishop-Wisecarver

Round shaft or profiled rail HOW TO CHOOSE?

This Rexroth CKL Compact Module incorporates a linear motor to deliver high force density with a compact package … for travel velocities up to 5 m/ sec. A Ball Rail with central relubrication helps the module deliver precise positioning and zero backlash.

50

WHEN DESIGNING a linear-motion system with recirculating linear guides, engineers have two main choices — round shaft or profiled rail.

Choosing the wrong one may necessitate structural changes or oversized components with unnecessarily high costs … or cause poor machine performance. Fortunately, key criteria dictate which technology is more appropriate.

Round shaft guides run successfully in virtually every industry. But their limitations in rigidity forced manufacturers of precision equipment (such as machine tools) to use machined ways or cross rollers to get required load capacities and accuracies. The introduction of profiled rail guides brought a less costly and time-consuming alternative for high load capacity and rigidity in a compact envelope. But for designers, the decision regarding when to use round shafts became less clear, as profiled rail guides were and are suitable for many of the applications once the province of round shafts.

In fact, the decision is still largely based on past successes (or failures) with a given technology … but performance criteria can make initial selection a bit more informed.

Load capacity advantage goes to profiled rail. With conformity between the balls and raceways, profiled rail systems have a larger contact area (and thus a higher load-carrying capacity for a given size) than round-shaft systems. Profiled rails also address moment loads better than round shafts, and typically have equal load capacities in all four directions. Conversely, the load capacity for round shafts depends on the direction of loading, which is the orientation of the load to the ball bushing.

Rigidity advantage goes to profiled rail again. The larger contact area between the balls and raceways yields less deflection for a profiled rail than for a round shaft. While round shaft guides can be lightly preloaded, profiled rail systems are often supplied with preload ranging from 2 to 8% which further boosts rigidity.

DESIGN WORLD — MOTION

Linear Guides — PT Ref Guide 02.17 V6.indd 50

2 • 2017

Accuracy advantage goes to profiled rail. With ground raceways and reference edges, profiled rails commonly get travel accuracies an order of magnitude better than round shaft guides. Here, round shafts are more commonly valued for their ability to handle inaccuracies (thanks to self-aligning) than for their travel accuracy.

Speed advantage goes to profiled rail. Round shaft guides can generally get speeds to 2 m/sec (limited by the ability to control the balls as they move in and out of the load zone). Profiled rail bearings, with a more sophisticated recirculation method, can reach speeds of 5 m/sec.

Mounting advantage goes to round shaft. Where profiled rail guides need full support and mounting along their length, round shaft guides can be supported only on their ends, for lengths to 20 times the shaft diameter. Round shafts don’t need machined surfaces for mounting either, because ball bushings inherently compensate for some misalignment, reducing cost and time for designing and preparing mounting surfaces.

The advantage in harsh environments goes to round shaft.

It’s generally less sensitive to debris than profiled rails and comes in myriad

motioncontroltips.com | designworldonline.com

2/9/17 12:59 PM

Swiss Precision to the Rescue

Components Precise & Affordable

Schneeberger Innovations Integrated Encoders Rack and Pinion

Custom Stages to Your Specifications

Schneeberger, Inc 44 6th road | Woburn, MA 01801 Info-usa@schneeberger.com www.schneeberger.com

800-854-6333

0117_Schneeberger_DW-wtwhFP.indd 1 Schneeberger 1-17.indd 51

1/11/2017 10:37:03 PM 2/9/17 2:15 PM

materials, coatings, and sealing options to withstand caustic or abrasive contamination.

The advantage for easy maintenance goes to round shaft. Due to the smaller contact area between the load-carrying balls and running tracks, round shafts have less demanding lubrication requirements than profiled rails.

SUMMARY OF ALL LINEAR-MOTION OPTIONS FOR MACHINE AXES

Linear-motion systems are essential in all sorts of applications, including everything from manually operated industrial drawers to advanced Cartesian robots. Mechanisms that include the former operate without power, using inertia or manual power to move loads. Components to complete the latter include ready-to-install drive and guidance designs … in the form of selfcontained actuators or linear-motion machinery subsections. Some designs simply rely on the rotary-to-linear mechanism or actuator structure for total load support.

Linear rails, rotary rails, guide rails, linear slides and linear ways are just a few options to facilitate single-axis motion. Their main function is to support and guide load with minimal friction along the way. Typical linear-motion arrangements consist of rails or shafts, carriages and runner blocks, and some type of moving element. Engineers differentiate these systems by the type of surface interaction (sliding or rolling), the type of contact points, and (if applicable) how the design’s rolling-element recirculation works. In fact, slides and rails are more advanced than ever, with advances in materials and lubrication setups (to help designs last longer in harsh applications), innovative rail geometries (to help designs withstand more misalignment and load than ever), and modular guide mounts (to boost load capacity and minimize deflection).

No matter the ultimate installation, MR, ARC, and HRC linear-profile rail with recirculating linear-motion rails, bearings from Lintech have two or four rows of recirculating guides, and ways enable balls. These are a 45° contact angle with the raceway for high rigidity under moment and torsional loads. motion along an axis or rail either through sliding

52

DESIGN WORLD — MOTION

Linear Guides — PT Ref Guide 02.17 V6.indd 52

2 • 2017

This Schaeffler INA Linear Technology is a linear recirculatingball bearing and guideway assembly. Called the KUVE-B-HS, it has conventional steel rolling elements for speeds to 10 m/sec. Plastic in the recirculation mechanism prevents rolling-element tilting and pulse loads. The guides run on standard guideways.

or rolling contact. Myriad moving elements can produce either sliding or rolling support: ball bearings, cam roller sliders, dovetail bearings, linear roller bearings, magnetic bearings, fluid bearings, X-Y tables, linear stages and machine slides.

One classic rail with sliding contact is a dovetail slide, and one classic rail with rolling contact is a ball rail with a recirculating system. Sliding-contact bearings are the more straightforward type of linear-motion component. These consist of a carriage or slide that rides over a surface known as a rail, way or guide. Sliding contact occurs when the moving part directly contacts the rail section. Older versions of these sliding-contact rails generated considerable friction during movement, so were only suitable for basic applications. However, newer versions have self-lubricating sleeves and other features to boost positioning accuracy and repeatability.

In contrast, rolling-element linear-motion systems are either recirculating or non-recirculating. Non-recirculating types use rolling elements such as bearing balls, rollers and cam followers for movement. Recirculating types use some type of moving platform that houses a bearing block. This bearing block contains raceways with rolling elements that let the platform move along the rail with little friction. Recirculating types include linear guides and ballbushing bearings.

More specifically, rolling-element linear guides come in two basic versions—those with circular arc grooves and those with Gothic arc grooves. These groove choices are a result of industry evolution that’s enabled new geometries for better load handling. Circular arc grooves contact bearing balls at two points. The Gothic arch contacts the balls at four points for bidirectional load capacity.

Another option for rolling-element linear motion is ball bushings that have a bushing nut lined with recirculating Water Dog Sliders from LM76 are bearing balls. This nut compliant with FDA, USDA, and 3A-Dairy regulations and have Corro-Slick-coated rides along a round shaft 300-series stainless rails and contoured to allow axial movement.

