Rod lens array, optical device, image sensor, printer, and inspection device

Abstract

This rod lens array 10a comprises a plurality of refractive index distribution-type rod lenses 1b arranged such that optical axes thereof are parallel to each other, and forms an erecting equal magnification image. A refractive index distribution-type rod lens 1b has a refractive index distribution in a radial direction. The radius of the refractive index distribution-type rod lens 1b is represented by r0. The central refractive index, which is the central refractive index of the refractive index distribution-type rod lens 1b, is represented by no. The refractive index distribution constant of the refractive index distribution-type rod lens 1b is represented by √A. The refractive index at a distance r from the center of the refractive index distribution-type rod lens 1b is approximated as n(r) = n0  {1 - (A / 2)  r2}. The opening angle θ represented by sin-1 (n0  √A  r0) is 3 to 6°. The imaging distance of the rod lens array 10a is 45 to 75 mm. The depth of field, in which the value of a modulation transfer function (MTF) at a spatial frequency of 6 lines / mm is 30% or more, is 1.5 to 3.0 mm.

Description

Technical Field

[0001] The present invention relates to a rod lens array, an optical device, an image sensor, a printer, an inspection apparatus, a base glass composition for a refractive index distribution type rod lens, and a method for manufacturing a refractive index distribution type rod lens.

Background Art

[0002] Conventionally, an apparatus for observing defects on the surface of a subject using an imaging device such as a Charge-Coupled Device (CCD) image sensor or a Complementary metal-oxide-semiconductor (CMOS) image sensor has been known. For example, Patent Document 1 describes a surface defect apparatus including a light source, an irradiation unit, a condensing unit, and an observation unit. The observation unit includes an imaging lens and an imaging device such as a CCD image sensor or a CMOS image sensor.

[0003] Patent Document 2 describes an inspection apparatus suitable for inspecting the appearance of a photoreceptor drum of an electrophotographic copying machine or a printer. This inspection apparatus includes a camera device that photographs the photoreceptor drum with a plurality of one-dimensional CCD cameras arranged in a row.

[0004] On the other hand, a contact image sensor (CIS) is also known as an imaging sensor. The CIS includes a rod lens array. Usually, a refractive index distribution type rod lens is used for the rod lens array.

[0005] For example, Patent Documents 3 to 5 describe a refractive index distribution type rod lens and a rod lens array in which a plurality of refractive index distribution type rod lenses are arranged. The refractive index distribution type rod lens is a rod-shaped (bar-shaped) lens having a refractive index distribution in which the refractive index continuously decreases from the center toward the outer periphery. In the refractive index distribution type rod lens described in Patent Document 3, the difference Δn between the refractive index on the peripheral surface of the lens and the refractive index on the central axis is 0.003 or more. According to Patent Document 3, when Δn becomes smaller than 0.003, the aperture angle (2θ) becomes smaller than about 10°, suggesting that this is not desirable. In other words, it is considered that Patent Document 3 suggests that an aperture angle (θ) of less than 5° is not desirable.

[0006] In Patent Document 4, the aperture angle of the refractive index distribution type rod lens according to the example is about 10.1 to 12.9°. In Patent Document 5, the aperture angle of the refractive index distribution type rod lens according to the example is 10.1 to 12.0°.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] Patent Documents 1 and 2 do not describe the use of a graded-index rod lens. The graded-index rod lenses described in Patent Documents 3 to 5 have a large aperture angle. This is hardly advantageous from the viewpoint of realizing a large depth of field in a graded-index rod lens, and it is considered that the depth of field of the graded-index rod lenses described in Patent Documents 3 to 5 is small.

[0009] In view of such circumstances, the present invention provides a rod lens array having a large depth of field. Further, the present invention provides an optical device, an image sensor, a printer, and an inspection device including such a rod lens array. In addition, the present invention provides a base glass composition for a graded-index rod lens that is advantageous for increasing the depth of field of a rod lens array. Further, the present invention provides a method that is advantageous for manufacturing a graded-index rod lens having a large depth of field.

Means for Solving the Problems

[0010] The present invention is a rod lens array that forms an erect and same-magnification image, comprising a plurality of graded-index rod lenses arranged such that their optical axes are parallel to each other, each of the plurality of graded-index rod lenses has a refractive index distribution in the radial direction, when the radius of the graded-index rod lens is represented by r0, the central refractive index that is the refractive index at the center of the graded-index rod lens is represented by n0, the refractive index distribution constant of the graded-index rod lens is represented by √A, and the refractive index at a distance r from the center of the graded-index rod lens is approximated by n(r)=n0·{1-(A / 2)·r 2}, the aperture angle θ represented by sin -1 (n0·√A·r0) is 3 to 6°, the imaging distance of the rod lens array is 45 to 75 mm, a depth of field in which the value of the modulation transfer function (MTF) at a spatial frequency of 6 line / mm is 30% or more is 1.5 to 3.0 mm, and provides a rod lens array.

[0011] The present invention provides an optical device including the above-described rod lens array.

[0012] The present invention provides an image sensor including: the above-described rod lens array; a line illumination device that linearly illuminates an object; and a line image sensor arranged such that light reflected from the object passes through the rod lens array and is condensed.

[0013]

[0014] The present invention provides a printer including a writing head having the above-described rod lens array. The present invention provides an inspection device including: a conveyance device for conveying an article; an illumination device for illuminating the article; an image sensor; and a controller, wherein the image sensor includes the above-described rod lens array for condensing light reflected from the article, acquires image information of the article conveyed by the conveyance device, and transmits the image information to the controller, and the controller specifies a defect of the article and determines acceptance or rejection of the article based on the image information.

[0015] The present invention provides, in mol%, 40% ≦ SiO2 ≦ 65% 0% ≦ TiO2 ≦ 10% 0.1% ≦ MgO ≦ 22% 0.15% ≦ ZnO ≦ 15% 0.5% ≦ Li2O < 4% 2% ≦ Na2O ≦ 20% 0% ≦ B2O3 ≦ 20% ​​​​​​0% ≤ Cs2O ≤ 3% 0% ≤ Y2O3 ≤ 5% 0% ≤ ZrO2 ≤ 2% 0% ≤ Nb2O5 ≤ 5% 0% ≤ In2O3 ≤ 5% 0% ≤ La2O3 ≤ 5% 0% ≤ Ta2O5 ≤ 5%, and contains at least two selected from the group consisting of CaO, SrO, and BaO, each in an amount of 0.1 mol% or more and 15 mol% or less, expressed in mol%, 2% ≤ MgO + ZnO, 0.07 ≤ ZnO / (MgO + ZnO) ≤ 0.93, 2.5% ≤ Li2O + Na2O < 24%, and satisfies the conditions of 0% ≤ Y2O3 + ZrO2 + Nb2O5 + In2O3 + La2O3 + Ta2O5 ≤ 11%, A base glass composition for a refractive index distribution type rod lens is provided.

[0016] The present invention is A method for manufacturing a refractive index distribution type rod lens, comprising forming a glass preform made of a glass composition containing an oxide of a first alkali metal element, immersing the glass preform in a molten salt containing a second alkali metal element different from the first alkali metal element, and performing an ion exchange treatment between the first alkali metal element in the glass preform and the second alkali metal element in the molten salt to form a refractive index distribution in the glass preform, The glass composition is expressed in mol% as 40% ≤ SiO2 ≤ 65% 0% ≤ TiO2 ≤ 10% 0.1% ≤ MgO ≤ 22% 0.15% ≤ ZnO ≤ 15% 0.5% ≤ Li2O < 4% 2% ≤ Na2O ≤ 20% 0% ≤ B2O3 ≤ 20% 0% ≤ Al2O3 ≤ 10% 0% ≤ K2O ≤ 3% 0% ≤ Cs2O ≤ 3% 0% ≤ Y2O3 ≤ 5% 0% ≤ ZrO2 ≤ 2% 0% ≤ Nb2O5 ≤ 5% 0% ≤ In2O3 ≤ 5% 0% ≤ La2O3 ≤ 5% including 0% ≤ Ta2O5 ≤ 5%, the glass composition contains at least two selected from the group consisting of CaO, SrO, and BaO, each in an amount of 0.1 mol% or more and 15 mol% or less, the glass composition is expressed in mol%, 2% ≤ MgO + ZnO, 0.07 ≤ ZnO / (MgO + ZnO) ≤ 0.93, 2.5% ≤ Li2O + Na2O < 24%, and satisfies the conditions of 0% ≤ Y2O3 + ZrO2 + Nb2O5 + In2O3 + La2O3 + Ta2O5 ≤ 11%, A method is provided.

Advantages of the Invention

[0017] The above rod lens array has a large depth of field. Further, the above base glass composition for a refractive index distribution type rod lens is advantageous for increasing the depth of field of the rod lens array.

Brief Description of the Drawings

[0018]

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[0019] Image data collected in the appearance inspection of a subject must have a resolution capable of identifying defects of the subject. When trying to obtain high-resolution image data using a camera equipped with a one-dimensional CCD sensor, the effective width that can be imaged by one camera becomes small. For this reason, it may be difficult to image the entire subject with one camera. For example, when the pixel size corresponding to the resolution required in the image data is 90 μm, the width of the area that can be imaged by a camera equipped with a one-dimensional CCD sensor of 4096 pixels is about 370 mm. In this case, in order to inspect a subject having a width of 1200 mm without omission, it is necessary to arrange four camera systems each equipped with a one-dimensional CCD sensor and a camera lens in the width direction. When mounting a plurality of camera systems equipped with one-dimensional CCD sensors, the manufacturing cost of the apparatus becomes high. In addition, every time the type of the subject is changed, adjustment and maintenance of a plurality of camera systems are required, and the running cost of the inspection also becomes high.

