Patent Publication Number: US-9421800-B2

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus that employs an image forming portion to form an image on a printing medium that is conveyed by a conveying portion. 
     2. Description of the Related Art 
     At present, image forming apparatuses that can form images on various types of printing media have been developed, and have been used in various different fields. These image forming apparatuses are also very frequently employed as, for example, coupon printers or small commodity label printers, for limited applications. Therefore, for installing the image forming apparatus, not only a usual desktop area, but also a shelf or another location tends to be selected in accordance with the use. 
     Since various applications and the installation locations can be selected, the situation where there is a restriction on the space for installing the image forming apparatus has also occurred. For example, in a printing apparatus wherein the cover portion needs to be pivoted upward to clear a paper jam, a space for allowing the upward movement of the lid must be obtained. Further, in a case wherein a location where the image forming apparatus must be moved when sheets are to be loaded is selected, there is a restriction that space for moving the image forming apparatus should be obtained near the installation location. 
     There is a proposal for reducing the installation space, and according to this proposal, one part of the conveying part that conveys a printing medium to a discharge part is to be extracted in one direction (e.g., in a direction in which the printing medium is to be discharged), and the space required to perform a paper jam clearing process and a sheet setting process is limited only to the front of the apparatus. In Japanese Patent Laid-Open NO. 2010-18406, for example, an apparatus where a sheet cassette is to be pulled out in a paper discharge direction is disclosed. 
     However, in the arrangement wherein the sheet cassette and the conveying part are to be extracted in one specific direction, the accuracy for positioning the sheet cassette and the conveying part in the conveying direction can be easily obtained, but the positioning accuracy in the vertical direction is difficult. When the satisfactory vertical positioning accuracy is not obtained, there is a possibility that sheet feeding, conveying and image forming may not be appropriately performed. Especially, the vertical positioning accuracy is reduced for the conveying part, the position relative to the image forming unit is deviated, and this deviation greatly affects the image quality. 
     SUMMARY OF THE INVENTION 
     While taking the above described shortcomings into account, one objective of the present invention is to provide an image forming apparatus wherein a medium moving portion that can be extracted from, and mounted to, the main body of the apparatus can be very accurately positioned. 
     In order to achieve this objective, the present invention includes the following arrangement. 
     Specifically, according to a first aspect of this invention, an image forming apparatus comprises: 
     a moving portion that moves a printing medium; 
     an image forming portion that ejects ink droplets to the printing medium that is moved by the moving portion, and forms an image thereon; 
     a supporting portion that supports the image forming portion, and supports the moving portion so as to be extracted from, or mounted to the supporting portion; and 
     an abutment mechanism that forces the moving portion, mounted to the supporting portion, to move toward the image forming portion and abut on a reference portion. 
     According to the present invention, for the image forming apparatus wherein the moving portion that moves the printing medium can be extracted from, or mounted to the image forming portion, the moving portion can be very accurately positioned relative to the image forming portion. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the external appearance of an image forming apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view of the image forming apparatus in  FIG. 1  from which a conveying unit is removed; 
         FIG. 3  is a cross-sectional view taken along line III-III in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along line IV-IV in  FIG. 1 ; 
         FIG. 5  is a perspective view of the positional relationship between a print head and the conveying unit during the printing operation performed for the first embodiment; 
         FIG. 6  is a perspective view of the state wherein a pinch rollers are released form a printing medium according to the first embodiment; 
         FIG. 7  is a perspective view of the state wherein a spur holder unit is removed according to the first embodiment; 
         FIG. 8  is a perspective view of the state wherein a spool is removed according to the first embodiment; 
         FIG. 9  is a perspective view of the state wherein a printing medium is being conveyed according to the first embodiment; 
         FIG. 10  is a perspective view of the positional relationship between discharge rollers and spurs when the spur holder unit is installed according to the first embodiment; 
         FIG. 11  is aside view in longitudinal cross section of the image forming apparatus according to the first embodiment wherein the conveying unit is mounted to the image forming apparatus main body; 
         FIG. 12  is an enlarged side view in longitudinal cross section of the structure of an abutment mechanism shown in  FIG. 11 ; 
         FIGS. 13A and 13B  are conceptual schematic diagrams showing the arrangement and the structure for the abutment mechanisms in  FIG. 11 ; 
         FIG. 14  is aside view in longitudinal cross section of the state wherein the print heads are closely covered with a recovery tub at a restoring position; 
         FIG. 15  is a schematic block diagram illustrating the arrangement of a control system for the first embodiment; 
         FIG. 16  is a flowchart showing the processing performed for the first embodiment, beginning with turning up an extraction lever until removing the conveying unit; 
         FIG. 17  is a flowchart showing the processing performed for the first embodiment when a jam of the printing medium occurs after print data has been received; 
         FIG. 18  is a flowchart showing the processing performed for the first embodiment when a medium exhaustion state occurs when print data has been received; 
         FIGS. 19A and 19B  are conceptual schematic diagrams showing the arrangement and the structure for abutment mechanisms according to a second embodiment of the present invention; 
         FIGS. 20A and 20B  are conceptual schematic diagrams showing the arrangement and the structure for abutment mechanisms according to a third embodiment of the present invention; and 
         FIGS. 21A and 21B  are conceptual schematic diagrams showing the arrangement and the structure for abutment mechanisms according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The embodiments of the present invention will now be specifically described while referring to drawings. The same reference numerals are employed for all of the drawings to denote the identical or corresponding portions. 
     (First Embodiment) 
       FIG. 1  is a perspective view of the external appearance of an image forming apparatus according to a first embodiment of the present invention. For an image forming apparatus  100  for the first embodiment, an image forming unit  102  to be described later and a conveying unit  103  that serves as a medium moving unit for moving a printing medium SH are arranged inside an image forming apparatus main body (hereinafter referred to as a main body)  101  that serves as an outer cover for the image forming apparatus  100 . The main body  101  of this embodiment includes a first housing  101 A where the image forming unit  102  is stored and a second housing  101 B where the conveying unit  103  is to be accepted. The image forming unit  102  is held and fixed at a specified location in the first housing  101 A of the main body  101 , while the conveying unit  103  is arranged to be extracted from, or inserted into the second housing  101 B of the main body  101 . The state in  FIG. 2  shows when the conveying unit  103  is removed from the main body  101  of the image forming apparatus  100 , and the conveying unit  103  thus extracted can be carried to an arbitrary place at a distance from the place where the main body  101  is installed. 
