JPH04169477A - Conveyer for sheet - Google Patents

Abstract

PURPOSE:To surely guide the second sheet or more in a sheet bundle, loaded on an intermediate tray, to a refuge position by temporarily slowing a conveying speed of the sheet bundle or stopping it, in the case that a conveying path switching means is moved from the first position to the second position. CONSTITUTION:There are provided a loading means 85 for successively loading a sheet P by each predetermined amount displaced in a conveying direction, refuge conveying path 27 providing the first conveying means 7 for giving conveying force to the forefront sheet of this sheet bundle and taking refuge partly of a sheet bundle conveyed in a forward direction to the second conveying means conveyable holding the sheet P in forward/reverse directions to the upstream of the first conveying means 7 and a conveying path switching means 9 for guiding the sheet bundle or partly the sheet bundle, conveyed in the forward direction, switched to the first position 9B for guiding to a conveying path 90 in the next step and to the second position 9A for guiding to a refuge conveying path 21. In a control means 11, a conveying speed of a sheet bundle P0 is controlled so as to be temporarily slowed or stopped in the case that the conveying path switching means 9 is moved from the first position 9B to the second position 9A.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a sheet conveying device in an image forming apparatus capable of forming images on both sides or multiple sides of a sheet.

(B) Conventional technology-M, in a double-sided image forming apparatus that performs double-sided copying,
Equipped with an intermediate tray that stores sheets on which images have been formed on the first side.After forming images on the first side of multiple sheets, the stack of sheets stacked on the intermediate tray is separated one by one. Then, the image is sent to the image forming section again, and a predetermined image is formed again.

An example of a conventional double-sided image forming apparatus of this type will be explained with reference to FIG.

In the figure, a photosensitive tram 3 that rotates in the direction of the arrow is disposed within an apparatus main body 2 of an image forming apparatus 1. As shown in FIG. An optical system consisting of a plurality of mirrors 62, 63, 65, 66, an imaging lens 67, etc. is disposed below a document table 61 provided at the top of the apparatus main body 2. Near the periphery of the photosensitive tram 3, there is a primary charger 69 for uniformly charging the photosensitive tram 3, and a developing device 70 for attaching toner to the latent image formed by the optical system to form a toner image. A transfer electrode 71 for transferring the toner image onto a sheet to be described later, a cleaner 72 for cleaning the photosensitive drum 3 after the transfer, and the like are sequentially provided.

The sheet P stored in the cassette 73 is fed out by a paper feed roller 75 and sent out by a registration roller 76 at a predetermined timing synchronized with the image on the photosensitive drum 3, and a toner image is formed on the first surface by the transfer electrode 71. transcribed. The sheet P after the toner image has been transferred is fixed by the fixing device 77.

When performing multiple copying by superimposing images again on the same side of the sheet on which an image has been formed on the first side, the sheet P is guided to the conveyance path 80a by the switching kite 79 and stored on the intermediate tray 85. Ru.

In addition, when forming an image on the side opposite to the first side,
The sheet 1-P is guided to the conveyance path 80a by the switching guide 79, and after being partially discharged by the discharge roller 81, the discharge roller 81 is reversed and the rear end of the sheet P is guided to the conveyance path 80C by the changeover guide 82. intermediate tray 85
stored above.

When stacking the sheets P on the intermediate tray 85, the sheets P stacked on the intermediate tray 85 are arranged and stacked in a stair-like manner with a slight shift each time one sheet P is stacked. . The sheet bundle P is thus stacked in a stair-like manner.

After the image forming operation for the first side is completed, the roller pair 86 is rotated to form the sheet bundle P. are conveyed all at once toward a pair of paper refeed rollers 87. By stopping the roller pair 86 at the same time that the bottom sheet Pl leaves the roller pair 86, only the bottom sheet P is conveyed by the refeeding roller pair 87, and the image forming operation for the second side is performed. It is done. According to this conventional example, it is possible to improve the performance of preventing double feeding of sheets P during refeeding.

In order to form images on both sides of the sheet P, a technique of stacking the 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. 58-178373, etc., and Japanese Patent Publication No. 6
It is published in Publication No. 3-18744, etc.

However, in the above conventional example, only the lowest sheet P1 to be re-fed is held between the re-feeding roller pair 87 and separated from the roller pair 86, and the other sheets P are held only by the roller pair 86. We have to create a situation where this is the case. For this purpose, it is necessary to set the distance between the pair of rollers 86 and the pair of refeeding rollers 87 to be slightly shorter than the length of the sheet P (see FIG. 11(a)). In this case, toner and the like attached to the sheets P are not rubbed against each other, and the sheets P are not soiled, but it is not possible to refeed sheets P of a plurality of sizes.

