Disk drive disturbance rejection using accelerometer and/or back-EMF measurements

• US 20040257693A1
• Filed: 06/04/2004
• Published: 12/23/2004
• Est. Priority Date: 06/05/2003
• Status: Abandoned Application

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ehrlich, Richard M.
• Application Number:
  US10/862,046
• Publication Number:
  US 20040257693A1
• Time in Patent Office: Days
• US Class Current: 360/77.02
• CPC Class Codes: G11B 5/5556 with track following after a "seek"
• CPC Class Codes: G11B 5/5582 system adaptation for working during or after external perturbation, e.g. in the presence of a mechanical oscillation caused by a shock
• CPC Class Codes: G11B 5/59605 Circuits G11B5/59627 - G11B5/59688 take precedence

Abstract

Track mis-registration (TMR) correction is conditionally made in a hard disk drive using servo data in a closed loop servo control scheme, along with one or more alternative sensing schemes when an external shock or vibration occurs. The alternative sensing schemes include measurement of spindle motor speed using a frequency of servo markers read from a rotating disk, voice control motor (VCM) back emf, spindle motor speed back emf, and accelerometer readings. The predicted TMR resulting from the signal generated by the alternative sensing scheme(s) is simulated based upon a model of the disk drive system, and corrections are applied only if the expected TMR due to the disturbances is large enough that application of the corrections using the alternative sensing scheme would be likely to reduce the overall TMR. In one case, actual operation is occasionally performed with and without corrective TMR feedback from the selected sensing scheme(s), and the actual values are compared with predictions from the system model and the results are used to update the system model.

Claims

1. The servo system for a hard disk drive that controls the track alignment of a read head relative to a desired tracking location using at least two measurements,

(a) a first measurement made from servo data position error signals (PES) read from the rotatable disk by the read head;

and

(b) a second measurement made from an accelerometer signal indicative of a disturbance applied to the hard disk drive, the second measurement being used to provide the track alignment correction only when the servo system determines that use of the second measurement reduces track alignment error.

2. The servo system of claim 1, wherein the accelerometer signal is provided from a linear accelerometer.

3. The servo system of claim 1, wherein the accelerometer signal is provided from a rotational accelerometer.

4. The servo system of claim 1, wherein the servo system determines use of the accelerometer signal will likely reduce track error when a disturbance threshold is exceeded.

5. The servo system of claim 4, wherein the disturbance threshold is a PES magnitude.

6. The servo system of claim 4, wherein the disturbance threshold is a magnitude of the accelerometer signal.

7. The servo system of claim 4, wherein when the disturbance is determined to exceed the threshold, track alignment correction is provided only using the accelerometer signal.

8. The servo system of claim 4, wherein when the disturbance is determined to exceed the threshold, track alignment correction is provided using both the accelerometer signal and the PES.

9. The servo system of claim 4, wherein the disturbance threshold is determined from a computer model that relates the PES and accelerometer signal.

10. The servo system of claim 4, wherein the disturbance threshold is set with a magnitude so that moving the transducer head to correct track alignment correction after the disturbance occurs would take less time than use of the PES alone.

11. The servo system of claim 4, further comprising:

a housing containing at least the rotatable disk, transducer head, processor and memory; and

an accelerometer attached to the housing, the accelerometer having a signal provided to the processor indicating when the disturbance is detected, and the magnitude of acceleration created by the disturbance.

12. The servo system of claim 4, wherein the disturbance threshold is provided with hysteresis.

13. The servo system of claim 4, wherein the disturbance comprises a physical shock.

14. The servo system of claim 4, wherein the disturbance comprises a vibration.

15. The servo system for a hard disk drive comprising:

a memory storing data indicating a disturbance threshold;

a processor coupled to the transducer head to read data from and write data to tracks on a rotatable disk, wherein track alignment correction of the head relative to a desired one of the tracks is determined by the processor using at least two measurements,

(a) a first measurement made from servo data position error signals (PES) read from the rotatable disk; and

(b) a second measurement made from an accelerometer signal provided to the processor indicating movement of the hard disk drive, the second measurement being used to provide the track alignment correction only when the disturbance threshold is exceeded.

16. A method providing servo control in a disk drive, the method comprising the steps of:

comparing a magnitude of disturbance determined from an accelerometer signal causing an acceleration of the disk drive with a threshold disturbance; and

performing track alignment correction to align a transducer head relative to a track on a disk by;

(a) using a position error signal (PES) determined from data read from the rotatable disk when the threshold is not exceeded without using the accelerometer signal, and

(b) using the accelerometer signal to perform the track alignment correction when the threshold is exceeded.

17. The method of claim 16, wherein the accelerometer comprises a linear accelerometer.

18. The method of claim 16, wherein the accelerometer comprises a rotational accelerometer.

19. A method providing servo control in a disk drive, the method comprising the steps of:

comparing an accelerometer signal magnitude with a threshold accelerometer signal; and

performing track alignment correction to align a transducer head relative to a track on a disk by;

(a) using the accelerometer signal when the threshold is exceeded, and

(b) using a position error signal (PES) determined from data read from a rotatable disk to perform the track alignment correction without the accelerometer signal when the threshold is not exceeded.

20. A method providing servo control in a disk drive, the method comprising the steps of:

comparing a position error signal (PES) value determined from data read from a rotatable disk with a threshold magnitude of the PES; and

performing track alignment correction to align a transducer head relative to a track on a disk by;

(a) using the accelerometer signal when the threshold is exceeded, and

(b) using a position error signal (PES) determined from data read from a rotatable disk to perform the track alignment correction without the accelerometer signal when the threshold is not exceeded.

21. The servo system for a hard disk drive that controls the track alignment of a read head relative to a desired tracking location using at least two measurements,

(c) a first measurement made from servo data position error signals (PES) read from the rotatable disk by the read head;

and

(d) a second measurement made from a back emf signal indicative of a disturbance applied to the hard disk drive, the second measurement being used to provide the track alignment correction only when the servo system determines that use of the second measurement reduces track alignment error.

22. The servo system of claim 21, further comprising:

a voice control motor (VCM) movably supporting the read/write head, wherein the back emf signal is provided from windings of the VCM.

23. The servo system of claim 22, further comprising:

a spindle motor rotabably supporting the disk,

wherein the track misalignment correction is further determined using a back emf signal provided from windings of the spindle motor when the servo system determines use of the VCM back emf signal will reduce track alignment error.

24. The servo system of claim 21, further comprising:

a spindle motor rotatably supporting the disk, wherein the back emf signal is provided from windings of the spindle motor.

25. The servo system of claim 24, further comprising:

a voice control motor (VCM) movably supporting the transducer head,

wherein the track misalignment correction is further determined using a back emf signal provided from windings of the VCM when the servo system determines use of the spindle motor back emf signal will reduce track alignment error.

26. The servo system of claim 21, wherein the servo system determines use of the back emf signal will likely reduce track error when a disturbance threshold is exceeded.

27. The servo system of claim 26, wherein the disturbance threshold is a PES magnitude.

28. The servo system of claim 26, wherein the disturbance threshold is a magnitude of the back emf signal.

29. The servo system of claim 26, wherein when the disturbance is determined to exceed the threshold, track alignment correction is provided only using the back emf signal.

30. The servo system of claim 26, wherein when the disturbance is determined to exceed the threshold, track alignment correction is provided using both the back emf signal and the PES.

31. The servo system of claim 26, wherein the disturbance threshold is determined from a computer model that relates a predicted PES to a back emf signal amount.

32. The servo system of claim 26, wherein the disturbance threshold is set with a magnitude so that moving the transducer head to make track alignment corrections after the disturbance occurs would take less time than use of the PES alone.

