Disk drive measuring stroke difference between heads by detecting a difference between ramp contact

• US 9,355,666 B1
• Filed: 06/08/2015
• Issued: 05/31/2016
• Est. Priority Date: 09/30/2013
• 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: Huang, Yanan, Zhang, Zhenyu, Ji, Chuanwen, Phan, Duc T.
• Primary Examiner(s): Agustin, Peter Vincent
• Application Number:
  US14/733,027
• Time in Patent Office: 358 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G11B 21/12 Raising and lowering; Back-spacing or forward-spacing along track; Returning to starting position otherwise than during transducing operation
• CPC Class Codes: G11B 5/59627 Aligning for runout, eccentricity or offset compensation G11B5/5534, G11B5/59677, G11B5/59688 take precedence

Abstract

A data storage device is disclosed comprising a plurality of disk surfaces including a first disk surface and a second disk surface. A first head is actuated over the first disk surface, and a second head is actuated over the second disk surface. A ramp is located proximate an outer diameter of the disk surfaces. A stroke difference between the first and second heads is measured by moving the first and second heads toward the ramp and detecting when the heads contact the ramp.

Claims

1. A data storage device comprising:

a plurality of disk surfaces including a first disk surface and a second disk surface;

a first head actuated over the first disk surface;

a second head actuated over the second disk surface;

a ramp proximate an outer diameter of the disk surfaces; and

control circuitry configured to measure a stroke difference between the first and second heads by moving the first and second heads toward the ramp and detecting when the heads contact the ramp.

2. The data storage device as recited in claim 1, wherein the data storage device further comprises a voice coil motor (VCM) configured to actuate the heads over the disk surfaces, and control circuitry is further configured to:

while moving the first and second heads toward the ramp, periodically sample a back electromotive force (BEMF) voltage of the VCM to generate a BEMF sample sequence;

after the heads contact the ramp, post-process the BEMF sample sequence to estimate a distance of movement for each of the heads; and

measure the stroke difference based on the distance of movement for each of the heads.

3. The data storage device as recited in claim 2, wherein the control circuitry is further configured to:

post-process the BEMF sample sequence by filtering the BEMF sample sequence using a non-causal filter to generate a filtered BEMF sample sequence; and

estimate the distance of movement for each of the heads based on the filtered BEMF sample sequence.

4. The data storage device as recited in claim 1, wherein the control circuitry is further configured to:

while moving the first head and the second heads toward the ramp, toggle between evaluating a first contact signal generated by the first head and a second contact signal generated by the second head; and

measure the stroke difference between the first head and the second head based on when the first contact signal indicates contact with the ramp and when the second contact signal indicates contact with the ramp.

5. The data storage device as recited in claim 1, wherein the first disk surface comprises a plurality of eccentric tracks and the control circuitry is further configured to:

measure a repeatable runout (RRO) of a reference track on the first disk surface representing the eccentricity of the reference track;

process the RRO of the reference track to servo the first head at a substantially fixed location as the disk rotates; and

measure a stroke of the first head by moving the first head toward the ramp from the fixed location.

6. The data storage device as recited in claim 5, wherein the control circuitry is further configured to measure a stroke of the first head multiple times by moving the first head toward the ramp from the fixed location starting from different rotation angles of the disk.

7. The data storage device as recited in claim 1, wherein the control circuitry is further configured to measure a stroke of the first head multiple times by moving the first head toward the ramp from a reference location starting from different rotation angles of the disk.

8. The data storage device as recited in claim 1, wherein the first head comprises a first touchdown sensor, the second head comprises a second touchdown sensor, and while moving the first and second heads toward the ramp the control circuitry is further configured to:

sample a first contact signal generated by the first touchdown sensor to generate a first contact sample sequence;

sample a second contact signal generated by the second touchdown sensor to generate a second contact sample sequence;

real-time detect the first head contacting the ramp based on the first contact sample sequence;

when the first head contacting the ramp is real-time detected, disable the first touchdown sensor;

real-time detect the second head contacting the ramp based on the second contact sample sequence; and

when contact the second head contacting the ramp is real-time detected, disable the second touchdown sensor.

