Measuring and testing – Instrument proving or calibrating – Speed – velocity – or acceleration
Patent
1999-03-16
2000-02-29
Raevis, Robert
Measuring and testing
Instrument proving or calibrating
Speed, velocity, or acceleration
G01P 2100
Patent
active
060294965
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for automatic calibration of a displacement sensor.
BACKGROUND INFORMATION
In a conventional vehicle navigation system, the calibration of the length measurement of a wheel sensor is based upon driving along a path of known distance. This calibration method requires, however, that the length of the calibration path be exactly known and that the path be driven along exactly (from beginning to end), in order to minimize length measurement errors. This procedure is necessary after initial installation of the navigation system in the vehicle, or when a tire change is made (such as, for example, after a changeover from summer to winter tires, or from old to new tires). In the situations described above, it is therefore necessary to have the displacement sensor length measurement calibrated at the repair shop.
SUMMARY OF THE INVENTION
The present invention provides a method for automatic calibration of a displacement sensor. The method is advantageous in that automatic calibration of the displacement sensor, for example in the event of a tire change, eliminates the need for laborious manual calibration. Costs are thereby reduced.
The method is further advantageous in that the displacement sensor is optimally calibrated regardless of vehicle load, tire pressure, or the like. Dead reckoning location thereby advantageously becomes more reliable.
The present invention also provides for the determination of vehicle speed by receiving satellite signals such as, for example, those transmitted from the Global Positioning System (GPS) system. At a given speed, the vehicle travels a defined distance within a predefined time period. The speed can, in this context, advantageously be measured using the Doppler effect. The distance traveled can then be calculated from the speed.
Even if the GPS data contain a certain error, the present invention contemplates the elimination of systematic error through mathematical techniques. It is, for example particularly favorable to determine the mean from a plurality of measurements, excluding those values which lie outside a predefined dispersion range. It appears advantageous in this context to take the standard deviation .sigma. as a basis for the dispersion range.
Using the mean and the standard deviation .sigma., the length measurement of an inductive wheel sensor or of a signal from the speedometer sensor can be calibrated within a predefined accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a block diagram of an exemplary embodiment.
DETAILED DESCRIPTION
FIG. 1 illustrates a block diagram of an exemplary embodiment according to the present invention, which will be used to explain its function in more detail. This block diagram may be part of a location system 10, supported on the basis of a digital map, in which the current vehicle position is determined as a function of distance traveled and direction of motion, and displayed on the digital map. Location system 10 is equipped, for example, with a radio receiver 1. Radio receiver 1 is preferably configured as a satellite receiver, and receives the signals of satellites of the Global Positioning System (GPS). Of course other satellite systems, for example, Glonass, may also be used.
In principle, the accuracy for the length measurement, i.e. for the distance traveled, should be very high. An error of, for example, less than 0.5% is desirable, so that, in destination guidance systems in particular, the necessary driving instructions can be output to the driver at the correct time. There arises in this context, however, the problem that the accuracy of the GPS satellite signals is not immediately sufficient for calibration of the displacement sensor, for example an inductive wheel sensor, since the GPS operator e.g., the Department of Defense has artificially degraded the signals. Without this artificial degradation it would be possible, for example using the Doppler effect, to determine the vehicle speed to an accuracy in the
REFERENCES:
patent: 5569848 (1996-10-01), Sharp
patent: 5917434 (1999-06-01), Murphy
Odometer Calibration, Research Disclosure, No. 364, p. 448, XP000468978.
Raevis Robert
Robert & Bosch GmbH
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