JPH07176713A - Contact-type image sensor - Google Patents

Abstract

PURPOSE:To prevent static electricity from discharging through a transparent conductive layer in a contact-type image sensor without imparing a shield effect of the transparent conductive layer. CONSTITUTION:A shielding layer 2 having a transparent window 3 is formed on a transparent substrate 1, and a photoelectric conversion element 4 is formed on the shielding layer. A protective layer 5a made of SiN film is formed on the photoelectric conversion element 4. A transparent conductive layer made of an ITO film is formed on a thin glass sheet as an abrasion-proof layer 6 and these layers are bonded with a transparent conductive adhesive 5b to the transparent substrate 1, on which the shielding layer 2 and the photoelectric conversion layer 4 have been formed. An overall sensor device part 14 is bonded to a frame 13 and put between each copy guide 12 while the shielding layer 2 and the copy guide 12 are grounded, and the copy guide 12 and the transparent conductive layer 7 are isolated to each other. Since the transparent conductive layer is grounded with impedance in between, the discharge can hardly take place through the transparent conductive layer.

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 a facsimile machine, an image scanner or the like for reading a two-dimensional image by closely moving a document, and particularly to static electricity generated by a moving document. The present invention relates to a contact-type image sensor that has taken measures.

[0002]

2. Description of the Related Art In a document reading device such as a facsimile or an image scanner for converting an image of a document into an electric signal,
A contact image sensor that does not have a reduction optical system and has a one-dimensional photoelectric conversion element array equal to the document width in the main scanning direction and mechanically scans in the sub scanning direction is a device that can be downsized at low cost. Widely adopted.
Among these, attention is paid to a device in which an element is formed on a thin glass plate without using an optical fiber array or a rod lens array.

FIG. 4 is a sectional view of a conventional contact-type image sensor of this type proposed in Japanese Utility Model Laid-Open No. 125562 / 1-1562. As shown in the figure, the conventional contact type image sensor has a light shielding layer 2 having a light transmitting window 3 on a light transmitting substrate 1.
Then, the photoelectric conversion element 4 is formed, and the entire transparent protective layer 5 is formed.
After being coated with d, the transparent conductive layer 7 is further formed thereon. Here, a plurality of photoelectric conversion elements 4 are arranged at a predetermined pitch in the vertical direction of the figure (that is, the main scanning direction). The original 9 is conveyed in the arrow direction by the roller 8. Illumination light emitted from the light source 10 is applied to the document surface through the translucent window 3, and the reflected light is reflected by the photoelectric conversion element 4.
Incident on. In this way, the photoelectric conversion elements 4 are arranged in the vertical direction of the drawing, and the original is conveyed in the vertical direction, so that the two-dimensional image information of the original can be read.

In this conventional example, a transparent conductive layer 7 is provided on the transparent protective layer 5d and is grounded. With this configuration, static electricity generated by a document that is conveyed in close contact is discharged, noise is superimposed on the image signal due to the electric field of the static electricity, signal level shift, photoelectric conversion element 4 and surroundings. This is to prevent the destruction of the circuit.

FIG. 5 is a sectional view of an image sensor proposed in Japanese Patent Laid-Open No. 64-71173. In this conventional example, a light-blocking layer 2 and a photoelectric conversion element 4 are formed on a transparent substrate 1, and a transparent conductive layer 7 is formed on the surface of the light-shielding layer 2 and a photoelectric conversion element 4 via a transparent adhesive 5c so that abrasion resistance The layer 6 is adhered. The abrasion resistant layer 6 is a thin glass plate having a thickness of about 50 μm, and prevents abrasion of the translucent conductive layer 7 made of ITO or the like. By keeping the translucent conductive layer 7 at a constant potential, the photoelectric conversion element 4 and peripheral circuits (not shown) are shielded from the electrostatic field, and image signal noise and element destruction are prevented.

