Abstract:
A liquid ejection apparatus includes a liquid ejection head, a conveyor, a recording controller, and a flashing controller. The conveyor conveys a recording medium along a conveyance path. The recording controller causes the conveyor to convey a recording medium, and controls liquid ejection from the liquid ejection head to form an image on the recording medium based on image data. The flashing controller causes the conveyor to temporarily stop conveyance of the recording medium, and causes liquid ejection from the liquid ejection head based on drive data which is unrelated to image formation. The flashing controller determines timing for executing a subsequent flashing control so that, within a print enforceable period between one flashing control and the subsequent flashing control, the number of pages subjected to image formation based on image data increases with a decrease in time interval between image formation on one page and on another page.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The application is a divisional application of U.S. patent application Ser. No. 12/625,545, filed on Nov. 24, 2009, which claims the benefit of Japanese Patent Application No. 2008-327660, which was filed on Dec. 24, 2008, the disclosures of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink-jet recording apparatus configured to conduct recording on a recording medium. 
     2. Discussion of Related Art 
     In a recording apparatus such as an ink-jet printer, a jam of a recording medium such as paper sometimes occurs when the recording medium is being conveyed between an ink-jet head for ejecting ink on the recording medium and a conveyor mechanism for conveying the recording medium. 
     In the light of the above, there is disclosed an apparatus in which the conveyor mechanism is configured to be moved away from the ink-jet head when the jam of the recording medium occurs, thereby ensuring a user easy removal of the jammed recording medium. 
     SUMMARY OF THE INVENTION 
     According to the arrangement described above, whether a jam-clearing processing for removing a jammed recording medium is conducted or not is up to a user, and the user sometimes does not conduct the jam-clearing processing. Further, even when the user has conducted the jam-clearing processing, there may be an instance in which a part of the jammed recording medium remains between the ink-jet head and the conveyor mechanism without being completely removed. In such an instance, if the conveyor mechanism which has been located away from the ink-jet head is moved near to the ink-jet head, the jammed recording medium remaining between the ink-jet head and the conveyor mechanism may come into contact with the ink-jet head, resulting in damage to the ink-jet head. 
     It is therefore an object of the invention to provide an ink-jet recording apparatus capable of preventing an ink-jet head from being damaged by a jammed recording medium. 
     The above-indicated object may be attained according to a principle of the invention, which provides an ink-jet recording apparatus, comprising: 
     an ink-jet head in which is formed an ejection surface from which ink is ejected; 
     a conveyor mechanism which has a conveyor surface opposed to the ejection surface and which is configured to convey a recording medium placed on the conveyor surface, in a medium conveyance direction; 
     a relative movement mechanism configured to move at least one of the conveyor mechanism and the ink-jet head relative to each other such that the conveyor mechanism and the ink-jet head are located selectively at one of: a recording position at which an image is recorded on the recording medium with the ink ejected from the ink-jet head; and a medium removal position at which a distance between the ejection surface and the conveyor mechanism is larger than that when the conveyor mechanism and the ink-jet head are located at the recording position and at which a jammed recording medium jammed between the ejection surface and the conveyor mechanism is allowed to be removed by a user; 
     a detecting device configured to detect an occurrence of a jam of the recording medium between the ink-jet head and the conveyor mechanism; 
     an output device configured to output a jam-clearing completion signal indicative of completion of a jam-clearing processing for clearing the jam of the recording medium, in response to a prescribed operation by a user; 
     a sensor for detecting the recording medium existing between the ink-jet head and the conveyor mechanism; and 
     a relative-movement control device configured to control the relative movement mechanism and including (a) a first control portion configured to control the relative movement mechanism such that the relative movement mechanism conducts a first operation in which said at least one of the conveyor mechanism and the ink-jet head is moved relative to each other such that the conveyor mechanism and the ink-jet head are located at the medium removal position from the recording position when the detecting device detects the occurrence of the jam of the recording medium and such that the relative movement mechanism conducts, after the first operation, a second operation in which said at least one of the conveyor mechanism and the ink-jet head is moved relative to each other such that the conveyor mechanism and the ink-jet head are located at the recording position from the medium removal position when the output device outputs the jam-clearing completion signal and (b) a second control portion configured to control the relative movement mechanism to prevent the conveyor mechanism and the ink-jet head from moving relatively toward each other where the sensor detects the recording medium in the second operation. 
     It is noted that “to move at least one of the ink-jet head and the conveyor mechanism relative to each other” means that only one of the ink-jet head and the conveyor mechanism is moved by the relative movement mechanism or both of the ink-jet head and the conveyor mechanism are moved relative to each other by the relative movement mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, advantages and technical and industrial significance of the present invention will be better understood by reading the following detailed description of preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective external view of an ink-jet printer according to a first embodiment of the invention; 
         FIG. 2  is a schematic side view showing an internal structure of the ink-jet printer of  FIG. 1 ; 
         FIG. 3  is a plan view of four ink-jet heads of  FIG. 2  and the vicinity thereof when viewed from the above; 
         FIG. 4  is a schematic side view showing an up/down moving mechanism; 
         FIGS. 5A and 5B  are perspective views showing a maintenance mechanism; 
         FIGS. 6A-6C  are side views showing a capping operation; 
         FIGS. 7A and 7B  are views showing a part of a return operation after the capping operation; 
         FIGS. 8A and 8B  are views showing a part of the return operation after the capping operation; 
         FIG. 9  is a diagram showing an electrical structure of the ink-jet printer; 
         FIG. 10  is a view showing a jam-clearing routine; 
         FIG. 11  is a view showing a routine for detecting a jam at a conveyor portion; and 
         FIG. 12  is a side view showing a part of an internal structure of an ink-jet printer according to a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     There will be hereinafter described preferred embodiments of the invention with reference to the drawings. 
     1. First Embodiment 
     &lt;Mechanical Structure of Ink-Jet Printer&gt; 
     As shown in the perspective view of  FIG. 1 , an ink-jet printer  1  as an ink-jet recording apparatus has a casing  1   a  which is a rectangular parallelepiped and which has two openings, i.e., upper and lower openings  3   a ,  3   b , that are formed on the front of the casing  1   a  (on the front surface of the casing  1   a  in  FIG. 1 ). In the opening  3   a , a first door  4  is provided so as to be openable and closable about a horizontal axis located at the lower end of the opening  3   a . The opening  3   a  and the first door  4  are disposed so as to be opposed to a conveyor mechanism  50  (a conveyor portion) in a depth direction of the casing  1 , namely, in a direction perpendicular to the plane of  FIG. 2 , i.e., in a main scanning direction. The arrangement allows a user easy access to the conveyor mechanism  50  by opening the first door  4  in an instance where a sheet P (as a recording medium) is jammed in the conveyor mechanism  50 , so that the jammed sheet P can be removed. 
     As shown in  FIG. 1 , an opening  3   c  is formed on one side surface of the casing  1   a  (on the right side surface of the casing  1   a  in  FIG. 1 ). In the opening  3   c , a third door  5  is provided so as to be openable and closable about a horizontal axis located at the lower end of the opening  3   c . As shown in  FIG. 2 , on the inner side of the third door  5 , an outer guide surface  18   a  that partially constitutes a sheet guide  18  (which will be described) is formed. The opening  3   c  and the third door  5  are disposed so as to be opposed to an inside of the sheet guide  18  in a sub scanning direction that is perpendicular to the main scanning direction. In this structure, where the sheet P is jammed in the sheet guide  18 , the user can access the inside of the sheet guide  18  by opening the third door  5 , so that the jammed sheet P can be removed. 
