Method and System for Calibrating and Detecting Offset of Rotary Encoder Relative to Rotor of Motor

• US 20150303845A1
• Filed: 12/23/2014
• Published: 10/22/2015
• Est. Priority Date: 04/16/2014
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Suda, Bharath, David, James
• Granted Patent: US 9,641,108 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 23/00 Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position

Abstract

Methods and systems for operating a motor having a rotor rotatable relative to a stator include commutating the motor to cause the rotor to rotate to a known position. While the rotor is at the known position, a position of an encoder magnet configured to rotate with the rotor is measured. Subsequent commutation of the motor is adjusted to take into account a difference between the known position of the rotor and the measured position of the encoder magnet.

Claims

1. A method for operating a motor comprising:

commutating the motor to cause a rotor to rotate relative to a stator to a known position;

while the rotor is at the known position, measuring a position of an encoder magnet configured to rotate with the rotor; and

adjusting subsequent commutation of the motor to take into account a difference between the known position of the rotor and the measured position of the encoder magnet.

2. The method of claim 1 further comprising:

detecting an alignment offset between the rotor and the encoder magnet as the difference between the known position of the rotor and the measured position of the encoder magnet.

3. The method of claim 2 further comprising:

using the measured position of the encoder magnet adjusted by the alignment offset to be a measured position of the rotor for the subsequent commutation of the motor.

4. The method of claim 1 further comprising:

repeating commutating the motor to cause the rotor to rotate to the known position and measuring the position of the encoder magnet for each commutation while the rotor is at the known position;

wherein adjusting subsequent commutation of the motor further includes taking into account a difference between the known position of the rotor and a value representative of the measured position of the encoder magnet for the commutations.

5. The method of claim 1 further comprising:

commutating the motor a second time to cause the rotor to rotate to a second known position; and

while the rotor is at the second known position, measuring a second position of the encoder magnet;

wherein adjusting subsequent commutation of the motor further includes taking into account an alignment offset value based on (i) the difference between the known position of the rotor and the measured position of the encoder magnet and (ii) a difference between the second known position of the rotor and the second measured position of the encoder magnet.

6. The method of claim 1 further comprising:

commutating the motor a second time to cause the rotor to rotate to a second known position; and

while the rotor is at the second known position, measuring a second position of the encoder magnet; and

detecting an amount of poles of the rotor based on a difference between the measured positions of the encoder magnet.

7. The method of claim 1 further comprising:

after the subsequent commutation of the motor, repeating commutating the motor to cause the rotor to rotate to a known position, measuring a position of the encoder magnet while the rotor is at the known position, and adjusting further subsequent commutation of the motor to take into account a difference between the known position of the rotor and the measured position of the encoder magnet of the repeated commutations.

8. The method of claim 1 wherein:

the motor is a permanent magnet brushless motor.

9. An assembly comprising:

a motor having a rotor rotatable relative to a stator;

a magnetic encoder assembly having an encoder magnet configured to rotate with the rotor; and

a controller configured to commutate the motor to cause the rotor to rotate to a known position, communicate with the magnetic encoder assembly to measure a position of the encoder magnet while the rotor is at the known position, and adjust subsequent commutation of the motor to take into account a difference between the known position of the rotor and the measured position of the encoder magnet.

10. The assembly of claim 9 wherein:

the controller is further configured to detect an alignment offset between the rotor and the encoder magnet as being the difference between the known position of the rotor and the measured position of the encoder magnet.

11. The assembly of claim 10 wherein:

the controller is further configured to use the measured position of the encoder magnet adjusted by the alignment offset to be a measured position of the rotor for the subsequent commutation of the motor.

12. The assembly of claim 9 wherein:

the controller is further configured to commutate the motor multiple times to cause the rotor to rotate to the known position multiple times, measure the position of the encoder magnet for each commutation while the rotor is at the known position, and adjust subsequent commutation of the motor to take into account a difference between the known position of the rotor and a value based on the measured position of the encoder magnet for the commutations.

13. The assembly of claim 9 wherein:

the controller is further configured to commutate the motor a second time to cause the rotor to rotate to a second known position, measure a second position of the encoder magnet while the rotor is at the second known position, and adjust subsequent commutation of the motor to take into account an alignment offset value based on (i) the difference between the known position of the rotor and the measured position of the encoder magnet and (ii) a difference between the second known position of the rotor and the second measured position of the encoder magnet.

14. The assembly of claim 9 wherein:

the controller is further configured to commutate the motor a second time to cause the rotor to rotate to a second known position, measure a second position of the encoder magnet while the rotor is at the second known position, and detect an amount of poles of the rotor based on a difference between the measured positions of the encoder magnet.

15. The assembly of claim 9 wherein:

the controller is further configured to, after the subsequent commutation of the motor, commutate the motor to cause the rotor to rotate to a known position, measure a position of the encoder magnet while the rotor is at the known position, and adjust further subsequent commutation of the motor to take into account a difference between the known position of the rotor and the measured position of the encoder magnet of the repeated commutation.

16. The assembly of claim 9 wherein:

the motor is a permanent magnet brushless motor.