JPH11334164A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate correction of a sheet position in a breadthwise direction of the sheet and transfer sheets of every size via a predetermined distance in the breadthwise direction by arranging a means for guiding the breadthwise direction of the sheet having an image formed at one face to a sheet re-transfer path which re-transfers the sheet to an image formation part. SOLUTION: A regulation guide 26 as a guide means standing vertically to a lower part 27 of a re-transfer part 16 is set in the vicinity of a transfer roller 24 of a first transfer roller pair of the re-transfer part 16 and a transfer roller 25 of a second transfer roller pair at the upstream of the transfer roller 24. When a transfer breadth at the upstream of the regulation is X, a maximum size in the breadthwise direction of a sheet is Y, marginal spaces are t1 , t2 , and a transfer breadth at the downstream of the regulation (predetermined distance) is [Y+(t1 +t2 )], the regulation guide 26 is set from the transfer roller 25 to the transfer roller 24 under a condition of X>[Y+(t1 +t2 )]. Accordingly, the regulation guide 26 can keep a correction breadth of the sheet within the predetermined distance.

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 having an automatic double-sided image forming function.

[0002]

2. Description of the Related Art In recent years, various types of image forming apparatuses have been manufactured and sold, and among them, those having an automatic double-sided image forming function have been considerably increased.

[0003] This is because there are more opportunities to form double-sided images due to diversification of uses of the image forming apparatus, and there is also an opportunity to form double-sided images for the purpose of reducing the number of sheets used from the viewpoint of environmental problems. Because it has increased further.

Accordingly, there is an increasing demand for an image forming apparatus having an automatic double-sided image forming function capable of easily forming a double-sided image. Further, in order to increase the speed and improve the image quality of the image forming apparatus, not only the automatic double-sided image forming function is provided, but also the improvement of the quality after image formation has been demanded.

[0005] Although the quality after image formation is the same as the image formation on the first side, the same image can be formed on both sides. Opportunities to form an image on both sides of the image have also been increasing, and at that time, a particularly problematic point is that the deviation between the image areas on the first and second surfaces becomes noticeable.

[0006] Further, with an increase in the mounting rate of a finisher or the like for performing bookbinding or the like, the deviation of the image area of the pages opened and opened when the bookbinding state is set becomes noticeable.

In order to solve this problem, in a conventional image forming apparatus, an apparatus for aligning the position of a sheet in an intermediate tray or the like in the sheet width direction (perpendicular to the sheet conveying direction) or detecting the sheet position in the sheet width direction is used. In some cases, the image is fed back to information, and the image on the second surface is formed by shifting the image and combining the image on the first surface and the image on the second surface.

[0008]

However, in the case of aligning the positions of the sheets on an intermediate tray or the like, it takes a long time to stop the conveyance of the sheets during the alignment, and the image forming speed may be reduced. Inevitably, the rollers must be released from being held during alignment, and once the rollers are released, it is difficult to align a sheet that has been greatly curled.

Further, when the images are aligned by detecting the sheet position in the sheet width direction, it is possible to align the image on the first surface and the image on the second surface with high accuracy, but it is actually shifted and conveyed. The sheet is conveyed as it is without returning the position of the sheet in the sheet width direction to the set position.

For this reason, it is necessary to secure a conveyance path having a width wider than the maximum sheet width in consideration of the positional deviation of the sheet expected at the maximum sheet width of the corresponding sheet size.

The required wide width in the sheet width direction must be ensured not only in the conveyance path but also in the image forming area of the photosensitive drum, and may have an effect that the size of the apparatus becomes large.

Further, when a finisher, a sorter, or the like is mounted, a surplus space for sheet displacement in the width direction of the sheet must be taken into consideration. There is also.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide an image forming apparatus which can convey a sheet within a predetermined interval to reduce the size of the apparatus. To provide.

[0014]

In order to achieve the above object, according to the present invention, in an image forming apparatus for forming an image on both sides of a sheet, a sheet on which an image is formed on one side is returned to an image forming section. A guide means is provided in the sheet re-conveying path for conveying and guides the sheet in the sheet width direction.

