JP4771475B2 - Bone conduction speaker - Google Patents

Description

  The present invention relates to a bone conduction speaker using a unimorph or bimorph type piezoelectric element, and more particularly to a bone conduction speaker having a piezoelectric element support structure capable of effectively using vibration energy and preventing sound leakage.

  There are few examples of the prior art as a bone conduction speaker using a unimorph or bimorph type piezoelectric element, and Patent Document 1 is disclosed as “an acoustic vibration generating element for a bone conduction speaker”. However, this is an example of performance improvement as a single vibration element, and when it is incorporated for use as an element of a bone conduction speaker in an information transmission device, how to support and install in order to reduce sound leakage It is not shown whether it is good. Considering from the viewpoint of the prior art, it is difficult to transmit vibration to the exterior structure of the device and to prevent an increase in sound leakage by supporting the vicinity of the position of the vibration node at the time of vibration with an elastic material and incorporating it in the device. is there.

  However, in this case, the amplitude of the bending vibration of the bimorph piezoelectric element is large at the center or both ends, and the difference in vibration phase is 180 degrees. Therefore, either one is applied to the human body to transmit the vibration, and only one half or less of the bending vibration energy of the piezoelectric element can be used. Therefore, a method that can effectively use the bending vibration is desired.

  On the other hand, when paying attention to the support structure of the vibration driving body using a piezoelectric element, there are many conventional cases of general speakers using air propagation. For example, it is a supporting method found in Patent Document 2 and Patent Document 3. The support structure of the piezoelectric element of the vibrating body in these cases is such that the outer periphery of the disk or both opposing sides of the rectangle are directly connected to a rigid body having a large mass via an elastic material, regardless of whether the piezoelectric element has a disk shape or a rectangular shape. The vibration of the central part is used for direct sounding or the other members are vibrated. In addition, as shown in Patent Document 4, there is a type in which the center is joined to the vibration member, and the others are free to vibrate the vibration member with the reaction force of the vibration operation of the piezoelectric element. Is a common case.

  The latter has a small excitation force compared to the ability of the piezoelectric element to generate a large force, and a technique for increasing the excitation force by joining a weight to the piezoelectric element to increase the excitation force is also disclosed. However, the amount of weight that can be added is relatively small, still insufficient for bone conduction speakers that vibrate the human body, and are inefficient and unsuitable.

  On the other hand, the former (Patent Documents 2 and 3) has a large force obtained from the central portion of the piezoelectric element by increasing the mass of the base, and can utilize the ability to generate a large force for the small size of the piezoelectric element. However, by attaching it to the base member via an elastic material, the loss due to the restraining force during vibration deformation of the piezoelectric element is reduced, while there is a degree of freedom of elastic displacement in the vibration direction, so that it can be used in the center. The vibration amplitude of the part is reduced.

  As a method for improving this point, there has been proposed a method in which a high-rigid sphere functioning as a roller is mixed in an elastic adhesive as shown in Patent Document 5. This method reduces the generated amplitude and force loss by strengthening the restraining force in the vibration direction and weakening the restraining force in the direction perpendicular to the vibration (the plane direction of the piezoelectric element) than when simply holding with an elastic adhesive. It is based on ideas.

  However, when it is intended to construct a small size by this method, it is necessary to reduce the diameter of the high-rigid sphere mixed in the elastic adhesive. When the diameter of the sphere is reduced, the dispersion of granular glass in plastic resembles the phenomenon that the rigidity increases in all directions, and tends to increase the restraint force in the planar direction of the piezoelectric element without weakening it. However, the effect of reducing loss is not yet sufficient.

JP 2005-175985 A JP 2000-201398 A JP 2000-305573 A JP 2004-104327 A Japanese Patent No. 3202169

  The characteristic required for a bone conduction speaker is that the vibration force that must be output is remarkably larger than that of an air conduction speaker used for an earphone. Further, in terms of differentiation, it is required that air conduction sound is not generated or is small (small sound leakage), and that the size is close to that of the air conduction speaker.

  Under such circumstances, piezoelectric elements that can produce a large force and have high energy efficiency are attracting attention. However, because the development of air-conducting loudspeakers is the main application, the increase in output has increased in size. As a result, the structure of a bone conduction speaker that has a strong tendency to increase sound leakage, is small in size, can produce the force necessary for bone conduction, and has little sound leakage even when incorporated into a small and lightweight plastic exterior structure device such as a mobile phone. Is required.

