Lens array unit and image reading device

Abstract

[Problem] To obtain excellent imaging performance at a low cost compared with conventional technologies. [Solution] The present invention is provided with a first lens array and a second lens array, at least one of the first lens array and the second lens array having a light-transmissive lens array substrate formed of a material having a linear expansion coefficient smaller than that of a resin forming the lens. A resin layer is formed in close contact with at least one of a light incident surface of the lens array substrate, and a light emission surface of the lens array substrate opposite from the light incident surface, and a plurality of the lenses are formed in the resin layer.

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 contact image sensor proposed is one that forms an erect, equal-magnification imaging optical system using a lens array unit composed of multiple resin lens arrays made by injection molding (see, for example, Patent Document 1).

[0003] JP 2013-45093 A

[0004] However, a contact-type image sensor with a resin lens array has a larger linear expansion coefficient than the image sensor substrate, such as FR-4 (glass epoxy board), on which the image sensor is mounted. For this reason, in conventional contact-type image sensors, the positions of the lens array and the image sensor can be significantly misaligned when the temperature changes, which can cause corrections such as shading correction for a certain pixel to become less than optimal, resulting in poor imaging performance.

[0005] In contrast, if the lens array is molded from glass, which has a smaller linear expansion coefficient than resin, it is possible to suppress misalignment between the lens array and the image sensor when the temperature changes, and better imaging performance can be obtained than when the lens array is molded from resin.However, on the other hand, producing a lens array from glass by cutting or other processes increases the cost.

[0006] 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 obtain good imaging performance at low cost.

[0007] In order to solve such problems, the lens array unit of the present invention comprises: a first lens array having a plurality of lenses, the plurality of lenses being arranged side by side along a first direction perpendicular to the optical axis direction of the lenses; and a second lens array arranged at a distance from the first lens array in the optical axis direction, the plurality of lenses being arranged side by side along the first direction so that the optical axes of the plurality of lenses coincide with the lenses of the first lens array; at least one of the first lens array and the second lens array has a light-transmitting lens array substrate formed from a material having a smaller linear expansion coefficient than the resin forming the lenses; and a resin layer is formed in close contact with at least one of one surface of the lens array substrate that is the light incident side and the other surface opposite to the first surface that is the light exit side, and the plurality of lenses are formed in the resin layer.

[0008] The image reading device of the present invention also comprises a lens array unit having a lens array in which a plurality of lenses are arranged in a line along a first direction perpendicular to the optical axis direction of the lenses, and an imaging element substrate on which an imaging element that receives light that has passed through the lens array unit is mounted, the lens array having a light-transmitting lens array substrate formed of a material having a linear expansion coefficient smaller than that of the resin forming the lenses, and a resin layer formed in close contact with at least one of one surface of the lens array substrate that is the light incident side and the other surface opposite to the one surface that is the light exit side, and the plurality of lenses are formed in the resin layer.

[0009] In the present invention, a lens array is constructed using a lens array substrate formed of a material with a linear expansion coefficient lower than that of the resin forming the lenses, and lenses formed in a resin layer that is in close contact with the lens array substrate. This reduces the difference in linear expansion coefficient between the lens array substrate and the image sensor substrate, thereby preventing misalignment between the lens array and the image sensor during temperature changes. Furthermore, rather than forming the entire lens array from a material with a linear expansion coefficient lower than that of resin and therefore more expensive, costs can be reduced by forming the lens array substrate from the material and then forming the lenses on the lens array substrate from resin.

[0010] According to the present invention, it is possible to realize a lens array unit and an image reading device that can obtain good imaging performance at a lower cost than conventional devices.

