JP2000272802A - Paper uncurling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uncurl the paper from its point end to its rear end while improving the uncurling effect toward the rear end by temporarily stopping the point of the paper in front of second feed rollers by a stopper, and then feeding the paper by the second feed rollers. SOLUTION: In an image forming device 1, a toner image formed on a photoreceptor 2 is transferred onto the fed paper, the transferred image is thermally fixed by a fixing unit, 3, and the paper having the image is fed out to a paper feeding-out portion 4. A paper feed passage 12 is provided with a paper sensor 10 detecting the paper, a pair of first feed rollers 18, a pair of second feed rollers 11 positioned at a downstream side of the first feed rollers 18, and a space 19 between the first feed roller 18 and the second feed roller for receiving the loop of the paper. A feed speed of the second feed rollers 11 is lower than that of the first feed rollers 18, and the second feed rollers 11 can be stopped for a predetermined time. Whereby the loop is formed on the fed paper, and the curling of the paper caused by the heat fixing can be uncurled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet curl correcting apparatus for correcting curl of a sheet caused by heat-fixing of a toner image in an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus.

[0002]

2. Description of the Related Art Conventionally, as this type of curl correction device, for example, as shown in Japanese Patent Publication No. 6-84223, a roller for conveying a sheet is stopped for a predetermined time to form a loop on the sheet. As disclosed in Japanese Patent No. 2637619, there is a technique for correcting a curl, and a technique for detecting a curl amount by a sensor and setting a speed difference between rollers to perform appropriate correction.

[0003]

By the way, the curl of the sheet caused by the fixing is generally larger toward the end face. If the paper edge is curled, staples,
In the case of performing binding or the like, since defects such as paper misalignment and staple failure tend to occur, it is necessary to correct the curl of the paper, particularly the end face. However,
In the technique disclosed in Japanese Patent Publication No. 6-84223, the rear end is corrected by stopping a roller near the rear end of the sheet. Therefore, the leading end of the sheet cannot be corrected. If the paper is stopped at the leading edge to solve this problem, the correcting effect at the trailing edge is insufficient.

Further, in the technique disclosed in Japanese Patent No. 2637619, a curl correction is performed by detecting a curl amount and fixing a speed difference between rollers to a certain value to form a loop. Since the speed difference is fixed in this manner, the loop amount becomes larger toward the rear end of the sheet, and a sufficient correction effect can be obtained at the rear end, but the loop is small at the front end, and a sufficient correction effect cannot be obtained. In each of the techniques, the time during which the loop is formed is short, and when the curl is extremely large, the correction effect may be insufficient even if the loop amount is increased. On the other hand, if the loop amount is too large, a side effect of the paper being wavy is generated.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a paper curl straightening apparatus capable of straightening from the leading edge to the trailing edge of a sheet and achieving a higher straightening effect toward the trailing edge. I do. It is another object of the present invention to provide a paper curl correcting device capable of appropriately performing curl correction on a paper curl having a large curl by controlling a loop amount according to a position of a paper.

[0006]

According to a first aspect of the present invention, there is provided a sheet curling device provided in a sheet conveying path for correcting the curl of a conveyed sheet. Between the first transporting means, the second transporting means located downstream of the first transporting means and set to a transporting speed lower than the transporting speed of the first transporting means, and the first and second transporting means. A stopping means for stopping the leading end of the sheet for a predetermined time, and a space for receiving a sheet loop generated between the first and second conveying means.

In the above construction, the second means is provided by the stopping means.
By temporarily stopping the leading edge of the sheet before the transporting unit and then transporting the sheet by the second transporting unit, transporting in a state where a loop is formed from the leading edge of the sheet becomes possible. Moreover, the first and second
Since the relationship between the speeds of the conveying means is set higher in the first conveying means than in the second conveying means, the loop amount becomes larger toward the rear end of the sheet, and a stronger correction effect can be obtained. As a result, the correction can be performed from the leading edge to the trailing edge of the sheet, and the correcting effect can be enhanced toward the trailing edge.

