JPH0573666B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, and more specifically to an image forming apparatus equipped with a sheet straightening path for correcting sheet warpage. Regarding.

(B) Prior Art Generally, when performing multiple copying or double-sided copying with an image forming apparatus, such as a copying machine, a sheet on which an image has been formed in an image forming section is fixed in a fixing device, and the copied sheet is then reused as a sheet. The image is then introduced into the image forming section via the conveyance path, and multiple copies or double-sided copies are made.

(C) Problems to be Solved by the Invention However, since the sheet passing through the fixing unit of the copying machine is heated and pressurized by the fixing device to perform fixing, upward warpage occurs at the leading edge of the sheet. This often results in a curled sheet, and
When the curled sheet is reintroduced to the image forming section via the sheet re-conveying path to perform multiple copying, the curled sheet is warped upward, causing it to touch the photoreceptor of the image forming section. It is easy to wrap around, and the separation of the sheet from the photoreceptor is significantly reduced. As a result, the sheet is not separated from the photoconductor and hits the cleaner in the image forming section, damaging the photoconductor or the rubber blade of the cleaner.
There was a risk that a jam would occur.

Therefore, it has been considered to improve the separation of the sheet on the photoreceptor by bringing separation claws into contact with the photoreceptor, but the separation claws may damage the photoreceptor, and the photoreceptor's durability is The lifespan will be reduced.
Furthermore, in order to correct the warpage of the sheet, there is a device in which a correction member is placed in the ejection roller part of the fixing device, but the correction member cannot sufficiently correct the warpage and the curled sheet is still sent to the image forming unit. was introduced.

(d) Means for solving the problem The present invention aims to solve the above-mentioned problem, and as shown in FIG. A sheet straightening path 41 having a sheet straightening member 40 is formed, and a conveying direction switching member 42 is arranged at a branch point of the straightening path 41 from the sheet re-conveying path 36, and the switching member 42 is connected to the main body of the image forming apparatus U. The sheet straightening path 41 is switched to the sheet straightening path 41 in accordance with the copy mode set, and the sheet straightening member 40 corrects the warpage of the sheet.

(E) Effect Based on the above-mentioned configuration, the conveyance direction switching member 42
However, the sheet correction path 4 corresponds to the predetermined copy mode.
The sheet switched to the 1 side and conveyed through the sheet re-conveyance path 36 is guided by the conveyance direction switching member 42 and conveyed to the sheet correction path 41. As a result, the sheet is corrected for its warpage by the sheet correction member 40, and then introduced into the image forming section again.

(f) Examples Examples of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the copying machine U has a document table 7,
Light source 9, lens system 10, two cassettes 11,1
2, and a cylindrical photoreceptor 13 is disposed within the main body of the copying machine. Furthermore, the photoreceptor 13
Near the periphery, there are two developing devices 15 and 16 each containing toner of a different color, a cleaner 17 and a primary charger 19, and a transfer charger 21 and a separation charger 22 are located at the tip of the conveyance device 20. It is arranged. In addition, paper feed rollers 23 and 25 are arranged in the cassettes 11 and 12, respectively, and feed rollers 23 and 25, respectively.
6 and 27, and is guided to a pair of registration rollers 29. Further, a fixing device 30 is disposed at the rear end portion of the conveyance device 20, and a first flapper 31 and a second flapper 32 are disposed downstream of the fixing device 30, and a roller pair 33 is disposed downstream of the fixing device 30. A sheet trailing edge detection sensor 35 for detecting the trailing edge of the sheet discharged from the roller pair 33 is installed near the discharge roller pair 33.

Further, a sheet re-conveying path 36 is formed by being branched and selected by the first flapper 31, and a sheet re-conveying path 36 is provided with a pair of conveying rollers 37, 39 and a pair of lateral registration rollers 1. A direct portion 36' of the sheet re-conveying path 36 and a sheet straightening path 41 are formed by branching into two directions from the downstream side of the pair of registration rollers 1, and communicate with the registration rollers 29, respectively.

As shown in FIGS. 2 and 3, a third flapper 42 is disposed at a two-way branch point on the downstream side of the pair of lateral registration rollers 1 so as to be switchable in two directions. The third flapper 42 is connected to the arm 43a of the solenoid 43, and the end of the arm 43a is urged by a spring 45 in the direction of the arrow.
It is switched and held on the 6' side (the solid line portion in FIG. 3). Further, the sheet straightening path 41 is formed to have a larger curvature than the direct sheet reconveying path 36', and a pair of sheet straightening rollers 40 is disposed in the straightening path 41. The pair of correction rollers 40 includes an upper roller 40a made of an inelastic material such as resin or metal, and a lower roller 40a made of an elastic material such as silicone sponge rubber or urethane.
An upper roller shaft 40a' fixing the upper roller 40a is rotatably supported by the side frame 38, and the upper roller shaft 40a' is driven by a drive means (not shown). Further, a lower roller shaft 40b' fixing the lower roller 40b is rotatably supported by the side frame 38 and slidably in the direction of the upper roller 40a, and the lower roller 40b is wound around the lower roller shaft 40a'. hung, and its both ends are attached to the side frame 38
The upper roller 40 is
The upper roller 40a is pressed and urged by the upper roller 40a.

Since the present embodiment has the above-described configuration, when the light source 9 moves, the document M placed on the document table 7 is irradiated by the light source 9, and the reflected light passes through the lens system 10 and is pre-charged by the charger 19. An image is formed on the uniformly charged surface of the photoreceptor 13 to form an electrostatic latent image, and as the photoreceptor 3 rotates in the direction of the arrow, the electrostatic latent image is transferred to the toner at the developing device 16 position. form an image. On the other hand, the sheets S loaded in the cassette 11 or 12 are sent to the paper feed roller 23 or 25, aligned with the toner image on the surface of the photoreceptor by the registration roller 29, and further transferred to the transfer charger 21. The toner image is transferred to the sheet surface. Further, the sheet S carrying the toner image is separated from the photoreceptor 13 by a separation charger 22, sent to a fixing device 30 by a conveyance device 20, and fixed there. At this time, the sheet S is heated and pressurized by the fixing device 30, and becomes a curled sheet S' having an upward warp at the leading edge of the sheet.

When the double-sided copy mode is selected, the curl sheet is fixed by the fixing device 30.
S' is guided by the first flapper 31 and conveyed toward the outside of the main body of the copying machine U by the forward rotation of the discharge roller pair 33. At this time, the second flapper 32 is blocking the sheet conveyance path, but since the flapper 32 is made of a light member and is supported rotatably in the direction of arrow F, the curl sheet
As S′ passes, it is pushed up by the sheet tip,
It is in a retracted state with respect to the curl sheet S', and does not interfere with the passage of the curl sheet S'. Furthermore,
The curl sheet is curled by the forward rotation of the discharge roller pair 33.
When the sheet S' is conveyed and the trailing edge of the sheet S' is detected by the sheet trailing edge detection sensor 35, the discharge roller pair 33 is rotated in the opposite direction, and the sheet S' is transferred to the second flapper 35 and the first flapper. 31 and then guided to a sheet re-conveying path 36. Furthermore, the sheet
S' is conveyed forward by the stopped horizontal registration roller pair 1 by the rotation of the conveyance roller pair 37, 39, and after the leading edge of the sheet S hits the registration roller pair 1, the conveyance roller pair 37, 39 is stopped. Then, the curl sheet S' is stopped in a state where it forms a loop in front of the pair of lateral registration rollers 1. Then, when the copying signal is sent from the copying machine to the other side,
The pair of horizontal registration rollers 1 is rotated, and further, with the pair of horizontal registration rollers biting the curled sheet S', the pair of horizontal registration rollers moves in a direction perpendicular to the sheet conveyance direction until the side edge of the sheet is detected by an optical sensor (not shown). Then, the lateral position of the curled sheet S' with respect to the conveying direction is adjusted. Furthermore, the curled sheet S' is guided to the third flapper 42 (solid line in FIG. 3) which has been switched to the sheet re-conveying path 36 side, and is guided to the sheet re-conveying path 36 side.
The pair of registration rollers 29 are connected to each other through a direct connection 36'
transported to. Further, the sheet S' is conveyed by a pair of registration rollers 29, and a toner image is transferred to the back surface (the non-copied surface) of the sheet by the photoreceptor 13, transfer charger 21, etc. in the same manner as described above. At this time, since the back surface of the curled sheet S' having an upward curvature comes into contact with the photoreceptor 13, the separation of the sheet S' from the photoreceptor 13 is good. After the sheet S' is fixed by the fixing device 30, the sheet copied on both sides is discharged to the outside of the copying machine main body by a pair of discharge rollers 33.

