Electronic compass and direction finding method

• US 20060190174A1
• Filed: 02/23/2006
• Published: 08/24/2006
• Est. Priority Date: 02/24/2005
• Status: Abandoned Application

• Current Assignee: Aichi Micro Intelligent Corporation
• Original Assignee: Aichi Micro Intelligent Corporation
• Inventors: Aoyama, Hitoshi, Tsuchida, Katsuhiko, Li, Xueping, Kako, Eiji, Honkura, Yoshinobu
• Application Number:
  US11/359,574
• Publication Number:
  US 20060190174A1
• Time in Patent Office: Days
• US Class Current: 701/224
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

An electronic compass and direction finding method includes a geomagnetic direction sensor having two sensor elements for detecting perpendicular components of the Earth'"'"'s magnetic field vector. A microcomputer is coupled to the geomagnetic direction sensor to compute a heading of a vehicle in software. Even if the electronic compass displays directional errors due to magnetization of the vehicle, a center of an azimuth circle can be immediately corrected by a center calculating means and a relatively accurate heading can be displayed. Later, the center of the azimuth circle can be corrected with a higher accuracy by a least squares calculating means. This frees a vehicle driver from uneasiness due to display of an intelligible direction.

Claims

1. An electronic compass, comprising:

a geomagnetic direction sensor having two magnetic sensor elements arranged perpendicular to each other for detecting two components of the Earth'"'"'s magnetic field vector, which varies with a heading direction θ

of a mobile object, as two-dimensional Cartesian coordinate data (X₁, Y₁), (X₂, Y₂) . . . (X_i, Y_i);

a direction calculating means for calculating said heading direction θ

of said mobile object from said two-dimensional coordinate data (X_i, Y_i);

a magnetic field judging means for determining whether the magnetic field is normal or abnormal; and

a correcting means for correcting a center of an azimuth circle plotted by said two-dimensional coordinate data (X_i, Y_i) in a turn of said mobile object, when said magnetic field judging means determines that the magnetic field is abnormal,

said correcting means having;

a center calculating means for calculating said center of said azimuth circle from at least three of said two-dimensional coordinate data (X_i, Y_i); and

a least squares calculating means for calculating said azimuth circle from a predetermined number of said two-dimensional coordinates data (X_i, Y_i), using the least square method,

said direction calculating means outputting said heading direction θ

calculated from said two-dimensional coordinate data (X_i, Y_i) when said magnetic field judging means determines that the magnetic field is normal, and calculating and outputting said heading direction θ

sequentially by using said center of said azimuth circle corrected by said correcting means when said magnetic field judging means determines that the magnetic field is abnormal.

2. An electronic compass according to claim 1, wherein said magnetic field judging means determines whether the magnetic field is normal or abnormal by comparing magnitude of said magnetic field vector obtained from said two-dimensional coordinate data (X_i, Y_i) and/or a time variation of said heading direction θ

calculated by said direction calculating means, with a predetermined threshold value.

3. An electronic compass according to claim 1, wherein said center calculating means obtains at least two perpendicular bisectors of at least two line segments connecting between different two-dimensional coordinate data, from said two-dimensional coordinate data (X_i, Y_i), and calculates an intersecting point of said at least two perpendicular bisectors.

4. An electronic compass according to claim 3, wherein said correcting means has an averaging means for averaging said intersecting point calculated by said center calculating means and a center point of said azimuth circle calculated by said least squares calculating means.

5. An electronic compass according to claim 1, wherein said center calculating means obtains a triangle connecting three data from said two-dimensional coordinate data (X_i, Y_i), and draws a perpendicular defined by a length of a longest side of said triangle and an apex angle opposite said longest side from a midpoint on said longest side, thereby calculating an end point of said perpendicular.

6. An electronic compass according to claim 5, wherein said correcting means has an averaging means for averaging said end point calculated by said center calculating means and a center point of said azimuth circle calculated by said least squares calculating means.

7. An electronic compass according to claim 1, wherein said magnetic sensor elements are magneto-impedance sensors.

8. A direction finding method, comprising:

a two-dimensional coordinate data detecting step for detecting two components of the Earth'"'"'s magnetic field vector, which varies with a heading direction θ

of a mobile object, as two-dimensional Cartesian coordinate data (X₁, Y₁), (X₂, Y₂) . . . (X_i, Y_i);

a direction calculating step for calculating said heading direction θ

of said mobile object from said two-dimensional coordinate data (X_i, Y_i) detected in said two-dimensional coordinate data detecting step;

a magnetic field judging step for determining whether the magnetic field is normal or abnormal; and

a correcting step for correcting a center of an azimuth circle plotted by said two-dimensional coordinate data in a turn of said mobile object, when said magnetic field judging step determines that the magnetic field is abnormal,

said correcting step having;

a center calculating step for calculating said center of said azimuth circle from at least three of said two-dimensional coordinate data (X_i, Y_i); and

a least squares calculating step for calculating said azimuth circle plotted in said turn of said mobile object from a predetermined number of said two-dimensional coordinate data (X_i, Y_i), using the least square method,

said direction calculating step outputting said heading direction θ

of said mobile object calculated from said two-dimensional coordinate data (X_i, Y_i) when said magnetic field judging step determines that the magnetic field is normal, and calculating and outputting said heading direction θ

sequentially by using said center of said azimuth circle corrected in said correction step when said magnetic field judging step determines that the magnetic field is abnormal.

9. A direction finding method according to claim 8, wherein said magnetic field judging step determines whether the magnetic field is normal or abnormal by comparing magnitude of said magnetic vector obtained from said two-dimensional coordinate data (X_i, Y_i) and/or a time variation of said heading direction θ

calculated in said direction calculating step, with a predetermined threshold value.

10. A direction finding method according to claim 8, wherein said center calculating step obtains at least two perpendicular bisectors of at least two line segments connecting between different two-dimensional coordinate data, from said two-dimensional coordinate data (X_i, Y_i), and calculating an intersecting point of said at least two perpendicular bisectors.

11. A direction finding method according to claim 10, wherein said correcting step has an averaging step for averaging said intersecting point calculated in said center calculating step and a center point of said azimuth circle calculated in said least squares calculating step.

12. A direction finding method according to claim 8, wherein said center calculating step obtains a triangle connecting three data from said two-dimensional coordinate data (X_i, Y_i), and draws a perpendicular defined by a length of a longest side of said triangle and an apex angle opposite said longest side from a midpoint on said longest side, thereby calculating an end point of said perpendicular.

13. A direction finding method according to claim 12, wherein said correcting step has an averaging step for averaging said end point calculated in said center calculating step and a center point of said azimuth circle calculated in said least squares calculating step.