Cylindrical body

Abstract

The objective is to provide a cylindrical body for a fluid pressure actuator with enhanced durability. [Solution] A cylindrical body 11 for a fluid pressure actuator, comprising a cylindrical elastic body 11a and a plurality of fiber bundles 11b arranged concentrically inside the elastic body 11a, configured to expand radially due to fluid pressure and contract axially, characterized in that the width of the elastic body 11a between adjacent fiber bundles 11b is 0.5 mm or more and 1.0 mm or less, and the circumferential pitch of the plurality of fiber bundles 11b is 1.0 mm or more and 1.5 mm or less.

Description

Technical Field

[0001] The present invention relates to a cylindrical body used for a fluid pressure actuator.

Background Art

[0002] There is known a fluid pressure actuator having a cylindrical body including a cylindrical elastic body and a plurality of fiber bundles arranged concentrically inside the elastic body (see, for example, Non-Patent Document 1). In such a fluid pressure actuator, the cylindrical body can be easily elastically deformed in the radial direction, but the elastic deformation accompanied by elongation in the axial direction is restricted by the plurality of fiber bundles. Further, in the fluid pressure actuator, both ends of the cylindrical body are closed by a sealing body. Thereby, when a pressurized fluid is supplied to the inside of the cylindrical body, the cylindrical body expands in the radial direction and contracts in the axial direction by the amount of expansion in the radial direction, and functions as a device for converting the pressure of the pressurized fluid into an axial mechanical contraction force.

[0003] However, in the above fluid pressure actuator, the expansion of the cylindrical body in the radial direction concentrates on the portions between adjacent fiber bundles of the elastic body (portions where no fiber bundles are arranged). Therefore, the stress applied to the elastic body becomes non-uniform in the circumferential direction, and as a result, the durability of the cylindrical body is reduced.

[0004] In response to the above problems, as a cylindrical body for a fluid pressure actuator, a structure in which a fiber layer is arranged in a layer over the entire circumference in the circumferential direction inside the elastic body (see, for example, Patent Document 1), or a structure in which a plurality of fiber bundles are arranged while being shifted from each other in the radial direction and the pitch of the circumferentially adjacent fiber bundles is made smaller (see, for example, Patent Document 2), etc., those having an increased amount of fibers or fiber bundles arranged in the circumferential direction have been developed. According to these cylindrical bodies, when a pressurized fluid is supplied, the stress applied to the elastic body can be made uniform in the circumferential direction, and the cylindrical body can be expanded evenly over the entire circumference.

Prior Art Documents

Non-Patent Documents

[0005] [Non-Patent Document 1] Matsushita: Notes on the Creation of Rubber Artificial Muscles; "Measurement and Control" Vol. 7, No. 12 (December 1968): pp. 110-116 [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2008 / 140032 [Patent Document 2] Japanese Patent Publication No. 2021-134873 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in the conventional cylindrical bodies for fluid pressure actuators described in Patent Documents 1 and 2, the elastic body constituting the cylindrical body is substantially divided into an inner layer portion radially inward and an outer layer portion radially outward, separated by a fiber layer or fiber bundle. Therefore, when the cylindrical body repeatedly expands and contracts, there is a risk that the inner and outer layers of the elastic body, sandwiching the fiber layer or fiber bundle, will undergo interfacial delamination with respect to the fiber layer or fiber bundle. Furthermore, if cracks occur in the delaminated inner layer portion, the fluid flowing into the delaminated portion through the cracks will cause the outer layer portion to undergo abnormal deformation. Thus, while the conventional cylindrical bodies for fluid pressure actuators described above can suppress the decrease in durability due to stress non-uniformity, they have the problem that their durability is impaired by a new mode of failure due to interfacial delamination, which is different from that described in Non-Patent Document 1.

