JPH048054A - Image sensor - Google Patents

Abstract

PURPOSE:To eliminate the need for an external circuit for shading correction by providing a luminous quantity correction pattern correcting luminous quantity unevenness for an optical system for a photodetector sensor to each lens at the light transmission of a transparent cover. CONSTITUTION:A transparent cover glass 3 is fitted to an upper face of a frame 2. A grating refractive index lens array 8 is fixed to an optical system fixing position 2a of the frame 2 by a screw or a resin. A luminous quantity pattern 4 is printed to a light transmission position 3a on the inner face of the cover glass 3 by the printing or the like. Uneven luminous quantity of the grating refractive index lens array 8 is cancelled by using a luminous quantity correction pattern 4 (4') having an opposite characteristic to the uneven luminous quantity of the grating refractive index lens array 8 so as to uniformize output levels of each picture element (nearly + or -5%). Thus, it is not required to apply shading correction to an image sensor output signal and the gamma correction gradation processing has only to be implemented.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an image sensor used for reading originals in facsimile terminals.

(b) Conventional technology FIG. 4 shows a cross-sectional view of a conventional image sensor.

In FIG. 4, 22 is a frame, and a transparent cover glass 23 is attached to the upper surface of the frame. Light source installation position of frame 22 i! A light source substrate 25 is attached to 22b. An LED chip 26 is bonded onto the light source substrate 25, and a lens 27 is attached to cover the LED chip 26.

A light receiving sensor substrate 30 is attached to the bottom surface of the frame 22. On this light-receiving sensor substrate 30, the scanning direction (
A light-receiving sensor with light-receiving parts arranged in the direction perpendicular to the paper (Fig. 4),
For example, a photodiode array chip 31 is bonded.

Further, at the optical system fixing position 22a of the frame 22, an optical system for the light receiving sensor, for example, a refractive index gradient type lens array (
A lens array (trade name: SELFOC Lens Array) 28 is fixed with screws (not shown) or the like.

As shown in FIG. 5(a), this lens array 28 is made by arranging cylindrical refractive index gradient type lenses Sl in the scanning direction (left-right direction in FIG. 5(a)). The two lenses SL serve as several light receiving sections corresponding to the range Bi on the document A.

The light emitted from the lens 27 passes through the cover glass 23 and is irradiated onto the reading position B on the document.

The light reflected from the original A passes through the cover glass 23 again and enters the lens array 28. This light is received by the corresponding light receiving portion by each lens Sf2 of the lens array 28, and is converted into an electrical signal.

(c) Problems to be Solved by the Invention In an image sensor, it is desirable that the output level of each light receiving section (pixel) be uniform, but in reality, unevenness and variation are unavoidable. The first factor that causes variations in the output level is variations in the characteristics of the LED chip 26 and photodiode array chip 31. However, in recent years, with the improvement of these quality, LED chips 26
, variations in output level caused by the photodiode 31 are suppressed to such an extent that there is no problem in actual use.

Another factor that causes variations in the output level is unevenness in the amount of light in the gradient index lens array 28.

This unevenness in the amount of light is caused by the amount of light received by the light receiving portion decreasing from the center C toward the ends e and e in the light receiving portion shared by one lens Sf, as shown in Fig. 5(a). It is caused by doing. For this reason, as shown in FIG. 5(b), there is unevenness in the output level of each pixel at each of the bright and dark levels, depending on the arrangement of the lenses Sp, and the degree of this is 10 to 15%. reach even.

Therefore, conventionally, shading correction is applied to correct this unevenness on a circuit. In this shading correction, a white reference plate is read by an image sensor in advance, and the obtained unevenness signal is digitally converted and stored in a memory. When actually reading a document, the unevenness signal stored in the memory is read out, converted into an analog signal, and used as a reference signal to correct the unevenness.

This shading correction requires chips such as a memory and an A/D converter, which has the problem of increasing the price of the image sensor.

The present invention has been made in view of the above, and aims at an image sensor HA that can uniformly correct the output level of each pixel with a simple configuration without causing an increase in price.

(d) Means and operation for solving the problems In order to solve the above problems, the image sensor of the present invention includes a light receiving sensor including a transparent cover, a light emitting element, and a light receiving part corresponding to each pixel arranged. A light-receiving sensor optical system including an array of lenses is provided in the frame, and the light from the light-emitting element passes through the transparent cover and is irradiated onto the original, and the optical system reflects the light from the original and illuminates the original. In the device in which the light transmitted through the transparent cover is received by the light receiving part of the light receiving sensor for each pixel, a light amount correction pattern for correcting light amount unevenness of the optical system for the light receiving sensor is provided at a light transmitting position of the transparent cover, It is characterized in that it is provided for each lens.

This light intensity correction pattern increases the attenuation of light at the center of the lens's distribution range, cancels out the uneven light intensity of the lens itself, and optically corrects the output level of each pixel. It is. Therefore, an expensive shading correction circuit is not required. Although it is necessary to newly provide a light amount correction pattern, this can be realized by inexpensive means such as printing.

(E) Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

2 and 3 are a sectional view and an exploded perspective view of the image sensor of the embodiment. 2 is a frame made of aluminum alloy or the like. A transparent cover glass 3 is attached to the upper surface of the frame 2. Here, transparent means that light of the wavelength used is transmitted, and is not necessarily limited to colorless and transparent in visible light.

