Position determination method and system

Abstract

A method of determining the geographical position of a rail vehicle travelling on a defined route that has a number of known stopping locations separated by known distances. The method comprises steps of: recording a linear speed signal of the vehicle; processing the linear speed signal to identify a plurality of preceding stationary periods when linear speed equals zero, including a last stationary period, and to calculate the distance traveled between the plurality of preceding stationary periods; comparing the calculated distances with the known distances between stopping locations, to match the last identified stationary period to a corresponding one of the known stopping locations and identify the direction of travel of the rail vehicle; and determining the geographical position of the rail vehicle by processing a portion of the speed signal obtained since the last identified stationary period, to calculate the distance traveled from the corresponding stopping location.

Claims

1. A method of determining the geographical position of a rail vehicle on a rail route having a number of known stopping locations that are separated by known distances, the method comprising steps of: recording a linear speed signal of the vehicle; processing the linear speed signal to: identify a plurality of preceding stationary periods when vehicle speed equals zero, including a last stationary period; and calculate the distance traveled between the plurality of preceding stationary periods; comparing the calculated distances with the known distances between stopping locations, to find a matching sequence that correlates the last identified stationary period to a corresponding one of the known stopping locations and identifies the direction of travel of the rail vehicle; and determining the geographical position of the rail vehicle by processing a portion of the speed signal recorded since the last identified stationary period to calculate the distance traveled from the corresponding stopping location, completing at least one of the steps with a processor.

2. The method of claim 1, wherein a pattern recognition algorithm is used in the step of comparing.

3. The method of claim 2, wherein the linear speed signal is obtained by measuring a rotational speed of a vehicle wheel and using a known diameter of the wheel to obtain the linear speed of the rail vehicle.

4. The method of claim 1, wherein the linear speed signal is obtained by measuring a rotational speed of a vehicle wheel and using a known diameter of the wheel to obtain the linear speed of the rail vehicle.

5. A position determination system for a rail vehicle, the system comprising: a database of defined routes within a rail network, each defined route having a number of scheduled stopping locations of known geographic position relative to a reference point; and a processor configured to receive a linear speed signal of the vehicle and to perform steps of recording a linear speed signal of the vehicle; processing the linear speed signal to: identify a plurality of preceding stationary periods when vehicle speed equals zero, including a last stationary period; and calculate the distance traveled between the plurality of preceding stationary periods; comparing the calculated distances with the known distances between stopping locations, to find a matching sequence that correlates the last identified stationary period to a corresponding one of the known stopping locations and identifies the direction of travel of the rail vehicle; and determining the geographical position of the rail vehicle by processing a portion of the speed signal recorded since the last identified stationary period to calculate the distance traveled from the corresponding stopping location.

6. A track condition monitoring system comprising: a position determination system, providing a database of defined routes within a rail network, each defined route having a number of scheduled stopping locations of known geographic position relative to a reference point; and a processor configured to receive a linear speed signal of the vehicle and to perform steps of recording a linear speed signal of the vehicle; processing the linear speed signal to: identify a plurality of preceding stationary periods when vehicle speed equals zero, including a last stationary period; and calculate the distance traveled between the plurality of preceding stationary periods; comparing the calculated distances with the known distances between stopping locations, to find a matching sequence that correlates the last identified stationary period to a corresponding one of the known stopping locations and identifies the direction of travel of the rail vehicle; and determining the geographical position of the rail vehicle by processing a portion of the speed signal recorded since the last identified stationary period to calculate the distance traveled from the corresponding stopping location, one or more sensors mounted to a rail vehicle for detecting rail surface defects and a processor configured to analyze a signal from the one or more sensors and identify the presence of a surface defect, wherein the position determination system is configured to determine the position of the rail vehicle at the time when the presence of a surface defect is identified.

7. The track condition monitoring system comprising the position determination system of claim 6, wherein a pattern recognition algorithm is used in the step of comparing.

