Patent Publication Number: US-11391277-B2

Title: Pump and fluid control device

Description:
This is a continuation of International Application No. PCT/JP2018/041611 filed on Nov. 9, 2018 which claims priority from Japanese Patent Application No. 2018-001965 filed on Jan. 10, 2018. The contents of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The present disclosure relates to a positive displacement pump using flexural vibration of a diaphragm and a fluid control device including the same, and more particularly to a piezoelectric pump using a piezoelectric element as a driving member for driving the diaphragm and a fluid control device including the same. 
     Description of the Related Art 
     A piezoelectric pump which is a type of a positive displacement pump has been known. In a piezoelectric pump, at least part of a pump chamber is formed by a diaphragm to which a piezoelectric element is attached, and an AC voltage having a predetermined frequency is applied to the piezoelectric element to drive the diaphragm at a resonant frequency, thereby causing pressure change in the pump chamber to enable a fluid to be suctioned and discharged. 
     An example of configuration of a piezoelectric pump is disclosed in International Publication No. 2016-013390 (Patent Document 1), for example. In the piezoelectric pump disclosed in Patent Document 1, a pump chamber is formed by diaphragms disposed facing each other and constituting a pair, and a piezoelectric element is attached to one of the diaphragms constituting the pair. 
     In the piezoelectric pump disclosed in Patent Document 1, in the diaphragms constituting the pair, provided is one hole portion to which a check valve is provided in a central region of the diaphragm without the piezoelectric element attached thereto, and provided are hole portions arranged in an annular shape with an interval therebetween in an intermediate region excluding a central region and a peripheral region of the other diaphragm with the piezoelectric element attached thereto. 
     In an embodiment of the piezoelectric pump disclosed in Patent Document 1, the check valve is provided to each of the hole portions arranged in an annular shape with an interval therebetween, and in another embodiment of the piezoelectric pump, the check valve is not provided to each of the hole portions. 
     In the piezoelectric pump according to any one of the embodiments described above, a pump function is achieved as follows. The diaphragms constituting the pair are caused to perform flexural vibration to be displaced in opposite directions by a piezoelectric element and pressure changes thus occur in a pump chamber. Due to the pressure changes in the pump chamber, fluid positioned outside the pump chamber is suctioned through hole portions provided to the diaphragm with the piezoelectric element attached thereto, and then the fluid is discharged through one hole portion provided to the diaphragm without the piezoelectric element attached thereto. 
     Patent Document 1: International Publication No. 2016-013390 
     BRIEF SUMMARY OF THE DISCLOSURE 
     Here, in the hole portion to which the check valve is provided, a flow path resistance becomes larger as the flow path becomes narrower than the hole portion to which the check valve is not provided. Therefore, as in the piezoelectric pump disclosed in Patent Document 1, when the hole portion with the check valve is provided in the central region of the diaphragm, an overall flow rate of the piezoelectric pump is determined by the hole portion, and therefore there arises a limitation in increasing the flow rate. 
     In a configuration in which the hole portions with the check valve are simply provided in the intermediate region excluding the central region and the peripheral region of the diaphragm in order to avoid the problem above, the flow path resistance is greatly reduced. However, an amount of displacement of the diaphragm in motion in the intermediate region is smaller than that in the central region, and therefore there arises a problem that an action of opening and closing of the check valve is not sufficient. Therefore, when the configuration above is adopted, also, it is difficult to increase the overall flow rate of the piezoelectric pump. 
     The present disclosure has been made in light of the aforementioned problem, and it is an object of the present disclosure to increase a flow rate in a positive displacement pump using flexural vibration of a diaphragm and in a fluid control device including the same, in comparison with the related art. 
     A pump according to the present disclosure includes a first plate member, a second plate member, a third plate member, a first circumferential wall member, a second circumferential wall member, a first pump chamber, a second pump chamber, and a driving member. The second plate member faces the first plate member. The third plate member is positioned on a side opposite from a side where the second plate member is positioned when viewed from the first plate member, and the third plate member faces the first plate member. The first circumferential wall member connects the peripheral region of the first plate member and the peripheral region of the second plate member. The second circumferential wall member connects the peripheral region of the first plate member and the peripheral region of the third plate member. The first pump chamber is positioned between the first plate member and the second plate member, and is formed by the first plate member, the second plate member and the first circumferential wall member. The second pump chamber is positioned between the first plate member and the third plate member, and is formed by the first plate member, the third plate member and the second circumferential wall member. The driving member causes a pressure change in both of the first pump chamber and the second pump chamber by causing the first plate member to perform flexural vibration. The first plate member is provided with two or more first hole portions to which a check valve is provided respectively, and each of the two or more first hole portions is arranged in a region not overlapping an axial line when viewed in an extending direction of the axial line orthogonal to a central region of the first plate member. In the second plate member, one or two or more second hole portions are provided, and in the third plate member, one or two or more third hole portions are provided. A check valve is provided to at least either of the one or the two or more second hole portions, or the one or the two or more third hole portions. 
     In the pump according to the present disclosure, the driving member may cause the first plate member to perform flexural vibration so that a standing wave is generated in the first plate member around the axial line and an antinode of vibration is formed in the central region of the first plate member. In this case, it is preferable that each of the two or more first hole portions be arranged in a region not overlapping a node of vibration formed in the first plate member. 
     In the pump according to the present disclosure, it is preferable that the two or more first hole portions be arranged with an interval therebetween in a position on a circumference around the axial line when viewed in the extending direction of the axial line. 
     In the pump according to the present disclosure, it is preferable that a distance between adjacent first hole portions among the two or more first hole portions be smaller than a distance between the axial line and each of the two or more first hole portions. 
     In the pump according to the present disclosure, the first plate member may be caused to perform flexural vibration by the driving member such that an antinode of vibration is further formed at a position excluding the central region of the first plate member. 
     In the pump according to the present disclosure, it is preferable that at least one of the two or more first hole portions be arranged in a region overlapping the antinode of vibration formed at a position excluding the central region of the first plate member. 
     In the pump according to the present disclosure, it is more preferable that each of the two or more first hole portions be arranged in the region overlapping the antinode of vibration formed at the position excluding the central region of the first plate member. 
     In the pump according to the present disclosure, each of the two or more first hole portions may be arranged in a region outside a node of vibration formed at a position farthest from the central region of the first plate member among nodes of vibration formed in a region excluding the peripheral region of the first plate member. 
     In the pump according to the present disclosure, when a check valve is attached to the one or the two or more second hole portions, it is preferable that the one or the two or more second hole portions be arranged in a region not overlapping the node of vibration formed in the first plate member when viewed in the extending direction of the axial line. 
     In the pump according to the present disclosure, when the check valve is provided to the one or the two or more second hole portions, it is more preferable that the one or the two or more second hole portions be arranged in a region overlapping the antinode of vibration formed at a position excluding the central region of the first plate member when viewed in the extending direction of the axial line. 
     In the pump according to the present disclosure, when the check valve is provided to the one or the two or more third hole portions, it is preferable that the one or the two or more third hole portions be arranged in a region not overlapping the node of vibration formed in the first plate member when viewed in the extending direction of the axial line. 
     In the pump according to the present disclosure, when the check valve is provide to the one or the two or more third hole portions, it is more preferable that the one or the two or more third hole portions be arranged in a region overlapping the antinode of vibration formed at a position excluding the central region of the first plate member when viewed in the extending direction of the axial line. 
     In a first aspect and a second aspect of the pump according to the present disclosure, the driving member causes the first plate member to perform flexural vibration such that a standing wave is generated in the first plate member around the axial line and an antinode of vibration is formed in the central region of the first plate member, each of the two or more first hole portions is arranged in a region not overlapping a node of vibration formed in the first plate member, and the two or more second hole portions are provided and the check valve is provided to each of the two or more second hole portions. The two or more first hole portions are arranged with an interval therebetween in a position on a circumference around the axial line when viewed in the extending direction of the axial line, and the two or more second hole portions are arranged with an interval therebetween in a position on a circumference around the axial line when viewed in the extending direction of the axial line. 
     In the first aspect, the first plate member may be caused to perform flexural vibration by the driving member such that an antinode of vibration is further formed at a position excluding the central region of the first plate member. In this case, it is preferable that the two or more second hole portions be arranged in a region not overlapping the node of vibration formed in the first plate member when viewed in the extending direction of the axial line. 
