Actuator

Abstract

The present invention provides an actuator that can easily adjust the electrostatic stress acting between electrodes. [Solution] The actuator comprises an insulating flexible bag that forms a housing, a liquid dielectric filled inside the flexible bag, a plurality of electrodes arranged on the inner circumferential surface of the flexible bag whose separation distance changes according to the applied voltage, an expansion section in which the liquid dielectric present between the electrodes flows in and expands in volume when the separation distance between the electrodes decreases, and a separator inserted between the electrodes. The separator is in the form of a film with its front and back surfaces facing the electrodes and has through holes that penetrate in the thickness direction. As a result, the applied voltage is directly applied to the capacitor portion where only liquid dielectric is filled between the electrodes, and by adjusting the relative permittivity of the liquid dielectric, the amount of charge induced between the electrodes can be adjusted accordingly.

Description

[Technical Field]

[0001] The present invention relates to an actuator, and more particularly to an actuator that utilizes electrostatic stress acting between electrodes. [Background technology]

[0002] In recent years, soft actuators, which enable more flexible movements compared to conventional mechanical actuators, have been attracting attention as a way to make the movements of industrial robots and other devices more similar to human movements. A soft actuator is a device that functions as an actuator by deforming through the deformation of a lightweight, flexible material, and is sometimes called an artificial muscle.

[0003] Soft actuators, compared to conventional mechanical actuators, (1) It is lightweight because it does not have mechanical drive parts that require rigidity. (2) Because it is driven via fluid, it is highly flexible. (3) It has no mechanical drive parts, so it is quiet. (4) Since it does not have a mechanical drive unit, there is no failure of a mechanical drive unit. It has the following advantages.

[0004] As an example of such a soft actuator, the HASEL (Hydraulically Amplified Self-healing Electrostatic) type actuator, as shown in Non-Patent Document 1, is known.

[0005] The document states that a typical HASEL type actuator is: An insulating flexible bag forming the housing, A liquid dielectric is filled inside the flexible bag, Multiple electrodes are arranged on the outer surface of the flexible bag, and their separation distance changes according to the applied voltage, When the distance between electrodes decreases, the liquid dielectric present between the electrodes flows in and expands in volume, forming an expansion region. A configuration including it is described.

[0006] Also, in the same document, as characteristics of the HASEL type actuator, (1) By applying a voltage between electrodes, positive and negative charges are induced on each electrode, and the distance between the electrodes changes due to the electrostatic stress (Maxwell stress) acting between the charges. (2) The displacement amount (amplification amount) of the expansion part can be defined by the relative relationship between the electrode size and the expansion part. (3) Even if dielectric breakdown occurs in the liquid dielectric, it can be self - repaired by the rearrangement of the liquid dielectric. etc. are described.

[0007] Also, for example, in Patent Document 2, a housing having an electrode region and an expandable fluid region, a dielectric fluid housed in the housing, an electrode pair including a first electrode and a second electrode disposed in the electrode region of the housing, and an electrode insulator having one or a plurality of insulating layers are included. The electrode insulator is disposed on the inner electrode surface of the first electrode of the electrode pair. A HASEL type actuator is described.

[0008] In the same document, it is described that when an electrode insulator is disposed only on one of the electrode pairs, asymmetry of the electrode insulator is formed, the decrease in the breakdown voltage of the electrode insulator material under stress is alleviated, and the reliability against breakdown short - circuit is improved.

[0009] In the HASEL type actuator as described above, (1) High responsiveness, (2) High deformation amplification amount, (3) High efficiency etc. have already been recognized as advantages.

[0010] However, on the other hand, in order to obtain the above advantages, there was a problem that a high voltage needs to be applied between the electrodes. As a countermeasure, one might consider increasing the relative permittivity of the dielectric between the electrodes to increase the charge induced on each electrode, thereby increasing the electrostatic stress acting between the electrodes and lowering the driving voltage. Therefore, the first thing to consider is increasing the relative permittivity of the liquid dielectric in order to increase the relative permittivity between the electrodes, but even if the relative permittivity of the liquid dielectric is increased, there are many cases in which the electrostatic stress actually decreases (driving voltage increases).

[0011] In HASEL-type actuators, a separator (flexible bag, electrode insulator) is typically inserted between the electrodes to prevent short circuits. Therefore, the equivalent circuit of the capacitor formed between the electrodes is a series connection of a capacitor consisting of a liquid dielectric and a separator. As a result, only the divided voltage portion of the voltage applied between the electrodes acts on the liquid dielectric, which can lead to a decrease in the charge induced on the electrodes. More specifically, even if the relative permittivity of the liquid dielectric is increased, if the decrease in the divided voltage of the applied voltage is greater due to its relationship with the capacitance of the separator, the charge induced at each electrode will decrease.

[0012] As a result, the electrostatic stress acting between the electrodes decreases, forcing an increase in the driving voltage. In other words, with conventional HASEL-type actuators, it is difficult to adjust the electrostatic stress acting between electrodes using a liquid dielectric with a relatively wide range of dielectric constants. [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] Philipp Rothemund; Nicholas Kellaris; Shane K. Mitchell; Eric Acome; Christoph Keplinger, HASEL Muscles for New Generation of Lifelike Robots-Recent Progress and Future Opportunities, Adv.Mater.,33,2003375(2021) [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2022-159168 [Overview of the Initiative] [Problems that the invention aims to solve]

[0015] The problem that this invention aims to solve is to provide an actuator that can easily adjust the electrostatic stress acting between electrodes. [Means for solving the problem]

[0016] To solve the above problems, the actuator according to the present invention An insulating flexible bag forming the housing, A liquid dielectric is filled inside the flexible bag, Multiple electrodes are arranged on the inner surface of the flexible bag, and their separation distance changes according to the applied voltage, When the distance between electrodes decreases, the liquid dielectric present between the electrodes flows in and expands in volume, creating an expansion region. A separator is inserted between the electrodes. It is equipped with. Here, the separator is a film-like material with its front and back surfaces facing the electrodes, and is equipped with through holes that penetrate in the thickness direction. However, "liquid dielectric" refers to a material that is liquid at room temperature ("25°C") and has a relative permittivity greater than that of air. [Effects of the Invention]

[0017] Therefore, since the separator is a film-like structure with its front and back surfaces facing the electrodes and has through-holes that penetrate in the thickness direction, the equivalent circuit of the capacitor formed between the electrodes will be a capacitor section in which only liquid dielectric is filled between the electrodes. More specifically, if the hole wall of the through-hole is formed parallel to the thickness direction of the separator, the projection portion of the hole wall onto the electrode becomes a capacitor portion consisting only of liquid dielectric. In the capacitor equivalent circuit, the configuration consists of a capacitor section made solely of liquid dielectric material and a capacitor section consisting of a series connection of liquid dielectric material and a separator, connected in parallel.