33. The servo system of claim 26, wherein the disturbance threshold is provided with hysteresis.

34. The servo system of claim 21, wherein the disturbance comprises a physical shock.

35. The servo system of claim 21, wherein the disturbance comprises a vibration.

36. A servo system for a hard disk drive comprising:

a voice control motor (VCM) configured to move a transducer head relative to tracks on a rotatable disk; and

a VCM back emf detection circuit that provides a VCM back emf signal measured from current provided from a winding of the VCM,

a processor coupled to receive the VCM back emf signal, wherein the VCM back emf signal magnitude is compared with a threshold, and

when the VCM back emf signal magnitude is greater than the threshold, the processor causes the VCM to make track alignment corrections to align a position of the head relative to one of the tracks using the VCM back emf signal, and

when the VCM back emf signal is less than the threshold, the processor does not use the VCM back emf signal to make the track alignment corrections.

37. The servo system of claim 36 further comprising:

a spindle motor rotatably supporting the disk;

a spindle motor back emf detection circuit that provides a spindle motor back emf signal measured from current provided from windings of the spindle motor,

wherein the processor is receives the spindle motor back emf signal, and when the VCM back emf signal is greater than the threshold, the processor further uses the spindle motor back emf signal to make track alignment corrections.

38. A servo system for a hard disk drive comprising:

a spindle motor rotatably supporting a disk;

a spindle motor back emf detection circuit that provides a spindle motor back emf signal measured from current provided from windings of the spindle motor,

a processor coupled to receive the spindle motor back emf signal, wherein the VCM back emf signal magnitude is compared with a threshold, and

when the spindle motor back emf signal magnitude is greater than the threshold, the processor causes track alignment corrections to align a position of a transducer head relative to a track on the disk using the spindle motor back emf signal, and

when the spindle motor back emf signal is less than the threshold, the processor does not use the spindle motor back emf signal to make the track alignment corrections.

39. The servo system of claim 38 further comprising:

a voice control motor (VCM) configured to move the transducer head relative to tracks on the disk; and

a VCM back emf detection circuit that provides a VCM back emf signal measured from current provided from a winding of the VCM

wherein the processor is receives the VCM back emf signal, and when the spindle motor back emf signal is greater than the threshold, the processor further uses the VCM back emf signal to make track alignment corrections.

40. The servo system for a hard disk drive comprising:

a memory storing data indicating a disturbance threshold;

a processor coupled to the transducer head to read data from and write data to tracks on a rotatable disk, wherein track alignment correction of the head relative to a desired one of the tracks is determined by the processor using at least two measurements,

(a) a first measurement made from servo data position error signals (PES) read from the rotatable disk, and

(b) a second measurement made from a back emf signal provided to the processor indicating movement of the hard disk drive, the second measurement being used to provide the track alignment correction only when the disturbance threshold is exceeded.

41. A method providing servo control in a disk drive, the method comprising the steps of:

comparing a magnitude of disturbance causing an acceleration of the disk drive with a threshold disturbance; and

performing track alignment correction to align a transducer head relative to a track on a disk by;

(c) using a position error signal (PES) determined from data read from the rotatable disk when the threshold is not exceeded without using the back emf signal, and

(d) using the back emf signal to perform the track alignment correction when the threshold is exceeded.

42. The method of claim 41, wherein the back emf signal is a VCM back emf signal.

43. The method of claim 41, wherein the back emf signal is a spindle motor back emf signal.

44. A method providing servo control in a disk drive, the method comprising the steps of:

comparing a back emf signal magnitude with a threshold magnitude of back emf; and

performing track alignment correction to align a transducer head relative to a track on a disk by;

(c) using the back emf signal when the threshold is exceeded, and

(d) using a position error signal (PES) determined from data read from a rotatable disk to perform the track alignment correction without the back emf signal when the threshold is not exceeded.

45. A method providing servo control in a disk drive, the method comprising the steps of:

comparing a position error signal (PES) determined from data read from a rotatable disk with a threshold magnitude of the PES; and

performing track alignment correction to align a transducer head relative to a track on a disk by;

(a) using the back emf signal when the threshold is exceeded, and

(b) using the PES to perform the track alignment correction without the back emf signal when the threshold is not exceeded.