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JP2006319612

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2006319612
An object of the present invention is to widen the range of linearity of an AC displacement output
with respect to an AC magnetic field input in a magnetostrictive element actuator. A
magnetostrictive element actuator (20) has a plurality of magnetostrictive elements in which
magnets for bias magnetic field are arranged at both ends arranged in the axial direction, and the
total amount of expansion and contraction of each magnetostrictive element is the total
expansion and contraction amount. An element cover 60 for guiding the same, a drive coil 40
disposed around the element cover 60, a vibration receiving plate 72 and a movable rod 74
arranged at the tip of the magnetostrictive movable element 50, and a housing for housing them
including. The housing accommodates a cylindrical case 30, a bottom plate 32 supporting the
end of the magnetostrictive movable element 50 on the bottom side, and a coil spring 76 biasing
the magnetostrictive movable element 50 toward the bottom via the vibration receiving plate 72.
The cover 34 is provided. A head 36 is attached to the tip of the movable rod 74 protruding from
the lid 34. [Selected figure] Figure 7
Magnetostrictive element actuator
[0001]
The present invention relates to a magnetostrictive element actuator, and more particularly to a
magnetostrictive element actuator which moves a mover by expanding and contracting the
magnetostrictive element by providing a magnetic field signal in the axial direction of the
magnetostrictive element.
[0002]
04-05-2019
1
As an electrically driven actuator for moving the mover by an electrical signal, a motor, a
solenoid plunger or the like is widely used as one using electromagnetic conversion.
In addition, a piezoelectric actuator using piezoelectric conversion is also known for downsizing
and the like. Also, with respect to a magnetostrictive actuator using a magnetostrictive element
that is expanded and contracted by a magnetic field, characteristics such as high-speed response
have attracted attention. Particularly in recent years, so-called giant magnetostrictive elements
have been developed, and the expansion and contraction rate with respect to the magnetic field
has been significantly improved. For example, one having an elongation of 1000 ppm at a
magnetic field strength of 80,000 A / m (1000 oersted) can be used.
[0003]
Patent Document 1 discloses a speaker unit and an audio output device, in which a
magnetostrictive material is used for a vibrating element contained in a drive coil, a magnet for
applying a bias magnetic field to both ends thereof is provided, and generated by the drive coil It
is stated that the vibrating element is extended and contracted in the axial direction by the
magnetic field. Here, the magnetostrictive material is a Laves-type cubic (RT2) material
composed of a large lanthanide element R and an iron group element T having a large magnetic
moment, and TbXDy1-XFeY (X = 0.25 to 0.50, It is stated that one having Y = 1.7-2.0) or SmFeY
(Y = 1.7-2.0) is used.
[0004]
Patent Document 2 discloses a pull-type actuator, in which a bias magnetic field to the giant
magnetostrictive rod is efficiently used in making the giant magnetostrictive rod expandable and
contractable by controlling the strength of the magnetic field applied by the electromagnetic coil.
The structure applied to is described. That is, since the giant magnetostrictive rod is elongated,
the bias magnetic field near the axial center is weaker than the bias magnetic field at both ends
of the shaft, and the bias magnetic field along the axial direction disperses. A second bias magnet
is provided at the end of the giant magnetostrictive rod. Here, as the giant magnetostrictive rod, a
magnetostrictive element made of a powder sintered alloy or a single crystal alloy containing as a
main component (for example, terbium, dysprosium, iron or the like) at least one of rare earth or
a specific transition metal is used.
04-05-2019
2
[0005]
JP, 2004-266307, A JP, 2004-266035, A
[0006]
A bias magnetic field is applied beforehand by a magnet or the like so that the operating point
comes to the substantially linear region of the "elongation rate-magnetic field strength"
characteristic of the giant magnetostrictive element, and an AC magnetic field is applied centered
on the operating point. It is well known as described above that it can be used for an actuator
such as a sound generator because it can generate substantially faithful alternating current
displacement.
In this case, the amplitude of the AC magnetic field may be increased to increase the output of
the sound generator or the like. However, in actual experiments, if the amplitude of the AC
magnetic field is increased, the output waveform is distorted even though the operating point is
set in the linear region. If the input AC magnetic field is limited so as not to distort the output
waveform, only a smaller output than expected can be obtained.
[0007]
The cause of this is also considered to be due to the dispersion of the bias magnetic field along
the axial direction because the giant magnetostrictive rod is elongated as suggested in Patent
Document 2. However, the solution of Patent Document 2 is in a structure unique to a pull type
actuator, and has a complicated structure such as using two types of bias magnets.
[0008]
An object of the present invention is to provide a magnetostrictive element actuator capable of
widening the range of linearity of AC displacement output with respect to AC magnetic field
input.
[0009]
The magnetostrictive element actuator according to the present invention is a magnetostrictive
element actuator which moves a movable element by providing a magnetic field signal in the
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3
axial direction of the magnetostrictive element to extend and contract the magnetostrictive
element, and magnets for bias magnetic field are disposed at both ends in the axial direction. Of
the plurality of magnetostrictive elements are arranged along the axial direction, and the
movable element portion and the movable element portion are accommodated such that the sum
of the axial expansion and contraction amounts of the magnetostrictive elements is the total axial
expansion and contraction; A cylindrical cover for guiding the magnetic field magnet movably in
the axial direction, a drive coil disposed around the cylindrical cover, for supplying an alternating
magnetic field signal in the axial direction to the movable element portion, and a tip portion of
the movable element portion An output mover to be disposed, a case supporting the end of the
movable element on the bottom side, and guiding the output mover axially movably on the upper
surface, and the movable element via the output mover Biasing means to bias the bottom side of
the case , Characterized in that it comprises a.
