JP2013060817A - Liquid feed pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable easy removal of air bubbles mixed into a pump chamber in a liquid feed pump driving a diaphragm by using a piezoelectric element.SOLUTION: The volume of the pump chamber is increased by applying a negative voltage to the piezoelectric element to contract the piezoelectric element, and decreased by releasing the applied negative voltage. When a fluid in the pump chamber is set to be pumped in this way, the volume of the pump chamber in the undeformed state (initial state) of the diaphragm can be indefinitely decreased. Thereby, since a location, in which the air bubbles are apt to be accumulated, in the pump chamber is set to be crushed in the initial state, the residence of the air bubbles in the pump chamber can be avoided.

Description

  The present invention relates to a liquid feed pump that pumps fluid.

  There is widely known a liquid feed pump that pumps a liquid in a pump chamber by forming a part of the pump chamber with a diaphragm and deforming the diaphragm with a piezoelectric element. In this liquid feed pump, when a positive voltage is applied to the piezoelectric element, the piezoelectric element expands to deform the diaphragm and reduce the volume of the pump chamber. As a result, the fluid in the pump chamber is pressurized and sent. When the applied voltage is removed and the piezoelectric element is returned to its original length, the diaphragm returns to its original shape and the volume of the pump chamber increases, and accordingly, liquid is supplied into the pump chamber. Thereafter, when a voltage is applied to the piezoelectric element again, the liquid supplied to the pump chamber is pressurized and fed.

  In such a liquid feed pump, when bubbles are mixed in the pump chamber, even if the diaphragm is deformed, the bubbles are crushed and it is difficult to pressurize the liquid, and the pump performance is lowered. Therefore, a technique (for example, Patent Document 1) has been proposed in which bubbles mixed into the pump chamber are sucked and removed together with the liquid in the pump chamber.

JP 2011-46015 A

  However, the liquid feed pump that drives the diaphragm using the piezoelectric element has a problem that it is difficult to remove bubbles mixed in the pump chamber. This is because a member having a relatively large area called a diaphragm is deformed by using an actuator with a small stroke called a piezoelectric element, so that a portion where the flow of liquid stagnates easily occurs in the peripheral portion of the pump chamber. Since the portion is fixed, once the bubbles are attached, it is difficult to remove the attached bubbles even if the diaphragm is driven.

  The present invention has been made to solve at least a part of the above-described problems of the prior art. In a liquid feed pump that drives a diaphragm using a piezoelectric element, it is easy to remove bubbles mixed in a pump chamber. The purpose is to provide removable technology.

In order to solve at least a part of the problems described above, the liquid feeding pump of the present invention employs the following configuration. That is,
A liquid feed pump that sucks fluid into the pump chamber by increasing the volume of the pump chamber and pumps the fluid in the pump chamber by decreasing the volume of the pump chamber,
A diaphragm for changing the volume of the pump chamber;
A piezoelectric element for deforming the diaphragm;
Voltage applying means for applying a voltage to the piezoelectric element;
With
The voltage applying means increases the volume of the pump chamber by applying a negative voltage to the piezoelectric element and contracting the piezoelectric element, and decreases the volume of the pump chamber by releasing the application of the negative voltage. It is a gist that it is a means to make it.

  In the liquid feed pump of the present invention having such a configuration, the negative voltage applied after the negative voltage is applied to the piezoelectric element is released to increase or decrease the volume of the pump chamber and pump the fluid from the pump chamber. Note that “releasing the application of the negative voltage” may cancel a part of the applied negative voltage. Therefore, it is not limited to completely canceling the applied negative voltage, but includes, for example, a case where most of the negative voltage is canceled (a little negative voltage is left).

