Image forming apparatus

Abstract

To provide an image forming apparatus that comprises a guide member for making a sheet bend at first to third curves in which even if a sheet is reversed in a transport direction its transport load is less apt to vary.SOLUTION: An image forming apparatus comprises inversion means that after transporting a sheet in a first direction, inverts it by a transport in an opposite, second direction, and also comprises a guide member including a first curve that guides a front end of the sheet fed from the inversion means in one direction, a second curve that guides the front end of the sheet guided by the first curve upward and a third curve that guides the front end of the sheet guided by the second curve in another direction, further comprising a first abutment member that is arranged to face the second curve and a second abutment member that is arranged to face the third curve.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus for forming an image on a sheet. [Background technology]

[0002] Image forming devices such as printers, copiers, and multifunction devices are provided with a reversing conveying mechanism such as a pair of reversing rollers that performs switchback conveying in order to reverse a sheet used as a recording material for the purpose of double-sided printing, face-down discharge, etc. In the case of double-sided printing, the sheet that has been switched back by the pair of reversing rollers is re-fed to the image forming section via a re-conveying path for double-sided printing in a state in which the first side on which an image has already been formed and the second side on which an image will be formed are reversed.

[0003] However, the evacuation space for evacuating the sheet needs to be large enough to accommodate the length of the sheet, and if the evacuation space is long enough to accommodate long sheets in particular, the image forming apparatus may become large. For this reason, a device has been proposed in which a guide member forming the evacuation space is provided with a first curved portion, a second curved portion, and a third curved portion, and the conveying direction is changed while the sheet is gently curved (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-184229 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of the above-mentioned Patent Document 1, in which the sheet is curved at the first to third curved portions, when a long sheet is evacuated to the evacuation space, the leading edge of the sheet is curved upward at the second curved portion, and then proceeds in a direction to be folded back horizontally at the third curved portion. However, depending on the rigidity of the sheet, the leading edge of the sheet may buckle or collapse downward. In this state, if the conveying direction of the sheet is reversed, the conveying load may fluctuate, which may cause the sheet to skew or be improperly conveyed.

[0006] Therefore, the present invention aims to provide an image forming device that is equipped with a guide member that curves a sheet at first to third curved portions, and that can prevent the transport load from fluctuating even when the sheet transport direction is reversed. [Means for solving the problem]

[0007] One aspect of the present invention is an image forming apparatus comprising: an image forming means for forming an image on a sheet being transported; an inversion means for transporting the sheet, on which an image has been formed on a first surface of the sheet by the image forming means, in a first direction and then inverting the sheet by transporting it in a second direction opposite to the first direction; a guide member including a first curved portion for guiding a leading edge of the sheet sent out from the inversion means in the first direction in one direction that intersects the vertical direction, a second curved portion for guiding upward the leading edge of the sheet guided in the one direction by the first curved portion, and a third curved portion for guiding upward the leading edge of the sheet guided upward by the second curved portion in another direction that intersects the vertical direction; a first abutment member arranged opposite the second curved portion and abutting a second surface of the sheet to be inverted that is opposite the first surface; and a second abutment member arranged opposite the third curved portion and abutting the second surface of the sheet to be inverted. Effect of the Invention

[0008] According to the present invention, a sheet conveying device is provided with a guide member that curves the sheet at the first to third curved portions, and even if the sheet conveying direction is reversed, the leading edge of the sheet is prevented from buckling or collapsing downward, making it possible to make the conveying load less likely to fluctuate. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a schematic view of an inversion mechanism according to the first embodiment. [Diagram 3] 4A and 4B are diagrams illustrating a state before a sheet is inverted by the inversion mechanism according to the first embodiment. [Figure 4] 4A to 4C are diagrams illustrating a state during reversing of a sheet by the reversing mechanism according to the first embodiment. [Diagram 5] 5A and 5B are diagrams illustrating a state after a sheet has been inverted by the inversion mechanism according to the first embodiment. [Figure 6] 5A to 5C are diagrams illustrating flapping of a leading edge of a sheet during a sheet inversion operation by the inversion mechanism according to the first embodiment. [Figure 7] FIG. 11 is a schematic view of an inversion mechanism according to a second embodiment. [Figure 8] 13A and 13B are diagrams illustrating a state during sheet inversion by a reversing mechanism that does not have first to third contact members. [Figure 9] 13 is a diagram showing a state after a sheet is inverted by a reversing mechanism that does not have first to third contact members. FIG. [Figure 10] 13 is a diagram showing a state after a sheet has been inverted by an inversion mechanism that does not have first and second contact members. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is shown as an example, and the present invention is not limited to the following embodiment.

