Method and apparatus for calibration of a distance sensor in a vehicle navigation system

• US 5,898,390 A
• Filed: 09/14/1995
• Issued: 04/27/1999
• Est. Priority Date: 09/14/1995
• Status: Expired due to Term

• Current Assignee: TomTom International BV (TomTom NV)
• Original Assignee: Zexel Corporation
• Inventors: Oshizawa, Hidekazu, Sakakibara, Toshikazu
• Primary Examiner(s): SWARTHOUT, BRENT
• Application Number:
  US08/528,075
• Time in Patent Office: 1,321 Days
• Field of Search: 340/988, 340/990, 340/995, 364/449.2, 364/449.4, 73/178 R, 235/95 R, 33/523.2, 324/171, 377/24.1, 701/207, 701/210
• US Class Current: 340/988
• CPC Class Codes: G01C 21/28 with correlation of data from several navigational instruments
• CPC Class Codes: G01C 22/02 by conversion into electric waveforms and subsequent integration, e.g. using tachometer generator G01C22/002, G01C22/004, G01C22/006 take precedence
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

Method and apparatus for modifying an odometer reading in a vehicle navigation system to compensate for odometer errors. A first distance measurement is obtained from the odometer, and a second distance measurement is obtained from at least one other sensor. The difference between the first and second distance measurements is determined and an adjustment amount is generated in response thereto. A modification factor is then adjusted by the adjustment amount, the modification factor being for modifying the odometer reading. The odometer reading is then modified with the modification factor. A method and apparatus for selecting a pulse rate setting in a vehicle navigation system to correspond to a pulse rate associated with the odometer are also described. A first distance measurement is obtained from the odometer and a second distance measurement is obtained from at least one other sensor. The difference between the first and second distance measurements is then determined. The pulse rate setting is changed to correspond to the odometer pulse rate if the difference is greater than a threshold level, and is left unchanged if the difference is less than the threshold level.

Claims

1. A method for modifying an odometer reading in a vehicle navigation system to compensate for odometer errors, the method comprising the steps of:

obtaining a first distance measurement from the odometer;

obtaining a second distance measurement from at least one other sensor;

determining a first difference between the first and second distance measurements;

generating an adjustment amount in response to the determining step; and

adjusting a modification factor by the adjustment amount, the modification factor being for modifying the odometer reading;

modifying the odometer reading with the modification factor; and

repeating the obtaining steps before generating the adjustment amount if the first difference is greater than a threshold level.

2. A method for modifying an odometer reading in a vehicle navigation system to compensate for odometer errors, the method comprising the steps of:

obtaining a first distance measurement from the odometer;

obtaining a second distance measurement from at least one other sensor;

determining a first difference between the first and second distance measurements;

generating an adjustment amount in response to the determining step; and

adjusting a modification factor by the adjustment amount, the modification factor being for modifying the odometer reading; and

modifying the odometer reading with the modification factor;

wherein a maximum value limit is placed on the adjustment amount and wherein the generating step comprises setting the maximum value limit to one of a plurality of levels, each of the plurality of levels corresponding to the number of repetitions of the adjusting step.

3. A method for modifying an odometer reading in a vehicle navigation system to compensate for odometer errors, the method comprising the steps of:

obtaining a first distance measurement from the odometer;

obtaining a second distance measurement from at least one other sensor;

determining a first difference between the first and second distance measurements;

generating an adjustment amount in response to the determining step; and

adjusting a modification factor by the adjustment amount, the modification factor being for modifying the odometer reading; and

modifying the odometer reading with the modification factor;

wherein the obtaining, determining, generating, adjusting, and modifying steps are repeated a plurality of times, and wherein the obtaining steps employ a first number of distance data points to obtain the first and second distance measurements, the first number varying according to the number of repetitions of the adjusting step.

4. A method for modifying an odometer reading in a vehicle navigation system to compensate for odometer errors, wherein the odometer has a pulse rate associated therewith and the vehicle navigation system has a pulse rate setting associated therewith, the method comprising the steps of:

obtaining a first distance measurement from the odometer;

obtaining a second distance measurement from at least one other sensor;

determining a first difference between the first and second distance measurements;

generating an adjustment amount in response to the determining step; and

adjusting a modification factor by the adjustment amount, the modification factor being for modifying the odometer reading;

modifying the odometer reading with the modification factor;

obtaining a third distance measurement from the odometer;

obtaining a fourth distance measurement from the at least one other sensor;

determining a second difference between the third and fourth distance measurements;

changing the pulse rate setting to correspond to the pulse rate if the second difference is greater than or equal to a threshold level; and

proceeding to the adjusting step if the second difference is less than the threshold level.

5. The method of claim 4 wherein the at least one other sensor comprises a global positioning satellite (GPS) sensor which receives a GPS signal.

6. The method of claim 5 further comprising the steps of:

determining whether reception of the GPS signal is stable for the third and fourth obtaining steps;

proceeding to the step of determining a second difference if the reception of the GPS signal is determined to be stable during the third and fourth obtaining steps; and

repeating the third and fourth obtaining steps if the reception of the GPS signal is determined to be unstable during the third and fourth obtaining steps.

7. The method of claim 5 further comprising the steps of:

determining a vehicle speed using the GPS signal;

proceeding to the step of determining a second difference if the vehicle speed is determined to be greater than or equal to a threshold level; and

repeating the third and fourth obtaining steps if the vehicle speed is determined to be less than the threshold level.

