Gel actuator and gel used therein

A gel actuator includes: a gel having a projected part made of an inductive high-polymer material; a positive electrode disposed so as to be in contact with a top of the projected part; and a negative electrode disposed in a position sandwiching the projected part in a height direction in cooperation with the positive electrode. When voltage is applied between the positive and negative electrodes, creep deformation occurs so that the projected parts adhere to the positive electrode side, and the gel contracts in the thickness direction.

BACKGROUND

1. Technical Field

The present invention relates to a gel actuator and a gel used for the same.

2. Related Art

Since a gel made of polyvinyl chloride (PVC) has an action that it is deformed when an electric field is applied, an actuator using the behavior is proposed.

FIGS. 11A and 11Billustrate a bending action of a flexible gel actuator.FIG. 11Aillustrates a state where a positive electrode6aand a negative electrode6bare disposed on both sides of a gel5formed in a flat plate shape so that one end side of the gel5extends from the electrode ends.FIG. 11Billustrates a state where voltage is applied between the positive electrode6aand the negative electrode6b.

When voltage is applied between the positive electrode6aand the negative electrode6b, electric charges are injected from the negative electrode6binto the gel5, the electric charges moved to the positive electrode6aside are accumulated in the positive electrode6aand a portion near the positive electrode6abefore being discharged, and the action of making the gel5electrostatically adhered near the positive electrode6ais made.

Deformation of the gel5is not simple bending but is induced by creep deformation and is deformation that the gel5is concentrated at the end portion of the positive electrode6a. When the electric field is eliminated, the electric charges are discharged, the action that the gel5is adhered to the positive electrode6ais lost, and the gel5returns to the original state by its intrinsic elasticity (FIG. 11A). Since the bending deformation occurs accompanying the application of voltage and the cancellation of the application of voltage, an actuator can be formed by using the deformation action.

FIGS. 12A and 12Billustrate an action when a mesh-state electrode is used as a positive electrode7aand voltage is applied between a negative electrode7bdisposed on the under face of the gel5and the positive electrode7a.FIG. 12Bis a state where voltage is applied. When voltage is applied, the gel5enters gaps in the mesh of the positive electrode7aby creep deformation. Since the gel5enters the gaps, the gel actuator becomes thinner as a whole. When the application of the voltage is stopped, the gel5returns to the original state. By performing the application of the voltage between the positive electrode7aand the negative electrode7band cancellation of the application as described above, the action that the gel actuator expands and contracts as a whole in the thickness direction is made. Consequently, the actuator can be constructed by using the expansion/contraction action.

PRIOR ART DOCUMENT

Patent Document

SUMMARY

The actuator having the mesh-shaped positive electrode has advantages such that a required displacement amount (stroke) can be obtained by employing a structure that an electrode and a gel are alternately stacked, a relatively large pressure force (action force) can be obtained, and periodical driving of a few Hz to tens of Hz can be performed.

However, the mesh-shaped positive electrode is provided also to assure the space in which the gel enters so that space has to be assured by using a line having a certain thickness. Consequently, there are a problem that the device becomes heavy and a problem that rigidity becomes higher and flexibility is disturbed.

The present invention is achieved to solve the problems and an object of the invention is to provide a gel which can contract in the thickness direction without using a mesh-shaped electrode as a positive electrode and a gel actuator using the gel.

A gel actuator according to the present invention includes: a gel having a projected part made of an inductive high-polymer material; a positive electrode disposed so as to be in contact with a top of the projected part; and a negative electrode disposed in a position sandwiching the projected part in a height direction in cooperation with the positive electrode. By applying voltage between the positive electrode and the negative electrode, creep deformation occurs in the projected part made of the inductive high-polymer material so that the material is adhered to the negative electrode side, and the interval between the positive and negative electrodes is reduced. When the application of voltage between the positive and negative electrodes is cancelled, the projected parts return to the original state by the elasticity of the inductive high-polymer material itself.

The gel actuator can be constructed as a gel actuator of a layer-stack type formed by stacking a plurality of the gel actuators in a layout of electrically insulating the positive electrode and the negative electrode between layers.

The gel actuator can be constructed in such a manner that the gel has the projected part formed on one of faces of a sheet part made of an inductive high-polymer material, and the negative electrode is disposed on a face opposite to the face provided with the projected part of the sheet part.

