JP4322282B2 - Liquid supply device - Google Patents

Description

  The present invention relates to a liquid supply apparatus.

  In particular, an apparatus using a syringe pump is used in order to supply a highly viscous liquid such as a paint. A conventional syringe pump sucks liquid by retreating a piston to reduce the pressure in the syringe. A liquid with high viscosity does not easily flow into the syringe, and a large negative pressure is generated in the syringe, so that outside air is inhaled from the joint of the pipe or the like, and gas dissolved in the liquid is bubbled. There is a case. Such bubbles cause a problem in that the amount of liquid supplied varies and causes problems such as a decrease in yield in subsequent processes.

Patent Document 1 discloses a technique for preventing the liquid from becoming atmospheric pressure or lower by pressurizing the liquid on the suction side of the syringe pump, but when air bubbles are mixed in the liquid from the beginning, It is not possible to prevent the discharge of liquid mixed with bubbles.
JP-A-8-182951 Japanese Patent Laid-Open No. 2003-56667 JP-A-5-285436

  In view of the above problems, an object of the present invention is to provide a liquid supply apparatus that does not mix bubbles in the liquid to be discharged.

In order to solve the above problems, a liquid supply device according to the present invention forms an internal space with a server tank capable of pressurizing stored liquid, a syringe and a piston, and retracts the piston by the pressure of the liquid. A syringe pump capable of introducing the liquid from the server tank into the internal space and discharging the liquid from the internal space by advancement of the piston; and a suction for introducing the liquid from the server tank into the internal space A switching valve that allows the internal space of the syringe pump to communicate with either the flow path or the discharge flow path for delivering the liquid to the outside, and is movable in the forward and backward directions of the piston. a drive mechanism having a pusher which can be brought into contact with the outside to advance the piston retracts the pusher at a predetermined speed When the sensor cannot detect the presence of the piston within a certain distance from the pusher, the pusher is temporarily stopped, and the sensor determines that the piston is within a certain distance from the pusher. If the sensor cannot detect again that the piston is within a certain distance from the pusher within the predetermined time, the pusher is retracted again at the predetermined speed. And control means for abnormally stopping .

  According to this configuration, when the pusher is retracted, the liquid flows into the syringe pump by retracting the piston by its own pressure. At this time, if air bubbles are mixed in the liquid, the speed at which the piston is retracted decreases due to the compressibility of the air bubbles. Therefore, the sensor detects the delay in the retraction of the piston with respect to the retraction of the pusher. When the mixing of bubbles is detected, the operation of the pusher is stopped, so that the liquid containing bubbles can be prevented from being discharged from the syringe pump.

  In the liquid supply apparatus of the present invention, the control means may be configured so that the sensor is located within a certain distance from the pusher before the predetermined determination time elapses after the sensor has passed the grace period. When this is detected, it may be determined that bubbles are mixed in the liquid.

  Since the piston retraction delay due to the compressibility of the bubbles falls within a certain range, it is possible to determine whether the delay of the piston is due to the mixing of bubbles or other troubles with this configuration.

  As described above, according to the present invention, air is mixed by pressurizing the liquid, retreating the piston by the pressure of the liquid, and detecting with the sensor the delay in the backward movement of the piston that occurs when the air bubbles are mixed. The operation can be stopped so as not to discharge the liquid.

Embodiments of the present invention will now be described with reference to the drawings.
In FIG. 1, the outline | summary of the liquid supply apparatus 1 which is one embodiment of this invention is shown. The liquid supply device 1 includes a server tank 2 that stores a liquid, for example, a paint L having a viscosity of 2500 to 4500 cps, and an external part that consumes the liquid L from the server tank 2 at a predetermined flow rate (for example, 500 to 1000 cc / min). Supply destination, for example, a syringe pump 3 to be supplied to the coating apparatus, and a drive mechanism 4 for driving the syringe pump 3.

  The server tank 2 has a sealed structure, and compressed air of a predetermined pressure (for example, 0.5 MPa) is introduced into the upper space of the liquid L to pressurize the stored liquid L.

  The liquid L is introduced into the syringe pump 3 from the suction channel 5 provided at the lower end of the server tank 2 through the switching valve 6 and the common channel 7. The switching valve 6 is a three-way valve, and selectively communicates the common flow path 7 with either the suction flow path 5 or the discharge flow path 8 leading to the supply destination.

  The syringe pump 3 is composed of, for example, a syringe 9 having an inner diameter of 80 mm, one end of which is connected to the common flow path 7, and a piston 11 that forms an internal space 10 that divides the inside of the syringe 9 and communicates with the common flow path 7. The piston 11 has a rod 12 that extends to the outside of the syringe 9.

  The drive mechanism 4 can move the pusher 14 in the same direction as the movable direction of the piston 11 by the motor 13, and the pusher 14 is brought into contact with the outside of the piston 11, that is, the rear end of the rod 12. 11 can be pushed into the back side (forward direction) of the syringe 9. Further, the drive mechanism 4 can confirm whether or not the rear end of the rod 12 is within a predetermined distance from the pusher 14 by the sensor 15 disposed on the pusher 14, and controls the motor 13 according to the output of the sensor 15. The control device 16 is provided.