[0008] This invention has been made in view of these problems, and its objective is to provide a cylindrical body for a fluid pressure actuator with enhanced durability. [Means for solving the problem]

[0009] The present invention provides a cylindrical body for a fluid pressure actuator, comprising a cylindrical elastic body and a plurality of fiber bundles arranged concentrically inside the elastic body, configured to expand radially due to fluid pressure and contract axially, characterized in that the width of the elastic body between adjacent fiber bundles is 0.5 mm or more and 1.0 mm or less, and the circumferential pitch of the plurality of fiber bundles is 1.0 mm or more and 1.5 mm or less.

[0010] In the tubular body of the present invention, it is preferable that, in the above configuration, the plurality of fiber bundles are formed by twisting together a plurality of fibers.

[0011] In the tubular body of the present invention, it is preferable that a plurality of fiber bundles are each bonded to the elastic body.

[0012] In the tubular body of the present invention, it is preferable that, in the above configuration, the plurality of fiber bundles are each arranged radially outward from the radial center position of the elastic body. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a cylindrical body for a fluid pressure actuator with enhanced durability. [Brief explanation of the drawing]

[0014] [Figure 1] This figure schematically shows the configuration of a fluid pressure actuator equipped with a cylindrical body according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view along line AA in Figure 1. [Figure 3] This is a magnified view of a portion of the cross-section of the cylindrical body shown in Figure 2. [Figure 4] This figure shows the cylindrical body of the fluid pressure actuator shown in Figure 1 in an expanded state. [Figure 5] This figure shows the relationship between circumferential strain and durability. [Figure 6] This figure shows the relationship between the pitch of the fiber bundle and the circumferential strain. [Figure 7] It is a diagram showing the relationship between the pitch of the fiber bundle and the decrease in the durability of the cylindrical body due to stress non-uniformity. [Figure 8] It is a diagram showing the process in which interfacial peeling occurs in the cylindrical body. [Figure 9] It is a diagram showing the relationship between the pitch of the fiber bundle and the occurrence frequency of interfacial peeling. [Figure 10] It is a diagram showing the relationship between the pitch of the fiber bundle and the decrease in the durability of the cylindrical body due to interfacial peeling. [Figure 11] It is a diagram showing the relationship between the pitch of the fiber bundle and the durability of the cylindrical body. [Figure 12] It is a diagram showing a partially enlarged cross-section of the cylindrical body according to the modified example. ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The elastic body 11a is the part that constitutes the outer shape of the cylindrical body 11. Various types of rubber can be used as the elastic body 11a, such as natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, nitrile rubber, butyl rubber, ethylene propylene rubber, chloroprene rubber, fluororubber, acrylic rubber, urethane rubber, and silicone rubber. Alternatively, a blend of two or more of the above types of rubber can be used as the elastic body 11a. Note that the elastic body 11a is not limited to the above and may be other materials such as elastomers.

[0021] As shown in Figures 1 and 2, the elastic body 11a is cylindrical in shape and extends along axis O. The outer diameter (diameter centered on axis O), thickness, length, etc. of the elastic body 11a can be appropriately set according to the output required for the fluid pressure actuator 1. In this embodiment, the outer diameter of the elastic body 11a is 60 mm in its natural state.

[0022] Each of the multiple fiber bundles 11b is a bundle of many fibers. The fiber bundles 11b are flexible and have high tensile strength. Preferably, the axial elongation of the fiber bundles 11b is 5% or less. As the fibers constituting the fiber bundles 11b, for example, organic fibers such as polyester, nylon, PET (polyethylene terephthalate), aromatic polyamides, and inorganic fibers such as carbon roving fibers can be used. In this embodiment, the fibers constituting the fiber bundles 11b are made of aromatic polyamide.

[0023] In this embodiment, each of the multiple fiber bundles 11b is formed by twisting together a large number of fibers. That is, in this embodiment, the fiber bundles 11b are twisted yarns. The cross-section of each fiber bundle 11b perpendicular to the axis O is approximately circular. By forming the fiber bundles 11b by twisting together a large number of fibers, the density is increased compared to the case where a large number of fibers are not twisted, while keeping the outer diameter D (see Figure 3) constant. In this embodiment, the outer diameter D of each fiber bundle 11b is 0.5 mm. Note that the outer diameter D of each fiber bundle 11b is not limited to 0.5 mm, but can be changed as appropriate as long as it is 1.0 mm or less, as will be described later. Furthermore, each of the multiple fiber bundles 11b may be composed of bundles of a large number of fibers, and these organic fibers may not be twisted.

[0024] As shown in Figures 1, 2, and 3, multiple fiber bundles 11b are arranged concentrically inside the elastic body 11a. The inside of the elastic body 11a is the portion between the inner surface facing radially inward and the outer surface facing radially outward of the cylindrical elastic body 11a. Figure 2 shows the case where 31 fiber bundles 11b are provided inside the cylindrical body 11, but the number of fiber bundles 11b provided inside the elastic body 11a can be set to any number, such as 180. For convenience, in Figures 1 and 2, only one fiber bundle 11b is labeled.

[0025] Each of the multiple fiber bundles 11b extends along the axial direction of the elastic body 11a from one end to the other. More specifically, the multiple fiber bundles 11b extend straight and parallel to each other from one end to the other of the elastic body 11a. Furthermore, the multiple fiber bundles 11b are arranged in a circumferential direction with spacing between them around the axis O. The circumferential pitch p of the multiple fiber bundles 11b is constant. Also, the radial positions of the multiple fiber bundles 11b around the axis O are the same. That is, inside the elastic body 11a, only multiple fiber bundles 11b arranged concentrically at equal circumferential intervals at the same radial position are provided. No fiber bundles are provided at positions radially offset from the multiple fiber bundles 11b inside the elastic body 11a.

[0026] The cylindrical body 11 can be elastically deformed to expand radially while bending the elastic body 11a and the multiple fiber bundles 11b. On the other hand, since the cylindrical body 11 has multiple fiber bundles 11b with high tensile strength inside, elastic deformation in the elongation direction along the axis O is restricted.

[0027] It is preferable that multiple fiber bundles 11b are each bonded to an elastic body 11a. That is, it is preferable to provide an adhesive layer 14 (see Figure 3) on the outer surface of the fiber bundles 11b that adheres to both the fiber bundles 11b and the elastic body 11a. This configuration can suppress the peeling of the elastic body 11a from the fiber bundles 11b. The adhesive layer 14 may be provided over the entire outer surface of the fiber bundles 11b, or only on a part of it.

[0028] The sealing bodies 12 and 13 are provided at the ends of the cylindrical body 11, respectively, to seal the openings 11c and 11d of the cylindrical body 11. More specifically, one sealing body 12 is provided at one end of the cylindrical body 11 in the axial direction (longitudinal direction along axis O), sealing one opening 11c of the cylindrical body 11. The other sealing body 13 is provided at the other end of the cylindrical body 11 in the axial direction, sealing the other opening 11d of the cylindrical body 11. Although not shown in detail, the sealing bodies 12 and 13 are configured to have a press ring on the outside of an inner cylinder positioned inside the end of the cylindrical body 11, and the end of the cylindrical body 11 is sandwiched and fixed between the outer surface of the inner cylinder and the inclined inner surface of the press ring by pressing the press ring with a nut member screw-connected to the inner cylinder. Furthermore, an internal unit is arranged inside the cylindrical body 11, which is supported by the inner cylinder and comprises a cylindrical inner tube coaxial with the cylindrical body 11, and a spring positioned inside the inner tube. Inside the cylindrical body 11, an internal space 15 (see Figure 2) is formed, partitioned by the cylindrical body 11, the sealing bodies 12 and 13, and the inner tube. The spring pushes the sealing bodies 12 and 13 apart from each other, thereby extending the cylindrical body 11.

[0029] Furthermore, the sealing bodies 12 and 13 are not limited to the above configuration, and can be configured as appropriate as long as they can seal the openings 11c and 11d of the cylindrical body 11. In addition, the configuration of the internal unit provided inside the cylindrical body 11, and the presence or absence of the internal unit, can also be changed as appropriate.

[0030] The fluid supply and discharge device 20 supplies pressurized fluid to the internal space 15 of the cylindrical body 11 and discharges the fluid supplied to the internal space 15 to the outside. As shown in Figure 1, the fluid supply and discharge device 20 has a pressurized fluid supply unit 21 and a discharge valve 22.

[0031] The pressurized fluid supply unit 21 communicates with the internal space 15 of the cylindrical body 11 through a supply pipe 23 connected to the sealing body 13. The pressurized fluid supply unit 21 can supply pressurized fluid to the internal space 15 through the supply pipe 23. In this embodiment, the pressurized fluid supply unit 21 is an air compressor. The pressurized fluid supply unit 21 can supply pressurized air to the internal space 15. Note that the fluid supplied to the internal space 15 by the pressurized fluid supply unit 21 is not limited to pressurized air, but may be other gases, liquids, etc.

[0032] A discharge pipe 24 is connected to the sealing body 13 separately from the supply pipe 23. A discharge valve 22 is provided in the discharge pipe 24. The discharge valve 22 is, for example, a solenoid valve. The discharge valve 22 can open and close the discharge pipe 24. When the discharge pipe 24 is opened by the discharge valve 22, the fluid supplied into the internal space 15 is discharged to the outside through the discharge pipe 24.

[0033] The operation of the pressurized fluid supply unit 21 and the discharge valve 22 is controlled by a control device (not shown).

[0034] Furthermore, the fluid supply and discharge device 20 is not limited to the above configuration; various configurations can be used as long as they can supply and discharge pressurized fluid into and out of the internal space 15.

[0035] The fluid pressure actuator 1 with the above configuration operates as follows.

[0036] From the state shown in Figure 1, the pressurized fluid supply unit 21 is activated to supply pressurized fluid to the internal space 15. At this time, the discharge valve 22 closes the discharge pipe 24. When pressurized fluid is supplied to the internal space 15, the pressure in the internal space 15 increases. As shown in Figure 4, when the pressure in the internal space 15 increases, the cylindrical body 11 expands radially outward. At this time, the elastic deformation of the cylindrical body 11 in the direction along the axis O is limited by multiple fiber bundles 11b. Therefore, the cylindrical body 11 expands radially outward while contracting in the direction of axis O, narrowing the distance between the sealant 12 and the sealant 13. In this way, the fluid pressure actuator 1 operates to generate a contraction force when pressurized fluid is supplied to the internal space 15 of the cylindrical body 11.

[0037] From the state shown in Figure 4, when the operation of the pressurized fluid supply unit 21 is stopped and the discharge valve 22 is activated to open the discharge pipe 24, the fluid inside the internal space 15 is discharged to the outside through the discharge pipe 24. As a result, the cylindrical body 11 returns to its original shape shown in Figure 1 from its radially expanded state due to the elastic force of the elastic body 11a and the spring force of the internal unit's spring.

[0038] In the cylindrical body 11 having the above configuration, the arrangement of fiber bundles 11b inside the elastic body 11a is determined by the balance of axial forces using the equation Fc = Ts × Nf. Here, Fc is the axial contractile force of the cylindrical body 11, Ts is the tension per fiber bundle, and Nf is the number of fiber bundles. In this equation, the tension of the fiber bundles (i.e., the fiber diameter) and the number of fiber bundles are inversely proportional, and the larger the outer diameter of the fiber bundles, the fewer fiber bundles there are.

[0039] Here, the inventors of the present invention, in determining the arrangement of fiber bundles 11b inside the elastic body 11a using the above formula, conducted experiments to find an arrangement of fiber bundles 11b that could further enhance the durability of the cylindrical body 11. These experiments involved a cylindrical body in which multiple fiber bundles were arranged inside at equal intervals in the circumferential direction, and the width of the elastic body between adjacent fiber bundles, i.e., the circumferential pitch of the fiber bundles, was varied to confirm the durability of the cylindrical body. In these experiments, a cylindrical body with the same configuration as the cylindrical body 11 shown in Figures 1 and 2 was used, the fiber bundles were made of aromatic polyamide with an outer diameter of 0.5 mm, and the number of fiber bundles provided inside the elastic body was 180. In these experiments, the cylindrical body was judged to have sufficient durability when it could withstand more than 10,000 expansion and contraction cycles.

