Actuator, actuator apparatus, and method of driving actuator

An actuator converts the pressure of a fluid into a change in the length of the actuator and is formed such that an elastic tube is spirally wound. The tube is wound around the axis of the actuator. One or more grooves are spirally formed on the outer surface of the tube along the axial center of the tube. When the fluid contained in the inside of the tube is pressurized, a torsional force is applied to the tube along the spirals of the one or more grooves and causes the actuator to contract in the axial direction. Even when an external force acts in a direction in which the actuator is bent, the volume of the inside of the tube is not substantially varied. Accordingly, the actuator can be allowed to freely move in a bending direction.

BACKGROUND

1. Technical Field

The present disclosure relates to an actuator, an actuator apparatus, and a method of driving the actuator.

2. Description of the Related Art

There is a growing need for machines that work close to humans such as domestic robots. Accordingly, expectations for artificial muscle actuators, which have characteristics of being light and being flexible such as in the case of muscle of humans, are growing. There are many different types of actuators called artificial muscle actuators. Many of these actuators use deformation of a rubber-like elastic material, which is likely to match the characteristics of being light and being flexible.

A McKibben-type actuator, which extends or contracts due to the pressure of a fluid, is known as one of the actuators that use the deformation of a rubber-like elastic material (see, for example, Japanese Unexamined Patent Application Publication No. 59-197605).

The McKibben-type actuator disclosed in Japanese Unexamined Patent Application Publication No. 59-197605 is formed of a rubber tube reinforced by a braided structure, and is caused to extend and contract in a manner in which the inside of the rubber tube is pressurized by the fluid, and expansion of the actuator in the radial direction is converted into contraction of the actuator in the axial direction while angles of braids are varied like a pantograph.

SUMMARY

However, free movement of the McKibben-type actuator in a bending direction is obstructed when the inside of the rubber tube is pressurized, although the McKibben-type actuator extends or contracts in the axial direction by increasing or decreasing the pressure of the fluid in the inside.

One non-limiting and exemplary embodiment provides an actuator that can extend and contract and allows free movement thereof in a bending direction.

In one general aspect, the techniques disclosed here feature an actuator including a hollow tube. The tube has a space therein which is located along a longitudinal axis of the tube. The tube is folded so as to have a coil shape. The tube has one or more grooves formed on an outer surface of the tube and/or an inner surface of the tube. The one or more grooves extend so as to be twisted along the longitudinal axis of the tube.

According to the present disclosure, the actuator can extend and contract and allows free movement thereof in a bending direction.

DETAILED DESCRIPTION

The present inventor uncovered the following problem in the McKibben-type actuator described in the description of the related art.

The McKibben-type actuator is formed of a rubber tube and has inherent flexibility in a bending direction. As the internal pressure of the rubber tube increases, the flexibility decreases and stiffness with respect to bending increases. Bending stiffness is increased presumably because when the actuator is bent, the volume of an interior space of the rubber tube is varied. In order to bend the actuator, it is necessary to compress a fluid in the interior space and to deform the rubber tube in response to a compressive force of the fluid. As the pressure in the interior space increases, a force required for the bend increases.

Such a property is advantageous in, for example, an action of holding a body by using bending stiffness but causes a problem, for example, when the actuator is installed on assisting wear in the form of clothes. More specifically, in the case where the actuator is installed so as to be bent along the shape of a human body part such as an arm or a leg, a force in an axial direction of the actuator and a force in a direction in which the bend of the actuator along the shape of the human body part is canceled are produced when the fluid is pressurized to cause the actuator to extend or contract. Accordingly, the installed actuator provides assistance with a force in the axial direction but obstructs free movement thereof in a bending direction.

To address such a problem, an actuator according to an aspect of the present disclosure includes a hollow tube. The tube has a space therein which is located along a longitudinal axis of the tube. The tube is folded so as to have a coil shape. The tube has one or more grooves formed on the outer surface of the tube and/or the inner surface of the tube. The one or more grooves extend so as to be twisted along the longitudinal axis of the tube.

With this structure, when a hollow portion of the tube contains a fluid and a pressure thereof is varied, the tube is elastically deformed outward or inward and is twisted along the spirals of the one or more grooves of the tube. The occurrence of the twist enables the actuator having a spirally wound shape to extend and contract. When an external force is applied to the actuator in a direction in which the actuator is bent, a portion whose volume is increased is created in the inside of the tube due to the twist of the tube in a given direction and a portion whose volume is decreased is created in the inside of the tube due to the twist of the tube in the opposite direction. Accordingly, variations in the total volume of the inside of the tube can be made small, and the actuator can be readily bent.

