JPH06252450A - Imaging device - Google Patents

Abstract

PURPOSE:To prevent a lens array from deteriorating in imaging performance due to flare light so as to improve an imaging device in performance by a method wherein the side faces of lenses are roughened as prescribed in average roughness, and a light absorbing resin layer specified in transmissivity to light of wavelengths larger than that of operating light is provided among lenses. CONSTITUTION:A lens array 2 is formed through such a manner that rod-like lenses 4 in continuous lengths are bound together, fixed by side plates 6, and cut into pieces. As the end face of the lens 4 is so roughened at cutting as to scatter light that travels through it, both the end faces of the lens 4 are covered with transparent resin layers 10 and 12. The side face 16 of the lens 4 is so roughened as to be 0.5 to 5mum in average roughness, and a light absorbing resin layer 18 whose transmissivity is below 20% to light of wavelengths larger than that of operating light is provided among the lenses 4. Therefore, flare light is restrained from being produced in a lens array, so that an imaging device of this constitution can be improved in image quality.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an LED head, a contact image sensor, a liquid crystal shutter array head, a PLZT.
The present invention relates to an image device using a light emitting / receiving element such as a head and a lens array. The invention particularly relates to improvements in the lens array used.

[0002]

2. Description of the Related Art Imaging devices such as LED heads and contact image sensors use lens arrays such as self-focusing lens arrays. This lens array uses a rod-shaped glass or plastic lens, and the lens has a refractive index distribution along its cross section to determine the optical path in the lens. Although the problems of the lens array have hardly been studied so far, the inventor has found that flare light travels in the lens array.
It has been found that this leads to a reduction in imaging performance. These flare lights provide, for example, a skirt of the imaged beam and broaden the beam. The spread of the hem of the beam becomes a problem in a regular pattern such as a graphic, and particularly in a pattern in which dots are continuous, the spread of the line width is caused and the resolution is reduced.
Flare light traveling from one lens to another in the lens array also results in a ghost image. This ghost image also remarkably appears as a figure in which many dots are continuous.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to block flare light in a lens array and improve image quality.

[0004]

According to the present invention, in an image device using a lens array in which a large number of rod-shaped lenses are bundled together and a large number of light emitting / receiving elements, the side surface of each lens is roughened and its average surface roughness is increased. Light absorption resin having a thickness of 0.5 to 5 μm and a transmittance of 20% or less for light having a wavelength longer than or equal to the wavelength of light used in the light emitting / receiving element between the lenses. It is characterized in that a layer is provided.

The surface roughness of the side surface of the lens is the average surface roughness measured by a surface roughness meter, and the rod-shaped lens before binding is treated by sandblasting or etching, particularly etching to give the surface roughness. When appropriate surface roughness is given to the side surface of the lens, flare light traveling in one lens is scattered by the unevenness of the side surface and does not travel in the lens, and flare light is emitted from the tip of the lens. Can be prevented. If the surface roughness is less than 0.5 μm, the roughness is shorter than the wavelength, so that the flare light scattering effect is small, and if it exceeds 0.5 μm, the flare light preventing effect becomes remarkable. For example, in the case of an image forming apparatus such as an LED head, flare light that travels through one lens causes the bottom of the beam to spread. This flare light is inconspicuous with respect to the isolated printing dots in the printing result viewed with the naked eye (for example, the printing result printed using the photosensitive drum), but can be detected by using a beam measuring device or the like. In continuous printing dots, the flare light overlaps the effect significantly, and even with the naked eye, it is felt that the printing quality deteriorates as the line width expands. On the other hand, when the surface average roughness on the side surface of the lens is 0.5 μm or more, it becomes impossible for the naked eye to feel the spread of the line width with respect to the continuous printing dots. Further, when the surface average roughness is 1 μm or more, the spread of the skirt of the beam becomes inconspicuous even when the intensity distribution of the beam of the isolated print dots is measured by the beam measuring machine.

