JP2006154766A - Double-sided paper feeding apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a double-sided paper feeding apparatus provided with constitution improving a transfer paper detecting condition in which interference sound or a jam is generated to an appropriate condition by surely restoring a clutch to its home position when a one-ration clutch is used. <P>SOLUTION: In a double-sided paper feeding route 9 and a manual paper feeding route 19, an operation panel 301 having detection means 16, 18 capable of detecting the existence of transfer paper and a start switch is arranged on the input side and a control part 300 to which a driving source 17 and a home position maintenance means 65 for the one-rotation clutch are connected is arranged on the output side. The control part 300 stops the one-rotation clutch 63 after rotating the clutch 63 at least one rotation without interrupting the driving source when a jam is generated in the manual paper feeding route, and at the time of redrive after solving the jam, rotates the one-rotation clutch 63 by one rotation in the manual feeding direction and then permits rotational drive in the reverse direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a double-sided sheet feeding device that can transfer a transfer sheet that has passed through a fixing device after an image is formed on one side of the transfer sheet to a double-sided sheet re-feeding path to form an image on both sides of the transfer sheet. And an image forming apparatus.

  In recent years, in image forming apparatuses such as printers and copying machines, the importance of double-sided image formation on transfer paper has been increasing from the viewpoint of saving paper resources. On the other hand, with an increase in the speed of image forming apparatuses, there is also a demand for improvement in productivity during double-sided image formation, that is, the number of double-sided images that can be formed per unit time. In order to meet such needs, an image forming apparatus capable of improving the productivity of double-sided image formation has been proposed (for example, Patent Document 1).

  The image forming apparatus disclosed in Patent Document 1 has a double-sided paper re-feeding path for switching back an image-formed transfer sheet on one side and feeding it again to form an image on the other side. When transferring the transfer paper to the double-sided paper re-feeding path, the conveyance speed is increased and the time for passing through the double-sided paper-feeding path is shortened, thereby improving the productivity of double-sided image formation. . In addition, it is intended to prevent the transfer paper from wrinkling or image rubbing.

  On the other hand, in an image forming apparatus having a configuration capable of duplex copying, there is also a demand to enable image formation on non-standard transfer paper. As a configuration for this purpose, manual feeding is performed separately from the existing paper feed mechanism. A configuration including a paper feed mechanism has been proposed (for example, Patent Document 2).

JP 2003-182907 A Japanese Patent Publication No. 2003-215874

  However, in the image forming apparatus described above, all of the plurality of transport rollers provided in the double-sided sheet re-feeding path are simultaneously driven and cannot be driven individually. For this reason, when the drive of the transport roller in the refeed path is stopped and the transfer paper in the refeed path is stopped, the transfer sheet that is transported next cannot be transported into the refeed path. . In this case, the distance between the trailing edge of the preceding transfer sheet and the leading edge of the succeeding transfer sheet that is transported next, that is, the gap between the sheets may become larger than necessary.

  The double-sided paper re-feed path is set to a minimum length from the viewpoint of downsizing the image forming apparatus. Therefore, if the sheet interval is wide, the refeed path cannot be used effectively, the number of transfer sheets that can be conveyed in the refeed path is reduced, and the productivity is insufficient. As one means for solving this problem, it is also conceivable to provide a drive source for each pair of transport rollers provided in the double-sided refeed path and to control the pair of transport rollers freely so as to close the gap between sheets. However, this means causes a cost problem because a drive source is provided for each pair of transport rollers.

  On the other hand, in a configuration in which a manual paper feed path is provided separately from the double-sided paper refeed path, it is conceivable to provide a driving device and a transfer paper transport member driven by this in each paper feed path. The complexity of the configuration is inevitable. Therefore, it is conceivable to use a pair of rollers of a driving roller and a driven roller as a transfer paper conveying member toward the registration rollers, and to transfer and convey the transfer paper. In the case of transporting the transfer paper, the following problem newly occurs.

  That is, the conveyance force in both paper feed paths is not uniform, and it is difficult to control this conveyance force. In other words, it is desirable that the roller, which is a conveying member used in the double-sided refeed path, does not increase the conveying force (clamping force) in order to avoid rubbing the image carried on one side. On the other hand, in the manual paper feed path, separation of the manually fed transfer paper is performed because friction separation is performed using the difference in frictional force between the transfer paper and the feeding roller provided in the manual paper feed path and the transfer paper. The conveying force (clamping force) must be large. As described above, it is difficult to distinguish the difference in conveying force in both paper feeding paths by a pair of rollers.

  In addition, the double-sided paper re-feeding path is often provided with a configuration for detecting the transfer paper introduced into this path, but as described above, the roller that is a conveying member in both paper feeding paths. When switching the rotation direction of the paper, for example, when a jam (paper jam) occurs in the double-sided refeed path, the direction opposite to the transport direction in the double-sided refeed path without detecting the jammed transfer paper If the roller is rotated during manual feed with `` '' set, the jammed transfer paper will move in the opposite direction, resulting in collision with the detection means and damage. In some cases, the transfer paper is caught in the joint of the conveyance guide portion used in the double-sided paper re-feeding path, and the transfer paper becomes accordion-like. In particular, it may be possible to slightly rotate the roller in order to determine whether or not the jammed transfer paper remains at the time of starting or the like, but in this case, there is a problem in the reverse transfer of the transfer paper described above. As described above, it is difficult to determine the rotation direction of the roller in advance.

  The above-described problems relating to jams are caused by the fact that in any case, the transfer paper causing the jam cannot be detected. Therefore, it is conceivable to increase the detection position of the transfer paper in the double-sided re-feeding path, that is, the detection means. The goal cannot be achieved.

  From the viewpoint of downsizing the apparatus, it is desired to reduce the space for the manual feed path. Therefore, a one-rotation clutch using an intermittent gear that is partially free of teeth in the circumferential direction is used instead of an electromagnetic clutch system that tends to become large because of the intermittent (one-by-one) feeding operation used in the manual feed path. Can be considered.

However, when this configuration is used, there are the following problems.
In other words, the missing gear has a home position in which the missing tooth portion faces the transmission gear between the gear and the transmission gear that can mesh with the gear, and this home position is, for example, missing using a biasing member. By energizing the toothed gear in one direction, the corresponding relationship with the transmission gear is maintained in a predetermined state, and an actuator such as a solenoid is provided in the missing gear to stop the missing gear at this position. It is designed to be maintained by engaging.

  For this reason, the transmission gear rotates in the manual feed direction, which is the opposite direction to the double-sided feed, in the state where it is not in the home position, in other words, the toothless gear is not locked, or immediately after assembly or maintenance. If it is driven to rotate in a state where the missing gear is not locked due to misalignment or the like after the transmission, the transmission gear rotates idle at the missing tooth portion, but corresponds to the tooth adjacent to the missing tooth portion. And the urging member for maintaining the home-position state of the tooth-missing gear is maintained in the direction of meshing with the transmission gear. The teeth adjacent to this part are in a state of being engaged with each other while alternately reciprocating meshing and disengagement. When the tooth adjacent to the missing tooth part corresponds to the tooth of the transmission gear, it collides with the biasing force of the biasing member. Te, so that it generates the interference sound.

  On the other hand, when manually feeding, when a jam occurs, the drive source is often stopped to minimize damage due to the jam. However, in such a case, as in the case described above, if the missing tooth gear is not returned to the home position, an interference sound is generated.

  As described above, when the 1-rotation clutch is used in order to save the space when the manual paper feed mechanism is provided, the 1-rotation clutch is not returned to the home position, and therefore, in an environment of interference noise. There is a risk of undesirable problems.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a plurality of transfer paper sheets on which images are formed on both sides without providing a drive source for each pair of transport rollers, in view of the problems in the conventional double-sided paper feeding device and the image forming apparatus using the same. A double-sided sheet feeding device capable of improving the productivity of double-sided image formation by configuring a drive mechanism for the refeed path so that the gap does not spread more than necessary and performing optimal control regarding transfer paper transfer The present invention provides an image forming apparatus to be used.

  Another object of the present invention is to optimize the detection conditions of transfer paper that generates interference noise or jamming by reliably returning to its home position when a one-rotation clutch is used. An object of the present invention is to provide a double-sided sheet feeding device and an image forming apparatus having a configuration capable of performing the above.

  In order to achieve the above object, the invention according to claim 1 is provided on the double-sided paper re-feeding path for feeding again the transfer paper on which the image is formed on one side to the image forming unit, and the double-sided paper re-feeding path. In a double-sided sheet feeder having a plurality of transport rollers driven by the same drive source and a transmission means for transmitting a driving force from the drive source to the transport rollers, a transport direction of the plurality of transport rollers The transport roller on the re-downstream side is connected to the drive source via a transmission means, and the transport roller on the most downstream side can be rotated in both forward and reverse directions by the drive source and can be idled with respect to the drive source. It is characterized by being.

  According to a second aspect of the present invention, the transmission means has a cavity, and the transmission means and the most downstream conveyance roller include the cavity and a pin provided on a shaft that supports the most downstream conveyance roller. It is characterized by being connected via.

  The invention of claim 3 is characterized in that the cavity has a sector shape having end faces with which the pins abut on both sides thereof.

  The invention according to claim 4 is characterized in that a transfer sheet from a manual sheet feeding path provided close to the double-sided sheet feeding path is introduced into the most downstream side conveyance roller.

  The invention according to claim 5 is characterized in that the transport roller on the most downstream side is also used as a drive roller for nipping and transporting the transfer paper from the manual paper feed path.

  According to a sixth aspect of the present invention, driven rollers are disposed on the most downstream side of the conveying roller so as to face each other, and one of the driven rollers is used for conveying the transfer paper to the double-sided sheet re-feed path. The other driven roller is provided for transferring the transfer paper in the manual paper feed path.

  According to a seventh aspect of the present invention, the transmission means for transmitting the driving force from the driving source to the conveying roller including the roller on the most downstream side corresponds to the both surfaces according to the forward and reverse rotations of the driving source. Transfer paper transfer through the re-feed path or transfer paper feed from the manual feed path can be selected, and the rotation direction of the drive source is set in the direction to transfer the transfer paper from the manual feed path And a one-way clutch for maintaining at least one of the conveying rollers in a non-rotating state when the roller is moved.

  According to an eighth aspect of the present invention, a feeding roller capable of feeding the transfer paper is provided on the transfer paper introduction side in the manual paper feeding path, and the feeding roller includes the most downstream roller. The driving force is intermittently transmitted via a one-rotation clutch using a toothless gear between the conveying roller and a transmission unit that transmits the driving force from the driving source. .

  According to a ninth aspect of the present invention, in the driving force transmission path for the one-rotation clutch, the driving source blocks the rotational driving force to the feeding roller when the driving source rotates in the transfer sheet conveyance direction in the double-sided refeed path. A one-way clutch capable of being arranged is arranged.

  According to a tenth aspect of the present invention, an image forming apparatus includes the double-sided sheet feeding device according to any one of the first to ninth aspects.

  According to the eleventh aspect of the present invention, an operation panel having detection means and a start switch capable of detecting the presence or absence of transfer paper in the double-sided refeed path and manual feed path is provided on the input side, and the drive source is provided on the output side. And a control unit to which the home position maintaining means of the one-rotation clutch is connected, and the control unit moves the transport roller on the most downstream side in the manual transfer sheet conveyance direction before manual sheet feeding during manual sheet feeding. It is characterized by rotating a predetermined amount.

  According to a twelfth aspect of the present invention, when a jam occurs in the manual sheet feeding path, the front control unit stops the driving source after the at least one rotation without stopping the driving source immediately.

  According to a thirteenth aspect of the present invention, in the control unit, when the drive source after the jam is removed is redriven, at least the transfer paper can be fed from the manual paper feed path. After the one-rotation clutch is rotated once, it is driven in the direction opposite to the above direction.

  According to a fourteenth aspect of the present invention, when the control unit drives the drive source at start-up, the control unit causes at least one rotation of the one-rotation clutch in a direction in which transfer paper can be fed from the manual paper feed path. Then, it is driven in a direction opposite to the direction.

  According to a fifteenth aspect of the present invention, the control unit issues a warning to the operation panel when the presence of the transfer paper is detected by the detecting means during the re-driving of the driving source or the driving at the start-up. Features.

  According to a sixteenth aspect of the present invention, in the control unit, when a double-sided paper feed command is input from the operation panel, the drive source is at least in a direction in which transfer paper can be fed from the manual paper feed path. The one-rotation clutch is rotated once.

  According to the first to third aspects of the present invention, even when the driving sources are stopped in the plurality of conveying rollers driven by the same driving source, only the conveying roller on the most downstream side in the conveying direction is idled, and the rollers on the downstream side It is possible to carry the transfer paper along with the drive. As a result, a drive mechanism for the refeed path is configured so that the gap between the plurality of transfer sheets on which images are formed on both sides is not unnecessarily widened without providing a drive source for each pair of transport rollers, and optimal control is performed. By doing so, productivity of double-sided image formation can be improved.

  According to the fourth aspect of the present invention, not only a double-sided paper refeed path is provided, but also a manual paper feed path is provided separately so that even non-standard transfer paper can be used as an object for double-sided copying. This makes it possible to expand the application of transfer paper capable of duplex copying.

