JP2003137467A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of reliably correcting a curled sheet without causing detrimental effects such as a defective conveyance of sheets, upsizing of the device, and decrease in the fixing temperature. SOLUTION: The image forming device is provided with a carrier belt 501 for carrying sheets and a pressing roller 502 coming into pressure contact with the carrier belt 501, and the curl generated on a sheet with an image heated and fixed by a fixing means is corrected by a curl correcting means 5 wherein the sheet is interposed and carried by the pressing roller 502 and the carrier belt 501 while the belt 501 is bent by the roller 502. When the curl is corrected, heat of the sheet is absorbed by the belt 501 and the belt 501 having absorbed the heat is cooled by a cooling means 503.

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, and more particularly to an image forming apparatus provided with a curl correcting device for correcting curl of a sheet on which an image is fixed.

[0002]

2. Description of the Related Art Conventionally, as an image forming process in an image forming apparatus such as a copying machine, a fax machine, a printer, etc., a toner image formed on a photosensitive drum of an image forming section is formed on a sheet fed one by one from a sheet feeding section. A well-known electrophotographic process in which a toner image on a sheet is pressed and heated at a fixing portion to be fixed as a permanent image is used.

By the way, in a conventional image forming apparatus for forming an image by using such an electrophotographic process, particularly in a case where an image is formed on both sides of a sheet, the sheet after image fixing has toner on the front and back sides. Curling is likely to occur due to differences in shrinkage rate, moisture absorption rate, and the like. Here, when the sheet is curled in this manner, a conveyance failure or an alignment failure may occur in a double-sided conveyance section located downstream of the fixing section or a sheet processing apparatus that performs processing such as binding on the sheet after image formation. May cause it. Therefore, conventionally, various curl correcting devices have been devised for correcting the curl of the sheet after fixing.

For example, in the curl correcting device disclosed in Japanese Unexamined Patent Publication No. 8-217313, a soft member such as a sponge roller or a conveyor belt is pressed against a hard member such as a metal roller and bent in the direction opposite to the curl direction of the sheet. A nip is formed, and the curl of the sheet is corrected by allowing the sheet to pass through the bent nip.

Further, in this curl correction device, the amount of toner that is a factor that changes the amount of curl, the environment of the device (temperature, humidity, etc.), the type of sheet (material, rigidity, thickness, size, crease direction, density, etc.) By predicting the curl amount of the sheet based on various information such as), and adjusting the bending amount of the nip based on the predicted curl amount, the transportability and consistency in the double-sided transport unit and the sheet processing device are always maintained. The sheet curl can be corrected to a level that does not cause any problems.

[0006]

However, in the image forming apparatus equipped with such a curl correcting device,
Since the curl correcting device is arranged near the fixing unit, before the heat applied to the sheet and the toner is sufficiently cooled,
That is, the sheet may be supplied to the curl correction device during the curl growth.

When the sheet is supplied to the curl correction device during the curl growth, the curl continues to grow even after the curl based on the predicted curl amount is given, and the correction effect is obtained. Sometimes it wasn't enough.

Therefore, in order to secure a sufficient sheet cooling time, for example, when the curl correcting device is arranged away from the fixing portion, not only the image forming apparatus becomes large, but also
The curl tip that has grown in the conveyance path to the curl correction device is caught in the guide joint part and bent at the corner, paper wrinkles, skew,
There was also the risk of jams and other conveyance defects. In addition, when the frontage of the seam is widened so as to allow the curl which has grown so that the curl tip does not catch on the guide seam, the image forming apparatus may be further increased in size. was there.

On the other hand, in order to sufficiently cool the sheet before reaching the curl correcting device, if a blowing fan or the like is provided to blow the cooling air directly onto the sheet, the sheet is cooled by the cooling air blown directly onto the sheet. There is a possibility that conveyance failure such as rattling, paper folding, paper wrinkles, and jam may occur, and that cooling air may enter the fixing section to lower the temperature of the fixing section.

