Lens array unit and image reading device

Abstract

[Problem] To reduce uneven illumination. [Solution] An optical system comprises: a first lens array provided closer to a subject and comprising a plurality of first lenses juxtaposed along a first direction perpendicular to the optical axis direction; a second lens array provided farther away from the subject and comprising a plurality of second lenses each having an optical axis aligned with the optical axis of a respective one of the plurality of first lenses; and a third lens array provided between the first lens array and the second lens array and comprising a plurality of third lenses each having an optical axis aligned with the optical axis of a respective one of the plurality of first lenses. The field-of-view width, which is the size in the first direction of the field of view of a unit optical system including a first lens, a second lens, and a third lens with the same optical axis, is at least twice the lens period of the first lens array. The first lens array, second lens array, and third lens array have positive refractive power.

Description

Lens array unit and image reading device

[0001] The present invention relates to a lens array unit and an image reading device.

[0002] Conventionally, contact image sensors (CIS) have been used as image reading devices in scanners and industrial cameras used in visual inspections. One proposed contact image sensor includes a lens array unit that forms an erect, equal-magnification imaging optical system using a first lens array that forms a reduced, equal-size image as an intermediate image and a second lens array that forms an enlarged, inverted image of the intermediate image (see, for example, Patent Document 1).

[0003] JP 2013-45093 A

[0004] As shown in FIG. 6 , the conventional technology uses a lens array in which circular lenses 200 are arranged in an array so as to be tangent to the Z direction, which is the optical axis direction, and the X direction, which is perpendicular to the Z direction. However, since the area Ar1 where light from a subject located on the optical axis of a certain lens 200 enters the lens 200 is different from the area Ar2 where light from a subject located on the boundary between two adjacent lenses 200 enters the lens 200, there is a problem of large unevenness in the amount of light.

[0005] To solve this problem, it is conceivable to use a lens array in which lenses 300 are arranged in an array so that the lenses 300 overlap in the X direction at a period that is half the lens diameter (length in the Y direction), as shown in Fig. 7. In this way, the area Ar3 through which light from an object located on the optical axis of a certain lens 300 enters the lens 300 is approximately equal to the area Ar4 through which light from an object located on the boundary between two adjacent lenses 300 enters the lens 300, thereby reducing unevenness in the amount of light.

[0006] 7, for example, in order to image all incident light having an area Ar3 by the lens 300, the field of view width, which is the size of the field of view in the X direction, needs to be at least twice the lens period (i.e., the lens width, which is the size of the lens 300 in the X direction). Furthermore, in the case of the lens array shown in FIG. 7, the field of view width is desirably large enough to image light from a subject located on the optical axis of the adjacent lens 300.

[0007] However, when the lens array unit is configured with two lens arrays as in the conventional technology, if the refractive power of the lenses 300 of the first lens array is small due to manufacturing reasons or the results of lens shape optimization, and the imaging magnification of the intermediate image formed by the first lens array is greater than 0.5, the imaging position of the intermediate image of light from a subject located on the optical axis of a lens 300 adjacent to a certain lens 300 will extend outside the lens width of that certain lens 300. In this case, the light extending outside the lens width will be cut off by a light blocking member (for example, an aperture array) intended to remove crosstalk light to the adjacent lens 300, ultimately resulting in large unevenness in the amount of light.

[0008] As described above, the conventional technology has had the problem that it is difficult to reduce unevenness in the amount of light in the lens array unit.

[0009] The present invention has been made in consideration of the above points, and aims to propose a lens array unit and an image reading device that can reduce unevenness in the amount of light.

[0010] In order to solve this problem, the lens array unit of the present invention is an optical system comprising: a first lens array provided on the side closer to the subject, having a plurality of first lenses, the first lenses being arranged side by side along a first direction perpendicular to the optical axis direction of the first lenses; a second lens array provided on the side farther from the subject, having a plurality of second lenses whose optical axes overlap with those of the first lenses, the second lenses being arranged side by side along the first direction; and a third lens array provided between the first lens array and the second lens array, having a plurality of third lenses whose optical axes overlap with those of the first lenses, the third lenses being arranged side by side along the first direction, wherein a field width, which is the size in the first direction of the field of view of a unit optical system including the first lenses, the second lenses, and the third lenses with the same optical axis, is at least twice the lens period of the first lens array, and the first lens array, the second lens array, and the third lens array have positive refractive power.

