Impedance control for dexterous space manipulators

Stable and robust execution of contact tasks is of paramount importance for dexterous manipulators operating in the unstructured space environment. Two adaptive schemes for controlling the end-effector impedance of dexterous manipulators are described. Each control system consists of two subsystems: a simple filter which characterizes the desired dynamic relationship between the end-effector position and the environmental contact force and modifies the reference trajectory according to this relationship, and an adaptive controller which produces the control input required to track this modified trajectory. The controllers are very general and computationally efficient since they do not require knowledge of the mathematical model or the parameter values of the robot dynamics or the environment and are implemented without calculation of the robot inverse kinematic transformation. The control strategies are globally stable in the presence of bounded disturbances, and the size of the tracking errors can be made arbitrarily small. It is demonstrated that the impedance controllers can be modified to provide accurate force regulation in the presence of uncertainty regarding the location and stiffness of the environment. Computer simulation results for a Robotics Research K-1607 redundant arm indicate that accurate and robust end-effect impedance control and effective redundancy utilization can be achieved simultaneously by using the proposed controllers