JPH04208947A - Image forming device - Google Patents

Abstract

PURPOSE:To carry even a long sheet without sending it double by synchronizing a resist roller with a sheet carrying means. CONSTITUTION:An image is formed on a sheet P, and sent to a roller 21. After the leading edge of a sheet Pa is detected and a prescribed time lapses, motor 22m and 23m are started. After the motors 22 and 23 are rotated only for the prescribed time, they are reversely rotated only for the prescribed time, and then, stopped. The tailing edge of the sheet Pa is located in the downstream side by a prescribed distance from the nipp of a pair of rollers 22. When the next sheet Pb is carried and reaches a pair of the rollers 22, they are operated like the last time while nipping one sheet P, and the leading edge of the second sheet Pb is located in the upper stream side than the nipp of a pair of the rollers 22. At this time, the first sheet Pa is carried together with the second sheet Pb, and the leading edge of the first sheet Pa is located in the downstream side compared with the leading edge of the second sheet Pb, by the prescribed distance. Thus, the two sheets Pa and Pb are overlapped in a state where they are shifted, this action is carried out with respect to all sheets P and they are piled up, and then, a motor 21m is stopped.

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying device, and more particularly to a sheet refeeding mechanism from an intermediate tray in an image forming apparatus that forms images on both sides and multiple times. [0002]

[Prior Art] Conventionally, in a double-sided image forming apparatus 1,
Generally, an intermediate tray is provided to store sheets on which images have been formed on the first side, and after the image formation on the first side is completed, the sheets stacked in the intermediate tray are separated and sent out one by one, and returned to the image forming section. image formation 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, reliability is a problem in the refeeding operation in which sheets on which images have been formed on the first side are separated one by one from the intermediate tray and sent out. [00031 FIG. 15 shows an example of a conventional double-sided image forming apparatus 1. In the figure, 1a 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, and 4. 5. 6. Reference numeral 7 indicates a mirror for forming an electrostatic latent image by forming an image of the original on the photosensitive drum 3. Reference numeral 8 indicates an imaging lens. [0004] Further, 9 is a transfer @ pole for transferring the toner image formed on the photosensitive drum 3 onto the sheet P. [00051 The sheet P stored in the cassette 10 is taken out by the paper feed roller 11, and after forming a loop around the nip portion of the registration roller 12 to regulate the posture of the sheet P, the registration roller 12 transfers the sheet P to the photosensitive drum 3. The toner image is sent out at a predetermined timing synchronized with the image, and after the toner image is transferred to the first surface by the transfer electrode 9, the toner image is fixed by the fixing device 13. When an image is to be superimposed again on the same side of the sheet P on which an image has been formed on the first side, the sheet P is guided to the conveyance path 15 by the switching guide 14 and stored in the intermediate tray 16. In addition, 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 ejected halfway by the ejection roller 18, the ejection roller 18 is reversed and switched. The trailing edge of the sheet is guided to the conveyance path 20 by the guide 19,
It is stored in the intermediate tray 16. [0006a] Next, when copying the first side or the second side again, the sheets P whose 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. [0007] Then, each time one sheet of paper is placed in the intermediate tray 16, the entire bundle of sheets P placed on the intermediate tray 16 is conveyed little by little by the pair of conveying rollers 22, and the sheets P are conveyed one by one.
It is constructed so that each sheet is stacked in a stair-like manner with slight deviations from each other. [0008] After the image forming operation on the first side is completed, the sheets stacked in a stepped manner are conveyed all together in the direction of the roller pair 23, and as shown in FIG. By stopping the roller pair 22 for the second sheet Pb and the bundle of sheets P above it at the same time as it leaves the second sheet Pb and the bundle of sheets P above it, the second sheet Pb and the bundle of sheets P above it are fixed. At this time, only the lowest sheet Pa held in the roller pair 23 is transferred to the roller pair 2.
3 to carry out the copying operation for the second side. According to this conventional example, it is possible to significantly improve the performance of preventing double feeding during paper refeeding. [0009]

