JPH0336176A - Sheet conveying device - Google Patents

Abstract

PURPOSE:To positively load, separate, and refeed different sized sheets by sending a bundle of the sheets to a first conveying means, and controlling a second conveying means so that the sheets except a foremost sheet are conveyed in the opposite direction after the foremost sheet is released from a state where it is held between a pair of rollers. CONSTITUTION:When a key board 61 indicates starting, a motor M114 and a CL 116 operate to send loaded sheets to a pair of paper-refeed rollers 116. When the rear end of a foremost sheet passes through a pair of rollers 114, the motor 114 is reversed. The timing of reversing the motor is determined by the time elapsed after the tip of the foremost sheet has been detected. By reversing the motor M114, the sheets except a lowermost sheet are held between the pair of rollers 114, conveyed in the opposite direction, and drawn out from the nip of the pair of rollers 116. Since a roller 116A is a resinous roller with small coefficient of friction, the sheets are drawn out, while the lowermost sheet is separated by a roller 116B with large coefficient of friction, and then conveyed.

Description

DETAILED DESCRIPTION OF THE INVENTION [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 and in multiple layers.

[Conventional technology]

Conventionally, double-sided image forming apparatuses are generally equipped with an intermediate tray that stores transfer material for image formation on the first side, and after image formation on the first side is completed, one sheet of the transfer material stacked in the intermediate tray is transferred from there. One sheet was separated and sent out, and then conveyed to the image forming section again to form an image on the second side. An important point in performing such double-sided image formation is the reliability of transfer material transportation, that is, whether or not the transfer material can be transported appropriately. In particular, reliability is a problem in the paper refeeding operation in which transfer materials on which images have been formed on the first side are separated one by one from the intermediate tray and sent out.

FIG. 2 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. 9 is a primary charger for uniformly charging the photosensitive drum 3 before image formation; 10
1 is a developing device that attaches toner to the electrostatic latent image formed on the photosensitive drum 3 to form a toner image; 11 is a transfer electrode that transfers the toner image formed on the photosensitive drum 3 onto a sheet; and 12 is a device that is unnecessary after the transfer. This is a cleaner that collects used toner.

The sheets stored in the cassette 106 are fed to the paper feed roller 1.
07, the toner image is sent out by the registration roller 109 at a predetermined timing synchronized with the image on the photosensitive drum 3, and after a toner image is formed on the first surface by the transfer electrode 11, the toner image is fixed by the fixing device 108. When an image is to be superimposed again on the same side of the sheet on which the image was formed on the second processing side, the sheet is guided to the conveyance path 113a by the switching guide 110 and stored in the intermediate tray 111. In addition, when forming an image on the second side opposite to the first side, the sheet is guided to the conveyance path 113C by the switching guide 110, and after the sheet is ejected halfway by the ejection roller 117, the ejection roller 117 is reversed and the switching guide The rear end of the sheet is guided to the conveyance path 113b and stored in the intermediate tray 111.

Next, when copying the first side or the second side again, the sheets on which the first side has been copied are re-fed one by one from the intermediate tray 111 and conveyed to the image forming section 107, where the second side is copied. Copying is performed. Here, the paper stacked in the intermediate tray 111 after copying has been performed on the first side passes through the fixing device 108 in order to fix the copied toner image. There may be cases where silicone oil is attached to one 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. 3 shows an example of a double-sided image forming apparatus configured to enhance such reliability. In this conventional example, each time a sheet of paper is placed in the intermediate tray, the entire sheet east placed on the intermediate tray is conveyed little by little by a pair of conveying rollers 114, and each sheet is moved up the stairs by a little bit. It is configured to be loaded in a shape.

After the image forming operation on the first side is completed, the sheets stacked in a stepwise manner are conveyed all together in the direction of the roller pair 116, and the roller pair 114 is stopped at the same time as the lowest sheet leaves the roller pair 114. By doing this, only the lowest sheet held by the roller pair 116 is conveyed by the roller pair 116, 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 during paper refeeding.

Note that, in order to form images on both sides, a technique of stacking sheets with an image formed on one side in a stepwise manner and refeeding the sheets is disclosed in Japanese Patent Application Laid-open No. 178373/1983 and Japanese Patent Publication No. 18744/1983.
It is stated in the publication number etc.

[Problems to be Solved by the Invention] However, in the conventional example described above, only the lower sheet to be re-fed is held by the pair of rollers 116 and separated from the pair of rollers 114, and the other sheets are held only by the pair of rollers 114. You have to create a situation where you are being held. For this purpose, it is necessary to set the distance between the pair of rollers 114 and 116 to be slightly shorter than the length of the sheet.

However, if the distance between the pair of rollers 114 and 116 is fixed, sheets of multiple sizes cannot be re-fed.

Additionally, when sheets with images formed on them are overlapped or separated and re-feeded, silicone oil, toner, etc. that have adhered to the sheets will rub against each other, resulting in the sheets becoming dirty. .

The present invention solves the problems in the conventional example.

SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet conveying device that has a simple configuration and is capable of reliably stacking, separating and refeeding sheets of a plurality of sizes despite being small.

Another object of the present invention is to provide a sheet conveying device that can prevent the sheet from becoming dirty when refeeding one sheet from a stack of sheets.

[Means for solving problems]

In order to solve the above problems, the present invention has a stacking means that sequentially stacks sheets by shifting them by a predetermined amount in the conveying direction, a stack of sheets stacked by shifting them by a predetermined length, and
A first conveyance means that selectively applies a conveyance force to the first sheet, and a sheet bundle stacked by the stacking means can be conveyed while being sandwiched between the stacking means and the first conveyance means in forward and reverse directions. a second conveying means, which conveys the sheet bundle to the first conveying means, and conveys the sheets other than the first sheet in the opposite direction after the first sheet is released from the nipping state. The conveying means is controlled to apply a conveying force to the sheet sent by the first conveying means, and while the sheet is being conveyed in the opposite direction, the conveying force to the first sheet is reduced to 1.
A sheet conveyance device characterized by comprising: a control means for controlling the first conveyance means so as to release the first conveyance means from time to time.

〔Example〕

FIG. 1 shows an embodiment of an image forming apparatus according to the present invention,
1 is a sectional view showing a copying device capable of double-sided and multiple copying in different colors; FIG.

In FIG. 1, the same components as those in FIG. 3 are designated by the same reference numerals, and their explanation will be omitted. Further, the operation when double-sided copying or multiple copying is performed on two sheets is the same as the conventional example shown in FIG.

Figure 4 shows a pair of paper refeed rollers 1 from the pair of rollers 112 in Figure 1.
FIG. 2 is a control block diagram of rollers and sensors arranged in a paper refeed path L20 up to 1G.

In Fig. 4, M112 and M (14 and M116
are motors that drive the roller pairs 112, 114 and the paper refeed roller 116, respectively, and are connected to each roller by a drive transmission means (not shown) such as a gear train.

Further, CL116 is a clutch that turns on and off the driving force transmitted from the motor M116 to the paper refeed roller 116, and when the clutch CL116 is in the OFF state, the paper refeed roller 116 can freely rotate in the forward and reverse directions. Yes, and when the clutch CL116 is in the ON state, the paper refeed roller 1
14A rotates in the forward direction (direction in which the sheet is conveyed downstream). Motors M112 and M11
Reference numeral 4 uses a stepping motor, which rotates by a predetermined angle according to the number of pulses sent from the control circuit 60, and can also be controlled in forward and reverse directions by the control circuit 60.

Reference numeral 61 is a keyboard for specifying to the control circuit 60 the number of copies, such as 1 duplex mode, multiplex mode, etc., and for instructing the start of copying.

51, 52, 53, 54, 55, and 56 are guides that guide the sheet.

The rollers 114A and 116A are supported by elongated holes in a side plate (not shown) of the main body, and are movable in the directions of arrows A and B, respectively. Furthermore, roller 114A.

116A are urged downward by leaf springs 114C and 116C, respectively.

114, which is the drive side roller. B, 116B is a rubber roller, and 114A is a driven roller.

116A is a resin roller whose coefficient of friction against the sheet is smaller than that of rubber.

Here, the nip between the roller pair 114, 116 is formed on the same plane as the guide member 52.55, and the surfaces of the rubber rollers 1.14B, 116B do not protrude onto the conveyance path.

] 1-2C, 1, and 16C are sensors that detect the presence or absence of a sheet.

Next, using the flowchart shown in FIG.
The operation of storing a plurality of sheets in 01 will be explained.

When the duplex or multiple copy mode is set using the keyboard 61 and a copy start is instructed, the sheet is taken out from the cassette 106 as described above, and the sheet with an image formed on one side by the photosensitive drum 3 starts rotating in step S61. It is sent to roller 112. A predetermined time 1 required from when the leading edge of the sheet is detected by the sensor 112C in step S62 in FIG. 5 until the leading edge of the sheet reaches the nip between the roller pair 45, forms a loop, and aligns the leading edges
+, the motor M114 is started (step 564). Then, in order to pull out the rear end of the sheet from the roller pair 112 and the guide 50, the motor M114 is rotated for a predetermined time t2 necessary to convey the sheet a preset distance 10 after it is gripped by the roller pair 114 (
Step S65, FIG. 6), after t2 elapses, motor M114
is reversed (step 566), and after being reversed for a predetermined time t2-Δt, which is shorter than t, motor M1 114 is stopped (step S67.68).

Due to the reverse rotation of the motor M114, the sheet is conveyed in the opposite direction by the roller pair 114, and the leading edge of the sheet is conveyed in the opposite direction by the roller pair 114.
It is located a predetermined distance l downstream from the nip portion of No. 4 (FIG. 7). The rear end of the sheet is guided on the guide 52 and enters the lower side of the roller pair 112.

Note that the rotation of the roller pair can also be controlled by the number of pulses sent from the control circuit to the motor M114.

That is, after the leading edge of the sheet reaches the nip between the pair of rollers 45, the sheet is moved a predetermined distance l. The pair of rollers 114 can be similarly controlled by sending a number of pulses corresponding to the rotation angle of the motor M114 necessary to convey the paper by the same amount.

Next, in step S69, it is determined whether or not the set number of sheets has been loaded, and if not, step S61
Return to Then, the next sheet is conveyed, and the roller pair 11
4, the pair of rollers 114 operates exactly as before while holding the first sheet, and positions the leading edge of the second sheet by l downstream from the nip between the rollers 2 and 114. At this time, the first sheet is conveyed together with the second sheet, and the sorting tip of the first sheet is located further downstream by l from the tip of the second sheet.

As a result, the two sheets are stacked one on top of the other with an offset of l. By performing this operation on a certain number of sheets, the sheets can be stacked one after another with the sheets shifted by l as shown in FIG.

In these processes, when the sheet hits the roller pair 114, the leading edge of the sheet smoothly slides into the nip of the roller pair 114 because the resin roller 114A with good sliding properties protrudes into the conveyance path. It is possible to get into it.

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

When a start is instructed by the keyboard 61, the motor M
11.4 and CL 116 are activated, and the stacked sheets are sent to the refeeding roller pair 116 (step S71).
．． 72). When the rear end of the first sheet has passed through the roller pair 114, the motor M114 is reversed (step 575).
(Figure 10). This timing is after the leading edge of the first sheet is detected by the sensor 116C (step 573).
) (step 574).

At this time, the sheets from the lowest sheet to the first several sheets are held between the pair of rollers 116. Then, as the motor M114 reverses, the rollers 114B rotate in the reverse direction, and since the sheets other than the lowest sheet are held by the roller pair 114, they are conveyed in the opposite direction and pulled out from the nip of the roller pair 116. Since the roller 116A is made of resin with a small coefficient of friction, the sheet can be pulled out from the pair of rollers 116 without being damaged. On the other hand, since the lowest sheet is in contact with the continuously rotating rubber roller 116B having a large friction coefficient, it is separated from the other sheets and conveyed downstream. After a predetermined time t4 has elapsed since the start of reverse rotation, the motor M114 is stopped (step 376.77), and after a predetermined time t4 has elapsed since the start of rotation.
After 5 elapses, clutch CL 11.6 is turned off (step S78.79). Then, the lowest sheet is conveyed to registration rollers 109, and the next image is formed. Then, it is determined in step 5710 whether refeeding of the set number of sheets has been completed, and if it has not been completed, the process returns to step S71.

With this configuration, sheets of different sizes can be stacked on the stairs, separated and re-fed without changing the distance between the roller pairs. That is, when stacking sheets on stairs, t2 in step S65 and t2-Δt in step S67 in the flowchart of FIG. 5 may be changed depending on the length of the sheet in the conveying direction. In order to remove the rear end of the sheet from the roller pair 112, how long should the long sheet be removed?
2 should be made longer. Similarly, if t2-Δt is also set according to the length of the sheets, sheets of different sizes can be stacked while being shifted by l.

In addition, in the case of separating and refeeding, j3+t, t5 in the flowchart of FIG. 9 are changed depending on the length of the sheet. Since t3 is the time required for the rear end of the lowest sheet to come out of the roller pair 114, the longer sheet is set to be longer. Similarly, t4 is the time for pulling out the unfed sheet from the roller pair 116, and is set longer for longer sheets. The sheet size is 63 in Figure 4.
j2+j2-Δt, j3+t4. t, M
Calculated by PU. The sheet size detection device may be of a type that detects the size from a known cassette, for example, or may be of a type that detects the size from the time the sheet passes through a sensor.

Separation and refeeding of the sheets can also be done by simply stopping the roller pair 114 in step S75 in FIG.
Figure 1). In other words, sorting that is not re-fed is performed by roller pair 1.
Only the lowest sheet that is held and stopped by the rollers 14 and re-fed is conveyed by the rubber drive roller 116B. However, at this time, since the second sheet from the lowest position is also held between the pair of rollers 6 116, the portion of the second sheet corresponding to the lower roller 116A is pressed against and rubbed against the lowest sheet. If the image side of the sheet is facing upward (double-sided copying), the portion of the second sheet held by the rollers on the back side will be stained. Furthermore, if the image surface of the sheet is facing downward (multiple copying), there is a risk that the portion of the image on the second sheet held between the rollers may disappear.

12th rI! J specifically indicates the above-mentioned content. Figure 12 (A) is the second sheet 121 from the bottom.
When stopping, FIG. 12(B) shows the case when pulling out.

In the figure, the area indicated by a indicates the width of the nip portion in the roller pair 116, and 120 and 121 indicate the lowest sheet and the second sheet from the lowest position, respectively. Further, V indicates the moving direction and speed of the sheet. Here, the width a of the holding part is 1 mm, the length of the sheet is 210 mm (the horizontal length of A4 size, which is frequently used), and the distance from the holding part to the rear end of the sheet 120 is 150 mm. In FIG. 12(A),
Since a 150mm sheet passes through a part with a nip width of 1mm, the amount of rubbing at part a is 150mrr per unit width.
It becomes r.

Also, in FIG. 12(B), the sheet 120°121
Assuming they are both moving at the same speed (in opposite directions),
While one point on the sheet passes through the nip width, the relative position of the sheet shifts by twice that amount, so the amount of shift per unit width is 2 mrr? Therefore, it is only 1/1 of the case in Figure 12 (A).
It can be seen that the amount of rubbing is 75.

In this way, by performing simple control such as once refeeding the second and subsequent sheet bundles when refeeding, it is possible to prevent the occurrence of stains on the sheets.

Furthermore, in the above embodiment, a case was described in which the roller 114B is reversed at the same time that the sheet bundle reaches the state shown in FIG. Top 8.

In order to consider in more detail the occurrence of stains due to the above-mentioned rubbing between sheets, the explanation will be made using simple model diagrams shown in FIGS. 13 and 14.

FIG. 13 is a model showing the state at the time of multiplexing, and black dots indicate groups of toner particles in an image. When the sheets 120 and 121 are fed forward and backward at the same time as described above at the timing of refeeding, the portions of the sheets within the shaded area in the figure rub against each other at the nip portion. At this time, the toner particles on the sheet 121 are peeled off and adhere to the back surface of the sheet 120 (assuming the second image transfer surface is the front surface) (FIG. 13(b)).

Next, FIGS. 14(a) and 14(b) are models showing the state of double-sided operation, and when sheets 120, 1, and 21 are simultaneously fed forward and backward at the timing of refeeding, the sheets in the shaded area in the figure is rubbed, and the toner particles (first transferred image) on the back surface of the sheet 120 are peeled off and deposited on the surface of the sheet 1-121 (4=1). The toner (= 1st place, that is, the dirt on this multiplexed single-sided sheet) can be significantly reduced to 9 and improved by the aforementioned control of once reversing the second and subsequent sheets, but further improvements can be made using the control described below. This can be easily achieved.

In the double-sided and multiple stains described above, the stains in particular on both sides not only adhere to the second image transfer surface, but also extend to the edges of the sheet. Therefore, even if the degree of dirt is slight, it becomes very noticeable when a plurality of sheets are stacked. Therefore, changes are made as shown in FIG.

That is, when the sheet 121 is reversely fed to the position shown in FIG. 15(b) (the sheet 121 is reversely fed by a distance A,
20), the signal of the clutch CL116 is cut off to set the refeeding roller in a free state.

At this time, since the roller 114 continues to feed backwards, the sheet 120 starts to feed backwards together with the sheet 121. Next, when the sheets 120 and 121 have been reversely fed by 12+Δl (when the sheet 121 has come off the roller pair 116), the clutch CL116 is turned ON again, and the sheet 120 and 121
is sent out in the forward direction and conveyed until it reaches the next conveyance roller. According to this, since the sheets 120 and 121 move together from the state shown in FIG. 15(b) to the 0 state shown in FIG. 15(C), the tip of the sheet 121 is not rubbed. No dirt is generated. Furthermore, stains occur only in the shaded area of the sheet 121 in FIG.
Compared to the case where 120 was continued to be sent in the forward direction, the area of dirt was reduced by half.

A flowchart at this time is shown in FIG.

When a start is instructed by the keyboard 61, the motor M
114 and CL116 are activated, and the stacked sheets are sent to the pair of refeed rollers 116 (steps S91 and 92).
). When the trailing edge of the first sheet has passed through the roller pair 114, the motor M114 is reversed (step 595) (first
Figure 0). This timing is determined by the elapsed time since the leading edge of the first sheet was detected by the sensor 116C (step 593) (step 594). At this time, the sheets from the lowest sheet to the first few sheets are roller pair 1.
It is held by 16. Then, as the motor M114 reverses, the roller pair 114B rotates in the reverse direction, and since the sheets other than the lowest sheet are held by the roller pair 114, they are conveyed in the opposite direction.

After a predetermined time t4 has elapsed since the start of reverse rotation, that is, when sheets other than the lowest sheet have been reversely fed by 11 (step 896),
In step S97, the clutch CL 11.6 is turned off, and the roller 116b is separated from the motor M114 to be in a free state. Then, the entire sheet bundle together with the lowest sheet is sent in the opposite direction by the roller pair 114.

Next, the time t required to reverse the sheet bundle by 12+Δl
5, after the sheets other than the lowest one have passed through the roller pair 116 (step 598), the clutch CL116 is turned on again in step S99, and the lowest sheet is sent out. Next, when the remaining sheet is located upstream of the sensor 116C, the motor M114 is turned to 0FFL (steps 5910, 911), and when the leading edge of the fed sheet hits the registration roller 109, which is the downstream conveyance means, and forms a loop, the clutch is activated. The CL 116 is turned off (steps 5912, 913). Then, it is determined in step 5914 whether or not refeeding of the set number of sheets has been completed, and if it has not been completed, the process returns to step S91.

Here, when the sheet 120 is reversely fed, t4≧
It is necessary that t.

Also, in order to reduce the area of dirt, the value of t4 i,)
It goes without saying that it is desirable to make the value of t6 as small as possible and to make the value of t6 as large as possible. Furthermore, although this embodiment describes the case of double-sided printing, even in the case of multiple printing, the same effect can be achieved in that the area where dirt occurs is halved, only the location where dirt occurs is different.

Further, in the above embodiment, the lowest sheet on the intermediate tray 111 is stacked in advance and the sheets are re-fed starting from the lowest sheet, but as shown in FIG. This method can also be easily applied to the case where the uppermost sheet (the sheet on which the operation of the negative side was last performed) is loaded in advance and the sheets are re-fed from the uppermost sheet.

Note that in the above embodiment, a spring clutch may be used as the clutch CL116. Alternatively, the connection may be made by pressing the rotating body on the driving side and the rotating body on the driven side against each other or separating them.

Alternatively, by connecting the motor to the roller 116b without using a clutch and cutting off the power supply to the motor, the roller 116b
may be in a freely rotatable state. However, in this case, it is necessary to sufficiently reduce the rotational resistance of the motor and the means for transmitting the driving force from the motor to the roller.

〔Effect of the invention〕

As described above, according to the present invention, sheets of a plurality of sizes can be reliably loaded, separated and re-feeded with a simple configuration and despite being small.

Further, it is possible to prevent the sheet from getting dirty when refeeding one sheet from a stack of sheets.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an image forming apparatus embodying the present invention, FIGS. 2 and 3 are conventional image forming apparatuses, FIG. 4 is a block diagram of an embodiment of the present invention, and FIG. 5 is a block diagram of an embodiment of the present invention. FIGS. 6 to 8 are operation explanatory diagrams of the embodiment of the present invention. FIG. 9 is a flowchart of sheet refeeding of the embodiment of the present invention. FIG. 10 is the embodiment of the present invention. FIG. 11 is a flowchart of sheet refeeding, FIGS. 12 to 15 are illustrations of effects of the present invention, FIG. 16 is a flowchart of an embodiment of the present invention, and FIG. 17 is another embodiment. An explanatory diagram.

Claims (2)

[Claims] (1) A stacking means that sequentially stacks sheets by shifting them by a predetermined length in the transport direction, and a first transporting means which clamps the stack of sheets stacked by shifting them by a predetermined length and applies a transport force to the first sheet. a second conveyance means capable of sandwiching and conveying the sheet bundle loaded by the stacking means in forward and reverse directions between the stacking means and the first conveyance means; After the first sheet is released from the clamped state, the second conveying means is controlled to convey the sheets other than the first sheet in the opposite direction, and after applying a conveying force to the first sheet. A sheet conveying device comprising: a control means for controlling the first conveying means so as to temporarily release the conveying force for the first sheet while the sheet is being conveyed in the opposite direction; . (2) The first conveying means has a rotating body that applies a conveying force to the sheet, and the conveying force can be released by making the rotating body freely rotatable.
The sheet conveyance device described in Section 1.