Patent Publication Number: US-7588432-B2

Title: Pump and inkjet printer

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The invention relates to a pump and an inkjet printer having the pump. 
   2. Description of Related Art 
   Inkjet printers eject ink drops from nozzles formed on inkjet heads by making use of various principles to print desired images on sheets, which are recording media. The inkjet heads are connected via tubes to ink tanks, which are ink sources. During printing, ink is sucked from the ink tanks using the capillary action of the nozzles and negative pressure generated by ejecting ink drops from the nozzles. However, when bubbles are trapped in the ink, it is tough to suck the ink from the ink tanks. As such, images cannot be printed on sheets using the inkjet heads. 
   An inkjet printer disclosed in Japanese Patent Publication No. 7-80304 (pp. 3-5, FIG. 1) can solve such a problem. This printer is provided with a pump for purging, and inkjet heads (recording heads) and ink tanks (ink cartridges) each containing ink that is communicated via flexible tubes inserted through the pump. The pump has a rotor rotatably attached inside to which three rollers are disposed on the circumference of the rotor. The rollers are placed away from each other at equivalent angles and are rotatably supported via respective shafts. In addition, the flexible tubes are disposed between the outside diameter of the rotor and the inside diameter of a circular hollow in the pump. During printing in such a printer, the rollers of the rotor are disposed so that they do not crush the tubes, and ink is sucked from the ink tanks via the tubes to the inkjet heads by the capillary action of the nozzles and negative pressure generated by ejecting ink drops from the nozzles as described above. Then, ink drops are ejected from the nozzles of the inkjet heads, and images are thereby printed on sheets. For a purging operation, the rotor of the pump is rotated so that ink is forcibly supplied from the pump to the inkjet heads. As this rotation enables ink containing bubbles to be eliminated from the inkjet heads, the reliability of the ink supply state can be recovered. 
   However, in the inkjet printer disclosed in Japanese Patent Publication No. 7-80304, when ink is forcibly supplied to the inkjet heads, the rotor crushes the flexible tubes at a position where the rotor contacts the flexible tubes when the rotor rotates. As a result, there is a problem in that the tubes disposed in the pump are damaged, and the ink supply to the inkjet heads fails. 
   There also exists a Cary&#39;s rotary pump, as a kind of rotary pump, as shown in  FIG. 1 . The pump  1070  has a case  1073  where a suction inlet  1071  and an exhaust outlet  1072  are formed and a rotor  1074  is rotatably provided so as to make contact with an inner surface of an upper portion of the case  1073  between the suction inlet  1071  and the exhaust outlet  1072 . The rotor  1074  is provided at an eccentric position in the case  1073 . Two vanes  1076   a ,  1076   b  connected by a spring  1075  are disposed in the rotor  1074  so as to slide in a direction of the diameter of the rotor  1074 . When the rotor  1074  rotates, the two vanes  1076   a ,  1076   b  rotate while making contact with the inner surface of the case  1073  by a spring force and a centrifugal force generated by rotating the rotor  1074 . 
   In the pump  1070  as described, when the rotor  1074 , which is located at the eccentric position, rotates, the volume gradually expands in a chamber communicating with the suction inlet  1071  (i.e., chamber  1077   a  in  FIG. 1 ), and fluid (liquid or gas) is sucked through the suction inlet  1071  therein to with the expansion of the volume. The chamber where the fluid is sucked then shifts to a position that is out of communication with the suction inlet  1071  and the exhaust outlet  1072  (i.e., chamber  1077   b  in  FIG. 1 ) by rotating the rotor  1074 . The chamber then moves to a position in communication with the exhaust outlet  1072  (i.e., chamber  1077   c  in  FIG. 1 ), where the volume is gradually decreased and the fluid is conveyed through the exhaust outlet  1072  with the decrease of the volume. 
   The above-described Cary&#39;s pump is disclosed in the following document: “27.13 Cary&#39;s rotary pump 1” in “Shin kikai no moto 10 pan 1977” [New Fundamentals of Machine 10th edition, 1977]. ed. Kikai no moto fukkan iinkai [Committee for republish of Fundamentals of Machine]. Rikogakusha Publishing Co., Ltd. p 203. 
   SUMMARY OF THE INVENTION 
   However, the Cary&#39;s rotary pump  1070  is intricately structured because the number of parts are large, and the manufacturing cost is thus expensive. If the spring  1075  becomes damaged, the vanes  1076   a ,  1076   b  do not move smoothly in the diameter direction by rotating the rotor  1074 . Thus, it becomes difficult to suck water or air through the suction inlet  1071 , resulting in a pump failure. 
   The invention thus provides, among other things, a pump that is not likely to malfunction and simply structured to thereby reduce manufacturing costs, and an inkjet printer including such a pump. 
   In one exemplary aspect of the invention, a pump includes a case having a hollow inside defined by an inner wall surface thereof and including a first through hole through which fluid is sucked in the hollow and a second through hole through which the fluid is ejected from the hollow; a rotor that is rotatable in the hollow and having a rotary shaft and a through groove formed on the rotor in a direction across the rotary shaft; and a partition in the through groove slidably in the direction across the rotary shaft, the partition being rotatable with the rotor with at least both ends of the partition, with respect to the direction across the rotary shaft, in constant contact with the inner wall surface defining the hollow upon rotation of the rotor. The hollow is partitioned into a plurality of chambers each enclosed by the case, the rotor, and the partition. 
   According to the above structure, upon rotation of the rotor, the partition slides in the direction across the rotor in accordance with a pressing force exerting on the inner wall surface of the case while expanding and contracting. Thus, as both ends of the partition is in constant contact with the inner wall surface of the case, the fluid can be sucked from the first through hole into the hollow and the sucked fluid can be ejected from the second through hole. Accordingly, the pump is simpler in structure and has less trouble when compared with the relevant prior art pump using two vanes urged by a spring instead of the partition member. In addition, as the pump does not use a spring, the number of parts can be decreased and manufacturing costs can be reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described in detail with reference to the following figures wherein: 
       FIG. 1  is a schematic sectional view of a conventional rotary pump; 
       FIG. 2  is a side view showing a general structure of an inkjet printer to which a pump according to an embodiment of the invention is applied; 
       FIG. 3  is a schematic diagram showing an ink supply passage of the inkjet printer shown in  FIG. 2 ; 
       FIG. 4A  shows a state of a pump applied to the inkjet printer shown in  FIG. 2 , during printing; 
       FIGS. 4B and 4C  show a rotation transition of a rotor in the pump during purging; 
       FIGS. 5A and 5B  show a rotation transition of a rotor in a pump, which is a first modification of the pump shown in  FIG. 4 , during purging; 
       FIG. 6A  is a schematic side view of a rotor of a pump, which is a second modification of the invention; 
       FIG. 6B  is a sectional view along the line VI-VI′ of  FIG. 6A ; 
       FIG. 7A  shows a state of the pump according to the second modification during printing; 
       FIGS. 7B and 7C  show a rotation transition of a rotor in the pump during purging; 
       FIG. 8A  shows a state of a pump according to a third modification during printing; 
       FIG. 8B  shows a state of the pump during purging; 
       FIG. 9A  shows a state of a pump according to a fourth modification during printing; 
       FIGS. 9B and 9C  show a rotation transition of a rotor in the pump during purging; 
       FIG. 10  is a schematic diagram showing an internal structure of a pump; 
       FIG. 11A  is a plan view of a partition member; 
       FIG. 11B  is a left side view of the partition member; 
       FIG. 11C  is a front view of the partition member; 
       FIG. 11D  is a right side view of the partition member; 
       FIG. 11E  is a bottom view of the partition member; 
       FIG. 11F  is an enlarged view of a left end part of  FIG. 11A ; 
       FIG. 11G  is an enlarged view of a right end part of  FIG. 11A ; 
       FIG. 11H  is an enlarged view of an upper part of  FIG. 11A ; 
       FIGS. 12A-12D  show rotational positions of the rotor and the partition member; 
       FIG. 13A  is a plan view of another partition member; 
       FIG. 13B  is a left side view of the partition member; 
       FIG. 13C  is a front view of the partition member; 
       FIG. 13D  is a right side view of the partition member; 
       FIG. 13E  is a bottom view of the partition member; 
       FIG. 13F  is an enlarged view of a left end part of  FIG. 13A ; 
       FIG. 13G  is an enlarged view of a right end part of  FIG. 13A ; and 
       FIG. 13H  is an enlarged view of an upper part of  FIG. 13A . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   An embodiment of the invention will be described in detail with reference to the accompanying drawings. A general structure of an inkjet printer  1  will be described with reference to  FIG. 2 . The inkjet printer  1  shown in  FIG. 2  is a color inkjet printer having four inkjet heads  2 . The printer  1  is provided with a sheet supplying unit  3  on the left of  FIG. 2  and a sheet ejecting unit  4  on the right. 
   Inside the printer  1 , a sheet conveying path is formed from the sheet supplying unit  3  toward the sheet ejecting unit  4 . A pair of conveying rollers  5  are disposed just downstream of the sheet supplying unit  3 . A sheet is conveyed by the pair of conveying rollers  5  from left to right in the figure (in the sheet conveying direction). Two belt rollers  6 ,  7  and a conveyor belt  8 , which is endless and looped around the two belt rollers  6 ,  7 , are disposed in the middle of the sheet conveying path. An outer surface (a conveying surface) of the conveyor belt  8  is treated with silicon so that the sheet conveyed by the pair of conveying rollers  5  is held on the outer surface of the conveyor belt  8  by its adhesive strength and is conveyed downstream (rightward in the figure) through a drive of the belt roller  6 . A pressing member  9  is disposed opposite the belt roller  6  with respect to the sheet conveying path. The pressing member  9  is used to bring a sheet into intimate contact with a conveying surface of the conveyor belt  8  by pressing the sheet against the conveying surface, so that the sheet is not raised from the conveying surface. 
   A sheet separation mechanism  10  is disposed rightward from the conveyor belt  8  as shown in the drawing. The sheet separation mechanism  10  is designed to separate a sheet adhered on the conveyor belt  8  from the conveyor belt  8  and convey the sheet to the sheet ejecting unit  4 . 
