JPH10123781A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically detect the curl direction of a paper irregularily curled upward or downward after fixing processing so as to adequately straightening the curl. SOLUTION: A first curl straightening member 28a straightening an upward curl paper S and a second curl straightening member 28b straightening a downward curl paper S are provided between two pairs of rollers 26, 26 and 27, 27. A path switching mechanism 30 is proved so that a posture can be changed to a first paper feeding posture C to the straightening path 21a of the upward curl paper S and to a second paper feeding posture to the straightening path 21b of the downward curl paper S. The mechanism 30 changes the posture to the first paper feeding posture C based on the upward curl detection result from a curl detecting means 33, and changes the posture to the second paper feeding posture based on the downward curl detection result.

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 an electrostatographic copier, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art In the above-described image forming apparatus, the paper on which a toner image is formed is curled upward after a fixing process due to the influence of environmental humidity, the amount of information of a toner image, or the like. Although it is considered that the influence is exerted on the sheet, the sheet after the fixing process may be irregularly curled upward or downward.

If the sheet after the fixing process curls irregularly upward or downward, in particular, the sheet is taken out to the sheet re-feeding means in the apparatus, and the sheet is re-supplied to the image forming section. When paper is formed and an image is formed on one side of a sheet by superimposition or an image is formed on both sides of the sheet, a jam is likely to occur in the re-feed section.

If the curled sheet is curled upward at the stage when the curled sheet is re-fed to the image forming unit, the leading end of the sheet may be wound around the photosensitive drum of the image forming unit, or may be reversed. When the sheet is curled downward, the leading end of the sheet is separated from the photosensitive drum, which may cause a transfer failure at the leading end of the sheet.

Japanese Patent Laid-Open No. Hei 6-115 discloses means for correcting the curl of an upwardly curled sheet.
No. 792. As shown in FIG. 13, the curl correcting means includes a pair of fixing rollers 5.
1, 51 pairs and paper discharge rollers 52, 52 pairs having a higher rotation speed than the rollers 51, 51 pairs are arranged.
The tension in the sheet transport direction is applied to the sheet S after the fixing process, and the two sets of rollers 51, 51,
A curl correcting member 53 for curving the tensioned sheet S to the front side is provided between the pair of rollers 52 and 52 to correct the curl of the sheet S curled upward.

[0006]

However, in such a curl correction technique, as described above, only the paper S curled upward is targeted for curl correction. There is an inconvenience that a sheet having a downward curl, which occurs irregularly under the conditions, cannot be subjected to the curl correction.

There is also a problem that the curl cannot be corrected over a long range of the trailing edge Sa of the sheet. That is, the curl correction by the above means is performed by the two sets of rollers 51 and 5.
While the sheet S is nipped by the pair 1, 52, 52, that is, after the leading end of the sheet is nipped by the downstream rollers 52, 52, the trailing end of the sheet is nipped by the rollers 51, 51 on the upstream side. This is performed until the curl correction member 5 is released.
3 and the curl correcting member 53 from the nip point b of the upstream rollers 51 and 51 to the nip point a of the downstream rollers 52 and 52. The curl correction is not performed on the rear end side Sa of the sheet in the range corresponding to the dimension L2 up to the curl correcting end.

In the above-described curl correcting means, since the curl correcting member 53 is arranged close to the downstream rollers 52, 52, the curl correcting member 53 starts from the nip point b of the upstream rollers 51, 51. The dimension L2 of the member 53 up to the curl correcting operation end is increased, and the curl correction of the rear end Sa of the sheet is not performed over a long range during this period.

However, even if the curl correcting member 53 is arranged close to the pair of rollers 51, 51 on the upstream side, the rollers 52, 52 on the downstream side from the curl correcting operation end of the curl correcting member 53 are reversed. By increasing the dimension L1 up to the nip point a by the pair, the curl correction of the sheet front end side Sb cannot be performed over a long range during this period.

[0010]

In order to solve the above-mentioned problems, according to the first aspect of the present invention, the curling direction of the paper is determined whether the paper is curled upward or curled downward after the fixing process. The paper is automatically detected and the upward or downward curl of the paper can be properly corrected. According to the second aspect of the present invention, the front side of the downward curl paper is handled and the paper is curved to the rear side. At this time, consideration is given not to damage the image forming surface of the downward curled paper.

According to the fifth aspect of the invention, similarly to the first aspect of the invention, the curl direction of the fixing paper is automatically detected, and
After the upward or downward curl of the sheet can be properly corrected, the cost of the curl correcting means can be reduced by using the curl correcting member for both purposes. In the invention according to claim 3 or 6, the range in which the curl correction on the front side and the rear end side of the paper curled upward or downward cannot be performed is shortened as much as possible, and the upward or downward curl of the paper is reduced. The curl can be corrected over a range near the entire surface from the leading edge to the trailing edge of the paper.

[0012]

More specifically, according to the first aspect of the present invention, two pairs of rollers for feeding a sheet after applying a tension in the sheet conveying direction to the sheet after the fixing process are disposed, and an upward facing paper is provided between the pair of rollers. A first curl correcting member for curling the curled sheet to the front side; and a second curling member for curving the downward curled sheet to the back side.
A first curl correcting member, and a first paper feeding posture for feeding paper to a straightening path for upward curled paper by the first curl correcting member; and a paper feeding to a straightening path for downward curled paper by the second curl correcting member. A path switching mechanism capable of changing the attitude of the second sheet feeding attitude to be provided,
Further, based on a paper upward curl detection result from a curl detecting unit that detects the curl direction of the fixing processing paper,
Changing the position of the path switching mechanism to the first sheet feeding position,
Alternatively, it is characterized in that the path switching mechanism is configured to change the attitude to the second paper feeding attitude based on the result of detecting the curl of the paper facing downward from the curl detecting means. At this time, it is desirable to provide a curl correcting roller that rolls in contact with the image forming surface of the sheet at the tip of the second curl correcting member.

According to a fifth aspect of the present invention, two pairs of rollers for feeding the paper after the fixing process in the paper feeding direction by applying tension thereto are arranged, and the upward curled paper is placed between the pair of rollers. A curl correcting member is provided so that the posture can be changed along with the rotation in a first correcting posture in which the curl correction member is bent to the first correction posture and a curl correcting member is bent in the second correction posture in which the paper curls downward. A path switching mechanism capable of changing a posture is provided between a first paper feeding posture for feeding the paper in the paper correction path and a second paper feeding posture for feeding the paper in the downward curling paper correction path,
Further, based on a paper upward curl detection result from a curl detecting unit that detects the curl direction of the fixing processing paper,
The position of the curl correcting member is changed to the first correcting position and the path switching mechanism is changed to the first sheet feeding position, or the curl correcting member is changed to the second correcting position based on the curl detection result from the curl detecting unit. The feature is that the path switching mechanism is configured to change the posture to the second paper feeding posture.

According to the third or sixth aspect of the present invention, the curl correcting member is provided with a first state in which the sheet is bent near the pair of rollers when the leading end of the sheet is nipped by the pair of rollers on the downstream side; Before the nip is released by the roller pair on the upstream side, the posture is changed with the rotation to the second state in which the sheet is curved near the roller pair.

According to the first aspect of the present invention, whether the sheet after the fixing process is curled upward or curled downward is automatically detected by the curl detecting means, and the paper curled upward. Based on the result of the curl detection, the sheet is fed to the upward curling paper correction path, and based on the downward curl detection result, the sheet is fed to the downward curl paper correction path.

When the leading end of the sheet is nipped by the pair of rollers on the downstream side, tension is applied to the sheet in the sheet conveying direction, and the curl correcting member moves the upward curled sheet toward the front side or downward curl. By curving the sheet to the back side, curl correction corresponding to upward curl or downward curl can be suitably achieved.

In the correction of the downward curl, the second curl correcting member comes into contact with the front side of the sheet, that is, the image forming surface, and curves the sheet toward the back side. As in the present invention, if the curl correcting roller that rolls in contact with the image forming surface of the sheet is provided at the tip of the second curl correcting member, the second curl correcting member handles the paper surface and damages the image forming surface. No more worries.