  This will pump the fluid by reducing the volume of the pump chamber filled with fluid, and then increase the volume of the pump chamber to suck in the fluid rather than pumping the pumped fluid into the pump chamber. After that, the fluid that has been sucked in is pumped. Accordingly, the volume of the pump chamber in the initial state (before the operation of the liquid feed pump) does not affect the amount of fluid delivered, and thus the volume of the pump chamber in the initial state can be reduced as much as possible. For this reason, for example, if there is a place where bubbles easily accumulate in the pump chamber, the portion of the pump chamber can be crushed in the initial state. Of course, the entire pump chamber can be crushed. As a result, in the liquid feeding pump of the present invention, it is possible to avoid bubbles remaining in the pump chamber.

  In the liquid feed pump of the present invention described above, a laminated piezoelectric element may be used as the piezoelectric element that deforms the diaphragm. By doing so, it is possible to improve the fluid pressure-feeding capability by increasing the stroke of the piezoelectric element, so that a high-performance liquid-feeding pump can be realized.

  Moreover, the liquid feeding pump of this invention mentioned above can drive a diaphragm with a big force by using a piezoelectric element. Therefore, it can be suitably used as a liquid feed pump for pumping liquid.

It is sectional drawing which showed the structure of the liquid feeding pump of a present Example. It is explanatory drawing which showed the operation | movement in which a liquid feeding pump pumps a fluid. It is sectional drawing which showed the structure of the conventional liquid feeding pump.

Hereinafter, in order to clarify the contents of the present invention described above, examples will be described in the following order.
A. Structure of liquid pump:
B. Fluid pump operation:

A. Liquid feed pump configuration:
FIG. 1 is a cross-sectional view showing the structure of the liquid feed pump 100 of this embodiment. As shown in the figure, the liquid feed pump 100 of this embodiment is roughly composed of a piezoelectric element case 110 and a flow path block 120.

  A piezoelectric element 112 is housed inside the piezoelectric element case 110. The bottom surface of the piezoelectric element 112 is bonded to the bottom portion of the piezoelectric element case 110, and the reinforcing plate 114 is bonded to the upper surface of the piezoelectric element 112. The piezoelectric element 112 has a property of expanding and contracting according to a voltage value when a voltage is applied. The reinforcing plate 114 and the piezoelectric element case 110 are polished so that the upper surface of the reinforcing plate 114 and the upper surface of the piezoelectric element case 110 are in a surface position when no voltage is applied to the piezoelectric element 112. .

  Further, on the upper surfaces of the reinforcing plate 114 and the piezoelectric element case 110, a disk-shaped diaphragm 116 formed of a stainless steel thin plate is bonded to the reinforcing plate 114 and the piezoelectric element case 110, respectively.

  The flow path block 120 is placed on the upper surface of the piezoelectric element case 110 and firmly attached to the piezoelectric element case 110 by screws or the like. An outlet connection pipe 122 is erected on the left side surface of the flow path block 120 in the drawing. An outlet channel 123 is formed inside the outlet connection pipe 122, and the outlet channel 123 is open on the bottom side of the channel block 120. An inlet-side buffer chamber 124 is formed on the upper surface side of the flow path block 120 (the side opposite to the piezoelectric element case 110). A passage penetrating to the bottom surface side (piezoelectric element case 110 side) is formed in the central portion of the inlet side buffer chamber 124, and a check valve 121 is provided at a position where this passage opens to the bottom surface side of the flow path block 120. Is provided. Further, an inlet connecting pipe 125 is erected on the right side surface of the channel block 120 in the drawing, and an inlet channel 126 is formed inside the inlet connecting pipe 125. The side buffer chamber 124 is opened. The inlet connection pipe 125 is connected to a fluid supply source (not shown) via, for example, a tube.

B. Fluid pump operation:
FIG. 2 is an explanatory view showing an operation in which the liquid feed pump 100 pumps fluid. When starting fluid pumping, first, the piezoelectric element 112 is contracted by applying a negative voltage to draw the diaphragm 116 toward the piezoelectric element case 110, and the bottom surface of the flow path block 120 and the diaphragm 116. The volume of the space (pump chamber 130) is increased. Then, as shown in FIG. 2A, the pump chamber 130, the inlet side buffer chamber 124, the inlet channel 126, and the outlet channel 123 are all filled with fluid.

