Cooperating manipulator control with feedforward dynamic compensation

Abstract

In this paper the transport of an object by two cooperating manipulators is simulated and performed experimentally. The controller used for each manipulator is the sum of two parts: (a) an off-line calculated feedforward part, which includes compensation of the manipulator and object rigid-body dynamics and (b) an on-line computed PID feedback part. The simulation problem is handled by first computing the open chain forward dynamics of each manipulator using an efficient O(n) recursive multibody dynamics algorithm. The closed chain problem is then solved through addition of a corrective joint acceleration term to the open chain solution, which is computed from the constraint forces. In the experiment an additional feedforward term is utilized, which takes into account viscous and Coulomb friction in the manipulators’ joints. The simulation and experiment are carried out using two PUMA 560 manipulators to move a steel cylinder along a sine wave path. Tracking performance results are given in Cartesian space for the simulation and experiment.