WDX Polymer blocks. They withstand washdown with chemicals and caustic foaming and run in temperatures from -400° to +180° F.

motioncontroltips.com | designworldonline.com

2/9/17 1:00 PM

SHAFT COLLARS & LOCKING DEVICES

Shaft collars & locking devices MECHANICAL CONNECTIONS attaching power-transmission parts, locking devices are a part of gears, drive shafts, sprockets, timing belt pulleys and more. Motion systems and rotary drive components rely on locking devices to remain running. Shaft collars work to set shaft position, space components on shafts and limit shaft movement.

In the world of power transmission and motion control, the connection of rotating components is either through positive form-fit connections or frictional connections. Positive form-fit connections are more traditional and the technology dates back centuries.

Most commonly they use a square key, which resides in notches cut into both the shaft and the hub. Another slightly more sophisticated positive form-fit connection is a spline with a mating star pattern instead of a square key. This boosts torque

density, as the stress is distributed across a larger number of small teeth rather than being concentrated on a relatively large single key. One caveat, they are more expensive to produce.

In more recent decades, mechanical engineers developed myriad frictional clamping devices as alternatives to positive form-fit connections. The advantage of frictional clamping is the shaft and hub are completely locked together in rotation, with no clearance between keys and keyways.

The shaft connections can withstand heavy vibration and alternating loads without wearing out.

Clamp style shaft collars with precise face to bore perpendicularity evenly distribute the axial load in impact situations making them suitable for mechanical stop applications.

motioncontroltips.com | designworldonline.com

Locking devices & shaft collars — PT Ref Guide 02.17 V2.indd 53

2 • 2017

DESIGN WORLD — MOTION

53

2/10/17 8:31 AM

Clamp-style collars use compressive forces to secure components to shafts without marring them like setscrews.

These collars distribute clamping force uniformly around the shaft (and not at one point) so users can easily adjust them without damaging the shaft. Clamp-style shaft collars are either one-piece or two-piece collars; the two-piece collar most evenly distributes force and creates the strongest hold.

While simple clamping collars are very common for light-duty applications, tapered conical clamping connections are preferred for transmission of higher torques. There are several different configurations, but all

This is a 30 RfN 4061 Shrink Disc from Ringfeder. Releasable mechanical shrink fits are often a better option than shrink fits with a torch and keyways or splines for reduced machining costs, easy installation and disassembly and easy adjustments for timing.

54

DESIGN WORLD — MOTION

Locking devices & shaft collars — PT Ref Guide 02.17 V2.indd 54

2 • 2017

rely on the same basic principle.

When two slightly tapered conical surfaces wedge against each other by flange screws, resulting radial pressure generated against the shaft and hub surfaces is sufficient to lock the components together with strength to transfer large forces.

Conical clamping type hubs provide further protection from torque overload and potential shaft slipping in high torque applications where a hard stop or aggressive load reversal takes place. These types of clamping hubs are typically manufactured from steel and generate high clamping pressure relative to normal application requirements.

Thus, conical clamping connections have become very popular as a way of reducing maintenance costs in heavy equipment, as well as increasing the level of precision in high speed manufacturing equipment.

Clamp-style shaft collars work as guides, spacers, and stops.

Clamp-style shaft collars distribute compressive forces evenly around the shaft for strong hold. Twopiece collars have more holding power than one-piece designs and install in place. In fact, machine integrators can add these collars to a design at any point in the manufacturing process.

Some shaft collars use fastening hardware that tests

The 1.25” RfN 7012 Locking Assembly shown here is typically used to lock gears, sheaves, flanges, rotors, wheels, sprockets, cams, propellers, impellers to shafts with a mechanical shrink fit by means of a torque wrench instead of a torch. Image courtesy Ringfeder.

motioncontroltips.com | designworldonline.com

2/10/17 8:31 AM

SHAFT COLLARS & LOCKING DEVICES

POWER TRANSMISSION

RETAINING DEVICES & maintenance & assembly tools BEARLOK

SHOELOK

BEARLOK Shrink Disc

BEARHUG

CLAMPNUT

TANGENTLOK

PRECISION NUTS & WASHERS

INCH and METRIC THREADS LEFT HANDED as well as RIGHT -HANDED

ADAPTER SLEEVE ASSEMBLIES

Materials of: CARBON, ALLOY and HARDENED ALLOY STEELS

Typically combining multiple functions to eliminate extra parts and improve mechanical efficiency and structural integrity, custom shaft collars like these can enhance drive system performance and add mounting or system integration capabilities. Image courtesy Stafford Manufacturing Corp.

Materials of: ALLUMINUM and CORROSION RESISTANT STEEL

beyond industry standards for maximum torque capabilities and holding power. For example, some stainless-steel shaft collars sport hardware that can also resist corrosion and satisfy regulatory standards; the stainless hardware undergoes surface treatment to prevent galling. Other clamp-style shaft collars come in steel with a black-oxide or zinc finish, aluminum, titanium, and engineered plastic. Black-oxide on steel resists corrosion and smooths screw installation to boost the transfer of screw clamping forces to the collar-shaft interface while preventing stick-slip.

Other keyless clamping devices include expansion shafts, fully split clamping hubs, as well as some others, each with their own unique purposes. As the field of precision motion control continues to develop faster, smaller, and more accurate systems, mechanical products are required to evolve to keep up with demands for acceleration and control that were not possible 50 years ago.

Performance issues related to backlash, size, inertia, and balance have all lead mechanical component suppliers to adapt to new standards and practices to eliminate shaft keys. While most keyless hub designs have existed for quite some time, their use in power transmission and motion control has increased widely over the past few years.

NUTS & WASHERS

HARDENED TONGUE WASHERS

SPLIT COLLAR

RETHREADING DIES

ADJUSTABLE SPANNER WRENCH

BEARING ASSEMBLY SOCKET

W

HI

TT

ET

-H

IG

GI

NS US

A

WHITTET-HIGGINS manufactures quality oriented, stocks abundantly and delivers quickly the best quality and largest array of adjustable, heavy thrust bearing, and torque load carrying retaining devices for bearing, power transmission and other industrial assemblies; and specialized tools for their careful assembly.

Visit our website–whittet-higgins.com–to peruse the many possibilities to improve your assemblies. Much technical detail delineated as well as 2D and 3D CAD models for engineering assistance. Call your local

or a good distributor.

33 Higginson Avenue, Central Falls, Rhode Island 02863 Telephone: (401) 728-0700 • FAX: (401) 728-0703 E-mail: info@whittet-higgins.com Web: www.whittet-higgins.com

2 • 2017

DESIGN WORLD — MOTION

Locking devices & shaft collars — PT Ref Guide 02.17 V2.indd 55

55

2/10/17 8:32 AM

Electric motors: THE BASICS

AC MOTORS Electric motors are usually divided into either ac – alternating current, or dc – direct current. The main difference is that ac motors take an input of ac current, while dc motors use dc current.

Speed control for ac motors is done by varying the voltage and frequency (along with the number of magnetic poles) while on dc motors control is achieved by varying voltage and current.

Another common way to categorize ac motors is by the magnetic principle that produces rotation. So there are two fundamental types of ac motors; induction and synchronous motors.

With induction motors, the key idea is the rotating magnetic field. The most common source of this is the squirrel cage configuration. This is essentially two rings, one at each end of the motor, with bars of aluminum or copper connecting the two ends.

