Remember that you have several choices. Once you have determined the style of cylinder, you can get to the details of your design. You probably know how you plan to mount the unit. But often times you find that mounting will require a special bolt pattern or mounting style that is non-standard. You’ll have to ask how the style of cylinder you have selected can be modified to fit the pattern for a minimum cost. Will it require that special parts be manufactured? Will it need unique mounting hardware, such as plates, flanges, or brackets? In cases where the mount is built into or uniquely attached to your cylinder, costs will increase along with manufacturing lead times. So beware. For example, nose mounting might require that unique end caps be produced. Integral lug mounts could require special extrusions, welding, or other creative attachment concept to be employed. In lieu of lugs, is there room to drill and tap your cylinder’s end caps (or body) with special bottom or side-mounting holes? Would you have enough depth of thread?
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Motion Elements
Now you’ll want to address the motion elements of your cylinder. Are there special movements, sensing, or side loads being applied that will require special modifications to the cylinder? If so, you’ll need to accommodate them. Must the load stop at any intermediate position?
3-Position Cylinders You’re in luck. You can get three or more rod positions from a single cylinder! Many cylinder styles are offered with 3-position options. The shortstroke tie rod cylinder shown in Fig. 8 is essentially two cylinder bodies combined in a single package. You can specify the same or different stroke lengths to set your work positions as required. Nice! 4-Position Cylinders More luck! You can also get numerous cylinder styles in back-to-back configurations that enable positioning at up to four end points. As the name implies, two single-rod cylinders are assembled with their back end caps attached. As shown in Fig. 9, by anchoring one rod end and allowing the cylinder body to “float,” four distinct end points can be obtained. Can the load be allowed to rotate slightly? Non-Rotating Options For applications in which anti-rotation and registration are critical, there are solutions. Maintaining the load’s fixed orientation can be accomplished in several ways. The drawing in Fig. 10 shows one method used on tie rod cylinders. Two guide pins incorporated inside the cylinder pass through the piston head. These guide pins prevent rotation of the rod with a tolerance of ±1°. A rubber disk is included at the end of each guide pin to take up end play and firmly seat the pins in the precision guide pin holes. Because the guide pins are inside the cylinder, they are protected from the environment, physical damage, and are lubricated by the system lubrication. They require no additional space, leaving the rod end area free for attachments and tooling as required by your application. Internal guide pins are also available on a number of short-stroke cylinder models like the Pancake® series shown in the figure. External Non-Rotating Options Another solution uses an external guide block securely attached to the piston rod. A steel guide shaft, attached to the guide block, assures anti-rotation of less than 0.8° (Fig. 11). Twin Rod, Non-Rotating Options Twin piston rods are incorporated into the cylinder head to provide anti-rotation. The rods are securely fastened to the piston and tied together externally by a rod end tool bar. The tool bar ensures that the rods move in tandem and provides an ideal mounting surface for attachments required by your application. The tool bar is furnished with threaded mounting holes or optional counter-bored mounting holes (Fig. 12). Stroke Adjustment Stroke adjust styles may also be needed when the stroke can change either on the extension or the retraction of the unit. Adjustable Retract Stroke An adjusting screw with a thread-sealing locknut mounted in the rear
Guide pin, Ground tool steel
Rubber disk
O’Ring, polyurethane Wrench flat random rotation Bushing, SAE 660 bearing bronze
Non-rotating option - internal guide pins Fig. 10
Guide block
Piston rod
Set screw
Guide shaft Fig. 11
Fig. 12
Thread sealing locknut
Adjusting screw Adjustable retract cross sectional view of metric cylinder Fig. 13
www.IFPS.org • Systems Integrator Directory 2015 • www.FluidPowerJournal.com
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