JP2019012264A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can stably convey an elongated sheet when forming images on both sides of the elongated sheet.SOLUTION: An image forming apparatus comprises: an image forming unit that forms toner images on an elongated sheet; a fixing unit that fixes the toner images formed on the elongated sheet; a main conveyance path that conveys the elongated sheet to the image forming unit and fixing unit; and a double-sided conveyance path that branches from the downstream side in a conveyance direction of the fixing unit in the main conveyance path, reverses the conveyance direction of the elongated sheet at a switchback point to turn the elongated sheet upside down, and conveys the elongated sheet toward upstream of the image forming unit. The downstream side in the conveyance direction in the double-sided conveyance path before the switchback includes a merging path connected to the upstream side of the image forming unit in the main conveyance path, and has a first introduction part that introduces the leading end in the conveyance direction of the elongated sheet to the merging path.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus.

  Conventionally, an image forming apparatus that forms an image on a sheet using toner is known. In such an image forming apparatus, in order to be able to form an image on both sides by reversing the front and back sides of the paper, a conveyance path is configured to reverse the front and back of the paper by switching back and forth (that is, reverse) in the front and back directions of the paper. Some have a reversing conveyance path (see, for example, Patent Document 1).

  In the conventional image forming apparatus, a sheet having a size that can be stored in the sheet feed tray unit can be switched back through the reverse conveyance path.

JP 2006-124100 A

  In recent years, there is an increasing demand for sheets that are called long paper exceeding the size that can be stored in the paper feed tray unit so that images can be formed on both sides. On the other hand, in order to realize double-sided printing of long paper, it is necessary to make the path length of the reverse conveyance path longer than before. When the path length of the reversing conveyance path is made longer than before, there are problems such as an increase in the size of the apparatus and measures against jams that are likely to occur compared to standard paper.

  As a configuration for facilitating the jam processing when the paper is jammed at the time of double-sided printing, for example, the above-mentioned reversing conveyance path and conveyance roller are configured as a single unit, and such a unit is configured as an apparatus main body. There is something that is configured to be able to be taken in and out. This unit is called, for example, an automatic duplex reversal transport unit (ADU: Auto Duplex Unit).

  On the other hand, when the reverse conveyance path can be taken in and out of the apparatus main body, there is a problem that the paper is easily jammed due to poor alignment accuracy with the conveyance path fixed to the apparatus main body side. In particular, when the reversal conveyance path is extended to a longer path than before and can be taken in and out of the apparatus main body, a gap forming the conveyance path, that is, a gap (clearance) between the guide members for conveying the sheet. Is an important issue to maintain with high accuracy over the entire length of the path.

  An object of the present invention is to provide an image forming apparatus capable of stably transporting long paper when images are formed on both sides of the long paper.

An image forming apparatus according to the present invention includes:
An image forming unit for forming a toner image on a long paper;
A fixing unit for fixing the toner image formed on the long paper;
A main conveyance path for conveying the long paper to the image forming unit and the fixing unit;
Branches from the downstream side of the fixing unit in the main conveyance path in the conveyance direction, and reverses the conveyance direction of the long paper at a switchback point so that the front and back of the long paper are reversed to the upstream side of the image forming unit. And a double-sided conveyance path for conveying to
The downstream side in the transport direction before switchback in the double-sided transport path includes a merging path connected to the upstream side of the image forming unit in the main transport path,
A first introduction unit configured to introduce a leading end of the long paper in the conveyance direction into the joining path;

  According to the present invention, when an image is formed on both sides of a long paper, the long paper can be stably conveyed.

1 is a configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment. FIG. 2 is a diagram illustrating a main part of a control system in the image forming apparatus of FIG. 1. It is a figure which extracts and shows the conveyance path | route for duplex printing. It is a figure which expands and shows a confluence | merging path | route. It is a perspective view which shows the structure of a guide plate. It is a figure which expands and shows the entrance side of a confluence | merging path | route. It is the figure which looked at the entrance side of the confluence | merging path | route from the lower side of FIG. It is a figure explaining the case where long paper is printed on both sides.

  Embodiments of an image forming apparatus to which the present invention is applied will be described below with reference to the drawings.

  FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 shows the main part of the control system of the image forming apparatus 1 in the present embodiment. FIG. 3 shows an extracted conveyance path for double-sided printing in the image forming apparatus 1.

  The image forming apparatus 1 according to the present embodiment is an apparatus that uses long paper LS or paper S (non-long paper) as a recording medium and forms an image on the long paper LS or paper S.

  In the present embodiment, the long paper LS is a sheet having a longer length in the transport direction than commonly used A4 size paper, A3 size paper, etc., and is stored in the paper feed tray units 51a to 51c. Has a length that cannot be. The size of the long sheet LS, that is, the dimension such as the length in the transport direction is stored as definition data in a memory or the like of the system. Hereinafter, when simply referred to as “paper”, both the long paper LS and the paper S may be included.

  The image forming apparatus 1 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 1 primarily transfers the Y (yellow), M (magenta), C (cyan), and K (black) toner images formed on the photosensitive drum 413 to the intermediate transfer belt 421. After the four color toner images are superimposed on the intermediate transfer belt 421, the toner images are formed by secondary transfer onto the paper.

  Further, in the image forming apparatus 1, the photosensitive drums 413 corresponding to the four colors of YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and the respective color toner images are sequentially transferred to the intermediate transfer belt 421 in one step. Tandem system is adopted.

  As shown in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100.

