A VARIABLE STRUCTURE ROBOT CONTROL ALGORITHM WITH AN OBSERVER

This paper proposes an algorithm combining variable structure control and observation for robot control using only joint position measurements. This algorithm investigates the interactions between the observer and the controller caused by system parameter uncertainties. The theorem in this paper gives sufficient conditions to ensure the stability of a closed-loop system composed of a robot, an observer, and a controller. This theorem shows that the joint velocity estimation errors are bounded and the joint position tracking errors are also bounded when time tends to infinite. The experimental results achieved with our direct-drive robot "DDR-1" verify the validity of the theoretical results. The experiments also demonstrate that when the end-effector of the robot tracks a 0.5-m-diameter circle at a speed of 0.5 m/s or tracks a 1-m straight line at a speed of 1 m/s, the maximum joint tracking errors are less than 0.05-degrees and the maximum trajectory tracking error is less than 0.5 mm.