Railway vehicle speed detection device and railway vehicle speed detection method

Abstract

To miniaturize an antenna necessary for detecting a speed of a railway vehicle using millimeter waves and avoid speed detection accuracy deterioration due to vehicle vibration and speed detection accuracy deterioration due to multiple reflections occurring at the bottom of the vehicle.SOLUTION: A railway vehicle speed detection device comprises: a transmission unit that transmits a chirp signal whose frequency changes over time; a reception unit that receives the chirp signal reflected from an object as a reception signal; and a digital processing unit that calculates a distance to the object and a Doppler speed of the object by Fourier transformation of the reception signal received by the reception unit. The transmission unit and the reception unit are installed at the bottom of a railway vehicle and located directly above a rail. The digital processing unit determines the fastest Doppler speed with the highest intensity of the reception signal among the reception signals from the object located at the equal distance within the calculated distance to the object and the Doppler speed of the object as the Doppler speed with the rail as the object, and calculates the vehicle speed of the railway vehicle from the Doppler speed of the rail.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a speed detection device and a speed detection method for a railway vehicle using millimeter waves. [Background technology]

[0002] In the railway business, safe operation and accurate timetable operation are important. Here, monitoring vehicle speed is essential for safe operation, and it is particularly important to monitor vehicle speed when stopping at platforms or around curves. Furthermore, in urban areas, timetables are becoming increasingly detailed, making vehicle speed monitoring important for accurate timetable operation. However, since GPS information cannot be obtained inside tunnels or subways, accurate vehicle speed information is required to detect the vehicle's position.

[0003] A common conventional technique for detecting the speed of railway vehicles is to use a tachograph attached to the wheels to measure the number of wheel revolutions and calculate the speed from the number of wheel revolutions. However, this tachograph-based method has the problem that the speed cannot be accurately detected due to wheel spin.

[0004] In recent years, development of a speed detection method using millimeter waves has been progressing in order to avoid the influence of wheel spin and to detect speed accurately. A known method of detecting speed using millimeter waves is to irradiate a millimeter sine wave onto the rail from a speed detection device installed on a vehicle and detect the speed from the Doppler shift of the sine wave reflected from the rail. In this method, the amount of Doppler shift changes depending on the angle at which the millimeter wave is irradiated onto the rail from the speed detection device, so to accurately detect speed, it is necessary to irradiate the millimeter wave at a known, designed irradiation angle within a narrow angular range.

[0005] Patent Document 1 proposes an antenna that generates a narrow beam to irradiate a narrow angular range. To achieve this narrow beam, a patch antenna is formed on a substrate and a lens antenna is placed on top of it.

[0006] Patent Document 2 discloses a technology to avoid the phenomenon whereby vehicle vibrations cause the irradiation angle to differ from the design value. Two types of millimeter wave irradiators are provided to form two different irradiation angles, which detect vibrations and cancel out the error in the irradiation angle caused by vibrations.

[0007] In Patent Document 3, when a speed detection device is provided at the bottom of a vehicle, in order to avoid the phenomenon where accurate speed cannot be detected due to the influence of multiple reflections that occur between the rail or ground and the bottom of the vehicle, the influence of multiple reflections is mitigated by providing a reflection control member at the bottom (floor) of the vehicle. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-226297 [Patent Document 2] International Publication No. 2018 / 163638 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-15474 Summary of the Invention [Problem to be solved by the invention]

[0009] The prior art described in the above patent documents has the following problems. The lens antenna described in Patent Document 1 needs to be large in size in order to achieve a narrow beam angle. The speed measurement device described in Patent Document 2 requires that two speed detection devices be installed on the vehicle. In the reflection control member described in Patent Document 3, the position at which the reflection control member is provided needs to be optimized according to the shape of the bottom of the vehicle.