On the other hand, according to the invention of claim 5, based on the result of detecting the upward curl of the sheet from the curl detecting means,
The paper is fed to the upward curl paper straightening path, and the curl correcting member is switched to a posture for correcting the upward curl of the paper. And the curl correcting member is switched to a posture for correcting the downward curl of the sheet. In a state where the tension in the sheet conveying direction is applied, the curl correcting member moves the upward curled sheet to the front side. In the same manner as in the first aspect of the present invention, the paper curled downward or downward is curved to the back side.
The curl correction corresponding to the upward curl or the downward curl can be suitably achieved. In particular, in the present invention, the curl correcting means can be reduced in cost by using the curl correcting member also for correcting the upward curl or the downward curl. Is done.

According to the third or sixth aspect of the present invention, when the leading end of the sheet is nipped by the pair of rollers on the downstream side, the curl correcting member starts to correct the curl of the sheet near the pair of rollers. Before the nip of the rear end of the sheet is released by the pair of rollers on the upstream side, the curl correcting member changes its position, and until the nip of the rear end of the sheet is released, the curl correcting member closes the paper near the pair of rollers. Continue curl correction.

That is, the curl correction is started in a state where the curl correcting member of the curl correcting member is located near the downstream roller pair, and the curl correcting member of the curl correcting member is positioned near the upstream roller pair. The curl correction is ended in a state where the curl correction member is changed in the posture over the first and second states, so that the curl correction range of the paper by the curl correction member is widened, and the front end side and the rear end side of the paper are adjusted. Since the range in which curl correction cannot be performed is extremely short, even if the paper is curled upward or curled downward, the curl correction can be performed substantially over the entire area from the leading edge to the trailing edge of the paper. It is preferably achieved.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an electrophotographic copying machine (an example of an image forming apparatus) configured to be capable of performing double-sided copying, in which a photosensitive drum 4 is horizontally mounted on an apparatus main body 3 having an original mounting table 1 and an original presser 2. Around the photosensitive drum 4, a charging device 5, a developing device 6, a transfer device 7, a paper separating device 8, and a cleaning device 9, which constitute an image forming unit, are arranged in this order. An optical system movable exposure apparatus 10 is arranged in an upper space of the main body 3.

Further, there is provided a paper feed transport path 12 for transporting the paper S in the paper feed deck 11 connected to the apparatus main body 3 to the transfer device 7 of the image forming section. A pair of registration rollers 14 for feeding the sheet S at a predetermined timing based on the detection information of the leading edge of the sheet from the sensor 13 is provided between them, and a fixing device (upper part) for transferring the toner image transfer sheet S after transfer and separation. ) And a lower pressure roller 15b.)
And a paper discharge roller pair 18 for discharging the paper S after the fixing process to a paper discharge tray 17 outside the apparatus.

On the lower side of the apparatus main body 3, an intermediate tray 19 for temporarily stocking the sheet S after the fixing process is provided.
A re-feeding means 20 for re-feeding the paper S stored in the intermediate tray 19 to the transfer device 7 of the image forming section is provided, and the paper S after the fixing process is provided upstream of the paper discharge roller pair 18. A paper feed path 21 for feeding the paper S toward the intermediate tray 19 is provided in a branched manner, and as shown in FIG. 2, a path switching means 22 is provided in this branched portion to discharge the paper S after the fixing process. It is possible to select between a mode in which the paper S is discharged to the paper tray 17 and a mode in which the paper S is introduced into the paper feed path 21. The reversing means 23 and the sheet S conveyed on the intermediate tray 19
And a merging conveyance path 24 for merging and feeding.

Therefore, when the single-sided copy image forming mode is selected, the sheet S fed from the sheet feeding deck 11 is
Is fed to the transfer device 7 of the image forming unit at a predetermined timing, and the toner image of the document is transferred to the surface of the paper, and is sent to the fixing device 15.
Is discharged to the discharge tray 17 as it is.

When the image forming mode for duplex copying is selected, the path switching means 22 is switched to a mode in which the sheet S after the fixing process is introduced into the sheet feeding path 21, and the sheet S after the fixing process is fed. The toner image is introduced into the path 21 and is stored in the intermediate tray 19 through the path reversing means 23 with the toner image forming surface facing upward.

Then, at a predetermined timing, the sheet re-feeding means 2
0 is activated, and the sheet S after the single-sided image formation is
4, the paper is re-fed to the transfer device 7 of the image forming unit while being turned upside down, and the toner image of the document is transferred to the back surface of the paper.
, And the sheet S on which the document image has been formed on both sides and has undergone the fixing process is ejected to the sheet ejection tray 17.

If a configuration for forming an image of a document on one side of a sheet in a multiplex manner is added, for example, a switchback sheet feeding path is provided in the middle of the sheet feeding path 21 and this switch is set on the basis of information on the multiple forming mode. A path switching unit for temporarily introducing the sheet S into the back sheet feeding path may be provided so that the sheet S after the fixing process is stored in the intermediate tray 19 with its toner image forming surface facing downward.

In the electrophotographic copying machine having the above-described configuration, if the paper S after the fixing process is curled up and down irregularly due to the influence of the environmental humidity and the amount of information of the recorded image, the double-sided copying is performed. Cause a jam in the re-feeding section, wrap the paper S around the photosensitive drum 4, or cause transfer failure at the leading end of the paper when the multi-copy composite image forming mode is set. become.

Therefore, in the present invention, the curl correcting means 25 for the fixing processing paper S is provided, the paper S after the fixing processing is taken out to the paper feeding path 21, and the paper S is re-fed by the re-feeding means 20 to the conveyed conveyance path. Until the sheet S is re-fed, the direction of the curl of the sheet S is detected and the upward or downward curl is automatically corrected.

That is, as shown in FIG. 2, a pair of upper and lower paper feed rollers 26, 26, one of which is a driving roller, is disposed immediately upstream of the path switching means 22, and is located immediately downstream of the path switching means 22. A pair of left and right paper feed rollers 27, one of which is a drive roller, is disposed in the middle of the paper feed path 21 on the side of
The rotation speed of the pair of rollers 27 and 27 is set to be higher than the rotation speed of the pair of rollers 26 and 26 on the upstream side. ,
In a state where the sheet S is nipped by the pairs 26, 27, and 27, tension is applied to the sheet S in the sheet transport direction.

Further, between the pair of rollers 26 and 26 on the upstream side and the pair of rollers 27 and 27 on the downstream side, the upward curl of the sheet S is curved toward the front side to correct the upward curl of the sheet S. A first curl correcting member 28a and a second curl correcting member 28b for curving the downward curl of the sheet S by curving the downward curled sheet S to the rear side are fixedly provided, and the upstream rollers 26, A path switching mechanism 30 is provided immediately downstream of the 26 pairs, and the path switching mechanism 30 is supplied to the correction path 21a of the upward curl sheet by the first curl correction member 28a by the driving means 29 such as a solenoid. A first paper feeding posture C for feeding paper and a second paper feeding posture D for feeding paper S to the correction path 21b of the downward curled paper by the second curl correction member 28b. And so as to energize change.

The first and second curl correcting members 28a, 28a
Each of the first curl correction members 28a has a curl correcting action end at the leading end which is rounded in the thickness direction. It is. The second curl correcting member 28b is provided with a curl correcting roller r that rolls in contact with the image forming surface of the sheet at its free end, and the roller r and the first curl correcting member 28a are provided.
The curvature radii of the curl correcting action end are almost equal.

When the path switching mechanism 30 is in the first paper feeding posture C and the sheet S fed from the pair of rollers 26 and 26 on the upstream side is taken out to the straightening path 21a for the upward curled sheet, the path S The paper feed guide 31 that guides the leading end of the paper S to the pair of rollers 27 and 27 on the downstream side and the path switching mechanism 30 are switched to the second paper feeding posture D, and are fed out from the pair of rollers 26 and 26 on the upstream side. A paper feed guide 32 is provided to guide the leading end of the sheet S to the pair of rollers 27 and 27 on the downstream side when the sheet S is taken out to the straightening path 21b for the downward curled sheet.

On the other hand, on the upstream side of the pair of rollers 26, 26 on the upstream side, a curl detecting means for detecting the curl direction of the fixing processing paper S (in this embodiment, the product name of OMRON Corporation is called Z4D-A). 33 is provided, and the path switching mechanism 30 is set to the first sheet feeding posture C based on the result of the upward curl detection of the sheet from the curl detecting means 33, and the curl detecting means is provided. Control means 34 is provided for changing the path switching mechanism 30 to the second paper feed attitude D based on the paper curl detection result from 33.

In the above configuration, when the image forming mode for duplex copying is selected, the curl direction of the sheet S fed from the fixing device 15 is detected by the curl detecting means 33, and the curl direction is upward. If
The path switching mechanism 30 changes the posture to the first paper feeding posture C,
The paper S fed from the upstream rollers 26, 26 is taken out to the upward curled paper correction path 21a, the leading end thereof is guided by the paper feed guide 31, and the nip is carried out by the downstream rollers 27, 27. Then, tension is applied to the paper S curled upward in the paper transport direction.

The first curl correcting member 28a is provided on the back surface of the upward curled paper S to which the tension is applied.
The curl correcting action end of the sheet C contacts the upward curled sheet S
The upward curl of the paper S is corrected by curling the curl correcting operation end toward the front side so as to handle the rear surface of the upward curled paper S with the paper feeding.

On the other hand, when the curl detecting unit 33 detects that the sheet S after the fixing process is curled downward, as shown in FIG. Change the posture and change the rollers 26 and 2 on the upstream side.
The paper S fed from the six pairs is taken out to the straightening path 21b for the downward curled paper, and the leading end thereof is fed to the paper feed guide 32.
, And nipped by the pair of rollers 27, 27 on the downstream side, and tension is applied to the sheet S curled downward in the sheet transport direction.

Then, on the front side of the downward curled sheet S to which the tension is applied, that is, on the image forming side, a second
The curl correcting roller 28 of the curl correcting member 28b comes into contact with the curl correcting member 28b, and the curl correcting roller r rolls and curls the downward curled sheet S to the back side as the downward curl sheet S is fed. Thus, the downward curl of the sheet S is corrected without damaging the image forming surface of the sheet S.

As described above, the second curl correcting member 28
In the case where a curl correcting roller r is provided at the leading end of b, the curl correcting roller r rolls in contact with the image forming surface of the sheet S, so that there is no fear of damaging the image forming surface of the sheet S. This is a preferred embodiment. If the fixing process is sufficiently performed before the sheet S reaches the second curl correcting member 28b, the second curl is not provided without the curl correcting roller r. It goes without saying that the correction member 28b can be implemented with the same configuration as the first curl correction member 28a.

Next, based on FIG. 4, the curl correcting means 25 is designed to reduce the cost of the curl correcting means 25 so that the upward curl or downward curl paper S can be corrected by one curl correcting member 28. 25 will be described.

In the curl correcting means 25, one curl correcting member 28 is driven by a driving means 35 such as a stepping motor, for example, to a first correcting posture X in which the paper S having an upward curl is curved to the front side; The curl detecting unit 33 is configured to drive and rotate the paper S having the downward curl to the second correction posture Y in which the paper S is curved to the back side.
The curl correction member 28 is in the first correction posture X, the path switching mechanism 30 is in the first paper supply posture C, and the paper curl detection from the curl detection means 33 is based on the upward curl detection result from the printer. Based on the result, the curl correction member 28 is set to the second correction posture Y and the path switching mechanism 3
The control means 34 is configured to change the position of each of the sheets 0 to the second sheet feeding position D.

According to the above configuration, the curl detecting means 33
As shown in FIG. 5, the paper S is fed to the upward curling paper straightening path 21a on the basis of the upward curl detection result of the paper S, and the curl correcting member 28 corrects the upward curl of the paper S. To the first correction posture X. Then, in the result of detecting the curl of the downward facing paper,
As shown in FIG. 6, the sheet S is fed to the downward curl sheet correction path 21b, and the curl correcting member 28 is switched to the second correction position Y for correcting the downward curl of the sheet S. In a state where the tension in the paper transport direction is applied, the curl correcting member 28 corresponds to the upward curl or the downward curl by curving the upward curl paper S toward the front side or the downward curl paper S toward the back side. Curl correction is preferably achieved.

FIGS. 7 and 8 show a curl correcting means 25 capable of expanding the curl correcting range of the sheet S by the curl correcting member 28. FIG. Specifically, the curl correcting means 25 has the following configuration and function added to the curl correcting means 25 shown in FIG.

That is, a paper edge detection sensor 38 for the fixing processing paper S is provided on the upstream side of the pair of rollers 26, 26 on the upstream side, and a predetermined information is detected based on the detection information of the paper edge from the edge detection sensor 38. The detecting means 36 for detecting the nip of the leading end of the sheet by the pair of rollers 27 and 27 on the downstream side with a time lag.
A nip release detecting unit 37 for detecting the release of the nip at the rear end of the sheet by 26 pairs is provided.

The curl correcting member 28, which can be switched to the first and second correction postures X and Y based on the curl detection result from the curl detecting means 33,
6, 37 based on the detection information from
A first method in which the sheet S is curved in the vicinity of the 9, 29 pairs of nip points a
The control means 34 is configured to change the posture between a state A and a second state B in which the sheet S is curved near the nip point b of the pair of rollers 26 and 26 on the upstream side.

Specifically, the first and second correction postures X,
In each of Y, the curl correcting member 28 is switched to the second state B based on the nip detection information of the leading edge of the paper from the nip detecting means 36, and the nip release detecting means 37 detects the nip release of the trailing edge of the paper. The control means 34 is configured to switch the curl correction member 28 to the first state A based on this.

As shown in FIG. 8, the curl correcting member 2
8 is in the second state B and the path switching mechanism 30 is switched to the second sheet feeding posture D, and a part of the curl correction member 28 and the path switching mechanism 30 is allowed to wrap in the direction of the rotation axis of the roller. For example, a slit may be formed in the curl correcting member 28, or a plurality of thin plates may be provided at predetermined intervals as the curl correcting member 28, and a path switching mechanism may be provided between the thin plates. 3
You may make it rush 0.

In the above configuration, the sheet S after the fixing process
Is a curl upward, as shown in FIG. 9, the curl correcting member 28 changes the posture to the first correcting posture X and the path switching mechanism 30 changes the posture to the first paper feeding posture C. , 26 are taken out to the straightening path 21a for the upward curled paper and nipped by the pair of rollers 27, 27 on the downstream side. Based on the information from the nip detecting means 36, the paper S shown in FIG. As shown, the curl correcting member 28 in the first state A is switched to the second state B.

That is, the leading end of the sheet is the roller 29,
When the nip is formed by the nine pairs, the curl straightening member 28
Near the nip point a of the rollers 27 and 27,
The curl correction member 28 is started to bend toward the front side, and the posture of the curl correction member 28 is changed to the second state B based on the nip detection information of the leading edge of the sheet from the nip detection means 36. Are the upstream rollers 26, 26
Until the nip at the rear end of the sheet by the pair is released, the curl correcting member 28 continues the curl correction of the sheet S near the nip point b of the pair of rollers 26 and 26 on the upstream side.

When the sheet S after the fixing process has a downward curl, as shown in FIG. 11, the curl correcting member 28 is changed to the second correcting posture Y and the path switching mechanism 30 is changed to the second paper feeding posture D. Then, the sheet S is taken out to the straightening path 21b for the downward curled sheet, and the leading end of the sheet is
At the time when the sheet S is nipped by the pairs 9 and 29, the curl correcting member 28 in the first state A starts the curl correction so that the sheet S bends to the back side near the nip point a of the pair of rollers 27 and 27. In addition, the posture of the curl correction member 28 is changed to the second state B, as shown in FIG. 12, based on the nip detection information of the leading end of the sheet from the nip detection means 36. Until the nip at the trailing end of the sheet by the pair of rollers 26 and 26 is released, the curl correcting member 28 moves the nip point b between the rollers 26 and 26 on the upstream side.
The curl correction of the sheet S is continued in the vicinity.

Thereafter, the nip at the rear end of the sheet by the pair of rollers 27, 27 on the downstream side is released, and when the release of the nip is detected by the detecting means 37, the curl correcting member 2
Reference numeral 8 denotes a posture return to the first state A to prepare for the curl correction of the next sheet S.

Therefore, according to the above-described configuration, the curl correction corresponding to the upward curl or the downward curl is performed based on the detection of the curl direction of the paper S regardless of whether the paper S is upward curl or downward curl. Will be done automatically.

