Filtered Disturbance Observer for High Backdrivable Robot Joint

Abstract

A collaborative robot is a robot that can work with humans in a shared workspace. It is expected that collaborative robots improve productivity and compensate for the shortage of working population. To make safe contact with the external environment, back-drivability is necessary. For high back-drivability, a robot with a joint torque sensor or a load-side encoder has been developed. Control methods using sensors effectively and improving collaborative robots performance are needed. It is known that disturbance suppression performance can be enhanced by disturbance observer (DOB). Disturbance suppression can make back-drivability higher by eliminating the effect of the contact force. However, a simple DOB cannot improve the disturbance suppression performance for a two-mass system like a robot joint. In this paper, we propose a method to enhance back-drivability significantly by simple filter design considering the structure of a two-mass system. The performance of the proposed method is evaluated by simulation and experiment.