JPWO2009119431A1 - Piezoelectric fan device and air cooling device using this piezoelectric fan device - Google Patents

Abstract

A piezoelectric fan device that uses a plurality of miniaturized piezoelectric fans and can reduce vibration generated in a support portion by driving a piezoelectric vibrator. Four piezoelectric fans (10a to 10d) are arranged in parallel in the width direction, and the ends of the piezoelectric fans on the side opposite to the extending side of the piezoelectric fans are connected and supported in parallel by a support body (11). Each piezoelectric fan includes piezoelectric vibrators 13a to 13d that bend and vibrate when a voltage is applied, and blades 12a to 12d that are coupled to the piezoelectric vibrators so as to be excited by the piezoelectric vibrators. Since the two piezoelectric fans 10b and 10c at the center are driven in the same phase by the voltage application means 15 and the two piezoelectric fans 10a and 10d at both ends are driven in the opposite phases, only the center of gravity vibration acting on the support 11 is required. In addition, moments around the three axes are canceled out. [Selection] Figure 5

Description

  The present invention relates to a piezoelectric fan device that generates a wind by bending and displacing a blade connected to the piezoelectric vibrator by bending and vibrating the piezoelectric vibrator.

  In recent years, with miniaturization and high-density mounting of parts in portable electronic devices, measures to dissipate heat generated in the electronic devices have become issues. An air cooling device using a piezoelectric fan has been proposed as means for efficiently radiating heat from such an electronic device.

  Patent Document 1 includes a piezoelectric bimorph vibrator in which a metal thin plate is sandwiched and bonded between a pair of plate-like piezoelectric elements, and an elastic thin plate is attached to both ends of the piezoelectric bimorph vibrator in a direction perpendicular to the piezoelectric bimorph vibrator. A piezoelectric fan having a structure in which a central portion of a vibrator is sandwiched and supported by a support portion is disclosed.

  In the case of the above structure, since the central part of one piezoelectric bimorph vibrator is supported by the support part, the piezoelectric vibrators on both sides of the support part deform symmetrically. In other words, if the left side of the support part is convexly convex upward, the right side is also convexly upward, and the center of gravity on the left and right sides of the support part is always the same in the direction perpendicular to the piezoelectric vibrator surface. Move. The reaction force generated by the vibration of the piezoelectric body (moving the center of gravity) is the same as the reaction force caused by the left-hand motion and the reaction force caused by the right-hand motion. It is subject to vibration of the power of. As a result, the support portion is very likely to vibrate, and this vibration is transmitted to other portions, which adversely affects the reliability of other components and contacts. For example, when this piezoelectric fan is used for the purpose of discharging warm air between a large number of radiating fins of a heat sink, the configuration of the piezoelectric fan becomes large, and the installation position is restricted.

  Patent Document 2 discloses a piezoelectric fan that discharges warm air between a large number of radiating fins of a heat sink by vibrating a wind-generating vibrator like a fan with a piezoelectric element. In this case, the structure is such that a wind generating plate is fixed between a pair of piezoelectric elements displaced in the opposite direction, the wind generating plate is protruded long from one end side of the piezoelectric element, and the other end side of the piezoelectric element is fixed to the case. Since it becomes (refer FIG. 2), the gravity center of the whole piezoelectric fan vibrates greatly with the vibration of a wind generating plate. Therefore, there is a problem that large vibration and moment act on the support portion supporting the piezoelectric element, and the vibration of the piezoelectric element is directly transmitted to the case main body, causing noise and impairing the durability of the case. . If the piezoelectric element is fixed to the case via an elastic body such as rubber, it is possible to suppress the ripple of vibration to the case. Becomes extremely small, and a desired air volume cannot be obtained.

  Patent Document 3 discloses a blower in which a plurality of piezoelectric fans are supported in parallel and alternating voltage phases supplied to the piezoelectric fans are alternately reversed in phase. In this case, since the piezoelectric fans arranged in the width direction are alternately driven in the opposite phase, the air volume can be increased as compared with the case of driving in the same phase. Incidentally, in addition to the center of gravity vibration, moments about three axes of the length direction axis, the width direction axis, and the thickness direction axis act on the support body supporting the plurality of piezoelectric fans. If the piezoelectric fans are alternately driven in opposite phases as in Patent Document 3 and the number of piezoelectric fans is an even number, the vertical center-of-gravity vibrations cancel each other, and the moments about the width direction and the thickness direction axis also occur. It is almost offset. However, moments around the longitudinal axis are not canceled out, and a load is applied to the support. For this reason, there is a problem that the support vibrates and the vibration spreads to other parts through the support or causes noise. Further, the vibration of the support means that a part of the vibration energy generated by the piezoelectric fan is lost.

FIG. 13 is a diagram showing three axes in the blower related to Patent Document 3. As shown in FIG. Here, four piezoelectric fans 101 to 104 are used to simplify the description. In FIG. 13, X is a length direction axis, Y is a width direction axis, and Z is a thickness direction axis. When the piezoelectric fans 101 to 104 are driven in opposite phases as indicated by arrows D1 to D4, the moments around the Y axis and the Z axis become almost zero, and the support 105 is hardly loaded. On the other hand, around the X axis, a counterclockwise moment ML is generated by the second and third piezoelectric fans 102 and 103, and a clockwise moment MR is generated by the first and fourth piezoelectric fans 101 and 104. To do. However, since the distance from the X axis to the first and fourth piezoelectric fans 101 and 104 is longer than the distance from the second and third piezoelectric fans 102 and 103, the moment MR is larger than the moment ML. Rotational vibration is generated in the support 105 due to the difference in these moments.
Japanese Patent Laid-Open No. 2-19700 JP 2002-339900 A Japanese Utility Model Publication No. 62-122199

  An object of the present invention is to provide a piezoelectric fan device that uses a plurality of miniaturized piezoelectric fans and can reduce vibration generated in a support portion by driving a piezoelectric vibrator.

  In order to achieve the above object, the present invention includes a piezoelectric vibrator that bends and vibrates when a voltage is applied, and a blade that is connected to or integrated with the piezoelectric vibrator and is excited by the piezoelectric vibrator. A piezoelectric fan device comprising: a plurality of piezoelectric fans arranged in parallel; and a support body for connecting and supporting in parallel the ends of the plurality of piezoelectric fans opposite to the extending side of the blade. The drive direction of the piezoelectric fans on both sides is axisymmetrical and the drive direction of half of the piezoelectric fans is the drive direction of the remaining half of the piezoelectric fans, with the piezoelectric fan located at the center in the width direction as the boundary. A piezoelectric fan device is provided, characterized in that voltage applying means for applying a voltage to each of the piezoelectric vibrators is provided so as to have an opposite phase.

  When multiple piezoelectric fans with the same vibration characteristics are supported on the support in parallel, and these piezoelectric fans are driven alternately in opposite phases, the center of gravity vibration can be canceled between the piezoelectric fans. Vibration generated in the body can be reduced. However, moments around the longitudinal axis are not canceled out, and the support vibrates, and the vibrations propagate to other parts through the support. In the present invention, among the plurality of piezoelectric fans, the driving directions of the piezoelectric fans on both sides are axisymmetric with respect to the piezoelectric fan located at the center (in the case of odd number) or between the piezoelectric fans located in the center (in the case of even number). In addition, a voltage is applied to the piezoelectric vibrator so that the driving direction of half of the piezoelectric fans is in an opposite phase to the driving direction of the remaining half of the piezoelectric fans. Therefore, not only the center-of-gravity vibration generated in the support but also the moments around the three axes can be eliminated or reduced, and the rotational vibration of the support can be suppressed. Thereby, it is possible to effectively suppress the vibration of the support body caused by the vibration of the blade from spreading to the case or the like, and to realize a piezoelectric fan with low noise and high reliability. Further, since it is possible to suppress the vibration of the piezoelectric fan from spreading to the outside, it is possible to efficiently convert the electric energy input to the piezoelectric vibrator into the vibration of the blade, thereby achieving an increase in the air volume and thus an improvement in cooling efficiency. Furthermore, since the load caused by vibration on the support is reduced, the blade can be driven with a large amplitude even if the fixing portion for fixing the support to the case or the like has low rigidity. Thereby, even if some vibration is generated in the support, the vibration can be absorbed by the vibration absorber, and the spread to the outside can be suppressed. That is, it is possible to achieve both an increase in the air volume and suppression of adverse effects caused by vibration.

  The piezoelectric fans used in the present invention have the same vibration characteristics. Here, the same vibration characteristic means that the resonance frequency and the amplitude characteristic substantially match when the piezoelectric fan is vibrated alone. The piezoelectric fans preferably have the same shape, but with regard to the width of the blade, equivalent vibration characteristics can be obtained if the width of the piezoelectric element is also increased or decreased in accordance with the increase or decrease of the width of the blade. For this reason, if the same vibration characteristic is obtained, it is not necessary to use blades having the same width.

  The piezoelectric vibrator in the present invention is one that bends and vibrates when an AC voltage is applied, but various configurations can be employed. For example, a unimorph type piezoelectric vibrator can be configured with the blade and the piezoelectric element by attaching a single-plate piezoelectric element to the main surface on one end side of the blade. Also, a bimorph type piezoelectric vibrator can be configured by adhering two piezoelectric elements expanding and contracting in opposite directions to both surfaces of the blade. Further, apart from the blade, a piezoelectric vibrator may be configured by bonding a single plate piezoelectric element and a metal plate, and the blade may be fixed to the piezoelectric vibrator. Although the amplitude itself accompanying the bending vibration of the piezoelectric vibrator is very small, the amplitude of the piezoelectric vibrator can be amplified many times by the resonance of the blade connected to the piezoelectric vibrator. The blade may be a metal plate or a resin plate. The thickness, length, Young's modulus, etc. of the blade may be set appropriately so that the blade can perform primary resonance by vibration of the piezoelectric vibrator. In order to drive the plurality of piezoelectric fans in opposite phases with each other, the voltage applying means may apply voltages having opposite phases to each piezoelectric vibrator, but the polarization directions of the piezoelectric elements constituting the piezoelectric vibrator are reversed. Then, even if the voltage of the same phase is applied, it can be driven in the opposite phase.

  The number of piezoelectric fans is not limited to an even number, and may be an odd number. In the case of an odd number, except for one piezoelectric fan located at the center in the width direction, the remaining half are driven in opposite phases. In the case of an odd number, the influence of the center of gravity vibration appears, but the influence decreases as the number of piezoelectric fans increases. In the case of an even number, it is particularly desirable to set a multiple of 4 such as 4, 8, or 12. In this case, since there are an even number of piezoelectric fans on both sides of the middle point in the width direction, it becomes easy to cancel the center-of-gravity vibration and the moment about the three axes.

  When four piezoelectric fans are arranged in parallel, the two central piezoelectric fans are driven in the same phase, and the two piezoelectric fans at both ends are driven in opposite phases with respect to the two central piezoelectric fans. Is desirable. In this case, the structure is simplified, and the movement of the center of gravity and the moment about the three axes can be effectively eliminated.

  Each piezoelectric fan includes an elongated strip-like blade and a piezoelectric element fixed to one end portion in the length direction of the blade, and a piezoelectric vibrator is configured by the one end portion in the length direction of the blade and the piezoelectric element. It is preferable that one end of the blade in the longitudinal direction is connected to and supported by a support. In this case, since the blade is directly supported by the support, the piezoelectric element is not restrained by the support, and the piezoelectric element can be displaced more freely. Further, the structure of the piezoelectric fan is simplified, and variations in vibration characteristics of individual piezoelectric fans are less likely to occur.

  Each piezoelectric vibrator has a first vibrator and a second vibrator. The first vibrator and one end in the length direction of the second vibrator are connected to each other, and the first vibrator A blade is connected to the other end in the length direction, the other end in the length direction of the second vibrator is supported on the support, and the first vibrator and the second vibrator are bent in opposite directions. The voltage application means may be connected to do so. In this case, the amplitude is doubled by the two vibrators, and the blade resonates with the vibration. Therefore, the amplitude of the blade is further amplified. As a result, a significant increase in air volume can be realized.

  It is desirable to use the piezoelectric fan device according to the present invention in combination with a heat sink. That is, this piezoelectric fan device is disposed in the vicinity of a heat sink having a plurality of heat dissipating fins arranged in parallel at intervals, and each blade is arranged so that its displacement direction is parallel to the side surface of the heat dissipating fin. Insert it in between. In this case, the warm air existing between the radiating fins is scraped off by the bending displacement of the blade, and can be efficiently discharged in the length direction of the blade. Since each blade is isolated by the heat radiating fin, the interaction between the blades via the air can be eliminated, and an unexpected vibration mode is not generated and a load is not applied to the support.

Effects of preferred embodiments of the invention

  As described above, according to the present invention, a plurality of piezoelectric fans are supported on the support in parallel, and the driving directions of the piezoelectric fans on both sides are axisymmetric with respect to the center in the width direction, and half of the piezoelectric fans Are driven in such a manner that their driving directions are opposite in phase to the driving directions of the remaining half of the piezoelectric fans, both the vibration of the center of gravity and the moment about the three axes are suppressed. Therefore, the amplitude of the blade is increased, the cooling efficiency is improved, and vibration propagation to other parts through the support due to the vibration is reduced. As a result, there is little adverse effect on the reliability of other parts and cases, and the noise is reduced.