Therefore, the sheet conveyed in a state where the position in the sheet width direction is shifted is guided in the sheet width direction by the guide means, and the sheet width of the sheet is accommodated at a predetermined interval in the sheet width direction of the guide means.

It is preferable that the guide means has a correction section in which the facing distance in the sheet width direction decreases from the upstream side to the downstream side in the sheet conveying direction.

Thus, the sheet width of the sheet is accommodated in the narrowed opposing distance as a predetermined interval in the correction unit.

It is preferable that the guide means has a changeable means for changing the facing distance according to the sheet width of the conveyed sheet.

Thus, the facing distance of the guide means can be set for different sheet widths of the sheets, and even if the sheet width is narrow, the sheet width is accommodated in the corresponding narrow facing distance. Correction of the sheet position in the width direction can be easily performed.

[0020] It is preferable that the image forming apparatus further includes a first conveying roller pair for conveying the sheet on the downstream side of the correcting section, and a second conveying roller pair for conveying the sheet on the upstream side of the correcting section.

Thus, a conveying force can be applied to the sheet before and after the sheet position is corrected.

When the sheet passes through the guide means,
When a sheet is pinched by a plurality of pairs of conveying rollers, it is preferable that a release unit is provided to cause the sheet to be pinched only by the first pair of conveying rollers and the second pair of conveying rollers, and to release the pinching of the other pairs of conveying rollers. .

As a result, the sheet passing through the guide means is nipped and conveyed by the first conveying roller pair and the second conveying roller pair, so that a strong conveying force is applied to the sheet before and after the sheet position is corrected. Can be prevented.

[0024] It is preferable that a loop forming means for forming a loop on the sheet is provided between the first conveying roller pair and the second conveying roller pair.

As a result, the sheet position is corrected and the first
Even when the position of the sheet is different between the pair of conveying rollers and the pair of second conveying rollers, the sheet can be easily conveyed by the loop formed on the sheet.

It is preferable that the length of the conveying roller of the second conveying roller pair in the sheet width direction is short.

Thus, when correcting the position of the sheet in the sheet width direction, it is possible to easily change the sheet advancing direction with the second conveying roller pair as the center of rotation without hindering the rotation of the sheet. Can be.

It is preferable that the sheet holding force of the second conveying roller pair is set to be weak.

Thus, when correcting the position of the sheet in the sheet width direction, the rotation of the sheet can be easily changed with the second conveying roller pair as the rotation center without hindering the rotation of the sheet. Can be.

It is preferable that the driven roller of the second conveying roller pair rotates in accordance with the sheet in the traveling direction of the sheet.

This makes it easy to change the sheet advancing direction with the second conveying roller pair as the center of rotation.

[0032]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The material, shape, relative arrangement, and the like are not intended to limit the scope of the present invention only to them unless otherwise specified.

(First Embodiment) FIG. 1 shows an image forming apparatus according to a first embodiment.
A sheet on which an image is to be formed is selectively fed from a manual feed tray 1 or a feed cassette 2, and the sheet is conveyed to a transport belt 3.
The electrophotographic photosensitive drums 4, 5, and 4 serving as image forming means are stacked on the sheet, transported to the image forming unit, and according to an electric signal of image information transmitted from a reader scanner, a personal computer, or the like (not shown). After the toner images formed on the surfaces of the sheets 6 and 7 are sequentially transferred to the sheet conveyed on the conveying belt 3, they are permanently fixed by a fixing device 8, and the sheet on which a monochrome or full-color image is formed is discharged to a discharge tray 9. The one that discharges to the top.

The image forming apparatus of the present embodiment has an automatic double-sided image forming function for forming a double-sided image without discharging the image to the outside of the image forming apparatus main body. Instead of discharging the formed sheet to the outside of the image forming apparatus main body, the sheet is reversed in the apparatus, and the second surface as the other surface is image-formed and discharged, so that image formation is performed on both sides of the sheet. Can be performed automatically.

