WO2008079456A1

WO2008079456A1 - System, method, and computer readable media for odometer calibration

Info

Publication number: WO2008079456A1
Application number: PCT/US2007/077344
Authority: WO
Inventors: Moreno Pieralli; Simone Bianchi; Giovanni Pacini
Original assignee: General Electric Company
Priority date: 2006-08-31
Filing date: 2007-08-31
Publication date: 2008-07-03
Also published as: ITMI20061661A1

Abstract

A system, computer readable media, and method for calibrating an odometer system of the type which measures distance traversed by a railway vehicle based on a number of wheel rotations. In an exemplary embodiment, a control unit is coupled to receive vehicle position information from a vehicle position device and one or more signals corresponding to a number of wheel rotations. The control unit is programmable to determine distance traveled by the vehicle based on position information acquired at different times. The distance information is used to provide a measure of distance traveled by the wheel during rotation.

Description

SYSTEM, METHOD, AND COMPUTER READABLE MEDIA FOR ODOMETER

CALIBRATION

FIELD OF THE INVENTION

This invention relates generally to railway management and, more particularly, to a system, method and computer readable media for calibration of measurement systems to assure accurate measurement of travel by railway vehicles.

BACKGROUND OF THE INVENTION

For numerous operational reasons it is necessary to monitor distances traveled by locomotives and railway cars. These include maintenance, assessment of performance and, generally, determination of transportation distances. Conventionally, odometers have been coupled to receive signals corresponding to rotation of railway wheels in order to measure distances based on number of wheel revolutions. This may be implemented with placement of a sensor adjacent a railway wheel, or other component which rotates therewith, to provide a signal each time the wheel completes a revolution. The sensor may be coupled directly to a processor or to a data transmission unit.

The data transmission unit may be used to transfer the signal information via an optical or rf link to a master control unit which processes the information and calculates distance traveled. For example, with the sensor providing a signal pulse for each rotation of the wheel, the distance traveled during a time period may be calculated based on the wheel diameter and the number of pulses counted during the period. However, the accuracy of such odometer measurement is subject to variation as vehicle parts undergo wear. For example, an initial wheel diameter of a railway vehicle may be on the order of 100 cm and then, through wear, become reduced by 10 or more centimeters during its useful life.

Since wheel wear is a gradual and continual process it can be difficult to determine when such wear begins to affect odometer accuracy. Moreover, if wheel wear is non- uniform, efforts to calibrate by periodically measuring the wheel diameter may not provide satisfactory odometer accuracy.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect a system for calibrating an odometer system includes a control unit coupled to receive vehicle position information from a GPS receiver and one or more signals corresponding to a number of wheel rotations. The control unit is programmable to determine distance traveled by the vehicle based on position information acquired at different times. The distance information provides the odometer system with a calibration measurement corresponding to distance traveled by the wheel during rotation, assuring that the odometer system measures distance traveled by the vehicle within desired tolerance limits. An associated method for calibrating an odometer system includes determining the number of rotations of the vehicle wheel during a measurable time period while moving the vehicle over a segment of track at a stable velocity and also acquiring position information from a GPS receiver for the vehicle location at the start of the time period as well as at the end of the time period. The position information is used to calculate distance traveled by the vehicle wheel during the time period. Calibration of the odometer system is adjusted in accord with the number of wheel rotations which occurred in the distance traveled. By way of example, when odometer measurement is based on the product of the number of wheel revolutions and the distance traveled by the wheel during one revolution, an updated value of the distance traveled per revolution may be provided to the odometer.

In another exemplary embodiment of the invention, a method for calibrating an odometer system of the type which measures distance traveled based on rotation of a wheel in a railway vehicle is disclosed. The method includes determining a number of rotations of the vehicle wheel occurring during a measurable time period while moving the vehicle over a segment of track at a stable speed. The method also includes acquiring vehicle position information from a vehicle position device at the start of the time period and at the end of the time period. Using the position information to calculate distance traveled by the vehicle is also disclosed. Further, the method discloses using the number of rotations of the vehicle wheel to adjust the odometer system by determining the distance traveled by the wheel during one rotation.

In yet another exemplary embodiment a computer readable media containing program instructions for calibrating an odometer system of the type which measures distance traveled based on rotation of a wheel in a railway vehicle with a computer as part of the railway vehicle is disclosed. The computer readable media includes a computer program code for determining the number of rotations of the vehicle wheel occurring during a measurable time period while moving the vehicle over a segment of track at a stable speed. A computer program code for acquiring vehicle position information at the start of the time period and at the end of the time period is also disclosed. A computer program code for using the position information to calculate distance traveled by the vehicle during the time period is further disclosed. Also disclosed is a computer program code for using the number of rotations of the vehicle wheel to adjust the odometer system by determining the distance traveled by the wheel during one rotation.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features will be apparent from the following description when read in conjunction with the drawings, in which:

Figure 1 illustrates portions of a railway processing system for calibrating an odometer; and

Figure 2 illustrates a calibration method for improved odometer accuracy.

