Method, system and device for calibrating a magnetic field sensor

• US 7,119,533 B2
• Filed: 04/20/2005
• Issued: 10/10/2006
• Est. Priority Date: 09/29/2004
• Status: Active Grant

• Current Assignee: Amosense Co., Ltd.
• Original Assignee: C & N Incorporated
• Inventors: Tamura, Yasuhiro, Ito, Masahito
• Primary Examiner(s): Patidar, Jay M.
• Application Number:
  US11/109,819
• Publication Number:
  US 20060066295A1
• Time in Patent Office: 538 Days
• Field of Search: 324/202, 324/249, 324/251, 324/252, 324/247, 324/260, 333/55.R, 333/61, 333/56, 702/150, 702 92- 93, 701/224
• US Class Current: 324/202
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• CPC Class Codes: G01R 33/0206 Three-component magnetometers
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

A control device 200 calibrates a magnetic-field sensor 100 by computation. A computation unit 210 calculates the magnetic-field intensity based upon the outputs of X-axis, Y-axis, and Z-axis magnetic-field detection devices of the magnetic-field sensor 100. Such calculation is performed for four or more different points. The calculation is performed such that at least one point is not positioned on a plane including the other points. The computation unit 210 converts the outputs from the X-axis, Y-axis, and Z-axis magnetic-field detection devices of the magnetic-field sensor 100 into three-dimensional spatial coordinate points. Then, the computation unit 210 creates a sphere on which the four or more coordinate points thus obtained are positioned. The coordinate point of the center of the sphere thus created represents the magnetic-field offset. The interfering magnetic-field components in the X-axis, Y-axis, and Z-axis directions thus obtained are subtracted from the outputs of the X-axis, Y-axis, and Z-axis magnetic-field detection devices of the magnetic sensor 100, whereby calibration is made.

Claims

1. A control method of controlling a magnetic-field sensor for detecting the three-axis components of the terrestrial magnetic-field vector, said method comprising:

calculating a reference coordinate point in a predetermined coordinate space by performing coordinate transformation for the three-axis components of the terrestrial magnetic field vector as a reference, and holding said reference coordinate point thus calculated;

acquiring the three-axis component outputs of said magnetic-field sensor occurring when said sensor assumes five or more attitudes;

performing coordinate transformation for the three-axis components thus obtained for each attitude to calculate five or more coordinate points in the same coordinate space as with said reference coordinate point;

selecting four points which are as far as possible from one another among the five or more coordinate points, creating a sphere on which said selected four coordinate points are positioned, and obtaining a magnetic-field offset by calculating the distance between the center of said sphere thus created and said reference coordinate point; and

calibrating said magnetic-field sensor using said magnetic-field offset.

2. A control device of a magnetic-field sensor for detecting three-axis components of the terrestrial magnetic-field vector, said device comprising:

a storage unit for holding a reference coordinate point in a predetermined coordinate space obtained by performing coordinate transformation for the three-axis components of the terrestrial magnetic field vector as a reference; and

a computation unit for performing coordinate transformation for the three-axis component output of said magnetic-field sensor occurring when said sensor assumes five or more attitudes to calculate five or more coordinate points in the same coordinate space as with said reference coordinate point, selecting four coordinate points which are as far as possible from one another from among the five or more coordinate points, and creating a sphere on which said selected four coordinate points are positioned,

wherein said computation unit obtains a magnetic-field offset by calculating the distance between the center of said sphere thus created and said reference coordinate point, and calibrates said magnetic-field sensor using said magnetic-field offset.

3. A mobile terminal device comprising:

a magnetic-field sensor for detecting the three-axis components of the terrestrial magnetic-field vector; and

a control device according to claim 2.

4. A system for calibrating a device containing a three-axis magnetic-field sensor, said system comprising:

a storage unit for storing a reference coordinate point in a predetermined coordinate space obtained by performing coordinate transformation for the three-axis components of the terrestrial magnetic field vector; and

a computation unit for;

calculating five or more coordinate points in the same coordinate space as the reference coordinate point by performing coordinate transformation for the three-axis component output of said magnetic-field sensor when said device assumes five or more attitudes;

selecting four points which are as far as possible from one another from among the five or more coordinate points;

creating a sphere on which said selected four coordinate points are positioned;

calculating a magnetic-field offset based on the distance between the center of said sphere thus created and said reference coordinate point; and

calibrating said device based on said magnetic-field offset.