8. The track condition monitoring system comprising the position determination system of claim 7, the track condition monitoring system comprising one or more sensors mounted to a rail vehicle for detecting rail surface defects and a processor configured to analyze a signal from the one or more sensors and identify the presence of a surface defect, wherein the position determination system is configured to determine the position of the rail vehicle at the time when the presence of a surface defect is identified.

9. The track condition monitoring system comprising the position determination system of claim 7, wherein the linear speed signal is obtained by measuring a rotational speed of a vehicle wheel and using a known diameter of the wheel to obtain the linear speed of the rail vehicle.

10. The track condition monitoring system comprising the position determination system of claim 9, the track condition monitoring system comprising one or more sensors mounted to a rail vehicle for detecting rail surface defects and a processor configured to analyze a signal from the one or more sensors and identify the presence of a surface defect, wherein the position determination system is configured to determine the position of the rail vehicle at the time when the presence of a surface defect is identified.

11. The track condition monitoring system comprising the position determination system of claim 6, wherein the linear speed signal is obtained by measuring a rotational speed of a vehicle wheel and using a known diameter of the wheel to obtain the linear speed of the rail vehicle.

12. The track condition monitoring system comprising the position determination system of claim 11, the track condition monitoring system comprising one or more sensors mounted to a rail vehicle for detecting rail surface defects and a processor configured to analyze a signal from the one or more sensors and identify the presence of a surface defect, wherein the position determination system is configured to determine the position of the rail vehicle at the time when the presence of a surface defect is identified.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 presents a schematic representation of a metro line constituting a route traveled by a rail vehicle; and

(2) FIG. 2 presents a plot of a linear speed signal that could be measured for a rail vehicle travelling on the route depicted in FIG. 1.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(3) FIG. 1 is a schematic representation of a route 10 of an underground railway line having ten stations S1, S2, . . . S10. A rail vehicle 20 travels back and forth along the route between the stations S1 and S10. The vehicle is equipped with a position determination system, to enable its location on the route to be determined at any given time or continuously monitored. The system implements an inventive method of position determination, based on using the signal from an on-board speed sensor to calculate the distance traveled during a number of previous trips and matching the calculated distances to a stored map of the route.

(4) A vehicle stopping point at station S1 is defined as the start of the route and is located at mile marker 0. The mile marker location of a vehicle stopping point at each subsequent station along the route is known, meaning that the corresponding distances d1, d2, . . . d9 between neighboring stations is also known. Assuming certain numerical values for the mile marker locations, the route of FIG. 1 can be represented in tabular form as follows:

(5) TABLE-US-00001 TABLE 1 Example of a route comprising 10 stations and 18 stopping points Mile Marker Distance from Stop No. Station (in metres) previous station (m) 1 S1 0 1050 (d.sub.1) 2 S2 1050 1050 (d.sub.1) 3 S3 2175 1125 (d.sub.2) 4 S4 3450 1275 (d.sub.3) 5 S5 4150 700 (d.sub.4) 6 S6 5200 1050 (d.sub.5) 7 S7 6100 900 (d.sub.6) 8 S8 6900 800 (d.sub.7) 9 S9 7650 750 (d.sub.8) 10 S10 8800 1150 (d.sub.9) 11 S9 7650 1150 (d.sub.9) 12 S8 6900 750 (d.sub.8) 13 S7 6100 800 (d.sub.7) 14 S6 5200 900 (d.sub.6) 15 S5 4150 1050 (d.sub.5) 16 S4 3450 700 (d.sub.4) 17 S3 2175 1275 (d.sub.3) 18 S2 1050 1125 (d.sub.2) 1 S1 0 1050 (d.sub.1)

(6) The position determination system may be linked to a track condition monitoring system for detecting defects in a surface of the rails. In the depicted example, the rail vehicle 20 is provided with track monitoring equipment such as disclosed in U.S. Pat. No. 668,239. The equipment includes vertical acceleration sensors mounted at each side of a bogie of the rail vehicle, above a wheel set, and displacement transducersone on each side of the bogiearranged to monitor the distance between the bogie and the wheel. The sensor data is processed to calculate the magnitude of undulations in a top surface of the track.

