JPH11255396A - Image forming apparatus and both-sided printing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute curl correction without any increase in size of an image forming apparatus by forming a paper guide forming a reversing path route for paper like an arch directed to correct a curl in the paper. SOLUTION: A paper guide formed by a lower guide member 33 and an upper guide member 34 is provided between two pairs of transport rollers 27 disposed in a both-sided printing unit 26 for conveying a paper sheet. In this arrangement, the lower guide member 33 and the upper guide member 34 are formed like an upward arch to curl in the reverse direction of the curl direction of the paper, and a space between both arch-like lower guide members 33 and upper guide member 34 is taken as a part of a reversing pass route 35. The lower guide member 33 and the upper guide member 34 are formed by ABS resin(acrylonitrile-butadiene styrene resin).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and a two-sided printing unit, and more particularly to a two-sided printing unit having a paper curl correcting mechanism used in an image forming apparatus such as a small laser printer and an optional unit. The present invention relates to an image forming apparatus to be incorporated in a computer.

[0002]

2. Description of the Related Art In recent years, with the spread and high performance of word processors and personal computers, high performance of output devices has been required, and small laser printers and the like have begun to spread along with the demand.

There is a demand for such a small laser printer to have a double-sided printing function. However, a large-sized copying machine having a reverse path route for double-sided printing in the apparatus itself is required. In contrast, in the case of a small laser printer, etc., incorporating it into the device itself leads to an increase in the size of the device.Therefore, a duplex printing unit is provided as an option, and this duplex printing unit can be used as needed. And are actually commercially available (for example, the trade names GL760 and GL740 of the present applicant).

Here, a conventional image forming apparatus with a double-sided printing unit will be described with reference to FIGS. In addition,
FIG. 5 is a schematic configuration diagram of a conventional image forming apparatus with a double-sided printing unit. In order to make it easier to understand the essence of the invention, FIG. Members that are not relevant are not shown. FIG. 6 is an explanatory diagram of a sheet reversing method in a conventional image forming apparatus with a double-sided printing unit, specifically showing a configuration in the vicinity of a reversing path route. The same members as in the figure are shown.

As shown in FIG. 5, a conventional image forming apparatus with a duplex printing unit, that is, a laser printer is, for example, a first paper cassette 11 and a second paper cassette so as to correspond to each paper size. 12 and a third paper cassette 13 including a third paper cassette 13.
Pick rollers 14 for feeding the paper stored in each paper cassette to a printing route indicated by a thick broken line in the drawing.
Are picked up by a pick roller 14 from a paper feed cassette corresponding to a sheet of a required size, and sent out to a printing route by a feed roller 15.

The leading edge of the paper fed to the printing route by the feed roller 15 is registered with a registration sensor 16.
, And is conveyed by a registration roller 17 to a transfer unit including a photoconductor 19 and a transfer unit 20 at a fixed timing. On the other hand, on the surface of the photoconductor 19, an electrostatic latent image is formed by exposing with a laser beam corresponding to an image signal from a laser diode housed in the LD unit 21. The toner is attached by the developing device 18, and the attached toner is transferred to a sheet by the transfer device 20. Incidentally, reference numeral 22 denotes a static elimination LED.

The toner transferred to the paper is fixed by a fixing unit 23 composed of a heat roller or the like.
The printed sheet is discharged to the stacker 25 through a sheet reversing mechanism 24 indicated by a dashed circle in the drawing. In an actual laser printer, a second sheet reversing mechanism, a second stacker, a third stacker, or the like is provided below the sheet reversing mechanism 24 in the printing route.
It is equipped with a multi-function feeder for supplying paper from other than a paper feed cassette.

In such a laser printer, when performing double-sided printing, the optional double-sided printing unit 26 of the uppermost first sheet feeding cassette 11 is mounted, and the sheet on which single-sided printing has been completed is turned into a sheet reversing mechanism. The sheet is switched back by 24 and taken into the duplex printing unit 26, sent out again from the duplex printing unit 26 to the printing route via the pick roller 14, and printed on the opposite side. Not discharged to other stackers.

FIG. 6 shows the sheet reversing mechanism 24 and the double-sided printing unit 26 in detail and specifically for explaining the sheet reversing method in duplex printing.
Is provided with a flap 30 and a reversing roller 31. First, when printing on one side, the flap 30 falls down to the reversing roller 31 side to form a paper discharge route,
When the trailing edge of the sheet is applied to the reversing roller 31, the flap 30 is raised as shown in the figure to form a route to the duplex printing unit 26, the reversing roller 31 is reversed, and the one-side printing is completed by switchback. The transported sheet is conveyed to the duplex printing unit 26. The inverted sheet is checked by the inversion sensor 32.

The duplex printing unit 26 to which the paper is fed
Is provided with two pairs of transport rollers 27 and a paper guide comprising a lower guide member 28 and an upper guide member 29 between the two pairs of transport rollers 27. The paper is formed by the paper guide while being fed out by the transport rollers 27. The paper is transported in the reversing pass route, and is again taken out by the pick roller 14 and sent out to the printing route.

As described above, by making the double-sided printing unit optional, double-sided printing can be performed without increasing the size of the main body of the image forming apparatus, and the configuration is optimal for an image forming apparatus such as a laser printer for personal use. If you don't need double-sided printing,
By removing the duplex printing unit, it can be used as a paper feed cassette as it is.

[0012]

However, such a small-sized image forming apparatus as described above does not have a curl correction mechanism. Therefore, when performing double-sided printing, the paper on one side is printed on the printing side. It takes curls to curve inwards,
This causes a jam (JAM) in the reversal path route formed by the paper guide, or causes damage or dirt. Further, since a curved paper is supplied to the transfer unit, a transfer failure occurs. There is.

In particular, when the printing target is a thick paper such as a postcard, which is a typical printing target of a small laser printer, poor transfer, trapping jam, etc. become remarkable due to the curl of the paper.

Some image forming apparatuses such as a laser printer are provided with a double-sided printing mechanism and a curl correcting mechanism (for example, Japanese Patent Application Laid-Open Nos. 60-114874 and 3-73770, or Kaihei 9-188
However, since such a double-sided printing mechanism and a curl correction mechanism are incorporated in the apparatus main body, there is a problem that the apparatus itself becomes large and is not suitable for an image forming apparatus for personal use. In the case of the curl correction mechanism described in the above document, when the paper is a thick paper such as a postcard, a jam may occur in the curl correction mechanism, and the intended effect may not be obtained.

Therefore, according to the present invention, a curl correction mechanism is provided externally as an option in the image forming apparatus.
An object of the present invention is to prevent occurrence of a jam due to the introduction of a curl correction mechanism.

[0016]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described. FIG. 1 is a cross-sectional view of a main part of a sheet cassette in which a duplex printing unit is mounted. Refer to FIG. 1 (1) The present invention is characterized in that, in a duplex printing unit 2 provided with a curl correction mechanism, a paper guide 4 constituting a paper reversal path route 3 is formed in an arch shape in a direction for correcting paper curl. And

As described above, the optional double-sided printing unit 2 in which the curl correction mechanism is arbitrarily incorporated in the paper feed cassette 1 is provided.
The paper guide 4 in which the curl correction mechanism is provided between the two pairs of transport rollers 5 and 6 constituting the reverse path route 3 can be used to curl the paper. Since the configuration is made by forming an arch shape in the direction to be corrected, the configuration is simplified, and furthermore, since the minimum curl correction is performed on the paper,
No extra stress is applied to the paper.

(2) Further, the present invention is characterized in that a sub-roller for correcting the curl of the paper is provided in the reverse path route 3 of the paper in the duplex printing unit 2 provided with the curl correcting mechanism.

As described above, the optional double-sided printing unit 2 in which the curl correction mechanism is arbitrarily incorporated in the paper feed cassette 1 is provided.
In this case, the size of the image forming apparatus can be reduced. In addition, since the curl correction mechanism is constituted by the sub-roller provided in the reversing path route 3, the structure is simplified, and the minimum required paper Since the curl correction is limited, no extra stress is applied to the paper. Note that, in this case, it is desirable to use in combination with the arch-shaped paper guide 4 in a direction to correct the curl of the paper.

(3) The present invention employs at least one of the above-mentioned constitution (2), in which the shape of the sub-roller is crowned or the pressing force of the sub-roller is adjustable. It is characterized by the following.

As described above, by making the shape of the sub-roller a crown shape, it is possible to correct the difference in the curl between the center and both ends of the paper.
By adjusting the pressing force of the sub roller, it is possible to correct the difference in how the paper is curled,
In particular, it is desirable to employ both of these configurations together.

(4) The present invention is characterized in that the double-sided printing unit 2 having the curl correction mechanism is provided with a belt transport mechanism for correcting the curl of the paper in the paper reversing path route 3. I do.

As described above, the optional double-sided printing unit 2 in which the curl correction mechanism is arbitrarily incorporated in the paper feed cassette 1 is provided.
The curl correction mechanism can be downsized, and the curl correction mechanism is constituted by the belt transport mechanism provided in the reversing path route 3, so that the curl correction is ensured. In this case, it is desirable to use in combination with a sub-roller that presses the sheet against the belt.

(5) According to the present invention, in the above (4), the shape of the side of the belt constituting the belt transport mechanism which comes into contact with the sheet may be a concave shape for correcting the curl of the sheet.
Alternatively, at least one of the configurations in which the pressing force of the belt can be adjusted is adopted.

As described above, by making the shape of the side of the belt that makes contact with the paper constituting the belt transport mechanism concave so as to correct the curl of the paper, the curl correction can be more reliably performed, and the pressing force of the belt can be improved. Is adjustable, it is possible to correct the difference in how the paper is curled, and it is particularly desirable to employ both of these configurations together.

(6) Further, according to the present invention, in an image forming apparatus, a sheet guide 4 constituting a sheet reversing path route 3 is provided.
Is characterized in that a double-sided printing unit 2 having a curl correction mechanism whose shape is arched in a direction for correcting the curl of a sheet is provided.

As described above, the sheet cassette 1 of the image forming apparatus
By optionally incorporating a double-sided printing unit 2 having a curl correction mechanism therein, it is possible to reduce the size of an image forming apparatus capable of performing double-sided printing in accordance with customer needs, and to minimize curl in a necessary minimum range. Can be reduced.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, a first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a cross-sectional view of a main part of a sheet cassette in which a double-sided printing unit is mounted. The configuration of the other laser printers is the same as the configuration shown in FIGS. Signs are attached. Referring again to FIG. 5, FIG. 5 is a diagram showing a schematic configuration of the image forming apparatus according to the embodiment of the present invention. As shown in FIG. To
A three-stage paper cassette including a first paper cassette 11, a second paper cassette 12, and a third paper cassette 13 is provided. A pick roller 14 is provided for feeding the sheet to a printing route indicated by a thick broken line in the drawing. Will be sent to

The sheet sent out to the printing route by the feed roller 15 has a leading end whose registration sensor 16
, And is conveyed by a registration roller 17 to a transfer unit including a photoconductor 19 and a transfer unit 20 at a fixed timing. On the other hand, on the surface of the photoconductor 19, an electrostatic latent image is formed by exposing with a laser beam corresponding to an image signal from a laser diode housed in the LD unit 21. The toner is attached by the developing device 18, and the attached toner is transferred to a sheet by the transfer device 20.

The toner transferred to the paper is fixed by a fixing unit 23 including a heat roller and the like.
The printed sheet is discharged to the stacker 25 through a sheet reversing mechanism 24 indicated by a dashed circle in the drawing. In an actual laser printer, a second sheet reversing mechanism, a second stacker, a third stacker, or the like is provided below the sheet reversing mechanism 24 in the printing route.
It is equipped with a multi-function feeder for supplying paper from other than a paper feed cassette.

In such a laser printer, when performing double-sided printing, the optional double-sided printing unit 26 of the uppermost first sheet feeding cassette 11 is mounted, and the sheet on which single-sided printing has been completed is turned into a sheet reversing mechanism. The sheet is switched back by 24 and taken into the duplex printing unit 26, sent out again from the duplex printing unit 26 to the printing route via the pick roller 14, and printed on the opposite side. Not to be discharged to other stackers.

