JP2898356B2 - Traffic flow measuring method and traffic flow measuring device by laser beam cutting method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for grasping and managing road conditions, and more particularly to a traffic flow measuring method using a laser beam cutting method and a traffic flow measuring device for implementing the method. Things.

[Conventional technology]

In planning and operating road traffic, measurement of traffic flow is indispensable to grasp traffic demand and traffic conditions, and to evaluate the results of road design and the effects of traffic control. As a method of measuring the traffic flow, an ultrasonic sensor has been generally used, and has a good track record among the traffic flow measurement sensors. However, since the ultrasonic sensor measures the traffic flow of the vehicle based on the time occupancy by point measurement, a measurement pulse output is emitted between the vehicles,
In addition, there is a drawback that a measurement error occurs when the vehicle is continuously fired at a vehicle that is stopped due to traffic congestion, and image processing that can perform measurement over a wider range in recent years because it is not possible to perform wide-area measurement. Sensors have also been studied, and some image processing sensors using natural lighting have reached the stage of practical use.

[Problems to be solved by the invention]

However, this type of image processing sensor uses sunlight in the daytime,
At night, natural lighting such as headlights and tail lamps are used to detect vehicles based on the luminance difference between the vehicle and the road surface. (A) Vehicles with a small luminance difference from the road surface (b) Vehicles and street trees Influence of shadows (c) Non-lighting vehicles at twilight or at night (d) Various effects such as anti-image due to mirroring of wet road surface easily cause measurement errors of tens of percent.

Further, the image processing sensor using natural lighting has a problem that since the programs used during the daytime and nighttime are different, it is difficult to determine the switching time of the program at dusk, and the error increases.

The present invention has been made in view of the above problems,
In recent years, with technological advances such as higher output of semiconductor lasers and higher sensitivity of CCD cameras, laser light that detects the vehicle by detecting the difference in altitude between the vehicle and the road surface by light cutting method using illumination by laser light It is an object of the present invention to propose a traffic flow measurement method using a cutting method and to provide a traffic flow measurement device used in the measurement method.

[Means for solving the problem]

(1) Principle of Traffic Flow Measurement Method by Light Cutting Method As shown in FIG. 1, a laser beam emitting device 2 and a CCD camera 3 of a traffic flow sensor 1 are installed above a road surface b to be measured and a laser beam. The beam emitting device 2 and the CCD camera 3 are located at a certain distance from each other. And
The light beam L1 on the light-emitting side and the light beam L2 on the light-receiving side are
It is an essential condition to have an angle θ for each position.
The semiconductor laser generator 8 that constitutes the laser beam emitting device 2 outputs a laser beam output from a road surface b by an appropriate optical system.
Are spread in the direction in which the vehicle flows, to form a planar fan-shaped beam B having an expansion angle α1, and project the beam onto the road surface b to be measured. The light beam L1 of the fan-shaped beam B (light emission side) is reflected from the road surface b or the vehicle a on the road surface b and forms an image on the image forming surface of the CCD camera 3 (see FIG. 4).

When there is no vehicle a on the measured road surface hb, the image A of the reflected (light receiving side) light beam L2 of the fan beam is a straight line (see arrow P in FIG. 4), and the vehicle a is on the road surface b. Since the fan-shaped beam B is "cut" by the vehicle a, the image of the reflected beam L2 is displaced in the width direction (arrow W) of the road surface b to be measured according to the reflection surface shape of the vehicle a. (See arrow P2 in FIG. 4). That is, the shooting direction C of the CCD camera 3
On the other hand, in the fan-shaped beam B, the portion on the vehicle a and the portion on the road surface b are shifted in the width direction (arrow w), and
The height difference between the vehicle a and the road surface b can be determined from the difference in the lateral coordinates of the camera 3. Therefore, by extracting this altitude difference as road information, it is possible to detect (a) the presence or absence of a vehicle.

Further, since the pattern of the arrow P2 in FIG. 4 substantially corresponds to the shape of the vehicle a in the vertical direction, (b) vehicle type classification can be performed.

 Furthermore, (c) the vehicle speed can be measured by monitoring the movement time of the pattern.

