Analysis of actuator in-phase property in terms of control performance and integrated plant/controller design using a novel model matching method

This paper is concerned with resonance in-phase property of a VCM (voice coil motor) plant system in the sense of control performance in HDDs (hard disk drives). Its relationships with the optimal performance level γ_opt, the stability margins and the disturbance rejection capability are revealed. It is found that the main resonance being in-phase is particularly beneficial to rejection of the narrow-band disturbances with frequencies near plant resonances. In order to meet the requirement on the inphase property, a partial model matching method is proposed. This model matching problem is solved by an H_∞ method using an linear matrix inequality approach. The partial model matching method is then applied to the VCM plant system. We especially take into account the in-phase case for the purpose to improve the system ability to attenuate high frequency disturbance. For the new system designed using the proposed model matching method, a feedback controller and a group peak filter are designed to attenuate the disturbance near the plant resonances. The advantages of the in-phase resonances are illustrated, when compared with the original plant.