JP2015197836A - Method and device for monitoring vehicle speed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable easy measurement of a vehicle travel speed regardless of the length of a vehicle, and proper determination of a timing for photographing the vehicle.SOLUTION: A speed monitoring device 1 comprising a Doppler radar receives a reflection wave of an electric wave transmitted obliquely downwardly toward a vehicle 7 travelling in a direction going away from an installation site, thereby obtaining a Doppler signal, calculates a travel speed from the Doppler signal, and if the travel speed exceeds a speed threshold, outputs a shutter signal to a photographing device 3, such that a numberplate at the rear end of the vehicle 7 can be photographed, when a voltage component of the Doppler signal has a value equal to or lower than a significant value and such a state continues for a reference period of time.

Description

  The present invention relates to a vehicle speed monitoring device used for photographing a vehicle exceeding a speed threshold, measuring traffic during a traffic jam, and the like.

  An apparatus that captures and records a vehicle that has traveled at a speed exceeding a speed threshold is known. For example, the apparatus disclosed in Patent Document 1 installs an imaging device at a predetermined site, measures the traveling speed of the vehicle in a situation where the vehicle approaches, and for a vehicle that exceeds the speed threshold, Along with taking a picture, the license plate at the rear end of the vehicle is also taken.

  In addition, when pulse radar is used to measure the running speed of a vehicle, problems of pulse cracking and vehicle resolution have been pointed out. Pulse cracking is a phenomenon in which the reflected wave does not return sufficiently depending on the vehicle shape or a part of the reflected wave is missing. The problem of vehicle resolution is a problem that if the distance between the preceding vehicle and the following vehicle is short, the two vehicles cannot be distinguished from the other vehicles. In order to solve such a problem, the apparatus disclosed in Patent Document 2 measures the vehicle length from moment to moment while sensing the presence of the vehicle, and the length of the reflected wave holding time according to the measured vehicle length. By changing the above, prevention of pulse cracking and improvement of vehicle resolution are achieved at the same time.

JP-A-4-149700 JP-A-3-231183

In each of the devices disclosed in Patent Document 1 and Patent Document 2, the traveling speed of the vehicle is measured in front of the vehicle approaching the radar. Therefore, the apparatus disclosed in Patent Document 1 cannot solve the above-described problems of pulse cracking and vehicle resolution. Further, when photographing the rear end of a vehicle, the distance that the vehicle travels from the position where the speed is measured to the photographing position is long, and it is not always possible to photograph the rear end of the vehicle when the traveling speed changes midway. There is also a problem of not.
In the apparatus disclosed in Patent Document 2, since it is necessary to change the method of calculating the vehicle speed by measuring the vehicle length from time to time, the processing becomes complicated, and the vehicle that travels at a speed exceeding the speed threshold is correctly photographed. Requires a considerably high-speed processing.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a technique for speed monitoring that can determine the timing for correctly photographing a target portion of a single vehicle regardless of the shape and length of the vehicle. And

The present invention provides a vehicle speed monitoring method and a speed monitoring apparatus.
In the speed monitoring method of the present invention, the radar generates a Doppler signal by transmitting a radio wave from a portion overlooking the rear of the traveling vehicle toward the rear of the vehicle and receiving the reflected wave, The connected signal processing unit determines whether or not the signal intensity of the Doppler signal exceeds a significant value, and when the signal intensity exceeds the significant value, the vehicle is changed between the time point and the change to the significant value or less. And determining whether or not the calculated traveling speed exceeds a predetermined speed threshold, and if so, the state in which the signal intensity is less than or equal to the significant value depends on the traveling speed. A shutter signal is output to a photographing device capable of photographing the vehicle when a predetermined reference period is continued.