Induction motors have properties that make them well suited to a number of industrial as well as home appliance applications. For starters, they are simple and rugged motors that are easy to maintain.

They also run at constant speed across a wide range of load settings, from zero to full-load.

The other type of ac motor is a synchronous motor. Synchronous motors are so named because they run synchronously with the frequency of the source. The motor speed is fixed and doesn’t change with changes to the load or voltage. These motors are primarily used where the requirement is precise and constant speed. Most synchronous motors are used in heavy industrial applications, with horsepower ratings ranging from the low hundreds up to thousands of hp.

Synchronous motors can be used in motion control applications, but there are some down sides to using these motors. Because of the rotor size, the motor’s response in incrementing applications is typically not good. Also, because acceleration of 56

DESIGN WORLD — MOTION

Motors — PT Ref Guide 02.17 V1.indd 56

2 • 2017

Brushed dc motors, such as the Athlonix 17DCT brush dc mini motor from Portescap, deliver high torque per ampere, resulting in longer battery life. With a 17-mm diameter, such small, powerful motors find use in a range of applications from medical and industrial pumps and drug delivery systems to miniature industrial power tools.

inertial loads may not be as high as other motor types, these motors may operate at irregular speeds and produce undesirable noise. And generally, synchronous motors are larger and more costly than other motors with the same horsepower rating.

DC MOTORS A dc motor generates a magnetic field via electromagnetic windings or permanent magnets.

According to most common industry naming conventions, there are three dc motor subtypes: brush motors, permanent-magnet (PM) motors, and universal motors. Many larger dc motors still employ brushes and wound fields, but PM motors dominate fractional and integral-horsepower applications below 18 hp.

In a brushed dc motor, the magnet acts as the stator. The armature is integrated onto the rotor and a commutator switches the current flow.

The commutator’s function is to transfer current motioncontroltips.com | designworldonline.com

2/10/17 2:13 PM

Right Choice.

Unparalleled Reliability.

Whether you’re designing a new material handling machine or replacing a unit that’s seen better days, Baldor•Reliance® industrial gearmotors are the right choice to put your application in motion.

• Drop-in Replacement

With unlimited custom capabilities and a wide array of drop-in replacement configurations in stock, every Baldor•Reliance industrial gearmotor features proven technology, quieter operation and unparalleled reliability.

• Right Angle and Parallel Shaft

baldor.com

• Unmatched Quality

479-646-4711

©2017 Baldor Electric Company

BAL DW gearmotors ad FVA.indd 1 Baldor —REL PT Ref Guide 02.17 V1.indd 57

• Unlimited Custom Designs

• Industry Proven Technology

http://esp.to/wPnBsI

1/10/17 9:29 2:09 AM PM 2/10/17

from a fixed point to the rotating shaft. Brushed dc motors generate torque straight from the dc power supplied to the motor by using internal commutation, fixed permanent magnets, and rotating electromagnets.

Brushless dc (BLDC) motors, on the other hand, do away with mechanical commutation in favor of electronic commutation, which eliminates the mechanical wear and tear involved with brushed dc motors. In BLDC motors, the permanent magnet is housed in the rotor and the coils are placed in the stator. The coil windings produce a rotating magnetic field because they’re separated from each other electrically, which enables them to be turned on and off. The BLDC’s commutator does not bring the current to the rotor. Instead, the rotor’s permanent magnet field trails the rotating stator field, producing the rotor field.

STEPPER MOTORS One of the most common motors used in motion control applications is the stepper motor. They’re used mostly in positioning applications and have the advantage of being able to be accurately controlled for the most precise positioning applications, down to fractions of a degree without the use of feedback devices such as encoders or resolvers. They operate open-loop (not closed-loop), without the need for tuning parameters as in closed-loop servo systems.

Steppers are generally classified by the number of allowable steps they can be commanded to move. For instance, a 1.8 degree step motor is capable of 200 steps/revolution (1.8 x 200 = 360 degrees, or one full revolution) in full-step mode. If operated in half-step mode, each step becomes 0.9 degrees and the motor can then turn 400 steps/revolution. Another mode called microstepping subdivides the degrees per step even further, allowing for extremely precise movements.

Stepper motor technologies including permanent magnet motors, variable reluctance, and hybrid types. The principle of operation for stepper motors is fairly straightforward. Traditional variable reluctance stepper motors have a large number of electromagnets arranged around a central gear-shaped piece of iron. When any individual electromagnet is energized, the geared iron tooth closest to that electromagnet will align with it. This makes them slightly offset from the next electromagnet so when it is turned on and the other switched off, the gear moves slightly to realign. This continues with the energizing and de-energizing of individual electromagnets, thus creating the individual steps of motion.

Stepper motors are relatively inexpensive and can be run open loop, requiring no feedback devices. Also, because the speed is proportional to the frequency of

the input pulses, a wide range of speeds is attainable. However, while stepper motors are capable of producing high torque at low speeds, they generally are well suited for lower power applications not for applications requiring lots of torque to move heavier loads. They are best for applications requiring the control of rotation angle, speed, and position.

A few drawbacks are that not properly controlling the motor can produce undesired resonance in the system. Also, stepper motors are generally not easy to operate at extremely high speeds. And as the motor speed increases, torque decreases.

A stepper motor’s low-speed torque varies directly with current. How quickly the torque falls off at higher speeds depends on a number of factors such as the winding inductance and drive circuitry including the drive voltage. Steppers are generally sized according to torque curves, which are typically specified by the manufacturer.

SERVOMOTORS The hallmark of any servomotor is the presence of feedback and closed-loop control. Servomotors provide precise control of torque, speed or position using closed-loop feedback. They can also operate at zero speed while maintaining enough torque to maintain a load in a given position.

Servomotors have several distinct advantages over other types of motors. For starters, they offer more precise control of motion. This means they can accommodate complex motion patterns and profiles more readily. Also, because the level of precision offered is high, the position error is greatly reduced.

Motor configurations go beyond standard rotary or linear, as shown here with an un-housed arc segmented frameless brushless torque motor from H2W Technologies. The low-inertia moving coil assembly is suitable for applications needing high angular acceleration.

58

DESIGN WORLD — MOTION

Motors — PT Ref Guide 02.17 V1.indd 58

2 • 2017

motioncontroltips.com | designworldonline.com

2/9/17 1:13 PM

MOTORS

All servomotors require a form of feedback, often with the feedback device, such as an encoder, built right into the motor frame. The feedback signal is needed by the control circuitry to close the control loop. It is this closed-loop control that gives servomotors their precise positioning ability.

Servomotors are used in many different industrial applications from machine tools, packaging machinery, communications and robotics applications to newer applications such as solar panel control and a broad range of automation control applications. The diversity of applications means that servomotors are designed for general-purpose indoor environments but also for specialized situations requiring them to withstand extreme temperatures and pressures outdoors as well as the special demands of food processing industries in washdown environments.

How are servomotors typically classified?

That’s not an easy question to answer, since there are many ways to categorize motors and manufacturers often use different terminology to describe the same type of motor. This can make deciphering motor classifications a bit confusing. To help cut through the confusion, here is a guide to motor terminology and a brief explanation of which types are most commonly used in servo systems.

