Sheet transport device and image forming apparatus

Abstract

To stabilize sheet transport and improve the productivity of double-sided printing. [Solution] The sheet conveying device (10) includes a first conveying section (1D) that conveys a sheet, a second conveying section (42) that conveys a sheet in a second conveying direction after conveying the sheet in a first conveying direction with the first roller and second roller in contact with the sheet, a first conveying path that guides the sheet being conveyed from the first conveying section to the second conveying section, a second conveying path connected to the first conveying path at a first connection section that guides the sheet being conveyed in the second conveying direction by the second conveying section, a drive section that drives the first conveying section and the second conveying section, and a control unit (1H) that controls the drive unit. The control unit controls the drive unit so that when conveying a preceding sheet from the second conveying section to the second conveying path and conveying a succeeding sheet to the first conveying path, the leading edge of the succeeding sheet reaches the first connection section while the trailing edge of the preceding sheet is positioned between the first connection section and the second conveying section.

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying apparatus for conveying sheets and an image forming apparatus. [Background Art]

[0002] There has been proposed an image forming apparatus including a sheet reversing means that switchbacks and feeds out a sheet fed into a reversing path from the leading end thereof with the trailing end of the sheet oriented to become the new leading end (see Patent Document 1). In the image forming apparatus of Patent Document 1, the sheet reversing means is constituted by a reversing roller arranged at an upper position and having a cutout portion, and a driven roller arranged at a lower position. When a succeeding sheet is fed into the sheet reversing means, the cutout portion of the reversing roller is oriented downward to bring the sheet reversing means into an open state, thereby allowing a portion of a preceding sheet and a portion of the succeeding sheet to overlap each other. [Prior Art Document] [Patent Document]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2003-192205 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, in an apparatus where the sheet reversing means is set to an open state as in Patent Document 1 described above, the leading end of the succeeding sheet is not nipped, so that the stability of conveyance of the succeeding sheet is lowered. On the other hand, for example, when an image forming apparatus is downsized, the length of a duplex conveyance path is shortened, and if alternate feeding, in which image formation is performed on a succeeding sheet while a preceding sheet is being conveyed again, cannot be performed, the productivity of double-sided printing is lowered.

[0005] Accordingly, it is an object of the present invention to provide a sheet conveying apparatus and an image forming apparatus that can achieve stabilization of sheet conveyance and improvement in productivity of double-sided printing. [Means for Solving the Problem]

[0006] One aspect of the present invention is a first conveying unit for conveying a sheet, a second conveying unit disposed downstream of the first conveying unit in the direction of sheet conveyance by the first conveying unit and including a first roller and a second roller capable of gripping and conveying the sheet, wherein the first roller and the second roller are in contact with the sheet and the sheet is conveyed in the first conveying direction, and then the sheet is conveyed in a second conveying direction opposite to the first conveying direction, a first conveying path for guiding the sheet being conveyed from the first conveying unit to the second conveying unit, and the first conveying path and a first connecting unit connected to the first conveying unit, The sheet conveying device comprises a second conveying path that guides a sheet being conveyed in the second conveying direction by a second conveying unit, a drive unit that drives the first conveying unit and the second conveying unit, and a control unit that controls the drive unit, wherein the control unit controls the drive unit so that when conveying a preceding sheet from the second conveying unit to the second conveying path and conveying a succeeding sheet to the first conveying path, the leading edge of the succeeding sheet reaches the first connection unit while the rear end of the preceding sheet is positioned between the first connection unit and the second conveying unit. [Effects of the Invention]

[0007] According to the present invention, it is possible to stabilize the transport of sheets and improve the productivity of double-sided printing. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing an image forming apparatus according to the first embodiment. [Figure 2] This diagram illustrates each transport path in the image forming apparatus according to the first embodiment. [Figure 3] This diagram illustrates the printing order in relation to the number of sheets fed and the printing surface in alternating feed. [Figure 4](a) is a diagram showing the position of the sheet when printing the first side of the first sheet in alternating feeding mode. (b) is a diagram showing the position of the sheet when printing the first side of the second sheet in alternating feeding mode. [Figure 5] (a) is a diagram showing the position of the sheets when printing the second side of the first sheet and when printing the first side of the third sheet in alternating feeding. (b) is a diagram showing the position of the sheets when printing the second side of the second sheet and when printing the first side of the fourth sheet in alternating feeding. [Figure 6] This is an enlarged cross-sectional view showing the vicinity of the first connection point between the fixed inversion transport path and the inversion double-sided transport path. [Figure 7] This diagram shows the sheet position when the leading edge of the following sheet reaches the margin at the rear end of the preceding sheet. [Figure 8] (a) is an enlarged cross-sectional view illustrating a reversing double-sided conveyor path. (b) is an enlarged cross-sectional view showing the case where the leading edge of the following sheet reaches the margin on the trailing edge side of the preceding sheet located in the reversing double-sided conveyor path. (c) is an enlarged cross-sectional view illustrating the shape of the guide surface of the guide member forming the reversing double-sided conveyor path. [Figure 9] This is an enlarged cross-sectional view showing the vicinity of the first connection point between the fixing / reversal transport path and the reversal / double-sided transport path in the image forming apparatus according to the second embodiment. [Modes for carrying out the invention]

[0009] <First Embodiment> The first embodiment will be described below with reference to the drawings.

[0010] [Configuration of the image forming apparatus] First, the configuration of the image forming apparatus according to the first embodiment will be described using Figure 1. Figure 1 is a schematic cross-sectional view showing the image forming apparatus according to the first embodiment. Here, as an example of the image forming apparatus according to this embodiment, an electrophotographic laser printer with double-sided printing (double-sided image formation) functionality will be described. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not limited to those unless specifically stated otherwise. In particular, the image forming apparatus according to this embodiment is not limited to a laser printer, but may be other image forming apparatus such as a copier or facsimile. Note that the schematic cross-sectional view shown in Figure 1 is a cross-sectional view in the width direction, which is perpendicular to the sheet transport direction. Similarly, the figures shown in Figures 2 and 4 to 9, which will be described in more detail later, are also drawings in the width direction.

[0011] As shown in Figure 1, the image forming apparatus 1 according to the first embodiment has a main body 1A. Inside the main body 1A, the image forming apparatus 1 roughly comprises a feeding and transporting unit 1B, an image forming unit 1C, a fixing unit 1D, a sheet inversion unit 1E, a re-transporting unit 1F, a sheet discharge unit 1G, and a control unit 1H. In this embodiment, the fixing unit 1D, the sheet inversion unit 1E, the re-transporting unit 1F, and the sheet discharge unit 1G constitute a sheet transporting device 10 that transports the sheet on which the image has been formed by the image forming unit 1C.

[0012] The feeding and transport unit 1B is detachably arranged on the main body 1A of the device and has a feeding cassette 32 as a sheet loading unit that loads and supports multiple sheets S before an image is formed. The feeding and transport unit 1B also has a sheet feeding unit 31 that separates and feeds the sheets supported by the feeding cassette 32 one by one. Furthermore, the feeding and transport unit 1B has a pair of registration rollers (hereinafter referred to as "registration roller pair") 8 as a skew correction unit whose rotation state is controlled by a registration motor M2.

[0013] The sheet feeding unit 31 is configured with a pickup roller 31a, a feed roller 31b, and a retard roller 31c, all driven by a feeding motor M1. The pickup roller 31a picks up the uppermost sheet from among the multiple sheets S supported by the feeding cassette 32. The feed roller 31b and the retard roller 31c are in contact with each other to form a separation nip section, and the sheet S picked up by the pickup roller 31a is conveyed by the feed roller 31b while the retard roller 31c applies a force in the opposite direction. As a result, even if multiple sheets S picked up by the pickup roller 31a are fed at once, they are separated one by one and fed towards the resist roller pair 8 via the conveying roller pair 7. In this embodiment, the retard roller 31c is driven by the same feeding motor M1 as the pickup roller 31a and feed roller 31b via a reversing gear (not shown), but it may be driven by a motor other than the feeding motor M1.

[0014] With the rotation of the register roller pair 8 stopped by the rotation control of the register motor M2, the leading edge of the sheet S, which has been transported by the sheet feeding unit 31 (or the re-transport unit 1F, which will be described in more detail later), comes into contact with it. This causes the leading edge of the sheet S to conform to the nip portion of the register roller pair 8. Subsequently, the rotation of the register roller pair 8 is started by the register motor M2, and the sheet S is transported toward the image forming unit 1C while correcting the skew of the sheet S.

[0015] The image forming unit 1C is configured to include a process cartridge 2 detachable from the apparatus main body 1A, a scanner unit 4, a transfer roller 9, and the like. The process cartridge 2 includes process means such as a photosensitive drum 3, a developing unit (not shown), and a charging roller (not shown). The scanner unit 4 is disposed vertically above the process cartridge 2, and exposes the photosensitive drum 3 based on image signals. The photosensitive drum 3 is rotated together with the transfer roller 9 by a transfer motor M3, charged to a predetermined negative potential by a charging roller (not shown), and then an electrostatic latent image is formed thereon by the scanner unit 4. This electrostatic latent image is reversal-developed by adhering negative toner thereto by a developing unit (not shown) in the process cartridge 2, whereby a toner image is formed on the surface of the photosensitive drum 3. A positive bias is applied to the transfer roller 9 rotated by the transfer motor M3 by a bias applying unit (not shown). As a result, the toner image is transferred as an unfixed image to the surface of the sheet S on the photosensitive drum 3 side, which passes through a nip portion formed by the photosensitive drum 3 and the transfer roller 9.

[0016] In the present embodiment, the fixing unit 1D constitutes a first conveyance unit that conveys a sheet. The fixing unit 1D includes a heating roller 11 serving as a fixing roller that is heated by a heater which is a heating means (not shown) and rotated by driving of a fixing motor M4, and a pressure roller 12 serving as a pressure member that rotates while being in pressure contact with the heating roller 11. That is, the sheet S to which the toner image has been transferred in the image forming unit 1C as described above is conveyed to the fixing unit 1D provided downstream of the image forming unit 1C in the conveyance direction. The sheet S conveyed to the fixing unit 1D is nipped and conveyed at a nip portion formed by the heating roller 11 and the pressure roller 12, and the toner image is fixed to the surface of the sheet S by application of heat and pressure. A fixing discharge sensor flag 13 is disposed downstream of the fixing unit 1D in the conveyance direction, which moves when the trailing end of the sheet S passes therethrough, and the movement of the flag is detected by a fixing discharge sensor SN1.

[0017] The sheet reversing unit 1E includes a double-sided reversing flapper 41 serving as a switching member whose position is switched by a reversing solenoid SL, and a reversing roller pair 42 serving as a second conveying unit that reverses the conveying direction of a sheet S. The double-sided reversing flapper 41 is arranged downstream of the fixing unit 1D in the sheet conveying direction of the fixing unit 1D, and switches the conveying path. That is, the double-sided reversing flapper 41 can be switched between a first position (the solid line position in FIG. 1) and a second position (the broken line position in FIG. 1). In the first position, the sheet conveyed from the fixing unit 1D is guided to the reversing roller pair 42, and in the second position, the sheet conveyed from the fixing unit 1D is guided to an intermediate conveying roller pair 21 serving as a third conveying unit of a sheet discharging unit 1G described later.

[0018] The double-sided reversing flapper 41 is switched to the second position under the control of the control unit 1H in the case of single-sided image formation (single-sided printing) in which an image is formed only on the first surface (single side) of the sheet S. Alternatively, in the case of double-sided image formation (double-sided printing) in which images are formed on the first surface and the second surface (both sides) of the sheet S, after an image is formed on the first surface of the sheet S, the double-sided reversing flapper 41 is switched to the second position under the control of the control unit 1H. Accordingly, the sheet S conveyed from the fixing unit 1D is conveyed to the sheet discharging unit 1G described later. On the other hand, in the case of double-sided image formation (double-sided printing) in which images are formed on the first surface and the second surface (both sides) of the sheet S, after an image is formed on the first surface of the sheet S, the double-sided reversing flapper 41 is switched to the first position under the control of the control unit 1H. Accordingly, the sheet S conveyed from the fixing unit 1D is conveyed to the reversing roller pair 42.

[0019] The reversing roller pair 42 is configured to have a drive roller 42a as a first roller rotated by a reversing motor M5 as a drive unit, and a driven roller 42b as a second roller that follows the drive roller 42a. That is, the sheet S can be gripped and conveyed by the drive roller 42a and the driven roller 42b. The drive roller 42a is rotated by a reversing motor M5 controlled by a control unit 1H so as to be able to change its rotation direction between a first rotation direction W1 and a second rotation direction W2 opposite to the first rotation direction W1. That is, when the drive roller 42a and the driven roller 42b are in contact with the sheet S and the drive roller 42a rotates in the first rotation direction W1, the reversing roller pair 42 conveys the sheet S in the first conveying direction V1. Furthermore, when the driving roller 42a rotates in a second rotation direction W2 opposite to the first conveying direction V1 while the driving roller 42a and the driven roller 42b are in contact with the sheet S, the reversing roller pair 42 conveys the sheet S in a second conveying direction V2 opposite to the first conveying direction V1. Note that the first conveying direction V1 and the second conveying direction V2 are tangential directions of the nip portion 42N formed by the driving roller 42a and the driven roller 42b, that is, the directions in which the sheet S is conveyed by the nip portion 42N of the reversing roller pair 42.

