Patent Publication Number: US-7725071-B2

Title: Both side printable printer

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority to Japanese Patent Application No. 2005-345766 filed on Nov. 30, 2005, the contents of which are hereby incorporated by reference into the present application. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a printer capable of printing on both sides of a piece of sheet (hereinafter, “a piece of sheer” may simply referred to as a sheet). The printer of the present invention is generic name of a device that transport cut sheets one after the other from a sheet case to a printing unit where characters, graphics, or photographs, etc., are sequentially printed on each sheet. It is not limited to a single-function printer and instead, a copier, a facsimile machine, a complex device (or a multifunction device) or the like that comprises a device for printing on a sheet corresponds to what we call a “printer” herein. 
   2. Description of the Related Art 
   Recently, in order to save resources, printers capable of printing on both sides of each sheet have been actively introduced into offices or homeplaces. 
   In general, a printer that prints on one side of a sheet has a cassette (or a sheet case), a printing unit, and a supply unit. Sheets not yet printed are accommodated in the cassette. The printing unit comprising a printing head which discharges ink droplets or toner on the sheet. The supply unit feeds a piece of sheet one by one from the cassette to the printing unit. Printing on both sides of sheets further requires a sheet returning mechanism for transporting sheet one side of which has been printed at the printing unit, to the printing unit once again. Japanese Patent Application Laid-Open No. 2004-102165 (see particularly  FIG. 2 ) discloses one example of a printer having a sheet returning mechanism that enables both side printing (double face printing). This printer is configured as described below. On the lower side of a case of a printer, the cassette in which stacked sheets are contained is located. On the tipper side of the case, the printing unit comprising a toner type printing head that discharges ink droplets by means of an electro photograph process is located. Between the printing unit located above and the cassette located below, the supply unit is located. The supply unit feeds a sheet from the cassette to the printing unit. The supply unit feeds sheets one by one from the cassette toward the printing unit. A sheet fed from the cassette runs through a U-shaped feed-in pathway. The U-shaped feed-in pathway guides the sheet to the printing unit. The sheet guided to the printing unit is printed on one side by the printing unit. The one side printed sheet is discharged (or pulled out) from the printing unit through a feed-out pathway. The one side printed sheet once stops on the feed-out pathway. Then, the sheet is back-fed through the feed-out pathway and transported to return pathway that diverges from the feed-out pathway. The feed-out pathway diverged from the feed-out pathway extends downward along with the lateral side of the printing unit. The return pathway bends from the side on the printing unit toward above the cassette. The return pathway passes between the cassette and the printing unit, and joins into feed-in pathway. Along the return pathway, a number of rollers are arranged for transporting sheets. Passing through the return pathway and feed-in pathway, the one side printed sheet is fed again to the printing unit. The return pathway and the number of rollers arranged along with the return pathway forms sheet returning mechanisms that enable both side printing. Passing through the U-shaped feed-in pathway, sheets are reversed upside down and transported to the printing unit. In other words, the surface that is the top face of the sheet when the sheet is in the cassette becomes the underside when the sheet is in the printing unit. Passing through the U-shaped feed-in pathway once again, the one side printed sheet will have other side printed. 
   BRIEF SUMMARY OF THE INVENTION 
   In the printer disclosed in Japanese Patent Application Laid-Open No. 2004-102165, the return pathway runs along the lateral side of the printing unit and between the printing unit and the cassette. The printer has such a structure that the printing unit, the return pathway, and the cassette overlap along with the vertical direction, which makes the printer grow in size. In addition, the printer has to carry the one side printed sheet along the long return pathway, a number of rollers should be arranged along the return pathway. This increases the number of components that enable both side printing. 
   The present invention is made to solve the conventional problems described above. It is an object of the present invention to provide a small-size both side printable printer that has a fewer number of components and a simple structure. 
   The printer of the present invention comprises a printing unit for printing onto a sheet, a cassette located below the printing unit and for containing stacked sheets, and a supply unit for discharging (feeding) one sheet from the cassette toward the printing unit. The printer also comprises a sheet support plate located in the printing unit. The sheet fed from the cassette by the supply unit is placed on the sheet support plate during being printed. An opening is formed on the sheet support plate. The printer also comprises a cover plate being movable between a covering position that covers the opening and an uncovering position that uncovers the opening. The printer also comprises a pair of feed-out rollers that nips a sheet at the exit of the printing unit. The pair of feed-out rollers pulls out the nipped sheet from the printing unit by rotating in a forward direction. The cover plate is moved at the covering position during printing. The cover plate moved at an uncovering position when the pair of feed-out rollers rotates in a reverse direction to return the sheet (nipped and pulled out by the pair of feed-out rollers) to the cassette through the opening of the sheet support plate. 
   What is herein meant by the rotation in a forward direction of the pair of feed-out rollers is the rotation direction of the pair of feed-out rollers when the nipped sheet is pulled out from the printing unit. If the pair of feed-out rollers continues to rotate in the forward direction after nipping the sheet, it can discharge the one side printed sheet out of the printer. 
   The pair of feed-out rollers feeds the one side printed sheet back to the printing unit. The back fed sheet passes through the opening formed on the sheet support plate and returns to the cassette located below the printing unit. A pathway of sheet from the opening formed on the sheet support plate to the cassette corresponds to a return pathway. The sheet support plate is arranged above the cassette. Therefore, the return pathway guides the one side printed sheet almost linearly from the opening formed on the sheet support plate to the cassette, which can shorten the return pathway. Thus, not only the number of rollers for carrying the one side printed sheet along the return pathway can be reduced but also size of the printer can be miniaturized. In addition, the one side printed sheet returned to the cassette can be fed again to the printing unit by the supply unit that feeds unprinted sheets from the cassette to the printing unit. In other words, the supply unit can be used for feeding both of unprinted sheets and one side printed sheets to the printing unit. It can reduce the number of components that enable both side printing. 
   The printer according to the present invention preferably has the following technical characteristics (A). 
   (A) The supply unit has a supply roller that is driven by motor to rotate. When the supply unit feeds a sheet, the supply roller is pressed against the top of the stacked sheets. A piece of sheet on the top of the stacked sheets is fed from the cassette by rotating supply roller. When the piece of sheet (the sheet is printed on its one side) returns to the top of the stacked sheets through the return pathway, the supply roller detaches from the top of the stacked sheets. The supply roller is pressed again against the top of the stacked sheets after the one side printed sheet returns to the top of the stacked sheet. The one side printed sheet is smoothly carried on the stacked sheets as the supply roller detaches from the top of the stacked sheets. 
   Instead of the technical characteristics (A), the printer may have the following technical characteristics (B). 
   (B) The supply unit has a supply roller that is pressed against the top of the stacked sheets. When the supply unit feeds a sheet, the supply roller is driven by motor to rotate. A piece of sheet on the top of the stacked sheets is fed from the cassette by rotating supply roller. When the piece of sheet (the sheet is printed on its one side) returns to the top of the stacked sheets through the return pathway, the supply roller becomes freely rotatable from the drive motor. The supply roller is driven again to rotate after the one side printed sheet returns to the top of the stacked sheet. The one side printed sheet is smoothly inserted between the supply roller and top of the stacked sheet as the supply roller becomes freely rotatable when the one side printed sheet returns to the cassette. 
   The printer according to the present invention preferably has the following technical characteristics in addition to the above technical characteristics (A). The pair of feed-out rollers releases the force of nipping when the supply roller is pressed again against the top of the stacked sheets. In addition to the above technical characteristics (B), it preferably has the following technical characteristics. The pair of the feed-out roller releases the force of nipping when the supply roller is driven again. 
   According to any of the above technical characteristics, the one side printed sheet returned to the cassette is smoothly fed again by the supply roller because the pair of feed-out rollers releases the one side printed sheet. 
   In addition, the printer of the present invention preferably has the following technical characteristics. When the cover plate is at the covering position, the top face thereof forms a plane (planar surface) together with the top face of the sheet support plate. In addition, when the cover plate is at the uncovering position, the top face thereof tilts to the top face of the sheet support plate. By forming the planar surface together with the top face of the sheet support plate, the cover plate does not prevent movement of a sheet being printed. On the one hand, as the cover plate tilts, one side printed sheet can smoothly enter the opening formed on the sheet support plate and transported to the cassette located below the sheet support plate. 
   It is preferable that the printer of the present invention further has a pair of feed-in rollers. The pair of the feed-in rollers nips a sheet in front of the inlet of the printing unit and carries the nipped sheet into the printing unit by rotating in the forward direction. The pair of feed-in rollers and the pair of feed-out rollers rotate simultaneously in the same direction. In other words, the pair of feed-in rollers rotates in the forward direction while the pair of feed-out rollers rotates in the forward direction, and the former rotates in the reverse direction when the latter rotates in the reverse direction. Such the configuration could eliminate the need for controlling the pair of feed-in rollers and the pair of the feed-out rollers independently during double-side printing and during intermittent feeding. The intermittent feeding will be described later. Control for conducting the double-side printing of the printer can be simplified. 
   The printing unit of the printer according to this invention preferably has a printing head of ink discharging method that selectively discharges ink droplets onto sheets. The sheet support plate, while having the function of defining a gap between a sheet lying thereon and the printing head, is also used as a member for guiding one side printed sheet to the cassette through the opening. This could enable reduction of the number of components and miniaturization of the printer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an overall perspective view of a multi-function device. 
       FIG. 2  is a perspective view of the lower case viewed from the back, with the upper case removed. 
       FIG. 3  is a plan view of the condition in which the cassette is attached to the lower case. 
       FIG. 4  is a perspective view of the printing unit with the guide plate on the rear side and the sheet support plate removed. 
       FIG. 5  is a view taken along V-V line of  FIG. 4 . 
       FIG. 6  is a perspective view viewed from the side of the pair of feed-out rollers of the condition in which a carriage is located on a maintenance unit. 
       FIG. 7  is an enlarged sectional view of the periphery of the opening on the sheet support plate (with the opening closed). 
       FIG. 8  is an enlarged sectional view of the periphery of the opening on the sheet support plate (with the opening opened). 
       FIG. 9  is an enlarged sectional view of the printing unit and the supply unit. 
       FIG. 10  is an enlarged perspective view of the vicinity of a roller holder. 
       FIG. 11  to  FIG. 14  are schematic sectional views illustrating the operation of carrying a sheet during double-side printing. 
       FIG. 15  is a front view illustrating power transmission while a sheet is fed in the intermittent feeding mode (first mode). 
       FIG. 16  is a perspective view illustrating power transmission while a sheet is fed in the intermittent feeding mode (first mode). 
       FIG. 17  is a side view illustrating power transmission while a sheet is fed in the intermittent feeding mode (first mode). 
       FIG. 18  is a perspective view of a first slider (first block) and a second slider (second block). 
       FIG. 19  is a perspective view of condition in which the first and second blocks are combined. 
       FIG. 20  is a front view of condition in which the first and second blocks are shallowly engaged. 
       FIG. 21  is a front view of condition in which the first and second blocks are deeply engaged. 
       FIG. 22  is a front view showing power transmission while a sheet is fed in continuous feeding mode (second mode). 
       FIG. 23  is a perspective view showing power transmission while a sheet is fed in the continuous feeding mode (second mode). 
       FIG. 24  is a side view showing power transmission while a sheet is fed in the continuous feeding mode (second mode). 
       FIG. 25  is a front view showing power transmission in return mode. 
       FIG. 26  is a perspective view showing power transmission in the return mode. 
       FIG. 27  is a side view showing power transmission in the return mode. 
       FIG. 28  is a front view showing power transmission in maintenance operation mode. 
       FIG. 29  is a perspective view showing power transmission in the maintenance operation mode. 
       FIG. 30  is a lateral view showing power transmission in the maintenance operation mode. 
       FIG. 31  is a schematic view of a power transmission switching means. 
       FIG. 32  is a front view schematically showing a stare in which the modes are switched by the power transmission switching means 
       FIG. 33  is a plan view showing a state in which the modes are switched by the power transmission switching means 
       FIG. 34  is a functional block diagram of a control device. 
       FIG. 35  is a flow chart that controls transportation of a sheet in double-side printing. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be described in detail with reference to the drawings.  FIG. 1  is an external perspective view of a multi-function device  1  equipped with the facsimile function, printing function, copying function, and scanner function. The multi-function device  1  transports one by one sheets contained in a cassette by a supply unit to a printing unit, and prints characters, graphics, photographs, etc. (hereinafter generically referred to as graphic patterns) on the transported sheets. 
   The multi-function device  1  has a lower case  2  and an upper case  3 . The lower case  2  is shaped almost like a box with a top face opened. Coupled to the left flank of the lower case  2  by way of hinges (not shown), the upper case  3  is rotatable from a position in  FIG. 1  in arrow  202  direction around a rotation axis  200 . When the upper case  3  rotates in an arrow  202  direction, interior of the lower case  2  becomes visible from the external. 
   In the following description, X direction of  FIG. 1  is referred to as a cross direction, Y direction is referred to as a horizontal direction, and Z direction is referred to as a vertical direction. 
   An operation panel  30  is located on the front of a top face of the upper case  3 . Various types of buttons such as numeric buttons, Start button, or Select Function buttons, etc. are provided on the operation panel  30 . Pressing these buttons, various operations can be executed. A liquid crystal display (LCD)  31  is provided on the operation panel  30  where set conditions of the multi-function device  1  or various operation messages, etc. are displayed, as necessary. 
   A scanner device  33  is placed inside the upper case  3 . The scanner device  33  comprises a glass plate (not shown) on which a script is placed, a graphic pattern reader unit (not shown) located beneath the glass plate, and a cover  34  covering a top face of the glass plate. The cover  34  is rotatable around a rotation axis  204  from a position in  FIG. 1  in an arrow  206  direction. When the cover  34  rotates in the arrow  206  direction, the glass plate is exposed so that the script can be placed thereon. The graphic pattern reader unit comprises a contact image sensor (CIS), extends along in the X direction. A rail (not shown) is provided to guide the graphic reader unit so as to reciprocate the graphic pattern reader unit along Y axis direction. The graphic pattern reader unit reads graphic patterns in the script placed on the glass plate by means of the contact image sensor. 
   When the facsimile function is selected, information read by the graphic pattern reader unit is sent to a facsimile unit at a destination through a telephone circuit. When the copy function is selected, information read by the graphic pattern reader unit is sent to a printing unit in the multi-function device  1 , and graphic patterns read by the graphic pattern reader unit are printed on a sheet. When the scanner function is selected, information read by the graphic pattern reader unit is sent to a computer (not shown). 
   There is provided a posture retention means to maintain the interior of the lower case  2  exposed, by widely rotating the upper case  3  around the rotation axis  200 . The posture retention means is comprised of a support rod (not shown) and a guide rail (not shown). One end of the support rod is attached to the vicinity of point  208  of the lower case  2  and can be swung with respect to the lower case  2 . The guide rail extends in the Y direction along a lower face of the backside of the upper case  3 . A channel extending in the Y direction is formed on the guide rail. A guide pin is fixed to the other end of the support rod and inserted into said channel. An engagement unit (not shown) for preventing the guide pin from sliding is formed in the vicinity of point  208 . When the upper case  3  is widely rotated around the rotating shaft  200 , the guide pin of the support rod fits into the engagement unit of the guide rail and prevents the upper case  3  from widely rotating downward. 
   Next, a structure for printing graphic patterns on sheets contained in the cassette will be described with reference to  FIG. 1  to  FIG. 14 . The structure is located in the lower case  2  of the multi-function device  1 . As shown in  FIG. 1 , a cassette  5  is arranged at the center part of the horizontal direction in the lower case  2 . The cassette  5  is such configured that it can be pulled out with respect to an opening  2   a  formed on the front face of the lower case  2 . The cassette  5  contains more than one sheet P in a stacked condition. A separation inclined surface  8  are provided at the front end of the cassette  5 . The separation inclined surface  8  is formed of material having a high coefficient of friction. 
   As shown in  FIG. 5 ,  FIG. 11  to  FIG. 14 , in the lower case  2 , a supply unit  6 , a U-shaped sheet guide  9 , and a printing unit  10  are arranged in addition to the cassette  5 . 
   The supply unit  6  and the printing unit  10  are attached to a metal frame  39  fixed into the lower case  2 . As shown in  FIG. 11 , the cassette  5  is located below the printing unit  10 . A sheet P is discharged from the cassette  5  and fed into the printing unit  10  through the U-shaped sheet guide  9 . 
   As shown in  FIG. 2  to  FIG. 5 , a frame  39  is located on the backside of the lower case  2  and above the cassette  5 . The frame  39  comprises a bottom surface  39   a  extending in the Y axis direction, a left wall  39   b  rising upward from the left end of the bottom surface  39   a , a right wall  39   c  rising upward from the right end of the bottom surface  39   a , a front side guide plate  41  connecting the left wall  39   b  and the right wall  39   c , and a back side guide plate  40  connecting the left wall  39   b  and the right wall  39   c . The front side guide plate  41  and the backside guide plate  40  extend in the Y direction. 
   The supply unit  6  is located above the cassette  5 . The supply unit  6  feeds a piece of sheet P on top of the stacked sheets in the cassette  5  toward the printing unit  10 . The sheet P fed from the cassette  5  by the supply unit  6  is guided along the U-shaped sheet guide  9  into the printing unit  10 . As shown in  FIG. 11 , the U-shaped sheet guide  9  flips the sheet that entered from the end thereof and guides it to the printing unit  10 . 
   As shown in  FIG. 9 , the supply unit  6  comprises an arm  6   a  and a supply roller  7 . One end of the arm  6   a  is rotatably coupled to the bottom surface  39   a  of the frame  39  by a drive shaft  14 . The supply roller  7  is attached to other end of the arm  6   a . The arm  6   a  is always biased downward by a biasing means (not shown) such as a torsion spring, etc. In other words, the supply roller  7  attached to the other end of the arm  6   a  is pressed against the top of the stacked sheets in the cassette  5 . 
   A plurality of gear groups (not shown) for transmitting power from the drive shaft  14  to the supply roller  7  is provided on the arm  6   a . Power of an LF motor  42  is transmitted to the drive shaft  14  and the supply roller  7  by the gear groups. When the LF motor  42  rotates in the reverse direction, the supply roller  7  rotates in the direction so as to discharge a top sheet P of the stacked sheets toward the printing unit  10 . The gear groups are such configured that the supply roller  7  can freely rotate around the drive shaft  14  when the LF motor  42  rotates in the forward direction. In other words, the supply roller  7  is disengaged from the LF motor  42 . To be specific, the gear groups have such structure that engagement among some gears is released when the LF motor  42  rotates in the forward direction. As shown in  FIG. 4 , the LF motor  42  is located at the left end of the frame  39 . 
   With reference to  FIG. 11 , the mechanism for discharging sheets one by one from the stacked sheets in the cassette  5  toward the printing unit  10  will be described. 
   First, let the LF motor  42  rotate in the reverse direction. When the LF motor  42  rotates in the reverse direction, the drive shaft  14  supporting the arm  6   a  of the supply unit  6  rotates clockwise. When the drive shaft  14  rotates clockwise, the supply roller  7  rotates anticlockwise. The supply roller  7  contacts the top of the stacked sheets in the cassette  5 . Thus, as the supply roller  7  rotates anticlockwise, a top sheet P of the stacked sheets is discharged to the U-shaped sheet guide  9  (discharged toward the printing unit  10 ). 
   At the end of the U-shaped sheet guide  9  on the side of the printing unit  10  is arranged a pair of feed-in rollers  20   a ,  20   b , to be discussed later. When the LF motor  42  rotates in the reverse direction, the feed-in roller  20   a  rotates anticlockwise (and the feed-in roller  20   b  rotates clockwise). Thus, the sheet P that reaches the pair of feed-in rollers  20   a ,  20   b  comes to rest, abutting against the pair of feed-in rollers  20   a ,  20   b , without getting caught up between the feed-in rollers  20   a ,  20   b.    
   Then, let the LF motor  42  rotate in the forward direction. When it does so, the feed-in roller  20   a  rotates clockwise (and the feed-in roller  20   b  rotates anticlockwise). The sheet P is get caught between the pair of feed-in rollers  20   a ,  20   b . In other words, sheet P is nipped by the pair of the feed-in rollers  20   a ,  20   b . Furthermore, when the feed-in roller  20   a  rotates clockwise, the sheet P is fed to the left. In fact, the sheet P is carried into the printing unit  10 . On the one hand, when the LF motor  42  rotates in the forward direction, the drive shaft  14  rotates anticlockwise. When the drive shaft  14  rotates anticlockwise, the supply roller  7  becomes freely rotatable around the drive shaft  14 , as described earlier. In other words, the supply roller  7  is disengaged from the LF motor  42 . Since the supply roller  7  is disengaged from the LF motor  42 , no sheet is discharged from the stacked sheets. This could make it possible to transport sheets one by one from the cassette  5  to the printing unit  10 . 
   The printing unit  10  comprises a printing head  12  of ink jet method that selectively jets ink droplets towards a surface of a sheet, a carriage  13  supporting the printing head  12 , and a sheet support plate  11  which supports sheets below the printing head  12 . The sheet support plate  11  is made of synthetic resin. Guided into the printing unit  10  by the U-shaped sheet guide  9 , the sheet P is carried onto the sheet support plate  11 . When the sheet P is carried onto the sheet support plate  11 , the printing head  12  prints given graphic patterns onto the sheet P. As described later, the printed sheet P is pulled out from the printing unit  10  by a pair of feed-out rollers  21   a ,  21   b . Structure of the sheet support plate  11  will be described later. In the following, in the printing unit  10 , the side into which the sheet P is carried from the cassette  5  may be referred to as an inlet of the printing unit. The side from which a printed sheet P is discharged after printing may be referred to as the exit of the printing unit  10 . An area that lies between the inlet and exit as well as between the printing head  12  and the sheet support plate  11  may be referred to as a printing area. 
   The carriage  13  supporting the printing head  12  is slidably supported by the front side guide plate  41  and the backside guide plate  40  of the frame  39 . 
   To have the carriage  13  reciprocate, on a top face of the front side guide plate  41  located downstream of a transport direction of the sheet P (an arrow A direction of  FIG. 4 ) is arranged a timing belt  25  extending in a main scanning direction (the Y axis direction) (See  FIG. 2 ). Respective ends of the timing belt  25  are supported by pulleys  25   a ,  25   b . The timing belt  25  is driven by a CR (carriage) motor  24 . The CR motor  24  (a DC motor in this embodiment) is fixed to the underside of the front side guide plate  41  (See  FIG. 2  and  FIG. 6 ). As shown in  FIG. 6 , a strip-shaped linear encoder (encoder strip)  37  is arranged on the front side guide plate  41  on the downstream side. The linear encoder  37  extends along the main scanning direction (Y axis direction). The linear encoder  37  detects a position or speed of the carriage  13  in the main scanning direction (Y axis direction). The linear encoder  37  has an inspection surface (a surface on which slits are arranged with same intervals in the Y axis direction). The linear encoder  37  is arranged on the front side guide plate  41  so that the inspection surface is opposed to the flank of the carriage  13 . 
   The multi-function device  1  is capable of color printing. Ink cartridges  26  for supplying ink to the printing head  12  for color printing are detachably arranged in the lower case  2 . The respective ink cartridges  26  contain ink of each color. In the case of the multi-function device  1 , ink of 4 colors, namely, black (B), cyan (C), magenta (M), and yellow (Y) is respectively contained in the four ink cartridges  26 . Needless to say, in a printer using more than 3 colors of ink may be such structured that as many ink cartridges as the number of ink colors can be accommodated. Ink is supplied from the respective ink cartridges  26  to the printing head  12  by way of flexible ink tubes  28  (See  FIG. 2 ). 
   As shown in  FIG. 3 , an ink receiver unit  35  is provided in a region that is outside of the width of a sheet P to be carried (shorter side of the sheet P) and close to the left wall  39   b  of the frame  39 . In addition, a maintenance unit  36  is provided in a region that is outside of the width of the sheet P to be carried and close to the right wall  39   c  of the frame  39 . 
   The printing head  12 , at fixed intervals, jets ink towards the ink receiver unit  35  to prevent clogging of nozzles. Ink jetted to prevent clogging is received by the ink receiver unit  35 . 
   If the printing head  12  is not used, the carriage  13  supporting the printing head  12  moves to a position opposed to the maintenance unit  36 . At this position, a capping unit  36   a  (See  FIG. 4 ) covers a nozzle surface of the printing head  12  from the lower side, and prevents ink from drying in the nozzles of the printing head  12 . In addition, recovery process, etc., for removing any air bubbles from a buffer tank (not shown) provided on the printing head  12  by actuating a suction pump (not shown) when necessary and sucking in ink from the nozzles is performed. In addition, when the carriage  13  moves in the lateral direction from the position opposed to the maintenance unit  36 , it wipes out the nozzle surface with a wiper blade  36   b  (See  FIG. 4 ) and cleans the printing head  12 . 
   Then, the pair of feed-in rollers  20   a ,  20   b  for carrying a sheet P feeds from the cassette  5  into the printing unit  10  (i.e., onto the sheet support plate  11 ) and the pair of feed-out rollers  21   a ,  22   b  for pulling the printed sheet P from the printing unit  10  will be described. 
   As shown in  FIG. 11 , the pair of feed-in rollers  20   a ,  20   b  are arranged on the side of inlet of the printing unit  10 . The pair of the feed-out rollers  21   a ,  21   b  are arranged on the side of exit of the printing unit  10 . The both ends of the feed-in roller  20   a  and of the feed-out roller  21   a  are supported by the left wall  39   b  and the right wall  39   c  of the frame  39 . 
   Of the pair of feed-in rollers  20   a ,  20   b , the feed-in roller  20   a  located in the upper side is driven to rotate by the LE motor  42 . The feed-in roller  20   b  located below the feed-in roller  20   a  is pressed with certain force to the feed-in roller  20   a , and also rotates accordingly when the feed-in roller  20   a  rotates. The feed-in roller  20   a  is a feed-in drive roller  20   a , while the feed-in roller  20   b  is a feed-in driven roller  20   b.    
   Of the pair of feed-out rollers  21   a ,  21   b , the feed-out roller  21   a  is also driven to rotate by the LF motor  42 . The feed-out roller  21   b  located above the feed-out roller  21   a  is pressed with certain force to the feed-out roller  21   a , and also rotates accordingly when the feed-out roller  21   a  rotates. The feed-out roller  21   a  is a feed-out drive roller  21   a , while the feed-out roller  21   b  is a feed-out driven roller  21   b . In addition, as shown in  FIG. 6 , the multi-function device  1  has a plurality of the feed-out driven rollers  21   b  attached to a roller holder  53 . The plurality of feed-out driven rollers  21   b  is aligned in the Y axis direction with a predetermined interval. The feed-out driven rollers  21   b  are attached to the roller holder  53  via coil springs (not shown). The roller holder  53 , to be described later, is movable relative to the frame  39 . 
   The sheet P guided by the U-shaped sheet guide  9  is nipped by the pair of feed-in rollers  20   a ,  20   b . The nipped sheet P is fed into the printing unit  10  (onto the sheet support plate  11 ) as the pair of feed-in rollers  20   a ,  20   b  rotates in the forward direction. 
   The sheet P printed at the printing unit  10  is further advanced by the pair of feed-in rollers  20   a ,  20   b  and reaches the pair of feed-out rollers  21   a ,  21   b . The sheet P that reaches the pair of feed-out rollers  21   a ,  21   b  is nipped by the pair of feed-out rollers  21   a ,  21   b . The nipped sheet P is pulled out from the printing unit  10  as the pair of feed-out rollers  21   a ,  21   b  rotate in the forward direction. 
   In addition, the pair of feed-in rollers  20   a ,  20   b  and the pair of feed-out rollers  21   a ,  21   b  rotate in synchronization. When the pair of feed-in rollers  20   a ,  20   b  rotates in the direction in which it carried the sheet P from the inlet side into the printing unit  10 , the pair of feed-out rollers  21   a ,  21   b  rotates in the direction in which it pulls our the sheet P from the exit of the printing unit  10 . At this time, the rotation direction of the pair of feed-in rollers  20   a ,  20   b  and that of feed-out rollers  21   a ,  21   b  is referred to as a forward direction. 
   The feed-in drive roller  20   a , the feed-out drive roller  21   a , the supply roller  7 , and the maintenance unit  36  as described above are drive by one LF (for carrying sheets) motor  42 . As shown in  FIG. 4 , the LF motor  42  is arranged in the vicinity of the left wall  39   b  of the frame  39 . Power of the LF motor  42  is transmitted to the feed-in drive roller  20   a , etc. by way of the gear groups  43 . The gear groups  43  will be described with reference to  FIG. 4  and  FIG. 5 . 
   A shaft of the LF motor  42  penetrates the left wall  39   b  of the frame  39  and extends to the outside of the frame  39 . A pinion  43   a  is fixed to the shaft of the LF motor  42 . The gears  43   b ,  43   c , and  43   d  are rotatably supported on the outside of the left wall  39   b.    
   The deceleration gear  43   b  engages with the pinion  43   a . The feed-in drive roller  20   a  is fixed to the deceleration gear  43   b . When the LF motor  42  rotates, the feed-in drive roller  20   a  rotates. As shown in  FIG. 4 , the gear  43   d  engages with the pinion  43   a  through the intermediate gear  43   c . The feed-out drive roller  21   a  is fixed to the gear  43   d . When the LF motor  42  rotates, the feed-out drive roller  21   a  rotates. 
   The deceleration gear  43   b  and the gear  43   d  rotate in opposite directions. Therefore, the feed-in drive roller  20   a  and the feed-out drive roller  21   a  also rotate in the opposite directions. The feed-n drive roller  20   a  is located on the upper side of the sheet P. while the feed-out drive roller  21   a  is located on the lower side of the sheet P. Thus, if the feed-in drive roller  20   a  and the feed-out drive roller  21   a  rotate in the opposite directions, the direction of feeding the sheet P by the feed-in drive roller  20   a  is identical to the direction of feeding the sheet P by the feed-out drive roller  21   a.    
   Power of the LF motor  42  is transmitted from the end of the feed-in drive unit  20   a  to the supply unit  6  through a power transmission switching means  100  to be discussed later. 
   A rotary encoder  44  is provided on the deceleration gear  43   b  for detecting travel distance of a sheet P carried by the pair of feed-in rollers  20   a ,  20   b . A CR motor  24  and the LF motor  42  are such configured that they can switch the rotation direction between in the forward and reverse directions. 
   In the multi-function device  1 , the U-shaped sheet guide  9  corresponds to feed-in pathway for guiding sheets in the cassette  5  to the printing unit  10 . To the left of the printing head  12  as shown in  FIG. 11 , that is, a pathway to which a printed sheet P is discharged from the printing unit  10  corresponds to a feed-out pathway. In normal single-side printing, a top sheet of stacked sheets contained in the cassette  5  is discharged (fed) by the supply unit  6 . The discharged sheet is guided to the printing unit  10  by the feed-in pathway (U-shaped sheet guide  9 ). A sheet printed at the printing unit  10  is guided outside of the multi-function device  1  by the feed-out pathway. 
   Next, both side printing function of the multi-function device  1  will be described. During both side printing, the multi-function device  1  returns to the cassette  5  a sheet P whose one side is printed at the printing unit  10  and which is discharged from the printing unit  10 . Passing through an opening  50  (described later) formed on the sheet support plate  11  arranged within the printing unit  10 , the sheet P discharged (or pulled out) from the printing unit  10  is returned to the top of the stacked sheets in the cassette  5 . As with the initial printing, the returned sheet P is fed to the printing unit  10  again by the supply unit  6  and the U-shaped sheet guide  9 , where other side of the sheet is printed. 
   Referring to  FIG. 7 ,  FIG. 8 , and  FIG. 11  to  FIG. 14 , the sheet support plate  11  arranged opposed to the underside (the surface on which nozzles for jetting ink are formed) of the printing head  12  will be described. The sheet support plate  11  is the plate for supporting a sheet when the printing head  12  prints on the sheet. In addition, the sheet support plate  11  defines an interval (gap length) between the printing head  12  and the sheet during printing. 
   The opening  50  is formed on the sheet support plate  11 . The opening  50  is the opening through which the sheet P nipped by the pair of feed-out rollers  21   a ,  21   b  and pulled out from the printing unit  10  passes when returning to the cassette  6 . As shown in  FIG. 8 , the opening  50  is a notch provided at the exit side end of the printing unit  10  of the sheet support plate  11 . The opening  50  has three sides thereof surrounded by the sheet support plate  11 , with the remaining one side surrounded by the feed-out roller  21   a.    
   The sheet support plate  11  is comprised of a main plate  45  and a sub-plate  46  (cover plate). The main plate  45  is arranged in the upstream of the transport path of a sheet P (on the side of inlet of the printing unit  10 ), while the sub-plate  46  is arranged in the downstream of the transport path (on the side of exit of the printing unit  10 ). The main plate  45  and the sub-plate  46  are formed long in a direction orthogonal to the transport direction of the sheet P. 
   The main plate  45  is fixed to the bottom surface  39   a  of the frame  39  so as to be opposed to the base (the surface on which the nozzles are formed) of the printing head  12 . 
   The sub-plate  46  has both ends thereof in the longitudinal direction (Y axis direction) coupled to the frame  39  by a pin  47 . As shown in  FIG. 7 , the pin  47  couples the end of the sub-plate  46  on the inlet side of the printing unit  10  to the frame  39 . The sub-plate  46  is vertically rotatable around the pin  47 . In other words, the sub-plate  46  can be inclined to the transport direction of the sheet P. The sub-plate  46  rotates vertically with the pin  47  as the rotating shaft by means of a solenoid  49  to be described later. The sub-plate  46  can be rotated (moved) between a position that forms an almost identical plane to the main plate  45  (See  FIG. 7 ) and a position inclined to the main plate  45  (See  FIG. 8 ), by means of the solenoid  49 . The former position is referred to as a covering position, while the latter position is referred to as an uncovering position. The covering position is to close (cover) the opening  50 , while the uncovering position is to open (uncover) the opening  50 . More specifically, at the covering position, the top face of the sub-plate  46  forms one plane together with the top face of the main plate  45 . This is to facilitate passage of the sheet over the sheet support plate  11 . The uncovering position is to open the opening  50  toward the exit of the printing unit  10  (in other words, toward the feed-out rollers  21   a ,  21   b ). This is to facilitate guiding to the opening  50  of the sheet being back fed from the exit side of the printing unit  10 . As shown in  FIG. 11  to  FIG. 14 , the lower face of the end in the downstream of the transport direction of the sub-plate  46  is preferably formed like a taper. With it shaped like this, when the sub-plate  46  rotates so that the end in the downstream of the transport direction of the sub-plate  46  moves upward (namely, when the sub-plate  46  moves to the uncovering position), the opening  50  can be widely opened toward the exit of the printing unit  10 . This makes it possible to smoothly guide the sheet P from the exit side of the printing unit  10  to the lower part of the arm  6   a.    
   The sheet P guided from the exit side of the printing unit  10  to the cassette  5  through the opening  50  and lower part of the arm  6   a  is fed toward the printing unit  10  once again by the supply unit  6  as described above. The fed sheet P is guided to the printing unit  10  by the U-shaped sheet guide  9 . It is carried from the U-shaped sheet guide  9  into the printing unit  10  again by the pair of feed-in rollers  20   a ,  20   b . Thus, graphic patterns are printed on both sides of the sheet P. 
   Then, the operation of the multi-function device  1  during both side printing of the sheet P will be described in detail with reference to  FIG. 11  to  FIG. 14 . 
   As shown in  FIG. 11 , the sheet P on top of the stacked sheets in the cassette  5  is fed (discharged) by the supply unit  6  toward the printing unit  10 . The discharged sheet P is guided by the U-shaped sheet guide  9 . The sheet P is nipped by the pair of feed-in rollers  20   a ,  20   b  at the end of the U-shaped sheet guide  9 . The nipped sheet P is carried into the printing unit  10  and positioned on the sheet support plate  11  as the pair of feed-in rollers  20   a ,  20   b  rotates in the forward direction. At this time, the sub-plate  46  is located at the covering position. The printing head  12  prints on one side of the sheet P located on the sheet support plate  11  in the printing unit  10 . Similar to the pair of feed-in rollers  20   a ,  20   b , the feed-out rollers  21   a ,  21   b  also rotate in the forward direction. Thus, when reaching the pair of feed-out rollers  21   a ,  21   b , the one side printed sheet P carried into the printing unit  10  by the pair of the feed-in rollers  20   a ,  20   b  is nipped by the pair of feed-out rollers  21   a ,  21   b . The one side printed sheet P nipped by the pair of feed-out rollers  21   a ,  21   b  is pulled out from the print area  10  as the pair of feed-out rollers  21   a ,  21   b  rotates in the forward direction. When the back end of the one side printed sheet P reaches the pair of feed-out rollers  21   a ,  21   b , the pair of feed-out rollers  21   a ,  21   b  stop rotating. Then, the pair of feed-out rollers  21   a ,  21   b  rotates in the reverse direction. At time same time, the sub-plate  46  moves to the uncovering position. When the pair of feed-out rollers  21   a ,  21   b  rotates in the reverse direction, the nipped sheer P (the one side printed sheet P) is back fed from the exit side to the inlet side of the printing unit  10 . The back fed sheet P abuts the lower surface of the sub-plate  46  and the travel direction thereof is oriented downward. Thus, the one side printed sheet P does not proceed to the inlet side of the printing unit  10  and proceeds down to the printing unit  10  ( FIG. 12 ). Through the opening  50  and under the arm  6   a , the one side printed sheet P is returned to the top of the stacked sheets in the cassette  5 . The one side printed sheer P returned to the cassette  5  is fed toward the printing unit  10  again by the supply unit  6 . The discharged one side printed sheet P is guided by the U-shaped sheet guide  9  and transported into the printing unit  10  with the same manner of initial printing. The other side of the one side printed sheet P is printed ( FIG. 13  and  FIG. 14 ). While the one side printed sheet P is passing through the U-shaped sheet guide  9 , it is flipped. Thus, out of the surfaces of the sheet P, the surface facing upward when initially passing through the printing unit  10  and printed thereon is reversed to face downward when passing though the U-shaped sheet guide  9  once again. This could enable double-side printing of the sheet P. 
   Now a mechanism for moving the sub-plate  46  will be described. In the lower part of the sub-plate  46  is provided a vertically slidable rod (not shown) that can be moved up and down by the solenoid  49 . Moving the rod up and down can rotate the sub-plate  46 . This can open and close (uncover and cover) the opening  50  of the sheet support plate  11 . The rod may be arranged above the sub plate  46  and the lower end of the rod may be coupled to the sub-plate  46 . Even such the configuration can rotate the sub-plate  46 . 
   A spur  51  is arranged between the printing head  12  and the feed-out rollers  21   a ,  21   b . The spur  51  is arranged having a predetermined gap to the top face of the sub-plate  46  (See  FIG. 7 ,  FIG. 8 , and  FIG. 11  to  FIG. 14 ). The spur  51  avoids floating of the sheet P from the sheet support plate  11  (the main plate  45  and the sub-plate  46 ). This prevents the surface of the sheet P from being contaminated as a result of contacting with the nozzles of the printing head  12 . 
   Next a capability of releasing the force of the pair of feed-out rollers  21   a ,  21   b  of nipping the sheet P will be described with reference to  FIG. 6  to  FIG. 10 . 
   The force of nipping the sheet P of the pair of feed-out rollers  21   a ,  21   b  can be released by separating the rollers  21   a  and  21   b  that press each other. 
   As described above, the feed-out driven roller  21   b  is rotatably attached to the roller holder  53 . The roller holder  53  is coupled to the bottom surface  39   a  of the frame  39  so that it can move up and down. The roller holder  53  is arranged in proximity to the lower surface of the front side guide plate  41 . In the tabular roller holder  53  made of synthetic resin, a plurality of feed-out driven rollers  21   b  are arranged at predetermined intervals along the rotation axis line of the feed-out drive roller  21   a . Hooks  55   a  are provided at both ends of the roller holder  53 . In addition, hooks  55   b  are provided at the both edges of the main plate  45  fixed to the bottom surface  39   a . The hooks  55   a  and  55   b  are coupled by a coil spring  54 . The coil spring  54  biases the roller holder  53  downward. With this, the feed-out driven rollers  21   b  attached to the roller holder  53  are always biased to the feed-out drive roller  21   a . The biasing force allows the sheet to be nipped between the pair of feed-out rollers  21   a ,  21   b.    
   To the edge in the downstream of the transport direction of the sheet P among the top faces of the roller holder  53  are attached L-shaped members  55  along Y axis direction at predetermined intervals. The L-shaped members penetrate the front side guide plate  41 . The L-shaped members  55  are arranged so that one side thereof is opposed to the top face of the front side guide plate  41  (See  FIG. 6  to  FIG. 8 ). At the edge in the downstream of the transport direction among the top faces of the front side guide plate  41 , a pivot shaft  56  extending along the Y axis direction is pivotally supported to the center of a shaft bush  57 . A droplet boost-up cam  58  is fixed to the pivot shaft  56  (See  FIG. 7  and  FIG. 8 ). In addition, a contact lever  59  extending upward in the vicinity of the maintenance unit  36  is fixed to the pivot shaft  56  (See  FIG. 6  to  FIG. 8 ). When the carriage  13  moves along the main scanning direction (Y axis direction) and enters the maintenance unit  36  from the print area (when it travels in the arrow E direction in  FIG. 6 ), and moves in the direction in which it exits from the maintenance unit  36  into the print area (the arrow C direction in  FIG. 6 ), a rear end face  13   c  (See  FIG. 6 ) of the carriage  13  presses the contact lever  59  and turns the pivot shaft  56  anticlockwise (the arrow F direction in  FIG. 8 ). By this, the cam  58  lifts the L-shaped member  55  upward. Then, the roller holder  53  rotates clockwise ( FIG. 8 ) against the biasing force of the coil spring  54 , thereby separating all the feed-out driven roller  21   b  from the top face of the feed-out drive roller  21   a . With this, the pair of feed-out rollers  21   a ,  21   b  releases the force of nipping the sheet P. 
   In the following, referring to  FIG. 15  to  FIG. 33 , configuration of the power transmission switching means  100  will be described. The power transmission switching means  100  transmits power of the LF motor  42  to the supply unit  6  or the maintenance unit  36 . The power transmission switching means  100  can selectively switch the following 4 types of power transmission modes:
     (a) Intermittent feeding mode: This mode is the power transmission mode for intermittently feeding sheets from the cassette  5  to the printing unit  10 . The intermittent feeding mode is used for printing on sheets with a high degree of accuracy.   (b) Continuous feeding mode: This mode is the power transmission mode for continuously feeding sheets from the cassettes  5 . The continuous feeding mode is used when continuously printing on a plurality of sheets at high speed.   (c) Return node: This mode is the power transmission mode for returning to the cassette  5  again a sheet one side of which has been printed and pulled from the printing unit  10 . This mode is used when printing on both sides of a sheet.   (d) Maintenance mode: This mode is the power transmission mode for moving to the maintenance unit  36  the carriage  13  that fixes the printing head  12 . The maintenance mode is used when cleaning the printing head  12 .   

   Unless the power transmission switching means  100  switches modes, a selected mode is maintained. 
   As described above, power of the LF motor  42  capable of rotating in the forward and reverse directions is transmitted to the pinion  43   a  and the deceleration gear  43   b  attached to the feed-in driver roller  20   a . In addition, power of the LF motor  42  is transmitted from the pinion  43   a  to the gear  43   c  attached to the feed-out drive roller  21   a  by way of the deceleration gear  43   b . In fact, the feed-in drive roller  20   a  and the feed-out drive roller  21   a  simultaneously rotate by the power of the LF motor  42 . 
   As shown in  FIG. 31 , the power (torque) of the LF motor  42  is transmitted to the feed-in drive roller  20   a  via deceleration gear  43   b . The gear  101  is fixed to a right end section of the feed-in drive roller  20   a  (upper section of the maintenance unit  36 ). A switching gear  102 , which is always engaged with the gear  101 , is provided at a position adjacent to the gear  101 . The switching gear  102  is slidable with respect to a spindle  103  extending in the Y-axis direction. 
   A first block  104  (first slider) and a second block  105  (second slider) are slidable with respect to the spindle  103 . The switching gear  102 , first block  104 , and second block  105  are slidable with respect to the spindle  103  independently of other members. The first block  104  contacts with or separates from the switching gear  102 . The second block  105  contacts with or separates from the first block  104 . The switching gear  102  and the first block  104  are rotatable with respect to the spindle  103 , and the second block  105  is prohibited to rotate with respect to the spindle  103 . 
   A surface with which the first block  104  and the second block  105  contact is inclined to the spindle  103 . When the second block  105  approaches the first block  104 , the first block  104  rotates around the spindle  103 . A connecting lever  104   a  protruding upward is fixed to the first block  104 . When the second block  105  approaches the first block  104  and the first block  104  rotates around the spindle  103 , the connecting lever  104   a  moves from top to bottom, in  FIG. 33 . 
   As shown in  FIG. 18  through  FIG. 21 , a plate-like engaging plate  104   b  is provided between a base section  104   c  of the first block  104  and the connecting lever  104   a  extending from the base section  104   c  in a radial outer direction. In the second block  105 , a section facing the engaging plate  104   b  in the base section  105   a  is provided with a notch section  105   b  in which the engaging plate  104   b  is buried. One surface of the notch section  105   b  is formed as an abutting surface  105   c  inclining from the center of radius of the base section  105   a  to the outside the radius of same. Further, the second block  105  is provided with a pair of corner sections  105   d  extending in the radial outer direction from the base section  105   a . The pair of corner sections  105   d  is provided so as to be able to abut on a bottom surface of the front side guide plate  41  on the downstream side so that the second block  105  does not rotate around the spindle  103 . The base section  104   c  of the first block  104  is formed so as to be buried in an inner diameter of the base section  105   a  of the second block  105 . 
   During a period between a state where the first block  104  and the second block  105  approach each other and the engaging plate  104   b  abuts against a section on the outer radius side in the abutting surface  105   c  of the notch section  105   b  (see  FIG. 20 ) and a state where the space between the first block  104  and the second block  105  becomes narrow and the engaging plate  104   b  abuts against a section on the center side of the radius in the abutting surface  105   c  of the notch section  105   b  (see  FIG. 21 ), the position of the first block  104  is forcibly caused to rotate in the direction of the arrow D (see  FIG. 19 ). If the first block  104  rotates, the connecting lever  104   a  also rotates When the first block  104  rotates in the direction of the arrow D, the connecting lever  104   a  also rotates in the direction of the arrow D. 
   As shown in  FIG. 31 , a first biasing spring  106   a  is disposed around the spindle  103 . The first biasing spring  106   a  presses the second block  105  in the direction of the arrow C. A second biasing spring  106   b  is disposed around the spindle  103 . The second biasing spring  106   b  presses the switching gear  102  in the direction of the arrow E. The biasing force of the first biasing spring  106   a  is larger than the biasing force of the second biasing spring  106   b.    
   As shown in  FIG. 33 , a first engaging step section  13   a  and a second engaging step section  13   b  are formed in the carriage  13 . When the carriage  13  moves in the direction of the arrow E, the connecting lever  104   a  of the first block  104  is engaged with either the first engaging step section  13   a  or the second engaging step section  13   b.    
   As shown in  FIG. 4 , a guide block  107  is fixed to the frame  39 . A guide groove  109  is formed in the guide block  107 , and the connecting lever  104   a  of the first block  104  is buried in the guide groove  109 . As shown in  FIG. 33 , the guide groove  109  comprises a linear groove section  109   a  which is elongated in the direction indicated by the arrows C and E (Y axis), and an circular groove section  109   b  which is communicated with a left end section of the linear groove section  109   a  via a connecting inclined surface  109   c . A regulating piece  110  which extends downward from an upper section of the guide block  107  is inserted in a central section of the circular groove section  109   b . The regulating piece  110  is elongated in the direction indicated with the arrows C and E. The circular groove section  109   b  is provided with a stair-like first set section  111 , second set section  112 , and third set section  108 . An inclined convex section  108   a  is provided between the second set section  111  and the third set section  108 . These three set sections  111 ,  112 , and  108  are, as a whole, referred to as a maintaining section. 
   As shown in  FIG. 33 , when the carriage  13  moves in the direction of the arrow E and contacts with the guide groove  109 , the first engaging step section  13   a  or the second engaging step section  13   b  of the carriage  13  is engaged with the connecting lever  104   a  of the guide groove  109 . As a result, the switching gear  102 , the first block  104 , and the second block  105  are caused to slide along the spindle  103  in the direction of the arrow C or E. Switching the operation modes by the power transmission switching means  100  will be described. 
   As shown in  FIG. 32 ,  33 , when the carriage  13  is located in a position facing the sheet P, the carriage  13  is away from the maintenance unit  36  in the direction of arrow C and does not press the connecting lever  104   a  in the direction of the arrow E. In this state, the first biasing spring  106   a  causes the second block  105 , first block  104  and switching gear  102  to slide along the spindle  103  in the direction of the arrow C. Then, the connecting lever  104   a  rotating in the direction of the arrow D is engaged with the first set section  111 . This position is called “position  1 ” (Po 1 ). At this moment, the switching gear  102  is engaged with the intermittent feeding gear  113  (see  FIG. 15-17 ). This state (the switching gear  102  is engaged with the intermittent feeding gear  113 ) is called “the intermittent feeding mode”. 
   When the carriage  13  moves in the direction of the arrow E, the first engaging step section  13   a  of the carriage  13  presses the connecting lever  104   a  in the direction of the arrow E. When the connecting lever  104   a  reaches the second set section  112 , the connecting lever  104   a  is engaged with the second set section  112 . This position (the connecting lever  104   a  is positioned at the second set section  112 ) is called “position  2 ” (Po 2 ). At this moment, the switching gear  102  is engaged with the continuous feeding gear  114  (see  FIG. 22-24 ). This state (the switching gear  102  is engaged with the continuous feeding gear  114 ) is called “the continuous feeding mode”. 
   When the carriage  13  further moves in the direction of the arrow E, the first engaging step section  13   a  of the carriage  13  presses the connecting lever  104   a  in the direction of the arrow E. The pressed abutting piece  104   a  climbs over a convex section  108   a  and reaches the third set section  108 , the connecting lever  104   a  is engaged with the third set section  108 . This position (the connecting lever  104   a  is positioned at the third set section  108 ) is called “position  3 ” (Po 3 ). At this moment, the switching gear  102  is engaged with the idle gear  121  (see  FIG. 25-27 ). This state (the switching gear  102  is engaged with the idle gear  121 ) is called “the return mode”. The idle gear  121  have no engaging gear except the switching gear  102 . Therefore, the power of LF motor  42  is not transmitted to the drive shaft  14 . The supply roller  7  that is fixed to the drive shaft  14  becomes free to rotate with respect to the LF motor  42 . 
   When the carriage  13  further moves from position  3  (Po 3 ) in the direction of the arrow E, the connecting lever  104   a  moves along with a connecting inclined surface  109   c  formed in the guide groove  109 . The connecting inclined surface  109   c  guides the connecting lever  104   a  from the circular groove section  109   b  to the linear groove section  109   a , while the connecting lever  104   a  moves along with the connecting inclined surface  109   c , the engaging partner of the connecting lever  104   a  changes from the second engaging step section  13   b  to the first engaging step section  13   a . When the connecting lever  104   a  reaches the position of the linear groove section  109   a  (this position is called “position  4 ” (Po 4 )), the switching gear  102  is engaged with the maintenance gear  115  (see  FIG. 28-30 ). 
   The switching gear  102 , the intermittent feeding gear  113 , the continuous feeding gear  114 , the idle gear  121  and the maintenance gear  115  are all spur gears. When the switching gear  102  gets to engage with one of those spur gears, phase of teeth may not synchronize. Therefore, when switching the position of the pressed abutting piece  104   a , the switching gear  102  is slightly rotated in the reverse direction in order to make engage smoothly. 
   The bevel gear  115   a  having a large diameter is fixed to a side surface of the maintenance gear  115 . 
   When the carriage  13  further moves from position  4  (Po 4 ) in the direction of the arrow E, the side surface of the switching gear  102  contacts with the bevel gear  115   a . The switching gear  102  is prevented to move in the direction of the arrow E. As a result, the switching gear  102  is detached from the first block  104  and is kept to engage with the maintenance gear  115  ( FIG. 28-30 ). On the other hand, the pressed abutting piece  104   a  is pushed by the second engaging step section  13   b  of the carriage  13  and reaches end portion (most right side in  FIG. 33 ) of the linear groove section  109   a . This position (the pressed abutting piece  104   a  is positioned at the end portion of the linear groove section  109   a ) is called “position  5 ” (Po 5 ). This state is called “the maintenance mode”. 
   Contrary to the above state, when the carriage position  13  moves from the position  5  (Po 5 ) in the direction of the arrow C, the connecting lever  104   a  moves from the linear groove section  109   a  to the circular groove section  109   b . At this moment, the connecting lever  104   a  is received by the first engaging step section  13   a  of the carriage  13 , thus the connecting lever  104   a  does not slides on the connecting inclined surface  109   c  but slides on the regulating piece  110  in the direction of the arrow C. Therefore, the connecting lever  104   a  abuts on a left inclined surface of the circular groove section  109   b  shown in  FIG. 33  while sliding on the regulating piece  110 , thereafter moves along the left inclined surface and then is engaged with the first set section  111 . In this manner, the connecting lever  104   a  repeats the cycle of moving from the position  1  to the position  4 . 
   The position  5  (Po 5 ) is called “the home position (original position)”. The home position is both stand-by position and maintenance position. At this home position, the capping unit  36   a  covers nozzle surfaces of the printing head  12  from the lower side. A recovery process, etc., for removing any air bubbles from a buffer tank (not shown) provided on the printing head  12 , for selectively sucking in ink from the nozzles by actuating a suction pump (not shown) by the LF motor  42  are performed. In addition, when the carriage  13  moves in the lateral direction from the position of the maintenance unit  36  to the printing area (left direction in  FIG. 6 ), at the position  4  (Po 4 ), the capping unit  36   a  uncovers nozzle surfaces and sucking in without ink is performed while wiping out the nozzle surface with a cleaner (wiper blade). In a state where power is not applied to the multifunction device  1 , the carriage  13  stops at an upper position (position  5  (Po 5 )) of the maintaining unit  36  and the nozzles of the printing head are covered by the capping unit  36   a.    
   A control section (controller or control means) of the multifunction device  1  is described next with reference to  FIG. 34 . The control section is for controlling the entire operation of the multifunction device  1 . 
   The control section is configured as a computer comprising mainly as a CPU  300 , ROM  301 , RAM  302 , and BEPROM  303 , and is connected to an application specific integrated circuit (ASIC)  306  via a bus  305 . 
   The ROM  301  has stored therein a program and the like for controlling various operations of the multifunction device  1 , and the RAM  302  is used as a storage region for temporarily storing various data items which are used when the CPU  300  executes these programs. 
   An NCU (Network Control Unit)  317  is connected to the ASIC  306 , and a communication signal which is inputted from a public circuit via the NCU  317  is demodulated by a MODEM  318  and then inputted to the ASIC  306 . Furthermore, when the ASIC  306  transmits image data to the outside by means of facsimile transmission or the like, the image data is modulated by the MODEM  318  and then outputted to the public line via the NCU  317 . 
   The ASIC  306  generates a phase excitation signal and the like which are communicated with, for example, the LF motor  42  in accordance with a command from the CPU  300 . These signals are provided to a drive circuit  311  of the LF motor  42  or a drive circuit  312  of the CR motor  24 , and a drive signal is communicated to the LF motor  42  or CR motor  24  via the drive circuit  311  or drive circuit  312  to control forward and reverse operation, stoppage and the like of the LF motor  42  and CR motor  24 . 
   Further, the scanner device  33  (CIS, for example) for reading images or characters on a script, a panel interface  313  for performing transmission of signals with a keyboard  30   a  and a liquid crystal display (LCD)  31  of the operation panel  30 , a parallel interface  315  and a USB interface  316  for performing transmission of data with external equipment such as a personal computer via a parallel cable or USB cable and the like are connected to the ASIC  306   
   Moreover, a switch  118  for detecting a rotation position of a cam (not shown) of the maintenance unit  36 , the sheet sensor  117  for detecting the front edge position and the back edge position of the sheet P when the sheet P is fed so as to approach the printing region via the U-shaped sheet guide  9 , the rotary encoder  44  for detecting the amount of rotation of the feed-in roller  20   a , the linear encoder  37  for detecting the position (present position) of the carriage  13  in the Y-direction, and the like are connected to the ASIC  306 . 
   A driver  314  is for selectively discharging the ink from the printing head  12  at a predetermined timing. The driver  314  receives a signal, which is generated in the ASIC  306  on the basis of a drive control procedure outputted from the CPU  300  and is then outputted, and drive-controls the printing head  12 . 
   Next, feeding of sheets by means of the above control means and control of the printing operation are described. The control mean can change a pattern of feeding the sheet P to either the intermittent feeding mode (the first mode) or continuous feeding mode (the second mode). In the first mode, a plurality of sheets are fed intermittently to the printing region  210 . The first mode is an accurate mode in which printing precision is prioritized. In the second mode, a plurality of sheets is fed to the printing area continuously and sequentially. The second mode is a speedy mode in which the printing speed is prioritized. 
   When power is applied to the multifunction device  1 , control is started. The user presses a mode setting button (not shown) of the operation panel  30  to select either the first mode or the second mode. When the first mode is selected, the front edge of a sheet P, which is fed by the supply roller  7 , is aligned with a contact line between the pair of feed-in rollers  20   a ,  20   b  rotating in the reverse direction, in which state feeding of the sheet P is stopped once. Even if the front edge of the sheet P is fed by the supply roller  7  such that the front edge of the sheet P is inclined with respect to the contact line between the pair of feed-in rollers  20   a ,  20   b , the front edge of the sheet P is aligned with the contact line. The first mode is suitable for print on a sheet designed for photograph because color heterogeneity or color drift can be prevented by the first mode. 
   When the first mode (precision priority mode, intermittent feeding mode) is selected, the controller set the power transmission switching means  100  to the first mode. The controller largely moves the carriage  13  positioned at the position  5  (Po 5 ) toward the printing area as shown by arrow C in  FIG. 33 . Thus, the first block  104  pressed by the biasing spring  106   a  moves in the direction C along with the regulating piece  110  of the circular groove section  109   b . As a result, the carriage  13  is disengaged from the circular groove section  109   b  and engaged with the first set section  111 . The carriage  13  is kept at position  1  (Po 1 ). 
   In this state, when the LF motor  42  is rotated in the reverse direction, the feed-in drive roller  20   a  is rotated in the reverse direction (counterclockwise direction in  FIG. 14 ). On the other hand, the supply roller  7  is rotated in the forward direction (counterclockwise direction in  FIG. 14 ) by the gear train inside the arm  6   a . When the supply roller  7  is rotated in the forward direction, the plurality of sheets P, which are stacked in the cassette  5 , are caused to abut on a separating member (not shown) of the separating inclined surface  15  provided at the front edge of the cassette  5 , the separating member having a high frictional coefficient. Then, only one uppermost sheet P is taken out from the cassette  5  and sent toward the U-shaped sheet guide  9 . At this moment, since the feed-in roller  20   a  is rotated in the reverse direction, the sheet P which is fed by the supply roller  7  cannot pass through between the feed-in drive roller  20   a  and the feed-in driven roller  20   b . The front edge of the sheet P is aligned with the contact line between the pair of feed-in rollers  20   a ,  20   b . Even if the front edge of the sheet P fed by the supply roller  7  is inclined, the front edge of the sheet P is aligned with the contact line between the pair of feed-in rollers  20   a ,  20   b.    
   Next, the LF motor  42  rotates in the forward direction through an appropriate number of steps, the switching gear  102  and the feed-in drive roller  20   a  rotates in the forward direction (clockwise rotation in  FIG. 11 ), and the sheet P between the feed-in drive roller  20   a  and the feed-in driven roller  20   b  is nipped and fed toward the printing area. The sheet P is fed by a predetermined distance after the LF motor  42  started rotation in the forward direction. As a result, the front edge of the sheet P is set at a print starting position inside the printing area. This process is called “heading process”. 
   At this time, the drive shaft  14  in the supply unit  6  rotates in the reverse direction, one of the gear among the gear train in the arm  6   a  are disengaged, and the supply roller  7  become free to rotate around the drive shaft  14 . The sheet P is released from between the top of the stacked sheets and supply roller  7  by setting the force of nipping between the pair of feed-in rollers  20   a ,  20   b  greater than keeping force to keep the sheet P between the top of the stacked sheets and supply roller  7 . The keeping force is caused by a torsion spring that press the supply roller  7  against the top of the stacked sheets. 
   Subsequently, when a printing command is inputted from an external computer or the like, which is not shown, the controller starts printing with discharging ink from the nozzles of the printing head  12  onto a surface of the sheet P while the carriage  13  is caused to move in the Y-direction, at the same time advancing the sheet P intermittently. When advancing the sheet P intermittently, the pair of feed-in rollers  20   a ,  20   b  and the pair of feed-out rollers  21   a ,  21   b  rotate in the same direction (forward direction). 
   When printing one sheet is finished, feeding out of the printed sheet P is started. In doing so, the LF motor  42  rotates in the forward direction through the number of steps in order to make the pair of feed-in rollers  20   a ,  20   b  and the pair of feed-out rollers  21   a ,  21   b  rotate continuously in the forward direction, and then the rotation of the LF motor  42  is stopped. 
   Next, it is determined whether printing data for a sheet (next page) is present or not. If the print data exists, the above described processes are repeated. In this manner, the sheets P are fed to the printing area (the printing unit  10 ) one by one. In this mode, a color picture, for example, can be printed accurately. 
   During above described processes, at the position  1  (Po 1 ), the connecting lever  104   a  pressed toward the direction shown by arrow C by the first biasing spring  106   a  is kept at the position of the first set section  111 . In the same way, at the position  2  (Po 2 ), the connecting lever  104   a  is kept at the position of the second set section  112  that is one step lower than the first set section  111 . In this manner, once the connecting lever  104   a  is kept at a given position, the carriage  13  is moved only for printing. Therefore, it is no need for the carriage  13  to move to the power transmission switching means  100  for heading process. Speeding up the whole printing process on the high quality (intermittent feeding) mode is achieved. 
   Next, a case in which the second mode is set is explained. The power transmission switching means  100  is set to the second mode. In the second mode, the quality of a print it not important, but the printing speed is prioritized, thus a plurality of sheets P are continuously and sequentially fed to the printing unit  10 . Therefore, the power of the feed-in roller  20   a  and the feed-in roller  20   b  nipping and feeding the sheets is set larger than the power of the supply roll  7  feeding the sheets, and the circumferential speed of the feed-in roller  20   a  is set higher than the circumferential speed of the supply roller  7 . The circumferential speed of the feed-in roller  20   a  is set, for example, based on the speed reduction ratio between the continuous feeding gear  114  and the intermediate gear  120 . 
   Then, the carriage  13  positioned at the position  1  (Po 1 ) is moved a predetermined amount in the direction of the arrow E, as shown in  FIG. 32 . Accordingly, the connecting lever  104   a  is pressed in the E direction at the first engaging step section  13   a  of the carriage  13 . During the period in which the connecting lever  104   a  is positioned at the second set section  112 , the switching gear  102  and the continuous feeding gear  114  are geared with each other, and the power is transmitted to the drive shaft  14  of the rear end of the arm  6   a  via one intermediate gear (not shown). After that, even if the carriage  13  moves in the direction of the arrow C (moves into the printing area), the connecting lever  104   a  is kept at the second set section  112  that is one step lower than the first set section  111 , because the connecting lever  104   a  is pressed by the first biasing spring  106   a.    
   When the LF motor  42  rotates in the forward direction in order to start feeding a sheet P, the switching gear  102  and the feed-in drive roller  20   a  rotates in the forward direction, and the supply roller  7  also rotates in the forward direction (counterclockwise direction in  FIG. 11 ). The supply roller  7  separates only one uppermost sheet P and feeds it to the U-shaped sheet guide  9 . When the front end section of the sheet P reaches the contact line between the feed-in drive roller  20   a  and the feed-in driven roller  20   b , the front end of the sheet P is nipped and drawn into between the feed-in drive roller  20   a  and the feed-in drive roller  20   b  since the feed-in roller  20   a  is rotated in the forward direction, and is then fed toward the printing area (printing unit  10 ). Then, printing starts. During the second mode, it is preferable that the ASIC  306  is set not to accept the output signals (ON or OFF signals) from the sheet sensor  117 . 
   When one piece of sheet P is held between the pair of feed-in rollers  20   a ,  20   b  and is in contact with the supply roller  7 , since the power of the pair of feed-in rollers  20   a ,  20   b  nipping and feeding the sheet is set larger than the power of the supply roller  7  pressing the sheet, and the circumferential speed of the feed-in drive roller  20   a  is set higher than the circumferential speed of the supply roller  7 , thus the sheet P is fed reliably toward the printing area at the feeding speed of the feed-in roller  20   a . The sheet P slides with respect to the supply roller  7 . 
   Next, when a command indicating that print data to be printed on the next page (subsequent sheet) exists is received from the external device, it is determined whether the current flag is the first mode or the second mode. When the fag is the second mode, the LF motor  42  continues to rotate in the forward direction and the feed-in drive roller  20   a , feed-out drive roller  21   a  and supply roller  7  are continued to rotate in the forward direction. Accordingly, the preceding sheet (preceding page) is discharged from the printing unit  10 , while the following sheet (subsequent page) is conveyed to the print starting position, and start printing on the following sheet. In this matter, the continuous rotation of the supply roller  7  and the pair of the feed-in roller makes the printing operation for a plurality of sheets faster without temporary stopping at the contact line between the pair of feed-in rollers  20   a ,  20   b.    
   Next, referring to a flowchart of  FIG. 35 , control of double-side printing will be described with the control section described above. In the double-side printing, after printing on one side of the sheet, the printing unit  10  prints on the other side of the sheet again. The printing on one side of the sheet and that on the other side are performed in the first mode, namely, the intermittent feeding mode. 
   When the multi-function device  1  is powered on and then there is any print command (Step S 1 : hereinafter referred to as S 1 . Same in other steps) from an external computer (not shown), the carriage  13  stopping at the above stand-by position (the home position; the position  5  (Po 5 )) is moved in the arrow C direction, as shown in  FIG. 33 . Thus, similarly to the above description, the power transmission switching means  100  is set to the first mode (S 2 ). 
   As shown in  FIG. 15  to  FIG. 17 , with the switching gear  102  engaged with an intermittent feeding gear  113 , sheet feeding from the cassette  5  is enabled. When the LF motor  42  rotates in the reverse direction for the sheet feed operation (S 3 ), the supply roller  7  rotates in the direction that feeds the sheet toward the printing unit  10 . 
   When the LF motor  42  rotates in the reverse direction, the feed-in drive roller  20   a  also rotates in the reverse direction. Thus, the sheet P fed by the supply roller  7  does not enter between the pair of feed-in rollers  20   a ,  20   b . A top sheet P of the stacked sheets in the cassette  5  is discharged toward the printing unit  10 . The discharged sheet is guided by the U-shaped sheet guide  9 . After the front end of the sheet P passes through a sheet sensor  117  located in the downstream of the U-shaped sheet guide  9 , the LF motor  42  rotates in the reverse direction till a predetermined number of steps is reached. In other words, the LF motor  42  continues to rotate in the reverse direction till the sheet P abuts the contact line between the pair of feed-in roller  20   a ,  20   b . Then, the LF motor  42  rotates in the forward direction as many steps as appropriate. Thus, the front end of the sheet P is positioned at a print start position (S 3 ). 
   Then, ink is selectively jetted onto one side of the sheet P from the nozzles of the print head  12 , while the sheet P advances intermittently, and the carriage  13  reciprocates along the main scanning direction. In other words, printing takes place (S 4 ). When the sheet P is positioned at the print start position and printed, the drive shaft  14  rotates in the reverse direction. Thus, the supply roller  7  is in a freely rotatable condition. In addition, as the pair of feed-in rollers  20   a ,  20   b  and that of feed-out rollers  21   a ,  21   b  rotate in the forward direction, the sheet P intermittently travels from the inlet to the exit of the printing unit  10 . 
   When printing on one side of the sheet P terminates, the one side printed sheet P is pulled out from the printing unit  10  by the pair of feed-out rollers  21   a ,  21   b . “The one side printed sheet P” is referred to as just “the sheet P” herein after. Until the rear and on the sheet P reaches at the pair of feed-out rollers  21   a ,  21   b , it is determined whether or not double-side printing is requested (S 5 ). If the double-side printing is not requested (S 5 : NO), the LF motor  42  continuously rotates in the forward direction. The sheet P is discharged to the discharge unit (arrow B direction in  FIG. 7 ) (S 6 ). In the case where single-side printing is requested, processes S 3  to S 6  are repeated. 
   When the double-side printing is requested (S 5 : YES), the LF motor  42  continuously rotates in the forward direction until the rear end of the sheet P is reaches the pair of feed-out rollers  21   a ,  21   b . When the rear end of the sheet P reaches the pair of feed-out rollers  21   a ,  21   b , the LF motor  42  stops (S 7 ). In fact, it suspends with the rear end of the sheet P nipped by the pair of feed-out rollers  21   a ,  21   b.    
   Then, the solenoid  49  is actuated ON, and the sub-plate  46  is moved to the uncovering position. In fact, the opening  50  is uncovered (S 8 ). Next, the carriage  13  travels laterally for a predetermined distance, and the power transmission switching means  100  is maintained in the condition in which the switching gear  102  is engaged with the idle gear  121  (see  FIG. 25  to  FIG. 27 ). Power transmission to the drive shaft  14  of the LF motor  42  is cut (S 9 ) in the condition where the switching gear  102  is engaged with the idle gear  121 . The supply roller  7  is in the freely rotatable condition. The processes in S 8  and S 9  may take place substantially at the same time. 
   Then, with the sub-plate  46  still retained in the uncovering position, the LF motor  42  rotates in the forward direction. The pair of feed-out rollers  21   a ,  21   b  rotates in the reverse direction (S 10 ). With this, the sheet P one side of which is printed travels with the rear end thereof as a head. The rear end of the sheet P is referred to as return side front end hereinafter. The sheet P is transferred through the opening  50  toward the cassette  5  (see  FIG. 12 ). 
   It is then determined whether or not the sheet P one side of which is printed has traveled a first predetermined amount (S 11 ). The first predetermined amount is a distance traveled by the return side front end of the one side printed sheet P from the position of being nipped between the pair of feed-out rollers  21   a ,  21   b  down to the position where the supply roller  7  is in contact with the top of the stacked sheet (to be more accurate, down to a position beyond the contact position of the supply roller  7  and the top of the stacked sheets. The first predetermined amount can be detected by the rotary encoder  44 . Traveling for the predetermined distance, the return side front end of the sheet P that passes below the arm  6   a  slides between the top of the stacked sheets and the supply roller  7  that is in the freely rotatable condition. 
   After the sheet P travels for a predetermined distance (S 11 : YES), the carriage  13  moves for a predetermined distance in the arrow C or E direction and the power transmission switching means is set to the first mode. Then, the switching gear  102  is engaged with the intermittent feeding gear  113 . In this condition, the LF motor  42  rotates in the forward direction, thereby turning the supply roller  7  in the forward direction (S 12 ). This discharges the one side printed sheet P from the cassette  5  to the printing unit  10 . The discharged sheet P is guided by the U-shaped sheet guide  9  and moves to the pair of feed-in rollers  20   a ,  20   b . In this condition, the pair of feed-in rollers  20   a ,  20   b  rotates in the reverse direction. 
   Then, the sheet P travels till it abuts the contact line of the pair of feed-in rollers  20   a ,  20   b  (S 13 ). When the front end of the sheet P reaches the contact line of the pair of feed-in rollers  20   a ,  20   b , the LF motor  42  stops (S 14 ). The supply roller  7 , the pair of feed-in rollers  20   a ,  20   b  and the pair of feed-out rollers  21   a ,  21   b  stops. 
   In this condition, the force of nipping the sheet P by the pair of feed-out rollers  21   a ,  21   b  is released (S 115 ). To be specific, the carriage  13  travels in the arrow C or E direction and the backend surface  13   c  of the carriage  13  presses the contact lever  59 . Then, as described earlier, the roller holder  53  raises, and the feed-out driven rollers  21   b  leave the top face of the feed-out drive roller  21   a.    
   Then, the carriage  13  moves in the arrow C or E direction in  FIG. 32 , the power transmission switching means  100  is switched to the first mode (intermittent feeding mode). In fact, the switching gear  102  engages with the intermittent feeding gear  113 . Then, the LF motor  42  rotates in the forward direction, thereby turning the pair of the feed-in rollers  20   a ,  20   b  and that of the feed-out rollers  21   a ,  21   b  in the forward direction. By doing so, the front end of the one side printed sheet P is carried between the printing head  12  and the main plate  45  (S 16 ). In this case, as the nipping force of the pair of feed-out rollers  21   a ,  21   b  is released, the one side printed sheet P does not return to the discharge direction (arrow B direction), even if the feed-out roller  21   a  rotates in the forward direction. 
   Then, after a predetermined time duration corresponding to length of the sheet P has passed (S 16 : YES), the pair of feed-out rollers  21   a ,  21   b  returns to the condition in which they can nip. In step S 16 , it may be determined that the sheet P travels for a second predetermined amount, rather than that the predetermined time duration has passed. When the step S 16  determines “YES”, the one side printed sheet P has already exited from the in-between the pair of feed-out rollers  21   a ,  21   b . Then, the carriage  13  travels to the arrow C. The backend surface  13   c  (back abutting area) of the carriage  13  leaves the contact lever  59 . Then, the roller holder  53  descends, and the feed-out driven rollers  21   b  come into contact with the feed-out drive roller  21   a . In fact, the pair of feed-out rollers  21   a ,  21   b  returns to the condition that they can nip the sheet (S 17 ). 
   Then, the solenoid  49  is actuated OFF to cover the opening  50  (S 18 ). In this condition, the rear end of the one side printed sheet P is already located below the sub-plate  46 . Even if the opening  50  is closed, the sheet P will not be sandwiched between the opening  50  and the sub-plate  46 . Then, same steps as steps S 3  and S 4  are repeated, and printing on the other side of the sheet P takes place. With the processes described above, the double-side printing takes place. 
   With the processes described above, the double-side printing takes place. The multi-function device  1  has enabled double-side printing of a sheet P with a fewer number of components. 
   In the above embodiment, the supply roller  7  is in contact with the top sheet of the stacked sheets in the cassette  5  even in the return mode. Preferably, the following configuration may replace this. In the return mode, the arm  6   a  raises and releases the supply roller  7  from the top of the stacked sheets. In such a condition, one side printed sheet passes through the opening  50 , and returns to the top of the stacked sheets. At this time, the supply roller  7  may rotate in the forward direction or in the reverse direction because the supply roller  7  is not in contact with the top of the stacked sheets. An actuator such as a separate electromagnetic solenoid, etc. may be utilized to raise the arm  6   a  in a predetermined timing. In addition, it is also preferable to elevate the arm  6   a  with mechanism similar to that for elevating the roller holder  53  by moving the carriage  13  in the direction approaching to the maintenance unit  36 . 
   As described above, the multi-function device  1  comprises a printing unit  10 , a cassette  5 , a supply unit  6 , a sheet support plate  11 , a cover plate  46 , and a pair of feed-out rollers  21   a ,  21   b . The printing unit  10  has a printing head  12  for jetting ink onto a sheet P. The cassette  5  is located below the printing unit  10  and contains stacked sheets. The supply unit  6  discharges a sheet from the cassette  5  to the printing unit  10 . The sheet transported into the printing unit  10  is placed on the sheet support plate  11  in the printing unit  10  during printing. An opening  50  is formed on the sheer support plate  11 . The cover plate  46  is movable between a position where it covers the opening  50  and a position where it uncovers the opening  50 . The pair of feed-out rollers  21   a ,  21   b  nips a sheet at the exit of the printing unit  10 , rotates in the forward direction, and pulls the nipped sheet from the printing unit  10 . In order to return the nipped and pulled out sheet to the cassette  5  through the opening  50  of the sheet support plate  11 , the cover plate  46  is located at the uncovering position when the pair of feed-out rollers  21   a ,  21   b  rotate in the reverse direction. 
   The multi-function device  1  having the above configuration returns one side printed sheet to the cassette  5  again through the opening  50  formed on the sheet support plate  11  that supports sheets during printing. The one side printed sheet returned to the cassette  5  is transported to the printing unit  10  again by the supply unit  6 . The multi-function device  1  can return the one side printed sheet to the cassette  5 , simply by conveying it for a short distance. The multi-function device  1  has enabled double-side printing with a fewer components than the conventional mechanism for double-side printing. 
   In addition, the multi-function device  1  returns the one side printed sheet P to the cassette  5  by reversely rotating the pair of feed-out rollers  21   a ,  21   b  arranged at the exit of the printing unit  10 . The return pathway for returning the one side printed sheet to the print area again can be shorter than a conventional printer that bypasses the printing unit. This can accelerate doubleside printing. Then, the pair of feed-in rollers  20   a ,  20   b  and that of feed-out rollers  21   a ,  21   b  are utilized as the rollers, etc. for transporting one side printed sheet to the printing unit  10  once again. This can reduce the number of components for double-side printing. 
   Until the front end of the one side printed sheet reaches between the supply roller  7  and the top of the stacked sheets, the supply roller  7  may be kept off the top face of stacked sheets in the cassette  5  or the supply roller  7  may be retained in a freely rotatable condition. Such the configuration could make it possible to effectively utilize the supply roller  7  for double-side printing. 
   The pair of feed-out rollers  21   a ,  21   b  releases the force of nipping a sheet when the supply roller  7  is pressed again against the top of the stacked sheets for double-side printing, or when the supply roller  7  is rotatably driven again for double-side printing. This could prevent the pair of feed-out rollers  21   a ,  21   b  from pulling a sheet when the supply roller  7  discharges one side printed sheet again. This can reliably discharge one side printed sheet to the printing unit  10  once again. 
   The multi-function device  1  comprises the pair of feed-in rollers  20   a ,  20   b  that nips a sheet in front of the inlet of the printing unit  10 , rotates in the forward direction, and thereby transports the nipped sheet into the printing unit  10 . The pair of feed-in rollers  20   a ,  20   b  rotates in the same direction as that of the pair of feed-out rollers  21   a ,  21   b . As there is no need of separately controlling the pair of feed-in rollers  20   a ,  20   b  and that of feed-out rollers  21   a ,  21   b , the controller can be simplified. 
   In the multi-function device  1 , when the sub-plate (cover plate)  46  covering the opening  50  at the covering position, the top face forms a plane together with the top face of the sheet support plate  11 . When the sub-plate  46  is at the uncovering position, the top face of the sub-plare  46  is inclined to the top face of the sheet support plate  11 . This could enable opening and closing of the opening  50  even in a smaller range of travel. In addition, a smaller actuator for moving and tilting the sub-plate  46  may be used. 
   The printing unit  10  of the multi-function device  1  has a printing head  12  of ink jet type that selectively jets ink droplets toward a sheet. The sheet support plate  11  have the capability of defining a gap between a sheet P to be placed thereon and the printing head  12 . At the same time, the sheet support plate  11  forms the opening  50  and has the capability of acting as a guide for directing one side printed sheet to the cassette  5 . The device can be miniaturized by having the sheet support plate  11  serve 2 functions. 
   The present invention shall not be limited to the embodiments illustrated in the above description and drawings, but may be carried out by making various changes without departing from the scope of the gist. 
   For instance, in the above embodiment, after the front end of the sheet P abuts to the contact line of the pair of feed-in rollers  20   a ,  20   b  that rotates in the reverse direction, the LF motor  42  is stopped. That is, the supply roller  7 , the pair of feed-in rollers  20   a ,  20   b  and that of the feed-out rollers  21   a ,  21   b  stop. In that condition, the roller holder  53  raises, thereby releasing the feed-out driven rollers  21   b  from the feed-out drive roller  21   a . It is not limited to the above timing when to release the feed-out driven rollers  21   b  from the feed-out drive roller  21   a . The feed-out driven rollers  21   b  may leave the feed-out drive roller  21   a  at any time between the following (a) and (b) timing:
     (a) When the front end of one side printed sheet P reaches a point between the supply roller  7  and the top of stacked sheets in the cassette  5 .   (b) When the pair of feed-in rollers  20   a ,  20   b  starts to rotate in the forward direction to transport the one side printed sheet P into the printing unit  10 .