Vibration control of piezoelectric microactuator

• US 6,600,619 B1
• Filed: 12/30/1999
• Issued: 07/29/2003
• Est. Priority Date: 02/22/1999
• Status: Expired due to Term

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Sluzewski, David A., Wright, John S., Morris, John C., Molloy, Brian G.
• Primary Examiner(s): Hudspeth, David
• Assistant Examiner(s): SLAVITT, MITCHELL R
• Application Number:
  US09/475,362
• Time in Patent Office: 1,307 Days
• Field of Search: 360/78.05, 360/75, 360/77.16, 360/78.12
• US Class Current: 360/75
• CPC Class Codes: G11B 5/5552 using fine positioning means for track acquisition separate from the coarse (e.g. track changing) positioning means
• CPC Class Codes: G11B 5/596 for track following on disks G11B5/5526, G11B5/5552, G11B5/5565, G11B5/5582 take precedence

Abstract

A system and method for controlling vibration of a piezoelectric microactuator in a disc drive are disclosed. The mechanical strain on the piezoelectric microactuator is ascertained and fed back to a controller which provides an electrical signal to the piezoelectric microactuator based upon the sensed strain. The electrical signal provided to the piezoelectric microactuator produces a mechanical force on the microactuator which counteracts the sensed strain. In one embodiment, a bridge circuit is coupled to the piezoelectric microactuator. The bridge circuit is adapted to sense a voltage across the piezoelectric microactuator and to separate the voltage across the piezoelectric microactuator into a voltage externally applied to the piezoelectric microactuator and a voltage induced on the piezoelectric microactuator by mechanical strain.

Claims

1. A method for controlling vibration of a piezoelectric microactuator in a disc drive, the piezoelectric microactuator adapted to finely position a read/write head relative to a track on a disc, the method comprising steps of:

(a) sensing the mechanical strain on the piezoelectric microactuator; and

(b) applying an electrical signal to the piezoelectric microactuator based on the sensed strain, whereby applying the electrical signal to the piezoelectric microactuator produces a mechanical force on the microactuator which at least reduces the sensed strain.

2. The method of claim 1 wherein the sensing step (a) comprises measuring a voltage induced on the piezoelectric microactuator by mechanical strain and wherein the applying step (b) comprises applying an electrical signal to the piezoelectric microactuator based on the voltage induced on the piezoelectric microactuator.

3. The method of claim 1 Wherein sensing step (a) further comprises steps of:

(a)(i) sensing a voltage across the piezoelectric microactuator; and

(a)(ii) separating the voltage across the piezoelectric microactuator into components comprising a voltage externally applied to the piezoelectric microactuator and a voltage induced on the piezoelectric microactuator by mechanical strain.

4. The method of claim 1 wherein the sensing step (a) includes sensing the mechanical strain directly from the microactuator.

5. The method of claim 1 wherein the disc drive comprises a plurality of heads and a plurality of piezoelectric microactuators and wherein the method is performed while one or more heads are writing a servo track to the disc and wherein sensing step (a) and applying step (b) are performed with respect to the plurality of piezoelectric microactuators concurrently, thereby reducing mechanical resonance of the plurality of piezoelectric microactuators.

6. The method of claim 1 wherein the method is performed while the head is involved with at least one of a group including seeking a selected track on the disc and following a selected track on the disc.

7. The method of claim 1 wherein the mechanical force on the microactuator counteracts the sensed strain.

8. The method of claim 1 further comprising a step (c) of repeating sensing step (a) and applying step (b) a plurality of times.

9. The method of claim 1 wherein applying step (b) further comprises calculating a magnitude of the electrical signal such that applying the electrical signal to the piezoelectric microactuator produces a mechanical force on the microactuator which minimizes the mechanical strain on the microactuator.

10. A disc drive comprising:

a disc adapted to store data;

a head adapted to be positioned adjacent the disc and adapted to read and write data to the disc;

a piezoelectric microactuator adapted to finely position the head relative to the disc;

a strain sensor adapted to sense the mechanical strain on the piezoelectric microactuator and to produce a sensed strain signal indicative of the sensed strain; and

a controller adapted to receive the sensed strain signal and to apply an electrical signal to the piezoelectric microactuator based on the sensed strain whereby the electrical signal applied to the piezoelectric microactuator produces a mechanical force on the microactuator which at least reduces the sensed strain.

11. The disc drive of claim 10 wherein the strain sensor is adapted to measure a voltage induced on the piezoelectric microactuator by mechanical strain and to produce a sensed strain signal indicative of the sensed strain based on the measured induced voltage.

12. The disc drive of claim 10 wherein the strain sensor comprises a bridge circuit coupled to the piezoelectric microactuator and adapted to sense a voltage across the piezoelectric microactuator.

13. The disc drive of claim 10 wherein the strain sensor is adapted to separate a voltage across the piezoelectric microactuator into components comprising a voltage externally applied to the piezoelectric microactuator and a voltage induced on the piezoelectric microactuator by mechanical strain.

14. The disc drive of claim 10 comprising:

a plurality of heads adapted to be positioned adjacent the disc and adapted to read and write data to the disc;

a plurality of piezoelectric microactuators, each adapted to finely position one of the plurality of heads relative to the disc; and

a plurality of strain sensors, each adapted to sense the mechanical strain on one of the piezoelectric microactuators and to produce a sensed strain signal indicative of the sensed strain, wherein the controller comprises a plurality of microactuator controllers, each adapted to receive the sensed strain signal produced by one of the plurality of strain sensors and to apply an electrical signal to the corresponding piezoelectric microactuator based on the sensed strain.

15. The disc drive of claim 10 comprising:

a plurality of heads adapted to be positioned adjacent the disc and adapted to read and write data to the disc;

a plurality of piezoelectric microactuators, each adapted to finely position one of the plurality of heads relative to the disc; and

a plurality of strain sensors, each adapted to sense the mechanical strain on one of the piezoelectric microactuators and to produce a sensed strain signal indicative of the sensed strain, wherein the controller is a multiple-input, multiple output servo controller adapted to receive the sensed strain signals produced by each of the plurality of strain sensors and to apply an electrical signal to each of the piezoelectric microactuators based on the sensed strain on the corresponding piezoelectric microactuator.

16. The disc drive of claim 10 further comprising a filter coupled to the strain sensor and adapted to remove frequencies from the sensed strain signal which are not within a prescribed range.

17. The disc drive of claim 16 wherein the filter is a high-pass filter adapted to remove frequencies from the sensed strain signal which are lower than a prescribed value.

18. The disc drive of claim 10 wherein the controller comprises a servo controller which is adapted to provide a first control signal to a voice coil motor to coarsely position the head relative to the disc and adapted to provide a second control signal to the piezoelectric microactuator to finely position the head relative to the disc.

19. The disc drive of claim 10 wherein the controller comprises a microactuator controller which is adapted to provide a control signal to the piezoelectric microactuator to finely position the head relative to the disc.

20. A disc drive comprising:

a piezoelectric microactuator adapted to finely position a head relative to a disc; and

means for reducing the mechanical strain on the piezoelectric microactuator.