JP4957480B2 - Piezoelectric micro pump - Google Patents

Description

The present invention relates to a piezoelectric micro pump, and more particularly to a piezoelectric micro pump using a diaphragm that is bent and displaced by a piezoelectric element.

Piezoelectric micropumps are used as cooling pumps for small electronic devices such as notebook computers and fuel transportation pumps for fuel cells. A piezoelectric micropump is a pump that uses a diaphragm that bends and deforms when a voltage is applied to a piezoelectric element. The piezoelectric micropump has an advantage that the structure is simple and thin, and the power consumption is low. In the case of a piezoelectric micropump that uses a piezoelectric element as a drive source, check valves are provided at the inlet and outlet of the micro pump. There is a problem that the foreign matter adheres and the fluid cannot be transported sufficiently. In general, rubber and resin with low elasticity are used as the check valve material. In this case, however, the check valve cannot follow up when the piezoelectric element is driven at a high frequency, and fluid cannot be transported. There was a problem.

Patent Document 1 discloses a piezoelectric pump in which a diaphragm is attached in a contact state on a pump body having an inlet and an outlet, and a plurality of piezoelectric elements are attached on the diaphragm so as to be arranged from the inlet to the outlet. Has been proposed. In the case of this pump, by sequentially driving the piezoelectric element close to the inlet side to the piezoelectric element close to the outlet side, the diaphragm is sequentially bent from the inlet to the outlet, and the fluid is transferred from the inlet. It can be pushed out toward the outlet. When the voltage application to the piezoelectric element is stopped, the flow path between the inlet and the outlet is closed by restoring the diaphragm, so that the check valves at the inlet and the outlet can be omitted.

Patent Document 2 discloses a fluid pump that does not have a check valve. In particular, in FIG. 10 of Patent Document 2, a pump chamber is formed between the pump main body and the diaphragm, a first opening is provided in the central portion of the pump main body, a second opening is provided in the peripheral portion, and the diaphragm A fluid pump is disclosed in which an elastic buffer is formed and the diaphragm is bent and deformed by reciprocating the central portion of the diaphragm by another driving means. When the diaphragm opens the first opening, fluid is sucked into the pump chamber from the first opening, and when the first opening is closed, the buffer corresponding to the second opening is bent, and the elastic restoring force of the buffer The fluid is discharged from the second opening.

In the piezoelectric pump as in Patent Document 1, it is necessary to arrange a plurality of piezoelectric elements in a planar shape, so that the piezoelectric pump becomes large and complicated, and the driver circuit for sequentially driving the piezoelectric elements also becomes complicated. There is a problem that it becomes expensive.

In the case of Patent Document 2, since the diaphragm is merely reciprocated by a single drive source, the structure is simplified. However, the part facing the first opening of the diaphragm, that is, only the center part of the diaphragm is displaced, and the peripheral part (buffer part) of the diaphragm is bent and deformed behind that displacement, so a soft material must be used as the diaphragm. The discharge pressure cannot be increased. In addition, when the fluid is a compressible fluid such as air, a very soft material such as rubber or resin must be used to elastically deform the buffer portion of the diaphragm, and the drive frequency may be increased. Can not. That is, when a soft material is used as the diaphragm, a delay time between the displacement of the central portion of the diaphragm and the displacement of the peripheral portion of the diaphragm is generated, and therefore, it cannot be driven at a frequency higher than the delay time. Therefore, it is difficult to obtain a desired flow rate.
JP-A-2-149778 JP 10-511165 A

An object of the present invention is to provide a piezoelectric micropump that can transport a fluid without using a check valve, has a simple structure, and can obtain a desired flow rate.