For example, the tube may include a cylindrical first elastic member and a cylindrical second elastic member that is disposed inside or outside the first elastic member and that is more flexible than the first elastic member, and the one or more grooves may be each formed of a through-hole extending from the inner surface of the first elastic member to the outer surface of the first elastic member and a surface of the second elastic member that closes the through-hole.

With this structure, the first elastic member having the through-hole is readily twisted and the tube can accordingly be reliably twisted. This enables the actuator to reliably extend and contract and enables the actuator to be readily bent.

For example, the first elastic member may include one or more spiral bone portions located between the grooves that are adjacent to each other in a circumferential direction of the first elastic member, and the thicknesses of the one or more bone portions may be lower than the widths of the one or more bone portions.

With this structure, when the hollow portion of the tube contains a fluid and a pressure thereof is varied, the first elastic member is readily deformed outward or inward and hence the tube is readily twisted. Accordingly, the actuator readily extends and contracts and is readily bent.

For example, spiral pitches of the one or more grooves may be larger than the length of an outer circumference of the first elastic member.

With this structure, the outward or inward deformation of the first elastic member is readily converted into the twist of the tube and the actuator readily extends and contracts.

For example, the first elastic member may be disposed outside the second elastic member, and ridges formed of the inner surface of the first elastic member and side surfaces of the one or more grooves may be chamfered.

This structure can mitigate stress concentration on the ridges formed of the inner surface of the first elastic member and the side surfaces of the one or more grooves when the first elastic member and the second elastic member are elastically deformed outward or inward. This enables the actuator to smoothly extend and contract and to be smoothly bent. In addition, the durability of the actuator can be improved.

For example, the depths of the one or more grooves may be larger than or equal to half of the thickness of the tube.

With this structure, one or more thick portions of the tube that are located at the bottom of the one or more grooves have decreased thicknesses and are readily deformed, the tube is readily elastically deformed outward or inward, and hence the tube is readily twisted. Accordingly, the actuator readily extends and contracts and is readily bent.

For example, the spiral pitches of the one or more grooves may be larger than the length of an outer circumference of the tube.

With this structure, the outward or inward deformation of the tube is readily converted into the twist of the tube and the actuator readily extends and contracts.

For example, the one or more grooves may be a plurality of grooves.

In the case where the one or more grooves are a plurality of grooves, the spiral pitches of spiral grooves can be increased compared with the case of one groove. This enables the outward or inward deformation of the tube to be readily converted into the twist of the tube and enables the actuator to readily extend and contract.

For example, the widths of the one or more grooves may be constant.

With this structure, a load applied to the tube can be balanced. Accordingly, the actuator can smoothly extend and contract and can be smoothly bent. In addition, the durability of the actuator can be improved.

To address the above problem, an actuator according to another aspect of the present disclosure includes a hollow tube. The tube has a space therein which is located along a longitudinal axis of the tube. The tube is folded so as to have a coil shape. The tube includes a cylindrical first elastic member and a second elastic member that is more flexible than the first elastic member. The first elastic member has a through-hole extending from the inner surface of the first elastic member to the outer surface of the first elastic member. The through-hole extends so as to be twisted along the longitudinal axis of the tube. The second elastic member is disposed in the through-hole.

With this structure, when a hollow portion of the tube contains a fluid and a pressure thereof is varied, the tube is elastically deformed outward or inward and is twisted along the spiral of the through-hole of the first elastic member. The occurrence of the twist enables the actuator having a spirally wound shape to extend and contract. When an external force is applied to the actuator in a direction in which the actuator is bent, a portion whose volume is increased is created in the inside of the tube due to the twist of the tube in a given direction and a portion whose volume is decreased is created in the inside of the tube due to the twist of the tube in the opposite direction. Accordingly, variations in the total volume of the inside of the tube can be made small, and the actuator can be readily bent. In addition, the thickness of the tube can be reduced, and the actuator can be downsized.

