JP2005130149A - Piezoelectric device for generation of acoustic signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric device for generation of an acoustic signal in which a generation frequency is lowered, miniaturization is realized, and fall shock resistance is improved. <P>SOLUTION: Force generated by centroid movement of an oscillator which comprises a piezoelectric element 11 with a fixed length and an elastic body 12 subjected to buckling deformation in correspondence to expansion/contraction in the length direction is used as driving force for an oscillated body 14. The piezoelectric element 11 to be used here does not need to undergo bend deformation but can adopt a strong structure and, by regulating elasticity coefficients of accompanying elastic body 12, the frequency can be lowered. Also, the weight of the oscillator itself functions as the weight of an oscillation system to contribute to the lowering of the frequency. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an acoustic vibration generating element using piezoelectric vibration, and particularly to a loudspeaker that generates an acoustic signal in the air, or a bone conduction speaker that propagates acoustic vibration to a skull or an arm and listens to it with an auditory nerve. The present invention relates to a suitable acoustic signal generating piezoelectric device.

  Conventionally, as an acoustic-related element using a piezoelectric element, for example, a thin piezoelectric plate having a diameter of 20 mm and a thickness of 0.1 to 0.2 mm on one or both sides of a thin metal plate having a circular shape of about 30 mm and a thickness of about 0.1 mm. There are elements based on a unimorph or bimorph structure in which ceramic elements are bonded together. In this case, a loud sound can be generated in the vicinity of a resonance frequency of several kHz, but if the drive frequency deviates from the resonance frequency, the volume that can be generated suddenly decreases, so that it can be used in the field of piezoelectric sounding bodies that generate specific acoustic signals. The Lord. Further, when the thickness of the piezoelectric ceramic is further reduced to, for example, 0.1 mm or less and the outer shape of the diaphragm is 50 mmφ, the function of a speaker having a high frequency of 1 kHz or more, that is, a tweeter can be realized.

  Furthermore, a sound generation method has been proposed and put into practical use in which a hole is formed in the center of a circular bimorph, that is, an antinode of vibration, and one end of a pillar is fixed to this portion and the other end is fixed to a housing or a panel. . In this configuration, for example, as disclosed in Patent Document 1, since the reaction force of vibration generated at the antinode of vibration is transmitted to the housing and the panel, the sound pressure increases by increasing the area of the vibration surface. In addition, the sound range that can be generated due to the combination of the vibration mode of the vibrator itself and the vibration mode of the housing and panel has a wide acoustic range that can be generated, so that it has a function as a practical loudspeaker. Is possible. The vibrator for this purpose does not necessarily have a circular shape. For example, Patent Document 2 describes the use of a rectangular piezoelectric bimorph.

JP 2000-209697 A JP 2000-201398 A

  In these applications, when emphasizing the low frequency range, it is necessary to lower the resonance frequency on the piezoelectric vibrator side as much as possible. As means for lowering the resonance frequency of the piezoelectric element, methods such as increasing the diameter and length of the element that determines vibration, lowering the flexural modulus of the element, or adding weight to the antinode portion of the vibration are conceivable. However, when the target is limited in the size of a portable device or the like, there is a limit to the means for increasing the size of the element.

  Another means of lowering the flexural modulus can be achieved by reducing the thickness of the element ceramics or metal plate (shim), but at the same time lowering the mechanical strength and reducing its own weight. There is no substantial effect because the resonance frequency is increased. It is possible to lower the elastic modulus of bending to some extent by selecting organic materials with low elastic modulus as shims, but generally the specific gravity of these materials is low, so the overall weight is lowered to increase the resonance frequency. It is easy to become. Moreover, when adding weight, it becomes easy to become weak with respect to an impact. Especially in the application to portable devices etc., a severe drop impact test is imposed, resulting in a disadvantageous configuration. From the above problems, there is a demand for means for generating acoustic vibrations that are basically different in configuration.

  Briefly, an object of the present invention is to provide a piezoelectric device for generating an acoustic signal, which has a low frequency, a small size, and an improved drop impact resistance.

  In view of such circumstances, the present invention provides an acoustic signal generating means that is different in principle from piezoelectric bimorphs and unimorphs, and aims to reduce frequency, reduce size, and drop impact resistance. The vibration system uses the weight of the elastic body that buckles and deforms in response to the expansion and contraction of the piezoelectric element having a certain length and the weight of the vibrator. The vibrator used here needs to bend and deform There is an advantage that a strong structure can be adopted without any problem and that the frequency can be lowered by adjusting the elastic coefficient of the accompanying elastic body. In addition, the weight of the vibrator itself functions as the weight of the vibration system and contributes to lowering the frequency.