  In this situation, the object of the present invention is to achieve a large output required for bone conduction using a unimorph or bimorph type piezoelectric element while preventing an increase in sound leakage when incorporated in a device. An object of the present invention is to provide a bone conduction speaker having excellent mass productivity.

  As a structure to solve the problem, the bending vibration of a strip-shaped bimorph piezoelectric element is close to the ideal free support at both ends (high rigidity in the vibration direction of the piezoelectric element and low in the longitudinal plane direction of the piezoelectric element). The rigidity of the piezoelectric element is maximized when an AC voltage is applied. In addition, the base side supporting both ends of the piezoelectric element has a large mass, the vibration amplitude due to the reaction force applied to the base side is reduced, the vibration transmitted to the exterior structure of the equipment supporting the base is reduced, and the exterior Sound leakage caused by vibration of the structure is reduced. At the same time, the vibration node position of the bending vibration of the piezoelectric element is brought close to both ends to maximize the amplitude of the central portion.

  According to the present invention, it is possible to obtain a large output vibration of a vibration energy required for a bone conduction speaker in a smaller size with a high-productivity component structure, and to increase output when incorporated in a use device. An increase in sound leakage can be prevented.

  Next, an embodiment of the present invention will be described with reference to FIG. In this bone conduction speaker, (1) a piezoelectric element portion comprising a rectangular bimorph or unimorph type piezoelectric element 1 having a length dimension of 2 or more when the width dimension is 1, and an insulating coating material 4 protecting the same, ( 2) a base weight 5 and a frame 3 that holds the base weight 5; a base portion having a mass larger than the mass of the piezoelectric element portion; and (3) a frame 3 that is joined to both ends of the piezoelectric element 1 in the longitudinal direction. Joined to the upper ends of the rising portions 3a and 3b of the piezoelectric element 1, the piezoelectric element 1 is formed so as to have a high rigidity in the plate thickness direction and low rigidity in the longitudinal direction perpendicular thereto. The two insulating support members 2a and 2b are provided, and when the vibration amplitude when the AC voltage is applied at the center of the piezoelectric element portion is 1, the vibration amplitude of the base portion (base weight 5 and frame 3) is 1/2 It is below.

  In this way, the unimorph or bimorph type rectangular planar piezoelectric element 1 is used, and this is used as a both-end support structure with little loss of vibration energy, and the mass of the support (base part) is increased. By reducing the vibration of the support, the phenomenon that the vibration is transmitted to the equipment and the sound leakage increases is reduced.

  At this time, if the length dimension is less than 2 with respect to the width dimension 1 of the rectangular shape of the piezoelectric element 1, the curved shape at the time of driving becomes a dish shape, and a curved vibration of an area more than necessary occurs, resulting in sound leakage. Becomes larger. On the other hand, when the length dimension exceeds 10 with respect to the width dimension 1, the usable range is narrowed due to the decrease in usability.

  Further, it is necessary to suppress the vibration amplitude of the base portion to ½ or less with respect to the vibration amplitude when the AC voltage is applied at the center of the piezoelectric element portion. This is because if the ratio exceeds 1/2, sound leakage that is practically unacceptable occurs. Ideally, the larger the mass of the base portion, the less the vibration of the base portion and the greater the vibration of the central portion of the piezoelectric element. However, the increase in the mass of the base part is limited due to restrictions on the overall size and the like, and the vibration amplitude of the base part is made less than 1/10 of the vibration amplitude at the center of the piezoelectric element part in order to satisfy the miniaturization condition. It's not easy.

  Further, the insulating covering material 4 is made of an elastic member having vibration damping characteristics, and is connected to the insulating support members 2a and 2b in the vicinity of the portion where the insulating support members 2a and 2b and the piezoelectric element 1 are joined. Thus, the vibration damping characteristic of resonance is enhanced.

  Further, as shown in FIG. 2, the piezoelectric element 1 has a flat plate shape, and the insulating coating material 4 is formed on the main surface opposite to the base portion (base weight 5 and frame 3) of the piezoelectric element 1 from the end portion in the longitudinal direction. Further, by forming a thick surface at the center and having a convex surface shape (convex surface 4a), transmission of vibration output to the human head can be facilitated.

