Azimuth calculation program and electronic compass

• US 8,577,636 B2
• Filed: 08/11/2009
• Issued: 11/05/2013
• Est. Priority Date: 03/06/2007
• Status: Active Grant

• Current Assignee: Alps Alpine Co., Ltd.
• Original Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Inventors: Hirobe, Kisei, Yamada, Yukimitsu, Kawarda, Katsuyuki
• Primary Examiner(s): HENSON, MISCHITA L
• Application Number:
  US12/539,212
• Publication Number:
  US 20090293295A1
• Time in Patent Office: 1,547 Days
• Field of Search: 702/92, 702/93, 702/150, 702/151
• US Class Current: 702/92
• CPC Class Codes: G01C 17/28 Electromagnetic compasses with north seeking magnetic elements and having electric pick-offs G01C17/26
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01R 33/0206 Three-component magnetometers

Abstract

An azimuth calculation program is a computer-executable program that performs an azimuth calculation using output of a magnetic sensor. The azimuth calculation program includes a first step of generating one triangle in three-dimensional space using three output values of a magnetic sensor unit, a second step of determining a circumcircle of the triangle, and a third step of performing an azimuth calculation using center coordinates of the circumcircle and output values of the magnetic sensor.

Claims

1. A method of determining an azimuth in an electronic compass, wherein the electronic compass performs functions, the electronic compass includes a compass module and a control unit, the compass module including a magnetic sensor unit, the control unit includes an azimuth calculation program and a calibration program, the method comprising:

using a control unit to perform an azimuth calculation utilizing output from the magnetic sensor unit, the magnetic sensor unit including magnetic sensor elements corresponding to at least three axes for magnetic detection, wherein the magnetic sensor unit outputs three dimensional output corresponding to X, Y, Z axes, wherein the azimuth calculation comprises;

selecting three points selected from random outputs of the magnetic sensor, wherein the three points constitute three corners of a triangle in a three dimensional space;

determining a circumcircle which passes through the three points, which are the three corners of the triangle; and

performing the azimuth calculation using a center coordinate of the circumcircle and an output value of the magnetic sensor, wherein the azimuth calculation is performed by rotating an output value A (Ax, Ay, Az) through coordinate rotation about X axis, the center of the circumcircle is moved on the Z axis by the rotation, the rotation renders the output value A (Ax, Ay, Az) to A′

(A′

x, A′

y, A′

z), wherein azimuth angle is obtained from the equation λ

=tan−

1 (A′

y/A′

x), wherein the azimuth calculation program determines the azimuth calculation using output of the magnetic sensor elements, and the calibration program determines a reference point of output of each magnetic sensor elements using output of the magnetic sensor unit.

2. The method according to claim 1, wherein when an angle between a plane containing an already determined circumcircle and another plane containing a newly determined circumcircle is within a predetermined range, center coordinates of the respective already determined circumcircles are used to perform the azimuth calculation.

3. The method according to claim 1, wherein when an angle between a plane containing an already determined circumcircle and another plane containing a newly determined circumcircle is within a predetermined range, center coordinates of the respective newly determined circumcircles are used to obtain a weighted average of center coordinates of the already determined circumcircle.

4. The method according to claim 1, wherein the circumcircle is determined by collecting multiple sets of three output values from the magnetic sensor, and averaging centers of virtual circumcircles determined from the respective collected sets of the three output values.

5. The method according to claim 1, comprising utilizing a plurality of buffers for storing the three output values which are selected from the random outputs of the magnetic sensor so that distances between two of the three output values are equal or greater than a specified value.