Patent Publication Number: US-2023158526-A1

Title: Liquid dispenser with plunger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of PCT Application No. PCT/JP2021/026160, filed on Jul. 12, 2021, which claims the benefit of priority from Japanese Patent Application No. 2020-120737, filed on Jul. 14, 2020, and Japanese Patent Application No. 2020-120741, filed on Jul. 14, 2020. The entire contents of the above listed PCT and priority applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to a liquid dispenser. 
     Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2014-163372 discloses a liquid dispense valve that dispenses a predetermined amount of liquid from a tip nozzle by reciprocally driving a plunger from above with respect to the pressurized liquid introduced into a liquid reservoir and a plunger guide. The liquid dispense valve has a connection portion between the plunger and a sliding body of a plunger driver so that a sliding direction of the plunger is not affected even if a sliding direction of the plunger driver is deviated from a sliding direction of the plunger. 
     SUMMARY 
     Disclosed herein is A dispenser. The dispenser may include: a plunger comprising a distal end surface facing an advance direction of the plunger and a proximal end surface facing a retraction direction of the plunger; a dispensing portion configured to dispense and suction liquid in response to an advance and a retraction of the distal end surface along an axial line intersecting the distal end surface and the proximal end surface, wherein the dispensing portion comprises: a surrounding portion surrounding the distal end surface of the plunger about the axial line to define an accommodation chamber; and an end portion facing the distal end surface of the plunger along the axial line, wherein the end portion comprises an outlet opening into the accommodation chamber to dispense the liquid out of the accommodation chamber, wherein the surrounding portion comprises an inlet opening into the accommodation chamber to receive the liquid into the accommodation chamber, and wherein a distance from the inlet to the end portion is less than or equal to half of a maximum stroke of the distal end surface of the plunger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram illustrating an example configuration of a dispenser. 
         FIG.  2    is a perspective view illustrating an example pump unit. 
         FIG.  3    is a cross-sectional view taken along line III-III. 
         FIG.  4    is an enlarged view of the vicinity of an example dispensing portion in  FIG.  3   . 
         FIG.  5    is an enlarged view of the vicinity of an example piston in  FIG.  3   . 
         FIG.  6    is an enlarged view of the vicinity of an example advance regulation unit in  FIG.  3   . 
         FIG.  7    is an enlarged view of the vicinity of an example retract regulating unit in  FIG.  3   . 
         FIG.  8    is an enlarged view around an example block assistance unit in  FIG.  3   . 
         FIG.  9    is a schematic view illustrating an example configuration of a connecting portion of a surrounding portion, a cylinder, and an outer cap. 
         FIG.  10    is a schematic diagram illustrating an example configuration of a piston driver. 
         FIG.  11    is a schematic diagram illustrating an example hardware configuration of control circuitry. 
         FIG.  12    is a flowchart illustrating an example control procedure by the control circuitry. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. 
      Dispenser 
     A dispenser  1  shown in  FIG.  1    is a device for intermittently dispensing liquid. For example, the dispenser  1  is a jet-type dispenser that intermittently ejects droplets toward a remote application target. Examples of the dispensed liquid include adhesives, lubricants, solder pastes, fluxes, silver pastes, reagents, and the like. 
     The dispenser  1  has a pump unit  10 , a barrel  20 , and a controller  30 . The pump unit  10  reciprocates a plunger by pressurizing the plunger by gas (hereinafter referred to as “driving gas”). Thus, suction and dispense of the liquid are repeated. The pump unit  10  reciprocates the plunger by switching the supply direction of the driving gas with respect to the plunger by driving power. The barrel  20  pressurizes liquid by gas (hereinafter referred to as “pumping gas”) to supply the liquid to the pump unit  10 . The controller  30  supplies the driving gas and the driving power to the pump unit  10 , and supplies the pumping gas to the barrel  20 . Hereinafter, configurations of the pump unit  10 , the barrel  20 , and the controller  30  will be described in detail. 
     Pump Unit 
     As shown in  FIGS.  2  and  3   , the pump unit  10  has a plunger  100 , a guide block  200 , a dispensing portion  300 , a driver  400 , an advance restricting unit  700 , a retraction restricting unit  500 , and a blocking assistance unit  600 . 
     The plunger  100  is a rod-shaped member formed of a metallic material such as stainless steel, titanium alloy, or cemented carbide, and includes a distal end surface  101  and a proximal end surface  102 . Hereinafter, a direction in which the distal end surface  101  of the plunger  100  faces is referred to as a “advance direction”, and movement in the direction is referred to as “advance”. In addition, a direction in which the proximal end surface  102  of the plunger  100  faces is referred to as a “retraction direction”, and movement in the direction is referred to as a “retraction”. 
     The plunger  100  has a flange  130  on its outer periphery. The flange  130  has a front surface  131  and a rear surface  132 . The front surface  131  faces the advance direction and the rear surface  132  faces the retraction direction. The flange  130  is positioned closer to the proximal end surface  102  between the distal end surface  101  and the proximal end surface  102 . For example, the distance from the distal end surface  101  to the front surface  131  is longer than the distance from the proximal end surface  102  to the rear surface  132 . 
     The guide block  200  (guide portion) guides the plunger  100  to advance and retract along an axial line L1 (for example, a center axial line of the plunger  100 ) that intersects (for example, is orthogonal to) the distal end surface  101  and the proximal end surface  102 . The guide block  200  is a cylindrical block member formed of, for example, a fluororesin or an engineering plastic material, and includes a distal end surface  213  and a proximal end surface  214 . The distal end surface  213  faces the advance direction and the proximal end surface  214  faces the retraction direction. 
     The guide block  200  has a guide hole  215  that penetrates between the distal end surface  213  and the proximal end surface  214  along the axial line L1. In the guide hole  215 , the plunger  100  is inserted from the proximal end surface  214  toward the distal end surface  213 , a distal end portion (the distal end surface  101  and its vicinity) of the plunger  100  is located anterior to the distal end surface  213 , and the flange  130  of the plunger  100  is located behind the proximal end surface  214  along the axial line L1. By engagement with the guide hole  215 , the plunger  100  is guided to advance and retract along the axial line L1. 
     A distal end fitting portion  211  is formed on an outer peripheral surface of a distal end portion (the distal end surface  213  and its vicinity) of the guide block  200 . A proximal end fitting portion  212  is formed on the outer peripheral surface of a proximal end portion (the proximal end surface  214  and its vicinity) of the guide block  200 . 
     The dispensing portion  300  accommodates the distal end portion (the distal end surface  101  and its vicinity) of the plunger  100  and dispenses and suctions liquid in response to advance and retraction of the distal end surface  101 . As shown enlarged in  FIG.  4   , for example, the dispensing portion  300  has a surrounding portion  310 , a nozzle unit  340 , a nozzle seal  351 , a nozzle holder  360 , a plunger seal  352 , and a barrel attachment portion  380 . 
     The surrounding portion  310  surrounds the distal end surface  101  around the axial line L1 to define an accommodation chamber  319 . The surrounding portion  310  is a block material formed of a metallic material such as stainless steel or an aluminum alloy, and contains a distal end surface  311  and a proximal end surface  312 . The distal end surface  311  faces the advance direction and the proximal end surface  312  faces the retraction direction. 
     A circular recess  313  centered on the axial line L1 is formed on the distal end surface  311 , and a circular recess  314  centered on the axial line L1 is further formed on the bottom surface of the recess  313 . A circular recess  316  centered on the axial line L1 is formed on the proximal end surface  312 , and a circular recess  317  centered on the axial line L1 is further formed on the bottom surface of the recess  316 . The surrounding portion  310  further includes a circular through-hole  321  extending along the axial line L1 between a bottom surface  315  of the recess  314  and a bottom surface  318  of the recess  317 . The through-hole  321  forms the accommodation chamber  319  and accommodates the distal end portion of the plunger  100 . 
     The surrounding portion  310  further includes an inlet  323 , a suction port  324 , and an inlet flow channel  325 . The inlet  323  opens into the accommodation chamber  319  and receives the liquid into the accommodation chamber  319 . For example, the inlet  323  opens onto the inner peripheral surface of the through-hole  321 . The suction port  324  opens onto the outer peripheral surface of the surrounding portion  310 . 
     The inlet flow channel  325  is formed within the surrounding portion  310  to provide communication between the suction port  324  and the inlet  323 . For example, the inlet flow channel  325  is formed by a circular through-hole penetrating between an outer peripheral surface of the surrounding portion  310  and an inner peripheral surface of the through-hole  321 , wherein the opening of the inlet flow channel  325  in the inner peripheral surface of the through-hole  321   forms the inlet  323  and the opening of the inlet flow channel  325  in the outer peripheral surface of the surrounding portion  310  forms the suction port  324 . The inlet flow channel  325  is inclined with respect to a plane vertical to the axial line L1 so that a portion of the inlet flow channel  325  moves away from the distal end surface  311  as the portion moves away from the axial line L1. Therefore, the inlet  323  and the suction port  324  have an elliptical shape extending along the axial line L1. 
     A holder attachment portion  331  is formed on the outer peripheral surface of a distal end portion of the surrounding portion  310  (the distal end surface  311  and its vicinity). The outer periphery of the holder attachment portion  331  is positioned inward from the outer peripheral surface of the surrounding portion  310  on which the suction port  324  is formed. As described above, the inlet flow channel  325  is inclined so that a portion of the inlet flow channel  325  moves away from the distal end surface  311  as the portion moves away from the axial line L1, thereby avoiding interference between the outer peripheral surface of the holder attachment portion  331  and the inlet flow channel  325 . 
     The nozzle unit  340  faces the distal end surface  101  of the plunger  100  along the axial line L1. The nozzle unit  340  includes an outlet  343 , a dispense port  344 , and a dispense flow channel  345 . The outlet  343  opens into the accommodation chamber  319  and leads the liquid out of the accommodation chamber  319 . The dispense port  344  opens to an outside of the accommodation chamber  319 . The dispense flow channel  345  connects the outlet  343  and the dispense port  344  without passing through the check valve. 
     For example, the nozzle unit  340  has a nozzle base  341  and a nozzle  342 . The nozzle base  341  is a disk-shaped portion formed of, for example, a fluororesin or an engineering plastic material, and is fitted into the recess  314 . The nozzle base  341  includes a through-hole  346  along the axial line L1. The nozzle  342  is a narrow tube formed of, for example, stainless steel or an aluminum alloy, and is fixed to the nozzle base  341  in a state of being passed through the through-hole  346 . The lumen of the nozzle  342  forms the dispense flow channel  345 , the opening of the nozzle  342  to the retraction direction forms the outlet  343 , and the opening of the nozzle  342  to the advance direction forms the dispense port  344 . 
     The nozzle seal  351  provides a seal between the nozzle unit  340  and the surrounding portion  310 . For example, the nozzle seal  351  is an annular seal member (e.g., an O-ring) formed of a rubber material or the like, and is accommodated in the recess  313  in a state of surrounding the nozzle base  341 . 
     The nozzle holder  360  holds the nozzle unit  340  and is attached to the surrounding portion  310 . For example, the nozzle holder  360  is a member formed of a metallic material such as stainless steel or an aluminum alloy, and includes a cover plate  361  and a peripheral wall  363 . The cover plate  361  covers the distal end surface  311  of the surrounding portion  310 . An opening  362  is formed in the central part of the cover plate  361 . The cover plate  361  holds the nozzle base  341  and the nozzle seal  351  from the advance direction with the nozzle  342  passed through the opening  362 . The peripheral wall  363  rises toward the retraction direction from the periphery of the cover plate  361  and surrounds the holder attachment portion  331 . 
     The peripheral wall  363  is attached to the holder attachment portion  331 . For example, a male screw  332  is formed on an outer periphery of the holder attachment portion  331 , a female screw  364  corresponding to the male screw  332  is formed on an inner periphery of the peripheral wall  363 , and the peripheral wall  363  is attached to the holder attachment portion  331  by screwing the male screw  332  into the female screw  364 . By screwing the male screw  332  into the female screw  364 , the cover plate  361  approaches the distal end surface  311  and presses the nozzle base  341  and the nozzle seal  351  toward the retraction direction. As the cover plate  361  approaches the distal end surface  311 , the nozzle seal  351  is pressed, thereby strengthening the seal between the nozzle unit  340  and the surrounding portion  310 . Further, the nozzle seal  351  suppresses the deviation between the center of the surrounding portion  310  and the center of the nozzle unit  340 . 
     The plunger seal  352  faces the nozzle unit  340  across the accommodation chamber  319  and provides a seal between the surrounding portion  310  and the plunger  100 . For example, the plunger seal  352  is an annular seal member formed of a plastic material or the like, and is accommodated in the recess  317  in a state of surrounding the distal end portion of the plunger  100 . 
     The guide block  200  is accommodated in the recess  316  of the surrounding portion  310 . The distal end fitting portion  211  of the guide block  200  is inserted into the recess  317  and sandwiches the plunger seal  352  with the bottom surface  318  of the recess  317 . This keeps the plunger seal  352  in the recess  317 . 
     The barrel attachment portion  380  connects the suction port  324  of the surrounding portion  310  and the barrel  20 . For example, the barrel attachment portion  380  has a support arm  381  and an attachment mouthpiece  382  (see  FIG.  3   ). The support arm  381  protrudes outward (toward a direction away from the axial line L1) from a portion of the outer periphery of the surrounding portion  310  where the suction port  324  is formed. The attachment mouthpiece  382  protrudes from the end portion of the suction port  324  toward the retraction direction and receives the liquid delivered from the barrel  20 . A relay flow channel  383  is formed in the support arm  381  to communicate the attachment mouthpiece  382  with the suction port  324 . 
     In the dispensing portion  300  constructed in this manner, the plunger seal  352  provides a seal between the surrounding portion  310  and the plunger  100  to substantially seal the accommodation chamber  319  except for the inlet  323  and the outlet  343 . Therefore, a volume of the accommodation chamber  319  is changed by the advance and retraction of the distal end surface  101  of the plunger  100 . 
