JP3413148B2 - Sheet conveying device and image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to a sheet conveying apparatus provided in an image forming apparatus such as a copying machine, a printer or a facsimile which forms an image on a sheet.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses for forming images on sheets such as copying machines, printers and facsimiles have become widespread. In these image forming apparatuses, there are various types of image forming methods, but in recent years, a type in which a toner image is transferred and fixed on a sheet by an electrophotographic method has become widespread. In this electrophotographic image forming apparatus, a thermal fixing device is provided to fix the toner image transferred on the sheet to the sheet. Further, in recent years when energy saving has been proclaimed, a double-sided printing function of forming an image on both sides of a sheet is becoming an essential function of an image forming apparatus.

A conventional image forming apparatus having the double-sided printing function will be described below with reference to the drawings by taking an electrophotographic laser beam printer as an example.

In the conventional image forming apparatus, as shown in FIG. 8 , a sheet cassette 20 as a sheet accommodating portion capable of accommodating and accommodating sheets P is formed inside a main body 1 of the image forming apparatus, and a toner image is formed on the sheet P. An image forming unit 2 serving as an image forming unit and a fixing unit 3 for fixing the formed toner image are provided.

Further, in this image forming apparatus, the sheet conveying path 21 formed from the sheet cassette 20 to the image forming section 2 and the sheet P which has passed through the fixing section 3 for double-sided printing are supplied to the image forming section 2 again. And a double-sided conveyance path 4 as a sheet re-feeding path. Further, on the downstream side of the fixing unit 3, a sheet discharge path 6 for discharging the sheet to the outside of the machine and a sheet reversal conveyance path 7 for guiding the sheet to the double-sided conveyance path 4 are arranged in a branched manner.

A transport path switching lever (not shown) is provided at each of the location where the sheet discharge path 6 and the sheet reverse transport path 7 branch and the location where the sheet reverse transport path 7 and the double-sided transport path 4 merge. Based on a control signal from a control means (not shown) that is arranged and controls the entire apparatus, each conveyance path switching lever is rotated to switch the sheet conveyance path.

A pair of transport rollers 22 for transporting a sheet is arranged in each of the above-described transport paths. Incidentally, 23 is a pickup roller for picking up the uppermost sheet P of the sheets stacked in the sheet cassette 20 from the sheet cassette 20, and 24 is the sheet P is intermittently conveyed to the transfer section 5 of the image forming section 2 at a predetermined timing. A pair of registration rollers for discharging the sheet P, a pair of discharge rollers 25 for discharging the sheet P passing through the fixing unit 3 to the outside of the apparatus, and a group 26 for conveying the sheet image-formed by the image forming unit 2 to the fixing unit 3. 2 is a belt conveyor unit including the conveyor belt and a plurality of pulleys.

In this image forming apparatus, the sheet cassette 2
The uppermost sheet P of the sheets stacked on 0 is picked up by the pickup roller 23, and the pair of conveyance rollers 2 arranged at the subsequent stage of the pickup roller 23.
2 is conveyed along the sheet conveying path 21 and is intermittently conveyed to the transfer portion 5 of the image forming portion 2 by the pair of registration rollers 24. After the toner image is transferred onto the upper surface of the transfer portion 5, the belt conveying portion 26 fixes the toner image. It is conveyed to the section 3.

The sheet P is heated and pressed by the fixing unit 3 so that the toner image is fixed, and in the case of performing normal one-sided printing, the sheet P is discharged by the discharge roller pair 25 to the outside of the apparatus.

On the other hand, when performing double-sided printing, the sheet P that has passed through the fixing unit 3 is guided to the downward sheet reversing conveyance path 7 branched at the latter stage of the fixing unit 3 by a conveyance path switching lever (not shown). Then, when the sheet P moves from the sheet reversal conveyance path 7 to the double-sided conveyance path 4, the traveling direction of the sheet P is reversed, and the sheet P is conveyed on the double-sided conveyance path 4 with the image surface facing upward. Then, the sheet P is conveyed from the double-sided conveyance path 4 to the sheet conveyance path 21 again, and the main surface is inverted here so that the image surface is up and the registration roller pair 2
4 is intermittently conveyed to the transfer section 5 of the image forming section 2, and after the toner image is transferred onto the upper surface of the transfer section 5, the fixing section 3
Then, the fixing process of the toner image is performed, and the sheet is discharged outside the apparatus by the pair of discharging rollers 25.

