JP2017137143A - Switch-back conveyance device and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switch-back conveyance device which can convey a sheet material by surely switching back the sheet material.SOLUTION: A switch-back conveyance device includes: a conveyance member which can be driven so as to hold and convey a sheet material by switching between the first conveyance direction of the sheet material and the second conveyance direction reverse to the first conveyance direction; drive means which drives the conveyance member by transmitting the first driving force such as the driving force in the normal conveyance direction to the conveyance member via a clutch that can be on-off controlled when the sheet material is conveyed in the first conveyance direction and drives the conveyance member by transmitting the second driving force to the conveyance member when the sheet material is conveyed in the second conveyance direction; and control means which controls the drive means. The switch-back conveyance device starts transmission of the second driving force to the conveyance member after turning the clutch off while the conveyance member holds and conveys sheet material in the first conveyance direction and before the rear end of the sheet material in the first conveyance direction passes through the holding position by the conveyance member.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switchback conveying apparatus and an image forming apparatus.

  2. Description of the Related Art Conventionally, there is known a switchback transport device that transports a sheet material sandwiched between a pair of rollers capable of rotating in the forward and reverse directions by switching back.

  Patent Document 1 discloses such a switchback transport device, which includes a forward rotation electromagnetic clutch and a reverse rotation electromagnetic clutch of a roller pair, and drives the roller pair by a rotational driving force transmitted through the electromagnetic clutch. It has been known. In this switchback conveying device, the forward electromagnetic clutch is turned off when the sheet material held between the roller pairs and conveyed in the direction of the first conveying direction is switched back. Then, after turning off the forward-rotating electromagnetic clutch, the reverse-rotating electromagnetic clutch is turned on to reversely rotate the roller pair, and the sheet material is conveyed in the second conveying direction opposite to the direction of the first conveying direction.

  In the switchback conveying device of the above-mentioned Patent Document 1, during the switchback operation, the forward electromagnetic clutch is turned off before the rear end portion of the sheet material held by the roller pair reaches the roller pair. However, even when the forward electromagnetic clutch is turned off in this way, the roller pair continues to rotate in the forward rotation direction, and the rear end of the sheet material may pass the nipping position (conveying nip) of the roller pair. For example, when the idling torque of the clutch is greater than the load torque on the clutch output side shaft, the driving force is transmitted to the output side even when the forward rotation electromagnetic clutch is turned off, and the roller pair continues to rotate in the forward direction. There is a possibility that the rear end of the sheet material passes through the holding position of the roller pair. Also, due to the inertia moment (inertia) of the output side of the clutch, the roller pair itself, etc., the roller pair continues to rotate in the forward direction even when the forward electromagnetic clutch is turned off, and the trailing edge of the sheet material holds the roller pair. There is a risk of passing the position. In this way, when the rear end of the sheet material passes the holding position of the roller pair, the sheet material is not held by the roller pair, so the sheet material is switched back and conveyed even if the roller pair is rotated in reverse. I can't.

  Note that the problem that the rear end of the sheet material cannot pass through the holding position of the roller pair to switch the sheet material in this way is at least the first regardless of the presence or absence of the reverse electromagnetic clutch. This can occur if the driving force for normal rotation when conveying the sheet material in the conveying direction is transmitted to the roller pair via a clutch that can be controlled on and off. For example, the driving force for forward rotation when the sheet material is conveyed in the direction of the first conveying direction is transmitted to the roller pair via a clutch that can be controlled on and off, and the second conveying direction is opposite to the first conveying direction. The above problem can also occur in a switchback conveying apparatus configured to transmit a driving force for reverse rotation when conveying a sheet material in a direction to a roller pair without passing through a clutch.

  In order to solve the above-described problem, the present invention switches between a first conveyance direction of a sheet material and a second conveyance direction opposite to the first conveyance direction so as to sandwich and convey the sheet material. When the transportable transport member and the sheet material are transported in the first transport direction, the first drive force is transmitted to the transport member via a clutch that can be controlled on and off, and the sheet material is driven. Switchback transport comprising drive means for transmitting a second drive force different from the first drive force to the transport member when transported in the second transport direction, and control means for controlling the drive means The apparatus is a device, wherein the rear end of the sheet material in the first transport direction is turned off after the clutch is turned off during transport in which the transport member holds the sheet material and transports the sheet material in the first transport direction. Pass the gripping position by the conveying member. Before, it is characterized in that to initiate transmission of said second driving force to the conveying member.

  According to the present invention, the sheet material can be reliably switched back and conveyed.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a partially enlarged plan view illustrating an example of a drive transmission unit of a paper discharge unit in the image forming apparatus according to the present embodiment. FIG. 4 is an explanatory diagram showing the operation direction of a sheet in a duplex printing mode in the image forming apparatus according to the present embodiment. FIG. 3 is an explanatory diagram illustrating a state in which a sheet is nipped and conveyed by a fixing unit toward a three-way unit in the image forming apparatus according to the present embodiment. FIG. 3 is an explanatory diagram illustrating a state in which a sheet is nipped and conveyed by a sheet discharge unit and is moving in a sheet discharge direction in the image forming apparatus according to the present embodiment. FIG. 4 is an explanatory diagram showing a state immediately after the rear end of the sheet passes through a switchback guide plate conveyance guide surface in the image forming apparatus according to the present embodiment. FIG. 7 is an explanatory diagram illustrating a state in which the sheet is further transported forward in the sheet discharge direction and temporarily stopped from the state illustrated in FIG. 6. FIG. 3 is an explanatory diagram illustrating a state in which a paper discharge driving roller rotates in the reverse direction in the image forming apparatus according to the present exemplary embodiment to convey a sheet into a double-sided conveyance path. FIG. 3 is an explanatory diagram illustrating a state in which a sheet is conveyed by an interleaf in the image forming apparatus according to the present embodiment. 5 is a timing chart at the time of interleaf in the image forming apparatus according to the present embodiment. FIG. 4 is an explanatory diagram illustrating a conveyance state of a sheet P when the interleaf operation is not performed in the duplex printing mode in the image forming apparatus according to the present embodiment. FIG. 12 is an explanatory diagram illustrating a state in which the sheet is transported in the reverse transport direction and the registration is stopped from the state illustrated in FIG. 11. 6 is a timing chart when no interleaf is performed in the image forming apparatus according to the present exemplary embodiment. FIG. 5 is a schematic configuration diagram illustrating an example of another image forming apparatus including two double-sided conveyance rollers in a double-sided conveyance path. FIG. 3 is a partially enlarged plan view of a configuration in which a discharge reverse motor and a one-way clutch are provided in a drive transmission unit of the discharge unit. FIG. 3 is a schematic configuration diagram in which a paper trailing edge detection sensor is provided in a paper discharge conveyance path. FIG. 3 is a block diagram illustrating an example of a main part of a control system that controls switchback conveyance in the image forming apparatus according to the embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. In the present embodiment, the case where the image forming apparatus 1 having a switchback conveying apparatus is a printer will be described. However, the present invention is not limited to a switch provided in another image forming apparatus such as a copier, a multifunction peripheral, or a FAX. It can also be applied to a back conveying device. The present invention can also be applied to a switchback conveyance device provided in an apparatus other than the image forming apparatus, or a single switchback conveyance apparatus that is not incorporated in another apparatus.

  In FIG. 1, an image forming apparatus 1 according to the present embodiment includes a switchback conveying device, and has a double-sided image forming function for forming images on both sides of a sheet P as a sheet material using the switchback conveying device. ing. The image forming apparatus 1 includes two sheet feeding units 2 including a front sheet feeding unit 2A and a manual sheet feeding unit 2B on the side of the apparatus, and both the front sheet feeding unit 2A and the manual sheet feeding unit 2B on the downstream side in the sheet conveyance direction. A registration roller 3 as a pair of registration rollers is provided. The transport paths of the front paper feed unit 2A and the manual paper feed unit 2B join the registration roller 3 in the vertical transport path R1 on the downstream side in the transport direction of the paper P. Therefore, the image forming apparatus 1 can feed the paper P if it includes at least one of the front paper feeding unit 2A and the manual paper feeding unit 2B.

  Further, the image forming apparatus 1 is provided with a transfer unit 4 and a fixing unit 5 along the vertical conveyance path R1, and with a three-way path unit 6, a paper discharge unit 7, and a paper discharge tray 8 along the paper discharge conveyance path R2. It has been. Further, the image forming apparatus 1 includes a control unit as a control unit to be described later that controls each unit.

  In addition, the image forming apparatus 1 includes a double-sided conveyance unit 9 that inverts and conveys the paper P in order to form images on both sides (front and back) of the paper P, and a conveyance roller is provided on the double-sided conveyance path R3. A double-sided conveying roller 9A as a pair is provided. By having the double-sided conveyance unit 9, the image forming apparatus 1 can select a single-sided print mode for forming an image on only one side of the paper P and a double-sided print mode for forming an image on both sides of the paper P. .

  In the single-sided printing mode, the paper P is fed from one of the two paper feeding units 2A and 2B, and the fed paper P is temporarily stopped at the leading edge by the registration roller 3 to bend. By doing so, the skew is corrected. Thereafter, the sheet P is re-conveyed at the timing when the position of the transfer unit 4 and the toner image on the photoconductor matches. The paper P onto which the image has been transferred by the transfer unit 4 is discharged to the paper discharge tray 8 through the fixing unit 5, the three-way path unit 6, the paper discharge conveyance path R 2, and the paper discharge unit 7.

  On the other hand, in the double-sided printing mode, the paper P on which an image is formed on one side is temporarily stopped at the paper discharge unit 7 before being discharged to the paper discharge tray 8 and then reversely reversed. The sheet is switched back in the direction and sent to the duplex conveyance path R3 of the duplex conveyance unit 9. The paper discharge unit 7 sandwiches and conveys the paper P between a paper discharge driving roller 7A and a driven roller 7B as a conveying member. The paper discharge roller 7A rotates the paper discharge driving roller 7A in the reverse direction so that the paper P is discharged to the paper discharge tray 8. Can be switched back in the reverse direction to the paper discharge direction.

  FIG. 2 is a partially enlarged plan view of the drive transmission unit of the paper discharge unit 7 in the image forming apparatus 1 according to the present embodiment. As shown in FIG. 2, a forward rotation electromagnetic clutch 7A1 and a reverse rotation electromagnetic clutch 7A2 are provided on the shaft of the paper discharge drive roller 7A, and the rotation of the main motor 10 rotating in one direction is provided. The driving force is transmitted by gear connection. More specifically, the forward rotation electromagnetic clutch 7A1 has a rotational driving force as the first driving force of the main motor 10 via the main motor output gear 10A, the first forward rotation idler gear 11 and the second forward rotation idler gear 12. Is transmitted. On the other hand, the rotational driving force as the second driving force of the main motor 10 is transmitted to the reverse electromagnetic clutch 7A2 via the main motor output gear 10A and the reverse idler gear 13.

  The normal rotation electromagnetic clutch 7A1 rotates the paper discharge driving roller 7A in the clockwise direction shown in FIG. 1 so that the paper P is normally conveyed in the direction of the paper discharge tray 8 when it is turned on. Further, when the reverse electromagnetic clutch 7A2 is turned ON, the paper discharge roller 7A is rotated counterclockwise as shown in FIG. 1 so as to reversely convey the sheet P in the direction of the double-sided conveyance path R3 (switchback conveyance). Rotate. The forward rotation electromagnetic clutch 7A1 and the reverse rotation electromagnetic clutch 7A2 rotate in opposite directions. The rotation of the main motor 10 is transmitted to the shaft of the discharge driving roller 7A. This is because the number is different by one. The forward rotation electromagnetic clutch 7A1 and the reverse rotation electromagnetic clutch 7A2 are controlled so as not to be simultaneously turned ON.

  In the image forming apparatus 1 configured as described above, the switchback conveying device includes a paper discharge drive roller 7A and a driven roller 7B of the paper discharge unit 7, a drive unit that drives the paper discharge drive roller 7A, and a drive unit that controls the drive unit, which will be described later. A control unit. The drive means for driving the paper discharge drive roller 7A is, for example, as described above, the forward rotation electromagnetic clutch 7A1, the reverse rotation electromagnetic clutch 7A2, the main motor 10, the first forward rotation idler gear 11, and the second forward rotation idler gear 12. The idler gear 13 is used.

Next, the operation in the duplex printing mode in the image forming apparatus 1 according to the present embodiment will be described in detail.
FIG. 3 is an explanatory diagram showing the operation direction of the paper P in the duplex printing mode in the image forming apparatus according to the present embodiment. 4 to 8 are explanatory views showing the operation of the paper P at each time point in the duplex printing mode of the image forming apparatus in time series.
In FIG. 3, in the double-sided printing mode, the paper P is transported in the direction of the vertical transport path R1, the three-way section 6, and the paper discharge section 7, temporarily stopped at the paper discharge section 7, and then switched back in the reverse direction. It is sent from the three-way section 6 to the duplex conveyance path R3.