According to a second aspect of the present invention, in the paper curl correcting apparatus according to the first aspect, there is provided a means for setting a transport speed of at least one of the first and second transport means. In this configuration, the transport speed can be appropriately set according to the degree of need for curl correction.

According to a third aspect of the present invention, in the paper curl correcting apparatus according to the first aspect, the stopping means stops the operation of the second conveying means, a stopper member for contacting the leading end of the paper, or a driving force. Is one of the roller pairs that do not have In this configuration, a loop is formed from the leading edge to the trailing edge of the sheet, and curl correction can be performed entirely.

According to a fourth aspect of the present invention, there is provided a sheet curling device according to the first aspect provided downstream of a heat fixing unit for fixing an image formed on a sheet, and a space is provided between the front and back of the sheet. The heat fixing means projects to the side where the temperature is set low. In this configuration, the direction of the curl generated on the sheet by heat fixing is usually on the side where the temperature of the heat fixing means is set high, but since a loop is formed in the opposite direction, the curl correction is performed. It can be done properly.

According to a fifth aspect of the present invention, there is provided the sheet curling device according to the first aspect, further comprising a heat fixing means for fixing an image formed on the sheet, and the first transport means is provided with a heat fixing means. This is an image forming apparatus arranged downstream. In this configuration, the curl correction of the sheet on which the image is formed can be properly performed.

According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, the first transporting means is a heat transporting type fixing transporting means. In this configuration,
One of the components of the curl correction device can be shared by the heat fixing and conveying means.

According to a seventh aspect of the present invention, in the paper curl correcting apparatus according to the first aspect, the first conveying means is located in a paper discharging device connected to the image forming apparatus.
With this configuration, a paper ejection device having a curl correcting function equivalent to that of the first aspect is obtained.

According to an eighth aspect of the present invention, in the paper curling device according to the first aspect, the first transporting means is a discharge roller of the image forming apparatus, and the second transporting means is connected to the image forming apparatus. It is located in the paper discharge device. In this configuration, a part of the components of the curl correction device is provided in the image forming apparatus, and a paper discharge device in which the number of components is reduced can be obtained.

According to a ninth aspect of the present invention, there is provided a sheet curl correcting device provided in a sheet conveying path for correcting curl of a sheet to be conveyed, comprising: a first conveying means for conveying the sheet;
A second transporting means located downstream of the first transporting means, a control means for controlling the transporting speed of the second transporting means, a detecting means located near the upstream of the first transporting means and detecting a sheet; And a space for receiving a loop of the paper, wherein the control means controls the transport speed of the second transport means to be lower than that of the first transport means within a range where the trailing edge of the paper does not interfere with the leading edge of the next paper. Is what you do.

In the above configuration, the correction of the correction effect is enhanced by stopping the conveyance of the second conveyance means and forming a loop at the rear end of the sheet and keeping the state long. In order to enhance this effect, the loop is detected by detecting the leading edge of the next sheet to be transported, detecting the leading edge reaching the first transport unit, and releasing the stop of the second transport unit to start transport. Calculate the time to cancel, compare these, and control to set the paper stop time to the maximum. It should be noted that the same operation can be obtained by controlling the second transport means to an extremely low speed instead of stopping.

According to a tenth aspect of the present invention, in the paper curl correcting apparatus according to the ninth aspect, when the transport speed of the second transport unit is switched to the low speed a plurality of times for one sheet, the low speed is finally determined. Is longer than the time of each of the other low-speed rotations. In this configuration, the loop state is maintained for the longest time on the rear end side of the sheet, and the correction effect at the rear end can be enhanced.

According to an eleventh aspect of the present invention, there is provided a sheet curl correcting device provided in a sheet conveying path for correcting the curl of a sheet to be conveyed. Lowering the transport speed of the sheet between the second transport unit located downstream and the first and second transport units;
A means for generating a loop in the sheet, a space for receiving the loop of the sheet to be generated, a sheet detecting means for detecting the sheet, and a conveying speed of at least one of the first and second conveying means based on an output of the sheet detecting means. And control means for controlling.

