JP2000072307A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the productivity of image formation by providing a clutch for interrupting the transmission of the driving force from a drive source in current carrying and transmitting the driving force in no-current carrying on a carrying roller in the outlet part from an intermediate tray. SOLUTION: A clutch 108 is provided concentrically with a carrying roller 107. The clutch 108 is disconnected in current carrying so as not to transmit the driving force of a motor to the carrying roller 107, and connected in no- current carrying to transmit the driving force of the motor to the carrying roller 107, so that the carrying of sheets can be performed. Accordingly, the current carrying is cut in case of reverse discharge, and the carrying roller 107 is rotated to carry the sheets. Thus, the sheet can be stopped in the outlet part from an intermediate tray by carrying a current to the clutch 108 in duplex image formation, and when non-stack interleaf duplex function is executed, sheets can be alternately fed from a paper feed part and a duplex re-feed part without spacing. Accordingly, the productivity in image formation can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an intermediate tray,
The present invention relates to an image forming apparatus including a switchback unit for switching back the sheet on the intermediate tray, and capable of forming an image on both sides of the sheet.

[0002]

2. Description of the Related Art In order to form an image on both sides of a sheet, it is necessary to turn the sheet on which the image is formed on one side once, move the sheet to an image forming position, and form an image on the inverted sheet. For this reason, a switchback mechanism for reversing the sheet has conventionally been provided. There are two cases where sheet reversal is required, in addition to the two-sided image formation described above, that is, reversal sheet ejection that requires ejection in the form that is turned upside down. Then, the sheet is conveyed to the image forming unit side, whereas the latter is conveyed to the sheet discharge tray side after reversal. As described above, since the operations after the inversion are different, the switchback mechanism is independently provided in each transport path for performing the operation.

[0003]

On the other hand, with the digitization of the image forming apparatus, a non-stacked interleaf double-sided function has been realized, and a single switchback mechanism has enabled reverse discharge and double-sided image formation. Has been able to provide an image forming apparatus at low cost. However, in order to improve the productivity of double-sided copying (image formation), it has been necessary to stop the paper in the double-sided path between the switchback unit and the image forming unit during both sides. That is,
In the non-stacked interleaf duplex mode, the paper is fed alternately between the paper feed unit and duplex refeed. (Image formation) productivity is reduced.
In particular, in a high-volume high-speed machine, it is necessary to increase the number of places where the sheets are stopped in order to prevent the entire conveyance path from becoming longer and the gap between the sheets being alternately fed. Further, if necessary, the paper must be stopped at the switchback portion. Therefore, it is necessary to provide a drive system that keeps driving at the time of reverse discharge and always stops driving only when the paper stops on both sides, or interrupts the transmission of the driving force.

If a jam occurs during execution of the non-stack interleaf double-sided mode, unless otherwise specified, the control device immediately cuts off the driving of the sheet conveying system and the image forming system. Remains, and the jam handling becomes a serious task.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances of the prior art, and has as its object to provide an image forming apparatus capable of improving the productivity of image formation and the operability of jam processing. Is to do.

[0006]

In order to achieve the above-mentioned object, a first means comprises an image forming means for forming an image on one side of a sheet and a sheet on which an image is formed on one side by the image forming means. An image forming apparatus comprising: a switchback means for switching back to a tray; and a control means for performing double-sided copying using the switchback means during both reverse discharge and double-sided copying. The transfer roller is provided with a clutch for interrupting the transmission of the driving force from the drive source when energized and for transmitting the driving force when not energized.

A second means is the first means, wherein the control means sets the clutch to a non-energized state to transmit the driving force when the sheet is reversed and discharges the power, and sets the clutch to an energized state when the sheet is stopped during duplex copying. The transmission of the driving force is interrupted.

A third means is the first means, wherein the control means keeps energizing the clutch at least as long as the transport rollers can rotate due to the inertia of the drive source at the time of paper jam. And

A fourth means is the first means, further comprising a torque limiter for preventing transmission of a driving force to the transport roller when a load of a predetermined value or more is applied to the drive of the transport roller. It is characterized by the following.

A fifth means is the first means, wherein the intermediate tray is provided with a regulating means for regulating a position in a direction orthogonal to the sheet conveying direction at the time of switchback, and the control means is provided with the regulating means at the time of sheet jam. Is set to be larger than the paper width.

In the embodiment described below,
The switchback means includes a pair of switchback rollers 103a and 103b, a transport roller 107 for a transport roller at an outlet from the intermediate tray, and a clutch 108 for a clutch.
However, the control means executes a predetermined control according to a program stored in a ROM (not shown).
U corresponds to the torque limiter 118, and the jogger fence 104 corresponds to the regulating means.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a main part of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, an image forming apparatus includes first and second sheet conveying apparatuses 1 and 2 for picking up and conveying sheets from sheet cassettes 1a and 2a extending over two stages, and one of these sheet conveying apparatuses 1 and 2 Photoreceptor drum 3 for transferring the toner image to the sheet conveyed from the printer, fixing device 4 for fixing the toner image transferred to the sheet, and sheet discharge for directly conveying the fixed sheet to a sheet discharge tray (not shown) A transport system 5, an intermediate transport system 6 for transporting the fixed sheet to the intermediate tray 105, and an intermediate tray 1.
Basically, each transport path of the re-feeding system 7 for transporting the sheet again from 05 to the photosensitive drum 3 side. In addition,
A device having various functions such as charging, exposure, development, transfer, separation, cleaning, and static elimination is arranged along the peripheral surface of the photosensitive drum 3, and an image is formed by an electrophotographic process. Since each of the devices is known, the description thereof is omitted here.

The sheet discharge conveyance system 5 and the intermediate conveyance system 6 are connected to a branch claw 8.
When the branching pawl is rotated counterclockwise in the figure to release the lower path in the figure, the sheet is guided to the intermediate transport system 6 and is rotated clockwise in the figure to rotate the upper path. When the path is released, the sheet is guided to the sheet discharge conveyance system 5. The intermediate conveyance system 6 is provided with a first path 6a for guiding the sheet to the intermediate tray 105 and a second path 6b for guiding the sheet from the intermediate tray 105 to the sheet discharge conveyance system 5. When the sheet is guided to the system 5, the discharge path of the sheet switched back by the switching claw 106 is selected. The intermediate transport system 6 includes a pair of transport rollers 119 and 1 along the branch claw 8 and the intermediate tray 105.
20, an intermediate tray entrance roller pair 101, 102 is provided, and a transport roller pair 107 is provided on the exit side of the intermediate tray 105, so that the paper can be transported to the discharge transport system 5 or the re-feed system 7. I have.

The re-feeding system 7 is provided with a horizontal transport unit 110, and a plurality of transport roller pairs 109 are used to feed the sheet transport devices 1 and 1.
2, the sheet can be sent out to the vertical conveyance path 100 common to the sheet 2, and can be fed again to the transfer position of the photosensitive drum 3 via the registration roller 100a. A pair of transport rollers is formed by the transport rollers 107 and the intermediate tray entrance rollers 102.

In the image forming apparatus constructed generally as described above, the photosensitive drum 3 fed from one of the first and second paper feed trays 1a and 2a via the paper transport devices 1 and 2 is used. The image formed on the photosensitive drum 3 at the transfer position is transferred and fixed by the fixing device 4. If the fixed sheet is not inverted, the branch claw 8 is switched clockwise to be directly conveyed to the sheet discharge conveyance system 5 and discharged to the sheet discharge tray. On the other hand, in the case of the reverse discharge, or in the case of double-sided copy (double-sided image formation), the branching claw 8 is switched in the counterclockwise direction and sent to the conveyance path of the intermediate conveyance system 6, and the conveyance roller pair 119,
The intermediate tray 105 is made to enter the intermediate tray 105 via the pair of intermediate tray entrance rollers 101 and 102 via 20. Intermediate tray 105
The paper conveyed inside the switchback roller 103a,
Switched back by 103b pair, transport roller pair 1
07 and 102, and are conveyed to the sheet discharge conveying system 5 or the re-feeding system 7. At this time, a jogging operation, that is, a so-called width direction alignment operation, is performed by a regulating member called a jogger fence 104 that regulates a position in a direction orthogonal to the transport direction. When a sheet enters the intermediate tray 105, a double-sided entrance sensor 113 disposed upstream of the pair of intermediate tray entrance rollers 101 and 102 in the sheet transport direction.
The jogger fence 104 and the switchback rollers 103a and 103b on the downstream side in the sheet conveying direction operate with the detection of the leading edge and the trailing edge of the sheet as triggers.

Thereafter, in the case of the reverse discharge, the sheet conveyed by the conveying roller pairs 107 and 102 is switched by the switching claw 1.
When the transport path is switched in 06, the sheet is transported in the direction of the sheet discharge roller 12 via the second path 6b. In addition, the transport roller 107
A clutch 108 is provided on the same axis as shown in FIG. 10 and FIG. This clutch 108 functions so as to be disconnected when energized so as not to transmit the driving force of the motor to the transport roller 107. Is made possible. Accordingly, in the case of the above-described reverse discharge, the power is turned off, and the transport rollers 107 rotate to transport the paper. Since the sheets on which images have been formed are stacked in page order with the image side facing down, the image forming apparatus having such a configuration is normally a reverse sheet discharge. On the other hand, at the time of double-sided printing, the sheet is conveyed to the horizontal conveyance unit 110 of the re-feeding system 7 by switching of the switching claw 106, re-feeded through the paper feeding unit 100 by the conveyance roller 109, and an image is formed on the back surface. Then, the paper is sent to the paper discharge transport system 5 and discharged from the paper discharge rollers 12 to a paper discharge tray.

The flow of paper transport on both sides in the non-stack double-sided function is as follows.

FIG. 2 is an explanatory view showing the image forming order of pages, and FIG.
FIGS. 7 to 7 are explanatory views showing the paper transport state at that time. The image forming order of the pages is “1”, “3”, “5”,
"7", "2" (back side of the first sheet), "9", "4" (2
The back of the third sheet), "11", "6" (the back of the third sheet),
"13", "8" (back side of the fourth sheet), "15", "1"
"0" (fifth back surface) and so on, the new paper on which an image is formed on the front surface and the next paper on which an image is formed on the back surface are alternately transferred to the transfer device 9 of the photosensitive drum 3. The images are supplied and image formation is performed in this order, and images are formed on both sides of the sheet.

More specifically, as shown in FIG. 3, four sheets are conveyed continuously from one of the sheet conveying devices 1 and 2, and an image is formed on the front surface (1, 3, 5). , P. 7)
It is made to enter the intermediate tray 105. Then, after switching back by the switchback rollers 103a and 103b, the switching claw 106 is switched to transfer the sheet to the horizontal transport unit 1.
Convey to 10. The first sheet (first page P1) is shown in FIG.
As shown in (1), the sheet is directly sent to the transfer device 9 side to form an image on the back side, and after the image is formed on the back side (second page P2), the sheet is conveyed to the sheet discharging roller 12 side of the sheet discharging and conveying system 5 as it is. Is discharged (FIG. 5).

The second (third page P3) and third (fifth page P5) sheets stop at a predetermined position of the horizontal transport unit 110,
I'm waiting. Therefore, a power transmission and transmission stop mechanism such as a clutch is used to drive the horizontal transport unit 110, so that the horizontal transport unit 110 can be stopped and waited. For the fourth sheet (page 7 P7), the leading end of the sheet is
It stops while being held by the nips 7, 102 and stands by in that state. As shown in FIG.
As shown at 0, a clutch 108 is provided. The clutch 108 is configured to be energized when the paper stops at the nip position of the pair of transport rollers 107 and 102 and waits, so that the driving force is not transmitted to the transport roller 107.

After the image is formed on the back side of the first sheet (P2 of the second page), the fifth sheet (P9 of the ninth page) is supplied from the sheet transport devices 1 and 2 as shown in FIG. To form an image,
The user directly enters the intermediate tray 105. After the image is formed on the ninth page P9, as shown in FIGS. 5 and 6, the second sheet which has been waiting in the horizontal transport unit 110 is directly transported to the transfer device 9 for backside image formation. An image is formed on the fourth page P4, which is the back side of the second sheet, and the sheet is discharged from the sheet discharge conveyance system 5 as it is. Then, the sixth sheet (page 11 P1
1) is supplied from the paper transport devices 1 and 2, and the 11th page P1
After the image is formed on the sheet No. 1, the sheet of the eleventh page P11 is conveyed to the intermediate tray 105. Subsequently, as shown in FIG. 7, the third sheet which has been waiting in the horizontal conveying unit 110 is conveyed to the transfer device 9 and an image is formed on the back surface (6th page P6). The paper is discharged via the system 5. This operation is alternately repeated as described above.

The above operation will be described in more detail.

As shown in the timing chart of FIG. 16, the leading edge of the sheet entering the intermediate tray 105 is detected by the double-sided entrance sensor 113. At the same time when the leading edge of the sheet is detected by the double-sided entrance sensor 113, the jogger fence 104 moves a predetermined distance from the sheet width position to a position widened in the width direction. When it is detected that the trailing edge of the sheet has gone out of the detection position of the double-sided entrance sensor 113, the jogger fence 104 returns to the sheet width position after a predetermined time, and is positioned in a direction perpendicular to the sheet conveying direction (alignment position).
And adjust the paper position. The movement distance of the jogger fence 104 from the alignment position is set in advance for each sheet size. The home position of the jogger fence 104 may be anywhere, but a position where the fence width is maximized is desirable.

FIG. 8 is a plan view showing the jogger fence 104, and FIG. 9 is a view taken in the direction of the arrow in FIG. 8A. The jogger fence 104 is driven by a stepping motor 111 and a timing belt 114 and reciprocates in a direction perpendicular to the transport direction. Therefore, the jogger fence 104 is fixed to a slider 116 that slides along a guide rod 112. In FIG.
When the stepping motor 111 is driven counterclockwise,
The jogger fence 104 moves in a direction that opens with respect to the paper width (arranged width), in other words, a direction in which the distance between the jogger fences increases, and stops when the home position sensor 115 detects the filler portion 104a of the jogger fence 104. .

The sheet that has entered the intermediate tray 105 is conveyed to the pair of conveying rollers 107 and 102 by the switchback rollers 103a and 103b, and proceeds to the next step. In this embodiment, the switchback rollers 103a and 103b are arranged such that the drive roller 103a is disposed below the sheet as shown in FIG. 1 and constantly rotates in a direction in which the sheet is fed to the pair of conveying rollers 107 and 102. . Driven roller 103b
Is moved up and down by a DC solenoid (not shown). That is, the DC solenoid is turned on when a sheet is conveyed to the next conveyance path by switchback, and a constant pressure is applied to the drive roller 103a by the driven roller 103b. In this case, the driving and following relationships are arbitrary.

As shown in the timing chart of FIG. 16, the on / off timing of the DC solenoid of the driven roller 103b is turned on when a predetermined delay time elapses when it is detected that the trailing edge of the sheet has passed through the double-sided entrance sensor 113. . At this time, it is desirable to set the delay time so that the jogger fence 104 is turned on after moving to the paper width position. For the off timing, an on-time is set in advance, and when the on-time elapses, the device turns off. For example, FIG.
In 3, the movement of the sheet on the seventh page P7 after the switchback is detected by the reversing sensor 117 provided near the pair of transport rollers 107 and 102. Since the sheet on the fifth page P5 exists on the downstream side for a predetermined time, The clutch 108 is energized to stop later. When the conveyance of the sheet of the fifth page P5 is started, the conveyance of the sheet of the seventh page P7 is started simultaneously or with a delay of a predetermined time, and the clutch 108 is turned off. As a result, the transport rollers 107 are
Power is transmitted by connecting the gear mechanism 122 from the main body side output coupling 121 as shown in FIG.
The clutch 108 is provided coaxially with the transport roller shaft 107a, and disconnects and connects the transmission of power from the gear mechanism 122 to the transport roller shaft 107a.

Further, as shown in FIG.
Is provided with a torque limiter 118, and when a load equal to or more than a certain value is applied between the roller portion and the shaft portion (transport roller shaft 107a), the transport roller 107 and the shaft portion 107a slip to slide from the transport roller shaft 107a. The driving force is not transmitted to the transport roller 107. In this embodiment,
Although the torque limiter 118 is provided in the transport roller unit 107, it may be provided in the gear unit of the clutch 108.

The jam clearance when the clutch 108 is provided in the drive transmitting portion of the transport roller 107 is as follows.

For example, as shown in FIG. 13, if a jam occurs while the sheet of the seventh page is stopped and in a standby state, the transport operation of the paper transport system is immediately stopped, and therefore, the power to the paper transport system is supplied. Is cut off immediately. Then, of course, the power supply to the clutch 108 is also turned off.
Indicates that the power is off and the driving force transmission is on, so the transfer roller pair 10
7, 102 is in a state where the driving force is transmitted. On the other hand, since the power of the transport system is turned off, the paper should not be transported even if the clutch 108 is connected, but actually, the paper is transported by the inertia of a drive motor (not shown). On the other hand, since the sheet of the fifth page of the preceding sheet is stopped, the leading end of the sheet of the seventh page conveyed with the clutch 108 engaged may collide with the rear end of the sheet of the fifth page. There is. Therefore, in this embodiment,
While the sheet is being conveyed by the inertia of the drive motor, the clutch 108 is energized to stop the sheet of the seventh page.

Further, as shown in FIG. 14, the fixing conveyance system and the double-sided conveyance system (illustrated M) are one driving source, in other words, one driving source.
In the case where the drive system is configured to be driven by two drive motors, and a jam processing knob 130 is provided in this system, when the above-described drive immediately-jam occurs, the transport on the upstream side of the intermediate tray 105 in the transport direction is performed. The remaining paper remaining on the road is discharged to the intermediate tray 105 by operating the knob 130. However, for the two-sided copy, 5
When the sheet of the page is stopped and the sheet of the seventh page is moved by the knob operation, the leading end of the seventh page collides with the trailing end of the fifth page, and the load increases, and the knob is further pushed. The sheet S cannot be fed, and the sheet S of the seventh page cannot be fed.
On the other hand, if an accordion-shaped jam occurs at the exit of the intermediate tray 105 as shown in FIG.
Is operated, the load increases, and it cannot be turned any further.

In such a situation, the clutch 108
, A load greater than the design value is applied, and the clutch 108 may be damaged. Therefore, the aforementioned torque limiter 11
8, the clutch 108 is not damaged, and the paper stopped at the exit of the intermediate tray 105 without being conveyed is operated by the knob 130 to operate the intermediate tray 105.
Transport to the side, and the operability of jam clearance is improved. At this time, if the jogger fence 104 is widened to a position wider than the paper width, the paper fed to the intermediate tray 105 by operating the knob 130 can smoothly enter without touching or contacting the jogger fence 104. This can also improve the jam clearance.

[0033]

As described above, the present invention has the following effects.

That is, according to the first aspect of the present invention,
The transfer roller at the exit from the intermediate tray is provided with a clutch that cuts off the transmission of the driving force from the drive source when energized, and that transmits the driving force when not energized. Paper can be stopped at the exit from the intermediate tray, and when the non-stack interleaf duplex function is executed, alternate paper can be fed from the paper feeding unit and the duplex refeeding unit without leaving a space between sheets. Thereby, the productivity of image formation can be improved.

According to the second aspect of the present invention, the driving force is transmitted with the clutch de-energized at the time of reverse discharge, and the transmission of the driving force is interrupted with the clutch energized at the time of stopping the paper during duplex copying. Therefore, the on-time of the clutch is shortened, whereby the life of the clutch can be extended, and the reliability can be improved.

According to the third aspect of the present invention, when a paper jam occurs, the power supply to the clutch is continued at least as long as the transport roller can rotate due to the inertia of the drive source, so that the sheet stops at the outlet from the intermediate tray. When a jammed paper collides with the trailing edge of the preceding paper, secondary jamming can be prevented.

According to the fourth aspect of the present invention, since the torque limiter for preventing transmission of the driving force to the transport roller when a load equal to or more than a preset value is applied to the drive of the transport roller is provided, the jam clearance is improved. It is possible to prevent an unnecessary load from being sometimes applied to the clutch and to be damaged, and to improve the operability of the jam processing when the remaining sheets enter the intermediate tray.

According to the fifth aspect of the invention, the intermediate tray is provided with a regulating means for regulating the position in the direction orthogonal to the sheet conveying direction at the time of switchback, and the regulating width by the regulating means is larger than the sheet width at the time of paper jam. To set,
It is possible to suppress interference between the regulating member and the remaining sheet when the remaining sheet on the upstream side in the transport direction from the intermediate tray is discharged to the intermediate tray, and it is possible to improve the operability of the jam processing.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram mainly showing a sheet conveyance system of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a page order of image formation of non-stacked duplex image formation executed by the image forming apparatus according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a position of a sheet in a sheet transport path, showing a state in which a first sheet is on standby in an intermediate tray and four sheets are present in the transport path.

FIG. 4 is an explanatory diagram showing a position of a sheet in a sheet transport path, showing a state in which an image is formed on a back surface of a first sheet and a fifth sheet is on standby at the transport device side.

FIG. 5 is an explanatory diagram showing a position of a sheet in a sheet transport path, showing a state where an image is formed on a surface of a fifth sheet and a second sheet is taken out from an intermediate tray.

FIG. 6 is an explanatory diagram illustrating a position of a sheet in a sheet conveyance path, showing a state where image formation on the back surface of a second sheet is completed and a sixth sheet is being conveyed from the conveyance device side.

FIG. 7 is an explanatory diagram illustrating a position of a sheet in a sheet conveyance path, and illustrates a state in which an image is formed on a back surface of a third sheet and a seventh sheet is conveyed from the conveyance device side.

FIG. 8 is a plan view showing a jogger fence provided on an intermediate tray and a driving mechanism thereof.

FIG. 9 is a front view showing the jogger fence and the jogger motor in FIG. 8;

FIG. 10 is a perspective view of a main part showing a transport roller provided at an intermediate tray outlet, a clutch provided on a drive shaft thereof, and a power drive system from the image forming apparatus main body side.

11 is a plan view showing a torque limiter attached to the transport roller unit in FIG.

FIG. 12 is a plan view showing a torque limiter laid on a clutch unit in FIG. 10;

FIG. 13 is a diagram illustrating a state of a sheet at an intermediate tray exit when a jam occurs.

FIG. 14 is a diagram illustrating a state of sheets on the entire conveyance path when a jam occurs.

FIG. 15 is a diagram illustrating a state of jam clearance at an intermediate tray exit.

FIG. 16 is a timing chart showing operation timings of mechanisms related to the intermediate tray.

[Explanation of symbols]

 1, 2 paper transport device 3 photoreceptor drum 4 fixing device 5 paper discharge transport system 6 intermediate transport system 7 re-feed system 8 branching claw 9 transfer device 100 vertical transport path 103a, 103b switchback roller 104 jogger fence 105 intermediate tray 106 Switching claw 107 Transport roller 108 Clutch 110 Horizontal transport section

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/14 G03G 21/00 372 3F100 F term (Reference) 2C059 AA22 AA49 AA51 AA55 AB09 AB12 2H027 DC14 ED16 EK10 FA13 2H028 BA06 BA07 BA12 BA14 2H072 AA02 EA02 JA02 3F053 BA03 BA14 BA18 EA03 EB04 ED02 LA03 LB03 3F100 AA02 BA14 CA12 EA02

Claims (5)

[Claims] 1. An image forming means for forming an image on one side of a sheet, a switchback means for switching back a sheet having an image formed on one side by the image forming means to an intermediate tray, An image forming apparatus comprising: a control unit for performing double-sided copying using the switchback unit at any time; and transmitting a driving force from a driving source to a conveying roller at an exit from the intermediate tray when energized. The image forming apparatus further comprises a clutch for transmitting the driving force when power is not supplied. 2. The control device according to claim 1, wherein the control unit controls the clutch to be in a non-energized state to transmit the driving force when the sheet is inverted and discharges the driving force to stop the transmission of the driving force when the sheet is stopped during duplex copying. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the control unit keeps energizing the clutch at least while the conveyance roller can be rotated by inertia of a driving source at the time of paper jam. . 4. The apparatus according to claim 1, further comprising a torque limiter for preventing transmission of a driving force to the transport roller when a load equal to or greater than a preset value is applied to the drive of the transport roller. Image forming device. 5. A regulating means for regulating a position in a direction orthogonal to a sheet conveying direction at the time of switchback in said intermediate tray, wherein said controlling means sets a regulation width by said regulating means to be larger than a sheet width when a sheet jam occurs. The image forming apparatus according to claim 1, wherein: