DECENTRALIZED ADAPTIVE COMPLIANCE CONTROL OF ROBOT MANIPULATORS

This paper presents two adaptive schemes for controlling the end-effec tor compliance of robot manipulators. Each controller possesses a dece ntralized structure, in which the control input for each configuration degree-of-freedom (DOF) is computed based on information concerning o nly that DOF. The first scheme is developed using an adaptive impedanc e control approach and consists of two subsystems: a simple ''filter'' which modifies the end-effector position trajectory based on the sens ed contact force and the desired dynamic relationship between the posi tion and force, and an adaptive controller that produces the joint tor ques required to track this modified trajectory. The second compliant motion control strategy is an adaptive admittance controller for posit ion-controlled manipulators. In this scheme a desired contact force is specified and then position setpoints for the ''inner-loop'' position controller are generated which ensure that this desired force is achi eved. The proposed controllers are extremely simple computationally, d o not require knowledge of the manipulator dynamic model or parameter values of the manipulator or the environment, and are implemented in d ecentralized form. It is shown that the control strategies are globall y stable in the presence of bounded disturbances, and that in the abse nce of disturbances the ultimate size of the controller errors can be made arbitrarily small. The capabilities of the proposed control schem es are illustrated through both computer simulations and actual hardwa re experiments with a Robotics Research Corporation Model K-1207 redun dant manipulator. These studies demonstrate that the first controller provides an accurate and robust means of ensuring that the desired end -effector impedance characteristics are realized, while the second sch eme represents a readily implementable method of obtaining high perfor mance force control.