   A guide member  11  is disposed in an area enclosed with the conveyor belt  8 . The guide member  11  has a substantially rectangular parallelepiped (having a width as nearly the same as the conveyor belt  8 ) and is placed opposite the inkjet heads  2  in contact with a lower surface of an upper portion of the conveyor belt  8 , thereby supporting the conveyor belt  8  from the inner surface of the conveyor belt  8 . 
   The four inkjet heads  2  are arranged corresponding to the four color inks (magenta, yellow, cyan, and black) along the sheet conveying direction. That is, the printer  1  is a line printer. Each of the inkjet heads  2  has a rectangular shape having a longitudinal direction perpendicular to the sheet conveying direction when viewed in a plan view, and includes a corresponding head body  18  on a lower end thereof. Each head body  18  is made by affixing a fluid passage unit, in which an ink passage including a pressure chamber is formed, to an actuator that applies pressure to ink in the pressure chamber. Each head body  18  has, on a bottom surface, a plurality of ejection nozzles having very minute diameters through which ink is ejected downward. 
   The inkjet heads  2  are arranged so as to create a small clearance between the bottom surfaces of the inkjet heads  2  and the outer surface of the conveyor belt  8 , with the sheet conveying path formed in the clearance. With this structure, a sheet conveyed on the conveyor belt  8  passes directly under the head bodies  18  of the four inkjet heads  2 , each color ink is ejected from the nozzles on an upper surface (print surface) of the sheet, and a desired color image can be formed on the sheet. 
   A structure for supplying ink to the inkjet heads  2  in the inkjet printer  1  will be described with reference to  FIG. 3 . To supply different color inks to the respective inkjet heads  2 , an ink tank  20  is provided in an appropriate position within the printer  1  as shown in  FIG. 3 . The inkjet head  2  and the ink tank  20 , which are positioned away from each other, are connected via a pump  30  and a flexible tube  13  connected to the pump  30 . Thus, an ink supply passage (ink passage) from the ink tank  20  to the inkjet head  2  is created. In  FIG. 3 , one ink tank  20 , one pump  30  and one tube  13  are illustrated. However, there are actually four ink tanks  20  and four pumps  30  to correspond to the number of the inkjet heads  2 . 
   As shown in  FIG. 3 , the ink tank  20  includes an ink bag  22  in a synthetic resin housing  21 . The ink bag  22  contains degassed ink. The ink bag  22  has a resin spout that seals an opening of the bag  22 . The spout is provided with a cap  23  made from silicon or butyl rubber. The ink bag  22  is constructed from a pouch film formed by sealing a plurality of flexible films by heat. The pouch film is structured wherein a polypropylene layer on an innermost side, a polyester layer as a base placed on the polypropylene layer, an aluminum foil layer as an impermeable layer placed on the polyester layer, and a nylon layer for improving the strength of the film are laminated in this order. 
   A hollow needle  25  passes through the cap  23 . When ink in the ink tank  20  runs out, the hollow needle  25  is separated from the cap  23 , and the ink tank  20  is replaced with a new one. 
   Each head body  18  of the inkjet heads  2  includes a tubular member  14  on one end with respect to a longitudinal direction thereof and on a surface opposite from the bottom surface where the ejection nozzles are formed. One end of the tube  13  connected to the pump  30  is connected to the tubular member  14 . Ink in the ink tank  20  is led to the ink passage inside the head body  18  and ejected from the nozzles. The tube  13  has a tubular shape and has sufficient flexibility because it is made from an elastomer. 
   Next, a structure of the pump  30  will be described with reference to  FIGS. 3 and 4A  to  4 C. The pump  30  shown in  FIG. 3  includes a cylindrical-shaped case  31  with end surfaces in an axial direction thereof. For that, a hollow  32  (i.e., an interior) is defined in the case  31 . An opening  33 , where a rotary shaft  43  of the rotor  40  passes through, is formed on one end surface of the case  31 . A suction inlet  31   a  through which ink is sucked from the ink tank  20  into the hollow  32  of the pump  30  is formed on a peripheral surface of the case  31  at a position facing the cap  23  of the ink tank  20 . The hollow needle  25 , which is made of metal and has a cylindrical shape, is directly coupled to the suction inlet  31   a . An end of the hollow needle  25 , which faces toward the ink tank  20 , is sharp because it is cut at a bevel. As shown in  FIG. 3 , the hollow needle  25  connected to the suction inlet  31   a  passes through the cap  23  of the ink tank  20  horizontally, thereby forming the ink passage between the ink tank  20  and the pump  30 . Ink in the ink bag  22  is taken in via the hollow needle  25  from the suction inlet  31   a  into the hollow  32  of the pump  30 . 
   An exhaust outlet  31   b  through which ink is ejected from the hollow  32  to the inkjet head  2  is formed at a place rotated 90 degrees clockwise in  FIG. 3  from the suction inlet  31   a  on the peripheral surface of the case  31  (in other words, in an upper vertical position on the peripheral surface of the case  31 ). The exhaust outlet  31   b  is connected to a filter storing portion  35 , which is connected to the tube  13  connected to the tubular member  14  of the head body  18 . Inside the filter storing portion  35 , a communication hole is formed so as to vertically face a passage from the exhaust outlet  31   b  to the tube  13 . The communication hole forms a part of the ink passage from the ink tank  20  to the inkjet head  2 . The communication hole expands horizontally at a substantially middle portion thereof, where a filter  36  is disposed such that its filter face is positioned horizontally. 
   The filter  36  is a mesh filter and is designed to filter ink supplied from the ink tank  20  to the inkjet head  2 . Thus, the filter  36  catches foreign materials, such as rubber leavings caused by the insertion and removal of the hollow needle  25  to and from the cap  23 , so that they can be removed from ink. As a result, there is no need to specially provide a filter structure to the ink tank  20  side, and a simplification of the ink tank can be obtained. 
   The horizontal arrangement of the filter  36  provides a structure in which bubbles, trapped in ink, easily pass through the filter  36  when ink is sucked in an empty hollow  32  of the pump  30  (when ink is initially sucked). This occurs because a comparatively great force combining the buoyancy of the bubbles and the rotation force of the pump  30  is applied to the bubbles in the ink. Thus, the supply of ink to the inkjet head  2  is less often interrupted due to stagnation of a large amount of bubbles at an upstream side of the filter  36 . Further, by forming the exhaust outlet  31   b  on an upper vertical side of the case  31 , bubbles trapped in the hollow  32  when ink is initially sucked can be smoothly ejected without opposing the buoyancy, thereby obtaining high ejection quality. 
   As shown in  FIG. 3 , the case  31  of the pump  30  includes a rotor  40  rotatably at a specified position therein. The rotor  40  is comprised of a rotating part  41  that rotates in the case  31  and the rotary shaft  43  that transmits a rotational force to the rotating part  41 . The rotating part  41  of the rotor  40  has a cylindrical shape and a thickness such that both end surfaces with respect to its axial direction are in contact with both end wall surfaces defining the hollow  32  (both inner end surfaces of the case  31 ). The rotary shaft  43  is cylindrically shaped and is formed on one end surface of the rotating part  41 , protruding in the axial direction of the rotating part  41  in engagement with an opening  33  formed on the one end surface of the case  31 . A gear (not shown) is disposed on a part of the peripheral surface of the rotary shaft  43  and is in constant contact with part of the peripheral surface of the rotary shaft  43 . When the gear is rotated by a drive unit (not shown), the rotating part  41  rotates via the rotary shaft  43 . 
   The rotating part  41  of the rotor  40  includes a through part  41   a , which is formed in a diameter direction of the rotating part  41  and passes through the peripheral surface of the rotating part  41  (a circumferential surface of a cylinder). The through part  41   a  is formed in such a shape as to have a very small clearance in which two sliding members  51   a ,  51   b  and a partition member  50  are disposed to overlay each other and move along the inner surface of the through part  41   a.    
   As shown in  FIG. 3 , the partition member  50 , made from an ethylene-propylene-diene-terpolymer (EPDM)-base synthetic rubber, and the two sliding members  51   a ,  51   b , disposed such as to sandwich the partition member  50  therebetween, are disposed in the through part  41   a  of the rotating part  41  across the rotating part  41  on the center thereof. The partition member  50  and the sliding members  51   a ,  51   b  are disposed such that both of their ends with respect to their longitudinal direction (with respect to a direction across the rotating part  41  of the rotor  40 ) extend from the peripheral surface of the rotating part  41 . The partition member  50  is a flexible member and can extend in its longitudinal direction. The sliding members  51   a ,  51   b  are made from acetal polyoxymethylene (POM) resin. 
   The partition member  50  has a rectangular, flat board shape, and at least, a length such that both end surfaces of the partition member  50  with respect to its longitudinal direction are in contact with at least the inner surface of the case  31  (wall surface defining the hollow  32  in the case  31 ). The partition member  50  has a thickness greater than that of one sliding member. With the partition member  50  constructed above, the hollow  32  in the case  31  is always divided into two chambers. 
   The two sliding members  51   a ,  51   b  are physically similar to the partition member  50  except for that the two sliding members  51   a ,  51   b  are shorter and thinner than the partition member  50 . As the sliding member  51   a ,  51   b  are constructed from resin, the sliding friction coefficient of the sliding members  51   a ,  51   b  to the through part  41   a  is smaller than the sliding friction coefficient of the partition member  50  to the through part  41   a . Thus, the partition member  50 , which is sandwiched between the sliding members  51   a ,  51   b  in the through part  41 , is able to move smoothly on the inner surface of the through part  41  in a direction across the rotating part  41  of the rotor  40 . Thus, when compared to a case without the sliding members  51   a ,  51   b , when the rotor  40  rotates, the sliding members  51   a ,  51   b  allow the partition member  50  to move smoothly in the rotating part  41 , resulting in an improvement of the reliability of the pump  30 . 
   As the sliding members  51   a ,  51   b  are shorter than the partition member  50 , when the rotor  40  rotates by the drive device (not shown), contact between both end surfaces of the sliding members  51   a ,  51   b  and the inner surface of the case  31  is controlled. In addition, the sliding members  51   a ,  51   b  can prevent the partition member  50  from becoming excessively curved at both ends by friction between both ends of the partition member  50  and the inner surface of the case  31 . Accordingly, both ends of the partition member  50  are prevented from becoming crimped between the peripheral surface of the rotating part  41  and the inner surface of the case  31 . Thus, during rotation of the rotor  40 , an excessive rotational torque is not generated and the contact between both end surfaces of the sliding members  51   a ,  51   b  and the inner surface of the case  31  can be stabilized, thereby the sealability of each chamber partitioned by the partition member  50  can be stabilized. 
   A cut portion  42 , which is partially a flat and level surface, is formed on the peripheral surface of the rotating part  41  of the rotor  40  (the circumferential surface of the cylinder) so as not to overlap the through part  41   a . As shown in  FIG. 4A , when the cut portion  42  is located in a chamber, where the suction inlet  31   a  and the exhaust outlet  31   b  are present and the hollow  32  is partitioned by the partition member  50 , the suction inlet  31   a  and the exhaust outlet  31   b  are in communication with each other. Thereby an ink passage is formed in the pump  30 . 
   The rotating part  41  of the rotor  40  is also disposed at a position such that the peripheral surface of the rotating part  41 , where the cut portion  42  is not formed, can contact an upper left portion (a specified position) of the inner peripheral surface of the case  31 . As shown in  FIGS. 4B and 4C , the rotating part  41  can contact an upper left portion of the inner peripheral surface of the case  31 . Thus, it is possible to close the ink passage from the suction inlet  31   a  to the exhaust outlet  31   b  by rotating the rotor  40 , thereby changing a flow resistance in the passage. 
   The following will describe how ink is supplied to the inkjet head  2  via the pump  30  during printing in the inkjet printer  1 . Ink drops are ejected from the inkjet head  2  onto a sheet fed by the conveyor belt  8 , so that a desired image is printed on the sheet. When ink drops are ejected from the nozzles of the head body  18 , a negative pressure is generated in the head body  18 , and the inkjet head  2  draws in ink from the ink bag  22  of the ink tank  20  by suction through the use of the negative pressure and capillary action of the nozzles. 
   Thus, in the pump  30  that forms a part of the ink passage between the inkjet head  2  and the ink tank  20  while the inkjet head  2  draws in ink, the rotor  40  is stopped at a position such that the cut portion  42  of the rotating part  41  are located in the chamber where the suction inlet  31   a  and the exhaust outlet  31   b  are present in the hollow  32  of the case  31 , which is divided by the partition member  50 , as shown in  FIGS. 3 and 4A . 
   That is, with the cut portion  42  of the rotating part  41 , a clearance is formed between the rotor  40  and the inner peripheral surface of the case  31 . The clearance provides the ink passage where the suction inlet  31   a  and the exhaust outlet  31   b  are in communication with each other in the pump  30  and where the ink passage from the inkjet head  2  to the ink tank  20  is provided, so that ink is supplied to the inkjet head  2 . In addition, the flow resistance in the passage from the suction inlet  31   a  to the exhaust outlet  31   b  in the pump  30  becomes low, and the ink tank  20  and the inkjet head  2  are communicated with low resistance in the pump  30 . Thus, during printing, ink is supplied as required from the ink tank  20  to the inkjet head  2  via the pump  30  in accordance with ejection of ink from the inkjet head  2 . 
   The following will describe the pump operation during purging in the inkjet printer  1 . When the purging of bubbles trapped in the ink is conducted, for example after replacing the ink tank  20 , the pump  30  causes the gear to be rotated by the drive device (not shown) and then the rotor  40  to be rotated from a state shown in  FIG. 4A . The pump  30  can forcibly send ink only with the rotation of the rotor  40 . In other words, when the rotor  40  is rotated in a direction of an arrow as shown in  FIG. 4B , the peripheral surface of the rotor  40 , except for the cut portion  42 , makes contact with the inner peripheral surface of the case  31  and the ink passage from the suction inlet  31   a  to the exhaust outlet  31   b  is closed. Thereby the hollow  32  is divided into three chambers: a chamber that is communicating with the suction inlet  31   a , a chamber communicating with the exhaust outlet  31   b , and a chamber not communicating with the suction inlet  31   a  or the exhaust outlet  31   b . Then, when the rotor  40  is further rotated in the direction of the arrow as shown in  FIG. 4C , the chamber communicating with the suction inlet  31   a  expands, a negative pressure is generated in the chamber, and ink is sucked from the ink tank  20 . On the other hand, the chamber communicating with the exhaust outlet  31   b  shrinks with the rotation of the rotor  40  and ink remaining in the chamber is forcibly sent from the exhaust outlet  31   b  to the inkjet head  2 . 
   With the rotation of the rotor  40 , the partition member  50  and the sliding members  51   a ,  51   b , disposed in the through part  41   a  of the rotating part  41 , slide on the inner surface of the through part  41   a  as shown in  FIG. 4C  from a state shown in  FIG. 4B  and move toward a direction across the through part  41   a  of the rotor  40 . Namely, by rotating the rotor  40 , on the partition member  50  shown in  FIG. 4B  with respect to the direction across the rotating part  41 , a downward pressing force, which is generated at the contact portion between the upper end surface of the partition member  50  and the inner peripheral surface of the case  31 , becomes greater than a upward pressing force, which is generated at the contact portion between the lower end surface of the partition member  50  and the inner peripheral surface of the case  31 . As a result, the partition member  50  and the sliding members  51   a ,  51   b  move downward in the direction across the rotor  40 . When the partition member  50  moves, the sliding members  51   a ,  51   b  slide on the inner surface of the through part  41   a , enabling the partition member  50  to move smoothly. 
   In addition, with the rotation of the rotor  40 , the partition member  50  moves while expanding and shrinking in the longitudinal direction, so that both end surfaces of the partition member  50  are in constant contact with the inner surface of the case  31 . By the movement, expansion and shrinkage of the partition member  50  with rotation of the rotor  40 , negative pressure can be generated within the chamber communicating with the suction inlet  31   a , and ink present in the chamber communicating with the exhaust outlet  31   b  can be ejected from the exhaust outlet  31   b.    
   In this way, when the rotor  40  is rotated with the peripheral surface of the rotating part  41  of the rotor  40 , except for the cut portion  42 , in contact with the inner surface of the case  31  such as to close the ink path from the suction inlet  31   a  to the exhaust outlet  31   b , ink in the ink tank  20  is forcibly sucked from the suction inlet  31   a  into the pump  30  and ejected from the exhaust outlet  31   b . Thereby ink can be forcibly sent to the inkjet head  2  via the tube  13  connected to the exhaust outlet  31   b . Therefore, bubbles initially present in ink or bubbles trapped in ink from the tube  13  connected to the exhaust outlet  31   b  in the pump  30  can be purged. 
   By a force of the pump  30  that sucks ink from the ink tank  20  while ejecting it toward the inkjet head  2 , bubbles trapped in ink are sent toward the inkjet head  2  with ink, such that bubbles are eliminated from the ink passage from the inkjet head  2  to the ink tank  20 . 
   When the rotor  40  is in a position that makes contact with the specified position of the wall surface defining the hollow  32  in the case  31 , the suction inlet  31   a  and the exhaust outlet  31   b  are always maintained out of contact with each other even when the rotor  40  is rotated. In other words, the resistance in the flow passage between the suction inlet  31   a  and the exhaust outlet  31   b  is maintained high. Thus, during purging, there is no reduction in the performance of the pump  30  to force ink to flow. 
   The above pump has comparatively few constitutional parts in number, and is thus structured simply, so that it can be easily manufactured in a larger size or smaller size and it is suitable to make up a pump for sending a small amount of fluid by pressure. Thus, the pump is extremely suitable as a pump for sending ink in inkjet printers. 
   Furthermore, to improve the performance of the pump  30  to force ink to flow during purging, that is, to improve the pump performance, for example, a pump  60  may be applied to the inkjet printer  1  as a modification of the pump  30 .  FIGS. 5A and 5B  show operational states of a first modification of the pump  30  according to the embodiment, in other words, a transition where a rotor  140  of a pump  130  is rotated during purging. In the first modification, the inkjet printer  1  has substantially the same structures except for the pump  130 . The pump  130  is designed for purging only. Thus, the inkjet printer  1  is structured such that ink is supplied from the ink tank  20  to the inkjet head  2  via an ink passage  19  (indicated by chain lines in  FIG. 3 ) formed to detour the pump  130  while printing is made onto a sheet at the inkjet head  2 . Both ends of the ink passage are provided with respective valves (not shown), which are structured to close when the pump  130  is in operation and open when the pump  130  is not in operation. Except for these points, the structure of the inkjet printer  1  including the pump  130  is substantially the same as that in the embodiment, and thus the description thereof is omitted for simplicity. As to the structure of the pump  130  in the first modification, the same parts as those of the pump  30  of the embodiment are designated by similar numerals and not described again. 
   The pump  130 , which is the modification shown in  FIGS. 5A and 5B , includes the case  31  having the suction inlet  31   a , the exhaust outlet  31   b  and the opening  33  as is the case with the pump  30 . A rotor  140  is provided in the hollow  32  in the case  31  such as to be rotatable at a fixed position, similarly to the above-mentioned pump  30 , however, the cut portion  42  is not formed on the peripheral surface of a rotating part  141  of the rotor  140 . This is the different point from the pump  30 . Besides the missing cut portion  42 , the rotary shaft  43 , the through part  41   a , the sliding members  51   a ,  51   b , the partition member  50 , the filter storing portion  35  connected to the exhaust outlet  31   b , and the hollow needle  25  directly coupled to the suction inlet  31   a , which are related to the rotor  140 , are the same as those as described above and designated by similar numerals. 
   The rotor  140  of the pump  130  is disposed at a position such that the peripheral surface of the rotating part  141  makes contact with the specified position on the inner peripheral surface of the case  31 . Even when the rotor  140  is rotated, the peripheral surface of the rotating part  141  of the rotor  140  is always in contact with the inner peripheral surface of the case  31 . Thus, as shown in  FIG. 5A , the suction inlet  31   a  and the exhaust outlet  31   b  formed at the case  31  are present in different chambers of three chambers in the hollow  32  partitioned by the case  31 , the rotor  140 , and the partition member  50 . 
   When the rotor  140  of the pump  130  is rotated, the surface contact between the rotating part  141  of the rotor  140  with the case  31  does not become intermittent because the cut portion  42  is not formed on the peripheral surface of the rotating part  141 . In other words, as a clearance for communication between the suction inlet  31   a  and the exhaust outlet  31   b  is not formed, the pump performance that draws in ink within the hollow  32  via the suction inlet  31   a  and ejects it from the hollow  32  via the exhaust outlet  31   b  is increased. 
   The following will describe the operation of the pump  130  during purging at the inkjet head  2 . During printing, the rotor  140  of the pump  130  is stopped and ink is supplied from the ink tank  20  to the inkjet head  2  via the ink passage  19  shown in  FIG. 3  as described above. 
   The pump  130  can forcibly send ink only with rotation of the rotor  140 . Namely, when the rotor  140  is rotated in a direction of an arrow indicated in  FIG. 5A , the chamber communicating with the suction inlet  31   a  expands as shown in  FIG. 5B , and a negative pressure is generated in the chamber. Thereby ink is sucked from the ink tank  20 . On the other hand, the chamber communicating with the exhaust outlet  31   b  shrinks with a rotation of the rotor  140 , and ink present in the chamber is forcibly sent from the exhaust outlet  31   b  to the inkjet head  2 . The movements of the partition member  50  and the sliding members  51   a ,  51   b , which are disposed in the through part  41   a , accompanied with the rotation of the rotor  140 , are the same as those accompanied with the rotation of the rotor  40  of the pump  30  described above. 
   The chamber communicating with the suction inlet  31   a  and the chamber communicating with the exhaust outlet  31   b  are always closed because the peripheral surface of the rotating part  141  of the rotor  140  is in contact with the specified position on the wall surface defining the hollow  32  in the case  31 . Even when the rotor  140  is continuously rotated, the suction inlet  31   a  and the exhaust outlet  31   b  are constantly maintained out of communication with each other. Thus, the performance of the pump  130  can be increased more than that of the above-described pump  30  without degradation of the sending ability of the pump  130  during purging. 
   A second modification of a pump included in the inkjet printer  1  according to the embodiment will be described with reference to  FIGS. 6A ,  6 B, and  7 A to  7 C. In the following, the inkjet printer  1  for the second modification has substantially the same structure as those of the inkjet printer  1  using the pump  30  except for a pump  230 , thus the description thereof is omitted for simplicity. As to the structure of the pump  230  in the second modification, parts equivalent to those in the pump  30  are designated by similar numerals and not described again. 
   The case  31  of the pump  230  of the second modification includes a rotor  240  rotatably therein. As shown in  FIGS. 6A and 6B , the rotor  240  is comprised of a rotating part  241  that rotates in the case  31  and a shaft  242  that transmits rotation force to the rotating part  241 . An opening  233  through which the shaft  242  passes is formed on one end surface of the case  31 . The rotating part  241  has a cylindrical shape and a thickness such that both end surfaces of the rotating part  241  with respect to its axial direction are in contact with end wall surfaces defining the hollow  32  (both inner end surfaces of the case  31 ). The through part  41   a  is formed on the peripheral surface thereof in a diameter direction of the rotating part  241 . 
   As shown in  FIG. 6B , the shaft  242  is cylindrically formed so as to protrude from one end surface of the rotating part  241 . The shaft  242  has a cylindrical protrusion  243  on the end surface opposite to a side where the rotating part  241  is provided. A grooved cam  245  is disposed on the right side of the protrusion  243  in  FIG. 6B . The protrusion  243  is in contact with a cam groove  246  formed on the end surface of the grooved cam  245 , which faces the rotor  240 . 
   The grooved cam  245  has a disk-like shape, and the cam groove  246  is formed on the end surface facing the rotor  240  such that it is circularly continuous. The center of the cam groove  246  is eccentric from the center of the cam  245  in a lower-right direction in  FIG. 6A . Thus, the center of the cam groove  246  is moved in a circle as the grooved cam  245  rotates. 
   A guide member  247  and a gear  249  are disposed between the rotating part  241  of the rotor  240  and the grooved cam  245 . The guide member  247  has an oval opening  248  formed through its thickness. The shaft  242  passes through the opening  248 . Thus, when the grooved cam  245  rotates, the cam groove  246  forces the protrusion  243  of the shaft  242  to move, and the rotating part  241  is also moved via the shaft  242 . Since the shaft  242  passes through the opening  248  of the guide member  247 , such a movement is made in a direction along the opening  248 . The movement of the rotor  240  caused by a rotation of the grooved cam  245  is restricted at the opening  248  of the guide member  247  when the peripheral surface of the rotating part  241  of the rotor  240  is in contact with an upper left portion (a specified position), shown in  FIG. 7B , of the inner surface of the case  31  (a wall surface defining the hollow  32  in the case  31 ). 
   The gear  249  is disposed in a position such that its side surface is maintained in constant contact with the peripheral surface of the shaft  242  partially, as shown in  FIG. 6B . Thus, the gear  249  is rotated by a drive device (not shown), a rotational force is applied to the shaft  242  in the direction opposite to a rotational direction of the gear  249 , and the rotating part  241  is also rotated. 
   The partition member  50  and the two sliding members  51   a ,  51   b  that sandwich the partition member  50  therebetween are disposed in the through part  41   a  of the rotating part  241  across the rotating part  241  on the center thereof, similarly to the above embodiment. 
   The partition member  50  shown in  FIG. 7A  has a rectangular plate-like shape in a plane, and a length such that both end surfaces of the partition member  50  with respect to its longitudinal direction (with respect to a direction across the rotating part  241 ) are in contact with the inner surface of the case  31 . The hollow  32  in the case  31  is always partitioned into two chambers by the partition member  50 . Of the partitioned chambers, one chamber where the suction inlet  31   a  is communicated with the exhaust outlet  31   b  provides an ink passage through which ink is supplied from the ink tank  20  toward the inkjet head  2 , as shown in  FIG. 7A . The chamber where the suction inlet  31   a  is communicated with the exhaust outlet  31   b  is further partitioned into two chambers by a half turn of the grooved cam  245  where the rotating part  241  of the rotor  240  moves in contact with the inner surface of the case  31 , as shown in  FIG. 7B , via the shaft  242  that moves along the opening  248  of the guide member  247 . Accordingly, resistance in the flow passage between the suction inlet  31   a  and the exhaust outlet  31   b  in this state becomes higher than that in a state shown in  FIG. 7A . 
   The following will describe how ink is supplied to the inkjet head  2  during printing in the inkjet printer  1 . The pump  230  forms a part of the ink passage between the inkjet head  2  and the ink tank  20 , as is the case of the pump  30 . During printing onto a sheet, in the pump  230 , the rotor  240  is disposed at a substantially center of the hollow  32  in the case  31  and stopped as shown in  FIG. 7A  such that the inkjet head  2  can draw in ink. That is, the rotor  240  is stopped at a position where the hollow  32  in the case  31  is partitioned by the partition member  50  disposed in the through part  41   a  of the rotor  240  such as to form the chamber where the suction inlet  31   a  and the exhaust outlet  31   b  are communicated. 
   While the suction inlet  31   a  and the exhaust outlet  31   b  are in communication with each other, the ink passage from the inkjet head  2  to the ink tank  20  is provided, so that ink is supplied to the inkjet head  2 . In other words, the resistance in the ink passage from the suction inlet  31  to the exhaust outlet  31   b  in the case  31  of the pump  230  becomes low, and during printing, an adequate amount of ink is supplied from the ink tank  20  via the pump  230  in response to an ejection of ink to the inkjet head  2 . 
   The following will describe the pump operation in the second modification during purging at the inkjet printer  1 . In the pump  230  during purging, the rotor  240  is moved from the position shown in  FIG. 7A  to the position shown in  FIG. 7B . In other words, by a half turn of the grooved cam  245 , which is in a state in that the center of the rotor  240  is located in substantially the center of the hollow  32  in the case  31 , the protrusion  243  of the shaft  242  of the rotor  240  moves along the cam groove  246 , the shaft  242  of the rotor  240  moves along the opening  248  of the guide member  247 , and the peripheral surface of the rotating part  241  of the rotor  240  make contact with the inner surface of the case  31  at the specified position as shown in  FIG. 7B . Thus, in the hollow  32  in the case  31  partitioned by the partition member  50  disposed in the through part  41   a  of the rotor  240 , the flow passage from the suction inlet  31   a  to the exhaust outlet  31   b  is closed. 
   The gear  249  is then rotated by the drive device (not shown) to rotate the rotor  240  in a direction of an arrow shown in  FIG. 7B , counterclockwise. As the rotor  240  is rotated in the direction of the arrow shown in  FIG. 7B , the chamber communicating with the suction inlet  31   a , which is partitioned by rotating the rotor  240 , expands as shown in  FIG. 7C , and negative pressure is generated in the chamber and ink is sucked from the ink tank  20 . On the other hand, the chamber communicating with the exhaust outlet  31   b  shrinks with a rotation of the rotor  240 , and ink present in the chamber is forced out through the exhaust outlet  31   b  to the inkjet head  2 . 
   The partition member  50  and the sliding members  51   a ,  51   b , which are disposed in the through part  41   a  of the rotor  240 , slide on the inner surfaces of the through part  41   a  from the state shown in  FIG. 7B  with a rotation of the rotor  240 , and move in the direction across the rotor  240  as shown in  FIG. 7C . That is, by rotating the rotor  240 , on the partition member  50  shown in  FIG. 7B  with respect to the direction across the rotor  240 , a downward pressing force, which is generated at the contact portion between the upper end surface of the partition member  50  and the inner surface of the case  31 , becomes greater than an upward pressing force, which is generated at the contact portion between the lower end surface of the partition member  50  and the inner surface of the case  31 . Thus, the partition member  50  moves downward with respect to the direction across the rotor  240 . When the partition member  50  moves, the sliding members  51   a ,  51   b  slide on the inner surface of the through part  41   a , enabling the partition member  50  to move smoothly. 