When the surface average roughness exceeds 5 μm, stress concentration occurs due to the impartation of irregularities, cracks occur in the lens where the stress concentration is concentrated, or the refractive index distribution becomes abnormal, degrading the imaging performance. To do. The cracks generated in the lens reduce the strength of the lens, resulting in insufficient strength in the process of cutting and bundling the lens to form a lens array. When stress concentration is completely prevented and the margin is taken into consideration,
The average surface roughness is preferably 3 μm or less. Therefore, the surface roughness of the lens side surface is 0.5 to 5 μm, more preferably 1 to 3 μm.
μm.

A light absorbing resin layer having a transmittance of 20% or less for light having a wavelength longer than the light wavelength used is provided between the lenses, and the lens is covered with such a light absorbing resin layer, for example. Such a light-absorbing resin layer is applied to the side surface of the lens in advance, for example, before binding the lenses, and the transmittance of the applied light-absorbing resin layer is defined. When the light absorbing resin layer is not applied to the lens surface and the gap between the bound lenses is filled with the light absorbing resin layer, the light absorbing resin having a thickness half the average gap between the lenses is used. Assuming that there is a layer, the transmittance is determined for the light absorbing resin layer having this thickness. For the transmittance, the transmittance for light having a wavelength equal to or longer than that used in the image device is used. For example, when an LED having a wavelength of 685 nm is used, the wavelength distribution of 685 nm ± 30 nm is taken into consideration, and the transmittance is 660 nm or more on the short wavelength side. It is defined by the transmittance with respect to the wavelength. The reason why the wavelength is equal to or longer than the wavelength is that the absorption coefficient of the pigment or the like is generally small on the long wavelength side (near infrared region), and flare light is likely to be generated on the long wavelength side of the emission wavelength.

Such a light absorbing resin layer has a thickness of, for example, 10 μm.
It is applied to an individual lens with a film thickness of about m, and for example, resin 95 to 6 such as silicone resin, epoxy resin, acrylic resin, etc.
A mixture of 0 wt% and 5 to 40 wt% of pigments such as carbon black, titanium-carbon and iron oxide is used. When the pigment concentration is 5 wt% and the film thickness is 10 μm, the transmittance becomes 20%, and when it exceeds 40 wt%, it becomes difficult to uniformly disperse the pigment in the resin, and the transmittance is locally increased. A more preferable composition is 10 to 30 wt% of the pigment with the total amount of the resin and the pigment being 100 wt%, and the transmittance is 4% or less in this range.

In such a lens array, a large number of lenses are involved in the image formation of one dot. Then, in a regular pattern such as a graphic, the flare light moving between the lenses causes a ghost image, which is perceived by the naked eye as a reduction in print quality. In an experiment by the inventor, when a light absorbing resin layer having a transmittance of 20% or less is provided,
Even with a regular pattern print, the ghost image could not be discriminated with the naked eye, and when the transmittance was 4% or less, the ghost image for the regular pattern print could not be detected even with a beam measuring machine.

As the image device, in addition to the LED head shown in the embodiment, an image device using a lens array and a light emitting / receiving element, such as a liquid crystal shutter array head, a contact type image sensor, a PLZT head, is used.

[0011]

According to the present invention, the lens side surface of the lens array is roughened. Due to the roughening, the flare light traveling in one lens is diffusely reflected by the unevenness on the side surface of the lens and does not travel in the lens. Then, the flare light is absorbed and disappears while being repeatedly scattered in the lens. Next, in order to absorb flare light that moves between the lenses, a black light absorbing resin layer is provided for the wavelength used. Therefore, the flare light that is about to move from one lens to another lens is absorbed by the light absorbing resin layer and disappears. Therefore, the flare light that travels in one lens and the flare light that moves between the adjacent lenses are removed, and the image quality is improved.

[0012]

1 to 3 show a first embodiment. In FIG. 1, 2 is a lens array, and 4 is a rod-shaped lens such as glass or plastic. 6 is a side plate made of black resin or the like, and 8 is a frame body made of the same black resin. 1
0 is a transparent resin layer on the incident light side, 12 is a transparent resin layer on the outgoing light side, the transparent resin layer 10 on the incident light side is preferentially provided, and the transparent resin layer 12 on the outgoing light side may not be provided. Further, a pigment or the like may be dispersed in the resin layers 10 and 12 to partially absorb light.