The gel actuator can be easily assembled as a layer-stack-type gel actuator, in which the gel is formed as a gel with a negative electrode in which the projected part is formed on one of faces of a sheet part made of an inductive high-polymer material and the negative electrode is embedded in the sheet part, or the gel is formed as a gel with a negative electrode in which the projected part is formed on both faces of a sheet part made of an inductive high-polymer material and the negative electrode is embedded in the sheet part.

The projected part may be provided directly on the negative electrode or the positive electrode, and the other electrode to be paired is disposed while sandwiching the projected part.

As a gel used for the gel actuator, a gel with a negative electrode having a configuration that the projected part is formed on one of faces of a sheet part made of an inductive high-polymer material, and the negative electrode is embedded in the sheet part, or a configuration that the projected part is formed on both faces of a sheet part made of an inductive high-polymer material, and the negative electrode is embedded in the sheet part is effectively used.

The gel actuator and the gel of the present invention perform the action of contraction (expansion/contraction) in the thickness direction by application of voltage between the positive and negative electrodes and cancellation of the application by using the creep deformation of the gel without using the mesh-shaped electrode, and an actuator can be constructed by using the action. Since the contraction action is performed by deformation of the gel itself, the size and weight of the device can be reduced.

EXPLANATIONS OF LETTERS OR NUMERALS

DETAILED DESCRIPTION

Configuration Example of Gel

A gel actuator according to the present invention is constructed by sandwiching a gel in a thickness direction by a positive electrode and a negative electrode and using an action that the gel contracts in the thickness direction when voltage is applied between the positive electrode and the negative electrode. The gel for use in the gel actuator of the present invention is formed in a flat plate shape having a number of projected parts formed in its surface. The positive electrode is disposed so as to be in contact with the top of the projected part formed in the surface of the gel, and the negative electrode is disposed on a face on the side opposite to the surface provided with the projected parts.

FIGS. 1A to 1Cillustrate an example of a gel10for use in a gel actuator according to the present invention.

In the gel10illustrated inFIG. 1A, a number of projected parts10aare formed on one of faces of a sheet part10bas a base part of the gel. The projected parts10aare formed so as to have the same height at equal intervals on the sheet part10b. The projected part10ain the gel10illustrated in the diagram is formed in a cylindrical object whose top part has a hemisphere shape. The shape of the projected part10amay be set to an arbitrary shape such as a cone, a frustum, a pyramid, a truncated pyramid, a spherical shape, or a hemispherical shape. The height, width (diameter), and disposition intervals (disposition density) of the projected parts10aare not also limited. The thickness, size, and the like of the sheet part10bcan be also properly set, and the plane shape of the sheet part10bcan be also set as an arbitrary shape such as a circular shape, an annular shape, a quadrangle shape, or a hexagonal shape.

FIG. 1Billustrates an example of a so-called gel with a negative electrode, in which a negative electrode20is embedded in advance in the sheet part10bsupporting the projected parts10a. In the case of constructing a gel actuator using the gel11with the negative electrode, it is sufficient to dispose the positive electrode so as to be in contact with the top of the projected parts10aon the side where the projected parts10aare provided in the gel11and apply voltage between the positive electrode and the negative electrode.

To construct a gel actuator by using the gel10illustrated inFIG. 1A, the positive electrode is disposed so as to be in contact with the top of the projected parts10a, and the negative electrode is made in contact with the face on the side opposite to the side of the sheet part10bwhere the projected parts10aare provided. When the gel11with the negative electrode illustrated inFIG. 1Bis used, a layer-stack-type gel actuator can be formed more easily as compared with the gel10illustrated in FIG1A.

The negative electrode20is provided in an entire plane region in which the projected parts10aare provided by using a conductive material such as metal foil. Since the negative electrode20makes an electric field acted on the projected parts10a, the material and thickness are not particularly limited. In place of metal foil, a conductive layer may be provided by a method such as vapor deposition to form the negative electrode20. Although the negative electrode20is usually provided on an entire face of the sheet part10b, the invention does not exclude a change such that a small hole is formed in the negative electrode20to control the electric field acted on the projected parts10a.

FIG. 1Cillustrates another example of the gel with the negative electrode, which is a gel12provided with the projected parts10aon both faces of the sheet part10b. With a shape in which the negative electrode20is embedded in the sheet part10band the projected parts10aare formed on both faces of the sheet part10b, at the time of making the electric field acted on the projected parts10aon both faces, the negative electrode20can be used as a common negative electrode20.