In the above arrangement, the transport speed of the first or second transport unit can be changed based on the output of the sheet detecting unit. A predetermined loop amount is maintained by switching the transport speed of the unit to the same speed as the first transport unit, or the loop is eliminated by switching to a high speed. The second at the trailing edge of the paper
By setting the transport speed of the transport unit to be lower than that of the first transport unit, the loop amount is increased or a loop is formed again. Thus, the leading and trailing edges of the sheet can be reliably corrected.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. The paper curl correcting apparatus according to the present embodiment is provided in an electrophotographic apparatus (image forming apparatus) such as a laser printer or a copying machine. FIG. 1 shows an image forming apparatus according to the first embodiment. The image forming apparatus 1 transfers the toner image formed on the photoreceptor 2 onto a sheet to be conveyed, heat-fixes the transferred image by a heat fixing device 3 (fixing unit), and removes the sheet on which the image is formed. The paper is discharged to the paper discharge unit 4.
Around the photoreceptor 2, electrophotographic processing means such as an exposure means 20, a developing means 21, and a transfer means 22 are arranged. The sheet feeding device 5 (sheet feeding means) includes a plurality of sheet feeding cassettes 5.
1, 52, and 53 and a manual paper feed unit 54. Sheets are fed one by one from one of the sheet feeding devices 5 by a sheet feeding roller 55, and are fed to a sheet feeding path 12 in which a feeding roller 56 is disposed.
Supplied through. The heat fixing device 3 includes a pair of heat rollers 3a and a pressure roller 3b.

The paper transport path 12 includes a paper sensor 10 (paper detection means) for detecting a paper and a pair of first transport rollers 18 (a paper detection means) in a path toward the paper discharge section 4 on the downstream side of the thermal fixing device 3. A first conveying unit), a pair of second conveying rollers 11 (second conveying unit; also serving as a paper discharging roller) positioned downstream thereof, a first conveying roller 18 and a second conveying roller 11.
There is provided a space 19 provided between them for receiving a paper loop. The transport speed of the second transport roller 11 is the first
The speed is set to be slower than that of the transport roller 18, and the second transport roller 11 can be stopped for a predetermined time (stop means). Thereby, a loop can be generated in the conveyed sheet. The above components constitute a paper curl correcting device for correcting curl generated on paper by thermal fixing. Note that at least one or both of the first transport roller 18 and the second transport roller 11 may be capable of speed control.

Here, the fixing operation of the heat fixing device 3 will be described with reference to FIGS. Since the heat fixing device 3 has a heater only inside the heat roller 3a on the image surface side, the temperature and the heat amount are different between the heat roller 3a on the image surface side and the pressure roller 3b on the back side. When a sheet containing a large amount of water is passed through the thermal fixing device 3 having such a configuration, uneven heat is applied to the front side (image side) and the back side of the sheet. The water moves and is dried while evaporating to the lower side (FIG. 2). Drying causes the fibers of the paper to shrink, but the moisture contained in the paper moves from the front to the back of the paper and is released from the back, eventually drying both sides of the paper to the same moisture content.

There are two types of fiber shrinkage: inter-fiber shrinkage, in which fibers are drawn by the surface tension of water when water evaporates, and intra-fiber shrinkage, in which the fiber diameter and length simply shrink.
In the case of the above fixing configuration, since the front side (image side) is directly heated, only shrinkage in the fiber occurs, and a large amount of water moves from the front side to the back side (non-image side), and the moisture between the fibers. Is interposed in a liquid state, so that inter-fiber contraction occurs in addition to intra-fiber contraction. Therefore, the degree of shrinkage of the front and back is different, and the degree of shrinkage of the fiber is larger on the back side. Therefore, the paper is largely curled toward the non-image side. Further, the curl is affected by the streaks of the paper and curls around the direction of the streaks (FIG. 3).

