System, method, device and computer code product for improving the readability of an electronic compass

• US 6,964,107 B1
• Filed: 05/27/2004
• Issued: 11/15/2005
• Est. Priority Date: 05/27/2004
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Ahola, Tom Mikael
• Primary Examiner(s): Fulton, Christopher W.
• Application Number:
  US10/856,206
• Publication Number:
  US 20050262713A1
• Time in Patent Office: 537 Days
• Field of Search: 333/56, 333/55.R, 333/57, 333/55.D, 33/1.E
• US Class Current: 33/356
• CPC Class Codes: G01C 17/28 Electromagnetic compasses with north seeking magnetic elements and having electric pick-offs G01C17/26

Abstract

A system, method, device and computer code product is disclosed for stabilizing compass heading under tilt error conditions from an uncorrected electronic compass reading. Exemplary embodiments include a stabilizing filter configured to filter out tilt errors incorporated into the uncorrected electronic compass reading and a filter adaptation module configured to control the stabilizing filter response based on the signal radius of the uncorrected compass reading and a pre-calibrated ideal radius for the compass. The filter adaptation module can be configured to calculate a filter response parameter as a function of the relative difference between the signal radius of the uncorrected compass reading and the pre-calibrated ideal radius. The filter response parameter can be passed to the stabilizing filter for controlling its operation.

Claims

1. An electronic compass configured to provide a compass heading based on the Earth'"'"'s magnetic field, the compass comprising:

a sensor configured to measure the Earth'"'"'s magnetic field and to provide sensor outputs signals indicative of the measured magnetic field;

a stabilizing filter configured to stabilize the compass heading in random tilt error conditions; and

a filter adaptation module configured to control the stabilizing filter response based on the sensor output signals and pre-calibrated compass radius information.

2. The compass of claim 1, wherein the stabilizing filter further comprises a first order infinite input response (IIR) filter.

3. The compass of claim 1, wherein the filter adaptation module is configured to provide the stabilizing filter with a filter response parameter.

4. The compass of claim 1, further comprising a warning indicator configured produce a warning signal if tilt error exceeds a predetermined threshold.

5. The compass of claim 1, wherein the stabilizing filter response is slowed down as tilt error increases.

6. A device for stabilizing a compass heading display in random tilt error conditions in an electronic compass configured to measure the Earth'"'"'s magnetic field and produce an uncorrected compass reading based on the measured field, the device comprising:

a stabilizing filter configured to filter random tilt error incorporated into the uncorrected compass reading; and

a filter adaptation module configured to control the stabilizing filter response based on the uncorrected compass reading and pre-calibrated compass radius information.

7. The device of claim 6, wherein the stabilizing filter further comprises a first order infinite response (IIR) filter.

8. The device of claim 6, wherein the filter adaptation module is configured to provide the stabilizing filter with a filter response parameter.

9. The device of claim 8, wherein the filter adaptation module is configured to calculate the filter response parameter as a function of the relative difference between a signal radius of the uncorrected compass reading and the pre-calibrated compass radius information.

10. The device of claim 9, wherein the filter adaptation module calculates the filter response parameter as follows:

$\sqrt{\frac{3<br><br><br><br>R_6-R<br><br>}{R}}$

wherein R_e is the signal radius of the uncorrected compass reading and R is the pre-calibrated compass radius information.

11. The device of claim 6, further comprising warning indicator configured for producing a warning signal if the tilt error exceed a predetermined threshold.

12. The device of claim 6, wherein the stabilizing filter response is slowed down as tilt error increases.

13. A method for filtering out tilt error in an electronic compass configured to produce an uncorrected compass reading indicative of compass heading, the method comprising:

calculating a signal radius of the uncorrected compass reading;

calculating a filter response parameter based on the calculated signal radius and a pre-calibrated ideal compass radius; and

stabilizing the compass reading in tilt error conditions with a stabilizing filter based on the calculated filter response parameter.

14. The method of claim 13, further comprising determining if the filter response parameter exceed a predetermined threshold and if so, activating a warning indicator.

15. The method of claim 13, wherein the filter response parameter is further calculated as a function of the relative difference between the signal radius and the pre-calibrated ideal compass radius.

16. The method of claim 15, wherein the filter response parameter is further calculated as:

$\sqrt{\frac{3<br><br><br><br>R_6-R<br><br>}{R}}$

where R_e is the signal radius and R is the pre-calibrated ideal compass radius.

17. A computer code product for filtering out tilt error in an electronic compass configured to produce an uncorrected compass reading indicative of compass heading, the computer code product comprising:

computer code configured to;

calculate a signal radius of the uncorrected compass reading;

calculate a filter response parameter based on the calculated signal radius and a pre-calibrated ideal compass radius; and

stabilize the compass reading in tilt error conditions based on the filter response parameter.

18. The computer code product of claim 17 further comprising computer code configured to determine if the filter response parameter exceeds a predetermined threshold, and if so, to activate a warning indicator.

19. The computer code product of claim 17, wherein the computer code configured to calculate the filter response parameter is further configured to calculate the filter response parameter as a function of the relative difference between the signal radius and the pre-calibrated ideal compass radius.

20. The computer code product of claim 19, wherein the computer code product is further configured to calculate the filter response parameter as:

$\sqrt{\frac{3<br><br><br><br>R_6-R<br><br>}{R}}$

where R_e is the signal radius and R is the pre-calibrated ideal compass radius.

21. A mobile electronic device, the device comprising:

an electronic compass configured to measure the Earth'"'"'s magnetic field and produce an uncorrected compass reading based on the measured field;

a stabilizing filter configured to filter random tilt error incorporated into the uncorrected compass reading; and

a filter adaptation module configured to control the stabilizing filter response based on the uncorrected compass reading and pre-calibrated compass radius information.

22. The device of claim 21, wherein the device further comprises a mobile telephone.

23. The device of claim 21, wherein the device further comprises a personal digital assistant.

24. The device of claim 21, wherein the device further comprises a portable computer.