Actuator position sensing

• US 9,680,348 B2
• Filed: 10/22/2014
• Issued: 06/13/2017
• Est. Priority Date: 10/22/2013
• Status: Active Grant

• Current Assignee: Ultra Motion, LLC
• Original Assignee: Ultra Motion, LLC
• Inventors: Rodger, Sean, Rodger, Erwin, Koch, Rob, Quartararo, Tom
• Primary Examiner(s): Luo, David S
• Application Number:
  US14/521,029
• Publication Number:
  US 20150108878A1
• Time in Patent Office: 965 Days
• Field of Search: 318721, 318720, 318700
• CPC Class Codes: G01D 18/00 Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
• CPC Class Codes: G01D 2205/26 Details of encoders or position sensors specially adapted to detect rotation beyond a full turn of 360°, e.g. multi-rotation
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: H02K 11/21 Devices for sensing speed or position, or actuated thereby specially adapted for machines having non-mechanical commutating devices H02K29/06, H02K29/14
• CPC Class Codes: H02K 7/116 with gears

Abstract

Methods and systems for measuring angular position include measuring an angular position within one rotation of a primary gear and a secondary gear that are meshed together. The primary gear and secondary gear have a first and second number of teeth respectively, where the first number of teeth and the second number of teeth are different. An angular position for the secondary gear is estimated using the measured primary gear angle and a reference value for each of the primary and secondary angle sensors. A number of primary gear rotations is calculated using the estimated angular position for the secondary gear and the measured angular position of the secondary gear. An angular position of the primary gear is calculated over multiple rotations using the calculated number of primary gear rotations, a reference value for the primary angle sensor, and the measured angle value of the primary gear within one rotation.

Claims

1. A position sensor, comprising:

a primary gear having a first number of teeth that is mounted to an input shaft;

a secondary gear having a second number of teeth that is meshed with the primary gear, wherein the second number of teeth is different from the first number of teeth;

a primary angular position sensor configured to measure the angular position of the primary gear within one rotation;

a secondary angular position sensor configured to measure the angular position of said secondary gear within one rotation; and

a control module configured to determine an angular position of the input shaft over multiple rotations using the measured angular positions of the primary and secondary gears and a reference value for each respective angle sensor,

wherein a maximum number of rotations of said input shaft (N), the number of teeth on the primary gear (PT), and the number of teeth on the secondary gear (ST) are configured such that N≦

LCM(PT, ST)/PT, where LCM( ) provides the lowest common multiple.

2. The position sensor of claim 1, wherein the number of teeth on the primary gear (PT), the number of teeth on the secondary gear (ST), a resolution of the primary angle sensor (RES_p), a resolution of the secondary angle sensor (RES_s), a maximum error of the primary angle sensor in units of digital output increments (ERR_p), and a maximum error of the secondary angle sensor in units of digital output increments (ERR_s) are configured such that:

3. The position sensor in claim 1, wherein the control module is configured to compute an error signal (ERRref) that represents deviation from an expected phase relationship between the primary and secondary angle sensors based on the reference values for each respective angle sensor and a determined number of full rotations of said primary gear.

4. The position sensor of claim 1, wherein the primary and secondary gears are each connected to a separate diametrically polarized magnet, and the primary and secondary angle sensors are non-contacting magnetic angle sensors that are configured to detect an angle of a respective magnet.

5. The position sensor of claim 4, wherein a gap exists between each gear and its respective magnetic sensor.

6. The position sensor of claim 1, wherein the first number of teeth and the second number of teeth differ by one.

7. The position sensor of claim 1, wherein the first number of teeth and the second number of teeth differ by greater than one.

8. The position sensor of claim 1, wherein the second number of teeth is a power of two.

9. The position sensor of claim 1, wherein the primary and secondary angle sensors have a same resolution.

10. The position sensor of claim 1, wherein a resolution of the secondary angle sensor (RESs) is a power of 2.

11. The position sensor of claim 1, wherein the first number of teeth (PT) and the second number of teeth (ST) are configured such that LCM(PT, ST)/PT is a power of 2.

12. The position sensor of claim 1, wherein the control module determines the multi-turn angular position using a reference position for each of the gears.

13. An electromechanical actuator, comprising:

an electric motor, comprising a rotor and a stator;

a mechanical output stage comprising a mechanical output limited to a finite range of motion;

a primary gear having a first number of teeth that is mounted to an input shaft that rotates in accordance with the electric motor to produce motion in the mechanical output;

a secondary gear having a second number of teeth that is meshed with the primary gear, wherein the second number of teeth is different from the first number of teeth;

a primary angular position sensor configured to measure the angular position of the primary gear within one rotation;

a secondary angular position sensor configured to measure the angular position of said secondary gear within one rotation; and

a control module configured to determine the angular position of the input shaft over multiple rotations using the measured angular positions of the primary and secondary gears and a reference value for each respective angle sensor,

wherein a maximum number of rotations of said input shaft (N), the number of teeth on the primary gear (PT), and the number of teeth on the secondary gear (ST) are configured such that N≦

LCM(PT,ST)/PT, where LCM( ) provides the lowest common multiple.

