An analysis of some fundamental problems in adaptive control of force and impedance behavior: theory and experiments

Force control in robotic mechanisms has been extensively researched. There have been several results which have concentrated either on explicit force control or impedance control. Further, many of these works require accurate identification of the stiffness of the environment. In this work the authors examine the role of adaptive controllers for force control with unknown system and environment parameters and clearly integrate several fundamental issues such as explicit force control, impedance control, and impedance control combined with a desired force control. All of these issues are treated using standard model-reference adaptive control (MRAC) approach. Within the same framework, the authors analyze other equally fundamental issues such as environment stiffness identification, stability of the complete system, and parameter convergence. The authors demonstrate the effectiveness of the proposed theory through experiments.