Process for compensating a magnetic interference field in a vehicle

• US 5,581,899 A
• Filed: 03/15/1994
• Issued: 12/10/1996
• Est. Priority Date: 09/17/1991
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Feigen, Patrick, Brehler, Markus
• Primary Examiner(s): Will, Thomas B.
• Application Number:
  US08/211,103
• Time in Patent Office: 1,001 Days
• Field of Search: 73/1 E, 33/356, 33/357, 33/361, 33/363 Q, 364/559, 364/571.05
• US Class Current: 33/356
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01R 33/025 Compensating stray fields G01R33/0017 takes precedence

Abstract

Process for compensating a magnetic interference field in a vehicle having a navigation installation. During a calibration run for initial compensation, a first set of interference field parameters is determined from the measurements of the magnetic field probe (interference field vector V1, axes a, b of the elliptical locus curve E1, oblique position) and transformed onto points of a circular locus curve with the radius a about the origin (0); the distance from the origin (0) and the angle are calculated for each pair of measurements. The calculated radius values and the circularly transformed pairs of measurements (MP) are averaged and entered in their appropriate memory cell in a segmented memory for 360° with a plurality of memory ceils (predetermined angular region). Variant 1: for each segment, the radius difference (Δa) is determined from the averaged radius values and the radius (a) and filtered; from this the maximum (MAX) is calculated according to direction and magnitude and the new center (M2) of the locus curve (K2) and thus the new interference field vector (V2=V1+V2'"'"') are calculated. The distances from the measurement points (MP) are calculated from M2 and compared with the radius; if there is adequately accurate agreement, compensation is carried out with the new interference field vector (V2). Variant 2: a straight line (g) is calculated from the averaged X and Y values by means of linear regression. Their correlation coefficient is determined and compared with an empirically found threshold; if the correlation coefficient is greater than the threshold, the center point (P) of the straight line section (S1,S2) is determined, which is given by the pairs of measurement points (MP). The perpendicular (L) at the center point (P), towards the origin (0), is constructed and the circle radius (a) is plotted, the end point of the radius forming the center (M2) of the new locus curve (circle K2) (new interference field vector V2).

Claims

1. A process for compensating for a magnetic interference field in a vehicle, in which, for navigation purposes, a direction of the earth'"'"'s magnetic field is determined by means of a magnetic field probe and a measuring and evaluating device, and a path distance traveled is determined by a wheel sensor and said direction and said path distance are processed in a navigation computer, said process comprising the following steps:

during a calibration run for initial compensation, determining a first set of interference field parameters from first measurements of the magnetic field probe, which parameters comprise values for an interference field vector, axes of an elliptical locus curve and an oblique position of this locus curve;

transforming the elliptical locus curve into a first circular locus curve having a radius and a center, the center being a coordinate origin;

during travel, taking second measurements with the magnetic field probe and transforming the second measurements into measured value pairs that are points on a second circular locus curve having a radius and a center

calculating for each measured value pair, a distance value from the origin and an angle;

defining a segmented memory having memory cells for a range of 0°

-360°

in which each memory cell corresponds to a predetermined angular region;

averaging the calculated distance values and the circularly transformed measured value pairs and storing the averaged distance values in the memory cells corresponding to their angle;

for each segment, determining a radius difference value from the averaged distance values and the radius of the first circular locus curve;

filtering the radius difference values with a low pass filter;

calculating a maximum value from the filtered radius difference values in terms of direction and magnitude and calculating a new center of the second circular locus curve and calculating a new interference field vector;

calculating further distances from the new circle center to the stored distance values and comparing said further distances with the radius of the first circular locus circle, and, in the event of substantially accurate agreement, carrying out compensation using the new interference field vector.

2. The process as claimed in claim 1, wherein the new interference field vector is calculated only if a minimum number of measurements is exceeded and at the same time a minimum number of angular regions are utilized in the segmented memory.

3. The process as claimed in claim 2, wherein one of a plurality of predetermined combinations of minimum number of measurements and minimum number of utilized angular regions in the segmented memory must be satisfied.

