Electrical phase compensation in BEMF spindle motor control

• US 20060097681A1
• Filed: 12/20/2005
• Published: 05/11/2006
• Est. Priority Date: 06/06/2003
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Ooi, KianKeong, Ding, MingZhong, Chiang, WingKong, Ang, June Christian
• Granted Patent: US 7,170,249 B2
• Time in Patent Office: Days
• US Class Current: 318/560
• CPC Class Codes: G11B 19/28 Speed controlling, regulating, or indicating G11B19/24 takes precedence
• CPC Class Codes: H02P 6/182 using back-emf in windings

Abstract

A method and apparatus for compensating for the asymmetrical phases of a spindle motor in a disc drive are provided. With the apparatus and method, compensation values are learned by sampling speed data during a period of operation of the disc drive where the speed is stable and only one control operation is performed per revolution of the disc. The sampled speed data is used to generate the compensation values for each of the phases of the spindle motor. The compensation values are stored in a compensation mechanism which is used by the spindle motor speed controller to provide compensation for the asymmetrical phases of the spindle motor. During Normal operation, the actual speed output of the spindle motor is measured and is subtracted from a reference speed to generate a difference speed value. Based on the corresponding electrical phase, the correct compensation value is fetched and is subtracted from the difference speed value to obtain a compensated difference speed value. A control signal based on this compensated difference speed value is generated and provided to the spindle motor to thereby control the output speed of the spindle motor.

Claims

1. A method comprising the steps of:

determining a speed of a motor;

determining a compensation value based on a phase of the motor, wherein the compensation value is a value that compensates for asymmetrical electrical phases of the motor;

generating a control signal based on the speed of the motor, the compensation value and a reference speed; and

providing the control signal to the motor to thereby control the speed of the motor.

2. The method of claim 1, wherein the speed of the motor is determined using a Back Electromotive Force (BEMF) zero-crossings methodology for determining speed.

3. The method of claim 1, wherein generating a control signal includes:

subtracting the speed of the motor from the reference speed to generate a difference speed value;

subtracting the compensation value from the difference speed value to generate a compensated difference speed value; and

generating the control signal based on the compensated difference speed value.

4. The method of claim 1, further comprising:

generating a matrix of compensation values based on sampled motor speed data, wherein the matrix of compensation values includes a compensation value for each phase of the motor.

5. The method of claim 4, wherein generating the matrix of compensation values includes:

sampling motor speed data for a period of time of operation of the motor where the motor speed is stable and only one control operation is performed per revolution of the motor;

calculating average speed error values for each phase of the motor; and

generating the matrix of compensation values as a difference between normalized average speed error values and a reference speed for each phase of the motor.

6. The method of claim 5, wherein the sampled motor speed data is stored in a matrix T having N×

P elements, where N is a number of revolutions of the motor and P is a number of electrical phases in the motor, and wherein the average speed error values is a matrix A are calculated using the following equation;

7. The method of claim 6, wherein the normalized average speed error values are determined using the following equation:

N(A)={N(a₁) . . . N(a_p)}, N(a_p)=(T_ref*a_p)/s

where N(A) is the normalized matrix of average speed error values, N(a_p) is the normalized average speed error value for phase p, T_ref is a reference speed, and s is the average speed of all sampled speed data.

8. The method of claim 7, wherein the matrix of compensation values is generated using the following equation:

C={c₁ . . . c_p}, c_p=N(a_p)−

T_ref

where C is the matrix of compensation values and c_p is the compensation value for phase p.

9. The method of claim 1, wherein the compensation value is determined by retrieving the compensation value from a data structure having compensation values for each phase of the motor, and wherein the compensation values for each phase of the motor are learned from sampling motor speed data for a period of time of operation of the motor where the motor speed is stable and only one control operation is performed per revolution of the motor.

10. The method of claim 1, wherein the motor is a spindle motor.

11. An apparatus comprising:

a motor

a measuring device for measuring the speed of the motor;

a controller coupled to the motor; and

an asymmetrical phase compensation device coupled to the controller, wherein the measuring device of the motor determines a speed of the motor, the asymmetrical phase compensation device determines a compensation value based on a phase of the motor, the compensation value being a value that compensates for asymmetrical electrical phases of the motor, and wherein the controller generates a control signal based on the speed of the motor, the compensation value and a reference speed and provides the control signal to the motor to thereby control the speed of the motor.

12. The apparatus of claim 11, wherein the speed of the motor is determined using a Back Electromotive Force (BEMF) zero-crossings methodology for determining speed.

13. The apparatus of claim 11, wherein the controller generates the control signal by subtracting the speed of the motor from the reference speed to generate a difference speed value, and subtracting the compensation value from the difference speed value to generate a compensated difference speed value.

14. The apparatus of claim 11, wherein the asymmetrical phase compensation device generates a matrix of compensation values based on sampled motor speed data, and wherein the matrix of compensation values includes a compensation value for each phase of the motor.

15. The apparatus of claim 14, wherein the asymmetrical phase compensation device samples motor speed data for a period of time of operation of the motor where the motor speed is stable and only one control operation is performed per revolution of the motor, and wherein the asymmetrical phase compensation device calculates average speed error values for each phase of the motor and generates the matrix of compensation values as a difference between normalized average speed error values and a reference speed for each phase of the motor.

16. The apparatus of claim 15, wherein the sampled motor speed data is stored in a matrix T having N×

P elements, where N is a number of revolutions of the motor and P is a number of electrical phases in the motor, and wherein the average speed error values is a matrix A are calculated using the following equation;

17. The apparatus of claim 16, wherein the normalized average speed error values are determined using the following equation:

N(A)={N(a₁) . . . N(a_p)}, N(a_p)=(T_ref*a_p)/s

where N(A) is the normalized matrix of average speed error values, N(a_p) is the normalized average speed error value for phase p, T_ref is a reference speed, and s is the average speed of all sampled speed data.

18. The apparatus of claim 17, wherein the matrix of compensation values is generated using the following equation:

C={c₁ . . . c_p}, c_p=N(a_p)−

T_ref

where C is the matrix of compensation values and c_p is the compensation value for phase p.

19. The apparatus of claim 11, wherein the compensation value is determined by retrieving the compensation value from a data structure having compensation values for each phase of the motor, and wherein the compensation values for each phase of the motor are learned from sampling motor speed data for a period of time of operation of the motor where the motor speed is stable and only one control operation is performed per revolution of the motor.

20. The apparatus of claim 11, wherein the motor is a spindle motor.