Multirate controller for dual actuated servomechanism in hard disk drive

This paper concerns the design and implementation of a multirate controller for a dual-actuated servomechanism used in hard disk drive (HDD). The design following the decoupled master-slave structure is carried out in two steps. A state feedback controller is designed for the coarse primary actuator, the voice coil motor (VCM), to obtain minimal performance and stability, and the controller is suitable for merging with time-optimal control for large seek. Bandwidth achievable at this stage is restricted by the presence of resonant modes. The secondary stage follows the residual error from the VCM loop, and we want its gain to be as close to unity as possible for a wide range of frequency. Two loops are designed independently, which ensures stable performance in the event of secondary actuator failure. The controller is realized using multirate sampling. Effectiveness of the design is underscored using both simulation and experimental results.