In the present embodiment, the photosensitive drums 4 to
As light source devices for forming toner images on the four surfaces of LED 7, light-emitting diodes (LEDs) 10, 11, 12, and 13 that are independently controlled face each of the surfaces of photosensitive drums 4 to 7. It is configured.

Next, a series of operations during automatic double-sided image formation in the image forming apparatus of the present embodiment will be described.

In the image forming apparatus according to the present embodiment, first, the image formation on the first side of the sheet is performed by the fixing unit 8 from the feeding operation.
Until the image is permanently fixed on the surface, the above-described sequence of operations is coincident with the above operation. From there, the sheet is transferred to the reversing section below the discharge section in the image forming apparatus main body by the flapper 14 disposed immediately after the fixing device 8. The sheet is fed, and the sheet is switched back by the reversing roller 15.

Then, the inverted sheet is sent to a re-conveying section 16 as a sheet re-conveying path disposed between the conveying belt 3 and the supply cassette 2, and skew correction is performed before the re-feed roller 17. The sheet is re-fed, and is sent out to the second side image formation.

The image forming operation on the second surface is performed by the re-feed roller 1.
7, the image forming of the first surface is completed, and the inverted sheet is re-fed, and the position of the sheet in the sheet width direction (vertical direction to the sheet conveying direction) is detected using the sheet position detecting device 18, By reflecting the information on the image information on the second surface, the deviation between the image on the first surface and the image on the second surface caused by the deviation of the sheet from the set position in the sheet width direction is corrected.

The subsequent operation coincides with the above-described operation until the sheet is stacked on the conveyor belt 3 of the image forming section and then discharged to the discharge tray 9, and the image forming operation on the second surface is completed.

The above-described sheet position detecting device 18 will be specifically described. FIG. 2 is a schematic diagram of the sheet position detecting device.

The sheet position detecting device 18 includes a photo interrupter 19 and a sensor flag 20, and includes a motor 2
1 is provided with a rack 22 capable of reciprocating in the sheet width direction.

The rack 22 has a stop position including a home position H and a start position S. The home position H is determined when the upper detection unit of the sensor flag 20 touches the protrusion 23 protruded from the image forming apparatus main body.

The start position S is a position at a fixed distance U from the end of the set sheet in the sheet width direction. That is, the start position S is determined by the sheet size (sheet width), and waits at this position immediately before detecting the sheet position.

The operation at the time of actually performing detection will be specifically described. First, the home position H is first set to the sensor flag 2 before the sheet arrives immediately below the sheet position detection device 18.
0 so that the lower detection part (sheet detection part) of the sensor flag 20 comes to the start position S which is a position away from the end of the sheet by a distance U in the sheet width direction. 22 is moved to a standby state.

When the re-fed sheet is present immediately below the sheet position detecting device 18, the rack 22 is moved until the lower detecting portion of the sensor flag 20 touches the sheet. Is detected in the sheet width direction.

In this embodiment, the motor 2
1 uses a stepping motor, and by using the characteristics of this motor, the distance from the start position S to the end of the sheet is determined by the motor 21 to move the sensor flag 20 from the start position S to touch the sheet. It is calculated from the number of required pulses.

Then, the detected position information is added to the image information, and the image forming position of the image on the second surface is moved. That is, the image forming area on the second surface is determined by the position of the sheet.

However, moving the image on the second surface by the sheet position detecting device 18 only corrects the image misalignment between the first and second surfaces. Therefore, this alone corresponds to the image forming device. For a sheet of a relatively small size (shorter sheet width) among the sheet sizes, if there is a position shift within the area that can be detected by the sheet position detecting device 18, even if only the image shift correction of the first surface and the second surface is performed, the sheet can be re-read. The width of the transport unit 16 is not significantly affected.

However, when a sheet of the maximum size (the sheet width is long) of the corresponding sheet size is conveyed, it is necessary to secure a surplus space in the sheet width direction in consideration of the expected positional deviation amount of the sheet in the sheet width direction. Will be needed.

The problem is not limited to the re-conveying section 16 and the feeding / conveying section. It is necessary to secure an image forming area in the sheet width direction in the image forming section.
This increases not only the size of the image forming apparatus such as increasing the length in the sheet width direction of Nos. 7 to 7, but also increases the cost.

