JP2013230889A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and low-cost image forming apparatus by decreasing the number of driving members.SOLUTION: A preceding sheet S and a following sheet S are brought into contact with nip parts of a registration roller pair 106 and a conveyance roller pair 131, for temporary stop. In this state, a controller starts driving a registration drive motor 137 and a preregistration drive motor 138 simultaneously. The preregistration roller pair is driven at a predetermined conveyance speed until the upstream end of the preceding sheet passes through the preregistration roller pair, while driving the preregistration roller pair 107 and the preregistration roller pair at the predetermined conveyance speed. The registration roller is controlled at an image forming speed lower than the predetermined conveyance speed when the upstream end of the preceding sheet passes through the preregistration roller pair.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination of these, and more specifically, an image forming apparatus having a configuration for conveying a sheet fed from a sheet feeding unit to an image forming unit. About.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, an image forming unit that forms an image on a sheet, a sheet feeding unit that feeds a sheet stored in the sheet storage unit, and an image forming unit that sends a sheet sent from the sheet feeding unit There is known a device provided with a sheet conveying device that conveys the ink to the sheet. Some sheet conveying apparatuses are configured to perform a pre-registration operation in order to eliminate the variation in conveyance when conveying a sheet to an image forming unit.

  An image forming apparatus having a configuration for performing this pre-registration operation is known. In this pre-registration operation, the sheet is temporarily stopped based on detection by a sensor arranged in the sheet conveyance path, a predetermined stop time is taken, and after the preceding sheet advances to a predetermined place, the subsequent Start the seat. As a result, the sheet can be conveyed to the image forming unit at a fixed interval (interval between sheets conveyed continuously). During this pre-registration operation, the stop time becomes longer if the sheet is conveyed early to a predetermined position, and the stop time becomes shorter if the sheet is conveyed later (see Patent Document 1).

JP 2002-29649 A

  However, in the conventional mechanism for performing the pre-registration operation, the following problems occur when trying to narrow the gap between the sheets as the conveyance speed increases. In other words, in order to narrow the gap between the sheets, the driving of the roller that performs the pre-registration operation, such as conveying the succeeding sheet when the preceding sheet is stopped, and the driving of the roller downstream of this roller are individually performed. Must be done. In that case, the increase in the number of drive units such as a drive motor may hinder the compactness of the apparatus or increase the cost.

  The present invention makes it possible to drive the roller for performing the pre-registration operation and the roller on the downstream side by the same drive unit, and reduce the number of the drive units to reduce the size of the apparatus and reduce the cost. An object of the present invention is to provide an image forming apparatus that enables the above.

  In the image forming apparatus, the image forming apparatus is disposed on an upstream side in the sheet conveying direction of the image forming unit, an image forming unit that forms an image on the sheet, a sheet feeding unit that feeds the sheet toward the image forming unit, A first conveying roller pair that performs a registration operation to stop the sheet and then send it to the image forming unit in accordance with the image forming operation, and is disposed downstream of the sheet feeding unit in the sheet conveying direction. A second conveyance roller pair that performs a pre-registration operation that is sent out after being stopped, and a sheet that is disposed between the first conveyance roller pair and the second conveyance roller pair and that is fed from the second conveyance roller pair. A third conveying roller pair that conveys toward the first conveying roller pair, a first drive unit that drives the first conveying roller pair, and the second and third conveying roller pairs that are conveyed in a predetermined manner. From the state where the leading edge of each of the preceding sheet and the succeeding sheet is brought into contact with each nip portion of the first and second conveying roller pairs and stopped temporarily, the first and second are driven at a speed. The drive unit is started to drive simultaneously, and the second and third transport roller pairs are driven at the predetermined transport speed, and the first transport roller pair is set so that the upstream end of the preceding sheet is the third transport roller. A control unit that controls to drive at the predetermined transport speed until the pair exits and to drive at the image forming speed slower than the predetermined transport speed from the time when the upstream end exits the third transport roller pair. It is characterized by that.

