JP2006227393A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the occurrence of a defective image such as image dust. <P>SOLUTION: The apparatus includes an image memory control part 22, an address converting means 24, an image judging part 23, a paper feeding means 21 and a mechanism part, and when it is judged by the image judging part 23 that image information is mainly composed of a main scanning direction line, an image rotating processing is performed by the address converting means 24, then, the apparatus is controlled so as to form an image on a transfer paper which is fed from a paper feeding cassette as the paper feeding means 21, and whose longitudinal direction in the set state is the same as the longitudinal direction of an image forming area in forming the image after the image rotating processing, and also, of the same size as that of the image forming area. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a printer, a copying machine, and a facsimile machine, and more particularly to an image forming apparatus that controls a transfer output of a transfer unit in accordance with a toner charge amount on a photoreceptor. .

An image forming apparatus using an electrophotographic system has been proposed that uses an image rotation process to prevent offset at the time of fixing for the purpose of improving the quality of an output image (see, for example, Patent Document 1).
In this technique, image rotation processing of 90 degrees or 270 degrees is performed at a timing according to the number of continuous sheets to be passed, and a transfer sheet having the same size and a different setting direction as the transfer sheet set in the currently selected sheet feeding port By changing to the paper feed slot where is set, vertical line images can be prevented from continuing indefinitely on the same circumference of the fixing roller, vertical line offsets can be avoided, and image quality can be improved. It is said that we can plan.
JP 2000-181283 A

By the way, the charge amount of the toner of the toner image on the photosensitive member has a distribution including strong to weak, and in the case where the charge amount of −20 μC / g or less, particularly −10 μC / g or less is weak, there is a large proportion. In the transfer process, the toner is charged up by peeling discharge, but the toner image on the transfer paper has a large amount of weak charge as it is. The weakly charged toner in the toner image on the transfer paper has a weak force (Coulomb force) acting on the toner and the transfer paper.
For this reason, in the conventional image forming apparatus, disturbance such as peeling discharge from the transfer unit or static electricity due to sliding between the transfer paper guide member and the transfer paper in the process after the toner image is transferred from the photoreceptor to the transfer paper. Due to the image, dust and unevenness are likely to occur. The degree of dust in the image differs depending on the solid image and the line image. Particularly, in the case of the main scanning direction line, the toner charge-up amount is smaller than that of the solid or sub-scanning direction line due to peeling discharge in the transfer process. Chile and unevenness are likely to occur.
Accordingly, the present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide an image forming apparatus capable of suppressing the occurrence of image defects such as image dust.

  In order to solve the above-mentioned problem, the invention described in claim 1 includes an image storage unit that stores input image information, an image reading unit that reads image information from the image storage unit, and an image storage unit. The image rotation means for converting the address when reading the image information and rotating the image data so that the image forming area at the time of image formation is rotated at a right angle, and the image information stored in the storage means are mainly used. Line direction determination means for determining whether or not the main line is a scanning direction line, and at least two paper feed cassettes capable of separately setting transfer sheets of the same size so that their longitudinal directions are perpendicular to each other An image forming unit for forming an image on a transfer sheet fed from the sheet feeding unit based on the image information read by the image reading unit, and the image forming unit Control means for controlling the image forming operation by the image rotation operation, and when the line direction determination means determines that the image information is mainly the main scanning direction line, the image rotation by the image rotation means The transfer paper fed by the paper cassette is processed, and in the set state, the longitudinal direction is the same as the longitudinal direction of the image formation area at the time of image formation after image rotation processing, and the image formation area And an image forming apparatus that controls to form an image on a transfer sheet having the same size as the image forming apparatus.

According to a second aspect of the present invention, there is provided an image storage means for storing inputted image information, an image reading means for reading out image information from the image storage means, and a main scanning direction in the image information stored in the image storage means A line direction determining means for obtaining a ratio of the line and the sub-scanning direction line, an image forming means having a transfer means for transferring an image onto a transfer sheet based on the image information read by the image reading means, and the image forming means Control means for controlling the image forming operation by the control means, wherein the control means determines the transfer current value of the transfer means according to the ratio of the main scanning direction line and the sub-scanning direction line obtained by the line direction determination means. The image forming apparatus is controlled.
According to a third aspect of the present invention, when the ratio of main scanning direction lines is large in the determination result of the line direction determination unit, the control unit sets the transfer current value of the transfer unit higher than usual. 2. An image forming apparatus according to item 2.
According to a fourth aspect of the present invention, there is provided image storage means for storing inputted image information, image reading means for reading out image information from the image storage means, and solid images in the image information stored in the image storage means. A solid line determination unit for obtaining a ratio of the lines, an image forming unit having a transfer unit for transferring an image onto a transfer sheet based on image information read by the image reading unit, and image formation by the image forming unit Control means for controlling the operation, wherein the control means transfers the transfer current of the transfer means for transferring the image onto the transfer paper in accordance with the ratio of the solid and line of the image obtained by the solid / line determination means. The image forming apparatus controls the value.
According to a fifth aspect of the present invention, in the determination result of the solid line determination unit, the control unit sets the transfer current value of the transfer unit higher than usual when the line ratio is large. It is the image forming apparatus described.

According to the first aspect of the present invention, when the line direction determining means determines that the image information is mainly the main scanning direction line, the image rotating process is performed by the image rotating means, and the original is the main scanning direction line. By replacing the existing image with the image in the sub-scanning direction when the image is formed, toner charge-up can be reliably performed when the transfer paper and the image carrier are separated, and the output image The occurrence of image defects such as image dust in the image can be suppressed.
According to the second or third aspect of the invention, when the result obtained by the line direction determination unit is an image having a large proportion of lines in the main scanning direction, the transfer current value of the transfer unit is set higher than usual. This makes it possible to reliably perform toner charge-up when the transfer paper and the image carrier are separated from each other in the main scanning direction line image, and to suppress the occurrence of image defects such as image dust in the output image.
According to the invention described in claim 4 or claim 5, when the result obtained by the solid line determination unit is an image having a large proportion of lines, the transfer current value of the transfer unit is set higher than usual. Thus, the toner charge can be reliably increased when the transfer paper and the image carrier are separated from each other in the line image, and the occurrence of image defects such as image dust in the output image can be suppressed.

The best mode for carrying out the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus as an embodiment of the present invention. The image forming apparatus 1 includes a mechanism unit as an image forming unit including a mechanism necessary for an image forming operation, and a control unit including a control circuit that controls each unit and the whole of the apparatus. First, the mechanism unit will be described, and then the control unit will be described.
The mechanism unit includes an image reading unit 20, a paper feeding unit 21, a developing unit 7, a transfer unit 6, a fixing unit 90, a cleaning unit 91, and the like.
The image reading means 20 reads and scans image information on a document set on the upper part of the apparatus. As input of image information, in addition to input by the image reading means 20, input from an external device through a network connection or the like is also possible.
The sheet feeding means 21 includes a plurality of sheet feeding cassettes (not shown), and can set a plurality of types of transfer sheets having different sizes. In addition, transfer sheets of the same size can be set so that their orientations are different. That is, a paper feed cassette for setting the transfer paper in the longitudinal direction to be the same as the transfer paper transport direction, and a paper feed cassette for setting the transfer paper in the longitudinal direction perpendicular to the transfer paper transport direction. Has a paper cassette. The controller 100 is instructed which paper feed cassette the transfer paper is used, and the transfer paper is automatically sent out from the selected paper feed cassette.

