JP2006072201A - Light receiving lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection measuring instrument which accurately measures a distance to a measurement object in a wide-angle range and is made small-sized and light-weight. <P>SOLUTION: In a light receiving lens, 9 or more luminous flux dividing lenses having toric faces are provided on one surface, and maximum angles of incidence (θx and θy) of light capable of being condensed, in directions of orthogonal axes (a y axis is an axis of a direction which gives a maximum value θy out of angles of incidence of light being capable of condensed, and an x axis is an axis orthogonal to the y axis) within a plane having an optical axis of the light receiving lens as the normal satisfy a relation of 0.05<¾θx/θy¾<1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light receiving lens that can collect light at a wide angle, and more particularly to a light receiving lens for a reflection measuring device that measures a distance, a speed, an angle, and the like between a measurement object and a measurement object. The present invention relates to a light receiving lens that can be used in a vehicle reflection measurement device.

  In the outgoing optical system used in the vehicle reflection measurement device, the irradiation range is expanded, so that the measurement target vehicle cannot be accurately detected from a large number of vehicles within the irradiation range, and measurement is performed with obstacles other than the vehicle such as guardrails. It may not be possible to accurately identify the target vehicle.

In order to solve such a problem, in the reflection measuring apparatus disclosed in Patent Document 1, reflected light from a non-measurement object that is not sufficiently refracted by the light receiving lens is reflected several times by a tapered optical waveguide to receive light. It is intended to improve the light receiving efficiency by focusing on the element. Further, a method of receiving a reflected light beam in a wide angle range with a wide angle lens used in a camera or the like is also considered.
Further, in the reflection measuring device disclosed in Patent Document 2, the distance between the light receiving lens and the object to be measured in a wide angle range using a Fresnel lens whose focal length circulates from the outer peripheral portion toward the central portion. Is intended to be measured.

Japanese Patent Application Laid-Open No. 64-80894 Japanese Patent Laid-Open No. 9-21874

  However, according to what is disclosed in Patent Document 1, when the number of times the reflected light is reflected by the optical waveguide is n, the optical power is attenuated to the optical power corresponding to the nth power of the reflectance, and the optical power is further increased by the optical waveguide. There is a problem of attenuation. Further, in order to form a polished surface on the optical waveguide that can narrow the light beam by reflection, there is a problem that a high-precision polishing process is required and the cost is increased.

  In addition, when a wide-angle lens used in a camera or the like is used, at least two or more lenses are required, so that there is a problem that the apparatus becomes large and becomes a complicated optical system. In order to solve such a problem, it is conceivable to use a Fresnel lens that is small, light and mass-produced at low cost as in Patent Document 2, but the light receiving performance is not good due to the characteristics of the Fresnel lens. Since the light receiving efficiency is significantly reduced with respect to no obliquely incident light, it is not suitable to use a Fresnel lens for a scanning reflection measuring apparatus for a vehicle that scans a wide angle range. Further, as shown in FIG. 10 of Patent Document 2, the relative detection distance decreases from around the horizontal incident angle of ± 5 °, and becomes extremely low when it approaches ± 10 °.

  The present invention has been made to solve such a problem, and provides a light receiving lens capable of condensing a wide angle light without distortion, and in a wide angle range using the light receiving lens. An object of the present invention is to provide a reflection measuring apparatus that accurately measures the distance to a measurement object and is reduced in size and weight.

  In order to achieve the above object, a light receiving lens according to the present invention comprises (1) a light beam splitting lens having a toric surface on the same surface, and an orthogonal axis direction (y-axis) in a plane normal to the optical axis of the light receiving lens. = The axis in the direction giving the maximum value θy among the incident angles of the condensable rays and the x axis = the axis orthogonal to the y axis), the maximum incident angles (θx and θy) of the condensing rays are 0.05 < The relationship | θx / θy | <1 is satisfied.