An actuator apparatus according to another aspect of the present disclosure includes an actuator, and a pressure source. The actuator includes a hollow tube that is elastic. The tube has a space therein which is located along a longitudinal axis of the tube. The tube is folded so as to have a coil shape. The tube has one or more grooves formed on the outer surface of the tube and/or the inner surface of the tube. The one or more grooves extend so as to be twisted along the longitudinal axis of the tube. The pressure source (a1) causes the actuator to contract by increasing the pressure of the inside of the tube and (a2) causes the actuator to extend by decreasing the pressure of the inside of the tube.

The pressure source may increase a pressure of the actuator by injecting a medium into the inside of the tube in the (a1) and decrease the pressure of the actuator by discharging the medium from the inside of the tube in the (a2).

To address the above problem, a method of driving an actuator according to the present disclosure includes (b1) preparing an actuator. The actuator includes a hollow tube that is elastic. The tube has a space therein which is located along a longitudinal axis of the tube. The tube is folded so as to have a coil shape. The tube has one or more grooves formed on the outer surface of the tube and/or the inner surface of the tube. The one or more grooves extend so as to be twisted along the longitudinal axis of the tube. The method includes (b2) causing the actuator to contract by increasing a pressure of a medium inside the tube.

With this feature, the actuator can reliably contract.

Moreover, (b3) the actuator may be caused to extend by decreasing the pressure of the medium inside the tube.

With this feature, the actuator can reliably extend.

To address the above problem, an actuator apparatus according to another aspect of the present disclosure includes a tube that is elastic and spirally wound and that has one or more grooves spirally formed on the outer surface of the tube and/or the inner surface of the tube. The central axes of the spirals of the one or more grooves are identical to a longitudinal axis of the tube. The inside of the tube contains a fluid. The actuator apparatus includes a pressure source that increases or decreases a pressure caused by the fluid, thereby increasing or decreasing a longitudinal length of the tube.

With this structure, the actuator can be readily bent by an external force while being caused to extend and contract.

It should be noted that general or specific aspects may be implemented as a system, a method, or any selective combination thereof.

The embodiments will be described below with reference to the drawings.

The embodiments described below are general or specific embodiments. Numerical values, shapes, materials, components, the arrangement and connection configuration of the components, steps, the order of the steps, and so on described in the following embodiments are examples and do not limit the present disclosure. Among the components in the following embodiments, components that are not recited in any one of independent claims showing the most generic concept are described as arbitrary components.

First Embodiment

The whole structure of an actuator apparatus1will be first described with reference toFIG. 1. The actuator apparatus1illustrated inFIG. 1includes an actuator2, a pressure source3, and a pipe4. The actuator apparatus1converts the pressure of the pressure source3into a change in the length of the actuator2.

The actuator2includes a hollow tube10. The tube10has a space therein which is formed in the longitudinal direction of the tube10. The tube10is spirally wound. In other words, the tube10is folded so as to have a coil shape. An example of the coil shape is a cylindrical shape. The inside of the tube10contains a medium. An example of the medium is a fluid, which includes liquid and gas. An example of the liquid is water. An example of the gas is air. An upper part of the actuator2is secured to a fixture not illustrated. The upper end of the actuator2is connected to the pipe4. The lower end of the actuator2is sealed by, for example, caulking. The structure of the actuator2will be described later in detail.

The pressure source3increases or decreases the pressure of the inside of the tube10of the actuator2by increasing or decreasing a fluid inside the tube10of the actuator2via the pipe4, thereby causing the actuator2to extend or contract.

An example of the pressure source3is a pump. Specific examples of the pump include a syringe pump (reciprocating pump). An exemplary syringe pump includes a cylindrical syringe, a movable plunger, and a controller that controls the position of the plunger. The syringe and the plunger act like an injector. The inside of the syringe is pressurized by the plunger and the fluid is delivered from the interior space of the syringe. The inside of the syringe is depressurized by the plunger and the fluid is collected. The syringe pump is operated to adjust (change) the amount of the fluid contained in the inside of the tube10of the actuator2so that the pressure of the inside of the tube10can be adjusted.

The phrase “to adjust (change) the amount of the fluid contained in the inside of the tube10” may be understood to be “to adjust (change) the density per unit volume of the fluid contained in the inside of the tube10”. “To increase the pressure of the fluid” may be “to increase the amount per unit volume of the fluid”. “To decrease the pressure of the fluid” may be “to decrease the amount per unit volume of the fluid”.

