JP2008212716

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DESCRIPTION JP2008212716
PROBLEM TO BE SOLVED: To improve the mechanical extension direction of an actuator.
SOLUTION: At least one of the boundary surfaces has a corrugated area provided with height and
depth as maximum and minimum parts extending in parallel to the lateral direction, the
corrugated area is covered by an electrode, and the electrode is maximum and minimum It covers
at least a part of the part entirely and is continuous over the corrugated area in the remaining
part. [Selected figure] Figure 1
アクチュエータ
[0001]
The present invention relates to an actuator in which the main bodies of elastomeric material are
provided with electrodes at the interfaces facing each other.
[0002]
An actuator of this type is known from US Pat. No. 5,977,685.
[0003]
This type of actuator is also simply called "artificial muscle", because under certain conditions its
behavior corresponds to that of human muscle.
[0004]
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Its function is relatively simple.
When a potential difference is applied to both electrodes, an electric field is generated to
penetrate the main body, where the electric field causes a mechanical attraction between the
electrodes.
For this reason, both electrode devices approach and compress a main body.
Access of both electrode devices is further facilitated if the material of the body has dielectric
properties. However, since the material has a substantially constant volume, upon compression,
i.e., as the thickness decreases, the body expands in size in both directions, i.e., parallel to the
electrodes.
[0005]
Now, assuming that the extension direction of the body is limited to one direction, the change in
thickness is completely replaced by the change in length in the longitudinal direction. In the
following description, the direction in which the length is changed is referred to as longitudinal
direction , and the direction in which the length is not changed is referred to as horizontal
direction . In the prior art, the electrode has a conductive layer of relatively low conductivity, on
which a laterally extending stripe of non-flexible material is deposited. In this case, the stripes are
spaced from one another in the longitudinal direction. The conductive layer serves to distribute
the electric field as uniformly as possible, while the stripes preferably consist of a material which
prevents the widening of the body in the lateral direction. However, in this case the kinetic
conductivity is somewhat limited due to the poor conductivity of the conductive layer.
[0006]
The object of the invention is to improve the mechanical extension of the actuator.
[0007]
This task is achieved in an actuator of the type described at the beginning, wherein at least one
of the interfaces has a corrugated area with height and depth as maxima and minima extending
parallel to the lateral direction, the corrugated area being The electrode is covered by the
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electrode, and the electrode covers the entire surface of at least a part of the maximum and
minimum parts, and the remaining part is continuous over the corrugated area.
[0008]
This configuration provides several advantages as follows.
[0009]
Since the electrodes are formed continuously in the lateral direction, they limit the direction in
which the body extends in this lateral direction.
Here, "continuous" means that the electrode has a shape that can not be stretched, for example, it
has a linear shape.
The overall deformation that occurs as the thickness of the body decreases is replaced by the
change in expansion in the longitudinal direction.
However, in practice, it changes slightly in the lateral direction due to the actual material.
However, this lateral change can be ignored compared to the longitudinal expansion. Since the
electrodes extend continuously throughout the corrugated area, the conductivity of the
electrodes is of sufficient magnitude so that the construction of the electric field necessary to
reduce the thickness of the body can be carried out rapidly Guaranteed. Therefore, high
frequency can be realized by the actuator according to the present invention. The surface of the
main body is corrugated at least in a predetermined area, and the corrugations extend in parallel
in the lateral direction, so in the longitudinal direction it is at least considerably larger than the
longitudinal part of the actuator in its resting state. A surface is provided. Therefore, if the
actuator is expanded in the longitudinal direction, only the corrugation is lowered, that is, the
difference between the maxima and minima becomes smaller, in other words, the difference
between the height tip and the depth valley becomes smaller. . Thus, the extension can be
continued without difficulty to the electrode deposited on this surface without the risk of the
electrode disengaging from the surface. The corrugated surface thus provides excellent stiffness
in the lateral direction and excellent flexibility in the longitudinal direction, making it easy to
evenly distribute the voltage supply to build up the electric field across the surface of the body it
can. The expression "waved" does not necessarily mean an arc-shaped contour or a sine-shaped
contour. Basically, what kind of structure if "peaks" and "valleys" are alternately located, and if
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the peaks and valleys extend in the lateral direction, ie, in the direction perpendicular to the
expansion direction, May be. It may therefore be sinusoidal, triangular, sawtooth, trapezoidal or
rectangular in cross section. The direction of extension is improved and the kinematics of the
actuator is not impaired.
