Path constrained robot control — experimental evaluation

Abstract Fast motion along a predefined path is important in many robot applications, and requires utilization of the maximum allowable torque range. If the torque is at the limit, there is no margin to cope with disturbances or modeling errors, which may result in deviation from the path. A path velocity controller outside the ordinary robot controller can improve path tracking. The path velocity controller modifies a nominal velocity profile, which is specified in advance, e.g. by minimum time optimization or by a robot operator/programmer. The path velocity controller modifies a scalar path parameter, giving computational efficiency and coordination of joint motions. The path velocity controller has been verified by experiments on an industrial robot, and some of the results are presented in this paper. The experiments were done on an industrial robot, where the original robot control system has been replaced by a VME-based computer system. The experimental results demonstrate how the path velocity controller can adjust a nominal minimum time velocity profile, such that the result is good path following and good utilization of the available torque range. The experiments also show how the path velocity controller is able to compensate for time variations in the robot dynamics.