The design and prototyping of a four degree of freedon, low-cost, high-speed, cartesian-motion robot

Today's robots are expensive, highly accurate, and use complex control techniques. However, industry lacks low-cost robots that can perform medium accuracy assembly operations and material handling. International Business Machines, through the Technical Interchange Program, supported the development of a low-cost, high-speed, cartesian motion robot to fill this niche. Several design requirements were specified; the most important was a total cost of $600. High speed was the next most important consideration. Stepper motors with open-loop control were specified. Four degrees of freedom were required: three translations, and one yaw rotation. The design also required modularity and ease of manufacture. The high volume production model will need to use plastic injection molded parts wherever possible to achieve minimal cost per part. Timing belts were required to minimize backlash, cost, and maintenance, and to increase reliability. An error detection/recovery capability was needed so that the robot could periodically recalibrate itself. The payload specified was three pounds. One possible application of the prototype is in an IBM circuit board manufacturing facility. A first prototype which performed only horizontal positioning, was developed as a master's thesis by Mark Granger, in the Department of Mechanical Engineering, at the University of Tennessee, Knoxville. For this second prototype, the bearings were replaced with rolling element bearings to increase its reliability. PVC plastic that has been bonded together is used to model the injection molded parts. This second prototype had a vertical arm that can also rotate. The cost of the proposed design has a projected cost of $1066 per robot, based on production of 200,000 robots. A maximum horizontal speed of the arm is 48 in/sec with an average velocity of 28 in/sec for a 12 inch move. This thesis discusses the design overview and methodology of the robot, projected performance and performance testing of the prototype, assembly instructions, failure modes and their correction, an analysis of the critical tolerances, a cost analysis and recommendations.