  In FIG. 4, after the paper P fed from the paper feeding unit 2 is temporarily stopped by the registration roller 3, an image is formed on one surface by the transfer unit 4, and the fixing roller 5 </ b> A and the pressure roller of the fixing unit 5 are formed. The state which has gone to the three-way part 6 is being pinched | interposed into 5B. Thereafter, the paper P is transported between the fixing roller housing first transport guide surface 5C and the switchback guide plate first transport guide surface 5E, and the leading end thereof contacts the switchback guide plate first transport guide surface 5E. Thus, the paper discharge conveyance path R2 is guided in the direction of the paper discharge unit 7.

  In FIG. 5, after the paper P is transported to the paper discharge transport path R <b> 2 through the three-way section 6, it is picked up by the paper discharge driving roller 7 </ b> A and the driven roller 7 </ b> B and transported in the paper discharge direction. Has reached the three-way section 6 and is in contact with the switchback guide plate first conveyance guide surface 5E. From this state, the paper P is further transported in the transport direction in the paper discharge direction as the first transport direction (hereinafter also referred to as “normal transport direction”). Then, the rear end of the paper P in the normal conveyance direction is separated from the switchback guide plate first conveyance guide surface 5E.

  FIG. 6 shows a state immediately after the rear end of the paper P has passed through the switchback guide plate first conveyance guide surface 5E. In the present image forming apparatus 1, a conveyance path switching member such as a displaceable switching claw operated by an actuator or an elastic member for preventing reverse feeding is used for switching the conveyance path of the paper P in the three-way section 6. Without being provided, the transport path is switched using the rigidity (stiffness) of the paper P. By not providing the conveyance path switching member, the cost of the apparatus can be reduced. In FIG. 5, the rear end of the paper P is in contact with the switchback guide plate first conveyance guide surface 5E and the rear edge is curved. In FIG. 6, the rear end of the paper P is the switchback guide plate first conveyance. It is straight from the guide surface 5E due to the rigidity (stiffness) of the paper P.

  FIG. 7 shows a state in which the paper P is further conveyed forward in the paper discharge direction and temporarily stopped from the state shown in FIG. The image forming apparatus 1 has the conveyance direction length information of the sheet P being conveyed by a known sheet size automatic detection method or a sheet size input setting by an operator. Using the length information in the transport direction of the paper P, the paper discharge drive roller 7A is stopped after the stop time TA has elapsed from when the registration sensor 3A detects the trailing edge of the paper P (paper detection signal OFF) (FIG. 10). 13). Specifically, the stop time TA is set by “(distance between the registration sensor 3A and the conveyance nip of the paper discharge roller 7−43.4 [mm]) / the conveyance speed of the paper P”. As a result, as shown in FIG. 7, the trailing edge of the paper P stops at 43.4 [mm] before reaching the conveyance nip as the nipping position of the paper discharge roller 7.

  FIG. 8 shows a state in which the paper discharge driving roller 7A rotates in the reverse direction (rotates counterclockwise) and conveys the paper P into the double-sided conveyance path R3. The paper P once stopped by the reverse rotation of the paper discharge driving roller 7A is a transport direction as a second transport direction opposite to the paper discharge direction (hereinafter also referred to as “reverse transport direction”). It is conveyed to. The leading edge of the sheet P in the reverse conveyance direction enters the double-sided conveyance path R3 by the three-way section 6 due to the rigidity (koshi) of the sheet P described above. Thereafter, the sheet P passes through the duplex conveying roller 9A and reaches the registration roller 3 again. Then, the front end of the paper P is temporarily stopped by the registration roller 3 and the skew is corrected by forming a bend, and then the paper P is held and conveyed by the registration roller 3, and the image is transferred to the other side by the transfer unit 4. The The sheet P on which the image is formed on the other side is fixed to the sheet discharge tray 8 after the image is fixed by the fixing unit 5 and then between the sheet discharge roller 7A and the driven roller 7B of the sheet discharge unit 7. Is done.

  In the image forming apparatus 1 configured as described above, the electromagnetic clutch 7A1 for normal rotation stops the rear end in the transport direction of the paper P at a position 43.4 [mm] before the transport nip position of the paper discharge unit 7. The forward electromagnetic clutch 7A1 is turned off. However, even if the forward rotation electromagnetic clutch 7A1 is turned off at a predetermined timing as described above, the discharge driving roller 7A is moved in the normal rotation direction by the inertia (moment of inertia) of the drive system on the discharge driving roller 7A side of the clutch. Stop after rotating. At this time, if the amount of rotation that the paper discharge drive roller 7A rotates in the forward rotation direction with inertia is too large, the rear end of the paper P passes through the conveyance nip of the paper discharge unit 7 and the paper discharge unit 7 is discharged. The paper P cannot be clamped by the roller pair of the paper driving roller 7A and the driven roller 7B. Then, the paper P is discharged from the paper discharge unit 7 and cannot be conveyed by being switched back in the reverse direction.

  Further, when the driving force of the main motor 10 is input to the forward electromagnetic clutch 7A1, the idling torque (also referred to as “co-rotation torque”) is generated on the drive output side (the sheet discharge driving roller 7A). May occur. When the idling torque of the normal rotation electromagnetic clutch 7A1 is larger than the load torque on the shaft of the normal rotation electromagnetic clutch 7A1, the normal rotation electromagnetic clutch 7A1 transmits the drive unintentionally during the switching time to the reverse rotation electromagnetic clutch 7A2. There is a risk that. Then, when the paper P is switched back, the paper P is unintentionally conveyed in the forward direction, and the rear end of the paper P may pass the conveyance nip of the paper discharge unit 7.

Therefore, in the present image forming apparatus 1, the operation condition at the time of switching back the paper P is set so that the rear end in the normal transport direction does not pass the transport nip of the paper discharge unit 7 when the paper P is switched back. It is set so as to satisfy the relationship 1).
L> Tmax × Vmax (1)
However,
L: The rear end position of the sheet P in the normal conveyance direction and the sheet discharge unit when the forward rotation electromagnetic clutch 7A1 is turned off and the transmission of the driving force is stopped while the sheet discharge driving roller 7A is conveying the sheet P in the normal conveyance direction. 7 (mm) from the holding position of the paper P by 7
Tmax: The forward rotation electromagnetic clutch 7A1 is turned off and the transmission of the driving force is stopped while the paper discharge driving roller 7A is transporting the paper P in the forward conveyance direction, and then the reverse rotation electromagnetic clutch 7A2 is turned on and the reverse conveyance direction is turned on. Maximum time until transmission of driving force starts (sec)
Vmax: Maximum transport speed (mm / sec) at which the paper discharge drive roller 7A transports the paper P in the forward transport direction.

