JP2001209885A - Number plate reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a number plate reader reading number plate information of a vehicle so as to keep illumination light from not being sensed by human eyes and to reduce the cost and the power consumption of a vehicle managing system provided with the reader. SOLUTION: In a traffic monitoring system 1 provided with an illuminator 13 for illuminating the number plate of a vehicle 8 and a CCD camera 2 for picking up the image of the number plate, an LED or a laser diode generating light including only a wavelength area over a visible limit or light of a central wavelength 900 to 1000 nm is used for the illuminator 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for reading a license plate of a vehicle, which is installed along a road or indoors, and more particularly to a license plate reader in which light illuminating the license plate is not detected by human eyes. .

[0002]

2. Description of the Related Art A license plate reader of a vehicle generally includes a pair of CCD cameras 2 and a lighting device 3 as shown in FIG. Installed beside the road 7 and the vehicle 8
The license plate is read.

FIG. 6 is an enlarged explanatory view of the configuration of the license plate reader shown in FIG.

In FIG. 1, an illuminating device 3 is realized by an LED, a laser diode, a halogen lamp, or the like, and is turned on when the illuminance of the surrounding environment is insufficient according to the synchronous control of the CCD camera 2 by the computer 4. An image of the vehicle 8 is captured by the CCD camera 2 having an optical system including a lens and an aperture (both not shown).

[0005] The image data picked up by the CCD camera 2 is transmitted to a reading device (not shown). The reading device cuts out an image near the license plate from the entire image area of the transmitted video data, and converts the cut out image. By processing
Recognize license plate information. The license plate information obtained by the recognition is transmitted to the computer 4,
Inquiry with registered data to find stolen vehicles,
It is used for grasping traffic conditions such as prediction of arrival time between predetermined points.

The CCD camera 2 captures the reflected light from the license plate, which is the subject, as an image. However, the amount of reflected light is insufficient when the surrounding environment is indoors or outdoors even after sunset. And the license plate cannot be accurately imaged. In such a case, with the lighting device 3 turned on, the CCD camera 2
Of the license plate is performed.

[0007]

Normally, light from an LED or laser diode used as a lighting device is near-infrared light having a center wavelength of 800 to 900 nm. FIG.
(B) shows an example of the light emission characteristics of an LED having a center wavelength of 850 nm.

As can be seen from FIG. 1, the center wavelength is usually 8
The spectral distribution of an optical device that emits near-infrared light of 00 to 900 nm is a visible light region on the shorter wavelength side, 78
It covers a wavelength range of 0 nm or less. Therefore, even at 780 nm, which is the long wavelength side of the visible light region, the light amount is not zero, and there are some individual differences, but the light of the LED is sufficiently recognized by human eyes.

[0009] Therefore, such a lighting device is used, for example, in a traffic monitoring system for detecting a crime vehicle or the like.
Not suitable if its presence cannot be revealed.

In order to solve the above-mentioned problem, a so-called infrared transmission filter that transmits only infrared light and blocks visible light among light emitted from a lighting device has been used. If the infrared transmission filter is provided, for example, at the light emitting portion of the lighting device, the light illuminating the vehicle transmits only the infrared light, so that the illumination light is not perceived by the driver.
Examples of the infrared transmission filter include a plastic filter in which a dye is dispersed in plastic, and a glass filter in which various materials are deposited on glass. In general, a glass filter is expensive while being excellent in infrared ray selection performance and infrared ray transmission performance.

However, the infrared transmission filter does not completely transmit infrared light. FIG. 7 shows transmission characteristics of a typical infrared transmission filter. As can be seen from the figure, the transmittance is almost zero from a low wavelength to 800 nm, and the transmittance rapidly increases from 800 nm,
After 850 nm, the transmittance is maintained at 80%.

For example, when the illumination light from the LED having the emission spectrum shown by the solid line in FIG. 8 is passed through the infrared transmission filter having the transmission characteristic shown in FIG. 7, the spectrum shown by the dotted line in FIG. Illumination light. As a result,
At 800 nm or less, the amount of light becomes zero, so that the illumination light is not recognized by the human eye, but the transmittance of the total transmitted light is 7%.
It is reduced to about 0%.

Accordingly, in order to provide an infrared transmitting filter and obtain sufficient brightness for recognizing the license plate, it is necessary to increase the lighting power of the lighting device or to reduce the number of optical devices such as LEDs constituting the lighting device. , The intensity of the illumination light needs to be increased. On the other hand, if the illumination light intensity is increased, there is a disadvantage that the cost of the illumination device is increased and the power consumption is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a license plate having low cost and low power consumption, because illumination light illuminating a license plate of a vehicle is not detected by human eyes. An object of the present invention is to provide a plate reader.

[0015]

According to a first aspect of the present invention, there is provided a license plate reading apparatus, comprising: an illuminating means for illuminating a license plate of a vehicle; an imaging means for imaging the license plate; In a license plate reader including an image reading unit that reads an image captured by an imaging unit, the illumination unit is an LED or a laser diode that generates light including only a wavelength range equal to or greater than a visible limit.

According to the above arrangement, even when the illumination means illuminates the vehicle in order to obtain the amount of light required for imaging, the light is not perceived by the driver or a third party. In this case, it is not necessary to use a high-cost member such as an infrared transmission filter, and the illumination light from the illumination means can be used without loss.

As a result, the license plate information of the vehicle can be read without being noticed by the driver or a third party, and the cost and power consumption of the license plate reader can be reduced.

According to a second aspect of the present invention, there is provided a license plate reading device, comprising: an illumination unit for illuminating a license plate of a vehicle; an imaging unit for imaging the license plate; and an image captured by the imaging unit. A license plate reading device comprising: an image reading unit that reads the image;
It is an LED or a laser diode that emits light of 0 nm.

According to the above arrangement, even when the illumination means illuminates the vehicle in order to obtain the amount of light required for imaging, the central wavelength of the illumination light from the illumination means is 900 nm or more, so that the light can be used for driving. Is not perceived by a person or a third party. Further, the center wavelength of the illumination light from the illumination means is 1000
Since it is not more than nm, the sensitivity of the imaging means can be made higher than a certain level, and the reflected light from the license plate can be used efficiently. Further, it is not necessary to use a high-cost member such as an infrared transmission filter, and the illumination light from the illumination means can be used without loss.

As a result, the license plate information of the vehicle can be read without being noticed by the driver or a third party, and the cost and power consumption of the license plate reader can be reduced.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
This will be described below with reference to the drawings. Note that members common to the drawings are denoted by the same reference numerals and description thereof will be simplified.

FIG. 1A shows the configuration of a traffic monitoring system 1 (number plate reader, vehicle management system) to which the number plate reader of the present invention is applied.

The traffic monitoring system 1 includes a mounting base 6 provided on a pillar 5 built beside a road 7, and a mounting base 6.
And a lighting device 13 (illuminating means). A loop coil 12 for detecting a passing vehicle is buried under the road 7.

The illuminating device 13 illuminates the license plate of the vehicle 8 when sufficient brightness cannot be obtained by the CCD camera 2 such as at night or indoors. As shown in FIG. 2, the illumination device 13 includes an LED array 9 in which LED elements having a center wavelength of 950 nm are arranged vertically and horizontally, a pulse generation circuit 10 for supplying a pulse voltage to the LED array 9, and an illumination power supply 11. Have been. Note that the lighting device 13 can use lighting means such as a laser diode instead of the LED element,
Further, an optical system such as a lens and a diaphragm may be appropriately provided.

FIG. 1B shows the emission characteristics of an LED element used as the LED array 9 and having a wavelength of 950 nm in a central region. As can be seen from the figure, the LED array 9 has light including only the wavelength region equal to or longer than the visible limit, specifically, the wavelength of the central region is 900 to 1000 nm.
Produces light. With such an LED element, an LED array 9 is provided.
Since the wavelength of the illuminating light from the illuminating device 13 is in a wavelength region equal to or longer than the visible limit, the light is not perceived by a driver or a third party.

In general, in the infrared region, the light receiving sensitivity of the imaging means represented by the CCD camera 2 is lower in the longer wavelength region, but the center wavelength of the illumination light from the illumination device 13 of the present embodiment is 1000 nm or less. Because there is, CCD camera 2
Can be made to have a sensitivity of a certain level or more, and the reflected light from the license plate can be used efficiently.

Furthermore, since there is no loss of illumination light due to the use of a high-cost member such as an infrared transmission filter, it is possible to reduce the cost and power consumption of the traffic monitoring system 1.

Further, as shown in FIG.
Is connected to a license plate reading processing unit 14 (image reading means). The license plate reading processing unit 14
An analog / digital conversion unit for converting an analog video signal sent from the D camera 2 into a digital value, a storage unit for storing the video signal converted to a digital value, and a video signal stored in the storage unit And an image processor for extracting image data of a license plate of the vehicle and reading license plate information (both not shown).

Further, the license plate reading processing section 14
Outputs a control signal for imaging trigger to the CCD camera 2, and outputs a control signal for lighting trigger from the CCD camera 2 to the lighting device 13, whereby LE is output.
The operation (ON / OFF) of the D array 9 and the operation (ON / OFF) of the CCD camera 2 are controlled, and the license plate reading processing unit 14 is connected to a monitor 16 as appropriate.

The loop coil 12 is connected to the traffic monitoring system 1
When a vehicle 8 passing through the vicinity is detected, a vehicle detection trigger signal is output. The vehicle detection trigger signal is transmitted to the vehicle management computer 15, and the vehicle management computer 15 instructs the license plate reading processing unit 14 to read a license plate. Put out.

Upon receiving the above instruction, the license plate reading processing section 14 outputs a control signal to the CCD camera 2 to cause the CCD camera 2 to start imaging, and the illuminating device 13 operates in response to a signal from the CCD camera 2. It is lit.

An analog video signal is sent from the CCD camera 2 during the imaging operation to the license plate reading processing unit 14. The license plate reading processor 14 analyzes the transmitted license plate image by image processing, recognizes the license plate information, and transfers the obtained license plate information to the vehicle management computer 15.

In the above configuration, the traffic monitoring system 1
The operation of is described below.

When the vehicle 8 approaches the traffic monitoring system 1, the loop coil 12 outputs a vehicle detection trigger signal to the vehicle management computer 15, and the vehicle management computer 15
Instructs the license plate reading processing unit 14 to read a license plate.

Upon receiving the above instruction, the license plate reading processor 14 outputs a control signal to the CCD camera 2 to cause the CCD camera 2 to start imaging, and the lighting device 13 is turned on by a signal from the CCD camera 2. Is done. Thus, the lighting device 13 is turned on only when the vehicle 8 is detected, so that the power consumption and the life of the lighting device 13 can be reduced.

In order to detect the vehicle 8, any means can be used without being limited to the configuration of the loop coil 12. For example, a change in the image sent from the CCD camera 2 is monitored, and when any change occurs in the image,
There is also a method of determining that the scene is likely to pass through the vehicle 8. In this case, in order to surely obtain an image including a license plate, it is preferable to continuously or repeatedly perform imaging with the CCD camera 2 while the image changes.

When the vehicle faces the license plate attached to the front of the vehicle 8, the illuminating device 13 illuminates the license plate of the vehicle 8 from a short distance, and the CCD camera 2 captures the license plate from the front. CCD
The image including the license plate captured by the camera 2 is converted into an analog video signal by the license plate reading processing unit 1.
4 to be subjected to image processing. The video signal is appropriately sent to the monitor 16 as a monitor output, and the administrator can check the captured image of the CCD camera 2 through the monitor 16.

Since the LED array 9 can be repeatedly turned on and off at a high speed, the illuminating device 13 is controlled in accordance with the exposure time of the image pickup means, that is, the CCD camera 2.
For example, pulse lighting may be performed at a video rate (a 1/60 or 1/30 second cycle) in accordance with the shutter opening time. In this case, the time during which the lighting device 13 is turned on can be suppressed to a necessary minimum, so that the power consumption of the lighting device 13 can be further reduced. In addition, by employing a pulse lighting method in which a large current is instantaneously supplied to the LED array 9, sufficient brightness can be obtained with a smaller number of LED elements.

The license plate reading processing section 14 converts the input analog video signal into a digital quantity,
Character (number) by binarizing each pixel data
Recognize patterns. Further, as shown in FIG. 4, the CCD camera 2 is adjusted in advance so that the luminance of the reflected light from the character portion of the license plate of the vehicle 8 is close to the lowest luminance level of the light receiving luminance range of the CCD camera 2. It is preferable to keep it.

When the license plate reading processing unit 14 completes the reading of the license plate information,
The CCD camera 2 and the lighting device 13 are controlled so that both the camera 2 and the lighting device 13 are turned off. Further, at this time, the license plate reading processing unit 14
The read license plate information is transmitted to the vehicle management computer 15.

The memory of the vehicle management computer 15 has
The license plate information received from the license plate reading processing unit 14 is stored. If various license plate information is registered in the vehicle management computer 15 in advance, for example, it is possible to determine whether the license plate information of the vehicle 8 matches the license plate information of the stolen vehicle.

The vehicle management computer 15 has a timer therein, adds time information such as a passing time to the license plate information of the vehicle 8, and stores the data in a predetermined storage area.

It should be noted that the traffic monitoring system 1
In some cases, the traffic monitoring system 1 may be installed in several places as well as in several places. In this case, each traffic monitoring system 1 may be connected online by a telephone line or another communication system. Alternatively, the data stored in each traffic monitoring system 1 may be taken out by a writable / readable data carrier or the like, or may be transferred online to another computer. . In this case, if the above-mentioned time information is added to the license plate information, the moving route and the moving speed of the vehicle 8 can be calculated from the time information obtained by the plurality of traffic monitoring systems 1.

The present invention relates to the reading of a license plate of a vehicle. However, the present invention can be applied to all application systems using the license plate, and one example is the above-described traffic monitoring system 1.

Examples of other systems include the following.

(1) A license plate reading device of the present invention is provided in a vehicle, and the obtained license plate information is compiled into a database together with time and vehicle position data to provide traffic information such as road congestion or to register information. A traffic system that detects license plate information that matches the number of a stolen or criminal car.

(2) The license plate reader of the present invention is provided, and while appropriately moving within the industrial waste disposal site, the obtained license plate information is compiled into a database together with time and vehicle position data, and the registered industrial license is registered. An industrial waste treatment plant system that distinguishes between vehicles with waste and unregistered vehicles and detects illegally dumped vehicles.

(3) A vehicle entrance / exit management system that includes the license plate reader of the present invention and manages license plate information of vehicles entering and exiting a parking lot installed in a hotel or the like.

[0049]

As described above, the license plate reading device according to the first aspect of the present invention reads out the image captured by the illuminating means for illuminating the license plate of the vehicle, the image capturing means for capturing the license plate, and the image captured by the image capturing means. In the license plate reading device including the image reading unit, the illumination unit is an LED or a laser diode that generates light including only a wavelength range equal to or greater than a visible limit.

Therefore, even when the illumination means illuminates the vehicle in order to obtain the amount of light required for imaging, the light is not perceived by the driver or a third party. In this case, it is not necessary to use a high-cost member such as an infrared transmission filter, and the illumination light from the illumination means can be used without loss.

Thus, the license plate information of the vehicle can be read without being noticed by the driver or a third party, and the cost and power consumption of the license plate reader can be reduced. Play.

As described above, the license plate reading device according to the second aspect of the present invention provides an illumination device for illuminating a license plate of a vehicle, an imaging device for imaging the license plate, and an image reading device for reading an image captured by the imaging device. In the license plate reader having the means, the illumination means is an LED or a laser diode that generates light having a center wavelength of 900 to 1000 nm.

Therefore, even if the illuminating means illuminates the vehicle in order to obtain the amount of light required for imaging, the central wavelength of the illuminating light from the illuminating means is not less than 900 nm, so that the light is transmitted to the driver or third Is not perceived by others. Further, since the center wavelength of the illumination light from the illumination means is 1000 nm or less, the sensitivity of the imaging means can be made higher than a certain level, and the light reflected from the license plate can be used efficiently. Further, it is not necessary to use a high-cost member such as an infrared transmission filter, and the illumination light from the illumination means can be used without loss.

