Velocity detection device and velocity detection method

Abstract

This velocity detection device comprises: a millimeter wave velocity sensor; a distance calculation unit for calculating the distance from the millimeter wave velocity sensor to a reflecting body on the basis of the delay time of reflected waves with respect to an irradiation wave; and a velocity calculation unit for calculating the velocity on the basis of the difference between a calculated beat frequency, which is calculated based on the difference between the irradiation wave and the reflected wave, and a beat frequency that has been calculated before said calculated beat frequency. The velocity calculation unit establishes a sampling condition on the basis of the distance from the millimeter wave velocity sensor to the reflecting body calculated by the distance calculation unit, and uses only a component of the reflected wave that satisfies the sampling condition to calculate the velocity.

Description

Speed ​​detection device and speed detection method

[0001] The present invention relates to a speed detection device and a speed detection method.

[0002] As a method for efficiently operating trains, the introduction of a train group control system is being considered, in which each train is given an operational target, such as a target time for arrival at the next station, and each train runs according to the target. This system is called an ATO (Automatic Train Operation) system.

[0003] Furthermore, as a method for safely operating trains, there are systems that set a speed limit for the train to travel to a point where it can run, depending on its location on the line, and allow the train to operate at or below this speed limit.Such systems include ATS (Automatic Train Stop) systems, ATC (Automatic Train Control) systems, and CBTC (Communications Based Train Control) systems, depending on the control method, and these systems are collectively called ATP (Automatic Train Protect) systems.

[0004] In order for these ATO and ATP systems to operate safely and accurately, it is necessary to accurately grasp the operating results and speed limits relative to operating targets, and it is particularly important to obtain accurate on-track positions.

[0005] In modern railways, it is common to use a tachograph or speed sensor to detect speed and calculate travel distance based on this. A tachograph has a gear that rotates with the axle and a coil placed close to the gear. The rotation of the gear generates a magnetic field in the coil that changes, outputting a sine wave and thereby detecting speed. In addition, a speed sensor has a magnetic sensor instead of the coil in the tachograph, outputting a square wave and thereby detecting speed.

[0006] The speed sensor can detect speed even at low speeds, which is difficult for a tachograph because the change in the magnetic field is small. However, because the speed detection method of the tachograph and speed sensor depends on the rotation and adhesion of the wheels, they can be affected by errors due to wheel wear, errors due to the resolution of the wheel diameter used to calculate the speed, and errors due to spinning and sliding.

[0007] Furthermore, Patent Document 1 discloses the following technology for detecting the speed of a railway vehicle based on the Doppler effect of a millimeter-wave speed sensor and the amount of Doppler shift: "The train control system 100 includes a speed detection device 1 that detects the speed of a train based on the reflected waves of electromagnetic waves irradiated onto a track, and a train control device (ATC device 2) that controls the running speed of the train based on the speed detected by the speed detection device 1. In particular, the speed detection device 1 includes a housing 11 installed under the floor of the train car and one or more speed sensors (transmitters / receivers 12) that have the function of transmitting and receiving electromagnetic waves, and at least one speed sensor is fixed to the housing 11 so that its irradiation axis 10 hits the end of the rail 7 when the vehicle is traveling on a straight section."

[0008] Furthermore, Patent Document 2 discloses the following technology as an information processing device that can reduce the capacity of the transmission path required for transmitting sensor data: "The information processing device extracts a portion of the sensor data based on the spectrum of a specific component of the sensor data from the distance measurement sensor, and generates extracted data. This technology can be applied to vehicle control systems that perform processing related to vehicle driving assistance and autonomous driving."

[0009] JP 2021-18205 A International Publication No. 2022 / 075075

[0010] The technology of Patent Document 1 makes it possible to detect the running speed of a train using a millimeter-wave speed sensor, thereby determining the distance traveled by the train and recognizing its location on the track relative to a specific point. However, with the technology of Patent Document 1, electromagnetic waves are irradiated onto the rails and track surface so that the center of the electromagnetic waves emitted from the millimeter-wave speed sensor is at the inner or outer edge of the rails that make up the track. Therefore, in cases where the rails are installed on members that raise the level above the roadbed, such as in certain sections of a rail depot, it is difficult to detect the train's speed accurately, and as a result, errors in the location of the train may occur.

