JPH06181504A - Picture reading unit - Google Patents

Abstract

PURPOSE:To suppress the deterioration of picture reading characteristics after heat cycle test processing by using the combination of a lens element array provided with a specific condition and a plastic-made case body. CONSTITUTION:The selection of thermal expansion coefficients of plastic bases 42, 43 in the range of 0.5X10<-5> to 10.0X10<-5>cm/cm/ deg.C is preferable for prepare a lens array with a small tolerance. A plastic case body is preferably used as the case body 41. For instance, resin allowed to be applied to projection molding is preferably used and the thermal expansion coefficient in the range of 0.5X10<-5> to 10.0X10<-5>cm/cm/ deg.C is preferably adopted. It is necessary to satisfy a difference between the thermal expansion coefficients of bases 42, 43 and the case body 41 with relation less than 5.0X10<-5>cm/cm/ deg.C. When a heat cycle test is executed in a state exceeding said condition, sensitivity is suddenly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an image reading unit having a lens array using a plastic substrate incorporated in a housing, which is lightweight and has high image reading accuracy. It is in the image reading unit which can be treated.

[0002]

2. Description of the Related Art A cross-sectional view of a conventionally developed image reading unit in which a large number of gradient index rod lens elements are arranged and a lens element array sandwiched and bonded between two substrates is incorporated in a housing. Is shown in FIG. In the figure, 11 is a housing incorporating the lens element array, which is usually made by die casting or drawing of a light metal such as aluminum. Reference numeral 14 is a lens element array, 12 and 13 are substrates constituting the lens element array, 15 is an optical sensor such as a CCD for converting image information read by the lens element array into an electric signal, and 16 is a light source. , 17 is cover glass, 18, 18 '
Is a pin for fixing the lens element array in the housing, and 19 and 19 'are projections for fixing the lens element array provided in the housing.

[0003]

Image reading units used in copying machines and facsimiles, which are becoming lighter in weight and smaller in size, are required to be lighter in weight and to use a lens element array having a constant lens conjugate length. As described above, in order to achieve these purposes, a lens element array in which an array of gradient index rod-shaped lens elements is bonded and sandwiched by a plastic substrate is assembled in a housing made of an aluminum die cast product. An image reading unit has been developed. Using this image reading unit, the MTF (modulation, transfer, function) measured using a grid of 4 line pairs / mm is 50% or more, which is extremely good.
After performing the thermal cycle test as shown in, it was found that the MTF measured in the same manner rapidly decreased to 30% or less, and the performance of the image reading unit was deteriorated.

[0004]

Therefore, the inventors of the present invention are currently investigating for the purpose of developing an image reading unit capable of solving the above-mentioned problems. The present invention has been completed by finding out that an image transmitting body which can achieve the object can be obtained by using it in combination with the case.

The gist of the present invention is to provide an image reading unit in which a lens array in which an array of gradient index rod-shaped lens elements is bonded and sandwiched between two plastic substrates is incorporated in a plastic housing. And the difference between the coefficient of thermal expansion of the lens array substrate and the coefficient of thermal expansion of the housing is 5.0 × 10
^It is an image reading unit characterized by being made of a material of ^-5 cm / cm / ° C or less.

The gradient index rod-shaped lens element used for carrying out the present invention can be manufactured by a method as shown in, for example, WO91 / 05274. Specifically, n (n is an integer of 3 or more) Each syrup-shaped plastic composition having a different refractive index was fed to a concentric spinning nozzle so that the refractive index was gradually decreased from the inside toward the outside, and a true conjugate was spun to form a yarn, By curing this yarn and cutting it into an appropriate length, a gradient index rod-shaped lens element can be obtained.

The gradient index lens element manufactured as described above has an extremely stable gradient index constant (g value), and the dimensional tolerance of the lens element length (Z ₀ ) used in the present invention is ±. It is suitable as a gradient index lens element used when forming a gradient index lens array in the range of 0.15 mm. Also in other manufacturing methods, both a plastic lens element and a glass lens element can be effectively used as long as the dimensional tolerance of the lens element length (Z ₀ ) is within ± 0.15 mm.