  The speed monitoring device of the present invention is installed together with a photographing device capable of photographing the rear end of the vehicle at a part overlooking the rear of the traveling vehicle, and transmits radio waves toward the rear of the vehicle traveling away from the installation part. When transmitting and receiving the reflected wave, a radar that generates a Doppler signal, signal acquisition means for acquiring the Doppler signal from the radar, and when the signal strength of the acquired Doppler signal becomes a significant value, The travel speed represented by the Doppler signal is calculated, and it is determined whether or not the travel speed exceeds a predetermined speed threshold. When the travel speed exceeds, the signal strength changes from the significant value to the value or less. And a shutter for the photographing device when the signal intensity after the change is continued for a reference period determined according to the traveling speed. Those having a signal output means for outputting a degree.

  In the speed monitoring apparatus, the detection means is configured to detect that the signal intensity has changed from the significant value to the value or less after calculating the traveling speed, and the signal output means, You may comprise so that a shutter signal may be output with respect to the imaging device which can image | photograph the said vehicle. Alternatively, the detection unit is configured to detect that the signal intensity has changed from the significant value to the value or less after calculating the traveling speed, and the signal output unit is configured to detect the signal intensity after the change. May be configured to output identification information that enables identification of the traveling speed and the vehicle to an external device when a reference period determined according to the traveling speed is continued.

  In the present invention, since attention is paid to the rear end of the vehicle to be monitored, speed monitoring can be performed regardless of the shape / size of the vehicle and the vehicle length. Also, when the signal intensity of the Doppler signal becomes less than a significant value represents the rear end of the vehicle, and it is found that there is no subsequent vehicle when the reference time continues from there, one vehicle is identified. It is possible to determine the timing for correctly photographing the target portion of the vehicle, for example, the rear end.

Explanatory drawing which shows the example of a use scene of the speed monitoring apparatus of this embodiment. The block diagram of a speed monitoring apparatus. Explanatory drawing of a Doppler signal. Processing procedure explanatory drawing in a signal processing part (control part). The conceptual explanatory drawing of back monitoring.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory diagram illustrating an example of a usage scene of the speed monitoring apparatus according to the present embodiment. The speed monitoring device 1 is installed together with the photographing device 3 on a part overlooking the rear of the traveling vehicle 7, for example, a pillar 5 having a height of 5 to 6 [m] from the road, and is separated from the installation part. The traveling speed of the vehicle 7 traveling in the direction is monitored in the measurement region. The measurement region is a region whose size is determined by the coverage of radio waves transmitted and received obliquely downward from the speed monitoring device 1. In the present embodiment, a measurement region having a size corresponding to the length of almost one vehicle to be monitored in the horizontal direction is formed on the road. The imaging device 3 is positioned so that a target part of the vehicle 7, for example, the installation part of the number plate at the rear end, enters the imaging screen in an area where the vehicle 7 slightly advances in the traveling direction from the measurement area.

  FIG. 2 is a diagram illustrating a configuration example of the speed monitoring device 1. The speed monitoring device 1 includes a radar 10, an ADC (analog / digital converter) 20, a signal processing unit 30, and an interface unit 40 with the imaging device 3. The interface unit 40 includes a wiring component such as a connector.

  The radar 10 is a Doppler radar having an antenna 11 and a Doppler module 12. The radar 10 is configured to form a measurement region having the above-described size on a road and to have specifications having a resolution of an assumed inter-vehicle distance. The “assumed inter-vehicle distance” is a distance between a preceding vehicle and a following vehicle that is assumed based on a speed threshold, that is, a distance at which the installation site of the number plate behind the preceding vehicle is not hidden by the following vehicle. . When the preceding vehicle is traveling at a speed that requires photographing, it is difficult to consider a situation in which the following vehicle is approaching it. Therefore, in this embodiment, the assumed inter-vehicle distance is set to 3 “m”.

In order to satisfy the above specifications, in this embodiment, the antenna 11 having a horizontal directivity of 4.8 degrees and a vertical directivity of 9.6 degrees is used. The Doppler module 12 generates a transmission wave by pulse-modulating a carrier having a frequency of 24.125 [GHz] (wavelength 12 [mm]) with a pulse width of 15 [ns] and a pulse interval of 4 [μs]. 11 and a reflected wave is received and compared to generate a Doppler signal having a Doppler frequency band of 895 [Hz] to 11.28 [kHz].
Under this Doppler frequency band, a traveling speed of 20 [km / h] to 250 [km / h] can be measured.