[0011] Furthermore, the technology of Patent Document 2 sets a region of interest in the distance / velocity spectrum of the reflected wave received by the millimeter-wave velocity sensor and extracts the components contained within this threshold, thereby compressing the volume of the millimeter-wave velocity sensor signal, which tends to be large, and as a result, making it possible to reduce the capacity of the transmission path required to transmit sensor data. However, Patent Document 2 focuses on a specific region to extract the distance / velocity spectrum, making it difficult to directly improve the accuracy of velocity detection.

[0012] Therefore, an object of the present invention is to provide a speed detection technique using a millimeter wave speed sensor that is capable of detecting an accurate speed regardless of road surface conditions.

[0013] To solve the above problems, one representative velocity detection device of the present invention includes a millimeter-wave velocity sensor having a transmitting function of irradiating electromagnetic waves and a receiving function of receiving reflected waves of the irradiated waves, a distance calculation unit that calculates a distance from the millimeter-wave velocity sensor to a reflecting object based on a delay time of the reflected wave relative to the irradiated wave, and a velocity calculation unit that calculates a velocity based on a phase difference between a beat signal calculated from the difference between the irradiated wave and the reflected wave and a beat signal calculated earlier than the calculated beat signal. The velocity calculation unit determines sampling conditions based on the distance from the millimeter-wave velocity sensor to the reflecting object calculated by the distance calculation unit, and calculates the velocity by using only components of the reflected wave that satisfy the predetermined sampling conditions.

[0014] According to the present invention, it is possible to provide a speed detection technique using a millimeter wave speed sensor that can accurately detect speed regardless of road surface conditions. Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiment of the invention.

[0015] FIG. 1 is a diagram illustrating an example of a speed detection device mounted on a train. FIG. 2 is a diagram illustrating the positional relationship between a millimeter-wave speed sensor and a road surface. FIG. 3 is a diagram illustrating the positional relationship between a millimeter-wave speed sensor and a road surface. FIG. 4 is a diagram illustrating the relationship between an irradiated wave and a reflected wave from a millimeter-wave speed sensor. FIG. 5 is a diagram illustrating the relationship between an irradiated wave and a reflected wave from a millimeter-wave speed sensor. FIG. 6 is a diagram illustrating an irradiated wave range used for speed detection. FIG. 7 is a diagram illustrating an example of sampling conditions. FIG. 8 is a diagram illustrating a speed conversion method. FIG. 9 is a diagram illustrating speed conversion processing. FIG. 10 is a diagram illustrating a second embodiment. FIG. 11 is a diagram illustrating a third embodiment.

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments. In the drawings, identical parts are denoted by the same reference numerals. When multiple components having the same or similar functions are present, the same reference numerals may be denoted by different subscripts. Furthermore, when it is not necessary to distinguish between these multiple components, the subscripts may be omitted. Furthermore, terms such as "first," "second," and "third" may be used to describe various elements or components in this disclosure, but it should be understood that these elements or components should not be limited by these terms. These terms are used only to distinguish one element or component from another. Therefore, a first element or component discussed below may also be referred to as a second element or component without departing from the teachings of the inventive concept. The position, size, shape, scope, etc. of each component shown in the drawings may not represent the actual position, size, shape, scope, etc., in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the position, size, shape, scope, etc. disclosed in the drawings.

[0017] <Millimeter-Wave Velocity Sensor> The millimeter-wave velocity sensor disclosed herein uses a frequency-modulated continuous wave (FMCW) system in which the emitted electromagnetic waves are modulated. Conventional millimeter-wave velocity sensors, known as continuous wave (CW) systems, are unable to obtain distance information from reflected waves and can only measure velocity. Therefore, for example, when multiple reflected waves are observed, it is difficult to determine whether each reflected wave is a primary reflection component from the measurement target, a secondary reflection component, or a reflection from another target. As a result, velocity measurement using the CW system suffers from velocity measurement errors due to multiple reflections. On the other hand, because the FMCW system requires complex signal processing after receiving reflected waves, it is often used by attaching radar to stationary or slowly moving objects, and has not been used as a velocity sensor by attaching it to a moving object. However, in recent years, the miniaturization and high performance of microcomputers have made high-speed signal processing possible, and the possibility of applying this to speed sensors is being investigated.

