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JP2002370069

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DESCRIPTION JP2002370069
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
vibration actuator which is used in a portable communication terminal or the like and has a
function of generating ringing tone, voice, vibration and the like.
[0002]
2. Description of the Related Art In recent years, the widespread use of portable communication
terminals represented by cellular phones, laptop personal computers, etc. has been remarkable.
As communication terminals are desired to be as small and lightweight as possible from the
viewpoint of portability, the demand for miniaturization and weight reduction has become
stricter year by year also for devices which are indispensable for making calls and calls. .
[0003]
For this reason, various vibration actuators that combine generation of ringing tone, voice and
vibration in one device have been developed and put to practical use. A cross-sectional view of a
conventional example of such a vibration actuator is shown in FIG. The configuration will be
described below with reference to FIG.
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1
[0004]
In a conventional vibration actuator, for example, as shown in FIG. 2, a suspension in which a
magnetic circuit in which a yoke 1, a permanent magnet 2 and a plate 3 are fitted to and
integrated with a central shaft 7 is an annular plate spring. 4 is fixed to the vibration
transmission unit 8 in a vibratable state. The vibrating body 5 is fixed to the vibration
transmitting unit 8 in the same manner as the suspension 4, and the coil 6 is integrated with the
vibrating body 5 by an adhesive or the like and disposed in the air gap of the magnetic circuit.
[0005]
When a drive current is supplied to the coil 6, the magnetic circuit or coil 6 vibrates in the
vertical direction in the figure, and the vibration transfer unit 8 functions as a fixed unit in a low
frequency region and as an elastic body in a high frequency region. Become part of and vibrate.
Thus, in each mode of vibration and sound, the magnetic circuit and the vibrating body 5 operate
so as to interfere with each other and transmit the vibration to the outside.
[0006]
In the vibration actuator having the structure shown in FIG. 2, most of the acoustic chamber
output is generated by the vibration of the vibrator 5. The vibrator 5 may be made of metal,
paper, polymer material, or any other material, but is required to have appropriate rigidity, be
light in weight, be easy to form, and be inexpensive. Therefore, a polymer material is used for the
conventional vibration actuator, and in particular, polycarbonate is often used.
[0007]
However, a vibration actuator using polycarbonate as a vibrator is not necessarily satisfactory in
terms of heat resistance. Various improvements have been made to polycarbonates, and those
having a very low thermal shrinkage even at temperatures of 140 to 150 ° C. have been
developed. However, even when thermal contraction is hardly observed, a change in the output
sound pressure characteristic of the vibration actuator may occur, which is presumed to be a
decrease in the rigidity of the vibrating body due to the thermal history.
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[0008]
FIG. 3 shows an example of the change in the output sound pressure characteristic of the
vibration actuator. This is the vibration actuator shown in FIG. 2 in which a 50 μm thick
polycarbonate film is used as a vibrating body and is operated at an environmental temperature
of 60 ° C. for 100 hours, and the output sound pressure before and after that It is the result of
measuring the characteristic.
[0009]
Although the shape change of the vibrating body could not be confirmed at all before and after
the operation for 100 hours, as shown in FIG. 3, the output sound pressure characteristic 10
after heating is compared with the output sound pressure characteristic 9 before heating. The
low frequency acoustic resonance frequency is increased, and the output sound pressure is
reduced by 3 to 4 dB in the frequency band of about 800 Hz or less.
[0010]
In addition, a vibration actuator using a polycarbonate vibration body also has a problem in
durability.
In the example, when a vibrator made by molding and processing polycarbonate with a diameter
of 16 mm and a thickness of 50 μm is incorporated into a vibration actuator and vibrated so
that the amplitude at the center of the vibrator is 0.9 mm, the variation is observed However, the
vibrator breaks in about 600 hours.
[0011]
Therefore, the technical problem of the present invention is that the output sound pressure
characteristic does not change even if the initial output sound pressure characteristic is equal to
or higher than that of the conventional one and a certain degree of heat history is added. It is
another object of the present invention to provide a vibration actuator with improved durability.
