JPH0618814A - Image reader unit - Google Patents

Abstract

PURPOSE:To automate an assembling process by fixing a lens element array having the dimensional tolerance of a lens length in a specified extent while almost keeping the exact cojugation length and the working distance of the lens array. CONSTITUTION:A lens length Zo and a working distance Io are determined by the conjugation length Tc of a lens element 24 specified for the respective image reader unit and the lens element array is composed of the lens element 24 having the dimensional tolerance of the lens length Zo within the range of + or -0.15mm. The array is fixed by the grasping projections 205, 205' in a case 21 comprizing the pairs of a grasping projection for lens element array 201, 2Ol', 202, 202', a pair of a grasping projection for linear light source 204, 204', a pair of a grasping projection for an image reader linear sensor 203, 203' and a pair of a grasping projection for a cover glass 205, 205'. The fluctuation ratio of the working distance Io of the lens element array having the lens tolerance larger than + or -0.15mm grows larger so that the image reader unit having the MTF larger than 50% is not realized.

Description

Detailed Description of the Invention

[0001]

The present invention relates is related to an image reading unit of a copying machine or a facsimile using a gradient index rod-lens array that dimensional tolerances with respect to the lens length Z _O is in the range of ± 0.15 mm, in particular The present invention relates to an image reading unit that does not require a work of aligning a mounting position of a lens element array when the lens element array is incorporated into a housing.

[0002]

2. Description of the Related Art A glass-made gradient index rod lens having an image transmitting capability is manufactured by a method as disclosed in Japanese Patent Publication No. 47-812. The gradient index lens manufactured by such a method is a batch manufacturing method, and if the conjugate length Tc of the lens is set to be constant, the lens length Z _O becomes different for each batch,
The lens length is inevitably large, with a dimensional tolerance of ± 0.3 mm.

An image reading system having a structure as shown in FIG. 1 in which a lens element array in which a large number of such array elements of the gradient index rod-shaped lens element are sandwiched and bonded between two substrates is incorporated in a housing. The unit is used as a sensor for copiers and the like. 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 a reading sensor such as a CCD for converting image information read by the lens element array into an electric signal, and 16 is an LED or the like. The line-shaped light sources are arranged in a line, 17 is the cover glass, 18 and 18 'are screws for fixing the lens element array inside the housing, and 19 and 19' are the lens element array fixed on the housing. It is a projection for use.

[0004]

In the assembly of the image reading unit shown in FIG. 1, the conjugation length Tc of the lens element is constant, but the lens element manufactured by the batch method such as the conventional method is Dimensional tolerance to length Z _O is ± 0.3m
Since m is large, if the installation location of the lens element array in the housing is fixed, there are many cases where the lens element array placement position does not match the lens element working distance l _O. Such an image reading sensor causes image blurring, and it is extremely difficult to exhibit its performance as an image reading sensor.

Therefore, in the conventional method, the lens array made by using the lens element having a large dimensional tolerance is incorporated into the housing as shown in FIG. 1, and the lens element array is provided with the fixing projections 19 and 19 '. However, by arranging them apart from these projections, the working distance of the lens element, which is the distance between the upper end surface of the lens element and the read image surface and the distance between the lower end surface of the lens element and the CCD sensor, is set. It is adjusted and fixed to the housing with screws 18 and 18'.Therefore, when assembling the image reading unit using the lens element array, manually install the lens element array in the housing. Position adjustment work is unavoidable, and it is the biggest factor that prevents automation of the assembly process of the image reading unit.

That is, the lens length Z of the lens element array
A lens element array with _O of 7.2 mm and a dimensional tolerance of ± 0.3 mm is used, and the lower end surface of the lens element array is fixed in the housing of FIG. 1 by a mold in contact with the lens element array fixing protrusions 19 and 19 '. The MTF (modulation, transfer, factor) of the image reading unit measured using a grid of 4 line pairs / mm is extremely low at 35%, and it cannot be said that the image reading unit has satisfactory characteristics. . On the other hand, the same lens element array is used, and when the lens element array is incorporated into the housing, the working length l _O of the lens is adjusted, and the lower end surface of the lens element array is fixed to the fixing projections 19 and 19 ′.
The MTF of the image reading unit made by fixing it to the housing with screws 18 and 18 'in a state of being lifted from the surface is 50% and has a performance usable as an image reading unit.

[0007]

Therefore, the present inventors have proposed an image reading unit that uses a lens element array and has an MTF of 50% or more, and an image reading unit that can automate its assembly process. Under development, we are constructing the lens element array with a dimensional tolerance of ± 0.15 mm with respect to the lens length Z _O , and use the lens element array as a housing to measure the conjugate length Tc of the lens array, which is almost accurate. The inventors have found that the object can be achieved by using a housing provided with a pair of lens element array gripping protrusions for fixing the working distance l _O in the housing and completed the present invention.