[0010]
Advantageously, the electrodes completely cover the corrugated area. That is, a plane electrode is
used. The use of a plane electrode makes charge build up at any point on the interface of the
body, thus making the construction of the electric field uniform. At the same time, the rigidity in
the lateral direction can be further improved. The reason is that the continuous electrodes cover
not only the local maxima, that is, the peaks and valleys, but also the side surfaces between the
peaks and valleys. However, there is no change in mobility in the longitudinal direction. When
the body expands in the longitudinal direction, the contours become flat, but it is not necessary
to make a change between the electrode attachment and the body.
[0011]
In this case, it is advantageous for the electrode to be directly connected to the body. As the
electrodes are used for electrical conduction to the entire interface, no auxiliary conductive layer
is required. When the electrode is directly connected to the body, the influence of the electrode
on the body is improved, in particular a change in the rigidity improvement or in the nonplasticity in the transverse direction.
[0012]
Advantageously, the maxima and minima have an amplitude not greater than 20% or more of the
thickness of the body between the interfaces. By means of such a dimensioning, a uniform
distribution of the electric field in the longitudinal direction of the actuator is achieved, ie the
force acts uniformly on the body and in particular does not stand out in a band. The amplitude is
half of the difference between adjacent maximum and minimum portions, that is, half of the
distance between one height and one depth.
[0013]
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Advantageously, the electrodes have a thickness which is at most 10% of the amplitude. The
plasticity factor (compliance factor) Q of the actuator is directly proportional to the ratio of the
electrode amplitude to the thickness. The greater this ratio, the greater the plasticity rate.
[0014]
Advantageously, the ratio of the amplitude to the period length is in the range 0.08 to 0.25. The
ratio of amplitude to period length affects the length of the surface of one period. The longer the
surface length, the higher the plasticity rate basically. In theory, if the surface electrode is
deformable, the body may be expanded until the surface is smooth. However, it goes without
saying that the plasticity rate is limited by other parameters in practice.
[0015]
Advantageously, the wave area has a rectangular profile. The rectangular profile was observed to
extend most in the longitudinal direction. This is because the electrode on the surface imparts a
certain degree of rigidity also in the longitudinal direction. For example, in the case of a
rectangular profile, the part lying parallel to the longitudinal extension of the rectangular profile
can not expand with respect to height and depth. In other words, the expansion of the body is
practically limited to the widening of the side slope and the associated reduction of the
amplitude.
[0016]
Advantageously, the rectangular profile has teeth and tooth gaps of the same length in the
longitudinal direction. This makes it possible to form the electric field as uniformly as possible. At
the same time, this configuration facilitates manufacture.
[0017]
In the case of methods of the type mentioned at the outset, the task is to press the elastomer in a
mold provided with a corrugated surface profile to form a film and to keep the film still short of
formable state. It is solved by time curing and then pressing the other mold with the corrugated
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surface against the other side of the film and applying the conductive layer to the surface after
forming the surface structure.
[0018]
The manufacture of this kind is relatively easy.
Basically, it is not necessary to process the electrode. It is only necessary to produce the desired
surface structure. This type of surface structure is produced by compression molding. For this
purpose, it is only necessary to prepare a mold with a suitable structure. This type of mold can be
obtained, for example, by known photolithographic processes as known from the manufacture of
compact discs (CDs).
[0019]
In this case, it is particularly advantageous to deposit the conductive layer. The deposited layer
can be realized with the desired thin thickness. Furthermore, the vapor also penetrates into the
narrow valleys, ensuring that there is an electrode formation.
[0020]
The invention will now be described in detail with regard to advantageous embodiments with the
aid of the drawings.
[0021]
FIG. 1 shows the individual stages of manufacture of the actuator 1, which comprises a body 2
having two interfaces 3, 4 facing one another.
