Digital servo control system for a data recording disk file with

Abstract

Disclosed is a digital control servo system for read/write head positioning in data recording disk files of the type which use voice coil motor (VCM) actuators for positioning the head, with improved modelling of the servo system in saturated seek mode. The VCM has a characteristic torque factor which varies in accordance with a predetermined relationship to head position and with age and temperature, and the servo system drives the VCM in a saturated seek mode at a maximum level of current which has a low frequency variation due primarily to temperature change. The servo system computes an estimated VCM control representing the VCM current, computes estimates of the state of the VCM including head position and velocity, and computes from an algorithmic model, predictions of head position and velocity. The improved modelling changes the algorithmic model to reflect the actual torque factor of the VCM and actual maximum level of current in saturated seek mode rather than nominal torque factor and VCM current. The preferred method is to employ scaling factors representing the ratio of measured torque factor to nominal torque factor, and representing the ratio of measured maximum level of current to nominal, to scale the model, and then to compute predictions of the state of the VCM in saturated seek mode from the scaled model and the current values of the states.