If the curl of the sheet is large, various problems occur in the sheet discharging device, such as an irregular sheet at the time of storage and an insufficient number of stacked sheets. If the moisture content of the paper is low,
Since the change in moisture is small, the curl itself is also small and poses no problem. The above is the case where the image is a text including only characters, and in the case of a solid image or a color image with a large amount of toner adhesion, in addition to the curl due to the above-mentioned change in moisture, the curl due to toner shrinkage is added. This is not the case.

The curl correcting apparatus according to the present invention can obtain a remarkable function and effect when the amount of moisture is large and abrupt because the relatively high wet paper is fixed. The effect is
Specifically, it utilizes the fact that the fibers of the paper are hydrogen-bonded, and the water rapidly changes due to the heat of the fixing means, so that the water intervenes between the fibers in a liquid state. This causes changes such as weakening of hydrogen bonds and increase of bonding points. Immediately after passing through the fixing means, it becomes an area in which the recombination between the fibers is performed, and by bending the paper to form a loop, the paper is distorted,
Correction is made possible by recombining in a distorted state. Therefore, the closer the correction is to the fixing unit, the higher the correction effect is, and if the correction is performed immediately after fixing or within the range up to the entrance of the paper discharge device, the curl can be corrected by forming only a small loop. Can be. However, since the recombination time between the fibers is long, even if the correction is performed near the exit of the sheet discharging device, the curl can be corrected by enlarging the formed loop. Further, if the paper is caused to pass through a curved path in the direction opposite to the loop before the loop is formed, the paper is curved and distortion is applied, so that the effect is weakened.

FIG. 4 shows a configuration of an embodiment of the curl correcting device. The sheet is heat-fixed with the toner image by the heat fixing unit 3 and passes through a sheet detection sensor 10 located downstream of the sheet.
It is transported to the first transport roller 18. Second transport roller 11
Is configured to be rotatable and stoppable by a motor, a clutch or the like (not shown), and based on a signal that the sheet detection sensor 10 detects the leading edge of the sheet, stops the rotation of the second transport roller 11 and forms a loop. After a predetermined time, the second transport roller 11 starts rotating at a transport speed lower than that of the first transport roller 18. By changing the stop time of the second transport roller 11, the loop amount at the leading end of the sheet can be adjusted.

It is the high-moisture paper that curls during fixing, and as described above, curls toward the opposite side of the image surface (roller side having a lower temperature) (in FIG. 4, the front and rear ends of the paper face upward). Since it is known that the paper P curls downward, the guide plate of the paper transport path 12 forms the space 19 so that the paper P forms a loop on the side opposite to the curl direction. However,
In the case where the fixing method is not a color image forming apparatus or a one-sided heater, the space may be formed in the opposite direction.

The driving of the second transport roller 11 is set to a speed slightly lower than that of the first transport roller 18. As the paper is transported, the loop amount sequentially increases due to the speed difference between the two rollers. As a result, the correction effect can be enhanced toward the rear end of the sheet. Also, the first transport roller 1
8, the second transport roller 11 may be configured to be able to set at least one of the transport speeds thereof, and by setting the speed difference between the second transport roller 11 and the first transport roller 18, the correction effect is obtained. Can be adjusted. The setting method is performed by input means such as an operation panel (FIGS. 8 to 10 described later).

FIG. 5 shows a configuration of another embodiment of the curl correcting device. A stopper 31 as a means for stopping the paper is provided so as to protrude and retract at a position immediately before the transport roller 11 by a driving means such as a motor, a solenoid, and a cam (not shown). When the sheet detection sensor 10 detects the leading end of the sheet P, the stopper 31 protrudes into the sheet conveyance path to stop the sheet P, and retreats after a predetermined time. By changing the stop time, the amount of loop at the leading end of the sheet can be adjusted.

