Robust hybrid position/force control of robot manipulators considering environment changes

Two types of robust hybrid position/force control methods for robot manipulators are proposed, which requires less computational effort and has robustness against the disturbance and parameter variations. In the case of position control, acceleration control is realized by a position-based disturbance observer; in the case of force control, control of second derivative of contact force is realized by a force-based disturbance observer or an environment observer. The position-based disturbance observer compensates the disturbance of robot manipulators. The environment observer and the force-based disturbance observer compensate the dynamic environments such as the parameter variation of stiffness and the movement of workpieces. One control system is based on the position-based disturbance observer in joint space and the environment observer in task space; the other one is based on the position-based disturbance observer and the force-based disturbance observer in task space, which are tested experimentally by a direct drive robot