[0010] Therefore, the present invention aims to provide a technology that reduces the size of the narrow beam antenna required for railway vehicle speed detection devices using millimeter waves, and avoids deterioration in speed detection accuracy caused by vehicle vibration and multiple reflections that occur at the bottom of the vehicle. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, one representative railway vehicle speed detection device of the present invention comprises a transmitter that transmits a chirp signal whose frequency changes over time, a receiver that receives the chirp signal reflected from a target as a received signal, and a digital processor that performs a Fourier transform on the received signal received by the receiver to calculate the distance to the target and the Doppler velocity of the target, the transmitter and receiver being installed at the bottom of the railway vehicle and located directly above the rail, and the digital processor further determines, as the Doppler velocity of the rail as the target, the Doppler velocity at which the received signal strength peaks and the Doppler velocity of the target, among the received signals from targets located at equal distances within the calculated distance to the target, and the Doppler velocity of the target, For each fixed distance traveled by the railway vehicle, the railway vehicle speed is estimated from the irradiation angle of the chirp signal transmitted to the rail and the Doppler velocity with the rail as the target. The estimated vehicle speed is weighted and averaged using the dispersion of the Doppler velocity with the rail as the target, which occurs at each fixed distance, and the strength of the received signal. This calculates the vehicle speed of a railway vehicle. [Effects of the Invention]

[0012] According to the present invention, a wide-angle antenna is used to detect vehicle speed at multiple distances, which allows for a smaller antenna and avoids the effects of vehicle vibration in the pitch direction. Furthermore, for long distances where multiple reflections are received, no digital processing is performed, thereby avoiding deterioration of speed detection accuracy due to multiple reflections. Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiment of the invention. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing the configuration of a railway vehicle speed detection device according to an embodiment of the present invention. [Figure 2]FIG. 2 is a diagram showing an image of a vehicle speed detection method and an image of an installation of a railway vehicle speed detection device. [Figure 3] FIG. 3 is a diagram showing the characteristics of the Doppler velocity distribution at equal distances from the railway vehicle speed detection device. [Figure 4] FIG. 4 is a diagram in which the characteristics of the Doppler velocity distribution shown in FIG. 3 are superimposed for each fixed distance traveled by the vehicle. [Figure 5] Figure 5 shows the relationship between rail distance and Doppler velocity as seen from a vehicle speed detector installed at a height of 20 cm. DETAILED DESCRIPTION OF THE INVENTION

[0014] Examples will be described below as representative embodiments of the present invention with reference to the drawings. Note that the present invention is not limited to these examples. In addition, in the description of the drawings, the same parts are designated by the same reference numerals. [Example]

[0015] FIG. 1 is a block diagram showing the configuration of a railway vehicle speed detection device (201) according to an embodiment of the present invention. The railway vehicle speed detection device 201 is composed of two blocks: an analog processing section (101) and a digital processing section (102).

[0016] The analog processing unit (101) comprises a synthesizer (103), a transmitting antenna (104), a receiving antenna (105), a mixer (106), and an A / D converter (107).

[0017] The synthesizer (103) generates a millimeter-wave chirp signal by linearly shifting the frequency over time, and the millimeter-wave chirp signal is transmitted from a transmitting antenna (104).

[0018] The transmitted signal is reflected by a target object, and a portion of the reflected wave returns to the receiving antenna (105) and is received.

[0019] The reflected wave signal received by the receiving antenna (105) is down-converted by a mixer (106) which is a frequency converter. At this time, the signal from the synthesizer (103) is input as a local signal to the mixer (106). As a result, a frequency corresponding to the time difference between the transmitted signal and the received signal, i.e., the distance to the target, is output from the mixer (106).

[0020] The output signal of the mixer (106) is converted into a digital signal by an A / D converter (107) and transmitted to the digital processing unit (102).

[0021] The digital processing unit (102) is composed of a time / frequency FFT processing unit (108), a rail extraction unit (109), a vehicle speed calculation unit (110), and a weighting processing unit (111).

