Control scheme for multi-actuator disc drive

• US 6,121,742 A
• Filed: 03/19/1999
• Issued: 09/19/2000
• Est. Priority Date: 03/20/1998
• Status: Expired due to Term

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Misso, Nigel F.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US09/273,005
• Time in Patent Office: 550 Days
• Field of Search: 318/562, 318/625, 360/75, 360/77.01, 360/77.02, 360/77.05, 360/78.04-78.14, 369/43, 369/44.11, 369/44.25, 369/44.35, 369/44.36
• US Class Current: 318/562
• CPC Class Codes: G11B 21/083 on discs
• CPC Class Codes: G11B 21/18 while the head is moving
• CPC Class Codes: G11B 5/4886 relative to rotating disc
• CPC Class Codes: G11B 5/553 Details
• CPC Class Codes: G11B 5/59605 Circuits G11B5/59627 - G11B5/59688 take precedence
• CPC Class Codes: G11B 5/59644 Acquisition or selection of servo format from a system reference after track seek G11B5/5556
• CPC Class Codes: G11B 5/59688 Servo signal format patterns or signal processing thereof, e.g. dual, tri, quad, burst signal patterns

Abstract

In a computer disc drive system having a plurality of voice coil motors for independently actuating a plurality of actuator arms or E-blocks, a single voice coil motor servo control circuit controls the plurality of voice coil motors. In a preferred embodiment, a single digital servo processor dynamically allocates servo bandwidth to the plurality of voice coil motors according to the present activity of each voice coil motor. In a preferred embodiment, the single digital servo processor allocates the greatest amount of bandwidth to a voice coil motor that is presently positioning an associated read/write head for writing, a lesser amount of bandwidth to a voice coil motor that is presently positioning a read/write head for reading, and the least amount of bandwidth to a voice coil motor that is presently seeking or idle.

Claims

1. An actuator assembly for a computer disc drive system having one or more magnetic discs adapted to store data, the actuator assembly comprising:

a plurality of actuator arms, each rotatable about a pivot axis independently from another one of the plurality of actuator arms;

a plurality of read/write heads, each mounted at a distal end of one of the actuator arms so as to be proximate a surface of one of the magnetic discs;

a plurality of voice coil motors, each coupled to at least one of the actuator arms, each adapted to controllably rotate its associated at least one actuator arm about the pivot axis independently from another one of the plurality of voice coil motors; and

a single servo control circuit adapted to control the plurality of voice coil motors, the servo control circuit adapted to dynamically allocate servo bandwidth to the plurality of voice coil motors according to a present activity of each voice coil motor.

2. The actuator assembly of claim 1 wherein the servo control circuit dynamically allocates to a given voice coil motor a first amount of servo bandwidth if said voice coil motor is presently positioning an associated read/write head for writing, a second amount of servo bandwidth, lesser than the first amount, if said voice coil motor is presently positioning an associated read/write head for reading, and a third amount of servo bandwidth, lesser than the first and second amounts, if said voice coil motor is presently seeking or idle.

3. The actuator assembly of claim 2 wherein the disc drive system includes only one read/write channel and two voice coil motors, and wherein the sum of the first amount of servo bandwidth and the third amount of servo bandwidth is equal to the total bandwidth of the servo control circuit.

4. The actuator assembly of claim 2 wherein the servo control circuit comprises:

a plurality of comparators, one for each voice coil motor, each adapted to determine a position error signal for its associated voice coil motor based on the actual position of a read/write head associated with the voice coil motor and on the desired position of said read/write head;

a plurality of status switches, one for each voice coil motor, adapted to express each position error signal with a number of bits dependent on the present activity of the corresponding voice coil motor; and

a modulator adapted to combine the plurality of position error signals into a combined position error signal comprising a predetermined number of bits.

5. The actuator assembly of claim 4 wherein the servo control circuit further comprises:

a servo processing algorithm adapted to generate a combined correction current signal based on the combined position error signal and indicative of the current required by the voice coil motors to achieve the desired position of the read/write heads; and

a demodulator adapted to separate the combined correction current signal into a plurality of independent correction current signals, one for each of the plurality of voice coil motors.

