Fluid pressure actuator

Abstract

To present effective configurations of a curved motion actuator using Warsaw-type artificial muscle and to embody various holding devices provided with the actuator.SOLUTION: An actuator 10 comprises: a multi-layered fiber reinforced tube 11 composed of two layers of a rubber base material layer and a fiber contained layer; cover members 12A, 12B attached to opposite ends of the tube 11, respectively; a binding member 20 in contact with a part of a lateral surface of the tube 11 and provided along an axial direction of the tube 11; an adhesive layer 31 connecting the tube 11 and the member; and fastening bands 13A, 13B. The cover members 12A, 12B close openings at the opposite ends of the tube 11, and maintains the inside thereof in a closed state. The fastening bands 13A, 13B are fastened to an outer peripheral surfaces at the opposite ends of the tube 11 and fastens the tube 11 with the binding member 20 such that no gap is present between the cover members 12A, 12B and the tube 11.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a hydraulic actuator that is optimized for end effector applications. [Background technology]

[0002] Soft actuators are materials, elements, and devices that function as actuators by deforming lightweight, flexible materials. These soft actuators, also known as artificial muscles, are characterized by their small size, light weight, ability to use various drive sources, silence, and ability to function under extreme conditions such as underwater and in the air. Great expectations are placed on them as a power source for wearable robots for power assist in rehabilitation, nursing care, and work assistance, as well as medical and surgical support robots, for which development has been in great demand in recent years.

[0003] One practical example of an end effector (robot arm) using a soft actuator is a gripping device using artificial muscles driven by fluid pressure (see Patent Document 1). Artificial muscles that operate by fluid pressure can be broadly divided into two types. One is a configuration consisting of a combination of an inner rubber tube and a braided sleeve, known as McKibben artificial muscle. The other is a configuration known as Warsaw artificial muscle, characterized by a rubber substrate tube layer that expands and contracts and a fiber-encapsulated layer that encapsulates threads or fibers to constrain the axial extension of the rubber tube, which are bonded together in a manner that prevents them from separating (see Non-Patent Document 2). The invention in Patent Document 1 adds a constraint member that can deform in a direction perpendicular to the axial direction to the McKibben artificial muscle, thereby constructing an actuator with a mechanism that curves (curls) in the radial direction perpendicular to the axial direction as the artificial muscle contracts, i.e., the constraint member is on the outside of the bend. A flexible gripping device is realized by constructing an effector consisting of multiple actuators arranged with this curvature direction as it abuts against an object. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-88999 [Patent Document 2] Matsushita: Notes on the production method of rubber artificial muscles; "Measurement and Control" Vol. 7, No. 12 (December 1968): pp. 110-116 Summary of the Invention [Problem to be solved by the invention]

[0005] A problem with bending actuators using Warsaw artificial muscles has been that no configuration that actually functions has been demonstrated.

[0006] The present invention has been made in consideration of these circumstances, and aims to provide an effective configuration for a bending motion actuator that uses Warsaw artificial muscles, and to realize various gripping devices that employ the actuator. [Means for solving the problem]

[0007] The fluid pressure actuator of the present invention, which solves the above problems, is characterized by combining two elements: a Warsaw-type axially contractible artificial muscle tube and a constraint member that converts the contraction motion of the tube into a bending motion.

[0008] The basic configuration of the Warsaw-type artificial muscle, i.e., axial fiber-reinforced artificial muscle shown in the previous section, has a two-layer structure consisting of a rubber-based tube layer and a fiber-encapsulated layer that restricts the axial extension of the tube layer, and when fluid pressure is applied, the tube expands significantly in the radial direction and contracts along the axial direction.

[0009] When the tube becomes approximately spherical due to the application of fluid pressure, the internal volume relative to the tube's length is maximized, and it does not contract further in the axial direction. Here, assuming that the free length (L1) before expansion is 100 mm and the diameter of the tube is 10 mm, the length (L2) at its maximum contraction is 68% of the free length (L1). In other words, a stroke of up to 32% can be achieved.

[0010] The fluid pressure actuator presented by the present invention is characterized in that a restraint member is provided which is in contact with a portion of the side surface of the tube, is continuously adhered to the outer surface of the tube from one end to the other in the axial direction of the tube so as not to separate when the tube contracts, resists radial expansion of the tube, and is elastically deformable in a direction perpendicular to the axial direction.

[0011] According to the configuration described above, the restraining member has a greater bending modulus than the tube. Therefore, even if the internal pressure of the tube increases, the radial expansion of the portion of the tube where the restraining member contacts a portion of the side surface and is continuously bonded to the outer surface of the tube from one end to the other in the axial direction is restricted by the restraining member. Therefore, the portion of the tube that can expand radially without being restricted, particularly the portion facing the restraining member, expands significantly. Therefore, the application of fluid pressure causes the tube to expand unevenly, and the actuator as a whole bends. The bending direction is such that the side with the bonded restraining member that exhibits low expansion is on the outside of the bend and the side with high expansion is on the inside of the bend. Therefore, by arranging the actuator in an end effector so that the bending direction is in the direction of contact with an object, it is possible to perform operations such as pushing, pulling, and grasping the object.

[0012] As explained in paragraph 0009, when the artificial muscle operates to its maximum contraction rate, the tube becomes approximately spherical, and the internal volume relative to the length of the tube becomes maximum, so the diameter of the tube becomes approximately equal to the length. For this reason, when the actuator bends, the tube expands and bulges out significantly toward the inside of the bend, which can be detrimental when the tube is incorporated into a device.

[0013] In addition to the configuration described in paragraph 0010, the fluid pressure actuator presented by the present invention may be configured such that one or more ring members for restraining radial expansion of the tube are provided in contact with the outer surface of the tube in a region from one end side to the other end side in the axial direction of the tube. When one or more radial restraint ring members are provided, the ring members cause the tube to constrict when expanding. When the tube is at its maximum radial expansion, it has a shape of approximately spheres connected by the ring members, and operates in a similar curved manner with approximately the same maximum contraction rate as when no ring members are present. This configuration solves the problem described in paragraph 0012.

[0014] Instead of the restraint member being continuously bonded from one end to the other end in the axial direction of the tube so as not to separate from the outer surface of the tube as described in the configuration shown in paragraph 0010, the restraint member may be embedded in and integrated with the tube. Even in the actuator having the configuration shown in this paragraph, the radial expansion of the portion where the restraint member is embedded is restricted by the restraint member even when the internal pressure of the tube increases, so that only the portion that can expand in the radial direction when the fluid pressure is applied, that is, the portion facing the restraint member, expands significantly, causing the tube to expand unevenly, and the actuator as a whole bends and operates in the same manner as the configuration shown in paragraph 0010.

[0015] Instead of the restraint member being continuously bonded from one end to the other end in the axial direction of the tube so as not to separate from the outer surface of the tube as described in the configuration shown in paragraph 0010, the restraint member may be bonded to the inner surface so as not to separate from the tube. Even in the actuator having the configuration shown in this paragraph, the radial expansion of the portion where the restraint member is bonded to the inner surface of the tube is restricted by the restraint member even when the internal pressure of the tube increases, so that only the portion that can expand radially when the fluid pressure is applied, that is, the portion facing the restraint member, expands significantly, causing the tube to expand unevenly, and the actuator as a whole bends and operates in the same manner as the configuration shown in paragraph 0010. [Effects of the Invention]