  According to the fifth and sixth aspects of the present invention, not only can the configuration be simplified by providing the drive roller common to the double-sided refeeding path and the manual sheet feeding path, but also the double-sided feeding path is provided on both sides of the driving roller. By providing driven rollers on the sheet feeding path side and the manual sheet feeding path side, it is possible to set the nipping and conveying force corresponding to each sheet feeding path. In other words, the driving force is common on the double-sided paper feed path side to have a clamping force that can prevent sliding of the image carried on one side of the transfer paper, and the manual feeding path side has a teaching force that can obtain the frictional force necessary for separation. It is possible to set each independently between the rollers.

  According to the seventh aspect of the present invention, when the transfer sheet is transported by selecting either the double-sided refeeding path or the manual sheet feeding path, the sheet is transported to the duplex sheet feeding path when transporting from the manual sheet feeding path. Since the state is interrupted, it is possible to prevent the transfer paper from being reversely fed and damaging the transfer paper detection means when the transfer paper remains in the double-sided refeed path. It becomes.

  According to the eighth aspect of the present invention, when a feeding roller that feeds transfer paper from the manual feeding path is used, a one-rotation clutch that uses a toothless gear is provided in the drive transmission path for the feeding roller. Since the drive force is transmitted intermittently, a large-sized electromagnetic clutch or the like is not required in the transmission path. Is possible.

  According to the ninth aspect of the present invention, the driving force to the feeding roller is interrupted when the transfer path using the one-rotation clutch is rotated in the direction in which the transfer sheet can be conveyed to the driving source surface feeding path. Since the one-way clutch is provided, when the drive source rotates in a direction in which the transfer sheet can be conveyed to the double-sided sheet re-feeding path, the missing tooth portion of the one-rotation clutch and the adjacent teeth face each other. By avoiding collision between the meshing members, that is, so-called gear teeth, it is possible to prevent the generation of interference sound, which is a collision sound.

  According to the tenth aspect of the present invention, the double-sided paper refeeding path can be provided with a manual paper feeding path without causing an increase in size, and transfer can be performed while preventing reverse transfer of the transfer paper through the double-sided paper refeeding path. It is possible to obtain an image forming apparatus capable of preventing paper damage.

  According to the eleventh aspect of the invention, the control unit rotates the transport roller on the most downstream side by a predetermined amount in the direction in which the transfer paper can be transported through the manual paper feed path during manual paper feed. It is possible to prevent play delays due to play by eliminating play, ie, play, at the transmission section of the downstream transport roller.

  According to the twelfth aspect of the present invention, when the jam of the transfer paper occurs in the control unit, the driving unit is not immediately cut off, but is stopped after at least one rotation of the one-rotation clutch. Thus, the home position of the one-rotation clutch can be set, and the operation of the one-rotation clutch from the home position can be enabled.

  According to the thirteenth aspect of the invention, when the jam is resolved and the drive source is re-driven by the control unit, the one-turn clutch is rotated at least once in the manual feed direction, and this direction is opposite to this direction. That is, by driving the drive source in the double-sided paper feeding direction, the one-rotation clutch can be positioned at the home position in the rotation process. As a result, when the drive source rotates in the double-sided paper feeding direction that is opposite to the manual paper feeding direction, it is possible to detect the presence / absence of the transfer paper that is moved by the operation of the conveyance roller that is linked to this rotation. It is possible to reliably transfer the transfer paper which is located between the detecting means and which could not be detected to the position of the detecting means and confirm whether or not the transfer paper exists on the transport path.

  According to the fourteenth aspect of the invention, since the drive source is controlled so that at least one rotation of the clutch rotates once in the manual feed direction at the time of starting, positioning is performed at the home position even when the one rotation clutch is not at the home position. be able to. As a result, the movement of the feeding roller on the side of the manual feeding path maintained at the home position can be stopped, so that the transfer paper that moves is moved by the operation of the conveying roller in the double-sided refeed path. Thus, it is possible to detect the remaining state of the transfer paper in the double-sided refeed path.

  According to the fifteenth aspect of the present invention, the control unit can determine the remaining state of the transfer paper in the surface re-feeding path and provide an alarm when it remains, so that the occurrence of a jam or the like can be prevented in advance. Is possible.

  According to the sixteenth aspect of the present invention, when the paper feed mode is executed in response to the double-sided paper feed command, the one-turn clutch rotates the drive source in the manual paper feed direction. Even when the one-rotation clutch is not at the home position, it can be returned to the home position during the rotation process, and this state can be maintained. Thus, it is possible to prevent the rotation of the transport roller from being disturbed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of an image forming apparatus showing an embodiment of the present invention. The image forming apparatus shown in the figure, like a normal image forming apparatus, is a paper feeding unit 1 that feeds transfer sheets one by one, an image transfer unit 2 that forms an image on the fed transfer paper, and an image forming unit. And a fixing unit 3 that fixes the image formed by the unit to the transfer paper.

  Downstream of the fixing unit 3 in the conveyance direction, there are a paper discharge path 23 for discharging the transfer paper to a paper discharge unit outside the apparatus, and a double-sided paper refeed path 9 for double-sided image formation. A branching claw 4 for branching the transfer sheet conveyed from the image transfer unit 2 to one of the paths is provided at the junction with the double-sided sheet refeeding path 9. The double-sided paper refeed path 9 includes a reverse roller 6 that reverses the transfer paper conveyance direction and a switchback path 5 that is a conveyance path for switching back the transfer paper. A sensor 8 is provided. When the reversing sensor 8 detects the trailing edge of the transfer paper moving on the switchback path 5, the reversing roller 6 transports the transfer paper to the image transfer unit 2 again. Is reversed.

  On the double-sided paper re-feeding path 9 downstream of the reversing roller 6, three conveyance roller pairs of an entrance roller 10, an intermediate roller 11, and an exit roller 12 are provided in order from the entrance side of the sheet feeding path. Thus, the transfer sheet sent to the double-sided sheet re-feeding path 9 is conveyed to the image forming unit 2. An inlet sensor 18 for detecting the leading edge of the transfer paper is provided in the vicinity of the upstream side of the inlet roller 10. An exit sensor 16 for detecting the leading edge of the transfer paper is also provided in the vicinity of the downstream side of the exit roller 12. Details of the inlet sensor 18 and the outlet sensor 16 will be described in the image forming operation described later.

  The exit roller 12 also serves as a transport roller for transporting transfer paper fed from the manual paper feed tray 22 provided on the side surface of the image forming apparatus toward the manual paper feed path 23, and from the manual paper feed tray 22. During manual paper feeding, the manually fed transfer paper is conveyed to the image transfer unit 2 by rotating in the opposite direction to that during double-sided image formation.

  The exit roller 12 is in contact with a pair of driven rollers arranged in a state of being opposed to each other, and one of these driven rollers is used for conveying the transfer paper to the double-sided sheet re-feeding path 9. The other of the driven rollers functions to convey transfer paper from the manual paper feed tray 22 toward the manual paper feed path 19.

  For this reason, the exit roller 12 corresponds to a drive roller for these driven rollers, and each driven roller rotates in opposite directions. It can be used as a transfer paper nipping and conveying member. Accordingly, unlike the case where the transfer paper nipping and conveying members are individually provided in different paper feed paths, the transfer paper can be shared, and the number of members used for nipping and conveying the transfer paper can be reduced.

  FIG. 2 shows a driving mechanism for each conveying roller on the reversing roller 6 and the double-sided sheet re-feeding path 9. The reversing roller 6 is driven by a reversing motor 7 provided on the back side of the apparatus. The entrance roller 10, the intermediate roller 11, and the exit roller 12 are connected to the double-sided motor 17 via timing belts 51 and 52 and a pulley, and are driven by the common double-sided motor 17. That is, the three roller pairs of the entrance roller 10, the intermediate roller 11, and the exit roller 12 are always driven simultaneously.

  However, the drive mechanism of the exit roller 12 is partially different from the other two rollers 10 and 11. As shown in FIG. 3, the pulley 15 that connects the exit roller 12 and the double-sided motor 17 via the timing belt 52 has a fan-shaped cavity having a central angle of about 240 degrees. The pulley 15 and the shaft 13 that supports the outlet roller 12 are connected to each other by a pin 14 provided in a radial direction on the shaft 13 having a predetermined amount of buffer in the cavity. That is, as shown in FIG. 4, since there is a buffer having a predetermined angular range in the rotational direction between the outlet roller 12 and the pulley 15, the driving force of the double-sided motor 17 is determined by the pin 14 as shown in FIG. As shown in FIG. 4 (c), it is transmitted to the pulley 15 only when it is in contact with both end faces of the cavity, and as shown in FIG. The pulley 15 idles by a predetermined angle, and during that time, the driving force of the double-sided motor 17 is not transmitted to the outlet roller 12. In this way, the exit roller 12 can freely rotate between the cavities of the buffer.

  Next, control of the so-called three-sheet interleaf method will be described with reference to FIG.

  The first transfer paper fed from the paper feed unit 1 is first formed on the surface thereof in the image transfer unit 2, and the image is fixed by the fixing unit 3. Guided to the refeed path 9. The transfer paper guided to the double-sided paper re-feed path 9 is conveyed to the switchback path 5 and when the rear end of the transfer paper is detected by the reverse sensor 8 (FIG. 5A), the reverse roller 6 It reverses, the conveyance direction is reversed to that before, and it is conveyed in the direction of the entrance roller 10 (FIG. 5B).

  The first transfer paper is conveyed to the position where the exit sensor 16 detects the leading edge of the first transfer paper (FIG. 5C), and when detected, the double-side motor 17 is temporarily stopped to form an image on the back surface. Therefore, it waits at that position until the conveyance timing (FIG. 5D). Since the conveyance of the transfer paper is stopped by stopping the double-sided motor 17, all of the entrance roller 10, the intermediate roller 11, and the exit roller 12 are stopped. Hereinafter, the stop position of the transfer paper is referred to as an exit stop position. This exit stop position is a position where the rear end of the transfer sheet having the longest length in the transport direction among the transfer sheets that perform three-sheet interleaf passes through the entrance roller 10, that is, near the downstream side of the entrance roller 10. Like that.

  In this embodiment, the outlet sensor 16 is arranged in consideration of this point. However, when the layout is restricted, the outlet sensor 16 is arranged on the upstream side of the arrangement position according to this embodiment, and the sensor 16 is disposed on the transfer paper. The transfer sheet may be stopped at a predetermined exit stop position by stopping after a predetermined time from detecting the leading edge.

  The second transfer sheet is conveyed to the image transfer unit 2 immediately after the image is formed on the surface of the first transfer sheet, and after the image is formed on the surface as in the first sheet, the double-sided refeed path 9 and is temporarily stopped when the inlet sensor 18 detects its tip (FIG. 5 (e)). Hereinafter, this stop position is referred to as an inlet stop position.

  The entrance stop position is in the vicinity of the upstream side of the entrance roller 10. The second transfer sheet is conveyed by the reversing roller 6 up to the entrance stop position, and when stopped at the entrance stop position, the rear end is sandwiched between the reversing rollers 6 and the rear end remains in the switchback path 5. Yes. The first transfer paper and the second transfer paper that are stopped in the vicinity of the downstream side of the entrance roller 10 are stopped with the exit roller 10 interposed therebetween, and thus the position of the transfer paper is controlled. Thus, the interval between the two transfer sheets can be shortened. In the present embodiment, the distance between the two transfer sheets is controlled to about 15 mm in the case of the maximum size (for example, A4 size width) capable of performing three-sheet interleaf.

The third transfer paper is transported to the image transfer unit 2 immediately after the image is formed on the surface of the second transfer paper, and after the image is formed on the surface, like the second transfer paper, both sides are fed again. It is conveyed to the entrance stop position in the paper path 9. Here, the first and second transfer sheets are resumed before the third transfer sheet reaches the switchback path 5. The conveyance resumption timing is controlled so that the trailing edge of the second transfer sheet passes through the switchback path 5 before the third transfer sheet reaches the switchback path 5 (FIG. 5 (f)). Is done.
The first and second transfer sheets whose conveyance has been resumed are conveyed by an entrance roller 10, an intermediate roller 11, and an exit roller 12, and the first transfer sheet is an image following the third transfer sheet. It is sent to the transfer unit 2 and an image is formed on the back surface thereof.

  Here, the entrance roller 10, the intermediate roller 11, and the exit roller 12 are controlled to stop when the second transfer sheet reaches the exit stop position (FIG. 5 (g)). However, when the second sheet reaches the exit stop position, the leading edge of the first transfer sheet is sandwiched between the registration rollers 20 and the trailing edge is sandwiched between the outlet rollers 12 and the trailing edge in the refeed path 9. Will remain. The registration roller 20 is driven by a roller (not shown) different from the double-sided motor 17, and conveys the first transfer sheet to the image transfer unit 2 even after the double-sided motor 17 stops driving. Here, if the exit roller 12 is a normal drive mechanism, the exit roller 12 cannot rotate due to the stop of the double-sided motor 17, but receives the force conveyed by the registration roller 20. May cause breakage.

  As described above, the outlet roller 12 in this embodiment is provided with the pulley 15 having a fan-shaped cavity as a mechanism for transmitting the driving force of the double-sided motor 17, thereby providing a buffer for the rotation direction. In a state where the driving force by the double-sided motor 17 is transmitted, as shown in FIG. 4A, the pulley 15, the shaft 13 that supports the outlet roller, and the pin 14 that is positioned in the cavity include the pin 14 and the pulley 15. The end face of the cavity is in contact, and the driving force of the double-sided motor 17 is transmitted from the pulley 15 to the outlet roller 12 through the pin 14 and the shaft 13, and the outlet roller 12 is rotated counterclockwise in FIG. Rotate.

  When the double-sided motor 17 stops, the pulley 15 also stops, but the shaft 13 and the pin 14 have a buffer that rotates counterclockwise as shown in FIG. Therefore, even if only the registration roller 20 rotates in a state where the transfer paper remains between the registration roller 20 as the downstream roller and the exit roller 12 as described above (FIG. 5G), The exit roller 12 can be rotated with the rotation and can convey the transfer paper. In the present embodiment, the required amount of idling is set from the trailing end length of the transfer paper remaining downstream of the exit roller 12 when stopped, and the central angle of the cavity provided in the pulley 15 is set to about 240 degrees. Needless to say, this angle can be appropriately set according to the remaining length of the transfer paper.

  By adopting such a driving mechanism, even if the driving source of the conveying roller in the double-sided sheet re-feeding path 9 is the same, one of the plural conveying rollers can be rotated independently. As a result, the double-sided motor 17 can be stopped so that the rear end of the second transfer sheet is in the vicinity of the downstream side of the entrance roller 10 in the same manner as the first sheet, and the vicinity of the upstream side of the second transfer sheet and the entrance roller 10. It is possible to shorten the sheet interval 1 with the third transfer sheet that stops at the entrance stop position (FIG. 5 (i)).

  After image formation on the surface of the third transfer sheet, the first back surface, the fourth surface, the second back surface, the fifth surface, the third back surface, The paper is conveyed alternately from the double-sided paper refeed path 9 to the image transfer unit 2. The transfer paper on which images are formed on both the front and back sides is guided to the paper discharge path 23 and discharged outside the apparatus. If the total number of jobs is N, the two-sided sheet re-feed path 9 continuously conveys the N-1st sheet, the Nth sheet, and the registration rollers 20 to complete the job. Until the end of the job, the movement of the transfer sheet is controlled as described above, and double-sided image formation is performed. FIG. 6 is a schematic diagram showing an image forming order when double-sided images are formed.

  The control is not performed as in the present embodiment, but it is not stopped when the leading edge of the second transfer paper reaches the exit stop position (FIG. 5 (g)) and after the first transfer paper. When the double-sided motor 17 is rotated until the end completely passes through the exit roller 12, the distance between the rear end of the second transfer sheet and the entrance roller 10 becomes longer. That is, the position of the second transfer sheet is closer to the registration roller 20, and the distance between the second and third transfer sheets is longer. In this case, when an image is formed on the back surface of the second sheet, the time until the leading edge of the second transfer sheet reaches the registration roller 20 is shortened, and the time required for conveyance by the double-sided roller 17 is shortened. Become. As a result, the transfer time of the third transfer sheet is also shortened, and the drive of the double-sided roller 17, that is, the transfer of the entrance roller 10 and the intermediate roller 11 is stopped before it is sufficiently transported into the double-sided paper refeed path 9. As a result, the rear end of the third transfer sheet remains in the switchback path 5 and may interfere with the front end of the fourth transfer sheet conveyed to the switchback path 5. .

  Instead of such a driving mechanism for the outlet roller 12, it is possible to idle only the outlet roller 12 by a one-way clutch or the like. However, when the exit roller 12 is also used as a manual feed conveyance roller as in this embodiment, a one-way clutch that can be driven only in one direction cannot be employed.

In this embodiment, when paper is fed from the manual paper feed tray 22, the exit roller 12, which is also used as a conveyance roller for manual paper feed, rotates in the opposite direction to that for duplex copying. At the end of the double-sided copying job, the shaft 13 and the pin 14 are in the position shown in FIG. For this reason, when the reverse rotation is attempted from that position, the pulley 15 is idled, and the transmission of the driving force of the double-sided motor 17 to the outlet roller 12 is delayed by the amount of the hollow buffer. In addition, if the exit roller 12 can idle during manual feeding, if the separation roller causes a variation in the leading edge of the transfer paper, the exit roller 12 idles and the transfer paper is conveyed in a dispersed state, resulting in poor conveyance. May also occur. In order to prevent this, the double-sided motor 17 is rotated in advance by the length that the exit roller 12 can idle, and then the manual feed roller 24 is rotated to prevent the transmission of the driving force from being delayed. it can. Further, even if the leading edge of the transfer paper fed from the manual paper feed tray 22 varies, the stopped exit roller 12 does not idle, so that the transfer paper is not conveyed in a dispersed manner.

Next, a driving force transmission mechanism for the transport rollers 10 to 12 in the double-sided paper feeder will be described in detail.
As shown in FIG. 7, the double-sided paper feeder is configured as an integrated unit including a double-sided paper refeed path, a transport roller, and a manual feed unit, and a part of the drive unit is provided on the unit side.
As shown in FIG. 10, a part of the drive unit corresponds to a double-sided motor 17, a motor pulley 69, a timing belt 78, and a reduction gear 74 corresponding to a drive source capable of rotating in the forward and reverse directions. Is provided. The rotation direction of the double-sided motor 17 is set according to the paper feed mode by the control unit 100 described later. In this embodiment, the rotation in the direction indicated by the symbol CW in FIG. The transfer paper is transported toward the paper feed path 9 (hereinafter also referred to as a double-sided paper feed direction), and the rotation in the direction indicated by the symbol CCW conveys the transfer paper from the manual paper feed tray 22 toward the manual paper feed path 19. Direction (hereinafter also referred to as a manual feed direction).

  On the other hand, FIG. 8 is a diagram showing a transfer paper introduction unit in the manual paper feed unit. In FIG. 8, the manual paper feed unit includes a paper feed roller shaft 61 (not shown) in a housing that also serves as a guide plate. The sheet feeding roller 24 is manually supported at the center of the sheet feeding roller shaft 61 in the axial direction, and the guide rollers 24 are provided on both sides of the sheet feeding roller 24. 60 are respectively attached.

  The paper supply roller 24 is fixed to the paper supply roller shaft 61 and rotates together with the coaxial 61. However, the guide roller 60 is rotatable with respect to the paper supply roller shaft 61.

One end of the feed roller shaft 61 is provided with a missing gear 63 that can mesh with a reduction gear 74 corresponding to a member that transmits the driving force from the double-sided motor 17 in FIG. A disk 62 is fixed to the disk.
As shown in FIG. 15, the missing gear 63 is a member that constitutes a one-rotation clutch that has a configuration having a missing tooth portion in the circumferential direction and can rotate intermittently. Further, a spring 66, which is a biasing member whose one end is hooked on a disk 62 fixed to the other end of the paper feed roller shaft 61, is given a rotational bias in the clockwise direction in FIGS. This rotation biasing allows the reduction gear 74 to be engaged. As shown in FIG. 15, this rotation direction corresponds to a direction in which the paper feed roller 24 is rotated in the manual paper feed direction (CCW).

In FIG. 9, the disk 62 located on the opposite side of the toothless gear 63 in the axial direction of the paper feeding roller shaft 61 is provided with a locking portion that can be engaged with the actuator of the solenoid 65 arranged in the vicinity. When the solenoid 65 is in the OFF state, the engaging portion is engaged with the actuator, so that the home position shown in FIG. 15, that is, the state where the teeth adjacent to the missing tooth portion are engaged with the reduction gear 74 is maintained. It has become so. Therefore, in this case, the solenoid 65 functions as a home position maintaining means.
Therefore, as shown by a two-dot chain line in FIG. 9, when the actuator 65 is instantaneously turned on by one activation pulse and the actuator is released from the engaging portion of the disk 62, the bias of the spring 66 is used. The disc 62, the paper feed roller shaft 61, and the toothless gear 63 rotate in the direction indicated by the symbol CCW in FIG. 9 and engage with the reduction gear 74, whereby the rotational force of the reduction gear 74 is transmitted and the paper supply roller is transmitted. The sheet feeding roller 24 provided on the shaft 61 is rotated in the direction in which the transfer sheet is conveyed toward the manual sheet feeding path 19. The solenoid 65 is brought into a state in which the actuator is moved back toward the engaging portion of the disk 62 when one start pulse is lost.

  At the stage where the missing tooth gear 63 makes one rotation and the missing tooth portion corresponds to the reduction gear 74, the engaging portion on the disk 62 side corresponds to the actuator of the solenoid 65, and the engaging portion is engaged with the actuator. As a result, the missing gear 63 is maintained at the home position.

At the time of intermittent rotation of the sheet feeding roller 24 by the one-rotation clutch using such a toothless gear 63, the cam indicated by reference numeral 64 in FIG. 8 is configured to rotate at the same time. Are repeatedly raised and lowered.
The transfer sheet that comes into contact with the sheet feeding roller 24 as the bottom plate of the sheet feeding tray 22 is repeatedly raised and lowered passes through a friction member 67 (see FIG. 8) that is in pressure contact with the lower peripheral surface side of the sheet feeding roller 24. At this time, one sheet is separated and fed out using the difference in friction coefficient between the transfer sheets, the transfer sheet, and the paper feeding roller 24 and between the lowermost transfer sheet and the friction member 67.

  The reduction gear 74 that transmits the rotational driving force of the double-sided motor 17 by meshing with the toothless gear 63 is pivotally supported by a bracket for mounting the double-sided motor 17 as shown in FIG. A timing pulley around which a timing belt 78 is wound around a timing pulley 69 integrated with an output shaft of the motor 17 is integrated. As a result, the driving force of the double-sided motor 17 is transmitted to the reduction gear 74 via the timing belt 78 and is transmitted to the toothless gear 63 via the reduction gear 74.

On the other hand, the following configuration is used to transmit driving force to the entrance roller 10, the intermediate roller 11, and the exit roller 12.
In FIG. 10, the idle gear 70 is engaged with the reduction gear 74, and the idle gear 71 integrated with the timing pulley is engaged with the idle gear 70. Although not shown, the idle gears 70 and 71 are supported by a rotation support shaft provided on the side wall of the double-sided conveyance unit, and a timing pulley integral with the idle gear 71 has one axial end on the rotation shaft of the intermediate roller 11. A timing belt 72 is provided between the timing pulley 73 and the timing pulley 73.

  A timing pulley is provided in a two-stage structure at the other axial end of the rotating shaft of the intermediate roller 11, and a timing pulley 15 a provided at the axial end of the rotating shaft of the inlet roller 10 is provided at the first stage. The timing belt 15b between which the timing belt 51 is wound and the timing belt 52 between the second stage and the timing pulley 15c provided at one end in the axial direction of the rotary shaft 13 of the outlet roller 12 Is hung around.

As shown in FIG. 11, a gear 68 that meshes with a reduction gear 74 is provided at the other end of the rotary shaft 13 of the exit roller 12, and the gear 68 is attached to the rotary shaft via a one-way clutch 68a. Yes.
The one-way clutch 68a has a function of interrupting the transmission relationship between the idle gear 68 and the reduction gear 74 when the double-sided motor 17 rotates in the direction in which the transfer paper is conveyed with respect to the double-sided paper re-feed path 9. have. The reason is as follows.
The exit roller 12 is used as a driving roller for both paper feed paths by contacting the driven roller located on the double-side paper feed path side and the manual paper feed path 19 side. For this reason, it is premised that the rotation directions when transporting transfer paper in each paper feed path are opposite to each other, and when transferring the transfer paper to the double-side paper feed path 9, It is necessary to cut off the conveyance state. For this reason, the one-way clutch 68a is used.

  As a result, when the double-sided motor 17 rotates in the direction for carrying the transfer paper in the double-sided paper re-feed path 9, the entrance roller 10 and the intermediate roller 11 are passed through the timing belts 72, 51, and 52 shown in FIG. And the exit roller 12 rotate in the direction in which the transfer paper can be conveyed toward the double-sided sheet re-feeding path 9, and the driving force from the gear 68 on the rotation shaft 13 of the exit roller 12 is not transmitted to the reduction gear 74. Is rotating, the situation where the reduction gear 74 repeatedly collides with the teeth adjacent to the missing tooth portion of the missing gear 63 corresponding to the reduction gear 74 is prevented, and the generation of interference noise is prevented. Will be prevented.

On the other hand, the one-way clutch is provided not only for the gear 68 described above but also for the timing pulley 15 a provided on the rotation shaft of the entrance roller 10.
The one-way clutch provided in the timing pulley 15a has a function of transmitting the rotational force to the rotation shaft only when the rotation in the rotation direction when the transfer paper is conveyed toward the double-sided paper feed path 9 is transmitted. is doing. The reason is as follows.
The case where the transfer paper is conveyed toward the double-sided paper feed path 9 by the entrance roller 10 means a state in which the transfer paper moves downward from the entrance roller 10 along the double-sided paper feed path 9 in FIG. For this reason, the transfer paper introduced into the double-sided paper feed path 9 by the entrance roller 10 is other than the direction in which the transfer paper is conveyed toward the path 9, in other words, the double-sided direction in the direction of conveying the transfer paper toward the manual paper feed path 19. When the motor 17 rotates, the transfer paper introduced into the double-sided paper feed path 9 is reversely fed. When such reverse feeding occurs, as indicated by a symbol FR in FIG. 10, if the end of the transfer paper collides with a detection sensor that detects the passage of the transfer paper, the detection sensor may be damaged. In particular, in the case of a limit switch type using a filler as the detection sensor FR, a bad effect such as breakage of the filler is caused.
Therefore, in the present embodiment, in order to prevent such a situation from occurring, the direction in which the transfer sheet is conveyed to the manual sheet feeding path 19 when transmission to each roller is performed via the timing belt. Is not transmitted to the rotation shaft of the entrance roller 10.

On the other hand, in the present embodiment, the double-sided motor 17 is driven and controlled by the control unit 100.
10, the control unit 100 is connected to a solenoid 65 as a home position maintaining means for the double-sided motor 17 and the toothless gear 63 on the output side, and on the input side, the outlet sensor 16 and the inlet sensor 18 shown in FIG. An operation panel 101 having a selection switch for giving a paper feed mode selection command and an alarm display unit is connected.

In the control unit 100, the following control is performed.
(1) When the manual feed mode is selected, the outlet roller 12 corresponding to the transport roller on the most downstream side in the transfer paper transport direction in the double-sided paper feed path 9 is directed in the manual transport direction before the manual paper feed. Rotate a predetermined amount.
This is to prevent the meshing delay between the reduction gear 74 and the toothless gear 63 during manual feeding, and the gear 68 via the one-way clutch 68a is used for the purchase of the outlet roller 12 via the timing belt. The reduction gear 74 that meshes with this by rotating is positioned so as to correspond to the tooth adjacent to the tooth missing portion of the tooth missing gear 63.
(2) When the exit sensor 16 detects that the transfer paper is jammed in the manual paper feed path, the one-rotation clutch constituted by the missing gear 63 is rotated at least once without immediately turning off the double-sided motor 17. After that, the double-sided motor 17 is stopped.
This is because the missing gear 63 constituting the one-rotation clutch is positioned at the home position. That is, if the double-sided motor 17 is immediately cut off, a state in which the tooth adjacent to the missing tooth portion does not correspond to the speed reducing gear 74 in the correspondence relationship between the reduction gear 74 and the missing tooth gear 63 occurs. In this case, the teeth of the reduction gear 74 repeatedly collide with the teeth of the missing gear 63, and an interference sound is generated. Therefore, in the present embodiment, the tooth adjacent to the missing tooth portion has a relationship corresponding to the reduction gear 74 so as to prevent occurrence of a collision sound when the reduction gear 74 rotates in the direction opposite to the manual feed direction. It has become.
(3) After the jam mentioned in (2) is resolved and the side wall of the device is opened to eliminate the jam, the double-sided motor 17 is re-driven when it is closed. After at least one rotation in the manual sheet feeding direction, rotation driving in the direction opposite to the sheet feeding mode can be performed.
As in the case of (2), this means that the missing gear 63 is surely returned to the home position, and the remaining state of the transfer paper in the double-sided paper feed path when rotated in the reverse direction in this state. This is to enable detection.
(4) When the double-sided motor 17 is driven when the image forming apparatus is started, after rotating the one-rotation clutch at least once in the manual paper feeding direction, the direction opposite to the manual paper feeding direction which is the double-sided paper feeding direction So that it can be rotated.
This is to correct the state where the missing gear 63 is not positioned at the home position when the operation of the image forming apparatus is stopped last time. Thus, as described above, it is possible to detect the case where the transfer paper remains in the double-sided paper feed path by performing a predetermined amount of rotation when the double-sided paper feed mode is set.
(5) A case in which transfer paper remains after a predetermined amount of rotation in the manual paper feeding direction after the above-described rotation control for the one-rotation clutch is completed when the double-sided motor 17 is redriven or started. This is to alert the user to clear the jam.
(6) When the double-sided paper feeding mode is selected, the one-rotation clutch is rotated at least one rotation in the manual paper feeding direction.
This is for positioning the toothless gear 63 of the one-rotation clutch at the home position as in the case described above. Accordingly, it is possible to detect the remaining transfer paper in the double-sided paper feed path when rotating a predetermined amount in the double-sided paper feed direction.

Next, another example of this embodiment will be described.
The driving force transmission form and configuration will be described with reference to FIGS. 12 to 14 as follows.
The double-sided motor 17 and the idler gear 74 have the same configuration as that of the above-described embodiment, but the driving system in the double-sided unit is different.
The idler gear 71 in the double-sided unit has a gear part and a timing pulley part integrally formed in two stages, and the timing belt 77 transmits the drive to the gear 75 attached to one end of the outlet roller. Yes.
In the gear 75, the timing pulley portion and the gear portion are integrally formed in two stages. The gear portion meshes with the idler gear 74, and the drive is transmitted to the toothless gear 63 of the manual sheet feeding portion. Unlike the gear 68 shown in FIG. 10, the gear 75 in this case does not incorporate a one-way clutch. In FIGS. 12 and 13, reference numeral 76 denotes a tighter (tension member) of the timing belt 77.

A timing pulley 15 c is attached to one end in the axial direction of the rotation shaft of the exit roller 12, and the drive is transmitted to the intermediate roller 11 by the timing belt 52.
A timing pulley 15 b is attached to the intermediate roller 11, and a timing pulley 15 a is attached to the entrance roller 10, and the drive is transmitted from the intermediate roller 11 to the entrance roller 10 by the timing belt 51. . Here, the timing pulley 15c of the exit roller 12 incorporates a one-way clutch (one-way clutch), and the double-sided motor 17 is rotated in the double-sided paper refeeding direction (the direction indicated by CW in FIG. 12B). Only occasionally, the rotary shaft 13 and the one-way clutch are locked, and the timing pulley 15c rotates to transmit the drive to the intermediate roller 11 and the entrance roller 10, respectively.

  Since the one-way clutch rotates idly with the rotary shaft 13 (the cavity range shown in FIG. 4 and the idling range shown in FIG. 14) when rotating in the manual feed direction, which is the rotation opposite to the double-sided sheet feeding direction. The pulley 15c does not rotate, and the entrance roller 11 and the exit roller 10 do not rotate. Thereby, it is possible to prevent the backflow of the remaining paper in the double-sided paper refeed path by the entrance roller 10 and the intermediate roller 11 when rotated in the manual paper feed direction.

  The present invention has been specifically described above based on the preferred embodiments of the present invention. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. Needless to say. For example, the driving force transmitted by the pulley 15 and the timing belt may be transmitted by a gear, and the gear connected to the shaft 13 may be configured as the pulley 15.

1 is a schematic view of a main body of an image forming apparatus such as a printer that embodies the present invention. FIG. 3 is an exploded perspective view illustrating a drive mechanism of the image forming apparatus according to the present invention. It is a perspective view which shows the drive mechanism of the exit roller in this invention. It is a side view which shows the idling operation | movement of the exit roller in this invention. It is the schematic explaining the motion of the transfer paper at the time of double-sided image formation in this invention. It is a schematic diagram which shows the image formation order in this invention. It is a figure which shows the external appearance of the double-sided paper feed unit which comprises the double-sided paper feeder in this invention. FIG. 8 is a diagram illustrating a transfer paper introduction unit in a manual sheet feeding unit provided in the double-sided sheet feeding unit illustrated in FIG. 7. It is the side view which looked at the manual feed part provided in the unit shown in Drawing 7 from one side. It is a figure for demonstrating the driving force transmission structure with respect to the member in the double-sided paper feed unit shown in FIG. It is a figure which shows the principal part in the driving force transmission structure shown in FIG. It is a figure equivalent to FIG. 10 for demonstrating the driving force transmission structure by another embodiment in this invention. It is a figure which shows the principal part of the driving force transmission structure shown in FIG. It is a figure which shows the structure of the clutch part used for the driving force transmission structure shown in FIG. It is a schematic diagram for demonstrating the principle structure of the 1 rotation clutch used for the structure shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Paper feed part 2 Image transfer part 3 Fixing part 5 Switchback path 6 Reverse roller 9 Both-sides re-feed path 10 Inlet roller 11 Intermediate roller 12 Outlet roller 13 Axis 14 Pin 15 Pulley 16 Outlet sensor 18 Inlet sensor 19 Manual feed Paper path 22 Manual feed tray 24 Feed roller 63 No-tooth gear 65 constituting one-rotation clutch Solenoid 66 equivalent to home position maintaining means Spring 300 Control unit 301 Operation panel

Claims (16)

A double-sided refeed path for feeding the transfer paper on which an image is formed on one side to the image forming unit again;
In the double-sided paper feeder having a plurality of transport rollers on the double-sided refeed path and driven by the same drive source, and a transmission means for transmitting the driving force from the drive source to the transport roller,
Among the plurality of transport rollers, the transport roller on the most downstream side in the transport direction is connected to the drive source via the transmission means, and the transport roller on the most downstream side is rotated in both forward and reverse directions by the drive source. A double-sided sheet feeding device characterized by being capable of idling with respect to a drive source.   The transmission means has a cavity, and the transmission means and the most downstream conveying roller are connected via the cavity and a pin provided on a shaft that supports the most downstream conveying roller. The double-sided sheet feeding device according to claim 1.   The double-sided sheet feeding device according to claim 2, wherein the cavity has a fan shape having end faces with which the pins abut on both sides thereof.   The transfer paper from a manual paper feed path provided close to the double-sided paper refeed path is introduced into the most downstream transport roller. Double-sided paper feeder.   5. The double-sided sheet feeding device according to claim 4, wherein the most downstream conveying roller is also used as a driving roller for nipping and conveying the transfer sheet from the manual sheet feeding path.   The most downstream transport rollers are respectively provided with driven rollers facing each other, and one driven roller is used for transporting transfer paper to the double-sided refeed path, and the other driven roller is manually fed. 6. The double-sided paper feeding device according to claim 4, wherein the double-sided paper feeding device is provided for conveying a transfer paper in a paper feeding path.   The transmission means for transmitting the driving force from the driving source to the transport roller including the most downstream roller is a transfer sheet in the double-sided refeed path according to the forward and reverse rotation of the driving source. Or transfer paper feeding from the manual paper feed path can be selected, and when the rotation direction of the drive source is set in the direction of transporting the transfer paper from the manual paper feed path, The double-sided sheet feeding device according to any one of claims 1 to 6, further comprising a one-way clutch that maintains at least one of the rollers in a non-rotating state.   A feeding roller capable of feeding out the transfer paper is provided on the transfer paper introduction side in the manual paper feeding path, and the feeding roller is driven by the drive source with respect to the transport roller including the most downstream roller. 8. The driving force is intermittently transmitted via a one-rotation clutch using a toothless gear to a transmission means for transmitting the driving force from the first gear. 8. Double-sided paper feeder described in 1.   In the driving force transmission path for the one-rotation clutch, a one-way clutch capable of interrupting the rotational driving force to the feeding roller when the driving source rotates in the transfer sheet conveyance direction in the double-sided refeed path. The double-sided paper feeder according to claim 8, wherein the double-sided paper feeder is arranged.   An image forming apparatus comprising the double-sided sheet feeding device according to claim 1.   An operation panel having detection means and a start switch capable of detecting the presence or absence of transfer paper in the double-sided paper refeed path and the manual paper feed path is provided on the input side, and the drive source and the home position of the one-rotation clutch are provided on the output side. And a control unit connected to the maintaining means, wherein the control unit rotates the transport roller on the most downstream side by a predetermined amount in the conveyance direction of the manual transfer paper before manual sheet feeding during manual sheet feeding. The image forming apparatus according to claim 10.   12. The image forming apparatus according to claim 10, wherein the front control unit stops the driving source after the at least one rotation without stopping the driving source immediately when a jam occurs in the manual sheet feeding path. .   The control unit makes at least one rotation of the one-rotation clutch in a direction in which the transfer paper can be fed from the manual paper feed path when the drive source is re-driven after the jam is resolved. 13. The image forming apparatus according to claim 10, wherein the image forming apparatus is driven in a direction opposite to the direction.   When the control unit drives the drive source at the time of starting, the control unit makes at least one rotation of the one-rotation clutch in a direction in which the transfer sheet can be fed from the manual sheet feeding path, and then reverses the direction. The image forming apparatus according to claim 10, wherein the image forming apparatus is driven in a direction.   The control unit alerts the operation panel when the detection means detects the presence of the transfer paper during re-driving of the driving source or driving at the time of starting. 14. The image forming apparatus according to claim 1. When a double-sided paper feed command is input from the operation panel, the control unit causes the drive source to rotate at least one rotation clutch in a direction in which transfer paper can be fed from the manual paper feed path. The image forming apparatus according to claim 10, wherein the image forming apparatus is an image forming apparatus.

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