JP2833264B2 - Paper transport device for image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suction guide device for guiding a sheet carrying a toner image immediately before a fixing device in an image forming apparatus such as an electronic copying machine. The present invention relates to an apparatus for forming a downward curl on a sheet by guiding while suctioning.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system, such as an electronic copying machine, a toner formed on a photosensitive drum is used.
Means are used in which an image is transferred to a sheet, and the sheet carrying the toner image is fixed through a fixing device to form a copy. In a general electronic copying machine or the like, after transferring a toner image from a photosensitive drum, the sheet is peeled off from the photosensitive drum, and the sheet is directed to a fixing device by a transport device using a suction transport belt or the like. We use means to provide guidance. As the suction conveyance device, for example,
An apparatus as shown in Japanese Utility Model Laid-Open No. 2-89459 is used. In the transfer device shown in the conventional example, a suction frame is disposed between an image transfer portion from a photosensitive drum and an insertion guide provided in a fixing device, and a large number of suction frames are provided on an upper surface of the frame. A suction hole is formed, and a plurality of conveying belts are arranged.

Then, a suction action is applied to the back surface of the paper carrying the toner image to press the belt, and the paper is conveyed by the frictional force between the belt and the paper. As described above, by providing the suction conveyance unit, the sheet carrying the unfixed toner image rises from the conveyance surface, and the image surface of the sheet is rubbed by a member arranged at the top of the sheet path, and the image is formed. Not to be disturbed. Also, by transferring the paper at a constant speed, the speed of the paper can be kept constant when transferring an image from the photosensitive drum, and the movement of the paper between the transport device and the fixing device can be maintained. It can be performed in a good condition.

[0004]

As described above, in a general apparatus such as an electronic copying machine, a space in which a suction conveyance device can be disposed between an image transfer portion from a photosensitive drum and a fixing device is provided. Therefore, it is possible to equip the device as shown in the conventional example. However, for example, as in a color copying machine as disclosed in Japanese Patent Application Laid-Open No. 1-107280, the position where the paper is to be peeled is arranged very close to the fixing device, and suction conveyance means may be used. It may not be possible. In the case of the conventional color copying machine, while the paper is held on a transfer drum, color toner images of different colors are superimposed and transferred, and the paper peeled from the transfer drum is transferred to a guide plate. And is moved toward the fixing device while sliding.

However, as described above, in the case where no means for sucking and conveying the sheet between the transfer drum and the fixing device is provided, the sheet carrying the unfixed toner image floats and the image surface thereof is raised. Is in contact with the upper member of the paper path, which disturbs the image. The problem of the lifting of the sheet is particularly noticeable at the leading edge and the trailing edge of the sheet.In addition, depending on the relationship between the rotation speed of the transfer drum and the sheet conveying speed in the fixing device, the sheet may face upward in the middle of the sheet. This is caused by forming a loop. And
There is a problem that an impact when the edge of the sheet jumps up or an image surface is rubbed against another member or the like at the upper part of the sheet path, thereby causing a defective copy. In order to solve such a problem, for example, it is conceivable to use a suction conveyance device as in the case of a conventional device. However, the transfer drum is a drum member having a very large diameter, and it is difficult to provide a mechanism for sucking a sheet because the transfer drum occupies a very large space.

[0006]

An object of the present invention is to prevent the occurrence of image defects in an apparatus in which there is no room for providing a suction belt device upstream of a fixing device as described above. It is an object of the present invention to provide a device capable of performing suction conveyance along a guide plate.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a toner image formed on a photosensitive drum is transferred onto a sheet held by suction on a transfer drum, and then the sheet carrying the toner image is transferred. The present invention relates to a device configured to be peeled, guided to a fixing device, and fixed. In the apparatus of the present invention, a guide plate that guides the back surface of the sheet is disposed between the sheet peeling section from the transfer drum and a nip section of the fixing device at a position lower than a line connecting the two, and the guide The plate is provided with a number of suction holes and is connected to suction means. Also, the suction force of the paper by the suction device can be changed according to the position of the paper, and the guide plate is arranged to be inclined upward toward the nip portion of the fixing device.

In the suction guide device of the present invention, until the leading end of the paper reaches the nip position by the fixing device,
Suction is performed with a force smaller than the suction force of the paper by the transfer drum, and after the rear end of the paper passes through the peeling portion of the transfer drum, the suction force is controlled so as to increase the suction force. I have. Further, in the present invention, the suction device disposed between the paper peeling portion from the transfer drum and the nip portion of the fixing device uses the same suction means as a suction mechanism provided on a cleaning brush for cleaning the transfer drum. The suction means for guiding the sheet and the suction means for the cleaning brush can be operated via a switching mechanism of an air suction path.

With the above-described configuration, in the present invention, a suction guide device can be configured according to the space of the apparatus and the like, and the paper is conveyed while sucking the paper between the transfer drum and the fixing device. can do. In addition, it is possible to prevent the rear end of the sheet from jumping up, and to prevent the sheet from rising significantly after the rear end of the sheet is peeled off from the transfer drum. Further, in the present invention, there is provided a means for forming a loop on a sheet between a sheet peeling portion from a transfer drum and a fixing device without using a suction belt device or the like, and there is a speed difference between the two devices. In this case, a loop can be formed downward with respect to the sheet.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sheet conveying device of an image forming apparatus according to the present invention will be described with reference to the illustrated example. The example shown in FIG. 1 shows a transfer drum 10 and a fixing device 1 in a color copying machine.
5 and a suction guide device 20 arranged between the two devices. In the apparatus of the present invention, as will be described later, the paper is electrostatically suction-held on the surface of the transfer drum 10 to transfer a color toner image in a superimposed manner. The fixing device 15 is used to peel off the sheet, transfer the sheet to the fixing device 15, and perform fixing. As described above, the sheet peeled from the transfer drum 10 by the peeling member 11 is guided by the guide plate 21 of the suction guide device 20 via the guide surface 12 formed on the upper surface of the peeling member.
Through the fixing device 15. The fixing device 20
Uses a device configured as a heat roller system, and passes heat, pressure and heat through a sheet carrying an unfixed toner image between a heating roller 16 and a pressure roller 17. Is added to form a color copy, and the copy is discharged to the outside via the discharge roller 19. Further, an upper guide plate 18 is provided above the paper introduction section of the fixing device 15 so that the leading end of the paper can be guided toward the nip portion of the roller via the upper guide plate. I do.

In the apparatus of the present embodiment configured as described above, when the paper transport speed of the transfer drum 10 and the paper transport speed of the fixing device 10 do not match, the speed of the fixing device is high. Then, the sheet is attracted between the transfer drum 10 and the fixing device 15. Then, there is an inconvenience that the sheet supported by the transfer drum is pulled from the fixing device side. On the other hand, when the speed on the side of the fixing device is low, a paper loop corresponding to the speed difference between the two members occurs. Further, when the loop of the paper is formed upward in a state indicated by a chain line Pa in FIG. 1, there arises a problem that the image surface is rubbed against the upper guide plate 18 of the fixing device. Therefore, in the present invention, the member provided as the lower guide plate of the conventional fixing device is configured as a device provided with a suction unit, and the suction guide device 20 sucks the sheet downward, and I'm going to guide you.

The suction guide device 20 is shown in FIGS.
Is used. In the suction guide device 20 of the present invention shown in FIG. 2, the guide plate 21 is arranged below the paper and a suction duct 23, and the guide plate 21 is, as shown in FIG. It is configured as having a large number of holes 22. In the guide plate 21 shown in FIG. 3, the suction holes 22 are provided with a large number of tapered openings from the upstream side to the downstream side in the paper transport direction, and the corners of the paper are caught. An opening having such a shape as to prevent slipping is provided. Further, a suction duct 23 is arranged below the guide plate 21 so as to suck air. An end of the suction duct 23 is connected to the air suction device 32 via the adjusting means 25. It is connected.

The adjusting means 25 includes a valve member 26 and a shaft 27.
The valve member 26 is provided with a drive mechanism by a solenoid 29 via a link 28. By turning on and off the solenoid 29, the valve member 26 can be set to a half-open state and a fully-open state. When the valve member 26 is set to the fully open state, a strong suction force is exerted on the sheet guided on the guide plate, and when the valve is set to the half-open state, the sheet is weak against the sheet. The suction action can be applied by force. Further, the adjusting means 25 is not limited to the configuration shown in the figure, and any other suction force adjusting means can be used.

The suction guide device 20 of the present invention can use, for example, the same suction source as the drum cleaner 30 provided on the transfer drum 10. As shown in FIG. It is connected to a device provided with a source and a common air suction device 32. As described above, even when the drum cleaner 30 and the suction guide device 20 are provided for one air suction unit, the two members are not used simultaneously. That is,
The cleaning action on the transfer drum is not performed when the copy is made, but the suction action by the suction guide device is performed when the copy is made. The suction means can be used effectively.

In the apparatus shown in FIG. 1 of the present invention constructed as described above, in the initial stage of peeling the sheet from the transfer drum 10, a weak suction force is applied to the suction guide device 20 to cause the transfer drum The sheet to be peeled is guided toward the fixing device 15 while being sucked onto the guide plate 21.
In this case, in the adjusting means 25 shown in FIG. 2, the valve member 26 is in a half-open state, and the suction force of the guide plate is smaller than the force of electrostatically sucking the paper to the transfer drum 10. Set. The sheet peeled off from the transfer drum 10 moves while sliding on the guide plate 21 according to the rotation of the transfer drum, and the sheet forms a loop downward without floating. At the fixing device. Therefore, as described above, by guiding the sheet with a weak suction force by the suction guide device, when the sheet conveyance speed in the fixing device 15 is low, a loop corresponding to the difference in the speed is formed on the sheet. This can prevent the paper from looping upward. Thereafter, the trailing end of the sheet to be peeled from the transfer drum is connected to a sheet sensor S provided at the peeling section.
When the detection is made by step 1, the valve member 26 of the adjusting means 25 is fully opened to generate a strong suction force on the suction guide device 20. Then, the sheet is conveyed by the conveying force of the fixing device 15 while preventing the rear end of the sheet from jumping up. Further, in the apparatus of the present invention, the guide plate 21 of the suction guide device 20 is provided to be inclined upward toward the nip portion of the fixing device. Therefore, as described above, when guiding the leading edge of the paper, the leading edge of the paper is first guided along the inclined path while being sucked by the guide plate 21, and the leading edge of the paper is nipped into the fixing device. After that, a function of forming a loop downward with respect to the sheet by a weak suction force is added, and accordingly, according to a difference in transport speed between the transfer drum and the fixing device,
The loop can be easily formed.

The suction device of the present invention configured as described above can be applied to, for example, a color copying machine 1 as shown in FIG. The color copying machine 1 shown in FIG. 4 is configured as a full-color copying machine. One photoconductor drum 2 is arranged for a transfer drum 10 and is adapted to correspond to the photoconductor drum 2. A plurality of developing devices 3 are arranged. The developing device 3 accommodates toner of each color so as to form color toner images of yellow, magenta, cyan, and black. A charged corotron 2a, a cleaning device 2b, and the like are arranged around the photosensitive drum 2 in the same manner as in a general copying machine, and a color toner image formed on the photosensitive drum is By the discharge of the transfer corotron 4, the operation of transferring the image to the sheet supported by the transfer drum 10 is repeated, and the color toner image is transferred onto the sheet in a superposed manner.

The paper is fed from a paper feed tray 5 to a paper feeder 6.
, And conveyed by a conveyance roller device 8 in a paper path 7, and transferred via a registration roller device 9 to a transfer drum 10.
Supplied to. In the transfer drum 10, an electrostatic sheet holding means is provided on the surface of the drum, and the transfer drum 10 is rotated once each time a toner image is transferred while the sheet is suction-held on the surface of the drum. Perform the operation. After all the color toner images have been transferred, the sheet is peeled off by the peeling member 11, and the sheet is guided along the guide surface 12 formed on the peeling member. To perform the fixing action.

The above-described apparatus of the present invention can be applied to a color copying machine as shown in the conventional example.
In addition, the present invention can be applied to an apparatus such as a small copying machine. The mechanism of the adjusting means provided in the suction guide device, the mode of controlling the suction pressure when performing the suction guide operation, and the like can be arbitrarily formed in accordance with the configuration of the image forming apparatus. Further, as for the configuration of the suction hole provided in the guide plate, any configuration other than the illustrated configuration can be used.

[0019]

Since the apparatus of the present invention is constructed as described above, the suction guide device can be constructed according to the space of the image forming apparatus and the like. Paper can be guided between. Then, it is possible to prevent the trailing end of the sheet from jumping up, and to prevent the sheet from rising significantly after the trailing end of the sheet is separated from the transfer drum. Further, in the present invention, a loop can be formed on a sheet between a sheet peeling section from a transfer drum and a fixing device without using a suction belt device or the like, and a speed difference between the two devices can be achieved. In some cases, a downward loop can be formed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of a sheet conveying device of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a suction guide device of the present invention.

FIG. 3 is a plan view showing a configuration of a guide plate of the present invention.

FIG. 4 is an explanatory diagram of a color copying machine to which the sheet conveying device of the present invention is applied.

[Explanation of symbols]

1 color copier, 2 photoreceptor drum, 3
Developing device, 10 transfer drum, 11 peeling member,
15 Fixing device, 20 Suction guide device, 21
Guide plate, 22 suction holes, 23 suction ducts,
25 adjusting means, 26 valve member, 30 drum cleaner.

Claims (2)

(57) [Claims] After transferring a toner image formed on a photosensitive drum onto a sheet held by suction on a transfer drum, the sheet carrying the toner image is peeled off, guided to a fixing device, and fixed. In the device configured to cause
A guide plate that guides the back surface of the sheet is disposed at a position lower than a line connecting the two between the sheet peeling unit from the transfer drum and the nip unit by the fixing device, and the guide plate has a number of suction holes. The suction plate is provided so as to be connected to suction means, and the suction force of the paper by the suction device is configured to be changeable according to the position of the paper, and the guide plate is directed upward toward the nip portion of the fixing device. A sheet conveying device for an image forming apparatus, wherein the sheet conveying device is arranged to be inclined. 2. A suction device disposed between a sheet peeling portion from the transfer drum and a nip portion of a fixing device includes the same suction means as a suction mechanism provided on a cleaning brush for cleaning the transfer drum. A suction unit for guiding the paper, and a suction unit with a cleaning brush,
2. The sheet conveying device of the image forming apparatus according to claim 1, wherein the sheet conveying device is configured to be operated via a switching mechanism of an air suction path.