Hybrid position/force control of manipulator using series elastic actuator with position controller

This paper proposes a method for designing a hybrid position/force control of a manipulator with a series elastic actuator (SEA) mounted on each joint. The actuator used in the SEA is assumed to be a low-cost servomotor with a built-in position controller. The hybrid position/force control is achieved by controlling the angle of the servomotor and the angular displacement of the SEA. Also, an algorithm is proposed to generate a target value for each of these states according to the position/force target value. To control these states, a state feedback system with an observer is designed for an extended system containing a position controller. Simulation results confirmed that hybrid control can be realized by giving the servomotor an appropriate target input according to the posture of the manipulator during the task execution. In addition, it is confirmed that the proposed control system has a certain robustness even when the initial posture and the environment parameters are different from the controller design.