Geometrical instruments – Indicator of direction of force traversing natural media – Magnetic field responsive
Reexamination Certificate
2000-12-15
2003-08-19
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Magnetic field responsive
C033S333000, C033S35500D, C033S357000
Reexamination Certificate
active
06606799
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic azimuth meter for calculating azimuth by detecting magnetic field of the geomagnetism by a magnetic sensor such as a magneto-resistive element.
2. Description of the Prior Art
According to an electronic azimuth meter, there is a concern in which a magnetic field generated at a location of a magnetic sensor is shifted from the magnetic field produced by the geomagnetism owing to the fact that a case of a battery normally comprising stainless steel such as SUS 304, or the like becomes more or less ferromagnetic by cold forming or the like and produces a magnetic field constituting noise in the geomagnetism. There has been a proposal per se for correcting an error by such noise by a correction table or the like (for example, Japanese Patent Laid-Open No. 170663/1998). According to technology proposed by the publication, actually, in order to correct errors in two orthogonal directions X and Y in a horizontal face, with regard to azimuth angle &thgr;, a correction calculating equation in the form of cos (2 &thgr;) is used and in the case in which the magnetic sensor can be arranged to separate from a battery having an outer shape substantially in a circular plate shape to some degree, the technology is regarded as appropriate qualitatively. Further, it is described in Japanese Patent Laid-Open No. 300869/1994 (Table 1 and
FIG. 13
of the publication) that in order to avoid an electronic part which is easy to bear magnetism or magnetize such as a case of a battery from effecting magnetic influence on a magnetic sensor, the electronic part which is easy to bear magnetism or magnetize is made remote from the magnetic sensor and a minimum limit distance which does not effect the magnetic influence is 2 cm (0.02 m) from an edge in the case of, for example, a sliver oxide battery.
However, the inventors have confirmed by experiment that when a case of a main body of an electronic azimuth meter is made as small as possible and a maximum size one is used for a battery, a distance between a magnetic part such as a case of the battery and a magnetic sensor is reduced and in an azimuth in which although a geomagnetic component in X (or Y) direction stays the same, a geomagnetic component in Y (or X) direction differs, an output of an X (or Y)-direction magnetic sensor, that is, a magnetic field detected value in X (or Y) direction by the magnetic sensor, in other words, an X (or Y) direction component of magnetic field formed at a location of the magnetic sensor differs.
SUMMARY OF THE INVENTION
The present invention has been carried out in view of the above-described point and it is an object thereof to provide an electronic azimuth meter which is compact and is capable of accurately measuring azimuth and an electronic time piece having the electronic azimuth meter.
In order to achieve the above-described object, according to an aspect of the invention, there is provided an electronic azimuth meter which is an electronic azimuth meter having an electronic azimuth meter main body and X-direction and Y-direction magnetic sensors for detecting magnetic field components of two orthogonal directions of X and Y of the main body, the electronic azimuth meter main body comprising a magnetic part forming at locations of the X-direction and the Y-direction magnetic sensors, magnetic fields Bmx and Bmy by being magnetized by geomagnetism and having components in oblique directions relative to a direction of the geomagnetism specified by magnetic field components Bx and By in an X-Y plane, approximate equation storing means for storing with regard to the respective directions of X and Y, pluralities of approximate equations calculated based on magnetic field detected values Vx and Vy of the X-direction and the Y-direction magnetic sensors with regard to a number of azimuths of the azimuth meter in the geomagnetism having the magnetic field components Bx and By, which are approximate equations (for example, Vxi (Bx, By), Vyj (Bx, By) or Bxi (Vx, Vy), Byj (Vx, Vy)) representing relationships between the detected values Vx and Vy of the magnetic sensors and the magnetic field components Bx and By of the geomagnetism, and azimuth calculating means for calculating the azimuth of the azimuth meter main body by selecting specific approximate equations in the pluralities of approximate equations with regard to the respective directions of X and Y based on the detected values Vx and Vy of the X-direction and the Y-direction magnetic sensors.
According to the electronic azimuth meter of the invention, there are provided “approximate equation storing means for storing with regard to the respective directions of X and Y, pluralities of approximate equations calculated based on magnetic field detected values Vx and Vy of the X-direction and the Y-direction magnetic sensors with regard to a number of azimuths of the azimuth meter in the geomagnetism having the magnetic field components Bx and By, which are approximate equations (for example, Vxi (Bx, By), Vyj (Bx, By) or Bxi (Vx, Vy), Byj (Vx, Vy)) representing relationships between the detected values Vx and Vy of the magnetic sensors and the magnetic field components Bx and By of the geomagnetism, and azimuth calculating means for calculating the azimuth of the azimuth meter main body by selecting specific approximate equations in the pluralities of approximate equations (for example, Vxi (Bx, By), Vyj (Bx, By) or Bxi (Vx, Vy), Byj (Vx, Vy) with regard to the respective directions of X and Y based on the detected values Vx and Vy of the X-direction and the Y-direction magnetic sensors” and therefore, even when there is provided “a magnetic part forming at locations of the X-direction and the Y-direction magnetic sensors, magnetic fields Bmx and Bmy by being magnetized by geomagnetism and having components in oblique directions relative to a direction of the geomagnetism specified by magnetic field components Bx and By in an X-Y plane”, influence by the magnetic part can be removed, the geomagnetic components of the geomagnetism can be detected and the azimuth of the azimuth meter can be calculated accurately. In this case, in order to calculate accurate azimuth, it is not necessary to know what noise magnetic field is formed by which part.
Therefore, according to the electronic azimuth meter of the invention, the magnetic part can be arranged in a state of being proximate to the magnetic sensor. That is, according to the electronic azimuth meter of the invention, a magnetic part such as a case of a battery typically comprising SUS 304 and easy to include more or less a ferromagnetic phase by a forming step, can be arranged to be proximate to the magnetic sensor and therefore, not only the size of the azimuth meter main body can be minimized but also a battery having a maximum capacity capable of being contained in the case can also be used and the electronic azimuth meter can be made compact and operable for a long period of time.
The electronic azimuth meter is provided with the X-direction and the Y-direction magnetic sensors for detecting respective geomagnetic components in two orthogonal directions of X and Y. The electronic azimuth meter is directed horizontally such that the magnetic field in the horizontal face can be detected by the X-direction and the Y-direction magnetic sensors. In this case, horizontally directing the electronic azimuth meter signifies directing the electronic azimuth meter in directions by which an X-Y plane becomes horizontal and the magnetic sensors detect the magnetic field in the horizontal face.
The magnetic field by the geomagnetism or the geomagnetism Bx, By and Bz differs according to locations on the earth. Strictly speaking, the magnetic field is varied over time. In the case of Japan, at a vicinity of Tokyo, horizontal magnetic force (magnitude of magnetic field (strictly speaking, “magnetic flux density”) component in a horizontal face of geomagnetism) {(Bx)
2
+(By)
2
}
½
, is about 30 &mgr;T, that
Adam & Wilks
Gutierrez Diego
Reis Travis
Seiko Instruments Inc.
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