Data processing: measuring – calibrating – or testing – Calibration or correction system – Direction
Patent
1997-12-18
1999-11-30
Hoff, Marc S.
Data processing: measuring, calibrating, or testing
Calibration or correction system
Direction
33349, 33359, G01C 1738
Patent
active
059959134
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION
This application is the national stage application of PCT/EP96/03681, filed Aug. 21, 1996, which is entitled to priority of German Application No. 195 32 122.7, filed Aug. 31, 1995.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of stabilizing the horizon of magnetic compasses.
2. Description of the Related Art
Customary compasses with a magnetic needle have no horizontal stabilization, but leveling is sometimes carried out, for example using a fluid support. The same effect would be achieved by suspending the compass from gimbles.
There are various known ways of stabilizing the horizon for magnetic compasses. For example, in the case of navigation systems, the horizon is stabilized using gyroscopic devices, but this is a complicated and expensive measure.
When there are faults in a system for stabilizing the horizon, a measuring error or reading error results, usually because of accelerations, when magnetic compasses of this type are used in motion, for example during a vehicle journey. The same errors may, however, also occur if the compass is only being held by hand.
In the case of a digital magnetic compass (DMC) known from DE 37 16 985 C1, the directional information is obtained from the projection of the geomagnetic field vector onto the horizontal plane. The DMC contains a separate sensor for each coordinate of the geomagnetic field. The horizontal plane is measured using two inclination sensors arranged perpendicular to one another. The inclination sensors are arranged in a common housing with the magnetic field sensors.
In actual fact, the inclination sensors are acceleration sensors. They are calibrated in the housing so that, in the stationary state, i.e. without additional acceleration forces acting, they only measure the components of the acceleration vector due to gravity in the X and Y directions of the DMC coordinate system, and determine therefrom the angle between the two said coordinate axes and the horizontal plane. The projection of the geomagnetic field vector is corrected in accordance with the current position of the DMC housing differing from the horizontal reference position.
The coordinate system of the DMC is a right-handed orthogonal cartesian coordinate system having origin O and three coordinate axes X, Y, Z. This coordinate system is regarded as fixed with respect to the DMC housing.
The X axis and the Y axis define a first plane which corresponds to the horizontal plane or reference plane when the DMC housing is aligned horizontally. The line of sight of the DMC coincides with the X axis. The Z axis is then parallel to the acceleration vector due to gravity.
If the DMC housing is inclined, then the DMC coordinate system must rotate with respect to a spatially fixed reference system which is likewise a right-handed orthogonal cartesian coordinate system having origin O, but now having three coordinate axes X', Y', Z'. In the horizontal state, the respectively corresponding coordinate axes and the origin of the two coordinate systems coincide.
After a rotation, the reference plane of the DMC would lie in a second plane which, for example, is obtained by one rotation through the angle .alpha. about the Y' axis and by one rotation through the angle .beta. about the X' axis. In the field of navigation, the angle .alpha. is referred to as the pitch angle, and the angle .beta. is referred to as the roll angle.
The XYZ coordinate system of the DMC can thus be converted into the spatially fixed X'Y'Z' coordinate system merely by a rotation. The pitch angle .alpha. and the roll angle .beta. are obtained as values measured by the inclination sensors.
Since the acceleration due to gravity varies only little over the surface of the earth, then, when the DMC is in a static state or in a state of uniform motion, particular inclination angles coincide everywhere with the actual position with respect to the acceleration vector due to gravity.
The behavior is different, however, if the DMC is built into a veh
REFERENCES:
patent: 5701259 (1997-12-01), Dittrich
Dittrich Frank
Gnepf Silvio
Nachbaur Peter
Hoff Marc S.
Leica Geosystems AG
Vo Hien
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