[0011] An image reading device of the present invention includes the above-described lens array unit and an imaging element board on which an imaging element that receives light that has passed through the lens array unit is mounted.

[0012] In the present invention, even if the refractive power of the first lens is small, by combining the first lens array with a third lens eye, the imaging magnification of the intermediate image can be made 0.5 times or less, and the field of view width can be made more than twice the lens period, thereby reducing unevenness in the amount of light.

[0013] According to the present invention, it is possible to realize a lens array unit and an image reading device that can reduce unevenness in the amount of light.

[0014] FIG. 1 is a perspective view showing the configuration of an image inspection device according to an embodiment. FIG. 2 is a perspective view showing the external configuration of an image reading device according to an embodiment. FIG. 3 is a cross-sectional view showing the internal configuration of an image reading device according to an embodiment. FIG. 4 is a table showing an example of the radius of curvature, conic constant, aspherical coefficient, and distance from an imaging element of each lens according to an embodiment. FIG. 5 is a cross-sectional view showing the path of light passing through a lens array unit according to an embodiment. FIG. 6 is a diagram showing the configuration (1) of a conventional lens array. FIG. 7 is a diagram showing the configuration (2) of a conventional lens array.

[0015] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0016] 1 shows the configuration of an image inspection device 10 according to this embodiment. This image inspection device 10 has a transport system 12 such as a belt conveyor that transports an inspection object 11, an image reading device 101 that reads an image of the inspection object 11 transported by the transport system 12, and a computing device 14 connected to the image reading device 101 via a cable 13.

[0017] The conveying system 12 has a conveying member 12a such as a belt, and is configured to place and convey the inspection object 11 on the conveying member 12a. Fig. 1 shows an example in which a plurality of inspection objects 11 are placed side by side in the conveying direction of the conveying member 12a, and also placed side by side in the width direction perpendicular to the conveying direction of the conveying member 12a.

[0018] The image reading device 101 is a contact type image sensor disposed above the conveying member 12a, and is a device that reads an image of one line along the width direction of the conveying member 12a (that is, a one-dimensional image).

[0019] In this image inspection device 10, while the inspection object 11 is transported by the transport system 12, the image reading device 101 continuously reads one line of images and sequentially transmits the read images to the calculation device 14 via the cable 13. The calculation device 14 forms a two-dimensional image (i.e., a planar image) by synthesizing the one-line images (i.e., one-dimensional images) continuously transmitted from the image reading device 101, and uses the formed image to detect flaws and inspect the dimensions of each inspection object 11. Note that by mounting an electronic component that performs calculation processing on the image reading device 101, the image reading device 101 may synthesize the read images and transmit the synthesized image to the calculation device 14.

[0020] [2. Configuration of Image Reading Device] Next, the configuration of the image reading device 101 used in the above-mentioned image inspection device 10, etc., will be described in more detail with reference to Figures 2 and 3. Figure 2 is a perspective view showing the external configuration of the image reading device 101, and Figure 3 shows a cross-sectional view showing the internal configuration of the image reading device 101 on the left side of the figure, and a partially enlarged view of a portion of the cross-sectional view on the right side of the figure. Note that, hereinafter, the optical axis direction of the optical system of the image reading device 101 is referred to as the Z direction. The +Z direction is the direction approaching the subject (upward in Figure 2), and the -Z direction is the direction moving away from the subject.

[0021] The image reading device 101 is a contact-type image sensor that is generally rod-shaped and long in the X direction, which is perpendicular to the Z direction (optical axis direction), and reads an image of a subject such as the above-mentioned inspection object 11 (FIG. 1) as one-dimensional data (one line's worth of data) along the X direction. A two-dimensional image can be obtained by continuously reading images using the image reading device 101 while displacing the subject in the Y direction, which is perpendicular to the Z and X directions, or while displacing the image reading device 101 in the Y direction.

[0022] In this embodiment, the distance from the subject to the lens (first lens 110a described later) of the image reading device 101 is set to 20 mm. The length of the image reading device 101 in the X direction is defined as the width of the image reading device 101.

[0023] As shown in the cross-sectional view of the image reading device 101 taken at a predetermined point in the X direction on the left side of Figure 3, the image reading device 101 is composed of an image sensor substrate 102, a lens array unit 103, and a holder 104.