[0010]
Preferably, the drive coil is a parallel drive coil configured by connecting in parallel a plurality of
coils respectively corresponding to a plurality of magnetostrictive elements.
[0011]
Further, in the magnetostrictive element actuator according to the present invention, the axial
length of each magnetostrictive element is the same as the axial length of the magnetostrictive
element in the nominal bias magnetic field by the bias magnetic field magnets disposed at both
axial ends of the magnetostrictive element. Preferably, the reduction rate which depends on the
length is set shorter than the axial length which is a predetermined reduction rate determined by
the amplitude of the alternating magnetic field signal supplied by the drive coil.
[0012]
In the magnetostrictive element actuator according to the present invention, the maximum value
of the AC magnetic field signal and the nominal bias magnetic field of the bias magnet each have
a magnetic field strength of 50,000 A / m to 100,000 A / m, and the magnetostrictive element
Preferably have a relative permeability of 6 or more and 8 or less and an axial length of 4 mm or
more and 9 mm.
[0013]
In addition, the drive coil is preferably sealed with a heat conductive resin inside the housing.
[0014]
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4
Further, in the magnetostrictive element actuator according to the present invention, it is
preferable to have a resin for damper disposed between the bottom surface on the movable
element side of the output mover and the drive coil.
[0015]
In the magnetostrictive element actuator according to the present invention, preferably, the
movable portion of the biasing means is covered by the flexible damper resin.
[0016]
In the magnetostrictive element actuator according to the present invention, preferably, the tip of
the output mover has a replaceable resin cover.
[0017]
According to the above configuration, in the movable element portion, a plurality of
magnetostrictive elements in which the bias magnetic field magnets are arranged at both ends
are arranged along the axial direction, and the total axial expansion and contraction amount of
each magnetostrictive element is the total axial expansion and contraction amount It becomes.
That is, the necessary output distortion is obtained not by one elongated magnetostrictive
element but by a plurality of magnetostrictive elements provided with bias magnets at both ends.
As a result, the axial length of each magnetostrictive element can be made shorter than the axial
length for the required output distortion, and the reduction of the bias magnetic field at the
central portion of each magnetostrictive element thus shortened can be reduced by one. This can
be reduced as compared with the case of the long and thin magnetostrictive element.
Therefore, it is possible to widen the range of linearity of the AC displacement output with
respect to the AC magnetic field input.
[0018]
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5
Further, the plurality of magnetostrictive elements in which the bias magnetic field magnets are
respectively disposed at both ends are movably guided in the cylindrical cover.
Since each magnetostrictive element expands and contracts in the axial direction and also
expands and contracts in the radial direction so that the entire volume does not substantially
change, it is preferable not to constrain both ends and the radial direction.
Actually, each magnetostrictive element is held by the attraction force between the bias magnets
at both ends, but in such free holding by the sandwiching force of such magnets, each
magnetostrictive element and each bias magnet are displaced in the radial direction along with
expansion and contraction. Things can happen.
By using the cylindrical cover, the axial and radial movements of the magnetostrictive elements
and the bias magnets are not unnecessarily restricted, and can be expanded and contracted in the
axial direction as a whole.
[0019]
Also, since the drive coil is a parallel drive coil configured by connecting in parallel a plurality of
coils respectively corresponding to a plurality of magnetostrictive elements, the same magnetic
field strength, ie, ampere-turn, is obtained as compared to using one coil. Low voltage driving is
possible to maintain the axial length, and heat generation and the like of the drive coil can be
suppressed.
[0020]
The axial length of each magnetostrictive element is set as follows.
That is, although the nominal bias magnetic field by the bias magnetic field magnet decreases
along the axial direction, the lowered bias magnetic field becomes the operating point of the AC
magnetic field signal supplied by the drive coil.
As a result, when the rate of decrease of the bias magnetic field is large, the operating point
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6
moves to the zero bias side too much, and the amplitude of the AC magnetic field signal capable
of maintaining the linearity of the output AC displacement decreases.
In order to prevent this, the axial length of each magnetostrictive element may be shortened.
Therefore, the axial length of each magnetostrictive element is set short so that the axial
decrease rate of the nominal bias magnetic field does not fall below a predetermined decrease
rate determined by the amplitude of the AC magnetic field signal supplied by the drive coil.
Thereby, the linearity of the output AC displacement can be secured in the range of the AC
magnetic field signal supplied by the drive coil.
[0021]
The maximum value of the AC magnetic field signal and the nominal bias magnetic field of the
bias magnet have magnetic field strengths of 50,000 A / m to 100,000 A / m, respectively, and
the magnetostrictive element has a relative permeability of 6 to 8 or less. It has a magnetic field,
and has an axial length of 4 mm to 9 mm. This condition is experimentally determined as being
able to ensure the linearity of the output AC displacement with respect to the input of this AC
magnetic field signal.
[0022]
Further, since the drive coil is sealed with the heat conductive resin inside the case, the heat
generated by the drive coil can be efficiently transferred to the case by the heat conductive resin
and dissipated to the outside.
[0023]
Further, since the resin for damper is disposed between the bottom surface on the movable
element side of the output mover and the drive coil, unnecessary vibration in the gap can be
suppressed.
[0024]
Further, since the movable portion is covered with the flexible damper resin, the urging means
can suppress unnecessary vibration in the movable portion.
04-05-2019
7
[0025]
In addition, since the resin cover at the tip of the output mover can be replaced, it is possible to
use a resin cover made of a material having a desirable output transfer characteristic according
to the characteristics of the other side.