In such an image forming apparatus of the electrophotographic system, the sheet P is curved (heat curl) due to heat as it passes through the fixing device 3, and further, is heated in the fixing device 3 and then conveyed to the conveying path. Curling also occurs by passing through the bent portions A, B, and the like. This curl is curved upwardly convex shape (the image surface) when conveyed on the duplex conveyance path 4 formed on the sheet P (see FIG. 1 1)
Tends to be. Then, in the image forming apparatus, when performing duplex printing, in order to prevent transfer defects, it is necessary to supply to the image forming unit 2 to remove the curl, as shown in FIG. 8, the sheet A curl correction mechanism 100 for imparting a curl in the opposite direction and correcting the above-described upward curl is arranged on the double-sided conveyance path 4.

[0012] The curl correction mechanism 100, as shown in FIG. 1 0, an endless belt 114 for conveying the sheet, the stretched shaft 111 and 112 which stretched rotatably the endless belt 114 is stretched The endless belt 114 has a rotatable pressing roller 113 that presses from the outside, and the sheet is conveyed while being sandwiched by the endless belt 114 and the pressing roller 113.

[0013] Here, sheet fed to the curl correction mechanism 100, FIG. 8, the curl correction mechanism 100 as shown in FIG. 1 0
By passing through the substantially V-shaped path formed by the pressing roller 113 and the endless belt 114, the curl convex upward is corrected, and the transfer failure of the second surface is prevented.

[0014]

However, the following problems have been pointed out in the above-mentioned conventional image forming apparatus.

A curl correction mechanism 10 of a conventional image forming apparatus.
At 0, if the reverse curl applied to the sheet P is too strong, the correction becomes excessive, and conversely, a curl convex downward is generated. In this case, when the second transfer is performed on the sheet P via the double-sided conveyance path 4, as shown in FIG. 9 , a curl (2) is used to distance the sheet P from the main surface of the photosensitive drum 2a to be transferred. A convex curl is generated on the first transfer surface, and a transfer failure is likely to occur. Therefore, in the curl correction mechanism 100, the sheet P
It is necessary to set the amount of curl in the reverse direction to be given to an appropriate strength. Conventionally, the strength of the curl and the amount of curl in the reverse direction are based on plain paper (basis weight 52 to 90 g / m 2). The settings were made.

On the other hand, in recent years, the types of sheets (materials) required for the image forming apparatus have increased, and in particular, it is desired to use thick sheets having a basis weight of 100 g / m ² or more (hereinafter referred to as thick paper). Is getting bigger.

However, even if the sheets have the same vertical and horizontal widths, the same fixing device is used for plain paper (basis weight 52 to 90 g / m ² ) and thick paper (basis weight 100 g / m ² or more).
Even if the curl passes through the bent portion, the curl generation states are different from each other, which often causes inconvenience when performing double-sided printing on thick paper.

That is, in the case of thick paper, the double-sided conveyance path 4
It is not necessary to perform curl correction by the curl correction mechanism 100, because the curl at the top does not become convex as in plain paper but becomes flat or slightly convex. However, the curl correction mechanism 100 of the conventional image forming apparatus is set so that the curl correction of plain paper can be optimally performed, and thick paper is not considered. Therefore, when the thick paper passes through the curl correction mechanism 100, The convex curl becomes large, and the leading edge of the sheet strongly abuts the main surface of the photosensitive drum 2a to be transferred, which may cause problems such as transfer failure (image misalignment) and paper jam.

As a countermeasure for this, a configuration may be considered in which the amount of entry of the pressing roller 113 is switched according to the thickness of the sheet, but means for detecting the thickness of the sheet and the pressing roller 113 are also possible.
Since a means for switching the entry amount of the device is required, the cost of the device is increased and the size is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sheet conveying device capable of performing a curl correction according to the thickness of a sheet without causing an increase in cost and an increase in size, and an image forming apparatus including the same.

[0021]

A first structure of a sheet conveying apparatus according to the present invention comprises an endless belt for conveying a sheet and at least two stretching shafts rotatably stretching the endless belt. And a rotatable pressing roller that presses the stretched endless belt from the outside, and in the sheet conveying device that conveys a sheet while sandwiching the sheet by the endless belt and the pressing roller, the pressing roller is Reaction force based on seat rigidity
By an elastic member so as to move in a pressing direction and a pressing release direction with respect to the endless belt according to the size of
It is characterized by being pressed by an endless belt .

A second structure of the sheet conveying device according to the present invention is the same as the first structure, wherein the pressing roller is a sheet transfer device.
As the reaction force based on the rigidity increases, the endless bell
It is characterized in that it moves in the direction of releasing the pressure against the press.

A third structure of the sheet conveying device according to the present invention is characterized in that, in the first structure, the elastic members are provided at both ends of the rotating shaft of the pressing roller.

A fourth construction of the sheet conveying apparatus according to the present invention is the construction of any one of the first to third constructions, wherein the endless belt has an upstream side and a downstream side on a sheet conveying surface formed with a pressing roller as a boundary. The angle α formed with the side is 2π / 6
It is characterized by being in the range of (rad) ≦ α ≦ 5π / 6 (rad).

A fifth constitution of the sheet conveying apparatus according to the present invention is the fourth constitution, wherein the pressing roller is arranged in the vicinity of an intersection connecting the upstream conveying passage and the downstream conveying passage. And

[0026]

A first configuration of the image forming apparatus according to the present invention is the sheet conveying device according to any one of the first to fifth aspects, and image forming means for forming an image on a sheet conveyed by the sheet conveying device. It is characterized by having and.

A second structure of the image forming apparatus according to the present invention is such that a sheet accommodating portion capable of accommodating and accommodating sheets, a sheet conveying path formed from the sheet accommodating portion to the image forming means,
A sheet re-feeding path for supplying the image-formed sheet to the image forming means again, and the sheet conveying device is arranged in the sheet re-feeding path.

A third structure of the image forming apparatus according to the present invention is characterized in that, in the second structure, the sheet re-feeding path has a downstream end connected to the sheet conveying path.

A fourth configuration of the image forming apparatus according to the present invention is the sheet of the second or third configuration, wherein the sheet re-feeding path reverses the traveling direction of the sheet on which the image is formed by the image forming means. It is characterized in that a reversing means is provided.

[0031]

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

[First Embodiment] First, the first embodiment of the present invention will be described.
Embodiments will be described with reference to FIGS. 1 to 3. The same members as those shown in FIGS. 9 to 12 of the conventional example are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

FIG. 1 shows the overall structure of an image forming apparatus to which the sheet conveying apparatus of the present invention is applied. The image forming apparatus according to the embodiment is a laser beam printer using an electrophotographic method, and as shown in FIG. 1, a sheet cassette 20 serving as a sheet storage unit capable of stacking and storing sheets P inside the image forming apparatus main body 1. An image forming unit 2 as an image forming unit for forming a toner image on the sheet P, and a fixing unit 3 for fixing the formed toner image.

Further, in this image forming apparatus, the sheet conveying path 21 formed from the sheet cassette 20 to the image forming section 2 and the sheet P passing through the fixing section 3 for double-sided printing are supplied to the image forming section 2 again. And a double-sided conveyance path 4 as a sheet re-feeding path. Further, on the downstream side of the fixing unit 3, a sheet discharge path 6 for discharging the sheet to the outside of the machine and a sheet reversal conveyance path 7 for guiding the sheet to the double-sided conveyance path 4 are arranged in a branched manner. And
A conveyance path switching lever 8 is arranged at a position where the sheet discharge path 6 and the sheet reversing conveyance path 7 branch, and a conveyance path switching lever 9 is arranged at a confluence of the sheet reversing conveyance path 7 and the double-sided conveyance path 4. Based on a control signal from a control means (not shown) that controls the entire apparatus, the respective conveyance path switching levers 8 and 9 are rotated in the arrow direction of FIG. To switch.

A pair of transport rollers 22 (22a to 22h) for transporting the sheet is arranged in each of the above-described transport paths. Incidentally, 23 is a pickup roller for picking up the uppermost sheet P of the sheets stacked in the sheet cassette 20 from the sheet cassette 20, and 24 is the sheet P is intermittently conveyed to the transfer section 5 of the image forming section 2 at a predetermined timing. A pair of registration rollers for discharging the sheet P, a pair of discharge rollers 25 for discharging the sheet P passing through the fixing unit 3 to the outside of the apparatus, and a group 26 for conveying the sheet image-formed by the image forming unit 2 to the fixing unit 3. 2 is a belt conveyor unit including the conveyor belt and a plurality of pulleys.