Next, a specific configuration of a double-sided printing unit having a curl correction mechanism according to the first embodiment of the present invention will be described with reference to FIG. Referring to FIG. 2, the duplex printing unit 2 mounted on the first paper feed cassette 11
6, two pairs of transport rollers 2 for transporting the paper
7, a paper guide including a lower guide member 33 and an upper guide member 34 is provided, and the shapes of the lower guide member 33 and the upper guide member 34 are adjusted upward so as to add a curl in a direction opposite to the curl direction of the paper. The space between the lower guide member 33 and the upper guide member 34 is formed as a part of a reverse path route 35. The lower guide member 33 and the upper guide member 34 are made of, for example, an ABS resin (acrylonitrile-butadiene styrene resin).

The lower guide member 33 and the upper guide member 34
The degree of curl of the sheet may be appropriately set according to the degree of curl of the sheet to be used. It is also desirable that the cross-sectional shape perpendicular to the vertical direction be arched upward.

As described above, in the first embodiment of the present invention, the lower guide member 3 constituting the reverse path route 35
Since the shape of the paper guide consisting of the upper guide member 3 and the upper guide member 34 is merely an arc shape, the configuration is simplified. Since no separate curl correction mechanism is provided, the curl correction can be performed without increasing the size of the laser printer itself. In addition, since the minimum curl required for double-sided printing is performed, no extra stress is applied to the paper.

Next, a duplex printing unit according to a second embodiment of the present invention will be described with reference to FIG. Note that FIG.
FIG. 3A is a cross-sectional view of a main part of a paper feed cassette in which a duplex printing unit is mounted. FIG. 3B is a cross-sectional view along the axial direction of a sub-roller. The configuration is the same as that shown in FIGS. 5 and 6, and the same members are denoted by the same reference numerals. See FIG. 3A. Duplex printing unit 2 mounted on first paper cassette 11
6, two pairs of transport rollers 2 for transporting the paper
7, a paper guide comprising a lower guide member 33 and an upper guide member 34 made of ABS resin is provided, and the shapes of the lower guide member 33 and the upper guide member 34 are changed in a direction opposite to the curl direction of the paper. The upper guide member 3 and the upper guide member 3 are formed into an upwardly facing arch shape so as to be attached.
4 is a part of the reversing path route 35, and a sub-roller 36 that is driven near the top of the lower guide member 33 is provided.

Referring to FIG. 3 (b), the sub-roller 36 is desirably formed in a crown shape as shown in the figure in order to correct the difference in the curl between the center and both ends of the sheet. In order to adjust the degree of curving of the lower guide member 33 according to the degree of curl of the sheet, the pressing force can be adjusted.

As described above, in the second embodiment of the present invention, since the sub-roller 36 is provided in the reversing path route 35, the transfer of the paper becomes smooth, and a jam occurs in the reversing path route 35. In addition, the curl correction is performed by the sub-roller 36 and the paper guide including the lower guide member 33 and the upper guide member 34, so that the correction accuracy can be improved.

In this case as well, the degree of curvature of the lower guide member 33 and the upper guide member 34 may be appropriately set in accordance with the degree of curl of the sheet to be used. In order to compensate for the difference in the manner in which
It is desirable to make it upwardly arched in accordance with the crown shape of No. 6.

Next, a duplex printing unit according to a third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view of a main part of a paper feed cassette in which a duplex printing unit is mounted. The configuration of the other laser printer is the same as the configuration shown in FIGS. Signs are attached. Referring to FIG. 4, the duplex printing unit 2 mounted on the first paper feed cassette 11
6, two pairs of transport rollers 2 for transporting the paper
7, a lower guide member 33 made of ABS resin is provided, and the shape of the lower guide member 33 is formed in an upward arch shape so as to add a curl in the direction opposite to the curl direction of the sheet, and the two pairs of transport rollers 27 are provided. Is a part of the reversing path route 35 and the sub-roller 36 driven near the top of the lower guide member 33
And a belt conveying means including pulleys 37 and 38 and a belt 39 for applying a pressing force so as to press the sub roller 36 downward. In this case, the belt 39 on the side in contact with the sheet is pressed by the sub-roller 36 and has a concave shape depressed upward.