As specific examples of the above formula (1), Tmax = 125 [msec], Vmax = 102.08 [mm / sec] (= conveyance linear velocity of the paper discharge driving roller 7A), L = 43.4 [mm] ] (See FIGS. 10 and 13). Therefore, the relationship of Formula (1) is satisfied as follows.
Tmax × Vmax = 0.125 × 102.08
= 12.76
<43.4 = L

By satisfying the relationship of the above formula (1), when the forward rotation electromagnetic clutch 7A1 is turned off, the rear end of the sheet P in the forward transport direction is not transported in the transport nip even if the discharge drive roller 7A is idled by the inertia of the drive system. Is reached, the reverse electromagnetic clutch 7A2 is turned on. As a result, the paper P is conveyed in the reverse direction before the rear end in the normal conveyance direction reaches the conveyance nip, so that the rear end in the normal conveyance direction does not pass through the conveyance nip of the paper discharge unit 7 and can be reliably obtained. It can be switched back and transported in the reverse direction.
Further, as described above, when the idling torque of the forward rotation electromagnetic clutch 7A1 is larger than the load torque on the axis of the forward rotation electromagnetic clutch 7A1, the forward rotation electromagnetic clutch 7A1 is switched during the switching time to the reverse rotation electromagnetic clutch 7A2. The drive may be transmitted unintentionally. Even in such a case, the reverse electromagnetic clutch 7A2 is turned ON before the rear end of the paper P in the forward transport direction reaches the transport nip and is transported in the reverse direction. It does not pass through the conveyance nip of the paper section 7. Therefore, the paper P can be reliably switched back and conveyed in the reverse direction.

  Further, as described above, since the formula (1) incorporates the sheet conveyance speed as a factor, the above-described merit can be obtained regardless of the sheet conveyance linear speed of the image forming apparatus 1. Further, by considering the paper conveyance speed at the initial maximum value, a switchback conveyance device that is not affected by deterioration with time of the paper ejection drive roller 7A and the driven roller 7B of the paper ejection section 7 due to paper dust or wear or the like is obtained. be able to.

  In the image forming apparatus 1, the conveyance jam due to the conveyance delay of the paper P is detected during the conveyance of the paper P in the reverse conveyance direction. For example, a detection sensor as a position detection unit that detects the rear end in the reverse conveyance direction of the paper P is provided in the double-sided conveyance path R3. When the detection sensor does not detect the trailing edge of the paper P within a predetermined time after the conveyance of the paper P in the reverse conveyance direction is started, the control unit detects a conveyance jam due to the conveyance delay of the paper P. The detection sensor and the control unit have a function as a clogging detection unit during conveyance of the paper P in the reverse conveyance direction.

  Note that the detection sensor is not limited to detecting the trailing edge of the paper P in the reverse conveyance direction on the double-sided conveyance path R3, and may be a sensor that detects the leading edge of the paper P in the reverse conveyance direction. The detection sensor may also be used as a sheet trailing edge detection sensor 7D that detects a trailing edge of the sheet P in the normal conveyance direction, which will be described later with reference to FIG.

  During the switchback conveyance of the paper P, the trailing edge in the forward conveyance direction of the paper P advances to the paper discharge unit 7 due to the idling torque of the electromagnetic clutch 7A1 for forward rotation and the inertia on the output side, and as a result, the reverse The conveyance start position in the conveyance direction may be closer to the paper discharge unit 7 than the target. Then, since the distance between the front end of the paper P in the reverse transport direction and the detection sensor becomes longer, the time from the start of transport of the paper P in the reverse transport direction until the detection sensor detects the rear end of the paper P Becomes longer. For this reason, after the conveyance of the paper P in the reverse conveyance direction is started, the detection sensor cannot detect the trailing edge of the paper P within a predetermined time, and the conveyance of the paper P is not delayed. There is a risk of erroneous detection that a jam has occurred.

  For this reason, in the present image forming apparatus 1, a jam detection margin M as a detection margin as a sheet conveyance delay allowable amount is prevented so that a conveyance jam due to a conveyance delay of the sheet P is not erroneously detected when the sheet P is conveyed in the reverse conveyance direction. Is set so as to satisfy the relationship of the following equation (2).

M> Tmax × Vmax (2)
However,
M: Jam detection margin when the paper P starts to be transported in the reverse transport direction (allowable paper transport delay) (mm)
Tmax: The forward rotation electromagnetic clutch 7A1 is turned off and the transmission of the driving force is stopped while the paper discharge driving roller 7A is transporting the paper P in the forward conveyance direction, and then the reverse rotation electromagnetic clutch 7A2 is turned on and the reverse conveyance direction is turned on. Maximum time to start transmission of driving force (s)
Vmax: Maximum transport speed (mm / s) at which the paper discharge driving roller 7A transports the paper P in the forward transport direction.

  The jam detection margin M is predicted to move the trailing edge of the paper P within a predetermined time after the paper P starts to be transported in the reverse transport direction when determining the paper jam based on the detection result of the detection sensor. It is added to the moving distance. That is, it is the allowable amount of paper conveyance delay when determining a paper jam based on the detection result of the detection sensor.

As a specific example of the above formula (2), Tmax = 125 [msec], Vmax = 102.08 [mm / sec] (= conveyance linear speed of the paper discharge driving roller 7A), and M = 70 [mm]. (See FIGS. 10 and 13). Therefore, the relationship of Expression (2) is satisfied as follows.
Tmax × Vmax = 0.125 × 102.08
= 12.76
<70 = M

  By satisfying the relationship of the above expression (2), the jam detection margin M is set to be larger than the maximum amount in which the rear end in the normal conveyance direction of the paper P is shifted toward the paper discharge unit 7 during switchback conveyance. It is possible to prevent erroneous detection of a conveyance jam due to conveyance delay.

  Further, as described above, since the formula (2) incorporates the paper conveyance speed as a factor, the above-described merit can be obtained regardless of the paper conveyance linear speed of the image forming apparatus 1. Furthermore, by considering the paper transport speed as a maximum value, a switchback transport device that is not affected by the temporal deterioration of the paper discharge drive roller 7A and the driven roller 7B of the paper discharge section 7 due to paper dust, wear, etc. Can do.

  Further, in the image forming apparatus 1 of the present embodiment, the registration roller 3 is installed on the downstream side of the double-sided conveyance path (third conveyance path) R3 in the paper conveyance direction, and a pair of double-sided conveyance rollers 9A is provided on the double-sided conveyance path R3. ing. The double-sided conveyance roller 9A can transmit a driving force as a third driving force via an electromagnetic clutch, and can stop the leading edge of the paper P conveyed from the double-sided conveyance path R3 by the registration roller 3.

  In the image forming apparatus 1, the paper P can be conveyed by the interleaf in the double-sided printing mode. Interleaf means that in the duplex printing mode, a sheet on which an image is formed on one side first forms an image on one side of the next sheet before it returns to the vertical conveyance path R1, and then conveys it. , A conveying method in which an image forming operation is repeatedly performed on the other side of the preceding sheet. In general, interleaf is a transport method performed on a sheet having a short length in the transport direction, and can improve productivity in the duplex printing mode.

  FIG. 9 is an explanatory diagram showing a state in which the paper P is being conveyed by the interleaf in the image forming apparatus 1 according to the present embodiment. FIG. 9 shows a state in which the preceding paper P conveyed from the double-sided conveyance path R3 is temporarily stopped by the registration roller 3, and the next paper P has been switched back and is conveyed to the double-sided conveyance path R3. When the leading edge of the preceding sheet is temporarily stopped by the registration roller 3, the trailing edge of the preceding sheet is located slightly upstream in the conveying direction with respect to the double-sided conveying roller 9A, but the discharge driving roller 7A and the driven roller of the discharging unit 7 It is not pinched by 7B.

  The electromagnetic clutch unit that drives the duplex conveying roller 9A sets a load on the electromagnetic clutch shaft larger than the idling torque of the electromagnetic clutch. Thereby, when the electromagnetic clutch is OFF, the electromagnetic clutch does not transmit the drive unintentionally. Therefore, it is possible to prevent the sheet P during registration standby from being unintentionally excessively fed by the double-sided conveyance roller 9A and causing the occurrence of undulation and conveyance direction registration error. Or the same effect can be acquired by satisfy | filling the relationship of following Formula (3).

Ts ≦ δ / VHmax (3)
However,
Ts: Stop time (sec) during which the double-sided conveyance roller electromagnetic clutch is stopped when the sheet P is temporarily stopped by the conveyance roller (registration roller) pair on the downstream side in the conveyance direction of the double-sided conveyance roller 9A
δ: Allowable amount of deflection of the sheet P between the conveyance nip of the double-sided conveyance roller 9A and the conveyance nip of the conveyance roller (registration roller) downstream in the conveyance direction (mm)
VHmax: Maximum conveyance speed (mm / sec) of the paper P by the double-sided conveyance roller 9A

Specific examples of the above formula (3) are: Ts = 0 [msec], δ = 7 [mm], VHmax = 101.73 [mm / sec] (= conveying linear velocity of the duplex conveying roller 9A). . Therefore, the relationship of Formula (3) is satisfied as follows.
δ / VHmax = 7 / 101.73
= 0.0688
≧ 0 = Ts

  By satisfying the relationship of the above expression (3), even when the sheet P in resist standby is unintentionally excessively fed by the electromagnetic clutch for driving the double-sided conveyance roller 9A, the deflection of the sheet P is the allowable amount of deflection of the sheet P. It is suppressed to the following. Therefore, it is possible to prevent the occurrence of the undulation of the paper P and the misregistration in the conveyance direction due to excessive feeding.

  Further, in the above equation (3), the sheet conveyance speed is a factor, so that the above-mentioned merit can be obtained regardless of the sheet conveyance linear speed of the image forming apparatus 1. Further, by considering the paper conveyance speed as a maximum value, it is possible to provide a switchback conveyance device that is not affected by deterioration with time of the double-sided conveyance roller 9A due to paper dust or wear.

FIG. 10 is a timing chart at the time of interleaf in the image forming apparatus 1 according to the present embodiment.
As shown in FIG. 10, the registration roller electromagnetic clutch 3 </ b> A <b> 1 is turned on after a lapse of time t <b> 1 after the registration sensor 3 </ b> A detects the paper P and is turned ON, and the registration roller 3 is rotationally driven to start conveying the paper P. . The registration roller electromagnetic clutch 3A1 is turned OFF after the time t3 has elapsed since the sheet P has passed the registration sensor 3A and turned OFF.

  The forward-rotating electromagnetic clutch 7A1 that normally rotates the paper discharge driving roller 7A is turned on after a lapse of time t2 since the registration-roller electromagnetic clutch 3A1 is turned on, and the time after the sheet P is turned off after passing the registration sensor 3A. Turns off after TA has elapsed.

  The reverse electromagnetic clutch 7A2 that reversely rotates the paper discharge driving roller 7A is turned on 100 [msec] after the forward electromagnetic clutch 7A1 is turned off, and the conveyance of the paper P in the reverse conveyance direction is started. Turns off after t4.

  Further, the double-sided conveyance roller electromagnetic clutch 9A1 as a driving means for transmitting the driving force to the double-sided conveyance roller 9A is turned on after a lapse of time t5 after the registration roller electromagnetic clutch 3A1 is turned on. Then, the double-sided transfer roller electromagnetic clutch 9A1 is turned off after the time t6 has elapsed from the second turn-on of the registration roller electromagnetic clutch 3A1. At this time, the paper P on which an image is formed on one side stops in a state where the paper P is sandwiched between the double-sided conveyance rollers 9 </ b> A just before the front end of the reverse conveyance direction hits the registration roller 3.

  In addition, the registration sensor 3A detects the succeeding paper P at the timing after the elapse of time t7 after the reverse rotation electromagnetic clutch 7A2 is turned on and is turned on. After the registration sensor 3A detects the succeeding paper P and is turned on, the registration roller electromagnetic clutch 3A1 is turned on after the elapse of time t1, and the registration roller 3 is rotationally driven to start conveying the succeeding paper P. To do. The registration roller electromagnetic clutch 3A1 is turned off after a lapse of time t3 after the succeeding paper P passes through the registration sensor 3A and is turned off.

  The forward-rotating electromagnetic clutch 7A1 is turned on after a lapse of time t2 after the registration-roller electromagnetic clutch 3A1 is turned on, and is turned off after a lapse of time TA after the succeeding paper P passes through the registration sensor 3A and is turned off.

Thereafter, the reverse electromagnetic clutch 7A2 is turned on and the succeeding paper P is conveyed to the double-sided conveyance path R3. Also, the registration roller electromagnetic clutch 3A1 is turned on, and the forward rotation electromagnetic clutch 7A1 is turned on, the preceding paper P is conveyed, an image is formed on the other surface, and the paper is discharged onto the paper discharge tray 8.
Thereafter, it is possible to efficiently form images on both sides of the plurality of sheets P by repeating the above-described interleaf operation.

