Geometrical instruments – Indicator of direction of force traversing natural media – Magnetic field responsive
Patent
1986-11-17
1988-04-19
Stearns, Richard R.
Geometrical instruments
Indicator of direction of force traversing natural media
Magnetic field responsive
33361, G01C 1738
Patent
active
047380314
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is based on a method for establishing the driving direction of a vehicle with an electronic compass in accordance with the type of the main claim. In a known navigation apparatus (DE-PS No. 27 54 888) the driving direction of a vehicle is established with a two-axis-magnetometer, whose output signals are fed to a correction unit for compensating magnetic interference fields in the vehicle. This solution is based on the assumption that an interference field is present in the vehicle which is superimposed to a ground field which is more or less screened by the chassis of the motor vehicle depending on the alignment of the vehicle. Thereby, a polar frequency is obtained for the measuring values of the magnetometer on the X and Y axis in the vector diagram by turning the vehicle, whose center point is displaced from the coordinate system of axes with the vector of the interference field and which forms an ellipse by the proportional change of the signals, whose axis extend parallel to the measuring axis in the vector diagram. Due to the proportional change of the one output signal, an ellipse should be formed into a circle and due to the zero point displacement the circle should be transferred to the coordinate system of the axes. This is checked by a control step in that the corrected signals are lifted to a square and must form a constant value when added (circular equation).
The correcting magnitudes which were established by the control stage must be established by scanning tests which are extremely cumbersome and erroneous. Moreover, in this manner only timely constant interference fields can be taken into consideration. A further, substantial disadvantage of the known method consists in that only an axis parallel displacement from the zero point has to be taken into consideration for the elliptical polar frequency of the weakened ground field, whereas the reality such an elliptical polar frequency is turned by an angular magnitude also in the vector diagram. Since this turning is not picked up in the known measuring method, a considerable deviation is obtained between the established and the actual driving direction with such an electronic compass.
SUMMARY OF THE INVENTION
It is a purpose of the present invention to establish the direction of the ground field or the driving direction of the vehicle as accurately as possible by establishing a very accurate actual polar frequency of the magnetic field which will become effective on the magnetometer.
A method in accordance with the invention for establishing the driving direction is advantageous in that measuring values are picked off a magnetic field effective on the magnetometer during the turning of the vehicle. All required parameters are established by a digital evaluation circuit. The values of dependent on the installation location of the magnetometer in the vehicle, which determines the center point displacement as well as the shape and the turning of the polar frequency of the magnetic field in the vector diagram. In this manner, it is possible to establish the exact direction of the ground field, the north direction or the driving direction, or the direction of a predetermined destination and to indicate the same in view of the constant measuring by the magnetometer through the established polar frequency.
It is particularly advantageous to pick up the changes of the driving direction while driving by an evaluation circuit, by measuring the magnetic field vector by means of a microcomputer when exceedng a predetermined value of a change in driving direction, the actually measured value is stored in the same vector diagram as a further measuring point of the polar frequency. The measuring points which were read-in are further processed by the computer for checking and, if need be, for correcting the established parameter of the polar frequency. Moreover, the values for the driving direction change together with the way signals of the vehicle may be used for determining the location of the vehicle. For e
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patent: 4497034 (1985-01-01), Kuno et al.
patent: 4611293 (1986-09-01), Hatch et al.
patent: 4660161 (1987-04-01), Okada
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Alberter Gunter
Bauer Harald
Helldorfer Reinhard
Ittner Peter
Rauch Hans
Stearns Richard R.
Striker Michael J.
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