[0018] <Summary of the present disclosure> The millimeter-wave speed sensor in the present disclosure employs the FMCW method, measures the distance to an object within the irradiation range of electromagnetic waves, and identifies the reflected wave from the rail from among the objects based on the distance information. By extracting only the reflected wave from the rail, components of the reflected wave from sources other than the rail, which are a cause of error in speed measurement, are eliminated, thereby achieving accurate speed detection based on the rail. The positional relationship between the millimeter-wave speed sensor mounted on the vehicle and the rail is always within a certain range of distance, although there is some deviation due to shaking during travel, etc. Therefore, in the FMCW method, the FFT Ｒ For the distance BIN calculated by the above, the sampling conditions are determined, and the distance BIN that satisfies the conditions and the distance BINs before and after it are extracted, and then the FFT is performed. ＶBy calculating the speed using this method, it is possible to measure the speed accurately by only using the waves reflected from the rails. Furthermore, since signal processing for speed calculation is not performed on all reflected waves, and only the extracted information is processed, high-speed processing is possible without using expensive hardware for calculations.

[0019] First, referring to FIG. 1 , an example of a speed detection device mounted on a train will be described. In FIG. 1 , a train 100 is a vehicle intended to operate on tracks with various road surface conditions, both at stations and outside stations. Generally, a train is composed of multiple cars coupled together. However, for simplicity's sake, FIG. 1 only shows the configuration of a single car (the lead car) that constitutes the train. Also, while FIG. 1 shows an example in which a train position recognition system that measures the speed of the vehicle is mounted on the lead car, in the train position recognition system according to the present invention, the speed measurement device may be mounted on another car. As shown in FIG. 1 , a train position recognition system 102 is mounted on a train 100 traveling on rails 101, and the train position recognition system is composed of a speed detection device 103 and an on-board control device 104.

[0020] As shown in Fig. 1, the train position recognition system is composed of a speed detection device 103 and an on-board control device 104, and the speed detection device 103 is equipped with a millimeter wave speed sensor 106. The on-board control device acquires the position at an arbitrary point using a transponder (not shown) installed on the ground, and calculates the running distance from the arbitrary point using the distance calculated from the speed information acquired from the speed detection device.

[0021] (On a normal route) Next, with reference to Figure 2, the positional relationship between the millimeter-wave speed sensor and the track bed when the train 100 is located on a normal route will be described. Figure 2 is a diagram illustrating the positional relationship between the millimeter-wave speed sensor 106, the rail 101, and the track bed when the rail 101 is installed at a position approximately at the same height as the track bed 220. The millimeter-wave speed sensor 106 is fixed within a housing 205 and includes a lens 207 that controls the irradiation range of the electromagnetic waves and a transparent window 208 that emits the electromagnetic waves of the millimeter-wave speed sensor to the outside of the speed measuring device. The millimeter-wave speed sensor 106 is installed under the vehicle so that the rail 101 is included in the irradiation range 214 of the electromagnetic waves emitted from the millimeter-wave speed sensor 106.

[0022] 2 and 3, wheels 209 are shown to make it easier to understand the relationship between the rail and the irradiation range of the electromagnetic waves emitted from millimeter-wave speed sensor 106, but this does not mean that the wheels are located within the irradiation range of the electromagnetic waves. The millimeter-wave speed sensor 106 is not installed directly above the wheels 209, but is installed in a position offset in the longitudinal direction of the traveling direction from the position directly above the wheels 209, and it is desirable that the electromagnetic waves emitted from the millimeter-wave speed sensor be irradiated from an oblique direction to the top of the rail.