As described above, in the third embodiment of the present invention, since the belt conveying means is provided in the reversing path route 35, the transfer of the paper becomes smooth and the paper is squeezed by the belt. Since the curl correction is performed by pressing down, the correction accuracy can be further improved.

In this case as well, in order to correct the difference in the curl between the center and both ends of the sheet, the cross-sectional shape of the pulleys 37 and 38 perpendicular to the sheet conveying direction is set to the crown shape of the sub-roller 36. It is desirable that the pressing force is adjustable in accordance with the degree of curl of the sheet to be used, and that the pressing force is desirably adjustable.

Also in this case, the degree of curl of the lower guide member 33 may be appropriately set in accordance with the degree of curl of the sheet to be used. In order to correct the above, it is desirable that the cross-sectional shape perpendicular to the sheet conveyance direction is formed in an upward arch shape in accordance with the crown shape of the sub-roller 36.

In this case, the sub-roller 36 is provided because the belt conveyance means including the pulleys 37 and 38 and the belt 39 assists the conveyance of the paper and corrects the curl.
Is not necessary.

The embodiments of the present invention have been described above. However, the present invention is not limited to the configurations shown in the above embodiments, and various modifications are possible.
The double-sided printing unit provided with the curl correction mechanism is not limited to a laser printer, but is also applied to other small electrophotographic recording apparatuses such as home copying machines.

[0045]

According to the present invention, since a simple curl correcting mechanism is provided at the reverse path route of the duplex printing unit which is optionally mounted on the image forming apparatus, the curl correction can be performed without increasing the size of the image forming apparatus. This can prevent poor transfer and jamming, and can adjust the pressing force of the curl correction mechanism so that various thicknesses from thick paper such as postcards to ordinary copy paper can be obtained. Since it is possible to flexibly cope with such paper sheets, it greatly contributes to the spread and development of small image forming apparatuses.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is a sectional view of the duplex printing unit according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a duplex printing unit according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a duplex printing unit according to a third embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of an image forming apparatus with a duplex printing unit.

FIG. 6 is an explanatory diagram of a sheet reversing method in a conventional image forming apparatus with a duplex printing unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 paper feed cassette 2 duplex printing unit 3 reverse path route 4 paper guide 5 transport roller 6 transport roller 11 first paper cassette 12 second paper cassette 13 third paper cassette 14 pick roller 15 feed roller 16 registration sensor 17 registration roller REFERENCE SIGNS LIST 18 developing device 19 photoreceptor 20 transfer device 21 LD unit 22 static elimination LED 23 fixing unit 24 paper reversing mechanism 25 stacker 26 double-sided printing unit 27 transport roller 28 lower guide member 29 upper guide member 30 flap 31 inversion roller 32 inversion sensor 33 lower guide Member 34 Upper guide member 35 Reverse path route 36 Sub-roller 37 Pulley 38 Pulley 39 Belt

Claims (6)

[Claims] 1. A double-sided printing unit provided with a curl correction mechanism, wherein a paper guide constituting a paper reversing path route is formed in an arch shape in a direction for correcting the curl of the paper. 2. A double-sided printing unit comprising a curl correction mechanism, wherein a sub-roller for correcting the curl of the paper is provided in a reverse path of the paper. 3. The curl according to claim 2, wherein at least one of a configuration in which the shape of the sub-roller is a crown shape and a configuration in which a pressing force of the sub-roller is adjustable is adopted. Double-sided printing unit with correction mechanism. 4. A double-sided printing unit provided with a curl correction mechanism, wherein a belt transport mechanism for correcting curl of the paper is provided in a paper reversal path. 5. A method according to claim 1, wherein a shape of a side of the belt constituting the belt conveying mechanism which is in contact with the sheet is a concave shape in a direction to correct the curl of the sheet, or a pressing force of the belt is adjustable. 5. A double-sided printing unit provided with a curl correction mechanism according to claim 4, wherein at least one of the configurations is adopted. 6. An image forming apparatus comprising: a double-sided printing unit having a curl correcting mechanism in which a shape of a paper guide forming a paper reversing path route is arch-shaped so as to correct the curl of the paper. .