Disk file digital servo control system with coil current modeling

摘要

A disk file digital servo control system utilizes a state estimator wherein the voice coil motor (VCM) current is modeled, rather than measured, thereby eliminating the need for analog-to-digital conversion of the actual VCM current. The VCM current is fed back directly to the input to the power amplifier where it is summed with the control signal output. This effectively changes the integrating power amplifier into a low pass filtering power amplifier, with linear input- output characteristics. Thus, during track following or short seeks, the VCM current is estimated based on this linear model. During long seeks, when the power amplifier is saturated, the VCM current is modeled based upon the known VCM characteristics during saturation, which include the effects of the back electromotive force and the coil current rise time. The microprocessor in the digital servo control system determines which VCM current model to use by a determination of when the power amplifier is in saturation. In the preferred embodiment, the microprocessor determines power amplifier saturation based upon a value of the head velocity error, which is the difference between the commanded velocity and the estimated velocity.