JPH0428676A - Sheet transfer device - Google Patents

Abstract

PURPOSE:To prevent contamination by attachment of toner and transfer a sheet stably by providing a means to separate and retract a bundle of sheets other than the foremost sheet, and a bending means to bend the forward end parts of all the sheets carried in. CONSTITUTION:Sheets are carried in by a sheet carrying in means 25, and the forward end parts of the sheets are bent by bending means 33a, 33b in the middle. The sheets carried in are transferred normally and inversely by sheet transfer means 28a, 28b in a predetermined quantity, they are mounted with a predetermined quantity deflected to form a bundle of the sheets, and the sheet bundle is transferred by the sheet transfer means 28a, 28b to sheet carrying out means 32a, 32b, where the foremost sheet P1 is carried out. At this time, the sheets other than the foremost sheet of the sheet bundle are separated by retracting means 37, 38, and when the foremost sheet P1 gets apart from the sheet transfer means 28a, 28b, the other sheets are sent inversely by the sheet transfer means 28a, 28b.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a sheet conveying device, and more particularly to a sheet refeeding mechanism for refeeding sheets from an intermediate tray in an image forming apparatus that forms images on both sides or in multiple layers. .

(■) Conventional technology Conventionally, double-sided image forming apparatuses generally include an intermediate tray for storing sheets on which an image has been formed on the first side, and the sheets are once stacked in the intermediate tray after the image formation on the first side is completed. From there, the sheets are separated one by one, sent out, and conveyed again to the image forming section to form an image on the second side. An important point in performing such double-sided image formation is the reliability of sheet conveyance, that is, whether or not the sheet can be conveyed appropriately. In particular, remove the sheet with an image formed on the first side from the intermediate tray.
Reliability in the refeeding operation of separating and feeding sheets one by one is a problem.

FIG. 9 shows an example of a conventional double-sided image forming apparatus. In the figure, 1 is the main body of the image forming apparatus, 2 is a document table on which a document is placed, 3 is a photosensitive drum that carries an image of the document, 4, 5, 6, .
Reference numeral 7 denotes an imaging lens, and mirror 8 forms an image of the original on the photosensitive drum 3 to form an electrostatic latent image.

Further, reference numeral 9 denotes a transfer electrode that transfers the toner image formed on the photosensitive drum 3 onto the sheet P.

The sheet P stored in the cassette 10 is fed to the paper feed roller 11
is taken out by the registration roller 12 at a predetermined timing synchronized with the image on the photosensitive drum 3,
After a toner image is formed on the first surface by the transfer electrode 9, the toner image is fixed by the fixing device 13. When overlapping and forming an image again on the same side of the sheet P on which the image has been formed on the first side, the sheet P is moved to the conveying path 1 by the switching guide 14.
5 and temporarily stored in the intermediate tray 16. Also the first
When forming an image on the second side opposite to the first side, the sheet P is guided to the conveyance path 17 by the switching guide 14, and after the sheet P is discharged halfway by the discharge roller 18, the discharge roller 1
8 is reversed, the rear end of the sheet is guided to the conveying path 20 by the switching guide 19, and is stored in the intermediate tray 16.

Next, when copying is to be performed on the first side or the second side again, the sheets P on which the first side has been copied are re-fed one by one from the intermediate tray 16 and conveyed to the image forming section. Copying is performed on two sides. Here, the sheet P stacked in the intermediate tray 16 after copying has been performed on the first side passes through the fixing device 13 in order to fix the copied toner image. Silicone oil may be attached to the first surface (first side), or curls may occur at the edges due to the heat and pressure applied during fixing.

For this reason, when refeeding paper from the intermediate tray, double feeding or jamming may occur.

FIG. 10 shows an example of a double-sided image forming apparatus configured to enhance such reliability. In this conventional example, the intermediate tray 1
Each time one sheet of paper is placed in the intermediate tray, the conveyor roller pair 21 transports the east metal body of the sheet P placed on the intermediate tray little by little, and the sheets P are stacked one by one in a stairway shape that is slightly shifted. It is configured to do so.

