JPH02107054A - Picture reader - Google Patents

Abstract

PURPOSE:To enhance the using efficiency of illumination, to decrease crosstalk to an adjacent picture element, and to improve S/N by arranging a fine lens on the light leading window, and its approximately doubling its focal distance to the distance between an original and a photodetector. CONSTITUTION:Fine lenses 8 are provided on respective light leading windows, illumination light is converged by the fine lenses, projected on the surface of an original 5, the reflected light is received by a photodetector 6, and the focal distance of the fine lens 8 is approximately doubled to the distance between the surfaces of the lens and the original 5. Consequently, the original surface is irradiated with a luminous flux converged by the fine lenses, even when the area of the lighting window is expanded, the irradiated area of the original surface is not expanded, and the expansion of the reflected and scattered light on the photodetector light receiving surface is reduced. Thus, the using efficiency of the illumination is increased, further the leakage of the light to the photodetector of the adjacent picture element is suppressed, and S/N can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reading device useful for facsimiles, image scanners, and the like.

[Conventional technology]

Conventionally, image reading devices are of the so-called "reduction type," which forms an image of the document in a reduced size using a reduction lens system and reads it with a CCD sensor, and the other is a "reduction type," which forms an erect image of the document with a lens array, which is then scanned over a long length. There was a so-called ``adhesive type'' that read with .

In addition to these methods, in recent years, the so-called "full contact type" has begun to be used, which reads by placing the sensor in close contact with the document surface without using a lens system.

The typical configuration of this complete contact type j is shown in Figures 4 to 6.
As shown in the figure. In the figure, l is a glass substrate, 2 is an illumination light source, 3 is a light shielding layer, 4 is an illumination window, 5 is a document, 6 is a photodetector,
7 is a surface protective layer.

The illumination windows 4 are arranged in one-to-one correspondence with the photodetectors 6, respectively.

The illumination light emitted from the illumination light source 2 illuminates the original 5 through the illumination window 4, and the reflected light is received by the photodetector 6, thereby photoelectrically detecting the image information of the original 5. Normally, unless the surfaces of the original 5 and the photodetector 6 are made into a conjugate relationship using an imaging lens, the image information of the original 5 will be blurred on the photodetector 6, but with this configuration, the image information of the original 5 and the light Detector 6
The surface is protected! Since they are very close to each other, on the order of several tens of micrometers with 117 in between, the amount of blurring is small and is at an acceptable level.

[Problem that the invention seeks to solve]

However, since the conventional image reading apparatus described above does not have an imaging lens system as described above, various considerations have been required to reduce image blur. That is, manuscript 5
In addition, if the illumination window 4 is made large, a wide area on the document surface is illuminated, as shown in FIG. The reflected and scattered light enters not only the photodetector 6A of the corresponding pixel but also the photodetector 6B of the adjacent pixel.
The illumination window 4 had to be made smaller because it caused "crosstalk" and the image became blurred.

Furthermore, if the area of the photodetector 6 is similarly increased, the reflected and scattered light will enter the adjacent photodetector and the image will be blurred, so the photodetector 6 cannot be made too large either.

As mentioned above, in order to reduce "crosstalk", in conventional devices, it is necessary to reduce the area of the illumination window and the photodetector, and therefore, there is a problem that the efficiency of use of illumination is low.

[Means for solving problems]

Microlenses are arranged in each light guide window, and the illumination light is converged by these microlenses and projected onto the image recording surface, and the reflected light is received by a photodetector. , approximately twice the distance between this lens and the image recording surface.

As the above-mentioned microlens, a flat plate microlens in which a substantially hemispherical refractive index distribution region is formed by ion exchange in a thin plate glass is suitable.

