Adaptation to environment stiffness in the control of manipulators

The dynamic performance of fixed-gain force or impedance manipulator control systems in constrained situations is very dependent on the environment parameters: e.g. the force response at low stiffnesses may be sluggish, while high stiffnesses give rise to bouncing and instability. An adaptive controller, based on the model reference approach, for multi-axis damping control is presented. Simulation results show that the adaptive scheme can significantly improve the performance in force tracking and enhance stability at high stiffnesses, by rendering the behavior independent of the environment stiffness. Experimentation on a PUMA manipulator shows the limitations of the approach when applied to industrial manipulators with significant nonlinearities and flexibility in the transmission.