Therefore, the present invention has been made in view of such a situation as described above, and does not bring about such problems as defective conveyance of sheets, enlargement of the apparatus main body, and lowering of the fixing temperature.
An object of the present invention is to provide an image forming apparatus capable of surely correcting the curl of a sheet.

[0011]

The present invention comprises an image forming portion for forming an image on a sheet, and a fixing means for heating and fixing the image formed on the sheet by the image forming portion onto the sheet. In the image forming apparatus, the image forming apparatus includes a conveyance belt that conveys the sheet on which the image is heated and fixed, and a pressure roller that is in pressure contact with the conveyance belt, and the pressure roller while bending the conveyance belt by the pressure roller. And a curl correction means for correcting the curl of the sheet by nipping and conveying the sheet with the conveyance belt, and a cooling means for cooling the conveyance belt.

The present invention is also characterized in that the conveyor belt is made of a material having good thermal conductivity so as to absorb heat of the sheet when the sheet is conveyed.

Further, the present invention is characterized in that the heat released from the conveyor belt by the cooling by the cooling means is discharged to the outside of the apparatus main body.

Further, the present invention is characterized in that the cooling means is a blowing means for blowing air to the inner peripheral surface of the conveyor belt to cool the conveyor belt which has absorbed the heat of the sheet. is there.

Further, the present invention is characterized in that the cooling means is a heat pipe for cooling the conveyor belt which has come into contact with the conveyor belt and has absorbed the heat of the sheet.

Further, the present invention is characterized in that at least one of the rollers for stretching the conveyor belt is constituted by the heat pipe.

Further, the present invention is characterized in that the pressure roller is constituted by the heat pipe.

Further, in the present invention, as the cooling means, air blowing means for blowing air to the inner peripheral surface of the conveyor belt to cool the conveyor belt which has absorbed the heat of the sheet, and to contact the conveyor belt. And a heat pipe for cooling the conveyor belt that has absorbed the heat of the sheet.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing the schematic arrangement of a digital copying machine which is an example of an image forming apparatus according to the first embodiment of the present invention.

In FIG. 1, 1A is a digital copying machine and 1 is a digital copying machine.
Is a main body of a digital copying machine (hereinafter referred to as an apparatus main body), a reader 2 for reading an image of a document is provided on an upper portion of the apparatus main body 1, an image forming unit 3 for forming an image on a sheet S is further provided at a central portion, A paper feeding unit 300 that feeds sheets to the image forming unit 3 is provided in the lower portion. Further, a sheet processing device 4 for performing alignment, sorting, stapling, folding, and the like on the discharged sheet after the image is formed by the image forming unit 3 is connected to the side end of the apparatus main body 1. .

Here, the image forming section 3 is arranged in parallel, and photoconductor drums 301a to 301d, which are image bearing members for respectively carrying toner images of four colors of yellow, magenta, cyan and black, and a charger 303a. ~ 303d,
Exposure devices 304a to 304d, developing units 305a to 305
d and the transfer belt 30 which is a transfer / conveying unit arranged in a vertical section below the photosensitive drums 301a to 301d.
Equipped with 2.

When the surfaces of the photoconductor drums 301a to 301d that are uniformly charged by the chargers 303a to 303d are scanned with laser light corresponding to the image information emitted from the exposure devices 304a to 304d, the photoconductor drums are scanned. A latent image is formed on the surface, and this latent image is further developed by the developing device 305a.
By developing with 305d to 305d, four color toner images of yellow, magenta, cyan and black are formed on the surface of the photosensitive drum.

After this, the photosensitive drums 301a-30
When the sheet S is conveyed to a transfer portion where 1d and the transfer belt 302 are in pressure contact with each other, as described later, the photosensitive drum 301a
The toner images formed on the sheets 301 to 301d are transferred to the sheet S.

The sheet feeding section 300 includes cassettes 306a to 306d for accommodating sheets S and cassettes 306a to 306d.
It has pickup rollers 307a to 307d for picking up the sheet S accommodated in. In addition, 30
A pair of registration rollers 8 conveys the sheet S to the transfer portion at a predetermined timing.