Further, the curl correction is started in a state where the curl correcting operation end of the curl correcting member 28 is located near the nip point a of the pair of rollers 27 and 27 on the downstream side, and the curl correcting operation end of the curl correcting member 28 is started. Is the upstream roller 2
Since the curl correction is completed in a state where the curl correction member 28 is located in the vicinity of the nip point b of the 6, 26 pairs, the curl correction member 28 changes the posture from the first state A to the second state B, and the paper by the curl correction member 28 The curl straightening range of S becomes wider,
The range in which the curl correction of the leading end side Sb and the trailing end side Sa of the paper S cannot be performed is extremely shortened, and the curl correction is preferably performed substantially over the range from the leading end to the trailing end of the paper S substantially close to the entire surface. Achieved.

In the above embodiment, the sensor 38 for detecting the leading edge of the paper is provided, and the nip detection for the leading edge of the paper and the nip release for the trailing edge of the paper are detected based on the detection information of the leading edge of the paper from the sensor 38. The detection sensor 38 at the leading end of the sheet is connected to the registration roller pair 14.
It is also possible to use the activation sensor 13 as a substitute.

The rollers r provided on the first curl correcting member 28a, ie, the first curl correcting member 28a shown in FIGS. 2 and 3 and the curl correcting member 28 shown in FIGS. Alternatively, a curl correction roller that contacts the paper surface and rolls with the feeding of the paper S may be provided.

Further, in the curl correcting means 25 shown in FIG. 2, the first and second curl correcting members 28a and 28b
The first and second curl correcting members 28a and 28b are provided so as to be changeable to the first and second states A and B by the driving means 35 as shown in FIG. In addition, a paper leading edge detecting sensor 38 is provided to switch the first or second curl correcting member 28a, 28b to the second state B based on the nip detecting information of the leading edge of the paper from the nip detecting means 36, and The first or second curl correcting member 28a, 28b is moved to the first or second curl correcting member 28a based on the detection information of the nip release of the rear end of the sheet from the release detecting means 37.
Control may be performed to switch to state A.

[0057]

As described above, in any of the first and fifth aspects of the present invention, the direction of the upward curl or the downward curl of the fixing paper is automatically detected, and the upward or downward curl of the paper is detected. In particular, according to the fifth aspect of the present invention, the curl correcting means can be reduced in cost by using the curl correcting member in common.

According to the second aspect of the present invention, when the curl is corrected by the second curl correcting member, there is no need to worry about damaging the image forming surface of the downward curled paper. According to the third or sixth aspect of the present invention, The area where curl correction cannot be performed on the leading and trailing edges of the paper curled upward or downward is shortened as much as possible, and the upward or downward curl of the paper is reduced from the leading edge to the trailing edge of the paper.適 正 It can be properly corrected over the whole area.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional side view of an electrostatographic copying machine as an example of an image forming apparatus.

FIG. 2 is a configuration diagram of curl correcting means.

FIG. 3 is an explanatory diagram illustrating a curl correction state of a downward curled sheet.

FIG. 4 is a configuration diagram of a curl correcting unit of another embodiment in which a curl correcting member is rotated to change the posture to a first and a second correcting posture.

FIG. 5 is an explanatory diagram illustrating a curl correction state of an upward curled sheet by the curl correction unit illustrated in FIG. 4;

FIG. 6 is an explanatory view showing a curl correction state of a downward curled sheet by the curl correction unit shown in FIG. 4;

FIG. 7 is a configuration diagram of a curl correcting unit according to another embodiment in which a curl correcting member in a first correcting posture is changed in posture into two states.

FIG. 8 is a configuration diagram of the curl correction member in the second correction position of the curl correction unit shown in FIG. 7 in which the posture is changed to two states.

9 is an explanatory diagram illustrating a curl correction state of an upward curl sheet near the downstream roller pair by the curl correction unit illustrated in FIG. 7;

FIG. 10 is an explanatory diagram illustrating a curl correction state of an upward curled sheet near the pair of rollers on the upstream side by the curl correction unit illustrated in FIG. 7;

11 is an explanatory diagram showing a curl correction state of a downward curl sheet near the downstream roller pair by the curl correction unit shown in FIG. 7;

12 is an explanatory diagram showing a curl correction state of a downward curled sheet near the pair of rollers on the upstream side by the curl correction unit shown in FIG. 7;

FIG. 13 is a configuration diagram of a curl correction unit of a conventional example.

[Explanation of symbols]

17: paper discharge tray, 20: re-feeding means, 21: paper feeding path, 22: path switching means, 26, 26: upstream pair of rollers, 27, 27: downstream pair of rollers, 28: curl correcting member , 30: path switching mechanism, 33: curl detecting means, 34: control means, 36: nip detecting means, 37 ...
Nip release detection means, r: roller, S: paper, A: first
State, B: second state, C: first sheet feeding attitude, D: second sheet feeding attitude, X: first correction attitude, Y: second correction attitude.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yasuhiro Michishita Mita Kogyo Co., Ltd. 1-2-28 Tamazo, Chuo-ku, Osaka-shi

Claims (7)

[Claims] 1. A pair of rollers for applying tension to a sheet after a fixing process in a sheet conveyance direction and feeding the sheet, and a first curling sheet curling upward is curved between the pair of rollers. A curl straightening member, and a second curl straightening member for curving the downward curled paper to the back side,
A first sheet feeding position in which the first curl correcting member feeds the sheet in the straightening path of the upward curled sheet; and a second sheet feeding position in which the second curl correcting member feeds the sheet in the straightening path of the downward curl sheet. A path switching mechanism capable of changing the orientation of each sheet, and further, the path switching mechanism is set to the first sheet feeding attitude based on a paper upward curl detection result from curl detecting means for detecting the curl direction of the fixing processing paper. An image forming apparatus characterized in that the path switching mechanism is configured to change the attitude to the second paper feeding attitude based on a result of detecting the curl of the sheet facing downward from the curl detecting means. 2. The image forming apparatus according to claim 1, wherein a curl correcting roller that rolls in contact with an image forming surface of the sheet is provided at an end of the second curl correcting member. 3. A first state in which the first and second curl correcting members are bent in the vicinity of the pair of rollers when the leading end of the sheet is nipped by the pair of rollers on the downstream side, and the trailing end of the sheet is upstream. 3. The image forming apparatus according to claim 1, wherein the posture is changed along with the rotation to a second state in which the sheet is curved near the roller pair before the nip is released by the roller pair on the side. 4. A first or second curl based on a nip detection means at a leading end of a sheet by a pair of rollers on a downstream side, a nip release detecting means at a trailing end of a sheet by a pair of rollers on an upstream side, and nip detection information on a leading end of a sheet. 4. The image forming apparatus according to claim 3, further comprising control means for switching the correction member to the second state and switching the first or second curl correction member to the first state based on the detection information of the nip release at the rear end of the sheet. . 5. A pair of rollers for applying tension to the paper after the fixing process in the paper transport direction and feeding the paper, and between the pair of rollers, a first curl paper curving upward is curved toward the front side. A straightening posture and a second straightening posture in which a downward curled sheet is curved to the back side are provided with a curl correcting member so that the posture can be changed along with the rotation. A path switching mechanism capable of changing the posture is provided between a first paper feeding posture for feeding the paper and a second paper feeding posture for feeding the paper on the correction path for the downward curled paper, and further, the curling of the fixing processing paper is performed. The curl correcting member is changed to the first correcting posture and the path switching mechanism is changed to the first paper feeding posture, based on the result of detecting the upward curl of the paper from the curl detecting means for detecting the direction of the paper. Moves the curl correcting member to the second position based on the result of detecting the downward curl of the sheet from the curl detecting means.
An image forming apparatus, wherein the image forming apparatus is configured to change a posture to a correction posture and a path switching mechanism to a second paper feeding posture. 6. A curl correction member comprising: a first state in which a sheet is curved near a pair of rollers when a leading end of the sheet is nipped by a pair of rollers on a downstream side; 6. The image forming apparatus according to claim 5, wherein before the nip is released, the posture is changed in accordance with the rotation to a second state in which the sheet is curved near the pair of rollers. 7. A nip detecting means for detecting a leading edge of a sheet by a pair of rollers on the downstream side, a nip release detecting means for detecting a nip of a trailing end of the sheet by a pair of rollers on the upstream side, and the curl correcting member based on nip detecting information of the leading end of the sheet. In the second state, the curl correcting member is moved to the first position based on the detection information of the nip release at the rear end of the sheet.
7. The image forming apparatus according to claim 6, further comprising control means for switching to a state.