Fluid pressure actuator

Abstract

This fluid pressure actuator comprises a cylindrical body and a cord disposed in a helical shape along the circumferential direction of the cylindrical body, and causes the cylindrical body to expand and contract by means of a pressurized fluid flowing in and out of a space on the inner peripheral side of the cylindrical body. At least a portion of the cylindrical body in the axial direction is a curving section, and the fluid pressure actuator has a restraint member fixed to the cylindrical body along the axial direction of the curving section from one end to the other end of the curving section in the axial direction at a portion of the curving section in the circumferential direction. The cylindrical body includes a crosslinked rubber composition. The cord includes fibers, is continuously connected from one end to the other end in the axial direction of the cylindrical body, and is fixed to an outer periphery of the cylindrical body or embedded in the cylindrical body. The restraint member includes a crosslinked rubber composition, canvas, or arranged cords. When the pressurized fluid flows in and out of the space on the inner peripheral side of the cylindrical body to expand and contract the cylindrical body along the axial direction, the axial expansion or contraction of the portion of the curving section to which the restraint member is fixed is restrained, thereby curving the curving section.

Description

Fluid pressure actuator

[0001] The present invention relates to a fluid pressure actuator that uses fluid pressure.

[0002] Conventionally, extensive research has been conducted on fluid pressure actuators that utilize fluid pressure, because they have a higher power-to-weight ratio, greater flexibility and higher compliance compared to electric actuators. A fluid pressure actuator is generally cylindrical in shape, with the space inside the cylindrical body serving as a chamber, and is configured such that a pressurized fluid such as air flows into and out of the chamber.

[0003] Fluid pressure actuators include expansion-contraction type actuators, typified by pneumatic artificial muscles, which utilize the expansion deformation of a rubber material to expand and contract (extend or contract) in the axial direction of the cylindrical body. Research is also progressing on bending-type actuators, which bend the cylindrical body by providing axial restraint with resin or metal on a part of the cylindrical body of an expansion-contraction type actuator.

[0004] Bending-type actuators enable smooth bending motion, can be easily reduced in diameter, and have a simple structure. Therefore, research is being conducted on their application in various fields, for example, applying them to the finger parts of robot arms to artificially reproduce the flexible bending motion of the finger parts.

[0005] For example, Patent Document 1 discloses an actuator comprising a silicone or rubber tube with a closed end that expands radially and axially under pressure, and a fibrous thread-like member spirally wound around the surface of the tube. When the expandable balloon is pressurized, it cannot expand radially and therefore stretches axially. It also discloses that the force attempting to stretch axially acts to further tilt the helix axially, resulting in the expandable balloon rotating around its axis. Furthermore, it states that this actuator can provide rotational motion, and the rotation angle can be controlled according to the pressure. It also describes that the thickness of the cross-section of the expandable balloon is non-uniform in the circumferential direction, and that the thinner side stretches more easily axially than the thicker side, causing the expandable balloon to curve as it stretches. Finally, it states that a fibrous restraining member similar to the thread-like member may be attached to the tube to introduce non-uniformity in axial stretchability into the expandable balloon.

[0006] Furthermore, Patent Document 2 discloses an actuator comprising an elastically deformable cylindrical body having a chamber inside which a working fluid can be contained, an injection pipe for bringing the working fluid into and out of the chamber, an elongation restricting wire fixed to the cylindrical body so as to extend axially and restrict the axial elongation of the inner curved portion of the cylindrical body, and an expansion restricting wire surrounding the chamber and arranged in a substantially symmetrical shape so as to restrict the lateral expansion of the cylindrical body. When a working fluid such as compressed air is injected into the chamber, the pressure inside the chamber increases and the cylindrical body is pushed outward. At this time, the elongation of the cylindrical body is partially restricted by the elongation restricting wire and the expansion restricting wire, so the actuator curves with the side having the elongation restricting wire facing inward. The patent document states that, for example, aramid fibers, threads, strings, ribbons such as cotton yarn, or plastic or metal rods or strips are preferred as the expansion restricting wire and elongation restricting wire, and that different types of materials may be combined.

[0007] Furthermore, Patent Document 3 discloses an actuator in which an axial reinforcing member made of metal plate or plastic is arranged on one side along the axial direction of an extendable cylindrical body to restrict axial elongation of that portion, and a helical reinforcing member is arranged around the periphery to restrict radial expansion. It is also described that by injecting high-pressure air into the cylindrical body of this actuator, the cylindrical body bends so that the axial reinforcing member faces inward.

[0008] Furthermore, Patent Document 4 discloses a fluid pressure actuator relating to a retractable actuator, in which a restraining member, which is a leaf spring made of carbon fiber reinforced plastic (CFRP), is provided on a part of the circumferential direction of the tube. According to this fluid pressure actuator, a portion that can be retracted and a portion that cannot be retracted are generated on the circumference of the actuator body, and when pressure is applied to the fluid pressure actuator, it is described that it bends on the side opposite to the side on which the restraining member is provided.

[0009] Japanese Patent Publication No. 2018-189169, Japanese Patent Publication No. 2008-19984, Japanese Patent No. 2993506, Japanese Patent Publication No. 2023-131052

[0010] However, as with the actuators described in Patent Documents 2 to 4, if the restraining member that constrains the curved portion of the cylindrical body has a high modulus of elasticity, such as metal, plastic, or carbon fiber reinforced plastic, the rigidity of the curved portion becomes too high. As a result, the curvature of the curved portion becomes small, and sufficient curvature cannot be obtained. Also, if the rigidity of the curved portion is high, when the curved portion of the cylindrical body is bent by applying pressure, it may not bend much in the initial stages of pressure application, and then suddenly begin to bend when the pressure exceeds a predetermined value. In such a bending motion, for example, if the actuator is applied to the finger portion of a robot arm, it may not be possible to provide the finger portion with a bending motion and holding force proportional to the pressure, which may hinder the smooth bending motion of the finger portion of the robot arm. On the other hand, as with the actuators described in Patent Documents 1 to 2, if the restraining member that constrains the curved portion of the cylindrical body has a low modulus of elasticity, such as fiber, thread, silicone, or rubber, the rigidity of the curved portion becomes low, but the restraining force of the curved portion becomes too weak. As a result, the curvature of the curved portion becomes small, and sufficient curvature cannot be obtained. For example, if the actuator is applied to the finger portion of a robot arm, the range of motion of the finger portion may become narrower.

[0011] Therefore, the present invention aims to provide a fluid pressure actuator that enhances the flexibility of a cylindrical body when it is expanded or contracted.

[0012] The present invention relates to a fluid pressure actuator comprising a cylindrical body and a cord helically arranged along the circumferential direction of the cylindrical body, wherein pressurized fluid flows in and out of the space on the inner circumference of the cylindrical body to expand and contract the cylindrical body, wherein at least a portion of the cylindrical body in its axial direction is a curved portion, and a restraining member is fixed along the axial direction of the curved portion from one end to the other in the axial direction of the curved portion in a portion of the circumferential direction of the curved portion, the cylindrical body comprises a crosslinked rubber composition, the cord comprises fibers and is continuously connected from one end to the other in the axial direction of the cylindrical body and is fixed to the outer circumference of the cylindrical body or embedded in the cylindrical body, the restraining member comprises a crosslinked rubber composition, canvas, or an array of cords, and when pressurized fluid flows in and out of the space on the inner circumference of the cylindrical body and the cylindrical body expands and contracts along the axial direction, the axial extension or contraction of the portion of the curved portion to which the restraining member is fixed is suppressed, thereby curving the curved portion.

[0013] In this configuration, when pressurized fluid flows into the cylindrical body, fluid pressure is applied to the inner circumference of the cylindrical body in all directions. Since the cylindrical body contains a cross-linked rubber composition which is an elastic material (elastomer), it stretches relatively large in the axial direction. At that time, the cylindrical body stretches in the axial direction and also tries to expand in the radial direction. Here, a cord containing fibers that are continuously connected from one end to the other in the axial direction of the cylindrical body is arranged helically along the circumferential direction of the cylindrical body. The cylindrical body that tries to expand radially is given helical fiber constraint by the cord along its entire axial direction. The helical fiber constraint by the cord is along the circumferential direction of the cylindrical body, and as a result, the fluid pressure that tries to expand the cylindrical body radially acts as a fluid pressure that tries to spread the portions between adjacent cords in the axial direction of the cylindrical body in the axial direction. Also, as the pressurized fluid flows out from the axially stretched cylindrical body and the fluid pressure decreases, the cylindrical body contracts in the axial direction. Here, at least a part of the cylindrical body in its axial direction is a curved portion. Furthermore, in a portion of the circumferential direction of this curved portion, a restraining member is fixed along the axial direction of the curved portion, from one end to the other in the axial direction of the curved portion. The portion of the curved portion to which the restraining member is fixed is restrained by the restraining member, and axial extension or contraction is suppressed. On the other hand, the portion of the curved portion to which the restraining member is not fixed is not restrained by the restraining member, and axial extension or contraction is not suppressed, so it extends or contracts in the axial direction. As a result, the curved portion of the cylindrical body curves when it extends or contracts in the axial direction. For example, in a state where the curved portion of the cylindrical body is not curved in the unpressurized state (see Figure 1(A)), when pressurized fluid is introduced into the inner circumferential space of the sealed cylindrical body, the cylindrical body extends in the axial direction. In this state, the axial extension of the portion of the curved portion to which the restraining member is fixed is suppressed, while the portion to which the restraining member is not fixed extends in the axial direction. As a result, the fluid pressure actuator becomes curved in the straightened state of the curved portion, and the axial direction of the curved portion becomes curved (see Figure 1(B)). On the other hand, when the pressurized fluid that has flowed into the inner circumferential space of the sealed cylindrical body is released, causing the cylindrical body to contract axially, the axial contraction of the portion where the restraining member of the curved section is fixed is suppressed, while the portion where the restraining member is not fixed contracts axially.As a result, the curved portion of the fluid pressure actuator straightens out, and the axial direction of the curved portion becomes linear (see Figure 1(A)). Also, when the curved portion is in a curved state without pressure (see Figure 8(A)), and pressurized fluid is introduced into the inner circumferential space of the sealed cylindrical body, causing the cylindrical body to extend axially, the axial extension of the portion of the curved portion where the restraining member is fixed is suppressed, while the portion of the curved portion where the restraining member is not fixed extends axially. As a result, the curved portion of the fluid pressure actuator straightens out, and the axial direction of the curved portion becomes linear (see Figure 8(B)). On the other hand, when the pressurized fluid introduced into the inner circumferential space of the sealed cylindrical body is released, causing the cylindrical body to contract axially, the axial contraction of the portion of the curved portion where the restraining member is fixed is suppressed, while the portion of the curved portion where the restraining member is not fixed contracts axially. As a result, the curved portion of the fluid pressure actuator, which was straightened out, curves, and the axial direction of the curved portion becomes curved (see Figure 8(A)). Furthermore, because the cord is fixed to the outer circumference of the cylindrical body containing the crosslinked rubber composition, or embedded in the cylindrical body, the fiber restraint is greater compared to cases where the cord is not fixed to the outer circumference of the cylindrical body or embedded in the cylindrical body. As a result, radial expansion of the cylindrical body is more suppressed compared to cases where the cord is not fixed to the outer circumference of the cylindrical body or embedded in the cylindrical body. In addition, the fiber-containing cord has lower rigidity and a higher elongation rate compared to a coil spring. Therefore, the fiber-containing cord can increase the axial elongation of the cylindrical body while providing helical fiber restraint to the cylindrical body. As a result, the cylindrical body can be curved significantly as the axial elongation of the cylindrical body increases, thereby improving its flexibility. Moreover, the restraining member is made of a crosslinked rubber composition, canvas, or arranged cord, and the restraining member has a lower elastic modulus and is more flexible than metals, plastics, or carbon fiber reinforced plastics, while having a higher elastic modulus and stronger restraining force compared to fibers, threads, silicone, or rubber. Therefore, when expanding or contracting the cylindrical body, the curvature of the part where the restraining member of the curved portion is fixed is increased, while enabling smooth bending motion proportional to the pressure applied.Therefore, the fluid pressure actuator of the present invention can enhance the flexibility of the cylindrical body when it is expanded or contracted. Note that "the cord is embedded in the cylindrical body" includes cases where a part of the cord is embedded in the cylindrical body and cases where the entire cord is embedded in the cylindrical body.

[0014] Furthermore, in the fluid pressure actuator of the present invention, the length of the restraining member in the circumferential direction of the curved portion may be in the range of 15% to 60% of the outer circumference length of the curved portion when no pressure is applied.

[0015] In the circumferential direction of the curved portion of a cylindrical body, if the length of the restraining portion relative to the outer circumference of the curved portion exceeds 60%, the curved portion becomes less flexible, and the curvature of the curved portion decreases. On the other hand, in the circumferential direction of the curved portion, if the length of the restraining portion relative to the outer circumference of the curved portion is less than 15%, the restraining force of the restraining portion of the curved portion weakens, and although the curved portion stretches, it does not curve properly. Therefore, with the above configuration, the curvature of the curved portion can be made appropriately large when the curved portion is bent.

[0016] Furthermore, in the fluid pressure actuator of the present invention, the ratio B / A of parameter B, defined by the following formula 1, which is an indicator of the elongation of the constrained portion constrained by the constraining member in the curved portion, and parameter A, defined by the following formula 2, which is an indicator of the elongation of the unconstrained portion not constrained by the constraining member in the curved portion, may be 0.5 or more and 150 or less. Parameter B [N] = (Tensile force [N] when the constrained portion is stretched by 10%) × (Proportion of the outer circumference of the curved portion occupied by the constrained portion) ... (Formula 1) Parameter A [N] = (Tensile force [N] when the unconstrained portion is stretched by 10%) × (Proportion of the outer circumference of the curved portion occupied by the unconstrained portion) ... (Formula 2)

[0017] Parameter B, which indicates the elongation of the constrained portion that is restrained by the restraining member, and parameter A, which indicates the elongation of the unconstrained portion that is not restrained by the restraining member, both indicate resistance to elongation as their values ​​increase. If the ratio of parameter B to parameter A is too small, the curved portion will stretch axially without curving; therefore, a larger ratio of parameter B to parameter A makes it easier to curve. For this reason, if the ratio B / A is 0.5 or higher, the restraining force acts sufficiently on the curved portion, allowing the curved portion to be curved appropriately.

[0018] Furthermore, in the fluid pressure actuator of the present invention, the restraining member may include a crosslinked rubber composition, and the crosslinked rubber composition may contain short fibers, wherein the orientation direction of the short fibers may be parallel to the axial direction of the cylindrical body.

[0019] According to the above configuration, the elastic modulus of the restraining member in the axial direction of the curved portion is improved. As a result, the restraining force of the restraining member is strengthened, and the axial elongation of the restrained portion in the curved portion is further suppressed. Consequently, when the cylindrical body is pressurized, the curvature of the curved portion can be increased.

[0020] Furthermore, the fluid pressure actuator of the present invention may have an axial elongation at break of 40% or more and 1000% or less of the cross-linked rubber composition forming the cylindrical body.

[0021] This configuration allows for a sufficiently large axial extension of the unconstrained portion when bending the curved section. As a result, the curved section can be curved more significantly as the axial extension of the unconstrained portion increases, thereby improving its flexibility.

[0022] Furthermore, in the fluid pressure actuator of the present invention, the cylindrical body may have an elongation index Y value defined by the following formula 3 that is 0.04 N / mm or more and 0.30 N / mm or less. Elongation index Y [N / mm] = (Tensile force [N] at 10% elongation of the unrestrained portion of the cylindrical body not restrained by the restraining member) / (Inner diameter of the cylindrical body [mm]) ... (Formula 3)

[0023] This configuration allows for a sufficiently large axial extension of the unconstrained portion when bending the curved section. As a result, the curved section can be curved more significantly as the axial extension of the unconstrained portion increases, thereby improving its flexibility.

[0024] Furthermore, the fluid pressure actuator of the present invention may have a tensile modulus of elasticity of the fibers constituting the cord that is 2 GPa or more and 150 GPa or less.

[0025] This configuration allows for a balance between the elongation rate and fracture safety of the tubular body for the fiber-containing cord. The cord provides sufficient helical fiber constraint to the tubular body while also providing the axial elongation rate necessary for the curvature of the curved portion of the tubular body. Therefore, as the axial elongation of the unconstrained portion increases, the curved portion can be curved more significantly, thereby improving the flexibility.

[0026] Furthermore, in the fluid pressure actuator of the present invention, the cords may be arranged such that, when no pressure is applied, the X value of the arrangement density of the cords is 60% or more and 90% or less.

[0027] This configuration allows the cords to be arranged within a cylindrical body while maintaining an appropriate amount of space between adjacent cords in the axial direction of the cylindrical body. As a result, when the cylindrical body expands radially, the cords create a larger helical fiber constraint. Consequently, the fluid pressure attempting to expand the cylindrical body radially acts as a fluid pressure that attempts to further widen the space between adjacent cords in the axial direction of the cylindrical body. This allows for increased axial elongation of the cylindrical body while suppressing radial expansion. Therefore, as the axial elongation of the unconstrained portion of the cylindrical body increases, the curved portion can be curved more significantly, thereby improving its flexibility.

[0028] Furthermore, in the fluid pressure actuator of the present invention, the cords may be arranged such that the distance between adjacent cords when no pressure is applied is 0 mm or more and 2.6 mm or less.

[0029] This configuration improves the pressure resistance of the cylindrical body because the cords are densely arranged in a spiral pattern within the cylindrical body. As a result, a greater fluid pressure can be applied to the cylindrical body, increasing its axial elongation. Consequently, the increased axial elongation of the unrestrained portion of the cylindrical body allows for greater curvature of the curved portion, thereby enhancing its flexibility.

[0030] Furthermore, the fluid pressure actuator of the present invention may be configured such that the value of the strain index Z, defined by the following formula 4, is between 1 [1 / GPa] and 400 [1 / GPa]. Strain index Z [1 / GPa] = (Inner diameter of the cylindrical body [mm]) × (Axial distance between adjacent cords when no pressure is applied [mm]) / { (Tensile modulus of elasticity of the cord [GPa]) × (Cord diameter [mm]) 2}...(Formula 4)

[0031] This configuration allows for reduced circumferential strain in the cylindrical body, thereby improving its pressure resistance. This enables the application of greater fluid pressure to the cylindrical body, increasing its axial elongation. Furthermore, the increased axial elongation in the unrestrained portion of the cylindrical body allows for greater curvature in the curved portion, thereby enhancing its flexibility.

[0032] Furthermore, the fluid pressure actuator of the present invention may also include untwisted fibers in its cord.

[0033] In this configuration, the inclusion of untwisted fibers in the cord results in a flattened cross-section. Compared to cords containing twisted fibers with a circular cross-section, cords arranged adjacent to each other in the axial direction of the tubular body overlap, increasing circumferential fiber constraint and improving pressure resistance. Therefore, when fluid pressure is applied, radial expansion of the tubular body is further suppressed. As a result, the fluid pressure acts more effectively against axial elongation, allowing for greater axial elongation of the tubular body while suppressing radial expansion. Consequently, the increased axial elongation of the unconstrained portion of the tubular body allows for greater curvature of the curved portion, thereby improving its flexibility.

[0034] Furthermore, the fluid pressure actuator of the present invention has a cord comprising a first cord and a second cord, and the first cord and the second cord may be fixed to the outer circumference of the cylindrical body or embedded in the cylindrical body, overlapping in the radial direction of the cylindrical body, such that when no pressure is applied, the orientation of their respective helices is axially symmetric with respect to the axial direction of the cylindrical body.

[0035] In this configuration, the spiral winding direction of the first and second cords is such that one is right-handed and the other is left-handed. This significantly suppresses axial twisting, which occurs when the cylindrical body expands or contracts, by preventing the cylindrical body from rotating in the direction of the spirals along the cords. By suppressing axial twisting of the cylindrical body, the axial elongation of the unconstrained portion of the cylindrical body can be increased. As the axial elongation of the unconstrained portion of the cylindrical body increases, the curved portion can be curved more significantly, thereby improving its flexibility. Note that "the spiral direction of the first and second cords" refers to the angle between the direction of the first and second cords and the radial direction of the cylindrical body, when viewed in a direction perpendicular to the axial direction of the cylindrical body. In other words, "the spiral direction of the first and second cords is axially symmetric with respect to the axial direction of the cylindrical body" means that when viewed in a direction perpendicular to the axial direction of the cylindrical body, if the intersection point of the first and second cords lies on the axis of the cylindrical body, the angle bisector of the angle between the first and second cords lies in the axial direction of the cylindrical body. In this case, the angle between the bisector and the axial direction of the cylindrical body is preferably 0 degrees, but it may include a range of about ±10 degrees.

[0036] This invention provides a fluid pressure actuator that enhances the flexibility of a cylindrical body when it is expanded or contracted.

[0037] Figure 1(A) is a side view of the fluid pressure actuator under no pressure according to the first embodiment. Figure 1(B) is a side view of the fluid pressure actuator under pressure according to the first embodiment. Figure 2(A) is a cross-sectional view of the cylindrical body in the thickness direction according to the first embodiment. Figure 2(B) is a side view of the cylindrical body according to the first embodiment. Figure 3(A) is a side view of the cylindrical body according to the first embodiment. Figure 3(B) is an enlarged cross-sectional view of the cylindrical body in Figure 3(A) along the axial direction. Figure 4(A) is a side view of the fluid pressure actuator under no pressure according to the second embodiment. Figure 4(B) is a side view of the fluid pressure actuator under pressure according to the second embodiment. Figure 5(A) is a cross-sectional view of the cylindrical body according to the second embodiment. Figure 5(B) is a side view of the cylindrical body according to the second embodiment. Figure 6(A) is a side view of the cylindrical body according to the second embodiment. Figure 6(B) is an enlarged cross-sectional view of the cylindrical body in Figure 6(A) along the axial direction. Figures 7(A) to 7(C) are explanatory diagrams of a method for manufacturing a fluid pressure actuator according to a modified example of the second embodiment. Figure 8(A) is a side view of the fluid pressure actuator under no pressure according to the third embodiment. Figure 8(B) is a side view of the fluid pressure actuator under pressure according to the third embodiment. Figure 9 is an explanatory diagram of an evaluation test regarding the lateral rigidity of the fluid pressure actuator according to the embodiment. Figure 10 is an enlarged view of the end of the fluid pressure actuator in Figure 9.

[0038] (First Embodiment) The fluid pressure actuator 1 according to the first embodiment will be described below with reference to the drawings.

[0039] (Fluid Pressure Actuator 1) As shown in Figure 1(A), the fluid pressure actuator 1 includes a cylindrical body 11 made of a cylindrical cross-linked rubber composition and a cord 12 helically bonded to the outer circumference of the cylindrical body 11 along the circumferential direction. The cylindrical body 11 has a curved portion 11c in which at least a part in its axial direction bends when pressurized. In this embodiment, the entire cylindrical body 11 is a curved portion 11c, and the cylindrical body 11 functions as a curved portion 11c along its entire length, but a part of the cylindrical body 11 in the axial direction may be a curved portion 11c. A restraining member 17 is fixed to a part of the circumferential direction of the curved portion 11c, extending from one end to the other along the axial direction. Furthermore, the fluid pressure actuator 1 includes bamboo shoot-shaped caps 13a and 13b, which are attached to one axial end 11a and the other end 11b of the cylindrical body 11, respectively, and hose bands 14a and 14b, which fix the cylindrical body 11 to the caps 13a and 13b. An air inlet is provided in the cap 13b. In the following description, the portion of the outer circumference of the curved portion 11c that is restrained by the restraining member 17 is defined as the restrained portion 11R (see Figures 1 and 2). The portion of the outer circumference of the curved portion 11c that is not restrained by the restraining member 17 is defined as the unrestrained portion 11N (see Figures 1 and 2).

[0040] Furthermore, the fluid pressure actuator 1 is connected to a control device (not shown) that controls the inflow and outflow of compressed air (pressurized fluid) into the inner circumferential space of the sealed cylindrical body 11 via an air inlet provided in the cap 13b. In this embodiment, pneumatic pressure from air is used as the pressurized fluid to be inflow and out of the inner circumferential space of the cylindrical body 11. However, this is not limited to air; other gases may be used as the pressurized fluid, or hydraulic pressure from oil or liquids such as water may be used. In other words, the inner circumferential space of the sealed cylindrical body 11 is a chamber through which pressurized fluid such as air is inflow and out.

[0041] The fluid pressure actuator 1 extends in the axial direction when compressed air is caused to flow into the space on the inner peripheral side of the sealed cylindrical body 11 by the control device. While the axial extension of the restrained portion 11R is suppressed, the unrestrained portion 11N extends in the axial direction. As a result, in the fluid pressure actuator 1 in the state shown in FIG. 1(A), the cylindrical body 11 in a straightly extended state bends, and as shown in FIG. 1(B), the axial direction of the cylindrical body 11 becomes a curved state. On the other hand, when the fluid pressure actuator 1 contracts in the axial direction due to the compressed air that has flowed into the space on the inner peripheral side of the sealed cylindrical body 11 flowing out by the control device, axial contraction of the restrained portion 11R is suppressed, while the unrestrained portion 11N contracts in the axial direction. As a result, in the fluid pressure actuator 1 in the state shown in FIG. 1(B), the cylindrical body 11 in a curved state extends straight, and as shown in FIG. 1(A), the axial direction of the cylindrical body 11 becomes linear. Accordingly, the fluid pressure actuator 1 can perform a smooth bending operation proportional to the pressure applied by the control device. As described above, the fluid pressure actuator 1 is capable of smooth bending operation, can be easily reduced in diameter, and has a simple structure. Therefore, for example, it can be applied as a bending actuator to a finger portion of a robot arm, and can be applied to various fields such as artificially reproducing the operation of a finger portion flexibly bending.

[0042] (Cylindrical body 11) The cylindrical body 11 is formed of a crosslinked rubber composition containing a rubber component. As one of the factors for increasing the axial elongation rate of the unrestrained portion 11N of the cylindrical body 11, designing the crosslinked rubber composition to be easily stretchable or less stretchable is important. In the present embodiment, tensile properties are cited as physical properties indicating the ease of stretching and resistance to stretching of the crosslinked rubber composition, and as index values thereof, "elongation at break (%)", "tensile stress at 100% elongation (MPa)", and "tensile stress at 50% elongation (MPa)", which can be measured by a method in accordance with JIS K6251 (2017), are used. Hereinafter, "tensile stress at 100% elongation (MPa)" may be referred to as 100% modulus (M100), and "tensile stress at 50% elongation (MPa)" may be referred to as 50% modulus (M50).

[0043] The crosslinked rubber composition forming the cylindrical body 11 has an elongation at break in the axial direction of, for example, 40% or more and 1000% or less, preferably 600% or more and 900% or less. As described above, by setting the elongation at break in the axial direction of the crosslinked rubber composition forming the cylindrical body 11 to 40% or more, when the cylindrical body 11 is curved, the elongation of the unconstrained portion 11N in the axial direction can be made sufficiently large. Therefore, the cylindrical body 11 can be greatly curved as the elongation of the unconstrained portion 11N in the axial direction increases, and the bendability can be improved.

[0044] In addition, for the cylindrical body 11, the value of the elongation index Y defined by the following formula is, for example, 0.04 N / mm or more and 0.30 N / mm or less, preferably 0.09 N / mm or more and 0.25 N / mm or less (see FIG. 2(A)). Elongation index Y [N / mm] = (tensile force [N] of the unconstrained portion 11N of the cylindrical body 11 at 10% elongation) / (inner diameter [mm] of the cylindrical body 11) By setting the value of the elongation index Y to 0.30 N / mm or less, when the cylindrical body 11 is curved, the elongation of the unconstrained portion 11N in the axial direction can be made sufficiently large. Therefore, the cylindrical body 11 can be greatly curved as the elongation of the unconstrained portion 11N in the axial direction increases, and the bendability can be improved.

[0045] Examples of the rubber component of the crosslinked rubber composition constituting the cylindrical body 11 include diene rubbers [natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), chloroprene rubber (CR), butyl rubber (IIR), styrene-butadiene rubber (SBR), vinylpyridine-styrene-butadiene rubber, acrylonitrile-butadiene rubber (nitrile rubber: NBR), acrylonitrile-chloroprene rubber, hydrogenated nitrile rubber (HNBR), etc.], ethylene-α-olefin elastomers [ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), etc.], chlorosulfonated polyethylene rubber (CSM), alkylated chlorosulfonated polyethylene rubber (ACSM), epichlorohydrin rubber, acrylic rubber, silicone rubber, urethane rubber, fluororubber, and the like. These rubber components can be used alone or in combination of two or more. In particular, natural rubber (NR) is preferable from the viewpoint of low cost.

[0046] Furthermore, the crosslinked rubber composition may further contain fillers in addition to the rubber components. Examples of fillers include carbon black, silica, clay, calcium carbonate, talc, and mica. Fillers often include reinforcing fillers, such as carbon black and reinforcing silica. Generally, the reinforcing properties of silica are less than those of carbon black. These fillers can be used individually or in combination of two or more.

[0047] Crosslinked rubber compositions contain crosslinking agents (vulcanizing agents) to crosslink rubber components, and, if necessary, co-crosslinking agents, crosslinking aids (vulcanization aids), crosslinking accelerators (vulcanization accelerators), crosslinking retarders (vulcanization retarders), etc.