[0020] Therefore, it is conceivable to perform an appearance inspection of a subject using a CIS. The CIS includes a plurality of one-dimensional light receiving elements arranged on a substrate and a rod lens array. In the CIS, the rod lens array forms an erect and life-size image. By using the CIS, a one-dimensional image with a width of 1200 mm can be obtained in one unit. The rod lens array is, for example, an array of a plurality of refractive index distribution type rod lenses. The refractive index distribution type rod lens has a refractive index distribution in its radial direction, and is a substantially cylindrical lens in which the refractive index changes from the center portion toward the peripheral portion in the radial direction of the refractive index distribution type rod lens. The CIS equipped with the rod lens array can reduce the distance between the imaging element and the object to be photographed to about one-tenth compared with a conventional camera system including a CCD sensor and a lens, and is advantageous in terms of miniaturization of the device. On the other hand, in the CIS, the depth of field (DOF), which is a characteristic value indicating the allowable range of the distance between the object to be photographed and the lens, is small. This causes a problem that when there is a variation in the thickness of the subject, a portion in focus and a portion out of focus occur in the subject. For this reason, the image of the portion out of focus is not clear, and there is a possibility of overlooking defects and misidentifying defects.

[0021] As described above, the aperture angle of the refractive index distribution type rod lens described in Patent Documents 3 to 5 is large, and it is difficult to say that this is advantageous from the viewpoint of increasing the DOF of the refractive index distribution type rod lens. Therefore, the present inventors fundamentally reviewed the conditions of the glass composition used for manufacturing the refractive index distribution type rod lens in order to realize a desired range of DOF in the refractive index distribution type rod lens. As a result of repeated extensive trial and error, the present inventors have finally found a refractive index distribution type rod lens capable of realizing a desired range of DOF. The refractive index distribution type rod lens according to the present invention can be used not only in the technical field of appearance inspection of a subject but also in the entire technical field of image formation such as image scanners, copiers, facsimiles, and printers.

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following description relates to an example of the present invention, and the present invention is not limited to the following embodiments.

[0023] The refractive index distribution type rod lens 1b has an opening angle θ of 3 to 6°. Let the radius of the refractive index distribution type rod lens 1b be r0. Let the central refractive index, which is the refractive index at the center of the refractive index distribution type rod lens 1b, be n0. Let the refractive index distribution constant of the refractive index distribution type rod lens 1b be √A. The refractive index n(r) at a distance r from the center of the refractive index distribution type rod lens is approximated by n(r)=n0·{1-(A / 2)·r 2}. In this case, the opening angle θ is represented by sin -1 (n0·√A·r0). In the refractive index distribution type rod lens 1b, when an erect and same magnification image is formed, the image formation distance (TC) of the erect image is 45 to 75 mm. The refractive index distribution type rod lens 1b has a depth of field (DOF) of 1.5 to 3.0 mm. The DOF of the refractive index distribution type rod lens 1b is determined by subtracting the minimum value from the maximum value of the working distance. At the working distance of the refractive index distribution type rod lens 1b, the value of the modulation transfer function (MTF) at a spatial frequency of 6 cycles / mm is 30% or more.

[0024] As shown in Fig. 1, the DOF of the refractive index distribution type rod lens 1b can be determined, for example, by arranging the rod lens array 10a, the line pattern 3, and the light receiving element 2 at predetermined intervals in the optical axis direction and obtaining the MTF value while varying the distance between the rod lens array 10a and the line pattern 3. The rod lens array 10a is configured by arranging a plurality of refractive index distribution type rod lenses 1b in a direction perpendicular to the optical axis. The line pattern 3 has black and white line pairs corresponding to a spatial frequency of 6 lines / mm. The light receiving element 2 is, for example, a CCD sensor. For example, the light emitted from a halogen lamp is irradiated onto the line pattern 3 after passing through a color filter and a light diffusing plate. The color filter may transmit light in the wavelength range of 500 to 600 nm, or may mainly transmit light with a wavelength of 530 nm. At this time, the MTF value can be determined as the reproduction rate of the image (output image) obtained by imaging on the light receiving element 2 by the rod lens array 10a with respect to the image (input image) of the line pattern 3 having a predetermined spatial frequency composed of bright and dark portions before entering the rod lens array 10a.

[0025] The distance (object point - imaging point distance) D between the line pattern 3 and the light receiving element 2 at which the MTF value becomes maximum max is determined. D max At this time, an erect and same - magnification image is obtained by the rod lens array 10a. Moreover, while keeping the distance between the rod lens array 10a and the light receiving element 2 fixed, the line pattern 3 is moved in the positive direction (ΔL > 0) and the negative direction (ΔL < 0) of the Z - axis parallel to the optical axis, and the MTF value is obtained at each position. By setting the allowable range of the MTF value in this way, the maximum value and the minimum value of the operating distance can be obtained. As a result, the DOF of the refractive index distribution type rod lens 1b can be determined. Note that when ΔL > 0, the distance between the line pattern 3 and the rod lens array 10a is larger than the operating distance corresponding to the distance D max On the other hand, when ΔL < 0, the distance between the line pattern 3 and the rod lens array 10a is the distance D maxis smaller than the operating distance corresponding thereto. At ΔL = 0, the distance between the line pattern 3 and the rod lens array 10a is the distance D max is equal to the operating distance corresponding thereto.

[0026] Since the DOF of the refractive index distribution type rod lens 1b and the rod lens array 10a is within the above range, for example, it is advantageous for obtaining image data suitable for the appearance inspection of a subject having a non-uniform thickness, step, or unevenness. Therefore, the refractive index distribution type rod lens 1b and the rod lens array 10a can contribute to improving the accuracy of the appearance inspection of the subject and enhancing the inspection standard.

[0027] The DOF of the refractive index distribution type rod lens 1b is desirably 1.5 mm or more, more desirably 1.8 mm or more, and still more desirably 2 mm or more. The DOF of the refractive index distribution type rod lens 1b is desirably 2.8 mm or less, more desirably 2.5 mm or less.

[0028] The lens - image formation position distance L at which the value of MTF becomes maximum when an erect and same - magnification image is formed by the refractive index distribution type rod lens 1b i is not limited to a specific value and is, for example, 13 to 28 mm. In this case, when a rod lens array including the refractive index distribution type rod lens 1b is incorporated into an inspection apparatus, it is easy to maintain the distance between the object to be inspected and the rod lens array at an appropriate distance. Therefore, the assembly of components such as the optical system can be facilitated. In addition, the refractive index distribution type rod lens 1b has a desired DOF and is advantageous from the viewpoint of inspecting an object having a step within a predetermined range.

[0029] The lens - image formation position distance L i is desirably 15 mm or more, more desirably 18 mm or more. The lens - image formation position distance L i is desirably 25 mm or less, more desirably 22 mm or less.

[0030] Since the refractive index distribution type rod lens 1b has an opening angle θ of 3 to 6°, the DOF of the refractive index distribution type rod lens 1b can be easily adjusted to a desired range. The opening angle θ of the refractive index distribution type rod lens 1b is defined, for example, as shown in FIG. 2. The opening angle θ is the maximum value of the angle formed by the optical axis and a light ray that can be incident on one end of the optical axis of the refractive index distribution type rod lens 1b. In FIG. 2, F1 is the object plane (object surface), and F2 is the light receiving surface (imaging surface) in a light receiving element or the like. Z0 is the length of the refractive index distribution type rod lens 1b. L o is the distance between the object plane F1 and the refractive index distribution type rod lens 1b when the value of MTF is maximum, and L i is the distance between the imaging surface F2 and the refractive index distribution type rod lens 1b when the value of MTF is maximum. In FIG. 2, the rod lens array 10a constitutes a substantially erect and same magnification imaging system, and the distance L i is substantially equal to the distance L o . In FIG. 2, X0 is the field radius of the refractive index distribution type rod lens 1b. The opening angle θ of the refractive index distribution type rod lens 1b can be determined, for example, according to the method described in the embodiment. In the method described in the embodiment, the opening angle θ may be determined using the refractive index n0 at the center of the refractive index distribution type rod lens 1b instead of the refractive index Nc of the glass wire before ion exchange. Nc or n0 can be obtained using the V-block method described in Japanese Industrial Standard (JIS) B 7071-2:2018.

[0031] The opening angle θ of the refractive index distribution type rod lens 1b may be 3.5° or more, and may be 3.7° or more. The opening angle θ of the refractive index distribution type rod lens 1b is desirably 5.5° or less, and more desirably 5.2° or less.

[0032] The maximum value of the MTF of the rod lens array 10a is not limited to a specific value, and is, for example, 60% or more, desirably 65% or more, and more desirably 70% or more.

[0033] The refractive index distribution type rod lens 1b has a refractive index distribution as shown in FIG. 3B, for example, in the radial direction. Here, in FIG. 3B, the refractive index n0 at the origin means the refractive index on the central axis of the refractive index distribution type rod lens 1b. r represents the position in the radial direction of the refractive index distribution type rod lens 1b.

[0034] The refractive index distribution of the refractive index distribution type rod lens 1b is represented by, for example, the following formula (1). In formula (1), r is the distance from the optical axis of the refractive index distribution type rod lens 1b, n(r) is the refractive index of the refractive index distribution type rod lens 1b at the distance r, n0 is the refractive index at the center of the refractive index distribution type rod lens 1b, and each of √A, h4, h6, and h8 is a refractive index distribution coefficient. n(r) 2 =n0 2 ·{1-(√A·r) 2 +h4·(√A·r) 4 +h6·(√A·r) 6 +h8·(√A·r) 8} Formula (1)

[0035] Furthermore, the refractive index distribution of the refractive index distribution type rod lens 1b can be approximated by formula (2). n(r)=n0·{1-(A / 2)·r 2} Formula (2)

[0036] The central refractive index n0 of the refractive index distribution type rod lens 1b is not limited to a specific value, and is, for example, 1.51 to 1.65. Thereby, the DOF tends to be large, and it is not so difficult to form the refractive index distribution by ion exchange of the base glass. The central refractive index n0 of the refractive index distribution type rod lens 1b is desirably 1.54 to 1.62.

