PES reduction in magnetic disk drives via a low-TMR HGA and servo loop shaping

This paper presents a servo-mechanically combined strategy to reduce the position error signal (PES) in high-track density magnetic disk drives. In this strategy, a special head-gimbal assembly (HGA) is designed so that it can move not only vertically to the disk but also across the data tracks. It is shown that such HGAs can reduce the track misregistration (TMR) due to disk vibration, by allowing the head to move in such a way that will compensate the off-track caused by disk bending. A further reduction in the final PES is then attempted by redesigning the servo loop shape taking the reduced disk-mode disturbance into consideration. The well-known random neighborhood search method is applied to find a set of servo gains that best approximates a desired loop shape determined based on empirical knowledge. Finally, the efficacy of the proposed strategy is demonstrated experimentally by using actual sample drives.