JP4027583B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus capable of duplex copying by a non-stack interleaf method, and more specifically, stores a plurality of document images obtained by reading with a scanner and the like on an arbitrary surface of an arbitrary transfer sheet. In a digital copying machine capable of forming images, it is ensured that transfer sheets collide with each other in a double-sided path extending from the front side to the upstream side of the registration roller during double-sided copying without stacking. The present invention relates to an image forming apparatus that can be prevented.
[0002]
[Prior art]
When performing double-sided copying in an image forming apparatus such as a copying machine, a printer, or a facsimile machine, the transfer paper that has undergone image formation on one side in the image forming unit is temporarily stacked on the intermediate tray without being discharged out of the apparatus, When the original image corresponding to the back side of the transfer sheet is read, the transfer sheet is re-fed to the image forming unit to form an image on the back side. That is, in a conventional analog type image forming apparatus or the like having no means for storing read original image information (for example, Japanese Patent Laid-Open Nos. 7-72683 and 7-209925), a plurality of originals are copied on both sides. In this case, since the reading operation of the original image and the image forming operation on the transfer paper are performed as a continuous inseparable process, the original image reading procedure is as follows: the first page, the third page, the fifth page,. Only the odd-numbered pages are sequentially read by the scanner, and image formation is sequentially performed on the surface of each corresponding transfer sheet immediately after the reading operation of each page. In this way, a plurality of transfer papers that have undergone image formation on one side are once stacked on the intermediate tray in a stacked state. Next, in order to form an image on the back side of the transfer paper, the scanner reads the even-numbered pages of the document, that is, the second page, the fourth page, the sixth page, and so on. By refeeding the transfer paper to the image forming unit one by one, an even page image is formed on the back surface of each transfer paper, and the transfer paper that has undergone image formation on both sides is discharged out of the apparatus. The document feeding operation in the image forming operation is performed by, for example, a circulation type automatic document feeder.
However, when a double-sided copy is obtained from a plurality of originals using the above-described conventional analog type image forming apparatus, a process of stacking single-sided recorded transfer paper on an intermediate tray is required, so that the time required for stacking is reduced. The entire copying time is increased by the amount of time, and transfer paper and image formation cannot be performed at a constant continuous short interval.
[0003]
On the other hand, in a digital copying machine equipped with a function for storing a read original image, a non-stack interleaf double-sided function that does not require stacking of single-sided recorded transfer paper is realized for double-sided copying. Can do. When performing double-sided copying in this type of digital copying machine, first, for example, all pages of a predetermined number of originals are read by a scanner by an automatic document feeder and stored in a storage unit. For example, in the case of a double-sided document, both front and back sides are read, and after this reading operation, images of odd-numbered pages (1st page, 3rd page, 5th page) of a predetermined number, for example, 3 documents are sequentially read from the storage unit. After sequentially forming an image on the surface of the transfer paper that is sequentially fed from the paper feed unit, the three transfer papers recorded on the surface are sequentially conveyed into the double-sided path from the switchback unit to the image forming unit. It is stopped in a front-rear position relationship (in a non-stacked state). Subsequently, when the first image of the even page is formed on the back surface of the transfer paper, the first (first) transfer paper of the three transfer papers stopped in the double-sided path is imaged. A toner image corresponding to the image of the second page read out from the storage unit and fed back to the forming unit is formed on the back surface of the first transfer sheet. At this time, the remaining two transfer sheets in the double-sided path are sequentially advanced to prepare for refeeding. Next, a fourth sheet of transfer paper is newly fed from the paper feed unit, a document image of the seventh page is formed on the surface, and then conveyed to the last part in the double-sided path to stop. Subsequently, the second sheet of transfer paper that has been stopped at the foremost part in the double-sided path is re-fed to the image forming unit, and the fourth page of the original image is formed on the back side. Subsequently, a fifth new transfer sheet is fed from the sheet feeding unit to the image forming unit, and a 9th page original image is formed on the surface. In other words, when the non-stack interleaf duplex function is implemented, after the double-sided path is filled with single-sided recorded transfer paper, a new transfer paper is fed from the paper feed unit and double-sided re-feeding. Therefore, if a single-side recorded transfer paper is not always kept waiting at the re-feeding position in the double-sided path, there will be a gap between the papers and copy productivity will be reduced.
[0004]
FIG. 7 is a schematic configuration and operation explanatory diagram of a conventional digital copying machine having a non-stack interleaf double-sided function, and is a reading optical system A, a writing optical system B, an image forming unit C, a reversing unit D, and a paper discharge unit E. , Double-sided path F, paper feeding unit G, and the like. The double-sided path F includes a branch transport path II, a path III before reverse reversal (switchback unit), a path IV after reversal, and a path V before registration. Further, the reverse paper discharge path II ′ is a path for discharging the transfer paper guided to the path III before reverse feed reverse to the paper discharge unit E with the front and back reversed. The transfer sheet fed from the sheet feeding section G to the pre-registration path V is fed to the image forming section C and is subjected to image formation, and then discharged from the sheet ejection path I to the sheet ejection section E or on the back surface. In order to receive image formation, it is guided from the branch conveyance path II to the double-side path F. A reverse roller 200 that reversely conveys the transfer paper in the pre-reverse reverse path III to the post-reverse path IV in the reverse portion between the pre-reverse reverse path III and the reverse reverse path IV, and the reverse pre-reverse reverse path III Are provided with a double-sided branching claw 201 that rotates to selectively distribute the transfer paper to either the reverse paper discharge path II ′ or the reverse-side path IV, and a solenoid that drives the double-sided branching claw.
FIG. 7A shows the first transfer sheet P1 after the first to third transfer sheets are sequentially fed from the sheet feeding section G and subjected to image formation on the surface by the image forming section C. Is shown in the double-sided path F from the branch conveyance path II, and in this state, the fourth transfer sheet P4 is in a state where the leading end protrudes from the sheet feeding section G to the pre-registration path V. In addition, each transfer sheet stands by with its leading end in contact with the registration roller pair 202 during a period required for image development in an image processing unit (not shown), and the toner formed on the photosensitive member after image development is completed. The image is fed by a registration roller that is driven according to the timing at which the image moves to the transfer position, and undergoes image formation.
Next, in FIG. 7B, the first, second, and third transfer papers P1, P2, and P3 that have undergone image formation on the surface sequentially enter the double-sided path F, and before reverse feed reversal. It is sequentially conveyed in the route III and the route IV after reversal.
Next, as shown in FIG. 7 (c), only the transfer paper P1 is fed again straight, undergoes image formation on the back surface, and is discharged out of the apparatus from the paper discharge path I. Then, the robot enters the pre-registration path V, abuts the front end against the registration roller pair 202, and waits until image development corresponding to the image on the first back surface is completed. During this waiting time, the second transfer sheet P2 stops at an appropriate position in the post-reversal path IV (a position that does not interfere with the rear end of the preceding first transfer sheet), and the subsequent third transfer sheet is reversely reversed. It will be located in the front path III. When the first sheet P1 is re-fed and subjected to image formation, the fourth sheet P4 is newly fed from the sheet feeding unit G toward the registration roller pair 202.
[0005]
However, since the reversing roller 200 used in the conventional double-sided path F of this type always rotates counterclockwise, even if the third transfer paper is stopped at the position shown in the drawing, the reversing roller 200 is rotated. Thus, there is a high risk that the two transfer sheets will be damaged by colliding with the trailing edge of the second transfer sheet that has been stopped.
In addition, as shown in FIG. 7C, when the third transfer paper P3 is positioned on the outer periphery of the reversing roller 200, the double-sided branching claw 201 does not interfere with the paper surface by operating the solenoid. However, since this means that energization of the solenoid is continued, there is an increased possibility of overloading and lowering durability such as temperature rise and breakage.
In this way, each stop position of a plurality of single-sided recorded transfer sheets that stop in the double-sided path collides with another transfer sheet that precedes when advancement is started for refeeding, or the interval is Although it is set so as not to open too much, depending on the stop position, movable parts located in the double-sided path, such as transport direction switching claws, rollers, etc. interfere with the transfer paper and damage the transfer paper, etc. In order to cause the above problem, control is performed so that the movable part is continuously operated and held at the non-interference position so that the movable part does not interfere with the transfer sheet at the stop position. However, when the drive source for operating such moving parts is a solenoid or the like, the drive source continues to be ON for a long time during double-sided image formation. It was.
The problem in the above-described double-sided copy operation also occurs when performing double-sided copying from a single-sided original.
[0006]
[Problems to be solved by the invention]
A problem to be solved by the present invention is to store a plurality of original images obtained by reading with a scanner, etc., and to form an arbitrary original image stored on an arbitrary surface of an arbitrary transfer paper In a copying machine, when double-sided copying is being performed in a non-stack, the following transfer paper collides with the preceding transfer paper that is stopped in the double-sided path, causing damage to the transfer paper. An object of the present invention is to solve the problem that the durability of the driving source is lowered by operating the movable part and keeping it in the non-interference position in order to avoid interference with the transfer paper stopped at a predetermined position in the path.
[0007]
[Means for Solving the Problems]
To solve the above problem, The invention described in claim 1 A double-sided path capable of reversing the transfer paper on which the image is formed on the surface by the image forming unit and refeeding the transfer paper to the image forming unit and stopping at least one transfer paper, and the double-sided path An image forming apparatus comprising: a control unit that controls the movable member provided on the double-sided path to hold the non-interfering position that does not interfere with the transfer paper on the double-sided path; When the period during which the movable member is held at the non-interference position exceeds a certain time, the transfer paper stop position is moved to a retreat position that does not interfere with the movable member, and the movable member is returned to the interference position to stop the operation. The image forming apparatus is controlled as described above.
Claim 2 According to the invention described above, an image forming unit for forming an image on a transfer paper, a transfer paper on which an image is formed on the surface by the image forming unit are reversed and re-fed to the image forming unit, and at least one sheet is provided. In an image forming apparatus having a double-sided path capable of stopping and waiting for the transfer paper and a control unit for controlling the double-sided path, the double-sided path is a branched transport that introduces transfer paper that has undergone image formation on the surface. A path, a reverse feed reverse path that receives and reversely transfers the transfer paper introduced from the branch conveyance path, and a reverse roller that reverses the front and back of the transfer paper that has been reversely fed from the reverse feed reverse path A reverse path for re-feeding the image forming unit after receiving the transfer paper whose front and back sides are reversed by the reversing roller, and a pre-registration that extends upstream a predetermined distance from a pair of registration rollers constituting the image forming unit. Route and When the preceding transfer paper is in a registration waiting state in which the leading end is in contact with the registration roller pair, the rotation of the reversing roller is stopped to prevent the transfer papers from colliding with each other in the double-sided path, A configuration in which the movable member is operated and held at a non-interference position in order to prevent the movable member on the double-sided path from interfering with the subsequent transfer paper stopped at a predetermined position in the double-sided path. And the controller moves the stop position of the subsequent transfer sheet to a retracted position that does not interfere with the movable member when the stop period of the subsequent transfer sheet transfer paper at the position exceeds a certain time. The travel length is defined as an image forming apparatus that controls the movable member to return to the interference position to stop the operation.
Claim 3 In the described invention, the control unit moves the transfer paper from the retracted position to the predetermined stop position immediately before the transfer paper stops at the retracted position and immediately starts to advance. Claim 1 to perform control Or 2 An image forming apparatus is characterized.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.
FIG. 1 is an explanatory diagram of an overall schematic configuration of a digital image forming apparatus to which the present invention is applied. A reading optical system A, a writing optical system B, an image forming unit C, a branching unit D, a paper discharge unit E, a double-sided path F, a feeding A schematic view centering on the paper portion G and the like is shown.
The image forming unit C includes a photoconductor 100, a charging unit 101, a developing unit 103, a transfer unit 104, a fixing unit 105, and the like. Image data read by the reading optical system A is temporarily captured by an image sensor such as a CCD. After the image is formed on 106, photoelectric conversion and A / D conversion are performed, and the image processing unit performs necessary image processing and then stores the image in the storage unit. The image data stored in the storage unit is read out by control from the control unit as necessary, and is output to the writing optical system B. The writing optical system B creates a laser beam based on the image data, and irradiates the laser beam onto the photoreceptor 100 that is uniformly charged in advance to form an electrostatic latent image. The electrostatic latent image is developed with toner supplied from the developing unit, and the toner image is transferred by the transfer unit 104 onto the transfer paper fed from the paper supply unit G and supplied to the transfer position by the registration rollers 33 and 34. The The transfer sheet that has received the transfer is conveyed to the fixing unit 105 and receives the toner image.
The branch portion D includes a paper discharge branch claw 3. When the paper discharge branch claw 3 rotates in the vertical direction about the axis, the transfer paper discharged from the fixing unit 105 is transferred to the paper discharge portion E and the double-side path F. It distributes and conveys to either. The paper discharge branch claw 3 is operated by a drive source such as a solenoid (not shown), and this drive source is operated based on a control signal from the control unit. The transfer paper guided downward by the paper discharge branch claw 3 is guided to the double-sided path F through the branch conveyance path II. The single-sided recorded transfer paper guided to the pre-reverse reverse path III in the double-side path F is reversed on the front and back by the reverse roller 13 and moved to the post-reverse path IV before being re-fed to the image forming unit C. As a result, after receiving image formation on the back surface, the paper is discharged to the paper discharge unit E via the paper discharge path I. The branch conveyance path II and the pre-reverse reverse path III constitute an intermediate tray 110.
[0009]
FIG. 2 is a diagram showing a detailed configuration centered on the double-sided path F of the image forming apparatus. At the front side of the paper discharge unit E, there is a paper discharge upper guide plate 1 for guiding the fixed transfer paper; A sheet discharge lower guide plate 2 that forms the branch conveyance path II, a sheet discharge branch claw 3 that switches the conveyance path of the fixed transfer paper to either the sheet discharge path I or the branch conveyance path II, and a sheet discharge lower guide plate A paper discharge intermediate guide plate 4 that forms a branch conveyance path II with the outer guide plate 2 and a reverse paper discharge route II ′ with the outer guide plate 42 is disposed. When the paper discharge branch claw 3 is at the position indicated by the dotted line, the fixed transfer paper is discharged straight to the paper discharge unit E, and when the paper discharge branch claw 3 is at the position indicated by the solid line, It is transported to the branch transport path II.
A double-sided entrance sensor 6 for detecting the passage of the rear end of the transfer sheet in the traveling direction is disposed on the guide plate 5 constituting the lower part of the branch conveyance path II, and an introduction roller 7 is rotatably disposed immediately downstream thereof. At the same time, the reversing branch claw 23 is rotatably arranged so as to face the introduction roller 7. The reversing branch claw 23 has a plurality of claw pieces arranged at a predetermined interval, and each claw piece can enter into a recess formed in the axial direction of the introduction roller 7. A pressure is applied toward the roller 7. For this reason, when the transfer paper enters between the introduction roller 7 and the reverse branch claw 23, the transfer paper is pressed against the peripheral surface of the introduction roller 7 by the pressure of the reverse branch claw 23 and is transported by generating a transport force. .
The paper discharge unit E has paper discharge rollers 40 and 41, and discharges the transfer paper on which image formation has been performed to a paper discharge tray outside the apparatus. In the reverse paper discharge path II ′, the transfer paper once sent to the branch conveyance path II and then redirected by the double-side branching claws 14 is received and then discharged from the paper discharge unit E, whereby the surface side of the transfer paper faces downward. Enables stacking in the specified page order. The intermediate tray 110 is parallel to the position immediately below the reverse feed reverse path III (switchback portion) that temporarily receives the single-sided recorded transfer paper that has been transported downward by the branch transport path II and the path III immediately before the reverse feed reverse path III. And a post-reversal path IV as a re-feed conveyance path. A switchback roller 8 that transports the transfer sheet between the large-diameter reversing roller 13 and the double-side driven roller 12 in contact with the upper surface of the transfer sheet that has been transported to the path III before reverse feed reverse, and the switchback roller A reversing drive roller 9 capable of rotating in the forward and reverse directions and transmitting a driving force in a nip with 8, a jogger fence 35 for performing a jogger operation for aligning the width direction position of the transfer paper during the switchback operation by the switchback roller 8, And a third conveyance detection sensor 38 provided in the vicinity of the reversing branch claw 23. The double-sided branching claw 14 is means for switching and transporting the transfer paper that has been switched back from the path III before reverse feed reverse to the reverse paper discharge path II ′ or the reverse path IV, and is indicated by a dotted line When rotating to the position, the transfer paper is guided to the post-reversal path IV along the outer peripheral surface of the large-diameter reversing roller 13.
[0010]
The post-reversal path IV is configured such that the transfer paper is fed in the middle of the vertical path (pre-registration path V) from the paper feeding unit G to the registration rollers 33 and 34, and is fed again to the transfer position (image forming unit). Has been. A plurality of conveying roller pairs 17, 18, 19, 20, and 21 and 22 are arranged at a required interval in the reverse path IV, and the conveying roller pairs 17, 18, 19, and 20 are not shown. The conveyance roller pair 21 and 22 are controlled to be independently driven and stopped by other clutches (not shown). Further, a first conveyance detection sensor 36 and a second conveyance detection sensor 37 are disposed in the reverse path IV, and the first conveyance detection sensor 36 is connected to the conveyance roller pairs 17, 18 and 19, 20. The second conveyance detection sensor 37 is disposed between the conveyance roller pairs 19, 20 and 21, 22.
The sheet feeding unit G is a unit that feeds and conveys an image-unformed transfer sheet to the image forming unit via the registration rollers 33 and 34. The sheet feeding unit G is provided in each sheet feeding tray and a sheet feeding tray 115 that stores the transfer sheet. Separating and conveying means 116.
A pre-registration path V extending from each separating and conveying means 116 toward the registration rollers 33 and 34 includes a refeed lower guide plate 24, a feed right guide plate 25, a feed upper left guide plate 26, a feed upper right guide plate 27, It has a relay driven roller 28, a relay driving roller 29, a pre-registration upper guide plate 30, a pre-registration lower guide plate 31, a pre-registration sensor 32, and the like. The rollers are configured so that they can be driven and stopped independently by a clutch, a stepping motor or the like (not shown).
A position where the post-inversion path IV joins the pre-registration path V is a joining portion 120.
In the present invention, the total route including the routes II, III, IV, and V is referred to as a double-sided route F.
[0011]
In FIG. 1, the transfer paper separated and fed from the paper feed tray 115 by the separation conveying means 116 and sent to the pre-registration path V passes through the nip portion of the relay driven roller 28 and the relay driving roller 29, and thereafter the image is transferred. It is conveyed to the photosensitive drum 100 by the registration rollers 33 and 34 in front of the forming unit.
After receiving the transfer of the toner image on the photosensitive drum 100, the transfer paper fixed by the fixing unit 105 is conveyed straight to the paper discharge roller pairs 40 and 41 when the front and back are not reversed.
When reverse paper discharge or double-sided copying is performed, the transfer paper is reversed by moving the paper discharge branch claw 3 to the reverse position, and the reverse reverse path constituting the intermediate tray 110 via the branch conveyance path II. Enter III.
The transfer paper conveyed to the path III before reverse feed reversal of the intermediate tray 110 is driven on both sides by the cooperation of the switchback roller 8 and the reverse drive roller 9 that descend based on the paper passing detection information from the double side entrance sensor 6. It is conveyed to the nip portion between the roller 12 and the reverse roller 13, and further to the reverse paper discharge path II ′ or the reverse path IV. A jogging operation is performed by a jogger fence 35 that regulates a direction perpendicular to the transport direction on the path III before reverse feed reversal. In other words, when the transfer paper enters the intermediate tray 110, the entrance of the transfer paper is detected by the double-sided entrance sensor 6 disposed upstream of the introduction roller 7, and the leading edge and the trailing edge of the transfer paper are detected. As a trigger, the downstream jogger fence 35 and the switchback roller 8 are operated.
[0012]
Thereafter, in the case of reverse paper discharge, the double-sided branching pawl 14 is moved to the solid line position so that the transfer paper is conveyed upward in the direction of the paper discharge roller pairs 40 and 41. Further, on the coaxial axis of the large-diameter reversing roller 13, a clutch (not shown) is provided which is not connected when energized but is coupled when deenergized. It is configured so that the drive is connected. Note that the reverse discharge is a mode for stacking the transfer paper discharged outside the apparatus on the discharge tray in the page order with the image surface facing downward.
At the time of double-sided copying, the transfer paper that has been switched back from the path III before reverse feed reverse is transported to the post-reverse path IV by the reverse roller 13 and the double-side branch claw 14, and each of the transport rollers 17, 18, 19 is further transferred. -It is conveyed to the junction part 120 by 20, 21 and 22. After conveyance to the junction, the sheet is fed to the image forming unit through registration rollers 33 and 34, undergoes image formation on the back surface, and is conveyed straight to the paper discharge rollers 40 and 41 as it is.
The image information formed by the laser beam irradiated on the photosensitive member is an original image originally read by a reading optical system (not shown). In a digital copying machine, the original image is converted into digital information as long as the capacity of the storage unit permits. In this embodiment, prior to the image forming operation, the image of the original is continuously read and stored in the storage unit within the capacity of the storage unit. For example, in the case of a single-sided original, one side is read continuously to store the required page image data. In the case of a double-sided original, the odd pages are read for the required pages, and the even pages of the same original are read for the required pages. Read and remember each one. After this document reading operation and storage operation, or in parallel, paper feeding and image forming operations for duplex copying are performed.
[0013]
Next, the flow of the transfer paper at the time of duplex copying using the non-stack duplex mechanism will be described with reference to FIG. FIG. 4 is a diagram for explaining the image forming order in the page order.
First, the transfer paper P on the paper feed tray 115 is conveyed one by one to the image forming unit C by the separating and conveying means 116 to form an image. In this case, for example, original images of pages 1, 3, and 5, which are odd-numbered pages, are sequentially formed on the surfaces of the first, second, and third transfer sheets P1, P2, and P3, respectively. Go (Figure 3 (a)). Subsequently, the three transfer sheets that have undergone image formation on one side sequentially enter the intermediate tray 110 and are switched back in the path III before reverse feed reverse, and then the double-side branching pawl 14, the transport driven roller 12, and the reverse roller 13 is conveyed to the post-reversal path IV, and the first transfer paper P1 is directly fed again to the image forming unit C to form an image on the back surface (FIG. 3B). As shown in FIG. 3 (c), the first transfer sheet P1 waits for image development of the second page of the original image with the leading end abutted against the pair of registration rollers 33, 34, and then the second page by the start of image formation. After the eye toner image is transferred and fixed on the back surface, it is discharged straight from the paper discharge 40 and 41 to the outside of the apparatus.
In the state of FIG. 3C, the transfer paper P2 on which the original image of the third page is formed on the surface is stopped in the reverse path IV, and the transfer paper P3 on which the original image of the fifth page is formed on the surface is reversed. Stop and wait on Route III before reversal. Further, the first transfer sheet P1 stops with its leading end abutting against the pair of registration rollers 33 and 34, and waits until the image of the second page is completely developed on the image processing unit and the image forming operation starts. To do. In the state shown in FIG. 3C, only one sheet of the transfer paper, for example, A4 size side can be stopped in the reverse path IV, and the transfer paper P3 is reversely fed from the outer periphery of the reverse roller 13. It extends to the previous route III and stops. As will be described later, the time required for image development is not uniform depending on the amount of image data and the like, and therefore the resist standby time of the transfer paper P1 is not uniform.