[0023] In Figure 2, the distance of the electromagnetic waves emitted from the millimeter-wave speed sensor is shown as h1, where h1 is the distance to the rail top 210a, and h2 is the distance to the rail bottom 210b. In Figure 2, when the vehicle and the ground are horizontal, the millimeter-wave speed sensor is positioned at the inner edge of the rail top. However, the positions of the center of the millimeter-wave speed sensor and the rail top are not limited to this; the center of the millimeter-wave speed sensor may be at the center of the rail top or at the outer edge of the rail top. Furthermore, in Figure 2, the millimeter-wave speed sensor emits electromagnetic waves to one rail, but the number and positions of the millimeter-wave speed sensors are not limited to this. For example, the millimeter-wave speed sensor may be installed on both the left and right rails.

[0024] (When the rail is raised) Next, referring to Figure 3, we will explain the positional relationship between the millimeter wave speed sensor, the rail 101, and the roadbed 320 when the rail is installed on a member 322 that raises the rail from the roadbed 320, such as a pit line at a vehicle depot.

[0025] Figure 3 differs from Figure 2 in that the rail 101 is not installed on the track bed 220 of Figure 2, but is placed on a member 322 that raises the rail 101 from the roadbed 320. Therefore, in the following description, components that are the same as or equivalent to those described in Figure 2 above will be assigned the same reference numerals, and their description will be simplified or omitted.

[0026] 3, the rail is installed on a member 322 that raises the rail from the roadbed 320, and so the distances from the millimeter wave speed sensor 106 to the irradiation target are the distance h1 to the rail top 210a, the distance h2 to the rail bottom 210b, and the distance h3 to the roadbed 320. In a rail depot or the like, the roadbed 320 is the ground where staff and others pass.

[0027] In the situation shown in Figure 3, when an FMCW millimeter-wave speed sensor is used to detect the speed of a train, the FMCW millimeter-wave speed sensor also receives reflected waves from the roadbed 320, which is far from the rails, and this can result in a decrease in the accuracy of the speed measurement. Furthermore, if all of the various reflected waves are to be signal-processed, the computational load may become excessive. The situation shown in Figure 3 can result in a decrease in the accuracy of the speed measurement not only at a railyard but also when the train is traveling on a bridge.

[0028] <Overview of Configuration and Processing of Millimeter-Wave Velocity Sensor> Next, the configuration and processing of the millimeter-wave velocity sensor used in the first embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a diagram illustrating the processing of the FMCW millimeter-wave velocity sensor in the first embodiment of the present invention. The millimeter-wave velocity sensor outputs a variable frequency from a synthesizer 415 and emits an irradiated wave 418, which is an electromagnetic wave to be irradiated, from an antenna 416. The antenna also receives a reflected wave 419, which is an electromagnetic wave that is the irradiated wave reflected by an object. Fig. 4 illustrates a configuration in which the irradiated wave and the reflected wave are transmitted and received by a single antenna, but a configuration in which the antenna that transmits the irradiated wave and the antenna that receives the reflected wave are separate may also be used.

[0029] The millimeter wave velocity sensor has a mixer 417 that combines two frequencies to generate a signal of a new frequency. The mixer receives the irradiated wave output by the synthesizer and the reflected wave received from the antenna, and converts the signal into an analog signal and a digital signal using an A / D 420 and a distance calculation unit 440. Ｒ 421 and performs distance conversion 422. Ｒ Reference numeral 421 denotes a Range FFT that obtains distance information by fast Fourier transforming the signal of the new frequency generated by the mixer 417. Thereafter, the velocity calculation unit 450 executes sampling selection 423, such as obtaining only the signal of a specific distance component from the distance conversion, or obtaining only the signal of a specific distance component (specific distance BIN) after performing power intensity extraction. Details of sampling selection will be described later. Furthermore, the velocity calculation unit 450 performs FFT on the extracted specific distance BIN. Ｖ 424 and performs speed conversion 425. Ｖ 424 denotes a Doppler FFT that obtains velocity information by fast Fourier transforming the Range FFT output of multiple repeated chirps. In this figure, FFT processing is performed in the process of distance conversion and velocity conversion, but since the processing contents are different, each FFT Ｒ and FFT Ｖ Also, FFT ＲAfter 421, an SNR measurement unit 430 may be provided to measure and determine whether the reflected wave components can be recognized as a signal, and the distance conversion 422 process may be performed only if the signal exceeds a set threshold.

