Cascade Position and Force Control via Saturation and a Compensator for Switching

This study presents a method to switch between position control and force control. Currently, robotic systems are being desired to perform versatile and dexterous tasks, achieving physical interaction with humans and/or environment. When robotic systems need to control position during unconstrained motion and force during constrained motion, switching between these control modes is required. In this study, a cascade position and force control scheme via saturation and a compensator for switching is proposed. The proposed method has an outer position controller and an inner force controller. A saturation function is inserted between the position controller and the force controller to modify the reference of motion. Moreover, the compensator is added to prevent the position tracking performance from deteriorating owing to the inserted saturation during the unconstrained motion. The experimental results show the validity of the proposed method.