Patent ID: 7106552

Claim:
A method for operating a dual-stage actuator disk drive, the disk drive including (a) a rotatable magnetic recording disk having a plurality of concentric data tracks containing servo positioning information; (b) a recording head movable across the disk, the head being capable of reading data and servo positioning information in the data tracks; (c) a voice-coil-motor (VCM) for moving the head; (d) a test location where movement of the VCM is limited; (e) a microactuator connected to the VCM, the head being connected to the microactuator; (f) a relative-position sensor for detecting the position of the microactuator relative to its neutral position; and (g) a servo control processor responsive to servo information read by the head and comprising (i) a dual-stage controller having a degraded-stability VCM controller with relatively high low-frequency gain and a microactuator controller for simultaneously generating a VCM control signal and a microactuator control signal, and (ii) a selectable single-stage controller for generating only a VCM control signal, the processor-implemented method comprising: detecting a potential failure of the microactuator; generating a location signal to the VCM to move the VCM to the test location and selecting the single-stage controller if a potential microactuator failure is detected; generating a first test signal to the microactuator; receiving a relative-position signal (RPS) from the relative-position sensor in response to the first test signal; calculating the stroke of the microactuator from the first test signal and the RPS; and posting a microactuator failure signal if the calculated stroke is outside a predetermined stroke range.