JP3315521B2 - 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 transfer paper on which an image is formed on one side in an image forming section having an image carrier, and selectively guides the transfer paper to a duplex unit. The present invention relates to an image forming apparatus which conveys the transfer paper to a switchback path, switches back the transfer paper, resends the transfer paper to the image forming unit, and forms an image on the back surface.

[0002]

2. Description of the Related Art An image forming apparatus having a switchback type double-sided mechanism as described above is known, and is attached to a printer, a copying machine or the like. In this type of image forming apparatus, when an image is formed and fixed on one side for double-sided printing, the transfer paper is dried. Then, the transfer paper may be wavy, or the transfer paper having an image formed on one side for double-sided printing may be reversed immediately after fixing, so that the curl in the reverse direction may be added.

The degree of the above-described undulation or curl in the reversal direction of the transfer paper varies depending on the type of transfer paper used, the environment, and the like. May occur.

[0004] When the transfer paper is fed to the switchback roller, the waving generated on the leading end side is apt to escape in the direction opposite to the curvature direction of the switchback roller when the transfer paper is reversed by the switchback roller. The occurrence rate of jams in the switchback roller was increased. Also,
As shown in FIG. 7, the wavy generated at the rear end portion when the transfer paper is re-sent to the image forming unit curls in the direction opposite to the curvature of the latent image carrier 100 during image formation on the back surface of the transfer paper 101. In such a case, transfer omission or transfer blurring occurred.

Further, as shown in FIG. 8, the transfer paper 101 is wrapped around the latent image carrier 100 as shown by a solid line, or the transfer paper 101 is drawn as shown by a dashed line.
Sometimes jammed just sitting down. Various countermeasures against the curl in the reversal direction have been proposed. For example, an image forming apparatus described in Japanese Patent Application Laid-Open No. 3-73770 has a curved path portion in the reverse direction of the curl.

[0006]

However, in the conventional image forming apparatus, the curl in the reverse direction can be corrected, but the double-sided unit must be provided with a curved path portion. Could not be resolved.

The present invention has been made in consideration of the above circumstances, and has as its object to provide an image forming apparatus capable of suppressing the occurrence of a problem caused by curling of transfer paper and waving of transfer paper of a device having a double-sided function. .

[0008]

According to the present invention, there is provided an image forming section having an image bearing member, wherein a transfer sheet having an image formed on one side thereof is selectively guided to a duplex unit. Wherein the transfer sheet is conveyed to a switchback path via a switchback roller, and the transfer sheet is switched back to be re-sent to the image forming section to form an image on the back surface thereof. A curving means is provided in the back path at a position where a rear end portion of the transfer sheet conveyed to the switchback path comes into contact with a rear end portion when the transfer sheet is retransmitted from the duplex unit to the image forming unit. When the sheet is re-transmitted to the image forming section, the transfer sheet is handled by the curving means to impart curl behavior in the same direction as the curvature direction of the image carrier.

According to another aspect of the present invention, there is provided an image forming section having an image bearing member, wherein a transfer sheet having an image formed on one side is selectively guided to a duplex unit. Is transported to a switchback path via a switchback roller, and the transfer paper is switched back, re-transmitted to the image forming unit, and an image is formed on the back surface thereof. And a detecting unit configured to detect that a rear end portion of the transfer sheet reaches the image forming unit when the transfer sheet is retransmitted to the image forming unit. At the time of retransmission, when the detecting means detects that the rear end portion of the transfer paper has reached the curving means, the curving means treats the transfer paper and is in the same direction as the curvature direction of the image carrier. Car It is characterized in that to grant the habit.

According to the present invention, in order to achieve the above object, the bending means abuts on the main roller and the main roller,
It is effective to have a sub roller that holds the transfer paper wound around the main roller.

Further, the present invention is effective when the main roller is a roller formed to have the same diameter over the width of the maximum size of the transfer paper on which an image is formed.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory front view showing a laser printer as an image forming apparatus according to the present invention.

