JPH01260366A - Space filter type speed detector - Google Patents

Abstract

PURPOSE:To enable stable highly accurate detection of speed under varied conditions, by providing a space filter with a wavelength selecting means to remove effect of extraneous light on the speed detection. CONSTITUTION:An infrared monochromatic ray with a specified wavelength band is irradiated to a measuring field of view of an object 7 to be measured such as a road surface from a light emitting diode 2. A reflection optical image of the infrared monochromatic ray corresponding to the measuring field of view is focused onto a space filter detector 4 with an objective lens 1 through an interference filter 3, which has a pass area somewhat broader than a half width of a radiation spectrum centered on the center wavelength of the light emitting diode 2. An output of the space filter detector 4 is applied to a signal processing circuit 6 through a pre-amplifier 5.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a speed detection device that optically detects the relative speed to an object to be measured in a non-contact manner using a spatial filter method. The present invention relates to a spatial filter speed detection device that measures speed with high precision without being affected by light.

[Prior Art] As a vehicle speed detection means, a method that detects the rotational speed of the wheels has mainly been used, but when considering anti-skid control etc., it is possible to detect the rotational speed of the wheels. It becomes necessary to detect speed, for example sensor technology; vol 6. No 7 (1986) p p 6
The spatial filter type speed detection devices described in Nos. 2 to 67 are attracting attention.

FIG. 3 shows the configuration of this conventional spatial filter type speed detection device, in which the surface of the object 7 to be measured, such as a running road surface, is irradiated with light from light g8, and an optical image of the object 7 to be measured is formed by the lens 1. It is adapted to be focused onto a spatial filter detector 4.

The detection signal from the spatial filter detector 4 is amplified by the preamplifier 5 and processed by the signal processing circuit 6, so that the relative velocity with respect to the object to be measured 7 is detected.

The above-mentioned spatial filter detector 4 has a configuration as shown in FIG. 4, and has a light receiving section 10 on the surface of a silicon solar cell.
is formed as a strip pattern.

These light receiving sections 10 have a so-called interdigital shape in which two sets of comb-like patterns are interlocked with each other on the surface of the Si substrate 9.

In this way, the common lead wire 14 provided on the Si substrate 9
Photodiodes are formed independently between lead wires 12 and 13 connected to the light receiving portions 1° arranged adjacent to each other. Therefore, photoelectric conversion signals are obtained between the lead wires 12 and 13 and the common lead wire 14, respectively.

When the object to be measured 7 moves with respect to the spatial filter type speed detection device having such a configuration, the image on the spatial filter detector 4 also moves accordingly. Then, depending on the optical brightness distribution on the surface of the object to be measured 7, a temporal change appears in the detection signal of the lead wires 12 and 13, and a signal that fluctuates at a frequency corresponding to the movement of the optical image of the object to be measured 7 is obtained. .

The projection magnification of the optical image of the object to be measured by the optical system is M.

When the arrangement pitch of the light receiving sections is P, the frequency f of the signal obtained here is given by the following equation.

f=MV/P...(1)
Conventionally, a halogen lamp having a wide emission spectrum in the visible light region is used as the light source 8, and the signal is detected by the spatial filter detector 4, which has high light reception sensitivity in the visible light region. .

[Problems to be Solved by the Invention] This type of speed detection device is often used in the presence of extraneous light other than the light intensity of the light source that illuminates the object to be measured.

Therefore, the extraneous light has the following adverse effect on speed detection by the speed detection device.

First, the intensity of the extraneous light varies greatly over time or location, and the detected current of the spatial filter detector varies significantly due to the variation in the intensity of the extraneous light.

For example, the intensity of the light irradiating the object to be measured differs by nearly two orders of magnitude when the speed detection device is used under sunlight during the day and when it is used at night. Furthermore, there is a large difference in the intensity of light irradiating the object to be measured, whether the speed detection device is used in the sun or in the shade.

In this way, if the intensity of the light that illuminates the object to be measured fluctuates significantly, the preamplifier and signal processing circuit connected to the spatial filter detector will be unable to follow the large fluctuations in the detection current of the spatial filter detector and will become inoperable. I sometimes fall into this situation.

Second, reflected light of external light at a location other than the measurement field of the object to be measured may enter the spatial filter detector as stray light, and the detected value of the speed detection device may change. FIG. 5 is a diagram showing the incidence of reflected light from external light on the spatial filter detector 4 in this case.

As shown in the figure, the external light 15 is reflected at a location other than the measurement field of view of the object to be measured 7, further reflected by the inner wall of the speed detection device, and is incident on the spatial filter detector 4 as stray light.

Since the optical brightness unevenness created by such stray light on the spatial filter detector 4 includes many low spatial frequency components,
This adversely affects speed measurements, especially at low speeds.

