JPH0314197A - Optical vehicle detector - Google Patents

Abstract

PURPOSE:To attain stabilization in detection and the miniaturization of a light receiver by using an infrared pulse laser diode as the light source of a projector. CONSTITUTION:As the light source of the projector 1, the infrared pulse laser diode is used instead of an infrared LED. Namely, a radiation power per element can be increased fro 50mW to 10W by using the infrared pulse laser diode having a feature capable of performing high output and fast pulse modulation. Thereby, stable detection even for a vehicle 14 with worse light reflectance can be performed. Also, it is possible to omit the sample-and-hold circuit, etc., of the light receiver 2 by utilizing the fast pulse modulation, and to miniaturize the light receiver 2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical vehicle detection device that uses light to detect the presence of a vehicle.

BACKGROUND OF THE INVENTION FIG. 4 shows the configuration of an optical vehicle viewing device, and FIG. 5 shows its installation method. Further, FIG. 6 shows temporal changes in the light level at each point in time.

In FIG. 4, 2 is a light receiver, 3 is a signal processing section, 4 is a light receiving element, 5, 6, 7.8 are sample and hold circuits, 9,
10 and 11 are operational amplifiers, 12 is a light receiver output, 13 is a control signal to the light receiver, 24 is a light projector using an infrared LED, and 25 is a control signal to the light projector. Next, in FIG. 5, 2,312.13, 24.25 are the same as in FIG. It is a reflection path of light.

In FIG. 6, d is the irradiation level of the projector, e is the light reception level of the light receiver, 26 to 32 are the light reception levels at each time point, and 34 indicated by diagonal lines is the light level due to external light.

Next, the above conventional example will be explained. First, in FIG. 6, when a vehicle is present with respect to the illumination level d of the projector, the light receiving level of the light receiving element 4 of the light receiver becomes e.

Here, the shaded line 34 is the light reception level due to external light, and unless this influence is eliminated, the vehicle cannot be accurately detected. In FIG. 4, the projector 24 is controlled by the control signal 25 to emit infrared radiation of 1 rn S and 3 m
The irradiation of S is repeatedly stopped (the state is shown in FIG. 6d). The light receiver 2 operates in synchronization with the control of the light emitter 24, and this will be explained using FIGS. 4 and 6.

First, the light reception level 26 at time 0 is held in the sample and hold circuit 5. Next, the sample and hold circuit 6 holds the received light level 27 at time 1, mS. At this moment, the output of the operational amplifier 10 becomes level 27 - level 26 - level 28, and this level 28 is bolded by the sample bold circuit 8. Furthermore, when the sample-and-hold circuit 8 is held, the bold state of the sample-and-hold circuits 5 and 6 is released. Next, when the time reaches 2 mS, the sample and hold circuit 6 holds the light reception level 29, and when the time reaches 3rnS, the sample and hold circuit 5 holds the light reception level 30. At this moment, the output of the operational amplifier 9 becomes level 30 - level 29 - level 31, and the sample and hold circuit 7 holds the level 3]. Here, since the external light fluctuates slowly and is linear over a very short period of time, levels 28 and 32 in FIG. 6 can be considered to be equal. Therefore, the output 12 of the operational amplifier 11 in FIG. 4 is level 31 - level 28 - level 31 - level 32 - level 33, and becomes level 33, which is the light receiving level of pure light from the projector without the influence of external light. The signal processing unit 3 can detect the presence of a vehicle based on the fluctuation of this level 33.

In this way, even the conventional optical vehicle detection device can detect the presence of a vehicle when it passes by.

Problems to be Solved by the Invention However, since the conventional optical vehicle sensing device described above uses an infrared LED as the light source of the floodlight, the light emission output is weak (about 50 mW per infrared LED) and the light output is low. When a vehicle with poor reflection efficiency (such as a vehicle with a black paint color) made an abnormal move such as changing lanes, it could be detected incorrectly. Furthermore, as explained in the above-mentioned conventional example, since a complicated sample-and-hold circuit and its control circuit are required, there is a problem in that there is a limit to the miniaturization of the light receiver.

The present invention solves these conventional problems,
It is an object of the present invention to provide an excellent optical vehicle sensing device that can stably detect even vehicles with poor light reflection efficiency and that allows the receiver to be made smaller than conventional ones.

Means for Solving the Problems In order to solve the above problems, the present invention uses an infrared pulsed laser diode instead of an infrared LED as a light source of a projector.