[0011] 7 is a perspective view showing the configuration of an image inspection device according to a first embodiment. FIG. 8 is a perspective view showing the external configuration of an image reading device according to a first embodiment. FIG. 9 is a cross-sectional view showing the internal configuration of an image reading device according to a first embodiment. FIG. 10 is an enlarged cross-sectional view of a portion of FIG. 3. FIG. 11 is a table showing an example of the radius of curvature, conic constant, aspherical coefficient, and distance from the imaging element of each lens according to the first embodiment. FIG. 12 is a table showing an example of the refractive index, Abbe number, and thickness of each lens and each substrate according to the first embodiment. FIG. 13 is a cross-sectional view showing the internal configuration of an image reading device according to a second embodiment. FIG. 14 is an enlarged cross-sectional view of a portion of FIG. 7. FIG. 15 is a table showing an example of the radius of curvature, conic constant, aspherical coefficient, and distance from the imaging element of each lens according to a second embodiment.

[0012] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0013] 1 shows the configuration of an image inspection device 10 according to this embodiment. The image inspection device 10 includes a conveyance system 12 such as a belt conveyor that conveys an inspection object 11, an image reading device 101 that reads an image of the inspection object 11 conveyed by the conveyance system 12, and a computing device 14 connected to the image reading device 101 via a cable 13.

[0014] 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.

[0015] 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).

[0016] 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.

[0017] [1-2. Configuration of Image Reading Device] Next, the configuration of the image reading device 101 used in the image inspection device 10 described above and the like 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 is a cross-sectional view showing the internal configuration of the image reading device 101. 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.

[0018] 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.

[0019] In this embodiment, the distance from the subject to the lens of the image reading device 101 (first lens 110d, described later) is set to 20 mm. The length of the image reading device 101 in the X direction is set to approximately 300 mm so that it can scan A3 size documents. The length of the image reading device 101 in the X direction is defined as the width of the image reading device 101.

[0020] As shown in FIG. 3, which is a cross-sectional view of the image reading device 101 taken at a predetermined point in the X direction, the image reading device 101 is composed of an image pickup element substrate 102, a lens array unit 103, and a holder 104.

[0021] 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).

[0022] 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).

[0023] 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.

[0024] The imaging element board 102 is a plate-shaped member, and is equipped with an imaging 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 imaging element 102a. The imaging element board 102 is a printed circuit board made of FR-4 (glass epoxy board) or the like, and generally, the linear expansion coefficient of printed circuit boards such as FR-4 is 14×10 －６ / ℃.

[0025] 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 of the image sensor substrate 102 in the +Z direction (the surface facing the lens array unit 103). In the present embodiment, 30 image sensors 102a are mounted in the X direction on one surface of the image sensor substrate 102, and these 30 image sensors 102a form a line sensor. The resolution of this line sensor is, for example, 600 dpi (42 μm period).

[0026] The lens array unit 103 is an optical system configured with 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, and an aperture array 112 provided between the first lens array 110 and the second lens array 111. In other words, the lens array unit 103 is an optical system in which the first lens array 110 and the second lens array 111 are arranged with a gap in the Z direction (optical axis direction), and the aperture array 112 is arranged between the first lens array 110 and the second lens array 111.

[0027] As shown in an enlarged view in Figure 4, the first lens array 110 is composed of a first lens array substrate 110a, which is a plate-shaped glass that is long in the X direction, a first resin layer 110b formed in close contact with one surface of the first lens array substrate 110a in the +Z direction (the surface closer to the subject), and a second resin layer 110c formed in close contact with one surface of the first lens array substrate 110a in the -Z direction (the surface farther from the subject).

[0028] A plurality of first lenses 110d are formed in an array on the first resin layer 110b so as to be in contact with each other in the X direction. A plurality of second lenses 110e are also formed in an array on the second resin layer 110c so as to be in contact with each other in the X direction.

[0029] The first resin layer 110b and the second resin layer 110c are layers of resin that has ultraviolet curing or heat curing properties, and the first lens 110d and the second lens 110e are formed by imprint technology.