Third, a shadow formed by external light may pass through the measurement field of view of the object to be measured, and the detected value of the speed detection device may change. For example, if a vehicle equipped with a speed detection device is illuminated by strong external light such as sunlight, a shadow of a part of the vehicle will be formed within the measurement field of view of the object to be measured, and this shadow will be affected by the movement of the vehicle. The shadow may pass within the measurement field of view and the speed detection device may detect the speed of this shadow. A similar problem may occur when a shadow caused by extraneous light from another object passing nearby passes through the measurement field of view of the object to be measured by the speed detection device.

The influence of shadows formed by extraneous light is particularly noticeable when detecting low speeds.

Fourthly, regarding foreign substances that have a transparent, smooth surface and a higher refractive index than air that exists within the measurement field of the object to be measured,
The detection signal-to-noise ratio may be reduced due to stray light generated by reflection of external light on the surface of this material.

FIG. 6 shows a state in which extraneous light 15 is reflected on the surface of a foreign substance 11 and enters the spatial filter detector 4 as stray light.
There is a puddle that exists on the road surface. When this puddle is irradiated with sunlight, which is the external light 15, the intensity of the light reflected from the surface of the puddle becomes greater than the light diffusely reflected inside or at the bottom of the puddle.

For this reason, this surface reflected light is mixed into the detection light that is the reflected light from the bottom of the puddle, and the spatial filter detector 4
Since the light is incident on the ground, the signal-to-noise ratio decreases, and in some cases, speed detection may become impossible.

The present invention has been made based on the current state of the spatial filter type speed detection device as described above, and its purpose is to eliminate the adverse effects of external light on speed detection, and to provide stable and highly accurate speed detection under various conditions. An object of the present invention is to provide a spatial filter type speed detection device that performs speed detection.

[Means for Solving the Problem] The above object is to use a light source that irradiates light in a predetermined wavelength band as a light source for irradiating the object to be measured, provide a wavelength selection means in the spatial filter, and use the wavelength selection means to control the spatial filter. This is accomplished by focusing only the optical image of the wavelength band of the light source on the detector.

[Function] In the present invention, light in a predetermined wavelength band (for example, infrared monochromatic light) is irradiated from a light source to the measurement field of the object to be measured, and the reflected light from the measurement field is reflected onto the spatial filter detector by the imaging optical system. However, only the optical image of the wavelength band of the light source is focused onto the spatial filter detector by the wavelength selection means provided in the spatial filter.

In this way, the light source irradiates the measurement field of the object with a predetermined wavelength band, and the wavelength selection means focuses the reflected optical image of the object in the predetermined wavelength band onto the spatial filter detector. Therefore, stable speed detection is performed without being affected by intensity fluctuations of external light in a wavelength band different from the predetermined wavelength band. Further, the wavelength selection means also prevents stray light based on external light and shadow components caused by external light from entering the spatial filter detector, and highly accurate detection is performed without false detection.

Furthermore, by selecting the wavelength of the irradiated light from the light source and the angle of incidence with respect to the measurement field of view of the object to be measured, light reflected from the surface of foreign substances (for example, puddles on the road surface) existing on the object to be measured can be reduced, and the Speed detection is performed with high sensitivity.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the present invention.

The same parts are given the same reference numerals as in FIG. 2, which has already been used to explain the conventional spatial filter type speed detection device.

As shown in FIG. 1, an infrared monochromatic light emitting diode 2 is attached to the open end side of the housing 17, and this light emitting diode 2 has a spectral characteristic in which the intensity of the radiation spectrum component of external light is low. , its emission intensity is selected to be relatively high at 50 mW. An objective lens 1 is attached so as to close the opening end of the housing 17, and an optical image of the measurement field of the object to be measured 7 is formed by the objective lens 1.
It is adapted to be focused onto a spatial filter detector 4.

This spatial filter detector 4 is a spatial filter detector that uses, for example, a silicon solar cell and has light receiving sensitivity in the visible light band and infrared light band. The aforementioned light emitting diode 2
The emission wavelength is selected to be a wavelength at which the spatial filter detector 4 has a high light receiving sensitivity.

In the housing 17, an interference filter 3 is disposed between the spatial filter detector 4 and the objective lens 1. FIG. 2 is a characteristic diagram showing the operating characteristics of the embodiment between wavelength, radiation spectrum intensity, and transmittance. As shown in the figure, the wavelength at which the transmittance of the interference filter 3 is maximum is the wavelength of the light emitting diode 2 The radiation spectrum intensity is set near the center wavelength where it is maximum.

The half-width of the passband of the interference filter 3 is set to be slightly wider than the half-width of the radiation spectrum of the light-emitting diode 2.

The configuration of other parts of the embodiment is the same as the conventional spatial filter type speed detection device already explained using FIG.

In an embodiment with such a configuration, 1 light emitting diode 2 serves as a light source, objective lens 1 serves as an imaging optical system, and interference filter 3 serves as a light source.
constitute the wavelength selection means.

Next, the operation of the embodiment will be explained.

In the embodiment, monochromatic infrared light having a center wavelength of approximately 0.9 μm is irradiated from the light emitting diode 2 onto the measurement field of view of the object to be measured 7 such as a road surface. A reflected optical image of monochromatic infrared light corresponding to this measurement field of view is focused by the objective lens 1 via the interference filter 3 onto the spatial filter detector 4 .

The interference filter 3 disposed between the objective lens 1 and the spatial filter detector 4 has a width slightly wider than the half-value width of the emission spectrum of the light emitting diode 2, centered on the center wavelength of the emission spectrum, as shown in Fig. 2. Since it has a passband, light of wavelengths other than the infrared monochromatic light of one light emitting diode 2 is almost never reflected directly or by the surface of the object to be measured 7 and reaches the spatial filter detector 4 .

Further, when the object to be measured 7 is a road surface, the incident angle of the light emitted from the light emitting diode 2 to the road surface is set so that the light emitted from the light emitting diode 2 is desired to be reflected on the surface of a puddle existing on the road surface. This can be done easily, so even if there is a puddle, the S/N ratio will not decrease and highly sensitive speed detection can be performed.

Furthermore, even if there are particles such as fog or dust floating between the objective lens 1 and the object to be measured 7, the transmittance is high because infrared monochromatic light with a longer wavelength than visible light is used. The object to be measured 7 is irradiated with light from the light emitting diode 2 very efficiently.

Similarly, even if microparticles adhere to the objective lens 1 or the like, infrared monochromatic light is rarely scattered by these particles, and the amount of light reaching the spatial filter detector 4 does not decrease.

In addition, in the example, a case was explained in which a light emitting diode that emits infrared monochromatic light was used as a light source, but the present invention is not limited to the example. Non-monochromatic infrared lamps with a spectrum can also be used. In this case,
G that has light receiving sensitivity in the infrared region as a spatial filter detector
An e-photodiode is used, and an infrared transmission filter is used as a wavelength selection means.

In addition to this, a semiconductor laser can also be used as the light source.

Further, in the embodiment, an interference filter is arranged after the objective lens as a wavelength selection means, but the present invention is not limited to the embodiment, and the interference filter may be arranged in front of the objective lens. I can do it. In this way,
Since the monochromatic light passes through the objective lens, it can solve the problem of chromatic aberration of the objective lens, improve the sharpness of the optical image focused on the spatial filter detector, and improve the S of the detection signal.
N ratio improves.

In addition, the spatial filter detector itself is used as a wavelength selection means.
It may also have wavelength selection characteristics that do not have light receiving sensitivity in the visible light band.

[Effects of the Invention] According to the present invention, without being affected by intensity fluctuations of external light,
Furthermore, it is possible to stably and accurately detect speed without being affected by stray light caused by external light. In addition, high-sensitivity speed detection is always performed without reducing the signal-to-noise ratio due to light reflected from the surface of a foreign substance present on the object to be measured.

Furthermore, by setting the irradiation light from the light source to the long wavelength side, there is no attenuation due to dirt on the opening of the detection device or fog or dust that exists between the detection device and the measured object, and speed detection is always highly sensitive. will be carried out.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a spatial filter in an embodiment of the present invention, Fig. 2 is a characteristic diagram between wavelength, radiation spectrum intensity, and transmittance showing the operation of an embodiment of the present invention, and Fig. 3 is a conventional diagram. FIG. 4 is an explanatory diagram of the spatial filter of the device, FIG. 4 is an explanatory diagram of the spatial filter detector of the conventional device, and FIGS. 5 and 6 are explanatory diagrams showing the influence of extraneous light in the conventional device. 1...Objective lens, 2...Light emitting diode, 3...Interference filter, 4...Spatial filter detector, 5...Preamplifier , 6...
... Signal processing circuit, 7... Defined object. Figure 1 Figure 2 Skin length (,um) Figure 3 / Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. A spatial filter detector including a light source that illuminates an object to be measured, and a plurality of light-receiving elements arranged at a predetermined pitch in the moving direction of an optical image of the object to be measured; A spatial filter is configured with an imaging optical system that focuses the optical image on the spatial filter detector, and a space that detects the relative velocity with the object to be measured based on the photoelectric conversion signal of the spatial filter detector. In the filter-type speed detection device, a light source that emits light in a predetermined wavelength band is used as the light source, and the spatial filter is provided with wavelength selection means, and the wavelength selection means causes the spatial filter detector to detect the wavelength of the light source. A spatial filter type speed detection device characterized in that it is configured so that only a band optical image is focused. 2. The spatial filter type speed detection device according to claim 1, wherein the light source is an infrared monochromatic light source.