JP2007101817A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a transfer output control means designed such that at least a two tarts of the leading end part of transfer paper and the rest of it can be separately controlled in terms of transfer output, a predetermined transfer output is assigned to the leading end of the transfer paper according to conditions for the transfer paper, and based on a gradation reproduction system selected by a selection means, the rest of the transfer paper is controlled so that a transfer current has a specific value suitable for transfer efficiency. <P>SOLUTION: The image forming apparatus includes a transfer device 2 for transferring a toner image, formed on the image carrier 1, onto transfer paper, and a separation device 3 for separating the transfer paper 7, subjected to the transfer, from the image carrier 1. In the image forming apparatus, a transfer output control means 2 is capable of separately controlling at least the leading end part of the transfer paper and the rest of the transfer paper in terms of transfer output. The predetermined transfer output is assigned to the leading end part of the transfer paper according to conditions for the transfer paper. Based on one of the gradation reproduction systems, selected according to a document type, the rest of the transfer paper is controlled so that the transfer current has the predetermined value suitable for transfer efficiency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus such as a copying machine or a printer that transfers a toner image on an image carrier onto a transfer sheet by a charging device or the like.

Conventionally, in a digital dry electrophotographic machine, it is known that an electrostatic latent image is formed with a minute dot pattern by exposing the charged photoreceptor surface with image data by an LED array or laser as a writing method. (For example, refer to Patent Documents 1 and 2).
In such a digital dry electrophotographic machine, the gradation of the image is expressed by the density of the minute dot pattern density, but in order to reproduce the gradation more faithfully, there are a plurality of recommended options for gradation reproduction. Thus, the operator can select from the operation unit.
JP 2002-323801 A JP 2002-214922 A

However, even if the toner image is accurately reproduced on the photosensitive drum by the gradation reproduction method, a high-quality image cannot be obtained unless it can be accurately transferred onto the transfer paper. Since the transfer is generally performed by bringing the photosensitive drum and the transfer paper into close contact with each other and further attracting and transferring the toner, there is also a problem that the transfer state changes depending on the amount of toner.
In addition, in the case of a gradation pattern with a low toner fine spot density on the photosensitive drum, if the transfer output is too strong, the toner is attracted before the transfer paper comes into close contact with the photosensitive drum, and the image is scattered. There is a problem that the toner is reversely charged and retransferred to the photosensitive drum.
In addition, depending on the transfer paper transport method, the end of the transfer paper is a free end, and because of its large behavior, it cannot be adhered to the photosensitive drum and is not transferred. is there.
Accordingly, an object of the present invention is to allow transfer output control by dividing the transfer paper leading end portion and the subsequent portion into at least two parts in consideration of the above-described situation, and the transfer paper leading end portion is a transfer paper. Image formation is provided with transfer output control means for controlling the transfer current to a predetermined value that increases transfer efficiency according to one gradation reproduction method selected by the selection means after that, depending on the paper conditions. To provide an apparatus.

In order to solve the above problems, the invention described in claim 1 separates the transfer device for transferring the toner image formed on the image carrier onto the transfer paper and the transferred transfer paper from the image carrier. In the image forming apparatus including the separating device, the transfer output control means sets the transfer output for the transfer paper leading end to a value corresponding to the transfer paper condition, and outputs the transfer output for the transfer paper after the leading end to the original. The transfer current is controlled to a predetermined value with high transfer efficiency according to one gradation reproduction method selected according to the type.
According to a second aspect of the present invention, in the first aspect, the separation device can perform separation output control by dividing the transfer paper leading end portion and the subsequent transfer paper portion into at least two parts, and the transfer paper leading end. The separation output for the part is a predetermined separation output according to the separation characteristics of the transfer paper, and the output for the transfer paper part after the leading edge is controlled to a separation output value with less image noise according to the selection of the gradation reproduction method. It is characterized by performing.
According to a third aspect of the present invention, in the second aspect of the present invention, the separation output is performed by simultaneously performing two types of output by a static elimination method using an AC corona output and a forced separation of a DC corona output having a polarity opposite to that of transfer. Regardless of the position of the transfer paper, the corona output always outputs a constant value and is controlled only by the DC corona output.

  According to the present invention, the transfer output control means prevents the transfer failure at the front end of the transfer paper by controlling the transfer output value at the front end of the transfer paper according to the conditions specific to the transfer paper. In addition, when one of a plurality of gradation reproduction methods is selected according to the type of the original, the transfer output is controlled so that the optimum condition corresponding to the selected one is selected for the portion after the leading edge of the transfer paper. The transfer paper is securely adhered to the photoreceptor, and a good image with little image dust and blur can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus. In FIG. 1, the role of the transfer / separation apparatus will be described along the entire flow.
The image forming apparatus in FIG. 1 uniformly charges the surface of the image carrier (photosensitive drum) 1 and selection means (not shown) for selecting one from a plurality of gradation reproduction methods according to the type of document. A charging unit (charging device) 4 and an exposure unit (exposure device) 5 that exposes the surface of the charged photosensitive drum 1 according to image data to form an electrostatic latent image with a minute dot pattern are provided.
Further, the image forming apparatus includes a developing unit (developing apparatus) 6 that develops a toner image by attaching toner (not shown) to the electrostatic latent image, and a transfer sheet 7 that transfers the toner image formed on the photosensitive drum 1. And a separating device 3 for separating the transferred transfer paper 7 from the photosensitive drum 1.
A toner image is formed on the surface of the photosensitive drum 1 serving as an image carrier by a known copying process, that is, charging, exposure, and development steps. For this image formation, a charging device 4, an exposure device 5, and a developing device 6 are arranged around the photosensitive drum 1.
The toner image formed on the photosensitive drum 1 is transferred onto the transfer paper 7 conveyed by a conveyance roller (not shown) by the transfer device 2, and the transfer paper 7 onto which the toner image has been transferred is photosensitive by the separation device 3. It is separated from the body drum 1 and sent to the conveying section and to the fixing device 10.
At this time, the transfer residual toner remaining on the photosensitive drum 1 is completely removed by the cleaning device 8. The electrical characteristics of the photosensitive drum 1 are restored to the original state by the charge removal value 9. This is repeated to obtain an image record.

FIG. 2 is a schematic perspective view showing the component configuration of the transfer / separation charger unit together with an enlarged portion. In FIG. 2, the transfer / separation charger unit includes a casing 13, a transfer corona wire 11, a separation corona wire 12, an end block 14, a guide (paper) 15, and a cover (end block) 16.
When a high voltage is applied to the corona wires 11 and 12, since the curvature of the corona wires 11 and 12 is large, the air in this portion is locally ionized with the casing 13 connected to the ground as a counter electrode, and a corona discharge phenomenon occurs. To do.
FIG. 3 is a schematic view showing the principle of the electrostatic transfer method. With reference to FIG. 3, the process in the transfer step will be described in detail next. The principle of the electrostatic transfer type transfer charger (transfer device) 2 is based on the fact that when positive corona discharge is performed from the back surface of the transfer paper (transfer body) 7, the transfer paper 7 is positively charged. The transfer charger 2 includes transfer output control means 21 schematically indicated by a block.
This charge induces an opposite negative charge on the aluminum base 1 of the photosensitive drum. As a result, the transfer paper 7 comes into close contact with the photosensitive drum 1. Next, due to the electric field generated between the transfer paper 7 and the photosensitive drum 1, the toner 17 overcomes the adhesive force with the photosensitive drum 1 and moves to the transfer paper 7 side.

FIG. 4 is a schematic diagram for explaining the principle in the separation step. Next, the process in the separation step will be described in detail. In the transfer process, the transfer paper 7 is in close contact with the photosensitive drum 1 and is very difficult to peel off. Accordingly, the charge is removed from the back surface of the transfer paper 7 by the separation charger (separation device) 3 to remove the attractive force between the photosensitive drum 1 and the transfer paper 7.
At this time, if the separation charger 3 is too weak, the transfer paper 7 cannot be completely discharged, so that separation jam is easily caused. If it is too strong, the charge of the transfer paper 7 is lost and the toner 17 cannot be attracted onto the transfer paper 7. In addition, the toner 17 is retransferred to the photosensitive drum 1 side, and a phenomenon that the image becomes thin occurs. For this purpose, the separation charger 3 includes a separation output control means 31.
FIG. 5 is a graph showing the relationship between transfer current and transfer efficiency. 3 and 5, in the transfer charger (transfer device) 2, if the corona discharge is weak, the charge of the transfer paper 7 decreases, so that the adhesion between the transfer paper 7 and the photosensitive drum 1 becomes weak, and the toner Since the power to absorb 17 is also weakened, the image becomes thin.
On the other hand, if it is too strong, the transfer paper 7 just approaches the photosensitive drum 1 and the toner 17 jumps to the transfer paper 7 and the image is distorted or the toner 17 is reversely charged and the image becomes thin. Become.
Further, the transfer efficiency varies depending on the amount of toner between the transfer paper 7 and the photosensitive drum 1, and therefore optimum control for each condition must be performed. However, at the leading edge of the transfer paper, the adhesion to the photosensitive drum 1 varies depending on the paper type.

FIG. 6 is a schematic diagram for explaining the entry of the leading edge of the transfer paper into the periphery of the photosensitive drum. As shown in FIG. 6, non-transfer due to poor adhesion tends to occur at the leading edge of the transfer paper. Therefore, the transfer control at the tip portion must be performed with priority given to close contact with the photosensitive drum 1.
For this reason, for example, in an apparatus with a linear velocity of 60 mm / sec, the transfer paper tip portion 8 mm has a drum (photosensitive member) current value of 60 ± 10 μA transfer output, and after the tip of the gradation portion, 50 ± 10 μA. To do.
As described above, in the transfer charger (transfer device) 2 of FIG. 3, the transfer output control means 21 controls the transfer output to be different between the leading end portion of the transfer paper and the two portions after the leading end. In this case, since the transfer paper 7 is fed after being timed by a registration roller (not shown), the passage of the front end portion of the transfer paper 7 is detected by the setting of the detection sensor 20 schematically shown in FIG. Can do.
In other words, the transfer output control means 21 sets the transfer output for the leading edge of the transfer paper to a value corresponding to the transfer paper condition, and selects the transfer output for the transfer paper portion after the leading edge according to the type of document. In accordance with the tone reproduction method, the transfer current is controlled to a predetermined value with high transfer efficiency.

FIG. 7 is a schematic diagram for explaining a close contact state between the transfer paper front end portion and the photosensitive drum. FIG. 8 is a schematic diagram for explaining the separation state of the transfer paper front end portion from the photosensitive drum in comparison with the front end portion and the subsequent portions. Since the leading end of the transfer paper 7 is a free end, once it comes into close contact with the photosensitive drum 1, it is difficult to separate along the curved surface of the photosensitive drum 1.
After the leading edge, it is easy to separate the curved surface of the photosensitive drum 1 by the stiffness of the paper and its own weight. In accordance with this situation, the separated output is controlled by the separated output control means 31 (FIG. 4). By controlling the separation output at the leading edge of the transfer paper according to the conditions specific to the transfer paper, separation failure can be prevented.
In addition, when one of a plurality of gradation reproduction methods is selected after the leading edge of the transfer paper according to the type of the original, the separation output is controlled so that the optimum condition corresponding to the selected one is selected, so that noise in the separation action can be obtained. A good quality image with less image quality can be obtained.
Furthermore, the separation characteristics vary depending on the paper type, and an appropriate separation output setting is required depending on the stiffness and the resistance value. Further, if the separation output is too high, there is a problem that the toner is not transferred to the transfer paper and is retransferred to the photosensitive drum.
In order to solve such a problem, the output is controlled to be low after the leading edge, and the optimum control condition with less noise adapted to the gradation is controlled. In other words, the separation apparatus can control the separation output by separating the output into at least two of the leading end portion of the transfer paper 7 and the subsequent portion by the separation output control means 31.

At this time, it is more effective and easier to control by DC having a polarity opposite to that of transfer having a higher separation effect than by controlling by AC for static elimination. With the AC corona output, stable neutralization separation is always performed regardless of the position of the transfer paper, and forcible separation is performed with the DC corona output at the leading edge of the transfer paper that is difficult to separate.
Further, in other image priority portions, the DC output is controlled to be low in order to prevent toner retransfer due to forced separation. In the transfer output control device that controls the transfer output, the transfer output value at the front end of the transfer paper is controlled according to the conditions specific to the transfer paper, thereby preventing transfer failure at the front end of the transfer paper.
Further, after the leading edge of the transfer paper, if one is selected from a plurality of gradation reproduction methods according to the type of the original, the transfer output is controlled so that the optimum condition corresponding to the selected one is selected, thereby reducing the image dust. Good images with less blur and blur can be obtained.

1 is a schematic diagram illustrating a configuration of an image forming apparatus. It is a schematic perspective view which shows the components structure of a transcription | transfer / separation charger unit with an enlarged part. It is the schematic which shows the principle of an electrostatic transfer system. It is the schematic explaining the principle in a separation process. It is a figure which shows the relationship between transfer current and transfer efficiency with a graph. FIG. 6 is a schematic diagram for explaining the entrance of a transfer paper tip into the periphery of a photosensitive drum. FIG. 6 is a schematic diagram illustrating a close contact state between a transfer paper front end portion and a photosensitive drum. FIG. 7 is a schematic diagram for explaining a separation state of a transfer paper front end portion from a photosensitive drum in comparison with a portion after the front end portion.

Explanation of symbols

1 Image carrier (photosensitive drum)
2 Transfer device (transfer charger)
3 Separation device (separation charger)
4 Charging means (charging device)
7 Transfer paper 21 Transfer output control means 31 Separation output control means

Claims (3)

  In the image forming apparatus including the transfer device for transferring the toner image formed on the image carrier to the transfer paper and the separation device for separating the transferred transfer paper from the image carrier, the transfer output control means is The transfer output with respect to the transfer paper leading edge is set to a value according to the transfer paper condition, and the transfer output with respect to the transfer paper portion after the leading edge is set according to one gradation reproduction method selected according to the type of the document, An image forming apparatus, wherein the transfer current is controlled to a predetermined value with high transfer efficiency.   The separation device can perform separation output control by dividing the transfer paper front end portion and the subsequent transfer paper portion into at least two or more, and the separation output for the transfer paper front end portion is based on the separation characteristics of the transfer paper. 2. The output according to claim 1, wherein the output to the transfer paper portion after the leading edge is controlled to a separation output value with less image noise according to the selection of the gradation reproduction method. Image forming apparatus.   As the separation output, two types of output are performed simultaneously by a static elimination method using an AC corona output and a forced separation of a DC corona output having a polarity opposite to that of the transfer. The AC corona output is always a constant value regardless of the position of the transfer paper. The image forming apparatus according to claim 2, wherein control is performed only by the DC corona output.

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