GA based high-order peak filter design with application to compensation of contact-induced vibration in HDD servo systems

Sensitivity loop shaping using add-on peak filters is a simple and effective method to reject narrow-band disturbances in hard disk drive (HDD) servo systems. The parallel peak filter is introduced to provide high gain magnitude in the concerned frequency range of open-loop transfer function. Different from almost all the known peak filters, which possess second-order linear system structures, in this paper we explore how high-order peak filters can be designed to improve the loop shaping performance. The main idea is to replace some of the constant coefficients of common second-order peak filter by frequency-related transfer functions, and then genetic algorithm (GA) is adopted to perform optimal pole and zero placement for those transfer functions. Owing to the remarkable searching ability of GA, the expected shape of sensitivity function can be achieved by incorporating the resultant high-order peak filter in parallel with baseline feedback controller. As an application, a well designed seventh-order peak filter is used to compensate contact-induced vibration in a high density HDD servo system, where the benefits of high-order filter are clearly demonstrated.