The gist of the present invention is that the dimensional tolerance of the lens length Z _O value in which an array of a large number of gradient index lens elements is bonded and sandwiched between two substrates is within a range of ± 0.15 mm. The lens element array, the line-shaped light source, the line-shaped image reading sensor and the cover glass have a structure capable of disposing the lens element array at a position satisfying the working distance l _O and the conjugate length Tc of the lens element array, And, a pair of lens element array holding projections, a pair of linear light source holding projections,
An image reading unit is characterized in that the housing is provided with a pair of line-shaped image reading sensor gripping projections and a pair of cover glass gripping projections, and is fixed by these gripping projections.

The lens element array used for carrying out the present invention determines the lens length Z _O and the working distance l _{O according} to the conjugate length Tc of the lens element specified for each image reading unit, and the dimensional tolerance with respect to the lens length Z _O. Is ± 0.15 mm
It is necessary for the lens element to be in the range. A lens element array having a large lens tolerance of ± 0.15 mm or more has a large fluctuation rate of its working distance l _O , and when mounting such a lens element array on a housing, the arrangement position of the lens element array is changed to the working distance l _o. The image reading unit cannot have an MTF of 50% or more unless it is arranged according to _O.

Dimensional tolerance to lens length Z _O is ± 0.15 mm
As a method of producing the lens element, the method described in Japanese Patent Publication No. 47-812 is used for a glass lens element, and WO91 / is used for a plastic lens element.
No. 05274 and WO91 / 05275 can be manufactured by a method such as that described above, and particularly at least 0 from the central axis of the gradient index optical transmission member toward the outer peripheral surface.
The refractive index distribution in the range of 25r _{O to} 0.70r _O has a refractive index distribution approximately similar to the refractive index distribution curve defined by [Equation 1],

[Equation 1] 1.4 <n _O <1.6 0.15 ≤ g ≤ 0.7 0.4 ≤ r _O ≤ 0.6, and the MTF measured using a grid of 4 line pairs / mm is 50% or more. n _O is 1.
If it is smaller than 4, it is difficult to make a lens element with high resolution, and if it exceeds 1.6, it becomes difficult to select the lens material. If the g value is less than 0.15, the resolution of the lens element is low. On the other hand, if the g value is greater than 0.7, the lens element has an appropriate conjugate length Tc and an appropriate lens length Z _O. Become. Especially, 0.25r _O ~ 0.70
A lens element having a refractive index distribution in the range of r _O that does not have an approximate distribution to the refractive index distribution curve defined by [Equation 1] has an MTF of 30%.
Only the following can be obtained, and a lens element with excellent resolution cannot be obtained.

In the present invention, the lens element array is made of lens elements having a dimensional tolerance of ± 0.15 mm with respect to the lens length Z _O.
Since the dimensional tolerance for _O can be ± 0.15 mm, the length can be made almost constant, and the working distance when mounting the lens element array in the housing
l No need to fine tune _O.

Therefore, according to the present invention, when mounting the lens element array, which has been considered impossible in the past, to the housing, it is unnecessary to adjust the mounting position. At the position where the working distance l _O and the conjugate length Tc are satisfied, the dimensional tolerance for the lens length Z _O is ± 0.15 m.
We have succeeded in making an image reading unit that engages with the housing by a throw-in method, instead of using the screw-fastening method, with a lens element array that has a pair of protrusions that grip the lens element array in the range of m. Of.

In the present invention, since the lens element array can be engaged with the housing by the pair of gripping projections of the lens element array, the working distance l _O of the lens element array is kept constant. Therefore, the fixing of the linear light source to the housing, the fixing of the linear reading sensor to the housing, and the fixing of the cover glass to the housing are performed by using a pair of grip projections of these members. The image reading unit can be automatically assembled in this way.

FIG. 2 is a sectional view showing the outline of the image reading unit of the present invention. In the figure, 24 is a lens element having a dimensional tolerance of ± 0.15 mm with respect to the lens length Z _O ,
Reference numerals 22 and 23 denote substrates which sandwich an array of a large number of these lens elements, and the lens element array is composed of 22, 23 and 24. Since this lens element array has a feature that the dimensional tolerance with respect to the lens length Z _O is ± 0.15 mm, the dimensional tolerance with respect to the lens length Z _O that has been developed so far is ± 0.3 m.
Compared to a lens element array having a large size of about m, the lens length of the lens element array can be made constant, and the working distance l _O of the lens element array is made almost constant with respect to the determined conjugate length Tc. Therefore, as shown in 201, 201 ′, 202, 202 ′ in FIG. 2, the lens element array can be thrown into a housing provided with a pair of lens element array holding projections without adjusting the position of l _O. Can be arranged in a manner.

As described above, in the image reading unit of the present invention, since the lens element array can be attached to the housing by the throwing method, a pair of long image reading sensors 25 shown in FIG. The projections 203, 203 'can be fixed by the throwing method, and the line-shaped light source 26 can also be fixed to the housing by the line-shaped light source gripping projections 204, 204', and the cover glass 27 can also be fixed by the cover glass gripping projections 205, 205 '. The image reading unit of the present invention has a great advantage in that the automatic assembling of the image reading unit of the present invention, which has been considered impossible in the past, is possible.