[0018] As a result, the applied voltage is directly applied to the capacitor section, where only liquid dielectric material is filled between the electrodes. Therefore, by adjusting the relative permittivity of the liquid dielectric material, the amount of charge induced on the electrodes can be adjusted accordingly. In other words, by increasing or decreasing the relative permittivity of the liquid dielectric, it becomes possible to create a region in which the electrostatic stress acting between the electrodes can be increased or decreased. Therefore, the electrostatic stress acting between the electrodes can be easily adjusted. [Brief explanation of the drawing]

[0019] [Figure 1] (a) A plan view of the actuator according to the first embodiment, (b) A cross-sectional view of the actuator taken by arrow bb, (c) A cross-sectional view of the actuator taken by arrow cc, and (d) A cross-sectional view of the actuator taken by arrow cc when voltage is applied. [Figure 2] This is a plan view of the actuator according to the second to ninth embodiment. [Figure 3] This is a plan view of the actuator according to the 10th to 13th embodiments. [Figure 4] (a) Capacitor model, (b) Equivalent capacitor model, and (c) Equivalent capacitor model of the equivalent capacitor model. [Figure 5](a) the HASEL capacitor model, (b) the separator-less capacitor model, (c) the porous capacitor model, and (d) the equivalent capacitor model of the porous capacitor model. [Figure 6] This is a capacitor model in which the hole wall of a through-hole is inclined with respect to the thickness direction. [Figure 7] This is an explanatory diagram of the narrowest opening ratio. [Figure 8] This is a specific example of the narrowest opening ratio.

[0020] [Figure 9] This is a diagram showing the electrostatic stress with respect to the relative permittivity εL of the liquid dielectric at various aperture ratios. [Figure 10] This is a diagram showing the electrostatic stress with respect to the relative permittivity εL of the liquid dielectric at various aperture ratios. [Figure 11] This is a diagram of electrostatic stress with respect to the relative permittivity εL of the liquid dielectric at the relative permittivity εS of each separator. [Figure 12] This is a diagram showing the electrostatic stress in response to changes in the inclination angle of the borehole wall. [Figure 13] This is a diagram showing the electrostatic stress with respect to the narrowest aperture ratio M.

[0021] [Figure 14] (a) Cross-sectional SEM image of sample 1, (b) Cross-sectional SEM image of sample 2, (c) Cross-sectional SEM image of sample 3, and (d) Planar optical microscope image of sample 3. [Figure 15] This is a schematic diagram of a stress measurement device. [Figure 16] This is an explanatory diagram of the actuator manufacturing method. [Figure 17] This is an explanatory diagram of the actuator manufacturing method. [Modes for carrying out the invention]

[0022] [Configuration 1] An insulating flexible bag forming the housing, A liquid dielectric is filled inside the flexible bag, Multiple electrodes are arranged on the inner surface of the flexible bag, and their separation distance changes according to the applied voltage, When the distance between electrodes decreases, the liquid dielectric present between the electrodes flows in and expands in volume, creating an expansion region. A separator is inserted between the electrodes. Equipped with, The separator is a film-like structure with its front and back surfaces facing the electrodes, and is equipped with through holes that penetrate in the thickness direction. Actuator. However, "liquid dielectric" refers to a material that is liquid at room temperature ("25°C") and has a relative permittivity greater than that of air.

[0023] [Configuration 2] The actuator according to configuration 1, wherein the through-hole occupancy rate is 0.1 or more and 0.9 or less.

[0024] [Configuration 3] The thickness of the separator is d (mm). The lower of the dielectric breakdown fields of the liquid dielectric or separator is denoted as E (kV / mm). If the voltage applied between the electrodes is V (kV), V <d×E The actuator described in configuration 1 or 2, used within an applied voltage range that satisfies the following relationship.

[0025] [Structure 4] An actuator according to any one of configurations 1 to 3, wherein the inclination angle of the hole wall of the through hole is 50 degrees or more with respect to the front and back surfaces.

[0026] [Composition 5] The actuator according to configuration 1, wherein the ratio of the narrowest opening ratio to the through-hole occupancy ratio is 0.1 or greater. However, "narrowest opening ratio" refers to the ratio of the total area of ​​the smallest opening perpendicular to the thickness direction of the through-hole to the area of ​​the surface or back surface of the separator.

[0027] [Composition 6] An actuator according to any one of configurations 1 to 5, wherein the relative permittivity of the separator is 2.0 or higher.

[0028] [Composition 7] An actuator according to any one of configurations 1 to 6, wherein the relative permittivity of the liquid dielectric is 1.5 or higher.

[0029] [Structure 8] The actuator according to configuration 7, wherein the relative permittivity of the liquid dielectric is 2.0 or higher.

[0030] The embodiments of the present invention will be described in detail below. [1. Actuator] The actuator according to the present invention is An insulating flexible bag forming the housing, A liquid dielectric is filled inside the flexible bag, Multiple electrodes are arranged on the inner surface of the flexible bag, and their separation distance changes according to the applied voltage, When the distance between electrodes decreases, the liquid dielectric present between the electrodes flows in and expands in volume, creating an expansion region. A separator is inserted between the electrodes. It is equipped with.

[0031] Figure 1 shows an actuator 1 according to the first embodiment of the present invention. The actuator 1 comprises a flexible bag 2, a liquid dielectric 3, an electrode 5, an expansion part 7, and a separator 8. Note that in Figure 1, for the sake of clarity, the dimensional ratios of each part are shown enlarged or reduced compared to the actual dimensional ratios.