As the polymer for manufacturing a plastic substrate for sandwiching the lens element array used for carrying out the present invention, polymethylmethacrylate, polyacetal, A
BS, polycarbonate, nylon, polyester, 4-
Various thermoplastic resins such as methylpentene-1 polymer, epoxy resin, unsaturated polyester resin, and crosslinkable resin can be used. A light-shielding additive such as carbon black or a reinforcing material such as carbon fiber, glass fiber or whiskers can be added to the resin for forming the substrate. The thermal expansion coefficient of the plastic substrate made in this way is 0.5 × 10
It is desirable to select a range of ^{-5 to} 10.0 × 10 ^-5 cm / cm / ° C in order to make a lens array with small dimensional tolerance.
These substrates can be manufactured by an injection molding method, an extrusion molding method, a press molding method, or the like.

Although various types of housings can be used for carrying out the present invention, the weight of the image reading unit of the present invention can be reduced, and the performance of the image reading unit does not deteriorate due to a thermal cycle test. For this purpose, it is preferable to use a plastic housing, for example, a housing made of an injection-moldable resin such as polycarbonate, poly-4-methylpentene-1, polyacetal, ABS, nylon, or polyester. The thermal expansion coefficient is preferably 0.5 × 10 ^{−5 to} 10.0 × 10 ⁻⁵ cm / cm / ° C. It is preferable that a reinforcing material such as carbon black, carbon fiber or glass fiber is added to the plastic constituting the housing to improve its dimensional stability.

The difference between the coefficient of thermal expansion of the substrate and the coefficient of thermal expansion of the housing is 5.0 × 10 ^-5 cm / cm / ° C or less, especially 3.0 × 10 ^-5 cm / cm / ° C.
It is necessary to satisfy the following relationships. The image reading sensor made by combining large ones with a difference in coefficient of thermal expansion exceeding 5.0 × 10 ^-5 cm / cm / ° C, the sensitivity of the image reading sensor suddenly decreases when subjected to a thermal cycle test. It cannot be an image reading unit with good performance.

Conventionally, the housing of the image reading sensor using the gradient index rod-shaped lens element array has been made of an aluminum die-cast product, an aluminum pultruded product or the like, but the image reading unit of the present invention is lighter in weight. It is necessary to have high-speed image reading characteristics and to have performance that does not deteriorate in the thermal cycle test. Conventionally, it was thought that the plastic housing, which was considered unusable, had its thermal expansion coefficient changed to the lens array. By specifying the thermal expansion coefficient of the substrate, it is possible to satisfy the above-mentioned requirements, which is a great feature.

The plastic housing can be manufactured by an extrusion molding method, an injection molding method, or the like, but it is necessary to have a housing with high dimensional accuracy, and in particular, a housing with high dimensional accuracy. It is preferable to adopt an injection molding method as the molding method. The housing is required to have high dimensional accuracy because a lens element array for image reading is provided in the housing,
This is because it is necessary to arrange the CCD sensor for converting the image information read by the lens element array into an electric signal and the lens array element and the cover glass surface in an accurate positional relationship, and this positional relationship is subjected to a thermal cycle test. This is because it is necessary to hold it accurately afterward.

When a housing is made by an injection molding method, in order to improve the dimensional accuracy of the housing, the housing has a length of 10 to 100 mm, preferably 10 to 50 mm. It is preferable to combine them into a housing. If the length of the casing unit is less than 10 mm, it is not preferable because a large number of casing units must be combined to form the casing, which increases the manufacturing cost of the finished casing. Also, in case units whose length is longer than 100 mm,
It is unavoidable that the flow of plastic into the mold during injection molding of plastic is uneven, and it becomes difficult to form a housing with high dimensional accuracy. As for the case, the length of the case unit should be in the range of 10 to 100 mm, especially 10 to 50 mm.
Join these housing units with 2 to 20 adhesives,
Alternatively, as shown by 502 and 503 in FIG. 5, it is preferable to use a case in which 2 to 20 case units having fastening parts to be fastened by a fitting structure are fastened to form a case. In particular, a case made by using a plurality of case units having a fastening portion as shown in FIG. 5 has extremely high dimensional accuracy, and a case using this case can have good image reading characteristics. .