There are three main ways to classify motors: by their current—ac or dc; by the way in which they achieve commutation—brushless or brushed; and by the speed of their rotating field (rotor)— synchronous or asynchronous.

Ac vs. dc The most basic classification of a motor is whether it’s an ac or dc motor. From a performance standpoint, the primary difference between ac and dc motors is in the ability to control their speed.

In a dc motor, speed is directly proportional to the supply voltage (given constant load, or torque, on the motor). Ac motor speed is determined by the frequency of the applied voltage and the number of magnetic poles.

While both ac and dc motors can be used in servo systems, ac motors can withstand higher current and are more commonly used in industrial servo applications.

Brushed vs. brushless When discussing dc motors, the next point of differentiation is whether the motor is commutated mechanically, with brushes, or electronically, without brushes. Brushed motors are generally less expensive and simpler to operate, while brushless designs are more reliable, have higher efficiency, and are less noisy.

Brushed dc motors are further sub-divided according to the construction of their stators: series-wound, shunt-wound, compound-wound, or permanent magnet. While the majority of motors used in servo systems are brushless designs, brushed

motioncontroltips.com | designworldonline.com

Motors — PT Ref Guide 02.17 V1.indd 59

permanent magnet dc motors are sometimes employed as servomotors for their simplicity and low cost. The most common type of brushed dc motor used in servo applications is the permanent magnet dc motor.

Brushless dc motors replace the physical brushes and commutator with an electronic means of achieving commutation, typically through the use of Hall effect sensors or an encoder. Brushless dc motors are also used in servo systems.

Ac motors are generally brushless, although there are some designs—such as the universal motor, which can run on either ac or dc power—that do have brushes and are mechanically commutated. Terminology for brushless ac (BLAC) motors can be quite confusing, as they are also referred to as permanent magnet ac (PMAC) motors or permanent magnet synchronous motors (PMSM).

Synchronous vs. asynchronous While dc motors are generally categorized as brushed or brushless, ac motors are more frequently differentiated by the speed of their rotating field— i.e. synchronous or asynchronous. In a synchronous motor, the rotor rotates at the same speed as the stator’s rotating magnetic field. In an asynchronous motor, normally referred to as an induction motor, the rotor rotates at a speed slower than the stator’s rotating magnetic field.

When induction motors are paired with variable frequency drives, they can achieve speed control and performance similar to servomotors, although they typically don’t incorporate feedback, and therefore, are not true servo devices.

Brushless ac (BLAC, aka PMSM or PMAC) and brushless dc (BLDC) motors are synchronous, and both types are frequently used as servomotors. In fact, some of the most common high-performance industrial servomotors are 3-phase, synchronous, brushless ac motors.

2 • 2017

DESIGN WORLD — MOTION

59

2/9/17 1:13 PM

The CXY-BS Series 150-mm Precision XY Motion Platform from Griffin Motion is a compact, lowprofile, ball-screw-drive stage with high levels of orthogonality (10 arc-sec) and parallelism, enabling 150 mm of precise XY travel with 10 µm linear accuracy and 1 µm linear repeatability.

Positioning stages: THE BASICS

POSITIONING STAGES and tables are a part of many motion systems. In fact, they’re used in a wide range of high-performance applications such as industrial robots, fiber optics and photonics, vision systems, machine tools, semiconductor equipment, micromachining, electronic manufacturing, and other industrial automation applications.

Stages have continued to improve with key developments including better mechanical components and innovations in feedback and control that are improving metrology, particularly in high-end stages. The result is that today’s positioning stages can do many things including making moves with incredible accuracy, synchronizing complicated axis commands, and optimizing travel from coarse and fine drives in tandem, closing the loop on one common position feedback.

Stages provide several different types of motion including linear, rotary, or lift types (Z-axis positioning stages). They can be configured in many different ways including movement in one direction (or axis) only, in multiple directions 60

DESIGN WORLD — MOTION

Positioning Stages — PT Ref Guide 02.17 V1.indd 60

2 • 2017

(X-Y positioning), or for extremely small and precise movements, as in nanopositioning applications where moves are in the micro- or nanometer range. (See sidebar on nanopositioning.)

Drive mechanisms for positioning stages can vary significantly, depending on a number of factors including cost and desired accuracy. For example, stages can be direct-drive types driven by linear servomotors or by a combination of motors and gearing and couplings, and can be linear or rotary actuator driven (either using electric actuators, or even pneumatic of hydraulic actuation). Other methods can include belt and pulley systems, ballscrews or leadscrews.

Precision and accuracy requirements can dictate design decisions involved in stage components. An example of this is the use of air bearings in stages where reliability and high accuracy are needed. These bearings support a load with a thin film of pressurized air between the fixed and moving elements.

Unlike ordinary bearings, the surfaces of an air bearing do not make mechanical contact, so these systems do not need to be lubricated. Because the surfaces do not wear, the systems don’t generate particulates, which makes them suitable for clean-room applications.

motioncontroltips.com | designworldonline.com

2/9/17 9:42 AM

POSITIONING STAGES

What are some options for nanopositioning?

Nanopositioning—positioning on the scale of onebillionth of a meter—is a common requirement in semiconductor and medical applications, such as metrology, scanning, dispensing, and pumping. But consistently achieving nanometer-level resolution is beyond the scope of most devices that use mechanical rolling or recirculating elements.

One of the most common solutions for nanopositioning is the piezo motor (also referred to as a piezo actuator), which uses no mechanical bearings or transmission components. Piezo motors operate on the reverse piezoelectric effect, which induces a mechanical stress on a piezo material when an electrical charge is applied. Piezo actuators take advantage of this effect to produce motion (expansion or contraction) and force.

But while their speed and force capabilities are relatively high for their small size, piezo actuators don’t fit all nanopositioning applications. In some cases, a linear motor stage or voice coil actuator is a better choice, depending on the performance criteria.

Linear motors Linear motors are direct-drive, non-contact devices, and as such, they don’t suffer from the effects of friction, compliance, or backlash. This allows them to produce nanometer-level motion. Linear motor stages can be driven by either ironless motors, for lower mass and higher acceleration, or by iron core motors, for higher forces. When used in nanopositioning applications, linear motor stages are typically integrated with either air bearings or crossed roller slides for support and guidance.

Linear motor stages offer two primary benefits over piezo actuators: stroke and load/force capability. In general, piezo actuators are when the application calls for strokes of a few inches or less, for rapid, oscillating motion, or for high holding force when powered off. Linear motors, on the other hand, are typically used for strokes greater than a few

motioncontroltips.com | designworldonline.com

Positioning Stages — PT Ref Guide 02.17 V1.indd 61

inches and can be built in lengths up to several meters. This is beneficial, for example, in medical imaging equipment, where the overall stroke is quite long, but the positioning resolution required is in the nanometer range. Linear motors can also achieve high acceleration and simultaneously produce thrust forces in the thousands of Newtons.

However, linear motor stages have a much larger footprint than piezo actuators, making them a challenge to integrate into small devices.

Voice coils Voice coil actuators are similar to piezo actuators in size and footprint, but their operating principle is more like that of linear motors, consisting of a coil and a permanent magnet field. When current is applied to the coil, the motor moves in one direction, generating a force proportional to the current. When the direction of the current is reversed, the actuator moves in the opposite direction.