Similarly, the image forming apparatus of the present embodiment
As described above, since an LED is used as a light source device, enlarging an image area requires a correspondingly large number of light-emitting diode elements, and accordingly, a control base and the like are also required. This leads to larger size and higher cost.

Further, when a device such as a sorter or finisher is mounted, the device must be large in consideration of the extra space in the sheet width direction of the device, in other words, a sorter or finisher that can be mounted. May be restricted.

Also, the function of aligning the position of the sheet in the sheet width direction, that is, temporarily discharging the sheet on which image formation on the first surface has been completed to an intermediate tray or the like, or transferring the sheet on the sheet conveyance path After releasing the restraint of the sheet such as temporarily releasing the pinch of the roller pair, the sheet is moved to the original set position by using a member capable of reciprocating in the sheet width direction, and then re-feeding is performed. In the case where a function of feeding the image to two-sided image formation is provided, an operation of picking up the sheet again is required at the same time.

When the image is formed on the first side, the quality of the sheet itself deteriorates due to the influence of heat of the fixing unit 8 or the sheet contains a large amount of fixing oil depending on the type of toner. It must be taken into account that this may lead to poor pickup.

The operation of actually aligning a sheet using a member (aligning member) that can reciprocate in the sheet width direction or correcting the position in the sheet width direction is performed for a full-color image in which a relatively large curl occurs. At the time of image formation, it is difficult to avoid the influence of curl, and it is often difficult to perform matching between settings and position correction in the sheet width direction.

Further, during alignment and correction of the position in the sheet width direction, it is necessary to temporarily stop the conveyance of the sheet. Therefore, it is necessary to take into account the effect of the reduction in the image forming speed due to this.

In this embodiment, in order to minimize the influence of sheet curl and the like, the holding of the rollers is not released, and
In order to minimize the interval in the sheet width direction that must be ensured in the image forming apparatus, the object is achieved by a configuration in which the sheet is conveyed only within a predetermined interval.

More specifically, referring to the drawings, as shown in FIGS. 3 and 4, the transport roller 24 of the first transport roller pair of the re-transport section 16 and the second transport roller upstream of the transport roller 24 The re-conveying unit 16
A restricting guide 26 is provided as a guide means that stands vertically to the lower part 27 of the guide.

The setting conditions of the regulation guide 26 in the conveyance rollers 25 to 24 are as follows: the upstream conveyance width before the regulation is X, the maximum size of the sheet in the sheet width direction is Y, and the remaining spaces are t ₁ and t ₂ . When the downstream conveyance width (predetermined interval) after the regulation is (Y + (t ₁ + t ₂ )), X>
(Y + (t ₁ + t ₂ ))...

As a result, the regulating guide 26 changes the sheet width of the sheet from the upstream conveying width through the sheet width direction position correcting section A as a correcting section at a predetermined interval (Y + (t ₁ + t ₂ )).
Can be put in.

Here, the extra spaces t ₁ and t ₂ need only be about the intersection of the sizes of the sheets in the sheet width direction, and the space corresponding to the amount of sheet displacement due to skewing or the like can be reduced as much as possible.

The length of the conveying rollers 24 and 25 in the sheet width direction for appropriately correcting the position of the sheet (the length of the surface rubber portion in the sheet width direction for applying a conveying force to the sheet)
Is that the length of the downstream conveying roller 24 in the sheet width direction is W, and the length of the upstream conveying roller 25 in the sheet width direction is V
, V ≧ V...

This condition is a condition when the conveying rollers 24 and 25 are compared. Actually, it is sufficient that the upstream conveying roller 25 is provided in a short sheet width direction.

As the actual position correction in the sheet width direction, when the position of the sheet having the largest sheet width is shifted in the sheet width direction, the sheet width direction position correction section A of the regulating guide 26 shown in FIG. Corners of the sheet abut, the sheet itself changes its advancing direction with the conveyance roller 25 as a rotation center, moves to a set position in the sheet width direction, and sets the sheet width at a predetermined interval by the conveyance direction regulating section B. Is to be transported.

