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DESCRIPTION JP2007336418

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DESCRIPTION JP2007336418
PROBLEM TO BE SOLVED: A small-sized, mass-produced bone conduction speaker which realizes
high output required for bone conduction using a unimorph or bimorph piezoelectric element
while preventing an increase in sound leakage when it is incorporated into a device. To provide.
SOLUTION: A bimorph-type rectangular planar piezoelectric element 1 is used as an end
supporting structure with little loss of vibration energy, and the mass of a base portion including
a base weight 5 and a frame 3 is increased. The rigidity of the piezoelectric element in the
thickness direction of the support including the insulating support members 2a and 2b is
increased by decreasing the rigidity of the piezoelectric element in the thickness direction,
thereby reducing the vibration of the base in the apparatus. Reduce the phenomenon that
vibration is transmitted and the sound leakage increases. [Selected figure] Figure 2
Bone conduction speaker
[0001]
The present invention relates to a bone conduction speaker using a unimorph or bimorph
piezoelectric element, and more particularly to a bone conduction speaker having a support
structure of a piezoelectric element capable of effectively utilizing vibrational energy and
preventing sound leakage.
[0002]
There are few examples of prior art as a bone conduction speaker using a unimorph or bimorph
piezoelectric element, and Patent Document 1 is disclosed as "acoustic vibration generating
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element for a bone conduction speaker".
However, this is an example of performance improvement as a single vibration element, and
when incorporated for use as an element of a bone conduction speaker in an information
transmission device, how to support and attach it in order to reduce sound leakage It is not
shown if it is good. Considering from the point of view of the prior art, it is difficult to transmit
the vibration to the exterior structure of the device by supporting the position near the position
of the node of the vibration at the time of vibration with an elastic material. is there.
[0003]
However, in this case, the amplitude of the bending vibration of the bimorph piezoelectric
element is large at the central portion or at both ends, and the difference in the vibration phase is
180 degrees. Therefore, either one of them is applied to the human body to transmit its vibration,
and only 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.
[0004]
On the other hand, when focusing on the supporting structure of the vibration driving body using
the piezoelectric element, there are many conventional cases of general speakers using air
propagation. For example, it is a support method seen in Patent Document 2 and Patent
Document 3. The support structure of the piezoelectric element of the vibrator in these is that the
outer periphery of the disc or both opposing sides of the disc are directly connected via the
elastic material to the large rigid body regardless of the disc shape and the rectangular shape of
the piezoelectric element. It is of a system of attaching and utilizing the vibration operation of the
central part directly for sound generation of air conduction or vibrating other members. In
addition, there is also a method of joining the center to the vibration receiving member and
vibrating the vibration receiving member with the reaction force of the vibration operation of the
piezoelectric element, as shown in Patent Document 4, and the others are free. Is a common case.
[0005]
In the latter case, the excitation force is small compared to the ability of the piezoelectric element
to produce a large force, and a method of joining a weight to the piezoelectric element to
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increase the excitation force and increasing the excitation force is also disclosed. However, the
amount of weight that can be added is relatively small and still insufficient for bone conduction
speakers that vibrate the human body, which is inefficient and unsuitable.
[0006]
On the other hand, in the former (patent documents 2 and 3), by increasing the mass of the base,
the force obtained from the central portion of the piezoelectric element is large, and a method
capable of utilizing the ability to exert a large force for the small size of the piezoelectric element
However, by attaching it to the base member via an elastic material, loss due to restraint force at
the time of vibration deformation of the piezoelectric element is reduced, while there is a degree
of freedom to be elastically displaced also in the vibration direction. The vibration amplitude of
the part is reduced.
[0007]
As a method of improving this point, there has been proposed a method of mixing a highly rigid
sphere acting as a roller in an elastic adhesive as disclosed in Patent Document 5.
This method strengthens the restraining force in the vibration direction more than simply
holding it with an elastic adhesive, and weakens the restraining force in the vibration
perpendicular direction (plane direction of the piezoelectric element) to reduce the loss of the
generated amplitude and force. It is based on ideas.
[0008]
However, in order to construct a compact one by this method, it is also necessary to reduce the
diameter of the highly 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 rigidity increases in all directions, and tends to strengthen the binding
force in the planar direction of the piezoelectric element without weakening it. And the loss
reduction effect is not sufficient yet.
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[0009]
JP, 2005-175985, JP, 2000-201398, JP, 2000-305573, JP, 2004-104, 327, JP, 3202169, A
[0010]
The characteristic required of the bone conduction speaker is that, compared to the air
conduction speaker used in the earphone, the vibration force which must be output is
significantly larger than that required.
Also, in terms of differentiation, it is required not to generate air conduction sound or to be small
(less sound leakage), and the size is required to be close to an air conduction speaker.
[0011]
Under these circumstances, piezoelectric elements that can exert a large force and have good
energy efficiency are attracting attention, but development for air-conducted speakers has been
advanced in main applications, and the increase in output has become an increase in size, As a
result, the structure of the bone conduction speaker has a strong tendency to increase sound
leakage, is small in size, can exert the force necessary for bone conduction, and has little sound
leakage even when incorporated into a device of small lightweight plastic exterior structure such
as a cellular phone. Is required.
[0012]
Under these circumstances, the object of the present invention is to realize a large output
required for bone conduction using a unimorph or bimorph piezoelectric element while
preventing an increase in sound leakage when incorporated into a device, thereby achieving
compactness. To provide a mass-produced bone conduction speaker.
[0013]
As a structure for solving the problem, the curved vibration of the strip-shaped bimorph type
piezoelectric element is close to the ideal free end support (with high rigidity in the vibration
direction of the piezoelectric element and low in the longitudinal plane direction of the
piezoelectric element As a rigid elastic property), the curvature of the piezoelectric element is
maximized when an AC voltage is applied.
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Also, a large mass is given to the base side supporting both ends of the piezoelectric element to
reduce the vibration amplitude due to the reaction force applied to the base side, and the
vibration transmitted to the exterior structure of the device supporting the base is further
reduced. It reduces sound leakage caused by vibration of the structure.
At the same time, the node position of the vibration of the bending vibration of the piezoelectric
element is brought close to both ends to maximize the amplitude of the central portion.
[0014]
According to the present invention, it is possible to obtain a large output vibration of vibration
energy required for a bone conduction speaker with a smaller size with a component
configuration with high mass productivity, and about an increase in output when incorporated in
a utilization device It is possible to prevent an increase in sound leakage.
[0015]
Next, an embodiment of the present invention will be described with reference to FIG.
In this bone conduction speaker, (1) a rectangular bimorph or unimorph piezoelectric element 1
having a length dimension of 2 or more when the width dimension is 1, and a piezoelectric
element portion comprising an insulating covering material 4 for protecting the same 2) A base
weight 5 and a frame 3 for holding the same, and a base portion having a mass larger than that
of the piezoelectric element portion, and (3) a frame 3 joined to both ends in the longitudinal
direction of the piezoelectric element 1 It is joined to the upper end of the rising parts 3a and 3b,
and has high rigidity in the thickness direction of the piezoelectric element 1 and low rigidity in
the longitudinal direction perpendicular to it. Provided with two insulated support members 2a
and 2b, and the vibration amplitude at the time of applying an alternating voltage 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.
[0016]
As described above, the unimorph or bimorph type rectangular planar piezoelectric element 1 is
used as an end supporting structure with little loss of vibrational energy, and the mass of the
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support (base portion) is increased. The vibration of the support is reduced to reduce the
phenomenon that the vibration is transmitted to the device and the sound leakage is increased.
[0017]
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 disk shape, and a curved vibration of an area more than necessary occurs, and sound leakage
Becomes larger.
On the other hand, if the length dimension exceeds 10 with respect to the width dimension 1, the
usability falls and so on, the usable application range becomes narrow.
[0018]
In addition, it is necessary to suppress the vibration amplitude of the base portion to 1/2 or less
of the vibration amplitude at the time of application of the alternating voltage at the center of the
piezoelectric element portion. When it exceeds 1/2, practically unacceptable sound leakage
occurs. Ideally, the larger the mass of the base portion is, the smaller the vibration of the base
portion is, and the larger the vibration of the central portion of the piezoelectric element.
However, the mass increase of the base is limited due to limitations such as the overall size, and
the vibration amplitude of the base is less than 1/10 of the vibration amplitude of the center of
the piezoelectric element in order to satisfy the condition of miniaturization It is not easy.
[0019]
Furthermore, the insulating covering material 4 is made of an elastic member having vibration
damping characteristics, and is connected to the insulating supporting members 2a and 2b in the
vicinity of the portions where the insulating supporting members 2a and 2b and the piezoelectric
element 1 are joined. Thus, the vibration damping characteristics of the resonance are enhanced.
[0020]
Further, as shown in FIG. 2, the piezoelectric element 1 has a flat plate shape, and the insulating
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covering material 4 is on the main surface of the piezoelectric element 1 on the opposite side to
the base (base weight 5 and frame 3) The transmission of the vibration output to the human head
can be facilitated by forming a thick and convex surface shape (convex surface 4a) at the central
portion.
[0021]
The piezoelectric element is not flat and can be curved in the longitudinal direction even when an
alternating voltage is not applied, and the main surface on the opposite side to the base weight 5
can have a convex shape.
[0022]
Further, as in the support structure shown in FIG. 2, the insulating support members 2a and 2b
are made of an insulating material, the support rigidity in the thickness direction of the
piezoelectric element is high, and the support rigidity in the longitudinal direction of the
piezoelectric element is low. It is preferable that the piezoelectric element has a shape that is not
easily deformed or displaced in the longitudinal direction and easily deformed or displaced in the
longitudinal direction of the piezoelectric element.
[0023]
Further, the support structure of FIG. 2 will be described. The support portion is composed of an
insulating material portion (insulation support members 2a and 2b) and a metal plate portion
connected to the bottom thereof (rising portions 3a and 3b of the frame 3) The part is joined to
the piezoelectric element 1 and the metal plate part is joined to the base part, but the metal sheet
part is integrally formed with the base part.
That is, an integrated form of the insulating support members 2a and 2b and the rising portions
3a and 3b 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.
[0024]
An embodiment of the present invention will be described based on the drawings.
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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 cross-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 the 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 in which the piezoelectric element 1 and the upper
half portions of the insulating support members 2a and 2b are molded and covered with the
elastic insulating covering material 4. FIG. 7 is a perspective view showing a completed state of
the bone conduction speaker in a state in which the frame 3 is further attached and the base
weight 5 is attached by a screw. FIG. 8 is a front view schematically showing a vibration state.
[0025]
The structure will be described. As shown mainly in FIG. 4, a unimorph type 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 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 structure is 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 It has a shape of 6 mm and a mass of about 0.28
g.
[0026]
As shown in FIG. 5, etc., both ends of the piezoelectric element 1 are inserted into the grooves of
the electrically insulating insulating support members 2a and 2b which can be manufactured by
plastic molding suitable for mass production, and the same as the material of the insulating
support member It is joined by an insulating adhesive of Young's modulus or more.
[0027]
As shown in FIG. 2 etc., the frame 3 which can be manufactured by press forming with high mass
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productivity with a metal plate material with a thickness of 0.3 mm has a width of 5 mm and a
size of 16 mm in the longitudinal direction and is about 2.5 mm at both ends. The rising portions
3a and 3b are press-fit and joined to elongated rectangular holes (not shown) formed on the
lower surface of the insulating support members 2a and 2b.
This bonding is not a press-in, but may be an adhesive bonding inserted into a hole together with
an adhesive, and in this case, the Young's modulus of the adhesive preferably has a characteristic
equal to or higher than the Young's modulus of the material of the insulating support member.
[0028]
Thus, the support rigidity of the piezoelectric element in the thickness direction is obtained by
adopting a structure in which the rising portions 3a and 3b (metal plate materials) of the frame 3
are press-fit into the elongated rectangular holes formed in the lower portions of the insulating
support members 2a and 2b. It is possible to make the support rigidity in the longitudinal
direction of the piezoelectric element low. That is, focusing on the insulating support members
2a and 2b, the shape and the structure are hard to be deformed or displaced in the thickness
direction of the piezoelectric element, and easily deformed or displaced in the longitudinal
direction of the piezoelectric element.
[0029]
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 by means of screws 6a and 6b, and the frame 3 and
the screws 6a and 6b and the base weight 5 The total mass is about 1.5 g.
[0030]
The outer periphery of the piezoelectric element 1 and the portions of the insulating support
members 2a and 2b that support the piezoelectric element 1 shown in FIG. 2 and the like have an
insulating property and good vibration damping (damping) characteristics from 60 degrees to 80
degrees (Hs 60-80 It is covered with the insulation covering material 4 which consists of rubber |
gum of JIS A) by the manufacturing method of vacuum casting.
The central portion of the upper surface, which is the contact portion with the human body, has a
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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 be part of it. Also, the total mass of this part is about 0.35 g.
[0031]
The curved surface for improving the contact with the human body is achieved with a curved
shape in which the central part of the insulating covering material 4 is thick, but the piezoelectric
element 1 itself is used to reduce the mass of the vibrating part including the piezoelectric
element 1 The piezoelectric material may be formed on one side or both sides of the curved thin
metal plate which is already in a curved shape at the time of non-operation, and the layer of the
insulating coating may be formed thin with a certain thickness.
[0032]
The insulating covering material 4 not only protects the mechanical covering of the piezoelectric
element 1 but also prevents short circuit failure caused by the migration phenomenon due to the
voltage application under the high temperature and high humidity environment of the silver
electrode relatively often used for the piezoelectric element It also serves as a cover for
preventing moisture and also serves as a damping material for reducing the degree of the
resonance phenomenon of the piezoelectric element.
In particular, the thickness of the coating and the hardness and material of the rubber are
important determinants in order to compromise at an appropriate level the increase in loss due
to the damping characteristics contrary to the reduction of the loss of vibration output.
[0033]
Next, the operating characteristics will be described. Strictly speaking, the elasticity and mass of
the support structure of the device and the human body transmission unit affect the vibration
state at the absolute position. However, here the whole is placed here on a sufficiently soft foam
sheet and allowed to operate freely, including being too complicated to argue up to that and not
being significantly different qualitatively. The vibration state will be described.
[0034]
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When an alternating voltage is applied to the piezoelectric element 1, it is bent and oscillated in
proportion to the applied voltage, and the influence acts on the whole. The vibration state is
schematically shown as shown in FIG. The piezoelectric element unit 10 including the
piezoelectric element 1 is a bending deformation operation along an applied voltage. Since the
support portions 20a and 20b configured by the insulating support members 2a and 2b
supporting the same and the left and right rising portions 3a and 3b of the frame 3 have high
rigidity in the Y-axis direction and low rigidity in the X-axis direction, The displacement of the
left and right ends of the piezoelectric element portion 10 in the Y-axis direction is the
displacement of both ends of the base portion 30 formed by the base weight 5 and the flat
portion (bottom portion) of the frame 3 in the Y-axis direction. The displacements of the support
portions 20a and 20b in the X-axis direction are balanced in the right and left directions, and
kinetic energy is balanced and does not affect the other. The displacement in the Y-axis direction
of both ends of the base portion 30 is parallel displacement of the base portion 30 because the
rigidity of the base portion 30 is high. There is theoretically no motion in the Z-axis direction. In
fact, it is very small and may not be considered.
[0035]
Here, since the mass of the base portion 30 is larger than the mass of the piezoelectric element
portion 10, the vibration nodes of the piezoelectric element portion 10 are closer to the left and
right ends than when both ends are not supported. In theory, when the base side is infinite mass,
the nodes become both ends. When the amplitude at the left and right ends (that is, equivalent to
the amplitude of the base 30) is compared with the amplitude at the center of the piezoelectric
element 10, the mass difference between the piezoelectric element 10 and the base 30 is 0.35 g
as a real number. On the other hand, it is about 4 times since it is 1.5 g, and the amplitude
difference is simply a quarter, but when comparing in kinetic energy, the vibration of the base
portion 30 is uniform overall, and the piezoelectric element portion Since the vibration of 10
changes depending on the place, it is considered that there is more difference. The prototype for
confirmation of the effect is different in length due to the trial manufacture of a pre-made
piezoelectric element, but the actual measurement value in this case is 1⁄5 to 1⁄8.
[0036]
FIG. 9 shows measured amplitude characteristics of the prototype (the vibration level on the
vertical axis is displayed based on an amplitude of 10 μm). That is, it is the figure which showed
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the difference of the vibration characteristic at the time of no load of the base part 30 and the
piezoelectric element part 10. FIG. FIG. 10 is a comparison of the amplitude characteristics in the
same manner, with the addition of a support and a pressure load assuming the incorporation into
the device and the pressure to the human body. That is, it is the figure which showed the
difference of the vibrational characteristic at the time of load of the base part 30 and the
piezoelectric element part 10. FIG. As can be seen from this, the characteristic assuming the
actual use condition is that there is no mass effect on the base side at 600 Hz or less where
sound leakage is unlikely, 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.
[0037]
FIG. 1 (a) is a plan view, FIG. 1 (b) is a front view, and FIG. 1 (c) is a right side view. Sectional
drawing in the AA of FIG. The disassembled perspective view which shows the separate
component state in one Example of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The
external appearance perspective view of the piezoelectric element in one Example of this
invention. The perspective view which inserted and adhered the insulation support member to
the both ends of the piezoelectric element in one Example of this invention. The perspective view
which shows the state which molding-molded and covered the upper half part of the piezoelectric
element and the insulation support member in one Example of this invention with an 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 no load of the base part and the
piezoelectric element part in the prototype of one Example of this invention. The figure which
shows the difference of the vibrational characteristic at the time of loading of the base part and
piezoelectric element part in the prototype of one Example of this invention.
Explanation of sign
[0038]
DESCRIPTION OF SYMBOLS 1 piezoelectric element 1a piezoelectric element wiring 2a, 2b
insulation support member 3 frame 3a, 3b rising 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
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