[0030] The first lens array 110 is held in the holder 104 so that the first lens 110d formed on one surface (the surface closer to the subject) of the first lens array substrate 110a in the +Z direction is exposed from the opening 104c of the holder 104.

[0031] As shown in Figure 3, the second lens array 111 has the same configuration as the first lens array 110, and is composed of a second lens array substrate 111a, a third resin layer 111b formed in close contact with one surface of the second lens array substrate 111a in the +Z direction, and a fourth resin layer 111c formed in close contact with the other end surface of the second lens array substrate 111a in the Z direction.

[0032] A plurality of third lenses 111d are formed in an array on the third resin layer 111b so as to be in contact with each other in the X direction. A plurality of fourth lenses 111e are also formed in an array on the fourth resin layer 111c so as to be in contact with each other in the X direction.

[0033] In this embodiment, the first lens 110d, the second lens 110e, the third lens 111d, and the fourth lens 111e are each a circular convex lens with a diameter of 1 mm, and are arranged in an array at a period of 1 mm in the X direction so that their optical axes coincide.

[0034] The radius of curvature r [mm], conic constant k, aspherical coefficient A, and distance [mm] from the image sensor 102a of each lens (first lens 110d, second lens 110e, third lens 111d, and fourth lens 111e) are shown in the table of Fig. 5. The first lens 110d and the third lens 111d are convex lenses that are convex on the +Z direction side (toward the subject), and the second lens 110e and the fourth lens 111e are convex lenses that are convex on the -Z direction side (toward the image sensor 102a).

[0035] 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.

[0036]

[0037] The lens array unit 103 forms an inverted, reduced image of the subject as an intermediate image using the first lens array 110, and then forms an inverted, enlarged image of the intermediate image using the second lens array 111, thereby forming an erect, equal-size image of the subject on the image sensor 102a.

[0038] 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 5 are examples, and the first lens array 110 and the second lens array 111 may be any optical system that can form an erect, life-size image of the subject on the image sensor 102a.

[0039] Furthermore, the refractive index, Abbe number, and thickness [mm] of each lens (first lens 110d, second lens 110e, third lens 111d, fourth lens 111e) and each substrate (first lens array substrate 110a, second lens array substrate 111a) are shown in the table of FIG. 6. The linear expansion coefficient of the glass forming the first lens array substrate 110a and the second lens array substrate 111a is generally 9×10 －６ / °C, and the linear expansion coefficient of the resin forming each resin layer (first resin layer 110b, second resin layer 110c, third resin layer 111b, fourth resin layer 111c) is generally 70×10 －６ / ℃.

[0040] 3 and 4, the aperture array 112 has apertures 112a formed by circular holes that are slightly smaller than the lenses of the first lens array 110 and the second lens array 111 penetrating in the Z direction, and the apertures 112a are arranged in an array at a period of 1 mm in the X direction. Each aperture array 112 is arranged so that the optical axis of each lens of the first lens array 110 and the second lens array 111 passes through the center of a circle as viewed in the Z direction.

[0041] In this embodiment, the aperture array 112 is formed by cutting stainless steel. The linear expansion coefficient of the stainless steel forming the aperture array 112 is generally 12×10 －６ / °C. Alternatively, the aperture array 112 may be made of another material such as aluminum. Generally, the linear expansion coefficient of aluminum is 25×10 －６ / ° C. The image reading device 101 has the above-described configuration.

[0042] [1-3. 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 to form an inverted, reduced intermediate image. The image reading device 101 then inverts and enlarges the inverted, reduced intermediate image formed by the first lens array 110 using the second lens array 111 to form an erect, life-size image on the image sensor 102a.

[0043] Here, light emitted from second lens 110e of first lens array 110 is incident on third lens 111d of second lens array 111, but at this time, aperture array 112 prevents the light emitted from second lens 110e from being incident on third lens 111d, which has an optical axis different from that of second lens 110e. In other words, aperture array 112 causes the light emitted from second lens 110e to be incident on third lens 111d, which has the same optical axis as second lens 110e.