The image forming apparatus 1 employs a reversal developing method (N / P developing method), and the surface of the photosensitive member (image carrier) 10 is uniformly negatively charged to about −900 V by the charging device 2, and then the original document. The signal read from the image memory in which the image information such as is stored is replaced with an electrostatic latent image of about −50 V by laser exposure 3. Then, a toner image is created by the negatively charged nonmagnetic toner.
The developing means 7 is a two-component developing device, and the developing means 7 contains a non-magnetic toner in a predetermined ratio (concentration) in a carrier made of a magnetic material. The developing means 7 includes developing rollers 71a and 71b for applying toner in the developer to the photosensitive member 10, a developing doctor 72 for regulating the amount of developer on the developing roller 71a, and stirring members 73 and 74 for stirring the developer. 75.
A toner replenishing unit 8 is provided on the right side of the developing unit 7 and gradually replenishes toner sent from a toner cartridge (not shown) into the developing unit 7 using a toner replenishing roller 81. The toner is replenished only for the shortage according to the developer concentration in the developing means 7. The replenished toner is agitated with the carrier by the agitating agents 73, 74, and 75, and is negatively charged on the carrier. Then, it is attracted by the magnet and adheres to the developing rollers 71a and 71b. The developing rollers 71a and 71b are rotated to the developing doctor 72 and are regulated to a predetermined amount, and then come to the developing area with the photoconductor 10. About −550V is supplied to the developing roller 71a from a developing bias power source (not shown), and only the negatively charged toner in the developer moves to the electrostatic latent image to become a toner image.
The toner that moves from the developing means 7 to the photoconductor 10 is likely to move from a toner having a low charge amount. Those having a high charge amount have a large Coulomb force and a strong adhesion to the carrier, so that it is difficult to move to the photosensitive member side in the developing electric field. The toner charge amount of the toner image on the photoreceptor 10 is slightly lower than the toner charge amount in the developing unit 7.
After the toner image on the photoconductor 10 is transferred to the transfer paper by the transfer belt 61, the toner on the transfer paper is charged up by the peeling discharge when the photoconductor 10 and the transfer paper are separated. The toner charge-up due to the peeling discharge is different between the solid image and the line image.

2 to 4 are graphs showing the toner charge amount by toner charge-up in each image form. The solid is 5 mm or more in width in the main scanning direction, and the line is 2 mm or less in width.
As can be seen by comparing these figures, the amount of charge-up in the main scanning direction line image in FIG. 2 is smaller than in the other images (solid image in FIG. 3 and sub-scanning direction line image in FIG. 4). .
The reason is that in the main scanning direction line image, the toner adhering portion in the sheet passing direction is discontinuous, and thus the peeling discharge current escapes to the portion where the toner is not adhering. As a result, when the toner is -15 μc / g on the photoreceptor, the toner on the transfer paper is only −16 to −18 μc / g.
In the case of a solid image or a vertical line image, since the toner adhering portion continuously exists in the sheet passing direction, the peeling discharge current flows to the toner, the toner is charged up, and −15 μc / g on the photoreceptor. In the case of toner, the toner on the transfer paper is −20 to −25 μc / g.
The toner on the transfer paper having a low toner charge amount (charge amount less than −20 μc / g), such as a line image in the main scanning direction, has a weak Coulomb force and a weak bond between the transfer paper and the toner. If there is a toner having a low toner charge amount on the transfer paper, before the toner is fixed, peeling discharge when the transfer paper is separated from the transfer belt 61, frictional charging by sliding between the transfer paper after transfer and the fixing entrance guide plate 66, or the like. As a result, image flickering is likely to occur. In order to cope with this, in the image forming apparatus 1 of the present embodiment, the processing described later in the control unit is performed.
Returning to FIG. 1, the transfer paper is conveyed from the paper feed cassette in the direction of arrow B along with the above-described toner image creation operation, and is temporarily stopped by the registration roller 5. In accordance with the timing of the toner image on the photoconductor 10, the transfer paper is sent from the registration roller 5, and the toner image on the photoconductor 10 is transferred to the transfer paper by the transfer belt 61 of the transfer unit 6. The transfer belt 61 is provided with a driving roller 62, a driven roller 63, and a bias roller 64 inside the belt. The transfer unit 6 includes a bias roller 64 and a transfer high-voltage power source 65. The bias roller 64 is connected to the transfer high-voltage power source 65, and is controlled so that a transfer bias is applied and the current flowing to the photoconductor 10 side becomes constant. ing.
The transfer paper on which the toner image is placed is fixed on the transfer paper by the fixing unit 90, and is then discharged to the image forming apparatus. The toner that has not been transferred to the transfer paper is collected by the brush roller 92 and the cleaning blade 93 of the cleaning means 91. Thereafter, the surface of the photoreceptor 10 is neutralized by a neutralizing lamp 94 which is a neutralizing unit.

Here, the configuration of the control unit of the image forming apparatus 1 of the present embodiment will be described.
The control unit of the image forming apparatus 1 according to the present embodiment includes an image memory control unit 22 as an image storage unit and an image reading unit, an image determination unit 23 as a line direction determination unit and a solid line determination unit, and an image rotation unit. The address conversion means 24 and the controller 100 are included.
The image memory control unit 22 includes an image memory for storing the acquired image information, and also has a function for reading the image information from the image memory.
The image determination unit 23 obtains the ratio of the main scanning direction line and the sub-scanning direction line in the image information stored in the image memory, determines whether or not the main scanning direction line is a main line, and the image memory Has the function of obtaining the ratio of the solid and line of the image in the stored image information.
The address conversion unit 24 converts the address when reading from the image memory control unit 22, and the direction in which the image forming area is rotated at a right angle when the image information is mainly composed of main scanning direction lines. So that the image data is rotated.
The controller 100 has a function of sending an instruction to the paper feeding means 21 so as to supply transfer paper having a direction corresponding to the direction of the image subjected to the rotation process, and a function of instructing a set value of the transfer current.

Hereinafter, operations of the control unit configured as described above will be described as first to third embodiments.
[First Embodiment]
In the first embodiment, when the read image is mainly composed of lines in the main scanning direction, the image is rotated, and a transfer sheet corresponding to the orientation of the image after the rotation process is selected to form an image on this. Like to do.
This operation will be described with reference to the flowchart of FIG. 5. First, in step S1, image information is read from the image memory control unit 22, and in step S2, it is determined whether or not the image is mainly composed of main scanning direction lines. Judgment by
In the case where the main scanning direction line is the main line, the process proceeds to step S3, where the address conversion unit 24 applies rotation processing to the image data so that the image at the time of image formation is rotated at a right angle, Proceeding to step S4, the size of the transfer sheet is the same as the size of the transfer paper selected when the rotation process is not performed, and the longitudinal direction when the image formation area is set in the image formation when the rotation process is performed is The selection of the paper feed cassette is changed so that paper feed is performed from the paper feed cassette containing the matching transfer paper. In step S5, printing is performed. If it is determined in step S2 that the main scanning direction line is not the main line, the process proceeds to step S5 without performing the rotation process, and the printing process is performed.
As described above, in the first embodiment, since the image originally in the main scanning direction line is replaced with the image in the sub scanning direction line when the image is formed, the transfer paper and the photoconductor 10 are separated. Therefore, it is possible to reliably perform the toner charge-up, and it is possible to suppress the occurrence of image defects such as image dust in the output image.

[Second Embodiment]
In the second embodiment, the ratio of the main scanning direction line and the sub scanning direction line of the read image is obtained by the image determination unit 23, and when the ratio of the main scanning direction line is large, the transfer current value is set higher than usual. I have to.
This operation will be described with reference to the flowchart of FIG. 6. First, in step S11, image information is read from the image memory control unit 22, and the ratio of main scanning direction lines and sub-scanning direction lines of the image read in step S12 is determined by the image determination unit 23. It is determined whether or not the ratio of main scanning direction lines is large.
If the ratio of lines in the main scanning direction is large, the process proceeds to step S13, and the controller 100 controls the transfer high-voltage power supply 65 to set the transfer current value higher than usual. For example, the transfer current value is usually 50 μA when the sub-scanning direction line is main, and is 100 μA when the main scanning direction line is main. In step S14, printing is performed. If the ratio of the main scanning direction line is not large in step S12, the process proceeds to step S14 without changing the transfer current value, and the printing process is performed.
As described above, in the case of an image having a large proportion of main scanning direction lines, by setting a transfer current value higher than usual, the toner charge when the transfer paper and the photoreceptor 10 are separated in the main scanning direction line image. The image can be reliably increased, and the occurrence of image defects such as image dust in the output image can be suppressed. The reason why the high transfer current value is not always set is that a high transfer current value decreases transfer efficiency and wastes toner.
[Third Embodiment]
In the third embodiment, the ratio between the solid and line of the read image is obtained, and in the case of an image with a large line ratio, the transfer current value is set higher than usual.
This operation will be described with reference to the flowchart of FIG. 7. In step S21, the image information is read from the image memory control unit 22, and the solid / line ratio of the image read in step S22 is obtained by the image determination unit 23. Determine whether.
If the line ratio is large, the process proceeds to step S23, where the controller 100 controls the transfer high-voltage power supply 65 to set the transfer current value higher than normal. For example, the transfer current value is 50 μA in the normal case, and 100 μA in the case where the main scanning direction line is main. In step S24, printing is performed. If the ratio of the main scanning direction line is not large in step S2, the process proceeds to step S24 without changing the transfer current value, and the printing process is performed.
As described above, in the case of an image with a large proportion of lines, by setting a transfer current value higher than usual, it is possible to reliably perform toner charge-up when the transfer paper and the photoreceptor 10 are separated in the line image. Thus, the occurrence of image defects such as image dust in the output image can be suppressed.

1 is a schematic configuration diagram of an image forming apparatus as the best mode for carrying out the present invention. The figure which shows the toner charge amount by the toner charge-up in the main scanning direction line image with a graph. The figure which shows the toner charge amount by the toner charge-up in a solid image with a graph. The figure which shows the toner charge amount by the toner charge-up in a subscanning direction line image with a graph. The flowchart which shows the operation | movement as 1st Embodiment. The flowchart which shows the operation | movement as 2nd Embodiment. The flowchart which shows the operation | movement as 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 2 Charging apparatus, 3 Laser exposure, 5 Registration roller, 6 Transfer means, 7 Developing means, 8 Toner replenishment part, 10 Photoconductor, 20 Image reading means, 21 Paper feed means, 22 Image memory control part, 23 Image determination unit, 24 Address conversion means, 61 Transfer belt, 62 Drive roller, 63 Drive roller, 64 Bias roller, 65 Transfer high voltage power supply, 66 Fixing entrance guide, 71a, 71b Development roller, 72 Development doctor, 73, 74, 75 Stirring member, 81 Toner supply roller, 90 fixing means, 91 cleaning means, 92 brush roller, 93 cleaning blade, 94 static elimination lamp, 100 controller

Claims (5)

Image storage means for storing input image information, image reading means for reading image information from the image storage means, and an image forming area at the time of image formation by converting an address when reading image information from the image storage means An image rotation means for rotating the image data so that the image is rotated at a right angle, and a line for determining whether or not the image information stored in the storage means is mainly a main scanning direction line Based on the direction determination means, a paper feed means having at least two paper feed cassettes capable of separately setting transfer paper of the same size so that the longitudinal directions thereof are perpendicular to each other, and image information read by the image reading means, Image forming means for forming an image on transfer paper fed from the paper feeding means, and control means for controlling an image forming operation by the image forming means,
When the line direction determination unit determines that the image information is mainly a main scanning direction line, the control unit performs image rotation processing by the image rotation unit and feeds the transfer sheet fed by the sheet feeding cassette. In the set state, the longitudinal direction is the same as the longitudinal direction of the image forming area at the time of image formation after image rotation processing, and control is performed so that image formation is performed on a transfer sheet having the same size as the image forming area. An image forming apparatus. Image storage means for storing input image information, image reading means for reading image information from the image storage means, and a ratio of main scanning direction lines and sub-scanning direction lines in the image information stored in the image storage means Line direction determining means, image forming means having transfer means for transferring an image onto transfer paper based on image information read by the image reading means, and control means for controlling an image forming operation by the image forming means With
The image forming apparatus according to claim 1, wherein the control unit controls a transfer current value of the transfer unit in accordance with a ratio of the main scanning direction line and the sub-scanning direction line obtained by the line direction determination unit.   3. The image formation according to claim 2, wherein when the ratio of main scanning direction lines is large in the determination result of the line direction determination unit, the control unit sets the transfer current value of the transfer unit to be higher than normal. apparatus. Image storage means for storing inputted image information, image reading means for reading out image information from the image storage means, and solid / line determination for obtaining a ratio of solid and line of the image in the image information stored in the image storage means And image forming means having transfer means for transferring an image onto a transfer sheet based on image information read by the image reading means, and control means for controlling an image forming operation by the image forming means. ,
The control means controls the transfer current value of the transfer means for transferring the image to the transfer paper according to the ratio of the solid and line of the image obtained by the solid / line determination means. apparatus. 5. The image forming apparatus according to claim 4, wherein the control unit sets the transfer current value of the transfer unit to be higher than normal when the line ratio is large in the determination result of the solid line determination unit.

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