For example, in the case of outputting voice, it is possible to use a resin cover with good damping
characteristics when the opposite side is a hard material, and use a hard resin cover when the
opposite side has appropriate softness.
[0026]
As described above, according to the magnetostrictive element actuator according to the present
invention, it is possible to widen the range of linearity of AC displacement output with respect to
AC magnetic field input.
[0027]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings.
In the following, as a giant magnetostrictive element, model PMT-1 manufactured by TDK, the
composition is TbXDy1-XFeY (X = 0.34, Y = 1.9), relative permeability 6, “axial elongation
percentage̶magnetic field "Strength" characteristics are used which are non-linear with
hysteresis but with a field strength of 1000 ppm elongation at 80,000 A / m (1000 oersted).
The other model PMS-1 and PMH-1 manufactured by TDK Ltd. differs in use temperature range
from PMT-1, but the relative permeability 6 to 10, almost the same "axial elongation percentagemagnetic field strength" characteristic As it has, these can also be used.
Moreover, as long as it has the same "axial direction elongation rate-magnetic field strength"
characteristic, things other than TDK company make may be used. In the following, an element
having such a characteristic is simply referred to as a magnetostrictive element.
04-05-2019
8
[0028]
First, the contents of the experiment on which the axial length of the magnetostrictive element
was determined will be described, and then the configuration and the like of a magnetostrictive
element actuator using the magnetostrictive element of that length will be described. FIG. 1 is a
diagram for explaining the contents of the experiment. Here, the cylindrical drive coil 12 is
disposed on the outer periphery of the columnar magnetostrictive movable element 10 whose
lower portion is fixed to the fixed portion. The magnetostrictive movable element 10 is provided
with a suitable bias magnetic field bias magnet. An alternating current signal having an
amplitude of 5 Vpp of 50 Hz is applied to the drive coil 12 from the alternating current power
supply 14, and the drive current can be varied. The total number of turns of the drive coil 12 is
600 turns, and its axial length is 13.77 mm. A capacitive displacement meter 16 is installed on
the free end side of the magnetostrictive movable element 10, and an amount of expansion and
contraction of the magnetostrictive movable element 10 in the axial direction is detected by an
AC magnetic field generated by the drive coil 12 by the AC power supply 14. Although the output
of the capacitive displacement meter 16 is an alternating voltage, it is converted to a
displacement amount and the alternating current displacement waveform is displayed on the
display.
[0029]
FIG. 2 is a diagram showing three types of configurations of the magnetostrictive movable
element 10 used in the experiment. In (a), a magnetostrictive movable element 10 is formed by
arranging a neodymium magnet with a diameter of 3 mm and a thickness of 1 mm as a bias
magnetic field magnet at both ends of a magnetostrictive element with a diameter of 3 mm and a
length of 16 mm. The neody magnets at both ends are mutually magnetically attracted by
sandwiching a magnetostrictive element having a length of 16 mm so that the opposing surfaces
have mutually opposite polarities. (B) uses two magnetostrictive elements with a diameter of 3
mm and a length of 8 mm in which similar neodymium magnets are disposed at both ends, and a
neodymium magnet-magnetostrictive element-neodymium magnet-magnetostrictive elementneodymium magnet The magnetostrictive movable element 10 is used as a magnet. (C) uses
three magnetostrictive elements with a diameter of 3 mm and a length of 5 mm in which similar
neodymium magnets are disposed at both ends, and uses neodymium magnet-magnetostrictive
element-neodymium magnet-magnetostrictive element-neodymium magnet-magnetostrictive
element-neodymium magnet One magnetostrictive movable element 10 is used.
04-05-2019
9
[0030]
FIG. 3 shows the experiment of FIG. 1 using these three types of magnetostrictive movable
elements 10, and changes the strength of the input AC magnetic field, that is, the amplitude of
the drive current, and the output AC displacement at that time maintains maximum linearity. The
growth rate of is calculated and the result is graphed. The axis of abscissa in FIG. 3 is the element
length of the magnetostrictive element constituting the magnetostrictive movable element 10,
that is, the interval sandwiched by the bias magnetic field magnets. The vertical axis is the
maximum elongation rate at which the linearity can be maintained, and the elongation rate is
calculated by the total axial elongation of the magnetostrictive movable element 10 / (sum of
lengths of all magnetostrictive elements constituting the magnetostrictive movable element 10) .
For example, if it is 15 μm of the magnetostrictive movable element 10 of FIG. 2C, the
elongation rate is 15 μm / 15 mm.
[0031]
As can be seen from FIG. 3, as the element length of the magnetostrictive element increases, the
elongation percentage in the range maintaining linearity decreases, but in particular, the one of
16 mm drops significantly. In this figure, when the average elongation rate at each element
length is determined, the element length of 5 mm is 1.04 μm / mm and that of 8 mm is 0.97
μm / mm, but the element length is 16 mm. Is 0.38 μm / mm.
[0032]
FIG. 4 shows an example of the waveform of the output AC displacement when the linearity is
broken. In this figure, an AC displacement waveform which is the output of the capacitive
displacement meter 16 is displayed on the display, the horizontal axis is time, and the vertical
axis is the output voltage. The drive current waveform which is an input signal is a 50 Hz sine
wave. For example, for a sample with a device length of 16 mm, when the amplitude of the drive
current is increased, the lower side of the waveform is thus distorted as if it were clipped.