FIG. 11 and FIG. 12 are explanatory diagrams showing the transport state of the paper P in time series when the interleaf operation is not performed in the duplex printing mode in the image forming apparatus 1 according to the present embodiment.
In general, what is not interleaved is a conveyance method performed on a sheet P having a long conveyance direction length. FIG. 11 shows a state where the paper P is temporarily stopped at the paper discharge unit 7 when the switchback conveyance is performed without the interleaf operation. FIG. 12 shows a state in which the paper P is conveyed in the reverse conveyance direction from the state shown in FIG. FIG. 12 shows a state in which the rear end of the paper P is sandwiched and held by the paper discharge unit 7. The paper P is transported to the vertical transport path R1 and an image is formed on the other surface, and then discharged from the paper discharge unit 7 to the paper discharge tray 8. After the preceding paper P is discharged, the process proceeds to image formation on the next paper P. Thereafter, this is repeated to form an image.

  FIG. 13 is a timing chart when the image forming apparatus 1 according to this embodiment does not interleave. Note that description of portions common to the timing chart of FIG. 10 is omitted. In FIG. 13, the registration sensor 3 </ b> A detects the paper P for the second time and turns on, which is the same paper as the paper P detected for the first time, not the next paper.

  When the leading edge of the paper P is temporarily stopped by the registration roller 3, the rear edge of the paper is positioned downstream of the double-sided conveyance roller 9A, and the longest paper P used in the image forming apparatus of this embodiment is shown in FIG. As shown, it is sandwiched between a paper discharge drive roller 7A and a driven roller 7B of the paper discharge section 7. It is desirable to set the electromagnetic clutch for driving the paper discharge driving roller 7A and the driven roller 7B so as to satisfy the following conditions.

  When the paper P is between the conveyance nip of the double-sided conveyance roller 9A and the conveyance nip of the registration roller 3, the electromagnetic clutch that drives the double-sided conveyance roller 9A has at least one of the same two conditions as when the interleaf operation is performed. It is desirable to set to satisfy one. That is, it is desirable that the electromagnetic clutch unit that drives the double-sided conveyance roller 9A sets a load on the clutch shaft larger than the idling torque of the electromagnetic clutch. Alternatively, it is desirable to satisfy the condition of the above formula (3). Accordingly, it is possible to prevent the paper P during registration standby from being unintentionally excessively fed by the double-sided conveyance roller 9A and causing the occurrence of rippling and conveyance direction registration error.

  Further, when the paper P is between the conveyance nip of the paper discharge unit 7 and the conveyance nip of the double-sided conveyance roller 9A, it is desirable to satisfy the relationships of the above formulas (1) to (3). Thereby, the effect mentioned above can be acquired. That is, the paper P can be reliably switched back and transported in the reverse direction without the rear end of the paper P in the forward transport direction passing through the transport nip of the paper discharge unit 7. In addition, erroneous detection of a conveyance jam can be prevented. In addition, it is possible to prevent the occurrence of rippling of the paper P and a conveyance direction registration error.

  In addition, with regard to the above formulas (1) to (3), since the sheet conveyance speed is taken into consideration, the above-described advantages can be obtained regardless of the sheet conveyance linear speed of the image forming apparatus 1. Furthermore, by considering the paper transport speed as a maximum value, a switchback transport device that is not affected by deterioration with time of the rollers such as the paper discharge drive roller 7A and the double-sided transport roller 9A due to paper dust, wear, etc. Can do.

  Note that the switchback conveyance device in which the length of the duplex conveyance path R3 is extremely short may not include the duplex conveyance roller 9A. In this case, the load torque on the clutch shaft of the reverse rotation electromagnetic clutch 7A2 may be set larger than the idling torque of the reverse rotation electromagnetic clutch 7A2 that drives the paper discharge drive roller 7A. Or you may satisfy | fill the relationship of following Formula (4).

TRs ≦ δR / VRmax (4)
However,
TRs: Stop time (sec) during which the reverse electromagnetic clutch 7A2 is stopped when the sheet P is temporarily stopped by the registration roller 3 on the downstream side in the transport direction of the paper discharge driving roller 7A.
δR: Allowable deflection (mm) of the sheet P between the conveyance nip of the paper discharge unit 7 and the conveyance nip of the registration roller 3 on the downstream side in the conveyance direction
VRmax: Maximum conveyance speed (mm / sec) of the paper P by the paper discharge driving roller 7A

  By setting the idling torque of the reverse electromagnetic clutch 7A2 or satisfying the relationship of the above equation (4), the sheet P during registration standby is unintentionally fed excessively by the reverse electromagnetic clutch 7A2 of the paper discharge driving roller 7A. It will never be done. Therefore, it is possible to prevent the occurrence of undulations and misregistration problems in the conveyance direction.

FIG. 14 is a schematic diagram of a configuration in which two duplex conveyance rollers 9A are provided in the duplex conveyance path R3.
In the case of the configuration shown in FIG. 14 as well, conditions are set in the same way as described above. Accordingly, it is possible to prevent the sheet P during registration standby from being unintentionally excessively fed by the electromagnetic clutch for driving each conveyance roller, and causing the occurrence of waving and conveyance direction registration error.

  In the above-described example, the configuration using the reverse rotation electromagnetic clutch 7A2 to rotate the paper discharge driving roller 7A in the reverse direction has been described. However, the configuration is not limited to this configuration, and other motors and one-way clutches are combined. You may tell the drive.

  FIG. 15 is a partially enlarged plan view of the drive transmission unit of the paper discharge unit 7. As shown in FIG. 15, in order to reversely rotate the paper discharge drive roller 7A, a one-way clutch 14 that transmits a drive force in the reverse direction is provided on the drive shaft of the paper discharge drive roller 7A. As a drive source for the one-way clutch 14, a paper discharge reverse motor 15 is provided. When the paper P is switched back, the forward rotation electromagnetic clutch 7A1 is turned off and the paper discharge reverse rotation motor 15 is turned on, so that the paper discharge drive roller 7A can be rotated in reverse via the one-way clutch 14.

  In the above-described example, the discharge driving roller 7A is stopped after the stop time TA has elapsed from when the registration sensor 3A detects the rear end of the paper P (paper detection signal OFF). A detection sensor for detecting and stopping the paper P may be provided.

  FIG. 16 is a schematic configuration diagram in which a sheet trailing edge detection sensor 7D for directly detecting the sheet trailing edge and stopping the sheet P is provided in the sheet discharge conveyance path R2. In the configuration example of FIG. 16, the stop accuracy of the paper P can be improved by detecting and controlling the trailing edge of the paper P by the paper trailing edge detection sensor 7D.

FIG. 17 is a block diagram illustrating an example of a main part of a control system that controls switchback conveyance in the image forming apparatus 1 according to the present embodiment.
The switchback transport apparatus includes a control unit 500 as a control unit configured by a computer device such as a microcomputer. The control unit 500 includes, via an I / O interface unit 505, a main motor 10, a registration sensor 3A for detecting the paper P of the registration roller 3, and a registration roller electromagnetic clutch 3A1 for turning on / off the rotation of the registration roller 3. Is connected. Further, the forward rotation electromagnetic clutch 7A1, the reverse rotation electromagnetic clutch 7A2, and the double-sided conveyance roller electromagnetic clutch 9A1 of the discharge driving roller 7A are connected to the control unit 500. Here, the registration sensor 3 </ b> A sends information detected by the sensor to the control unit 500.

  The control unit 500 includes a CPU (Central Processing Unit) 501. In addition, a ROM (Read Only Memory) 503 and a RAM (Random Access Memory) 504 as storage means connected to the CPU 501 via the bus line 502, and an I / O interface unit 505 are provided. The CPU 501 executes various calculations and drive control of each unit by executing a control program which is a computer program incorporated in advance. The ROM 503 stores in advance fixed data such as computer programs and control data. The RAM 504 functions as a work area for storing various data in a rewritable manner. Note that the control unit 500 may be configured using, for example, an IC or the like as a semiconductor circuit element manufactured for control in a switchback transfer device, instead of a computer device such as a microcomputer.

  As shown in the timing chart of FIG. 10, the control unit 500 configured as described above rotates the main motor 10 by starting the image forming operation of the printer 1, for example. Based on the ON signal of the registration sensor 3A, ON / OFF of the registration roller electromagnetic clutch 3A1, the forward rotation electromagnetic clutch 7A1, the reverse rotation electromagnetic clutch 7A2, and the double-sided conveyance roller electromagnetic clutch 9A1 is controlled.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect A)
Drives so that the sheet material is nipped and conveyed by switching between a first conveyance direction such as a normal conveyance direction of a sheet material such as paper P and a second conveyance direction such as a reverse conveyance direction opposite to the first conveyance direction. When the sheet material is conveyed in the first conveyance direction and the conveyance member such as the sheet ejection drive roller 7A of the possible sheet ejection unit 7, the forward rotation direction is controlled via the clutch such as the forward rotation electromagnetic clutch 7A1 that can be controlled on and off. A second driving force such as a driving force in a reverse conveying direction that is different from the first driving force when the sheet material is conveyed in the second conveying direction. A switchback conveying apparatus comprising: a driving unit that transmits a force to the conveying member to drive; and a control unit such as a control unit that controls the driving unit, wherein the conveying member holds the sheet material in the first conveying direction. Clutch off during transport After, before the trailing edge of the sheet material in the first transport direction passes through the support position by the conveying member, to start the transfer of the second driving force to the conveying member.
According to this, as described in the above embodiment, when switching back the sheet material that is nipped by the conveying member to which the first driving force is transmitted via the clutch and conveyed in the first conveying direction, The clutch is turned off during the conveyance. After the clutch is turned off, the sheet material is held by the conveying member before the rear end of the sheet material in the first conveying direction passes the holding position by the conveying member, and is opposite to the first conveying direction. The transmission of the second driving force to the conveying member is started so as to convey in the second conveying direction. Thus, by starting transmission of the second driving force to the conveying member in a state where the sheet material is held by the conveying member, the sheet material held by the conveying member is reliably switched in the second conveying direction. It can be transported back.
(Aspect B)
In the above aspect A, the distance between the rear end of the sheet material in the first conveyance direction and the holding position of the sheet material by the conveyance member when the clutch is turned off during conveyance of the sheet material in the first conveyance direction is L, and the clutch When Tmax is the maximum time from when turning off to start transmission of the second driving force to the conveying member, and Vmax is the maximum conveying speed when the conveying member conveys the sheet material in the first conveying direction, The relational expression represented by L> Tmax × Vmax is satisfied.
According to this, as described in the above embodiment, the sheet material is not affected by the deterioration of the conveying member with time, regardless of the conveying speed when the conveying member conveys the sheet material in the first conveying direction. 2. It can be transported by reliably switching back in the transport direction.
(Aspect C)
In the above-described aspect A or B, position detection means such as a detection sensor for detecting the leading or trailing end position of the sheet material in the second conveyance direction of the sheet material, and the second conveyance of the sheet material based on the detection result of the position detection means Clogging detection means such as a control unit for detecting clogging in the direction.
According to this, as described in the above embodiment, it is possible to reliably detect the jam of the sheet material in the second conveyance direction at the time of switchback conveyance.
(Aspect D)
In the above-described aspect C, the clogging detection unit detects clogging of the sheet material based on a moving distance that the front end or the rear end position of the sheet material moves within a predetermined time after the conveyance of the sheet material in the second conveyance direction. When the detection margin such as a jam detection margin added to the moving distance when the jam detection unit detects jam of the sheet material is M, the relational expression M> Tmax × Vmax is satisfied.
According to this, as described in the above embodiment, the detection margin M is set to be larger than the maximum amount by which the rear end of the sheet material in the first conveyance direction is shifted toward the conveyance member during conveyance in the second conveyance direction. In addition, it is possible to prevent erroneous detection of clogging due to a delay in conveyance of the sheet material.
(Aspect E)
In any of the above-described aspects A to D, the clutch is an electromagnetic clutch such as a normal rotation electromagnetic clutch 7A1.
According to this, as described in the above embodiment, the driving force can be easily and electrically controlled on and off.
(Aspect F)
In any of the above aspects A to E, the conveying member is a pair of discharge rollers such as a discharge driving roller 7A and a driven roller 7B that discharges the sheet material.
According to this, since the discharge roller pair can also be used as the conveying member as described in the above embodiment, the apparatus can be reduced in size and cost compared to a configuration in which a separate conveying member is provided.
(Aspect G)
In any one of the above aspects A to F, the sheet is disposed in the conveyance path that conveys the sheet material in the second conveyance direction, and is disposed downstream of the conveyance path that conveys the sheet material in the second conveyance direction. A registration roller pair such as a registration roller 3 for temporarily stopping the sheet material by abutting the leading end portion in the second conveyance direction of the material, and double-sided conveyance that is disposed in the conveyance path and conveys the sheet material toward the registration roller pair A pair of conveying rollers such as a roller 9A.
According to this, as described in the above embodiment, the skew of the sheet material can be corrected by abutting the front end of the sheet material conveyed in the second conveyance direction against the registration roller pair.
(Aspect H)
In the above-described aspect G, when the sheet material is conveyed toward the registration roller pair, the third driving force is transmitted to the conveyance roller pair via a clutch such as the electromagnetic clutch 9A1 for double-sided conveyance rollers that can be controlled on and off. Drive output side provided with drive means and connected to the pair of conveying rollers against idling torque generated on the drive output side when the third driving force is input to the clutch while the clutch stops driving transmission The load torque on the shaft is set large.
According to this, as described in the above embodiment, when the clutch is off, the drive is not unintentionally transmitted to the pair of conveying rollers due to the idling torque of the clutch. Therefore, the sheet material that is waiting while hitting the registration roller pair is not unintentionally excessively fed by the conveyance roller pair, and the occurrence of the sheet material waving and the conveyance direction registration misalignment is prevented. Can do.
(Aspect I)
In the above aspect G, when conveying the sheet material toward the registration roller pair, a driving unit that transmits and drives the third driving force to the conveying roller pair via a clutch such as an electromagnetic clutch that can be controlled on and off is provided. When the allowable amount of deflection of the sheet material between the conveying roller pair and the registration roller pair is δ and the maximum conveying speed of the sheet material by the conveying roller pair is VHmax, the registration roller pair temporarily stops the sheet material. The stop time Ts during which the clutch is off satisfies the relational expression represented by Ts ≦ δ / VHmax.
According to this, as described in the above-described embodiment, even when the sheet material is on standby while abutting against the registration roller pair, even if the sheet material is unintentionally excessively fed by the clutch of the conveying roller pair, the sheet material The bending of is suppressed to an allowable amount or less. Therefore, it is possible to prevent the sheet material from waving and the conveyance direction registration error caused by the excessive feeding.
(Aspect J)
An image forming apparatus such as the image forming apparatus 1 comprising the switchback conveying device according to any one of the above aspects A to I.
According to this, as described in the above embodiment, the sheet material can be reliably switched back and conveyed, and images can be formed on both sides of the sheet material.

1 Image forming device (printer)
2A Front sheet feeding unit 2B Manual sheet feeding unit 3 Registration roller 3A Registration sensor 3A1 Registration roller electromagnetic clutch 4 Transfer unit 5 Fixing unit 5A Fixing roller 5B Pressure roller 5C Fixing roller housing first conveyance guide surface 5D Fixing roller housing second Conveyance guide surface 5E Switchback guide plate 1st conveyance guide surface 5F Switchback guide plate 2nd conveyance guide surface 6 Three-way section 7 Discharge portion 7A Discharge drive roller 7A1 Forward rotation electromagnetic clutch 7A2 Reverse rotation electromagnetic clutch 7B Discharge driven roller 7C Discharge upper guide plate 7D Paper trailing edge detection sensor 8 Discharge tray 9 Double-sided part 9A Double-sided conveyance roller 9A1 Double-sided conveyance roller electromagnetic clutch 9B Double-sided entrance upper guide plate 10 Main motor 500 Control unit P Paper R1 Vertical conveyance path R2 Paper ejection Transport path R3 Double-sided transport path

JP 2008-209624 A

Claims (10)

A transport member that can be driven to switch between a first transport direction of the sheet material and a second transport direction opposite to the first transport direction to sandwich and transport the sheet material;
When the sheet material is conveyed in the first conveying direction, the first driving force is transmitted to the conveying member via a clutch that can be controlled to be turned on and off, and the sheet material is conveyed in the second conveying direction. Drive means for transmitting a second driving force, sometimes different from the first driving force, to the conveying member;
A control means for controlling the drive means, and a switchback transport device comprising:
After the conveying member holds the sheet material and conveys it in the first conveying direction, the clutch is turned off, and the rear end of the sheet material in the first conveying direction is held by the conveying member. Before passing through the position, transmission of the second driving force to the transport member is started. In the switchback conveying apparatus of claim 1,
Let L be the distance between the rear end of the sheet material in the first transport direction and the holding position of the sheet material by the transport member when the clutch is turned off during transport of the sheet material in the first transport direction. Tmax is the maximum time from when the clutch is turned off until the transmission of the second driving force to the conveying member is started, and the maximum time when the conveying member conveys the sheet material in the first conveying direction. When the conveyance speed is Vmax,
L> Tmax × Vmax
A switchback transfer device, characterized by satisfying the relational expression shown in FIG. In the switchback conveying device according to claim 1 or 2,
Position detecting means for detecting a leading edge or a trailing edge position of the sheet material in the second conveying direction of the sheet material;
A switchback conveyance device comprising: a clogging detection unit that detects clogging of the sheet material in the second conveyance direction based on a detection result of the position detection unit. In the switchback conveying apparatus of Claim 3,
The clogging detection unit detects clogging of the sheet material based on a moving distance that the leading or trailing end position of the sheet material moves within a predetermined time after the sheet material starts conveying in the second conveying direction. Is what
When the detection margin added to the moving distance when the clogging detection means detects clogging of the sheet material is M,
M> Tmax × Vmax
A switchback transfer device, characterized by satisfying the relational expression shown in FIG. In the switchback conveyance apparatus in any one of Claims 1 thru | or 4,
The switchback transport device, wherein the clutch is an electromagnetic clutch. In the switchback conveyance apparatus in any one of Claims 1 thru | or 5,
The switchback conveying device, wherein the conveying member is a pair of discharge rollers for discharging the sheet material. In the switchback conveyance apparatus in any one of Claims 1 thru | or 6,
A second conveyance direction of the sheet material is arranged on a conveyance path that conveys the sheet material in the second conveyance direction, and is disposed downstream of the conveyance path that conveys the sheet material in the second conveyance direction in the second conveyance direction. A pair of registration rollers for temporarily stopping the sheet material by abutting the tip,
A switchback conveying apparatus comprising: a conveying roller pair disposed in the conveying path and configured to convey the sheet material toward the registration roller pair. The switchback transport device of claim 7,
Drive means for transmitting and driving a third driving force to the pair of conveying rollers via a clutch capable of on / off control when conveying the sheet material toward the pair of registration rollers;
While the clutch stops driving transmission, the driving load of the conveying roller pair is set to be greater than the idling torque generated on the drive output side when the third driving force is input to the clutch. A switchback transfer device characterized by comprising: The switchback transport device of claim 7,
Drive means for transmitting and driving a third driving force to the pair of conveying rollers via a clutch capable of on / off control when conveying the sheet material toward the pair of registration rollers;
When the allowable amount of bending of the sheet material between the conveying roller pair and the registration roller pair is δ, and the maximum conveying speed of the sheet material by the conveying roller pair is VHmax, the sheet material is applied to the registration roller pair. The stop time Ts during which the clutch is turned off to stop once is
Ts ≦ δ / VHmax
A switchback transfer device, characterized by satisfying the relational expression shown in FIG.   An image forming apparatus comprising the switchback conveying device according to claim 1.

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