Patent ID: 7209321

Claim:
A disk drive comprising: (a) a disk; (b) a head; (c) a voice coil motor (VCM) for actuating the head radially over the disk, the VCM comprising a voice coil; (d) a plurality of driver switches for controlling a voltage applied to the voice coil; (e) a pulse width modulated (PWM) signal generator for generating PWM control signals applied to the driver switches, the PWM signal generator comprises: a control law block for generating an acceleration command in response to a commanded current and at least one estimated state of the VCM; a command to timing block for generating a plurality of PWM timing signals in response to the acceleration command; a PWM controller for generating the PWM control signals applied to the driver switches in response to the PWM timing signals, wherein the command to timing block, PWM controller, driver switches, and voice coil comprise a plant transfer function; a current detector for detecting a current flowing through the voice coil; a plant model comprising a model transfer function for generating the estimated state of the VCM in response to the detected current flowing through the voice coil; and a correction block, responsive to the detected current, for adjusting the PWM timing signals so that the plant transfer function substantially matches the model transfer function.