DETAILED DESCRIPTION OF THE INVENTION

As used herein the term odometer refers to any type of measuring device which measures distance traveled by a wheel, or a wheeled vehicle, based on the product of the distance traveled by the wheel per revolution and the number of wheel revolutions which occur during traversal of the distance. Control unit is understood to mean any unit capable of providing control functions or processing functions in relation to measurement and storage of information including distance, velocity, rpm, direct or indirect counting of wheel revolutions or, generally, collection of data during measurable periods of time. The phrase "stable speed" as used herein means a vehicle speed which varies within acceptable limits for purposes of acquiring reliable data.

Those skilled in the art will recognize that the invention can be practiced with many variations relative to the examples provided herein. Numerous details relating to specific configurations, structures, components, and operations are not shown in order to avoid obscuring aspects of the invention.

The Global Positioning System (GPS) is widely used in conventional navigation, e.g., for aviation and shipping activities. In fact, it is common to determine the location of a train with a GPS system in order to advise passengers of the approximate time that the train will reach a destination. The accuracy of such estimates is dependent on the accuracy of the measured vehicle velocity. Over short distances, e.g., less than 25 miles, errors on the order of even a few percent typically do not affect estimated arrival times by more than a minute. Errors in estimated arrival times may be based on inaccuracies in position determination and inaccuracies in train speed. On-board systems for measuring both speed and distance are influenced by variations in wheel diameter due to wear. Figure 1 shows a railway processing system 10 configured to collect data from a number of subsystems in order to reduce such error.

The system 10 provides functions of monitoring, control and communication, many details of which are omitted from the figures. In this exemplary embodiment, the railway processing system includes a control unit 14 which, in this example, is positioned on a locomotive and configured to measure distances traveled by the locomotive, based on rotation of at least one wheel 12, e.g., a locomotive wheel. Generally, the system 10 may be configured to collect data from subsystems located on other railway vehicles including various cars (freight, passenger, etc.) which form a train with the locomotive. The control unit 14 may be microprocessor-based, or may comprise one or more digital signal processors under the control of a microprocessor which may be remotely located from the unit 14. In the illustrated examples the unit 14 is located in a locomotive and comprises a microprocessor and memory. The unit 14 may be located in any railway car or may be positioned in a terminal or non-mobile control center or station in order to perform processing or control in relation to multiple trains via rf links. Moreover, for some embodiments, the various functions attributed to the control unit 14 may be distributed, e.g., with some associated components located on one or more railway vehicles and other components possibly located in a non-mobile control center.

Still referring to Figure 1, the system 10 may share components with other systems including an on-board odometer system 18 which includes a counter 20 coupled to a sensor 24. The sensor 24 provides a signal pulse to the counter 20 for each revolution of the wheel 12. The counter 20 increments a value "C" based on rotation of the wheel through each revolution. In this example, each incrementation is an integer value corresponding to one revolution of the wheel 12, but the system 10 may be configured to increment the counter 20 based on lesser or greater wheel rotation or by an estimated distance traversed by wheel rotations. Operation of the sensor 24 may be based on any of several well-known mechanisms including optical, magnetic and electro-mechanical generation of signals. The odometer system 18 may be coupled to receive data from multiple sensors each coupled to a different wheel of the railway vehicle.

For the embodiment of Figure 1, the odometer system 18 indicates cumulative distances traveled by the locomotive, e.g., by periodically updating a distance value based on the product of a stored value "K" and the number of counts, "C". The stored value "K" is the estimated distance the wheel 12 travels in one complete revolution, and the value C corresponds to the number of wheel revolutions counted. The count, C, may be a resetable value or the display may provide dual readings corresponding, for example, to both a cumulative distance over the useful life of the locomotive and a resetable distance.

As noted, the odometer accuracy is dependent in part on variation in the distance the wheel 12 travels in one complete revolution, i.e., the value of K, as the wheel 12 wears. This distance K may be periodically revised based on timed changes in position of the train as measured with a vehicle position device, such as but not limited to a GPS receiver, 28 mounted within the railway vehicle and connected to an antenna 30 to receive available satellite data. Specifically, the control unit 14 may be programmed to periodically go into a calibration mode to determine a new value for K, e.g., for every ten thousand km of travel by the wheel 12, or upon command by an operator. Once in the calibration mode, determination of a new value for K is effected by measuring the distance traveled by the wheel 12 during a brief period of relatively constant speed, e.g., more than 70 km per hour stable to within one km per hour or one percent. The period during which data is collected can be relatively short, e.g., 3 seconds or less.