  Thereafter, when the negative charge applied to the piezoelectric element 112 is removed, the piezoelectric element 112 returns to its original length and the diaphragm 116 attempts to return to its original shape as shown in FIG. The fluid in the pump chamber 130 is pressurized. Here, since the check valve 121 is provided between the pump chamber 130 and the inlet side buffer chamber 124, the fluid in the pump chamber 130 does not flow back into the inlet side buffer chamber 124. As a result, the fluid pressurized by the diaphragm 116 is pushed out from the outlet channel 123.

  Subsequently, as shown in FIG. 2C, when a negative voltage is applied to the piezoelectric element 112, the piezoelectric element 112 contracts, the volume of the pump chamber 130 increases, and the pump chamber 130 becomes negative pressure. This negative pressure acts in the direction in which the fluid (inlet side fluid) in the inlet side buffer chamber 124 is sucked into the pump chamber 130 and at the same time in the direction in which the fluid (outlet side fluid) in the outlet channel 123 is sucked. Works. However, in reality, the fluid on the outlet side is hardly sucked, and the fluid on the inlet side is sucked into the pump chamber 130 as shown in FIG. This is because, compared to the inertance of the outlet-side channel (exit channel 123), the inlet-side channel (the passage part penetrating from the inlet-side buffer chamber 124 and the inlet-side buffer chamber 124 to the bottom surface side of the channel block 120) ) Because the inertance is significantly smaller.

Here, inertance is a characteristic value of the flow path, and indicates the ease of fluid flow when the fluid in the flow path is about to flow when pressure is applied to one end of the flow path. For example, in the simplest case, a fluid having a density ρ (here, a liquid) is filled in a channel having a cross-sectional area S and a length L, and a pressure P (exactly, It is assumed that a pressure difference P) at both ends is added. A force of pressure P × cross-sectional area S acts on the fluid in the channel, and as a result, the fluid in the channel flows out. If the acceleration of the fluid at that time is a, the mass of the fluid in the flow path is density ρ × cross-sectional area S × length L.
P = ρ × L × a (1)
Is obtained. Furthermore, when the volume flow rate flowing through the flow path is Q and the flow velocity of the fluid flowing through the flow path is v,
Q = v × S So
dQ / dt = a × S (2)
Holds. Substituting equation (2) into equation (1),
P = (ρ × L / S) × (dQ / dt) (3)
It becomes. This equation is an equation representing the equation of motion of the fluid in the flow path using the pressure P applied to one end of the flow path (more precisely, the pressure difference at both ends) and dQ / dt. Equation (3) indicates that if the same pressure P is applied, dQ / dt increases (that is, the flow velocity changes greatly) as (ρ × L / S) decreases. This (ρ × L / S) is a value called inertance.

  In the liquid feed pump 100 of the present embodiment, the inertance of the outlet channel 123 has a large value because the inner diameter is small and the passage length is long. On the other hand, the inertance of the flow path on the inlet side of the pump chamber 130 has a small value because the length of the passage portion penetrating from the inlet side buffer chamber 124 to the bottom surface side of the flow path block 120 is short. For this reason, when the pump chamber 130 has a negative pressure, the liquid on the outlet side with a large synthetic inertance is hardly sucked, and the liquid on the inlet side with a small synthetic inertance is sucked into the pump chamber 130 exclusively.

  When the fluid is sucked into the pump chamber 130 in this way, the negative voltage applied to the piezoelectric element 112 is removed, and the diaphragm 116 is returned to its original shape, thereby pushing out the fluid in the pump chamber 130 from the outlet flow path 123 and then the piezoelectric element. By applying a negative voltage again to the element 112, the fluid is sucked into the pump chamber 130. In this way, applying a negative voltage to the piezoelectric element 112 and removing the applied negative voltage are repeated, and the operation of pushing the fluid sucked into the pump chamber 130 from the inlet-side channel into the outlet-side channel is repeated. Thus, the fluid is pumped.