In addition to the above, the contact image sensor provided with a countermeasure against static electricity uses a conductive adhesive instead of the transparent conductive layer 7 (Japanese Patent Laid-Open No. 2-29116).
No. 9), and a static elimination brush arranged immediately before the contact image sensor (Japanese Patent Laid-Open No. 3473/1993).

[0007]

[Problems to be Solved by the Invention]
In the prior art described in Japanese Patent No. 562, the SnO ₂ film and the ITO film used as the translucent conductive layer 7 are soft and the film thickness is reduced by friction with the original, so that static electricity is stable for a long period of time. It was difficult to maintain the preventive effect.

In the prior art disclosed in Japanese Patent Laid-Open No. 64-71173, when the original 9 is continuously read, the abrasion resistant layer 6 and the original 9 are charged with different polarities due to friction. Since the electric field due to this static electricity is shielded by the transparent conductive layer 7 held at a predetermined potential as described above, the transparent substrate 1 including the photoelectric conversion element 4 is provided.
It does not affect the upper peripheral circuits (not shown). However, when the original is continuously read, the potential on the abrasion resistant layer 6 rises, and finally discharge is generated between the place where the discharge is most easy. The place where the discharge is generated is the end of the transparent conductive layer 7 on the end face of the sensor device on the entrance side or the discharge side of the document 9. The reason will be described below.

Although the structure of the image reading apparatus is not specified in this prior art publication, the structure is generally shown in FIG. That is, the light source 10 and the frame 13 are provided on the printed circuit board 16, the sensor device unit 14 is arranged on the frame, and the document guides 12 are attached to both sides to form the contact image sensor 17. In order to smoothly convey the original, the original guide 12 is attached to the sensor device portion 14 without forming a step. Here, the sensor device unit 14 is the translucent substrate 1 shown in FIG.
To the wear resistant layer 6 are laminated structures.

This sensor device unit has a length in the main scanning direction of about 257 mm and a length in the sub scanning direction of several millimeters required for peripheral circuits and wirings, as long as the B4 width document is read. In general, a large-sized light-transmitting substrate is collectively formed into a film, which is then cut into pieces. Therefore,
The end of the translucent conductive layer 7 is exposed at the end face of the cut. Then, this end face is abutted against and adhered to the end face of the document guide 12. At this time, since the abrasion resistant layer 6 has a thickness of about 50 μm in order to be mounted without a step on the plane, the translucent conductive film is used. It is difficult to ensure that the edges of the layers are not exposed to the air at all. Thus, on the discharge side of the document 9, when the charged document 9 separates from the sensor device unit 14, the potential sharply rises. This is because the surfaces of the document 9 and the sensor device unit 14 can be regarded equivalently as a capacitor, and as the distance between the document 9 and the sensor device unit 14 increases, the electrode interval increases and the capacitance decreases.
= If the charge amount does not change from the relational expression of CV,
The voltage will rise. Then, since different charges are charged on the upper and lower surfaces of the abrasion resistant layer 6, the electric field changes sharply at the ends thereof, and moreover, the transparent conductive layer 7
Is grounded, a low-impedance discharge path is formed therethrough through the transparent conductive layer 7, and the charge on the abrasion resistant layer is discharged.

When this discharge occurs, the following problems occur. The discharge current enters the translucent conductive layer 7, but the ITO film or the SnO ₂ film cannot be made too thick in order not to reduce the light transmittance, and its sheet resistance value is several hundred Ω / □. Therefore, the translucent conductive layer 7 that has been discharged locally generates heat to expand the abrasion resistant layer 6 and the translucent protective layer 5c, and the thin glass of the abrasion resistant layer 6 is broken by a shock and partially May peel off. This causes the document 9 to be caught and causes a jam.

Further, since this kind of discharge phenomenon becomes a high frequency current of several hundred MHz, when there are few places where the transparent conductive layer 7 is grounded, the transparent conductive layer serves as a distributed constant line. Since the discharge current is less likely to flow due to the inductance, a partial increase in potential occurs in the translucent conductive layer 7,
This causes a local dielectric breakdown of the translucent protective layer 5c, which causes a problem that the photoelectric conversion element 4 and surrounding electric circuits and wirings (not shown) are destroyed. Even if such a breakdown does not occur, when a high-frequency current pulse flows to the ground portion, the ground potential of the device equipped with the contact image sensor partially changes. This phenomenon causes a malfunction of a document reading apparatus equipped with a large number of digital circuits.

