JPH04233864A - Adherence type image sensor - Google Patents

Abstract

PURPOSE:To increase the light quantity of an LED radiated to a document, to enlarge a detecting signal of an element train, and also, to reduce the variance of an output voltage, and to improve the read photographic printing quality of halftone density of the document by performing a light reflection preventive processing to the surface of an inner wall of a through-hole of a supporting body. CONSTITUTION:Light generated by light emission of a light emitting element, that is an LED 2 enhances a reflection factor of the inner wall surface 4B of a housing, therefore, a part thereof is reflected by the inner wall surface, and also, its reflected light is radiated to the inner wall surface 9 of a through- hole 8 of a supporting body and the light reflection preventive surface 10. In this case, since a light reflection preventive processing is performed to the inner wall surface 9, it does not occur that a secondary reflection is furthermore generated from these surfaces 9, 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type image sensor used in facsimile reading heads and the like.

0002

2. Description of the Related Art The basic structure of a light source for illuminating a document in a contact type image sensor is known from Japanese Patent Application Laid-Open No. 62-285569 and No. 62-291257, and is disclosed in Japanese Patent Application Laid-Open No. 62-291257. An example of an image sensor is shown in FIG. In the same figure, 2 is an LED, 3 is an LED
A printed circuit board 2 is mounted, and a detection head 6 is a board on which an array of photodetecting elements is formed, which detects light reflected from the LED 2 on a paper surface or the like and reads an image. A support body 5 supports the detection head 6 and the printed circuit board 3 and also serves as a housing for the LED 2. This support 5 is made of Al
Made of metal materials such as 4A is a cavity, and 4C is a silver tape attached to the wall of the cavity, which is provided to reflect the light from the LED 2 and use a part of it effectively for illuminating the original. Increasing the amount of light irradiated onto the original in this way and increasing the reading output signal is
This is an important requirement in that the number of D chips is relatively small, the current consumption of the sensor body is reduced, and the amplifier gain of the circuit has a margin.

0003

[Problems with the Prior Art] However, according to the image sensor having this structure, although the light from the LED 2 is reflected on the wall surface of the cavity 4A, it is not focused toward the document, so the increase in the amount of illumination light is still unsatisfactory. It's not possible. Furthermore, attaching the silver tape 4C to the wall surface of the cavity 4A increases the number of steps and increases the cost during mass production.

[0004] Also, Japanese Patent Laid-Open No. 62-291257 introduces the provision of a condensing lens in the cavity 4A as a prior art, but installing the condensing lens complicates the structure of the image sensor and The number of parts increases, which causes an increase in costs.

[0005] Another problem that has recently received particular attention is that there are variations in the output voltage (hereinafter referred to as Vth) for each photodetector element with respect to the light reflected from the black original portion. It's here.

[0006] If the variation in Vth is large, the Vt
Corresponding to the abnormal portion of h, there is a problem in that a portion with higher or lower density than the surrounding halftone portion is printed as a white or black strip pattern.

The inventors of the present invention have conducted extensive research in view of the above circumstances, and have found that the cause of this variation in Vth may be due to variation in characteristics between dots of the reading element, but there are also other causes, from the light emitting element to the document. We found that the structure of the light guide part of the sensor body has a large influence.

[0008]

OBJECTS OF THE INVENTION Therefore, the present invention has been completed based on the above findings, and its purpose is to increase the amount of light irradiated onto a document without impairing the mass productivity of contact image sensors, and to improve the light detection element array. In addition to increasing the output signal of
The purpose of this invention is to reduce the variation in Vth and improve the quality of reading and printing of halftone densities of originals.