     As shown in  FIG. 2 , the conveying unit  103  includes: a feeding part  118  that feeds the printing medium SH to a conveying path R along a platen  406 ; a conveying part  119  that conveys, in a conveying direction A1, the printing medium SH that is fed to the conveying path R; and a discharge part  120  that discharges the printing medium SH to the outside of the conveying unit  103 . When the conveying unit  103  is to be removed from the main body  101 , first, a conveying lever  304  is pulled and turned down. Then, the conveying unit  103  is pulled forward (the conveying direction A1) by holding the conveying lever  304 , so that the conveying unit  103  is extracted from the main body  101  in the direction A1 in which the printing medium SH is to be conveyed. In  FIG. 2 , A represents a direction in which the conveying unit  103  can be moved relative to the main body  101 . The conveying unit  103  can be completely separated from the main body  101 . Therefore, when the jam of the printing medium SH occurs, a user can obtain a large space area to clear the jam. 
     When the conveying unit  103  has been inserted into the main body  101  as shown in  FIG. 1 , the conveying unit  103  is connected to a main board  201  (see  FIG. 4 ) by a drawer connector  117  (see  FIG. 3 ), and electric power required for driving the individual sections, such as a conveying motor  115  (see  FIG. 3 ) and a roll drive motor  116  (also see  FIG. 3 ), is supplied by the main board  201 . When the conveying unit  103  is to be extracted from the main body  101 , the conveying lever  304  is pulled in the above described manner, and a conveyance ON/OFF detecting switch  121  (see  FIG. 3 ) internally provided for the conveying lever  304  cuts off the supply of power from the power source to the conveying unit  103 . As a result, a phenomenon (hot swapping) that the conveying unit  103  is removed by a user while the power is running through the conveying unit  103  can be prevented. The discharge part  120  includes a discharge port and a cutter unit that cuts off the portion of the printing medium SH that is discharged from the discharge port. 
     Next, the internal arrangement of the image forming apparatus  100  of this embodiment will be described while referring to  FIGS. 3 and 4 .  FIG. 3  is a cross-sectional view taken along line III-III in  FIG. 1 , and  FIG. 4  is a cross-sectional view taken along line IV-IV in  FIG. 1 . The image forming apparatus  100  employed for this embodiment is an ink jet printing apparatus that ejects ink from ink jet print heads to form an image. Further, in the specification of this invention, the side of the main body  101  where the conveying lever  304  in  FIG. 1  and the discharge port are provided serves as a manipulation side that is to be operated by a user (the front side of the image forming apparatus  100 ). Further, a left side L of the image forming apparatus  100  represents the rear side shown in  FIGS. 3 and 4 , and a right side R represents the front side in  FIGS. 3 and 4 . 
     For the image forming apparatus  100  of this embodiment, long paper provided in a rolled form is employed as the printing medium SH; however, Z-fold paper or fanfold paper can also be employed as a printing medium SH, or cut sheets may also be employed. The available sheet size ranges from one inch wide to 63 mm wide, and various types of paper, such as glossy paper, matte paper and synthetic paper, can also be employed. For setting the printing medium SH, the left side L (see  FIG. 1 ) with respect to the discharge side (operation side) of the image forming apparatus  100  is employed as a reference. It should be noted that the printing medium SH employed for this embodiment includes continuous belt-shaped backing paper and a plurality of labels that are adhered to one side of the backing paper at predetermined intervals in the longitudinal direction. 
     As described above, the image forming apparatus  100  includes the image forming unit  102  and the conveying unit  103 , and also includes the main board  201  located on the left side L of the image forming unit  102  and a maintenance cartridge  202  provided below the image forming unit  102 . The image forming unit  102  includes ink tanks  104  to  107 , print heads  108  to  111 , a recovery tub  112  that serves as a cap for covering the ejection ports of the print heads  108  to  111 , and a pump unit  113 . 
     Of the four ink tanks, the ink tank  104  is used to store yellow (Y) ink, the ink tank  105  is used to store magenta (M) ink, the ink tank  106  is used to store cyan (C) ink, and the ink tank  107  is used to store black (BK) ink. The individual ink tanks  104  to  107  are correlated respectively with the print heads  108  to  111 . Specifically, ink in the ink tank  104  is supplied to the print head  108 , ink in the ink tank  105  is supplied to the print head  109 , ink in the ink tank  106  is supplied to the print head  110  and the ink in the ink tank  107  is supplied to the print head  111 . In the following description, the ink tanks  104  to  107  are collectively referred to as ink tanks T and the print heads  108  to  111  are collectively referred to as print heads H, unless the individual ink tanks and the print heads need be particularly identified. 
     The individual print heads H are ink jet print heads, each of which prints an image on the printing medium SH by ejecting ink based on image data. For each print head H, an ejection port array (nozzle array) that is a predetermined arrangement of a plurality of ejection ports is formed on the ejection port face, opposite the printing medium SH. The ejection port array is extended in a direction across the conveying direction A 1  (in this embodiment, a direction perpendicular to the conveying direction A 1 ). Ejection energy generation elements are arranged along liquid paths that communicate with the individual ejection ports of the ejection port array, and when the ejection energy generation elements are selectively driven based on image data to eject ink droplets, a desired image is formed. The ejection energy generation elements can be, for example, electro-thermal conversion elements (heaters) or electro-mechanical conversion elements (piezoelectric elements). 
