JP2003066749A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device with which the back end of a sheet material can be surely transferred even when the sheet material such as roll paper has a curled part. SOLUTION: In the image forming device having a transfer unit 7 for transferring a toner image formed on an image carrier 2 to the sheet material 6 at a transfer section 10, and an fixing unit 11 composed of a heating roller 12 for fixing the toner image supported on the sheet material 7 and a pressurizing roller 13 pressure-contacting with the heating roller 12, a bending forming means 21 for forming the bending in the sheet material 6 between the transfer section 10 and the fixing unit 11 immediately before the end part of the sheet material passes through the transfer section 10 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field 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 transfer omission at the rear end of a sheet material.

[0002]

2. Description of the Related Art An image forming apparatus has a charging device, an exposure device, a developing device, and a transfer device around an image carrier.
These sequentially act on the image bearing member to form a toner image on the image bearing member, and the toner image is transferred by the transfer unit to the sheet material conveyed from the paper feeding unit at a predetermined timing by the transfer unit, After that, the transfer material passes through a nip portion of a fixing device including a heating roller and a pressure roller that is in pressure contact with the heating roller, and is discharged to the outside as a permanent image. Between the transfer unit, which is provided with a transfer device for transferring the toner image on the image carrier to the sheet material, and the fixing device, there is provided means for conveying or guiding the sheet material to the fixing device. A suction / conveyance belt that conveys the bottom surface of the sheet material while suctioning the bottom surface of the sheet material, a guide plate that guides the sheet material on the conveyance path, and the like are provided.

In an image forming apparatus in which the length of the sheet material is longer than the distance between the transfer portion 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. Has been done. When the sheet material passes over the transfer portion, the conveying means or the guiding means, and the fixing device and passes through the conveying path, it is preferable that the sheet material passes through the conveying path without any bending. That is, when the sheet material is bent, there is a risk of retransfer that the sheet material approaches the image carrier even if the sheet material passes through the transfer portion and the image transferred to the sheet material moves to the image carrier again. There is a problem that wrinkles easily occur in the sheet material passing through the fixing device.

On the other hand, when an image is formed on a sheet material that has been curled due to the curl of the roll paper, it is preferable to use the curl in a downward direction. By curling the sheet material downward, the sheet material curls away from the image carrier during the transfer process, and the sheet material is easily peeled off from the image carrier after the transfer. There is almost no risk of paper jams in.

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 formed of a flat plate having a width larger than the width of the maximum size sheet material, and the tip of the guide member is positioned near the inlet of the nip portion between the heating roller and the pressure roller that is in pressure contact with the heating roller to remove the sheet material. Guided 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 curls upward, the leading edge of the sheet material is guided away from the upper surface of the guide member, the sheet material cannot be guided to a predetermined position, and the sheet jams due to abutting against the heating roller. Paper jams and wrinkles may occur. As described above, even if the sheet material is curled, the problem of preventing the wrinkle of the sheet material from being peeled off from the image carrier and being fixed can be almost eliminated by making the sheet material face down.

[0006]

However, in such an image forming apparatus, the sheet material on the conveying path is conveyed so as to be pulled by sandwiching the heating roller and the pressure roller of the fixing device. For this reason, it is difficult for the trailing edge of the sheet material to contact the image carrier to the end due to the curling strain in the transfer portion. That is, the sheet material is attempted to be electrostatically attracted to the surface of the image bearing member during transfer holding, but it cannot be attracted to the surface of the image bearing member due to the curl strength of the sheet material, and the moving force of the image bearing member is further increased. Therefore, before the curled portion of the sheet material acts on the surface of the image carrier at the transfer portion, the sheet material is pinched by the fixing device so that the sheet material is pulled and conveyed by the conveying force. . Therefore, there is a problem that the toner image cannot be transferred onto the sheet material. A so-called transfer omission occurs.

This transfer omission occurs irregularly in the width direction of the sheet material, and is often seen especially in the central portion. Therefore, there is a problem that image information such as prints and drawings is missing at the rear end portion of the sheet material, and the appearance is not good. The sheet material contracts due to the heat of fixing when passing through the fixing device. Particularly in the case of forming a long image, the contraction amount of the sheet material increases and the fixing device acts to pull the sheet material in the latter half of the output, and due to this influence, the sheet material is conveyed in a stretched state. . When the trailing edge 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 a non-magnetic one-component toner, the toner image that has been transferred and left remains on the image bearing member, and static electricity removal and exposure at this portion leave a memory image. This may adversely affect image formation.

The present invention has been made in view of the above problems, and can reliably transfer the trailing edge of a sheet material even when the sheet material such as roll paper is curled. An object is to provide an image forming apparatus.

[0009]

In order to solve the above problems, the present invention relates to a transfer device for transferring a toner image formed on an image carrier to a sheet material at a transfer portion, and a toner image carried on the sheet material. An image forming apparatus having a fixing device including a heating roller for fixing a sheet and a pressure roller in pressure contact with the heating roller, the transfer unit and the fixing device immediately before the trailing edge of the sheet material passes through the transfer unit. And a flexure forming means for forming a flexure of the sheet material.

Further, the deflection forming means guides the sheet material in the upward direction of the entrance of the nip portion formed by the pressure contact between the heating roller and the pressure roller, and the rear end of the sheet material transfers the transfer material. It is characterized in that a guide member for changing the invasion angle into the fixing device downward to form the deflection is provided immediately before passing through the section.

Further, a means for conveying or guiding the sheet material is provided between the transfer section and the fixing device, and the suction conveying belt for conveying the sheet material while the means sucks the sheet material. Is characterized in that.

Further, the flexure forming means makes the transport speed of the fixing device slower than the transport speed of the image carrier immediately before the trailing edge of the sheet material passes through the transfer part, and the transfer part and the transfer part. A flexure is formed between the sheet material and a fixing device, and means for conveying the sheet material is provided between the transfer portion and the fixing device. Immediately before passing through the transfer portion, the conveyance 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 form a bend between the transfer portion and the means. It is characterized by

With such a structure, the guide member for guiding the sheet material to the fixing device is formed so as to form a bend between the transfer portion and the fixing device immediately before the rear end of the sheet material passes through the transfer portion. Change the angle. Alternatively, the speed of the fixing device is set to be slower than the moving speed of the image carrier so as to form a bend between the transfer part and the fixing device immediately before the trailing edge of the sheet material passes through the transfer part. The flexure 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 by the movement of the image carrier at the transfer unit. While transcribing. As a result, the sheet material moves on the image carrier so as to be pushed out, and even at the rear end of the curled sheet material, the sheet material comes into contact with the image carrier to transfer the toner image on the image carrier.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows 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 of the image carrier 2 (direction of arrow A) around the image carrier 2. An exposure device 4 having a light source such as a laser or an LED array for forming an electrostatic latent image on the image carrier 2, and toner is attached based on the electrostatic latent image to form a toner image on the image carrier 2. A developing device 5, a transfer device 7 that transfers a toner image to a sheet material 6 that comes into contact with and passes through 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 in the process is transferred onto the conveyed sheet material 6. A cleaning device for removing the toner remaining on the image carrier after the transfer may be provided between the transfer device 7 and the eraser lamp 8.

In the embodiment, as the sheet material 6, a roll paper provided in a paper feeding portion (not shown) is cut into a predetermined length by a cutter, and the leading end of the sheet material 6 is used as a registration roller 9. Then, the registration roller 9 is driven at a predetermined timing from the start of the image exposure by the exposure device 4, the sheet material 6 is conveyed, and the sheet material 6 is sent to the transfer portion 10 of the transfer device 7.

Reference numeral 11 is a fixing device for fixing, as a permanent image, the sheet material 4 carrying an unfixed toner image. The fixing device 11 is composed of a heating roller 12 having a heater therein and an elastic pressure roller 13 which is in pressure contact with the heating roller 11, and by this pressure contact, the nip 1 having a predetermined width is provided.
4, the sheet material carrying the unfixed toner image is passed therethrough, 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 feeding speed of the image carrier 2.

Between the transfer device 7 and the fixing device 11, means 15 for conveying the sheet material 6 toward the fixing device 11 is provided. As the means 15, for example, a suction conveyance belt 16 is preferably used. The suction / conveyance belt 16 stretches a plurality of or one belt 18 made of rubber or synthetic resin on a pair of rollers 17, and moves the belt 18 in the arrow direction by transmitting drive to the roller 17 connected to a drive source. There is. The belt 18 is provided with a plurality of holes, a box-shaped frame body 19 is arranged inside, and the bottom surface of the sheet material 6 conveyed by a suction fan 20 provided inside the frame body 19 is conveyed while being sucked. ing. Suction conveyor belt 16
Is set to be the same as the feeding speed of the image carrier 2 and the fixing device 11. By providing the transporting means such as the suction transport belt, the sheet material is reliably transported, and the transport path can be formed without any bending.

As an example of the flexure forming means 21 for forming a flexure of the sheet material 6 between the transfer portion 10 and the fixing device 11, the suction conveyance belt 16 is conveyed between the suction conveyance belt 16 and the fixing device 11. Guide member 22 for guiding the leading edge of the sheet material 6 to a predetermined position of the fixing device 11.
Is mentioned.

The guide member 22 is provided so as to be pivotable around a fulcrum 23, and a sheet material 6 is provided by a plunger 26.
It is provided so that the entry angle can be changed. Guide member 2
Reference numeral 2 denotes a metal plate or a synthetic resin flat plate having a width larger than the maximum size of the sheet material 6, and when the sheet material 6 enters the fixing device 11, the front end of the sheet material 6 is fixed to the fixing device 1.
The first position 2 so as to be guided to the heating roller 12 slightly above the first nip 14 and then guided to said nip.
Located at 4. At the first position 24 of the guide member 22, the front end of the sheet material is guided to the fixing device 11 and the heating roller is crowned so that the sheet material is fixed so as to be squeezed toward both ends, and wrinkles occur. Pass through the nip 14 so as not to. Immediately before the rear end of the sheet material 6 passes through the transfer section 10, the guide member 22 changes the angle around the fulcrum 23 by the action of the plunger 26 and positions it at the second position 25 (broken line). By changing the angle of the guide member 22 from the first position 24 to the second position 25, it is possible to form a bend in the sheet material 6 being conveyed.

Although there is no limitation on the amount of deflection of the sheet material, in the embodiment, the angle of the guide member 22 is changed from the first position 24 to the second position 25, so that the transfer portion from the transfer portion to the fixing device can be changed. More preferably about 0.5 mm to 3 mm
The sheet material is bent to make it longer. In the embodiment, when the conveying speed of the sheet material is 100 mm / sec, 0.5 sec from when the rear end of the sheet material passes the transfer portion
The deflection forming means is operated before 1.0 sec to form the deflection on the sheet material. That is, 5 from the rear edge of the sheet material
A bend is formed between 0 mm and 1000 mm. The range of the above-mentioned numerical values is preferable immediately before the sheet material passes through the transfer portion, but this numerical value is not limited, and the tension of the sheet material by the fixing device is eliminated when the sheet material passes through the transfer portion. Just go. The amount of deflection of the sheet material may be any 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 section. When the amount of deflection is large, the sheet material carries the image. Re-transfer occurs in which the toner image transferred to the sheet material comes into contact with the body even after passing the transfer portion and moves again to the image carrier.

With this structure, the sheet material 6 passes through the transfer section 10, and the toner image carried on the image carrier 2 is transferred by the well-known image forming method to the transfer section 10 by the action of the corona discharger 27. Transfer to the material 6. The transferred sheet material 6 is conveyed toward the fixing device 11 by the sheet material conveying unit 15. The leading end 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 sheet material 6 passing through the transfer unit 10, the sheet material conveying means 15 and the fixing device 11 has a moving speed of the image carrier 2, a conveying speed of the sheet material conveying means 15 and a fixing device 11 feeding speed. Is the same, and the sheet material 6 conveyed on the conveying path in these sections is conveyed so as to be in close contact with the conveying path, and is conveyed without being bent. Therefore, 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 sandwiching it.

When the trailing edge of the sheet material 6 reaches just before the transfer portion 10, for example, the guide member 22 which is the deflection forming means 21 receives a signal of cutting the sheet material 6 or a signal of passing the registration roller. From the first position 24 to the second position 25, the guide member 22 pivots around the fulcrum 23 by the action of the plunger 26 to change the penetration angle of the sheet material 6 into the fixing device 11. By changing the angle of the guide member 22, a bend is formed between the means 15 and the fixing device 11. Due to this bending, the sheet material 6 is moved by the movement of the image carrier 2 so as to send out the sheet material 6 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 removed. It is transcribed without any. 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, the rear end of the sheet material 6 in the transfer portion 10 is not hindered from coming into contact with the image carrier 2 so as to be wound. .

FIG. 1 shows an example in which the suction conveyance belt 16 having a driving force is used as the means 15, but instead of this, a plate-shaped guide plate for guiding the sheet material may be used, or the sheet may be used. The same effect can be obtained by using a guide plate provided with a plurality of ribs along the carrying direction so as to reduce the contact area with the bottom surface of the material. Alternatively, the main member for conveying or guiding the sheet material may be omitted and only the guide member may be configured.

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. The position 1 is fixed at the position 24. Descriptions of other reference numerals having the same operation will be omitted.

In FIG. 2, for example, the rear end of the sheet material 6 is detected by a sensor 30 provided near the registration roller 9 so that the rear end of the sheet material 6 is just before reaching the transfer portion 10. Based on the signal, the driving of the fixing device 11 and the means 15 is temporarily decelerated or stopped after a predetermined time or at the same time. As a result, the conveyance speed of the suction conveyance belt 16 as the means 15 and the feeding speed of the fixing device 11 are slower than the movement speed of the image carrier 2 and a bend is formed between the transfer portion 10 and the means 15. Due to this bending, the sheet material 6 passes through the transfer portion 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 sheet material 6 of the fixing device 11 due to the pulling of the sheet material at the transfer portion 10. 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 inertia gradually decelerates and the deflection height is 0.5 mm.
The fixing speed is not affected because the distance is set to 3 mm so that the speed becomes the same as the moving speed of the image carrier again.

In FIG. 2, an example in which the suction conveyance belt 16 having a driving force is used as the means 15 is shown. However, instead of this, a plate-shaped guide plate may be used, or contact with the bottom surface of the sheet material is possible. The same effect can be obtained even if the feeding speed of the fixing device is reduced or stopped by using a guide plate provided with a plurality of ribs along the transport direction so as to reduce the area. A configuration in which the means is omitted may be used.

[0027]

According to the image forming apparatus of the present invention, the 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 by the deflection forming means.
It is possible to transfer even at the trailing edge of the sheet material without affecting the transfer portion by the pulling of the sheet material of the fixing device. In addition, a stable amount of deflection can be formed by a simple configuration in which a guide member for guiding the sheet material is pivotally provided in the fixing device to form the deflection. Further, by providing a means for conveying or guiding the sheet material between the transfer portion and the fixing device, the sheet material can be conveyed or guided to the fixing device without any deflection on the conveying path, and the transfer of the sheet material can be performed. Make it optimal.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an image forming apparatus according to the present invention.

FIG. 2 is a schematic view showing another embodiment.

[Explanation of symbols]

1 Image forming device 2 Image carrier 6 sheet materials 10 Transfer part 11 Fixing device 15 means 16 suction conveyor belt 21 Deflection forming means 22 Guide member 24 First position 25 Second position

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 G03G 21/00 372 3F101 F term (reference) 2H027 DA32 DC04 DC05 DE09 EC06 EC18 ED16 ED24 ED25 EE01 EE03 EE05 EE07 EF09 ZA07 2H033 AA14 AA15 BA08 BA09 BA12 BA59 BB01 BB37 CA09 CA22 CA30 CA36 CA37 CA40 2H071 BA03 BA19 BA29 CA01 DA09 DA12 DA15 DA23 DA26 DA32 EA06 2H200 FA04 FA06 FA20 GA05 GA10 GA23 GA02 HA02 GB25 GA02 GA22 GA44 GA44 GA44 JB06 JB12 JB18 JB39 JB49 KA02 KA07 LA12 LA19 PA10 PA11 PA12 PA20 PB12 3F049 AA01 BA04 LA02 LA05 LA07 LB03 3F101 FA01 FB07 LA02 LA07 LB03

Claims (6)

[Claims] 1. A transfer device for transferring a toner image formed on an image bearing member 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 for pressing the heating roller. An image forming apparatus having a fixing device including a deflection device for forming a deflection of the sheet material between the transfer portion and the fixing device immediately before the rear end of the sheet material passes through the transfer portion. An image forming apparatus having. 2. The deflection forming means guides the sheet material upward of an entrance of a nip portion formed by pressure contact between the heating roller and the pressure roller, and a rear end of the sheet material transfers the transfer material. 2. The image forming apparatus according to claim 1, further comprising a guide member that forms the deflection by changing an invasion angle into the fixing device downward immediately before passing through the fixing unit. 3. The image forming apparatus according to claim 2, wherein means for conveying or guiding the sheet material is provided between the transfer portion and the fixing device. 4. The image forming apparatus according to claim 3, wherein the means is a suction conveyance belt that conveys the sheet material while suctioning the sheet material. 5. The flexure forming means sets the conveyance speed of the fixing device to be slower than the conveyance speed of the image carrier immediately before the trailing edge of the sheet material passes through the transfer portion, and the transfer portion and the fixing portion. The image forming apparatus according to claim 1, wherein a flexure is formed between the apparatus and the apparatus. 6. A means for conveying the sheet material is provided between the transfer portion and the fixing device, and the deflection forming means is configured to fix the fixing material immediately before a rear end of the sheet material passes through the transfer portion. 2. The flexure is formed between the transfer section and the means by making the carrying speed of the apparatus and the carrying speed of the means for carrying the sheet material slower than the carrying speed of the image carrier. Image forming device.