FIG. 6 shows a configuration of a curl correction device according to still another embodiment. The second downstream of the first transport roller 18
Immediately upstream of the transport roller 11, a roller pair 32 having no driving force is provided as stopping means. This roller pair 3
Numeral 2 is configured to rotate when the paper P is sent from the upstream and reaches a predetermined rotation torque. Until the sheet P is nipped by the pair of rollers 28 and the pair of rollers 28 starts to rotate, the sheet P is temporarily stopped and a loop is formed.

FIG. 7 shows an embodiment in which a curl correcting device is provided in a paper discharging device. In this embodiment, a paper discharge device 40 such as a sorter that receives a paper discharge after image output is connected to the image forming apparatus 1. The paper discharge device 40 includes a plurality of bins 41 for receiving paper, a passage switching mechanism 42 for sorting paper discharge,
The image forming apparatus 1 includes a carry-in roller 43 (second carrying means) for receiving a sheet discharged by the paper discharging roller 11 (here, it corresponds to the first carrying means instead of the second carrying means). By controlling the downstream carrying roller 43 to be driven at a speed lower than the carrying speed of the paper discharging roller 11, the carrying of the leading end side of the paper is delayed, so that the space between the image forming apparatus 1 and the paper discharging device 40 ( A paper loop is formed in the space 19 formed between the carry-in roller 43 and the paper discharge roller 11). Thereby, a correction effect is obtained. In this embodiment,
Although the paper discharge roller 11 of the image forming apparatus 1 is used as the first transport roller, a configuration in which the first transport roller is provided in the paper discharge device 40 is also possible.

FIG. 8 shows a panel 15 provided as an input unit of paper characteristics provided in the image forming apparatus 1. The operation panel 15 has an operation key and a display LCD 16, by which an operator or a serviceman can set whether or not to apply a curl correction effect to the sheet passed through each sheet feeder. it can. 9 and 10 show display examples of the LCD 16. In the display state of FIG. 10, the curl correction effect can be set.

Next, a loop amount control operation in the curl correction device as described above will be described with reference to FIGS. FIGS. 11 and 12 show time charts of loop amount control in the embodiments of FIGS. 4 and 5, respectively (corresponding to claim 1). At the timing when the sheet detection sensor 10 detects the leading edge of the sheet and the signal is turned on, the rotation of the second conveying roller 11 is stopped, or the stopper 31 is moved to the sheet conveying path 12.
The rotation starts again after a predetermined time t1, or the stopper 31 is retracted. Here, the first transport roller 18
Is faster than the transport speed of the second transport roller 11, the loop position formed on the sheet moves between the two rollers, and the loop amount gradually increases. Thereafter, after the sheet detection sensor 10 detects the trailing edge of the sheet and its signal is turned off, when the trailing edge of the sheet is separated from the first transport roller 18, the loop is gradually eliminated. By performing such control, a curl correction can be performed by forming a loop from the leading end side of the sheet, and the correction effect can be enhanced toward the trailing end side.

FIG. 13 shows a time chart of another loop amount control (corresponding to claim 9). In this control, the transport speed of the second transport roller 11 is maintained lower (or stopped) than the first transport roller 18 within a range where the trailing edge of the first sheet does not interfere with the leading edge of the second sheet. Control. That is, at the timing when the sheet detection sensor 10 detects the trailing edge of the first sheet and the sensor signal is turned off, the rotation of the second conveyance roller 11 is stopped.
A loop is formed at the trailing edge of the sheet, and that state is temporarily maintained. Before the leading edge of the second sheet arrives, the rotation of the second transport roller 11 is started to eliminate the loop of the trailing edge of the first sheet.

In such control, the transport of the second transport roller 11 is stopped, a loop is formed at the trailing end of the sheet, and the state is maintained for a long time to improve the correction effect. The time required for the leading edge of the next transported paper to reach the first transport roller 18 and the second transport roller 1
It is sufficient to calculate the time until the loop is eliminated by releasing the stop of No. 1 and starting the conveyance, compare these, and control to set the paper stop time to the maximum. In addition,
The same effect can be obtained by controlling the second transport roller 11 to an extremely low speed instead of stopping it.