Therefore, if the length of the upstream conveying roller 25 in the sheet width direction is short, the nipped sheet can easily change the sheet advancing direction about the conveying roller 25 as a rotation center, and the position of the sheet in the sheet width direction can be corrected. It can be suitably performed.

In other words, the configuration in which the transport roller 25 transports the sheet in the transport direction rather than favorably in the transport direction, rather than the configuration in which the transport is unstable and the skewing easily occurs in any direction, is a point of correcting the position of the sheet. Is preferred.

Further, the conditions for the pinching force of the roller pair for suitably correcting the position of the sheet are as follows: the pressure of the driven roller (not shown) of the downstream transport roller 24 is P ₂₃ ; When the pressing force of the roller is P ₂₄ , P ₂₃ ≧ P ₂₄ .

This condition is a condition when the transport rollers 24 and 25 are compared. Actually, it is sufficient that the sheet gripping force of the upstream transport roller 25 is weak.

Under the same conditions, the traveling direction of the sheet in the sheet width direction position correction area can be easily changed.

In the sheet width direction position correction area, the width of the restriction guide 26 becomes narrower from the upstream side to the downstream side of the sheet width direction position correction portion A in order to perform the sheet width direction position correction smoothly. The angle α formed by the tapered surface with respect to the transport direction is preferably in a setting range of 0 ° <α ≦ 45 °. The configuration is not limited to this, and any configuration may be used as long as the tapered surface of the sheet width direction position correction unit A becomes narrower from the upstream side to the downstream side.

However, as a condition for performing the position correction in the sheet width direction more preferably, the angle α to be formed is an acute angle closer to 0 ° when the corner of the sheet contacts the position correction unit A in the sheet width direction. Due to the reaction force applied locally, it is possible to avoid as much as possible a factor that hinders the position correction in the sheet width direction, such as bending near the corners of the sheet.

Further, the tapered surface of the sheet width direction position correcting portion A which contacts the corner of the sheet may be a curved surface instead of a flat surface.

Under the above conditions, no matter which sheet of the corresponding sheet size is conveyed to the re-conveying section 16 in a state of being shifted in the sheet width direction, the sheet is moved in the sheet width direction by the regulating guide 26. At a predetermined interval (Y + (t
₁ + t ₂ )), it is not necessary to secure a particularly large extra space in the sheet width direction in the feeding / conveying unit and the image forming unit.

Accordingly, sheets of all sizes can be conveyed at a predetermined interval in the sheet width direction, and the size of the apparatus can be reduced.

In the case of the present embodiment, the transport rollers 2
It is more effective to form a loop between the sheet and the transport roller 25 in the sheet.

More specifically, when a sheet abuts on the stopped transport roller 24, the sheet is further transported from the upstream side, the sheet is bent, and the transport roller 24 is rotated to form a loop in the sheet. After the conveyance direction of the sheet is changed to a direction different from the sheet conveyance direction around the conveyance roller 25 as the rotation center, and the leading end of the sheet is returned to the original sheet width position, the conveyance roller is moved as described above. 24
By forming a loop in the sheet, the traveling direction of the sheet can be easily returned to the transport direction.

Even if it is not possible to change the traveling direction of the sheet about the transport roller 25 as the center of rotation, the sheet itself is allowed to have a degree of freedom (become loose) between the transport roller 25 and the transport roller 24. By changing the position in the sheet width direction, the stress applied to the sheet can be avoided,
The position in the sheet width direction can be easily moved.

In addition, even when the seat has a relatively weak waist, when the corners of the sheet abut against the control guide 26, the control guide 26 may be used as shown in FIG. The upper end of 26 is closely attached to the upper part 33, or is made into one member, or the gap between the upper part 33 and the lower part 27 is gradually narrowed as shown in the figure to restrain the sheet so as not to hinder the position correction. Thus, the position can be suitably corrected.

Further, as shown in FIG. 6, the driven roller 28 of the transport roller 25 of the second transport roller pair of the re-transport section 16
However, when the position of the sheet in the sheet width direction is adjusted by the regulation guide 26, the driven roller 28 is provided so as to rotate in accordance with the direction of movement of the sheet that slightly changes.

