Patent Publication Number: US-2020282726-A1

Title: Liquid agent application device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. national stage of PCT Application No. PCT/JP2018/025146, filed on Jul. 3, 2018, and priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is claimed from Japanese Application No. 2017-188842, filed Sep. 28, 2017; the entire disclosures of each of which are hereby incorporated herein by reference. 
    
    
     1. FIELD 
     The present disclosure relates to a liquid agent application device. 
     2. BACKGROUND 
     Since the piezoelectric element that converts energy from electrical energy to mechanical energy by the piezoelectric effect are excellent in responsiveness, it is used in a liquid agent application device that discharges a liquid agent onto the surface of an object in wide fields such as semiconductor, printing, chemicals, etc. 
     The liquid agent application device includes a liquid agent reservoir having a discharge port, a diaphragm for changing the volume in the liquid agent reservoir, and a piezoelectric element that pressurization vibrates the diaphragm. 
     Here, since the ease of discharging the liquid agent from the discharge port varies depending on the viscosity of the liquid agent, there is a desire to appropriately adjust the displacement amount of the diaphragm. 
     However, since the amount of expansion and contraction of the piezoelectric element is very small, and the displacement amount of the diaphragm is small, adjusting the displacement amount of the diaphragm only by the piezoelectric element is limited. 
     SUMMARY 
     A liquid agent application device according to an example embodiment of the present disclosure includes a liquid agent reservoir, a diaphragm, and a driver. The liquid agent reservoir includes a liquid agent discharge port. The diaphragm changes an internal volume of the liquid agent reservoir. The driver is located on the diaphragm. The driver includes a driving piezoelectric element that vibrates in response to application of a drive voltage signal and a horn that vibrates together with the driving piezoelectric element. 
     The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a configuration of a liquid agent application device according to a first example embodiment of the present disclosure. 
         FIG. 2  is a schematic diagram showing a configuration of a liquid agent application device according to a second example embodiment of the present disclosure. 
         FIG. 3  is a schematic diagram showing a configuration of a liquid agent application device according to a third example embodiment of the present disclosure. 
         FIG. 4  is a schematic diagram showing a configuration of a liquid agent application device according to a fourth example embodiment of the present disclosure. 
         FIG. 5  is a schematic diagram for explaining a method of fixing a driving piezoelectric element with a fastener. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, referring to the drawings, liquid agent application devices according to example embodiments of the present disclosure will be described. Note that the scope of the present disclosure is not limited to the example embodiments described below, but includes any modification thereof within the scope of the technical idea of the present disclosure. Further, in the following drawings, to easily understand each component, a scale, the number, etc. of each structure may be different from those of actual structures. 
     In this specification, “connection” means a state in which two members are fixed or coupled to each other. Thus, when two members are connected, they always operate together. “Contact” means a state where the two members are not fixed or connected to each other although the two members are in direct contact. When two members are in contact with each other, there is a case where both operate together and a case where both do not operate together. In the present specification, the “end portion” of each member means an end portion in the expansion/contraction direction of the piezoelectric element. 
       FIG. 1  is a schematic diagram showing the configuration of a liquid agent application device  10  according to the first example embodiment. 
     The liquid agent application device  10  includes a liquid agent reservoir  11 , a diaphragm  12 , a drive unit  13 , a fixing member  14 , and a control unit  15 . The liquid agent reservoir  11 , the diaphragm  12 , the drive unit  13 , and the fixing member  14  constitute a head  16 . 
     The liquid agent reservoir  11  includes a housing  11   a  and a nozzle lib. 
     The housing  11   a  is formed in a hollow shape. In the present example embodiment, the housing  11   a  is formed in a tubular shape, but is not limited thereto. The housing  11   a  can be made of, for example, an alloy material, a ceramic material, and a synthetic resin material, and the design is made to enhance the rigidity so that it is prevented from being deformed by the application of a pressing force by the drive unit  13  described later. The rigidity of the housing  11   a  can be appropriately adjusted by optimizing the thickness according to the constituent material. Also, when manufacturing the housing  11   a  by molding and casting, the rigidity of the housing  11   a  can be effectively improved by providing ribs on the outer peripheral face. 