FIG. 14 is a time chart of still another loop amount control, in which the transport speed of the second transport roller 11 is switched to a low speed a plurality of times (here, the leading edge and the trailing edge) on one sheet. And the last time t2 during which the motor rotates (or stops) at low speed is the other low-speed rotation (or stops).
The time is longer than the time t1 (corresponding to claim 10). With this control, the loop position of the sheet moves, and the loop state is maintained for the longest time on the rear end side of the sheet, and the correction effect at the rear end can be enhanced.

FIGS. 15 and 16 are time charts of still another loop amount control, wherein the transport speed of the second transport roller 11 is controlled based on the output of the sheet detection sensor 10. 11). In this example, after the predetermined loop is formed in the same manner as described above, the transport speed of the second transport roller 11 is switched to the same speed as the first transport roller 18 to maintain the predetermined loop amount (or by switching to high speed). The loop is eliminated; FIG. 16).
The amount of loop is increased (or a loop is formed again) by setting the transport speed of the first transport roller 18 to be lower than that of the first transport roller 18.
I do. Thereby, the leading and trailing edges of the sheet can be corrected.

FIGS. 17 and 18 show a case in which the stopper 31 and the second transport roller 11 are used as the stopping means, and the same operations as those in FIGS. 15 and 16 are obtained.

As described in the above embodiments, the means for stopping the paper is configured to be able to rotate and stop the second transport roller by a motor, a clutch, or the like. The rotation of the two transport rollers may be stopped. By changing the stop time of the roller, it is possible to adjust the loop amount at the leading end of the sheet. When a stopper is used, the stopper is configured to protrude and retract with respect to the conveyance path by driving means such as a motor, a solenoid, and a cam. May be stopped, and evacuation may be performed for a predetermined time. By changing the time for stopping the paper, the same operation as described above can be obtained. In addition, the timing of switching the speed of the second transport roller may be determined by detecting the leading edge and trailing edge of the sheet and performing it after a predetermined time, detecting the leading edge of the sheet and counting the pulses of the motor, and other known methods. Is applicable.

In the above description, the case where the curl of the sheet end face is large, which is a general case, has been described as an example. However, if the curl of another tendency occurs due to the configuration of the fixing device and other requirements, the case is considered. It is also possible to control so as to obtain an appropriate effect on curling.

[0041]

As described above, according to the present invention, it is possible to temporarily stop the leading edge of the sheet in front of the second transport means located on the downstream side and transport the sheet in a state where a loop is formed from the leading edge of the sheet. Further, since the transport speed of the second transport unit is set lower than that of the first transport unit, the loop amount becomes larger toward the rear end of the paper, and the curl correction effect can be obtained from the leading end side of the paper to the trailing end. Moreover, a high curl correction effect can be obtained on the rear end side. The curl correction effect at the trailing edge of the paper is enhanced by controlling the suspension so that the loop is formed at the trailing edge of the paper within a range that does not interfere with the leading edge of the next paper. be able to. Further, by controlling the loop amount in accordance with the position of the sheet, it is possible to appropriately correct the curl of the end face of the sheet having a large curl.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image forming apparatus equipped with a curl correction device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state change of a sheet passing through a one-sided heater fixing device.

FIG. 3 is an explanatory diagram showing a change in the state of a sheet due to the eyes of the sheet.

FIG. 4 is a configuration diagram of a curl correction device according to an embodiment of the present invention.

FIG. 5 is a configuration diagram of a curl correction device according to another embodiment.

FIG. 6 is a configuration diagram of a curl correction device according to still another embodiment.

FIG. 7 is a configuration diagram in which a curl correction device is provided in a paper discharge device.

FIG. 8 is a configuration diagram showing input means for a curl correction effect.

FIG. 9 is a diagram showing a display example of a curl correction effect input unit.

