Force Control for Robotic Rigid Disk Grinding

The design and implementation of through-arm force control for the robotic rigid disk grinding process are presented. A PUMA 762 industrial robot equipped VAL II software, a 4 Hp pneumatic grinder, and a JR³ six degree of freedom force sensor was used in the experiments. Through-arm control was accomplished using VAL II´s capabilities for real time path control, and an external 386-based microcomputer for control algorithm calculations. Experimental results are compared with simulations. The models for the system consisted of a mechanistic description of the robotic grinding process and an experimentally determined gain-delay model for the robot dynamics. The gain-delay model is, without question, an oversimplified representation of the robot dynamics, however, it has proved to be quite useful for tuning and simulating the controller. The response predicted by the simulation closely resembles the experimental response of the system under PID control. In the tests, the controller was able to effectively maintain the grinding forces at the setpoint value. The process was found to be very sensitive to the robot stiffness, and the robot path tracking error was also found to be a significant factor affecting the grinding forces. The experimental results show that a finely tuned PID controller is robust enough to compensate for force errors caused by both step force disturbances and robot path tracking errors.