JP5030146B2 - Piezoelectric device for generating acoustic signals - Google Patents

Description

  The present invention relates to a piezoelectric device for generating an acoustic signal used for a speaker that emits acoustic vibration in the air, a headphone that directly listens to the ear, or a bone conduction speaker that propagates acoustic vibration to the skull and listens to it with an auditory nerve. More particularly, the present invention relates to a piezoelectric device for generating an acoustic signal having a structure for protecting a piezoelectric element from destruction against a large impact force such as a drop impact of the device.

  Conventionally, piezoelectric unimorph elements and piezoelectric bimorph elements have been mainly used as piezoelectric devices for generating acoustic signals using piezoelectric elements, but they are not simply devices that generate air vibration, but generate larger vibration energy. A device that can be used for a bone conduction speaker that propagates acoustic vibrations to the human body and listens to the vibrations with auditory nerves is becoming more popular due to the expansion of the elderly population and the aging of audio information equipment. . As a device that can be used more efficiently for this bone conduction speaker, a device that obtains a large amplitude and vibration force by combining a laminated piezoelectric element and a mechanical enlargement mechanism has been proposed.

  The essential form of a bone conduction speaker that comes from a difference from a general acoustic speaker is that a vibration output section for propagating acoustic vibration to the human body must be exposed in a protruding manner on the outer surface of the device. For this reason, when a strong impact such as an object colliding with the built-in device or a collision with the floor due to the falling of the device itself is applied, the vibration output part is unavoidably subject to this impact. There are important issues that must be addressed.

  When an impact force is applied to the vibration output section, naturally a large force acts on the structure for vibrating it, and a large force (impact force) is also applied to the piezoelectric element that is the vibration drive element. Become. As an example, when a call device is naturally dropped from the height of a human head onto a hard floor, there is an example in which an impact of about 1000 G (1000 times gravitational acceleration) is applied to the internal structure of the device. Even if the difference in the device structure is taken into consideration, it is not much lower than this. Compared with the impact applied to the device during transportation in the normal product packaging state, or the impact applied to the fixed installation equipment, etc., it is several to 10 times or more.

  On the other hand, the contact part between the piezoelectric element that drives vibration and the driven object is generally firmly fixed, and the vibration of the drive element during normal operation, chatter noise due to vibration, and wear damage due to friction Is achieved, and a reliable transmission of driving force is realized.

  By the way, this device uses a laminated piezoelectric element that can obtain a large displacement at a low voltage, but this kind of piezoelectric element is hard and brittle, and has a strong characteristic to compressive force in the laminating direction. It is a general characteristic that the tensile force in the stacking direction is weak. Therefore, in the case of a columnar stacked piezoelectric element elongated in the stacking direction, it is strong against simple compression but weak against bending, tensile force and torsional force. Therefore, it is necessary to adopt a structure in which these forces are difficult to work structurally.

  As a method of attaching the laminated piezoelectric element disclosed, (1) as shown in Patent Document 1, the fixed part structure and the movable part structure forming a completely parallel surface are directly and closely joined to each other, (2) As shown in Patent Document 2, the end face of the piezoelectric element is fixed to a completely parallel block (adhesion is suggested), and the side face is an elastic plate. Examples of reinforcement with members, (3) The upper and lower ends of the piezoelectric element, as seen in Patent Document 3, are only abutting on both the fixed side and the movable side, and the movable side is a rotation operation of a minute angle. There is a structure in which the parallel contact surfaces of the piezoelectric element on the fixed side and the movable side are adjusted and held in a state where a large preload is applied to the piezoelectric element.

  (1) In the case of a close-bonded support structure as described in Patent Document 1, the structure moves even when the movable side is at a minute angle, so when a large impact force is applied to the drive transmission system. Since not only the tensile force works but also the bending force works, there is a great risk that the laminated piezoelectric element will be delaminated.

  (2) In the support structure as described in Patent Document 2, when a large impact force is applied by making the strength and rigidity not to damage the reinforcing material (elastic plate) on the added side surface. Although the risk of breakage is reduced, the structural complexity of adding a reinforcing material increases the cost.

