Symmetry compensation for encoder pulse width variation

• US 6,510,396 B1
• Filed: 09/13/2000
• Issued: 01/21/2003
• Est. Priority Date: 09/16/1999
• Status: Expired due to Fees

• Current Assignee: Pacific Century Motors, Inc. (Aviation Industry Corporation of China, Ltd.), GM Global Technology Operations Incorporated (General Motors Company)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Colosky, Mark Philip
• Primary Examiner(s): Hilten, John S.
• Assistant Examiner(s): LE, JOHN H
• Application Number:
  US09/661,221
• Time in Patent Office: 860 Days
• Field of Search: 702/85, 702/86, 702/87, 702/88, 702/89, 702/90, 702/94, 702/95, 702/96, 702/105, 702/106, 731/180.1, 180/421, 180/422, 180/443, 180/446, 701/22, 701/41
• US Class Current: 702/85
• CPC Class Codes: B62D 5/046 Controlling the motor
• CPC Class Codes: G01D 18/001 Calibrating encoders
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position

Abstract

A method of compensating for errors in the measurement of the kinematic properties of an electric power steering motor for an automobile is disclosed. The method comprises generating a set of M-ary signals; measuring the pulse width of the set of M-ary signals; and measuring the time between the edges of the set of M-ary signals. The motor velocity may be directly measured by a tachometer or other such device. The motor position signal can be used to estimate the angular velocity of the motor, by determining the change in angular position of the motor divided by the change in time.

Claims

1. A method of compensating for errors in the measurement of the kinematic properties of an electric power steering motor for an automobile, the method comprising:

generating a set of M-ary signals comprising a set of pulses indicative of the angular position of the motor, wherein the pulse widths of the M-ary signals comprise a fraction of a cycle of the M-ary signals;

measuring the pulse width of the set of M-ary signals;

measuring the time between the edges of the set of M-ary signals; and

calculating a compensated value of a first kinematic property of the motor;

wherein calculating the compensated value of the first kinematic property of the motor comprises calculating the compensated value of the angular velocity, ν

_c, of the motor according to the equation

2. The method as set forth in claim 1 further comprising determining an uncompensated value of a second kinematic property of the motor.

3. The method as set forth in claim 2 further comprising calibrating the duty cycles of the set of M-ary signals.

4. The method as set forth in claim 3 further comprising calculating

an uncompensated value of the first kinematic property of the motor.

5. The method as set forth in claim 4 wherein calculating

an uncompensated value of the first kinematic property of the motor comprises calculating the uncompensated value of the angular velocity, ν

_u, of the motor according to the equation

6. The method as set forth in claim 5 wherein calculating a

compensated value of a first kinematic property of the motor includes calculating the compensated value of the angular velocity of the motor according to the equation ν

_c=D_s×

ν

_u wherein D_s is the duty cycles of the M-ary signals.

7. The method as set forth in claim 6 wherein the set of M-ary signals comprise binary signals.

8. The method as set forth in claim 7 further comprising assigning a fractional equivalent to the duty cycles of the M-ary signals according to the equation

9. A storage medium encoded with machine-readable program code for compensating for errors in the measurement of the kinematic properties of an electric power steering motor for an automobile, the computer code being executable whereby the computer code when run by a computer system will compensate for errors in the measurement of the kinematic properties of an electric power steering motor for an automobile, the program code including instructions for causing the computer system to implement a method comprising:

generating a set of M-ary signals comprising a set of pulses indicative of the angular position of the motor, wherein the pulse widths of the M-ary signals comprise a fraction of a cycle of the M-ary signals;

measuring the pulse width of the set of M-ary signals;

measuring the time between the edges of the set of M-ary signals; and

calculating a compensated value of a first kinematic property of the motor;

wherein calculating the compensated value of the first kinematic property of the motor comprises calculating the compensated value of the angular velocity, ν

_c, of the motor according to the equation

10. The method as set forth in claim 9 further comprising determining an uncompensated value of a second kinematic property of the motor.

