JPH07253462A - Distance measuring instrument - Google Patents

Abstract

PURPOSE:To provide a distance measuring instrument which can measure the distance to an obstacle with high accuracy by reducing the error resulting from the intensity distribution of the light emitted from a light source. CONSTITUTION:A transmission optical system 14 is composed of an optical element which flattens the intensity distribution of the luminous flux of light with a plurality of parallel principal points and the light 15 emitted from a light source 3 is projected upon an obstacle with a flat intensity distribution. The obstacle is detected from the light returning from the obstacle after reflection and the distance to the obstacle is measured by measuring the turnaround time of the light from the difference between the transmitting timing S1 the light and receiving timing S4 of the reflected light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device. More specifically, the present invention relates mainly to a vehicle using a laser radar, and relates to a device for measuring a distance to a target object such as an obstacle.

[0002]

2. Description of the Related Art A conventional vehicle distance measuring device detects the presence of an obstacle using a laser radar and measures the distance to the obstacle. The structure of such an apparatus is as shown in FIG. The pulse train output from the pulse generator 1 serves as a lighting trigger, and the pulse amplifier 2 outputs the light source drive signal S1.
Sent to. Laser light is emitted from the laser light source 3, and output light 5 is transmitted via the transmission lens 4. When the output light 5 is reflected from the obstacle, a part of the reflected light 6 is received by the receiving lens 7
And enters the light receiving element 8. The signal S2 photoelectrically converted by the light receiving element 8 is amplified by the amplifier 9 to become an analog amplifier output signal S3, which is converted into a digital rectangular wave reception signal S4 by the comparator 10 and then input to the time difference measuring circuit 11. The time difference measuring circuit 11 includes a light source drive signal S1 and a clock pulse S5 from the clock 12.
Is input, and the time delay of the received signal S4 with respect to the light source drive signal S1 is measured.

Comparator 10 and time difference measuring circuit 11
10, the amplifier output signal S3 input to the comparator 10 is compared with a predetermined threshold level, and when it exceeds the threshold level, the reception signal S3 is received.
Converted to 4. The clock pulse S5 is input to the time difference measuring circuit 11, and the clock pulse S5 between the rising edges of the light source drive signal S1 and the received signal S4 input to the time difference measuring circuit 11 is counted. When the number N of the counted clock pulses S5 is multiplied by the period of the clock pulse S5, the round-trip time of the laser light to the obstacle is obtained, and since the light speed is known, the distance to the obstacle can be obtained.

[0004]

SUMMARY OF THE INVENTION In such a device,
A semiconductor laser has a high oscillation efficiency as a laser light source,
It is small, lightweight, and can operate with low power consumption, and has come into widespread use along with cost reduction due to mass production. As shown in FIG. 11, when the laser light emitted from the semiconductor laser 21 is emitted from the end face 22 of the active layer, it rapidly spreads due to the Fraunhofer diffraction phenomenon, and the cross-sectional shape of the beam is generally elliptical. The intensity distribution in the vertical direction and the intensity distribution in the horizontal direction of the ellipse are not uniform like the curves 23 and 24, respectively, and both have a Gaussian distribution in which the central portion is strong and the peripheral portion sharply decreases. With such a light source,
As shown in FIG. 12, the laser light emitted from the semiconductor laser 21 is transmitted via the transmission lens 25. When the semiconductor laser 21 is placed near the focal point of the transmission lens 25, the light flux from the semiconductor laser 21 may be transmitted as a measurement light flux having a slight spread because the light source may have a slight spread instead of a point light source. It In this case, the intensity distribution of the measurement light flux has a Gaussian distribution as shown by the curve 26, similarly to that shown in FIG. 11, and the intensity of the peripheral portion of the measurement light flux is significantly lower than that in the central portion. When a laser beam having such a non-uniform intensity distribution is used to measure the distance using a conventional transmission optical system, even if the same obstacle is located at the same distance, the central portion of the beam is The distance measurement values are different between the projected obstacle and the obstacle projected on the periphery.

This will be described with reference to FIG. (A) is the amplifier output signal S when the obstacle is in the center of the measurement light beam
3 shows the relationship between the intensity and time of (3), (b) shows the relationship between the intensity of the received signal S4 and the time when the obstacle is at the center of the measurement light beam, (c) shows the obstacle of the measurement light beam. FIG. 6 is a diagram showing the relationship between the intensity of the amplifier output signal S3 and the time when it is in the peripheral part, and (d) a diagram showing the relation between the intensity of the received signal S4 and the time when an obstacle is in the peripheral part of the measurement light beam. is there. Since the intensity of the laser beam is larger in the central part of the measurement light beam than in the peripheral part, even if the obstacle is the same, the peripheral part of the measurement light beam is projected when the central part of the measurement light beam is projected on the obstacle. The amount of light reflected and incident on the light receiving element 8 is larger than that in the case described above, and the intensity of the amplifier output signal S3 is larger in the case shown in (a) than in the case shown in (c). As shown in (a) and (c), if the threshold levels are the same,
As shown in (b) and (d), the rising of the reception signal S4 is faster when the obstacle is in the central portion of the measurement light flux and faster than when the obstacle is in the peripheral portion of the measurement light flux.
The trailing edge of 4 is slower when the obstacle is at the center of the measurement light flux than when it is at the periphery of the measurement light flux.