[0044] 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.

[0045] In the image reading device 101, the linear expansion coefficients of the first lens array substrate 110a and the second lens array substrate 111a are 9×10 －６ / °C, and the linear expansion coefficient of the imaging element substrate 102 is 14×10 －６ / °C, the difference in the linear expansion coefficient between the first lens array substrate 110a and the second lens array substrate 111a and the imaging element substrate 102 is 5×10 －６ / ℃.

[0046] For this reason, when the temperature of the image reading device 101 rises from 25 degrees to 50 degrees, for example, if the total length (total width) in the X direction of 300 mm is divided in half at the center of the X direction to 150 mm, the first lens array substrate 110 a, the second lens array substrate 111 a, and the image sensor 102 a on the image sensor substrate 102 will be misaligned by approximately 20 μm in the X direction.

[0047] [1-4. Summary and Effects] As described above, the image reading device 101 according to the first 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.

[0048] Furthermore, the lens array unit 103 is an optical system that forms an erect, equal-magnification image of a subject on the imaging element 102a using a first lens array 110 and a second lens array 111. The first lens array 110 has a first lens array substrate 110a, which is an example of a lens array substrate that transmits light. A first resin layer 110b is tightly formed on one surface of the first lens array substrate 110a that is the light incident side (the surface closer to the subject), and a second resin layer 110c is tightly formed on the other surface opposite to the first surface that is the light exit side. A plurality of first lenses 110d are formed on the first resin layer 110b, and second lenses 110e are formed on the second resin layer 110c.

[0049] On the other hand, the second lens array 111 has a second lens array substrate 111a, and a third resin layer 111b is tightly formed on one surface (the surface closer to the subject) of the second lens array substrate 111a, and a fourth resin layer 111c is tightly formed on the other surface opposite to the one surface, and a plurality of third lenses 111d are formed on the third resin layer 111b, and a fourth lens 111e is formed on the fourth resin layer 111c.

[0050] Furthermore, the plurality of first lenses 110d, second lenses 110e, third lenses 111d, and fourth lenses 111e are arranged side by side along the X direction, which is an example of a first direction perpendicular to the optical axis direction, so that their optical axes coincide with each other.

[0051] Furthermore, the first lens array substrate 110a of the first lens array 110 and the second lens array substrate 111a of the second lens array 111 are formed from glass, which is an example of a material having a smaller linear expansion coefficient than the first resin layer 110b, the second resin layer 110c, the third resin layer 111b, and the fourth resin layer 111c (i.e., a material having a smaller linear expansion coefficient than the resin that forms the lenses).

[0052] In this way, in the image reading device 101 of the first embodiment, the lens arrays (first lens array 110, second lens array 111) are configured from lens array substrates (first lens array substrate 110a, second lens array substrate 111a) formed of glass having a linear expansion coefficient lower than that of the resin forming the lenses, and lenses (first lens 110d, second lens 110e, third lens 111d, fourth lens 111e) formed in resin layers (first resin layer 110b, second resin layer 110c, third resin layer 111b, fourth resin layer 111c) that are in close contact with the lens array substrates.

[0053] By doing this, in the image reading device 101 of the first embodiment, the difference in linear expansion coefficient between the lens array substrate (first lens array substrate 110a, second lens array substrate 111a) and the image sensor substrate 102 is reduced, thereby suppressing misalignment between the lens array (first lens array 110, second lens array 111) and the image sensor 102a when the temperature changes.

[0054] Specifically, for example, when a lens array is made of resin, the linear expansion coefficient of the resin is generally 70×10 －６ / °C, and the linear expansion coefficient of the imaging element substrate 102 is 14×10 －６ / °C, the difference in the linear expansion coefficient between the lens array and the image sensor substrate 102 is 56×10 －６ / ° C. In this case, for example, if the temperature rises from 25° C. to 50° C., the lens array and the image sensor 102 a on the image sensor substrate 102 will be misaligned in the X direction by approximately 210 μm.

