JPH06265561A - Spatial filter type speed measuring equipment - Google Patents

Abstract

PURPOSE:To provide a spatial filter type speed measuring equipment in which a light emitting element capable of high speed modulation can be employed as a light source for illuminating an object and the speed can be measured accurately. CONSTITUTION:Light emitted from a semiconductor light emitting element 2 capable of intensity modulation is reflected on an object 1 to pass through first and second lenses 3, 4 and impinges on a prism array 5 where the light is split alternately into two directions at a predetermined pitch and then condensed by a third lens 6. The light then passes through two diaphragms and received by two light receiving elements 9. Since the detected light is received by a light receiving system, the light receiving element 9 having small light receiving area can be employed and quick response can be realized.

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 optically measuring the ground speed of an automobile or the like in a non-contact manner, and more particularly to an optical system thereof.

[0002]

2. Description of the Related Art In an optical measuring apparatus, in order to prevent the influence of ambient light, it is common to employ a modulated light system using light whose intensity is modulated as used in a photoelectric switch. Moreover, in order to make the measuring device strong against ambient light,
High-speed modulated light must be used. As one type of such an optical measuring device, there is a velocity measuring device that receives light from a measurement object with a spatial filter and measures a relative movement velocity (see, for example, Japanese Patent Laid-Open No. 52-143081). . Also in this kind of speed measuring device, similar to the above,
In order to prevent malfunction due to the effects of sunlight, street lights, and lighting in tunnels, it is necessary to adopt a modulated light method.

[0003]

However, in this type of spatial filter type velocity measuring device, generally, a comb-tooth type light receiving element is used, and this light receiving element has a large light receiving area and a slow response speed. However, when the modulated light is used for illuminating the measuring object so as to adopt the above-described modulated light system, there is a problem that the modulated light cannot be received at high speed.

The present invention solves the above-mentioned problems, and is an optical system capable of accurately measuring the speed even when a light emitting element capable of high speed modulation is used as a light source for illuminating an object to be measured. Therefore, it is possible to provide a spatial filter type velocity measuring device that is less likely to malfunction due to the influence of ambient light and that can maintain high measurement accuracy even when the distance between the measuring device and the measurement object changes. To aim.

[0005]

In order to achieve the above object, the invention of claim 1 uses a light emitting element capable of intensity modulation as a light source for illuminating an object to be measured, and reflects light reflected from the object to be measured. In a spatial filter type velocity measuring device comprising a light receiving lens for receiving light and a spatial filter for detecting a relative velocity of the measuring object from the light received by the light receiving lens, the light receiving lens is a first lens. An optical element that is composed of a lens group and a second lens group, is arranged so that the focal positions of both lens groups match, and the spatial filter alternately divides light in at least two directions at a constant pitch; A lens having at least two aperture stops arranged in the vicinity of the focal point of the third lens group, and a light beam that has passed through the aperture stop. At least 2 to be received by the respectively separate
It is composed of two light receiving elements.

A second aspect of the present invention is the spatial filter type velocity measuring device according to the first aspect, wherein the at least two aperture stops have a shape narrow in the velocity measuring direction and wide in the direction orthogonal thereto. The invention of claim 3 is at least the above 2
2. The spatial filter type velocity measuring device according to claim 1, wherein the member having one aperture stop is made of one metal member, and is fixed to a printed wiring board on which the light receiving element is fixed and wired. According to a fourth aspect of the present invention, a light-shielding plate having an aperture stop is arranged between the first lens group and the second lens group, and each light divided by the optical element in at least two directions is The spatial filter type velocity measuring device according to any one of claims 1 to 3, wherein the light is incident only on each of the light receiving elements.

[0007]

According to the structure of the above-mentioned claim 1, the light-emitting element capable of intensity modulation irradiates the object to be measured with light, and the light is reflected by the object to be measured, and the light is reflected by the first lens group and the second lens group. The light passes through the lens group and is incident on the optical element. The light incident on the optical element is alternately divided into two directions at a constant pitch in the optical element and is condensed by the third lens group. This light becomes a signal component obtained as a spatial filter. This light passes through the two aperture stops to remove noise components, and then is received by the two light receiving elements separately. The speed of the relative moving measurement object is calculated based on the detection signal from the light receiving element. In this way, since the signal light is received by the light receiving system through the aperture stop, it is possible to adopt a small light receiving area capable of high-speed response. According to the configuration of claim 2, it is possible to block light as a noise component that is not necessary for speed measurement, and
In the direction orthogonal to the velocity measurement direction, even if the aperture stop is wide, it does not affect the characteristics of the spatial filter, and the amount of detected signal increases corresponding to the wide aperture, so that the sensitivity is improved.

According to the third aspect of the invention, the metal member can be grounded to the printed wiring board, and an electrical shield effect can be provided. According to the structure of claim 4, since the light blocking plate having the aperture stop is provided between the first lens group and the second lens group, the light split by the optical element is simultaneously received as a plurality of stray lights. Incident on the device is prevented.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment embodying the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of a spatial filter type velocity measuring device. This speed measuring device
A semiconductor light emitting element 2 which is arranged so as to face the measurement object 1 whose velocity is to be measured, and which is capable of intensity modulation for irradiating the measurement object 1 with light, and a first lens 3 for receiving reflected light from the measurement object 1. A second lens 4 for collimating the light passing through the first lens 3, and a prism array 5 as an optical element for alternately splitting the light in at least two directions at a constant pitch.
A third lens 6 for condensing the divided light, an aperture stop member 8 having two aperture stops 7, and two aperture stops 7
And two light receiving elements 9 that receive the light that has passed through. The focal length of the first lens 3 is f1, and the second lens 4 is
Let f2 be the focal length of the third lens 6 and f3 be the focal length of the third lens 6, so that the focal positions of the first lens 3 and the second lens 4 match, that is, the distance from the first lens 3 to the second lens 4. Both lenses are arranged so that is (f1 + f2). The aperture stop member 8 is arranged at the focal position of the third lens 6, that is, the distance from the third lens 6 to the aperture stop member 8 is f3.

Next, the operation of the above configuration will be described.
The light emitted from the semiconductor light emitting element 2 capable of intensity modulation is reflected by the measuring object 1, and the reflected light is reflected by the first lens 3
And is collimated by the second lens 4 and is incident on the prism array 5. The component parallel to the light receiving optical system in the reflected light from the measurement target 1 is the ratio of the focal lengths of the lens (f2 /
It is reduced in f1) and is incident on the prism array 5. The light that has entered the prism array 5 is split into two directions according to the individual prisms that have entered. The light of the component parallel to the light receiving optical system is condensed by the third lens 6 on the two aperture stops 7 located at the focal position. Then, the light passes through the two aperture stops 7 and is individually received by the two light receiving elements 9. The output of the two light receiving elements 9 is a detected signal, and the velocity of the object 1 which is moving relatively can be calculated by obtaining the periodic signal by taking the differential of these signals. it can. Therefore, the first
Since the lens 3 and the second lens 4 are arranged so that their focal positions coincide with each other, the imaging magnification of the optical system is determined by the ratio (f2 / f1) of the focal lengths of the two lenses, so that the space to be measured The frequency is uniquely determined by the focal lengths of the first lens 3 and the second lens 4 and the period of the prism array.

Next, the reason why the aperture stop member 8 having the two aperture stops 7 is provided will be described. There are lights in various directions from the measurement object 1, and the light of one point of the measurement object 1 that has passed through the first lens 3 passes through a plurality of prism surfaces in the prism array 5 and is split. When the light receiving element 9 is large without the aperture stop member 8, the light may enter the light receiving element 9. As described above, when the light receiving element 9 simultaneously detects the light split through the plurality of prism surfaces, the noise component is included in the signal component obtained as the spatial filter, and the accurate spatial filter signal is obtained. Can not be detected.

On the other hand, as in the present embodiment, by disposing the aperture stop member 8 having the two aperture stops 7 narrow in the speed measurement direction on the front surface of the two light receiving elements 9, the light as the noise component can be obtained. Can be shielded. Aperture stop 7
Has a finite magnitude such that, of the reflected light from the measurement object 1, only the light component that can be regarded as having passed through only one surface of the prism is reflected by one point of the measurement object 1. It is an opening. It should be noted that if the aperture stop 7 is small enough to be about the diffraction limit of light, the optical system will have ideal performance. However, if the aperture stop 7 is small, the received light signal will be weak, so that a strong illumination amount A light emitting element and a highly sensitive light receiving element 9 capable of detecting a weak light signal are required, which is expensive. Therefore, the light from one point of the measuring object 1 passes through the two prism faces, but the light passing through the prism faces required as the signal component is designed to be sufficiently larger than the light as the noise component. do it. For example, if the prism pitch of the prism array 5 is 3 mm, the size of the aperture stop 7 in the speed measurement direction is about 0.5 mm.

FIG. 2 shows details around the aperture stop member 8.
The aperture stop member 8 has a slit shape having two aperture stops 7 and is made of a metal member. The aperture stop member 8 is fixed to a printed wiring board (hereinafter abbreviated as PWB) 10 on which the light receiving element 9 is fixed and wired. The two aperture stops 7 are narrow in the speed measurement direction and wide in the direction orthogonal to the speed measurement direction. With such a shape, most of the light passing through the aperture stop becomes light having a component substantially parallel to the speed measurement direction, while the signal of the orthogonal component has a wider signal amount. Expected to increase. This aperture stop member 8 is a PWB 10.
Since it is fixed to, the electric shield effect can be provided and the S / N ratio of the detected electric signal can be improved. Further, since the present measuring device is a device that detects only the light component that is substantially parallel to the speed measurement direction and the imaging magnification does not change, the distance between the present measuring device and the measuring object 1 varies. However, the fluctuation of the amount of received light is small and the load on the signal processing circuit is light.

FIG. 3 shows a modified example of FIG.
This is a case where the light receiving area of the light receiving element 19 is made smaller than the size of the aperture of No. 7 and a substantial aperture stop is configured by a combination of these. The two aperture stops 17 of the aperture stop member 8 are formed to have the same length as the length of the light receiving element 9 in the speed measurement direction in FIG. In this example as well, the same effect as in FIG. 2 is obtained, and in addition, the light receiving element 19 becomes smaller, so that the cost can be reduced. As described above, by adopting the light receiving element having a small light receiving area, it is possible to deal with high speed modulated light, noise is reduced, and measurement accuracy is improved.

In the above embodiment, the prism array 5
Shows an example in which the light is divided into two and is condensed at two points by the third lens 6 accordingly.
Although the number of the aperture diaphragms 7 is two, the present invention is not limited to this, and a prism array 5 that divides light into three or more divisions can be used. The number of aperture stops 7 of the member 8 is provided corresponding to that, and the number of light receiving elements 9 is also provided.

Next, a second embodiment will be described with reference to FIG. In this embodiment, a compound lens is used as the first lens group 13, and a light shielding plate 18 having an aperture stop is provided between the first lens group 13 and the second lens 4 at the focal position of both lenses.
Is provided. Since the light blocking plate 18 is provided, it is possible to prevent the light split into two by the prism array 5 from entering the plurality of light receiving elements 9 as stray light. Two
When the divided light is incident on the plurality of light receiving elements 9 as stray light, the signal component is reduced and the load on the signal processing circuit is increased, which is not desirable, but the provision of the light shielding plate 18 solves the problem. To be done.

If a lens with large aberration is used,
Light may pass through multiple prism surfaces due to the effects of aberration,
Even if the prism array 5 is configured with a constant pitch, if it operates as a spatial filter having a different period depending on the location, the velocity measurement error will increase. In order to minimize the aberration, it is desirable to construct an aspherical lens,
If the outer shape of the lens becomes large, it becomes difficult to manufacture the lens. Therefore, as in the present embodiment, the first lens having the largest lens outer shape is formed of a spherical lens to form a combined lens (first lens group 13) having a small aberration, thereby suppressing a speed measurement error and measuring accuracy. Can be prevented from dropping.

[0018]

As described above, according to the invention of claim 1,
By providing an aperture stop in front of the light receiving element that receives the light that has passed through the spatial filter from the measurement object, it is possible to block the light of the noise component and, by extension, to use a small light receiving element, so high speed It becomes possible to deal with modulated light, and it becomes a strong device against ambient light. Also, since the focal positions of the first lens group and the second lens group are arranged so as to coincide with each other, the imaging magnification of the optical system is determined by the ratio of the focal lengths of both lenses, so the space to be measured Frequency
It is uniquely determined by the focal lengths of the first lens group and the second lens group and the period of the prism array. In addition to this, since the measuring device detects only light components that are substantially parallel to the velocity measurement direction, and the imaging magnification does not change, the distance between the measuring device and the measurement target such as the road surface varies. Even if the amount of received light is small, the load on the signal processing circuit is light. According to the invention of claim 2, since the aperture stop is narrow in the speed measurement direction and wide in the direction orthogonal thereto, most of the light passing through the aperture stop is light having a component substantially parallel to the speed measurement direction. The light of the noise component is shielded, and the measurement accuracy is improved. Further, since the aperture stop is wide in the orthogonal direction, the amount of detection signal of the directional component increases, so that it is not necessary to use a highly sensitive light receiving element capable of detecting a weak light signal, and the cost can be suppressed.

According to the third aspect of the present invention, the member having the aperture stop is composed of one metal member, and this member can be grounded to the printed wiring board. With this member, the electric shield effect can be obtained. The S / N ratio of the electric signal can be improved. According to the invention of claim 4, since the light-shielding plate having the aperture stop is arranged between the first lens group and the second lens group, each light divided by the optical element becomes stray light. It is possible to prevent the light from entering the light receiving element, and thus the load on the signal processing circuit is reduced.

[Brief description of drawings]

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

FIG. 2 is a detailed view of the vicinity of an aperture stop member in the same apparatus, in which (a) is a front view and (b) is a side sectional view.

FIG. 3 is a detailed view of the vicinity of an aperture stop member in a modified example, (a) is a front view and (b) is a side sectional view.

FIG. 4 is a configuration diagram of a spatial filter type velocity measuring device according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Measurement Object 2 Semiconductor Light Emitting Element 3 First Lens 4 Second Lens 5 Prism Array 6 Third Lens 7,17 Aperture Stopper 8 Aperture Stopper Member 9,19 Photosensitive Element 10 Printed Wiring Board 13 First Lens Group 18 Shading Plate

Claims (4)

[Claims] 1. A light receiving element which uses a light emitting element capable of intensity modulation as a light source for illuminating an object to be measured and receives a reflected light from the object to be measured, and the object to be measured from the light received by the light receiving lens. In a spatial filter type velocity measuring device including a spatial filter for detecting a relative velocity of an object, the light receiving lens is composed of a first lens group and a second lens group, and focal positions of both lens groups are provided. And the spatial filters are alternately arranged at a constant pitch for at least 2
An optical element for splitting light in a direction, a third lens group for collecting the light split by the optical element, and at least two aperture stops arranged near the focal position of the third lens group. A spatial filter type velocity measuring device, comprising: a member; and at least two light receiving elements that separately receive the light that has passed through the aperture stop. 2. The spatial filter type velocity measuring device according to claim 1, wherein the at least two aperture stops have a shape narrow in a velocity measuring direction and wide in a direction orthogonal thereto. 3. The member having at least two aperture stops is made of one metal member and is fixed to a printed wiring board on which the light receiving element is fixed and wired. 1. The spatial filter type velocity measuring device according to 1. 4. A light-shielding plate having an aperture stop is disposed between the first lens group and the second lens group, and each light split by the optical element in at least two directions is the light-receiving element. 4. The spatial filter type velocity measuring device according to claim 1, wherein the spatial filter type velocity measuring device is made to enter only each of the above.