[0009]

[Means for Solving the Problems] According to the present invention, there are provided a light emitting element row for document illumination, a light guide housing disposed corresponding to the light emitting element row, and a through hole that fits into the housing and allows illumination light to pass through. In a contact image sensor comprising a support having a hole, and a substrate mounted on the support and having a photodetection element array formed thereon for detecting reflected light from a document and converting it into an electrical signal, A contact image sensor is provided, the inner wall surface of which is subjected to light reflection prevention treatment.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows a schematic cross-sectional view of a contact type image sensor 1 according to the present invention, and FIG. 2 shows an enlarged view of the vicinity of the light guide section in FIG.

In FIG. 1, 2 is an LED, and 3 is a printed circuit board, on which the LED 2 and other incidental circuits are mounted. A detection head 6 detects light reflected from the original 7 from the LED 2 and reads images such as character information and graphic information. Note that, in this drawing, the IC connected to the detection head 6 and the cover covering the IC are omitted.

Reference numeral 5 denotes a support body that directs the light from the LED 2 to the document 7.
A through-hole 8 is formed for guiding in the direction of. and,
The inner wall surface 9 of this through hole 8 is treated to prevent light reflection.

Further, in the present invention, when the light reflection prevention surface 10 is formed over the interface between the detection head 6 and the support body 5, the object of the present invention can be further achieved. For example, as the light reflection prevention surface 10, a light reflection prevention treatment may be applied to the surface of the support 5 that comes into contact with the detection head 6, or the surface of the detection head 6 that comes into contact with the support 5.

The material constituting the support 5 is, for example, a mixture of engineering plastic such as polyphenylene sulfide and carbon fiber and metal powder such as zinc, nickel, and stainless steel. The purpose of mixing carbon fiber and metal powder is to make the support 5 conductive and use it as a ground or ground shield for the detection head 6. Furthermore, engineering plastics are used because their shapes are complex and shape accuracy such as surface flatness is required. The support body 5 can be made of a metal member such as an extrusion molded product or a press molded product such as Al or iron, but these materials require additional machining such as drilling and deburring, and also require high shape accuracy. Because of the harsh conditions, secondary processing such as surface polishing is also required. Of course, the use of metal members is not excluded.

[0016] As a method for the anti-reflection treatment, for example, when engineering plastic is used as the support material, it is possible to have an anti-reflection function by simply adjusting the content of metal powder or carbon fiber for conductive treatment. I can do it. When using metal materials, if the metal is Al, there is alumite impregnated with black dye, and if the metal is iron, there is a so-called black dyeing treatment. As an essential requirement of the present invention, the anti-reflection treatment is required at least on the inner wall surface 9 of the through hole, but the same treatment may of course be applied to the entire surface of the support 5.

A housing 4 is brought into contact with the through hole 8 of the support 5, and a cavity 4A provided on the inner surface of the housing 4 is tapered to narrow the tip to direct the light from the LED 2 to the document 7. Focuses light in the direction of

That is, the light generated by the LED 2 is emitted in a divergent manner, but the housing 4 is provided with the tapered cavity 4A, and the inner wall surface 4B is colored white to increase the reflectance. Then, the light is repeatedly reflected diffusely on the inner wall surface 4B, and as a result, the light is focused in the direction of the document 7.

In FIG. 1, a taper is provided over the entire surface of the cavity 4A, but it is not necessarily necessary to provide a taper over the entire surface as long as the desired effect of the present invention can be obtained. Moreover, the surface roughness of the housing inner wall surface 4B is JI
It is preferable that the S code is approximately ▽▽▽ or more to make the surface smooth and to facilitate light reflection. The taper angle of the cavity 4A is preferably 40° or less, more preferably,
The angle should be 5 to 30 degrees. Within this range, the light from the LED 2 can be effectively focused in the direction of the document 7. In addition,
Here, the taper angle is defined as the angle formed between the optical axis direction from the LED 2 to the document surface and the housing inner wall surface 4B.