  (3) The support structure described in Patent Document 3 is an example of a displacement magnifying mechanism whose driving form is a minute rotation operation. In the support structure of the piezoelectric element in this example, in the case where the support surface is simply parallel and sandwiched by the preload, if the operating frequency is about 100 Hz as in this example, the positional displacement of the piezoelectric element does not occur. However, since a driving frequency is at least 3 kHz when an audio signal is handled and at least 10 kHz when a music signal is handled, a positional deviation due to driving occurs. In addition, when a large impact force is applied, the preload is lost due to the inertial force due to the mass of the components of the drive mechanism, and there is a danger that the pinching state will be released and the piezoelectric element will be disengaged from the required position. In addition, an adjustment mechanism that makes perfect parallelism is also necessary. If it is not parallel, the force of the component that causes the positional deviation works, so that the positional deviation is likely to occur in the case of high frequency driving.

  Furthermore, the configuration that combines a piezoelectric element and a mechanical displacement expansion mechanism has a structure in which it is generally contradictory to efficiently expand vibration and to reduce the impact force applied to the piezoelectric element by the impact force applied from the outside. Become. If an attempt is made to reduce the force or displacement applied to the piezoelectric element by an external impact force, the displacement enlargement mechanism will be increased in rigidity or the enlargement rate will be reduced, while the displacement force will be reduced or the displacement amount will be reduced. Therefore, the efficiency is lowered and the piezoelectric element has a characteristic that the displacement amount is small but the generated force to be displaced is large.

  The characteristics of the support structure of the piezoelectric element used in such a displacement magnifying mechanism will be specifically described with reference to the principle structure diagram shown in the perspective view of FIG. 1 and the front view of FIG. 1 is a multilayer piezoelectric element, 2 is a generally U-shaped displacement magnifying mechanism, 2a is a base member of the displacement magnifying mechanism, has relatively high rigidity and large structural characteristics, and 2b is vibration of the displacement magnifying mechanism. The output member has structural characteristics that are relatively high in rigidity and low in mass, and 2c is an elastic member of a displacement magnifying mechanism and has deformation elastic characteristics.

  The lower end 1 a and the upper end 1 b of the multilayer piezoelectric element 1 are coupled to the displacement enlarging mechanism 2, respectively. In general, they are bonded to each other with a highly rigid adhesive to prevent misalignment during operation and to ensure transmission of driving force. It is said that the adhesive used has the best rigidity equivalent to that of the piezoelectric ceramic that is the basic constituent material of the piezoelectric element 1.

  In this structure, since the vibration output member 2b is directly connected to a member exposed to the outside of the apparatus, an external force in the A direction and an external force in the B and C directions are easily applied. When an external force in the A direction is applied, a compressive force in the stacking direction is applied to the piezoelectric element 1, but when an external force in the B or C direction is applied, the tip direction of the piezoelectric element 1 is pushed sideways. Since a bending force acts on the piezoelectric element 1 and the lower end 1a and the upper end 1b of the piezoelectric element 1 are bonded and fixed, the piezoelectric element 1 that is harder than the material of the displacement magnifying mechanism 2 and has a higher elastic coefficient will be deformed. Will receive most of the power. As a result, when the external force is large, the laminated piezoelectric element 1 is damaged due to delamination due to a large bending force, and there is a high risk that it will not function.

JP-A-5-151580 Japanese Patent Application Laid-Open No. 5-96755 JP 2003-224745 A

  In the prior art, the elastic output portion is dealt with by the peripheral structure so that the impact force in the B and C directions in FIG. For example, the gap between the periphery of the portion where the vibration output unit is exposed and the exterior member of the apparatus is increased, and the step in the protruding direction is reduced. Furthermore, the support cushioning material for reducing vibration transmission is hardened against its purpose so that it does not collide with the exterior member due to the inertia of the entire mass of the piezoelectric device for generating acoustic signals, such as during a drop impact. Ingenuity has been devised to balance the deterioration of the original performance (deterioration of appearance due to widening of the gap or increase of leakage sound due to vibration transmission) and the resistance to impact force within the allowable range.

  Bone conduction speakers, which often use piezoelectric devices for generating acoustic signals, are different from speakers that generate air conduction sound, or in order to make the advantages more prominent, reduce leakage sound that changes to air conduction sound, appearance, etc. The improvement of usability and the usability to the device is desired. For this purpose, the acoustic signal generating piezoelectric device itself needs to have a stronger structure against external impacts.

  That is, an object of the present invention is to provide an acoustic signal generating piezoelectric device that is excellent in impact resistance while ensuring a large amplitude output and displacement force.

  In the present invention, the external force and deformation in the directions B and C in FIG. 1 are not increased, the displacement due to the external force is less likely to act on the piezoelectric element, and the external force is not received as it is. A structure that is dispersed in a portion other than the piezoelectric element is adopted.

That is, in the piezoelectric device for generating an acoustic signal according to the present invention, the piezoelectric element that converts an electrical signal into mechanical vibration, the displacement expansion mechanism that expands the displacement of the mechanical vibration generated by the piezoelectric element, and the displacement expansion mechanism are expanded. An acoustic signal generating piezoelectric device having an acoustic vibration part for transmitting mechanical vibration displacement as acoustic vibration, wherein the displacement enlarging mechanism is plate-shaped and opposed to the base member in a plate shape. one of the consists of a vibration output member that upright bent is provided to face each other by bending in a direction where there is the base member in the long side, and an elastic member having one end coupled to the base member and the vibration output member, said base the said vibration output member and the member has a high rigidity than the elastic member, from the other end of the base member and the vibration output member, the piezoelectric element, and the weight member is inserted in sequence, to said base member Serial weight member is coupled with high stiffness, the piezoelectric element is arranged between the central portion of the end portion and the vibration output member of the vibration output member of a side of the elastic member, and the piezoelectric said piezoelectric element to compress the displacement in the same direction, means for applying a preload between the base member and the vibration output member provided, position regulating means for unchanged the position of the piezoelectric element in the piezoelectric displacement direction substantially perpendicular one end of the piezoelectric element at the addition of structure, fixed to said base member or said vibration output member, the other end of the piezoelectric element on the opposite side to the fixed side with the addition of the position regulating means, the vibration output characterized in that in pressure contact without adhesive bonding to the member or the base member.

And in the fixed side end portion to the position regulating means is provided with a piezoelectric element, and a side member for the fixed and the piezoelectric element, may Shore D hardness is bonded through 30 or more 70 or less of the adhesive.

Wherein one end pressing surface of the piezoelectric element, when the surface treatment for reducing the contact friction coefficient of each other in at least one of the pressing surface of the vibration output member or said base member is pressed against the one end of the piezoelectric element is performed Good.

Wherein one end pressing surface of the piezoelectric element, between the pressing surface of the vibration output member or said base member is pressed against one end of the piezoelectric element, the friction reducing material may be interposed.

The displacement enlarging mechanism is formed by press forming of a metal plate material, and a bending portion which is a boundary portion between the vibration output member and the elastic member is not only bent on a flat plate but also processed to increase rigidity, and the weight member is wherein the portion of section and the weight member for coupling the base member is attached from the outside to the vicinity of the boundary between the elastic member and the base member, the coupling portion using an adhesive agent having 80 or more hardness in Shore D hardness It is preferable to increase the rigidity of the displacement enlargement mechanism and increase the overall resonance frequency of the displacement enlarging mechanism.

  According to the present invention, while the large amplitude output and the displacement force are ensured by the displacement enlarging mechanism, the multilayer piezoelectric element peels between the layers even when a large impact is caused by a drop or a collision applied to the incorporated device. It is possible to provide a piezoelectric device for generating an acoustic signal with a low risk of breakage. In addition, the method is realized by the structure of a structural part that can be manufactured by a general mass production method without any additional parts and additional work steps that are specially expensive compared to the conventional method. Moreover, there is no need to deal with additional changes in the appearance of the apparatus, and the usability is not deteriorated.

