JPH1097107A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of transfer defect on a transfer tip part of the rear side at the both-side copying time with a very simple constitution. SOLUTION: In this image forming device capable of transfer-fixing a toner image formed on an intermediate transfer belt onto the rear side of a transfer paper 10 too, after transfer-fixing the toner image onto the front side of the transfer paper, the image tip missing on the rear side derived from curling caused at the time of copying the front side is prevented by making the image missing width in the tip on the front side of the transfer paper, and the image missing width in the tip on the rear side of the transfer paper, possible to be severally independently set.

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 capable of transferring an image to both sides of a transfer sheet.

[0002]

2. Description of the Related Art With the spread of color copying machines, image forming apparatuses represented by copying machines require low-cost machines, and the need for double-sided copying as well as monochrome or monochrome copying machines is increasing. The transfer method of a color copying machine is a method in which recording paper is wound around a transfer drum and images of each color are directly transferred to transfer paper. The images of each color are sequentially transferred to an intermediate transfer body, and then the image of the intermediate transfer body is transferred to a transfer paper. A typical method is to collectively transfer the images. Among them, the advantage of the latter method using the intermediate transfer member is that the paper transfer property is high. As a transfer method to transfer paper in the method using the intermediate transfer body, there are a corona charge method, a roller transfer method, and the like. The corona charge method has a merit of lower cost than the roller transfer method, and is widely used. .

On the other hand, in double-sided copying, after a toner image is transferred onto the surface of a transfer sheet, the image is fixed by a fixing device, and the image is temporarily stacked on a reversing tray. The reversing tray changes the surface of the transfer paper so that the back surface is in contact with the intermediate transfer member, and transfers and fixes the toner image on the back surface. In the two-sided copy mode, if there is a solid image on the surface of the transfer paper, the transfer paper may be deformed, that is, curled, due to the difference in the heat shrinkage between the transfer paper and the fixed toner. In particular, in the case of a color copy, toner of four colors is applied and the amount of adhesion is large, so that the toner is easily curled. The curl direction is a face curl in which the image surface is inward and curls, and when this is copied on the back side of the transfer paper, it becomes a back curl. Copies are charged by corona discharge immediately after the transfer paper is brought into contact with the transfer belt, and are brought into close contact with the transfer belt. It may be defective, and the leading end may be defective in transfer. Therefore, for example, JP-A-7-128938 and JP-A-8-1015
As can be seen in Japanese Patent Publication No. 35, a mechanism for mechanically correcting curl has been proposed.

[0004]

However, since the conventional curl correcting mechanism performs double-sided copying, there is a disadvantage that a transfer paper reversing device for reversing the transfer paper copied on the surface is complicated.

The present invention has been made in view of such circumstances of the prior art, and a first object of the present invention is to prevent a transfer failure at the transfer front end portion on the back surface in the case of double-sided copy with an extremely simple configuration. Is to prevent it.

A second object of the present invention is to make it possible to separately set the image missing area at the leading edge and the trailing edge of the transfer paper in color copying or monochrome copying in double-sided copying, and to set an appropriate image missing width depending on the type of copy. Is to form.

A third object of the present invention is to provide an image forming apparatus provided with an image carrier having stable transferability.

[0008]

In order to achieve the first object, the first means is to transfer and fix a toner image formed on an image carrier to a first surface of a transfer material, and then fix the toner image. In an image forming apparatus capable of transferring and fixing a toner image also on a second surface of a transfer material, an image notch width at a front end on the first surface of the transfer material and an image notch width at a front end on the second surface of the transfer material are determined. There is a means for setting each independently.

In order to achieve the first object, the second means may be configured such that the image chipping width at the tip of the second surface of the transfer material in the first means is determined by the image chipping at the tip of the first surface of the transfer material. Set wider than width.

In order to achieve the first object, the third means is to transfer the toner image formed on the image carrier to the first material of the transfer material.
A single-sided mode in which the toner image is fixed on the first surface by the single-sided mode in which the toner image is fixed on the first surface by the single-sided mode, and the stacked transfer papers are fed to the image carrier again. An image forming apparatus capable of switching to an automatic double-sided mode for transferring and fixing the toner image formed on the image bearing member to the second surface thereof, the image forming apparatus comprising: Means are provided for independently setting the image chipping width and the image chipping width at the rear end of the first surface of the transfer material in the single-sided mode.

In order to achieve the first object, the fourth means is the third means, wherein the width of the image notch at the rear end of the first surface of the transfer material in the automatic double-sided mode is set to the one-sided mode. The width is set to be wider than the image chipping width at the rear end of the first surface of the transfer material.

