JP2008160454A - Far-infrared imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a far-infrared imaging apparatus capable of preventing a lens from being damaged by a scatter, such as a fly stone without lowering light transmittance. <P>SOLUTION: The far-infrared imaging apparatus is provided with one or a plurality of lenses that converge, a plurality of imaging elements arranged in a matrix shape, an image processing circuit for forming an image on the basis of an output value in each of the imaging elements, and is provided with a net member at a prescribed position in front of the one or a plurality of lenses, for example, a net member configured in the shape of a grid. The net member is made of metal material and is provided at a position that is 5 mm or below from the front of the lenses. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a far-infrared imaging device that images the outside. In particular, the present invention relates to a far-infrared imaging device capable of preventing lens damage due to flying objects such as flying stones without reducing light transmittance.

  Many night vision systems using far infrared imaging devices capable of detecting the presence of obstacles such as pedestrians and bicycles at night have been developed in order to ensure the safety of vehicles such as automobiles. Usually, two far-infrared imaging devices are installed at a predetermined position in front of the vehicle, and the distance to the obstacle detected by stereo vision is calculated.

  The far infrared imaging device includes a lens, a shutter, an imaging device, and an image processing circuit. At the time of imaging, the shutter is opened and external light is condensed through the lens, and the luminance value detected by the imaging element is A / D converted by the image processing circuit and output as a digital signal.

However, when the far-infrared imaging device is installed on the front grill or the like of the vehicle, the lens is exposed from the vehicle, and there is a possibility that the surface of the lens may be damaged by scattered objects such as bounced stones. As a method for protecting the lens surface, for example, as disclosed in Patent Document 1, a method including a movable shutter for protecting the lens surface is disclosed.
JP 2002-327263 A

  However, in the method of protecting the lens surface by opening and closing the movable shutter, it is not possible to take an image with the shutter closed. It is also possible to provide a light-transmitting optical window in place of the shutter, but it is difficult to avoid attenuation of the amount of light because there is no substance with a far-infrared transmittance of 100%. There was a problem.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a far-infrared imaging device capable of preventing lens damage due to flying objects such as flying stones without reducing light transmittance. And

  In order to achieve the above object, a far-infrared imaging device according to a first aspect of the present invention is based on one or a plurality of condensing lenses, a plurality of imaging elements arranged in a matrix, and an output value for each imaging element. A far-infrared imaging device comprising an image processing circuit for forming an image, wherein a net member is provided at a predetermined position on the front surface of the lens.

  The far-infrared imaging device according to the second invention is characterized in that, in the first invention, the mesh member is made of a metal material.

  The far-infrared imaging device according to the third invention is characterized in that, in the first or second invention, the net member is provided at a position of 5 mm or less of the front surface of the lens.

  In the far-infrared imaging device according to the fourth aspect of the invention, the mesh member has a mesh interval of 5 (mm) or less, the tensile strength of the wire constituting the mesh member is a (N), and the wire member at the elastic limit When elongation is b (%) and the length of the wire is c (m), (a × 0.7) · b · c / 2 ≧ 1.5 (N · m) is satisfied. To do.

  In the first invention, far-infrared imaging including one or a plurality of condensing lenses, a plurality of imaging elements arranged in a matrix, and an image processing circuit that forms an image based on an output value for each imaging element A mesh member is provided at a predetermined position on the front surface of the lens of the apparatus. When a mesh member is installed at a position closer to the lens than the focal length of the lens and further away from the lens, the mesh member is not imaged, and only an image excluding the mesh member is captured. On the other hand, the scattered matter larger than the arrangement interval of the wire members constituting the net member can be prevented from reaching the lens, and damage to the lens surface due to the scattered matter can be suppressed.

  In the second invention, the net member is made of a metal material. By being composed of a metal material having high thermal conductivity, the ambient temperature and the temperature of the mesh member are substantially the same, and the mesh member is not reflected in an image captured by far infrared rays. Therefore, it is possible to capture an image excluding the net member while protecting the lens surface from scattered objects.

  In the third aspect of the invention, the net member is provided at a position equal to or smaller than the front surface 5 (mm) of the lens. By installing the mesh member at a position shorter than the focal length of the lens and not more than 5 mm in front of the lens, the image of the mesh member is not formed, and the image is taken without experimental blurring. The It is also possible to avoid indirectly damaging the surface of the lens due to the scattered object colliding with the net member.

  In the 4th invention, since the stitch | interval space | interval is 5 (mm) or less, the scattered matter which has an outer dimension of 5 (mm) or more collides with a net | network member. Further, the tension at the elastic limit of the wire constituting the net member is about 0.7 times the tensile strength (N), and the elongation of the wire at the elastic limit is b (%). Energy of 1/2) × (tensile strength a × 0.7) × (elongation b × length c) can be absorbed. And (a * 0.7) * b * c / 2 is 1.5 or more. Accordingly, it is possible to prevent the scattered matter having an outer dimension of 5 (mm) or more and having an energy of 1.5 (N · m) or less from reaching the lens. That is, the net member can almost block pebbles and the like that may fly while the vehicle is running, and can protect the lens from pebbles and the like.

  According to the present invention, when a mesh member is installed at a position closer to the lens than the focal length of the lens and at a position separated from the lens, the mesh member is not imaged and an image excluding the mesh member Only is imaged. On the other hand, the scattered matter larger than the arrangement interval of the wire members constituting the net member can be prevented from reaching the lens, and damage to the lens surface due to the scattered matter can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a far-infrared imaging device 1 according to an embodiment of the present invention. In addition, the far-infrared imaging device 1 which concerns on this Embodiment is an imaging device using the infrared light whose wavelength is 7-14 micrometers.

  In FIG. 1, the far-infrared imaging device 1 includes an objective lens 31 made of germanium, zinc sulfide, or the like, and an image imaging unit 11 is disposed on the back side of the objective lens 31. The image pickup unit 11 includes image pickup elements that convert optical signals into electric signals in a matrix. As the far-infrared imaging device, an infrared sensor such as a vanadium oxide bolometer type or a barium titanate pyroelectric type using a micromachining technique is used.

  The image capturing unit 11 reads an infrared light image around the vehicle as a luminance signal (a luminance value for each pixel), and transmits the read luminance signal to a signal processing unit 12 that is an LSI substrate. FIG. 2 is a block diagram showing a configuration of the signal processing unit 12 of the far-infrared imaging device 1 according to the embodiment of the present invention. The signal processing unit 12 includes an A / D conversion unit 121, a NUC (Non-Uniformity Correction) processing unit 122, a BPR (Bad-Pixel Replacement) processing unit 123, a non-volatile memory such as a flash memory, and a temporary storage such as an SRAM. The RAM 125 is a memory.

  The signal processing unit 12 converts the luminance value received from the image capturing unit 11 into a digital signal by the A / D conversion unit 121, and corrects the output luminance value for each image sensor by the NUC (Non-Uniformity Correction) processing unit 122. .

  In the NUC processing unit 122, as a correction coefficient by calibration, an offset correction value for correcting an output value for a predetermined temperature for each image sensor, and a gain correction for correcting a difference in output value for a predetermined temperature change rate for each image sensor. The value is calculated and the output luminance value is corrected. For example, when the output luminance value for each imaging element arranged in a matrix of i rows and j columns is Vij, the NUC processing unit 122 performs the calculation shown in (Equation 1) to obtain the output luminance value for each imaging element as V. Correct to 'ij.

  In (Expression 1), Gij represents a gain correction value, and Oij represents an offset correction value. For example, an output luminance value for each image sensor when an object having a uniform temperature distribution such as a black body furnace or a shutter is imaged. Is a value calculated based on

  The output luminance value V′ij for each image sensor corrected by the NUC processing unit 122 is corrected for defective pixels by the BPR processing unit 123 and is output via the communication interface unit 14 as a corrected luminance value V ″ ij. The output luminance value may be stored in the image memory 13 in units of frames.

  In the present embodiment, a cover 32 made of a net member is provided so as to cover the front surface of the objective lens 31. FIG. 3 is a plan view of the cover 32 as viewed from the front.

  The cover 32 has a wire rod 321 knitted in a lattice shape fixed by a lens frame 322 that is an annular support member. The lens frame 322 has a predetermined height so that the cover 32 is fixed and separated from the objective lens 31 by a distance L shorter than the focal length of the objective lens 31. Therefore, even when the grid-like wire 321 is imaged, the image of the wire 321 is not imaged by the image imaging unit 11, and only the object that is located further away is imaged. It will be in the same state.

  Further, in order to avoid the formation of an image in the image pickup unit 11 even when the image is not in focus and the image is blurred, the wire 321 of the cover 32 is preferably a metal material having high thermal conductivity. Since the thermal conductivity is high, the temperature of the wire 321 of the cover 32 is substantially the same as the surrounding temperature, and the difference from the background temperature is very small. It is possible to avoid erroneously detecting the wire 321 as an object.

Further, the wire 321 has a diameter of 0.7 (mm), a length of 5 (cm), a tensile strength of 820 (N / mm ² ), and an elastic limit elongation of 30% or more, such as stainless steel (SUS316). ). The tensile strength is 820 × 0.35 × 0.35 × 3.14 = 315 (N). In general, since the tension applied to the wire 321 at the elastic limit is about 0.7 times the tensile strength, it is 315 × 0.7 = 220 (N). The energy that can be absorbed by the wire 321 is (1/2) × (tension at the elastic limit) × (elongation of the wire 321 at the elastic limit) = 0.5 × 220 × (0.05 × 0.3) = 1.65. It is. Therefore, it is possible to prevent scattered objects having an outer dimension of 5 (mm) or more and energy of 1.65 or less from reaching the objective lens 31. For example, since the kinetic energy of a flying object having a weight of 2 g and a relative speed of 140 km / h with respect to the objective lens 31 is 1.51 (N · m), such a flying object is prevented from reaching the objective lens 31. can do.

  FIG. 4 is a diagram showing an example of an MTF diagram for comparing a modulation transfer function MTF (Modulation Transfer Function) with and without the lattice-like cover 32 attached. The spatial frequency F (cycle / mm) in FIG. 4 is a value obtained by converting the number of patterns per millimeter with respect to 1. FIG. 5 is an MTF diagram obtained by measuring the MTF when the various mesh members of FIGS. 4B to 4D are fixed to the front surface of the lens frame 322 and imaged. The distance between the objective lens 31 and the net member is about 5 (mm).

  FIG. 4A is an MTF diagram in a normal use state in which a mesh member is not provided on the front surface of the lens frame 322. At the spatial frequency F = 0.3, the MTF is approximately 0.28. FIG. 4B is an MTF diagram in the case where a net member using stainless steel (SUS316) having a wire diameter of 0.25 (mm) and a line spacing of approximately 5 (mm) is provided on the front surface of the lens frame 322. It is. At the spatial frequency F = 0.3, the MTF is approximately 0.22, and it can be seen that the degree of blur of the captured image is not so deteriorated despite the provision of the net member.

  FIG. 4C is an MTF diagram in the case where a net member using stainless steel (SUS316) having a wire diameter of 0.5 (mm) and a distance of approximately 5 (mm) is provided on the front surface of the lens frame 322. It is. At the spatial frequency F = 0.3, the MTF is approximately 0.18, and the MTF is deteriorated as compared with FIG. However, it is not greatly deteriorated as compared with the case where no mesh member is provided, and it can be seen that the degree of blur of the captured image is not so much deteriorated. FIG. 4D shows an MTF in the case where a mesh member made of a square member having a lattice interval of about 3 (mm) using a synthetic resin member and a side of about 1 (mm) is provided on the front surface of the lens frame 322. FIG. At the spatial frequency F = 0.3, the MTF is approximately 0.18, and the MTF is deteriorated as compared with FIG. However, it is not greatly deteriorated as compared with the case where no mesh member is provided, and it can be seen that the degree of blur of the captured image is not so much deteriorated.

  From the above measurement results, although the MTF deteriorates as the thickness of the wire constituting the mesh member increases, there is practically no difference from the case where the mesh member is not provided on the front surface of the objective lens 31. It is considered to be a fully usable range according to the required performance. Of course, it goes without saying that the thickness of the wire member of the mesh member that can be used is specified according to the required performance.

  Furthermore, by installing a net member at a position approximately 5 (mm) in front of the objective lens 31, damage to the lens due to a flying stone or the like during traveling can be prevented, and an expensive window capable of transmitting far-infrared rays. The objective lens 31 can be protected by an inexpensive net member without using a member.

  Furthermore, it is possible to prevent a scattered object having an outer dimension of 5 (mm) or more and an energy of 1.65 or less from reaching the objective lens 31.

In the present embodiment, the case where the mesh member is configured in a lattice shape is described, but the arrangement interval of the wire constituting the mesh member can maintain the same interval as in the above-described embodiment. If it is, it will not be limited in particular to comprise in a grid | lattice form.
In the embodiment, the wire rod is a stainless steel having a diameter of 0.7 (mm) and a length of 5 (cm), a tensile strength of 820 (N / mm ² ), and an elongation at the elastic limit of 30% or more ( SUS316) is adopted, but if (1/2) × (tension at the elastic limit) × (elongation of the wire at the elastic limit) ≧ 1.5 is satisfied, even if the wire is constituted by other members good.
Furthermore, in the present embodiment, the objective lens made of germanium or zinc sulfide has been described. However, the objective lens may be made of other materials such as chalconide glass.

It is a block diagram which shows the structure of the far-infrared imaging device which concerns on embodiment of this invention. It is a block diagram which shows the structure of the signal processing part of the far-infrared imaging device which concerns on embodiment of this invention. It is the top view which looked at the cover from the front. It is a figure which shows an example of the MTF diagram for comparing the modulation transfer function MTF with the case where a lattice-like cover is attached, and the case where it is not attached.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Far-infrared imaging device 11 Image pick-up part 12 Signal processing part 13 Image memory 14 Communication interface part 15 Internal bus 31 Objective lens 32 Cover 321 Wire material 322 Lens frame

Claims (4)

One or more lenses for focusing;
A plurality of imaging devices arranged in a matrix;
In a far-infrared imaging device comprising: an image processing circuit that forms an image based on an output value for each imaging element;
A far-infrared imaging device comprising a mesh member at a predetermined position on the front surface of the lens.   The far-infrared imaging device according to claim 1, wherein the net member is made of a metal material.   The far-infrared imaging device according to claim 1, wherein the mesh member is provided at a position of 5 mm or less in front of the lens. The mesh member has a mesh interval of 5 mm or less,
When the tensile strength of the wire constituting the mesh member is a (N), the elongation of the wire at the elastic limit is b (%), and the length of the wire is c (m), (a × 0.7 4. The far-infrared imaging device according to claim 1, wherein b · c / 2 ≧ 1.5 (N · m) is satisfied.

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