[0032] [1.1. Flexible bag] The flexible bag 2 is a flexible insulator and forms the housing. In Figure 1, the flexible bag 2 is constructed by laminating a first flexible insulating sheet 2a and a second insulating sheet 2b. However, the structure of the flexible bag 2 is not limited to this embodiment. For example, the flexible bag 2 may be formed by an inflation molding method. Furthermore, in order to arrange electrodes 5, separators 7, etc., inside the flexible bag 2 according to the present invention, it is preferable that the bag 2 be constructed by laminating a first insulating sheet 2a and a second insulating sheet 2b together.

[0033] Furthermore, although the flexible bag 2 has a rectangular shape in plan view, we are not particularly limited to this configuration. The shape of the flexible bag 2 can be appropriately selected according to the purpose. For example, the shape of the flexible bag 2 may be circular, elliptical, or a polygon such as a triangle, pentagon, or hexagon.

[0034] The material of the flexible bag body 2 (first insulating sheet 2a, second insulating sheet 2b) is not particularly limited as long as it is flexible and insulating, and the most suitable material can be selected as appropriate depending on the purpose. For example, the material of the flexible bag 2 is: (1) Polyolefin resins such as polypropylene and polyethylene, (2) Amide resins such as polyamides and aromatic polyamides, (3) Ester resins such as polyester and aromatic polyester. (4) Fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride, (5) Chlorine-based resins such as polyvinylidene chloride, (6) Inorganic compounds such as glass These are some examples. Furthermore, the material of the flexible bag 2 (first insulating sheet 2a, second insulating sheet 2b) may consist of one of these types, or it may be a mixture of two or more types, or a laminate.

[0035] [1.2. Liquid Dielectrics] The liquid dielectric 3 is a liquid dielectric that is filled inside the flexible bag 2. More specifically, a "liquid dielectric" is a material that is liquid at room temperature (25°C) and has a relative permittivity greater than that of air. The type of liquid dielectric 3 is not particularly limited, and the most suitable one can be selected as appropriate depending on the purpose.

[0036] Examples of liquid dielectric materials 3 include those shown in Table 1. The relative permittivity of each liquid dielectric is also shown. Note that the relative permittivity is measured at a frequency of 1 kHz. The liquid dielectric 3 may be any one of the following compounds, or a mixture of two or more compounds. [Table 1]

[0037] Here, the relative permittivity of the liquid dielectric 3 is related to the amount of charge induced in the electrode 5 when a voltage is applied, and is related to the electrostatic stress acting between the electrodes 5. Therefore, in order to enable adjustment of electrostatic stress over a wider range, the relative permittivity of the liquid dielectric 3 is preferably 1.5 or higher. Furthermore, in order to increase the amount of charge induced on the electrode 5 when a voltage is applied and generate sufficient driving force as an actuator, the relative permittivity of the liquid dielectric 3 is more preferably 2.0 or higher.

[0038] [1.3. Electrodes] Multiple electrodes 5 are arranged on the inner circumferential surface of the flexible bag 2, and are movable parts whose separation distance changes according to the applied voltage. In Figure 1, of the multiple electrodes 5, the first electrode 5a is attached to the inner surface of the first insulating sheet 2a, and the second electrode 5b is attached to the inner surface of the second insulating sheet 2b. A lead wire 5c is connected to the first electrode 5a, and a lead wire 5d is connected to the second electrode 5b. The lead wires 5c and 5d are led out of the flexible bag 2 and connected to an external power supply. Note that both leader lines 5c and 5d extend in the x direction.

[0039] In Figure 1, the first electrode 5a and the second electrode 5b are square in plan view, and the first electrode 5a and the second electrode 5b are arranged to overlap in the z-direction view. However, the arrangement of the first electrode 5a and the second electrode 5b is not limited to this configuration. The shape, size, and arrangement of the first electrode 5a and the second electrode 5b are not particularly limited, as long as they can generate electrostatic stress between the electrodes 5 when a voltage is applied. The most appropriate shape, size, and arrangement can be selected as appropriate depending on the purpose.

[0040] For example, the shapes of the first electrode 5a and the second electrode 5b may be circular, elliptical, or polygonal, such as a triangle, pentagon, or hexagon. Furthermore, the shapes of the first electrode 5a and the second electrode 5b may be annular, for example, a circular ring or a polygonal ring. Furthermore, the shapes of the first electrode 5a and the second electrode 5b may be the same or different.

[0041] Furthermore, the first electrode 5a and the second electrode 5b may be arranged to completely overlap in the z-direction view, or they may be arranged to partially overlap. If at least a portion of the first electrode 5a and the second electrode 5b overlap in the z-direction, electrostatic stress can be applied between the electrodes 5 when a voltage is applied between them.

[0042] [1.3.1. Material] The materials of the electrodes 5 (first electrode 5a, second electrode 5b) and the lead wires 5c and 5d are not particularly limited, and the most suitable materials can be selected as appropriate depending on the purpose. Furthermore, the material of electrode 5 is preferably one that has low electrical resistance and flexibility to follow the movement of the flexible bag 2, and more preferably a thin metal film. Possible materials for electrode 5 include, for example, Al, Cu, Ag, and Au.

[0043] [1.3.2. Thickness] The thicknesses of the first electrode 5a, the second electrode 5b, the leader wire 5c, and the leader wire 5d are not particularly limited, as long as they do not hinder the flexibility of the flexible bag 2. If the thickness of the first electrode 5a, the second electrode 5b, the leader wire 5c, and the leader wire 5d becomes too thick, it may affect the flexibility of the flexible bag 2. Therefore, it is preferable that the thickness of the first electrode 5a, the second electrode 5b, the leader wire 5c, and the leader wire 5d be 200 μm or less.

[0044] [1.4. Expansion Section] The expansion section 7 is a movable section attached to the electrode 5, and when the distance between the electrodes 5 decreases, the liquid dielectric 3 present between the electrodes 5 flows in and expands in volume. More specifically, as shown in Figure 1(d), when a voltage is applied between the first electrode 5a and the second electrode 5b, electrostatic stress acts between the first electrode 5a and the second electrode 5b, causing the first electrode 5a and the second electrode 5b to attract each other. As a result, the liquid dielectric 3 that was between the first electrode 5a and the second electrode 5b is pushed out of the electrodes 5. As a result, the expansion portion 7 expands in the z direction and contracts in the x and y directions.

[0045] In this regard, considering the responsiveness to the displacement of electrode 5, it is preferable that the expansion portion 7 be adjacent to electrode 5. Furthermore, by making the electrode 5 annular, an expanded portion 7 can also be formed on the inside of the electrode 5. Furthermore, the expansion portion 7 may involve a change in the volume of the flexible bag 2.

[0046] [1.5. Separator] The separator 8 is a component inserted between the electrodes 5 to suppress short circuits between the electrodes 5 when a voltage is applied to the electrodes 5. Therefore, it is preferable that the separator 8 be made of a material with high insulating properties.

[0047] Here, "inserted between electrodes 5" means (1) The electrodes 5 are arranged in a floating state. (2) The electrode 5 is partially or entirely fixed. (3) The flexible bag 2 is partially or entirely fixed to it. It represents one of the following.

[0048] Furthermore, there is no limit to the number of separators 8, and multiple separators 8 may be inserted between the electrodes 5. For example, the separator 8 can be fixed to the first electrode 5a so as to cover half of the first electrode 5a, and the separator 8 can be fixed to the second electrode 5b so as to cover half of the second electrode 5b, so that when the first electrode 5a and the second electrode 5b are in close proximity, the entire surface of each electrode is protected by the separator 8.

[0049] Examples of materials for separator 8 are shown in Table 2. The relative permittivity of each material is also shown. Note that the relative permittivity is measured at a frequency of 1 kHz. [Table 2] Furthermore, the material of the separator 8 may consist of one of these types, a mixture of two or more types, or a laminate.

[0050] Here, the separator 8 is a film-like structure with its front and back surfaces facing the electrodes 5, and is equipped with through-holes 10 that penetrate in the thickness direction. Furthermore, since the separator 8 is part of the soft actuator, it is preferable that it be flexible. The configuration of the through-hole 10 will be described in detail later.

[0051] Furthermore, the separator 8 exists between the electrodes 5 together with the liquid dielectric 3, forming a capacitor. Therefore, the relative permittivity of the separator 8 is related to the amount of charge induced in the electrodes 5 when a voltage is applied, and is related to the electrostatic stress acting between the electrodes 5. Therefore, in order to increase the amount of charge induced in electrode 5 when voltage is applied and generate sufficient driving force as an actuator, it is preferable that the relative permittivity of separator 8 be 2.0 or higher.

[0052] Furthermore, the liquid dielectric 3 has a wider range of selectable relative permittivity compared to the separator 8. Therefore, it is preferable to adjust the relative permittivity of the dielectric between the electrodes 5 by adjusting the relative permittivity of the liquid dielectric 3.

[0053] [2. Actuator (2)] Figure 2 shows a plan view of the actuator 1 according to the second to ninth embodiments of the present invention. Figure 3 shows a plan view of the actuator 1 according to the tenth to thirteenth embodiments of the present invention. In the diagram, the part labeled "electrode 5" represents the electrode pair where the first electrode 5a and the second electrode 5b overlap in a view in the z direction.

[0054] In the second embodiment shown in Figure 2(a), unlike the first embodiment, the leader wire 5c extends in the y direction. This reduces the area occupied by actuator 1 in the x-direction, thereby increasing the degree of freedom in installation in the x-direction.

[0055] In the third embodiment shown in Figure 2(b), unlike the first embodiment, the leader wire 5c extends to the same side as the leader wire 5d. Note that the leader wires 5c and 5d are not parallel. This reduces the area occupied by actuator 1 in the x-direction, thereby increasing the degree of freedom in installation in the x-direction. Furthermore, since the leader lines 5c and 5d are drawn from the same side of the flexible bag 2, the flexible bag 2 can also be formed by the inflation molding method, increasing the degree of freedom in selecting the flexible bag 2.

[0056] In the fourth embodiment shown in Figure 2(c), the electrode 5 is circular, unlike in the first embodiment. This makes it possible to suppress the generation of discharge between electrode pairs starting from the sharp corners.

[0057] In the fifth embodiment shown in Figure 2(d), unlike the first embodiment, the electrode shape is circular, and the lead wire 5c extends in the y direction. This makes it possible to suppress the generation of discharge between electrode pairs starting from the sharp corners. Furthermore, the area occupied by actuator 1 in the x-direction can be reduced, increasing the degree of freedom in installation in the x-direction.

[0058] In the sixth embodiment shown in Figure 2(e), unlike the first embodiment, the electrode shape is circular, and the leader wire 5c extends to the same side as the leader wire 5d. Note that the leader wires 5c and 5d are not parallel. This makes it possible to suppress the generation of discharge between electrode pairs starting from the sharp corners. Furthermore, the area occupied by actuator 1 in the x-direction can be reduced, increasing the degree of freedom in installation in the x-direction.

[0059] Furthermore, since the leader lines 5c and 5d are drawn from the same side, the flexible bag 2 can also be formed by the inflation molding method, increasing the degree of freedom in selecting the flexible bag 2. Furthermore, because the electrode shape is circular, the positions of the first electrode 5a and the second electrode 5b can be superimposed in the z-direction view regardless of the direction of the lead wire, thereby increasing the electrostatic stress acting between the electrode pair.

[0060] In the seventh embodiment shown in Figure 2(f), unlike the first embodiment, the electrode shape is elliptical, and the area of ​​electrode 5 is larger. This makes it possible to suppress the generation of discharge between electrode pairs starting from the sharp corners. Furthermore, because the electrode area is large, the electrostatic stress acting between the electrode pairs can be increased.

[0061] In the eighth embodiment shown in Figure 2(g), unlike the first embodiment, the electrode shape is elliptical. This makes it possible to suppress the generation of discharge between electrode pairs starting from the sharp corners. Furthermore, even when the flexible bag 2 is long in the axial direction, the electrode area can be increased, and the electrostatic stress acting between the electrode pairs can be increased.

[0062] In the ninth embodiment shown in Figure 2(h), unlike the first embodiment, the electrode shape is circular, the electrode area is small, and the placement position is eccentric. This makes it possible to suppress the generation of discharge between electrode pairs starting from the sharp corners. Furthermore, because the electrode area is small, the electrostatic stress acting between electrode pairs can be reduced, enabling minute movements. Furthermore, by offsetting the placement position, the expansion rate (contraction rate) can be changed depending on the position of the expansion section 7, allowing various expansion rates (contraction rates) to be achieved with a single actuator 1.

