Hydraulic actuator

Abstract

Provided is a hydraulic actuator having a cylindrical body and a cord disposed spirally along the circumferential direction of the cylindrical body, wherein a pressurized fluid flows into and out of a space on the inner peripheral side of the cylindrical body. The cylindrical body includes a crosslinked rubber composition. The cord includes fibers, is continuously connected from one end to the other end of the cylindrical body in the axial direction, and is fixed to the outer periphery of the cylindrical body or embedded in the cylindrical body.

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, since they have a higher output-to-weight ratio, greater flexibility and higher compliance compared to electric actuators. Actuators that use fluid pressure are primarily cylindrical in shape, with a space inside the cylindrical body serving as a chamber, and are configured to allow fluid such as pressurized air to flow into and out of the chamber.

[0003] As a conventionally studied fluid pressure actuator, there is a telescopic actuator represented by pneumatic artificial muscles, which utilizes the expansion deformation of a rubber material to expand and contract (contract or extend) the cylindrical body in the axial direction. When the air pressure in the chamber formed by the inner space of the cylindrical shape is increased or decreased, the actuator expands and contracts.

[0004] Studies on conventional telescopic pneumatic actuators include: McKibben actuators that generate axial deformation of rubber via a braided sleeve; axially fiber-reinforced actuators that contract by applying axial fiber restraint to a rubber tube; actuators that expand and contract by forming the inside of a bellows structure as a chamber; actuators composed of a cylindrical sleeve that expands and contracts axially and a rubber tube; and actuators that expand and contract axially by applying spiral fiber restraint to a cylindrical rubber tube.

[0005] Regarding telescopic actuators, for example, Patent Documents 1 to 3 disclose an actuator of the type that applies spiral restraint to a rubber tube and expands and contracts axially by fluid pressure. Patent Document 1 discloses an arrangement including a tube with a closed end that expands in the radial direction and axial direction when pressurized, and a thread-like member spirally wound around the surface of the tube, wherein when the expandable balloon is pressurized, it cannot expand in the radial direction and thus extends in the axial direction. In addition, Patent Document 2 discloses an arrangement that expands and contracts in the axial direction by applying pressure or decompression of air pressure to a cylindrical expansion body while limiting the expansion of the cylindrical expansion body in the outer circumferential direction with a coil spring.

[0006] In recent years, there has been a demand for high-elongation, expandable-tension actuators in fluid pressure actuators that can significantly increase the axial elongation rate of a cylindrical body. Conventional expandable-tension actuators require a large expansion rate in the axial direction of the cylindrical body to achieve a large elongation rate, which necessitates a large radial wall thickness of the cylindrical body. As a result, a relatively large space is required to mount the actuator. Furthermore, coil springs that restrict the circumferential expansion of the expandable body, such as those in Patent Document 2, tend to have higher rigidity and smaller elongation rates compared to fibers that provide fiber constraints, such as those in Patent Document 1.

[0007] Therefore, in expandable actuators, high-elongation actuators have been developed that can increase the axial elongation rate of a cylindrical body by utilizing the stretch deformation of a rubber material. For example, Patent Document 3 discloses an embodiment that includes a cylindrical part made of an elastic material and a fiber layer wound circumferentially within the cylindrical part and extending continuously in the axial direction, in which the fiber layer restricts the radial expansion of the cylindrical part, thereby increasing the axial elongation rate and flexibility. However, the actuator in Patent Document 3 has an elongation rate of only 53%.

[0008] Japanese Patent Publication No. 2018-189169, Japanese Patent Publication No. 2019-207017, Japanese Patent Publication No. 2012-176126

[0009] Therefore, if a method for increasing the axial elongation rate while suppressing radial expansion of a cylindrical body, as described in Patent Document 3, could achieve an even higher elongation rate (for example, 200-300%), it would broaden the range of applications, such as allowing installation in space-saving locations like confined spaces. However, an actuator capable of achieving such a high level of elongation rate has not yet been developed, and the selection of applicable rubber materials and restraint methods is required.

[0010] The present invention aims to provide a fluid pressure actuator that can increase the axial elongation rate to a high level while suppressing radial expansion of a cylindrical body, in order to broaden its range of applications.

[0011] 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 side of the cylindrical body, the cylindrical body comprising a crosslinked rubber composition, and the cord comprising fibers, continuously connected from one end to the other in the axial direction of the cylindrical body, and fixed to the outer circumference of the cylindrical body or embedded in the cylindrical body.

[0012] 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 crosslinked 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 tends 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 tends to expand radially is subjected to 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 axially expand the portions between adjacent cords in the axial direction of the cylindrical body. Here, since 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 constraint is greater compared to cases where the cord is not fixed to the outer circumference of the cylindrical body or is not embedded in the cylindrical body. This further suppresses the radial expansion of the cylindrical body compared to cases where the cord is not fixed to the outer circumference of the cylindrical body or is not embedded in the cylindrical body. Furthermore, a cord containing fibers has lower rigidity and a higher elongation rate compared to a coil spring. Therefore, a cord containing fibers can extend in the axial direction of the cylindrical body while providing helical fiber constraint to the cylindrical body. As a result, the fluid pressure actuator of this configuration can increase the axial elongation rate while suppressing the radial expansion of the cylindrical body. 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.

[0013] Furthermore, in the fluid pressure actuator of the present invention, the cord may be arranged such that the angle between the direction parallel to the circumferential direction of the cylindrical body and the direction parallel to the axial direction of the cord is greater than 0 degrees and 10 degrees or less.

[0014] In this configuration, the cords are arranged spirally at a predetermined pitch, approximately parallel to the circumferential direction of the cylindrical body. This allows for more cords to be placed on a cylindrical body of the same axial length compared to a case where the angle of the cords with respect to the circumferential direction of the cylindrical body is greater than 10 degrees, and also increases the number of spaces between the cords. Therefore, when the cylindrical body expands radially, the cords create larger helical fiber constraints. As a result, the fluid pressure attempting to expand the cylindrical body radially acts as a fluid pressure that attempts to further widen the spaces between adjacent cords in the axial direction of the cylindrical body. Thus, the fluid pressure actuator in this configuration can further suppress the radial expansion of the cylindrical body while further increasing the axial elongation rate.

[0015] Furthermore, the fluid pressure actuator of the present invention may also have a crosslinked rubber composition containing short fibers, and the orientation direction of the short fibers may range from a direction parallel to the circumferential direction of the cylindrical body to a direction parallel to the axial direction of the cord.

[0016] In this configuration, the short fibers are oriented along the circumferential direction of the tubular body. As a result, the oriented short fibers do not increase the axial stiffness (elastic modulus) of the tubular body, but increase the circumferential stiffness (elastic modulus). In particular, in the portions between adjacent cords in the axial direction of the tubular body, the increased circumferential stiffness makes the tubular body less susceptible to radial deformation, thus further suppressing radial expansion of the tubular body when fluid pressure is applied. As a result, the fluid pressure acts more strongly on the portions between adjacent cords in the axial direction of the tubular body. Consequently, the spacing between cords in the axial direction of the tubular body widens further, causing the tubular body to elongate further in the axial direction. In other words, by suppressing radial expansion of the tubular body, the tubular body will not expand radially even when a larger fluid pressure is applied, allowing for greater pressure to be applied to the axial elongation of the tubular body and increasing the elongation rate. Therefore, compared to the case where the cylindrical body contains a crosslinked rubber composition without short fibers, the fluid pressure actuator of this configuration can further suppress radial expansion of the cylindrical body while further increasing the axial elongation rate.