The image forming section 2 is an electrophotographic photosensitive drum (hereinafter referred to as a photosensitive drum) 2a as an image bearing member on which an electrostatic latent image is formed by an electrophotographic method, and a photosensitive drum 2a.
A laser scanner 2b for forming a latent image, a reflection mirror 2c, a developing device 2d, a transfer charger 2e for charging the photosensitive drum 2a, and the like are provided. In the image forming unit 2, the laser beam corresponding to the image information emitted and scanned by the laser scanner 2b is supplied to the surface of the photosensitive drum 2a, so that the surface of the photosensitive drum 2a uniformly charged by the transfer charger 2e. A latent image is formed on. In the image forming unit 2, the latent image is developed by the developing device 2d to form a toner image.

Further, this toner image is recorded on the photosensitive drum 2.
The transfer charger 2e disposed below the photosensitive drum 2a performs a transfer process on the sheet P conveyed by the pair of registration rollers 24 in synchronism with the rotation of a. Is transcribed to. The sheet P on which the toner image has been transferred is conveyed by the belt conveying unit 26 disposed substantially in the center of the apparatus.
The toner image on the sheet surface is fixed by being conveyed to a fixing unit 3 whose details will be described later and being heated and pressed by the fixing unit 3.

The sheet P on which the toner image has been fixed by the fixing unit 3 is usually printed on only one side,
The sheet passes through the sheet discharge path 6 and is discharged outside the image forming apparatus main body 1 by the discharge roller pair 25 with the image forming surface as the upper surface, and is sequentially discharged and stacked on a discharge tray (not shown).
In this case, the transport path switching lever 8 is held at the initial position shown in FIG.

On the other hand, during double-sided printing, the sheet P is re-supplied to the image forming section 2 by the following operation.
That is, at the time of double-sided printing, the conveyance path switching lever 8 rotates upward in FIG. 1 to close the sheet discharge path 6, so that the sheet P passing through the fixing unit 3 moves toward the sheet reversal conveyance path 7. Be guided. When the sheet P is conveyed in the sheet reversing conveyance path 7 by the pair of conveyance rollers 22d and 22e, and the trailing end of the sheet P passes through the conveyance path switching lever 9, the conveyance path switching lever 9 is moved from the initial position shown in FIG. The sheet is turned clockwise to close the sheet reversal conveyance path 7. Then, the conveyance roller pair 22e rotates in the opposite direction, so that the sheet P moves up and its traveling direction is reversed. Subsequently, the sheet P is guided to the double-sided conveying path 4 with the image forming surface facing upward, and the conveying roller pairs 22f, 22g, 2 are conveyed.
After being conveyed by 2 h, the curl is corrected by the curl correcting unit 10, the sheet is guided to the sheet conveying path 21, and is again supplied to the image forming unit 2 via the conveying roller pair 22 c and the registration roller pair 24. At this time, the image forming surface of the sheet P is on the lower side, and after the image is formed on the upper surface of the image forming unit 2 and the fixing process is performed by the fixing unit 3, as described above, the sheet discharge path is formed. 6 and is discharged to the outside of the image forming apparatus main body 1 by the discharge roller pair 25.

Here, the curl correcting means 10 in the image forming apparatus according to the embodiment is arranged on the downstream side in the double-sided conveying path 4 as shown in FIG. 1, and its details will be described below with reference to FIGS. 2 and 3. Will be described with reference to.

As shown in FIG. 2, the curl correcting means 10 includes an endless belt 14 for conveying a sheet,
The belt driven shaft 11 and the belt drive shaft 12 function as a stretching shaft that rotatably stretches the endless belt 14, and a rotatable pressing roller 13 that presses the stretched endless belt 14 from above and outside. When the belt drive shaft 12 is rotationally driven in the clockwise direction in FIG. 2 by a drive means (not shown) such as a motor, the endless belt 14 and the belt driven shaft 11 rotate in the same direction,
The pressing roller 13 that is in pressure contact with the endless belt 14 rotates in the counterclockwise direction.

Here, as shown in FIG. 2, the portion of the double-sided conveying path 4 where the belt driven shaft 11 and the belt drive shaft 12 are arranged is a lower guide member of the guide members forming the double-sided conveying path 4. While 30b and 31b are cut out,
The upper guide members 30a and 31a are curved in the direction of the pressing roller 13. Hereinafter, the double-sided transport path 4 on the upstream side of the pressing roller 13 will be referred to as an upstream transport path 30,
The double-sided transport path 4 on the downstream side of the pressing roller 13 is called a downstream transport path 31.

