JP7308171B2 - Gradient index lenses, rod lens arrays, image scanners, printers, and inspection equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gradient index lens, an optical product, an optical device, a glass composition for a gradient index lens, and a method for producing a gradient index lens.

2. Description of the Related Art Conventionally, there has been known an apparatus for observing defects on the surface of an object using a Charge-Coupled Device (CCD). For example, Patent Literature 1 describes a surface defect device that includes a light source, irradiation means, light collection means, and observation means. The observation means consists of an imaging lens and a CCD.

Japanese Unexamined Patent Application Publication No. 2002-100001 describes an inspection apparatus suitable for visual inspection of a photosensitive drum of an electrophotographic copier or printer. This inspection apparatus includes a camera device that photographs the photosensitive drum with a plurality of one-dimensional CCD cameras arranged in a line.

On the other hand, a contact image sensor (CIS) is also known as an imaging sensor. The CIS has a rod lens array. A gradient index lens is usually used for the rod lens array.

For example, patent documents 3 to 5 describe gradient index lenses. A gradient index lens or a gradient index rod lens is a rod-shaped (rod-shaped) lens having a refractive index distribution in which the refractive index continuously decreases from the center to the outer periphery. In the gradient index lens described in Patent Document 3, the difference Δn between the refractive index at the peripheral surface of the lens and the refractive index at 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°, which suggests that this is undesirable. In other words, it is believed that Patent Document 3 suggests that an aperture angle ([theta]) of less than 5[deg.] is undesirable.

The aperture angle of the gradient index lens according to the example in Patent Document 4 is about 10.1 to 12.9 degrees. The aperture angle of the gradient index lens according to the example in Patent Document 5 is 10.1 to 12.0°.

JP-A-7-27709 Japanese Unexamined Patent Application Publication No. 2003-75906 Japanese Patent Publication No. 51-21594 JP 2005-289775 A JP 2008-230956 A

Patent Documents 1 and 2 do not describe the use of gradient index lenses. The gradient index lenses described in Patent Documents 3 to 5 have large aperture angles. This is hardly advantageous from the viewpoint of achieving a large depth of field in the gradient index lens, and the gradient index lenses described in Patent Documents 3 to 5 are considered to have a small depth of field. If the depth of field of the gradient index lens is small, for example, when the thickness of the object varies, the object may have an in-focus portion and an out-of-focus portion.

In view of such circumstances, the present invention provides a gradient index lens that makes it difficult for an object to have an in-focus portion and an out-of-focus portion even if the object has variations in thickness.

The present invention
A gradient index lens,
has a depth of field of 1.5 to 3.0 mm,
The depth of field is determined by subtracting the minimum value from the maximum value of the working distance while maintaining a constant distance between the gradient index lens and the imaging position,
At the working distance, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines/mm is 30% or more,
The refractive index n(r) at the radius r of the gradient index lens and the refractive index n 0 at the center of the gradient index lens are _n (r)=n ₀ ×{1−(A/ 2) satisfies the relationship xr ² },
The refractive index distribution constant, which is the square root of A in the above relationship, is 0.130 to 0.230 mm ⁻¹ ,
having an opening angle of 3° to 6°,
A gradient index lens is provided.

The present invention
Provided is a rod lens array comprising the gradient index lenses arranged in one or more rows in the main scanning direction so that the optical axes are parallel.

The present invention
a rod lens array as described above;
a line-shaped light receiving element;
a line-shaped illumination device;
Provide an image scanner.

The present invention
A printer is provided comprising the above rod lens array .

The present invention
An inspection apparatus comprising the above rod lens array is provided .

According to the gradient index lens described above, even when the thickness of the object varies, it is difficult for the object to have an in-focus portion and an out-of-focus portion.

FIG. 1 is a diagram illustrating a method of determining the depth of field of an example of a gradient index lens according to the present invention. FIG. 2 is a diagram showing an aperture angle of an example of a gradient index lens according to the present invention. FIG. 3A is a diagram showing ion exchange treatment in an example of the method for manufacturing a gradient index lens according to the present invention. FIG. 3B is a graph conceptually showing a refractive index distribution in a gradient index lens. FIG. 4 is a perspective view showing an example of an optical product according to the present invention. FIG. 5 is a cross-sectional view showing an example of an optical device according to the present invention. FIG. 6 is a cross-sectional view showing another example of the optical device according to the present invention. FIG. 7 is a diagram showing still another example of the optical device according to the present invention. FIG. 8 is a diagram showing still another example of the optical device according to the present invention. FIG. 9 is a graph showing the relationship between the MTF value and the working distance of the gradient index lenses according to Example 2, Comparative Example 3, and Reference Example 1. FIG.

Image data collected in visual inspection of a subject must have a resolution that allows identification of defects in 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. Therefore, it may be difficult to image the entire subject with one camera. For example, if 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 thoroughly inspect a subject having a width of 1200 mm, it is necessary to arrange four camera systems with one-dimensional CCD sensors and camera lenses in the width direction. Mounting multiple camera systems with one-dimensional CCD sensors increases the manufacturing cost of the device. In addition, it requires adjustment and maintenance of a plurality of camera systems each time the type of subject is changed, which increases the running cost of inspection.

