Design and construction of a microcomputer-controlled light-weight robot arm

This paper describes current research on a computer-controlled light-weight mechanical arm. This mechanical arm is a self-contained, autonomous system capable of executing high-level commands from a supervisory computer. The links used in the experimental model are made of aluminium, while the actuators of the joints are permanent magnet type dc motors driven by servo-amplifiers via Pulse Width Modulation. To avoid the use of tachometers and thus reduce the link masses, a method for velocity estimation based on a position history was developed which can be implemented in digital circuitry. The design of the full-servo-loop is described, as well as the interface between the arm and an IBM-XT type microcomputer. Experimental results show that the link masses can be reduced by replacing the joint tachometers with a velocity estimator and very fast response can be achieved using light-weight structures without compromising rigidity.