Therefore, when refeeding sheets P of multiple types of sizes, the distance between the roller pair 86 and the refeeding roller pair 87 should be adjusted to the optimal roller pair position shown in FIG. 11(a) for the smallest size sheet P. For a sheet P of a larger size that satisfies this requirement, it must be in a state as shown in FIG. 11(c). In other words, the lowest sheet P to be re-fed is separated from the roller pair 86, and the other sheets P are held between the roller pairs 86.

A sheet bundle P that is sufficiently large compared to the smallest size sheet P.

In the case of feeding R, a plurality of sheets P including the lowest sheet P are held between the pair of rollers 86. From this state, the lowest sheet P is fed by the rubber drive roller 87b. Another sheet bundle P. is held between the pair of rollers 86 and is not fed.

However, at this time, since the second sheet P2 from the lowest position is also held between the pair of refeeding rollers 87, the portion of the bottom surface of the second sheet P2 corresponding to the pair of refeeding rollers 87 is the lowest sheet. Since it is not pressed against the sheet P, it will rub.

If the image forming portion of the sheet P is facing upward (in the case of double-sided copying), the portion of the second sheet P held between the rollers on the back side will be soiled. Also, if the image forming side of sheet P is facing downward (in the case of multiple copying), the second sheet P
There is a risk that the part of the image 2 that is held between the rollers may disappear.

Regarding the occurrence of stains due to rubbing between the sheets 2 mentioned above,
This will be explained using a simple model shown in FIGS. 12 and 13.

FIG. 12 is a model showing the state at the time of multiplexing, and black dots in the figure indicate groups of toner particles in an image. When the sheet P1 is fed forward in the forward direction shown by the arrow 91a as described above at the timing of refeeding, the parts of the sheet in the diagonally shaded area in the figure are rubbed against each other at the nip (range a) not shown by the arrow. Ru. At this time, the toner particles on the sheet 2 are peeled off and attached to the back surface of the sheet P1 (the second image transfer surface is the front surface) (see FIG. 12(b)).

Next, Figure 13 shows a model showing the state when both sides are in use.
When the sheet P1 is fed forward at the timing of re-feeding, the sheet in the shaded area in the figure is rubbed, and the toner particles (first transferred image) on the back side of the sheet P are peeled off and attached to the surface of the sheet P2. .

Therefore, in order to prevent the sheets P 1 and P 2 from becoming dirty, an evacuation bus is provided on the sheet conveyance path and a flapper serving as a conveyance switching means is operated to remove the sheets sandwiched between the pair of refeed rollers 87. A mechanism for reducing the number of sheets to one or less has been proposed. FIG. 14 shows an example of a conveyance path diagram provided with the above-mentioned evacuation path and flapper.

In the figure, a guide member 21 serving as a retracted position is provided near the upper side of the paper refeeding roller pair 87. Between the upstream end of the guide member 21 and the intermediate tray 85, there is a sheet bundle P conveyed on the intermediate tray 85. A flapper 89 is disposed to guide the robot to the retracted position 21 at a predetermined timing.

The flapper 89 is driven by a solenoid (not shown), and can be selectively placed in either position 89A or 89B by turning the solenoid ON or OFF. In this case, when the leading edge of the lowest sheet P1 passes the flapper 89, the flapper 89 is at position 89B, and the leading edge of the lowest sheet P1 passes the flapper 89.
By guiding the refeeding roller pair 87 to the retraction value 121,
A sheet bundle P is held between the sheet bundles P. is limited to the first sheet P1 only.

(c) Problem to be solved by invention However, in the above-mentioned conventional example, the flapper 89
Depending on the timing difference in the operation of the flapper 89, the operation may not be performed normally as shown in FIG. As shown in FIG. 15(c), the tip of the flapper 89 sneaks under the lowest sheet P1,
This may result in sheet feeding failure.

This is thought to be due to variations in the response time from when a signal is input to the solenoid that operates the flapper 89 to when the flapper 89 actually operates. For example, the staggered stacking interval of sheet bundle P0 is 10 m.
If the conveyance speed is 200mm/s, the time it takes for the flapper 89 to operate accurately is at most 50mm5l,
Or it will not exist. Furthermore, in consideration of the skew of the sheet, etc., the flapper 89 is required to have even more accurate response. Furthermore, in order to improve the responsiveness of the flapper 89, attempts have been made to increase the operating speed of the flapper 89 (increasing the suction force of the solenoid in this conventional example); Since the sheet is hit hard, problems such as scratches and damage to the sheet P may occur.

Therefore, the present invention makes it possible to reliably guide the second and higher sheets of the sheet bundle stacked on the intermediate tray to the retracted position, and also to prevent damage to the sheets when switching the sheet conveyance direction. The object of the present invention is to provide a sheet conveying device that has the following features.

(:) Means for Solving the Problems The present invention has been made in view of the above-mentioned circumstances, and as shown in FIGS. 1 and 2, for example, the sheet (P) is (n) stacking means (85) that sequentially stacks the sheets with a shift of a predetermined amount; and a first conveyance means (85) that applies a conveying force to the first sheet (Pl) of the sheet bundle (Po) stacked with a shift of a predetermined amount. 7) and the first conveying means (7)
a second conveying means (6) located upstream of the sheet (P) and capable of sandwiching and conveying the sheet (P) in forward and reverse directions;
7), an evacuation conveyance path (21) located on the upstream side of the conveyance path (21) for evacuating a part of the sheet bundle (Po) conveyed in the forward direction;
A first position (90) for guiding the sheet bundle (Po) or a part thereof conveyed in the forward direction to the next conveyance path (90).
B) and a second position (9A) leading to the evacuation conveyance path (21).
) and a conveyance path switching means (9) for guiding the
When the conveyance path switching means (9) moves from the first position (9B) to the second position (9A), the sheet bundle (
It is characterized by having a control means (11) for controlling the conveyance speed of the P O) to be temporarily slowed or stopped.

(e) Effect Based on the above configuration, the sheet (P
) is loaded with the loading means (8
5) They are stacked on top one after another. When a predetermined number of sheets have been stacked, the sheet bundle (Po) on the stacking means (85) is conveyed to the re-feeding roller pair (7). During this conveyance, the leading edge of the sheet bundle (Po) is stopped near the upstream side of the pair of re-feeding rollers or is conveyed at a slow conveyance speed, thereby moving the sheet bundle (Po) to the evacuation conveyance path ( 2]) The permissible timing of the operation of the switching means (9)) leading to
By reliably guiding the sheet (P), stable conveyance performance of the sheet (P) can be achieved during double-sided and multiple copying.

Note that the above-mentioned symbols in parentheses are shown for reference to the drawings, and do not limit the structure of the present invention in any way.

(F) Example Hereinafter, an example of the present invention will be described based on the drawings. Components having the same meaning as those shown in FIGS. 10 and 14 are denoted by the same reference numerals, and the explanation thereof will be omitted.

FIG. 1 shows a control block diagram of a sheet conveying device of the present invention, and FIG. 2 shows an example of a double-sided image forming apparatus to which the present invention is applied. The operation of performing duplex or multiple copying on one sheet in the image forming apparatus shown in FIG. 2 is performed in the same manner as in the apparatuses shown in FIGS. 10 and 14, and therefore a description thereof will be omitted.

In FIG. 2, a pair of rollers 6 that can rotate in forward and reverse directions is provided on the upstream side of the intermediate tray 85, and a pair of refeed rollers 7 that refeed the sheets on the intermediate tray 85 are provided on the downstream side. Furthermore, a flapper (switching means) 9 for guiding the sheet to the guide member 21 is disposed upstream of the paper refeeding roller pair 7, respectively.

In FIG. 1, reference numeral M112 represents a motor for driving the roller pair 83, M114 represents a motor for driving the roller pair 6, and M116 represents a motor for driving the paper refeeding roller pair 7. The rollers are connected to each roller via a drive transmission means (not shown) such as a gear train. Also, the motor M112. M114. A stepping motor is used as M116, and the control circuit 11
It rotates by a predetermined angle in accordance with the number of pulses sent from the control circuit 11, and forward and reverse rotation control is also possible under the control of the control circuit 11. Reference numeral 12 designates a keyboard for specifying the number of copies, duplex mode, multiple mode, etc. to the control circuit 11, and for supporting copy start.

The rollers 6a and 7a of the roller pair 6 and paper refeed roller pair 7 are movable in the directions of arrows A and B (in the vertical direction in the figure) along long holes (not shown) drilled in the main body 2 of the apparatus. ing. Further, the roller 6a is urged downward by a leaf spring 25, and the roller 7a is urged downward by a leaf spring 26.

The drive rollers 6b and 7b are made of rubber rollers, and the driven rollers 6a and 7a are made of resin rollers whose coefficient of friction with respect to the sheet P is smaller than that of rubber. Here, the nip portion between the opening roller pair 6 and the paper refeeding roller pair 7 is connected to an intermediate tray 85 which also serves as a sheet kite.
The rubber rollers 6a and 7a are formed on a unified plane.
The upper circumferential surface of the carrier does not protrude onto the conveyance path.

A sensor 22 is provided near the downstream side of the pair of rollers 83, and a sensor 23 is provided near the upstream side of the flapper 9, and these sensors detect the presence or absence of the sheet P. A guide member (retreat conveyance path) 21 for moving the sheet P to a retracted position is disposed near the upper side of the paper refeeding roller pair 7, and an intermediate tray 85 is disposed between the upstream portion of the guide member 21 and the intermediate tray 85. Sheet bundle P on 85. A flapper (switching means) 9 is provided for guiding the air to the retracted position 21. The above-mentioned flapper 9 is rotatable around a support shaft 10, and this flapper 9 is connected to a control circuit (
It is actuated by a solenoid 27 controlled by the MPU (MPU) 11, and can be positioned at a first position 9B leading to the next stage conveyance path 90 and a second position 19A leading to the apparatus main body 21.

Next, the operation of storing a plurality of sheets P in the paper refeed path 15 will be explained using the flowchart shown in FIG.

When duplex or multiple copy mode is set using the keyboard 12 and a copy start is instructed, the sheet P is taken out from the cassette 73, an image is formed on one side by the photosensitive tram 3, and is fixed by the fixing device 77. The sheet P after fixing is sent to the roller pair 83 which starts rotating in S61.

After the leading edge of the sheet P is detected by the sensor 22 at 362 in FIG. 3, a loop is formed in which the leading edge of the sheet reaches the nip of the roller pair 6, and after the time t1 necessary for aligning the leading edges, the motor M114 is started. (S6
4, see Figure 4).

Then, the rear end of the sheet P is moved between the roller pair 83 and the conveyance path 80.
The straddling motor M114 is rotated for a required predetermined time t to transport the sheet P a predetermined distance ff, which is preset after it is pinched by the pair of rollers 6, in order to pull it out from the sheet P (S65
, see FIG. 5), and after t2 has elapsed, the motor M114 is reversed (S66).

After the motor M114 is reversed by a predetermined time t2-Δt shorter than t2, the motor M114 is stopped (S67.68).

Due to the reverse rotation of the motor M114, the sheet P is conveyed in the opposite direction by the pair of rollers 6, and the leading edge of the sheet P is located a predetermined distance @ρ on the downstream side from the nip portion of the pair of rollers 6 (see FIG. 6). The rear end of the sheet is guided on the intermediate tray 85 and enters below the roller pair 83.

Note that the rotation of the roller pair 6 is controlled by a motor M from a control circuit 11.
It can also be controlled by the number of pulses sent to 114. That is, after the leading edge of the sheet reaches the nip between the roller pair 6, the sheet P is moved a predetermined distance lIlρ. Motor M required for vertical conveyance
The rotation of the roller pair 6 can be similarly controlled by sending several pulses corresponding to the rotation angle of the roller pair 6.

Next, in S69, it is determined whether or not the set number of sheets has been stacked, and if the stacking is within the set number, the process returns to S61.

Then, when the next sheet P is conveyed and reaches the roller pair 6, the roller pair 6 moves in exactly the same way as the previous time while holding the first sheet P, and the leading edge of the second sheet P is moved between the rollers. It is located downstream of the nip portion of No. 6 by ρ. On this occasion,
The first sheet P is conveyed together with the second sheet P, and the leading edge of the first sheet P is located further downstream than the leading edge of the second sheet P by β.

As a result, the two sheets P are stacked on top of each other with a distance of Ω. By performing this operation for a predetermined number of sheets P, the sheets P can be stacked one after another with the sheets P shifted by ρ.

In these processes, when the sheet P hits the roller pair 6, the tip of the sheet P smoothly hits the roller pair 6 because the resin roller 6a with good slipperiness protrudes into the conveyance path. It is possible for it to enter the nip.

Next, Section 7 describes the operation when refeeding the stacked sheets P for the second image formation of double-sided or multiple copying.
This will be explained based on the flowchart shown in the figure.

When a signal for forming an image on the second side is issued, rotation of the motor M114 is started (71), and the stacked sheets P are sent in the direction of the pair of refeed rollers 7.

After the motor M114 starts rotating and the sensor 23 issues an ON signal, the motor M11 starts rotating after a predetermined time t3 necessary for reaching the first seat P1 or the point S in FIG.
4 stops rotating 574), and then the flapper 9 is activated 575) to take a state in which the first sheet P1 is separated, that is, a first position 9B. As shown in FIG. 8 and FIG. 15(a), the S point is located at the seat P1.
It is set at a position suitable for separating the sheet bundle P.
. By stopping the separation operation, stable separation operation can be performed regardless of variations in the operation timing of the flapper 9.

After a sufficient time t4 has elapsed for the flapper 9 to operate,
The motor M114 starts rotating again (577), and the time t until the rear end of the first sheet P□ leaves the roller pair 6,
After a period of time, the motor M114 reverses (580), and only the first sheet P1 is further conveyed to the conveyance path 90 by the pair of refeeding rollers 7, and the sheet bundle P other than the wrinkled sheet P1 is further conveyed to the conveyance path 90. is returned to the upstream side by the pair of rollers 6 to the position where the leading edge is detected by the sensor 23, in preparation for the operation for the second and subsequent sheets. Next, it is determined whether or not the operation for the set number of sheets has been completed, and if the operation has not been completed, the process returns to (S71) and the same operation is repeated again.

(G) As described in detail, according to the present invention, the sheet bundle on the intermediate tray of the paper refeeding path has a conveyance path switching means (flapper).
By a simple method of temporarily stopping at the operating position, it is possible to feed only the lowest sheet to the refeeding roller pair without being affected by the timing of the switching means operation, and it is possible to stabilize the sheet during refeeding. It is possible to realize conveyance performance.

In addition, by slowing down the conveyance speed of the sheet bundle only in the vicinity of the switching means without stopping the sheet bundle at the operating position of the switching means, the allowable range of the operation timing of the switching means relative to the sheet smoothing amount C can be widened. Then, only the lowest sheet can be transported to the pair of refeed rollers. For example, in the case where the sheet bundle conveyance speed in the conventional device is 200 mm/sec and the sheet leading edge shift amount ρ is 10+nm, the switching means (flapper) has a maximum permissible timing of only 50 mm5. The conveyance speed is increased to 50 in/see only near the switching means activation position.
By doing so, the switching means is at most 200+++
It is possible to secure an acceptable timing of n+s.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram of rollers, sensors, etc. arranged in a sheet refeeding path according to an embodiment of the sheet conveying device of the present invention, and FIG. 2 is an example of a double-sided image forming device to which the present invention is applied. FIG. 3 is a flow chart, FIGS. 4 to 6 are action diagrams, FIG. 7 is a flow chart, FIGS. 8 and 9 are action diagrams, and FIG. 10 is a flow chart. 11 is a side view of the next stage showing an example of a conventional double-sided image forming apparatus, FIG. 11 is an operational view, and FIGS. 12 and 13 are enlarged views of important parts of the sheet in the pair of refeed rollers.
FIG. 14 is a side view of the next stage of a paper refeeding passage section of a conventional sheet conveying device having a retraction position switching means, and FIG. 15 is a side view of the switching means and the leading end of a sheet bundle. 1... Sheet conveyance device, P... Sheet, Po
...sheet bundle, Pl...lowest sheet, P2
...Second sheet, 6...Second conveyance means (
roller pair), 7... first conveyance means (paper refeeding roller pair), 15... paper refeeding path, 9... switching means (flapper), 9B... first position,
9A...Second position, 11...Control circuit (
MPU), 21... Evacuation conveyance path (guide member as evacuation position), 22.23... Sensor, 27... Solenoid, M112, Ml
14. Ml 16...Pulse motor, 90...Conveyance path for paper refeeding.・Figure 7 F step Figure 11 (a) (b) (C) Figure 13

Claims (1)

[Scope of Claims] 1. A stacking means for sequentially stacking sheets by shifting them by a predetermined amount in the conveying direction; and a first means for applying a conveying force to the first sheet of the bundle of sheets stacked by shifting them by a predetermined amount. a conveying means; a second conveying means located upstream of the first conveying means and capable of sandwiching and conveying the sheet in forward and reverse directions; a second conveying means located upstream of the first conveying means and capable of conveying the sheet in the forward direction; an evacuation conveyance path for evacuating a part of the sheet bundle being conveyed; a first position for guiding the sheet bundle or a part thereof conveyed in the forward direction to the next stage conveyance path; and the evacuation conveyance path. a conveyance path switching means for switching and guiding the sheet bundle to a second position; and the conveyance path switching means temporarily changing the conveyance speed of the sheet bundle when moving from the first position to the second position. A sheet conveying device comprising: a control means for controlling the speed to slow down or stop.