Vehicle speed measurement system

Abstract

The present disclosure relates to a vehicle speed measurement system that acquires signals measured by an optical fiber vibration measuring instrument connected to an optical cable having a plurality of crossing sections, which are laid across a road or railway at known intervals that are longer than a vehicle to be measured, calculates vibration waveforms at the plurality of crossing sections using the acquired signals, and measures the speed of the vehicle that has passed the plurality of crossing sections on the basis of time intervals at which the vibration waveforms were detected at the plurality of crossing sections.

Description

Vehicle speed measurement system

[0001] This disclosure relates to traffic monitoring technology using optical fiber sensing.

[0002] A method for estimating road traffic conditions using a distributed acoustic sensing (DAS) optical fiber vibration measuring instrument has been proposed (see, for example, Non-Patent Document 2). DAS is a technique for measuring the vibration distribution in the longitudinal direction of an optical fiber, which is a sensing probe (see, for example, Non-Patent Document 1).

[0003] Non-patent document 2 describes laying optical cables underground along the road and measuring the vibration distribution transmitted through the optical cables using DAS. Non-patent documents 2 and 3 describe using artificial intelligence to derive the vehicle's trajectory from the vibration distribution.

[0004] "Distributed Acoustic Nibration Sensing (DAS / DVS)", AP SENSING https: / / www.apsensing.com / technology / distributed-acoustic-sensing-das-dvs "NEC delivers high-precision traffic monitoring system utilizing optical fiber sensing technology to NEXCO Central Japan", NEC press release, May 24, 2022 http: / / jpn.nec.com / press / 202205 / 20220524_01.html#top "Road monitoring using optical fiber sensing", #deep learning-Qiita https: / / qiita. com / d_ike / items / 08492b3ba5d3c83adccf

[0005] However, even with artificial intelligence, it was not possible to measure vehicle speed for each lane when there were two or more lanes in one direction. Even with a single lane in each direction, complex calculations are required (see, for example, Non-Patent Document 3).

[0006] This disclosure aims to enable the measurement of vehicle speed for each lane without using complex calculations when estimating traffic conditions on roads or railway tracks using DAS.

[0007] The vehicle speed measurement system of the present disclosure includes a plurality of transverse sections laid across a road or a railway track in an optical cable laid on the road or the railway track. For example, at a point on the road or track where a vehicle is to be detected, two or more parallel optical cables laid at a known interval longer than the target vehicle are used to cross the road or track.

[0008] Specifically, the vehicle speed measurement system of the present disclosure includes an optical cable, an optical fiber vibration measuring device that measures the vibration of the optical cable, and a signal processing device of the present disclosure that acquires a signal from the optical fiber vibration measuring device.

[0009] The signal processing circuit of the present disclosure executes the vehicle speed measurement method of the present disclosure. In the vehicle speed measurement method of the present disclosure, the signal processing device acquires a signal measured by an optical fiber vibration measuring device connected to an optical cable having a plurality of transverse sections laid across a road or a railway track at a known interval longer than the vehicle to be measured, calculates the vibration waveforms of the plurality of transverse sections using the acquired signal, and measures the speed of the vehicle passing through the plurality of transverse sections based on the time interval between the times when the vibration waveforms are detected in the plurality of transverse sections.

[0010] In the present disclosure, since the optical cable has transverse sections, even when a plurality of lanes or railway tracks are included in the transverse sections, the passage of the vehicle can be detected for each lane and track. Therefore, the present disclosure can measure the speed of each vehicle without using complicated calculations in the estimation of traffic conditions using DAS.

[0011] In the present disclosure, the optical cables of the plurality of transverse sections may be laid in parallel. Further, each of the plurality of transverse sections may be provided with a mechanism for increasing the vibration generated when a vehicle passes.

[0012] Note that the above disclosures can be combined as much as possible. [[ID=十七]]

[0013] According to the present disclosure, in the estimation of traffic conditions on a road or a railway track using DAS, the vehicle speed can be measured for each lane without using complicated calculations.