[0030] <FMCW Millimeter-Wave Velocity Sensor> Next, the relationship between the irradiated wave and the reflected wave in the FMCW millimeter-wave velocity sensor that is the premise of this disclosure will be described with reference to Fig. 5. Fig. 5 is a diagram illustrating the relationship between the irradiated wave and the reflected wave from a general millimeter-wave velocity sensor, with the vertical axis representing frequency and the horizontal axis representing time. The synthesizer of the millimeter-wave velocity sensor is ０ [Hz] 526 to f ０ A frequency change up to +BW [Hz] 527 occurs for each Chirp 528, and the time it takes for the frequency to change within one Chirp is t [s] 529.

[0031] Because the irradiated wave is reflected by hitting an object, a time delay occurs between the irradiated wave and the reflected wave, and the reflected wave is attenuated by the material of the object and the humidity of the space. Therefore, at any given time, a frequency difference Δf [Hz] occurs between the irradiated wave 418 and the reflected wave. Furthermore, due to differences in the irradiation distance, the reflected waves are divided into reflected wave a: 419a, which has the shortest distance to be reflected from the millimeter-wave velocity sensor, reflected wave b: 419b, which has the next shortest distance, and reflected wave c: 419c, which has the longest distance to be reflected, and when compared to the irradiated wave, the frequency difference between each wave is different.

[0032] (Irradiation Wave Range) Fig. 6 is a diagram illustrating the irradiation wave range used for velocity detection in the first embodiment. The millimeter wave velocity sensor detects the delay time Δt of the reflected wave as shown in equation (1). ｌ From [s], it is possible to calculate (distance conversion) the distance to the object for each reflected wave. In addition, R in formula (1) indicates the distance, and c indicates the speed of light. R = (Δt ｌ [s]*C) / 2...Formula (1)

[0033] (Velocity Conversion) Figure 6 is a diagram illustrating the mechanism for performing velocity conversion from two chirp frequencies, an irradiated wave and one reflected wave. The millimeter-wave velocity sensor calculates a beat frequency 633 from the frequency difference Δf [Hz] between the irradiated wave and the reflected wave at time t [s] when the frequency within one chirp changes. In this diagram, the frequency acquired by the first chirp is designated beat frequency a: 633a, and the frequency acquired by the next chirp is designated beat frequency b: 633b, and beat frequencies are compared between two or more chirps. Because the beat frequency is the difference between the irradiated wave and the reflected wave, a change in beat frequency means that the distance between the millimeter-wave velocity sensor and the object has changed.

[0034] Next, we will explain beat frequency and velocity conversion. The beat frequency is the difference between the irradiated wave and the reflected wave. The reflected wave is attenuated to a certain extent depending on the environmental conditions, and the irradiated wave is attenuated to a certain extent by the frequency of the reflected wave. ０ If the beat frequency is based on a frequency of 100 Hz, the beat frequency changes depending on the distance to the object. This indicates a delay in the reflected wave, i.e., a change in phase. When a train is not running, the phase of the beat frequency does not change, so the millimeter-wave speed sensor determines that the speed is 0 km / h based on the fact that the phase is always the same. When a train is running, the phase changes, so the speed is determined from the magnitude of the phase change.

[0035] Specifically, in the mixer of the millimeter wave velocity sensor, the irradiated wave (x １ ) and reflected wave (x ２ ) and the new frequency (x ｏｕｔ ) can be expressed by the following equations (2) to (4), where ω is the angular frequency and Φ is the phase. １ = sin(ω １ t+Φ １ )...Formula (2) x ２ = sin(ω ２ t+Φ ２ )...Equation (3) x ｏｕｔ = sin((ω １ -ω ２ )t+(Φ １ -Φ ２ )) ...Formula (4)

[0036] In other words, from equations (2) to (4), when the phases of the irradiated wave and the reflected wave are the same, the phase difference is 0, so the new frequency (x ｏｕｔ ) Chirp is equal to the irradiating wave.