[0024] The holder 104 is a member that holds the imaging element substrate 102 and the lens array unit 103. The holder 104 is a hollow member that is long in the X direction and has a generally convex cross section in which a first portion 104a on the +Z direction side (the side closer to the subject, which is the upper portion in the drawing) is shorter in the Y direction than a second portion 104b on the −Z direction side (the side farther from the subject, which is the lower portion in the drawing).

[0025] The holder 104 holds the lens array unit 103 inside a first portion 104a, and holds the image pickup element substrate 102 inside a second portion 104b. The lens array unit 103 and the image pickup element substrate 102 are held in close contact with the inside of the holder 104 by, for example, an adhesive (not shown).

[0026] The holder 104 also has an opening 104c on one surface in the +Z direction (the top surface in the figure), and the opening 104c is closed by one surface of the lens array unit 103 (i.e., one surface of the lens array unit 103 is exposed through the opening 104c). The holder 104 also has an opening 104d on one surface in the -Z direction (the bottom surface in the figure), and the opening 104d is closed by the imaging element substrate 102.

[0027] The holder 104 of this embodiment is produced by, for example, metal cutting, sheet metal processing, or resin injection molding.

[0028] The image pickup element board 102 is a plate-shaped member, and is equipped with an image pickup element 102a that converts the optical image formed by the lens array unit 103 into an image signal, a connector (not shown) for electrically connecting to an external control device (not shown), and various electronic components (not shown) for driving the image pickup element 102a. The image pickup element board 102 is a printed circuit board made of FR-4 (glass epoxy board) or the like.

[0029] The image sensor 102a is, for example, a CCD (Charge Coupled Device) with a length in the X direction of about 10 mm. The image sensors 102a are mounted continuously in the X direction on one surface in the +Z direction of the image sensor substrate 102 (the surface facing the lens array unit 103). If the width of the image reading device 101 is, for example, 250 mm, 25 image sensors 102a are mounted in the X direction on one surface of the image sensor substrate 102, and these 25 image sensors 102a form a line sensor.

[0030] The lens array unit 103 is an optical system consisting of a first lens array 110 provided on the side closer to the subject, a second lens array 111 provided on the side farther from the subject, a third lens array 112 provided between the first lens array 110 and the second lens array 111, a first aperture array 113 provided between the first lens array 110 and the third lens array 112, and a second aperture array 114 provided between the third lens array 112 and the second lens array 111.

[0031] As shown in a partially enlarged view of the lens array unit 103 on the right side of Figure 3, the first lens array 110 is a plate-shaped member that is long in the X direction, and multiple first lenses 110a are formed in an array on one surface in the +Z direction (the surface closer to the subject) so that they are in contact with each other in the X direction.

[0032] The first lens array 110 is held by the holder 104 so that the first lenses 110a formed on one surface in the +Z direction (the surface closer to the subject) are exposed from the opening 104c of the holder 104.

[0033] The second lens array 111 is also a plate-shaped member that is long in the X direction, and has a plurality of subject-side second lenses 111a formed in an array on one surface in the +Z direction (the surface closer to the subject) so that they are in contact with the X direction, and a plurality of image-capturing-element-side second lenses 111b formed in an array on one surface in the -Z direction (the surface closer to the image-capturing element 102a) so that they are in contact with the X direction.

[0034] The third lens array 112 is also a plate-like member that is long in the X direction, and a plurality of third lenses 112a are formed in an array on one surface in the +Z direction (the surface closer to the subject) so as to be in contact with the X direction. The third lens array 112 is provided so that the third lenses 112a are located at positions closer to the first lens array 110 in the Z direction than the position at which the intermediate image of the subject is formed by the first lens array 110.

[0035] The second lens array 111 and the third lens array 112 are arranged so that the optical axis of each lens (the subject-side second lens 111a, the image sensor-side second lens 111b, and the third lens 112a) coincides with the optical axis of each first lens 110a of the first lens array 110. In other words, the lens arrays (the first lens array 110, the second lens array 111, and the third lens array 112) are arranged so that the optical axes of each lens (the first lens 110a, the subject-side second lens 111a, the image sensor-side second lens 111b, and the third lens 112a) coincide.

[0036] In this embodiment, as an example, the thickness (length in the Z direction) of first lens array 110, second lens array 111, and third lens array 112 is set to 1 mm. Also in this embodiment, as an example, first lens 110a, subject-side second lens 111a, image-capturing-element-side second lens 111b, and third lens 112a are each convex lenses having a diameter (length in the Y direction) of 1 mm and a width (length in the X direction) of 0.5 mm, and having a substantially racetrack shape (see FIG. 7 ), and are each arranged in an array at a period of 0.5 mm in the X direction.