Also by the gel12with the negative electrode illustrated inFIG. 1C, it is easy to form a gel actuator in a layer stack type, and there is an advantage that an electrode for making the electric field acted on the gel12can be commonly used between the layers.

Method of Manufacturing Gel

As a gel for use in a gel actuator, an inductive high-polymer material in which a bending deformation and/or creep deformation occurs when an electric field is acted can be used. As such an inductive high-polymer material, polyvinyl chloride (PVC), polymethylmethacrylate, polyurethane, polystyrene, polyvinyl acetate, nylon 6, polyvinyl alcohol, polycarbonate, polyethylene terephthalate, polyacrylonitrile, or the like is used.

In the embodiment, polyvinyl chloride (PVC) is used as the material of a gel used for a gel actuator. Polyvinyl chloride has advantages such that a deformation amount by the action of an electric field is large, durability is high, and it is easy to handle.

In practice, dibutyl adipate (DBA) is added as a plasticizer to PVC, and the resultant is completely dissolved in tetrahydrofuran (THF) as a solvent to form a gel solution. The gel solution is casted on a petri dish. The petri dish is disposed horizontally. The gel solution is covered with a forming die and left for a few days to make THF completely evaporated and dried. After that, the gel is detached from the forming die, thereby obtaining a gel provided with projected parts.

FIG. 2illustrates a forming die15used for forming the gel used in an experiment. The forming die15has a flat-face recessed part15bfor forming the sheet part10bin one of faces of a base material15ahaving a flat plate shape, and has recessed parts15cfor forming projected parts in an under face of the flat-face recessed part15b. When the forming die15is put on the gel solution casted on the petri dish (the forming die15inFIG. 2faces downward), the gel solution enters the flat-face recessed part15band the recessed parts15cfor forming the projected parts. In this state, the gel solution is turned into a gel. In such a manner, a gel having the projected parts10ais formed.

The forming die15has air holes15dcommunicating the top part of the recessed part15cfor forming a projection (a part corresponding to the top of a projected part) and the outside. The air holes15dare provided so that, when the forming die15is put on the gel solution, air escapes from the recessed parts15cfor forming projected parts, the top part of the recessed part15cfor forming a projected part is reliably filled with the gel solution, and the projected parts10aare formed in the predetermined shape.

With the forming die15illustrated inFIG. 2, the recessed part15cfor forming a projected part is formed in a cone shape, the depth (height of the projected part) of the recessed part15cfor forming a projected part is 0.8 mm, diameter is 2 mm, and a pitch (interval between top parts of the projected parts) is 3 mm. The diameter of the air hole15dis 0.3 mm. The depth of the flat-face recessed part15b(thickness of the sheet part10b) is 1 mm.

As the forming die used to form a gel, a forming die of a proper shape can be used in accordance with the size and shape of a projected part formed in the gel. For example, by using a mesh-shaped die in place of forming a recessed part for forming a projected part, projected parts may be formed in the gel. By applying the gel solution by a printing method such as screen printing, projected parts can be formed.

For an experiment of the characteristic of a gel actuator which will be described later, the gel11with the negative electrode illustrated inFIG. 1Bwas used.

The gel11with the negative electrode was formed as follows. 10 g of a PVC gel solution was casted on a petri dish and left for a few days so as to be dried (to form a sheet part on the lower side of the negative electrode). Subsequently, stainless steel foil (having a thickness of 0.01 mm) as the negative electrode was put on the dried gel, and 4 g of the gel solution was casted on the stainless steel foil to fix the stainless steel foil. Subsequently, 20 g of the gel solution was casted on the gel thinly remained on the surface of the stainless steel foil, the forming die15illustrated inFIG. 2was put on the gel solution, and the gel solution was dried. The gel was taken from the forming die15to form the gel11in which the negative electrode20is embedded.

FIGS. 3A and 3Billustrate a gel actuator40constructed by disposing a positive electrode30for the gel11with the negative electrode illustrated inFIG. 1Band the action when voltage is applied to the gel actuator40.

To contract the gel11in the thickness direction, the positive electrode is made in contact with the top of the projected part10a, and voltage is applied between the positive electrode and the negative electrode.FIG. 3Aillustrates a state where the positive electrode30is disposed on the face provided with the projected parts10aof the gel11, and the positive electrode30is made in contact with the projected parts10a. In reality, the stainless steel foil as the positive electrode30was disposed on a glass plate, and the gel11was put on the stainless steel foil while the projected parts10awere turned downward to make the stainless steel foil (positive electrode30) come into contact with the top of each of the projected parts10a.

