Phase design of an IIR filter and its application to an inverse system

To suppress external vibration from affecting position error for a hard disk drive, shock sensor feed forward techniques are proposed by White and Tomizuka (1997). To design the feed forward controller, its phase should be within a certain specified range. Usually there is an analog low pass filter to suppress resonance frequency of the shock sensor output. The filter causes phase delay and makes it difficult to design the feed forward controller. We need to design a filter that can compensate the phase delay caused by the low pass filter. In this paper a method to design the phase of a digital infinite response (IIR) filter is proposed. The method uses linear matrix inequalities (LMI), so that the result can be global optimum. The stability of the filter is obtained by the phase of a target transfer function