     In response to the advance of the distal end surface  101 , the volume of the accommodation chamber  319  decreases, and the internal pressure of the accommodation chamber  319  increases accordingly. This pressurizes liquid toward both the inlet  323  and the outlet  343 , but since the inlet  323  is pressurized by the barrel  20 , the liquid flows out of the outlet  343  and is dispensed from the dispense port  344 . In response to the retraction of the distal end surface  101 , the volume of the accommodation chamber  319  increases, and the internal pressure of the accommodation chamber  319  decreases accordingly. As a result, liquid flows in from the inlet  323 . 
     The behavior of the liquid in the dispense flow channel  345  is based on a relationship between the decompression caused by the retraction of the distal end surface  101  and the pressurization caused by the barrel  20  (hereinafter referred to as “pressurization relationship”). For example, if the pressurization relationship is adjusted such that a pressure inside the accommodation chamber  319  is less than or equal to a pressure outside the accommodation chamber  319  (for example, atmospheric pressure) during at least a part of a period during the retraction of the plunger  100  (hereinafter referred to as a “retraction period”), the dispense of liquid from the dispense port  344  ceases during at least a part of the retraction period. 
     Here, the inlet  323  may be positioned closer to the nozzle unit  340  between the plunger seal  352  and the nozzle unit  340 . The distance from the inlet  323  to the nozzle unit  340  (a distance D1 in  FIG.  4   ) may be less than or equal to half of a maximum stroke H1 of the distal end surface  101  of the plunger  100 . The maximum stroke H1 is a distance from the most retracted position of the end surface  101  to the most advanced position of the distal end surface  101 . 
     More than half of the maximum stroke H1 may overlap the inlet  323 . For example, an opening height H2 of the inlet  323  in the direction along the axial line L1 may be half or more of the maximum stroke H1, and the most retracted position of the distal end surface  101  may be located behind the inlet  323 , and the most advanced position of the distal end surface  101  may be located anterior to the inlet  323  along the axial line L1. The inlet  323  can be opened at the beginning of the retraction period, so that liquid is suctioned quickly into the accommodation chamber  319 . Also, in most of the retraction period, the opening of the inlet  323  becomes larger as the distal end surface  101  retracts, so that the liquid is suctioned more quickly. Further, since the opening of the inlet  323  becomes smaller as the distal end surface  101  advances in most of a period of the advance of the distal end surface  101 , a pressure into the inlet  323  can be suppressed and the liquid can be rapidly dispensed from the outlet  343 . 
     The driver  400  causes the driving gas to advance and retract the proximal end portion of the plunger  100 . As shown enlarged in  FIG.  5   , for example, the driver  400  has a cylinder  410 , a piston  450 , an outer seal  471 , an inner seal  472 , and a piston driver  480 . 
     The cylinder  410  accommodates the proximal end portion of the plunger  100 . The cylinder  410  is a cylindrical member formed of a metallic material such as stainless steel or an aluminum alloy, and includes a distal end surface  411  and a proximal end surface  412  (see  FIG.  3   ). The distal end surface  411  faces the advance direction and the proximal end surface  412  faces the retraction direction. The cylinder  410  has a second pressurizing hole  432  and a first pressurizing hole  431  arranged in order from the advance direction to the retraction direction. Each of the second pressurizing hole  432  and the first pressurizing hole  431  penetrates between an inner peripheral surface and an outer peripheral surface of the cylinder  410 . 
     With the cylinder  410  accommodating the proximal end portion of the plunger  100 , the distal end portion (the distal end surface  411  and its vicinity) of the cylinder  410  is connected to the dispensing portion  300 . For example, the distal end portion of the cylinder  410  fits to the proximal end fitting portion  212  of the guide block  200  and is connected to the surrounding portion  310  around the recess  316 . 
     The piston  450  is provided to the cylinder  410  to partition the cylinder  410  along the axial line L1 into a first space  413  and a second space  414 . The first space  413  is a space located behind the piston  450  along the axial line L1, and the second space  414  is a space located anterior to the piston  450  along the axial line L1. The piston  450  causes the plunger  100  to advance in response to the first space  413  pressurized and the plunger  100  to retract in response to the second space  414  pressurized. 
     The piston  450  is annular and may partition the cylinder  410  into the first space  413  and the second space  414  between the outer peripheral surface of the plunger  100  and the inner peripheral surface of the cylinder  410 . For example, the piston  450  is an annular plate member formed of a metallic material such as stainless steel or an aluminum alloy, and includes a distal end surface  452 , a proximal end surface  453 , and a through-hole  454 . The distal end surface  452  faces the advance direction and the proximal end surface  453  faces the retraction direction. The through-hole  454  penetrates along the axial line L1 between the distal end surface  452  and the proximal end surface  453 . An inner radius of the through-hole  454  is greater than an outer radius of the proximal end portion of the plunger  100 . On an outer peripheral surface  451  of the piston  450 , a groove  455  is formed over the entire circumference around the axial line L1. A recess  456  centered on the axial line L1 is formed in the distal end surface  452 . 
     The piston  450  is attached to the proximal end portion of the plunger  100  so that the piston  450  can float (move) in a direction vertical to the axial line L1. For example, the driver  400  further comprises a holder  461 . The holder  461  holds the piston  450  around the proximal end portion of the plunger  100  while allowing the piston  450  to float in the direction vertical to the axial line L1. For example, the holder  461  sandwiches the piston  450  with the flange  130  with the proximal end portion of the plunger  100  passed through the through-hole  454 . 
     For example, a holding groove  121  is formed on the outer peripheral surface of the proximal end portion of the plunger  100  over an entire circumference around the axial line L1. With the piston  450  in contact with the rear surface  132  of the flange  130 , the holding groove  121  is located behind the piston  450  along the axial line L1. The holder  461  is, for example, a C-shaped snap ring, which is fitted into the holding groove  121  that is located behind the piston  450   along the axial line L1. Thus, the piston  450  is sandwiched between the flange  130  and the holder  461 . As described above, the inner radius of the through-hole  454  is greater than the outer radius of the proximal end portion of the plunger  100 . The piston  450  is allowed to float in the direction vertical to the axial line L1 by the difference between the inner radius of the through-hole  454  and the outer radius of the proximal end portion of the plunger  100 . 
     The outer seal  471  seals between the piston  450  and the cylinder  410 . For example, the outer seal  471  is an annular seal member (e.g., an O-ring) formed of a rubber material or the like, and is accommodated in the groove  455 . The outer seal  471  seals between the piston  450  and the cylinder  410  by contacting the bottom surface of the groove  455  and the inner peripheral surface of the cylinder  410 . 
     The inner seal  472  (seal portion) seals between the piston  450  and the plunger  100  while allowing the piston  450  to float in the direction vertical to the axial line L1. For example, the inner seal  472  is an annular seal member (for example, an O-ring) formed of a rubber material or the like, and is accommodated in the recess  456  in a state of surrounding the plunger  100 . The inner seal  472  seals between the piston  450  and the plunger  100  by contacting a bottom surface  457  (annular first seal surface) of the recess and the rear surface  132  (annular second seal surface facing the first seal surface) of the flange  130 . 