[0014] An example of a system using DAS is shown. A configuration example of the vehicle speed measurement system according to this embodiment is shown. A configuration example of the vehicle speed measurement system according to this embodiment is shown. A waterfall diagram of the vibration intensity according to this embodiment is shown. An example of the vibration waveform of the cross-sectional section is shown. It is an explanatory diagram of the laying mode of the optical cable.

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These examples are merely illustrative, and the present disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In the present specification and drawings, components with the same reference numerals indicate the same components as each other.

[0016] FIG. 1 shows an example of a system using DAS. This system includes an optical fiber vibration measuring device (DAS) 11 and a signal processing device 12. As a preliminary preparation, the present disclosure lays an optical cable 13 on a road. The optical cable 13 houses an optical fiber (sensing probe) connected to the DAS 11. When estimating the traffic situation on the road, the optical cable 13 is connected to the DAS 11, and the DAS 11 is used to measure the vibration of the optical cable 13.

[0017] The DAS 11 can employ any device capable of measuring the vibration distribution in the longitudinal direction of the optical fiber. For example, an optical coherent time domain reflectometer (C-OTDR: Coherent-Optical Time Domain Reflectometer) can be exemplified.

[0018] The signal processing device 12 is a device that analyzes the vibration distribution in the longitudinal direction of the optical cable 13 using the signal obtained by the DAS 11 and performs arbitrary arithmetic processing. For example, the signal processing device 12 detects and extracts the vibration of the vehicle 100 from the vibration distribution in the longitudinal direction of the optical cable 13.

[0019] In the DAS 11, the temporal change in vibration intensity can be measured for each longitudinal section of the optical cable 13. Therefore, if the optical cable 13 is laid across the road, the vibration waveforms of vehicles can be calculated for each lane of the road. Thus, in the present disclosure, an optical cable 13 having a plurality of transverse sections laid across a road or a railway at a known interval longer than the vehicle 100 to be measured is connected to the DAS 11, and the vehicle speed measurement method of the present disclosure is executed.

[0020] In the vehicle speed measurement method of the present disclosure, the signal processing device 12 acquires the signal measured by the DAS 11, calculates the vibration waveforms of the plurality of transverse sections using the acquired signal, and measures the speed of the vehicle 100 that has passed through the plurality of transverse sections based on the time interval between the times when the vibration waveforms are detected in the plurality of transverse sections. This will be described in detail below.

[0021] (First Embodiment) FIG. 2 shows a configuration example of the vehicle speed measurement system of the present embodiment. This figure shows the state of the road as seen from above. The optical cable 13 connected to the DAS 11 is laid in the longitudinal direction so as to cross the road to be measured, and has two transverse sections S

[0022] , Ｎ１ , ,

[0021] , Ｎ , , Ｎ , Ｎ１ , , Ｎ２ , Ｎ１ , Ｎ２ , Ｎ１ , Ｎ２ ,

[0023] and S Ｎ２ are provided. The transverse sections S Ｎ１ and S Ｎ２ are laid so as to cross the lanes of the road where the vehicle 100 is to be detected, and a transverse underground optical cable that does not change its laid state over a long period in an environment where it receives the vibration of the vehicle 100 can be adopted.

[0022] The two transverse sections S Ｎ１ and S Ｎ２ are parallel, and the interval therebetween is D Ｎ . The interval D Ｎ can use a known value that is longer than the vehicle 100 to be measured. Also, it is desirable that there is no road where vehicle 100 merging is assumed between the points where the optical cable 13 crosses. Under this condition, the system of the present embodiment measures the vibration of the optical cable 13 using the DAS 11. [[ID=??]] [[ID=??]]