4. The process as claimed in claim 1, wherein a quality of the interference field vector is determined from the comparison of the radius values of all participating magnetic field measurements with the radius of the first circular locus curve obtained from the initial compensation and, in the event of the quality being below a specified value, all original measurements from the magnetic field probe and from the wheel sensor are stored, in order subsequently to correct vehicle position using the new interference field vector and data stored in the segmented memory.

5. A process for compensating for a magnetic interference field in a vehicle, in which, for navigation purposes, a direction of the earth'"'"'s magnetic field is determined by means of a magnetic field probe and a measuring and evaluating device, and a path distance traveled is determined by a wheel sensor and said direction and said path distance are processed in a navigation computer, said process comprising the following steps:

during a calibration run for initial compensation, determining a first set of interference field parameters from first measurements of the magnetic field probe, which parameters comprise values for an interference field vector, axes of an elliptical locus curve and an oblique position of this locus curve;

transforming the elliptical locus curve into a first circular locus curve having a radius and a center, the center being a coordinate origin;

during travel, taking second measurements with the magnetic field probe and transforming the second measurements into measured value pairs that are points on a second circular locus having a radius and a center;

calculating for each measured value pair, a distance value from the origin and an angle;

defining a segmented memory having memory cells for a range of 0°

-360°

, in which each memory cell corresponds to a predetermined angular region;

averaging the calculated distance values and the circularly transformed measured value pairs and storing the averaged distance values in the memory cells corresponding to their angle;

calculating a straight line from averaged X and Y values of the measured value pairs using linear regression;

determining a correlation coefficient of this straight line and comparing the correlation coefficient with an empirically found threshold;

if the correlation coefficient is greater than this threshold, determining a center of gravity a straight line section, which is established by the circularly transformed measured value pairs in the segmented memory;

constructing a perpendicular to the straight line at the center of gravity in a direction of the origins;

plotting the radius of the first circular locus curve on the perpendicular, an end point of this plotted radius forming a center of the second circular locus curve, and determining a new interference field vector from a sum of a previous interference field vector and the shift of the center of the second locus curve, and revising the set of interference field parameters with the new interference field vector and using the revised set of interference field parameters in the transformation of measured values.

6. The process as claimed in claim 5, wherein the new interference field vector is calculated only if a minimum number of measurements is exceeded and at the same time a minimum number of angular regions are utilized in the segmented memory.

7. The process as claimed in claim 6, wherein one of a plurality of predetermined combinations of minimum number of measurements and minimum number of utilized angular regions in the segmented memory must be satisfied.

8. The process as claimed in claim 5, wherein a quality of the interference field vector is determined from the comparison of the radius values of all participating magnetic field measurements with the radius of the first circular locus curve obtained from the initial compensation and, in the event of the quality being below a specified value, all original measurements from the magnetic field probe and from the wheel sensor are stored, in order subsequently to correct the vehicle position using the new interference field vector and using data stored in the requested memory, with the utilization of the stored data.

9. A method for compensating for magnetic interference field in a vehicle wherein, for navigation purposes, a direction of the earth'"'"'s magnetic field is determined with a magnetic field probe and a measuring and evaluating device, and a path distance traveled is determined by a wheel sensor and are processed in a navigation computer, comprising the following method steps:

determining a first set of interference field parameters from first measured values of the magnetic field probe during a calibration drive for an initial compensation, said parameters being composed of values for a first interference field vector, axes of an elliptical locus curve and an oblique attitude of this locus curve;

transforming the elliptical locus curve determined during the calibration drive into a first circular locus curve having a radius and a center that is a coordinate origin;

during travel, taking second measurements with the magnetic field probe and transforming the second measurements into measured value pairs that are points on a second circular locus curve having a radius and a center, taking a set of interference field parameters into account;

calculating a distance value from the origin and an associated angular range for every circularly transformed measured value pair;

defining a segmented memory having memory cells for a range from 0°

through 360°

, each memory cell corresponding to a predetermined angular range or, respectively, segment;

averaging the calculated distance values and the circularly transformed measured value pairs and storing the averaged distance values in the memory cells corresponding to their angle;

calculating a straight line from average X and Y values of the measured value pairs using a linear regression;

determining a correlation coefficient of the straight line and comparing the correlation coefficient with an empirically found threshold;

if the correlation coefficient is greater than this threshold, determining a center of gravity of a straight line segment that is established by the circularly transformed measured value pairs in the segmented memory;

constructing a perpendicular to the straight line at the center of gravity in a direction of the origin;

entering the circle radius of the first circular locus curve on the perpendicular, an end point thereof forming a center of the second circular locus curve, a new interference field vector being determined from a sum of a previous interference field vector and the shift of the center of the second locus curve, and the new interference field vector being entered into the set of interference field parameters and being taken into account in the transformation of measured values.