[0055] In contrast, in the image reading device 101 according to the first embodiment, the lens array substrates (first lens array substrate 110a, second lens array substrate 111a) are made of glass, so the difference in linear expansion coefficient between the lens array substrates and the image pickup element substrate 102 is 5×10 －６ / ° C. In this case, for example, if the temperature rises from 25° C. to 50° C., the lens array and the image sensor 102 a on the image sensor substrate 102 will be misaligned by about 20 μm in the X direction.

[0056] In this way, in the image reading device 101 of the first embodiment, the X-direction positional deviation between the lens array and the image sensor 102a on the image sensor substrate 102 due to temperature changes can be significantly reduced compared to when the lens array is formed from resin.

[0057] Furthermore, in the image reading device 101 of the first embodiment, instead of forming the entire lens array (first lens array 110, second lens array 111) from glass, which has a smaller linear expansion coefficient and is more expensive than resin, the lens array substrate (first lens array substrate 110a, second lens array substrate 111a) is formed from glass, and the lenses (first lens 110d, second lens 110e, third lens 111d, fourth lens 111e) are formed from resin on the lens array substrate, thereby reducing costs.

[0058] Thus, the image reading device 101 of the first embodiment can provide good imaging performance at low cost.

[0059] In addition, the lens array unit 103 of the first embodiment has an aperture array 112 between the first lens array 110 and the second lens array 111, and the aperture array 112 is also made of stainless steel or aluminum, which has a linear expansion coefficient lower than that of the resin that forms the lenses.

[0060] By doing so, the image reading device 101 according to the first embodiment can also suppress misalignment in the X direction between the aperture array 112 and the image sensor 102a on the image sensor substrate 102 due to temperature changes.

[0061] [2. Second Embodiment] Next, a second embodiment will be described. In the first embodiment, the first lens array 110 and the second lens array 111 are configured to have convex lenses on the incident side (side closer to the subject) and the exit side (side farther from the subject). In contrast, in the second embodiment, the first lens array 210 corresponding to the first lens array 110 is configured to have a convex lens on the incident side (side closer to the subject) and a concave lens on the exit side (side farther from the subject). The other configurations are the same between the first embodiment and the second embodiment.

[0062] 7, which corresponds to the cross-sectional view of Fig. 3, an image reading device 201 according to the second embodiment is composed of an image pickup element substrate 202, a lens array unit 203, and a holder 204. Here, the image pickup element substrate 202 and the holder 204 are similar to the image pickup element substrate 102 and the holder 104 according to the first embodiment, and therefore a description thereof will be omitted.

[0063] The lens array unit 203 is an optical system configured with a first lens array 210 provided on the side closer to the subject, a second lens array 211 provided on the side farther from the subject, and an aperture array 212 provided between the first lens array 210 and the second lens array 211. Here, the aperture array 212 is an optical system in which the aperture array 112 of the first embodiment is elongated in the Z direction, and therefore a description thereof will be omitted.

[0064] As shown in an enlarged view in Figure 8, the first lens array 210 is composed of a first lens array substrate 210a, which is a plate-shaped glass that is long in the X direction, a first resin layer 210b formed in close contact with one surface of the first lens array substrate 210a in the +Z direction (the surface closer to the subject), and a second resin layer 210c formed in close contact with one surface of the first lens array substrate 210a in the -Z direction (the surface farther from the subject).

[0065] A plurality of first lenses 210d are formed in an array on the first resin layer 210b so as to be in contact with each other in the X direction. A plurality of second lenses 210e are also formed in an array on the second resin layer 210c so as to be in contact with each other in the X direction.

[0066] The first resin layer 210b and the second resin layer 210c are layers of resin having ultraviolet curing or heat curing properties, and the first lens 210d and the second lens 210e are formed by imprint technology.

[0067] The first lens array 210 is held in the holder 204 so that the first lens 210d formed on one surface (the surface closer to the subject) of the first lens array substrate 210a in the +Z direction is exposed from the opening 204c of the holder 204.

[0068] The second lens array 211 has the same configuration as the second lens array 111 of the first embodiment. That is, the second lens array 211 is composed of a second lens array substrate 211a, a third resin layer 211b formed in close contact with one surface of the second lens array substrate 211a in the +Z direction, and a fourth resin layer 211c formed in close contact with the other end surface of the second lens array substrate 211a in the Z direction. A plurality of third lenses 211d are formed in an array on the third resin layer 211b so as to be in contact with each other in the X direction, and a plurality of fourth lenses 211e are also formed in an array on the fourth resin layer 211c so as to be in contact with each other in the X direction.

[0069] In this embodiment, the first lens 210d, the second lens 210e, the third lens 211d, and the fourth lens 211e are each a circular lens with a diameter of 1 mm, and are arranged in an array at a period of 1 mm in the X direction so that their optical axes coincide. The first lens 210d, the third lens 211d, and the fourth lens 211e are convex lenses, and the second lens 210e is a concave lens.

[0070] The radius of curvature r [mm], conic constant k, aspherical coefficient A, and distance [mm] from the image sensor 102a of each lens (first lens 210d, second lens 210e, third lens 211d, and fourth lens 211e) are shown in the table of FIG. 9. The first lens 210d and the third lens 211d are convex lenses that are convex toward the +Z direction (the subject side), the second lens 210e is a concave lens that is concave toward the +Z direction, and the fourth lens 211e is a convex lens that is convex toward the −Z direction (the image sensor 202a side). The shape of each lens can be expressed by equation 1, which was described in the first embodiment.

[0071] The lens array unit 203 forms an inverted, reduced image of the subject as an intermediate image using the first lens array 210, and forms an inverted, enlarged image of the intermediate image using the second lens array 211, thereby forming an erect, equal-size image of the subject on the image sensor 202a.

[0072] 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 9 are examples, and the first lens array 210 and the second lens array 211 may be any optical system that can form an erect, life-size image of the subject on the image sensor 202a.

[0073] Furthermore, the refractive index, Abbe number, and thickness [mm] of each lens (first lens 210d, second lens 210e, third lens 211d, fourth lens 211e) and each substrate (first lens array substrate 210a, second lens array substrate 211a) are shown in the table of FIG. 10.

[0074] 9 and 10, in the first lens array 210 of the second embodiment, the refractive index of the second lens 210e, which is a concave lens, is larger than that of the first lens 210d, which is a convex lens, and the Abbe number is smaller, thereby satisfying the conditions for an achromatic lens. The configuration of the image reading device 101 is as described above. The operation of the image reading device 201 is similar to that of the image reading device 101 of the first embodiment, and therefore a description thereof will be omitted.

[0075] [2-2. Summary and Effects] As explained above, the image reading device 201 according to the second embodiment includes the lens array unit 203 having the first lens array 210 and the second lens array 211 .

[0076] The first lens array 210 has a first lens array substrate 210a, and a first resin layer 210b is tightly formed on one surface of the first lens array substrate 210a that is the light incident side (the surface closer to the subject), and a second resin layer 210c is tightly formed on the other surface opposite to the first surface that is the light exit side, and a plurality of first lenses 210d are formed on the first resin layer 210b, and second lenses 210e are formed on the second resin layer 210c.

[0077] Furthermore, in the first lens array 210, the first lens 210d is a convex lens and the second lens 210e is a concave lens, and the second lens 210e has a higher refractive index and a smaller Abbe number than the first lens 210d, so that it functions as an achromatic lens.

[0078] In this way, in the image reading device 201 according to the second embodiment, the first lens array 210 is an achromatic lens, so that the first lens array 210 can correct chromatic aberration.

