Backdrivability improvement method based on angular transmission error in a high reduction gear

Abstract

The actuators in robot joints are often equipped with reduction gears for increasing the power output. However, a high reduction ratio is required to decrease the backdrivability. In this paper, the backdrivability is improved by installing motor- and load-side encoders in the reduction gear. The proposed method comprises a backdrive assist control, feedforward friction compensation, and estimation and feedback of the load-side disturbance by using a multiencoder-based disturbance observer. The angular transmission error in the reduction gear is treated as a disturbance that affects the motor. This disturbance is estimated from the motor- and load-side angular accelerations, and provides feedback assistance to the backdrive. The effectiveness of the proposed method is verified through experiments.