Therefore, it is conceivable to use the CIS to inspect the appearance of the subject. A CIS includes a plurality of one-dimensional light receiving elements arranged on a substrate and a rod lens array. In CIS, a rod lens array forms an erect equal-magnification image. With CIS, a one-dimensional image with a width of 1200 mm can be obtained with one unit. A rod lens array is, for example, an arrangement of a plurality of rod-shaped gradient index lenses. A gradient index lens has a refractive index distribution in its radial direction, and the refractive index changes from the center to the periphery in the radial direction of the gradient index lens. A CIS equipped with a rod lens array can reduce the distance between the imaging device and the object to be photographed to about one-tenth of that of a conventional camera system equipped with a CCD sensor and a lens, and the size of the device can be reduced. It is advantageous in terms of conversion. On the other hand, in 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 the thickness of the subject varies, there are portions in focus and portions out of focus on the subject. For this reason, the image of the out-of-focus portion is not clear, and there is a possibility that the defect may be overlooked or the defect may be misidentified.

As described above, the gradient index lenses described in Patent Documents 3 to 5 have large aperture angles, which is not advantageous from the viewpoint of increasing the DOF of the gradient index lenses. Therefore, the present inventors fundamentally reviewed the conditions of the glass composition used for manufacturing the gradient index lens in order to realize the DOF in the desired range in the gradient index lens. The inventors of the present invention have finally found a graded refractive index lens capable of realizing a DOF within a desired range after much trial and error. The gradient index lens according to the present invention can be used not only in the technical field of visual inspection of a subject, but also in the general technical field of image formation such as image scanners, copiers, facsimiles, and printers.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the following description relates to an example of the present invention, and the present invention is not limited to the following embodiments.

The gradient index lens 1b has a depth of field (DOF) of 1.5-3.0 mm. The DOF of the gradient index lens 1b is determined by subtracting the minimum working distance from the maximum working distance. At the working distance of the gradient index lens 1b, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines/mm is 30% or more.

As shown in FIG. 1, the DOF of the gradient index lens 1b includes, for example, a lens array 10a, a line pattern 3, and a light receiving element 2 arranged at predetermined intervals in the optical axis direction. can be determined by obtaining the value of MTF while varying the distance from . The lens array 10a is constructed by arranging a plurality of gradient index lenses 1b in a direction perpendicular to the optical axis. 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 line pattern 3 is irradiated with light emitted from a halogen lamp after passing through a color filter and a light diffusion plate. The color filter may, for example, transmit light in the wavelength range of 500 to 600 nm, or may transmit mainly a wavelength of 530 nm. At this time, the value of MTF is the image (input image) of the line pattern 3 having a predetermined spatial frequency consisting of bright and dark portions formed on the light receiving element 2 by the lens array 10a before entering the lens array 10a. can be determined as the reproduction rate of the image (output image) obtained by

A distance (object point-image point distance) D _max between the line pattern 3 and the light receiving element 2 that maximizes the MTF value is determined. Then, the positive direction (ΔL>0) and negative direction (Δ
The line pattern 3 is moved to L<0), and the MTF value is obtained at each position. Thus, by setting an allowable range of values for a given MTF, it is possible to determine the maximum and minimum values of the working distance. As a result, the DOF of the gradient index lens 1b can be determined. In addition, when ΔL>0, the distance between the line pattern 3 and the lens array 10a is the distance D _max
greater than the working distance corresponding to . On the other hand, when ΔL<0, the distance between the line pattern 3 and the lens array 10a is smaller than the working distance corresponding to the distance D _max . At ΔL=0, the distance between the line pattern 3 and the lens array 10a is equal to the working distance corresponding to the distance D _max .

Since the DOF of the gradient index lens 1b is within the above range, it is advantageous in obtaining image data suitable for visual inspection of a subject having uneven thickness, steps, and unevenness. Therefore, the gradient index lens 1b can contribute to improving the accuracy of the visual inspection of the subject and enhancing the inspection criteria.

The DOF of the gradient index lens 1b is desirably 1.5 mm or more, more desirably 1.8 mm or more, and even more desirably 2 mm or more. The DOF of the gradient index lens 1b is preferably 2.8 mm or less, more preferably 2.5 mm or less.

The working distance corresponding to the object point-image point distance D _max that maximizes the MTF value is, for example, 15
mm or more, preferably 18 mm or more. When the distance D _max between the object point and the imaging point is within these ranges, the DOF is within an appropriate range. By incorporating a rod lens array including such a gradient index lens 1b into an inspection apparatus, an object having steps can be inspected. In addition, the rod lens array can maintain an appropriate distance from the object, which facilitates the assembly of the optical system.

The gradient index lens 1b has an aperture angle θ of 3 to 6°, for example. This facilitates adjustment of the DOF of the gradient index lens 1b to a desired range. The aperture angle θ of the gradient index lens 1b is defined, for example, as shown in FIG. The aperture angle θ is the maximum value of the angle formed by the optical axis and a ray that can be incident on one end of the optical axis of the gradient index lens 1b. In FIG. 2, F1 is an object surface, and F2 is a light receiving surface (image forming surface) of a light receiving element or the like. Z ₀ is the length of the gradient index lens 1b. _Lo is the object plane F
1 and the gradient index lens 1b, and L _i is the distance between the image plane F2 and the gradient index lens 1b when the MTF value is maximized. In FIG. 2, the lens array 10a constitutes a substantially erect equal-magnification imaging system, and the distance _Li is substantially equal to the distance _Lo . In FIG. 2, X ₀ is the field radius of the gradient index lens 1b. The aperture angle θ of the gradient index lens 1b can be determined, for example, according to the method described in Examples. In the method described in the Examples, the aperture angle θ may be determined using the refractive index n ₀ at the center of the gradient index lens 1b instead of the refractive index Nc of the glass wire before ion exchange. . Nc or n ₀ can be determined using the V-block method described in Japanese Industrial Standards (JIS) B 7071-2:2018.

The aperture angle θ of the gradient index lens 1b may be 3.5° or more, or may be 3.7° or more. The aperture angle θ of the gradient index lens 1b is preferably 5.5° or less, more preferably 5.2° or less.

