Rejection of Unknown Periodic Disturbances in Magnetic Hard Disk Drives

Magnetic hard disk drive (HDD) has become a primary choice as a cost effective means for digital audio players, portable computers, car navigation systems and other portable electronic products. A particular problem an HDD faces in such applications is periodic disturbances caused by the vibrations from the environment. The frequencies of these external vibrations are often not known a priori and/or vary in time. Typical feedback controllers have limitations on addressing such disturbances, and for unknown frequency cases, some sort of adaptive control scheme is called for. While there are algorithms proposed for HDD to address unknown periodic disturbances, ever-increasing demand for higher areal density requires further improvements on the performance. In this paper, a new adaptive method to identify and reject unknown periodic disturbances is applied to a mobile HDD and simulation and experimental results are presented in comparison with a scheme proposed in the literature