     Since the bottom surface  457  and the rear surface  132  intersect (for example, are orthogonal to) the axial line L1, even if the piston  450  floats in a vertical direction in the axial line L1, the inner seal  472  is kept in contact with the bottom surface  457  and the rear surface  132 . Therefore, both the float property of the piston  450  and the seal property between the piston  450  and the plunger  100  can be achieved. 
     The piston driver  480  switches between a first state in which a pressure from a pressurizing source (a pressure of the above mentioned driving gas) is applied to the first space  413  and a second state in which the pressure from the pressurizing source is applied to the second space  414  in accordance with the supply of the driving power. For example, the piston driver  480  may pressurize the first space  413  when there is no supply of the driving power and pressurize the second space  414  when there is the supply of the driving power. An example structure of the piston driver  480  will be described later. 
     The advance restricting unit  700  regulates an advance of the plunger  100 . For example, the advance restricting unit  700  is provided between the guide block  200  and the flange  130 , and regulates an advance of the flange  130 . For example, the advance restricting unit  700  may be placed in the second space  414  to provide a seal between the inner peripheral surface of the cylinder  410  and the outer peripheral surface of the plunger  100  while restricting the advance of the flange  130 . As shown enlarged in  FIG.  6   , by way of example, the advance restricting unit  700  has an advance restricting block  710 , outer seals  721 ,  722 , and inner seals  731 ,  732 . 
     The advance restricting block  710  (advance regulating portion) is a cylindrical block member formed of a metallic material such as stainless steel or an aluminum alloy, and includes a distal end surface  711  and a proximal end surface  712 . The distal end surface  711  faces the advance direction and the proximal end surface  712  faces the retraction direction. The advance restricting block  710  has a guide hole  713  that penetrates between the distal end surface  711  and the proximal end surface  712  along the axial line L1. The plunger  100  is inserted into the guide hole  713  from the proximal end surface  712  toward the distal end surface  711 . The proximal end surface  712  of the advance restricting block  710  faces the front surface  131  of the flange  130  to regulate the advance of the flange  130 . 
     A groove  714  is formed on an outer peripheral surface of a distal end portion (the distal end surface  711  and its vicinity) of the advance restricting block  710  over an entire circumference around the axial line L1. A groove  715  is formed on an outer peripheral surface of a proximal end portion (the proximal end surface  712  and its vicinity) of the advance restricting block  710  over an entire circumference around the axial line L1. Grooves  716 , 717  arranged along the axial line L1 are formed on an inner peripheral surface of the guide hole  713 . Each of the grooves  716   717  extends around an entire circumference of the axial line L1. 
     Each of the outer seals  721 , 722  is an annular seal member (for example, an O-ring) formed of a rubber material or the like and seals between the advance restricting block  710  and the cylinder  410 . For example, an outer seal  721  may be accommodated in the groove  714  in a state of surrounding the advance restricting block  710 , and may be in contact with a bottom surface of the groove  714  and the inner peripheral surface of the cylinder  410  to seal between the advance restricting block  710  and the cylinder  410 . An outer seal  722  may be accommodated in the groove  715  in a state of surrounding the advance restricting block  710 , and may be in contact with the bottom surface of the groove  715  and the inner peripheral surface of the cylinder  410  to seal between the advance restricting block  710  and the cylinder  410 . 
     Each of the inner seals  731   732  is an annular seal member (for example, an O-ring) formed of a rubber material or the like, and seals between the advance restricting block  710  and the plunger  100 . For example, an inner seal  731  may be accommodated in the groove  716  in a state of surrounding the plunger  100 , and may be in contact with the bottom surface of the groove  716  and the outer peripheral surface of the plunger  100  to seal between the advance restricting block  710  and the plunger  100 . An inner seal  732  may be accommodated in the groove  717  in a state of surrounding the plunger  100 , and may be in contact with the bottom surface of the groove  717  and the outer peripheral surface of the plunger  100  to seal between the advance restricting block  710  and the plunger  100 . 
     The pump unit  10  further comprises an advance limit adjuster  420 . The advance limit adjuster  420  adjusts the position of the advance restricting unit  700  relative to the cylinder  410  in a direction along the axial line L1. For example, the advance limit adjuster  420  has a male screw  718 , a female screw  421 , and an adjustment window  422 . The male screw  718  is formed around the outer peripheral surface of the advance restricting block  710  between the groove  714  and the groove  715 . The female screw  421  is formed on a portion of the inner peripheral surface of the cylinder  410  corresponding to the male screw  718 . The advance restricting unit  700  is placed in the cylinder  410  with the male screw  718  screwed into the female screw  421 . 
     The adjustment window  422  (see  FIG.  2   ) penetrates between the inner peripheral surface and the outer peripheral surface of the cylinder  410  at a position located anterior to the groove  714  along the axial line L1. The adjustment window  422  exposes a portion of the outer peripheral surface of the advance restricting block  710  to the exterior of the cylinder  410 . Thus, an operation force around the axial line L1 can be applied to the outer peripheral surface of the advance restricting block  710  from the outside of the cylinder  410 , and the advance restricting block  710  can be rotated around the axial line L1. 
     Rotating the advance restricting block  710  rotates the male screw  718  relative to the female screw  421  and displaces the advance restricting block  710  along the axial line L1. This adjusts the position of the advance restricting unit  700  relative to the cylinder  410 . The above-described maximum stroke H1 is a stroke in a state in which the advance restricting unit  700  is located at the most advanced position along the axial line L1. 
     The retraction restricting unit  500  regulates the retraction of the plunger  100 . For example, the retraction restricting unit  500  is connected to the proximal end portion of the cylinder  410  and regulates the retraction of the proximal end surface  102  of the plunger  100 . As shown enlarged in  FIG.  7   , for example, the retraction restricting unit  500  has an outer cap  510 , a regulating rod  520 , a retraction limit adjustment portion  530 , an inner cap  540 , an outer seal  551 , and an inner seal  552 . 
     The outer cap  510  is a plate-shaped member formed of a metallic material such as stainless steel or an aluminum alloy, and closes the proximal end portion of the cylinder  410 . The outer cap  510  has an opening  511  in its center. 
     The regulating rod  520  is a rod-shaped member formed of a metallic material such as stainless steel or an aluminum alloy, and is inserted into the opening  511  along the axial line L1. The regulating rod  520  has a distal end surface  521  and a proximal end surface  522 . The distal end surface  521  faces the advance direction and the proximal end surface  522  faces the retraction direction. The distal end surface  521  (retraction restricting portion) faces the proximal end surface  102  of the plunger  100  in the cylinder  410  and restricts the retraction of the plunger  100 . The proximal end surface  522  is positioned outside the cylinder  410 . 
     The retraction limit adjustment portion  530  accommodates the regulating rod  520  outside the cylinder  410 . The retraction limit adjustment portion  530  has a handle  531  and causes the regulating rod  520  to advance and retract in response to the rotation of the handle  531  about the axial line L1. This adjusts the position of the distal end surface  521  in a direction along the axial line L1. The above-described maximum stroke H1 is a stroke in a state in which the distal end surface  521  is located at the most retracted position along the axial line L1. 
