Adaptive Control of a Hybrid Servo System for Magnetic Disk Drives

Digital servo systems for small magnetic disk drives with high track-densities must overcome poor control performance caused by mechanical gain variations of both the position detectors and the voice coil motor in each disk drive. This paper presents a method for adaptive control of the digital track following servo system. A reduced model for the magnetic disk drive plant is introduced that includes actuator dynamics and a time-delay element for both computation time-delay and several notch filters. A design procedure for adaptive control of the mechanical gain estimator is based on an estimator model consisting of the reduced plant model and uses the recursive least-squares algorithm with low-pass filters. This adaptive control method provides good control and is implemented using a digital signal processor.