[0037] Next, the initial phase of the beat frequency Φ ０ is the frequency f corresponding to the start time of the new frequency, as shown in equation (5). ｘ Instantaneous time Δt in [Hz] １ Also, the initial phase Φ ０ can also be expressed by equation (6) using the distance R and the wavelength λ of the irradiated wave.

[0038] Φ ０ = 2 * π * f ｘ *△t １ ...Formula (5) Φ ０ =(4*π*R) / λ...Formula (6)

[0039] The beat frequency for an object at a distance R is a sine wave expressed by equation (7): Beat frequency = A sin(2 * π * f ０ *△t １ +Φ ０ )...Formula (7)

[0040] Next, the phase difference ΔΦ of the beat frequency can be expressed by equation (8) using equation (6), and therefore the velocity can be calculated by equation (9). However, equation (9) only holds when |ΔΦ|<π, and if |ΔΦ|<<π, it can be expressed by equation (10).

[0041] △Φ ０ = (4 * π * V * Δt １ ) / λ...Formula (8) V=(λ*△Φ) / (4*π*△t １ )...Formula (9) V=λ / (4*△t １ ) ...Formula (10)

[0042] First Embodiment Hereinafter, a first embodiment of the present disclosure will be described, which performs accurate speed detection, taking into account the distance relationship between the millimeter-wave speed sensor installed in the vehicle and the rail or roadbed, and the relationship with the FMCW millimeter-wave speed sensor, as described above.

[0043] (Sampling Conditions) First, with reference to Figure 7, an example of the sampling conditions for the reflected wave required for accurate speed detection will be described. The delay time of the reflected wave from the millimeter-wave speed sensor from the emitted wave increases depending on the distance from the millimeter-wave speed sensor to the object. Therefore, as shown in Figure 7, the delay time differs when the emitted wave is reflected by the top of the rail, the bottom of the rail, and the roadbed. In Figure 7, the rail is installed on a member 322 that raises the rail from the roadbed 320, so the range 731 desired to acquire the reflected wave that is used as the basis for speed conversion is the area above the bottom of the rail.

[0044] In the first embodiment of the present disclosure, the speed detection device can set a distance condition (Threshold 732) for a specific distance to determine the sampling condition for data to be used for speed conversion among the distances to the object. This allows only reflected wave components whose distance conversion results are within a distance range equal to or less than the Threshold to be specified as data to be used for speed conversion. Note that, as a method for setting the sampling condition, the distance condition may be pre-registered in the millimeter-wave speed sensor, provided that the reflected wave is within a level at which it can be recognized as a signal, or may be set after measuring the signal level of the received reflected wave. Furthermore, if the sampling condition needs to be limited to reflected waves from the top of the rail, the sampling condition can be set to be equivalent to the shortest distance level calculated by the distance calculation unit.

[0045] Next, referring to FIG. 8, a method will be described in which the speed calculation unit calculates the speed by using only the reflected wave components that satisfy a predetermined distance condition based on the distance calculated by the distance calculation unit. FIG. 8 is a diagram illustrating a speed conversion method in the first embodiment. FIG. 8(a) shows the results of distance conversion in a situation in which the rail is installed on a member 322 that raises the height from the roadbed 320 as shown in FIG. 3, in which a 1-chirp irradiated wave is emitted from the millimeter wave speed sensor 106, and reflected waves are received from the distance h1 to the rail top 210a, the distance h2 to the rail bottom 210b, and the distance h3 to the roadbed 320. When distance conversion is performed from the 1-chirp reflected wave, three types of peaks 837a, 837b, and 837c can be obtained as distance-converted peaks corresponding to the reflected waves from the distances h1, h2, and h3 shown in FIG. However, since peak 837c is determined to be due to a wave reflected from somewhere other than the rail, a range 850 including peaks 837a and 837b is set as the distance condition.

[0046] Then, velocity conversion is performed on the distance conversion data in the range including the peaks 837a and 837b. FIG. 8B is a diagram showing a model of the distance BIN that is the basis for calculating the peaks of the distance conversion in FIG. 8A. Ｒ By this, the FFT on the distance Ｒ The results are shown as distance BINs 801, 802, 803, 804, 805, and 806. Each distance BIN stores complex number data, and includes information on the phase and radio wave intensity related to the distance.

[0047] Therefore, in the speed conversion in the first embodiment of the present disclosure, of the BINs 801 to 806 obtained from 1 Chirp, 801, 802, and 803, which are distance BINs corresponding to the distance condition 850 described above, are selected as components that satisfy the distance condition 850, and speed conversion processing is performed on these.

[0048] Next, the speed conversion process will be described with reference to Fig. 9. Fig. 9(a) is a diagram showing distance BINs for multiple chirps. As explained in Fig. 8, distance conversion is performed for each chirp for distance BINs that satisfy distance condition 850 (white BINs in Fig. 9(a)), and distance information for multiple chirps shown in Fig. 9(b) can be obtained. Then, FFT is performed on the beat signals of multiple chirps. ｖ The velocity can be converted by performing the following.

[0049] Then, the millimeter wave velocity sensor performs FFT using two or more Chirps with specified sampling ranges. Ｖ Velocity can be detected by calculating the peak values ​​of the Doppler amplitude at distances 837a and 837b, calculating the average peak value of the sampling data of all chirps, and converting the average value into velocity. The number of chirps used for velocity conversion can be set appropriately within the range of the allowable time for one velocity conversion.

[0050] (Effects of the First Embodiment) In a typical FMCW millimeter-wave velocity sensor, beat frequencies are calculated for different distances to an object using all received reflected waves, and velocity conversion is performed from the phase difference of the beat frequencies for each reflected wave.

[0051] For this reason, as shown in Figure 7, when the rail is raised, the distance from the millimeter-wave velocity sensor to the ground is longer than usual, so a mixture of reflected waves from objects with short distances and reflected waves from objects is generated. In this case, the attenuation of the emitted wave and reflected wave is greater than that of reflected waves from objects with long distances and reflected waves from objects with short distances, and the S / N ratio, which is the ratio of signal components required for accurate calculation to other noise components, is smaller. For this reason, if the beat frequency is calculated based on reflected waves from objects with long distances and then converted into velocity, errors are likely to occur.

[0052] Furthermore, since the results of velocity conversion from the beat frequency difference for each reflected wave do not match, the average velocity conversion value that is finally output will deviate from the true velocity conversion value. In this regard, in the first embodiment of the present disclosure, the target range of signal processing is limited as a distance condition, thereby enabling accurate velocity detection with little load.

[0053] <Second Embodiment> Next, a second embodiment will be described with reference to Fig. 10. The second embodiment differs from the first embodiment in that, after distance BINs satisfying the distance condition are extracted, a peak BIN is further detected from among them, and speed conversion is performed only on this peak BIN. Fig. 10 is a diagram showing a procedure in sampling selection, in which, after distance BINs satisfying the distance condition are extracted, the peak BIN is detected, and FFTv processing is performed only on the peak BIN. In the following description, components that are the same as or equivalent to those in the first embodiment described above are given the same reference numerals, and their description will be simplified or omitted. As shown in Fig. 10, after distance BINs satisfying the distance condition are extracted, a peak BIN is detected, and speed conversion is performed only on the peak BIN, thereby Ｖ The processing load is significantly reduced, and the accuracy of the peak BIN is expected to be higher than that of other distance BINs, so it is possible to further improve the accuracy of speed detection.

[0054] Third Embodiment Next, a third embodiment will be described with reference to FIG. 11 . The third embodiment differs from the first embodiment in that, after distance conversion, power intensity extraction 1100 is performed for all BINs, and velocity conversion is performed for all distance BINs that exceed a predetermined power intensity threshold. Note that the power intensity of each BIN can be easily calculated as the absolute value of the complex component of each BIN. In the following description, components that are the same as or equivalent to those in the first embodiment described above are designated by the same reference numerals, and their description will be simplified or omitted.

