Implementation of a discontinuous control law on a robot during collision with a stiff environment

Practical tasks may require making transitions from free motion to contact motion and from contact motion to free motion. Recently, a discontinuous control law has been shown to provide stability during these transitions. The theory is extended by modifying the discontinuous control law to account for bounded parameter uncertainty. A facility for testing contact task control laws has been designed and built. The facility consists of a two-degree-of-freedom robot, a machine which stimulates a one-degree-of-freedom spring-mass-damper system, and a microcomputer for controlling both of these in real time. The robot has a horizontal, parallel link construction. High-precision direct-drive motors are used which reduce the backlash and friction associated with gear-driven joints. The spring-mass-damper machine is used to create a contact surface with dynamics that can be specified. Software has been designed to make implementation of a wide variety of control laws possible