Railway vehicle speed detection device and railway vehicle speed detection method
Patent Information
- Application Number
- JP2022183486
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-11-16
- Publication Date
- 2025-03-04
- Estimated Expiration
- 2042-11-16
AI Technical Summary
Existing railway vehicle speed detection methods using millimeter waves face challenges such as the need for large-sized lens antennas, requiring multiple speed detection devices, and optimizing reflection control members based on vehicle shape, which can lead to accuracy issues due to vehicle vibration and multiple reflections.
A railway vehicle speed detection device using a wide-angle antenna and digital processing to transmit a chirp signal, calculate Doppler velocity, and perform Fourier transforms to determine vehicle speed, minimizing the effects of vehicle vibration and multiple reflections by installing components directly above the rail.
The solution allows for a smaller antenna design, reduces accuracy deterioration from vehicle vibration, and avoids errors from multiple reflections, enhancing speed detection accuracy by averaging and weighting processed signals.
Smart Images
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Abstract
Description
[Technical field]
[0001] The present invention relates to a railway vehicle speed detection device and speed detection method using millimeter waves. [Background technology]
[0002] In the railway business, safe operation and accurate schedule operation are important. Here, monitoring of vehicle speed is essential for safe operation, and it is especially important to monitor vehicle speed when stopping at platforms or around curves. In urban areas, timetables are becoming more and more precise, so monitoring vehicle speed is also important for accurate schedule 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 wheel to measure the number of revolutions of the wheel and calculate the speed from the number of revolutions of the wheel. However, a problem with this method using a tachograph is that the wheel may not be able to detect the correct speed due to wheel slippage.
[0004] In recent years, in order to avoid the influence of wheel spin and detect speed accurately, speed detection methods using millimeter waves have been developed. A known method of detecting speed using millimeter waves is to irradiate a millimeter sine wave onto the rail from a speed detector installed on a vehicle and detect the speed from the Doppler shift of the sine wave reflected from the rail. In this method, the Doppler shift varies depending on the angle of the millimeter wave irradiated onto the rail from the speed detector, so in order to detect the speed accurately, it is necessary to irradiate the rail at a known designed irradiation angle and within a narrow angle range.
[0005] Patent Document 1 proposes an antenna that generates a narrow-angle beam to irradiate a narrow angular range. To achieve this narrow-angle 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 in which vehicle vibration causes an irradiation angle that differs from the design value. Two types of millimeter wave irradiators are prepared to form two different irradiation angles, which detects vibration and cancels the error in the irradiation angle caused by vibration.
[0007] In Patent Document 3, when a speed detection device is provided at the bottom of a vehicle, in order to avoid the phenomenon in which 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 on the bottom (floor surface) of the vehicle. [Prior art documents] [Patent documents]
[0008] [Patent Document 1] JP 2015-226297 A [Patent Document 2] International Publication No. 2018 / 163638 [Patent Document 3] JP 2017-15474 A Summary of the Invention [Problem to be solved by the invention]
[0009] The prior art described in each of 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 technology that miniaturizes the narrow-angle beam antenna required for a railway vehicle speed detection device 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 problems, one representative railway vehicle speed detection device of the present invention comprises a transmitting unit 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, and a digital processing unit that performs a Fourier transform of the received signal received by the receiving unit to calculate the distance to the target and the Doppler velocity of the target, where the transmitting unit and receiving unit 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 at the same distance within the calculated distance to the target and the Doppler velocities of the target, the Doppler velocity at which the received signal strength peaks 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. Effect of the Invention
[0012] According to the present invention, since a wide-angle antenna is used to detect vehicle speed at multiple distances, the antenna can be made smaller and the influence of vehicle vibration in the pitch direction can be avoided. 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 description of the drawings]
[0013] [Figure 1] FIG. 1 is a block diagram showing a configuration of a railway vehicle speed detection device according to an embodiment of the present invention. [Diagram 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. [Diagram 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. [Diagram 5] FIG. 5 is a diagram showing the relationship between the rail distance and the Doppler velocity as seen from a vehicle speed detector installed at a height of 20 cm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Hereinafter, examples will be described 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 denoted by the same reference numerals. EXAMPLES
[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 section (101) is composed of 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 chirp signal in the millimeter wave band by linearly shifting the frequency over time. This chirp signal in the millimeter wave band 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 that 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 installation image of a railway vehicle speed detection device (201). The railroad vehicle speed detection device (201) is assumed to be installed on the bottom (206) of the railroad vehicle and directly above the rail (207), as shown in the lower diagram of Fig. 2. However, while at least the transmitting antenna (104) and the receiving antenna (105) need to be installed on the bottom (206) of the railroad vehicle and located directly above the rail (207), it is not necessary that all of the components constituting the railroad vehicle speed detection device (201) be installed on the bottom (206) of the railroad 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 formula (A), where the vehicle speed is Vcar (204) and 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) is θ (205). Vdpr = Vcar cosθ (A)
[0025] As is clear from formula (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 smaller the value of θ becomes, the larger the value of the calculated Doppler velocity Vdpr (203) becomes, and the smaller the value of the ... the closer the vehicle speed Vcar (204) becomes.
