Method and apparatus for measuring azimuth

• US 5,052,116 A
• Filed: 02/28/1990
• Issued: 10/01/1991
• Est. Priority Date: 02/23/1988
• Status: Expired due to Fees

• Current Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Original Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Inventors: Nakajima, Ryoichi, Oide, Sakuji
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Gutierrez, Diego F. F.
• Application Number:
  US07/486,627
• Time in Patent Office: 580 Days
• Field of Search: 33/361, 33/362, 33/356, 324/247, 324/253, 324/254, 324/255
• US Class Current: 33/361
• CPC Class Codes: G01C 17/30 Earth-inductor compasses

Abstract

A method of measuring an azimuth by detecting the earth'"'"'s magnetism by using two perpendicular coils to detect the azimuth according to the outputs of the coils, including the steps of converting the outputs of the coils by multiplying them by a constant so as to vary in a range determined by a reference value, dividing the converted signal by the reference value, and measuring the azimuth at each coil output according to an inverse trigonometric function, with the divided result as a variable. An azimuth measuring apparatus for executing the method is also provided. Thus, the method and apparatus can accurately detect the azimuth and can further detect an error due to a disorder of the earth'"'"'s magnetism or the inclination of the apparatus.

Claims

1. A method for measuring an azimuth relative to the earth'"'"'s magnetic field, comprising the steps of:

providing two coils perpendicular to each other;

measuring an output signal from each of said coils;

multiplying the output signal of each of said coils by a constant to provide a converted signal having a value within a predetermined range;

dividing the converted signal by a predetermined value to provide a normalized signal value;

computing a smaller value for the azimuth using said normalized signal value from one of said coils and computing a larger value for azimuth from said normalized signal value from the other one of said coils by substituting each said value into an inverse trigonometric function; and

adding to the smaller one of said azimuth values a product equal to a difference of said smaller and larger values of azimuth multiplied by a factor proportional to a ratio of the output signals of the two coils.

2. A method for determining an azimuth as in claim 1 which further includes the steps of:

rotating both of said coils to generate a periodic function of the output signal versus rotation for each coil wherein each periodic function has a particular phase;

comparing a displacement angle between said phases to a particular value; and

correcting said phase of one function by an angle corresponding to said displacement angle.

3. An azimuth measuring apparatus comprising:

two perpendicular coils each emitting a signal proportional to components of the earth'"'"'s magnetic field;

means for rotating said coils;

means for multiplying a constant by each of the outputs of said coils, thereby converting the multiplied value to a value within a range of a reference value;

means for dividing said multiplied value by said reference value to provide an output value;

means for computing a value of azimuth for every output of each of the coils as said coils are rotated as an inverse trigonometric function of said output value;

means for storing signals as said coils are rotated, thereby producing a first and a second periodic signal function, one for each coil, said functions having respectively first and second phases;

means for computing a phase difference between said phases;

means for comparing said phase difference to a predetermined value; and

means for displacing said first phase toward said second phase when said phase difference exceeds said predetermined value.