Adaptive force control of position/velocity controlled robots: theory and experiment

This paper addresses the problem of achieving exact dynamic force control with manipulators possessing low-level position and/or velocity controllers typically employed in industrial robot arms. Previously reported approaches and experimental results are reviewed. A new adaptive force control algorithm for velocity/position controlled robot arms in contact with surfaces of unknown linear compliance is reported. The controller provably guarantees global asymptotic convergence of force trajectory tracking errors to zero when the robot is under exact or asymptotically exact inner loop velocity control. An additional result which guarantees arbitrarily small force errors for bounded inner loop velocity tracking errors is presented. Comparative experiments show the new adaptive velocity (position) based controller and its nonadaptive counterpart to provide performance superior to that of previously reported position-based force controllers.