  In a preferred aspect of the light receiving lens of the present invention, (2) the incident angle in the y-axis direction or the x-axis direction has an angle distribution that is symmetric with respect to a plane including the optical axis and the x-coordinate axis or the y-coordinate axis. (3) The light beam splitting lens is rectangular, and the lens surface shape of the cross section formed by the optical axis and the x axis of the light beam splitting lens is a straight line, a part of an aspherical cross section arc, or a part of a perfect circle arc The lens surface shape of the cross section formed by the optical axis and the y axis of the light beam splitting lens is formed by a straight line, a part of an aspherical cross section arc, or a part of a perfect circle arc, and the entire light receiving lens Is rectangular. (4) The angle formed by the optical axis of the light beam splitting lens and the optical axis of the light receiving lens gradually increases as the distance from the optical axis of the light receiving lens increases. (5) The maximum thickness d is 2 mm <d <15 mm. (6) The light receiving lens body is made of resin, and an antireflection layer is formed on the surface of the light receiving lens body. (7) A slope parallel to the direction of the light incident angle at the boundary is provided at the boundary between adjacent beam splitting lenses.

  According to the light receiving lens of the present invention, even if the incident angle of the reflected light incident on the light receiving lens changes, preferably nine or more light beam splitting lenses having a toric surface are provided, and the surface having the optical axis of the light receiving lens as a normal line The maximum incident angle (θx and the maximum incident angle of the light beam that can be collected in the direction of the orthogonal axis (y axis = the axis in the direction that gives the maximum value θy among the incident angles of the condensing light beam and x axis = the axis that is orthogonal to the y axis)) Since the light beam that has passed through the light receiving lens satisfying the relationship of θy) 0.05 <| θx / θy | <1 is condensed to the light receiving unit with almost equal light amount, the incident angle of the reflected light beam becomes a wide angle. However, a relatively flat light receiving efficiency characteristic can be maintained.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a sectional view of a light receiving lens according to an embodiment of the present invention, and FIG. 3 is a perspective view thereof.
As shown in FIGS. 1 and 3, the light receiving lens 51 includes nine or more light beam splitting lenses 101 and has a rectangular shape from the front. These light beam splitting lenses have a toric surface and are rectangular when viewed from the front. In this embodiment, the light-receiving lens has an uneven shape of the light beam splitting lens formed on only one surface, and the other surface is flat. The light beam enters the toric surface of the beam splitting lens and exits from the plane. Light rays at each incident angle are transmitted through a corresponding light beam splitting lens and can be condensed at one point or a plurality of focal points. By providing the light receiving element 52 as shown in FIG. 5 at the focal point, it is possible to sense the collected light and calculate the distance. In the case of focusing on a plurality of focal points, a plurality of light receiving parts can be provided.

FIG. 2 shows the arrangement of the light beam splitting lens of the light receiving lens of this embodiment. For example, the light splitting lens 1 is arranged in the a row and the A column, and the light splitting lens 6 is arranged in the c row and the B column. The light receiving lens of this embodiment has a rectangular shape. 1 is a cross-sectional view taken along the plane y0 in FIG. 2, and the cross-sectional view x0 in FIG. 1 is a cross-sectional view taken along the plane x0 in FIG. The portion of the light receiving lens of this embodiment without a circled number in FIG. 2 is symmetrical with respect to the x0 plane or the y0 plane.
The toric surface of each beam splitting lens is expressed by Formula A and Formula B.

By inputting a desired numerical value to each coefficient of C _X , C _Y , K, A, and B, a three-dimensional curved surface shape is defined. Table 1 shows the coefficients of the light receiving lens according to the embodiment of the present invention. X, Y, and Z indicate local coordinates (X, Y, Z) of the light beam splitting lens.
The toric surface is preferably formed by a lens surface shape of a cross section formed by the optical axis and the x axis of the light beam splitting lens being a straight line, a part of an arc of an aspherical cross section, or a part of an arc of a perfect circle, It is preferable that the lens surface shape of the cross section formed by the optical axis and the y axis of the beam splitting lens is formed by a straight line, a part of an aspherical cross section arc, or a part of a perfect circle arc.