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads a program corresponding to the processing content from the ROM 102 and develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program. At this time, various data stored in the storage unit 72 is referred to. The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 100 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Do. For example, the control unit 100 receives image data transmitted from an external device, and forms a toner image on a sheet based on the image data (input image data). The communication unit 71 is composed of a communication control card such as a LAN card, for example.

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

  The automatic document feeder 11 transports the document D placed on the document tray by a transport mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents D placed on a document tray all at once.

  The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

  The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as the display unit 21 and the operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like in accordance with a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table LUT) in the storage unit 72 under the control of the control unit 100. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, a compression process, and the like on the input image data in addition to the gradation correction. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 is based on the input image data, and image forming units 41Y, 41M, 41C, 41K, and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component. Etc.

  The Y component, M component, C component, and K component image forming units 41Y, 41M, 41C, and 41K have the same configuration. For convenience of illustration and description, common components are denoted by the same reference numerals, and in order to distinguish each, Y, M, C, or K is added to the reference numerals. In FIG. 1, only the components of the Y-component image forming unit 41Y are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 has, for example, an undercoat layer (UCL), a charge generation layer (CGL), a charge transport layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). It is a negatively charged organic photoreceptor (OPC: Organic Photo-conductor) in which CTL (Charge Transport Layer) is sequentially laminated. The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges by exposure by the exposure device 411. The charge transport layer consists of a material in which a hole transport material (electron donating nitrogen-containing compound) is dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The control unit 100 controls the drive current supplied to a drive motor (not shown) that rotates the photosensitive drum 413 to rotate the photosensitive drum 413 at a constant peripheral speed (linear speed).

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity. The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. A positive charge is generated in the charge generation layer of the photosensitive drum 413 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 413 is neutralized. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 is, for example, a two-component developing type developing device, and forms a toner image by visualizing the electrostatic latent image by attaching toner of each color component to the surface of the photosensitive drum 413.

  The drum cleaning device 415 includes a cleaning member that is in sliding contact with the surface of the photosensitive drum 413. The drum cleaning device 415 removes the transfer residual toner remaining on the surface of the photosensitive drum 413 after the primary transfer with a cleaning member.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421 as an image carrier, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, it is preferable that the roller 423A disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face the backup roller 423B disposed on the downstream side in the belt traveling direction of the drive roller 423A. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photoconductive drum 413 are primarily transferred onto the intermediate transfer belt 421 in sequence. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet. Specifically, by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the paper (the side in contact with the secondary transfer roller 424), the toner image becomes It is electrostatically transferred to the paper. The sheet on which the toner image has been transferred is conveyed toward the fixing unit 60.

  The belt cleaning device 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421 and removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Instead of the secondary transfer roller 424, a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller is adopted. Also good.

  The fixing unit 60 is arranged on the upper fixing unit 60A having a fixing surface side member arranged on the fixing surface (surface on which the toner image is formed) side of the paper, and on the back surface (surface opposite to the fixing surface) side of the paper. A lower fixing unit 60B having a back-side support member and a heating source 60C. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the sheet is formed.

  The fixing unit 60 fixes the toner image on the sheet by secondarily transferring the toner image and heating and pressurizing the conveyed sheet at the fixing nip. The fixing unit 60 is disposed in the fixing device F as a unit. The fixing device F is provided with an air separation unit 60D that separates the sheet S from the fixing surface side member by blowing air.

  The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. In the three paper feed tray units 51a to 51c constituting the paper feed unit 51, paper S (standard paper, special paper) identified based on basis weight (rigidity), size, etc. is set for each preset type. Be contained. The conveyance path unit 53 includes a plurality of conveyance rollers such as a pair of registration rollers 53a, a double-sided conveyance path for forming an image on both sides of a sheet, and the like. Details of the transport path unit 53 will be described later.

  The sheets S stored in the sheet feed tray units 51 a to 51 c are sent one by one from the top and are conveyed to the image forming unit 40 by the conveyance path unit 53. At this time, the registration roller portion provided with the registration roller pair 53a corrects the inclination of the fed paper S and adjusts the conveyance timing. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred onto one side of the sheet S at a time, and a fixing process is performed in the fixing unit 60. The sheet S on which the image has been formed is discharged out of the apparatus by a discharge unit 52 having a discharge roller 52a.

  Next, the conveyance path unit 53 will be described in detail.

  The conveyance path unit 53 is a path through which a sheet of paper forms an image on one side (upper surface), and includes a main conveyance path 530 through which a sheet on which a toner image is formed by the image forming unit 40 is conveyed. . The main conveyance path 530 is a path through which the sheet is conveyed via the registration roller 53a, the secondary transfer nip of the image forming unit 40, and the fixing unit 60. The conveyance path unit 53 includes a reverse conveyance path 533 that reverses the front and back of the sheet.

  The conveyance path unit 53 is fed from an external sheet feeding conveyance path 531 that conveys a sheet such as a long sheet LS fed from the external sheet feeding port 2a to the main conveyance path 530, and the sheet feeding tray units 51a to 51c. A paper feed conveyance path 532 is provided for conveying the sheet S to the main conveyance path 530.

  The main transport path 530 is provided above the paper feed tray units 51 a to 51 c inside the apparatus main body 2 and extends from one side of the apparatus main body 2 to the other side. One end of the main transport path 530 is connected to the external paper feed transport path 531 and the paper feed transport path 532. Further, the other end of the main transport path 530 is connected to the discharge port of the discharge unit 52 provided on the other side of the apparatus main body 2.

  One end of the external sheet feed conveyance path 531 is connected to the external sheet feed port 2 a, and the other end is connected to the main conveyance path 530. The paper feed conveyance path 532 is provided in the vicinity of one side in the apparatus main body 2, and extends vertically from the paper feed tray units 51 a to 51 c to the main conveyance path 530. In the paper feed conveyance path 532, an unillustrated open / close door provided on one side of the apparatus main body 2 is opened, so that a part of the path of the paper feed conveyance path 532 is exposed to the outside, jam processing, etc. Is possible. The paper feed transport path 532 has an upper end connected to the main transport path 530 and a lower end connected to the paper feed tray units 51a to 51c.

  The reverse conveyance path 533 is provided between the paper feed tray units 51 a to 51 c and the main conveyance path 530 inside the apparatus main body 2, and extends from the other side of the apparatus main body 2 to one side. The reverse conveyance path 533 includes a first reflux conveyance path 533 a that branches downward from the main conveyance path 530 on the downstream side of the fixing unit 60 in the conveyance direction of the sheet conveyed through the main conveyance path 530, and the image forming unit 40. A second reflux conveyance path 533b that joins the main conveyance path 530 is provided upstream of the secondary transfer nip.

  One end of the reverse conveyance path 533 is connected to the first reflux conveyance path 533a and the second reflux conveyance path 533b. Here, one end of the reverse conveyance path 533 connected to the first reflux conveyance path 533a and the second reflux conveyance path 533b is a switchback that switches between forward and reverse of the paper traveling direction (conveyance direction) during duplex printing. Point SBP. Hereinafter, in the reverse conveyance path 533, the conveyance direction indicated by the arrow a in which the sheet is conveyed from the first reflux conveyance path 533a is referred to as a positive direction, and is indicated by the arrow b in which the sheet is conveyed to the second reflux conveyance path 533b. The conveyance direction is referred to as the reverse direction.

  Further, the reverse conveyance path 533 includes a conveyance roller 53b as a switchback roller on the downstream side in the normal conveyance direction with respect to the switchback point SBP. The conveyance roller 53b receives a driving force of a motor (not shown) and conveys the paper in both the forward direction and the reverse direction.

  Further, on the downstream side of the transport roller 53b in the forward transport direction of the reverse transport path 533, a confluence transport path 533c that joins the main transport path 530 and connects the reverse transport path 533 and the main transport path 530 is provided. Is provided. FIG. 4 shows an enlarged portion of the confluence conveyance path 533c. This merging conveyance path 533c is a curved conveyance path having a curved shape so as to be folded upward in the conveyance direction of the sheet before being switched back.

  The confluence conveyance path 533c is a double-sided path used for duplex printing of paper (mainly long paper LS), and the main conveyance path 530 is upstream of the registration roller 53a in the conveyance direction of the sheet conveyed in the forward direction. To join. In this example, the merging conveyance path 533c merges on the upstream side from the merging point between the main conveyance path 530 and the second reflux conveyance path 533b. Further, the merging conveyance path 533 c merges with the main conveyance path 530 in a direction in which the sheet is conveyed in the left direction of the main conveyance path 530 in the drawing.

  As described above, by joining the reverse conveyance path 533 to the main conveyance path 530, it is possible to realize double-sided printing of the long sheet LS while preventing the apparatus body 2 and the image forming apparatus 1 from being enlarged. That is, in the present embodiment, the downstream side of the transport path in the transport direction before the switchback is provided so as to be folded back into the apparatus main body 2, thereby preventing the image forming apparatus 1 (the apparatus main body 2 or the like) from becoming large. However, the path length of the reverse conveyance path 533 can be made longer than before. In addition, when the converging conveyance path 533c of the reverse conveyance path 533 is connected to the upstream side of the image forming unit 40 in the main conveyance path 530, it is possible to perform double-sided printing on a long sheet LS having a longer size in the conveyance direction. .

  As shown in the figure, the confluence conveyance path 533c is curved to extend upward so as to fold back the conveyed sheet. For this reason, depending on the length of the long paper LS, the long paper LS is transported in a direction in which the leading edge of the first surface on which the toner image is formed climbs the merging transport path 533c before switchback at the time of duplex printing. The At this time, although depending on the type (rigidity, length, etc.) of the long paper LS, a case where the conveyance force of the conveyance roller 53b is insufficient may occur. If the conveyance force of the conveyance roller 53b before the switchback is insufficient, the leading edge of the first sheet of the long sheet LS cannot climb up the merging conveyance path 533c, and the trailing end of the long sheet LS can pass the switchback point SBP. Cases such as disappearance may occur.

  Therefore, in the present embodiment, the conveyance roller 53c that conveys the long paper LS is additionally provided in the merging conveyance path 533c. Here, the conveyance roller 53c is a pair of rollers facing each other, and one of the rollers is provided at the opening of the inner paper guide 537 constituting the merging conveyance path 533c, as shown in FIG. It is driven by a motor 540 which is a drive source separate from the transport roller 53b. The other roller of the transport rollers 53c is provided at the opening of the outer paper guide 536 constituting the merged transport path 533c, and is driven to rotate as the one roller rotates. Specifically, the transport rollers 53b and 53c rotate synchronously under the control of the control unit 100, and are driven to rotate so that the transport direction and the peripheral speed (paper transport speed) are the same.

  Thus, by providing the drive source of the transport roller 53c separately from the drive source of the transport roller 53b, the drive source (motor) for the transport roller 53b after the leading edge of the long paper LS enters the transport roller 53c. The load can be reduced.

  Note that when the long paper LS is transported in the reverse direction after the switchback compared to before the switchback, the transport is performed in the direction of going down the transport path, so that only the transport force by the transport roller 53b is sufficient. On the other hand, if the long paper LS is sandwiched between the transport rollers 53c at this time, the load on the transport rollers 53b increases and the transport force may be insufficient. Therefore, in the present embodiment, an actuator (not shown) or the like is connected to the transport roller 53c so that the transport roller 53c can be retracted from the merging transport path 533c. And the control part 100 outputs a control signal to this actuator so that the conveyance roller 53c may be spaced apart from the long paper LS at the time of conveyance in the reverse direction after switchback.

  In the present embodiment, an actuator (not shown) is also connected to the transport roller 53e (see FIG. 3) arranged in the main transport path 530 so that the transport roller 53e can be retracted from the main transport path 530. . Here, the transport roller 53e is originally a roller for printing on one side (first side) of a sheet, and is not configured to be able to reverse the type of motor. For this reason, when the leading edge of the long paper LS enters the transport roller 53e in the forward transport before the switchback, the control unit 100 separates the transport roller 53e from the long paper LS during the reverse transport after the switchback. The control signal is output to the actuator of the transport roller 53e.

  Referring to FIG. 3, the distance between the transport roller 53b and the transport roller 53c is set to a distance longer than the size of the paper S (standard paper) in the transport direction, for example, a distance of about 400 mm. Therefore, in the present embodiment, when double-sided printing is performed on the paper S that is a non-long paper, the control unit 100 does not perform drive control of the motor 540 for the transport roller 53c. For this reason, power saving and simplification of control can be achieved at the time of duplex printing of non-long paper.

  According to the present embodiment having such a configuration, when performing double-sided printing of the long paper LS, when the long paper LS before switchback is climbed toward the main transport path 530, the transport force is sufficient. Can be secured.

  Further, in transporting the long paper LS after the switchback, the transport roller 53c is separated from the long paper LS and the motor 540 of the transport roller 53c is not operated, so that power saving during transport after the switchback is achieved. It is done.

  By the way, the merging / conveying path 533c is curved so as to fold back the conveyed sheet, so that the guide (the right sheet in FIG. 4) faces the first surface of the long sheet LS on which the toner image is formed. Guide) may rub. In this case, there is a possibility that scratches may occur on the first surface of the long paper LS depending on the rigidity (strength of stiffness) of the long paper LS.

  More specifically, generally, when the distance from the conveyance roller 53b to the merging conveyance path 533c is large as in this example, the free length of the long paper LS from the conveyance roller 53b can be secured, so Even if the paper guide rubs, the long paper LS is less likely to be scratched. On the other hand, in this embodiment, since the conveyance roller 53c is provided in the merging conveyance path 533c, the portion of the long paper LS that has passed downstream of the conveyance roller 53c in the conveyance in the forward direction is merged and conveyed with a short free length. It is pressed against the paper guide of the path 533c. That is, the portion of the long paper LS pressed against the paper guide in a state where the free length is short has an apparent stiffness, that is, a pressing force against the paper guide, and as a result, scratches are likely to occur.

  In view of such a problem, in the present embodiment, a roller 53d that rotates in contact with the image forming surface of the long sheet LS is provided in the region of the merging conveyance path 533c where the scratch damage or the like described above may occur. Yes. With this configuration, the first surface of the long paper LS is prevented from rubbing against the conveyance guide, and as a result, the occurrence of scratches and the like is prevented.

  As shown in FIGS. 3 and 4, the roller 53d is located on the downstream side of the transport roller 53c in the forward transport direction. The roller 53d is positioned in the vicinity of the conveyance roller 53c in the merged conveyance path 533c, and the axis of the roller 53d is parallel to the axis of the conveyance roller 53c. The roller 53d forms the merged conveyance path 533c and faces the merged conveyance path 533c (the first surface of the long paper LS) from an opening provided in the outer paper guide 536 facing the first surface of the long paper LS. Are arranged as follows. Since the roller 53d forms a part of the ADU, it can be taken in and out of the apparatus main body 2.

  In the merging conveyance path 533c, the upstream side of the conveyance roller 53c in the positive conveyance direction is a region where the leading end of the long paper LS in the conveyance direction linearly strikes, in other words, the long paper LS and the conveyance guide. This is an area where rubbing is likely to occur. Therefore, it is conceivable that the rollers 53d are provided alternatively or additionally in such areas. On the other hand, the experimental results of the present inventors have found that when a roller is provided in this region, the long paper LS is caught and jamming is likely to occur. For this reason, in the present embodiment, as described above, the roller 53d is disposed in the vicinity of the downstream side of the transport roller 53c in the positive transport direction in the merging transport path 533c.

  In the present embodiment, a sheet guide member serving as a first introducing portion that faces the start end in the conveyance direction before switching back in the merge conveyance path 533c and introduces the leading edge in the conveyance direction of the long paper LS into the merge conveyance path 533c. 535 is provided. The paper guide member 535 is provided in the vicinity of the lower end portion of the guide plate 536 of the confluence conveyance path 533c, and has a function of assisting or supporting the conveyance of the long paper LS during double-sided printing. The paper guide member 535 is a step forming member that forms a step with respect to the lower end of the opposing guide plate 536 so that the leading end in the transport direction of the long paper LS is received by the guide plate 536. That is, the downstream end portion of the paper guide member 535 along the positive conveyance direction is positioned above the lower end portion of the guide plate 536. The configuration of the guide plate 536 will be described later.