As described above, since the clock pulse S5 is counted between the rising edges of the light source drive signal S1 and the received signal S4, the intensity of the amplifier output signal S3 at which the central portion of the measurement light beam is projected on the obstacle. Is larger than that of the amplifier output signal S3 on which the peripheral portion of the measurement light beam is projected.
When the intensity of is smaller, the number of clock pulses S5 is larger, the distance measurement value is larger, and an error occurs due to the obstacle being in the peripheral portion of the measurement light beam. If the clock pulse S5 is counted during each fall of the light source drive signal S1 and the received signal S4, the magnitude relationship is reversed, but an error still occurs in the distance measurement value. When the distance of an obstacle is measured by the laser light having the non-uniform intensity distribution as described above, there is a problem that different distance measurement values can be obtained even for the same obstacle.

In view of such a situation, it is an object of the present invention to provide an obstacle detecting device which reduces errors due to the intensity distribution of light emitted from a light source and has a high distance measuring accuracy.

[0008]

To achieve the above object, the distance measuring apparatus of the present invention includes a transmission optical system for transmitting light emitted from a light source and a light transmitted from the transmission optical system which is reflected from an object. The receiving means for receiving the returned light and outputting the received signal, the detecting means for detecting the target object by the received signal, and the round trip time to the target object from the difference between the transmission timing and the reception timing of the light In a distance measuring device including a calculating unit that measures and calculates a distance to the object, the transmission optical system has a plurality of main points arranged in parallel, and is an optical device that flattens a luminous flux intensity distribution of the light. It is provided with an element.

The optical element is preferably a fly-eye lens.

[0010]

According to the distance measuring device of the present invention, the light emitted from the light source is transmitted to the obstacle through the optical element having a plurality of principal points, the intensity distribution of which is flattened by the transmission optical system.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. The pulse train output from the pulse generator 1 serves as a lighting trigger, and the light source drive signal S1 is output from the pulse amplifier 2 and the light source drive signal S1 is sent to the laser light source 3. Laser light is emitted from the laser light source 3, and output light 15 is transmitted from the transmission lens 14. When the output light 15 is reflected from the obstacle, a part of the reflected light 6 enters the receiving lens 7 and is focused on the light receiving element 8. Signal S2 photoelectrically converted by the light receiving element 8
Is amplified by the amplifier 9 and is an analog amplifier output signal S3
Then, it is input to the comparator 10. Comparator 1
At 0, the amplifier output signal S3 is converted into a rectangular wave reception signal S4 which rises when a predetermined threshold level is exceeded, and is input to the time difference measuring circuit 11.

The reception signal S4, the light source drive signal S1 and the clock pulse S5 are input to the time difference measuring circuit 11, and the number of pulses between the rising edges of the light source drive signal S1 and the reception signal S4 of the clock pulse S5 is counted. . The counted number of clock pulses S5 is input to the arithmetic circuit 16, and the number of clock pulses S5 is multiplied by the cycle of the clock pulses S5 to obtain the round-trip time of the laser light to the obstacle,
Find the distance from the speed of light to the obstacle. The obtained distance measurement value is displayed on the display unit 17, and when no obstacle is detected, it is displayed as no distance measurement value.

The transmitting lens 14 is an optical element which has a plurality of principal points and flattens the intensity distribution of laser light. 2 and 3 show a front view and a side view of the transmission lens 14, respectively. A plurality of hexagons 18 are gathered on the plan view to form a figure like a compound eye "flying eye". The cross-sectional view shows a plane 14a on one side and a plane 14b formed from many small spherical surfaces 19 on the other side. In this way, the optical element formed by gathering a large number of parallel single lenses is a so-called fly-eye lens.

