Patent Publication Number: US-9845214-B2

Title: Image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to and claims the benefit of Japanese Patent Application No. 2014-174352, filed on Aug. 28, 2014, the disclosure of which including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus for forming an image on a long sheet. 
     2. Description of Related Art 
     Conventionally, image forming apparatuses (such as a printer, a copier, and a facsimile machine) which can form an image on a long sheet such as a roll sheet and a continuous sheet (continuous form paper) are known. For example, an electrophotographic image forming apparatus is configured to irradiate (expose) a uniformly-charged photoconductor (for example, a photoconductor drum) with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet through an intermediate transfer belt, followed by heating and pressurization for fixing at a fixing section, whereby an image is formed on the sheet. 
     In general, the interior of an image forming apparatus is contaminated and damaged by paper dust and preprinted ink component, and therefore cleaning of the sheet feeding path is required. In particular, when an image is formed on a tack roll sheet (a roll sheet including a surface base material, adhesive, and a release sheet) used for making labels, adhesive that comes off from the sheet adheres to parts (for example, a conveyance roller and a conveyance guide disposed in the sheet width direction) that make contact with an end portion of the sheet, and therefore it is necessary to frequently clean up the sheet feeding path. 
     When the sheet feeding path is cleaned, the sheet feeding path is exposed by widely exposing the exterior portion of the image forming apparatus, or by pulling a sheet conveyance section including a conveyance roller section and a conveyance guide part in the sheet width direction from a front door of the image forming apparatus, for example (see, for example, Japanese Patent Application Laid-Open No. 2007-172014). 
     However, when the interior of the apparatus is exposed by widely exposing the exterior of the image forming apparatus to perform cleaning, a long sheet still presents in the sheet feeding path, and therefore the cleaning of the parts under the long sheet cannot be performed. In addition, since the cleaning has to be performed while avoiding the structural parts, it is difficult to ensure a sufficient space for the cleaning. Furthermore, in electrophotographic image forming apparatuses having complicated internal structures, parts which can be exposed are limited, and therefore the workability is poor. 
     In the case where cleaning is performed by pulling out the sheet conveyance section in the sheet width direction, the sheet conveyance section cannot be pulled when the long sheet exists in the feeding path since the long sheet is torn if the sheet conveyance section is pulled in the state where the long sheet exists in the feeding path. For this reason, the long sheet has to be removed from the sheet feeding path to pull out the sheet conveyance section, and thus removal of the long sheet and resupply of the sheet after the cleaning are required, and as a result, the cleaning operation is complicated. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an image forming apparatus in which cleaning of a sheet feeding path can be readily performed when a long sheet is used. 
     To achieve at least one of the abovementioned objects, an image forming apparatus reflecting one aspect of the present invention includes: a sheet conveyance section configured to convey a long sheet along a sheet feeding path; and an image forming section configured to form an image on the long sheet conveyed by the sheet conveyance section, the sheet conveyance section including a conveyance unit that includes a first conveyance roller and a second conveyance roller for conveying the long sheet in a sandwiching manner, and is movable along a sheet conveyance direction in a state where the long sheet is conveyed through the sheet feeding path. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
         FIG. 1  illustrates an image forming apparatus according to an embodiment of the present invention; 
         FIG. 2  illustrates a general configuration of an image forming apparatus main body; 
         FIG. 3  illustrates a principal part of a control system of the image forming apparatus main body; 
         FIG. 4A  illustrates a state where a sheet introduction unit and a sheet ejection unit are mounted in the image forming apparatus main body; 
         FIG. 4B  illustrates a state where the sheet introduction unit and the sheet ejection unit are dismounted from the image forming apparatus; 
         FIGS. 5A to 5C  illustrate an example of the sheet introduction unit; 
         FIGS. 6A to 6C  illustrate another example of the sheet introduction unit; 
         FIG. 7A  illustrates a state where the sheet introduction unit is mounted in the image forming apparatus main body; and 
         FIG. 7B  illustrates a state where the sheet introduction unit is pulled out from the image forming apparatus main body. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a configuration of image forming apparatus  1  according to the embodiment of the present invention. 
     Image forming apparatus  1  illustrated in  FIG. 1  includes sheet feeding apparatus  1 A, image forming apparatus main body  1 B, and winding apparatus  1 C. Image forming apparatus  1  forms an image on a roll sheet, and the present invention is suitable for an image forming apparatus that forms an image on a long sheet such as a roll sheet and a continuous sheet, that is, a sheet that is always being conveyed through a sheet feeding path. 