  In the liquid feed pump 100 of this embodiment that pumps the fluid in this manner, the volume of the pump chamber 130 is increased to suck the fluid into the pump chamber 130, and then the pumped fluid is pumped from the pump chamber 130. . Therefore, since the volume of the pump chamber 130 before the fluid is sucked (initial state) does not affect the amount of fluid delivered, the volume of the pump chamber 130 in the initial state can be reduced as much as possible. For this reason, for example, the volume of the pump chamber 130 in the initial state can be made almost zero, so that even when bubbles are mixed in the pump chamber 130, it is avoided that bubbles remain in the pump chamber 130. Can do. As a result, when the diaphragm 116 is returned to its original shape, it can be avoided that the bubbles in the pump chamber 130 are crushed and it is difficult to pressurize the fluid. It is possible to maintain the ability to pump.

  FIG. 3 is a cross-sectional view showing the structure of a conventional liquid feed pump 300. As shown in FIG. 3A, in the conventional liquid feed pump 300, a pump chamber 330 is formed above the diaphragm 316, and a positive voltage is applied to the piezoelectric element 312 to extend the piezoelectric element 312. Therefore, the fluid in the pump chamber 330 is pressurized. Further, when the positive voltage applied to the piezoelectric element 312 is removed and the piezoelectric element 312 is returned to its original length, fluid is supplied from the inlet side buffer chamber 324 to the pump chamber 330.

  In such a conventional liquid feed pump 300, even if the piezoelectric element 312 is extended to deform the diaphragm 316, a region that cannot be crushed by the diaphragm 316 is generated in the peripheral portion of the pump chamber 330 (FIG. 3B). See). If bubbles enter such a portion, it is difficult to expel the bubbles no matter how much the diaphragm 316 is deformed. On the other hand, such a portion does not occur in the liquid feed pump 100 of the present embodiment. As a result, it is possible to reliably avoid the bubbles from staying in the pump chamber 130 and the pump performance from deteriorating.

  Further, in the liquid feed pump 100 of the present embodiment, a very slight gap is formed between the upper surface of the diaphragm 116 and the bottom surface of the flow path block 120 in a state where no voltage is applied to the piezoelectric element 112. (See FIG. 1). Therefore, every time the diaphragm 116 returns to its original shape while the fluid is being pumped, the bottom surface of the flow path block 120 and the diaphragm 116 do not contact each other, and it is possible to prevent the diaphragm 116 from being deteriorated by the contact. .

  Although various embodiments have been described above, the present invention is not limited to all the above embodiments, and can be implemented in various modes without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 100 ... Liquid feed pump, 110 ... Piezoelectric element case, 112 ... Piezoelectric element,
116 ... Diaphragm, 120 ... Channel block, 121 ... Check valve,
122: outlet connection pipe, 123: outlet channel, 124: inlet side buffer chamber,
125 ... Inlet connection pipe, 126 ... Inlet flow path, 127 ... Recess,
130 ... Pump chamber, 300 ... Liquid feed pump, 312 ... Piezoelectric element,
316 ... Diaphragm, 320 ... Channel block, 323 ... Outlet channel,
324 ... Inlet side buffer chamber, 330 ... Pump chamber

Claims (3)

A liquid feed pump that sucks fluid into the pump chamber by increasing the volume of the pump chamber and pumps the fluid in the pump chamber by decreasing the volume of the pump chamber,
A diaphragm for changing the volume of the pump chamber;
A piezoelectric element for deforming the diaphragm;
Voltage applying means for applying a voltage to the piezoelectric element;
With
The voltage applying means increases the volume of the pump chamber by applying a negative voltage to the piezoelectric element and contracting the piezoelectric element, and decreases the volume of the pump chamber by releasing the application of the negative voltage. A liquid feed pump that is a means to make   The liquid feeding pump according to claim 1, wherein the piezoelectric element is a laminated piezoelectric element.   The liquid feeding pump according to claim 1, wherein the fluid is a liquid.

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