     An opening  3   d  (not shown) is formed on another side surface of the casing  1  (on the left side surface of the casing  1   a  in  FIG. 1 ). In the opening  3   d , a second door  6  is provided so as to be openable and closable about a horizontal axis located at the lower end of the opening  3   d . As shown in  FIG. 2 , on the inner side of the second door  6 , an outer guide surface  17   a  that partially constitutes a sheet guide  17  (which will be described) is formed. The opening  3   d  and the second door  6  are disposed so as to be opposed to an inside of the sheet guide  17  in the sub scanning direction. In this structure, where the sheet P is jammed in the sheet guide  17 , the user can access the inside of the sheet guide  17  by opening the second door  6 , so that the jammed sheet P can be removed. 
     The ink-jet printer  1  is a color ink-jet printer having four ink-jet heads  2  which respectively eject inks of different colors, i.e., magenta, cyan, yellow, and black. The ink-jet printer  1  has a sheet supply device  10  at its lower portion and a discharged-sheet receiving portion  15  at its upper portion. The conveyor mechanism  50  for conveying the sheet P in a sheet conveyance direction A is disposed between the sheet supply device  10  and the discharged-sheet receiving portion  15 . The ink-jet printer  1  further has a controller  100  for controlling operations thereof. 
     Each of the four ink-jet heads  2  has a generally rectangular parallelepiped shape that is long in the main scanning direction. The four ink-jet heads  2  are disposed so as to be spaced apart from each other in the sub scanning direction and are fixed to a frame  7 . That is, the ink-jet printer  1  is a line-type printer. In the present embodiment, the sub scanning direction is a direction parallel to the sheet conveyance direction A while the main scanning direction is a direction perpendicular to the sub scanning direction and is horizontal, namely, the main scanning direction coincides with the vertical direction in  FIG. 3 . 
     Each ink-jet head  2  has a laminar body having; a flow-passage unit in which are formed ink passages that include pressure chambers; and an actuator for giving pressure to ink in the pressure chambers. The flow-passage unit and the actuator (both not shown) are bonded to each other so as to provide the laminar body. The bottom surface of each ink-jet head  2  is formed as an ejection surface  2   a  from which the ink is ejected. As shown in  FIG. 3 , the ejection surface  2   a  has a plurality of ejection holes  2   b , an ejection area  2   c  within which the ejection holes  2   b  are disposed, and a non-ejection area  2   d  which surrounds the ejection area  2   c . The ejection area  2   c  has a dimension as measured in the main scanning direction that is slightly larger than the dimension of the sheet P as measured in the same direction. Accordingly, it is possible to form an image over an entire surface of the sheet P conveyed by the conveyor mechanism  50 , namely, it is possible to conduct marginless printing. In  FIG. 3 , a maintenance mechanism  30  (which will be explained) is not shown. 
     As shown in  FIG. 2 , the sheet supply device  10  includes a sheet cassette  11  in which a stack of sheets P can be accommodated, a sheet supply roller  12  configured to supply an uppermost one of the sheets P from the sheet cassette  11 , and a sheet supply motor (not shown) configured to rotate the sheet supply roller  12 . The sheet cassette  11  is disposed so as to be attachable to and detachable from the casing  1   a  in a direction perpendicular to the plane of  FIG. 2 . In a state in which the sheet cassette  11  is installed on the casing  1   a , the sheet cassette  11  overlaps the conveyor mechanism  50  when viewed from the top of the printer  1 . The sheet supply roller  12  is configured to supply the uppermost one of the sheets P from the sheet cassette  11  while being held in rolling contact therewith. The sheet supply motor configured to rotate the sheet supply roller  12  is controlled by the controller  100 . 
     At the left-side portion of the ink-jet printer  1  as seen in  FIG. 2 , namely, at a portion of a sheet transfer path between the sheet cassette  11  and the conveyor mechanism  50 , there are disposed: the sheet guide  17  which extends in a curved form from the sheet cassette  11  toward the conveyor mechanism  50 ; and two feed rollers  23   a ,  23   b  provided on the downstream side of the sheet guide  17 . The sheet guide  17  is constituted by the outer guide surface  17   a  formed on the second door  6  and an inner guide surface  17   b  opposed to the outer guide surface  17   a . The feed roller  23   b  is rotatably driven by a feed motor (not shown) controlled by the controller  100  while the feed roller  23   a  is a driven roller configured to be rotated as the sheet is transferred. 
     In the structure described above, the sheet supply roller  12  is rotated clockwise in  FIG. 2  by being controlled by the controller  100 , whereby the sheet P contacting the sheet supply roller  12  is transferred upward in  FIG. 2  through the sheet guide  17 . The sheet P is supplied to the conveyor mechanism  50  while being held by the feed rollers  23   a ,  23   b.    
     A sensor  73  is disposed at a position which is downstream of the sheet supply roller  12  and is upstream of the sheet guide  17  while a sensor  74  is disposed at a position which is downstream of the sheet guide  17  and is upstream of the feed rollers  23   a ,  23   b . Each of the sensors  73 ,  74  is disposed such that its detecting surface is opposed to the sheet P passing through the sheet guide  17 . Each sensor  73 ,  74  is an optical sensor of reflection type configured to detect the sheet P by sensing a light reflected on the surface of the sheet P. The two sensors  73 ,  74  are disposed at the respective positions at which the two sensors  73 ,  74  are opposed to the inner central portion of the sheet guide  17  in the main scanning direction. These two sensors  73 ,  74  are configured to detect the leading end of the sheet P passing through the sheet guide  17 . It is noted that each sensor  73 ,  74  is not limited to the optical sensor of reflection type, but may be an optical sensor of transmission type. 
     In an instance where the sensor  74  does not detect the leading end of the sheet P even though a prescribed time has been passed after detection of the leading end of the sheet P by the sensor  73 , the controller  100  judges that a jam of the sheet P (so-called paper jam) has occurred in the sheet guide  17 . In this case, the controller  100  stops rotation of the sheet supply roller  12  and the feed roller  23   b.    
     As shown in  FIG. 2 , the conveyor mechanism  50  includes two belt rollers  51 ,  52 , an endless conveyor belt  53  wound around the two belt rollers  51 ,  52  so as to be stretched therebetween, a tension roller  55  configured to give tension to the conveyor belt  53 , a feed motor (not shown) configured to rotate the belt roller  52 , and an adhesion device  60 . The two belt rollers  51 ,  52  are arranged along the sheet conveyance direction indicated “A” in  FIG. 2 . As shown in  FIG. 3 , the conveyor belt  53  is opposed to the ejection surfaces  2   a  and has an outer circumferential surface functioning as a conveyor surface  54  on which the sheet P is held. 
     The belt roller  52  is a drive roller and is configured to be rotated clockwise in  FIG. 2  by a feed motor (not shown). The belt roller  51  is a driven roller configured to be rotated clockwise in  FIG. 2  by the movement of the conveyor belt  53  in accordance with the rotation of the belt roller  52 . As shown in  FIG. 2 , the tension roller  55  is rotatably supported by the casing  1   a  so as to give tension to the conveyor belt  53  while contacting the inner circumferential surface of the conveyor belt  53  at the lower portion of the loop of the same  53 . The tension roller  55  is configured to be rotated clockwise in  FIG. 2  by the movement of the conveyor belt  53 . 
     As shown in  FIG. 2 , the adhesion device  60  is disposed in a region enclosed by the conveyor belt  53  and includes a platen  61  having a generally rectangular parallelepiped shape and a fan  62  disposed below the platen  61 . On the upper surface of the platen  61 , a plurality of holes (not shown) are formed through the thickness of the platen  61 . The plurality of holes are distributed over the entirety of the area of the upper surface of the platen  61 , which area is opposed to the conveyor belt  53 . The platen  61  has a dimension as measured in the main scanning direction slightly larger than dimensions of the sheet P and the conveyor belt  53  as measured in the same direction. 
     As shown in  FIG. 2 , the upper surface of the platen  61  is held in contact with the inner circumferential surface of the conveyor belt  53  at the upper portion of the loop of the belt  53  so as to support the belt  53  from the inside of the loop. According to the arrangement, the conveyor belt  53  at the upper portion of the loop and the ejection surfaces  2   a  of the ink-jet heads  2  are opposed to each other so as to be parallel to each other, and there is formed a slight clearance therebetween. The clearance partially constitutes the sheet transfer path. 
     The fan  62  has a generally rectangular parallelepiped shape shown in  FIG. 2 . The fan  62  is configured to suck in the air through suction ports (not shown) formed in its upper surface by rotation of rotary vanes provided in its inside. The fan  62  is controlled by the controller  100 . 
     A pressing roller  48  is located on the upstream side of one of the four ink-jet heads  2  that is disposed on the most upstream side in the sheet conveyance direction A among the four ink-jet heads  2 , so as to be opposed to the belt roller  51  with the conveyor belt  53  interposed therebetween. The pressing roller  48  is biased toward the conveyor surface  54  by an elastic member such as a spring (not shown) and is configured to press the sheet P supplied from the sheet supply device  10  onto the conveyor surface  54 . The pressing roller  48  is a driven roller configured to be rotated in accordance with the rotary movement of the conveyor belt  53 . 
     In this structure, the conveyor belt  53  rotates by rotation of the belt roller  52  clockwise in  FIG. 2  under the control of the controller  100 . In this instance, the belt roller  51 , the tension roller  55 , and the pressing roller  48  are also rotated by the rotary movement of the conveyor belt  53 . Further, the fan  62  is driven under the control of the controller  100 , so that the air is drawn into the suction ports formed in the fan  62  through all of the plurality of holes formed in the platen  61 . According to the arrangement, the sheet P supplied from the sheet supply device  10  is conveyed in the sheet conveyance direction A while adhering to the conveyor surface  54 . In the structure, when the sheet P conveyed by and held on the conveyor surface  54  of the conveyor belt  53  passes right below the four ink-jet heads  2 , the ink-jet heads  2  controlled by the controller  100  eject the respective inks toward the sheet P, so that an intended color image is formed on the sheet P. 
     The conveyor mechanism  50  is configured to be moved upward and downward relative to the ink-jet heads  2  by an up/down moving mechanism  80  ( FIG. 4 ) as a relative movement mechanism between a recording position at which an image is recorded or printed on the sheet P with the inks ejected from the ink-jet heads  2  and a sheet removal position (as a medium removal position) at which a distance by which the ejection surfaces  2   a  and the conveyor mechanism  50  are spaced apart from each other is larger than that when the ink-jet heads  2  and the conveyor mechanism  50  are located at the recording position and at which a user is allowed to remove the sheet P when the sheet P is jammed between the ejection surfaces  2   a  and the conveyor mechanism  50 . Each of the recording position and the sheet removal position corresponds to relative positions of the ink-jet heads  2  and the conveyor mechanism  50 . In other words, the conveyor mechanism  50  is moved upward and downward between the recording position shown in  FIG. 2  at which the conveyor mechanism  50  is located close to the ink-jet heads  2  and the sheet removal position at which the conveyor mechanism  50  is located at a height level lower than the recording position. 
     As shown in  FIG. 4 , the up/down moving mechanism  80  includes an up/down moving portion  81  configured to move the belt roller  51  upward and downward and an up/down moving portion  85  configured to move the belt roller  52  upward and downward. The up/down moving portion  81  has an up/down motor  82 , two rings  83 , and wires  84  each as a connecting member. The rings  83  are disposed near respective opposite axial ends of a roller shaft  51   a  of the belt roller  51  and rotatably support the roller shaft  51   a . Each wire  84  is fixed at one end thereof to the upper end of the corresponding ring  83  and is fixed to and wound around a motor shaft  82   a  of the up/down motor  82  at the other end thereof. At respective positions of the casing  1   a  facing the opposite axial ends of the roller shaft  51   a  of the belt roller  51 , guides  91  are formed for guiding the opposite axial ends of the roller shaft  51   a  of the belt roller  51  when the belt roller  51  is moved upward and downward. Each guide  91  is formed such that its upper end coincides with the position of the roller shaft  51   a  at a time when the conveyor mechanism  50  is located at the recording position. The guide  91  extends downward from its upper end. 
     Similarly, the up/down moving portion  85  has an up/down motor  86 , two rings  87 , and wires  88 . The rings  87  are disposed near respective opposite axial ends of a roller shaft  52   a  of the belt roller  52  and rotatably support the roller shaft  52   a . Each wire  88  is fixed at one end thereof to the upper end of the corresponding ring  87  and is fixed to and wound around a motor shaft  86   a  of the up/down motor  86  at the other end thereof. At respective positions of the casing  1   a  facing the opposite axial ends of the roller shaft  52   a  of the belt roller  52 , guides  92  are formed for guiding the opposite axial ends of the roller shaft  52   a  of the belt roller  52  when the belt roller  52  is moved upward and downward. Each guide  92  is formed such that its upper end coincides with the position of the roller shaft  52   a  at a time when the conveyor mechanism  50  is located at the recording position. The guide  92  extends downward from its upper end. 
     In the structure, when the two up/down motors  82 ,  86  are simultaneously driven under the control of the controller  100  and the motor shafts  82   a ,  86   a  are rotated counterclockwise in  FIG. 4 , the wires  84 ,  88  are unwound from the respective motor shafts  82   a ,  86   a , whereby the conveyor mechanism  50  moves downward along the guides  91 ,  92 . That is, the conveyor mechanism  50  is moved from the recording position to the sheet removal position. On the other hand, when the motor shafts  82   a ,  86   a  are rotated clockwise in  FIG. 4  under the control of the controller  100 , the wires  84 ,  88  are wound around the respective motor shafts  82   a ,  86   a , whereby the conveyor mechanism  50  moves upward along the guides  91 ,  92 . That is, the conveyor mechanism  50  is moved from the sheet removal position to the recording position. 
     The movement of the conveyor mechanism  50  from the recording position to the sheet removal position is conducted in an instance where a jam of the sheet P occurs at the conveyor mechanism  50  in a printing or recording operation in which an image is printed or recorded on the sheet P with the conveyor mechanism  50  located at the recording position. When the conveyor mechanism  50  is located at the sheet removal position, the distance between the ejection surfaces  2   a  and the conveyor mechanism  50  is large, thereby allowing the user easy access to the conveyor mechanism  50  by opening the first door  4 , so that the jammed sheet P can be easily removed. Subsequently when the user conducts a prescribed operation such as closing of the first door  4 , the controller  100  outputs a jam-clearing completion signal indicative of completion of a jam-clearing processing for clearing the jam of the sheet P, and the conveyor mechanism  50  located at the sheet removal position returns to the recording position. 
     While the conveyor mechanism  50  is configured to be moved relative to the ink-jet heads  2  by the up/down moving mechanism  80  in the present embodiment, the ink-jet heads  2  may be configured to be moved upward and downward relative to the conveyor mechanism  50  by the up/down moving mechanism  80 . Further, both of the ink-jet heads  2  and the conveyor mechanism  50  may be configured to be moved upward and downward such that the conveyor mechanism  50  and the ink-jet heads  2  approach each other or separate away from each other. 
     As shown in  FIG. 2 , a separation plate  9  is disposed on the immediately downstream side of the conveyor mechanism  50  in the sheet conveyance direction A. The separation plate  9  is configured to separate the sheet P from the conveyor surface  54  such that the edge of the separation plate  9  is inserted between the sheet P and the conveyor belt  53 . 
     At a portion of the sheet transfer path between the conveyor mechanism  50  and the discharged-sheet receiving portion  15 , there are disposed: four feed rollers  21   a ,  21   b ,  22   a ,  22   b ; and the sheet guide  18  located between the feed rollers  21   a ,  21   b  and the feed rollers  22   a ,  22   b . The feed rollers  21   b ,  22   b  are rotatably driven by a feed motor (not shown) controlled by the controller  100 . The feed rollers  21   a ,  22   a  are driven rollers configured to be rotated as the sheet is transferred. The sheet guide  18  is constituted by the outer guide surface  18   a  formed on the third door  5  and an inner guide surface  18   b  opposed to the outer guide surface  18   a.    
     In the arrangement described above, the feed motor is driven under the control of the controller  100  so as to rotate the feed rollers  21   b ,  22   b , whereby the sheet P conveyed by the conveyor mechanism  50  is transferred upward in  FIG. 2  through the sheet guide  18  while being held by the feed rollers  21   a ,  21   b . Subsequently, the sheet P is discharged to the discharged-sheet receiving portion  15  while being held by the feed rollers  22   a ,  22   b.    
     A sensor  75  is disposed at a position which is downstream of the separation plate  9  and is upstream of the feed rollers  21   a ,  21   b  while a sensor  76  is disposed at a position which is downstream of the sheet guide  18  and is upstream of the feed rollers  22   a ,  22   b . Each of the sensors  75 ,  76  is disposed such that its detecting surface is opposed to the sheet P passing through the sheet guide  18 . Each sensor  75 ,  76  is an optical sensor of reflection type configured to detect the sheet P by sensing a light reflected on the surface of the sheet P. The two sensors  75 ,  76  are disposed at respective positions at which the two sensors  75 ,  76  are opposed to the inner central portion of the sheet guide  18  in the main scanning direction. These two sensors  75 ,  76  are configured to detect the leading end of the sheet P passing through the sheet guide  18 . It is noted that each sensor  75 ,  76  is not limited to the optical sensor of reflection type, but may be an optical sensor of transmission type. 
     In an instance where the sensor  76  does not detect the leading end of the sheet P even though a prescribed time has been passed after detection of the leading end of the sheet P by the sensor  75 , the controller  100  judges that a jam of the sheet P (so-called paper jam) has occurred in the sheet guide  18 . In this case, the controller  100  stops rotation of the feed rollers  21   b ,  22   b.    
     As shown in  FIG. 2 , the maintenance mechanism  30  (as an intervening-member moving mechanism) is disposed between the four ink-jet heads  2  and the conveyor mechanism  50 . The maintenance mechanism  30  has four caps  31  each as an intervening member configured to cover the ejection surfaces  2   a  of the respective ink-jet heads  2 . Each of the caps  31  is formed of an elastic material such as rubber and having a rectangular shape in plan view whose longitudinal direction is parallel to the longitudinal direction of each ink-jet head  2 . Each cap  31  is located, in its initial state, on the immediately upstream side of the corresponding ink-jet head  2 , and is moved, in accordance with the movement of the maintenance mechanism  30 , in the leftward and rightward direction and in the upward and downward direction as seen in  FIG. 2 , relative to the corresponding ink-jet head  2 . 
     As shown in  FIG. 5A , the maintenance mechanism  30  includes: four plate members  32  which are equally spaced apart from each other in the sub scanning direction and each of which has the cap  31  disposed on its upper surface; and a pair of inner frames  33  between which the plate members  32  are held. Each inner frame  33  has protruding corner portions  33   a  that extend upward at respective opposite ends thereof. On one corner portion  33   a  of each inner frame  33 , a pinion gear  34  that is fixed to a shaft of a drive motor (not shown) is disposed so as to mesh with a rack gear  35  disposed horizontally. In  FIG. 5A , the pinion gear  34  of only one of the inner frames  33  (that is located on the front side as seen in  FIG. 2 ) is shown. 
     As shown in  FIG. 5B , the maintenance mechanism  30  further includes an outer frame  36  disposed so as to enclose the pair of inner frames  33 . Inside the outer frame  36 , the rack gear  35  shown in  FIG. 5A  is fixed. A pinion gear  37  that is fixed to a shaft of a drive motor (not shown) is disposed so as to mesh with a rack gear  38  disposed vertically. The rack gear  38  is disposed so as to extend upright in the casing  1   a.    
     In the arrangement described above, when the two pinion gears  34  are synchronously rotated, the inner frames  33  are moved in the sub scanning direction. Further, when the pinion gear  37  is rotated, the outer frame  36  is moved in the vertical direction. 
     More specifically, when the maintenance mechanism  30  is located at an initial position shown in  FIG. 2 , each plate member  32  is located on the immediately upstream side of the corresponding ink-jet head  2 , and three openings  39   a  between any adjacent two plate members  32  and one opening  39   b  between the plate member  32  located on the most downstream side and the corner portions  33   a  of the inner frame  33  are opposed to the respective ejection surfaces  2   a . When a capping operation for covering the ejection surfaces  2   a  with the corresponding caps  31  is conducted, the outer frame  36  is moved downward in the vertical direction, so that the maintenance mechanism  30  is moved to an intervening position at which the maintenance mechanism  30  is located between the ink-jet heads  2  and the conveyor mechanism  50 , as shown in  FIG. 6A . On this occasion, the caps  31  are located at a retracted position at which the caps  31  are disposed between the corresponding ink-jet heads  2  and the conveyor mechanism  50  but are not opposed to the ejection surfaces  2   a.    
     Thereafter, the pair of inner frames  33  are moved downstream in the sub scanning direction. On this occasion, the caps  31  are located at a facing position at which the caps  31  face the corresponding ejection surfaces  2   a , as shown in  FIG. 6B . Then the outer frame  36  is moved upward in the vertical direction, whereby the caps  31  are located at a capping position at which the caps  31  contact the corresponding ejection surfaces  2   a  so as to cover the same  2   a , as shown in  FIG. 6C . According to this procedure, the ejection surfaces  2   a  are covered with the respective caps  31 . The caps  31  return back to the initial position by conducting the procedure in a reverse order. 
     The capping operation described above is conducted with the conveyor mechanism  50  located at the sheet removal position after having been moved downward from the recording position or with the conveyor mechanism  50  located at the recording position. Further, the capping operation is conducted in an instance where a jam of the sheet P occurs at any of the sheet guide  17 , the sheet guide  18 , and the conveyor mechanism  50 .  FIGS. 6A-6C  show a state in which the conveyor mechanism  50  has been moved by the up/down moving mechanism  80  from the recording position to the sheet removal position after occurrence of a jam of the sheet P at the conveyor mechanism  50 . 
