Back-drivability Improvement of Geared System Based on Disturbance Observer and Load-side Disturbance Observer

Abstract

This paper proposes a method of improving the back-drivability of torque control according to the dynamic characteristic of forward-drivability based on the concept of proposed equivalent expression. The control strategy is composed of disturbance observer (DOB), a load-side DOB (LDOB) and the designed controller for torque control. The DOB realizes robust motion control by compensating for the friction and modeling error of the system, and the LDOB estimates the external torque input from the load-side. According to the designed controller, the proposed method constructs the back-drivability as forward-drivability via each transfer function of the equivalent expression. In addition, a scaling factor is introduced to quantitatively adjust the back-drivability to adapt to different application demands. Moreover, the decision basis of parameters in the proposed control is discussed and the effect on the control system is clarified. The experimental results are compared with the conventional torque control method, and show the consistency in the quantitative improvement of back-drivability effectively with the scaling factor.