Therefore, according to the present invention, by using an infrared pulsed laser diode, which has the characteristics of high output (10 W or more) and high-speed pulse modulation, as the light source of the projector, the element 1
The radiation power per unit can be increased from 50 mW to more than IOW, and even vehicles with poor light reflection efficiency can be stably detected. Furthermore, by utilizing high-speed pulse modulation, the sample bold circuit function of the photoreceiver can be omitted and the photoreceiver can be miniaturized.

Embodiment FIG. 1 shows the configuration of an embodiment of the present invention, FIG. 2 shows the installation method of the same embodiment, and FIG. 3 shows temporal changes in the light level at each point in time. In Fig. 1, 1 is a floodlight (infrared pulsed laser diode), 17 is a small capacitor, and 18 is a small capacitor.
is an amplifier, and 2, 3, 412 are the same as in FIG. Next, in FIG. 2, 1 is the same as in FIG. 1, and the other parts are the same as in FIG. 5. In FIG. 6, a is the irradiation level of the infrared pulsed laser diode, and b is the light receiving element 4 of the light receiver.
C is the level of light received after passing through the small capacitor 17. Further, the shaded line 23 is the light receiving level of the light receiving element 4 due to external light.

Next, the operation of one embodiment of the present invention will be explained. First, in FIG. 3, when a vehicle is present at the irradiation level a of the infrared pulsed laser diode, the light receiving level of the light receiving element 4 of the light receiver becomes b. Here, the shaded 2
3 is the light reception level due to external light, and unless this influence is eliminated, the vehicle cannot be detected with high accuracy. 1st
In the figure and FIG. 3, the projector] is 1. as shown in a.
Infrared irradiation is repeated with a pulse width of 100 nS every mS. When a vehicle is present, the light receiving element 4 of the light receiver receives light at a level shown in FIG. Here, while the external light reception level 23 changes very slowly,
The level of light received by the irradiated light from the infrared pulsed laser diode has a pulse width of 100 nS, that is, a frequency component of about 5 MHz. It is very easy to separate signals with widely different frequency bands in this way, and by simply passing the signal through a small-capacity capacitor 17, the received light level 23 completely eliminates the influence of external light. The waveform is as shown in C. The amplifier 18 is an amplifier that amplifies the waveform C to a sufficient size, and its output becomes the output 12 of the optical receiver. Therefore, the signal processing section 3 can detect the presence of a vehicle based on fluctuations in the level of the output 12.

As described above, according to the above embodiment, an infrared pulsed laser diode can be used as a light source of a floodlight, thereby increasing the irradiation output from approximately 50 mW of a conventional infrared LED.
It has the advantage that it is improved over OW and can stably detect vehicles with poor light reflection efficiency. In addition, high-speed pulse modulation of the infrared pulsed laser diode has made it possible to add a high-frequency component to the light receiving level of the photoreceiver. In the example, only the small capacitance capacitor 5) can be removed, and the sample bold circuit and its control circuit as in the conventional example can be completely omitted, which has the effect that the light receiver can be miniaturized.

Effects of the Invention As is clear from the above embodiments, the present invention utilizes an infrared pulsed laser diode as the light source of a floodlight, and thereby emits an overwhelmingly large amount of light compared to conventional floodlights. This makes it possible to stably detect vehicles with poor light reflection efficiency. Furthermore, the receiver circuit is simplified by using high-speed pulse modulation,
The light receiver can be downsized.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an optical vehicle detection device according to an embodiment of the present invention, Fig. 2 is an installation diagram of the same embodiment, Fig. 3 is a signal waveform diagram of a floodlight of the same embodiment, and Fig. 4 is a conventional FIG. 5 is an installation diagram of the optical vehicle detection device, and FIG. 6 is a signal waveform diagram of the floodlight of the detection device. 1... Floodlight (infrared pulsed laser diode)
, 2... Light receiver, 3... Signal processing section,
4... Light receiving element, 5 6,7. -8・・・・・・
・Sample hold circuit, 9.10.11...
Operational amplifier, 12...Receiver output, 13...
...Receiver control signal, i 4...Vehicle, 15
....Reflection path of light when a vehicle is present, 16.
....Reflection path of light when no vehicle is present, 17.
...Small capacity capacitor, 18...Amplifier, 23...Light reception level due to external light, 24...
...Light emitter (infrared LED), 25...Light emitter control signal, 26-33...Light reception level at each time, 34...Light reception level due to external light.

Claims (1)

[Claims] An optical vehicle detection device that has a projector that emits light and a receiver equipped with a light-receiving element that detects the level of reflected light from the vehicle. An optical vehicle detection device that detects a vehicle by applying high-speed pulse modulation with a light emission pulse width of 200 nS or less using a laser diode and detecting changes in the light level of the modulated component.