Dual-stage actuator disk drive with method for secondary-actuator failure detection and recovery using a relative-position sensor while track following

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;
• (e) a relative-position sensor for detecting the position of the secondary actuator relative to its neutral position;
• and (f) 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 series of dynamic test signals, each of the dynamic test signals in the series having a fixed frequency different from the other dynamic test signals in the series;
• receiving, in response to each dynamic test signal in the series, a relative-position signal (RPS) from the relative-position sensor;
• calculating the frequency response of the secondary actuator from the RPS received for each dynamic test signal in the series;
• recording the gains and corresponding frequencies from each of the calculated secondary-actuator frequency responses;
• and
• posting a secondary-actuator failure signal if the maximum recorded gain is outside a predetermined range.

A magnetic recording disk drive comprising:

• a rotatable magnetic recording disk having a plurality of concentric data tracks containing servo positioning information;
• a recording head movable across the disk, the head being capable of reading data and servo positioning information in the data tracks;
• a voice-coil-motor (VCM) for moving the head;
• a secondary actuator connected to the VCM, the head being connected to the secondary actuator;
• a relative-position sensor for generating a relative-position signal (RPS) representing the position of the secondary actuator relative to its neutral position;
• and
• a servo control processor responsive to servo information read by the head and to the RPS and comprising (i) a dual-stage controller for simultaneously generating a VCM control signal and a secondary-actuator control signal, (ii) a single-stage controller for generating only a VCM control signal, and (iii) a program of instructions readable by the processor for undertaking method acts comprising:
• detecting a potential failure of the secondary actuator;
• generating from the single-stage controller a VCM control signal to cause the head to follow a data track;
• generating a series of dynamic test signals to the secondary actuator, each of the dynamic test signals in the series having a fixed frequency different from the other dynamic test signals in the series;
• receiving the RPS in response to each dynamic test signal in the series;
• calculating the frequency response of the secondary actuator from the RPS for each dynamic test signal in the series;
• recording the gains and corresponding frequencies from each of the calculated secondary-actuator frequency responses;
• and
• posting a secondary-actuator failure signal if the maximum recorded gain is outside a predetermined range.