JP2006007818A - Railroad crossing obstacle detection device - Google Patents

Abstract

A radar-type crossing obstacle detection device capable of detecting both a vehicle and a person on a crossing road at a low cost, and increasing the distance measurement speed and measurement accuracy.
A distance measuring unit 80 for measuring a distance from a rotation mechanism unit 70 that rotates an irradiation wave S in a horizontal direction within a railroad crossing to a detection target 13 fixes the frequency f of the irradiation wave S at a high and low frequency. The modulator 81 that can sweep the signal, the beat signal extraction circuit 56 + 57 that extracts the beat signal b related to the irradiation wave S and the reflected wave R, and the distance in the two-frequency CW system from the beat signals b1 and b2. And a signal processing device for calculating appropriate distance information by determining the distance in the FMCW method from the beat signal b3 and further combining these distances.
[Selection] Figure 1

Description

  The present invention relates to a railroad crossing obstacle detection apparatus that detects an obstacle such as a person or a vehicle on a railroad crossing by irradiating an aerial propagation wave such as a millimeter wave or a microwave into a railroad crossing. The present invention relates to a crossing obstacle detection device that uses a CW (Continuous Wave, continuous wave) type distance measuring sensor to measure the distance of the vehicle.

As a general method of detecting an obstacle on a level crossing, an optical system that detects an obstacle by blocking the light beam between the light emitter and the receiver by an automobile and a loop coil installed under the road of the level crossing There is known a loop type that detects an obstacle using the increase of the oscillation frequency of a loop coil built-in oscillation circuit in response to a metal such as the above. These systems are dissatisfied with the high equipment cost and the inability to detect vulnerable traffic people staying on level crossings, and improvements are required.
As a method for solving these problems, a radar-type crossing obstacle detection device shown in FIG. 4 has been proposed (see, for example, Patent Document 1).

  FIG. 4 shows a schematic structure and the like of such a level crossing obstacle detection device, where (a) is a perspective view of the level crossing obstacle detection device and a level crossing where the level crossing obstacle detection device is installed, and (b) is a level crossing obstacle detection device. It is a perspective view of a rotation mechanism part. This level crossing obstacle detection device includes a rotation mechanism 40 that is installed in a track and faces the railroad crossing 10, a transmission / reception unit (51 to 57 or 61 to 57) built in the rotation mechanism 40, and an instrument box beside the track. 12 is provided with a distance measuring unit (50 or 60) comprising a signal processing device (58 or 68) built in the unit 12. The rotation mechanism unit 40 includes a rotating disk that supports the antenna of the transmission / reception unit so as to be rotatable about a vertical axis, and an orientation detection unit such as a rotary encoder that detects the rotation position. The irradiation direction of the irradiation wave S is rotated in the horizontal direction within the railroad crossing, and the direction of the rotation is detected at any time.

In addition, the distance measuring unit irradiates an aerial propagation wave such as a radio wave into the railroad crossing, and receives the reflected wave R returned from the irradiation wave S reflected by the detection target 13 or the like on the railroad crossing 10, Specifically, the beat signal is extracted using the relationship between the reflected wave R and the original irradiation wave S, and the distance from the rotation mechanism 40 to the detection target 13 is measured. Yes.
Furthermore, the signal processing device performs an operation such as processing a beat signal and calculating distance information as a part of the distance measuring unit, and based on the distance information and the direction information obtained by the rotation mechanism unit 40. Thus, it is also determined whether or not there is an obstacle between the barrier bars 11 on both sides on the railroad crossing 10.

As a specific example of such a CW distance measurement method, a two-frequency CW distance measuring sensor 50 shown in FIG. 5 and an FMCW (Frequency Modulated Continuous Wave) frequency measurement shown in FIG. A distance sensor 60 is known. Conventionally, either of these methods has been adopted without being used together (see, for example, Patent Document 1 and Patent Document 2).
Here, the CW type distance measuring sensors 50 and 60 will be described by scratching the configuration and characteristics useful for explaining the present invention.

5A is a block diagram of a general two-frequency CW system distance measuring sensor 50, and FIG. 5B is an explanatory diagram of a distance measurement state using the same.
The two-frequency CW type distance measuring sensor 50 (see FIG. 5 (a)) switches the modulation signal at a fixed time to fix the frequency f of the irradiation wave S to a low frequency f1 in order to irradiate the aerial propagation wave into the railroad crossing. And a modulator 51 that alternately fixes the signal to a high frequency f2, and a sinusoidal transmission signal s1 having a frequency f1 and a sinusoidal transmission signal s2 having a frequency f2 when generating the transmission signal s according to the modulation signal. Are alternately generated at fixed time intervals, a signal distributor 53 that divides the transmission signal s, sends a part thereof to the transmission antenna 54, and sends the remainder to the mixer 56, and a transmission signal s of an electrical signal Is emitted into the air as an irradiation wave S such as a millimeter wave or a microwave (radio wave), so that the irradiation wave S1 having the frequency f1 and the irradiation wave S2 having the frequency f2 are alternately irradiated into the railroad crossing for a predetermined time. And an antenna 54.

  Further, the two-frequency CW system distance measuring sensor 50 generates a reception signal r of an electrical signal from the reflected wave R of the airborne wave in order to receive the reflected wave R bounced back when the irradiation wave S hits the detection target 13. A receiving antenna 55 is provided. As a result, a received signal r1 having the frequency f1 is obtained from the reflected wave R1 having the frequency f1, and a received signal r2 having the frequency f2 is obtained from the reflected wave R2 having the frequency f2. Furthermore, as a beat signal extraction circuit for extracting the beat signal b related to the irradiation wave S and the reflected wave R, a mixer 56 for mixing (multiplying) the transmission signal s and the reception signal r, and a low-pass filter 57 subsequent thereto. The beat signal b1 related to the irradiation wave S1 and the reflected wave R1 and the beat signal b2 related to the irradiation wave S2 and the reflected wave R2 are alternately generated.

  Further, the two-frequency CW system distance measuring sensor 50 obtains the distance from the rotation mechanism unit 40 to the detection object 13 by the two-frequency CW system based on the beat signal b in order to calculate distance information for determination. A signal processing device 58 is provided. The signal processing device 58 is mainly composed of a microprocessor or a digital signal processor as an arithmetic means, and an A / D conversion circuit that digitizes and inputs the beat signal b, and the frequency spectrum of the beat signal b is converted into a digital calculation. FFT (Fast Fourier Transform) calculating means is calculated or incorporated. The distance d2 in the two-frequency CW method is calculated by a known predetermined formula from the phase difference between the phase of the beat signal b1 and the phase of the beat signal b2.

  Using such a two-frequency CW system distance measuring sensor 50 (see FIG. 5 (b)), the detection range distance dx required for detecting an obstacle at a level crossing is set to 36 m, for example, and the object 13 on the level crossing 10 is reached. If the distance is measured, the minimum detection unit is as small as about 0.5 ° in phase difference (about 10 cm in distance), so fine distance measurement can be performed, but 180 ° in phase difference (detection range distance dx = Distance measurement exceeding 36m) is not possible. For the detection target 13 farther than the detection range distance dx, the distance from the rotation mechanism unit 40 to the detection target 13 is the distance to the virtual image 14 near the detection range distance dx, that is, from the correct distance to the detection range distance dx. This is because the lie distance minus the integer multiple is calculated.

6A is a block diagram of a general FMCW range sensor 60, and FIG. 6B is an explanatory diagram of a distance measurement state using the same.
The FMCW range sensor 60 (see FIG. 5A) differs from the above-described two-frequency CW range sensor 50 in that the modulator 51 is changed to the modulator 61, and the signal processing device 58 is a signal. This is the point that the processing device 68 is used.

The modulator 61 continuously changes the modulation signal in order to sweep without fixing the frequency f of the airborne wave. Therefore, even if the other members 52 to 57 remain the same, the transmission signal s, the irradiation wave S, the reflected wave R, and the reception signal r increase or decrease the frequency f by the frequency modulation width B every frequency modulation period T. Yes.
In this specification, when the transmission signal s, the irradiation wave S, the reflected wave R, the reception signal r, and the beat signal b in the FMCW system are distinguished from those in the two-frequency CW system, the transmission signal s3 and the irradiation wave are distinguished. S3, reflected wave R3, received signal r3, and beat signal b3 are described. The measurement distance d from the rotation mechanism 40 to the detection target 13 also includes the distance d3 in the FMCW method and the distance d2 in the two-frequency CW method.

  The signal processing device 68 includes calculation means such as an A / D conversion circuit, FFT calculation means, and a microprocessor, and is the same as the signal processing device 58 in terms of hardware, but the calculation contents in the microprocessor and the like. Is different from the signal processing device 58. That is, the modulator 61 sweeps the frequency f3 of the irradiation wave S3 and at the same time, obtains the beat signal b3 obtained by the beat signal extraction circuit from the reception signal r3 of the reflected wave R3 and the transmission signal s3 of the original signal of the irradiation wave S3. The distance d3 in the FMCW system is obtained from the input frequency. Specifically, the distance d3 in the FMCW method is calculated from a beat frequency fu when the frequency f is high and a beat frequency fd when the frequency f is low using a known predetermined formula.

  Using such an FMCW range sensor 60 (see FIG. 6 (b)), the allowable value of the occupied frequency bandwidth, that is, the frequency modulation width B is 76 MHz, for example, and the distance to the object 13 on the railroad crossing 10 , The minimum detection unit is as large as about 2 m regardless of the detection range distance dx required for detecting the obstacle at the railroad crossing, so that it is a rough distance measurement, but the distance measurement exceeding the detection range distance dx of 36 m is also possible. Is possible. Even for the detection target 13 farther than the detection range distance dx, the distance of the real image is obtained in the same manner as the detection target 13 closer to the detection range distance dx without measuring the near virtual image as in the two-frequency CW method. Can do.