  By using the radar 10 having the above-described configuration, the coverage of the radio wave becomes a beam. For example, on the road ahead of 15 [m] (30 [m] by reciprocation of the transmitted wave and the reflected wave) A measurement region having a width of 5 [m] and a width of 5 to 10 [m] (including the road surface) in the vertical direction can be formed, and a resolution of 3 [m] or less can be realized.

  As shown in FIG. 3, the Doppler signal generated by the Doppler module 12 is a frequency difference between the transmitted wave and the reflected wave due to the Doppler effect, that is, the Doppler frequency component f1 and the signal intensity of the reflected wave that changes in time series. A voltage component e1 is included. As is well known, the Doppler frequency component f1 represents the traveling speed of the vehicle, and the voltage component e1 represents the shape / size of the vehicle, the traveling position, and the like.

  The ADC 20 acquires a Doppler signal from the Doppler module 12 of the radar 10, digitally samples the acquired Doppler signal at a high speed (sample time 44.8 [ms], number of samples 1024), and can process this with the signal processing unit 30. Convert to data.

  The signal processing unit 30 is an information processing device configured by a field-programmable gate array (FPGA), a digital signal positioner (DSP), or the like. In the present embodiment, an analysis unit 31 and a shutter signal generation unit 32 configured by hardware elements, and a control configured by firmware elements including digital data such as a CPU (Central Processing Unit), a memory, and a computer program. The signal processing unit 30 includes the unit 33.

The signal processing unit 30 is provided with an input terminal IN and output terminals OUT-1 and OUT-2. The input terminal IN is connected to the ADC 20, and the output terminals OUT- 1 and OUT- 2 are connected to the photographing apparatus 3 via the interface unit 40.
The control unit 33 comprehensively controls the operation of each unit of the signal processing unit 30 by reading and executing the digital data recorded in the memory.

The analysis unit 31 acquires the Doppler signal sampled by the ADC 20 and input from the input terminal IN, and performs signal analysis of the Doppler signal. In other words, an FFT (Fast Fourier Transform) function for performing Doppler frequency component analysis in 0.5 [km / h] steps and a function for performing intensity analysis of the voltage component of the Doppler signal are executed. The results of these analyzes are transmitted to the control unit 33 as needed.
Note that the ADC 20 may be configured to be included in the signal processing unit 30.

  The shutter signal generation unit 32 generates a control signal (“shutter signal”) for causing the photographing apparatus 3 to release the shutter, and outputs the shutter signal to the photographing apparatus 3 through the output terminal OUT-1 and the interface 40. As will be described later, information such as measurement time is also added to the shutter signal. The output timing of the shutter signal and the like is controlled by the control unit 33.

The control unit 33 functions as a “detection unit” by cooperating with the analysis unit 31, and functions as a “signal output unit” by cooperating with the shutter signal generation unit 32. A procedure example of processing executed in the control unit 33 will be described with reference to FIG.
The control unit 33 is in a standby state until a Doppler signal is detected (S1: No). Here, “the Doppler signal is detected” means that the Doppler signal is generated by the radar 10, that the Doppler signal is sampled by the ADC 20, and then input to the analysis unit 31 is transmitted to the control unit 33. Say. When the Doppler signal is detected (S1: Yes), the control unit 33 determines whether or not the voltage component e1 of the Doppler signal exceeds a significant value (S2). The “significant value” refers to a value at which the voltage component e1 becomes meaningful as a signal, not a noise level. Specifically, a value indicating that the vehicle has started to enter the measurement area of the radar 10 is a “significant value”.