[0020] In the case of double-sided image formation (double-sided printing), the reversing roller pair 42 configured as described above causes the drive roller 42a to rotate in the first rotation direction W1 by the reversing motor M5, and the sheet S is transported in the first transport direction V1. Subsequently, the reversing roller pair 42 rotates in the second rotation direction W2, opposite to the first rotation direction W1, to reverse (swap) the transport direction of the sheet S to the second transport direction V2 and transport it. As a result, the leading and trailing ends of the sheet S are swapped, and the sheet S is transported to the re-transport section 1F.

[0021] The re-transport unit 1F has a pair of double-sided transport rollers 51 as a fourth transport unit driven by a double-sided motor M6, and a pair of re-feeding rollers 52. The re-transport unit 1F re-transports the sheet S, which has been transported from the sheet inversion unit 1E by the inversion roller pair 42, to the pair of register rollers 8 of the feeding transport unit 1B. That is, the sheet S has been inverted by the inversion roller pair 42 of the sheet inversion unit 1E so as to swap its leading and trailing ends, and this inverted sheet S is re-transported to the pair of register rollers 8. As a result, the image forming unit 1C forms a toner image on the second surface of the sheet S opposite to the first surface in the image forming process described above, and the fixing unit 1D fixes the toner image on the second surface of the sheet S. A double-sided transport sensor flag 58 is positioned upstream of the transport direction of the double-sided transport roller pair 51, which moves when the trailing end of the sheet S passes, and whose movement is detected by the double-sided transport sensor SN2.

[0022] The sheet discharge unit 1G includes an intermediate transport roller pair 21 and an discharge roller pair 22 driven by a discharge motor M7, and an discharge tray 60 formed on the upper surface of the device body 1A for loading the discharged sheets. The sheets are discharged from the discharge port (paper discharge port) of the device body 1A to the discharge tray 60 by the discharge roller pair 22. In the case of single-sided printing, after an image is formed on the front surface (first surface) of the sheet S, the double-sided inversion flapper 41 is switched to the second position and the sheet S is transported from the fuser unit 1D to the sheet discharge unit 1G. Alternatively, in the case of double-sided printing, after an image is formed on the back surface (second surface) of the sheet S, the double-sided inversion flapper 41 is switched to the second position and the sheet S is transported from the fuser unit 1D to the sheet discharge unit 1G. The sheet discharge unit 1G then transports the transported sheet S to the discharge tray 60 by the intermediate transport roller pair 21 and the discharge roller pair 22 and discharges it, loading the printed sheet S onto the discharge tray 60. This completes single-sided or double-sided printing in the image forming apparatus 1.

[0023] The control unit 1H is a controller that performs various controls in the image forming apparatus 1, and includes a CPU 71, which is an example of a processor, and memory units such as RAM 72, ROM 73, and HDD 74. The CPU 71, RAM 72, ROM 73, and HDD 74 are connected to each other by a bus so that they can communicate information with one another, and are connected to controllers of each part and operation units (not shown) via interfaces (not shown) so that they can communicate information with one another. The control unit 1H is also connected to various drive motors, various solenoids, various sensors, etc. via interfaces (not shown). Specifically, the control unit 1H is electrically connected to the above-mentioned feed motor M1, register motor M2, transfer motor M3, fixing motor M4, inversion motor M5, double-sided motor M6, discharge motor M7, inversion solenoid SL, fixing discharge sensor SN1, double-sided transport sensor SN2, etc. The control unit 1H sends signals to them to control them freely. In particular, in this embodiment, the control unit 1H can freely control the transport direction and transport position of the sheet S that is inverted by the inversion roller pair 42. Details regarding the control of the sheet S by this control unit 1H will be described later in accordance with the explanation of the sheet S transport operation.

[0024] [Definition of the transport path in an image forming apparatus] Next, the definition of each transport path in the image forming apparatus 1 according to the first embodiment will be explained using Figure 2. Figure 2 is a diagram illustrating each transport path in the image forming apparatus according to the first embodiment. In the image forming apparatus 1 according to this embodiment, there are multiple transport paths that are continuously connected from the supply cassette 32 to the discharge tray 60, and are partitioned so that the sheet S is guided by transport guide members, flappers, etc. Furthermore, in the image forming apparatus 1 according to this embodiment, there are multiple connection points where two of these multiple transport paths are connected. In order to explain the position of the sheet S in such a transport path, the explanation will be given using transport paths and connection points that are conveniently partitioned as follows.

[0025] In detail, in the image forming apparatus 1, it is defined as follows: Feeding register transport path 105: A transport path from the sheet feeding unit 31 to the register roller pair 8. Register fixing transport path 106: A transport path from the register roller pair 8 to the fixing section 1D (the nip section between the heating roller 11 and the pressure roller 12). Fixing and reversing transport path 101: A transport path from the fixing section 1D to the reversing roller pair 42 (nip section 42N between the drive roller 42a and the driven roller 42b). Reversing double-sided conveying path 102: A conveying path from the reversing roller pair 42 through the double-sided conveying roller pair 51 and the refeeding roller pair 52 to the resist roller pair 8. Fixing and discharge transport path 103: A transport path from the fixing section 1D, via the intermediate transport roller pair 21, to the discharge roller pair 22. Reversal downstream transport path 104: A transport path downstream from the reversal roller pair 42 in the transport direction when the sheet S is transported from the fixing section 1D to the reversal roller pair 42. First connection section CN1: A connection section in which the reversing double-sided transport path 102 is connected to the fixing reversing transport path 101. Second connection section CN2: A connection section in which the fixing discharge transport path 103 is connected to the fixing inversion transport path 101. Third connection section CN3: A connection section in which the reversal double-sided transport path 102 is connected to the feed / transport register transport path 105.

[0026] In this embodiment, the fixing and reversing transport path 101 constitutes a first transport path that guides the sheet being transported from the fixing unit 1D to the reversing roller pair 42. Furthermore, the reversing double-sided transport path 102, which is connected to the first transport path (fixing and reversing transport path 101) at the first connection part CN1 and connected to the feed and feed register transport path 105 at the third connection part CN3, constitutes a second transport path that guides the sheet S in the second transport direction V2. Here, the first connection part CN1 is located between the fixing unit 1D and the reversing roller pair 42 in the transport direction. Strictly speaking, the second transport path is the reversing double-sided transport path 102 from the first connection part CN1 to the third connection part CN3. The third connection part CN3 is located between the sheet feed and feed unit 31 and the image forming unit 1C in the transport direction. Furthermore, the fixing discharge transport path 103, which is connected to the first transport path (fixing inversion transport path 101) at the second connection section CN2, constitutes a third transport path that branches off from the first transport path (fixing inversion transport path 101) and guides the sheet S toward the discharge tray 60. Here, the second connection section CN2 is located between the fixing section 1D and the first connection section CN1 in the transport direction. Then, the feeding register transport path 105 and the register fixing transport path 106 constitute a fourth transport path that guides the sheet S from the sheet feeding section 31 through the image forming section 1C to the fixing section 1D, and merges with the second transport path at the third connection section CN3. As shown in Figure 2, the leading edge of the sheet S1 transported to the inversion downstream transport path 104 by the inversion roller pair 42 may protrude to the outside of the device body 1A through the opening of the device body 1A. The opening of the device body 1A at this time is different from the discharge port of the device body 1A.

