Method and apparatus for automatic calibration of the wheel track of a movable vehicle
First Claim
1. A method for calibrating a wheel track of a movable vehicle in which a navigation system is installed, said system including a global positioning satellite (GPS) receiver and a dead reckoning (DR) system, said DR system including sensors coupled to wheels of the movable vehicle, said method comprising the steps of:
- estimating an initial value of the wheel track;
determining a heading change derived from said DR system based on said initial estimate for the wheel track of the movable vehicle;
determining a heading change derived from said GPS receiver;
using said heading changes derived from said GPS and DR systems to generate a refined value of said wheel track; and
updating said initial value of the wheel track with said refined value.
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Accused Products
Abstract
This invention reduces the navigation error associated with the use of wheel sensor based DR as an augmentation to GPS. In order to derive accurate heading information from the wheel speeds, the distance between the centers of the tires, or the wheel track, must be known to high precision. Unfortunately, the wheel track may not be precisely known whereby different classes of the same vehicle type can produce variations of up to 5%. The current invention removes the error growth associated with wheel track error by automatically estimating and calibrating the wheel track. The wheel track is measured by computing a heading rate directly from the GPS Doppler measurements, and comparing it with the heading rate derived from the wheel sensors whereby subsequent refinements to the estimated wheel track are computed by filtering each measured track.
13 Citations
22 Claims
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1. A method for calibrating a wheel track of a movable vehicle in which a navigation system is installed, said system including a global positioning satellite (GPS) receiver and a dead reckoning (DR) system, said DR system including sensors coupled to wheels of the movable vehicle, said method comprising the steps of:
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estimating an initial value of the wheel track; determining a heading change derived from said DR system based on said initial estimate for the wheel track of the movable vehicle; determining a heading change derived from said GPS receiver; using said heading changes derived from said GPS and DR systems to generate a refined value of said wheel track; and updating said initial value of the wheel track with said refined value. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for calibrating the wheel track of a movable vehicle in which a navigation system is installed, the system including a global positioning satellite (GPS) receiver and a dead reckoning (DR) system, the DR system including sensors coupled to wheels of the movable vehicle, said method comprising the steps of:
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estimating an initial value of the wheel track; determining a heading change using said DR system using said initial value for a wheel track of the movable vehicle; determining a heading change using said GPS system; estimating an error in said wheel track using said heading changes as determined from said GPS and DR systems; refining said error in said wheel track at a predetermined time interval; and updating said initial value of the wheel track with a refined value. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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15. An apparatus for estimating a wheel track of a movable vehicle, comprising:
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means for storing an initial value for the wheel track; sensors coupled to wheels of the movable vehicle for determining a first heading of the movable vehicle based upon said initial value for the wheel track of the movable vehicle; a global positioning satellite (GPS) receiver for determining a second heading of the movable vehicle based upon GPS data; and processing means for receiving said first and second headings and updating said initial value of said wheel track with a refined value. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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Specification