Servo loop gain calibration using Model Reference Adaptation in HDD servo systems

An automatic gain calibration method based on model reference adaptation (MRA) for hard disk drive (HDD) servo is presented in this paper. The servo loop gain in the HDD servo control depends on magnetic flux density of actuator, head flying height, temperatures and other factors. Variations in VCM gain may cause variations in servo control stability margins and thus need to be compensated. The traditional MRA method is modified in this paper to generate the compensation gain adaptively. Experimental results show the effectiveness of the MRA compensation method. After the compensation, the DC gain of the HDD open loop responses can be maintained nearly constant despite the variations in head position and operating temperature.