FIG. 10 is a diagram showing a display example of a curl correction effect input unit.

FIG. 11 is a timing operation diagram of loop amount control.

FIG. 12 is a timing operation diagram of loop amount control.

FIG. 13 is a timing operation diagram of loop amount control.

FIG. 14 is a timing operation diagram of loop amount control.

FIG. 15 is a timing operation diagram of loop amount control.

FIG. 16 is a timing operation diagram of loop amount control.

FIG. 17 is a timing operation diagram of loop amount control.

FIG. 18 is a timing operation diagram of loop amount control.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Thermal fixing device (fixing means) 10 Paper sensor (paper detection means) 11 2nd conveyance roller (2nd conveyance means, but the 1st conveyance means in FIG. 7) 12 Paper conveyance path 18 1st conveyance roller ( (First transporting means) 19 space 31 Stopper (stopping means) 32 Roller pair having no driving force (stopping means) 40 Paper discharge device 43 Loading roller (second transporting means)

Claims (11)

[Claims] 1. A paper curl correction device provided in a paper transport path for correcting curl of a transported paper, comprising: a first transport unit for transporting the paper; a first transport unit downstream of the first transport unit; A second conveying unit set to a conveying speed lower than the conveying speed of the first conveying unit; a stopping unit for stopping a leading end of the sheet between the first and second conveying units for a predetermined time; A paper curl correcting device, comprising: a space for receiving a paper loop generated between conveying means. 2. The paper curl correcting device according to claim 1, further comprising means for setting at least one of the first and second conveying means. 3. The method according to claim 2, wherein the stopping unit stops the operation of the second conveying unit, is a stopper member that comes into contact with the leading edge of the sheet, or is a pair of rollers having no driving force. 2. The paper curl correcting device according to 1. 4. A space provided downstream of a heat fixing unit for fixing an image formed on a sheet, wherein the space projects from a front side and a back side of the sheet to a side where a temperature of the heat fixing unit is set low. The paper curl correcting device according to claim 1, wherein: 5. A sheet curling device according to claim 1, further comprising: a heat fixing unit for fixing an image formed on a sheet, wherein the first conveying unit is disposed downstream of the heat fixing unit. An image forming apparatus comprising: 6. The image forming apparatus according to claim 5, wherein the first transport unit is a thermal transport type fixing transport unit. 7. The image forming apparatus according to claim 1, wherein the first transport unit is located in a paper discharge device connected to the image forming apparatus.
Paper decurling apparatus according to 1. 8. The image forming apparatus according to claim 1, wherein the first transport unit is a discharge roller of the image forming apparatus, and the second transport unit is located in a paper discharge device connected to the image forming apparatus. Paper curl straightener. 9. A paper curl correction device provided in a paper transport path for correcting curl of a transported paper, wherein the first transport means transports the paper, and the second transport means is located downstream of the first transport means. Transport means; control means for controlling the transport speed of the second transport means; detection means located near the upstream of the first transport means for detecting paper; and a space for receiving the generated paper loop. Wherein the control means controls the transport speed of the second transport means to be lower than that of the first transport means within a range in which the trailing edge of the paper does not interfere with the leading edge of the next paper. Straightening equipment. 10. The method according to claim 1, wherein the second step is performed a plurality of times on one sheet.
10. The paper curl correcting device according to claim 9, wherein when the transport speed of the transport unit is switched to a low speed, the time of the last low-speed rotation is longer than the time of each of the other low-speed rotations. 11. A paper curl correcting device provided in a paper transport path for correcting curl of a transported paper, wherein the first transport means transports the paper, and the second transport means is located downstream of the first transport means. Transport means; means for reducing the transport speed of the paper between the first and second transport means to generate a loop in the paper; space for receiving the generated paper loop; and paper detection means for detecting the paper A sheet curling device, comprising: a control unit that controls a conveying speed of at least one of the first and second conveying units based on an output of the sheet detecting unit.