Direction finding method and apparatus for correcting magnetization of a vehicle

• US 5,276,626 A
• Filed: 04/11/1991
• Issued: 01/04/1994
• Est. Priority Date: 04/12/1990
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ihara, Yasuhiro, Yamashita, Mitsuhiro
• Primary Examiner(s): Trans, Vincent N.
• Application Number:
  US07/685,392
• Time in Patent Office: 999 Days
• Field of Search: 364/424.02, 364/443, 364/449, 364/453, 364/457, 364/454, 364/571.2, 340/995, 340/988
• US Class Current: 701/224
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 21/28 with correlation of data from several navigational instruments

Abstract

The direction finding apparatus provided in the vehicle (10) computes average data and variance data from output data of the terrestrial magnetism sensor (1) in straight moving, and determines reliability of the detected output data of the terrestrial magnetism sensor (1). The error due to the magnetization of the vehicle (10) is corrected by computing the examined data on each of plural center candidates and selecting a center candidate as a new center coordinate of the present output circle of the terrestrial magnetism. Then, the magnetization of the vehicle (10) is inferred from the new center coordinate, thereby to infer a precise terrestrial magnetism direction.

Claims

1. A method for correcting magnetization of a vehicle comprising the steps of:

detecting terrestrial magnetism in a moving vehicle by terrestrial magnetism sensor means having two sensor elements arranged orthogonally to each other and generating a plurality of corresponding output data;

detecting an angular velocity of said moving vehicle and calculating a direction change angle which is equal to or larger than a predetermined angle from said detected angular velocity;

detecting a wheel speed of said moving vehicle and calculating a straight moving distance which is equal to or larger than a predetermined distance from said detected wheel speed;

determining a straight moving state of said moving vehicle from said direction change angle and said straight moving distance;

storing said output data from said terrestrial magnetism sensor means in basic data memory means when said straight moving state of said moving vehicle is determined;

determining average data and variance data from said stored output data in said basic data memory means and storing said determined average data and variance data in data calculation means;

determining reliability data from said variance data and an order number of said output data from said terrestrial magnetism sensor means;

determining an intensity and a direction of a magnetization of said moving vehicle from said average data, said variance data and said reliability data with magnetization calculation means by setting a plurality of center candidates and selecting a center coordinate from said plurality of center candidates having the smallest sum total, said sum total being calculated by multiplying said reliability data by a difference between an intensity of said detected average data and a radius of an output circle of said terrestrial magnetism;

storing said intensity and said direction of said magnetization in magnetization memory means;

determining a course of said moving vehicle from said output data from said terrestrial magnetism sensor means and said intensity and direction of said magnetization stored by said magnetization memory means; and

outputting to data output means a corrected direction of terrestrial magnetism.

2. A method for correcting magnetization of a vehicle in accordance with claim 1, wherein

said reliability calculation means obtains a final reliability data on the basis of a plurality of reliability data responding to said variance data and said order number of said output data.

3. A method for correcting magnetization of a vehicle in accordance with claim 1, wherein

said reliability calculation means obtains a final reliability data based on said variance data, said order number and a distance data determined according to said straight moving state in said straight moving detection means.

4. A method for correcting magnetization of a vehicle in accordance with claim 1, wherein

in said magnetization calculation means, all direction of said output circle are divided into a plurality of sectors, so that said magnetization calculation means selects an average data having the high reliability data in said divided direction and thereby computes said intensity and direction of said magnetization of said moving vehicle.

5. A direction finding apparatus comprising:

terrestrial magnetism sensor means, having two sensor elements arranged orthogonally to each other, for detecting terrestrial magnetism from locations passed by a moving vehicle and for generating a plurality of corresponding output data;

turn rate sensor means for detecting an angular velocity of said moving vehicle and calculating a direction change angle which is equal to or larger than a predetermined angle from said detected angular velocity;

wheel speed sensor means for detecting a wheel speed of said moving vehicle and calculating a straight moving distance which is equal to or larger than a predetermined distance from said detected wheel speed;

straight moving detection means for determining a straight moving state of said moving vehicle from said direction change angle and said straight moving distance;

basic data memory means for storing said output data from said terrestrial magnetism sensor means when said straight moving state of said moving vehicle is determined by said straight moving detection means;

data calculation means for calculating average data and variance data from said stored output data of said basic data memory means and for storing said calculated average data and variance data;

reliability calculation means for determining a reliability data from said variance data and an order number of said output data of said terrestrial magnetism sensor means;

magnetization calculation means for determining an intensity and a direction of a magnetization of said moving vehicle from said average data, said variance data and said reliability data by setting a plurality of center candidates, and selecting a center coordinate from said center candidates having the smallest sum total, said sum total being calculated by multiplying said reliability data by a difference between an intensity of said detected average data and a radius of an output circle of said terrestrial magnetism;

magnetization memory means for storing said intensity and direction of said magnetization determined by said magnetization calculation means;

direction calculation means for determining a course of said moving vehicle from said output data of said terrestrial magnetism sensor means and said intensity and direction of said magnetization stored by said magnetization memory means; and

data output means for outputting a corrected direction of terrestrial magnetism computed by said direction calculation means.

6. A direction finding apparatus in accordance with claim 5, wherein

said reliability calculation means obtains a final reliability data on the basis of a plurality of reliability data corresponding to said variance data and said order number of said output data.

7. A direction finding apparatus in accordance with claim 5, wherein

said reliability calculation means obtains a final reliability data based on said variance data, said order number and a distance data determined according to said straight moving state in said straight moving detection means.

8. A direction finding apparatus in accordance with claim 5, wherein

in said magnetization calculation means, all direction of said output circle are divided into a plurality of sectors, so that said magnetization calculation means selects an average data having high reliability in said divided direction and thereby computes said intensity and said direction of the magnetization of said vehicle.