Design For Assembly Evaluation of 1986 Technics Compact Disk Player Kyle Morrissette Nick O’Sullivan Doug Carder Charlie Hunter Jason Runkle
University of Notre Dame
ABSTRACT This report discusses the research, findings, approaches and conclusions regarding the design for assembly of the Technics SL-P110, a CD player launched in 1986. Additional topics discussed include the CD player’s fundamental components and how they function together, the techniques used by Technics to construct the CD player to make it’s assembly efficient, and suggested potential improvements in the design for assembly of the CD player. In order to insightfully analyze the CD player, detailed assembly drawings, figure 1, are also included in the report. Overall, this report provides a critical analysis of the design for assembly behind the Technics SLP110.
I. INTRODUCTION Design For Assembly, or DFA, is the practice of designing a product with maximum ease of assembly and optimize efficiency of assembly. DFA analyzes the constraints of putting together a product, such as assembly time, assembly cost, and people needed piece the components together, and then attempts to minimize each by improving the initial design. DFA Guidelines are available to engineers in order for them to make their products more assembly friendly. Some of these guidelines include: minimizing overall part count, maximize part functionality, avoid unnecessary complications like tangling and nesting, making parts symmetric, and installing the parts in a pattern where they will be easy to access in case of part failure. If these DFA guidelines are properly incorporated into a product, they can cut assembly costs dramatically, and simultaneously make a product’s functionality easier to understand for the customer.
II. APPROACH The goal of this project was to understand and use the practice of design for assembly on an older model compact disk player. To begin with, the product was carefully disassembled to its basic components so that the group could analyze how each worked and which components did which tasks. Assembly drawings of each fundamental component were then created through Google Sketch in order to document how the various components mated and how they functioned together. Next, the DFA techniques that Technics used to assemble the product were documented, and improvements to strengthen the product’s DFA were discussed. Finally, an improvement potential was calculated based off the number of necessary components and the number of components actually used. A. Fundamental Components and Functions Once the power is turned on, current enters the player through the rear and immediately reaches the transformer where its voltage is lowered to a usable value. It then runs to the circuit board where it splits into five paths as shown in Figure 2. The first path takes power to a battery on the disk drive. This battery stores power that is used for a motor that turns a tray wheel. The tray wheel opens and closes the CD tray. The second path sends power to a
solenoid on the SORD, which is the laser-reading device that reads the CD data. The solenoid produces a magnetic field that transports the SORD along a magnetic track so that it can read the entire radius of a CD. The third path sends power to the user interface (buttons) on the front of the player. The Central Processing Unit, or CPU, executes the commands given to it through the user interface. The fourth path sends power to three solenoids that make up the CD motor. This causes a coaxial magnet attached to the disk holder to spin, turning the CD. The last path sends power to the audio outputs of the CD player. These convert the digital signals of the CD, interpreted by the laser, into analog signals that can be displayed and interpreted by external speakers.
Figure 2. Power Flow Chart
B. DFA Techniques Technics intended to create a simple, efficient assembly for the SL-P110. First, the base of the unit is comprised of one sheet of metal that was machine bent in order to form a box. Notches and holes were also formed by machine in the base in order to support the interior components of the unit. Although constructing the base unit from one sheet of metal mandated a large amount of machining, it reduced the number of components required to form the base from several different sheets to one base component. Second, many interior components were easily put together by hand. The CD slips into position on the disk holder without fasteners, the wire leads snap into place, and the CD tray clips in and out. Furthermore, the more complicated components in the unit have multiple functions. For example, the tray wheel drives multiple processes. It opens and closes the tray, raises and lowers the CD holder, and raises and lowers the CD fork, a device connected to the tray that sets the disk precisely on the disk holder. By integrating all these functions into one complicated component instead of multiple complicated components the unit is more efficiently built and has a simpler assembly process. These all ensure a simple assembly process. Considering the time period of the machineâ€™s creation, the group assumed the player was not constructed robotically. Therefore, it must have been constructed by hand, and by keeping the assembly process simple, mistakes are less likely to occur.
III. RESULTS DFA Improvements Many improvements can be made to improve the DFA of the 1986 Technics compact disc player. The most effective improvement is the incorporations of the disc tray, disc drive assembly, and circuit board into a single component. This change would allow for a
significant size reduction of the compact disk player by eliminating several, unnecessary parts. One such example is the disk tray. Instead of the current design’s disk tray, the user could place the disk directly onto the disk holder where it would snap into place, eliminating the need for a disk tray and CD holder. This would also remove the need for its functional components, including the motor to power the tray, the battery to power the motor, and all the necessary wiring. Another improvement is the elimination of separate springs to absorb shock. In the redesign of the compact disk player the damping system will be more effective with springs between the disk tray and the chassis to minimize vibrations instead of the larger springs used in the design. The motor board could be made all plastic instead of a composite of metal and plastic. If it were, it could be molded into one piece, instead of the current method, which consists of many glued plastic pieces on the metal foundation. This would save time, money, and weight. Similarly, the top could be made of plastic with lower thermal conductivity than the current metal top. This change would reduce weight and heat transfer to the player’s environment. The redesign will use latches to lock the lid in place when it is closed instead of a disk tray moving in and out. Another potential change in the design is the positioning and design of the screws used to put the player together. The redesign will use fewer screws, all of which would be of the same type and the screws will be fastened in the same orientation. An improvement potential equation was used to calculate the improvement potential. Potential = (Actual # of Components) – (Theoretical minimum # of Components) (Actual # of Components)
There were fifty-nine parts identified, not including minor pieces such as individual resistors or capacitors, which would be difficult to quantify, and the group estimated that twelve parts could be eliminated. According to equation (1), the CD player had 20.43% room for improvement, which was good according to the grade scale of David G. Ullman1. Snaps and latches could be used in several locations instead of screws. For example, the lid that was fastened with four screws could easily be snapped into place. In order to increase the portability of the compact disk player, a battery compartment could be added into the design. The AC adapter would still be necessary, but could be used as an option to the user. Another improvement would be to minimize the space required for the AC adapter jack. The line-out jacks in the old design can be minimized and the addition of a headphone jack would be necessary for increased portability. Another problem with the old design is the tangling of the wiring between the systems. The single piece redesign eliminates several wires that have become unnecessary and decreased the distance the wires need to stretch between connections.
IV. CONCLUSION In conclusion, the group was able to grasp the intricate functions and analyze the fundamental components of the Technics SL-P110 Compact Disk player. The technological limitations of 1986 were the greatest detriment to the CD player’s DFA. Lack of sophisticated assembly machinery necessitated the need for human construction, which handicapped the product’s design for assembly. However, careful analysis of the CD player yielded improvements for future designs that would incorporate a more streamlined assembly process, making the product’s assembly simpler and faster.
Ul lma n, D G. ( 199 4) . T he Me cha n i cal Des i g n P rocess . N e w York : McGraw - H il l. Pa g e 3 34
1986 Technics CD Player design review