Further, in the one disclosed in Japanese Patent Application Laid-Open No. 2-291169, in which a conductive adhesive is used instead of the transparent conductive layer 7, the conductive adhesive is a material having a high resistance, so that a shielding effect is obtained. It has a drawback that it is weak and cannot fully prevent the influence of the electrostatic charge. Furthermore, in the one disclosed in JP-A-3-3473 in which a static elimination brush is arranged immediately in front of the image sensor, charging on the abrasion resistant layer is prevented. Since the discharge cannot be performed immediately after the sensor unit, the above-mentioned problems related to the discharge cannot be solved.

[0014]

In order to solve the above problems, according to the present invention, a light-shielding film (2) having a transparent window (3) on a transparent substrate (1) and a photoelectric conversion element ( 4)
And a light-transmissive coating layer (5a, 5b), a light-transmissive conductive layer (7) and an abrasion resistant layer (6) are laminated in this order on the light-transmissive conductive layer (7). Is resistance and /
Alternatively, there is provided a contact image sensor which is grounded via a capacitance. And, it is preferable that the light shielding film (2) is a grounded conductor and the translucent coating layer (5b) is conductive.

[0015]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a sectional view showing a state near a sensor device portion according to a first embodiment of the present invention. In the figure, reference numeral 1 is a light-transmissive substrate made of a glass plate, on which Cr, Al or the like is formed and a light-transmissive window 3 is opened to form a light-shielding layer 2. Amorphous silicon is used to form the photoelectric conversion element 4 thereon (the electrodes and peripheral circuits are not shown in order to avoid complication of the drawing). In the case of the contact type image sensor for the B4 plate, the contact type image sensor is arranged, for example, at a density of 8 elements per 1 mm over a length of 257 mm in the main scanning direction.

The photoelectric conversion element 4 is partially covered with a transparent protective layer 5a made of SiNx. The translucent protective layer 5a may be formed of another insulating material such as polyimide or acrylic. Similar to the conventional method, an ITO film or a SnO ₂ film to be the translucent conductive layer 7 is formed on the abrasion resistant layer 6 made of a glass thin plate having a thickness of about 50 μm by the sputtering method, etc. The adhesive 5b is applied to the light-shielding film 2 and the light-transmissive substrate 1 on which the photoelectric conversion elements 4 are formed. Here, as the translucent / conductive adhesive 5b, it is possible to use a material in which an additive is added to a polymer material to impart conductivity, and an adhesive such as an epoxy-based material is mixed therein.

The sensor device portion 1 thus formed
4 is adhered onto the frame portion 13 to form the sensor device portion 1
The document guides 12 are attached before and after 4. Document guide 1
Reference numeral 2 is made of a conductive material and is grounded by a ground wiring. Further, the light shielding layer 2 is grounded by a ground wiring (not shown). The transparent conductive layer 7 is insulated from the document guide. In the contact image sensor thus assembled, the light from the light source 10 is applied to the original 9 through the light-transmitting window 3 formed in the light-shielding layer 2, and the reflected light is incident on the photoelectric conversion element 4. It is converted into an electric signal. The original 9 is conveyed in the sub-scanning direction by the roller 8, and thus two-dimensional image reading can be performed.