[0079] That is, in the image reading device 201 of the second embodiment, in addition to the same effect as the image reading device 101 of the first embodiment (the effect of being able to significantly reduce the misalignment in the X direction between the lens array and the image sensor 102 a on the image sensor substrate 102), chromatic aberration can be corrected without increasing the number of lens arrays, and therefore better imaging performance can be obtained than in the image reading device 101 of the first embodiment.

[0080] [3. Other Embodiments] [3-1. Other Embodiment 1] In the first embodiment described above, the lens array unit 103 is an optical system configured with the first lens array 110, the second lens array 111, and the aperture array 112, but is not limited to this, and may be an optical system having, for example, three or more lens arrays. The same applies to the second embodiment.

[0081] In the first embodiment described above, the image reading device 101 is configured to include the lens array unit 103 of an erect, equal-magnification optical system composed of the first lens array 110, the second lens array 111, and the aperture array 112, and the image sensor 102a. However, the image reading device may also be configured to include an optical system having at least one lens array, an image sensor that converts an image formed by the lens array into an image signal, and an image processing unit that performs image processing on the image signal obtained from the image sensor (for example, image processing that inverts and magnifies an inverted, reduced image formed by a single lens array). The same applies to the second embodiment.

[0082] In the first embodiment described above, the first lens array substrate 110a of the first lens array 110 and the second lens array substrate 111a of the second lens array 111 are formed of glass having a linear expansion coefficient lower than that of the resin forming the lenses. However, the first lens array substrate 110a and the second lens array substrate 111a may be formed of another material (e.g., calcium fluoride) having a linear expansion coefficient lower than that of the resin forming the lenses. In this way, forming the lens array substrates (first lens array substrate 110a, second lens array substrate 111a) from a material having a linear expansion coefficient lower than that of at least the resin can suppress misalignment in the X direction between the lens array and the image sensor 102a on the image sensor substrate 102 compared to when the lens arrays (first lens array 110, second lens array 111) are formed from resin. The same applies to the second embodiment.

[0083] In the first embodiment described above, the first lens array 110 and the second lens array 111 are configured such that lenses are formed in a resin layer that is in close contact with the lens array substrate, but this is not limiting, and one of the first lens array 110 and the second lens array 111 may be configured such that lenses are formed in a resin layer that is in close contact with the lens array substrate, and the other may have another configuration (for example, a configuration in which the entire lens array is formed from a material (glass, etc.) that has a lower linear expansion coefficient than resin). The same applies to the second embodiment.

[0084] Furthermore, in the first embodiment described above, the first lens array 110 is configured such that a resin layer is adhered to both one and the other surfaces of the lens array substrate, and lenses are formed in both the resin layer on the one surface and the resin layer on the other surface. However, this is not limiting, and the first lens array 110 may be configured such that a resin layer is adhered to one surface of the lens array substrate, and lenses are formed in the resin layer. The same applies to the second lens array 111; for example, lenses may be formed on both surfaces of the first lens array 110 and lenses may be formed on one surface of the second lens array 111. The same applies to the second embodiment.

[0085] Furthermore, the lenses formed in the resin layer are not limited to being circular, but may be in a racetrack shape, such as a circle with both ends cut off in the diameter direction, or a honeycomb shape, in which regular hexagons are arranged without gaps.

[0086] [3-2. Alternative Embodiment 2] Furthermore, in the second embodiment described above, only the first lens array 210 is an achromatic lens, but this is not limiting, and both the first lens array 210 and the second lens array 211 may be achromatic lenses, or only the second lens array 211 may be an achromatic lens.

[0087] [3-3. Other Embodiment 3] Furthermore, in the first embodiment described above, 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 and the second lens array 111 and the apertures 112a of the aperture array 112 may be arranged side by side in the X direction and the Y direction, respectively.

[0088] Furthermore, in the first embodiment described above, 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.

[0089] Furthermore, in the first embodiment described above, 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.