As a result, the license plate information of the vehicle can be read without being noticed by the driver or a third party, and the cost and power consumption of the license plate reader can be reduced. Play.

The illuminating means of the license plate reader according to the present invention is illuminated only when, for example, a vehicle is detected.

According to this structure, the illuminating means is turned on only when the vehicle is detected and the vehicle appears in the field of view of the imaging means. When the vehicle is not detected, the illuminating means is not lit.

As a result, the time for lighting the lighting means for illuminating the license plate of the vehicle can be suppressed to a short time, so that the power consumption and the life of the lighting means can be reduced.

Further, in the license plate reader according to the present invention, the illuminating means may be turned on, for example, in accordance with the exposure time of the imaging means.

As described above, when the exposure time of the imaging means is extremely short, or when the exposure of the imaging means is performed intermittently rather than continuously, L can be turned on / off at a high speed.
By making use of the characteristics of the ED and the laser diode, the illumination unit is turned on at a timing and a time synchronized with the exposure time of the imaging unit.

This makes it possible to minimize the time required for turning on the illuminating means for illuminating the license plate of the vehicle, thereby reducing the power consumption of the illuminating means. Furthermore, when the exposure of the image pickup means is repeated at high speed and intermittently, a pulse lighting method in which a large current is instantaneously applied to the LED or laser diode as the lighting means is adopted, so that the LED or laser having a smaller number of elements There is an effect that sufficient brightness can be obtained with the diode.

A vehicle management system according to the present invention includes the above-described license plate reader, and manages license plate information obtained from the license plate reader.

[0062] Therefore, the license plate information of the vehicle is collected and managed without the driver or a third party sensing the light illuminating the license plate. The license plate information is stored as a database or compared with registered information as necessary. Further, it is not necessary to use a high-cost member such as an infrared transmission filter, and the illumination light from the illumination means can be used without loss.

As a result, the license plate information of the vehicle can be read, managed and utilized without being noticed by the driver or a third party, and the cost of the lighting device can be reduced and the power consumption can be reduced. It works.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram illustrating an appearance of a traffic monitoring system according to an embodiment of the present invention. (B) is (a)
It is explanatory drawing which shows the light emission characteristic of the LED element used for the illumination device of the traffic monitoring system of FIG.

FIG. 2 is an explanatory diagram showing a configuration of a lighting device of the traffic monitoring system.

FIG. 3 is a block diagram illustrating a configuration of the traffic monitoring system.

FIG. 4 is an explanatory diagram for explaining sensitivity adjustment of a CCD camera of the traffic monitoring system.

FIG. 5A is an explanatory view showing the appearance of a conventional license plate reader. (B) is an explanatory view showing the light emission characteristics of the LED element used in the license plate reader of (a).

FIG. 6 is an explanatory diagram showing a configuration of a conventional license plate reading device.

FIG. 7 is an explanatory diagram showing transmission characteristics of a typical infrared transmission filter.

FIG. 8 is an explanatory diagram showing a spectrum change of illumination light from an LED by the infrared transmission filter.

[Explanation of symbols]

Reference Signs List 1 traffic monitoring system (license plate reader, vehicle management system) 2 CCD camera (imaging means) 8 vehicle 12 loop coil 13 lighting device (lighting means) 14 license plate reading processing unit (image reading means)

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[Procedure amendment]

[Submission date] February 25, 2000 (200.2.2
5)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

Claims (2)

[Claims] 1. A license plate reading apparatus comprising: illuminating means for illuminating a license plate of a vehicle; imaging means for imaging the license plate; and image reading means for reading an image taken by the imaging means. A license plate reader, which is an LED or a laser diode that generates light including only a wavelength region exceeding a limit. 2. A license plate reading apparatus comprising: illuminating means for illuminating a license plate of a vehicle; imaging means for imaging the license plate; and image reading means for reading an image captured by the imaging means. A license plate reader, which is an LED or a laser diode that emits light having a wavelength of 900 to 1000 nm.