Dual-stage actuator disk drive with secondary actuator failure detection and recovery using relative-position signal

A disk drive comprising:

• a rotatable magnetic recording disk having a plurality of concentric data tracks, the 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 primary actuator for moving the head;
• a test location where movement of the primary actuator is substantially limited;
• a secondary actuator connected to the primary actuator, the head being connected to the secondary actuator;
• a relative-position sensor coupled to the secondary actuator for generating a secondary actuator 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 comprising a dual-stage controller comprising a degraded-stability primary actuator controller having relatively high low-frequency open-loop gain and a selectable single-stage controller for generating only a primary actuator control signal, the servo control processor including a model of the dynamic response of the primary actuator and a model of the dynamic response of the secondary actuator, the models providing a modeled head-position output when the control signals from the dual-stage controller are input to the models;
• and
• wherein the processor is capable of sending a location signal to the primary actuator for moving the primary actuator to the test location and, when the primary actuator is at the test location, generating a test signal to the secondary actuator and receiving the RPS in response to the test signal, wherein the single-stage controller is selected by the processor when the difference between the modeled head-position output and the measured head-position from the servo information detected by the head is greater than a predetermined value, and wherein the processor sends a location signal to the primary actuator when the single-stage controller is selected.

A disk drive comprising:

• a rotatable magnetic recording disk having a plurality of concentric data tracks, the 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 test location where movement of the VCM is substantially limited;
• a microactuator connected to the VCM, the head being connected to the microactuator;
• a relative-position sensor coupled to the microactuator for generating a microactuator relative-position signal (RPS) representing the position of the microactuator relative to its neutral position;
• and
• a servo control processor responsive to servo information read by the head and comprising a dual-stage controller for generating a VCM control signal and a microactuator control signal, the processor capable of sending a location signal to the VCM for moving the VCM to the test location and, when the VCM is at the test location, generating a test signal to the microactuator, receiving the RPS in response to the test signal, calculating the stroke of the microactuator from the RPS, and generating a failure signal if the calculated stroke is outside a predetermined stroke range.