In order to achieve the first object, the fifth means is to transfer the toner image formed on the image carrier to the first material of the transfer material.
A single-sided mode in which the toner image is fixed on the first surface by the single-sided mode in which the toner image is fixed on the first surface by the single-sided mode, and the stacked transfer papers are fed to the image carrier again. An image forming apparatus capable of switching to an automatic double-sided mode for transferring and fixing the toner image formed on the image bearing member to the second surface thereof, the image forming apparatus comprising: The image chipping width was set larger than that in the single-sided mode, and the image chipping width at the tip of the second surface was set larger than the image chipping width at the tip of the first surface.

In order to achieve the second object, the sixth means is the image processing apparatus according to the second or fourth means, wherein the image forming apparatus has a monochrome mode and a color mode, and the image lacking width is in the monochrome mode. And color mode can be set separately.

In order to achieve the first object, the seventh means is the sixth means, wherein the image missing width in the color mode is set to be larger than the image missing width in the monochrome mode.

In order to achieve the third object, an eighth means comprises the image carrier in the first to seventh means,
An intermediate transfer member made of a medium resistance material was used.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. First, the overall configuration of the image forming apparatus will be described with reference to FIGS. In this embodiment, a color electrostatic image forming apparatus is taken as an example. FIG. 6 is a schematic diagram for explaining the entire configuration of the image forming apparatus, FIG. 7 is a schematic diagram for explaining the relationship between the intermediate transfer belt and the photoconductor, and FIG. 8 shows the structure of the main part of the reversing tray. It is sectional drawing.

At the top of the color electrostatic image forming apparatus, there is provided a color scanner 200 for reading a document image after separating it into colors and converting it into color image data as electrical signals. The color scanner 200 is a contact glass 2
02 on an illumination lamp 20 (not shown).
4. An image is formed on the color sensor 210 via the mirror group 206 and the lens 208, and the color image information of the original is
For example, the image data is read for each color separation light of blue (B), green (G) and red (R), and is converted into an electric image signal. In this example, the color sensor 210 includes blue, green, and red color separation means and a photoelectric conversion element such as a CCD, and performs simultaneous reading of three colors. The color scanner 200 includes an image processing control unit (not shown) including a CPU and a ROM storing operation programs and the like. The image processing control unit includes the blue, green, Color conversion processing is performed based on the intensity level of the red color separation image signal to obtain black (Bk), cyan (C), magenta (M), and yellow (Y) color image data.

The color image data obtained in this manner is written by a writing optical unit 400 described below.
Visualization of black, cyan, magenta and yellow is performed to obtain a final color copy. The operation method of the color scanner 200 for obtaining the image data of black, cyan, magenta and yellow is such that the operation of the writing optical unit 400 is synchronized with the operation of the writing optical unit 400 by receiving a scanner start signal from the image processing control unit. FIG.
In, the illumination / mirror optical system scans the document in the direction of the left arrow, and obtains one color image data for each scan. By repeating this operation four times in total, image data of four colors is sequentially obtained. Each time, the writing optical unit 40
While the images are sequentially visualized at 0, they are superimposed to form a four-color full-color image.

The writing optical unit 400 includes a photosensitive member 402 serving as an image carrier for forming an electrostatic latent image, a laser light emitting unit 404 including a laser diode and the like, a light emission drive control unit (not shown), and a polygon mirror 406. And a rotation motor 408, an f / θ lens 410, a reflection mirror 412, and the like. Although not shown, the writing optical unit 400 is also provided with an image forming control means constituted by a CPU and a ROM storing the operation program and the like.

The photosensitive member 402 rotates counterclockwise as shown by the arrow. Around the photoconductor cleaning unit 414, a neutralization lamp 416, a charger 418, a potential sensor 420, and a rotary developing device 422 as a developing unit.
Of the developing devices (the developing device 43 in the example of FIG. 6).
8), a development density pattern detector 424, an intermediate transfer belt 426 as an intermediate transfer medium, and the like are arranged. The intermediate transfer belt 426 has a volume resistivity of 1 × 10 ⁸ to 10 ¹² Ω.
Cm, surface resistivity 1 × 10 ⁸ -10 ¹¹ Ω (JISK6
911), a medium resistance belt, ethylene tetrafluoroethylene (ETFE), epichlorohydrin rubber or the like is used. The intermediate transfer belt 426 may be formed in a drum shape instead of a belt shape. The reason why the volume resistance of the intermediate transfer belt 426 is set to 10 ¹² Ω · cm or less is that if the volume resistance is higher than that, the optimal range of the transfer current is narrowed. This is because an excessively transferred image is obtained without being obtained. When the volume resistance of the intermediate transfer belt 426 increases,
Since the charge having the opposite polarity to the charge injected into the transfer paper does not flow into the intermediate transfer belt 426 from the ground, the adhesion between the intermediate transfer belt 426 and the transfer paper is weakened, and the optimum transfer current area is narrowed. Become. Therefore, the transfer resistance is stabilized by setting the volume resistance of the intermediate transfer belt 426 to 10 ¹² Ω · cm or less.

The rotary developing device 422 includes a developing device 428 for black, a developing device 430 for cyan, and a developing device 4 for magenta.
32, a yellow developing unit 434, and a rotation drive unit (not shown) for rotating each of these developing units. Each developing device includes a developing sleeve that rotates by contacting the ears of the developer with the surface of the photoconductor 402 to visualize the electrostatic latent image, and a developing sleeve that rotates to pump and agitate the developer. It is composed of battles.

In the standby state, the rotary developing device 422
When the copying operation is started by the above-described image forming control means, the reading of the black image data is started at a predetermined timing by the color scanner 200, and a laser beam is read based on the image data. Optical writing by light and latent image formation begin.
(Hereinafter, an electrostatic latent image based on black image data is referred to as a black latent image. The same applies to cyan, magenta, and yellow.) In order to develop from the leading end of this black latent image, the developing unit 428 for black develops the image. Before the leading end of the latent image reaches the position, the rotation of the developing sleeve is started to develop the black latent image with black toner. Thereafter, the developing operation of the black latent image area is continued. When the rear end of the latent image has passed the black position, the rotary developing device 422 is quickly moved from the black developing position to the next color developing position. Rotates. The rotation operation of the rotary developing device 422 is also controlled by the image forming control unit, and the operation is completed at least before the leading end of the latent image based on the next image data arrives.

When the image forming cycle is started, first, the photosensitive member 402 rotates counterclockwise as indicated by an arrow, and the intermediate transfer belt 426 is rotated clockwise by a drive motor (not shown). Intermediate transfer belt 426
, A black toner image formation, a cyan toner image formation, a magenta toner image formation, and a yellow toner image formation are performed, and finally black, cyan, magenta, and yellow are superimposed on the intermediate transfer belt 426 in this order. And a toner image is formed.

Here, in order to reduce the time required to align the leading edge of the image when forming a superimposed toner image as described above, the support roller of the intermediate transfer belt 426 is moved, as shown in FIG. As shown by the two-dot chain line, the intermediate transfer belt 426 is separated from the photoconductor 402, and under this separated state, the intermediate transfer belt 426 is rapidly fed.

First, a black image is formed as follows. The charger 418 as a charging unit uniformly charges the photoconductor 402 with negative charges to about -700 V by corona discharge (charging step). Subsequently, the laser diode of the laser emitting means 404 performs raster exposure based on the black signal (exposure step). As described above, when the raster exposure is performed, the exposed portion of the photoconductor 402 that is initially uniformly charged loses the charge proportional to the amount of exposure light, and an electrostatic latent image is formed.

The toner in the rotary developing device 422 is negatively charged by stirring with the ferrite carrier, and the black developing sleeve of the rotary developing device 422 is shown in FIG. A bias of a potential in which a negative direct current potential and an alternating current are superimposed is applied by a power supply unit that does not.

As a result, no toner adheres to the portion of the photoconductor 402 where the charge remains, and the black toner is adsorbed to the portion having no charge, that is, the exposed portion. A visual image is formed (development step).

The intermediate transfer belt 426 is connected to the drive roller 44
4, transfer opposed roller 446, cleaning opposed roller 4
48, and is stretched around a driven roller group, and is driven and controlled by a drive motor (not shown) and the image forming control means.

The black toner image formed on the photoconductor 402 is transferred to the surface of the intermediate transfer belt 426 which is driven at a constant speed in contact with the photoconductor 402 by a belt corona discharger 450 as a primary transfer unit. (Primary transfer step, hereinafter, transfer of the toner image from the photoconductor 402 to the intermediate transfer belt 426 is referred to as primary transfer). The discharge efficiency (distribution ratio) of the belt corona discharger 450 is about 15 to 30%.

A small amount of untransferred residual toner present on the photoconductor 402 is cleaned by the photoconductor cleaning unit 414 in preparation for reuse of the next color of the photoconductor 402. The collected toner is stored in a waste toner tank (both not shown) via a collection pipe.

On the intermediate transfer belt 426, black, cyan, magenta, and yellow toner images sequentially formed on the photosensitive member 402 are accurately and sequentially aligned.
A four-color superimposed belt transfer image is thus formed, and thereafter,
Using a transfer corona discharger 454 as a secondary transfer means, batch transfer is performed on transfer paper as a recording medium (secondary transfer step).

On the photoconductor 402 side, the process proceeds to the cyan process after the black process. At a predetermined timing, the reading of cyan image data by the color scanner 200 starts, and the cyan latent image is written by laser light writing based on the image data. Image formation is performed.

The cyan developing device 430 is moved to the developing position after the rear end of the previous black development passes and
Rotary developing device 422 before the leading end of the cyan latent image arrives
Is performed to visualize the cyan latent image with cyan toner. Thereafter, the development in the cyan development area is continued, but when the rear end of the latent image passes, the black developing device 428
The rotation operation of the cyan developing unit is performed in the same manner as in the case of.
This is also completed before the leading end of the magenta latent image arrives.

In the magenta and yellow processes, the operations of reading the image data, forming the latent image, and developing are the same as those in the above-described black and cyan processes, and thus the description thereof is omitted.

Corona discharger 454 as secondary transfer means
Applies a DC or AC + DC component by a corona discharge method to transfer the overlapping toner image on the intermediate transfer belt 426 onto a recording medium. The distribution ratio is about 15 to 30%, which is the same as that of the belt corona discharger 450.

In a paper supply bank 456 located below the writing optical unit 400, three transfer paper cassettes 4 are provided.
58, 460 and 462 are provided. Transfer papers of different sizes are accommodated in these cassettes. Of these, from the accommodation cassette of the designated (selected) size paper, the writing optical unit 40 is fed by the paper feed roller 466.
The sheet is fed and conveyed in the direction of the registration roller of No. 0. Reference numeral 468 in the figure denotes a manual paper feed tray for OHP paper, thick paper, and the like.

At the time when image formation is started, the transfer paper is fed from the paper feed port of any of the above-mentioned cassettes, and waits at the nip portion of the pair of registration rollers 470. Then, when the leading end of the toner image on the intermediate transfer belt 426 approaches the corona discharger 454, the registration roller pair 470 is positioned so that the leading end of the image is located at a position shifted by a predetermined length from the leading end of the transfer paper. Drive control is performed by paper feed control means (not shown), and image registration is performed at a predetermined position on the transfer paper. The paper feed control means controls the drive of the transfer paper conveyance means such as the registration roller pair 470 in order to convey the transfer paper at a predetermined timing. Similar to the above-described image processing control means and image formation control means, the CPU and its CPU are provided. It is composed of a ROM or the like in which an operation program and the like are stored.

In this way, the transfer paper is superimposed on the intermediate transfer belt 426 and passes over the corona discharger 454 connected to the positive potential. At this time, the transfer paper is charged with a positive charge by the corona discharge current, and a substantial part of the toner image is transferred onto the transfer paper. Subsequently, when passing through a portion of a corona discharger 454 on a left side in FIG. 6 of a not-shown discharging brush, the transfer paper is discharged, separated from the intermediate transfer belt 426 and moved to the paper transport belt 472.

The transfer paper on which the four-color superimposed toner images are collectively transferred from the intermediate transfer belt 426 is conveyed to a fixing device 474 by a paper conveyance belt 472, and is transferred between a fixing roller 476 and a pressure roller 478 controlled to a predetermined temperature. The toner image is melted and fixed in the nip portion, sent out of the apparatus by a discharge roller pair 480, stacked face up on a copy tray (not shown), and a full-color copy can be obtained on one side of the transfer paper.

After the image has been transferred to the intermediate transfer belt 426, the surface of the photoconductor 402 is cleaned by a photoconductor cleaning unit 414 including a brush roller and a rubber blade, and is uniformly discharged by a discharge lamp 416.

The surface of the intermediate transfer belt 426 after the transfer of the toner image to the transfer paper is cleaned by pressing the blade again by the blade contacting / separating mechanism in the cleaning device 542.

In the case of a repeat copy, the operation of the color scanner 200 and the image formation on the photosensitive member 402 are performed after the first image process, and the process proceeds to the second first color image process at a predetermined timing. become. In the intermediate transfer belt 426, the second black toner image is primarily transferred to the surface area cleaned by the cleaning device 452 following the batch transfer step of the first four-color superimposed image onto the transfer paper. Is done. Thereafter, the same operation as that of the first sheet described above is performed.

The above is an explanation for obtaining a four-color full-color copy on one side of the transfer paper.
In the case of the color copy mode, the same operation as described above is performed for the designated color and the number of times.

In the case of the single-color copy mode, until the predetermined number of sheets is completed, only the developing device of the predetermined color of the rotary developing device 422 is in the developing operation state, that is, the developing position of the predetermined color is set to the cleaning device. The copying operation is continuously performed in a state where the blade 452 is kept pressed against the intermediate transfer belt 426.

Furthermore, the longest size A3
Next, a case where full-color copying is performed on transfer paper of a size will be described. One color image is formed each time the intermediate transfer belt 426 makes one rotation, and the four-color image formation is completed when the intermediate transfer belt 426 rotates four times. However, if the peripheral length of the intermediate transfer belt 426 is shortened to the maximum size as much as possible, there is a problem that, in the copying operation of the maximum size, there is no time to return to the scanner. On the other hand, the intermediate transfer belt 4 is supposed to perform a copying operation at a maximum size that is not frequently used such as an A3 size.
If the size 26 is taken, there arises a problem that, in the case of a copy of A4 or B5 size frequently used which is smaller than the size, a waste time not contributing to the work increases. Therefore, in the case of A3 size copy, the intermediate transfer belt 4
It is configured so that one operation is performed during the two rounds of 26.
That is, after the black toner image is transferred to the intermediate transfer belt 426, the rotation is performed without performing the development and transfer in the next one rotation, and the development and primary transfer are performed in the next one rotation.

On the other hand, when copying is also performed on the back surface of the transfer paper, the transfer paper having the toner image fused and fixed on the front surface in the fixing device 474 is temporarily stacked on the reversing tray 500 provided in the writing optical unit 400. For this reason, a branch claw unit 482 is provided between the fixing device 474 and the discharge roller pair 480, and the transfer paper is sent to the discharge roller pair 480 side by the branch claw unit 482,
I send it to the side. That is, the branching pawl unit 482 switches to transfer the transfer paper on which the one-sided copy has been completed in the one-sided copy mode and the transfer paper on which the double-sided copy has been completed in the double-sided copy mode to the discharge roller pair 480 side. In the case of the double-sided copy mode, switching is performed so that the transfer sheet on which single-sided copying has been completed is sent to the reversing tray 500 side. These switching controls are performed by the above-described sheet feeding control means.

As shown in FIG. 8, a transport path 502 for transporting the transfer paper guided by the branching claw means 482 is provided above the reversing tray 500, and transport paths provided at two locations on the transport path 502 are provided. It has a pair of rollers 504, a paper input detection sensor 506 provided on the entrance side of the transport path 502 for detecting the intrusion of the transfer paper, and an inversion detection sensor 508 for detecting that the transfer paper is inverted and sent out. . A feed roller 510 for stacking transfer paper in the reversing tray 500 and sending the stacked transfer paper to the nip portion of the registration roller pair 470 again is provided at the exit side of the transport path 502. This feed roller 51
Numeral 0 is supported on the reversing tray 500 by a reversible step motor (not shown) so as to be able to rotate forward and backward. Reversing tray 50
A stack portion 512 for stacking transfer paper on which one side is copied is formed at a lower portion of the stacking portion 0. One end of the stack portion 512 is provided so that the outer peripheral surface of the feed roller 510 and the outer peripheral surface thereof are in contact with each other. Separated separation roller 514,
When the transfer paper stacked in the stack portion 512 is sent out to the nip portion between the feed roller 510 and the separation roller 514, a bottom plate 516 provided to rise, a paper end detection sensor 518 for detecting an end portion of the transfer paper, and a stack portion 512 And a side fence HP detection sensor 522 for detecting the position of the side fence 520. When the feed roller 510 rotates clockwise, the separation roller 514 rotates in a counterclockwise direction, and when the feed roller 510 rotates in the counterclockwise direction, the one-way clutch 514 prevents rotation. (Not shown) is attached. A retractable end fence 524 for aligning the rear end of the transfer sheet and an end fence HP detection sensor 526 for detecting the state of the end fence 524 are provided on the rear end side of the stack portion 512.

At one end of the upper portion of the reversing tray 500, there is provided a switching claw 528 for switching the transfer paper transported on the transport path 502 so as to be stacked on the stack portion 512. Reference numeral 530 denotes a grip transport roller pair for transporting the transfer paper to the nip portion of the transport roller pair 504.

On this reversing tray 500, the transfer paper copied on one side is sent from the direction shown by the arrow in FIG. This transfer paper is transported by a transport roller pair 504 to a transport path 5.
02 is conveyed, and the transfer paper is lowered by the switching claw 528 rising so that the transfer paper is not sent to the grip conveyance roller pair 300, and is sent to the nip portion between the feed roller 510 and the separation roller 514. At this time, the feed roller 510
Is rotated clockwise, whereby the transfer paper passes through the space between the feed roller 510 and the separation roller 514 and is stacked on the stack portion 512. The transfer papers stacked in the stacking section 512 are positioned such that the upper surface, that is, the already copied surface, faces upward. The bottom plate 516
Is falling. When re-feeding the transfer paper to the nip portion of the registration roller pair 470 in order to copy the back surface of the transfer paper stacked in the stack unit 512 in this manner, the bottom plate 516 is raised and the feed roller 510 is fed. Is rotated counterclockwise. At this time, the separation roller 514 does not rotate clockwise in conjunction with the one-way clutch. Accordingly, the transfer paper is sent by the feed roller 510 to the grip conveyance roller pair 530, discharged as indicated by the dotted arrow, and conveyed to the nip portion of the registration roller pair 470. The separation roller 5
Numeral 14 is stopped and functions to separate and feed the transfer paper one by one based on the principle of the friction pad. The rotation direction of the feed roller 510, the vertical movement of the bottom plate 516, and the switching of the switching claw 528 are controlled in a predetermined sequence by the above-described sheet feeding control means.

The copy on the back side of the transfer paper is performed through a charging step, an exposure step, a development step, a primary transfer step, and a secondary transfer step in the same manner as the above-described front side copy, and the transfer paper copied on both sides is discharged. Branch claw means 482 switched to the side
Through the discharge roller pair 480 to the outside of the machine.

In the case of double-sided copying using the manual paper feed tray 468, the transfer paper sent to the outside from the discharge roller pair 480 after one-sided copying has been completed is manually fed with its back side up. It is inserted into the tray 468 and the back side is copied. At this time, when the operator presses a back surface designation key on an operation panel (not shown), the machine can check the back surface.

As described above, when two-sided copying is performed automatically or manually, particularly when a color is formed on the surface,
Since a large amount of toner adheres to the surface, the surface is easily curled.
This is because the transfer paper that has passed through the fixing device 476 has a different heat shrinkage rate between the toner and the paper. Here, the setting of the image missing width will be described with reference to FIGS. FIG. 3 is a diagram for explaining the state of the transfer paper that has been copied on one side, FIG. 4 is a table showing the relationship between the screen width on the front side of the transfer paper and the screen width on the back side, and FIG. 6 is a table showing set values of image missing widths of FIG.

That is, as shown in FIG. 3, the transfer paper 10 on which the color copy is made on the front surface curls the toner image 11, that is, the front surface side due to heat shrinkage at the time of fixing, the face curls on the front side, and the back side on the back side. It becomes curl. The transfer paper 10 has the end 12 at the front end when the front side copy is performed, but when copying onto the back side, the transfer paper 10 is temporarily stacked on the reversing tray 500 and pulled out again therefrom. Part 13
Is the tip. As described above, the front end of the back surface of the transfer paper 10 corresponds to the rear end of the front surface, so that the toner image is not applied to this portion, or the front end position of the toner image is shifted to the center of the transfer paper 10 at all. Let it. Therefore, the curl state was observed by changing the image chipping width formed at the rear end of the front surface of the transfer paper 10 and the image chipping width generated at the front end of the back surface during color copying. The results are shown in the chart of FIG. In this chart, x indicates that the transfer loss at the front end of the back surface is large, Δ indicates that some transfer omission occurs at the back end portion, but there is no problem in the transfer state, and o indicates that transfer omission occurs at the back end portion. Indicates that it cannot be seen.

According to the chart of FIG. 6, when the transfer position of the rear end of the front surface is 4.0 mm or less, the transfer position of the front end of the rear surface is 8 m.
If it is set to m or more, noticeable transfer omission does not occur, and if the rear end transfer position of the front surface is set to 6.0 mm, there is no problem even if the front end transfer position of the back surface is 6 mm. The reason why the width of the image notch on the back side needs to be larger than that on the front side is that the adhesion between the transfer paper (white) and the intermediate transfer belt 426 is larger than the adhesion between the toner and the intermediate transfer belt 426. In the case of a mono-color image, there is no problem even if the width of the missing image is slightly reduced. This is because the amount of toner adhered is smaller than in full color.

It is well known that in a laser writing type image forming apparatus, if the laser is not turned on, an erase will occur (image loss). Therefore, the setting of the notch width at the front end and the rear end of the image as described above can be performed by controlling the lighting of the laser. Therefore, the setting of the notch width at the front end and the rear end of the image is performed by the image forming control unit of the writing optical unit 400 by the laser emission unit 40.
The light emission of No. 4 may be controlled. In this embodiment, the rotation of the registration roller pair 470 is also controlled by the image forming control means.
By controlling the transfer timing of the transfer paper with 0, the image transfer start position on the transfer paper can also be set. Therefore, if this is set as the image notch width, the transfer timing of the transfer paper can be controlled by the paper feed control means. Control also allows for installation.

From the above table, as shown in FIG. 5, the set value of the image missing width is determined according to various modes of the image forming apparatus. In FIG. 5, A to G indicate setting codes, and the setting codes are changed depending on the mode even with the same numerical value. These setting codes and numerical values are stored in the image forming control means in advance.

Next, the setting of the leading edge image chipping width in the image forming apparatus in which the setting codes and numerical values shown in the chart of FIG. 5 are stored in the image forming control means will be described with reference to the flowchart shown in FIG. FIG. 1 is a flowchart showing the setting of the image missing width at the leading end of the transfer paper.

First, it is selected whether the transfer sheet is the front side or the back side (step 1001). If it is the back side, it is selected whether the transfer sheet is a manually inserted transfer sheet or a transfer sheet automatically sent out (step 1001). Step 1002). In the case of manual feed, the image missing width is set to 8.0 mm (step 1003).
If automatic is selected in step 1002,
Select whether the surface is colored or not (step 100)
4) For color, go to step 1003. In the case of a monochrome image, the image missing width is set to 4.0 mm (step 1005). If the surface of the transfer paper is selected in step 1001, the process proceeds to step 1005 irrespective of color or monocolor, and the image cutout width is 4.0 m.
Set to m. In this manner, the image chip width at the leading end of the back surface of the transfer paper is set to 8.0 mm for manual feed, to 8.0 mm only when the chart is in color in the automatic mode, and to 4.0 mm in other cases. You.

On the other hand, the setting of the image missing width at the rear end of the transfer paper is set according to the flowchart of FIG. FIG. 2 is a flowchart showing the setting of the image missing width at the rear end of the transfer sheet.

Here, first, whether the transfer paper is one-sided copy or automatic double-sided copy is selected (step 2001). In the case of automatic double-sided copy, whether the side to be copied is front or back is selected (step 2002). If the side to be copied is a table, select whether it is monocolor or full color (step 2003).
In the case of full color, the image missing width is set to 8.0 mm (step 2004). On the other hand, if one side is selected in step 2001, the back side is selected in step 2002, and the monocolor is selected in step 2003, the image missing width is set to 2.5 mm (step 2004). In this way, the rear end of the transfer paper is the surface of the double-sided mode, and the image chipping width is 8.0 in the case of the color mode.
mm and in other modes it is set to 2.5 mm.

As described above, the optimum image notch width can be automatically set depending on whether two-sided copying is performed automatically or manually, or whether color copying or monochrome copying is performed. Occurrence of a chipping situation can be reliably prevented.

In the above-described embodiment, the image processing control means, the image formation control means and the paper feed control means are separately provided, but these three controls may be performed by one CPU.

[0063]

As is apparent from the above description, according to the first aspect of the present invention, the width of the leading end image of the transfer paper can be set separately for the first surface and the second surface. Also, even when the image missing width becomes large, only one surface can be used.

According to the second aspect of the present invention, when the first surface is the front surface and the second surface is the back surface, the width of the front end image notch on the back surface is larger than that of the front surface. The transfer force at the front end of the back surface can be suggested.

According to the third aspect of the present invention, in an apparatus capable of performing automatic double-sided copying, the width of the image notch at the rear end of the first side can be set separately in the single-sided copy mode and the double-sided copy mode. Even when the image missing width becomes large, only the double-sided copy mode is required.

According to the fourth aspect of the present invention, at the time of automatic double-sided copying, the image chipping width at the leading end of the first side of the transfer paper is increased, so that the transfer omission at the leading end of the second side can be reduced. .

According to the fifth aspect of the present invention, at the time of automatic double-sided copying, both the trailing edge of the first surface and the leading edge of the second surface of the transfer sheet are made large in the image chipping width. Can be demonstrated.

According to the sixth aspect of the present invention, since the setting of the image chipping width can be set separately in the monochrome mode and the color mode, when the image chipping width is increased, the chipping width in a mode other than necessary is not increased. Only needs to be done.

According to the seventh aspect of the present invention, since the image missing width is increased only in the color mode, it is possible to prevent the image missing width from increasing in the monochrome mode in which curling is relatively small.

According to the eighth aspect of the present invention, since the image carrier is formed of an intermediate transfer body of a medium resistance material, the adhesion between the intermediate transfer body and the transfer paper is ensured and the transfer property is stabilized. be able to.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating setting of a chip width at an image leading end of a transfer sheet according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating setting of a cutout width at the rear end of an image on a transfer sheet according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining a state of a transfer sheet that has been copied on one side;

FIG. 4 is a diagram illustrating a relationship between a cutout width of a screen on a front surface of a transfer sheet and a cutout width of a screen on a back surface.

FIG. 5 is a diagram showing a setting value of a screen missing width for each copy mode.

FIG. 6 is a schematic diagram illustrating the overall configuration of the image forming apparatus.

FIG. 7 is a schematic diagram for explaining a relationship between an intermediate transfer belt and a photoconductor in FIG. 6;

8 is a cross-sectional view showing a structure of a main part of the reversing tray in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Transfer paper 200 Color scanner 210 Color sensor 400 Writing optical unit 402 Photoreceptor 404 Laser light emitting means 422 Rotary developing device 426 Intermediate transfer belt 456 Feed bank 468 Manual feed tray 470 Registration roller pair 474 Fixing device 480 Ejection roller pair 482 Branch Claw Means 500 Reverse Tray 510 Feed Roller 512 Stack Unit 514 Separation Roller 528 Switching Claw

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G03G 15/01 G03G 15/01 S 21/00 370 21/00 370

Claims (8)

[Claims] An image forming apparatus capable of transferring and fixing a toner image formed on an image carrier to a first surface of a transfer material, and then transferring and fixing the toner image to a second surface of the transfer material. An image forming apparatus comprising: means for independently setting an image chipping width at a front end of a first surface of the transfer material and an image chipping width at a front end of a second surface of the transfer material. 2. The image according to claim 1, wherein an image chipping width at a front end of the second surface of the transfer material is set wider than an image chipping width at a front end of the first surface of the transfer material. Forming equipment. 3. A single-sided mode in which a toner image formed on an image carrier is transferred and fixed to a first surface of a transfer material, and the transfer paper having the toner image fixed on the first surface by the single-sided mode is used. An image that can be switched to an automatic double-sided mode in which the transfer paper stacked on a tray is fed to the image carrier again and the toner image formed on the image carrier is transferred and fixed to the second surface thereof. In the forming apparatus, the image chipping width at the rear end of the first surface of the transfer material in the automatic double-sided mode and the image chipping width at the rear end of the first surface of the transfer material in the single-sided mode are independently set. An image forming apparatus comprising: 4. An image chipping width at a rear end of the first surface of the transfer material in the automatic double-sided mode is set wider than an image chipping width at a rear end of the first surface of the transfer material in the single-sided mode. The image forming apparatus according to claim 3, wherein: 5. A single-sided mode in which a toner image formed on an image carrier is transferred and fixed to a first surface of a transfer material, and the transfer paper having the toner image fixed on the first surface by the single-sided mode is used. An image that can be switched to an automatic double-sided mode in which the transfer paper stacked on a tray is fed to the image carrier again and the toner image formed on the image carrier is transferred and fixed to the second surface thereof. In the forming apparatus, the image chipping width at the rear end of the first surface of the transfer material in the automatic double-sided mode is larger than that in the single-sided mode, and the image chipping width at the front end of the second surface is set to the front-end image of the first surface. An image forming apparatus characterized by being set to be larger than a notch width. 6. The image forming apparatus according to claim 2, wherein the image forming apparatus has a monochrome mode and a color mode, and the image missing width can be set separately for the monochrome mode and the color mode. Image forming device. 7. The image forming apparatus according to claim 2, wherein the image missing width in the color mode is set to be larger than the image missing width in the monochrome mode. . 8. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer member made of a medium resistance material.