[0037] The refractive index distribution constant (√A) of the refractive index distribution type rod lens 1b is not limited to a specific value. √A means the square root of A. The refractive index distribution constant √A of the refractive index distribution type rod lens 1b is, for example, 0.130 to 0.230 mm -1That is, if the refractive index distribution constant √A is within such a range, the aperture angle θ of the refractive index distribution type rod lens 1b is likely to fall within a desired range. As a result, the DOF of the refractive index distribution type rod lens 1b is easily adjusted to a desired range.

[0038] The refractive index distribution constant √A of the refractive index distribution type rod lens 1b may be 0.140 mm -1 or more, and may be 0.150 mm -1 or more, and may be 0.170 mm -1 or more. The refractive index distribution constant of the refractive index distribution type rod lens 1b is preferably 0.210 mm -1 or less, and more preferably 0.205 mm -1 or less.

[0039] The imaging distance (TC) of the erect image in the refractive index distribution type rod lens 1b being 45 to 75 mm is advantageous from the viewpoint of adjusting the DOF of the refractive index distribution type rod lens 1b to a desired range.

[0040] The imaging distance (TC) of the erect image in the refractive index distribution type rod lens 1b is desirably greater than a predetermined value from the viewpoint of adjusting the aperture angle and the DOF to a desired range while considering the balance with the lens length Z0. From this viewpoint, the imaging distance (TC) of the erect image in the refractive index distribution type rod lens 1b may be 47 mm or more, may be 50 mm or more, may be 53 mm or more, and may be 54 mm or more. From the viewpoint of avoiding an increase in the size of the optical device incorporating the refractive index distribution type rod lens 1b, the imaging distance of the erect image in the refractive index distribution type rod lens 1b may be 70 mm or less, and may be 67 mm or less. In this case, when the refractive index distribution type rod lens 1b is used in a close-contact type image sensor using an LED or the like as illumination light, the refractive index distribution type rod lens 1b has a size suitable for reproducing uniform illumination with less unevenness while suppressing an excessive decrease in its intensity.

[0041] The refractive index distribution type rod lens 1b may have a structure that prevents incident light having an incident angle larger than the numerical aperture from being reflected by the side surface of the lens and generating noise light (so-called white noise (stray light)) as needed. Such a structure can be, for example, a light absorption layer or a light scattering layer provided on the side surface of the lens. For example, the refractive index distribution type rod lens 1b may have a core-clad structure in which a colored layer serving as a light absorption layer is disposed on the side surface of the lens. When the refractive index distribution type rod lens 1b has a core-clad structure, the outer diameter of the lens and the effective diameter of the lens that substantially contributes to image formation may be different. Further, the refractive index distribution type rod lens 1b may have a structure in which fine uneven portions serving as a light scattering layer are formed on the side surface near the outermost peripheral surface thereof.

[0042] The refractive index distribution type rod lens 1b is typically a glass lens. The glass composition at the center of the refractive index distribution type rod lens 1b satisfies the conditions of, for example, 40% ≤ SiO2 ≤ 65%, 0% ≤ TiO2 ≤ 10%, 0.1% ≤ MgO ≤ 22%, 0.15% ≤ ZnO ≤ 15%, 0.5% ≤ Li2O < 4%, 2% ≤ Na2O ≤ 20%, 0% ≤ B2O3 ≤ 20%, 0% ≤ Al2O3 ≤ 10%, and 0% ≤ K2O ≤ 3% when expressed in mol%. The base glass composition for the refractive index distribution type rod lens contains, for example, 40% ≤ SiO2 ≤ 65%, 0% ≤ TiO2 ≤ 10%, 0.1% ≤ MgO ≤ 22%, 0.15% ≤ ZnO ≤ 15%, 0.5% ≤ Li2O < 4%, 2% ≤ Na2O ≤ 20%, 0% ≤ B2O3 ≤ 20%, 0% ≤ Al2O3 ≤ 10%, 0% ≤ K2O ≤ 3%, 0% ≤ Cs2O ≤ 3%, 0% ≤ Y2O3 ≤ 5%, 0% ≤ ZrO2 ≤ 2%, 0% ≤ Nb2O5 ≤ 5%, 0% ≤ In2O3 ≤ 5%, 0% ≤ La2O3 ≤ 5%, and 0% ≤ Ta2O5 ≤ 5% when expressed in mol%. In addition, this base glass composition contains at least two selected from the group consisting of CaO, SrO, and BaO, each in an amount of 0.1 mol% or more and 15 mol% or less. Further, this base glass composition satisfies the conditions of 2% ≤ MgO + ZnO, 0.07 ≤ ZnO / (MgO + ZnO) ≤ 0.93, 2.5% ≤ Li2O + Na2O < 24%, and 0% ≤ Y2O3 + ZrO2 + Nb2O5 + In2O3 + La2O3 + Ta2O5 ≤ 11% when expressed in mol%. By using such a base glass composition, a refractive index distribution type rod lens having a desired DOF can be obtained.

[0043] The refractive index distribution type rod lens 1b can be manufactured, for example, by subjecting a glass preform made of the above glass composition to an ion exchange treatment.

[0044] (SiO2) SiO2 is an essential component that forms the network structure of glass. When the content of SiO2 is less than 40 mol%, the content of other components necessary to exhibit the optical properties as a refractive index distribution type rod lens after ion exchange becomes relatively large, and devitrification is likely to occur. Also, when the content is less than 40 mol%, the chemical durability as a glass composition significantly decreases. On the other hand, when the content exceeds 65 mol%, the content of other components, such as alkali components for forming the refractive index distribution, refractive index increasing components, and physical property value adjusting components, is limited, and it becomes difficult to obtain a practical glass composition. Therefore, the content of SiO2 is 40 mol% or more and 65 mol% or less.

[0045] (TiO2) TiO2 is an essential component that has the effect of increasing the refractive index of the glass composition. By increasing the refractive index of the base glass composition, the central refractive index of the refractive index distribution type rod lens obtained from the glass composition can be increased. Also, by increasing the content of TiO2, the refractive index distribution in the refractive index distribution type rod lens can be made closer to an ideal state, enabling the production of a refractive index distribution type rod lens with excellent resolution. When the content of TiO2 is 10 mol%, no decrease in the resolution of the image based on the obtained lens is observed, but when the content is less than 1 mol%, the resolution of the image clearly decreases and a practical lens cannot be obtained. On the other hand, when the content exceeds 10 mol%, the coloration becomes stronger, resulting in a larger chromatic aberration and a practical lens cannot be obtained. Therefore, in order to obtain a lens with high resolution and small chromatic aberration, the content of TiO2 is 1 mol% or more and 10 mol% or less. The content of TiO2 is desirably 2 mol% or more and 8 mol% or less.

[0046] (MgO) MgO is an essential component that has the effect of lowering the melting temperature of the glass composition and increasing the refractive index difference (Δn) between the central part and the peripheral part of the lens after ion exchange. When the content of MgO exceeds 22 mol%, devitrification is likely to occur. Also, when the content of MgO exceeds 22 mol%, the contents of other components excessively decrease, and a practical glass composition cannot be obtained. For this reason, the content of MgO is 0.1 mol% or more and 22 mol% or less. From the viewpoint of realizing a sufficient refractive index difference, the content of MgO is desirably 2 mol% or more. When the content of MgO is 2 mol% or more, the contents of alkaline earth metal oxides (CaO, SrO, BaO) can be more appropriately controlled for the purpose of further reducing the mobility of alkali ions. That is, the content of MgO is desirably 2 mol% or more and 22 mol% or less, and more desirably 2 mol% or more and 16 mol% or less.

[0047] (ZnO, MgO + ZnO, ZnO / (MgO + ZnO)) ZnO has the effect of improving the weather resistance of the glass composition and the refractive index distribution type rod lens. In the glass composition according to the present invention, ZnO may be added to substitute for a part of MgO. From the viewpoint of enhancing the weather resistance of the glass composition and the refractive index distribution type rod lens, the content of ZnO is 0.15 mol% or more and 15 mol% or less. At this time, the contents of MgO and ZnO are adjusted so that the total content of MgO and ZnO (MgO + ZnO) is 2 mol% or more. In addition, the contents of MgO and ZnO are adjusted so that the ratio of the content of ZnO to the total content of MgO and ZnO (ZnO / (MgO + ZnO)) satisfies 0.07 ≦ ZnO / (MgO + ZnO) ≦ 0.93. From the viewpoint of further enhancing the weather resistance of the glass composition and the refractive index distribution type rod lens, the content of ZnO is desirably 3 mol% or more and 15 mol% or less. In this case, MgO + ZnO may be 6 mol% or more, and the condition of 0.12 ≦ ZnO / (MgO + ZnO) ≦ 0.93 may be satisfied. From the viewpoint of devitrification resistance, the content of ZnO is desirably 8 mol% or less. From the viewpoint of further enhancing the weather resistance of the glass composition and the refractive index distribution type rod lens, the content of ZnO is more desirably 4 mol% or more and 15 mol% or less. In this case, MgO + ZnO may be 6 mol% or more, and MgO + ZnO may be 6 mol% or more and 22 mol% or less. MgO + ZnO may be 15 mol% or less. Also, ZnO / (MgO + ZnO) is desirably 0.07 or more and 0.9 or less, more desirably 0.25 or more and 0.85 or less, further desirably 0.25 or more and 0.8 or less, and particularly desirably 0.3 or more and 0.8 or less.

