Multi-turn sensor

1. A multi-turn angular position sensor comprising:

a main gear configured to couple to and rotate, in response to rotation of a rotation member, over a main gear rotation range;

a first sensor gear engaged with the main gear and configured to experience more angular rotation than the main gear in response to rotation of the main gear;

a second sensor gear engaged with the main gear and configured to experience more angular rotation than the main gear and less angular, rotation than the first sensor gear in response to rotation of the main gear;

a first angular position sensor configured and disposed to sense rotation of the first sensor gear and to generate a first output signal indicative of rotation of the first sensor gear;

a second angular position sensor configured and disposed to sense rotation of the second sensor gear and to generate a second output signal indicative of rotation of the second sensor gear;

wherein the main gear and the first and second sensor gears are configured such that a difference in a number of 360 degree revolutions experienced by the first sensor gear and the second sensor gear will be one 360 degree revolution or less in response to the main gear rotating through an expected full main gear rotation range greater than 360 degrees; and

a processor communicatively coupled to the first and second angular position sensors and configured to:

receive the first and second output signals,

determine a difference between rotation of the first sensor gear and rotation of the second sensor gear based on the first and second outputs,

determine an overall angular rotation of the first or second sensor gear from an initial angular position of the first or second sensor gear based on the difference and a present angular position of the first or second sensor gear, respectively, and

determine an angular position of the main gear based on the overall angular rotation of the first or second sensor gear.

2. The multi-turn angular position sensor of claim 1 , wherein the processor is further configured to:

determine a number of 360 degree revolutions that the first or second sensor gear has experienced from the initial angular position of the first or second sensor gear based on the difference; and

determine the overall angular rotation of the first or second sensor gear based on the present angular position of the first or second sensor gear, respectively, and the number of 360 degree revolutions that the first or second sensor gear has experienced.

3. The multi-turn angular position sensor of claim 2 , wherein the processor determines the difference between the rotations of the first and second sensor gears, DIFF, based on an algorithm comprising:

DIFF=sen1−sen2

IF (DIFF>180°) THEN DIFF=DIFF −360°

ELSE IF (DIFF <−180°) THEN DIFF=DIFF +360°

ENDIF; and

determines the number of 360 degree revolutions, TURN, that the first or second sensor gear has experienced based on a relationship comprising:

TURN

=

TRUNC

⁡

[

DIFF

+

180

-

sen

N

360

N

]

;

wherein:

sen 1 is the sensed rotation of the first sensor gear, sen 2 is the sensed rotation of the second sensor gear and sen is the sensed rotation of the first sensor gear or the second sensor gear, and

N is the number of 360 degree revolutions that the first or second sensor gear experiences in response to the main gear rotating through the desired full main gear rotation range.

4. The multi-turn angular position sensor of claim 3 wherein the processor determines the angular position of the main gear, MAIN_GEAR_POSITION, based on equations comprising:

OVERALL_SEN_POSITION=TURN*360+sen; and

MAIN_GEAR_POSITION=OVERALL_SEN_POSITION/GR;

wherein GR is a gear ratio between the main gear and the first sensor gear.

5. The multi-turn angular position sensor of claim 1 , wherein the first and second outputs of the first and second angular position sensors are known for the initial angular positions of the first and second sensor gears when the main gear is in an initial angular position in the main gear rotation range, the first angle of rotation is relative to the initial angular position of the first sensor gear, and the second angle of rotation is relative to the initial angular position of the second sensor gear.

6. The multi-turn angular position sensor of claim 1 , wherein the main gear has a number of teeth Nm, the first sensor gear has a number of teeth Ns 1 and the second sensor gear has a number of teeth Ns 2 , and the expected full main gear rotation range is a number of 360 degree revolutions Tm or less, wherein Nm, Ns 1 , Ns 2 and Tm are integers, and further wherein the product (Tm*Nm) is evenly divisible by Ns 1 and Ns 2 .

7. The multi-turn angular position sensor of claim 6 wherein the number of teeth Ns 2 is one greater than the number of teeth Ns 1 .

8. The multi-turn angular position sensor of claim 7 wherein Ns 2 is eighteen, Ns 1 is seventeen, Tm is six and Nm is fifty-one.

9. The multi-turn angular position sensor of claim 1 , wherein at least one of the first or second angular position sensors is a Hall-effect sensor.

10. A method of determining an angular position of an object, the method comprising:

receiving a first output from a first angular position sensor, the first output being indicative of rotation of a first sensor gear engaged with a main gear, the main gear being configured to couple to and rotate, in response to rotation of a rotation member, over a main gear rotation range, the first sensor gear being configured to experience more angular rotation than the main gear in response to rotation of the main gear;

receiving a second output from a second angular position sensor, the second output being indicative of rotation of a second sensor gear engaged with the main gear, the second sensor gear being configured to experience more angular rotation than the main gear and less angular rotation than the first sensor gear in response to rotation of the main gear;

determining a difference between rotation of the first sensor gear and rotation of the second sensor gear based on the first and second outputs;

determining an overall angular rotation of the first or second sensor gear from an initial angular position of the first or second sensor gear based on the difference and a present angular position of the first or second sensor gear, respectively; and

determining an angular position of the main gear based on the overall angular rotation of the first or second sensor gear,

wherein the main gear and the first and second sensor gears are configured such that a difference in a number of 360 degree revolutions experienced by the first sensor gear and the second sensor gear will be one 360 degree revolution or less in response to the main gear rotating through an expected full main gear rotation range greater than 360 degrees.

11. The method of claim 10 further comprising:

determining a number of 360 degree revolutions that the first or second sensor gear has experienced from an initial angular position of the first or second sensor gear based on the difference; and

determining the overall angular rotation of the first or second sensor gear based on the present angular position of the first or second sensor gears, respectively, and the number of 360 degree revolutions that the first or second sensor gear has experienced.

12. The method of claim 11 further comprising:

determining the difference between the rotations of the first and second sensor gears, DIFF, based on an algorithm comprising:

DIFF=sen1−sen2

IF (DIFF>180°) THEN DIFF=DIFF −360°

ELSE IF (DIFF<−180°) THEN DIFF=DIFF +360°

ENDIF; and

determining the number of 360 degree revolutions, TURN, that the first or second sensor gear has experienced based on a relationship comprising:

TURN

=

TRUNC

⁡

[

DIFF

+

180

-

sen

)

N

360

N

]

;

wherein:

sen 1 is the sensed rotation of the first sensor gear, sen 2 is the sensed rotation of the second sensor gear and sen is the sensed rotation of the first sensor gear or the second sensor gear, and

N is the number of 360 degree revolutions that the first or second sensor gear experiences in response to the main gear rotating through the desired full main gear rotation range.

13. The method of claim 12 further comprising:

determining the angular position of the main gear, MAIN_GEAR_POSITION, based on equations comprising:

OVERALL_SEN_POSITION=TURN*360+sen; and

MAIN_GEAR_POSITION=OVERALL_SEN_POSITION/GR;

wherein GR is a gear ratio between the main gear and the first sensor gear.

14. The method of claim 10 , wherein the first and second outputs of the first and second angular position sensors are known for the initial angular positions of the first and second sensor gears when the main gear is in an initial angular position in the main gear rotation range, the first angle of rotation is relative to the initial angular position of the first sensor gear, and the second angle of rotation is relative to the initial angular position of the second sensor gear.

15. The method of claim 10 , wherein the main near has a number of teeth Nm, the first sensor gear has a number of teeth Ns 1 and the second sensor gear has a number of teeth Ns 2 , and the expected full main gear rotation range is a number of 360 degree revolutions Tm or less, wherein Nm, Ns 1 , Ns 2 and Tm are integers, and further wherein the product (Tm*Nm) is evenly divisible by Ns 1 and Ns 2 .

16. The method of claim 15 wherein the number of teeth Ns 2 is one greater than the number of teeth Ns 1 .

17. The method of claim 16 wherein Ns 2 is eighteen, Ns 1 is seventeen, Tm is six and Nm is fifty-one.

18. The method of claim 10 , wherein at least one of the first or second angular position sensors is a Hall-effect sensor.

19. A multi-turn angular position sensor comprising:

first sensor means for sensing a rotation of a first sensor gear engaged with a main gear and for outputting a first output indicative of the rotation of the first sensor gear, the main gear being configured to couple to and rotate, in response to rotation of a rotation member, over a main gear rotation range, the first sensor gear being configured to experience more angular rotation than the main gear in response to rotation of the main gear;

second sensor means for sensing a rotation of a second sensor gear engaged with the main gear and for outputting a second output indicative of the rotation of the second sensor gear, the second sensor gear being configured to experience more angular rotation than the main gear and less angular rotation than the first sensor gear in response to rotation of the main gear; and

processor means for:

receiving the first output,

receiving the second output,

determining a difference between rotation of the first sensor gear and rotation of the second sensor gear based on the first and second outputs,

determining an overall angular rotation of the first or second sensor gear from an initial angular position of the first or second sensor gear based on the difference and a present angular position of the first or second sensor gear, respectively, and

determining an angular position of the main gear based on the overall angular rotation of the first or second sensor gear;

wherein the main gear and the first and second sensor gears are configured such that a difference in a number of 360 degree revolutions experienced by the first sensor gear and the second sensor gear will be one 360 degree revolution or less in response to the main gear rotating through an expected full main gear rotation range greater than 360 degrees.