The pipe4is a tubular member that connects the pressure source3to the actuator2and is a channel through which the fluid flows into and out. In the case where the actuator2is directly connected to the pressure source3, the actuator apparatus1may not include the pipe4. The pipe4with a branch pipe may connect the pressure source3to a plurality of the actuators2.

The actuator2according to the embodiment will now be described.

FIG. 2is a partial view of the tube10of the actuator2.FIG. 3is a cross-sectional view of the tube10of the actuator2.

The actuator2is formed such that the hollow tube10that is elastic is spirally wound. The tube10is wound around the longitudinal axis A1of the actuator2. Grooves c are spirally formed on the outer surface10bof the tube10such that the central axes of the grooves are the axial center A2of the tube10. In other words, the grooves c extend so as to be twisted along the circumference of the longitudinal axis of the tube10. In the embodiment, the tube10is spirally wound clockwise with respect to the axis A1, and the grooves c are spirally wound clockwise with respect to the axial center A2. That is, the direction in which the tube10is spirally wound is matched to the direction in which the grooves c are spirally wound.

As illustrated inFIG. 3, the tube10includes a cylindrical first elastic member11, and a cylindrical (tubular) second elastic member12that is more flexible than the first elastic member11. The second elastic member12is hollow. A hollow portion of the second elastic member12(inside an inner surface12a) contains a fluid5.

The first elastic member11has through-holes11cextending from the inner surface11aof the first elastic member11to the outer surface11bof the first elastic member11. The second elastic member12is disposed inside the first elastic member11so as to be in contact with the first elastic member11and closes the through-holes11c. Accordingly, the grooves c are formed of side surfaces of the through-holes11cof the first elastic member11and a surface (outer surface12b) of the second elastic member12. It is to be noted that the first elastic member11and the second elastic member12do not adhere to each other.

The first elastic member11includes bone portions b located between the grooves c that are adjacent to each other in the circumferential direction of the first elastic member11. The bone portions b each have an arc shape in section and are disposed so as to be spaced apart from each other in the circumferential direction. The bone portions b are four bone portions b and are spirally wound around the axial center A2so that four grooves c are spirally formed.

The first elastic member11is disposed outside the second elastic member12. Ridges formed of the inner surface11aof the first elastic member11and the side surfaces of the grooves c (through-holes11c) are chamfered. Although the ridges are formed so as to be rounded in the embodiment, the ridges may be tapered.

A member that is more flexible than the first elastic member11is used as the second elastic member12as described above. Examples of the member that is flexible include a soft member as a material, a structurally soft member such as a deformable member that is formed, for example, so as to be thin or so as to be corrugated.

In the embodiment, nylon is used as the material of the first elastic member11, and silicon rubber is used as the material of the second elastic member12. The materials, however, are not limited to these materials, and various resin materials or metallic materials may be used. The first and second elastic members11and12are appropriately selected in consideration of required pressure resistance, flexibility, or resistance against the fluid5(chemical resistance, solvent resistance, and oil resistance), and so on. For example, the use of a resin material for the first and second elastic members11and12enables the actuator2to be lightweight. The use of an engineering plastic material or a metallic material, which has high stiffness, enables the actuator2to be operated at a high pressure and a low flow rate and enables a loss due to the flow of the fluid5to be reduced.

The pipe4of the actuator apparatus1has a pressure resistance higher than the pressure resistance of the first and second elastic members11and12for the purpose of an improvement in responsiveness in operation of the actuator2.

FIG. 4is a view of the tube10of the actuator2when the tube10is straightened.FIG. 5is a longitudinal sectional view of the tube10illustrated inFIG. 4.

As illustrated inFIG. 4andFIG. 5, the tube10has a multi-groove structure, specifically, the four grooves c (c1, c2, c3, and c4) and the four bone portions b (b1, b2, b3, and b4). The grooves c1, c2, c3, and c4are parallel to one another and have constant widths. The distance between the adjacent grooves c (for example, the distance between the groove c1and the groove c2) is appropriately designed in accordance with the number of the grooves c. The bone portions b1, b2, b3, and b4are parallel to one another and have constant widths wb. The thicknesses tb of the bone portions b are smaller than the widths wb of the bone portions b.