  According to the present invention, the third transport roller pair is controlled by switching the drive of the first transport roller pair that may pinch the sheet with the third transport roller pair from the predetermined transport speed to the image forming speed. It can drive with a 2nd drive part common with 2 conveyance roller pairs. For this reason, it is possible to reduce the number of driving units, reduce the size of the apparatus, and reduce the cost, while enabling conveyance with a shorter interval between sheets.

1 is a schematic configuration diagram showing a digital composite copying machine (image forming apparatus) according to an embodiment of the present invention. The schematic block diagram which expands and shows the characteristic part in FIG. 6 is a diagram for explaining an operation during sheet conveyance in the digital composite copying machine of the embodiment. FIG. 6 is a timing chart showing a driving state during sheet conveyance in the present embodiment. The diagram for demonstrating the operation | movement at the time of the sheet conveyance in a comparative example. FIG. 6 is a diagram illustrating in detail an operation during sheet conveyance in FIG. 5.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. First, a digital composite copying machine 200 to which an image forming apparatus according to the present invention is applied will be described with reference to FIG.

  As shown in FIG. 1, a digital composite copying machine (image forming apparatus) 200 includes a copying machine main body 1 as an image forming apparatus main body and a large-capacity deck 40 connected to the copying machine main body 1. The digital composite copying machine 200 includes a document reading unit 4 that reads an image of a document, and an image forming unit 42 that forms an image on a sheet by electrophotography based on image information read by the document reading unit 4.

  Further, the digital multi-functional copying machine 200 includes deck feeding units 34 and 35, cassette feeding units 36 and 37, and a large-capacity deck feeding unit 39 as sheet feeding units that feed sheets toward the image forming unit 42. doing. The digital composite copying machine 200 is configured to be able to continuously feed a plurality of sheets from each sheet feeding unit to the image forming unit 42.

  Inside the copying machine main body 1, there is disposed a control unit 130 that controls each part of the digital composite copying machine 200 in an integrated manner. On the upper part of the copying machine main body 1, a document table 2 made of a transparent glass plate fixedly provided is arranged. A document feeder 3 for conveying a document to a predetermined position on the document table 2 is disposed on the document table 2, and the document reading unit 4 is disposed on the bottom of the document table 2.

  In the digital composite copying machine 200, an image of a document on the document table 2 is read by the document reading unit 4, and based on the data, the writing laser unit 5 emits a laser beam to uniformly charge the photosensitive member. By scanning the drum 12, an electrostatic latent image is formed on the photosensitive drum 12.

  In the digital composite copying machine 200, the deck storage units 30 and 31 built in the copying machine main body 1 and the sheets S stacked in the sheet cassettes 32 and 33 are loaded into the deck feeding units 34 and 35 and the cassette feeding units 36 and 37. To the image forming unit 42.

  The deck feeding unit 34 includes a pickup roller 101 that feeds the sheets S stacked and stored in the deck storage 30, a feed roller 102 that separates and feeds the sheets S sent by the pickup roller 101, and a retard roller 103. Is provided. These rollers are similarly provided in the deck feeding unit 35 and the cassette feeding units 36 and 37.

  The image forming unit 42 includes a photosensitive drum 12, a charger 13 for uniformly charging the surface of the photosensitive drum, and an electrostatic latent image formed on the surface of the photosensitive drum 12 charged by the charger 13. And a developing device 14 that forms a toner image to be transferred onto the sheet S. Further, the image forming unit 42 includes a transfer charger 19 that transfers the toner image developed on the surface of the photosensitive drum 12 to the sheet S. The image forming unit 42 is in close contact with the sheet, passes between the transfer charger 19 and the photosensitive drum 12, and separates the sheet having the toner image transferred from the photosensitive drum 12, and the transfer of the toner image. Thereafter, a cleaner 26 for removing toner remaining on the photosensitive drum 12 is provided.

