Advanced disk drive servo system design for improved transient responses

The continuing increase of recording density of a magnetic hard disk drive relies heavily on the advancement in the servo system. In this thesis we developed new technologies including algorithms as well as novel instruments for improving the transient response of servo systems. These new technologies covers three aspects of the disk drive servo systems related to transient responses during seeking-tracking hand-offs, disturbance rejection during tracking, and compensation of position run-outs. First, we proposed a time-optimal feed-forward algorithm which makes use of a simple feedforward control signal applied at the seeking-tracking hand-off to minimize the settling time. The effectiveness of the algorithm is based partly on the fact that the seeking controller and the tracking controller are optimized with different design objectives, and that exact cancellation of bias disturbance does not result in time-optimal settling performance. Second, we developed a generalized disturbance observer structure which enables us to break the otherwise highly correlated design of the disturbance observer and the design of the main control loop into two independent procedures. The proposed structure let us study the effects of the disturbance rejection rate and the measurement noise attenuation under the well-studied classical unity feedback structure. Consequently the design compromise between the performance and stability margin for a disturbance observer is made more intuitive and easier. Finally, we proposed an instrumented suspension together with the active vibration control method to improve the bandwidth of the servo system. We developed technologies for optimal sensor placement, a multi-rate active vibration control with an instrumented suspension, and robustness analysis methods for mix-signal system for high frequency spill-overs and flexible mode variation.