Next, the detailed structure of the curl correcting means 10 will be described with reference to FIG. As shown in FIG. 3, the curl correcting means 10 includes the belt driven shaft 1 described above.
1, the belt drive shaft 12, and the pressing roller 13 are the sheet P
Is longer than the width of the belt and is attached to the frame 15, and the belt driven shaft 11 and the belt drive shaft 12 are
A plurality of endless belts 14 (four in this embodiment) are attached. Each endless belt 14 is stretched over belt conveying rollers 11a and 12a which are integrally formed with the belt driven shaft 11 and the belt drive shaft 12. The material of the endless belt 14 is CR,
Rubbers such as EPDM and polyurethane are suitable. In addition,
In this embodiment, the number of endless belts 14 is four, but the number is not particularly limited.

The frame 15 is provided with the belt driven shaft 11, the belt driving shaft 12, and the parts on both end sides (hereinafter, referred to as both side plates) to which the pressing roller 13 is attached, which are formed to rise, and the belt driven shaft 11 and the belt driving shaft are formed. Both ends of the pressing roller 12 and the pressing roller 13 are rotatably attached to the both side plates.

Specifically, the belt driven shaft 11 and the belt drive shaft 12 are attached to both side plates of the frame 15 via bearings 11b and 12b composed of ball bearings, slide bearings and the like. Further, the belt drive shaft 12 is provided at one end thereof with a drive gear 28 that meshes with a drive gear 27 to which the drive force of a drive means (not shown) is transmitted, and is driven to rotate by the drive means. There is.

The pressing roller 13 presses the endless belt 14 by being biased by the coil spring 17 as an elastic member. More specifically, the pressing roller 13 has an outer diameter of φ8, is formed of free-cutting steel or stainless steel as a material, and is a bearing 13 such as a ball bearing or a slide bearing.
b and the pressing roller holding body 16 holding the bearing 13b. Here, the holder 16 is the frame 1
It is configured such that it can reciprocate in the vertical direction in the notch 15a formed on both side plates of No. 5. And the holder 1
The coil spring 17 is arranged on the upper part of the coil spring 6.
When the holding body 16 is urged downward by the urging force of, the pressing roller 13 independently presses the endless belt 14 at both end sides. Here, since the pressing roller 13 is pressed upward by receiving a reaction force due to the tension of the endless belt 14, it is held at a position where the force of the coil spring 17 and the tension of the endless belt 14 are balanced. It will be.

The operation of the curl correcting means 10 during sheet conveyance will be described below. During double-sided printing of the image forming apparatus, the sheet P guided to the double-sided conveyance path 4
Is supplied to the curl correcting means 10 by each pair of rotating conveying rollers 22f, 22g, 22h.

Here, the sheet P is conveyed in the direction of the arrow shown in FIG. 1 to FIG. 3 and rides on the main surface portion of the endless belt 14 on the belt driven shaft 11 where the lower side of the sheet front end portion is rotating, and the endless belt. It is conveyed by 14. At this time, the sheet P moves along the upper guide member 30 a that is inclined downward, and the leading end of the sheet is supplied to the nip portion between the pressing roller 13 and the endless belt 14,
The sheet is conveyed by the main surface of the endless belt 14 (hereinafter referred to as a sheet conveying surface) while being sandwiched between the pressing roller 13 and the endless belt 14. And the sheet P is
By passing through the curl correction unit 10, the curl correction according to the angle formed between the upstream side and the downstream side of the sheet conveying surface having the substantially V-shaped cross section of the endless belt 14 formed with the pressing roller 13 as a boundary is performed. After that, the sheet is guided to the sheet conveying path 21 as described above, and is again supplied to the image forming unit 2 via the conveying roller pair 22c and the registration roller pair 24.

Here, the curl correction means 10 of the embodiment
Since the pressing roller 13 is held at a position where the force of the coil spring 17 and the tension of the endless belt 14 are balanced as described above, the sheet P is swung in the vertical direction when passing. Will be done. Specifically, as shown in FIGS. 4 and 5, the pressing roller 13 moves up and down according to the value of the reaction force of the sheet P, and when the sheet P is plain paper, as shown in FIG. On the other hand, when the sheet P is a thick sheet that is thicker than the plain sheet, it hardly moves up and down, and as shown in FIG. 5, a reaction force larger than that of the plain sheet is generated, so that the pressing roller 13 moves upward when the sheet passes. Will be done.

In this embodiment, the curl correction means 10
The coil spring 17 of is smaller than the reaction force of the thick paper,
Further, a spring having a biasing force (pressing force) larger than the reaction force of the plain paper is used, and when the sheet P is the plain paper, by passing through the nip portion between the belt 14 and the pressing roller 13, as shown in FIG. When the sheet P is thick paper, the pressing roller 13 escapes upward due to the reaction force (rigidity) of the thick paper, and as shown in FIG. 5, the curl correction function is hardly exhibited.

Therefore, according to the image forming apparatus of the embodiment provided with the curl correcting means 10 having such a structure, it is possible to perform more appropriate curl correction on both plain paper and thick paper.

In this embodiment, about 6N is provided on one side.
(600gf) Coil spring 1 to which a load of around 600gf is applied
By setting the value to 7, suitable curl correction for both plain paper and thick paper was realized. It should be noted that this numerical value changes depending on the arrangement of the components, the material, etc., and the present invention is not limited to this value.

As described above, in the curl correcting means 10 of the embodiment, since the pressing roller 13 is pressed by the coil spring 17 so as to be movable in the pressing direction and the pressing releasing direction with respect to the endless belt 14, the sheet P is pressed. The pressing roller 1 according to the change in the reaction force based on the thickness (rigidity) of the roller.
When the sheet P is plain paper, the pushing amount of the pressing roller 13 is large and the curl correction capability is high, while when the sheet P is thick paper, Due to the large reaction force, the entering amount of the pressing roller 13 becomes small, and the curl correction capability becomes low. As a result, optimal curl correction is realized while utilizing the performance of both plain paper and thick paper.

Further, the curl correction means 10 of the present embodiment
According to this, since the coil springs 17 are provided at both ends of the pressing roller 13 and both ends of the pressing roller 13 are independently pressurized, the belt drive shaft 12, the belt driven shaft 11, and the belt conveying rollers 11a, 1 are provided. , Endless belt 1
4, the tension of the endless belt 14 is kept substantially constant at both ends, and the curl correction function is stabilized.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. The same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be appropriately omitted.

In the image forming apparatus of the second embodiment, as shown in FIG. 6, the curl correction means 1 of the first embodiment is used.
The curl correcting means 10A having substantially the same configuration as that of 0 is provided in the bending path portion near the exit portion of the double-sided conveyance path 4. In the curl correcting means 10A of the second embodiment, as shown in FIG. 7, an angle α formed by the upstream side conveyance path 30 and the downstream side conveyance path 31 on the sheet conveyance path surface formed with the pressing roller 13 as a boundary. However, in the initial state where the sheet does not pass, 2π / 6
(Rad) ≦ α ≦ 5π / 6 (rad), that is, 60 °
The range is not less than 150 ° and not more than 150 °.

The pressing rollers 13 are arranged at both ends of the upper guide members 30a and 31a, and near the intersection of the upstream side conveyance path 30 and the downstream side conveyance path 31.

[0058]

According to the curl correcting means 10A having such a structure, the sheet P can smoothly enter the substantially V-shaped conveying path formed by the endless belt 14 and the pressing roller 13, and the sheet can be discharged smoothly, and the sheet can be discharged smoothly. It is less likely that P receives a force in the direction opposite to the curl correction direction on the conveyance path before and after the V-shaped path of the curl correction means 10A, and the curl correction function is more efficiently exhibited.

The upstream transport path 30 and the downstream transport path 3
The angle α formed with 1 is a value in the initial state in which the sheet does not pass as described above, and when the passing sheet P is thick paper, the pressing roller 13 escapes due to a relatively large reaction force, and α It may be> 5π / 6 (rad).

Further, in the present embodiment, α = 7π
Although it is set to / 12 rad (105 ° ), the effect of the present invention is in a wider range (α = 2π / 6 rad or more 5π /
It can be expected in the 60rad below). Therefore, the present invention is not limited to the above values.

In each of the above-described embodiments, an example in which the present invention is applied to a printer has been described, but the present invention is not limited to this, and can be applied to a copying machine, a facsimile machine, or a composite machine of these. Of course. Also,
The image forming process is not limited to the electrophotographic system, but can be applied to various systems such as an inkjet system.