The grooves c are formed such that inclinations θ with respect to the axial center A2of the tube10are less than 45° when a pressure applied by the fluid is equal to 0. The diameter d of the tube10is 4 mm. The spiral pitches p2of the grooves c are 14.4 mm. The spiral pitches p2of the grooves c are set to be larger than the length πd of the outer circumference of the tube10(length of the outer circumference of the first elastic member11in the embodiment) in a manner in which the inclinations θ of the grooves c are set to be less than 45°.

An outline of a method of driving the actuator2will be next described.

FIG. 6is a flow chart illustrating a method of driving the actuator2.FIG. 8AandFIG. 8Bare schematic views of the actuator2illustrating extension and contraction of the actuator2. InFIG. 8AandFIG. 8B, illustration of the grooves c is omitted.

The method of driving the actuator includes a step (a) of preparing the actuator apparatus1, and a step (b) of increasing and/or decreasing the length of the actuator2in the longitudinal direction (direction of the axis A1).

After the actuator apparatus1is prepared and before the fluid5inside the tube10is pressurized, as illustrated inFIG. 8A, the actuator2is in a steady state (S1inFIG. 6). The steady state is a state in which the fluid5inside the tube10has been pre-pressurized. In the steady state, the length of the actuator2is obtained by adding a contraction due to the pre-pressurization and a deformation due to an external force to a natural length of the actuator2.

In a state illustrated inFIG. 8A, the fluid5is pressurized at, for example, 0.5 MPa by using the pressure source3, and the fluid5is additionally supplied to the inside of the tube10of the actuator2. As illustrated inFIG. 8B, this causes the actuator2to contract in the direction of the axis A1(S2inFIG. 6). For example, the actuator2is caused to contract by injecting the fluid5into the inside of the tube10by using the pressure source3.

The actuator2is caused to extend in the direction of the axis A1by depressurizing the fluid5by using the pressure source3so that the length of the actuator2is returned to the original length (S3inFIG. 6). For example, the actuator2is caused to extend by discharging the fluid5from the inside of the tube10by using the pressure source3. These steps are repeated to decrease the length of the actuator2and subsequently to increase the length of the actuator2(to cause the actuator2to contract and subsequently to extend). Only one of extension and contraction may be performed, and the order of extension and contraction may be reversed. Only one of extension and contraction may be repeated multiple times.

A mechanism of driving the actuator2will be next described.

FIG. 7Ais a sectional view of one of the bone portions b of the first elastic member11before the fluid5inside the tube10is pressurized.FIG. 7Bis a sectional view of the bone portion b of the first elastic member11illustrating deformation of the bone portion b after the fluid5inside the tube10is pressurized.

FIG. 7AandFIG. 7Bboth illustrate a winding of the bone portion b from the direction of the axial center A2.

As illustrated inFIG. 7A, the radius of the bone portion b is r before the fluid5is pressurized. When the fluid5is pressurized, the first elastic member11of the tube10is expanded (deformed) in the radial direction due to a pressure applied via the second elastic member12of the tube10, and, as illustrated inFIG. 7B, the radius of the bone portion b accordingly becomes r+Δr. At this time, the bone portion b is twisted at an angle of φ=2πΔr/(r+Δr) per a winding. The twist causes the entire tube10mainly including the first elastic member11to be twisted about the axial center A2.

In the embodiment, the grooves c of the tube10are wound around the axial center A2clockwise, and the actuator2is wound around the axis A1clockwise. Accordingly, as illustrated inFIG. 8B, the twist of the tube10acts so as to cause the actuator2to contract in the direction of the axis A1.

That is, the entire tube10is twisted counterclockwise about the axial center A2with the expansion due to the pressurization and the actuator2is wound around the axis A1clockwise. Accordingly, the tube10is twisted counterclockwise such that portions located out of the page toward the reader are rotated in the direction of solid arrows when attention is paid to the right side of the actuator2inFIG. 8B. The tube10is twisted counterclockwise such that portions located into the page away from the reader are rotated in the direction of dashed arrows when attention is paid to the left side of the actuator2. Accordingly, the twist occurring over the entire length of the tube10acts such that a pitch angle a of the tube10is decreased (spiral pitch p1of the tube10is decreased) so that the length of the actuator2is decreased.

When the pressurization of the fluid5is stopped, the tube10deformed in the radial direction and twisted is returned to the original state and the length of the actuator2is also returned to the original length due to elastic forces of the first elastic member11and the second elastic member12.