The gradient index lens 1b may have, for example, a gradient index constant (√A) of 0.130 to 0.230 mm ⁻¹ . √A means the square root of A. If n(r) is the refractive index at radius r of the gradient index lens, n(r)=n ₀ ×{1−(A/2)×r ² } holds in the paraxial region of the lens. If the gradient index constant √A is within such a range, the aperture angle θ of the gradient index lens 1b is likely to fall within a desired range. As a result, the DOF of the gradient index lens 1b is easily adjusted to a desired range.

The gradient index constant of the gradient index lens 1b may be 0.140 mm ⁻¹ or more, or may be 0.145 mm ⁻¹ or more. The refractive index distribution constant of the gradient index lens 1b is preferably 0.210 mm ^-1 or less, more preferably 0.205 mm ^-1 or less.

The imaging distance of the erected image in the gradient index lens 1b is, for example, 45 to 80 mm. This is advantageous from the viewpoint of adjusting the DOF of the gradient index lens 1b to a desired range.

The imaging distance of the erect image in the gradient index lens 1b may be 47 mm or longer, 50 mm or longer, 53 mm or longer, or 54 mm or longer. The imaging distance of the erected image in the gradient index lens 1b may be 75 mm or less, 70 mm or less, or 67 mm or less.

The gradient index lens 1b is typically a rod-like or fiber-like lens. The gradient index lens 1b has, for example, a refractive index distribution in the radial direction as shown in FIG. 3B. Here, the refractive index n ₀ at the origin in FIG. 3B means the refractive index at the central axis of the gradient index lens 1b. r represents the radial position of the gradient index lens 1b.

The graded refractive index lens 1b prevents noise light (so-called white noise (stray light)) from being reflected by the side surface of the lens when incident light having an incident angle larger than the aperture angle is generated. You may have a structure. Such structures can be, for example, light-absorbing or light-scattering layers provided on the sides of the lens. For example, the graded refractive index lens 1b may have a core-clad structure in which a colored layer serving as a light absorbing layer is arranged on the side surface of the lens, or a fine uneven portion serving as a light scattering layer may be provided on the side surface. It may have a formed structure.

The gradient index lens 1b is typically a lens made of glass. The glass composition for a graded refractive index lens, expressed in mol %, has 40%≦SiO ₂ ≦65%, 0%≦TiO ₂ ≦10%, 0.1%≦MgO≦22%, and 0.15%≦ ZnO≦15%, 0.5%≦Li ₂ O<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% _≤La2 O ₃ ≦5% and 0%≦Ta ₂ O ₅ ≦5%. In addition, the glass composition for a gradient index lens contains at least two selected from the group consisting of CaO, SrO, and BaO in an amount of 0.1 mol % or more and 15 mol % or less. Furthermore, the glass composition for a graded refractive index lens has a
ZnO, 0.07≦ZnO/(MgO+ZnO)≦0.93, 2.5%≦ _Li2O + _Na2O <24%, and 0%≦ _{Y2O3 + ZrO2} + _{Nb2O5 + In2O3 + La2 O3 + Ta2O5≤}
Satisfies the 11% condition. By using such a glass composition, a gradient index lens having a desired DOF can be obtained.

The gradient index lens 1b can be manufactured, for example, by subjecting a glass wire made of the glass composition described above to an ion exchange treatment.

( _SiO2 )
SiO ₂ is an essential component that forms the network structure of glass. If the content of SiO ₂ is less than 40 mol %, the content of other components necessary for exhibiting the optical properties of a gradient index lens after ion exchange becomes relatively large, and devitrification tends to occur. Become. Also, if the content is less than 40 mol %, the chemical durability of the glass composition is significantly reduced. On the other hand, when the content exceeds 65 mol%, the content of other components such as an alkali component for forming a refractive index profile, a refractive index increasing component, and a physical property value adjusting component is limited and practical. It becomes difficult to obtain a suitable glass composition. Therefore, the content of SiO ₂ is 40 mol % or more and 65 mol % or less.

( _TiO2 )
TiO ₂ is an essential component that acts to increase the refractive index of the glass composition. By increasing the refractive index of the base glass composition, it is possible to increase the center refractive index of the gradient index lens obtained from the glass composition. Also, by increasing the content of TiO ₂ , the refractive index distribution in the gradient index lens can be brought closer to an ideal state, and a gradient index lens with excellent resolution can be manufactured. When the content of TiO ₂ is 10 mol %, no deterioration 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 deteriorates, which is not practical. I can't get the lens. On the other hand, if the content exceeds 10 mol %, coloring becomes strong, chromatic aberration becomes large, and a practical lens cannot be obtained. Therefore, the content of TiO ₂ is 1 mol % or more and 10 mol % or less in order to obtain a lens with small chromatic aberration and capable of enhancing image resolution. The TiO ₂ content is desirably 2 mol % or more and 8 mol % or less.

(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 center and periphery of the lens after ion exchange. When the MgO content exceeds 22 mol %, devitrification tends to occur. On the other hand, when the MgO content exceeds 22 mol %, the content of other components is excessively decreased, and a practical glass composition cannot be obtained. Therefore, the content of MgO is 0.1 mol % or more and 22 mol % or less. From the viewpoint of achieving a sufficient refractive index difference, the MgO content is desirably 2 mol % or more. When the content of MgO is 2 mol % or more, the content 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 MgO content is desirably 2 mol % or more and 22 mol % or less, and more desirably 2 mol % or more and 16 mol % or less.