[0011] First Embodiment (Image forming device) First, the structure of the image forming apparatus according to the first embodiment will be described. Fig. 1 is a cross-sectional view showing the structure of a laser beam printer (hereinafter referred to as printer) 100, which is the image forming apparatus according to the first embodiment. The printer 100 has a housing 101, which houses each mechanism constituting an engine section and a control board housing section 103 that houses an engine control section 103a and a printer controller 103b. The engine control section 103a controls the operation of each mechanism constituting the engine section. The printer controller 103b develops print data received from an external computer and executes a print job by controlling the engine control section 103a in an integrated manner.

[0012] In this embodiment, the mechanisms constituting the engine section refer to the optical development processing mechanisms 120, 121, 122, and 123, the intermediate transfer mechanism 152, the secondary transfer section 140, the fixing processing mechanism 160, the feeding and conveying mechanism 110, the discharge mechanism 170, the reversing mechanism 200, and the double-sided conveying mechanism 220. Of these, the optical development processing mechanisms 120, 121, 122, and 123, the intermediate transfer mechanism 152, the secondary transfer section 140, and the fixing processing mechanism 160 constitute a tandem-type intermediate transfer type electrophotographic mechanism 100A that forms an image on a sheet.

[0013] The optical development processing mechanisms 120, 121, 122, and 123 are stations that perform the steps of charging, exposing, and developing in the electrophotographic process to create a monochrome visible image (toner image). The intermediate transfer mechanism 152 is a mechanism that performs primary transfer of the visible images created by the optical development processing mechanisms 120, 121, 122, and 123, and causes the intermediate transfer body 150 to carry the images, thereby creating a full-color toner image. The secondary transfer unit 140 is a mechanism that performs secondary transfer of the toner image carried by the intermediate transfer body 150 onto a sheet P, which is a recording material. The fixing processing mechanism 160 is a mechanism that performs fixing processing on the toner image transferred onto the sheet P, thereby fixing the image onto the sheet P.

[0014] The feeding and conveying mechanism 110 is a mechanism that feeds and conveys the sheet P toward the secondary transfer unit 140. The discharge mechanism 170 is a mechanism that discharges or sorts the conveying direction of the sheet on which an image has been formed by passing through the secondary transfer unit 140 and the fixing processing mechanism 160. The reversing mechanism 200 has a reversing and evacuation section 300 as an evacuation section for temporarily evacuating the sheet when switching back, and is a mechanism that reverses and conveys the sheet P in the case of double-sided printing. The double-sided conveying mechanism 220 as a re-conveying means is a mechanism that conveys the sheet P inverted by the reversing mechanism 200 again to the secondary transfer unit 140.

[0015] The basic operation of the image forming apparatus will be described. Each laser scanner unit 107 of the optical development processing mechanisms 120, 121, 122, and 123 has a laser driver that drives a laser beam emitted from a semiconductor laser (not shown) on and off in response to image data supplied from the printer controller 103b. The laser beam emitted from the semiconductor laser is scanned in the main scanning direction by a rotating polygon mirror. The laser beam deflected in the main scanning direction is guided to the photosensitive drum 105 via a reflecting polygon mirror 109, and exposes the photosensitive drum 105 in the main scanning direction. Meanwhile, the electrostatic latent image formed on the surface of the photosensitive drum 105 by the scanning exposure with the laser beam as described above, which is charged by a primary charger 111, is visualized into a toner image by a toner supplied by a developer 112.

[0016] Thereafter, the toner image carried on the photosensitive drum 105 is transferred (primary transfer) to an intermediate transfer body 150 provided in an intermediate transfer mechanism 152 by applying a voltage having reverse characteristics to that of the toner image. When forming a color image, the single-color toner images of yellow, magenta, cyan, and black formed in each of the optical developing processing mechanisms 120 to 123 are transferred sequentially to the intermediate transfer body 150, and a full-color visible image is formed on the surface of the intermediate transfer body 150.

[0017] In parallel with this toner image creation operation, the feeding and conveying mechanism 110 separates and conveys sheets P one by one from the sheet stack stored in the storage 110a, and conveys them to the secondary transfer unit 140. The path from the feeding and conveying mechanism 110 to the discharge mechanism 170 via the secondary transfer unit 140 and the fixing processing mechanism 160 is a main conveying path 190 where an image is formed on the sheet.

[0018] Next, the visible image carried on the surface of the intermediate transfer body 150 is transferred (secondary transfer) in a secondary transfer section 140 constituted by a pair of secondary transfer rollers 151 onto a sheet P transported by the feeding and transporting mechanism 110. The pair of secondary transfer rollers 151 presses the sheet P against the intermediate transfer body 150 and simultaneously applies a bias having opposite characteristics to the toner, thereby performing secondary transfer.