10. The method according to claim 9, wherein the second interference field vector is only calculated when a minimum plurality of measured values is exceeded and a minimum plurality of angular ranges is simultaneously utilized in the segment memory.

11. The method according to claim 9, wherein one of a plurality of predetermined combinations of minimum number of measured values and minimum number of utilized angular ranges in the segment memory are satisfied.

12. The method according to claim 9, wherein a quality of an interference field vector is determined from the comparison of the radius values of all magnetic field measured values to the radius of the locus curve from the initial compensation, and, when the quality drops below a specific value, all original measured values from the magnetic field probe and from the wheel sensor are stored in order to subsequently correct vehicle position with the second interference field vector using data stored in the segmented memory.

13. A method for compensating for magnetic interference field in a vehicle wherein, for navigation purposes, a direction of the earth'"'"'s magnetic field is determined with a magnetic field probe and a measuring and evaluating device, and a path distance traveled is determined by a wheel sensor and are processed in a navigation computer, comprising the following method steps:

determining a first set of interference field parameters from first measured values of the magnetic field probe during a calibration drive for an initial compensation, said parameters being composed of values for a first interference field vector, axes of an elliptical locus curve and an oblique attitude of this locus curve;

transforming the elliptical locus curve determined during the calibration drive into a first circular locus curve having a radius and a center that is a coordinate origin;

during travel, taking second measurements with the magnetic field probe and transforming the second measurements into measured value pairs that are points on a second circular locus curve having a radius and a center, taking a set of interference field parameters into account;

calculating a distance value from the origin and an associated angular range for every circularly transformed measured value pair;

defining a segmented memory having memory cells for a range from 0°

through 360°

, each memory cell corresponding to a predetermined angular range or, respectively, segment;

averaging the calculated distance values and the circularly transformed measured value pairs and storing the averaged distance values in the memory cells corresponding to their angle;

calculating a straight line from average X and Y values of the measured value pairs using a linear regression;

determining a correlation coefficient of the straight line and comparing the correlation coefficient with an empirically found threshold;

if the correlation coefficient is greater than this threshold, determining a center of gravity of a straight line segment that is established by the circularly transformed measured value pairs in the segmented memory;

constructing a perpendicular to the straight line at the center of gravity in a direction of the origin;

entering the circle radius of the first circular locus curve on the perpendicular, an end point thereof forming a center of the second circular locus curve, a new interference field vector being determined from a sum of a previous interference field vector and the shift of the center of the second locus curve, and the new interference field vector being entered into the set of interference field parameters and being taken into account in the transformation of measured values;

calculating radius difference between the averaged radius values and the radius of the first circular locus curve for each segment;

filtering the radius difference values are filtered with a low-pass filter;

calculating a maximum value in terms of direction and magnitude from the filtered radius difference values and the center of the second circular locus curve and calculating a new interference field vector therefrom;

calculating distances to the stored, circularly transformed measured value pairs proceeding from the center of the second circular locus curve and comparing the calculated distances to the radius of the first circular locus curve, the new interference field vector being inserted into the set of interference field parameters given adequately precise coincidence and being taken into account in the transformation of measured values.

14. The method according to claim 13, wherein the second interference field vector is only calculated when a minimum plurality of measured values is exceeded and a minimum plurality of angular ranges is simultaneously utilized in the segment memory.

15. The method according to claim 13, wherein one of a plurality of predetermined combinations of minimum number of measured values and minimum number of utilized angular ranges in the segment memory are satisfied.

16. The method according to claim 13, wherein a quality of an interference field vector is determined from the comparison of the radius values of all magnetic field measured values to the radius of the locus curve from the initial compensation, and, when the quality drops below a specific value, all original measured values from the magnetic field probe and from the wheel sensor are stored in order to subsequently correct vehicle position with the second interference field vector using data stored in the segmented memory.