(ZnO, MgO+ZnO, ZnO/(MgO+ZnO))
ZnO has the effect of improving the weather resistance of the glass composition and the gradient index lens. In the glass composition according to the invention, ZnO may be added to partially replace MgO. From the viewpoint of enhancing the weather resistance of the glass composition and the gradient index lens, the content of ZnO is 0.15 mol % or more and 15 mol % or less. At this time, the content of MgO and ZnO is adjusted so that the total content of MgO and ZnO (MgO+ZnO) is 2 mol % or more. In addition, the ratio of the content of ZnO to the sum of the content of MgO and ZnO (ZnO
The contents of MgO and ZnO are adjusted such that /(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 gradient index 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 ZnO content is desirably 8 mol % or less. From the viewpoint of further enhancing the weather resistance of the glass composition and the gradient index lens, the ZnO content 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. ZnO/(MgO+ZnO) is preferably 0.07 or more and 0.9 or less, more preferably 0.25 or more and 0.85 or less, still more preferably 0.25 or more and 0.8 or less, Especially preferably, it is 0.3 or more and 0.8 or less.

( _Li2O )
Li ₂ O is an essential component and one of the most important components for ion-exchanging the glass composition of the present invention to obtain a gradient index lens. Conventionally, Li ₂ O in glass compositions
It has been thought that if the content of is low, a sufficient concentration distribution, that is, a sufficient refractive index distribution cannot be developed by ion exchange, and a suitable graded index lens cannot be obtained. However, the present inventors have found that even a glass composition having a Li ₂ O content of 4 mol % or less has an appropriate refractive index distribution and , newly found that a gradient index lens having a large DOF can be produced. If the content of Li ₂ O exceeds 4 mol % or less, the resulting gradient index lens tends to have a large aperture angle and a small DOF. The Li ₂ O content is 0.5 mol % or more, preferably 0.7 mol % or more, and more preferably 1 mol % or more. The Li ₂ O content is 4 mol % or less, preferably 3.5 mol % or less, more preferably 3 mol % or less, and even more preferably 2 mol % or less.

One of the features of the gradient index lens 1b is that the content of _Li2O is less than various prior arts. Conventionally, there was a manufacturing process reason that the content of Li ₂ O could not be reduced.
The inventors of the present invention have found that the amount of glass filaments processed per batch by the ion exchange method is limited, and the original content of Li in the molten salt is reduced. The present inventors have newly found that a gradient index lens having a smaller aperture angle than before and a practical resolution can be obtained while suppressing lens aberration.

( _Na2O )
During ion exchange, Na ₂ O aids ion exchange between Li and ions of ion-exchange species (ions contained in the molten salt) substituting Li ions due to the so-called mixed alkali effect, and facilitates ion exchange. Keep your mobility moderate. By keeping the ion mobility moderate, the ion exchange rate can be moderately adjusted, and the optical properties of the gradient index lens can be adjusted. If the content of Na ₂ O in the glass composition is less than 2 mol %, the glass becomes hard during molding, making molding difficult. In addition, the melting temperature of the glass rises significantly, making lens production difficult. In addition, it is difficult to sufficiently obtain the effect of maintaining the ion mobility at an appropriate level. On the other hand, when the content of Na ₂ O exceeds 20%, the chemical durability of the glass is lowered and the glass lacks practicality. Therefore, the Na ₂ O content is 2 mol % or more, preferably 5 mol % or more, and more preferably 10 mol % or more. Also, the content of Na ₂ O is 20 mol % or less, preferably 17 mol % or less.

( _Li2O + _Na2O )
As described above, the sum of the Li ₂ O content and the Na ₂ O content in the glass composition (Li ₂
O+Na ₂ O) is 2.5 mol % or more and less than 24 mol %. When Li ₂ O+Na ₂ O is within this range, an image with good resolution can be obtained with a gradient index lens manufactured using this glass composition. Li ₂ O+Na ₂ O is desirably 6 mol % or more, more desirably 10 mol % or more.

( _Li2O / _Na2O )
When the ratio of the Li ₂ O content to the Na ₂ O content (Li ₂ O/Na ₂ O) is large, the resolving power of the gradient index lens manufactured using the glass composition may be improved. . On the other hand, when the ratio of Li ₂ O/Na ₂ O is excessively large (for example, 1.0 or more), the gradient index lens produced using the glass composition tends to have a large aperture angle and a small DOF. be. Therefore, Li ₂ O/Na ₂ O is, for example, 0.2 or less, preferably 0.15 or less, and more preferably 0.1 or less.

The above glass composition may further contain the following components.

_{( B2O3} )
B ₂ O ₃ is an optional component that forms the network structure of the glass, and promotes vitrification of the glass composition without substantially changing the resolving power and the aperture angle θ of the gradient index lens obtained, has the effect of adjusting the It also has the effect of slowing down the ion exchange rate of the glass composition, albeit slightly. For B ₂ O ₃ , for example, the content of each of the essential components described above is within the scope of the present invention, but when viewed as a composition, the content of some components is relatively high, making it difficult to use as glass. It may be added when the stability decreases (for example, devitrification tends to occur). By adding B ₂ O ₃ , it is possible to reduce the contents of some of the above relatively large components without changing the ratio of the contents of the essential components. The content of B ₂ O ₃ that can be added without changing the resolving power and aperture angle of the gradient index lens obtained is, for example, 20% mol or less. Therefore, the content of B ₂ O ₃ is 0% mol or more and 20 mol% or less. The content is desirably 0 mol % or more and 10 mol % or less, and when the glass composition contains B ₂ O ₃ , the content is desirably 1 mol % or more and 10 mol % or less.

_{( Al2O3} )
The glass composition for a gradient index lens may contain Al ₂ O ₃ as an optional component, and its content is 0 mol % or more and 10 mol % or less.

_{( SiO2} + _TiO2 + _B2O3 )
In the glass composition for a gradient index lens, the total content of SiO ₂ , TiO ₂ and B ₂ O ₃ (SiO ₂ +TiO ₂ +B ₂ O ₃ ) is, for example, 41 mol % or more and 70 mol % or less. , desirably from 50 mol % to 70 mol %.

( _{Y2O3 , ZrO2 , Nb2O5 , In2O3 , La2O3} , _{Ta2O5 )}
The glass composition for a gradient index lens contains Y ₂ O ₃ , ZrO ₂ , Nb ₂ O ₅ , In for the purpose of adjusting the refractive index of the gradient index lens obtained after ion exchange or improving the weather resistance. At least one component selected from the group consisting of ₂ O ₃ , La ₂ O ₃ and Ta ₂ O ₅ may be included. The total content of these components is 0 mol % or more and 11 mol % or less, and when the glass composition for a gradient index lens contains these components, the total content of these components is desirably 0. .2 mol % or more and 6 mol % or less. In addition, it is desirable that the sum of the content of these components and the content of ZnO be 15 mol % or less.

_{( Y2O3} )
The content of Y ₂ O ₃ is desirably 0 mol % or more and 5 mol % or less.

( _ZrO2 )
The content of ZrO ₂ is desirably 0 mol % or more and 2 mol % or less, and when the glass composition for a gradient index lens contains ZrO ₂ , the content is 0.2 mol % or more and 2 mol % or less. is.

Each of the contents of Nb ₂ O ₅ , In ₂ O ₃ , La ₂ O ₃ and Ta ₂ O ₅ is desirably 0 mol % or more and 5 mol % or less.

( _K2O , _Cs2O )
K ₂ O and Cs ₂ O are optional components that have the effect of reducing the mobility of alkali ions, similar to MgO, CaO, SrO, and BaO, due to the mixed alkali effect. Each of the K ₂ O and Cs ₂ O contents is, for example, 0 mol % or more and 3 mol % or less. From the viewpoint of increasing the water resistance of the glass composition for a gradient index lens, the content of Cs ₂ O is preferably less than 2 mol %, more preferably 0 mol % or more and 1 mol % or less, and even more preferably. is 0.5 mol % or less. From the viewpoint of enhancing the water resistance of the glass composition for a gradient index lens, it is desirable that the glass composition for a gradient index lens does not substantially contain Cs ₂ O. As used herein, "substantially free" means that the content of the component is less than 0.1 mol %.

(other ingredients)
The glass composition for a gradient index lens may contain GeO ₂ as another component. The content of GeO ₂ may range from 0 mol % to 10 mol %. Further, the glass composition for a gradient index lens may contain at least one selected from the group consisting of SnO ₂ , As ₂ O ₃ and Sb ₂ O ₃ as an additive. _SnO2 , _As2O3 , and _S
Each of the contents of b ₂ O ₃ can be 0 mol % or more and 1 mol % or less. The glass composition for a gradient index lens may consist essentially of the above components. In this case, the content of each component contained in the glass composition and the relationship between the content of each component (total and content ratio) satisfy the conditions described above. As used herein, the phrase "consisting essentially of" means that the impurity content is allowed to be less than 0.1 mol %.

(PbO)
The glass composition for a gradient index lens does not substantially contain lead (PbO as a typical compound). Also, the gradient index lens 1b does not substantially contain lead.

In the glass composition for a gradient index lens, for example, the water resistance determined according to the Japanese Optical Glass Industry Standard (JOGIS) 06-2009 is first class. In this case, the glass composition for a gradient index lens has high water resistance, and the gradient index lens manufactured using the glass composition for a gradient index lens also tends to have high water resistance. The glass forming the gradient index lens may also have first-class water resistance determined according to JOGIS 06-2009.

The glass composition for a gradient index lens contains an oxide of a primary alkali metal element. The gradient index lens 1b can be manufactured, for example, by a method including the following steps (I) and (II).
(I) A glass strand 1a made of the above glass composition for a graded index lens is formed.
(II) The glass wire 1a is immersed in a molten salt S containing a second alkali metal element R different from the first alkali metal element Q contained in the glass composition for a gradient index lens, and The first alkali metal element Q and the second alkali metal element R in the molten salt are ion-exchanged to form a refractive index distribution in the glass wire 1a.

In the step (II), for example, as shown in FIG. 3A, the glass wire 1a is put into the molten salt S inside the container V, and the glass wire 1a is immersed in the molten salt S for a predetermined time. At least one of potassium nitrate and sodium nitrate is melted in the molten salt S, for example. When the glass wire 1a is immersed in the molten salt S, cations of the first alkali metal element Q such as Li (lithium) contained in the glass wire 1a dissolve into the molten salt S, for example. On the other hand, cations of the second alkali metal element R such as K (potassium) in the molten salt S enter the glass wire 1a. By adjusting the temperature of the molten salt S and the immersion time of the glass wire 1a in the molten salt S, 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 performed. You can control it. A specific monovalent cation concentration distribution occurs inside the glass wire 1a, and a refractive index distribution as shown in FIG. 3B is formed in the glass wire 1a according to this concentration distribution. Thereby, the gradient index lens 1b can be manufactured from the glass wire 1a.