[0027] [Regarding the printing order during alternating feed] Next, the printing order in relation to the number of sheets fed and the printing surface during alternating feeding in the image forming apparatus 1 according to this embodiment will be explained using Figures 3 to 5. Figure 3 is a diagram illustrating the printing order in relation to the number of sheets fed and the printing surface during alternating feeding. Figure 4(a) is a diagram showing the position of the sheet when printing the first side of the first sheet in alternating feeding. Figure 4(b) is a diagram showing the position of the sheet when printing the first side of the second sheet in alternating feeding. Figure 5(a) is a diagram showing the position of the sheet when printing the second side of the first sheet in alternating feeding and when printing the first side of the third sheet in alternating feeding. Figure 5(b) is a diagram showing the position of the sheet when printing the second side of the second sheet in alternating feeding and when printing the first side of the fourth sheet in alternating feeding. In the following explanation, in order to distinguish sheets S, the number of sheets fed continuously by the feeding and transport unit 1B in a series of printing jobs will be added to the reference numerals. Furthermore, the symbol "n" indicates that the number of sheets being fed is the "nth sheet".

[0028] (The number of sheets being fed is set to print the first side of the first sheet.) As shown in Figures 3 and 4(a), when a print job for printing multiple double-sided sheets is started by the control unit 1H, for example, the control unit 1H feeds the first sheet S1 from the feed cassette 32 to the image forming unit 1C via the registration roller pair 8. This first sheet S1 passes through the feed registration transport path 105 and the registration fixing transport path 106 (see Figure 2), where an image is formed on the first surface in the image forming unit 1C, and the image is fixed in the fixing unit 1D. After that, this first sheet S1 passes through the double-sided reversing flapper 41, which has been switched to the first position, and is transported from the fixing reversing transport path 101 to the reverse downstream transport path 104 by the rotational drive of the fixing unit 1D and the reversing roller pair 42 (see Figure 2). Then, the control unit 1H stops transporting the sheet S1 when the rear end of the first sheet S1 is upstream of the reversing roller pair 42 in the transport direction, according to the timing detected by the fixing discharge sensor SN1 (fixing discharge sensor flag 13) when the rear end of the sheet S1 is upstream.

[0029] (The feed rate is set to print the first side of the second sheet.) Next, as shown in Figures 3 and 4(b), the control unit 1H switches the double-sided reversing flapper 41 to the second position, reverses the rotation direction of the reversing roller pair 42 and drives it to rotate, so that the first sheet S1 is transported to the reversing double-sided transport path 102 (see Figure 2). Subsequently, the control unit 1H feeds the second sheet S2 from the feed cassette 32 towards the image forming unit 1C via the register roller pair 8. At this time, the control unit 1H controls the process so that the trailing end of the second sheet (the subsequent sheet) passes through the third connection section CN3 before the leading end of the first sheet (the preceding sheet) reaches the third connection section CN3. Similarly, this second sheet S2 also passes through the feed register transport path 105 and the register fixing transport path 106 (see Figure 2), an image is formed on the first surface in the image forming unit 1C, and the image is fixed in the fixing unit 1D. Subsequently, this second sheet S2 is also transported to the fixing and reversing transport path 101 via the double-sided reversing flapper 41, which has been switched to the first position, by the rotational drive of the fixing unit 1D and the reversing roller pair 42.

[0030] (The number of sheets being fed is set to print the second side of the first sheet.) Next, as shown in Figures 3 and 5(a), the control unit 1H transports the second sheet S2 from the fixing reversal transport path 101 to the reverse downstream transport path 104 by the rotational drive of the reversal roller pair 42 (see Figure 2). Subsequently, the control unit 1H feeds the first sheet S1, located on the reverse double-sided transport path 102, toward the image forming unit 1C. The transport direction of this first sheet S1 is reversed by the reversal roller pair 42, and its front and back sides are reversed when it is transported from the reverse double-sided transport path 102 to the register roller pair 8. Then, the first sheet S1 passes through the feed register transport path 105 and the register fixing transport path 106 (see Figure 2), an image is formed on the second surface in the image forming unit 1C, and the image is fixed in the fixing unit 1D.

[0031] (The feed is set to print the first side of the third sheet.) Subsequently, as shown in Figures 3 and 5(a), the control unit 1H transports the first sheet S1 via the double-sided reversing flapper 41, which has been switched to the second position, from the fixing and discharge transport path 103 towards the discharge tray 60 (see Figure 2). The control unit 1H also reverses the rotation direction of the reversing roller pair 42 and drives it to rotate, transporting the second sheet S2 to the reversing double-sided transport path 102 (see Figure 2). Then, the control unit 1H feeds the third sheet S3 from the feed cassette 32 via the register roller pair 8 towards the image forming unit 1C. This third sheet S3 also travels similarly via the feed register transport path 105 and the register fixing transport path 106 (see Figure 2), where an image is formed on the first surface in the image forming unit 1C, and the image is fixed in the fixing unit 1D. Subsequently, this third sheet S3 is also transported to the fixing and reversing transport path 101 via the double-sided reversing flapper 41, which has been switched to the first position, by the rotational drive of the fixing unit 1D and the reversing roller pair 42.

[0032] (The feed rate is set to print the second side of the second sheet.) Next, as shown in Figures 3 and 5(b), the control unit 1H transports the third sheet S3 from the fixing reversal transport path 101 to the reverse downstream transport path 104 by the rotational drive of the reversal roller pair 42 (see Figure 2). Subsequently, the control unit 1H feeds the second sheet S2, located on the reverse double-sided transport path 102, toward the image forming unit 1C. This second sheet S2 also has its transport direction reversed by the reversal roller pair 42 and is transported from the reverse double-sided transport path 102 to the register roller pair 8, where its front and back sides are reversed. Then, the second sheet S2 passes through the feed register transport path 105 and the register fixing transport path 106 (see Figure 2), where an image is formed on the second surface in the image forming unit 1C, and the image is fixed in the fixing unit 1D.

[0033] (The feed is set to print the first side of the fourth sheet.) Next, as shown in Figures 3 and 5(b), the control unit 1H transports the second sheet S2 from the fixing and discharge transport path 103 towards the discharge tray 60 via the double-sided reversing flapper 41 which has been switched to the second position (see Figure 2). The control unit 1H also reverses the rotation direction of the reversing roller pair 42 and drives it to transport the third sheet S3 to the reversing double-sided transport path 102 (see Figure 2). Then, the control unit 1H feeds the fourth sheet S3 from the feed cassette 32 via the register roller pair 8 towards the image forming unit 1C. This fourth sheet S4 is similarly transported via the feed register transport path 105 and the register fixing transport path 106 (see Figure 2), where an image is formed on the first surface in the image forming unit 1C, and the image is fixed in the fixing unit 1D. Subsequently, this fourth sheet S4 is also transported to the fixing and reversing transport path 101 via the double-sided reversing flapper 41, which has been switched to the first position, by the rotational drive of the fixing unit 1D and the reversing roller pair 42.

[0034] (This describes the state of double-sided printing using alternating feed from this point onward.) After the process described above, which involves printing the first side of the fourth sheet, the sheet transport operation shown in Figures 3, 5(a), and 5(b) is repeated, forming images on the first and second sides of each sheet S. In other words, the order in which the first side of the nth sheet is printed is "2n-2", and the order in which the second side of the nth sheet is printed is "2n+1".

[0035] [Features of conveyance control in alternating feeding according to this embodiment] Next, the overlap between the preceding sheet (hereinafter referred to as "preceding sheet S(n)") and the following sheet (hereinafter referred to as "following sheet S(n+1)"), which is a feature of the transport control in the alternating feeding according to this embodiment, will be explained using Figures 6 and 7. Figure 6 is an enlarged cross-sectional view showing the vicinity of the first connection between the fixed inversion transport path and the inversion double-sided transport path. Figure 7 is a diagram showing the sheet position when the leading edge of the following sheet reaches the margin on the rear end side of the preceding sheet. The preceding sheet S(n) and following sheet S(n+1) shown in Figure 7 are sheets of the size that maximizes the length in the transport direction that enables alternating feeding. The transport control described below controls the transport position of the sheets by controlling each motor as a drive unit, which is performed by the control unit 1H.

[0036] As shown in Figure 7, the leading sheet S(n) enters the reversed double-sided transport path 102 when the rotation of the reversing roller pair 42 reverses. Subsequently, the double-sided transport sensor SN2 (double-sided transport sensor flag 58) detects the leading edge S(n)-R of the leading sheet S(n). Depending on the timing of the detection of the leading edge S(n)-R by the double-sided transport sensor SN2, the rotation of the double-sided transport roller pair 51 and the re-feeding roller pair 52 is stopped so that the leading edge S(n)-R is positioned downstream of the re-feeding roller pair 52, and the transport of the leading sheet S(n) is stopped.

[0037] In this state, the preceding sheet S(n) is stopped with its rear end S(n)-T positioned between the first connecting part CN1 and the reversing roller pair 42 in the second transport direction V2 (see Figure 1). Subsequently, the following sheet S(n+1) passes through the fixing and reversing transport path 101, and as shown in Figure 6, its front end S(n+1)-R contacts the rear end portion of the preceding sheet S(n) at the first connecting part CN1. Then, the following sheet S(n+1) is transported by the fixing part 1D toward the reversing roller pair 42 with its front end S(n+1)-R overlapping with the preceding sheet S(n). Further on, when the following sheet S(n+1) reaches the reversing roller pair 42 with its front end S(n+1)-R in contact with the drive roller 42a and driven roller 42b, it is gripped and transported in the first transport direction V1. Furthermore, the rear end portion of the preceding sheet S(n) that the leading edge S(n+1)-R of the succeeding sheet S(n+1) contacts is an area outside the image printing area where the image is printed by the image forming unit 1C, which is an area where image printing is not possible, in other words, a margin. In other words, the control unit 1H controls the process so that when the leading edge S(n+1)-R of the succeeding sheet S(n+1) reaches the first connection part CN1, the image formed on the first surface of the preceding sheet S(n) passes through the first connection part CN1.

[0038] As described above, in the transport control in the alternating feeding according to this embodiment, an overlapping region where the preceding sheet S(n) and the succeeding sheet S(n+1) overlap is provided between the first connection part CN1 and the reversing roller pair 42. This makes it possible to shorten the length of the reversing double-sided transport path 102, enabling miniaturization of the image forming apparatus 1 (sheet transport apparatus 10) and improving the productivity of double-sided printing.

[0039] Furthermore, the subsequent sheet S(n+1) transported from the fixed inversion transport path 101 is transported by the inversion roller pair 42 in the first transport direction V1 to the inverted downstream transport path 104, and then inverted in the second transport direction V2 and transported towards the inverted double-sided transport path 102. When the subsequent sheet S(n+1) is transported in this way, the drive roller 42a and driven roller 42b of the inversion roller pair 42 are always in contact with (nip) the subsequent sheet S(n+1) and grip it during transport. As a result, the distance between the position where the inversion roller pair 42 grips the subsequent sheet S(n+1) and the leading edge S(n+1)-R of the subsequent sheet S(n+1) is shorter than, for example, when the sheet is transported by the fixed section 1D without being gripped by the inversion roller pair 42. Therefore, the transport of the subsequent sheet S(n+1) can be stabilized.

[0040] Furthermore, the trailing edge of the preceding sheet S(n) has an area where image printing is not possible (a margin), and the position where the subsequent sheet S(n+1) contacts the preceding sheet S(n) at the first connection part CN1 is set to be within this area where image printing is not possible. Therefore, the subsequent sheet S(n+1) is not rubbed against the printed image on the first surface of the preceding sheet S(n), thus preventing image distortion.

[0041] Furthermore, for example, when inserting a preceding sheet S(n) and a succeeding sheet S(n+1) into the reversing roller pair 42 while overlapping, it would be necessary to provide a separation mechanism to separate the drive roller 42a and the driven roller 42b, or to make the roller shape D-shaped when viewed in the width direction. This would increase the cost of the separation mechanism and the rollers themselves, potentially leading to an increase in the cost of the image forming apparatus 1. However, in this embodiment, since an overlapping region where the preceding sheet S(n) and the succeeding sheet S(n+1) overlap is provided between the first connection part CN1 and the reversing roller pair 42, the preceding sheet S(n) and the succeeding sheet S(n+1) do not overlap in the reversing roller pair 42. This makes it possible to avoid an increase in the cost of the image forming apparatus 1.