     In the first aspect, it is more preferable that each of the two or more first hole portions be arranged in a region overlapping the antinode of vibration formed at the position excluding the central region of the first plate member. Further, it is more preferable that each of the two or more second hole portions be arranged in a region overlapping the antinode of vibration formed in the first plate member when viewed in the extending direction of the axial line. 
     In the first aspect, it is preferable that the total number of the two or more second hole portions be smaller than the total number of the two or more first hole portions. 
     In the second aspect, the two or more third hole portions are provided, and the check valve is provided to each of the two or more third hole portions. The two or more third hole portions are arranged with an interval therebetween in a position on a circumference around the axial line when viewed in the extending direction of the axial line. 
     In the second aspect, the first plate member may be caused to perform flexural vibration by the driving member such that the antinode of vibration is further formed at a position excluding the central region of the first plate member. In this case, it is preferable that the two or more second hole portions be arranged in a region not overlapping the node of vibration formed in the first plate member when viewed in the extending direction of the axial line, and it is preferable that the two or more third hole portions be arranged in a region not overlapping the node of vibration formed in the first plate member when viewed in the extending direction of the axial line. 
     In the second aspect, it is more preferable that each of the two or more first hole portions be arranged in a region overlapping the antinode of vibration formed at the position excluding the central region of the first plate member. Further, it is more preferable that each of the two or more second hole portions be arranged in a region overlapping the antinode of vibration formed in the first plate member when viewed in the extending direction of the axial line, and it is more preferable that each of the two or more third hole portions be arranged in a region overlapping the antinode of vibration formed in the first plate member when viewed in the extending direction of the axial line. 
     In the second aspect, it is preferable that the total number of the two or more second hole portions be smaller than the total number of the two or more first hole portions, and that the total number of the two or more third hole portions be smaller than the total number of the two or more first hole portions. 
     In the first aspect and the second aspect, the driving member may cause the second plate member to perform flexural vibration such that a standing wave is generated in the second plate member around the axial line and the antinode of vibration is formed in the central region of the second plate member, and the driving member also may cause the third plate member to perform flexural vibration such that a standing wave is generated in the third plate member around the axial line and an antinode of vibration is formed in a central region of the third plate member. 
     In the pump according to the present disclosure, it is preferable that a hole other than the two or more first hole portions, the one or the two or more second hole portions, and the one or the two or more third hole portions be not provided in any of the first plate member, the second plate member, the third plate member, the first circumferential wall member, and the second circumferential wall member. 
     In the pump according to the present disclosure, the driving member may include a piezoelectric element having a substantially flat plate shape, and in this case, it is preferable that the piezoelectric element be attached to the central region of the first plate member. 
     In the pump according to the present disclosure, it is preferable that any of each of the two or more first hole portions be arranged outside relative to the piezoelectric element when viewed in the extending direction of the axial line. 
     The fluid control device according to the present disclosure is provided with the pump according to the present disclosure. 
     According to the present disclosure, in the positive displacement pump using flexural vibration of a diaphragm and the fluid control device including the same, an increase in the flow rate can be achieved in comparison with the related art. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of a piezoelectric blower according to Embodiment 1. 
         FIG. 2  is an exploded perspective view of the piezoelectric blower illustrated in  FIG. 1 . 
       Each of  FIGS. 3A, 3B and 3C  is a schematic diagram describing a configuration of a driving unit in the piezoelectric blower illustrated in  FIG. 1 , an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber. 
       Each of  FIGS. 4A and 4B  is a schematic diagram describing an operation status of the driving unit in the piezoelectric blower illustrated in  FIG. 1  and the direction of the gas flow generated in each status over time. 
         FIG. 5  is a plan view of a first diaphragm illustrated in  FIG. 1 . 
         FIG. 6  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower and an approximate direction of a gas flow generated during operation according to Modification 1. 
         FIG. 7  is an exploded perspective view of a piezoelectric blower according to Modification 2. 
       Each of  FIGS. 8A, 8B and 8C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 2. 
       Each of  FIGS. 9A, 9B and 9C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 3. 
       Each of  FIGS. 10A, 10B and 10C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 4. 
       Each of  FIGS. 11A, 11B and 11C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 5. 
       Each of  FIGS. 12A, 12B and 12C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 6. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The following embodiments exemplify a case where the present disclosure is applied to a piezoelectric blower as a pump for suctioning and discharging of gas. In the following embodiments, the same or common portions are denoted by the same reference numerals, and the description thereof will not be repeated. 
     Embodiment 1 
       FIG. 1  is a schematic sectional view of a piezoelectric blower according to Embodiment 1 of the present disclosure, and  FIG. 2  is an exploded perspective view of the piezoelectric blower illustrated in  FIG. 1 . First, the configuration of a piezoelectric blower  1 A according to the present embodiment will be described with reference to  FIG. 1  and  FIG. 2 . 
     As illustrated in  FIG. 1  and  FIG. 2 , the piezoelectric blower  1 A according to the present embodiment mainly includes a case  10  and a driving unit  20 A. A housing space  13 , which is a flat substantially cylindrical space, is provided inside the case  10 , and the driving unit  20 A is disposed therein. 
     The case  10  has a disk shaped first case member  11  made of resin, metal or the like, and a bottomed substantially cylindrical shaped second case member  12  made of resin or metal. The first case member  11  and the second case member  12  are combined and bonded to each other by such as an adhesive or the like to make the case  10 , and the case  10  includes the housing space  13  therein. 
     In a central region of the first case member  11  and in a central region of the second case member  12 , a first nozzle portion  14  and a second nozzle portion  15  projecting outward are provided, respectively. A space outside the piezoelectric blower  1 A and the housing space  13  communicate with each other through the first nozzle portion  14  and the second nozzle portion  15 . 
     The driving unit  20 A mainly includes a first diaphragm  30  as a first plate member, a second diaphragm  40  as a second plate member, a third diaphragm  50  as a third plate member, a first spacer  60 A as a first circumferential wall member, a second spacer  60 B as a second circumferential wall member, a first valve supporting member  70 A, a second valve supporting member  70 B, a third valve supporting member  70 C, a first check valve  80 A, a second check valve  80 B, a third check valve  80 C, and a piezoelectric element  90  as a driving member. The driving unit  20 A is configured by integrating the members described above in a state in which the members of the driving unit  20 A are stacked one another, disposed in the housing space  13  of the case  10 , and supported by the case  10 . The housing space  13  of the case  10  is partitioned into a space on the first nozzle portion  14  side and a space on the second nozzle portion  15  side by the driving unit  20 A. 
     The first diaphragm  30  is formed of a metal thin plate made of such as stainless steel or the like, and has a substantially circular outer shape in a plan view. The outermost end of a peripheral region of the first diaphragm  30  is bonded to the case  10  by such as an adhesive or the like. First hole portions  31  are arranged in an annular shape with an interval therebetween in an intermediate region excluding the central region and the peripheral region of the first diaphragm  30 . 
     The second diaphragm  40  faces the first diaphragm  30 , and more specifically, is disposed on a side where the first case member  11  is positioned when viewed from the first diaphragm  30 . The second diaphragm  40  is formed of a metal thin plate made of such as stainless steel or the like, and has a substantially circular outer shape in a plan view. Second hole portions  41  are arranged in an annular shape with an interval therebetween in the intermediate region excluding the central region and the peripheral region of the second diaphragm  40 . 
     The third diaphragm  50  faces the first diaphragm  30 , and more specifically, is disposed on a side where the second case member  12  is positioned when viewed from the first diaphragm  30  (that is, opposite to the side where the second diaphragm  40  is positioned when viewed from the first diaphragm  30 ). The third diaphragm  50  is formed of a metal thin plate made of such as stainless steel or the like, and has a substantially circular outer shape in a plan view. Third hole portions  51  are arranged in an annular shape with an interval therebetween in the intermediate region excluding the central region and the peripheral region of the third diaphragm  50 . 
     The first spacer  60 A is positioned between the first diaphragm  30  and the second diaphragm  40 , and is sandwiched by the first diaphragm  30  and the second diaphragm  40 . The first spacer  60 A is formed of a metal member made of such as stainless steel or the like, and has a substantially annular plate outer shape. 
     The first spacer  60 A connects the peripheral region excluding the outermost end of the first diaphragm  30  and the peripheral region of the second diaphragm  40 . Thus, the first diaphragm  30  and the second diaphragm  40  are placed with a predetermined distance determined by the first spacer  60 A. The first spacer  60 A and the first diaphragm  30  are bonded by such as an adhesive or the like, and the first spacer  60 A and the second diaphragm  40  are bonded by such as an adhesive or the like. 