It is a perspective view of the reference example of a piezoelectric fan apparatus. It is a perspective view of the drive state of the piezoelectric fan apparatus shown in FIG. It is a vibration model figure of the piezoelectric fan apparatus shown in FIG. 1 is a perspective view of a first embodiment of a piezoelectric fan device according to the present invention. It is a perspective view of the drive state of the piezoelectric fan apparatus shown in FIG. It is sectional drawing of the air-cooling apparatus which combined the piezoelectric fan apparatus shown in FIG. 4 with the heat sink. It is the side view which looked at the air cooling apparatus shown in FIG. 6 from the length direction. It is a figure which shows the moment added to the support body of the piezoelectric fan apparatus shown in FIG. The experimental structure for comparing blade amplitude is shown, (a) is a plan view, (b) is a front view, and (c) is a right side view. It is an amplitude comparison figure of the braid | blade front-end | tip part when the thickness of a coupling tool is 0.3 mm and 0.6 mm. It is a figure which shows the drive method of the piezoelectric fan apparatus using eight piezoelectric fans. It is a figure which shows the various aspects of the structure of a piezoelectric fan. It is a figure explaining the triaxial moment in the conventional piezoelectric fan apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

  Before describing the piezoelectric fan device according to the present invention, the basic structure of the piezoelectric fan device will be described with reference to FIGS.

  In FIG. 1, two piezoelectric fans 1 a and 1 b having the same vibration characteristics are connected and fixed to a support 6 side by side in the width direction. The piezoelectric fans 1a and 1b are connected to a plurality of blades 2a and 2b that can be bent and displaced in the thickness direction, and one end in the length direction of each blade 2a and 2b, and a plurality of piezoelectric vibrators 3a and 3b that bend and vibrate when a voltage is applied. 3b. Weights 4a and 4b are fixed to the free ends of the blades 2a and 2b, respectively. The piezoelectric vibrators 3a and 3b are bimorph vibrators in which piezoelectric elements are attached to both surfaces of a metal plate serving as an intermediate electrode. Voltage applying means 5 is electrically connected to the piezoelectric vibrators 3a and 3b, and by applying an AC voltage from the voltage applying means 5 to the piezoelectric vibrators 3a and 3b, the piezoelectric vibrators 3a and 3b are bent. By vibrating, the blades 2a and 2b can be primarily resonated to bend and displace larger than the piezoelectric vibrators 3a and 3b. The ends of the piezoelectric fan opposite to the extending direction of the blades 2a, 2b, here the ends of the blades 2a, 2b on the side where the piezoelectric vibrators 3a, 3b are arranged are connected and supported in parallel by the support body 6. ing. The support 6 is fixed to a fixing part such as a case (not shown). The reaction force due to the movement of the blades 2a and 2b in the opposite phase is transmitted in the width direction of the support body 6, and the reaction force cancels out. Therefore, the support body 6 is rigid enough to transmit the reaction force. is necessary.

  The voltage applying means 5 includes an AC power source 5a and wirings 5b and 5c for supplying a signal whose phase is inverted from the power source 5a to the piezoelectric vibrators 3a and 3b. That is, one end of the AC power supply 5a is connected to the upper and lower electrodes of the piezoelectric vibrator 3a and the intermediate electrode of the piezoelectric vibrator 3b via the wiring 5b, and the other end of the AC power supply 5a is connected to the piezoelectric vibrator 3a via the wiring 5c. And the upper and lower electrodes of the piezoelectric vibrator 3b. Therefore, when the free end of one piezoelectric vibrator 3a is displaced downward, the free end of the other piezoelectric vibrator 3b is displaced upward. As a result, as shown in FIG. 2, the blade 2a connected to the free end of one piezoelectric vibrator 3a and the blade 2b connected to the free end of the other piezoelectric vibrator 3b are displaced in mutually opposite phases. Then, an air flow in the direction indicated by arrow A in FIG. 2 is generated. Since the vibration characteristics (length, thickness, resonance frequency, etc.) of the two piezoelectric fans 1a, 1b are the same, the vibration frequencies and amplitudes of both blades 2a, 2b are also equal. Since the weights 4a and 4b are fixed to the free ends of the blades 2a and 2b, the resonance frequency becomes lower and the amplitude becomes larger than that of the blade alone.

