Patent Publication Number: US-9889463-B2

Title: Liquid material discharge device and discharge method

Description:
TECHNICAL FIELD 
     The present invention relates to a liquid material discharge device and discharge method, which can supply compressed air in amount sufficient to continuously perform a discharge operation at a high speed. 
     BACKGROUND ART 
     As a device for continuously discharging a liquid material in the form of droplets at a high speed, there is known the type of quickly advancing a plunger in a liquid chamber, which has a discharge port, toward the discharge port and then abruptly stopping the plunger such that the liquid material is discharged in the form of a droplet from the discharge port. 
     A device disclosed in Patent Document 1, proposed by the applicant, is one example of a droplet dispensing device in which a tip of a plunger is abruptly stopped by abutting the tip against a valve seat, thus causing a liquid to be discharged in the form of a droplet flying from a discharge port of a valve. 
     A device disclosed in Patent Document 2, proposed by the applicant, is one example of a droplet discharge device in which a plunger is advanced and then stopped in a state where a tip of the plunger and an inner wall of a liquid chamber are not contacted with each other, thus applying an inertial force to a liquid material and discharging the liquid material in the form of a droplet. 
     LIST OF PRIOR-ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent No. 4663894 
     Patent Document 2: International Publication Pamphlet No. WO2008/108097 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The above-mentioned devices of prior art can continuously discharge the liquid material in the form of a droplet at a high speed. In practical fields, however, a discharge device capable of continuously discharging the liquid material at a higher tact is demanded from the viewpoint of increasing productivity. 
     One effective solution for realizing the higher tact is to increase the pressure of air for operating the plunger. However, this solution requires flow passages, etc. in the discharge device to be endurable against the higher pressure, thus leading to the problem that the size and the weight of the device are increased. Assuming the case of carrying out work on a desk, an increase in the size and the weight of the device has to be avoided. 
     In consideration of the above-described state of the art, an object of the present invention is to provide a liquid material discharge device and discharge method, which can perform continuous discharge at a higher tact than in the past while the device size is held small. 
     Means for Solving the Problems 
     With attention focused on a solenoid valve having a relatively small in the entire device, the inventor has accomplished the present invention based on the finding that a higher tact in the continuous discharge can be realized by arranging a plurality of solenoid valves in parallel. Thus, the present invention is constituted by the following technical means. 
     According to a first invention, there is provided a liquid material discharge device comprising a liquid chamber that is communicated with a discharge port and is supplied with a liquid material, a plunger that is coupled to a piston, and that has a tip advancing and retreating within the liquid chamber in a state not in contact with a lateral surface of the liquid chamber, a resilient member that applies a biasing force to the plunger, a main body including a piston chamber in which the piston is disposed, a solenoid valve that supplies a pressurized gas, supplied from a pressurized gas source, to the piston chamber, or that exhausts the pressurized gas from the piston chamber, and a controller that controls operation of the solenoid valve, wherein the solenoid valve is constituted by a plurality of solenoid valves that are connected to the piston chamber in parallel. 
     According to a second invention, in the first invention, the liquid material discharge device further comprises a holder including a holding member that holds the plural solenoid valves, and a relay member that has an inner flow passage communicating the plural solenoid valves with the piston chamber, wherein the holding member has a supply port communicating with the pressurized gas source and has a plurality of delivery ports that distribute the pressurized gas, supplied to the supply port, to the plural solenoid valves, and the relay member has an inner flow passage that communicates the plural solenoid valves with the piston chamber. 
     According to a third invention, in the second invention, the relay member has a plurality of inner flow passages that communicate the plural solenoid valves individually with the piston chamber. 
     According to a fourth invention, in the second or third invention, the holder is detachably fixed to the main body. 
     According to a fifth invention, in any one of the first to fourth inventions, the solenoid valve is constituted by three or four solenoid valves. 
     According to a sixth invention, in any one of the first to fifth inventions, the controller establishes communication between the pressurized gas source and the piston chamber by the solenoid valves at timing different for each of the solenoid valves. 
     According to a seventh invention, in any one of the first to sixth inventions, the liquid material discharge device is of desk-top type. 
