Compensation system for electronic compass
First Claim
1. A method for compensating for the effect of a deviating magnetic field in a vehicle compass, said compass comprising:
- first and second magnetoresistive sensors responsive to an external magnetic field for developing electronic signals representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle,said first and second sensors being oriented in a predetermined angular relation with each other, and being aligned in a predetermined angular relation with respective axes of said vehicle,each of said sensors including means for nullifying at least part of a deviating magnetic field which impinges on it, said method comprising the steps of;
determining whether the value of the sensor signal of each sensor is different from a nominal value which corresponds approximately to the value of the earth magnetic field,if it is, using said nullifying means for adjusting the magnetic field impinging on each sensor to adjust the sensor signal to a value approximately equal to the nominal value,determining the maximum and minimum peak values of each sensor signal,determining the average of said peak values of each sensor signal,and mathematically compensating the actual value of each sensor signal in accordance with the respective average value.
1 Assignment
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Accused Products
Abstract
An electronic compass is described for use in vehicles. The compass employs a magnetoresistive sensor for sensing the earth magnetic field and the sensor is operated in alternate set/reset bias modes. In a first embodiment, the compass is provided with deviation compensation by a closed loop system including measurement of the sensor output signals and an offset current strap for nullifying the vehicle deviation field. In a second embodiment, deviation compensation is provided by operation in an initial calibration mode and by operation in a normal calibration mode to adjust compensation, as needed, on a long term basis during normal operation of the compass. In the initial calibration mode, while the vehicle is being driven, the signal peak values are adjusted to a nominal earth field level by changing the offset current. Then, compensating signal reference values for each axis are determined as each peak for that axis is determined. The system automatically exits the initial calibration mode when certain criteria have been met. In the normal compensation mode, the signal reference value for each axis is adjusted at least once during the time interval between turn-on and turn-off of the vehicle ignition switch.
257 Citations
34 Claims
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1. A method for compensating for the effect of a deviating magnetic field in a vehicle compass, said compass comprising:
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first and second magnetoresistive sensors responsive to an external magnetic field for developing electronic signals representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said first and second sensors being oriented in a predetermined angular relation with each other, and being aligned in a predetermined angular relation with respective axes of said vehicle, each of said sensors including means for nullifying at least part of a deviating magnetic field which impinges on it, said method comprising the steps of; determining whether the value of the sensor signal of each sensor is different from a nominal value which corresponds approximately to the value of the earth magnetic field, if it is, using said nullifying means for adjusting the magnetic field impinging on each sensor to adjust the sensor signal to a value approximately equal to the nominal value, determining the maximum and minimum peak values of each sensor signal, determining the average of said peak values of each sensor signal, and mathematically compensating the actual value of each sensor signal in accordance with the respective average value.
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2. A method for compensating for the effect of a deviating magnetic field in a vehicle compass, said compass comprising:
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first and second magnetoresistive sensors responsive to an external magnetic field for developing electronic signals representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said first and second sensors being oriented in a predetermined angular relation with each other, and being aligned in a predetermined angular relation with respective axes of said vehicle, each of said sensors including means for nullifying at least part of a deviating magnetic field which impinges on it, a digital electronic circuit including means for measuring said signals when said signals are within a predetermined measurement range, said method comprising the steps of; determining whether the value of the sensor signal of each sensor is within said measurement range, if it is not, using said nullifying means for nullifying at least part of magnetic field impinging on said sensor to reduce the sensor signal to a value within said range. - View Dependent Claims (3, 4)
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5. A method for updating the deviation compensation of a vehicle compass comprising:
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first and second sensors responsive to an external magnetic field for developing electronic signals representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said first and second sensors being oriented in a predetermined angular relation with each other, and being aligned in a predetermined angular relation with respective axes of said vehicle, and a memory which stores a reference value for each sensor signal, said reference value for each sensor being equal to an offset value for providing deviation compensation for the respective sensor at a previous time, said method comprising the steps of; detecting the occurrence of a peak in the sensor signal of one of the sensors, measuring the value of the sensor signal of the other sensor which occurs at the same time as the occurrence of said peak, and if there is a difference between the measured value and said reference value, adjusting the reference value in accordance with the difference. - View Dependent Claims (6, 7)
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8. A method for compensating an electronic compass in a vehicle of the type comprising first and second sensors oriented in a predetermined angular relation with each other and with respective axes of the vehicle,
said method comprising the steps of: -
determining a compensating reference signal value for each sensor, detecting the occurrence of a peak in the sensor signal of one of the sensors, measuring the value of the sensor signal of the other sensor which occurs at the same time as the occurrence of said peak, and, if there is a difference between the measured value and the reference value, adjusting the reference value in accordance with the difference.