The reason why the center of gravity vibration acting on the support 6 can be reduced by driving the two piezoelectric fans 1a and 1b in opposite phases as described above will be described below. Due to the vibration of the piezoelectric vibrator 3 and the blade 2, the center of gravity of one piezoelectric fan 1 periodically moves in the thickness direction (z) and the length direction (x). Considering the piezoelectric fan vibration model as shown in FIG. Here, a concentrated mass M (= center of gravity) is considered at a distance R from the support 6 and it is assumed that the vibration is θ = Θsin ωt. In this case, the motion of the center of gravity in the x and z directions is
x = Rcos (Θsin ωt)
z = Rsin (Θsin ωt)
It can be written as Here, the amplitude in the x direction is (R / 2) sin Θ tan Θ, and the amplitude in the z direction is R sin Θ. That is, when Θ is small, the amplitude in the x direction becomes a very small square, and can be ignored. On the other hand, the ones that are oscillating in antiphase are
x = Rcos (−Θsin ωt) = Rcos (Θsin ωt)
z = Rsin (−Θsin ωt) = − Rsin (Θsin ωt)
It becomes. The center of gravity when these two piezoelectric fans are combined is
x = (MRcos (Θsin ωt) + MRcos (Θsin ωt)) / (M + M)
= Rcos (Θsin ωt)
z = (MRsin (Θsin ωt) −MRsin (Θsin ωt)) / (M + M)
= 0
Can be calculated.

  Thus, it can be seen that the center of gravity does not vibrate in the thickness direction in the pair of two piezoelectric fans 1a and 1b moving in opposite phases. Therefore, no force in the thickness direction is applied to the support 6 supporting the pair of two piezoelectric fans. Although vibration in the length direction remains, it is negligible when Θ is small as described above. Accordingly, the force acting on the support 6 is almost canceled.

  As described above, by driving the two piezoelectric fans 1a and 1b in opposite phases, the load acting on the support body 6 can be canceled, but vibration due to the reaction force caused by the amplitude of the blades 2a and 2b is generated in the support body 6. To do. However, unlike the conventional piezoelectric fan, sufficient amplitude can be obtained for the blades 2a and 2b without the support 6 being strongly fixed to the case or the like. That is, a vibration absorber such as rubber can be interposed between the support 6 and the case. Therefore, it is possible to effectively suppress the vibration generated in the support 6 from spreading to the case or the like, and to realize a piezoelectric fan with low noise and high reliability.

  FIG. 1 shows an example in which the piezoelectric fans 1a and 1b are fixed to the support 6 in the same direction in the thickness direction, and voltages having opposite phases are applied from the voltage applying means 5 to the piezoelectric fans 1a and 1b. When the piezoelectric fans 1a and 1b are fixed to the support 6 in the direction opposite to the thickness direction, voltages having the same phase may be applied. Further, when the piezoelectric vibrators 3a and 3b of the piezoelectric fans 1a and 1b have opposite characteristics, that is, when the polarization directions of the piezoelectric elements constituting the piezoelectric vibrators 3a and 3b are opposite, the piezoelectric vibrations Even when voltages having the same phase are applied to the sub-elements 3a and 3b, both the piezoelectric fans 1a and 1b can be vibrated in opposite phases.

[First Embodiment]
4 to 7 show an example in which the first embodiment of the piezoelectric fan device according to the present invention is used as an air cooling device for a heat sink. In FIG. 4, four piezoelectric fans 10 a to 10 d having the same vibration characteristics are connected and fixed to the support 11 in the width direction at equal intervals. The piezoelectric fans 10a to 10d have the same structure as the piezoelectric fans 1a and 1b shown in FIG. That is, a plurality of blades 12a to 12d that can be bent and displaced in the thickness direction, and a plurality of bimorph piezoelectric vibrators 13a to 13d that are connected to one end in the length direction of each blade 12a to 12d and bend and vibrate when voltage is applied. Each has. Weights 14a to 14b are fixed to the free ends of the blades 12a to 12d, respectively. A voltage applying means 15 is connected to the piezoelectric vibrators 13a to 13d. By applying an alternating voltage from the voltage applying means 15 to the piezoelectric vibrators 13a to 13d, the piezoelectric vibrators 13a to 13d are vibrated, and the blade 12a-12d can be resonated. The ends of the piezoelectric vibrators 13 a to 13 d opposite to the extending direction of the blades 12 a to 12 d are connected and supported in parallel by the support 11.

  In this embodiment, the voltage application means 15 includes an AC power supply 15a and wirings 15b and 15c for applying signals whose phases are inverted from the power supply 15a to the piezoelectric vibrators 13a to 13d. That is, one end of the AC power supply 15a is connected to the upper and lower electrodes of the first and fourth piezoelectric vibrators 13a and 13d and the intermediate electrode of the second and third piezoelectric vibrators 13b and 13c via the wiring 15b. The other end of the AC power supply 15a is connected to the intermediate electrode of the first and fourth piezoelectric vibrators 13a and 13d and the upper and lower electrodes of the second and third piezoelectric vibrators 13b and 13c via the wiring 15c. Therefore, when the first and fourth piezoelectric vibrators 13a and 13d are displaced downward, the second and third piezoelectric vibrators 13b and 13c are displaced upward. As a result, as shown in FIG. The blades 12a and 12d connected to the first and fourth piezoelectric vibrators 13a and 13d and the blades 12b and 12c connected to the second and third piezoelectric vibrators 13b and 13c are displaced in mutually opposite phases. . Since the vibration characteristics (length, thickness, resonance frequency, etc.) of the piezoelectric fans 10a to 10d are the same, the vibration frequencies and amplitudes of all the blades 12a to 12d are also equal.