[0090] [3-4. 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.

[0091] The present invention can be widely used in, for example, contact type image sensors.

[0092] 10...Image inspection device, 101, 201...Image reading device, 102, 202...Image pickup element substrate, 102a, 202a...Image pickup element, 103, 203...Lens array unit, 104, 204...Holder, 110, 210...First lens array, 110a, 210a...First lens array substrate, 110b, 210b...First resin layer, 110c, 210c...Second resin layer, 110d, 210d...First lens, 110e, 210e...Second lens, 111, 211...Second lens array, 111a, 211a...Second lens array substrate, 111b, 211b...Third resin layer, 111c, 211c...Fourth resin layer, 111d, 211d...Third lens, 111e, 211e...Fourth lens, 112, 212...Aperture array.

Claims

1. A lens array unit comprising: a first lens array having a plurality of lenses, the plurality of lenses being aligned along a first direction perpendicular to the optical axis direction of the lenses; and a second lens array, spaced apart from the first lens array in the optical axis direction, having a plurality of lenses, the plurality of lenses being aligned along the first direction so that their optical axes coincide with those of the lenses of the first lens array; at least one of the first lens array and the second lens array having a lens array substrate that transmits light and is formed from a material with a linear expansion coefficient smaller than that of a resin that forms the lenses; a resin layer formed in close contact with at least one of one surface of the lens array substrate that is the light incident side and the other surface opposite to the first surface that is the light exit side; and the plurality of lenses being formed on the resin layer.

2. The lens array unit according to claim 1, wherein the optical system including the first lens array and the second lens array is an erect unity magnification optical system.

3. The lens array unit described in claim 2, further comprising an aperture array between the first lens array and the second lens array, the aperture array being formed of a material having a linear expansion coefficient smaller than that of the resin forming the lenses, and having a plurality of apertures that penetrate in the optical axis direction of the lenses arranged in a line along the first direction.

4. The lens array unit described in claim 2, characterized in that at least one of the first lens array and the second lens array has the resin layer formed in close contact with both the one surface and the other surface of the lens array substrate, and a plurality of the lenses are formed in each of the resin layers.

5. The lens array unit described in claim 4, characterized in that in at least one of the first lens array and the second lens array, the lenses formed in the resin layer on the incident side are convex lenses, and the lenses formed in the resin layer on the exit side are concave lenses.

6. The lens array unit described in claim 5, characterized in that at least one of the first lens array and the second lens array has a higher refractive index and a smaller Abbe number for the lenses formed in the resin layer on the exit side than for the lenses formed in the resin layer on the incident side.

7. An image reading device comprising: a lens array unit having a lens array in which a plurality of lenses are arranged in a first direction perpendicular to the optical axis direction of the lenses; and an imaging element substrate on which an imaging element that receives light that has passed through the lens array unit is mounted, wherein the lens array has a lens array substrate that transmits light and is formed from a material with a linear expansion coefficient smaller than that of the resin that forms the lenses, and a resin layer is formed in close contact with at least one of one surface of the lens array substrate that is the light incident side and the other surface opposite to the one surface that is the light exit side, and the plurality of lenses are formed in the resin layer.

8. The image reading device according to claim 7, wherein the imaging element substrate is made of a material having a linear expansion coefficient smaller than that of the resin forming the lens.

9. The image reading device according to claim 8, wherein the lens array has a resin layer formed in close contact with both the one surface and the other surface of the lens array substrate, and a plurality of lenses are formed in each of the resin layers.

10. An image reading device as described in claim 9, characterized in that the lenses formed in the resin layer on the incident side of the lens array are convex lenses, and the lenses formed in the resin layer on the exit side are concave lenses.

11. An image reading device as described in claim 10, characterized in that the lens array has a higher refractive index and a smaller Abbe number for the lenses formed in the resin layer on the exit side than for the lenses formed in the resin layer on the incident side.

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