The material constituting the housing 4 includes, for example, a transparent resin such as ABS resin as a basic material to which a small amount of white pigment is added. When using titanium white powder, which is a typical white pigment, the amount of the pigment added is, for example, about 0.5 g per 1 kg of resin, and more generally 0.1 g or more. When ABS resin is used, the optical density is 0 with addition of 0.5g per 1kg.
．． It becomes 05. The optical density is approximately inversely proportional to the amount of pigment added. The preferred optical density range is 0.1 or less. In addition,
Here, the optical density is determined by the following formula.

D=-Log10I/I0 where I0
represents the intensity of incident light, and I represents the intensity of reflected light from the object to be measured. According to experiments conducted by the inventors, the optical density may be 0.1 or less, and if the optical density is made larger than that, the light that has entered the cavity 4A is absorbed by the inner wall surface 4B, and the amount of light irradiating the original 7 is reduced. .

Next, the present inventors will explain the reason why the variation in Vth can be reduced with reference to FIG.

In the figure, the detection head 6 includes a common electrode layer 6B made of Cr or the like on a glass substrate 6A, a photoconductive layer 6C made of amorphous silicon or the like, an individual electrode layer 6D made of laminated ITO, Cr, Al, etc. It has a structure in which transparent resin layers 6E such as epoxy resin are sequentially laminated, and furthermore, a thin glass plate 6F for preventing abrasion caused by the original 7 is arranged. 8 indicates a light guiding window. Further, 11 indicates a part of the path of the light emitted by the LED 2. Other numbers are the same as in FIG.

Since the reflectance of the housing inner wall surface 4B is increased, a portion of the light generated by the LED 2 is reflected from the inner wall surface, and the reflected light is further reflected as shown in 11 in the figure. The inner wall surface 9 of the through hole 8 of the support and the anti-reflection surface 10 are irradiated. Here, since the inner wall surface 9 is subjected to light reflection prevention treatment, no further secondary reflection occurs from these surfaces 9 and 10. As a result, LED2
The light is irradiated onto the original 7 from a light guide window 8 provided in the detection head, and only the light reflected from the original 7 is detected by the photoconductive layer 6C.

Therefore, it is possible to obtain a large brightness ratio of the output of the detection head corresponding to the black and white density of the original, and to reduce variations in Vth. As described above, even halftone originals can be faithfully reproduced in their shading, and white or black striped patterns do not occur, making it possible to improve the quality of reading and printing.

[0026] Here, if the inner wall surface 9 of the through hole 8 of the support body 5 is not subjected to anti-reflection treatment,
In addition, if there is no anti-reflection surface 10, the light path 11
As shown by the dotted line, a portion of the secondary reflected light from the LED 2 finally enters the photoconductive layer 6C, producing a constant output to the detection head even if there is no reflected light from the original. The intensity of this secondary reflected light differs from detection element to detection element due to the influence of variations in the geometrical positional relationship between the through hole 8 and the detection element. Therefore, if the influence of this secondary reflected light is large, the variation in Vth becomes large, causing a problem in the reproducibility of halftones of the original.

It can also be said that variations in Vth have a greater effect on the density unevenness of read prints, especially when the output level of the bright output is low than when it is high.

Note that in FIG. 2, it appears that the common electrode portion 6B, which also serves as a light-shielding film, can be expanded to prevent the secondary reflected light from entering the photoconductive layer 6C; however, in this case, The area of overlap with the individual electrode 6D increases, increasing the probability of short-circuiting and causing an increase in defects.

Next, an experimental example will be described.

[0030] The support body 5 is made of an Al material having a through hole for light guiding and whose entire surface is subjected to black alumite treatment, and a resin to which titanium white is added at a rate of 0.5 g per 1 kg of ABS resin. A housing 4 having a cavity tapered at an angle of 10° was prepared.

[0031] Furthermore, the detection head was manufactured according to the following procedure. First, apply C to a completely cleaned glass substrate.
A thin film of r was formed by sputtering, and a common electrode layer 6B was provided by photoprocessing. Next, amorphous silicon was formed as a photoconductive layer 6C by plasma CVD. Next, ITO, Cr, and Al were sequentially formed by sputtering, and an individual electrode layer 6D was formed by a photo process. Next, a light guide window 8 was further formed by a photo process, and then an epoxy resin was applied onto the substrate around the light guide window, and finally, a protective glass was bonded and hardened to finish.