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

[0017]

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 stock solution is 2.2
It was × 10 ⁴ poise. The temperature of the composite spinning nozzle is
It was 55 ° C. Then, each layer was passed through the layer interdiffusion treatment section of 90 cm length, and then 12 fluorescent lamps of 120 cm length and 40 W were passed through the strand fiber at the center of the light irradiation section arranged in a circle at 50 cm / Radius (r _O ) 0.50 mm at speed of minute
The light transmission body of the above was taken up by a nip roller. The discharge amount ratio was 1st layer: 2nd layer: 3rd layer = 1: 1: 1. The obtained gradient index rod-shaped lens has a radius (r _O ) of 0.50 mm, a refractive index distribution of 1.512 at the center (n _O ) and 1.470 at the periphery,
The refractive index distribution in the range of 0.25r _{O to} 0.70r _O has almost the same distribution as the quadratic curve of [Equation 1], and the refractive index distribution constant (g)
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 and its working distance was 4.1 mm. The image of the obtained grating was a clear image with little distortion.

Lens lengths 7.12 to 7 made as described above.
A large number of 28mm lens elements are arranged and bonded between two substrates made of blackened ABS plate, the lens end surface is polished and surface-treated to give a lens length Z _O of 7.2mm and a dimensional tolerance of ± 0.08mm. An element array was used. 200 lens element arrays were prepared, a cross-linking curable resin mainly composed of pentaerythritol hexaacrylate was coated on the lens end surface side, and an ultraviolet irradiation treatment was performed to form a surface-cured coating.

It has a sectional shape as shown in FIG. 2, the distance between the projections for gripping the lens element array is 7.2 mm, and the working distance of the lens is l.
_O is 4.1mm, conjugate length Tc is 15.4mm, line CCD
200 housings with sensor-holding projections, linear LED light source-holding projections, and cover glass-holding projections are made of carbon black ABS resin, and these housings are provided with a lens element array, a linear LED light source, and a linear shape. A CCD sensor and a cover glass were incorporated as a built-in image reading unit. The obtained image reading unit is 4
Image reading unit M using a line pair / mm grid
When TF was measured, it was confirmed that all of them were image reading units with excellent resolution of 55% or more. Moreover, it was confirmed that the assembly is extremely simple and can be automatically assembled.

[0021]

[Embodiment 2] Lens length 7.04 produced in the same manner as in Embodiment 1.
A gradient index lens element having a diameter of up to 7.34 mm is produced, and these lens elements are used in the same manner as in Example 1 to form a lens element array.
I made 200 books. The lens length Z _O of the lens element array is 7.
It was 2 mm and the dimensional tolerance was ± 0.14 mm. In the same manner as in Example 1, a housing having a conjugation length Tc of 15.4 mm, a working distance l _O 4.1 mm, a distance between the lens element array gripping projections of 7.2 mm, and a cross-sectional structure as shown in FIG. Then, the lens element array, the linear LED light source, the linear CCD sensor and the cover glass were assembled by an injection method to form an image reading unit, and the MTF was measured in the same manner as in Example 1. All were 50% or more. .

[0022]

Comparative Example 1 Lens length 7.04 to 7.36 in the same manner as in Example 1.
mm lens elements were made, and using these lens elements, 200 lens elements having a lens length of 7.2 mm and a dimensional tolerance of ± 0.16 mm were made in the same manner as in Example 1. Using the housing prepared in Example 1, the lens element, the linear LED light source, and the linear C
Assemble the CD sensor and cover glass by throwing in,
An image reading unit was created. The MTF of these image reading units was 35%, and the minimum value was extremely low at 28%.

[0023]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a conventionally used image reading unit.

FIG. 2 is a sectional view of the image reading unit of the present invention.

[Explanation of symbols]

11,21 ………… Case 12,22 ………… Substrate 13,23 ………… Substrate 14,24 ………… Index rod lens 15,25 ………… CCD sensor 16,26 …… ...... Light source 17,27 ………… Cover glass 18,18 '………… Lens array fixing screw 19,19', 201,201 ', 202,202' ………… Protrusion 203,203 '…… ...... CCD sensor fixing protrusion 204,204 '………… Light source fixing protrusion 205,205' ………… Cover glass fixing protrusion

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayuki Tanaka 20-1 Miyuki-cho, Otake-shi, Hiroshima Mitsubishi Rayon Co., Ltd. Central Research Laboratory

Claims (1)

[Claims] 1. A lens element array having a dimensional tolerance of a lens length Z _O value within a range of ± 0.15 mm in which a plurality of arrays of gradient index lens elements are bonded and sandwiched between two substrates, and a linear light source. The linear image reading sensor and the cover glass have a structure capable of disposing the lens element array at a position satisfying the working distance l _O and the conjugate length Tc of the lens element array, and a pair of lens element arrays. It is characterized in that it is fixed by a gripping projection in a housing provided with a gripping projection, a pair of linear light source gripping projections, a pair of linear image reading sensor gripping projections, and a pair of cover glass gripping projections. Image reading unit.