[0063] In the tenth embodiment shown in Figure 3(i), unlike the first embodiment, the electrode shape is a square ring. This allows the expansion portion 7 to be formed on the inside of the electrode 5 as well.

[0064] In the 11th embodiment shown in Figure 3(j), unlike the first embodiment, the electrode shape is a circular ring. This makes it possible to suppress the generation of discharge between electrode pairs starting from the sharp corners. Furthermore, an expanded portion 7 can also be formed on the inside of the electrode 5.

[0065] In the twelfth embodiment shown in Figure 3(k), unlike the first embodiment, four pairs of electrodes with a square shape are arranged inside the flexible bag 2. This allows a single actuator 1 to handle various operations; for example, if fine movements are required, current can be supplied to a single electrode pair, and if a large driving force is required, current can be supplied to multiple electrode pairs.

[0066] In the 13th embodiment shown in Figure 3(l), unlike the first embodiment, a first electrode 5a with a square electrode shape and a second electrode 5b that includes the projection of all of the first electrodes 5a are arranged inside the flexible bag 2. This allows for a reduction in the number of components in the actuator 1, for example, by using the second electrode 5b as ground.

[0067] [3. Terms of use] The actuator according to the present invention is The thickness of the separator is d (mm). The lower of the dielectric breakdown fields of the liquid dielectric or separator is denoted as E (kV / mm). If the voltage applied between the electrodes is V (kV), V <d×E It is preferable to use an applied voltage range that satisfies the following relationship. This is to prevent short circuits between electrodes and maintain the electrostatic stress acting between them, thereby ensuring sufficient driving force for the actuator. Furthermore, using the actuator within the above-mentioned applied voltage range prevents damage to the separator and allows for longer-term use of the actuator.

[0068] [4. Characteristics] [4.1. Electrostatic stress] The actuator according to the present invention can be simplified and represented as a parallel plate capacitor model, as shown in Figure 4. Here, ε0: Permittivity of vacuum ε L : Relative permittivity of liquid dielectrics ε S : Relative permittivity of the separator (solid part) D: Electrode spacing d: Thickness of the separator S: Electrode area w: Opening ratio That is the case.

[0069] Here, "opening ratio" refers to the ratio of the total opening area of ​​the through-hole to the area of ​​the separator surface or back surface, assuming that the hole wall of the through-hole is parallel to the thickness direction and the opening diameter of the through-hole does not change in the thickness direction. Therefore, the "opening ratio" of the separator surface and back surface are equal. In this case, the "through-hole occupancy rate," which is the ratio of the total volume of through-holes to the volume of the separator, is equal to the "opening rate."

[0070] On the other hand, when the opening diameter of a through-hole changes in the thickness direction, the "opening ratio" of the front and back surfaces of the separator is usually different. In this case, even if the opening diameter in the thickness direction changes for each through-hole, if the volume of the through-hole does not change, the through-hole occupancy ratio will not change. Therefore, in cases where the opening diameter of the through hole changes in the thickness direction, the "opening ratio" shall be defined as the "through hole occupancy ratio." Note that the volume of the separator includes the through-hole, and the surface area of ​​the separator's front or back surface includes the opening area of ​​the through-hole.

[0071] A simplified actuator according to the present invention can be represented by a parallel plate capacitor model as shown in Figure 4(a). Furthermore, the parallel plate capacitor in Figure 4(a) is equivalent to the parallel plate capacitor in Figure 4(b). Furthermore, the parallel plate capacitor in Figure 4(b) is equivalent to the parallel plate capacitor in Figure 4(c).

[0072] In other words, the parallel plate capacitor shown in Figure 4(a) has a relative permittivity ε L , ε of electrode spacing D L Single-layer capacitor section and relative permittivity ε L , a capacitor section with electrode spacing D-d, and relative permittivity ε S This is equivalent to a capacitor connected in parallel with a series-connected HASEL-type capacitor section with an electrode spacing d.

[0073] Here, the applied voltage between the electrodes is V, ε L The electrostatic stress acting on the single-layer capacitor is F. L, let the electrostatic stress acting on the HASEL type capacitor part be F S Then, the electrostatic stress F acting between the electrodes is the resultant force of F S and F L , so it becomes the value shown in Equation 1.

Equation

[0074] Also, in the single-layer capacitor part, for example, when increasing the relative permittivity ε L of the liquid dielectric, since all the applied voltage acts, F L increases monotonically. In other words, by increasing or decreasing the relative permittivity ε L of the liquid dielectric, F L can be increased or decreased. L That is, in the HASEL type capacitor part, even if the relative permittivity ε of the liquid dielectric is increased, F L does not necessarily increase. That is, in the HASEL type capacitor part, since only a part of the applied voltage acts on the liquid dielectric part, even if ε S is increased, F L may instead decrease. S There may be cases where F

[0075] Note that when the separator does not have through holes as shown in Fig. 5(a), the aperture ratio w is 0, so the electrostatic stress F acting between the electrodes when voltage is applied is the value shown in Equation 2.

Equation

[0076] Also, as shown in Fig. 5(b), when the separator is not arranged between the electrodes, the aperture ratio w is 1 and the thickness d of the separator is 0, so the electrostatic stress F acting between the electrodes when voltage is applied is the value shown in Equation 3.

Equation

[0077] Furthermore, as shown in Figure 5(c), if the separator is a porous material of the bubble type, and the porosity is p and the separator thickness is t, then the effective separator thickness d is equivalent to t × (1 - p), as shown in Figure 5(d). Therefore, the stress F acting between the electrodes when a voltage is applied is the value shown in Equation 4. Furthermore, "porosity" refers to the ratio of the total volume of voids to the volume of the separator.

number

[0078] [4.1.1. Aperture ratio] As shown in Figure 4(c), as the aperture ratio increases, ε L The area of ​​the single-layer capacitor increases. Therefore, ε L With the adjustment of F L The range over which the electrostatic stress F can be adjusted increases, making it easier to adjust the electrostatic stress F. For example, ε L As F increases, L This allows for an increase in the electrostatic stress F, making it easy to increase the electrostatic stress F. To obtain such effects, the aperture ratio is preferably 0.1 or higher. It is preferable that the aperture ratio be 0.2 or higher, and more preferably 0.5 or higher.

[0079] On the other hand, if the opening ratio becomes too high, the rigidity of the separator may decrease. Therefore, it is preferable that the opening ratio be 0.9 or less. It is preferable that the opening ratio be 0.8 or less, and more preferably 0.7 or less.

[0080] [4.1.2. Inclination of through holes] The walls of a through-hole are not necessarily parallel to the thickness direction. In soft actuators, it is preferable for the separator to be flexible, and under normal operating conditions, deformation and displacement over time may cause the hole wall of the through-hole to become misaligned with the thickness direction.

[0081] In this case, by considering a parallel plate capacitor model in which the holes of the through-holes are inclined with respect to the thickness direction, as shown in Figure 6, the electrostatic stress acting between the electrodes can be determined. If the hole wall of the through-hole is inclined with respect to the thickness direction, that is, if the angle between the hole wall of the through-hole and the front and back surfaces of the separator is less than 90 degrees, the area in the thickness direction that is not shielded by the hole wall decreases, and therefore the effective opening ratio is likely to decrease. Therefore, in order to ensure an effective opening ratio, it is preferable that the angle between the hole wall of the through-hole and the front and back surfaces of the separator be 50 degrees or more. Preferably, the angle between the hole wall of the through-hole and the front and back surfaces of the separator be 60 degrees or more, and more preferably 80 degrees or more.

[0082] [4.1.3. Opening ratio of the narrowest part of the through hole] Through holes do not necessarily have a uniform diameter in the thickness direction. Note that the opening diameter of a through hole refers to the diameter of the through hole perpendicular to the thickness direction. In soft actuators, the separator is preferably flexible, and under normal operating conditions, deformation and displacement over time may cause the opening diameter of the through-hole to become uneven in the thickness direction.

[0083] In this case, by considering a parallel plate capacitor model as shown in Figure 7, the relationship between the narrowest aperture ratio and electrostatic stress can be determined. Here, "narrowest opening ratio" refers to the ratio of the total area of ​​the smallest opening perpendicular to the thickness direction of the through-hole to the area of ​​the surface or back surface of the separator.

[0084] First, consider the equivalent capacitor (HASEL type capacitor section and ε) of a capacitor with a separator interposed, as shown in Figure 7(a), where the aperture ratio is w. L Consider a capacitor connected in parallel with a single-layer capacitor section.

[0085] Next, as shown in Figure 7(b), the separator section of the HASEL type capacitor (relative permittivity ε SThe α region, which is part of the (section), is deleted, and a new β region is added to the separator section. Here, by making the volumes of the α region and the β region equal, the opening ratio (through-hole occupancy ratio) can be maintained to be the same as in Figure 7(a). In other words, by creating a portion where the opening diameter widens and a portion where the opening diameter narrows without changing the volume of the through-hole, the smallest possible opening can be formed. In this case, a new parallel plate capacitor will be formed with an aperture ratio (through-hole occupancy ratio) w, a narrowest aperture ratio M, and a β region thickness td, as shown in Figure 7(c).

[0086] Figure 8 shows an example of the separator configuration when the value of t is changed (the thickness of the β region is changed) with an opening ratio (through-hole occupancy rate) of 0.3 and an opening ratio of 0.15 at the narrowest part. Note that the volumes of regions α and β in the figure are identical. Furthermore, the configuration for t=0.25 shown in Figure (c) is equivalent to each of the configurations shown in Figure (g).

[0087] In Figure 7(c), if we consider the capacitor as a parallel capacitor of capacitor sections A, B, and C, the electrostatic stress F acting between the electrodes when a voltage is applied is the value shown in Equation 5.

number

[0088] To ensure an effective aperture ratio, the ratio of the narrowest aperture ratio to the total aperture ratio is preferably 0.1 or higher. The ratio of the narrowest aperture ratio to the total aperture ratio is preferably 0.2 or higher, and more preferably 0.5 or higher.

[0089] [5. Effect] The separator is a film-like structure with its front and back surfaces facing the electrodes, and is equipped with through holes that penetrate in the thickness direction. Therefore, the equivalent circuit of the capacitor formed between the electrodes is the relative permittivity ε between the electrodes. L ε filled only with liquid dielectric L A single-layer capacitor section will appear. More specifically, if the hole wall of the through hole is formed parallel to the thickness direction of the separator, the projection portion of the hole wall onto the electrode consists only of the liquid dielectric. L This is the single-layer capacitor section. In the capacitor equivalent circuit, the ε consists only of this liquid dielectric. L The configuration consists of a single-layer capacitor section and a HASEL-type capacitor section, which is a series connection of a liquid dielectric and a separator, connected in parallel.

[0090] This means that ε L In the single-layer capacitor section, the applied voltage is directly applied, and therefore the relative permittivity ε of the liquid dielectric is... L By adjusting this, the amount of charge induced on the electrodes can also be adjusted accordingly. In other words, the relative permittivity ε of a liquid dielectric is L By increasing or decreasing this value, it becomes possible to create a region where the electrostatic stress acting between the electrodes can be increased or decreased. Therefore, the electrostatic stress acting between the electrodes can be easily adjusted.

[0091] As a result, for example, the relative permittivity ε of a liquid dielectric L By increasing this factor, it becomes possible to easily increase the electrostatic stress acting between the electrodes. Furthermore, since liquid dielectrics have a wider range of selectable relative permittivity compared to separators, it is preferable to adjust the relative permittivity of the liquid dielectric when adjusting the relative permittivity of the dielectric between electrodes. [Examples]

[0092] [1. Check the characteristics] [1.1. Relationship between aperture ratio and electrostatic stress] First, in the parallel plate capacitor model shown in Figure 4, the relative permittivity ε of the liquid dielectric at each aperture ratio is given. L We investigated the electrostatic stress F for [the given material]. The electrostatic stress F was calculated based on Equation 1. The parameters used in deriving the electrostatic stress F are shown in Table 3. Here, the relative permittivity ε of the separator SThe material was assumed to be polypropylene (dielectric constant: 2), and the electrode was assumed to be circular with a diameter of 23 mm. Note that an aperture ratio of 0 corresponds to the configuration shown in Figure 5(a) and Equation 2, while an aperture ratio of 1 corresponds to the configuration shown in Figure 5(b) and Equation 3. The results are shown in Figures 9 and 10.

[0093] [Table 3]

[0094] From the results in Figures 9 and 10, the following was found: (1) As the aperture ratio increases, the relative permittivity ε of the liquid dielectric increases L The increase in electrostatic stress becomes larger in proportion to the increase in [something]. (2) When the aperture ratio is 0.1 or higher, the electrostatic stress is equal to the relative permittivity ε of the liquid dielectric. L It increases monotonically with increasing . (3) When the aperture ratio is 0.05 or less, the relative permittivity ε of the liquid dielectric L If the relative permittivity is 2 or less, then the relative permittivity ε L As the relative permittivity ε increases, the electrostatic stress increases monotonically, but L When it exceeds 2, the relative permittivity ε L Increasing the value actually decreases the electrostatic stress. (4) When the aperture ratio is 0 (all parts are HASEL type capacitor parts), the value of the electrostatic stress acting between the electrodes is extremely low.

[0095] Furthermore, when the aperture ratio is 0.05 or less, the relative permittivity ε of the liquid dielectric is... L Despite the increase, the electrostatic stress is decreasing because of the relative permittivity ε of the liquid dielectric. L This is thought to be due to a decrease in the voltage division of the applied voltage to the liquid dielectric as the amount of liquid dielectric increases.

[0096] [1.2. Relative permittivity ε of the separator S [Relationship between electrostatic stress] Next, in the parallel plate capacitor model shown in Figure 4, the relative permittivity ε of each separator SRelative permittivity ε of a liquid dielectric in L We investigated the electrostatic stress F for [the given material]. The electrostatic stress F was calculated based on Equation 1. The parameters used to derive the electrostatic stress F are shown in Table 4. Here, the relative permittivity ε of the separator S The materials used were assumed to be polypropylene (dielectric constant: 2) and polyvinylidene fluoride (dielectric constant: 10), and the electrodes were assumed to be disc-shaped with a diameter of 23 mm. Furthermore, the aperture ratio w was set to 0.4. The results are shown in Figure 11.

[0097] [Table 4]

[0098] From the results in Figure 11, the following was found: (1) Relative permittivity ε of a liquid dielectric L If they are equal, the relative permittivity ε of the separator S The higher the value, the greater the electrostatic stress.

[0099] [1.3. Relationship between the inclination of through holes and electrostatic stress] Next, in a parallel plate capacitor model where the angle between the hole wall of the through-hole and the front and back surfaces of the separator is 90 degrees or less, as shown in Figure 6, we investigated the change in electrostatic stress F when the inclination angle of the hole wall was changed. The electrostatic stress F was calculated using the μ-Excel electrostatic field software manufactured by Mutec. The parameters used to derive the electrostatic stress F are shown in Table 5. Here, the relative permittivity ε of the separator S This refers to polypropylene (relative permittivity: 2) and the relative permittivity ε of a liquid dielectric. L We assumed that the material was octanitrile (dielectric constant 50) and that the electrode was rectangular in shape, measuring 1 m x 25 mm. Furthermore, the aperture ratio w was set to 0.4. The results are shown in Figure 12.

[0100] [Table 5]

[0101] The results in Figure 12 revealed the following: (1) The less the angle between the hole wall and the front and back surfaces of the separator is less than 90 degrees, the less electrostatic stress is generated. (2) If the angle between the hole wall and the front and back surfaces of the separator is up to 50 degrees, the reduction in electrostatic stress is small.

[0102] Furthermore, the reason why electrostatic stress decreases as the angle between the hole wall and the front and back surfaces of the separator decreases is thought to be because the area in the thickness direction that is not shielded by the hole wall decreases, thus reducing the effective opening ratio.

[0103] [1.4. Relationship between the narrowest opening ratio of through holes and electrostatic stress] Next, in the parallel plate capacitor model shown in Figure 7(c), we investigated the relationship between the narrowest opening ratio M of the through-hole and the electrostatic stress F. The electrostatic stress F was calculated based on Equation 5. The parameters used to derive the electrostatic stress F are shown in Table 6. Here, the relative permittivity ε of the separator S This assumes polypropylene (relative permittivity 2) and the relative permittivity ε of the liquid dielectric. L We assumed the material to be octanitrile (dielectric constant 50) and the electrode to be circular with a diameter of 23 mm. Furthermore, the aperture ratio w was set to 0.3. The results are shown in Figure 13.

[0104] [Table 6]

[0105] The results in Figure 13 revealed the following: (1) The smaller the ratio of the narrowest opening, the less electrostatic stress acts between the electrodes. (2) As the value of t increases (as the thickness of the β region increases), the electrostatic stress acting between the electrodes decreases. (3) When considering an aperture ratio of 0.3 and an aperture ratio of 0.15 at the narrowest point, the electrostatic stress acting between the electrodes decreases as the value of t increases, but it never falls below the electrostatic stress at an aperture ratio w of 0.15 (F=1.425N). (4) Even the minimum electrostatic stress (F=0.36N at t=0.95) when the aperture ratio is 0.3 and the narrowest aperture ratio is 0.03 is greater than the electrostatic stress (F=0.05N) when the aperture ratio is 0.

[0106] Furthermore, the reason why the electrostatic stress acting between electrodes decreases as the narrowest aperture ratio decreases is thought to be because the area in the thickness direction that is not shielded by the hole wall decreases, thus reducing the effective aperture ratio.

[0107] [2. Electrostatic stress measurement] (Samples 1-4) To verify the aforementioned simulation results, we measured the stress generated between electrodes using various separators.

[0108] Sample 1 is a porous separator made of polytetrafluoroethylene (H050A293D (manufactured by ADVANTEC)), and a cross-sectional SEM image is shown in Figure 13(a). Sample 2 is a porous separator made of polyimide (TAPM-CL10 (manufactured by Tokyo Ohka Kogyo)), and a cross-sectional SEM image is shown in Figure 13(b). Sample 3 is a separator made of polyimide with through-holes formed therein. A cross-sectional SEM image is shown in Figure 13(c), and a planar microscope image is shown in Figure 13(d). Sample 4 is a separator made of polypropylene.

[0109] Stress was measured for samples 1 to 4 using the stress measuring device shown in Figure 14. The measurements were performed by filling the space between 25 mmφ electrode pairs (200 μm) with octanitrile or silicone as a liquid dielectric, and inserting the separators for samples 1-4. The measurement results are shown in Table 7. The properties of samples 1-4 are also shown. Note that the porosity in sample 3 is equal to the aperture ratio.

[0110] [Table 7]

[0111] From the results in Table 7, the following was found: (1) The electrostatic stress acting between the electrodes of sample 4, where the entire region is a HASEL type capacitor, is low. (2) In sample 4, where the entire region is a HASEL-type capacitor, the electrostatic stress acting between the electrodes becomes extremely low as the relative permittivity of the liquid dielectric increases. (3) In sample 3, which is a separator with through holes, the electrostatic stress acting between the electrodes depends on the relative permittivity of the liquid dielectric. In other words, the electrostatic stress acting between the electrodes can be adjusted by the relative permittivity of the liquid dielectric. (4) In sample 3, which is a separator with through holes formed therein, the electrostatic stress acting between the electrodes is high when the relative permittivity of the liquid dielectric is high.

[0112] Furthermore, as can be seen in Figure 13(c), in sample 3, the through-holes are approximately parallel to the thickness direction, and the opening diameter is approximately constant. Also, as can be seen in Figure 13(d), the opening ratio is high, and the configuration further enhances the effect of the through-holes, as shown in the simulation results mentioned earlier.

[0113] (Example 1, Comparative Example 1) [3. Fabrication of the actuator] The method for manufacturing the actuator will be explained with reference to Figure 16. First, as shown in Figure 16(a), an adhesive was applied to the back surface of the Al thin film (thickness: 11 μm). Here, the composition of the adhesive is: Adhesive: Unistol (registered trademark) XP01B (manufactured by Mitsui Chemicals, Inc.) Hardener: HD-02A Catalyst: DBU (diazabicycloundecene) That's what I decided. Then, after applying the adhesive, it was dried at 100°C for 1 minute.

[0114] Next, as shown in Figure 16(b), an electrode-forming structure was cut out from the Al thin film. The electrodes were 25mm x 25mm squares, and the electrode lead wires were 10mm x 45mm rectangular.

[0115] Next, as shown in Figure 16(c), an electrode-formed material was attached to a biaxially oriented polypropylene sheet (OPP sheet, heat-cut T-type (manufactured by Fukusuke Kogyo)), and the sheet was passed through a laminator to produce an OPP sheet with electrodes.

[0116] Next, as shown in Figure 16(d), adhesive was applied so as to straddle the electrode lead wires of the electrode-attached OPP sheet. The adhesive application area was 10 mm away from the electrode end, with a width of 10 mm and a length of 30 mm. Then, after applying the adhesive, it was dried at 100°C for 1 minute.

[0117] Next, as shown in Figure 16(e), two OPP sheets with adhesive-coated electrodes were placed on top of each other with a separator in between, and the three sides of the separator were heat-sealed to create an open bag. After heat sealing, the open bags were left to stand at 60°C for 3 days.

[0118] Next, as shown in Figure 17(f), liquid dielectric was injected through the opening of the open bag, and the opening was sealed with a heat seal. Then, by cutting off the unnecessary parts as shown in Figure 17(g), the actuator shown in Figure 17(h) was fabricated.

[0119] Note that the only difference between Example 1 and Comparative Example 1 is the separator configuration. Comparative Example 1 uses a porous separator made of polyimide, while Example 1 uses a through-hole separator made of polyimide. For Comparative Example 1, the separator used was from the same lot as Sample 2, and for Example 1, the separator used was from the same lot as Sample 3.

[0120] [4. Test Method] [4.1. Driving Voltage] The drive voltage was investigated for Example 1 and Comparative Example 1. The results are shown in Table 8. The properties of the separator are also shown.

[0121] [Table 8]

[0122] From the results in Table 8, the following was found: (1) Example 1 has a low drive voltage. This is thought to be due to the fact that the through-holes are approximately parallel to the thickness direction, the opening diameter is approximately constant, the opening ratio is high, and the relative permittivity of the liquid dielectric is also high, resulting in an increase in electrostatic stress acting between the electrodes. Although not shown in Table 8, for separators where the entire region is a HASEL-type capacitor section, the drive voltage was approximately 5kV.

[0123] Although embodiments of the present invention have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Industrial applicability]

[0124] The actuator according to the present invention can be used in soft actuators (artificial muscles), etc.

Claims

1. An insulating flexible bag forming the housing, A liquid dielectric is filled inside the flexible bag, Multiple electrodes are arranged on the inner surface of the flexible bag, and their separation distance changes according to the applied voltage, When the distance between the electrodes decreases, the liquid dielectric present between the electrodes flows into an expansion portion, causing its volume to expand. A separator interposed between the electrodes Equipped with, The separator is a film-like material with its front and back surfaces facing the electrodes, and is provided with through holes that penetrate in the thickness direction. Actuator. However, the term "liquid dielectric" refers to a material that is liquid at room temperature ("25°C") and has a relative permittivity greater than that of air.

2. The actuator according to claim 1, wherein the through-hole occupancy rate is 0.1 or more and 0.9 or less.

3. The thickness of the separator is d (mm), The lower of the dielectric breakdown fields of the liquid dielectric or the separator is defined as E (kV / mm). When the voltage applied between the movable electrodes is V (kV), V < d × E The actuator according to claim 1, used in an applied voltage range that satisfies the relationship.

4. The actuator according to claim 1, wherein the inclination angle of the hole wall of the through hole is 50° or more with respect to the front and back surfaces.

5. The actuator according to claim 1, wherein the ratio of the narrowest opening ratio to the through-hole occupancy ratio is 0.1 or more. However, the "narrowest opening ratio" refers to the ratio of the total area of ​​the smallest openings perpendicular to the thickness direction of the through-hole to the area of ​​the surface or back surface of the separator.

6. The actuator according to claim 1, wherein the relative permittivity of the separator is 2.0 or greater.

7. The actuator according to claim 1, wherein the relative permittivity of the liquid dielectric is 1.5 or more.

8. The actuator according to claim 7, wherein the relative permittivity of the liquid dielectric is 2.0 or more.

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