(7) Let us assume that an unacceptable value is calculated at a point in time when the vehicle 20 is travelling from station S8 to S7 as shown in FIG. 1. To enable a maintenance crew to be sent to the location of the track defect, the position determination system is configured to determine the position of the vehicle at the time when a track defect has been detected. In an embodiment, the position determination system implements the following method:

(8) A linear speed signal of the vehicle is measured and recorded. This may be done using a tachometer, such as a magnetic pulse encoder attached to a wheel shaft or to a wheel bearing that supports the wheel shaft. A known value of the wheel diameter is then used to convert the angular speed in rotations per unit time to distance per unit time. Other methods of measuring linear speed may also be employed.

(9) An example of a speed signal that could be measured is shown in FIG. 2. The method comprises a step of processing the speed signal, firstly to identify a last stationary period SPL when the vehicle speed was equal to zero and a number of preceding stationary periods SPL-1, SPL-2, SPL-3, SPL-4, SPL-5. The speed signal between consecutive stationary periods corresponds to a number of previous trips T1, T2, T3, T4, T5.

(10) The step of processing further comprises integrating the speed signal with respect to time, to obtain the distance traveled during each of the previous trips T1-T5. Let us assume that the following distances are calculated: 749 m, 1152 m, 1151 m, 753 m, 801 m.

(11) In a next step, the calculated distances (+/ a certain allowable error of e.g. 6 m) are compared against the known distances between stations on the stored route, to identify which station corresponds to the last stationary period SPL and determine the direction of travel of the rail vehicle. Any suitable pattern recognition algorithm may be employed.

(12) In the given example, a match is found between the calculated trip history and the distances highlighted in Table 1. The distance traveled to reach the last stopping location was approximately equal to 750 m. This trip distance on its own is not sufficient to determine which was the last station, given that this distance is traveled to reach stations S8 and S9, depending on the rail vehicle's direction of travel. Furthermore, in other examples of rail routes, the individual distances between stations may not be unique. At least the distance traveled in the preceding trip (approx. 1150 m) is needed in the present example in order to identify that station S8 was the last station and that the vehicle is travelling back to the start of the route. As will be understood, the number of trips included in the trip history is at least sufficient to enable a unique sequence to be identified within the route in question.

(13) Preferably, a greater number of trips than the minimum number is included in the trip history, to improve accuracy and account for erroneous measurement results. For example, it the vehicle makes an unscheduled stop between stations within the calculated trip history, it is likely that the calculated distance traveled to reach that stopping location will not correspond to one of the values d1, d2, . . . d9 in the stored route. Or, if by coincidence it does correspond to a stored value, then the preceding or subsequent calculated distance will not.

(14) The pattern recognition algorithm used in the step of comparing may be adapted to ignore a non-matching calculation result or sequence of results, and seek a match based on a smaller number of calculated distances. Additionally, the pattern recognition algorithm may be adapted to add non-matching calculation results and compare the sum with the stored distances, to find a match which identifies the last station and the direction travel.

(15) In a final step, the location of the rail vehicle 20 is determined by calculating the distance traveled since the last station (S8 in the present example) using a portion of the speed signal Vp measured since the last identified stationary period SPL. Let us assume that integration of this signal portion Vp results in a distance of 350 m

(16) We know that the last station S8 is located at mile marker 6900 m and that the vehicle is travelling back towards the start of the route. The train positioning system thus determines that at the time of implementing the inventive method, i.e. at the time when a surface defect was detected, the rail vehicle's location is 6550 m from the zero mile marker. A maintenance crew can thus be sent to the right location in order to carry out necessary track repairs.