     Sheet feeding apparatus  1 A includes roll sheet feeding section  91 , sheet feeding side buffer section  94  and the like, and feeds a sheet under the instruction of image forming apparatus main body  1 B. In sheet feeding side buffer section  94 , for example, slackening of the roll sheet is absorbed with a vertically movable tension roller, an air blasting device that applies air to the roll sheet, a suction device that sucks the roll sheet or the like, and thus a proper tensile force is given to the roll sheet. 
     The roll sheet fed from sheet feeding apparatus  1 A is conveyed along sheet feeding path  93 . Image forming apparatus main body  1 B forms an image on a roll sheet fed from sheet feeding apparatus  1 A. The way of image formation of image forming apparatus main body  1 B is not limited, and an electrophotographic method, an ink-jetting method, a thermal method or the like may be adopted. In the present embodiment, image forming apparatus main body  1 B adopting an electrophotographic method will be described. 
     Winding apparatus  1 C includes roll winding section  92  and winding side buffer section  95 , and winds up a roll sheet on which an image has been formed by image forming apparatus main body  1 B. Winding side buffer section  95  has a configuration similar to that of sheet feeding side buffer section  94 . 
       FIG. 2  illustrates a general configuration of image forming apparatus main body  1 B.  FIG. 3  illustrates a principal part of a control system of image forming apparatus main body  1 B. 
     Image forming apparatus main body  1 B illustrated in  FIGS. 2 and 3  is a color image forming apparatus of an intermediate transfer system using electrophotographic process technology. A longitudinal tandem system is adopted for image forming apparatus main body  1 B. In the longitudinal tandem system, respective photoconductor drums  213  corresponding to the four colors of YMCK are placed in series in the travelling direction (vertical direction) of intermediate transfer belt  221 , and the toner images of the four colors are sequentially transferred to intermediate transfer belt  221  in one cycle. 
     That is, image forming apparatus main body  1 B transfers (primary-transfers) toner images of yellow (Y), magenta (M), cyan (C), and black (K) formed on photoconductor drums  213  to intermediate transfer belt  221 , and superimposes the toner images of the four colors on one another on intermediate transfer belt  221 . Then, image forming apparatus main body  1 B transfers (secondary-transfers) the resultant image to a sheet, to thereby form an image. 
     As illustrated in  FIGS. 2 and 3 , image forming apparatus main body  1 B includes operation display section  12 , image processing section  13 , image forming section  20 , sheet introduction section  14 , sheet ejection section  15 , main conveyance section  16 , and control section  17 . 
     Control section  17  includes central processing unit (CPU)  171 , read only memory (ROM)  172 , random access memory (RAM)  173  and the like. CPU  171  reads a program suited to processing contents out of ROM  172  or storage section  182 , develops the program in RAM  173 , and integrally controls the operation of each block of image forming apparatus  1 B, sheet feeding apparatus  1 A and winding apparatus  1 C in cooperation with the developed program. 
     Communication section  181  has various interfaces such as network interface card (NIC), modulator-demodulator (MODEM), and universal serial bus (USB), for example. 
     Storage section  182  is composed of, for example, a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive. Storage section  182  stores therein a look-up table which is referenced when the operation of each block is controlled, for example. 
     Control section  17  transmits and receives various data to and from an external apparatus (for example, a personal computer) connected to a communication network such as a local area network (LAN) or a wide area network (WAN), through communication section  181 . Control section  17  receives image data (input image data) of page description language (PDL) that has been sent from an external device, and controls the apparatus to form an image on a sheet on the basis of the data, for example. 
     Operation display section  12  includes, for example, a liquid crystal display (LCD) with a touch panel, and functions as display section  121  and operation section  122 . Display section  121  displays various operation screens, image conditions, operating statuses of functions, and the like in accordance with display control signals received from control section  17 . Operation section  122  includes various operation keys such as numeric keys and a start key, receives various input operations performed by a user, and outputs operation signals to control section  17 . By operating operation display section  12 , the user can perform setting relating to the image formation such as document setting, image quality setting, multiplying factor setting, application setting, output setting, and sheet setting. 
     Image processing section  13  includes a circuit that performs a digital image process suited to initial settings or user settings on the input image data, and the like. For example, image processing section  13  performs tone correction on the basis of tone correction data under the control of control section  17 . Image processing section  13  also performs various correction processes such as color correction and shading correction on the input image data. Image forming section  20  is controlled on the basis of the image data that has been subjected to these processes. 
     Image forming section  20  includes: toner image forming section  21  configured to form toner images of colored toners respectively containing a Y component, an M component, a C component, and a K component on the basis of the input image data; intermediate transfer section  22  configured to transfer a toner image formed by toner image forming sections  21  to a sheet; fixing section  23  configured to fix a transferred toner image to a sheet; and the like. 