  FIG. 2 shows details of the syringe pump 3 and the drive mechanism 4. The drive mechanism 4 causes the pusher 14 to move in a forward direction or a backward direction (direction in which the piston 11 is pulled out from the syringe 9) by a feed screw 17 that is rotated by a motor 13, respectively (for example, 200 to 600 mm / min in the backward direction). , In the forward direction at 100 to 200 mm / min). The retraction speed of the pusher 14 is set so as to substantially match the speed at which the liquid L pressurized in the server tank 2 flows into the internal space 10 of the syringe 9 while retreating the piston 11 by the pressure. The pusher 14 is formed with a seat 18 that receives the rear end of the rod 12, and the sensor 15 is, for example, a photoelectric sensor that outputs a potential when the rear end of the rod 12 is in the seat 18.

  When the common flow path 7 is communicated with the suction flow path 5 by the switching valve 6, the liquid L pressurized by the server tank 2 presses the piston 11. At this time, if the rear end of the rod 12 is in contact with the pusher 14, the pusher 14 resists the pressure of the liquid L and causes the piston 11 to stay in place. As shown in FIG. When the pusher 14 is retracted, the piston 11 is retracted by the pressure of the liquid L. If the pressure of the liquid L is sufficiently large, the piston 11 moves backward at the same speed as the pusher 14 moves backward.

  As shown in FIG. 4, when bubbles B are mixed in the liquid L, the pressure transmitted from the server tank 2 to the piston 11 due to the contraction of the bubbles B is reduced, so that there is a delay in the backward movement of the piston 11. Arise.

  FIG. 5 shows a model of pressure propagation of viscous fluid. As shown in the figure, the pressures at two points away from the pipe line filled with the viscous fluid are P1 and P2. As shown in FIG. 6, when pressure is applied to the fluid from one of the pipes and the upstream pressure P1 rises, the downstream pressure P2 rises with a slight delay. Even if the pressures P1 and P2 are stabilized, the pressure P2 on the downstream side remains slightly lower than the pressure P1 on the upstream side due to pressure loss in the pipe.

  In FIG. 6, the pressure on the downstream side when the bubbles B are mixed in the liquid L is shown as P2 '. As shown in the figure, since the bubbles contract due to the increase in pressure and the apparent volume of the liquid L is reduced, the increase in the pressure P2 ′ on the downstream side is further increased compared to the pressure P2 when there is no bubble. Ascend late.

  When this is applied to the syringe pump 3, the upstream pressure P 1 is the pressure of the liquid L in the server tank 2, and the downstream pressures P 2 and P 2 ′ are the liquid L that causes the piston 11 in the internal space 10 of the syringe 9 to retreat. Become pressure. FIG. 6 shows the pressure Pp necessary to overcome the friction with the syringe 9 and retract the piston 11. As shown in the figure, the delay T2 when the bubble B is mixed from when the upstream pressure rises to Pp until the downstream pressure rises to Pp is the case where the bubble B is not mixed. It becomes larger than the delay T1. The delays T1 and T2 vary greatly depending on the viscosity of the liquid L, the flow path resistance of the flow paths 5 and 7 and the switching valve 6, the inner diameter of the syringe 9, and the like.

  FIG. 7 shows the flow of operation of the drive mechanism 4 controlled by the control device 16 when the liquid L is sucked into the internal space 10 of the syringe pump 3 (pressurized and introduced from the server tank 2) in this embodiment. Show. As shown in the figure, if the sensor 15 detects the rod 12 of the piston 11, the control device 16 reverses the motor 13 to retract the pusher 14, and the piston 11 retracts due to the pressure of the liquid L, so that the liquid It is possible to introduce L into the internal space 10.

  However, if the sensor 15 cannot detect the rod 12 of the piston 11, the control device 16 stops the rotation of the motor 13 and stops the pusher 14. The control device 16 measures the time from when the motor 13 is stopped until the sensor 15 detects the rod 12 of the piston 11. When the time until the sensor 15 detects the rod 12 is within a predetermined delay time T1 (for example, 3 seconds) corresponding to the delay time when the bubbles in FIG. 6 are not mixed, the motor 13 is reversed again. The pusher 14 is retracted by rotating to allow the piston 11 to be further retracted by the pressure of the liquid L.

  If the sensor 15 cannot re-detect the rod 12 within the grace period T1, there is a suspicion that there is a delay due to air bubbles mixing, so the control device 16 stops the operation of the drive mechanism 4 as abnormal suction, and for example, the control device 16 An abnormality is displayed on the display device provided in

  When the suction abnormality that the sensor 15 cannot re-detect the rod 12 for longer than the grace time T1 does not occur, the control device 16 detects that the pusher 14 has moved back to the end of the feed screw by a retract limit sensor (not shown). When this happens, stop the suction operation.

