JP2015122935A - Actuator element and actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an actuator element capable of increasing recovery stress while reducing an applied voltage.SOLUTION: An actuator element 5 includes: a dielectric layer 10; and a pair of electrodes 12, 14 disposed by sandwiching the dielectric layer 10 in a thickness direction. The dielectric layer 10 is composed of a gelatinous dielectric substance that is creep-deformed when a voltage is applied to the electrodes 12, 14. A surface on a side in contact with at least the positive electrode 12 out of the pair of electrodes 12, 14 is a dielectric layer formed on an uneven surface that absorbs the creep deformation. The surface shrinks in a thickness direction when a voltage is applied between the electrodes 12, 14, and recovers to an original thickness when the applied voltage is released.

Description

  The present invention relates to an actuator element using a dielectric layer having a dielectric layer in which the surface on the side in contact with an anode is an uneven surface, and an actuator using the same.

  In recent years, next-generation actuators using polymer materials have attracted attention. For example, a conductive polymer that is excellent in expansion and contraction force and generated force but low in response, and a dielectric elastomer that is excellent in generated force and response but requires a high applied voltage. Compared with these, the PVC gel actuator developed by the inventor of the present application is flexible and rich in elasticity, and can be driven to contract in the atmosphere (Non-patent Document 1). It has excellent characteristics such as a shrinkage of 25% at an applied voltage of 100 V and a recovery stress of 24.4 kPa / cm (Non-patent Document 2).

  The PVC gel can be obtained by mixing polyvinyl chloride (PVC) and a plasticizer dibutyl adipate (DBA) in a solvent tetrahydrofuran (THF), and casting the mixture into a petri dish. As shown in FIG. 15, the PVC gel undergoes creep deformation near the anode when a voltage is applied. A PVC gel actuator is constructed by using this property and having a structure in which a gel is sandwiched between a mesh-like anode and a foil-like cathode.

  FIG. 16 shows the most basic structure of a gel actuator, in which a mesh electrode (anode) is sandwiched between gel sheets, and foil electrodes (cathodes) are provided on the outer surfaces of both gel sheets. In this gel actuator, when a voltage is applied between the anode and the cathode, the gel is drawn into the space of the mesh and contracts in the thickness direction as a whole. It works to return to the original thickness. When the actuator shown in FIG. 16 is stacked in the thickness direction, the displacement amount and recovery stress of the actuator can be increased.

JP 2009-273204 A JP2012-130201A JP 2012-161221 A

Misaki Yamano, Naoki Ogawa, Satoshi Hashimoto, Midori Takasaki, Toshihiro Hirai: “Structure and Drive Characteristics of Contraction Type PVC Gel Actuator”, Journal of the Robotics Society of Japan, Vol.27 No.7 pp718-24,2009 Satoshi Hayasaka, Siryu Ryu, Yukinari Tsuchiya, Satoshi Hashimoto: “Development of high-performance PVC gel actuator by thinning”, 18th Robotics Symposia Proceedings, 4A4, pp361-366,2013

Regarding gel actuators using PVC gel, various improvements have been studied, such as improving the shrinkage rate and recovery stress of gel actuators by reducing the thickness of the gel, and accurately controlling displacement by feedback control. . For this gel actuator, in order to improve the safety in use, it is required to further reduce the applied voltage and further increase the generated force assuming application to a robotic suit or the like.
An object of the present invention is to provide an actuator element and an actuator having a novel configuration that can reduce applied voltage and increase recovery stress.

An actuator element according to the present invention includes a dielectric layer and a pair of electrodes arranged with the dielectric layer sandwiched in the thickness direction, and the dielectric layer applies a voltage between the electrodes. The dielectric layer is formed of a gel-like dielectric material that creep-deforms, and at least the surface in contact with the anode of the pair of electrodes is an uneven surface that absorbs the creep deformation, and a voltage is applied between the electrodes. When applied, the film shrinks in the thickness direction, and when the voltage application is canceled, the original thickness is restored.
As the dielectric layer, for example, a dielectric layer (hereinafter sometimes referred to as gel nonwoven fabric) formed in a three-dimensional net structure can be used by utilizing an electrospinning method. In the dielectric layer, when a voltage is applied between the electrodes, the gel-like dielectric deformed by the creep phenomenon is drawn (absorbed) into the concave portion of the dielectric layer, thereby contracting in the thickness direction as a whole. When the voltage is removed, the dielectric layer returns to its original state due to the elasticity of the gel.

  The gel nonwoven fabric produced by electrospinning has a fine net shape in which fibers are folded. The thickness of this gel nonwoven fabric, the diameter of a fiber, the porosity, etc. can be selected suitably. By using a gel nonwoven fabric by an electrospinning method, it is easy to reduce the thickness as compared with a gel sheet conventionally used as a dielectric layer, and mass production of the dielectric layer is also easy. In addition, since the dielectric layer can be made thin, it can be formed compactly even in the case of a laminated structure, and as a result, the applied voltage can be reduced, and the contraction rate compared to conventional actuator elements. It is possible to improve the recovery stress (generated force).

In the actuator element, the dielectric layers and the electrodes are alternately stacked in the thickness direction, so that the contraction amount (displacement amount) when the voltage application is turned on and off can be increased, The recovery stress when the voltage is OFF can be increased.
Both of the pair of electrodes can be configured as foil-shaped electrodes, and one of the electrodes can be a mesh-shaped electrode.
The dielectric layer can be appropriately formed from a dielectric material. However, a gel nonwoven fabric containing polyvinyl chloride as a polymer component is easy to manufacture and can be used as a dielectric layer that produces suitable creep deformation. It is useful because it works.

  The actuator according to the present invention includes a dielectric layer and a pair of electrodes arranged with the dielectric layer sandwiched in the thickness direction, and the dielectric layer applies a voltage between the electrodes. An actuator element comprising a gel-like dielectric that creep-deforms, and at least a surface in contact with the anode of the pair of electrodes is a dielectric layer formed on an uneven surface that absorbs the creep deformation, and the electrode Voltage applying means for applying a voltage by ON-OFF control, and contracts in the thickness direction when a voltage is applied between the electrodes, and the original thickness when the voltage is released. It is characterized by returning to.

As described above, a dielectric layer (gel nonwoven fabric) that forms a three-dimensional net structure can be used as the dielectric layer by using, for example, an electrospinning method. The actuator includes an actuator element in which the dielectric layers and electrodes are alternately stacked in a thickness direction, and the pair of electrodes includes an actuator element formed of a foil-shaped electrode. One of the pair of electrodes includes an actuator element formed of a mesh electrode.
Further, the dielectric layer includes an actuator element made of a gel nonwoven fabric containing polyvinyl chloride as a polymer component.

According to the actuator element and the actuator according to the present invention, an actuator element including a dielectric layer and a pair of electrodes arranged with the dielectric layer sandwiched in the thickness direction, the dielectric layer being an electrode By using an actuator element that is made of a gel-like dielectric that undergoes creep deformation when a voltage is applied between them, and the surface on the side in contact with the anode is a dielectric layer formed on an uneven surface that absorbs creep deformation, In this way, the mesh-like electrode (anode) is sandwiched from both sides by a gel sheet, and the thickness can be reduced compared to the case where a foil-like electrode (cathode) is provided on the outer surface of both gel sheets. Can be reduced, the contraction rate of the actuator element can be improved, and the recovery stress can be increased.
Further, by using a gel nonwoven fabric by electrospinning for the dielectric layer, it is possible to easily mass-produce the dielectric layer.

It is explanatory drawing which shows the structure of an actuator element and an actuator. It is explanatory drawing which shows the structure of a laminated actuator element and an actuator. It is a SEM image of the surface side of a gel nonwoven fabric. It is explanatory drawing which shows the sample preparation method from a gel nonwoven fabric. It is explanatory drawing which shows the state which attached the lead wire to the gel nonwoven fabric sample. It is explanatory drawing which shows the unit structure of an actuator. It is a graph which shows the response characteristic of an actuator. It is a graph which shows the displacement amount of an actuator. It is a graph which shows the displacement amount of an actuator. It is a graph which shows the displacement amount of an actuator. It is a graph which shows the contraction rate of an actuator. It is a graph which shows the recovery stress of an actuator. It is a graph which shows the recovery stress of an actuator. It is a graph which shows the recovery stress of an actuator. It is explanatory drawing which shows a mode that a dielectric material layer carries out creep deformation. It is explanatory drawing which shows the structure of the conventional actuator element.

[Configuration of actuator]
FIG. 1 shows a basic configuration of an actuator according to the present embodiment. The actuator according to the present embodiment includes actuator element 5 using a gel nonwoven fabric as a dielectric layer, and voltage applying means 8 for applying a voltage to the dielectric layer of actuator element 5.

The actuator element 5 has a basic configuration in which the gel nonwoven fabric 10 is sandwiched between an anode (Anode) 12 and a cathode (Cathode) 14 in the thickness direction. The gel nonwoven fabric 10 functions as a dielectric layer, and is formed of a gel-like dielectric material that creep-deforms when a voltage is applied, for example, gel-like polyvinyl chloride (PVC).
The voltage applying means 8 applies ON / OFF control between the anode 12 and the cathode 14 of the actuator element 5 and applies a voltage applied between the DC power source and the anode 12 and the cathode 14. And means for switching on and off (switching means).

The actuator element according to the present embodiment is greatly different from the conventional gel actuator in that a gel nonwoven fabric is used instead of a gel sheet used as a dielectric layer sandwiched between an anode and a cathode.
The gel sheet is formed of a material that creep-deforms when a voltage is applied. Similarly to the gel sheet, the gel non-woven fabric is formed of a gel-like dielectric that creeps when a voltage is applied. Materials having the property of creep deformation when a voltage is applied include polyvinyl chloride (PVC), polymethyl methacrylate, polyurethane, polystyrene, polyvinyl acetate, nylon 6, polyvinyl alcohol, polycarbonate, polyethylene terephthalate, polyacrylonitrile, Examples include silicone rubber.

A gel nonwoven fabric can be produced by an electrospinning method using a dielectric material. When a solution in which a material having a creep deformation action such as PVC is dissolved is used as the anode side and a high voltage is applied between the anode and the cathode plate, the polymer is moved toward the cathode plate from the nozzle on the anode side by the electrostatic force. The gel nonwoven fabric is formed on the cathode plate by spraying. According to the electrospinning method, the fiber-like polymer sprayed from the nozzle of the spinneret toward the cathode plate is bound one after another so as to be folded on the cathode plate, so the gel nonwoven fabric is a three-dimensional net structure. (Non-woven fabric) (FIGS. 3A and 3B).
The diameter of the fiber constituting the gel nonwoven fabric and the thickness of the nonwoven fabric can be appropriately set depending on the spinning conditions of electrospinning. The gel nonwoven fabric used for the actuator is cut out from a nonwoven fabric produced by electrospinning into an appropriate shape and size according to the intended use.
Although the gel nonwoven fabric does not have to be prepared by the electrospinning method, the surface side in contact with the anode may be formed as an uneven surface that absorbs the gel-like dielectric deformed by the creep phenomenon.

1A shows a state in which the voltage application between the anode 12 and the cathode 14 of the actuator element 5 is released, and FIG. 1B shows a state in which a voltage is applied between the anode 12 and the cathode 14. . When a voltage is applied between the anode 12 and the cathode 14, as shown in the figure, the thickness of the gel nonwoven fabric 10 that is a dielectric layer becomes thinner than before the voltage application (Δh). That is, it acts to contract in the thickness direction by applying a voltage.
The action of contracting the dielectric layer made of the gel nonwoven fabric 10 in the thickness direction by applying a voltage is similar to the action of the conventional gel actuator, and the voltage is applied between the anode 12 and the cathode 14 so that the gel nonwoven fabric is This is because 10 is creep-deformed.

  In a conventional actuator element using a gel sheet, a mesh electrode is used for the anode. However, in the actuator element of this embodiment, a mesh electrode may be used for the anode 12 or a simple foil. A shaped electrode may be used. Since the gel nonwoven fabric 10 has gaps between the fibers, even when a foil-like electrode is used, it can be easily creep-deformed when a voltage is applied, and the deformation penetrates into the gaps between the fibers, resulting in a thickness increase. It can easily shrink in the vertical direction. As will be described later, an actuator is actually constructed using a gel nonwoven fabric, and the action of contracting in the thickness direction by applying a voltage is confirmed.

FIG. 2 is an example of an actuator using a laminated actuator element 6 in which gel nonwoven fabrics and electrodes as dielectric layers are alternately laminated in the thickness direction. In the laminated actuator element 6, the electrodes laminated with the gel nonwoven fabric 10 are the anode 12 and the cathode 14 alternately. The illustrated example is an example in which the gel nonwoven fabric 10 has five layers. The number of stacked actuator elements 6 can be set as appropriate.
The anode 12 and the cathode 14 are connected to a power source in common, and are wired so that the voltage between the anode 12 and the cathode 14 is turned on and off in common when the power is turned on and off.

  2A shows the case where the voltage applied between the anode 12 and the cathode 14 of the actuator element 6 is OFF, and FIG. 2B shows the voltage between the anode 12 and the cathode 14 of the actuator element 6. Applied (ON) state. By applying a voltage, each of the laminated gel nonwoven fabrics 10 contracts in the thickness direction, and the actuator element 6 as a whole contracts in the thickness direction (ΔH). By superimposing the shrinkage amount of each gel nonwoven fabric 10, the shrinkage amount becomes larger than that of the actuator element composed of a single layer, and the recovery stress is also increased.

  Since the actuator element according to the present embodiment uses a gel non-woven fabric as the dielectric layer, it can be easily reduced in thickness as compared with the gel sheet used in the conventional actuator element. Even in the case of an actuator element, the thickness can be effectively reduced. Moreover, the shrinkage | contraction rate and recovery stress of an actuator element can be increased by using a gel nonwoven fabric.

As described above, the gel nonwoven fabric can be easily produced by an electrospinning method or the like, and can be easily mass-produced.
Further, when a gel nonwoven fabric is used as the dielectric layer, a foil-like electrode can be used, so that it is easy to form an actuator element having a laminated structure.
As a method of forming an actuator having a laminated structure, it is possible to use a method of alternately laminating separately formed gel nonwoven fabrics and conductive foils, or to form a conductive layer to be an electrode by a film forming method such as plating or sputtering. By using the forming method, a structure in which gel nonwoven fabrics and conductive layers are alternately laminated can be used.
Moreover, it is possible to produce the gel nonwoven fabric which has electroconductivity by mixing an electroconductive substance with the preparation solution of a fiber. By using a gel nonwoven fabric layer having conductivity as a conductive layer and alternately laminating with a gel nonwoven fabric serving as a dielectric layer, a multilayer actuator element can be easily produced.

[Making PVC gel nonwoven fabric]
First, PVC, dibutyl adipate (DBA: plasticizer), and tetrahydrofuran (THF: solvent) were mixed to prepare a PVC gel solution. In this example, the weight ratio of PVC: DBA: THF was 1: 2: 9 and 1: 2: 11.5. In the following, the actuator fabricated using the former is called THF9, and the latter is called THF11.5.
A gel non-woven fabric was prepared using an electrospinning device (MECC, NANON-02) from a PVC gel solution. The environmental conditions were a temperature of 22-25 degrees and a humidity of 14%. The spinning conditions were an applied voltage of 10 kV, a solution delivery rate of 1 mL / h, and a needle-collector distance of 12 cm. When spinning, a plate-type collector was used, and spinning was performed by placing an aluminum foil on the collector. The aluminum foil has a glossy surface on the top. As a result, some adhesion was observed. The diameter of THF9 gel fiber is 1.78μm (Fig. 3 (A)), and THF11.5 is 1.04μm (Fig. 3 (B)). A gel nonwoven fabric consisting of body was obtained.

Spinning times were 1.0 h, 1.5 h, and 2.0 h, and nonwoven fabrics with thicknesses of 30 μm, 45 μm, and 60 μm were produced. After spinning, the aluminum foil was left in a thermostatic bath for about 2 days, and then the gel nonwoven fabric was punched out together with the aluminum foil using a φ15 punch (FIG. 4). Also, only aluminum foil was punched with a punch, and lead wires were bonded to each using a conductive adhesive (FIG. 5).
From the above, a total of 6 types of PVC gel nonwoven fabric samples with 2 types of fiber diameters and 3 types of thickness were prepared. The actuator weight was 9.32 mg when the nonwoven fabric thickness (d) of THF9 was 30 μm, and 8.51 mg for THF11.5 (Table 1).

[Measuring method]
[Measurement of displacement]
The displacement measurement system consists of a high-voltage amplifier (MATSUSADA, HOPS-1.5B2-L2) for applying an electric field, and an interface board (JUSTWARE) for outputting signals from a displacement sensor (KEYENCE, LK-G30) and a PC. , JIF-171-1). The voltage was increased by 20 V every 10 s and continuously applied to 100 V, and the displacement at that time was measured using a laser displacement meter.

[Calculation method of shrinkage]
FIG. 6 shows a unit structure of the actuator. The shrinkage rate is obtained based on the amount of displacement. The method is to multiply the displacement (D) divided by the actuator height (h) by 100. The height of the actuator is a value obtained by adding half of the thickness (d) of the gel non-woven fabric and the thickness of the anode and cathode (c).

[Measurement of recovery stress]
The system for measuring the recovery stress (generated force) consists of an insulation resistance tester (KIKUSUI, TOS201), a load cell (KYOWA, LMA-A-5N), which is a power source for applying voltage, and a voltage signal obtained from the sensor on a PC It consists of an AD converter (CONTEC, AI-1608AY) and a PC.
In this embodiment, the recovery stress refers to a force that causes the actuator during voltage application to return to the original height when the voltage is removed. The recovery stress is measured by applying a voltage to the actuator for about 10 s, bringing the load cell closer to the actuator, applying a certain load (initial load), and removing the voltage applied to the PVC gel actuator.

[Measure response time]
The response time is calculated using a displacement measurement system. Here, the response time is defined as the time required for the actuator to move from 10% to 90% of the displacement (FIG. 7).

[Measurement result]
[Displacement]
From the results, except for THF9 (d = 30μm), the displacement of the actuator increased in proportion to take the maximum value when the applied voltage was 80V, and then decreased (Figs. 8-10). In the graph, 20V, 40V, 60V, 80V, 100V from the left).
Looking at the influence of the nonwoven fabric thickness, it was found that both THF9 and THF11.5 have a large displacement when the nonwoven fabric thickness is 45 μm (FIG. 9). At this time, it was found that at an applied voltage of 80 V, THF9 showed a maximum displacement of 11.7 μm and THF11.5 showed 11.1 μm.
As for the fiber diameter of the gel nonwoven fabric, when the thickness of the nonwoven fabric was 45 μm and 60 μm, THF9 tended to show a larger displacement. On the other hand, when the nonwoven fabric thickness was 30 μm, it was found that THF11.5 showed a larger displacement.

[Shrinkage factor]
As with the displacement, the shrinkage rate tended to increase proportionally up to an applied voltage of 80 V (FIG. 11). When the thickness of the nonwoven fabric was 30 μm, THF11.5 tended to show a higher shrinkage at the same applied voltage.
On the other hand, when the thickness of the nonwoven fabric was 45 μm and 60 μm, THF9 tended to show a higher shrinkage rate.
The maximum displacement was 21.4% for THF9 and 21.6% for THF11.5 when the nonwoven fabric thickness was 45μm at an applied voltage of 80V. When the thickness of both THF9 and THF11.5 was 45 μm or less, the shrinkage rate exceeded 10% at an applied voltage of 60 V. It was found that a higher shrinkage rate was obtained at a lower voltage than the PVC gel actuator.

[Recovery stress]
The recovery stress also tended to increase in proportion to the applied voltage (FIGS. 12 to 14: 20V, 40V, 60V, 80V, 100V from the left side in each graph). When the thickness of the nonwoven fabric was 30 μm and 45 μm, the recovery stress was greater for THF 11.5, and when it was 60 μm, the recovery stress was greater for THF 9.
On the other hand, the recovery stress was also maximized when the nonwoven fabric thickness was 45 μm, as was the displacement and shrinkage.
The maximum recovery stress value was 92 Pa at an applied voltage of 100 V when THF was 11.5.

[Response time The response time was measured using a non-woven fabric having a thickness of 45 μm in which a recovery stress tended to increase. As a result of examining the response time when the applied voltage was 80 V and 100 V, it was found that the higher the applied voltage, the faster the response time for both THF9 and THF11.5 (Table 2).
However, there was little change in response time due to the difference in fiber diameter.

As described above, in this example, it was found that the PVC gel nonwoven fabric actuator has a tendency that the displacement amount and the contraction rate increase proportionally when the applied voltage is 80 V and the maximum value is obtained. This is considered to be due to the difference in how to apply the applied voltage when measuring the displacement amount and the contraction rate. In this example, when measuring the displacement amount and the contraction rate, the applied voltage was continuously applied up to 100 V within a predetermined time. Therefore, it is considered that when the voltage was removed, the actuator applied the voltage again without returning to the original height.
On the other hand, the recovery stress, which is supposed to increase in proportion to the shrinkage, tends to increase almost in proportion to the applied voltage of 00V. This may be because the voltage application method at the time of measuring the displacement amount and the contraction rate is different.

  In the future, it will be necessary to unify the voltage application method and measure each characteristic value. Table 3 compares the results of this example with the characteristics of a conventional PVC gel actuator.

The characteristics of the conventional PVC gel actuator were 14% shrinkage at an applied voltage of 80V, whereas the PVC gel nonwoven fabric actuator showed a shrinkage of 21.4% at an applied voltage of 80V.
In addition, in FIG. 11, since the shrinkage rate was 14.8% when the applied voltage was 60 V, it can be said that the PVC gel nonwoven fabric actuator can be driven at a low voltage.

In this example, a PVC gel nonwoven fabric actuator was produced and the characteristics were evaluated. It was found that the PVC gel nonwoven fabric actuator has the characteristics that the displacement, shrinkage, and recovery stress increase with increasing applied voltage. In this example, it was found that the nonwoven fabric actuator had relatively good shrinkage and recovery stress characteristics when the thickness of the nonwoven fabric was 45 μm.
The non-woven actuator weighs about one-tenth of the conventional weight, and is very lightweight. The shrinkage rate was 14.8% at an applied voltage of 60 V, enabling driving at a lower voltage than before, and improving the characteristics. It can be said that it was possible.

5, 6 Actuator element 8 Voltage application means 10 Nanofiber nonwoven fabric 12 Anode 14 Cathode

Claims (14)

A dielectric layer, and a pair of electrodes arranged with the dielectric layer sandwiched in the thickness direction,
The dielectric layer is made of a gel-like dielectric that creep-deforms when a voltage is applied between the electrodes, and at least the surface of the pair of electrodes that contacts the anode absorbs the creep deformation. A dielectric layer formed on
An actuator element characterized by contracting in the thickness direction when a voltage is applied between the electrodes, and returning to the original thickness when the voltage application is canceled.   2. The actuator element according to claim 1, wherein the dielectric layer forms a three-dimensional net structure.   3. The actuator element according to claim 2, wherein the dielectric layer is formed in a net structure by electrospinning.   The actuator element according to any one of claims 1 to 3, wherein the dielectric layers and electrodes are alternately stacked in a thickness direction.   The actuator element according to claim 1, wherein the pair of electrodes are both foil-shaped electrodes.   The actuator element according to any one of claims 1 to 4, wherein the anode is a mesh electrode among the pair of electrodes.   The actuator element according to any one of claims 1 to 6, wherein the dielectric layer is made of polyvinyl chloride. A dielectric layer and a pair of electrodes arranged with the dielectric layer sandwiched in the thickness direction, and the dielectric layer is made of a gel-like dielectric material that undergoes creep deformation when a voltage is applied between the electrodes. An actuator element in which at least a surface in contact with the anode of the pair of electrodes is a dielectric layer formed on an uneven surface that absorbs the creep deformation;
A voltage applying means for applying a voltage ON-OFF control between the electrodes;
An actuator that contracts in the thickness direction when a voltage is applied between the electrodes and returns to the original thickness when the voltage application is canceled.   The actuator according to claim 8, wherein the dielectric layer includes an actuator element forming a three-dimensional net structure.   The actuator according to claim 9, wherein the dielectric layer includes an actuator element formed in a net structure by electrospinning.   The actuator according to any one of claims 8 to 10, further comprising an actuator element in which the dielectric layers and electrodes are alternately stacked in a thickness direction.   The actuator according to any one of claims 8 to 11, wherein the pair of electrodes includes an actuator element made of a foil electrode.   The actuator according to any one of claims 8 to 11, wherein, of the pair of electrodes, the anode includes an actuator element including a mesh electrode.   The actuator according to claim 8, wherein the dielectric layer includes an actuator element made of polyvinyl chloride.