Acceleration feed-forward correction enabled or disabled based on track follow loop signals

Abstract

Disturbances to actuator control caused by external vibrations are corrected using feed-forward techniques that are selectively enabled or disabled based on signal values within a track follow loop. An increase in data integrity and reliability may be achieved by reducing off-track reads and writes caused by physical disturbances to disk drives during operation. Accelerometers detect external forces imparted on a disk and an acceleration feed-forward (AFF) signal is generated to compensate for disturbances to the location of a head caused by such external forces. Application of the AFF signal to an actuator may be based on whether signal values along the track follow loop exceed a certain threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exploded perspective view of a disk drive of an embodiment of the present invention;

FIG. 2 illustrates a functional block diagram of a disk drive of an embodiment of the present invention in communication with a host system;

FIG. 3 illustrates a block diagram of a track follow loop and an acceleration feed-unit forward control unit of a servo controller in accordance with an embodiment of the present invention.

FIG. 4 illustrates a block diagram of a servo vibe detect unit of an embodiment of the present invention.

Claims

1. An acceleration feed-forward (AFF) system comprising: an acceleration feed-forward (AFF) unit configured to selectively provide an AFF signal based on track follow loop signal samples; anda track follow system for at least partially controlling motion of an actuator relative to the selected track of the storage medium, based on the acceleration feed-forward (AFF) signal.

2. The system of claim 1, wherein the track follow loop signal samples are position error signal (PES) samples.

3. The system of claim 1, wherein the track follow loop signal samples are current drive signal (CDS) samples.

4. The system of claim 1, wherein the track follow loop signal samples are both PES samples and CDS samples.

5. The system of claim 1, wherein the acceleration feed-forward (AFF) unit comprises: a counter having a counter cycle for counting from an initial value;an absolute value unit for providing an absolute value of the track follow loop signal samples;a summation unit for generating a sum value representing the total value of the absolute values of the track follow loop signal samples added together within one counter cycle;a filter unit configured to provide output values from one or more sum values generated by the summation unit;a comparator unit for comparing the filter output values with a threshold value;wherein the AFF unit provides the AFF signal if one or more filter output values exceed the threshold value so that the actuator is able to be at least partially controlled by the AFF signal.

6. The system of claim 5, wherein the counter count is altered each time the summation unit adds the absolute value of a track follow loop signal sample to the sum value, and is reset to the initial value when the counter count reaches a predefined value.

7. The system of claim 5, wherein: while the storage system is in a seek mode, addition of the absolute value of the track follow loop signal samples by the summation unit is suspended, the counter has a count value that remains constant, filtering by the filter unit is suspended, and comparing of the filter output values to the threshold value by the comparator unit is suspended;upon the storage system re-entering a tracking mode, addition of the absolute value of the track follow loop signal samples by the summation unit resumes, the counter count value continues to decrement from the same counter count when last suspended, filtering by the filter unit resumes, and comparing of the filter output values to the threshold value resumes.

8. The system of claim 5, wherein: while an error condition is present, addition of the absolute value of the track follow loop signal samples by the summation unit is suspended, the counter count value remains constant, filtering by the filter unit is suspended, and comparing of the filter output values to the threshold value is suspended;upon removal of the error condition, addition of the absolute value of the track follow loop signal samples by the summation unit resumes, the counter count value continues to decrement from the same counter count when last suspended, filtering by the filter unit resumes, and comparing of the filter output values to the threshold value resumes.

9. The system of claim 5, wherein the threshold value is automatically adjusted based on the hostility of the environment the magnetic storage system is in.

10. The system of claim 5, wherein the initial value of the counter is equal to the number of servo sectors around one disk revolution along one track.

11. The system of claim 5, wherein the filter is a low-pass filter.

12. The system of claim 1, wherein the track follow loop signal samples are coarse actuator compensator signal samples.

13. The system of claim 1, wherein the AFF unit comprises: a variance calculating unit that generates a variance value of more than one of the track follow loop signal samples;a filter unit configured to provide filter output values by filtering one or more variance values generated by the variance calculating unit;a comparator unit for comparing the filter output values with an adjustable threshold value;wherein the AFF unit provides the AFF signal if one or more filter output values exceed the threshold value so that the coarse actuator is able to be at least partially controlled by the AFF signal.

14. The system of claim 13, wherein the more than one of the track follow loop signal samples are PES samples and CDS samples.

15. The system of claim 1, wherein in the event that the AFF unit provides the AFF signal so that the actuator is able to be at least partially controlled by the AFF signal, the AFF unit stops providing the AFF signal after a period of time, the period of time being adjustable.

16. The system of claim 15, wherein the period time is automatically adjusted based on the hostility of the environment of the system is in.

17. A storage system comprising: a storage medium having a surface with one or more tracks for storing data;a read/write device for reading data from the storage medium and/or for writing data to the storage medium;an actuator for positioning the read/write device relative to a selected track of the one or more tracks;a sensor for providing a signal based on the sensed forces; andan acceleration feed-forward (AFF) system as recited in claim 1, for providing an AFF signal based on the signal provided by the sensor.

18. An acceleration feed-forward (AFF) system comprising: an acceleration feed-forward (AFF) unit configured to selectively provide an AFF signal based on whether a storage system employing the acceleration feed-forward (AFF) system is in a read or write retry state; anda track follow system for at least partially controlling motion of an actuator relative to the selected track of the storage medium, based on the acceleration feed-forward (AFF) signal.

19. A method for providing an acceleration feed-forward (AFF) signal to compensate for any disturbances to a position of a head of a storage system relative to a selected track of a storage medium, the method comprising: selectively providing an acceleration feed-forward (AFF) signal based on (i) track follow loop signal samples and/or (ii) whether a storage system employing the method is in a read or write retry state; andat least partially controlling motion of an actuator relative to the selected track of the storage medium, based on the acceleration feed-forward (AFF) signal.

20. The method of claim 19, wherein selectively providing an AFF signal comprises providing an AFF signal based on track follow loop signal samples and wherein the track follow loop signal samples are one or both of position error signal (PES) samples and current drive signal (CDS) samples.