   Further, as the partition member  50  moves while expanding and shrinking in the longitudinal direction thereof by rotating the rotor  240 , both end surfaces of the partition member  50  are in constant contact with the inner surface of the case  31 . By the movement, expansion and shrinkage of the partition member  50  with rotation of the rotor  240 , negative pressure can be generated within the chamber communicating with the suction inlet  31   a , and ink present in the chamber communicating with the exhaust outlet  31   b  can be ejected from the exhaust outlet  31   b.    
   Thus, as the chamber where the suction inlet  31   a  and the exhaust outlet  31   b  are communicated with each other is partitioned with a movement of the rotor  240 , once the rotor  240  is rotated with the passage from the suction inlet  31   a  to the exhaust outlet  31   b  closed, ink in the ink tank  20  is forcibly sucked from the suction inlet  31   a  into the pump  230  and ejected from the exhaust outlet  31   b . Thereby ink is forcibly sent toward the inkjet head  2  via the tube  13  connected to the exhaust outlet  31   b . Therefore, bubbles initially present in ink or bubbles trapped in ink from the tube  13  connected to the exhaust outlet  31   b  in the pump  230  can be purged. 
   By a force of the pump  230  that sucks ink from the ink tank  20 , while ejecting it toward the inkjet head  2 , bubbles trapped in ink are sent toward the inkjet head  2  with ink, such that bubbles are eliminated from the ink passage from the inkjet head  2  to the ink tank  20 . 
   When the rotor  240  is in a position making contact with the specified position of the wall surface defining the hollow  32  in the case  31 , the suction inlet  31   a  and the exhaust outlet  31   b  are maintained out of communication with each other even when the rotor  240  is rotated. In other words, the resistance in the flow passage between the suction inlet  31   a  and the exhaust outlet  31   b  is maintained high. Thus, during purging, there is no reduction in the performance of the pump  230  to force ink to flow. 
   A third modification of a pump included in the inkjet printer  1  according to the embodiment will be described with reference to  FIGS. 8A and 8B .  FIG. 8A  shows a state of a pump  330  during printing.  FIG. 8B  shows a state of the pump  330  during purging. In the following, as the inkjet printer  1  for the third modification has substantially the same structure as that of the inkjet printer  1  using the pump  30  except for the pump  330 , thus the description thereof is omitted for simplicity. In addition, as to the structure of the pump  330  in the third modification, parts equivalent to those in the pump  30  are designated by similar numerals and thus are not described again. 
   The pump  330  of the third modification shown in  FIGS. 8A and 8B  is provided with a case  61  having the suction inlet  31   a  and the exhaust outlet  31   b  as is the case with the pump  30  described above. The hollow  32  is defined in the case  61 . Of the wall surface defining the hollow  32 , a part of the wall surface between the suction inlet  31   a  and the exhaust outlet  31   b  is composed of a movable wall member  65 . In the case  61 , a rotor  340 , which is similar to that in the pump  30 , is provided. The rotor  340 , however, does not move as in the pump  230 , and is provided rotatably at a fixed position. The through part  41   a , the sliding members  51   a ,  51   b , the partition member  50 , the filter storing portion  35  connected to the exhaust outlet  31   b , the hollow needle  25  directly connected to the suction inlet  31   a , which are related to the rotor  340 , are the same as those as described above and designated by the same numerals. 
   The rotor  340  of the pump  330  is disposed such that the peripheral surface of the rotor  340  can make contact with the movable wall member  65  when the movable wall member  65  is on the circumference of the inner surface of the case  61  as shown in  FIG. 8B . This position is substantially similar to the specified position on the inner surface of the case  31 , which the rotor  240  of the pump  230 , the second modification, moves in contact with. The rotor  340  is rotated by a drive device (not shown) at the position. That is, the pump  330  is not provided with parts required for moving the rotor  240  in the second modification, such as the grooved cam  245  and the guide member  247 . 
   The case  61  is provided with a through portion  61   a , which is on the peripheral surface of the case  61  on the side where the distance between the suction inlet  31   a  and the exhaust outlet  31   b  is shorter. The through portion  61   a  guides the movable wall member  65  slidably. The case  61  has a shape similar to that of the case  31  in the pump  30  according to the embodiment except for which the through portion  61   a  is formed. 
   The movable wall member  65 , which is guided slidably by the through portion  61   a  of the case  61 , has an outer peripheral shape substantially similar to an inner peripheral shape of the through portion  61   a , which is substantially a rectangular solid shape. The movable wall member  65  is provided with a sealing member (not shown) around an outer peripheral surface thereof. This sealing member prevents bubbles from being trapped in ink in the pump  330  in between the movable wall member  65  and the through portion  61   a , and further prevents ink from leaking out of the pump  330 . An end surface  65   a  of the movable wall member  65 , which faces the rotor  340 , has a spherical shape similar to that of the inner surface of the case  61  (the wall surface defining the hollow  32  in the case  61 ), and constitutes a part of the inner surface of the case  61 . 
   An arm  66  is connected to other end surface of the movable wall member  65 , which is the opposite side of the end surface  65   a . A grooved cam  68  is connected to an end of the arm  66  that is the opposite side to which the movable wall member  65  is connected. The grooved cam  68  includes, on a surface facing the arm  66 , a cam groove  69  whose center is eccentric as is the case with the grooved cam  245  in the second modification. Thus, as the grooved cam  68  is rotated, the center of the cam groove  69  moves in a circle. 
   A protrusion  66   a  is formed on an end portion of the arm  66 , which faces toward the grooved cam  68 . The protrusion  66   a  protrudes toward the cam groove  69  and fits in the cam groove  69 . Thus, as the grooved cam  68  is rotated, the protrusion  66   a  is moved along the cam groove  69 , so that the arm  66  moves in a direction A as shown in  FIG. 8B  and thus the movable wall member  65  also moves similarly. By moving the movable wall member  65  in this way, the movable wall member  65  can be moved to a position making contact with the rotor  340  of the pump  330  and a position out of contact with the rotor  340 . Thereby changing the flow resistance in the chamber where the suction inlet  31   a  and the exhaust outlet  31   b  are communicated with each other of the hollow  32  in the case  61 , which is partitioned by the partition member  50  disposed in the through part  41   a  of the rotor  340 . 
   The following will describe the operation of the pump  330  during printing and purging at the inkjet head  2 . As described above, while printing is made on a sheet at the inkjet head  2 , ink is supplied from the ink tank  20  as the inkjet head  2  sucks ink, so that the movable wall member  65  of the pump  330  reaches a state where it is placed in isolation at the position out of contact with the rotor  340 . That is, by rotating the grooved cam  68 , the protrusion  66   a  of the arm  66  moves along the cam groove  69 , and thus the movable wall member  65  also moves along the through part  61   a  via the arm  66 . When the movable member  65  is isolated from the peripheral surface of the rotor  340 , the grooved cam  68  is stopped, and the suction inlet  31   a  and the exhaust outlet  31   b  are brought into communication with each other. At this time, the rotor  340  of the pump  330  is stopped such that the partition member  50  is in the position to form the chamber where the suction inlet  31   a  and the exhaust outlet  31   b  are in communication with each other. 
   The movable wall member  65  is separated from the rotor  340  so that the suction inlet  31   a  and the exhaust outlet  31   b  are communicated with each other. As a result, the fluid resistance in the passage from the suction inlet  31   a  to the exhaust outlet  31   b  becomes low, and ink is spontaneously supplied as required from the ink tank  20  to the inkjet head  2  via the pump  330  in accordance with an ejection of ink from the inkjet head  2 , as is the case with the pump  30  according to the embodiment. 
   An operation of the pump  330  during purging will be described. The movable wall member  65  is moved from the position shown in  FIG. 8A  to the position shown in  FIG. 8B . In other words, when the grooved cam  68 , which is in a state where the movable wall member  65  is separated from the rotor  340 , is rotated a half-turn, the protrusion  66   a  of the arm  66  is moved along the cam groove  69 , the arm  66  is moved to the rotor  340 , and the end surface  65   a  of the movable wall member  65  makes contact with the peripheral surface of the rotor  340 . In this way, as is the case with the pump  30  described above, the passage from the suction inlet  31   a  to the exhaust outlet  31   b , which is formed in the hollow  32  partitioned by the partition member  50  disposed in the through part  41   s  of the rotor  340 , is closed. 
   The rotor  340  is rotated in a direction of an arrow in  FIG. 8B  (counterclockwise) by the drive device (not shown), as is the case with the pump  30  described above. The chamber communicating with the suction inlet  31   a  expands to suck ink into the chamber from the ink tank  20 , and the chamber communicating with the exhaust outlet  31   b  shrinks to forcibly eject ink present in the chamber from the exhaust outlet  31   b  to send it to the inkjet head  2 . The movements of the partition member  50  and the sliding members  51   a ,  51   b  accompanied with a rotation of the rotor  340  are the same as those accompanied with a rotation of the rotor  40  of the above-mentioned pump  30 . 
   The chamber where the suction inlet  31   a  and the exhaust outlet  31   b  are communicated with each other is partitioned in accordance with the movement of the movable wall member  65 , so that the passage from the suction inlet  31   a  to the exhaust outlet  31   b  is closed. As the rotor  340  is rotated with the passage closed, the pump  330  can forcibly send ink to the inkjet head  2 , as is the case with the pump  30 . Therefore, as is the case with the pump  30  described above, bubbles initially present in ink or bubbles trapped in ink from the tube  13  connected to the exhaust outlet  31   b  in the pump  330  can be purged with ink, so that it is possible to eliminate the bubbles from ink. In addition, as is the case with the pump  30 , even when the rotor  340  is rotated, the suction inlet  31   a  and the exhaust outlet  31   b  are always maintained out of communication with each other. In other words, the resistance in the passage between the suction inlet  31   a  and the exhaust outlet  31   b  is maintained extremely high, so that, during purging, there is no reduction in the performance of the pump  330  to force ink to flow. 
   A fourth modification of a pump included in the inkjet head printer  1  according to the embodiment will be described with reference to  FIGS. 9A to 9C .  FIG. 9A  shows a state of a pump  430  during printing, and  FIGS. 9B and 9C  show a transition where a rotor  440  of the pump  430  is rotated during purging. In the following, as the inkjet printer  1  for the fourth modification has substantially the same structure as that of the inkjet printer  1  using the pump  30  except for the pump  430 , thus the description thereof is omitted for simplicity. In addition, as to the structure of the pump  430  in the fourth modification, parts equivalent to those in the pump  30  are designated by similar numerals and thus are not described again. 