[0022] The first-stage time / frequency FFT processor (108) of the digital processor (102) performs a time FFT and a frequency FFT on the received signal. That is, the frequency FFT is performed to calculate the distance R (202), and the time FFT is performed to calculate the Doppler velocity Vdpr (203).

[0023] FIG. 2 is a diagram showing an image of a vehicle speed detection method and an image of the installation of a railway vehicle speed detection device (201). The railway vehicle speed detection device (201) is assumed to be installed on the bottom (206) of the railway vehicle and directly above the rail (207), as shown in the lower diagram of Figure 2. However, although at least the transmitting antenna (104) and the receiving antenna (105) must be installed on the bottom (206) of the railway vehicle and located directly above the rail (207), it is not necessary that all of the components constituting the railway vehicle speed detection device (201) be installed on the bottom (206) of the railway vehicle and located directly above the rail (207).

[0024] In this case, the Doppler velocity Vdpr (203) calculated by the time FFT is expressed by the following equation (A), where Vcar (204) is the vehicle speed and θ (205) is the angle (illumination angle) between the irradiation vector from the railway vehicle speed detection device (201) to the target and the velocity vector of the vehicle speed Vcar (204). Vdpr=Vcar·cosθ (A)

[0025] As is clear from equation (A), the value of the Doppler velocity Vdpr (203) calculated by the time FFT changes depending on the irradiation angle θ (205). In addition, the smaller the value of θ, the larger the value of the calculated Doppler velocity Vdpr (203) becomes, and the closer it becomes to the vehicle speed Vcar (204).

[0026] The railway vehicle speed detection device (201) is installed directly above the rail (207), and since the rail (207) is generally convex in the height direction from the ground, θ (205) at the rail (207) is the smallest among targets with the same distance R (202) calculated by frequency FFT.

[0027] For example, the upper diagram in Figure 2 shows the angle θ1 (205(1)) with respect to the rail (207) and the angle θ2 (205(2)) with respect to the ground or sleepers at an equal distance R (202) from the railway vehicle speed detection device (201). The magnitude relationship between the two is that θ1 (205(1)) is smaller than θ2 (205(2)) (θ2>θ1).

[0028] In addition, since there are no targets in a typical railway environment in the range where the angle θ is shallower than the rail (207) at the same distance R, the Doppler velocity Vdpr (203) calculated at the rail (207) is the largest within the range of the same distance R (202).

[0029] 3 is a diagram showing the characteristics of the Doppler velocity distribution at equal distances R from the railway vehicle speed detection device (201). This is the result of processing by the time / frequency FFT processing unit, with the horizontal axis representing the Doppler velocity and the vertical axis representing the spectral intensity.

[0030] The rail extraction unit (109) treats the distribution range of Doppler velocities in which no target is considered to exist as noise, among the characteristics shown in FIG. 3, and determines that a target exists when the spectrum intensity has a higher SNR than the threshold value (301), for example, an SNR of 10 dB.

[0031] Since rails (207) are made of metal, they show a high spectral intensity value where the reflection of millimeter waves is strongly received. Therefore, the rail extraction unit (109) determines that the target that shows the peak value (302 in FIG. 3) with the fastest Doppler velocity among the peak values ​​(the portion indicated by the downward arrow in FIG. 3) in the region of spectral intensity higher than the threshold value is a rail.

[0032] In the case of a rail (207), the distance R (202) and the height H (208) from the rail surface of the rail (207) to the rail vehicle speed detection device (201) attached to the bottom (206) of the rail vehicle are known, so the angle θ (205) can be calculated and is known.

[0033] Therefore, the vehicle speed calculation unit (110) calculates the vehicle speed Vcar (204) by dividing the rail Doppler speed Vdpr (203) by cos θ using the above equation (A).

[0034] FIG. 4 is a diagram in which the characteristics of the Doppler velocity distribution shown in FIG. 3 are superimposed for each fixed distance traveled by the vehicle. Since the vehicle speed Vcar (204) can be calculated for the distance R obtained by frequency FFT, the detection accuracy can be improved by averaging the vehicle speed Vcar (204) calculated for each fixed distance traveled by the vehicle, as shown in FIG. 4.

[0035] Here, the resolution of the distance R is determined by the bandwidth of the chirp signal generated by the synthesizer (103), and the wider the bandwidth, the higher the resolution. For example, the resolution of the distance R is 20 cm when the bandwidth of the chirp signal is 0.75 GHz, and 6 cm when it is 2.5 GHz. In other words, the wider the bandwidth, the higher the distance resolution, and therefore the detection accuracy of the vehicle speed Vcar (204) can be improved.

[0036] 5 shows the characteristics of the Doppler velocity of the rail (207) versus distance, assuming a distance resolution of 5 cm (corresponding to a chirp signal bandwidth of 3 GHz) and a height H (208) of 20 cm from the rail surface of the rail (207) to the railway vehicle speed detection device (201). The vertical axis represents the Doppler velocity Vdpr (203) normalized by the vehicle speed Vcar (204), and the horizontal axis represents the distance (cm).

[0037] The solid line (501) is the theoretical value of the Doppler velocity Vdpr (203). Under ideal conditions, the Doppler velocity Vdpr (203) on this solid line would be detected. The white circle points (503) are the Doppler velocity Vdpr (203) detected at 5 cm intervals, which is the distance resolution. Here, due to the nature of the distance resolution, each white circle point will include a Doppler velocity component within the range of the arrow line (502) shown in Figure 5.

[0038] From the above, it can be seen that there is a large spread (dispersion) in the detected Doppler velocity near the minimum distance of 20 cm (the range indicated by the arrow line (502)), but as the distance increases, the spread (dispersion) of the detected Doppler velocity also decreases. On the other hand, since the received signal strength of the irradiated millimeter waves increases at short distances, it can be said that the fluctuation in the detection accuracy of vehicle speed caused by noise is small.

[0039] Taking these conditions into consideration, a weight is calculated by multiplying the received signal strength by the inverse of the Doppler velocity spread (dispersion), and this weighting process is applied to the vehicle speed calculated for each fixed distance traveled by the vehicle, followed by averaging. The weighting process (111) of the digital processing unit (102) shown in Figure 1 performs this process. This makes it possible to calculate an accurate vehicle speed.

[0040] As described above, in the digital processing unit (102) of the railway vehicle speed detection device (201), the time / frequency FFT processing unit (108) calculates the distance R (202) and the Doppler velocity Vdpr (203), and then the rail extraction unit (109) extracts the fastest peak (302) from the Doppler velocity distribution at the same distance R to extract the rail.

[0041] Next, the vehicle speed detection unit (110) calculates the vehicle speed from the rail illumination angle θ at each distance, and then the weighting processing unit (111) performs weighting processing based on the received signal strength and Doppler velocity spread (502) and then averaging processing. These processes enable accurate calculation of the vehicle speed Vcar (204).

[0042] In this invention, a narrow-beam antenna is not required because it is assumed that a millimeter-wave chirp signal will be irradiated onto the rail over a fairly wide distance range. However, because the ground and sleepers outside the rails can be noise sources, it is preferable to use an antenna that has a wide beam angle in the direction of the rails but a fairly narrow beam angle in the perpendicular direction.

[0043] Furthermore, vibrations (210) occurring in the vehicle's pitch direction, as shown in the lower diagram of Figure 2, are not affected because the antenna has a wide angle in the direction of the rails. On the other hand, in the case of a railway vehicle that experiences vibrations in the height direction, it is possible to detect vibrations in the height direction and avoid their effect on speed detection by estimating the offset in the horizontal axis direction of the solid line (501) shown in Figure 5 from the white circle points (503) that represent the Doppler speeds detected for each distance.

[0044] Furthermore, as shown in the lower diagram of Figure 2, the influence of multiple reflections (209) that occur between the bottom of the railway vehicle (206) and the ground can be avoided by not performing processing after the frequency FFT in the digital processing unit (102) for the long distance R calculated by the frequency FFT, i.e., by setting a limit on the distance R.

[0045] Furthermore, the above-described embodiment encompasses at least the following technical aspects. <Technical matters 1> The railway vehicle speed detection device comprises a transmitter that transmits a chirp signal whose frequency changes over time, a receiver that receives the chirp signal reflected from a target as a received signal, and a digital processing unit that performs a Fourier transform on the received signal received by the receiver to calculate the distance to the target and the Doppler velocity of the target. The transmitter and receiver are installed at the bottom of the railway vehicle and located directly above the rail, and the digital processing unit further determines, among the received signals from targets located equidistant within the calculated distance to the target and the Doppler velocities of the targets, the Doppler velocity at which the received signal shows a peak and is the fastest, as the Doppler velocity of the rail as the target, and calculates the vehicle speed of the railway vehicle from the Doppler velocity of the rail.

[0046] <Technical matters 2> In the railway vehicle speed detection device described in Technical Item 1 above, when calculating the vehicle speed of the railway vehicle, the digital processing unit calculates an estimated vehicle speed of the railway vehicle from the irradiation angle of the chirp signal transmitted to the rail and the Doppler speed of the rail for each fixed distance traveled by the railway vehicle, weights the estimated vehicle speed using the dispersion of the Doppler speed occurring for each fixed distance and the strength of the received signal, and further averages it to calculate the vehicle speed.

[0047] <Technical matters 3> In the railway vehicle speed detection device according to the above technical feature 1 or 2, the receiving unit is configured with an antenna having a wide angle in the direction of the rails.

[0048] <Technical matters 4> A railway vehicle speed detection device according to any one of technical matters 1 to 3 above, wherein the digital processing unit does not perform processing to calculate a vehicle speed estimate for a long distance where the received signal includes signals from multiple reflections occurring between the bottom of the railway vehicle and the ground.

[0049] <Technical matters 5> In the railway vehicle speed detection device according to any one of Technical Item 1 to Technical Item 4, the chirp signal transmitted by the transmitter is a chirp signal in the millimeter wave band.

[0050] <Technical matters 6> A railway vehicle equipped with a railway vehicle speed detection device according to any one of technical matters 1 to 5 above.

[0051] <Technical matter 7> The railway vehicle speed detection method includes transmitting a chirp signal whose frequency changes over time from an antenna installed on the bottom of the railway vehicle and positioned on the rail, receiving the chirp signal reflected from a target as a received signal, performing a Fourier transform on the received signal to calculate the distance to the target and the Doppler velocity of the target, and determining the fastest Doppler velocity at which the strength of the received signal peaks among the Doppler velocities of targets located at equal distances within the calculated distance to the target as the Doppler velocity of the rail as the target, The vehicle speed of the railway vehicle is calculated from the Doppler velocity of the rail as a target.

[0052] <Technical matters 8> The railway vehicle speed detection method described in Technical Item 7 above, which calculates the vehicle speed of a railway vehicle, calculates an estimated vehicle speed of the railway vehicle from the irradiation angle of a chirp signal transmitted to the rail and the Doppler speed of the rail for each fixed distance traveled by the railway vehicle, weights the estimated vehicle speed using the dispersion of the Doppler speed occurring for each fixed distance and the strength of the received signal, and then calculates the vehicle speed by averaging it.

[0053] <Technical matters 9> The railway vehicle speed detection method described in Technical Item 8 above does not perform the process of calculating a vehicle speed estimate for long distances where the received signal includes signals from multiple reflections occurring between the bottom of the railway vehicle and the ground.

[0054] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0055] 101 Analog Processing Section 102 Digital Processing Unit 103 Synthesizer 104 transmitting antenna 105 Receiving Antenna 106 Mixer 107 A / D converter 108 Time / Frequency FFT Processing Section 109 Rail extraction section (extracts the fastest peak) 110 Vehicle speed calculation unit 111 Weighting processing unit 201 Railway vehicle speed detection device 202 Distance (R) 203 Doppler velocity (Vdpr) 204 Vehicle Speed ​​(Vcar) 205 Angle between the irradiation vector and the vehicle speed vector (θ) 206 Underside of a railway car 207 Rail 208 Height from the rail surface to the railway vehicle speed detection device (H) 209 Multiple reflections on the bottom of the vehicle 210 Pitch vibration 301 Threshold (determines the presence of a target) 302 Peak (indicates the fastest) 501 Solid line (Theoretical value showing the relationship between distance to rail and Doppler velocity) 502 Arrowed line (indicating the spread (dispersion) of detected Doppler velocity) 503 White circle points (indicating detected Doppler velocity)

Claims

1. a transmitter that transmits a chirp signal whose frequency changes over time; a receiving unit that receives the chirp signal reflected from a target as a received signal; a digital processing unit that performs a Fourier transform on the received signal received by the receiving unit to calculate the distance to the target and the Doppler velocity of the target; Equipped with the transmitting unit and the receiving unit are installed at the bottom of the railcar and positioned directly above the rails; the digital processing unit further determines, as the Doppler velocity of the rail as the target, the Doppler velocity at which the strength of the received signal peaks and the Doppler velocity of the target are the highest among the received signals from targets located at equal distances within the calculated distance to the target, and the Doppler velocities of the targets; calculating an estimated vehicle speed of the railway vehicle from an irradiation angle of the chirp signal transmitted to the rail and a Doppler speed of the rail as a target for each fixed distance traveled by the railway vehicle; The vehicle speed estimate is weighted using the dispersion of the Doppler velocity of the rail target occurring at each fixed distance and the strength of the received signal, and is then averaged to calculate the vehicle speed of the railway vehicle. A railway vehicle speed detection device characterized by:

2. 2. The railway vehicle speed detection device according to claim 1, The receiving unit is configured with an antenna having a wide angle in the direction of the rail. A railway vehicle speed detection device characterized by:

3. 2. The railway vehicle speed detection device according to claim 1, The digital processing unit does not execute a process for calculating the estimated vehicle speed value for a long distance where the received signal includes signals of multiple reflections occurring between the bottom of the railcar and the ground. A railway vehicle speed detection device characterized by:

4. 4. The railway vehicle speed detection device according to claim 1, The chirp signal transmitted by the transmitter is a chirp signal in the millimeter wave band. A railway vehicle speed detection device characterized by:

5. A railway vehicle equipped with the railway vehicle speed detection device according to claim 4.

6. A method for detecting a frequency of a chirp signal, the frequency of which changes over time, transmitted from an antenna installed at the bottom of a railway vehicle and positioned directly above the rails, and receiving the chirp signal reflected from a target as a received signal; Fourier transforming the received signal to calculate the distance to the target and the Doppler velocity of the target; determining, as the Doppler velocity of the rail as the target, the Doppler velocity at which the strength of the received signal peaks and the Doppler velocity of the target are the received signals from targets located at equal distances within the calculated distance to the target and the Doppler velocity of the target; calculating an estimated vehicle speed of the railway vehicle from an irradiation angle of the chirp signal transmitted to the rail and a Doppler speed of the rail as a target for each fixed distance traveled by the railway vehicle; The vehicle speed estimate is weighted using the dispersion of the Doppler velocity of the rail target occurring at each fixed distance and the strength of the received signal, and is then averaged to calculate the vehicle speed of the railway vehicle. A railway vehicle speed detection method comprising:

7. A railway vehicle speed detection method according to claim 6, The process of calculating the estimated vehicle speed value is not performed for a long distance where the received signal includes signals of multiple reflections occurring between the bottom of the railcar and the ground. A railway vehicle speed detection method comprising:

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