FIG. 1 shows the measurement state of the first lane.
By scanning the fan-shaped beam B in the width direction W of the road surface b to be measured using the scanning mechanism, a plurality of lanes can be measured. At this time, when considering a vehicle whose lane is being changed, it is needless to say that the swing angle α2 needs to be adjusted so that the scanning beam interval is smaller than the vehicle width of the small vehicle.

The information output from the CCD camera 3 is configured to be output to a control / processing device 20 described later.

(2) Sensitivity of CCD Camera 3 The semiconductor laser generator 8 uses a GaAlAs semiconductor laser (oscillation wavelength: 830 nm) that oscillates at a wavelength near the peak value of the spectral characteristics of the CCD in order to use the output of the laser light at the maximum efficiency. It is preferable to use the near infrared rays used.

The light intensity is calculated according to the visible light as follows.

E = (P · K · τ · ρ) / (L · 2L / n) (1) In the above equation (1), E is the irradiance (reflected light) by the laser light, and P is the light output of the laser light. Power, K = 680 [1m /
W] is the maximum visibility constant, τ is the transmittance of the optical system, ρ is the reflectivity of the subject (vehicle a or the measured road surface b), L is the length of the measured range (road direction), and n is the number of pixels of the CCD camera. (N × n CCD camera), and the coefficient 2 is obtained when the width of the fan-shaped beam B is set to 2 pixels in order to reliably detect the beam.

As a calculation example, P = 1W, τ = 0.8, ρ = 0.3, L = 50m, n = 5
Substituting 12 into equation (1) gives E = 16.7 [Lux]. Therefore, if the lowest illuminance of the subject that can be photographed by the CCD camera 3 is smaller than this, it can be detected. Currently available general-purpose surveillance CCD cameras have a minimum subject illuminance of 1 to 10 Lux, which is within a detectable range.

(3) Removal of sunlight background In the traffic flow measurement method by the laser beam cutting method, CCD
Illumination other than the laser light in the light incident on the camera 3 becomes the background. Among them, sunlight is considered to be the strongest background light and is very strong compared to laser light, so sunlight is removed by the following two methods.

(A) Optical removal using an interference filter The laser light used has a wavelength characteristic of a very narrow bandwidth, and most of the solar light is obtained by using an interference filter having a narrow transmission bandwidth corresponding to the band. Light can be removed. For example, when a laser beam having a wavelength width of 5 nm is used and a corresponding interference filter having a transmission band of 10 nm is used, the illuminance on the road surface due to sunlight is 10 ⁵ Lux (summer,
Sunlight, direct radiation, detection wavelength width of illuminometer = 400 to 1150 nm), and ρ = 0.3 in the same manner as above, the irradiance (reflected light) E ′ due to sunlight in the transmission bandwidth of the interference filter is
It is given by the following equation.

E ′ = (10 ⁵ Lux · 0.3 · 10 nm) / (1150 nm−400 nm) = 400 [Lux] (2) This is obtained by calculating the irradiance (reflected light) by the laser beam given in the above calculation example. Compared to 16.7 [Lux], E '/ E ≒ 24 [times]. This value is for CCD camera 3
It can be seen that the value is such that the background can be sufficiently removed as compared with the resolution for the irradiance.

(B) Removal of the background by data processing (operation) Since the remaining sunlight removed by the interference filter is approximately 24 times the illuminance of the irradiating laser light, the remaining is removed by the control / processing circuit and software. Remove.

Specifically, as shown in the timing chart of FIG. 5, after driving and scanning the step motor of FIG. 2, a background image (see FIG. 6a) of one frame is taken, and then the laser is scanned at the same position. A signal image (see FIG. 6b) of one frame is taken by irradiating light, and a background image is subtracted from the signal image and processed to obtain a measurement image (see FIG. 6c).

[Action]

Thus, according to the traffic flow measuring method by the laser beam cutting method, the light beam is cut from the image data obtained by using the illumination by the laser beam through the optical light selecting means by the interference filter and the post-processing means by the subtraction. Since the altitude difference between the vehicle and the road surface is obtained and detected by the method, reliable measurement can be performed without being affected by natural light. In addition, the processing system is simple, and measurement based on the space occupancy of the vehicle can be performed in real time. Therefore, measurement errors do not occur even on a road surface where the vehicle is congested, and accurate traffic flow can be informationized. it can.