     The maintenance mechanism  30  is provided with two sensors  71 ,  72 , as shown in  FIG. 2 . More specifically, the sensor  71  is disposed at a location that is upstream of the most upstream inkjet head  2  in the sheet conveyance direction A while the sensor  72  is disposed at a location that is downstream of the most downstream ink-jet head  2  in the sheet conveyance direction A, such that the detecting surface of each of the sensors  71 ,  72  faces the conveyor surface  54 . That is, the sensors  71 ,  72  are disposed integrally with the caps  31 , namely, provided so as to be immovable relative to the caps  31 . Each sensor  71 ,  72  is an optical sensor of reflection type configured to detect the sheet P by sensing a light reflected on the surface of the sheet P. The two sensors  71 ,  72  are disposed at respective locations at which the two sensors  71 ,  72  are opposed to the middle portion of the conveyor surface  54  in the main scanning direction. These two sensors  71 ,  72  are configured to detect the leading end of the sheet P conveyed by the conveyor belt  53 . It is noted that each sensor  71 ,  72  is not limited to the optical sensor of reflection type, but may be an optical sensor of transmission type. 
     In an instance where the sensor  72  does not detect the leading end of the sheet P even though a prescribed time has been passed after detection of the leading end of the sheet P by the sensor  71 , the controller  100  judges that a jam of the sheet P (so-called paper jam) has occurred at the conveyor mechanism  50 . In this case, the controller  100  stops ejection of the inks from the respective ink jet heads  2 .  22   b.    
     In addition to the sensors  71 ,  72 , the maintenance mechanism  30  includes sensors  41 R,  41 L, sensors  42 R,  42 C,  42 L, sensors  43 R,  43 C,  43 L, sensors  44 R,  44 C,  44 L, and sensors  45 R,  45 L, which are disposed integrally with the caps  31 , namely, provided so as to be immovable relative to the caps  31 . Hereinafter, the sensors  71 ,  72 ,  41 - 45  are collectively referred to as a sensor group where appropriate. Here, one of opposite sides of the conveyor surface  54  which extends along the sub scanning direction and which is located on the right-hand side when viewed from the upstream side toward the downstream side of the sheet conveyance direction A is referred to as a right side. The other of the opposite sides of the conveyor surface  54  which extends along the sub scanning direction and which is located on the left-hand side when viewed from the upstream of the sheet conveyance direction is referred to as a left side. The sensor  41 R is disposed on the right side of the sensor  71  in the main scanning direction so as to be opposed to the right-side region of the conveyor surface  54 . The sensor  41 L is disposed on the left side of the sensor  71  in the main scanning direction so as to be opposed to the left-side region of the conveyor surface  54 . The sensors  42 R,  42 C,  42 L are disposed between the most upstream ink-jet head  2  and its neighboring ink-jet head  2  located downstream of the most upstream ink-jet head  2 , in the sheet conveyance direction A. The sensors  42 R,  42 C,  42 L are located so as to be opposed respectively to the right-side region, the middle region interposed between the right-side region and the left-side region, and the left-side region, of the conveyor surface  54 . The sensors  43 R,  43 C,  43 L are disposed between the second ink-jet head  2  from the upstream side and its neighboring ink-jet head  2  located downstream of the second ink-jet head  2 , in the sheet conveyance direction A. The sensors  43 R,  43 C,  43 L are located so as to be opposed respectively to the right-side region, the middle region, and the left-side region, of the conveyor surface  54 . The sensors  44 R,  44 C,  44 L are disposed between the second ink-jet head  2  from the downstream side and its neighboring ink-jet head  2  located most downstream, in the sheet conveyance direction A. The sensors  44 R,  44 C,  44 L are located so as to be opposed respectively to the right-side region, the middle region, and the left-side region, of the conveyor surface  54 . The sensor  45 R is disposed on the right side of the sensor  72  in the main scanning direction so as to be opposed to the right-side region of the conveyor surface  54 . The sensor  45 L is disposed on the left side of the sensor  72  in the main scanning direction so as to be opposed to the left-side region of the conveyor surface  54 . In other words, the sensors are arranged in a plurality of rows each of which extends in a direction perpendicular to the sheet conveyance direction and parallel to the ejections surfaces  2   a  and each of which includes three sensors. 
     The sensors of the sensor group are configured to detect the sheet P existing between the ink-jet heads  2  and the conveyor mechanism  50 . 
     When the user conducts the prescribed operation such as closing of the first door  4  in a state in which the conveyor mechanism  50  is located at the sheet removal position and in which the capping operation has been conducted, there are conducted a return operation in which the maintenance mechanism  30  returns back to the initial position after the capping operation and a return operation in which the conveyor mechanism  50  located at the sheet removal position returns back to the recording position, as described below. Initially, as shown in  FIG. 7A , the outer frame  36  is moved downward in the vertical direction, so that the maintenance mechanism  30  is moved to the intervening position at which the maintenance mechanism  30  is located between the ink-jet heads  2  and the conveyor mechanism  50 . On this occasion, the sensors of the sensor group start a detecting or sensing operation for detecting or sensing the sheet P existing between the ink-jet heads  2  and the conveyor mechanism  50 . At the same time, the conveyor mechanism  50  located at the sheet removal position starts to move upward to the recording position by the up/down moving mechanism  80 . The speed at which the conveyor mechanism  50  is moved upward is lower than the speed at which the conveyor mechanism  50  is moved downward. Further, during the upward movement of the conveyor mechanism  50 , the adhesion device  60  is placed, under the control of the controller  100 , at its operating state for enabling the sheet P to adhere to the conveyor surface  54  if the sheet P exists on the conveyor surface  54 . 
     Subsequently, the inner frames  33  are moved toward the downstream side in the sub scanning direction, so that the caps  31  are moved toward the downstream side in a direction parallel to the sheet conveyance direction, by a distance “b” that is larger than a pitch “a” at which the four ink-jet heads  2  are arranged in the sheet conveyance direction A, as indicated in  FIG. 7B . On this occasion, the detecting operation by the sensors of the sensor group for detecting the sheet P existing between the ink-jet heads  2  and the conveyor mechanism  50  is being continued, and the upward movement of the conveyor mechanism  50  toward the recording position by the up/down moving mechanism  80  is being continued. Further, on this occasion, the adhesion device  60  is kept in the operating state. 
     Thereafter, the inner frames  33  are moved toward the upstream side in the sub scanning direction, so that the caps  31  are moved toward the upstream side in the direction parallel to the sheet conveyance direction, as indicated in  FIG. 8A . Accordingly, the caps  31  are placed at the retracted position at which the caps  31  are not opposed to the corresponding ejection surfaces  2   a . On this occasion, the detecting operation by the sensors of the sensor group for detecting the sheet P existing between the ink-jet heads  2  and the conveyor mechanism  50  is being continued, and the upward movement of the conveyor mechanism  50  toward the recording position by the up/down moving mechanism  80  is being continued. Further, on this occasion, the adhesion device  60  is kept in the operating state. 
     Subsequently, the outer frame  36  is moved upward in the vertical direction, so that the caps  31  return back to the initial position, as shown in  FIG. 8B . Further, the conveyor mechanism  50  is placed at the recording position by the up/down moving mechanism  80 . Then the detection of the sheet P by the sensors of the sensor group is stopped, and the adhesion device  60  stops operating. According to the procedure described above, the caps  31  return back to the initial position and the conveyor mechanism returns back to the recording position. 
     Here, when at least one of the sensors of the sensor group detects, in the upward movement of the conveyor mechanism  50  from the sheet removal position to the recording position, the sheet P existing between the ink-jet heads  2  and the conveyor mechanism  50 , the up/down moving mechanism  80  stops the upward movement of the conveyor mechanism  50  so as to prevent the conveyor mechanism  50  and the ink-jet heads  2  from approaching relative to each other. 
     In the arrangement described above, in an instance where a jam of the sheet P (paper jam) occurs between the ink-jet heads  2  and the conveyor mechanism  50 , the conveyor mechanism  50  and the ink-jet heads  2  are moved relative to each other so as to be placed at the sheet removal position from the recording position for allowing the user to clear the jam. Specifically, in the present embodiment, the conveyor mechanism  50  is moved relative to the ink-jet heads  2 . After completion of the jam-clearing processing, the conveyor mechanism  50  and the ink-jet heads  2  are moved relative to each other from the sheet removal position back to the recording position. In this instance, where any of the sensors detects the sheet P jammed between the conveyor mechanism  50  and the ink-jet heads  2  in the relative movement of the conveyor mechanism  50  and the ink-jet heads  2  from the sheet removal position to the recording position, the conveyor mechanism  50  and the ink-jet heads  2  are stopped from approaching relative to each other. Thus, where the jammed sheet P exists between the ink-jet heads  2  and the conveyor mechanism  50 , the conveyor mechanism  50  is inhibited from approaching the ink-jet heads  2  any more, so that the jammed sheet P is prevented from contacting the ink-jet heads  2 . Accordingly, it is possible to protect the ink-jet heads  2  from being damaged by the jammed sheet P. 
     In the present embodiment, the conveyor mechanism  50  is moved upward from the sheet removal position back to the recording position at a speed lower than a speed at which the conveyor mechanism  50  is moved downward from the recording position to the sheet removal position. The arrangement increases a time period during which the sensors can detect the jammed sheet P, resulting in an enhanced accuracy of detecting the jammed sheet P by the sensors of the sensor group. 
     The sensors of the sensor group are provided integrally with the caps  31  located between the ink-jet heads  2  and the conveyor mechanism  50 . Accordingly, the jammed sheet P can be detected well before the jammed sheet P contacts the ink-jet heads  2 . 
     In the upward movement of the conveyor mechanism  50  from the sheet removal position to the recording position, the caps  31  on which the sensors of the sensor group are integrally provided are moved toward the downstream side in the direction parallel to the sheet conveyance direction, whereby the jammed sheet P can be detected over a wide range in the direction parallel to the sheet conveyance direction. 
     The caps  31  on which the sensors of the sensor group are integrally provided are moved by the distance “b” larger than the pitch “a” at which the ink-jet heads  2  are arranged in the sheet conveyance direction A. Accordingly, even if the jammed sheet P exists between any adjacent two heads  2 , the jammed sheet P can be detected. 
     The adhesion device  60  is kept in its operating state for permitting the jammed sheet P to adhere to the conveyor surface  54 , in the upward movement of the conveyor mechanism  50  from the sheet removal position to the recording position, whereby the jammed sheet P can be prevented from contacting the ink-jet heads  2 . 
     The sensors of the sensor group are arranged in a plurality of rows each including three sensors in the present embodiment and each extending in the direction perpendicular to the sheet conveyance direction and parallel to the ejection surfaces  2   a , namely, in a depth direction of the sheet P. Accordingly, even if the jammed sheet P is not located evenly in the depth direction, the jammed sheet P can be detected. 
     &lt;Electric Structure of Ink-Jet Printer&gt; 
     The operations of the ink-jet printer  1  are controlled by the controller  100 , as shown in  FIG. 9 . The controller  100  is constituted by a microcomputer  101  as its main constituent element disposed on a circuit board, and various circuits. The microcomputer  101  includes a CPU  102  for controlling various operations according to preset programs, a ROM  103  for storing various programs, and a RAM  104  as a temporary memory device. 
     To the CPU  102 , there are connected: a head control circuit  106  for controlling the ink-jet heads  2 ; a conveyor-mechanism control circuit  107  for controlling the conveyor mechanism  50 , the feed rollers  21   b ,  22   b ,  23   b , and the sheet supply roller  12 ; an up/down-moving-mechanism control circuit  108  for controlling the up/down moving mechanism  80 ; a maintenance-mechanism control circuit  109  for controlling the maintenance mechanism  30 ; an interface circuit  111  to which sheet detection signals from the sensors  71 - 76  and the sensors  41 - 45  are inputted; and a communication circuit  112  for performing communication with a general-purpose personal computer (not shown) or the like via a communication portion  20 . 
     The head control circuit  106  controls the ink-jet heads  2  to eject the inks toward the sheet P, on the basis of recording or printing data transmitted from the personal computer or the like via the communication portion  20 . In this instance, the head control circuit  106  as a recording control device controls the ink-jet heads  2  to start ejection of the inks toward the sheet P a predetermined time after the sensor  71  has detected the leading end of the sheet P conveyed by the conveyor mechanism  50 . The above-indicated predetermined time is equal to a time obtained by dividing a distance, along the sheet transfer path, between the position of the leading end of the sheet P when the sensor  71  detects the leading end and the position of the ejection holes  2   b  which are located most upstream in the most upstream one of the four ink-jet heads  2 , by a speed at which the sheet P is transferred. 
     Thus, the sensor  71  used in detecting the sheet P existing between the ink-jet heads  2  and the conveyor mechanism  50  is also used in detection of the sheet P in the recording operation as described above, resulting in a reduction of the number of required components and the cost of the ink-jet printer  1 . 
     The conveyor-mechanism control circuit  107  is configured to control the conveyor mechanism  50 , the feed rollers  21   b ,  22   b ,  23   b , and the sheet supply roller  12  such that the sheet P is transferred from the sheet supply device  10  to the discharged-sheet receiving portion  15 . In particular, the conveyor-mechanism control circuit  107  when functioning as an adhesion control device is configured to control the adhesion device  60  so as to permit the sheet P to adhere to the conveyor surface  54  in a second operation explained below. 
     The up/down-moving-mechanism control circuit  108  is configured to control the up/down moving mechanism  80  such that the conveyor mechanism  50  is moved away from the ink-jet heads  2  when a jam of the sheet P that is being conveyed has occurred in the conveyor mechanism  50 , for instance. Further, the up/down-moving-mechanism control circuit  108  is configured to control the up/down moving mechanism  80  such that the conveyor mechanism  50  is moved toward the ink-jet heads  2  when the jam-clearing processing by the user has completed, for instance. 
     The up/down-moving-mechanism control circuit  108  as a relative-movement control device has a first control portion to control the up/down moving mechanism  80  to conduct a first operation in which the conveyor mechanism  50  and the ink-jet heads  2  are moved relative to each other from the recording position to the sheet removal position when a jam of the sheet P occurs between the ink-jet heads  2  and the conveyor mechanism  50 . The CPU  102  as an output device is configured to output the jam-clearing signal indicative of completion of the jam-clearing processing for removing the jammed sheet, in response to the prescribed operation by the user. Further, the first control portion is configured to control the up/down moving mechanism  80  to conduct, after the first operation, a second operation in which the conveyor mechanism  50  and the ink-jet heads  2  are moved relative to each other from the sheet removal position back to the recording position when the jam-clearing signal is outputted. In this respect, the first control portion is configured to control the up/down moving mechanism  80  to conduct the second operation at a speed less than a speed at which the first operation is conducted. The up/down-moving-mechanism control circuit  108  as the relative-movement control device further has a second control portion to control the up/down moving mechanism  80  to prevent the relative movement of the conveyor mechanism  50  and the ink-jet heads  2  toward each other where the sensors of the sensor group detect the sheet P in the second operation. 
     The maintenance-mechanism control circuit  109  is configured to control the maintenance mechanism  30  to conduct the capping operation when a jam of the sheet P that is being conveyed or transferred occurs. In particular, the maintenance-mechanism control circuit  109  as an intervening-member-movement control device is configured to control the maintenance mechanism  30  such that the caps  31  move, in the second operation, in the direction parallel to the sheet conveyance direction. Further, the maintenance-mechanism control circuit  109  is configured to control the maintenance mechanism  30  such that the caps  31  are moved by the distance “b” larger than the pitch “a” at which the four ink-jet heads  2  are arranged in the sheet conveyance direction A. 
     The CPU  102  judges that a jam of the sheet P has occurred only when a time interval of detection of the sheet P by the two sensors in each of the three sets of sensors, i.e., the sensors  71  and  72 , the sensors,  73  and  74 , and the sensors  75  and  76 , exceeds respective preset values. In other words, the CPU  102  judges that a jam of the sheet P has occurred in an instance where the downstream-side sensor of each set does not detect the leading end of the sheet P before a prescribed time elapses after detection of the leading end of the sheet P by the upstream-side sensor of the set. The prescribed time is equal to a time obtained by diving the distance between the two sensors in each set along the sheet transfer path, by the sheet transfer speed. 
     More specifically, the CPU  102  initially judges that a jam of the sheet P has occurred in the sheet guide  17  in an instance where the sensor  74  does not yet detect the leading end of the sheet P at an expected time point at which the prescribed time has elapsed from the time point of detection of the leading end of the sheet P by the sensor  73 , namely, in an instance where the sensor  74  does not detect the leading end of the sheet P before the prescribed time elapses after detection of the leading end of the sheet P by the sensor  73 . Here, the prescribed time is equal to a time obtained by dividing the distance between the sensor  73  and the sensor  74 , by the sheet transfer speed. That is, the CPU  102  detects an occurrence of the sheet jam in the sheet guide  17 . The CPU  102  next judges that a jam of the sheet P has occurred at the conveyor mechanism  50  in an instance where the sensor  72  does not detect the leading end of the sheet P before the prescribed time elapses after detection of the leading end of the sheet P by the sensor  71 . Here, the prescribed time is equal to a time obtained by dividing the distance between the sensor  71  and the sensor  72 , by the sheet transfer speed. That is, the CPU  102  when functioning as an output device with the sensors  71 ,  72  judges an occurrence of the sheet jam between the ink-jet heads  2  and the conveyor mechanism  50 . The CPU  102  then judges that a jam of the sheet P has occurred in the sheet guide  18  in an instance where the sensor  76  does not detect the leading end of the sheet P before the prescribed time elapses after detection of the leading end of the sheet P by the sensor  75 . Here, the prescribed time is equal to a time obtained by dividing the distance between the sensor  75  and the sensor  76 , by the sheet transfer speed. That is, the CPU  102  detects an occurrence of the sheet jam in the sheet guide  18 . 
     The head control circuit  106  and the conveyor-mechanism control circuit  107  stop ejection of the ink from each ink-jet head  2  and stop conveyance of the sheet P by the conveyor mechanism  50  where the CPU  102  judges that the sheet jam has occurred. Where the time interval of detection of the sheet P by the two sensors in each of the three sets of sensors is held within the prescribed time and the CPU  102  does not judge the occurrence of the sheet jam, the inks are ejected to the sheet P in a state in which the ink-jet heads  2  are opposed to the sheet P, whereby an image is formed on the sheet P. The image-formed sheet P is discharged onto the discharged-sheet receiving portion  15 . 
     &lt;Operations of the Ink-Jet Printer&gt; 
     There will be next explained operations of the thus constructed ink-jet printer  1  referring to a jam-clearing routine shown in  FIG. 10 . The jam-clearing routine of  FIG. 10  is a routine for dealing with a sheet jam at the conveyor mechanism  50 . Sheet jams in the sheet guides  17 ,  18  are dealt with according to respective routines, which are not explained here. 
     The jam-clearing routine shown in  FIG. 10  starts with step S 1  (hereinafter “step” is omitted where appropriate) in which a conveyor-portion-jam detecting processing (that will be explained with reference to the routine of  FIG. 11 ) is conducted. S 1  is followed by S 2  to judge whether a sheet jam has occurred at the conveyor mechanism  50 . Where it is judged that the sheet jam has not occurred, the control flow goes back to S 1 . On the other hand, where it is judged that the sheet jam has occurred, S 3  is implemented in which the head control circuit  106  controls the ink-jet heads  2  so as to stop the recording operation and S 4  is implemented in which the conveyor-mechanism control circuit  107  controls the conveyor mechanism  50 , the feed rollers  21   b ,  22   b ,  23   b , and the sheet supply roller  12  so as to stop conveyance or transfer of the sheet P. Then S 5  is implemented in which an error signal is transmitted from the communication circuit  112  to the exterior via the communication portion  20 . 
     Subsequently, S 6  is implemented in which the up/down-moving-mechanism control circuit  108  controls the up/down moving mechanism  80  to move the conveyor mechanism  50  downward, so that the conveyor mechanism  50  is placed at the sheet removal position distant from the ink-jet heads  2 . S 6  is followed by S 7  in which the maintenance-mechanism control circuit  109  controls the maintenance mechanism  30  to conduct the capping operation in which the ejection surfaces  2   a  are covered with the caps  31 . In this state, the user is allowed to conduct the jam-clearing processing to remove the jammed sheet P, by opening the first door  4 . 
     Thereafter, it is judged in S 8  whether the jam-clearing completion signal indicative of completion of the jam-clearing processing by the user has been received. Where it is judged that the jam-clearing completion signal is not received yet, S 8  is repeatedly implemented until the jam-clearing completion signal is received. On the other hand, where it is judged that the jam-clearing completion signal has been received, S 9  is implemented in which the conveyor-mechanism control circuit  107  controls the conveyor mechanism  50  such that the adhesion device  60  is placed in its operating state for permitting the sheet P to adhere to the conveyor surface  54  if the sheet P exists at the conveyor mechanism  50 . Subsequently, the sensors of the sensor group start detecting or sensing the sheet P. 
     Thereafter, S 11  is implemented in which the up/down-moving-mechanism control circuit  108  controls the up/down moving mechanism  80  to move the conveyor mechanism  50  upward. It is noted that the speed of the upward movement of the conveyor mechanism  50  is lower than the speed of the downward movement of the same  50 . Then S 12  is implemented in which the maintenance-mechanism control circuit  109  controls the maintenance mechanism  30  to start a movement of the caps  31  back to the initial position, in which the caps  31  are initially moved to the downstream side in the direction parallel to the sheet conveyance direction by a distance “b” larger than the pitch “a” at which the ink-jet heads  2  are arranged in the sheet conveyance direction A. Then S 13  is implemented to judge whether any of the sensors of the sensor group has detected or sensed the sheet P. 
     Where it is judged in S 13  that the sheet P has not been detected, S 14  is implemented in which the maintenance-mechanism control circuit  109  controls the maintenance mechanism  30  such that the caps  31  return to the initial position. Then S 15  is implemented in which the up/down-moving-mechanism control circuit  108  controls the up/down moving mechanism  80  such that the conveyor mechanism  50  stops at the recording position. Subsequently, S 16  is implemented to stop the operation by the adhesion device  60  which permits the sheet P to adhere to the conveyor surface  54 , and S 17  is implemented to stop the sensors of the sensor group from detecting or sensing the sheet P. Them the control flow goes back to S 1 . 
     In an instance where it is judged in S 13  that the sheet P has been detected, S 18  is implemented in which the up/down-moving-mechanism control circuit  108  controls the up/down moving mechanism  80  to stop the upward movement of the conveyor mechanism  50 . Subsequently, S 19  is implemented in which the maintenance-mechanism control circuit  109  controls the maintenance mechanism  30  to stop the movement of the caps  31 . Thereafter, S 20  is implemented to stop the operation by the adhesion device  60  which permits the sheet P to adhere to the conveyor surface  54 , and S 21  is implemented to stop the sensors of the sensor group from detecting or sensing the sheet P. Then the control flow goes back to S 5 , and the capping operation is again conducted to cover the ejection surfaces  2   a  with the caps  31 . In this state, the user is allowed to again conduct the jam-clearing processing to clear the jam of the sheet P. 
     There will be next explained a conveyor-portion-jam detecting routine executed in S 1  of the routine of  FIG. 10 , with reference to  FIG. 11 . As shown in  FIG. 11 , a flag is set at “0” in S 101 . The flag is used for judging in S 2  of the routine of  FIG. 10  whether the sheet jam has occurred or not. In an instance where the sheet jam has occurred, the flag is changed to “1”. That is, where the flag is “1”, it is judged that the sheet jam has occurred at the conveyor mechanism  50 . 
     Subsequently, it is judged in S 102  whether the upstream-side sensor  71  has detected the leading end of the sheet P. Where it is judged in S 102  that the upstream-side sensor  71  has not yet detected the leading end of the sheet P, the sub routine is ended and goes back to the jam-clearing routine of  FIG. 10 . 
     On the other hand, where it is judged in S 102  that the upstream-side sensor  71  has detected the leading end of the sheet P, it is judged in S 103  whether the downstream-side sensor  72  has detected the leading end of the sheet P. Where it is judged in S 103  that the downstream-side sensor  71  has detected the leading end of the sheet P, the sub routine is ended and goes back to the jam-clearing routine of  FIG. 10 . 
     On the other hand, where it is judged in S 103  that the downstream-side sensor  72  has not yet detected the leading end of the sheet P, it is judged in S 104  that the prescribed time has elapsed. Where it is judged in S 104  that the prescribed time has not elapsed, the control flow goes back to S 103 . On the other hand, where it is judged in S 104  that the prescribed time has elapsed, it is judged that the sheet jam has occurred and the flag is changed from “0” to “1” in S 105 . Thus, the sub routine is ended and the control flow goes back to the jam-clearing routine of  FIG. 10 . 
     2. Second Embodiment 
     &lt;Mechanical Structure of Ink-Jet Printer&gt; 
     Next, there will be explained an ink-jet printer  1  according to a second embodiment with reference to  FIG. 12 . The ink-jet printer of the second embodiment differs from the ink-jet printer of the first embodiment in that the ink-jet printer of the second embodiment does not have the maintenance mechanism  30  and that the sensors of the sensor group are disposed integrally with the ink-jet heads  2 , namely, disposed so as to be immovable relative to the ink-jet heads  2 , at the lower surface of the frame  7  to which the ink-jet heads  2  are fixed. 
     More specifically, the sensors  71 ,  41 L,  41 R are disposed upstream of the most upstream ink-jet head  2 . The sensors  42 L,  42 C,  42 R are disposed between the most upstream ink-jet head  2  and its neighboring ink-jet head  2  located downstream of the most upstream ink-jet head  2 . The sensors  43 L,  43 C,  43 R are disposed between the second ink-jet head  2  from the upstream side and its neighboring ink-jet head  2  located downstream of the second ink-jet head  2 . The sensors  44 L,  44 C,  44 R are disposed between the most downstream ink-jet head  2  and its neighboring ink-jet head  2  located upstream of the most downstream ink-jet head  2 . The sensors  72 ,  45 L,  45 R are disposed downstream of the most downstream ink-jet head  2 . 
     These sensors of the sensor group are configured to detect the jammed sheet existing between the conveyor mechanism  50  and the ink-jet heads  2  which are moved relative to each other from the sheet removal position to the recording position. 
     As described above, the sensors of the sensor group are disposed integrally with the ink-jet heads  2 , namely, disposed so as to be immovable relative to the ink-jet heads  2 , whereby it is possible to detect the jammed sheet P before the jammed sheet comes into contact with the ink-jet heads  2 . Further, the sensors  42 L,  42 C,  42 R, the sensors  43 L,  43 C,  43 R, and the sensors  44 L,  44 C,  44 R are disposed between corresponding adjacent two ink-jet heads  2 , whereby the jammed sheet P can be detected even when the jammed sheet P exists between any adjacent two ink-jet heads  2 . 
     The ink-jet printer of the second embodiment is identical with the ink-jet printer of the first embodiment except for the above structure, and a detailed explanation is dispensed with. 
     &lt;Modifications&gt; 
     While the presently preferred embodiments have been described, it is noted that the invention is not limited to the details of the illustrated embodiments, but may be embodied with various changes and modifications, which may occur to those skilled in the art, without departing from the spirit and scope of the invention defined in the attached claims. It is further noted that the effects of the invention described in the illustrated embodiments are preferable ones arising from the invention and that the effects of the invention are not limited to those described in the illustrated embodiments. 
     In the illustrated embodiments, the upward movement of the conveyor mechanism  50  is stopped where the jammed sheet P is detected in the second operation in which the conveyor mechanism  50  is moved to the recording position. In this instance, the conveyor mechanism  50  may be configured to be moved downward to the sheet removal position. 
     The second operation in which the conveyor mechanism  50  is moved to the recording position may be conducted at a speed not lower than the speed at which is conducted the first operation in which the conveyor mechanism  50  is moved to the sheet removal position. 
     In the illustrated embodiments, the sensors  71   72  for detecting the sheet P between the ink-jet heads  2  and the conveyor mechanism  50  are configured to be used for detecting the sheet P in the recording operation of recording an image on the sheet P. Other sensors may be provided to be used for detecting the sheet P in the recording operation. 
     In the illustrated embodiments, the adhesion device  60  may be configured not to be placed in the operating state in the second operation in which the conveyor mechanism  50  is moved to the recording position. 
     In the illustrated embodiments, the sensors may not be arranged in a plural number in the direction perpendicular to the sheet conveyance direction and parallel to the ejection surfaces  2   a.    
     The ink-jet recording apparatus according to the present invention is not limited to the ink-jet type, but may be applicable to a thermal type. Further, the ink-jet recording apparatus according to the present invention is not limited to the line type, but may be applicable to a serial type in which the heads are reciprocated. The principle of the invention may be applicable to not only the printer, but also a facsimile machine, a copying machine, and the like. While the conveyor mechanism  50  in the illustrated embodiments is configured to convey the sheet P in the horizontal direction, the conveyor mechanism  50  may be configured to convey the sheet P in directions other than the horizontal direction such as a direction inclined with respect to the horizontal direction, the vertical direction, etc., by arranging the conveyor surface  54  such that the conveyor surface  54  that is parallel to the ejection surfaces  2  is inclined or vertical with respect to the horizontal direction.