[0019] The sheet P that has passed through the secondary transfer unit 140 is transported to a fixing mechanism 160. The fixing mechanism 160 has a heating roller 161 and a pressure roller 162 that sandwich and transport the sheet P, and a heat source (e.g., a halogen lamp) for heating the toner image on the sheet via the heating roller 161. As the sheet P passes through the fixing nip formed by the heating roller 161 and the pressure roller 162, the toner transferred to the sheet P is heated and melted, and then cooled and solidified, thereby obtaining an image fixed on the sheet P.

[0020] The sheet P that has passed through the fixing process mechanism 160 is transported to the discharge mechanism 170. In the discharge mechanism 170, the transport path of the sheet P is switched depending on whether or not double-sided printing is performed on the sheet P. In the case of single-sided printing, the sheet P is guided by a first switching flap 173 toward a pair of discharge rollers 171 as a discharge means, and is discharged to the outside of the printer 100 by the pair of discharge rollers 171.

[0021] In double-sided printing, the sheet P with an image formed on the first side is guided to the reversal inlet rollers 172 by the first switching flap 173, and is transported to the reversal mechanism 200 via the reversal inlet rollers 172. The reversal mechanism 200 performs switchback transport while temporarily retracting the sheet P using the reversal evacuation section 300, and transports the sheet P to the double-sided transport mechanism 220.

[0022] The double-sided conveying mechanism 220 joins the feeding and conveying mechanism 110 upstream of the secondary transfer unit 140, and conveys the sheet P, whose first and second sides have been switched by the reversing mechanism 200, back to the feeding and conveying mechanism 110. The sheet P switched back by the reversing mechanism 200 is conveyed again toward the main conveying path 190 by the reversing mechanism 200 and the double-sided conveying mechanism 220. Then, after the sheet P passes through the secondary transfer unit 140 and the fixing processing mechanism 160 to form an image on the second side, the sheet P is then guided to the discharge roller pair 171, and is discharged to the outside of the printer 100 by the discharge roller pair 171.

[0023] Incidentally, various sheets such as ordinary plain paper, recycled paper, glossy paper, coated paper (paper with a surface treatment such as resin coating), thin paper, thick paper, etc. can be used as the sheet P used as the recording material. In addition, in this embodiment, a long sheet (for example, a sheet longer than 420 mm, which is the long side of an A3 sheet) whose length in the conveying direction is longer than a general standard size can be used as the recording material. Incidentally, the long sheet is not necessarily stored in the illustrated storage 110a, and for example, the long sheet may be set on a manual feed tray protruding from the side of the housing 101 and fed one by one to the feeding and conveying mechanism 110 by a feeding roller.

[0024] The printer 100 is also provided with an operation unit 180 that serves as a user interface. The operation unit 180 includes a display device such as a liquid crystal panel that displays information to the user, and an input device such as physical keys or a touch panel function unit of the liquid crystal panel that allows the user to input commands and data to the printer 100. By operating the operation unit 180, the user can change settings such as whether the sheet used in the current print job is a long sheet or not. The printer controller 103b, which serves as a control means, controls the engine control unit 103a based on information received from the operation unit 180 to execute the print job.

[0025] The tandem type / intermediate transfer type electrophotographic mechanism 100A (optical development processing mechanisms 120, 121, 122, 123, intermediate transfer mechanism 152, secondary transfer section 140, fixing processing mechanism 160) described above is an example of an image forming means for forming an image on a sheet. When applying the technology described below, for example, a direct transfer type electrophotographic mechanism that transfers a toner image formed on a photosensitive member to a sheet without passing through an intermediate transfer member may be used as the image forming means. Also, in addition to the electrophotographic mechanism, an inkjet type printing unit or an offset printing mechanism may be used as the image forming means.

[0026] (Reversal mechanism) Next, the reversing mechanism 200 will be described. Fig. 2 is a schematic diagram of the periphery of the reversing mechanism 200 as viewed from the front of the main body. The reversing mechanism 200 includes an upstream conveying path 201, a duplex conveying path 202, a pair of reversing rollers 230, a duplex switching flap 231, a reversing and retreating section 300, and duplex conveying rollers 206 and 207. The upstream conveying path 201 is a part of the second conveying path through which the sheet guided to the reversing entrance roller 172 by the first switching flap 173 (Fig. 1) passes. The duplex conveying path 202 is formed by an upper surface guide 202a and a lower surface guide 202b, and is connected to a junction with the main conveying path 190 via the duplex conveying mechanism 220.

[0027] The reversing roller pair 230 as a reversing means is provided downstream (vertically below) of the place where the upstream conveying path 201 and the double-sided conveying path 202 join together in terms of the conveying direction in the upstream conveying path 201. The reversing roller pair 230 is configured to be able to switch the conveying direction of the sheet, for example, by being drivingly connected to a motor capable of forward and reverse rotation. In addition, the motor is controlled by the printer controller 103b, that is, the driving of the reversing roller pair 230 is freely controlled. In other words, the printer controller 103b can control the sheet conveying speed by the reversing roller pair 230 and the acceleration at which the sheet accelerates from a stopped state to the conveying speed.

[0028] The double-sided switching flap 231 is provided at a location where the upstream conveying path 201 and the double-sided conveying path 202 join together, and prevents the sheet inverted by the reversing roller pair 230 from flowing back into the upstream conveying path 201 .

[0029] The double-sided conveying path 202 is provided with double-sided conveying rollers 206, 207, and 208. The double-sided conveying rollers 206, 207, and 208, which are conveying means in this embodiment, convey the sheet, which is inverted by the reversing roller pair 230 and sent to the double-sided conveying path 202, via the double-sided conveying path 202 toward the double-sided conveying mechanism 220.

[0030] The reversing and evacuation section 300 serving as an evacuation section is provided downstream of the pair of reversing rollers 230 in the conveying direction in the upstream conveying path 201. The reversing and evacuation section 300 forms an evacuation area for temporarily evacuating a part of the sheet when the pair of reversing rollers 230 switches back the sheet.

[0031] In this embodiment, as shown in FIG. 1, the main transport path 190 and the duplex transport path 202 both extend in a substantially horizontal direction. In the range shown in FIG. 2, the duplex transport path 202 also extends from one side (left side in the figure) to the other side (right side in the figure) in the horizontal direction. In the vertical direction, the duplex transport path 202 is provided below the main transport path 190, and the reversing and evacuation section 300 is provided below the duplex transport path 202. In this embodiment, the fixing mechanism 160 and the discharge mechanism 170 located above the reversing and evacuation section 300 are both at least partially overlapped with the reversing and evacuation section 300 when viewed in the vertical direction. In addition, the reversing and evacuation section 300 and the storage 110a are arranged side by side in the horizontal direction, and their occupied areas in the vertical direction overlap. Such an arrangement is effective in suppressing the increase in size of the printer 100 caused by the arrangement of the reversing and evacuation section 300.

[0032] Here, we will explain the basic operation of the sheet P in the inversion mechanism 200. Figures 3, 4, and 5 are schematic diagrams showing the operation of the sheet P in the inversion mechanism 200, respectively showing the state before the sheet is inverted, the state during the inversion, and the state after the sheet is inverted.

[0033] The sheet P (dashed line) with an image formed on its first surface that has been transported from the reversing entrance rollers 172 to the reversing mechanism 200 is transported along the upstream transport path 201 and handed over to the reversing roller pair 230 (FIG. 3). The reversing roller pair 230 continues transporting the sheet P in the forward feed direction A (first direction) when receiving the sheet P from the reversing entrance rollers 172. At this time, the portion of the sheet P that is sent out in the forward feed direction A from the reversing roller pair 230 is stored in the reversing evacuation section 300 and is thus in an evacuated state.

[0034] When the rear end of the sheet P in the forward conveying direction A passes the double-sided switching flap 231, the reversing roller pair 230 pauses. After that, the double-sided switching flap 231 rotates in the direction of the arrow B to switch the orientation of the double-sided switching flap 231 so as to regulate the reverse flow of the sheet P in the upstream conveying path 201 and guide the sheet P to the double-sided conveying path 202 (FIG. 4). After switching the orientation of the double-sided switching flap 231, the reversing roller pair 230 switches the conveying direction to the reverse conveying direction C (second direction) to convey the sheet P. As a result, the sheet P is carried into the double-sided conveying path 202 and is conveyed by the double-sided conveying rollers 206 and 207 (FIG. 5).

[0035] In the above, a case has been described in which a sheet inverted by the inversion mechanism 200 is transported via the double-sided transport path 202, but the inversion mechanism 200 is also used in face-down discharge. Face-down discharge refers to an operation in which a sheet is discharged with the side on which an image is formed facing down in the case of single-sided printing. In the case of this embodiment, as shown in FIG. 1, a second switching flap 174 is provided upstream of the inversion entrance rollers 172, and in the case of face-down discharge, the sheet inverted by the inversion mechanism 200 is guided to the discharge roller pair 171 by the second switching flap 174.

[0036] (Reverse evacuation section) Next, the reversing and retracting section 300 as the retracting section of this embodiment will be described with reference to Figures 2 to 6. Figure 6 is a diagram showing flapping of the leading edge of the sheet when the reversing mechanism 200 reverses the sheet.