  An embodiment of the present invention is shown in FIGS. 3 to 6 and will be described in detail. 3 is an overall perspective view of the piezoelectric device for generating an acoustic signal to which the present invention is applied, FIG. 4 is an exploded perspective view of the piezoelectric device, and FIG. 5 is a vibration output unit pad and an anti-vibration support sheet for supporting the device. 6 is a plan view of the piezoelectric device for generating an acoustic signal in a state, and FIG. 6 is a view showing a cross section taken along the line XX shown in FIG.

  First, the structure will be described. As shown in FIGS. 4 and 6, the multilayer piezoelectric element 10 has a structure in which a piezoelectric material and an electrode are laminated in the longitudinal direction, and has a characteristic of extending in the longitudinal direction when a voltage is applied. The displacement enlarging lever 11 has a substantially U-shaped overall shape made by press-molding a metal plate, and both side portions of the base portion 11a are formed with standing bends that are twice as high as the plate pressure. The rigidity is increased. A screw hole for screwing a preload screw 12 for applying preload and a hole for screwing the base weight 13 are provided. Both side portions of the vibration output portion 11b on the upper side of the displacement magnifying lever 11 as the displacement magnifying mechanism are provided with standing bends having a height of 1.5 to 2.5 times the plate thickness to increase its rigidity. . The elastic portion 11c that connects one end of the base portion 11a and the vibration output portion 11b is not bent at both sides, and is configured to be relatively easily deformed in the thickness direction. However, a standing bend may be provided in the vicinity of the bent portion, which is a boundary portion between the elastic portion 11c and the vibration output portion 11b, to increase the rigidity of the bent portion.

  A base weight 13 is attached to the base portion 11 a of the displacement magnifying lever 11 by a weight fixing screw 14, and a coil bobbin 16 of a plastic molded product is coupled to the outer periphery of the base weight 13. A coil 21 is wound. The coil 21 is formed by winding an enamel wire having a diameter of about 80 μm for about 1000 turns, and is used to send a signal to a hearing aid compatible with the T coil, but functions as a weight member together with the base weight 13. In addition, an attenuation sheet 18 for relaxing resonance is disposed on the base weight 13. As a result, the mass of the base weight 13, the coil bobbin 16, and the coil 21 is coupled to the base portion 11a in a highly rigid state. Therefore, the masses of the base part 11a, the base weight 13, the coil bobbin 16, the coil 21, the weight fixing screw 14 and the preload screw 12 are combined, and the base part has a mass about 10 times larger than that of the vibration output part 11b. ing.

  The multilayer piezoelectric element 10 is disposed in a U-shaped inner space of the displacement magnifying lever 11, and the upper end surface of the multilayer piezoelectric element 10 is in contact with the inner surface (lower surface) of the vibration output member 11b. A thin film of solid lubricant is formed on the vibration output side contact portion E of the multilayer piezoelectric element for the purpose of reducing the friction coefficient. The lower end of the multilayer piezoelectric element 10 is in contact with the end face of the tip of the preload screw 12 that applies a preload in the compression direction to the multilayer piezoelectric element 10.

  The preload screw 12 is screwed and supported in the screw hole of the base member 11a. Furthermore, the periphery of the lower end portion of the multilayer piezoelectric element 10 is surrounded by a positioning plate 15 so that the multilayer piezoelectric element 10 does not rotate or move, and the positioning plate 15 is positioned at the lower bending position of the displacement enlarging lever 11. The formed square hole and the stepped portion of the base weight 13 are fixed to the inner surface of the base portion 11a. The base-side contact portion D of the multilayer piezoelectric element, which is the contact surface between the multilayer piezoelectric element 10 and the preload screw 12, is a space that can be made microscopically at the end surface contact portion of the preload screw 12 and the multilayer piezoelectric element 10 and its surroundings. The adhesive is a one-pack type epoxy adhesive having a Shore D hardness of 60. The adhesive is also present at the contact portion between the base portion 11a and the positioning plate 15 and the contact portion between the preload screw 12 and the base portion 11a, and these are bonded to each other. By the way, the Shore D hardness of this adhesive can be selected in the range of 30 or more and 70 or less. If it is less than 30, the fixing force is not sufficient, and if it exceeds 70, when an impact force is applied from the outside, the laminated piezoelectric An excessive force is applied to the element 10, which is not preferable.

  As shown in FIG. 4, a pad 17 of a plastic molded product is attached to the outer surface of the vibration output portion 11b as an acoustic vibration portion, and a portion that contacts the human body and transmits vibration is formed. The coil bobbin 16 is fitted with a lower anti-vibration support sheet 19 and an upper anti-vibration support sheet 20 punched from a special rubber sheet. The lower surface of the support sheet 19 and the upper surface of the vibration-proof support sheet 20 are guided by a device appearance member (not shown) that houses the entire device, and elastically supports the bone conduction speaker on the device.

  Also, as shown in FIGS. 4, 5, and 6, a so-called square bevel 11d is applied to a right-angled bending portion that becomes a boundary portion between the vibration output portion 11b and the elastic portion 11c of the displacement magnifying lever 11, and the rigidity of the bending portion is increased. Improvements are being made. In addition, the space between the lower bent portion, which is the boundary portion between the base portion 11a of the displacement enlarging lever 11 and the elastic portion 11c, and the coil bobbin 16, protrudes from the inner side surface of the coil bobbin 16 to a position where it contacts the surface of the elastic portion 11c. The stopper rib 16a is provided, and a substantially prismatic corner space F is formed below the stopper rib 16a. By embedding the corner space F with a highly rigid adhesive having a Shore D hardness of 80 or more, the displacement expanding lever 11 and the coil bobbin 16 are The required part is adhered. In addition, since the corner space F exists in the other side and near side of the cross section of FIG. 6, the shape is not shown in FIG. Moreover, when the Shore D hardness after hardening of the adhesive agent used at this time is 90, it has confirmed that it was especially effective in forming a highly rigid structure.

  The assembly process will be described. First, a solid lubricant, which is a friction reducing material, is applied to the surface of the vibration output side contact portion E of the displacement magnifying lever 11, and then, at a required position in the inner space of the displacement magnifying lever 11, at the lower end of the multilayer piezoelectric element 10. Temporary positioning is performed with a jig in the form in which the positioning plate 15 is inserted. At this time, on the pressure contact surface of the displacement magnifying lever 11 and the pressure contact surface of the end of the multilayer piezoelectric element 10 that are pressure-contacted by the vibration output side contact portion E, a surface that reduces a contact friction coefficient due to formation of a surface modification layer or the like It is even better if it is processed.

  Next, an adhesive is injected into the screw hole for the preload screw 12, and then the preload screw 12 is screwed. The preload screw 12 is screwed in by a pre-measured amount so that the reaction force of the elastic deformation of the displacement expanding lever 11 becomes a necessary preload while observing the displacement dimension of the tip of the lever 11b. Thereafter, the temporary positioning jig is removed, the base weight 13 is attached with the weight fixing screw 14, an adhesive is applied to the outer periphery of the base weight 13, and the assembly in which the coil 21 is wound around the coil bobbin 16 is brought to a required position. insert. Next, the corner space F is filled with an adhesive, and further, the adhesive is applied and attached to the pad 17 and the upper surface required portion of the vibration output portion 11b of the displacement magnifying lever 11, and finally heated for curing the adhesive. . This heating may be performed separately for each bonding process depending on the heatable temperature conditions, or several bonding processes may be performed collectively.

  Next, the functional operation will be described. When a voltage is applied to the multilayer piezoelectric element, expansion and contraction occurs in the length of the multilayer piezoelectric element corresponding to the applied voltage. Due to this expansion and contraction, the vibration output part 11b is subjected to a minute rotational displacement that opens the U-shaped tip side relative to the base part 11a. Due to the rotational displacement, a displacement larger than the expansion / contraction amount of the multilayer piezoelectric element is generated in the direction of the tip of the vibration output unit 11b. That is, as a result of arranging the upper end of the multilayer piezoelectric element 10 between one end of the vibration output part 11b on the elastic part 11c side and the central part of the vibration output part 11b, the displacement of the multilayer piezoelectric element is expanded. It becomes operation. Thus, when an acoustic signal voltage is applied to the multilayer piezoelectric element 10, a vibration displacement is generated in accordance with an acoustic signal that is enlarged by the displacement of the piezoelectric element.

  The base side including the base portion 11a has a mass about ten times larger than that of the vibration output portion 11b, and has a large moment of inertia including the shape effect. Accordingly, the absolute displacement of the vibration output portion 11b at this time is sufficiently larger than the base side in absolute amount. Conversely, the absolute displacement of the base portion 11a is sufficiently smaller than the vibration output portion 11b. Furthermore, since the bone conduction speaker can further reduce the conduction of vibrations due to the vibration-proofing effect of the vibration-proofing support sheets 19 and 20, the structure of the device incorporating the bone-conduction speaker vibrates and generates undesired air vibrations. Thus, it is possible to effectively suppress the occurrence of so-called leakage sound. Of course, on the contrary, the vibration displacement of the vibration output portion 11b can be obtained greatly, and the desired bone conduction vibration can be obtained efficiently.

  Now, an operation when a large impact force is applied to the apparatus incorporating the bone conduction speaker when it is dropped or collides with another object will be described. For example, when the impact force in the direction A shown in FIG. 1 is directly applied to the pad 17, the operation is roughly described. The elastic strain of the displacement expanding lever 11, the elastic strain in the compression direction of the laminated piezoelectric element, and each part of the bone conduction speaker The impact force is received by the energy absorption effect due to the displacement of the inertia mass and the deformation of the vibration-proof support sheet 19 on the lower side. In this case, the laminated piezoelectric element 10 generally has a hard and brittle characteristic, but a compressive force corresponding to the only strong characteristic acts, and there are few problems at this time. As the subsequent operation, the movement in the opposite direction occurs in which the energy absorbed by the elastic strain of each part is released. In this case, the displacement magnifying lever 11 performs a deformation operation in a direction in which the U-shape opens, and when both ends of the multilayer piezoelectric element 10 are bonded, a force in the tensile direction acts on the multilayer piezoelectric element 10. In a laminated piezoelectric element that is weak against tension, there is a high risk of peeling between the laminated layers. However, in the case of the structure of the present invention, the one end surface (upper end surface) of the multilayer piezoelectric element 10 is merely in pressure contact with or in contact with the displacement enlarging lever 11, so that only the surface of the vibration output portion 11b is separated. The tensile force due to the repulsive inertial force of other parts does not work. Thereafter, the vibration operation due to the impact is rapidly attenuated while performing the operation of the opposite repulsion phenomenon. As a result, only a large compressive force acts on the multilayer piezoelectric element 10, no tensile force acts, and there is little risk of damage to the multilayer piezoelectric element 10 which is strong against the compressive force.

  Next, the operation when the impact force in the B or C direction shown in FIG. 1 acts will be described. First, under what circumstances such impact force works is as follows. When an impact force in the B or C direction is applied to the device incorporating this bone conduction speaker, the entire bone conduction speaker moves relative to the device while deforming each other due to the inertial force and rigidity of each part. . Here, the anti-vibration support sheet 19 and the anti-vibration support sheet 20 have a Shore D hardness of 30 to 70 (general rubber is 80 or more), which is softer than ordinary rubber. This causes the pad 17 to collide. In this case, due to the inertia energy of the base portion having a large inertial mass, a force that relatively displaces in the B or C direction or in combination acts on the base portion 11a and the vibration output portion 11b.

  When such a force is applied, if the upper and lower ends of the multilayer piezoelectric element 10 are bonded to the displacement magnifying lever 11, the multilayer piezoelectric element 10 is bent and twisted depending on the rigidity strength of the adhesive. The deformable force is applied to the laminated piezoelectric element 10 having high rigidity, and most of the force is received. As a result, there is a high risk of breaking the form in which the laminated layers are separated, and the actual condition in the apparatus is damaged. Is out.