The lens array 2 is a modification of the self-focusing lens array, and is formed by, for example, bundling long rod-shaped lenses, fixing them with side plates, and cutting. Due to the influence of cutting, the end surface of the lens 4 is roughened and light is scattered. In order to prevent light from being scattered by the end surface of the lens 4,
The transparent resin layers 10 and 12 cover both end surfaces of the lens 4. The transparent resin layers 10 and 12 are made of resin such as epoxy, acryl, polyester, etc.
Since it is close to, it is possible to prevent light from being scattered at the end surface of the lens 4. This is because the end surfaces of the lenses 4 are covered with the transparent resin layers 10 and 12 having a similar refractive index to that of the lenses 4, and the roughness of the end surfaces of the lens 4 is not felt by the light. If the thickness of the transparent resin layers 10 and 12 is not uniform, a lens effect occurs, and the optical path changes from a straight line. Therefore, the frame bodies 8 and 8 are provided and the transparent resin layers 10 and 12 are poured to make the thickness uniform. To

FIG. 2 shows an individual lens 4. Lens 4
Has a refractive index distribution along its cross section, and light travels while being guided by the refractive index distribution. The lens 4 is made of glass, plastic, or the like and has a diameter of, for example, about 1.1 mm. The side surface of the lens 4 is roughened as shown in FIG. 2, and the surface roughness is 0.5 to 5 μm, more preferably 1 to 3 μm as the average surface roughness measured by a surface roughness meter. Etching is used for roughening, for example. The roughened surface is shown as surface layer 16.

As shown in FIG. 3, the lens 4 is covered with a light absorbing resin layer 18. For example, a silicone resin is used as the resin component of the resin layer 18, and a black pigment in the near infrared region such as carbon black, titanium-carbon, and black iron oxide is used as the pigment. The amount of pigment added is 100 based on the total weight of resin 18.
5% to 40% by weight of pigment, more preferably 1% by weight
It is set to 0 to 30 wt%. If it is less than 5 wt%, the transmittance is 20.
% (When the film thickness is 10 μm), flare light moving from the lens 4 to another lens 4 cannot be sufficiently absorbed. On the other hand, when the pigment content exceeds 40 wt%, it becomes difficult to uniformly disperse the pigment, making it difficult to apply the pigment, and locally producing a portion having a high transmittance. When the pigment content is 10 to 30 wt%, the transmittance becomes less than 4% and the flare light can be almost completely absorbed.
In FIG. 3, it is shown that the gap between the lenses 4 and 4 is filled with the light absorbing resin layer 18, but the lens 4 is covered with the light absorbing resin layer 18 before binding with a film thickness of, for example, about 10 μm. It is preferable to bind with a black resin. By doing so, the lenses 4 and 4 do not come into direct contact with each other even at the closest portions of the lenses 4 and 4, and the light absorbing resin layer 18 can be provided between them to absorb light. Further, the transmittance is measured, for example, by applying it on a glass plate with the same thickness as that applied on the lens 4.

Returning to FIG. 1, other parts of the image device will be described. Reference numeral 20 denotes a head cover made of plastic or the like, and it is preferable to coat the inner surface with black or use a black resin to block stray light. 22 is a protrusion for positioning, and 2
Reference numeral 4 is a substrate such as glass or ceramic whose surface is glass glaze, 26 is an LED array, and 28 is a light emitter thereof.
Reference numeral 30 is a transparent resin layer for molding the LED array 26, and 32 is a flow stop frame for preventing the transparent resin layer 30 from flowing out. By using the flow stop frame 32, the surface of the transparent resin layer 30 is made flat, and the optical path is prevented from being bent because the surface of the transparent resin layer 30 is not smooth. The other parts of the LED head are well known and will not be described.