[0040] First, the inventors conducted experiments to investigate the relationship between the maximum circumferential strain (hereinafter simply referred to as "strain") generated in the elastic body when the cylindrical body expands and contracts, and the durability of the cylindrical body. As shown in Figure 5, there was a correlation between strain and the durability of the cylindrical body, with the durability of the cylindrical body decreasing as the strain increased. In particular, it was confirmed that the strain needed to be less than 0.8 in order for the cylindrical body to have sufficient durability to withstand more than 10,000 expansions and contractions. Next, experiments were conducted to investigate the relationship between the circumferential pitch of the fiber bundles in the cylindrical body and strain. As shown in Figure 6, it was confirmed that the wider the width of the elastic body between adjacent fiber bundles, that is, the wider the circumferential pitch of the fiber bundles, the more the radial expansion of the cylindrical body concentrated in the area between adjacent fiber bundles (the area where no fiber bundles are placed) when pressurized fluid is supplied to the internal space of the cylindrical body, resulting in a large strain in that area. This is the mechanism of durability reduction due to stress concentration. Furthermore, it was confirmed that in order to keep the strain below 0.8, the circumferential pitch of the fiber bundles needs to be smaller than 1.5 mm. Based on these results, experiments were conducted to check the durability of the cylindrical body by changing the circumferential pitch of the fiber bundles in various ways. As shown in Figure 7, it was confirmed that when the circumferential pitch of the fiber bundles becomes larger than 1.5 mm, the stress applied to the elastic material constituting the cylindrical body becomes non-uniform, resulting in a decrease in the durability of the cylindrical body.

[0041] Furthermore, the inventors found through this experiment that when the circumferential pitch of the fiber bundles in the cylindrical body becomes smaller than 1.0 mm, interfacial delamination occurs between the inner and outer layers of the elastic body and the fiber layer, reducing the durability of the cylindrical body. To explain interfacial delamination, when the circumferential pitch of the fiber bundles becomes narrower, the width of the elastic body between adjacent fiber bundles becomes smaller. In other words, when the circumferential pitch of the fiber bundles becomes narrower, the area in which the inner layer (radially inward) and the outer layer (radially outward) of the elastic body constituting the cylindrical body are connected to each other between adjacent fiber bundles becomes smaller. As a result, as shown in Figure 8(a), the multiple fiber bundles 11b are arranged in layers between the inner and outer layers of the elastic body 11a. Note that in Figure 8, for convenience, the multiple fiber bundles 11b are shown as a single layer. As a result, when the cylindrical body 11 repeatedly expands and contracts, as shown in Figure 8(b), the inner and outer layers of the elastic body 11a undergo interfacial delamination with respect to the layered fiber bundle 11b. Subsequently, as shown in Figure 8(c), cracks form in the inner layer of the elastic body 11a, supplying air to the delamination area. This supplied air is blocked by the layered fiber bundle 11b and cannot be released, so as shown in Figure 8(d), the outer layer of the elastic body 11a undergoes large, abnormal expansion and eventually breaks. This is the mechanism of reduced durability due to interfacial delamination. The inventors then investigated the relationship between the frequency of interfacial delamination occurring between the inner and outer layers of the elastic body and the fiber layer, and the circumferential pitch of the fiber bundle of the cylindrical body. As shown in Figure 9, it was confirmed that when the circumferential pitch of the fiber bundle of the cylindrical body becomes smaller than 1.0 mm, the frequency of interfacial delamination increases sharply. Based on the above results, experiments were conducted to check the durability of the cylindrical body by changing the circumferential pitch of the fiber bundles in various directions. As shown in Figure 10, it was confirmed that when the circumferential pitch of the fiber bundles of the cylindrical body becomes smaller than 1.0 mm, the frequency of interface isolation increases, leading to a problem of decreased durability of the cylindrical body. This is a novel problem that the inventors discovered for the first time through the above experiments.

[0042] The inventors combined the experimental results regarding the relationship between the circumferential pitch of the fiber bundles and the durability of the cylindrical body due to stress concentration (shown in Figure 7) and the experimental results regarding the relationship between the circumferential pitch of the fiber bundles and the durability of the cylindrical body due to interfacial delamination (shown in Figure 10) to obtain the graph shown in Figure 11, which shows the relationship between the circumferential pitch of the fiber bundles and the durability of the cylindrical body. In the graph shown in Figure 11, it was confirmed that the cylindrical body can obtain sufficient durability when the fiber bundle pitch is in the range of 1.0 mm to 1.5 mm, for both the durability of the cylindrical body due to stress concentration (shown by circles in the figure) and the durability of the cylindrical body due to interfacial delamination (shown by squares in the figure). Thus, by conducting the above experiments, the inventors found that by setting the fiber bundle pitch to the range of 1.0 mm to 1.5 mm, that is, by setting the width of the elastic body between adjacent fiber bundles to 0.5 mm to 1.0 mm, a remarkable effect is obtained in that the durability of the cylindrical body is significantly improved. Note that the numerical values ​​for the width of the elastic body between adjacent fiber bundles and the pitch of the fiber bundles are values ​​for the tubular body in its natural state, when it is not expanding radially.

[0043] The inventors conducted similar experiments on cylindrical bodies with different outer diameters of fiber bundles and elastic bodies. From these results, they confirmed that setting the width of the elastic body between adjacent fiber bundles to a range of 0.5 mm to 1.0 mm, and the pitch of the fiber bundles to a range of 1.0 mm to 1.5 mm, resulted in a remarkable improvement in the durability of the cylindrical body.

[0044] Based on the above findings, in the fluid pressure actuator 1 according to this embodiment, the width W (see Figure 3) of the elastic body 11a between adjacent fiber bundles 11b is set to 0.5 mm or more and 1.0 mm or less, and the multiple fiber bundles 11b provided inside the elastic body 11a are arranged in the circumferential direction at a pitch p of 1.0 mm or more and 1.5 mm or less.

[0045] This configuration allows the stress applied to the elastic body 11a when pressurized fluid is supplied to the internal space 15 to be uniformly distributed in the circumferential direction, enabling the cylindrical body 11 to expand uniformly around its entire circumference. Furthermore, this configuration suppresses the occurrence of interfacial delamination between the elastic body 11a and the multiple fiber bundles 11b, even when the cylindrical body 11 repeatedly expands and contracts.

[0046] As described above, in the fluid pressure actuator 1 according to this embodiment, the width W of the elastic body 11a between adjacent fiber bundles 11b is set to 0.5 mm or more and 1.0 mm or less, and the multiple fiber bundles 11b provided inside the cylindrical body 11 are arranged in the circumferential direction at a pitch p of 1.0 mm or more and 1.5 mm or less. As a result, the durability of the cylindrical body 11 can be significantly improved compared to conventional ones.

[0047] Furthermore, in the fluid pressure actuator 1 according to this embodiment, multiple fiber bundles 11b are arranged concentrically, that is, at the same radial position, with spacing in the circumferential direction. This configuration is simpler compared to cases where fibers are arranged in layers over the entire circumference of the elastic body 11a, or where multiple fiber bundles are arranged in multiple rows offset from each other in the radial direction. This reduces the manufacturing cost of the cylindrical body 11.

[0048] In this embodiment, the outer diameter D of the fiber bundle 11b is 0.5 mm, but the outer diameter D of the fiber bundle 11b can be set to an appropriate value as long as it is 1.0 mm or less. Preferably, the outer diameter D of the fiber bundle 11b is 0.5 mm or more and 1.0 mm or less. By setting the outer diameter D of the fiber bundle 11b to a range of 0.5 mm or more and 1.0 mm or less, when the cylindrical body 11 expands radially, it is possible to prevent the elastic body 11a from breaking due to the shear force that the fiber bundle 11b applies to the elastic body 11a, thereby further increasing the durability of the cylindrical body 11.

[0049] As described above, in the fluid pressure actuator 1 according to this embodiment, multiple fiber bundles 11b are formed by twisting multiple fibers together. This increases the density when the outer diameter D of the fiber bundles 11b is kept constant, thereby making the fiber bundles 11b have higher tensile strength. In other words, a fiber bundle 11b with a smaller outer diameter D can be used to obtain a fiber bundle 11b with high tensile strength.

[0050] Furthermore, as described above, in the fluid pressure actuator 1 according to this embodiment, multiple fiber bundles 11b are bonded to the elastic body 11a, so that when the cylindrical body 11 repeatedly expands and contracts, the elastic body 11a does not peel off from the fiber bundles 11b. This makes it possible to further improve the durability of the cylindrical body 11.

[0051] In the modified fluid pressure actuator 1 shown in Figure 12, multiple fiber bundles 11b are arranged radially outward from the radial center of the elastic body 11a. That is, in the modified fluid pressure actuator 1, when the portion of the elastic body 11a radially inward from the virtual circle C passing through the centers of each of the multiple fiber bundles 11b is designated as the inner layer 11e and the portion outside of it as the outer layer 11f, the thickness t1 of the inner layer 11e is greater than the thickness t2 of the outer layer 11f.

[0052] According to this modified configuration, even if the elastic body 11a undergoes interfacial delamination with respect to the fiber bundle 11b, crack formation in the inner layer 11e can be suppressed. Therefore, the durability of the cylindrical body 11 can be further enhanced.

[0053] Furthermore, the inventors of the present invention conducted experiments to confirm the durability of a cylindrical body in which multiple fiber bundles are arranged inside at equal intervals in the circumferential direction, by changing the ratio of the thickness of the inner layer to the thickness of the outer layer in various ways. In these experiments, the cylindrical body used was one with the same configuration as the cylindrical body 11 shown in Figure 12.

[0054] As a result of the above experiment, as shown in Figure 13, it was confirmed that the durability of the cylindrical body 11 is highest when the ratio of the thickness t1 of the inner layer 11e to the thickness t2 of the outer layer 11f is 3:1.

[0055] Based on the above findings, in the modified fluid pressure actuator 1 shown in Figure 12, the elastic body 11a is configured such that the ratio of the thickness t1 of the inner layer 11e to the thickness t2 of the outer layer 11f is 3:1. This configuration more reliably suppresses the occurrence of cracks in the inner layer 11e when the elastic body 11a undergoes interfacial delamination with respect to the fiber bundle 11b, thereby further improving the durability of the cylindrical body 11.

[0056] The present invention is not limited to the embodiments described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0057] 1. Fluid pressure actuator 10 Actuator body 11. Cylindrical body 11a Elastic body 11b Fiber bundle 11c aperture 11d aperture 11e Inner layer 11f outer layer 12 Sealing body 13 Sealing body 14 Adhesive layer 15 Interior space 20 Fluid supply / discharge device 21 Pressurized fluid supply unit 22 Discharge valve 23 Supply pipe 24 Discharge pipe O axis D Outer diameter p pitch W width C Virtual Yen t1 Thickness t2 thickness

Claims

1. A cylindrical body for a fluid pressure actuator comprises a cylindrical elastic body and a plurality of fiber bundles arranged concentrically inside the elastic body, and is configured to expand radially due to fluid pressure and contract axially, A cylindrical body characterized in that the width of the elastic body between adjacent fiber bundles is 0.5 mm or more and 1.0 mm or less, and the circumferential pitch of the plurality of fiber bundles is 1.0 mm or more and 1.5 mm or less.

2. The cylindrical body according to claim 1, wherein each of the multiple fiber bundles is formed by twisting together multiple fibers.

3. The cylindrical body according to claim 1 or 2, wherein each of the multiple fiber bundles is bonded to the elastic body.

4. The cylindrical body according to claim 1, wherein each of the multiple fiber bundles is arranged radially outward from the radial center of the elastic body.

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