     Toner image forming section  21  includes four toner image forming sections  21 Y,  21 M,  21 C, and  21 K for the Y component, the M component, the C component, and the K component, respectively. Since toner image forming sections  21 Y,  21 M,  21 C, and  21 K have similar configurations, common elements are denoted by the same reference signs for ease of illustration and description. Only when elements need to be discriminated from one another, Y, M, C, K is added to their reference signs. In  FIG. 2 , reference signs are given to only the elements of toner image forming section  21 Y for the Y component, and reference signs are omitted for the elements of other toner image forming sections  21 M,  21 C, and  21 K. 
     Toner image forming section  21  includes exposing device  211 , developing device  212 , photoconductor drum  213 , charging device  214 , drum cleaning device  215  and the like. 
     Photoconductor drum  213  is, for example, a negative-charge-type organic photoconductor (OPC) formed by sequentially laminating an under coat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) on the circumferential surface of a conductive cylindrical body (aluminum-elementary tube) made of aluminum. 
     The charge generation layer is made of an organic semiconductor in which a charge generating material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charge and negative charge through light exposure by exposure device  211 . The charge transport layer is made of a layer in which a hole transport material (electron-donating nitrogen compound) is dispersed in a resin binder (for example, polycarbonate resin), and transports the positive charge generated in the charge generation layer to the surface of the charge transport layer. 
     Charging device  214  is composed of a corona discharging generator such as a scorotron charging device and a corotron charging device, for example. Charging device  214  evenly negatively charges the surface of photoconductor drum  213  by corona discharge. 
     Exposing device  211  is composed of, for example, an LED print head including an LED array having a plurality of linearly laid out light-emitting diodes (LED), an LPH driving section (driver IC) for driving each LED, and an lens array that brings light radiated from the LED array into an image on photoconductor drum  213 , and the like. Each of the LEDs of LED array  1  corresponds to one dot of an image. 
     Exposure device  211  irradiates photoconductor drum  213  with light corresponding to the image of each color component. The positive charge generated in the charge generation layer of photoconductor drum  213  irradiated with light is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of photoconductor drum  213  is neutralized. Thus, an electrostatic latent image of each color component is formed on the surface of photoconductor drum  213  by the potential difference from its surroundings. 
     Developing device  212  stores developers of respective color components (for example, a two-component developer composed of toner and magnetic carrier). Developing device  212  attaches toner of respective color components to the surfaces of photoconductor drums  213 , and visualizes the electrostatic latent image to form a toner image. To be more specific, a developing bias voltage is applied to a developer bearing member (developing roller), and an electric field is formed between photoconductor drum  213  and developer bearing member. By the potential difference between photoconductor drum  213  and the developer bearing member, the charging toner on the developer bearing member is caused to move and attach to a light exposure section on the surface of photoconductor drum  213 . 
     Drum cleaning device  215  includes a drum cleaning blade that is brought into sliding contact with the surface of photoconductor drum  213 , and removes residual toner that remains on the surface of photoconductor drum  213  after the primary transfer. 
     Intermediate transfer section  22  includes intermediate transfer belt  221 , primary transfer roller  222 , a plurality of support rollers  223 , secondary transfer roller  224 , belt cleaning device  225  and the like. 
     Intermediate transfer belt  221  is composed of an endless belt, and is stretched around the plurality of support rollers  223  in a loop form. At least one of the plurality of support rollers  223  is composed of a driving roller, and the others are each composed of a driven roller. When driving roller rotates, intermediate transfer belt  221  travels in arrow A direction at a constant speed. 
     Primary transfer rollers  222  are disposed on the inner periphery side of intermediate transfer belt  221  in such a manner as to face photoconductor drums  213  of respective color components. Primary transfer rollers  222  are brought into pressure contact with photoconductor drums  213  with intermediate transfer belt  221  therebetween, whereby a primary transfer nip (hereinafter referred to as “primary transfer section”) for transferring a toner image from photoconductor drums  213  to intermediate transfer belt  221  is formed. 
     Secondary transfer roller  224  is disposed on the outer periphery side of intermediate transfer belt  221  in such a manner as to face one of support rollers  223 . In the plurality of support rollers  223 , support roller  223  that is so disposed as to face intermediate transfer belt  221  is referred to as a backup roller (hereinafter referred to as “backup roller  223 ”). Secondary transfer roller  224  is brought into pressure contact with backup roller  223  with intermediate transfer belt  221  therebetween, whereby a secondary transfer nip (hereinafter referred to as “secondary transfer section”) for transferring a toner image from intermediate transfer belt  221  to a sheet is formed. 
     In the primary transfer section, the toner images on photoconductor drums  213  are sequentially primary-transferred to intermediate transfer belt  221 . To be more specific, a primary transfer bias is applied to primary transfer rollers  222 , and electric charge of the polarity opposite to the polarity of the toner is applied to the rear side (the side that makes contact with primary transfer rollers  222 ) of intermediate transfer belt  221 , whereby the toner image is electrostatically transferred to intermediate transfer belt  221 . 
     Thereafter, when the sheet passes through the secondary transfer section, the toner image on intermediate transfer belt  221  is secondary-transferred to the sheet. To be more specific, a secondary transfer bias is applied to secondary transfer roller  224 , and an electric charge opposite to that of the toner is applied to the rear side (the side that makes contact with secondary transfer roller  224 ) of the sheet, whereby the toner image is electrostatically transferred to the sheet. The sheet on which the toner image has been transferred is conveyed toward fixing section  23 . 
     Belt cleaning device  225  includes a belt cleaning blade configured to make sliding contact with the surface of intermediate transfer belt  221 , and the like, and removes transfer residual toner remaining on the surface of intermediate transfer belt  221  after the secondary transfer. 
     Alternatively, in intermediate transfer section  22 , it is also possible to adopt a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is installed in a stretched state in a loop form around a plurality of support rollers including a secondary transfer roller in place of secondary transfer roller  224 . 
     Fixing section  23  includes upper fixing section  231  having a fixing side member disposed on a fixing surface (the surface on which a toner image is formed) side of a sheet, lower fixing section  232  having a back side supporting member disposed on the rear surface (the surface opposite to the fixing surface) side of a sheet, heating source  233  configured to heat the fixing side member, a pressure contact separation section (not illustrated) configured to bring the back side supporting member into pressure contact with the fixing side member, and the like. 
     For example, when upper fixing section  231  is of a roller heating type, the fixing roller serves as the fixing side member, and when upper fixing section  231  is of a belt heating type, the fixing belt serves as the fixing side member. In addition, for example, when lower fixing section  232  is of a roller pressing type, the pressure roller serves as the back side supporting member, and when lower fixing section  232  is of a belt pressing type, the pressing belt serves as the back side supporting member.  FIG. 2  illustrates a configuration in which upper fixing section  231  is of a roller heating type, and lower fixing section  232  is of a roller pressing type. 
     Upper fixing section  231  includes upper fixing section-driving section (not illustrated) for rotating the fixing side member. When control section  17  controls the operation of the upper fixing section-driving section, the fixing side member rotates (travels) at a predetermined speed. Lower fixing section  232  includes lower fixing section-driving section (not illustrated) for rotating the back side supporting member. When control section  17  controls the operation of the lower fixing section-driving section, the back side supporting member rotates (travels) at a predetermined speed. It is to be noted that, in the case where the fixing side member follows the rotation of the back side supporting member, the upper fixing section-driving section is not required. 
     Heating source  233  is disposed inside or near the fixing side member. When control section  17  controls the output of heating source  233 , the fixing side member is heated, and maintained at a predetermined temperature (for example, a fixable temperature, or a fixation idling temperature). On the basis of the detection result of a fixing temperature detection section (not illustrated) disposed at a position near the fixing side member, control section  17  controls the output of heating source  233 . 
     A pressure contact separation section (not illustrated) presses the back side supporting member against the fixing side member. The pressure contact separation section makes contact with both ends of a shaft that supports the back side supporting member to separately press each end. With this structure, the balance of the nip pressure in the direction along the shaft in the fixing nip can be adjusted. When control section  17  controls the operation of the pressure contact separation section (not illustrated) such that the back side supporting member is brought into pressure contact with the fixing side member, a fixing nip for conveying a sheet in a tightly sandwiching manner is formed. 
     Heat and pressure are applied to a sheet on which a toner image has been secondary-transferred and which has been conveyed along a sheet feeding path at the time when the sheet passes through fixing section  23 . Thus, the toner image is fixed to the sheet. 
     Sheet introduction section  14  is configured as a unit (hereinafter referred to also as “sheet introduction unit  14 ”) in which sheet introduction roller section  141 , sheet-introduction rolling member  143 , sheet introduction guide part  142  and the like are fixed to frame  144  (see  FIG. 5 ) for example. Sheet introduction unit  14  is detachably mounted in image forming apparatus main body  1 B, and is configured to send a roll sheet fed from sheet feeding apparatus  1 A into main conveyance section  16 . 
     Sheet introduction roller section  141  includes a pair of rollers (upper sheet introduction roller  141 A and lower sheet introduction roller  141 B, see  FIG. 4A  and  FIG. 4B ) that are brought into pressure contact with each other. One of the rollers (here, upper sheet introduction roller  141 A) is a drive roller, and the other (here, lower sheet introduction roller  141 B) is a driven roller. Upper sheet introduction roller  141 A and lower sheet introduction roller  141 B are kept in a pressure contact state or a separated state by a pressure contact separation section (not illustrated). 
     Sheet-introduction rolling member  143  is disposed on the downstream side of sheet introduction roller section  141  in the sheet conveyance direction, and helps the conveyance of the roll sheet. 
     Sheet introduction guide part  142  includes a pair of guide members (upper side sheet introduction guide  142 A and lower side sheet introduction guide  142 B, see  FIG. 5 ) that face each other in the vertical direction (a direction perpendicular to the surface of the roll sheet). The sheet feeding path in sheet introduction section  14  is configured by sheet introduction guide part  142 . 
     Sheet ejection section  15  is configured as a unit (hereinafter referred to also as “sheet ejection unit  15 ”) in which sheet ejection roller section  151 , sheet ejection rolling member  152 , sheet ejection guide part  153  and the like are fixed to a frame (not illustrated). Sheet ejection unit  15  is detachably mounted in image forming apparatus main body  1 B, and is configured to send the roll sheet output from main conveyance section  16  into winding apparatus  1 C. The configuration of sheet ejection section  15  is similar to that of sheet introduction section  14 . 
     Sheet ejection roller section  151  includes a pair of rollers (upper sheet ejection roller  151 A and lower sheet ejection roller  151 B, see  FIG. 4 ) that are brought into pressure contact with each other. One of the rollers (here, upper sheet ejection roller  151 A) is a drive roller, and the other (here, lower sheet ejection roller  151 B) is a driven roller. Upper sheet ejection roller  151 A and lower sheet ejection roller  151 B are kept in a pressure contact state or a separated state by a pressure contact separation section (not illustrated). 
     Sheet ejection rolling member  152  is disposed on the upstream side of sheet ejection roller section  151  in the sheet conveyance direction, and helps the conveyance of the roll sheet. 
     Sheet ejection guide part  153  includes a pair of guide members (an upper side sheet ejection guide and a lower side sheet ejection guide, not illustrated) that face each other in the vertical direction (a direction perpendicular to the surface of the roll sheet). The sheet feeding path in sheet ejection section  15  is configured by sheet ejection guide part  153 . 
     Main conveyance section  16  includes a plurality of conveyance roller sections serving as sheet-conveyance elements for conveying sheets in a sandwiching manner. The conveyance roller sections include entry roller section  161  disposed on the upstream side of the secondary transfer section in the sheet conveyance direction. Main conveyance section  16  conveys a roll sheet introduced from sheet introduction section  14  through image forming section  20  (a secondary transfer section and fixing section  23 ), and conveys a sheet output from image forming section  20  (fixing section  23 ) toward sheet ejection section  15 . 
     When an image is formed on a roll sheet, a roll sheet fed from sheet feeding apparatus  1 A is introduced through sheet introduction section  14 . The roll thus introduced is conveyed to image forming section  20  by sheet main conveyance section  16 . Thereafter, a toner image on intermediate transfer belt  221  is secondary-transferred to a surface of the roll sheet at one time at the time when the roll sheet passes through the secondary transfer section, and then a fixing process is performed in fixing section  23 . The roll sheet on which an image has been formed is ejected out of the apparatus from sheet ejection section  15 , and wound by roll winding section  92  of winding apparatus  1 C. As described, the sheet conveyance section of image forming apparatus main body  1 B is configured by sheet introduction section  14 , sheet ejection section  15 , and main conveyance section  16 . 
     Image forming apparatus  1  requires cleaning of sheet feeding path  93  since the interior of the apparatus is contaminated and damaged with paper dust and preprinted ink component. In particular, in the case where an image is formed on a tack roll sheet (a roll sheet having a surface base material, adhesive, and a release sheet) used for making labels, adhesive that comes off from the sheet adheres to parts (for example, sheet introduction roller section  141 , sheet ejection roller section  151  and the like) that make contact with an end portion of the sheet, and therefore it is necessary to frequently clean up sheet feeding path  93 . 
     The present embodiment adopts a configuration in which sheet introduction unit  14  and sheet ejection unit  15  can be readily mounted or dismounted to or from image forming apparatus main body  1 B to facilitate the cleaning. 
       FIG. 4A  illustrates a state where sheet introduction unit  14  and sheet ejection unit  15  are mounted in image forming apparatus main body  1 B.  FIG. 4B  illustrates a state where sheet introduction unit  14  and sheet ejection unit  15  are dismounted from image forming apparatus main body  1 B. Sheet introduction unit  14  and sheet ejection unit  15  correspond to “conveyance unit” of the embodiment of the present invention. 
     As illustrated in  FIG. 4A  and  FIG. 4B , sheet introduction unit  14  includes upper sheet introduction unit  14 A (first conveyance unit) in which upper sheet introduction roller  141 A (first conveyance roller) is disposed, and lower sheet introduction unit  14 B (second conveyance unit) in which lower sheet introduction roller  141 B (second conveyance roller) is disposed. A roll sheet is conveyed between upper sheet introduction unit  14 A and lower sheet introduction unit  14 B. 
     Sheet ejection unit  15  includes upper side sheet ejection unit  15 A (which corresponds to first conveyance unit) in which upper sheet ejection roller  151 A (which corresponds to first conveyance roller) is disposed, and lower side sheet ejection unit  15 B (which corresponds to second conveyance unit) in which lower sheet ejection roller  151 B (which corresponds to second conveyance roller) is disposed. A roll sheet is conveyed between upper side sheet ejection unit  15 A and lower side sheet ejection unit  15 B. 
     In image forming apparatus main body  1 B, sheet introduction unit  14  and sheet ejection unit  15  can be moved along the sheet conveyance direction, that is, can be mounted or dismounted to or from image forming apparatus main body  1 B in a state where a roll sheet presents in the apparatus. It is to be noted that the phrase “can be moved along the sheet conveyance direction” means that the units can move in the “sheet conveyance direction” and “a direction opposite to the sheet conveyance direction.” 
     Sheet introduction unit  14  and sheet ejection unit  15  each include an engaging part (for example rolling member not illustrated) that is slidably engaged with a guide part (for example, guide rail not illustrated) disposed in image forming apparatus main body  1 B, and when the engaging parts slide along the guide part, sheet introduction unit  14  and sheet ejection unit  15  move along the sheet conveyance direction, for example. 
     As described, image forming apparatus  1  includes a sheet conveyance section (sheet introduction section  14 , sheet ejection section  15 , and main conveyance section  16 ) that conveys a roll sheet (long sheet) along the sheet feeding path, and image forming section  20  that forms an image on a roll sheet conveyed by the sheet conveyance section. The sheet conveyance section includes upper sheet introduction roller  141 A (first conveyance roller) and lower sheet introduction roller  141 B (second conveyance roller) for conveying a roll sheet, and includes sheet introduction unit  14  (conveyance unit) that can move along the sheet conveyance direction in a state where a roll sheet is being conveyed in the sheet feeding path. In addition, the sheet conveyance section includes upper sheet ejection roller  151 A (first conveyance roller) and lower sheet ejection roller  141 B (second conveyance roller) for conveying a roll sheet, and sheet ejection unit  15  (conveyance unit) that can move along the sheet conveyance direction in a state where a roll sheet is being conveyed in the sheet feeding path. 
     In image forming apparatus  1 , sheet introduction unit  14  and sheet ejection unit  15  can be mounted or dismounted to or from image forming apparatus main body  1 B without cutting the roll sheet, and therefore the cleaning of the sheet feeding path of sheet introduction unit  14  and sheet ejection unit  15  can be readily performed when a roll sheet is used. In addition, since it is not necessary to again convey the roll sheet, efficiency of the cleaning improves. In particular, image forming apparatus  1  is suitable for the case where a tack roll sheet is used. 
     In addition, upper sheet introduction unit  14 A and lower sheet introduction unit  14 B are connected with each other such that the interior of sheet introduction unit  14  can be exposed. Upper side sheet ejection unit  15 A and lower side sheet ejection unit  15 B are connected with each other such that the interior of sheet ejection unit  15  can be exposed. 
     With this configuration, components for sheet conveyance such as sheet introduction roller section  141  and sheet ejection roller section  151  can be readily exposed, and cleaning efficiency can be further improved. 
     The following describes specific configurations for exposing the interior of the units in sheet introduction unit  14  and sheet ejection unit  15 . It is to be noted that, since sheet introduction unit  14  and sheet ejection unit  15  may have configurations similar to each other, only sheet introduction unit  14  will be described below. 
       FIGS. 5A to 5C  illustrate an exemplary sheet introduction unit  14 .  FIG. 5A  is a plan view of sheet introduction unit  14  as viewed from upward.  FIG. 5B  is a side view of sheet introduction unit  14  as viewed from a near side (a front surface side of image forming apparatus main body  1 B, or this side of  FIG. 2 ).  FIG. 5C  is a front view illustrating a state where sheet introduction unit  14  is exposed. The left-and-right direction in  FIGS. 5A to 5C  is the sheet conveyance direction. 
     As illustrated in  FIG. 5A  to  FIG. 5C , in upper sheet introduction unit  14 A, upper sheet introduction roller  141 A, upper side sheet introduction guide  142 A and the like are attached to upper frame  144 A, for example. In lower sheet introduction unit  14 B, lower sheet introduction roller  141 B, lower side sheet introduction guide  142 B, sheet-introduction rolling member  143  and the like are attached to lower frame  144 B. 
     Upper frame  144 A and lower frame  144 B are connected together with shaft part  145  (for example, a hinge) disposed at an one end in the sheet conveyance direction (here, an end on image forming apparatus main body  1 B side). A locking part (not illustrated) configured to keep a closed state of sheet introduction unit  14  is provided at both ends in the sheet width direction or at the other end in the sheet conveyance direction of sheet introduction unit  14 . Shaft parts  145  are disposed in a spaced relationship in the sheet width direction, and a roll sheet is conveyed therebetween. 
     At the time of cleaning of sheet introduction roller section  141  and the like, as illustrated in  FIG. 5C , lower sheet introduction unit  14 B is turned frontward with respect to upper sheet introduction unit  14 A about shaft part  145 , and the interior of sheet introduction unit  14  is exposed. 
     As described, upper sheet introduction unit  14 A (first conveyance unit) and lower sheet introduction unit  14 B (second conveyance unit) are connected together with shaft parts  145  disposed along the sheet width direction at an end in the sheet conveyance direction, and upper sheet introduction unit  14 A or lower sheet introduction unit  14 B turns about shaft part  145 , whereby the interior of sheet introduction unit  14  (conveyance unit) is exposed. The same applies to sheet ejection unit  15 . 
     With this configuration, the user can easily clean up the components for sheet conveyance such as sheet introduction roller section  141  and sheet ejection roller section  151 . 
       FIGS. 6A to 6C  illustrate another example of sheet introduction unit  14 .  FIG. 6A  is a plan view of sheet introduction unit  14  as viewed from upward.  FIG. 6B  is a side view of sheet introduction unit  14  as viewed from a near side (image forming apparatus main body  1 B front surface side, in  FIG. 2  paper surface front side).  FIG. 6C  is a front view illustrating a state where sheet introduction unit  14  is exposed. The horizontal direction in  FIGS. 6A to 6C  is the sheet conveyance direction. 
     In sheet introduction unit  14  illustrated in  FIG. 6 , upper frame  144 A and lower frame  144 B are connected together with a shaft part  146  (for example, a hinge) disposed at one end in the sheet width direction (here, an end of the far side on image forming apparatus main body  1 B side). At both ends in the sheet conveyance direction or at the other end in the sheet width direction of sheet introduction unit  14 , a locking part (not illustrated) for keeping a closed state of sheet introduction unit  14  is provided. Other configurations are similar to those of sheet introduction unit  14  illustrated in  FIG. 5 . 
     At the time of cleaning of sheet introduction roller section  141  and the like, lower sheet introduction unit  14 B is turned to the far side with respect to upper sheet introduction unit  14 A about shaft part  146  as illustrated in  FIG. 6C , and the interior of sheet introduction unit  14  is exposed. 
     As described, upper sheet introduction unit  14 A (first conveyance unit) and lower sheet introduction unit  14 B (second conveyance unit) are connected together with shaft parts  146  disposed at an end in the sheet width direction along the sheet conveyance direction, and upper sheet introduction unit  14 A or lower sheet introduction unit  14 B turns about shaft part  145 , whereby the interior of sheet introduction unit  14  (conveyance unit) is exposed. The same applies to sheet ejection unit  15 . 
     With this configuration, the user can easily clean up the components for sheet conveyance such as sheet introduction roller section  141  and sheet ejection roller section  151 . 
     When a roll sheet is pinched by sheet introduction roller section  141  or sheet ejection roller section  151  during operation for mounting or dismounting sheet introduction unit  14  and sheet ejection unit  15 , the roll the roll sheet may be torn or slackened by being pulled. In view of this, when sheet introduction unit  14  and sheet ejection unit  15  are mounted or dismounted to or from image forming apparatus main body  1 B, it is desired that the roll sheet be not pulled. 
     For example, upper sheet introduction roller  141 A (first conveyance roller) and lower sheet introduction roller  141 B (second conveyance roller) may be configured such that they are brought into a separation state from a pressure contact state when sheet introduction unit  14  (conveyance unit) is pulled out of the apparatus, and that they are brought into a pressure contact state from a separation state when sheet introduction unit  14  is mounted in the apparatus. In this case, the pressure contact separation section (not illustrated) may automatically control the rollers to perform pressure contact operation or separation operation along with mounting or dismounting of sheet introduction unit  14 . 
     During mounting or dismounting of sheet introduction unit  14 , upper sheet introduction roller  141 A and lower sheet introduction roller  141 B are kept in the separation state, and therefore the roll sheet is not pulled. As a result, the roll sheet can be prevented from being torn or slackened by being pulled. The same applies to sheet ejection unit  15 . 
     In addition, for example, upper sheet introduction roller  141 A (first conveyance roller) and lower sheet introduction roller  151 A (second conveyance roller) may be configured to rotate in conjunction with the pulling operation when sheet introduction unit  14  (conveyance unit) is pulled out of the apparatus, and to rotate in conjunction with mounting operation when sheet introduction unit  14  is mounted in the apparatus. 
     As illustrated in  FIG. 7A  and  FIG. 7B , pinion gear G may be disposed at both ends of the roller shaft of upper sheet introduction roller  141 A serving as a drive roller such that pinion gear G is engaged with rack L disposed in image forming apparatus main body  1 B along with mounting or dismounting of sheet introduction unit  14 . When sheet introduction unit  14  is mounted in image forming apparatus main body  1 B, the engaging state of pinion gear G and rack L is released, and pinion gear G is connected to conveyance drive motor M. That is, rack L is disposed in such a manner that the conveyance operation is not interfered. 
     Upper sheet introduction roller  141 A rotates along the direction same as that of the sheet conveyance at the time when sheet introduction unit  14  is pulled out from image forming apparatus main body  1 B, and rotates along the direction opposite to that of the sheet conveyance at the time when sheet introduction unit  14  is mounted in image forming apparatus main body  1 B. The same applies to sheet ejection unit  15 . Thus, the roll sheet can be prevented from being torn or slackened by being pulled. 
     Meanwhile, in the case of sheet ejection unit  15 , upper sheet ejection roller  151 A rotates along the direction opposite to that of the sheet conveyance at the time when sheet ejection unit  15  is pulled out from image forming apparatus main body  1 B, and rotates along the direction same as that of the sheet conveyance at the time when sheet ejection unit  15  is mounted to image forming apparatus main body  1 B. 
     In addition, when a roll sheet is slacken at the time when sheet introduction unit  14  or sheet ejection unit  15  is mounted to image forming apparatus main body  1 B, conveyance error of the roll sheet may be caused. In view of this, it is preferable to perform sheet advancement prior to image formation by adjusting the drive timing of the conveyance roller section including sheet introduction roller section  141  and sheet ejection roller section  151 . With this configuration, slack of the roll sheet is readily removed. The length corresponding to the sheet advancement is absorbed by buffer sections  94  and  95  provided in sheet feeding apparatus  1 A and winding apparatus  1 C. 
     While the invention made by the present inventor has been specifically described based on the preferred embodiments, it is not intended to limit the present invention to the above-mentioned preferred embodiments but the present invention may be further modified within the scope and spirit of the invention defined by the appended claims. 
     For example, it is possible to adopt a configuration in which only one of sheet introduction unit  14  and sheet ejection unit  15  can be mounted or dismounted to or from image forming apparatus main body  1 B. Further, it is possible to adopt a configuration in which a part of main conveyance section  16  can be mounted or dismounted to or from image forming apparatus main body  1 B together with sheet introduction unit  14  or sheet ejection unit  15 . 
     In addition, in sheet introduction unit  14  and sheet ejection unit  15 , a guide part (side guide) that restricts the conveyance state of a roll sheet may be disposed at both ends in the sheet width direction. While, in the case where an image is formed on a tack roll sheet, the side guide is easily contaminated and damaged by adhesive that comes off from an end portion of the sheet in the width direction, the side guide can be readily cleaned up since sheet introduction unit  14  and sheet ejection unit  15  can be pulled out from image forming apparatus main body  1 B. 
     The present invention is applicable not only to image forming apparatuses utilizing an image formation method described in the embodiment, but also to image forming apparatuses utilizing an ink jetting method and a thermal method. 
     The embodiment disclosed herein is merely an exemplification and should not be considered as limitative. The scope of the present invention is specified by the following claims, not by the above-mentioned description. It should be understood that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors in so far as they are within the scope of the appended claims or the equivalents thereof.