FIG. 3Aillustrates a state where no voltage is applied between the positive electrode30and the negative electrode20, andFIG. 3Billustrates a state where voltage is applied between the positive electrode30and the negative electrode20. When voltage is applied between the positive electrode30and the negative electrode20, electric charges are injected from the negative electrode20into the gel11and the electric charges passing through the projected parts10aare accumulated near the positive electrode30. When the electric charges are accumulated near the positive electrode30, the gel is electrostatically attracted to the positive electrode30side, and creep deformation occurs in the projected parts10aso that the projected parts10aare adhered to the positive electrode30. That is, when voltage is applied, the height of the projected parts10adecreases, and the thickness of the gel actuator40decreases as a whole (contraction occurs). When the application of voltage is cancelled, the electric charges disappear by the discharge, the action that the projected parts10aare adhered to the positive electrode30is lost, and the gel actuator40returns to the original state by the elasticity of the gel itself.

In such a manner, by repeating the operation of applying the voltage between the positive electrode30and the negative electrode20of the gel actuator40and cancelling the application of the voltage, the gel actuator40alternately enters a state where it contracts in the thickness direction and a state where it returns to the original thickness.

FIGS. 3A and 3Billustrate the action (operation) when voltage is applied between the positive electrode30and the negative electrode20in the gel actuator40using the gel11with the negative electrode illustrated inFIG. 1B. Also with respect to the gels10and12illustrated inFIGS. 1A and 1B, by making the voltage acted between the positive electrode30and the negative electrode20, a gel actuator which similarly operates can be constructed.

In the gel actuator constructed by using the gel having the projected parts10a, when voltage is applied between the positive electrode30and the negative electrode20, creep deformation occurs in the projected parts10aand the projected parts10acontract by using the action that the projected parts10aare adhered to the negative electrode20side. Consequently, a gel in any form can be used as long as it can perform the action. For example, as the form of the gel with the negative electrode, the present invention is not limited to the form that the negative electrode20is embedded in the sheet part10bbut may employ a form that the negative electrode20is provided on one of faces of the sheet part10bso as to be exposed and the projected parts10amade of gel are provided directly on the negative electrode20. The invention may also employ a configuration that the projected parts10amade of gel are provided directly on the negative electrode20or the positive electrode30without providing the sheet part10band the electrodes are a pair which are disposed while sandwiching the projected parts10a.

Driving Characteristic of Gel Actuator

Hereinafter, a result of examining the drive characteristic of the gel actuator40(single-layer structure) using the gel11with the negative electrode illustrated inFIGS. 3A and 3Bwill be described.

Displacement Characteristic

FIG. 4illustrates a result of measuring how a displacement amount in the thickness direction changes when voltage is applied to the gel actuator. The measurement result relates to the case where the application voltage was 1200V. The displacement amount of the gel actuator was measured by using a laser displacement measuring device. It is understood that the gel actuator contracts when the voltage is applied and returns to the original thickness when the voltage application is cancelled.

FIG. 5illustrates displacement amounts when application voltage was set to 600V, 1200V, and 1800V for the same sample as that used in the experiment ofFIG. 4.

The measurement result indicates that the displacement amount increases as the application voltage increases. The displacement amount of the gel actuator when the application voltage is set to 1800V is 0.17 mm at the maximum, The displacement amount corresponds to about 14% of the thickness of the entire gel actuator.

Generation Force

A pushing force (generation force) which is generated when the gel actuator returns from the contraction state to the original state was measured. The measurement was made by a method of eliminating voltage from a state where the gel actuator contracts due to application of voltage to make the gel actuator expand and measuring the pushing force at the time of expansion by a force sensor.

A sample of the gel actuator has a circular disc shape having a size of 50 mm, thickness of a gel (including the projected parts) is 1.15 mm, and stainless steel foil having a thickness of 0.01 mm was used as the positive electrode.

FIG. 6illustrates a result of measuring a pushing force (generation force) when the application voltage was 1200V. As the pushing force, about 350 Pa was obtained.

FIG. 7illustrates a result of examining how the pushing force changes by the application voltage.FIG. 7illustrates that as the application voltage increases, the pushing force increases.