[0016] According to the configuration of the fluid pressure actuator described above, it is possible to realize a novel bending motion actuator by utilizing the contraction characteristics of the Warsaw artificial muscle. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of an actuator 10 and a driving device 20 that perform bending operation using fluid pressure. [Figure 2] FIG. 2 is a side view of the actuator 10. [Figure 3] FIG. 3 is a side view of the actuator in a state where it is bent by application of fluid pressure. [Figure 4] FIG. 4 is a cross-sectional view of the actuator 10 taken along the axial direction. [Figure 5] FIG. 5 is a perspective view of the actuator 10. As shown in FIG. [Figure 6] FIG. 6 is a perspective view of the actuator 10 in an exploded state. [Figure 7] FIG. 7 is a cross-sectional view of a multi-layer fiber-reinforced tube, which is a component of the actuator. [Figure 8-a] FIG. 8-a is a schematic diagram of one of the processes for forming the fiber encapsulation layer 11b. [Figure 8-b]FIG. 8-b is a schematic diagram of one of the processes for forming the fiber encapsulation layer 11b. [Figure 9-c] FIG. 9-c is a cross-sectional view showing one way of combining the layers of the tube. [Figure 9-d] FIG. 9-d is a cross-sectional view showing one way of combining the layers of the tube. [Figure 9-e] FIG. 9-e is a cross-sectional view showing one way of combining the layers of the tube. [Figure 10] FIG. 10 is a side view of one of the multiple configurations of the actuator, in which a radial restraint ring member 22 is added. [Figure 11] FIG. 11 is a perspective view of the actuator having the configuration shown in FIG. [Figure 12] FIG. 12 is a side view of the actuator having the configuration shown in FIG. 10 in a state where it is bent by application of fluid pressure. [Figure 13] FIG. 13 is a cross-sectional view taken along line AA' of a configuration in which the restraining member is embedded in the tube, among the multiple configurations of the actuator. [Figure 14] FIG. 14 is a cross-sectional view taken along line AA' of a configuration in which the restraining member is bonded to the inside of the tube, among the multiple configurations of the actuator. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below with reference to the following embodiments, but the invention is not limited to the scope of the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the present invention.

[0019] Fig. 1 is a schematic diagram of a fluid pressure actuator system that performs bending motion by adjusting fluid pressure. Actuator 10 and drive unit 30 are connected by a fluid supply / discharge pipe 31. The detailed configuration of actuator 10 is shown in a side view in Fig. 2, a cross-sectional view in Fig. 4, a perspective view in Fig. 5, and an exploded perspective view in Fig. 6.

[0020] It is desirable to select a working fluid for the actuator system that is suitable for the application and environment of the actuator. Specifically, water, oil, air, steam, product gases generated from reactive substances, etc. can be used.

[0021] The actuator 10 includes a multilayer fiber-reinforced tube 11, which is composed of a rubber base layer 11a and a fiber-encapsulating layer 11b. The tube 11 is fitted with cap members 12A and 12B at both ends, respectively. A restraining member 20 is attached to a portion of the side surface of the tube 11 and extends along the axial direction of the tube. An adhesive layer 31 connects the tube and the restraining member 20, and tightening bands 13A and 13B. The cap members 12A and 12B close the openings at both ends of the tube 11 to maintain a sealed interior. The tightening bands 13a and 13b are fastened to the outer peripheral surfaces of both ends of the tube 11 and tighten the tube 11 together with the restraining member 20 to prevent gaps from forming between the cap members 12A and 12B and the tube 11. The tube 11 is thus sealed by the cap members 12A and 12B and the tightening bands 13A and 13B. The tube 11 is operated by introducing a working fluid into the sealed space. The cover member 12B has a hole penetrating from the inside to the outside, into which a fluid supply / discharge pipe 31 is fitted. The drive device 20 includes a solenoid valve 32a for injecting fluid, a solenoid valve 32b for discharging fluid, a working fluid supply means 33, and a control means 34, and the fluid supply / discharge pipe 31 is fitted into the solenoid valve 32b. The control means 34 controls the opening and closing of the solenoid valve 32a for injecting fluid and the solenoid valve 32b for discharging fluid, thereby controlling the bending operation of the actuator.

[0022] The actuator 10 performs a bending operation by transitioning between two states, a non-pressurized state shown in FIG. 2 and a pressurized state shown in FIG. 3, as the working fluid is supplied and discharged via the fluid supply and discharge pipe 31 under the control of the drive device 30.

