Patent Publication Number: US-9405256-B2

Title: Roll sheet image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority based on Japanese Patent Application No. 2014-159126, filed on Aug. 5, 2014, the entire contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a roll sheet image forming apparatus configured to feed and guide a continuous sheet wound in a roll shape even when the continuous sheet has a large roll diameter incapable of being accommodated in a preset mounting unit. 
     2. Description of the Related Art 
     In an image forming apparatus such as a printer, a copier, a facsimile and the like, an inkjet type configured to discharge ink to form an image on a medium to be printed and an electrophotographic type configured to form an image on a medium to be printed by using toner have been generally used. There is an image forming apparatus configured to selectively use both a cut sheet and a continuous sheet wound in a roll shape (hereinafter, also referred to as ‘roll sheet’), as the medium to be printed. 
     For example, JP-A-H10-198096 discloses a copier  10  in which a roll sheet unit  70  configured to accommodate therein a roll sheet  72  is provided to be displaceable between a pulled-out state and an incorporated state, the roll sheet  72  accommodated in the roll sheet unit  70  is precut to a predetermined size by a cutter  100  provided in the roll sheet unit  70  and is fed to an image forming unit in the apparatus and an image is formed thereon. 
     The image forming apparatus configured to form an image is widely available in the market. Since the image forming apparatus available in the market is mass-produced, the cost thereof is decreasing. 
     For this reason, it may be possible to cost down a roll sheet image forming apparatus capable of forming an image on a roll sheet and the like by adopting a configuration of the image forming apparatus for the image forming unit configured to form an image on the roll sheet and the like. 
     For example, JP-A-2014-052433 suggests a label printer  1  in which a printer main body  10  is placed on a mount unit  82  having an unwinder  84  arranged therein, which is a roll sheet unwinding device, a roll sheet  200  is unwound by the unwinder  84 , an image is formed thereon by an upper image forming unit (printer main body  10 ), the roll sheet is wound at one time by a rewinder  86 , which is a winding device, and a large amount of labels or seals can be continuously printed. 
     In the meantime, for example, JP-A-2012-000815 discloses a configuration of, when a remaining amount of a continuous recording medium such as roll sheet is insufficient, splicing a new continuous recording medium to the continuous recording medium being used until then by a splicing tape and the like for a replacement operation of the continuous recording medium, and control of a splicing part. 
     However, when a roll sheet accommodation area is configured in the apparatus, such as the lower part of the printing unit, like the image forming apparatus using the roll sheet disclosed in JP-A-H10-198096 and JP-A-2014-052433, a maximum outer diameter of the useable roll sheet is physically determined depending on an apparatus main body. That is, since the entire apparatus is designed to normally reduce an equipment area and an overall height of the apparatus, the roll sheet accommodation space is naturally determined by a size of the apparatus main body. For example, in JP-A-H10-198096, a diameter of the roll sheet  72  corresponds to a size (height) of the roll sheet unit  70 , and in JP-A-2014-052433, a diameter of the unwinder  84  corresponds to a size (height) of the mount unit  82 . 
     However, a user may want to print (to feed a large capacity of continuous sheet) a roll sheet having a large diameter incapable of being accommodated in the apparatus. In this case, it is considered to configure a feeding unit (external feeding unit) of a roll sheet at an outside of the apparatus, to add an opening on a side surface of the apparatus and to guide a front end of the roll sheet to a sheet setting position. However, the structure is complicated and an operation thereof is troublesome. In particular, when an operation space in the vicinity of the sheet setting position is narrow or when the roll sheet is set and the front end of the sheet is manually guided to a predetermined position, the operation is difficult. 
     Regarding the above technical problems, JP-A-H10-198096 and JP-A-2014-052433 do not disclose favorable measures, i.e., do not suggest the configuration of feeding the continuous sheet from the outside and do not recognize the problems. 
     In the meantime, JP-A-2012-000815 discloses a technology of splicing the continuous recording media each other. However, as described above, when the operation space of the feeding guide unit is narrow, it is difficult to perform the splicing operation. Also, it does not disclose the configuration of feeding the continuous sheet from the outside. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a roll sheet image forming apparatus capable of easily feeding and guiding a continuous sheet wound in a roll shape from an outside, even when the continuous sheet has a large roll diameter incapable of being accommodated in a preset mounting unit. 
     In order to achieve the above object, a roll sheet image forming apparatus of the present invention has following configurations. 
     A roll sheet image forming apparatus includes an image forming unit, a holding unit, a feeding unit and an introduction opening. The image forming unit forms an image on a sheet being conveyed. The holding unit holds a sheet wound into a roll shape. The feeding unit is pulled out in a predetermined direction from a storage chamber together with the holding unit and feeds the sheet held at the holding unit towards the image forming unit. The introduction opening is provided on a side surface of the storage chamber and introduces a sheet provided in an external feeding unit into the storage chamber. 
     Also, in order to achieve the above object, a roll sheet image forming apparatus of the present invention has following configurations. 
     A roll sheet image forming apparatus includes an image forming unit, a holding unit, a feeding unit and an introduction opening. The image forming unit forms an image on a sheet being conveyed. The holding unit holds a sheet wound into a roll shape. The feeding unit is pulled out in a predetermined direction from a storage chamber together with the holding unit and feeds the sheet held at the holding unit towards the image forming unit. The introduction opening is provided on a side surface of the storage chamber and guides a sheet from an outside of the storage chamber towards the feeding unit, instead of the sheet held at the holding unit. 
     Further, in order to achieve the above object, a roll sheet image forming apparatus of the present invention has following configurations. 
     A roll sheet image forming apparatus includes an image forming unit, a holding unit, a feeding unit, a storage chamber and an introduction opening. The image forming unit forms an image on a sheet being conveyed. The holding unit holds a sheet wound into a roll shape. The feeding unit feeds the sheet held at the holding unit towards the image forming unit. The storage chamber is provided below the image forming unit and accommodates the holding unit and the feeding unit to be pulled out in a predetermined direction. The introduction opening is provided on a side surface of the storage chamber and guides a sheet from an outside of the storage chamber towards the image forming unit via the feeding unit, instead of the sheet held at the holding unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system configuration view of a roll sheet image forming apparatus and an external feeding unit according to an illustrative embodiment of the present invention. 
         FIGS. 2A and 2B  illustrate a feeding guide method according to the illustrative embodiment of the present invention (illustrates a state before a sheet for lead and a continuous sheet for option feeding are spliced). 
         FIGS. 3A and 3B  illustrate the feeding guide method according to the illustrative embodiment of the present invention (illustrates a state after the sheet for lead and the continuous sheet for option feeding are spliced). 
         FIGS. 4A to 4D  illustrate a guide plate according to the illustrative embodiment of the present invention and a relation between the sheet for lead and the sheet for option feeding. 
         FIGS. 5A and 5B  illustrate an image forming unit (printer) according to the illustrative embodiment of the present invention. 
         FIGS. 6A to 6C  are front views of the roll sheet image forming apparatus according to the illustrative embodiment of the present invention. 
         FIGS. 7A to 7C  are perspective views of the roll sheet image forming apparatus according to the illustrative embodiment of the present invention. 
         FIG. 8  is a partially cutaway system configuration view illustrating a roll sheet image forming apparatus according to another illustrative embodiment of the present invention and a configuration where a continuous sheet is used as the continuous sheet for option feeding. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, illustrative embodiments of the present invention will be described in detail with reference to the accompanying drawings. Meanwhile, in below descriptions, the same elements are denoted with the same reference numerals. 
     An image forming unit (printer) to which a roll sheet image forming apparatus of the illustrative embodiment is applied will be first described and the roll sheet image forming apparatus, an external feeding unit and a feeding guide method of a continuous sheet for option feeding will be then described. 
     Image Forming Unit 
       FIG. 5A  is a perspective view illustrating an outward appearance of a printer  100 , which is an image forming unit, and  FIG. 5B  is a sectional view illustrating an internal structure of the printer  100 . 
     As shown in  FIG. 5B , the printer  100  is a general tandem-type electrophotographic color printer of a secondary transfer type, and has an image forming main unit  102 , a transfer belt unit  103 , a toner supply unit  104 , a feeding unit  105 , a belt-type heat fixing unit  106 , a conveyance unit  107  for duplex printing, and the like. 
     The image forming main unit  102  has four developing devices  109  ( 109   k ,  109   c ,  109   m ,  109   y ) arranged side by side in a multi stage form from right to left in  FIG. 5B , which are in contact with a lower traveling surface  108   a  of a transfer belt  108  of the transfer belt unit  103 . The image forming main unit  102  is held at a frame of the printer  100  so that it can be moved up and down between a position upon printing execution shown in  FIG. 5B  and a repair position lower than the position. 
     The three developing devices  109   c ,  109   m ,  109   y  of the four developing devices  109 , which are positioned at a downstream side (left side in  FIG. 5B ), are configured to form a mono-color image by color toners of cyan (C), magenta (M) and yellow (Y), which are three subtractive primary colors, and the developing device  109   k  is configured to form a monochrome image by black toner (K), which is mainly used for a character, a black part of an image, and the like. 
     The respective developing devices  109  have the same configuration, except for colors of toners for image developing. Therefore, in the below, the corresponding configuration is described with reference to the developing device  109   y  for yellow (Y) toner. 
     The developing device  109  has a photosensitive drum  110  at the uppermost part. The photosensitive drum  110  has a circumferential surface made of an organic photoconductive material, for example. A cleaner  111 , a charging roller  112 , an optical writing head  113  and a developing roller  115  of a developing member  114  are arranged to contact the circumferential surface of the photosensitive drum  110  or to surround a vicinity thereof. 
     The developing member  114  has a housing  116  configured to cover an external part, a partition wall  117  provided therein, the developing roller  115 , a first agitation conveying screw  118  and a second agitation conveying screw  119 . Although not particularly shown, the first agitation conveying screw  118  and the second agitation conveying screw  119  have a screw shaft and a fin integrally formed with the screw shaft and configured to rotate, respectively. 
     To the developing member  114 , any one toner of black (K), cyan (C), magenta (M) and yellow (Y) toners denoted with K, C, M, Y in  FIG. 5B  is supplied from a toner cartridge  121  of the toner supply unit  104  arranged above the transfer belt unit  103 . 
     The transfer belt unit  103  has the endless transfer belt  108 , which extends in a flat loop shape in a left-right direction of  FIG. 5B  at a substantial center of a main body apparatus, and a driving roller  122  and a driven roller  123 , on which the transfer belt  108  is put and which are configured to circulate the transfer belt  108  in a counterclockwise direction denoted with an arrow ‘a’. 
     A secondary transfer roller  124  is pressed against the driving roller  122  via the transfer belt  108 , and forms a secondary transfer unit for secondarily transferring a primary transfer toner image on the transfer belt  108  to a sheet being conveyed thereto, which is a medium to be printed. 
     A first transfer roller  125  is integrally incorporated to the transfer belt  108 . The first transfer roller  125  is arranged to face the photosensitive drum  110  with the transfer belt  108  being interposed therebetween. 
     The first transfer roller  125  is configured to directly transfer (primary transfer) a toner image to the lower traveling surface  108   a  of the transfer belt  108  circulating. The transfer belt  108  further conveys the toner image to the secondary transfer unit so as to transfer the toner image to the sheet (secondary transfer). 
     Also, a belt cleaner  126  is arranged at the transfer belt  108  so that it contacts a surface of the transfer belt put on the driven roller  123 . A waste toner collection receptacle  127  configured to accommodate therein waste toner removed from the transfer belt  108  by the belt cleaner  126  is detachably arranged below the belt cleaner  126 . 
     The toner supply unit  104  has four toner cartridges  121  arranged above an upper traveling surface of the transfer belt  108 . Although not particularly shown, the toner supply unit  104  is held at the frame of the printer  100  so that it can be moved up and down between the position upon printing execution shown in  FIG. 5B  and a repair position higher than the position. 
     The four toner cartridges  121  of the toner supply unit  104  are configured to accommodate therein the black (K), cyan (C), magenta (M) and yellow (Y) toners, respectively. 
     The toner cartridges  121  can be attached and detached to and from the printer  100  by inserting and demounting the same in a front-side surface direction, i.e., a forward direction of a depth direction of the drawing sheet. Although not seen in a sectional view of  FIG. 5B , the toner cartridges  121  are formed with toner discharge openings for supplying the toners to the developing devices  109 . 
     When the toner cartridges  121  are mounted to the printer  100 , the toner discharge openings communicate with a toner supply path extending upwards from the rear of the developing devices  109  and the toners are supplied to the developing devices  109  through the toner supply path. Although not seen in the sectional view of  FIG. 5B , the toner supply path is arranged to go around at the rear of the transfer belt unit  103 . 
     An electrical unit  129  is arranged at the left of the toner supply unit  104  from the left of the belt cleaner  126  to the upper part. The electrical unit  129  is mounted with a circuit board having a control device consisting of a plurality of electronic components mounted thereon. 
     The feeding unit  105  has one feeding cassette  131 . A sheet pickup roller  132 , a conveying roller  133 , a separation roller  134  and a pair of standby conveying rollers  135  are arranged in the vicinity of a feeding opening (right in  FIG. 5B ) of the feeding cassette  131 . 
     The second transfer unit is formed in a sheet conveying direction (vertically upward direction in  FIG. 5B ) of the standby conveying rollers  135 . The belt-type heat fixing unit  106  is arranged downstream (upper in  FIG. 5B ) of the secondary transfer unit. 
     The belt-type heat fixing unit  106  has a fixing roller  106   a  and a heating roller  106   b  in a fixing frame  106   e . The fixing belt  106   c  is put on the fixing roller  106   a  and the heating roller  106   b . Also, a pressing roller  106   d  is pressed against the fixing roller  106   a  via the fixing belt  106   c , so that a fixing nip portion is formed. 
     A pair of carrying-out rollers  136  configured to carry out the fixed sheet from the heat fixing unit  106  and a pair of sheet discharge rollers  138  configured to discharge the carried out sheet to a sheet discharge tray  137  formed on an upper surface of the apparatus are arranged further downstream of the belt-type heat fixing unit  106 . 
     The conveyance unit  107  for duplex printing also serves as an opening/closing member of which an outer surface (right outer surface in  FIG. 5B ) opens outwards or closes an inside of the printer  100  from a side. 
     The conveyance unit  107  for duplex printing has a conveying path  139  having a conveying start path  139   a  branching from a portion just before the sheet discharge rollers  138  in a rightward lateral direction of  FIG. 5B , a conveying intermediate path  139   b  bent downwards from the conveying start path  139   a  and a conveying end path  139   c  bent in a further leftward lateral direction and configured to reverse the sheet being conveyed. 
     Also, in the printer  100  of this illustrative embodiment, a switching device  140  configured to switch and guide a roll sheet  23  (which will be described later) to a guide conveying path shown with a dotted line b direction is arranged in a conveying path between the carrying-out rollers  136  and the sheet discharge rollers  138 , and a pair of roll sheet discharge rollers  141  is arranged in a sheet discharge opening  100   b.    
     Also, a feeding opening  100   a  configured to introduce the roll sheet  23  from a lower direction shown with an arrow c is formed at the lower part of the printer  100  at which the separation roller  134  and the conveying end path  139   c  are arranged. 
     In the printer  100 , when forming an image on a normal sheet (for example, A4 sheet) such as a cut sheet, a normal sheet picked up from the feeding cassette  131  of the feeding unit  105  by the sheet pickup roller  132  is conveyed by the feeding roller  133  and the separation roller  134 , and is sent to the secondary transfer unit by the standby conveying rollers  135 , so that a toner image on the transfer belt  108  is secondarily transferred to the normal sheet by the secondary transfer unit having the driving roller  122 , on which the transfer belt  108  is put, and the secondary transfer roller  124 . 
     In the meantime, when a medium on which an image is to be formed is a roll sheet, for example, the roll sheet is fed from the feeding opening  100   a  provided on the bottom of the printer  100 . The fed roll sheet is conveyed to the secondary transfer unit via the standby conveying rollers  135 , so that the toner image on the transfer belt  108  is secondarily transferred to the roll sheet. 
     The normal sheet for which the secondary transfer has been made is conveyed to the belt-type heat fixing unit  106  positioned above the secondary transfer unit, in which the fixing processing of the toner image is then performed, and is then discharged to the sheet discharge tray  137  via the sheet discharge rollers  138 . On the other hand, when the medium is the roll sheet, the roll sheet is conveyed to the belt-type heat fixing unit  106 , in which the fixing processing of the toner image is then performed, and is then discharged in the dotted line b direction from the sheet discharge opening  100   b  via the switching device  140  and the roll sheet discharge rollers  141 , as described above. 
     Therefore, the configuration of the printer  100  is basically the same as a general printer, and has the features that the switching device  140 , the sheet discharge opening  100   b , the roll sheet discharge rollers  141  and the feeding opening  100   a  formed at the lower part of the apparatus, through which the roll sheet can be fed, are provided. 
     Roll Sheet Image Forming Apparatus 
     In the below, a configuration of the roll sheet image forming apparatus is described in detail. 
       FIGS. 6A to 6C  are front views of the roll sheet image forming apparatus according to the illustrative embodiment of the present invention.  FIG. 6A  illustrates a state where a prescribed roll sheet is not mounted yet,  FIG. 6B  illustrates a state where the prescribed roll sheet is set to be fed, and  FIG. 6C  illustrates a state where an image is being formed with the prescribed roll sheet being unwound and wound. 
     As shown in  FIG. 6A , the roll sheet image forming apparatus  1  has a roll sheet feeding device  1   a , the printer  100  arranged above the roll sheet feeding device  1   a , and a winding device  9 . 
     As shown in  FIGS. 6B and 6C , the roll sheet feeding device  1   a  is configured to feed the roll sheet  23  to the printer  100 . The printer  100  functions as an image forming unit configured to form a multi-color image on the roll sheet  23  by the toners of four YMCK (yellow (Y), magenta (M), cyan (C) and black (K)) colors on the basis of image data of a printing target. 
     The roll sheet feeding device  1   a  is configured to continuously unwind the roll sheet  23 , which is wound into a roll shape around a predetermined winding core (sheet tube), and to convey the same to the image forming main unit  102  of the printer  100  along a predetermined conveying path. Specifically, the roll sheet feeding device  1   a  has a slide plate  7 , a holding unit  8 , a serpentine detection sensor  11 , a side guide  12 , a pair of conveying rollers  13 , an auto cutter  14 , a mark sensor  15 , a pair of entrance rollers  16 , an entrance sensor  17  and driven rollers  18   a ,  18   b . Here, the conveying rollers  13 , the entrance rollers  16 , the driven rollers  18   a ,  18   b , the side guide  12  and the like function as a feeding means. 
     Also, the holding unit  8  functions as a sheet holding means, and is configured to hold the roll sheet  23  before an image is formed by the printer  100 . The holding unit  8  has a rotary shaft  8   a , which is configured to penetrate the winding core positioned at a center of winding of the roll sheet  23  and to hold the roll sheet  23 , and a support plate configured to support the rotary shaft, and is configured to rotatably hold the roll sheet  23 . 
     The holding unit  8  is mounted with a motor (not shown) for rotating the rotary shaft  8   a . The holding unit  8  functions as an unwinder configured to rotate the rotary shaft  8   a  with an instructed rotation number per unit time (the number of rotations per unit time) by the driving of the motor and to unwind the roll sheet  23  being held. 
     Also, a powder brake (not shown) is attached to the rotary shaft  8   a  of the holding unit  8 . The powder brake is configured to brake the rotation of the rotary shaft  8   a  so that tension (tensile force) applied to the roll sheet  23  unwound and conveyed from the holding unit  8  is constant. By the function of the powder brake, the roll sheet  23  unwound from the holding unit  8  is stably conveyed without being loosened. 
     The slide plate  7  has slide bearings at both sides thereof, and is configured to slide the holding unit  8  in a direction of the rotary shaft  8   a  (a width direction of the roll sheet  23 ). When the serpentine detection sensor  11  detects serpentine movement of the roll sheet  23  being conveyed in the roll sheet feeding device  1   a , the slide plate  7  is applied with a driving force from an actuator and moves the holding unit  8  in a direction of cancelling the detected serpentine movement. 
     The serpentine detection sensor  11  is configured to detect the serpentine movement of the roll sheet  23  being conveyed in the roll sheet feeding device  1   a . Specifically, the serpentine detection sensor  11  has a plurality of sets light emitting elements and light receiving elements arranged to face each other so that end portions of the roll sheet  23  in a width direction are positioned therebetween. The serpentine detection sensor  11  is configured to determine whether the light emitted from the light emitting element is received by the light receiving element without being blocked, for each of the multiple sets, thereby measuring positional deviation of the end portions of the roll sheet  23  in the width direction without contacting the roll sheet  23 . 
     The pair of conveying rollers  13  is configured to sandwich and convey the roll sheet  23  unwound from the holding unit  8  and conveyed via the driven rollers  18   a ,  18   b  and the side guide  12 , thereby feeding the roll sheet to the pair of entrance rollers  16 . The pair of entrance rollers  16  is configured to sandwich and convey the roll sheet  23  fed from the pair of conveying rollers  13 , thereby feeding the same to the printer  100  through the feeding opening  100   a  of the printer  100 . 
     The auto cutter  14  is configured to cut the roll sheet  23 , as required. For example, when the roll sheet  23  of a length necessary for image formation in the printer  100  is completely conveyed, the auto cutter  14  cuts a longitudinal end (rear end) of the roll sheet  23 . Also, the cutting operation of the auto cutter  14  is controlled by a control means (not shown) so as to cut a sheet  5  for lead from a continuous sheet  4  for option feeding. 
     The mark sensor  15  is configured to detect an original mark that is recorded on a surface of the roll sheet  23  and is used as a position reference for image formation by the printer  100 . 
     The entrance sensor  17  is configured to detect a start end (front end) of the roll sheet  23  entering the feeding opening  100   a  of the printer  100  from the pair of entrance rollers  16 . Specifically, the entrance sensor  17  has a light emitting element and a light receiving element, and determines that a start end of the roll sheet  23  is detected, when the light generated from the light emitting element is blocked by the start end of the roll sheet  23  and is not thus detected by the light receiving element. When the entrance sensor  17  detects the start end of the roll sheet  23 , the printer  100  starts to drive a variety of the pairs of rollers and to convey the roll sheet  23  introduced therein. 
     In the meantime, as can be clearly seen from  FIGS. 6A to 6C , the serpentine detection sensor  11 , the driven roller  18   b , the side guide  12 , the pair of conveying rollers  13 , the auto cutter  14 , the mark sensor  15 , the pair of entrance rollers  16 , the entrance sensor  17  and the like form a substantially vertical conveying path. 
     An area shown with the dotted line at the right of the roll sheet feeding device  1   a  is partitioned by a partition wall  1   b  and is used as a storage chamber  1   e  of disposables such as the roll sheet, the toner and the like. 
     Therefore, in order to sandwich the front end of the roll sheet between the pair of conveying rollers  13  and to manually set the roll sheet to a feedable state, after attaching the roll sheet  23  to the rotary shaft  8   a  of the holding unit  8 , as shown in  FIG. 6B , from the state shown in  FIG. 6A  where the roll sheet  23  is not mounted yet, the partition wall  1   b  becomes an obstacle, so that an operation space is narrow and it is difficult to perform the operation. 
     Thus, according to the roll sheet image forming apparatus  1  of this illustrative embodiment, although described in detail later with reference to  FIGS. 7A to 7C , the slide plate  7 , the holding unit  8 , the driven rollers  18   a ,  18   b , the serpentine detection sensor  11 , the side guide  12 , the pair of conveying rollers  13 , the auto cutter  14 , the mark sensor  15 , the pair of entrance rollers  16 , the entrance sensor  17  and the like are configured to be integrally moveable with respect to a main body of the roll sheet feeding device  1   a , i.e., configured to function as a drawable and receivable feeding unit, and the entire feeding unit is pulled out forwards and is thus set to the feedable state. 
     In the meantime, a main body side  1   c  of the roll sheet feeding device  1   a  is formed with an introduction opening  1   d  of a continuous sheet for option feeding (which will be described later). An openable guide plate  2  (refer to a two-headed arrow d) is provided in the vicinity of the introduction opening  1   d . In  FIGS. 6A to 6C , the guide plate  2  is closed along the main body side  1   c  of a left surface of the roll sheet feeding device  1   a . However, as described later with reference to  FIG. 1 , the guide plate  2  is opened horizontally by 90° and serves as a feeding guide plate when handling a continuous sheet for option feeding. 
     In the meantime, the winding device  9  functions as a winding means (rewinder), and is configured to wind and hold the roll sheet  23  discharged from the printer  100  around a winding shaft  9   a.    
     In the below, a method of mounting the roll sheet  23  having a preset size (diameter) to the holding unit  8  in the roll sheet image forming apparatus  1  and operating the apparatus is described. 
     As shown in  FIG. 7A , before the printing, a user pulls out the entire feeding unit in an arrow e direction from the apparatus main body of the roll sheet feeding device  1   a  and mounts the roll sheet  23  before the printing of which a start end  27  is fixed by a fixing tape  24 , for example, to the rotary shaft  8   a  of the holding unit  8  (refer to an outline arrow). Then, the user sandwiches the start end  27 , from which the fixing tape  24  has been removed, between the pair of conveying rollers  13 , as shown with the dotted line in  FIG. 6B  and returns the entire feeding unit to the original state (refer to an arrow f direction) to complete a preparation operation. 
     At this state, when a feeding request is received from the printer  100  having received print data from a host device (not shown), the rotary shaft  8   a  of the holding unit  8 , the pair of conveying rollers  13 , the pair of entrance rollers  16  and the like are driven to convey the roll sheet  23  to the printer  100 . 
     Here, an original mark  25  is recorded in advance on the roll sheet  23 . The original mark  25  functions as a first reference mark, which becomes a position reference when an image is formed on the roll sheet  23  by the printer  100 . The original mark  25  recorded on the roll sheet  23  being conveyed is detected by the mark sensor  15 . 
     The original mark  25  is recorded at a constant interval at a plurality of positions from the start end  27  to a termination  28  (refer to  FIG. 7C ) when the roll sheet  23  is configured by a label sheet. The interval is set to a length corresponding to a pitch of each label in the image data to be output so that the printer  100  can adjust a position of image formation for each label. 
     The roll sheet  23  conveyed to the printer  100  is formed thereon with a predetermined image and is then discharged from the sheet discharge opening  100   b  of the printer  100 , as shown in  FIG. 7B . 
     An overall operation of the winding device  9  is controlled by a control unit (not shown). For example, when the winding request of the roll sheet  23  is received from the printer  100 , the winding shaft  9   a  is rotated to wind the roll sheet  23  being discharged to the printer  100 , as shown with the dotted line in  FIG. 6C . 
     When the winding is completed, the normal printing is also over. The termination  28  of the completely wound roll sheet  23  is temporarily fixed by the fixing tape  24  and is removed from the winding device  9 . 
     In the roll sheet image forming apparatus  1 , the roll sheet  23  to be mounted on the holding unit  8  has a preset size (diameter). That is, the size of the roll sheet is set to a size mountable to a size of the holding unit  8 , in other words, a size (height, width) of the roll sheet feeding device  1   a . In this illustrative embodiment, a size of about 350 mm is a storage limitation, and a roll sheet having a larger size cannot be printed. 
     As described above, some users may want to use a roll sheet having a size (diameter) that cannot be accommodated in the roll sheet feeding device  1   a . Therefore, in an illustrative embodiment of the present invention, a configuration of option feeding considering the roll sheet having a large diameter (large capacity) is suggested. 
     That is, according to an illustrative embodiment of the present invention, a special configuration is added to the roll sheet image forming apparatus  1  so that the roll sheet having a large diameter incapable of being accommodated in the holding unit  8  of the roll sheet feeding device  1   a  can be used as a continuous sheet for option feeding through an external feeding unit  3 , and a special feeding guide method is also adopted. 
     Feeding Guide Method of Continuous Sheet for Option Feeding 
     As described above, according to the roll sheet image forming apparatus  1  of the illustrative embodiment of the present invention, the roll sheet feeding device  1   a  has the right storage chamber  1   e  for disposables such as roll sheet and toner, which is partitioned by the partition wall  1   b , and the left drawable and receivable feeding unit. 
     The user pulls out the entire feeding unit and sets the roll sheet  23  to a feedable state. 
     Here, the holding unit  8  configured to mount and hold the roll sheet  23  thereto has the rotary shaft  8   a  at a substantial center thereof. A maximum size (diameter) of the roll sheet  23  to be mounted thereto is about 350 mm (refer to D in  FIG. 1 ), as described above. Therefore, a roll sheet having a larger size (diameter) cannot be accommodated in the roll sheet feeding device  1   a.    
     In order to cope with this situation, according to the illustrative embodiment of the present invention, as shown in  FIG. 1 , a following configuration is provided on the assumption that the external feeding unit  3  is configured to be coupled to the roll sheet feeding device  1   a  (refer to a two-headed outline arrow). 
     That is, the external feeding unit  3  that is applied to the present invention has a support shaft  3   a  and a guide roller  3   b , and is configured to feed a continuous sheet  4  for option feeding. A mountable size (diameter) E of the continuous sheet  4  for option feeding is set to be larger than the maximum size (diameter) D of the roll sheet  23 . 
     In the meantime, although the description of the specific structure of the external feeding unit  3  is omitted, it has substantially the same configuration as the holding unit  8  of the roll sheet feeding device  1   a . That is, the external feeding unit  3  functions, instead of the holding unit  8 . 
     In the below, a feeding guide method of the continuous sheet for option feeding according to the present invention is described. As described above, according to the illustrative embodiment of the present invention, the introduction opening  1   d  is provided so that a continuous sheet can be introduced into the roll sheet feeding device  1   a  from the external feeding unit  3 . However, even when the introduction opening  1   d  is just provided, it is not possible to feed the continuous sheet  4  for option feeding from the external feeding unit  3 . 
     The reason is as follows: even though the external feeding unit  3  is fixedly arranged to be coupled to the introduction opening  1   d  and the continuous sheet  4  for option feeding is introduced into the roll sheet feeding device  1   a  through the introduction opening  1   d , the operation space is narrow, as described above, so that it is not possible to manually sandwich a front end  4   a  of the continuous sheet  4  for option feeding between the pair of conveying rollers  13  and to manually set the same to a feedable state. 
     In contrast, like the case of the roll sheet  23  having the preset size (diameter) described with reference to  FIG. 7A , it is considered to pull out the entire feeding unit in an arrow e direction from the apparatus main body of the roll sheet feeding device  1   a , to arrange the external feeding unit  3  in correspondence to the pulled-out feeding unit and then to feedably set the continuous sheet  4  for option feeding at this state. 
     However, in this case, when returning the entire feeding unit to the original state (the arrow f direction) to complete the preparation operation, it is also required to move the heavy external feeding unit  3  in association with the movement of the feeding unit. Thereby, the apparatus is complicated and larger and positional deviation between the continuous sheet  4  for option feeding and the roll sheet feeding device  1   a  may be caused due to the movement of the external feeding unit  3 . That is, the above consideration is not practical. 
     Therefore, in this illustrative embodiment, as shown in  FIGS. 2A, 2B, 3A, 3B and 4A to 4D , a special configuration is provided. That is, a sheet  5  for lead is prepared and a feeding guide method as described below is adopted. 
     First, when performing the feeding from the continuous sheet  4  for option feeding, the external feeding unit  3  is fixedly connected to the introduction opening  1   d  of the roll sheet feeding device  1   a  of which the guide plate  2  is opened, as shown in  FIG. 2A . That is, it is premised that the external feeding unit  3  is arranged at a predetermined position together with the roll sheet image forming apparatus  1 . 
     Then, the front end  4   a  of the continuous sheet  4  for option feeding is placed on the guide plate  2  and the entire feeding unit in which the roll sheet  23  is not mounted yet is pulled out (or when the roll sheet  23  is already mounted, the entire feeding unit is pulled out and the roll sheet  23  is removed). 
     Subsequently, as shown in  FIG. 2B , the sheet  5  for lead prepared in advance is placed on the slide plate  7 , a front end  5   a  of the sheet  5  for lead is sandwiched between the pair of conveying rollers  13  and is thus set to a feedable state. Then, the entire feeding unit is returned to the original state (the entire feeding unit is accommodated). Here, a size of the sheet  5  for lead is set so that a rear end  5   b  of the sheet  5  for lead protrudes outwards from the introduction opening  1   d  by a predetermined length at a state where the front end  5   a  is set to be feedable, i.e., to be conveyable to the image forming unit by the feeding means. 
     At this state, as shown in  FIG. 3A , the rear end  5   b  of the sheet  5  for lead is pulled out onto the external guide plate  2  from the introduction opening  1   d , and the front end  4   a  of the continuous sheet  4  for option feeding and the rear end  5   b  of the sheet  5  for lead are bonded using a bonding member  5   c  such as a splicing tape, as shown in  FIG. 3B . In the meantime, regarding the bonding method, the rear end  5   b  of the sheet  5  for lead may be formed with an adhesive layer having a peeling member, the peeling member may be peeled off after pulling out the rear end  5   b  of the sheet  5  for lead onto the guide plate  2  and then the front end of the continuous sheet  4  for option feeding may be overlapped and bonded, instead of separately providing the bonding member  5   c.    
     The continuous sheet  4  for option feeding bonded in this way is guided to the sheet  5  for lead, instead of the roll sheet  23  intended to normally use, and is guided to the printer  100  in the same manner as the roll sheet  23 , and then an image is formed thereon. 
     The continuous sheet  4  for option feeding having an image formed thereon is wound onto the winding shaft  9   a  of the winding device  9 . At this time, the continuous sheet  4  for option feeding may be wound including the preceding sheet  5  for lead. However, in this illustrative embodiment, as shown in  FIG. 1 , a slightly backward position of the spliced part of the sheet  5  for lead and the continuous sheet  4  for option feeding is cut by the auto cutter  14 , and the switching device  140  of the printer  100  is controlled to switch the sheet discharge direction to the left side in  FIG. 1 , so that the cut preceding sheet  5  for lead is discharged onto the sheet discharge tray  137 . In the meantime, the switching device  140  is controlled to switch the sheet discharge direction to the right side in  FIG. 1  and only the continuous sheet  4  for option feeding from which the continuous sheet  4  for option feeding has been cut is wound around the winding shaft  9   a.    
     In this way, the sheet  5  for lead can be used several times, so that it is possible to prevent the resource from being wasted. 
       FIGS. 4A to 4D  illustrate the guide plate according to the illustrative embodiment of the present invention and a relation between the sheet for lead and the sheet for option feeding.  FIGS. 4A and 4B  illustrate a state where the sheet  5  for lead and the continuous sheet  4  for option feeding are spliced. Here, in this illustrative embodiment, a rubber sheet  2   a , for example, is bonded to the upper surface of the guide plate  2 . The rubber sheet (a rubber lining is also possible) is made of a urethane-based rubber material, for example, and a surface thereof is slightly adhesive. Therefore, the rubber sheet can be easily detached even though it has the adhesiveness. 
     Also, a central line  2   c  is printed at a substantial center of the rubber sheet, so that it is possible to temporarily fix and position an end portion of a sheet in conformity to the central line (instead of the central line  2   c , the rubber sheet may be formed to have a step and the positioning may be performed by butting an end portion of a sheet thereto). Further, the upper surface of the guide plate  2  is provided with width restraint guides  2   d ,  2   d  for aligning a width of a sheet. The width restraint guides are configured to move in conformity to a sheet width (refer to a two-headed arrow g in  FIG. 4B ). 
       FIGS. 4C and 4D  illustrate an operation of splicing the sheet  5  for lead and the continuous sheet  4  for option feeding on the guide plate  2 . That is, as described above, the unwound continuous sheet  4  for option feeding is placed onto the guide plate  2  in conformity to the width restraint guides  2   d ,  2   d  moved in an arrow h direction, as shown in  FIG. 4C , and then a front end portion thereof is temporarily fixed in conformity to the central line. On the other hand, the sheet  5  for lead is pulled out onto the guide plate  2 , the rear end portion  5   b  thereof is temporarily fixed in conformity to the central line  2   c , as shown in  FIG. 4D , and then the front end portion and the rear end portion are bonded using the bonding member  5   c.    
     The guide plate  2  is provided, so that it is possible to securely splice the sheet  5  for lead and the continuous sheet  4  for option feeding without the positional deviation and to secure the stability of the feeding conveying. 
     In the above illustrative embodiment, the continuous sheet  4  for option feeding is placed on the guide plate  2  and then the sheet  5  for lead is placed thereon. Then, both are bonded. However, the operation sequence may be changed so that the sheet  5  for lead is first placed on the guide plate  2  and then the continuous sheet  4  for option feeding is placed thereon. Also, in the illustrative embodiment of the present invention, the guide plate  2  is arranged on the main body side  1   c  of the roll sheet feeding device  1   a . However, the guide plate  2  may be provided for the external feeding unit  3 . 
     In the above descriptions, the sheet mounted on the external feeding unit  3  and wound in a roll shape has been exemplified as the continuous sheet  4  for option feeding. However, the present invention is not limited to the roll-shaped continuous sheet. 
       FIG. 8  illustrates another illustrative embodiment of the present invention, in which a continuous sheet is used as the continuous sheet for option feeding. 
     As shown in  FIG. 8 , a continuous sheet  6  of this illustrative embodiment is loaded and accommodated with being folded in a receptacle  6   a , like the external feeding unit  3 , and can be pulled out from an opening  6   b.    
     Here, the continuous sheet  6  of this illustrative embodiment has a folded size larger than the maximum size (diameter) D of the roll sheet  23  to be originally mountable to the roll sheet feeding device  1   a , as seen from a feeding direction. Therefore, it is not possible to feed the continuous sheet  6  with being loaded on the slide plate  7 , as it is. 
     Therefore, although the specific descriptions are omitted, the continuous sheet  6  can also be fed via the pulling out operation of the feeding unit and the sheet  5  for lead, like the above illustrative embodiment. 
     As described above, according to the present invention, it is not necessary to provide a mechanism for moving the heavy external feeding unit  3  in association with the movement of the feeding unit. The continuous sheet for option feeding is fixed on the guide plate  2  in the vicinity of the introduction opening  1   d , so that it can be easily fed and guided. Therefore, the positional deviation between the continuous sheet  4  for option feeding and the roll sheet feeding device  1   a  is not caused. As a result, the present invention can be effectively applied to a roll sheet having a large size and a long continuous sheet, which cannot be accommodated in the preset mounting unit. 
     Having described and illustrated the principles of this application by reference to one preferred embodiment, it should be apparent that the preferred embodiment may be modified in arrangement and detail without departing from the principles disclosed herein and that it is intended that the application be construed as including all such modifications and variations insofar as they come within the spirit and scope of the subject matter disclosed herein.