Response Characteristic

A sine wave of voltage 900V was applied to the gel actuator using the gel with the negative electrode illustrated inFIG. 3and a response characteristic of the gel actuator was measured. While changing the frequency of the sine wave voltage applied from 0.1 Hz to 10 Hz, the amplitude of the displacement at that time was measured.FIG. 8is a gain chart of the displacement. The bandwidth is 2 Hz until the gain becomes −3 dB. The measurement result indicates that the above-described gel actuator sufficiently follows when the frequency of the application voltage is about 2 Hz.

Another Configuration Example of Gel Actuator

The gel actuator used in the above-described experiment is of the single-layer structure formed by a single gel. The gel actuator can be used as a single-layer structure or a stacked-layer structure in which gel actuators each as a unit are stacked in the thickness direction.

FIGS. 9A and 9Billustrate an example of constructing a gel actuator50of a layer stack type using the gel11(FIG. 1B) with the negative electrode and having the projected parts10aon one face. The gel actuator50is formed by setting the projected parts10aof gels to be stacked in the same direction and stacking the gels11each with the negative electrode while the positive electrode30is interposed so that the positive electrode30comes into contact with the top of each of the projected parts10a.

The positive electrodes30of gel actuators40aand40bas units constructing the gel actuator50are connected to the positive electrode of a power supply, the negative electrodes20are connected to the negative electrode of the power supply, and voltage is applied.

FIG. 9Billustrates a state where the voltage is applied. When voltage is applied to the gel actuator50, each of the gel actuators40aand40bcontracts in the thickness direction, and the gel actuator50as a whole contracts in the thickness direction. Since the contraction amounts of the gel actuators40aand40bare cumulated, the contraction amount (deformation amount) of the gel actuator50of a layer stack type can be made larger than that in the case of using a single gel actuator.

FIGS. 10A and 10Billustrate an example of a gel actuator60formed by using the gel12with the negative electrode and having the projected parts10aon both faces of a gel illustrated inFIG. 1C. Also in the gel actuator60of the embodiment, the gels12are stacked while the positive electrode30is interposed between the projected parts10aof the gels12stacked so that the positive electrode30comes into contact with the top of each of the projected parts10a.

In the gel actuator60of the embodiment, when voltage is applied, the negative electrode20acts as an electrode common to the projected parts10aon its both sides and the positive electrode30acts as an electrode common to the projected parts10aon its both sides.

FIG. 10Billustrates a state where voltage is applied to the gel actuator60. The gel actuators40cand40das units contract in the thickness direction, and the gel actuator60as a whole contracts in the thickness direction.

The gel actuator60of the embodiment uses the gel with the negative electrode and having the projected parts10aon both faces of the gel. Consequently, as compared with the case of using the gel with the negative electrode and having the projected parts10aon its one face, a large displacement amount can be obtained while reducing the size in the thickness direction.

Although the gel actuator50illustrated inFIG. 9is an example of stacking two gels11as units and the gel actuator60illustrated inFIG. 10is an example of stacking two gels12as units, an arbitrary number can be selected for gels stacked in the gel actuator. By increasing the number of gels as units stacked in the gel actuator, the displacement amount of the entire gel actuator can be increased. By setting a gel actuator of a layer-stack structure, the generation force (pushing force) accompanying the displacement of the gel actuator can be also increased.

In the gel actuator50illustrated inFIGS. 9A and 9B, the sheet part10balso has an action of electrically insulating the positive electrode30and the negative electrode20at the time of stacking the gels11between the layers. At the time of forming the layer-stack-type gel actuator by stacking gels having the projected parts10a, electric insulation has to be provided between the layers so that the positive electrode30and the negative electrode20are not electrically short-circuited. A gel may be used as an insulating layer like the gel11or a configuration of stacking gels while providing a specific insulating layer may be employed.

The gel actuator according to the present invention has the layout that a gel having the projected parts is sandwiched between a positive electrode and a negative electrode in the thickness direction and uses an action that the projected parts are deformed when voltage is applied between the positive electrode and the negative electrode. Consequently, a thin conductive material such as metal foil can be used as each of the positive and negative electrodes. Thus, the electrode can be made thinner as compared with the case of using a mesh electrode. Also in the case of stacking a number of gel actuators, the size (thickness) and weight can be reduced. Since a gel is very flexible and an electrode is also thinly formed and flexible, they can be used effectively as components for driving which are requested to have flexibility.