FIG. 2 is an electrical equivalent circuit diagram of the sensor device portion of this embodiment. As shown in the figure, the light-shielding layer 2 and the transparent conductive layer 7 are opposed to each other, and a resistor R and a capacitor C are formed between them, so that the transparent conductive layer 7 is made of R and C. Internal impedance consisting of parallel circuit 1
It is grounded by 1. Here, the volume resistivity of the translucent / conductive adhesive 5b is ρ [Ω · m], the area between the translucent conductive layer 7 and the light shielding layer 2 is S [m ² ] and the distance is d [m].
Then, the resistance R of the internal impedance 11 is obtained by the following equation. R = ρ · (d / S) [Ω] Further, when the relative permittivity of the light transmitting / conductive adhesive 5b is ε _r , the capacitance C of the capacitor is C = ε _r ε ₀ (S / d) (ε ₀ : Dielectric constant of vacuum). Since the internal impedance 11 is interposed between the translucent conductive layer 7 and the ground, the impedance of the discharge path through the translucent conductive layer 7 becomes large, and it becomes difficult to perform the discharge through this discharge path. The discharge is mainly performed through the document guide which is grounded. On the other hand, the translucent conductive layer covering the photoelectric conversion element 4 and the peripheral circuit has a relatively low resistance value because it is made of ITO or the like, and is grounded via the capacitor C.
It has a low impedance in terms of alternating current, and in the above configuration, the transparent conductive layer 7 can achieve substantially the same shield effect as in the case of the conventional example directly grounded.

When the original 9 is conveyed in the direction of the arrow,
As shown in FIG. 2, static electricity is generated on the abrasion resistant layer 6, and the original 9 is charged with static electricity of the opposite polarity. The polarity of this static electricity depends on the materials of the original 9 and the abrasion resistant layer 6,
Here, the abrasion resistant layer 6 is shown as negatively charged and the original 9 is shown as positively charged. The transparent conductive layer 7 is positively charged by the static electricity on the abrasion resistant layer 6. The movement of the charges is performed through the resistance of the internal impedance 11, and the potential of the translucent conductive layer 7 fluctuates by this, but since the potential fluctuates with a time constant determined by the capacitor component of the internal impedance 11, the fluctuations are compared It is gentle. Therefore, it is possible to prevent noise from being superimposed on the image signal and malfunction of the document reading device due to the potential variation of the transparent conductive layer 7.

Here, assuming that the total capacitance of the capacitor in the internal impedance 11 is C and the electrostatic charge is -Q, the charge of Q is induced in the transparent conductive layer 7,
This potential V _ITO becomes V _ITO = Q / C and is inversely proportional to the capacitor capacity C. Therefore, if the capacitance value is set so that the voltage of the translucent conductive layer 7 at the maximum expected charge falls within a range that does not induce malfunction or damage of the photoelectric conversion element 4 or the like, electrostatic image reading apparatus The influence can be eliminated.

FIG. 3 is a sectional view showing the main part of the second embodiment of the present invention. In the figure, parts corresponding to those of the previous embodiment are designated by the same reference numerals, and a duplicate description will be omitted, but in the present embodiment,
A parallel circuit of a lumped resistor R ′ and a capacitor C ′ is connected as an external impedance 15 between the transparent conductive layer 7 and the ground. Therefore, in this embodiment, the parallel circuit of the internal impedance 11 and the external impedance 15 is connected between the transparent conductive layer 7 and the ground.

The capacitance and resistance value of the capacitor and resistor to be connected between the transparent conductive layer 7 and the ground are the type of the photoelectric conversion element 4 to be used, the abrasion resistant layer 6 and the transparent / conductive adhesive 5b.
The wear resistance layer 6 is 50 μm in the sensor device portion 14 having an effective area of about 260 mm × 3 mm for B4, and the translucent / conductive adhesive 5
If b is a film thickness of about 5 μm and the document feed speed for G3 is C = 10 ⁻¹⁰ to 10 ⁻⁷ [F], R = 10 ³ to 10
It is desirable to set it to about ⁶ [Ω]. Here, the resistance value may be too high or the capacity may be insufficient only with the light transmitting / conductive adhesive 5b. In such a case, the external impedance 15 is added as in the present embodiment to eliminate the above shortage. If supplemented, an image sensor unit having desired characteristics can be constructed.