  That is, the piezoelectric device for generating an acoustic signal according to the present invention has a plate-like or curved plate-like shape that is disposed substantially in parallel with both ends in the longitudinal direction of a plate-like piezoelectric element having a certain length. At least one elastic body is coupled to both ends, and a vibration system is formed that vibrates in a direction perpendicular to the longitudinal direction by buckling deformation of the elastic body in accordance with expansion and contraction in the longitudinal direction of the piezoelectric element, The force generated by the movement of the center of gravity of the vibration system is used as the driving force to the vibrating body.

  The piezoelectric element may be a stacked piezoelectric element that is stacked in the longitudinal direction or in a direction perpendicular to the longitudinal direction.

  A central portion of one of the elastic bodies may be joined to a casing or panel as a vibrating body.

  The elastic body is arranged on both sides of the main surface of the piezoelectric element, and the central portion of the elastic body arranged on one side is joined to a casing or panel as a vibrating body and arranged on the other side. A weight may be added to the center of the elastic body.

  According to the present invention, the vibration system uses the weight of an elastic body that buckles and deforms in response to expansion and contraction in the length direction of a piezoelectric element having a certain length, and the vibrator used here. There is an advantage that a strong structure can be adopted without the need for bending deformation and the frequency can be lowered by adjusting the elastic coefficient of the accompanying elastic body. In addition, the weight of the vibrator itself functions as the weight of the vibration system and contributes to lowering the frequency.

  As a result, according to the present invention, it is possible to provide a loudspeaker having a robust structure with improved impact resistance and a wide sound range and a piezoelectric speaker for bone conduction at the same time.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a basic configuration of the present invention, in which 11 is a piezoelectric element, 12 is a plate-like elastic body, 13 is a mounting jig, and 14 is a panel or housing that is acoustically driven as a body to be vibrated. . The piezoelectric element 11 generates a displacement in the length direction (displacement in the left-right direction on the paper surface) by using a lateral effect or a longitudinal effect of piezoelectricity. When the lateral effect is used, the element is rectangular and polarized in the thickness direction, and causes expansion and contraction in accordance with electric signals applied to the upper and lower surfaces. In addition, when the electrode is divided into two groups for each layer and the polarization and voltage can be applied for each layer in the configuration in which the layers are stacked in the thickness direction, there is an advantage that the driving voltage can be greatly reduced. Electrical connections are omitted from the figure.

  When the longitudinal effect is used, polarization is performed in the longitudinal direction, and expansion and contraction in the longitudinal direction is performed by applying a driving voltage from the electrodes on both end faces. This configuration also has an advantage that the driving voltage can be greatly reduced in the case of a laminated piezoelectric element that is laminated in the longitudinal direction and can apply a voltage to each layer.

 An elastic plate made of a metal or an organic material is arranged in an arc shape with a certain curvature along the longitudinal direction of the piezoelectric element, and is fixed near both ends. Displacement with a small but powerful force generated by the piezoelectric element causes buckling deformation of the elastic plate, and this deformation is converted into an arc bulge. At this time, the amount of displacement is expanded to several tens of times the displacement of the element. It is possible. In order to perform the deformation of the elastic plate stably, it is preferable that the elastic plate is disposed on both sides of the element because the balance of force is good. The basic configuration is a configuration in which the bulging portion of one elastic plate and the casing or panel are fixed by means such as bolts, soldering, and bonding.

 When the acoustic signal is applied to the piezoelectric element, a deformation in the length direction according to the acoustic signal is generated, and this is expanded to the bulge of the elastic plate orthogonal to the displacement. Since the bulge portion is coupled to a panel or casing which is a body to be vibrated, the piezoelectric element moves away or approaches according to vibration when viewed from the body to be vibrated. The piezoelectric element has a constant weight, and the inertial force accompanying this movement is transmitted to the body to be vibrated through the elastic plate and can be a driving source for vibration.

  If a weight with a constant mass is added to the center of the elastic plate on the side not in contact with the vibrating body, the center of gravity shifts from the center axis to the weight side in a direction perpendicular to the center axis of the vibrator. In addition, as the distance from the center axis of the vibrator increases, the amount of vibration displacement increases and a large center of gravity moves, resulting in a large inertial force and a greater effect on the body to be vibrated, enabling greater sound generation. .

  By the way, the piezoelectric device for generating an acoustic signal according to the present invention is basically mechanically robust and includes a piezoelectric element and an elastic plate, and is excellent in drop impact resistance.

  Further, the resonance frequency can be adjusted by controlling the elastic coefficient of the elastic plate.

  Next, this invention is demonstrated based on an Example. An NEC TOKIN piezoelectric ceramic, a vibrator having 30 mm in length, 6 mm in width, and 3 mm in thickness using a brand name Nepec 10 and laminated in 30 layers in the thickness direction was used. FIG. 2A is a perspective view showing an appearance of a lateral effect type laminated element laminated in the thickness direction. FIG. 2B is a perspective view showing the appearance of a longitudinal effect type laminated element laminated in the length direction, and such a laminated element may be used.