An electromagnetic clutch (not shown) is provided on the drive shaft of the reversing roller 13 capable of rotating in the forward and reverse directions. Since the electromagnetic clutch is energized while the reversing roller 13 is stopped or in standby, a driving force from the motor is applied to the reversing roller 13. It is configured not to be transmitted. Accordingly, the reversing roller 13 is not continuously driven in the state of FIG. 3C as in the prior art, but can be stopped, so that the load on the motor that drives the reversing roller 13 can be reduced. Further, by stopping the reversing roller 13, it is possible to eliminate the problem that the transfer paper P3 is rotated along with the reversing roller 13 and collides with the preceding transfer paper P2.
During the period from the state of FIG. 3C to the state of FIG. 3D, the first transfer sheet P1 that has undergone image formation on the back surface is discharged straight out of the apparatus, and the fourth transfer sheet P4. New paper feeding, refeeding of the second transfer paper P2, forward movement of the third transfer paper P3, and the like are sequentially performed.
[0014]
FIG. 3D shows the subsequent transfer sheet conveyance sequence. After the image of the seventh page of the original image is formed on the surface of the fourth transfer sheet P4, the transfer sheet waits in the reverse path IV. The second transfer sheet P2 is re-fed to the image forming unit C and undergoes image formation for the fourth page on the back side. Subsequently, feeding of the fifth transfer sheet P5 from the sheet feeding tray 115 is started, and after a resist standby period in which the leading ends of the pair of registration rollers 33 and 34 are abutted to wait for image development, the surface of the transfer sheet P5 is transferred. An image of the 9th page original image is formed, and the transfer paper P5 enters the double-sided path F. At this time, the transfer paper P4 preceding the transfer paper P5 has already entered the intermediate tray 110. After the 9th page of the original image is formed on the front surface of the transfer paper P5, the third transfer paper P3 waiting in the post-reversal path IV is conveyed to the image forming unit C for the backside image formation. Then, after waiting for registration, a document image of the sixth page is formed on the back side of the image. Thereafter, a new transfer sheet is fed from the sheet feeding unit G and a re-feed from the reverse path IV is alternately performed to form an image.
The transfer sheet conveyance and stop operations are performed by a control unit (not shown) based on detection information about the position of each transfer sheet detected by each conveyance detection sensor 36, 37, 38, 32. That is, in each of the transport and stop operations described above, the drive stop timing of the registration roller pair 33 and 34 and the relay roller pair 28 and 29 at the time of registration standby with the tip contacted with the registration roller pair 33 and 34 is the pre-registration sensor. This is performed based on the detection information of the transfer paper by 32. Further, the timing of stopping the transfer paper by stopping the driving of each of the conveyance roller pairs 17, 18, 19, 20 is performed based on the sheet passing detection information by the first conveyance detection sensor 36. The timing of stopping the transfer and stopping the transfer paper is performed based on the detection of paper passing by the second conveyance detection sensor 37.
[0015]
As apparent from FIGS. 3 and 4, in the image forming apparatus of the present invention, after the image formation on the first sheet front is performed, the image formation on the back of the first sheet is performed 2 Image formation is performed on the sheet table and the third sheet table. In other words, in this embodiment, image formation is performed on the surface of the transfer paper (for example, the first sheet) after image formation is performed on the back surface of the transfer paper. Assuming that the number of transfer sheets is N, N = 2 sheets (second sheet and third sheet). During the continuous double-sided image forming operation, at least three transfer sheets that have undergone image formation on the surface, that is, N + 1 sheets or more, are always present in the image transport path.
Here, N = 2 sheets is merely an example, and the present invention can be applied to an image forming apparatus of a type where N = 1 sheet or N = 3 sheets or more.
That is, for example, as shown in FIG. 3C, when one transfer sheet P1 that has undergone image formation on the surface is in a resist standby state, the subsequent second transfer sheet P2 is in the post-reversal path IV, Further, the succeeding third transfer sheet P3 is in the path III before reverse feed reverse. For this reason, it is possible to avoid a problem that the transfer sheets collide in the double-sided path when the transfer sheet P1 is stopped before the image is formed on the back surface.
[0016]
Next, FIG. 5 is a diagram for explaining a characteristic control method in the image forming apparatus of the present invention. The paper is re-feeded from the inside of the path IV after reversal, and the tip is brought into contact with the registration roller pair 33 and 34. The fourth transfer sheet (recorded on the front side) in the state of being in the standby state is in resist standby during the image development time of the original image corresponding to the back side, but the time required for image development is not uniform depending on the amount of image information, etc. It may take a long time. At this time, the subsequent surface-recorded fifth transfer sheet P5 is reversed by the conveyance roller pairs 17, 18, 19 and 20 whose driving is stopped based on the sheet passing detection information from the first conveyance detection sensor 36. It is stopped in the rear route IV. Further, the succeeding sixth surface-recorded transfer sheet P6 is moved to the illustrated position by the pair of rollers 8, 9, 12, and 13 whose driving is stopped based on the sheet passing detection information from the third conveyance detection sensor 38. Be stopped. At this time, since the leading portion of the sixth transfer sheet P6 is placed on the outer peripheral surface of the reversing roller 13, the conventional reversing roller 13 is rotated without being stopped completely by the control method in which the reversing roller 13 is always rotated. Along with the roller 13, it moves forward and collides with the rear end of the fifth transfer sheet P5, causing a problem that the colliding part of both transfer sheets is damaged. Therefore, in this embodiment, when the sixth transfer sheet P6 is stopped in such a state, the driving force transmission to the reversing roller 13 is temporarily interrupted using an electromagnetic clutch (not shown) and stopped. Let
[0017]
Next, as shown in FIG. 5, when the leading portion of the sixth transfer paper P <b> 6 is in a position where it interferes with the double-sided branching claw (movable member) 14, the transfer paper is damaged by contact with the double-sided branching claw 14. In order to prevent this, it is necessary to continue to retract the double-sided branching pawl 14 to the non-interference position as shown. In order to continue retracting the double-sided branching pawl 14 to the non-interference position, it is necessary to keep the solenoid that is the driving source turned on. In this case, since the solenoid is energized for a long time and overloaded, Durability tends to decrease. Therefore, in the present invention, as shown in FIG. 6, when the resist waiting time of the transfer paper P4 waiting for registration is prolonged according to the time required for image development, the position of the sixth transfer paper P6 is determined. 5 can be retracted from the position shown in FIG. 5 to the rear position shown in FIG. 6 and stopped to avoid interference with the double-sided branching claws 14, and the double-sided branching claws can be returned to the interference position indicated by the dotted line. When the double-sided branching pawl 14 is in the interference position, the drive solenoid is in the OFF state, so that the problem of deterioration in durability due to overload is eliminated. Note that when the sixth transfer sheet P6 is stopped at the interference position in FIG. 5 for a certain period of time and is controlled to move to the position in FIG. 6, the third conveyance detection sensor 38 counts the stop time. Is performed based on the sheet passing detection information for the sixth transfer sheet P6.
However, if the sixth transfer sheet P6 is started from the retracted position shown in FIG. 6 and is advanced to the post-reversal path IV, an interval from the preceding fifth transfer sheet P5 is increased. In the present invention, the development of the image corresponding to the back surface of the transfer paper P4 waiting for registration is completed and the registration roller pairs 33 and 34 start to drive. Before the transfer paper P4 starts the registration portion, the double-sided branching pawl 14 that has been lowered to the interference position indicated by the dotted line is retracted to the non-interference position indicated by the solid line, and then the switchback roller 8 is lowered. Thereafter, by rotating the reverse drive roller 9 and the reverse roller 13 by a predetermined amount in the normal conveying direction, the sixth transfer paper P6 is returned to the position shown in FIG. The switchback roller 8 is raised to the original position. After that, the registration of the fourth transfer sheet is started, and each of the conveying roller pairs 17, 18, 19, 20, and 21, 22 is driven to bring the fifth transfer sheet and the sixth transfer sheet to the required positions. Move forward. For this reason, when the sixth transfer sheet P6 resumes moving forward, there is no problem that productivity is lowered due to an excessive interval between the transfer sheet and the preceding transfer sheet. In addition, it is possible to prevent a collision caused by an excessively narrow interval with another transfer sheet positioned further rearward of the sixth transfer sheet P6.
Each of the above embodiments is merely an example, and the scope of application of the present invention is not limited to the above.
[0018]
【The invention's effect】
As described above, the present invention stores a plurality of original images obtained by reading with a scanner and the like, and can form an arbitrary original image stored on an arbitrary surface of an arbitrary transfer paper. In non-stack double-sided copying, the following transfer paper collides against the preceding transfer paper that is stopped in the double-sided path, resulting in damage or jamming of the transfer paper. It is possible to solve the problem that the durability of the driving source is lowered by operating the movable part and keeping it at the non-interference position in order to avoid the interference with the transfer paper stopped at a predetermined position in the path.
That is, in the first aspect of the invention, the transfer sheet stopped in the double-sided path is in a position where it interferes with other movable members, and it is necessary to keep the movable member retracted to the non-interference position in order to avoid interference. In some cases, when the stop time exceeds a certain time, at least one stop position of the stopped transfer paper is retracted to the non-interference position, thereby preventing the drive unit of the movable member from operating for a long time. Thus, the occurrence of damage to the movable member due to overload is prevented.
Claims 2 In this invention, the transfer paper that is stopped in the path before reverse feed reversal moves along with the reverse roller and collides with the transfer paper that stops in advance and breaks the edge or jam occurs. Can be prevented. That is, the above problem is solved by controlling the driving of the reversing roller, which has been controlled so as to always rotate, to stop while the transfer paper is stopped. In addition, when the transfer paper stopped in the double-sided path is in a position where it interferes with other movable members, and it is necessary to keep the movable member retracted to the non-interference position in order to avoid interference, the stop time When at least a certain period of time, the stop position of at least one of the stopped transfer papers is retracted to the non-interference position, thereby preventing the long-time operation of the drive unit of the movable member and causing the overload. Prevents damage to the movable member.
Claims 3 In the invention of claim 1, Or 2 Then, when the stop time of the transfer paper in the double-sided path becomes a certain time or more, the stop position of at least one stop of the transfer paper that has been stopped is retracted. Immediately after the stop is completed and immediately before the movement starts, the stop position is advanced, the transfer paper stop position is moved to the original stop position, and the movement is resumed, thereby improving the productivity of the image forming apparatus. In addition, it is possible to prevent a rear-end collision with another transfer sheet, and to prevent a decrease in the margin between sheets during conveyance.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus as an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a main configuration of the image forming apparatus of FIG.
FIG. 3 is a diagram showing a double-sided image forming procedure in the image forming apparatus of the present invention.
4 is a diagram showing an image forming procedure for the transfer paper in the example of FIG. 3;
FIG. 5 is a diagram for explaining a characteristic control method of the present invention.
FIG. 6 is a diagram for explaining another characteristic control method of the present invention.
FIG. 7 is a diagram showing a double-sided image forming procedure in a conventional image forming apparatus.
[Explanation of symbols]
A reading optical system, B writing optical system, C image forming unit, D branching unit, E paper discharging unit, F double-sided path, G paper feeding unit, I paper discharging path, II branching conveyance path, II 'reverse paper discharging path, III Path before reverse feed, IV Path after reverse, V Pre-registration path, 3 Discharge branch claw, 5 Guide plate, 6 Double-side entrance sensor, 7 Introduction roller, 8 Switchback roller, 9 Reverse drive aura, 12 Double-side driven roller , 13 Reverse roller, 14 Double-branch claw, 17, 18, 19, 20, 21, 22 Conveying roller pair, 28/29 Relay roller pair, 32 Pre-registration sensor, 33/34 Registration roller pair, 36 First conveyance detection Sensor 37 37 second conveyance detection sensor 40/41 discharge roller pair 100 photoconductor 101 charging unit 103 developing unit 104 transfer unit 105 fixing unit 106 image sensor 110 double-sided tray 115 paper feed tray B, 116 Separating and conveying means.

Claims (3)

A double-sided path capable of reversing the transfer paper on which the image is formed on the surface by the image forming unit and refeeding the transfer paper to the image forming unit and stopping at least one transfer paper, and the double-sided path An image forming apparatus comprising:
The control unit operates a movable member provided on the double-sided path to hold it at a non-interfering position that does not interfere with the transfer paper on the double-sided path, and a period during which the movable member is held at the non-interfering position is constant. An image forming apparatus, wherein when the time is exceeded, the transfer sheet is moved to a retracted position where it does not interfere with the movable member, and the movable member is returned to the interference position to stop the operation. An image forming unit for forming an image on the transfer paper, and the transfer paper on which the image is formed on the surface by the image forming unit are turned upside down and re-fed to the image forming unit, and at least one transfer paper is stopped and waited In an image forming apparatus having a double-sided path that can be controlled and a control unit that controls the double-sided path,
The double-sided path includes a branch conveyance path for introducing transfer paper having undergone image formation on the surface, a path before reverse reversal for receiving and reversely feeding the transfer paper introduced from the branch conveyance path, and the reverse reversal. A reversing roller that reverses the front and back of the transfer paper that has been fed back from the previous path, and a reversing path that re-feeds the transfer paper that has been reversed by the reversing roller and then re-feeds the image forming unit, A pre-registration path extending a predetermined distance upstream from a pair of registration rollers constituting the image forming unit,
When the preceding transfer sheet is in a registration waiting state in which the leading end is in contact with the registration roller pair, the rotation of the reversing roller is stopped to prevent the transfer sheets from colliding with each other in the double-sided path. In order to prevent the movable member on the double-sided path from interfering with the succeeding transfer paper stopped at a predetermined position in the path, the movable member is operated and held at the non-interference position. The control unit moves the stop position of the subsequent transfer paper at the position to a retreat position that does not interfere with the movable member when the stop period of the subsequent transfer paper transfer paper exceeds a certain time. An image forming apparatus that controls to return the member to the interference position and stop the operation. The control unit performs control to move the transfer sheet from the retracted position to the predetermined stop position immediately before the transfer sheet is stopped at the retracted position and immediately starts to advance. the image forming apparatus according to claim 1 or 2, characterized in.

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