JP3815533B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus provided with a mechanism for switching back sheets conveyed one by one.
[0002]
[Prior art]
2. Description of the Related Art Image forming apparatuses represented by printers and copiers capable of performing automatic double-sided printing by switching back sheets conveyed one by one have been put into practical use. In such an image forming apparatus, a sheet handling apparatus connected to the latter stage of the image forming apparatus discharges the printed surface of a single-side printed sheet downward (hereinafter referred to as “face down”) in order to facilitate page alignment. Called “discharge”).
[0003]
In addition, when a sheet with binding holes is used, the single-sided printed sheet is discharged face-down and the final printed side of the double-sided printed sheet is used in order to discharge the single-sided printing and double-sided printing with the binding hole direction aligned. There is a demand for a function capable of selectively separating the discharge upward (hereinafter referred to as “face-up discharge”). Therefore, in recent image forming apparatuses, a function of selectively switching between face-up discharge and face-down discharge as well as a function of inverting the front and back surfaces of the printed sheet in the final-stage discharge unit are indispensable.
[0004]
An example of the configuration of the paper discharge unit of a conventional image forming apparatus that satisfies the above functions will be described with reference to FIG. In FIG. 3, a fixing device 9 provided in the image forming apparatus 1 includes a heat roller 9a and a pressure roller 9b that are pressed against each other, and fixes a toner image transferred to a sheet. A gate 10 has a function of switching the direction of the conveyed sheet. The sheet conveyance path 12 that connects the fixing device 9 and the discharge port 11 of the image forming apparatus 1 is referred to as a “sheet feeding path”. Reference numeral 13 a denotes a “pull-in path”, which is branched from the sheet feeding path 12 on the downstream side in the sheet conveying direction with respect to the fixing device 9, and is sent out from the fixing device 9 by switching control of the gate 10. Select the sheet. Further, 13b is referred to as a “reversed paper discharge path”, and is branched from the middle of the drawing path 13a, and its end is joined to the paper feed path 12 upstream of the sheet discharge port 11 of the image forming apparatus 1. Yes. In FIG. 3, 15 is a pair of transport rollers provided at the front stage of the gate 10, 16 is a pair of discharge rollers provided at the rear stage of the gate 10, and 17 is a transport provided on the drawing path 13a and the reverse discharge path 13b. A driving roller 18 of the roller pair is a reversing roller pair provided on the drawing path 13a and capable of switching between normal rotation and reverse rotation.
[0005]
With the above configuration, when the printed sheet is discharged face-up, the sheet sent from the fixing device 9 is discharged from the discharge port 11 as it is along the paper feeding path 12 and sent to the sheet handling device 2 side. When the printed sheet is discharged face down, the sheet sent from the fixing device 9 is drawn into the drawing path 13a by the guidance of the gate 10, and at the timing when the trailing edge of the sheet reaches a predetermined position in the drawing path 13a. The reversing roller pair 18 is rotated in the direction opposite to that at the time of drawing, the sheet is conveyed from the reversing path 13b to the discharge roller pair 16 side, discharged from the discharge port 11, and sent to the sheet handling device 2 side.
[0006]
When the image forming apparatus 1 is printed by thermal fixing using a laser beam printer or the like, large out-of-plane deformation (hereinafter referred to as “heat curl”) occurs in the sheet. In many cases, the direction of the heat curl is curved toward the heat roll 9 a in the fixing device 9, and is curved in the direction of the conveyance path in the conveyance path downstream of the fixing device 9. In the fixing device 9, the size of the heat curl increases as the diameter of the heat roll decreases and the applied pressure increases. In the curved portion of the conveyance path, the larger the curvature of the conveyance path is, and the higher the sheet temperature is, the more easily affected by the curvature of the conveyance path.
[0007]
In the configuration of FIG. 3, the curl state of the sheet discharged to the sheet handling device 2 is discharged by upward heat curl generated in the fixing device 9 in the case of face-up discharge. Further, in the case of face-down discharge, the downward heat curl generated by the curvature of the lead-in path 13a is reversed and discharged as an upward heat curl. In general, the sheet handling apparatus 2 often employs a stacking method in which the sheets are sequentially stacked on the preceding sheet. Therefore, when the stacked sheets have an upward heat curl, the front of the succeeding sheet at the time of stacking is used. A stacking failure is likely to occur at the trailing edge of the stacked sheets, which causes a decrease in the reliability of the apparatus. As a means for removing heat curl, a configuration in which a curl correction device (hereinafter referred to as “decurler”) 19 is provided as shown in FIG.
[0008]
[Problems to be solved by the invention]
In the above prior art, upward heat curl is likely to occur in the sheet discharged to the sheet handling apparatus, which is a factor of reducing the reliability of the apparatus. Further, when the decurler is provided to remove the heat curl, the configuration of the image forming apparatus is complicated, and there are disadvantages that the apparatus becomes large and the manufacturing cost increases.
[0009]
The object of the present invention is to eliminate the disadvantages of the prior art as described above, and by devising the shape of the conveyance path of the paper discharge unit of the image forming apparatus, without providing a decurler at the subsequent stage of the image forming apparatus, An object of the present invention is to provide an image forming apparatus having a sheet reversing sheet discharge device that can discharge without occurrence of upward heat curl in both cases of face-up discharge and face-down discharge and is composed of a small number of parts.
[0010]
[Means for Solving the Problems]
The above object is to discharge a sheet fed from the fixing device (9) having a heat roller (9a) and a pressure roller (9b) provided in pressure contact with the heat roller. A discharge port (11), a paper feed path (12) for connecting the fixing device and the discharge port, and a branch from the paper feed path are provided, and the sheet can be guided upward with respect to the paper feed path. The sheet feeding path (13a) is formed in a switchback manner with respect to the drawing path, and the sheet is reversed so that the leading edge of the sheet drawn into the drawing path becomes the rear end. In the image forming apparatus including the reverse discharge path (13b) to be merged with the path, the paper feed path includes a branch point between the paper feed path and the pull-in path, the reverse discharge path, and the paper feed path. The paper feed path that exists between the merging points and the radius of curvature is 30 mm or less It is bent upward is achieved by forming.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 2, a sheet handling apparatus 2 is connected to the subsequent stage of the image forming apparatus 1. In this embodiment, the image forming apparatus 1 is exemplified by a laser printer that uses a photoreceptor and records and forms a toner image on a sheet material by a known electrophotographic process. Further, as the sheet handling device 2, a stacker that stacks and holds sheets discharged from the printer 1 on a tray is exemplified.
[0012]
In the printer 1, reference numerals 3, 4, and 5 denote sheet storage units that store sheets as sheet materials. Reference numeral 6 denotes a photosensitive drum, which starts rotating in the direction of an arrow based on a signal from a controller (not shown). When the photosensitive drum 6 starts rotating, the surface of the photosensitive drum 6 is uniformly charged by a corona charger (not shown). An electrostatic latent image is formed on the charged photosensitive drum 6 by a laser beam emitted from an exposure device (not shown). When the electrostatic latent image reaches the position of the developing device 7, the electrostatic latent image is developed with toner and visualized as a toner image on the photosensitive drum 6. Thus, the toner image formed by the well-known electrophotographic process is transferred by the transfer device 8 to the sheet sent out from the sheet accommodating portions 3, 4, 5 or the return path 14 described later. Reference numeral 9 denotes a fixing device. In this embodiment, the fixing device is composed of a heat roller 9a and a pressure roller 9b that are brought into pressure contact with each other, and fixes the toner image transferred to the paper. Reference numerals 10a and 10b denote gates which have a function of switching the direction of the conveyed paper. Reference numeral 13 denotes an inverter that reverses the sheet to be discharged by switching back, and has a function of changing the sheet discharge direction.
[0013]
In the following description, regarding the sheet conveyance path configured in the printer 1, for convenience, the sheet storage units 3, 4, 5 -image forming units 6, 7, 8-communicate with the sheet discharge port 11 of the printer 1. The paper transport path 12 is referred to as a “paper feed path”. Further, 13a is referred to as a “pull-in path”, and is branched from the sheet feeding path 12 on the downstream side in the sheet conveyance direction by the gate 10b with respect to the image forming units 6, 7, and 8, and the gate 10b switching control is provided. Thus, the sheet sent out from the fixing device 9 is selectively drawn. Reference numeral 13b denotes a “reversed paper discharge path”, which is branched from the middle of the drawing path 13a, and its end is joined to the paper feed path 12 upstream of the sheet discharge port 11 of the printer 1. 14 is referred to as a “return path”, and branches from the paper feeding path 12 upstream of the drawing path 13a by the gate 10a with respect to the drawing path 13a, and ends at the upstream of the image forming means 6, 7, and 8 in the paper conveying direction. It is provided so as to merge with the paper feeding path 12 on the side.
[0014]
In FIG. 2, reference numeral 15 denotes a pair of conveying rollers provided in front of the gates 10a and 10b, and 17 is configured to be able to switch between forward and reverse rotations, so that the feeding immediately before the drawing path 13a, the reverse discharge path 13b, and the sheet discharge port 11 is configured. The transport drive roller 17a of the discharge roller pair provided on the paper path 12 is configured to be brought into pressure contact with the drive roller 17 so as to be able to be rotated according to the rotation of the transport drive roller 17, and to be an introduction roller pair of the drawing path 13a. The pinch roller 17b is configured to be brought into pressure contact with the conveyance drive roller 17 so that it can be rotated according to the rotation of the drive roller 17. The pinch roller 17c constituting the feed roller pair of the reverse discharge path 13b is conveyed. It is configured so that it can be brought into pressure contact with the driving roller 17 and rotated according to the rotation of the conveying driving roller 17, and is provided on the paper feeding path 12 immediately before the sheet discharge port 11. Pinch rollers constituting the obtained discharge roller pair, 18 is a positive reverse switchable reversing roller pair provided on the retraction path 13a.
[0015]
With the above configuration, when the printed sheet is discharged face up, the sheet sent from the fixing device 9 is discharged from the discharge port 11 as it is through the discharge roller pair 17 and 17 c along the sheet feeding path 12, and is stacked. Send to 2 side. Further, when the printed sheet is discharged face down, the conveyance drive roller 17 is rotated in the direction opposite to that during face up discharge, and the sheet fed from the fixing device 9 is guided by the gate 10b through the introduction roller pair 17, The sheet is switched by rotating the reversing roller pair 18 in the direction opposite to that at the time of pulling in at the timing when the trailing end of the sheet reaches a predetermined position in the pulling path 13a through the pulling path 13a of the reversing machine 13 through 17a. The sheet is reversed, and the sheet is discharged from the reverse discharge path 13b through the discharge roller pair 17 and 17b and discharged from the discharge port 11, and is sent to the stacker 2 side.
[0016]
Further, when printing on both sides of the sheet, the sheet sent out from the fixing device 9 is drawn into the return path 14 by the guidance of the gate 10a, and the one-side printed sheet is imaged again by switching back the drawn paper. The sheet is fed to the forming means 6, 7, and 8, whereby double-sided printing is executed.
[0017]
In FIG. 2, 3a, 4a, and 5a are pick rollers that feed out the paper stored in the sheet storage portions 3, 4, and 5, and 3b, 4b, and 5b are generally known to be composed of a feed roller and a retard roller. A pair of paper feed rollers. The pair of paper feed rollers 3b, 4b, and 5b supplies the paper one by one to the paper feed path 12 while preventing the paper fed out by the pick rollers 3a, 4a, and 5a from being conveyed in a state where a plurality of sheets are overlapped. It has a function.