  In the vicinity of the piezoelectric fans 10a to 10d, a heat sink 20 having five heat dissipating fins 21a to 21e arranged in parallel at intervals is disposed. The blades 12a to 12d are inserted between the radiation fins 21a to 21e, and are arranged so that the displacement direction thereof is parallel to the side surfaces of the radiation fins 21a to 21e. As shown in FIGS. 6 and 7, the heat sink 20 is attached in a state of being thermally coupled to the upper surface of a heating element (CPU or the like) 23 mounted on the circuit board 22. Therefore, the heat generated from the heat generating element 23 is conducted to the heat sink 20, and the air between the radiation fins 21a to 21e is heated. Since the blades 12a to 12d inserted between the radiation fins 21a to 21e are displaced in parallel with the side surfaces of the radiation fins 21a to 21e, the warm air between the radiation fins 21a to 21e is scraped off by the blade, and the blades 12a to 12d It is discharged in the length direction. As a result, as indicated by an arrow A in FIG. 6, heat between the radiation fins 21a to 21e is efficiently discharged by the air flow in the length direction of the blades 12a to 12d, and an air cooling device having an excellent heat radiation effect can be realized. . Further, since adjacent blades are displaced in opposite phases, there is a possibility that unexpected vibration modes such as twisting may occur in the blades 12a to 12d due to the interaction via air. However, as shown in FIG. Since the blades 12a to 12d are isolated by ˜21d, the interaction between the blades via the air can be eliminated, and an unexpected load is not applied to the support 11.

  In the present embodiment, since half of the four piezoelectric fans 10a to 10d vibrate in opposite phases, the center-of-gravity vibration acting on the support 11 can be reduced to almost zero as in the reason shown in FIG. Further, in the case of the present embodiment, the two piezoelectric fans 10b and 10c at the center are driven in the same phase, and the two piezoelectric fans 10a and 10d at both ends are compared with the two piezoelectric fans 10b and 10c at the center. Therefore, the moment about the three axes of the support 11 can be eliminated. The reason will be described with reference to FIG.

  FIG. 8A is a view of the four piezoelectric fans 10a to 10d as viewed from the length direction (X direction). When the fans 10a to 10d are driven in the directions of arrows D1 to D4, a clockwise moment is generated in the first and third piezoelectric fans 10a and 10c around the longitudinal axis (X axis), and the second and A counterclockwise moment is generated in the fourth piezoelectric fans 10b and 10d. Since these moments are the same, these moments cancel each other and the moment about the longitudinal axis becomes zero.

  FIG. 8B is a view of the piezoelectric fans 10a to 10d viewed from the width direction (Y direction). Centering on the width direction axis (Y-axis), a counterclockwise moment is generated in the first and fourth piezoelectric fans 10a and 10d, and a clockwise moment is generated in the second and third piezoelectric fans 10b and 10c. As a result, both moments cancel each other, and the moment about the width direction axis becomes zero.

  (C) of FIG. 8 is the figure which looked at the piezoelectric fans 10a-10d from the thickness direction (Z direction). As described above, when the piezoelectric fans 10a to 10d are driven, the longitudinal vibration of each piezoelectric fan is almost negligible, and therefore the moment of each piezoelectric fan around the thickness direction axis (Z axis) is small. In addition, since the moments acting on the first and second fans 10a and 10b and the third and fourth fans 10c and 10d are canceled out, the moment about the thickness direction axis (Z axis) is also zero. Since all the moments around the three axes acting on the support 11 are canceled in this way, a support structure with less vibration and load can be realized.

Regarding the piezoelectric fan, in order to obtain a large blade amplitude, it is preferable that the torsional rigidity of the coupler satisfies the following relationship.
D> kmAf ² LW
Here, D: Torsional rigidity [Nm ² / rad]
m: Mass other than fan connector [kg]
A: Blade tip amplitude (tip-to-tip) [m]
f: Drive frequency [Hz]
L: Length of fan [m]
W: Connector width [m]
k: a coefficient. When canceling the triaxial moment, if the coefficient k has a value of 10 or more, vibration propagation can be made smaller, the reliability of other parts, cases, etc. is hardly adversely affected, and noise is reduced. .

