Magnetic Sensor With Compensation

• US 20080290859A1
• Filed: 01/12/2007
• Published: 11/27/2008
• Est. Priority Date: 01/12/2006
• Status: Active Grant

• Current Assignee: Timken US Corp. (The Timken Company)
• Original Assignee: Timken US Corp. (The Timken Company)
• Inventors: LaCroix, Mark E.
• Granted Patent: US 7,999,533 B2
• Time in Patent Office: Days
• US Class Current: 324/207.13
• CPC Class Codes: G01R 33/02 Measuring direction or magnitude of magnetic fields or magnetic flux G01R33/20 takes precedence
• CPC Class Codes: G01R 33/025 Compensating stray fields G01R33/0017 takes precedence

Abstract

A sensing assembly. The sensing assembly is spaced apart from a magnet that has a magnet length, and includes a compensation module and a string of magnetic sensors that has a string length. The magnetic sensors are grouped into a plurality of magnetic sensor groups. Each of the magnetic sensors generates a respective intermediate signal based on the magnet. The compensation module assigns a plurality of respective gains to the respective magnetic sensor groups based on a difference between the magnet length and the string length, and applies the respective gains to the respective intermediate signals of the respective magnetic sensor groups to generate respective adjusted signals.

Claims

1. A sensing assembly adapted to be spaced apart from a magnet having a magnet length, the sensing assembly comprising:

a string of magnetic sensors having a string length, the magnetic sensors grouped into a plurality of magnetic sensor groups, each of the magnetic sensors configured to generate a respective intermediate signal based on the magnet; and

a compensation module configured to assign respective gains to the respective magnetic sensor groups based on a difference between the magnet length and the string length, and to apply the respective gains to the respective intermediate signals of the respective magnetic sensor groups to generate respective adjusted signals.

2. The sensing assembly of claim 1, further comprising an output module configured to sum the respective adjusted signals based on the magnetic sensor groups to generate a plurality of sine and cosine signals.

3. The sensing assembly of claim 1, wherein the magnet comprises a plurality of poles, and wherein the magnetic sensors are arranged relatively symmetrically with respect to the poles.

4. The sensing assembly of claim 3, wherein the string of sensors are grouped into an inner group configured to include a plurality of sensors closest to the poles, an outer group configured to include a plurality of sensors farthest from the poles, and an intermediate group configured to include a plurality of sensors between the inner group and the outer group.

5. The sensing assembly of claim 4, wherein the respective intermediate signals of the inner group are amplified by a gain value when the magnet length is less than the string length, the respective intermediate signals of the outer group are attenuated with the gain value when the magnet length is less than the string length, the respective intermediate signals of the inner group are attenuated by a gain value when the magnet length is greater than the string length, and the respective intermediate signals of the outer group are amplified with the gain value when the magnet length is greater than the string length.

6. The sensing assembly of claim 1, wherein the compensation module comprises a memory configured to store the respective gains.

7. The sensing assembly of claim 1, wherein the groups of magnetic sensors have equal lengths.

8. A method of compensating for a dimensional difference between a magnet and a sensor string having a plurality of sensors, the method comprising:

assigning a reference to the magnet;

determining a respective distance between each of the sensors and the reference;

assigning a respective weight to each of the sensors based on the respective distance; and

applying the assigned respective weights to respective outputs of the sensors.

9. The method of claim 8, wherein applying the assigned respective weights to respective outputs results in a plurality of adjusted signals, the method further comprising summing the plurality of adjusted signals to generate a plurality of sine and cosine signals.

10. The method of claim 8, wherein the magnet comprises a plurality of poles, and wherein assigning a reference to the magnet comprises assigning a reference relatively symmetrically with respect to the poles.

11. The method of claim 10, further comprising determining a difference between a length of the sensors and a length of the magnet.

12. The method of claim 11, wherein assigning a respective weight to each of the sensors based on the respective distance comprises:

assigning an amplification factor to a plurality of respective sensors having relatively shorter distances when the magnet length is less than the string length;

assigning an attenuation factor to a plurality of respective sensors having relatively greater distances when the magnet length is less than the string length;

assigning an attenuation factor to a plurality of respective sensors having relatively shorter distances when the magnet length is greater than the string length; and

assigning an amplification factor to a plurality of respective sensors having relatively greater distances when the magnet length is greater than the string length.

13. A method of compensating for a dimensional difference between a magnet and an adjacent sensor string having a plurality of sensors, the method comprising:

measuring the dimensional difference between the magnet and the sensor string;

grouping the sensors into a plurality of sensor groups;

generating a respective intermediate signal at each of the sensors based on the magnet; and

applying a gain to the respective intermediate signals based on the dimensional difference and the groups.

14. The method of claim 13, wherein applying a gain to the respective intermediate signals results in a plurality of adjusted signals, the method further comprising summing the plurality of adjusted signals to generate a plurality of sine and cosine signals

15. The method of claim 13, wherein the magnet comprises a plurality of poles, the method further comprising arranging the magnetic sensors relatively symmetrically with respect to the poles.

16. The method of claim 15, wherein grouping the sensors into a plurality of sensor groups comprises:

grouping into an inner group the plurality of sensors closest to the poles; and

grouping into an outer group the plurality of sensors farthest from the poles.

17. The method of claim 16, wherein the dimensional difference comprises a length difference, wherein applying a gain to the respective intermediate signals based on the dimensional difference and the groups comprises:

assigning an amplification factor to the inner group when the magnet length is less than the string length;

assigning an attenuation factor to the outer group when the magnet length is less than the string length;

assigning an attenuation factor to the outer group when the magnet length is greater than the string length; and

assigning an amplification factor to the inner group when the magnet length is greater than the string length.

18. The method of claim 13, wherein the sensor groups comprise an equal number of sensors.