A wind-up restraint control of disturbance observer system for saturation of actuator torque

When a control system has integral compensators and saturation in the control object, the response will become unstable for the worst case, known as the wind-up phenomenon. There is little research about wind-up phenomenon for a disturbance observer system, which realizes high speed and high accuracy control. The wind-up phenomenon of the disturbance observer system is more violent than that of a PI control system because of the positive feedback of the disturbance compensation loop. In this paper an easy method, which prevents the wind-up phenomenon using a saturation model in the disturbance observer is proposed. When the saturation model in the disturbance observer is used and the input to the control object with saturation is much larger than the saturation value, the response becomes oscillatory due to the outer loop PD controller. To prevent the oscillation a new method which inverts the servo motor torque at a proper time using a predicted future response, is proposed. This method is applied to both intermittent motion and continuous motion. The simulation results and experimental results show the effectiveness of the proposed method