[0042] [Regarding the reversing double-sided transport path 102] Next, the configuration of the reversing double-sided conveying path 102 and the shape of the guide surface 55s of the conveying guide 55 will be explained with reference to Figure 8. Figure 8(a) is an enlarged cross-sectional view illustrating the reversing double-sided conveying path. Figure 8(b) is an enlarged cross-sectional view showing the case where the leading edge of the following sheet reaches the margin on the rear end side of the preceding sheet located in the reversing double-sided conveying path. Figure 8(c) is an enlarged cross-sectional view illustrating the shape of the guide surface of the guide member forming the reversing double-sided conveying path.

[0043] As shown in Figure 8(a), the reversing double-sided conveying path 102 is broadly composed of a first straight section 1021, a curved section 1022, and a second straight section 1023. The first straight section 1021 is formed to extend linearly from the reversing roller pair 42 toward the second conveying direction V2 (see Figure 1). More specifically, in an axial view, the first straight section 1021 is the part that extends linearly from the first connecting section CN1 in the direction of a virtual line VL connecting the nip sections 42N of the drive roller 42a and the driven roller 42b with the first connecting section CN1, and guides the sheet S.

[0044] The curved section 1022 is located downstream of the first straight section 1021 in the transport direction and upstream of the second straight section 1023 in the transport direction, and is formed with a curvature that curves to connect them. That is, the curved section 1022 communicates with the first straight section 1021 and extends in a curved shape that curves toward the intersection direction X (left-right direction in the figure) that intersects the imaginary line VL in the width direction view, guiding the sheet S. The second straight section 1023 communicates with the curved section 1022 and is formed with a shape that extends linearly from the curved section 1022 toward the intersection direction X, that is, it is a part that guides the sheet S linearly toward the intersection direction X.

[0045] The first straight section 1021 described above has one side surface formed by a transport guide 55, that is, the transport guide 55 is configured to include a guide surface 55s, which is a guide surface located on the opposite side of the curved section 1022 in the intersecting direction X when viewed in the width direction. The guide surface 55s has a concave shape formed in an arc shape so as to be recessed on the opposite side of the curved section 1022 in the intersecting direction X when viewed in the width direction.

[0046] Here, the connection between the first straight section 1021 and the curved section 1022 is called the connection section Cp. As shown in Figure 8(b), when the subsequent sheet S(n+1) contacts the preceding sheet S(n) at the first connection section CN1, the portion of the preceding sheet S(n) located at the curved section 1022 is bent at the curved section 1022. The guide surface 55s of the transport guide 55 is formed in an arc shape so as to be concave on the opposite side from the curved section 1022, as described above. In other words, in the transport direction, the guide surface 55s between the first connection section CN1 and the connection section Cp is separated from the imaginary line VL, as shown in Figure 8(c), forming a space Sp between the preceding sheet S(n) and the guide surface 55s.

[0047] Here, when the leading sheet S(n) is bent by the curved portion 1022, its rigidity may cause the rear end S(n)-T of the leading sheet S(n) to float away from the guide surface 55s due to the deflection of the leading sheet S(n). In other words, the rear end S(n)-T of the leading sheet S(n) may move towards the double-sided inverting flapper 41 near the first connection portion CN1.

[0048] However, since the guide surface 55s is formed in an arc shape, creating a space Sp that is separated from the imaginary line VL, the rear end S(n)-T of the preceding sheet S(n) moves along the guide surface 55s in the direction of arrow X1. Therefore, the rear end S(n)-T of the preceding sheet S(n) is transported along the transport guide 55 near the first connection part CN1. As a result, when the subsequent sheet S(n+1) is transported from the first connection part CN1 to the reversing roller pair 42, it is guided by the preceding sheet S(n) which is being transported along the guide surface 55s. In particular, since the preceding sheet S(n) is stopped at this time, the subsequent sheet S(n+1) is transported stably, as if it were directly guided by the guide surface 55s of the transport guide 55. Note that the shape of the transport guide 55 between the first connection part CN1 and the connection part Cp in the transport direction does not have to be an arc shape, but may be a plane parallel to the imaginary line VL.

[0049] In the first embodiment described above, the subsequent sheet S(n+1) is brought into contact with the first connecting part CN1 while the transport of the preceding sheet S(n) is stopped. However, the subsequent sheet S(n+1) may be brought into contact with the preceding sheet S(n) while it is being transported without stopping the transport of the preceding sheet S(n). This makes it possible to shorten the distance between the trailing end S(n+1)-T of the subsequent sheet S(n+1) heading from the fixing / reversal transport path 101 to the reverse downstream transport path 104 and the leading end S(n)-R of the preceding sheet S(n) heading from the reverse double-sided transport path 102 to the register fixing transport path 106. In other words, the distance between sheets can be shortened, which makes it possible to improve the productivity of double-sided printing.

[0050] <Second Embodiment> Next, a second embodiment, which is a modified version of the first embodiment described above, will be explained with reference to Figure 9. Figure 9 is an enlarged cross-sectional view showing the vicinity of the first connection between the fixing / reversal transport path and the reversal / double-sided transport path in the image forming apparatus according to the second embodiment. In this second embodiment, the same reference numerals are used for the same parts as in the first embodiment, and their descriptions are omitted.

[0051] In the sheet transport device 10 of the image forming apparatus 1 according to this second embodiment, compared to the first embodiment, the double-sided reversing roller 43 is provided with the double-sided reversing flapper 41 as a rotating body that contacts the sheet S and is driven to rotate.

[0052] More specifically, as shown in Figure 9, the double-sided reversing roller 43 is located near the first connection portion CN1, and its outer peripheral surface 43s protrudes beyond the guide surface 41g of the double-sided reversing flapper 41. For example, suppose the rear end S(n)-T of the preceding sheet S(n) curls, and the preceding sheet S(n) presses the subsequent sheet S(n+1), which is being conveyed to the downstream conveying path 104, against the guide surface 41g of the double-sided reversing flapper 41. Even in this case, the subsequent sheet S(n+1) is guided by the driven rotating double-sided reversing roller 43, and the guide surface 41g and the subsequent sheet S(n+1) do not come into contact. Therefore, by contacting the driven rotating double-sided reversing roller 43, the sliding resistance of the portion of the subsequent sheet S(n+1) that is in contact with the subsequent sheet S(n+1) is reduced, and the distortion of the image on the first surface of the subsequent sheet S(n+1) can be reduced.

[0053] In this second embodiment, a double-sided reversing roller 43, which is the rotating body, is described in relation to the double-sided reversing flapper 41, but the invention is not limited to this. For example, the double-sided reversing roller 43 may be fixedly supported to the main body 1A of the device near the base of the double-sided reversing flapper 41. In other words, the double-sided reversing roller 43 is positioned between the fixing section 1D and the reversing roller pair 42, and is positioned to rotate in contact with the side of the sheet that is guided along the fixing reversing transport path 101 that is opposite to the reversing double-sided transport path 102.

