Extension of ILQ Design Method by Using a Free Parameter in the Feedforward Path

Abstract

ILQ optimal servo design method has been generalized so far in many ways. Noting that a general control structure of robust servo systems has a free feedforward parameter, such a free parameter is introduced here in the usual ILQ design method for further generalization. As a result, the proposed method inherits two characteristics of an existing ILQ design method; one is that we can specify directly a desired closed loop transfer function from reference input to output in a larger class than usual; the other is that design results are expressed analytically in terms of system parameters and design specifications. Moreover, the proposed method can decouple those servo systems of type one that cannot be decoupled by state feedback and hence inapplicable by the usual ILQ design. Finally we clarify the class of transfer functins which can be decoupled in general servosystems. The class shows there is essentially no difference between ILQ servo systems and general servo systems.