The present invention uses a rod-shaped lens element having a uniform conjugate length as compared with the refractive index distribution type rod-shaped lens element which has been conventionally developed, and these lens elements are sandwiched between substrates having a specific coefficient of thermal expansion. Since the bonded lens array is an image reading unit with a structure that is built in a plastic housing with a specific coefficient of thermal expansion,
The image reading unit has good workability when incorporating the CCD sensor, the light source, and the cover glass, and has a small difference between the image reading characteristic at high temperature and the image reading characteristic at low temperature. .

Hereinafter, the present invention will be described in more detail with reference to examples.

[0016]

Example 1 Polymethylmethacrylate ([η] = 0.5
6, measured in methyl ethyl ketone (MEK) at 25 ° C) 46 parts by weight, benzyl methacrylate 44 parts by weight, methyl methacrylate 10 parts by weight, 1-hydroxycyclohexyl phenyl ketone 0.2 parts by weight and hydroquinone 0.1 parts by weight 70 parts by weight
The mixture was heated and kneaded at 0 ° C. to prepare a first layer (central portion) forming stock solution.
In addition, polymethylmethacrylate ([η] = 0.41, MEK
(Measured at 25 ° C in medium) 50 parts by weight, methyl methacrylate 50 parts by weight, 1-hydroxycyclohexyl phenyl ketone 0.2
Parts by weight and 0.1 parts by weight of hydroquinone are heated and kneaded to 70 ° C. to prepare a second layer forming stock solution, and further 45 parts by weight of polymethylmethacrylate ([η] = 0.34, measured at 25 ° C. in MEK), 2,2 , 3,3,4,4,5,5-octafluoropentyl methacrylate 35 parts by weight, methyl methacrylate 20 parts by weight, 1-
A mixture of 0.2 parts by weight of hydroxycyclohexyl phenyl ketone and 0.1 parts by weight of hydroquinone was kneaded by heating at 70 ° C. to obtain a stock solution for forming the third layer (outer layer part). Using a composite spinning machine equipped with a concentric three-layer composite spinning nozzle, three types of stock solutions were sequentially arranged from the center so that the refractive index of the uncured product was lowered, and simultaneously extruded strand fibers were obtained.
The viscosity of the first layer is 4.5 × 10 ⁴ poise when extruded,
The second layer is 2.0 × 10 ⁴ poise, and the third layer undiluted solution is 2.2
It was × 10 ⁴ poise. The temperature of the composite spinning nozzle is
It was 55 ° C.

Next, each layer was passed through a layer mutual diffusion treatment section of 90 cm in length, and then 12 fluorescent lamps of 120 cm in length and 40 W were passed through the strand fiber through the centers of the light irradiation sections arranged in a circle at equal intervals. The optical transmission medium having a radius (r 2 _{O 3} ) of 0.50 mm was pulled by a nip roller at a speed of 50 cm / min. The discharge amount ratio was 1st layer: 2nd layer: 3rd layer = 1: 1: 1. Refractive index profile in the center of the obtained refractive index distribution type rod-shaped lenses (n _O) is 1.
512, the peripheral part is 1.470, and the refractive index distribution constant (g) is
It was 0.52.

The rod-shaped lens obtained as described above had a lens length of 7.2 mm, and its both end surfaces were polished, and the MTF measured using a grating of 4 line pairs / mm was 57%, and the conjugate at that time was 57%. The length was 15.4 mm. The image of the obtained grating was a clear image with little distortion.

As shown in the perspective view of FIG. 2, a large number of these rod-shaped lens elements are bonded between two grooved substrates 12 and 13 with a sandwiching adhesive 25 to form a lens array. The dimensions of the lens array were 230 mm in length, 7.2 mm in width, and 2.8 mm in thickness, and the lens end surface was mirror-polished. The substrates 12 and 13 were made of carbon black-containing ABS resin by injection molding, and the adhesive 201 was an epoxy adhesive. The coefficient of thermal expansion of this lens array substrate was measured between −20 ° C. and 60 ° C.
It was 10 ^-5 cm / cm / ° C. Below, all thermal expansion coefficients are −20
The measurement was performed between ℃ and 60 ℃. Further, as shown in FIG. 4, a casing 235 having a length of 235 mm having two pairs of projections 49, 49 ', 401, 402 for fixing the lens array was made from ABS resin containing carbon black, and the thermal expansion coefficient was measured to be 7.5. × 10
^{It was -5} cm / cm / ° C. Also, the warp between both ends of the housing is 1 mm
Was a small one. The above-mentioned lens array is mounted on the housing 41, and the CCD sensor 45, the light source 46, and the glass cover are attached.
With 47 as an image reading unit, 4 line pairs / mm
When the MTF was measured with the following grating, it was 50% or more over the entire width of the lens array. When the image reading unit was subjected to a thermal cycle test as shown in FIG. 3, the MTF of the image reading sensor was measured again, and it was 47% or more over the entire width of the lens array.

[0020]

Example 2 A case 41 shown in FIG. 4 was manufactured using a carbon black-containing polycarbonate, and the coefficient of thermal expansion thereof was measured and found to be 4 × 10 ⁻⁵ cm / cm / ° C. The warp between both ends of this housing was about 1.5 mm. Using this case 41, an image reading unit was manufactured in the same manner as in Example 1, and 4
When the MTF was measured using a line pair / mm grating, it was 50% or more over the entire lens array width. This image reading sensor was subjected to a thermal cycle test as shown in FIG. 3 and then its MTF was measured again, and it was 45% or more, and there was no practical problem.

[0021]

Example 3 a housing 41 in FIG. 4 manufactured by using a carbon black-containing ABS resin reinforced with glass fibers (20% glass fiber content), was measured the thermal expansion coefficient, 5.2 × 10 ^{- It was 5} cm / cm / ° C, and the warp between both ends of this casing was 1.0 mm. Using this casing 41, an image reading unit was manufactured in the same manner as in Example 1, and 4 line pairs /
When the MTF was measured with a grating of mm, it was 48% or more over the entire lens array width. When the image reading unit was subjected to a thermal cycle test as shown in FIG. 3 and its MTF was measured again, it was 47%, which was practically no problem.

[0022]

[Example 4] A lens array was manufactured in the same manner as in Example 1 except that the substrates 42 and 43 in Example 1 were made of ABS resin containing glass fiber reinforced carbon black (glass fiber content 20%). The coefficient of thermal expansion of the substrate was measured and found to be 4.9 × 10 ^-5 cm / cm / ° C. Using this lens array and the housing 41 manufactured in Example 1, an image reading unit was manufactured in the same manner as in Example 1 and its MTF was measured with a grid of 4 line pairs / mm. That was all. This image reading unit was subjected to a thermal cycle test as shown in FIG.
When F was measured, MTF was 45% at the screws 18 at both ends of the lens array, but there was no problem in practical use.

[0023]

Fifth Embodiment In the first embodiment, the substrates 42 and 43 are manufactured by using carbon fiber reinforced ABS resin (carbon fiber content rate 30%),
A lens array was manufactured in the same manner as in Example 1. The coefficient of thermal expansion of the substrate of this lens array was measured and found to be 1.2.
It was × 10 ^-5 cm / cm / ° C. In addition, the case 41 of FIG.
Carbon fiber reinforced ABS resin (carbon fiber content
30%) and measured the coefficient of thermal expansion,
It was 1.1 × 10 ^-5 cm / cm / ° C, and there was almost no warp between both ends. An image reading unit was manufactured using this lens array and the housing in the same manner as in Example 1, and the MTF was measured with a grid of 4 line pairs / mm, and it was 50% or more over the entire width of the lens array. When the image reading sensor was subjected to a thermal cycle test as shown in FIG. 3 and its MTF was measured again, it was 50% or more over the entire width of the lens array.

[0024]

Comparative Example 1 The housing 41 of FIG. 4 was made of aluminum and its thermal expansion coefficient was measured and found to be 2.2 × 10 ⁻⁵ cm / cm / ° C. An image reading unit was manufactured in exactly the same manner as in Example 1 except that this housing 41 was used, and 4 line pairs / mm
When the MTF was measured with the grating of No. 2, it was 50% or more over the entire lens array width. Further, when the image reading sensor was subjected to a thermal cycle test as shown in FIG. 3 and its MTF was measured, the MTF was measured at both ends of the lens array.
Was as low as 40%.

[0025]

Comparative Example 2 Using the lens array used in Example 1 and the housing 41 used in Example 5, an image reading unit was manufactured in the same manner as in Example 1, and the MTF was formed with a grid of 4 line pairs / mm. Was measured, and over the entire width of the lens array
It was over 50%. The difference in thermal expansion coefficient between the lens array substrate and the housing was 5.9 × 10 ^-5 cm / cm / ° C. Also, when the image reading unit was subjected to a thermal cycle test as shown in FIG. 3 and then its MTF was measured, the MTF at both ends of the lens array was reduced to 25%, and it could be used as an image reading sensor. There wasn't.

[0026]

Comparative Example 3 Using the lens array used in Example 5 and the housing 41 used in Example 1, an image reading unit was manufactured in the same manner as in Example 1, and the MTF was formed with a grid of 4 line pairs / mm. Was measured, and over the entire width of the lens array
It was over 50%. Further, when the MTF was measured after the thermal cycle test as shown in FIG. 3 was performed on this image reading unit, the MTF was reduced to 25% at both ends of the lens array, and it could not be used as an image reading sensor. It was

[0027]

Example 6 A lens array substrate having a length of 235 mm, a width of 7.2 mm and a thickness of 2.8 mm was made of ABS resin containing carbon black, and its thermal expansion coefficient was measured to be 7 × 10 ⁻⁵ cm / cm /
It was ℃. 2 for fixing the lens array as shown in FIG.
Twelve 20 mm long housing units having a pair of protrusions 59, 59 ′, 501, 501 ′ and fastening claws 502 for fastening a plurality of housing units 500 and fastening holes 503 are made of carbon black ABS resin. Using the injection molding method, the thermal expansion coefficient of the housing unit was 7.4 × 10 ^-5 cm / cm / ° C.
A fastening member was engaged with these 12 housing units using an epoxy resin adhesive to form a housing having a length of 240 mm, and the warp between the both ends was measured and found to be 1 mm or less. Using the case and lens array element obtained as described above, an image reading unit was produced in the same manner as in Example 1, and the image reading unit M
When TF was measured, it was 50% or more. After subjecting this image reading unit to a thermal cycle test as shown in FIG. 3, its MTF was measured and found to be 50% over the entire length.
It was above, and it had the outstanding performance.

[0028]

[Comparative Example 4] The take-up speed at the nip roller was 60 cm /
A gradient index rod-shaped lens element was manufactured in the same manner as in Example 1 except that the difference was set. The refractive index distribution of the obtained gradient index lens element is 1.515 in the central part (n ₀ ) and 1.15 in the peripheral part.
462, and the refractive index distribution constant (g) was 0.53. Example 1 except that the lens length of this rod-shaped lens was 7.0 mm
The same evaluation as was done. MTF at this time is 60%,
The conjugation length was 15.4 mm. The image of the obtained grating was a clear image with little distortion. This gradient index rod lens element was formed into a lens array in the same manner as in Example 1. The dimensions of the lens array were 230 mm long, 7.0 mm wide and 2.8 mm thick. Using this lens array, the housing used in Example 1 was used to fabricate an image reading unit in the same manner as in Example 1, and M was formed using a grid of 4 line pairs / mm.
When TF is measured, it is 30% over the entire width of the lens array.
Was low.