[0054] <Possibility of other embodiments> In the first and second embodiments described above, the image forming apparatus 1 was described as a small, desktop-type laser printer as an example, but it is not limited to this. For example, it may be an image forming apparatus used in an office multifunction printer, a commercial printing image forming system, etc. Furthermore, it is not limited to monochrome printing, but may also be a color printing apparatus. In addition, the sheet transport device is not limited to one equipped with an image forming unit that forms an image, but may also be a sheet transport device such as a processing device such as a finisher, or a scanner device that reads an image.

[0055] Furthermore, while the first and second embodiments described a sheet reversal unit 1E that reverses the front and back sides of the sheet for double-sided printing, the invention is not limited to this. For example, the sheet reversal unit 1E may reverse the front and back sides in order to discharge the sheet to the discharge tray with the front surface facing up, or to discharge the sheet to the discharge tray with the front surface facing down. In addition, while the sheet reversal unit 1E described a system in which the sheet is transported upwards, then reversed and transported downwards, these directions may be reversed vertically, or even horizontally, in other words, any direction is acceptable.

[0056] This disclosure can also be implemented by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be implemented by a circuit (e.g., an ASIC) that implements one or more functions.

[0057] Summary of this disclosure This disclosure includes at least the following: (Composition 1) A first conveying unit that transports the sheets, A second conveying unit is positioned downstream of the first conveying unit in the direction of sheet transport by the first conveying unit and includes a first roller and a second roller capable of gripping and transporting the sheet, wherein the second conveying unit transports the sheet in the first conveying direction while the first roller and the second roller are in contact with the sheet, and then transports the sheet in a second conveying direction opposite to the first conveying direction. A first transport path that guides the sheet being transported from the first transport unit to the second transport unit, A second transport path is connected to the first transport path at the first connection section and guides the sheet being transported in the second transport direction by the second transport section, A drive unit that drives the first transport unit and the second transport unit, The system comprises a control unit for controlling the drive unit, When the control unit transports a preceding sheet from the second transport unit to the second transport path and a succeeding sheet to the first transport path, it controls the drive unit so that the leading edge of the succeeding sheet reaches the first connect unit while the rear end of the preceding sheet is positioned between the first connect unit and the second transport unit. A sheet conveying device characterized by the following features. (Configuration 2) The second conveying unit conveys the sheet in the first conveying direction when the first roller rotates in the first rotational direction while the first roller and the second roller are in contact with the sheet, and conveys the sheet in the second conveying direction when the first roller rotates in the second rotational direction opposite to the first rotational direction while the first roller and the second roller are in contact with the sheet. A sheet conveying device according to configuration 1, characterized by the features described above. (Composition 3) A third transport path connected to the first transport path at the second connection between the first transport section and the first connection section, The system comprises a third transport unit that transports the sheet guided along the third transport path, A sheet conveying device according to configuration 1 or 2, characterized by the above. (Composition 4) The device includes a switching member that can switch between a first position for guiding the sheet that has been transported to the second connection section to the second transport section, and a second position for guiding the sheet that has been transported to the second connection section to the third transport path. A sheet conveying device according to configuration 3, characterized by the features described above. (Composition 5) The switching member in the second position guides the sheet being transported in the second transport direction by the second transport unit to the second transport path. The sheet conveying device according to configuration 4, characterized by the features described above. (Composition 6) The switching member is provided with a rotating body that is in contact with the sheet and rotates, The sheet conveying device according to configuration 5, characterized by the features described herein. (Composition 7) The main body of the device, The device comprises a discharge section for loading sheets discharged from the main body of the device, The third transport path guides the sheet toward the discharge section. A sheet conveying device according to any one of configurations 3 to 6, characterized by the above. (Composition 8) The device comprises a rotating body positioned between the first transport section and the second transport section, which is rotated in contact with the side of the sheet on the opposite side of the second transport path from the first transport path, which is guided along the first transport path. A sheet conveying device according to configuration 1 or 2, characterized by the above. (Composition 9) The control unit, The drive unit is controlled so that the preceding sheet stops when the leading edge of the subsequent sheet reaches the first connection portion. A sheet conveying device according to any one of configurations 1 to 8, characterized by the above. (Composition 10) The control unit, When the leading edge of the subsequent sheet reaches the first connection part, the drive unit is controlled so that the preceding sheet is being transported. A sheet conveying device according to any one of configurations 1 to 8, characterized by the above. (Composition 11) The second transport path is, In a view in the width direction perpendicular to the conveying direction, a first straight section extends linearly from the first connecting section in the direction of a virtual line connecting the nip portion of the first roller and the second roller and the first connecting section, and guides the sheet. It has a curved portion that communicates with the first straight portion and extends in a curved shape so as to curve in the direction of intersection that intersects the imaginary line in the width direction view, and guides the sheet, The first straight section includes a guide surface located on the opposite side of the curved section in the intersecting direction when viewed in the width direction, The guide surface has a concave shape formed in an arc shape so as to be recessed on the opposite side of the curved portion in the intersecting direction when viewed in the width direction. A sheet conveying device according to any one of configurations 1 to 10, characterized by the above. (Composition 12) The second transport path has a second straight section that communicates with the curved section and extends linearly from the curved section in the intersecting direction to guide the sheet. It includes a fourth transport section for transporting the sheet guided to the second straight section, A sheet conveying device according to configuration 11, characterized by the features described above. (Composition 13) A sheet transport device as described in any one of configurations 1 to 12, It comprises an image forming unit that forms an image on a sheet, An image forming apparatus characterized by the following features. (Composition 14) The sheet on which the image has been formed by the image forming unit is equipped with a fixing unit for fixing the image, The fixing section includes a fixing roller, The first transport unit includes the fixing roller, The image forming apparatus according to configuration 13, characterized by the features described above. (Composition 15) The second transport path guides the sheet, on which an image has been formed on the first surface by the image forming unit, back towards the image forming unit. The image forming apparatus according to configuration 13 or 14, characterized by the above. (Composition 16) The control unit controls the drive unit such that when the leading edge of the subsequent sheet reaches the first connection portion, the image formed on the first surface of the preceding sheet passes through the first connection portion. The image forming apparatus according to configuration 15, characterized in that... (Composition 17) The seat loading area, A sheet feeding unit that feeds sheets from the sheet loading unit, The system includes a fourth transport path that guides the sheet being transported from the sheet feeding unit to the first transport unit, The second transport path is connected to the fourth transport path at the third connection point between the sheet feeding unit and the image forming unit. The control unit controls the drive unit so that the leading edge of the preceding sheet reaches the third connection portion after the trailing end of the following sheet has passed the third connection portion. The image forming apparatus according to configuration 15 or 16, characterized by the above. [Explanation of symbols]

[0058] 1…Image forming apparatus / 1A…Apparatus body / 1C…Image forming section / 1D…Fixing section (first transport section) / 1G…Discharge section / 1H…Control unit / 10…Sheet transport device / 11…Heating roller (fixing roller) / 21…Intermediate transport roller pair (third transport section) / 31…Sheet feeding section / 32…Feeding cassette (sheet loading section) / 41…Double-sided reversing flapper (switching member) / 42…Reversing roller pair (second transport section) / 42a…Driven roller (first roller) / 42b…Driven roller (second roller) / 42N…Nip section / 43…Double-sided reversing roller (rotating body) / 51…Double-sided transport roller pair (fourth transport section) / 55s…Guide surface (guiding surface) / 101…Fixing reversing transport path (first transport path) / 102…Reversing double-sided transport path (second transport path) / 10 3…Fixing and discharge transport path (3rd transport path) / 105…Feeding and feeding register transport path (4th transport path) / 106…Register fixing transport path (4th transport path) / 1021…1st straight section / 1022…Curved section / 1023…2nd straight section / CN1…1st connection section / CN2…2nd connection section / CN3…3rd connection section / M4…Fixing motor (drive unit) / M5…Reversing motor (drive unit) / S…Sheet / S(n+1)…Successor sheet (following sheet) / S(n)…Preceding sheet (preceding sheet) / S(n)-T…Rear end of preceding sheet (rear end of preceding sheet) / S(n+1)-R…Front end of succeeding sheet (front end of succeeding sheet) / V1…1st transport direction / V2…2nd transport direction / VL…Imaginary line / W1…1st rotation direction / W2…2nd rotation direction

Claims

1. A first conveying unit that transports sheets, A second conveying unit is positioned downstream of the first conveying unit in the direction of sheet conveyance by the first conveying unit, and includes a first roller and a second roller capable of gripping and conveying the sheet, wherein the second conveying unit conveys the sheet in the first conveying direction while the first roller and the second roller are in contact with the sheet, and then conveys the sheet in a second conveying direction opposite to the first conveying direction. A first transport path that guides the sheet being transported from the first transport unit to the second transport unit, A second transport path is connected to the first transport path at the first connection section and guides the sheet being transported in the second transport direction by the second transport section, A drive unit that drives the first transport unit and the second transport unit, The system comprises a control unit for controlling the drive unit, When the control unit transports a preceding sheet from the second transport unit to the second transport path and a succeeding sheet to the first transport path, it controls the drive unit so that the leading edge of the succeeding sheet reaches the first connect unit while the rear end of the preceding sheet is positioned between the first connect unit and the second transport unit. A sheet conveying device characterized by the following features.

2. The second conveying unit conveys the sheet in the first conveying direction when the first roller rotates in the first rotational direction while the first roller and the second roller are in contact with the sheet, and conveys the sheet in the second conveying direction when the first roller rotates in the second rotational direction opposite to the first rotational direction while the first roller and the second roller are in contact with the sheet. The sheet conveying device according to feature 1.

3. A third transport path connected to the first transport path at the second connection between the first transport section and the first connection section, The system comprises a third transport unit that transports the sheet guided along the third transport path, The sheet conveying device according to feature 1.

4. The device includes a switching member that can switch between a first position for guiding the sheet that has been transported to the second connection section to the second transport section, and a second position for guiding the sheet that has been transported to the second connection section to the third transport path. The sheet conveying device according to feature 3.

5. The switching member located at the second position guides the sheet being transported in the second transport direction by the second transport unit to the second transport path. The sheet conveying device according to feature 4.

6. The switching member is provided with a rotating body that is in contact with the sheet and rotates, The sheet conveying device according to feature 5.

7. The main body of the device, The device comprises a discharge section for loading sheets discharged from the main body of the device, The third transport path guides the sheet toward the discharge section. The sheet conveying device according to feature 3.

8. The device comprises a rotating body positioned between the first transport section and the second transport section, which is rotated in contact with the side of the sheet on the opposite side of the second transport path from the first transport path, which is guided along the first transport path. The sheet conveying device according to feature 1.

9. The control unit, The drive unit is controlled so that the preceding sheet stops when the leading edge of the subsequent sheet reaches the first connection part. The sheet conveying device according to feature 1.

10. The control unit, When the leading edge of the subsequent sheet reaches the first connection part, the drive unit is controlled so that the preceding sheet is being transported. The sheet conveying device according to feature 1.

11. The second transport path is, In a view in the width direction perpendicular to the conveying direction, a first straight section extends linearly from the first connection portion in the direction of a virtual line connecting the nip portion of the first roller and the second roller to the first connection portion, and guides the sheet. It has a curved portion that communicates with the first straight portion and extends in a curved shape so as to curve in the direction of intersection that intersects the imaginary line when viewed in the width direction, and guides the sheet, The first straight section includes a guide surface located on the opposite side of the curved section in the intersecting direction when viewed in the width direction, The guide surface has a concave shape formed in an arc shape so as to be recessed on the opposite side of the curved portion in the intersecting direction when viewed in the width direction. The sheet conveying device according to feature 1.

12. The second transport path has a second straight section that communicates with the curved section and extends linearly from the curved section in the intersecting direction to guide the sheet. The system includes a fourth transport unit for transporting the sheet guided to the second straight section, The sheet conveying device according to feature 11.

13. A sheet conveying device according to any one of claims 1 to 12, It comprises an image forming unit that forms an image on a sheet, An image forming apparatus characterized by the following features.

14. The sheet on which the image has been formed by the image forming unit is equipped with a fixing unit for fixing the image, The fixing section includes a fixing roller, The first transport unit includes the fixing roller, The image forming apparatus according to feature 13.

15. The second transport path guides the sheet, on which an image has been formed on the first surface by the image forming unit, back towards the image forming unit. The image forming apparatus according to feature 13.

16. The control unit controls the drive unit such that when the leading edge of the subsequent sheet reaches the first connection portion, the image formed on the first surface of the preceding sheet passes through the first connection portion. The image forming apparatus according to feature 15.

17. The seat loading area and A sheet feeding unit that feeds sheets from the sheet loading unit, The system includes a fourth transport path that guides the sheet being transported from the sheet feeding unit to the first transport unit, The second transport path is connected to the fourth transport path at the third connection point between the sheet feeding unit and the image forming unit. The control unit controls the drive unit so that the leading edge of the preceding sheet reaches the third connection portion after the trailing end of the following sheet has passed the third connection portion. The image forming apparatus according to feature 15.

Images