In addition to the above support, housing, and detection head, there is also a printed circuit board, L, on which a drive circuit is mounted.
Prepare the printed circuit board and cover equipped with the ED element array,
A set of these members was assembled to complete a contact type image sensor, which was designated as Sample A.

[0033] As another example, a sample that was the same as sample A was also produced, except that the support was made of Al without anti-reflection treatment, and the inner wall of the housing was painted black. , this was designated as sample B. The purpose of sample B is to eliminate reflection on the inner wall surface of the housing to prevent the LED light from going around to the photoconductive layer.

Furthermore, a sample identical to Sample A was produced, and this was designated as Sample C, except that the support was made of Al and not subjected to anti-reflection treatment.

When bright output and dark output were measured using these sensors, the results shown in Table 1 were obtained. In Table 1, (maximum value - minimum value) of dark output indicates the variation in Vth.

[0036]

[Table 1]

From Table 1, it can be seen that sample A according to the present invention has a high bright output and a small variation in Vth. On the other hand, in sample B, the variation in Vth is
Although there was a similar improvement effect as in sample A, the bright output itself was reduced to about 1/2 compared to sample A. Therefore, when the gain is approximately doubled and the bright output is adjusted to 1.5V, the variation in Vth becomes 0.113V, and the actual improvement effect is relatively small. Further, in sample C, although the bright output was sufficiently high, the variation in Vth was about twice that of sample A.

On the other hand, when manufacturing the support, a black alumite treatment is performed before forming the through hole, and then the through hole is processed, so that only the inner wall surface of the through hole is subjected to antireflection treatment. A sensor similar to that of Sample A was also prepared using a support with no support, but as a result of evaluating this sensor in the same manner as in Table 1, the variation in Vth was approximately 50% compared to Sample A.
It was big.

As described above, it is desirable that the inner wall surface of the through hole of the support body and the plane near the opening on the side where the substrate is mounted are subjected to anti-reflection treatment, and in addition, the anti-reflection surface 10
It can be seen that forming this has a great effect on reducing the variation in Vth.

In the above embodiment, Al was used as the support material and ABS resin was used as the housing material.
The present inventors do not limit the combination of these materials and other members to the embodiments, but believe that various configurations can be adopted without departing from the gist of the present invention.

Finally, when sample A was installed in a fax machine and a photographic original was read and printed on the thermal fax machine, a test was conducted in which the halftone density was faithfully reproduced in the original and white and black striped patterns were produced. did not occur. However, sample C had problems in that the gradation of the original was not sufficiently reproduced and a white or black band pattern appeared.

[0042]

As described above, according to the contact type image sensor of the present invention, at least the inner wall surface of the through hole of the support body is subjected to anti-reflection treatment, so that the surface of the original can be improved without impairing its mass productivity. It was possible to increase the incident light intensity of the LED emitted light and to reduce the relative variation in Vth, and it was possible to improve the halftone reading and print quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a contact type image sensor according to the present invention.

FIG. 2 is an enlarged detailed view of a cross section of a contact type image sensor according to the present invention.

FIG. 3 is a schematic cross-sectional view of a conventional contact type image sensor.

[Explanation of symbols]

2 Light emitting element 4 Housing 5 Support 6 Detection head 8 Through hole

Claims (1)

[Claims] 1. A light emitting element array for document illumination, a light guide housing disposed corresponding to the light emitting element array, a support that fits into the housing and has a through hole for allowing illumination light to pass through, and the support. In a contact image sensor that is mounted on a body and includes a substrate formed with a photodetection element array that detects light reflected from a document and converts it into an electrical signal, the inner wall surface of the through hole is subjected to light antireflection treatment. A close-contact image sensor that is characterized by: