Robust critical control for servo systems using disturbance observers

This paper develops a computationally efficient method to design a controller for servo systems which require that tracking errors and control inputs are strictly maintained within pre-specified constant bounds. To ensure these bounds in the presence of unknown disturbances and parameter variations of a plant, the disturbance observer is introduced. In the framework of the principle of matching, a controller is designed as a 2-degree-of-freedom controller including the disturbance observer under the condition that reference signals and disturbances are restricted in rate of change and magnitude, respectively. Through a case study of servo controller design for the actively-controlled bed for ambulances, it is shown that the 2-degree-of-freedom controller can compensate wider parameter variations compared to a 1-degree-of-freedom controller and that the proposed method is computationally efficient.