In FIG. 1, the laser printer comprises a printer main body 10, a double-sided unit 30 and a paper feed cassette 50 which are sequentially arranged below the printer main body 10. The duplex unit 30 and the paper cassette 50 are interchangeable. When the duplex unit 30 is not provided, the duplex unit 30 includes the printer body 10 and the paper cassette 50.
This laser printer is provided with a sheet feeding device 1 of a sheet feeding cassette 50.
The transfer paper 2 fed in the direction of arrow A from FIG. 1 is conveyed to a latent image carrier composed of a belt-shaped photoconductor 4 at a timing by a pair of registration rollers 3. Photoreceptor belt 4
Is driven clockwise by driving means (not shown),
At that time, the surface is charged by the charging charger 5. Then, the laser beam L from the laser unit 6 is irradiated,
An electrostatic latent image is formed on the photoconductor. This latent image is visualized by toner when passing through the developing device 7, and a toner image is formed. This toner image is transferred to the transfer paper 2 conveyed to the photoreceptor belt 4 under the action of the transfer charger 8, and the transfer paper 2 after the transfer is separated by the curvature of the photoreceptor 4. Thereafter, the transfer paper 2 is conveyed by the first paper discharge roller 11 after the toner image is fixed by the fixing device 9.

The printer main body 10 is provided with a branch claw 12 following the first paper discharge roller 11. In the case of normal single-sided printing, the transfer paper 2 is transferred to the second paper in accordance with the direction switching of the branch claw 12. The paper is conveyed by the paper discharge roller 13. Then, the transfer paper 2 is discharged to the paper discharge tray 19 in the direction of arrow C with the image side up according to the direction switching of the switching claw 14, or the printer main body is moved in the B direction via the third paper discharge roller 15. The paper is discharged onto the paper discharge tray 16 above the printer 10 with the image side down.

On the other hand, the photoreceptor belt 4 after the transfer is cleaned of residual toner by a cleaning device 17 and residual charge is removed by a discharge lamp 18 to prepare for the next print.

Next, when the double-sided printing is selected, the transfer paper 2 having been fixed passes through the reversing conveyance path constituted by the reversing guides 21 and 22 according to the switching of the direction of the branching claws 12 to the two-sided unit 30 described above. Sent. In the double-sided unit 30, a switchback roller 34 is disposed on the opposite side of the reverse transport path, that is, the reverse transport path is disposed on the left side and the switchback roller 34 is disposed on the right side in FIG. Therefore, the transfer paper 2 sent to the duplex unit 30 passes through the transport path 31 and is transported to the switchback roller 34 by the transport rollers 32 and 33 provided in the transport path. Then, the transfer paper 2 is reversed in image side by the switchback roller 34, and is again
And is printed on the back surface following the same path as above, and is discharged in the direction of arrow C or arrow B.

The configuration of the above-described laser printer is the same as the conventional one. In such a printer, the transfer paper fixed by the fixing device 9 may be dried and wavy. Further, it has been described above that the transfer paper 2 passes through the reversing conveyance path immediately after the fixing, thereby giving a curl habit and causing various troubles.

Therefore, in the present embodiment, it is intended to solve the problem due to the waving on the rear end side of the transfer sheet when the sheet is fed again from the duplex unit 30 to the image forming section.

In FIG. 2, the switchback path 40 is provided with a curve guide 41 as a curve means at a position where a rear end portion of the transfer paper 2 conveyed to the path comes into contact with the photosensitive member 4 when the sheet is resent. ing. The curved guide 41 has a pair of rollers 42, 4 at a position where the bending starts and a position where the bending is stopped.
The roller pair 42 and 43 are each configured to be driven to rotate in a direction that gives a transfer force in a direction of drawing the transfer paper 2 into the switchback path 40.