     A space positioned between the first diaphragm  30  and the second diaphragm  40  functions as a first pump chamber  21 . The first pump chamber  21  is formed by the first diaphragm  30 , the second diaphragm  40 , and the first spacer  60 A, and is configured with a flat substantially cylindrical space. Here, the first spacer  60 A corresponds to a circumferential wall member forming the first pump chamber  21  and connecting the first diaphragm  30  and the second diaphragm  40 . 
     The second spacer  60 B is positioned between the first diaphragm  30  and the third diaphragm  50 , and is sandwiched by the first diaphragm  30  and the third diaphragm  50 . The second spacer  60 B is formed of a metal member made of such as stainless steel or the like, and has a substantially annular plate outer shape. 
     The second spacer  60 B connects the peripheral region excluding the outermost end of the first diaphragm  30  and the peripheral region of the third diaphragm  50 . Thus, the first diaphragm  30  and the third diaphragm  50  are placed with a predetermined distance determined by the second spacer  60 B. The second spacer  60 B and the first diaphragm  30  are bonded by such as an adhesive or the like, and the second spacer  60 B and the third diaphragm  50  are bonded by such as an adhesive or the like. 
     A space positioned between the first diaphragm  30  and the third diaphragm  50  functions as a second pump chamber  22 . The second pump chamber  22  is formed by the first diaphragm  30 , the third diaphragm  50 , and the second spacer  60 B, and is configured with a flat substantially cylindrical space. Here, the second spacer  60 B corresponds to the circumferential wall member forming the second pump chamber  22  and connecting the first diaphragm  30  and the third diaphragm  50 . 
     The first valve supporting member  70 A is attached to the central region of the first diaphragm  30  by such as an adhesive or the like, and more specifically, the first valve supporting member  70 A is disposed on a side where the third diaphragm  50  is positioned when viewed from the first diaphragm  30 . The first valve supporting member  70 A is formed of a metal thin plate made of such as stainless steel or the like, and has a substantially circular outer shape in a plan view. The first valve supporting member  70 A includes a first annular step portion  71   a  that recedes in a direction apart from the first diaphragm  30  on the peripheral region of a main surface positioned on the first diaphragm  30  side, and the first annular step portion  71   a  faces the first hole portions  31  provided to the first diaphragm  30 . 
     The first check valve  80 A is formed of a member made of resin such as polyimide resin or the like, and has a substantially annular plate outer shape. The first check valve  80 A is loosely fitted to the first annular step portion  71   a  of the first valve supporting member  70 A to be housed in the first annular step portion  71   a . That is, the first check valve  80 A is positioned between the first annular step portion  71   a  of the first valve supporting member  70 A and a portion of the first diaphragm  30  facing the first annular step portion  71   a.    
     Thus, the first check valve  80 A is movably supported by the first valve supporting member  70 A such that the first check valve  80 A is able to open and close the first hole portions  31  provided to the first diaphragm  30 . More specifically, the first check valve  80 A closes the first hole portions  31  in a state that the first check valve  80 A moves in proximity to and is in close contact with the first diaphragm  30 , and opens the first hole portions  31  in a state that the first check valve  80 A is moved away from the first diaphragm  30 . 
     The second valve supporting member  70 B is attached to the central region of the second diaphragm  40  by such as an adhesive or the like, and more specifically, the second valve supporting member  70 B is disposed on a side where the first diaphragm  30  is positioned when viewed from the second diaphragm  40 . The second valve supporting member  70 B is formed of a metal thin plate made of such as stainless steel or the like, and has a substantially circular outer shape in a plan view. The second valve supporting member  70 B includes a second annular step portion  71   b  that recedes in a direction apart from the second diaphragm  40  on the peripheral region of a main surface positioned on the second diaphragm  40  side, and the second annular step portion  71   b  faces the second hole portions  41  provided to the second diaphragm  40 . 
     The second check valve  80 B is formed of a member made of resin such as polyimide resin or the like, and has a substantially annular plate outer shape. The second check valve  80 B is loosely fitted to the second annular step portion  71   b  of the second valve supporting member  70 B to be housed in the second annular step portion  71   b . That is, the second check valve  80 B is positioned between the second annular step portion  71   b  of the second valve supporting member  70 B and a portion of the second diaphragm  40  facing the second annular step portion  71   b.    
     Thus, the second check valve  80 B is movably supported by the second valve supporting member  70 B such that the second check valve  80 B is able to open and close the second hole portions  41  provided to the second diaphragm  40 . More specifically, the second check valve  80 B closes the second hole portions  41  in a state that the second check valve  80 B moves in proximity to and is in close contact with the second diaphragm  40 , and opens the second hole portions  41  in a state that the second check valve  80 B is moved away from the second diaphragm  40 . 
     The third valve supporting member  70 C is attached to the central region of the third diaphragm  50  by such as an adhesive or the like, and more specifically, the third valve supporting member  70 C is disposed on a side opposite to a side where the first diaphragm  30  is positioned when viewed from the third diaphragm  50 . The third valve supporting member  70 C is formed of a metal thin plate made of such as stainless steel or the like, and has a substantially circular outer shape in a plan view. The third valve supporting member  70 C includes a third annular step portion  71   c  that recedes in a direction apart from the third diaphragm  50  on the peripheral region of a main surface positioned on the third diaphragm  50  side, and the third annular step portion  71   c  faces the third hole portions  51  provided to the third diaphragm  50 . 
     The third check valve  80 C is formed of a member made of resin such as polyimide resin or the like, and has a substantially annular plate outer shape. The third check valve  80 C is loosely fitted to the third annular step portion  71   c  of the third valve supporting member  70 C to be housed in the third annular step portion  71   c . That is, the third check valve  80 C is positioned between the third annular step portion  71   c  of the third valve supporting member  70 C and a portion of the third diaphragm  50  facing the third annular step portion  71   c.    
     Thus, the third check valve  80 C is movably supported by the third valve supporting member  70 C such that the third check valve  80 C is able to open and close the third hole portions  51  provided to the third diaphragm  50 . More specifically, the third check valve  80 C closes the third hole portions  51  in a state that the third check valve  80 C moves in proximity to and is in close contact with the third diaphragm  50 , and opens the third hole portions  51  in a state that the third check valve  80 C is moved away from the third diaphragm  50 . 
     The piezoelectric element  90  is attached to the first valve supporting member  70 A with such as an adhesive or the like, and consequently the piezoelectric element  90  is attached to the central region of the first diaphragm  30  with the first valve supporting member  70 A interposed therebetween. Thus, the piezoelectric element  90  is attached to the main surface side positioned on a side facing the second pump chamber  22  of the first diaphragm  30 . The piezoelectric element  90  is formed of a thin plate made of a piezoelectric material such as lead zirconate titanate (PZT) or the like, and has a substantially circular outer shape in a plan view. 
     The piezoelectric element  90  performs flexural vibration by application of an AC voltage, and the flexural vibration generated in the piezoelectric element  90  is propagated to the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50 , so that the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50  also perform flexural vibration. That is, the piezoelectric element  90  corresponds to the driving member for causing flexural vibration in the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50 , and when an AC voltage with a predetermined frequency is applied to the piezoelectric element  90 , the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50  are respectively caused to vibrate at resonant frequency, thereby generating standing waves in the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50 , respectively. 
     Here, the piezoelectric element  90  does not necessarily have a substantially circular shape in a plan view, and may have a substantially regular polygonal shape in a plan view. When the piezoelectric element  90  has a substantially circular shape or a substantially regular polygonal shape in a plan view, it is preferable that the first diaphragm  30  and the piezoelectric element  90  be arranged such that a center of the first diaphragm  30  and a center of the piezoelectric element  90  coincide with each other. With the configuration above, the standing wave can more reliably and easily be generated in the first diaphragm  30 . 
     With having the configuration above, in the piezoelectric blower  1 A according to the present embodiment, the first pump chamber  21  and the second pump chamber  22  are positioned between the first nozzle portion  14  and the second nozzle portion  15 . Of the housing space  13  of the case  10 , a space, which is closer to the first nozzle portion  14  side than a position where the first pump chamber  21  is provided, and the first pump chamber  21  communicate through the second hole portions  41  in a state that the second hole portions  41  provided to the second diaphragm  40  is not closed by the second check valve  80 B. Of the housing space  13  of the case  10 , a space, which is closer to the second nozzle portion  15  side than a position where the second pump chamber  22  is provided, and the second pump chamber  22  communicate through the third hole portions  51  in a state that the third hole portions  51  provided to the third diaphragm  50  is not closed by the third check valve  80 C. Further, the first pump chamber  21  and the second pump chamber  22  communicate with each other through the first hole portions  31  in a state that the first hole portions  31  provided to the first diaphragm  30  is not closed by the first check valve  80 A. 