On the other hand, the reader 2 illuminates an original placed on the original glass 201 with an illumination lamp 202 and a CCD in the image sensor 207 by reflecting the reflected light from the original.
Reflecting mirrors 203, 204, 205 for forming an image on the sensor
And a lens 206 and the like.

In the figure, 2A is an automatic document feeder which is provided on the upper surface of the reader 2 so as to be openable and closable, and places the document D on the platen glass 201. This automatic document feeder 2A The reader 2 can be opened and closed centering on a hinge (not shown).

Next, an image forming operation of the multi-function digital copying machine 1A having the above-mentioned structure will be described.

First, when the copy button is turned on in the operation section (not shown), the original is placed on the original glass 201 by the automatic original feeder 2A, and the original is illuminated by the illumination lamp 202 of the reader 2. .

Then, the reflected light from this original is imaged on the CCD sensor in the image sensor 207 via the reflection mirrors 203, 204, 205 and the lens 206, and is separated into each color component of yellow, magenta, cyan and black. The pixel data is stored in an image memory (hard disk) (not shown) as pixel data. The pixel data stored in this memory is thereafter output to (the exposure devices 304a to 304d of) the image forming unit 3 in the order according to the editing mode designated by the operation unit (not shown) of the digital copying machine 1A. To be done.

Next, the photosensitive drums 301a to 301d driven by a motor (not shown) are chargers 303a to 303d.
03d, the exposure device 304a-
A predetermined laser beam based on the pixel data decomposed into each color component is irradiated by 304d, and a latent image is formed on the surface of the photoconductor drum. Then, each latent image is developed by the developing device 3.
The toner images of yellow, magenta, cyan, and black are sequentially formed on the photoconductor drum by being developed by 05a to 305d.

Further, in parallel with the toner image forming operation, the sheets S stored in the sheet cassettes 306a to 306d are picked up by the pickup rollers 307a to 307d, guided to the registration roller pair 308, and then the registration rollers. The pair 308 is placed on the transfer belt 302 in synchronism with the image forming operation, and is conveyed to the transfer unit where the photosensitive drums 301a to 301d and the transfer belt 302 are in pressure contact with each other.

Next, with respect to the sheet S conveyed to the transfer section in this way, the photosensitive drums 301a to 301d are operated by the transfer blades 309a to 309d arranged in each transfer section and applied with a voltage having a polarity opposite to that of the toner. The toner images of the respective colors above are sequentially superposed and transferred onto the sheet. Then, the sheet S on which the toner images of four colors are transferred in this manner is separated from the leading end in the conveying direction at the bent portion of the transfer belt 302 and is conveyed to the fixing device 310.

Next, the sheet is heated and pressed in the fixing device 310, whereby the toners of respective colors on the sheet are melt-mixed and fixed on the sheet. As a result, the full-color print image is fixed on the sheet as a permanent image.

Here, the digital copying machine 1A is capable of forming images on both sides, and the sheet S having an image formed on one side is conveyed again to the image forming section 3 by a double-sided conveyance path. 313 is provided.

As a result, when the one-sided copy is selected by the operation unit (not shown), the sheet S on which the toner image is fixed is formed.
After that, the sheet S is ejected to the outside of the image forming unit 3 through the sheet ejection path 314 by the sheet ejection roller 311, and the toner image is fixed on the sheet S when the double-sided copy mode is selected.
The sheet is guided to the double-sided conveying path 313 after the front and back sides are reversed by the reverse rotation of the reverse roller 312.

The sheet S guided to the double-sided conveyance path 313 in this way passes through the registration rollers 308 again, and the toner image is transferred and fixed by the same process as in the one-sided copying, and then is transferred to the outside of the image forming section 3. Is discharged.