  As shown in FIG. 4, the light receiving lens according to the embodiment of the present invention has an orthogonal axis direction in the plane with the optical axis as a normal line (y axis = direction in which the maximum value θy of the incident angles of condensing light rays is given). The maximum incident angles (θx and θy) of rays that can be collected on the axis and the x-axis = axis perpendicular to the y-axis satisfy the relationship of 0.05 <| θx / θy | <1. In this embodiment, the maximum incident angle θy in the y-axis direction is 10 °, and the maximum incident angle in the x-axis direction is 1 °. The incident angles θy and θx have an angle distribution that is symmetric with respect to the optical axis. That is, the incident angle is ± 10 ° in the y-axis direction and ± 1 ° in the x-axis direction. The incident angle in the x-axis direction may be asymmetric in the angle distribution, such as + 2 ° to −1 °.

To measure the distance between a vehicle equipped with the reflection measuring device 1 and a vehicle that is the object to be measured on a road that is relatively straight and has a long inter-vehicle distance, such as an expressway, measure within an angle range of ± 6 °. Although it is sufficient if possible, on a road with many curves and a short inter-vehicle distance such as a general road, a flat received light amount characteristic is required while maintaining a constant received light amount within an angle range of ± 10 °. By combining a beam splitting lens that collects the refracted light beam on the light receiving element 52 at incident angles of 0 °, 4 °, and 8 °, the characteristics of the amount of received light with respect to the incident angle are substantially flat within a range of ± 10 °. Become.
In addition, it is preferable to install the light receiving lens of the embodiment of the present invention so that the y-axis direction is a horizontal direction. In the vehicle reflection measurement apparatus, the light receiving efficiency can be increased by widening the detection angle with respect to an object in the horizontal direction and decreasing the detection angle in the vertical direction.

  In order to have such an incident angle distribution, preferably the angle formed by the optical axis of the light beam splitting lens and the optical axis of the light receiving lens gradually increases as the distance from the point through which the optical axis of the light receiving lens passes is increased. To do. In this embodiment, the toric surface is inclined at a specific rotation angle with the Y-axis and the X-axis as the rotation axis with the intersection point between the optical axis and the toric surface of the light beam splitting lens as the origin, and enters the light beam splitting lens. Has an angular distribution. In this embodiment, as shown in Table 1, the light splitting lens 1 of a row A column condenses light rays having an incident angle of 0 ± 2 ° in the y-axis direction and an incident angle of 0 ± 0.4 ° in the x-axis direction on the light receiving unit. It can be done. The light splitting lens 4 in the a row and the B column has an X-axis rotation angle of 8.92 °, a Y-axis rotation angle of 0 °, and a y-axis direction incident angle of 4 ± 2 ° and an x-axis direction incident angle of 0 ± 0.4 °. The light beam can be condensed on the light receiving part. The light splitting lens 7 in a row C column has an X-axis rotation angle of 16.94 °, a Y-axis rotation angle of 0 °, and a y-axis direction incident angle of 8 ± 2 ° and an x-axis direction incident angle of 0 ± 0.4 °. The light beam can be condensed on the light receiving part. The light splitting lens 2 in the b-row A-column has a Y-axis direction incident angle of 0 ± 2 ° and an x-axis direction incident angle of 0.55 ± 0.15 on a plane with an X-axis rotation angle of 0 ° and a Y-axis rotation angle of 20.44 °. The light beam of ° can be focused on the light receiving part. The light splitting lens 3 in the c-row A-column has a Y-axis direction incident angle of 0 ± 2 ° and an x-axis direction incident angle of 0.85 ± 0.15 on a plane with an X-axis rotation angle of 0 ° and a Y-axis rotation angle of 31.78 °. The light beam of ° can be focused on the light receiving part. The other light beam splitting lenses 5, 6, 8, and 9 have their toric surfaces inclined at the rotation angles shown in Table 1. The center thickness of each light beam splitting lens of this example is as shown in Table 1. The maximum thickness d of the light receiving lens is preferably 2 mm <d <15 mm. When the maximum thickness is within this range, a light receiving lens with high productivity can be obtained. The minimum thickness is usually 0.7-1 mm. The X-axis rotation angle is an angle obtained by rotating the X-axis as a rotation axis, and the Y-axis rotation angle is an angle obtained by rotating the Y-axis as a rotation axis. The X-axis and Y-axis of each beam splitting lens are in a positional relationship parallel to the x-axis and y-axis of the light receiving lens.

  It is preferable that the boundary between adjacent beam splitting lenses has a slope parallel to the direction of the light incident angle at the boundary. In this embodiment, as shown in FIG. 1, a slope parallel to the direction of the light incident angle of 2 ° in the y-axis direction is formed at the boundary between the light beam splitting lens 1 and the light beam splitting lens 4. On the boundary between the light beam splitting lens 4 and the light beam splitting lens 7, a slope parallel to the y-axis direction light incident angle of 6 ° is formed. Although not shown in the figure, a slope parallel to the direction of the light incident angle of 0.4 ° in the x-axis direction is formed at the boundary between the light beam splitting lens 1 and the light beam splitting lens 2. At the boundary between the light beam splitting lens 2 and the light beam splitting lens 3, a slope parallel to the direction of the light incident angle of 0.7 ° in the x-axis direction is formed. Similarly, slopes parallel to the y-axis and x-axis direction beam incident angles are formed on the other boundaries.

The material constituting the light receiving lens of the present invention is not particularly limited, and can be formed of a transparent resin or glass. The light receiving lens body of this embodiment is made of a transparent resin.
Examples of the transparent resin include polycarbonate resin, acrylic resin, polyester resin, polyolefin resin, and polycycloolefin resin. Of these, polycarbonate resin or polycycloolefin resin is preferred. Specific examples of the polycycloolefin resin include norbornene resins (ring-opening polymers and addition polymers of norbornene monomers), addition polymers of monocyclic olefins, addition polymers of vinylcycloolefins, aromatic vinyl monomers Examples thereof include a product obtained by hydrogenating an aromatic addition polymer with an aromatic ring. The body of the light-receiving lens formed of a transparent resin can be formed by a known molding method such as an injection molding method using a mold or the like, a compression molding method, or by cutting out the shape of the beam splitting lens by a cutting method or the like. .
The material constituting the light receiving lens preferably contains a pigment or the like for shielding transmission of visible light. By including a pigment or the like that blocks visible light, noise due to visible light can be removed and accurate measurement can be performed.

  In the light receiving lens of the present invention, it is preferable that an antireflection layer is formed on the surface of the lens body. The antireflection layer is not particularly limited as long as it can reduce the reflectance of the light beam on the lens surface. For example, the antireflective layer is formed by laminating alternately and repeatedly a high refractive index film and a low refractive index film. Examples thereof include a film whose refractive index is lowered by having a hollow part (for example, an airgel film, a film in which hollow particles are dispersed in a resin matrix, and the like).