Electrodes 5 and 6 are provided on both boundary surfaces 3 and 4 respectively. The electrodes
5, 6 are directly coupled to the body 2. The body is formed from an elastomeric material, such as
silicone elastomer, and advantageously has dielectric properties. Although the material of the
body 2 is deformable, the volume is constant. That is, when the main body 2 is compressed in the
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direction of thickness d, the spread of the main body 2 is expanded in the other two directions.
Now, assuming that the expansion of the main body 2 is limited in one direction, the expansion of
the main body 2 is only in the other direction due to the reduction of the thickness d. In the case
of the embodiment of FIG. 1, the possibility of expansion in the direction perpendicular to the
plane of the drawing (lateral direction) is limited or completely prevented. On the other hand (in
FIG. 1) an extension from the left to the right, ie in the longitudinal direction, is possible. In order
to achieve this anisotropic behavior, both interfaces 3, 4 of body 2 have a corrugated structure.
In FIG. 1, this waveform structure is illustrated as a rectangular profile. However, the corrugated
structure may be formed by a sinusoidal profile, a triangular profile, a sawtooth profile or a
trapezoidal profile.
[0022]
As is further apparent from the drawings, the non-inflatable electrodes 5, 6 directly coupled to
the body 2 and thus fixedly coupled to the body 2 are shown in the drawing when the body 2 is
compressed in the direction of its thickness d It prevents the expansion of the body 2 in the
direction perpendicular to the plane. The main body 2 expands in a direction perpendicular to
the plane of the drawing on the premise that the electrodes 5 and 6 are also expandable in this
direction, but such a case does not correspond by definition. The electrodes 5 and 6 are given a
potential difference to compress the main body. As a result, an electric field is formed between
the two electrodes 5 and 6, and the electric field exerts a force to attract the two electrodes 5 and
6 to each other. The premise in this case is that the body 2 is not too thick. The thickness d of the
main body 2 is advantageously varied in the range of several tens of μm or less.
[0023]
Table 1 below shows typical values for the electrode layer and the elastomer and typical values
of the actuation voltage of the actuator.
[0024]
[0025]
In the following, a 20 μm thick silicon elastomer film with an elastomer module of 0.7 MPa and
a dielectric constant of 3 was observed.
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The electrodes are made of gold and have a thickness of 0.05 μm and an elastomer module of
80,000 MPa.
The volume of such an actuator is 0.1 nF / cm 2 and the step response is on the order of
microseconds for an unloaded actuator. Assuming that the plasticity of the electrode is 4000,
1000 V is required to stretch on the order of 10%. On the other hand, in the case of the nonexpandable electrode, that is, in the case of the electrode having a plasticity of 1, an elongation of
0.05% or less occurs. In other words, it is possible to reduce the operating voltage according to
the invention.
[0026]
The manufacture of a body 2 of this kind is relatively simple. A mold 7 having a suitable negative
structure (here a rectangular structure) is coated with an elastomer solution to form a thin film 9
typically 20 μm to 30 μm thick. Next, when the film 9 is cured for a short time, the film
becomes a relatively soft layer. This layer can be molded at any time. Then, on the other side of
the elastomeric film 9, a second film 10 with a corresponding surface structure 11 is pressed. In
this case both pressing steps are carried out under vacuum so that air is not trapped at the
interface between the mold and the film. Thereafter, the entire sandwich structure of the film 9
and the molds 7 and 10 is cured in a set. When the molds 7, 10 are mechanically separated, the
film 9 will have the corrugated boundary surfaces 3, 4 shown. Finally, conductive layers can be
deposited on the corrugated interfaces 3, 4 respectively. For example, a metal layer consisting of
gold, silver or copper can be deposited.
[0027]
The effect of the corrugated surface structure is apparent from the schematic of FIG. What is
indicated by a broken line is a rectangular profile in the resting position. That is, it is a
rectangular profile when no voltage is applied to the electrodes 5 and 6. The rectangular profile
has an amplitude a and a period length L. The thickness of the conductive layer 5 is h. The
amplitude is half of the difference between the height 13 and the depth 14. The height 13 and
the depth 14 can also be called "mountain" or "valley". In short, both concepts are called "local
maxima". As can be seen from FIGS. 1 and 2, the height 13 and the depth 14 have the same
extent in the longitudinal direction 12. The longitudinal direction 12 extends from left to right in
FIG.
