Force Sensorless Hybrid Position/Force Control with Equivalent Mass Matrices Switching for Decoupled Rubbing Motion

This paper presents a force sensorless workspace hybrid position/force control method with equivalent mass matrices switching for rubbing motion. The equivalent mass matrices express an interference between control axes. Since the determinant of the matrix computed from the design values of robots becomes near zero around the singular configuration of robots, the utilized matrices are often arbitrarily designed. However, inappropriate matrices conditions deteriorate control performance and could cause vibration during rubbing motion. This study reveals suitable equivalent mass matrices for rubbing motion depending on the velocity of the force control axes. Moreover, a hybrid controller with equivalent mass matrices switching depending on the expected velocity of the force control axes in tasks is proposed. The validity of the proposed hybrid controller is demonstrated by the experimental response of rubbing motion with a parallel link type direct-drive four-link manipulator.