The optical product according to the present invention is not limited to a specific product as long as it includes the gradient index lens 1b. For example, a predetermined lens array can be provided using the gradient index lens 1b. In this case, the lens array can have a 0-dimensional arrangement, a 1-dimensional arrangement, or a 2-dimensional arrangement with respect to the arrangement of the gradient index lenses 1b. The 0-dimensional arrangement is, for example, a configuration in which a single graded index lens 1b is arranged, and a desired effect is expected from an optical product composed of the single graded index lens 1b. A one-dimensional arrangement is a configuration in which a plurality of gradient index lenses 1b are arranged in a row in a specific direction. The 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. The plurality of gradient index lenses 1b are arranged such that their optical axes are substantially parallel. A two-dimensional array is a configuration in which a plurality of lenses are arranged in a direction different from the one-dimensional array. For example, a configuration in which a plurality of gradient index lenses 1b are arranged in two or more rows along the main scanning direction can correspond to a two-dimensional arrangement. According to the lens array 10b, even if the diameter of each gradient index lens is small, it is possible to obtain a wide-ranging erect equal-magnification image.

For example, a gradient index lens 1b can be used to provide the lens array 10b shown in FIG. In the lens array 10b, a plurality of gradient index lenses 1b are arranged such that their optical axes are substantially parallel. In the lens array 10b, a plurality of gradient index lenses 1b are arranged in two rows so as to form a two-dimensional array. In the lens array 10b, a plurality of gradient index lenses 1b are arranged between a pair of fiber reinforced plastic (FRP) substrates 5, for example. Between the pair of FRP substrates 5, a black resin 7 is filled in the space between the plurality of gradient index lenses 1b and the space between the FRP substrate 5 and the gradient index lens 1b. Thus, between the pair of FRP substrates 5, a plurality of gradient index lenses 1b are integrated. Such a lens array 10b can be produced, for example, as follows. First, on the surface of one FRP substrate 5, a plurality of gradient index lenses 1b are arranged substantially parallel, and the other FRP substrate 5 sandwiches the lenses. After that, the space between the pair of FRP substrates 5 is filled with black resin 7 to integrate the whole. Further, the end face of the gradient index lens 1b is polished as necessary.

The lens array 10b can be modified from various points of view, and materials known in the manufacture of lens arrays may be used for the materials of the parts that constitute the lens array. Also, the arrangement of the plurality of gradient index lenses 1b is not limited to two rows. The plurality of gradient index lenses 1b may be arranged in one row, or may be arranged in three or more rows. By arranging the gradient index lenses 1b in multiple rows, it is possible to provide a lens array that can accommodate a large area.

The gradient index lens 1b can be a plastic rod lens having the above optical performance. Plastic rod lenses can be produced by methods such as copolymerization, sol-gel, and interdiffusion. In the interdiffusion method, in particular, resins whose refractive index gradually decreases from the center to the periphery are laminated concentrically, and materials between the layers are mutually diffused so that the refractive index becomes continuous. After such treatment, the film is further heated and stretched to obtain a rod-shaped rod lens. Plastic rod lenses are easy to handle and generally inexpensive due to the characteristics of their materials, and in some cases have merits.

A lens array equipped with a gradient index lens 1b has a large DOF and excellent weather resistance in some cases, and can be widely used in optical equipment such as scanners, copiers, facsimiles, printers, CIS, and line cameras. can. Furthermore, since the lens array provided with the gradient index lens 1b is particularly excellent in water resistance (humidity resistance), it can be used not only in general air conditioning such as offices, but also in factories, storage warehouses, and transportation that are exposed to high temperature and humidity. It can be applied to the above-mentioned optical equipment and the like in various environments including physical distribution such as trucks.

Lens array 10b can be used, for example, to provide CIS scanner 100 shown in FIG. The CIS scanner 100 includes, for example, a lens array 10b, a housing 11, a linear light-receiving element 12, a linear illumination device 13, and a document table . The linear light receiving elements 12 extend in the main scanning direction of the lens array 10b. In FIG. 5, 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 lens array 10b. The platen 14 is made of a glass plate. A glass plate forming document platen 14 is arranged so as to cover the opening of housing 11 . The lens array 10b, the linear light receiving elements 12, and the linear illumination device 13 are arranged inside the housing 11. As shown in FIG. A document P placed on a document platen 14 is irradiated with linear illumination light from the linear illumination device 13 . The lens array 10 b is arranged so that the light reflected by the surface of the document P is incident on the linear light receiving elements 12 . A two-dimensional image of the document P is obtained by scanning the scanner mechanism including the lens array 10b and the linear light-receiving elements 12 in the sub-scanning direction or by conveying the document P placed on the document table 14 in the sub-scanning direction. data can be obtained.

Since the lens array 10b is equipped with a gradient index lens 1b having a large DOF, the quality of the read image is maintained even in a portion of the document P that is partially lifted due to, for example, wrinkles or a double-page spread. tend to get better.

Lens array 10b can be used, for example, to provide scanner 300 shown in FIG. The scanner 300 includes a housing 31 , a linear light receiving element 32 , a linear illumination device 33 , a first spacer 34 a, a second spacer 34 b, and a substrate 35 . In the scanner 300 , the linear illumination device 33 is arranged outside the housing 31 . For example, in the scanner 300, in order to appropriately adjust the optical arrangement between the portions of the document P to be read and the linear light receiving elements 32, the lens array 10b is formed by the first spacer 34a and the second spacer 34b. 31 are positioned and fixed. The scanner 300 may be applied to an apparatus for inspecting the appearance of a subject, and may be used to obtain an image from the subject (inspection object) instead of the manuscript P. In this case, the subject is irradiated with light rays emitted from the linear illumination device 33, and the light reflected from the surface of the subject is imaged on the linear light receiving element 32 by the imaging action of the lens array 10b. The linear light-receiving element 32 can sequentially convert one-dimensional image information of the surface of the subject into electrical signals and output them.

Lens array 10b can be used to provide, for example, printer 500 shown in FIG. The printer 500 includes a write head 51 , a photosensitive drum 52 , a charger 53 , a developer 54 , a transfer device 55 , a fuser 56 , an erase lamp 57 , a cleaner 58 and a paper feed cassette 59 . I have. The lens array 10b is arranged inside the write head 51 . The printer 500 is an electrophotographic printer. The write head 51 includes a lens array 10b and a light emitting element array (not shown). The lens array 10b constitutes an imaging optical system that exposes the photosensitive drum 52 to the light emitted from the light emitting element array. Specifically, the lens array 10b has its focal point positioned on the surface of the photosensitive drum 52, and constitutes an erecting equal-magnification optical system. A photosensitive layer made of a photoconductive material (photoreceptor) such as amorphous Si is formed on the surface of the photosensitive drum 52 . First, the surface of the rotating photosensitive drum 52 is uniformly charged by the charger 53 . Next, the writing head 51 irradiates the photosensitive layer of the photosensitive drum 52 with light of a dot image corresponding to the image to be formed, neutralizes the charge in the area of the photosensitive layer irradiated with the light, and creates a latent charge in the photosensitive layer. An image is formed. Next, when toner is caused to adhere to the photosensitive layer by the developing device 54, the toner adheres to the portion of the photosensitive layer where the latent image is formed according to the charged state of the photosensitive layer. Next, the attached toner is transferred by the transfer device 55 to the paper sent from the cassette, and then the paper is heated by the fixing device 56, so that the toner is fixed on the paper and an image is formed. On the other hand, the charge on the photosensitive drum 52 that has completed 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 cleaning device 58. FIG.

Using the lens array 10b, for example, an inspection apparatus 700 shown in FIG. 8 can be provided. The inspection apparatus 700 includes a CIS scanner 71 , a linear illumination device 72 , a controller 73 , an output device 74 , a transport device 75 and a transport control device 76 . Inside the CIS scanner 71, a lens array 10b is arranged. The conveying device 75 is, for example, a belt conveyor. The transport device 75 transports a subject T such as a printed circuit board, textile, paper, or the like. The transport control device 76 is a digital computer for controlling the transport device 75 and outputs control signals to the transport device 75 for adjusting the transport speed of the transport device 75 . The CIS scanner 71 and the linear illumination device 72 are arranged, for example, above the carrier device 75 , and the subject T passes directly below the CIS scanner 71 by the carrier device 75 . The CIS scanner 71 and linear 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. FIG. The controller 73 continuously acquires one-dimensional image information from the CIS scanner 71 when the subject T passes directly under the CIS scanner 71 . In addition, the controller 73 acquires transport position information of the subject T from the transport control device 76 . The controller 73 performs calculation processing based on the one-dimensional image information acquired from the CIS scanner 71 and the transport position information acquired from the transport control device 76 to form two-dimensional image information. The formed two-dimensional image information is compared with pre-stored information in the controller 73 characterizing defects such as foreign objects, cracks, pinholes and the like. Thereby, the controller 73 identifies the presence/absence of defects, the number of defects, and the positions of defects in the subject T. FIG. The controller 73 may judge whether the subject T is good or bad based on this comparison result. The output device 74 is, for example, a monitor, and displays two-dimensional image information formed by the controller 73 .

The present invention will be described in more detail below with reference to examples. In addition, the present invention is not limited to the following examples.

(Preparation of glass composition and production of gradient index lens)
Glass raw materials were mixed so as to have the composition shown in Table 1, and the mixture was melted to obtain glass melts (glass compositions) according to Examples 1 to 4, Comparative Examples 1 to 3, and Reference Example 1. The numbers in Table 1 indicate mol %. Table 2 shows the relationship between the contents of predetermined components in each glass composition on a mol % basis. Each molten glass was spun into a fiber shape, the obtained glass fiber was cut into a predetermined length, and the cut surface was polished. Thus, the glass strands according to each example, each comparative example, and reference example 1 were obtained. The diameter (wire diameter) of each glass wire was 560 μm. Next, each glass wire was immersed in a sodium nitrate molten salt heated to around the glass transition temperature of the glass composition constituting each glass wire to perform an ion exchange treatment. Thereby, a refractive index distribution was formed in each glass strand. Thereafter, the glass strands after the ion exchange treatment were cut into one period length, and the cut end surfaces were polished to obtain gradient index lenses according to each example, each comparative example, and reference example 1.

(characteristic evaluation)
A cut surface of a sample obtained by cutting the graded index lens manufactured as described above into an appropriate length was mirror-polished. Next, a sheet on which a lattice pattern is written is brought into contact with one end face of this sample, and an erected image of the pattern is observed from the other end face of the sample to determine the periodic length P of each gradient index lens. Decided. Next, the refractive index distribution coefficient √A of each gradient index lens was determined based on the relationship √A=2π/P. Next, based on the values of the refractive index distribution coefficient √A, the radius r ₀ of the gradient index lens, and the refractive index Nc of the glass wire before the ion exchange treatment, and the relationship shown in the following formula (1), The aperture angle θ of each gradient index lens was determined. Table 3 shows the results. The refractive index Nc was 1.60 and could be regarded as the refractive index of each gradient index lens on the optical axis.
θ=sin ⁻¹ {√A·Nc·r ₀ } Equation (1)

The refractive index Nc was obtained by evaluating the refractive index 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 prepared by cutting out the 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, a sample is placed on a V-block prism, and the angle of deviation of the ray that is bent by the sample when the dispersed ray passes through it is measured. This method is a method of relatively calculating the refractive index of the sample from the value of this deflection angle and the known refractive index of the V-block prism. KPR-3000 manufactured by Shimadzu Corporation was used for the evaluation.

(Water resistance evaluation)
The water resistance of each glass composition was evaluated according to JOGIS 06-2009. A sample prepared from each glass composition was 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. According to JOGIS 06-2009, water resistance is classified into grades 1 to 6, and it can be said that glass having grade 1 water resistance has excellent weather resistance, particularly durability against moisture.

(Measurement of DOF)
For each gradient index lens, the side surface thereof was subjected to a predetermined treatment (unevenness formation treatment) for the purpose of removing noise light. After that, a plurality of gradient index lenses were arranged two-dimensionally to produce a lens array in which a plurality of gradient index lenses were arranged in two rows as shown in FIG. Thus, lens arrays according to each example, each comparative example, and reference example 1 were obtained. A line pattern was prepared having six black and white line pairs at intervals of 1 mm. That is, this line pattern had a spatial frequency of 6 lines/mm. The light emitted from the halogen lamp was passed through a color filter (transmission central wavelength: 530 nm, full width at half maximum: 15 nm) to irradiate the line pattern. As shown in FIG. 1, the line pattern, each lens array, and the light-receiving element are arranged at the position where the MTF value is maximized. The distance between the lens array and the light-receiving element at this time was determined as the lens-imaging position distance _Lo . Table 3 shows the results. After that, while moving the line pattern in the optical axis direction, the MTF value was obtained at each position, and the working distance range in which the MTF value was 30% or more was specified from the relationship between ΔL and the MTF value. Then, the depth of field (DOF) of each gradient index lens was determined by subtracting the minimum working distance from the maximum working distance. Table 3 shows the results. 9 shows the relationship between the MTF value and ΔL in the lens arrays according to Example 2, Comparative Example 3, and Reference Example 1. In FIG.

As shown in Table 1, the DOF in the lens array provided with the gradient index lenses according to each example is in the range of 1.5 to 3.0 mm, and the gradient index lenses according to each example are desired. It was suggested to have DOF. In addition, the water resistance of the glass composition according to each example was grade 1. On the other hand, the DOF in the lens array provided with the gradient index lens according to each comparative example was small. The DOF of the lens array including the gradient index lenses according to Reference Example 1 was 2.4 mm. However, the water resistance of the glass composition according to Reference Example 1 is grade 4,
It was suggested that the glass composition according to Reference Example 1 was inferior in water resistance to the glass compositions according to the Examples.

1a Glass wire 1b Gradient index lens 2 Light receiving element 3 Line pattern 10a, 10b Lens array 100 CIS scanner 300 Scanner 500 Printer 700 Inspection device

Claims (8)

A gradient index lens,
has a depth of field of 1.5 to 3.0 mm,
The depth of field is determined by subtracting the minimum value from the maximum value of the working distance while maintaining a constant distance between the gradient index lens and the imaging position,
At the working distance, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines/mm is 30% or more,
The refractive index n(r) at the radius r of the gradient index lens and the refractive index n ₀ at the center of the gradient index lens are n(r)=n ₀ ×{1−(A/ 2) satisfies the relationship xr ² },
The refractive index distribution constant, which is the square root of A in the above relationship, is 0.130 to 0.230 mm ⁻¹ ,
having an aperture angle of 3.5° to 5.5°;
The imaging distance of the erect image is 54 to 67 mm,
Gradient index lens. 2. A rod lens array comprising the gradient index lens according to claim 1, arranged in one or more rows in the main scanning direction so that the optical axes are parallel. a rod lens array according to claim 2;
a line-shaped light receiving element;
an image scanner, comprising: a linear illumination device; A printer comprising the rod lens array according to claim 2. An inspection apparatus comprising the rod lens array according to claim 2. 2. The gradient index lens according to claim 1, wherein the graded refractive index lens has a water resistance of grade 1 as determined in accordance with Japan Optical Glass Industry Standard (JOGIS) 06-2009. A rod lens array used in a visual inspection device,
The visual inspection apparatus includes a CIS scanner equipped with the rod lens array,
a transport device for transporting an object to be inspected;
a controller;
Used in the appearance inspection device that forms two-dimensional image information of the inspection object by continuously acquiring one-dimensional image information of the inspection object transported by the transport device,
3. A rod lens array according to claim 2. A method for manufacturing the gradient index lens according to claim 1, comprising:
providing a glass strand having a composition comprising a first alkali metal oxide and one or more other metal oxides;
By immersing the glass wire in a molten salt containing a second alkali metal for a predetermined time and exchanging the first alkali metal and the second alkali metal in the glass wire and in the molten salt, the forming a refractive index profile within the glass strand;
A method for manufacturing a gradient index lens, wherein the glass strands have the following composition.
expressed in mole %,
40%≦SiO ₂ ≦65%
1 % _≤TiO2≤10 %
0.1%≦MgO≦22%
0.15%≦ZnO≦15%
0.5%≦Li ₂ O<4%
2%≦Na ₂ O≦20%
0 _{% ≤B2O3≤20} %
0%≦Al ₂ O ₃ ≦10%
0%≦K ₂ O≦3%
0% _≤Cs2O≤3 %
0 _{%≤Y2O3≤5 %}
0% _≤ZrO2≤2 %
0 _{%≤Nb2O5≤5 %}
0 _{%≤In2O3≤5 %}
0%≦La ₂ O ₃ ≦5%
0% ≤ Ta ₂ O ₅ ≤ 5%,
CaO, SrO, and at least two selected from the group consisting of BaO, each containing 0.1 mol% or more and 15 mol% or less,
expressed in mole %,
2%≦MgO+ZnO,
0.07≦ZnO/(MgO+ZnO)≦0.93,
The conditions of 2.5%≦Li ₂ O+Na ₂ O<24% and 0%≦Y ₂ O ₃ +ZrO ₂ +Nb ₂ O ₅ +In ₂ O ₃ +La ₂ O ₃ +Ta ₂ O ₅ ≦11% are satisfied.

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