By the way, the digital copying machine 1 described above is used.
In the above, the sheet S on which the toner image is fixed is in a state in which curling easily occurs. It should be noted that the curl mainly occurs due to the toner heated and melted by the fixing device being air-cooled and contracted during the transportation. Also, this curl amount is
The amount of toner on the sheet S (the difference between the front and back toner amounts in the case of double-sided copy paper), the type of the sheet S (material, rigidity, thickness, size, crevice direction, etc.) and the surrounding temperature and humidity environment, There is a correlation between the change factor and the curl amount.

Here, if such curl occurs, there is a risk of causing conveyance failure or misalignment in the double-sided conveyance path 313, the sheet processing apparatus 4, etc. located downstream of the fixing device 310, and therefore, downstream of the fixing device 310. Near the side,
A curl correction device 5 for correcting the sheet curl after fixing is provided.

In the present embodiment, when the sheet S passes through the transfer portion, for example, the photosensitive drums 301a to 301a-3.
The curl correcting device 5 is configured to correct the upward curl because the curl is made in a state in which the front end portion and the rear end portion face upward according to the shape of 01d.

FIG. 2 is a diagram showing the configuration of such a curl correcting device 5. The curl correcting device 5 has an endless conveyor belt 501 and a pressure roller 502 which is in pressure contact with the conveyor belt 501. I have it.

The conveyor belt 501 is made of, for example, a metal material such as aluminum, copper or silver in a thin film form by a method such as electroforming or thermal spraying, a silicon rubber sheet, or Japanese Examined Patent Publication No. 1-49642. It is formed of a material having excellent flexibility and thermal conductivity, such as a graphite sheet formed by graphitizing a polymer film whose manufacturing method has been disclosed in the publication. The pressure roller 502 is made of a hard material such as metal.

Here, in the curl correction device 5,
The pressure roller 502 is in pressure contact with the conveyor belt 501,
As the pressure roller 502 presses in this manner, the conveyor belt 501 bends upward along the outer diameter of the pressure roller 502. The sheet S having the upward curl opposite to the nip shape is conveyed in the nip between the upwardly bent conveyor belt 501 and the pressure roller 502, and the sheet S is conveyed to curl the sheet S. Can be modified.

The curl correction device 5 having such a configuration
The curl correction capability in is based on the curl amount predicted in advance using the above-mentioned curl change factor as curl information,
The pressure roller 502 can be adjusted by changing the pressure contact force of the pressure roller 502 with respect to the conveyor belt 501 and changing the bending amount.

On the other hand, in the curl correcting device 5, as shown in FIG.
Blower fan 50 which is a blower unit as a cooling unit that blows air to the inner peripheral surface of No. 1 and cools the conveyor belt 501.
3 are provided.

By the way, the heat of the sheet S is transferred to the conveying belt 501 from the outer peripheral surface which is in contact with the sheet S while the sheet S is being conveyed. That is, the conveyor belt 501 absorbs the heat of the sheet S from the outer peripheral surface. Note that, as described above, the transport belt 501 is made of a material having good thermal conductivity, so that the heat can be efficiently absorbed from the sheet S.

In this embodiment, the heat of the sheet S is efficiently absorbed by the conveyor belt 501 as described above, and the blower fan 5 is provided inside the conveyor belt 501.
03 is provided and air is blown to the inner peripheral surface of the transport belt 501, so that the heat of the sheet S is absorbed by the transport belt 501 and the heat absorbed by the transport belt 501 while the sheet S is being transported. So that it can be released. The released heat is exhausted to the outside by a cooling fan (not shown) provided in the apparatus body.

As described above, the pressure roller 502 is pressed against the conveyor belt 501 to bend the conveyor belt 501, and the blower fan 503 is disposed inside the conveyor belt 501, so that the heat of the conveyed sheet S is reduced. After being sufficiently cooled, the curl can be properly corrected according to the predicted curl amount. As a result, the growth of sheet curl due to insufficient cooling, corner crease due to it, paper wrinkles,
It is possible to prevent conveyance defects such as skew and jam.

The air blown by the air blower fan 503 of the curl correction device 5 acts only on the inner peripheral surface of the conveyor belt 501 and does not directly blow on the sheet S. There is no risk of paper conveyance failure such as paper folding, paper wrinkles, or jam, and there is no risk of the fixing temperature of the fixing device 310 being lowered by getting around the fixing device 310.