[Effect]

According to the above configuration, the document surface (image recording surface) is illuminated with a light beam converged by a microlens, so even if the area of the illumination window is large, the area of the document surface that is illuminated is large (because it does not become large). , the blur of the image will not become large and the efficiency of illumination usage can be increased.Also, since the focal length of the microlens is approximately twice the distance between the microlens and the document surface, there will be no reflection or scattering from the document surface. Of the light beams thus generated, the light beams in the direction of specular reflection from the document surface are focused on approximately one point on the light-receiving surface of the photodetector.

Therefore, the spread of reflected and scattered light on the light-receiving surface of the photodetector is reduced, light leakage to the photodetector of an adjacent pixel is suppressed, and the S/N ratio can be improved.

〔Example〕

The present invention will be explained in more detail below.

As mentioned above, in the conventional so-called "complete contact type" shown in FIGS. 4 to 6, the leakage of light into adjacent pixels of the photodetector leads to blurring of the read image, that is, deterioration of the MTF. . The key points to keep this low are firstly to reduce the distance between the document surface and the photodetector, secondly to reduce the illumination area for each pixel on the document surface, and thirdly to reduce the illumination area for each pixel on the document surface. The first step is to reduce the area of the photodetector.

Of course, making the illumination area smaller means making the illumination window smaller, which means reducing the efficiency of lighting use, and making the photodetector smaller means reducing the amount of light received.
Both lead to a decrease in the S/N ratio, and the leakage of light to adjacent pixels (hereinafter referred to as crosstalk) mentioned earlier.
The optimal value for each dimension is selected in consideration of the above.

- As an example, for a reading device with 8 pixels per millimeter (pixel pitch 125 μm), the distance between the document and the photodetector is approximately 80 μm, the size of the light guiding window for illumination is approximately 80A1m square, and the size of the photodetector is approximately 60 μm. To be elected.

The key point of the present invention is that a microlens is arranged in the light guide window of the illumination, and its focal length is approximately 2 times the distance between the original and the photodetector.
That's doubled. This will be explained using FIG. For simplicity, diffraction is ignored by assuming that the illumination is a parallel beam of light. It is also assumed that the document surface is not a diffusive surface but a mirror surface.

Further, it is assumed that the distance between the document surface and the illumination window and the distance between the document surface and the photodetector are equal, and the light receiving surface of the photodetector is expressed at a position that is a mirror image of the document surface.

FIG. 8(a) shows a conventional "complete contact type" as shown in FIGS. 4 to 6.

If we consider it simply from a geometric optics perspective, the light beam that passes through the illumination window directly illuminates the document surface, and then enters the light-receiving surface of the photodetector.

The area through which the rays pass through each surface is equal.

On the other hand, FIG. 8(b) shows the trajectory of the light ray when a microlens having the aforementioned focal length is placed in the illumination window.

Figure 8 (B) shows that the area of the illumination area on the document surface is as shown in Figure 8 (B).
(b), but since the luminous flux is refracted inward by a microlens placed in the illumination window,
The area of the corresponding illumination window is about four times larger than that in FIG. 8(a).

That is, by placing the microlens, the area of the illumination window can be increased without increasing the illumination area on the document surface, thereby greatly improving the efficiency of illumination use.

Furthermore, as is clear from Figure 8 (b), by making the focal length of the microlens approximately twice the distance between the illumination window and the document surface, the light beam reflected from the document surface is directed onto the light receiving surface of the photodetector. The light is focused on one point. Of course, the actual document surface is normal paper and has a diffusive surface, so there is no specular reflection like this, but since the center of the amount of scattered light is in the direction of regular reflection, that is, specular reflection, as shown in the figure. With this configuration, the spread of reflected and scattered light from the original can be suppressed to a small extent, thereby reducing crosstalk to adjacent pixels.

As described above, by providing a microlens 4J in the illumination window and setting its focal length as described above, it is possible to improve the efficiency of illumination usage and reduce crosstalk to adjacent pixels.

In reality, there are some points that do not match the above explanation, such as the fact that the illumination light is not parallel but diffused light with a certain degree of curvature, but this does not significantly change the above operations and effects.