[0033]
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10
FIG. 5 is a diagram showing the maximum amplitude of the input drive current at which the
output AC displacement can maintain linearity, that is, the current limit of maintaining the
linearity. The horizontal axis represents the element length of the magnetostrictive element
constituting the magnetostrictive movable element 10 as in FIG. As can be seen from this figure,
the input current limit capable of maintaining linearity decreases as the element length increases,
and although there is little difference between the element lengths of 5 mm and 8 mm, the
element length of 16 mm is significantly limited. In other words, in the magnetostrictive actuator,
even if the current supplied to the drive coil is increased to increase the output displacement to
increase the output, the linearity is broken, and if the linearity is maintained, a large output can
be obtained. It can not be
[0034]
FIG. 6 is a figure which infers the cause from the results of FIG. 4 and FIG. 5 and explains one
possible idea. In this figure, the horizontal axis represents the strength of the magnetic field
applied to the magnetostrictive element, and the vertical axis represents the elongation of the
magnetostrictive element, and shows the characteristic curve 2 of “axial direction elongationmagnetic field strength” of the magnetostrictive element. is there. Using this figure, the designer
determines the operating point A to be in the first quadrant of FIG. 6 so that the full amplitude of
the input AC magnetic field 4 by the drive coil 12 is included in the linear region of the
characteristic curve 2. . Then, for the operating point A, a bias magnet having a nominal value of
the strength of the magnetic field is selected. Therefore, according to this design, the output AC
displacement whose lower limit is clipped as shown in FIG. 4 should not appear. The waveform as
shown in FIG. 4 is estimated that the designed operating point A is shifted to an operating point B
where the magnetic field strength is closer to zero in actual driving. If the input AC magnetic field
5 is given at the estimated operating point B, the corresponding lower limit of the output AC
displacement 6 is clipped and distorted. In order to avoid this distortion, the amplitude of the
input alternating magnetic field 5 will be reduced, but this will reduce the current amplitude to
the drive coil 12, thereby creating a current limit to ensure linearity.
[0035]
Thus, assuming that the operating point A designed based on the nominal magnetic field strength
of the bias magnet moves to the operating point B in actual driving, as shown in FIG. The
effective bias magnetic field strength of the magnetostrictive element sandwiched by magnets is
determined by the distance between the bias magnets at both ends, that is, the axial length of the
magnetostrictive element, and it is predicted that the longer the length, the weaker the magnetic
04-05-2019
11
field. Ru. A theoretical analysis of how the axial reduction rate of the nominal magnetic field due
to the bias magnets at both ends is related to the length of the magnetostrictive element having a
predetermined magnetic permeability interposed therebetween has not been performed yet.
[0036]
Therefore, it can be said from FIGS. 3 and 5 that the axial length of each magnetostrictive
element is the same as that of the magnetostrictive element in the axial direction of the nominal
bias magnetic field due to the bias magnetic field magnets disposed at both axial ends of the
magnetostrictive element. It is preferable that the reduction rate which decreases depending on
the length is set shorter than the axial length which is a predetermined reduction rate
determined by the amplitude of the alternating magnetic field signal supplied by the drive coil.
[0037]
Here, in the case of the element lengths of 5 mm and 8 mm in FIG. 5, the strength of the
magnetic field corresponding to 3.7 App to 3.0 App which is the average value of the current
limit is the number of turns of the drive coil and its axial direction. Using length, the strength of
the magnetic field corresponds to approximately 65,000 A / m to 80,000 A / m, as determined
by the single-sided current amplitude.
Considering the variation range of the elements, the current limit does not change much
depending on the element length within the range of 50,000 to 100,000 A / m, and the linearity
can be practically maintained. Also, as understood from FIG. 6, the strength of the bias magnetic
field when maintaining linearity can be approximately the same as the strength of the magnetic
field due to this current limit.
[0038]
Therefore, more specifically, with the maximum value of the AC magnetic field signal and the
nominal bias magnetic field of the bias magnet as the magnetic field strength of 50,000 A / m to
100,000 A / m, respectively, each magnetostrictive element It is preferable to have a relative
permeability of 8 or less and to have an axial length of 4 mm to 9 mm.
[0039]
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12
Next, the configuration of the magnetostrictive element actuator reflecting the above
experimental results will be described.
Here, a magnetostrictive movable element having the configuration of FIG. 2C, that is, a
magnetostrictive movable element having a configuration in which three magnetostrictive
elements, each having a bias magnetic field magnet disposed at both ends in the axial direction,
are arranged along the axial direction. . FIG. 7 is a cross-sectional view of the magnetostrictive
element actuator 20, and FIGS. 8 and 9 are diagrams illustrating an assembly process of the
magnetostrictive element actuator 20. As shown in FIG.
[0040]
The magnetostrictive element actuator 20 has a cylindrical housing having a diameter of about
30 mm and a height of about 45 mm, and an umbrella-shaped output with a flat top on a
movable rod protruding from the upper surface of the housing. A configuration is provided in
which the transmission head is attached.
[0041]
The housing of the magnetostrictive element actuator 20 includes a case 30 having a cylindrical
outer shape, a bottom plate 32 attached to cover the bottom of the case 30, and a lid 34 attached
to cover the top of the case 30.
An open hole is provided on the upper surface of the lid 34, and the movable rod 74 protrudes
through a suitable bearing, and a head 36 for output transmission is attached thereon. The drive
coil 40, the magnetostrictive movable element 50, and the element cover 60 are disposed inside
the housing. The lower portion of the magnetostrictive movable element 50 is supported by the
bottom plate 32, the upper surface thereof is in contact with the vibration receiving plate 72
connected to the lower portion of the movable rod 74, and the vibration receiving plate 72 is
biased toward the bottom plate by a coil spring 76.
[0042]
Further, in the magnetostrictive element actuator 20, the gap between the bottom of the drive
coil 40 and the bottom plate 32 and the gap between the upper surface of the bobbin and the
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vibration receiving plate 72 are filled with damper resin 90 and 92, respectively. Further, the
flexible resin 94 fills the movable portion of the coil spring 76, that is, the gap between the coil
wires. Further, the gap between the drive coil 40 and the case 30 is sealed with a heat conductive
resin 96.
[0043]
The contents of the elements constituting the magnetostrictive element actuator 20 and their
interrelationships will be described with reference to FIG. 8 and FIG. FIG. 8 is a front half portion
of the assembly of the magnetostrictive element actuator 20, mainly showing each process until
the magnetostrictive movable element 50 is incorporated. FIG. 9 is a rear half portion after that,
mainly the magnetostrictive movable element 50. It is a figure which shows each process of
assembling and an output transmission rod etc.
[0044]
As shown in FIG. 8A, first, a case 30 is prepared. The case 30 is a cylindrical member made of a
metal material such as aluminum or stainless steel, and has an outer diameter of about 30 mm
and a wall thickness of about 1 mm. It has an opening 31 for the lower shank of 72 to pass
through. The inner diameter of the opening hole 31 is larger than the outer shape of the
vibration receiving plate 72 so that it can be used for positioning of the drive coil 40 in the next
process, and it is in the upper portion of the bobbin 42 of the drive coil 40. It is set according to
the dimension of the positioning part 47. In addition, an appropriate number of resin injection
holes 95 for sealing of a heat conductive resin 96 described later are provided in the cylindrical
portion.
[0045]
Also, the drive coil 40 is prepared. The drive coil 40 is obtained by winding a coil winding 44
around a bobbin 42 made of a suitable heat resistant resin. The bobbin 42 has an axial hole 46
axially penetrating at the central portion. The magnetostrictive movable element 50 and the
element cover 60 disposed therearound are inserted into the axial hole 46, so that the inner
diameter thereof is set to a size that allows the insertion. A step is provided around the shaft hole
46 at the upper part of the bobbin 42 and this becomes the above-mentioned positioning part
47. The total number of turns of the drive coil 40 is 600 turns, and the height in the axial
04-05-2019
14
direction is about 14 mm. As described above, the value actually measured for use in the
experiment of FIG. 1 is 13.77 mm. As the drive current flows about 3 App, it is preferable to use
a copper wire or the like coated with a heat resistant insulating resin as the coil winding.
[0046]
Next, the drive coil 40 is inserted and arranged from the bottom side of the case 30. The
positioning is performed by aligning the positioning portion 47 of the drive coil 40 with the
inner periphery of the opening hole 31 of the case 30. The situation is shown in FIG. 8 (b). Then,
a bottom plate 32 prepared separately is attached so as to cover the bottom of the case 30. The
attachment can be performed with a mounting screw or the like not shown. Alternatively, the
case 30 and the bottom plate 32 may be joined using an adhesive. FIG. 8C shows how the bottom
plate 32 covers the bottom of the case 30 with the drive coil 40 housed.
[0047]
The bottom plate 32 is preferably a disk-shaped member, and the material is preferably a
magnetic body. When the material of the case 30 is magnetic, the same material as that of the
case 30 can be used, but another material may be used. The central portion of the upper surface
of the bottom plate 32 has a function of supporting the lower portion of the magnetostrictive
movable element 50 as described later. And since the lowermost part of the magnetostrictive
movable element 50 used is a bias magnet, the grooves 33 are provided around the magnet
support portion of the bottom plate 32 in order to reduce the leakage of the generated magnetic
flux to the outside. Further, a shoulder portion inside the groove 33 corresponds to the
positioning portion 48 on the bottom surface side of the bobbin 42 of the drive coil 40, and
functions to position the drive coil 40 on the bottom surface when assembling the bottom plate
32 to the case 30. Also have.
[0048]
When or before the bottom plate 32 is attached to the case 30, the gap between the bottom plate
32 and the bottom surface of the bobbin 42 of the drive coil 40 is filled with the damper resin
90. This gap may occur due to dimensional dispersion or the like of the bobbin formation of the
drive coil 40. The damper resin 90 has a function of suppressing the occurrence of extra
vibration due to the bobbin 42 rattling with the bottom plate 32 due to the gap. As the damper
04-05-2019
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resin 92, a rubber-like resin, a gel-based resin, or the like can be used.
[0049]
In this manner, when the bottom plate 32 is attached to the case 30 and the drive coil 40 is
positioned and stored in the inside thereof, the magnetostrictive movable element 50 and the
element cover 60 are then inserted into the shaft hole 46 of the drive coil 40. Be inserted.
[0050]
The magnetostrictive movable element 50 corresponds to a movable element portion that
expands and contracts in the axial direction in the magnetostrictive element actuator 20
according to the strength of the applied magnetic field.
Here, the magnetostrictive movable element 50 is not composed of one elongated
magnetostrictive element as described above, but a magnetostrictive element having a diameter
of 3 mm and a length of 5 mm in which the neody magnet 54 as a bias magnet for bias magnetic
field is disposed at both ends. Three moving members 52 are disposed in the axial direction with
the neody magnet 54-the magnetostrictive element 52-the neodymium magnet 54-the
magnetostrictive element 52-the neodymium magnet 54-the magnetostrictive element 52-the
neodymium magnet 54 to form one movable element. The sum of the displacement amounts of
the three magnetostrictive elements 52 is the displacement amount of the entire
magnetostrictive movable element 50. It can be determined that the strength of the nominal bias
magnetic field of the neodymium magnet 54 is determined in accordance with the maximum
value of the drive current supplied to the drive coil 40. When the maximum value of the AC
magnetic field signal generated by the drive coil 40 in the above example is a magnetic field
strength of 50,000 A / m to 100,000 A / m, the nominal bias magnetic field strength is also
comparable to this. Is desirable.