[0023] The tube 11 is cylindrical and open at both ends. It is a multilayer structure consisting of at least one rubber substrate layer 11a and at least one fiber encapsulation layer 11b. The fiber encapsulation layer 11b is formed by forming a fiber sheet 11s into a cylindrical shape. The fiber encapsulation layer 11b is formed by uniformly dispersing multiple reinforcing fibers 11k in a binder material 11r or by uniformly attaching the fibers to the surface (see Figures 8-a and 8-b). Note that the orientation of the fibers 11k should be approximately parallel to the axial direction of the tube 11, more specifically, within an angle of 5 degrees from the axial direction. The fibers 11k constituting the fiber layer 11b may be any fibrous or thread-like material that has sufficient tensile strength to withstand expansion due to internal pressure of the tube 11 and restrict tube elongation, and is flexible enough not to impede radial expansion of the tube. Specifically, the material may be selected from a variety of high-strength fibers, such as glass fiber, nylon fiber, aramid fiber, carbon fiber, and piano wire. The binder material 11r may be a soft material that can hold the reinforcing fibers 11k without separation or displacement and that can follow the contraction and expansion of the tube 11. More specifically, the binder material may be selected from natural rubber or synthetic rubber latex, silicone, polyurethane, vinyl polymer, etc.

[0024] The layer structure of the tube 11 may be any structure that prevents the rubber base layer 11a and the fiber encapsulation layer 11b from peeling off during expansion and contraction. The structure may be selected according to the material of each layer, such as bonding the layers 11a and 11b together through tackiness or bonding them together with an adhesive. The inside and outside of each layer and the number of layers may be selected as appropriate for the application. More specifically, the rubber base layer 11a and the fiber encapsulation layer 11b may be either on the inside or the outside (Fig. 9-c), or multiple layers of the same type may be stacked (Fig. 9-d), or different layers may be stacked alternately (Fig. 9-e).

[0025] The dimensions of the restraint member 20 are not particularly limited and can vary depending on the dimensions of the fluid pressure actuator 10, and the driving force and operating stroke of the actuator. The material used to make the restraint member 20 is preferably an elastic rubber material or a material with a greater flexural modulus than the tube 11 made of untwisted fibers. Specifically, materials that can be used as leaf springs, such as various general-purpose plastics, engineering plastics, glass fiber reinforced resins, carbon fiber reinforced plastics, spring stainless steel, and spring copper alloys, can be processed into a member of the same length as the tube 11 and used.

[0026] The restraint member 20 is adhered via an adhesive layer 21 on the outer surface of the tube 11 so that it does not separate when the tube 11 expands or contracts. The material of the adhesive layer 21 is desirably selected taking into consideration the respective materials of the tube 11 and the restraint member 20. Specifically, it is possible to select and use an adhesive selected from epoxy resin adhesives, acrylic resin adhesives, styrene butadiene rubber adhesives, chloroprene rubber adhesives, silicone rubber adhesives, etc.

[0027] Up to this point, the simplest basic configuration of the actuator 10 proposed by the present invention, which performs bending motion by adjusting fluid pressure, has been shown and explained in Figures 2, 3, 4, 5, 6, and 7. In this basic configuration, the radial expansion of the tube 11 is restricted in the area where the outer surface of the tube 11 and the restraining member 20 are continuously bonded, so the area that can expand radially without restriction, particularly the area facing the restraining member 20, expands greatly. This expansion of the tube 11 can sometimes hinder installation in equipment.

[0028] Figures 10 and 11 show a side view and a perspective view of a configuration of the actuator 10, one of several configurations, in which two radial restraint ring members 22 are added. Figure 12 shows the actuator in this configuration in a pressurized bending operation. The ring members 22 cause the tube 11 to constrict when pressurized and expanded. Therefore, the shape of the tube 11 at maximum expansion is a roughly spherical shape connected by the ring members, and the maximum contraction rate is approximately the same as when the ring members are not added, resulting in a similar bending and operation. The diameter of the tube 11 at maximum expansion is reduced to approximately 37% of that without the ring members 22, enabling the actuator 10 to operate in a space-saving manner. The material of the ring members 22 is preferably one with a tensile strength sufficient to withstand the radial expansion of the tube 11. More specifically, a material selected from high-strength fiber constricted into a ring shape, a steel hose band, a rubber ring, etc. can be used. The ring member 22 can be attached to the actuator 10 by tightening it from the outside of the tube 11 and fixing it by friction, by gluing it to the tube 11 or the restraining member 20, or by sandwiching it between the tube 11 and the restraining member 20 and fixing it by friction.Any attachment method can be selected as long as it does not come apart or shift in position when the tube 11 expands or contracts.

