Patent Publication Number: US-10773911-B2

Title: Conveyor and recording apparatus including same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 14/670,094, filed Mar. 26, 2015, which further claims priority from Japanese Patent Application No. 2014-073621, which was filed on Mar. 31, 2014, the disclosure of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to: a conveyor capable of performing position adjustment of a sheet-shaped medium; and a recording apparatus including the conveyor. 
     2. Description of Related Art 
     There has been known a conveyor for conveying a sheet (recording medium) on which an image is recorded. The conveyor may include an upstream roller pair and a lateral misregistration correcting unit configured to set a sheet at a predetermined width-directional position along a reference plane. The lateral misregistration correcting unit includes a reference plate having the reference plane and a downstream roller pair constituted by a lateral misregistration correction roller and an inclined conveyor roller. The rotation shafts of the paired upstream rollers are both orthogonal to the reference plane, whereas the rotation shaft of the inclined conveyor roller is inclined with respect to the reference plane. The downstream roller pair is positioned between the reference plane and the center of the sheet and is closer to the reference plane than to the center of the sheet, in the width direction of the sheet. 
     In the conveyor using such a lateral misregistration correcting unit, when the downstream roller pair nips a sheet, to begin with, the sheet rotates so that the tail end of the sheet approaches the reference plane. Thereafter, as the sheet contacts with the reference plane, the sheet reversely rotates on account of the reaction to the contact, so that the leading end of the sheet approaches the reference plane. As a result, the sheet is positioned so that the side edge thereof extends along the reference plane, and the sheet is conveyed along the reference plane. In this way, the correction of the width-directional position of the sheet (so-called side registration) is carried out. 
     SUMMARY OF THE INVENTION 
     In the above-described conveyor, the side registration by the downstream roller pair by which the position adjustment is carried out by rotating and reversely rotating the sheet mainly occurs when the sheet is pinched only by the downstream roller pair. To put it differently, because the upstream roller pair always operates to convey the sheet in the direction along the reference plane, the side registration exerted by the downstream roller pair is obstructed by the upstream roller pair when the sheet is pinched by both the upstream roller pair and the downstream roller pair, and hence the side registration may not be properly carried out. 
     An object of the present invention is to provide a conveyor in which a side registration is less likely to be obstructed, and a recording apparatus including such a conveyor. 
     A conveyor according to a first aspect of the invention comprises: a first conveyor roller unit which includes a drive roller and a first driven roller which holds a sheet-shaped medium with the drive roller and is rotated in accordance with conveyance of the sheet-shaped medium by rotation of the drive roller; and a side position adjustment mechanism which is positioned downstream of the first conveyor roller unit in a conveyance direction in which the sheet-shaped medium is conveyed by the drive roller. The side position adjustment mechanism includes: a guide member having a guide face which extends in the conveyance direction to be able to contact with one side edge of the sheet-shaped medium; and a position adjustment roller unit which is positioned between the guide face and the center of a conveyance path on which the sheet-shaped medium is conveyed and is closer to the guide face than to the center of the conveyance path, in an axial direction which is in parallel to a rotational axial line of the drive roller. The position adjustment roller unit includes a first position adjustment roller and a second position adjustment roller which holds the sheet-shaped medium with the first position adjustment roller. An angle between a rotational axial line of the first position adjustment roller and a part of the guide face which part is on the downstream in the conveyance direction of an intersection between the rotational axial line of the first position adjustment roller and the guide face is an acute angle. The conveyor further comprises a first support member which supports the first driven roller to allow a rotational axial line of the first driven roller to be swingable. 
     A recording apparatus according to a second aspect of the invention comprises: a recording unit configured to record an image onto a sheet-shaped medium which is a recording medium; a conveyance unit configured to convey the sheet-shaped medium to cause the sheet-shaped medium to pass a recording position where recording is carried out on the sheet-shaped medium by the recording unit; and a re-conveyance unit configured to re-convey, to a position before passing the recording position, the sheet-shaped medium having been conveyed by the conveyance unit and having passed the recording position. The re-conveyance unit includes the conveyor according to the first aspect of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other and further objects, features and advantages of the invention will appear more fully from the following description taken in connection with the accompanying drawings in which: 
         FIG. 1  is a schematic profile showing an internal structure of an inkjet printer including a conveyor of First Embodiment of the present invention. 
         FIG. 2  is a virtual plan view showing the positional relationship between two conveyor roller units which are along a sheet re-conveyance path and a side position adjustment mechanism in the printer shown in  FIG. 1 . 
         FIG. 3  is a plan view showing the details of the side position adjustment mechanism shown in  FIG. 2 . 
         FIG. 4  is a partial oblique perspective of the first conveyor roller unit shown in  FIG. 2 . 
         FIGS. 5A to 5D  show a first driven roller and a second driven roller in the first conveyor roller unit and an important part of a first support member. 
         FIGS. 6A to 6D  are plan views showing a positioning operation of a sheet in First Embodiment of the present invention step by step. 
         FIGS. 7A and 7B  are virtual plan views which relate to Second and Third Embodiments of the present invention and are equivalent to  FIG. 2 . 
         FIG. 8  is a cross section which relates to Fourth Embodiment of the present invention and is equivalent to  FIG. 5A . 
         FIG. 9  is a profile which relates to Fifth Embodiment of the present invention and is equivalent to  FIG. 5A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     &lt;Overall Structure of Printer&gt; 
     To begin with, with reference to  FIG. 1 , the following will describe the overall structure of an inkjet printer  1  which is a recording apparatus including a re-conveyance guide unit which is a conveyor of First Embodiment of the present invention. 
     The printer  1  includes a rectangular parallelepiped casing  1   a . At the top plate of the casing  1   a  is provided a sheet output unit  4 . The internal space of the casing  1   a  is divided into spaces A and B in this order from above. In the spaces A and B, a sheet conveyance path from a sheet feeding unit  23  toward the sheet output unit  4  and a sheet re-conveyance path from the downstream to the upstream of the sheet conveyance path are formed. As shown in  FIG. 1 , a sheet P is conveyed along black thick arrows on the sheet conveyance path, and is conveyed along outlined thick arrows on the sheet re-conveyance path. In the space A, image recording onto the sheet P, conveyance of the sheet P to the sheet output unit  4 , and re-conveyance of the sheet P are carried out. In the space B, sheet feeding from the sheet feeding unit  23  to the sheet conveyance path is performed. 
     In the space A, members such as a head (recording unit)  2 , a conveyance mechanism  3 , and a controller  100  are provided. The head  2  is configured to eject black ink. To the space A, an unillustrated cartridge storing black ink is detachably attached. The cartridge is connected with the head  2  via an unillustrated tube and pump to supply ink to the head  2 . 
     The head  2  is a line-type head which is substantially rectangular parallelepiped in shape and is long in the main scanning direction. The lower surface of the head  2  is an ejection surface  2   a  where ejection openings are formed. In recording, the black ink is ejected from the ejection surface  2   a . The head  2  is supported by the casing  1   a  via a head holder  2   b . The head holder  2   b  supports the head  2  so that a predetermined gap suitable for recording is formed between the ejection surface  2   a  and a later-described platen  3   d.    
     The conveyance mechanism  3  includes an upstream guide unit  3   a , a downstream guide unit  3   b , a re-conveyance guide unit  3   c , and a platen  3   d . The platen  3   d  is positioned to oppose the ejection surface  2   a  of the head  2 . The platen  3   d  has a flat upper surface, supports the sheet P from below. A recording position where recording is carried out on the sheet P by the head  2  is formed between the flat upper surface of the platen  3   d  and the ejection surface  2   a  of the head  2 . The recording position is a part of the sheet conveyance path. The upstream guide unit  3   a  and the downstream guide unit  3   b  are positioned to sandwich the platen  3   d . The upstream guide unit  3   a  includes two guides  31  and  32  and two conveyor roller units  41  and  42  and connects the recording position with the sheet feeding unit  23 . The downstream guide unit  3   b  includes two guides  33  and  34  and three conveyor roller units  43  to  45 , and connects the recording position with the sheet output unit  4 . The sheet conveyance path is defined by the four guides  31  to  34 , the platen  3   d , and the head  2 . 
     The re-conveyance guide unit  3   c  includes three guides  35  to  37 , three conveyor roller units  46  to  48  (including later-described first conveyor roller unit  47  and second conveyor roller unit  46 ), and a side position adjustment mechanism  50  having a so-called side registration, and connects the downstream guide unit  3   b  with the upstream guide unit  3   a  while circumventing the recording position. The guide  35  is connected to a non-end part of the guide  33  to connect the re-conveyance guide unit  3   c  with the downstream guide unit  3   b . The guide  37  is connected to a non-end part of the guide  31  to connect the re-conveyance guide unit  3   c  with the upstream guide unit  3   a . The sheet re-conveyance path is defined by the three guides  35  to  37  and the side position adjustment mechanism  50 . 
     Each of the above-described conveyor roller units  41  to  48  is made up of a drive roller and a plurality of driven rollers which holds the sheet P with the drive roller and are rotated in accordance with the conveyance of the sheet P by the rotation of the drive roller. In the present embodiment, the drive rollers of the conveyor roller units  41  to  45  are rollers that contact with a surface of the sheet P conveyed from the sheet feeding unit  23  to the sheet output unit  4  without passing the sheet re-conveyance path, the surface opposing the platen  3   d  and no recording being performed thereon. The drive rollers of the conveyor roller units  46  to  48  are rollers which contact with a surface of the sheet P supplied to the sheet re-conveyance path on which surface no recording is performed. (i.e., contact with a surface of the sheet P to be supplied to the sheet conveyance path, which surface opposes the ejection surface  2   a ). Examples of the drive rollers include rubber rollers and resin rollers. Details of the conveyor roller units  46  and  47  will be given later. 
     In the present embodiment, the upstream guide unit  3   a , the downstream guide unit  3   b , the platen  3   d , and the conveyor roller units  41  to  45  constitute a conveyance unit which conveys the sheet P to cause the sheet P to pass the recording position. Furthermore, the re-conveyance guide unit  3   c  constitutes a re-conveyance unit which re-conveys, to a position before passing the recording position, the sheet P having been conveyed by the conveyance unit and having already passed the recording position. 
     The drive roller of the conveyor roller unit  44  is controlled by the controller  100  so that the conveyance direction of the sheet P is switched. To put it differently, the drive roller of the conveyor roller unit  44  rotates to convey the sheet P upward when the sheet P is conveyed from the recording position toward the sheet output unit  4 . In the meanwhile, when the sheet P is conveyed from the sheet conveyance path to the sheet re-conveyance path, the rotational direction of this drive roller is switched so that the sheet P is conveyed downward with the tail end of the sheet P being the leading end, when the tail end of the sheet P is positioned between the junction of the guides  33  and  35  and the conveyor roller unit  44  and the tail end is detected by the sheet sensor  27 . The sheet P having been conveyed from the sheet conveyance path to the sheet re-conveyance path is re-conveyed to the upstream guide unit  3   a . The re-conveyed sheet P conveyed to the recording position again is reversed as compared to the sheet P having passed the recording position for the first time. In this way, images are formed on the respective surfaces of the sheet P. 
     In the sheet re-conveyance path, the three conveyor roller units  46  to  48  are positioned in this order from the upstream. The side position adjustment mechanism  50  is positioned downstream of the conveyor roller unit  47  and upstream of the conveyor roller unit  48  in the conveyance direction E of the sheet P conveyed by the drive roller of the conveyor roller unit  47 , i.e., the side position adjustment mechanism  50  is positioned between the conveyor roller units  47  and  48 . In the vertical direction, the side position adjustment mechanism  50  is positioned between the recording position and the sheet feeding unit  23  (specifically, positioned between the platen  3   d  and the sheet feeding unit  23 ). The side position adjustment mechanism  50  includes an upper guide  51 , a lower guide  52  (guide member), and a position adjustment roller unit  60 . The side position adjustment mechanism  50  performs the positioning of the sheet P in the width direction in such a way as to convey the sheet P while causing side edge in the width direction of the sheet P having conveyed between the guides  51  and  52  (i.e., side edges in the orthogonal direction which is the main scanning direction and is orthogonal to the conveyance direction E of the sheet P) to contact a guide face  54   a   1  (see  FIG. 2 ). The details of the side position adjustment mechanism  50  will be given later. 
     In the space B is provided the sheet feeding unit  23 . The sheet feeding unit  23  includes a sheet tray  24  and a pickup roller  25 . The sheet tray  24  is detachable to the casing  1   a . The sheet tray  24  is an open top box and is able to store sheets P which are positionally adjusted with reference to the center (so that the center of each sheet P in the width direction corresponds to a later-described center line C 1 ). The pickup roller  25  sends out the topmost sheet P in the sheet tray  24 . 
     The sub scanning direction is a direction in parallel to the conveyance direction D in which a sheet is conveyed by the conveyor roller units  42  and  43  and in parallel to the conveyance direction E in which a sheet is conveyed by the conveyor roller units  47  and  48 . The main scanning direction is a direction in parallel to the horizontal plane and orthogonal to the sub scanning direction, and is in parallel to a later-described axial direction (i.e., the direction of axial lines M 1 , M 2 , and M 3 ). 
     Now, the controller  100  will be described. The controller  100  controls the overall operations of the printer  1  by controlling operations of components of the printer  1 . The controller  100  controls a recording operation based on a recording command supplied from an external apparatus (e.g., a PC connected to the printer  1 ). To be more specific, the controller  100  controls operations such as conveyance of a sheet P and ink ejection in sync with the conveyance of the sheet P. 
     When, for example, a recording command instructing to perform recording on one surface of a sheet P is received from the external apparatus, the controller  100  drives, based on the recording command, the sheet feeding unit  23  and the drive rollers of the conveyor roller units  41  to  45  by using an unillustrated drive mechanism (constituted by members such as a drive motor and a gear transferring a rotational force of the drive motor). The sheet P sent out from the sheet tray  24  is guided by the upstream guide unit  3   a  and is sent to the recording position (between the platen  3   d  and the head  2 ). When the sheet P passes a position directly below the head  2 , the head  2  is controlled by the controller  100  so that ink droplets are ejected from the head  2 . With this, a desired image is formed on a surface of the sheet P. A timing to eject ink is determined based on a detection signal from a sheet sensor  26 . The sheet sensor  26  is positioned upstream of the head  2  in the conveyance direction D to detect the leading end of each sheet P. The sheet P on which the image has been recorded is guided by the downstream guide unit  3   b  and is ejected to the sheet output unit  4  from an upper part of the casing  1   a.    
     When, for example, receiving a recording command instructing to perform recording on both surfaces of the sheet P from the external apparatus, the controller  100  drives, based on the recording command, the sheet feeding unit  23  and the drive rollers of the conveyor roller units  41  to  45  by using the unillustrated drive mechanism. To begin with, as with the single-surface recording, an image is formed on the surface of the sheet P and the sheet P is conveyed toward the sheet output unit  4 . As shown in  FIG. 1 , a sheet sensor  27  is positioned upstream of and close to the conveyor roller unit  44 . When the sheet sensor  27  detects the tail end of the sheet P, the drive roller of the conveyor roller unit  44  reversely rotates under the control of the controller  100 , so that the direction of the conveyance of the sheet P is reversed. At this stage, the drive rollers of the conveyor roller units  46  to  48  (including the drive rollers  111  and  121  of later-described roller units  46  and  47  (see  FIG. 2 )) and the drive roller  61  of the position adjustment roller unit  60  (see  FIG. 2 ) are also driven. As a result, the path of the sheet P is switched and the sheet P is conveyed along the sheet re-conveyance path (indicated by the outlined arrows). At this stage, the side position adjustment mechanism  50  performs the positioning of the sheet P in the main scanning direction, and the positioned sheet P is re-conveyed to the recording position. The sheet P having been reversed and re-conveyed from the sheet re-conveyance path to the upstream guide unit  3   a  is supplied again to the recording position, and an image is recorded on the back surface. When the leading end of the sheet P is detected by the sheet sensor  26  prior to the image recording on the back surface, the rotation of the drive roller of the conveyor roller unit  44  is returned to the regular rotation. The sheet P having the surfaces for both of which the recording has been done is ejected to the sheet output unit  4  via the downstream guide unit  3   b.    
     &lt;Outline of First and Second Conveyor Roller Units&gt; 
     Now, referring to  FIG. 2 , the outline of the first conveyor roller unit  47  and the second conveyor roller unit  46  will be described.  FIG. 2  is a virtual plan view showing the positional relationship between the two conveyor roller units  46  and  47  along the sheet re-conveyance path and the side position adjustment mechanism  50 . In  FIG. 2 , a path between the conveyor roller units  46  and  47  is indicated to extend along the conveyance direction E. 
     As shown in  FIG. 2 , the conveyor roller units  46  and  47  have drive rollers  111  and  121 , respectively. Each of the drive rollers  111  and  121  is longer than the width of a sheet Pmax which is the maximum-sized sheet which can be conveyed at the side position adjustment mechanism  50 . The drive rollers  111  and  121  are identical in length and the axes thereof (i.e., axial lines M 1  and M 2  which are in parallel to each other) are orthogonal to the conveyance direction E. The drive rollers  111  and  121  are driven by an unillustrated drive mechanism. 