[0048] (Li2O) Li2O is an essential component and is one of the most important components for obtaining a refractive index distribution type rod lens by ion-exchanging the glass composition of the present invention. Conventionally, it has been considered that when the content of Li2O in the glass composition is low, a sufficient concentration distribution, that is, a sufficient refractive index distribution, cannot be expressed by ion exchange, and an appropriate refractive index distribution type rod lens cannot be obtained. However, the present inventors have newly found that even a glass composition having a Li2O content of 4 mol% or less can produce a refractive index distribution type rod lens having an appropriate refractive index distribution and a large DOF by performing ion exchange under predetermined conditions. When the content of Li2O exceeds 4 mol%, the aperture angle of the obtained refractive index distribution type rod lens tends to be large and the DOF tends to be small. The content of Li2O is 0.5 mol% or more, desirably 0.7 mol% or more, more desirably 1 mol% or more. Further, the content of Li2O is 4 mol% or less, desirably 3.5 mol% or less, more desirably 3 mol% or less, and still more desirably 2 mol% or less.

[0049] One of the characteristics of the refractive index distribution type rod lens 1b is that the content of Li2O is less than that of various prior arts. Conventionally, there were reasons in the manufacturing process that the content of Li2O could not be reduced. The present inventors have newly found that by new devices such as restricting the processing amount of glass preforms per batch by the ion exchange method and reducing the initial content of Li in the molten salt, while suppressing lens aberrations such as field curvature, a refractive index distribution type rod lens having a smaller aperture angle than before and a practical resolution can be obtained.

[0050] (Na2O) During ion exchange, Na₂O helps the ion exchange between Li and the ions of the ion exchange species that replace Li ions (the ions contained in the molten salt) due to the so-called mixed alkali effect, and appropriately maintains the ionic mobility. By appropriately maintaining the ionic mobility, the ion exchange rate can be appropriately adjusted, and the optical properties of the refractive index distribution type rod lens can be adjusted. When the content rate of Na₂O in the glass composition is less than 2 mol%, the glass becomes hard during glass forming, so the forming becomes difficult. In addition, the melting temperature of the glass rises significantly, making it difficult to fabricate the lens. Also, it is difficult to sufficiently obtain the effect of appropriately maintaining the ionic mobility. On the other hand, when the content rate of Na₂O exceeds 20%, the chemical durability of the glass decreases, lacking practicality. Therefore, the content rate of Na₂O is 2 mol% or more, desirably 5 mol% or more, and more desirably 10 mol% or more. Also, the content rate of Na₂O is 20 mol% or less, desirably 17 mol% or less.

[0051] (Li₂O + Na₂O) As described above, the total of the content rate of Li₂O and the content rate of Na₂O in the glass composition (Li₂O + Na₂O) is 2.5 mol% or more and less than 24 mol%. When Li₂O + Na₂O is within this range, an image with good resolution can be obtained by the refractive index distribution type rod lens manufactured using this glass composition. Li₂O + Na₂O is desirably 6 mol% or more, and more desirably 10 mol% or more.

[0052] (Li₂O / Na₂O) When the ratio of the content rate of Li₂O to the content rate of Na₂O (Li₂O / Na₂O) is large, the resolution of the refractive index distribution type rod lens manufactured using the glass composition may be improved. On the other hand, when Li₂O / Na₂O is excessively large (for example, 1.0 or more), the aperture angle of the refractive index distribution type rod lens manufactured using the glass composition becomes large, and its DOF tends to become small. For this reason, Li₂O / Na₂O is, for example, 0.2 or less, desirably 0.15 or less, and more desirably 0.1 or less.

[0053] The above glass composition may further contain the following components.

[0054] (B2O3) B2O3 is an optional component that forms the network structure of the glass. It has the effect of promoting the vitrification of the glass composition and adjusting its viscosity without substantially changing the resolution and the aperture angle θ of the resulting refractive index distribution type rod lens. It also has a slight effect of slowing down the ion exchange rate of the glass composition. B2O3 may be added, for example, when the content ratios of the above-described essential components are within the scope of the present invention, but when the content ratios of some components become relatively large when viewed as the composition and the stability as glass decreases (for example, devitrification is likely to occur). By adding B2O3, the content ratios of the above-described relatively large components can be reduced without changing the ratio of the content ratios between the essential components. The content ratio of B2O3 that can be added without changing the resolution and the aperture angle of the resulting refractive index distribution type rod lens is, for example, 20 mol% or less. Therefore, the content ratio of B2O3 is 0 mol% or more and 20 mol% or less. The content ratio is preferably 0 mol% or more and 10 mol% or less. When the glass composition contains B2O3, the content ratio is preferably 1 mol% or more and 10 mol% or less.

[0055] (Al2O3) The base glass composition for the refractive index distribution type rod lens may contain Al2O3 as an optional component, and the content ratio thereof is 0 mol% or more and 10 mol% or less.

[0056] (SiO2+TiO2+B2O3) In the base glass composition for the refractive index distribution type rod lens, the total content ratio of SiO2, TiO2, and B2O3 (SiO2+TiO2+B2O3) is, for example, 41 mol% or more and 70 mol% or less, and preferably 50 mol% or more and 70 mol% or less.

[0057] (Y2O3, ZrO2, Nb2O5, In2O3, La2O3, Ta2O5) The base glass composition for a refractive index distribution type rod lens may contain at least one component selected from the group consisting of Y2O3, ZrO2, Nb2O5, In2O3, La2O3, and Ta2O5 for the purpose of adjusting the refractive index of the refractive index distribution type rod lens obtained after ion exchange or improving the weather resistance. The total content of these components is 0 mol% or more and 11 mol% or less. When the base glass composition for a refractive index distribution type rod lens contains these components, the total content of these components is desirably 0.2 mol% or more and 6 mol% or less. Further, it is desirable that the total of the content of these components and the content of ZnO is 15 mol% or less.

[0058] (Y2O3) The content of Y2O3 is desirably 0 mol% or more and 5 mol% or less.

[0059] (ZrO2) The content of ZrO2 is desirably 0 mol% or more and 2 mol% or less. When the base glass composition for a refractive index distribution type rod lens contains ZrO2, the content thereof is 0.2 mol% or more and 2 mol% or less.

[0060] The content of each of Nb2O5, In2O3, La2O3, and Ta2O5 is desirably 0 mol% or more and 5 mol% or less.

[0061] (K2O, Cs2O) K2O and Cs2O are optional components that, due to the mixed alkali effect, have the effect of reducing the mobility of alkali ions, similar to MgO, CaO, SrO, and BaO. The content of each of K2O and Cs2O is, for example, 0 mol% or more and 3 mol% or less. From the perspective of enhancing the water resistance of the base glass composition for the refractive index distribution type rod lens, the content of Cs2O is preferably less than 2 mol%, more preferably 0 mol% or more and 1 mol% or less, and even more preferably 0.5 mol% or less. From the perspective of enhancing the water resistance of the base glass composition for the refractive index distribution type rod lens, it is desirable that the base glass composition for the refractive index distribution type rod lens substantially does not contain Cs2O. As used herein, "substantially does not contain" means that the content of the component is less than 0.1 mol%.

[0062] (Other components) In the base glass composition for the refractive index distribution type rod lens, as other components, it may contain GeO2. The content of GeO2 can be 0 mol% or more and 10 mol% or less. Also, the base glass composition for the refractive index distribution type rod lens may contain at least one selected from the group consisting of SnO2, As2O3, and Sb2O3 as additives. The content of each of SnO2, As2O3, and Sb2O3 can be 0 mol% or more and 1 mol% or less. The base glass composition for the refractive index distribution type rod lens may substantially consist of the above components. In this case, the content of each component contained in the glass composition, as well as the relationship (total and content ratio) between the contents of the respective components, satisfy the above-described conditions. As used herein, "substantially consists of" means allowing the inclusion of impurities with a content of less than 0.1 mol% in terms of content.

[0063] (PbO) The base glass composition for the refractive index distribution type rod lens substantially does not contain lead (a typical compound is PbO). Also, the refractive index distribution type rod lens 1b substantially does not contain lead.

[0064] In the base glass composition for a refractive index distribution type rod lens, for example, the water resistance determined in accordance with the Japan Optical Glass Industry Association Standard (JOGIS) 06 - 2009 is Class 1. In this case, the base glass composition for a refractive index distribution type rod lens has high water resistance, and the refractive index distribution type rod lens manufactured using the base glass composition for a refractive index distribution type rod lens also tends to have high water resistance. Also, in the glass forming the refractive index distribution type rod lens, the water resistance determined in accordance with JOGIS 06 - 2009 may be Class 1.

[0065] The base glass composition for a refractive index distribution type rod lens contains an oxide of a first alkali metal element. The refractive index distribution type rod lens 1b can be manufactured, for example, by a method including the following steps (I) and (II). (I) Form a glass preform 1a made of the above base glass composition for a refractive index distribution type rod lens. (II) Immerse the glass preform 1a in a molten salt S containing a second alkali metal element R different from the first alkali metal element Q contained in the base glass composition for a refractive index distribution type rod lens, and perform an ion exchange treatment between the first alkali metal element Q in the glass preform 1a and the second alkali metal element R in the molten salt, thereby forming a refractive index distribution in the glass preform 1a.

[0066] In the step of (II), for example, as shown in Fig. 3A, the glass preform 1a is introduced into the molten salt S inside the container V, and the glass preform 1a is immersed in the molten salt S for a predetermined time. In the molten salt S, for example, at least one of potassium nitrate and sodium nitrate is molten. When the glass preform 1a is immersed in the molten salt S, for example, cations of the first alkali metal element Q such as Li (lithium) contained in the glass preform 1a dissolve into the molten salt S. On the other hand, cations of the second alkali metal element R such as K (potassium) in the molten salt S penetrate into the glass preform 1a. By adjusting the temperature of the molten salt S and the immersion time of the glass preform 1a in the molten salt S, the ion exchange between the cations of the first alkali metal element Q and the cations of the second alkali metal element R can be appropriately controlled. Inside the glass preform 1a, a concentration distribution of specific monovalent cations occurs, and according to this concentration distribution, a refractive index distribution as shown in Fig. 3B is formed in the glass preform 1a. Thereby, the refractive index distribution type rod lens 1b can be manufactured from the glass preform 1a.

[0067] As shown in Fig. 3B, typically, the refractive index is the highest at the center of the refractive index distribution type rod lens 1b. Note that at the center of the refractive index distribution type rod lens 1b, r = 0. The refractive index n0 at the center of the refractive index distribution type rod lens 1b may be the same as the refractive index Nc of the base glass composition for the refractive index distribution type rod lens before the ion exchange treatment. At this time, in the glass preform 1a, since cations such as alkali metal elements do not substantially move, the composition of the glass at the center of the refractive index distribution type rod lens may be the same as the composition of the base glass before the ion exchange.

[0068] The optical product according to the present invention is not limited to a specific product as long as it includes the refractive index distribution type rod lens 1b. Using the refractive index distribution type rod lens 1b, for example, a predetermined rod lens array can be provided. The rod lens array forms an erect and same magnification image. In this case, the rod lens array may have a 0-dimensional array, a 1-dimensional array, or a 2-dimensional array with respect to the arrangement of the refractive index distribution type rod lenses 1b. The 0-dimensional array is, for example, a configuration in which a single refractive index distribution type rod lens 1b is arranged, and a desired effect is expected from an optical product composed of a single refractive index distribution type rod lens 1b. The 1-dimensional array is a configuration in which a plurality of refractive index distribution type rod lenses 1b are arranged in a row in a specific direction. That specific direction is called the main scanning direction, and the direction perpendicular to the main scanning direction and perpendicular to the optical axis is called the sub-scanning direction. In the rod lens array, the plurality of refractive index distribution type rod lenses 1b are arranged such that their optical axes are substantially parallel. The 2-dimensional array is a configuration in which, in addition to the 1-dimensional array, a plurality of lenses are arranged in a direction different from that. For example, a configuration in which a plurality of refractive index distribution type rod lenses 1b are arranged in two or more rows along the main scanning direction may correspond to the 2-dimensional array. According to the rod lens array 10b, even if the diameter of each refractive index distribution type rod lens is small, a wide range of erect and same magnification images can be obtained. As described above, in the refractive index distribution type rod lens 1b, the imaging distance (TC) is 45 to 75 mm. In other words, the imaging distance of the rod lens array is 45 to 75 mm. In addition, the refractive index distribution type rod lens 1b has a depth of field (DOF) of 1.5 to 3.0 mm. In other words, the depth of field (DOF) in the rod lens array is 1.5 to 3.0 mm.

[0069] For example, using the refractive index distribution type rod lens 1b, a rod lens array 10b shown in FIG. 4 can be provided. In the rod lens array 10b, a plurality of refractive index distribution type rod lenses 1b are arranged such that their optical axes are substantially parallel. In the rod lens array 10b, the plurality of refractive index distribution type rod lenses 1b are arranged in two rows so as to form a two-dimensional array. In the rod lens array 10b, the plurality of refractive index distribution type rod lenses 1b are arranged, for example, between a pair of fiber reinforced plastic (FRP) substrates 5. Between the pair of FRP substrates 5, the space between the plurality of refractive index distribution type rod lenses 1b and the space between the FRP substrate 5 and the refractive index distribution type rod lens 1b are filled with a black resin 7. Thereby, between the pair of FRP substrates 5, the plurality of refractive index distribution type rod lenses 1b are integrated. Such a rod lens array 10b can be manufactured, for example, as follows. First, a plurality of refractive index distribution type rod lenses 1b are arranged substantially in parallel on the surface of one FRP substrate 5, and the lenses are clamped by the other FRP substrate 5. Then, the space between the pair of FRP substrates 5 is filled with the black resin 7 to integrate the whole. Further, the end faces of the refractive index distribution type rod lenses 1b are polished as necessary.

[0070] As shown in FIG. 2, an erect and same magnification image is formed in the range of the visual field radius X0 by one refractive index distribution type rod lens 1b. In the image formed by one refractive index distribution type rod lens 1b, the amount of light on the optical axis of the refractive index distribution type rod lens 1b is the largest, and the amount of light decreases as the distance from the optical axis increases. For this reason, a change in the amount of light occurs within the visual field represented by the visual field radius X0. Since the rod lens array is formed by arranging such refractive index distribution type rod lenses 1b, unevenness in the amount of light occurs depending on the arrangement pitch of the refractive index distribution type rod lenses 1b.

[0071] When a rod lens array having a large amount of light unevenness is used in an inspection apparatus and optical devices such as an image sensor, the brightness of the image may vary periodically in the main scanning direction (the arrangement direction of the rod lenses) depending on the arrangement pitch of the rod lenses in the rod lens array. As a result, there is a possibility that the optical device may not exhibit the desired performance.

[0072] FIG. 5 schematically shows the relationship between the field of view and the light quantity distribution of an erect image of a refractive index distribution type rod lens 1b having a diameter D. The light quantity distribution E(x, y) in the field of view of the erect image is represented by the following formula (3). In formula (3), E0 is the light intensity at the center of the field of view of the erect image. At the center of the field of view of the erect image, x = y = 0. E(x,y)=E0·√{1-(x 2 +y 2 ) / X0 2} Formula (3)

[0073] FIG. 6 schematically shows the light quantity distributions E M1 and E M2 in a rod lens array in which refractive index distribution type rod lenses 1b having the above light quantity distribution E(x, y) are arranged in an array. The light quantity distribution E M1 shows the light quantity distribution of the refractive index distribution type rod lens 1b individually, and the light quantity distribution E M2 is the synthesized light quantity distribution of the refractive index distribution type rod lens 1b. The light quantity distribution in the rod lens array exhibits periodic light quantity unevenness corresponding to the arrangement pitch of the refractive index distribution type rod lenses 1b along the main scanning direction (x direction). The light quantity unevenness ΔE (0,0) along the reference line is represented by, for example, the following formula (4). In formula (4), E max and E min are the maximum value and the minimum value, respectively, in the light quantity distribution along the reference line. The light quantity unevenness ΔE (0,0) can be obtained by actually manufacturing the rod lens array and measuring the light quantity distribution. Also, if the optical constants of the refractive index distribution type rod lens 1b are known, ΔE (0,0)can be calculated. The rod lens array has, for example, a lens group in which a plurality of refractive index distribution type rod lenses 1b are arranged in a row along the main scanning direction. The light amount unevenness ΔE (0,0) Regarding, the reference line is the imaging plane of the erect same magnification image and the intersection line with the plane that is equidistant from one end and the other end of the lens group (rod lens array) in the sub-scanning direction (y direction) when looking at the end face of the refractive index distribution type rod lens 1b along the direction parallel to the central axis of the refractive index distribution type rod lens 1b. FIGS. 7A and 7B show the reference line L of the rod lens array having a lens group in which a plurality of refractive index distribution type rod lenses 1b are arranged in one row R conceptually. FIGS. 8A and 8B show the reference line L of the rod lens array having a lens group in which a plurality of refractive index distribution type rod lenses 1b are arranged in two rows R conceptually. FIGS. 9A and 9B show the reference line L of the rod lens array having a lens group in which a plurality of refractive index distribution type rod lenses 1b are arranged in three rows R conceptually. In FIGS. 7A to 9B, the reference line L R extends in the main scanning direction (x direction) and is a straight line with a position of y = 0 in the sub-scanning direction (y direction). In FIGS. 7A to 9B, P is an object such as a document and an inspection object, f1 can be the reading surface or the inspection surface of the object, and f2 is the imaging surface ΔE (0,0) =(E max -E min ) / E min Equation (4)

[0074] In a rod lens array having a lens group in which a plurality of refractive index distribution type rod lenses 1b are arranged in a row along the main scanning direction, the light amount unevenness ΔE along the reference line (0,0) is not limited to a specific value. The light amount unevenness ΔE along the reference line (0,0) is, for example, 6% or less. Thereby, an erect same magnification image is easily formed with a desired light amount in an optical device using the rod lens array. The predetermined range is within the range where the light amount distribution has substantially periodicity in the main scanning direction (x direction), and ΔE along the reference line (0,0)For example, it may be obtained within a predetermined range. The predetermined range is a range in which the light quantity distribution has substantially periodicity in the main scanning direction (x direction). In an example of the predetermined range, y = 0, and the range of x is 10 mm, y = 0, and the range of x is 4 mm, or y = 0, and the range of x may be 2 mm. Also, when the position in the middle of the above range of x is defined as x = 0, examples of the predetermined range can be expressed as y = 0, and -5 mm ≤ x ≤ 5 mm, y = 0, and -2 mm ≤ x ≤ 2 mm, y = 0, and -1 mm ≤ x ≤ 1 mm, respectively. Also, the position equidistant from the lenses at one end and the other end of the rod lens array, or the center of the lens closest to the position may be defined as x = 0. At this time, since the position of x = 0 is determined in advance, a predetermined range in the x direction may be obtained so as to include the position.

[0075] Light quantity unevenness ΔE along the reference line (0,0) is desirably 5% or less, and more desirably 4% or less. On the other hand, the light quantity unevenness ΔE (0,0) along the reference line is, for example, 1% or more. Thereby, in the refractive index distribution type rod lens 1b, it is easy to avoid adjusting the aperture angle that causes a decrease in the DOF.

[0076] The rod lens array 10b can be changed from various viewpoints, and for the material of each part constituting the rod lens array, a material known in the production of the rod lens array may be used. Also, the arrangement of the plurality of refractive index distribution type rod lenses 1b is not limited to two rows. The plurality of refractive index distribution type rod lenses 1b may be arranged in a single row, or may be arranged in two rows, or three or more rows. When a large number of refractive index distribution type rod lenses 1b are arranged in multiple rows, a rod lens array capable of corresponding to a large area can be provided.

[0077] The refractive index distribution type rod lens 1b can be a plastic rod lens having the above optical performance. The plastic rod lens can be manufactured by methods such as copolymerization method, sol-gel method, and mutual diffusion method. In particular, in the mutual diffusion method, resins with a refractive index decreasing stepwise from the center to the outer periphery are laminated concentrically, and then mutual diffusion of substances between layers is performed so that the refractive index becomes continuous. After performing such a process, it is further heat-stretched to obtain a rod-shaped rod lens. The plastic rod lens is easy to handle and generally inexpensive due to the characteristics of its material, and has advantages in some cases.

[0078] The rod lens array provided with the refractive index distribution type rod lens 1b has a large DOF, and in some cases, is excellent in weather resistance, and can be widely used in optical devices such as scanners, copiers, facsimiles, printers, CISs, and line cameras. In other words, an optical device provided with a rod lens array can be provided. Furthermore, since the rod lens array provided with the refractive index distribution type rod lens 1b is particularly excellent in water resistance (moisture resistance), it can be applied to the above optical devices and the like not only in general air-conditioned offices but also in various environments including factories, storage warehouses, or transportation trucks exposed to high-temperature and high-humidity situations.

[0079] The optical device provided with a rod lens array further includes, for example, a linear light source and a photosensor.

[0080] For example, using the rod lens array 10b, the close contact type image sensor (CIS) 100 shown in FIG. 10 can be provided. The CIS 100 includes, for example, a rod lens array 10b, a housing 11, a linear light sensor 12, a linear illumination device 13, and an original platen 14. The linear light sensor 12 extends in the main scanning direction of the rod lens array 10b. In FIG. 10, the direction parallel to the X-axis is the main scanning direction, and the direction parallel to the Y-axis is the sub-scanning direction. The linear illumination device 13 extends in the main scanning direction of the rod lens array 10b. The original platen 14 is formed of a glass plate. The glass plate forming the original platen 14 is disposed so as to cover the opening of the housing 11. The rod lens array 10b, the linear light sensor 12, and the linear illumination device 13 are disposed inside the housing 11. Linear illumination light is irradiated from the linear illumination device 13 onto the original P placed on the original platen 14. The rod lens array 10b is disposed such that the light reflected from the surface of the original P is incident on the linear light sensor 12. In other words, the linear light sensor 12 is disposed such that the light reflected from the original is transmitted through the rod lens array 10b and condensed. By scanning the mechanism including the rod lens array 10b and the linear light sensor 12 in the sub-scanning direction or by conveying the original P placed on the original platen 14 in the sub-scanning direction, two-dimensional image data regarding the original P can be obtained. The image sensor 100 may be configured to be able to image an object other than the original.

[0081] Since the rod lens array 10b includes the refractive index distribution type rod lens 1b having a large DOF, for example, even in a portion where a part of the original P floats due to wrinkles or a separated portion, the quality of the read image tends to be good.

[0082] Using the rod lens array 10b, for example, an image sensor 300 shown in FIG. 11 can be provided. The image sensor 300 includes a housing 31, a line-shaped optical sensor 32, a line-shaped illumination device 33, a first spacer 34a, a second spacer 34b, and a substrate 35. In the image sensor 300, the line-shaped illumination device 33 is disposed outside the housing 31. For example, in the image sensor 300, in order to appropriately adjust the optical arrangement between the portion of the document P to be read and the line-shaped optical sensor 32, the rod lens array 10b is positioned and fixed to the housing 31 by the first spacer 34a and the second spacer 34b. The image sensor 300 may be applied to a device for inspecting the appearance of a subject, or may be used to obtain an image from a subject (object to be inspected) instead of the document P. In this case, the light beam emitted from the line-shaped illumination device 33 irradiates the subject, and the light reflected from the surface of the subject is imaged on the line-shaped optical sensor 32 by the imaging action of the rod lens array 10b. The line-shaped optical sensor 32 can sequentially convert the one-dimensional image information on the surface of the subject into electrical signals and output them.

[0083] Using the rod lens array 10b, for example, a printer 500 shown in FIG. 12 can be provided. The printer 500 includes a writing head 51, a photosensitive drum 52, a charger 53, a developing device 54, a transferrer 55, a fixing device 56, an erasing lamp 57, a cleaner 58, and a paper feed cassette 59. The rod lens array 10b is disposed inside the writing head 51. The printer 500 is an electrophotographic printer. The writing head 51 includes the rod lens array 10b and a light emitting element array (not shown). The rod lens array 10b constitutes an imaging optical system that exposes the light emitted from the light emitting element array onto the photosensitive drum 52. Specifically, the focal point of the rod lens array 10b is located on the surface of the photosensitive drum 52, and it constitutes an erect and same magnification optical system. On the surface of the photosensitive drum 52, a photosensitive layer made of a material (photoconductor) having photoconductivity such as amorphous Si is formed. First, the surface of the rotating photosensitive drum 52 is uniformly charged by the charger 53. Next, the light of the dot image corresponding to the image to be formed is irradiated onto the photosensitive layer of the photosensitive drum 52 by the writing head 51, the charge in the area irradiated with light in the photosensitive layer is neutralized, and a latent image is formed in the photosensitive layer. Next, when toner is attached to the photosensitive layer by the developing device 54, the toner adheres to the portion where the latent image is formed in the photosensitive layer according to the charged state of the photosensitive layer. Next, the attached toner is transferred onto the paper sent from the cassette by the transferrer 55, and then, when the paper is heated by the fixing device 56, the toner is fixed to the paper and an image is formed. On the other hand, the charge of the photosensitive drum 52 after the transfer is neutralized over the entire area by the erasing lamp 57, and then, the toner remaining on the photosensitive layer is removed by the cleaner 58.

[0084] Using the rod lens array 10b, for example, an inspection apparatus 700 shown in FIG. 13 can be provided. The inspection apparatus 700 includes an image sensor 71, a line illumination device 72 as a light source, a controller 73, an output device 74, a transport device 75, and a transport control device 76. The rod lens array 10b is disposed inside the image sensor 71. The transport device 75 is, for example, a belt conveyor. The transport device 75 transports a subject T such as a printed circuit board, a textile, and paper. The transport control device 76 is a digital computer for controlling the transport device 75, and outputs a control signal for adjusting the transport speed of the transport device 75 toward the transport device 75. The image sensor 71 and the line illumination device 72 are disposed, for example, above the transport device 75, and the subject T passes directly below the image sensor 71 by the transport device 75. The image sensor 71 and the line illumination device 72 are arranged so that clear image data of the subject T can be obtained. The controller 73 is a digital computer for forming image data of the subject T. When the subject T passes directly below the image sensor 71, the controller 73 continuously acquires one-dimensional image information from the image sensor 71. In addition, the controller 73 acquires the transport position information of the subject T from the transport control device 76. The controller 73 performs a calculation process based on the one-dimensional image information acquired from the image sensor 71 and the transport position information acquired from the transport control device 76, and forms two-dimensional image information. The formed two-dimensional image information is compared with information stored in advance in the controller 73 that characterizes defects such as foreign matter, cracks, and pinholes. Thereby, the controller 73 specifies the presence or absence of defects, the number of defects, and the positions of the defects in the subject T. The controller 73 may determine the pass or fail of the subject T based on this comparison result. The output device 74 is, for example, a monitor, and displays the two-dimensional image information formed by the controller 73.

[0085] The above-mentioned optical devices such as CIS, image sensors, and inspection devices may be configured to acquire color images of objects such as objects to be inspected, subjects, and originals. For example, as shown in FIG. 14, an optical device 900 using a color filter method can be provided. The optical device 900 includes a rod lens array 10a, a white light source (not shown), and a photosensor 92. The white light source emits light having different wavelengths such as RGB. The white light source is, for example, a line light source. The photosensor 92 is arranged along the main scanning direction of the rod lens array 10a and has a plurality of segments having different main wavelengths. The photosensor 92 is, for example, a sensor such as a photodiode provided with color filters corresponding to R (red), G (green), and B (blue). Each of the plurality of segments is arranged, for example, in the sub-scanning direction (y direction) and is provided with a color filter corresponding to each of R, G, and B. As shown in FIG. 14, the plurality of segments of the photosensor 92 are arranged in the main scanning direction (x direction), and pixel information corresponding to RGB is formed in each segment, and they are combined to obtain a color image of the object.

[0086] As an image sensor capable of acquiring a color image, it is also conceivable to configure an image sensor using a sequential light source lighting method. On the other hand, a color filter type image sensor has advantages such as small color shift in the sub-scanning direction and good color reproducibility corresponding to each color of RGB.

[0087] In the rod lens array of a color filter type image sensor, not only the shift from the reference position in the axial direction of the rod lens but also the optical performance when shifted by a predetermined distance from the reference position in the sub-scanning direction (y direction) is important. Regarding the light amount unevenness, it is important that the light amount unevenness along the main scanning direction is small when shifted by a predetermined distance in the sub-scanning direction (y direction) of the rod lens array. Let the light amount unevenness when shifted by a predetermined distance y in the sub-scanning direction be ΔE (y,0) and represent it.

[0088] In a rod lens array having a lens group in which a plurality of refractive index distribution type rod lenses 1b are arranged in a row along the main scanning direction, a reference line L in the sub-scanning direction R the amount of light unevenness ΔE in the range of the imaging surface when it is separated from 0 to 0.5 mm (y = 0 to 0.5) (y,0) is, for example, 12% or less. It is understood that the smaller the value of the amount of light unevenness ΔE (y,0) , the better the performance of the rod lens array. On the other hand, from the perspective of the amount of light unevenness ΔE (y,0) , if the performance of the rod lens array is excessively high, in the refractive index distribution type rod lens 1b, it becomes extremely difficult to form the refractive index distribution, and it becomes difficult to suppress variations in performance in the actual manufacturing process. By setting the aperture angle of the refractive index distribution type rod lens 1b within a predetermined range, ΔE (y,0) , which is one of the optical performances in the axial direction of the refractive index distribution type rod lens 1b, can be easily reduced.

[0089] In the above rod lens array, the amount of light unevenness ΔE in the range of the imaging surface when it is separated from 0 to 0.5 mm (y = 0 to 0.5) with respect to the reference line L in the sub-scanning direction R is desirably 10% or less. In the above rod lens array, the amount of light unevenness ΔE in the range of the imaging surface when it is separated from 0 to 0.3 mm (y = 0 to 0.3) with respect to the reference line L in the sub-scanning direction (y,0) is, for example, 6% or less, and desirably 5% or less. In the above rod lens array, the amount of light unevenness ΔE in the range of the imaging surface when it is separated from 0 to 0.1 mm (y = 0 to 0.1) with respect to the reference line L in the sub-scanning direction R is, for example, 5% or less, and desirably 4% or less. (y,0) is, for example, 5% or less, and desirably 4% or less. R the amount of light unevenness ΔE in the range of the imaging surface when it is separated from 0 to 0.1 mm (y = 0 to 0.1) with respect to the reference line L in the sub-scanning direction (y,0) is, for example, 5% or less, and desirably 4% or less.

[0090] As described above, the light quantity unevenness ΔE can be calculated from each parameter of a known rod lens in addition to measurement using a rod lens array. Further, in order to evaluate the light quantity unevenness ΔE of the rod lens array, the overlapping degree M of the rod lens array, which is the array pitch ratio of the field of view radius, can be used. The overlapping degree M is expressed as M = X0 / 2R. One of the causes of the light quantity unevenness is the light quantity distribution in the image formed by one rod lens. Therefore, assuming a case where a plurality of rod lenses are arranged so that the low light quantity field region of a specific rod lens is compensated by another rod lens, it is understood that it is appropriate to use the value obtained by dividing the radius of the field of view by the array pitch of the rod lens. X0 is the field of view radius, 2R is the array pitch of the rod lens array, and is the distance between the central axes of adjacent rod lenses. As will be described later, the light quantity unevenness along the main scanning direction when shifted in the sub-scanning direction can be evaluated by the overlapping degree M.

[0091] The overlapping degree M of a rod lens array including a plurality of refractive index distribution type rod lenses 1b is not limited to a specific value, and is, for example, 1.4 to 3.6. Thereby, it is easy to reduce the light quantity unevenness while keeping the DOF within a desired range. From the viewpoint of reducing the light quantity unevenness, the overlapping degree M of the rod lens array is desirably 1.6 or more, more desirably 1.8 or more, and still more desirably 2.0 or more. From the viewpoint of the DOF, the overlapping degree M of the rod lens array is desirably 3.4 or less, more desirably 3.2 or less.

[0092] When using a rod lens array in an inspection apparatus for industrial products or the like, high reliability and sufficient tolerance are important. There are allowable ranges for various industrial products in consideration of quality variations. Therefore, in an inspection apparatus using a rod lens array, it is important to maintain the reliability of the inspection assuming such quality variations.

[0093] The characteristics such as the light quantity unevenness of the rod lens array and the degree of overlap M related to the light quantity unevenness are indicators used for evaluation in expanding the range of products applicable to the rod lens array. On the other hand, these characteristics are limited to the characteristics for evaluating the optical performance regarding the shift in the sub-scanning direction (y direction). In an optical device using a rod lens array, it is important that the variation in light quantity unevenness is small even when the height of the original and the object to be inspected varies, such as the depth of field (DOF).

[0094] Regarding the variation in light quantity unevenness related to the shift in the optical axis direction of the rod lenses in the rod lens array, for example, an index of the light quantity unevenness depth is used. The light quantity unevenness depth is measured from the reference line L in the sub-scanning direction R at a distance y, and when the position of the object plane in the direction parallel to the optical axis of the rod lenses in the rod lens array is shifted by ΔL from the position of the object plane when the MTF value is maximum, the maximum value of the light quantity unevenness is represented as ΔE (y,ΔL) ΔL becomes a negative value when the distance between the object plane and the rod lens array in the direction parallel to the optical axis is smaller than L i and becomes a positive value when the distance is larger than L i .

[0095] In a rod lens array having a lens group in which a plurality of refractive index distribution type rod lenses 1b are arranged in a row along the main scanning direction, when the value of y representing the shift in the sub-scanning direction (y direction) is 0 to 0.5 mm and ΔL is -1.5 mm to 1.5 mm, the light quantity unevenness depth ΔE (y,ΔL) is, for example, 25% or less. Thereby, in an optical device equipped with a rod lens array, even when the height of an object such as an original and an object to be inspected varies, the variation in light quantity unevenness is likely to be small.

[0096] The light quantity unevenness depth ΔE within the above range of the values of y and ΔL (y,ΔL) is desirably 15% or less, more desirably 10% or less, and even more desirably 8% or less. The required light quantity unevenness depth ΔE for the rod lens array (y,ΔL)may vary depending on the quality level of objects such as manuscripts and objects to be inspected. For example, when the values of ΔL or y are not so large and the acquisition of a high-quality image is required, the depth of light amount unevenness ΔE when y is 0 to 0.3 mm and ΔL is -1.0 mm to 1.0 mm (y,ΔL) is, for example, 8% or less, desirably 6% or less. Further, ΔE when y is 0 to 0.2 mm and ΔL is -0.5 mm to 0.5 mm (y,ΔL) is, for example, 6% or less, desirably 4% or less.

Example

[0097] Hereinafter, the present invention will be described in more detail with reference to examples. Note that the present invention is not limited to the following examples.

[0098] (Preparation of glass composition and production of refractive index distribution type rod lens) Glass raw materials were mixed so as to have the compositions shown in Table 1, and the mixture was melted to obtain molten glass (glass compositions) according to Examples 1 to 4, Comparative Examples 1 to 3, and Reference Example 1. The numerical values in Table 1 indicate mol%. Table 2 shows the relationship of the content ratios of predetermined components in each glass composition based on mol%. Each molten glass was spun and formed into a fiber shape, the obtained glass fiber was cut to a predetermined length, and the cut surface was polished. Thereby, glass element wires according to each example, each comparative example, and Reference Example 1 were obtained. The diameter (wire diameter) of each glass element wire was 560 μm. Next, each glass element wire was immersed in a molten sodium nitrate salt heated near the glass transition temperature of the glass composition constituting each glass element wire, and ion exchange treatment was performed. Thereby, a refractive index distribution was formed in each glass element wire. Thereafter, the glass element wire after the ion exchange treatment was cut into a one-period length, and the cut end face was polished to obtain refractive index distribution type rod lenses according to each example, each comparative example, and Reference Example 1.

[0099] (Characteristic evaluation) The cut surface of a sample obtained by cutting the refractive index distribution type rod lens fabricated as described above to an appropriate length was mirror polished. Next, a sheet with a lattice pattern was brought into contact with one end face of this sample, and an erect image of the pattern was observed from the other end face of the sample to determine the period length P of each refractive index distribution type rod lens. Next, based on the relationship of √A = 2π / P, the refractive index distribution coefficient √A of each refractive index distribution type rod lens was determined. Next, based on the values of the refractive index distribution coefficient √A, the radius r0 of the refractive index distribution type rod lens, and the refractive index Nc of the glass preform before the ion exchange treatment, and the relationship shown in the following formula (5), the aperture angle θ of each refractive index distribution type rod lens was determined. The results are shown in Table 3. Note that the refractive index Nc was 1.60 and could be regarded as the refractive index n0 on the optical axis of each refractive index distribution type rod lens. θ = sin -1 {√A·Nc·r0} Formula (5)

[0100] The refractive index Nc was determined by evaluating the refractive indices of the glass compositions according to each example, each comparative example, and Reference Example 1. A rectangular parallelepiped sample having a cross-sectional area of 15 mm square was fabricated by cutting out a base glass made of the glass composition, and the refractive index Nc was evaluated according to the V-block method described in JIS B 7071-2:2018. In this method, the sample is placed on a V-block prism, and the deflection angle of the light ray bent by the sample when the spectrally separated light ray passes through is measured. This method is a method of calculating the refractive index of the sample relatively from the value of this deflection angle and the refractive index of the known V-block prism. A KPR-3000 manufactured by Shimadzu Corporation was used for the evaluation.

[0101] (Water resistance evaluation) The water resistance of each glass composition was evaluated in accordance with JOGIS 06-2009. Samples made from each glass composition were placed in boiling water for 1 hour to measure the weight loss rate, and the water resistance of each glass composition was evaluated according to the weight loss rate. The water resistance in JOGIS 06-2009 is classified from Grade 1 to Grade 6, and it can be said that a glass with a water resistance of Grade 1 has excellent durability against weathering, particularly against moisture.

[0102] (Measurement of DOF) A predetermined treatment (unevenness forming treatment) was performed on the side of each gradient index rod lens for the purpose of removing noise light. Then, a plurality of gradient index rod lenses were arranged two-dimensionally to produce a rod lens array in which a plurality of gradient index rod lenses were arranged in two rows as shown in FIG. 4. In this manner, rod lens arrays according to each embodiment, each comparative example, and reference example 1 were obtained. A line pattern having six pairs of black and white lines spaced at intervals of 1 mm was prepared. That is, this line pattern had a spatial frequency of 6 lines / mm. The light emitted from a halogen lamp was passed through a color filter (transmission center wavelength: 530 nm, full width at half maximum: 15 nm) and irradiated onto the line pattern. As shown in FIG. 1, the line pattern, each rod lens array, and the light receiving element were arranged at a position where the MTF value of the erect life-size image was maximized. The distance between the rod lens array and the light receiving element at this time was defined as the lens-imaging position distance L. o The results are shown in Table 3. Then, while keeping the distance between the rod lens array and the light receiving element constant, the line pattern was moved in the optical axis direction to obtain the MTF value at each position, and the range of the working distance in which the MTF value is 30% or more was specified from the relationship between ΔL and the MTF value. Then, the depth of field (DOF) of each gradient index rod lens was determined by subtracting the minimum value from the maximum value of the working distance. The results are shown in Table 3 together with the image formation distance TC, the field radius X0, and the overlap degree M. FIG. 15 also shows the relationship between the MTF value and ΔL in the rod lens arrays according to Example 2, Comparative Example 3, and Reference Example 1.

