Vibration analysis and control in hard-disk drive servo systems

Abstract

With the trend of increasing track densities in Hard-Disk Drives (HDDs), disk platter vibrations and other mechanical disturbances causing slider/head off-track have to be suppressed for better servo positioning. This require excellent actuator track following to reduce Track Mis-Registration (TMR) achieve higher Tracks-Per-Inch (TPI). This dissertation studies and analyses the axial disk fluttering phenomenon with its effect on the head positioning mechatronics and a disk fluttering vibration model is constructed for the design of track following controllers. With this model, a control strategy by modeling the secondary actuator in a Decoupled Master-Slave (DMS) dual-stage servo system as a pure gain for many frequencies is employed to bypass the sensitivity limitation from Bodea??s Integral theorem (BIT). The hump of the sensitivity transfer function is usually unavoidable and causes amplification of head off-track disturbances which increases TMR. Experimental results show suppression and even attenuation of high frequency vibrations via reducing the hump.