JP4662111B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus capable of preventing a transfer omission at the rear end of a sheet material.
[0002]
[Prior art]
The image forming apparatus includes a charging device, an exposure device, a developing device, and a transfer device around an image carrier, which sequentially act on the image carrier to form a toner image on the image carrier. The transfer device transfers the toner image to the sheet material conveyed from the paper feeding unit at a predetermined timing by the transfer unit, and then the transfer material is a fixing composed of a heating roller and a pressure roller pressed against the heating roller. It passes through the nip portion of the apparatus and is discharged to the outside as a permanent image.
Means for conveying or guiding the sheet material to the fixing device is provided between the transfer unit provided with the transfer device for transferring the toner image of the image carrier to the sheet material and the fixing device. A suction conveyance belt for conveying the sheet material while sucking the bottom surface of the sheet material as conveying means, a conveyance plate for guiding the sheet material on the conveyance path, and the like as a guiding means.
[0003]
In an image forming apparatus configured such that the length of the sheet material is longer than the distance between the transfer unit and the fixing device, the moving speed of the image carrier and the fixing speed of the fixing device are set to be the same speed. .
When the sheet material passes through the conveyance path on the transfer unit, the conveyance unit or guide unit, and the fixing device, it is preferable that the sheet material pass on the conveyance path without bending.
That is, if the sheet material is bent, there is a risk of retransfer that the sheet material approaches the image carrier even if it passes through the transfer portion, and the image transferred to the sheet material moves to the image carrier again. There is a problem that the sheet material that is generated or passes through the fixing device is likely to be wrinkled.
[0004]
On the other hand, when forming an image on a sheet material on which curling has occurred due to roll paper curling or the like, it is preferable to use the curling direction downward. By setting the curl of the sheet material downward, the sheet material is curled away from the image carrier in the transfer process, so that the sheet material is easily peeled off from the image carrier after transfer, and the periphery of the transfer device There is almost no risk of paper jams.
[0005]
Further, a guide member for guiding the leading edge of the sheet material to the upper side of the nip portion of the fixing device is provided in order to perform stable fixing without wrinkles. The guide member is made of a flat plate having a width larger than that of the maximum size sheet material, and the guide member has a leading end positioned in the vicinity of the entrance of the nip portion between the heating roller and the pressure roller pressed against the heating roller. Guides to the fixing device. In this case, even if there is a downward curl, the leading edge of the sheet material is guided to the fixing device without being separated from the upper surface of the guide member, so that the leading edge of the sheet material can be always guided to a predetermined position. However, when the sheet material is curled upward, the leading edge of the sheet material is guided away from the upper surface of the guide member, and the sheet material cannot be guided to a predetermined position. Paper jams and wrinkles may occur. Thus, even if the sheet material has a curl, the problem relating to the peeling of the sheet material from the image carrier and the prevention of wrinkles of fixing is almost eliminated.
[0006]
[Problems to be solved by the invention]
However, in such an image forming apparatus, the sheet material on the conveyance path is conveyed so as to be pulled by nipping between the heating roller and the pressure roller of the fixing device . For this reason, it becomes difficult for the rear end of the sheet material to be in contact with the image carrier to the end due to curling by the curl. In other words, the sheet material is electrostatically adsorbed on the surface of the image carrier during transfer , but cannot be adsorbed on the surface of the image carrier due to the curl strength of the sheet material. Therefore, before the curled portion of the sheet material acts on the surface of the image carrier at the transfer portion, the conveying force that pulls and conveys the sheet material by the nipping of the sheet material by the fixing device acts on the transfer portion. . For this reason, there is a problem that the toner image cannot be transferred onto the sheet material. So-called transfer omission occurs.
[0007]
This transfer omission occurs irregularly in the width direction of the sheet material, and is often observed particularly in the central portion. For this reason, there is a problem that image information such as printing and drawings is lost at the rear end portion of the sheet material, and the appearance is not good.