[0048] As crosslinking agents, conventional components can be used depending on the type of rubber component. Examples include metal oxides (magnesium oxide, zinc oxide, lead oxide, etc.), organic peroxides (diasyl peroxide, peroxyester, dialkyl peroxide, etc.), and sulfur-based crosslinking agents. Examples of sulfur-based crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and sulfur chloride (sulfur monochloride, sulfur dichloride, etc.). These crosslinking agents can be used alone or in combination of two or more. When the rubber component is chloroprene rubber, metal oxides (magnesium oxide, zinc oxide, etc.) may be used as crosslinking agents. Metal oxides may also be used in combination with other crosslinking agents (sulfur-based crosslinking agents, etc.), and metal oxides and / or sulfur-based crosslinking agents may be used alone or in combination with crosslinking accelerators.

[0049] The crosslinked rubber composition constituting the cylindrical body 11 may further contain various conventional additives as needed. Commonly used additives include, for example, metal oxides (calcium oxide, barium oxide, iron oxide, copper oxide, titanium oxide, aluminum oxide, etc.), softeners (oils such as paraffin oil and naphthenic oils), processing agents or processing aids (stearic acid or its metal salts, waxes, paraffin, fatty acid amides, etc.), plasticizers [aliphatic carboxylic acid plasticizers (adipate ester plasticizers, sebacate ester plasticizers, etc.), aromatic carboxylic acid ester plasticizers (phthalate ester plasticizers, trimellitic acid ester plasticizers, etc.), oxycarboxylic acid ester plasticizers, phosphate ester plasticizers, ether plasticizers, ether ester plasticizers, etc.], antioxidants (antioxidants, heat aging inhibitors, flex crack inhibitors, ozone degradation inhibitors, etc.), colorants, tackifiers, plasticizers, coupling agents (silane coupling agents, etc.), stabilizers (ultraviolet absorbers, heat stabilizers, etc.), flame retardants, and antistatic agents. Furthermore, the crosslinked rubber composition may optionally contain adhesion improvers (such as resorcinol-formaldehyde cocondensates or amino resins). These additives can be used individually or in combination of two or more.

[0050] The cylindrical body 11 preferably has a thickness of 0.01 to 10 mm, an inner diameter of 1 to 1000 mm, and an axial length of 3 to 3000 mm. The 50% modulus (M50) of the cylindrical body 11 in the circumferential direction is preferably 0.3 to 10 MPa. The 100% modulus (M100) of the cylindrical body 11 in the axial direction is preferably 0.3 to 5 MPa. The elongation at break in the axial direction of the cylindrical body 11 is preferably 40% or more.

[0051] (Code 12) In this embodiment, the code 12 is an example of a tensile body that restrains the stretching of the cylindrical body 11, and is composed of a fiber-containing material. That is, various materials can be used as tensile bodies, but in this embodiment, a fiber-based code 12 is used as the tensile body. As shown in Figure 1, the code 12 is bonded to the outer circumference of the cylindrical body 11 in a spiral shape along the circumferential direction, and is bonded in a continuous state from one end 11a to the other end 11b in the axial direction. More specifically, as shown in Figure 3, the code 12 is bonded to the outer circumference of the cylindrical body 11 from one end 11a to the other end 11b in the axial direction, with a portion of it embedded in the cross-linked rubber composition constituting the cylindrical body 11 in a cross-section perpendicular to the axial direction of the code 12. In other words, the code 12 is embedded in the cross-linked rubber composition constituting the cylindrical body 11 with a portion of it exposed in a cross-section perpendicular to the axial direction of the code 12. Furthermore, the cord 12 is integrated with the cross-linked rubber composition constituting the cylindrical body 11 by cross-linking molding during the manufacturing process of the fluid pressure actuator 1, thereby strengthening the adhesion between a portion of the cord 12 in the circumferential direction and the cross-linked rubber composition constituting the cylindrical body 11. It should be noted that the cord 12 does not necessarily need to be bonded to the outer circumference of the cylindrical body 11; it is sufficient that it is held in a state where relative movement to the cylindrical body 11 is suppressed. In other words, the cord 12 may be provided in a manner that it is fixed to the outer circumference of the cylindrical body 11.

[0052] In this configuration, when compressed air flows into the cylindrical body 11, air pressure is applied to the inner circumference of the cylindrical body 11 in all directions. Since the cylindrical body 11 is made of a crosslinked rubber composition which is an elastic body (elastomer), it stretches relatively large in the axial direction. At that time, the cylindrical body 11 stretches in the axial direction and also tries to expand in the radial direction. Here, the cord 12, which acts as a tensile body, is made of a member containing fibers that are continuously connected from one end 11a to the other end 11b in the axial direction of the cylindrical body 11, and is arranged spirally along the circumferential direction on the outer circumference of the cylindrical body 11. Therefore, the cylindrical body 11, which tries to expand radially, is given helical fiber constraint along its entire axial direction by the cord 12. The helical fiber constraint by the cord 12 is along the circumferential direction of the cylindrical body 11, and as a result, the air pressure that tries to expand the cylindrical body 11 radially acts as air pressure that tries to spread the portion between adjacent cords 12 in the axial direction of the cylindrical body 11 in the axial direction. Here, the restraining member 17 is fixed to the cylindrical body 11 in a portion of its circumferential direction, extending axially from one end 11a to the other end 11b. As a result, the restrained portion 11R of the cylindrical body 11 is restrained by the restraining member 17, and its axial elongation is suppressed. On the other hand, the unrestrained portion 11N of the cylindrical body 11 is not restrained by the restraining member 17, and its axial elongation is not suppressed, so it stretches in the axial direction. As a result, the cylindrical body 11 curves in the direction from the central axis of the cylindrical body 11 in the radial direction toward the restrained portion 11R of the cylindrical body 11. In addition, since the cord 12 is bonded to the outer circumference of the cylindrical body 11 containing the crosslinked rubber composition, the fiber restraint is greater compared to when the cord 12 is not bonded to the cylindrical body 11. This further suppresses the radial expansion of the cylindrical body 11 compared to when the cord 12 is not bonded to the cylindrical body 11. Furthermore, by using a fiber cord 12 as the tensile body, the stiffness is lower and the elongation rate is higher compared to a coil spring. Therefore, the fiber cord 12 can provide helical fiber constraint to the cylindrical body 11 while increasing the axial elongation of the unconstrained portion 11N of the cylindrical body 11. As a result, the cylindrical body 11 can be curved significantly as the axial elongation of the unconstrained portion 11N increases, thereby improving its flexibility.

[0053] Furthermore, as shown in Figure 2(B), the angle α between the direction parallel to the circumferential direction of the cylindrical body 11 and the direction parallel to the axial direction of the cord 12 is, for example, greater than 0 degrees and 10 degrees or less, preferably greater than 0 degrees and 5 degrees or less. The closer the angle α is to 0 degrees, the better. With this configuration, the cords 12 are arranged spirally at a predetermined cord pitch P (details will be described later) parallel to the approximately circumferential direction of the cylindrical body 11. As a result, compared to the case where the angle α between the direction parallel to the circumferential direction of the cylindrical body 11 and the direction parallel to the axial direction of the cord 12 is greater than 10 degrees, more cords 12 can be bonded to a cylindrical body 11 of the same axial length, and the number of spaces between the cords 12 also increases. Therefore, when the cylindrical body 11 expands radially, the cords 12 create larger helical fiber constraints. Consequently, the air pressure that attempts to expand the cylindrical body 11 radially acts as air pressure that attempts to further widen the space between adjacent cords 12 in the axial direction of the cylindrical body 11 in the axial direction. As a result, the fluid pressure actuator 1 can further suppress the radial expansion of the cylindrical body 11 while increasing the axial elongation of the unrestrained portion 11N, thereby improving the curvature of the cylindrical body 11.

[0054] Furthermore, the tensile modulus of the fibers constituting the cord 12 is, for example, 2 GPa or more and 150 GPa or less, preferably 4 GPa or more and 150 GPa or less, and more preferably 5 GPa or more and 150 GPa or less. With this configuration, the cord 12 made of fibers can achieve both the elongation rate of the tubular body 11 and the fracture safety. The cord 12 provides sufficient helical fiber restraint to the tubular body 11 while also providing the axial elongation rate necessary for the curvature of the tubular body 11. As a result, the tubular body 11 can be curved significantly as the axial elongation of the unrestrained portion 11N increases, thereby improving its flexibility.

[0055] Furthermore, as shown in Figure 3, it is preferable that the cords 12 are arranged such that, when no compressed air is flowing into the cylindrical body 11 and there is no pressure, the spacing d between adjacent cords 12 in the axial direction from one end 11a to the other end 11b of the cylindrical body 11 is 2.6 mm or less. With this configuration, the arrangement of the cords 12 arranged spirally in the cylindrical body 11 is dense, which improves the pressure resistance of the cylindrical body 11. As a result, a larger air pressure can be applied to the cylindrical body 11, and the axial elongation of the unrestrained portion 11N of the cylindrical body 11 can be increased. Then, as the axial elongation of the unrestrained portion 11N of the cylindrical body 11 increases, the cylindrical body 11 can be curved more significantly, thereby improving its flexibility.

[0056] Furthermore, the cord 12 preferably has an average wire diameter (outer diameter D of the cord 12) of 0.1 to 5 mm.

[0057] Furthermore, with respect to the cord 12, by adjusting the outer diameter D of the cord 12 and the spacing d between adjacent cords 12 in the axial direction, or the cord pitch P which is the interaxial distance between adjacent cords 12 in the axial direction, the X value (%) of the cord 12 arrangement density can be appropriately adjusted to control the constraint on the helical fibers, that is, the constraint that further increases the elongation rate in the axial direction while suppressing the radial expansion of the cylindrical body 11. In this embodiment, the X value (%) of the cord 12 arrangement density is defined as "the ratio of areas where cords are not arranged (total spacing d) to the axial length W of the cylindrical body 11," that is, "the ratio of the total spacing d between adjacent cords 12 in the axial direction to the axial length W of the cylindrical body 11." A larger X value means that the cords 12 are sparsely arranged in the axial direction of the cylindrical body 11. On the other hand, a smaller X value means that the cords 12 are densely arranged in the axial direction of the cylindrical body 11.

[0058] More specifically, as shown in Figure 3, which illustrates the axial length W of the cylindrical body 11, the outer diameter D of the cord 12, the spacing d between adjacent cords 12 in the axial direction, and the cord pitch P of this embodiment, adjacent cords 12 in the cylindrical body 11 are arranged with a predetermined spacing d in the axial direction. The total spacing d between adjacent cords 12 in the axial direction of the cylindrical body 11 includes the spacing between one end 11a of the cylindrical body 11 and the cord 12, and the spacing between the other end 11b of the cylindrical body 11 and the cord 12. In other words, the total spacing d between adjacent cords 12 in the axial direction of the cylindrical body 11 means the value obtained by subtracting the value of "total outer diameter D of the cords 12 (outer diameter D of the cord 12 × number of turns of the cord 12)" from the value of "axial length W of the cylindrical body 11". Therefore, the X value (%) can be replaced by the relationship between the outer diameter D of the cord 12 and the cord pitch P, as shown in the following formula.

[0059] X value (%) = (Sum of intervals d / Length W) × 100 = [(Length W - Sum of cord outer diameters D) / Length W] × 100 = {[Length W - (Cord outer diameter D × Number of cord turns)] / Length W} × 100 = <{Length W - [Cord outer diameter D × (Length W / Cord pitch P)]} / Length W> × 100 = [1 - (Cord outer diameter D / Cord pitch P)] × 100

[0060] In this embodiment, the axial length W of the cylindrical body 11, the outer diameter D of the cord 12, the distance d between adjacent cords 12, and the cord pitch P are determined based on the axial cross-sectional view (cross-sectional perspective) of the cylindrical body. The cord pitch P is the distance between adjacent cords 12 in the axial direction of the cylindrical body 11 in the cross-sectional view, as shown in Figure 3. If the cord 12 is an untwisted cord, the cross-sectional area of ​​the cord 12 embedded in the cross-linked rubber composition is measured, and assuming a perfect circle with an area equivalent to the measured cross-sectional area, the diameter of that perfect circle is calculated as the outer diameter D. The cross-sectional area of ​​the cord 12 is measured by cutting the cross-linked rubber composition in which the cord 12 is embedded perpendicular to the winding direction of the cord 12 and observing the cut surface with a microscope.

[0061] Furthermore, as shown in Figure 3, the cord 12 is arranged such that the cord pitch P of each cord 12, which is arranged spirally from one end 11a to the other end 11b in the width direction, is a constant value. Each cord pitch P only needs to be larger than the outer diameter D of the cord 12. In this embodiment, as shown in Figure 3, the apparent number of cords 12 arranged in the width direction of the cylindrical body 11 with a predetermined cord pitch P in a cross-sectional view is treated as the "number of cord turns". That is, the "number of helices" of a single cord 12 arranged spirally is taken as the "number of cord turns".

[0062] Here, it is desirable to count only the number of turns of the cord that affect the helical fiber constraint on the cylindrical body 11. Therefore, it is desirable to not include the cut cords 12 that are placed at one end 11a and the other end 11b in the width direction of the cylindrical body 11 and have a non-circular cross-section in the "number of turns of the cord," but to count only the cords 12 that have not been cut in cross-section as the "number of turns of the cord."

[0063] Specifically, the approximate "number of cord turns" is calculated by dividing the axial length W of the cylindrical body 11 by the cord pitch P, and then truncating the decimal part of the result. For example, if the axial length W of the cylindrical body 11 is 100 mm and the cord pitch P is 2.9 mm, the calculated value is 34.48, and "34" is considered the "number of cord turns".

[0064] It is preferable that the cords 12 are arranged such that the X value of the arrangement density of the cords 12 is in the range of 60% to 90% when no pressure is applied. By arranging the cords 12 in this range on the cylindrical body 11, the cords 12 can be arranged on the cylindrical body 11 while maintaining an appropriate amount of space between adjacent cords 12 in the axial direction of the cylindrical body 11. As a result, when the cylindrical body 11 expands radially, the cords 12 create a larger helical fiber constraint. Consequently, the air pressure that attempts to expand the cylindrical body 11 radially acts as air pressure that attempts to further widen the space between adjacent cords 12 in the axial direction of the cylindrical body 11 in the axial direction. This allows for increased axial elongation of the unconstrained portion 11N of the cylindrical body 11 while suppressing radial expansion of the cylindrical body 11. Therefore, the cylindrical body 11 can be curved significantly as the axial elongation of the unconstrained portion 11N increases, thereby improving its curvature.