With the railway vehicle in motion and the control unit 14 in the calibration mode, the control unit acquires data at and between selected time intervals. For example, both position data and changes in the count, C, can be monitored and recorded every three seconds. Speed data may be acquired at a higher data rate to check for stability, e.g., to determine whether the speed varies by less than one percent over a three second interval. Once a three second interval is identified during which time it is determined that the train speed has met stability criteria, GPS position data acquired for the beginning and end of that period is processed to determine the distance the wheel traveled during that same period. The number of counts, C, occurring during the same time period is used to calculate a new value for K, the distance traveled per revolution of the wheel 12, and the new value may be used to replace the existing value of K.

It may be desirable to improve odometer accuracy to less than one percent error, i.e., having an error of less than 100 meters over a 10 km distance. In the past, GPS data has not been found useful to provide position accuracy such as needed to effect such tolerance. A feature of the example embodiment is that accuracy of the position data is recognized to be a function of the number of satellites, Z, from which position information is simultaneously acquired. In the example embodiment, GPS position and velocity data may be acquired when the data is simultaneously available from at least three satellites 34. To further improve accuracy, the position or velocity data can be acquired from multiple data sets which are taken sequentially. The value used to update K may be based on a simple average or may be determined with a weighting function. By way of example, ten values of K may be computed, each designated K₁, (i = 1,10), wherein each K₁ is calculated during a different three second time interval. The values K₁ can be sorted and re-numbered by magnitude, with the three largest values (now designated K₈, K₉, Ki₀) as well as the three smallest values (now designated Ki₁ K₂, K3) each discarded, such that the new value of K is computed as an arithmetic average of the remaining values:

K = (K₄ + K₅ + K₆ + K₇)/4

Figure 2 illustrates an exemplary calibration methodology incorporating this algorithm. Initially, the control unit 14 enters the calibration mode and checks to determine whether the number of GPS satellites 34 is greater than or equal to a threshold number, Z, required to assure desired accuracy. Once this threshold condition is met, the system sets i to zero and begins collecting data during consecutive three second intervals. For each three second interval, if the speed, V_GPS, is found to meet speed and stability criteria (e.g., greater than 70 kph and not varying by more than one percent), the collected data is used to compute a value K₁.

In the exemplary example of Figure 2, the speed V_GPS is based on GPS data, but speed data may be provided to the unit 14 from an on-board speedometer which directly monitors speed of the railway car with electro-mechanical instrumentation. It is to be understood that speed determination with an on-board speedometer may be based on a relatively inaccurate value of K because the speed is monitored to assure that a minimum speed criteria are met. On-board speed measurement is not used directly in the computation OfK₁.

Each time the speed criteria are met a value K₁ is stored in memory of the control unit and i is incremented. Once ten values of K₁ are determined, the values are re-ordered by magnitude and the values Of K₁ for i = 4, 5, 6 and 7 are arithmetically averaged to provide a new odometer value K, which is stored in a designated odometer register for access by the odometer system.

Based on the foregoing specification, the methods described above may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof, wherein the technical effect is to provide a system, method, and computer readable media for calibrating measurement systems to assure accurate measurement of travel by railway vehicles. Any such resulting program, having computer-readable code means, may be embodied or provided within one or more computer-readable media, thereby making a computer program product, i.e., and an article of manufacture, according to the invention. For example, as disclosed herein, the computer-readable media may include a computer program code for using position information to calculate distance traveled by the vehicle during a time period.

The computer-readable media may be, for example, a fixed (hard) drive, diskette, optical disk, magnetic tape, semiconductor memory, such as read-only memory (ROM), etc., or any transmitting/receiving medium, such as the Internet or other communication network or link. The article of manufacture containing the computer code may be made and/or used by executing the code directly from one medium, by copying the code from one medium to another medium, or by transmitting the code over a network.

One skilled in the art of computer science will be able to combine the software created as described with appropriate general purpose or special purpose computer hardware, such as a microprocessor, to create a computer system or computer subsystem embodying the method of the invention. An apparatus for making, using or selling the invention may be one or more processing systems including, but not limited to, a central processing unit (CPU), memory, storage devices, communication links and devices, servers, I/O devices, or any sub-components of one or more processing systems, including software, firmware, hardware or any combination or subset thereof, which embody the invention.