In the laser printer having the above-described configuration, when the transfer paper 2 printed on one side as described above is sent to the switchback roller 34 and enters the switchback path 40, the transfer paper 2 is sequentially held by the roller pairs 42 and 43. When the rear end of the transfer paper 2 passes through the reversing film 36 and reaches the switchback path 40, the switchback roller 3
4 is stopped, and then the switchback roller 34
, The driving of the roller pairs 42 and 43 is stopped by, for example, a clutch or the like. And transfer paper 2
Is transported toward the image forming section while being sandwiched between the switchback roller 34 and the roller 35. At this time, the transfer sheet 2 is transported while being held down by the stopped roller pairs 42 and 43 when the paper 2 is re-fed. Therefore, it is handled by the curved guide 41 and the curl of the curved surface of the guide is forcibly applied. As a result, as shown in FIG. 3, the rear end of the transfer paper 2 is curled in the same direction as the curvature of the photoconductor 4, and the transfer paper 2
And the photoreceptor 4 are improved in adhesion, and transfer omission and transfer blur can be prevented.

When the size of the transfer paper 2 that can be printed by the laser printer is plural, the position where the rear end side of the transfer paper 2 is located in the switchback path 10 is not constant. In this case, the roller pair 4 in the switchback path 10
The rear end detection sensor 44 is provided on the back side of the third position. In addition, the roller pairs 42 and 43 are configured to be reversibly driven in the same manner as the switchback roller 34.

When the transfer paper 2 reaches the switchback path 40 in the same manner as described above during double-sided printing, the laser printer having the above configuration also drives the switchback roller 34 to rotate in the reverse direction.
At this time, the roller pairs 42 and 43 are simultaneously driven in reverse rotation. When the rear end of the transfer sheet 2 is detected by the sensor 44, the reverse rotation of the pair of rollers 42 and 43 is stopped by the signal, whereby the rear end side of the transfer sheet 2 is handled by the curved guide 41 in the same manner as described above. . Therefore, even if the size of the transfer paper 2 varies, the curl can be added only to the rear end side.

FIG. 4 shows a modification of the embodiment shown in FIG. 2, in which a decurling roller 45 as a rotatable main roller is provided instead of the curved guide 41. The decal roller 45 has driven rollers 46, 4 as sub-rollers at positions corresponding to the positions of the roller pairs 42, 43 in the above embodiment.
7 are provided. In this case, the driven rollers 46 and 47 are divided into a plurality of portions, but the decurling roller 45 is formed to have the same diameter over the entire width as shown in FIG. If such a decurling roller 45 is used, the transfer load can be reduced by performing two handlings of the transfer paper by the roller, and furthermore, when the transfer paper 2 is handled, the transfer paper may be broken or a roller mark may be formed. Can be prevented.

In the laser printer thus constructed, when the transfer paper 2 printed on one side is sent to the switchback roller 34 and enters the switchback path 40, the rear end of the transfer paper when re-feeding the transfer paper is connected to the decurling roller 45. Driven roller 4
6, 47. Then, the rear end of the transfer paper 2 passes through the reversing film 36 and the transfer paper 2 is moved to the switchback path 4.
0, the drive of the switchback roller 34 is stopped, and then the reverse drive of the switchback roller 34 is started.
Is stopped. When the transfer paper 2 is conveyed toward the image forming section, its trailing end is driven rollers 46 and 4.
Since the transfer paper 2 is conveyed while being pressed by the decurling roller 45 stopped by 7, the transfer paper 2 is handled by the decurling roller 45 and has a curl habit due to its curvature. Also, in this embodiment, when the rear end position of the transfer paper 2 in the switchback path 40 is not constant, a sensor can be provided to perform the same control as in the above embodiment.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, but can be variously modified. For example, as shown in FIG.
When transferring at the top of the paper, it is necessary to reverse the curl. In this case, the transfer paper 2 is fed in the reverse direction with respect to the decurling roller 45, so that the curl can be curled by the curvature of the decurling roller 45.

[0026]

According to the first aspect of the present invention, a curl in the same direction as the curvature of the photoreceptor is applied to the leading end of the transfer paper fed to the duplex unit, that is, the rear end of the transfer paper at the time of refeeding. As a result, the adhesiveness of the transfer paper to the photoconductor is improved, and transfer omission and transfer blur, which are likely to occur at the rear end of the transfer paper during duplex printing, can be prevented.