     The inner cap  540 , the outer seal  551  and the inner seal  552  provide a seal between the cylinder  410  and the regulating rod  520  in the cylinder  410 . For example, the inner cap  540  has a through-hole  542  in its center. The inner cap  540  is placed in the cylinder  410  and secured to the outer cap  510  with the regulating rod  520  passed through the through-hole  542 . 
     The outer seal  551  seals between the inner cap  540  and the cylinder  410  by contacting the outer peripheral surface of the inner cap  540  and the inner peripheral surface of the cylinder  410 . A flange  543  is formed on an outer peripheral surface of the inner cap  540  and the outer seal  551  is held between the flange  543  and the outer cap  510 . 
     The inner seal  552  seals between the inner cap  540  and the regulating rod  520  by contacting an inner peripheral surface of the through-hole  542  and an outer peripheral surface of the regulating rod  520 . An inward flange  544  is formed on the inner peripheral surface of the through-hole  542  and the inner seal  552  is held between the inward flange  544  and the outer cap  510 . 
     When the pressurizing source is not supplied to the piston driver  480 , the blocking assistance unit  600  applies a repulsive force to the piston  450  toward the advance direction to keep the plunger  100  at the most advanced position (the position in which the front surface  131  is in contact with the advance restricting block  710 ). This keeps the distal end surface  101  of the plunger  100  in close proximity to the nozzle unit  340 , thereby keeping the outlet  343  substantially blocked and preventing leakage of liquid from the outlet  343 . 
     For example, the blocking assistance unit  600  has a spring  620  and a pusher  630 . For example, the spring  620  applies a repulsive force to the plunger  100  toward the advance direction. For example, the spring  620  is a coil spring that surrounds the regulating rod  520  and generates a repulsive force against compression along the axial line L1 direction. The pusher  630  intervenes between the spring  620  and the piston  450  and transmits the repulsive forces generated by the spring  620  to the piston  450 . In this configuration, the spring  620  applies the repulsive force to the piston  450  between the outer peripheral surface of the plunger  100  and the inner peripheral surface of the cylinder  410  via the pusher  630 . 
     As shown enlarged in  FIG.  8   , the pusher  630  is a cylindrical block member formed of a metallic material such as stainless steel or aluminum alloy, and is disposed in the cylinder  410  along the axial line L1. The pusher  630  has a distal end surface  641  and a proximal end surface  642 . The distal end surface  641  faces the advance direction and the proximal end surface  642  faces the retraction direction. A recess  634  centered on the axial line L1 is formed in the proximal end surface  642 . The spring  620  is accommodated in the recess  634 . The spring  620  exerts a repulsive force on the bottom surface of the recess  634 . 
     A recess  635  centered on the axial line L1 is formed in the distal end surface  641 , and a recess  636  centered on the axial line L1 is further formed in the bottom surface of the recess  635 . An opening  637  centered on the axial line L1 is formed between the bottom surface of the recess  636  and the bottom surface of the recess  634 , and the regulating rod  520  is passed through the opening  637 . A plurality of vent holes  638  are formed between the bottom surface of the recess  635  and the bottom surface of the recess  634 . Thus, the space in which the piston  450  is disposed and the space in which the spring  620  is disposed communicate with each other. When the pusher  630  contacts the piston  450 , the recess  635  receives the holder  461  and the recess  636  receives the proximal end portion of the plunger  100 . 
     The pump unit  10  further comprises a release portion  440 . The release portion  440  releases the application of a repulsive force to the piston  450  by the spring  620  by the pressure of the pressurizing source (for example, the pressure of the driving gas). Therefore, when the pressure of the pressurizing source is supplied, the repulsive force of the spring  620  does not act as resistance against the sliding of the piston  450 , and the piston  450  can slide at high speed. For example, the release portion  440  forms a third space, between the pusher  630  and the cylinder  410 , to which the pressure of the pressurizing source is applied in both the first state and the second state, and releases the application of the repulsive force by the spring  620  by pressurizing of the third space. As an example, the release portion  440  has switching seals  651 ,  652 , and a third pressurizing hole  443 . 
     In the cylinder  410 , an inner diameter of a portion that accommodates a distal end portion (the distal end surface  641  and its vicinity) of the pusher  630  (hereinafter referred to as “a first accommodation portion  441 ”), and an inner diameter of a portion that accommodates a proximal end portion (the proximal end surface  642  and its vicinity) of the pusher  630  (hereinafter referred to as “a second accommodation portion  442 ”) are different with each other. In particular, the inner diameter of the second accommodation portion  442  is greater than the inner diameter of the first accommodation portion  441 . On the inner peripheral surface of the first accommodation portion  441 , a groove  444  is formed over an entire circumference around an axial line L1. A flange  631  is formed on the outer peripheral surface of the proximal end portion of a pusher  630 . On the outer peripheral surface of the flange  631 , a groove  633  is formed over an entire circumference around the axial line L1. 
     A switching seal  651  provides a seal between the pusher  630  and the first accommodation portion  441 . For example, the switching seal  651  may be an annular seal member (e.g., an O-ring) formed of a rubber material or the like and accommodated in the groove  444  surrounding the distal end portion of the pusher  630 . The switching seal  651  seals between the pusher  630  and the first accommodation portion  441  by contacting the bottom surface of the groove  444  and the outer peripheral surface of the pusher  630 . 
     A switching seal  652  provides a seal between the pusher  630  and the second accommodation portion  442 . For example, the switching seal  652  is an annular seal member (for example, an O-ring) formed of a rubber material or the like, and is accommodated in the groove  633  surrounding the flange  631  of the pusher  630 . The switching seal  652  seals between the pusher  630  and the second accommodation portion  442  by contacting the bottom surface of the groove  633  and the inner peripheral surface of the second accommodation portion  442 . The third pressurizing hole  443  penetrates between the inner peripheral surface and the outer peripheral surface of the cylinder  410  between the switching seal  651  and the switching seal  652 . The third pressurizing hole  443  is connected to the pressurizing source in both the first state and the second state. 
     With the above configuration, the third space  445  is formed between the switching seal  651  and the switching seal  652 , which is sealed except for the third pressurizing hole  443  and is connected to the pressurizing source in both of the first state and the second state. As the third pressurizing hole  443  is pressurized by the pressurizing source, the pusher  630  retracts with the switching seal  652  to correspondingly enlarge the third space  445 . This moves the pusher  630  away from a piston  450  and releases the application of the repulsive force by the spring  620  to the piston  450 . As described above, since the space in which the piston  450  is disposed and the space in which the spring  620  is disposed communicate with each other by the plurality of vent holes  638  formed in the pusher  630 , a difference in pressures between these two spaces is less likely to occur. Therefore, the pusher  630  smoothly rebounds in response to the pressurizing of the third space  445 . 