Although examples of how the invention may be implemented have been illustrated, this is not to be regarded as limiting and the scope of the invention is defined by the claims which follow.

Claims

WHAT IS CLAIMED IS:

1. A system for calibrating an odometer system of the type which measures distance traversed by a railway vehicle based on a number of wheel rotations, comprising:

a) a control unit coupled to receive vehicle position information and one or more signals corresponding to a number of wheel rotations, said control unit programmable to determine distance traveled by the vehicle based on said position information acquired at different times, said control unit using the distance information to provide a measure of distance traveled by the wheel during rotation.

2. The system of claim 1 wherein said measure of distance is used to assure that the odometer system is calibrated to measure distance traveled by the vehicle within desired tolerance limits.

3. The system of claim 1 wherein the control unit and the odometer system are positioned on a locomotive.

4. The system of claim 1 wherein the control unit receives position data based on information received from a GPS receiver.

5. The system of claim 4 wherein the control unit receives position data based on information from at least three GPS satellites.

6. The system of claim 1 further including a vehicle position device for receiving one or more signals relating to vehicle position.

7. The system of claim 1 wherein the vehicle position device is a GPS receiver.

8. The system of claim 1 wherein the control unit estimates distance traveled by the wheel during rotation based on computation of position data taken during multiple time intervals.

9. The system of claim 1 wherein the control unit only calculates said measure of distance with data taken during time intervals in which the speed of the railway vehicle varies less than one kilometer per hour.

10. The system of claim 1 wherein the signals corresponding to a number of wheel rotations are provided by the odometer system to the control unit.

11. A method for calibrating an odometer system of the type which measures distance traveled based on rotation of a wheel in a railway vehicle, comprising:

a) determining a number of rotations of the vehicle wheel occurring during a measurable time period while moving the vehicle over a segment of track at a stable speed;

b) acquiring vehicle position information from a vehicle position device at the start of the time period and at the end of the time period;

c) using the position information to calculate distance traveled by the vehicle; and

d) using the number of rotations of the vehicle wheel to adjust the odometer system by determining the distance traveled by the wheel during one rotation.

12. The method of claim 11 wherein the stable speed is a speed stable to within one kilometer per hour.

13. The method of claim 11 wherein the stable speed is stable to within one percent.

14. The method of claim 11 wherein the number of rotations of the wheel is counted by the odometer system and provided to a microprocessor-based control unit.

15. The method of claim 11 wherein the step of acquiring position information includes acquiring position information based on data from at least one of a vehicle position device and three GPS satellites.

16. The method of claim 11 wherein the step of determining the distance traveled by the wheel during one rotation is accomplished by acquiring position information during a plurality of time intervals, calculating the distance traveled by the wheel during one rotation based on data from each time interval and finding an average based on at least some of the calculated distances.

17. The method of claim 11 wherein the position data is collected from a plurality of GPS satellites and data is taken during multiple time intervals in order to provide an estimate of the distance traveled by the wheel during one rotation which is accurate to within one percent.

18. Computer readable media containing program instructions for calibrating an odometer system of the type which measures distance traveled based on rotation of a wheel in a railway vehicle with a computer as part of the railway vehicle, the computer readable media comprising:

a) a computer program code for determining the number of rotations of the vehicle wheel occurring during a measurable time period while moving the vehicle over a segment of track at a stable speed;

b) a computer program code for acquiring vehicle position information at the start of the time period and at the end of the time period;

c) a computer program code for using the position information to calculate distance traveled by the vehicle during the time period; and

d) a computer program code for using the number of rotations of the vehicle wheel to adjust the odometer system by determining the distance traveled by the wheel during one rotation.

19. The computer readable media of claim 18 wherein the stable speed is stable to within one kilometer per hour.

20. The computer readable media of claim 18 wherein the stable speed is stable to within one percent.

21. The computer readable media of claim 18 wherein the computer program code for acquiring position information includes a computer program code for acquiring position information based on data from at least one of a vehicle position device and three GPS satellites.

22. The computer readable media of claim 18 wherein the computer program code for determining the distance traveled by the wheel during one rotation is accomplished by a computer program code for acquiring position information during a plurality of time intervals, a computer program code for calculating the distance traveled by the wheel during one rotation based on data from each time interval and finding an average based on at least some of the calculated distances.

23. The computer readable media of claim 18 wherein the position data is collected from a plurality of GPS satellites and data is taken during multiple time intervals in order to provide an estimate of the distance traveled by the wheel during one rotation which is accurate to within one percent.