In order to achieve the above object, the present invention comprises a pump body, a diaphragm having an outer peripheral portion fixed to the pump body and a piezoelectric element fixed to the center portion, and a pump chamber formed between the pump body and the diaphragm. A piezoelectric micro pump having a first wall portion in contact with the diaphragm is formed at a portion of the pump body facing the outer peripheral portion of the pump chamber with the diaphragm interposed therebetween, and the diaphragm in contact with the first wall portion. A first opening is provided at the site, and a second opening is provided on the side wall of the pump main body, which is in contact with the side surface of the diaphragm on the pump chamber side. The first opening is closed by the first wall of the pump body, and the second opening is closed by the diaphragm, and is caused by the bending displacement of the diaphragm accompanying the vibration of the piezoelectric element. Opening the first opening and the second opening are alternately draws fluid from one aperture to provide a piezoelectric micro pump, characterized by discharging the fluid from the other opening.

In the present invention, the fluid is discharged by forcibly bending and deforming the diaphragm by a piezoelectric element, instead of pushing out the fluid by using the elastic restoring force of the diaphragm itself as in Patent Document 2. A first opening is provided in a portion of the diaphragm that is in contact with the first wall of the pump body facing the outer periphery of the pump chamber, and the second wall of the pump body that is in contact with the side of the diaphragm on the pump chamber side Two openings are provided. At rest, both the first opening and the second opening are closed, but when the piezoelectric element is vibrated, the diaphragm is bent and displaced, and the first opening and the second opening are alternately opened. . Due to the volume change of the pump chamber accompanying the bending displacement of the diaphragm, the fluid can be sucked from one opening and discharged from the other opening. As described above, since the diaphragm portion facing the first opening and the diaphragm portion facing the second opening can be efficiently bent and deformed in the opposite directions, the check valve can be omitted and the discharge pressure can be reduced. The fluid can be reliably discharged even under conditions where the pressure on the discharge side is high. Since a hard material can be used as the diaphragm, the diaphragm can follow the piezoelectric element well, and can be operated at a high frequency. Therefore, a large flow rate can be obtained.

The frequency of the voltage applied to the piezoelectric element can be selected arbitrarily. However, when driven at a frequency near the resonance frequency of the entire diaphragm (including the piezoelectric element), the displacement volume of the diaphragm becomes very large and a large flow rate is obtained. Is desirable. When the diaphragm is driven in the primary resonance mode, the entire diaphragm is displaced in a uniform direction, so that the fluid can be sucked from the second opening and discharged from the first opening. When driven in the tertiary resonance mode, the central portion and the peripheral portion of the diaphragm are displaced in opposite directions, so that the fluid can be sucked from the first opening and discharged from the second opening.

Both the primary resonance mode and the tertiary resonance mode can be driven at a high frequency, but particularly when the tertiary resonance mode is used, it can operate at a very high frequency of about three times the primary resonance mode. This makes it possible to drive at a frequency exceeding the audible range, thereby preventing noise. In particular, when driving in the third resonance mode exceeding the human audible range, no noise is generated and a large flow rate is obtained. Further, since the displacement is small, the stress generated in the fixed portion between the pump body and the diaphragm is reduced, and the reliability is improved.

When driving in the primary resonance mode, a top plate that covers the diaphragm may be provided at a portion of the pump body facing the pump chamber with the diaphragm interposed therebetween, and a discharge hole may be formed in the top plate. In this case, another fluid chamber is formed on the side facing the pump chamber with the diaphragm interposed therebetween, and the fluid discharged from the first opening is temporarily stored in the fluid chamber, and is discharged from the fluid chamber through the discharge hole. Therefore, the fluid can be discharged from one place.

The piezoelectric micropump of the present invention is suitable for transporting a compressive fluid such as air and can be used as a so-called piezoelectric microblower. When discharging an incompressible fluid such as liquid, check valves using soft materials such as rubber and resin are provided at the inlet and outlet, respectively, and the piezoelectric element is driven at a low frequency of about several tens of Hz. It is common. However, when a pump having a check valve is used to discharge a compressive fluid such as air, the displacement of the piezoelectric element is very small, and the fluid can hardly be discharged. When the piezoelectric element is driven in the vicinity of the resonance frequency (primary resonance frequency or tertiary resonance frequency) of the diaphragm, the maximum displacement is obtained, but the check valve cannot follow up because the resonance frequency is a high frequency on the order of kHz. Since the present invention does not have a check valve, even if the piezoelectric element is driven at a frequency near the resonance frequency, there is no restriction by the check valve, and the compressible fluid can be transported efficiently. In addition, a highly reliable piezoelectric micro pump can be provided without concern that dust or the like may adhere to the check valve and cause malfunction.

