Abstract:
An image forming apparatus includes cap members for capping ejection outlets of an ejection portions for ejecting liquid to a recording material; pump diviec including suction inlets in fluid communication within the cap members; discharging outlets for discharging the liquid; cylinder member including a plurality of cylinders having the suction inlets and the discharging outlets, respectively; a seal member for dividing inner space in the cylinder divice into the cylinders; and a plurality of pistons reciprocable in the spaces in contact with the inner surfaces of the cylinders to produce pressure change in the inner spaces; wherein in each of the cylinders, the suction inlet is disposed more away from seal member than the discharging outlet.

Description:
This application is a continuation of application Ser. No. 09/640,382, filed Aug. 17, 2000, now abandoned. 
    
    
     FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus which forms an image on recording medium by ejecting liquid such as ink from a printing head, and a pump for such an image forming apparatus. 
     In an image forming apparatus such as an ink jet printer, ink is ejected from the ejection orifices of a printing head to form an image on a piece of recording medium. During the operation of such an image forming apparatus, ink (with increased viscosity), dust, and the like, adhere to the ejection orifices of the printing head. Thus, in order to remove these contaminants, an ink jet printer is generally provided with a recovery means to keep stable the ink ejection performance of the printer. 
     A recovery means generally comprises a capping means, a wiping means, and a pumping means. The capping means comprises a plurality of caps for covering the printing head, across the surface with ejection orifices, while the apparatus is not recording. It prevents ink from drying or evaporating while the apparatus is not recording. The wiping means comprises a blade or the like for removing the ink adhering to the printing head surface with ejection orifices. The pumping means suctions the ink with increased viscosity, and the like, from the ejection orifices and their adjacencies, through the capping means. 
     Generally speaking, a conventional pumping means comprises a cylinder and a piston which shuttles within the cylinder, with its peripheral surface remaining in contact with the internal surface of the cylinder. Technology regarding such a pumping means is disclosed in Japanese Laid-Open Patent Application No. 067,121/1998. 
     FIG. 18 is a schematic sectional drawing which presents an example of a conventional pumping means for an image forming apparatus. As depicted in FIG. 18, the pumping means comprises a cylinder  160 , and a piston  164  which shuttles within the cylinder  160 . The cylinder  160  is provided with two ink suction holes  161  and  162  and one ink discharge hole  163 . The ink suction holes  161  and  162  are connected to two capping members (unillustrated), one for one. 
     When the pumping means structured as described above is in operation, the piston  164  shuttles within the internal space of the cylinder  160 , with its peripheral surface remaining in contact with the internal surface of the cylinder  160 . As the piston  164  shuttles, ink is suctioned into the cylinder  160  through the ink suction holes  161  and  162 , and then is discharged from the cylinder  160  through the ink discharge hole  163  as a common ink discharge hole. This pumping means is superior in space utilization efficiency, compared to a pumping means which comprises two caps, and two cylinders parallelly disposed corresponding one for one to the two caps. In other words, this pumping means has an advantage over the latter, in that it makes it possible to reduce the overall size of an image forming apparatus. 
     However, the pumping means structured as described has a problem. That is, after the ink is suctioned into the cylinder, the ink is left alone to discharge itself out of the cylinder by its own weight. As a result, a certain amount of ink remains within the cylinder. If the ink which is remaining in the cylinder adheres to the internal surface of the cylinder and solidifies there, there is a possibility that the gap between the cylinder and piston fails to be properly sealed. If the gap fails to be properly sealed, air is allowed to leak through the gap, causing the pumping means to fail to properly suction ink. There is also a possibility that the ink will remain between the cylinder and piston and solidifies there. If the ink which is remaining between the cylinder and piston solidifies, the force required to make the piston slide on the internal surface of the cylinder sometimes becomes large enough to prevent the piston from being driven, which results in ink suction failure. 
     SUMMARY OF THE INVENTION 
     A principal object of the present invention is to provide an image forming apparatus pump which does not suffer from leakage and waste liquid solidification which lead to suction failure, and to provide an image forming apparatus equipped with such a pump. 
     Another object of the present invention is to provide an image forming apparatus pump capable of easily discharging waste liquid, and to provide an image forming apparatus equipped with such a pump. 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising cap members for capping ejection outlets of an ejection portions for ejecting liquid to a recording material; pump means including suction inlets in fluid communication within said cap members; discharging outlets for discharging the liquid; cylinder means including a plurality of cylinders having said suction inlets and said discharging outlets, respectively; a seal member for dividing inner space in the cylinder means into said cylinders; and a plurality of pistons reciprocable in the spaces in contact with the inner surfaces of the cylinders to produce pressure change in the inner spaces; wherein in each of said cylinders, said suction inlet is disposed more away from seal member than said discharging outlet. 