[0029]

[Embodiment 7] As shown in FIG. 7, the lens array fixing protrusions 601, 69, 69 'and the CCD sensor fixing protrusion 60 are shown in the housing.
AB containing carbon black with 2,602 ', light source fixing protrusions 603, 603', and cover glass fixing protrusions 604, 604 '
An image reading sensor was produced using the housing made of S resin and having a thermal expansion coefficient of 7.5 × 10 ⁻⁵ cm / cm / ° C. and the lens array used in Example 1. When making this image reading unit,
No position adjustment was required for the arrangement of the lens array, CCD sensor, light source and cover glass. When the MTF of this image reading sensor was measured using a grid of 4 line pairs / mm, it was 50% or more over the entire width of the array.
After performing a thermal cycle test as shown in FIG. 3, MT
When F was measured, it was 50% over the entire lens array width.
That was all.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an image reading unit incorporating a conventionally used gradient index rod lens array.

FIG. 2 is a perspective view of a gradient index rod-shaped lens array.

FIG. 3 is a time chart of a heat cycle test.

FIG. 4 is a sectional view of an example of an image reading unit of the present invention.

FIG. 5 is a perspective view showing an example of a housing unit for creating an image reading unit of the present invention.

FIG. 6 is a sectional view of an example of an image reading unit of the present invention.

[Explanation of symbols]

11, 41, 51, 61 ………… Housing 12, 22, 42, 62 ………… Substrate 13, 23, 43, 63 ………… Substrate 14, 24, 44, 64 ………… Refractive index Distributed rod lens 15, 45, 65 ……… CCD sensor 16, 46, 66 ……… Light source 17, 47, 67 …………… Glass cover 18, 18 '……… Lens array Fixing screw 19, 19 ', 49, 49', 59, 59 ', 401, 401', 501, 50
1 ', 601, 69, 69' ………… Protrusions for fixing the optical transmitter array 201 …………………… Adhesives 502, 503 ………… Fasteners for fastening housing units 602, 602 '… ………… CCD sensor fixing protrusion 603, 603 ′ ………… Light source fixing protrusion 604 604 ′ ………… Cover glass fixing protrusion

Front page continued (72) Inventor Takayuki Tanaka 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Otake Office

Claims (9)

[Claims] 1. An image reading unit in which a lens array, in which an array of gradient index rod-shaped lens elements is sandwiched and joined by a plastic substrate, is incorporated in a plastic housing, the thermal expansion coefficient of the lens array substrate. The image reading unit is made of a material having a difference in thermal expansion coefficient between the housing and the housing of 5.0 × 10 ^-5 cm / cm / ° C or less. 2. The image reading unit according to claim 1, wherein the difference between the coefficient of thermal expansion of the lens array substrate and the coefficient of thermal expansion of the housing is 3.0 × 10 ⁻⁵ cm / cm / ° C. or less. 3. The image reading unit according to claim 1, wherein a lens array having a dimensional tolerance of the gradient index lens element length (Z ₀ ) constituting the lens array within a range of ± 0.15 mm is used. . 4. The image reading unit according to claim 1, wherein the case is composed of a case unit divided into two or more parts in a longitudinal direction thereof. 5. The image reading unit according to claim 4, wherein the housing unit is made by an injection molding method. 6. The image reading unit according to claim 4, wherein the housing unit has a length of 1 to 10 cm. 7. The image reading unit according to claim 1, wherein a housing provided with a protrusion for holding the lens array is used. 8. The image reading unit according to claim 7, wherein a housing provided with a projection for holding at least one of a linear light source, a linear sensor, and a cover glass is used in the housing. 9. The image reading unit according to claim 4, wherein the case unit is provided with a fastening portion for connecting two or more case units.