  In this way, the liquid supply apparatus 1 according to the present embodiment can prevent the risk of generating a defect in a subsequent process by supplying the liquid L mixed with bubbles.

  Moreover, in the liquid supply apparatus 1 of this embodiment, the control apparatus 16 may perform control as shown in FIG. In this control, if the sensor 15 cannot detect the rod 12, the control device 16 stops the rotation of the motor 13 and stops the pusher 14, and the time until the sensor 15 detects the rod 12 again is a grace period T1. Is within the same range as in the control of FIG.

  However, in this control, even when the sensor 15 cannot redetect the rod 12 within the delay time T1, the output of the sensor 15 is further monitored, and the pressure rise delay time when bubbles are mixed in FIG. If the sensor 15 can re-detect the rod 12 within the corresponding determination time T2 (for example, 10 seconds), the processing is stopped and a warning display indicating that air bubbles are mixed is displayed. When the determination time T2 elapses without the sensor 15 re-detecting the rod 12, the process is immediately stopped and a suction abnormality warning is displayed.

  As a result, the operator can know whether the cause of the operation stop is high that air bubbles are likely to be mixed in, or whether there is a high possibility of other mechanical troubles, and the trouble treatment can be performed efficiently. .

  In the present embodiment, when the liquid L is sucked into the syringe 9, the piston 11 moves backward while pressing the pusher 14. For this reason, the reaction force of the pusher 14 acts on the liquid L, and when the bubble B is mixed, the reaction force of the pusher 14 compresses the bubble B in advance. That is, the delay time of the backward movement of the piston 11 due to the contraction of the bubble B is shortened by the amount that the bubble B is compressed in advance, and the detection sensitivity of the bubble B is reduced.

  In order to solve this problem, when the liquid L is sucked into the syringe 9, first, the motor 13 is started with the switching valve 6 communicating the internal space 10 of the syringe 9 with the discharge flow path 8. It is effective to retract the pusher 14 and wait for the pusher 14 to move away from the rod 12 by about 1 to 3 mm, for example, and then operate the switching valve 6 to connect the internal space 10 to the suction flow path 5.

  In this way, when the bubble L is not mixed in the liquid L and the retreating speed of the piston 11 coincides with the retreating speed of the pusher 14, the piston 11 keeps a certain distance from the pusher 14 while keeping the pusher 14. You can retreat without receiving the reaction force.

  By preventing the piston 11 from receiving the reaction force of the pusher 14 when the piston 11 is retracted, it is possible to easily detect the delay in the retracting of the piston 11 when the bubbles B are mixed. For this purpose, the sensor 15 needs to be able to detect the rod 12 even when the pusher 14 is several mm away from the rod 12.

1 is a schematic view of a liquid supply apparatus according to one embodiment of the present invention. FIG. 2 is a detailed view of the syringe pump of FIG. 1. FIG. 3 is a detailed view showing when the piston of the syringe pump of FIG. 2 moves. FIG. 3 is a detailed view showing air bubbles mixed in the syringe pump of FIG. 2. The figure which shows the model of the pressure transmission of a viscous fluid. The figure which shows the change of the pressure in the model of FIG. 2 is a flowchart of a liquid suction operation in the liquid supply apparatus of FIG. FIG. 8 is a flowchart of an alternative liquid suction operation in FIG. 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid supply apparatus 2 Server tank 3 Syringe pump 4 Drive mechanism 5 Suction flow path 6 Switching valve 7 Shared flow path 8 Discharge flow path 9 Syringe 10 Internal space 11 Piston 12 Rod 13 Motor 14 Pusher 15 Sensor 16 Control apparatus 17 Feed screw

Claims (2)

A server tank capable of pressurizing the liquid to be stored;
An internal space is formed by the syringe and the piston, the piston is retracted by the pressure of the liquid, the liquid is introduced from the server tank into the internal space, and the liquid can be discharged from the internal space by the advance of the piston. A syringe pump,
A switching valve that communicates the internal space of the syringe pump with any one of a suction flow channel for introducing the liquid from the server tank into the internal space and a discharge flow channel for delivering the liquid to the outside;
A drive mechanism having a pusher that is movable in the forward and backward directions of the piston and capable of advancing the piston in contact with the outside of the piston;
A sensor for detecting that the piston is within a certain distance from the pusher;
When the pusher is retracted at a predetermined speed and the sensor cannot detect that the piston is within a certain distance from the pusher, the pusher is temporarily stopped, and the sensor is within a certain distance from the pusher. If the presence of the piston can be detected again within a predetermined grace period, the pusher is retracted again at the predetermined speed, and it is within the grace period that the sensor is within a certain distance from the pusher. And a control means for abnormally stopping the apparatus if it cannot be detected again . When the sensor detects that the piston is within a certain distance from the pusher after the grace period has elapsed and before a predetermined determination time has elapsed, the control means The liquid supply apparatus according to claim 1 , wherein it is determined that bubbles are mixed.

Images