     According to another aspect of the present invention, there is provided a pump for an image forming apparatus which includes cap members for capping ejection outlets of an ejection portions for ejecting liquid to a recording material, said pump comprising suction inlets in fluid communication within said cap members; discharging outlets for discharging the liquid; cylinder means including a plurality of cylinders having said suction inlets and said discharging outlets, respectively; a seal member for dividing inner space in the cylinder means into said cylinders; and a plurality of pistons reciprocable in the spaces in contact with the inner surfaces of the cylinders to produce pressure change in the inner spaces; wherein in each of said cylinders, said suction inlet is disposed more away from seal member than said discharging outlet. 
     As described above, according to the present invention, an image forming apparatus pump comprises a plurality of cylindrical portions which are provided with the suction hole or holes and discharge hole or holes, and are aligned in a straight line; a single or plural sealing members which serve as a divider between the internal spaces of the adjacent two cylinder portions, and a plurality of pistons which shuttle within the correspondent cylinder portions, with the peripheral surface thereof remaining in contact with the internal surfaces of the cylinder portions, to change the internal pressures of the cylinder portions. After being suctioned into the internal spaces of the plurality of cylinder portions, liquid is almost completely discharged through the discharge holes by the pressure generated in the space between the pistons and correspondent sealing members. In other words, according to the present invention, it is possible to prevent leakage and solidification of waste liquid, which lead to suction failure, by reducing the amount of the liquid which remains in the cylinder. 
     Further, the present invention eliminates the need for arranging a plurality of the cylinder portions in parallel corresponding to a plurality of capping member, making it possible to reduce the overall size and cost of an image forming apparatus. 
     Further, according to the present invention, in each cylinder portion, the suction hole is disposed on the far side, with respect to the discharge hole, from the sealing member, making it possible to place the discharge holes closer to each other to make it easier to dispose waste liquid. 
     Further, according to the present invention, a plurality of rings are on the peripheral surface of each of the plurality of pistons so that only the peripheral surfaces of the rings make contact with the internal surface of each cylinder portion, reducing the size of the contact area between the internal surface of the cylinder and the peripheral surface of the piston. Therefore, even if liquid enters between the internal surface of a cylinder portion and a piston, and solidifies there, it does not occur that liquid fails to be satisfactorily suctioned due to the insufficiency in the piston driving force. 
     Further, according to the present invention, among the plurality of the rings on the peripheral surface of each of the plurality of pistons, the ring on the upstream side in terms of the direction in which the piston moves for suctioning is rendered greater in external diameter than the ring on the downstream side, equalizing both rings in their contact pressure upon the internal surface of the cylinder portion to prevent leakage. Therefore, liquid is reliably suctioned. 
     In addition, the force required to drive the pistons is smaller, making it possible to employ a motor, or the like, with relatively low torque as a driving force source to reduce noise level compared to when a high torque motor is employed. 
     These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is an external perspective view of the image forming apparatus in an embodiment of the present invention. 
     FIG. 2 is a schematic plan view of the sheet conveyance mechanism for conveying the sheets placed in the sheet feeder tray illustrated in FIG. 1, onto the platen illustrated in FIG.  1 . 
     FIG. 3 is an external perspective view of the driving mode switching means illustrated in FIG. 1, and depicts the structure of the driving mode switching means. 
     FIG. 4 is a plan view of the driving mode switching means illustrated in FIG.  3 . 
     FIG. 5 is a plan view of the right side of the driving mode switching means illustrated in FIG.  3 . 
     FIG. 6 is a sectional view of the pumping means illustrated in FIG. 3, and depicts the structure of the pumping means. 
     FIG. 7 is a drawing for describing the operational sequence through which ink is suctioned into, or discharged from, the cylinder  516  illustrated in FIG.  6 . 
     FIG. 8 is a drawing for describing the operational sequence through which ink is suctioned into, or discharged from, the cylinder  517  illustrated in FIG.  6 . 
     FIG. 9 is a schematic drawing for describing the shape of the piston illustrated in FIG.  6 . 
     FIG. 10 is a graph for describing the relationship between the external diameter D 1  of the ring portion  519   a  illustrated in FIG. 9, and the contact pressure P 1  applied by the ring portion  519   a  upon the cylinder  517 , and the relationship between the external diameter D 1  of the ring portion  519   a  and the contact pressure P 2  applied by the ring portion  519   b  upon the cylinder  517 . 
     FIG. 11 is a plan view of the adjacencies of the joint between the pumping means and capping means illustrated in FIG.  3 . 
     FIG. 12 is a sectional view of the capping means illustrated in FIG.  11 . 
     FIG. 13 is a plan view of the front side of the driving mode switching means illustrated in FIG.  3 . 
     FIG. 14 is a plan view of the left side of the driving mode switching means illustrated in FIG.  3 . 
     FIGS. 15, ( a ) and ( b ), are graphs for describing the movements of the capping means, carriage lock, and P sensor transmission lever, with respect to the rotational angle of the P output gear illustrated in FIG. 3, and the movement of the ink suctioning movement of the pumping means with respect to the rotational angle of the P output gear, respectively. 
     FIG. 16 is a perspective view of a head cartridge integrally comprising a printing head and an ink container; FIGS. (a), (b), and (c) correspond to a black cartridge, a color cartridge, and a photographic cartridge. 
     FIG. 17 is a perspective view of the essential portion of an ink jet recording head in accordance with the present invention, with some portions, omitted. 
     FIG. 18 is a schematic sectional view of an example of a conventional pumping means to be placed in an image forming apparatus, and depicts the structure of the pumping means. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the preferred embodiments of the present invention will be described with reference to the appended drawings. 
     FIG. 1 is an external perspective view of the image forming apparatus in an embodiment of the present invention. FIG. 2 is a plan view of the sheet conveyance mechanism for conveying the sheets placed in the sheet feeder tray  101  illustrated in FIG. 1, onto the platen  301  illustrated in FIG.  1 . 
     FIG. 16 is a perspective view of a head cartridge integrally comprising a printing head and an ink container. In FIG. 16, FIGS. (a), (b), and (c), correspond to a black cartridge, a collar cartridge, and a photographic cartridge. The number of ejection orifices is different for a black head, a color head, and a photographic head, and will be described later in detail. These printing heads are optionally mounted on a carriage  201 ; one of them is mounted according to the printing objective. 
     FIG. 17 is a perspective view of the essential portion of one of the image forming apparatuses in accordance with the present invention, with some portions omitted. The top member of an ink jet recording head H ( 400 ) is made of resinous material, and integrally comprises: a top plate portion, in which a liquid chamber  1104  for storing recording liquid, and a plurality of liquid paths, are formed; an ejection outlet plate portion  1101 , in which a plurality of ejection orifices  1102  correspondingly connected to the plurality of liquid paths  1103  are formed; and a recording liquid receiving portion  1105 . A heater board  1107  comprises: a substrate formed of silicone; a plurality of heaters (electrothermal transducers)  1106 , which are aligned on the silicone substrate to generate the thermal energy to be used for causing the so-called film boiling in the ink to eject ink; and unillustrated wiring for supplying these heaters with electrical power. These heaters and the wiring are formed by a known film formation technology. The heater board  1107  is fixed to a base plate  1110  by a known die bonding technology. The wiring substrate  1108  is provided with the wiring connected to the wiring of the heater board  1107  by a known wire bonding technology, and with a plurality of pads  1109  which are positioned one for one at both ends of the wiring to receive electrical signals from the main assembly of the image forming apparatus. The top plate  1100  and heater board  1107  are bonded to each other, with the plurality of the liquid paths  1103  and heaters  1106  aligned one for one to each other, and are fixed to the base plate  1110 , along with the wiring substrate  1108 , forming the ink jet recording head H. 
     Referring to FIGS. 1 and 2, the image forming apparatus in this embodiment comprises: a sheet feeder roller  102  for conveying the sheets (medium on which recording is made) placed in a sheet feeder tray  101 ; a conveyer roller  302  for conveying the sheets onto the platen  301  after the sheets are fed into the apparatus by the sheet feeder roller  102 ; a carriage  201  on which a printing head comprising a portion from which ink is ejected, and an ink container  203 , are mounted; a rail  360  on which the carriage  201  is slidably supported to be shuttled in the longitudinal direction of the rail  360 ; a recovery means for restoring the performance of the plurality of printing heads mounted on the carriage  20 ; a driving mode switching means  600  driven by the conveyer roller  302 ; and a chassis  350 . 
     In an image forming apparatus structured as described above, as the sheets placed in the sheet feeder tray  101  are conveyed onto the platen  301  by the sheet feeder roller  102  and conveyer roller  302 , ink is ejected onto the sheets from the plurality of printing heads on the carriage  201  which are being shuttled on the rail  360 . As a result, an image is formed on the sheets. 
     Next, the sheet feeder mechanism, illustrated in FIG. 1, for conveying the sheets from the sheet feeder tray  101  onto the platen  301  will be described. 
     The rotational force from a pulse motor  305  is transmitted by way of a speed reduction gear  306  to a conveyer gear  303  fixed to one of the longitudinal ends of the conveyer roller  302 , in order to rotate the conveyer roller  302 . 
     On the other hand, an LF output gear  304  is fixed to the other end of the conveyer roller  302 . Therefore, the rotational force transmitted to the conveyer roller  303  is transmitted to the recovery means and sheet feeder gear  105  disposed within a switching means  600 , by way of the LF output gear  30 . 
     As the driving force is transmitted to the sheet feeder gear  105 , the sheet feeder roller  102  rotates, and the sheets placed in the sheet feeder tray  101  are conveyed to the conveyer roller  302  by the rotation of the sheet feeder roller  102 . After being conveyed to the conveyer roller  302 , the sheets are conveyed onto the platen  301  by the conveyer roller  302 . 
     Next, the driving mode switching means  600  illustrated in FIG. 1 will be described in detail. 
     FIG. 3 is an external perspective view of the driving mode switching means  600  illustrated in FIG. 1, and depicts the structure of the driving mode switching means  600 . FIG. 4 is a plan view of the driving mode switching means  600  illustrated in FIG. 3, and FIG. 5 is a plan view of the right side of the driving mode switching means  600  illustrated in FIG.  3 . 
     As shown in FIGS. 3-5, in order to prevent the drying or evaporation of ink, the printing head in this embodiment is provided with a capping means comprising caps  528  and  529  for capping the printing head surface which has the ejection orifices. The caps  528  and  529  are selectively activated depending on the configuration of the printing head surface which has ejection orifices. Further, the image forming apparatus in this embodiment is provided with a recovery means  500 , which comprises a pumping means  503  and a wiping means  502 . The pumping means  503  suctions ink, and the like, from the ejection orifices and the adjacencies thereof. The wiping means  502  removes the ink adhering to the printing head surface with ejection orifices, using of a blade (unillustrated). The capping means  501  and pumping means  503  are driven as the driving force is transmitted to the P output gear  604  and piston gear  510  from the LF output gear  304  (FIG.  2 ). 
     The P output gear  604  is a gear rotationally fitted around a P output gear shaft  509 , the longitudinal ends of which are supported by a driving mode switching means base  601 . 
     Further, the P output gear  604  comprises: a cam portion  604   b  for regulating the vertical movement of a carriage lock  511  which is under the pressure generated in the direction of the carriage  201  (FIG. 1) by a pressure generating means  543  such as a spring, and also, for regulating the phase of the toothless portion of the P outlet gear  604 ; a cam portion  604   c  for regulating the vertical movement of the caps  528  and  529 ; and a cam portion (unillustrated) for regulating a P sensor transmission lever  512  which engages with a P sensor lever (unillustrated), which detects the rotational angle of the cam  604   c.    
     Next, the sequential steps through which the driving force from the LF output gear  304  (FIG. 2) is transmitted to the P output gear  604  and piston gear  510  will be described. 
     After being transmitted to an LF transmission gear  602  meshed with the LF output gear  304 , the driving force is transmitted to a P clutch gear  630 , by way of the LF transmission gear  602 , a transmission shaft  605 , and a P transmission gear  606 . 
     When the pumping means  503  is driven, and immediately after the capping means  503  begins to be driven, a P clutch trigger gear  632  is slid by the carriage  201  (FIG.  1 ), whereby the latchet portion of the P clutch trigger gear  632  is meshed with the latchet portion of the P clutch gear  630 . 
     Therefore, when the pumping means  503  is driven, and immediately after the capping means  503  begins to be driven, the driving force transmitted to the P transmission gear  606  is transmitted to the P output gear  604 , and then is transmitted to the piston gear  510 , rotating the piston gear  510 . 
     The P output gear  604  is provided with a toothless portion, which is on the P clutch gear  630  side. Thus, when the pumping means  503  is not being driven, that is, when the sheets are being fed, when the sheets are discharged, when images are being printed, and when the like operations are carried out, the P output gear  604  is not in mesh with the P clutch gear  630 . 
     Therefore, the driving force from the LF output gear  304  is transmitted to the P output gear  604 , as the P output gear  604  is meshed with the P clutch gear  630  or P clutch trigger gear  632  when the pumping means  503  is driven, or immediately after the capping means  503  begins to be driven. 
     Next, the pumping means  503  illustrated in FIG. 3 will be described in detail. 
     FIG. 6 is a sectional view of the pumping means  503  illustrated in FIG. 3, and depicts the structure of the pumping means  503 . 
     As shown in FIG. 6, the pumping means  503  in this embodiment comprises: a cylinder portion  516  (which hereinafter may be simply called “cylinder”) provided with an ink suction hole  516   a  and an ink discharge hole  516   b ; a cylinder portion  517  (which hereinafter may be simply called “cylinder”) provided with an ink suction hole  517   a  and an ink discharge hole  517   b ; a sealing member  523  which is disposed between washers  522  and  524 , being sandwiched by them, and serves as the divider between the cylinder portions  516  and  517 ; pistons  518  and  519  which shuttle within the cylinder portions  516  and  517 , respectively; and a piston shaft  513  which supports the pistons  518  and  519 . 
     In this embodiment, as the driving force from the piston gear  510  is transmitted to the piston shaft  513 , the pistons  518  and  519  supported by the piston shaft  513  shuttle. As a result, ink is suctioned into the cylinder portions  516  and  517  through the ink suction holes  516   a  and  517   a , and then is discharged through the discharge holes  516   b  and  517   b  by the pressure generated between the piston  518  and sealing member  523 , and between the piston  519  and sealing member  523 , respectively. 
     The surface of the center hole of the piston gear  510  has a guide portion  510   a , so that the driving force from the piston gear  510  is transmitted to a screw portion  513   a  through the guide portion  510   a  in order to cause the piston shaft  513  to shuttle in the horizontal direction. 
     The piston shaft  513  is provided with a piston stopper  520  and a stopper rubber  521  for regulating the movement of the piston  518 . 
     Between the cylinder portion  517  and cylinder cap  515 , a sealing member  526  and a washer  525  are sandwiched. 
     The piston shaft  513  is provided with a guide pin  514 , which has been pressed into a hole  513   b  with which the piston shaft  513  is provided. The guide pin  514  shuttles along a guide portion  515   a  with which the cylinder cap  515  is provided, preventing the piston shaft  513  from rotating. 
     Also, in order to prevent the piston shaft  513  from rotating, a projection (unillustrated) on the cylinder cap  515  is engaged in a recess (unillustrated) in the cylinder portion  517 . 
     Next, the ink suctioning and discharging operations of the pumping means structured as described above will described in detail. 
     FIG. 7 is a drawing for describing the processes through which ink is suctioned or discharged by the pumping means. At this time, the sequential steps will be described with reference to the cylinder portion  516 . 
     As the piston  518  passes by the ink suction hole  516   a , while moving from the initial position (FIG. 7, ( a )) toward the ink discharge hole  516   b , ink  591  is suctioned into the cylinder portion  516  by the accumulated negative pressure through the ink suction hole  516   a . As the amount of the ink  591  reaches a predetermined value, the piston  518  stops there (FIG.  7 ( b )). 
     Next, the moving direction of the piston  518  reverses; the piston begins to move toward the initial position illustrated in FIG. 7, ( a ) (FIG.  7 ( c )). During this movement of the piston  518 , the ink  591 , which has been suctioned into the cylinder portion  516 , moves toward the ink discharge hole  516   b  through the ink path provided between the piston  518  and piston shaft  513 . The piston  518  moves to the end of its stroke (FIG. 7, ( d )). 
     Next, the piston  518  begins to move toward the ink discharge hole  516   b . As the piston  518  moves, the ink  591 , which has moved toward the ink discharge hole  516   b , is forcefully discharged through the ink discharge hole  516   b  by the pressure generated as the space between the sealing member  523  sandwiched by the washers  522  and  523 , and piston  518  becomes less (FIG. 7, ( e )). 
     Thereafter, the piston  518  shuttles a predetermined number of times (dry strokes). As the piston  518  goes through the dry strokes, the ink within the cylinder  516  is almost completely discharged through the ink discharge hole  516   b.    
     The position from which the piston  518  begins to move, and the position of the other end of the piston stroke, may be varied depending on printing head type (in terms of color, capacity, and the like), so that the amount by which ink is suctioned into the cylinder portion is optimized, depending on the printing head type. 
     FIG. 8 is a drawing for describing the processes through which ink is suctioned into, or discharged from, the cylinder  517  illustrated in FIG.  6 . 
     Since the processes through which ink is suctioned into, or discharge from, the cylinder portion  517  are the same as those for the cylinder portion  516 , the detailed description thereof will be omitted. 
     As shown in FIG. 6, there are a few internal spaces in the cylinder portion  517 . One of the longitudinal ends of the piston shaft  513  is in the left most internal space in the cylinder portion  517 . With this arrangement, the aforementioned leftmost internal space is greater in volume than the rightmost internal space in the cylinder portion  517 . The leftmost and rightmost internal spaces are connected to the relatively large cap  528  (FIG.  3 ), and the relatively small cap  529  (FIG.  3 ), respectively. The relatively large cap  528  and relatively small cap  529  are used to cap a color ink head (FIG. 16) which is relatively large in the total number of ejection orifices, and a black ink head (FIG. 16) which is relatively small in the total number of ejection orifices, respectively. In this embodiment, the color ink head comprises 48 ejection orifices for black ink, 48 ejection orifices for cyan ink, 48 ejection orifices for magenta ink, and 48 ejection orifices for yellow ink, totaling 192 ejection orifices. The black ink head has 160 ejection orifices. In other words, a head having the greater number of ejection orifices to be capped is capped with the relatively large cap, which is connected to the cylinder portion larger in the volume of the internal space into which ink is suctioned. This is because it is desired that the greater a printing head is in the total number of ejection orifices to be capped together, the larger the amount of liquid to be suctioned must be, so that ejection orifices are equalized in the amount of the ink suctioned through them. The photographic head is the same as the color ink head in the total number of ejection orifices. In other words, the photographic ink head is provided with 48 ejection orifices for photographic black ink, 48 ejection orifices for photographic cyan ink, 48 ejection orifices for photographic magenta ink, and 48 ejection orifices for photographic yellow ink, totaling 192 ejection orifices. The photographic ink head is capped by the cap  528 , that is, the same cap as the one for the color ink head, and is suctioned by the leftmost most portion of the cylinder, which is relatively large in the internal space. 
     In this embodiment, in order to make the color ink head and photographic ink head greater in the total amount of suction than the black ink head, the pumping means is structured so that the length of the stroke of the piston  518  between the position from which the piston  518  begins to move, and the position of the other end of the stroke, can be adjusted depending on head type. In other words, the length of the stroke of the piston  518  is made greater when the color ink head or photographic ink head is suctioned than when the black ink head is suctioned. 
     Next, the pistons  518  and  519  illustrated in FIG. 6 will be described in detail. 
     FIG. 9 is a drawing for describing the configurations of the pistons  518  and  519  illustrated in FIG.  6 . At this time, the description will be given with reference to the piston  519 . 
     Referring to FIG. 9, the piston  519  is provided with ring portions  519   a  and  519   b , which are on the peripheral surface of the piston  519 , and are the only portions of the piston  519  which make contact with the internal surface of the cylinder portion  517 . 
     With the provision of the above described structure, the size of the contact area between the piston  519  and the internal surface of the cylinder portion  517  is smaller than when the piston  519  is not provided with the rings  519   a  and  519   b.    
     Therefore, even if the piston  519  is caused to temporarily stick to the cylinder portion  517  by the ink which has solidified in the gap between the cylinder portion  517  and piston  519  after flowing into the gap, the force required to loosen the piston  519  from the cylinder portion  517  is smaller, making this structural arrangement advantageous in that it is unlikely to make the pumping means  503  impossible to drive. 
     The relationship among the external diameter D 1  of the ring portion  519   a , the external diameter D 2  of the ring portion  519   b , and the internal diameter D 3  of the cylinder portion  517  is: D 3 &lt;D 2 &lt;D 1 . In other words, the ring portion  519   a  with the external diameter of D 1 , which is on the upstream side in terms of the direction in which the piston  519  is moved to suction ink, is greater in the external diameter than the ring portion  519   b  with the external diameter of D 2 , which is on the downstream side. 
     This structural arrangement is made so that the contact pressure P 1  between the ring portion  519   a  and cylinder portion  517  remains the same as the contact pressure P 2  between the ring portion  519   b  and cylinder portion  517  while the piston shaft  513  moves in the cylinder portion  517  in the direction indicated by an arrow mark A, that is, the ink suctioning direction. 
     As the piston shaft  513  moves in the direction of the arrow mark A, a reactive force P, the direction of which is opposite to the direction of the arrow mark A, applies to the piston  519  due to the friction between the internal surface of the cylinder portion  517  and the peripheral surface of the piston  519 . This sometimes causes the deformation of the piston  519 , which makes the contact pressure P 1  smaller than the contact pressure P 2 . 
     In the above described situation, the piston  519  becomes unstable, threatening to increase the possibility that suction failure or the like will occur due to leakage. 
     The piston  518  is also provided with ring portions, which are on the peripheral surface of the piston  518 . The external diameter D 1  of the ring portion located on the upstream side in terms of the direction in which the piston  518  moves to suction ink is greater than the external diameter of the ring portion on the downstream side. 
     Next, the relationship between the external diameter D 1  of the ring portion  519   a  and the contact pressure P 1 , and the relationship between the external diameter D 1  of the ring portion  519   a  and the contact pressure P 2 , will be described. 
     FIG. 10 is a drawing for describing the relationship between the external diameter D 1  of the ring portion  519   a  illustrated in FIG.  9  and the contact pressure P 1  of the ring portion  519   a  upon the cylinder  517 , and the relationship between the external diameter D 1  of the ring portion  519   a  and the contact pressure P 2  of the ring portion  519   b  upon the cylinder  517 . 
     FIG. 10 represents a case in which the value of the internal diameter D 3  of the cylinder portion  517 , and the value of the external diameter D 2  of the ring portion  519   b , were preset so that the external diameter D 2  of the ring portion  519   b  became larger than the internal diameter D 3  of the cylinder portion  517 , and only the external diameter D 1  of the ring portion  519   a  was varied. 
     As shown in FIG. 10, as the external diameter D 1  of the ring portion  519   a  was varied from a small size to a larger size, the contact pressure P 1  increased, whereas the contact pressure P 2  decreased. Eventually, the contact pressures P 1  and P 2  became equal to each other at a point at which the value of the external diameter D 1  was “Q (&gt;external diameter D 2 )”. 
     In other words, the contact pressures P 1  and P 2  can be rendered equal to each other by setting the value of the external diameter D 1  of the ring portion  519   a  to “Q”, so that the piston  519  can be stabilized in its shuttling movement. 
     Next, the positional relationship between the pumping means  503  and capping means  501  illustrated in FIG. 3 will be described, along with the structure of the capping means  501 . 
     FIG. 11 is a plan view of the joint between the pumping means and capping means  501  illustrated in FIG. 3, and its adjacencies. FIG. 12 is a sectional view of the cap  529  illustrated in FIG.  11 . 
     The capping means  501  is rotationally supported. More specifically, the caps  528  and  529  are fixed to a cap holder  527  provided with two bosses. The two bosses are fitted one for one in the hole of an arm portion  516   c  integrally formed with the cylinder portion  516  and the hole of the arm portion  517   c  integrally formed with the cylinder portion  517 . 
     The cap holder  527  has two positioning bosses  527   a  and  527   b , in addition to the aforementioned two bosses. These bosses  527   a  and  527   b  are fitted in a groove (unillustrated) which is U-shaped in cross section and with which the base  601  (FIG. 4) is provided. 
     Further, the cap holder  527  is provided with a hole  527   c  as a positioning hole in which the boss portion (unillustrated) of the base  601  is fitted. 
     The cap  528  is provided with a tube portion  528   a , which is integrally formed with the cap  528 . This tube portion  528   a  is connected to the ink suctioning portion, in the form of a projection, with which the cylinder portion  516  is provided; the tube portion  528   a  is press-fitted around the projection. 
     The cap  528  has an internal absorbent member  530  for absorbing and retaining the ink within the cap  528 . 
     The cap  529  has a tube portion  529   a , which is integrally formed with the cap  529 . This tube portion  529   a  is connected to the ink suctioning portion, in the form of a projection, with which the cylinder portion  517  is provided; the tube portion  529   a  is press-fitted around the projection. 
     Further, the cap  529  has an internal absorbent member  531  for absorbing and retaining the ink within the cap  529 . 
     The pumping means  503  is rotationally supported by the base  601 . More specifically, the shaft portion  510   b  of the piston gear  510  is fitted in the hole of the base  601 , and the shaft portion  516   d  of the cylinder portion  516  is fitted in the hole of a bearing  532  (FIG. 4) with which the base  601  is provided. 
     The pumping means  503  is under the pressure applied from the back side of the cap holder  527 , in the direction to rotate the pumping means  503 , by the spring  544  (FIG. 5) with which the base  601  is provided. 
     An arm portion  517   d  is an integrally formed portion of the cylinder portion  517 , and regulates the rotation of the pumping means  503 , in coordination with the cam portion  604   c  (FIG. 4) of the P output gear  604  (FIG.  4 ). 
     While the pumping means  503  suctions ink, the cap  528  or  529  is kept in contact with the printing head mounted on the carriage  201  (FIG.  1 ). The amount of the pressure with which the cap  528  or  529  is pressed upon the printing head is set at a predetermined value. 
     Also during this period, the arm portion  517   d  remains separated from the cam portion  604   c  of the P output gear  604 . 
     Next, the wiping means  502  illustrated in FIG. 3 will be described in detail. 
     FIG. 13 is a plan view of the front side of the driving mode switching means  600  illustrated in FIG.  3 . FIG. 14 is a plan view of the left side of the driving mode switching means  600  illustrated in FIG.  3 . 
     FIG. 13 shows the state of the driving mode switching means  600 , in which the wiping means  502 , disposed within the driving mode switching means  600 , is at the wiping position for wiping the printing head mounted on the carriage  201  (FIG.  1 ). 
     First, referring to FIGS. 13 and 14, the steps for setting the wiping means  502  in the driving mode switching means  600 , at the wiping position, and the steps for disengaging the wiping means  502 , will be described. 
     As a B trigger lever  532  is moved in the direction of an arrow mark B by the movement of the carriage  201 , the cam portion (unillustrated) of the B trigger lever  532  engages with the boss portion  534   b  of a B lever  534 , causing the B lever  534  to move in the direction of an arrow mark E. 
     The B lever  534  is between the base  601  and a base cover  640 , being sandwiched between them. 
     A B lock  536  is rotationally supported by the B lever  534 . As the B lever  534  rotates at a predetermined angle, the B lock  536  slides onto the projecting portion of the base  601 , becoming locked in order to complete the steps for setting the wiping means  502  for wiping. 
     The B lock release lever  538  is a lever for dissolving the locked state of the B lock  536 . As the carriage  201  moves in the direction of an arrow mark C after the completion of the wiping operation, the carriage  201  comes into contact with the B lock release lever  538 , causing the B lock release lever  538  to move in the direction of an arrow mark F. As a result, the B lock  536  rotates in the lock releasing direction, allowing the B lever  534  to be set at the no-wiping position by a pressure generating means  535  such as a spring placed between the base  601  and B lever  534 , dissolving the state in which the wiping means  502  is ready for wiping. 
     Next, the structure of the wiping means  502  will be described. 
     Referring to FIGS. 13 and 14, the wiping means  502  has blades  541   a  and  541   b  for removing the ink adhering to the printing head surface with the ejection orifices, a B holder  539  which supports the blades  541   a  and  541   b  through a spacer (unillustrated), and supports a B retainer  542  for retaining the B holder  539 . The B holder  539  is under pressure generated in the direction of an arrow mark G by a pressure generating means  540  such a spring placed between the B holder  539  and the B lever  534 . 
     In the wiping operation of the wiping means  502  structured as described above, the striking surface  539   a  of the B holder  539  comes in contact with the bottom surface of the carriage  201  to control the amount of the overlap between the surface (with the ejection orifices) of the printing head mounted on the carriage  201 , and the blades  541   a  and  541   b , so that the surface (with the ejection orifices) of the printing head is properly wiped by the blades  541   a  and  541   b.    
     FIG. 15 is a graph for describing the movements of the various components disposed within the driving mode switching means, with respect to the rotational angle of the P output gear  604  illustrated in FIG. 3; Figure (a) depicts the movements of the capping means  501 , a carriage lock  511  (FIG.  4 ), and the P sensor transmission lever  512  (FIG.  3 ), and Figure (b) depicts the ink suctioning movement of the pumping means  503 . 
     The P output gear  604  can be rotated either forward or in reverse within a range of 0°-330°. The rotational angle of 0° corresponds to the home position, which is used as the referential position for the capping operation of the capping means  501 , for the ink suctioning operation of the pumping means  503 , and for the like operations. 
     For example, when ink is suctioned by the pumping means  503  through the cap  528 , the P output gear  604  rotates in reverse from the position corresponding to a rotational angle of 299° to the position corresponding to a rotational angle of 82°, whereas when ink is suctioned through the cap  529 , the P output gear  604  rotates forward from the position corresponding to a rotational angle of 35° to a position corresponding to a rotational angle of 250°. 
     In terms of the rotational angle, the position from which the P output gear  604  begins to rotate, and the position at which it stops rotating, correspond to the amount of ink to be suctioned into the cylinder portions during the ink sucking strokes of the pistons and during the dry strokes of the pistons, and also correspond to the amount of the negative pressure which applies to the printing head while ink is suctioned. The pumping means  503  is provided with a plurality of operational modes inclusive of the number of pumping strokes to be repeated for ink suction and virtually dry suction, so that an optimal operation mode is selected from among the plurality of operation modes according to the aforementioned factors. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.