〔Example〕

Hereinafter, an embodiment of a traffic flow measuring device that implements a traffic flow measuring method by a laser beam cutting method according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, the laser beam emitting device 2 and the CCD camera 3 of the traffic flow sensor 1 are supported by a pillar 4 established on the road side or on the road, or installed on the roof or wall of a building near the road. In addition, the laser beam emitting device 2 and the CCD camera 3 are, for example, at the height (H = 10
1212 m) and a fixed distance (l = 2 to 5 m) away from the arm 5 that is horizontally mounted at the position.
The light beam L1 on the light emitting side and the light beam L2 on the light receiving side are angled with respect to each position of the road surface b in the measurement range.
(Depending on the position of the measured road surface b). The CCD camera 3 has a fixed imaging range S including a measured road surface b indicated by a two-dot chain line, and the laser beam emitting device 2 has a structure in which a beam irradiation direction is driven by a scanning mechanism 6 described later. I have.

FIG. 2 shows an example of the scanning mechanism 6 of the laser beam emitting device 2. A semiconductor laser generator 8 controlled by a drive circuit 7 includes a swing substrate 10 mounted on a drive shaft of a step motor 9. The laser beam output is expanded in the direction in which the vehicle a flows on the road surface b to be measured by an optical system in which a cylindrical lens 11 is disposed on the forward light beam L1 of the semiconductor laser generator 8 so that the spread angle α1 Is swung in the width direction W of the road surface b to be measured in the width direction W (arrow α2), and a predetermined lane is sequentially irradiated with the sector beam B by scanning, and the reflected light beam L2 including the irradiation light beam L1 is CC through the interference filter 12 having a selective transmission characteristic corresponding to the irradiation light beam L1
The image is input to the D camera 3 and formed into an image. And CCD
The information output from the camera 3 is transmitted to a control / processing device 20 described later.
Is output to the central control unit CPU.

The above CCD camera 3 uses a GaAlAs semiconductor laser (oscillation wavelength: 830 nm) that oscillates at a wavelength near the peak value of the spectral characteristics of the CCD in order to use the laser light output of the semiconductor laser generator 8 with maximum efficiency. It is preferred to use

FIG. 3 shows an embodiment of the control / processing device 20, which will be described with reference to the operation timing chart of FIG.

The CPU is a central control unit that controls and drives the semiconductor laser generator 8 and the step motor 9 by a control signal so as to correspond to the vertical synchronizing output of the CCD camera 3.
The video signal input to the D camera 3 is converted into a video signal processing circuit 2
1 and output by a processing result output device 22 a processing result usable for traffic flow measurement.
The video signal processing circuit 21 subtracts the background frame signal transferred by the background frame signal storage device 23 by the CCD camera 3 and performs a background removal,
A comparator 25 for removing noise by a comparison output with a preset threshold value 26 and outputting a binary value signal;
The central control unit CP uses the output of the counter 28, which is divided by the horizontal synchronization output of the
It is constituted by a latch 29 for outputting coordinate data to U.

The control / processing device 20 converts the horizontal coordinates into simple one-dimensional waveform data as shown in the pattern of the vehicle a in FIG. 3 by the counter 28 controlled by the horizontal synchronization signal. By inputting the waveform data to the central control unit CPU, processes such as vehicle detection, vehicle type classification, and vehicle speed calculation can be performed.

The laser beam used in the laser beam cutting method according to the present invention is expanded into a fan-shaped beam B, and the irradiance at a position corresponding to the road surface b to be measured is several tens of lux. Because it can be much smaller than the maximum allowable exposure (MPE) set in the proposed safety standard, there is no concern about human eye damage.

Further, in the description of the above embodiment, one laser beam emitting device 2 is arranged on the road surface b to be measured, and the laser beam emitting device 2 is swung in the width direction W of the road surface b to be measured to cope with a plurality of lanes. Although the method of measuring the traffic flow of the vehicle a to be disclosed is disclosed, a plurality of laser beam emitting devices 2 corresponding to each lane of the road surface b to be measured are arranged and measured for each lane, or beyond the lane. Of course, it can be configured to enable measurement of the running vehicle a.

〔The invention's effect〕

The traffic flow measuring method and the traffic flow measuring device by the laser beam cutting method according to the present invention are different from the conventional image processing sensors that detect the vehicle by the luminance difference between the vehicle and the road surface using natural illumination, and are active by the laser light. Since the vehicle can be detected by obtaining the altitude difference between the vehicle and the road surface by the light cutting method using illumination, the problem of the conventional image processing sensor can be solved.

In addition, the processing system is simpler, real-time measurement based on the space occupancy is possible, and the laser light used in the laser beam cutting method of the present invention has low irradiance, so that there is no fear of obstruction to human eyes. It has features such as no
The effect after implementing the present invention is extremely large.

[Brief description of the drawings]

FIG. 1 is a principle diagram showing one embodiment of a traffic flow measuring device for implementing a traffic flow measuring method by a laser beam cutting method according to the present invention, FIG. 2 is a front view of a main part in FIG. 1, and FIG. FIG. 4 is a block diagram showing a configuration of a control / processing device of the same device. FIG. 4 is an explanatory diagram showing a pattern of a vehicle to be measured on a CCD camera imaging plane. FIG. 5 is an explanatory diagram showing driving timing. FIGS. 7A, 7B and 7C are explanatory diagrams showing the operation of the subtracter of the control / processing device. DESCRIPTION OF SYMBOLS 1 ... Traffic flow sensor 2 ... Laser beam emitting device 3 ... CCD camera 4 ... Support, 5 ... Arm 8 ... Semiconductor laser generator, 9 ... Step motor 10 ... Swing board, 11 ... Cylindrical lens 12 ... Interference filter, 20 ... Control / processing device 21 ... Video signal processing circuit 22 ... Processing result output device 23 ... Background frame signal storage device 24 ... Subtractor, 25 ... Comparator 27 ... Oscillator, 28 ... Counter 29 ... Latch, CPU ... Central control device A … Image of reflected light beam, B… fan beam a… vehicle, b… road surface to be measured

Continuation of the front page (56) References JP-A-53-41251 (JP, A) JP-A-53-146618 (JP, A) JP-A-2-68098 (JP, A) Jpn. , U) (58) Fields surveyed (Int. Cl. ⁶ , DB name) G08G 1/00-1/16

Claims (2)

(57) [Claims] 1. A laser beam emitting device and a CCD camera are provided at a predetermined distance above a road surface facing a road surface to be measured, and a flat fan-shaped beam expanded in a direction in which vehicles flow from the laser beam emitting device. The image is projected onto the measurement road surface and captured by the CCD camera via an interference filter having a transmission wavelength characteristic of a bandwidth of a laser beam irradiated with reflected light from the road surface including the fan beam and the vehicle, and a video signal of the CCD camera is taken. A subtraction process of a background image of one frame not irradiated with laser light at the same position from a signal image of one frame irradiated with laser light to obtain a measurement image, thereby obtaining a measurement image by a laser light cutting method. 2. A scanning device for providing a flat fan-shaped beam forming means such as a cylindrical lens for expanding a beam in a specific wavelength band in a direction in which a vehicle flows on an optical axis, and displacing the fan beam in a width direction of a road surface. A laser beam emitting device that constitutes the driving means, and a CCD camera with an interference filter with a transmission wavelength characteristic of the bandwidth of the laser light interposed on the optical axis are provided at a fixed distance above the road surface facing the road surface to be measured. A traffic flow sensor that captures reflected light from a road surface and a vehicle including a fan-shaped beam emitted from a laser beam emitting device to a measured road surface to a CCD camera, and does not output a laser beam from an image output from the CCD camera. A laser beam characterized by being configured by a control / processing device configured to drive and control the laser beam emitting device and the CCD camera while subtracting and removing a background output. Traffic flow measuring device according to the cross-sectional method.