     In the piezoelectric blower  1 A according to the present embodiment, the piezoelectric element  90  causes the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50  to perform flexural vibration such that standing waves are generated in the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50 , respectively, around an axial line  100  orthogonal to a central region of the first diaphragm  30 , a central region of the second diaphragm  40 , and a central region of the third diaphragm  50 . More specifically, the piezoelectric element  90  causes the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50  to perform flexural vibration such that the antinode of vibration is formed in the central region of the first diaphragm  30 , the central region of the second diaphragm  40 , and the central region of the third diaphragm  50  respectively, and such that the antinode of vibration is also formed at a position excluding the central region of the first diaphragm  30 , a position excluding the central region of the second diaphragm  40 , and a position excluding the central region of the third diaphragm  50 . In the piezoelectric blower  1 A according to the present embodiment, the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50  are driven such that the one antinode of vibration is respectively formed in a radial direction at a position excluding the central region of each diaphragm. 
     The piezoelectric element  90  directly drives the first diaphragm  30  to which the piezoelectric element  90  is attached. The piezoelectric element  90  indirectly drives the second diaphragm  40  and the third diaphragm  50  to which the piezoelectric element  90  is not attached through the first spacer  60 A as the first circumferential wall member and the second spacer  60 B as the second circumferential wall member. At this time, with an appropriate design of a shape of the first diaphragm  30  and a shape of the second diaphragm  40  (in particular, thickness of diaphragms), the first diaphragm  30  and the second diaphragm  40  are respectively displaced in opposite directions. Similarly, with an appropriate design of a shape of the first diaphragm  30  and a shape of the third diaphragm  50  (in particular, thickness of diaphragms), the first diaphragm  30  and the third diaphragm  50  are respectively displaced in opposite directions. 
     The first pump chamber  21  repeats expansion and contraction due to the vibration of the first diaphragm  30  and the second diaphragm  40  in opposite directions, and the second pump chamber  22  repeats expansion and contraction due to the vibration of the first diaphragm  30  and the third diaphragm  50  in opposite directions. As the result, resonance occurs inside the first pump chamber  21  and inside the second pump chamber  22  respectively, so that a large pressure change occurs in each of the first pump chamber  21  and the second pump chamber  22 . Thus, positive pressure and negative pressure are generated in the first pump chamber  21  and the second pump chamber  22  alternately in terms of time, and a pump function of pressure feed of gas is realized by the pressure change. 
     Each of  FIGS. 3A, 3B and 3C  is a schematic diagram describing a configuration of the driving unit in the piezoelectric blower illustrated in  FIG. 1 , an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber. Each of  FIGS. 4A and 4B  is a schematic diagram describing an operation status of the driving unit in the piezoelectric blower illustrated in  FIG. 1  and a direction of a gas flow generated in each status over time. Next, the operation status of the piezoelectric blower  1 A according to the present embodiment will be described in detail with reference to  FIGS. 3A, 3B and 3C , and  FIGS. 4A  and  4 B. 
     As described in  FIGS. 3A, 3B and 3C , in the piezoelectric blower  1 A according to the present embodiment, the first check valve  80 A is provided to each of the first hole portions  31  provided to the first diaphragm  30 , the second check valve  80 B is provided to each of the second hole portions  41  provided to the second diaphragm  40 , and the third check valve  80 C is provided to each of the third hole portions  51  provided to the third diaphragm  50  as described above. 
     Here, the first check valve  80 A provided to each of the first hole portions  31  enables a gas flow from the first pump chamber  21  toward the second pump chamber  22 , but is configured so as to disable the gas flow in the opposite direction. The second check valve  80 B provided to each of the second hole portions  41  enables a gas flow from a space in the first nozzle portion  14  side of the housing space  13  of the case  10  toward the first pump chamber  21 , but is configured so as to disable the gas flow in the opposite direction. The third check valve  80 C provided to each of the third hole portions  51  enables a gas flow from the second pump chamber  22  toward a space in the second nozzle portion  15  side of the housing space  13  of the case  10 , but is configured so as to disable the gas flow in the opposite direction. Therefore, the direction of the gas flow generated during the operation of the piezoelectric blower  1 A is determined by an action of the first check valve  80 A, the second check valve  80 B, and the third check valve  80 C, and the approximate direction of the gas flow is illustrated with an arrow in  FIG. 3A . 
     Specifically, as illustrated in  FIG. 4A , when the central region of the first diaphragm  30  and the central region of the second diaphragm  40  are displaced in a direction to which they move close to each other and the central region of the first diaphragm  30  and the central region of the third diaphragm  50  are displaced in a direction to which they move apart from each other, negative pressure is generated in the vicinity of the first hole portions  31  of the first pump chamber  21  and positive pressure is generated in the vicinity of the first hole portions  31  of the second pump chamber  22 , whereby the first check valve  80 A closes the first hole portions  31 . In the state above, since the negative pressure is generated in the vicinity of the second hole portions  41  of the first pump chamber  21 , the second check valve  80 B opens the second hole portions  41 . In addition, in the state above, since the positive pressure is generated in the vicinity of the third hole portions  51  of the second pump chamber  22 , the third check valve  80 C opens the third hole portions  51 . At this time, since the volume of the first pump chamber  21  is decreased as a whole and the volume of the second pump chamber  22  is increased as a whole, gas is suctioned into the first pump chamber  21  through the second hole portions  41  provided to the second diaphragm  40 , and gas is discharged from the second pump chamber  22  through the third hole portions  51  provided to the third diaphragm  50 . 
     Then, as illustrated in  FIG. 4B , when the central region of the first diaphragm  30  and the central region of the second diaphragm  40  are displaced in a direction to which they move apart from each other, and the central region of the first diaphragm  30  and the central region of the third diaphragm  50  are displaced in a direction to which they move close to each other, positive pressure is generated in the vicinity of the first hole portions  31  of the first pump chamber  21  and negative pressure is generated in the vicinity of the first hole portions  31  of the second pump chamber  22 , whereby the first check valve  80 A opens the first hole portions  31 . In the state above, since the positive pressure is generated in the vicinity of the second hole portions  41  of the first pump chamber  21 , the second check valve  80 B closes the second hole portions  41 . In addition, in the state above, since the negative pressure is generated in the vicinity of the third hole portions  51  of the second pump chamber  22 , the third check valve  80 C closes the third hole portions  51 . Thus, the gas is transferred from the first pump chamber  21  to the second pump chamber  22  through the first hole portions  31 . 
     Since the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50  are vibrated so that the state described in  FIG. 4A  and the state described in  FIG. 4B  are alternately repeated, the gas flow direction described in  FIG. 3A  is generated in the piezoelectric blower  1 A. Therefore, the first nozzle portion  14  provided to the case  10  functions as a suction nozzle for suctioning gas from the outside, and the second nozzle portion  15  provided to the case  10  functions as a discharge nozzle for discharging the gas to the outside, whereby the gas is pressure-fed by the piezoelectric blower  1 A. 
       FIG. 3B  schematically illustrates the pressure distribution in each of the first pump chamber  21  and the second pump chamber  22  in the state described in  FIG. 4A  (hereinafter referred to as the first state), and  FIG. 3C  schematically illustrates the pressure distribution in each of the first pump chamber  21  and the second pump chamber  22  in the state described in  FIG. 4B  (hereinafter referred to as the second state). 
     As is evident from  FIG. 3B  and  FIG. 3C , in the piezoelectric blower  1 A according to the present embodiment, when the first diaphragm  30 , the second diaphragm  40  and the third diaphragm  50  are driven with the condition described above that the resonance occurs in each of the first pump chamber  21  and the second pump chamber  22 , an antinode and a node of the pressure change occur as follows. An antinode of the pressure change in the first pump chamber  21  is formed in the central region of the first pump chamber  21 , a node of the pressure change in the first pump chamber  21  is formed in an outer side of the antinode, another antinode of the pressure change in the first pump chamber  21  is formed in an outer side of the node, and another node of the pressure change in the first pump chamber  21  is formed in an outermost end portion of the first pump chamber  21 . An antinode of the pressure change in the second pump chamber  22  is formed in the central region of the second pump chamber  22 , a node of the pressure change in the second pump chamber  22  is formed in an outer side of the antinode, another antinode of the pressure change in the second pump chamber  22  is formed in an outer side of the node, and another node of the pressure change in the second pump chamber  22  is formed in an outermost end portion of the second pump chamber  22 . 
     Here, in the piezoelectric blower  1 A according to the present embodiment, the first hole portions  31  provided to the first diaphragm  30 , the second hole portions  41  provided to the second diaphragm  40 , and the third hole portions  51  provided to the third diaphragm  50  satisfy the following conditions as described in  FIG. 3A . 
     The first hole portions  31  are provided to the first diaphragm  30  in a region not overlapping the axial line  100  when viewed in the extending direction of the axial line  100  and not overlapping the node of vibration formed in the first diaphragm  30 , and the first check valve  80 A is provided to the first hole portions  31 . More specifically, the first hole portions  31  are provided to a region overlapping the antinode of vibration formed at a position excluding the central region of the first diaphragm  30 . The first hole portions  31  are arranged with an interval therebetween in a position on a circumference around the axial line  100  when viewed in the extending direction of the axial line  100 . 
     The second hole portions  41  are provided to the second diaphragm  40  in a region not overlapping the axial line  100  when viewed in the extending direction of the axial line  100  and not overlapping the node of vibration formed in the second diaphragm  40  (in other words, each of the second hole portions  41  are not provided in a region overlapping the node of vibration formed in the first diaphragm  30  when viewed in the extending direction of the axial line  100 ), and the second check valve  80 B is provided to the second hole portions  41 . More specifically, the second hole portions  41  are provided to a region overlapping the antinode of vibration formed at a position excluding the central region of the second diaphragm  40  (in other words, each of the second hole portions  41  are provided to a region overlapping the antinode of vibration formed in the first diaphragm  30  when viewed in the extending direction of the axial line  100 ). The second hole portions  41  are arranged with an interval therebetween in a position on a circumference around the axial line  100  when viewed in the extending direction of the axial line  100 . 
     The third hole portions  51  are provided to the third diaphragm  50  in a region not overlapping the axial line  100  when viewed in the extending direction of the axial line  100  and not overlapping the node of vibration formed in the third diaphragm  50  (in other words, each of the third hole portions  51  is not provided in a region overlapping the node of vibration formed in the first diaphragm  30  when viewed in the extending direction of the axial line  100 ), and the third check valve  80 C is provided to the third hole portions  51 . More specifically, the third hole portions  51  are provided in a region overlapping the antinode of vibration formed at a position excluding the central region of the third diaphragm  50  (in other words, each of the third hole portions  51  is provided in a region overlapping the antinode of vibration formed in the first diaphragm  30  when viewed in the extending direction of the axial line  100 ). The third hole portions  51  are arranged with an interval therebetween in a position on a circumference around the axial line  100  when viewed in the extending direction of the axial line  100 . 
     Note that the first diaphragm  30 , the second diaphragm  40 , the third diaphragm  50 , the first spacer  60 A, and the second spacer  60 B which form the first pump chamber  21  and the second pump chamber  22  are not provided with holes other than holes in the first hole portions  31 , the second hole portions  41 , and the third hole portions  51 . 
     With the configuration above, the piezoelectric blower  1 A according to the present embodiment can increase the flow rate in comparison with the related art. The reason will be described in detail below. 
     In the piezoelectric blower  1 A according to the present embodiment, the first check valve  80 A, the second check valve  80 B, and the third check valve  80 C for determining the direction of the gas flow in the piezoelectric blower  1 A are respectively provided to the first hole portions  31  provided in the intermediate region excluding the central region and the peripheral region of the first diaphragm  30 , to the second hole portions  41  provided in the intermediate region excluding the central region and the peripheral region of the second diaphragm  40 , and to the third hole portions  51  provided in the intermediate region excluding the central region and the peripheral region of the third diaphragm  50 . With the configuration above, in comparison with a configuration in which the hole portions with a check valve are provided in the central region of the diaphragm, the flow path resistance to the gas passing through the first hole portions  31 , the second hole portions  41 , and the third hole portions  51  is significantly reduced, so that the flow rate through these portions can be increased. 
     However, as described above, since the displacement amount in the intermediate region excluding the central region and the peripheral region of the diaphragm is smaller than that in the central region of the diaphragm, the action of opening and closing of the check valve is likely to be insufficient by adopting the above-described configuration alone. 
     In order to solve the problem, in the piezoelectric blower  1 A according to the present embodiment, particularly, a pair of the second diaphragm  40  and the third diaphragm  50  are disposed so as to face the first diaphragm  30  to which the first hole portions  31  with the first check valve  80 A are provided, so that the first diaphragm  30  is sandwiched by the first pump chamber  21  and the second pump chamber  22 . With this, it is possible to reliably open and close the first check valve  80 A using a differential pressure between the positive pressure and the negative pressure generated in the first pump chamber  21  and the second pump chamber  22 . 
     That is, as described in  FIG. 3B , in the first state, the negative pressure is generated in the vicinity of the first hole portions  31  of the first pump chamber  21 , and the positive pressure is generated in the vicinity of the first hole portions  31  of the second pump chamber  22 , so that the differential pressure ΔP makes it possible to more reliably achieve a state in which the first check valve  80 A is closed. As described in  FIG. 3C , in the second state, the positive pressure is generated in the vicinity of the first hole portions  31  of the first pump chamber  21 , and the negative pressure is generated in the vicinity of the first hole portions  31  of the second pump chamber  22 , so that the differential pressure ΔP makes it possible to more reliably achieve a state in which the first check valve  80 A is opened. 
     Further, by providing the second check valve  80 B to the second hole portions  41  provided to the second diaphragm  40  and providing the third check valve  80 C to the third hole portions  51  provided to the third diaphragm  50 , in the second state described above, the second hole portions  41  and the third hole portions  51  are closed by the second check valve  80 B and the third check valve  80 C, respectively. Thus, in the second state, the positive pressure in the vicinity of the first hole portions  31  of the first pump chamber  21  is maintained to be higher, and the negative pressure in the vicinity of the first hole portions  31  of the second pump chamber  22  is maintained to be lower. As the result, the above-described differential pressure ΔP becomes particularly large, and accordingly, the state in which the first check valve  80 A is opened is made to be achieved more reliably. 
     Here, in the piezoelectric blower  1 A according to the present embodiment, as described above, since the first hole portions  31  are provided so as to overlap the antinode of vibration formed at a position of the first diaphragm  30  excluding the central region of the first diaphragm  30 , the differential pressure ΔP between the first pump chamber  21  and the second pump chamber  22  can be secured to be larger, and the action of opening and closing of the first check valve  80 A can also be made to be more reliable in this respect. 
     Further, in the piezoelectric blower  1 A according to the present embodiment, as described above, since the second hole portions  41  provided to the second diaphragm  40  are arranged so as to overlap the antinode of vibration formed in the second diaphragm  40 , and the third hole portions  51  provided to the third diaphragm  50  are arranged so as to overlap the antinode of vibration formed in the third diaphragm  50 , it is possible to reliably open and close the second check valve  80 B provided to the second hole portions  41  and also open and close the third check valve  80 C provided to the third hole portions  51 . 
     Therefore, in the piezoelectric blower  1 A according to the present embodiment, the flow path resistance in the driving unit  20 A is lowered and the action of opening and closing of the first check valve  80 A, the second check valve  80 B, and the third check valve  80 C may be ensured, so that the flow rate may be increased in comparison with the related art. Further, since the second check valve  80 B is provided to each of the second hole portions  41  provided to the second diaphragm  40 , and the third check valve  80 C is provided to each of the third hole portions  51  provided to the third diaphragm  50 , the pressure amplitude due to the pressure change in the first pump chamber  21  and the pressure amplitude due to the pressure change in the second pump chamber  22  can be increased in comparison with the related art, and a piezoelectric pump with high suction pressure and high discharge pressure can be realized. 
     In the piezoelectric blower  1 A according to the present embodiment, as described above, since the second hole portions  41  provided to the second diaphragm  40  and the third hole portions  51  provided to the third diaphragm  50  are arranged in an annular shape with an interval therebetween, the axial symmetricity of the gas flow in the piezoelectric blower  1 A is improved and turbulence is not easily generated in the gas flow. Thus, an efficient air flow can be achieved, and as the result, the flow rate can be increased. 