[0023] The signal processing device 12 acquires the signal measured by the DAS 11, and uses the acquired signal for the two transverse sections S Ｎ１ and SＮ２ The vibration waveform is calculated. Specifically, the signal processing device 12 calculates the vibration waveform of the cross section S. Ｎ１ Vibration waveform F generated by vehicle 100 passing through １ The vibration waveform F is calculated and １ time t １ The signal processing device 12 records the data onto a recording medium. The signal processing device 12 also processes the crossing section S Ｎ２ Vibration waveform F generated by vehicle 100 passing through ２ Calculate the time t ２ Record it onto a recording medium.

[0024] In this embodiment, the cross section S Ｎ１ and S Ｎ２ interval D Ｎ Since the crossing section S is longer than the vehicle 100, the signal processing device 12 Ｎ１ After the vibration waveform is detected, the cross section S Ｎ２ The vibration waveform is detected. The signal processing device 12 detects the cross section S Ｎ１ The vibration waveform was detected at time t. １ From, cross section S Ｎ２ The vibration waveform was detected at time t. ２ Measure the time interval Δt up to that point.

[0025] Interval D Ｎ Since the time interval Δt and the distance D between crossing points are known values, the signal processing device 12 determines the time interval Δt and the distance D between crossing points. Ｎ Therefore, calculate the speed of vehicle 100 using the following formula: (Mathematics 1) Vehicle speed = D Ｎ / Δt

[0026] The signal processing device 12 uses only the time variation of vibration intensity in its calculation process, eliminating the need for complex calculations used in machine learning, etc. Furthermore, the DAS 11 can identify which section of the optical cable 13 the vibration is from. Therefore, the cross section S Ｎ１ and S Ｎ２ When crossing two or more lanes, crossing section S Ｎ１ and S Ｎ２ It is possible to identify which of the crossing sections the vibration is occurring in. Therefore, the system of this embodiment makes it possible to measure vehicle speed separately for each lane with only a simple analysis.

[0027] As described above, the system of this disclosure has a function to measure the vibration distribution in the longitudinal direction of an optical fiber, and a function to measure the cross section S of the measured vibration distribution. Ｎ１ and S Ｎ２ It has a function to calculate vibration waveforms, and with only a simple analysis, it becomes possible to measure vehicle speed separately for each lane, even when there are two or more lanes on one side.

[0028] In this embodiment, there are two crossing sections S at two points. Ｎ１ and S Ｎ２ An example is shown that includes this configuration, but the crossing section may have three or more points. Furthermore, although this embodiment shows an example of traffic conditions for cars traveling on a road, it is also applicable to the conditions of trains traveling along railway tracks. The same applies to the following embodiments.

[0029] (Second Embodiment) Figure 3 shows an example of the configuration of the vehicle speed measurement system of this embodiment. In this embodiment, as shown in the vibration intensity waterfall diagram in Figure 4, there is a cross section L in the middle of the optical cable 13. ＡＢ , L ＣＤ An example of the arrangement is shown. The signal processing device 12 is located in the cross section L ＡＢ and L ＣＤ Calculate the vibration waveform.

[0030] Figure 5 shows the cross section L. ＡＢ , L ＣＤ An example of the vibration waveform is shown. In this embodiment, the transverse section L ＡＢ and L ＣＤ The vibration waveform is calculated for each section, and based on this, the cross section L ＡＢ Vibration waveform F ＡＢ and crossing section L ＣＤ Vibration waveform F ＣＤ These are obtained individually. The signal processing device 12 processes the vibration waveform F ＡＢ The time t obtained ＡＢ and vibration waveform F ＣＤ The time t obtained ＣＤ The time interval Δt is calculated, and the vehicle 100 is in section L ＢＣ interval D Ｎ The vehicle speed is calculated by dividing this value by the time interval Δt.

[0031] Here, at time tＡＢ The vibration waveform F ＡＢ This could be the time when the maximum amplitude of the vibration waveform F is obtained, or the time when the vibration waveform F is obtained. ＡＢ The vibration intensity in section L ＡＢ It may also be the time when the threshold is exceeded at time t. ＣＤ The same applies to this matter.

[0032] Furthermore, as shown in Figure 3, a single optical cable 13 is laid in a single continuous line to create two parallel cross-sectional sections L. ＡＢ , L ＣＤ Alternatively, you could configure it using two different optical cables 13 and two DAS 11 to cross the section L ＡＢ , L ＣＤ You may also configure it as follows:

[0033] (Third Embodiment) The laying of the optical cable 13 in this disclosure can be carried out in any manner that can detect road vibrations. For example, as shown in Figure 1, it may be underground under the road, or it may be realized using road surface wiring optical fiber cable design technology.

[0034] In particular, this disclosure describes laying the optical cable 13 across a road. Therefore, as shown in Figure 6(a), a groove 14 may be provided on the road surface, and the optical cable 13 may be housed in the groove 14. Alternatively, as shown in Figure 6(b), a laying layer 15 may be provided on the road surface, and the optical cable 13 may be housed in a cutout in the laying layer 15. The laying layer 15 can use any means to fix the optical cable 13 to the road, for example, resin can be used.

[0035] The grooves 14 and the laying layer 15 may be equipped with a mechanism that generates specific vibrations without hindering the movement of the vehicle 100. For example, vibrations may be reflected within the grooves 14, or irregularities may be provided on the surface of the laying layer 15.

[0036] Furthermore, the system may be equipped with a mechanism to amplify the vibrations generated when the vehicle 100 passes. For example, a speed bump (a structure that raises a part of the road) may be placed directly in front of the optical cable 13. This makes the vibration waveform when the vehicle 100 passes clearer, and also makes it possible to measure the vibrations of slow-moving vehicles and small vehicles such as motorcycles.

[0037] Furthermore, the groove 14 and the laying layer 15 do not need to be present along the entire length of the optical cable 13. When laid along the longitudinal direction of a road, they can be buried underground, and the groove 14 and laying layer 15 can be provided only in the sections that cross the road.

[0038] (Other Embodiments) The signal processing device 12 of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. The program of this disclosure is a program that causes a computer to realize each of the functions provided in the signal processing device 12 according to this disclosure, and is a program that causes a computer to execute each of the procedures provided in the method executed by the signal processing device 12 according to this disclosure.

[0039] 11: DAS 12: Signal processing unit 13: Optical cable 14: Groove 15: Laying layer 100: Vehicle

Claims

1. A signal processing device that acquires signals measured by an optical fiber vibration measuring instrument to which an optical cable having multiple crossing sections laid at known intervals longer than the vehicle being measured crosses a road or railway, is connected, calculates vibration waveforms of the multiple crossing sections using the acquired signals, and measures the speed of a vehicle passing through the multiple crossing sections based on the time intervals at which vibration waveforms were detected in the multiple crossing sections.

2. A vehicle speed measurement system comprising: an optical cable having multiple crossing sections laid at known intervals longer than the vehicle to be measured, so as to cross a road or railway; an optical fiber vibration measuring instrument for measuring the vibration of the optical cable; and a signal processing device according to claim 1 for acquiring a signal from the optical fiber vibration measuring instrument.

3. The vehicle speed measurement system according to claim 2, wherein the optical cables in the plurality of crossing sections are laid in parallel, and each of the plurality of crossing sections is provided with a mechanism for amplifying vibrations generated when vehicles pass over it.

4. A vehicle speed measurement method comprising: a signal processing device acquiring signals measured by an optical fiber vibration measuring instrument to which an optical cable having multiple cross sections laid at known intervals longer than the vehicle to be measured crosses a road or railway; the signal processing device using the acquired signals to calculate vibration waveforms of the multiple cross sections; and the signal processing device measuring the speed of a vehicle passing through the multiple cross sections based on the time intervals at which vibration waveforms were detected in the multiple cross sections.

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