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JPH09168197

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DESCRIPTION JPH09168197
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of applying a magnetic bias to a magnetostrictive material used as an acoustic sensor or
actuator.
[0002]
2. Description of the Related Art As a product using a magnetostrictive material, for example, an
acoustic transmitter that generates an acoustic wave by vibration based on the magnetostriction
phenomenon and transmits the acoustic wave, or conversely receives an acoustic wave and
converts it into an electrical signal. There is an acoustic receiver that outputs, and an actuator
that drives a drive part of an industrial product (for example, an autofocus mechanism of a
camera). When magnetostrictive material is used for an acoustic sensor or actuator as described
above, in general, static distortion characteristics (characteristic showing the relationship
between the strength of the magnetic field applied to the magnetostrictive material and the
amount of distortion) suitable for the purpose of use In order to improve the energy conversion
efficiency at the time of exciting (or driving) the magnetostrictive material as well as applying an
appropriate amount of mechanical stress (this is called prestress) to the magnetostrictive
material in advance, The magnetostrictive material is provided with a magnetic bias that
optimizes the
[0003]
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1
FIG. 3 is a view showing an example of the configuration of an underwater sound source using a
conventional magnetostrictive material, and this underwater sound source can be used, for
example, as a transmitter of sound waves propagating at low frequencies and long distances. It is
a thing. In FIG. 3, 1 is a permanent magnet, 2 is a yoke material, 3 is a solenoid coil, 4 is a
magnetostrictive material, and 5 is an AC power supply (or AC amplifier) for exciting the solenoid
coil 3. Further, 11 is a waterproof container when used as an underwater sound source.
[0004]
The configuration and operation of FIG. 3 will be described. Conventionally, when driving the
magnetostrictive material 4, in order to reduce leakage of the magnetic field and to improve
energy efficiency, as shown in FIG. 3, a solenoid coil 3 is provided around the magnetostrictive
material 4 and an AC power supply is provided thereto. The magnetic field was applied by
supplying an alternating current for excitation from 5. Further, in order to concentrate the
magnetic flux in the magnetostrictive material 4, a DC magnetic bias is applied from the
permanent magnet 1 to the magnetostrictive material 4 via the yoke material 2 having the
property of high permeability.
[0005]
The magnetostrictive material 4 is given a prestress for obtaining a desired static distortion
characteristic, and the permanent magnet 1 is adjusted so that the magnetic bias applied from
the permanent magnet 1 becomes an optimum operating point in the static distortion
characteristic. The mounting position of is adjusted. As a result, the magnetostrictive material 4
expands and vibrates in the direction and the magnitude shown by the arrows in FIG. 3 from the
magnetic bias position in the static distortion characteristic, according to the excitation
frequency of the AC power supply 5 and the current value of the AC current. Acoustic waves can
be generated.
[0006]
However, in the method of giving a magnetostrictive bias to a magnetostrictive material by a
permanent magnet as shown in FIG. 3, only applying a fixed magnetic bias by a magnetic field of
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2
a certain strength to the magnetostrictive material could not. For example, when a
magnetostrictive material is used as an acoustic sensor for underwater acoustic waves,
depending on the structure of the transducer, the stress applied to the magnetostrictive material
as the acoustic sensor may change due to a change in water pressure.
[0007]
FIG. 4 is a view for explaining a change in stress applied to the magnetostrictive material due to a
change in water pressure. That is, in the underwater transducer having the structure as shown in
FIG. 4, when the depth at which the underwater transmitter is installed is different, the stress
(prestress) applied to the magnetostrictive material 4 changes due to the change in water
pressure, and the static strain characteristic Since it changes, it is necessary to readjust to the
magnetic bias which adapts to this changed static distortion characteristic. In such an
underwater acoustic wave transducer, although it is desired to adjust the magnetic bias of the
magnetostrictive material to be variable according to the change in depth used, in the prior art,
the magnetic bias is fixed. There is a problem that the usable depth range of the transducer is
limited.
