Navigation system and method

• US 6,014,610 A
• Filed: 01/30/1998
• Issued: 01/11/2000
• Est. Priority Date: 01/31/1997
• Status: Expired due to Term

• Current Assignee: Continental Automotive Systems, Inc. (Continental AG)
• Original Assignee: Greenfield Enterprises, Inc.
• Inventors: Hatch, Ronald, Judge, Kevin
• Primary Examiner(s): ASSOUAD, PATRICK J
• Application Number:
  US09/016,609
• Time in Patent Office: 711 Days
• Field of Search: 702/92, 702/93, 702/104, 33/316, 33/319, 33/355 R, 33/356, 33/357, 33/352, 701/1, 701/200, 701/224, 701/205, 701/213, 701/214, 73/1.76, 73/1.75, 324/260
• US Class Current: 702/92
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

An electronic compass system and method in which an automatic calibration process is available while the vehicle is in use. The procedure uses a binning process to collect and count data points which automatically triggers the automatic calibration process, and which is also used for manual calibration. Also, there is a procedure for detecting and rejecting anomalous magnetic events outside the vehicle through a jitter phenomenon.

Claims

1. Apparatus for calibrating the distortions in the readings of a magnetic compass having a plurality of magnetic field sensors and for characterizing and rejecting readings caused by transient magnetic disturbances comprising:

first means coupled to the compass sensors for obtaining the outputs from each of the sensors as a function of time by weighting and combining the outputs from each of the sensors at a first time and for a predetermined number of the next previous times to said first time to obtain a time filtered output for each of the sensors;

second means coupled to said first means to form from said sensors outputs measurement parameters having sensitivity values;

said sensitivity values being variables in a generalized equation that represents the configuration and location of a geometrical figure defined by the focus of coordinates of said outputs, said outputs having distortions due to permanent and induced magnetism of the vehicle and distortions due to sensor imbalance between the misorientation of the magnetic compass sensors;

said second means for defining calibration coefficients of said measurement parameters in said equation;

third means coupled to said second means to incorporate said measurement parameters and said calibration coefficients into a least squares matrix and to solve for said calibration coefficients;

fourth means coupled to said third means for computing calibration parameters from said calibration coefficients that are to be applied to said outputs;

fifth means coupled to said first means and said fourth means for applying said calibration parameters to said outputs from said f&

Art means to form an output from each of two sensors;

said two sensors being orthogonally related to one another;

sixth means coupled to said fifth means for obtaining the calibrated compass heading from said two sensors outputs; and

further comprising means for obtaining said outputs separately from said sensors at a selected rate sufficient to characterize the high frequency signature of transient magnetic disturbances and said characterization means further comprising means for analyzing the output separately from each of said sensors by comparing sensor reading magnitudes by application of a selected difference in magnitude as an acceptability threshold and using readings for heading determination which are within the acceptability threshold.

2. The apparatus of claim 1 including seventh means coupled between said fifth means and said sixth means for normalizing said two sensors outputs by dividing each of said two sensors outputs by dividing each of said two sensors outputs by the square root of the sum of the squares of each of said two sensors outputs.

3. The apparatus of claim 1 including eighth means coupled between each of said compass sensors and each of said first means and said second means for sensing the amplitude of the sensors outputs and increasing or creasing the amplitudes of the sensors outputs to fit within a predetermined sensor scale of amplitudes.

4. The apparatus of claim 3 wherein said eighth means comprises integrating means for integrating the sensors incremental outputs and increasing the number of sensors incremental outputs Integrated when the sensors outputs fall below the sensor scale and decreasing the number of sensors incremental outputs integrated when the sensors outputs are above the sensor scale.

5. The apparatus of claim 1 wherein said geometrical figure for the distorted vector outputs is In the shape of an ellipse and the geometric figure for the undistorted vector outputs is in the shape of a circle;

said generalized equation in said second means being;

x² +y² =b₁ +b₂ (x² -y²)+b₃ (-2xy)+b₄ (2x)+b₅ (2y) in said second means said measurement parameters being m₀, m₁, m₂, m₃, m₄, m₅ and

having the sensitivity values x² +y², 1, x² -y², -2xy,2x and 2y, respectively;

in said second means said calibration coefficients comprise;

b₁ =[a₁ -(1-a₂)x²₀ -(1+a₂)y²₀ -2a₂ x₀ y₀ ]

b₂ =a₂

b₃ =a₃

b₄ =[(1-a₂)x₀ +a₃ y₀ ]

b₅ =[(1+a₂)y₀ +a₃ x₀ ]

where

a₁ =2b² /(2-e²)

a₂ =e² (C₂ /(2-3²)

a₃ =e² S₂ /(2-e²)

a=semimajor axis of ellipse

b=semiminor axis of ellipse ##EQU1## C₂ =cosine (2θ

) and S₂ =sine (2θ

) θ

=rotation angle of ellipse

x,y=coordinates of center of ellipse prior to offset

x₀,y₀ =coordinates of offset center of ellipse said least squares matrix in said third means comprises;

##EQU2## B=[Σ

(M^T M)]^-1 [Σ

(M^T m₀)]where the matrix [Σ

(M^T M)]^-1 is the inverse of the matrix Σ

(M^T M)

said calibration parameters in said fourth means comprise;

##EQU3##

6. The apparatus of claim 5 wherein the number of sensors in the compass is three and the three sensors are arcuately spaced 120°

from one another and the outputs from the three sensors are U, Y, W respectively, said first means comprises push down stack means for obtaining time filtered outputs U", V", W" having the form;

space="preserve" listing-type="equation">F=P.sub.1 -P.sub.2 -2P.sub.3 +4P.sub.4 -2P.sub.5 -P.sub.6 +P.sub.7

where for the U reading F=U"(t), P₁ =U(t),

P₂ =V(t-1), P₂ =W(t-2), P₄ =U(t-3),

P₅ =V(t-4), P₆ =W(t-5), P₇ =U(t-6);

where for the V reading F=V"(t), P₁ =V(t), P₂ =W(t-1), P₃ =U(t-2), P₄ =V(t-3), P₅ =W(t-4), P₆ =U(t-5), P₇ =V(t-6);

where for the W reading F=W"(t), P₁ =W(t), P₂ =U(t-1), P₃ =V(t-2), P₄ =W(t-3), P₅ =U(t-4), P₆ =V(t-5), P₇ =W(t-6) and where t= present time and (t-n) is the time equal to the present time t minus the next previous n times units.

7. The apparatus of claim 6 wherein said filtered outputs from said three sensors are U", V", W" respectively and said two sensor outputs are X, Y respectively, and said fifth means converts to the said two sensor outputs by obtaining:

X=α

₁₁ (U"-B_u)+α

₁₂ (V"-B_v)+α

₁₃ (W"p31 B_w)

Y=═

₂₁ (U"-B_u)+α

₂₂ (V"-B_v)+α

₂₃ (W"-B_w).

8. The apparatus of claim 7 wherein said fifth means is for normalizing the X, Y outputs to obtain X'"'"', Y'"'"', respectively, as follows:

##EQU4##

9. The apparatus of claim 8 wherein said sixth means is for obtaining the heading are tangent from X'"'"', Y'"'"'.

10. The apparatus of claim 1 wherein the number of sensors in the compass is three and the three sensors are arcuately spaced 120°

from one another and the outputs from the three sensors are U, V, W respectively, said first means comprises push don stack means for obtaining time filtered outputs U", V", W" having the form;

space="preserve" listing-type="equation">F=P.sub.1 -P.sub.2 -2P.sub.3 +4P.sub.4 -2P.sub.5 -P.sub.6 +P.sub.7

where for the U reading F=U"(t), P₁ =U(t), P₂ =V(t-1), P₃ =W(t-2), P₄ =U(t-3), P₅ =V(t-4), P₆ =W(t-5), P₇ =V(t-6);

where for the W reading F=W"(t), P₁ =W(t), P₂ =U(t-1), P₃ =V(t-2), P₄ =W(t-3), P₅ =U(t-4), P₆ =V(t-5), P₇ =W(t-6) and where t=present time and (t-n) is the time equal to the present time t minus the next previous n time units.

11. The apparatus of claim 10 wherein said filtered outputs from said three sensors are U", V", W" respectively and said two sensor outputs are X, Y respectively, and said fifth means converts to the said two sensor outputs by obtaining:

X=a₁₁ (U"-B_u)+a₁₂ (V"-B_v)+a₁₃ (W"-B_w)

Y=a₂₁ (U"-B_u)+a₂₂ (V"-B_v)+a₂₃ (W"-B_w).