[0065] Furthermore, the fluid pressure actuator 1 of this embodiment takes into account the cord pitch P, which is the distance between adjacent cords 12 in the axial direction of the cylindrical body 11 when no pressure is applied, and calculates the strain index Z as "(inner diameter of cylindrical body 11 [mm]) × (cord pitch P [mm]) / {(tensile modulus of elasticity of cord 12 [GPa]) × (cord diameter [mm]) 2The value of "}" is set. The value of the strain index Z is, for example, 1 [1 / GPa] or more and 400 [1 / GPa] or less, preferably 1 [1 / GPa] or more and 110 [1 / GPa] or less, and more preferably 1 [1 / GPa] or more and 50 [1 / GPa] or less. With this configuration, the circumferential strain in the cylindrical body 11 can be reduced. Specifically, when air pressure is applied to the cylindrical body 11, the "circumferential stress of the cylindrical body 11 receiving internal pressure" is almost entirely borne by the cord 12, so if the thickness of the cylindrical body 11 is ignored, the "circumferential stress of the cylindrical body 11 receiving internal pressure" can be considered as (inner diameter of the cylindrical body 11) × (air pressure). On the other hand, the "circumferential stress of the cylindrical body 11 receiving internal pressure" is (strain) × (elastic modulus of the cylindrical body 11). Therefore, (inner diameter of cylindrical body 11) × (air pressure) = (strain) × (elastic modulus of cylindrical body 11). Thus, (strain) can be considered as (inner diameter of cylindrical body 11) × (air pressure) / (elastic modulus of cylindrical body 11). Here, "elastic modulus of cylindrical body 11" is [(tensile modulus of cord 12 × (cord diameter) 2 It is proportional to (inner diameter of the cylindrical body 11) × (cord pitch P) / [(tensile modulus of elasticity of the cord 12) × (cord diameter)]. Therefore, when the cylindrical body 11 is subjected to internal pressure, the circumferential "strain" of the cylindrical body 11 is (inner diameter of the cylindrical body 11) × (cord pitch P) / [(tensile modulus of elasticity of the cord 12) × (cord diameter)] 2 It is proportional to ]. Therefore, it is preferable for the circumferential "strain" of the cylindrical body 11 to be small, so the strain index Z is "(inner diameter of cylindrical body 11 [mm]) × (cord pitch P [mm]) / {(tensile modulus of cord 12 [GPa]) × (cord diameter [mm]) 2 It is preferable to set the value of} to 400 [1 / GPa] or less. In this way, the circumferential strain in the cylindrical body 11 can be reduced, thereby improving the pressure resistance of the cylindrical body 11. As a result, a larger air pressure can be applied to the cylindrical body 11, and the axial elongation of the restraining portion 11R of the cylindrical body 11 can be increased. Then, as the axial elongation of the cylindrical body 11 increases, it can be curved more significantly, thereby improving its curvature.

[0066] Furthermore, the cord 12 can be composed of a twisted cord formed by twisting together multiple strands or multifilament yarns (fibers), an untwisted cord formed by not twisting together multiple strands or multifilament yarns (fibers), a cord made of monofilaments, or a cord with a braided structure. If the cord 12 is a twisted cord, a twisted cord of strands is preferred, and one strand may be formed by bundling filaments (long fibers). The material of the filaments is a polyester fiber [polyalkylene arylate fiber (for example, C2-4 alkylene C8-14 arylate fibers such as polyethylene terephthalate (PET) fiber, polytrimethylene terephthalate (PTT) fiber, polybutylene terephthalate (PBT) fiber, polyethylene naphthalate (PEN) fiber); polyarylate fiber, liquid crystal polyester fiber, or other fully aromatic polyester fiber], which has a sufficiently lower tensile modulus of elasticity than conventionally widely used E glass fiber (general-purpose alkali-free glass fiber) and a higher tensile modulus of elasticity than aliphatic polyamide fiber.

[0067] If the cord 12 is a twisted cord, there are no particular restrictions on the thickness of the filaments forming the twisted cord, the number of filaments converged, the number of strands, and the twisting method (e.g., double twist, single twist, Lang twist). For example, a polyester cord with a total fineness of 230 to 710 dtex can be used, which is double-twisted with a group of filaments (strands) of 75 to 235 dtex at an upper twist count of 40 to 60 turns / 10 cm and a lower twist count of 50 to 90 turns / 10 cm. Alternatively, an aramid cord with a total fineness of 200 to 1600 dtex can be used, which is single-twisted with a group of filaments (strands) of 200 to 400 dtex at an upper twist count of 30 to 100 turns / 10 cm. Additionally, nylon cords with a total fineness of 165 to 1760 dtex can be used, which are made by twisting together filament groups (strands) of 165 to 330 dtex with 10 to 50 twists per 10 cm on the top and 20 to 80 twists per 10 cm on the bottom.

[0068] When the cord 12 is an untwisted cord, there are no particular restrictions on the composition, such as the thickness of the filaments forming the untwisted cord, the number of filaments converged, and the number of strands. For example, an untwisted nylon cord with a fineness of 33 to 2100 dtex (10 to 312 filaments), an untwisted polyester cord with a fineness of 1100 to 1670 dtex (60 to 240 filaments), or an untwisted p-aramid cord with a fineness of 420 to 17000 dtex (250 to 5000 filaments) can be used. When the cord 12 is a monofilament cord, for example, a cord made of polyester monofilament with 330 to 890 dtex, a cord made of polypropylene monofilament with 220 to 1330 dtex, or a cord made of nylon monofilament with 370 to 1330 dtex can be used. If the cord 12 is a braided cord, for example, a braided cord made of ultra-high molecular weight polyethylene with a diameter of 0.053 to 0.69 mm can be used.

[0069] The twisted or untwisted cord used as the cord 12 may be subjected to an adhesive treatment to enhance its adhesion to the crosslinked rubber composition constituting the tubular body 11. For example, the adhesive treatment may involve immersing the twisted or untwisted cord in a resorcinol-formaldehyde-latex treatment solution (RFL treatment solution), followed by heating and drying to form a uniform adhesive layer on the surface of the twisted or untwisted cord. The RFL treatment solution is a mixture of latex and an initial condensate of resorcinol and formalin. The latex may be, for example, chloroprene, styrene-butadiene-vinylpyridine terpolymer (VP latex), nitrile rubber, or hydrogenated nitrile rubber. Furthermore, the adhesive treatment may involve pre-treating with an epoxy compound or isocyanate compound before treatment with the RFL treatment solution.

[0070] Here, it is preferable that the cord 12 is made of an untwisted cord rather than a twisted cord. By making the cord 12 an untwisted cord, the cross-section of the cord 12 becomes flat. Compared with a cord made of twisted fibers whose cross-section is circular, the cords 12 that are arranged adjacent to each other in the axial direction of the cylindrical body 11 overlap, and the circumferential fiber constraint is increased, improving the pressure resistance. Therefore, when air pressure is applied, the radial expansion of the cylindrical body 11 is further suppressed. As a result, the air pressure acts more effectively against axial elongation, so that the radial expansion of the cylindrical body 11 is suppressed while the axial elongation of the unconstrained portion 11N of the cylindrical body 11 can be increased. Therefore, the cylindrical body 11 can be curved more as the axial elongation of the unconstrained portion 11N increases, thereby improving its curvature.

[0071] (Restraining member 17) The restraining member 17 is formed from a crosslinked rubber composition, canvas, or an array of cords.

[0072] When the restraining member 17 is formed from a crosslinked rubber composition, the restraining member 17 is in the shape of a sheet. The materials that can be used for the restraining member 17 are the same as those used for the cylindrical body 11 described above. Since the restraining member 17 is a crosslinked rubber composition, the adhesion between it and the crosslinked rubber composition constituting the cylindrical body 11 is strengthened and integrated by the crosslinking molding process in the manufacturing process of the fluid pressure actuator 1.

[0073] Furthermore, if the restraining member 17 is formed from a crosslinked rubber composition, the restraining member 17 may contain short fibers. When the restraining member 17 contains short fibers, it is preferable that the orientation direction of the short fibers is parallel to the axial direction of the cylindrical body 11. This improves the elastic modulus of the restraining member 17. As a result, the restraining force of the restraining member 17 on the restraining portion 11R of the cylindrical body 11 is strengthened, so that the axial elongation of the restraining portion 11R in the cylindrical body 11 is further suppressed. As a result, when the cylindrical body 11 is pressed, the curvature of the cylindrical body 11 can be further increased.

[0074] Examples of short fibers contained in the restraining member 17 include polyolefin fibers (polyethylene fibers, polypropylene fibers, etc.), polyamide fibers (nylon fibers such as polyamide 6 fibers, polyamide 66 fibers, polyamide 46 fibers, etc., aramid fibers, etc.), and polyalkylene arylate fibers [polyethylene terephthalate (PET) fibers, polyethylene naphthalate (PEN) fibers, etc., polyC 2-4 Alkilen C 6-14Synthetic fibers such as arylate fibers, vinylon fibers, polyvinyl alcohol fibers, and poly(p-phenylenebenzobisoxazole (PBO)) fibers; natural fibers such as cotton, linen, and wool; and inorganic fibers such as carbon fibers are commonly used. These short fibers can be used alone or in combination of two or more types. Among these short fibers, polyalkylene arylate fibers such as PET fibers, polyamide fibers such as polyamide 66 fibers and aramid fibers, and cellulose fibers such as cotton are preferred, and nylon fibers such as polyamide 66 fibers are particularly preferred. The average fiber diameter of the short fibers is, for example, 0.5 to 1000 μm, preferably 3 to 100 μm, more preferably 5 to 50 μm, and more preferably 10 to 30 μm. If the fiber diameter is too large, the hardness and modulus of the crosslinked rubber may decrease, and if it is too small, it may be difficult to disperse it inside the crosslinked rubber composition constituting the restraining member 17. The average fiber length of the short fibers is, for example, 0.1 to 20 mm, preferably 1.5 to 10 mm, more preferably 2 to 5 mm, and more preferably 2.5 to 4 mm. If the average length of the short fibers is too short, there is a risk that the mechanical properties in the direction of the fibers, such as modulus, cannot be sufficiently enhanced, and conversely, if it is too long, there is a risk that the dispersibility of the short fibers in the rubber composition will decrease. From the viewpoint of the dispersibility and adhesion of the short fibers in the rubber composition, it is preferable that at least the short fibers be bonded or surface-treated. It is not necessary for all short fibers to be bonded, and bonded short fibers and unbonded short fibers may be mixed or used in combination. In the bonding treatment of short fibers, various bonding treatments can be used, such as a treatment solution containing an initial condensate of phenols and formalin (such as a prepolymer of novolac or resol-type phenolic resin), a treatment solution containing a rubber component (or latex), a treatment solution containing the initial condensate and a rubber component (latex), a treatment solution containing a silane coupling agent, an epoxy compound (such as epoxy resin), or a reactive compound (adhesive compound) such as an isocyanate compound. In a preferred bonding treatment, the short fibers are treated with a treatment solution containing the initial condensate and a rubber component (latex), particularly with at least a resorcinol-formaldehyde-latex (RFL) solution.These treatment solutions may be used in combination. For example, short fibers may be pretreated with a conventional adhesive component, such as an epoxy compound (epoxy resin, etc.) or a reactive compound (adhesive compound) such as an isocyanate compound, and then treated with the RFL solution.

[0075] When the restraint member 17 is formed from canvas, it may be formed from, for example, woven fabric, knitted fabric, or nonwoven fabric. Conventionally, it is often woven fabric, and the weave structure of the woven fabric is not particularly limited as long as the warp and weft threads intersect regularly in the vertical and horizontal directions. It may be plain weave, twill weave (or diagonal weave), satin weave, or a combination of these structures. Organic fibers are commonly used as fibers to form the canvas, and examples include cellulose fibers such as cotton and rayon, polyester fibers (PET fibers, etc.), polyamide fibers (aliphatic polyamide fibers such as polyamide 66 fibers, aramid fibers, etc.), PBO fibers, and fluororesin fibers [polytetrafluoroethylene (PTFE) fibers, etc.]. These fibers can be used alone or in combination of two or more. To improve adhesion with the tubular body 11, the canvas forming the restraint member 17 may be treated with adhesive. Examples of bonding treatments include immersing the canvas in an RFL treatment solution followed by heat drying; treating it with an epoxy compound or isocyanate compound; dissolving a rubber composition in an organic solvent to make a rubber glue, immersing the canvas in this glue, and then heat drying; and combining these treatment methods. These methods can be performed individually or in combination, and the order and number of treatments are not limited. For example, the canvas may be pretreated with an epoxy compound or isocyanate compound, then immersed in an RFL treatment solution, and then heat dried.

[0076] For example, if the restraint member 17 is a treated canvas made of 6,6-nylon plain weave fabric that has been subjected to RFL treatment, the restraint member 17 is bonded to the crosslinked rubber composition constituting the cylindrical body 11 by crosslink molding in the manufacturing process of the fluid pressure actuator 1, and is integrated with it.

[0077] When the restraint member 17 is formed by an array of cords, the array of cords consists of a plurality of cords arranged axially from one end 11a to the other end 11b of the cylindrical body 11, arranged in the circumferential direction of the cylindrical body 11. The material of the cords used for the array of cords is the same as that of the cord 12 described above. In order to improve the adhesion between the restraint member 17 formed by the array of cords and the cylindrical body 11, each cord is subjected to an adhesive treatment, and the adhesion between the restraint member 17 and the cross-linked rubber composition constituting the cylindrical body 11 is strengthened and integrated by cross-linking molding in the manufacturing process of the fluid pressure actuator 1.

[0078] As described above, the restraining member 17 is made of a cross-linked rubber composition, canvas, or arrayed cord. The restraining member has a lower elastic modulus and is more flexible than metal, plastic, or carbon fiber reinforced plastic, and has a higher elastic modulus and stronger restraining force than fiber, thread, silicone, or rubber. Therefore, when the cylindrical body 11 is expanded or contracted, the curvature of the restraining portion 11R of the cylindrical body 11 can be increased, while a smooth bending movement proportional to the pressure can be achieved. Thus, the fluid pressure actuator 1 can enhance the curvature when the cylindrical body 11 is expanded or contracted.

[0079] Furthermore, it is preferable that the length of the restraining member 17 in the circumferential direction of the cylindrical body 11 is in the range of 15% to 60% of the outer circumference length of the curved portion 11c when no pressure is applied. If the length of the restraining portion 11R relative to the outer circumference length of the curved portion 11c is greater than 60% in the circumferential direction of the curved portion 11c, the curved portion 11c will be less likely to bend, and the curvature of the curved portion 11c will be smaller. On the other hand, if the length of the restraining portion 11R relative to the outer circumference length of the curved portion 11c is less than 15% in the circumferential direction of the curved portion 11c, the restraining force of the restraining portion 11R of the curved portion 11c will be weaker, and although the curved portion 11c will stretch, it will not bend properly. Therefore, with the above configuration, the curvature of the curved portion 11c when the curved portion 11c is bent can be made appropriately large. Also, if the restraining member 17 is canvas, it is preferable that the thickness of the restraining member 17 is in the range of, for example, 0.2 mm to 1.5 mm. Furthermore, if the restraining member 17 is a rubber sheet, the thickness of the restraining member 17 is preferably in the range of, for example, 0.5 mm or more and 2.0 mm or less.

[0080] Furthermore, in the curved portion 11c, it is preferable that the ratio B / A of the following parameter B, which is an indicator of the elongation of the constrained portion 11R, and the following parameter A, which is an indicator of the elongation of the unconstrained portion 11N in the curved portion 11c, is between 0.5 and 150. Parameter B [N] = (Tensile force [N] when the constrained portion 11R is stretched by 10%) × (Percentage of the outer circumference of the cylindrical body 11 (curved portion 11c) occupied by the constrained portion 11R) Parameter A [N] = (Tensile force [N] when the unconstrained portion 11N is stretched by 10%) × (Percentage of the outer circumference of the cylindrical body 11 (curved portion 11c) occupied by the unconstrained portion 11N)

[0081] Parameter B and parameter A represent resistance to stretching as their values ​​increase. If the ratio of parameter B to parameter A is too small, the curved portion 11c will stretch axially without curving; therefore, a larger ratio of parameter B to parameter A makes it easier to curve. For this reason, if the ratio B / A is 0.5 or greater, the restraining force of the restrained portion 11R by the restraining member 17 acts sufficiently, and the curved portion 11c can be curved appropriately.

[0082] (Method for manufacturing the fluid pressure actuator 1) First, an uncrosslinked rubber sheet made of a rubber composition is wrapped around the outer circumference of a cylindrical molding mold with a smooth surface. Next, a cord 12 is spun spirally around the outer circumference of the uncrosslinked rubber sheet at a predetermined pitch to produce an uncrosslinked cylindrical molded body. Next, a restraining member 17 is placed in a predetermined range on the outer circumference of the cylindrical molded body, from one end to the other. If the restraining member 17 contains short fibers, the orientation of the short fibers is arranged to coincide with the axial direction of the cylindrical molded body. After that, with a flexible jacket placed on the outside of the uncrosslinked cylindrical molded body, the molding mold is placed in a vulcanizing apparatus and crosslinking is performed to produce a crosslinked sleeve. When crosslinking is performed, crosslinks are formed between the cord 12 and the crosslinked sleeve, which is made of a crosslinked rubber composition, and between the restraining member 17 and the crosslinked sleeve, resulting in strong adhesion through chemical crosslinking bonds. After demolding the obtained cylindrical crosslinking sleeve from the molding mold, the crosslinking sleeve is cut to a predetermined size to produce a cylindrical body 11 with the restraining member 17 bonded along the axial direction.

[0083] Next, the caps 13a and 13b are fitted onto both ends of the cylindrical body 11. Then, the hose clamp 14a is fastened around the outer circumference of one end 11a of the cylindrical body 11 to secure that end 11a to the cap 13a. Similarly, the hose clamp 14b is fastened around the outer circumference of the other end 11b of the cylindrical body 11 to secure that end 11b to the cap 13b. The fluid pressure actuator 1 is manufactured through the above process.

[0084] Furthermore, short fibers may be incorporated into the crosslinked rubber composition that constitutes the cylindrical body 11 of the fluid pressure actuator 1. The same short fibers as those contained in the restraining member 17 described in the first embodiment can be used as the short fibers incorporated into the crosslinked rubber composition that constitutes the cylindrical body 11. The orientation direction of the short fibers contained in the cylindrical body 11 is preferably in the range from the direction parallel to the circumferential direction of the cylindrical body 11 to the direction parallel to the axial direction of the cord 12 (see Figure 2(B)). Here, as mentioned above, the cord 12 is preferably arranged such that the angle α between the direction parallel to the circumferential direction of the cylindrical body 11 and the direction parallel to the axial direction of the cord 12 is greater than 0 degrees and 10 degrees or less, and furthermore, the closer the angle α is to 0 degrees, the better. Therefore, the orientation direction of the short fibers contained in the cylindrical body 11 is preferably in the range of 0 degrees or more and 10 degrees or less for the angle between the direction parallel to the circumferential direction of the cylindrical body 11 and the orientation direction of the short fibers, and furthermore, the closer the angle is to 0 degrees, the better.

[0085] In this configuration, the short fibers are oriented along the circumferential direction of the cylindrical body 11. As a result, the oriented short fibers do not increase the axial stiffness (elastic modulus) of the cylindrical body 11, but increase the circumferential stiffness (elastic modulus). In particular, in the portion between adjacent cords 12 in the axial direction of the cylindrical body 11, the increased circumferential stiffness makes it more difficult for the cylindrical body 11 to deform radially, thus further suppressing radial expansion of the cylindrical body 11 when air pressure is applied. As a result, the air pressure acts more strongly on the portion between adjacent cords 12 in the axial direction of the cylindrical body 11. Consequently, the spacing between the cords 12 in the axial direction of the cylindrical body 11 widens further, causing the cylindrical body 11 to stretch further in the axial direction. In other words, by suppressing radial expansion of the cylindrical body 11, the cylindrical body 11 will not expand radially even when greater air pressure is applied, allowing greater pressure to be applied to the axial stretching of the cylindrical body 11, and thus increasing the elongation rate. Therefore, with a fluid pressure actuator 1 containing short fibers oriented along the circumferential direction of the cylindrical body 11, compared to the case where the cylindrical body 11 contains a crosslinked rubber composition without short fibers, it is possible to further suppress the radial expansion of the cylindrical body 11, increase the axial elongation of the unrestrained portion 11N, and improve the curvature of the cylindrical body 11.

[0086] (Second Embodiment) As shown in Figure 4(A), the fluid pressure actuator 201 includes a cylindrical body 211 made of a cylindrical cross-linked rubber composition and a cord 212 helically bonded to the outer circumference of the cylindrical body 211 along the circumferential direction. The cylindrical body 211 has a curved portion 211c in which at least a part in the axial direction bends when pressurized. In this embodiment, the entire cylindrical body 211 is a curved portion 211c, and the cylindrical body 211 functions as a curved portion 211c along its entire length, but a part in the axial direction of the cylindrical body 211 may be a curved portion 211c. A restraining member 217 is fixed to a part in the circumferential direction of the curved portion 211c, extending from one end to the other along the axial direction. In the fluid pressure actuator 1 of the first embodiment described above, the cord 12, which is helically bonded to the outer circumference of the cylindrical body 11 along the circumferential direction, is partially embedded in the cross-linked rubber composition constituting the cylindrical body 11 in a cross section perpendicular to the axial direction of the cord 12, as shown in Figure 3. On the other hand, in the fluid pressure actuator 201 of the second embodiment, the cord 212 is helically bonded to the inside of the cylindrical body 211 along the circumferential direction, and is bonded in a state where it is continuously connected from one end 211a to the other end 211b in the axial direction (see Figures 4 to 6). In detail, as shown in Figure 6, the cord 212 is bonded to the inside of the cylindrical body 211 from one end 211a to the other end 211b in the axial direction, with the entire cord 212 embedded in the cross-linked rubber composition constituting the cylindrical body 211 in a cross section perpendicular to the axial direction of the cord 212. That is, the cord 212 is embedded in the cross-linked rubber composition constituting the cylindrical body 211 in a state where it is not exposed to the outside. Furthermore, the statement that the code 212 is embedded in the cylindrical body 211 includes cases where a part of the code 212 is embedded in the cylindrical body 211, and cases where the entire code 212 is embedded in the cylindrical body 211.

[0087] Furthermore, the cord 212 is bonded to the crosslinked rubber composition constituting the cylindrical body 211 by a crosslinking reaction during the manufacturing process of the fluid pressure actuator 201, thereby strengthening the adhesion between the entire circumferential direction of the cord 212 and the crosslinked rubber composition constituting the cylindrical body 211, and integrating them. For this reason, the cord 212 is more firmly bonded to the crosslinked rubber composition constituting the cylindrical body 211 than the cord 12 in the first embodiment. The restraining member 217 is fixed to the outer circumference of the cylindrical body 211 along the axial direction from one end 211a to the other end 211b in a portion of the circumferential direction of the cylindrical body 211. The other configurations of the fluid pressure actuator 201 according to the second embodiment are the same as those of the first embodiment.

[0088] (Method for manufacturing the fluid pressure actuator 201) First, an uncrosslinked rubber sheet made of a rubber composition is wrapped around the outer circumference of a cylindrical molding mold with a smooth surface. Next, a cord 212 is spun spirally around the outer circumference of the uncrosslinked rubber sheet at a predetermined pitch. Next, an uncrosslinked rubber sheet made of a rubber composition is wrapped around the outer circumference of the cord 212 spun around the outer circumference of the uncrosslinked rubber sheet to produce an uncrosslinked cylindrical molded body. Next, a restraining member 217 is placed in a predetermined range on the outer circumference of the cylindrical molded body, from one end to the other. If the restraining member 217 contains short fibers, the orientation of the short fibers is arranged to coincide with the axial direction of the cylindrical molded body. After that, with a flexible jacket placed on the outside of the uncrosslinked cylindrical molded body, the molding mold is placed in a vulcanizing apparatus and crosslinked to produce a crosslinked sleeve. When crosslinking molding is performed, a crosslinking reaction causes crosslinks to form between the cord 212 and the crosslinked rubber composition, which is the crosslinked sleeve, and between the restraint member 217 and the crosslinked sleeve, resulting in strong adhesion through chemical crosslinking bonds. After demolding the obtained cylindrical crosslinked sleeve from the molding mold, the crosslinked sleeve is cut to a predetermined size to produce a cylindrical body 211 in which the cord 212 is helically bonded inside and the restraint member 217 is bonded along the axial direction. The other steps are the same as in the first embodiment. The fluid pressure actuator 201 is manufactured by the above steps.

[0089] In this configuration, when compressed air flows into the cylindrical body 211, air pressure is applied to the inner circumference of the cylindrical body 211 in all directions. Since the cylindrical body 211 is made of a crosslinked rubber composition with a higher elastic modulus than a non-crosslinked rubber composition, it stretches relatively large in the axial direction. At that time, the cylindrical body 211 stretches in the axial direction and also tries to expand in the radial direction. Here, a cord 212 made of fibers that are continuously connected from one end 211a to the other end 211b in the axial direction of the cylindrical body 211 is arranged spirally along the circumferential direction inside the cylindrical body 211. Therefore, the cylindrical body 211 that tries to expand radially is given helical fiber constraint along its entire axial direction by the cord 212. The helical fiber constraint by the cord 212 is along the circumferential direction of the cylindrical body 211, and as a result, the air pressure that tries to expand the cylindrical body 211 radially acts as air pressure that tries to spread the portions between adjacent cords 212 in the axial direction of the cylindrical body 211 in the axial direction. Here, the restraining member 217 is fixed to the cylindrical body 211 in a portion of its circumferential direction, extending axially from one end 211a to the other end 211b. As a result, the restrained portion 211R of the cylindrical body 211 is restrained by the restraining member 217, and its axial elongation is suppressed. On the other hand, the unrestrained portion 211N of the cylindrical body 211 is not restrained by the restraining member 217, and its axial elongation is not suppressed, so it extends axially. As a result, the cylindrical body 211 curves in the direction from the central axis of the cylindrical body 211 in the radial direction toward the restrained portion 211R of the cylindrical body 211. Here, since the cord 212 is bonded inside the cylindrical body 211 made of a cross-linked rubber composition, the fiber restraint is greater compared to when the cord 212 is not bonded to the cylindrical body 211. As a result, radial expansion of the cylindrical body 211 is more suppressed compared to when the cord 212 is not adhered to the cylindrical body 211. This makes it possible to increase the axial elongation rate of the unrestrained portion 211N of the cylindrical body 211 while suppressing radial expansion of the cylindrical body 211. As a result, the cylindrical body 211 can be curved more significantly as the axial elongation of the unrestrained portion 211N increases, thereby improving its flexibility.

[0090] (Modification of the Second Embodiment) In the modified fluid pressure actuator 1201 of the second embodiment, a cord 216 (corresponding to a second cord) is further bonded in a helical manner along the circumferential direction of the cylindrical body 1211 to the outer circumference of the cord 212 (corresponding to a first cord) of the fluid pressure actuator 201 of the second embodiment (see Figure 4). The cord 216 may be bonded in a continuous manner from one end 211a to the other end 211b in the axial direction.

[0091] In detail, when no pressure is applied, the cords 212 and 216 may be bonded to the cross-linked rubber composition constituting the cylindrical body 1211, overlapping radially within the cylindrical body 1211, such that the orientation of their respective helices is axially symmetric with respect to the axial direction of the cylindrical body 1211 (see Figure 7). For example, if the helical direction of cord 212 is right-handed (Z-winding), then the helical direction of cord 216 is left-handed (S-winding), forming a double helix structure. Also, if the helical direction of cord 212 is left-handed, then the helical direction of cord 216 is right-handed, forming a double helix structure. In other words, the helical winding of the first cord, cord 212, and the second cord, cord 216, is such that one is right-handed and the other is left-handed. Note that the same material may be used for code 216 as for code 212, or a different code may be made using the materials described above for the constituent materials of code 12. Furthermore, code 212 and code 216 do not necessarily need to be bonded to the cylindrical body 1211; they only need to be held in a state where relative movement with respect to the cylindrical body 1211 is suppressed. In other words, code 212 and code 216 may be fixed to the outer circumference of the cylindrical body 1211, or embedded inside the cylindrical body 1211.