     According to an eighth invention, there is provided a liquid material discharge method comprising a step of preparing a liquid material discharge device including a liquid chamber that is communicated with a discharge port and is supplied with a liquid material, a plunger that is coupled to a piston, and that has a tip advancing and retreating within the liquid chamber in a state not in contact with a lateral surface of the liquid chamber, a resilient member that applies a biasing force to the plunger, a main body including a piston chamber in which the piston is disposed, a solenoid valve that supplies a pressurized gas, supplied from a pressurized gas source, to the piston chamber, or that exhausts the pressurized gas from the piston chamber, and a controller that controls operation of the solenoid valve; a step of constituting the solenoid valve by a plurality of solenoid valves that are connected to the piston chamber in parallel; a first step of operating the plural solenoid valves to communicate the pressurized gas source with the piston chamber at desired timings; a second step of operating the plural solenoid valves to communicate the piston chamber with the atmosphere at the same timing; and a third step of continuously discharging droplets by repeating the first and second steps. 
     According to a ninth invention, in the eighth invention, in the first step, the plural solenoid valves communicate the pressurized gas source with the piston chamber at the same timing. 
     According to a tenth invention, in the eighth invention, in the first step, the plural solenoid valves successively communicate the pressurized gas source with the piston chamber. 
     According to an eleventh invention, in the eighth, ninth or tenth invention, the pressurized gas distributively supplied to the plural solenoid valves from one pressurized gas source is supplied to the piston chamber through one flow passage communicating with each of the plural solenoid valves. 
     According to a twelfth invention, in the eighth, ninth or tenth invention, the pressurized gas distributively supplied to the plural solenoid valves from one pressurized gas source is supplied to the piston chamber through a plurality of flow passages communicating with the plural solenoid valves in one-to-one relation. 
     According to a thirteenth invention, in any one of the eighth to twelfth inventions, the solenoid valve is constituted by three or four solenoid valves. 
     According to a fourteenth invention, in any one of the eighth to thirteenth inventions, in the second step, the plunger is advanced and stopped in a state that the plunger tip is not contacted with an inner wall of the liquid chamber, the inner wall being present in an advancing direction of the plunger, thereby applying an inertial force to the liquid material and discharging the liquid material in form of a droplet. 
     According to a fifteenth invention, in any one of the eighth to fourteenth inventions, in the third step, the droplets are continuously discharged at a rate of 300 shots or more per sec. 
     Advantageous Effect of the Invention 
     With the present invention, the discharge device capable of performing continuous discharge at a higher tact than in the past can be obtained while the device size is held small. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates, in a way partially sectioned in principal parts, a discharge device according to a first embodiment. 
         FIG. 2  is a perspective view to explain a solenoid valve device. Specifically,  FIG. 2( a )  is a perspective view of the solenoid valve device, and  FIG. 2( b )  is a perspective view in a dismantled state of the solenoid valve device illustrated in  FIG. 2( a ) . 
         FIG. 3  is a rear view of individual members constituting a holder. Specifically,  FIG. 3( a )  is a rear view of a grasping member, and  FIG. 3( b )  is a rear view of a relay member. 
         FIG. 4  is a graph plotting the relation among the number of solenoid valves, opening timings thereof, and a pressure reaching time. Specifically,  FIG. 4( a )  represents the case where the solenoid valves are opened at the same timing, and  FIG. 4( b )  represents the case where the solenoid valves are opened at different timings. 
         FIG. 5  illustrates, in a way partially sectioned in principal parts, a discharge device according to a second embodiment. 
         FIG. 6  illustrates, in a way partially sectioned in principal parts, a discharge device according to a third embodiment. 
         FIG. 7  illustrates, in a way partially sectioned in principal parts, a discharge device according to a fourth embodiment. 
         FIG. 8  illustrates, in a way partially sectioned in principal parts, a discharge device according to a fifth embodiment. 
         FIG. 9  illustrates, in a way partially sectioned in principal parts, a discharge device according to a sixth embodiment. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Examples of the mode for carrying out the present invention will be described below. 
     First Embodiment 
     A discharge device  1  according to a first embodiment relates to a discharge device including two solenoid valves, which are connected in parallel and which supply a compressed gas to a piston chamber.  FIG. 1  illustrates, in a way partially sectioned in principal parts, the discharge device  1  according to the first embodiment. In the following, the side nearer to a discharge port  11  is called the front side, and the side nearer to a micrometer  42  is called the rear side in some cases for convenience of explanation. 
     Description is now made about a discharge unit  10  and a pressure supply unit  50  which are constituting the discharge device  1 . 