[0017] Furthermore, the fluid pressure actuator of the present invention may also have a short fiber content of 2 to 20 parts by mass relative to 100 parts by mass of the rubber component of the crosslinked rubber composition.

[0018] With this configuration, the short fibers moderately improve the circumferential rigidity (elastic modulus) of the tubular body.

[0019] Furthermore, in the fluid pressure actuator of the present invention, the tensile stress at 50% elongation in the orientation direction of the short fibers may be greater than the tensile stress at 100% elongation in the direction perpendicular to the orientation direction of the short fibers.

[0020] This configuration allows for a balance between the axial stiffness (elastic modulus) and circumferential stiffness (elastic modulus) of the cylindrical body, making it less prone to radial expansion while allowing for easier axial elongation.

[0021] Furthermore, the fluid pressure actuator of the present invention may also include untwisted fibers in its cord.

[0022] 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 on axial elongation, causing the tubular body to elongate further in the axial direction.

[0023] 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.

[0024] This configuration allows for both high elongation and fracture safety in the fiber-containing cord. Furthermore, the cord provides sufficient helical fiber restraint to the tubular body while allowing for a large elongation rate in the axial direction of the tubular body.

[0025] Furthermore, the cords of the fluid pressure actuator of the present invention 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 85% or less.

[0026] 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 a further increase in the axial elongation rate while suppressing the radial expansion of the cylindrical body.

[0027] Furthermore, the cords of the fluid pressure actuator of the present invention may be arranged such that the distance between adjacent cords when no pressure is applied is 0 mm or more and 2.0 mm or less.

[0028] This configuration, with its densely arranged, spirally connected cords within the cylindrical body, improves the body's pressure resistance. As a result, a greater fluid pressure can be applied to the cylindrical body, and its maximum elongation rate can also be increased.

[0029] Furthermore, the fluid pressure actuator of the present invention may have a cross-linked rubber composition whose elongation at break in the axial direction of the cylindrical body is 300% or more and 1000% or less.

[0030] This configuration allows the cylindrical body itself to be significantly extended in the axial direction.

[0031] Furthermore, the cylindrical body of the fluid pressure actuator of the present invention may be configured such that the value of the elongation index Y, defined by the following formula 1, is 0.01 MPa or more and 0.50 MPa or less. Elongation index Y [MPa] = (Tensile stress at 100% elongation in the axial direction of the cylindrical body [MPa]) × (Thickness of the cylindrical body [mm]) / (Inner diameter of the cylindrical body [mm]) ... (Formula 1)

[0032] With this configuration, the elongation rate of the cylindrical body can be increased to 100% or more at a fluid pressure of less than 0.50 MPa.

[0033] 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 2, 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 2)

[0034] This configuration allows for reduced circumferential strain in the cylindrical body.

[0035] 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.

[0036] In this configuration, the winding direction of the helices 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 helices along the cords. By suppressing axial twisting of the cylindrical body, the axial expansion rate of the fluid pressure actuator can be further increased. Note that "the direction of the helices 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 direction of the helices 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 is 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.

[0037] This invention provides a fluid pressure actuator that can suppress radial expansion of a cylindrical body while significantly increasing its axial elongation rate.

[0038] 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 is a side view of the cylindrical body according to the third embodiment. Figure 9 is a side view of the cylindrical body according to the fourth embodiment.

[0039] (First Embodiment) The fluid pressure actuator 1 according to the first embodiment will be described below with reference to the drawings.

[0040] (Fluid Pressure Actuator 1) As shown in Figure 1(A), the fluid pressure actuator 1 comprises a cylindrical body 11 made of a cross-linked rubber composition, a cord 12 helically bonded to the outer circumference of the cylindrical body 11 along the circumferential direction, bamboo shoot-shaped caps 13a and 13b attached to one end 11a and the other end 11b of the cylindrical body 11 in the axial direction, and hose bands 14a and 14b that fix the cylindrical body 11 to the caps 13a and 13b. An air inlet is provided in the cap 13b.

[0041] Furthermore, the fluid pressure actuator 1 controls the inflow and outflow of compressed air (pressurized fluid) into and out of the space on the inner peripheral side of the sealed cylindrical body 11 via an air introduction port provided in the cap 13b. It is connected to a control device (not shown). In the present embodiment, air pressure from air is used as the pressurized fluid that flows into and out of the space on the inner peripheral side of the cylindrical body 11. However, the present invention is not limited thereto: a gas other than air may be used as the pressurized fluid, or hydraulic pressure using oil or liquid pressure using a liquid such as water may be used. That is, the space on the inner peripheral side of the sealed cylindrical body 11 is a chamber through which air or the like, which is a pressurized fluid, flows in and out.

[0042] The fluid pressure actuator 1 described above is used as an artificial muscle that expands and contracts in the axial direction when the control device controls the inflow and outflow of compressed air into and out of the space on the inner peripheral side of the sealed cylindrical body 11 (see FIGS. 1(A) and 1(B)). Examples of applications of the fluid pressure actuator 1 as an artificial muscle include human body assistance aimed at reducing work load, extrusion mechanisms in distribution lines, replacements for air cylinders, and robot arms.

[0043] (Cylindrical Body 11) The cylindrical body 11 is formed of a crosslinked rubber composition containing a rubber component. As one of the factors that increase the axial elongation rate of the cylindrical body 11, the design of the ease and difficulty of elongation of the crosslinked rubber composition is important. In the present embodiment, tensile properties are cited as physical properties indicating the ease and difficulty of elongation 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. Specifically, the measurement can be performed by the method described in the Examples mentioned later. 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).

[0044] The crosslinked rubber composition forming the cylindrical body 11 has an axial elongation at break of, for example, 300% or more and 1000% or less, preferably 600% or more and 900% or less. According to this configuration, the cylindrical body itself can be greatly elongated in the axial direction.

[0045] Furthermore, the value of the elongation index Y of the cylindrical body 11, which is "(tensile stress [MPa] at 100% elongation in the axial direction of the cylindrical body 11) × (thickness [mm] of the cylindrical body 11) / (inner diameter [mm] of the cylindrical body 11)", is, for example, 0.01 MPa or more and 0.50 MPa or less, preferably 0.03 MPa or more and 0.20 MPa or less, and more preferably 0.05 MPa or more and 0.15 MPa or less (see FIG. 2(A)). According to this configuration, the elongation percentage of the cylindrical body can be made 100% or more with a fluid pressure lower than 0.50 MPa. Specifically, the force balance in the cylindrical body 11 when the fluid pressure actuator 1 is elongated satisfies the equation "force for elongation" = "force of the crosslinked rubber composition". The "force for elongation" is expressed by (cross-sectional area of the cylindrical body 11) × (fluid pressure), and the "force of the crosslinked rubber composition" is expressed by (inner circumferential length of the cylindrical body 11) × (thickness of the cylindrical body 11) × (modulus of elasticity of the crosslinked rubber composition). Therefore, (cross-sectional area of the cylindrical body 11) × (fluid pressure) = (inner circumferential length of the cylindrical body 11) × (thickness of the cylindrical body 11) × (modulus of elasticity of the crosslinked rubber composition). Accordingly, (fluid pressure) = (inner circumferential length of the cylindrical body 11) × (thickness of the cylindrical body 11) × (modulus of elasticity of the crosslinked rubber composition) / (cross-sectional area of the cylindrical body 11). The (inner circumferential length of the cylindrical body 11) and the (cross-sectional area of the cylindrical body 11) are values obtained from the (inner diameter of the cylindrical body 11). Therefore, (fluid pressure) is proportional to (modulus of elasticity of the crosslinked rubber composition) × (thickness of the cylindrical body 11) / (inner diameter of the cylindrical body 11). Here, the (modulus of elasticity of the crosslinked rubber composition) is the (tensile stress at 100% elongation in the axial direction of the cylindrical body 11). Therefore, in order to achieve an elongation percentage of 100% or more for the cylindrical body 11 with a fluid pressure lower than 0.50 MPa, it is preferable to reduce the value of the elongation index Y, which is "(tensile stress [MPa] at 100% elongation in the axial direction of the cylindrical body 11) × (thickness [mm] of the cylindrical body 11) / (inner diameter [mm] of the cylindrical body 11)", to 0.50 MPa or less.

[0046] Examples of rubber components in 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 individually or in combination of two or more. Natural rubber (NR) is particularly preferred from the viewpoint of low cost.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 300% or more.

[0052] (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 tubular body 11 by cross-linking molding during the manufacturing process of the fluid pressure actuator 1, which strengthens the adhesion between a portion of the cord 12 in the circumferential direction and the cross-linked rubber composition constituting the tubular body 11. However, the cord 12 does not necessarily need to be bonded to the outer circumference of the tubular body 11; it is sufficient that it is held in a state in which relative movement with respect to the tubular body 11 is suppressed. In other words, the cord 12 may be provided in a manner that is fixed to the outer circumference of the tubular body 11.

[0053] 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, since the cord 12 is bonded to the outer circumference of the cylindrical body 11 made of a cross-linked rubber composition, the fiber restraint is greater compared to when the cord 12 is not bonded to the cylindrical body 11. As a result, the radial expansion of the cylindrical body 11 is more suppressed compared to when the cord 12 is not bonded to the cylindrical body 11. Furthermore, by using the cord 12 made of fibers as the tensile body, the rigidity is lower and the elongation rate is higher compared to a coil spring. Therefore, the cord 12 made of fibers can stretch in the axial direction of the cylindrical body 11 while providing helical fiber restraint to the cylindrical body 11. As a result, the fluid pressure actuator 1 of this configuration can increase the axial elongation rate while suppressing the radial expansion of the cylindrical body 11.

[0054] 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) substantially parallel to the 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 further increasing the axial elongation rate.

[0055] Furthermore, the tensile modulus of the fibers constituting the cord 12 is, for example, 2 GPa or more and 150 GPa or less, preferably 3 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 a large elongation rate and fracture safety. The cord 12 provides sufficient helical fiber restraint to the tubular body 11 while also providing a large elongation rate in the axial direction of the tubular body 11.

[0056] 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 0 mm or more and 2.0 mm or less. With this configuration, the number of helices of the cords 12 arranged spirally in the cylindrical body 11 is large (the arrangement of the cords 12 becomes denser), 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 maximum extension rate of the fluid pressure actuator 1 can also be increased.

[0057] Furthermore, the cord 12 preferably has an average wire diameter (outer diameter D of the cord 12) of 0.1 to 5 mm.

[0058] Furthermore, in this embodiment, the helical fiber constraint (i.e., a constraint that further increases the axial elongation rate while suppressing radial expansion of the cylindrical body 11) can be appropriately adjusted 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. In this embodiment, the X value (%) of the cord arrangement density of the cord 12 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.

[0059] 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.

[0060] 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

[0061] 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 used as the outer diameter D to calculate the X value. 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.

[0062] 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".

[0063] 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."

[0064] 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".

[0065] 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 85% 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 greater 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 makes it possible to further increase the axial elongation rate while suppressing the radial expansion of the cylindrical body 11.

[0066] Furthermore, the fluid pressure actuator 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]) ２ The 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 ] / (cord pitch P). Therefore, when the cylindrical body 11 is subjected to internal pressure, the circumferential "strain" of the cylindrical body 11 is (inner diameter of cylindrical body 11) × (cord pitch P) / [(tensile modulus of elasticity of 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] The twisted or untwisted cord used as 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 incyanate compound before treatment with the RFL treatment solution.

[0071] 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 to a twisted cord whose cross-section is circular, the cords 12 that are arranged adjacent to each other in the axial direction of the cylindrical body 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 on axial elongation, causing the cylindrical body 11 to elongate further in the axial direction.

[0072] (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. Then, 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, a crosslinking reaction causes crosslinks to be formed between the cord 12 and the crosslinked sleeve, which is a crosslinked rubber composition, 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 11 with the cord 12 spirally bonded to its outer circumference.

[0073] 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.

[0074] (Second Embodiment) The fluid pressure actuator 201 according to the second embodiment will be described.

[0075] 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 Figures 1 to 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, corresponding to Figures 1 to 3). 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. In other words, the code 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. Note 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.

[0076] Furthermore, the cord 212 is bonded to the crosslinked rubber composition constituting the cylindrical body 211 through 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 of the first embodiment. The other components of the fluid pressure actuator 201 according to the second embodiment are the same as those of the first embodiment.

[0077] (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. Then, an uncrosslinked rubber sheet made of a rubber composition is wrapped around the outer circumference of the cord 212 that was spun around the outer circumference of the uncrosslinked rubber sheet to produce an uncrosslinked 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, a crosslinking reaction is carried out, and crosslinks are formed between the cord 212 and the crosslinked sleeve, which is a crosslinked rubber composition, 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 spirally embedded inside. The other steps are the same as in the first embodiment. The fluid pressure actuator 201 is manufactured through the above process.

[0078] According to the fluid pressure actuator 201 described above, 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 spiral fiber constraints along its entire axial direction by the cord 212. The helical fiber restraint provided by the cords 212 is along the circumferential direction of the cylindrical body 211. As a result, the air pressure attempting to expand the cylindrical body 211 radially acts as air pressure attempting to axially expand the space between adjacent cords 212 in the axial direction of the cylindrical body 211. Here, since the cords 212 are bonded inside the cylindrical body 211, which is made of a cross-linked rubber composition, the fiber restraint is greater compared to when the cords 212 are not bonded to the cylindrical body 211. This further suppresses the radial expansion of the cylindrical body 211 compared to when the cords 212 are not bonded to the cylindrical body 211. Furthermore, the fiber cords 212 have lower rigidity and a higher elongation rate compared to coil springs. Therefore, the fiber cords 212 can stretch in the axial direction of the cylindrical body 211 while providing helical fiber restraint to the cylindrical body 211. This makes it possible to increase the axial elongation rate while suppressing the radial expansion of the cylindrical body 211. Therefore, the fluid pressure actuator 201 with this configuration can be applied to a wide range of applications.

[0079] (Modification of the second embodiment) In the modified fluid pressure actuator 201A of the second embodiment, a cord 216 (corresponding to a second cord) is further bonded in a spiral manner along the circumferential direction of the cylindrical body 211A 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 is bonded in a continuous manner from one end 211a to the other end 211b in the axial direction.

[0080] In detail, when no pressure is applied, the cords 212 and 216 are bonded to the cross-linked rubber composition constituting the cylindrical body 211A, overlapping radially within the cylindrical body 211A, such that the orientation of their respective helices is axially symmetric with respect to the axial direction of the cylindrical body 211A (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 code 216 may be used as 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 211A; they only need to be held in a state where relative movement with respect to the cylindrical body 211A is suppressed. In other words, code 212 and code 216 may be fixed to the outer circumference of the cylindrical body 211A, or embedded inside the cylindrical body 211A.

[0081] (Manufacturing method for fluid pressure actuator 201A) 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, as shown in Figure 7(C), 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, 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, a crosslinking reaction forms crosslinks between the cords 212 and 216 and the crosslinked sleeve, which is made of a crosslinked rubber composition, resulting in strong adhesion through chemical crosslinking bonds. After demolding the obtained cylindrical crosslinked sleeve from the molding mold 281, the crosslinked sleeve is cut to a predetermined size to produce a cylindrical body 211A in which the cords 212 and 216 are embedded inside in a double helix shape. The other steps are the same as in the first embodiment. The fluid pressure actuator 201A is manufactured by the above steps.

[0082] According to the fluid pressure actuator 201A described above, axial twisting of the cylindrical body 211A can be significantly suppressed. By suppressing axial twisting of the cylindrical body 211A, the axial extension rate of the fluid pressure actuator 201A can be further increased.

[0083] (Third Embodiment) The fluid pressure actuator 301 according to the third embodiment will be described.

[0084] The fluid pressure actuator 301 of the third embodiment is obtained by incorporating short fibers into the crosslinked rubber composition that constitutes the cylindrical body 11 of the fluid pressure actuator 1 of the first embodiment (see Figure 1). That is, the crosslinked rubber composition that constitutes the cylindrical body 311 of the fluid pressure actuator 301 contains short fibers 15 (see Figure 8).

[0085] The orientation direction of the short fibers 15 is preferably in the range from the direction parallel to the circumferential direction of the cylindrical body 311 to the direction parallel to the axial direction of the cord 312, as shown in Figure 8. Here, as shown in Figure 8, the angle α between the direction parallel to the circumferential direction of the cylindrical body 311 and the direction parallel to the axial direction of the cord 312 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. Therefore, the orientation direction of the short fibers 15 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 311 and the orientation direction of the short fibers 15, it may be 5 degrees or less, and even more preferably closer to 0 degrees.

[0086] In this configuration, the short fibers 15 are oriented along the circumferential direction of the cylindrical body 311. As a result, the oriented short fibers 15 do not increase the axial stiffness (elastic modulus) of the cylindrical body 311, but increase the circumferential stiffness (elastic modulus). In particular, in the portion between adjacent cords 312 in the axial direction of the cylindrical body 311, the increased circumferential stiffness makes it more difficult for the cylindrical body 311 to deform radially, thus further suppressing radial expansion of the cylindrical body 311 when air pressure is applied. As a result, the air pressure acts more strongly on the portion between adjacent cords 312 in the axial direction of the cylindrical body 311. Consequently, the spacing between the cords 312 in the axial direction of the cylindrical body 311 widens further, causing the cylindrical body 311 to stretch further in the axial direction. In other words, if the radial expansion of the cylindrical body 311 can be suppressed, the cylindrical body 311 will not expand radially even when a larger air pressure is applied, so a larger pressure can be applied to the axial elongation of the cylindrical body 311, and the elongation rate can be increased. Therefore, the fluid pressure actuator 301 of this configuration can further suppress the radial expansion of the cylindrical body 311 and further increase the axial elongation rate compared to the case in which the cylindrical body 311 is made of a cross-linked rubber composition that does not contain short fibers 15.

[0087] Examples of short fibers 15 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. Of these short fibers 15, 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 15 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 tubular body 11. The average fiber length of the short fibers 15 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 15 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 15 in the rubber composition will decrease. From the viewpoint of the dispersibility and adhesion of the short fibers 15 in the rubber composition, it is preferable that at least the short fibers 15 be bonded or surface-treated. It is not necessary for all short fibers 15 to be bonded, and bonded short fibers 15 and unbonded short fibers 15 may be mixed or used in combination. In the bonding treatment of the short fibers 15, various bonding treatments can be performed, for example, 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), a reactive compound (adhesive compound) such as an isocyanate compound, etc. In a preferred bonding treatment, the short fibers 15 are treated with a treatment solution containing the initial condensate and a rubber component (latex), in particular with at least a resorcinol-formaldehyde-latex (RFL) solution.These processing solutions may be used in combination. For example, the short fibers 15 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.

[0088] When the crosslinked rubber composition constituting the cylindrical body 311 contains short fibers 15, the proportion of short fibers 15 per 100 parts by mass of the rubber component of the crosslinked rubber composition is, for example, 2 parts by mass or more and 20 parts by mass or less, preferably 3 parts by mass or more and 15 parts by mass or less. This is because if the content of short fibers 15 per 100 parts by mass of the rubber component of the crosslinked rubber composition constituting the cylindrical body 311 is less than 2 parts by mass, a sufficient improvement in the circumferential elastic modulus of the cylindrical body 311 cannot be expected. In this way, by setting the content of short fibers 15 per 100 parts by mass of the rubber component of the crosslinked rubber composition to 2 parts by mass or more, the circumferential rigidity (elastic modulus) of the cylindrical body 311 due to the short fibers 15 is appropriately improved.

[0089] Furthermore, it is preferable that the tensile stress of the cylindrical body 311 at 50% elongation in the orientation direction of the short fibers 15 is greater than the tensile stress of the cylindrical body 311 at 100% elongation in the direction perpendicular to the orientation direction of the short fibers 15. With this configuration, the balance between the axial stiffness (elastic modulus) and circumferential stiffness (elastic modulus) of the cylindrical body 311 is appropriately adjusted, with the viewpoint of making the cylindrical body 311 less prone to radial expansion and more prone to axial elongation.

[0090] Furthermore, the other configurations of the fluid pressure actuator 301 according to the third embodiment are the same as those of the first embodiment.

[0091] (Fourth Embodiment) The fluid pressure actuator 401 according to the fourth embodiment will be described.

[0092] That is, the cross-linked rubber composition constituting the cylindrical body 411 of the fluid pressure actuator 401 contains short fibers 415 (see Figure 9). The short fibers 415 are the same as those in the fluid pressure actuator 301 according to the third embodiment. In addition, the components of the fluid pressure actuator 401 according to the fourth embodiment, other than the short fibers 415, are the same as those in the fluid pressure actuator 201 according to the second embodiment.

[0093] Furthermore, the fluid pressure actuator 401 may have a cord 416 (corresponding to a second cord) embedded in a spiral shape along the circumferential direction of the cylindrical body 411, on the outer circumference of a cord 412 (corresponding to a first cord) embedded in the cylindrical body 411 of the fluid pressure actuator 401, similar to the fluid pressure actuator 201A according to a modification of the second embodiment. Specifically, the cords 412 and 416 may be bonded to the crosslinked rubber composition constituting the cylindrical body 411 in a state where they overlap radially within the cylindrical body 411, such that the orientation of their respective helices is axially symmetric with respect to the axial direction of the cylindrical body 411 (see Figure 7). The configuration of the cords 412 and 416 is the same as that of the fluid pressure actuator 201A according to a modification of the second embodiment.

[0094] In this example, the fluid pressure actuators according to Comparative Examples 1 to 4 and Examples 1 to 33, as shown in Tables 5 to 9 later, were fabricated using the following materials, and performance and durability evaluations were conducted and comparative verifications were performed as described later. The present invention will be described in more detail below based on the examples, but the present invention is not limited to these examples.

[0095] (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 4 and Examples 1 to 33.

[0096] 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 SRF: "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.

[0097] [Preparation of Uncrosslinked Rubber Sheets] To prepare uncrosslinked rubber sheets for forming tubular bodies, each rubber composition shown in Table 1 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. If the uncrosslinked rubber sheet contained short fibers, the short fibers were oriented in the rolling direction.

[0098] [Tensile properties of crosslinked rubber compositions: Axial tensile properties (M100, elongation at break)] An uncrosslinked rubber sheet was press-heated at a temperature of 165°C, a pressure of 2 MPa, and a time of 30 minutes to produce a crosslinked rubber sheet (100 mm × 100 mm × 2 mm thickness). Test specimens were punched out in a dumbbell shape (Type 3) in accordance with JIS K6251 (2017). For samples containing short fibers, a dumbbell-shaped test specimen was taken from the crosslinked rubber sheet such that the longitudinal direction of the short fibers and the longitudinal direction of the test specimen were approximately perpendicular to each other, so that the tensile direction was perpendicular to the direction of arrangement of the short fibers. Then, in accordance with JIS K6251 (2017), the tensile stress at 100% elongation (100% modulus, M100) and the elongation at break Eb were measured. The tensile speed was set to 500 mm / min, the test temperature to 23°C, and a Shimadzu Corporation "Autograph AG-5000A" tensile testing machine was used.

[0099] [Tensile properties of crosslinked rubber composition: circumferential tensile properties (M50)] Dumbbell-shaped test specimens (Type 3) were prepared in accordance with JIS K6251 (2017) using the same method as described above for the axial direction. For samples containing short fibers, dumbbell-shaped test specimens were taken from the crosslinked rubber sheet so that the longitudinal direction of the short fibers and the longitudinal direction of the test specimen were approximately parallel, with the arrangement direction of the short fibers being the tensile direction. Then, the tensile stress (50% modulus, M50) at 50% elongation was measured in accordance with JIS K6251 (2017). The tensile speed was 500 mm / min, the test temperature was 23°C, and a Shimadzu Corporation "Autograph AG-5000A" tensile testing machine was used.

[0100] [Tonic body] The configurations of the tensile bodies used in the fluid pressure actuators of Examples 1 to 33 and Comparative Examples 1 to 4 are shown in Tables 2 and 3.

[0101] [Tonic material: fiber cord] The tensile modulus was calculated by dividing the force at 1% of the tensile test of the cord by the cross-sectional area of ​​the cord to determine 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] When the cord type was nylon, two under-twisted yarns were prepared by twisting a multifilament yarn of nylon fiber with a fineness of 175 dtex 26 times / 10 cm in the S direction. The two prepared under-twisted yarns were brought together and twisted 45 times / 10 cm in the Z direction to prepare a multi-twisted cord with a total fineness of 350 dtex, which was then subjected to RFL impregnation treatment with the RFL treatment solution shown in Table 4.

[0105] [Tumrosians: Others]

[0106] [RFL treatment solution]

[0107] (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 30 and 31), a rubber thickness of 2.0 mm (0.6 mm for Examples 30 and 31), and an axial length of 100 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 1 to 3 and Examples 1 to 11, the fluid pressure actuators were fabricated using the manufacturing method described in the first embodiment in the section on "Modes for Carrying Out the Invention," in Comparative Examples 4 and Examples 12 to 16 and 19 to 33, the manufacturing method described in the second embodiment, and in Examples 17 and 18, the manufacturing method described in the modified version of the second embodiment. Tables 5 to 9 below show the materials for the fluid pressure actuators related to Comparative Examples 1 to 4 and Examples 1 to 33, as well as the results of performance evaluation and durability evaluation.

[0108]

[0109]

[0110]

[0111]

[0112]

[0113] [Fluid pressure actuator of the first or third embodiment] (Examples 1 to 6) An uncrosslinked rubber sheet (R1, sheet thickness 2.0 mm) that does not contain short fibers was used as the uncrosslinked rubber sheet. A PET twisted cord (1 x 3 twists of PET fibers) was used as the tensile material and was spun in a spiral pattern on the outer circumference (surface layer) of the uncrosslinked rubber sheet so that the angle α, cord pitch P, and distance d between adjacent cords were as shown in Table 5.

[0114] (Example 7) A fluid pressure actuator was fabricated in the same manner as in Example 5, except that an aramid twisted cord (0 x 2 single twist of aramid fibers) was used as the tensile material.

[0115] (Example 8) A fluid pressure actuator was fabricated in the same manner as in Example 5, except that a nylon twisted cord (1x2 twisted nylon fibers) was used as the tensile material.

[0116] (Examples 9-11) Fluid pressure actuators were manufactured in the same manner as in Example 5, except that an uncrosslinked rubber sheet (R2) containing 10 parts by mass of short fibers was used as the uncrosslinked rubber sheet, and the uncrosslinked rubber sheet was arranged so that the short fibers were oriented in the direction shown in Table 6.

[0117] (Comparative Example 1) In the manufacturing method of Example 9, a fluid pressure actuator was manufactured without using a tensile material (twisted cord).

[0118] (Comparative Example 2) In the manufacturing methods of Examples 1 to 6, a fluid pressure actuator was fabricated using a metal cord (coil spring; angle α is 1.6 degrees, cord pitch P is 2.6 mm, and the distance d between adjacent cords is 0 mm) as the tensile body.

[0119] (Comparative Example 3) In the manufacturing methods of Examples 1 to 6, a mesh 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 to manufacture a fluid pressure actuator.

[0120] [Fluid pressure actuator of the second or fourth embodiment] (Example 12) A PET twisted cord (1x3 twist of PET fibers) was spun spirally around the outer circumference of an uncrosslinked rubber sheet (R1, sheet thickness 1.30 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. An uncrosslinked molded body was then crosslinked by winding an uncrosslinked rubber sheet (R1, sheet thickness 0.7 mm) around the outer circumference to create a fluid pressure actuator in which the cord is spirally embedded inside a cylindrical body.

[0121] (Example 13) A fluid pressure actuator was fabricated in the same manner as in Example 12, except that an aramid twisted cord (0 x 2 single twist of aramid fibers) was used as the tensile material.

[0122] (Example 14) A fluid pressure actuator was fabricated in the same manner as in Example 12, except that a nylon twisted cord (1x2 twisted nylon fibers) was used as the tensile material.

[0123] (Example 15) A fluid pressure actuator was fabricated in the same manner as in Example 12, except that a PET untwisted cord was used as the tensile material, the angle α was set to 0.7 degrees, the cord pitch P to 1.0 mm, and the spacing d between adjacent cords was set to 0 mm.

[0124] (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.