[0092] (Method for manufacturing the fluid pressure actuator 1201) First, an uncrosslinked rubber sheet made of a rubber composition is wrapped around the outer circumference of a cylindrical molding mold 281 with a smooth surface. Next, as shown in Figure 7(A), a cord 212 is spun spirally around the outer circumference of the uncrosslinked rubber sheet at a predetermined pitch. Next, as shown in Figure 7(B), a cord 216 is spun spirally around the outer circumference of the cord 212 spun around the outer circumference of the uncrosslinked rubber sheet at a predetermined pitch, such that the direction of the spiral is opposite to that of the cord 212. For example, if the spiral direction of the cord 212 is right-handed, the cord 216 is spun around the outer circumference of the cord 212 so that the spiral direction of the cord 216 is left-handed. On the other hand, if the spiral direction of the cord 212 is left-handed, the cord 216 is spun around the outer circumference of the cord 212 so that the spiral direction of the cord 216 is right-handed. Next, an uncrosslinked rubber sheet made of a rubber composition is wrapped around the outer circumference of the cord 216 to produce an uncrosslinked cylindrical molded body 210. Then, a restraining member 217 is placed in a predetermined area on the outer circumference of the cylindrical molded body 210, from one end to the other. If the restraining member 217 contains short fibers, the orientation of the short fibers is aligned with the axial direction of the cylindrical molded body 210. After that, with a flexible jacket placed on the outside of the uncrosslinked cylindrical molded body 210, the molding mold 281 is placed in a vulcanizing apparatus to perform crosslinking molding and produce a crosslinked sleeve. When crosslinking molding is performed, crosslinking reactions cause crosslinks to form between the cords 212 and 216 and the crosslinked sleeve, which is made of a crosslinked rubber composition, as well as between the restraining member 217 and the crosslinked sleeve, resulting in strong adhesion through chemical crosslinking bonds. After demolding the obtained cylindrical bridging sleeve from the molding mold 281, the bridging sleeve is cut to a predetermined size to produce a cylindrical body 1211 in which the cords 212 and 216 are bonded inside in a double helix shape, and the restraining member 217 is bonded along the axial direction. The other steps are the same as in the first embodiment. The fluid pressure actuator 1201 is manufactured by the above steps.

[0093] According to the fluid pressure actuator 1201 described above, axial twisting of the cylindrical body 1211 can be significantly suppressed. By suppressing axial twisting of the cylindrical body 1211, the axial elongation of the unrestrained portion 1211N of the fluid pressure actuator 1201 can be increased, thereby improving the curvature of the cylindrical body 1211.

[0094] (Third Embodiment) The fluid pressure actuator 301 of the third embodiment, as shown in Figure 8(A), includes a cylindrical body 311 containing a cylindrical crosslinked rubber composition and a cord 312 helically bonded to the outer circumference of the cylindrical body 311 along the circumferential direction. The cylindrical body 311 is a curved portion 311c in which at least a part in its axial direction is curved in the absence of pressure. In this embodiment, the entire cylindrical body 311 is a curved portion 311c, and the cylindrical body 311 functions as a curved portion 311c along its entire length, however, a part of the cylindrical body 311 in the axial direction may be a curved portion 311c. The cord 312 may be fixed to the outer circumference of the cylindrical body 311, or it may be embedded inside the cylindrical body 311. In the fluid pressure actuator 1 of the first embodiment described above, as shown in Figure 1(A), the restraining member 17 is fixed to the cylindrical body 11 along the axial direction from one end 11a to the other end 11b of the curved portion 11c of the cylindrical body 11, in a part of the circumferential direction of the curved portion 11c of the cylindrical body 11, when the cylindrical body 11 is not extended in the axial direction. As a result, when the fluid pressure actuator 1 extends in the axial direction by controlling the inflow and outflow of compressed air into the inner circumferential space of the sealed cylindrical body 11 by the control device, the axial extension of the restraining portion 11R of the cylindrical body 11 is suppressed, while the unrestrained portion 11N of the cylindrical body 11 extends in the axial direction, causing the cylindrical body 11 to curve (see Figures 1(A) and 1(B)). On the other hand, in the fluid pressure actuator 301 of the third embodiment, as shown in Figures 8(A) and 8(B), the restraining member 317 is fixed to the cylindrical body 311 along the axial direction from one end 311a to the other end 311b of the curved portion 311c of the cylindrical body 311, in a part of the circumferential direction of the curved portion 311c of the cylindrical body 311 when the cylindrical body 311 is extended in the axial direction. In the following description, the portion of the outer circumference of the curved portion 311c of the cylindrical body 311 that is restrained by the restraining member 317 is defined as the restrained portion 311R, and the portion of the outer circumference of the curved portion 311c of the cylindrical body 311 that is not restrained by the restraining member 317 is defined as the unrestrained portion 311N.As a result, in the fluid pressure actuator 301, the axial contraction of the constrained portion 311R of the cylindrical body 311 is suppressed when no pressure is applied, while the unconstrained portion 311N of the cylindrical body 311 contracts axially, thereby maintaining the cylindrical body 311 in a curved state (see Figure 8(A)).

[0095] When the fluid pressure actuator 301 extends axially by the control device introducing compressed air into the inner circumferential space of the sealed cylindrical body 311, the axial extension of the constrained portion 311R is suppressed, while the unconstrained portion 311N extends axially. As a result, in the state shown in Figure 8(A), the curved portion 311c of the fluid pressure actuator 301 straightens out, and the axial direction of the curved portion 311c becomes straight, as shown in Figure 8(B). On the other hand, when the fluid pressure actuator 301 contracts axially by the control device releasing the compressed air that has flowed into the inner circumferential space of the sealed cylindrical body 311, the axial contraction of the constrained portion 311R is suppressed, while the unconstrained portion 311N contracts axially. As a result, in the state shown in Figure 8(B), the straightened cylindrical body 311 of the fluid pressure actuator 301 curves out, and the axial direction of the cylindrical body 311 becomes curved, as shown in Figure 8(A). As a result, the fluid pressure actuator 301 can perform a smooth bending motion proportional to the pressure applied by the control device. The other configurations of the fluid pressure actuator 301 according to the third embodiment are the same as those of the first embodiment.

[0096] In this example, the fluid pressure actuators according to Comparative Examples 1 to 5 and Examples 1 to 42, shown in Tables 5 to 9 later, were fabricated using the following materials, and tensile force evaluation and performance evaluation at 10% elongation, as described later, were performed for comparative verification. The present invention will be described in more detail below based on the examples, but the present invention is not limited to these examples.

[0097] (Cylindrical body) [Raw materials for the rubber composition constituting the cylindrical body] Table 1 shows the raw materials for the rubber composition constituting the cylindrical body of the fluid pressure actuator according to Comparative Examples 1 to 5 and Examples 1 to 42.

[0098] Natural rubber: SVR-L Nylon staple fibers: "Leona" manufactured by Asahi Kasei Corporation, average fiber diameter 27 μm, average fiber length 3 mm Zinc oxide: "Zinc Oxide (JIS Standard 2)" manufactured by Hakusui Tech Co., Ltd. Stearic acid: "Tsubaki Stearic Acid" manufactured by NOF Corporation Anti-aging agent A: "Ozonon 6C" manufactured by Seiko Chemical Co., Ltd. Anti-aging agent B (microcrystalline wax): "Santight C" manufactured by Seiko Chemical Co., Ltd. Calcium carbonate: "Super #1500" manufactured by Maruo Calcium Co., Ltd., average particle size 1.5 μm Carbon black: "Seasto S" manufactured by Tokai Carbon Co., Ltd., average particle size 66 nm, iodine adsorption amount 26 mg / g Plasticizer (naphthenic oil): "SUNTHENE 410" manufactured by Nippon Sun Oil Co., Ltd. Crosslinking accelerator CBS (N-cyclohexyl-2-benzothiazolyl sulfenamide): "Noxellar CZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: "Sulfur" manufactured by Hosoi Chemical Industry Co., Ltd.

[0099] [Preparation of Uncrosslinked Rubber Sheets] To prepare uncrosslinked rubber sheets for forming tubular bodies, each rubber composition shown in Table 2 was kneaded using a Banbury mixer, and the resulting kneaded rubber was rolled to a predetermined thickness using a calender roll to produce uncrosslinked rubber sheets.

[0100] [Tensile material] Tables 2 and 3 show the twist configurations of the cords used in the fluid pressure actuators according to Comparative Examples 1 to 5 and Examples 1 to 42.

[0101] [Tonic material: fiber cord] The tensile modulus was determined by dividing the force at 1% of the cord's tensile strength by the cord's cross-sectional area to find the stress, and then dividing this by 1%.

[0102] [Polyester (PET)] When the cord type was polyester (PET), three under-twisted yarns were prepared by under-twisting a PET multifilament yarn with a fineness of 167 dtex 32 times / 10 cm in the S direction. The three prepared under-twisted yarns were then aligned and over-twisted 55 times / 10 cm in the Z direction to prepare a multi-twisted cord with a total fineness of 501 dtex, which was then subjected to RFL impregnation treatment with the RFL treatment solution shown in Table 4.

[0103] [Aramid] When the cord type is aramid, two multifilament yarns of aramid fibers with a fineness of 400 dtex are held together and twisted 35 times / 10 cm in the S direction to produce a single-twist cord with a total fineness of 800 dtex, and then subjected to RFL impregnation treatment with the RFL treatment solution shown in Table 4.

[0104] [Nylon] (1) 1 x 2 double-twisted nylon cord: When the type is nylon, a multifilament yarn of nylon fiber with a fineness of 175 dtex was twisted 26 times / 10 cm in the S direction to produce two under-twisted yarns. The two under-twisted yarns were brought together and twisted 45 times / 10 cm in the Z direction to produce a double-twisted cord with a total fineness of 350 dtex, which was then impregnated with RFL treatment solution shown in Table 4. (2) 1 x 3 double-twisted nylon cord: When the type is nylon, a multifilament yarn of nylon fiber with a fineness of 235 dtex was twisted 38 times / 10 cm in the S direction to produce three under-twisted yarns. Three pre-twisted yarns were aligned and twisted 6045 times / 10cm in the Z direction to produce a double-twisted cord with a total fineness of 705 dtex. This cord was then impregnated with RFL treatment solution as shown in Table 4.

[0105] [Tumrosians: Others]

[0106] [RFL treatment solution]

[0107] [Restraining Members] In Examples 1-9, 24, 25, and Comparative Examples 4-5, the restraining members used were the raw materials of the rubber compositions shown in Table 1. When the restraining member contained short fibers, the arrangement direction of the short fibers was set to the axial direction of the tubular body. In Examples 10-23, 27, 29-42, and Comparative Examples 2-3, the following treated canvas was used as the restraining member. In Example 26, a blind-like aramid cord (circumferential density 80 strands / 10 cm, axial density 10 strands / 10 cm) was used as the restraining member. In Example 28, a PET film was used as the restraining member. In Comparative Example 1, no restraining member was used.

[0108] [Nylon Canvas] A canvas fabric (0.6 mm thick) was plain woven using 66 nylon yarn with a fineness of 235 dtex as the warp and 30 mm with a yarn density of 92 threads / 30 mm. This treated canvas was then immersed in the RFL treatment solution shown in Table 4 and dried to perform an adhesive treatment.

[0109] [Aramid Canvas] A canvas (0.6 mm thick) was plain woven using 20-count meta-aramid yarn as both warp and weft threads at a yarn density of 40 threads / 30 mm. This canvas was then subjected to an RFL treatment, which involved immersion in the RFL treatment solution shown in Table 4 and drying.

[0110] (Fabrication of Fluid Pressure Actuators) Fluid pressure actuators were fabricated by creating cylindrical bodies with an inner diameter of 25 mm (5 mm for Examples 37 and 38, and 50 mm for Examples 39 and 40), a rubber thickness of 2.0 mm (0.6 mm for Examples 37 and 38), and an axial length of 150 mm, using uncrosslinked rubber sheets formed from the rubber compositions shown in Table 1 and tensile materials shown in Tables 2 and 3, according to the manufacturing method described in the section on [Modes for Carrying Out the Invention]. In Comparative Examples 2, 4, and 5 and Examples 41 and 42, the manufacturing method described in the first embodiment in the section on [Modes for Carrying Out the Invention] was used to fabricate the fluid pressure actuators. In Comparative Examples 1 and 3 and Examples 1 to 16 and 19 to 40, the manufacturing method described in the second embodiment was used, and in Examples 17 and 18, the manufacturing method described in the modified version of the second embodiment was used to fabricate the fluid pressure actuators.

[0111]

[0112]

[0113]

[0114]

[0115]

[0116] [Fluid pressure actuator of the second embodiment] (Comparative example 1) A PET twisted cord (1x3 twist of PET fibers) was spun spirally around the outer circumference of an uncrosslinked rubber sheet (R1, sheet thickness 1.3 mm) with an angle α of 0.5 degrees, a cord pitch P of 0.8 mm, and a spacing d between adjacent cords of 0.5 mm. Then, an uncrosslinked rubber sheet (R1, sheet thickness 0.7 mm) was wrapped around the outer circumference to produce an uncrosslinked cylindrical molded body. Without using a restraining member, the cylindrical molded body was crosslinked to produce a fluid pressure actuator in which the cord was spirally embedded inside the cylindrical body.

[0117] (Examples 1-5) In the manufacturing method of Comparative Example 1, restraining members were arranged around the outer circumference of an uncrosslinked cylindrical molded body so that the ratio of the restraining portion (the ratio of the length of the restraining member to the outer circumference of the cylindrical body) was as shown in Table 5, from one end to the other of the uncrosslinked cylindrical molded body. Then, the cylindrical molded body was crosslinked to produce a fluid pressure actuator in which a cord was helically embedded inside the cylindrical body. An uncrosslinked rubber sheet containing short fibers (R2, sheet thickness 0.6 mm) was used as the restraining member.

[0118] (Example 6) A fluid pressure actuator was fabricated in the same manner as in Example 1, except that an uncrosslinked rubber sheet (R1, sheet thickness 0.6 mm) that did not contain short fibers was used as the restraining member.

[0119] (Example 7) A fluid pressure actuator was manufactured in the same manner as in Example 6, except that the sheet thickness of the restraining member (uncrosslinked rubber sheet R1) was set to 1.2 mm and the proportion of the restraining portion was set to 25%.

[0120] (Example 8) A fluid pressure actuator was manufactured in the same manner as in Example 7, except that the proportion of the constrained portion was set to 33.3%.

[0121] (Example 9) A fluid pressure actuator was manufactured in the same manner as in Example 6, except that the sheet thickness of the restraining member (uncrosslinked rubber sheet R1) was set to 1.8 mm and the proportion of the restraining portion was set to 50%.

[0122] (Example 10) A fluid pressure actuator was manufactured in the same manner as in Example 1, except that nylon canvas was used as the restraining member and the proportion of the restrained portion was set to 12.5%.

[0123] (Example 11) A fluid pressure actuator was manufactured in the same manner as in Example 1, except that aramid canvas was used as the restraining member and the proportion of the restrained portion was set to 15.0%.

[0124] (Example 12) A fluid pressure actuator was fabricated in the same manner as in Example 11, except that a nylon twisted cord (1x2 twisted nylon fibers) was used as the tensile material, the angle α was 0.3 degrees, the cord pitch P was 0.4 mm, and the spacing d between adjacent cords was 0.5 mm.

[0125] (Example 13) A fluid pressure actuator was fabricated in the same manner as in Example 11, except that a nylon twisted cord (1x3 twisted nylon fibers) was used as the tensile material.

[0126] (Example 14) A fluid pressure actuator was fabricated in the same manner as in Example 11, except that an aramid twisted cord (0 x 2 single twist of aramid fibers) was used as the tensile material.

[0127] (Example 15) A fluid pressure actuator was fabricated in the same manner as in Example 11, except that a PET untwisted cord was used as the tensile material, the angle α was 0.7 degrees, the cord pitch P was 1.0 mm, and the spacing d between adjacent cords was 0 mm.

[0128] (Example 16) A fluid pressure actuator was fabricated in the same manner as in Example 15, except that an aramid untwisted cord was used as the tensile material.

[0129] (Example 17) A fluid pressure actuator was fabricated in the same manner as in Example 16, except that the aramid untwisted cord was double-wound (double helix) with an angle α of 1.1 degrees, a cord pitch P of 1.6 mm, and a spacing d between adjacent cords of 0 mm, so as to be axially symmetric with respect to the axial direction of the molding mold.

[0130] (Example 18) A fluid pressure actuator was manufactured in the same manner as in Example 11, except that a PET twisted cord (1 x 3 twists of PET fibers) was double-wound (double helix) with an angle α of 1.1 degrees, a cord pitch P of 1.6 mm, and a spacing d between adjacent cords of 0 mm, so as to be axially symmetric with respect to the axial direction of the molding mold.

[0131] (Comparative Example 2) In the manufacturing method of Example 11, a fluid pressure actuator was manufactured without using a tensile material (twisted cord).

[0132] (Comparative Example 3) In the manufacturing method of Example 11, a fluid pressure actuator was fabricated using a tensile body in which aramid cords arranged in a blind-like shape (circumferential density 80 cords / 10 cm, axial density 10 cords / 10 cm) were arranged along the circumferential direction.

[0133] (Examples 19-23) Fluid pressure actuators were manufactured in the same manner as in Example 16, except that the proportion of the restrained portion was changed to the values ​​shown in Table 7.

[0134] (Example 24) A fluid pressure actuator was manufactured in the same manner as in Example 16, except that the restraining member was an uncrosslinked rubber sheet (R1, sheet thickness 1.8 mm, not containing short fibers) and the proportion of the restraining portion was set to 50%.

[0135] (Example 25) A fluid pressure actuator was manufactured in the same manner as in Example 16, except that the restraining member was an uncrosslinked rubber sheet (R2 containing short fibers, sheet thickness 0.6 mm) and the proportion of the restraining portion was set to 50%.

[0136] (Example 26) A fluid pressure actuator was manufactured in the same manner as in Example 21, except that the restraining member was made of aramid cord in the shape of a bamboo blind.

[0137] (Example 27) A fluid pressure actuator was manufactured in the same manner as in Example 21, except that the restraining member was made of nylon canvas.

[0138] (Example 28) A fluid pressure actuator was manufactured in the same manner as in Example 21, except that the restraining member was made of PET film.

[0139] (Example 29) A fluid pressure actuator was manufactured in the same manner as in Example 21, except that the uncrosslinked rubber sheets wrapped around the inner and outer circumferences of the aramid untwisted cord were changed to uncrosslinked rubber sheets (R2) containing short fibers, and the uncrosslinked rubber sheets were arranged so that the orientation direction of the short fibers was parallel to the circumferential direction of the molding mold.

[0140] (Example 30) A fluid pressure actuator was fabricated in the same manner as in Example 21, except that the uncrosslinked rubber sheets wrapped around the inner and outer circumferences of the aramid untwisted cord were changed to uncrosslinked rubber sheets (R2) containing short fibers, and the uncrosslinked rubber sheets were arranged so that the orientation direction of the short fibers was parallel to the helical direction of the cord (angle α of 0.7 degrees).

[0141] (Example 31) A fluid pressure actuator was manufactured in the same manner as in Example 21, except that the uncrosslinked rubber sheet wrapped around the outer circumference of the aramid untwisted cord was changed to an uncrosslinked rubber sheet (R2) containing short fibers, and the uncrosslinked rubber sheet was positioned so that the orientation direction of the short fibers was parallel to the circumferential direction of the molding mold.

[0142] (Examples 32-36) Fluid pressure actuators were manufactured in the same manner as in Example 21, except that the angle α, code pitch P, and the distance d between adjacent codes were changed to the values ​​shown in Table 8.

[0143] (Examples 37, 38) In the manufacturing method of Example 21, a molding mold with an inner diameter of 5 mm was used, and the thickness of the uncrosslinked rubber sheet wrapped around the inner and outer circumferences of the cord was set to 0.3 mm. The PET untwisted cord was spun in a spiral shape so that the angle α, cord pitch P, and distance d between adjacent cords were as shown in Table 8, and a fluid pressure actuator was manufactured.

[0144] (Examples 39, 40) In the manufacturing method of Example 21, a molding mold with an inner diameter of 50 mm was used to spin a nylon twisted cord (1 x 3 twisted nylon fiber) in a spiral shape so that the angle α, cord pitch P, and distance d between adjacent cords were as shown in Table 8, and a fluid pressure actuator was manufactured.

[0145] [Fluid Pressure Actuator of the First Embodiment] (Examples 41, 42) An uncrosslinked cylindrical molded body was fabricated by helically spinning PET twisted cords (1x3 twisted PET fibers) around the outer circumference of an uncrosslinked rubber sheet (R1, sheet thickness 2.0 mm) with an angle α of 0.5 degrees, a cord pitch P of 0.8 mm, and a spacing d between adjacent cords of 0.5 mm. After arranging restraining members around the outer circumference of the uncrosslinked cylindrical molded body so that the proportion of the restrained portion from one end to the other matches the values ​​shown in Table 9, the cylindrical molded body was crosslinked to fabricate a fluid pressure actuator in which the cords are helically fixed to the outer circumference of the cylindrical body.

[0146] (Comparative Example 4) In the manufacturing method of Example 41, a metal cord (coil spring; angle α is 1.6 degrees, cord pitch P is 2.6 mm, distance d between adjacent cords is 0 mm) was used as the tensile body, and an uncrosslinked rubber sheet (R2 containing short fibers, sheet thickness 0.6 mm) was used as the restraining member, and a restraining portion ratio of 33.3% was used to produce a fluid pressure actuator.

[0147] (Comparative Example 5) In the manufacturing method of Example 41, a mesh-like braided sleeve described in the example of a McKibben type actuator disclosed in Japanese Patent Application Publication No. 2024-131802 was used as the tensile material, and an uncrosslinked rubber sheet (containing short fibers R2, sheet thickness 0.6 mm) was used as the restraining member, and a restraining portion ratio of 33.3% was used to produce a fluid pressure actuator.

[0148] (Evaluation of tensile force at 10% elongation) From the cylindrical bodies of the fluid pressure actuators according to Comparative Examples 1 to 5 and Examples 1 to 42, test specimens were taken by punching out pieces with a width of 5 mm and a length of 100 mm from both the constrained and unconstrained portions, with the axial direction of the cylindrical body being the longitudinal direction. Tensile tests were performed on a tensile testing machine at a speed of 50 mm / min, and the tensile force when the test specimen was elongated by 10% was measured. The elongation of the test specimen was confirmed by the change in the gauge length (e.g., 50 mm).

[0149] (Performance Evaluation) (1) Bending Angle β The fluid pressure actuators in Comparative Examples 1 to 5 and Examples 1 to 42 have caps fitted to both ends and secured with hose clamps to prevent gaps. These caps are shaped like bamboo shoots, improving the pressure resistance of the crimping. An air inlet is provided in the cap fitted to the other end of the cylindrical body. The other end of the fluid pressure actuator was fixed, and one end was allowed to be freely displaced and rotated in the axial and torsional directions. Air pressure was applied to the fluid pressure actuator in this state. The bending angle β (see Figure 1(B)) at an air pressure of 1.5 MPa was measured. The bending angle β was measured by taking photographs of the fluid pressure actuator and performing image analysis, and was judged according to the following criteria.

[0150] [Curving Angle β: Judgment Criteria] a. Greater than 120 degrees b. Greater than 100 degrees and 120 degrees or less c. Less than or equal to 100 degrees

[0151] (2) Lateral stiffness As shown in Figure 9, if the fluid pressure actuator 501 is easily deformed in a direction perpendicular to the bending direction K, when the fluid pressure actuator 501 is bent and brought into contact with the object, the tip of the fluid pressure actuator 501 will slide laterally along the surface of the object, resulting in insufficient work being done on the object. Therefore, lateral stiffness was evaluated as an indicator of whether the desired work can be done on the object.

[0152] First, the fluid pressure actuator 501 shown in Figure 9 was fabricated as follows. As shown in Figure 10, a cap 502 was fitted 10 mm into one end of the cylindrical body 511, so that the cap 502 protruded 15 mm from the end of the cylindrical body 511. Near the center of the longitudinal direction of the cylindrical body 511, the end of a hose clamp 514 (Oetica: 9 mm wide) was aligned with the end of the cap 502, and the hose clamp 514 was fitted around the outer circumference of the cylindrical body 511 and crimped with an air chuck. The same procedure was followed for the other end of the cylindrical body 511. At this time, the distance between the inner ends of the pair of hose clamps 514 was set to 150 mm. Then, as shown in Figure 9, the fluid pressure actuator 501 was placed on the stand so that the bending direction K was in the horizontal plane. One end of the cylindrical body 511 was fixed to the frame, and one end of the wire 503 was fastened to the cap 502 attached to the other end of the cylindrical body 511 at a position 10 mm away from the end of the cylindrical body 511 and perpendicular to the bending direction K (upper end in the vertical direction). A load cell 504 was attached to the other end of the wire 503. At this time, the length of the wire 503 from the fastening position with the fluid pressure actuator 501 to the load cell 504 was set to 300 mm. The fluid pressure actuator 501 was bent, and the load at which the wire 503 was pulled 20 mm at 100 mm / min from a direction perpendicular to the bending direction K (vertical direction) was measured with the load cell 504 and judged according to the following criteria. The total weight of the cap 502 and hose band 514 was 15 g.

[0153] [Lateral rigidity: Judgment criteria] a. Judgment: 10N or more b. Judgment: 3N or more but less than 10N c. Judgment: Less than 3N

[0154] (3) A cycle of applying pressure-resistant air for 1 second and exhausting it for 1 second was defined as one cycle, and this cycle was repeated 100 times to verify that there were no abnormalities (damage, changes in bending angle, etc.) in the fluid pressure actuator. The pressure was increased from 0.15 MPa by 0.05 MPa every 100 cycles, and verified up to 0.30 MPa.

[0155] [Overall Evaluation Criteria] Table 10 shows the overall evaluation criteria based on the performance evaluation of bending angle, lateral rigidity, and pressure resistance.

[0156] [Fluid pressure actuator of the second embodiment] (Evaluation results for Table 5) (Comparative example 1) This is an example of the second embodiment in which a cylindrical body (crosslinked rubber composition) is formed from composition R1 that does not contain short fibers, and a PET twisted cord (1 x 3 twists of PET fibers) is embedded spirally inside the cylindrical body (crosslinked rubber composition) as a tensile body without being exposed to the outside. This is an example of the first embodiment in which the cord is arranged spirally along the circumferential direction on the outer circumference of the cylindrical body. Comparative example 1 is an example without a restraining member, and since there is no restraining part, it stretches but does not bend, and the bending angle β was 0°.

[0157] (Examples 1-5) Examples 1-5 are examples in which an uncrosslinked rubber sheet (R2) containing short fibers was used as the restraining member, compared to Comparative Example 1. The bending angle β tends to increase as the proportion of the restrained portion increases, but when the proportion of the restrained portion exceeds 50%, the bending angle β tends to decrease. The reason why the bending angle β in Examples 4 and 5 was smaller than in Example 3 is thought to be that the proportion of the restrained portion became too large, making it difficult for the cylindrical body to bend. In these examples, the lateral rigidity was rated as c, so the overall rating was rank C.

[0158] (Examples 6-9) Examples 6-9 are examples in which an uncrosslinked rubber sheet (R1) that does not contain short fibers was used as the restraining member. The curvature angle β tends to increase as the proportion of the restrained portion increases. Example 1 and Example 6 had the same proportion of the restrained portion (16.7%), and Example 2 and Example 8 had the same proportion of the restrained portion (33.3%), but Example 6 had a smaller curvature angle β than Example 1, and Example 8 had a smaller curvature angle β than Example 2. This is thought to be because the restraining force on the cylindrical body was weak due to the low elastic modulus of the restraining member. Example 3 and Example 9 had the same proportion of the restrained portion (50%), and the curvature angle β was about the same. In these examples, the lateral stiffness was rated as c, so the overall rating was rank C.

[0159] (Example 10) Example 10 is an example in which nylon canvas was used as the restraining member. Compared to Examples 1 and 6, which had a similar proportion of restrained portion, Example 10 showed a larger curvature angle β. This is thought to be because the canvas had a high modulus of elasticity, resulting in a large restraining force on the tubular body. However, since the lateral rigidity was rated as c, the overall rating was C.

[0160] (Example 11) Example 11 is an example in which aramid canvas was used as the restraining member. In Example 11, the curvature angle β was the same as in Example 1, but the lateral rigidity improved to a B rating, and the overall rating was B rank. From these results, it can be said that using "aramid canvas" as the restraining member is a particularly preferred embodiment.

[0161] (Evaluation results for Table 6) (Examples 12-14) Examples 12-14 are examples of configurations similar to Example 11 (composition R1, PET twisted cord, angle α = 0.5 degrees, spacing d = 0.5 mm) which used "aramid canvas" as a restraining member, but with a change in the tensile strength member. Example 12 is an example using a nylon twisted cord with a low modulus of elasticity (less than 4 GPa) (1 x 2 twisted nylon fibers), and although the bending angle β and lateral stiffness were judged as a or b, the pressure resistance was insufficient and the overall judgment was rank C. Example 13 is also an example using a nylon twisted cord with a low modulus of elasticity (4-5 GPa) (1 x 3 twisted nylon fibers), and although the bending angle β and lateral stiffness were judged as a or b, and there was no abnormality in the pressure resistance, the overall judgment was rank B. Example 14 uses a high modulus aramid stranded cord. Although the bending angle β was improved compared to Example 13, the lateral stiffness was rated as b, resulting in an overall rating of B.

[0162] (Examples 15 and 16) Example 15 is an example in which a PET untwisted cord was used in contrast to Example 11 (PET twisted cord). With the untwisted cord, the cords were arranged flat, resulting in a slightly different helical arrangement compared to the twisted cord (angle α = 0.7 degrees, cord pitch P = 1.0 mm, spacing between adjacent cords d = 0 mm). Compared to Example 11 using the twisted cord, the bending angle β and lateral stiffness were slightly reduced, but the overall evaluation was a B rank. Example 16 is an example in which an aramid untwisted cord was used in contrast to Example 14. Similar to Example 14, the overall evaluation was a B rank, but the level of the bending angle β was improved. From these results, it can be said that PET twisted cord and aramid untwisted cord are particularly preferred as tensile materials.

[0163] (Examples 17 and 18) Example 17 is an example in which an aramid untwisted cord was double-wound (double helix) with an angle α of 1.1 degrees, a cord pitch P of 1.6 mm, and a spacing d between adjacent cords of 0 mm, so as to be axially symmetric with respect to the axial direction of the molding mold, compared to Example 16. Similar to Example 16, the overall evaluation was rank B, but the level of the curvature angle β was slightly lower than that of Example 16. Example 18 is an example in which a PET twisted cord was double-wound (double helix) with an angle α of 1.1 degrees, a cord pitch P of 1.6 mm, and a spacing d between adjacent cords of 0 mm, so as to be axially symmetric with respect to the axial direction of the molding mold, compared to Example 11. Similar to Example 11, the overall evaluation was rank B, but the level of the curvature angle β was slightly improved.

[0164] (Comparative Example 2) Comparative Example 2 is an example in which a tubular body (crosslinked rubber composition) was formed with composition R2 containing short fibers, with the short fibers oriented in the circumferential direction, but without a tensile body. The bending angle β was rated as a, but the lateral stiffness was rated as a c, and the pressure resistance was also insufficient, so the overall rating was D.

[0165] (Comparative Example 3) Comparative Example 3 is an example in which a tensile material was used in which a blind-like aramid cord (circumferential density 80 strands / 10 cm, axial density 10 strands / 10 cm) was arranged along the circumferential direction, in the configuration of Examples 11 to 16. The bending angle β was judged as a, but the lateral stiffness was judged as a c, and the pressure resistance was also insufficient, so the overall judgment was rank D.

[0166] (Evaluation results for Table 7) (Examples 19-23) Examples 19-23 are examples in which the proportion of the restraining portion was changed from the configuration of Example 16, which was a particularly preferred embodiment in Table 6, in which the restraining member was "aramid canvas" and the tensile body was "aramid untwisted cord". As the proportion of the restraining portion increased to 10% (Example 19), 15% (Example 16), 30% (Example 20), and 45% (Example 21), the lateral rigidity improved, and the overall evaluation also improved, with Example 21 at 45% achieving an A rank. However, when the proportion of the restraining portion was further increased to 60% (Example 22) and 65% (Example 23), while the lateral rigidity remained at an A rank, the curvature angle β decreased, causing the overall evaluation to drop to a B or C rank. From these results, it can be said that it is preferable to set the proportion of the restraining portion to around 45% (approximately 50%).

[0167] (Examples 24-28) Examples 24-28 are examples in which the restraining member was changed from the configuration of Example 21 (an example in which the tensile body was an aramid untwisted cord, the restraining member was an aramid canvas, and the proportion of the restrained part was about 50%). Example 24 used an uncrosslinked rubber sheet (R1 without short fibers, sheet thickness 1.8 mm) as the restraining member, and Example 25 used an uncrosslinked rubber sheet (R2 containing short fibers, sheet thickness 0.6 mm) as the restraining member. In both cases, the bending angle β was larger than in Example 21, but the lateral stiffness decreased to a c rating, resulting in an overall rating of C. Example 26 is an example in which a blind-like aramid cord was used as the restraining member. Compared to Example 21, the lateral stiffness was larger, but the bending angle β decreased to a b rating, resulting in an overall rating of B. Example 27 uses nylon canvas as the restraining member. Compared to Example 21, the curvature angle β increased, but the lateral stiffness decreased to a b rating, resulting in an overall rating of B. Example 28 uses PET film as the restraining member. Compared to Example 21, the curvature angle β increased, but the lateral stiffness decreased to a b rating, and an abnormality occurred in the pressure resistance test, resulting in an overall rating of C. From these results, it can be said that a configuration using aramid untwisted cord for the tensioning member and aramid canvas for the restraining member is a particularly preferred combination.

[0168] (Examples 29-31) Examples 29-31 are examples in which the tubular body (crosslinked rubber composition) is formed from composition R2 containing 10 parts by mass of short fibers, compared to the configuration of Example 21 (an example in which the tensile body is made of aramid untwisted cord, the restraining member is made of aramid canvas, and the proportion of the restraining portion is about 50%). Compared to Example 21, which does not contain short fibers, Example 29, in which the short fibers are oriented in the circumferential direction of the tubular body, showed improved lateral rigidity and received an a rating, but the bending angle β decreased to a b rating, resulting in an overall rating of B. In Example 30, in which the short fibers are oriented parallel to the helical arrangement of the cord, the bending angle β further decreased to a c rating, resulting in an overall rating of C. Example 31 is an example in which only the outer layer of the tubular body is formed from composition R2 containing short fibers, compared to Example 21. Although the bending angle β decreased slightly, it received an a rating, and the overall rating was A. These results indicate that orienting short fibers circumferentially in a tubular structure improves lateral rigidity, but reduces the bending angle β. Therefore, if the goal is to increase flexibility, it is preferable to omit the short fibers.

[0169] (Evaluation results for Table 8) (Examples 32-36) Examples 32-36 are examples in which the angle α between the direction parallel to the circumferential direction of the cylindrical body and the direction parallel to the axial direction of the cord was varied (and the cord pitch P was also varied in conjunction with it) compared to Example 21 (aramid untwisted cord, angle α = 0.7 degrees, spacing d = 0 mm). When the angle α was greatly varied in the order of 0.4 degrees (Example 32), 0.5 degrees (Example 33), 0.7 degrees (Example 21), 1.0 degrees (Example 34), 1.9 degrees (Example 35), and 2.3 degrees (Example 36), the bending angle β and lateral rigidity were judged as "a" in the range of angle α from 0.5 degrees to 1.9 degrees, similar to Example 21, and there were no abnormalities in pressure resistance, resulting in an overall judgment of rank A. In Example 32 with an angle α of 0.4 degrees and in Example 36 with an angle α of 2.3 degrees, the result was rank B.

[0170] (Examples 37 and 38) Examples 37 and 38 are examples of forming a small-diameter cylindrical body with an inner diameter of 5 mm, with a configuration similar to that of Example 21. In Example 37, PET untwisted cords were arranged spirally at a relatively large angle, with an angle α of 9.4 degrees (cord pitch P of 2.9 mm, and spacing d between adjacent cords of 2.6 mm). The bending angle β and lateral rigidity were rated as b, and there were no abnormalities in the pressure resistance test, resulting in an overall rating of B. In Example 38, compared to the configuration of Example 37, the angle α of the PET untwisted cords was 11.3 degrees (cord pitch P of 3.5 mm, and spacing d between adjacent cords of 3.2 mm), resulting in a larger angle of spiral arrangement. The bending angle β and lateral rigidity were rated as b, but abnormalities occurred in the pressure resistance test, resulting in an overall rating of C. Based on these results, a configuration in which the gap d between tensile members is 2.6 mm or less and the angle α is 10 degrees or less is considered a more preferable configuration.

[0171] (Examples 39 and 40) Examples 39 and 40 are examples of forming a large-diameter cylindrical body (inner diameter 50 mm) using a nylon twisted cord (1 x 3 twist) with a low tensile modulus, as an example of a large strain index Z. In Example 39, a nylon twisted cord (tensile modulus 4.6 GPa, diameter 0.3 mm) was arranged helically with an angle α of 0.3 degrees (cord pitch P of 0.8 mm, spacing d between adjacent cords of 0.5 mm), resulting in a strain index Z value of 109.2 [1 / GPa]. The bending angle β was rated as b, the lateral stiffness as a, and there were no abnormalities in pressure resistance, resulting in an overall rating of B. Example 40 is an example where a nylon twisted cord (tensile modulus of elasticity 4.6 GPa, diameter 0.3 mm) was helically arranged with an angle α of 0.5 degrees (cord pitch P of 1.5 mm, spacing d between adjacent cords of 1.2 mm), resulting in a strain index Z value of 204.8 [1 / GPa]. The bending angle β and lateral stiffness were rated as A, but an abnormality occurred in the pressure resistance test, resulting in an overall rating of B. From these results, it can be said that a configuration with a strain index Z value of 110 [1 / GPa] or less is a more preferable embodiment.

[0172] [Fluid Pressure Actuator of the First Embodiment] (Evaluation Results for Table 9) (Examples 41-42) This is an example of the first embodiment in which a cylindrical body (crosslinked rubber composition) is formed from a composition R1 that does not contain short fibers, and a tensile member is arranged spirally along the circumferential direction on the outer circumference of the cylindrical body. Example 41 is an example in which the configuration is similar to Example 11 of the second embodiment (PET twisted cord, angle α = 0.5 degrees, spacing d = 0.5 mm, restraining member is aramid canvas, restraining portion 15%), but modified from the first embodiment. The same trend as Example 11 of the second embodiment was observed, and it was confirmed that the first embodiment also achieves a level that is not problematic for practical use (rank B). It can be said that the same effect can be obtained whether the cord is arranged on the outer circumference of the cylindrical body (crosslinked rubber composition) or embedded inside. Example 42 is an example in which the proportion of the restraining portion is increased to 45% compared to Example 41. Compared to Example 41, the curvature angle β increased, and the lateral rigidity also improved to a rating, resulting in an overall rating of A.

[0173] (Comparative Examples 4 and 5) Comparative Example 4 is an example in which a coil spring disclosed in Japanese Patent Publication No. 2019-207017 was used as the tensile body. The bending angle β was judged as c (100 deg or less), the lateral stiffness was judged as b (b), and the pressure resistance was also insufficient, resulting in an overall judgment of rank D. Comparative Example 5 is an example in which a braided sleeve of a McKibben type actuator disclosed in Japanese Patent Publication No. 2024-131802 was used as the tensile body. There was no abnormality in the pressure resistance, but the bending angle β was judged as c (100 deg or less), and the lateral stiffness was also judged as c (c), resulting in an overall judgment of rank D. From these results, it can be said that an embodiment using a cord containing fibers as the tensile body is preferable.

[0174] From the above results, it was found that the configuration of the present invention can provide a fluid pressure actuator capable of achieving a large degree of bending.

[0175] This application is based on Japanese Patent Application No. 2025-054102 filed on 27 March 2025 and Japanese Patent Application No. 2026-046567 filed on 19 March 2026, the contents of which are incorporated herein by reference.

[0176] 1, 201, 1201, 301 Fluid pressure actuator 11, 211, 1211, 311 Cylindrical body (crosslinked rubber composition) 11a, 211a, 1211a, 311a One end 11b, 211b, 1211b, 311b Other end 12, 212, 216, 312 Code 17, 217, 317 Restraining member

Claims

A fluid pressure actuator comprising a cylindrical body and a cord helically arranged along the circumferential direction of the cylindrical body, wherein pressurized fluid flows in and out of the space on the inner circumference of the cylindrical body, thereby causing the cylindrical body to expand and contract, The cylindrical body has a curved portion in at least a part of its axial direction, In a portion of the circumferential direction of the curved portion, a restraining member is provided which is fixed along the axial direction of the curved portion from one end to the other in the axial direction of the curved portion. The tubular body contains a crosslinked rubber composition, The aforementioned cord contains fibers and is continuously connected from one end to the other in the axial direction of the cylindrical body, and is fixed to the outer circumference of the cylindrical body or embedded in the cylindrical body. The restraining member comprises a crosslinked rubber composition, canvas, or an array of cords. A fluid pressure actuator that, when pressurized fluid flows in and out of the space on the inner circumference of the cylindrical body and the cylindrical body expands and contracts along the axial direction, suppresses axial extension or contraction of the portion of the curved portion to which the restraining member is fixed, thereby curving the curved portion. 　 The fluid pressure actuator according to claim 1, characterized in that the length of the restraining member in the circumferential direction of the curved portion occupies a range of 15% to 60% of the outer circumference length of the curved portion when no pressure is applied. 　 The fluid pressure actuator according to claim 1 or 2, characterized in that, in the curved portion, parameter B, defined by the following formula 1, which serves as an indicator of the stretchability of the restrained portion restrained by the restraining member, and parameter A, defined by the following formula 2, which serves as an indicator of the stretchability of the unrestrained portion not restrained by the restraining member in the curved portion, have a ratio B / A value of 0.5 or more and 150 or less. Parameter B [N] = (Tensile force [N] when the constrained portion is elongated by 10%) × (Proportion of the constrained portion to the outer circumference of the curved portion) ... (Equation 1) Parameter A [N] = (Tensile force [N] when the unrestrained portion is elongated by 10%) × (Proportion of the unrestrained portion to the outer circumference of the curved portion) ... (Equation 2) 　 The restraining member comprises a crosslinked rubber composition, The fluid pressure actuator according to any one of claims 1 to 3, characterized in that the crosslinked rubber composition contains short fibers, and the orientation direction of the short fibers is parallel to the axial direction of the cylindrical body. 　 The fluid pressure actuator according to any one of claims 1 to 4, characterized in that the axial elongation at break of the crosslinked rubber composition forming the cylindrical body is 40% or more and 1000% or less. 　 The fluid pressure actuator according to any one of claims 1 to 5, characterized in that the cylindrical body has an extension index Y defined by the following formula 3 that is 0.04 N / mm or more and 0.30 N / mm or less. Elongation index Y [N / mm] = (Tensile force [N] at 10% elongation of the unrestrained portion of the cylindrical body not restrained by the restraining member) / (Inner diameter of the cylindrical body [mm]) ... (Equation 3) 　 The fluid pressure actuator according to any one of claims 1 to 6, characterized in that the tensile modulus of the fibers constituting the cord is 2 GPa or more and 150 GPa or less. 　 The fluid pressure actuator according to any one of claims 1 to 7, characterized in that the code is arranged such that the X value of the arrangement density of the code is 60% or more and 90% or less when no pressure is applied. 　 The fluid pressure actuator according to any one of claims 1 to 8, characterized in that the cords are arranged such that the distance between adjacent cords when no pressure is applied is 0 mm or more and 2.6 mm or less. 　 The fluid pressure actuator according to any one of claims 1 to 9, characterized in that the value of the strain index Z, defined by the following formula 4, is configured to be between 1 [1 / GPa] and 400 [1 / GPa]. Strain index Z [1 / GPa] = (Inner diameter of the cylindrical body [mm]) × (Axial distance between adjacent cords when no pressure is applied [mm]) / { (Tensile modulus of elasticity of the cord [GPa]) × (Cord diameter [mm]) 2 }...(Formula 4) 　 The fluid pressure actuator according to any one of claims 1 to 10, characterized in that the code includes the untwisted fibers. 　 The aforementioned code has a first code and a second code, The fluid pressure actuator according to any one of claims 1 to 11, characterized in that, when no pressure is applied, the first code and the second code are fixed to the outer circumference of the cylindrical body or embedded in the cylindrical body, overlapping in the radial direction of the cylindrical body such that the orientation of their respective helices is axially symmetric with respect to the axial direction of the cylindrical body.

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