The preferred embodiment has been described above.
The present invention is not limited to these examples, and various modifications can be made without departing from the scope of the invention. For example, although both the resistor and the capacitor are used in the embodiment, only one of them may be used. When only the resistor is used, the potential changes according to the time constant determined by the parasitic capacitance, and when only the capacitor is used, the electric charge is charged and discharged by the leak current. Further, instead of the translucent conductive layer, illumination light using a non-translucent conductor,
An aperture can be formed in the optical path of the reflected light, and a mesh conductor can be used. Further, the charge may be discharged by using a charge eliminating brush. The photoelectric conversion element may be formed of a material other than amorphous silicon, and its type may be either a photoconductive type or a photovoltaic type.

[0024]

As described in detail above, in the contact type image sensor of the present invention, the light-transmissive conductive layer under the abrasion resistant layer is grounded by the resistor and the capacitor. The potential fluctuation can be made gentle according to the time constant. Therefore, according to the present invention, it is possible to avoid a situation in which noise is superimposed on an image signal due to static electricity and the document reading apparatus malfunctions. Further, according to the present invention, since the light transmissive conductive layer is grounded via the impedance, the impedance of the discharge path via the conductive layer is increased, and the discharge is less likely to occur. Therefore, overheating and overvoltage due to discharge can be avoided, and damage or malfunction of the device can be prevented.

Further, since the photoelectric conversion element and the like are covered with a translucent conductive layer having a relatively low resistance and the conductive layer is grounded by the capacitor, a good shielding effect can be obtained by this conductive layer. You can Further, since the portion that comes into contact with the original is the abrasion resistant layer made of glass, deterioration due to abrasion can be prevented and stable characteristics can be maintained for a long period of time.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is an electrical equivalent circuit diagram of FIG.

FIG. 3 is a sectional view of a main portion of a second embodiment of the present invention.

FIG. 4 is a sectional view of a first conventional example.

FIG. 5 is a sectional view of a second conventional example.

FIG. 6 is a cross-sectional view showing the overall configuration of a contact image sensor.

[Explanation of symbols]

1 Light-transmissive substrate 2 Light-shielding layer 3 Light-transmissive window 4 Photoelectric conversion element 5a, 5d Light-transmissive protective layer 5b Light-transmissive / conductive adhesive 5c Light-transmissive adhesive 6 Abrasion resistant layer 7 Light-transmissive conductive layer 8 Roller 9 original 10 light source 11 internal impedance 12 original guide 13 frame 14 sensor device section 15 external impedance 16 printed circuit board 17 contact image sensor

Claims (8)

[Claims] 1. A light-shielding film having a light-transmitting window and a photoelectric conversion element are formed on a light-transmitting substrate, and a light-transmitting coating layer is formed thereon.
In the contact-type image sensor in which a light-transmissive conductive layer and a wear-resistant layer are laminated in this order, the light-transmissive conductive layer is grounded via resistance and / or capacitance. Image sensor. 2. The contact image sensor according to claim 1, wherein the light transmissive conductive layer is grounded by a distributed constant resistance and / or a distributed constant capacitance. 3. The light transmissive conductive layer is grounded by a distributed constant type resistance and / or a distributed constant type electrostatic capacitance and a lumped constant type resistance and / or a lumped constant type electrostatic capacitance. Item 3. The contact image sensor according to Item 1. 4. The contact image sensor according to claim 1, wherein the light-shielding film is a grounded conductor, and the translucent coating layer has conductivity. 5. The contact image sensor according to claim 1, wherein the light-transmissive conductive layer is any one of a transparent conductive film, a net-shaped conductor, and a conductor with a light-transmitting opening. 6. The contact image sensor according to claim 1, further comprising a document guide which is a grounded conductor and is disposed adjacent to the document discharge side of the abrasion resistant layer. 7. The contact type image sensor according to claim 1, wherein a document guide, which is a grounded conductor, is disposed adjacent to the document entrance side and the document discharge side of the abrasion resistant layer. 8. The contact type image sensor according to claim 1, wherein a static elimination brush is arranged adjacent to the document entrance side and / or the document discharge side of the abrasion resistant layer.