  FIG. 9 shows an experimental structure for confirming the cooling performance of the piezoelectric fan device. Each of the four piezoelectric fans 30a to 30d includes elongated strip-like blades 31a to 31d, and one end in the length direction of these blades is fixed to one end of the holders 33a to 33d. Piezoelectric elements 32a to 32d are fixed in the vicinity of one end fixed to the blade holder to constitute a piezoelectric vibrator. The other ends of the holding tools 33a to 33d are connected to a connecting tool (support) 34 extending in the width direction. The connector 34 extends to one side in the width direction and is fixed to the fixing portion 35.

  In the piezoelectric fan device having the above-described structure, the amplitude of the blade tip portion (the phase of the fan 1 is set to 0 °) in the case where the phase relationship of vibration of each fan is four types shown in Table 1 was evaluated. The applied voltage to the piezoelectric body was fixed at 45 Vpp, and 42Ni was used as a blade, and a glass epoxy plate was used as a holder and a connector. In order to see the influence of the torsional rigidity of the coupler, two types of couplers having a thickness of 0.3 mm and 0.6 mm were used. The dimensions of each part are as shown in FIG. CASE 1 is an example in which all fans are driven in the same phase, CASE 2 is an example in which the left and right halves are in reverse phase from the center, CASE 3 is an example in which opposite phases are alternated, and CASE 4 (invention) is in the width direction This is an example in which the opposite phase is axisymmetric with respect to the center.

  10A and 10B show the amplitude of the blade tip in CASE1 to CASE4 when the thickness of the coupler is 0.3 mm and 0.6 mm. As is clear from FIG. 10, CASE 2 has a larger amplitude and CASE 3 is larger than CASE 1. It can be seen that in CASE 4 that can cancel the triaxial moment, the blade amplitude is maximized.

  In CASE 1, since it is necessary to support the vibrations of all the fans with the coupler, a large amplitude cannot be obtained if the rigidity of the coupler is lowered. In CASE 2, the reaction force from the fan moving in the opposite phase is supported through the connector. However, it is only the center of gravity vibration that cancels out, and the moment remains. Therefore, if the coupler has rigidity, a certain amount of center-of-gravity vibration can be suppressed, and a larger amplitude than CASE 1 can be obtained. However, since the moment is not canceled out, the coupler is rotationally vibrated as a whole. When the rigidity of the coupler is lowered, the amplitude is greatly reduced. CASE 3 has the same situation as CASE 2, but since the distance between the fans moving in the opposite direction is smaller than CASE 2, the moment is reduced and the rotational vibration is also reduced. Therefore, if there is the same connector rigidity, a larger amplitude than CASE 2 can be obtained. In CASE4, both the center-of-gravity vibration and the moment vibration can cancel each other out in the coupler, so that a larger amplitude can be obtained compared to CASE3.

  The amplitude difference between the blades of CASE 3 and CASE 4 is slight when the thickness of the coupler is 0.6 mm, but the amplitude difference is about 5% at 0.3 mm. The lower the torsional rigidity of the coupler, the greater the amplitude difference between CASE3 and CASE4. Although the amplitude difference of 5% is numerically small, there is a difference of about 15% in the cooling performance depending on the installation position of the fan with respect to the heat source. Therefore, if the rigidity of the coupler that supports the fan is reduced in order to suppress the spread of vibrations to the outside, a large difference in cooling performance occurs.

  FIG. 11 shows an example of a driving method when eight piezoelectric fans are arranged in parallel. The first to eighth fans 41 to 48 are arranged at equal intervals in the width direction, and are connected and held by a support body (not shown). Arrows D1 to D8 indicate the driving direction. The X axis is the longitudinal axis at the center in the width direction, and the Z axis is the thickness direction axis. In (a), the two fans 44 and 45 at the center are driven in the same phase, and the other fans are alternately driven in opposite phases with respect to adjacent fans. In this case, not only the center-of-gravity vibration in the Z direction but also the moments around the X, Y, and Z axes cancel each other, so that a large amplitude can be obtained even if the rigidity of the support connecting the fans 41 to 48 is low. Can do. In (b), the fans 41 and 48 at both ends and the two fans 44 and 45 at the center are driven in the same phase, and the second, third, sixth and seventh fans 42, 43, 46 and 47 are reversed. Driven in phase. Also in this case, the center-of-gravity vibration and the triaxial moment cancel each other, so that the rigidity of the support can be lowered and a large amplitude can be obtained.

  FIG. 12 shows various aspects of the structure of the piezoelectric fan. A piezoelectric fan 50 shown in FIG. 12A is an example in which a main surface of one end of a blade 52 made of a metal plate is attached to one main surface of a single-plate piezoelectric element 51 to form a unimorph type vibrator. The end of the piezoelectric fan 50 opposite to the blade protruding side is fixed to the support 53. By applying an alternating voltage between the piezoelectric element 51 and the blade 52, the piezoelectric fan 50 as a whole is bent and deformed by the piezoelectric element 51 that expands and contracts and the blade 52 that does not expand and contract. In this case, one electrode of the piezoelectric element 51 can be shared by the blade 52.

