A PASSIVITY APPROACH TO CONTROLLER-OBSERVER DESIGN FOR ROBOTS

Passivity-based control methods for robots, which achieve the control objective by reshaping the robot system's natural energy via state fee dback, have, from a practical point of view, some very attractive prop erties. However, the poor quality of velocity measurements may signifi cantly deteriorate the control performance of these methods. In this p aper we propose a design strategy that utilizes the passivity concept in order to develop combined controller-observer systems for robot mot ion control using position measurements only. To this end, first a des ired energy function for the closed-loop system is introduced, and nex t the controller-observer combination is constructed such that the clo sed-loop system matches this energy function, whereas damping is inclu ded in the controller-observer system to assure asymptotic stability o f the closed-loop system. A key point in this design strategy is a fin e tuning of the controller and observer structure to each other, which provides solutions to the output-feedback robot control problem that are conceptually simple and easily implementable in industrial robot a pplications. Experimental tests on a two-DOF manipulator system illust rate that the proposed controller-observer systems enable the achievem ent of higher performance levels compared to the frequently used pract ice of numerical position differentiation for obtaining a velocity est imate.