9. The data storage device as recited in claim 8, wherein the control circuitry is further configured to real-time detect the first head contacting the ramp based on:

10. The data storage device as recited in claim 8, wherein after moving the first and second heads toward the ramp the control circuitry is further configured to:

post-time detect the first head contacting the ramp based on the first contact sample sequence; and

post-time detect the second head contacting the ramp based on the second contact sample sequence.

11. The data storage device as recited in claim 8, wherein the control circuitry is further configured to post-time detect the first head contacting the ramp based on:

12. The data storage device as recited in claim 11, wherein the control circuitry is further configured to post-time detect the first head contacting the ramp based on a difference between LPF(n) and RPF(n).

13. The data storage device as recited in claim 12, wherein the control circuitry is further configured to post-time detect the first head contacting the ramp based on when the difference between LPF(n) and RPF(n) reaches an extremum.

14. A method of operating a data storage device, the method comprising:

moving first and second heads over respective disk surfaces to generate a contact signal; and

measuring a stroke difference between the first and second heads by detecting when the heads contact a ramp based on the contact signal.

15. The method as recited in claim 14, further comprising:

while moving the first and second heads toward the ramp, periodically sampling a back electromotive force (BEMF) voltage of the VCM to generate a BEMF sample sequence;

after the heads contact the ramp, post-processing the BEMF sample sequence to estimate a distance of movement for each of the heads; and

measuring the stroke difference based on the distance of movement for each of the heads.

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

post-processing the BEMF sample sequence by filtering the BEMF sample sequence using a non-causal filter to generate a filtered BEMF sample sequence; and

estimating the distance of movement for each of the heads based on the filtered BEMF sample sequence.

17. The method as recited in claim 14, further comprising:

while moving the first head and the second heads toward the ramp, toggling between evaluating a first contact signal generated by the first head and a second contact signal generated by the second head; and

measuring the stroke difference between the first head and the second head based on when the first contact signal indicates contact with the ramp and when the second contact signal indicates contact with the ramp.

18. The method as recited in claim 14, wherein the first disk surface comprises a plurality of eccentric tracks and the method further comprises:

measuring a repeatable runout (RRO) of a reference track on the first disk surface representing the eccentricity of the reference track;

processing the RRO of the reference track to servo the first head at a substantially fixed location as the disk rotates; and

measuring a stroke of the first head by moving the first head toward the ramp from the fixed location.

19. The method as recited in claim 18, further comprising measuring a stroke of the first head multiple times by moving the first head toward the ramp from the fixed location starting from different rotation angles of the disk.

20. The method as recited in claim 14, further comprising measuring a stroke of the first head multiple times by moving the first head toward the ramp from a reference location starting from different rotation angles of the disk.

21. The method as recited in claim 14, wherein while moving the first and second heads toward the ramp the method further comprises:

sampling a first contact signal generated by a first touchdown sensor of the first head to generate a first contact sample sequence;

sampling a second contact signal generated by a second touchdown sensor of the second head to generate a second contact sample sequence;

real-time detecting the first head contacting the ramp based on the first contact sample sequence;

when the first head contacting the ramp is real-time detected, disabling the first touchdown sensor;

real-time detecting the second head contacting the ramp based on the second contact sample sequence; and

when contact the second head contacting the ramp is real-time detected, disabling the second touchdown sensor.

22. The method as recited in claim 21, further comprising real-time detecting the first head contacting the ramp based on:

23. The method as recited in claim 21, wherein after moving the first and second heads toward the ramp the method further comprises:

post-time detecting the first head contacting the ramp based on the first contact sample sequence; and

post-time detecting the second head contacting the ramp based on the second contact sample sequence.

24. The method as recited in claim 21, further comprising post-time detecting the first head contacting the ramp based on:

25. The method as recited in claim 24, further comprising post-time detecting the first head contacting the ramp based on a difference between LPF(n) and RPF(n).

26. The method as recited in claim 25, further comprising post-time detecting the first head contacting the ramp based on when the difference between LPF(n) and RPF(n) reaches an extremum.