  However, in the embodiment of the present invention, one end of the multilayer piezoelectric element 10 is only in pressure contact with or in contact with the displacement expanding lever 11 and is not adhesively bonded. When the force is exceeded, a slip phenomenon occurs, and as a result, bending and twisting forces acting on the multilayer piezoelectric element 10 are reduced. Furthermore, when a lubricant that lowers the coefficient of friction is present on the pressure contact surface (contact surface), the force is greatly reduced. Therefore, the risk of damaging the multilayer piezoelectric element 10 is greatly reduced as compared with the case of bonding.

  In actuality, there are cases where the impact force in the A direction, B, and C directions is generated in combination. In this case, a surface pressure greater than the preload is generated at the vibration output side contact portion E on the laminated piezoelectric element 10 by the force due to the impact in the A direction, and a large resistance force is maintained even if the friction coefficient of the surface is lowered. As a result, a larger bending or twisting force acts on the multilayer piezoelectric element 10 as described above, combined with the force caused by the impact force in the B and C directions. However, the lower part of the multilayer piezoelectric element 10 and the base part 11a of the displacement magnifying lever 11 are joined by a relatively soft adhesive (a one-component epoxy adhesive having a Shore D hardness of about 60). Because of the support, the entire laminated piezoelectric element 10 is tilted or twisted, and all the upper displacement is prevented from being applied as bending force or torsional force of the laminated piezoelectric element 10. become. The force that the multilayer piezoelectric element 10 no longer receives is received by another member having high strength such as the displacement magnifying lever 11. For this reason, the risk of damage to the multilayer piezoelectric element 10 is reduced.

  (1) The upper and lower ends of the laminated piezoelectric element 10 are bonded and fixed to the displacement magnifying lever 11 with a highly rigid adhesive, and (2) one end is merely in pressure contact or contact, and the other end is Compared with a structure fixed through a relatively soft adhesive as a vibrating structure. If the conditions other than the fixing conditions of the upper and lower ends of the multilayer piezoelectric element 10 are completely the same, a sinusoidal voltage is applied to the multilayer piezoelectric element 10 and the resonance frequency is compared. The resonance frequency is lowered.

  If this resonance frequency is 3 kHz or less, particularly 2.5 kHz or less, there is a resonance point in the main band of the audio frequency, and the amplitude characteristic due to the applied voltage is greatly distorted near the resonance point. In the case of the bone conduction speaker using the acoustic signal generating piezoelectric device according to the present invention, the displacement enlarging lever 11 formed by pressing an iron plate is used in consideration of productivity, so that the upper and lower ends of the laminated piezoelectric element 10 are displaced. When fixed to the magnifying lever 11 with a highly rigid adhesive, the resonance frequency is around 2.9 kHz. ) And relatively soft adhesive fixation, the range is 2.4 kHz to 2.7 kHz.

  This greatly distorts the characteristics of the audio frequency band, and even if the characteristics of the drive circuit are adjusted, the sound quality is deteriorated, which is not preferable. Therefore, in the present embodiment, in order to increase the rigidity of the entire structure and make a vibration body having a resonance frequency of 3 kHz or more, the bending portion that is the boundary between the vibration output portion 11b and the elastic portion 11c of the displacement magnifying lever 11 is pressed. As shown in FIG. 6, the corner 11d that can be easily worked is added, the length of the elastic portion 11c occupying most of the spring characteristics is shortened, the constant as a spring is improved, and the resonance frequency is increased. A highly rigid adhesive was added to the corner space F to improve the rigidity of the displacement expansion lever against the required vibration displacement. As a result, the resonance frequency was improved to be between 2.9 and 3.1 kHz.

  In the above embodiment, the upper end of the multilayer piezoelectric element 10 is pressed against the vibration output portion 11b of the displacement magnifying lever, and the lower end of the multilayer piezoelectric element 10 is fixed to the base portion 11a of the displacement magnifying lever. One end of the piezoelectric element 10 may be fixed to the vibration output portion 11b of the displacement magnifying lever, and the other end of the stacked piezoelectric element 10 may be pressed against the base portion 11a of the displacement magnifying lever.

The perspective view which shows a principle structure. The front view which shows a principle structure. The perspective view which shows the external appearance of the piezoelectric device for acoustic signal generation in embodiment of this invention. The disassembled perspective view of the piezoelectric device for acoustic signal generation in embodiment of this invention. The top view of the piezoelectric device for acoustic signal generation | occurrence | production except the pad part in embodiment of this invention. Sectional drawing of the XX plane of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 1a Lower end part 1b Upper end part 2 Displacement expansion mechanism 2a Base member 2b Vibration output member 2c Elastic member 10 Multilayer piezoelectric element 11 Displacement expansion lever 12 Preload screw 13 Base weight 14 Weight fixing screw 15 Positioning plate 16 Coil bobbin 17 Pad 18 Damping sheet
19, 20 Anti-vibration support sheet 21 Coil 11a Base part 11b Vibration output part 11c Elastic part 11d Square striker 16a Stopper rib D Base side contact part E Vibration output side contact part F Corner space

Claims (5)

A piezoelectric element that converts electrical signals into mechanical vibration, a displacement expansion mechanism that expands the displacement of the mechanical vibration generated by the piezoelectric element, and an acoustic vibration unit that transmits the displacement of the mechanical vibration expanded by the displacement expansion mechanism as acoustic vibration A piezoelectric device for generating an acoustic signal comprising:
The displacement enlarging mechanism includes a plate-like base member , a vibration output member that is plate-like and opposed to the base member, and has two long sides that are bent in the direction in which the base member is located and opposed to each other. The base member and an elastic member to which one end of the vibration output member is coupled ,
Said base member and said vibration output member having a higher rigidity than the elastic member,
From the other end of the base member and the vibration output member, the piezoelectric element and the weight member are sequentially inserted,
The weight member is coupled with a high rigidity to said base member,
The piezoelectric element is arranged between the central portion of the end portion and the vibration output member of the vibration output member of a side of the elastic member,
And, wherein the piezoelectric element so as to compress the piezoelectric displacement in the same direction, a means for applying a preload between the base member and the vibration output member,
One end of the piezoelectric element at adapted to be added to the position regulating means for unchanged the position of the piezoelectric element in the piezoelectric displacement direction substantially perpendicular direction is fixed to the base member or the vibration output member,
The other end of the piezoelectric element on the opposite side to the position restricting stationary added with means for generating an acoustic signal piezoelectric, characterized in that in pressure contact without adhesive bonding to the vibration output member or said base member apparatus. And in the fixed side end portion to the position regulating means is provided in the piezoelectric element, wherein a side of the member to the fixed and the piezoelectric element was bonded Shore D hardness through 30 or more 70 or less of the adhesive The acoustic signal generating piezoelectric device according to claim 1. Pressure contact surface of one of said piezoelectric element, a surface treatment for reducing the contact friction coefficient of each other in at least one of the pressing surface of the vibration output member or said base member is pressed against one end of the piezoelectric element is subjected The piezoelectric device for generating an acoustic signal according to claim 1, wherein: Pressure contact surface of one of said piezoelectric elements, said between pressing surface of the vibration output member or said base member is pressed against the one end of the piezoelectric element according to claim 1, characterized in that interposed friction reducing material The acoustic signal generating piezoelectric device according to any one of to 3. The displacement enlarging mechanism is formed by press molding of a metal plate material,
The bending part which is a boundary part between the vibration output member and the elastic member is not only bent on a flat plate, but also processed to increase rigidity,
The part portion and said weight member, wherein the weight member is coupled to the base member is coupled from the outside to the vicinity of the boundary between the elastic member and the base member, an adhesive having a 80 hardness of at least Shore D hardness 5. The acoustic signal generating piezoelectric device according to claim 1, wherein the rigidity of the coupling portion is increased by using the first and second components to increase the overall resonance frequency of the displacement magnifying mechanism.

Images