JPH0674959A - Speed measurement device - Google Patents

Abstract

PURPOSE:To provide a space filter type speed measurement device having a light receiver quick in response speed, and an improved light utilization factor. CONSTITUTION:Light is irradiated from an illuminant 1 to a measurement object 2, and the reflected light thereof is received with the first lens 3. This light passes an open diaphragm 4 and made incident on a prism array 7. The light is then separated through the array 7 in two directions alternately at a constant pitch, and separately received with two photo detectors 9. As a result, the speed of the object 2 giving a relative travel can be calculated on the basis of data detected with the detectors 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for contactlessly measuring a ground speed of an automobile or the like by using a spatial filter system composed of a prism or the like, and particularly to an optical system thereof.

[0002]

2. Description of the Related Art Conventionally, a spatial filter type speed measuring device has been known as a device for measuring the ground speed of an automobile or the like in a non-contact manner. As an optical system in this device,
For example, there is one disclosed in Japanese Patent Laid-Open No. 52-143081. In this velocity measuring device, the reflected light from the object to be measured is introduced into the spatial filter system detector through the lens, and a light blocking plate having a small hole on the lens focus between the lens and the spatial filter system detector is provided. It is the configuration provided.

[0003]

However, in such a conventional optical system, since the comb-teeth type photodiode having the function of the spatial filter is used as the photodetector, the area of the photodiode is wide. Become. Therefore, the response speed of the light receiver is slow, it is difficult to cope with the modulation on the light projecting side, and the photodetector is relatively expensive.

In order to speed up the response of the photodetector,
A combination of pure optical spatial filter and high-speed photodetector is effective. As an example using a pure optical spatial filter,
For example, there is a speedometer using a prism type spatial filter as disclosed in JP-A-58-2662. The spatial filter of this velocimeter is composed of a laminated prism, and the light from the object to be measured enters this prism, and the light spreads largely after exiting the prism, so it is difficult to efficiently guide the light to the photodetector. Therefore, there is a problem that the utilization efficiency of light is poor.

As a conventional prism array type spatial filter, there is a spatial filter disclosed in Japanese Utility Model Laid-Open No. 62-133164, in addition to the above-mentioned Japanese Patent Laid-Open No. 58-2662. However, in the above-mentioned conventional prism array type spatial filter, it is difficult to manufacture it accurately because it has a structure in which a plurality of prisms or columnar lenses are stacked. In addition, the light is dispersed by the reflection on the refracting surface and a loss occurs in the amount of received light. Furthermore, since the ratio of the aperture period to the aperture width is not limited, it is inevitably 2: 1 (the ratio of the aperture and the non-aperture of the aperture limiting member is 1: 1), and the triple frequency component of the spatial frequency. Becomes a harmonic noise and causes a deterioration of the SN ratio.

On the other hand, conventionally, as a measure for preventing malfunctions when water is present on an object to be measured, there is a practical use as a 63-190957.
There is a velocity sensor using polarized light as disclosed in Japanese Patent Publication No. However, in such a sensor, since light needs to be incident on the water surface at the Brewster's angle in order to eliminate reflection loss, it is necessary to separate the light projecting unit and the light receiving unit from each other, which results in a large measuring device. There's a problem.

The present invention solves the above-mentioned problems, using a prism array type spatial filter, at low cost, with good manufacturing accuracy, and with a fast response speed of a photodetector, thus improving the utilization efficiency of light. It is an object of the present invention to provide a spatial filter type velocity measuring device aiming at this.

[0008]

In order to achieve the above object, the invention of claim 1 is such that light projecting means for irradiating a measuring object with light and reflected light from the measuring object are alternately arranged at a constant pitch. In a spatial filter type velocity measuring device having an optical element that separates in at least two directions and at least two light receiving elements that separately receive light separated in the two directions, reflected light from the measurement object A light receiving lens for receiving light and an aperture stop provided at a focal position of the light receiving lens are provided, and light passing through the aperture stop is made incident on the optical element. The invention of claim 2 is
A collimator lens is provided between the optical element and the aperture stop to collimate the light passing through the aperture stop and make it enter the optical element. The invention of claim 3 is
The optical element is arranged at a position where an image of the measurement object is formed via the light receiving lens and the collimating lens. According to the invention of claim 4, one condenser lens is arranged between the optical element and the two light receiving elements, and each of the lights separated by the optical element in two directions alternately at a constant pitch, The light is condensed on each of the light receiving elements by the one condenser lens. According to the invention of claim 5, the focal length of the condenser lens is shorter than the focal length of the collimator lens. The invention of claim 6 is
The light projecting means includes a plurality of pulse-modulated infrared light emitting diodes. According to a seventh aspect of the invention, the aperture stop is a slit having a narrow width with respect to the relative movement direction of the measurement object. According to an eighth aspect of the invention, the light projecting means is arranged on both sides of the light receiving lens along the relative movement direction of the measurement object. A ninth aspect of the present invention uses, as the optical element, a prism array in which light emission surfaces having different emission directions are alternately arranged at a constant pitch. According to the invention of claim 10, the prism array is configured such that an angle formed by the optical axes of the light emitting surfaces with respect to incident light is a Brewster angle. According to the eleventh aspect of the present invention, as the prism array, one in which at least one of the light incident surface and the light emitting surface is provided with an antireflection coating is used. According to the invention of claim 12, as the prism array,
At least one of the light incident surface side and the light emitting surface side is provided with an aperture limiting member such that the ratio of the aperture period to the aperture width is 3: 1. According to a thirteenth aspect of the present invention, the prism array includes a light shielding member between the light emitting surfaces having different emission directions. Claim 14
In the invention, the above-mentioned prism array is integrally molded.

[0009]

According to the structure of the first aspect, light is emitted to the object to be measured by the light projecting means, and this light is reflected by the object to be measured and enters the optical element through the light receiving lens and the aperture stop. The incident light is alternately separated in at least two directions at a constant pitch in the optical element, and is separately received by at least two light receiving elements. Based on the data detected by the light receiving element, the speed of the measurement object that is moving relatively can be calculated. According to the structure of claim 2, the light passing through the aperture stop is collimated by the collimator lens and is incident on the optical element. As a result, the light is not dispersed and the light utilization efficiency is improved. According to the structure of claim 3, the light reflected by the measuring object passes through the light receiving lens and the collimating lens, is imaged, and is incident on the optical element arranged at the image forming position. The incident light is alternately separated in at least two directions at a constant pitch in the optical element, and is separately received by at least two light receiving elements. According to the structure of claim 4, the respective lights, which are alternately separated by the optical element in the two directions at the constant pitch, are condensed on the respective light receiving elements by the condenser lens, and the light can be easily condensed. According to the structure of claim 5, the light reflected by the measuring object is incident on the optical element through the light receiving lens and the aperture stop. This light is split into at least two directions in the optical element, and is condensed on each light receiving element by a condenser lens having a focal length shorter than the focal length of the collimator lens. According to the structure of claim 6, by projecting light using the pulse modulation type infrared light emitting diode, the influence of ambient light can be prevented and the SN ratio can be improved. According to the configuration of claim 7, it is possible to reduce the size of the optical filter installed downstream of the aperture stop in the light traveling direction.
According to the structure of claim 8, since the light is projected onto the object to be measured by the light projecting means arranged on both sides of the light receiving lens, the light receiving area is determined by the light receiving lens and the aperture stop. It becomes possible to irradiate light, and the loss of the amount of received light is reduced. According to the structure of claim 9, light collection by the optical element becomes easy. According to the structure of claim 10, there is no reflection loss on the refracting surface of the prism array. According to the structure of claim 11, it is possible to reduce the reflection loss of light at the prism array. According to the configurations of claims 12 and 13, the loss of the amount of received light is reduced and the SN ratio is improved. According to the structure of claim 14, the prism array can be easily manufactured.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment embodying the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of the speed measuring device, and FIG. 2 is a sectional view of the speed measuring device. This velocity measuring device is arranged so as to face a measurement object 2 whose velocity is to be measured, and includes a light source (projection means) 1 including a light emitting diode for irradiating the measurement object 2 with light, and the measurement object 2. An optical system that processes the reflected light of the
It is composed of two photodetectors (light receiving elements) 9 that separately receive the light beams separated and condensed in the respective directions.

The above optical system includes a first lens (light receiving lens) 3 for receiving the reflected light from the measuring object 2 and an aperture stop 4.
An optical filter 5, which is a wavelength selection filter that transmits only light having a wavelength equal to the wavelength of the light source 1 or a polarization filter in a polarization utilizing method, an aperture stop 4 and an optical filter 5.
Second lens (collimating lens) 6 for collimating light that has passed through and prism array (optical element) for alternately separating the reflected light from the measuring object 2 into two directions at a constant pitch
7 and a third lens 8 that causes the separated photodetectors 9 to receive the separated lights. Further, mirrors 10 for improving the light collection efficiency are arranged on the side surfaces of the two photodetectors 9. The aperture stop 4 is a slit having a narrow width with respect to the relative movement direction of the measuring object 2. Further, the prism array 7 is a pure optical spatial filter, and light emitting surfaces having different emitting directions are alternately arranged at a constant pitch.

The light sources 1 are arranged on both sides of the first lens 3 along the relative movement direction of the measuring object 2, and the illumination light is emitted when the distance between the speed measuring device and the measuring object 2 is maximum. It is fixed at a constant inclination with respect to the reflection optical axis so that the light is irradiated to the center of the light receiving area 2a on the measurement object 2 which is most condensed and is determined by the aperture stop 4 and the first lens 3. Although the light sources 1 are arranged on both sides of the first lens 3 in this embodiment, they may be arranged on only one side.

Next, the operation of the above configuration will be described. Light source 1
The light emitted from is reflected by the measuring object 2 that moves relatively in the direction of the arrow in FIG. 1, and this reflected light is centered on the component parallel to the reflected optical axis by the first lens 3 and the aperture stop 4. Only the components with a slight angle are selected. The reflected light collected by the first lens 3 passes through the aperture stop 4, passes through the optical filter 5, is collimated by the second lens 6, and is incident on the prism array 7. Prism array 7
The light incident on is split into parallel light in two directions according to the individual prisms incident on. In FIG. 2, one of the light rays separated in the two directions is shown by a one-dot chain line, and the other light ray is shown by a broken line. The parallel light in these two directions is reflected by the third lens 8
Are focused on the two corresponding photodetectors 9. Mirror 1
With 0, a portion of the light passing through the slit in the long axis direction that cannot be condensed by the third lens 8 is also incident on the photodetector 9.
When the traveling speed is V, the arrangement pitch of the two photodetectors 9 is P, and the magnification of the lens is m, the obtained frequency f is f = (m
/ P) V is used to obtain the periodic signal by taking the differential of the outputs of the two photodetectors 9, and is disclosed, for example, in the above-mentioned Japanese Patent Laid-Open No. 52-143081. By such a general method, the speed of the measurement object 2 can be detected.

By using the optical system having the above structure, the area of the photodetector 9 may be small, and therefore, the detection response becomes fast and the modulated light can be easily dealt with. Moreover, since the gain in the photocurrent-voltage converter can be increased, the SN ratio of the circuit system can be improved. Further, it becomes easy to collect the light emitted from the prism array 7.

Next, a second embodiment will be described with reference to FIG. In this embodiment, a prism array 7 (or an aperture limiting member) as a spatial filter is placed at a position where the object 2 to be measured forms an image through the first lens (light receiving lens) 3 and the second lens (collimating lens) 6. It is arranged.
When the distance to the measurement object 2 fluctuates within a certain range, the image of the measurement object 2 is at an arbitrary distance within the range and the image of the measurement object 2 is the first lens (light receiving lens) 3 and the second lens (collimate). The prism array 7 may be arranged at a position where an image is formed via the lens 6. In addition to the above configuration, the focal length F3 of the third lens 8 is equal to the focal length F of the second lens 6.
It is set to be shorter than 2. In addition, the light source 1 includes the first lens 3 along the relative movement direction of the measuring object 2.
On both sides or on one side of the measuring object 2 when the distance between the speed measuring device and the measuring object 2 is the largest, and the illumination light is most condensed, and is determined by the aperture stop 4 and the first lens 3 on the measuring object 2. It is fixed at a constant inclination with respect to the reflection optical axis so that the center of the light receiving area 2a is irradiated with light.

In the present embodiment, light is emitted from the light source 1 to the center of the light receiving area 2a on the measuring object 2, and the reflected light from the measuring object 2 is imaged by the second lens 6 to form an image forming position. The light is incident on the prism array 7 arranged at. This light is split into light in two directions according to the individual prisms that have entered. The light in the two directions is condensed on the corresponding two photodetectors 9 by the third lens 8 having the focal length F3 shorter than the focal length F2 of the second lens 6.

According to this embodiment, the blur of the image can be suppressed to the minimum, and the spatial filter output obtained on the basis of the contrast of the image, that is, the intensity difference of the light separated by the spatial filter becomes maximum, Signal processing becomes easy. Also,
Since the slit aperture is reduced and an image is formed on the side of the light receiving element, the light receiving area of the light receiving element can be reduced and the response speed becomes faster.
Moreover, an inexpensive light receiving element can be used. When water is present on the object to be measured, even if the specularly reflected light on the water surface passes through the light receiving lens, it is blocked by the slit opening and is not received by the light receiving element, so that the water surface is not erroneously detected. Even if the water surface has waves and is specularly reflected in various directions, most of the specularly reflected light can be blocked, so that erroneous detection can be prevented. At the same time, the measuring device can be significantly downsized.

Next, an embodiment of the prism array type spatial filter will be described with reference to FIGS. In any of the prism array type spatial filters 7 and 17, light is incident on the back surfaces 21 and 31 which are processed into flat surfaces and emitted from the refracting surfaces 22 and 32 which are alternately arranged. In the prism array type spatial filter 17, the refraction surfaces 32 are arranged by alternately changing the inclination with respect to the bottom surface of the filter. The light emitted from the refracting surfaces 22 and 32 of the spatial filters 7 and 17 is adapted to converge on a first point or a second point on the opposing flat surfaces (not shown). The filters 7 and 17 can be easily manufactured as an integral body by molding or the like, and the cost can be reduced.

Another embodiment of the prism array will be described with reference to FIG. In a speed sensor using a spatial filter, in order to avoid the influence of direct reflection from a puddle on the road surface when used as a vehicle speed meter, etc.
In many cases, polarized light is used as shown in Japanese Patent Publication No.
In that case, the refracting surface 2 of the prism array type spatial filter 7
An optical element is arranged so that P-polarized light is incident on 2 and processed so that the angle θ with respect to the optical axis of the refracting surface 22 of the prism array type spatial filter 7 forms a Brewster angle with respect to P-polarized light. Then, the reflected light disappears and the reflection loss on the refracting surface becomes zero theoretically (Brewster's law).
For example, in FIG. 6, the prism array type spatial filter 7
If the refractive index of is 1.51, then the Brewster angle θ = 3
It may be 3.5 (degrees). Further, an antireflection coating may be applied to the incident surface and the reflecting surface of the prism array type spatial filter 7. Thereby, the reflection loss of light can be reduced.

Yet another embodiment of the prism array is shown in FIG.
Will be described. It is known that the ratio of the aperture period T to the aperture width D of the spatial filter 7 is preferably 3: 1. Therefore, in this embodiment, the slits 40 satisfying the condition are attached to the prism array type spatial filter 7. is there. This slit 40 may be arranged on the refraction surface 22 side of the prism array type spatial filter 7, or may be realized by applying metal vapor deposition to the back surface 21.

Yet another embodiment of the prism array is shown in FIG.
Will be described. In this embodiment, the slit 50 is attached to the prism array type spatial filter 27. Partitions 52 functioning as a light shielding plate are provided between the openings 51 of the slit 50. Further, the rear surface 21 of the prism array type spatial filter 27 is provided with a recess 23 having a slit shape so as to fit with the partition 52 of the slit 50. By fitting these, the light enters into one opening 51. The light is always emitted from one corresponding refracting surface 22. By adding the slit 50, it is possible to reduce harmonic noise. Furthermore, in order to reduce the loss of light absorbed by the partition 52 in the prism array type spatial filter 27 and the slit 50, the partition 52 may be mirror-finished.
This can further increase the light utilization efficiency.

[0022]

As described above, according to the invention of claim 1,
Since the reflected light from the object to be measured can be efficiently collected, the area of the light receiver can be reduced, the detection response can be made faster, and the modulated light can be easily dealt with. Further, since a general-purpose photodiode can be used as the light receiver, the cost can be reduced. Since the response speed of the photodetector is fast, the detection speed range is widened and higher speeds can be detected. According to the invention of claim 2, the incident light to the optical element is collimated, so that the light is not dispersed and the utilization efficiency of the light is high. According to the invention of claim 3, the reflected light from the measurement object is incident on the optical element in a state of being imaged, so that the light can be efficiently condensed and the light receiving area of the light receiving element is reduced. Claim 4
According to the invention, the light can be condensed easily, and the light utilization efficiency becomes high. According to the invention of claim 5, it is possible to minimize the blurring of the image of the measuring object on the light receiving element, and to obtain the spatial filter output obtained based on the difference in brightness of the image, that is, the light separated by the spatial filter. The intensity difference is maximized, which facilitates signal processing. Further, since the slit aperture is reduced and an image is formed on the side of the light receiving element, the light receiving area of the light receiving element can be reduced and the response speed becomes faster. And an inexpensive light receiving element can be used. According to the invention of claim 6, the influence of ambient light can be prevented and the SN ratio can be improved. Further, since the projection direction is set so that the illumination light is most condensed on the measurement target, the fluctuation of the received light amount is small with respect to the distance fluctuation between the measurement targets. Therefore, the load on the circuit side such as gain control is lightened. According to the invention of claim 7, since the aperture stop is a slit having a narrow width, the optical filter installed downstream of the aperture stop in the light traveling direction can be made small, resulting in a low cost.