Also, if multiple copy mode is selected,
The first flapper 31 is switched to the sheet re-conveying path 36 side, the solenoid 43 is energized, the third flapper 42 is switched to the sheet straightening path 41 side (dotted line in Figure 3), and the fixing unit 30 fixes the sheet. The copied curled sheet S' is guided by the first flapper 31 and led to the sheet re-conveying path 36. Then, as in the case of double-sided copying described above, the lateral position of the sheet S' is adjusted by the lateral registration roller pair 1, and the third flapper 42 (see the dotted line in FIG. ), the curled sheet S' is conveyed through a sheet straightening path 41 with a large curvature, and the curled sheet S' is guided by a pair of sheet straightening rollers 4.
0, the warp is corrected, and the corrected sheet S is transferred to the registration roller pair 29.
transported to. Furthermore, the sheet S is conveyed by a pair of registration rollers 29, and a second image is superimposed and copied on the surface of the sheet S that has been copied once.
At this time, since the sheet S whose warp has been corrected comes into contact with the photoreceptor 13, the sheet S can be easily separated from the photoreceptor 13. Furthermore, after the multiple copied sheet is fixed by the fixing device 30, it is guided by the first flapper 31 which has been switched to the ejection roller pair 33 side, and is ejected to the outside of the copying machine main body by the ejection roller pair 33. .

In this embodiment, a sheet straightening roller pair 40 consisting of an upper roller 40a and a lower roller 40b was used as the sheet straightening member, but as shown in FIG. A similar effect can be obtained by pressurizing and urging the rollers 40c and 40d.

(G) Effects of the Invention As explained above, according to the present invention, a sheet straightening path is formed which communicates with the sheet re-conveyance path and has a sheet straightening member, and furthermore, a sheet straightening path is formed at a branch point between the straightening path and the direct re-conveyance path. A conveyance direction switching member is disposed, and the switching member is switched to the sheet straightening path side in accordance with the copy mode set in the main body of the image forming apparatus, and the sheet straightening member corrects the warpage of the sheet. When it is necessary to correct the warpage of a sheet, for example, only in the case of multiple copying, a curled sheet having a warp can be conveyed to a sheet straightening path and the warp can be corrected by a sheet straightening member, and the sheet photoreceptor, etc. The separability of the image carrier from the image carrier can be maintained in a good condition, and a reliable and durable image forming apparatus can be constructed without generating a jam.

[Brief explanation of the drawing]

1 is a side view showing the image forming apparatus according to the present invention, FIG. 2 is a perspective view showing the area around the sheet correction path, FIG. 3 is a side view thereof, and FIG. 4 is the area around the sheet correction path of another embodiment. FIG. 36...Sheet re-conveyance path, 36'...Sheet re-conveyance direct path, 40...Sheet correction member (sheet correction roller pair), 41...Sheet correction path, 4
2...Conveyance direction switching member (third flapper),
U...Image forming device.

Claims (1)

[Scope of Claims] 1. In order to perform multiple image formation or double-sided image formation on the same transfer sheet, a transferred sheet that has been conveyed out through an image forming section and a fixing section is subjected to image formation again via a sheet re-conveying path. In the image forming apparatus configured to be introduced into the sheet re-conveying section, a sheet straightening path having a sheet straightening member is formed in parallel with a part of the sheet re-conveying path, and further a sheet straightening path is formed from the sheet re-conveying path of the straightening path. A conveyance direction switching member is disposed at a branch point of the image forming apparatus, and the switching member is switched to the sheet straightening path side in accordance with a copy mode set in the main body of the image forming apparatus, so that the sheet straightening member corrects the warping of the sheet. image forming device. 2. The image forming apparatus according to claim 1, wherein the copy mode is a multiple copy mode.