[0051]
The magnetostrictive movable element 50 having a configuration in which the magnetostrictive
element 52 is sandwiched by the neodyme magnets 54 is held by the magnetic attraction force
between the facing neodymium magnets 54. However, since the magnetostrictive element 52 is
expanded and contracted in the axial direction and its dimension is also changed in the radial
direction by the AC magnetic field signal of the drive coil 40, in some cases, the holding may be
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broken. The element cover 60 has a function of guiding the movement of the magnetostrictive
element 52 and the neodymium magnets 54 in the axial direction as the whole magnetostrictive
movable element 50 without being unnecessarily restricted from axial and radial movements.
[0052]
10A and 10B show the relationship between the magnetostrictive movable element 50 and the
element cover 60, where FIG. 10A is a sectional view and FIG. 10B is a top view. As described
above, the element cover 60 is a cylindrical member, and is an elongated cylindrical case that
guides the magnetostrictive movable element 50 in the axial direction so as to be movable in the
central through portion. This guide is normally noncontact rather than contacting or slidingly
guiding, and a guide for preventing the magnetostrictive element 52 and the neodymium magnet
54 which are included in the magnetostrictive movable element 50 from being largely deviated
in the radial direction in any case. It is. Therefore, in terms of its function, as in the element cover
61 shown in FIG. 10C, it may be a longitudinal direction guide member in which a cylinder is
divided into a plurality of pieces in the axial direction, and a sheet is wound and used It is also
good. The element cover 60 is preferably made of a material having good lubricity, and for
example, a Teflon (registered trademark) material may be molded into a predetermined shape, or
a Teflon tube of a predetermined size may be used. Alternatively, a silicon-based flexible sheet,
such as Geltech's trade name “α-gel sheet”, may be wound in a cylindrical shape and used.
[0053]
Returning to the assembling flow of FIG. 8 again, FIG. 8D is a view showing how the
magnetostrictive movable element 50 and the element cover 60 are inserted into the shaft hole
46 of the drive coil 40. As described above, the lowermost portion of the magnetostrictive
movable element 50 is placed at the support portion surrounded by the groove 33 in the central
portion of the upper surface of the bottom plate 32. In this manner, a structure in which the
drive coil 40 is disposed outside the magnetically biased movable magnetostrictive element 50 is
assembled.
[0054]
Next, the output mover 70 is disposed on the top surface of the magnetostrictive movable
element 50. The output mover 70 is a transmission shaft for transmitting the expansion and
04-05-2019
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contraction movement of the magnetostrictive movable element 50 to the head 36, and is
constituted of a vibration receiving plate 72 and a movable rod 74. The vibration receiving plate
72 is a substantially disk-shaped member having a diameter substantially close to the outer
diameter of the drive coil 40, and a shaft portion in contact with the neodyme magnet 54 at the
top of the magnetostrictive movable element 50 protrudes It is a member provided with an
annular recess at the periphery of the upper surface which receives the biasing force of the coil
spring 76. The material is preferably a magnetic material in order to reduce the leakage of the
magnetic flux generated from the neodymium magnet 54 at the top of the magnetostrictive
movable element 50 to the outside.
[0055]
As described above, the vibration receiving plate 72 receives the biasing force of the coil spring
76 in the wide upper surface portion, and efficiently transmits this to the top of the
magnetostrictive movable element 50. Thereby, the entire magnetostrictive movable element 50
is pressed in the direction of the bottom plate 32 to determine its initial length, and when the
magnetostrictive movable element 50 is driven by the drive coil 40 to generate an elastic force in
the axial direction, the biasing force of the coil spring 76 The balance force is output as the
movement of the tip of the movable rod 74 as an axial output. FIG. 9A shows how the output
mover 70 is disposed on the top surface of the magnetostrictive movable element 50. FIG.
[0056]
FIG. 9B is a view showing a state in which a coil spring 76 is placed around the upper surface of
the vibration receiving plate 72 of the output mover 70, and the lid 34 is covered from above
and assembled to the case 30. The lid 34 has a recess on the bottom surface side, and is
constituted by a lid main body 35 having a through hole at the center of the upper surface and a
bearing 37 fixedly attached to the through hole of the lid main body 35. The recess on the
bottom side of the lid body 35 accommodates the coil spring 76 in the recess space, and when
the lid 34 is assembled to the case 30, the coil spring 76 is contracted with the vibration
receiving plate 72 and pinched. It has a function to generate power. The lid body 35 can be made
of the same material as the case 30 by machining or molding, or a combination thereof. The
bearing 37 is a member for slidingly supporting the movable rod 74, and a metal bush bearing or
the like having good lubricity can be used.
[0057]
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Before or after covering the lid 34, a damper resin 92 is filled in the gap between the bottom
surface side of the vibration receiving plate 72 and the top surface side of the bobbin 42 of the
drive coil 40. When the magnetostrictive movable element 50 is displaced, the damper resin 92
vibrates the vibration receiving plate 72 in accordance with the displacement, but has a function
of suppressing the extra vibration. As the damper resin 92, a rubber-like resin, a gel-based resin,
or the like can be used. FIG. 9 (b) also shows the damper resin 90 filled in the gap between the
bottom plate 32 and the bottom surface of the bobbin 42 of the drive coil 40 described in FIG. 8
(c). ing.
[0058]
The coil spring 76 is an urging means for urging the magnetostrictive movable element 50
toward the bottom plate 32 via the vibration receiving plate 72 as described above. The coil
spring 76 is filled with a flexible resin 94 so as to fill the space between the spiral wires at or
before the cover 34 is covered. The flexible resin 94 performs AC vibration via the vibration
receiving plate 72 when the magnetostrictive movable element 50 is driven to perform AC
displacement in the axial direction, and at that time, it has a function of suppressing the
occurrence of resonance vibration. Have. Although depending on the spring constant and the like
of the coil spring 76, the coil spring having an appropriate size from the above-described casing
size and the like resonates at, for example, around 10 kHz. Since the flexible resin 94 acts as a
damper that suppresses this, it is possible to faithfully transmit the vibration component of the
magnetostrictive movable element 50 to the output mover 70. As the flexible resin 94, a rubberlike resin, a gel-based resin or the like can be used.
[0059]
In order to cover the lid 34, the movable rod 74 of the output mover 70 is inserted into the
bearing 37 and the coil spring 76 is pressed, and the assembly with the case 30 can be
performed with a mounting screw or the like not shown. Alternatively, the case 30 and the
bottom plate 32 may be joined using an adhesive.
[0060]
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19
As described above, when each predetermined element is accommodated in the housing, as
shown in FIG. 9C, the thermally conductive resin 96 is injected from the resin injection hole 95
provided in the cylindrical portion of the case 30, and the housing The gap around the drive coil
40 inside the body is filled. This gap mainly exists around the coil winding 44 of the drive coil 40
in the case 30. Therefore, the heat conductive resin 96 encloses the coil winding 44 so as to
surround the coil winding 44 and, if there is a gap between the coil windings, enter the gap as
well. As packed. The heat conductive resin 96 has a function of efficiently transmitting the heat
generated in the coil winding 44 to the casing such as the case 30 when the drive current is
large, and efficiently radiating the heat to the outside air. As such a heat conductive resin, for
example, trade name "high thermal conductivity silicone gel" manufactured by GE Toshiba
Silicone Co., Ltd. can be used.
[0061]
Thereafter, the head 36 is attached by screwing or the like to the end of the movable rod 74 of
the output mover 70 protruding from the housing, and the assembly of the magnetostrictive
element actuator 20 is completed. The head 36 is exchangeably attached to the movable rod 74
by the screw portion 39, and the flat top of the resin cover 38 having a flat top is made to
contact the flat surface of the wide area of the resin cover 38 with the object. It has a function of
efficiently transmitting the AC displacement output of the mover 70 to the object.
[0062]
The head 36 can cope with various objects by preparing different materials of the resin cover 38
in advance. That is, the head 36 of the resin cover 38 having a preferable material of the output
transfer characteristic can be selected and attached to the output mover 70 in accordance with
the characteristics of the object. For example, in the case of outputting voice, it is possible to use
a resin cover with good damping characteristics when the opposite side is a hard material, and
use a hard resin cover when the opposite side has appropriate softness.
[0063]
The operation of the magnetostrictive element actuator 20 having such a structure will be
described. Since two input terminals of the drive coil 40 are provided from the magnetostrictive
element actuator 20, these are connected to an appropriate drive circuit. The drive circuit can be
04-05-2019
20
designed in accordance with the application of the magnetostrictive element actuator 20. Here,
the case where the magnetostrictive element actuator 20 is used as a sound generator will be
described. In that case, the drive circuit is a circuit that generates an alternating current drive
signal corresponding to the audio signal. The drive circuit determines the frequency and the
amplitude of the drive current supplied to the drive coil 40 according to the frequency of the
audio signal and the amplitude thereof, and supplies it as a drive signal between two input
terminals.
[0064]
The drive coil 40 generates an alternating magnetic field according to the frequency and the
amplitude of the supplied drive current. The alternating magnetic field acts on the
magnetostrictive movable element 50 to which the bias magnetic field is applied in advance. The
magnetostrictive movable element 50 is configured by arranging in the axial direction three
magnetostrictive elements 52 with a length of 5 mm in the axial direction, in which neodye
magnets 54 for generating a bias magnetic field are arranged at both ends. Therefore, if the
strength of the input AC magnetic field is about 50,000 A / m to about 100,000 A / m, AC
displacement with good linearity can be output. That is, displacement vibration that is faithful to
a desired audio signal is output. The output displacement vibration is transmitted to the output
mover 70, and the resin cover 38 of the head 36 outputs the displacement vibration faithful to
the desired audio signal. At this time, noise such as vibration due to excessive resonance or
rattling is effectively removed by the action of the damper resins 90 and 92 and the flexible resin
94.
[0065]
The material of the resin cover 38 of the head 36 can be exchangeably adapted to an object
which generates a sound wave by attaching the magnetostrictive element actuator 20 as a
sounding body and actually vibrating it. The resin cover 38 may be entirely made of a resin
material, or may be made by resin coating on the surface of a metal material other than resin. For
example, when the magnetostrictive element actuator 20 is attached to a window glass and the
window glass is vibrated to generate an actual sound wave, the glass has a fairly hard mechanical
vibration characteristic, so a resin of a flexible resin material with good damping characteristics.
A head 36 having a cover 38 is used. Also, when the magnetostrictive element actuator 20 is
attached to a wood board and the wood board is vibrated to generate an actual sound wave, the
wood board has mechanical vibration characteristics that easily absorb the sound wave, so there
is not much damping property. A head 36 having a resin cover 38 of hard resin material can be
04-05-2019
21
selected.
[0066]
When a large output displacement vibration is used, the amplitude of the current flowing
through the drive coil 40 also becomes considerably large, and the drive coil 40 generates heat.
This heat generation is efficiently transmitted to the casing such as the case 30 by the heat
conductive resin that encloses the drive coil 40 and dissipates heat to the outside air, so that the
temperature rise of the magnetostrictive element actuator 20 can be suppressed. When the
temperature of the drive coil 40 rises, the resistance of the coil winding 44 rises and the drive
current that can be supplied is limited. However, by suppressing the temperature rise, the drive
current that can be supplied can be made larger.
[0067]
In the above, although a drive coil demonstrated as what uses a single coil with respect to three
magnetostriction elements, you may use a drive coil as what connects a some coil in parallel. FIG.
11 is an explanatory view in the case where coils are provided corresponding to the respective
magnetostrictive elements and they are connected in parallel. FIG. 11 (a) shows a drive coil 40 of
a single coil winding 44 used in FIG. 7 and the like for comparison. The two input terminals of
the drive coil 40 are connected to the amplifier 13 of the drive circuit. FIG. 11B shows an
example in which three coil windings 43 are connected in parallel corresponding to three
magnetostrictive elements 52 to configure one drive coil 41. That is, two input terminals of each
of the three coil windings 43 are respectively connected in parallel to form two input terminals
as a whole, and are connected to the amplifier 13 of the drive circuit. The number of turns of
each coil winding 43 / the axial length of the coil is set to be the same as the number of turns of
the single coil winding 44 of FIG. 11A / the axial length of the coil. In the above example, both
the coil winding 44 and the coil winding 43 are set to the number of turns / axial length of the
coil = 600 turns / 13.77 mm = 200 turns / 4.923 mm.
[0068]
Therefore, if the drive current input from the amplifier 13 is the same, the strength of the
magnetic field generated by the drive coil 40 in FIG. 11A is also generated by each coil winding
43 of the drive coil 41 in FIG. The strength of the magnetic field is also the same, and the
04-05-2019
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expansion and contraction of the magnetostrictive movable element 50 are the same. At this
time, the voltage between the two output terminals of the amplifier 13 in FIG. 11B is 1/3 of that
in the case of FIG. Therefore, since the output current is the same in both FIG. 11 (a) and FIG. 11
(b), the output power can be reduced to 1/3. Further, since the inductance of each coil winding
43 of FIG. 11B is smaller than the inductance of the coil winding 44 of FIG. 11A, it is possible to
flow a larger current.
[0069]
In the case where the drive coil is a "plurality of coil windings" connected in parallel, the number
of the plurality of coils and the number of the "plurality of magnetostrictive elements" may not be
the same. For example, in the example of FIG. 11, two coil windings may be connected in parallel
to the three magnetostrictive elements.
[0070]
As described above, a plurality of magnetostrictive elements, each having a bias magnetic field
magnet disposed at both ends in the axial direction, are arranged along the axial direction, and
the sum of the axial expansion and contraction amounts of the magnetostrictive elements is the
total axial expansion and contraction By using the magnetostrictive movable element, it is
possible to widen the range of linearity of the AC displacement output with respect to the AC
magnetic field input. Therefore, a wide range of AC magnetic field input is possible, and a larger
output can be obtained. Further, by appropriately using the damping resin, it is possible to
suppress extra vibration and maintain the linearity of the output signal with respect to the input
signal. Furthermore, heat generation accompanying a large output can be suppressed by sealing
the drive coil with a heat conductive resin.
[0071]
It is a figure explaining the contents of the experiment used as the basis which sets the axial
direction length of the magnetostriction element used as the premise of the embodiment
concerning the present invention. It is a figure which shows three types of structures of the
magnetostriction movable element used for experiment. It is a figure which shows the
relationship between the element length of the magnetostriction element which comprises a
magnetostriction movable element, and the maximum elongation rate which can maintain the
04-05-2019
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linearity of input-output by one of the experimental results. It is a figure which shows the
example of the waveform of output alternating current displacement when the linearity of inputoutput is broken in experiment. It is a figure which shows the mode of the input drive current
limit which can maintain the element length of the magnetostriction element which comprises a
magnetostriction movable element, and the linearity of input-output by one of the experimental
results. It is a figure which infers a cause from the result of FIG. 4, FIG. 5, and demonstrates one
possible idea. It is a sectional view of a magnetostrictive element actuator in an embodiment
concerning the present invention. FIG. 7 is a diagram for explaining the first half of the assembly
process of the magnetostrictive element actuator in the embodiment according to the present
invention. FIG. 7 is a view for explaining the second half of the assembly process of the
magnetostrictive element actuator in the embodiment according to the present invention. FIG. 7
is a view showing a relationship between a magnetostrictive movable element and an element
cover in the embodiment according to the present invention. In another embodiment, it is a
figure showing an example which comprises a plurality of coil winding by which drive coil was
connected in parallel.
Explanation of sign
[0072]
4, 5 input AC magnetic field, 6 output AC displacement, 10, 50 magnetostrictive movable
elements, 12 drive coils, 13 amplifiers, 14 AC power supplies, 16 capacitive displacement meters,
20 magnetostrictive element actuators, 30 cases, 31 opening holes, 32 bottom plates , 33 groove,
34 lid, 35 lid main body, 36 head, 37 bearing, 38 resin cover, 39 screw portion, 40, 41 drive coil,
42 bobbin, 43, 44 coil winding, 46 shaft hole, 47, 48 positioning portion , 52 magnetostrictive
element, 54 neodymium magnet, 60, 61 element cover, 70 output mover, 72 vibration receiving
plate, 74 movable rod, 76 coil spring, 90, 92 damper resin, 94 flexible resin, 95 resin injection
hole, 96 Thermal conductive resin.
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