       FIG. 5  is a plan view of the first diaphragm illustrated in  FIG. 1 . Hereinafter, with reference to  FIG. 5 , a more preferable configuration for increasing the flow rate in the piezoelectric blower  1 A according to the present embodiment will be described. 
     As illustrated in  FIG. 5 , in the piezoelectric blower  1 A according to the present embodiment, as described above, the first hole portions  31  are provided in an annular shape with an interval therebetween in the intermediate region excluding the central region and the peripheral region of the first diaphragm  30 . With the configuration above, since the flow path resistance in the first hole portions  31  provided to the first diaphragm  30  is reduced, it can be possible to increase the flow rate. 
     Here, it is preferable that the first hole portions  31  be formed of substantially cylindrical holes with the same opening diameter and be arranged with the same intervals. With the configuration above, the axial symmetricity of the gas flow in the piezoelectric blower  1 A is improved, so that the turbulence is not easily generated in the gas flow, and the efficient gas flow can be realized, and as the result, the flow rate can be increased. 
     In addition, it is preferable that a distance D1 between the adjacent first hole portions among the first hole portions  31  is smaller than a distance D2 between the axial line  100  and each of the first hole portions  31 . The reason is as follows. Part of the gas positioned in the vicinity of the first hole portions  31  of the first pump chamber  21  moves toward the central region of the first pump chamber  21  due to the pressure change in the first pump chamber  21 , and is reflected at the center region to return to the original position. However, by adopting the configuration described above, large part of the gas positioned in the vicinity of the first hole portions  31  flows into the first hole portions  31  preferentially, whereby proportion of the gas moving toward the central region of the first pump chamber  21  can be reduced, and as the result, an overall flow rate of the piezoelectric blower  1 A can be increased. 
     In the piezoelectric blower  1 A according to the present embodiment, each of the first hole portions  31  arranged in an annular shape with an interval therebetween is positioned outside the piezoelectric element  90  when viewed in the extending direction of the axial line  100 . With the configuration above, the first pump chamber  21  and the second pump chamber  22  may easily communicate with each other without providing a through-hole or the like in the piezoelectric element  90 . When the through-hole is provided in the piezoelectric element  90 , it is not necessarily advantageous in terms of manufacturing cost, reliability, and the like. By contrast, with the configuration described above, there is no need to provide the through-hole in the piezoelectric element  90 , and it is possible to provide a piezoelectric blower with lower cost and high reliability. 
     Although the dimensions of the piezoelectric blower  1 A according to the present embodiment described above and such as the number of various holes provided to the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50  are not particularly limited, examples thereof are as follows. 
     The diameter of the first diaphragm  30  is about 25 mm, for example, and in that, the diameter of the portion forming the first pump chamber  21  and the second pump chamber  22  is about 19 mm, for example. The diameter of the second diaphragm  40  is about 23 mm, for example, and in that, the diameter of the portion forming the first pump chamber  21  is about 19 mm, for example. The diameter of the third diaphragm  50  is about 23 mm, for example, and in that, the diameter of the portion forming the second pump chamber  22  is about 19 mm, for example. The thicknesses of the first diaphragm  30 , the second diaphragm  40 , and the third diaphragm  50  are the same, and is about 0.2 mm, for example. The outer diameter and inner diameter of each of the first spacer  60 A and the second spacer  60 B are about 23 mm and about 19 mm, respectively, and the thickness thereof is about 0.3 mm, for example. 
     The first hole portions  31  provided to the first diaphragm  30  are arranged in an annular shape with an interval therebetween, spaced apart from the central region of the first diaphragm  30  by about 6 mm, for example, and each opening diameter thereof is about 0.4 mm, for example, and the number thereof is about 50. The second hole portions  41  provided to the second diaphragm  40  are arranged in an annular shape with an interval therebetween, spaced apart from the central region of the second diaphragm  40  by about 6 mm, for example, and each opening diameter thereof is about 0.4 mm, for example, and the number thereof is about 50. The third hole portions  51  provided to the third diaphragm  50  are arranged in an annular shape with an interval therebetween, spaced apart from the central region of the third diaphragm  50  by about 6 mm, for example, and each opening diameter thereof is about 0.4 mm, for example, and the number thereof is about 50. 
     (Modification 1) 
       FIG. 6  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower and an approximate direction of a gas flow generated during operation according to Modification 1 based on Embodiment 1. With reference to  FIG. 6 , a piezoelectric blower  1 A′ according to Modification 1 will be described. 
     As illustrated in  FIG. 6 , the piezoelectric blower  1 A′ according to Modification 1 includes a driving unit  20 A′ having a configuration different from that of the piezoelectric blower  1 A according to Embodiment 1. As with the driving unit  20 A of the piezoelectric blower  1 A according to Embodiment 1, the driving unit  20 A′ includes the first diaphragm  30 , the second diaphragm  40 , the third diaphragm  50 , the first spacer  60 A, the second spacer  60 B, the first check valve  80 A, the second check valve  80 B, the third check valve  80 C, the piezoelectric element  90 , and the like. However, the position and the configuration of the piezoelectric element  90  in the driving unit  20 A′ are different from those in the driving unit  20 A. 
     Specifically, in the piezoelectric blower  1 A′ according to the Modification 1, the piezoelectric element  90  is attached to the main surface positioned on a side facing the first pump chamber  21  of the first diaphragm  30  with an adhesive, for example. That is, unlike the piezoelectric blower  1 A according to Embodiment 1, the piezoelectric element  90  is directly attached to the first diaphragm  30  without the first valve supporting member  70 A interposed therebetween. 
     With the configuration above, the same effects as those described in Embodiment 1 can also be obtained, and it is possible to provide a piezoelectric blower with an increased flow rate in comparison with the related art. 
     (Modification 2) 
       FIG. 7  is an exploded perspective view of a piezoelectric blower according to Modification 2 based on Embodiment 1. Hereinafter, with reference to  FIG. 7 , a piezoelectric blower  1 A″ according to the Modification 2 will be described. 
     As illustrated in  FIG. 7 , the piezoelectric blower  1 A″ according to Modification 2 includes a driving unit  20 A″ having a configuration different from that of the piezoelectric blower  1 A according to Embodiment 1. As with the driving unit  20 A of the piezoelectric blower  1 A according to Embodiment 1, the driving unit  20 A″ includes the first diaphragm  30 , the second diaphragm  40 , the third diaphragm  50 , the first spacer  60 A, the second spacer  60 B, the first check valve  80 A, the second check valve  80 B, the third check valve  80 C, the piezoelectric element  90 , and the like. However, in those, the number of holes provided to the second diaphragm  40  and the third diaphragm  50  are different from those in the driving unit  20 A. 
     Specifically, in the piezoelectric blower  1 A″ according to Modification 2, the number of the second hole portions  41  provided to the second diaphragm  40  and the number of the third hole portions  51  provided to the third diaphragm  50  are significantly reduced respectively in comparison with the piezoelectric blower  1 A according to Embodiment 1, and each of the total number is 10. Thus, the total number of the second hole portions  41  and the total number of the third hole portions  51  are respectively smaller than the total number of the first hole portions  31 . 
     With the configuration above, large dispersion of the pressure change is not easily generated between the region in the vicinity of the second hole portions  41  provided to the second diaphragm  40  of the first pump chamber  21  and the region in the vicinity of the third hole portions  51  provided to the third diaphragm  50  of the second pump chamber  22 . Thus, the second check valve  80 B provided to the second hole portions  41  and the third check valve  80 C provided to the third hole portions  51  may also reliably be opened and closed. The flow rate is increased also in this respect. 
     With the configuration above, it is also possible to obtain effects similar to those described in Embodiment 1, and it is possible to provide a piezoelectric blower with an increased flow rate in comparison with the related art. Thus, the number of holes provided to the second diaphragm  40  and the third diaphragm  50  is not limited to any specific number, and may be at least one or more. 
     In the present modification, in comparison with the piezoelectric blower  1 A according to Embodiment 1, exemplified is a case where the number of the second hole portions  41  provided to the second diaphragm  40  and the number of the third hole portions  51  provided to the third diaphragm  50  are both reduced, however, either one alone of the number of the second hole portions  41  provided to the second diaphragm  40  and the number of the third hole portions  51  provided to the third diaphragm  50  may be reduced. 
     Embodiment 2 
     Each of  FIGS. 8A, 8B and 8C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 2 of the present disclosure. Hereinafter, with reference to  FIGS. 8A, 8B and 8C , a piezoelectric blower  1 B according to the present embodiment will be described. 