8. A method for modifying an odometer reading in a vehicle navigation system to compensate for odometer errors, wherein the odometer has a pulse rate associated therewith and the vehicle navigation system has a pulse rate setting associated therewith, the method comprising the steps of:

obtaining a first distance measurement from the odometer;

obtaining a second distance measurement from at least one other sensor;

determining a first difference between the first and second distance measurements;

changing the pulse rate setting to correspond to the pulse rate if the first difference is greater than or equal to a threshold level;

obtaining a third distance measurement from the odometer;

obtaining a fourth distance measurement from the at least one other sensor;

determining a second difference between the third and fourth distance measurements;

generating an adjustment amount in response to the step of determining a second difference;

adjusting a modification factor by the adjustment amount, the modification factor being for modifying the odometer reading;

modifying the odometer reading with the modification factor thereby generating a modified odometer reading;

repeating th e third and fourth obtaining steps, the second determining step, the generating step, the adjusting step, and the modifying step a plurality of times.

9. The method of claim 8 wherein the at least one other sensor comprises a global positioning satellite (GPS) sensor which receives a GPS signal.

10. The method of claim 9 further comprising the steps of:

determining whether reception of the GPS signal is stable for the first and second obtaining steps;

proceeding to the step of determining a first difference if the reception of the GPS signal is determined to be stable during the first and second obtaining steps; and

repeating the first and second obtaining steps if the reception of the GPS signal is determined to be unstable during the first and second obtaining steps.

11. The method of claim 9 further comprising the steps of:

determining a vehicle speed using the GPS signal;

proceeding to the step of determining a first difference if the vehicle speed is determined to be greater than or equal to a threshold level; and

repeating the first and second obtaining steps if the vehicle speed is determined to be less than the threshold level.

12. The method of claim 9 further comprising the steps of:

determining whether reception of the GPS signal is stable for the third and fourth obtaining steps;

proceeding to the adjusting step if the reception of the GPS signal is determined to be stable during the third and fourth obtaining steps; and

repeating the third and fourth obtaining steps if the reception of the GPS signal is determined to be unstable during the third and fourth obtaining steps.

13. The method of claim 9 further comprising the steps of:

determining a vehicle speed using the GPS signal;

proceeding to the adjusting step if the vehicle speed is determined to be greater than or equal to a threshold level; and

repeating the third and fourth obtaining steps if the vehicle speed is determined to be less than the threshold level.

14. The method of claim 8 wherein a maximum value limit is placed on the adjustment amount and wherein the generating step comprises setting the maximum value limit to one of a plurality of levels, each of the plurality of levels corresponding to a number of repetitions of the adjusting step.

15. The method of claim 8 wherein the third and fourth obtaining steps employ a first number of distance data points to obtain the third and fourth distance measurements, the first number varying according to the number of repetitions of the adjusting step.

16. The method of claim 8 further comprising the steps of:

determining a first vehicle position based on the third distance measurement;

determining a second vehicle position based on the fourth distance measurement, the second vehicle position having a relative relationship with the first vehicle position;

determining whether the relative relationship is consistent with the modification factor;

proceeding to the adjusting step if the relative relationship is consistent with the modification factor; and

repeating the third and fourth obtaining steps if the relative relationship is inconsistent with the modification factor.

17. A method for selecting a pulse rate setting in a vehicle navigation system to correspond to a pulse rate associated with an odometer, comprising the steps of:

obtaining a first distance measurement from the odometer;

obtaining a second distance measurement from at least one other sensor;

determining a difference between the first and second distance measurements;

changing the pulse rate setting to correspond to the pulse rate if the difference is greater than or equal to a threshold level; and

leaving the pulse rate setting unchanged if the difference is less than the threshold level.

18. The method of claim 17 wherein the at least one other sensor comprises a global positioning satellite (GPS) sensor which receives a GPS signal.

19. The method of claim 18 further comprising the steps of:

determining whether reception of the GPS signal is stable for the obtaining steps;

proceeding to the step of determining a difference if the reception of the GPS signal is determined to be stable during the obtaining steps; and

repeating the obtaining steps if the reception of the GPS signal is determined to be unstable during the obtaining steps.

20. The method of claim 18 further comprising the steps of:

determining a vehicle speed using the GPS signal;

proceeding to the step of determining a difference if the vehicle speed is determined to be greater than or equal to a threshold level; and

repeating the obtaining steps if the vehicle speed is determined to be less than the threshold level.

21. A vehicle navigation system operable to select a pulse rate setting to correspond to a pulse rate associated with an odometer comprising:

an odometer;

at least one other sensor;

means for determining a difference between a first distance measurement from the odometer and a second distance measurement from the at least one other sensor; and

means for changing the pulse rate setting to correspond to the pulse rate if the difference is greater than or equal to a threshold level, and for leaving the pulse rate setting unchanged if the difference is less than the threshold level.

22. A method for selecting a pulse rate setting to correspond to a pulse rate associated with an odometer in a vehicle navigation system, the method comprising:

determining a difference between a first distance measurement from the odometer and a second distance measurement from at least one other sensor; and

changing the pulse rate setting to correspond to the pulse rate if the difference is greater than or equal to a threshold level, and for leaving the pulse rate setting unchanged if the difference is less than the threshold level.