     A pressure chamber  11   c  is formed inside the housing  11   a . A liquid agent is stored in the pressure chamber  11   c . Examples of the liquid agent include solder, thermosetting resin, ink, coating liquid for forming functional thin films (oriented film, resist, color filter, organic electroluminescence, etc.), but are not limited to this. 
     A liquid agent supply port  11   d  is formed in the side wall of the housing  11   a . A liquid agent supplied from a liquid agent supply device (not shown) passes through the liquid agent supply port  11   d  and is replenished into the pressure chamber  11   c.    
     The nozzle lib is formed in a plate shape. The nozzle lib is disposed so as to close one end opening of the housing  11   a . A discharge port  11   e  is formed in the nozzle lib. The liquid agent in the pressure chamber  11   c  is discharged as a droplet from the discharge port  11   e.    
     The diaphragm  12  is disposed so as to close the other end opening of the housing  11   a . The diaphragm  12  vibrates elastically when a pressurization vibration is applied from the drive unit  13  described later. Accordingly, the diaphragm  12  changes the volume of the pressure chamber  11   c  formed in the liquid agent reservoir  11 . 
     When the diaphragm  12  curves convexly toward the inside of the pressure chamber  11   c , the volume of the pressure chamber  11   c  decreases. As a result, the liquid agent is discharged from the discharge port  11   e . Thereafter, when the diaphragm  12  returns to a steady state by its own elasticity, the volume of the pressure chamber  11   c  also returns to the original state. At this time, the liquid agent is replenished to the pressure chamber  11   c  from the liquid agent supply port  11   d.    
     Although the constituent material of the diaphragm  12  is not particularly limited, for example, an alloy material, a ceramic material, a synthetic resin material, or the like can be used. 
     The drive unit  13  is a member for expansion and contraction driving the diaphragm  12 . The drive unit  13  is located on the diaphragm  12 . The drive unit  13  is disposed between the diaphragm  12  and the fixing member  14 . The drive unit  13  is sandwiched between the diaphragm  12  and the fixing member  14 . 
     A first end portion  13   p , of the drive unit  13 , opposite to the diaphragm  12  is connected to the fixing member  14 . That is, the first end portion  13   p  of the drive unit  13  is fixed to the fixing member  14 . Accordingly, the first end portion  13   p  of the drive unit  13  is a fixed end portion. The first end portion  13   p  of the drive unit  13  can be connected to the fixing member  14  via an adhesive such as an epoxy resin, for example. In the present example embodiment, the first end portion  13   p  of the drive unit  13  is part of a horn  21  described later. 
     A second end portion  13   q , of the drive unit  13 , toward the diaphragm  12  is in contact with the diaphragm  12 . That is, the second end portion  13   q  of the drive unit  13  is not fixed to the diaphragm  12 . In the present example embodiment, the second end portion  13   q  of the drive unit  13  is part of a driving piezoelectric element  20  described later. 
     The drive unit  13  includes the driving piezoelectric element  20  and the horn  21 . 
     The driving piezoelectric element  20  is located on the diaphragm  12 . The driving piezoelectric element  20  is disposed between the diaphragm  12  and the horn  21 . The driving piezoelectric element  20  is sandwiched between the diaphragm  12  and the horn  21 . 
     The driving piezoelectric element  20  is connected to the horn  21 . The driving piezoelectric element  20  is connected to the horn  21  via an adhesive such as an epoxy resin. 
     The driving piezoelectric element  20  is in contact with the diaphragm  12 . That is, the driving piezoelectric element  20  is not connected to the diaphragm  12 . However, the driving piezoelectric element  20  may be connected to the diaphragm  12 . 
