JPH07287492A - Image forming device - Google Patents

Abstract

(57) [Summary] [Objective] The residual charge on the photoconductor drum 7 can be removed by the pre-exposure means 42, but the charging effect by the charger 23 at a portion adjacent to the pre-exposure means 42 is not hindered. And A charger 23 is provided on the outer circumference of a rotatable photosensitive drum 7, and a scanner unit 17 for forming a latent image on the surface of the photosensitive drum 7 charged by the charger 23.
And a developing device 10 for forming a toner image on the surface of the photoconductor drum 7, and a photoconductor drum 7 by applying a transfer voltage.
And a transfer roller for transferring the toner image to the paper P in this order, and a pre-exposure unit 42 composed of a row of light-emitting diodes is arranged adjacent to the upstream side of the charger 23, and the charger 23 and the pre-exposure unit 42 And the partition wall 5 in the charging case 51.
1a was made to face the surface of the photosensitive drum 7. As a result, the light emitted from the pre-exposure unit 42 is not disturbed by the partition wall 51 a and does not enter the charging area of the charger 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a copying machine and a facsimile machine.

[0002]

2. Description of the Related Art Conventionally, the surface of a rotating photosensitive drum as an image carrier is uniformly charged in advance by corona charging means, and the charged surface is exposed according to image data.
An electrostatic latent image is formed, charged toner is supplied from the developing device to the latent image to form a toner image, and then paper is supplied to the pressing contact portion between the transfer roller and the photoconductor drum. A transfer voltage is applied to the paper to transfer the toner image to the paper surface, and then the fixing device on the downstream side of the paper conveyance fixes the toner image on the paper surface by heating and pressing, while the toner not transferred to the paper is The removal is performed with a cleaner blade that is in sliding contact with the surface of the photosensitive drum.

It has been conventionally proposed to pre-exposure the surface of the photosensitive drum with a pre-exposure means as a process for removing the residual charge remaining on the surface of the photosensitive drum on the downstream side of the transfer section. ing.

[0004]

However, while the corona charging means uniformly charges the surface of the photoconductor drum to one polarity, the area irradiated with light by the pre-exposure means is not charged. Because it can be removed
If the light emitted from the pre-exposure means overlaps (or enters) the area to be charged by the corona charging means, the charging effect of the corona charging means is hindered.

The present invention has been made to solve this technical problem, and provides an image forming apparatus capable of removing the residual charge on the image bearing member while not hindering the charging effect by the charging means. The purpose is to do.

[0006]

In order to achieve the above object, the invention according to claim 1 provides a charging means for charging the image carrier on the outer periphery of a rotatable image carrier, and a charging means therefor. Exposure means for forming a latent image on the image bearing body charged by the toner, developing means for forming a toner image on the image bearing body, and transfer of the toner image on the image bearing body by applying a transfer voltage. In an image forming apparatus in which a transfer unit for transferring to a recording medium is sequentially arranged at a portion, a pre-exposure unit is arranged adjacent to the upstream side of the charging unit, and a pre-exposure unit is provided between the both units. It is characterized in that a partition for preventing the light from the means from entering the charging area by the charging means is brought close to the surface of the image carrier.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the front end portion of the partition wall, which is close to the surface of the image bearing member, has an appropriate width dimension along the rotation direction of the image bearing member. It is characterized by being formed. Claim 3
The described invention is the image forming apparatus according to claim 1,
The charging unit and the pre-exposure unit are supported on a case extending in parallel with the rotation axis of the image carrier, and the case integrally includes the partition wall.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the charging means includes a corona wire for corona discharge, which is installed in parallel with the partition wall at a distance.
The grit electrode is located between the corona wire and the image carrier, and the partition wall projects toward the image carrier from the grid electrode.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect, the pre-exposure unit is composed of a plurality of light emitting diodes arranged in parallel with a rotation axis of the image carrier, and the partition wall. It is characterized in that it is placed close to. According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, the case has a frame-like shape that cooperates with one side of the partition wall to form a box-shaped space open to the image carrier side. Of the partition wall and a support wall integrally projecting laterally from the other side of the partition wall, the corona wire is installed in the box-shaped space, and the opening of the box-shaped space is covered. The grid electrode is mounted on the support wall, and the light emitting diode is supported on the support wall.

[0010]

EXAMPLES Next, examples embodying the present invention will be described. FIG. 1 is a schematic side sectional view of a printer 1 as an image forming apparatus, and FIG. 2 is a side sectional view of a developing device 10 and a photoconductor unit 9. In the printer 1 of this embodiment, a paper feed cassette 3 is detachably mounted on one side of the main body case 2, and a recording medium stacked in the paper feed cassette 3 by a paper feed roller 4 and a separation pad 5. The paper P as a sheet is separated sheet by sheet, and is fed to the photoconductor unit 9 including the photoconductor drum 7 as an image carrier and the transfer roller 8 as a transfer unit via the feed roller pair 6. . A developing device 10 as a developing means is disposed adjacent to the photoconductor unit 9 on the side close to the sheet feeding cassette 3, and on the opposite side to the heating roller 1
A fixing unit 13 including 1 and a pressing roller 12 is arranged.

Below the photoconductor unit 9, a scanner unit 17 including a laser emitting section 14, a lens 15, a reflecting mirror 16 and the like, control boards 18 and 19, and a power supply unit 20.
Etc. are arranged, and the cover body 21 is provided with a keyboard 22 having a plurality of operation buttons. As will be described later, the scanner unit 17 fires the image data on the surface of the photoconductor drum 7 that has been precharged by the corona charger 23 as a charging unit according to image data transmitted from an external device such as a computer (not shown). By irradiating light, an electrostatic latent image is formed on the surface of the photosensitive drum 7, and then the developing sleeve 32 in the developing device 10 rotates to supply the magnetized powdery toner to form the latent image. After the development for visualizing is performed, the toner image is transferred onto the paper P supplied between the photosensitive drum 7 and the transfer roller 8, and then the transferred image is transferred by the fixing unit 13. Heat and pressure are applied to the sheet P to fix the toner image on the sheet P, and the sheet P is discharged from the sheet discharge roller pair 24 to the sheet discharge tray 25 of the printer 1.

The case 27 made of synthetic resin or the like in the developing device 10 has a stirring chamber 30 and a developing chamber 34 as shown in FIG.
Are separated by a partition wall, and an opening 36 is opened in the partition wall so as to face one side of the peripheral surface of the developing sleeve 32. The toner box 26, which serves as a toner supply chamber for supplying non-magnetic toner or magnetic toner to the stirring chamber 30, is attachable to and detachable from a pair of left and right bracket portions (not shown) protruding from one side of the case 27. The supplied toner is agitated by the second agitating member 31 formed of rotating blades in the agitating chamber 30.

In the developing chamber 34, a magnet roller 38 is provided on the inner diameter portion.
Has a first stirring member 33 composed of a developing sleeve 32 containing therein and a rotating blade and the like below the developing sleeve 32, and is arranged so that one side of the rotatable developing sleeve 32 faces the outer peripheral surface of the photosensitive drum 7. There is. A regulating member 37 is attached in the vicinity of the opening 36, and a midway portion of the regulating member 37 extends downward in the developing chamber 34 to face the outer peripheral surface of the developing sleeve 32 and regulate. The member 37 is arranged so that its free end is close to the outside of the rotation trajectory of the first stirring member 33.

As shown in FIG. 2, the second stirring member 31 as an agitator rotates in the direction of arrow B to move the stirring chamber 30.
The toner inside is scraped from the bottom toward the opening 36. The first stirring member 33 rotates in the direction of arrow C, and while stirring the toner supplied from the opening 36 and the magnetic carrier previously stored in the developing chamber 34, the toner is once developed through the bottom of the developing chamber 34. It flips up toward the lower surface of the sleeve 32.
The developing sleeve 32 rotates in the direction of arrow D, while the magnet roller 38 (where N poles and S poles are radially arranged alternately) in the inner diameter portion rotates in the direction of arrow E, and the developing sleeve 32 moves in the direction of arrow F. Is close to the photoconductor drum 7 rotating in the direction.

At a portion of the developing chamber 34 near one side of the outer peripheral surface of the photosensitive drum 7, the outer peripheral surface of the developing sleeve 32 has a layer thickness of the toner carried by the magnetic carrier (developer layer thickness). ) Is provided for trimmer blade 39. The developing method used in this embodiment is a so-called two-component developing method in which the magnetic carrier is 95 to 98% (weight ratio) and the non-magnetic toner is 2 to 5% (weight ratio), and the magnetic carrier is 30 to 50%. Any of the so-called 1.5-component developing method in which the magnetic toner is 80% (weight ratio) and the magnetic toner is 20 to 70% (weight ratio) may be used.

The transfer roller 8 located on the upper side of the circumferential surface of the photosensitive drum 7 is a conductive sponge roller,
A portion where the transfer roller 8 presses the paper P against the surface (circumferential surface) of the photosensitive drum 7 is a transfer portion. The toner that has not been transferred to the sheet P at the transfer portion is wiped off by a cleaner 41 having a cleaning blade 40 that is in sliding contact with the other peripheral surface of the photosensitive drum 7. This cleaner 41
A light emitting element (light emitting diode, LED) 50 as the pre-exposure means 42 of the present invention is provided between the charger and the charger 23.

The charger 23 of this embodiment is a scorotron composed of a corona wire 52 such as a tungsten thin wire and a grid electrode 53 for controlling charging, and a corona discharge emitted from the corona wire 52 when a high voltage of several kV is applied. The surface of the photoconductor drum 7 is positively charged by the ions generated in 1. At this time, the charging is controlled by applying a voltage of several hundreds V to the grid electrode 53.

The light emitting element 50 as the pre-exposure means 42 is
A plurality of chargers 23 are provided outside the charging case 51 along the rotation axis direction of the photoconductor drum 7 (see FIG. 3).
The charger 23 and the light emitting element 50 are supported by a single case 51 made of an insulating material having a light shielding property. The case 51 has a box shape extending in parallel with the rotation axis of the photosensitive drum 7 and over the entire length thereof, and has a partition wall 51 a so as to separate the charger 23 and the light emitting element 50. The tip of the partition wall 51a extends so as to approach the surface of the photosensitive drum 7. In the case 51, a side wall 51b extending in parallel with one side of the partition wall 51a and end walls 51c, 51c connecting both walls at both ends of the partition wall 51b and the side wall 51b are integrally formed in a frame shape to form a partition wall 5
Together with 1a, a box-shaped space that opens to the side of the photosensitive drum 7 is formed. The corona wire 52 has end walls 51c and 51 at both ends.
It is supported by c and is installed in a box-shaped space. Grid electrode 5
3 is attached to cover the drum side opening of the box-shaped space.
The tip of the partition wall 51 a projects toward the drum side with respect to the grid electrode 53. Further, the case 51 has a support wall 51d integrally protruding outward from the other side of the partition wall 51a, and the wiring board 50a on which the light emitting elements 50 are arranged at intervals is fixed on the support wall 51d. The row of light emitting elements 50 is a partition wall 51a.
And is arranged in parallel with the rotation axis of the photosensitive drum 7, and emits light toward the drum 7 so as to expose the photosensitive drum 7 over its entire length.

The case 51 is a pair of side walls 9a, 9a of the photoconductor unit 9 which rotatably supports the photoconductor drum 7.
Are fixed at the end walls 51c at both ends. Further, a wall 50e extending in a slanted shape is integrally provided outside the side wall 50b,
Between the wall 50e and the bottom wall 9b of the photoconductor unit 9,
A passage 56 is formed for introducing the light emitted from the scanner unit 17 to the photosensitive drum 7.

FIG. 5 is a functional block diagram of the control means of the image forming operation on the paper P by the photoconductor unit 9 and the pre-exposure means 42. The controller 44 rotates the photoconductor drum 7 in the direction of arrow F. A drive motor 43, a charger 23 that charges the surface of the photosensitive drum, a pre-exposure unit 42, a scanner unit 17 that exposes the surface of the photosensitive drum 7 according to image data, a developing device 10, and a transfer roller 8. The voltage is applied to the charger 23 from the high voltage unit 45 having a high voltage of about 4 kV to 7 kV. The scanner unit 17 is operation-controlled via a video controller 46 and a scanner controller 47 which are controlled by image data from an external device such as a host computer.

Next, the image forming mode of the printer 1 thus constructed will be described. When the photosensitive drum 7 is rotating in the direction of arrow F at a constant rotation speed, first, the charger 23 is operated. +8 on the surface of the photoconductor drum
It is charged to about 00V. Next, the scanner unit 17
Is neutralized so that the charge potential on the surface of the photosensitive drum is lowered to about +100 V in the bright portion by exposure from
Dark areas that are not exposed remain at the same charged potential (+800
V). Toner that is positively charged at the position of the developing device 10 at the same time is transferred to the surface of the photoconductor drum 7 by the electric field formed between the developing sleeve 32 and the photoconductor drum 7, and becomes visible. An image is formed. Then, at the transfer roller 8, -1 kV to -4
A transfer voltage of about kV is applied, and the toner image is transferred to the sheet P passing between the pressing portions (transfer portion) between the transfer roller 8 and the photosensitive drum 7 by the force of this electric field.

By the way, since the charge potential on the surface of the photosensitive drum 7 is unevenly distributed based on the image data by the exposure from the scanner unit 17, even if it is suddenly charged by the charger 23, the charge remains. The influence of the electric charge remains, and it is impossible to charge it to a uniform positive electric charge.
Therefore, by the exposure of the pre-exposure means 42, the remaining positive charges are neutralized to a potential equal to or lower than the exposed portion potential by laser exposure.

At this time, when the partition wall 51a does not extend so as to approach the surface of the photosensitive drum 7 as described above, the portion of the pre-exposure means 42 which irradiates the surface of the photosensitive drum 7 with light is charged by the charger 23. As a result, the charging effect by the charger 23 is impaired. As in the above embodiment, one of the gaps formed on both sides of the flat grid electrode 53 facing the cylindrical photosensitive drum 7 can be made as small as possible by extending the partition wall 51a. Then, the partition wall 51a disposed between the charger 23 and the pre-exposure means 42 is placed at the end of the partition wall 51a so that the gap between the front end of the partition wall 51a and the surface of the photosensitive drum 7 is, for example, about 1.5 mm. If it is arranged so as to be extremely close to the surface of the drum 7, the light emitted from the pre-exposure means 42 to the photosensitive drum 7 will pass through the case 51 of the charger 23 and directly enter the inside, or will pass over the partition wall 51a. This prevents the charging device 23 from penetrating into the charging region and does not reduce the charging effect of the charger 23 in the charging region.

In the embodiment of FIG. 4, the tip portion 55 of the partition wall 51a of the case 51 is formed wide so as to have an appropriate dimension L1 (for example, 1 mm or more) in the rotation direction of the photosensitive drum 7. By forming in this way, it is possible to completely prevent the light emitted from the pre-exposure means 42 from directly or indirectly entering the charging area of the charger 23. .

If the partition wall 51a is formed by the side plate of the charging case 51, a separate component as a partition wall material is not required, so that the number of components can be reduced. In addition, due to the combination of the photosensitive layer of the photosensitive drum 7 and the conductive layer on the inner diameter side, the charging polarity of the surface of the photosensitive drum 7 by the charger 23 is negative,
Even when the charging by the pre-exposure means 42 is positive,
It goes without saying that the same action and effect as described above can be obtained.

[0026]

As described above, claim 1
In the invention, a charging means for charging the image bearing body is provided on the outer periphery of the rotatable image bearing body, and an exposing means for forming a latent image on the image bearing body charged by the charging means,
Image formation in which developing means for forming a toner image on an image carrier and transfer means for transferring a toner image on the image carrier to a recording medium at a transfer site by applying a transfer voltage are sequentially arranged. In the apparatus, a pre-exposure unit is arranged adjacent to the upstream side of the charging unit, and a partition wall is provided between the both units so as to prevent light from the pre-exposure unit from entering the charging area of the charging unit. Since it is made to face the body surface so that the residual charges on the image bearing member can be removed by the pre-exposure means, the light irradiated from the pre-exposure means is obstructed by the partition walls, and the charging means. Since it does not enter the charging area due to, the excellent effect that the charging effect by the charging means in the portion adjacent to the pre-exposure means is not hindered is exhibited. Further, as a result, the charging unit and the pre-exposure unit can be arranged close to each other, so that there is an effect that the entire image forming apparatus can be downsized.

The invention described in claim 2 is the same as claim 1.
In the image forming apparatus described in the above, since the partition wall is formed to have an appropriate width dimension along the rotational direction of the image carrier, the tip portion facing the surface of the image carrier is easily formed. With the structure, it is possible to further enhance the effect of preventing the light emitted from the pre-exposure unit from entering the charging area by the charging unit.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the charging means and the pre-exposure means are supported on one case extending in parallel with the rotation axis of the image carrier, Since the case is integrally provided with the partition wall, the charging means and the pre-exposure means can be arranged closer to each other, and the entire apparatus can be further downsized, and both means can be integrated into the apparatus. It has an effect that it can be manufactured easily.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the corona wire for corona discharge is provided in which the charging means is installed in parallel with the partition wall at a distance, the corona wire and the image. It is characterized in that it is composed of a grid electrode located between the carrier, and the partition wall is projected to the image carrier side from the grid electrode, so that a cylindrical image carrier and a planar grid. The gap formed between the electrodes can be reduced, and the effect of not hindering the charging effect can be further enhanced.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect, the pre-exposure means comprises a plurality of light emitting diodes arranged in parallel with the rotation axis of the image carrier, and the partition wall is provided. Since they are characterized in that they are arranged close to each other, the size of the pre-exposure means can be made smaller, and the pre-exposure means can be arranged closer to the charging means, and the size of the entire apparatus can be reduced.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, a box-shaped space that opens to the image carrier side is formed in the case in cooperation with one side of the partition wall. A frame-shaped wall is integrally provided, and a support wall integrally protruding laterally from the other side of the partition wall is provided, and the corona wire is installed in the box-shaped space, and the opening of the box-shaped space is formed. It is characterized in that the grid electrode is attached to cover the light emitting diode and the light emitting diode is supported on the support wall, so that the charging means and the pre-exposure means can be easily incorporated in a case having a simple structure. This is advantageous in that it can be manufactured at low cost and the size of the entire device can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view of a laser printer.

FIG. 2 is a partially cutaway side sectional view of a main part of a photoconductor unit.

FIG. 3 is a view taken along the line III-III in FIG.

FIG. 4 is a side sectional view of another embodiment.

FIG. 5 is a functional block diagram of a control device.

[Explanation of symbols]

 1 Printer 7 Photoreceptor Drum 8 Transfer Roller 9 Photoreceptor Unit 10 Developing Device 23 Charger 42 Pre-exposure Means 44 Controller 50 Light Emitting Element 51 Charging Case 51a Partition

Claims (6)

[Claims] 1. A charging means for charging the image bearing body on the outer periphery of a rotatable image bearing body, and an exposing means for forming a latent image on the image bearing body charged by the charging means. An image in which a developing unit that forms a toner image on the image carrier and a transfer unit that transfers the toner image on the image carrier to a recording medium at a transfer site by applying a transfer voltage are sequentially arranged. In the forming apparatus, a pre-exposure unit is arranged adjacent to the upstream side of the charging unit, and a partition wall is provided between the both units so as to prevent light from the pre-exposure unit from entering the charging area of the charging unit. An image forming apparatus, characterized in that it faces the surface of a carrier. 2. The image forming apparatus according to claim 1, wherein a front end portion of the partition wall, which is close to the surface of the image carrier and faces the image carrier, is formed to have an appropriate width along the rotation direction of the image carrier. 3. The charging unit and the pre-exposure unit are supported on one case extending parallel to the rotation axis of the image carrier, and the case integrally includes the partition wall. The image forming apparatus according to item 1. 4. The charging means comprises a corona wire for corona discharge, which is installed in parallel with the partition wall at a distance from the partition wall, and a grit electrode positioned between the corona wire and the image carrier. The image forming apparatus according to claim 3, wherein the image forming device protrudes toward the image carrier side from the grid electrode. 5. The pre-exposure unit is composed of a plurality of light emitting diodes arranged in parallel with the rotation axis of the image carrier, and is arranged in the vicinity of the partition wall. Image forming apparatus. 6. The case integrally has a frame-shaped wall that forms a box-shaped space that opens to the image carrier side in cooperation with one side of the partition wall, and extends laterally from the other side of the partition wall. Having a supporting wall protruding integrally, the corona wire is installed in the box-shaped space, the grid electrode is attached to cover the opening of the box-shaped space, and the light-emitting diode is mounted on the supporting wall. The image forming apparatus according to claim 4, wherein the image forming apparatus supports the image forming apparatus.