When the tube10of the actuator2is expanded (deformed), the tube10tries to expand (deform) also in the radial direction and the direction of the axis A2, and the grooves c located on the outer circumferential side of the tube10try to expand in the width direction of the grooves c. However, when the inclinations θ of the grooves c are less than 45° (spiral pitches p2are larger than the length πd of the outer circumference of tube10) as in the embodiment, the tube10is sufficiently twisted even when the grooves c are expanded in the width direction. Accordingly, the actuator2can sufficiently contract.

A case where the actuator2is deformed so as to be bent by applying an external force to the actuator2will be next described. The actuator2according to the embodiment is also featured such that, when an external force is applied to the actuator2in the lateral direction, the actuator2is deformed so as to be bent due to the elasticity of the actuator2itself without being affected by the pressure of the fluid5.

FIG. 9Ais a schematic view of the actuator2before an external force is applied to the actuator2.FIG. 9Bis a schematic view of the actuator2illustrating a state in which the actuator2is bent after an external force is applied to the actuator2. InFIG. 9AandFIG. 9B, illustration of the grooves c is omitted.

As illustrated inFIG. 9B, a pitch angle α1of the tube10is decreased and a pitch angle α2of the tube10is increased on the assumption that an external force is applied to the actuator2in the vertical direction with respect to the axis A1of the actuator2to bend and deform the actuator2. Thus, portions on the right side of the tube10are twisted counterclockwise such that the portions located out of the page toward the reader are rotated in the direction of solid arrows, and portions on the left side of the tube10are twisted clockwise such that the portions located into the page away from the reader are rotated in the direction of dashed arrows.

When the twist occurs in the direction opposite the direction in which the grooves c are spirally wound, the diameter of the tube10is increased, and the volume of the inside of the tube10is increased. In contrast, when the twist occurs in the direction in which the grooves c are spirally wound, the diameter of the tube10is decreased, and the volume of the inside of the tube10is decreased. In the embodiment, the volume of the inside of the tube10is increased and decreased at the same time. Accordingly, the variations in the total volume of the inside of the tube10can be made small and the actuator2can be readily bent.

In other words, stiffness when the actuator2is bent and deformed does not substantially depend on the pressure acting on the fluid5and the stiffness of the actuator2itself is dominant. Accordingly, the use of a soft material for the actuator2enables the actuator2to be readily bent and deformed.

A method of manufacturing the actuator2will be next described.

As illustrated inFIG. 10, a cylindrical member that is made of a thermoplastic resin and that includes bone portions b is first prepared. The cylindrical member is heated to a glass-transition temperature or more. In this state, the cylindrical member is twisted and rotated about the axis. The cylindrical member is then cooled to form the first elastic member11including spiral bone portions b. The cylindrical second elastic member12is next inserted into the inside of the cylindrical first elastic member11to form the tube10being straightened. The tube10is again heated to the glass-transition temperature or more. In this state, the tube10is wound around a core material (not illustrated). The tube10is then cooled and the core material is extracted. In this way, the actuator2that is spirally wound can be manufactured.

The first elastic member11can be manufactured by another manufacturing method. For example, the bone portions b made of a thermoplastic resin are spirally wound around a mandrel, which is the core material, and an anneal process is performed. The mandrel is then removed to form the first elastic member11. Other than these methods, the first elastic member11may be manufactured by a three-dimensional modeling method.

Modifications to the actuator2according to the first embodiment will now be described.

As illustrated in a first modification inFIG. 11, in the tube10of the actuator2, the second elastic members12may be formed such that the through-holes11cof the first elastic member11are filled with the second elastic members12. In other words, the second elastic members12may be disposed in the through-holes11cextending from the inner surface11aof the first elastic member11to the outer surface11b. The thicknesses of the second elastic members12are equal to the thickness of the first elastic member11. There is no step between the outer surfaces of the second elastic members12and the outer surface11bof the first elastic member11. With this structure, the tube10can be formed to be thin and the actuator2can be downsized. The thicknesses of the second elastic members12are not necessarily equal to the thickness of the first elastic member11, and there may be a difference between the thicknesses.

As illustrated in a second modification inFIG. 12, in the tube10of the actuator2, the second elastic member12is joined to the outside of the first elastic member11by, for example, adhesion, so as to close the through-holes11cof the first elastic member11. In this case, the grooves c are formed of the side surfaces of the through-holes11cof the first elastic member11and a surface (inner surface12a) of the second elastic member12. With this structure, the tube10can carry out the same function as the tube10illustrated inFIG. 3.

Although the direction in which the tube10is spirally wound is matched to the direction in which the grooves c are spirally wound in the embodiment, the directions of the spirals may be opposite. For example, the tube10may be spirally wound around the axis A1clockwise and the grooves c may be spirally wound around the axial center A2counterclockwise.

In an actuator with the above structure (third modification not illustrated), when the fluid5inside the tube10is pressurized, a torsional force is applied to the tube10clockwise and acts to cause the actuator2to extend in the direction of the axis A1.

FIG. 13Ais a schematic view of the actuator2before the fluid5inside the tube10is pressurized.FIG. 13Bis a schematic view of the actuator2illustrating extension and contraction of the actuator2after the fluid5inside the tube10is pressurized. InFIG. 13AandFIG. 13B, illustration of the grooves c is omitted.

In this actuator2, the grooves c are spirally wound counterclockwise. Accordingly, the entire tube10is twisted clockwise about the axial center A2of the tube10with the expansion due to the pressurization. The tube10is wound around the axis A1clockwise. Accordingly, the tube10is twisted clockwise such that the portions located out of the page toward the reader are rotated in the direction of solid arrows when attention is paid to the right side of the actuator2inFIG. 13B. In contrast, the tube10is twisted clockwise such that the portions located into the page away from the reader are rotated in the direction of dashed arrows when attention is paid to the left side of the actuator2. Accordingly, the twist occurring over the entire length of the tube10acts such that the pitch angle α of the tube10is increased (spiral pitch p1of the tube10is increased) so that the length of the actuator2is increased.

That is, in the case where the direction in which the tube10is spirally wound is opposite to the direction in which the grooves c are spirally wound, the actuator2can extend with the expansion due to the pressurization. The same is true in the case where the tube10is wound around the axis A1counterclockwise.

The actuator may be caused to contract or extend by increasing the pressure of the inside of the tube10in a manner in which the inside of the syringe is pressurized by using the plunger and the fluid or an additional fluid is delivered to the inside of the tube10of the actuator2to increase the amount of the fluid (amount per unit volume of the fluid) contained in the inside of the tube10of the actuator2. The phrase “inside of the syringe is pressurized by using the plunger” may be understood to be “distance between an end of the syringe (at which the fluid is discharged from the syringe) and the plunger is decreased”.

The actuator may be caused to contract or extend by decreasing the pressure of the inside of the tube10in a manner in which the inside of the syringe is depressurized by using the plunger and the fluid or part of the fluid is collected from the inside of the tube10of the actuator2to decrease the amount of the fluid (amount per unit volume of the fluid) contained the inside of the tube10of the actuator2. The phrase “inside of the syringe is depressurized by using the plunger” may be understood to be “distance between the end of the syringe and the plunger is increased”.

Second Embodiment

An actuator according to a second embodiment differs from the actuator according to the first embodiment in that a first elastic member11and a second elastic member12are integrally formed as a single piece.

FIG. 14is a partial view of a tube10of an actuator2A.FIG. 15is a cross-sectional view of the tube10of the actuator2A. In the following drawings, like symbols designate like components to those in the first embodiment, and description of these components is omitted.

The actuator2A is formed such that the hollow tube10that is elastic is spirally wound. The tube10is wound around the axis A1of the actuator2A. Grooves c are spirally formed on the outer surface10bof the tube10such that the central axes of the grooves are the axial center A2of the tube10.

The grooves c formed on the tube10are a plurality of grooves having constant widths. The depths of the grooves c are larger than or equal to half of the thickness of the tube10. That is, portions at which the grooves c are formed are flexible compared with portions at which no groove c is formed. The spiral pitches p2of the grooves c are larger than the length πd of the outer circumference of the tube10.

The tube10is hollow. A hollow portion of the tube10contains a fluid5. The tube10includes bone portions b located between the grooves c that are adjacent to each other in the circumferential direction of the tube10. The bone portions b are disposed so as to be spaced apart from each other in the circumferential direction. The bone portions b are four bone portions b1, b2, b3, and b4. Nylon, for example, is used as the material of the tube10.

In the actuator2A according to the second embodiment, the tube10is integrally formed as a single piece, and the actuator can thus have a simple structure. The actuator2A achieves the same effects as the actuator2according to the first embodiment.

A modification to the actuator2A according to the second embodiment will now be described.

As illustrated in a fourth modification inFIG. 16, in the tube10of the actuator2A, grooves may be formed on the inner surface10aof the tube10. As illustrated in a fifth modification inFIG. 17, the grooves c may be formed on both the inner surface10aand outer surface10bof the tube10. As illustrated in a sixth modification inFIG. 20, the grooves c may be formed on both the inner surface10aand outer surface10bof the tube10so as to alternate. With these structures, the same functions as the tube10illustrated inFIG. 15can be carried out. In the fifth modification, the grooves on the inner surface10aare formed at positions corresponding to the grooves on the outer surface10b. The grooves, however, are not limited thereto. Forming the grooves at different positions are also acceptable.

Third Embodiment

An actuator according to a third embodiment differs from the actuator according to the first embodiment in having a single groove c.

FIG. 18is a partial view of a tube10of an actuator2B according to the third embodiment.

The actuator2B is formed such that the hollow tube10that is elastic is spirally wound. The tube10is wound around the axis A1of the actuator2B. The groove c is spirally formed on the outer surface10bof the tube10such that the central axis of the groove is the axial center A2of the tube10.

Specifically, the tube10includes a cylindrical first elastic member11and a cylindrical second elastic member12that is more flexible than the first elastic member11. In the first elastic member11, a through-hole11cextending from the inner surface11a of the first elastic member11to the outer surface11b is formed. The second elastic member12is disposed inside the first elastic member11so as to be in contact with the first elastic member11and closes the through-hole11c. The first elastic member11includes a bone portion b having an arc shape in section. The bone portion b is spirally wound around the axial center A2so that the groove c is spirally formed.

A method of manufacturing the actuator2B will be next described.

As illustrated inFIG. 19, a cylindrical member that is made of a thermoplastic resin and that includes the bone portion b is first prepared. The cylindrical member is heated to the glass-transition temperature or more. In this state, the cylindrical member is twisted and rotated about the axis. The cylindrical member is then cooled to form the first elastic member11including spiral bone portion b. The cylindrical second elastic member12is next inserted into the inside of the cylindrical first elastic member11to form the tube10being straightened. The tube10is again heated to the glass-transition temperature or more. In this state, the tube10is wound around a core material. The tube10is then cooled and the core material is extracted. In this way, the actuator2B that is spirally wound can be manufactured.

The first elastic member11can be manufactured by another manufacturing method. For example, the bone portion b made of a thermoplastic resin is spirally wound around a mandrel, which is the core material, and an anneal process is performed. The mandrel is then removed to form the first elastic member11. Other than these methods, the first elastic member11may be manufactured by a three-dimensional modeling method.

The actuator2B can achieve effects corresponding to the effects of the actuator2according to the first embodiment.

The actuators according to the aspect or the aspects are described above based on the embodiments. The present disclosure, however, is not limited to the embodiments. Modifications to the embodiments that a person skilled in the art thinks of and any embodiment obtained from the combination of the features of the embodiments may be included in the range of the aspect or the aspects without departing from the concept of the present disclosure.

For example, in the above embodiments, water is used as the fluid. The fluid, however, is not limited to water, and any one of known liquids is acceptable. Not only a liquid but also any one of gasses that is a compressible fluid is acceptable.

In the above embodiments, the spiral groove has a constant width. The width is not limited to being constant, and the width of the groove may be varied in the longitudinal direction and/or the width direction of the groove. The spiral groove is not necessarily a continuous groove such as in the case of the embodiments and may be divided at some positions.

In the above embodiments, the syringe pump is used as the pressure source. The pressure source is not limited to the syringe pump, and any known art and combination thereof can be applied thereto, provided that the pressure source can discharge the fluid from and inject the fluid into an interior space.

In the above embodiments, water is discharged from and injected into a coil body whose one end is sealed via the other end. This is not a limitation. Water may be discharged from and injected into coil body via the other end and a port via which water is discharged from and injected into the coil body may be formed at a midway portion of the coil body. An increase in the number of the ports via which water is discharged from and injected into enables the responsiveness of the actuator to be improved.

The actuator according to the aspect of the present disclosure can be used as an artificial muscle actuator that drives a machine that works close to humans and can be applied to the field of assisting equipment that is wearable like clothes. Other than these, the actuator can be used as a linear actuator that is flexible against an external force and a lightweight linear actuator.