[0037] The radius of curvature r [mm], conic constant k, aspheric coefficient A, and distance [mm] from the image sensor 102a of each lens (first lens 110a, subject-side second lens 111a, image sensor-side second lens 111b, and third lens 112a) are shown in the table of Fig. 4. The first lens 110a, subject-side second lens 111a, and third lens 112a are convex lenses that are convex in the +Z direction (toward the subject), and the image sensor-side second lens 111b is a convex lens that is convex in the -Z direction (toward the image sensor 102a).

[0038] Furthermore, the shape of each lens can be expressed by the following equation 1, where z is the displacement from the vertex of the surface in the optical axis direction, r is the radius of curvature, h is the height from the optical axis in a direction perpendicular to the optical axis, k is the conic constant, and A is a fourth-order aspherical coefficient.

[0039]

[0040] The lens array unit 103 is an erect equal-size optical system in which the first lens array 110, the second lens array 111, and the third lens array 112 have positive refractive power, and the first lens array 110 and the third lens array 112 form an inverted, reduced image of the subject as an intermediate image, and the second lens array 111 forms an inverted, enlarged image of the intermediate image, thereby forming an erect equal-size image of the subject on the image sensor 102a.

[0041] Note that the radius of curvature r [mm], conic constant k, aspherical coefficient A, and distance [mm] from the image sensor 102a of each lens shown in the table of Figure 4 are examples, and the first lens array 110, second lens array 111, and third lens array 112 may be optical systems that can form an erect, life-size image of the subject on the image sensor 102a.

[0042] In addition, the first lens array 110, the second lens array 111, and the third lens array 112 in this embodiment are formed by injection molding of a transparent resin, for example, and APL5514ML from Mitsui Chemicals, Inc. is used as the transparent resin.

[0043] In addition, the lens array unit 103 is an optical system in which the field of view width, which is the size in the X direction of the field of view (the field of view of the unit optical system including the first lens 110a, the subject-side second lens 111a, the image sensor-side second lens 111b, and the third lens 112a on the same optical axis), is at least twice the lens period in the X direction.

[0044] As will be described in more detail later, the lens array unit 103 of this embodiment is configured so that the third lens array 112 changes the direction of light that has passed through the first lens array 110 so that light that enters from a subject on the optical axis of a lens adjacent to the first lens 110a of the first lens array 110 and passes through the first lens array 110 enters the second lens array 111 without going outside the lens width of the first lens 110a, i.e., so that the imaging magnification of the intermediate image is 0.5 times or less.

[0045] 3 , the first aperture array 113 has first apertures 113a formed by holes having a substantially racetrack shape that is slightly smaller than the first lenses 110a of the first lens array 110 (i.e., holes having a shape similar to the outer shape of the first lenses 110a) that penetrate the first aperture array 113 in the Z direction, and the first apertures 113a are arranged in an array at a period of 0.5 mm in the X direction. The period of the first apertures 113a is the same as the period of the first lenses 110a. In other words, the first aperture array 113 is arranged so that the optical axis of the first lens 110a passes through the center of each first aperture 113a when viewed in the Z direction.

[0046] The second aperture array 114 has second apertures 114a formed by holes having a generally racetrack shape that is slightly smaller than the third lenses 112a of the third lens array 112 (i.e., holes having a shape similar to the outer shape of the third lenses 112a) that penetrate the array in the Z direction, and the second apertures 114a are arranged in an array at a period of 0.5 mm in the X direction. The period of the second apertures 114a is the same as the period of the third lenses 112a. In other words, the second aperture array 114 is arranged so that the optical axis of the third lenses 112a passes through the center of each second aperture 114a when viewed in the Z direction.

[0047] The first aperture array 113 and the second aperture array 114 of this embodiment are produced by, for example, cutting metal or injection molding resin, etc. The image reading device 101 is configured as described above.

[0048] [3. Operation of Image Reading Device] Next, a brief description will be given of the operation of the image reading device 101. The image reading device 101 collects light from a subject using the first lens array 110, and forms an inverted, reduced intermediate image using the first lens array 110 and the third lens array 112. Furthermore, the image reading device 101 inverts and enlarges the inverted, reduced intermediate image formed by the first lens array 110 and the third lens array 112 using the second lens array 111, and forms an erect, life-size image on the image sensor 102a.

