JPH08314235A - Image forming device - Google Patents

Abstract

(57) [Abstract] An object of the present invention is to provide an image forming apparatus which reduces stains on the end portion of the photosensitive belt and prevents erroneous detection of the seam position to stabilize the image quality. [Structure] Charger 2 for charging photosensitive belt 10 to a constant potential
The width of 1 is larger than the width of development by the developing device 22 and smaller than or equal to the width of the photosensitive belt 10 and smaller than the width of the intermediate transfer drum 30, and the seam position detection marker 65 provided at the end of the photosensitive belt 10. Charge to the surrounding area. [Effect] By charging the periphery of the joint position detection marker, it is possible to prevent the scattered toner from adhering to the non-image area, keep the periphery of the marker clean, and prevent erroneous detection.
Further, even if the scattered toner adheres, it is transferred to the intermediate transfer drum due to the high transfer potential, and the area around the marker is always kept clean, and erroneous detection by the sensor can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a laser beam.

[0002]

2. Description of the Related Art Generally, an electrophotographic image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer is provided with a charger for uniformly charging the surface of the photosensitive drum with the photosensitive drum as the center. An exposing device that exposes the surface of the charged photosensitive drum according to image information to form an electrostatic latent image; a developing device that develops the electrostatic latent image to convert it into a toner image; A transfer device for transferring the toner image and a thermal fixing device for passing the recording paper on which the toner image is transferred and fixing the toner image on the recording paper are provided.

However, in recent years, an image forming apparatus of this kind has been required to perform color printing, and various methods have been attempted as a method for realizing the color printing.

By the way, in order to form a color image,
As shown in JP-A-5-142955, four toner images of different colors (yellow, magenta, cyan, black) are formed on the surface of the photosensitive belt, and the four toner images are superposed on the surface of the intermediate transfer drum. A method of completing a color toner image on the surface of the intermediate transfer drum by transfer is adopted.

In such an electrophotographic image forming apparatus, the photosensitive belt has a joint for making it endless. Further, since an image is not formed on the seam, a marker for detecting the position of the seam is provided. This marker is detected by an optical sensor or the like.
The photosensor is installed in the main body because the photosensitive belt is a life component and is regularly replaced.
Therefore, the marker needs to be on the image forming surface of the photosensitive belt. However, the image forming portion of the photosensitive belt is easily soiled with toner. To prevent false detection of the sensor,
It is required to always keep the area around the marker clean. Therefore, conventionally, the width of the cleaning device for the photoconductor is increased to clean the end portion of the photosensitive belt, or brush-like cleaning members are provided at both ends of the cleaning device to clean the end portion of the photosensitive belt.

[0006]

However, in the electrophotographic image forming apparatus, increasing the width of the photosensitive belt cleaning device is disadvantageous in terms of cost and volume occupied by the device. In addition, in the case of a blade type cleaning device that is advantageous in terms of cost and occupied volume, when cleaning the non-image part, if there is no toner that works as a lubricant, the blade will turn over due to an increase in the friction coefficient, and the device will malfunction. Cause of. Furthermore, when auxiliary cleaning members such as brushes are provided at both ends of the cleaning device, the cleaning member itself is contaminated, and conversely, the photosensitive belt is contaminated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic image forming apparatus capable of preventing the above-mentioned seam position detection marker of the photoconductor from being soiled and erroneously detecting the sensor.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and each color toner is formed on an endless photosensitive belt having a photoconductive surface capable of forming an electrostatic latent image. In an image forming apparatus that sequentially superimposes on a transfer drum after being made visible, and then simultaneously transfers to a recording sheet, the photosensitive belt, a charger for charging the photosensitive belt to a constant potential, and an exposure for forming an electrostatic latent image. It is equipped with a device, a developing device for making the toner visible on the photosensitive belt, and an intermediate transfer drum for sequentially superposing the toner images on the photosensitive belt. The width of the photosensitive belt is shorter than or equal to the width of the photosensitive belt.

Further, the photosensitive belt is characterized in that it has a joint for making it endless and a marker for detecting the position of the joint at the end of the photosensitive belt, and is charged up to the marker portion by a charger. .

Further, by charging the marker portion and the periphery thereof, it is possible to prevent the scattered toner from adhering from the developing device, and to keep the periphery of the marker portion clean to prevent erroneous detection of the sensor.

Further, by charging the marker portion and the periphery thereof, the toner adhering to the periphery of the marker portion is transferred to the intermediate transfer drum, and the periphery of the marker portion is always kept clean to prevent erroneous detection of the sensor. Characterize.

Further, the charger for charging the photosensitive belt to a constant electric potential comprises a constant voltage element for uniformly charging the electric potential and a grid arranged in parallel with the photosensitive belt. The portion corresponding to the image area is in a mesh shape and is characterized in that holes are provided in the portion for stretching the grid.