     The driving piezoelectric element  20  includes a plurality of piezoelectric bodies  20   a , a plurality of internal electrodes  20   b , and a pair of side surface electrodes  20   c  and  20   c . The piezoelectric bodies  20   a  and the internal electrodes  20   b  are alternately stacked. Each of the piezoelectric bodies  20   a  is made of, for example, piezoelectric ceramic such as lead zirconate titanate (PZT). Each of the internal electrodes  20   b  is electrically connected to one of the pair of side surface electrodes  20   c  and  20   c . That is, the internal electrode  20   b  electrically connected to one side surface electrode  20   c  is electrically insulated from the other side surface electrode  20   c . Such a structure is generally referred to as a partial electrode structure. However, the driving piezoelectric element  20  only needs to include at least one piezoelectric body and a pair of electrodes, and various known piezoelectric elements can be used as the driving piezoelectric element  20 . 
     The driving piezoelectric element  20  vibrates according to a drive voltage signal (that is, a drive pulse) applied from the control unit  15  described later. In particular, when a drive voltage signal is applied from the control unit  15  to the pair of side surface electrodes  20   c  and  20   c , each of the piezoelectric bodies  20   a  expands and contracts. Along with the expansion and contraction of each of the piezoelectric bodies  20   a , a pressurization vibration is applied to the diaphragm  12 . 
     The horn  21  is located on the driving piezoelectric element  20 . The horn  21  is disposed between the fixing member  14  and the driving piezoelectric element  20 . The horn  21  is sandwiched between the fixing member  14  and the driving piezoelectric element  20 . In the present example embodiment, the horn  21  is a tubular metal rod. 
     The horn  21  is connected to the fixing member  14  and the driving piezoelectric element  20 . The horn  21  can be connected to the fixing member  14  via an adhesive such as an epoxy resin. 
     The horn  21  is a vibrating body which vibrates with the driving piezoelectric element  20  to increase the amount of displacement of the diaphragm  12  due to expansion and contraction of the driving piezoelectric element  20 . The natural vibration frequency F 1  of the horn  21  is equal to or lower than the drive critical frequency F 2  of the driving piezoelectric element  20 . 
     The natural vibration frequency F 1  of the horn  21  is a frequency at which the horn  21  performs free vibration. The natural vibration frequency F 1  of the horn  21  is a frequency specific to the horn  21 . The natural vibration frequency F 1  of the horn  21  is determined by the shape, material, mass, and the like of the horn  21 . Accordingly, the shape, material, mass and the like of the horn  21  are not particularly limited, and it is sufficient that the natural vibration frequency F 1  is set to a desired value. 
     The drive critical frequency F 2  of the driving piezoelectric element  20  is the maximum value of the critical frequency at which the driving piezoelectric element  20  can be driven with a stable amplitude. The drive critical frequency F 2  of the driving piezoelectric element  20  is a frequency specific to the driving piezoelectric element  20 . The drive critical frequency F 2  of the driving piezoelectric element  20  is determined by the configuration of the driving piezoelectric element  20 . The frequency (hereinafter referred to as “drive voltage signal frequency”) F 3  of the drive voltage signal applied to the driving piezoelectric element  20  is set to the drive critical frequency F 2  or less. 
     Here, when the natural vibration frequency F 1  of the horn  21  is equal to or lower than the drive critical frequency F 2  of the driving piezoelectric element  20 , and the natural vibration frequency F 1  and the drive voltage signal frequency F 3  are in a multiple relationship, the horn  21  resonates with the driving piezoelectric element  20 . In this case, the closer the natural vibration frequency F 1  of the horn  21  is to the drive voltage signal frequency F 3 , the higher the degree of resonance between the horn  21  and the driving piezoelectric element  20 , and the greater the amplitude between the horn  21  and the driving piezoelectric element  20 . When the natural vibration frequency F 1  of the horn  21  is the same as the drive voltage signal frequency F 3 , the degree of resonance between the horn  21  and the driving piezoelectric element  20  is maximized, and the amplitude between the horn  21  and the driving piezoelectric element  20  is also maximized. 
