Patent ID: 7079338

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 secondary actuator connected to the VCM, the head being connected to the secondary actuator; and (e) a servo control processor responsive to servo information read by the head and comprising (i) a dual-stage controller for simultaneously generating a VCM control signal and a secondary-actuator control signal, and (ii) a selectable single-stage controller for generating only a VCM control signal, the processor-implemented method comprising: selecting the single-stage controller if a potential failure of the secondary actuator is detected; generating from the single-stage controller a VCM control signal to cause the head to follow a data track; generating a dynamic test signal to the secondary actuator; receiving, in response to the dynamic test signal, a position error signal (PES) from the servo positioning information in the data track being followed; calculating from the PES the response of the secondary actuator to the dynamic test signal; and posting a secondary-actuator failure signal if the calculated response is outside the range of the expected response.