[0013]

According to the present invention, in the means for solving the above problems, the width that can be charged by the charger is longer than the width that can be developed by the developing device and is shorter than or equal to the width of the photosensitive belt in the width direction. . As a result, the non-image forming portions at both ends of the photosensitive belt can be charged, and the scattered toner from the developing device can be prevented from adhering.

Further, provided at the end of the photosensitive belt,
It is possible to charge up to the marker portion for detecting the position of the seam. As a result, it is possible to prevent the scattered toner from adhering from the developing device and always keep the periphery of the marker portion clean, so that the erroneous detection of the sensor can be prevented.

Further, by charging the marker portion and its periphery, the toner adhering to the periphery of the marker portion is transferred to the intermediate transfer drum, and the periphery of the marker portion is always kept clean to prevent erroneous detection by the sensor. it can.

Further, the charger for charging the photosensitive belt to a constant electric potential comprises a constant voltage element for uniformly charging the electric potential and a grid arranged parallel to the photosensitive belt. The portion corresponding to the image area has a mesh shape, and a hole is provided in a portion for stretching the grid. As a result, the width of the charger remains unchanged,
The width that can be charged to the photosensitive belt can be expanded,
It is possible to reduce stain around the marker portion and prevent erroneous detection of the sensor.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a color laser printer according to the present invention, in which the photosensitive belt 10 is provided at the center of the frame 100.
Is rotatably installed by being stretched around the driving roller 11 and the driven rollers 12 to 14, and around the photosensitive belt 10,
The photosensitive belt 10 is exposed by exposing the photosensitive belt 10 by turning on / off a laser according to information from the charger 21 and the host.
An exposing device 25 for forming an electrostatic latent image, a developing device 22Y for yellow color, a developing device 22M for magenta color, a developing device 22C for cyan color, a developing device 22K for black color, a belt cleaner 24 and the like are arranged on the top. Developing device 22Y for each color
Each of the rollers 22K has a developing roller 23Y to 23K, which forms a magnetic brush made of a developer, rotatably supported therein. The lengths of the developing rollers 23Y to 23K in the width direction are shorter than the length of the photosensitive belt 10 in the width direction. That is, the developing rollers 23Y to 23K have a widthwise length corresponding to an image area described later.

On the left side of the photosensitive belt 10, there is an intermediate transfer drum 30 which rotates in contact with the photosensitive belt 10 by electrostatic force or the like.
Is provided. A paper cassette 41 for accommodating the paper 40 and a paper feed roller 42 are provided on the lower side of the frame 100, and a registration roller 43, a transfer roller 27,
A static eliminator 28, a conveyance guide 44, a fixing device 51, a paper discharge roller 52 are provided, and a paper discharge tray 53 is provided on the upper side. A drum cleaner 35 is provided above the intermediate transfer drum 30 so that it can be brought into contact with and separated from the surface of the intermediate transfer drum. The peeling claw 32 is provided for peeling the sheet 40 that is about to be attracted to the intermediate transfer drum 30.

Next, the operation of this color laser printer will be described. Since the object of the present invention is to improve the prevention of stains on both end portions of the photoconductor, detailed description of electrostatic latent image formation, development and transfer is omitted.

When color image printing (monochrome image printing is almost the same) is started, the laser generated from the exposure device 25 is turned on / off according to the image information for each color sent from the host, so that each color is printed on the photosensitive belt 10. To form an electrostatic latent image of. The developing devices 22Y to 22K develop corresponding electrostatic latent images to form toner images. The toner images of the respective colors are transferred onto the intermediate transfer drum 30 so as to be superposed and transferred.
0 is combined into a color toner image. Photosensitive belt 10
The toner image remaining on the photosensitive belt without being completely transferred from the intermediate transfer drum 30 to the intermediate transfer drum 30 projects from the cleaning device 24 and is scraped off by the elastic blade 61 contacting the photosensitive belt 10.

On the other hand, the paper 40 is fed from the paper cassette 41 by the paper feed roller 42 and conveyed to the registration roller 43. The registration roller 43 starts rotating in synchronization with the movement timing of the color toner image on the intermediate transfer drum 30, and sends the sheet 40 to the transfer roller 27.

The transfer roller 27 is energized at the same time as the paper 40 moves in the direction of contacting the intermediate transfer drum 30 at the timing when the paper 40 arrives at the transfer position, and the paper 40 is pressed against the color toner image on the intermediate transfer drum 30 to cause color transfer. The toner image is transferred to the paper 40. At this time, the sheet 40 is charged by the voltage application of the transfer roller 27 and tends to be electrostatically attracted to the intermediate transfer drum 30 in relation to the potential of the intermediate transfer drum 30. The static eliminator 28 acts to neutralize a part of the electric charge charged on the sheet 40 in order to reduce the electrostatic attraction force. The leading edge of the paper 40 whose electrostatic attraction force has decreased in this way forms a slight gap with the intermediate transfer drum 30, so that the peeling claw 32 enters the gap and reliably peels the paper 40. After that, the paper 40 is fixed by the fixing device 51 and is discharged to the paper discharge tray 53.