     As illustrated in  FIG. 8A , the piezoelectric blower  1 B according to the present embodiment includes a driving unit  20 B having a configuration different from that of the piezoelectric blower  1 A according to Embodiment 1. As with the driving unit  20 A of the piezoelectric blower  1 A according to Embodiment 1, the driving unit  20 B includes the first diaphragm  30 , the second diaphragm  40 , the third diaphragm  50 , the first spacer  60 A, the second spacer  60 B, the first check valve  80 A, the second check valve  80 B, the third check valve  80 C, the piezoelectric element  90 , and the like. However, the configuration of holes provided to the second diaphragm  40  and the third diaphragm  50  is different from that in the driving unit  20 A. 
     Specifically, the second diaphragm  40  is provided with the second hole portions  41  in a region outside relative to the central region of the second diaphragm  40  and inside relative to the innermost node of vibration among nodes of vibration formed in the second diaphragm  40 . The second hole portions  41  are arranged with an interval therebetween in a position on a circumference around the axial line  100  when viewed in an extending direction of the axial line  100 . 
     In addition, the third diaphragm  50  is provided with the third hole portions  51  in a region outside relative to the central region of the third diaphragm  50  and inside relative to the innermost node of vibration among nodes of vibration formed in the third diaphragm  50 . The third hole portions  51  are arranged with an interval therebetween in a position on a circumference around the axial line  100  when viewed in the extending direction of the axial line  100 . 
     When the configuration above is adopted, the pressure changes in the first pump chamber  21  and the second pump chamber  22  can also be obtained in the first state and the second state respectively, as illustrated in  FIG. 8B  and  FIG. 8C , and as the result, the gas flow as illustrated in  FIG. 8A  is generated in the piezoelectric blower  1 B. 
     Here, both in the region of the second diaphragm  40  provided with the second hole portions  41  and in the region of the third diaphragm  50  provided with the third hole portions  51 , a displacement generated during operation is smaller than an antinode of vibration formed in the second diaphragm  40  and an antinode of vibration formed in the third diaphragm  50 . However, with the configuration above, the effects similar to those described in Embodiment 1 can also be obtained and it is possible to provide a piezoelectric blower with an increased flow rate in comparison with the related art. 
     Embodiment 3 
     Each of  FIGS. 9A, 9B and 9C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 3. Hereinafter, with reference to  FIGS. 9A, 9B and 9C , a piezoelectric blower  1 C according to the present embodiment will be described. 
     As illustrated in  FIG. 9A , the piezoelectric blower  1 C according to the present embodiment includes a driving unit  20 C having a configuration different from that of the piezoelectric blower  1 A according to Embodiment 1. As with the driving unit  20 A of the piezoelectric blower  1 A according to Embodiment 1, the driving unit  20 C includes the first diaphragm  30 , the second diaphragm  40 , the third diaphragm  50 , the first spacer  60 A, the second spacer  60 B, the first check valve  80 A, the second check valve  80 B, the third check valve  80 C, the piezoelectric element  90 , and the like. However, the configuration of holes provided to the second diaphragm  40  and the third diaphragm  50  is different from that in the driving unit  20 A. 
     Specifically, the second diaphragm  40  is provided with the one second hole portion  41  in a region overlapping the axial line  100  when viewed in the extending direction of the axial line  100 , and the third diaphragm  50  is provided with the one third hole portion  51  in a region overlapping the axial line  100  when viewed in an extending direction of the axial line  100 . 
     When the configuration above is adopted, the pressure changes in the first pump chamber  21  and the second pump chamber  22  can also be obtained in the first state and the second state respectively, as illustrated in  FIG. 9B  and  FIG. 9C , and as the result, the gas flow as illustrated in FIG.  9 A is generated in the piezoelectric blower  1 C. 
     Here, both in the region of the second diaphragm  40  provided with the one second hole portion  41  and in the region of the third diaphragm  50  provided with the one third hole portion  51 , the larger displacement is generated during operation, so that the effects similar to those described in Embodiment 1 can also be obtained with the configuration above, and it is possible to provide a piezoelectric blower with an increased flow rate in comparison with the related art. 
     Since the region of the second diaphragm  40  provided with the one second hole portion  41  and the region of the third diaphragm  50  provided with the one third hole portion  51  are the central regions of the second diaphragm  40  and the third diaphragm  50  respectively, the flow path resistance is basically larger than that in the case where the second hole portions  41  and the third hole portions  51  are provided in a region other than the central region. On the other hand, since both these regions are the antinodes of vibration, when the configuration above is adopted, it is possible to obtain an effect that not only the first check valve  80 A provided to the first hole portions  31  provided to the first diaphragm  30  but also the second check valve  80 B provided to the one second hole portion  41  and the third check valve  80 C provided to the one third hole portion  51  can reliably be opened and closed. 
     Thus, with the configuration above, it is also possible to obtain effects similar to those described in Embodiment 1, and it is also possible to provide a piezoelectric blower with the increased flow rate in comparison with the related art. 
     Embodiment 4 
     Each of  FIGS. 10A, 10B and 10C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 4. Hereinafter, with reference to  FIGS. 10A, 10B and 10C , a piezoelectric blower  1 D according to the present embodiment will be described. 
     As illustrated in  FIG. 10A , the piezoelectric blower  1 D according to the present embodiment includes a driving unit  20 D having a configuration different from that of the piezoelectric blower  1 C according to Embodiment 3. As with the driving unit  20 C of the piezoelectric blower  1 C according to Embodiment 3, the driving unit  20 D includes the first diaphragm  30 , the second diaphragm  40 , the third diaphragm  50 , the first spacer  60 A, the second spacer  60 B, the first check valve  80 A, the third check valve  80 C, the piezoelectric element  90 , and the like. However, the configuration of the driving unit  20 D is different from that of the driving unit  20 C only in that the driving unit  20 D is not provided with the second check valve  80 B. 
     When the configuration above is adopted, the pressure changes in the first pump chamber  21  and the second pump chamber  22  can be obtained in the first state and the second state respectively, as illustrated in  FIG. 10B  and  FIG. 10C , and as the result, the gas flow as illustrated in  FIG. 10A  is generated in the piezoelectric blower  1 D. 
     With the configuration above, by providing the third check valve  80 C to the third hole portion  51  provided to the third diaphragm  50 , in the second state described above, the third hole portion  51  are also closed by the third check valve  80 C. Thus, in the second state, the negative pressure in the vicinity of the first hole portions  31  of the second pump chamber  22  is maintained to be lower, and as the result, the differential pressure ΔP between the first pump chamber  21  and the second pump chamber  22  becomes particularly large, and accordingly, the state in which the first check valve  80 A is opened may be made to be achieved reliably. 
     Thus, with the configuration above, it is also possible to obtain effects similar to those described in Embodiment 1, and it is possible to provide a piezoelectric blower with an increased flow rate in comparison with the related art. 
     Embodiment 5 
     Each of  FIGS. 11A, 11B and 11C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 5 of the present disclosure. Hereinafter, with reference to  FIGS. 11A, 11B and 11C , a piezoelectric blower  1 E according to the present embodiment will be described. 
     As illustrated in  FIG. 11A , the piezoelectric blower  1 E according to the present embodiment includes a driving unit  20 E having a configuration different from that of the piezoelectric blower  1 C according to Embodiment 3. As with the driving unit  20 C of the piezoelectric blower  1 C according to Embodiment 3, the driving unit  20 E includes the first diaphragm  30 , the second diaphragm  40 , the third diaphragm  50 , the first spacer  60 A, the second spacer  60 B, the first check valve  80 A, the second check valve  80 B, the piezoelectric element  90 , and the like. However, the configuration of the driving unit  20 E is different from that of the driving unit  20 C only in that the driving unit  20 E is not provided with the third check valve  80 C. 
     When the configuration above is adopted, the pressure changes in the first pump chamber  21  and the second pump chamber  22  can be obtained in the first state and the second state respectively, as illustrated in  FIG. 11B  and  FIG. 11C , and as the result, the gas flow as illustrated in  FIG. 11A  is generated in the piezoelectric blower  1 E. 
     With the configuration above, by providing the second check valve  80 B to the second hole portion  41  provided to the second diaphragm  40 , in the second state described above, the second hole portion  41  are also closed by the second check valve  80 B. Thus, in the second state, the positive pressure in the vicinity of the first hole portions  31  of the first pump chamber  21  is maintained to be higher, and as the result, the differential pressure ΔP between the first pump chamber  21  and the second pump chamber  22  becomes particularly large, and accordingly, the state in which the first check valve  80 A is opened may be made to be achieved reliably. 