If the voltage component e1 is not a significant value, the process returns to S1 (S2: No). When the value exceeds a significant value, the traveling speed is calculated based on the analysis result of the Doppler frequency component, that is, the Doppler frequency component f1 shown in FIG. 3 (S2: Yes, S3).
Then, it is determined whether or not the calculated traveling speed exceeds a “speed threshold value” recorded in the memory in advance, that is, a speed set as a speed limit that needs to be recorded by shooting (S4). If not, it is not necessary to photograph the vehicle, and the process is immediately terminated (S4: No). On the other hand, when the traveling speed exceeds the speed threshold, the traveling speed data at that time and the data of the measurement time acquired from the timer (not shown) held by the CPU are held in the memory (S5). ).

The control unit 33 also dynamically determines the reference period based on the calculated traveling speed, and stores this in the memory (S6). “Dynamically” means not a fixed period, but changes from time to time. The “reference period” is a period in which the state in which the voltage component e1 of the Doppler signal is less than or equal to a significant value continues, and the final period is a time point for determining the output timing of the shutter signal to the imaging device 3. Specifically, the reference period is a value obtained by dividing the above-mentioned assumed inter-vehicle distance by the traveling speed. That is, the reference period becomes shorter as the traveling speed is higher. For example, in this embodiment, since the assumed inter-vehicle distance is 3 [m], it is assumed that the traveling speed exceeding the speed threshold is set to 140 [km / h] (38.9 [m / s]). The reference period is 77.1 [ms]. When the traveling speed is higher than that, the reference period is further shortened.
Note that the assumed inter-vehicle distance is set in the memory in advance, and is read by the control unit 33 when the reference period is calculated.

  The control unit 33 stands by when the voltage component e1 of the Doppler signal maintains a significant value (S7: No), and monitors the passage of time from that point when the voltage component e1 is no longer significant. And it waits until a reference period passes (S8: No). When the reference period has elapsed (S8: Yes), the control unit 33 outputs a detection signal indicating that the optimum shooting timing has been detected to the shutter signal generation unit 32. Thereafter, the vehicle data (running speed, measurement time, reference time) held in the memory is discarded, and the process ends (S9). When the shutter signal generation unit 32 receives this detection signal, the shutter signal generation unit 32 outputs the shutter signal to the photographing apparatus 3 via the interface unit 40. In addition, the traveling speed data and measurement time data previously held in the memory are added to the output shutter signal as identification information for enabling identification of the vehicle.

  The photographing device 3 can photograph the license plate at the rear end of the vehicle almost at the center of the photographing screen by releasing the shutter at the reception timing of the shutter signal. In addition, since the traveling speed data and the measurement time data are added to the shutter signal in the process of S9 and output to the photographing device 3, it is possible to identify which vehicle the photographed image belongs to, and the photographed image and the measurement time. Data and traveling speed data can be stored together in one electronic file or transmitted to an external device.

  If the voltage component e1 of the Doppler signal returns to a significant value before the reference period elapses, it is considered that the significant value is continuous and the detection signal is not output. As described above, in the case of a traveling speed that exceeds the speed threshold, for example, 140 [km], it is difficult to realistically think that the assumed inter-vehicle distance with the following vehicle is less than 3 [m]. This is because it can be regarded as missing pulses.

  FIG. 5 monitors the traveling speed of the vehicle 7 traveling in a direction away from the speed monitoring device 1 (that is, rearward monitoring) and photographs the rear end of the vehicle 7 with the photographing device 3 as in this embodiment. It is a figure explaining a state. In FIG. 5, for convenience, the Doppler signal is shown as a signal waveform before sampling by the ADC 20 and processing by the signal processing unit 30.

  In FIG. 5, when the front end of the vehicle 7 starts to enter the measurement area on the road, the Doppler effect appears, and the voltage component of the Doppler signal (voltage component e1 in FIG. 3) starts to change. Eventually, when the voltage component becomes a significant value at point A due to the reflected wave from the roof portion of the vehicle 9, the speed monitoring device 1 determines the traveling speed from the analysis result of the Doppler frequency component (Doppler frequency component f1 in FIG. 3). v is calculated. When the calculated traveling speed v exceeds the speed threshold, the traveling speed v and the measurement time are output to the photographing device 3, and the assumed inter-vehicle distance is divided by the traveling speed v to calculate the reference period Δt. , Keep it in memory.

  In the case of rear monitoring, the intensity of the reflected wave becomes maximum immediately before the rear end of the vehicle 7, and then the voltage component suddenly becomes a significant value or less at the point B that has passed through the measurement region. Therefore, the point B can be detected with relatively high accuracy as compared with the monitoring of the traveling speed of the vehicle that is heading toward the speed monitoring device 1 (that is, forward monitoring). However, although the rear end of the vehicle 7 can be recognized at the point B, it is not known whether there is a following vehicle. Therefore, the speed monitoring device 1 waits until the reference period Δt calculated based on the assumed inter-vehicle distance from the point B, and outputs a shutter signal to the photographing device 3 at the elapsed point C. Thereby, the imaging device 3 can capture the rear end of the vehicle 7 that is not hidden by the presence of the following vehicle, and can reliably capture the license plate.

In such rear monitoring, the traveling speed v is calculated in a period T in which A is the beginning and B point is the end, and when the traveling speed v exceeds the speed threshold, the information is output to the photographing device 3. The end of the reference period Δt can be calculated and held. Therefore, there is a time margin more than in the case of forward monitoring. This means that information such as the shutter signal and the traveling speed v can be output to the photographing apparatus 3 with a relatively lighter load than in the case of forward monitoring, that is, high specifications are not required for the signal processing unit 30. To do.
Further, since it is not necessary to measure the shape and the vehicle length of the vehicle 7 every moment and reflect the result in the correction of the reflected wave, the rear end of the vehicle 7 is hidden by the following vehicle while using almost uniform signal processing. The shutter signal can be output to the photographing apparatus at a timing that is not present. In addition, since the reference period Δt can be dynamically determined according to the calculated traveling speed v, the number plate at the rear end of the vehicle 7 can be reliably photographed regardless of the traveling speed of the vehicle 7. Can do.

  In addition to the above, the advantage of the backward monitoring is that the speed monitoring device 1 and the photographing device 3 are difficult to see from the driver, so that the presence of these devices is not noticed. Therefore, it becomes possible to monitor the vehicle speed in accordance with the actual situation and to photograph the vehicle exceeding the speed threshold. This can contribute to the driver's own safety because the driver who recognizes the photographing device 3 or the like can suddenly step on the brake or suddenly change the traveling course.

  In the present embodiment, an example in which the assumed inter-vehicle distance is 3 [m] and the reference period is calculated by dividing this value by the traveling speed has been described. However, the distance may be shorter than that. Alternatively, a table in which the traveling speed is associated with the reference period corresponding thereto may be created in advance, and the reference period corresponding to the calculated traveling speed may be read from the table and used.

Moreover, although this embodiment demonstrated the example in case both the speed monitoring apparatus 1 and the imaging device 3 were installed in the same support | pillar 5, implementation of installing an imaging device in a site | part different from a speed monitoring apparatus. It is also possible to adopt a form in which the photographing apparatus 3 and another photographing apparatus installed in another part are linked to perform photographing.
For example, the travel speed is measured by a rearward monitoring with a speed monitoring device, and the shutter signal is taken at a position different from the speed monitoring device that can take a picture of the vehicle when the reference period has passed. It is also possible to output to a device.

  Alternatively, the recording device or the communication device is not used when the comparison between the traveling speed and the speed threshold value is not performed, and the shutter signal is not output, and the state in which the voltage component becomes a significant value or less continues for the reference period. For example, the running speed and identification information (measurement time, etc.) for enabling identification of the vehicle may be output to an external device. In such a configuration, the monitoring result of the vehicle monitoring device 1 can be effectively used for monitoring the traffic flow in a traffic jam.

  DESCRIPTION OF SYMBOLS 1 ... Speed monitoring apparatus, 3 ... Imaging device, 5 ... Support | pillar, 7 ... Vehicle, 10 ... Radar, 11 ... Antenna, 12 ... Doppler module, 20 ... ADC 30... Signal processing unit 31... Analysis unit 32. Shutter signal generation unit 33. Control unit 40.

Claims (8)

A method performed by a radar and a signal processing unit connected to the radar,
The radar generates a Doppler signal by transmitting a radio wave toward the rear of the vehicle from a part overlooking the rear of the traveling vehicle and receiving the reflected wave,
The signal processing unit determines whether or not the signal intensity of the Doppler signal exceeds a significant value, and when the signal intensity exceeds the significant value, the vehicle is changed from the time point to the significant value or less. And determining whether or not the calculated traveling speed exceeds a predetermined speed threshold, and if so, the state in which the signal intensity is less than or equal to the significant value depends on the traveling speed. A shutter signal is output to a photographing device capable of photographing the vehicle at a point of time when a reference period determined by
Vehicle speed monitoring method. It is installed together with a photographing device capable of photographing the rear of the vehicle at a part overlooking the rear of the traveling vehicle, transmits radio waves toward the rear of the vehicle traveling away from the installation part, and receives the reflected waves A radar that generates a Doppler signal by
Signal acquisition means for acquiring the Doppler signal from the radar;
When the signal strength of the acquired Doppler signal becomes a significant value, the travel speed represented by the Doppler signal is calculated, and it is determined whether or not the travel speed exceeds a predetermined speed threshold. A detecting means for detecting that the signal intensity has changed from the significant value to the value or less;
A signal output means for outputting a shutter signal to the imaging device when the signal intensity after the change continues for a reference period determined according to the traveling speed;
A vehicle speed monitoring device comprising: The radar forms a measurement area of the size of almost one vehicle to be monitored and has a resolution of an assumed inter-vehicle distance that is a distance between a preceding vehicle and a succeeding vehicle assumed based on the speed threshold. It is a Doppler radar having,
The speed monitoring apparatus according to claim 1. The detection means calculates the traveling speed in a period starting from a time when the signal intensity of the Doppler signal exceeds a significant value in the measurement region, and ending when the signal intensity becomes less than or equal to the significant value, The reference period is dynamically determined from a value obtained by dividing an assumed inter-vehicle distance by the calculated traveling speed,
The speed monitoring apparatus according to claim 3. The assumed inter-vehicle distance is characterized in that the number plate at the rear end of the preceding vehicle is not hidden by the following vehicle,
The speed monitoring apparatus according to claim 4. The signal output means outputs identification information enabling identification of the vehicle to the photographing apparatus together with the shutter signal.
The speed monitoring apparatus according to any one of claims 1 to 5. A radar that is installed in a part overlooking the back of the traveling vehicle, transmits a radio wave toward the rear of the vehicle traveling in a direction away from the installation part, and generates a Doppler signal by receiving the reflected wave; and
Signal acquisition means for acquiring the Doppler signal from the radar;
When the signal strength of the acquired Doppler signal becomes a significant value, the travel speed represented by the Doppler signal is calculated, and it is determined whether or not the travel speed exceeds a predetermined speed threshold. A detecting means for detecting that the signal intensity has changed from the significant value to the value or less;
And a signal output means for outputting a shutter signal to a photographing device capable of photographing the vehicle when the signal intensity after the change continues for a reference period determined according to the traveling speed.
Vehicle speed monitoring device. A radar that is installed in a part overlooking the back of the traveling vehicle, transmits a radio wave toward the rear of the vehicle traveling in a direction away from the installation part, and generates a Doppler signal by receiving the reflected wave; and
Signal acquisition means for acquiring the Doppler signal from the radar;
When the signal strength of the acquired Doppler signal becomes a significant value, the detection means calculates the traveling speed represented by the Doppler signal and detects that the signal strength has changed from the significant value to the value or less. When,
When the signal intensity after the change continues for a reference period determined according to the traveling speed, the identification information that enables the traveling speed and the vehicle to be identified is output to an external device.
Vehicle speed monitoring device.

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