Reduction of Acoustic Noise in a Head-Positioning Servo System of a Magnetic Disk Drive by Using Initial Value Compensation and Determining Optimal Mode Switching Conditions

The head-positioning control system of a magnetic disk drive must enable precise positioning and high-speed access. To meet these control requirements, a Mode-Switching Control (MSC) system composed of two or three control modes and a mode-switching function has been used widely in current head-positioning control systems. One of the issues concerning MSC is to improve the transient response after it switches the mode. Although the mode switching is a non-linear action, the transient response can be improved if the control system considers the initial state response after mode switching. Initial-Value Compensation (IVC), which is based on this condition, can improve the transient response after mode switching. In the current study, we applied IVC to reduce acoustic noise during the seek operation of the head-positioning control system. Furthermore, we developed a new method for the mode switching condition; this method considers a trade-off between the peak value of operation current (which is an important factor in the reduction of acoustic noise during seek), the overshoot of displacement response, and the settling-time after mode switching. Acoustic noise during seek was experimentally found to be significantly reduced by IVC and the new switching method.