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[0028]
The solid line shows the shape of the rectangular profile when the body is expanded in the
longitudinal direction 12. Since the material of the main body 2 has a constant volume,
expansion in the longitudinal direction 12 simultaneously means that the profile has become
thinner in the thickness direction. In the figures, the reduction in thickness is exaggerated for
emphasis. Such a profile is shown as a solid line.
[0029]
As can be seen from the figure, the profile does not extend substantially in the region of height
13 and depth 14. Thus, stretching of the body 2 is only possible at the sides 15, 16, and there is
no need to expand the electrodes fixed thereto in any way.
[0030]
At this point, various relationships with particularly advantageous properties can be established.
[0031]
That is, the ratio of the amplitude a of the profile to the thickness h of the conductive layer
forming the electrodes 5, 6 determines the direction in which the corrugated electrodes extend
and thus the expansivity of the body 2.
For a waveform profile, the plasticity factor Q is directly proportional to the square of the ratio.
By optimizing the above ratio, theoretically, it is possible to increase the extending direction by a
factor of 10000 or more. For example, if the coating thickness is 0.02 μm and the amplitude is 2
μm, the ratio is 100 and the plasticity is 10000.
[0032]
For a rectangular profile as illustrated in FIG. 2, the plasticity factor Q can be easily calculated
from the bending bar theory.
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[0033]
[0034]
Here, γ = a / L.
[0035]
The same equations apply basically to sinusoidal or triangular profiles.
However, the constant for sinusoidal or triangular profiles (16 for rectangular profiles) is smaller.
Furthermore, it is necessary to consider the ratio between the total length s of the profile period
and the length L of the period itself.
The total length s is said to "pull straight" the profile. In the case of a rectangular profile, the total
length s is s = L + 4a. If the ratio s / L is close to 1, the actuator does not move much, even if the
electrode is very flexible.
[0036]
In FIG. 3 and FIG. 4, the ratio of the amplitude a to the period length L is represented to the right,
and the ratio 100% × (s−L) / L is represented to the upper Are for sinusoidal profiles, FIG. 4 is
for rectangular profiles. In fact, for an "artificial muscle" to perform 10% to 25% of exercise, a
maximal stretch of 20% to 50% is required. That is, when using a rectangular profile, the ratio γ
= a / L needs to change in the range of 0.1 to 0.2.
[0037]
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In theory, approximately 32% stretching can be achieved using a sinusoidal profile, and
approximately 80% stretching can be achieved using a rectangular profile. However in practice
this is not the case. For example, although a rectangular profile is composed of vertical and
horizontal parts, only the former is responsible for flexibility or plasticity. The horizontal part of
the electrode itself does not stretch.
[0038]
In a practical embodiment, the mold 7 is produced by exposing and developing a positive
photoresist by photolithography. In this case, the mask used for exposure is relatively simple.
The mask consists of a plurality of parallel quadrilaterals with a width of 5 μm and a length
determined by the size of the substrate. The individual quadrilaterals are uniformly spaced 5 μm
apart and are compounded in the expansion direction. The height, or amplitude, of the profile is
defined as half the thickness of the photoresist layer deposited on the substrate. This height can
also be selected to be approximately 5 μm.
[0039]
However, it is advantageous for the amplitude to be at least 10 times smaller than the thickness d
of the body 2 in order to make the electric field uniform. For an elastomeric film with a thickness
of 20 μm, an amplitude of at most 2 μm is chosen for this purpose.
[0040]
FIG. 5 is a schematic view of individual method steps for manufacturing an actuator. It is a
sectional view of one cycle. It is a graph for demonstrating the ratio in a sine profile. It is the
same graph for demonstrating the ratio in a rectangular profile.
Explanation of sign
[0041]
Reference Signs List 1 actuator 2 main body (silicone elastomer) 3 interface 4 interface 5
electrode 6 electrode
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