  On the downstream side of the image forming unit 42, a conveyance unit 21 that conveys the sheet S on which the toner image is transferred by belt and a fixing unit 22 that fixes the toner image on the sheet conveyed by the conveyance unit 21 as an image are disposed. Has been. Further, a discharge roller 24 for discharging the sheet S on which the toner image is fixed by the fixing device 22 from the copying machine main body 1 is disposed. Further, a discharge tray 25 for receiving the sheet S discharged by the discharge roller 24 is disposed outside the copying machine main body 1.

  On the conveyance path for conveying the sheet from the sheet feeding unit to the image forming unit 42, various roller pairs 105, 107, 108, 109 to 112, 123 and a sheet path sensor 116 for detecting the leading edge and the trailing edge of the sheet, 117, 118, 119 are arranged. The sheet S fed by each roller pair is sent to the image forming unit 42 by the registration roller pair 106.

  A registration sensor 120 that detects the leading edge of the sheet is disposed in the vicinity of the upstream side of the registration roller pair 106 in the sheet conveyance direction. The registration roller pair 106 is disposed upstream of the image forming unit 42 in the sheet conveyance direction, and performs a registration operation in which the sheet S is temporarily stopped and then sent to the image forming unit 42 in accordance with the image forming operation. One transport roller pair is configured.

  The roller pair 107 is a pre-registration roller pair for feeding the sheet S sent from each sheet feeding unit to the registration roller pair 106. The pre-registration roller pair 107 is disposed between the registration roller pair 106 and the large-capacity deck conveying roller pair 131, and conveys the sheet S sent from the roller pair 131 toward the roller pair 106. Three transport roller pairs are configured.

  In the upstream conveyance path of the pair of pre-registration rollers 107 in the copying machine main body 1, a conveyance roller pair 105, a sheet path sensor 104, conveyance roller pairs 108 and 109, a sheet path sensor 116, a conveyance roller pair 110, and a sheet path sensor. 117 are arranged in this order.

  From the conveyance path between the pre-registration roller pair 107 and the conveyance roller pair 105, a sheet conveyance path that is continuous with the deck feeding unit 35 is branched. In this sheet conveyance path, a conveyance roller pair 111, a conveyance roller 112, a sheet path sensor 118, and a conveyance roller pair 123 are arranged in this order from the downstream side.

  A sheet reversing path is branched from the conveyance path between the conveyance roller 112 and the conveyance roller pair 123. In this sheet reversing path, a sheet path sensor 119, a pair of double-sided conveyance rollers 113 and 114, a reversing roller 115 that rotates in the forward and reverse directions, and a sheet reversing unit 121 are arranged in this order from the downstream side.

  A registration driving motor 137 for driving the registration roller pair 106 is disposed in the copying machine main body 1. The registration drive motor 137 constitutes a first drive unit that drives the registration roller pair (first transport roller pair) 106.

  In the copying machine main body 1, a pre-registration driving motor that simultaneously drives a pair of pre-registration rollers 107 in the copying machine main body and a pair of large-capacity deck conveying rollers 131 in a large-capacity deck 40 that is a sheet feeding unit. 138 is arranged.

  The large-capacity deck conveyance roller pair 131 is disposed in the large-capacity deck 40 (in the sheet feeding unit) on the downstream side in the sheet conveyance direction of the large-capacity deck feeding unit 39, and temporarily stops the sheet S. A second conveyance roller pair that performs a pre-registration operation to be sent out from the first is configured. The large-capacity deck feeding unit 39 constitutes a sheet feeding unit. The pre-registration drive motor 138 drives the large-capacity deck transport roller pair (second transport roller pair) 131 and the pre-registration roller pair (third transport roller pair) 107 at a transport speed (predetermined transport speed) β. A second drive unit is configured. Normally, the separation and feeding of sheets in the sheet feeding unit has a large variation in feeding timing, so the sheets are fed at intervals shorter than the set sheet interval, and the sheet is temporarily stopped halfway in the conveyance path. The interval is adjusted. A stop operation for stopping the succeeding sheet at a predetermined position in the transport path in order to transport the succeeding sheet at an appropriate interval according to the transport state of the preceding sheet is referred to as a pre-registration operation.