[0125] (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.

[0126] (Example 18) A fluid pressure actuator was manufactured in the same manner as in Example 12, 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.

[0127] (Comparative Example 4) In the manufacturing method of Example 12, a tensile body was used in which a tensile body was embedded inside a cylindrical body, using a tensile body made of aramid cords arranged in a blind-like shape (circumferential density 80 cords / 10 cm, axial density 10 cords / 10 cm) along the circumferential direction.

[0128] (Example 19) A fluid pressure actuator was manufactured in the same manner as in Example 12, except that an uncrosslinked rubber sheet (R2) containing short fibers was used, and the uncrosslinked rubber sheet was arranged so that the orientation direction of the short fibers was parallel to the circumferential direction of the molding mold.

[0129] (Example 20) A fluid pressure actuator was fabricated in the same manner as in Example 12, except that the uncrosslinked rubber sheet was arranged so that the orientation direction of the short fibers was parallel to the helical direction of the cord (angle α is 0.5 degrees).

[0130] (Example 21) A fluid pressure actuator was fabricated in the same manner as in Example 12, except that the uncrosslinked rubber sheet was arranged so that the orientation direction of the short fibers was at a larger angle than the helical direction of the cord (angle α is 0.5 degrees) (parallel to the direction where angle α is 1.0 degrees).

[0131] (Example 22) A fluid pressure actuator was fabricated in the same manner as in Example 12, except that the uncrosslinked rubber sheet was arranged so that the orientation direction of the short fibers was axially symmetric with respect to the helical direction of the cord (angle α of 0.5 degrees) and the axial direction of the molding mold.

[0132] (Examples 23 and 24) Fluid pressure actuators were fabricated in the same manner as in Example 19, except that uncrosslinked rubber sheets (R3 and R4) with different short fiber contents were used.

[0133] (Examples 25-29) In the manufacturing method of Example 16, which uses aramid untwisted cord as the tensile material, a fluid pressure actuator was fabricated by spinning the cord in a helical shape so that the angle α, cord pitch P, and distance d between adjacent cords were as shown in Table 9.

[0134] (Example 32) A fluid pressure actuator was manufactured in the same manner as in Example 16, 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.

[0135] (Example 33) A fluid pressure actuator was manufactured in the same manner as in Example 27, 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.

[0136] (Examples 30 and 31) In the manufacturing method of Example 16, which uses aramid untwisted cord as the tensile material, a molding mold with an inner diameter of 5 mm was used, and the cord was spun into a spiral shape to achieve the angle α, cord pitch P, and distance d between adjacent cords shown in Table 9, thereby producing a fluid pressure actuator.

[0137] (Performance Evaluation) The fluid pressure actuators in Comparative Examples 1-4 and Examples 1-33 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. In this state, air pressure was applied to the fluid pressure actuator. The axial length of the fluid pressure actuator in its natural length state was 100 mm, the inner diameter was 25 mm (5 mm for Examples 30 and 31), and the rubber thickness was 2.0 mm (0.6 mm for Examples 30 and 31). While increasing the air pressure, the maximum pressure at which the fluid pressure actuator fails due to air leakage, the axial elongation at the maximum pressure (maximum elongation rate), the radial expansion rate at the maximum pressure (maximum expansion rate), and the axial twist angle at the maximum pressure were measured. Calipers and a measuring tape were used for the measurements. The following are the criteria for evaluating maximum pressure, maximum elongation, and maximum expansion rate as performance criteria. Note that the measurement of maximum pressure was stopped at a maximum of 500 kPa.

[0138] [Maximum Pressure: Criteria] a. 300 kPa or higher b. 200 kPa or higher but less than 300 kPa c. Less than 200 kPa

[0139] [Maximum Growth Rate: Criteria] a: 300% or more b: 200% or more but less than 300% c: Less than 200%

[0140] [Maximum expansion rate: Criteria] a. 10% or less b. Greater than 10% and 20% or less c. Greater than 20%

[0141] (Durability Evaluation) Air pressure was applied to the fluid pressure actuator in the same manner as in the performance evaluation described above. The air pressure was set so that the axial elongation of the fluid pressure actuator was 100%. One cycle consisted of applying air for 2 seconds and exhausting it for 2 seconds. This cycle was repeated, and the number of cycles until the fluid pressure actuator failed due to air leakage was measured. In Examples 8 and 14, which used nylon twisted cord, the axial elongation of the fluid pressure actuator was set to 80%. Furthermore, if the axial elongation of the fluid pressure actuator was less than 80%, the durability evaluation was not performed. The criteria for determining durability are shown below.

[0142] (Judgment Criteria) a. More than 100,000 times b. More than 20,000 times but 100,000 times or less c. Less than 20,000 times

[0143] [Overall Assessment] The criteria for the overall ranking of a fluid pressure actuator capable of solving this problem were determined based on the results of the assessments of the four evaluation items above: maximum pressure, maximum elongation rate, maximum expansion rate, and durability. The following criteria were used, with a rank of C or higher considered a pass. Rank A: If all of the above evaluation items received an "a" rating, it was judged to be completely practical and therefore the best rank. Rank B: If there were no "c" ratings in the above evaluation items, but one or more "b" ratings were given, it was considered practically usable but slightly inferior. Rank C: If one or more of the above evaluation items received a "c" rating, it was considered practically usable but slightly inferior to rank B. Note that cases where all ratings were "c" were excluded. Rank D: If all of the above evaluation items received a "c" rating, or if the maximum elongation rate was less than 80%, it was considered insufficient to solve this problem, i.e., a fail.

[0144] [Fluid Pressure Actuator of the First or Third Embodiment] (Evaluation Results for Table 5) Table 5 shows Examples 1 to 6 and Comparative Examples 1 to 3, which are examples of the first embodiment. (Examples 1 to 6) This is an example of the first embodiment in which a tubular body (crosslinked rubber composition) is formed from a composition R1 that does not contain short fibers, and a PET twisted cord (1 x 3 twists of PET fibers) is arranged spirally along the circumferential direction on the outer circumference of the tubular body as a tensile body. The angle α between the direction parallel to the circumferential direction of the tubular body and the direction parallel to the axial direction of the cord was changed to a small amount in the order of 1.8 degrees (Example 1), 1.5 degrees (Example 2), 1.4 degrees (Example 3), 0.8 degrees (Example 4), 0.5 degrees (Example 5), and 0.3 degrees (Example 6). As a result, the cord pitch P and the distance d between adjacent cords also decreased in order. In these examples, the overall judgment in the four evaluation items of maximum pressure, maximum elongation, maximum expansion rate, and durability was at a level that is not problematic for practical use (rank B or C). As the spacing d between adjacent cords decreased, the maximum pressure and maximum elongation increased, and durability also tended to improve. However, in Example 6, where the spacing d was reduced to 0.1 mm, the maximum pressure and maximum elongation decreased slightly. The reason why Example 6 had lower maximum pressure and maximum elongation than Example 5 is thought to be that the increased amount of fiber relative to the rubber material reduced the adhesive strength between the rubber and the fibers. Furthermore, when the strain index Z value was large, at 135.6 (Example 1) and 112.2 (Example 2), each evaluation item received a b or c rating, resulting in an overall rating of C. However, when the Z value was small, at 102.9 (Example 3), 56.1 (Example 4), and 37.4 (Example 5), the maximum pressure was 300 kPa or more (a rating), and the maximum elongation was 200% or more (a or b rating), resulting in an overall rating of B. From these results, it can be said that a strain index Z of 110 or less is preferable.

[0145] (Comparative Examples 1-3) Comparative Example 1 is an example in which a tubular body (crosslinked rubber composition) is formed from composition R2 containing short fibers, and the short fibers are oriented in the circumferential direction, but it does not have a tensile body. The maximum pressure, maximum elongation, and maximum expansion rate all received a c rating, and the overall rating was D. Comparative Example 2 is an example in which a coil spring disclosed in an embodiment of Patent Document 2 is used as the tensile body. The maximum elongation rate was less than 80%, resulting in a c rating, and the overall rating was D. Comparative Example 3 is an example in which a braided sleeve of a McKibben type actuator disclosed in Japanese Patent Application Publication No. 2024-131802 is used as the tensile body. The maximum elongation rate was less than 80%, resulting in a c rating, and the overall rating was D. From these results, it can be said that an embodiment using a cord containing fibers as the tensile body is preferable.

[0146] (Evaluation results for Table 6) Table 6 shows Examples 7-8, which are examples of the first embodiment, and Examples 9-11, which are examples of the third embodiment. (Examples 7-8) Compared to Example 5 (composition R1, PET twisted cord, angle α = 0.5 degrees, spacing d = 0.5 mm), Example 7 is an example in which a high modulus aramid twisted cord was used as the tensile material. Maximum pressure, maximum elongation, and maximum expansion rate all improved to an a rating, but durability was a b rating, and the overall rating was B rank. On the other hand, Example 8 is an example in which a low modulus (less than 5 GPa) nylon twisted cord was used. Maximum expansion rate was a rating, but maximum pressure and maximum elongation rate were c ratings, and the overall rating was C rank. It was confirmed that even if the material of the twisted cord is changed, it will reach a level that is not problematic for practical use (B or C rank).

[0147] (Examples 9-11) Examples 9-11 are examples of the third embodiment in which a tubular body (crosslinked rubber composition) was formed with composition R2 containing 10 parts by mass of short fibers, compared to Example 5 (composition R1, PET twisted cord, angle α = 0.5 degrees, spacing d = 0.5 mm). In Example 9, the short fibers were oriented in the circumferential direction of the tubular body, in Example 10, the short fibers were oriented parallel to the helical arrangement of the cord, and in Example 11, the short fibers were oriented axially symmetric with respect to the helical arrangement of the cord (with respect to the axial direction of the molding mold). In Example 9, the maximum pressure, maximum elongation, and maximum expansion rate all received an A rating, but the durability received a B rating, resulting in an overall rating of B. The decrease in the maximum expansion rate in Example 9 compared to Example 5 indicates that radial expansion (elongation) was suppressed by the short fibers. In Example 10, the maximum pressure and maximum elongation rate received an A rating, but the maximum expansion rate and durability received a B rating, resulting in an overall rating of B. Compared to Example 9, in which the short fibers were arranged circumferentially in the composite, the maximum expansion rate increased. This suggests that the slight deviation of the short fiber arrangement direction from the circumferential direction of the tubular body reduced the elastic modulus in the circumferential direction of the tubular body. In Example 11, the maximum pressure and maximum elongation rate received an A rating, but the maximum expansion rate received a B rating and the durability a C rating, resulting in an overall rating of C. From these results, it can be said that the orientation direction of the short fibers is preferably in the range from a direction parallel to the circumferential direction of the tubular body to a direction parallel to the helical arrangement of the cord.

[0148] [Fluid Pressure Actuator of the Second or Fourth Embodiment] (Evaluation Results for Table 7) Table 7 shows Examples 12 to 18 and Comparative Example 4, which are examples of the second embodiment. (Examples 12 to 14) These are examples of the second embodiment in which a cylindrical body (crosslinked rubber composition) is formed from composition R1 that does not contain short fibers, and the tensile material is embedded spirally inside the cylindrical body (crosslinked rubber composition) in a state in which the tensile material is not exposed to the outside. Examples 12 to 14 are examples that have been modified to the second embodiment, with configurations similar to Examples 5, 7, and 8 of the first embodiment (composition R1, angle α = 0.5 degrees, spacing d = 0.5 mm). The same trend as Examples 5, 7, and 8 of the first embodiment was observed, and it was confirmed that the second embodiment also achieves a level that is practically acceptable (rank B or C). It can be said that the same effect can be obtained whether the cord is placed on the outer circumference of the cylindrical body (crosslinked rubber composition) or embedded inside.

[0149] (Examples 15 and 16) Example 15 is an example in which a PET untwisted cord was used in contrast to Example 12 (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 12 using a twisted cord, the maximum pressure, maximum elongation, maximum expansion rate, and durability all received an "a" rating, and the overall rating improved to an A rank. Example 16 is an example in which an aramid untwisted cord was used in contrast to Example 15. Similar to Example 15, the overall rating was an A rank, but the levels of maximum pressure, maximum elongation, maximum expansion rate, and durability all improved. From these results, it can be said that untwisted cords are preferable to twisted cords, and that aramid fiber untwisted cords are particularly preferable.

[0150] (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 A rank, but the durability was improved compared to 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 15. Similar to Example 15, the overall evaluation was A rank, but the levels of maximum pressure, maximum elongation, maximum expansion, and durability were slightly lower. However, since the maximum twist angle in Example 15 was 70°, compared to 5° in Example 18, it can be said that twisting is significantly suppressed by using a double-wound (double helix) cord.

[0151] (Comparative Example 4) Comparative Example 4 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 12 to 16. The maximum pressure, maximum elongation, and maximum expansion rate all received a C rating, and the maximum elongation rate was very small at 30% (less than 80%), resulting in a D rank. From these results, it can be said that an arrangement of fiber-containing cords in a helical shape as a tensile material is preferable.

[0152] (Evaluation results for Table 8) Table 8 shows Example 12, which is an example of the second embodiment, and Examples 19 to 24, which are examples of the fourth embodiment. (Examples 19 to 22) Examples 19 to 22 are examples of the fourth embodiment in which a tubular body (crosslinked rubber composition) is formed with composition R2 containing 10 parts by mass of short fibers, compared to Example 12 (composition R1, PET twisted cord, angle α = 0.5 degrees, spacing d = 0.5 mm). In Example 19, the short fibers are oriented in the circumferential direction of the tubular body; in Example 20, the short fibers are oriented parallel to the helical arrangement of the cord; in Example 21, the short fibers are oriented parallel to a direction in which the angle is larger than the helical arrangement of the cord (angle α = 0.5 degrees) (direction in which angle α = 1.0 degrees); and in Example 22, the short fibers are oriented axially symmetric with respect to the helical arrangement of the cord (with respect to the axial direction of the molding mold). Compared to Example 12, which did not contain short fibers, Example 19, in which short fibers were oriented circumferentially in the tubular body, received a B rating for durability, but improved maximum pressure, maximum elongation, and maximum expansion rate, all of which received an A rating (overall rating was B). Example 20, in which short fibers were oriented parallel to the helical arrangement of the cord, improved maximum pressure and maximum elongation, but, like Example 12, received a B rating. On the other hand, in Example 21, in which short fibers were oriented at a slight angle to the direction of the helical arrangement of the cord, the maximum pressure and maximum elongation rate decreased slightly, and the durability dropped to a C rating. Furthermore, in Example 22, in which short fibers were oriented axially symmetric to the direction of the helical arrangement of the cord (relative to the axial direction of the molding mold), the maximum pressure and maximum elongation rate decreased even further, and the durability dropped to a C rating. In Example 19, the maximum expansion rate decreased compared to Example 12, indicating that radial expansion (elongation) was suppressed by the short fibers. Examples 20-22 show that the elastic modulus in the circumferential direction of the tubular body decreased because the arrangement direction of the short fibers was slightly deviated from the circumferential direction of the tubular body. From these results, it can be said that the orientation direction of the short fibers is preferably in the range from the direction parallel to the circumferential direction of the tubular body to the direction parallel to the helical arrangement of the cord.

[0153] (Examples 23 and 24) Examples 23 and 24 are examples in which the content of short fibers in the tubular body was reduced compared to Example 19 (composition R2, 10 parts by mass of short fibers, PET twisted cord, angle α = 0.5 degrees, spacing d = 0.5 mm). In Example 23, which used composition R3 (3.0 parts by mass of short fibers), and Example 24, which used composition R4 (2.0 parts by mass of short fibers), the overall evaluation was a B rank, at the same level as Example 19.

[0154] (Evaluation results for Table 9) Table 9 shows Examples 25 to 31, which are examples of the second embodiment, and Examples 32 and 33, which are examples of the fourth embodiment. (Examples 25 to 29) Examples 25 to 29 are examples of the second embodiment, in which the angle α between the direction parallel to the circumferential direction of the tubular body and the direction parallel to the axial direction of the cord is varied (and the cord pitch P is also varied in conjunction with it), compared to Example 16 (composition R1, aramid untwisted cord, angle α = 0.7 degrees, spacing d = 0 mm). When the angle α was significantly varied in the following order: 0.4 degrees (Example 25), 0.5 degrees (Example 26), 0.7 degrees (Example 16), 1.0 degrees (Example 27), 1.2 degrees (Example 28), and 1.6 degrees (Example 29), in the range of angle α from 0.5 degrees to 1.2 degrees, all four evaluation items—maximum pressure, maximum elongation, maximum expansion rate, and durability—received an "a" rating, similar to Example 16, resulting in an overall rating of A. In Example 25 (0.4 degrees) and Example 29 (1.6 degrees), the ratings were B.

[0155] (Examples 32 and 33) Example 32 is an example in which only the outer layer of the tubular body is formed with composition R2 containing short fibers, compared to Example 16 (composition R1, aramid untwisted cord, angle α = 0.7 degrees, spacing d = 0 mm). Compared to Example 16, the maximum elongation rate improved, and durability tended to decrease, but the overall rating was A. Example 33 is an example in which the tubular body is formed with composition R2 containing short fibers, compared to Example 27 (composition R1, aramid untwisted cord, angle α = 1.0 degrees, spacing d = 0.2 mm). Compared to Example 16, the maximum elongation rate improved, but durability decreased to a B rating, and the overall rating was B.

[0156] (Examples 30 and 31) Example 30 is an example in which a small-diameter cylindrical body with an inner diameter of 5 mm (composition R1, aramid untwisted cord) is formed using the configuration of the second embodiment. In Example 30, the aramid untwisted cord is helically arranged at a relatively large angle, with an angle α of 9.4 degrees (cord pitch P of 2.9 mm, and the distance d between adjacent cords of 1.6 mm). The maximum pressure and maximum expansion rate were rated as a, but the maximum elongation rate and durability were rated as b, resulting in an overall rating of B. In Example 31, the aramid untwisted cord is helically arranged at a larger angle, with an angle α of 11.3 degrees (cord pitch P of 3.5 mm, and the distance d between adjacent cords of 2.2 mm), compared to the configuration of Example 30. The maximum pressure and maximum expansion rate were rated as a, but the maximum elongation rate and durability were rated as c, resulting in an overall rating of C. From these results, it can be said that a relatively excellent (B-rank) fluid pressure actuator can be obtained in a helical arrangement where 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 is up to about 10 degrees, so an angle of 10 degrees or less is preferable.

[0157] From the above results, it has been found that the configuration of the present invention can provide a fluid pressure actuator that can increase the axial elongation rate to a high level while suppressing the radial expansion of the cylindrical body.

[0158] This application is based on Japanese Patent Application No. 2025-054096 filed on 27 March 2025 and Japanese Patent Application No. 2026-046493 filed on 19 March 2026, the contents of which are incorporated herein by reference.

[0159] 1, 201, 201A, 301, 401 Fluid pressure actuator 11, 211, 211A, 311, 411 Cylindrical body (crosslinked rubber composition) 11a, 211a One end 11b, 211b Other end 12, 212, 312, 412, 416 Cord 15, 415 Short fiber

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 side of the cylindrical body, The tubular body contains a crosslinked rubber composition, The fluid pressure actuator is characterized in that the cord contains fibers, 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 fluid pressure actuator according to claim 1, characterized in that the cord is arranged such that the angle between the direction parallel to the circumferential direction of the cylindrical body and the direction parallel to the axial direction of the cord is greater than 0 degrees and 10 degrees or less. 　 The fluid pressure actuator according to claim 1 or 2, characterized in that the crosslinked rubber composition contains short fibers, and the orientation direction of the short fibers is in the range from a direction parallel to the circumferential direction of the cylindrical body to a direction parallel to the axial direction of the cord. 　 The fluid pressure actuator according to claim 3, characterized in that the content of the short fibers relative to 100 parts by mass of the rubber component of the crosslinked rubber composition is 2 parts by mass or more and 20 parts by mass or less. 　 The fluid pressure actuator according to claim 3 or 4, characterized in that the tubular body has a tensile stress at 50% elongation in the orientation direction of the short fibers that is greater than the tensile stress at 100% elongation in a direction perpendicular to the orientation direction of the short fibers. 　 The fluid pressure actuator according to any one of claims 1 to 5, characterized in that the cord includes the untwisted fibers. 　 The fluid pressure actuator according to any one of claims 1 to 6, characterized in that the fibers constituting the cord have a tensile modulus of 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 85% 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 2.0 mm or less. 　 The fluid pressure actuator according to any one of claims 1 to 9, characterized in that the crosslinked rubber composition has an elongation of 300% or more and 1000% or less at break in the axial direction of the cylindrical body. 　 The fluid pressure actuator according to any one of claims 1 to 10, characterized in that the cylindrical body is configured such that the value of the extension index Y, defined by the following formula 1, is 0.01 MPa or more and 0.50 MPa or less. Elongation index Y [MPa] = (Tensile stress at 100% elongation in the axial direction of the cylindrical body [MPa]) × (Thickness of the cylindrical body [mm]) / (Inner diameter of the cylindrical body [mm]) ... (Equation 1) The fluid pressure actuator according to any one of claims 1 to 11, characterized in that the value of the strain index Z defined by the following formula 2 is configured to be 1 [1 / GPa] or more and 400 [1 / GPa] or less. 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 2) 　 The aforementioned code has a first code and a second code, The fluid pressure actuator according to any one of claims 1 to 12, 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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