  As shown in the front view of FIG. 3, two brass elastic bodies 32 having a length of 35 mm, a width of 6 mm, and a thickness of 0.2 mm at the thinnest portion are used and curved with a certain curvature to form a C shape. Thus, an elastic metal fitting 30 for buckling deformation having a structure in which both ends are welded to the U-shaped metal fitting 31 was prepared. The distance from the bottom to the bottom of the concave inner surface of the U-shaped part at both ends is matched to the length of the piezoelectric element, and the U-shaped opening width (the vertical width on the paper) matches the thickness of the piezoelectric element. It is.

  The structure of this example formed by bonding both with an adhesive is as shown in the front view of FIG. 4A, and 41 is a laminated piezoelectric element. Each part was given a pattern such as a diagonal line to distinguish it from other parts. A mounting hole is formed in the central portion of the metal fitting projecting to the side, and is fixed to the body to be vibrated 44, that is, the casing or panel to be vibrated, with screws. That is, the outer shape is a 10 mm thick wooden plate with a 60 mm square cutout in the center of a 100 mm square, and the periphery of an acrylic plate of 70 mm square and 2 mm thickness is supported and fixed by a rubber frame and used as an acoustic vibration plate. The acrylic plate was fixed with a 3 mm screw at the center. Also, 42 in the figure is a weight and is screwed by being arranged in a direction located outside the central axis of the piezoelectric element. This weight 42 was effective in increasing the sound pressure by lowering the resonance frequency of the vibration system and increasing the reaction force accompanying the vibration.

  Further, the structure of the elastic body can be a flat plate, and this example is shown in a front view in FIG. Reference numeral 45 denotes a flat plate elastic body.

  Next, the characteristic measurement results of the acoustic signal generating piezoelectric device of this embodiment will be described. The driving condition was a PP voltage of 30 V, and the distance was 300 mm from the vibration surface, and the generated sound pressure was measured at a frequency in the range of 100 Hz to 10 kHz. The measurement results are shown in FIG. Even when there was no weight, a high sound pressure was obtained at 400 kHz, but there was a clear difference between the sound pressure in the low frequency range and the sound pressure in the entire frequency range when there was no weight. In this structure, the impact at the time of dropping can generally be absorbed by deformation of the elastic body, and damage to the piezoelectric element can be greatly reduced as compared with the bimorph structure. Further, the number of elastic bodies can be three or more.

The schematic diagram which shows the basic composition of the piezoelectric device for acoustic signal generation of this invention. The perspective view which shows the basic structure of the lamination type piezoelectric element used for this invention. 2A is a diagram of a lateral effect multilayer element, and FIG. 2B is a diagram of a vertical effect multilayer element. The front view which shows the elastic body metal fitting for buckling deformation used for this invention. The front view which shows the structure of the piezoelectric device for acoustic signal generation of the Example of this invention. FIG. 4A shows a case where a curved elastic body is used, and FIG. 4B shows a case where a flat plate type elastic body is used. The figure which shows an acoustic characteristic measurement result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Piezoelectric elements 12 and 32 Elastic body 13 Attachment jigs 14 and 44 Vibrated body 30 Elastic body bracket for buckling deformation 31 U-shaped bracket 41 Multilayer piezoelectric element 42 Weight
43 Mounting screw 45 Flat elastic body

Claims (4)

  The both ends in the longitudinal direction of the plate-like piezoelectric element having a certain length are combined with the both ends of at least one elastic body having a flat plate shape or a curved plate shape arranged substantially parallel to the piezoelectric element, A vibration system that vibrates in a direction perpendicular to the longitudinal direction is formed by buckling deformation of the elastic body according to the expansion and contraction of the piezoelectric element in the longitudinal direction, and the force generated by the movement of the center of gravity of the vibration system is vibrated. A piezoelectric device for generating an acoustic signal, characterized in that the driving force is applied to the body.   2. The piezoelectric device for generating an acoustic signal according to claim 1, wherein the piezoelectric element comprises a laminated piezoelectric element laminated in a longitudinal direction or a direction perpendicular to the longitudinal direction.   3. The piezoelectric device for generating an acoustic signal according to claim 1, wherein a central portion of one of the elastic bodies is joined to a casing or a panel as a vibrating body.   The elastic body is arranged on both sides of the main surface of the piezoelectric element, and the central part of the elastic body arranged on one side is joined to a casing or a panel as a vibrating body and arranged on the other side. 3. The acoustic signal generating piezoelectric device according to claim 1, wherein a weight is added to a central portion of the acoustic signal generating device.

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