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9. A method for compensating an electronic compass in a vehicle, said compass being of the type comprising first and second sensors oriented in a predetermined angular relation with each other and in a predetermined angular relation with respective axes of the vehicle, the first and second sensors each having an adjustable offset magnetic field generator for generating an offset magnetic field and being responsive to said offset magnetic field and to an external magnetic field for developing first and second electronic signals, respectively, representative of the combination of said magnetic fields, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said method comprising the steps of:
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adjusting the magnetic field generator so that the value of the sensor signal of each sensor is approximately equal to a nominal value, measuring the maximum and minimum peak values of the sensor signal of each sensor, determining a compensating reference signal value for each sensor as the average of the maximum and minimum peak values, storing said reference value for each sensor, and combining said reference value for each sensor with the value of the sensor signal for providing a deviation compensated signal corresponding to each sensor. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A method for maintaining the deviation compensation of an electronic compass which has been compensated for deviation in a vehicle, said compass being of the type comprising first and second sensors oriented in a predetermined angular relation with each other and in a predetermined angular relation with the respective axes of the vehicle, said first and second sensors being responsive to an external magnetic field for developing first and second sensor signals, respectively, representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and the deviating field of the vehicle, said method comprising the steps of:
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storing first and second compensating reference signal values for the first and second sensors, respectively, for combining with the value of the first and second sensor signals, respectively, for deviation compensation of the respective sensors, driving said vehicle on a road trip, detecting the occurrence of a peak value in each one of the first and second sensor signals and measuring the value of the other one of the sensor signals at the time of said occurrence, and, if there is a difference between the measured value of either of the sensor signals and the respective compensating reference signal value, adjusting reference value in accordance with the difference. - View Dependent Claims (26, 27, 28)
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29. A method for compensating an electronic compass in a vehicle, said compass being of the type comprising first and second sensors oriented in a predetermined angular relation with each other and in a predetermined angular relation with respective axes of the vehicle, the first and second sensors each having an adjustable offset magnetic field generator and being responsive to said offset magnetic field and to an external magnetic field for developing first and second electronic signals, respectively, representative of the combination of said magnetic fields, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said method comprising the steps of:
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(1) driving the vehicle through a path with direction changes equivalent to about two circles for initial deviation compensation of the compass by performing the following method steps 2, 3, 4 and 5; (2) adjusting the magnetic field generator so that the value of the sensor signal of each sensor is approximately equal to a nominal value, (3) measuring the maximum and minimum peak values of the sensor signal of each sensor, (4) determining -a compensating reference signal value for each sensor as the average of the maximum and minimum peak values, (5) storing first and second compensating reference signal values for the first and second sensors, respectively, for combining with the value of the first and second sensor signals, respectively, for deviation compensation of the respective sensors, (6) operating the compass while the vehicle is being driven through a path having direction changes for updating the deviation compensation of the compass by performing the following method steps; (7) detecting the occurrence of a peak value in each one of the first and second sensor signals and measuring the value of the other one of the sensor signals at the time of said occurrence, (8) and, if there is a difference between the measured value of either of the sensor signals and the respective compensating reference signal value, adjusting reference value in accordance with the difference. - View Dependent Claims (30, 31)
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32. A system for compensating an electronic compass in a vehicle, said compass being of the type comprising first and second sensors oriented in a predetermined angular relation with each other and in a predetermined angular relation with respective axes of the vehicle, the first and second sensors each having an adjustable offset magnetic field generator for generating an offset magnetic field and being responsive to said offset magnetic field and to an external magnetic field for developing first and second electronic signals, respectively, representative of the combination of said magnetic fields, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said system comprising:
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means for adjusting the magnetic field generator so that the value of the sensor signal of each sensor is approximately equal to a nominal value, means for measuring the maximum and minimum peak values of the sensor signal of each sensor as the heading of the vehicle is changed, means for determining a compensating reference signal value for each sensor as the average of the maximum and minimum peak values, means for storing said reference signal value for each sensor, and means for combining said reference signal value for each sensor with the value of the sensor signal for providing a deviation compensated signal corresponding to each sensor.
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33. A system for maintaining the deviation compensation of an electronic compass which has been compensated for deviation in a vehicle, said compass being of the type comprising first and second sensors oriented in a predetermined angular relation with each other and in a predetermined angular relation with the respective axes of the vehicle, said first and second sensors being responsive to an external magnetic field for developing first and second sensor signals, respectively, representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and the deviating field of the vehicle, said system comprising:
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means for storing first and second compensating reference signal values for the first and second sensors, respectively, for combining with the value of the first and second sensor signals, respectively, for deviation compensation of the respective sensors, means for detecting, during operation of the vehicle, the occurrence of a peak value in each one of the first and second sensor signals and for measuring the value of the other one of the sensor signals at the time of said occurrence, and means for adjusting the reference value in accordance with a difference between the measured value of either of the sensor signals and the respective compensating reference signal value.
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34. A system for compensating an electronic compass in a vehicle, said compass being of the type comprising first and second sensors oriented in a predetermined angular relation with each other and in a predetermined angular relation with respective axes of the vehicle, the first and second sensors each having an adjustable offset magnetic field generator for generating an offset magnetic field and being responsive to said offset magnetic field and to an external magnetic field for developing first and second electronic signals, respectively, representative of the combination of said magnetic fields, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said system comprising:
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means for adjusting the magnetic field generator so that the value of the sensor signal of each sensor is approximately equal to a nominal value, means for measuring the maximum and minimum peak values of the sensor signal of each sensor as the heading of the vehicle is changed, means for determining a compensating reference signal value for each sensor as the average of the maximum and minimum peak values, means for storing first and second compensating reference signal values for the first and second sensors, respectively, for deviation compensation of the respective sensors, means for updating the deviation compensation of the compass during compass operation while the vehicle is being driven including means for detecting the occurrence of a peak value in each one of the first and second sensor signals and measuring the value of the other one of the sensor signals at the time of said occurrence, and means for adjusting the reference signal value in accordance with a difference between the measured value of either of the sensor signals and the respective compensating reference signal value.
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Specification