[0049] Here, light incident on a first lens 110a of the first lens array 110 passes through the first lens array 110 and is incident on a third lens 112a of the third lens array 112, but at this time, the first aperture array 113 prevents the light incident on the first lens 110a from being incident on a third lens 112a which has an optical axis different from that of the first lens 110a. In other words, the first aperture array 113 causes the light incident on the first lens 110a to be incident on a third lens 112a which has the same optical axis as the first lens 110a.

[0050] Furthermore, the light incident on the third lens 112a passes through the third lens array 112 and enters the subject-side second lens 111a of the second lens array 111, but at this time, the second aperture array 114 prevents the light incident on the third lens 112a from entering the subject-side second lens 111a, which has a different optical axis from the third lens 112a. In other words, the second aperture array 114 causes the light incident on the third lens 112a to enter the subject-side second lens 111a, which has the same optical axis as the third lens 112a.

[0051] The image reading device 101 then converts the erect, life-size image formed on the image sensor 102a into an image signal, thereby reading the image of the subject as one-dimensional data (one line's worth of data) along the X direction. The operation of the image reading device 101 is as described above.

[0052] Next, the operation of the third lens array 112 will be described in more detail with reference to Fig. 5. Fig. 5 is a cross-sectional view showing an XZ cross section of the first lens array 110, the first aperture array 113, the third lens array 112, and the second aperture array 114 as viewed from the Y direction.

[0053] The solid line L1 shown in Figure 5 indicates the path of light from a subject located on the optical axis of a first lens 110a (shown as 110a2 in the figure) adjacent to a first lens 110a (shown as 110a1 in the figure) in the first lens array 110 when the light is incident on the first lens 110a1.

[0054] Furthermore, the dotted line L2 shown in Figure 5 indicates the path of light when light from a subject located on the optical axis of the first lens 110a2 adjacent to the first lens 110a1 of the first lens array 110 is incident on the first lens 110a1 when the third lens array 112 is not present.

[0055] The farther away from the optical axis the light is incident, the greater the inclination of the light ray incident on the first lens 110a relative to the optical axis direction (Z direction) (the inclination of the solid line L1 and dotted line L2 relative to the Z direction).

[0056] Here, if the refractive power of first lens array 110 is insufficient due to reasons such as the fact that lenses can only be formed on one side due to limitations in lens manufacturing costs or lens manufacturing technology, and the imaging magnification when an intermediate image is formed using only first lens array 110 is greater than 0.5, then without third lens array 112, the image position when light from a subject located on the optical axis of first lens 110a2 adjacent to first lens 110a1 enters first lens 110a1 will extend outside the lens width of first lens 110a1, as shown by dotted line L2. In this case, the light extending outside the lens width is blocked by the wall surface of second opening 114a of second opening array 114 and does not enter second lens array 111.

[0057] Therefore, in this embodiment, as shown by the solid line L1, when light from a subject located on the optical axis of the first lens 110a2 adjacent to the first lens 110a1 is incident on the first lens 110a1, the imaging position is such that it does not extend outside the lens width of the first lens 110a1, i.e., the imaging magnification of the intermediate image is 0.5 times or less (more strictly, so that it does not come into contact with the wall surface of the second opening 114a of the second opening array 114), and the light that has passed through the first lens array 110 is bent by the third lens array 112 toward the center of the lens width (i.e., inside the second opening 114a).

[0058] In this way, light from a subject located on the optical axis of first lens 110a2 adjacent to first lens 110a1 (light incident from the edge of the field of view when the field of view width is twice the lens period) enters first lens 110a1, passes through first lens array 110, and is then incident on second lens array 111 without being blocked by the wall surfaces of second openings 114a of second aperture array 114. In other words, the field of view width of lens array unit 103 can be made twice the lens period. The operation of third lens array 112 is as described above.

[0059] [4. Summary and Effects] As described above, the image reading device 101 according to the present embodiment includes the lens array unit 103 and the image sensor board 102 on which the image sensor 102 a that receives light that has passed through the lens array unit 103 is mounted.

[0060] The lens array unit 103 is an optical system that forms an erect, life-size image of a subject on the image sensor 102a using the first lens array 110, the second lens array 111, and the third lens array 112.

[0061] The first lens array 110 is provided on the side closer to the subject and has a plurality of first lenses 110a, and the plurality of first lenses 110a are arranged side by side along the X direction, which is a first direction perpendicular to the optical axis direction of the first lenses 110a.