When the sheet material passes through the fixing device, it contracts due to the heat of fixing. In particular, in the case of forming a long image, the shrinkage amount of the sheet material increases as the latter half of the output is performed, and the fixing device acts to pull the sheet material, and the sheet material is conveyed in a stretched state due to this influence. . When the rear end of the sheet material passes through the transfer portion in the stretched state, many transfer omissions occur.
Further, in an image forming apparatus that does not have a cleaner using non-magnetic single component toner, the transferred toner image remains on the image carrier, and this portion remains as a memory image due to the effect of charge removal or exposure. There is a risk of adversely affecting image formation.
[0008]
The present invention has been made in view of the above-described problems, and an image forming apparatus capable of reliably transferring the trailing edge of a sheet material even when the sheet material such as roll paper has curl. It is an issue to provide.
[0009]
[Means for solving problems]
In order to solve the above problems, the present invention provides a transfer device that transfers a toner image formed on an image carrier onto a sheet material at a transfer unit, a heating roller that fixes the toner image carried on the sheet material, In an image forming apparatus having a fixing device comprising a pressure roller that is in pressure contact, a deflection forming means for forming a deflection of the sheet material between the transfer portion and the fixing device immediately before the trailing edge of the sheet material passes through the transfer portion. The deflection forming means guides the sheet material upward at the entrance of the nip portion formed by the pressure contact between the heating roller and the pressure roller, and fixes immediately before the trailing edge of the sheet material passes through the transfer portion. A guide member for forming a deflection by changing an intrusion angle into the apparatus downward is provided .
[0011]
Further, means for conveying or guiding the sheet material is provided between the transfer unit and the fixing device, and the means is a suction conveyance belt that conveys the sheet material while sucking it. It is characterized by.
[0012]
Furthermore, the deflection forming means temporarily decelerates or temporarily stops the driving of the fixing device and the means after a predetermined time or simultaneously, and immediately before the trailing edge of the sheet material passes through the transfer portion. The conveyance speed of the fixing device is made slower than the conveyance speed of the image carrier, and a deflection is formed between the transfer unit and the fixing device. The drive of the means is temporarily decelerated or temporarily stopped, and the conveyance speed of the fixing device and the conveyance speed of the means for conveying the sheet material are set immediately before the trailing edge of the sheet material passes through the transfer unit. It is characterized in that a deflection is formed between the transfer section and the means at a slower speed than the conveying speed of the image carrier.
[0013]
With this configuration, the angle of the guide member that guides the sheet material to the fixing device is changed so that a deflection is formed between the transfer portion and the fixing device immediately before the rear end of the sheet material passes through the transfer portion. Let Alternatively, the speed of the fixing device is made slower than the moving speed of the image carrier so that a deflection is formed between the transfer portion and the fixing device immediately before the rear end of the sheet material passes through the transfer portion. The deflection formed between the transfer unit and the fixing device acts so as not to pull the remaining sheet material by driving the fixing device, and the sheet material is conveyed by the driving force only for the movement of the image carrier in the transfer unit. Transcript while. As a result, the sheet material moves on the image carrier so as to be pushed out, and the toner image on the image carrier is transferred by contacting the image carrier even at the rear end of the curled sheet material.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic sectional view of an image forming apparatus 1 according to the present invention. The image forming apparatus 1 includes a charging device 3 that charges the surface of the image carrier 2 so as to have a predetermined surface potential along the moving direction (arrow A direction) of the image carrier 2 around the image carrier 2; An exposure device 4 having a light source such as a laser or LED array that forms an electrostatic latent image on the image carrier 2 and a toner image is formed on the image carrier 2 by attaching toner based on the electrostatic latent image. A developing device 5, a transfer device 7 that transfers a toner image to a sheet material 6 that passes in contact with the image carrier 2, and an eraser lamp 8 that neutralizes the surface of the image carrier 2 are sequentially arranged. The toner image formed on the image carrier 2 by the process is transferred onto the conveyed sheet material 6.
A cleaning device for removing toner remaining on the image carrier after transfer may be provided between the transfer device 7 and the eraser lamp 8.
[0015]
In the embodiment, the sheet material 6 is obtained by cutting a roll paper provided in a paper feeding unit (not shown) to a predetermined length with a cutter, and the front end of the sheet material 6 is temporarily stopped by a registration roller 9. Then, the driving of the registration roller 9 is started at a predetermined timing from the start of the image exposure by the exposure device 4, the sheet material 6 is conveyed, and sent to the transfer unit 10 of the transfer device 7.
[0016]
Reference numeral 11 denotes a fixing device for fixing the sheet material 4 carrying an unfixed toner image as a permanent image. The fixing device 11 includes a heating roller 12 provided with a heater therein and an elastic pressure roller 13 that is in pressure contact with the heating roller 11. By this pressure contact, a nip 14 having a predetermined width is formed, and unfixed toner is formed. The sheet material carrying the image is passed, and the sheet material 6 is fixed by heat and pressure by the heating roller 12 and the pressure roller 13. The peripheral speed of the fixing device 11 is set to be the same as the feed speed of the image carrier 2.
[0017]
A means 15 for conveying the sheet material 6 toward the fixing device 11 is provided between the transfer device 7 and the fixing device 11. For example, the suction conveyance belt 16 is preferably used as the means 15. The suction conveyance belt 16 stretches a belt 18 made of a plurality or one rubber and synthetic resin between a pair of rollers 17, and moves the belt 18 in the direction of the arrow by transmission of drive to the roller 17 connected to a drive source. Yes. The belt 18 is provided with a plurality of holes, and a box-shaped frame body 19 is disposed inside the belt 18 and conveyed while sucking the bottom surface of the sheet material 6 conveyed by the suction fan 20 provided in the frame body 19. ing. The suction conveyance belt 16 is set to have the same speed as the feeding speed of the image carrier 2 and the fixing device 11. By providing a conveying means such as a suction conveying belt, the sheet material can be reliably conveyed, and the conveying path can be formed without any deflection.
[0018]
As an example of the deflection forming means 21 for forming the deflection of the sheet material 6 between the transfer unit 10 and the fixing device 11, the sheet material conveyed by the suction conveyance belt 16 between the suction conveyance belt 16 and the fixing device 11. 6 is a guide member 22 that guides the tip of 6 to a predetermined position of the fixing device 11.
[0019]
The guide member 22 is provided so as to be pivotable about the fulcrum 23, and is provided so that the penetration angle of the sheet material 6 can be varied by the plunger 26. The guide member 22 is made of a metal plate having a width larger than the maximum size of the sheet material 6 or a synthetic resin flat plate, and when the sheet material 6 enters the fixing device 11, the leading end of the sheet material 6 is a nip of the fixing device 11. 14 is positioned at the first position 24 so as to be guided to the nip after abutting the slightly upper heating roller 12.
At the first position 24 of the guide member 22, the leading edge of the sheet material is guided to the fixing device 11, and the heating roller is crowned to be fixed so that the sheet material is creased toward both ends, thereby generating wrinkles. Pass through the nip 14 so as not to. Immediately before the rear end of the sheet material 6 passes through the transfer portion 10, the guide member 22 changes the angle around the fulcrum 23 by the action of the plunger 26 and is positioned at the second position 25 (broken line). When the guide member 22 changes the angle from the first position 24 to the second position 25, the sheet material 6 being conveyed can be bent.
[0020]
The amount of sheet material deflection is not limited, but in the embodiment, by changing the angle of the guide member 22 from the first position 24 to the second position 25, it is more preferable than the length of the conveyance path of the fixing device from the transfer portion. The sheet material is bent so as to be about 0.5 mm to 3 mm longer.
In the embodiment, when the conveyance speed of the sheet material is 100 mm / sec, the deflection forming means is operated 0.5 sec to 1.0 sec before the trailing edge of the sheet material passes through the transfer portion to cause the sheet material to bend. Forming. That is, the deflection is formed between 50 mm and 1000 mm from the rear end of the sheet material. The above numerical range is preferable immediately before the sheet material passes through the transfer portion, but this value is not limited, and the tension of the sheet material fixing device when the sheet material passes through the transfer portion is eliminated. Just do it.
The amount of deflection of the sheet material may be an amount that does not affect the pulling of the sheet material by the fixing device when the trailing edge of the sheet material passes through the transfer portion. When the amount of deflection is large, the sheet material supports the image. Even if the body passes the transfer portion, re-transfer occurs in which the toner image transferred to the sheet material in contact with the body moves to the image carrier again.
[0021]
With this configuration, the sheet material 6 passes through the transfer unit 10, and the toner image carried on the image carrier 2 by a known image forming method is transferred to the sheet material 6 by the transfer corona discharger 27 in the transfer unit 10. Transcript. The transferred sheet material 6 is conveyed toward the fixing device 11 by means 15 for conveying the sheet material. The leading edge of the sheet material reaches the first position 24 of the guide member 22 and is guided upward in the nip 14 of the fixing device 11. The transfer unit 10, the sheet material transporting means 15, and the sheet material 6 passing through the fixing device 11 are moved by the image carrier 2, the sheet material transporting means 15, and the fixing device 11 feeding speed. The sheet material 6 conveyed on the conveyance paths in these sections is conveyed so as to be in close contact with the conveyance path, and is conveyed without bending. For this reason, the sheet material is conveyed on the conveyance path so as to be pulled by the fixing device 11 that conveys the sheet material 6 while pinching it.
[0022]
When the rear end of the sheet material 6 reaches just before the transfer unit 10, for example, the guide member 22 which is the deflection forming means 21 in response to a signal that cuts the sheet material 6 or a signal that has passed through the registration roller is the first member. The guide member 22 pivots about the fulcrum 23 by the action of the plunger 26 from the position 24 to the second position 25 to vary the angle of entry of the sheet material 6 into the fixing device 11. By changing the angle of the guide member 22, a deflection is formed between the means 15 and the fixing device 11. Due to this deflection, the sheet material 6 moves so as to send out the sheet material 6 by the movement of the image carrier 2 without being affected by the fixing device 11 having the highest conveyance force, and the rear end of the sheet material 6 is transferred and missed. It is transcribed without any problems. Further, since the conveying force of the sheet material 6 of the means 15 is weaker than the conveying force of the fixing device 11, it does not prevent the rear end of the sheet material 6 in the transfer unit 10 from coming into contact with the image carrier 2. .
[0023]
Although FIG. 1 shows an example in which the suction conveyance belt 16 having a driving force is used as the means 15, a plate-shaped guide plate for guiding the sheet material may be used instead, or the bottom surface of the sheet material may be used. Even if a guide plate provided with a plurality of ribs along the transport direction so as to reduce the contact area with is provided, the same effect is obtained. Alternatively, the main member d that conveys or guides the sheet material may be omitted and only the guide member may be configured.
[0024]
Another embodiment will be described with reference to FIG.
Instead of the deflection forming means 21 pivoting the guide member 22 to form the deflection, the deflection is formed by the speed change of the fixing device 11 and the means 15, and the guide member 22 shown in FIG. 1 is fixed at position 24. Descriptions of other symbols that perform the same function are omitted.
[0025]
In FIG. 2, for example, the rear end of the sheet material is detected by a sensor 30 provided in the vicinity of the registration roller 9 so that the rear end of the sheet material 6 is just before reaching the transfer unit 10, and based on the detection signal from the sensor 30. Then, after a predetermined time or simultaneously, the driving of the fixing device 11 and the means 15 is temporarily decelerated or temporarily stopped. As a result, the conveying speed of the suction conveying belt 16 as the means 15 and the feeding speed of the fixing device 11 are slower than the moving speed of the image carrier 2, and a deflection is formed between the transfer unit 10 and the means 15. By this deflection, the sheet material 6 passes through the transfer unit 10 so that the sheet material 6 is pushed out by the moving force of the image carrier 2 without being affected by the conveyance of the fixing device 11 due to the pulling of the sheet material. Even the trailing edge of the curled sheet material can be transferred. Even if the driving of the fixing device 11 and the means 15 is temporarily stopped, the speed is gradually reduced by the inertia, the height of the deflection is reduced to 0.5 mm to 3 mm, and the speed again becomes the same as the moving speed of the image carrier. Therefore, there is no effect on fixing.
[0026]
In FIG. 2, an example in which the suction conveyance belt 16 having a driving force is used as the means 15 is shown, but instead of this, a plate-shaped guide plate may be used, or the contact area with the bottom surface of the sheet material is reduced. As described above, even if the feeding speed of the fixing device is reduced or stopped using the guide plate provided with a plurality of ribs along the transport direction, the same effect is obtained. The structure which a means was abbreviate | omitted may be sufficient.
[0027]
【The invention's effect】
In the image forming apparatus of the present invention, the deflection by the sheet material feeding of the fixing device is formed by forming a deflection between the transfer unit and the fixing device immediately before the trailing edge of the sheet material passes the transfer unit by the deflection forming unit. Can be transferred even at the rear end of the sheet material without affecting the transfer portion.
Further, a stable amount of deflection can be formed by a simple configuration in which a guide member for guiding the sheet material is provided in the fixing device so as to be pivotable to form the deflection.
Further, by providing means for conveying or guiding the sheet material between the transfer unit and the fixing device, the sheet material can be conveyed or guided to the fixing device without being bent on the conveying path, and the sheet material can be transferred. It shall be optimal.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an image forming apparatus according to the present invention.
FIG. 2 is a schematic diagram showing another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image carrier 6 Sheet material 10 Transfer part 11 Fixing device 15 Means 16 Suction conveyance belt 21 Deflection forming means 22 Guide member 24 First position 25 Second position

Claims (5)

A transfer device for transferring a toner image formed on an image carrier onto a sheet material at a transfer portion, a heating roller for fixing the toner image carried on the sheet material, and a pressure roller in pressure contact with the heating roller In the image forming apparatus comprising: a deflection forming means for forming a deflection of the sheet material between the transfer unit and the fixing device immediately before the rear end of the sheet material passes through the transfer unit;
The deflection forming means guides the sheet material upward of the entrance of the nip portion formed by the pressure contact between the heating roller and the pressure roller, and immediately before the rear end of the sheet material passes through the transfer portion. The image forming apparatus according to claim 1, further comprising a guide member configured to change the angle of entry into the fixing device downward to form the deflection . 2. The image forming apparatus according to claim 1 , wherein means for conveying or guiding the sheet material is provided between the transfer unit and the fixing device. The image forming apparatus according to claim 2, wherein the means is a suction conveyance belt that conveys the sheet material while sucking the sheet material. A transfer device for transferring a toner image formed on an image carrier onto a sheet material at a transfer portion, a heating roller for fixing the toner image carried on the sheet material, and a pressure roller in pressure contact with the heating roller In the image forming apparatus comprising: a deflection forming means for forming a deflection of the sheet material between the transfer unit and the fixing device immediately before the rear end of the sheet material passes through the transfer unit;
The deflection forming means temporarily decelerates or temporarily stops the driving of the fixing device and the means after a predetermined time or simultaneously, and immediately before the rear end of the sheet material passes through the transfer portion. The image forming apparatus is characterized in that a bend is formed between the transfer unit and the fixing device by lowering the conveying speed of the image carrier than the conveying speed of the image carrier. A transfer device for transferring a toner image formed on an image carrier onto a sheet material at a transfer portion, a heating roller for fixing the toner image carried on the sheet material, and a pressure roller in pressure contact with the heating roller In the image forming apparatus comprising: a deflection forming means for forming a deflection of the sheet material between the transfer unit and the fixing device immediately before the rear end of the sheet material passes through the transfer unit;
Means for conveying the sheet material is provided between the transfer unit and the fixing device, and the deflection forming means temporarily decelerates or temporarily drives the fixing device and the means after a predetermined time or simultaneously. Immediately before the trailing edge of the sheet material passes through the transfer unit, the transfer speed of the fixing device and the conveyance speed of the means for conveying the sheet material are made slower than the conveyance speed of the image carrier to stop the transfer. An image forming apparatus, wherein a deflection is formed between the portion and the means.

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