[0012]
SUMMARY OF THE INVENTION The present invention focuses on the fact that the above-
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mentioned problems are derived from the heat resistance characteristics and mechanical
strength of the material used for the vibrator, and materials having high characteristics for these,
It is the result of various studies.
[0013]
That is, according to the present invention, a magnetic circuit including a permanent magnet and
a coil disposed in an air gap of the magnetic circuit, a suspension having elasticity for fixing the
magnetic circuit to a vibration transmission part in a vibratable state, and a coil are integrated. In
the vibration actuator including the vibration body and capable of vibration output, the vibration
body is a vibration actuator characterized by comprising a polymer compound having a glass
transition temperature of 180 ° C. or more.
[0014]
The present invention is the above-mentioned vibration actuator, wherein the polymer compound
has a thickness of 30 to 50 μm.
[0015]
Further, the present invention is the vibration actuator according to the above-mentioned
vibration actuator, wherein the polymer compound is polyetherimide.
[0016]
As described above, polycarbonate has been widely used as the vibrating body of the
conventional vibration actuator.
A high molecular compound such as polycarbonate is a material suitable for use as a vibrator
because it is lightweight, flexible, and easy to be molded into any shape.
[0017]
And in order to control change of the output sound pressure characteristic by heat history,
although heat resistance improvement is required, glass transition temperature is one of the
indices which show heat resistance of a polymer material.
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In the polymer compound, the specific volume, the thermal expansion coefficient, the specific
heat, etc. change at a fixed ratio with respect to the temperature change, but the ratio changes
remarkably with the glass transition temperature as the boundary.
[0018]
This phenomenon is caused by the thermal movement of the molecular chain, and in the region
below this temperature, the thermal movement of the molecular chain of the polymer compound
is in a frozen state.
That is, it is presumed that the higher the temperature, the smaller the change in physical
properties associated with the thermal history of the polymer compound.
[0019]
Most of the polycarbonates have a glass transition temperature of 180 ° C. or less, but in recent
years they are widely used in areas where high heat resistance is required, so-called engineering
plastics have a glass transition temperature in a temperature range higher than this There is one
that has
That is, the above problem can be solved by selecting an appropriate material from among these
as the vibrating body of the vibration actuator.
[0020]
From these examination results, it has been found that, by using a polymer compound having a
glass transition temperature of 180 ° C. or more as a vibrator, it is possible to suppress the
change in output sound pressure characteristics due to the heat history of the vibration actuator
to a considerable extent. In the invention, the above problem was solved by using polyether
imide.
[0021]
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, specific embodiments of the
present invention will be described.
[0022]
FIG. 1 shows a vibrating body of a vibration actuator of the present invention, and FIG. 1 (a) is a
front view, and FIG. 1 (b) is a cross-sectional view.
This vibrator has a corrugation structure as shown in FIG. 1 (b) so as to obtain desired acoustic
characteristics.
Note that the method of incorporating the vibrator into the vibration actuator, the structure of
the other portions of the vibration actuator, and the like are the same as those shown in FIG.
[0023]
The vibrator shown in FIG. 1 is made of a polyetherimide film having a diameter of 16 mm and a
thickness of 50 μm.
Here, Ultem 1000 manufactured by General Electric Company, having a chemical structure as
shown in Chemical Formula 1, was used as the polyetherimide.
[0025]
Here, the thickness of the polyetherimide film is 50 μm, but if the thickness is more than this,
the lower acoustic resonance frequency of the vibration actuator becomes too high as the rigidity
increases. The required acoustic characteristics can not be obtained. In addition, when the
thickness of the polyetherimide film is 30 μm or less, not only the required acoustic
characteristics can not be obtained but also the handling at the time of production becomes
difficult due to the decrease in rigidity and the decrease in mechanical strength. In addition, the
amplitude at the time of operation as a vibration actuator becomes too large, which causes a
problem in durability.
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[0026]
The vibration actuator was operated at an environmental temperature of 60 ° C. for 100 hours,
and changes in output sound pressure characteristics before and after that were examined. As a
result, no difference was found before and after the operation.
[0027]
As described above, according to the present invention, by constituting the vibrator with
polyetherimide, it is possible to obtain a vibratory actuator excellent in heat resistance and
durability.
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