[0029] Figure 13 is a cross-sectional view taken along line AA' of one of the multiple configurations of the actuator described above, in which the constraint member 20 is embedded in the tube 11. The constraint member 20 may be embedded in either the rubber base material layer 11a or the fiber encapsulation layer 11b inside the tube 11, or may be embedded across both layers. Even in the actuator 10 having the configuration shown in Figure 13, the radial expansion of the portion where the constraint member 20 is embedded is restricted by the constraint member 20 even if the internal pressure of the tube 11 increases. Therefore, only the portion facing the constraint member 20 expands significantly, causing the tube 11 to expand unevenly, and the actuator as a whole bends and operates in the same way as the basic configuration.

[0030] Figure 14 is a cross-sectional view taken along the line AA' of a configuration, among the multiple configurations of actuator 10, in which restraint member 20 is adhered so as not to separate from the inner surface of tube 11. Even in actuator 10 having the configuration of Figure 14, the radial expansion of the portion where restraint member 20 is adhered to the inner surface of tube 11 is restricted by restraint member 20 even if the internal pressure of tube 11 increases, so only the portion facing restraint member 20 expands significantly, causing tube 11 to expand unevenly, and the actuator as a whole bends and operates in the same way as in the basic configuration.

[0031] Although not explained in the above embodiment, it is of course possible to construct an actuator system by combining the various configurations of actuator 10, such as an actuator that combines the configuration of the embedded restraint member shown in FIG. 13 with the configuration of the constricted ring member shown in FIG. 10, or an actuator that combines the configuration of the inner surface-bonded restraint member shown in FIG. 14 with the configuration of the constricted ring member shown in FIG. 10. [Explanation of symbols]

[0032] 10. Fluid pressure actuator 11 Multi-layer fiber reinforced tube 11a Rubber base layer 11b Fiber encapsulation layer 11k reinforced fiber 11r binder material 11s fiber sheet 12A Lid member 12B Supply and exhaust pipe side cover member 13A Tightening Band 13B Supply and exhaust pipe side tightening band 20 Restraining member 21 Adhesive layer 22 Restraining ring member 30 Drive unit 31 Fluid supply and discharge pipe 32a Fluid injection solenoid valve 32b Fluid discharge solenoid valve 33 Fluid supply means 34 Control Means

Claims

1. a fluid pressure actuator configured to expand the tube radially by the pressure of a fluid supplied to a space defined by a multi-layer fiber-reinforced tube, which expands and contracts in response to fluid pressure, and lid members provided at both ends of the tube, thereby generating a contraction force in the axial direction of the tube; the tube having a multi-layer structure comprising a combination of at least one rubber-based tube layer and at least one fiber-encapsulated layer that restricts the axial extension of the tube layer; a restraining member that resists the radial expansion of the tube and is deformable in a direction perpendicular to the axial direction, the restraining member contacting a portion of the side of the tube and continuously adhering to the outer surface of the tube from one end to the other in the axial direction so as not to separate from the tube; and therefore, even if the internal pressure of the tube increases due to the application of the fluid pressure, the radial expansion of the tube is partially restricted by the restraining member, resulting in uneven radial expansion of the tube; and the actuator as a whole operates by bending in a direction such that the side where the restraining member is adhered and exhibiting low expansion is on the outside of the bend and the side where high expansion is on the inside of the bend.

2. 2. The fluid pressure actuator according to claim 1, wherein one or more ring members for restraining radial expansion of the tube are provided in a region from one end side to the other end side in the axial direction of the tube.

3. 2. The fluid pressure actuator according to claim 1, wherein the restraint member is embedded in the tube and integrated therewith, instead of being adhered to the outer surface so as not to separate from the tube.

4. 2. The fluid pressure actuator according to claim 1, wherein the restraint member is adhered to the inner surface so as not to separate from the outer surface, instead of being adhered to the outer surface so as not to separate from the inner surface.

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