     Therefore, when the frequency difference between the natural vibration frequency F 1  of the horn  21  and the drive voltage signal frequency F 3  is reduced, the amplitude between the horn  21  and the driving piezoelectric element  20  increases, so that the amount of displacement of the diaphragm  12  by the driving piezoelectric element  20  can be increased. As a result, since a sufficient amount of displacement can be secured even when the voltage applied to the driving piezoelectric element  20  is reduced, the power consumption (including the amount output as displacement force and the amount consumed as heat) for the driving piezoelectric element  20  can be reduced. 
     On the other hand, since the amplitude between the horn  21  and the driving piezoelectric element  20  can be reduced when the frequency difference between the natural vibration frequency F 1  of the horn  21  and the drive voltage signal frequency F 3  is increased, the amount of displacement of the diaphragm  12  can be reduced. In this way, the amount of displacement of the diaphragm  12  can be adjusted as appropriate by controlling the degree of resonance between the horn  21  and the driving piezoelectric element  20 . 
     The fixing member  14  is a member that fixes the first end portion  13   p  of the drive unit  13 . The fixing member  14  is located on the liquid agent reservoir  11 . However, the fixing member  14  only needs to fix the first end portion  13   p  of the drive unit  13 , and may be separated from the liquid agent reservoir  11 . Further, the shape of the fixing member  14  is not limited to the shape shown in  FIG. 1 , and can be appropriately changed in consideration of the positional relationship with the peripheral members. 
     The control unit  15  is realized by a power amplifier composed of a microprocessor such as a central processing unit (CPU) and a digital signal processor (DSP), or an arithmetic device such as an application specific integrated circuit (ASIC), a power metal-oxide-semiconductor field-effect transistor (MOSFET) and the like. 
     The control unit  15  generates a drive voltage signal for driving the driving piezoelectric element  20 . The control unit  15  sends the generated drive voltage signal to the power amplifier to amplify the power, and applies the power to each of the pair of side surface electrodes  20   c  and  20   c  of the driving piezoelectric element  20  to vibrate the driving piezoelectric element  20 . 
     The control unit  15  sets the drive voltage signal frequency F 3  of the drive voltage signal to be equal to or lower than the drive critical frequency F 2  of the driving piezoelectric element  20 , and sets the natural vibration frequency F 1  of the horn  21  and the drive voltage signal frequency F 3  to have a multiple relationship. As mentioned above, the amount of displacement of the diaphragm  12  can be changed as appropriate by controlling the frequency difference between the natural vibration frequency F 1  of the horn  21  and the drive voltage signal frequency F 3 . 
     The control unit  15  preferably adjusts the drive voltage signal frequency F 3  of the drive voltage signal in accordance with the displacement of the driving piezoelectric element  20 . For this adjustment, a method of performing control so that the peak value is constant from the current and voltage in the waveform of the drive voltage signal or a method of performing control so that the phase difference between the current and voltage in the waveform of the drive voltage signal is constant can be used. In particular, in control by the phase difference, the feedback is performed so that the phase difference at the resonance frequency which is obtained in advance is set as the control target value, and the phase difference detected in actual driving matches the control target value. As a result, since the drive voltage signal frequency F 3  can be matched with the natural vibration frequency F 1 , the driving piezoelectric element  20  can be vibrated more efficiently. 
       FIG. 2  is a schematic diagram showing a configuration of a liquid agent application device  10   a  according to the second example embodiment. The difference between the liquid agent application device  10  according to the first example embodiment and the liquid agent application device  10   a  according to the second example embodiment is that the driving piezoelectric element  20  and the horn  21  are arranged in reverse. Therefore, the difference will be mainly described below. 