[0055] When the power intensity is above a certain level, it can be predicted that the signal accuracy is high, so Doppler FFT is performed on all BINs with high power intensity, and the results are weighted according to the power intensity and converted into velocity.

[0056] As described above, according to the embodiment of the present disclosure, by selecting only low-noise signals using the SNR measurement unit 430, it is possible to improve the accuracy of speed detection in the subsequent process.

[0057] The present invention has been described in detail above using the drawings. However, the present invention is not limited to these, and modifications can be made freely within the scope of the invention. For example, the functions performed by the distance calculation unit and velocity calculation unit described as functional units can be performed by other functional units, or the division of functions between the distance calculation unit and the velocity calculation unit can be changed. Furthermore, the functions of the distance calculation unit and the velocity calculation unit can be performed in common by one of the functional units. Furthermore, methods other than those described in the embodiments can be used for setting sampling conditions and calculating the velocity conversion. Furthermore, when multiple velocity sensors are used, the velocity can be detected by integrating the velocity conversion results from each sensor.

[0058] 100: Train 101: Rail 102: Train position recognition system 103: Speed ​​detection device 104: On-board control device 106: Millimeter wave speed sensor 205: Housing 207: Lens 208: Transparent window 209: Wheel 210a: Rail top 210b: Rail bottom 415: Synthesizer 416: Antenna 417: Mixer 418: Irradiated wave 419: Reflected wave 420: A / D conversion processing 421: FFT Ｒ Processing 422: Distance conversion 423: Sampling selection 424: FFT Ｖ 425: Speed ​​conversion 528: Chirp

Claims

1. A speed detection device that detects the speed of a train based on a reflected wave of an electromagnetic wave irradiated towards a track on which the train runs, comprising: a millimeter wave speed sensor having a transmitting function of irradiating an electromagnetic wave of the irradiated wave and a receiving function of receiving a reflected wave of the irradiated wave; a distance calculation unit that calculates a distance from the millimeter wave speed sensor to a reflecting object based on a delay time of the reflected wave relative to the irradiated wave; and a speed calculation unit that calculates the speed based on a beat frequency calculated from the difference between the irradiated wave and the reflected wave and a difference between a beat frequency calculated earlier than the calculated beat frequency, wherein the speed calculation unit determines a sampling condition based on the distance from the millimeter wave speed sensor to the reflecting object calculated by the distance calculation unit, and calculates the speed in the speed calculation unit by using only the components of the reflected wave that satisfy the sampling condition.

2. A speed detection device as claimed in claim 1, characterized in that the millimeter wave speed sensor is provided with an SNR determination unit which determines whether or not the reflected wave component can be recognised as a signal.

3. A speed detection device according to claim 1 or 2, characterized in that the sampling condition is equivalent to the shortest distance level calculated by the distance calculation section.

4. A speed detection device according to claim 1 or 2, characterized in that the sampling condition is a peak BIN extracted from distance BINs that satisfy a distance condition.

5. A speed detection device according to claim 1 or 2, characterized in that the sampling condition is that the power intensity calculated from the distance BIN exceeds a predetermined level.

6. A velocity detection device comprising: a millimeter wave velocity sensor having a transmission function of emitting an electromagnetic wave and a reception function of receiving a reflected wave of the emitted wave; a distance calculation unit that calculates a distance from the millimeter wave velocity sensor to a reflecting object based on a delay time of the reflected wave relative to the emitted wave; and a velocity calculation unit that calculates a velocity based on a beat frequency calculated from the difference between the emitted wave and the reflected wave and a difference between a beat frequency calculated earlier than the calculated beat frequency, the velocity detection method comprising: a first step of selecting a component of the reflected wave that satisfies a sampling condition consisting of a predetermined distance condition based on the distance from the millimeter wave velocity sensor to the reflecting object calculated by the distance calculation unit; and a second step of calculating a velocity in the velocity calculation unit by using only the component of the reflected wave selected in the first step.

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