     The above-described plunger  100 , guide block  200 , dispensing portion  300 , driver  400 , advance restricting unit  700 , retraction restricting unit  500 , and blocking assistance unit  600  are integrated by connecting the surrounding portion  310 , the cylinder  410 , and the outer cap  510 . 
     As shown in  FIG.  9   , the surrounding portion  310 , the cylinder  410 , and the outer cap  510  may be connected by a plurality of through bolts  11  (fastening members) that are inserted into the outer cap  510  from the retraction direction toward the advance direction and reach the surrounding portion  310 . Since the removal of the through bolts  11  can be performed from the opposite side of the nozzle unit  340  dispensing the liquid, the maintenance workability is improved. 
     Here, the configuration of the above piston driver  480  will be described. As shown in  FIG.  10   , the piston driver  480  has a pressurizing port  481 , exhaust ports  482 ,  483 , a first flow channel  484 , a second flow channel  485 , a third flow channel  486 , a solenoid valve  487 , an elastic member  488 , and a solenoid  489 . 
     The pressurizing port  481  is a port for supplying the driving gas. Exhaust ports  482 ,483 are ports for exhausting gas in the cylinder  410 . The first flow channel  484  is a flow channel connected to the first pressurizing hole  431 , and the second flow channel  485  is a flow channel connected to the second pressurizing hole  432 . The third flow channel  486  is a flow channel connecting the pressurizing port  481  and the third pressurizing hole  443 . 
     The solenoid valve  487  moves between a first position and a second position. The solenoid valve  487  connects the first flow channel  484  and the pressurizing port  481 , and connects the second flow channel  485  and the exhaust port  482  in the first position. Hereinafter, this state is referred to as a first state. In the first state, the first space  413  is pressurized by the driving gas, gas of the second space  414  is exhausted from the exhaust port  482 , and the piston  450  advances. 
     The solenoid valve  487  connects the second flow channel  485  and the pressurizing port  481 , and connects the first flow channel  484  and the exhaust port  483  in the second position. Hereinafter, this state is referred to as a second state. In the second state, the second space  414  is pressurized by the driving gas, gas of the first space  413  is exhausted from the exhaust port  483 , and the piston  450  retracts. 
     The elastic member  488  applies an elastic repulsive force from the second position toward the first position to the solenoid valve  487 . The solenoid  489  applies a driving force from the first position toward the second position to the solenoid valve  487  by the supplied driving power. Therefore, in a state in which the driving power is not supplied to the solenoid  489 , the solenoid valve  487  is disposed at the first position by the elastic repulsive force of the elastic member  488 . In a state where the driving power is supplied to the solenoid  489 , the solenoid valve  487  is arranged at the second position by the driving force against the elastic repulsive force. 
     According to such a configuration, even in a case where the driving power is not supplied due to a failure of a controller  30  described later or the like, the plunger  100  is maintained in the most advanced state as long as the supply of the driving gas is continued. This prevents leakage of liquid since the outlet  343  is substantially blocked. 
     The third pressurizing hole  443  is directly connected to the pressurizing port  481  by the third flow channel  486 . Therefore, in both the first state and the second state, the third space  445  is pressurized by the driving gas. Therefore, as long as the driving gas is supplied to the pressurizing port  481 , the application of the repulsive force to the piston  450  by the spring  620  is released, and the piston  450  can readily be operated at high speed. 
     When the supply of the driving gas to the pressurizing port  481  is stopped due to a failure of the controller  30  or the like, since the driving gas is not supplied to the third space  445 , the application of the repulsive force to the piston  450  by the spring  620  is resumed and the plunger  100  is kept in the most advanced state. This prevents leakage of liquid since the outlet  343  is substantially blocked. 
     Barrel 
     The barrel  20  pumps liquid from outside the accommodation chamber  319  to the inlet  323 . As shown in  FIG.  1   , for example, the barrel  20  has a delivery port  21  and a pressurizing port  22 . The delivery port  21  is attached to the attachment mouthpiece  382  of the barrel attachment portion  380  and pumps liquid through the attachment mouthpiece  382  to the relay flow channel  383 . The pressurizing port  22  receives the pumping gas described above. The barrel  20  pressurizes the liquid with pumping gas coming from the pressurizing port  22  and pumps the liquid through the delivery port  21 , the attachment mouthpiece  382 , the relay flow channel  383 , the suction port  324 , and the inlet flow channel  325  into the inlet  323 . 
     Control Device 
     As shown in  FIG.  10   , the controller  30  has air circuitry  40  and control circuitry  50 . The air circuitry  40  supplies the driving gas to the pump unit  10  and the pumping gas to the barrel  20 . For example, the air circuitry  40  is connected to a gas source via an input hose  73 , to the pressurizing port  481  in the pump unit  10  via an output hose  71 , and to the pressurizing port  22  of the barrel  20  via an output hose  72 . 
     The air circuitry  40  outputs a portion of gas (hereinafter referred to as “input gas”) that flows in from the input hose  73 , and output remaining portion of the input gas to the output hose  72  as the pumping gas. The air circuitry  40  has a regulator  41 , an electropneumatic regulator  42 , a valve  43 , and pressure sensors  44 ,  45 , 46 . 
     The regulator  41  reduces pressure of the input gas to a supply pressure of the driving gas and outputs it to the output hose  71  and the electropneumatic regulator  42 . The electropneumatic regulator  42  further reduces the pressure reduced by the regulator  41  to a supply pressure of the pumping gas and outputs it to the output hose  72 . 
     The electropneumatic regulator  42  changes the supply pressure of the pumping gas according to a control command. The valve  43  is, for example, a solenoid valve, and opens and closes a flow path between the electropneumatic regulator  42  and the output hose  72  according to a control command. 
     The pressure sensor  44  detects the pressure of the input gas prior to passing through the electropneumatic regulator  42 . The pressure sensor  45  detects the pressure of the driving gas between the electropneumatic regulator  42  and the output hose  71 . The pressure sensor  46  detects the pressure of the pumping gas between the electropneumatic regulator  42  and the valve  43 . 
     The control circuitry  50  controls the air circuitry  40 . The control circuitry  50  is also connected to the piston driver  480  via a cable  74  and controls the piston driver  480 . For example, the control circuitry  50  has a pressure monitoring unit  51 , a barrel pressure control unit  52 , and a dispense control unit  53  as a functional elements(hereinafter referred to as a “functional block”). 
     The pressure monitoring unit  51  adjusts the pressures applied by the barrel  20  to the liquid. For example, the pressure monitoring unit  51  switches between supplying and stopping the pumping gas by opening and closing the valve  43 . The barrel pressure control unit  52  controls the electropneumatic regulator  42  to cause the supply pressure of the pumping gas to follow a target pressure. The target pressure is determined based on, for example, a setting input of a user. The setting input is acquired by an input device  66  that is described later. The dispense control unit  53  supplies the driving power to the piston driver  480  so as to repeat switching between the first state and the second state at a predetermined cycle at a predetermined period. For example, the dispense control unit  53  supplies the driving power to the piston driver  480  according to a dispense command from a host controller  80 . The dispense command includes, for example, the predetermined cycle and the predetermined period. 
       FIG.  11    is a block diagram illustrating the hardware configuration of the control circuitry  50 . As shown in  FIG.  11   , the control circuitry  50  includes a processor  61 , a memory  62 , a storage  63 , an input / output port  64 , a display device  65 , the input device  66 , and a communication port  67 . Although one processor  61  is shown in the figure, the control circuitry  50  may have a plurality of processors  61 . The control circuitry  50  may have the memory  62  and the storage  63  for each the processor  61 . 
     The storage  63  may include one or more storage devices each of which include one or more non-transitory and computer-readable storage mediums, such as a nonvolatile semiconductor memory. The storage  63  stores a program for causing the control circuitry  50  to configure the functional blocks described above. The memory  62  may include one or more memory devises each of which temporarily stores the program loaded from the storage medium of the storage  63  and the calculation result by the processor  61 . The one or more memory devices are, for example, a random access memory. The processor  61  may include one or more processing devices and configures the functional blocks of the control circuitry  50  by executing the program in cooperation with the memory  62 . The input / output port  64  inputs and outputs electrical signals to and from the valve  43 , pressure sensors  44 ,  45 ,  46  and the solenoid valve  487  in accordance with instructions from the processor  61 . The display device  65  includes, for example, a liquid crystal panel or an organic EL panel, and displays an interface image in accordance with instructions from the processor  61 . The input device  66  includes, for example, an input key and acquires an input (key input) to the input key. The display device  65  and the input device  66  may be integrated as a touch panel  33  (see  FIG.  1   ). The communication port  67  performs information communication with the host controller  80  in accordance with instructions from the processor. 
     The control circuitry  50  may not be limited to one in which each function is configured by a program. For example, at least a part of the functions of the control circuitry  50  may be configured by a dedicated logic circuit or an application specific integrated circuit (ASIC) in which the dedicated logic circuit is integrated. 
     Control Procedure 
     Hereinafter, a control procedure by the control circuitry  50  will be described. As shown in  FIG.  12   , the control circuitry  50  first executes operations S 01  and S 02 . In the operation S 01 , the pressure monitoring unit  51  acquires the detection results of the pressures by the pressure sensors  44 ,  45 ,  46 . In the operation S 02 , the pressure monitoring unit  51  checks whether the pressures detected by the pressure sensors  44 ,  45 ,  46  are within a normal range. 
     When it is determined that at least one of the detection results of the pressures in the operation S 02  is not within the normal range, the control circuitry  50  performs a operation S 21 . In the operation S 21 , the pressure monitoring unit  51  notifies the host controller  80  of the error. The control circuitry  50  then terminates the control procedure. 
     When it is determined that the detection results of the pressures in the operation S 02  is within the normal range, the control circuitry  50  executes operations S 03 , S 04 . In the operation S 03 , the barrel pressure control unit  52  opens the valve  43  to start the supply of pumping gas to the barrel  20 . In the operation S 04 , the dispense control unit  53  checks whether or not there is a dispense command from the host controller  80  or the like. 
     When it is determined that there is the dispense command in the operation S 04 , the control circuitry  50  executes a operation S 05 . In the operation S 05 , the dispense control unit  53  supplies the driving power to the piston driver  480  so as to repeat dispense and suction of the liquid according to the dispense command. 
     Next, the control circuitry  50  performs operations S 06 , S 07 . If it is determined that there is no dispense command in the operation S 04 , the control circuitry  50  executes the operations S 06 , S 07  without executing the operation S 05 . In the operation S06, the pressure monitoring unit  51  acquires the detection results of the pressures by the pressure sensors  44 ,  45 ,  46 . In the operation S 07 , the pressure monitoring unit  51  checks whether the pressures detected by the pressure sensors  44 ,  45 ,  46  are within the normal range. 
     When it is determined that the detection results of the pressures in the operation S 07  is within the normal range, the control circuitry  50  performs a operation S 08 . In the operation S 08 , the barrel pressure control unit  52  checks whether a control stop command is received from the host controller  80 . 
     When it is determined that the control stop command is not received in the operation S 08 , the control circuitry  50  returns the processing to the operation S 04 . Thereafter, until an abnormality occurs in the detection results of the pressure sensors  44 ,  45 ,  46  or the control stop command is received from the host controller  80 , the control of dispensing the liquid to the pump unit  10  according to the dispense command is repeated. 
     When it is determined that at least one of the detection results of the pressures in the operation S 07  is not within the normal range, the control circuitry  50  executes a operation  511 . In the operation S 11 , the pressure monitoring unit  51  notifies the host controller  80  of the error. 
     If it is determined that the control stop command is received in the operation S 08 , or after the operation S 11 , the control circuitry  50  executes a operation S 12 . In the operation S 12 , the barrel pressure control unit  52  closes the valve  43  and stops the supply of the pumping gas to the barrel  20 . The control circuitry  50  then terminates the control procedure. 
     As described above, the dispenser  1  includes: a plunger  100  comprising a distal end surface  101  facing an advance direction and a proximal end surface  102  facing a retraction direction; a guide block  200  configured to guide an advance toward the advance direction and retraction toward the retraction direction of the plunger  100  along an axial line L1 intersecting the distal end surface  101  and the proximal; a dispensing portion  300  configured to dispense and suction liquid in response to the advance and the retraction of the distal end surface  101 ; a driver  400  configured to cause the plunger  100  to advance toward the advance direction and retract toward the retraction direction. The dispensing portion  300  includes: a surrounding portion  310  surrounding the distal end surface  101  of the plunger  100  about the axial line L1 to define an accommodation chamber  319 ; a nozzle unit  340  facing the distal end surface  101  of the plunger  100  along the axial line L1; and a plunger seal  352  facing the nozzle unit  340  so that the accommodation chamber  319  is located between the plunger seal  352  and the nozzle unit  340 , and sealing between the surrounding portion  310  and the plunger  100 . The nozzle unit  340  includes an outlet  343  opening into the accommodation chamber  319  to dispense the liquid out of the accommodation chamber  319 . The surrounding portion  310  includes an inlet  323  opening into the accommodation chamber  319  to receive the liquid into the accommodation chamber  319 . The inlet  323  is located closer to the nozzle unit  340  between the plunger seal  352  and the nozzle unit  340 . 
     According to this dispenser  1 , the inlet  323  is opened at the beginning of a period during which the plunger retracts (hereinafter referred to as a “retraction period”), so that liquid is rapidly suctioned into the accommodation chamber  319 . In addition, since the opening areas of the inlet  323  are increased as the plunger  100  retracts, the liquid can be suctioned more quickly. Further, the opening areas of the inlet  323  become smaller as the plunger  100  advances in a period during which the plunger  100  advance (hereinafter referred to as “advance period”), the pressure from escaping to the inlet  323  can be suppressed and the liquid can be dispensed more quickly from the outlet  343 . Therefore, dispensing may be sped up. 
     A distance from the inlet  323  to the nozzle unit  340  is less than or equal to half of a maximum stroke H1 of the distal end surface  101  of the plunger  100 . Liquid can be suctioned more quickly. 
     More than half of the maximum stroke H1 of the distal end surface  101  of the plunger  100  may overlap the inlet  323  along the axial line L1. Liquid can be suctioned more quickly. 
     The nozzle unit  340  may further include: a dispense port  344  opening to outside of the accommodation chamber  319 ; and a dispense flow channel  345  connecting the outlet  343  and the dispense port  344  without passing through a check valve. Since there is no resistance of the check valve, the liquid can be dispensed more quickly. In addition, since the inlet  323  opens early when sucking the liquid, the liquid can be suppressed from being drawn into the outlet  343  even without the check valve. 
     The driver  400  may include: a cylinder  410  accommodating the plunger  100 ; a piston  450  partitioning an inside of the cylinder  410  into a first space  413  and a second space  414 , configured to: advance the plunger  100  toward the advance direction according to a pressure of the first space  413 ; and retract the plunger  100  toward the retraction direction according to a pressure of the second space  414 ; and a piston driver  480  configured to switch between a first state in which a pressure of a pressurizing source is applied to the first space  413  and a second state in which the pressure of the pressurizing source is applied to the second space  414 . Even when the driving power is not supplied due to a failure of the control system, the cylinder  410  can be held at the most advanced position as long as the pressurizing is continued, and leakage of the liquid from the outlet  343  can be suppressed. Therefore, both of an increase in dispensing speed and an improvement in reliability can be achieved. 
     The piston driver  480  may pressurize the first space  413  or the second space  414  by a pressure of a pressing source. The dispenser  1  may further include a spring  620  configured to apply a repulsive force to the plunger  100  toward the advance direction; and a release portion  440  configured to release, by the pressure of the pressurizing source, an application of the repulsive force from the spring  620  to the plunger  100 . When the pressurizing source is supplied, the repulsive force applied to the piston  450  by the spring  620  may be released to allow the piston  450  to slide at high speed, and when the pressurizing source is not supplied, the plunger  100  may be maintained at the most advanced position by the repulsive force of the spring  620 . Accordingly, leakage of the liquid from the outlet  343  can be more reliably suppressed. 
     The dispenser  1  may further comprise a barrel  20  configured to pump the liquid from outside the accommodation chamber  319  to the inlet  323 ; and a pressure monitoring unit  51  configured to adjust a pressure applied to the liquid by the barrel  20 . The dispensing speed can be increased by optimizing the relationship between the pressurizing and depressurizing by the advance and retract of the plunger  100  and the pressurizing by the barrel  20 . 
     As described above, the dispenser  1  includes: a plunger  100  comprising a distal end surface  101  facing an advance direction and a proximal end surface  102  facing a retraction direction; a guide block  200  configured to guide an advance toward the advance direction and retraction toward the retraction direction of the plunger  100  along an axial line L1 intersecting the distal end surface  101  and the proximal; a dispensing portion  300  configured to dispense and suction liquid in response to the advance and the retraction of the distal end surface  101 ; a cylinder  410  accommodating the plunger  100 ; a piston  450  partitioning an inside of the cylinder  410  into a first space  413  and a second space  414 , configured to: advance the plunger  100  toward the advance direction according to a pressure of the first space  413 ; and retract the plunger  100  toward the retraction direction according to a pressure of the second space  414 ; a piston driver  480  configured to switch between a first state in which a pressure of a pressurizing source is applied to the first space  413  and a second state in which the pressure of the pressurizing source is applied to the second space  414 ; a spring  620  configured to apply a repulsive force to the plunger  100  toward the advance direction; and a release portion  440  configured to release, by the pressure of the pressurizing source, an application of the repulsive force from the spring  620  to the plunger  100 . 
     According to this dispenser  1 , when the pressurizing source is supplied, the repulsive force applied to the piston  450  by the spring  620  is released to enable high-speed sliding in the piston  450 , and when the pressurizing source is not supplied, the plunger  100  can be held at the most advanced position by the repulsive force of the spring  620 . Therefore, both high speed dispensing and reliability can be achieved. 
     The release portion  440  may form a third space  445  in the cylinder  410 , so that the pressure of the pressurizing source is applied to the third space  445  in both the first state and the second state. The application of the repulsive force may be released by the pressure of the third space  445 . The configuration of the release portion  440  can be simplified. 
     The piston  450  may have an annular shape and partitions the inside of the cylinder  410  into the first space  413  and the second space  414  between an outer peripheral surface of the plunger  100  and an inner peripheral surface of the cylinder  410 . The spring  620  may apply the repulsive force to the piston  450  between the outer peripheral surface of the plunger  100  and the inner peripheral surface of the cylinder  410 . By utilizing the space around the proximal end portion of the plunger  100  as the arrangement space of the spring  620  and the release portion  440 , increase in size due to the addition of the spring  620  and the release portion  440  can be suppressed. 
     The dispenser  1  may further comprise a holder  461  holding the piston  450  on the outer peripheral surface of the plunger  100  while allowing the piston  450  to move in a direction vertical to the axial line L1. By the holder  461  that allows the axial line L1 to float the piston  450  in the vertical direction, both the position of the plunger  100  with respect to the guide block  200  and the position of the piston  450  with respect to the cylinder  410  can be optimized, and the speed of sliding of the piston  450  and the plunger  100  can be increased. 
     The driver  400  may further have an annular inner seal  472  sealing between the piston  450  and the plunger  100  while allowing the piston  450  to move in the direction vertical to the axial line L1. By sealing the piston  450  formed by the annular shape over the entire circumference, the first space  413  and the second space  414  may be firmly pressurized and the piston  450  may be driven at a higher speed. 
     The piston  450  may have an annular bottom surface  457  along a plane intersecting the axial line L1. The plunger  100  may have an annular rear surface  132  facing the bottom surface  457 . The plunger seal  352  may contact the bottom surface  457  and the rear surface  132  to seal between the piston  450  and the plunger  100 . By interposing the inner seal  472  between the bottom surface  457  and the rear surface  132 , both the float property in the direction vertical to the axial line L1 and the seal property of the piston  450  can be achieved. In addition, since the inner seal  472  is interposed between the bottom surface  457  and the rear surface  132  over the entire circumference around the axial line L1, the place where the driving force acts between the plunger  100  and the piston  450  is dispersed over the entire circumference. As a result, the postures of both the plunger  100  and the piston  450  are stabilized, so that the plunger  100  and the piston can slide at higher-speed. 
     The dispenser  1  may further comprise a through bolt  11  for attaching the guide block  200  to the cylinder  410 . The floatability of the piston  450  is more beneficial because the guide block  200  and the cylinder  410  are separate members from each other and a positional deviation of the cylinder  410  relative to the guide block  200  is likely to occur. 
     The dispenser  1  may further include a distal end surface  521  facing the proximal end surface  102  of the plunger  100  in the cylinder  410  to restrict the retraction of the plunger  100 ; and a retraction limit adjustment portion  530  configured to adjust the position of the distal end surface  521  in a direction along the axial line L1. The distal end surface  521  acts directly on the cylinder  410 , and the most retracted position of the plunger  100  can be adjusted accurately. 
     It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail.