Electronic compass

Details Electronic compass Electronic compass

2000-04-11

2004-07-06

Barlow, John (Department: 2863)

Data processing: measuring, calibrating, or testing

Calibration or correction system

Direction

C033S356000, C033S361000

Reexamination Certificate

active

06760678

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to an electronic compass and, more particularly, to a system for and a method of calibrating the compass and displaying a designation of direction heading on the display of the compass.
BACKGROUND OF THE INVENTION
Although its cause is still the subject of dispute, it is well understood among scientists that planet Earth has its own natural magnetic field. As was discovered early in world history, the Earth's magnetic field can be used to indicate directional heading. A device that senses the Earth's magnetic field and aligns a ferromagnetic pointer with the flux lines of the Earth's magnetic field is generally referred to as a compass. This alignment allows for an identification of directional heading. Compasses are classified within a family of instruments referred to as magnetometers, which function to detect and measure the magnitude and/or direction of magnetic fields.
Modern mechanical compasses typically include a needle mounted for rotational movement that aligns itself with the magnetic flux lines of Earth's magnetic field. As is well understood, by convention, the magnetic flux lines are said to terminate at the Earth's magnetic north pole. Typically, during operation, a compass needle points towards the Earth's magnetic north pole, which is located in Canada.
The ability to identify direction, which is provided for by a compass, has proven to be invaluable for navigators and other travelers. Accordingly, since the development of the very first compasses, navigators have used such devices to sense and identify the directional heading traversed by their vehicles. Today, besides being a favorite among campers, compasses are found on board a variety of vehicles, including airplanes, ships, boats and automobiles. Compasses are increasingly used in position and navigation systems for vehicles.
One drawback of modern mechanical compasses is their inability to be calibrated to eliminate errors due to the magnetic field signature of nearby ferromagnetic material having relatively high permeability. It is understood by those skilled in the art that vehicles ordinarily have their own unique and distinct magnetic field signatures. In other words, the material from which a vehicle is made produces magnetic interference, which combines with the Earth's magnetic field. As will be appreciated, a compass installed in the vehicle will read the combined magnetic field (i.e., the Earth's magnetic field and the magnetic field corresponding to the vehicle's magnetic signature), and will in all likelihood generate inaccurate results as to the vehicle heading. In some cases, the effect of the vehicle magnetic field on the compass reading substantially overrides the effect of the Earth's magnetic field on the compass reading. When that occurs, the compass is rendered useless as a directional heading identification instrument.
With the advent of electronic technology in modem consumer products, electronic compasses have been developed. Electronic compasses provide substantial benefits over mechanical compasses for several reasons. One such reason is that electronic compasses can be more readily calibrated so that they eliminate the aforementioned vehicle signature magnetic field effect.
Electronic compasses produce electrical signals indicative of directional heading, based upon a measurement of the magnetic field intensity of the Earth's magnetic field relative to the orientation of the compass. Conventionally, electronic compasses include two distinct data channels defined by two orthogonally disposed magnetic field sensors aligned in the same plane. As a practical matter, the sensors are mounted on the same printed circuit board (PCB) positioned inside the housing of the electronic compass. As is well known in the art, the sensors generate electrical signals representative of the sensed magnetic field intensity of the Earth's magnetic field.
For purposes of representation and to facilitate an understanding of those signals, the respective magnitudes of the output electrical signals for each sensor may be represented by the magnitudes of component vectors on respective axes of a reference Cartesian coordinate system. In particular, the magnitude of the electrical signal for a first magnetic sensor may be represented by the magnitude of a first component vector extending in the same direction as the abscissa axis of a reference Cartesian coordinate system. On the other hand, the magnitude of the electrical signal for the second magnetic sensor may be represented by the magnitude of a second component vector extending in the same direction as the ordinate axis of that reference Cartesian coordinate system.
When the vector sum of the two aforementioned component vectors is determined, a resultant vector is produced, which ideally corresponds with the Earth's magnetic field vector, both in magnitude and direction. As will be appreciated, the electronic compass performs this vector summing operation to determine the directional heading.
In the ideal case (i.e., in the absence of any interfering magnetic fields), as the compass is rotated full circle (360 degrees) while being subjected to the Earth's magnetic field, the Earth's magnetic field vector will trace a circle having its center positioned at the origin of the reference Cartesian coordinate system. In that regard, the magnetic field intensity of the Earth's magnetic field, which corresponds with the magnitude of the Earth's magnetic field vector, is uniform. Therefore, as the compass is rotated full circle, the magnitude of the Earth's magnetic field vector is constant. On the other hand, although the Earth's magnetic field flux lines maintain constant direction, the orientation of those flux lines relative to the orientation of the magnetic sensors in the electronic compass varies while the compass is rotated. This relative difference is represented by the direction (i.e., angle) of the Earth's magnetic field vector. Therefore, as the compass is rotated fill circle, the direction of the Earth's magnetic field vector varies, and more particularly, rotates full circle as well.
FIG. 1
illustrates a reference Cartesian coordinate system
20
that is used to represent the ideal electrical signals for each of the two data channels of an electronic compass. Those electrical signals are produced by the two orthogonally disposed magnetic sensors of the compass. The reference Cartesian coordinate system
20
includes a point of origin
22
. Extending from origin
22
in opposite directions are the two opposing sides
24
,
26
of an abscissa
28
(e.g., x-axis). Likewise, the two opposing sides
30
,
32
of an ordinate
34
(e.g., y-axis) extend in opposite directions from origin
22
. As shown, the opposing sides
24
,
26
of abscissa axis
28
are orthogonally positioned with respect to the opposing sides
30
,
32
of ordinate axis
34
.
Still referring to
FIG. 1
, the electrical signal outputs for the orthogonally disposed magnetic sensors are represented by component vectors Vx and Vy, respectively. As shown, component vector Vx is a vector having a magnitude Vx, which corresponds to the magnetic field intensity sensed by one of the orthogonally disposed magnetic sensors. Component vector Vx extends in a direction from origin
22
to a point along one of the sides
24
,
26
of abscissa
28
. As further shown, component vector Vy is a vector having a magnitude Vy, which corresponds to the magnetic field intensity sensed by the other of the orthogonally disposed magnetic sensors. Component vector Vy extends in a direction from origin
22
to a point along one of the sides
30
,
32
of ordinate
34
. Component vectors Vx and Vy represent the magnetic field intensities measured by the two orthogonally disposed magnetic sensors, respectively. The two vector components Vx and Vy are added together to form a resultant vector Vm, which defines the total compass output. Resulta

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