A study of equivalence between AFC and feedback control with resonant filter

This paper describes theoretical analysis of adaptive feed-forward cancellation (AFC) for a disturbance suppression method. AFC is known as an adaptive control method, and the adaptive algorithm can estimate a sinusoidal disturbance. Therefore, AFC was mainly applied to suppress periodic disturbances. In a previous study, we developed an enhanced AFC that has a damping function. This AFC can be applied to suppress not only a periodic disturbance but also a non-periodic disturbance. On the other hand, feedback control has been widely implemented to suppress periodic and non-periodic disturbances. To suppress disturbances, a feedback controller is designed to achieve loop shaping for disturbance rejection. The enhanced AFC and feedback control can suppress these disturbances similarly. In this paper, we compare the enhanced AFC and the feedback control method. As a result, the characteristic of the enhanced AFC is consistent with that of a resonant filter, which is a feedback control method. The results of a track-following simulation of a hard disk drive showed that the enhanced AFC is equal to that of a resonant filter in terms of time and frequency domain. The adaptive algorithm of AFC functions the same as the feedback control method, which indicates that AFC is a feedback control method.