     Thus, with the configuration above, it is also possible to obtain effects similar to those described in Embodiment 1, and it is also possible to provide a piezoelectric blower with an increased flow rate in comparison with the related art. 
     Embodiment 6 
     Each of  FIGS. 12A, 12B and 12C  is a schematic diagram describing a configuration of a driving unit in a piezoelectric blower, an approximate direction of a gas flow generated during operation, and a pressure change generated in a first pump chamber and a second pump chamber according to Embodiment 6 of the present disclosure. Hereinafter, with reference to  FIGS. 12A, 12B and 12C , a piezoelectric blower  1 F according to the present embodiment will be described. 
     As illustrated in  FIG. 12A , the piezoelectric blower  1 F according to the present embodiment includes a driving unit  20 F having a configuration different from that of the piezoelectric blower  1 B according to Embodiment 2. As with the driving unit  20 F of the piezoelectric blower  1 B according to Embodiment 2, the driving unit  20 B includes the first diaphragm  30 , the second diaphragm  40 , the third diaphragm  50 , the first spacer  60 A, the second spacer  60 B, the first check valve  80 A, the second check valve  80 B, the third check valve  80 C, the piezoelectric element  90 , and the like. However, the configuration of holes provided to the first diaphragm  30  is different from that in the driving unit  20 B. 
     Specifically, the first hole portions  31  are provided to the first diaphragm  30  in a region not overlapping the axial line  100  when viewed in an extending direction of the axial line  100 , outside relative to the antinode of vibration formed at a position excluding a central region of the first diaphragm  30 , and inside relative to the peripheral region of the first diaphragm  30 . The first hole portions  31  are arranged with an interval therebetween in a position on a circumference around the axial line  100  when viewed in the extending direction of the axial line  100 . 
     When the configuration above is adopted, the pressure changes in the first pump chamber  21  and the second pump chamber  22  can also be obtained in the first state and the second state respectively, as illustrated in  FIG. 12B  and  FIG. 12C , and as the result, the gas flow as illustrated in  FIG. 12A  is generated in the piezoelectric blower  1 F. 
     Here, in the region of the first diaphragm  30  provided with the first hole portions  31 , a displacement generated during operation is smaller than an antinode of vibration formed in the first diaphragm  30 . However, with the configuration above, the effects similar to those described in Embodiment 1 can be obtained and it is possible to provide a piezoelectric blower with an increased flow rate in comparison with the related art. 
     When the first hole portions  31  are arranged in a region not overlapping the antinode of vibration formed in the first diaphragm  30 , it is preferable that the first hole portions  31  be arranged in a region outside relative to the node of vibration formed in the position furthest from the central region of the first diaphragm  30  among the nodes of vibration formed in the region excluding the peripheral region of the first diaphragm  30 , as in the present embodiment. This is because, at the time of driving, a volume change in the portion of the first pump chamber  21  and the second pump chamber  22  corresponding to the region described above becomes larger as a whole than the volume change in the portion of the first pump chamber  21  and the second pump chamber  22  corresponding to the region inside the nodes. Thus, with the configuration above, it is possible to obtain larger differential pressure. 
     (Other) 
     In Embodiments 1 to 6 and modifications thereof of the present disclosure, there has been exemplified and described the case where the first hole portions provided to the first plate member are arranged in an annular shape with an interval therebetween, however, the layout of the first hole portions is not limited to this arrangement and may be changed as appropriate. 
     In Embodiments 1 to 6 and modifications thereof of the present disclosure, there has been exemplified and described the case where both of the second hole portions provided to the second plate member and the third hole portions provided to the third plate member are arranged in an annular shape with an interval therebetween, however, the layout of the second hole portions and the third hole portions are not limited to this arrangement and may be changed as appropriate. 
     In Embodiments 1 to 6 and modifications thereof of the present disclosure, there has been exemplified and described the case where the piezoelectric element serving as the driving member is attached to one main surface side of the first plate member, however, a pair of piezoelectric elements may be provided and attached to both of the main surface sides of the first plate member. In this case, since the displacement of the first plate member can be increased, a further increase in the flow rate can be achieved. 
     In Embodiments 1 to 6 and modifications thereof of the present disclosure, there has been exemplified and described the case where the piezoelectric element serving as the driving member is attached to the first plate member, however, the piezoelectric element may be attached to the second plate member or to the third plate member or to both of the second and third plate member. In this case, it is possible to obtain an effect of facilitating wiring to the piezoelectric element. 
     In Embodiments 1 to 6 and modifications thereof of the present disclosure, there has been exemplified and described the case where the piezoelectric element causes the first, second, and third plate members to perform flexural vibration in which the antinode of vibration is formed in the central region of each of the first, second, and third plate members, and in addition to that, the one antinode of vibration in the radial direction is formed at a position excluding the central region of each of the first, second, and third plate members. However, the piezoelectric element may cause the first, second, and third plate member to perform flexural vibration so that the antinode of vibration is formed only in each of the central regions of the first, second, and third plate members. Further, the piezoelectric element may cause the first, second, and third plate member to perform flexural vibration in which the antinode of vibration is formed in the central region of each of the first, second, and third plate members, and in addition to that, two or more of the antinode of vibration in the radial direction is formed at a position excluding the central region of each of the first, second, and third plate members. 
     In Embodiments 1 to 6 and modifications thereof of the present disclosure, there has been exemplified and described the case where not only the first plate member but also the second plate member and the third plate member are caused to perform flexural vibration, however, the second plate member and the third plate member are not necessarily caused to perform the flexural vibration, and the first plate member alone may be caused to perform the flexural vibration. 
     Further, the characteristic configurations in Embodiments 1 to 6 and modifications thereof of the present disclosure can be appropriately combined without departing from the spirit and scope of the present disclosure. 
     Additionally, in Embodiments 1 to 6 and modifications thereof of the present disclosure, there has been exemplified and described the case where the present disclosure is applied to an piezoelectric blower which sanctions and discharges gas, however, the present disclosure may be applied to a pump which sanctions and discharges liquid and to a pump using other than a piezoelectric element as a driving member (obviously limited to a positive displacement pump using flexural vibration of a diaphragm). 
     In Embodiments 1 to 6 and modifications thereof of the present disclosure, the pump to which the present disclosure is applied alone is described in detail among pumps and fluid control devices to which the present disclosure is applied, however, the fluid control device to which the present disclosure is applied includes the pump to which the present disclosure is applied. That is, the fluid control device to which the present disclosure is applied is a fluid system including the pump to which the present disclosure is applied as a part (for example, the piezoelectric blower according to Embodiments 1 to 6 and modifications thereof of the present disclosure). The pump and other fluid control parts cooperatively control fluid behavior depending on application. 
     The embodiments and the modifications of the present disclosure are illustrative in all respects and are not intended to limit the scope of the present disclosure. The technical scope of the present disclosure is defined by the scope of the appended claims, and all changes that fall within the same essential spirit as the scope of the claims are intended to be included therein as well.
           1 A to  1 F,  1 A′, and  1 A″ PIEZOELECTRIC BLOWER     10  CASE     11  FIRST CASE MEMBER     12  SECOND CASE MEMBER     13  HOUSING SPACE     14  FIRST NOZZLE PORTION     15  SECOND NOZZLE PORTION     20 A to  20 E,  20 A′, and  20 A″ DRIVING UNIT     21  FIRST PUMP CHAMBER     22  SECOND PUMP CHAMBER     30  FIRST DIAPHRAGM     31  FIRST HOLE PORTION     40  SECOND DIAPHRAGM     41  SECOND HOLE PORTION     50  THIRD DIAPHRAGM     51  THIRD HOLE PORTION     60 A FIRST SPACER     60 B SECOND SPACER     70 A FIRST VALVE SUPPORTING MEMBER     70 B SECOND VALVE SUPPORTING MEMBER     70 C THIRD VALVE SUPPORTING MEMBER     71   a  FIRST ANNULAR STEP PORTION     71   b  SECOND ANNULAR STEP PORTION     71   c  THIRD ANNULAR STEP PORTION     80 A FIRST CHECK VALVE     80 B SECOND CHECK VALVE     80 C THIRD CHECK VALVE     90  PIEZOELECTRIC ELEMENT     100  AXIAL LINE