   The pump  430  shown in  FIG. 9A  is substantially the same as the pump  30  according to the above-mentioned embodiment, and is provided with a tunnel  442  that connects two places on the peripheral surface of the rotor  440 , instead of the cut portion  42  formed in the rotor  41  of the pump  30 . 
   As shown in  FIG. 9A , the rotor  440  of the pump  430  is provided in the case  31  such as to be rotatable at a fixed position similar to that of the rotor  40  in the embodiment, and a part of the peripheral surface of the rotor  440  always making contact with the inner surface of the case  31 . The tunnel  442  is cut through in the direction across the rotor  440  between the through part  41   a  and a contact between the peripheral surface of the rotor  440  and the inner surface of the case  31  such that the tunnel  442  should not overlap the through part  41   a.    
   When the tunnel  442  of the rotor  440  is placed in the chamber where the suction inlet  31   a  and the exhaust outlet  31   b  exist in the hollow  32  partitioned by the partition member  50  as shown in  FIG. 9A , the suction inlet  31   a  and the exhaust outlet  31   b  are brought in communication with each other. When the rotor  440  is rotated so that the peripheral surface of the rotor  440  can make contact with the inner surface of the case  31 , as shown in  FIG. 9B , on a side where there is not the tunnel  442  opposing a side where the tunnel  442  is formed across the through part  41   a , the ink passage from the suction inlet  31   a  to the exhaust outlet  31   b  can be closed. Thus, the pump  430  that changes the fluid resistance in the ink passage from the suction inlet  31   a  to the exhaust outlet  31   b  by the rotation of the rotor  440  can be easily manufactured by only providing the tunnel  442  that connects the two places on the peripheral surface of the rotor  440 . 
   The following will describe the operation of the pump  430  during printing at the inkjet head  2 . While printing is made on a sheet at the inkjet head  2 , the inkjet head  2  sucks ink, so that ink is supplied from the ink tank  20 , as described above. As shown in  FIG. 9A , the rotor  440  is stopped such that the tunnel  442  is placed in the chamber where the suction inlet  31   a  and the exhaust outlet  31   b  exist in the hollow  32  partitioned by the partition member  50 . 
   The tunnel  442  of the rotor  440  allows communication between the suction inlet  31   a  and the exhaust outlet  31   b , thereby providing the ink passage in the pump  430 . In addition, the resistance in the ink passage from the suction inlet  31   a  to the exhaust outlet  31   b  becomes low, and ink is spontaneously supplied as required from the ink tank  20  to the inkjet head  2  via the pump  430  in accordance with an ejection of ink from the inkjet head  2 , as is the case with the pump  30  according to the embodiment. 
   An operation of the pump  430  during purging will be described. The pump  430  can force ink to flow by only rotating the rotor  440  counterclockwise from the state shown in  FIG. 9A . That is, as shown in  FIG. 9B , when the rotor  440  is rotated counterclockwise, the peripheral surface of the rotor  440  is in contact with the inner surface of the case  31  on the side where there is not the tunnel  442  opposing the side where the tunnel  442  is formed across the through part  41   a , and the passage from the suction inlet  31   a  to the exhaust outlet  31   b  is closed. With this state, when the rotor  440  is rotated counterclockwise as shown in  FIG. 9C , the chamber communicating with the suction inlet  31   a  expands and ink is sucked in the chamber from the ink tank  20 , whereas the chamber communicating with the exhaust outlet  31   b  shrinks and ink present in the chamber is forcibly ejected from the exhaust outlet  31   b  and conveyed to the inkjet head  2 . The movements of the partition member  50  and the sliding members  51   a ,  51   b  accompanied with a rotation of the rotor  440  are the same as those accompanied with a rotation of the rotor  40  of the above-mentioned pump  30 . 
   Thus, when the rotor  440  is rotated with the peripheral surface of the rotor  440  brought in contact with the inner surface of the case  31  on the side where there is not the tunnel  442  opposing the side where the tunnel  442  is formed across the through part  41   a , such that the ink passage from the suction inlet  31   a  to the exhaust outlet  31   b  may remain closed, ink can be forcibly sent to the inkjet head  2  as is the case with the pump  30 . Accordingly, as in the case of the pump  30 , bubbles initially present in ink or bubbles trapped in ink from the tube  13  connected to the exhaust outlet  31   b  in the pump  430  can be purged with ink. 
   As described above, while the ink passage from the suction inlet  31   a  to the exhaust outlet  31   b  is closed in the pump  30 ,  130 ,  230 ,  330 ,  430 , continuous rotation of the rotor  40 ,  140 ,  240 ,  340 ,  440  enables ink to forcibly supply from the ink tank  20  to the inkjet head  2  even without printing, and bubbles remaining in the inkjet head  2  can be also purged with ink. In addition, both printing and purging at the inkjet head  2  can be performed easily by making the fluid resistance between the suction inlet  31   a  and the exhaust outlet  31   b  variable. The pump performance that sends ink toward the inkjet head  2  and an amount of ink to be conveyed toward the inkjet head  2  can be adjusted by controlling the number of rotations of the rotor  40 ,  140 ,  240 ,  340 ,  430 . 
   In contrast to the use of a flexible tube, a space in the ink tank  20  and an ink passage in the inkjet head  2  are connected at the hollow  32  in the pump  30 ,  230 ,  330 ,  430  without segmentation, thereby preventing malfunctions regarding ink supply to the inkjet head  2  caused by pump trouble. As there is no need to dispose a flexible tube in the pump  30 ,  230 ,  330 ,  430 , a barrier effect to prevent bubbles in the pump  30 ,  230 ,  330 ,  430  can be improved. As only the hollow needle  25  is interposed between the ink tank  20  and the pump  30 ,  230 ,  330 ,  430 , bubbles are seldom trapped in ink between the ink tank  20  and the pump  30 ,  230 ,  330 ,  430 . 
   While the invention has been described with reference to the preferred embodiment, it is to be understood that the invention is not restricted to the particular forms shown in the foregoing embodiment. Various modifications and alternations can be made thereto without departing from the scope of the invention. For example, in the pump operation during purging, while the rotor  40 ,  240 ,  340 ,  440  is rotated, the peripheral surface of the rotor  40 ,  240 ,  340 ,  440  of the pump  30 ,  230 ,  330 ,  430  and the inner surface of the case  31 ,  61  (the wall surface defining the space in the case) may be always out of contact with each other so as to have a slight clearance therebetween. That is, in the chamber where the suction inlet  31   a  and the exhaust outlet  31   b  are present, of the two chambers that are partitioned by the partition member  50  in the hollow  32  in the case  31 ,  61  of the pump  30 ,  230 ,  330 ,  440 , the peripheral surface of the rotor  40 ,  240 ,  340 ,  440  may be brought as close to the inner surface of the case  31 ,  61  of the pump  30 ,  230 ,  330 ,  440  as possible, thereby making the fluid resistance from the suction inlet  31   a  to the exhaust outlet  31   b  go high. When the rotor  40 ,  240 ,  340 ,  440  is rotated in this status, it is possible to suck ink through the suction inlet while ejecting ink through the exhaust outlet. 
   In the above embodiment and modifications, the rotor  40  of the pump  30  and the movable wall member  65  of the pump  330  are moved through the use of a grooved cam. However, they can be moved by a cylinder. 
   The filter storing portion  35  may not be provided. In addition, there is no need to provide the sliding members  51   a ,  51   b  which put therebetween the partition member  50  disposed in the through part  41   a  of the rotor  40 ,  240 ,  340 , and  440 . The partition member  50  may be formed of several sheets in stack. Furthermore, a coating agent may be applied to the surface of the partition member  50  which contacts the inner surface of the through part  41   a , as a sliding agent. The invention may be applicable to not only line-type inkjet printers but also serial-type inkjet printers. 
   The invention can be applied to not only inkjet printers but also anything required pump function that draws in fluid from a suction inlet and ejects the fluid from an exhaust outlet. Further, the fluid sucked and ejected from the pump is not limited to ink, and can be a different fluid or air. 
   The partition member  5  may be constructed of not only EPDM but also a different synthetic rubber such as SBR (styrene butadiene rubber), NBR (nitrile-butadiene rubber), CR (chloroprene rubber), and fluorine rubber. In addition, the sliding members  51   a ,  51   b  may be constructed of not only acetal polyoxymethylene (POM) resin but also other engineering resins such as poly-carbonate (PC) resin, polypropylene (PP) resin, and polyethylene (PE) resin. 
   The partition member  50  may be formed in the following shape. In the following description, it is assumed that the basic structures of a pump are those applied to the pump  30  of the embodiment. Thus, the parts except for the partition member  50  are designated by the same numerals as used in the pump  30  of the embodiment, and not described again. 
   As shown in  FIGS. 11A-11E , the partition member  50  is a plate-like member of which edge portions are cut at a bevel facing in the opposite direction to a rotational direction R ( FIG. 11E ) of the partition member  50 , so that slopes ( 50   a ,  50   b ,  50   c  of  FIG. 11 ) are formed each having approximately 30 degrees with respect to the front and back surfaces of the partition member  50 , and thereby the edge portions are formed thinner toward the edges. The very edges of the partition member  50  are rounded. The partition member  50  is disposed at such a position as to pass through the inside of the rotor  40  with its front and back surfaces orientated parallel to the rotational axis of the rotor  40 . The partition member  50  is maintained in the rotor  40  such as to be slidable in a direction perpendicular to the rotational axis of the rotor  40  and along the front and back surfaces of the partition member  50 . The partition member  50  makes contact with the inner surface of the case  31  at its edge portions to partition the hollow  32  into two. 
   When the partition member  50  rotates with the rotor  40  upon the rotation of the rotor  40 , it slides in a sliding direction in accordance with a pressing force exerting on the inner surface of the case  31 . Thus, the partition member  50  rotates while remaining in contact with the inner surface of the case  31 . As the edge portions of the partition member  50  are tapered so as to be thinner toward the edges, when they make contact with the inner surface of the case  31 , they flexibly deform to bend in a direction opposite to the rotational direction of the rotor  40  as shown in  FIG. 10 . Thus, the partition member  50  is in intimate contact with the inner surface of the case  31 . 
