JPS6247509A - Optical system for range finding - Google Patents

Abstract

PURPOSE:To control so as to output an optimum photoelectric signal within the infinite range from very close distance by providing as well a diaphragm plate on at least either projecting lens or photodetecting lens and by performing the adjustment of the light quantity by limiting one part of the irradiating luminous flux at close distance side. CONSTITUTION:The light from the light emitting diode 1 emitting a near infrared ray is condensed by a projecting lens 2, propagated linearly according to an optical axis 3 and irradiated on a material body 6 as a spot light 5. The spot light 5 is reflected with diffusion on the surface of the body 6 and one part thereof is made incident on a photodetecting lens 8 according to optical axis 7. A line sensor 10 is arranged so that the longitudinal direction is allowed to coincide with the base line length direction at the rear part of the photodetecting lens arranged apart from the projecting lens 2 and base line length lambda, then. The optical axis 7 is inclined largely for an optical axis 11 when the body 6 is located at very close distance and the inclination of the optical axis 7 becomes smaller as the body 6 becomes at remote distance. And the luminous flux converged by the lens 8 is focused on the different position on the sensor 10 corresponding to the body distance and the sensor 10 outputs the focused position thereof as electrical signal, so by utilizing it, the distance upto the body 6 can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ranging optical system used in an active type ranging device.

[Conventional technology]

An active type distance measuring device used in an autofocus device of a camera, etc. includes a light projector and a light receiver. The light projecting unit includes a light source such as a light emitting diode that emits infrared light, and a light projecting lens disposed in front of the light source. Further, the light receiving section includes a light receiving body having a function of detecting a light receiving position, such as a line sensor combining a light receiving element and a CCD, and a light receiving lens disposed in front of the light receiving body. The light receiving section is arranged at a distance of a certain base line length from the light projecting section, and is arranged so that the longitudinal direction of the light receiving body coincides with the base line length direction.

When the light source is turned on, a spot light is irradiated onto the object by the projection lens. This spot light is reflected by the surface of the object, and a portion of the reflected light beam is imaged on the photoreceptor via the photoreceptor lens. At this time, the reflected optical axis from the object to the light receiving lens enters the light receiving lens at an angle corresponding to the object distance, and the spot light is imaged at different positions on the light receiving body accordingly. By detecting the image position, the distance to the object can be determined.

[Problem that the invention seeks to solve]

The photoreceptor used in the distance measuring device described above receives spot light from an object at an infinite distance of 5 m or more, for example, to a close range of about 50 cm, and outputs the light receiving position as an electrical signal. It has the effect of By the way, the amount of light irradiated from the light source to the object and the amount of light reflected by the object and incident on the photoreceptor are inversely proportional to the square of the distance to the object, so as the object distance becomes longer, the amount of light that is reflected on the photoreceptor increases. The amount of incident light will be drastically reduced.

Therefore, in order to obtain photoelectric output from the photoreceptor even at long distances, it is necessary to make the photosensitivity of the photoreceptor extremely high.

However, the dynamic range of the photoreceptor is naturally limited, so the sensitivity level of the photoreceptor is set so that it can respond to the amount of reflected light from an object distance of, say, 5 meters, which is considered to be infinite. If this is done, the photoelectric output from the photoreceptor will be saturated for light from a close distance, making it impossible to obtain an appropriate distance measurement signal. On the other hand, if the sensitivity level of the photoreceptor is set for light from a close distance, the photoreceptor may not be able to capture weak light from an infinite distance.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and is designed to output an appropriate photoelectric signal from the photoreceptor within a range from a close distance to a predetermined distance considered to be infinite. It is an object of the present invention to provide a distance measuring optical system that controls the amount of light irradiated onto an object or reflected light from the object.

[Means for solving problems]

In order to achieve the above object, the present invention disposes an aperture between the light source and the emitter lens stop or between the light receiver lens and the light receiver, and the aperture partially blocks the light flux depending on the object distance. I'm trying to make it possible. For this reason, the light source or the light receiving body includes a light projecting lens disposed in front of the light source or the light receiving body.
It is fixedly placed on the focal plane of the light-receiving lens, and when the object distance is a predetermined distance that is considered to be infinite, the light flux from the light source or the light flux reflected from the object is used without loss. ing. Then, as the object distance becomes closer, the amount of light is adjusted by blocking part of the light beam irradiating the subject or the light beam entering the photoreceptor by the aperture. It is.

In carrying out the present invention, it is not necessary to provide the aperture for both the light projecting lens and the light receiving lens. For example, when the optical axis of the light irradiated by the projecting lens is fixed and the distance is measured by the inclination of the reflected optical axis reflected from the object and incident on the receiving lens, it is preferable to provide the aperture on the receiving lens side. Effective. In addition, if the light-receiving optical axis of the light-receiving lens is fixed and distance measurement is performed by scanning the irradiation optical axis of the light beam from the light source to the object in the baseline length direction, a diaphragm may be provided on the light-emitting lens side.

Note that the pattern of the light flux irradiated onto the object is not limited to a spot-like pattern, but may be, for example, a slit-like pattern. As described above, by blocking a part of the light beam that is irradiated to the object when the object distance is short or a part of the light beam that is incident on the photoreceptor, when the object distance is short distance, Since the depth of focus of each lens is deepened, the secondary effect is that the pattern of the light flux irradiating the object or the pattern of the light flux formed on the photoreceptor becomes clearer, making it easier to measure at short distances. This makes it possible to further improve distance accuracy.

Embodiments of the present invention will be described below based on the attached drawings.

〔Example〕

In FIG. 3 showing a distance measuring device to which the present invention is applied, light from a light emitting diode 1 that emits near-infrared light is condensed by a projecting lens 2, travels straight along an optical axis 3, and forms a spot light 5. The object 6 is irradiated as follows. The spot light 5 is diffusely reflected on the surface of the object 6, and a part of the light beam is incident on the light receiving lens 8 along the optical axis 7.

Light projection lens 2 and baseline length! Light receiving lenses 8 arranged apart from each other
At the rear, the longitudinal direction matches the baseline length direction.
A line sensor 10 is arranged. As shown in the figure, when the object 6 is at a close distance, the optical axis 7 is tilted greatly with respect to the optical axis 11 of the light receiving lens, and as the object 6 becomes far away, the tilt of the optical axis 7 becomes smaller. Therefore, the light beam converged by the light receiving lens 8 is imaged at different positions on the line sensor 10, corresponding to the object distance.The line sensor 10 outputs the imaged position as an electrical signal. Using this electrical signal, the distance to the object 6 can be measured.As the object distance approaches infinity, the optical axis 7 becomes the optical axis 11 of the light receiving lens 8. getting closer.

In FIG. 1 showing an embodiment of the present invention, the line sensor 10 is placed on the focal plane of the light receiving lens 8 with a diaphragm plate 15 in between. Therefore, when the object distance is infinite, the light beam 16 that enters the light receiving lens 8 along the optical axis 11 is converged by the light receiving lens 8 and is transmitted to the line sensor 1.
0 is clearly imaged. Note that the diaphragm plate 15 has an aperture diameter that allows the convergent light beam produced by the light-receiving lens 8 to pass through to the line sensor 10 as it is, as shown in the figure.

On the other hand, when the object distance is short, the light beam 17 reflected from the object 6 enters the light receiving lens 8 along the optical axis 7 tilted with respect to the optical axis 11. A portion of the light beam 17 thus incident is restricted by the diaphragm plate 15 . As a result, the brightness of the spot light imaged on the line sensor 10 is adjusted to an appropriate level that takes into account the photoelectric conversion efficiency of the line sensor 10, and less blur is obtained, which improves distance measurement accuracy. It is very effective in maintaining

The light-receiving lens 8 shown in FIG. 1 can be configured as a single lens having an aspherical surface on the object side and a spherical surface on the image side, for example. The aspherical shape in this case is expressed by the following equation.

In the above equation, X is the coordinate in the direction from the object side to the image side along the optical axis with the apex of the aspherical surface as the origin, and h is the coordinate in the direction orthogonal to the X axis with the apex of the aspherical surface as the origin. It is. Furthermore, C is the reciprocal of the paraxial radius of curvature r of the surface (C=1
/r), k is a conical coefficient, and A-D is an aspherical coefficient, which are set to the following values.

r 11.34382 k -3,07563 A 1.83702X10-' B -6,54607xlO-7C-7,983
03X10-9 D 1.11105X10-10 The radius of curvature of the spherical surface on the image side and the axial thickness of the lens are -63,2
0574.5,000, the focal length of this light receiving lens 8 is 20.0000 mm'z F number is 1
．． It becomes 6667. The light-receiving surface of the line sensor 10 is installed to coincide with the focal plane of the light-receiving lens 8, and a diaphragm plate 15 with an aperture of 1°86 is located 14 degrees from the apex of the spherical surface.
．． It is located at position 5. This light receiving lens 8 is made by resin molding and has a refractive index of 1.4917.

The optical system configured in this way is set at a close distance of 50 cm and 5
When the distance beyond m is used as infinity, and the base line length l (Fig. 3) between the projection lens 2 and the projection lens 2 is used as 30 mm, the line sensor 10
The amount of light reaching the object is 43% of that when the object distance is infinite. Further, when the focal length of the light receiving lens 8 is 1 and the distance from the line sensor 10 to the diaphragm plate 15 is X, the installation position of the diaphragm plate 15 is adjusted as appropriate within the range of 0.07<x<0.3. It is also possible.

FIG. 2 shows another embodiment of the present invention, in which the optical system is comprised of lenses 20. Aperture plate 21. It consists of a second lens 22. Runs 20. Each of the second lenses 22
The figure shows the resin lenses used in the embodiment, and the object side surfaces of each lens 20° and 22 are aspherical.

The object-side surface of the second lens 20 is composed of an aspheric surface expressed by the formula shown in the embodiment of FIG. 1, and has a paraxial curvature radius r
, the aspherical coefficients, and the respective values of A-D are as follows.

r 15.01887 k -4,24318 A 8.26341X10-5B
-1,93993X10-6C3,37013X10-
' D -3,45419xlO-'' Further, the image side surface of the lune 20 is a spherical surface with a radius of curvature of -22,72526, and the axial thickness of the lunse 20 is 5.5115.

On the other hand, as for the second lens 22, its object-side surface is an aspherical surface expressed by the same formula as the second lens 20, and each coefficient is as follows.

r -9,64087 k -871,9336 A 9.27761X10-'B
-2,06510X10-'c -7,920
67xlO-I3D 0.00000 The image side of the second lens 22 has a radius of curvature of -3,36486
The axial thickness of this second lens 22 is 2.458.
It is 03.

Runs 20 above. The focal length of the entire system of the second lens 22 is 20.0000 mm, the F number is 1°6667, and the aperture plate 21 with an aperture diameter of 2.22 is placed at a distance of 14.0 mm from the apex of the image-side spherical surface of the second lens 20. When installed and used under the same conditions as the embodiment shown in FIG. 1, the amount of light reaching the line sensor 10 when the object distance is close is 25% of that when the object distance is infinite, An image with even less blur was obtained on the sensor 10.

Incidentally, since the light flux blocking effect by the aperture plates 15 and 21 is effective in the base line length direction, the aperture between them may be changed as appropriate in the direction perpendicular to the base line length direction. Furthermore, the present invention is not limited to the above-described line sensor 10, but is equally applicable to distance measuring devices using other 4-degree light receiving bodies that have the function of detecting the irradiation position of patterned light beams such as spot-like or slit-like light beams. I can do it. Furthermore, contrary to the above-described embodiment, in the case where the distance measurement is performed without scanning the irradiation optical axis by the light emitting diode 1 and the light projecting lens 2, an aperture plate 15 as described above is provided on the projecting lens 2 side. Of course, by installing 21, similar effects can be obtained.

〔Effect of the invention〕

As explained above, in the distance measuring optical system of the present invention, a diaphragm plate is attached to at least one of the light emitting lens and the light receiving lens, so that a part of the irradiated light flux or the received light flux on the short distance side is The amount of light is adjusted by limiting the amount of light. Therefore, by adjusting the sensitivity level of the photoreceptor for a predetermined distance that is considered to be infinite distance, it becomes possible to obtain an appropriate photoelectric conversion output even when the object distance is close, and also to Since the pattern formed on the body becomes clearer, it is very effective in obtaining accurate ranging signals.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention. FIG. 2 is a sectional view showing another embodiment of the present invention. FIG. 3 is a principle diagram showing an example of an active type distance measuring device using the present invention. 1...Light emitting diode 2...Light emitting lens 5...Spot light 8...Light receiving lens 10...Line sensor 15.21...Aperture plate 20...Second lens 22...Second lens.

Claims (1)

[Scope of Claims] (1) A measurement method in which a light beam from a light source is irradiated onto an object through a light projecting lens, and a part of the light beam reflected from the object is made to enter a light receiving body through a light receiving lens. In the range device, a diaphragm is disposed between the light emitting lens and a light source fixed on the focal plane of the light emitting lens, or between the light receiving lens and a light receiving body fixed on the focal plane of the light receiving lens, and 1. A distance measuring optical system characterized in that when the distance is short, a part of the light beam irradiated onto the object or the light beam incident on the photoreceptor is partially blocked by the aperture. (2) When the focal length of the light projecting lens or the light receiving lens is 1, and the distance between the light source or the light receiving body and the aperture is x, 0.07<x<0.3 is satisfied. A light-receiving optical system for distance measurement according to claim 1. (3) The light projecting lens or the light receiving lens including the aperture is composed of two groups, a first lens and a second lens, and the aperture is disposed between the first lens and the second lens. A light-receiving optical system for distance measurement according to claim 2.