     A drive unit  13   a  is located on the diaphragm  12 . The drive unit  13   a  is disposed between the diaphragm  12  and the fixing member  14 . The first end portion  13   p  of the drive unit  13   a  is connected to the fixing member  14 . The second end portion  13   q  of the drive unit  13   a  is in contact with the diaphragm  12 . In this example embodiment, the first end portion  13   p  of the drive unit  13   a  is part of the driving piezoelectric element  20 , the second end portion  13   q  of the drive unit  13   a  is part of the horn  21 . 
     The drive unit  13  includes the driving piezoelectric element  20  and the horn  21 . 
     The driving piezoelectric element  20  is located on the horn  21 . The driving piezoelectric element  20  is disposed between the fixing member  14  and the horn  21 . The driving piezoelectric element  20  is sandwiched between the fixing member  14  and the horn  21 . The driving piezoelectric element  20  is connected to the fixing member  14  and the horn  21 . 
     The horn  21  is located on the diaphragm  12 . The horn  21  is disposed between the diaphragm  12  and the driving piezoelectric element  20 . The horn  21  is sandwiched between the diaphragm  12  and the driving piezoelectric element  20 . 
     The horn  21  is connected to the driving piezoelectric element  20 . In addition, the horn  21  may be in contact with the driving piezoelectric element  20 . The horn  21  is in contact with the diaphragm  12 . However, the horn  21  may be connected to the diaphragm  12 . 
     As above, even when the horn  21  and the driving piezoelectric element  20  are sequentially arranged from the diaphragm  12  side, the displacement amount of the diaphragm  12  by the driving piezoelectric element  20  can be appropriately changed by the horn  21  by adjusting the frequency difference between the natural vibration frequency F 1  of the horn  21  and the drive voltage signal frequency F 3  as described in the first example embodiment. 
       FIG. 3  is a schematic diagram showing the configuration of a liquid agent application device  10   b  according to the third example embodiment. The difference between the liquid agent application device  10  according to the first example embodiment and the liquid agent application device  10   b  according to the third example embodiment is that the drive unit  13   b  includes an oscillating piezoelectric element  22 . Therefore, the difference will be mainly described below. 
     The drive unit  13   b  is located on the diaphragm  12 . The drive unit  13   b  is disposed between the diaphragm  12  and the fixing member  14 . The first end portion  13   p  of the drive unit  13   b  is connected to the fixing member  14 . The second end portion  13   q  of the drive unit  13   b  is in contact with the diaphragm  12 . In this example embodiment, the first end portion  13   p  of the drive unit  13   b  is part of the oscillating piezoelectric element  22  described later, and the second end portion  13   q  of the drive unit  13   a  is part of the driving piezoelectric element  20 . 
     The drive unit  13   b  includes the driving piezoelectric element  20 , the horn  21 , and the oscillating piezoelectric element  22 . 
     The configuration of the driving piezoelectric element  20  and the horn  21  is as described in the first example embodiment. Therefore, also in this example embodiment, the amount of displacement of the diaphragm  12  can be changed as appropriate by controlling the frequency difference between the natural vibration frequency F 1  of the horn  21  and the drive voltage signal frequency F 3 . 
     The oscillating piezoelectric element  22  is located on the horn  21 . The oscillating piezoelectric element  22  is disposed between the fixing member  14  and the horn  21 . The oscillating piezoelectric element  22  is sandwiched between the fixing member  14  and the horn  21 . 
     The oscillating piezoelectric element  22  is connected to the horn  21 . The oscillating piezoelectric element  22  is connected to the horn  21  via an adhesive such as an epoxy resin. 
     The oscillating piezoelectric element  22  is connected to the fixing member  14 . The oscillating piezoelectric element  22  can be connected to the fixing member  14  via an adhesive such as an epoxy resin. 
     The oscillating piezoelectric element  22  includes at least one piezoelectric body and a pair of electrodes. Examples of the oscillating piezoelectric element  22  can include various known piezoelectric elements. The oscillating piezoelectric element  22  vibrates according to the high-frequency signal applied from the control unit  15 . The high-frequency signal applied to the oscillating piezoelectric element  22  is a signal having a higher frequency than that of the drive voltage signal applied to the driving piezoelectric element  20 . The amplitude (potential difference) of the high-frequency signal is preferably smaller than the amplitude (potential difference) of the drive voltage signal. 
     The oscillating piezoelectric element  22  to which the high-frequency signal is applied applies a minute pressurization vibration to the diaphragm  12  such that the liquid agent is not discharged from the discharge port  11   e . As a result, while improving the fluidity of the liquid agent stored in the liquid agent reservoir  11 , it is possible to improve the dripping properties of the liquid agent discharged from the discharge port  11   e.    
     From the viewpoint of improving the fluidity of the liquid agent, the amplitude of the high-frequency signal is preferably between 1% to 20% of the amplitude of the drive voltage signal, and the frequency of the high-frequency signal is preferably between 1 kHz to 30 kHz. In the case of a liquid agent exhibiting thixotropy, in general, as the frequency of the high-frequency signal increases, the fluidity can be improved. 
     From the viewpoint of improving the dripping properties, the amplitude of the high-frequency signal is preferably between 1% to 20% of the amplitude of the drive voltage signal, the frequency of the high-frequency signal is preferably between 1 kHz to 5 kHz. 
     In  FIG. 3 , the form in which the oscillating piezoelectric element  22  is disposed between the fixing member  14  and the horn  21  is exemplified, but the present disclosure is not limited to this. The oscillating piezoelectric element  22  may be disposed between the driving piezoelectric element  20  and the horn  21 , or may be disposed between the diaphragm  12  and the driving piezoelectric element  20 . 
     In  FIG. 3 , the form in which the driving piezoelectric element  20  and the horn  21  are sequentially arranged from the diaphragm  12  side is exemplified. As explained in the second example embodiment, the arrangement of the driving piezoelectric element  20  and the horn  21  may be reversed. 
       FIG. 4  is a schematic diagram showing a configuration of a liquid agent application device  10   c  according to the fourth example embodiment. The difference between the liquid agent application device  10  according to the first example embodiment and the liquid agent application device  10   c  according to the fourth example embodiment is that a preload spring  17  is disposed between the drive unit  13  and the fixing member  14 . Therefore, the difference will be mainly described below. 
     The preload spring  17  is located on the drive unit  13 . The preload spring  17  is disposed between the drive unit  13  and the fixing member  14 . The preload spring  17  is sandwiched between the drive unit  13  and the fixing member  14 . 
     A first end portion  17   p , of the preload spring  17 , opposite to the drive unit  13  is connected to the fixing member  14 . That is, the first end portion  17   p  of the preload spring  17  is fixed to the fixing member  14 . Accordingly, the first end portion  17   p  of the preload spring  17  is a fixed end portion. The first end portion  17   p  of the preload spring  17  may be directly fastened to the fixing member  14 , or, for example, may be connected to the fixing member  14  via an adhesive such as an epoxy resin. 
     A second end portion  17   q , of the preload spring  17 , toward the drive unit  13  is connected to the first end portion  13   p  of the drive unit  13 . That is, the second end portion  17   q  of the preload spring  17  is fixed to the first end portion  13   p  of the drive unit  13 . Therefore, in the present example embodiment, the first end portion  13   p  of the drive unit  13  is not a fixed end portion. The second end portion  17   q  of the preload spring  17  may be directly fastened to the drive unit  13 , or, for example, may be connected to the drive unit  13  via an adhesive such as an epoxy resin. 
     In  FIG. 4 , the case where a coil spring is used as the preload spring  17  is illustrated, but the present disclosure is not limited to this. Examples of the preload spring  17  may include known springs such as a disc spring, a leaf spring, or a spiral spring. The spring constant of the preload spring  17  is preferably larger than the spring constant of the diaphragm  12 . 
     The preload spring  17  presses the drive unit  13  against the diaphragm  12 . The preload spring  17  constantly presses the drive unit  13  against the diaphragm  12  regardless of whether the driving piezoelectric element  20  is expanded or contracted. 
     Here, since the second end portion  13   q  of the drive unit  13  is only in contact with the diaphragm  12 , when the expanded driving piezoelectric element  20  contracts, not only a tensile force due to expansion occurs inside the driving piezoelectric element  20 , but also ringing of the drive unit  13  itself may occur. However, in this example embodiment, as mentioned above, the drive unit  13  can be pressed against the diaphragm  12  by the pressing force of the preload spring  17 . For this reason, while suppressing the tensile force generated in the driving piezoelectric element  20 , ringing of the drive unit  13  can be suppressed. 
     Also, when the second end portion  13   q  of the drive unit  13  is connected to the diaphragm  12 , in a case where the expanded driving piezoelectric element  20  contracts, the contraction speed of the drive unit  13  is faster than the return speed of the diaphragm  12 , so that there is a possibility that the drive unit  13  may be separated from the diaphragm  12 . However, as in this example embodiment, the drive unit  13  is pressed against the diaphragm  12  by the pressing force of the preload spring  17 , so that the drive unit  13  can be prevented from being separate from the diaphragm  12 . 
     Although the present disclosure has been described according to the above example embodiments, the discussion and drawings that form part of this disclosure should not be construed as limiting the disclosure. From this disclosure, various alternative example embodiments, examples and operational techniques will be apparent to those skilled in the art. 
     In the first to third example embodiments, the first end portion  13   p  of the drive unit  13  is connected to the fixing member  14 , but it may be only in contact with the fixing member  14 . 
     In the first to fourth example embodiments, the second end portion  13   q  of the drive unit  13  is in contact with the diaphragm  12 , but it may be connected to the diaphragm  12 . 
     In the first to fourth example embodiments, the second end portion  13   q  of the drive unit  13  is in direct contact with the diaphragm  12 , but an intermediate member that is in surface contact with the drive unit  13 , and which is in point contact with the diaphragm  12  may be sandwiched between the second end portion  13   q  and the diaphragm  12 . The intermediate member is fixed to the second end portion  13   q  of the drive unit  13 , and can be brought into and out of contact with the diaphragm  12 . Since it is possible to prevent the pressing force from being concentrated on part of the second end portion  13   q  of the drive unit  13  by sandwiching such an intermediate member, damage to the drive unit  13  can be suppressed. 
     In the second example embodiment, the driving piezoelectric element  20  is connected to the fixing member  14  and the horn  21 , but as shown in  FIG. 5 , may be fixed between the fixing member  14  and the horn  21  through a fastener  30 . Example of the fastener  30  may include a screw and the like. The fastener  30  passes through the driving piezoelectric element  20  and is fastened to the horn  21 . In order to efficiently transmit the vibration of the driving piezoelectric element  20  to the horn  21 , the fastener  30  preferably has a sufficient fastening force. The driving piezoelectric element  20  is formed in a shape (for example, a hollow ring shape) that allows the fastener  30  to pass therethrough. The end portion, of the driving piezoelectric element  20 , toward the fixing member  14  is a fixed end portion. In this way, the vibration of the driving piezoelectric element  20  can be efficiently transmitted to the horn  21  by fixing the driving piezoelectric element  20  between the fixing member  14  and the horn  21  through the fastener  30 , compared to, for example, the case where the both are connected via an elastic body such as an adhesive. 
     Features of the above-described preferred example embodiments and the modifications thereof may be combined appropriately as long as no conflict arises. 
     While example embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.