Like linear motors, voice coils can be integrated with crossed roller slides or, more commonly, with air bearings for guidance and load support. Unlike ironcore linear motors, voice coil actuators don’t suffer from the effects of cogging, giving them extremely smooth motion. Although they can achieve longer strokes than piezo actuators, voice coil actuators are still somewhat limited in stroke length. Maximum stroke for a voice coil actuator is typically 5 to 6 inches. Longer strokes are possible, but efficiency decreases in proportion to the actuator’s length.

Voice coil actuators, like piezo actuators, can be configured to provide either linear or rotary motion. In linear motion applications, they’re commonly used to supply force or pressure control, whereas in rotary applications they supply torque.

Although voice coils supply high force (or torque) for their size, piezo actuators generally provide higher continuous, intermittent, and holding forces.

2 • 2017

DESIGN WORLD — MOTION

61

2/9/17 9:42 AM

sto Fe g e. m f ro l i n k a p ion etu r s -pin d pe rip k-an g c s Thi s a ra use

rack-and-pinion HOW

SETS WORK

This roller-pinion system from Nexen Group acts a cam and follower. Its cycloidal contact curves means there’s no slipping.

Rack-tooth geometry minimizes backlash by loading pairs of pinion rollers in opposition.

62

Today’s rack-and-pinion sets are precision mechanical devices that can deliver performance rivaling that of electromechanical alternatives. They are useful in everything from small consumer devices that move a few ounces to large industrial machinery that moves tons of load. That includes off-highway machinery, food-processing, packaging lines and other applications that involve reciprocating motion.

Here’s how rack and pinions work: A parallelaxis gearset converts rotary motion to linear motion through a motor-driven pinion (essentially a specialty spur gear or engineered roller) that engages the rack (which is essentially a gear of infinite diameter).

In rare cases, an input moves the rack to get pinion rotation. Usually, rack-and-pinion sets get paired with servomotors or (less commonly) with step motors.

One rack-and-pinion variation is based on a roller pinion. These ultra-quiet rack-and-pinion sets have a pinion of bearing-supported rollers instead of a spur gear. Rollers ride the rack-tooth surfaces for 99% and repeatability to about 2.5 μm from one direction (or better than 5.8 μm from both). Manufacturers also make the rollers with meshing geometry to trace paths tangent to tooth faces. So, the rollers glide into engagement with the rack teeth, which eliminates the wear and inaccuracy from sliding friction and tooth slap of some rack-and-pinion sets.

Rack-and-pinion sets can operate without enclosures or protective covers; they are efficient to 98% or better; and many exhibit backlash of 1 arc-min or less. Another strength is that they’re often less expensive than comparable linear motors when stroke lengths are long … so that a rack-and-pinion set may cost half of what a linear motor costs … especially for many-meter strokes. Rack-and-pinion sets sometimes perform better than ballscrew actuators

DESIGN WORLD — MOTION

Rack & Pinion — PT Ref Guide 02.17 V4.indd 62

2 • 2017

because they’re not affected by adjacent bearings, couplings, or bores; they’re also immune to stiffness degradation, even over long lengths.

ADDRESSING THE ISSUE OF BACKLASH Manufacturers often preload rack-and-pinion sets to boost stiffness and eliminate backlash. There are a few ways to do this. One option is to run twin pinions concurrently, with a slave pinion that gently opposes the drive force. This setup usually reduces efficiency, but boosts machine dynamics and stiffness. A more sophisticated variation of this approach is to use the motion controller to apply preload electronically. Such controls maximize preload but reduce opposing slavepinion force when the drive pinion accelerates. During constant-speed strokes, the slave pinion mirrors the action of master pinion, and the two drive in tandem.

When the axis decelerates, the slave pinion engages the opposite tooth flank, increases force opposing drive force, and helps slow the load.

This dynamic rack-and-pinion system from Wittenstein can drive linear motion to unlimited travel lengths. Some preassembled versions run true to 10 µm; those with actuators and servogears exhibit less backlash than standard setups.

motioncontroltips.com | designworldonline.com

2/9/17 1:17 PM

RETAINING RINGS

In this assembly, keys and retaining rings secure gears to the shaft. Image courtesy Konstantinos Oikonomopoulos

HOW TO

SPECIFY

retaining rings

RETAINING RINGS are fasteners that (when installed in a groove) hold components on shafts or in a housing. Three types are tapered section, constant section and spiral retaining rings.

Tapered section rings typically show a decreasing thickness from the center of the ring out to the ends. They can be mounted either axially or radially. The taper is there to ensure full contact with the groove when installed.

Constant section retaining rings have a constant width around the circumference of the ring. When installed, these rings do not maintain uniform contact with the entire component. They take on an elliptical shape and contact the groove at three points. Spiral retaining rings are installed into the housing or onto the shaft, making full contact with the groove and component. Their grooves are relatively shallow, so their load bearing capability is reduced. Spiral rings are often selected when full contact with the retained component or a lower axial profile is required.

Spiral rings have no protruding ears to interfere with mating components in an Spiral retaining rings do not need special tools for removal. The removal notches on the rings make it easy to extract from a groove. Image courtesy Smalley Steel Ring Co.

motioncontroltips.com | designworldonline.com

Retaining Rings — PT Ref Guide 02.17 V3.indd 63

assembly. The ring has a uniform cross-section and no gap or lugs for a functional and aesthetically pleasing ring. Unlike traditional fasteners, retaining rings eliminate machining and threading, reducing costs and weight. Spiral retaining rings do not require special tools for removal and are supplied standard with removal notches for easy extraction from a groove.

When selecting a retaining ring for an application, answer these questions to determine which retaining ring is most suitable.

What kind of assembly is the application — housing or shaft?

Next, determine the main critical dimensions. These include the housing or shaft diameter, groove diameter and the groove width.

What is the rotational speed of the assembly?

After calculating this value, determine the maximum thrust applied to the ring. (Designers define this thrust as either a light, medium or heavy-duty load.) Maximum thrust value helps determine if groove deformation or ring shear could be a problem. Basically, groove deformation occurs because the groove material is soft, which in turn limits maximum capacity. Ring shear occurs when the groove material is hardened but the load exceeds the ring’s maximum capacity.

Will the retaining ring be exposed to temperature and presence of corrosive substances?

This dictates the most suitable choice for ring material.

2 • 2017

DESIGN WORLD — MOTION

63

2/9/17 1:34 PM

Wire rope isolators, such as these designs from ITT Enidine, are a cost-effective way to reduce vibration and fatigue on machnes. Usually constructed of carbon steel, stainless steel or aluminum, they are highly resistant to corrosive and harsh environments.

shock & vibration damping OVERVIEW OF

TECHNOLOGIES

MOTION IS PRESENT in almost all industrial automation systems, and changing this motion’s direction or stopping it altogether can create damaging shock and vibration. Sometimes this damage may be immediate and sometimes it can cause fatigue over extended periods of time.

This is why using shock and vibration attenuating components to decelerate a load smoothly and precisely is a necessity.

64

DESIGN WORLD — MOTION

Shock Absorbers — PT Ref Guide 02.17 V4.indd 64

2 • 2017

The most common types of shock and vibration attenuating components are shock absorbers, linear dampers, wire rope or spring isolators, elastomeric isolators, air springs, and structural damping materials.

These devices help manufacturers reduce equipment downtime and costly cycle time limitations.

Most shock absorbers achieve their damping characteristics through the use of hydraulic fluids. The fluid is pushed by a piston and rod through small orifice

motioncontroltips.com | designworldonline.com

2/9/17 9:50 AM

ITT Enidine 1-17.indd 65

2/10/17 9:14 AM

Depiction of Frequency Waves

holes to create damping, and this action compresses some type of gas.

This in turn creates a spring force to return the rod back to its starting position when the load is removed.

Shock absorbers and dampers are generally made of high-strength steel to handle the pressures from the internal hydraulic forces.

Elastomeric seals prevent the fluid from leaking out of the cylinder, and special plating and coatings keep the units protected from harsh operating environments.

Vibration isolation products rely generally on mechanical designs to achieve their isolation characteristics. A spring function provides support for the mounted equipment, while decoupling it from the vibration source. Friction and elastomeric material properties give the isolators their damping characteristics.

Isolators can be made from a variety of materials. Wire rope and spring isolators can be made from carbon steel, stainless steel or aluminum. Elastomeric isolators generally have metallic components that function as mounting brackets, separated by an elastomeric material that provides the stiffness and damping desired. Common elastomeric compounds include natural rubber, neoprene and silicone; however, a vast selection of compounds and compound blends can be used to achieve different characteristics specific to the application.

Air springs are comprised of metallic end fittings coupled by a composite elastomericbased bladder that contains the compressed air used to provide isolation. These singleacting designs are comprised of a pressurized bladder and two end plates. As air is directed into the air bladders, they are expanded VIBRATION linearly.

Energy or power dissipation is key when selecting a damper or shock-absorbing device. The size and characteristics of the device are based on these inputs, so it is generally the first consideration to make.

Dynamic spring rate and damping are the two biggest considerations when selecting an MADE IN THE U.S.A. isolator. These characteristics will define the natural frequency (sometimes referred to as 800.838.3906 resonant frequency) of the isolation system and are important in achieving the desired performance.

INNOVATING SHOCK & SOLUTIONS

www.sorbothane.com 66

DESIGN WORLD — MOTION

Shock Absorbers — PT Ref Guide 02.17 V4.indd 66

2 • 2017

motioncontroltips.com | designworldonline.com

2/9/17 9:50 AM

SHOCK & VIBRATION DAMPING

Deceleration & & Vibration VibrationDeceleration & V Deceleration Deceleration & Vibration Technology: Technology: Technology: Technology:

Expect more more Expect Expect moreExpect mo than Automation Automation than than Autom than Automation Control!

Control!

Control!

Control!

Motion Control Motion Control CustomMotion controlControl Custom control of handCustom forces control of hand forces of hand forces

Elastomeric and synthetic pads reduce shock and vibration

Motion Co Custom con of hand forc

Vibration Control Vibration Control Vibration Isolate unwantedControl Isolate unwanted Isolate unwanted vibrations vibrations vibrations

Elastomer and other synthetic and rubber pads can also damp vibration and isolate shock loads. They are available in a number of shapes, including tubes, bushings, blocks, pads and washers. These components are commonly used in heavy-duty applications to create strong cushioning plates or foundations in heavy machinery such as cranes, presses, and also for vibration reduction in lab and testing equipment, aerospace, and for pipelines and bridges.

The rubber-like materials with which they are designed allow these padding materials to meet specific requirements, such as natural frequency, load, and area. And because they are soft, they are forgiving in most environments.

Predicting the natural frequency of an application lets material manufacturers target known disturbance frequencies to dissipate energy.

The lower the ratio of natural system frequency to disturbance frequency, the more it’s possible to isolate problem vibrations. These cushioning plates can protect machinery subsystems against impacts and isolate vibration and structure-borne noise. For example, PAD plates from ACE Controls withstand compressive loads to 10,000 psi (69 N/mm2) depending on plate form and size.

Safety Safety Safety Safety Products Products Products Products Protection Protection Protection Automation for all Protection Automation for all for all Automation Control for all machine Control machine machine Control Optimum tuning designsmachine under Optimumdesigns tuning under designs under Optimum for any design tuning designs under any condition for anyany design any condition condition for any design any condition

Another custom product called Sorbothane (from a company with the same name) is a thermoset that attenuates shock with near-faultless memory. That means its deformation is elastic and not plastic, so pads of the material reliably return to their original shape. Custom pieces of the material work for vibration damping, acoustic damping and isolation. Sorbothane works by turning mechanical energy into heat as the material is deformed. Molecular friction generates heat energy that translates perpendicularly away from the axis of incidence.

07.01.16 18:07 07.01.16 18:07

com com or our product ww.acecontrols.com

67

ontrols.com

ol l

Shock Absorbers — PT Ref Guide 02.17 V5.indd 67

DESIGN WORLD — MOTION

More Info?

More Info?

More Info?

Tel. 800-521-3320 More Info?

Tel. 800-521-3320 Tel. 800-521-332 Email: shocks@acecontrols.com Tel. 800-521-3320 Email: shocks@acecontrols.com Email: shocks@a Email: shocks@acecontrols.com Download a CAD file or our product Download a CAD file or our product Download a CAD sizing software at: awww.acecontrols.com Download CAD file or our product sizing software at: www.acecontrols.com sizing software a sizing software at: www.acecontrols.com

y ACE

2 • 2017

by ACE

by ACE

by ACE

Automation Control Optimum tuning for any design

ibration Control Isolate unwanted vibrations

Anti-Vibration Leveling Mounts like these from Sorbothane are designed to handle a wide range of loads and varying environmental conditions.

2/10/17 2:31 PM

How do you specify industrial shock absorbers?

Several criteria should be considered when selecting industrial shock absorbers. Typically the most important is the physical space that is available to mount the device.

Incorporating a shock absorber that has the longest stroke available will make it easier for the shock absorber to achieve the desired goal of a smooth, continuous deceleration. Other attributes that should be considered are the environment where the unit will be installed, whether there will be significant contaminants that will come into contact with the shock, and the temperature where the shock will be installed.

Extreme heat or cold can have dramatic effects on the shock absorber and should always be taken into account when sizing a new application.

A highly corrosive environment may require the use of anticorrosion measures to prevent a premature failure. Materials such as stainless steel and aluminum may be available to ensure proper operation of the shock absorber. Additionally, coatings and treatments are available that can also be used to prevent a shock absorber from prematurely rusting.

Industrial shock absorbers are properly sized based on the load being controlled, the velocity at which the load is traveling upon contact, and any additional, external forces

Everything we do hinges on you.

being applied (e.g., a hydraulic cylinder providing an additional amount of propelling force). The combination of these inputs results in the amount of energy that the shock absorber will be required to deal with. This energy, typically noted as the “Energy per Cycle” will determine the size and stroke of the shock absorber required. It is also important to calculate the number of cycles that the shock absorber will be used in an hour. This will determine the necessary “Energy per Hour” calculation and will also be used to properly size the application. A shock absorber converts the energy of the impact into heat and the more that the shock is hit, the more heat it will generate. Too much heat can lead to a failure.

Shock absorbers and gas springs extend machine life and boost machine quality by reducing the banging, slamming, or bouncing that can occur when a machine has to make a sudden change in direction or a complete stop. Image courtesy of ACE Controls.

Weber Knapp, leading manufacturer of mechanical motion control solutions, invites you to explore your possibilities with the first Design Your Own (DYO) custom online application.

Vectis™ utilizes standard parts while taking advantage of computer numerically controlled (CNC) capabilities; providing custom characteristics unique to your application. You design it - we build it.

Using our proprietary DYO software, simply plug in your product’s critical load parameters - lid weight plus lid center of gravity (CG) to hinge pivot axis dimensions. The slide bar variables will calculate the optimum torque curve to fine tune the open and close feel; making products more reliable and user friendly.

Select the model and quantity desired. Order one or as many as your project requires without the costly expense of tooling or engineering.

See the new Vectis™ line at vectiscounterbalance.com or call the Vectis™ Help Line at 800.828.9254 x263

A proud US employer and manufacturer since 1909, Weber Knapp provides the highest quality engineering and performance in all the products we manufacture.

Made in the USA

Weber Knapp Company weberknapp.com

Shock Absorbers — PT Ref Guide 02.17 V5.indd 68

2/10/17 2:18 PM

WAVE SPRINGS

wave springs

THE BASICS OF

A SPRING is a device that stores mechanical energy. There are almost as many variations of wave springs as there are spring applications.

Although often out of sight, these springs are essential in many motion-control applications— including gear assemblies, actuators, rotary unions and different kinds of clutches—and consumer applications.

There are three types: tension, compression and torsion. Tension springs operate in tension with a load attached, so as the application applies load, this spring stretches out. Compression springs, as the name implies, operate under compression, so as the application applies load, this spring becomes shorter. Torsion springs operate under twisting loads, which means the application applies torque to the spring.

UPDATE FOR 2017: DEVELOPMENTS IN WAVE-SPRING TECHNOLOGY

There’s been a move to miniaturize assemblies, and wave springs help on this front. That’s because they provide a lot of spring force from compact designs. That lets designers reduce the size and weight of their finished assemblies.

More recent changes in the design of wave springs include new materials and end configurations that offer weight and space benefits for critical applications. All wave springs act as a stack of wave washers that maintain alignment, and some newer wavespring designs (including nested and interlaced variations) boost fatigue and load ratings.

MORE ON LEADING VARIATIONS FOR INDUSTRIAL DESIGNS

Compression springs are the most common wave spring type. Manufacturers make these out of coiled flat wire with waves added along the coils for more spring effect. Such wave springs can replace conventional round-wire compression springs in applications that have

motioncontroltips.com | designworldonline.com

Wave Springs — PT Ref Guide 02.17 V2.LE.indd 69

One advantage of wave springs is that they save space. Because the springs have shorter operating heights, they can fit into smaller spring cavities. That lets engineers make assemblies lighter and more compact, which in turn reduces overall design cost.

minimal space but need tight load deflection. As an alternative to other coil springs, wave springs occupy 30 to 50% of the compressed height space of comparable round-wire springs with the same deflection and load specifications. Manufacturers typically make wave springs from a single filament of flat wire formed in continuous precise coils with uniform diameters and waves … most commonly out of 17-7pH hardened stainless steel.

Manufacturers make the springs with either plain ends (for wavy) or squared-flat ends (with shim ends).

Wave springs operate as load bearing devices. They take up play and compensate for dimensional variations within assemblies. They can produce a range of forces whereby loads build either gradually or abruptly to reach a predetermined working height. This establishes a precise spring rate in which load is proportional to deflection.

Some manufacturers offer single, nested and multi-turn wave springs. A singleturn wave spring with overlapping ends saves axial space so that more space is given for travel. The spring clings to the bore, which saves more radial space. The overlapping ends prevent radial jamming because a circumferential movement is allowed. The spring ends could move against each other so that the specification load at work height is always given.

Nested wave springs suit applications requiring higher forces to meet safety regulations, such as those in government or military applications. A nested wave spring provides a higher load than a single-turn wave spring (a stamped wave washer) and uses the same radial space as a single-turn design.

Multiple-turn wave springs do not cling to the bore, because radial jamming affects the specified load at work height. If the design of the multi-turn wave spring results in peripheral movement of the turns against each other, this can render the spring unstable.

Compared to a single-turn design, longer travel or deflection is possible because the deflection in total is split. Every turn must tolerate less deflection than a single-turn design. Use of a multi-turn wave spring can also save 50% in axial space compared to a traditional coil spring. What’s more, these springs eliminate the risk of torsional movements during compression to work height … a real problem with coil springs. In contrast, a wave spring always applies its load in an axial direction.

Wave springs also apply very consistent loads within a small tolerance range at different work heights. That lets design engineers easily adjust the application to meet given requirements when needed.

HOW TO SELECT A WAVE SPRING?

Although wave spring applications abound, there is a basic set of rules to define spring requirements and determine whether a design can use a stock or standard spring or needs a special wave spring. The first and most important consideration is the load the application will apply to the wave spring. Required load is defined as the amount of axial force the spring must produce when installed at its work height.

2 • 2017

DESIGN WORLD — MOTION

69

2/9/17 1:48 PM

Some applications require multiple working heights so that there are critical loads at two or more operating heights.

Often minimum and maximum loads are satisfactory solutions, particularly where tolerance stack-ups are inherent in the application.

In any case, remember to consider whether the This is a Smalley wave spring in an industrial application. The crest-to-crest spring will be subject to spring applies force to keep a seal and high temperature, dynamic prevent leakage from one pressurized side of a rotary union to the other. loading (fatigue), corrosive media or other unusual operating conditions.

Solutions to various environmental conditions typically call for special materials that withstand operating stresses.

Wave springs install into working cavities. These usually consist of a bore (in which the spring operates) or a shaft that the spring clears. The spring stays positioned by piloting in the bore or on the shaft. The distance between the loading surfaces defines the axial working cavity or the spring’s work height. This is where the spring’s material cross-section is important to the overall design.

Four critical factors dictate the most suitable wave spring for a given application: physical design constraints (including bore geometry, shaft, ID, OD and so on), the application load, the working height at which the design applies load, and the spring material that will best withstand the application environment.

If a spring is designed for a static application, make sure that the percent stress at working height is less than 100%. Springs will take a “set” or length loss in operation due to the high stress condition of the spring, if subjected to a higher stress. If a spring is designed for a dynamic application, make sure that the percent stress at working height is less than 80%. Springs will take a set if put under higher stress. If the work height per turn is less than twice the wire thickness, the spring operates in a non-linear range and actual loads may exceed calculated loads.

• Number of turns must be between 2 and 20 • Number of waves per turn (N) must be in half-turn increments • Minimum radial wall = (3 times the wire thickness) • Maximum radial wall = (10 times the wire thickness) One caveat: It’s best to avoid situations that compress a wave spring to solid. In addition, account for the expansion of the OD as well as the OD tolerance when designing a spring to fit in a bore or over a shaft.

70

DESIGN WORLD — MOTION

Wave Springs — PT Ref Guide 02.17 V2.LE.indd 70

2 • 2017

Here are basic formulas to narrow down the wave spring type, shape and size that best suit an application. Note that wave springs are helping today’s push toward design miniaturization. Smaller designs need shorter and smaller diameter wave springs. That’s spurred some developers to make wave springs less than 0.250 in. in diameter.

Formulas: Operating Stress: S = (3πPDm)/4bt2 N2 Where: S = operating stress P = load in pounds Dm = mean diameter in inches b = radial width of material in inches t = thickness of material in inches N = number of waves per turn Fatigue Stress Ratio: x = s-s1/s-s2 Where: s = Material tensile strength s1 = Calculated operating stress at lower working height (must be less than s) s2 = Calculated operating stress at upper working height Deflection: f = ((PKZDm3)/(Ebt3N4)) x (ID/OD) Where: f = deflection in inches P = load in pounds K = multiple wave factor Dm = mean diameter in inches Z = number of turns E = modulus of elasticity b = radial width of material in inches t = thickness of material in inches N = number of waves per turn Spring Rate: R = (P/f) = (Ebt3N4)/(KZDm3) x (ID/OD) Where: R = Spring rate in pounds/inch P = load in pounds f = deflection in inches E = modulus of elasticity b = radial width of material in inches t = thickness of material in inches N = number of waves per turn K = multiple wave factor Dm = mean diameter in inches Z = number of turns

motioncontroltips.com | designworldonline.com

2/9/17 1:49 PM

HOW DO I KNOW IF I’M TALKING TO AN ENGINEER OR A SALESMAN? Ask Smalley. We have nothing against sales people. But when it comes to differentiating Inconel from Elgiloy or overcoming dimensional variations within a complex assembly, wouldn’t you rather work with an engineer?

Our customers would. That’s why they collaborate directly with our world-class team of Smalley engineers—experienced professionals whose only focus is helping you specify or design the ideal wave spring, Spirolox® retaining ring or constant section ring for your precision application.

Smalley wave springs reduce spring operating height by 50%, saving space and weight, fitting tight radial and axial spaces. We offer more than 4,000 stock sizes in carbon and stainless steel.

Visit smalley.com for your no-charge test samples.

Smalley Wave Spring

Coil Spring

THE ENGINEER’S CHOICE™

38139_Smalley_BrandAd_DesignWorld_r3.indd 1 Smalley 10-15.indd 71

9/1/15 2:16 3:43 PM PM 2/9/17

M O T I O N C O N T R O LT I P S. C O M

AD INDEX

SALES

ACE Controls Inc. .............................................................................. 67 All Motion ............................................................................................ 2 Altra Industrial Motion Corp. ............................................................. 11 Applied Motion Products .................................................................. 14 AutomationDirect ................................................................................ 3 Baldor Electric ............................................................................ 57, BC BellowsTech, LLC ............................................................................... 33 Bison Gear & Engineering Corp. ..................................................... IBC C-Flex Bearing Company .................................................................. 22 CGI ...................................................................................................... 1 Custom Machine and Tool Co. Inc. ................................................... 24 DIEQUA Corporation ........................................................................ 46 Dynatect Manufacturing, Inc. ............................................................ 18 Encoder Products Company .............................................................. 38 GAM Gear ......................................................................................... 41 igus, inc. ...................................................................................... 20, 21 Intech ................................................................................................. 43 ITT Enidine ........................................................................................ 65 Mach III Clutch Inc. ............................................................................ 28 Master Bond ...................................................................................... 26 NSK Precision .................................................................................... 17 Power Transmission Distributors Association ...................................... 7 R+W America .................................................................................... 34 Schneeberger .................................................................................... 51 Stock Drive Products/Sterling Instrument ......................................... 25 Serapid Inc. ....................................................................................... 15 Servometer® ..................................................................................... 33 SEW Eurodrive ................................................................................... 36 Smalley Steel Ring Company............................................................. 71 Sorbothane ........................................................................................ 66 THK America, Inc. ............................................................................ IFC Weber Knapp Company .................................................................... 68 Whittet-Higgins.................................................................................. 55 Zero-Max, Inc. ...................................................................................... 5

Mike Caruso

David Geltman

mcaruso@wtwhmedia.com

dgeltman@wtwhmedia.com

469.855.7344

516.510.6514 @wtwh_david

Garrett Cona gcona@wtwhmedia.com

Neel Gleason

213.219.5663

ngleason@wtwhmedia.com 312.882.9867

Jessica East

@wtwh_ngleason

jeast@wtwhmedia.com 330-319-1253

Tom Lazar

@wtwh_MsMedia

tlazar@wtwhmedia.com 408.701.7944

Michael Ference

@wtwh_Tom

mference@wtwhmedia.com 408.769.1188

Jim Powers

@mrference

jpowers@wtwhmedia.com 312.925.7793 @jpowers_media

Michelle Flando mflando@wtwhmedia.com

Courtney Seel

440.670.4772 @mflando

cseel@wtwhmedia.com 440.523.1685

Mike Francesconi

@wtwh_CSeel

mfrancesconi@wtwhmedia.com 630.488.9029

LEADERSHIP TEAM Publisher

EVP

Mike Emich

Marshall Matheson

memich@wtwhmedia.com

mmatheson@wtwhmedia.

508.446.1823

com

@wtwh_memich

805.895.3609

Managing Director

@mmatheson

Scott McCafferty smccafferty@wtwhmedia.com 310.279.3844 @SMMcCafferty

find us on Twitter

@DESIGNWORLD

72

DESIGN WORLD — MOTION

ad index — PT Guide 2-17 v1.indd 72

2 • 2017

motioncontroltips.com | designworldonline.com

2/10/17 11:24 AM

THE BEST JUST GOT BETTER...

DC

AC Runs Cooler & Longer Lasting than Traditional Right Angle Gearmotors AC and DC options available now 1/15 - 1/2 HP; 35-1780 in-lbs • AC MOTOR OPTIONS: 115V 1PH, 115/230V 1PH 230V 3PH Inverter Duty, 230/400-460 50/60HZ 3PH • DC MOTOR OPTIONS 720 frame size: 12V, 24V, 90V, 130V and 180V 725 frame size: 12V, 24V, 90V, 130V and 180V 730 frame size: 24V, 90V and 130V • Maximum power density means a compact profile without compromising performance • Ground gearing provides whisper quiet operation, low backlash precision • Latest hypoid gear technology ensures less friction/heat and extends product life • Versatile mounting interchangeability to easily upgrade your installed drives • Exclusive PowerSTAR® EP lubricant for extended life To learn more about PowerSTAR® right-angle gearmotors, please visit Bison’s NEW WEBSITE at www.bisongear.com or call 1-800-AT-BISON.

©2014 Bison Gear and Engineering Corp.

Bison Gear 1-17.indd 1

We make your products go.™

2/9/17 2:16 PM

The First Name in Power Transmission

Baldor•Dodge® power transmission products offer reliable service and low maintenance to help reduce your total cost of ownership. Our innovative bearings, gearing and power transmission products have solved the toughest applications for over 130 years.

• Unmatched Quality

Our technical sales team can help you with the most challenging applications, and our worldwide distributor network ensures immediate delivery.

• Improved Uptime

When it comes to PT solutions, Baldor•Dodge is the first name in power transmission. baldor.com

479-646-4711

• Superior Reliability

• Quick Delivery • American Made Since 1880

©2013 Baldor Electric Company

Baldor 1-14.indd 47

2/9/17 2:17 PM