SYSTEM AND METHOD FOR CALIBRATING A ROTARY ABSOLUTE POSITION SENSOR

• US 20110067479A1
• Filed: 09/22/2009
• Published: 03/24/2011
• Est. Priority Date: 09/22/2009
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust), Oceaneering International Incorporated
• Inventors: Davis, Donald R., Permenter, Frank Noble
• Granted Patent: US 8,250,901 B2
• Time in Patent Office: Days
• US Class Current: 73/1.75
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G01D 5/2449 using hard-stored calibration data
• CPC Class Codes: G05B 2219/34136 Ellipse, hyperbola

Abstract

A system includes a rotary device, a rotary absolute position (RAP) sensor generating encoded pairs of voltage signals describing positional data of the rotary device, a host machine, and an algorithm. The algorithm calculates calibration parameters usable to determine an absolute position of the rotary device using the encoded pairs, and is adapted for linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters. A method of calibrating the RAP sensor includes measuring the rotary position as encoded pairs of voltage signals, linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters, and calculating an absolute position of the rotary device using the calibration parameters. The calibration parameters include a positive definite matrix (A) and a center point (q) of the ellipse. The voltage signals may include an encoded sine and cosine of a rotary angle of the rotary device.

Claims

1. A system comprising:

a rotary device;

a rotary absolute position (RAP) sensor operable for generating encoded pairs of voltage signals describing positional data of the rotary device;

a host machine; and

an algorithm adapted for calculating calibration parameters for determining an absolute position of the rotary device using the encoded pairs of voltage signals;

wherein the algorithm is executed via the host machine, and is adapted for linearly-mapping an ellipse defined by the encoded pairs of voltage signals to thereby calculate the calibration parameters.

2. The system of claim 1, wherein the system includes a humanoid robot having a robotic joint, and wherein the rotary device is a rotary portion of a series elastic actuator (SEA).

3. The system of claim 1, wherein the encoded pair of voltage signals includes a first voltage signal encoding the cosine of a rotary angle of the rotary device, and a second voltage signal encoding the sine of the rotary angle.

4. The system of claim 1, wherein the rotary device has an input side and an output side, and wherein RAP sensor includes a pair of RAP sensors positioned on opposite sides of the rotary device and adapted for measuring a rotary position of a respective one of the input and output sides.

5. The system of claim 1, wherein the calibration parameters includes a positive definite matrix (A) and a center point (q) of the ellipse.

6. A calibration module adapted for calibrating a rotary absolute position (RAP) sensor for a system having a rotary device, the RAP sensor being adapted for measuring a rotary position of the rotary device, and for outputting encoded pairs of voltage signals describing the rotary position, the calibration module comprising:

a host machine in communication with the RAP sensor and adapted for processing the encoded pairs of voltage signals from the RAP sensor; and

an algorithm executed via the host machine and adapted for calculating calibration parameters for determining an absolute position of the rotary device using the encoded pairs of voltage signals;

wherein the algorithm is adapted for linearly-mapping an ellipse defined by the encoded pairs of voltage signals to thereby calculate the calibration parameters.

7. The calibration module of claim 6, wherein the encoded pairs of voltage signals each include a first voltage signal encoding the cosine of a rotary angle, and a second voltage signal encoding the sine of the rotary angle.

8. The calibration module of claim 6, wherein the RAP sensor includes a pair of RAP sensors positioned on opposite sides of the rotary portion, and wherein the pair of RAP sensors are adapted for measuring the rotary position before and after the rotary portion.

9. The calibration module of claim 6, wherein the rotary device is at least one of a motor portion and a spring portion of a series elastic actuator.

10. The calibration module of claim 6, wherein the calibration parameters include a positive definite matrix (A) and a center point (q) of the ellipse.

11. A method of calibrating a rotary absolute position (RAP) sensor adapted for measuring a rotary position of a rotary device, the method comprising:

measuring the rotary position as encoded pairs of voltage signals using the RAP sensor;

linearly-mapping an ellipse defined by the encoded pairs of voltage signals to thereby calculate calibration parameters suitable for calibrating the RAP sensor using a host machine; and

calculating an absolute position of the rotary device using the calibration parameters.

12. The method of claim 11, wherein measuring the rotary position as encoded pairs of voltage signals includes transmitting a first voltage signal that encodes the cosine of a rotary angle of the rotary device, and transmitting a second voltage signal that encodes the sine of the rotary angle.

13. The method of claim 11, wherein measuring the rotary position includes measuring the rotary position before and after a spring portion of a series elastic actuator using a pair of the RAP sensors positioned on opposite sides of the spring portion.

14. The method of claim 11, wherein the calibration parameters include a positive definite matrix (A) and a center point (q) of the ellipse.