Internal model control (IMC) approach for designing disk drive servo-controller

This paper presents the design procedure for disk drive servomechanism using internal model control (IMC) structure. A typical disk drive actuator can be modeled as a second order dynamics for low frequencies. However, the higher frequency response shows resonant behavior which are difficult to model. We discuss the use of IMC structure for designing servo-controllers for disk drives. In this method, a second order nominal model of the plant is used to design an H ₂-optimal controller to attain minimum integral-error-square (ISE) performance. Multiplicative uncertainty bound is defined by the difference between the actual frequency response and the response of the nominal model. The uncertainty bound is used to decide robust stability and robust performance bounds. The H₂-optimal control is then augmented by a low-pass filter with sufficient high frequency roll-off to ensure robust stability and robust performance. Tuning of only one parameter of the IMC filter makes this design method easy and convenient. Simulation results for the designed controller are presented