Further, since the curl correction device 5 has a simple structure in which the blower fan 503 is arranged on the inner peripheral surface of the existing conveyor belt 501, the image forming device 1 is increased in size. Nor.

The position where the curl correction device 5 is provided is not limited to the position described in the present embodiment, and may be provided at another position downstream of the fixing device 310. It goes without saying, however, that the closer to the fixing device 310 as in the present embodiment, the more the curl growth can be prevented and the transport stability is improved.

Further, as shown in the figure, the curl correcting device 5 is arranged upstream of the branch point between the discharge path 314 and the double-sided conveying path 313, so that each path 31
It is not necessary to provide the curl correction device 5 on the 3,314, and
This is effective because the curl correction device 5 can surely correct the curl of all the sheets S.

In the present embodiment, the case where the pressure roller 502 is pressed against the conveying belt 501 to bend the conveying belt 501 upward has been described, but the present invention is not limited to this. Instead, by reversing the upper and lower arrangements of the conveyor belt 501 and the pressure roller 502, the conveyor belt 501 can be bent downward, which causes a downward curl of the sheet in which the leading end and the trailing end face downward. It goes without saying that it can be modified.

Further, as shown in FIG. 3, the conveyor belt 50
The pressure rollers 502a and 502b are arranged above and below the sheet No. 1, and the sheet S is directed between the curl correcting device 5 and the fixing device 310 toward the nip portion between the transport belt 501 and the upper pressure roller 502a. The first conveying path 51 and the second conveying path 52 that directs the sheet S toward the nip portion between the conveying belt 501 and the lower pressure roller 502b are provided, and the sheet S is rotated by a flapper (not shown) according to the curl direction of the sheet S. The first
Alternatively, it may be selectively conveyed to the second passages 51 and 52.

By thus selectively conveying the sheet S to the first or second passages 51 and 52 in accordance with the curl direction, the curl of both the upward and downward sheets S is surely achieved. Can be modified to

Further, as shown in FIG. 4, the conveyor belt 50
1a and 501b and pressure rollers 502a and 502b are vertically reversed, and a plurality of curl correction devices 5a and 5b are arranged in parallel on the same conveyance path.
Even if the pressure contact force of 502b is selectively switched according to the direction and amount of curl, the curl of both the upward and downward sheets S can be reliably corrected.

With such a structure, if the upstream curl correcting device 5a can sufficiently cool the sheet S, the blower fan 503 is provided to the downstream curl correcting device 5b.
It is not necessary to provide b.

Next, a second embodiment of the present invention will be described.

In the above-described first embodiment, the cooling of the conveyor belt 501 is performed by the blower fan 503 (503a, 503).
However, in the present embodiment, for example, as shown in FIG. 5, in the present embodiment, a tube having a configuration in which a gas or a liquid is hermetically sealed inside the conveyor belt 501 as a cooling means for cooling the conveyor belt 501. The heat pipes 504 are contacted with each other.

By bringing the heat pipe 504 into contact with the conveyor belt 501 in this manner, the heat absorbed by the conveyor belt 501 from the sheet S is transferred to the heat pipe 504.
Can be absorbed by. As a result, the sheet S can be sufficiently cooled, and appropriate curl correction can be performed according to the predicted curl amount. The heat absorbed through the heat pipe 504 is discharged to the outside of the main body of the apparatus by a heat conducting means (not shown) or the like.

In the above description, the heat pipe 504 is arranged in contact with the upper outer peripheral surface of the conveyor belt 501 as shown in FIG.
The arrangement position is not limited to this as long as the heat can be transferred from No. 1 and may be arranged on the inner peripheral surface of the conveyor belt 501.

Further, the curl correcting device 5 according to the present embodiment, which is configured to cool the sheet by the heat pipe 504, is provided with the blower fan 503 shown in the above-described first embodiment. Even better, in the case of such a configuration, the sheet can be cooled more efficiently.

Next, a third embodiment of the present invention will be described.

In the above-described second embodiment, the case where the heat pipe 504 for cooling the conveyor belt 501 is provided as a separate body has been described, but in the present embodiment, as shown in FIG. 6, for example, By configuring one or both of the plurality of stretched conveyor belts 501, two stretch rollers 505 in the figure with a heat pipe,
A similar sheet cooling effect can be obtained.

In the case of such a configuration, it is not necessary to additionally dispose the heat pipe 504, and it is possible to reduce the cost and downsize the apparatus main body 1.

Further, the curl correction device 5 according to the present embodiment, which is configured to cool the sheet by the heat pipe 504, is provided with the blower fan 503 shown in the above-described first embodiment. Even better, in the case of such a configuration, the sheet can be cooled more efficiently.

Further, the pressure roller 502 facing the conveyor belt 501 may be constituted by a heat pipe. In this case, cooling can be performed from both sides of the sheet, and the cooling efficiency is further improved.

[0068]

As described above, when the curl is corrected by the curl correcting device which nips and conveys the sheet by the pressure roller and the conveyor belt while bending the conveyor belt by the pressure roller as in the present invention, the sheet is corrected. By cooling the conveyor belt that has absorbed the heat of the sheet by the cooling means, it is possible to surely correct the curl of the sheet without causing any adverse effects such as poor conveyance of the sheet, upsizing of the main body of the apparatus, and lowering of the fixing temperature. You can

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a digital copying machine that is an example of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a curl correction device provided in the digital copying machine.

FIG. 3 is a diagram showing another configuration of the curl correcting device according to the present embodiment.

FIG. 4 is a diagram showing another configuration of the curl correcting device according to the present embodiment.

FIG. 5 is a diagram showing a configuration of a curl correction device provided in a digital copying machine according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a curl correction device provided in a digital copying machine according to a third embodiment of the present invention.

[Explanation of symbols]

1A digital copier 1 device body 5 (5a, 5b) Curl correction device 310 Fixer 331 Image forming unit 501 (501a, 501b) conveyor belt 502 (502a, 502b) pressure roller 503 (503a, 503b) blower fan 504 heat pipe 505 tension roller

Claims (8)

[Claims] 1. An image forming unit for forming an image on a sheet,
An image forming apparatus comprising: a fixing unit configured to heat and fix an image formed on the sheet by the image forming unit, wherein a transport belt that transports the sheet on which the image is heat-fixed, and the transport belt. A curl correcting unit that has a pressure roller that is in pressure contact, and that corrects the curl of the sheet by nipping and transporting the sheet while the pressure roller and the conveyor belt bend the conveyor belt. An image forming apparatus comprising: a cooling unit that cools the conveyor belt. 2. The image forming apparatus according to claim 1, wherein the conveyor belt is formed of a material having a good thermal conductivity so as to absorb heat of the sheet when the sheet is conveyed. 3. The image forming apparatus according to claim 1, wherein the heat released from the conveyor belt by the cooling by the cooling unit is discharged to the outside of the apparatus main body. 4. The air-blowing means for blowing air to the inner peripheral surface of the conveyor belt to cool the conveyor belt having absorbed the heat of the sheet. The image forming apparatus according to claim 1. 5. The heat pipe according to claim 1, wherein the cooling means is a heat pipe that cools the conveyor belt that comes into contact with the conveyor belt and absorbs heat of the sheet. The image forming apparatus described. 6. The image forming apparatus according to claim 5, wherein at least one of the rollers that stretches the conveyor belt is formed of the heat pipe. 7. The image forming apparatus according to claim 5, wherein the pressure roller is constituted by the heat pipe. 8. As the cooling means, a blowing means for blowing air to the inner peripheral surface of the conveyor belt to cool the conveyor belt which has absorbed the heat of the sheet, and a blowing means for contacting the conveyor belt to convey the sheet. The image forming apparatus according to any one of claims 1 to 3, further comprising a heat pipe that cools the conveyor belt that has absorbed heat.