According to the invention of claim 8, the loss of the amount of light received by the light receiving lens is reduced. Further, when there is water on the object to be measured, even if specularly reflected light on the water surface passes through the light receiving lens, it is blocked by the slit opening and is not received by the light receiving element, so the water surface is not erroneously detected. On the other hand, even when there are waves on the water surface and specular reflection is performed in various directions, most of the specular reflection light can be blocked, and therefore false detection can be prevented. At the same time, the measuring device can be significantly downsized. According to the invention of claim 9, the light emitted from the prism array is parallel light, so that it is easy to condense, and the light utilization efficiency becomes higher when the condensing component by the mirror is also added. According to the invention of claim 10, since the reflection loss on the refracting surface becomes almost zero, the light utilization efficiency becomes high. According to the eleventh aspect of the invention, since the loss of the amount of received light is small, the SN ratio can be improved. According to the invention of claim 12, the spatial frequency is 3
Since the doubled component does not become harmonic noise, the SN ratio can be improved. According to the thirteenth aspect of the invention, since the loss of the amount of received light is small, the SN ratio can be improved. According to the fourteenth aspect of the invention, since the prism array is integrally molded, it can be easily manufactured, is inexpensive, and the manufacturing accuracy is improved.

[Brief description of drawings]

FIG. 1 is a perspective view of a speed measuring device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the speed measuring device.

FIG. 3 is a sectional view of a speed measuring device according to a second embodiment.

FIG. 4 is a perspective view of a prism array type spatial filter.

FIG. 5 is a perspective view of a prism array type spatial filter of another embodiment.

FIG. 6 is a diagram showing a refraction state of light in a prism array type spatial filter.

FIG. 7 is a perspective view of a slit and prism array type spatial filter.

FIG. 8 is a perspective view of a slit and prism array type spatial filter.

[Explanation of symbols]

 1 Light Source 2 Measurement Target 3 First Lens 4 Aperture Stop 5 Optical Filter 6 Second Lens 7, 17, 27 Prism Array 8 Third Lens 9 Photo Detector 40, 50 Slit 52 Partition

Claims (14)

[Claims] 1. A light projecting means for irradiating an object to be measured with light,
A spatial filter type having an optical element that alternately separates the reflected light from the measurement object in at least two directions at a constant pitch, and at least two light receiving elements that separately receive the light separated in the two directions. In the speed measuring device, the light receiving lens for receiving the reflected light from the measurement object and the aperture stop provided at the focal position of the light receiving lens are provided, and the light passing through the aperture stop is incident on the optical element. A speed measuring device characterized in that 2. The speed according to claim 1, further comprising a collimator lens between the optical element and the aperture stop, which collimates the light passing through the aperture stop and makes the light enter the optical element. measuring device. 3. The speed measuring device according to claim 2, wherein the optical element is arranged at a position where an image of the measuring object is formed through the light receiving lens and the collimating lens. 4. One condensing lens is arranged between the optical element and two light receiving elements, and each of the lights separated by the optical element in two directions alternately at a constant pitch is 4. The speed measuring device according to claim 1, wherein the light is collected on each of the light receiving elements by a single condenser lens. 5. The speed measuring device according to claim 4, wherein the focal length of the condenser lens is shorter than the focal length of the collimator lens. 6. The speed measuring device according to claim 1, wherein the light projecting means comprises a plurality of pulse modulation type infrared light emitting diodes. 7. The aperture stop is a slit having a narrow width with respect to a relative movement direction of the measurement object, wherein the aperture stop is a slit. Speed measuring device. 8. The light projecting means is arranged on both sides of the light receiving lens along a relative movement direction of the object to be measured. The speed measurement device according to 6 or 7. 9. The optical element is a prism array in which light emitting surfaces having different emitting directions are alternately arranged at a constant pitch.
The speed measuring device according to 7 or 8. 10. The speed measurement according to claim 9, wherein the prism array is configured such that an angle formed by an optical axis of the light emitting surface with respect to incident light is a Brewster angle. apparatus. 11. The velocity measuring device according to claim 9, wherein the prism array has an antireflection coating on at least one of a light incident surface and a light emitting surface. 12. The prism array comprises an aperture limiting member having a ratio of an aperture cycle to an aperture width of 3: 1 on at least one of the light incident surface side and the light emission surface side. The speed measuring device according to claim 9, 10, or 11. 13. The speed measuring device according to claim 9, 10, 11 or 12, wherein the prism array includes a light shielding member between the light emitting surfaces having different emitting directions. 14. The speed measuring device according to claim 9, 10, 11, 12, or 13, wherein the prism array is integrally molded.