     Further, the print head H in  FIG. 3  forms a so-called line head where the ejection ports are arranged in a range equivalent to, or beyond the maximum width of the printing medium to be employed (the “width of the printing medium” is the length of the printing medium in a direction that intersects the conveying direction A 1 ). The image forming apparatus  100  of this embodiment is an ink jet printing apparatus of full-line printing type that employs the line head and forms an image for one line on a printing medium that is sequentially conveyed. It should be noted, however, that the present invention can also be applied for a so-called serial ink jet printing apparatus that performs printing by moving a print head in the direction that intersects the direction in which a printing medium is to be conveyed. 
     The print head H is to be moved upward and downward (a direction from the conveying path R to be described later toward the print head H, and a direction from the print head H to the conveying path R) by a head moving mechanism that is driven by the drive force of a head elevating motor  1210 . For forming an image on the printing medium H, the head elevating motor  1210  is driven to move the print head H down from an elevated position P 1  in  FIG. 3  to an image formation position P 3  (see  FIG. 5 ) that is appropriate for image forming for the printing medium SH and that is closer to the conveying path R than to the P 1 , and the print head H thereafter ejects ink droplets from the ejection ports to form an image. When image forming has been performed, the print head H is elevated to the elevated position P 1 . Thereafter, the recovery tub  112  is horizontally moved to a position below the print head H, and the print head H is moved down to the recovery tub  112 . As a result, the ejection port face of the print head H closely contacts the recovery tub  112  and is blocked from the external air, and the ejection ports and the ejection port face are protected. 
     The pump unit  113  that performs a suction operation is connected to the recovery tub  112 . Occasionally, tiny dust, for example, is attached to the ejection ports of the print head H, and causes printing defects. In this case, the pump unit  113  performs suction by bringing the ejection port face of the print head H in close contact with the recovery tub  112 , and as a result, tiny dust attached to the ejection ports can be removed. When the pump unit  113  performs the suction operation for the print head H in this manner, not only tiny dust attached to the ejection ports, but also ink remaining in the print head H is drawn by suction. The ink thus drawn by suction is transmitted through the recovery tub  112  to the maintenance cartridge  202 , and is absorbed by and stored in an absorber  203  of the maintenance cartridge  202 . A conductivity sensor for detecting the amount of absorbed waste ink is provided for the maintenance cartridge  202 . 
     The conveying unit  103  includes the feeding part  118 , the conveying part  119  and the discharge part  120 . The conveying unit  103  also includes the conveying motor  115 , the roll drive motor  116 , the cutter unit  114 , and a printing medium detection unit that detects the printing medium SH. The printing medium detection unit includes an upstream medium detector, which is located at a position opposite a light transmission window  702 U (see  FIG. 7 ) arranged upstream of the printing medium conveying path R, and a downstream medium detector, located at a position opposite a light transmission window  702 D (see  FIG. 7 ) arranged downstream of the conveying path R. The upstream medium detector includes a thru-beam sensor  1221  and a reflective sensor  1222  (see  FIG. 12 ) located at positions opposite the light transmission window  702 U. The downstream medium detector includes a reflective sensor  1224  located at the position opposite the light transmission window  702 D. The thru-beam sensor  1221  includes a projector and a photodetector that are arranged opposite to each other with the light transmission window  702 U in between, and light emitted by the projector is transmitted through the backing paper portion of the printing medium SH, and is received by the photodetector, but the light is blocked on labels on the backing paper, and is not received by the photodetector. Therefore, in a case wherein a signal transmitted by the photodetector is changed at a predetermined interval, it can be ascertained that the printing medium SH is being moved along the conveying path R. Further, the reflective sensor  1222  includes a projector and a photodetector provided opposite the light transmission window  702 U, and light emitted by the projector is reflected at the backing paper portion of the printing medium SH, and the reflected light is received by the photodetector. Therefore, based on the output of the photodetector of the reflective sensor  1222 , whether the printing medium SH is located above the light transmission window  702 U or not can be determined. 
     As shown in  FIG. 8 , the feeding part  118  includes a spool  801  that serves as a medium supply source, in which the printing medium SH in a continuous sheet form is rolled, and a spool holder  802  that rotatably supports the spool  801 . 
     Furthermore, as shown in  FIG. 6 , the conveying part  119  includes conveying rollers  602 , pinch rollers  601 , and a platen  406 , which is provided on the upper face of a conveying frame  407  that is a support structure of the conveying unit  103 . 
     The discharge part  120  includes discharge rollers  1001  shown in  FIG. 10  and a spur holder unit  701  (see  FIG. 7 ) that holds spurs  1002  that can be pressed against the discharge rollers  1001 . The spur holder unit  701  has a structure wherein a pair of spurs  1002  and the rotary plate of an encoder are securely fitted to a rotary shaft that is rotatably supported to a shaft support portion. The spur holder unit  701  is detachably attached relative to the conveying frame  407 . The conveying path R is formed for the conveying unit  103 , and is extended from the conveying rollers  602  of the conveying part  119  across the platen  406  to the discharge rollers  1001  of the discharge part  120 . 
     The printing medium SH is sandwiched between the pinch rollers  601  of the pinch roller unit  605  and the conveying rollers  602 , and is conveyed, in accordance with rotations of the conveying rollers  601 , from the feeding part  118  along the conveying path R of the conveying unit  103 . That is, the conveying unit  103  includes two conveying mechanisms: the upstream conveying mechanism that has the conveying rollers  602  to perform feeding and conveying of the printing medium SH, and the downstream conveying mechanism that has the discharge rollers  1002  to perform discharging of the printing medium SH. The conveying rollers  602  and the discharge rollers  1001  interact with each other to rotate and convey the printing medium SH. When the printing medium SH is conveyed by the conveying rollers  602  and the pinch rollers  601 , the leading edge of the printing medium SH is detected by the upstream medium detector, and controls the start to drive the print head H based on the detection position as a reference, and then, the print head H forms an image at the appropriate location of the printing medium H. When an image has been formed on the printing medium SH, the printing medium SH is held by the discharge rollers  1001  and the spurs  1002  of the spur holder unit  701 , and is discharged outside of the conveying unit  103  in accordance with the rotations of the discharge rollers  1001 . 
     The state shown in  FIG. 9  is the state wherein the printing medium SH is conveyed in the conveying direction A 1  along the conveying path R by being sandwiched between the conveying rollers  602  and the pinch rollers  601  of the pinch roller unit  605  in the above described manner. In a case wherein a paper jam occurs at the feeding part  118  of the conveying unit  103  during the conveying operation, the user pulls the conveying unit  103  out of the main body  101  in the conveying direction A 1 , as described above (see  FIG. 2 ). Then, as shown in FIG.  6 , a pinch roller base  604  of the pinch roller unit  605  is pivoted upward at a rotation center  604   a  to a retraction position. When the pinch roller base  604  is pivoted, the pinch rollers  601  are moved to a higher position, and are separated from the conveying rollers  602 . As a result, since the printing medium SH sandwiched between the roller  602  and the pinch roller  601  is released, the printing medium SH jammed inside the feeding part  118 , or the spool  801 , can be removed, and the paper jam can be cleared. Likewise, in a case wherein a paper jam has occurred in the conveying part  119  of the conveying unit  103 , the conveying unit  103  is also pulled from the main body  101  in the conveying direction A 1  (indicated by the arrow), and the printing medium SH is released, as needed, by moving the pinch rollers  601  upward to clear the paper jam. 
       FIG. 10  is a perspective view of the positional relationship between the discharge rollers  1001  and the spurs  1002  of the discharge part  120  when the spur holder unit  701  is mounted to the conveying unit  103 . During the conveying operation, the discharge rollers  1001  are rotated by interlocking with the conveying rollers  602 , while the rotation of the pinch rollers  601  is performed, following the rotation of the discharge rollers  1001 . In a case wherein the conveying of the printing medium SH is correctly performed, the printing medium SH conveyed along the conveying path R by being sandwiched between the conveying rollers  602  and the pinch rollers  601  is discharged outside the conveying unit  103  by the discharge rollers  1001  and the spurs  1002  that are rotated by interlocking with the conveying rollers  602 . 
     Furthermore, when a paper jam has occurred in the discharge part  120 , a pulse signal is generated by an encoder  1225 , which includes a rotatory plate that is rotated together with the spurs  1002  fitted to the rotary shaft of the spur holder unit  701 , and a projector/photodetector that detects the slit formed in the rotary plate. This pulse signal is transmitted to a CPU  1202 , which then employs the count value of the pulse signals and the output of the reflective sensor  1224  to determine whether the spurs  1002  are appropriately rotated, i.e., whether the printing medium SH is properly conveyed by the discharge part  120  (i.e., whether a paper jam has occurred). 
     In a case wherein it is determined that a paper jam has occurred in the discharge part  120  of the conveying unit  103 , the conveying unit  103  is pulled from the main body  101  in the conveying direction A 1 , as shown in  FIG. 2 , and the spur holder unit  701  is removed from the conveying unit  103 , as shown in  FIG. 7 . As a result, the portion around the conveying path R is exposed, and a paper jam clearing process can be easily performed. 
       FIG. 8  is a perspective view of the state wherein the replacement or replenishment of the printing medium SH is performed at the feeding part  118  of the conveying unit  103 . When exhaustion of the printing medium SH in the feeding part  118  occurs as the result of printing, or replacement of the printing medium SH is required, first, the conveying unit  103  is pulled out of the main body  101  in the conveying direction A1 (see  FIG. 2 ). Thereafter, as shown in  FIG. 6 , the pinch roller base  604  of the pinch roller unit  605  is pivoted upward at the rotation center  604   a . As a result, the spool  801  to which a roll of the printing medium SH is to be fitted can be removed from the spool holder  802  of the main body  101 , and the replacement or replenishment of the printing medium SH is enabled. 
       FIG. 11  is a cross-sectional view of the state wherein the conveying unit  103  is arranged inside the second housing  101 B of the main body  101 . A plurality of protruded portions  1104  (conveying unit side protrusions) are formed on the upper side of the conveying unit  103  along the conveying path R, and are employed to perform vertical positioning for the conveying unit  103  with respect to the print head H when the conveying unit  103  is inserted into the main body  101 . Further, a plurality of abutment mechanisms  200  are formed on the lower side of the conveying unit  103 , and are employed to force the protruded portions  1104  to abut upon the lower face of a reference plate  1103  of the main body  101  when the conveying unit  103  is mounted to the main body  101 . 
       FIG. 12  is an enlarged side view in cross section of the structure of the abutment mechanism  200  in  FIG. 11  for the first embodiment. The abutment mechanism  200  includes a sliding member (a movable contact member)  201  made of, for example, a resin, an elastic member  202  that exerts an elastic force to push the sliding member  201  in a direction Z 1 , and a guide member  203  that guides the sliding member  201  in a direction Z (Z 1  or Z 2 ). The guide member  203  is provided for the conveying frame  407  of the conveying unit  103 . In this embodiment, the direction Z corresponds to a direction that intersects the printing medium passage face of the conveying path R (in  FIG. 11 , the vertical direction that intersects the printing medium passage face), and the direction Z 1  represents the downward direction (a direction from the print head H to the conveying path R), and the direction Z 2  represents the upward direction (a direction from the conveying path R to the print head H). 
       FIGS. 13A and 13B  are conceptual schematic diagrams illustrating the arrangement and the structure for the abutment mechanisms  200  in this embodiment.  FIG. 13A  is a schematic top view of the image forming apparatus  100  (viewed in the direction Z 1 ), and  FIG. 13B  is a schematic diagram showing the image forming apparatus  100  viewed from the right side R. In this embodiment, the abutment mechanisms  200  are arranged at a plurality of upstream and downstream locations in the conveying direction (direction A 1 ), and referring to  FIG. 13A , the total four abutment mechanisms  200 , two each for the upstream and downstream, are provided. In  FIG. 13A , abutment mechanisms  200 U 1  and  200 U 2  are those located upstream in the conveying direction, while abutment mechanisms  200 D 1  and  200 D 2  are those located downstream. In this embodiment, the conveying unit  103  is to be inserted into the second housing part  101 B in the direction (direction A 2 ) opposite, in plan view, to the direction (direction A 1 ) in which the printing medium SH is to be conveyed. Therefore, the upstream position or the upstream side in the conveying direction corresponds to the rear position or rear side in the direction in which the conveying unit  103  is to be inserted (hereinafter, simply referred to as an insertion direction), and the downstream position or the downstream side in the conveying direction corresponds to the front position or the front side in the insertion direction. Therefore, the abutment mechanisms  200 U 1  and  20 U 2  can be also referred to as abutment mechanisms located at the rear in the insertion direction, while the abutment mechanisms  200 D 1  and  200 D 2  can be referred to as abutment mechanisms located in front in the insertion direction. 
     Further, the two abutment mechanisms  200 U 1  and  200 D 1  are arranged on the same linear line that is parallel to the insertion direction (direction A2). Similarly, the other two abutment mechanism  200 U 2  and  200 D 2  are arranged on the same linear line that is parallel to the insertion direction (conveying direction). The distance between the abutment mechanisms  200 U 1  and  200 U 2  is equal to the distance between the abutment mechanisms  200 D 1  and  200 D 2 . Furthermore, the upstream abutment mechanisms  200 U 1  and  200 U 2  are arranged by being shifted from the downstream abutment mechanisms  200 D 1  and  200 D 2  in the direction Z 2  (upper direction). 
     The lower face of the reference plate  1103  described above serves as a reference position in the direction that intersects the printing medium passage face of the conveying path R (in  FIG. 11 , the vertical direction (direction Z) that intersects the printing medium passage face). That is, the Z-directional position of the ejection port face of the print head H that is held in the first housing  101 A and the Z-directional position of the conveying unit  103  for the printing operation are determined by employing, as a reference, the lower face of the reference plate  1103  that serves as a reference member. 
     Two rails (support members)  204  projected in the direction Z 2  (upper direction) and extended in the insertion direction (direction A 2 ) are arranged at the bottom of the second housing  101 B where the conveying unit  103  can be accepted. As shown in  FIG. 11 , the two rails  204  each includes a slope face  204 A, a raised portion  204 B, a recessed portion  204 C, a slop face  204 D and a raised portion  204 E that are sequentially formed in the insertion direction (direction A 2 ) that is opposite the printing medium conveying direction (direction A 1 ). In a case wherein the conveying unit  103  is to be mounted to the second housing  101 B, the conveying unit  103  is inserted in a direction B by guiding the sliding member  201  along the two rails  204 . Then, the sliding members  201  are moved in the direction Z 2  along the slope faces  204 A and  204 B of the rails  204 , and finally, the upstream abutment mechanisms  200 U 1  and U 2  reach the raised portions  204 E of the rails  204 , while the downstream abutment mechanisms  200 D 1  and  200 D 2  are moved from the raised portions  204 B and reach the recessed portions  204 C on the downstream side. At this time, since the elastic members  202  of the individual abutment mechanisms  200  that are compressed push the conveying unit  103  in the direction Z 2  (upper direction), the raised portions  1104  of the conveying unit  103  are brought in contact with the lower face of the reference plate  1103 . As a result, the distance between the surface of the platen  406 , serving as the medium passage face of the conveying unit  103 , and the reference face is obtained as a distance required for the printing operation, and mounting of the conveying unit  103  to the main body  101  has been completed. In the state wherein the conveying unit  103  has been mounted, when the print head H is lowered to a printing ready position (image forming position), the distance between the ejection port face of the print head H and the platen  406  of the conveying unit  103  is set to the distance at which appropriate printing for the printing medium can be performed. 
     Furthermore, when the conveying unit  103  has been mounted to the main body  101 , the downstream abutment mechanisms  200 D 1  and  200 D 2  are in the state wherein the outer middle portions of the sliding members  201  are caught in contact with upstream ends  204 B 1  of the raised portions (projected portions)  204 B. Therefore, so long as a force of a predetermined level or higher is not applied to the conveying unit  103  in the conveying direction (direction A 1 ), movement of the conveying unit  103  in the conveying direction can be prevented. For example, even when the main body  101  is tilted after the conveying unit  103  has been mounted, and a gravitational force is applied to the conveying unit  103  in a direction to slip off from the main body  101 , the conveying unit  103  can be held at the mounting position by contacting the raised portions  204 B. In other words, sufficiently strong engagement force against the weight of the conveying part  103  is to be exerted between the conveying unit  103  and the upstream ends  204 B 1  of the raised portions  204 B. 
     In the standby state wherein the printing operation is not performed, the print head H closely contacts the recovery tub  112  at a standby position higher than the printing ready position in  FIG. 5 , and the ejection port face is protected at this position (see  FIG. 14 ). Therefore, in a case wherein the print head H is to be moved from the standby position to the printing ready position, the print head H is first moved upward from the standby position in  FIG. 14 , and thereafter, the recovery tub  112  is moved from the cap position immediately below the ejection port face in the lateral direction (direction opposite the conveying direction A 1  in  FIG. 3 ) to the retraction position, at which the recovery tub  112  does not bother the movement of the print head H to the printing ready position. In this state, the print head H is moved to the printing ready position. 
     Further, in the state wherein the print head H is at the printing ready position, the platen  406  of the conveying unit  103  is near the ejection port face of the print head H. Therefore, when the conveying unit  103  is to be removed in this state, the upper portion of the conveying unit  103  might interfere with the ejection port face of the print head H, and damage the ejection port face. In this embodiment, when the print head H is at the printing ready position, the print head H is set to the location that interferes with the area where the conveying unit  103  passes at the time of detachment relative to the second housing  101 B. Therefore, in a case wherein removal of the conveying unit  103  is performed for this embodiment, the print head H is moved, prior to the removal process, to the retraction position, such as the elevated position in  FIG. 3  or the standby position in  FIG. 14 , at which insertion or drawing of the conveying unit  103  relative to the second housing  103  is not bothered. This control operation is performed by a control system that will be described below. In this embodiment, the recovery tub  112  is provided not to interrupt the detachment of the conveying unit  103  relative to the second housing  101 B, regardless of whether the recovery tub  112  is located at the cap position, the retraction position, or a position between the cap position and the retraction position. That is, the recovery tub  112  is arranged at a location at which the recovery tub  112  does not interfere with the area where the conveying unit  103  passes (the recovery tub  112  is located in the direction Z2 for the conveying unit  103 ). 
       FIG. 15  is a schematic block diagram illustrating the arrangement of a control system provided for the image forming apparatus  100  of this embodiment. In  FIG. 15 , print data and commands are transmitted by a host PC  1213  via an interface controller  1201 , and are received by the CPU  1202 . The CPU  1202  is an operation processing part that controls the operations of the entire apparatus, such as reception of print data for the image forming apparatus  100  and control for the feeding part  118 , the conveying part  1129  and the discharge part  120 . The CPU  1202  analyzes a received command, and draws, in an image memory  1205 , a bit map of image data for the individual color components of the print data. For performing the pre-processing for printing, a capping motor  1211  that operates the recovery tub  112  and the head elevating motor  1210  that operates the print head H are driven via an output port  1208  and a motor driver  1209 , and these motors separate the print heads  108  to  111  from the recovery tub  112 , and move the print heads  108  to  111  to the printing ready position. 
     Sequentially, the roll drive motor  116  that winds the printing medium SH and the conveying motor  115  that conveys the printing medium SH are driven through the output port  1208  and the motor driver  1209 , and these motors convey the printing medium SH to the printing ready position. The upstream printing medium detector detects the leading edge of the printing medium SH to determine a timing (printing timing) for start of ejection of ink to the printing medium SH that is conveyed at a predetermined speed. Thereafter, in synchronization with conveying of the printing medium SH, the CPU  1202  reads, in order, print data of corresponding colors from the image memory  1205 , and transmits the print data to the print heads  111 ,  110 ,  109  and  108  via a print head control circuit  1203 . 
     The operation of the CPU  1202  is performed based on process programs stored in a program ROM  1204 . The process programs and tables corresponding to various control operations are stored in the program ROM  1204 . Further, a work RAM  1206  is employed as a work memory. In the cleaning operation or the recovery operation of the print heads  111 K,  110 C,  109 M and  108 Y, the CPU  1202  drives a pump motor  1212  via the output port  1208  and the motor driver  1209  to exercise control, such as application of pressure to ink and performance of suction. 
     The CPU  1202  also receives detection signals from the thru-beam sensor  1221 , the reflective sensor  1222  and the encoder  1223 , all of which are included in the upstream medium detector, and receives detection signals from the reflective sensor  1224  and the encoder  1225 , both of which are included in the downstream medium detector. Furthermore, a conveying lever switch  1226  is connected to the CPU  1202 , and outputs an ON/OFF signal in accordance with the operating state of the conveying lever  304  that is provided on the front face of the conveying unit  103 . Based on the signals received from the sensors and the switch, CPU  1202  controls the individual motors described above, the print heads H and a display device  1232 . The display device  1232  is driven by the CPU  1202  through the output port  1208  and a drive circuit  1231 , and displays various statuses, such as the occurrence of a paper jam in the main body  101  and the exhaustion of sheets in the feeding part  118 . The upstream medium detector, the downstream medium detector and the CPU  1202  constitute conveyance defect detection unit that detects a paper jam and the absence of sheets, described above. 
     The control operation performed by the control system will now be described based on flowcharts in  FIGS. 16 to 18 . The processing in the flowcharts in  FIGS. 16 to 18  is performed by the CPU  1202 . 
       FIG. 16  is a flowchart showing the control operation performed when the conveying lever  304  is pulled up. When the conveying lever  304  of the conveying unit  103  is pulled up, the conveying lever switch  1226  that is set ON or OFF by interlocking with the conveying lever  304  is set to the ON state (S 001 ), and the CPU  1202  cuts off the supply of power to the conveying unit  103  (S 002 ). Through this control operation, the occurrence of hot swapping can be prevented when the conveying unit  103  is extracted. Following the operation at S 002 , the CPU  1202  moves the print head H to the retraction position (either the elevated position or the standby position) (S 003 ), and allows the conveying unit  103  to be extracted while preventing the conveying unit  103  from contacting the print head H. At this time, the CPU  1202  displays, on the display device  1232 , a message that removing of the conveying unit  103  is ready (S 004 ). In a case wherein the print head H is already located at the retraction position after the process at S 002  has been performed, program control skips step S 003  and performs the process at step S 004 . Further, at step S 003 , the print head H may be moved to the standby position, and the ejection ports of the print head H may be covered with the recovery tub  112 , or the print head H may be moved to the elevated position. 
       FIG. 17  is a flowchart showing the control operation performed when a jam of the printing medium SH is detected based on the outputs of the upstream medium detectors ( 1221  and  1222 ) and the encoder  1223  and the output of the reflective sensor  1224  that serves as the downstream medium detector. When the print data is transmitted by the host PC  1213  through the interface controller  1202 , and is received by the CPU  1202  (S 011 ), the CPU  1202  drives the conveying drive motor  115  (S 012 ) to begin the feeding operation and the conveying operation for the printing medium SH. Thereafter, based on the signals output by the thru-beam sensor  1221  and the reflective sensor  1222  and the pulse signal output by the encoder  1223 , the CPU  1202  determines whether the printing medium SH has been property conveyed and has reached the upstream light transmission window  702 U. 
     Specifically, in a case wherein the pulse signal is received from the encoder  1223  and the printing medium SH is detected by the reflective sensor  1222 , but the signal transmitted by the thru-beam sensor  1221  does not continuously change, the CPU  1202  determines that a paper jam has occurred in the upstream conveying mechanism (S 013 ). At this time, in a case wherein the leading edge of the printing medium SH is not detected by the reflective sensor  1221 , the CPU  1202  determines that a paper jam has occurred in the upstream conveying mechanism. Furthermore, in a case wherein a pulse signal is not output by the encoder  1223  after the conveying operation has been initiated, or in a case wherein the number of pulses that corresponds to the time elapsed from the start of the conveying operation is not obtained, the CPU  1202  also determines that a paper jam has occurred. 
     When it is ascertained at step S 013  that a paper jam has occurred, at S 014  driving of the conveying drive motor  115  is halted, and an error message is displayed on the display device  1232 . Thereafter, the CPU  1202  moves the print head H to the retraction position, such as the elevated position in  FIG. 3 , or the standby position in  FIG. 14  (S 018 ). Following the process at S 018 , the CPU  1202  examines the signal of the conveying lever switch  1226  to determine whether the conveying lever  304  has been pulled up (S 019 ). When the conveying lever  304  has been pulled up, supply of electric power to the conveying unit  103  is halted (S 020 ). As a result, the conveying unit  103  is ready for being extracted, and a message for this effect is displayed on the display device  1232  (S 021 ). When it is ascertained at step S 016  that a paper jam does not occur, at S 022  a check is performed to determine whether a printing halt instruction is received. When a printing halt instruction is received, the printing operation is stopped, and thereafter, the print head H is moved either to the standby position, at which the ejection ports of the print head H are covered with the recovery tub  112 , or to the elevated position (S 023 ), and the processing is terminated. 
     In a case wherein it is ascertained at decision step S 013  that a paper jam does not occur in the upstream conveying mechanism, the CPU  1202  drives the conveying drive motor  115 , and also drives the individual print heads H based on the print data to begin the printing operation (S 015 ). Further, based on the pulse signals received from the reflective sensor  1224  and the encoder  1225  that constitute the downstream medium detector, the CPU  1202  determines whether a paper jam has occurred in the downstream conveying mechanism (S 016 ). Specifically, when the printing operation is begun, CPU  1202  starts counting the pulse signals output by the encoder  1225 . In a case wherein the reflective sensor  1224  does not detect the printing medium SH although the number of pulses counted has reached a value that should be obtained before the leading edge of the printing medium SH arrives at the downstream light transmission window  702 D, it is determined that a paper jam has occurred (YES at S 016 ). Furthermore, in a case wherein a pulse signal is not output by the encoder  1225  after the printing operation has begun, or a case wherein the number of pulse signals that corresponds to predetermined elapsed time is not obtained although the predetermined time has been elapsed from the start of the printing operation, it is also determined that a paper jam has occurred (YES at S 016 ). 
     When it is ascertained at step S 013  that a paper jam has occurred, driving of the conveying drive motor  115  is halted, and an error message is displayed on the display device  1232 . Following this, the print head H is moved to the elevated position, or the standby position (S 018 ), and when the conveying lever  304  is thereafter pulled up (YES at S 019 ), the supply of power to the conveying unit  103  is cut off (S 020 ), and a message indicating the effect that the conveying unit  103  is ready for being extracted is displayed on the display device  1232  (S 021 ). 
       FIG. 18  is a flowchart showing the control operation performed for determining whether the rolled printing medium SH in the feeding part  118  has been exhausted, and therefore, an error indicating exhaustion of the printing medium SH is detected, and the control operation performed when an error indicating exhaustion of the printing medium SH has occurred. In  FIG. 18 , the same step numbers are provided for the same processes as those in  FIG. 17 . Upon receiving print data transmitted by the host PC  1213  (S 111 ), the CPU  1202  drives the conveying drive motor  115  (S 112 ) to initiate the feeding operation and the conveying operation for the printing medium SH. Then, based on the signal output by the reflective sensor  1222  and the output of the encoder  1223 , the CPU  1202  determines whether the roll of the printing medium SH at the spool of the feeding part  118  is exhausted (S 113 ). Specifically, the CPU  1202  counts the number of pulse signals output by the encoder  1225  that begins the conveying operation. When the number of pulse signals thus counted has reached a count value that should be obtained before the leading edge of the printing medium SH arrives at the upstream light transmission window  702 U, the CPU  1202  determines whether the printing medium SH is detected by the reflective sensor  1222  (S 113 ). When the leading edge of the printing medium SH is not detected by the reflective sensor  1222 , the CPU  1202  determines that the printing medium SH in the feeding part  118  is exhausted. 
     In a case wherein it is ascertained that the rolled printing medium SH in the feeding part  118  is exhausted, at S 014 , the driving of the conveying drive motor  115  is halted, and also an error message is displayed on the display device  1232 . Thereafter, program control moves to step S 018  to perform the same processing as the processing at S 018  to S 021  in  FIG. 17  performed for clearing a paper jam. When exhaustion of the printing medium SH is not detected at S 113 , the processing at S 015  to S 023  in  FIG. 18  that correspond to that at S 015  to S 023  in  FIG. 17  is performed. 
     As described above, according to the image forming apparatus  100  of this embodiment, when the conveying unit  103  is removed from the main body  101  of the image forming apparatus  100 , the conveying unit  103  is physically and electrically, completely separated from the main body  101  and the image forming unit  102 . Therefore, in the paper jam clearing operation, for example, the conveying unit  103  thus extracted can be placed in a large work area to fix a paper jam, or to replace the printing medium or other units, and the operation can be efficiently performed. Furthermore, in this embodiment, since the direction in which the conveying unit  103  is to be pulled is designated as the same direction as the conveying direction for the printing medium, the space in the widthwise direction (direction W) need not be obtained for removing the conveying unit, and the installation area to the front can be reduced. It should be noted, however, that the present invention is not limited to this embodiment, and the direction in which the conveying unit is to be pulled out can also be designated as a direction (e.g., the lateral direction) that intersects the conveying direction. 
     Moreover, according to a conventional image forming apparatus, a feeding part that feeds a printing medium, a conveying part that conveys the printing medium that is fed, and a discharge part that discharges the conveyed printing medium are provided as individual, different units, i.e., respectively as a feeding unit, a conveying unit and a discharge unit. As a result, the number of units included in the image forming apparatus is increased, and accordingly, the number of constituents is also increased. By contrast, for the image forming apparatus of the embodiment of this invention, the feeding part  118 , the conveying part  119  and the discharge part  120  are integrally formed together to provide a single unit referred to as a conveying unit. With this arrangement, the individual parts can be formed by employing a member used in common, and the number of required parts can be reduced. Further, since the interlocking mechanism for the individual members can be simplified, the apparatus manufacturing cost can be greatly reduced, compared with the cost required for the conventional apparatus. 
     (Second Embodiment) 
     A second embodiment of the present invention will now be described based on  FIGS. 19A and 19B . The same reference numerals as used for the first embodiment are employed to denote identical or corresponding components. 
     As shown in  FIG. 19 , for an image forming apparatus for the second embodiment, upstream abutment mechanisms  200 U 1  and  200 U 2  and downstream abutment mechanisms  200 D 1  and  200 D 2  are arranged at the same positions in a direction Z (at the same height). Further, two rails  204  are arranged at the bottom of a second housing  101 B where a conveying unit  103  is to be accepted, and each include a slope face  204 A, a raised portion  204 B and a recessed portion  204 C. The depths (heights) of the recessed portions  204 C in the direction Z are uniform. 
     When the conveying unit  103  is to be inserted into the second housing  101 B, the upstream abutment mechanisms  200 U 1  and  200 U 2  and the downstream abutment mechanisms  200 D 1  and  200 D 2  sequentially slide up along the slope faces  204 A of the rails  204 , pass the raised portions  204 B and reach the recessed portions  204 C. In the state wherein the conveying unit  103  is completely accepted to the second housing  101 B, all of the abutment mechanisms  200  are held at the same height in contact with the recessed portions  204 C. As a result, the elastic members of the individual abutment mechanisms  200  are in the same compressed state, and uniformly push up the conveying unit  103 , and therefore, protruded portions  1104  formed on the upper face of the conveying unit  103  are brought in contact with the lower face of a reference plate  1103 . Thus, an appropriate distance can be maintained between the ejection port face of a print head H and a platen  406  included in the conveying unit  103 . 
     As descried above, according to the second embodiment, compared with the first embodiment, the shape of the rail is simplified, and the abutment mechanisms can be arranged at the same positions in the direction Z. Therefore, as additional effects, the arrangement can be simplified, and design layout and manufacturing can be easily performed. 
     (Third Embodiment) 
     A third embodiment of the present invention will now be described based on  FIGS. 20A and 20B . The same reference numerals used for the first embodiments are also employed to denote identical or corresponding components. 
     In the first and second embodiments, the abutment mechanisms  200 U 1  and  200 D 1  are arranged along the same linear line that is parallel to the insertion direction (direction A2), and the abutment mechanisms  200 U 2  and  200 D 2  are arranged another same linear line that is parallel to the insertion direction. That is, the distance between the abutment mechanisms  200 U 1  and  200 U 2  is equal to the distance between the abutment mechanisms  200 D 1  and  200 D 2 . By contrast, according to the third embodiment, abutment mechanisms  200 U 1  and  200 D 1  and abutment mechanisms  200 U 2  and  200 D 2  are arranged so as not to be located on the same linear lines that are parallel to the insertion direction. With this arrangement, the distance between the upstream abutment mechanisms  200 U 1  and  200 U 2  is shorter than the distance between the downstream abutment mechanisms  200 D 1  and  200 D 2 . As a result, the upstream abutment mechanisms  200 U 1  and  200 U 2  can pass along rails  204  at different positions in the widthwise direction from those where the downstream abutment mechanisms  200 D 1  and  200 D 2  pass. 
     Further, a slope face  204 A, a raised portion  204 B and a recessed portion  204 C are formed for each of the rail portions along which the downstream abutment mechanisms  200 D 1  and  200 D 2  pass. However, for the rail portion along which the upstream abutment mechanisms  20  U 1  and  200 U 2  pass, the raised portion  204 B is not formed, and only the recessed portion  204 C is formed. 
     Therefore, when a conveying unit  103  is to be mounted to a second housing  101 B of a main body  101  for an image forming apparatus  100 , the upstream abutment mechanisms  200 U 1  and  200 U 2  do not contact the raised portions  204 B, and therefore, there is no moment at which the elastic members are greatly compressed. Thus, when the conveying unit  103  is to be inserted, the sliding friction caused by the abutment mechanisms against the rails, and by the reference plate and the raised portions can be reduced, and the mounting operation can be smoothly and easily performed. Further, also in this embodiment, after the conveying unit  103  has been mounted, the projected portions  1104  formed for the individual abutment mechanisms  200  are brought in contact with the reference plate  1103 , so that the appropriate distance can be maintained between the ejection port face of the print head H and a platen  406 . The distance between the downstream abutment mechanisms  200 D 1  and  200 D 2  may be set greater than the distance between the upstream abutment mechanisms  200 U 1  and  200 U 2 . Furthermore, the abutment mechanisms  200 U 1 ,  200 U 2 ,  200 D 1  and  200 D 2  may also be arranged respectively at different locations in the widthwise direction (the direction on the conveyance plane perpendicular to the conveying direction). 
     (Fourth Embodiment) 
     A fourth embodiment of the present invention will now be described based on  FIGS. 21A and 21B . The same reference numerals used for the first embodiment are also employed to denote identical or corresponding components. 
     In the fourth embodiment, when abutment mechanisms  200 U 1 ,  200 U 2 ,  200 D 1  and  200 D 2  projected on the bottom face of a conveying unit  103  abut upon two rails (movable supporting members)  204 , the two rails are pushed upward by elastic members  212 . With this arrangement, when the conveying unit  103  is inserted into a second housing  101 B of a main body  101 , protruded portions  1104  of the conveying unit  1103  can be pressed against the lower face of a reference plate  1103  by the urging force of the elastic members  212  through the rails  204 . Therefore, in the fourth embodiment, as well as in the other embodiments, an appropriate distance can be maintained between the ejection port face of a print head H and a platen  406 . 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-185325, filed on Sep. 6, 2013, which is hereby incorporated by reference herein in its entirety.