JP 2003-11824 A JP 2003-35768 A

The above-mentioned radar level crossing obstacle detection device can detect not only vehicles and people (especially those with weak traffic) staying on the level crossing road, but also the detection with one radar. There is a feature that maintenance costs are also reduced.
In such a level crossing obstacle detection device, a car or a wheelchair person who is captivated on the level crossing is an important detection target, and therefore it is generally suitable for distance measurement radars to detect stationary objects. An FMCW range sensor is used (see, for example, Patent Document 1).
However, there is still room for improvement in the distance measurement method of such a crossing obstacle detection device. This will be described in detail below.

An automobile front obstacle detection sensor is known as an application of a distance measurement sensor (see, for example, Patent Document 2). This distance measurement sensor must be able to detect a distance of up to 150 m, but has a detection accuracy (resolution). Since about 1 m is sufficient, either the 2-frequency CW system or the FMCW system can be arbitrarily adopted.
On the other hand, the detection range of the level crossing obstacle detection device is limited to the level crossing 10 inside the barrier bar 11 on both sides of the double line up and down as shown in FIG. Is about 36 m at maximum. However, if the detection target 13 is located inside the crossing barrier 11 from the level crossing barrier 11, it is determined as an obstacle, and if the detection target 13 is outside the level crossing barrier 11, it is determined as an obstacle. Don't be. For this reason, the distance accuracy requires ± 15 cm or less, and the distance resolution is required to be 15 cm or less.

  Further, in the radar type crossing obstacle detection device, as shown in FIG. 4, the rotation mechanism 40 is installed in the track so that the antenna of the distance measuring sensor is swung (oscillated), and a stationary object By performing minute vibrations of the antenna etc. in the front-rear direction for the measurement, the entire railroad crossing 10 extending about 180 ° in front is irradiated in the air in a short time, specifically within 2 seconds, It is desired to measure the distance d to the detection target 13 that reflects radio waves. When the horizontal spread of the distance measuring sensor beam (irradiation wave S) is 4 °, the distance d is measured for each direction divided by 45 (= 180 ° / 4 °). The time required for measurement is 44 ms. Here, the reason why the 180 ° rotation time is set to 2 seconds or less is that, according to the regulation of level crossing fault detection, “when obstacles are detected for 6 seconds or more, fault information is output”. This is to improve the accuracy of obstacle detection by performing a series of propagation wave irradiation and distance measurement three times in 6 seconds until output and further combining, for example, majority decision.

However, the distance resolution Δd of the FMCW range sensor is defined by the frequency sweep width Δf = frequency modulation width B as expressed by the following equation. C is the speed of light.
Δd = c / (2 · Δf)
When using the FMCW type distance measuring sensor having such a distance resolution, it is necessary to further consider the distance measurement accuracy in consideration of the following two elements (1) and (2) in the signal processing system.

(1) The radar reflected wave R capture time Tin (time required for measurement per one position) must be considered. This is because 1 / Tin is the lowest signal frequency that can be appropriately processed by the FFT calculation means.
(2) The signal sampling time Ts of the A / D conversion circuit of the signal processing device of the distance measuring unit must be considered. This is because 1 / (2 · Ts) is the highest signal frequency that can be appropriately processed by the FFT operation means.
In consideration of these, if the measurement time allowed for each of the azimuths into which the rotation range is divided becomes short, the distance measurement accuracy deteriorates. As described above, in order to shorten the measurement time per one position to 44 ms, it is necessary to be prepared to sacrifice the distance measurement accuracy.

  Further, since the frequency sweep width Δf = frequency modulation width B is limited by the occupied frequency bandwidth in the operating frequency range, and the occupied frequency band is regulated by the Radio Law, for example, even when a frequency of 76.5 GHz band is used The allowable frequency bandwidth is 500 MHz, and in this case, the distance resolution Δd is about 30 cm. Since the detection error (distance measurement accuracy) due to the roughness of the resolution is not related to the length of the detection distance (detection range distance dx), the detection range (detection range distance dx) of the level crossing obstacle detection device is 36 m. It is not improved even in the following cases.

Moreover, since the use of the 76.5 GHz band is currently limited to in-vehicle ranging sensors, it cannot be used for ground facilities. For this reason, the frequency equipment 24.15 GHz band for the ground equipment is used for the level crossing obstacle detection device which is the ground equipment. In this frequency domain, the allowable value of the occupied frequency bandwidth is only 76 MHz. The distance resolution Δd is about 2 m.
From any point of view, that is, from the viewpoint of both measurement speed and measurement accuracy, if the FMCW distance measuring sensor is used in the distance measuring unit as before, sufficient improvement of the level crossing obstacle detection device (ie distance High speed and high accuracy of measurement) cannot be expected.

  On the other hand, if a two-frequency CW system distance sensor is adopted instead of the FMCW system distance sensor, the minimum detection unit (distance resolution) increases or decreases depending on the size of the detection range distance dx. It seems that a crossing obstacle detection device with a small crossing can easily solve problems such as measurement accuracy, but as described above, in the two-frequency CW system distance measurement, the detection object 13 farther than the detection range distance dx is brought closer. Due to the characteristic of false detection, it is important to determine whether the object to be detected is inside or outside the railroad crossing, unlike in the case of a car that measures only the front far. The level crossing obstacle detection device that changes greatly in accordance with the direction of wave irradiation (direction of rotation) cannot be adopted to some extent by modifying a general two-frequency CW rangefinder.

  Therefore, in order to improve the accuracy of obstacle detection without compromising the feature that it is possible to detect both vehicles and people on a railroad crossing with a radar type railroad crossing obstacle detection device that has characteristics superior to optical and loop types In addition, we devised to increase the distance measurement speed and measurement accuracy so that accurate determination can be made by performing as many precise distance measurements as possible within the specified time, and the scale of the equipment should be kept down in order to reduce costs In addition, it is a technical problem to make further efforts to avoid an increase in circuit scale.

  The level crossing obstacle detection device of the present invention has been devised to solve such a problem, and irradiates an aerial propagation wave into the level crossing and receives the reflected wave to determine the distance to the detection target. A distance measuring unit for measuring, and a rotating mechanism unit for rotating the irradiation direction in the horizontal direction and detecting the direction of the rotation at any time, the distance information obtained by the distance measuring unit and the rotating mechanism unit In the crossing obstacle detection device that determines whether or not there is an obstacle in the crossing based on the azimuth information obtained in the above, the distance measurement unit includes the following modulation means, beat signal extraction circuit, and signal processing And a device.

That is, the modulation means controls an oscillation circuit or a transmission circuit that generates a transmission signal that is an original signal of the irradiation wave, and can change the frequency of the air propagation wave including a radio wave or an electromagnetic wave such as a millimeter wave or a microwave. It is possible to adjust the frequency of the airborne wave to a high or low frequency, and it is also possible to sweep without fixing the frequency of the airborne wave.
The beat signal extraction circuit extracts a beat signal related to the irradiation wave and the reflected wave. Specifically, the signal obtained by dividing or replicating the transmission signal and the reception signal of the reflected wave are mixed by a mixer or the like, and then a beat signal having a low frequency component is extracted by a low-pass filter or the like. .

Further, the signal processing apparatus calculates the distance information by combining the two-frequency CW method and the FMCW method as follows.
That is, the modulation means fixes the frequency of the airborne wave to a high frequency to determine the phase of the beat signal, and the modulation means fixes the frequency of the airborne wave to a low frequency and the beat signal And the distance in the two-frequency CW method is obtained from the phase difference.
Further, the frequency of the airborne wave is swept by the modulation means, and the distance in the FMCW method is obtained from the frequency of the beat signal.
Further, the distance information is calculated by combining the distance in the FMCW method and the distance in the two-frequency CW method as being able to exceed the detection range and not exceeding the detection range.

  In such a crossing obstacle detection device of the present invention, distance measurement is performed by both the FMCW method and the two-frequency CW method while following the distance measurement by the radar method. The measurement results are integrated so that the characteristics live. That is, the distance in the two-frequency CW method that allows high-precision detection but cannot exceed the detection range distance at the level crossing, and the limitation of the occupied frequency band that can be used although it can exceed the detection range distance at the level crossing By appropriately combining the distance in the FMCW system, which tends to be low in distance measurement accuracy due to the limitation of the hit measurement time, it can be repeated as many times as desired within the specified time with high accuracy up to the detection range distance at the level crossing Distance measurement can be performed as quickly as possible.

In addition, the 2-frequency CW system distance sensor and the FMCW system distance sensor may have almost the same hardware such as the beat signal extraction circuit, so the 2-frequency CW system distance sensor and the FMCW system distance sensor By performing the time division, the hardware of the distance measuring unit can be shared, so that an increase in the scale of the electronic circuit or the like can be suppressed and an increase in cost can be avoided. The specific modification points are the expansion of the function of the modulation means and the expansion of the calculation contents of the signal processing device, but the modulation means are both fixed-frequency and frequency-swept because they are originally small circuits. However, the increase in the circuit scale is only slight, and the calculation means of the signal processing apparatus is usually embodied by a program, so that the expansion of calculation contents hardly causes an increase in the circuit scale or the apparatus scale.
Therefore, according to the present invention, it is possible to realize a level crossing obstacle detection device that can detect a vehicle and a person on a level crossing quickly and accurately while being inexpensive.

  A specific configuration of such a crossing obstacle detection device of the present invention will be described with reference to the drawings. 1A is a perspective view of a level crossing including a level crossing obstacle detection device, and FIG. 1B is a block diagram of a distance measuring unit. FIG. 2 is a flowchart showing a signal processing procedure for distance measurement. In the drawings, the same reference numerals are given to the same components as those in the prior art, and therefore, repeated explanations are omitted. Hereinafter, the differences from the prior art will be mainly described.

In this level crossing obstacle detection device (see FIG. 1), the above-described rotation mechanism unit 40 (see FIG. 4) becomes a rotation mechanism unit 70 capable of high-speed rotation (see FIG. 1 (a)). The radar-type distance measuring units 50 and 60 (see FIGS. 5 and 6) are replaced with a distance measuring unit 80 that uses both the two-frequency CW method and the FMCW method (see FIG. 1B).
The rotation mechanism unit 70 is different from the rotation mechanism unit 40 in that the swinging speed of the antenna and the like of the transmission / reception unit is increased by increasing the driving ability of the rotating disk. Others are the same. Thereby, rotation (oscillation) over about 180 °, that is, one irradiation of the irradiation wave S to the entire area within the railroad crossing is performed in 2 seconds or less.

The distance measuring unit 80 is different from the two-frequency CW-type distance measuring sensor 50 and the FMCW-type distance measuring sensor 60 in that the modulators 51 and 61 are changed to the modulator 81 and the signal processing devices 58 and 68 perform signal processing. This is the point where the device 88 is obtained.
As for the other parts, the part constituting the transmission circuit such as the oscillation circuit 52 and the signal distributor 53, the part constituting the beat signal extraction circuit such as the mixer 56 and the low-pass filter 57 as well as the transmission antenna 54 and the reception antenna 55 are already described. Same as ok. The distance measurement is performed by two methods of the two-frequency CW method and the FMCW method, but since it is time-division, one set of hardware is sufficient.

  The modulator 81 receives the measurement mode switching signal M from the signal processing device 88 and switches the modulation signal to the high frequency oscillator 52. Specifically, in order to enable measurement of the distance d2 in the two-frequency CW method, when the distance measurement sensor 50 measurement mode switching signal M is the two-frequency CW mode M1, the frequency f of the transmission signal s and the irradiation wave S Is fixed to a low frequency f1, the transmission circuit s1 is generated by the transmission circuit, and the irradiation wave S1 is emitted from the transmission antenna 54. When the measurement mode switching signal M is the two-frequency CW mode M2, the transmission signal s2 and the irradiation wave S are fixed at a high frequency f2, and the transmission circuit s2 is generated by the transmission circuit. The irradiation wave S2 is emitted.

  Further, when the measurement mode switching signal M is the FMCW mode M3, the modulator 81 sweeps the frequency f3 instead of fixing the frequency f of the transmission signal s and the irradiation wave S. That is, the frequency f3 is linearly increased by the frequency modulation width B = frequency sweep width Δf during the frequency modulation period T, and the frequency f3 is increased by the frequency modulation width B = frequency sweep width Δf during the frequency modulation period T. Lowering linearly is repeated alternately. Thereby, when measuring the distance d3 in the FMCW system, the transmission circuit generates a transmission signal s3 having a variable frequency and emits the irradiation wave S3 swept in frequency from the transmission antenna 54.

  The signal processing device 88 includes arithmetic means such as an A / D conversion circuit, FFT arithmetic means, and a microprocessor, and is the same as the signal processing devices 58 and 68 in terms of hardware, The calculation contents are different from those of the signal processing devices 58 and 68. That is, (see FIG. 2), the signal processing device 88 calculates the distance d2 by measuring the distance by the two-frequency CW method while sharing the hardware by time division (steps ST1 to ST6), and also measures by the FMCW method. The distance d3 is calculated by performing the distance (steps ST7 to ST9), and the distances d2 and d3 are integrated to finally calculate one distance d (steps ST10 to ST11). A specific procedure for signal processing will be described in detail later when the operation is described.

The reason why the distance d2 is obtained by the two-frequency CW method is to measure the distance d as accurately as possible to a detection range distance dx as short as 36 m. According to this, the distance d3 is obtained by the FMCW method. This is because the distance measurement can be performed beyond the distance dx, and by combining these, the weak point of the two-frequency CW method that the detection range distance dx cannot be exceeded is covered. The reason will be described in detail. In the case of distance measurement by the two-frequency CW method, the initial phases of the transmission signals s1 and s2 are φ1 and φ2, the time is t, and the transmission signals are respectively
s1 = sin (2 · π · f1 · t + φ1)
s2 = sin (2 · π · f2 · t + φ2)

After the irradiation wave S corresponding to the transmission signal s is reflected by the detection target 13, the reception signals r1 and r2 of the reflected wave R received by the reception antenna 55 are distances from the rotation mechanism unit 70 to the detection target 13. Is d2, the Doppler shift frequency generated by the relative speed with respect to the detection target 13 is Fd1 = Fd2 = Fd, and the light speed is c, the received signal (demodulated wave) is
r1 = sin (2 · π · (f1 + Fd) · t + φ1−4 · π · f1 · d2 / c)
r2 = sin (2 · π · (f2 + Fd) · t + φ2−4 · π · f2 · d2 / c)
It becomes.

When these received signals r1 and r2 are mixed with the transmission signals s1 and s2 by the mixer 56 and then the low-frequency component beat signal b is extracted by the low-pass filter 57, the obtained beat signals b1 and b2 are respectively
b1 = sin (2 · π · Fd · t-4 · π · f1 · d2 / c)
b2 = sin (2 · π · Fd · t−4 · π · f2 · d2 / c)
Therefore, by obtaining the phase difference Δφ = 4 · π · (f1−f2) · d2 / c between the beat signals b1 and b2, the distance from the rotation mechanism unit 70 to the detection target 13 is
d2 = c · Δφ / (4 · π · (f1−f2))

The phase difference Δφ can be obtained by extracting the respective phases φ1 and φ2 from the frequency spectrum obtained by processing the received signals r1 and r2 by FFT calculation.
When the value of the phase difference Δφ exceeds π radians, that is, 180 °, the phase difference Δφ cannot be determined. Therefore, the detection range distance dx is a value when the phase difference Δφ is π radians = 180 °.
In the case of this distance measuring unit 80, since it is assumed to be applied to the general level crossing described above, the detection range distance dx is 36 m. In addition, since the phase resolution can be set to 0.5 ° by normal signal processing without using an expensive signal processing device, the minimum detection unit is 10 cm, and thus the two-frequency CW method distance measuring unit 80 is required. It satisfies the distance resolution. In order to measure a stationary object in the two-frequency CW method that requires the detection target to move relatively, a vibration mechanism that causes the transmitting antenna 54 and the like to vibrate slightly in the front-rear direction, that is, the irradiation direction, is about several millimeters. The distance measurement unit 80 may be integrated with the transmission antenna 54 or the like, or may be provided in the scanning mechanism unit 70 separately from the transmission antenna 54 or the like.

As described above with reference to FIG. 6B, in the two-frequency CW method, a precise distance can be detected if the detection target 13 is within the detection range distance dx. However, with the two-frequency CW method alone, when the detection target 13 is outside the detection range distance dx, the phase difference Δφ exceeds π radians and becomes π + α radians (180 ° + β °). Since it is obtained as α radians (β °) less by π radians (180 °), the distance d2 is erroneously detected closer to the actual distance.
Therefore, although the minimum detection unit (distance resolution) is as bad as 2 m, erroneous detection is prevented by combining the FMCW method without such inconvenient characteristics.

That is, the detailed position of the detection target 13 is detected by the two-frequency CW method, and whether or not it is within the detection range is detected by the FMCW method. Thereby, the distance measurement unit 80 determines that “there is an obstacle” when the head of the automobile enters the railroad crossing from the barrier, and otherwise determines “no obstacle”. Can be performed accurately.
In the distance measurement by the FMCW method, when the frequency f3 of the transmission signal s3 is alternately swept up and down in the frequency modulation width B with the frequency modulation period T, the beat at the time of ascending sweep from the frequency spectrum of the received signal r3. Obtain the frequency fu and the beat frequency fd during the downward sweep,
d3 = (c · T / 4 · B) · (fu−fd)
By performing this calculation, a distance d3 that exceeds the detection range distance dx is obtained.

About the level crossing obstacle detection apparatus 70 + 80 of this embodiment, its usage and operation will be described with reference to the drawings. FIG. 1A is a perspective view showing an installation state of the level crossing obstacle detection device 70 + 80 on the level crossing and an outline of the operation of the distance measuring unit 80, and FIG. 2 is a flowchart showing a signal processing procedure at the time of distance measurement. FIG. 3 is a waveform example of each signal during distance measurement.
Hereinafter, the installation of the device at the level crossing, the series of operations at the time of crossing the level crossing, and the distance measurement operation therein will be described in order.

The level crossing obstacle detection device 70 + 80 (see FIG. 1) may be entirely installed in the track so that the entire area of the level crossing road 10 can be seen. However, in most cases, the rotation mechanism unit 70 is configured so that the number of structures in the track is reduced. Is installed in the track, but the portion that may be outside the track is stored in the instrument box 12 beside the track and connected to the rotation mechanism unit 70 by a cable for power supply or signal transmission. Of the distance measurement unit 80, the transmission antenna 54 and the reception antenna 55 are mounted on the rotation mechanism unit 70, the signal processing device 88 is stored in the instrument box 12, and the other circuit portions are appropriately stored in any one of them.
In addition, for the operation check and azimuth correction of the rotation mechanism unit 70, and the operation check and distance correction of the distance measurement unit 80, reflectors 41 are erected at important points of the crossing, for example, at the four corners.

When the train approaches the railroad crossing, a warning sound is emitted by the railroad crossing safety device and an operation start command is issued to the railroad crossing obstacle detection device 70 + 80. When about 4 seconds have passed since then, the crossing fence 11 is lowered by the level crossing safety device, and the level crossing 10 is blocked.
During these 4 seconds, the level crossing obstacle detection device 70 + 80 performs one propagation wave irradiation and distance measurement for the level crossing twice. That is, while the distance measurement unit 80 measures the distance every 4 °, the rotation mechanism unit 70 swings 180 ° for the reciprocation.

  At this stage, the presence / absence determination of the obstacle is not performed, and the distance and direction are corrected by comparing the measurement distance and the measurement direction related to the reflector 41 with known values (see Patent Document 1). Specifically, the calculation parameters for correction used for calculating the distance and direction are finely adjusted. What is the correction? This is performed only when the reflection plate 41 can be detected, and is not performed when detection of the reflection plate 41 is hindered by a passerby or the like. In this level crossing obstacle detection device 70 + 80, since the irradiation and measurement for correction are performed a plurality of times each time the operation is started, detection of the reflector 41 is likely to be hindered by passersby. Even if there is, corrections are frequently made.

  After that, that is, after the barrier bar 11 is lowered, a propagation wave irradiation and a distance measurement for the railroad crossing by the railroad crossing obstacle detection device 70 + 80 are repeated every 2 seconds. For each irradiation, the rotation mechanism unit 70 swings 180 ° with azimuth detection, and the distance measurement unit 80 performs four-degree distance measurement 45 times. Based on the distance information obtained in this way and the azimuth information obtained by the rotation mechanism unit 70, it is determined whether or not there is an obstacle in the level crossing. This determination is made by tracing a sequence of 45 distance data to grasp the shape and size of the detection target 13, and determining whether the detection target 13 is a car or a person based on the trace. The determination accuracy can be increased (see Patent Document 1).

  If any part of the road crosses the barrier fence 11 on the railroad crossing 10, it is determined that there is an obstacle in the railroad crossing. If it is 6 seconds, the level crossing obstacle detection device 70 + 80 according to the present invention can determine that the rotation is about three times. Therefore, in order to improve the determination accuracy and minimize the detection of obstacles as much as possible, a majority decision is adopted for this level crossing obstacle detection device 70 + 80, and there are obstacles in two or more of the three determinations. Is determined, a final determination to that effect is made and an alarm sound is emitted. On the other hand, when the obstacle is detected only once out of three times, it is highly likely that something that has run away quickly or a large piece of paper flying in the wind is detected. It is determined that it is not.

  Finally (see FIGS. 2 and 3), the measurement of the distance d from the rotation mechanism unit 70 to the detection target 13 will be described. The measurement time per time is 44 ms, during which time the distance d2 is calculated sequentially by the two-frequency CW method (steps ST1 to ST6), and the distance is measured by the FMCW method. The distance d3 is calculated (steps ST7 to ST9), and the distances d2 and d3 are integrated so as not to exceed the detection range and the final distance d is calculated (step ST10). To ST11) are performed.

  Specifically, first, the signal processing device 88 sets the measurement mode switching signal M to the modulator 81 to the two-frequency CW mode M1 (step ST1 in FIG. 2). Then (see the left part of FIG. 3), an irradiation wave S1 having a low frequency f1, for example 24.150 GHz, is emitted from the transmitting antenna 54 into the railroad crossing, and a reflected wave R1 having substantially the same frequency is applied to the receiving antenna 55. The beat signals b1 are extracted by the beat signal extraction circuit 56 + 57. This beat signal b1 is taken into the signal processor 88 for the first 14 ms out of 44 ms, and data is accumulated. The signal sampling time Ts at that time is, for example, 10 μs. Thereafter, FFT processing is performed on the accumulated data, and the fixed phase φ1 of the reflected wave R1 is obtained from the frequency spectrum after the FFT processing (step ST2 in FIG. 2).

  Next, the signal processing device 88 sets the measurement mode switching signal M to the modulator 81 to the two-frequency CW mode M2 (step ST3 in FIG. 2). Then (see the central portion of FIG. 3), an irradiation wave S2 having a high frequency f2, for example 24.152 GHz, is emitted from the transmitting antenna 54 into the railroad crossing, and a reflected wave R2 having substantially the same frequency is received by the receiving antenna 55. The beat signals b2 are received and extracted by the beat signal extraction circuit 56 + 57. This beat signal b2 is taken into the signal processor 88 for 14 ms after 14 ms of 44 ms, and data is also accumulated. Thereafter, the accumulated data is subjected to FFT processing, and the fixed phase φ2 of the reflected wave R2 is obtained from the frequency spectrum after the FFT processing (step ST4 in FIG. 2).

When these phases φ1 and φ2 are aligned, the signal processing device 88 determines the distance d2 in the two-frequency CW system distance measurement. Specifically, the phase difference Δφ = (φ1-φ2) is calculated (step ST5 in FIG. 2), and the distance d2 = c · Δφ / (4π (f1-f2)) is calculated (step ST6 in FIG. 2). ).
Then, the distance d3 in the FMCW system distance measurement is obtained in the last 16 ms out of the 44 ms measurement time per time.

  That is, the signal processing device 88 sets the measurement mode switching signal M to the modulator 81 to the FMCW mode M3 (step ST7 in FIG. 2). Then (see the portion on the right side of FIG. 3), the frequency f3 of the irradiation wave S3 is swept accordingly. The sweep is performed between 24.100 GHz and 24.176 GHz, for example, and the frequency modulation width B = frequency sweep width Δf is 76 MHz, and the frequency modulation period is repeated twice in 16 ms. T = take-in time Tin is 4 ms.

Then, every 4 ms, the beat signal b3 relating to the irradiation wave S3 and the reflected wave R3 is taken into the signal processing device 88 and accumulated, and the accumulated data is subjected to FFT calculation processing, and the frequency after the FFT processing. Beat frequencies fu and fd are obtained from the spectrum (step ST8 in FIG. 2). Since two beat frequencies fu and fd are obtained, if both are in the normal range, they are collected by averaging or the like, and if not, either one is adopted.
When a set of beat frequencies fu and fd are obtained, the signal processor 88 calculates d3 = (c · T / 4 · B) · (fu−fd), and the distance d3 in the FMCW ranging is obtained. Is obtained.

  As described above, since the distance d2 in the two-frequency CW method and the distance d3 in the FMCW method are aligned, finally, the integration calculation to the final distance d is performed. There are various ways of integration, but one simple method that can be performed by arithmetic operation is a method of converting the distances d2 and d3 into integers by the detection range distance dx. Specifically, an integer value dn is calculated by calculating Int (d3 / dx) −Int (d2 / dx) using an Int function that is rounded off to an integer twice (step ST10 in FIG. 2). The distance d is calculated by calculating d2 + (dn · dx) (step ST11 in FIG. 2). Thus, the final distance d is obtained. This is a measurement that is not possible to exceed the detection range distance dx but is accurate to the two-frequency CW method (distance resolution) to the extent possible with the FMCW method, that is, to the place that exceeds the detection range distance dx.

[Others]
The above numerical values are merely examples, and may be changed as appropriate according to the purpose of application, the release of regulations, etc. in practical use.
Further, millimeter waves, microwaves, radio waves in the radar frequency band, and the like are suitable as the air propagation waves.
Further, in the above embodiment, the transmission antenna 54 and the reception antenna 55 are separate from each other. However, a transmission / reception unit using a transmission / reception shared antenna in which they are integrated is well known. It is also possible to adopt it.

  As a method of combining the distance d2 in the two-frequency CW method and the distance d3 in the FMCW method, in addition to the above-described method, for example, the distance measurement accuracy of the FMCW method is ± 2 m, and the measurement of the two-frequency CW method is performed. If the distance accuracy is ± 10 cm, d3 + d2 is set to d if d3 ≧ dx + 2, and d2 + d3 is set to d if dx−2 ≦ d3 <dx2 and 2-d2 ≧ 0, and dx−2 ≦ d3 <dx2 For example, there is a method for obtaining the distance d by setting d2 to d if 2-d2 <0, and d2 to d if d3 <dx + 2. This also makes it possible to perform measurement exceeding the detection range distance dx of the two-frequency CW method while maintaining the distance measurement accuracy of the two-frequency CW method.

The embodiment of the present invention shows a structure of a level crossing obstacle detection device, wherein (a) is a perspective view of the level crossing obstacle detection device and a level crossing where the level crossing obstacle detection device is installed, and (b) is a block diagram of a distance measuring unit. It is a flowchart which shows the signal processing procedure for distance measurement. It is an example of a waveform of each signal at the time of distance measurement. (A) is a perspective view of a level crossing obstacle detection device and a level crossing provided with the conventional level crossing obstacle detection device, and (b) is a perspective view showing an operation state of the level crossing obstacle detection device. (A) is a block diagram of a general two-frequency CW system distance measuring sensor, and (b) is an explanatory diagram of a distance measurement state using the same. (A) is a block diagram of a general FMCW distance measuring sensor, and (b) is an explanatory diagram of a distance measurement state using the same.

Explanation of symbols

10 ... Railroad crossing, 11 ... Barrier, 12 ... Instrument box, 13 ... Object to be detected, 14 ... Virtual image,
40 ... Rotation mechanism part (crossing obstacle detection device), 41 ... Reflector,
50 ... 2 frequency CW type distance measuring sensor (crossing obstacle detection device),
51 ... Modulator, 52 ... High frequency oscillator, 53 ... Signal distributor, 54 ... Transmitting antenna,
55 ... receiving antenna, 56 ... mixer, 57 ... low pass filter, 58 ... signal processing device,
60 ... FMCW range sensor, 61 ... modulator, 68 ... signal processing device,
70: Rotation mechanism (railway crossing obstacle detection device),
80 ... Distance measuring unit (crossing obstacle detection device), 81 ... modulator, 88 ... signal processing device,
M ... measurement mode, f ... frequency, s ... transmission signal, S ... irradiation wave,
R ... reflected wave, r ... received signal, b ... beat signal, φ ... phase, d ... distance

Claims (1)

  A distance measurement unit that irradiates the level crossing with an airborne wave and receives the reflected wave to measure the distance to the detection target, and a rotation that rotates the irradiation direction horizontally and detects the direction of rotation at any time And a crossing that determines whether or not there is an obstacle in the crossing based on the distance information obtained by the distance measurement unit and the azimuth information obtained by the rotation mechanism unit. In the obstacle detection device, the distance measuring unit can fix the frequency of the aerial propagation wave at a high or low frequency, or can sweep without fixing, the irradiation wave, and the reflected wave. A beat signal extraction circuit for extracting a beat signal according to the above, and a phase of the beat signal is obtained by fixing the frequency of the air propagation wave to a high frequency by the modulation means, and a frequency of the air propagation wave is obtained by the modulation means The low The frequency of the beat signal is fixed and the phase of the beat signal is obtained, the distance in the two-frequency CW method is obtained from the phase difference thereof, and the frequency of the airborne wave is swept by the modulation means to obtain the FMCW from the frequency of the beat signal. A signal processing device for calculating the distance information by determining the distance in the system and further combining the distance in the FMCW system and the distance in the two-frequency CW system as exceeding the detection range and not exceeding the detection range, respectively. A crossing obstacle detection device characterized by comprising:

Images