12. The apparatus of claim 11 wherein said fifth means is for normalizing the X, Y outputs to obtain X'"'"', Y'"'"', respectively, as follows:

##EQU5##

13. The apparatus of claim 12 wherein said sixth means is for obtaining the heading arc tangent from X'"'"', Y'"'"'.

14. A method for calibrating the distortions in the readings of a magnetic compass having a plurality of magnetic field sensors and for characterizing and rejecting readings caused by transient magnetic disturbances comprising:

a first step of obtaining the outputs from each of the sensors;

a second step of forming from said sensors outputs measurement parameters having sensitivity values;

said sensitivity values being variables in a generalized equation that represents the configuration and location of a geometrical figure defined by the locus of coordinates of said outputs, said outputs having distortions due to permanent and induced magnetism of the vehicle and distortions due to sensor imbalance between and misorientation of the magnetic compass sensors;

said second step defining calibration coefficients of said measurement parameters in said equation;

a third step of incorporating said measurement parameters and said calibration coefficients into a least squares matrix and solving for said calibration coefficients;

a fourth step of computing calibration parameters from said calibration coefficients that are to be applied to said outputs;

a fifth step of applying said calibration parameters to said outputs from said first step to form an output from each of two sensors;

said two sensors being orthogonally related to one another;

a sixth step of obtaining the calibrated compass heading from said two sensors outputs; and

further comprising the steps of obtaining said outputs separately from said sensors at a selected rate sufficient to characterize the high frequency signature of transient magnetic disturbances and said characterization further comprising analyzing the output separately from each of said sensors by comparing sensor reading magnitudes by application of a selected difference in magnitude as an acceptability threshold and using readings for heading determination which are within the acceptability threshold.

15. The method of claim 14 wherein said first step comprises obtaining the outputs from each of the sensors as a function of time by weighting and combining the outputs from each of the sensors at a first time and for a predetermined number of the next previous times to said first time to obtain a time filtered output for each of the sensors.

16. The method of claim 14 including a seventh step of normalizing said two sensors outputs by dividing each of said two sensors outputs by the square root of the sum of the squares of each of said two sensors outputs.

17. The method of claim 14 including an eighth step of sensing the amplitude of the sensor outputs and increasing or decreasing the amplitudes of the sensor outputs to fit within a predetermined sensor scale of amplitudes.

18. The method of claim 17 wherein said eighth step comprises integrating the sensor incremental outputs and increasing the number of sensor incremental outputs integrated when the sensor outputs fall below the sensor scale and decreasing the number of sensor incremental outputs integrated when the sensor outputs are above the sensor scale to fit the outputs within a predetermined sensor scale of amplitudes.

19. The method of claim 14 wherein said geometrical figure for the distorted vector outputs is in the shape of an ellipse and the geometric figure for the undistorted vector outputs is in the shape of a circle;

said generalized equation being;

space="preserve" listing-type="equation">x.sup.2 +y.sup.2 =b.sub.1 b.sub.2 (x.sup.2 -y.sup.2)+b.sub.3 (-2xy)+b.sub.4 (2x)+b.sub.5 (2y)

said measurement parameters being m₀, m₁, m₂, m₃, m₄, m₅ and having the sensitivity values x² +y², 1, x² -y², 2xy, 2x and 2y, respectively;

said calibration coefficients comprise;

##EQU6##20.

20. The method of claim 14 wherein said first step comprises compensating for the origin offset due to the permanent magnetic distortion effect of the vehicle on the compass vector outputs, id offset being the difference between the vector origin location of the distorted vector outputs for all headings of the compass and the vector origin location of the undistorted vector outputs for all headings of the compass;

said first step further comprising compensating for the difference in configuration of geometric figures defined by the distorted vector outputs and the undistorted vector outputs due to the induced magnetic distortion effects of the vehicle on the compass vector outputs for all headings of the compass.

21. Apparatus for calibrating the distortions in the readings of a magnetic compass having a plurality of magnetic field sensors and for characterizing and rejecting readings caused by transient magnetic disturbances comprising:

first means coupled to the compass sensors for obtaining the outputs from each of the sensors;

second means coupled to said first means to form from said sensors outputs measurement parameters having sensitivity values;

said sensitivity values being variable in a generalized equation that represents the configuration and location of a geometrical figure defined by the locus of coordinates of said outputs, said outputs having distortions due to permanent and induced magnetism of the vehicle and distortions due to sensor imbalance between and misorientation of the magnetic compass sensors;

said second means for defining calibration coefficients of said measurement parameters in said equation;

third means coupled to said second means to incorporate said measurement parameters and said calibration coefficients into a least squares matrix and to solve for said calibration coefficients;

fourth means coupled to said third means for computing calibration parameters from said calibration coefficients that are to be applied to said outputs;

fifth means coupled to said first means and said fourth means for applying said calibration parameters to said outputs from said first means to form an output from each of the two sensors;

said two sensors being orthogonally related to one another;

sixth means coupled to said fifth means for obtaining the calibrated compass heading from said two sensors outputs; and

further comprising means for obtaining said outputs separately from said sensors at a selected rate sufficient to characterize the high frequency signature of transient magnetic disturbances and said characterization means further comprising means for analyzing the output separately from each of said sensors by comparing sensor reading magnitudes by application of a selected difference in magnitude as an acceptability threshold and using readings which are within the acceptability threshold for heading determination.

