Patent ID: 7835106

Claim:
A method of controlling the position of a read/write head relative to a disk in a test apparatus, the test apparatus having a positioner for positioning the head, the positioner having a sensor for measuring the actual position achieved by the positioner, the method comprising: generating a sensor signal measuring the actual position achieved by the positioner; generating a position error signal of the head relative to the disk detected at the head; high pass filtering the head position error signal and low pass filtering the sensor signal so that there is substantially no overlap in frequency between them; deriving a low frequency head error signal from the head position error signal corresponding to any drift of the head; feeding forward the low frequency head error signal to generate a compensated commanded position of the head; generating a position error signal of the positioner in accordance with the compensated commanded position of the head and the filtered sensor signal; providing both said positioner error signal and said high frequency head error signal to a hybrid servo controller; and, controlling the position of the head by causing said hybrid servo controller to signal said positioner with a movement control signal generated in accordance with both of said provided error signals used simultaneously.