After the image forming operation on the first side is completed, the stack of sheets stacked in a stepwise manner is conveyed all at once toward the roller pair 22, and the lowest sheet P leaves the roller pair 21 at the same time. By stopping, only the lowest sheet held by the pair of rollers 22 at this time is conveyed by the pair of rollers 22, and the operation for the second side is performed. According to this conventional example, it is possible to improve the performance of preventing double feeding when the paper is fully fed.

In order to form images on both sides, a technique of stacking sheets P with an image formed on one side in a stepwise manner and refeeding them is disclosed in Japanese Patent Application Laid-open No. 58-1 '78373 and Japanese Patent Publication No. 63-18.
It is described in Publication No. 744, etc.

However, in the conventional example described above, it is necessary to create a state in which only the lowest sheet P to be re-fed is held between the pair of rollers 22 and separated from the pair of rollers 21, and the other sheets P are held only between the pairs of rollers 21. Must be.

For this purpose, as shown in FIG. 11(a), a pair of rollers 2
It is necessary to set the distance between 1 and 22 to be slightly shorter than the length of sheet P. In this case, the toner etc. attached to the sheet P will not rub against each other,
Check that the sheet P is clean and has multiple sizes.
cannot be re-fed. Therefore, when feeding sheets P of multiple sizes, the distance between the roller pairs 21 and 22 should be adjusted to satisfy the optimum opening-ra pair position for the smallest size sheet, as shown in FIG. 11(a). When doing so, for a sheet P of a larger size, see Figure 11(b).
must be in a state like this. That is, when feeding a bundle of sheets P that is large enough for the smallest size sheet P, two or more sheets P including the lowest sheet P□ will be sandwiched between the pair of rollers 22. . In this state, the rubber drive roller 22b feeds the lowest sheet P1. The other bundles of sheets P are held between the pair of rollers 21 and are therefore not fed. Therefore, Fig. 12(a)
, As shown in (b), it moves in the direction of the arrow while rubbing against the lowest sheet P1 or the second sheet P2. Therefore, during multiple copying, as shown in FIG. 12(a), the toner from the bottom surface of the nip of the sheet P2 of the two-sheet sheet adheres to the upper surface of the sheet P1 in the shaded area in the figure, and the toner of the sheet P2 of the two-sheet sheet also adheres to Peel off from P2.

In addition, during double-sided copying, as shown in FIG. 12(b), toner adheres to the lower surface of the nip portion of the two-sheet sheet P2, and the toner on the upper surface of the lowest sheet P1 in the area shown by diagonal lines is peeled off. . There was a problem.

In order to prevent the sheet P from becoming dirty due to the above-mentioned adhesion, as shown in FIG. A separating claw C for separating the sheets P is pivotally supported on a shaft d, and a guide e for retracting the bundle of sheets P separated by the separating claw C is provided in the opening.

Then, when the bundle of sheets P is carried out to the right, immediately after the leading edge of the first sheet P1 passes the tip of the separating claw C at the position indicated by the dotted line, the separating claw C is lowered to the position indicated by the dotted line,
The second sheet P2 is separated upward by the tip of the separation claw C, and the bundle of sheets P after the second sheet P2 is guided e.
A proposal has been made to move the sheet P1 upward and carry out only the first sheet P1 without soiling it.

(C) Problems to be Solved by the Invention However, in the above method, the first sheets P1 and 2
When separating the sheet bundle after sheet P2, 2
There is a possibility that the leading edge of the second sheet P2 may get caught in the leading edge of the separating claw C, resulting in failure to separate the sheet P2 properly.

Moreover, during separation, the separation is easily influenced by the state of the leading edge of the sheet P2, the curl of the sheet P2, etc., and is not reliable, so that jams are likely to occur.

Therefore, one aspect of the present invention is to provide a means for separating and retracting a bundle of sheets other than the first sheet, and also to provide a folding means for folding the leading ends of all the sheets being carried in, thereby achieving folding that is effective for separation. It is an object of the present invention to provide a sheet conveying device that can reliably separate the first sheet from other sheets to prevent adhesion of toner and the like by providing a curvature, and can also stably convey the sheet.

(:) Means for Solving the Problems The present invention has been made in view of the above circumstances, and includes:
For example, Fig. 1, Fig. 4(b), Fig. 5, Fig. 7(b)
FIG. 8 shows a sheet carrying means (25) for carrying in a sheet (P), and a
) in forward and reverse directions by a required amount, and stack the stacked sheets by shifting them by a predetermined amount (I2) at a time, and also transport a bundle of stacked sheets (P), and the transported sheets. sheet carrying means (32a, 32b) for carrying out the first sheet (Pl) of the bundle (P), the sheet carrying means (32a, 32b) and the sheet carrying means (28a
, 28b), and when carrying out the first sheet (P□) of the bundle of sheets conveyed in the carrying out direction,
Evacuation means (37,
38), and folding means (33a, 3
3b).

The bending means (33a, 33b) includes a cradle (33a) made of an elastic body, and a pressing member (33b) made of a rigid body that can move between a position where the cradle is pressed and a position where it is evacuated from the cradle. It is characterized by being more.

Further, it is characterized in that the pedestal (33a) and the pressing member (44) are formed in the shape of a roller.

Further, the pressing member (33b) made of the rigid body is pressed against the retracting means (37, 3) with respect to the sheet conveyance path (23).
8).

(N) Function Based on the above structure, the sheet (P) is carried in by the sheet carrying means (25), and the folding means (33a
, 33b), bend the leading end of the sheet (P).

Then, the transported sheet (P) is transferred to the sheet conveying means (2).
8a, 28b) in the forward and reverse directions, and stack the sheets by shifting them by a predetermined amount (I2) to form a bundle of sheets (P).
8a, 28b), the sheet delivery means (32a.

32b), and the sheet is conveyed to the sheet carrying-out means (32a.

32b), the first sheet (Pl) is carried out. At this time, other sheets (P) other than the first sheet (Pl) of the bundle of sheets (P) are separated by the evacuation means (37, 38), and the first sheet (Pl) is separated by the sheet conveying means (28a).
, 28b), the other sheet (P) is reversely fed by the sheet conveying means (28a, 28b).

Note that the reference numerals in parentheses are for illustrative purposes only, and do not limit equivalent configurations.

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

FIG. 1 is an image forming apparatus to which the present invention is applied, and shows a copying apparatus that performs duplex and multiple copying in different colors.

In FIG. 1, the configuration is common to the conventional example shown in FIG.
The same reference numerals are given to the members that act, and the description thereof will be omitted.

Therefore, the portion from the conveyance path 23 where the conveyance paths 15 and 20 merge to the registration roller 12 will be described with reference to FIGS. 1 and 2.

A sensor 24 for detecting the leading edge of the sheet P is provided at the downstream end of the transport path 23, and a pair of transport rollers 25 is provided slightly upstream of this sensor 24. Further, the upper guide 26 of the conveyance path 23 is provided to extend diagonally downward, and a substantially horizontal lower guide 27 is provided below the upper guide 26 to face the upper guide 26, and is substantially flush with the upper surface of the lower guide 27. A driving roller 28a made of rubber having a nip portion is provided, and a driven roller 28b made of resin having a lower coefficient of friction than rubber is provided above the driving roller 28a so as to be movable up and down. It is biased downward.

Further, a vertical guide 26 is provided on the right side of the roller pair 28a, 28b.
．． An upper guide 30 and a lower guide 31 similar to those shown in FIG.
The roller 32a is pivotally supported by a fixed shaft, and the roller 32b is biased downward by a leaf spring 34 so as to be able to move up and down, and is brought into pressure contact with the roller 32a.

On the right side of the pair of rollers 32a, 32b, upper and lower guides 35 and 36 curved upward from the flat surface are arranged on the lower guide 3.
6 is provided so that the upper surface thereof is substantially flush with the nip portion of the roller pair 32a, 32b.

Further, a branch guide 37 is provided near the roller pair 32a, 32b of the upper guide 30 so as to face diagonally upward to the downstream side, and a separation claw 38 is attached to the base end of the branch guide 37 on the shaft 38a.
is supported by.

Further, a sensor 39 for detecting the sheet P is attached to the lower guide 31.

A cylindrical pedestal 33a made of low-hardness rubber is provided below the lower guide 23 near the downstream side of the sensor 24, and a pressing member 33b for pressing the pedestal 33a is attached to the upper side of the upper guide 26. This pressing member 33
b is driven by a solenoid 40 to form an upwardly concave crease at the leading end of the sheet P.

The driving roller of the roller pair 25 is the roller 28a.
10-ra 32a are stepping motors 25m and 28, respectively.
The stepping motors 25m, 28m, and 32m are connected to the motors 25m, 28m, and 32m by a gear train or the like, and their signal circuits are connected to the control unit 41, allowing forward and reverse rotation and rotation at a predetermined angle. Further, the separation claw 38 is driven by a solenoid 38s, and a signal circuit between the solenoid 38s and a solenoid 40s that drives the pressing member 33b is connected to the control section 41.

Further, the rollers 28a and 32a are made of rubber or the like with a large friction coefficient, and the rollers 28b and 32b are made of resin or the like with a small friction coefficient.

Further, 42 is a keyboard for instructing the number of copies, duplex mode, multiplex mode, copy start, etc., and 43 is a size detection device, each of which has a signal circuit connected to the control section 41.

Next, the operation of this embodiment will be explained.

First, the operation of storing a bundle of sheets (P) in the lower guide 27 (sheet refeeding path) will be explained with reference to the flowchart of FIG.

When the duplex or multiple copy mode is set using the keyboard 42 and a copy start is instructed, the sheet P, which is taken out from the cassette 10 as described above and has an image formed on one side by the photosensitive tram 3, starts rotating in step S1. It is sent to the roller 25 where it is placed. Step S in Figure 3
2, after the leading edge of the sheet P is detected by the sensor 24, the leading edge of the sheet is a predetermined distance m from the leading edge of the pressing member 33b.
After the predetermined time t1 necessary for the vehicle to pass through the
3b is pressed against the pedestal 33a from the retracted position (steps S3 and S4). The pressing member 33b operates and the predetermined time I
After 2, the leading end of the sheet P is bent by approximately the length m (see FIG. 4(b)), and the solenoid 40s is turned off (step S5.36) (see FIG. 4(c)). Step S2 (
The sensor 24 detects the leading edge of the sheet P) and then the sheet P
After the tip reaches the nip between the rollers 28a and 28b to form a loop and the predetermined darkness t3 necessary for aligning the tips has elapsed (step S7), the motor 28m is started (
Step S8), and in order to pull out the rear end of the sheet from the roller pair 25 and the lower guide 23, the sheet P is moved to the roller pair 25 and the lower guide 23.
8a.

A predetermined distance from being held by 28b! . The motor 28m is rotated for a predetermined time t4 required for conveyance (Step 39, Figure 4 (d)), and after t4 has elapsed, the motor 28m is reversed (Step 5IO). motor 2 after
Stop 8m (step Sll, 12), motor 28
The sheet P is conveyed in the opposite direction by the roller pair 28a and 28b due to the reversal of the rotation speed m, and the leading edge of the sheet P is conveyed by the roller pair 28
It is located on the downstream side by a predetermined distance lII from the nip portion of a and 28b (FIG. 4(e)). The rear end of the seat is the guide 27
It is guided above and enters the lower side of the roller pair 25.

Note that the rotation of the roller pair can also be controlled by the number of pulses sent from the control section 33 to the motor 28m.

That is, the roller pair 28a, 28b can be similarly moved by sending the number of pulses corresponding to the rotation angle of the motor 28m necessary to convey the sheet P a predetermined distance after the leading edge of the sheet reaches the nip between the roller pair 28a, 28b. 28b can be controlled.

Next, in step 813, it is determined whether or not the set number of sheets has been loaded, and if not, the process returns to step S2. Then, the next sheet P is conveyed, and the roller pair 28
When reaching a and 28b and forming a loop, the roller pair 2
8a and 28b operate exactly the same as before while holding the first sheet P, and the roller 2 at the tip of the second sheet P
8a.

12. from the nip part of 28b. Position it on the downstream side.

At this time, the first sheet P8 is conveyed together with the second sheet P2, and the leading edge of the first sheet P1 is located further downstream by I2 than the leading edge of the second sheet P2.

As a result, the two sheets P are stacked on top of each other with a distance β shifted from each other. By performing this operation on a set number of sheets P, the sheets can be stacked one after another with the sheets shifted by a distance β as shown in FIG. The motor 25m then stops (step 514).

In these processes, when the sheet P hits the roller pair 28a, 28b, since the resin roller 28b with good sliding properties protrudes into the conveyance path, the leading edge of the sheet P smoothly hits the roller pair. It is possible to enter the nip of 28a, 28b. Further, the rotation angle of the motor 28 can be controlled by the number of pulses sent.

Next, regarding the operation when refeeding the stacked sheets P for the second image formation of duplex or multiple copying,
This will be explained based on the flowchart shown in FIG.

When a start is instructed by the keyboard 42, the motor 2
The rotations of 8 m and 32 m begin, and the stacked bundle of sheets P is sent to the rollers 32a and 32b (step 821.
22) At this time, the leading edge of the lowest sheet P is the sensor 3.
9 (step 523), and a predetermined time t has elapsed since the motor 28m started (at this time,
When the leading edge of the sheet P1 passes the leading edge of the separating claw 38 in FIG. 7(a) (step 324), the separating claw 38 is activated (step 525). The state shown in Figure (a) is reached. and,
Branch guide 3 branches a bundle of sheets P other than the lowest sheet P1
7 (see FIG. 7(b)). lowest sheet P
At a predetermined time t6 when the rear end of
27), the bundle of sheets P other than the lowest sheet P1 is fed backwards, and only the lowest sheet P1 is carried out.

At this time, only the lowest sheet P□ is held between the roller pair 32a and 32b, and the other sheets, that is,
There is no rubbing from the second sheet P2. The motor 28m stops after a time t7 has elapsed since the start of the reverse rotation of the motor 28m (step 828.29). Furthermore, the motor 32m stops when the time t8 elapses until the lowest sheet PI is sent to the next conveyance roller (step 531). ).

The times t3...t are set based on the size of the sheet P, the roller arrangement distance of the device, the size of the rollers, etc., and are stored in the control section 41, which controls the sheet size detection device 43. The motor 2
It also indicates 8m and 32m. Note that the sheet size detection device may be of a type that detects the size from a cassette, or may be of a type that detects the size from the time the sheet passes through a sensor.

The copying operation ends after repeating the steps from step 821 until the set number of copies is completed (step 5).
32) Next, another embodiment will be described with reference to FIG.

In the embodiment described above, the tip of the pressing member 33b is formed to be sharp so as to bend the tip of the sheet P, or instead of the pressing member 33b, a cylindrical body made of a rigid body such as metal is used. The pressing member 44 may also be used.

In this manner, when the sheet P is pressed against the receiving table 33a by the pressing member 44, the leading end of the sheet P becomes an upwardly concave curved surface as shown in FIG.

The effect is similar to that of the previous embodiment.

(G) Effects of the Invention As explained above, according to the present invention, the leading edge of the sheet is creased by the folding means while the sheet is being carried in by the sheet carrying means, so that the stacked sheets are shifted by a predetermined amount. While transporting the sheets by the sheet transport means, only the first sheet is reliably separated, and when the rear end of the first sheet leaves the sheet transport means, the sheet transport means separates the sheets other than the first sheet. When a stack of sheets is fed backwards, the first sheet is transported without rubbing against other sheets, so the sheets that have been brought in can be carried out without getting dirty, and the first sheet can be transported without rubbing against other sheets. Since the paper is separated reliably from the sheet, it is possible to obtain stable conveyance performance without jamming or the like. Further, since the leading edge of the sheet is curved, it is effective for separating it from a photosensitive drum, for example.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional front view of a copying machine embodying the present invention, Fig. 2 is a cross-sectional front view of its sheet conveying device, Fig. 3 is a flowchart of its sheet stacking, and Fig. 4 (a) shows the vicinity of its folding means. A cross-sectional front view showing a state in which the sheet has been carried into the
Figure 4(b) is a cross-sectional front view showing the sheet being folded, Figure 4(c) is a cross-sectional front view showing the sheet being folded, and Figure 4(d) is the sheet being carried in and conveyed. 4(e) is a sectional front view when the sheet is stopped at a position shifted by a predetermined amount; FIG. 5 is a sectional front view showing a state in which the sheets have been loaded; Figure 6 is a flowchart of sheet unloading, Figure 7 (a)
7(b) is a sectional front view showing a state in which the stacked sheets are close to the evacuation means, and FIG. 7(b) is a sectional front view showing a state in which the first sheet is carried out and the other sheets are evacuated. FIG. 8 is a cross-sectional front view of another embodiment, FIG. 9 is a cross-sectional front view of a conventional example, FIG. 10 is a cross-sectional front view of another conventional example, and FIG.
Figure 1 (a) is a front view showing the roller arrangement for the smallest sheet, Figure 11 (b) is a front view showing the drawbacks of the same roller arrangement, and Figures 12 (a) and (b) are the states of sheet stains. FIG. 13 is a cross-sectional front view of a proposed example for preventing dirt. 25... Sheet carrying means (conveying roller pair) 28a, 2
8b... Sheet conveying means (driving roller, driven roller)
32a, 32b - Sheet delivery means (conveyance roller) 33a, 33b...Bending means (receptacle, pressing member) 33b, 44...Pressing member 37
．． 38... Evacuation means (branch guide, separation claw) Q
...Predetermined amount P-... Sheet Po... First sheet

Claims (1)

[Scope of Claims] 1. A sheet carrying means for carrying in sheets, which carries the carried sheets by a required amount in forward and reverse directions, shifts them by a predetermined amount and stacks them, and also conveys a bundle of stacked sheets. a sheet conveying means; a sheet conveying means for conveying out the first sheet of the bundle of sheets; and a sheet conveying means located between the sheet conveying means and the sheet conveying means, for conveying the sheet in the conveying direction. The present invention is characterized by comprising: a retracting means for separating the other sheet bundles when carrying out the foremost sheet of the bundle; and a folding means for creating a crease at the leading edge of a sheet that is being carried in by the carrying means. Sheet conveyance device. 2. The sheet conveyance according to claim 1, wherein the bending means comprises a pedestal made of an elastic body, and a pressing member made of a rigid body that is movable between a position where the pedestal is pressed and a position where it is evacuated from the pedestal. Device. 3. The sheet conveying device according to claim 2, wherein the receiving table and the pressing member are formed in the shape of a roller. 4. The sheet conveying device according to claim 2, wherein the pressing member made of a rigid body is arranged on the side of the retracting means with respect to the conveying path of the sheet.