The first opening and the second opening may be formed at the maximum displacement position of the diaphragm excluding the portion where the piezoelectric element in the third-order resonance mode is disposed or on the outer peripheral side thereof. The maximum displacement position of the diaphragm in the third-order resonance mode varies depending on the area ratio of the piezoelectric element and the diaphragm, the Young's modulus of the diaphragm, and the like. By providing the second opening, the lift amount of the first opening and the second opening can be sufficiently obtained and the sealing performance can be sufficiently obtained in the operation cycle of the piezoelectric micropump. Therefore, the back flow of the fluid can be prevented, and not only the discharge pressure but also the discharge flow rate is increased.

According to the present invention, the first opening is provided in the diaphragm portion in contact with the first wall portion of the pump body facing the outer peripheral portion of the pump chamber, and the second of the pump body in contact with the side surface of the diaphragm on the pump chamber side. A second opening is provided on the wall of the diaphragm, both openings are closed when stationary, and an electric signal is applied to the piezoelectric element to oppose the first opening and the second opening of the diaphragm. By bending and deforming the diaphragm part in the same direction, the other opening is closed when one opening is open, so that the discharge pressure can be increased and the fluid can be fluid even under conditions where the discharge side pressure is high. Can be discharged reliably. In addition, the diaphragm can be driven at a high frequency, and a large flow rate can be obtained. In addition, the piezoelectric micropump can be configured with only the diaphragm with the pump body and piezoelectric element attached, and no auxiliary parts such as a check valve are required, so the structure is very simple, small and thin, and highly reliable. Can be realized.

Hereinafter, preferred embodiments of the present invention will be described based on examples.

1 to 3 show a first embodiment of the present invention, which shows an example of a piezoelectric microblower that transports air, which is a compressible fluid. Here, FIG. 1 is a sectional view of the piezoelectric microblower, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is an exploded perspective view.

The piezoelectric micro blower B of this embodiment is composed of a pump body 10 and a diaphragm 20. The pump body 10 is obtained by laminating and bonding a bottom plate 11, a lower frame plate 12, an upper frame plate 13 and a top plate 14 in order from the bottom, and is formed of a hard material such as a resin material or a metal material. The lower frame plate 12 has a hollow portion 12a in which half is elliptical and the other half is circular, and a pump chamber 15 is formed by the hollow portion 12a. The upper frame plate 13 is also formed with a hollow portion 13a in which half is elliptical and the other half is circular, and a fluid chamber 16 is formed by the hollow portion 13a. The pump chamber 15 is indicated by a broken line in FIG. 2, the fluid chamber 16 is indicated by a solid line in FIG. 2, and both chambers 15, 16 are asymmetrical. A pedestal portion (corresponding to the second wall portion) 12b that protrudes slightly outside the piezoelectric element 22 is formed on the side wall of the lower frame plate 12 and facing the circular portion of the fluid chamber 16. A second opening 12c that is closed by the diaphragm 21 is formed in the pedestal 12b. The pedestal portion 12b is located inside the outer peripheral adhesion region of the diaphragm 20, and the second opening portion 12c can be opened by the displacement of the diaphragm 20.

The bottom plate 11 is formed with a hole 11 a communicating with the second opening 12 c of the lower frame plate 12. A communication hole 14 a for communicating the fluid chamber 16 and the outside air is formed at the center of the top plate 14. The top plate 14 can be omitted, and the fluid chamber 16 may be directly open to the outside air.

The diaphragm 20 includes a vibration plate 21 made of a metal plate or a hard resin plate, and a disk-shaped piezoelectric element 22 attached to the upper surface of the center portion. The configuration of the diaphragm 20 may be a configuration in which a bimorph type piezoelectric element is bonded to a vibration plate, or may be a configuration in which a single plate piezoelectric element is bonded up and down across the vibration plate. Alternatively, a unimorph type piezoelectric element in which a single plate piezoelectric element is bonded to a metal plate may be used. Further, the diaphragm 20 may be composed of only the piezoelectric element 22. That is, the configuration is not limited as long as it is a diaphragm that applies an alternating electric field (sine wave or rectangular wave) to the piezoelectric element 22 and performs bending displacement using the vibration of the piezoelectric element. A first opening 21 a made of a through hole is formed in the outer peripheral side of the region of the diaphragm 21 to which the piezoelectric element 22 is attached and in the inner peripheral side of the region bonded to the pump body 10. The first opening 21a of this embodiment is formed at a 180 ° symmetrical position with respect to the second opening 12c formed in the lower frame plate 12. A pedestal portion (corresponding to the first wall portion) 13 b that protrudes to a position slightly outside the piezoelectric element 22 is formed on the side wall of the upper frame plate 13 and facing the circular portion of the pump chamber 15. The first opening 21a is closed by the pedestal 13b.

The outer shape of the diaphragm 21 is formed in the same quadrangle as the lower frame plate 12 and the upper frame plate 13, and the outer peripheral portion thereof is bonded and fixed between the lower frame plate 12 and the upper frame plate 13. The adhesion region of the diaphragm 21 is a region on the outer peripheral side from the pump chamber 15 and the fluid chamber 16 as indicated by hatching in FIG. Therefore, the periphery of the first opening 21a and the periphery of the second opening 12c are not bonded, and the diaphragm 20 can be freely displaced. The vibration plate 21 may be a metal plate or a resin plate, but it is preferable to use a hard plate having a Young's modulus of about 10 ⁹ Pa or more so that it can follow the displacement of the piezoelectric element 22 when driven in the resonance mode.

FIG. 4 shows the displacement of the piezoelectric microblower B having the above structure when the diaphragm 20 is driven in the primary resonance mode. The primary resonance mode is a mode in which the entire diaphragm 20 is displaced so as to be uniformly convex upward or convex downward. FIG. 4A shows the first quarter period of the voltage applied to the piezoelectric element 22, and the diaphragm 20 is displaced so as to protrude upward. The second opening 12c is opened, and the first opening 21a is closed by the pedestal 13b. Since the volume of the pump chamber 15 on the lower side of the diaphragm 20 increases, the fluid is sucked into the pump chamber 15 from the second opening 12c. When the diaphragm 20 is displaced upward, the volume of the fluid chamber 16 is reduced, so that the fluid is discharged from the communication hole 14 a of the top plate 14. FIG. 4B shows the next quarter period, and the diaphragm 20 has returned to a flat posture. Both the first opening 21a and the second opening 12c are closed, and there is no fluid movement. FIG. 4 (c) further shows the next quarter cycle, and the diaphragm 20 is displaced so as to protrude downward, so that the volume of the pump chamber 15 below the diaphragm 20 decreases, and at the same time the first Since the opening 21 a is separated from the pedestal 13 b, the fluid in the pump chamber 15 is pushed out from the first opening 21 a to the fluid chamber 16. At this time, since the second opening 12c is closed by the diaphragm 20, the fluid does not flow backward. Thereafter, the operation of the diaphragm 20 returns to (b) of FIG. 4, and thereafter, the operations of (b) → (a) → (b) → (c) are periodically repeated.

As described above, when the diaphragm 20 is driven in the primary resonance mode, the fluid can be sucked from the second opening 12c and discharged from the communication hole 14a through the first opening 21a. Since the diaphragm 20 resonates, a very large displacement can be obtained, and the fluid can be efficiently transported because the diaphragm 20 is driven at a high frequency.