  A piezoelectric fan 60 shown in FIG. 12B is an example in which a piezoelectric element 62, 63 is attached to both main surfaces of one end of a blade 61 made of a metal plate to form a bimorph type vibrator. The end of the piezoelectric fan 60 opposite to the blade protruding side is fixed to the support 64. When the piezoelectric elements 62 and 63 are polarized in the same direction in the thickness direction, the piezoelectric fan 60 is bent and deformed as a whole by applying an AC voltage between the electrodes on both main surfaces and the blade 61.

  A piezoelectric fan 70 shown in FIG. 12C has a first vibrator 71 and a second vibrator 72, and one end in the length direction of the first vibrator 71 and the second vibrator 72. By connecting them together via a spacer 73, a U-shaped structure is formed, the blade 74 is connected to the other longitudinal end of the first vibrator 71, and the other longitudinal end of the second vibrator 72 is connected. It is supported by the support body 75. The first vibrator 71 and the second vibrator 72 are vibrators having the same vibration characteristics, and are bent and displaced in directions opposite to each other. For example, when the first vibrator 71 is bent and displaced convexly upward, the second vibrator 72 is bent and displaced convexly downward. The blade 74 is vibrated with twice the amplitude of each of the vibrators 71 and 72, and the amplitude of the blade 74 is increased accordingly, so that a significant increase in air volume can be realized.

  A piezoelectric fan 80 shown in FIG. 12 (d) is a modification of the piezoelectric fan 70 shown in FIG. 12 (c). A blade 81 connected to the other longitudinal end of the first vibrator 71 is bent in a V shape. In this case, since the two vibrators 71 and 72 have a U-shaped structure and the blade 74 is folded back toward the vibrators 71 and 72, the length dimension can be shortened, and a compact piezoelectric fan as a whole can be obtained. realizable.

Explanation of symbols

10a to 10d Piezoelectric fan 11 Supports 12a to 12d Blades 13a to 13d Piezoelectric vibrators 14a to 14d Weight 15 Voltage applying means 15a AC power supply

Claims (6)

A plurality of piezoelectric fans arranged in parallel in the width direction, each having a piezoelectric vibrator that bends and vibrates when voltage is applied, and a blade that is connected to or integrated with the piezoelectric vibrator and is excited by the piezoelectric vibrator;
In the piezoelectric fan device comprising: a support body for connecting and supporting in parallel the ends of the plurality of piezoelectric fans opposite to the extending side of the blade;
Piezoelectric fans located in the center in the width direction or the piezoelectric fans located in the center in the width direction as a boundary, the driving directions of the piezoelectric fans on both sides are axisymmetric, and the driving directions of half of the piezoelectric fans are the remaining half A piezoelectric fan device comprising voltage applying means for applying a voltage to each of the piezoelectric vibrators so as to have an opposite phase with respect to the driving direction.   The piezoelectric fan device according to claim 1, wherein the number of the piezoelectric fans is a multiple of four.   The four piezoelectric fans are arranged in parallel, the two central piezoelectric fans are driven in the same phase, and the two piezoelectric fans at both ends are driven in the opposite phase with respect to the two central piezoelectric fans. The piezoelectric fan device according to claim 2. Each piezoelectric fan includes an elongated strip-like blade and a piezoelectric element fixed to one end in the length direction of the blade,
The one end of the blade in the length direction and the piezoelectric element constitute the piezoelectric vibrator,
4. The piezoelectric fan device according to claim 1, wherein one end portion of the blade in the length direction is connected to and supported by the support body. 5.   Each of the piezoelectric vibrators includes a first vibrator and a second vibrator. The first vibrator and the second vibrator are connected to each other at one end in the length direction, and the first vibrator The blade is connected to the other longitudinal end of the vibrator, and the other longitudinal end of the second vibrator is supported by the support, and the first vibrator, the second vibrator, 5. The piezoelectric fan device according to claim 1, wherein voltage applying means is connected so as to bend and vibrate in a reverse direction. 6.   The piezoelectric fan device according to any one of claims 1 to 5, wherein the piezoelectric fan device is disposed in the vicinity of a heat sink having a plurality of heat dissipating fins arranged in parallel at intervals, and each blade has a displacement direction of the heat dissipating fins. An air-cooling device, wherein the air-cooling device is inserted between the radiating fins so as to be parallel to the side surface.

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