Before describing the structure and operation of the transmitting lens 14 in detail, here, the main points of the lens are described in "Laser & Optics Guide 3 (1)", Hideaki Yamada, published by Keno Melles Griot Co., Ltd., 1993. In July, a brief explanation will be given according to the description on pages P1-2 to P1-3. There is a theorem that "a ray that passes through one of the two focal points is parallel to the optical axis on the opposite side of the lens", and the two focal points are determined based on this theorem. Strictly speaking, the ray from the front focus (that is, the ray that is parallel to the optical axis after reaching the opposite side of the lens) is refracted once on each surface of the lens, but once on an imaginary surface. Can be considered to be done. Such an imaginary surface can be regarded as a substantially flat surface for paraxial rays, and this is called a principal plane. The point where the principal plane intersects the optical axis is called the principal point.

This will be described with reference to FIG. In the figure, lens 30
There is a front focus 31 and a rear focus 32 on the optical axis 33 of the.
A ray 34 from an object at infinity parallel to the optical axis 33 is refracted at the second principal plane 37 and passes through the rear focal point 32. The back ray 35 to the front focal point 31 is refracted by the first principal plane 36 and passes through the front focal point 31. The points where the first principal plane 36 and the second principal plane 37 intersect the optical axis are the first principal point 38 and the second principal point 39, respectively.
Is.

The expression "having a plurality of principal points" is used in the present invention. However, this is not because there is a plurality of first principal points and second principal points of each single lens that constitutes the transmitting lens 14. Absent. This means that the transmission lens including a set of a plurality of single lenses has a plurality of first principal points (or second principal points), and the transmission lens 14 has a plurality of first principal points (or a plurality of second principal points). ) Means that the lens is formed by a plurality of curved surfaces.

Next, how the light from the light source is transmitted by the fly-eye lens will be described with reference to FIG. One surface 63a of the fly-eye lens 63 is a flat surface and the other surface 63b is
Has a large number of parallel convex spherical surfaces having the same curvature, and has a shape in which a large number of single lenses (not shown) are arranged in parallel. FIG. 5 shows a cross section of five single lenses among them. A light source 61 having a predetermined light emitting area is arranged on a focal plane 62 formed by the focal points of the single lenses. The fly-eye lens 63 has a first main surface 64 near the light source 61, and the light source 6
There is a second principal surface 65 on the side away from the first principal point 66 and the second principal point corresponding to each single lens.
8, 70, 72, 74 and the second principal points 67, 69, 71,
73 and 75.

A light ray 82 emitted from a point 81 on the light source 61 and reaching the first principal point 68 passes through the fly-eye lens 63 as a light ray 83 parallel to the light ray 82 because the light source 61 is placed on the focal plane 62. Sent. Also, a point 81 on the light source 61
From the first principal point 68 to a point 76 away from
Since the light source 61 is located in the focal plane 62, it is transmitted as a ray 85 parallel to the ray 83. In this case, the ray 85 is apparently transmitted from the point 77 on the second principal surface 65, but the distance between the second principal point 69 and the point 77 is equal to the distance between the first principal point 68 and the point 76. As a result, the intensity distribution of the light flux on the surface 91 is a curve 92 when the light source is a semiconductor laser having a Gaussian intensity distribution as shown in FIG.
Gaussian distribution like.

Other light rays emitted from other points on the light source 61 also pass through the fly-eye lens 63 and undergo similar effects. In the above description, the aberration of the lens and the influence of the light source deviating from the optical axis are omitted for simplification.

As shown in FIG. 6, the laser light emitted from the laser light source 3 is transmitted through the transmission lens 14 having a plurality of principal points. When the laser light source 3 is placed near the focal point of the transmission lens 14, the light flux from the laser light source 3 is transmitted as a plurality of measurement light fluxes having a slight spread. The intensity distribution of each measuring light flux is a Gaussian distribution as shown by the curve 27. The total intensity distribution of the measurement light flux in this case is shown by a flattened curve 28 in the form formed by superimposing the individual measurement light fluxes whose intensity distribution is a Gaussian distribution.

Next, another embodiment will be described with reference to FIG. The detailed description of the same or similar points as in the above-described embodiment will be omitted. The optical element used in this embodiment is a combination of a reflection type optical element 51 and a reflecting mirror 52. The laser light emitted from the laser light source 3 has a hole 51 a in the optical element 51.
Is transmitted, reflected by the reflecting mirror 52, and then reflected by the surface 51a of the optical element 51 and transmitted. A large number of concave spherical surfaces are formed on the surface 51a, and the intensity distribution of the reflected light from each concave spherical surface becomes a Gaussian distribution like the curve 53, and the intensity distribution of the reflected light from the entire surface 51a becomes the curve 54. It has a flat distribution like.

Further, another embodiment will be described with reference to FIG. Detailed description of the same or similar points as those of the above-described embodiments will be omitted. The optical element used in this embodiment is a combination of the convex lens 55 and the optical element 56. The laser light emitted from the laser light source 3 passes through the convex lens 55, is condensed, and then passes through the optical element 56 to be transmitted. A large number of small prisms are formed on the surface 56a of the optical element 56. The intensity distribution of light from each small prism is shown by the curve 57.
However, the total intensity distribution of the transmitted light is a flat distribution like the curve 58.

Needless to say, each of the embodiments is applicable not only to the semiconductor laser light source but also to other light sources having an uneven intensity distribution.

Although the optical axes of the respective small lenses are parallel to each other in the embodiment, they may not be necessarily parallel as long as they are substantially parallel.

The present invention may use not only a lens having a plurality of principal points of plano-convex configuration as in the embodiment but also a lens having curved surfaces on both sides.

Although the embodiment of the book has been mainly described with the convex surface of the plano-convex lens as the object surface, the present invention can be carried out with the convex surface as the light source side. In this case, since the flat surface is arranged on the outer side, there is an effect that cleaning is easy.

As the material of the lens, general optical materials such as glass and plastic can be used, and the present invention can be applied to not only colored lenses but also colored lenses.

In the present invention, the curved surface of the lens having a plurality of principal points is often not a single continuous curved surface but a discontinuous curved surface as in the embodiment shown in FIG. A lens having such a surface is advantageously manufactured by plastic molding.

When a lens having a plurality of colored principal points is used as a receiving lens, it can also serve as a filter for removing unnecessary light from the background other than the light reflected by the object.

Further, the present invention is not limited to the semiconductor laser of the embodiment as the light source, and a light source having another wavelength range may be used.

Although the present embodiment has been described as an on-vehicle device, the present invention can be applied to other devices such as a robot for measuring the distance to an object.

[0032]

According to the present invention, the light emitted from the light source is transmitted with its intensity distribution flattened through the optical element having a plurality of principal points. The intensity does not differ regardless of whether the light projected onto the same obstacle is the central part of the measurement light beam or the peripheral part. Therefore, the error due to the intensity distribution of the light emitted from the light source is reduced, and an obstacle detection device with high distance measurement accuracy can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a front view of a transmission optical element according to an embodiment of the present invention.

FIG. 3 is a side view of a transmission optical element according to an embodiment of the present invention.

FIG. 4 is a sectional view of a lens for explaining the principal points.

FIG. 5 is a diagram for explaining the operation of the transmission optical element according to the embodiment of the present invention.

FIG. 6 is a diagram illustrating an intensity distribution of transmission light via a transmission optical element according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating an intensity distribution of transmission light via a transmission optical element according to another embodiment of the present invention.

FIG. 8 is a diagram illustrating an intensity distribution of transmission light via a transmission optical element according to still another embodiment of the present invention.

FIG. 9 is a block diagram of a conventional example.

FIG. 10 is a diagram illustrating counting of clock pulses.

FIG. 11 is a diagram showing an intensity distribution of laser light emitted from a semiconductor laser.

FIG. 12 is a diagram for explaining the intensity distribution of transmission light via a transmission optical element according to a conventional example.

FIG. 13 is a diagram illustrating an error caused by an obstacle existing in the peripheral portion of the measurement light beam in the conventional example.

[Explanation of symbols]

 2 ・ ・ ・ ・ Pulse amplifier 3 ・ ・ ・ ・ ・ ・ Laser light source 4, 14 ・ ・ ・ ・ Transmission lens 5, 15 ・ ・ ・ ・ Output light 9 ・ ・ ・ ・ Amplifier 10 ・ ・ ・ ・ ・ ・ Comparator 11 ・ ・ ・ ・ ・ ・ Time difference Measuring circuit 38, 66, 68, 70, 72, 74 ... First principal point 39, 67, 69, 71, 73, 75 ... Second principal point 51, 56 ... Optical element 52・ ・ ・ Reflector 55 ・ ・ ・ ・ Convex lens 63 ・ ・ ・ Fly eye lens S1 ・ ・ ・ ・ Light source drive signal S3 ・ ・ ・ Amplifier output signal S4 ・ ・ ・ Reception signal S5 ・ ・ ・ Clock pulse

Claims (2)

[Claims] 1. A transmission optical system for transmitting light emitted from a light source toward an object, and light received from the object which is reflected and returned from the object among the light transmitted from the transmission optical system. The receiving means for outputting, the detecting means for detecting the object by the received signal, and the distance to the object by measuring the round-trip time to the object from the difference between the transmission timing and the reception timing of the light. In the distance measuring device including a calculating means for calculating, the transmitting optical system includes an optical element having a plurality of main points arranged in parallel to flatten the luminous flux intensity distribution of the light. measuring device. 2. The distance measuring device according to claim 1, wherein the optical element is a fly-eye lens.