Torque Control for Sensor Equipped Motor-harmonic Drive System

In this paper, the torque control algorithm for Sensor Equipped Motor-Harmonic Drive System is proposed. For the model-based control, the dynamic equation of the harmonic drive and the electric motor was derived as a lumped model, and the frictions of the harmonic drive and the bearings were regarded as disturbance. Consequently, a linear model in which the disturbance acts on the second order system without damping was formulated. The disturbance was estimated from the disturbance observer (DOB) and forward-compensated. Subsequently, the second order system without damping was stabilized by the three different kind of feedback algorithms. First, the integral differentiator control (ID control) algorithm was developed by using pole-zero cancellation. When the model parameters are incorrect, however, the system becomes unstable. To resolve this, the PID controller was considered to make the closed loop system as a second order standard form with damping. The PID controller is stable but has some chattering in steady state. Lastly, PD control with feed-forward augmentation was examined. Among the three controllers, the Feed-forward Augmented PD controller (FAPD controller) gived best result even with parameter inaccuracy. Control performances were verified by computer simulations and experiments with the developed.