Sensor calibration method and system

• US 10,352,725 B2
• Filed: 06/18/2015
• Issued: 07/16/2019
• Est. Priority Date: 06/18/2015
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Hallberg, Bryan Severt
• Primary Examiner(s): Kundu, Sujoy K
• Assistant Examiner(s): Anderson, L.
• Application Number:
  US14/742,852
• Publication Number:
  US 20160370203A1
• Time in Patent Office: 1,489 Days
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 19/00 Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration

Abstract

A sensor calibration method and system dynamically compute a bias offset which is subtracted from field strength readings generated by a sensor to correct them. The three-dimensional space around a sensor is seeded with orientation targets. As the sensor is rotated to different orientations, field strength readings are generated by the sensor and assigned to different targets based on estimated proximity. Once occupancy of targets conforms to a first state of occupancy, a coarse bias offset is computed for the sensor using readings from occupied targets. Once occupancy of targets conforms to a second state of occupancy, a refined bias offset is computed for the sensor using readings from occupied targets. Multiple sensors may be calibrated concurrently. Moreover, a user interface provides a real-time graphic showing the location and occupancy status of individual targets and highlighting the individual target best aligned with a most recent corrected sensor reading.

Claims

1. A method for calibrating a sensor, the method comprising:

generating a plurality of orientation targets in three-dimensional space around the sensor;

generating field strength readings by the sensor when at different orientations;

assigning the readings to different ones of the targets based on estimated proximity between the readings and the targets whereby different ones of the targets are occupied by the readings, wherein the assigning step comprises assigning the readings to tentative targets having an estimated shortest distance from the readings in a positive X, Y, Z octant of the three-dimensional space around the sensor and combining the tentative targets with X, Y, Z sign values from the readings to identify the assigned targets in a final octant of the three-dimensional space around the sensor;

comparing a current occupancy of targets by readings for conformance with a predetermined state of target occupancy; and

computing a bias offset to correct at least one of the field strength readings generated by the sensor when the current occupancy conforms with the predetermined state of target occupancy.

2. The method of claim 1, wherein the targets are grouped in a plurality of zones and conformance of the current occupancy with the predetermined state of target occupancy is determined based on occupancy of the zones by readings.

3. The method of claim 1, wherein the targets are paired with diametrically opposing targets and conformance of the current occupancy with the predetermined state of target occupancy is determined based on occupancy of the paired targets by readings.

4. The method of claim 1, wherein the bias offset is computed as an average of minimum and maximum readings for each of three spatial dimensions among readings from occupied targets.

5. The method of claim 1, wherein the bias offset is computed as an average of readings for each of three spatial dimensions among readings from only diametrically opposed occupied targets.

6. The method of claim 1, wherein the bias offset is computed using readings from targets occupied by single readings.

7. The method of claim 1, wherein the bias offset is computed using readings from targets occupied by multiple readings.

8. The method of claim 1, wherein the bias offset is computed using filtered readings from targets occupied by multiple readings.

9. The method of claim 1, wherein the bias offset is subtracted from a field strength reading taken by the sensor.

10. The method of claim 1, wherein the method is applied to calibrate a plurality of sensors concurrently.

11. The method of claim 1, further comprising displaying on a user interface a graphic showing locations and occupancy status of individual ones of the targets.

12. The method of claim 1, further comprising displaying on a user interface a graphic showing locations of individual ones of the targets and highlighting one of the individual targets best aligned with a most recent corrected sensor reading.

13. The method of claim 1, wherein the sensor is a magnetometer.

14. The method of claim 1, wherein the sensor is an accelerometer.

15. The method of claim 1, wherein the sensor resides on an inertial measurement unit.

16. A method for calibrating a sensor, the method comprising:

generating a plurality of orientation targets in three-dimensional space around the sensor;

generating field strength readings by the sensor when at different orientations;

assigning the readings to different ones of the targets based on estimated proximity between the readings and the targets whereby different ones of the targets are occupied by the readings;

comparing a current occupancy of targets by readings for conformance with a predetermined state of target occupancy; and

computing a bias offset to correct at least one of the field strength readings generated by the sensor when the current occupancy conforms with the predetermined state of target occupancy wherein the computing step comprises computing a coarse bias offset for the sensor when the current occupancy conforms with a first predetermined state of target occupancy and computing a refined bias offset for the sensor when the current occupancy conforms with a second predetermined state of target occupancy.

17. A method for calibrating a sensor, the method comprising:

generating a plurality of orientation targets in three-dimensional space around the sensor;

generating field strength readings by the sensor when at different orientations;

assigning the readings to different ones of the targets based on estimated proximity between the readings and the targets whereby different ones of the targets are occupied by the readings;

comparing a current occupancy of targets by readings for conformance with a predetermined state of target occupancy;

computing a bias offset to correct at least one of the field strength readings generated by the sensor when the current occupancy conforms with the predetermined state of target occupancy, and buffering the readings and reassigning at least one of the buffered readings to a different one of the targets based on an updated estimated proximity between the buffered reading and the different target determined using the computed bias offset.

18. A sensor calibration system, comprising:

a sensor configured to measure a physical property at different orientations of the sensor and generate field strength readings for the sensor based on measurements of the physical property;

a processor communicatively coupled with the sensor, wherein under control of the processor the system is configured to generate a plurality of orientation targets in three-dimensional space around the sensor, assign the readings to different ones of the targets based on estimated proximity between the readings and the targets whereby different ones of the targets are occupied by the readings, compare a current occupancy of targets by readings with a predetermined state of target occupancy and compute a bias offset to correct at least one of the field strength readings generated by the sensor, when the current occupancy of targets by readings conforms with the predetermined state of target occupancy; and

buffer the readings and reassign at least one of the buffered readings to a different one of the targets based on an updated estimated proximity between the buffered reading and the different target determined using the computed bias offset.