Rejection of repeatable runout in hard disk drives using mixed-radix algorithm

Suppression of repeatable run-out (RRO) in the following control of hard disk drives (HDDs) is indispensable to improve the motion performance and to increase the disk density. The authors have already presented algorithms to suppress the effects of RRO on the following control performance, where the fast Fourier transform (FFT) has been applied to identify the frequency characteristics of RRO. Based on the identified characteristics, an inverse dynamics in frequency domain could be achieved to reject the effect of RRO. This approach, however, leads to computational intensity and requires the long data length to acquire the inverse dynamics with higher resolution. This paper presents an improvement approach to solve the above problems by applying a mixed-radix FFT. Experimental results show the effectiveness of the proposed suppression