     (Discharge Unit) 
     The discharge unit  10  includes, as main components, a main body  2  having a piston chamber  20 , a piston  30  disposed in the piston chamber  20 , and a nozzle block  3  in which a nozzle member  4  is disposed. 
     The piston chamber  20  is partitioned by the piston  30  into a front piston chamber  21  and a rear piston chamber  22 . A sealing member is fitted over a lateral circumferential surface of the piston  30 , and the piston  30  is slidable within the piston chamber  20  in a state closely contacted with the piston chamber  20 . 
     The front piston chamber  21  is communicated with the pressure supply unit  50  through an air flow passage  49 . When compressed air is supplied to the front piston chamber  21 , the piston  30  is retreated, and when the compressed air in the front piston chamber  21  is released from the air passage  49 , the piston  30  is advanced by a biasing force of a spring  40 . The piston  30  is coupled to a rod (plunger)  33  such that a rod tip  35  is also reciprocally moved within a liquid chamber  13  together with reciprocal movement of the piston  30 . On that occasion, the rod  33  is reciprocally moved in a state not in contact with a lateral surface of the liquid chamber  13 . When the rod tip  35  abuts against a valve seat  15  that is provided in a bottom surface of the liquid chamber  13  at the front side (or in an inner wall thereof positioned in an advancing direction of the plunger), the liquid material is separated and discharged in the form of a flying droplet. 
     The piston  30  is further coupled to a rear abutment member  32 . 
     A rear stopper  41  extending to enter a spring chamber  23  is disposed in a rear end portion of the main body  2 . The rear stopper  41  comes into abutment against a rear end of the rear abutment member  32 , thereby limiting rearward movement of the piston  30 . A rear end of the rear stopper  41  is connected to the micrometer  42 . A position of the rear stopper  41  in the forward and rearward direction can be adjusted by operating the micrometer  42 . 
     The spring chamber  23  is communicated with the atmosphere through an air flow passage  24 . 
     The nozzle block  3  is fixed to the front side of the main body  2 . The nozzle member  4  is screwed to the nozzle block. A liquid material supply passage  12  communicating with a liquid reservoir (not illustrated) is provided in a lateral portion of the nozzle block. The liquid material is supplied to the liquid chamber  13  inside the nozzle block through the liquid material supply passage  12 . 
     (Pressure Supply Unit) 
       FIG. 2  is a perspective view to explain a solenoid valve device constituting the pressure supply unit  50 , and  FIG. 3  is a rear view of individual members constituting a holder. 
     A solenoid valve device is arranged integrally with the discharge unit  10  at the lateral side thereof, and it includes a solenoid valve A  61 , a solenoid valve B  62 , and a holder  70  that holds the solenoid valves A and B. 
     The solenoid valves  61  and  62  are each a selector valve that is switchable over between a first position at which a pressurized gas source (not illustrated) is communicated with the piston chamber  20  and a second position at which the piston chamber  20  is communicated with the atmosphere. The solenoid valves  61  and  62  have the same valve opening/closing speed and the same flow rate. Operations of the solenoid valves  61  and  62  are controlled by a controller  90  (not illustrated in  FIG. 1 ). The solenoid valves  61  and  62  are constituted as an integral unit in a state held by the holder  70  such that they can be handled as one unit. Alternatively, the holder  70  may include a pressure reducing valve such that air pressure having been adjusted to a desired level is supplied to the solenoid valves. 
     The solenoid valve A  61  has an air supply port A  66 , an air exhaust port A  67 , and an air delivery port (not illustrated) formed at the rear side. The air delivery port is communicated with one of the air supply port A  66  and the air exhaust port A  67  by the action of the solenoid valve A  61 . 
     The solenoid valve B  62  has an air supply port B  68 , an air exhaust port B  69 , and an air delivery port (not illustrated) formed at the rear side. The air delivery port is communicated with one of the air supply port B  68  and the air exhaust port B  69  by the action of the solenoid valve B  62 . 
     The holder  70  is constituted by a grasping member (holding member)  71  and a relay member  72 . The grasping member  71  and the relay member  72  are fixed to each other in a detachable manner. 
     The grasping member  71  has an air supply port  73  and an exhaust port  74  at the front side, and has an air delivery port A  75 , an air inlet port A  76 , an air delivery port B  77 , and an air inlet port B  78  at the rear side. A flow passage for branching air supplied to the air supply port  73  is formed inside the grasping member  71 . The length of a flow passage from the air supply port  73  to the air delivery port A  75  is the same as that of a flow passage from the air supply port  73  to the air delivery port B  77 . Furthermore, the length of a flow passage from the air inlet port A  76  to the exhaust port  74  is the same as that of a flow passage from the air inlet port B  78  to the exhaust port  74 . 
     The relay member  72  has an air reception port A  79  and an air reception port B  80  at the front side, and an air delivery port  81  at the rear side. The relay member  72  serves also to fix the solenoid valves A and B to the lateral surface of the main body  2  in a detachable manner. The relay member  72  is constituted such that the length of a flow passage from the air supply port A  66  to the air flow passage  49  is the same as that of a flow passage from the air supply port B  68  to the air delivery port  81 . Furthermore, the length of a flow passage from the air delivery port  81  to the air exhaust port A  67  is the same as that of a flow passage from the air delivery port  81  to the air exhaust port B  69 . 
     Description is now made about a route through which air supplied to the air supply port  73  from the pressurized gas source (not illustrated) via a pressure reducing valve is delivered to the front piston chamber  21 . It is here assumed that the solenoid valves A and B are operated to be opened and closed at the same timing by the controller  90 . 
     The compressed air supplied to the air supply port  73  is branched within the grasping member  71  to be supplied from the air delivery port A  75  to the air supply port A  66  and further from the air delivery port B  77  to the air supply port B  68 . 
     The compressed air supplied to the air supply port A  66  passes through an inner flow passage of the solenoid valve A  61 , and is delivered from an air delivery port (not illustrated) of the solenoid valve A  61  to the air reception port A  79  of the relay member  72 . Similarly, the compressed air supplied to the air supply port B  68  passes through an inner flow passage of the solenoid valve B  62 , and is delivered from an air delivery port (not illustrated) of the solenoid valve B  62  to the air reception port B  80  of the relay member  72 . The air supplied to the air reception port A  79  and the air supplied to the air reception port B  80  are merged together in an inner flow passage of the relay member  72 , and then supplied to the air flow passage  49  from the air delivery port  81  of the relay member  72 . 
     As described above, it is possible to branch the air received from one pressure supply port to be supplied to two solenoid valves, which are arranged in parallel, through branched flow passages, to merge two streams of air together after passing through the solenoid valves, and to deliver the merged air to the discharge unit from one pressure delivery port. 
     Alternatively, timings of opening and closing the solenoid valves A and B may be shifted from each other. For example, the start of the retreat operation of the piston (plunger) can be moderated by slightly shifting the timings of opening the solenoid valves A and B such that the flow rate of the air flowing into the air chamber is changed over time. This is effective in preventing the occurrence of cavitation in the liquid chamber when the piston (plunger) is retreated. 
       FIG. 4  is a graph plotting the relation among the number of solenoid valves, opening timings thereof, and a pressure reaching time. The graph plots pressure change in a pressure chamber when the solenoid valve is opened and pressure is supplied to the pressure chamber. Specifically,  FIG. 4( a )  is a graph plotting pressure change when one solenoid valve is opened, and pressure change when two solenoid valves arranged in parallel are opened at the same timing.  FIG. 4( b )  is a graph plotting pressure change when one solenoid valve is opened, and pressure change when two solenoid valves arranged in parallel are opened at different timings. In each the graphs of  FIGS. 4( a ) and 4( b ) , a dotted line represents the pressure change when one solenoid valve is opened. 
     As seen from  FIG. 4( a ) , when two solenoid valves (valve 1 and valve 2) having the same specifications are opened at the same timing, the pressure in the pressure chamber is increased to a higher level than the case of opening one solenoid valve from the start immediately after the opening of the solenoid valves. As a result, the plunger is moved at a higher speed in the case of opening the two solenoid valves at the same timing. 
       FIG. 4( b )  is a graph representing the case where two solenoid valves (valve 1 and valve 2) having the same specifications are opened at different timings shifted from each other. In this case, at the beginning, because only one solenoid valve (valve 1) is opened, the pressure in the pressure chamber is increased along the same curve as that in the case of opening one solenoid valve. When the second solenoid valve (valve 2) is opened, a pressure rising rate is increased, and the pressure in the pressure chamber can reach the desired pressure at earlier timing than in the case of employing one solenoid valve. 
     When the plunger is abruptly retreated so as to generate negative pressure, cavitation tends to occur in some cases depending on the type of the liquid material. In such a case, by opening the two solenoid valves successively at different timings shifted from each other, a tact time can be shortened while prevention of the occurrence of cavitation is ensured. When finer control is desired, it is preferable to increase the number of solenoid valves as in a sixth embodiment described later. 
     In the above-described discharge device according to this embodiment, since plural solenoid valves each operating at a high speed are arranged in parallel to increase an amount of supplied air without increasing the supply pressure of the pressurized gas source, the tact time can be shortened without increasing the size and the weight of the device. 
     Furthermore, ultra-high speed discharge of droplets (e.g., 300 shots or more per sec, preferably 400 shots or more per sec, and more preferably 500 shots or more per sec) can be realized without increasing the device size. With the high-speed operation of the plunger rod, it is possible to not only increase efficiency of work, but also to discharge the liquid material in a smaller amount. 
     Second Embodiment 
     A discharge device  1  according to a second embodiment relates to a discharge device in which the plunger is advanced and then stopped in a state where the rod tip  35  and the bottom surface of the liquid chamber  13  at the front side (or the inner wall thereof positioned in the advancing direction of the plunger) are not contacted with each other (i.e., in a manner not abutting against the valve seat), thus applying an inertial force to the liquid material and discharging the liquid material in the form of a flying droplet. In the following, only different features from those in the first embodiment are described, and duplicate description of the same features is omitted. 
       FIG. 5  illustrates, in a way partially sectioned in principal parts, the discharge device  1  according to the second embodiment. The discharge device  1  according to the second embodiment is different from the first embodiment in that the piston  30  includes a collision portion  31  formed at the side in the advancing direction thereof, and the advance of the piston  30  is abruptly stopped upon the collision portion  31  colliding against the inner wall (bottom surface) of the piston chamber  20  at the front side. Because the rod tip  35  is not abutted against the valve seat, there is no risk that abrasion pieces or particles may be generated due to abutting of the rod tip against the valve seat. Furthermore, even when the liquid material contains a solid such as a filler, reduction of discharge accuracy caused by collapse or damage of the solid can be prevented, and the liquid material can be discharged without deteriorating the function and properties of the liquid material. 
     Though not illustrated in  FIG. 5 , the discharge device may include a plunger position determining mechanism (see Patent Document 2) that specifies the tip position of the plunger at the time when the advance of the plunger is stopped, to a desired position near the inner wall (bottom surface) of the liquid chamber, which is located in the advancing direction of the plunger. 
     The solenoid valves  61  and  62  and the holder  70  have the same structures as those in the first embodiment. 
     Also in this embodiment, the tact time can be shortened by increasing an amount of supplied air without increasing the supply pressure of the pressurized gas source. Furthermore, ultra-high speed discharge of droplets (e.g., 300 shots or more per sec, preferably 400 shots or more per sec, and more preferably 500 shots or more per sec) can be realized without increasing the device size. 
     Third Embodiment 
     A discharge device  1  according to a third embodiment relates to a discharge device in which two solenoid valves connected in parallel and supplying the compressed gas are connected to the piston chamber through different flow passages. In the following, only different features from those in the second embodiment are described, and duplicate description of the same features is omitted. 
       FIG. 6  illustrates, in a way partially sectioned in principal parts, the discharge device  1  according to the third embodiment. In  FIG. 6 , components corresponding to the pressure supply unit  50  in  FIG. 1  are omitted, and the solenoid valve A  61 , the solenoid valve B  62 , and the controller  90  are mainly illustrated. 
     The discharge device  1  according to the third embodiment is different from the second embodiment in that the relay member  72  constituting the holder  70  has two air delivery ports  81  and  81  each of which is communicated with the air flow passage  49 . More specifically, an air delivery port  81   a  formed in the relay member  72  is communicated with the air reception port A  79 , and an air delivery port  81   b  formed therein is communicated with the air reception port B  80 . 
     Also in this embodiment, the tact time can be shortened by increasing an amount of supplied air without increasing the supply pressure of the pressurized gas source. Furthermore, ultra-high speed discharge of droplets (e.g., 300 shots or more per sec, preferably 400 shots or more per sec, and more preferably 500 shots or more per sec) can be realized without increasing the device size. 
     Fourth Embodiment 
     A discharge device  1  according to a fourth embodiment relates to a discharge device in which a spring  40  is disposed under the piston  30 . In the following, only different features from those in the first embodiment are described, and duplicate description of the same features is omitted. It is to be noted that, in  FIG. 7 , a syringe  8  is connected to the liquid material supply passage  12  through a tube  9 , and this arrangement is similarly applied to the first to third embodiments. 
       FIG. 7  illustrates, in a way partially sectioned in principal parts, the discharge device  1  according to the fourth embodiment. The discharge device  1  according to the fourth embodiment is different from the first embodiment in that a spring  40  is arranged at the side in the advancing direction of the piston  30 , and the piston  30  is advanced by supplying the compressed gas to the rear piston chamber  22 . More specifically, when the compressed gas is supplied to the piston chamber through the solenoid valves  61  and  62 , the piston  30  is advanced. When the compressed gas is released from the piston chamber through the solenoid valves  61  and  62 , the piston  30  is retreated by a biasing force of the spring  40 . Upon the rod tip  35  abutting against the valve seat  15  that is disposed in the inner wall (bottom surface) of the liquid chamber  13  at the front side, the liquid material is separated and discharged in the form of a flying droplet. 
     Furthermore, in this embodiment, the solenoid valves  61  and  62  are incorporated in a pressure supply unit  51 . The pressure supply unit  51  has an air delivery port  81  formed at the rear side, and it is attached to the main body  2  such that the air delivery port  81  and the air flow passage  24  are communicated with each other. The pressure supply unit  51  has an air supply port  73  and an air exhaust port  74  both formed at the front side, and the air supply port  73  is communicated with the pressurized gas source through a pressure reducing valve  94 . 
     Also in this embodiment, the tact time can be shorted by increasing an amount of supplied air without increasing the supply pressure of the pressurized gas source. Furthermore, ultra-high speed discharge of droplets (e.g., 300 shots or more per sec, preferably 400 shots or more per sec, and more preferably 500 shots or more per sec) can be realized without increasing the device size. 
     Fifth Embodiment 
     A discharge device  1  according to a fifth embodiment relates to a discharge device of the type that the liquid material comes into contact with a work before the liquid material departs from the discharge port (i.e., of the type opening and closing a discharge flow passage by a tip of a shaft member). In the following, only different features from those in the fourth embodiment are described, and duplicate description of the same features is omitted. 
       FIG. 8  illustrates, in a way partially sectioned in principal parts, the discharge device  1  according to the fifth embodiment. In the discharge device  1  according to the fifth embodiment, a liquid is discharged when a flow passage communicating with the discharge port  11  is opened and closed by the tip  35  of the rod  33  that is coupled to the piston  30 . Thus, a liquid is discharged by the action of air pressure applied to a reservoir tank  97  instead of being discharged by the action of an inertial force applied to the rod  33 . 
     Air pressure supplied from a pressure supply source is supplied to the reservoir tank  97 , in which the liquid material is stored, through an air tube  6  after being adjusted to the desired pressure by a pressure reducing valve  95 . The liquid material pressurized in the reservoir tank  97  is supplied to the liquid material supply passage  12  of the discharge device  1  through the liquid tube  9  from a pipe  96  having a fore end that is arranged near a bottom surface of the reservoir tank  97 . The liquid material is then supplied to the liquid chamber  13  communicating with the liquid material supply passage  12 . The liquid chamber  13  is constituted to be opened and closed at its end in the discharge direction by the tip  35  of the rod  33  of the discharge device  1 . Upon the tip  35  of the rod  33  abutting against the valve seat  15 , the flow passage connecting the liquid chamber  13  and the discharge port  11  of the nozzle member  4  is shut off. 
     Subsequently, when the rod  33  of the discharge device  1  is ascended, the liquid chamber  13  and the discharge port  11  of the nozzle member  4  are communicated with each other. Therefore, the liquid material is discharged from the discharge port  11  of the nozzle member  4  while it is pressed by the air pressure, which has been adjusted by the pressure reducing valve  95 . The discharge is ended by descending the rod tip  35  to be abutted against the valve seat  15 . The reservoir tank  97  stores the liquid material of several liters to several tens liters, for example. 
     The pressure supply unit  51  has the same structure as that in the fifth embodiment. The start of the retreat operation of the rod  33  can be moderated and the occurrence of cavitation can be prevented by slightly shifting operation timings of the two solenoid valves so as to open them successively. 
     Sixth Embodiment 
     A discharge device  1  according to a sixth embodiment relates to a discharge device including four solenoid valves connected in parallel. In the following, only different features from those in the second embodiment are described, and duplicate description of the same features is omitted. 
       FIG. 9  illustrates, in a way partially sectioned in principal parts, the discharge device  1  according to the sixth embodiment. In  FIG. 9 , components corresponding to the pressure supply unit  50  in  FIG. 1  is omitted, and the solenoid valve A  61 , the solenoid valve B  62 , a solenoid valve C  63 , a solenoid valve D  64 , and the controller  90  are mainly illustrated. 
     The discharge device  1  according to the sixth embodiment is different from the second embodiment in that the device includes four solenoid valves and the holder  70  has a structure for holding the four solenoid valves. 
     The solenoid valves  61  to  64  have the same structure as the solenoid valves in the first and second embodiments. The grasping member  71  has the air supply port  73  and the exhaust port  74  at the front side, and has four air delivery ports A to D and four air inlet ports A to D at the rear side. The relay member  72  has four air reception ports A to D. Flow passages communicating with the air reception ports A to D are merged together such that the pressurized air is delivered to the discharge unit from one pressure delivery port  81 . When the number of solenoid valves is large, it is preferable from the viewpoint of reducing the device size to deliver the pressurized air to the discharge unit after merging the flow passages communicating with the individual solenoid valves together. 
     The discharge device  1  according to this embodiment is suitable for opening the solenoid valves in a stepwise manner. In more detail, of the four solenoid valves arranged in parallel, the first solenoid valve is opened first, and then the second, third and fourth solenoid valves are opened successively in the mentioned order. As a result, the flow rate of the pressurized air at the start of the air supply to the air chamber can be reduced and the start of the retreat operation of the piston  30  can be made more moderate in comparison with the case of opening the four solenoid valves at the same timing. 
     Also in this embodiment, the tact time can be shortened by increasing an amount of supplied air without increasing the supply pressure of the pressurized gas source. Furthermore, ultra-high speed discharge of droplets (e.g., 300 shots or more per sec, preferably 400 shots or more per sec, and more preferably 500 shots or more per sec) can be realized without increasing the device size. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to the technique of discharging the liquid material by repeatedly operating a shaft member, which is called, e.g., a plunger, a valve shaft, or rod, in a reciprocal way at a high speed. 
     Furthermore, the present invention can be applied to not only the discharge technique of the type that the liquid material comes into contact with a work after the liquid material has departed from the discharge unit, but also to the discharge technique of the type that the liquid material comes into contact with a work before the liquid material departs from the discharge unit (i.e., of the type opening and closing the discharge flow passage by a tip of the shaft member). 
     LIST OF REFERENCE SYMBOLS 
     
         
         
           
               1 : discharge device  2 : main body  3 : discharge block  4 : nozzle member  5 : air supply device  6 : air tube  7 : adapter  8 : liquid reservoir (syringe)  9 : liquid tube  10 : discharge unit  11 : discharge port  12 : liquid material supply passage  13 : liquid chamber  14 : discharge flow passage  15 : valve seat  20 : piston chamber  21 : front piston chamber  22 : rear piston chamber  23 : spring chamber  24 : air flow passage  30 : piston  31 : collision portion,  32 : rear abutment member  33 : rod  35 : tip  40 : spring  41 : rear stopper  42 : micrometer  49 : air flow passage  50 : pressure supply unit (solenoid valve)  51 : pressure supply unit  61 : solenoid valve A  62 : solenoid valve B  63 : solenoid valve C  64 : solenoid valve D  65 : solenoid valve E  66 : air supply port A  67 : air exhaust port A  68 : air supply port B  69 : air exhaust port B  70 : holder  71 : grasping member  72 : relay member  73 : air supply port  74 : air exhaust port  75 : air delivery port A  76 : air inlet port A  77 : air delivery port B  78 : air inlet port B  79 : air reception port A  80 : air reception port B  81 : air delivery port  90 : controller  94 : pressure reducing valve  95 : pressure reducing valve  96 : pipe  97 : reservoir tank