Disk drive comprising a per-drive and per-head fly height filter

• US 9,053,749 B1
• Filed: 03/15/2013
• Issued: 06/09/2015
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: JP Morgan Chase Bank, N.A. (JP Morgan Chase & Co)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Haralson, Phillip S., Anderson, Kent D.
• Primary Examiner(s): Sniezek, Andrew L
• Application Number:
  US13/840,225
• Time in Patent Office: 816 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G11B 27/36 Monitoring, i.e. supervising the progress of recording or reproducing for digital recording G11B20/00 and s.gr.; for monitoring, testing or measuring of TV recorders of the type covered by H04N5/76 and subgroups, see H04N17/06
• CPC Class Codes: G11B 5/5534 Initialisation, calibration, e.g. cylinder "set-up"
• CPC Class Codes: G11B 5/6011 Control of flying height
• CPC Class Codes: G11B 5/6029 Measurement using values derived from the data signal read from the disk

Abstract

A disk drive is disclosed comprising a plurality of disk surfaces, and a head actuated over each disk surface, where each head comprises a fly height actuator (FHA) operable to control a fly height of the head over the corresponding disk surface. A fly height is measured for each head to generate a plurality of fly height measurements. An average value is generated in response to the plurality of fly height measurements, and a first control value is generated for a first head based on the average value and the fly height measurement for the first head. The first FHA of the first head is controlled in response to the first control value.

Claims

1. A disk drive comprising:

a plurality of disk surfaces;

a head actuated over each disk surface, where each head comprises a fly height actuator (FHA) operable to control a fly height of the head over the respective disk surface; and

control circuitry operable to;

measure a fly height for each head to generate a plurality of fly height measurements;

calculate an average value in response to the plurality of fly height measurements;

generate a first control value for a first head as a function of the calculated average value and the fly height measurement for the first head; and

control the first FHA of the first head in response to the first control value.

2. The disk drive as recited in claim 1, wherein the control circuitry is further operable to generate the first control value as a function of the calculated average value and the fly height measurement for the first head and a previous control value for the first head.

3. The disk drive as recited in claim 1, wherein the control circuitry is further operable to:

generate a second control value for a second head as a function of the calculated average value and the fly height measurement for the second head; and

control the second FHA of the second head in response to the second control value.

4. The disk drive as recited in claim 1, wherein the control circuitry is further operable to:

measure a fly height delta for each head, wherein the fly height delta represents a difference between the measured fly height and a target fly height for each head;

generate the average value by averaging the fly height deltas; and

generate the first control value for the first head based on the average value and the fly height delta for the first head.

5. The disk drive as recited in claim 4, wherein the control circuitry is further operable to:

generate a first deviation value for the first head based on a difference between the fly height delta for the first head and the average value; and

generate the first control value for the first head based on the average value and the first deviation value for the first head.

6. The disk drive as recited in claim 5, wherein the control circuitry is further operable to:

amplify the average value by a first gain to generate a first amplified value;

amplify the first deviation value for the first head by a second gain less than the first gain to generate a second amplified value; and

generate the first control value for the first head by summing the first amplified value with the second amplified value.

7. The disk drive as recited in claim 5, wherein the control circuitry is further operable to:

compare the first deviation value for the first head to a threshold; and

when the first deviation value for the first head exceeds the threshold, set the second amplified value to zero in order to generate the first control value independent of the first deviation value for the first head.

8. The disk drive as recited in claim 1, wherein the control circuitry is operable to:

periodically measure the fly height for each head at a sampling rate; and

adjust the sampling rate based on the periodic fly height measurements.

9. The disk drive as recited in claim 8, wherein the control circuitry is operable to:

periodically measure a fly height delta for each head at the sampling rate, wherein the fly height delta represents a difference between the measured fly height and a target fly height for each head; and

adjust the sampling rate based on the periodic fly height delta measurements.

10. The disk drive as recited in claim 9, wherein the control circuitry is operable to increase the sampling rate when the periodic fly height delta exceeds a threshold.

11. The disk drive as recited in claim 9, wherein the control circuitry is operable to increase the sampling rate when a derivative of the periodic fly height delta exceeds a threshold.

12. The disk drive as recited in claim 9, wherein the control circuitry is operable to:

filter the periodic fly height delta to generate a filtered fly height delta; and

increase the sampling rate when the filtered fly height delta exceeds a threshold.

13. A method of operating a disk drive comprising a plurality of disk surfaces and a head actuated over each disk surface, where each head comprises a fly height actuator (FHA) operable to control a fly height of the head over the respective disk surface, the method comprising:

measuring a fly height for each head to generate a plurality of fly height measurements;

calculating an average value in response to the plurality of fly height measurements;

generating a first control value for a first head as a function of the calculated average value and the fly height measurement for the first head; and

controlling the first FHA of the first head in response to the first control value.

14. The method as recited in claim 13, further comprising generating the first control value as a function of the calculated average value and the fly height measurement for the first head and a previous control value for the first head.

15. The method as recited in claim 13, further comprising:

generating a second control value for a second head as a function of the calculated average value and the fly height measurement for the second head; and

controlling the second FHA of the second head in response to the second control value.

16. The method as recited in claim 13, further comprising:

measuring a fly height delta for each head, wherein the fly height delta represents a difference between the measured fly height and a target fly height for each head;

generating the average value by averaging the fly height deltas; and

generating the first control value for the first head based on the average value and the fly height delta for the first head.

17. The method as recited in claim 16, further comprising:

generating a first deviation value for the first head based on a difference between the fly height delta for the first head and the average value; and

generating the first control value for the first head based on the average value and the first deviation value for the first head.

18. The method as recited in claim 17, further comprising:

amplifying the average value by a first gain to generate a first amplified value;

amplifying the first deviation value for the first head by a second gain less than the first gain to generate a second amplified value; and

generating the first control value for the first head by summing the first amplified value with the second amplified value.

19. The method as recited in claim 17, further comprising:

comparing the first deviation value for the first head to a threshold; and

when the first deviation value for the first head exceeds the threshold, setting the second amplified value to zero in order to generate the first control value independent of the first deviation value for the first head.

20. The method as recited in claim 13, further comprising:

periodically measuring the fly height for each head at a sampling rate; and

adjusting the sampling rate based on the periodic fly height measurements.

21. The method as recited in claim 20, further comprising:

periodically measuring a fly height delta for each head at the sampling rate, wherein the fly height delta represents a difference between the measured fly height and a target fly height for each head; and

adjusting the sampling rate based on the periodic fly height delta measurements.

22. The method as recited in claim 21, further comprising increasing the sampling rate when the periodic fly height delta exceeds a threshold.

23. The method as recited in claim 21, further comprising increasing the sampling rate when a derivative of the periodic fly height delta exceeds a threshold.

24. The method as recited in claim 21, further comprising:

filtering the periodic fly height delta to generate a filtered fly height delta; and

increasing the sampling rate when the filtered fly height delta exceeds a threshold.