Disk drive adjusting phase of adaptive feed-forward controller when reconfiguring servo loop

A method of operating a disk drive comprising a disk comprising tracks defined by servo sectors, a head, and control circuitry comprising a servo control system operable to actuate the head over the disk in response to the servo sectors, the method comprising:

• configuring the servo control system into a first state so as to comprise a first input sensitivity function;
• generating a position error signal (PES) representing a difference between a target location for the head and a measured location for the head;
• generating an actuator control signal in response to the PES;
• adapting a feed-forward control signal in response to the servo sectors;
• adjusting the actuator control signal using the feed-forward control signal;
• configuring the servo control system from the first state to a second state so as to comprise a second input sensitivity function different from the first input sensitivity function;
• and
• adjusting a phase of the adaptation of the feed-forward control signal based on the second state.

A disk drive comprising:

• a disk comprising tracks defined by servo sectors;
• a head;
• and
• control circuitry comprising a servo control system operable to actuate the head over the disk in response to the servo sectors, the control circuitry operable to:
• configure the servo control system into a first state;
• generate a position error signal (PES) representing a difference between a target location for the head and a measured location for the head;
• generate an actuator control signal in response to the PES;
• adapt a feed-forward control signal in response to the servo sectors;
• adjust the actuator control signal using the feed-forward control signal;
• configure the servo control system from the first state to a second state;
• adjust a phase of the adaptation of the feed-forward control signal based on the second state;
• prior to configuring the servo control system into the second state, save the phase of the adaptation of the feed-forward control signal;
• configure the servo control system from the second state to the first state;
• and
• restore the phase of the adaptation of the feed-forward control signal based on the saved phase.

A method of operating a disk drive comprising a disk comprising tracks defined by servo sectors, a head, and control circuitry comprising a servo control system operable to actuate the head over the disk in response to the servo sectors, the method comprising:

• configuring the servo control system into a first state;
• generating a position error signal (PES) representing a difference between a target location for the head and a measured location for the head;
• generating an actuator control signal in response to the PES;
• adapting a feed-forward control signal in response to the servo sectors;
• adjusting the actuator control signal using the feed-forward control signal;
• configuring the servo control system from the first state to a second state;
• adjusting a phase of the adaptation of the feed-forward control signal based on the second state;
• prior to configuring the servo control system into the second state, saving the phase of the adaptation of the feed-forward control signal;
• configuring the servo control system from the second state to the first state;
• and
• restoring the phase of the adaptation of the feed-forward control signal based on the saved phase.