[0026] The railway vehicle speed detection device (201) is installed directly above the rail (207), and the rail (207) is generally convex in the height direction from the ground. Therefore, among targets with the same distance R (202) calculated by frequency FFT, θ (205) at the rail (207) is the smallest.
[0027] As an example, the upper diagram of Figure 2 shows an angle θ1 (205(1)) with respect to the rail (207) and an angle θ2 (205(2)) with respect to the ground and 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 maximum within the equal 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 in a time / frequency FFT processing unit, with the horizontal axis representing the Doppler velocity and the vertical axis representing the spectrum intensity.
[0030] The rail extraction unit (109) treats the distribution range of Doppler speeds 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, SNR=10 dB.
[0031] Since rails (207) are made of metal, they show a high spectral intensity value where the reflection of millimeter waves is strong. Therefore, the rail extraction unit (109) determines that a target object showing a peak value (302 in FIG. 3) with the fastest Doppler velocity among peak values (the downward arrow in FIG. 3) in a region of spectral intensity higher than a 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 velocity 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 band of the chirp signal generated by the synthesizer (103), and the wider the band, the higher the resolution. For example, the resolution of the distance R is 20 cm when the band of the chirp signal is 0.75 GHz, and 6 cm when it is 2.5 GHz. In other words, the wider the band, the higher the distance resolution, and therefore the detection accuracy of the vehicle speed Vcar (204) can be improved.
[0036] 5 is a diagram showing 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 value obtained by normalizing the Doppler velocity Vdpr (203) 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 intervals of 5 cm, which is the distance resolution. Here, due to the nature of the distance resolution, each white circle point includes a Doppler velocity component within the range of the arrow line (502) shown in FIG. 5.
[0038] From the above, near the minimum distance of 20 cm, there is a large spread (degree of dispersion) in the detected Doppler velocity (range of the arrow line (502)), but as the distance increases, the spread (degree of dispersion) of the detected Doppler velocity also becomes smaller. On the other hand, at short distances, since the received signal strength of the irradiated millimeter waves becomes strong, it can be said that the fluctuation in the detection accuracy of the vehicle speed caused by noise is small.
[0039] Taking these conditions into consideration, the received signal strength is multiplied by the inverse of the spread (dispersion) of the Doppler velocity to obtain a weighting factor, which is then applied to the vehicle speed calculated for each fixed distance traveled by the vehicle, and then averaged. The weighting factor processing unit (111) of the digital processing unit (102) shown in Fig. 1 performs these processes. 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) determines 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 of the equal distance R to extract the rail.
[0041] Next, the vehicle speed detection unit (110) calculates the vehicle speed from the rail irradiation angle θ at each distance, and then the weighting processing unit (111) performs weighting processing based on the received signal strength and the Doppler velocity spread (502) and further performs averaging processing. These processes make it possible to calculate an accurate vehicle speed Vcar (204).
[0042] In the present invention, since it is assumed that the rail is irradiated with a chirp signal in the millimeter wave band over a relatively wide distance range, a narrow-angle antenna is not required. However, since the ground and sleepers outside the rail may be noise sources, it is more preferable to use an antenna that has a wide angle in the direction of the rail but a relatively narrow angle in the perpendicular direction.
[0043] Also, vibrations (210) occurring in the pitch direction of the vehicle, as shown in the lower diagram of Figure 2, are not affected because the antenna has a wide angle in the direction of the rail. 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 direction of the solid line (501) shown in Figure 5 from the white circle points (503), which are the Doppler velocities detected for each distance.
[0044] Furthermore, as shown in the lower diagram of FIG. 2, the influence of multiple reflections (209) occurring between the bottom of the railway vehicle (206) and the ground can be avoided by not performing processing subsequent to 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, according to the above embodiment, at least the following technical matters are included. <Technical matters 1> The railway vehicle speed detection device comprises a transmitting unit that transmits a chirp signal whose frequency changes over time, a receiving unit that receives the chirp signal reflected from a target object as a received signal, and a digital processing unit that performs a Fourier transform on the signal received by the receiving unit to calculate the distance to the target and the Doppler velocity of the target, where the transmitting unit and receiving unit 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 at the same distance within the calculated distance to the target and the Doppler velocities of the target, the one where the received signal strength peaks and the fastest Doppler velocity is the Doppler velocity of the rail as the Doppler velocity of 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 vehicle speed estimate using the dispersion of the Doppler speed occurring for each fixed distance and the strength of the received signal, and further averages the vehicle speed.
[0047] <Technical matters 3> In the railway vehicle speed detection device according to the above Technical Item 1 or Technical Item 2, the receiving unit is configured with an antenna having a wide angle in the direction of the rail.
[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 for calculating a vehicle speed estimate for a long distance where the received signal includes signals of multiple reflections occurring between the bottom of the railway vehicle and the ground.
[0049] <Technical matters 5> A railway vehicle speed detection device according to any one of Technical 1 to Technical 4 above, wherein the chirp signal transmitted by the transmitting unit 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 Item 1 to Technical Item 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 located 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 with 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 vehicle speed estimate using the dispersion of the Doppler speed occurring for each fixed distance and the strength of the received signal, and further averages the vehicle speed.
[0053] <Technical matters 9> The railway vehicle speed detection method described in Technical Item 8 above does not perform a process of calculating a vehicle speed estimate for long distances where the received signal includes signals of 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 without departing from the gist of the present invention. [Explanation of symbols]
[0055] 101 Analog Processing Section 102 Digital Processing Section 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 railway car 207 Rail 208 Height from rail surface to railway vehicle speed detection device (H) 209 Multiple reflections on the bottom of the vehicle 210 Pitch Vibration 301 Threshold (to determine 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 Arrows (indicating the spread (dispersion) of detected Doppler velocities) 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 reception signal received by the receiving unit to calculate a distance to the target and a 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 is at a peak and which is the fastest among the received signals from targets located at an equal distance 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 speed of the rail target generated at each fixed distance and the strength of the received signal, and is then averaged to calculate the vehicle speed of the rail vehicle. A railway vehicle speed detection device comprising:
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 comprising:
3. 2. The railway vehicle speed detection device according to claim 1, The digital processing unit does not execute a process for calculating the vehicle speed estimate 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 comprising:
4. 4. A railway vehicle speed detection device according to claim 1, The chirp signal transmitted by the transmitting unit is a chirp signal in the millimeter wave band. A railway vehicle speed detection device comprising:
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 varies with 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, among the received signals from targets located at equal distances within the calculated distance to the target and the Doppler velocities of the targets, the Doppler velocity at which the received signal has a peak and is the fastest, as the Doppler velocity of the rail as 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 speed of the rail target generated at each fixed distance and the strength of the received signal, and is then averaged to calculate the vehicle speed of the rail vehicle. A railway vehicle speed detection method comprising:
7. A railway vehicle speed detection method as claimed in claim 6, comprising: The process of calculating the vehicle speed estimate 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: