Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2001-11-06
2003-12-02
Black, Thomas G. (Department: 3663)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S200000, C701S210000, C701S215000, C340S988000, C073S17800T, C342S358000
Reexamination Certificate
active
06658353
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Application
The invention relates to a vehicle navigation apparatus which estimates the current position of a vehicle by utilizing GPS (Global Positioning Satellite) position measurement data, for correction of relative position and travel direction information obtained by dead reckoning navigation calculations based on signals produced from sensors which are mounted on the vehicle.
2. Description of Prior Art
Types of vehicle navigation apparatus are now widely utilized, whereby the current position and travel path of the vehicle are indicated on a display device, superimposed upon a displayed road map of the region in which the vehicle is currently travelling. The apparatus may also be capable of determining and displaying the optimum route between that current position and a destination which is specified by the vehicle driver. With such an apparatus it is of course essential to determine the current position as accurately as possible under various different driving conditions. Typically with such an apparatus, an output signal produced from a gyroscope, indicative of changes in the vehicle course direction (i.e., detected as amounts of turning of the vehicle about a predetermined axis of the gyroscope) is used, with each such change representing a change in the travel direction of the vehicle in relation to a previously determined absolute travel direction (where, for brevity of description, the term “travel direction” is used herein to refer to an estimated instantaneous direction of travel of a vehicle, derived together with an estimated current position of the vehicle). The direction change information from the gyroscope is used in conjunction with distance information expressing a distance that has been traveled by the vehicle relative to some preceding (absolute) estimated position of the vehicle, i.e., distance information obtained based on an output signal from a vehicle speed sensor, to perform dead reckoning calculations to obtain the estimated current position and travel direction of the vehicle. Such methods are described for example in Japanese patent HEI 8-54248, etc.
With such a method, on-board sensors of the vehicle itself are used to detect the vehicle position and travel direction, so that there is the disadvantage that it is not possible to obtain absolute position values.
Furthermore, when a gyroscope is utilized to measure changes in vehicle travel direction, the measurement is based on detecting values of angular velocity of rotation about the aforementioned predetermined axis of the gyroscope. When that axis does not correspond to the axis about which the vehicle actually rotates when performing a turn, then the conversion gain of the gyroscope (which is a proportionality constant, predetermined beforehand as a conversion factor for conversion to angular velocity) will differ from the correct conversion factor. Thus a conversion gain error (referred to in the following simply as the gain error) will arise. Moreover when a gyroscope is utilized, the value of output voltage of the signal produced from the gyroscope when the detected angular velocity is 0 (deg/s) is used as a reference voltage value, with that value being referred to in the following as the offset. However this offset may vary, due to various factors, so that when actual angular velocity is 0 (deg/s), the difference between the output voltage from the gyroscope and the offset may not be zero. As a result, a drift error will arise the in angular velocity detection results. Due to the above reasons, errors may arise in determining an amount of change in the vehicle travel direction, and the accuracy of detecting the current position of the vehicle will thereby be reduced. The effects of such drift and offset errors will be cumulative.
Because of the sources of inaccuracy described above, methods of vehicle position detection are utilized whereby position measurement data conveyed by radio waves transmitted from a source such as the GPS system are used to periodically obtain absolute position and travel direction information, for use in correcting the positions and directions that are derived by dead reckoning based on the on-board sensor outputs as described above. Specifically, while the vehicle is being driven in a condition in which such radio waves conveying the GPS position measurement data can be received, successive absolute positions and corresponding travel directions of the vehicle are derived based on these data at periodic intervals, with each set of information thus obtained being used to correct the positions and travel directions which are derived by dead reckoning using the vehicle on-board sensors.
However with the GPS system (as available for public use), the absolute position and direction estimates which are obtained thereby contain substantial amounts of randomly varying error, which may have a magnitude of up to approximately 100 meters in the case of position estimates. The successive relative position and travel direction estimates which are obtained from the dead reckoning calculations on the other hand will contain relatively small amounts of such randomly varying error, under a normal condition of operation of the vehicle, but may contain significant amounts of drift and offset error, for the reasons mentioned above.
For that reason, position and travel direction information derived based on the GPS data are generally subjected to a form of filter processing for reducing the effects of the random errors in these data, with the result being applied to correct the estimated positions and travel directions derived by dead reckoning. The most widely utilized form of such processing is the Kalman filter.
Successive sets of corrected vehicle position and travel direction estimates which are thereby derived are combined to obtain an estimate of the path which has been traveled by the vehicle up to the current position. Periodically, that estimated travel path is applied in map matching processing, i.e., the path is compared with data expressing a road map of a region in which the vehicle is currently travelling, to make use of the fact that the vehicle location is in general constrained to streets or freeways, etc., and thereby further increase the accuracy of a finally estimated current position of the vehicle. In that way it becomes possible to accurately obtain and display the route which is being traversed by the vehicle and its current position.
Under normal driving conditions, such a type of vehicle navigation apparatus can provide accurate results. However substantial amounts of error may arise in the estimated vehicle travel direction that is derived by such an apparatus, under some special circumstances. A first case of such special circumstances is when the vehicle is driven into a location such as a multistory car park, then performs a number of successive turns during a short time interval, e.g., while driving up and around a series of ramps within the car park. This can result in substantial error for the following reasons:
(a) The gain error of the gyroscope will cumulatively increase as the successive turns are executed, even if the detection axis of the gyroscope is correctly oriented with the turning axis of the vehicle and the gyroscope is mounted correctly in relation to the direction of the action of gravity under normal driving conditions. Specifically, when driven up the ramps within a multistory car park, and thereby performing successive turns, the attitude of the vehicle will be altered due to vehicle roll to the left or right side as the successive turns are executed, and due to the lateral axis of the vehicle becoming tilted (i.e., occurrence of pitch) by the slope of the ramps. Such changes in the vehicle attitude may cause changes in the orientation of the detection axis of the gyroscope in relation to the direction of action of gravity. As a result, the conversion factor of the gyroscope will change, so that the conversion gain will contain a gain error. Furthermore, errors due to variations in offs
Shimizu Yasuhiro
Tsurumi Kiyoshi
Black Thomas G.
Denso Corporation
Donnelly Arthur D.
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