A light source substrate 5 is attached to the light source mounting position 2b of the frame 2. On this light source substrate 5, LED chips 6 are die-bonded at predetermined intervals in the image sensor scanning direction (direction perpendicular to the plane of the paper in the second figure). A plastic lens 7 is attached on the light source substrate 5.

Illuminance at the document reading position fiB is ensured.

A refractive index gradient lens array 8 is fixed to the optical system fixing position 2a of the frame 2 with screws or resin (not shown). As shown in FIG. 3, this refractive index gradient lens array 8 is formed by arranging cylindrical lenses Sl in the scanning direction.

A light receiving sensor substrate 10 is attached to the lower surface of the frame 2. On this light-receiving sensor substrate 10, photodiode array chips 11, .

For example, 64 light receiving sections are arranged on the photodiode array chip 11, forming a straight line in the scanning direction. Furthermore, elements constituting a processing circuit for the light reception signal of the photodiode array chip 11 are also mounted on the light reception sensor substrate 10, but they are omitted in FIGS. 2 and 3.

A connector 9 is also attached to the frame 2 (see FIG. 2). The terminals 9a of the connector 9 are connected to the light source board 5 and the light receiving sensor board 1 by lead wires (not shown).
Connected to 0.

At the light transmission position 3a on the inner surface of the cover glass 3,
Alternatively, a light amount correction pattern 4 as shown in (C) is provided by means such as printing. There is another light transmitting position on the inner surface of the cover glass 3 at 3b, but 3a is preferable for providing a light amount correction pattern because it is not affected by the refractive index of the cover glass 3.

Of course, it is also possible to provide a light amount correction pattern at the position 3b or integrally from 3a to 3b.

FIG. 1 [Ex.] shows an example of a light amount correction pattern 4, in which the left-right direction on the paper corresponds to the scanning direction.

This light amount correction pattern 4 is composed of a straight line pattern that is perpendicular to the scanning direction, has a uniform thickness, and does not transmit light or hardly transmits light, and the pattern 4i corresponds to one lens S21. Each pattern 4. The structure is such that the density of the linear patterns is large, that is, the interval between the linear patterns is small, at a location corresponding to the center of each lens Sl of the refractive index gradient lens array, and the amount of light transmitted is small.

Note that, instead of changing the interval between the linear patterns, it is also possible to have a configuration in which the amount of light transmitted is reduced by keeping the interval constant and changing the thickness of the linear pattern (increasing the thickness toward the center of the lens SR).

FIG. 1C shows another example 4' of the light amount correction pattern. In this light amount correction pattern 4', each pattern 4
", is a short line pattern extending in the scanning direction,
! , and are arranged in parallel in a direction perpendicular to the scanning direction at a position corresponding to the center of , and the amount of light transmitted in this portion is configured to be small.

Both light intensity correction patterns 4 and 4' are printed on the inner surface of the cover glass 3 in advance, and when attaching the cover glass 3 to the frame 2, the portions of each pattern 4° (4'i) where the amount of light transmitted is small are printed. In the image sensor of this embodiment, which is positioned with respect to the center of each lens Sl, by using a light amount correction pattern 4 (4°) having a characteristic opposite to the light amount unevenness of the refractive index gradient type lens array 8. , to cancel out the unevenness in the amount of light of the gradient index lens array 8 and to equalize the output level of each pixel (about ±5%). Therefore, there is no need to perform shading correction on the image sensor output signal, and gamma correction gradation processing can be performed as is.

Note that the light amount correction pattern is not limited to that of the above embodiment, and the design can be changed as appropriate. However, from the standpoint of positioning accuracy, it is preferable to configure the pattern from a plurality of straight lines as in the embodiment.

(f) Detailed Description of the Invention As described in detail, the image sensor of the present invention is provided with a light intensity correction pattern for each lens at the light transmitting position of the transparent cover to correct unevenness in light intensity of the optical system for the light receiving sensor. This feature has the advantage that the output level can be uniformly corrected with a simple configuration, an external circuit for shading correction is not required, and the price can be reduced.

Furthermore, since no external circuit for shading correction is required, space is also advantageous.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a light amount correction pattern of an image sensor according to an embodiment of the present invention in correspondence with a lens of a refractive index gradient lens array, FIG. 2 is a cross-sectional view of the image sensor, and FIG. The figure is an exploded perspective view of the same image sensor, FIG. 4 is a sectional view of a conventional image sensor, and FIG. 5(a)
FIG. 5 is a diagram explaining the action of the gradient refractive index lens array, and FIG. 2: frame, 3: cover glass, 4.4゛: light intensity correction pattern, 6: LED chip, 8: refractive index gradient lens array, SL: lens, 11: photodiode array. Patent applicant Lome Co., Ltd. Agency, Shigenobu Nakamura, Figure 2 Frame Cap <-Plica ゛ 4 ': LED Sen Tsubu IJI In Ordinary Led IL Home Type Lence イ オ Hoto 9 Iodo Array Figure 2b Q Figure (a) Figure (b)

Claims (1)

[Claims] (1) A frame is provided with a transparent cover, a light-emitting element, a light-receiving sensor formed by arranging a light-receiving section corresponding to each pixel, and an optical system for the light-receiving sensor formed by arranging lenses, and the light-emitting element is The light transmitted through the transparent cover is irradiated onto the document, and the optical system is configured to cause the light receiving portion of the light receiving sensor to receive the light reflected from the document and transmitted through the transparent cover for each pixel. An image sensor characterized in that a light amount correction pattern for correcting light amount unevenness of the light receiving sensor optical system is provided for each lens at a light transmitting position of the transparent cover.