Switching based repetitive control for hard disk drives: experiments on RIDR and RPTC methods

In this paper, two switching based repetitive controllers are proposed with multirate control, namely, repetitive intersample disturbance rejection (RIDR) and repetitive perfect tracking control (RPTC). The former method offers excellent intersample performance and the latter method can reduce the computation cost significantly. The proposed methods are applied to high-order repeatable runout (RRO) rejection problem in hard disk drive (HDD). First, the proposed RIDR method is compared with a conventional feedback (FB) control in the case of single-mode disturbance rejection at 770 [Hz]. This experiments show that the switching mechanism enables the rejection of periodical disturbance without any sacrifice of the closed-loop characteristics. Next, RPTC method is applied to cancel the broad-band disturbance. The final experiments show that the switching based RPTC eliminates 32.6 [%] tracking error than the conventional method.