   The sliding members  51   a ,  51   b  are thin plate-like members made of acetal polyoxymethylene (POM) resin, thereby the friction resistance generated between the sliding members  51   a ,  51   b  and the rotor  40  is smaller than that generated between the partition member  50  and the rotor  40 , as described above. The sliding members  51   a ,  51   b  are interposed between the partition member  50  and the rotor  40 . 
   The partition member  50  and the sliding members  51   a ,  51   b  are disposed such that both end portions of the partition member  50  and the sliding members  51   a ,  51   b  with respect to their longitudinal direction protrude from the peripheral surface of the rotor  40 . The partition member  50  can extend and contract in its longitudinal direction because it is a flexible member. The sliding members  51   a ,  51   b  are shorter than the partition member  50  with respect to their longitudinal direction, thereby controlling such as to keep both end surfaces of the sliding members  51   a ,  51   b  from contacting with the inner surface of the case  31 . 
     FIGS. 12A to 12D  show rotational positions of the rotor  40  at 0 degrees, 45 degrees, 90 degrees, and 135 degrees, respectively. After the rotational position of the rotor  40  reaches 180 degrees, the partition member  50 , rotational symmetry 180 degrees, is located in a similar position as is the case with the rotor  40  is at 0 degrees, except that the chambers  32   a ,  32   b  in  FIG. 12  change places. 
   When the rotor  40  rotates in the eccentric position in the hollow  32 , in the chambers  32   a ,  32   b  partitioned by the partition member  50 , the rotor  40 , and the case  31 , the volume gradually increases at the position communicating with the suction inlet  31   a , and ink is sucked through the suction inlet  31   a  with the increase of the volume (refer to the chamber  32   a  in  FIGS. 12A and 12B ). When the rotor  40  further rotates, the chamber where ink has been sucked reaches a position where there is no communication with the suction inlet  31   a  (refer to the chamber  32   a  in  FIG. 12C ), and then reaches a position communicating with the exhaust outlet  31   b  (refer to the chamber  32   a  in  FIG. 12D ). In the chamber that reaches the position communicating with the exhaust outlet  31   b , the volume is gradually decreased, and ink is sent through the exhaust outlet  31   b  with the decrease of the volume (refer to the chamber  32   b  in  FIGS. 12A to 12D ). 
   As described above, according to the pump  30 , the partition member  50  maintains in contact with the inner surface of the case  31  by sliding in the sliding direction in accordance with a pressing force that acts on the inner surface of the case  31  accompanied with the rotation of the rotor  40 . Thus, the pump  30  is simpler in structure and has less trouble when compared with the relevant prior art pump using two vanes urged by a spring. In addition, as the pump  30  does not use a spring, the number of parts can be decreased and manufacturing costs can be reduced. 
   In addition, the edges of the partition member  50  deform in the direction opposite to the rotational direction of the rotor  40  in contact with the inner surface of the case  31 , so that they are easy to stick to the inner surface of the case. Thus, this enhances the degree of contact (air tightness or fluid tightness) between the partition member  50  and the inner surface of the case  31  and improves the pump performance, when compared with the prior art pump using the two vanes that make contact with the inner surface of the case  31  without deformation. 
   Especially, the edges of the partition member  50  are tapered toward the edges and the partition member  50  is easy to deform toward the edges. Even when there are minute bumps and dips on the inner surface of the case  31 , the partition member  50  is easy to deform to fit the bumps and dips at its edges, and the degree of contact (air tightness or fluid tightness) between the partition member  50  and the inner surface of the case  31  becomes extremely high, when compared with a case without such tapered edges. In addition, differing from a case when the partition member  50  is thin in its entirety, the partition member  50  according to the embodiment does not bend excessively further beyond the edge portions. Thus, the partition member  50  does not bend excessively with the increase of the internal pressure. 
   Further, as the sliding members  51   a ,  51   b  are interposed between the partition member  50  and the rotor  40 , the partition member  50  can smoothly slide with the sliding members  51   a ,  51   b  with respect to the rotor  40 . Thus, the movement of the partition member  50  with respect to the rotor  40  becomes smooth, thereby improving the reliability of the pump, when compared with a case without the sliding members  51   a ,  51   b.    
   According to the inkjet printer  1  equipped with the pump  30  structured, as described above, the pump  30  is comparatively simple in structure, and can be manufactured with less manufacturing costs by just that much, developing a smaller size of the pump  30  is also easy, malfunction is unlikely to occur, and the pump performance is also excellent. Thus, these factors contributes to reduced manufacturing costs of the inkjet printer  1 , enabling the pump to accommodate in a limited space inside the inkjet printer  1  compactly, and preventing trouble such as ink supply failure. 
   Although the two sliding members  51   a ,  51   b  are adopted in the above embodiment to enhance the slidability of the partition member  50 , there may be no need to provide the sliding members  51   a ,  51   b  in the pump  30  if the slidability of the partition member  50  is sufficiently high. 
   As a structure where the slidability of a partition member can be enhanced sufficiently, a partition member  70  shown in  FIGS. 13A to 13H , for example, can be provided where a contact part  72  formed of fluorine rubber is provided around the edges of a core member  71  formed of POM resin. 
   The partition member  70  is a combination of the core member  71  and the contact part  72 , which are integrally formed by the so-called outsert molding technique where the core member  71  is arranged in a mold in advance and then composite raw material of fluorine rubber is injected in the mold so that the contact part  72  is molded. A plurality of through holes  71   a  are formed on the core member  71 , and the material to produce the contact part  72  are embedded in the through holes  71   a . Thus, the core member  71  and the contact part  72  never separate from each other although delamination only occurs at an interface between the core member  71  and the contact part  72 . The core member  71  and the contact part  72  are excellent in strength when compared with a case that they are separately produced and bonded with adhesive agent. 
   Even in the partition member  70  structured above, as is the case with the partition member  50 , edge portions of the partition member  70  are cut at a bevel so that slopes ( 70   a ,  70   b ,  70   c  of  FIG. 13 ) are formed having approximately 30 degrees with respect to the front and back surfaces of the partition member  70 , and thereby the edge portions are formed thinner toward the edges. The edge portions of the partition member  70  deform in contact with the inner surface of the case  31  in a direction opposite to the rotational direction of the rotor  40 , thereby bringing into intimate contact with the inner surface of the case  31 . 
   The core member  71  is slightly thicker than the contact part  72 . When the partition member  70  is disposed in the rotor  40 , the front and back surfaces of the core member  71  mainly make contact with the inner surface of the through part  41   a  of the rotor  40 . Thus, in contrast with the partition member  50  entirely made of fluorine rubber, the partition member  70  has a sufficiently high slidability relative to the rotor  40  without having to interpose the sliding members  51   a ,  51   b.    
   Thus, the partition member  70  can be smoothly slid with respect to the rotor  40  as long as it is structured as described above, when compared with a case that it is constructed of only a material selected in terms of the degree of contact with respect to the case  31 . Thus, the reliability of the pump  30  can be improved. In addition, when compared with a case where the partition member is formed of only a material selected in terms of the slidability with respect to the rotor  40 , the partition member  70  can be brought in contact with the case  31 , thereby improving the pump performance. Furthermore, there is no need to interpose the sliding members  51   a ,  51   b . The dimensional accuracy of the core material  71  is higher than that of the partition member formed of a rubber-base material, so that a play between the rotor  40  and the partition member  70  can be minimized without detriment to the slidability, and that backlash of the partition member  70  can be controlled. These have also effects to stabilize the operation of the pump  30  and improve the reliability of the pump  30 . 
   A pump concerning the embodiment and modifications of the invention includes a case having a hollow inside defined by an inner wall surface and including a suction inlet through which ink is sucked in the hollow and an exhaust outlet through which ink is ejected from the hollow; a rotor that is rotatable in the hollow and having a through groove formed on the rotor in a direction across the rotor; and a partition that is rotatable with the rotor and slidably supported with respect to the rotor in a direction across the rotor such that edge portions of the partition is in constant contact with the inner wall surface defining the hollow. 
   According to this structure, when the rotor is rotated, sliding of the partition in the direction across the rotor and expansion and shrinkage of the partition in the direction across the rotor make the edge portions contact with the inner wall surface defining the hollow, thereby ink can be sucked through the suction inlet into the hollow, and the sucked ink can be ejected through the exhaust outlet from the hollow. Accordingly, the pump is simpler in structure and has less trouble when compared with the relevant prior art pump using two vanes urged by a spring instead of the partition. In addition, as the pump does not use a spring, the number of parts can be decreased and manufacturing costs can be reduced. 
   In the above pump, the rotor is rotatable and in constant or intermittent contact with the specified position of the inner wall surface defining the chamber. When the rotor is in contact with the specified position of the inner wall surface, the hollow is divided into the plurality of chambers each enclosed by the case, the rotor, and the partition, and the suction inlet and the exhaust outlet are present in the respective chambers. When ink is sucked in the hollow through the suction inlet and ejected from the hollow through the exhaust outlet, suction and ejection of ink is conducted efficiently thereby improving the pump performance. 
   According to the structure, when the rotor is in contact with the specified position of the inner wall surface, the suction inlet and the exhaust outlet are present in the different chambers respectively enclosed by the case, the rotor, and the partition member. Thus, when ink is sucked through the suction inlet inside the hollow and ejected through the exhaust outlet from the hollow, efficiency of suction and ejection of ink is improved thereby the performance of the pump is improved. 
   In the above pump, sliding members of which sliding friction coefficient between the sliding members and the partition is smaller than a sliding friction coefficient between the rotor and the partition, are disposed such as to place the partition therebetween. 
   According to the structure, the partition placed between the sliding members slides smoothly with the sliding members with respect to the rotor. When compared with the case where the sliding members are not disposed, the movement of the partition with respect to the rotor accompanied with the rotation of the rotor is smooth and the reliability of the pump is improved. 
   In the above pump, the length of the sliding members are shorter than that of the partition with respect to the direction across the rotor. According to the structure, as the partition protrudes from both ends of the sliding members, the partition  50 , which protrudes from the rotor is not curved excessively at both ends. Thus, the partition becomes easy to slide, thereby enabling stable sealability between the partition and the case as well as preventing the generation of an excessive rotational torque. 
   The above pump is structured such that, when the suction inlet and the exhaust outlet are on the same side with respect to the partition (in the same chamber in the hollow partitioned by the partition member), a fluid resistance between the suction inlet and the exhaust outlet is variable. According to the structure, a space in the ink tank and an ink passage in the inkjet head are communicated with each other in the pump with a low resistance. During printing, an adequate amount of ink is supplied from the ink tank via the pump in response to ejection of ink to the inkjet head. 
   On the other hand, by setting the fluid resistance in the chamber too high and rotating the rotor continuously, ink can be forcibly supplied from the ink tank to the inkjet head even when printing is not performed, and bubbles remaining in the inkjet head can be also purged with ink. Thus, with a simple way of making a fluid resistance variable, the inkjet head can cope with both printing and purging. 
   Contrasted with a case of using a flexible tube, the space in the ink tank and the ink passage in the inkjet head are connected in the pump without separation, thereby preventing trouble such as ink supply failure traceable to pump failure. In addition, as there is no need to provide a flexible tube in the pump, the impermeability for bubbles in the pump can be improved. 
   The pump may be structured such that the fluid resistance can be changed when the rotor is moved between the position making contact with the specified position on the inner wall surface and the position out of contact with the specified position on the inner wall surface, as shown in the second modification of the invention. According to the structure, when the rotor is in the position making contact with the specified position on the inner wall surface, the fluid resistance is always maintained high even when the rotor is rotated, and there is no reduction in the performance of the pump when purging is performed. 
   The pump may be structured such that the fluid resistance may be changed when a wall surface near the specified position on the inner wall surface is moved between the position making contact with the rotor and the position out of contact with the rotor, as shown in the third modification of the invention. According to the structure, when the wall surface near the specified position on the inner wall surface is in the position making contact with the rotor, the fluid resistance is always maintained high even when the rotor is rotated, and there is no reduction in the performance of the pump when purging is performed. 
   The pump may be structured such that the rotor may include a cut portion on the peripheral surface of the rotor and rotate in constant or intermittent contact with the specified position of the inner wall surface defining the chamber, as shown in the embodiment of the invention, and the fluid resistance may be changed in response to the position of the cut portion changing by rotation of the rotor, with respect to the suction inlet and the exhaust outlet. According to the structure, the pump can be manufactured simply by providing the cut portion on the peripheral surface of the rotor. 
   The pump may be structured such that the rotor may include a tunnel that connects two places on the peripheral surface of the rotor and rotate in constant or intermittent contact with the specified position of the inner wall surface defining the chamber, as shown in the fourth modification of the invention, and the fluid resistance may be changed in response to the position of the tunnel changing by rotation of the rotor, with respect to the suction inlet and the exhaust outlet. According to the structure, the pump can be easily manufactured only by providing the tunnel that connects the two places on the peripheral surface of the rotor. 
   According to an inkjet printer having the pump disclosed in the above embodiment and modifications, the pump is comparatively simple in structure, can be manufactured with less manufacturing costs by just that much, developing a smaller size of the pump is also easy, malfunction is unlikely to occur, and the pump performance is also excellent. Thus, these factors contributes to reduced manufacturing costs of the inkjet printer, enabling the pump to accommodate in a limited space inside the inkjet printer compactly, and preventing trouble such as ink supply failure. 
   In this inkjet printer, ink can be supplied from the ink tank to the inkjet head by pressure using the pump. When ink is initially supplied from the ink tank to the inkjet head, it can be filled in a passage from the ink tank to the inkjet head using the pump. When purging is performed to remove thickened ink remaining in the nozzles of the head, ink is forcibly sent to the head using the pump, so that the thickened ink is ejected from the nozzles of the head, thereby restoring the performance of the head. 
   Furthermore, in the inkjet printer, the rotor is structured such as to stop at a rotational position when the pump is not in operation and has a passage that provides communication between the suction inlet and the exhaust outlet at the stopped state. When ink is ejected from the head in the stopped state of the rotor, ink is supplied from the ink tank via the passage to the head. 
   According to the inkjet printer structured above, the rotor built in the pump is structured at the rotational position when the pump is not in operation, and the suction inlet and the exhaust outlet are in communication with each other via the passage. When ink is ejected from the head, ink is supplied from the ink tank to the head via the passage, and the pump never hinders the flow of ink. 
   That is, in this kind of the inkjet printer, when ink is ejected from the head, for example, to execute usual printing, ink is accordingly decreased from the ink passage in the head, the pressure of the ink passage in the head is lowered, a difference in pressure is generated between the ink tank side and the head side, and ink flows from the ink tank to the head. In this case, if the pump is structured to interrupt the flow of ink between the ink tank and the head, a bypass passage should be provided to detour the pump and to secure the passage form the ink tank to the head. 
   However, as the pump includes a rotor having a passage structured above, there is no need to provide a bypass passage, and the ink passage can be secured from the ink tank to the head. Thus, the structure of the ink passage is simplified by just that much, and this also contributes to reduced manufacturing costs and improved maintenance of the inkjet printer. 
   In the inkjet printer concerning the embodiment and modifications of the invention, a metal needle having a fluid passage inside is directly connected to the suction inlet and the tip of the needle is stuck in the ink tank. According to the structure, as the metal needle only is disposed between the ink tank and the pump, air bubbles are hardly trapped in ink between the ink tank and the pump. 
   In addition, the above inkjet printer includes an ink passage connecting the pump and the inkjet head. The ink passage is formed with a portion that is connected to the exhaust outlet and faces toward a vertical direction, and a filter is disposed in the portion such that a filter face is placed horizontally. 
   According to the structure, as the filter is disposed in the portion that is connected to the exhaust outlet and faces toward the vertical direction with its filter face positioned horizontally, bubbles trapped in ink when ink is initially let in the empty hollow of the pump, for example, are to easily pass through the filter, because a comparatively great force combining the buoyancy of the bubbles and the rotation force of the pump is applied to the bubbles in ink. Thus, ink supply to the inkjet head is less often interrupted due to stagnation of a large amount of bubbles at an upstream side of the filter. 
   In the above inkjet printer, the exhaust outlet is formed on an upper vertical side of the case. According to the structure, bubbles trapped in the hollow when ink is initially let in can be smoothly ejected without opposing the buoyancy, thereby obtaining a high ejection quality. 
   In the pump according to the embodiment and modifications of the invention, both ends, at least, of the partition make contact with the inner wall surface of the case, and flexibly deform to bend in a direction opposite to the rotational direction of the rotor. Thus, the partition is in intimate contact with the inner surface of the case. According to the structure, both ends, at least, of the partition member are fully in intimate contact with the inner wall surface of the case. Thus, this enhances the degree of contact (air tightness or fluid tightness) between the partition and the inner wall surface of the case and improves the pump performance, when compared with the prior art pump using the two vanes that make contact with the inner surface of the case without deformation. Furthermore, as the flexure of the partition increases, the partition slides less in the rotor compared with a non-flexible partition of the same length. Thus, the motion of the rotor becomes smooth 
   Further, in the pump, the partition is shaped thinner toward the edges. According to the structure, the partition is likely to deform toward the edges. Even when there are minute bumps and dips on the inner wall surface of the case, the partition is easy to deform to fit the bumps and dips at its edges, and the degree of contact (air tightness or fluid tightness) between the partition and the inner wall surface of the case becomes extremely high, when compared with a case without such tapered edges. In addition, differing from an entirely thin partition member, the partition does not bend excessively further beyond the edge portions. Thus, the partition does not bend excessively with the increase of the internal pressure. 
   In the pump, the partition has a first portion formed of a first material that allows the first portion to flexibly deform in contact with the case and a second portion formed of a second material that allows the second portion to deform less flexibly than the first portion, and a friction resistance between the first portion and the rotor is greater than a friction resistance between the second portion and the rotor. 
   In the pump thus structured, the first material is preferably a material excellent for contact mainly with the case, that is, a rubber-base material, such as fluorine rubber, ethylene-propylene-diene-terpolymer (EPDM)-base rubber, styrene butadiene rubber (SBR), nitrile-butadiene rubber (NBR), and chloroprene rubber (CR). Above all, fluorine rubber is preferable in its high slidability. The second material is preferably a material with low friction resistance and high wear resistance, for example, an engineering resin such as acetal polyoxymethylene (POM), poly-carbonate (PC) resin, polypropylene (PP) resin, and polyethylene (PE) resin. 
   For the first portion, a portion required for contact mainly with the case is selected. For the second portion, a portion required for small friction resistance mainly to the rotor is selected. For example, the partition member may be made up of a core member formed of the second material and a contact portion formed of the first portion, which is shaped like a frame around the core material, in order that the edges are formed of the first material and the front and back surfaces are formed of the second material. In this case, the partition member is preferably structured such that the front and back surfaces of the core member are thickened more than the contact portion, in order that the rotor can make contact with the front and back surfaces of the core member mainly, and the contact portion around the core member can make intimate contact with the inner wall surface of the case. Alternatively, the structure of the partition member may be that projections formed of the second material may protrude from the front and back surfaces formed of the first material. The first portion and the second portion can be designed in any form or any size as long as they can play their own roles. No matter how the partition member is shaped in a concrete manner, the partition member formed of two materials can improve both the degree of contact with the case and the slidability relative to the rotor, compared with formation of a single material. 
   According to the pump, the partition can be slid smoothly with respect to the rotor thereby improving the performance of the pump, compared with a case of forming the partition of a material selected in terms of the degree of contact with the case. 
   The first portion and the second portion can be molded separately and bonded later if the materials of the first portion and the second portion are a combination to provide high adhesion properties to each other. However, combinations of rigid cellular plastics and rubbers do not generally in most provide high adhesion. In this case, it is preferable that the first portion and the second portion are integrally formed by insert molding (sometimes called outsert molding) in such a manner that they never separate from each other although delamination only occurs at an interface therebetween.