A design method of a robust controller for hydraulic actuation with disturbance observers

In this paper, a design method of a robust controller for hydraulic actuators is proposed. Generally speaking, the hydraulic actuator generates hydraulic force, and a load is driven by the hydraulic force. In order to control the hydraulic actuators, non-linearity caused by chamber pressures and natural feedback meaning the effect by the load velocity on the hydraulic pressure dynamics should be considered. A controller with feedback linearization is one of the methods to compensate the effects of the non-linearity and the natural feedback. However, since the method is based on the model parameters of the hydraulic actuator, the control performance is affected by modeling errors and modeling uncertainties. Therefore, a robust controller for the hydraulic actuator is proposed to complement the disadvantage of the conventional method. To design the proposed controller, a part of the feedback linearization, that is, pressure (nonlinearity) compensation is used to linearize the hydraulic pressure dynamics virtually. By using the virtually linearized hydraulic dynamics and the nominal mass, the nominal model of the hydraulic pressure and that of the load motion dynamics model are designed. Then, the effects which prevent each dynamics from behaving as the nominal models are defined as disturbances. In the proposed controller, two types of the observers are designed to compensate the disturbances. In this paper, the design details are shown and the validity of the proposed method is shown by simulation and experiments.