JPH06138133A - Spatial filter type speed measuring apparatus - Google Patents

Abstract

PURPOSE:To provide a spatial filter-type speed measuring apparatus of which measuring accuracy can be kept always high even against a change in the uneven situation of a road surface by removing a low spatial frequency component. CONSTITUTION:A beam of light reflected by an object 2 under test is transmitted through a transmissivity distribution filter 11 provided with a transmissivity distribution, and it is received by a photodetector 9. On the basis of an output signal from the photodetector 9, the relative movement speed of the object 2 under test is detected. When the transmissivity distribution of the transmissivity distribution filter 11 is set so as to be reduced from the central part in a filter periodic direction toward both end parts, a low frequency component can be removed even when the situation of a road surface is changed unevenly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial filter type speed measuring device for detecting the ground speed of an automobile or the like in a non-contact manner, and to a technique for improving the measuring accuracy.

[0002]

2. Description of the Related Art A spatial filter type velocity measuring device of this type is used, for example, in an anti-skid control system for automobiles, in which reflected light that changes due to unevenness of the road surface is incident on the light receiving portion of the spatial filter. The relative speed of the road surface is detected from the change in the reflected light caused by the same unevenness as the pitch. When measuring the ground speed using this speed measuring device, when crossing the traffic sign paint or the asphalt joint drawn on the road surface, the low spatial frequency component signal generated by the sudden change of the road surface condition,
It is known to make velocity measurement by the device instantaneously difficult. In order to deal with this problem, for example, as disclosed in Japanese Patent Laid-Open No. 63-233375, attention is paid to the sensitivity pattern of the entire light receiving portion in the spatial filter, and the sensitivity pattern is set in the moving direction of the image. It is known to change symmetrically from the center to the front-rear direction. That is, as shown in FIG. 8 (a), the light receiving portion of the spatial filter 101 on which an image of the road surface is formed is elliptical with a major axis in the moving direction, or as shown in FIG. The width of each filter of the filter 105 is gradually changed in the moving direction. With this configuration of the spatial filter, the amount of light received by the spatial filter can be gradually reduced from the center to both ends in the array direction of the light receiving section, so that the signal component of a low frequency with respect to the center frequency can be reduced. Can be eliminated, and the ground speed can be detected with high accuracy even if the road surface environment changes abruptly.

[0003]

However, in the former elliptical spatial filter 101, as shown in FIG. 9A, a light receiving area on the road surface where a change in the condition of the road surface 104 is imaged on the spatial filter 101. Although it is effective in the case where it covers the entire area 103, the change in the road surface condition is
As shown in FIG. 9B, only a part of the edge of the light receiving area 103 on the road surface, or as shown in FIG. The elliptical effect does not appear, and similarly to the conventional one, there is a problem that a low spatial frequency component occurs and the accuracy of speed measurement deteriorates. Note that FIG. 9 is a perspective view of the optical system of the apparatus, and a hatched portion P indicates a paint portion of the road surface 104 and the like. Further, in the latter spatial filter 105 in which the width of each filter is gradually changed, low spatial frequency components can be removed, but other spatial frequency components are transmitted, resulting in a problem that measurement accuracy deteriorates. .

The present invention solves the above-mentioned problems, and by removing low spatial frequency components, it is possible to always maintain a high measurement accuracy even when the road surface condition changes unevenly. An object is to provide a speed measuring device.

[0005]

In order to achieve the above object, the invention according to claim 1 provides a light source for irradiating a measuring object with light, and a specific spatial frequency component of light from the measuring object. A spatial filter type velocity measuring device comprising a spatial filter for selectively receiving light and detecting a relative moving velocity of the measurement object based on an output signal of the spatial filter, and transmitting the light in a light passing direction upstream of the spatial filter. An optical filter having a rate distribution is provided, and the spatial filter receives light reflected by the measurement object and transmitted through the optical filter. The invention according to claim 2 is characterized in that the spatial filter alternately separates the reflected light from the measurement object into two directions at a constant pitch,
The spatial filter type velocity measuring device according to claim 1, further comprising: two light receiving elements that receive light separated in two directions by the optical element for each direction. According to a third aspect of the present invention, the spatial filter includes two light receiving portions, each of the two light receiving portions has a plurality of light receiving areas, and the light receiving areas are alternately arranged at a constant pitch. The spatial filter type velocity measuring device according to claim 1.

[0006]

According to the structure of claim 1, light is emitted from the light source toward the object to be measured, and the light reflected by the object to be measured passes through an optical filter having a transmittance distribution, and the transmitted light is Among them, only the light of a specific spatial frequency component is selectively received by the spatial filter. This transmittance distribution may be set so that the transmittance decreases from the center to both ends in the spatial filter cycle direction, which allows light with a lower spatial frequency component than that without the transmittance distribution filter. Therefore, the relative movement speed can be measured without being affected by the light of a large low frequency component generated when the road surface condition changes nonuniformly. According to the structure of claim 2, in the above operation, the light transmitted through the optical filter is alternately separated into two directions by the optical element at a constant pitch, and is received by each light receiving element.
Similar to the operation of claim 1, the relative moving speed of the measurement object is detected without being affected by the light of the low frequency component. Since the light from the measurement object is separated into two directions by using the optical element in this way, it is possible to easily collect the light in each light receiving element. According to the configuration of claim 3, the light transmitted through the optical filter is received by the comb-shaped light receiving element, and is not affected by the light of the low frequency component as in the case of the above-described operation of claim 1. Then, the relative moving speed of the measuring object is detected.

[0007]

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 a spatial filter type velocity measuring device. The speed measuring device is a light source 1 including a light emitting diode or the like for irradiating the measuring object 2 with light at a position facing the measuring object 2 requiring speed measurement.
And an optical system that processes reflected light from the measurement target 2 and separates and collects the light in two directions, and two photodetectors 9 that separately receive the lights separated and collected in the two directions. Has been done. The light source 1 is fixed at a constant inclination with respect to the optical axis so that the illumination light is most condensed when the distance between the speed measuring device and the measurement object 2 is maximum.

The above optical system includes a first lens 3 for receiving the reflected light from the object to be measured 2, an aperture stop 4, a wavelength selection filter for transmitting only light having a wavelength equal to the wavelength of the light source 1, and a polarization utilizing system. The optical filter 5, which is a polarization filter, a second lens 6 that collimates the light passing through the aperture stop 4 and the optical filter 5, a transmittance distribution filter 11 having a transmittance distribution, and reflected light from the measurement target 2. Array 7 that separates light in two directions alternately at a fixed pitch
And the third lens 8 that allows the separated photodetectors 9 to receive the separated light. 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.

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 the figure, and this reflected light is reflected by the first lens 3
And the aperture stop 4 selects only the component parallel to the reflected optical axis. The reflected light collected by the first lens 3 passes through the aperture stop 4, then passes through the optical filter 5, is collimated by the second lens 6, and is given an intensity distribution by the transmittance distribution filter 11, and then the prism. It is incident on the array 7. The light that has entered the prism array 7 is split into parallel light in two directions according to the individual prisms that have entered. The parallel light in the two directions is condensed by the third lens 8 on the corresponding two photodetectors 9. The 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 by the mirror 10. Since the periodic signal can be obtained by taking the differential of the outputs of the two photodetectors 9, the Japanese Patent Application Laid-Open No.
The velocity of the measuring object 2 is detected by a general method as disclosed in Japanese Patent Publication No. 143081.

FIG. 2 shows the positional relationship between the transmittance distribution filter 11 and the prism array 7 which is a spatial filter. In the figure, the horizontal axis (position) corresponds to the relative movement direction of the object. The transmittance distribution filter 11 is arranged on the upstream side of the light passing direction of the prism array 7, and the transmittance distribution is set so that the transmittance decreases from the central portion to both ends in the filter cycle direction. This transmittance distribution may be one in which the transmittance distribution changes continuously as shown in FIG. 3, or one which changes stepwise as shown in FIG. The transmittance distribution filter may be configured as shown in FIG. That is,
The filter 11a shown in (a) of the figure is an example in which two identical filter pieces having a certain transmittance are arranged with the vicinity of the reflection optical axis open, and the transmittance distribution has three stages. ,
The filter 11b shown in (b) is an example in which the number of overlapping filter pieces is changed depending on the position so that the transmittance decreases from the center to both ends in the filter cycle direction. By using a plastic sheet or tape as the transmittance distribution filter,
The filter can be easily attached at low cost.

FIG. 6 shows the calculated values of the transmittance characteristics with respect to the spatial frequency in the case where the transmittance distribution filter is added to the differential spatial filter having the slit period number N of 6 and the slit width of 1/3 of the period. ing. Further, the transmittance without the transmittance distribution filter is also shown by a dotted line. When the transmittance distribution filter is provided, the transmittance of low spatial frequency components near 0 is suppressed as compared with the case where the transmittance distribution filter is not provided. Therefore, when measuring the ground speed using this speed measuring device, accurate speed measurement can be performed without being affected by the large low-frequency component signal generated when the road surface changes suddenly. It will be possible.

Next, a second embodiment will be described with reference to FIG. The present embodiment is a velocity measuring device using a comb-teeth shaped light receiving element which has been conventionally used, instead of the optical spatial filter and the light receiving element shown in the first embodiment. Above the optical filter 5, a transmittance distribution filter 11 having a transmittance distribution and a comb-tooth-shaped light receiving element 12 are provided. The light source 1 is fixed at a constant inclination with respect to the optical axis so that the illumination light is most condensed when the distance between the speed measuring device and the measurement object 2 is maximum. The light emitted from the light source 1 is reflected by the measurement object 2, and the reflected light is selected by the first lens 3 and the aperture stop 4 only in the component parallel to the reflected optical axis. The reflected light collected by the first lens 3 passes through the aperture stop 4, passes through the optical filter 5, and is given an intensity distribution by the transmittance distribution filter 11,
The light is received by the comb-shaped light receiving element 12. The speed of the measuring object 2 is detected based on the received light output signal. In the present embodiment as well, similar to the first embodiment, accurate speed measurement can be performed without being affected by a large low-frequency component signal generated when the road surface condition changes abruptly.

[0013]

As described above, according to the invention of claim 1,
By making the transmittance of the spatial filter decrease from the central part to the both ends in the filter cycle direction, a low spatial frequency component generated due to uneven road surface conditions that often exist on the actual road surface. Can be removed. Therefore, it is possible to always measure the speed with high accuracy. Further, since the low spatial frequency component can be removed, the processing circuit for detecting the speed becomes simple, and the cost of the entire apparatus can be reduced. Further, by using a plastic sheet or tape as the optical filter, the optical filter having the transmittance distribution can be easily attached at low cost. According to the second aspect of the present invention, in addition to the same effect as the above, by using the optical element, the light can be condensed easily and the light utilization efficiency is improved. According to the invention of claim 3, even if a comb-tooth shaped light receiving element which has been generally used in the past is used,
The same effect as that of the invention can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of a spatial filter type velocity measuring device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a positional relationship between a transmittance distribution filter and a spatial filter of the apparatus.

FIG. 3 is a diagram showing a transmittance distribution state in a transmittance distribution filter.

FIG. 4 is a diagram showing a transmittance distribution state in a transmittance distribution filter.

FIG. 5 is a diagram showing an example of a transmittance distribution filter,
(A) is an example in which the transmittance distribution has three levels, and (b) is an example in which the transmittance distribution has multiple levels.

FIG. 6 is a diagram showing a transmission characteristic of a spatial frequency in a spatial filter.

FIG. 7 is a perspective view of a spatial filter type velocity measuring device according to a second embodiment.

FIG. 8 is a diagram showing a light receiving portion of a conventional spatial filter,
(A) shows an ellipse, (b) shows what gradually changed the width of each filter.

FIG. 9 is a diagram showing a change in road surface condition when speed is measured using a conventional elliptical spatial filter, and FIG. 9A shows a case where the road surface condition changes over the entire light receiving area on the road surface. (B) shows the case where only a part of the light receiving area on the road surface changes, and (c) shows the case where only the central portion of the light receiving area on the road surface changes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Object to be measured 7 Prism array 9 Photodetector 11 Transmittance distribution filter 12 Comb-shaped photodetector

Claims (3)

[Claims] 1. A light source for irradiating a measurement object with light, and a spatial filter for selectively receiving light of a specific spatial frequency component of light from the measurement object, and an output signal of the spatial filter. In the spatial filter type velocity measuring device for detecting the relative moving speed of the measurement object based on, an optical filter having a transmittance distribution upstream of the light passage direction of the spatial filter, the spatial filter, by the measurement object A spatial filter type velocity measuring device, characterized in that light reflected and transmitted through the optical filter is received. 2. The spatial filter receives an optical element that separates the reflected light from the object to be measured alternately into two directions at a constant pitch, and receives the light separated into two directions by the optical element in each direction. The spatial filter type velocity measuring device according to claim 1, further comprising two light receiving elements. 3. The spatial filter comprises two light receiving parts, each of the two light receiving parts has a plurality of light receiving regions, and these light receiving regions are alternately arranged at a constant pitch. The spatial filter type velocity measuring device according to claim 1, wherein the velocity measuring device is a spatial filter type velocity measuring device.