The piezoelectric micro blower having the structure shown in FIG. 1 was prototyped under the following conditions, and the characteristics were evaluated.
Upper frame plate: glass epoxy plate with a thickness of 1.5 mm, half of the cavity is a circle with a diameter of 52 mm (10 mm margin for the piezoelectric element), and the other half is an ellipse with a 6 mm margin for the piezoelectric element Shape lower frame plate: a glass epoxy plate having a thickness of 0.1 mm and a shape symmetrical to the upper frame plate, and a hole (second opening) having a diameter of 2 mm is formed at a position 1.5 mm from the end of the ellipse side. A 1.5 mm thick glass epoxy plate, a hole top plate at the same position as the lower frame plate: None Piezoelectric element: Diameter 32 mm: Bimorph type piezoelectric element diaphragm in which two circular piezoelectric ceramics of 0.2 mm thickness are laminated: Piezoelectric element thickness Bonded to a 0.1 mm glass epoxy plate and formed a hole (first opening) with a diameter of 2 mm at a position 1.5 mm from the elliptical end of the upper frame plate A rectangular wave with a driving voltage of ± 60 V

In order to evaluate the characteristics of the micro-blower prototyped under the above conditions, when the piezoelectric element was driven at a driving frequency of 2.2 kHz (primary resonance mode), a static pressure of 900 Pa and a no-load flow rate of 0.4 ml / sec were obtained. As a result, it was confirmed that it operates at a high frequency. This time, a piezoelectric element with a diameter of 32 mm was used, but the resonance frequency of the piezoelectric element increases if the piezoelectric element is miniaturized, and also increases if the diaphragm material is hardened. By setting these conditions, Driving at a higher frequency is also possible. Therefore, the problem of noise can be solved by increasing the frequency beyond the audible range.

FIG. 5 shows a case where the diaphragm 20 is driven in the tertiary resonance mode. The tertiary resonance mode is a mode in which the center portion and the peripheral portion of the diaphragm 20 are displaced so as to be upside down. In this case, it is preferable to form the first opening 21a and the second opening 12c at a position corresponding to the peripheral portion where the maximum displacement occurs in a portion where the piezoelectric element of the diaphragm 20 is not disposed or outside thereof. FIG. 5A shows the first quarter period of the voltage applied to the piezoelectric element 22, and the center portion of the diaphragm 20 is displaced so as to protrude upward. Since the deformation of the piezoelectric element 22 and the pressure in the pump chamber 15 are reduced, the peripheral portion of the diaphragm 20 is pulled downward. Therefore, the first opening 21 a is opened and the second opening 12 c is closed by the diaphragm 20. Here, only the peripheral part of the diaphragm 20 is pulled downward, and the entire piezoelectric element 22 is not displaced downward. The mass of the piezoelectric element 22 is larger than the mass of the diaphragm 21. This is because it does not change. The movement in which the peripheral portion of the diaphragm 20 is pulled downward is the direction in which the first opening 21a opens more widely, so that the fluid is smoothly introduced into the pump chamber 15. FIG. 5B shows the next ¼ period, and the diaphragm 20 returns to a flat posture. In this state, both the first opening 21a and the second opening 12c are closed, and there is no fluid movement. (C) of FIG. 5 is the next quarter cycle, and the center portion of the diaphragm 20 is displaced so as to protrude downward. Since the pressure in the pump chamber 15 is increased, the peripheral portion of the diaphragm 20 is pushed upward, and the second opening 12c is opened, so that the fluid in the pump chamber 15 is pushed out from the second opening 12c. At this time, the first opening 21a is closed by the pedestal 13b, so that the fluid does not flow backward. Thereafter, the operation of the diaphragm 20 returns to (b) of FIG. 5 and thereafter the operations of (b) → (a) → (b) → (c) are periodically repeated.

As described above, when the diaphragm 20 is driven in the tertiary resonance mode, the fluid can be sucked from the first opening 21a and discharged from the second opening 12c. In the tertiary resonance mode, the excluded volume per stroke is reduced as compared with the primary resonance mode, but the number of strokes can be increased and the flow rate can be increased by increasing the frequency. Although the top plate 14 is used in FIG. 5, the top plate 14 can be omitted because the fluid chamber 16 may be open to the atmosphere when driven in the tertiary resonance mode.

6, 7 and 8 show a piezoelectric microblower according to a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. In this embodiment, the lower frame plate 12 and the upper frame plate 13 are formed with cavity portions 12a and 13a constituting the pump chamber 15 and the fluid chamber 16, respectively. The pump chamber 15 and the fluid chamber 16 are 90 ° out of phase with each other. It has an oval shape. A first opening 21 a that contacts the pedestal portion 13 b of the upper frame plate 13 is formed in a portion of the diaphragm 20 that faces two locations on the long axis side of the pump chamber 15, and two locations on the long axis side of the fluid chamber 16 A second opening 12c is formed in the pedestal 12b of the opposed lower frame plate 12. In this embodiment, since the first opening 21a and the second opening 12c are formed at two locations, the flow path can be enlarged and the flow rate can be increased. As in the first embodiment, the fluid transport direction can be reversed by driving the diaphragm 20 in the primary resonance mode and the tertiary resonance mode.

In the above-described embodiment, an example in which the first opening 21a and the second opening 12c are round holes has been described. However, the shape of the openings is arbitrary, and the number, size, and length are also arbitrary.
As the structure of the pump body, an example in which a bottom plate 11, a lower frame plate 12, an upper frame plate 13 and a top plate 14 are laminated and the diaphragm 20 is sandwiched between the lower frame plate 12 and the upper frame plate 13 is shown. However, the structure is arbitrary. The outer shape is not limited to a quadrangle.
In the above embodiment, the piezoelectric micro pump of the present invention is used as a blower for transporting a compressible fluid such as air. However, the present invention can also be applied to an incompressible fluid such as a liquid.

1 is a cross-sectional view of a first embodiment of a piezoelectric micropump according to the present invention. It is the II-II sectional view taken on the line of FIG. It is a disassembled perspective view of the piezoelectric micro pump shown in FIG. It is sectional drawing which shows a displacement when the piezoelectric micropump shown in FIG. 1 is driven by a primary resonance mode. It is sectional drawing which shows a displacement when the piezoelectric micropump shown in FIG. 1 is driven by a tertiary resonance mode. It is a cross-sectional view of the second embodiment of the piezoelectric micropump according to the present invention. It is the VII-VII sectional view taken on the line of FIG. It is the VIII-VIII sectional view taken on the line of FIG.

Explanation of symbols

B Piezoelectric micro pump (piezoelectric micro blower)
10 Pump body 11 Bottom plate 12 Lower frame plate 12b Pedestal part (second wall part)
12c 2nd opening part 13 Upper frame board 13b Pedestal part (1st wall part)
14 Top plate 15 Pump chamber 16 Fluid chamber 20 Diaphragm 21 Diaphragm 21a First opening 22 Piezoelectric element

Claims (5)

A piezoelectric micropump having a pump body, a diaphragm whose outer peripheral part is fixed to the pump body, and a piezoelectric element fixed to the center part, and a pump chamber formed between the pump body and the diaphragm,
A first wall portion in contact with the diaphragm is formed at a portion of the pump body facing the outer peripheral portion of the pump chamber with the diaphragm interposed therebetween,
A first opening is provided in a portion of the diaphragm in contact with the first wall;
A second opening is provided in a second wall portion of the pump body, which is in contact with a side surface of the diaphragm on the pump chamber side;
At rest, the first opening is closed by the first wall of the pump body, and the second opening is closed by the diaphragm,
According to the bending displacement of the diaphragm accompanying the vibration of the piezoelectric element, the first opening and the second opening are alternately opened, the fluid is sucked from one opening, and the fluid is discharged from the other opening. Piezoelectric micro pump. The fluid is sucked from the second opening and discharged from the first opening by applying an electric signal that causes the diaphragm to be displaced in the primary resonance mode to the piezoelectric element. The piezoelectric micropump described. The top plate that covers the diaphragm is provided at a portion of the pump body that faces the pump chamber with the diaphragm interposed therebetween, and a discharge port is formed in the top plate. Piezoelectric micro pump. The fluid is sucked from the first opening and discharged from the second opening by applying an electric signal that causes the diaphragm to be displaced in the third resonance mode to the piezoelectric element. The piezoelectric micropump described. The first opening and the second opening are formed at the maximum displacement position of the diaphragm excluding the portion where the piezoelectric element in the third-order resonance mode is disposed or on the outer peripheral side thereof. Item 5. The piezoelectric micropump according to Item 4.

Images