A preferred embodiment of the present invention based on the above-mentioned principle will be described below.
This is shown in Figures 3 to 3.

Reference numbers 1 to 6 in the figures are the same as those in FIGS. 4 to 6. In addition to these, a microlens 8 is fabricated in the light guide window for illumination. Its focal length is set to approximately twice the distance between the document surface 5 and the photodetector 6. The microlens 8 can obtain the function of a microlens by forming a substantially hemispherical high refractive index distribution region in the glass substrate 9 using, for example, an ion exchange method, and by a convex lens effect due to this refractive index distribution.

If a microlens is produced in this way, a convex lens effect can be obtained even if the surface is flat, so it is easy to bond the thin glass 9 on which the microlens has been produced to the substrate 1 as shown in the figure.

According to the configuration shown in the figure, illumination is applied to the original 5 through the illumination window 4 and the microlens 8, and this reflected light is received by the photodetector 6, thereby displaying the original. Can read f&5 image information.

The definition of the focal length of the microlens mentioned here was discussed without taking into account the refractive index of the material between the microlens 8 and the original 5, but as is clear from the gist of the present invention, it is actually This means that, taking into account the refractive index, the focal position is at a distance from the surface of the microlens by approximately twice the distance between the microlens and the document surface.

It should also be noted that the optimum value of this focal length may vary somewhat from twice depending on the size of the illumination window, changes in the diffusion of illumination light, light diffusion conditions on the paper surface, etc.

Furthermore, it is desirable that the position of the photodetector be slightly shifted from the position where the specularly reflected light rays converge (point O in FIG. 8(b)) in order to suppress noise due to irregularities on the surface of the thin glass 9.

〔Effect of the invention〕

According to the present invention, it is possible to significantly improve the low efficiency of illumination in conventional fully contact type image reading devices, reduce crosstalk between adjacent pixels, and improve the S/N ratio.

As a result, it is possible to obtain a clear image signal even if the light emission output of the illumination light source is lowered, and it is expected to improve the S/N ratio, reduce the size and cost of the lighting system, and simplify measures to prevent heat generation in the lighting system. can.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, in which FIG. 1 is a side sectional view, FIG. 2 is a plan view, and FIG. 3 is a Y-Y line in FIG.
Figures 4 to 6 show the conventional device, Figure 4 is a side sectional view, Figure 5 is a plan view, and Figure 6 is a cross-sectional view taken along line Y-Y' in Figure 5. FIG. 7 is a cross-sectional view illustrating problems occurring in the conventional device, and FIGS. 8(a) and 8(b) are perspective views schematically showing the principles of the conventional device and the device of the present invention, respectively. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Illumination light source, 3... Light shielding layer, 4
...Illumination window, 5... Original, 6... Photodetector, 7.
... Surface protective layer, 8... Microlens, 9... Lens substrate. Figure ζ Figure B A Photodetector light-receiving surface Photodetector light-receiving surface

Claims (1)

[Claims] A large number of photodetector arrays are arranged on the substrate in one or two dimensions, and the photodetector array photoelectrically detects incident light from one side of the substrate, and detects incident light from the other side. The incident light is blocked by a light shielding layer, etc.
and an illumination light source on the side of the substrate that cannot be photoelectrically detected,
The substrate is provided with a light guide window that corresponds one-to-one with each detector in the photodetector array in order to guide illumination light emitted from the illumination light source to the opposite side of the substrate, and Each of these light guide windows is equipped with a microlens, and the illumination light emitted from the illumination light source is converged by the microlens array, and is brought close to the surface of the substrate where the photodetector array is arranged. The photodetector array is arranged to photoelectrically detect reflected light from the image recording surface, and the focal length of the microlens is set so that the focal length of the microlens is between the lens and the image recording surface. Approximate distance between 2
An image reading device characterized by being about twice as large.