6. A computer disc drive system comprising:

a spindle;

at least one magnetic disc adapted to store data and rotatable about the spindle;

a spindle motor adapted to rotate the at least one magnetic disc;

a plurality of actuator arms, each rotatable about a pivot axis independently from another one of the plurality of actuator arms;

a plurality of read/write heads, each mounted at a distal end of one of the actuator arms so as to be proximate a surface of one of the magnetic discs;

a plurality of voice coil motors, each attached to at least one of the actuator arms, each adapted to controllably rotate its associated at least one actuator arm about the pivot independently from another one of the plurality of voice coil motors; and

a single servo control circuit adapted to control the plurality of voice coil motors, the servo control circuit adapted to dynamically allocate servo bandwidth to the plurality of voice coil motors according to a present activity of each voice coil motor.

7. The computer disc drive system of claim 6 wherein the single servo control circuit dynamically allocates to a given voice coil motor a first amount of servo bandwidth if said voice coil motor is presently positioning an associated read/write head for writing, a second amount of servo bandwidth, lesser than the first amount, if said voice coil motor is presently positioning an associated read/write head for reading, and a third amount of servo bandwidth, lesser than the first and second amounts, if said voice coil motor is presently seeking or idle.

8. The computer disc drive system of claim 7 wherein the disc drive system includes only one read/write channel and two voice coil motors, and wherein the sum of the first amount of servo bandwidth and the third amount of servo bandwidth is equal to the total bandwidth of the single servo control circuit.

9. The computer disc drive system of claim 7 wherein the single servo control circuit comprises:

a plurality of comparators, one for each voice coil motor, each adapted to determine a position error signal for its associated voice coil motor based on the actual position of a read/write head associated with the voice coil motor and on the desired position of said read/write head;

a plurality of status switches, one for each voice coil motor, adapted to express each position error signal with a number of bits dependent on the present activity of the corresponding voice coil motor; and

a modulator adapted to combine the plurality of position error signals into a combined position error signal comprising a predetermined number of bits.

10. The computer disc drive system of claim 9 wherein the single servo control circuit further comprises:

a servo processing algorithm adapted to generate a combined correction current signal based on the combined position error signal and indicative of the current required by the voice coil motors to achieve the desired position of the read/write heads; and

a demodulator adapted to separate the combined correction current signal into a plurality of independent correction current signals, one for each of the plurality of voice coil motors.

11. A method of providing servo control for a plurality of voice coil motors in a computer disc drive system, each voice coil motor adapted for independently positioning at least one read/write head relative to a disc surface, the method comprising:

(a) controlling the plurality of voice coil motors with a single digital servo processor; and

(b) dynamically allocating servo bandwidth to the plurality of voice coil motors according to a present activity of each voice coil motor.

12. The method of claim 11 wherein the dynamically allocating step (a) comprises:

dynamically allocating a first amount of servo bandwidth to a given voice coil motor if said voice coil motor is presently positioning an associated read/write head for writing;

dynamically allocating a second amount of servo bandwidth, lesser than the first amount, to a given voice coil motor if said voice coil motor is presently positioning an associated read/write head for reading; and

dynamically allocating a third amount of servo bandwidth, lesser than the first and second amounts, to a given voice coil motor if said voice coil motor is presently seeking or idle.

13. The method of claim 12 wherein the disc drive system includes only one read/write channel and two voice coil motors, and wherein the sum of the first amount of servo bandwidth and the third amount of servo bandwidth is equal to the total bandwidth of the single digital servo processor.

14. The method of claim 11 wherein the dynamically allocating step (a) comprises:

determining a plurality of position error signals, one for each of the plurality of voice coil motors, by comparing the actual position of a read/write head associated with the corresponding voice coil motor with the desired position of said read/write head;

expressing each position error signal with a number of bits dependent on a present activity of the corresponding voice coil motor; and

combining the plurality of position error signals into a combined position error signal consisting of a predetermined number of bits.

15. The method of claim 14 wherein the controlling step (a) comprises:

generating a combined correction current signal based on the combined position error signal and indicative of the current required by the voice coil motors to achieve the desired position of the read/write heads;

separating the combined correction current signal into a plurality of independent correction current signals, one for each of the plurality of voice coil motors; and

applying a correction current to each of the plurality of voice coil motors based on the independent correction current signals.

16. An actuator assembly in a computer disc drive comprising:

a plurality of voice coil motors, each coupled to at least one actuator arm, each adapted to controllably rotate its associated at least one actuator arm independently from another one of the plurality of voice coil motors;

a single servo control circuit adapted to control the plurality of voice coil motors; and

means for allocating servo bandwidth to the plurality of voice coil motors according to a present activity of each voice coil motor.