11. The method as set forth in claim 10 further comprising calibrating the duty cycles of the set of M-ary signals.

17. An error compensating system for compensating for errors in the measurement of a kinematic property of an electric power steering motor, the error compensating system comprising:

a motor position sensor system receptive of a signal indicative of the kinematic property of the motor and operative thereby to provide as output a set of M-ary phase shifted signals comprising a set of pulses indicative of the angular position of the motor, wherein the pulse widths of the M-ary signals comprise a fraction of a cycle of the M-ary signals; and

a signal processing system receptive of the set of M-ary phase shifted signals for compensating for errors in the measurement of the kinematic property of the motor, providing as output thereby a signal indicative of a compensated value of the angular velocity, ν

_c, of the motor.

12. The method as set forth in claim 17 further comprising calculating

an uncompensated value of the first kinematic property of the motor.

13. The method as set forth in claim 12 wherein calculating

an uncompensated value of the first kinematic property of the motor comprises calculating the uncompensated value of the angular velocity, ν

_u, of the motor according to the equation

14. The method as set forth in claim 13 wherein calculating a compensated value of a first kinematic property of the motor includes calculating the compensated value of the angular velocity of the motor according to the equation ν

_c=D_s×

ν

_u wherein D_s is the duty cycles of the M-ary signals.

15. The method as set forth in claim 14 wherein the set of M-ary signals comprise binary signals.

16. The method as set forth in claim 15 further comprising assigning a fractional equivalent to the duty cycles of the M-ary signals according to the equation

18. The error compensating system as set forth in claim 17 wherein the motor position sensor system comprises:

a pulse encoded position sensor attached to a shaft of the motor and receptive of the signal indicative of the kinematic property of the motor providing as output a signal indicative of the angular position of the motor; and

a position sensor receiver attached to a stationary part of the motor and receptive of the output signal from the pulse encoded sensor providing as output the set of M-ary phase shifted signals.

19. The error compensating system as set forth in claim 18 wherein the position sensor receiver comprises a Hall effect sensor.

20. The error compensating system as set forth in claim 17 wherein the pulse encoded position sensor comprises a slotted disk or an etched glass disk or a magnetic disc.

21. The error compensating system as set forth in claim 17 wherein the signal processing system comprises:

a timing device for measuring the time between the M-ary phase shifted signals providing thereby a signal indicative of the time between the M-ary phase shifted signals;

a computing device receptive of the signal indicative of the time between the M-ary phase shifted signals from the timing device for computing the uncompensated angular velocity of the motor providing thereby a signal indicative of the uncompensated angular velocity of the motor; and

a symmetry compensator receptive of the signal indicative of the uncompensated angular velocity of the motor from the computing device and the set of M-ary phase shifted signals from the motor position sensor system for generating a compensated velocity of the motor according to the equation

22. The error compensating system as set forth in claim 21 wherein the timing device comprises an edge triggered timing device.

23. A method of compensating for errors in the measurement of the kinematic properties of a motor, the method comprising:

generating a set of M-ary signals comprising a set of pulses indicative of the angular position of the motor, wherein the pulse widths of the M-ary signals comprise a fraction of a cycle of the M-ary signals;

measuring the pulse width of the set of M-ary signals;

measuring the time between the edges of the set of M-ary signals; and

calculating a compensated value of a first kinematic property of the motor;

wherein calculating the compensated value of the first kinematic property of the motor comprises calculating the compensated value of the angular velocity, ν

_c, of the motor according to the equation

24. The method as set forth in claim 23 further comprising determining an uncompensated value of a second kinematic property of the motor.

25. The method as set forth in claim 24 further comprising calibrating the duty cycles of the set of M-ary signals.

26. The method as set forth in claim 25 further comprising calculating an uncompensated value of the first kinematic property of the motor.

27. The method as set forth in claim 27 wherein calculating an uncompensated value of the first kinematic property of the motor comprises calculating the uncompensated value of the angular velocity, ν

_u, of the motor according to the equation;

28. The method as set forth in claim 27 wherein calculating a compensated value of a first kinematic property of the motor includes calculating the compensated value of the angular velocity of the motor according to the equation ν

_c=D_s×

ν

_u wherein D_s is the duty cycles of the M-ary signals.

29. The method as set forth in claim 28 wherein the set of M-ary signals comprise binary signals.

30. The method as set forth in claim 29 further comprising assigning a fractional equivalent to the duty cycles of the M-ary signals according to the equation: