JPH02247663A - Sheet conveyance device - Google Patents

Abstract

PURPOSE:To reduce the space for a device and to miniaturize the device by recarrying sheets in such a way that a small-sized sheet is switched back when synthesized copying is performed thereon and recarrying a large-sized sheet while holding electrostatically it on a transfer belt. CONSTITUTION:In the case of the synthesized copying on the small-sized sheet, the transfer belt 13 is normally rotated counterclockwise and a first image is transferred. Then the transfer belt 13 is reversely rotated clockwise, the sheet is switched back and carried till the top edge of the sheet is positioned in the downstream of an image transfer part A and a second image is transferred. Then, the transfer belt 13 is normally rotated again and the sheet is ejected to an ejected paper tray 12 through a fixing device 10 and a paper ejecting roller 11. In the case of the synthesized copying on the large-sized sheet, the sheet on which the first image is formed is recarried toward the prescribed position in the upstream of the image transfer part A while being electrostatically held by the transfer belt 13. When the second image is transferred, a destaticizing charger 15 is turned on, electric charges on the transfer belt 13 are removed and the sheet is ejected to the ejecting paper tray 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sheet conveying device in an electrostatic transfer type copying apparatus having a composite copying function.

(Prior art) A static copying machine equipped with a composite copying function that repeatedly conveys a sheet fed by a paper feeding means to an image transfer unit to form multiple (or multicolor) images on the same sheet. 2. Description of the Related Art Electric transfer type copying devices are known.

This type of copying device has a sheet conveyance path in normal copy mode that forms a single image on a sheet, a sheet conveyance path in composite copy mode that forms multiple images on a sheet, and two sheet conveyance paths. This requires a sheet conveyance device having sheet path switching means for selectively switching paths. For this reason, this type of copying device has become complicated and large.
The cost also tended to be high.

In order to solve this problem, conventionally an endless belt for conveying the sheet is placed between the image transfer section and the image fixing section.
The forward side surface of this endless belt is made to function as part of the sheet conveyance path in the normal copy mode, and the reverse side surface of the endless belt is made to function as part of the sheet conveyance path in the composite copy mode. A sheet conveying device configured as follows has been proposed (Japanese Patent Laid-Open No. 60-227272).

(Problem to be Solved by the Invention) However, in the conventional sheet conveying device described above, a part of the sheet conveying path in each mode is composed of one endless belt, so it is difficult to simplify the structure. However, the sheet conveyance span during composite copying is still as long as before, resulting in poor copy productivity.Furthermore, the sheet is re-transported to the image transfer unit while being fixed each time during composite copying. Shrinkage of the sheet due to this fixing process causes misalignment in the combined image, and this misalignment has the drawback of causing a significant deterioration in image quality, particularly in color copying.

Furthermore, in the conventional sheet conveying device described above, the sheet path switching means consisting of a mechanical means such as a flap is an essential element, so that the occurrence rate of sheet jams increases.

In addition, as a sheet conveyance device that realizes composite copying without newly installing the above-mentioned sheet path switching means and sheet conveyance path for composite copying, a transfer belt stretched in a loop shape is rotated in forward and reverse directions to transfer images. There is also a sheet conveyance device configured to cause the transfer section to convey the sheet in a switchback manner. However, in this sheet conveying device, it is necessary to secure enough sheet conveying space on both sides of the image transfer section to switch back the sheet, so the device itself has the disadvantage of being extremely large.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention, when making composite copies on small-sized sheets, switches back and conveys the sheets by forward and reverse rotation of the transfer belt. When performing composite copying on a large-sized sheet, the sheet is electrostatically held on the transfer belt by the charges on the transfer belt, and the transfer belt is rotated in the forward direction to be conveyed again.

(Function) According to the present invention, since the sheet conveyance method during composite copying can be selected according to the size of the sheet, the space for switching back the sheet on both sides of the image transfer section can be shortened, and Since the sheet is electrostatically held and conveyed by the transfer belt, the conveyance path of the sheet can be switched without using a mechanical sheet path switching means.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows an outline of a copying machine to which a sheet conveying device according to the present invention is applied. As is well known, an optical system 1,
Charger 2, photoreceptor 3, developing device 4, cleaning device 5, sheet cassette 6, paper feeding device 7, registration roller 8, belt transfer device 9, fixing device 10. Paper ejection roller 11. and a paper discharge tray 12. Here, the belt transfer means 9 includes a transfer belt I3 which is stretched in a loop and is rotatable in forward and reverse directions and which guides the sheet fed by the paper feed means 7 to the image transfer section A, and a back surface of the transfer belt 13. The transfer charger 14 is disposed at a location corresponding to the image transfer section A, and a static elimination charger 15 removes the charge on the transfer belt 13 charged by the transfer charger 14.

The sheet conveying device according to the present invention has this belt transfer means 9.
is configured to function as a sheet conveying means. That is, in FIG. 1, the transfer belt 13 is
The image transfer portion AL of the photoreceptor 3 is rotatably stretched by a plurality of belt rollers 6 so that the corresponding surface thereof is along the sheet conveyance path between the registration roller 8 and the fixing device 10 . Also.

The transfer belt 13 is rotated in forward and reverse directions by moving at least one of the belt rollers 6 into forward and reverse directions. Furthermore, this transfer belt 1
3, the length of both sides of the image transfer section A is long enough to place a small-sized sheet such as a postcard.

Further, a belt contact/separation roller 17 is provided on the back side of the image transfer portion A of the transfer belt 13. This belt contact/separation roller 17 is connected to a solenoid 18 as shown in FIG.
It is rotatably mounted on the free end of a lever 19 that swings when the solenoid 18 is turned on and off, and when the solenoid 18 is turned on and off, it is displaced as shown by chain lines and solid lines in FIG. The belt 13 is moved toward and away from the photoreceptor 3. Further, during composite copying of small-sized sheets, the belt roller 6 is immediately rotated forward and reverse at a predetermined timing by a control means (not shown), and the transfer belt 13 is rotated forward and reverse. On the other hand, during composite copying of large-sized sheets, the static elimination charger 15 is turned on and off at predetermined timing by the control means.

The sheet conveying device configured as described above operates as follows.

First, the conveyance operation of a small size sheet will be explained with reference to FIGS. 1 to 4.

In Figure 1, when you turn on the print key after setting the original and small-sized sheets, the sheet cassette 6
The inner sheet is fed by the pickup roller and separation feed roller of the paper feeding means 7, and is fed onto the transfer belt 13 by the registration roller 8 in synchronization with the rotation of the photoreceptor 3. on the other hand.

During this time, a cleaning device 5, a charger 2. The optical system 1 and the developing device 4 operate to form an original image. Here, the transfer belt 13 is rotated in the counterclockwise direction in FIG. 1 in synchronization with the rotational speed of the photoreceptor 3 so that the leading edge of the image on the photoreceptor 3 and the leading edge of the sheet coincide with each other. Further, at this time, the transfer charger 14 is turned on and the solenoid 18 is also turned on. As a result, as shown in FIG.
transported upstream. Here, in the case of normal copy mode, the static elimination charger 15 is turned on and the transfer belt 1
3 is removed, the sheet is separated from the transfer belt 13, the image transferred to the sheet is fixed by the fixing device 10, and then the sheet is discharged onto the paper discharge tray 12 by the paper discharge roller 11. On the other hand, in the composite copy mode, when the transfer of the first image to the sheet is completed (the state shown in FIG. 3), the solenoid 18 is turned off and the sheet is separated from the surface of the photoreceptor 3. At the same time, the belt roller 6 is activated to rotate in the reverse direction, and the transfer belt 13 is rotated in the reverse clockwise direction in FIG. As a result, the transfer belt 13 is transferred to the fourth
As shown in the figure, the sheet is conveyed in a switchback manner until the leading edge of the sheet is located on the downstream side of the image transfer section A, and then the sheet is stopped. The stopping position of the sheet at this time is controlled by the above-mentioned control device based on the on/off state of a well-known position sensor disposed on the sheet conveyance path. Then, a second image is formed on the surface of the photoreceptor 3 in the same way as the first image described above.

The transfer belt 13 is rotated forward again, and the sheet to which the first image has been transferred is conveyed again, and the second image is transferred.

In this way, the sheet is conveyed in a switchback manner according to the number of images to be combined by forward and reverse rotation of the transfer belt 13.
When the transfer of the composite image onto the sheet is completed, the sheet is ejected onto the ejection tray 12 through the fixing device IO and ejection roller 11 in the same manner as in the normal copy mode described above.

Next, the conveyance operation of a large-sized sheet will be explained.

During composite copying onto a large-sized sheet, the sheet to which the first image has been transferred is conveyed while being electrostatically held on the transfer belt 13, in the same manner as in the normal copy mode described above. That is, in this composite copy mode, the charger 15 is controlled so as not to operate until composite copying onto the sheet is completed, and the transfer belt 13 is rotated counterclockwise a number of times corresponding to the number of images to be composited. It is rotated forward in return. Therefore, in this composite copy mode, the sheet onto which the first image has been transferred remains electrostatically held on the transfer belt 13 by the charge applied by the transfer charger 14, as shown in FIG. It is conveyed again toward a predetermined position on the upstream side of the transfer section A. Then, the second image is transferred onto the sheet in the same manner as when the first image was transferred.

When the transfer of a predetermined image is completed in this manner, the static elimination charger 15 is turned on to remove the electric charge from the transfer belt 13, and the sheet holding force of the transfer belt 13 is lost. As a result, the sheet is conveyed toward the fixing device 10 and is discharged onto the paper discharge tray 12 by the paper discharge roller 11 .

As described above, the sheet conveyance device according to the present invention can select the conveyance method during composite copying on a sheet depending on the size of the sheet to be transferred, so that the conveyance method on the side of the transfer belt where the sheet is switched back can be selected depending on the size of the sheet to be transferred. The path can be extremely shortened, and large-sized sheets can be repeatedly conveyed without using mechanical sheet path switching.

(Effects of the Invention) According to the present invention, the space and size of the apparatus can be saved and the composite image can be transferred without fixing.
It is possible to obtain high-quality composite copies with fewer occurrences of copy image misalignment and sheet jams.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIG. 2 is a configuration diagram of essential parts of the embodiment, and FIGS. 3 to 5 are explanatory diagrams of the operation of the embodiment. 13... Transfer belt, 14... Transfer charger, 1
5... Static elimination charger, 6... Belt roller, 17
...Belt contact/separation roller, A image transfer section. Tsu 〒5 I し 3〕 Ki 2 Figure

Claims (1)

[Claims] A transfer belt stretched in a loop shape and capable of forward and reverse rotation guides the sheet fed by the paper feeding means to the image transfer section; In a copying apparatus having a belt transfer means constituted by a transfer charger and a charge eliminating charger for removing electric charge on the transfer belt charged by the transfer charger, and a composite copying function for forming a plurality of images on the same sheet, When performing composite copying onto a small-sized sheet, the transfer belt is rotated in the forward direction to switch back the sheet onto which the first image has been transferred to a position downstream of the upper image transfer section by rotating the transfer belt in the reverse direction, and then the above-mentioned transfer is performed. The belt is rotated in the normal direction again to transport the sheet to the image transfer section again, while at the same time, when composite copying is performed on a large size sheet, the operation of the static elimination charger is stopped when the sheet on which the first image has been transferred is transferred. A sheet conveying device characterized in that the sheet is re-transported to the image transfer section by rotating the transfer belt in the forward direction while the sheet is electrostatically held by the transfer belt.