Rotational vibration compensation using a dedicated surface with a constant frequency pattern

• US 6,285,522 B1
• Filed: 12/18/1998
• Issued: 09/04/2001
• Est. Priority Date: 06/05/1998
• Status: Expired due to Fees

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Wilson, Nathaniel B., Francis, Stuart K., McKenzie, Lealon R., Douglas, D. Brent
• Primary Examiner(s): Hudspeth, David
• Assistant Examiner(s): HABERMEHL, JAMES LEE
• Application Number:
  US09/215,470
• Time in Patent Office: 991 Days
• Field of Search: 360/77.05, 360/60, 360/75, 360/77.02, 360/77.08
• US Class Current: 360/77.05
• CPC Class Codes: G11B 33/08 Insulation or absorption of undesired vibrations or sounds
• 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 5/59627 Aligning for runout, eccentricity or offset compensation G11B5/5534, G11B5/59677, G11B5/59688 take precedence

Abstract

An apparatus and method for minimizing the effects of rotational vibration upon a disc drive having first and second heads supported adjacent first and second disc recording surfaces, respectively. A frequency modulation (FM) demodulator generates a rotational velocity signal indicative of application of rotational vibration to the base deck in relation to changes in frequency of a readback signal generated from a circumferentially extending frequency pattern written to the first disc recording surface at a constant frequency. A servo circuit controllably positions the first and second heads in response to servo information stored on the second disc recording surface and the rotational velocity signal from the FM demodulator. The servo circuit further interrupts a data transfer operation between the second disc recording surface and a host device when a magnitude of the rotational velocity signal exceeds a predetermined threshold.

Claims

1. In a disc drive having a rotary actuator supporting at least first and second heads adjacent first and second disc recording surfaces, respectively, the actuator and the first and second disc recording surfaces supported by a base deck, an apparatus for reducing effects of rotational vibration applied to the base deck, comprising:

a frequency modulation (FM) demodulator, operably coupled to the first head, which generates a rotational velocity signal indicative of application of rotational vibration to the base deck in relation to changes in frequency of a readback signal generated from a circumferentially extending frequency pattern written to the first disc recording surface at a constant frequency;

a servo circuit, operably coupled to the second head and the FM demodulator, which controllably positions the first and second heads in response to servo information stored on the second disc recording surface and the rotational velocity signal from the FM demodulator;

a gain block, operably coupled to the FM demodulator, which applies a gain to the rotational velocity signal to generate an adjusted rotational velocity signal; and

a differentiator block, operably coupled to the gain block, which differentiates the adjusted rotational velocity signal to generate a rotational acceleration signal indicative of a tangentially directed acceleration component of the rotational vibration applied to the base deck, wherein the servo circuit selects the gain to reduce error in the positioning of the second head induced by the application of rotational vibration to the base deck.

2. The apparatus of claim 1, wherein the servo circuit interrupts a data transfer operation between the second disc recording surface and a host device associated with the disc drive when a magnitude of the rotational velocity signal exceeds a predetermined threshold.

3. The apparatus of claim 1, wherein the actuator further supports a magnetic coil and wherein the servo circuit uses the rotational acceleration signal to generate a current command signal indicative of current applied to the magnetic coil to position the first and second heads.

4. The apparatus of claim 1, wherein the servo circuit selects the gain to minimize error in the positioning of the second head induced by the application of rotational vibration to the base deck.

5. The apparatus of claim 1, wherein the servo circuit comprises a processor having associated programming to:

set the gain to an initial value; and

selectively vary the value of the gain while measuring an average position error signal indicative of error in the positioning of the second head to identify an optimum value of the gain.

6. The apparatus of claim 5, wherein the optimum gain is selected while the disc drive is operated in a rich vibrational environment wherein both rotational and translational vibration components are imparted to the disc drive.

7. The apparatus of claim 6, wherein the disc drive is mechanically coupled to a plurality of additional disc drives so that at least portions of the rotational and translational components are established by the operation of the additional disc drives.

8. The apparatus of claim 7, wherein the servo circuit determines the optimum value of the gain during manufacture of the disc drive.

9. The apparatus of claim 8, wherein the servo circuit determines the optimum value of the gain during subsequent operational use of the disc drive.

10. A disc drive, comprising:

a base deck;

a rotatable disc, supported by the base deck, having oppositely disposed first and second recording surfaces, the first recording surface having a circumferentially extending frequency pattern written at a constant frequency and the second recording surface having a plurality of servo fields interspersed with data fields;

a rotary actuator, supported by the base deck, which supports first and second heads adjacent the first and second recording surfaces, respectively;

a frequency modulation (FM) demodulator, operably coupled to the first head, which generates a rotational velocity signal indicative of application of rotational vibration to the base deck in relation to changes in frequency of a readback signal generated from the circumferentially extending frequency pattern;

a servo circuit, operably coupled to the second head and the FM demodulator, which controllably rotates the first and second heads with respect to the disc in response to servo information stored on the second recording surface and the rotational velocity signal from the FM demodulator,

a gain block which applies a gain to the rotational velocity signal to generate an adjusted rotational velocity signal; and

a differentiator block which differentiates the adjusted rotational velocity signal to generate a rotational acceleration signal indicative of a tangentially directed acceleration component of the rotational vibration applied to the base deck, wherein the servo circuit selects the gain to reduce error in the positioning of the second head induced by the application of rotational vibration to the base deck.

11. The disc drive of claim 10, wherein the servo circuit interrupts a data transfer operation between the data fields of the second recording surface and a host device associated with the disc drive when a magnitude of the rotational velocity signal exceeds a predetermined threshold.

12. The disc drive of claim 10, wherein the circumferentially extending frequency pattern on the first recording surface radially extends substantially from an innermost radius to an outermost radius of the disc.

13. A method for minimizing effects of rotational vibration on a disc drive comprising a base deck supporting a rotary actuator which supports first and second heads adjacent first and second disc recording surfaces, respectively, comprising steps of:

(a) operating the disc drive in a rich vibrational environment wherein both rotational and translational vibration components are imparted to the disc drive,

(b) generating a readback signal as the first head reads a circumferentially extending frequency pattern previously written at a constant frequency to the first recording surface;

(c) applying frequency demodulation to the readback signal to derive a rotational velocity signal indicative of application of rotational vibration to the base deck in relation to changes in frequency of the readback signal; and

(d) controlling the position of the first and second heads in relation to the rotational velocity signal, comprising steps of;

(d1) applying a gain to the rotational velocity signal to generate an adjusted rotational velocity signal;

(d2) differentiating the adjusted rotational velocity signal to generate a rotational acceleration signal indicative of a tangentially directed acceleration component of the rotational vibration applied to the base deck;

(d3) using the rotational acceleration signal to generate a current command signal which controls a magnitude of current applied to a coil of the actuator to control the position of the first and second heads.

(d4) setting the gain to an initial value;

(d5) selectively varying the value of the gain while measuring an average position error signal indicative of error in the positioning of the second head to identify an optimum value of the gain; and

(d6) using the optimum value of the gain in the applying step (d1).

14. The method of claim 13, further comprising a step of:

(e) interrupting a data transfer operation between the second recording surface and a host device associated with the disc drive when a magnitude of the rotational velocity signal exceeds a predetermined threshold.

15. The method of claim 13, wherein the operating step (a) further comprises mechanically coupling the disc drive to a plurality of additional disc drives so that at least portions of the rotational and translational components are established by operation of the additional disc drives.