4 to 6 show various modifications of the lens array 2. In the lens array 42 of FIG. 4, the side plate 44 also serves as a frame. However, this is the lens 4 side plate 4
Since it is tied and cut without using 4, it is more difficult to manufacture than the lens array 2 of FIG. 46 and 48 are new transparent resin layers.

In the lens array 52 of FIG. 5, the transparent resin layers 10 and 12 are formed by using the head cover 20 also as a frame body. In this modification, an appropriate jig is used as a mold for the transparent resin layers 10 and 12, and the transparent resin layers 10 and 12 are poured and cured using the head cover 20 and the jig as a mold.

In the lens array 62 shown in FIG. 6, microlens arrays 64 and 66 are provided above and below the lens 4. 64
Is a microlens array on the incident light side, and 66 is a microlens array on the outgoing light side. Micro lens array 6
4, 66 are the frame body 8 and the microlens arrays 64, 66.
The transparent resin is poured into a mold by using a mold corresponding to the surface shape of. These microlenses are compound eye lenses,
A lens having a smaller diameter than the individual lens 4 is used. The microlens arrays 64 and 66 are arrays of microconvex lenses, and convex portions are provided on the outside of the lens 4 as illustrated.

In the embodiment, the transparent resin layers 10 and 12 have a uniform thickness, but it is difficult to know the thickness itself. This is because of variations in the thickness of the frame body 8 and the like. It is also difficult to know the thickness of the transparent resin layer 30. Therefore, after the image device is assembled, an optimum image forming position is searched for by using a photoconductor drum, a CCD camera, or the like (not shown), and the optimum mounting position of the head cover 20 on the photoconductor drum is stored. The head cover 20 is provided with a mounting screw or the like (not shown) so that the distance between the head cover 20 and the photosensitive drum or the like can be finely adjusted.
Then, the mounting screw is finely adjusted based on the optimum mounting position measured at the time of assembly, and the light emitting body 28 with respect to the center of the lens array 2 is adjusted.
The distance is adjusted with the fine adjustment screw so that the optical distance from the lens array 2 and the optical distance from the center of the lens array 2 to the photosensitive drum match. In this way, the transparent resin layers 10, 1
Optimal imaging performance can be obtained even if the optical distance changes due to the change in the thickness of 2, 30.

The operation of the embodiment will be described with reference to FIGS. FIG. 7 shows the absorption of flare light. The rod-shaped lens 4 has a refractive index distribution, and light entering the range of the aperture angle of the lens 4 travels as shown by the solid line in the figure and does not reach the lens side surface. On the other hand, flare light (broken line in the figure) has a larger incident angle than the aperture angle, reaches the surface layer 16 of the lens 4, and is scattered because the surface layer 16 has unevenness comparable to the wavelength of light. The beam of scattered light is shown by the dashed line in the figure. Since the flare light has to be repeatedly scattered in order to travel in the lens 4, the flare light cannot travel in the lens 4, and the flare light emitted from the tip of the lens 4 becomes a very small part. For example, the flare light scattered forward by one scattering is about a fraction, and the flare light is attenuated by a fraction for each scattering. Then, if the scattering is repeated several times, the flare light becomes extremely small, and the output light from the lens 4 becomes almost zero.

When light moves from one lens 4 to another lens 4 and flare light is generated, the flare light is absorbed by the light absorbing resin layer 18 between them. The light-absorbing resin layer 18 has a transmittance of 20% or less, and the total transmittance is 4 to transfer to another lens.
% Or less (a layer having a transmittance of 20% or less is passed twice).

The inventors of the present invention have examined the degree of roughness of the surface layer 16 and the effect of the transmittance of the resin layer 18 by using L at a wavelength of 685 nm.
It was examined using the ED array 26. For the lens 4, there are two types of flare light that travels in one lens and flare light that travels between the lenses. The flare light that travels in one lens causes the line width of an image to spread. This effect is small in isolated print dots, and is felt as a spread of the line width in a regular pattern such as a graphic, and is particularly noticeable for continuous print dots. The flare light is generated due to the variation of the lens 4 and the variation of the light emitter 28, and there is no regularity in the degree, and the variation of the line width also varies, so that it is felt as uneven density. Here, the surface layer 16 of the lens 4
If the average surface roughness of the above is 0.5 μm or more, the irregularity in density when printed using an a-Si photosensitive drum is not perceptible to the regular continuous printing dots with the naked eye, and if it is 1 μm or more, the beam measuring device is used. Even when used, the spread of the hem of the beam became inconspicuous.

The lens array 2 is formed by bundling the lenses 4 into, for example, two rows, and about seven lenses 4 are involved in forming one dot. The flare light traveling between the lenses 4, 4 leads to a ghost image, which appears strongly in the area of the continuous printing dots, especially in a regular pattern. When the lens 4 is covered with the light absorbing resin layer 18 having a transmittance of about 20% at a wavelength of 660 nm, a ghost image is not felt by the naked eye even with respect to the printing result of continuous printing dots of a graphic pattern, and the transmittance is 4%. Under the following conditions (when the pigment concentration is 10 wt% or more), the ghost image cannot be detected even by the beam measuring device.

These are the results when the transparent resin layers 10 and 12 and the black frame 8 are removed. If these are used, the cause itself of flare light such as scattering at the end face of the lens 4 is eliminated, The influence of flare light can be further reduced.

8 to 10, the end surface of the lens 4 is rough due to the influence of cutting. Although the light is scattered when the roughness is left, the influence of the roughness is prevented by using the fact that the transparent resin layers 10 and 12 are coated and the refractive indices of the transparent resin layers 10 and 12 and the lens 4 are close to each other.

As shown in FIG. 8, the refractive index of the transparent resin layer 10 is higher than that of the surrounding air, so that the light from the light emitting body 28 approaches the parallel resin when entering the transparent resin layer 10, and the light beam is focused. . For this reason, even wide-angle incident light that cannot be originally used by the lens 4 can be imaged by the lens 4, and a brighter image can be formed. In addition, the transparent resin layer 10
When the incident light is brought closer to the parallel beam in advance, the load on the lens 4 is reduced and the imaging performance can be improved. Furthermore, the light that causes the ghost image is the frame 8 of black resin.
Is incident on and absorbed. The meaning of black here is
In the case of the embodiment, it means that the light having a wavelength longer than the wavelength of the light used is black, and the light having a wavelength longer than the emission wavelength of the LED array 26 may be black. Further, when a black pigment or the like is dispersed in the transparent resin layer 10, light incident on the transparent resin layer 10 at a wide angle is preferentially absorbed because the moving distance within the transparent resin layer 10 is long, and flare light is further removed. Can be done.

In the embodiment, in order to protect the LED array 26 and to enhance the light incident on the lens array 2, the LED array 26 is covered with the transparent resin layer 30. This is because the difference in the refractive index between the light emitter 28 and the air is large, so that part of the output light is reflected at the interface with the air and is confined in the light emitter 28. Therefore, the resin layer 30 having an intermediate refractive index between the light emitter 28 and air is interposed to prevent the effect of confining light in the light emitter 28. Next, the flow stop frames 32 are provided on both sides of the transparent resin layer 30, the transparent resin layer 30 is formed using a low viscosity resin, and the surface of the transparent resin layer 30 is made flat.
When the transparent resin layer 30 is not provided, the light emitted from the light-emitting body 28 spreads like a beam indicated by a chain line in the lower right of FIG. On the other hand, when the transparent resin layer 30 is provided, since the refractive index is larger than that of air, the beam can be narrowed as shown by the broken line in FIG. 8 and a light beam with high directivity can be extracted. In addition, the transparent resin layer 30
When the LED is provided, only the product of the difference between the refractive index of the transparent resin layer 30 and the refractive index of air and the thickness of the transparent resin layer 30 is used for the LED.
This means that the array 26 is optically brought close to the lens array 2 side. As a result, the spread of the light beam on the way can be prevented and the light incident on the lens array 2 can be strengthened.

Light emitted from the lens array 2 to the side of the photosensitive drum (not shown) passes through the transparent resin layer 12. The fact that the refractive index of the transparent resin layer 12 is close to the refractive index of the lens 4 eliminates the influence of the roughness of the end surface of the lens 4 on the exit side.

A measure against the variation between the lenses 4 and 4 will be described with reference to FIG. The lens 4 has a variation in image forming performance, and the greater the number of the lenses 4 involved in image formation, the greater the influence of the variation. Since the refractive index of the transparent resin layer 10 is larger than the refractive index of air, the light from the light emitter 28 approaches the parallel light rays when entering the transparent resin layer 10, and is related to image formation as shown by the solid line in FIG. The number of lenses 4 is reduced. As a result, the influence of the characteristic variation between the lenses 4 and 4 is reduced.

FIG. 10 shows the microlens arrays 64, 6
The action of 6 is shown. The microlens arrays 64 and 66 are convex lens arrays, and the microlens array 6 on the incident side is used.
In 4, the light incident from the light emitter 28 while spreading is brought closer to a parallel light beam, and in the emission side microlens array 66, the emitted light is further focused toward the focus. The bending of the optical path toward the center in this way is performed by the microlens array 6
4, 66 is the action. In this way, the luminous body 28
Light from the lens is made to be parallel rays by the microlens array 64, more light is made to enter the aperture angle of the lens 4 to make a brighter image, and the incident rays are made to be parallel rays to improve the imaging performance. be able to. Similarly, the number of lenses 4 related to image formation can be reduced to reduce the influence of characteristic variations. In the microlens array 66 on the outgoing light side, the optical path of outgoing light is bent toward the focus,
Further improve the imaging performance.

The microlens arrays 64 and 66 are formed by injecting transparent resin using the frame 8 and a jig (not shown). Then, a jig (not shown) is used to form irregularities corresponding to the microlenses. Therefore, the microlens arrays 64 and 66 can be made uniform in thickness and easily formed.

In the embodiment, as a countermeasure against flare light, a surface roughness of 0.5 to 5 μm is given to the lens side surface, and LE is used.
It was covered with a black light absorbing resin layer for D light. Other than this, the transparent resin layers 10 and 12 and the black frame 8 and the like are shown, but the transparent resin layers 10 and 12 and the frame 8 and the like may not be provided.

[0034]

According to the present invention, the flare light on the lens array can be removed and the image quality can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of an image device according to an embodiment.

FIG. 2 is a perspective view of an individual rod-shaped lens according to an embodiment.

FIG. 3 is a sectional view of a main part of a lens array used in an example.

FIG. 4 is a sectional view of a lens array according to a second embodiment.

FIG. 5 is a cross-sectional view of the essential parts of the third embodiment.

FIG. 6 is a sectional view of a lens array according to a fourth embodiment.

FIG. 7 is a diagram showing cutting of flare light due to unevenness on the lens side surface in the example.

FIG. 8 is a diagram showing a flare light cutting and a light beam diaphragm mechanism in the embodiment.

FIG. 9 is a diagram showing a mechanism for reducing the number of lenses related to image formation in the example.

FIG. 10 is a diagram showing a diaphragm of a light beam by a microlens array.

[Explanation of symbols]

 2 lens array 4 lens 6 side plate 8 frame 10 transparent resin layer 12 transparent resin layer 14 lens body 16 surface layer 18 light absorbing resin layer 20 head cover 22 protrusions 24 glass substrate 26 LED array 28 light emitter 30 transparent resin layer 32 flow stop frame 42 lens array 44 side plate 46 transparent resin layer 48 transparent resin layer 52 lens array 62 lens array 64 microlens array 66 microlens array

Claims (1)

[Claims] 1. In an image device using a lens array in which a large number of rod-shaped lenses are bundled together and a large number of light emitting / receiving elements, the side surface of each lens is roughened so that the average surface roughness thereof is less than 0.1. In addition to 5 to 5 μm, a light absorbing resin layer having a transmittance of 20% or less with respect to light having a wavelength equal to or longer than the wavelength of light used in the light emitting / receiving element is provided between each lens. An imaging device characterized by the above.