In the electrophotographic color laser printer as described above, the toners are visualized by color toners on an endless photosensitive belt having a photoconductive surface capable of forming an electrostatic latent image, and then sequentially superposed on a transfer drum. After that, the method of simultaneously transferring to recording paper is used.

FIG. 3 shows a photosensitive belt 10 according to the present invention. In terms of productivity and cost, the photosensitive belt 10 includes a flexible sheet-shaped member such as a polyethylene terephthalate film 61 (hereinafter referred to as a PET film) on which a layer is formed in the order of an aluminum electrode 62 and a photoconductor 63. It is general that these are joined by a method such as ultrasonic welding. Therefore, there is a seam 64 by joining. A step is formed on the seam 64 due to the overlap of the PET films 61, and the toner is deposited on the step. Therefore, when an image is formed on the seam 64, the seam 6 is formed on the printed image.
The line 4 appears, which significantly deteriorates the image quality. In order to prevent this, the photosensitive belt 10 is provided with a marker 65 for detecting the position of the seam 64. The marker 65 is detected by a sensor (not shown) so that the electrostatic latent image does not overlap the seam 64.

However, the joint position detection marker 65 is
Since the photoconductive surface at the end of the photosensitive belt 10 is provided, scattered toner from the developing device 22 adheres to the marker 6
Soil 5. Therefore, the sensor may erroneously detect the printed image and the printed image may overlap the seam 64. An embodiment for solving this problem will be described below.

FIG. 1 shows the relationship between the width of the photosensitive belt 10, the charger 21, the developing device 22, and the intermediate transfer drum 30 in the width direction, and the distribution of the surface potential of the photosensitive belt 10 in the width direction at that time. Shows.

The widthwise length of the charger 21 for charging the photosensitive belt 10 to a constant potential is longer than the developing width by the developing device 22, that is, the widthwise width of the image area, and the widthwise direction of the photosensitive belt 10 is equal. Shorter than or equal to the length,
The length is made shorter than the width of the intermediate transfer drum 30. For example, the width of the image area in the width direction corresponds to A4 size which is the width of the printable paper, and the length of the photosensitive belt in the width direction is about 10% longer than that. Therefore, the length of the charger in the width direction is 5 to 10 with respect to the length of the image area in the width direction.
% Longer. As a result, almost the entire width of the photosensitive belt 10 in the width direction is charged, and since the length in the width direction is longer than the length in the width direction of the image area, toner adhesion to the non-image area outside the image area is reduced. To do. Therefore, the contamination of the joint position detection marker 65 provided in the non-image area with toner is also reduced. Since the area around the marker 65 is always kept clean, erroneous detection of the sensor can be prevented. FIG. 4 is an example of a scorotron type charger according to the present invention.

The charger 21 for charging the photosensitive belt 10 to a constant electric potential comprises a constant voltage element 73 for uniformly charging the electric potential and a grid 71 arranged in parallel with the photosensitive belt 10. 71 has a mesh shape in a portion corresponding to the length of the image area in the width direction, and has a hole 72 in a portion for stretching the grid 71. This allows
It is possible to discharge the corona from the outside of the mesh portion of the grid 71, that is, the inside of the cases 74 and 75 that are originally hidden and cannot be seen, to charge the photosensitive belt 10. Therefore, the width of the charging device 21 in the width direction can be increased, and the chargeable width of the photosensitive belt 10 can be increased.
It is possible to reduce stains on the periphery and prevent erroneous detection by the sensor.

FIG. 5 shows the principle of toner image transfer from the photosensitive belt 10 to the intermediate transfer drum 30. A bias Vt (for example, -500 V) for transfer is applied to the aluminum electrode 62 of the photosensitive belt 10. A potential Vo (for example, −600 V) charged by the charger 21 is superposed on the transfer bias Vt, and the surface potential with respect to the ground potential is Vt + Vo. When the surface of the photosensitive belt 10 is irradiated with laser light from the exposure device 25, the charging potential V
o drops to Vr (eg, -100V). When this portion is developed with the developing bias Vb (for example, -350V), the toner is adsorbed by the potential difference of Vb-Vr and developed. The toner adhering to the surface of the photosensitive belt 10 is transferred to the intermediate transfer drum 30 due to the potential difference between the potential Vd of the transfer drum 30 (0 V because it is grounded) and the surface potential Vt + Vr of the exposed portion.

On the other hand, the toner attached to the non-image area of the photosensitive belt 10 has a surface potential of Vt + Vo.
Alternatively, since the potential is close to that, the intermediate transfer drum 3
The potential difference from 0 is Vt + Vo ', the transfer potential is high,
It is easily transferred to the intermediate transfer drum 30. This allows
Since the transfer potential around the marker 65 is high, the adhered toner is transferred to the intermediate transfer drum 30, and the marker 65 is always
The surroundings are kept clean and it is possible to prevent erroneous detection by the sensor.

[0032]

As described above, according to the present invention, the width of the charging device is larger than the developing width by the developing device and smaller than or equal to the width of the photosensitive belt, and further smaller than the width of the intermediate transfer drum. As a result, the non-image forming portions on both ends of the photosensitive belt can be charged, and the effect of preventing the scattered toner from adhering from the developing device can be prevented.

Further, provided on the end portion of the photosensitive belt,
It is possible to charge up to the marker portion for detecting the position of the seam, prevent the scattered toner from adhering to the developing device, and always keep the periphery of the marker portion clean, which is effective in preventing erroneous detection by the sensor. Further, by charging the marker portion and its periphery, the toner adhering to the periphery of the marker portion can be transferred to the intermediate transfer drum, and keeping the periphery of the marker portion clean at all times has the effect of preventing erroneous detection by the sensor. is there.

[Brief description of drawings]

FIG. 1 is a diagram showing a length in a width direction and a surface potential distribution of a photosensitive belt of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of a photosensitive belt according to an exemplary embodiment of the present invention.

FIG. 4 is a configuration diagram of a charger according to an exemplary embodiment of the present invention.

FIG. 5 is a diagram showing a principle of toner transfer according to an embodiment of the present invention.

[Explanation of symbols]

10 ... Photosensitive belt, 11 ... Driving roller, 12, 13, 1
4 ... Driven roller, 19 ... Gap setting member, 21 ... Charger, 22, 22Y, 22M, 22C, 22K ... Developing device, 23, 23Y, 23M, 23C, 23K ... Developing roller, 24 ... Cleaner, 25 ... Exposure device , 26 ... Laser light, 27 ... Transfer roller, 28 ... Static eliminator, 30 ... Intermediate transfer drum, 31 ... Separation claw, 35 ... Intermediate transfer drum cleaner, 40 ... Paper, 41 ... Paper cassette, 42 ... Paper feed roller, 43 ... Registration roller, 44 ... Conveyance guide, 51
... Fixing device, 52 ... Ejection roller, 53 ... Ejection tray, 64
... seam, 65 ... seam position detection marker, 71 ... grid, 72 ... hole, 73 ... constant voltage element.

Front Page Continuation (72) Inventor Katsumasa Mikami 1-1-1, Higashitagacho, Hitachi City, Ibaraki Prefecture Incorporated company Hitachi Ltd. Electric Appliances Division Taga Headquarters (72) Inventor Masashi Yamamoto Omika Town, Hitachi City, Ibaraki Prefecture 7-1-1, Hitachi, Ltd. Hitachi Research Laboratory

Claims (5)

[Claims] 1. An image forming apparatus in which an endless photosensitive belt having a photoconductive surface capable of forming an electrostatic latent image is exposed by color toners, respectively, and then sequentially superposed on a transfer drum and simultaneously transferred to a recording paper. In the above, the photosensitive belt, a charging device for charging the photosensitive belt to a constant potential, an exposure device for forming an electrostatic latent image, and a developing device for being exposed by toner on the photosensitive belt,
An intermediate transfer drum for sequentially superposing the visualized toner images is provided, and the chargeable width by the charger is longer than the developable width by the developing device and shorter than or equal to the widthwise direction of the photosensitive belt. An image forming apparatus characterized in that there is. 2. The photosensitive belt according to claim 1, further comprising: a joint for making the photosensitive belt endless, a marker provided at an end of the photosensitive belt for detecting a position of the joint, and a sensor for detecting the marker. An image forming apparatus having the charging unit, wherein the charging unit charges the marker unit. 3. The erroneous detection of the sensor according to claim 2, wherein charging of the marker portion and the periphery thereof prevents adhesion of scattered toner from the developing device and keeps the periphery of the marker portion clean. An image forming apparatus characterized by preventing. 4. The toner according to claim 2, wherein the toner adhering to the periphery of the marker portion is transferred to the intermediate transfer drum by charging the periphery of the marker portion and keeping the periphery of the marker portion clean. An image forming apparatus that prevents erroneous detection of a sensor. 5. The charging device according to claim 1, wherein the charger for charging the photosensitive belt to a predetermined potential is installed in parallel with the constant voltage element for charging the potential substantially uniformly and the photosensitive belt. An image forming apparatus comprising: a grid, wherein a portion of the grid corresponding to an image area is a mesh shape, and a hole is provided in a portion for stretching the grid.