[0037] The reversing and retracting section 300 is composed of a guide member 310 arranged to surround an evacuation area where the sheet sent out from the reversing roller pair 230 is evacuated. The guide member 310 forms an evacuation conveying path along which the leading edge of the sheet is guided to trace the inner surface when the sheet is conveyed to be evacuated to the evacuation area, that is, the guide member 310 is arranged only on one side of the evacuation conveying path. Therefore, except for the portion where the first to third opposing rollers 412, 413, and 414 described later are present, the first surface of the sheet slides only on one side of the evacuation conveying path, and the conveying resistance is reduced, for example, compared to the case where the guide members are arranged on both sides of the evacuation conveying path.

[0038] The guide member 310 is shown as an integrated unit in FIG. 2, but is composed of three members, a first guide member 310A, a second guide member 310B, and a third guide member 310C, arranged in order in the forward feed direction A of the pair of reversing rollers 230. In particular, to retreat a longer sheet to the reversing and retreating section 300, it is necessary to utilize the area below the lower surface guide 202b as an evacuation area. For example, when a long sheet is retreated to the reversing and retreating section 300, the leading end of the sheet will be left over from the third curved section 313. Therefore, the third guide member 310C is arranged below the lower surface guide 202b, and a guide surface is provided to guide the sheet proceeding further beyond the third curved section 313.

[0039] The first guide member 310A is formed with a first curved portion 311, the second guide member 310B is formed with a second curved portion 312 and a third curved portion 313, and the third guide member 310C is formed with a fourth curved portion 314. The fourth curved portion 314 is formed by bending the lower surface of the third guide member 310C into two planes, and is called the fourth curved portion 314 in this embodiment in the sense that a curved surface (inscribed circle) that changes the direction of the leading end of the sheet is formed in a pseudo manner by these two planes. As described above, the guide member 310 has four curved portions, the first curved portion 311, the second curved portion 312, the third curved portion 313, and the fourth curved portion 314, in the order of proximity to the reverse roller pair 230 with respect to the forward feed direction A of the reverse roller pair 230.

[0040] If the sheet P is a long sheet, the leading edge of the sheet P sent from the reversing roller pair 230 to the reversing and retracting section 300 is guided while contacting the first curved portion 311, the second curved portion 312, the third curved portion 313, and the fourth curved portion 314. Specifically, the leading edge of the sheet P sent downward from the reversing roller pair 230 is guided by the first curved portion 311 in a direction from the upstream side to the downstream side of the sheet conveying direction in the double-sided conveying path 202 in the horizontal direction (one direction intersecting the vertical direction). Next, the leading edge of the sheet P is guided upward in the vertical direction by the second curved portion 312. Furthermore, the leading edge of the sheet P is guided by the third curved portion 313 in a direction opposite to the sheet conveying direction in the double-sided conveying path 202 in the horizontal direction (the other direction intersecting the vertical direction). Then, the leading edge of the sheet P is guided downward in the vertical direction by the fourth curved portion 314. Therefore, when a relatively long sheet such as a long sheet is switched back by the pair of reversing rollers 230, the sheet is retreated in a curved, rolled state along these curved portions inside the reversing and retreating section 300 (see FIG. 4).

[0041] As shown in FIG. 2, a first opposing roller 412 is disposed as a first contact member that contacts the second surface of the sheet at a position opposite to the second curved portion 312. The first opposing roller 412 is rotatably supported by a pair of support members 422 disposed on both sides of the outside of the second guide member 310B in the width direction perpendicular to the sheet conveying direction, that is, the first opposing roller 412 is configured as a driven roller. In addition, the support members 422 position the outer peripheral surface of the first opposing roller 412 so that it is 5 mm or more away from the inner peripheral surface of the second curved portion 312. That is, a conveying path (for example, the upstream conveying path 201 or the double-sided conveying path 202) that conveys a general sheet is configured so that the distance between the two guides is 3 mm to 5 mm. Therefore, the shortest distance between the outer peripheral surface of the first opposing roller 412 and the inner peripheral surface of the second curved portion 312 is configured to be 5 mm or more, which is greater than the distance (3 mm to 5 mm) between the upper surface guide 202a and the lower surface guide 202b.

[0042] Also, when viewed from the width direction, a line connecting the center P1, which is the first center of the arc shape of the second curved portion 312, and the upstream end 312a of the second curved portion 312 in the forward feed direction A is defined as a first virtual line L1. Furthermore, when viewed from the width direction, a line connecting the center P1 of the arc shape of the second curved portion 312 and the downstream end 312b of the second curved portion 312 in the forward feed direction A is defined as a second virtual line L2. At this time, the first opposing roller 412 is contained within an area surrounded by the first virtual line L1, the second virtual line L2, and the arc of the second curved portion 312, when viewed from the width direction. In other words, the first opposing roller 412 does not face the entire opposing area from the second curved portion 312 toward the center P1, but faces only a part of it.

[0043] Similarly, a second opposing roller 413 is disposed as a second contact member that contacts the second surface of the sheet at a position opposite the third curved portion 313. The second opposing roller 413 is rotatably supported by a pair of support members 423 disposed on both sides of the outside of the second guide member 310B in the width direction of the sheet, that is, the second opposing roller 413 is configured as a driven roller. In addition, the second opposing roller 413 is disposed so that the outer peripheral surface of the second opposing roller 413 is separated from the inner peripheral surface of the third curved portion 313 by the support members 423 by 5 mm or more. Similarly, the shortest distance between the outer peripheral surface of the second opposing roller 413 and the inner peripheral surface of the third curved portion 313 is configured to be 5 mm or more, which is greater than the distance (3 mm to 5 mm) between the upper surface guide 202a and the lower surface guide 202b, for example.

[0044] Also, when viewed from the width direction, a line connecting the center P2, which is the second center of the arc shape of the third curved portion 313, and the upstream end 313a of the third curved portion 313 in the forward feed direction A is defined as a third virtual line L3. Furthermore, when viewed from the width direction, a line connecting the center P2 of the arc shape of the third curved portion 313 and the downstream end 313b of the third curved portion 313 in the forward feed direction A is defined as a fourth virtual line L4. At this time, the second opposing roller 413 is contained within an area surrounded by the third virtual line L3, the fourth virtual line L4, and the arc of the third curved portion 313, when viewed from the width direction. In other words, the second opposing roller 413 does not face the entire opposing area from the third curved portion 313 toward the center P2, but faces only a part of it.

[0045] A third opposing roller 414 is disposed at a position opposite to the fourth curved portion 314 as a third abutting member that abuts against the second surface of the sheet. The third opposing roller 414 is rotatably supported by a pair of support members 424 disposed on both sides of the outside of the third guide member 310C in the width direction of the sheet, that is, the third opposing roller 414 is configured as a driven roller. The support members 424 also position the third opposing roller 414 so that its outer peripheral surface is 5 mm or more away from the inner surface of the fourth curved portion 314. In short, the shortest distance between the outer peripheral surface of the third opposing roller 414 and the inner peripheral surface of the fourth curved portion 314 is configured to be 5 mm or more, which is greater than the distance (3 mm to 5 mm) between the upper surface guide 202a and the lower surface guide 202b.

[0046] Next, a detailed operation of retracting a long sheet to the reversing and retracting section 300 and reversing and conveying it will be described. As shown in FIG. 3, when a long sheet P is conveyed from the reversing roller pair 230 in the forward conveying direction A to the reversing and retracting section 300 and retracted, the sheet P is guided so as to trace the inner circumferential surface of the guide member 310. That is, the leading end of the sheet P is guided by the first curved portion 311, the second curved portion 312, the third curved portion 313, and the fourth curved portion 314, and is reversed in the state shown in FIG. 4. As described above, the first opposing roller 412, the second opposing roller 413, and the third opposing roller 414 are respectively 5 mm or more away from the second curved portion 312, the third curved portion 313, and the fourth curved portion 314. Therefore, the sheet P conveyed in the forward conveying direction A is unlikely to come into contact with the first opposing roller 412, the second opposing roller 413, and the third opposing roller 414, and is conveyed stably.

[0047] As described above, the first opposing roller 412 partially faces the second curved portion 312, and the second opposing roller 413 also partially faces the third curved portion 313. Therefore, even if the sheet P is sandwiched between the guide member 310 and the sheet P while being fed in the forward feed direction A, causing resistance to conveyance, the resistance to conveyance is reduced, and further, even if the sheet P jams, ease of jamming and visibility are improved.

[0048] 4, when the sheet P is to be reversed, the reversing roller pair 230 is stopped by the printer controller 103b, and the double-sided switching flap 231 is switched to the direction of the arrow B. Thereafter, the reversing roller pair 230 is reversed and the sheet P is conveyed in the reverse feed direction C.

[0049] Here, when the reversing roller pair 230 is stopped, there is no longer any conveying force for the sheet P to trace the guide member 310. For example, as shown in Fig. 8, if the first opposing roller 412, the second opposing roller 413, and the third opposing roller 414 are not provided, the sheet P will sag downward as shown in the direction of the arrow Y, and the sheet P will buckle and fall downward. In this state, if the rotation of the reversing roller pair 230 is reversed and the sheet P is conveyed in the reverse feed direction C, the leading edge of the sheet P will be pulled into the reversing roller pair 230 in the direction of the arrow Z, as shown in Fig. 9.

[0050] Also, for example, as shown in FIG. 10, assume that the first opposing roller 412 and the second opposing roller 413 are not provided, and only the third opposing roller 414 is provided. Even in this case, when the rotation of the reversing roller pair 230 is reversed and the sheet P is conveyed in the reverse feed direction C, the sheet P is rolled up in the direction of the arrow W, and the leading edge of the sheet P may fall downward. Then, there is a risk that the load on the reversing roller pair 230 may fluctuate, or the sheet may be pulled into the reversing roller pair 230. In particular, when the load fluctuation becomes large, the torque of the motor driving the reversing roller pair 230 may become large, or the reversing roller pair 230 may not be able to clamp the sheet. This may cause the sheet to be misaligned, bent, or skewed when reversed. In addition, if the clamping force of the reversing roller pair 230 is increased, problems such as the need to increase the motor torque, image defects due to roller marks, and reduced durability may occur.

[0051] 5, in this embodiment, a first opposing roller 412, a second opposing roller 413, and a third opposing roller 414 are provided to support the sheet P inward, thereby maintaining the shape of the sheet P along the inner side of the guide member 310. This prevents the long sheet P from sagging downward during or after the sheet P is inverted, and prevents the sheet P from folding, the load fluctuation on the reversing roller pair 230, and the leading end from being pulled into the reversing roller pair 230.

[0052] Incidentally, if the length of a long sheet P is a normal length (first length, third length) such as A3 size or 18 inches or less, it will not reach the third curved portion 313. However, if the length of the long sheet P is longer than the normal length (second length, fourth length), it will pass over the third curved portion 313 and reach the fourth curved portion 314. If the length of the sheet P reaches the fourth curved portion 314, as shown in FIG. 6, the leading end of the sheet P bent horizontally by the third curved portion 313 and bent downward by the fourth curved portion 314 is likely to flutter in the direction of the arrow X.

[0053] Therefore, when the sheet P is a long length (fourth length) longer than the normal length (third length), the printer controller 103b sets the stop time (first stop time) for stopping before reversing the rotation to a stop time (second stop time) longer than the normal time. This prevents the sheet P from being reversed until the fluttering at the leading edge of the sheet P stops, and after that, the reversed sheet P can be stably transported and the fluctuation in the transport load can be reduced.

[0054] Furthermore, when the sheet P is a long sheet P having a length (second length) longer than the normal length (first length), the printer controller 103b sets the conveying speed and acceleration after reversal of the reversing roller pair 230 to half that of the normal length. In other words, when the sheet is of normal length, the printer controller 103b controls the conveying speed (first conveying speed) and acceleration (first acceleration). When the sheet is longer than the normal length, such as A3 size or 18 inches or less, the printer controller 103b controls the conveying speed (second conveying speed) and acceleration (second acceleration) slower than the normal conveying speed and acceleration. This makes it possible to reduce the influence of inertia caused by the weight, friction, and shape of the long sheet P.

[0055] <Second embodiment> Next, a second embodiment, which is a partial modification of the first embodiment, will be described with reference to Fig. 7. Fig. 7 is a schematic diagram of an inversion mechanism according to the second embodiment. In the description of the second embodiment, the same reference numerals are used for the same parts as those in the first embodiment, and the description thereof will be omitted.

[0056] In the above first embodiment, the first opposing roller 412, the second opposing roller 413, and the third opposing roller 414 are provided, but in this second embodiment, as shown in Fig. 7, these are configured in a plate shape having opposing surfaces that face the guide member 310. That is, the first opposing surface 512 is arranged to face the second curved portion 312, the second opposing surface 513 is arranged to face the third curved portion 313, and the third opposing surface 514 is arranged to face the fourth curved portion 314.

[0057] In detail, a first opposing surface 512 serving as a first contact member is disposed at a position opposing the second curved portion 312. The first opposing surface 512 is supported by a pair of support members 522 disposed on both sides of the outside of the second guide member 310B in the width direction of the sheet. The support members 522 also dispose the outer surface of the first opposing surface 512 so as to be 5 mm or more away from the inner peripheral surface of the second curved portion 312. That is, the shortest distance between the outer surface of the first opposing surface 512 and the inner peripheral surface of the second curved portion 312 is configured to be 5 mm or more, which is greater than the distance (3 mm to 5 mm) between the upper surface guide 202a and the lower surface guide 202b, for example.

[0058] Further, when viewed from the width direction, the first opposing surface 512 is contained within a region surrounded by the first virtual line L1, the second virtual line L2, and the arc of the second curved portion 312. In other words, the first opposing surface 512 does not face the entire opposing region from the second curved portion 312 toward the center P1, but faces only a portion of it.

[0059] Similarly, a second opposing surface 513 serving as a second contact member is disposed at a position opposing the third curved portion 313. The second opposing surface 513 is supported by a pair of support members 523 disposed on both sides of the outside of the second guide member 310B in the width direction of the sheet. The support members 523 also dispose the outer surface of the second opposing surface 513 so as to be 5 mm or more away from the inner circumferential surface of the third curved portion 313. That is, the shortest distance between the outer surface of the second opposing surface 513 and the inner circumferential surface of the third curved portion 313 is configured to be 5 mm or more, which is greater than the distance (3 mm to 5 mm) between the upper surface guide 202a and the lower surface guide 202b, for example.

[0060] Further, when viewed from the width direction, the second opposing surface 513 is contained within a region surrounded by the third virtual line L3, the fourth virtual line L4, and the arc of the third curved portion 313. In other words, the second opposing surface 513 does not face the entire opposing region from the third curved portion 313 toward the center P2, but faces only a portion of it.

[0061] A third opposing surface 514 serving as a third contact member is disposed at a position facing the fourth curved portion 314. The third opposing surface 514 is supported by a pair of support members 524 disposed on both sides of the outside of the third guide member 310C in the sheet width direction. The support members 524 also dispose the outer surface of the third opposing surface 514 so as to be 5 mm or more away from the inner surface of the fourth curved portion 314. That is, the shortest distance between the outer peripheral surface of the third opposing surface 514 and the inner peripheral surface of the fourth curved portion 314 is configured to be 5 mm or more, which is greater than the distance (3 mm to 5 mm) between the upper surface guide 202a and the lower surface guide 202b, for example.

[0062] In the reversing and retracting section 300 of the second embodiment configured as described above, the shape of the sheet P is maintained by the first opposing surface 512, the second opposing surface 513, and the third opposing surface 514 during or after the sheet P is reversed. This makes it possible to prevent the sheet P from falling over or the leading edge of the sheet P from being pulled into the pair of reversing rollers 230, reduce fluctuations in the conveying load, and enable stable conveyance.

[0063] Other than this, the configuration, operation, and effects of the second embodiment are similar to those of the first embodiment, so a description thereof will be omitted.

[0064] (Possible other embodiments) In the above-described first and second embodiments, the reversing and retracting section 300 is disposed next to the storage 110a on the lower side of the printer 100. However, the present invention is not limited to this, and the reversing and retracting section 300 may be disposed anywhere inside the printer 100.

[0065] In the first and second embodiments, the guide member 310 is described as having the first curved portion 311, the second curved portion 312, the third curved portion 313, and the fourth curved portion 314 formed of the first guide member 310A, the second guide member 310B, and the third guide member 310C. However, this is not limiting, and for example, the guide member 310 may be formed as a single unit, or may be divided in any manner.

[0066] In the second embodiment, the first opposing surface 512, the second opposing surface 513, and the third opposing surface 514 are described as being planar. However, this is not limiting, and it is also possible to provide a conveying rib on the surface corresponding to the guide member 310, or to arrange a plurality of small rollers.

[0067] In the first and second embodiments, the first to third curved portions 311 to 313 are formed of a curved surface that is arc-shaped when viewed from the width direction. However, the present invention is not limited to these, and the first to third curved portions may be formed by connecting a plurality of planes at different angles, that is, the conveying path may be curved. Conversely, the present invention is not limited to these, and the fourth curved portion 314 is formed by connecting two planes, that is, the conveying path may be curved. However, the present invention is not limited to these, and the fourth curved portion may be formed of a curved surface that is arc-shaped when viewed from the width direction, that is, the conveying path may be curved. [Explanation of symbols]

[0068] 100...image forming apparatus (printer) / 100A...image forming means (electrophotographic mechanism) / 103b...control means (printer controller) / 230...reversing means (reversing roller pair) / 310...guide member / 311...first curved portion / 312...second curved portion / 312a...upstream end / 312b...downstream end / 313...third curved portion / 313a...upstream end / 313b...downstream end / 314...fourth curved portion / 412...first contact member / 413...second contact member / 414...third contact member / A...first direction (forward feed direction) / C...second direction (reverse feed direction) / L1...first virtual line / L2...second virtual line / L3...third virtual line / L4...fourth virtual line / P...sheet / P1...first center / P2...second center

Claims

[Claim 1] an image forming means for forming an image on a conveyed sheet; an inversion means for inverting a sheet having an image formed on a first surface of the sheet by the image forming means by transporting the sheet in a first direction and then transporting the sheet in a second direction opposite to the first direction; a guide member including a first curved portion for guiding a leading edge of the sheet sent out in the first direction from the inversion means in one direction intersecting the vertical direction, a second curved portion for guiding upward the leading edge of the sheet guided in the one direction by the first curved portion, and a third curved portion for guiding the leading edge of the sheet guided upward by the second curved portion in another direction intersecting the vertical direction; a first contact member disposed opposite the second curved portion and contacting a second surface of the sheet to be inverted, the second surface being opposite to the first surface; a second contact member disposed opposite the third curved portion and contacting the second surface of the sheet to be inverted; 1. An image forming apparatus comprising:

Images