[0062] The second lens array 111 is provided on the side farther from the subject (the side closer to the image sensor 102a), and has a plurality of subject-side second lenses 111a and a plurality of image sensor-side second lenses 111b as a plurality of second lenses whose optical axes overlap with those of the plurality of first lenses 110a, respectively, so that the plurality of subject-side second lenses 111a are arranged side by side along the X direction, and the plurality of image sensor-side second lenses 111b are also arranged side by side.

[0063] The third lens array 112 is provided between the first lens array 110 and the second lens array 111, and has a plurality of third lenses 112a whose optical axes overlap with those of the plurality of first lenses 110a, and the plurality of third lenses 112a are arranged side by side along the X direction.

[0064] Furthermore, the lens array unit 103 has a field of view width, which is the size of the field of view in the X direction, that is at least twice the lens period, and the first lens array 110, the second lens array 111, and the third lens array 112 have positive refractive power. Furthermore, the first lens 110a has an imaging magnification of more than 0.5 times for the subject.

[0065] Furthermore, the third lens array 112 changes the direction of light that has passed through the first lens array 110 so that light that enters the first lens 110a of the first lens array 110 from a subject on the optical axis of an adjacent lens and passes through the first lens array 110 enters the second lens array 111 without going outside the lens width of the first lens 110a, i.e., so that the magnification of the intermediate image of the subject formed by the first lens array 110 and the third lens array 112 is 0.5x or less.

[0066] Specifically, the light passing through the first lens array 110 is bent by the third lens array 112 toward the center of the lens width (inside the wall surface of the second opening 114a) so that the intermediate image of a subject located on the optical axis of the first lens 110a2 adjacent to a certain first lens 110a1 (the edge of the field of view when the field of view width is twice the lens period) does not extend outside the lens width of the first lens 110a1 (more precisely, so as not to come into contact with the wall surface of the second opening 114a of the second opening array 114).

[0067] As described above, in image reading device 101 of the present embodiment, in order to ensure that at least the intermediate image of the subject on the optical axis of the adjacent lens (the edge of the field of view when the field of view width is twice the lens period) does not extend outside the lens width of first lens 110a1 (more strictly speaking, does not come into contact with the wall surface of second aperture 114a of second aperture array 114), third lens 112a bends light inward so that when the image is formed by first lens 110a1, it is not cut off by second aperture array 114. In other words, the magnification of the intermediate image of the subject formed by first lens array 110 and third lens array 112 is set to 0.5 times or less, and as a result, the field of view width is set to be twice the lens period or more.

[0068] Thus, in the image reading device 101 of this embodiment, even if the refractive power of the first lens 110a is small, by combining it with the third lens array 112, the imaging magnification of the intermediate image can be made 0.5 times or less, and the field of view width can be made more than twice the lens period, thereby reducing unevenness in the amount of light.

[0069] [5. Other embodiments] [5-1. Other embodiment 1] In the above-described embodiment, the lens array unit 103 is an optical system configured of the first lens array 110, the second lens array 111, the third lens array 112, the first aperture array 113, and the second aperture array 114, but the present invention is not limited to this and may be an optical system having at least three lens arrays, or may be an optical system having four or more lens arrays.

[0070] In the above-described embodiment, the first lens array 110 is configured to have a plurality of first lenses 110a formed on the surface closer to the subject, but this is not limiting, and lenses may be formed on one or both of the surface closer to the subject and the surface farther from the subject. The same applies to the second lens array 111 and the third lens array 112.

[0071] Furthermore, although the lenses formed in each lens array have a racetrack shape like a circle with both ends cut off in the diametric direction, other shapes may be used.Furthermore, although the apertures formed in each aperture array have been described as holes similar in shape to the lenses formed in each lens array penetrating in the optical axis direction, the present invention is not limited to this and may have other shapes.

[0072] [5-2. Other embodiment 2] Furthermore, in the above-described embodiment, the field of view width, which is the size of the field of view of the lens array unit 103 in the X direction, is set to twice the lens width of the first lenses 110a of the first lens array 110. However, the field of view width of the lens array unit 103 may be set to at least twice the lens width (lens period), which is the size of the first lenses 110a in the X direction.

[0073] [5-3. Alternative Embodiment 3] Furthermore, in the above-described embodiment, the present invention is applied to the image reading device 101 as a line sensor that reads an image of a subject as one-dimensional data by arranging lenses and image sensors side by side in the X direction perpendicular to the optical axis, but is not limited to this. The present invention can also be applied to an image reading device as an area sensor that reads an image of a subject as two-dimensional data by arranging lenses and image sensors side by side in the X direction and Y direction perpendicular to the optical axis. In this case, for example, the lenses of the first lens array 110, the second lens array 111, and the third lens array 112 and the apertures of the first aperture array 113 and the second aperture array 114 can be arranged side by side in the X direction and the Y direction, respectively.

[0074] Furthermore, in the above-described embodiment, the image reading device 101 equipped with the lens array unit 103 is used in the image inspection device 10, but the present invention is not limited to this, and the image reading device 101 may be used in devices other than the image inspection device 10. For example, the image reading device 101 may be used in devices such as a copy machine or a scanner. The same applies to the second embodiment.

[0075] Furthermore, in the above-described embodiment, the lens array unit 103 is used as the optical system of the image reading device 101, but the present invention is not limited to this, and the lens array unit 103 may be used as the optical system of a device other than the image reading device 101. For example, the lens array unit 103 may be used as the optical system of an exposure device employed in an image forming device such as a printer.

[0076] [5-4. Other Embodiment 4] Furthermore, the present invention is not limited to the above-described embodiments and other embodiments. That is, the scope of application of the present invention extends to embodiments in which the above-described embodiments and part or all of the above-described other embodiments are arbitrarily combined, or embodiments in which a part is extracted.

[0077] The present invention can be widely used in, for example, contact type image sensors.

[0078] 10...Image inspection device, 11...Object to be inspected, 14...Calculation device, 101...Image reading device, 102...Image capture element substrate, 102a...Image capture element, 103...Lens array unit, 104...Holder, 110...First lens array, 110a...First lens, 111...Second lens array, 111a...Second lens on the subject side, 111b...Second lens on the image capture element side, 112...Third lens array, 112a...Third lens, 113...First aperture array, 113a, 114a...Apertures, 114...Second aperture array.

Claims

1. An optical system comprising: a first lens array provided on the side closer to the subject, having a plurality of first lenses, the plurality of first lenses being arranged in a first direction perpendicular to the optical axis direction of the first lenses; a second lens array provided on the side farther from the subject, having a plurality of second lenses whose optical axes overlap with those of the plurality of first lenses, the plurality of second lenses being arranged in a first direction; and a third lens array provided between the first lens array and the second lens array, having a plurality of third lenses whose optical axes overlap with those of the plurality of first lenses, the plurality of third lenses being arranged in a first direction; wherein the field width, which is the size in the first direction of the field of view of a unit optical system including the first lenses, the second lenses, and the third lenses with the same optical axis, is at least twice the lens period of the first lens array, and the first lens array, the second lens array, and the third lens array have positive refractive power.

2. The lens array unit according to claim 1, wherein the first lens has an imaging magnification of an object greater than 0.5 times.

3. The lens array unit according to claim 1, wherein the optical system formed by the first lens and the third lens has an imaging magnification of 0.5 times or less.

4. The lens array unit described in claim 3 is an erect equal-magnification optical system in which the first lens array and the third lens array form an inverted, reduced image of the subject as an intermediate image, and the second lens array forms an inverted, enlarged image of the intermediate image.

5. The lens array unit according to claim 4, wherein the third lens array is arranged at a position closer to the first lens array in the optical axis direction than the position at which the subject is imaged by the first lens array.

6. The lens array unit described in claim 5, further comprising: a first aperture array provided between the first lens array and the third lens array, in which a plurality of first apertures formed to penetrate in the optical axis direction are aligned along the first direction at the same period as the first lenses; and a second aperture array provided between the third lens array and the second lens array, in which a plurality of second apertures formed to penetrate in the optical axis direction and have holes similar in shape to the third lenses are aligned along the first direction at the same period as the third lenses.

7. The lens array unit according to claim 6, wherein the first opening is an opening formed by passing through a hole having a shape similar to that of the first lens in the optical axis direction.

8. The lens array unit described in claim 6, characterized in that the intermediate image of a subject located on the optical axis of an adjacent optical system formed by the optical system consisting of the first lens and the third lens is located inside the wall surface of the second opening of the second aperture array.

9. An image reading device comprising: the lens array unit according to claim 1; and an imaging element board on which an imaging element that receives light that has passed through said lens array unit is mounted.

Images