  Further, in the present embodiment, as the second introduction unit that faces the end in the conveyance direction before the switchback in the merging conveyance path 533c and receives the leading edge in the conveyance direction of the long paper LS and introduces it into the main conveyance path 530. The opening 530 a is provided in the paper guide below the main conveyance path 530. The opening 530a is bent so that a part of the lower sheet guide of the main conveyance path 530 protrudes to a position below the upper end of the upper guide member 537, and as shown in FIG. The bent portion of the guide forms a step with respect to the upper end of the upper guide member 537. In this way, by forming a merge path with the merge conveyance path 533c on the same surface and a lower position of the lower sheet guide of the main conveyance path 530 constituting the first sheet path, the first sheet is passed. Sometimes, the sheet is prevented from being caught at the opening 530a, and the long sheet LS can be smoothly taken in and out between the merging conveyance path 533c and the main conveyance path 530.

  FIG. 5 shows a guide plate 536 that forms part of the sheet guide member in the merging conveyance path 533c. As illustrated, the guide plate 536 is curved so as to have a curvature, and a plurality of openings 536a (three in this example) into which one of the rollers (right side in FIGS. 1 and 4) in the transport roller 53c is inserted. One) is provided. As shown in the drawing, the inner side of the guide plate 536 on the side facing the paper is a flat lower area, and a plurality of ribs 536b are raised in the upper area so as to extend in the transport direction.

  As shown by a dotted line in FIG. 1, the reverse conveyance path 533 and the rollers disposed in the reverse conveyance path 533 are configured as components of an automatic duplex reverse conveyance unit (Auto Duplex Unit: ADU) with respect to the apparatus main body 2. It can be pulled out toward you.

  More specifically, for example, by pulling out an operation lever (not shown) of the ADU during jam processing, a plate-like frame 533f on the back side of the apparatus shown in FIG. 3 and a confluence conveyance path 533c attached to the frame 533f are included. Most of the paper guide members, rollers and the like constituting the reverse conveyance path 533 are pulled out. On the other hand, among the paper guide members constituting the reverse conveyance path 533, a part of the guide members 534 serving as the bottom surface is fixed to the apparatus main body 2 side. Hereinafter, the guide member 534 fixed to the apparatus main body 2 side is referred to as a main body side lower guide. Further, the sheet guide member 535 described above is attached to the main body side lower guide 534 and remains on the apparatus main body 2 side even when the ADU is pulled out.

  In the present embodiment, a configuration in which a part of the guide member constituting the double-sided conveyance path is fixed (remains) on the apparatus main body 2 side as described above, thereby improving the jam handling performance when the ADU is pulled out. In addition, the ADU and the entire image forming apparatus 1 are prevented from being enlarged.

  In the image forming apparatus 1 of the present embodiment, the long paper LS can be printed on both sides of the longer paper LS in the transport direction by passing the long paper LS through the merge transport path 533c before and after the switchback operation. . Further, according to the present embodiment, since the double-sided conveyance path is substantially annular, the long paper LS is held so as to be wound around the inner guide member when the frame 533f or the like is pulled out during jam processing. Is done. Therefore, according to the present embodiment, there is an advantage that the paper can be easily taken out while preventing the paper from being damaged (guillotine or the like) at the time of removing the jammed paper.

  By the way, as described above, a sheet conveyance guide member (hereinafter referred to as a sheet guide) is divided between the ADU and the apparatus main body 2 side, and a sheet conveyance path is formed in a clearance (gap) between the sheet guides. Due to the following problems, an area in which it is difficult to accurately maintain the clearance of the sheet conveyance path is generated.

  That is, the rear side of the ADU can be accurately aligned with the apparatus main body 2 by, for example, fitting the end of the frame 533f on the apparatus main body 2 side. On the other hand, it is not easy to provide such an alignment mechanism on the front side of the ADU. Specifically, the front side of the ADU is a side on which an opening / closing door (not shown) of the apparatus main body 2 is opened to expose a sheet conveyance path and the like. For this reason, if a member that closes the paper conveyance path such as the frame 533f is provided on the front side of the ADU, it becomes difficult to visually recognize the state of the paper during the jam processing, and the work of taking out the paper becomes complicated. In addition, since the opening / closing door of the apparatus main body 2 is a movable member and is not rigid, even when a mechanism for aligning the front side portion of the ADU with the opening / closing door of the apparatus main body 2 is provided, It is difficult to ensure the accuracy of alignment.

  In general, in the configuration in which the ADU is taken in and out of the image forming apparatus 1 in the front-rear direction (front side and back side), the paper guide fixed to the apparatus main body 2 side and the paper guide opposed to or connected to the paper guide 2 It is not easy to ensure the accuracy of the gap between the ADU side paper guide and the front side of the apparatus. Specifically, depending on the weight of the ADU, the distance between the main body side lower guide 534 and the paper guide member 535 on the front side of the apparatus and the upper guide member 537 on the ADU side facing these members tends to be narrowed. Similarly, it is not easy to always maintain the clearance accurately at the connection portion of the main conveyance path 530 and the merging conveyance path 533c of the ADU on the front side of the apparatus. As described above, in the configuration in which the ADU is taken in and out of the apparatus main body 2, there is a problem that it is difficult to appropriately maintain the gap in the conveyance path of the long paper LS.

  In view of such a problem, in this embodiment, as shown in FIGS. 6 and 7, a sheet conveyance space (gap) is provided between the main body side lower guide 534 and the upper guide member 537 as a pair of sheet guides. A roller 533g is provided as a gap holding portion to hold. Here, FIG. 7 is a view of the entrance side of the merging conveyance path 533c as viewed from the lower side of FIG. 6, and the right side of FIG.

  The roller 533g is disposed at a position outside the width of the long paper LS conveyed through the gap between the main body side lower guide 534 and the upper guide member 537. In this example, the roller 533 g is rotatably supported on the front side of the apparatus on the lower surface of the upper guide member 537, that is, on the end side in the front direction of the apparatus main body 2.

  The roller 533g is provided in the vicinity of the paper guide member 535 and is disposed at a position where it does not interfere with the paper guide member 535. The shaft of the roller 533g is supported by the upper guide member 537 so that the roller 533g contacts the main body side lower guide 534 and does not contact the upper guide member 537. Here, the axis of the roller 533g is parallel to the paper conveyance direction and is in a direction orthogonal to the axis of a roller (for example, conveyance rollers 53b and 53c) that conveys the paper.

  According to such a configuration, the upper guide member 537 moves relative to the lower guide 534 on the main body side when the ADU accommodated in the main body 2 is pulled out to the front side of the apparatus (left side in FIG. 5). During such movement, the roller 533 g that is pivotally supported by the upper guide member 537 and is in contact with the main body side lower guide 534 moves on the main body side lower guide 534 as the upper guide member 537 and the main body side lower guide 534 move relative to each other. It functions as a driven rotating wheel. Therefore, according to the present embodiment, the rotation of the roller 533g can reduce the frictional resistance with the apparatus main body 2 side when the ADU is pulled out, and can smoothly pull out the ADU.

  In the operation of returning the ADU thus drawn out into the apparatus main body 2, if the roller 533 g gets on the main body side lower guide 534, the roller 533 g similarly functions as a wheel, and the back side of the ADU It rotates on the lower guide 534 on the main body side until the positioning of the (frame 533f) is completed. When the ADU is completely returned into the apparatus main body 2, the roller 533g stops at a position in front of the paper guide member 535 (see FIG. 4), and supports or presses the upper guide member 537 from below. A gap (clearance) between the main body side lower guide 534 and the upper guide member 537 is kept constant.

  As described above, according to the present embodiment in which the roller 533g is used as a gap holding member that holds the gap between the pair of paper guides, the clearance of the paper conveyance path is kept constant with a simple and low-cost configuration. Accuracy can be improved. As a result, the transportability of the long paper LS during double-sided printing can be stabilized or improved.

  Further, in the present embodiment, as described above, there is a step at the connection portion between the end portion of the guide plate 536 forming the confluence conveyance path 533c and the guide member of the main body side lower guide 534 and the main conveyance path 530. Provided. That is, in the present embodiment, by providing a step between each guide in a region where there is a possibility that an error may occur in the clearance between the guides and there is no space for placing the rollers 533g, The clearance error between the two guides is absorbed. As a result, it is possible to stabilize the transportability of the long paper LS during duplex printing.

  Next, the conveyance operation at the time of duplex printing will be described.

  First, a case where duplex printing is performed on the paper S fed from the paper feed tray units 51a to 51c will be described. In the image forming apparatus 1, the paper S that has been transported in the forward direction (left direction in FIG. 1) through the main transport path 530 and passed through the image forming unit 40 and the fixing unit 60 has a surface facing upward (first surface). The toner image is transferred and fixed. Subsequently, the sheet S is transported and controlled by the control unit 100 so that the sheet S is transported from the main transport path 530 to the reverse transport path 533 via the first reflux transport path 533a. Further, when the trailing end of the sheet S in the transport direction passes the switchback point SBP, the control unit 100 switches the rotation direction of the transport roller 53b to reverse the transport direction, and the sheet S is transferred from the reverse transport path 533 to the second reflux. The conveyance control is performed so as to convey to the main conveyance path 530 via the conveyance path 533b.

  With this conveyance control, the sheet S, which is a non-long sheet, is conveyed in the forward direction indicated by the arrow a, before the leading edge of the sheet S enters the merging conveyance path 533c, and the trailing edge of the sheet S is the switchback point. Pass SBP. Subsequently, the sheet S passes through the second reflux conveyance path 533b, and is conveyed to the main conveyance path 530 with the first surface, which is the image forming surface, facing downward, and the image is formed on the second surface facing upward. The The sheet S on which the toner images are formed on both sides is transport-controlled by the control unit 100 so that the sheet S is discharged from the main transport path 530 to the paper discharge unit 52. Therefore, when the paper S, which is a non-long paper, is printed on both sides, the paper S is not transported to the merging transport path 533c.

  Next, a case where double-sided printing of the long paper LS is performed using the merging conveyance path 533c will be described. The following is an example of transporting a long sheet LS having a length that is transported to the main transport path 530 through the merge transport path 533c in transport in the forward direction on the reverse transport path 533.

  The long sheet LS is conveyed in the forward direction (left direction in FIG. 1) from the external sheet feed port 2a of the apparatus main body 2 via the external sheet feed conveyance path 531. Thereafter, in the same manner as described above, the long paper LS that has passed through the image forming unit 40 and the fixing unit 60 has the toner image transferred and fixed on the upper first surface, and the first reflux conveyance path from the main conveyance path 530. It is conveyed to the reverse conveyance path 533 via 533a. When the long sheet LS is conveyed in the forward direction indicated by the arrow a in the reverse conveyance path 533, the conveyance roller 53b is driven and controlled by the control unit 100 so that the leading end in the conveyance direction enters the merging conveyance path 533c.

  At this time, as shown in FIG. 4, the long paper LS slides on the paper guide member 535 (step forming member) and is conveyed so that the leading end side of the long paper LS rises due to the inclination of the paper guide member 535. The Subsequently, the front end of the long paper LS abuts on the lower plane area (see FIG. 5) of the guide plate 536, and then moves (rises) along the curved shape of the guide plate 536, and is moved to the transport roller 53c. storm in. At this time, the leading edge of the long paper LS is received by the flat portion of the guide plate 536, and the stress of the long paper LS abutted against the guide plate 536 is evenly distributed by the flat surface. For this reason, the buckling of the long paper LS in the curved merging conveyance path 533c is suppressed.

  Further, the control unit 100 outputs a drive signal to the drive source (motor 540) so that the transport roller 53c starts rotating when the leading edge of the long paper LS enters the transport roller 53c, and the transport rollers 53b and 53c. The long paper LS is conveyed in the forward direction by both of the above. Here, the control unit 100 outputs a drive signal to each drive source so that the peripheral speeds of the transport roller 53b and the transport roller 53c are the same.

  Subsequently, the long paper LS is transported by both the transport rollers 53b and 53c while being in contact with the ribs 536b of the guide plate 536, and the leading end side in the traveling direction of the long paper LS passes through the above-described opening 530a. Enter Road 530. Here, since the roller 53d that faces the merged conveyance path 533c from the outer paper guide that forms the merged conveyance path 533c is provided, the leading end of the first surface of the long sheet LS has passed through the conveyance roller 53c. The roller 53d is contacted without contacting the paper guide. Thereafter, the roller 53d rotates following the clockwise direction in FIG. 4 with the movement of the first surface of the long paper LS that has come into contact therewith. According to the present embodiment, the function of the roller 53d can effectively prevent the occurrence of scratches caused by rubbing the first surface of the long paper LS against the paper guide. In addition, since a step is provided between the upper end of the upper guide member 537 forming the merging conveyance path 533c and the lower paper guide (opening 530a) of the main conveyance path 530, the long paper LS is It is smoothly introduced into the main transport path 530 from the stepped portion of the opening 530a (see FIG. 8).

  Then, when the trailing end of the long paper LS in the conveyance direction passes the switchback point SBP, the control unit 100 performs a switchback operation that switches the rotation direction of the conveyance rollers 53b and 53c to reverse the conveyance direction. Here, the control unit 100 outputs a drive signal to the motor 540 so as to reversely rotate the transport roller 53c at substantially the same peripheral speed as that of the transport roller 53b during transport in the reverse direction after the switchback. In this operation, the long paper LS is transported and controlled by the control unit 100 so as to be transported from the reverse transport path 533 to the main transport path 530 via the second reflux transport path 533b.

  As another example of the switchback operation, the following operation may be performed. That is, when the trailing end of the long paper LS in the transport direction passes the switchback point SBP, the control unit 100 separates (withdraws) the transport roller 53c from the long paper LS and switches the rotation direction of the transport roller 53b. The operation to reverse the conveyance direction is executed.

  In general, regarding a conveyance roller into which a long sheet LS enters before and after the switchback, a conveyance path that rotates only in one direction depending on the type of a drive source (motor) that drives rotation of the conveyance roller. If it is a conveyance roller which can be separated from the direction and can be rotated in both forward and reverse directions, it may be configured not to be separated from the conveyance path.

  By this conveyance control, the traveling direction of the long paper LS is reversed and conveyed in the reverse direction, and the rear end of the long paper LS in the conveyance direction moves in the reverse direction (right direction in FIG. 4) on the main conveyance path 530. The leading end in the transport direction is transported from the reverse transport path 533 to the main transport path 530 via the second reflux transport path 533b.

  Thereafter, as in the case of the sheet S, the long sheet LS is conveyed to the main conveyance path 530 through the second reflux conveyance path 533b with the first surface, which is the image forming surface, facing downward. The toner image is transferred and fixed on the second surface facing upward. The long paper LS on which the toner images are formed on both sides is transported and controlled by the control unit 100 so as to be discharged from the main transport path 530 to the paper discharge unit 52.

  As described above, according to the present embodiment, the long paper LS can be stably transported in the transport operation when the long paper LS is printed on both sides, and the transportability of the long paper LS is improved. As a result, jamming of the long paper LS can be prevented or suppressed.

  In the above-described embodiment, the roller 533g is attached to the upper guide member 537 (that is, the ADU side), and is configured to rotate following the main body side lower guide 534 that is relatively moved when the ADU is put in and out. As another configuration example, the roller 533g may be attached to the main body side lower guide 534 (that is, the apparatus main body 2 side) and rotated following the upper guide member 537 of the ADU.

[Appendix]
According to the above-described embodiment, technical ideas or configurations as described in the following (1) to (11) are derived.

(1) an image forming unit 40 that forms a toner image on the long paper LS;
A fixing unit 60 for fixing the toner image formed on the long paper LS;
A main conveyance path 530 for conveying the long paper LS to the image forming unit 40 and the fixing unit 60;
The main conveyance path 530 branches from the downstream side in the conveyance direction of the fixing unit 60 and reverses the conveyance direction of the long paper LS at the switchback point SBP, thereby reversing the front and back of the long paper LS. A double-sided conveying path 533 for conveying upstream;
With
The double-sided conveyance path 533 has a curved conveyance path 533c that curves so as to be folded back in the conveyance direction before the long paper LS is switched back.
The curved conveyance path 533c includes a conveyance roller 53c that conveys the long paper LS.
Image forming apparatus.

(2) In the configuration of (1) above,
The curved conveyance path 533 c is connected to the upstream side of the image forming unit 40 in the main conveyance path 530.

(3) In the configuration of (1) or (2) above,
A roller 53d that rotates in contact with the image forming surface of the long paper LS conveyed to the curved conveyance path 533c is provided.

(4) In any one of the constitutions (1) to (3),
The distance between the transport roller 53c and the switchback roller 53b that reverses the transport direction of the long paper LS at the switchback point SBP is shorter than the length of the long paper LS in the transport direction and is longer than the length of the standard paper in the transport direction. Also long.

(5) In the configuration of (4) above,
The transport roller 53c transports the long paper LS at the same peripheral speed as the switchback roller 53b before the long paper LS is reversed at the switchback point SBP.

(6) In the configuration of (4) or (5) above,
The transport roller 53c and the switchback roller 53b are driven by different drive sources.

(7) In any one of the constitutions (1) to (6),
The transport roller 53c is separated from the long paper LS when the long paper LS is switched back.

(8) In the configuration of (3) above,
The roller 53d is disposed in the curved conveyance path 533c downstream of the conveyance roller 53c in the conveyance direction before being switched back.

(9) In the transport direction before the long paper LS is reversed at the switchback point SBP in order to form an image by the image forming unit 40 on both sides of the long paper LS having a length in the transport direction of a predetermined length or more. A paper conveyance control method in the image forming apparatus 1 including a double-sided conveyance path 533 having a curved conveyance path 533c that is bent so as to be folded,
When a toner image is formed on both sides of the long paper LS, before the long paper LS is reversed at the switchback point SBP, the transport roller 53c disposed in the curved transport path 533c is driven to perform the long paper LS. Transport LS,
Paper transport control method.

  The above-described embodiments and modifications are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. . That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Apparatus main body 2a External paper feed port 10 Image reading part 20 Operation display part 30 Image processing part 40 Image forming part 50 Paper transport part 51 Paper feed part 51a-51c Paper feed tray unit 52 Paper discharge part 53 Transport path Part 53a Registration roller pair 53b Transport roller (switchback roller)
53c Conveying roller 53d Roller 53e Conveying roller 530 Main conveying path 530a Opening (second introduction part)
531 External paper feed path 532 Paper feed path 533 Reverse feed path (both sides transport path)
533a 1st recirculation conveyance path 533b 2nd recirculation conveyance path 533c Merged conveyance path (merging path, curved conveyance path)
533f frame 533g roller (gap holding part)
534 Main body side lower guide (paper guide)
535 paper guide member (first introduction part)
536 Guide plate (paper guide)
536a Opening 536b Rib 537 Upper guide member (paper guide)
540 Motor (drive source)
60 fixing unit 100 control unit (conveyance control unit)
ADU automatic duplex reversing conveyance unit SBP Switchback point LS Long paper

Claims (9)

An image forming unit for forming a toner image on a long paper;
A fixing unit for fixing the toner image formed on the long paper;
A main conveyance path for conveying the long paper to the image forming unit and the fixing unit;
Branches from the downstream side of the fixing unit in the main conveyance path in the conveyance direction, and reverses the conveyance direction of the long paper at a switchback point so that the front and back of the long paper are reversed to the upstream side of the image forming unit. And a double-sided conveyance path for conveying to
The downstream side in the transport direction before switchback in the double-sided transport path includes a merging path connected to the upstream side of the image forming unit in the main transport path,
A first introduction portion for introducing a leading end of the long paper in the conveyance direction into the merging path;
Image forming apparatus. The first introduction portion is a step forming member that forms a step with respect to the paper guide so that the leading end of the long paper in the transport direction is received by the paper guide of the merging path.
The image forming apparatus according to claim 1. The step forming member is fixed to the apparatus main body,
The image forming apparatus according to claim 2. One of the pair of paper guides forming the double-sided conveyance path is arranged in a unit that can be taken in and out of the apparatus main body, and the other of the paper guides is fixed to the apparatus main body,
Between the pair of paper guides, a gap holding unit that holds the gap is provided on the end side outside the width of the long paper that is conveyed through the gap between the paper guides.
The image forming apparatus according to claim 1. The gap holding portion is a roller that is pivotally supported by one of the pair of paper guides and is in contact with the other, and rotates in accordance with the loading and unloading.
The image forming apparatus according to claim 4. The gap holding portion is disposed on the end side in the front direction of the apparatus main body,
The image forming apparatus according to claim 4 or 5. A second introduction portion for introducing a leading end of the long paper in the conveyance direction into the main conveyance path;
The image forming apparatus according to claim 6. The second introduction part forms a step with respect to the paper guide inside the merging path so as to receive the leading edge of the long paper in the transport direction.
The image forming apparatus according to claim 7. The double-sided conveyance path has a curved conveyance path that curves so as to be folded back in the conveyance direction before the long paper is switched back;
The curved conveyance path includes a conveyance roller that conveys the long paper.
The image forming apparatus according to claim 1.

Images