JPS63171758A - Image forming device - Google Patents

Abstract

PURPOSE:To pile a number of sheets in staircase form onto a transport passage by installing a means for transporting the sheets in transport in the normal and reverse directions, retreat part for the retreat of the rear edge of the sheet and a control means for operating the transport means, into a multiple image forming device. CONSTITUTION:The first sheet S1 on which an image is formed is transported to the prescribed positions of the transport means 29 and 30 through a sheet transport passage. A control means operates the transport means 29 and 30 according to the arrival of the sheet S1, and after the sheet S1 is normally transported by a prescribed length L1, said sheet S1 is reversely transported by a prescribed length L2 furthermore. Therefore, the sheet S1 is held with the top edge projecting from the transport means 29 by the difference gamma between the prescribed length L1 and the prescribed length L2, and the rear edge part is retreated into a sheet retreat part 50. The sheet S2 advances on the sheet S1 and arrives at the transport means 29. The transport means 29 and 30 normally revolve by the prescribed length L1 and then reversely revolve by the prescribed length L2, with the sheets S1 and S2 in held state. Through the repetition of these operations, the sheets are piled in staircase on the transport passage, and sent into an image formation part again, and each image is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer. The present invention relates to a double-sided or multiple image forming apparatus having a structure in which sheets are stacked in a stepwise manner in a 1-m conveyance path in order to further form images on the back side or the same side.

(b) Prior art - In this type of image forming apparatus, in order to continuously form images on a desired number of sheets, a predetermined conveyance roller provided in the sheet conveyance path is used, and the activation of the roller is used. By repeatedly stopping, the desired number of sheets on which image formation has been completed on one side are stacked in a stepwise manner, and the sheets are once docked in the sheet transport path, and from there, the sheets are fed again to the image forming section. There is.

On the other hand, in the image forming apparatus, various sheets of different sizes are used, and when the image forming apparatus uses sheets with different sheet lengths, which are the lengths of the sheets in the conveying direction, the edge positions of the stacked sheets change. I will do it. On the other hand, since the intervals between the conveyance rollers arranged in the sheet Sakaki conveyance path are constant, the conveyance path is changed using a switching means such as a flapper in order to correspond to the change in the sheet end position. Or, change the difference between each step of stacked sheets and see! - It was necessary to maintain the consistency of the end position.

←→ Problems to be Solved by the Invention However, with the above-mentioned means of changing the conveyance route,
The disadvantage is that the structure is complicated, making the device larger and more expensive.Also, with the latter method, the difference per stage changes, so the number of sheets that can be loaded changes depending on the sheet length, and the device becomes more expensive. At the same time, the sheet conveyance becomes difficult for the operator to understand, and at the same time, the distance between the conveyance rollers provided in the conveyance path is small.

The disadvantage is that as the length of the paper increases, the number of sheets that can be stacked and held decreases rapidly.

(c) Means for solving the problem The present invention aims to solve the above-mentioned problems,
A conveyance means capable of conveying the sheet in both forward and reverse directions in the sheet conveyance path, a sheet retraction section where the rear end of the displaced sheet in the conveyance direction is retracted on the upstream side of the conveyance means, and a sheet retraction section smaller than the length of the sheet to be conveyed. The present invention is characterized in that a control means is provided for operating the above-mentioned conveyance means to cause the sheet to be forward-fed for a predetermined length and then reverse-fed for a predetermined length smaller than that length.

(E) Effect By employing the above means, the first sheet on which the image has been formed in the image forming section is conveyed through the sheet conveyance path to the position of the predetermined conveyance means. In response to the arrival of the sheet, the control means operates the conveying means to forward the sheet by a predetermined length smaller than the sheet length, and then to reverse feed the sheet by a predetermined length smaller than the predetermined length. As a result, the sheet is held by the conveying means with the leading end portion protruding from the predetermined length smaller than the sheet length and the predetermined length further smaller than the predetermined length, and at the same time, the trailing end portion is retracted into the sheet retracting section.

Then, the second sheet that is subsequently sent advances over the first sheet held by the conveying means and reaches the conveying means, and as it reaches the conveying means, the second sheet is moved to the conveying means. While holding the first and second sheets, these sheets are forwardly fed by a predetermined length smaller than the sheet length, and then reversely fed again by a predetermined length smaller than the predetermined length. The above operation is repeated for a desired number of sheets, and as a result, each sheet is stacked in the sheet conveyance path in a stepwise manner at intervals of the above-mentioned difference. After that, the loaded Sea! Starting with the first sheet located at the leading edge, the sheets are sent to the image forming section again and image formation is performed.

(F) Embodiments Hereinafter, embodiments embodying the present invention will be described with reference to the drawings.

A copying apparatus 1 configured to perform multiple copies or double-sided copies on the same transfer sheet includes a copying apparatus main body 3 having a built-in copying section (image forming section) 2 and having a configuration as shown in FIG. have.

The main body 3 of the device consists of a base f^ [mounting table 4, light source 5, lens system 6.
The apparatus includes two cassettes 1-7a, 7b, etc., and the copying section 2, which includes a cylindrical photoreceptor 8, etc., is disposed approximately at the center of the main body 3 of the apparatus. Near the periphery of the photoreceptor 8, two developing units 9a and 9b each containing toner of a different color can be set and reset by moving in the direction of the arrow so that copies can be made in a desired color. established,
Further, a transfer charger 10 is provided on the downstream side of the photoreceptor 8 in the rotational direction.
and separation charging Wg 11 , and cleaner 12 and -
The next band 'y411113 is arranged. In addition, paper feed rollers 14a and 14b are arranged in the cassettes 7a and 7b, and the transfer sheet S is guided to a register roller pair 17 via transport roller pairs 15a and 15bS paths 16a and 16b, respectively. In addition, the transfer sheet 1-3 to be subjected to multiple copies or double-sided copies is guided by the pair of registration rollers 17 via a sheet conveying path 19 disposed below the main body 3 of the apparatus. There is. Further, a fixing device 20 is disposed at the rear of the conveying device 18 having a conveyor belt 18a following the separation charger 11, and furthermore, a first discharge roller pair 21 is disposed on the rear side of the fixing device 20. The transfer plate is normally disposed to be discharged to a tray or the like outside the machine via a second discharge roller pair 22.

A flapper 23 and an auxiliary flapper 2 are provided between the first pair of discharge rollers 21 and the second pair of discharge rollers 22.
Normally, the transfer sheet S discharged from the first pair of discharge rollers 21 is conveyed along the upper side of the flapper 23 at the solid line position, and its conveying force moves the transfer sheet S to the auxiliary flapper 2.
4 in the direction of the arrow, and based on that, the detection arm 25
While the optical sensor 26 is activated to detect the passage of the transfer sheet, the transfer sheet is discharged outside the machine by a second pair of discharge rollers 22 that rotate normally. On the other hand, during double-sided copying, the transfer sheet S is partially ejected out of the machine by normal rotation of the second ejecting roller pair 22, as in the normal case, but the rear end of the transfer sheet When the transfer sheet leaves the auxiliary flapper 24, the detection arm 25 and the optical sensor 26 operate to drive the second discharge roller pair 22 in the reverse direction, and the transfer sheet is thereby guided to the left side of the auxiliary flapper 24 and the flapper 23. It is now ready to be introduced into route 27. Therefore, during double-sided copying, the second discharge roller pair 22, the detection arm 25, the optical sensor 26
The transfer sheet is then fed again through the path 27. Further, when performing multiple copying, the flapper 23 is switched to the dotted line position, and the transfer sheet S discharged from the first discharge roller pair 21 is directly introduced into the path 27 by the guiding action of the right side of the flapper 23. ing. Therefore, during multiple copying, the first ejection roller pair 21 and the flapper 23
The transfer sheet is then fed again through the path 27. Then, the transfer rate S introduced into the path 27 is adjusted in the axial direction in order to align the transport roller pair 28, cliff roller pair 29, 30 constituting the transport means, and one lateral end of the transfer sheet at the reference position. Sea! having a pair of registration rollers 31 configured to be movable relative to the seat! - It is designed to be guided by the pair of registration rollers 17 via the conveyance path 19.

In the sheet conveyance path 19 described above, the conveyance roller pair 28 consists of a driving roller 28a and a driven roller 28b supported between the front and rear side plates of the main body, and the driving roller 28a is driven in synchronization with the apparatus main body 3 by a driving means (not shown). is,
While the main body 3 of the apparatus is in operation (always rotating in the direction of the arrow shown in the figure), a sheet detection sensor 3 consisting of a detection arm 32a and a photodetection element 32b is installed immediately before the pair of rough feed rollers 24.
2 are arranged.

A pair of conveying rollers 29 disposed downstream of the pair of Song conveying rollers 28
, 30 has a configuration as shown in detail in FIG. 2, and this transport roller pair 29 is movable up and down and rotatable between the drive roller 29a supported between the front and rear side plates of the main body, and between the same side plates. The upper roller 29b is supported by the upper roller 29b and is pressed against the drive roller 29a by a spring 33 which is passed through the bearing part.
It consists of The drive roller 29a and the upper roller 29b are controlled in circumferential speed by a gear train consisting of a gear 34 fixed to the drive roller 29a, idler gears 35 and 36, and a gear 37 fixed to the upper roller 29b. Both rollers 29a and 29b are connected equally.
Even if there is a gap of 1 to 211 Im, the rotational connection relationship is maintained by the gear train.

The drive roller 29a is driven by a drive pulse motor 3 which rotates forward and backward in response to a signal from a control means (not shown) via a gear 39.
8 and can rotate forward or backward according to the rotation of the motor, and the amount of rotation can be controlled by a control means. A driving roller 30a of the transporting roller pair 30 provided downstream of the transporting roller pair 29 is supported in the same way as the driving roller 29a, and an input gear 40 fixed to the driving roller 30a is supported.
is rotated in the same direction and at the same circumferential speed as the drive roller 29a by meshing with a gear 39 provided on the drive pulse motor 38. On the other hand, the upper roller 3ob is pivotally supported on an arm 41.41 rotatably disposed on the axis of the upper roller 29b of the pair of conveying rollers 29, and is connected to a gear 37 fixed to the upper roller 29b and the arm 41. A gear 4 is fixed to the upper roller 30b via a shaft-supported idler gear 42.
The driving force is transmitted by the drive roller 30a.
It is configured to rotate at a constant speed. Also, arm 4
1 is hung by a balance spring 44 whose one end is fixed to the main body 3 of the apparatus, so that the weight of the upper roller 30b and the arm 41 is canceled out, and the arm 41 hits a stopper provided above and stops. Both rollers of the transport roller pair 30 do not contact each other and are spaced apart from each other by approximately 2 mm, and furthermore, a spring 47 is provided on the opposite side 1ζ of the balance spring 44 to connect the link 46 of the solenoid 45 and the arm 41. The solenoid 45 is operated to press the upper roller 30b against the drive roller 30a.

An upper guide plate 48 and a lower guide plate 49 are disposed between the conveyance roller pair 28 and the conveyance roller pair 29 (see FIG. 1), and the upper guide plate 48 guides the sheet that has passed through the production roller pair 28 to the conveyance roller pair. Further, one end of the lower guide plate 49 extends below the drive roller 28a, and the lower guide plate 49
A retraction portion 50 is formed by the gap between the g-roller 28a and the g-roller 28a. The distance 11 between the pair of conveying rollers 28 and the pair of conveying rollers 29 is 11, and the minimum length in the conveying direction is 4. . Considering a slight margin a so that the sheet can be conveyed, l = L,...
-α, and if the distance e2 between the pair of feed rollers 30 and the pair of registration rollers 31 is set to a certain margin β, 12=L.
.

1n-β, and the distance 13 between the conveying roller pair 29 and the registration roller pair 31 is the maximum length in the conveying direction, 1, = L, , , -β so that an 85-sized sheet can be conveyed.
is set to . Note that the minimum length in the transport direction is 11. .

is the minimum length that can pass through the sheet transport path 19 (which does not match the minimum length in the case of only one side), and is also the minimum length that can be stacked in a stepwise manner. Similarly, the maximum length L in the transport direction
m m x is the maximum length that can be loaded in a stairway,
It is not necessarily the maximum length that can pass through sheet transport @19.

Next, a pair of registration rollers 3 are movable in the axial direction and have the function of correcting the position of the sheet in a direction perpendicular to the conveying direction.
1 has a configuration as shown in FIGS. 3 and 4, and consists of a lower roller 31a and an upper roller 31b that are pressed against each other. Then, the upper roller 31b and the lower roller 31
a is rotatably and slidably supported on the front and rear side plates la and Ib of the copying device 1 via bearings 52 and 52, respectively, and a collar 5 provided on each bearing 52 and the shaft of each roller.
3. A spring 55 disposed between the two is biased toward the left in FIG. 4. Further, the rollers 31a and 31b are respectively inserted into a block body 56 so as to be able to rotate freely, and the block body 56 has a roller member 5 disposed in its upper portion.
It comes into contact with a cam member 57 via 6a. The cam member 57 is of a type in which an inclined cam is formed on the circumference of the end of a cylindrical body, and when the spring clutch 59 is turned on by the solenoid 59s,
The rotational force of the drive gear 60 is transmitted to the shaft 61 via the clutch 59 to rotate the cam member 57, and as the cam member rotates once, the upper roller 3 is transferred via the block body 56.
1b and the lower roller 31a are moved in left and right directions A and B (see FIG. 3) against a spring 55. Normally, the light shielding plate 62 provided at the end of the shaft 61 The cam member 5 is
The center portion 57a of the inclined surface 7 is brought into contact with the roller member 56a, and the upper roller 31b and lower roller 31n are stopped at the center position of the left-right movement stroke, that is, the home position. Further, a gear 65 is fixed to the lower roller 31a, and when an electromagnetic clutch 66 is turned on, the drive gear 6
7 is transmitted to the shaft 69 via the clutch 66 and the transmission gear 70 is rotated, thereby rotating the gear 65 meshing with the gear 7°, thereby rotating the lower 0-
The roller 31a is rotated, and the transfer sheet 1-S, which had been stopped with its tip abutting the tip of the upper roller 31b and the lower roller 3111, is now subjected to the conveyance action.

Furthermore, as shown in FIG. 3, a light emitting section 71a has a large number of light emitting elements arranged in parallel close to the contact area between the upper roller 31b and the lower roller 31a, and a large number of light emitting elements are arranged. An optical sensor 71 consisting of a light receiving section 71b is provided, and the lateral position of the transfer sheet is detected by the optical sensor 71. As shown in FIG. 5, an optical sensor 75 corresponding to this optical sensor 71 is arranged in front of the pair of registration rollers 17, and detects the lateral position of the sheet when the first copy is made on the sheet. In order to
It is disposed near the pair of registration rollers 17 so as to be orthogonal to each other, and is composed of a light emitting section 75a in which a large number of light emitting elements are arranged, and a light receiving section 75b in which a large number of light receiving elements are arranged. In FIG. 3, reference numeral 72 is an upper guide plate for guiding the transfer sheet toward the contact area between the upper roller 31b and the lower roller 31a. It is integrally fixed to the roller 31b, and a detection arm 74b cooperates with the photodetection element 74a to detect the conveyed sheet as a sensor 74.

Since this embodiment has the above-described configuration, when multiplexing or double-sided copying is to be performed on one sheet, when the copy button (not shown) is pressed to start the copying operation, the copies supplied from the cassette 7a or 7b are The transfer sheet S passes between the light emitting part 75a and the light receiving part 75b of the optical sensor 75,
After being positioned in the sheet conveying direction by a pair of registration rollers 17 , the sheet is conveyed to the copying section 2 , where the toner image is transferred, and then further conveyed to the fixing device 20 .

At this time, the lateral position of the transfer sheet S in the direction perpendicular to the conveyance direction is detected by the light-shielded portion and the unshielded portion of the light-receiving section 75b by the transfer sheet S, and the detected lateral position A corresponding electrical signal is stored from the optical sensor 75 in a storage section of a microprocessor unit (MPU) that controls the copying apparatus 1 . Then, preparations are made in the MPU to move the pair of registration rollers 31 in the axial direction in accordance with the detected lateral position. Next, the transfer sheet +-S that has undergone the fixing action in the fixing device 20 is conveyed to the sheet conveying path 19 by the flapper 23 or the like for multiple copying or double-sided copying. The minimum length in the feeding direction that can be conveyed in the sheet feeding path 19 L T+l i 11
If it is detected by the time it takes to pass through the optical sensor 71 or by the detection of the cassette size that it is shorter than
The sheet S is discharged onto the tray regardless of the operator's designation of double-sided copying or the like. L, 1. A sheet with a length greater than n is conveyed by a pair of conveying rollers 28 via a conveying path 27, and after the leading edge of this transfer sheet S reaches a pair of conveying rollers 29, the pair of conveying rollers 29 rotates normally after a predetermined time. By starting, a loop is formed between the pair of conveying rollers 28 and 29, and the skew of the sheet is corrected. When the sheet length is UNI + n, the solenoid 45 is operated at the same time as the conveyance roller pair 29 rotates, and the conveyance roller pair 30 is rotated.
Keep it under pressure. Conveyance roller pair 28, 29, 30
When the transfer sheet +-S that has been re-fed by the sensor 73 enters the pair of registration rollers 31, it is detected by the sensor 73 immediately before the pair of registration rollers 31, and based on this, the leading edge of the transfer sheet is stopped. Even after the upper roller 31b and the lower roller 31a come into contact with the contact portion, the transporting action of the transfer sheet by normal rotation of the transport roller pair 29, 30 continues for a predetermined period of time, and after the elapse of the predetermined time, the transport roller pair 29, 3
0 is stopped, thereby forming an appropriate amount of flexure, that is, a loop, in the transfer sheet with the leading edge of the transfer sheet in contact with the contact portion between the upper roller 31b and the lower roller 31a. Next, when the transport roller pair 29 and 30 rotate normally again and the electromagnetic clutch 66 is turned on at the same time, the drive gear 6
7 is transmitted to the gear 65 via the shaft 69 and the gear 70, the lower roller 31a starts rotating, and the transfer sheet is held between the rotating upper roller 31b and the lower roller 31a, forming the above-mentioned loop. Transport will begin in this state. At the same time, the spring clutch 59 is turned on, and the rotation of the drive gear 60 is transmitted to the cam member 57 via the shaft 61.
Due to the rotation of the cam member 57, the block body 56 is moved from its stop position, that is, the home position, in the direction B via the roller member 56a, and if necessary, the block body 56 is moved to the rightmost end.
The transfer sheet is moved in the A direction to the leftmost end, and then moved again in the B direction, and while the transfer sheet is being conveyed, it is moved in a direction perpendicular to the conveyance direction. At that time, due to the existence of the above-mentioned loop, even if the rear end of the sheet is held between the pair of conveying rollers 29, the lateral movement of the transfer sheet does not apply any unreasonable force or deform the transfer sheet. Make it happen smoothly. When the transfer sheet S moves in the lateral direction, the lateral position of the transfer sheet S is checked by the optical sensor 71, and the lateral position of the transfer sheet S is detected by the optical sensor 75 and stored in the MPU. When the lateral position of the transfer sheet S matches the position of the transfer sheet S during the first copying, the spring clutch 59 is disconnected by a command from the MPU, and the lateral movement of the upper roller 31b and the lower roller 31a is stopped. Thereafter, by the rotational conveyance action of the upper roller 31b and the lower roller 31a that continues for a predetermined period of time, the transfer sheet is conveyed from the sheet conveyance path 19 to the pair of registration rollers 17 with the lateral position corrected and corrected. After the transfer sheet is conveyed, the electromagnetic clutch 66 is disengaged and the rotation of each roller 31b, 31a is stopped, and the pair of registration rollers 31 is moved to the central home due to the reset action by the light shielding plate 62, optical sensor 63, etc. It is returned to the position and is in a standby state in order to correct the position of the next transfer sheet S.

Next, the operation when double-sided copying or multiple copying is performed continuously on a plurality of sheets will be described for a sheet having a length LM in the transport direction. After setting the first original on the document table and instructing the desired number of copies N, pressing the copy button (not shown) to instruct the copying operation will cause the cassette 7a to
Alternatively, the length in the transport direction L M A X supplied from 7b
The transfer sheet S is the light emitting part 75a and 75b of the optical sensor 75.
After passing through the gap and having its lateral position measured, the image forming process sequentially passes through the second image forming process and reaches the pair of conveying rollers 28 . At this time, if it is detected that the length of the sheet S in the transport direction is larger than , , , based on the time it takes for the sheet to pass through the optical sensor 75, etc., the copying device 1 will not accept continuous double-sided copying, etc., and will warn the operator. emits. When the sheet) S reaches the conveying roller pair 28, the conveying roller pairs 29 and 30 are stopped, and after a predetermined time after the sheet 1 detection sensor 32 detects the sheet, that is, in FIG. As shown, the leading edge of the sheet S1 contacts the contact portion between the upper and lower rollers of the transport roller pair 29 to form a loop, and after the skew of the sheet is corrected, the transport roller pair 29 is corrected by the command Cζ of the control means. Begin full transfer. At this time, the transport roller pair 30 also rotates in synchronization, but the upper roller 30b is in a retracted state and does not act on the sheet. And sh!・So that the rear end of Sl is completely let out from the pair of conveying rollers 28.

Greater than -11, only sea 1-3. After feeding out (Fig. 6 (bl) i#? feed roller pair 29, stop once,
This time, the sheet S is reversed and returned to the upstream side by an amount L2 such that L2<L, thereby causing the rear end of the sheet S to enter the sheet retracting portion 50 (FIG. 6(C)). Subsequently, when the second sheet S2 is conveyed after the first copying, it is formed into a loop at the printing roller pair 29 in the same way as the first sheet S (FIG. 6 fd )), the first sheet S is conveyed to the downstream side (Fig. 6)), and is returned to the upstream side by L2 by the conveying roller pair 29 which is reversed again (Fig. 6 (f)). ). Such an action is repeated for a set number of sheets N, and if L, -L2 = 7, a bundle of N sheets stacked in a stepwise manner with each step γ is formed (Figure 6 (g)). . At this time, since the stacked sheets are slightly corrected for skew by abutting against the pair of feed rollers 29, the parallelism is good, and the skew is corrected to a large extent by the pair of registration rollers 31 located next. Since this is not necessary, it is possible to reduce γ and place sheets at high density. After the sheet I/bundle is formed, the copying machine 1 temporarily stops, so the operator must replace the originals on the document table 4, and then press the suppression button to
Make the second copy. Then, as shown at ta+ in FIG. 7, the conveyance roller pair 29 starts normal rotation and feeds the N sheets in the east direction, and the leading edge of the first sheet S1 reaches the sensor 74 of the registration roller pair 31 located downstream. After the first sheet S1 is detected and fed by a predetermined amount, that is, the leading edge of the first sheet S1 leaves the conveying roller pair 29, and before the second sheet S2 reaches the sensor 74, the conveying roller pair 29 is stopped. . In addition,
When conveying the sheets as a bundle in this way, the upper roller 29b and lower roller 29a of the conveying roller pair 29 are connected by a gear train, so even if the conveying roller pair 29 repeats forward and reverse rotation, the sheet I/bundle remains unchanged. Transport it without collapsing. When the pair of conveyance rollers has stopped as described above, as shown in FIG.
As shown in l, the first sheet has registration roller pair 31.
A loop is formed with the tip in contact between the rollers,
The other sheet bundles after the second sheet are held between the pair of conveyance rollers 29, and then, while the pair of conveyance rollers 29 is stopped, the pair of registration rollers 31 rotates, in the same way as when feeding one sheet. While correcting the horizontal position, move the first sea +
-S is sent to the image forming section 2 (FIG. 7(C)).

At this time, the rear end of the first sheet whose position is corrected is N-1.
Although the weight of the sheet is only a few tens of grams at most, it does not interfere with the correction using the registration roller pair 31.Then, the second and subsequent sheets are repeated in the same manner as described above. It is transported, subjected to double-sided copying, etc., and then discharged from the apparatus.

Next, the operation when double-sided copying is performed continuously on a sheet having a length LM□ in the conveyance direction will be described. @Sheets 1-L, , N, which have undergone the -th image forming process sequentially in the same way as the sheet L 11 A described above, are conveyor roller pair 2
8, and is sent to the stopped conveyance roller pair 29.degree. 30, but when it is detected that this sheet is the smallest sheet L, 11N, the solenoid 45 is activated, and the rollers 30a, 30 of the conveyance roller pair 30 are conveyed. 30b are joined, and the conveying roller pair 30 enters the operating state. After a predetermined period of time after the sheet detection sensor 32 detects the sheet, the leading edge of the sheet comes into contact with the contact portion between the upper and lower rollers of the m feed roller pair 29, forming a slight loop, and the skew of the sheet is corrected. The pair of rear feeding rollers 29 starts normal rotation according to a command from the control means.

After the trailing end of the sheet S is completely fed out from the conveying roller pair 28, the conveying roller pair 29 stops once after feeding out L't1 sheets S larger than LMl+1'l, and then reverses itself so that L2< L, becomes 1kL2 only sea 1-
S is returned to the upstream side, and the rear end of the sheet is caused to enter the sea 1-retreat part 50 so that the second sheet sent subsequently does not enter the downstream of the first sheet. Then 2
After a certain period of time has elapsed since the sheet detection sensor 32 detects the entry of the first sheet, the pair of transport rollers 29 rotates by a predetermined amount, and when the leading edge of the first sheet moves from the nip of the rollers to the position γ mentioned above, Stop. Next, the leading edge of the second sheet reaches the nip between the stopped transport roller pair 29, and the same operation as for the first sheet is performed, and this is repeated for the set number N of sheets, so that the sheet moves one step on the sheet transport path 19. A step-like bundle of N sheets with γ is formed. This Sea I・
After forming the bundle, when the second copying operation is performed, the pair of conveyor rollers 2
9 and 30 start normal rotation to feed N sheets as a bundle, and after the leading edge of the first sheet is detected by the sensor 74 of the registration roller pair 31 located downstream, the sheet is fed by a predetermined amount. That is, the trailing edge of the first sheet leaves the pair of conveying rollers 30, and the pair of conveying rollers 29, 30 are stopped before the rate of the second sheet reaches the sensor 74. In this state, a loop is formed with the leading end of the first sheet in contact with the rollers of the pair of registration rollers 31, and the other sheets after the second sheet are held between the pair of transport rollers 29 and 30. Then, while the pair of transport rollers 29 and 30 are stopped, the pair of registration rollers 31 rotates, and image formation is performed on the first sheet while correcting the position in the lateral direction in the same way as when feeding one sheet. Send to section 2. Subsequently, the second and subsequent sheets are repeatedly conveyed in the same manner as described above, subjected to double-sided copying, and then discharged from the apparatus.

In the above embodiment, the conveying means capable of conveying the sheet in the forward and reverse directions are two pairs of conveying rollers 29.degree. 30, but a larger number of pairs of conveying rollers may be provided. Further, although the upper and lower rollers of the pair of conveying rollers are drivingly connected, one roller may be simply a driven roller depending on the material of the sheet. Furthermore, the rotational speed of the pair of conveying rollers is set to a low speed regardless of the sheet conveying speed within the copying machine. It is also possible to perform accurate positioning.

(G) As described in detail, according to the present invention, there is provided a continuous conveying means capable of conveying sheets in both forward and reverse directions in a sheet conveying path, and a continuous conveying means which is located upstream of the continuous conveying means and which is arranged to carry a notebook. A sheet retracting section where the rear end in the feeding direction retracts, and a sheet having a predetermined length smaller than the length of the sheet that is slowly fed by the conveying means! Since a control means is provided for forward feeding and then reverse feeding by a predetermined length smaller than the predetermined length, it is possible to stack a large number of sheets at high density regardless of the sheet length.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the image forming apparatus according to the present invention and an overall configuration diagram thereof; Figure 7 (al~(c
) is an explanatory diagram of the operation when the value is zero. 1. Image forming section M (copying device), 2. Image forming section, 17. Registration roller pair, 19.
・Sheet conveyance path, 28... Conveyance roller pair, 2
9.30 - Conveying means (conveying roller pair), 31...
Regis) Laura vs., 50... Sea 1 - Retired [I
S.

Claims (3)

[Claims] (1) In an image forming apparatus having an image forming section and a sheet conveyance path for feeding a sheet on which an image has been formed to the image forming section again, a conveyance means capable of conveying the sheet in both forward and reverse directions in the sheet conveyance path. a sheet retracting section located upstream of the conveying means, from which the trailing end of the sheet in the conveying direction retreats; An image forming apparatus comprising: a control means for reverse feeding by a smaller predetermined length. (2) The image forming apparatus according to claim 1, wherein the conveying means includes a plurality of pairs of conveying rollers arranged at intervals in the conveying direction. (3) The sheet retraction portion is provided between a pair of sheet conveying rollers provided upstream of the conveying means and a guide extending downward from the vicinity of the conveying means and below the pair of conveying rollers. The image forming apparatus according to scope 1 or 2.