In this manner, the re-conveying unit 16 can transfer any sheet having a sheet width among the corresponding sheet sizes between the conveying roller 25 and the conveying roller 24.
After passing through, a predetermined interval (Y + (t ₁
The position of the sheet width of the sheet is adjusted within the range of + t ₂ )).

For example, when the distance in the sheet conveyance direction of the correction area of the position in the sheet width direction such as the position correction section A in the sheet width direction of the regulation guide 26 shown in FIG. Even in the case where the stiffness of the sheet is weak, the position correction in the sheet width direction can be performed more suitably.

More specifically, in the case of a sheet having a relatively low waist, even if the end of the sheet comes into contact with one of the restriction guides 26, the sheet is pushed down, and the position of the sheet in the sheet width direction is changed. Without correction, the corners of the sheet may break.

For this reason, when the position of the sheet is corrected in the sheet width direction, there is a degree of freedom at the center of rotation in order to cope with a slight change in the traveling direction of the sheet with the conveyance roller 25 as the center of rotation. Need to be done. However, it is difficult to allow the driving-side conveying roller 25 to have a degree of freedom so as to be rotatable.

Therefore, as described above, the driven roller 28 of the transport roller 25 is provided so as to follow the subtle change in the traveling direction of the sheet and to rotate.

Thus, when the vicinity of the leading end of the sheet abuts on the regulating guide 26 to correct the sheet width position of the sheet, the conveying roller 25 on the drive side with respect to the slightly changing sheet conveying direction Even if the driven roller 28 does not rotate, the driven roller 28 is provided with a degree of freedom so that the driven roller 28 can rotate. The position of the sheet in the sheet width direction can be suitably corrected by changing the traveling direction of the sheet around the rotation center 25.

(Second Embodiment) The second embodiment is characterized in that the regulating guide 26 moves in accordance with the size of the sheet to be conveyed. The description is omitted because it is almost the same as the first embodiment.

That is, as shown in FIG.
6 is moved in advance according to the size of the conveyed sheet, and the position in the sheet width direction is corrected regardless of the size of the conveyed sheet.

By providing this method, it is basically possible to prevent a certain degree of image misalignment between the first surface and the second surface without providing a sheet position detecting device. Is expected to be shifted by the extra space (t ₁ + t ₂ ) in the sheet width direction described with reference to FIG. 4 in the first embodiment. Image shift between the surface and the second surface can be minimized.

When the sheet position detecting device 18 is used after correcting the position in the sheet width direction, the start position S of the rack 21 of the sheet position detecting device 18 described with reference to FIG. 2 in the first embodiment is used. It is possible to shorten the set value of the distance U from the sheet to the edge of the sheet.

Accordingly, the operation time required to detect the sheet position can be shortened, and the sheet position detecting device can be arranged at a position closer to the image forming section, so that the accuracy of correcting the image shift is improved. .

(Third Embodiment) The third embodiment has the same configuration as the image forming apparatus described in the first embodiment except for the re-conveying section 16, and a restriction guide 26.
Since the basic configuration for correcting the position of the sheet such as the maximum size in the sheet width direction using the same is the same, the description is omitted.

Normally, the pitch between the conveying rollers is determined by the sheet having the shortest length in the conveying direction among the corresponding sheet sizes. Therefore, when the difference between the longest sheet and the shortest sheet in the conveying direction is large, the position correction in the sheet width direction described in the first embodiment and the like is performed in a state where the plurality of conveying roller pairs sandwich the sheet. Must be done.

In fact, it is difficult to correct the sheet conveyance position only by the regulation guide 26 in a state where a plurality of pairs of conveyance rollers hold the sheet. If possible, if the sheet is nipped by a pair of conveyance rollers, the position in the sheet width direction can be suitably corrected as described in the first embodiment.

Therefore, in the present embodiment, the length of the sheet in the sheet width direction which requires the position correction in the sheet width direction by the conveyance direction regulating guide 26 and the sheet width of the sheet considerably longer in the sheet conveyance direction than between the conveyance roller pitches. A description will be specifically given of how to appropriately perform the directional position correction.