[0103] table 3 As shown in FIG. 1, a rod lens array including a gradient index rod lens according to each embodiment is The DOF in (a) is in the range of 1.5 to 3.0 mm, and the refractive index distribution type It was suggested that the glass lens had a desired DOF. The water resistance of the composition was grade 1. On the other hand, the composition equipped with the gradient index rod lens according to each comparative example The DOF in the rod lens array was small. The DOF in the rod lens array equipped with lenses was 2.4 mm. However, in the reference example the water resistance of the glass composition according to 1 was grade 4, and it was suggested that the glass composition according to Reference Example 1 was inferior in terms of water resistance compared to the glass compositions according to each of the examples.

[0104] (Light quantity unevenness and overlap degree) For each of the examples, comparative examples, and the rod lens array according to Reference Example 1 having the respective parameters as shown in Table 3, the light quantity unevenness was determined. Considered as a model was an arrangement of rod lenses having the respective parameters of Table 3 in two rows as shown in FIG. 4. FIGS. 16A and 16B schematically show the optical system for calculating the light quantity unevenness. In FIGS. 16A and 16B, the rod lens 10 corresponds to the refractive index distribution type rod lens in the rod lens arrays according to each of the examples, comparative examples, and Reference Example 1. Considering a model in which the MTF of the rod lens array is maximized, the refractive index distribution type rod lens was arranged according to the values shown in Table 3 with respect to the imaging distance TC and the distance L between the lens and the imaging position. In FIGS. 16A and 16B, the x direction is the main scanning direction of the rod lens array, and the y direction is the sub-scanning direction of the rod lens array. The straight line representing y = 0 is the axis of the rod lens array, and on this straight line, the lengths of the perpendiculars from the centers of the rod lenses arranged in two rows in the sub-scanning direction are equal. The value of y is the distance shifted from the axis of y = 0. i

[0105] Table 4 shows the values of the light quantity unevenness ΔE of the rod lens arrays according to each of the examples, comparative examples, and Reference Example 1 calculated based on Expression (3) and Expression (4). The value of this light quantity unevenness is the value when ΔL = 0, and was obtained from the light quantity distribution at a specific y at the imaging position L. The value of ΔE when y = 0 mm is ΔE (y,0) i (y,0) (0,0) . Table 3 shows the overlap degree M of each rod lens array.

[0106] Regarding the rod lens arrays according to Examples 1, 2, and 3, the light quantity distributions obtained along the reference line of the light quantity unevenness are shown in FIGS. 17, 18, and 19, respectively.

[0107] (Light quantity unevenness depth) Similar to the calculation of the light quantity unevenness, based on the optical systems shown in FIGS. 16A and 16B, the light quantity unevenness was determined for a plurality of sets of ΔL and y in the rod lens arrays according to Examples 1 to 3 and Comparative Example 4. The results are shown in Tables 5 and 6. The maximum value of the light quantity unevenness ΔE within a predetermined range of ΔL and y is the light quantity unevenness depth ΔE (y,ΔL) is. The optical parameters of the rod lens array according to Comparative Example 4 are as follows. Central refractive index n0 = 1.450 Optical constant √A = 0.1500 mm -1 Lens length Z0 = 27.75 mm Manuscript, etc. - Distance between lenses L O = 8.211 mm Field of view radius X0 = 0.8187 mm Overlap degree M = 0.9097

[0108] In the range of -1.5 mm ≤ ΔL ≤ 1.5 mm and 0 ≤ y ≤ 0.5 mm, the light quantity unevenness depth ΔE of the rod lens array according to Example 1 (y,ΔL) is 13.2%, and the light quantity unevenness depth ΔE of the rod lens array according to Example 2 (y,ΔL) is 6.4%, and the light quantity unevenness depth ΔE of the rod lens array according to Example 3 (y,ΔL) is 6.0%, and the light quantity unevenness depth ΔE of the rod lens array according to Comparative Example 4 (y,ΔL) was 120.8%.

[0109] In the range of -1.0 mm ≤ ΔL ≤ 1.0 mm and 0 ≤ y ≤ 0.3 mm, the light quantity unevenness depth ΔE of the rod lens array according to Example 1 (y,ΔL) is 7.5%, and the light quantity unevenness depth ΔE of the rod lens array according to Example 2 (y,ΔL) is 5.4%, and the light quantity unevenness depth ΔE of the rod lens array according to Example 3 (y,ΔL)is 4.8%, and the light quantity unevenness depth ΔE of the rod lens array according to Comparative Example 4 (y,ΔL) was 120.8%.

[0110] In the range of -0.5 mm ≤ ΔL ≤ 0.5 mm and 0 ≤ y ≤ 0.2 mm, the light quantity unevenness depth ΔE of the rod lens array according to Example 1 (y,ΔL) is 4.3%, and the light quantity unevenness depth ΔE of the rod lens array according to Example 2 (y,ΔL) is 3.6%, and the light quantity unevenness depth ΔE of the rod lens array according to Example 3 (y,ΔL) is 3.6%, and the light quantity unevenness depth ΔE of the rod lens array according to Comparative Example 4 (y,ΔL) was 57.7%.

[0111]

Table 1

[0112]

Table 2

[0113]

Table 3

[0114]

Table 4

[0115]

Table 5

[0116]

Table 6

Claims

1. A rod lens array that forms an erect same-magnification image, comprising a plurality of refractive index distribution type rod lenses arranged such that their optical axes are parallel to each other, each of the plurality of refractive index distribution type rod lenses having a refractive index distribution in the radial direction, Let the radius of the refractive index distribution type rod lens be r 0 and represent the central refractive index, which is the refractive index at the center of the refractive index distribution type rod lens, as n 0 and represent the refractive index distribution constant of the refractive index distribution type rod lens as √A. When the refractive index at a distance r from the center of the refractive index distribution type rod lens is approximated by n(r) = n 0 ·{1 - (A / 2)·r 2}, the half-angle of the cone of light θ represented by sin -1 (n 0 ·√A·r 0 ) is 3 to 5.5°, and the imaging distance of the rod lens array being 45 to 75 mm, The array pitch of the rod lens array is represented as 2R, and when the field of view radius is represented as X 0 when represented as, X 0 The overlap degree M represented by / 2R is 1.4 to 3.6, the depth of field being 1.5 to 3.0 mm with the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines / mm being 30% or more, rod lens array.

2. The refractive index distribution constant √A is 0.130 to 0.230 mm -1 and The central refractive index n 0 is 1.51 to 1.65, and the rod lens array according to claim 1.

3. The rod lens array according to claim 1 or 2, wherein the maximum value of the MTF is 60% or more.

4. The rod lens array according to any one of claims 1 to 3, wherein the distance between the lens and the imaging position at which the value of the MTF is maximum is 13 to 28 mm.

5. When looking at the end face of the refractive index distribution type rod lens along the direction parallel to the central axis of the refractive index distribution type rod lens and the imaging plane of the erect same magnification image, the intersection line with the plane that is equidistant from one end and the other end of the rod lens array in the sub-scanning direction is defined as the reference line L R When expressed as R the light quantity unevenness ΔE (0,0) in the reference line L is 6% or less. The rod lens array according to any one of claims 1 to 4

6. When the imaging plane of the erect same-magnification image is intersected with a plane that is equidistant from one end and the other end of the rod lens array in the sub-scanning direction when viewing the end face of the refractive index distribution type rod lens along a direction parallel to the central axis of the refractive index distribution type rod lens, a reference line L R is represented as In the sub-scanning direction, the reference line L R The light amount unevenness ΔE in the range of the imaging surface that is 0 to 0.5 mm away from (y,0) is 12% or less. The rod lens array according to any one of claims 1 to 5.

7. When the imaging plane of the erect same-magnification image is intersected with a plane that is equidistant from one end and the other end of the rod lens array in the sub-scanning direction when viewing the end surface of the refractive index distribution type rod lens along a direction parallel to the central axis of the refractive index distribution type rod lens, the intersection line is defined as reference line L R When expressed as The maximum value of the light quantity unevenness ΔE is the value when it is separated from the reference line by 0 to 0.5 mm in the sub-scanning direction and the position of the object surface in the direction parallel to the optical axis of the refractive index distribution type rod lens is shifted by -1.5 mm to 1.5 mm from the position of the object surface when the value of the MTF is maximum. (y,ΔL) is 25% or less. The rod lens array according to any one of claims 1 to 6.

8. The glass composition at the center of the refractive index distribution type rod lens, expressed in mol%, 40% ≤ SiO 2 ≤ 65% 0% ≤ TiO 2 ≤ 10% 0.1% ≤ MgO ≤ 22% 0.15% ≤ ZnO ≤ 15% 0.5% ≤ Li 2 O < 4% 2% ≤ Na 2 O ≤ 20% 0% ≤ B 2 O 3 ≤ 20% 0% ≤ Al 2 O 3 ≤ 10% 0% ≤ K 2 O ≤ 3% The rod lens array according to any one of claims 1 to 7, satisfying the above conditions.

9. An optical device comprising the rod lens array according to any one of claims 1 to 8.

10. The rod lens array according to any one of claims 1 to 8, a line illumination device for illuminating an object in a line shape, and a line light sensor arranged such that light reflected from the object passes through the rod lens array and is condensed, image sensor.

11. The line light sensor has a plurality of segments arranged in the sub-scanning direction and provided with color filters corresponding to each of R, G, and B, the plurality of segments being arranged in the main scanning direction of the rod lens array, image sensor according to claim 10.

12. A printer comprising a writing head having the rod lens array according to any one of claims 1 to 8.

13. A conveying device for conveying an article, an illumination device for illuminating the article, an image sensor, and a controller, the image sensor comprising the rod lens array according to any one of claims 1 to 8 for condensing light reflected from the article, acquiring image information of the article conveyed by the conveying device and transmitting it to the controller, the controller specifying a defect of the article and determining the pass / fail of the article based on the image information, inspection device.

Images