[0063]

As described above, according to the present invention,
It is possible to provide a sheet conveying apparatus that can perform curl correction according to the thickness of a sheet and an image forming apparatus including the sheet conveying apparatus without increasing cost and increasing size.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the overall configuration of a first embodiment of an image forming apparatus to which the present invention has been applied.

FIG. 2 is a cross-sectional view showing a configuration of curl correction means.

FIG. 3 is an external perspective view showing a detailed configuration of curl correction means.

FIG. 4 is a diagram showing a state when plain paper passes through a curl correction unit.

FIG. 5 is a diagram showing a state in which thick paper passes through a curl correction unit.

FIG. 6 is a sectional view showing the overall configuration of a second embodiment of an image forming apparatus to which the present invention has been applied.

FIG. 7 is a side view for explaining an angle of an upper surface of an endless belt formed with a pressing roller as a boundary in the curl correcting unit.

FIG. 8 is an overall cross-sectional view showing a conventional image forming apparatus having a double-sided printing function.

FIG. 9 is a diagram illustrating a case where a transfer failure occurs.

FIG. 10 is a diagram illustrating a configuration of a curl correction unit.

FIG. 11 is a diagram showing a curled state of the sheet.

[Explanation of symbols]

P sheet 1 Image forming device body 2 Image forming unit (image forming means) 2a Photosensitive drum 2b laser scanner 2c reflective mirror 2d developing device 2e Transfer charger 3 fixing section 4 Double-sided transport path (sheet re-feed path) 5 Transfer part 6 sheet discharge path 7 Sheet reversal conveyance path 8, 9 Conveyor path switching lever 10, 10A Curl correction means 11 Belt driven shaft 11b, 12b, 13b Bearings 11a, 12a Belt transport roller 12 Belt drive shaft 13 Pressing roller 14 Endless belt 15 frames 16 Press roller holder 17 Coil spring (elastic member, pressurizing means) 20 sheet cassettes (sheet accommodating parts) 21 sheet transport path 22 (22a to 22h) Transport roller pair 23 Pickup roller 24 Pair of registration rollers 25 Ejection roller pair 26 Belt conveyor 27, 28 drive gear 30 upstream transport path 31 Downstream transport path 30a, 31a Upper guide member 30b, 31b Lower guide member

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Claims (9)

(57) [Claims] 1. An endless belt for conveying a sheet, at least two stretching shafts for rotatably stretching the endless belt, and a rotatable press for pushing the stretched endless belt from outside. Laura,
In the sheet conveying device, which conveys a sheet while sandwiching the sheet by the endless belt and the pressing roller, the pressing roller has a magnitude of reaction force based on the rigidity of the sheet.
Endre by an elastic member to move in the pressing direction and the pressing release direction with respect to the endless belt in response to
A sheet conveying device characterized by being pressed by a belt . 2. The pressing roller is based on sheet rigidity.
As the reaction force increases, the endless belt
It moves in the pressing release direction.
Sheet transport device. Wherein said elastic member is a sheet conveying apparatus according to claim 1, characterized in that provided on both ends of the rotation shaft of the pressing roller. 4. The endless belt has an angle α of 2π / 6 (rad) ≦ α ≦ 5π / 6 formed between an upstream side and a downstream side of a sheet conveying surface formed with a pressing roller as a boundary.
(Rad) range.
The sheet conveying device according to any one of 3 above. 5. The sheet conveying apparatus according to claim 4 , wherein the pressing roller is arranged in the vicinity of an intersection connecting the upstream side conveying path and the downstream side conveying path. 6. A sheet conveying device according to any one of claims 1 to 5, the image formation characterized by comprising an image forming means for forming an image on a conveyed sheet by the sheet conveying device apparatus. 7. A sheet accommodating portion capable of accommodating and accommodating sheets, a sheet conveying path formed from the sheet accommodating portion to the image forming means, and a sheet on which an image is formed by the image forming means, to the image forming means again. 7. The image forming apparatus according to claim 6 , further comprising: a sheet re-feeding path for supplying the sheet, wherein the sheet conveying device is arranged in the sheet re-feeding path. 8. The sheet re-feeding path has a downstream end connected to the sheet conveying path.
7. The image forming apparatus according to item 7 . The method according to claim 9, wherein the sheet refeed path, claim 7 also <br/>, characterized in that the sheet reversing means for reversing the traveling direction of the sheet with an image formed by the image forming means provided Is an image forming apparatus according to item 8 .