  The piezoelectric element is not a flat plate, but can be curved in the longitudinal direction even when no AC voltage is applied, and can have a convex shape on the main surface opposite to the base weight 5.

  In addition, as in the support structure of FIG. 2, the insulating support members 2a and 2b are made of an insulating material, and the piezoelectric element thickness is such that the support rigidity in the piezoelectric element thickness direction is high and the support rigidity in the piezoelectric element longitudinal direction is low. It is preferable that the shape is not easily deformed or displaced in the vertical direction and is easily deformed or displaced in the longitudinal direction of the piezoelectric element.

  Further, the supporting structure of FIG. 2 will be described. The supporting portion is composed of an insulating material portion (insulating supporting members 2a and 2b) and a metal plate material portion (the rising portions 3a and 3b of the frame 3) connected to the bottom portion thereof. The portion is joined to the piezoelectric element 1 and the metal plate material portion is joined to the base portion, but the metal plate material portion is formed integrally with the base portion. That is, a configuration in which the insulating support members 2a and 2b and the rising portions 3a and 3b are integrated is regarded as a support portion, and a base portion including the base weight 5 and the bottom surface portion of the frame 3 is connected to the support portion. It is.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the appearance of a bone conduction speaker according to an embodiment of the present invention. FIG. 1 (a) is a plan view, FIG. 1 (b) is a front view, and FIG. 1 (c) is a right side view. FIG. 2 is a sectional view taken along line AA in FIG. FIG. 3 is an exploded perspective view showing an individual component state. FIG. 4 is a perspective view of the piezoelectric element 1, and 1a is a piezoelectric element wiring. FIG. 5 is a perspective view in which insulating support members 2 a and 2 b are inserted and fixed to both ends of the piezoelectric element 1. FIG. 6 is a perspective view showing a state where the piezoelectric element 1 and the upper half portions of the insulating support members 2a and 2b are molded and covered with an elastic insulating covering material 4. FIG. 7 is a perspective view showing a completed state of the bone conduction speaker with the frame 3 attached and the base weight 5 attached with screws. FIG. 8 is a front view schematically showing a vibration state.

  The structure will be described. As shown mainly in FIG. 4, a unimorph type piezoelectric element 1 in which a piezoelectric material plate and an electrode are stacked on a metallic thin plate, or a bimorph type piezoelectric element 1 in which a piezoelectric material plate and an electrode are stacked on both sides of a metal thin plate, or a metallic thin plate A laminated bimorph type piezoelectric element 1 formed by stacking a plurality of piezoelectric materials and electrodes on one side or both sides of a rectangular plane having a width of about 4.4 mm and a length of about 15 mm and a total thickness of about 0. .6mm shape with a mass of about 0.28g.

  As shown in FIG. 5 and the like, both ends of the piezoelectric element 1 are inserted into the grooves of electrically insulating insulating support members 2a and 2b that can be manufactured by plastic molding suitable for mass production, and the same material as the insulating support member is used. It is joined with an insulating adhesive having a Young's modulus of a degree or more.

  As shown in FIG. 2 and the like, the frame 3 that can be produced by press molding with high productivity of a metal plate material having a thickness of 0.3 mm has a width of 5 mm, a length of 16 mm, and approximately 2.5 mm at both ends. The rising portions 3a and 3b are press-fitted and joined to elongated rectangular holes (not shown) formed on the lower surfaces of the insulating support members 2a and 2b. This bonding may not be press fit, but may be adhesive bonding inserted into the hole together with an adhesive. In this case, the Young's modulus of the adhesive is preferably equal to or higher than the Young's modulus of the material of the insulating support member.

  In this way, by adopting a structure in which the rising portions 3a, 3b (metal plate material) of the frame 3 are press-fitted into elongated rectangular holes formed in the lower portions of the insulating support members 2a, 2b, the support rigidity in the piezoelectric element thickness direction can be increased. The support rigidity in the longitudinal direction of the piezoelectric element can be increased and the support rigidity can be decreased. That is, when attention is paid to the insulating support members 2a and 2b, it has a shape and structure that is difficult to be deformed or displaced in the piezoelectric element thickness direction and is easily deformed or displaced in the longitudinal direction of the piezoelectric element.