[0018]
Reference numerals 12a, 12b, 12c, and 12d denote a pair of conveying rollers that convey the sheet in the sheet feeding path 12, and 12e conveys the sheet in synchronism with the timing at which the toner image formed on the photosensitive drum 6 is transferred to the sheet. A pair of registration rollers. Reference numerals 14 a, 14 b, 14 c, 14 d, 14 e, and 14 f are conveyance roller pairs that convey the paper in the return path 14.
[0019]
Next, the sheet conveyance state in the conveyance path downstream of the fixing device will be described with reference to FIG. In FIG. 1, in the part P of the paper feed path 12, a curved conveyance path having a curvature radius of 30 mm or less is formed on the lower side with respect to the conveyance surface so as to surround the pinch roller 17 c of the pair of paper discharge rollers. Further, the lead-in path 13a is branched from the paper feeding path 12 to the upper side with respect to the conveying surface by the gate 10b guide. Empirically, when the radius of curvature of the conveyance path downstream of the fixing device is 30 mm or less, the curvature of the conveyance path is transferred to the curl shape of the sheet, so the sheet discharged face-up passes through the P portion. The upward heat curl generated in the fixing device 9 can be corrected by being sometimes curled in a direction that curves downward with respect to the conveyance surface.
[0020]
Further, since the sheet discharged face down is drawn in by a drawing path 13a curved in the same direction as the upward heat curl generated in the fixing device 9, the heat curl generated in the fixing device 9 is curled inside the reversing device 13. The shape is maintained or promoted. As a result, the paper switchback inverted by the inverter 13 is discharged to the stacker 2 by downward heat curl.
[0021]
As described above, by configuring the paper discharge path downstream of the fixing device and the inverter 13 for switchback inversion, the following effects can be obtained. First, there is no need for a decurler mechanism as in the prior art, and no postcurler is provided, and in the case of both face-up discharge and face-down discharge, no upward heat curl is generated with respect to the post-processing apparatus. The sheet can be discharged.
[0022]
Secondly, the reverse paper discharge device can be configured with a small number of parts, and the configuration of the image forming apparatus can be saved.
[0023]
【The invention's effect】
As described above, according to the present invention, it is possible to perform discharge without generating upward heat curl in both face-up discharge and face-down discharge without providing a decurler at the subsequent stage of the image forming apparatus, and a small number. It is possible to provide an image forming apparatus having a sheet reversing and discharging apparatus composed of these parts.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating a sheet conveyance state downstream of a fixing device in an image forming apparatus of the present invention.
FIG. 2 is an overall configuration diagram of an image forming apparatus according to the present invention.
FIG. 3 is an explanatory diagram showing a configuration of a paper discharge unit in the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Sheet handling apparatus, 9 ... Fixing apparatus, 11 ... Discharge port, 12 ... Paper feeding path, 13 ... Inverter, 13a ... Pull-in path, 13b ... Reverse discharge path.

Claims (1)

A fixing device including a heat roller and a pressure roller provided in pressure contact with the heat roller;
A discharge port for discharging the sheet fed from the fixing device;
A paper feed path that connects the fixing device and the discharge port;
A pull-in path provided so as to be branched from the paper feed path, and configured to be capable of guiding the sheet upward with respect to the paper feed path;
A reverse discharge path that is branched in a switchback manner with respect to the pull-in path, reverses the sheet so that the leading edge of the sheet pulled into the pull-in path becomes a rear end, and merges with the paper feed path. In the provided image forming apparatus,
The paper feeding path is located above the paper feeding path existing between the branch point of the paper feeding path and the drawing path and the junction of the reverse paper discharge path and the paper feeding path with a radius of curvature of 30 mm or less. An image forming apparatus formed by curving to the side .

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