22. An apparatus for automatically calibrating a mobile compass having a combination of a compass for providing heading outputs, said compass having a plurality of magnetic field sensors, electronic circuitry, and a programmed computer for calibration of the compass comprising;

an electronic compass having sensor elements which respond to magnetic fields and provide output signals related to the earth'"'"'s magnetic field and distortions sensed by the sensor element;

means to translate the sensor output signals into digital values;

a computer portion programmed to receive the digital values of the sensor output signals and to perform an ellipse fit and a computer portion programmed to receive the digital values of the sensor output signals and to perform a circularization of the ellipse defined by the output signals to define an origin centered circle and to determine heading;

a computer portion programmed to define a selected number of angular segments of the circle as bins and to count the sensor outputs as data points according to the bin in which they fall;

a compute portion programmed to offset parameters of the ellipse as required by the data points as they are acquired in order to determine the bin for the data point;

a computer portion programmed to perform a least squares calibration of said compass being executed upon the counting of a selected number of one or more data points to a selected maximum in every bin, said calibration using all data points up to the maximum number per bin.

23. The apparatus of claim 22 wherein said computer is programmed to process incoming data from the compass at a rate at least about 5 per second.

24. The apparatus of claim 23 wherein said rate is about 12 per second.

25. A method of automatically calibrating a mobile compass system mounted in a vehicle, the system having a compass for providing heading outputs, said compass having a plurality of magnetic field sensors electronic circuitry, and a programmed computer comprising;

providing output signals from said electronic compass sensors;

allowing the vehicle to be driven without any regulation of its path;

performing an ellipse fit and circularization procedure on the output data to define an origin centered circle for the data points;

selecting a number of angular segments of the circle to define bins;

identifying data points to a bin according to its position on the circle;

offsetting ellipse parameters as data points are acquired in order to determine the bin for the data point;

calibrating the compass by a least squares calibration when each bin has at least one data point identified said calibration using all data points acquired.

26. The method of claim 25 wherein said computer is programmed to process incoming date from the compass at a rate at least about 5 per second.

27. The method of claim 26 wherein said rate is about 12 per second.

36. The method of claim 25 in which a maximum number of data points for each bin is selected and the data points used for calibration are all data points acquired up to the maximum identified in each bin.

28. A system for detection and rejection for use in heading determination of transient magnetic anomalies in a mobile compass system having a programmed computer and having angularly separated magnetic field sensors comprising;

a computer portion programmed to receive readings separately from each of said sensors and to characterize from said readings the magnetic signature of the anomaly and to reject use for heading determination of readings that fall with said characterization;

said characterization flier comprising separately for each sensor selecting an upper limit of frequency of change of readings and a threshold in magnitude of change of readings to define readings to be retained as those falling under said upper limit and below said threshold for use in determining heading.

29. The system of claim 28 wherein said computer is programmed to process incoming data from the compass at a rate of at least about 5 per second.

30. The system of claim 29 wherein said rate is about 12 per second.

31. A method for detection and rejection of transient magnetic anomalies in a mobile electronic compass system having magnetic sensors to provide components of sensed magnetic field location comprising;

in a programmed computer, receiving readings from a compass and characterizing from said readings, the high frequency signature of the anomaly and rejecting use of sensor readings that fall within said characterization, said characterization comprising;

taking said sensor output signals at a selected sufficiently high frequency to enable distinguishing the rapid sensor changes caused by the anomaly; and

comparing the difference in magnitude of selected sequential readings against a selected magnitude difference threshold to define readings to be used for heading determination as those falling under the upper limit of frequency and below the threshold.

32. The method of claim 31 wherein said computer is programmed to process incoming data from the compass at a rate of at least about 5 per second.

33. The method of claim 32 wherein said rate is about 12 per second.

34. The method of claim 31 in which said frequency of taking sensor output signals is at least about 5 per second.

35. The method of claim 34 in which said frequency of taking sensor output signals is up to about 12 per second.