  As shown in FIGS. 2 and 3, a base weight 5 made of a metal plate having a relatively large specific gravity is attached to the frame 3 with screws 6 a and 6 b, and the frame 3, the screws 6 a and 6 b, and the base weight 5 are connected to each other. The total mass is about 1.5 g.

  The outer periphery of the piezoelectric element 1 shown in FIG. 2 and the portion of the insulating support members 2a and 2b that support the piezoelectric element 1 are insulative and have a hardness of 60 degrees to 80 degrees (Hs 60 to 80 degrees) with good vibration damping (damping) characteristics. It is covered with an insulating coating material 4 made of JIS A) rubber by a vacuum casting method. The central portion of the upper surface that becomes the contact portion with the human body forms a curved convex surface 4a that protrudes about 1 mm above the peripheral portion, and the center of contact with the human body is the center of the piezoelectric element portion 10 (FIG. 8). I try to become a part. The total mass of this part is about 0.35 g.

  The curved surface for improving the contact with the human body is achieved by a curved shape in which the central portion of the insulating coating material 4 is thickened. However, in order to reduce the mass of the vibration part including the piezoelectric element 1, the piezoelectric element 1 itself is When not in operation, it may be already curved, that is, a piezoelectric material may be formed on one or both sides of a curved metal thin plate, and the insulating coating layer may be thin with a constant thickness.

  The insulating coating 4 is not only for mechanical covering protection of the piezoelectric element 1, but also for preventing a short-circuit failure caused by a migration phenomenon due to voltage application in a high temperature and high humidity environment in a silver electrode that is relatively often used for the piezoelectric element. It also serves as a cover for moisture prevention, and also serves as a damping material that reduces the degree of resonance phenomenon of the piezoelectric element. In particular, the thickness of the coating, the hardness of the rubber, and the material are important determinants in compromising the increase in loss due to the damping characteristics that contradict the reduction in vibration output loss at an appropriate level.

  Next, operation characteristics will be described. Strictly speaking, the support structure of the device and the elasticity and mass of the human body transmission part affect the vibration state at the absolute position. However, including the fact that it is too complicated to discuss and that it does not differ greatly qualitatively, here is the case where the whole is placed on a sufficiently soft foam sheet and freely operated The vibration state will be described.

  When an alternating voltage is applied to the piezoelectric element 1, it bends and vibrates in proportion to the applied voltage, and the effect acts on the whole. FIG. 8 schematically shows the state of vibration. The piezoelectric element portion 10 including the piezoelectric element 1 performs a bending deformation operation along the applied voltage. Since the support portions 20a and 20b constituted by the insulating support members 2a and 2b and the left and right rising portions 3a and 3b of the frame 3 supporting this are high in the Y-axis direction and low in the X-axis direction, The displacement in the Y-axis direction at the left and right ends of the piezoelectric element portion 10 becomes the displacement in the Y-axis direction at both ends of the base portion 30 formed by the base weight 5 and the flat portion (bottom surface portion) of the frame 3 as it is. The displacements in the X-axis direction of the support portions 20a and 20b are balanced left and right and are balanced in terms of kinetic energy and do not affect others. The displacement in the Y-axis direction at both ends of the base portion 30 becomes parallel displacement of the base portion 30 because the rigidity of the base portion 30 is high. There is no theoretical movement in the Z-axis direction. Actually, it is negligible and need not be considered.

  Here, since the mass of the base portion 30 is larger than the mass of the piezoelectric element portion 10, the vibration node of the piezoelectric element portion 10 is closer to the left and right ends than when both ends are not supported. Theoretically, if the base side has an infinite mass, the node will be at both ends. When comparing the amplitude of the left and right ends (that is, equivalent to the amplitude of the base portion 30) with respect to the central amplitude of the piezoelectric element portion 10, the mass difference between the piezoelectric element portion 10 and the base portion 30 is 0.35 g as a real number. On the other hand, since it is 1.5 g, there are about four times, and the amplitude difference is simply a quarter, but when compared in terms of kinetic energy, the vibration of the base part 30 is uniform throughout, and the piezoelectric element part Since 10 vibrations change depending on the location, it is considered that there is a further difference. Prototypes for confirming the effect are different in length because of trial manufacture with an off-the-shelf piezoelectric element, but the actual measurement value is 1/5 to 1/8.

  FIG. 9 shows the actually measured amplitude characteristics of the prototype (the vibration level on the vertical axis is displayed with an amplitude of 10 μm as a reference). That is, it is a diagram illustrating a difference in vibration characteristics between the base unit 30 and the piezoelectric element unit 10 when there is no load. FIG. 10 shows a comparison of amplitude characteristics in the same manner by adding support and pressing load assuming installation into equipment and pressing on the human body. That is, it is a diagram illustrating a difference in vibration characteristics when the base portion 30 and the piezoelectric element portion 10 are loaded. As can be seen from this, the characteristics assuming the actual use state are that the mass effect on the base side is not seen at 600 Hz or less, which is unlikely to cause sound leakage, but at 1 kHz or more where sound leakage is likely to occur, The mass effect works and an amplitude difference of 15 dB or more is observed.

FIG. 1A is a plan view, FIG. 1B is a front view, and FIG. 1C is a right side view of a bone conduction speaker according to an embodiment of the present invention. Sectional drawing in the AA of FIG. The disassembled perspective view which shows the individual component state in one Example of this invention. 1 is an external perspective view of a piezoelectric element in one embodiment of the present invention. The perspective view which inserted and fixed the insulating support member to the both ends of the piezoelectric element in one Example of this invention. The perspective view which shows the state which carried out the molding shaping | molding and covered the upper half part of the piezoelectric element and the insulation support member in one Example of this invention with the elastic insulation coating material. The perspective view which shows the external appearance of the completion state of the bone conduction speaker in one Example of this invention. The front view which shows typically the vibration state in one Example of this invention. The figure which shows the difference of the vibration characteristic at the time of the no load of the base part and piezoelectric element part in the prototype of one Example of this invention. The figure which shows the difference of the vibration characteristic at the time of the load of the base part and piezoelectric element part in the prototype of one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 1a Piezoelectric element wiring 2a, 2b Insulation support member 3 Frame 3a, 3b Standing part 4 Insulation coating material 4a Convex surface 5 Base weight 6a, 6b Screw 10 Piezoelectric element part 20a, 20b Support part 30 Base part

Claims (7)

A bone conduction speaker that is a vibration driving body that transmits vibration to a human head and transmits sound information, and a rectangular bimorph or unimorph type piezoelectric element having a length dimension of 2 or more when the width dimension is 1, and the same A piezoelectric element portion made of a covering material for protecting
A base portion having a mass larger than the mass of the piezoelectric element portion;
Bonded to both ends of the piezoelectric element in the longitudinal direction and bonded to the base portion, the rigidity is high in the plate thickness direction of the piezoelectric element, and rigid in the longitudinal direction perpendicular thereto. Are provided with two support parts having low support characteristics,
The bone conduction speaker according to claim 1, wherein the vibration amplitude of the base portion is ½ or less when the vibration amplitude at the time of applying an alternating voltage at the center of the piezoelectric element portion is 1.   2. The bone conduction speaker according to claim 1, wherein the covering material is made of an elastic member having vibration damping characteristics, and is connected to the support portion in the vicinity of a portion where the support portion and the piezoelectric element are joined. .   The piezoelectric element has a flat plate shape, and the covering material has a convex surface shape formed on the main surface opposite to the base portion of the piezoelectric element so as to be thicker at the center than at the longitudinal end. The bone conduction speaker according to claim 2, wherein   3. The bone conduction speaker according to claim 1, wherein the piezoelectric element is curved in a longitudinal direction when no AC voltage is applied, and has a convex shape on a main surface opposite to the base portion.   The support portion includes an insulating support member, and is not easily deformed or displaced in the piezoelectric element thickness direction so that the support rigidity in the piezoelectric element thickness direction is high and the support rigidity in the piezoelectric element longitudinal direction is low. The bone conduction speaker according to any one of claims 1 to 4, wherein the bone conduction speaker is shaped to be easily deformed or displaced in a direction.   The support portion includes an insulating material portion and a metal plate material portion connected to a bottom portion thereof, the insulating material portion being joined to the piezoelectric element, and the metal plate material portion being joined to the base portion. The bone conduction speaker according to any one of 1 to 4.   The bone conduction speaker according to claim 6, wherein the metal plate member is formed integrally with the base.

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