Data processing: vehicles – navigation – and relative location – Navigation – Determination of along-track or cross-track deviations
Reexamination Certificate
1999-10-21
2002-03-19
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Determination of along-track or cross-track deviations
C701S213000
Reexamination Certificate
active
06360165
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of Invention
The present invention relates generally to vehicle navigation systems. More specifically, the invention relates to methods and apparatus which provide on-the-fly calibration of readings from a vehicle's odometer sensor to ensure accurate determination of the vehicle's position by the navigation system.
Current vehicular navigation systems are hybrids which utilize several independent position determining means to locate a vehicle. The position determining means include: global positioning system satellites (GPS), dead reckoning systems, and map databases. Typically, one among these systems will serve the primary navigation system function while the remaining determining means are utilized to recalibrate cumulative errors in the primary system. Each determining means has its advantages and limitations.
GPS is an electromagnetic wave positioning system utilized to determine a vehicle's position. GPS includes Navstar GPS and its successors, i.e., differential GPS (DGPS), WAAS, or any other electromagnetic wave positioning system. Navstar is a GPS system which uses space-based satellite radio navigation developed by the U.S. Department of Defense. Navstar GPS receivers provide users with continuous three-dimensional position, velocity and time data. Navstar GPS consists of three major segments: space, control, and end-user segments. The space segment consists of a constellation of 24 operational satellites placed in six orbital planes above the Earth's surface. The satellites are in circular orbits and in such an orientation as to normally provide a GPS user with a minimum of five satellites in view from any point on earth at any one time. The satellite broadcasts an RF signal, which is modulated by a precise ranging signal and a coarse acquisition code ranging signal to provide navigation data. This navigation data, which is computed and controlled by the GPS control segment for all GPS satellites, includes the satellite's time, clock correction and ephemeris parameters, almanac and health status. The user segment is a collection of GPS receivers and their support equipment, such as antennas and processors, which allow users to receive the code and process information necessary to obtain position, velocity and timing measurements. There are two primary disadvantages to GPS positioning as it pertains to vehicular navigation. First, errors are imposed on the portion of the GPS signals accessible to civilians. The government imposes position errors in the range of 100 meters. In urban environments, this can result in inadequate navigation capabilities due to the close proximity of streets, some of which are spaced apart by less than 100 meters. The second disadvantage of GPS is that when the user is in urban environments with many scattering objects, such as buildings, it may not be possible to receive information from enough satellites to make an adequate position determination. Even where enough satellites are present, the presence of multipath errors due to the multiple reflections of the satellite signals from buildings, etc., may prevent adequate positioning on the basis of GPS alone. For this reason, GPS is typically utilized in a hybrid navigation system with other position determining means, such as dead reckoning and map databases.
Prior systems use a road network stored in a map database to calculate current vehicle positions. These systems send distance and heading information derived from either GPS or dead reckoning to perform map matching. Map matching calculates the current position based on the road network stored in the database and the input position and heading data. These systems also use map matching to calibrate sensors. The map matching, however, has inaccuracies due to map errors as well as inherent inaccuracies resulting from the fact that map matching must look back in time and match data to a location. As such, map matching can only calibrate the sensors or serve as a position determining means when an absolute position is identified on the map. However, on a long, straight stretch of highway, sensor calibration or position determination using map matching may not occur for a significant period of time.
Current land-based dead reckoning systems use vehicle speed sensors, rate gyros, reverse gear hookups, and wheel sensors to “dead reckon” the vehicle position from a previously known position. It is evident that the accuracy of the data received from these various sensors is essential to the reliable determination of the vehicle's position.
The accuracy of data received from a vehicle's odometer is influenced by a number of factors, including wheel size and pulse rate. An odometer typically detects wheel revolutions as representative of traveled distance, the tire size is directly related to the accuracy of the reported travel distance. For current navigation Systems, once the vehicle's tire size is known, it can be manually programmed into the navigation system to properly correlate wheel revolutions to traveled distance. However, it is well known that the size of a vehicle's tires change over time as they wear down from contact with the road. Moreover, factors such as the air pressure of the tires and the weight loaded on the vehicle at any given time produce variation in travel distances reported by the odometer. The tire size may be periodically reprogrammed into the system to account for such variations, but this is obviously impractical in that a difficult manual reprogramming would frequently be required, possibly every time the navigation system is used.
Another potential source of error in measured distance reported by an odometer is a mismatch between the odometer's pulse rate and the pulse rate setting of the navigation system. Odometers generate a pulse train in which a specific number of pulses (e.g., 2000) represent a unit distance (e.g., a mile). For example, Nissan vehicles employ a pulse rate of 2000 pulses/mile while Ford vehicles employ a pulse rate of 8000 pulses/mile. Therefore, each navigation system must be configured to correspond to the type of vehicle in which it is installed, otherwise very large-scale errors may result. If, for example, the pulse rate setting in a navigation system installed in a Ford corresponded to the pulse rate of a Nissan, an error factor of four would be introduced. The pulse rate setting is typically done before a navigation system is installed and is difficult to change where, for example, the odometer in the vehicle is changed, or the navigation system is installed in a different vehicle. Thus, while detection of the error may be elementary, correction of the error remains problematic.
U.S. Pat. No. 5,898,390 entitled “
Method and Apparatus for Calibration of a Distance Sensor in a Vehicle Navigation System
” discloses a method and apparatus for modifying an odometer reading to compensate for odometer errors resulting from pulse rate and tire size. The method and apparatus provides for correction of a first distance estimate derived from the odometer reading with a second distance estimate, typically produced by an external navigation system, i.e., GPS. Additionally, the pulse rate setting may be adjusted so as to reduce deviations between the first and second distance estimates. If pulse rate settings and tire size were the only significant sources of odometer error, the teachings of the '390 patent would allow the production of a reliable navigation system. However, there are other far more significant sources of odometer error which the '390 patent fails to account for, as will be discussed shortly. This failing is particularly critical in urban environments where scattering objects, such as buildings, reduce the possibility of frequent GPS initiated recalibration of the odometer based distance estimates. Absent these recalibrations, the other far more significant sources of odometer error will result in unacceptable cumulative errors in the odometer distance estimate during intervals in which G
Beyer Weaver & Thomas,LLP
Cuchlinski Jr. William A.
Pipala Edward
Visteon Technologies, LLC
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