NEW RESULTS ON ADAPTIVE IMPEDANCE CONTROL FOR DEXTEROUS MANIPULATORS

Stable and robust execution of contact tasks is of paramount importanc e for robot manipulators in many applications. This paper presents two adaptive schemes for controlling the end-effector impedance of dexter ous manipulators to enable reliable execution of contact tasks. The fi rst scheme, position-based adaptive impedance control, consists of two subsystems: a simple ''filter'' that modifies the end-effector positi on trajectory based on the sensed contact force and the desired dynami c relationship between the position and force, and an adaptive control ler that produces the joint torques required to track this modified tr ajectory. The second control strategy is developed using a model refer ence adaptive impedance control approach by formulating the desired re lationship between the end-effector position and contact force as a '' reference model,'' and then devising a control scheme to ensure that t he end-effector dynamics emulates this reference model. The proposed c ontrollers are very general and computationally efficient since they d o not require knowledge of the manipulator dynamic model or parameter values of the manipulator or the environment, and are implemented with out calculation of the robot inverse dynamics or inverse kinematic tra nsformation. It is shown that the control strategies are globally stab le in the presence of bounded disturbances, and that in the absence of disturbances the ultimate bound on the size of the controller errors can be made arbitrarily small. Computer simulation results are given f or a Robotics Research Corporation Model K-1607 redundant arm and demo nstrate that accurate end-effector impedance control and effective red undancy utilization can be achieved simultaneously by using the propos ed control schemes.