A variable structure robot control algorithm with an observer

An algorithm is proposed that combines variable structure control and observation for robot control using only joint position measurements. This algorithm is used to investigate the interactions between the observer and the controller caused by system parameter uncertainties. The theorem underlying the present work 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 infinity. The experimental results achieved with the 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° and the maximum trajectory tracking error is less than 0.5 mm