14. The electromechanical actuator of claim 13, wherein the number of teeth on the primary gear (PT), the number of teeth on the secondary gear (ST), a resolution of the primary angle sensor (RES_p), a resolution of the secondary angle sensor (RES_s), a maximum error of the primary angle sensor in units of digital output increments (ERR_p), and a maximum error of the secondary angle sensor in units of digital output increments (ERR_s) are configured such that:

15. The electromechanical actuator of claim 13, wherein the control module is configured to compute an error signal (ERRref) that represents deviation from an expected phase relationship between the primary and secondary angle sensors based on the reference values for each respective angle sensor and the determined number of full rotations of said primary gear.

16. The electromechanical actuator of claim 13, wherein the primary and secondary gears are each connected to a separate diametrically polarized magnet, and the primary and secondary angle sensors are non-contacting magnetic angle sensors that are configured to detect an angle of a respective magnet.

17. The electromechanical actuator of claim 13, wherein a gap exists between each gear and its respective magnetic sensor.

18. The electromechanical actuator of claim 13, wherein the first number of teeth and the second number of teeth differ by one.

19. The electromechanical actuator of claim 13, wherein the second number of teeth is a power of two.

20. The electromechanical actuator of claim 13, wherein the primary and secondary angle sensors have a same resolution.

21. The electromechanical actuator of claim 13, wherein a resolution of the secondary angle sensor (RESs) is a power of 2.

22. The electromechanical actuator of claim 13, wherein the first number of teeth (PT) and the second number of teeth (ST) are configured such that LCM(PT,ST)/PT is a power of 2.

23. The electromechanical actuator of claim 13, wherein the rotor of said electric motor is mounted to said primary gear, and is used to drive the said input shaft.

24. The electromechanical actuator of claim 13, wherein the rotor of said electric motor is rotatably mounted to the secondary gear, and drives said input shaft by transmitting torque through the meshing of the primary and secondary gears.

25. The electromechanical actuator of claim 13, wherein the control module is further configured to compute a rotor angle by combining an angle sensor value that corresponds to the rotor of said electric motor with an offset value.

26. The electromechanical actuator of claim 25, wherein the control module is further configured to commutate said electric motor using the computed rotor angle.

27. The electromechanical actuator of claim 25, wherein the control module is further configured to perform Field Oriented Control of said electric motor using the computed rotor angle.

28. The electromechanical actuator of claim 13, wherein the control module is further configured to perform closed-loop control of said electric motor using the computed angular position of said input shaft over multiple rotations as feedback.

29. A method of determining angular position over multiple rotations, comprising:

measuring an angular position within one rotation of a primary gear and a secondary gear that are meshed together, said primary gear and secondary gear having a first and second number of teeth respectively, wherein the first number of teeth and the second number of teeth are different;

estimating an angular position for the secondary gear by multiplying a difference between the measured primary gear angle and the reference value for the primary angle sensor by a ratio of the first number of teeth to the second number of teeth, and combining the result with the reference value for the secondary angle sensor;

calculating a number of primary gear full rotations using the estimated angular position for the secondary gear and the measured angular position of the secondary gear; and

calculating an angular position of the primary gear over multiple rotations using the calculated number of primary gear full rotations, a reference value for the primary angle sensor, and the measured angle value of the primary gear within one rotation.

30. The method of claim 29, wherein the second number of teeth is a power of two.

31. The method of claim 29, wherein the first and second numbers of teeth differ by one.

32. The method of claim 31, wherein calculating the number of primary gear full rotations comprises:

calculating a difference between the estimated angular position for the secondary gear and the measured position of the secondary gear;

dividing said difference between the estimated position and measured position of the secondary gear by a window size, wherein the window size is equal to a resolution of the secondary angle sensor multiplied by the first number of teeth that is divided by the least common multiple of the first number of teeth and the second number of teeth; and

rounding the result of said divide to the nearest integer.

33. The method of claim 32, wherein the window size is a power of 2.

34. The method of claim 29, wherein the first number of teeth and the second number of teeth differ by a number greater than one.

35. The method of claim 34, wherein calculating the number of primary gear full rotations comprises changing a window position until the measured position of the secondary gear is inside the window.

36. The method of claim 35, wherein a window size is equal to a resolution of the secondary angle sensor multiplied by the first number of teeth, divided by the least common multiple of the first number of teeth and the second number of teeth.

37. The method of claim 35, wherein a window position is changed by an amount equal to a resolution of the secondary angle sensor multiplied by the first number of teeth and divided by the second number of teeth.

38. The method of claim 29, wherein the resolution of the primary angle sensor is equal to the resolution of the secondary angle sensor.

39. The method of claim 29, wherein the number of teeth on the primary gear (PT) and the number of teeth on the secondary gear (ST) are configured such that LCM (PT,ST)/PT is a power of 2.

40. The method of claim 29, wherein the resolution of the secondary angle sensor is a power of 2.

41. The method of claim 29, further comprising computing an error signal (ERRref) that represents deviation from an expected phase relationship between the primary and secondary angle sensors based on the reference values for each respective angle sensor and the determined number of full rotations of said primary gear.