[0008]
In the method of applying a magnetic bias applied to a magnetostrictive material according to the
present invention, there is provided a method of applying a magnetic bias applied to a
magnetostrictive material used as an acoustic sensor or actuator, the method comprises applying
magnetic bias to both ends of the magnetostrictive material. The permanent magnets are
respectively provided, and the permanent magnets at both ends form a magnetic field of constant
strength through the magnetostrictive material, and a solenoid coil is provided around the
magnetostrictive material to pass a direct current to the solenoid coil and the current By making
the value variable and forming a magnetic field of variable strength, it is possible to apply an
optimum magnetic bias to the magnetostrictive material. Therefore, when the magnetostrictive
material is subjected to stress or changes in temperature under the environment where the
magnetostrictive material is used, and the static strain characteristics change, the static strain is
adjusted by adjusting the value of the direct current supplied to the solenoid coil. An optimum
magnetic bias corresponding to the change in characteristics can be applied to the
magnetostrictive material.
[0009]
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3
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a view showing an
example of the construction of an underwater sound source using a magnetostrictive material
according to the present invention, and FIG. 2 is a view for explaining the optimum magnetic bias
of the magnetostrictive material of FIG. In FIG. 1, 1 to 5 and 11 are the same as in FIG. 6 is a
choke coil, 7 is a block capacitor, 8 is a DC power supply, 9 is a strain gauge as a stress detection
sensor attached to a magnetostrictive material 4, and 10 is an A / D converter 10a and a D / A
converter 10b. Computer, 12 is a waterproof cable.
[0010]
The configuration and operation of FIG. 1 will be described. In FIG. 1, the underwater sound
source connected to one end of the waterproof cable 12 is installed in the water, and the device
connected to the other end is installed on the water. In order to allow direct current and
alternating current to flow simultaneously to the solenoid coil 3, a choke coil 6 for blocking an
alternating current component is connected in series to the direct current power supply 8 side,
and a direct current component is connected to the alternating current power supply 5 side. The
block capacitor 7 for the purpose of interrupting is connected in series. The stress detection
signal of the magnetostrictive material 4 detected by the strain gauge 9 is input to the computer
10 via the A / D converter 10a. The computer 10 calculates the amount of distortion of the
magnetostrictive material 4 from this input signal, and controls the DC power supply 8 to control
the DC power supply 8 to apply an optimum magnetic bias to the magnetostrictive material 4 in
accordance with the amount of distortion. The DC power supply 8 is supplied via the D / A
converter 10b.
[0011]
FIG. 2 shows the static distortion characteristics of the direct current (corresponding to the
strength of the magnetic field) supplied to the solenoid coil 3 versus the amount of distortion. In
FIG. 2, the curves indicated by C1, C2 and C3 indicate that the static distortion characteristics
change as the installation depth of the underwater sound source is gradually increased, and the
straight line portion where the slope is maximum in each of the characteristic curves It is the
most efficient method of adjusting the magnetic bias (for example, in the case of an underwater
sound source, the maximum sound pressure can be obtained at the output) by setting the
magnetic bias so that the central position of is the operating point. In the example of the
characteristic curves C1, C2 and C3 of FIG. 2, it is shown that the optimum magnetic bias can be
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4
obtained by setting the values of the direct current on the horizontal axis to I1, I2 and I3,
respectively. Then, the computer 10 stores the correspondence between the measured distortion
amount as shown in FIG. 2 and the direct current value for giving the optimum magnetic bias in a
built-in table memory or the like in advance.
[0012]
Next, a specific method of adjusting the magnetic bias will be described. First, in a state where
the underwater sound source is used in the air, the position of the permanent magnet 1 is
adjusted so that an optimum magnetic bias is applied to the magnetostrictive material 4 (for
example, position adjustment screws not shown on both ends of the permanent magnet 1) The
mounting position of the permanent magnet 1 can be adjusted by advancing or retracting this
screw. Next, since the stress applied in the longitudinal direction (vibration direction) of the
magnetostrictive material 4 changes as the underwater sound source sinks into water, the
computer 10 measures the amount of distortion sequentially using the strain gauge 9 and stores
the table memory in advance. A control signal for controlling the direct current power supply 8 is
sequentially supplied to the direct current power supply 8 so as to obtain a direct current value
for applying an optimal magnetic bias corresponding to the distortion amount stored in the
above. When the depth finally becomes constant, an optimum magnetic bias corresponding to
the static strain based on the depth is applied to the magnetostrictive material 4.
[0013]
With the configuration as shown in FIG. 1, the excitation AC current and the bias DC current of
the magnetostrictive material 4 are simultaneously supplied to the solenoid coil 3 and static of
the magnetostrictive material 4 due to stress received from water pressure based on the
detection signal of the stress sensor. Since the value of the direct current supplied to the solenoid
coil 3 is controlled so that the optimum magnetic bias can be applied to the magnetostrictive
material 4 in response to the distortion, the optimum magnetic bias is obtained even if the
underwater sound source is used at any depth Be Further, since the magnetic bias of the
magnetostrictive material 4 is used in combination with the magnetic field by the permanent
magnet 1 and the magnetic field by the DC power source flowing to the solenoid coil 3, the
amount of heat generation of the solenoid coil 3 can be small.
[0014]
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In the embodiment of FIG. 1, the magnetostrictive material is subjected to stress in the use
environment of water, and this stress changes the static strain characteristics of the
magnetostrictive material. Therefore, a stress sensor is attached to the magnetostrictive material,
and the detection signal of this stress sensor is An example of using is shown. However, the static
strain characteristics of the magnetostrictive material also change depending on, for example, the
environmental temperature used in addition to the stress. In such a case, a sensor for detecting
the temperature is attached to the magnetostrictive material, and the detection signal of this
temperature sensor To control the value of the direct current supplied to the solenoid coil so that
the optimum magnetic bias can be applied to the magnetostrictive material in response to the
change in the static strain characteristic of the magnetostrictive material due to the temperature
change of the environment. Good.
[0015]
Furthermore, in the present invention, the sensor attached to the magnetostrictive material is not
limited to the stress sensor or the temperature sensor. For example, a magnetostrictive material
or a member driven by this magnetostrictive material is attached with a sensor for detecting its
displacement or acceleration, and based on the detection signal of this displacement or
acceleration sensor, the magnetostrictive material of the most efficient by the alternating current
flowing in the solenoid coil The value of the direct current flowing simultaneously to the solenoid
coil may be controlled so that excitation can be performed (for example, when the sensor is a
displacement sensor, a maximum displacement amount is obtained in the magnetostrictive
material).
[0016]
Finally, the application form of the present invention will be described. The present invention is
applicable to various industrial products that use a magnetostrictive material as a means for
vibrating or driving a member by the magnetostriction phenomenon, and in particular, the
magnetostrictive characteristic of the magnetostrictive material based on the change in the use
environment (such as environmental pressure and temperature). The effects of applying the
present invention are significant in applications where the optimum magnetic bias changes
significantly with changes. For example, good results can be obtained when the present invention
is applied to an underwater high-power sound source used for ocean acoustic tomography, an
actuator of various drive members, a speaker, and the like. Further, in a magnetostrictive material
based on a rare earth alloy such as TbDyFe alloy, which is used as a giant magnetostrictive
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6
material, the property change due to the axial stress (prestress) of the material is large, so the
utility value of the present invention is large.
[0017]
As described above, according to the present invention, in the method of applying a magnetic
bias applied to a magnetostrictive material used as an acoustic sensor or actuator, permanent
magnets are respectively provided at both ends of the magnetostrictive material, and A
permanent magnet forms a magnetic field of constant strength through a magnetostrictive
material, and a solenoid coil is provided around the magnetostrictive material, a direct current is
supplied to the solenoid coil, and the current value is made variable to change the magnetic field
of variable strength. By forming the magnetostrictive material, it is possible to apply an optimum
magnetic bias to the magnetostrictive material, so that the static strain characteristics are
changed due to stress or temperature change under the environment where the magnetostrictive
material is used. In this case, by adjusting the value of the direct current supplied to the solenoid
coil, the optimum magnetic bias corresponding to the change in the static distortion
characteristic is applied to the magnetostrictive material, and the sound is generated. It is
possible to perform the most efficient operation in sensors and actuators.
[0018]
Brief description of the drawings
[0019]
1 is a diagram showing a configuration example of an underwater sound source using a
magnetostrictive material according to the present invention.
[0020]
2 is a diagram for explaining the optimum magnetic bias of the magnetostrictive material of FIG.
[0021]
3 is a diagram showing a configuration example of an underwater sound source using a
conventional magnetostrictive material.
[0022]
4 is a diagram for explaining the change in stress applied to the magnetostrictive material by the
change in water pressure.
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[0023]
Explanation of sign
[0024]
DESCRIPTION OF SYMBOLS 1 permanent magnet 2 yoke material 3 solenoid coil 4
magnetostrictive material 5 AC power supply 6 choke coil 7 block capacitor 8 DC power supply 9
strain gauge 10 computer 10 a A / D converter 10 b D / A converter 11 waterproof container 12
waterproof cable
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