However, when the length of the sheets P is sufficiently long as shown in FIG. However, since it cannot perform any operation other than synchronized operation with respect to the photosensitive drum 3 as in the prior art, it cannot perform synchronized operation with the roller pair 22, 23, so there is a drawback that it is not possible to refeed the sheet bundle. [00101, that is, the tip of the sheet bundle is located at registration roller 1
There is a drawback that only sheets P whose length does not reach 2 can be re-fed, and the size of the sheet P to be re-fed is limited. [00111] Therefore, it is an object of the present invention to provide an image forming apparatus having a sheet refeeding device which is provided with a control means for controlling the registration rollers to be synchronized with the sheet conveying means and conveys even long sheets without double feeding. The purpose is to [0012]

[Means for Solving the Problems] The present invention has been made in view of the above-mentioned circumstances, and includes, for example, FIGS.
4. Referring to FIG. 15, an intermediate tray (on which a sheet (P) on which an image has been formed in the image forming section (3, 9) of the image forming apparatus (1) is temporarily loaded for double-sided or multiple copying) is shown. 1
6), a sheet carrying means (21) for carrying the sheet (P) into the intermediate tray (16), and shifting the carried sheet (P) by a predetermined amount by conveying the carried sheet (P) by a predetermined amount in forward and reverse directions. Sheet stacking/conveying means (22) for stacking sheets (P) in a staggered manner and conveying a stack of sheets (P) stacked in a staggered manner.
and the first sheet (P) of the bundle of sheets (P) conveyed.
a); and a refeeding device comprising a sheet ejecting means (23) that operates to eject the sheet (Pa) when the rear end of the sheet (Pa) escapes from the sheet stacking/conveying means (22); In the forming apparatus (1), when the sheet (P) is longer than a predetermined length, a registration roller (12) is provided that conveys the sheet (P) in synchronization with the operation of the image forming section (3, 9). The present invention is characterized in that a control means (32) is provided for controlling in synchronization with the sheet conveyance means (23). [0013] The present invention is also characterized in that the sheet delivery means (23) and the registration rollers (12) are not synchronized when forming an image on the first side of the sheet (P). [0014] Further, the image forming section (3, 9) includes a photoreceptor (3) and a transfer charger (9), and the intermediate tray (
16), when the leading edge of the bundle of sheets (P) has reached the image forming section (3, 9), the transfer charger (9) By reducing the current to zero, the residual toner on the photoreceptor (3) is removed from the sheet (
P) is characterized in that it is prevented from being transferred to P). Further, the image forming section (3, 9) is provided with a flapper (35) that guides the sheet (P) in a direction away from the image forming section (3, 9), so that the bundle of sheets (P) is When the leading edge of the bundle of sheets (P) has reached the image forming section (3, 9) when stacked on the tray (16), the leading edge of the bundle of sheets (P) is The flapper (3) is removed from the image forming section (3, 9).
5). [0015]

[Operation] Based on the above configuration, after an image is formed on the sheet (P) by the image forming section (3, 9) of the image forming apparatus (1), the image is transferred to the intermediate tray (16) for duplex or multiple copying. The sheet (P) is carried in by the sheet carrying-in means (21), and the carried-in sheet (P) is transported by a required amount in the forward and reverse directions by the sheet loading/unloading means (22), thereby being shifted by a predetermined amount (d) and stacked. Then, the staggered stack of sheets (P) is transported by the sheet stacking/transporting means (22), and the rear end of the first sheet (P a) of the stack of sheets (P) is conveyed by the sheet stacking/transporting means. (22), the sheet is carried out from the intermediate tray (16) by the sheet carrying means (23). At this time, when the sheet (P) is longer than a predetermined length, the control means (32) synchronizes the registration roller (12) with the sheet delivery means (23). [0016] Furthermore, when forming an image on the first side of the sheet (P), the registration roller (12) is not synchronized with the sheet delivery means (23). [0017] Also, a sheet (P
) is loaded and the leading edge of the bundle of sheets (P) has reached the image forming section (3, 9), the current of the transfer charger (9) becomes zero and the sheet (P) is stacked. ) The residual toner on the photoreceptor (3) is not transferred to the leading edge of the bundle. [0018] Also, a sheet (P
) is stacked and if the leading edge of the sheet (P) has reached the image forming unit (3, 9), the leading edge of the sheet (P) is moved from the image forming unit (3, 9) to the flapper (35). ) to remove. [0019] Note that the reference numerals in parentheses are for illustrative purposes only and do not limit the configuration in any way. [00201

[Embodiments] Examples of the present invention will be described below with reference to the drawings. [00211 In the prior art section, FIGS. 15 and 1
The present invention can be applied to the image forming apparatus 1 described with reference to 7, and members having the same configurations and functions as those already used will be designated by the same reference numerals and the description thereof will be omitted. [0022] The control block diagram shown in FIG. 1 is related to the present invention, and relates to the conveyance path 24 where the conveyance paths 15 and 20 merge and the portion thereof from the conveyance roller pair 21 to the registration roller 12. explain. [0023] A sheet sensor 25 is provided on the downstream side of the transport roller pair 21, a sheet sensor 26s is provided on the upstream side of the roller pair 23, and a sheet sensor 27s is provided on the upstream side of the registration rollers 1. [0024] Then, the upper guide of the conveyance path 24 is extended to form an upper guide 28 , the upper guide 29 is provided between the roller pair 22 and 23 , and the upper guide 29 is provided between the roller pair 23 and the registration roller 12 . An upper guide 30 and a lower guide 31 are provided. [0025] A rubber drive roller 22a having a nip portion is provided on substantially the same upper surface as the upper surface of the intermediate tray 16, and a resin driven roller 22b having a small coefficient of friction faces above the drive roller 22a. , is provided to be movable up and down, and is biased downward by a plate spring or the like (not shown), forming a pair of rollers 22. Like the roller pair 22, the roller pair 23 also includes a driving roller 23a and a driven roller 23b.
It is formed by [0026] Further, the drive rollers 22a, 23a and the drive rollers of the registration roller 12 are each driven by a stepping motor 2.
2m, 23m, and 12m via a gear train, etc., and a signal circuit from a control unit 32 is connected to the drivers of these motors 22m, 23m, and 12m, and a signal circuit from a control unit 32 is connected to the drivers of these motors 22m, 23m, and 12m. signal circuit is connected. A keyboard 33 for instructing the number of copies, duplex mode, multiplex mode, copy start, etc., and a sheet size detection device 34 are connected to the control section 32 by signal lines. In addition, the sheet size detection device 3
4 may be detected by the time during which the sheet P passes through the sheet sensor, or by sheet size detection means provided in the cassette. In addition, the drive roller 2 with a large friction coefficient
2a and 23a are almost submerged in the intermediate tray 16, and the smooth driven rollers 22b and 23b guide the ends of the sheet P, so that the sheet P can easily enter the nip between the roller pair 22 and 23. It is configured as follows. [00271] Next, the operation of stacking and storing the 'sheets P whose first side has been copied in stages on the intermediate tray 16 will be explained with reference to the flowchart shown in FIG. [0028] When the duplex or multiple copy mode is set using the keyboard 33 and a copy start is instructed, the sheet P is taken out from the cassette 10, an image is formed on one side by the photosensitive drum 3, and rotation is started in step S1. It is sent to the roller 21 where it is placed. In step S2, the predetermined time ta necessary for the leading edge of the sheet P to reach the nip portion of the roller pair 22, form a loop, and align the leading edges after the leading edge of the sheet Pa is detected by the sensor 25S (step S3). After that, the motors 22m and 23m are started (step S4). [0029] Then, in order for the trailing end of the sheet Pa to pass through the conveyance path 24, the sheet Pa passes through the roller pair 22 or 22.
The motor 22 is moved for a predetermined time tb necessary to convey the predetermined distance do after being held between the motor 22 and the motor 23.
Or rotate 22 and 23 (step S5), tb
After a period of time, reverse the motors 22m and 23m (step S
6), After reversing for a time (tb-△t), stop the motors 22m and 23m (37. S8). By reversing the motors 22m and 23m, the sheet Pa is moved to the roller pair 2.
The sheet Pa is conveyed in the opposite direction by 2.degree. 23, and the rear end of the sheet Pa is located downstream by a predetermined distance d from the nip portion of the roller pair 22 (FIG. 3). [00301] Next, in step S9, it is determined whether or not stacking of the set number of sheets has been completed, and if the stacking has not been completed, the process returns to step S2. Then, when the next sheet Pb is conveyed and reaches the roller pair 22, the roller pair 22 operates in the same way as the previous time while holding one sheet Pa, and the leading edge of the second sheet Pb is placed in the nip of the roller pair 22. d from the part
only on the upstream side. At this time, the first sheet Pa
is conveyed together with the second sheet Pb, and the leading edge of the first sheet Pa is located downstream by d from the leading edge of the second sheet Pb. As a result, the two sheets Pa and pb are stacked on top of each other with an offset of d. This operation is performed for all the sheets P, so that the sheets P are stacked as shown in FIG. 4, and then the motor 21m is stopped (step 510). [00311 Furthermore, the motors 21m, 22 from the control unit 32
It is controlled by the number of pulses sent to the 23m and 23m drivers. [00321] Next, the operation when refeeding the stacked sheets P for image formation on the second side of double-sided or multiple copying will be described based on the flowchart shown in FIG. [0033] When a start instruction is given from the keyboard 33 (step 511), the motors 22m and 23m start rotating, and the stacked bundle of sheets P is moved to the roller pair 23.
(step 512). When the trailing edge of the lowest and first sheet Pa has completely passed through the pair of conveying rollers 22, the motor 22m is reversed (step 515) (FIG. 6). This timing is determined by the elapsed time tc since the leading edge of the first sheet was detected by the sensor 26S (step 513) (step 514). At this time, the sheets P from the lowest sheet Pa to several sheets are handled by the roller pair 23.
is held between. Then, due to the reverse rotation of the motor 22m, the pair of conveying rollers 22 is reversely rotated, and the sheets P other than the lowest sheet Pa are conveyed in the opposite direction, so that the leading edge of the top sheet P of the bundle of sheets P is brought into the nip of the pair of conveying rollers 22. It is located a predetermined distance d downstream from the section. Then, after the predetermined time td has elapsed (step 816), the motor 22m stops (step 517). In this case, sheets other than the lowest sheet Pa are held between the roller pair 22, and the lowest sheet P
Only the roller a is free from being pinched by the roller pair 22. Therefore, only the lowest sheet Pa in a free state is separated from the other bundles of sheets P and conveyed downstream by the roller pair 23, while the other bundles of sheets P are stopped. roller pair 22
It does not move as it is held between the two. After a predetermined time te has elapsed since the start of rotation, the motor 23m is stopped (step S18, 519). Then, after an elapsed time tf after the leading edge of the lowest sheet Pa is detected by the sensor 27 (step 520), the leading edge of the lowest sheet Pa hits the nip portion of the registration roller 12 to form a loop, and then the motor 12m rotation is started, the lowest sheet Pa is conveyed, and the next image formation is performed. In other words, the rear end of the lowest sheet Pa is the registration roller 1.
Stop the rotation of motor 12m when it passes through 2 (
Step 524). The timing is the first seat Pa
It is determined by the elapse of a predetermined time tg (step 523) after the leading edge of is detected by the sensor 27S. Then, it is determined in step S25 whether refeeding of the set number of sheets has been completed, and if not, the process returns to step SL2. [0034] In such a configuration, sheets P of different sizes can be stacked in a stepwise manner and re-fed after one separation without changing the interval between the roller pairs. That is, when stacking sheets in a stairway, tb in step S5 and tb in step S7 in the flowchart of FIG.
-Δt may be changed depending on the length of the sheet P in the conveying direction. In order to remove the rear end of the sheet P from the conveyance path 24, the longer the sheet P, the longer tb may be. Similarly, tb△
If t is also set according to the length of the sheet P, sheets of different sizes can be stacked while being shifted by d. [0035] Furthermore, when the sheets are separated and re-fed, the times tc, td, te, and tf in the flowchart of FIG. 5 are changed depending on the length of the sheet P. tc is the time it takes for the trailing edge of the lowest sheet Pa to come out of the roller pair 22, td is the time it takes to pull out the bundle of sheets P that will not be re-fed from the roller pair 23, and te is the time it takes for the trailing edge of the lowest sheet Pa to come out from the roller pair 23. , and tf is the lowest sheet P from the registration roller 12.
This is the time required for the rear end of sheet a to come out, and in each case, the longer sheet P is set to be longer. [0036] Separation and re-feeding of the sheet P can be performed simply by stopping the roller pair 22 in step 515 in FIG. That is, the sheet P that is not to be re-fed is stopped while being nipped by the pair of rollers 22, and only the lowest sheet Pa that is to be re-fed is conveyed by the pair of rubber drive rollers 23a. The sheet size is detected by the sheet size detection device shown in 34 in FIG. 1, and tb and t are determined according to the detected size.
The control unit 32 calculates b-Δt, tc, td, te, and tg. The sheet size detecting device 34 detects a predetermined length La having a sheet size La.
If it is detected that the length is shorter (L≦La), it is possible to stack and refeed the sheet P by carrying out the control shown in the flowcharts of FIGS. 2 and 5 above. Become. In this case, the predetermined length La is a length that does not reach the registration rollers 12 when a plurality of sheets are stored in the paper refeed path. [0037] Next, FIGS. 7 and 8 describe stacking and refeeding operations when the sheet detection device 34 detects that the sheet size L is longer than the predetermined length La (L>La). This will be explained with reference to the flowchart shown in FIG. In this case, the loading operation shown in FIG. 7 is the same as that shown in FIG. 2, but the difference in control is step S34. S36. As shown in S38, the motor 22
The point is that m, 23m, and 12m are synchronously controlled. By performing such control, the roller pair 22
Furthermore, even sheets P that are long enough to reach the registration rollers 12 when stacked by the roller pair 23 can be stacked. In step S35, the sheet Pa is moved through the roller pair 22 and 23 in order to remove the rear end of the sheet Pa from the conveyance path 24.
, furthermore, the motors 22m, 23m, 12m are used to convey the preset distance do after being held by the 12.
This indicates that the required time th to rotate the . [00381 Next, FIG. 8 describes the operation control when refeeding the stacked sheets P for image formation on the second side of double-sided or multiple copying when the sheet length La is longer than a certain predetermined length. This will be explained with reference to the flowchart shown in . [0039] When the start is instructed by the keyboard 33 (step 541), the motors 22m, 23m, 12
The rotation of the sheet P is started, and the stacked sheets P are sent to the registration rollers 12 (step 542). When the rear end of the lowest and first Pa has passed through the roller pair 22, the motor 22m is reversed (step 45). This timing is determined by the elapsed time ti from the time when the first sheet Pa is detected by the sensor 27S (step 543).
step 544). Then, due to the reverse rotation of the motor 22m, the roller pair 22 is reversely rotated, and the sheets P other than the lowest sheet Pa are conveyed in the opposite direction, so that the leading edge of the top sheet of the bundle of sheets P is moved from the nip portion of the roller pair 22 to a predetermined position. It is located downstream by a distance d. The motor 22m is stopped after a predetermined time tj has elapsed since the start of the reverse rotation of the motor 22m (step S46).
, 547), the motors 23m and 12m are stopped after a predetermined time tk has elapsed from the start of rotation (steps S48 and 5).
49). In this case, the predetermined times ti, tj, and tk are changed depending on the length of the sheet. And the lowest sheet P
While the photosensitive drum 3a is being conveyed, the photosensitive drum 3 is synchronized with the roller 12 by a signal from the sensor 27S, and the next image formation is performed. Step S determines whether refeeding of the set number of sheets has been completed.
It is determined in step 50 that if the process is not completed, step S
Return to 42. [00401 With the above configuration, it is possible to form a plurality of double-sided and multiple image forming apparatuses 1 with a simple configuration and space saving, without being limited by the sheet size. [0041] In order to improve reliability by transferring the toner image on the photosensitive drum 3 to the correct position on the sheet P when performing image formation on the second and subsequent sides on the sheet P which is longer than the predetermined length La, FIG. The part A of the flowchart shown in FIG. 9 is changed to the control shown in the flowchart of FIG. [00421 When refeeding sheets, first, when a start instruction is given from the keyboard 33 (step 551), rotation of the motors 22m and 23m is started, and the sheets P loaded on the intermediate tray 16 are sent to the registration rollers 12. (
Step 552). After the leading edge of the lowest and first sheet Pa is detected by the sensor 27S1 (step 553), the leading edge of the sheet Pa reaches the registration roller 12 and the rule starts.
After a predetermined time tm necessary for forming the image and adjusting the position timing of the leading edge of the image has elapsed (step 554), the motor 12m is started (step 555). Then, when the trailing end of the sheet Pa has passed through the conveyance roller 22 (step 556), the motor 22m is reversed (step 557), that is, (step 5 of FIG.
45), the flowchart of FIG. 8 is followed below. [00431 When the leading edge of the sheet Pa reaches the registration rollers 12 and forms a loop, if a loop as shown in FIG. 10A is formed, the sheet position can be aligned more reliably. Furthermore, when a loop is formed in the direction shown in FIG.
a easily enters the nip portion of the registration roller 12. [0044] By controlling in this manner, the reliability of transferring the toner image on the photosensitive drum 3 to the correct position can be improved. [0045] Next, another embodiment will be described with reference to FIG. 11. [0046] In this embodiment, the paper refeed drive roller 2
3a is provided with an on/off mechanism, and when the size detection device 34 detects that the size of the sheet P is larger than a predetermined size, the sheet Pa is turned off by the roller only when refeeding in duplex or multiple copy mode. When the sheet Pa passes through the pair 22, the driving roller 23a is turned off (the biasing force of the driven roller 23b is also released).
2, and the other bundles of sheets P are conveyed by roller pair 2.
By reversing step 2, it is transported in the opposite direction. [0047] By doing this, the pinching between the roller pair 23 is eliminated, and the sheet Pa does not rub against other bundles of sheets P in the roller pair 23, so that the image disturbance of the sheet Pa,
That is, it is possible to prevent image distortion due to the pinching of the roller pair 23 when refeeding the paper. [00481 Next, still another embodiment will be described with reference to FIG. 12 and the above embodiment. In the embodiment described above, when stacking sheets, the next sheet P is placed downstream from the nip portion of the roller pair 22 by a predetermined distance d, but if the roller pair 23 is used instead of the roller pair 22, refeeding is difficult. In the case of paper, only the lowest sheet Pa is conveyed by the pair of rollers 23.12, and the other bundles of sheets are reversely conveyed to the pair of rollers 22 by reverse rotation. [0049] By doing this, the time required to reversely feed the stacked sheets P can be shortened compared to the embodiment described above, and the intermediate tray 16 can be adjusted to a length corresponding to the length of the sheets P. There is no need to increase the length, and space can be saved. [00501 Note that when performing image formation on the second or higher side, if the bundle of sheets P loaded on the roller pairs 22 and 23 passes through the registration rollers 12 and reaches the photosensitive drum 3 as shown in FIG. , photosensitive drum 3 without being transferred.
In order to prevent residual toner that could not be completely collected by the cleaner from being transferred onto the sheet P and losing image clarity, the current of the transfer charger 9 is set to zero when image formation is not performed. , remove the residual toner on the drum 3 from the sheet P without placing a negative charge on the back side of the sheet P.
Avoid attracting. [00511 Also, as shown in FIGS. 14(a) and 14(b), the registration roller 12, the transfer charger 9, and the drum 3
A flapper 35 is provided between the sheet P and the transfer section, and when forming an image, the sheet P is guided to the transfer section as shown in FIG. 14(a), and when not forming an image, as shown in FIG. 14(b). Avoid the sheet P from the transfer section. [0052] By doing so, it becomes possible to convey a longer sheet P with a simple configuration. [0053] [Effects of the Invention] As explained above, according to the present invention,
When the length of the sheet is longer than a predetermined length, the registration rollers are synchronized with the sheet delivery means according to instructions from the control means, so even if the leading edge of a stack of sheets reaches the registration rollers during sheet stacking, the sheets can be secured. The paper can be separated and re-feeded. [0054] Furthermore, when the sheets are stacked in a stepped manner on the intermediate tray, if the leading edge of the stack of sheets has reached the image forming section, no current flows to the transfer charger, so the residual toner on the photoreceptor is This prevents the image from being transferred to the sheet and staining the sheet. Further, since the leading end of the sheet bundle is removed from the image forming section by the flapper, it is possible to prevent the leading end of the sheet bundle from becoming dirty. In this way, it is possible to prevent the image forming apparatus from increasing in size in order to refeed long sheets, and this has the effect of reducing the cost of the apparatus.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram of a paper refeeding section showing an embodiment of the present invention.

FIG. 2 is a flowchart for stacking sheets on the intermediate tray in a stepwise manner.

FIG. 3 is a longitudinal side view showing a state in which sheets are stacked on an intermediate tray while being shifted by a predetermined amount.

FIG. 4 is a longitudinal sectional side view showing a state where the stacks are shifted by a predetermined amount.

FIG. 5 is a flowchart for refeeding the short sheet.

FIG. 6 is a longitudinal side view showing the state of the paper re-feeding timing.

FIG. 7 is a flowchart for stacking the long sheets on the intermediate tray in a stepped manner.

FIG. 8 is a flowchart for refeeding long sheets.

9 is a flowchart showing a flowchart for conveying the sheet to an image forming unit after forming a loop in the registration rollers when refeeding a long sheet, and is a modified flowchart of the flowchart in FIG. 8;

FIGS. 101(a) and 101(b) are side views showing the state in which the first sheet hits the nip portion of the registration rollers, respectively. FIG. 11 is a vertical sectional side view showing another embodiment.

FIG. 12 is a longitudinal sectional side view showing still another embodiment.

FIG. 13 is a side view showing a case where no current is applied to the transfer charger.

FIG. 141(a) is a side view showing the state of the flapper during image formation on the first side, and FIG. 141(b) is a side view showing the state of removing the leading edge of the sheet bundle from the image forming unit by the flapper during refeeding. FIG. 15 is a longitudinal sectional side view of a conventional copying apparatus.

FIG. 16 is a side view showing the state at the beginning of sheet re-feeding.

FIG. 17 is a side view showing a state in which the long sheet is re-fed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Image forming apparatus, 3... Photoreceptor (photosensitive drum), 3.9... Image forming part (photosensitive drum, transfer charger), 9... Transfer charger, 12... Resist Roller, 16... Intermediate tray, 22... Sheet loading/conveying means (roller pair), 23... Sheet discharging means (roller pair), 32... Control means (control unit), 35... Flapper, P... Sheet Pa.
・First seat

[Figure 5]

[Figure 9]

[Figure 15]

Claims (4)

[Claims] 1. An intermediate tray on which sheets on which images have been formed in an image forming section of an image forming apparatus are temporarily loaded for double-sided or multiple copying; sheet carrying means for carrying the sheets into the intermediate tray; and a sheet carrying means for carrying the sheets into the intermediate tray. Sheet stacking, in which the stacked sheets are shifted by a predetermined amount by conveying the required amount in the forward and reverse directions, and the stack of sheets stacked in the shifted manner is conveyed.
a conveying means; a sheet ejecting means that operates to eject the foremost sheet of the bundle of sheets when the trailing edge of the sheet escapes from the sheet stacking and conveying means; In an image forming apparatus having a paper device, when the sheet is longer than a predetermined length, control is performed to control a registration roller that conveys the sheet in synchronization with the operation of the image forming unit to synchronize with the sheet discharging means. An image forming apparatus characterized by comprising means. 2. When forming an image on the first side of the sheet,
2. The image forming apparatus according to claim 1, wherein said sheet conveyance means and said registration rollers are not synchronized. 3. When the image forming section includes a photoreceptor and a transfer charger, and when the sheets are stacked on the intermediate tray, the leading edge of the bundle of sheets has reached the image forming section. 2. The image forming apparatus according to claim 1, wherein the current of the transfer charger is set to zero to prevent residual toner on the photoreceptor from being transferred to the sheet. 4. The image forming unit includes a flapper that guides the sheet in a direction away from the image forming unit, so that when the bundle of sheets is stacked on the intermediate tray, the leading edge of the bundle of sheets is When the image forming section has been reached,
2. The image forming apparatus according to claim 1, wherein the flapper is operated so that the leading end of the sheet bundle is removed from the image forming section.