  The large-capacity deck 40 includes a large-capacity deck storage 38 and a large-capacity deck feeding unit 39 that feeds sheets S loaded and stored in the large-capacity deck storage 38 toward the image forming unit 42. Yes. The large-capacity deck feeding unit 39 includes a pickup roller 134 that feeds the sheet S in the large-capacity deck storage 38, a large-capacity deck feed roller 133 that separates and feeds the fed sheet S, and a retard roller 135. A separating roller pair is arranged. The large-capacity deck feeding unit 39 is provided with a large-capacity deck drive motor 139 that drives the large-capacity deck transport roller pair 132 and the large-capacity deck feed roller 133.

  A large-capacity deck conveyance roller pair 131 for feeding the sheet S from the large-capacity deck 40 side to the copying machine main-body 1 side is disposed at the connection portion of the large-capacity deck 40 with the copying machine body 1. A conveyance detection sensor 136 is disposed in the vicinity of the upstream side of the large-capacity deck conveyance roller pair 131.

  The large capacity deck 40 is detachably connected to the copying machine main body 1. When the large-capacity deck 40 is coupled as shown in FIG. 1, the driving force of the pre-registration drive motor 138 is transmitted to the drive gear train (not shown) of the large-capacity deck conveying roller pair 131. The gear on the pre-registration drive motor 138 side is meshed. In this state, the pre-registration roller pair 107 and the large-capacity deck transport roller pair 131 can be driven simultaneously by the pre-registration drive motor 138.

  Each of the rollers other than the registration roller pair 106 and the pre-registration roller pair 107 in the copying machine main body 1 is rotationally driven by transmitting a driving force of a driving motor (not shown). The rotation operation of each of these rollers is controlled by the control unit 130 based on the detection result of each corresponding sheet path sensor.

  In this embodiment, the pre-registration drive motor 138 in the copier body 1 simultaneously drives the pre-registration roller pair 107 in the copier body 1 and the large-capacity deck transport roller pair 131 in the large-capacity deck 40. It is configured as follows. This eliminates the need for a complicated configuration in which two motors for individually driving the roller pairs 107 and 131 are disposed, simplifying the configuration of the apparatus, making it compact, and reducing costs.

  In this embodiment, the large-capacity deck drive motor 139 in the large-capacity deck 40 is configured to drive the large-capacity deck transport roller pair 132 and the large-capacity deck feed roller 133 in common. A one-way clutch 41 is disposed between the conveying roller pair 132 and the large capacity deck drive motor 139 (see FIG. 2). The one-way clutch 41 can pull out the sheet S bitten by the conveying roller pair 132 from the downstream side even when the large-capacity deck drive motor 139 is stopped. As a result, it is not necessary to use two motors for individually driving the roller pairs 132 and 133, the apparatus configuration is simplified and made compact, and the cost can be reduced.

  Next, an operation at the time of sheet feeding in the digital multi-functional copying machine 200 will be described by taking as an example a case of feeding from the deck feeding unit 34.

  That is, at the start of sheet feeding, the pickup roller 101, the feed roller 102, the retard roller 103, the conveyance roller pair 105, and the pre-registration roller pair 107 are driven to rotate by a drive motor (not shown). At this time, the registration roller pair 106 is still in a stopped state.

  At the time of sheet feeding, the pickup roller 101 first feeds the sheet S stacked and stored in the deck storage 30 to the nip portion between the feed roller 102 and the retard roller 103. Here, the sheet S is separated into only the uppermost sheet by a retard roller 103 provided facing the feed roller 102 and applied with a force that rotates in a direction opposite to the conveying direction with a constant torque.

  The leading edge of the uppermost sheet S is detected by the sheet path sensor 104 and is conveyed by the conveying roller pair 105. At this time, the digital multi-functional copying machine 200 performs a so-called pre-registration operation that corrects variations at the leading edge of the sheet and adjusts the interval between sheets (inter-sheet spacing). Therefore, the control unit 130 temporarily stops the rotation of the conveying roller pair 105 based on the detection timing of the leading edge of the sheet by the sheet path sensor 104. Thus, the leading edge of the sheet S being nipped and conveyed by the conveyance roller pair 105 is stopped at a predetermined position on the conveyance path, and the rotation of the conveyance roller pair 105 is started again after a predetermined time has elapsed.

  That is, in the sheet feeding unit, not only the sheet whose leading edge is at the normal stacking position of the deck storage 30 but also a sheet whose back is returned to the deck storage 30 by the retard roller 103 and is near the feed roller 102. Will also be fed. Therefore, there is a variation in the front end position of the sheet at the start of feeding, and it is necessary to eliminate this variation on the front side of the registration roller pair 106. This pre-registration operation needs to be performed on the sheet S sent from the large-capacity deck storage 38 in the large-capacity deck 40.

  In the digital composite copying machine 200, when image formation is performed on both sides of a sheet, the sheet S formed by the image forming unit 42 is reversed by the sheet reversing unit 121 and the reversing roller 115 and sent to the sheet reversing path. Then, it is sent again to the image forming unit 42 through the paths of the double-sided roller pairs 114 and 113, the conveying roller 112, the conveying roller pair 111, the pre-registration roller pair 107, and the registration roller pair 106.

  Next, a sheet conveyance sequence from sheet feeding to transfer will be described in detail with reference to FIGS. 2 and 3 by taking the large-capacity deck feeding unit 39 as an example. 2 is an enlarged schematic configuration diagram showing the characteristic portion in FIG. 1, and FIG. 3 is a diagram showing the positional relationship between the leading edge and the trailing edge of each sheet during continuous feeding of the sheet.

  The registration roller pair 106, the pre-registration roller pair 107, the large-capacity deck transport roller pairs 131 and 132, and the large-capacity deck feed roller 133 are configured to be rotatable at a process speed α and a transport speed β. The process speed α is an image forming speed corresponding to the image forming operation of the image forming unit 42, and the transport speed β is set to a speed higher than the process speed α.

  The control unit 130 (see FIG. 1) drives each of the registration drive motor 137, the pre-registration drive motor 138, and the large-capacity deck drive motor 139 so that the rollers can rotate at the process speed α and the conveyance speed β. To control each. As shown in FIG. 3 and FIG. 4, when accelerating to the conveyance speed β, the control unit 130 starts rotation of each drive motor 137, 138, 139 at an initial speed β 1 that is slower than the conveyance speed β and accelerates the acceleration time. Acceleration drive control is performed so that the rotation continues for Tb. Thereby, each of the roller pairs 106, 107, 131 (first to third transport roller pairs) is controlled to be accelerated so as to reach the transport speed β after a predetermined time (Tb) has elapsed from the initial speed β1.

  The control unit 130 according to the present embodiment starts from the state in which the leading ends of the preceding sheet and the succeeding sheet are brought into contact with the nip portions of the registration roller pair 106 and the large-capacity deck conveying roller pair 131 and stopped temporarily. 137 and 138 are simultaneously driven. Further, the control unit 130 keeps driving the roller pairs 106 and 131 at the conveyance speed (predetermined conveyance speed) β until the upstream end of the preceding sheet passes through the pre-registration roller pair 107. Is driven at a conveyance speed β. Then, the control unit 130 drives the registration roller pair 106 at a process speed (image forming speed) α that is slower than the conveyance speed β from the time when the upstream end of the preceding sheet passes through the pre-registration roller pair 107.

  When feeding a sheet from the large-capacity deck storage 38, first, the large-capacity deck drive motor 139 is driven, and the pickup roller 134 is rotated so that the sheet S is changed from the initial speed β1 to the transport speed β and the large capacity deck feed roller. 133 (arrow a part in FIG. 3). At this time, the sheet is separated only into the uppermost sheet by a retard roller 135 provided opposite to the large-capacity deck feed roller 133 and applied with a force that rotates in a direction opposite to the conveying direction with a constant torque. The

  The uppermost sheet is fed through the large-capacity deck transport roller pair 132, and the leading end is detected by the transport detection sensor 136. Under the control of the control unit 130, the leading end abuts the large-capacity deck transport roller pair 131 and reaches a predetermined level. It stops when the loop is formed (arrow b part in FIG. 3). Thereby, a so-called pre-registration operation is performed. At this time, the preceding sheet S is stopped in a state where the leading end abuts against the registration roller pair 106 to form a predetermined loop, and the upstream side is sandwiched between the pre-registration roller pair 107. Thereby, a so-called registration operation is performed. The preceding sheet S and the subsequent sheet S are in a state indicated by a two-dot chain line in FIG.

  That is, the pre-registration operation is performed in order to eliminate variations in sheet conveyance due to the sheet S being returned by the retard roller 135 or the start position at the start of sheet feeding being varied. Here, at the time of pre-registration, if the sheet S is conveyed early from the large-capacity deck storage 38, the stop time at the large-capacity deck conveyance roller pair 131 becomes long, and if it is conveyed late, the large-capacity deck. The stop time at the conveying roller pair 131 is shortened. By appropriately adjusting the length of the stop time at the large-capacity deck conveyance roller pair 131 in this way, the arrival time of the sheet S from the large-capacity deck storage 38 is made uniform, and there is no variation. It can be sent to the pair of ration rollers 106.

  Then, the control unit 130 simultaneously drives the registration drive motor 137, the pre-registration drive motor 138, and the large-capacity deck drive motor 139 simultaneously. As a result, the preceding sheet S stopped by the registration roller pair 106 and the succeeding sheet S stopped by the large-capacity deck conveying roller pair 131 are simultaneously started (part A of FIG. 3).

  At this time, the drive motors 137, 138, and 139 that are simultaneously driven are all at the initial speed β1, and are accelerated within the acceleration time Tb to the transport speed β (the end of acceleration is indicated by the arrow B in FIG. 3). As a result, the preceding sheet S and the succeeding sheet S are simultaneously conveyed in a state where a certain gap is left. The preceding sheet S is conveyed to the image forming unit 42 by the registration roller pair 106, and the leading edge of the subsequent sheet S is detected by the registration sensor 120 via the pre-registration roller pair 107.

  Then, the succeeding sheet S is stopped when the leading end abuts against the nip portion of the registration roller pair 106 and is fed a predetermined amount, and this time, the preceding sheet S is in contact with the nip portion of the registration roller pair 106 as a preceding sheet. Create a quantification loop. As a result, the skew of the preceding preceding sheet S is corrected so as to follow the extending direction of the nip portion.

  Next, under the control of the control unit 130, the registration drive motor 137, the pre-registration drive motor 138, and the large-capacity deck drive motor 139 are simultaneously started to drive from the initial speed β1 to the transport speed β as described above. The

  When the trailing edge of the preceding preceding sheet passes through the roller pair 107 (the portion indicated by arrow C in FIG. 3), the driving motor 137 is driven at the time before the leading edge of the preceding sheet transfers the toner image. The roller pair 106 that rotates at a speed is reduced to a process speed α. That is, when the trailing edge of the preceding sheet passes through the roller pair 107 and is released from the conveying state by the drive motor 138, the registration roller motor 106 is now switched to the process speed α by driving the registration drive motor 137. Can do.

  Then, when the trailing edge of the preceding sheet S passes through the registration roller pair 106 and stops, the succeeding sheet S abuts the leading edge against the registration roller pair 106 in the same manner as described above. To form a predetermined loop. Then, the succeeding sheet S is stopped in a state where the upstream side is sandwiched between the pair of pre-registration rollers 107, and becomes the next preceding sheet.

  Next, a comparative example for the above-described embodiment will be described with reference to FIGS. 5 and 6. FIG. 5 is a diagram for explaining the operation at the time of sheet conveyance in the comparative example, and FIG. 6 is a diagram showing the operation at the time of sheet conveyance in FIG. 5 in detail.

If the sheet S is temporarily stopped downstream of the large-capacity deck transport roller pair 132 (the portion indicated by D in both figures), the sheet S is moved to the large-capacity deck transport roller pair 132 during acceleration (acceleration time Tb). When entering, the sheet S loops due to the speed difference. Therefore, it is necessary to increase the sheet interval time by Tc in FIG. 6 (arrow E portion in FIG. 6). In FIG. 6, Tc is
[(Β1 + β) / 2] × [Tb / β]
It is expressed.

  Also, it is necessary to increase the sheet interval time for the transport variation Ta from the position to the large capacity deck transport roller pair 131. Therefore, according to this comparative example, it is not possible to control the distance between the Ta + Tc sheets in total (arrow F portion in FIG. 6).

Taking the difference between this comparative example and this embodiment as an example, for example:
β = 750 mm / s
β1 = 250 mm / s
From Tb = 50 ms to Tc = 33 ms,
If Ta = 12ms,
Ta + Tc = 45 ms.

  Thus, for example, if the present invention is applied to a digital composite copying machine of 110 sheets (545 ms / sheet), 120 sheets (500 ms / sheet) can be obtained.

  As described above, according to the present embodiment, the driving of the registration roller pair 106 that holds the sheet S together with the pre-registration roller pair 107 can be switched from the conveyance speed β to the process speed α. Thus, the pre-registration roller pair 107 can be driven by the common pre-registration drive motor 138 together with the large-capacity deck transport roller pair 131. For this reason, the number of drive units such as a drive motor can be reduced as compared with the case where the roller pairs 106, 107, 131 are individually driven by a drive motor while enabling conveyance with a shorter interval between sheets. As a result, the device can be made compact and the cost can be reduced.

  39: Sheet feeding unit (large capacity deck feeding unit), 40: Sheet feeding unit (large capacity deck), 42: Image forming unit, 106: First transport roller pair (registration roller pair), 107: First 3 conveying roller pair (pre-registration roller pair), 131... Second conveying roller pair (large capacity deck conveying roller pair), 130... Control unit, 137... First driving unit (registration driving motor), 138. Drive unit (drive motor before registration), 200... Image forming apparatus (digital composite copying machine), S... Sheet, preceding sheet, subsequent sheet

Claims (4)

An image forming unit for forming an image on a sheet;
A sheet feeding unit that feeds the sheet toward the image forming unit;
A first conveying roller pair that is disposed upstream of the image forming unit in the sheet conveying direction and performs a registration operation of temporarily stopping the sheet and then feeding the image forming unit in accordance with the image forming operation;
A second conveying roller pair that is disposed downstream of the sheet feeding unit in the sheet conveying direction, and that performs a pre-registration operation for sending out the sheet after temporarily stopping;
A third conveyance roller pair that is disposed between the first conveyance roller pair and the second conveyance roller pair and conveys the sheet sent from the second conveyance roller pair toward the first conveyance roller pair;
A first drive unit for driving the first conveying roller pair;
A second drive section for driving the second and third transport roller pairs at a predetermined transport speed;
From the state where the leading ends of the preceding sheet and the succeeding sheet are brought into contact with the nip portions of the first and second conveying roller pairs and temporarily stopped, the first and second driving units are started to be driven at the same time. With the second and third transport roller pairs being driven at the predetermined transport speed, the first transport roller pair is moved at the predetermined transport speed until the upstream end of the preceding sheet passes through the third transport roller pair. A control unit that drives and controls the upstream end to drive at an image forming speed slower than the predetermined conveying speed from the time when the upstream end passes through the third conveying roller pair;
An image forming apparatus. The control unit controls the first and second drive units to accelerate the first to third transport roller pairs so that the transport speed becomes the transport speed after a predetermined time has elapsed from the initial speed,
The image forming apparatus according to claim 1. An image forming apparatus main body including the image forming unit, and a sheet feeding unit connected to the image forming apparatus main body, and a sheet fed from the sheet feeding unit provided in the sheet feeding unit. Causing the pre-registration operation to be performed by the second conveying roller pair disposed in the sheet feeding unit;
The image forming apparatus according to claim 1, wherein the image forming apparatus includes: The first driving unit is disposed in the image forming apparatus main body, and the second driving unit is disposed in the sheet feeding unit;
The image forming apparatus according to claim 3.

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