The light-receiving lens of the present invention can be used in a reflection measuring device to measure the distance to an object to be measured.
This reflection measuring device usually includes a light source, an exit lens, the light receiving lens that collects the light beam that has passed through the exit lens and reflected by the object to be measured, and the light receiving device that receives the light beam collected by the light receiving lens. And a calculating means for calculating a distance between the object to be measured and the light source from a difference between a light reception time at the light receiving unit and an emission time of the light beam emitted from the light source.
As the light source, a semiconductor laser is preferably used, and one that emits an infrared ray having a wavelength of about 860 nm is usually used.
The emitted infrared ray is reflected by the surface of the object to be measured and collected through the light receiving lens of the present invention. The light receiving lens 51 is preferably provided with nine or more light beam splitting lenses having a toric surface on the same surface, and an orthogonal axis direction (y-axis = condensable ray of light that is normal to the optical axis of the light-receiving lens). The maximum incident angle (θx and θy) of light that can be collected on the axis in the direction that gives the maximum value θy among the incident angles and the x-axis = axis that is orthogonal to the y-axis is 0.05 <| θx / θy | <1 It satisfies the relationship. The condensed light is detected by the light receiving element 52. The light receiving element 52 is composed of, for example, a PIN photodiode, an avalanche photodiode, or the like.

The distance to the object to be measured is calculated from the difference between the light reception time and the light emission time of the light beam reflected by the object to be measured and incident on the light receiving element 52 through the light receiving lens 51 using the formula C 1.
Measurement distance = (time when light is received−time when light is emitted) × speed of light × 1/2 (formula C)

  6 and 7 show the condensing characteristics of the light receiving lens according to the embodiment of the present invention. The horizontal direction shows a substantially flat light receiving efficiency of 16% or more in a range of ± 10 °. The vertical direction shows a light receiving efficiency of 16% or more in a range of ± 1 °. It can be seen that wide-angle light can be collected without distortion.

It is the y-axis sectional view and x-axis sectional view which show the light-receiving lens of the present invention example. It is a figure which shows the position of the light beam splitting lens of the light reception lens of this invention Example. It is a perspective view which shows the light reception lens of this invention Example. It is a figure explaining an example of the range of the incident angle of the light reception lens of this invention Example. It is a figure which shows the positional relationship of the light reception lens of this invention Example, and a light-receiving part. It is a figure which shows the light reception efficiency of the y-axis direction (horizontal direction) of the light reception lens of this invention Example. It is a figure which shows the light reception efficiency of the x-axis direction (vertical direction) of the light reception lens of this invention Example.

Explanation of symbols

51: Light receiving lens 101: Light beam splitting lens 52: Light receiving element

Claims (8)

A beam splitting lens having a toric surface is provided on the same surface,
In the plane orthogonal to the optical axis of the light-receiving lens as a normal line (y-axis = axis that gives the maximum value θy of incident angles of condensing rays and x-axis = axis perpendicular to the y-axis) A light-receiving lens in which the maximum incident angle (θx and θy) of a light beam that satisfies light satisfies a relationship of 0.05 <| θx / θy | <1. The light receiving lens according to claim 1, wherein the incident angle in the y-axis direction has an angle distribution that is symmetric with respect to a plane including the optical axis and the x-coordinate axis. The light receiving lens according to claim 1, wherein the incident angle in the x-axis direction has an angle distribution that is symmetric with respect to a plane including the optical axis and the y-coordinate axis. The light beam splitting lens is rectangular, and the lens surface shape of the cross section formed by the optical axis and the x axis of the light beam splitting lens is formed by a straight line, a part of an aspherical cross section arc, or a part of a perfect circle arc. The lens surface shape of the cross section formed by the optical axis and the y axis of the light beam splitting lens is formed by a straight line, a part of an aspherical cross section arc, or a part of a perfect circle arc, and the entire light receiving lens is rectangular. The light-receiving lens according to any one of claims 1 to 3. 5. The light receiving lens according to claim 1, wherein an angle formed by the optical axis of the light beam splitting lens and the optical axis of the light receiving lens gradually increases as the distance from the point through which the optical axis of the light receiving lens passes. The light receiving lens according to claim 1, wherein the maximum thickness d is 2 mm <d <15 mm. The light receiving lens according to claim 1, wherein the lens body is made of resin, and an antireflection layer is formed on the surface of the lens body. The light receiving lens according to claim 1, wherein the light receiving lens has a slope parallel to a direction of a light incident angle at which the light can be condensed at a boundary between adjacent beam splitting lenses.

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