According to the second aspect of the present invention, even if the length of the transfer paper is different, a curl in the same direction as the curvature of the photosensitive member is applied to the rear end of the transfer paper at the time of re-feeding, so that transfer omission and transfer occur. Shake can be prevented.

According to the configuration of the third aspect, the transfer load can be reduced by handling the transfer paper by the roller. According to the configuration of the fourth aspect, since the rollers are not divided when the transfer paper is handled, it is possible to prevent a problem that the transfer paper is bent or a roller mark is formed at the rear end portion.

[Brief description of the drawings]

FIG. 1 is an explanatory front view showing a laser printer as an image forming apparatus according to the present invention.

FIG. 2 is an explanatory front view showing an embodiment of the image forming apparatus according to the present invention.

FIG. 3 is an explanatory diagram showing a relationship between a transfer sheet having a curl habit at a rear end and a photoconductor;

FIG. 4 is an explanatory front view showing a modified example of FIG. 2;

FIG. 5 is a perspective view showing the decurling roller of FIG. 4;

FIG. 6 is an explanatory front view showing still another modified example of FIG. 2;

FIG. 7 is an explanatory diagram showing a relationship between a transfer paper and a photoconductor according to a conventional method by waving.

FIG. 8 is an explanatory diagram showing a relationship between a conventional transfer sheet and a photoconductor by reverse curl.

[Explanation of symbols]

 2 Transfer Paper 4 Photoconductor 30 Double-sided Unit 34 Switchback Roller 40 Switchback Path 41 Curved Guide 42,43 Roller Pair 45 Decal Roller 46,47 Follower Roller

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI G03G 15/00 510 G03G 15/00 510 (72) Inventor Nobuo Inoue 1-3-6 Nakamagome 1-chome, Ota-ku, Tokyo Inside Ricoh Company Limited ( 56) References JP-A-6-51587 (JP, A) JP-A-3-73770 (JP, A) JP-A-64-48772 (JP, A) JP-A-61-282254 (JP, A) (58) ) Field surveyed (Int.Cl. ⁷ , DB name) B65H 29/58 B65H 5/02 B65H 5/06 B65H 29/70 G03G 15/00

Claims (4)

(57) [Claims] An image forming section having an image carrier selectively guides a transfer sheet having an image formed on one side thereof to a duplex unit,
In the image forming apparatus, the transfer paper is conveyed to a switchback path via a switchback roller in the double-sided unit, and the transfer paper is switched back and re-sent to the image forming unit to form an image on the back surface. A bending means is provided in the switchback path at a position where a rear end portion of the transfer sheet conveyed to the switchback path comes into contact with the rear end when retransmitted from the duplex unit to the image forming unit; An image forming apparatus, wherein when the transfer paper is re-transmitted to the image forming section, the curl means treats the transfer paper to impart curl behavior in the same direction as the curvature direction of the image carrier. 2. A transfer sheet having an image formed on one side in an image forming section having an image carrier is selectively guided to a duplex unit.
In the image forming apparatus, the transfer paper is conveyed to a switchback path via a switchback roller in the double-sided unit, and the transfer paper is switched back and re-sent to the image forming unit to form an image on the back surface. A curving means disposed in the switchback path; and a detecting means for detecting that a rear end portion of the transfer sheet reaches the curving means when the transfer paper is retransmitted to the image forming unit,
When retransferring the transfer paper to the image forming unit, and when the detecting means detects that the rear end portion of the transfer paper has reached the curving means, the curving means handles the transfer paper and An image forming apparatus that imparts curl behavior in the same direction as the curvature direction of an image carrier. 3. The curving device according to claim 1, wherein the bending means includes a main roller and a sub roller which is in contact with the main roller and holds the transfer paper wound around the main roller. An image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 3, wherein the main roller is a roller formed to have the same diameter over a width of a maximum size of a transfer sheet on which an image is formed.