The structure of the re-conveying section 16 shown in FIG.
By using a solenoid (not shown), the driven roller 30 and the driven roller 32 of the transport roller 31 provided further upstream than the transport roller 25 provided immediately before the sheet width direction position correction area are separated from each other. Release the pinch of the roller pair when correcting the position in the sheet width direction, and
The first conveying roller pair and the second conveying roller pair provided with the rollers 4 and 25 are used for nipping and conveying.

Therefore, similarly to the first embodiment, the position of the sheet in the sheet width direction can be suitably corrected.

Also, in the present embodiment, the driven roller 28 of the transport roller 25 described in the first embodiment is similarly provided so as to rotate in accordance with the traveling direction of the sheet. Since the details have already been described, they are omitted here.

FIG. 9 shows the conditions for releasing the nipping of the transport rollers.
More specifically, the length of the sheet (not shown) for correcting the position in the sheet width direction in the sub-scanning direction using the regulating guide 26 is L _K , and the conveying roller immediately before the sheet width direction position correction area is used. L ₁ , the distance between the pitches of the transport roller 25 and the transport roller 29 in the sheet width direction position correction area is L ₂ , and the distance between the pitches of the transport roller 31 and the transport roller 31 in the sheet width direction position correction area is L ₁ . the pitch distance of the conveying roller 24 in the regulation region as L _3, the conditions for releasing the holding of the sheet conveying roller 29 and the driven roller _{30, L K> L 2 + L} 3 ... is as.

Next, the conveying roller 31 and the driven roller 32
The condition for releasing the holding of the sheet is as follows: L _K > L ₁ + L ₂ .
become that way.

There is no problem if the sheet is released before the sheet is conveyed to this area, so it may be immediately after setting the sheet size before image formation or immediately before being conveyed to this area.

In this manner, similarly to the first embodiment, correction of the position of the sheet in the sheet width direction can be suitably performed, and sheets of all sizes are conveyed at predetermined intervals in the sheet width direction. Therefore, the size of the device can be reduced.

[0103]

According to the present invention, there is provided a sheet re-conveying path for re-conveying a sheet having an image formed on one surface to an image forming section, and a guide means for guiding the sheet in the sheet width direction. The sheet conveyed in a state where the position in the sheet width direction is shifted is guided in the sheet width direction by the guide means, the sheet width of the sheet is set at a predetermined interval in the sheet width direction of the guide means, and the sheet in the sheet width direction is The position can be easily corrected, and sheets of all sizes can be conveyed at predetermined intervals in the sheet width direction, whereby the size of the apparatus can be reduced.

Since the guide means has a correction section in which the facing distance in the sheet width direction decreases from the upstream side to the downstream side with respect to the sheet conveying direction, the sheet becomes narrow as a predetermined interval in the correction section. The sheet width is accommodated in the opposed distance, and the sheet position in the sheet width direction can be easily corrected, and sheets of all sizes can be conveyed at predetermined intervals in the sheet width direction. The size of the device can be reduced.

The guide means can change the facing distance, and has a changing means for changing the facing distance in accordance with the sheet width of the sheet to be conveyed. The distance can be set individually, and even if the sheet has a small sheet width, the sheet width can be accommodated in the corresponding narrow opposing distance, and the sheet position in the sheet width direction can be easily corrected.

A first conveying roller pair for conveying a sheet downstream of the correction unit and a second conveyance roller for conveying a sheet upstream of the correction unit.
With the provision of the conveying roller pair, a conveying force can be applied to the sheet before and after the sheet position is corrected.

When a sheet is nipped by a plurality of pairs of conveying rollers when the sheet passes through the guide means, the sheet is nipped only by the first pair of conveying rollers and the second pair of conveying rollers, and the other pair of conveying rollers Is provided, the sheet passing through the guide means is nipped and conveyed by the first pair of conveying rollers and the second pair of conveying rollers, so that the sheet is not moved before and after the sheet position is corrected. It is possible to prevent the transfer force from being applied.

By providing a loop forming means for forming a loop on the sheet between the first conveying roller pair and the second conveying roller pair, the sheet position is corrected, and the first conveying roller pair and the second conveying roller Even when the sheet position differs between the pair, the sheet can be easily conveyed by the loop formed on the sheet.

Since the length of the conveying roller of the second conveying roller pair in the sheet width direction is shortened, the rotation of the sheet is not hindered when correcting the position of the sheet in the sheet width direction. The sheet advancing direction can be easily changed with the second conveying roller pair as the center of rotation.

Since the sheet holding force of the second conveyance roller pair is set to be weak, the correction of the sheet position of the sheet does not hinder the rotation of the sheet, and the second conveyance roller pair is used as the rotation center. The sheet advancing direction can be easily changed.

The driven roller of the second conveying roller pair corresponds to the traveling direction of the sheet and rotates following the sheet to change the traveling direction of the sheet about the second conveying roller pair. Can be easier.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an image forming apparatus according to a first embodiment.

FIG. 2 is a perspective view showing a sheet position detecting device.

FIG. 3 is a perspective view showing a re-transport unit according to the first embodiment.

FIG. 4 is a plan view showing a re-transport unit according to the first embodiment.

FIG. 5 is a perspective view showing an example of a re-transport unit according to the first embodiment.

FIG. 6 is a perspective view showing an example of a re-transport unit according to the first embodiment.

FIG. 7 is a perspective view showing a re-transport unit according to a second embodiment.

FIG. 8 is a perspective view showing a re-transport unit according to a third embodiment.

FIG. 9 is a plan view showing a re-transport unit according to a third embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 manual feed tray 2 supply cassette 3 transport belt 4, 5, 6, 7 photosensitive drum 8 fixing device 9 discharge tray 10, 11, 12, 13 LED 14 flapper 15 reverse roller 16 re-transport section 17 re-feed roller 18 sheet position detection Apparatus 19 Photointerrupter 20 Sensor flag 21 Motor 22 Rack 23 Projection 24, 25, 29, 31 Conveyance roller 26 Regulation guide 27 Lower part 28, 30, 32 Follower roller 33 Upper part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03G 15/00 510 G03G 15/00 510

Claims (9)

[Claims] An image forming apparatus for forming an image on both sides of a sheet is provided in a sheet re-conveying path for re-conveying a sheet having an image formed on one side to an image forming section, and guides the sheet in a sheet width direction. An image forming apparatus comprising: 2. The apparatus according to claim 1, wherein the guide unit includes a correction unit that reduces a facing distance in a sheet width direction from an upstream side to a downstream side with respect to a sheet conveying direction.
An image forming apparatus according to claim 1. 3. The image according to claim 2, wherein said guide means is capable of changing an opposing distance, and is provided with changing means for changing the opposing distance in accordance with the sheet width of a sheet to be conveyed. Forming equipment. 4. The apparatus according to claim 1, further comprising a first pair of transport rollers for transporting a sheet downstream of said correction unit, and a second pair of transport rollers for transporting a sheet upstream of said correction unit. Item 4. The image forming apparatus according to item 2 or 3. 5. When the sheet is nipped by a plurality of pairs of conveying rollers when the sheet passes through the guide means, the sheet is nipped only by the first pair of conveying rollers and the second pair of conveying rollers. The image forming apparatus according to claim 4, further comprising a release unit configured to release the nipping of the pair of transport rollers. 6. The image forming apparatus according to claim 4, further comprising a loop forming unit that forms a loop on a sheet between the first pair of conveying rollers and the second pair of conveying rollers. apparatus. 7. The image forming apparatus according to claim 4, wherein a length of the conveying roller of the second conveying roller pair in a sheet width direction is shortened. 8. The image forming apparatus according to claim 4, wherein a sheet holding force of the second conveying roller pair is weakened. 9. The driven roller of the second conveying roller pair,
The image forming apparatus according to any one of claims 4 to 8, wherein the image forming apparatus rotates in accordance with the sheet in the advancing direction.