     The first conveyor roller unit  47  further includes nine driven rollers  123  and  124  which are lined up at regular intervals to form a single line in the axial direction. The drive roller  121  opposes the nine driven rollers  123  and  124 . Seven driven rollers (hereinafter, first driven rollers  123 ) which are partial rollers and are not the third and seventh rollers among the nine driven rollers are supported by a later-described first support member  130  so that the rotational axial lines of these seven driven rollers are swingable (see  FIG. 5A ). To the outer circumferential surface of each first driven roller  123 , two spurs  126  are attached. The details of the spurs  126  will be given later. The third and seventh driven rollers (hereinafter, second driven rollers  124 ) are supported by the first support member  130  so that the rotational axial lines of these two driven rollers are in parallel to the rotational axial line of the drive roller  121  and do not swing (see  FIG. 5D ). The separation distance between the first conveyor roller unit  47  and the position adjustment roller unit  60  in the conveyance direction E is shorter than the length in the conveyance direction E of a sheet Pmin and is longer than a half of the length of the sheet Pmin in the conveyance direction E. The sheet Pmin is the minimum-sized sheet which can be conveyed at the side position adjustment mechanism  50 . 
     The second conveyor roller unit  46  further includes nine driven rollers (upstream driven rollers)  113  which are partial rollers and are lined up at regular intervals to form a single line in the axial direction. The drive roller  111  (upstream drive roller) opposes the nine upstream driven rollers  113 . Each of the rotational axial lines of the driven rollers  113  are in parallel to the rotational axial line of the drive roller  111 . The nine driven rollers  113  are supported by a second support member  150  so that the each of the rotational axial lines of the driven rollers  113  does not swing. The second support member  150  is identical in terms with the structure with a part of the first support member  130  supporting the second driven rollers  124 . To the outer circumferential surface of each upstream driven roller  113 , two spurs  117  which are identical in terms of the structure with the spurs  126  are attached. In the present embodiment, the side edges of the maximum-sized sheet Pmax are positioned to correspond to the driven rollers  113  and  123  which are the outermost ones of the nine driven rollers, in each of the conveyor roller units  46  and  47 . The separation distance between the second conveyor roller unit  46  and the position adjustment roller unit  60  in the conveyance direction E is shorter than the length of the sheet Pmax in the conveyance direction E and longer than a half of the length of the sheet Pmax in the conveyance direction E. Furthermore, the separation distance is longer than the length of the sheet Pmin in the conveyance direction E. 
     &lt;Side Position Adjustment Mechanism&gt; 
     Now, the side position adjustment mechanism  50  will be described referring further to  FIG. 3 . The upper guide  51  and the lower guide  52  of the side position adjustment mechanism  50  are both plate-shaped components and are distanced from each other in the vertical direction. The space between these guides  51  and  52  corresponds to “the conveyance path” of the present invention and forms a part of the sheet re-conveyance path. 
     The position adjustment roller unit  60  includes a driven roller  71  (first position adjustment roller) and a drive roller  61  (second position adjustment roller) which is positioned below the first position adjustment roller  71  to hold a sheet P with the first position adjustment roller  71 . In the main scanning direction, the position adjustment roller unit  60  is positioned between the guide face  54   a   1  and the center of the conveyance path and is closer to the guide face  54   a   1  than to the center of the conveyance path. Here, the center of the conveyance path corresponds to the center line C 1  indicated by a broken line in  FIG. 2 . The first position adjustment roller  71  is driven either by the rotation of the drive roller  61  or in accordance with the conveyance of a sheet P conveyed by the drive roller  61 . 
     As shown in  FIG. 3 , the lower guide  52  has a hole  52   a  which penetrates the lower guide  52  in the thickness direction. The hole  52   a  is slightly smaller than the drive roller  61  in plan view. The lower guide  52  has a conveyance surface  52   b  which supports the lower surface of a conveyed sheet P. At one end in the main scanning direction of the lower guide  52 , a vertical portion  54  is formed to extend in the vertical direction. This vertical portion  54  includes an extending portion  54   a  which extends in the sub scanning direction and a tapered portion  54   b . The extending portion  54   a  has a guide face  54   a   1  which is a vertical surface in which the sub scanning direction is one of the in-plane directions thereof. The guide face  54   a   1  is a side surface of the extending portion  54   a  which surface faces the position adjustment roller unit  60 . The guide face  54   a   1  is configured to contact with one side edge of a sheet P. In the conveyance direction E, the tapered portion  54   b  is connected to the upstream end portion of the extending portion  54   a . The tapered portion  54   b  has a tapered face  54   b   1  which intersects with the guide face  54   a   1 . The tapered face  54   b   1  is a side surface of the tapered portion  54   b  which surface faces the position adjustment roller unit  60 . The tapered face  54   b   1  is connected to the guide face  54   a   1  at a border line H. 
     In the present embodiment, the first position adjustment roller  71  is positioned to overlap the guide face  54   a   1  in the conveyance direction E. With this arrangement, the sheet P is certainly brought onto the guide face  54   a   1  by the position adjustment roller unit  60 . Provided that the first position adjustment roller  71  is positioned upstream or downstream of the guide face  54   a   1  in the conveyance direction E, the distance in which the sheet P is conveyed while contacting with the guide face  54   a   1  is short, and hence the sheet P is less likely to be sufficiently brought onto the guide face  54   a   1 . 
     The drive roller  61  includes a cylindrical roller main body  62  and a shaft  63  which rotates together with the roller main body  62 . The roller main body  62  is positioned to oppose the hole  52   a  and to be below the first position adjustment roller  71 . The upper end of the roller main body  62  slightly protrudes upward from the conveyance surface  52   b  of the lower guide  52 , and contacts with the lower surface of a sheet P conveyed to the conveyance surface  52   b . The shaft  63  is fixed to the roller main body  62  in the state of being inserted into the roller main body  62 , and functions as a rotation shaft of the drive roller  61 . The shaft  63  is rotatably supported by the casing  1   a . The side position adjustment mechanism  50  is driven by the above-described drive mechanism. This drive mechanism is driven under the control of the controller  100 , and rotates the roller main body  62  via the shaft  63 . An axial line M 3  (in parallel to the above-described two axial lines M 1  and M 2 ) of the shaft  63  is in parallel to the main scanning direction. To put it differently, the axial line M 3  of the shaft  63  is orthogonal to the guide face  54   a   1 . This simplifies the structure of the drive mechanism. Provided that the axial line M 3  of the shaft  63  intersects with the main scanning direction, components of the drive mechanism such as a gear must correspond to the inclination of the axial line M 3 , and hence the structure of the drive mechanism becomes complicated. 
     As shown in  FIG. 3 , the first position adjustment roller  71  includes a cylindrical roller main body  73  and four spurs  72  on the outer circumferential surface of the roller main body  73 . The first position adjustment roller  71  overlaps the guide face  54   a   1  in the conveyance direction E. Each of the spurs  72  is a thin plate in shape and includes an annular portion attached to the outer circumferential surface of the roller main body  73  and protrusions protruding outward from the annular portion. Each of the protrusions narrows toward a point. With this arrangement, as the sharp points of the protrusions of the first position adjustment roller  71  contact with the sheet P in a piercing manner, the first position adjustment roller  71  rotates in accordance with the conveyance of the sheet P. The spurs  72  are identical in terms of the structure with the spurs  126  of the first driven roller  123  (see  FIG. 5C ). 
     The first position adjustment roller  71  is supported to be rotatable about the shaft by a supporting mechanism including a shaft  81  which is inserted into and fixed to the roller main body  73 . This supporting mechanism is attached to the lower surface of the upper guide  51  and includes a spring which is a biasing member (e.g., an elastic member such as a coil spring). On this account, the supporting mechanism is able to press the first position adjustment roller  71  contacting with the drive roller  61  downward toward the drive roller  61 . As a result, a predetermined nipping force for holding the sheet P is generated between the first position adjustment roller  71  and the drive roller  61 . This restrains the slipping of the sheet P with respect to the drive roller  61 , and the sheet P is conveyed in the conveyance direction E. 
     As shown in  FIG. 3 , the first position adjustment roller  71  is supported by the supporting mechanism in such a way that an angle θ 1  between the axial line L 1  and a part of the guide face  54   a   1 , which part is on the downstream in the conveyance direction E of an intersection between the axial line L 1  of the shaft  81  and the guide face  54   a   1 , is an acute angle (e.g., 85 to 89 degrees, preferably 88 degrees). With this arrangement, the sheet P sandwiched between the first position adjustment roller  71  and the drive roller  61  receives a force with which the side edge of the sheet P is positioned along the guide face  54   a   1 , in accordance with the rotation of the drive roller  61 . 
     In the present embodiment, the vertical portion  54  of the lower guide  52  and the position adjustment roller unit  60  are movable in the main scanning direction by an unillustrated mechanism, in accordance with an operation by the user. On the assumption that the center of the sheet P in the width direction corresponds to the center line C 1 , the user moves the guide face  54   a   1  in the main scanning direction in accordance with the size of the sheets P stored in the sheet tray  24  so that the position of the side edge of each sheet P corresponds to the guide face  54   a   1  in the main scanning direction. 
     &lt;First Support Member of First Conveyor Roller Unit&gt; 
     Now, the structure of the first support member  130  of the conveyor roller unit  47  will be described referring further to  FIG. 4  and  FIGS. 5A to 5D .  FIG. 4  is a partial oblique perspective of the conveyor roller unit  47  in which only one first driven roller  123  is depicted.  FIGS. 5A to 5D  are drawings for explaining the first driven roller  123  and an important part of the first support member  130  and for explaining the second driven roller  124  and an important part of the first support member  130 . While  FIG. 4  shows that the first support member  130  supports only one first driven roller  123 , the first support member  130  actually supports the seven first driven rollers  123  and the two second driven rollers  124  as described below. 
     As shown in  FIG. 4 , the first conveyor roller unit  47  includes the first support member  130  supporting the first driven rollers  123 . The first support member  130  has nine supporter main bodies  131  ( FIG. 4  shows only one of them) attached to the lower surface of the upper guide  51 . On the lower surface of each supporter main body  131 , a pair of flanges  132  is formed to protrude downward. In each flange  132 , a long hole  132   a  which is narrow and vertically long is formed. 
     As shown in  FIG. 5A , the first support member  130  further includes, for each first driven roller  123 , a supporting shaft  133  (shaft) which horizontally extends and a pair of coil springs  135  which are elastic members positioned between the supporter main body  131  and the supporting shaft  133 . The supporting shaft  133  is inserted into the long holes  132   a  at the both ends. As shown in  FIG. 5B , the supporting shaft  133  is vertically movable within the range of each long hole  132   a . Between the flanges  132  and the first driven roller  123 , the coil springs  135  are connected to the supporter main body  131  and the supporting shaft  133 . 
     As shown in  FIG. 5A , the first driven roller  123  includes a cylindrical roller main body  125  and two spurs  126 . The roller main body  12  has a through hole  125   a  which horizontally extends. The two spurs  126  are attached to the outer circumferential surface  125   b  of the roller main body  125 . The inner circumferential surface of the first driven roller  123  defines the through hole  125   a . At a central part of the inner circumferential surface of the first driven roller  123 , an annular protrusion  137  is provided together with the roller main body  125 . The annular protrusion  137  is a part of the first support member  130 . The protrusion  137  forms, in the through hole  125   a , a circular opening which is smaller in diameter than the through hole  125   a . The inner diameter of this circular opening is substantially identical with the outer diameter of the supporting shaft  133 . 
     The supporting shaft  133  is inserted into the through hole  125   a , and the outer circumferential surface  133   a  of the supporting shaft  133  contacts with the leading end of the protrusion  137  throughout the range of 360 degrees. In the meanwhile, the outer circumferential surface  133   a  of the supporting shaft  133  does not contact with the inner circumferential surface of the first driven roller  123  which surface faces the through hole  125   a , and a gap is formed therebetween. As a result, the leading end of the protrusion  137  functions a a fulcrum of the swing of the roller main body  125  with respect to the supporting shaft  133 . That is to say, the first driven roller  123  is swingable about the leading end of the protrusion  137  to the extent that the inner circumferential surface of the first driven roller  123  does not contact with the outer circumferential surface  133   a  of the supporting shaft  133 . Each first driven roller  123  is supported so that the rotational axial line L 2  thereof swings, in a plane which is orthogonal to a plane including the rotational axial line of the drive roller  121  and a tangent of the drive roller  121  and the first driven roller  123 . To put it differently, the orthogonal plane includes the rotational axial line of the drive roller  121  and the conveyance direction E. To put it further differently, the orthogonal plane is in parallel to the sheet P conveyed by the first conveyor roller unit  47  and is in parallel to the conveyance surface  52   b . When a later-described θ 2  is 90 degrees, the rotational axial line L 2  of the first driven roller  123  (the central axis of the through hole  127   a ) is in parallel to the axial direction of the drive roller  121 . Furthermore, in the present embodiment, the supporter main body  131 , the flanges  132 , the supporting shaft  133 , the coil springs  135 , and the protrusion  137  are provided independently for each first driven roller  123 . For this reason, the first support member  130  supports the seven first driven rollers  123  so that the rotational axial lines L 2  of the seven first driven rollers  123  independently swing. Furthermore, the supporting shaft  133  supports the roller main body  125  at the leading end of the protrusion  137  so that the roller main body  125  is rotatable about the shaft. 
     As shown in  FIG. 5C , each of the spurs  126  is a flat plate in shape and has an annular portion  126   a  attached to the outer circumferential surface  125   b  of the roller main body  125  and protrusions  126   b  protruding outward from the annular portion  126   a . Each of the protrusion  126   b  is narrowed toward a point. With this arrangement, as the sharp points of the protrusion  126   b  contact with the sheet P in a piercing manner, the first driven roller  123  rotates in accordance with the conveyance of the sheet P. 
     The pair of coil springs  135  biases the supporting shaft  133  downward when the first driven roller  123  contacts with the drive roller  121 . The biasing force of the coil springs  135  generates a pressure from the first driven roller  123  to the drive roller  121 . 
     As shown in  FIG. 5D , at a part of the first support member  130  which part supports the second driven roller  124 , a pair of flanges  142  protruding downward is formed at the lower surface of the supporter main body  131 . Each of the flanges  142  has a long hole  142   a  which is narrow and long in the vertical direction. 
     In addition to the above the first support member  130  includes, for each second driven roller  124 , a supporting shaft  143  (shaft) which horizontally extends and a pair of coil springs  145  which are elastic members positioned between the supporter main body and the supporting shaft  143 . The supporting shaft  143  is inserted into the long holes  142   a  at the both ends. The supporting shaft  143  is vertically movable within the range of each long hole  142   a . Between the flanges  142  and the second driven roller  124 , the coil springs  145  are connected to the supporter main body and the supporting shaft  143 . 
     The second driven roller  124  includes a cylindrical roller main body  127  in which a horizontally-extending through hole  127   a  is formed. The inner diameter of the through hole  127   a  is slightly longer than the outer diameter of the supporting shaft  143 , and the supporting shaft  143  is inserted into the through hole  127   a . With this, the second driven roller  124  does not swing and is supported by the supporting shaft  143  to be rotatable about the shaft. The rotational axial line of the second driven roller  124  (i.e., the central axis of the through hole  127   a ) is always in parallel to the axial direction of the drive roller  121 . No spur is attached to the outer circumferential surface of the second driven roller  124  because a sheet tends to be damaged in a later-described positioning operation when a spur is provided on the second driven roller  124  which do not swing. 
     The pair of the coil springs  145  biases the supporting shaft  143  downward while the second driven roller  124  contacts with the drive roller  121 . The biasing force of the coil springs  145  generates a pressure from the second driven roller  124  to the drive roller  121 . In the present embodiment, spring constants of the coil springs  135  and  145  are adjusted so that the pressure from the second driven roller  124  to the drive roller  121  is smaller than the pressure from the first driven roller  123  to the drive roller  121 . 
     As described above, the second support member  150  supporting the upstream driven rollers  113  is structurally identical with a part of the first support member  130  which part supports the second driven roller  124  ( FIG. 5D ). As with the first support member  130 , the pressure from the upstream driven rollers  113  to the upstream drive roller  111  is generated by a biasing force of the coil springs. In the present embodiment, as the spring constants of the coil springs  145  and the coil springs in the second support member  150  supporting the upstream driven rollers  113  are adjusted, the pressure from the first driven rollers  123  to the drive roller  121  is smaller than the pressure from the upstream driven rollers  113  to the upstream drive roller  111 . Furthermore, on the outer circumferential surface of the upstream driven roller  113 , two spurs  117  which are identical with the spurs  126  shown in  FIG. 5C  are attached. 
     &lt;Positioning Operation for Sheet in Sheet Re-Conveyance Path&gt; 
     Now, a positioning operation (side registration) for a sheet P conveyed on the sheet re-conveyance path will be described referring further to  FIGS. 6A to 6D . The description below assumes that a sheet P which is relatively long in the conveyance direction and is equal to or longer than the distance between the second conveyor roller unit  46  and the position adjustment roller unit  60  in length is used. The positioning operation described below, however, remains the same even if a sheet P which is relatively short in the conveyance direction and is shorter than the distance between the second conveyor roller unit  46  and the position adjustment roller unit  60  is used. 
     To begin with, the sheet P is conveyed from the second conveyor roller unit  46  to the first conveyor roller unit  47 . At this stage, the seven first driven rollers  123  of the first conveyor roller unit  47  are rotating in accordance with the rotation of the drive roller  121 . For this reason, as shown in  FIG. 6A , the rotational axial line L 2  of each first driven roller  123  is inclined with the respect to the supporting shaft  133  so that the rotational axial line L 2  of each first driven roller  123  is in parallel to the axial line M 1  of the drive roller  121 . As a result, the rotational axial line L 2  and a part of the guide face  54   a   1  which part is on the downstream in the conveyance direction E of an intersection between the rotational axial line L 2  and a virtual flat plane including the guide face  54   a   1  form an angle θ 2  of substantially 90 degrees (right angle). On this account, at the contact point between each first driven roller  123  and the drive roller  121 , the rotational direction of the first driven roller  123  is substantially identical with the rotational direction of the drive roller  121 . As a result, the load from each first driven roller  123  to the sheet P is reduced. 
     The two second driven rollers  124  do not swing and the rotational axial lines thereof are always orthogonal to the virtual flat plane including the guide face  54   a   1 . For this reason, even if the first driven rollers  123  are inclined for some reason so that the angle θ 2  becomes not at 90 degrees, the second driven rollers  124  always apply a force by which the sheet P is conveyed in the conveyance direction E to the sheet P, with the result that the rotation of the sheet P or the movement of the sheet P in the main scanning direction before the leading end of the sheet P reaches the position adjustment roller unit  60  are restrained. 
     When the leading end of the sheet P reaches the position adjustment roller unit  60  and the tail end of the sheet P has passed the second conveyor roller unit  46 , the sheet P is conveyed while being pinched by the position adjustment roller unit  60 . At this stage, as shown in  FIG. 6B , the position adjustment roller unit  60  holds the left part of the sheet P, and hence an angular moment around the center of gravity of the sheet P is generated in the sheet P. As a result, the sheet P is conveyed by the position adjustment roller unit  60  and the two conveyor roller units  46  and  47  in the conveyance direction E while rotating in a rotational direction F 1  (counterclockwise rotation in the figure) about the center of gravity G, until a side P 1  of the sheet P which side faces the guide face  54   a   1  contacts with the border line H between the guide face  54   a   1  and the tapered face  54   b   1 . 
     In regard to the above, the rotational axial line L 2  of each first driven roller  123  which contacts with the sheet P and rotates in accordance with the conveyance of the sheet P changes its angle with respect to the supporting shaft  133  by following the traveling direction Q 1  of the sheet P (i.e., a direction formed by synthesizing the rotational direction F 1  at the contact point between the spur  126  and the sheet P and the conveyance direction E). To be more specific, the rotational axial line L 2  of the first driven roller  123  is inclined with respect to the supporting shaft  133  so that the direction of the rotational axial line L 2  of the first driven roller  123  becomes close to a direction orthogonal to the traveling direction Q 1  of the sheet P. In other words, the angle θ 2  is an obtuse angle. For this reason, at the contact point between each first driven roller  123  and the sheet P, the rotational direction of the first driven roller  123  becomes close to the traveling direction Q 1  of the sheet P. As a result, the load from the first driven rollers  123  to the sheet P is reduced and hence the rotation of the sheet P is less likely to be obstructed, with the result that the sheet P easily rotates. 
     The side P 1  of the sheet P then contacts with the border line H. When the sheet P is further conveyed by the position adjustment roller unit  60  and the conveyor roller unit  47  while the side P 1  of the sheet P is contacting with the border line H, as shown in  FIG. 6C , an angular moment is generated in the sheet P with the border line H functioning as a rotation center. As a result, the sheet P is conveyed by the position adjustment roller unit  60  and the conveyor roller unit  47  in the conveyance direction E while rotating in the rotational direction F 2  (clockwise direction in the figure) about the border line H, until the leading end of the sheet P (the leading end of the side P 1 ) contacts with the guide face  54   a   1 . At this stage, the rotational axial line L 2  of each first driven roller  123  changes its angle with respect to the supporting shaft  133  by following the traveling direction Qw of the sheet P (i.e., a direction formed by synthesizing the rotational direction F 2  at the contact point between the spur  126  and the sheet P and the conveyance direction E). To be more specific, the rotational axial line L 2  of the first driven roller  123  is inclined with respect to the supporting shaft  133  so that the direction of the rotational axial line L 2  of the first driven roller  123  becomes close to a direction orthogonal to the traveling direction Q 2  of the sheet P. In other words, the angle θ 2  is an acute angle. On this account, at the contact point between the first driven roller  123  and the sheet P, the rotational direction of the first driven roller  123  becomes close to the traveling direction Q 2  of the sheet P. As a result, the rotation of the sheet P is less likely to be obstructed because the load from the first driven rollers  123  to the sheet P is reduced, and hence the sheet P easily rotates. 
     Subsequently, as shown in  FIG. 6D , when the leading end of the sheet P contacts with the guide face  54   a   1 , most of the side P 1  contacts with the guide face  54   a   1 . For this reason, the traveling direction of the sheet P conveyed by the position adjustment roller unit  60  and the first conveyor roller unit  47  becomes identical with the conveyance direction E. Furthermore, at this stage, by following the traveling direction (conveyance direction E) of the sheet P, the rotational axial line L 2  of the first driven roller  123  changes its angle with respect to the supporting shaft  133  so that the rotational axial line L 2  of the first driven roller  123  becomes in parallel to the axial line M 1  of the drive roller  121 . In other words, the angle θ 2  is substantially 90 degrees (right angle). For this reason, at the contact point between the first driven roller  123  and the sheet P, the rotational direction of the first driven roller  123  becomes substantially identical with the traveling direction (conveyance direction E) of the sheet P. As a result, the load from the first driven rollers  123  to the sheet P is reduced. The sheet P is positioned in this way in the main scanning direction, and the sheet P in this state is conveyed in the conveyance direction E while the side P 1  of the sheet P contacts with the entirety of the guide face  54   a   1 . 
     As described above, in the printer  1  of the present embodiment, side registration, i.e., skew correction (positioning) performed by conveying the sheet P along the guide face  54   a   1  is carried out by utilizing the arrangement that the position adjustment roller unit  60  is closer to the guide face  54   a   1  than to the center (center line) of the conveyance path in the main scanning direction. In so doing, because the first driven rollers  123  are arranged to be swingable with respect to the supporting shafts  133 , the first driven rollers  123  swing in accordance with the traveling direction of the sheet P when the sheet P is pinched by both the first conveyor roller unit  47  and the position adjustment roller unit  60 . To be more specific, the first driven rollers  123  swing so that the axial line direction L 2  of the first driven roller  123  becomes close to a direction orthogonal to the traveling direction of the sheet P. Such swing reduces the load from the first driven rollers  123  to the sheet P and hence the rotation of the sheet P is less likely to be obstructed, with the result that the sheet P easily rotates in the states shown in  FIGS. 6B and 6C . Consequently, the side registration of causing the side P 1  of the sheet P to be along the guide face  54   a   1  by the position adjustment roller unit  60  is less likely to be obstructed by the first conveyor roller unit  47 . 
     In particular, when the sheet P is relatively long in the conveyance direction, the rotation of the sheet P is obstructed if the first driven rollers  123  do not swing, because the force of binding the sheet P by the first conveyor roller unit  47  is relatively large when the sheet P is pinched by the first conveyor roller unit  47 . In other words, the side registration is likely to be obstructed when the sheet P is pinched by the first conveyor roller unit  47 . When the tail end of the sheet P has just passed the first conveyor roller unit  47 , most of the sheet P is on the downstream of the position adjustment roller unit  60  in the conveyance direction E, and hence the side registration is difficult. In this regard, according to the present embodiment, because the first driven rollers  123  are arranged to swing, the side registration is unlikely to be obstructed even if the sheet P is pinched by both the first conveyor roller unit  47  and the position adjustment roller unit  60 , and hence the side registration is properly carried out even if the sheet P is relatively long in the conveyance direction. In other words, because the first driven rollers  123  are arranged to be swingable, the side registration is properly done no matter whether the sheet P is relatively short or relatively long in the conveyance direction. 
     In the above-described positioning operation of the sheet P, the second driven rollers  124  do not swing as the rotational axial line of each of these rollers is identical with the axial line M 1  of the drive roller  121 , and hence these rollers  124  are more likely to obstruct the rotation of the sheet P in the rotational directions F 1  and F 2 , as compared to the first driven rollers  123 . However, because the pressure from the second driven rollers  124  to the drive roller  121  is smaller than the pressure from the first driven rollers  123  to the drive roller  121  as described above, the obstruction of the rotation by the second driven rollers  124  is moderate, and hence the position adjustment is certainly carried out. Furthermore, each second driven roller  124  which is not provided with a spur has a smaller force of binding the sheet P in the rotational axial line than each first driven roller  123  provided with a spur. For this reason, the obstruction of the rotation by the second driven rollers  124  is moderate, and the position adjustment is certainly carried out. 
     In the present embodiment, the supporting shaft  133  inserted into each first driven roller  123  supports the first driven roller  123  to be rotatable about the shaft. The first driven rollers  123  are supported to be swingable with respect to the supporting shafts  133 . As such, the structure in which the rotational axial line L 2  of each first driven roller  123  swings is easily realized. 
     In addition to the above, according to the present embodiment, because the leading end of an annular protrusion  137 , which is a part of the first support member  130 , formed on the inner circumferential surface of the first driven roller  123 , and faces the through hole  125   a , functions as the fulcrum of the swinging of the first driven roller  123  and contacts with the outer circumferential surface of the supporting shaft  133 , the fulcrum of the swinging of each first driven roller  123  is unchanged even if the first driven roller  123  is slightly deviated in the direction of the axial line of the supporting shaft  133 . With this, the swinging of each first driven roller  123  is stabilized. 
     In addition to the above, in the present embodiment, because the first driven rollers  123  which are partial rollers separated from each other in the axial direction independently swing, resistance by which each first driven roller  123  is swung is relatively small as compared to a case where a single long roller is used as the first driven roller. For this reason, the side registration is further effectively carried out. 
     In addition to the above, in the present embodiment, the pressures from the first driven rollers  123  and the second driven rollers  124  to the drive roller  121  are smaller than the pressure from the upstream driven rollers  113  to the upstream drive roller  111 . For this reason, the rotation of the sheet P becomes less obstructed as the conveyance force exerted by the first conveyor roller unit  47  is reduced, with the result that the side registration of the sheet P is further certainly carried out. In case of a sheet P which is relatively long in the conveyance direction and is equal to or longer than the distance between the second conveyor roller unit  46  and the position adjustment roller unit  60  in length, such a sheet P is successfully conveyed by a conveyance force of the second conveyor roller unit  46 , even if the conveyance force exerted by the first conveyor roller unit  47  is small. On the other hand, in case of a relatively short sheet P in the conveyance direction which is shorter than the distance between the second conveyor roller unit  46  and the position adjustment roller unit  60 , such a sheet P is successfully conveyed by a small conveyance force exerted by the first conveyor roller unit  47 , because this sheet P is short and light. 
     In the present embodiment, because each of the first driven rollers  123  and upstream driven rollers  113  has at least one spur on the outer circumferential surface, these driven rollers  123  and  113  are less likely to slip on the surface of the sheet P. The sheet P is therefore more certainly conveyed. 
     Because the printer  1  includes a re-conveyance guide unit  3   c  which is the conveyor of the present embodiment in a re-conveyance unit, the lateral position of the sheet P is appropriate even when printing is performed on the back surface. 
     In the present embodiment, each upstream driven roller  113  is supported so as not to swing. On this account, the sheet P is conveyed in the conveyance direction E by the second conveyor roller unit  46 . To restrain the occurrence of inappropriate conveyance of the sheet P, the second conveyor roller unit  46  preferably conveys the sheet P in the conveyance direction E. Provided that each upstream driven roller  113  is supported to be swingable in the same manner as the first driven rollers  123 , the sheet P may be erroneously conveyed in a direction orthogonal to the conveyance direction E, when the sheet P is being conveyed by the first conveyor roller unit  47  and the second conveyor roller unit  46  before the sheet P is passed to the position adjustment roller unit  60 . If the sheet P is conveyed in the direction orthogonal to the conveyance direction E before the sheet P is passed to the position adjustment roller unit  60 , the sheet P may contact with a wall defining the conveyance path or the like in the main scanning direction, with the result that inappropriate conveyance such as jamming may occur. In the present embodiment, while each first driven roller  123  of the first conveyor roller unit  47  is supported to be swingable, each upstream driven roller  113  of the second conveyor roller unit  46  on the upstream of the first conveyor roller unit  47  in the conveyance direction E is supported not to be swingable. With this, the sheet P is conveyed in the conveyance direction E. 
     When the sheet Pmax is conveyed, the leading end of the sheet Pmax reaches the position adjustment roller unit  60  and then the tail end of the sheet Pmax passes the second conveyor roller unit  46 . While the sheet Pmax is being conveyed by the second conveyor roller unit  46 , each upstream driven roller  113  does not swing, and hence the sheet Pmax is conveyed in the conveyance direction E. After the tail end of the sheet Pmax passes the second conveyor roller unit  46 , the sheet Pmax starts to rotate on account of the function of the position adjustment roller unit  60 . At this stage, the sheet Pmax is pinched by the first conveyor roller unit  47 . In this regard, because each first driven roller  123  of the first conveyor roller unit  47  is arranged to swing, the rotation of the sheet Pmax is unlikely to be obstructed. 
     When the sheet Pmin is conveyed, the leading end of the sheet Pmin reaches the position adjustment roller unit  60  after the tail end of the sheet Pmin passes the second conveyor roller unit  46  and before the tail end passes the first conveyor roller unit  47 . Because each first driven roller  123  of the first conveyor roller unit  47  is supported to be swingable, the sheet Pmin starts to rotate due to the function of the position adjustment roller unit  60 , when the leading end of the sheet Pmin reaches the position adjustment roller unit  60 . Because each upstream driven roller  113  does not swing while the sheet Pmin is being conveyed by the second conveyor roller unit  46 , the sheet Pmin is conveyed in the conveyance direction E. 
     Second Embodiment 
     Now, the following will mainly describe differences between the printer of First Embodiment and a printer including a conveyor of Second Embodiment of the present invention with reference to  FIG. 7A .  FIG. 7A  is a virtual plan view which relates to Second Embodiment and is equivalent to  FIG. 2 , and does not illustrate spurs. In the description below, members identical with those in First Embodiment will be denoted by the same reference numerals and the explanations thereof will be omitted. 
     Second Embodiment is different from First Embodiment in the structure of the first conveyor roller unit. In Second Embodiment, as shown in  FIG. 7A , a first conveyor roller unit  247  includes a drive roller  221  and five driven rollers (first driven rollers)  223 . In the second embodiment, the drive roller  221  of the first conveyor roller unit  247  is shorter than the drive roller  111  of the second conveyor roller unit  46  and these drive rollers are positioned to be symmetrical with each other about the center line C 1 . 
     The drive roller  221  opposes five first driven rollers  223  which are partial rollers and are lined up at regular intervals to form a single line in the axial direction. These first driven rollers  223  are supported by a support member which is identical in structure with the above-described first support member  130  so that the rotational axial line of each first driven roller  223  is swingable. The center in the axial direction of the third first driven roller  223  which is the central one of the five first driven rollers  223  corresponds to the center in the axial direction of the fifth driven roller  113  which is the central one in the second conveyor roller units  46 . These centers are on the center line C 1 . 
     As such, in the present embodiment, the center of the region in which the five first driven rollers  223  are provided corresponds in the axial direction to the center of the region in which the nine upstream driven rollers  113  are provided, and the region in which the five first driven rollers  223  are provided is shorter than the region in which the nine upstream driven rollers  113  are provided. Furthermore, in the present embodiment, the first conveyor roller unit  247  does not include a non-swinging second driven roller which is included in First Embodiment. 
     In the present embodiment, as with First Embodiment, the vertical portion  54  of the lower guide  52  and the position adjustment roller unit  60  are movable by an unillustrated mechanism in the main scanning direction in response to an operation by a user. For this reason, by moving the vertical portion  54  and the position adjustment roller unit  60  to positions indicated by full lines in case of a wide sheet P or to positions indicated by broken lines in case of a narrow sheet P, the position of the side edge of a sheet P on which printing is to be done is adjusted to correspond to the guide face  54   a   1 . 
     A positioning operation for a sheet in the present embodiment is identical with the operation described with reference to  FIGS. 6A to 6D  in First Embodiment. That is to say, to begin with, the five first driven rollers  223  are inclined so that the angle θ 2  becomes a right angle (see  FIG. 6A ), the first driven rollers  223  are then inclined so that the angle θ 2  becomes an obtuse angle when the leading end of the sheet P reaches the position adjustment roller unit  60  (see  FIG. 6B ), the first driven rollers  223  are then inclined so that the angle θ 2  becomes an acute angle when the side P 1  of the sheet P contacts with the border line H (see  FIG. 6C ), and then the first driven rollers  223  are inclined so that the angle θ 2  becomes a right angle when the leading end of the sheet P contacts with the guide face  54   a   1  (see  FIG. 6D ). In this way, in the present embodiment, as with First Embodiment, the side registration of causing the side P 1  of the sheet P to be along the guide face  54   a   1  is less likely to be obstructed by the first conveyor roller unit  247 . 
     Because the first driven rollers  223  swing so that the angle θ 2  is serially changed in accordance with the conveyance of the sheet, the load from the first driven rollers  223  to the sheet P is reduced and the rotation of the sheet P is less likely to be obstructed, with the result that the sheet P easily rotates. The sheet P, however, still receives a small load from the first driven rollers  123 . For this reason, the load from the first driven rollers  223  to the sheet P which is wider than five first driven rollers  223  in total in the positioning operation of the sheet is further reduced as compared to First Embodiment, by arranging the region in which the five first driven rollers  223  are provided as in the present embodiment to be shorter than the region in which the upstream driven rollers  113  are provided. This allows the side registration to be more smoothly performed. In the meanwhile, even if the conveyance force from the first conveyor roller unit  247  to the sheet is smaller than the conveyance force in First Embodiment, the sheet P which is not wider than the five first driven rollers  223  is light in weight, and hence a suitable conveyance force is exerted by the five first driven rollers  223 , as the sheet P is adjusted with reference to the center and conveyed. Furthermore, the load to the sheet P is small because the non-swing second driven roller  124  in the first conveyor roller unit  47  of First Embodiment is not provided, and hence this arrangement is preferable in terms of smooth side registration. In the present embodiment, at least one of the five first driven rollers  223  may be a non-swing second driven roller described in First Embodiment. In this case, the second driven rollers are preferably arranged to be symmetrical with respect to the center line C 1  to apply a symmetrical force onto the sheet. 
     Third Embodiment 
     Now, the following will mainly describe differences between the printer of First Embodiment and a printer including a conveyor of Third Embodiment of the present invention with reference to  FIG. 7B .  FIG. 7B  is a virtual plan view which relates to Third Embodiment and is equivalent to  FIG. 2 , and does not illustrate spurs. In the description below, members identical with those in First Embodiment will be denoted by the same reference numerals and the explanations thereof will be omitted. 
     In the first place, Third Embodiment is different from First Embodiment in the structure of the first conveyor roller unit. In Third Embodiment, a first conveyor roller unit  347  includes, as shown in  FIG. 7B , a drive roller  321  and five driven rollers  323  and  324  which are lined up at regular intervals to form a single line in the axial direction. In the present embodiment, the drive roller  321  of the first conveyor roller unit  347  is shorter than the drive roller  111  of the second conveyor roller unit  46  and these rollers are arranged to be non-symmetrical with respect to the center line C 1 , more specifically, most of each roller is between the center line C 1  and the guide face  54   a   1 . 
     The drive roller  321  opposes the five driven rollers  323  and  324 . The five driven rollers  323  and  324  are classified into four first driven rollers  323  which are partial rollers supported by a first support member to be swingable in the same manner as the first driven rollers  123  of First Embodiment and one second driven roller  324  which is supported by the first support member not to be swingable in the same manner as the second driven rollers  124  of the First Embodiment. The second driven roller  324  is positioned to be closest to the guide face  54   a   1  in the axial direction. Among the four first driven rollers  323 , the first driven roller  323  farthest from the second driven roller  324  is arranged such that the center in the axial direction of this roller corresponds to the center line C 1 . Furthermore, the center in the axial direction of the driven roller  323  at the center of the five driven rollers  323  and  324  corresponds to the center in the axial direction of a driven roller  113  which is the third roller from the guide face  54   a   1  in the second conveyor roller unit  46 . A linear line which passes this position and is in parallel to the center line C 1  is indicated as C 2  in  FIG. 7B . 
     In the present embodiment, being different from First Embodiment, a sheet tray  24  is able to store sheets P which are adjusted with reference to the side edge (i.e., the position of the side edges of the stored sheets P corresponds to a virtual linear line which passes the guide face  54   a   1  and is in parallel to the center line C 1 ). On this account, the vertical portion  54  of the lower guide  52  and the position adjustment roller unit  60  are fixed to be immovable. For example, in case of a prescribed large sheet P, the center in the width direction of the sheet P is on the center line C 1  when the side edge of the sheet P contacts with the guide face  54   a   1 , and in case of a prescribed small sheet P, the center in the width direction of the sheep P is on the linear line C 2  when the side edge of the sheet P contacts with the guide face  54   a   1 . The position adjustment roller unit  60  is closer to the guide face  54   a   1  than to the center line C 1  and the linear line C 2 . 
     The positioning operation for the sheet in the present embodiment is identical with the positioning operation described in First Embodiment with reference to  FIGS. 6A to 6D . That is to say, to begin with, the first driven rollers  323  are inclined so that the angle θ 2  becomes a right angle (see  FIG. 6A ), the first driven rollers  323  are then inclined so that the angle θ 2  becomes an obtuse angle when the leading end of the sheet P reaches the position adjustment roller unit  60  (see  FIG. 6B ), the first driven rollers  323  are then inclined so that the angle θ 2  becomes an acute angle when the side P 1  of the sheet P contacts with the border line H (see  FIG. 6C ), and then the first driven rollers  323  are inclined so that the angle θ 2  becomes a right angle when the leading end of the sheet P contacts with the guide face  54   a   1  (see  FIG. 6D ). In this way, in the present embodiment, as with First Embodiment, the side registration of causing the side P 1  of the sheet P to be along the guide face  54   a   1  is less likely to be obstructed by the first conveyor roller unit  347 . 
     As the first driven rollers  323  swing to serially change the angle θ 2  in accordance with the conveyance of the sheet, the load from the first driven rollers  323  to the sheet P is reduced and the rotation of the sheet P is less likely to be obstructed, with the result that the sheet P easily rotates. The sheet P, however, still receives a small load from the first driven rollers  323 . For this reason, the load from the first driven rollers  323  to the sheet P which is wider than the total length of four first driven rollers  323  and one second driven roller  324  in the positioning operation of the sheet is further reduced as compared to First Embodiment, by arranging the region in which first driven rollers  323  and a second driven roller  324 , the total number of which is five, are provided as in the present embodiment to be shorter than the region in which the upstream driven rollers  113  are provided. This allows the side registration to be more smoothly performed. In the meanwhile, even if the conveyance force from the first conveyor roller unit  347  to the sheet is smaller than the conveyance force in First Embodiment, the sheet P which is not wider than the total length of four first driven rollers  323  and one second driven roller  324  is light in weight, and hence a suitable conveyance force is exerted by the four first driven rollers  323  and the one second driven roller  324  as the sheet P is adjusted on the basis of the side edge and conveyed. 
     In addition to the above, the second driven roller  324  does not swing, and the rotational axial line thereof is always orthogonal to a virtual flat plane including the guide face  54   a   1 . For this reason, even if the first driven rollers  323  swing for some reason so that the angle θ 2  becomes not at 90 degrees before the leading end of the sheet P reaches the position adjustment roller unit  60  (i.e., the timing identical with the timing shown in  FIG. 6A ), the second driven roller  324  always applies a force by which the sheet P is conveyed in the conveyance direction E to the sheet P, with the result that the rotation of the sheet P or the movement of the sheet P in the main scanning direction before the leading end of the sheet P reaches the position adjustment roller unit  60  are restrained. 
     In addition to the above, because no spur is attached to the outer circumferential surface of the second driven roller  124  as described above in order to prevent the sheet P from being damaged, the second driven roller  124  tends to slip on the sheet P. In this regard, in the present embodiment, the outermost one of the five driven rollers  323  and  324 , which faces a region which is likely to be a blank region where no image recording is performed by the head  2  in the sheet P irrespective of the size of the sheet P (in the present embodiment, a side edge closer to the guide face  54   a   1  in case of position adjustment with reference to the side edge), is selected as the second driven roller  324 . For this reason, the occurrence of disturbance in the image is prevented even if the second driven roller  324  slips. 
     Fourth Embodiment 
     Now, the following will mainly describe differences between the printer of First Embodiment and a printer including a conveyor of Fourth Embodiment of the present invention with reference to  FIG. 8 .  FIG. 8  is a cross section which relates to Fourth Embodiment and is equivalent to  FIG. 5A . In the description below, members identical with those in First Embodiment will be denoted by the same reference numerals and the explanations thereof will be omitted. 
     Fourth Embodiment is different from First Embodiment in the structure of a part of a first support member which part supports first driven rollers  123 . In the present embodiment, a first support member  430  supporting first driven rollers  123  includes nine supporter main bodies  131  (see  FIG. 4 ) attached to the lower surface of an upper guide  51 . On the lower surface of each supporter main body  131 , a pair of flanges  432  is formed to protrude downward. In each flange  432 , a long hole  432   a  which is narrow and long in the vertical direction is formed. 
     As shown in  FIG. 8 , the first support member  430  further includes, for each first driven roller  123 , a supporting shaft  433  (shaft) which horizontally extends and a pair of coil springs  435  which are elastic members positioned between the supporter main body and the supporting shaft  433 . The supporting shaft  433  is inserted into the long holes  432   a  at the both sides. The supporting shaft  433  is arranged to be vertically movable in the range of each long hole  432   a . The coil springs  435  are connected to the supporter main body  131  and the supporting shaft  433  between the flanges  432  and the first driven roller  123 . 
     As described in First Embodiment, each first driven roller  123  includes a cylindrical roller main body  125  in which a horizontally-extending through hole  125   a  is formed and two spurs  126  attached to the outer circumferential surface  125   b  of the roller main body  125 . At a central part of the outer circumferential surface  433   a  of the supporting shaft  433  which part faces the through hole  125   a , an annular protrusion  437  which is a part of the first support member  430  is formed to be integrated with the supporting shaft  433 . The diameter of a circle formed by the leading end of the protrusion  437  is substantially identical with the inner diameter of the through hole  125   a.    
     The supporting shaft  433  is inserted into the through hole  125   a  and the protrusion  437  contacts across 360 degrees with the inner circumferential surface of the first driven roller  123  facing the through hole  125   a . In the meanwhile, the outer circumferential surface  433   a  of the supporting shaft  433  does not contact with the inner circumferential surface of the first driven roller  123 , and a gap is formed therebetween. As a result, the leading end of the protrusion  437  functions as a fulcrum of the swing of the roller main body  125  with respect to the supporting shaft  433 . That is to say, the first driven roller  123  is swingable about the leading end of the protrusion  437  to the extent that the inner circumferential surface of the first driven roller  123  does not contact with the outer circumferential surface  133   a  of the supporting shaft  433 . Also in the present embodiment, the first support member  430  supports the seven first driven rollers  123  so that the rotational axial lines L 2  (i.e., the central axes of the through holes  125   a ) of the first driven rollers  123  swing independently from one another. Furthermore, the supporting shaft  433  supports the roller main body  125  at the leading end of the protrusion  437  to be rotatable about the shaft. The positioning operation for the sheet in the present embodiment is identical with the positioning operation described with reference to  FIGS. 6A to 6D . 
     In this way, in the present embodiment, because the supporting shaft  433  has the protrusion  437  functioning as a fulcrum of the swinging of the roller main body  125 , the arrangement that allows the roller main body  125  to swing with respect to the supporting shaft  433  is easily realized. That is to say, because it is unnecessary to provide the protrusion  137  on the inner circumferential surface of the first driven roller  123 , the manufacturing of the first support member  430  is simplified. 
     Fifth Embodiment 
     Now, the following will mainly describe differences between the printer of First Embodiment and a printer including a conveyor of Fifth Embodiment of the present invention with reference to  FIG. 9 .  FIG. 9  is a profile which relates to Fifth Embodiment and is equivalent to  FIG. 5A . In the description below, members identical with those in First Embodiment will be denoted by the same reference numerals and the explanations thereof will be omitted. 
     In Fifth Embodiment, a first conveyor roller unit is not provided with the two second driven rollers  124  which are provided in First Embodiment, and nine first driven rollers  123  are lined up at regular intervals to form a single line in the axial direction. Fifth Embodiment is different from First Embodiment in the structure of the first support member. As shown in  FIG. 9 , a first support member  530  supporting nine first driven rollers  123  in the present embodiment includes nine attaching shafts  531  (only one of them is shown in  FIG. 9 ) each vertically penetrating the upper guide  51 , rotatably attached to the upper guide  51 , and having an upper end portion which horizontally extends, and nine shaft retaining members  532  (only one of them is shown in  FIG. 9 ) which is connected to the lower end of each attaching shaft  531  and has a U-shaped side surface which is open downward. In each of parts of the shaft retaining member  532  which parts vertically extend and oppose each other, a circular hole  532   a  is formed. 
     In addition to the nine attaching shafts  531  and the nine shaft retaining members  532 , the first support member  530  further includes, for each first driven roller  123 , a supporting shaft  533  (shaft) which horizontally extends and a coil spring  535  which is an elastic member positioned around the attaching shaft  531  and between the upper guide  51  and the shaft retaining member  532 . The upper end of the coil spring  535  is fixed to the upper guide  51  whereas the lower end of the coil spring  535  is fixed to the shaft retaining member  532 . The supporting shaft  533  is inserted into the holes  532   a  at the both sides. 
     As described in First Embodiment, each first driven roller  123  includes a cylindrical roller main body  125  in which a horizontally-extending through hole  125   a  is formed and two spurs  126  fixed to the outer circumferential surface  125   b  of the roller main body  125 . In the present embodiment, the inner diameter of the through hole  125   a  is slightly longer than the outer diameter of the supporting shaft  533 , and the supporting shaft  533  is inserted into the through hole  125   a . With this, each first driven roller  123  is supported by the supporting shaft  533  so as not to swing with respect to the supporting shaft  533  and to be rotatable about the shaft. 
     When the first driven roller  123  contacts with the drive roller  121 , the coil spring  535  biases the shaft retaining member  532  downward. On account of the biasing force of this coil spring  535 , the pressure from the first driven roller  123  supported by the shaft retaining member  532  to the drive roller  121  via the supporting shaft  533  is generated. 
     In addition to the above, because the upper end of the coil spring  535  is fixed to the upper guide  51  whereas the lower end of the coil spring  535  is fixed to the shaft retaining member  532 , the attaching shaft  531  receives a rotational force which is caused by the circumferential elastic force of the coil spring  535  to reversely rotate the attaching shaft  531  to return to the original angular orientation, and hence the attaching shaft  531  is rotated in one direction. When no external rotational force is exerted to the attaching shaft  531 , the rotational axial line (the axis of the through hole  125   a  of each first driven roller  123 ) and the supporting shaft  533  are in parallel to the axial line M 1  of the drive roller  121 . By this elastic force of the coil spring  535 , the first driven roller  123  swings in a horizontal plane (i.e., a plane including the axial line M 1  of the drive roller and the conveyance direction) so as to rotate the attaching shaft  531  together with the supporting shaft  533  and the shaft retaining member  532 . As a result, as with First Embodiment, the side registration of causing the side P 1  of the sheet P to be along the guide face  54   a   1  is less likely to be obstructed by the first conveyor roller unit. Also in the present embodiment, the first support member  530  supports the nine first driven rollers  123  so that the rotational axial lines L 2  (central axes of the through holes  125   a ) of the first driven rollers  123  independently swing. 
     Other Modifications 
     For example, the first driven rollers and the upstream driven rollers may not have spurs. Furthermore, the position adjustment roller unit  60  of the side position adjustment mechanism  50  may be positioned upstream or downstream of the guide face  54   a   1  in the conveyance direction E. Furthermore, the first driven rollers may not be arranged so that one roller main body is provided for one supporting shaft. Two or more roller main bodies may be provided for one supporting shaft. Furthermore, while each of the first driven rollers and upstream driven rollers has two spurs in the embodiments above, each roller may have one, three, or more spurs. Furthermore, the structure from the second conveyor roller unit  46  to the side position adjustment mechanism  50  in the re-conveyance guide unit  3   c  may be provided in the downstream guide unit  3   b . In such a case, a sheet P having been positioned is ejected to the sheet output unit  4 . 
     In addition to the above, the above-described embodiments may be altered as below. In the first conveyor roller unit  47 , only one first driven roller  123  may be provided for one drive roller  121 , and the length of the first driven roller  123  may be changed at will. The magnitude relationship between the pressures from the driven rollers to the drive rollers may be different from those described above and may be suitably changed. The first driven rollers  123  and the driven roller  71  (first position adjustment roller) may be provided in an opposite manner with respect to the sheet P. When the sheet leading end reaches the position adjustment roller unit  60 , the sheet tail end may have already passed the pinching position of the second conveyor roller unit  46 . Instead of arranging the positions of the vertical portion  54  of the lower guide  52  and the position adjustment roller unit  60  to be changeable, detachable units each of which includes these members and the distance from the center line C 1  in each unit is different from the other units may be prepared, and the attached unit may be replaced with a suitable one in accordance with the size of a conveyed sheet. Alternatively, the position of the vertical portion  54  of the lower guide  52  may be changeable whereas the position of the position adjustment roller unit  60  may be fixed. The number and the positions of the second driven rollers may be changed. For example, as the second driven roller, a single driven roller in which the center thereof in the axial direction corresponds to the position of the center line C 1  may be used. The second driven rollers are preferably positioned in a symmetrical manner with respect to the center line C 1 . In the axial direction, the region in the second conveyor roller unit in which region the upstream driven rollers are provided may be shorter than the region of the first conveyor roller unit in which the first driven rollers are provided. In Third Embodiment, all of the five driven rollers may be swingable first driven rollers  323 . In Fifth Embodiment, the upper end of the coil spring  535  may not be fixed to the upper guide  51  and the lower end of the coil spring  535  may not be fixed to the shaft retaining member  532 . That is to say, when the attaching shaft  531  is rotated in one direction, the rotational force of returning the attaching shaft  531  to the original angular orientation by means of the circumferential elastic force of the coil spring  535  may not be applied to the attaching shaft  531 . The second support member may support the driven rollers (upstream driven rollers) of the second conveyor roller unit  46  to be swingable. The first support member may be arranged to be different from those described in the embodiments and modifications above, on condition that the first driven rollers are supported so that the rotational axial lines of the first driven rollers are swingable. 
     The conveyor of the present invention may be employed in an apparatus which is not a recording apparatus. When the conveyor is employed in the recording apparatus, the recording apparatus may be a line-type or a serial-type, and may be not only a printer but also a facsimile machine or a photocopier. As long as the recording apparatus performs image recording, the conveyor can be employed in any types of recording apparatuses such as laser-types and thermal types. The recording medium is not limited to the sheet P, and may be various types of recordable media. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.