Disturbance observer based path tracking control of robot manipulator considering torque saturation

This paper proposes a path-tracking algorithm to compensate for path deviation due to torque limits. The algorithm uses a disturbance observer with an additional saturation element at each joint of n degrees of freedom (DOF) manipulator to obtain a simple equivalent robot dynamic (SERD) model. This model is represented as an n independent double integrator system and is designed to ensure stability under input saturation. For an arbitrary trajectory generated for a given path in Cartesian space whenever any of the actuators is saturated, the desired acceleration of the nominal trajectory in Cartesian space is modi®ed on-line by using SERD. An integral action with respect to the di€erence between the nominal and modi®ed trajectories is utilized in the nonsaturated region of actuators to reduce the path error. To verify the e€ectiveness of the proposed algorithms, real experiments were performed for a two DOF SCARA-type direct-drive arm. 7 2000 Published by Elsevier Science Ltd.