McKIBBEN ARTIFICIAL MUSCLE

Abstract

A McKibben artificial muscle that relaxes and contracts by fluid pressure, the McKibben artificial muscle comprising: an elastic tube that is a hollow and cylindrical elastic casing member; and a braided tube formed by circularly knitted threads with a predetermined knitting angle that are movably wound over a circumference of the elastic tube, the braided tube having a contraction region and a restriction region that are continuously alternately provided, and the braided tube is circularly knitted in the contraction region with a knitting angle that allows the elastic tube to expand radially and contract in a longitudinal direction to thereby obtain a contraction force, and the braided tube is circularly knitted in the restriction region with a knitting angle that suppresses radial expansion near an end portion of the elastic tube.wherein the braided tube has a mark to mark a portion of the restriction area intended to be cut off, in a case where the contraction area and the restriction area are continuously provided alternately.,

Description

Technical FieldThe present invention relates to an McKi artificial muscle, and more particularly to an McKi artificial muscle having improved durability in an end portion thereof.Background ArtAn artificial muscle McKi is a fluid actuator-driven artificial muscle such as an air cylinder, an artificial muscle, etc. driven by a change in fluid pressure. These muscles have a higher weight specific output than electromagnetic actuators and the like. For example, in Patent Document 1, an artificial muscle McKi using compressed air is disclosed. The artificial muscle comprises a hollow and cylindrical elastic tube, and a braided covering member for covering the elastic tube as a reinforcing layer. When the air from a compressor is introduced into such an artificial muscle, the elastic tubular casing member expands radially and contracts in the longitudinal direction, thereby generating contracting forces.In such an artificial muscle of McKi, an end portion is fixed with silicone adhesives or the like, or a cap-shaped cap is set on the end portion. There is connected an air supply pipe for supplying the air into the elastic tube via the end portion.Prior Art DocumentPatent DocumentPatent Document 1: Japanese Patent Application Kokai Publication No. Sho 48-24175.SUMMARY OF THE INVENTIONProblems Solved by the InventionIn the case of the conventional McKi artificial muscle, since the artificial muscle is steeply radially expanded from its end portions, there is a risk that the artificial muscle may come into strong contact with the peripheral portion of the silicone adhesive or the cap at the end portion, thereby wearing and damaging the end portion.An object of the present invention is therefore to eliminate the problems occurring in the prior art and to provide an McKi artificial muscle having an improved durability in an end portion.Means for Solving the ProblemsIn order to achieve the above object of the present invention, an artificial muscle McKi according to the present invention that relaxes and contracts by fluid pressure may include: an elastic tube that is a hollow and cylindrical elastic housing part; A braided tube formed by circular knitted yarns having a predetermined knitting angle and movably wound around a periphery of the elastic tube, wherein the braided tube has a contraction portion and a restriction portion, and wherein the braided tube is circular knitted in the contraction portion, having a knitting angle that allows the elastic tube to radially expand and contract in a longitudinal direction, thereby obtaining a contraction force, and wherein the braided tube is circular knitted in the restriction portion, having a knitting angle that suppresses a radial expansion near an end portion of the elastic tube.The knitting angle suppressing the radial strain of the braided tube may be an equilibrium angle.The braided tube may be circular knitted in such a manner that the knitting angle continuously increases from the contraction portion toward the restriction portion.The restriction portion may be used as an air supply pipe that supplies air into the elastic tube.The braided tube may have a mark to mark a portion of the restriction area intended to be cut off in a case where the contraction area and the restriction area are sequentially provided alternately.Advantages of the InventionAccording to the present invention, the McKiben artificial muscle has an advantage of improving its end portions in terms of durability.BRIEF DESCRIPTION OF THE DRAWINGFIGS. 1A and 1B are schematic side views for explaining an McKi artificial muscle of the present invention, in which FIG. 1A shows a relaxed state and FIG. 1B shows a contracted state. FIG. 2 illustrates an enlarged schematic partial lateral view of an end portion of the McKi artificial muscle of the present invention in a contracted state.FIGS. 3A and 3B are schematic side views for explaining a case where an end portion of the McKi artificial muscle of the present invention is formed as an air supply line, FIG. 3A showing a relaxed state and FIG. 3B showing a contracted state. FIG. 4 is a schematic side view for explaining a case where an elastic tube and a braided tube of the McKi artificial muscle of the present invention are continuously provided.Embodiments for Carrying Out the InventionIn this document, an embodiment for implementing the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic side view for explaining an McKi artificial muscle according to the present invention, wherein FIG. 1A shows a relaxed state and FIG. 1B shows a contracted state. As illustrated, an artificial muscle McKi 1 of the present invention that relaxes and contracts by fluid pressure includes an elastic tube 10 and a braided tube 20. The fluid supplied into the elastic tube 10 is not limited to air, but oil or other liquids may be used.The elastic tube 10 is a hollow and cylindrical elastic housing member. The air is supplied into its cavity, for example, via an air supply line 30 from a compressor (not shown). A rubber tube, silicone tube or other materials used in conventional McKi artificial muscles, as well as any other elastic housing parts that will be developed in the future, may be suitable as the elastic housing part.The braided tube 20 is composed of circular knitted yarns having a predetermined knitting angle θ that are movably wound around a circumference of the elastic tube 10. More specifically, for example, yarns may be spirally wound by a braiding machine, and other yarns may be reversely wound to thereby cross the former, so that braiding and circular knitting may be performed. The braided tube 20 may have a so-called pantograph structure which can expand in the radial direction (or the direction perpendicular to its longitudinal direction) while contracting in the longitudinal direction. As shown in FIG. 1B, when air is supplied from the compressor, for example, the elastic tube 10 stretches, but its movement is restricted by the braided tube 20. Thereby, the elastic tube 10 contracts to be shorter in the longitudinal direction. It should be noted that the angle, number and spacing of the filaments as shown in the drawing are depicted for the purpose of illustration only and the present invention is thus not limited to the examples shown.The braided tube 20 includes a contraction portion 21 and a restriction portion 22 as illustrated in the drawing. In the contraction portion 21, the braided tube 20 is circular knitted at a knitting angle that allows the elastic tube 10 to radially expand and contract in a longitudinal direction, thereby obtaining a contracting force. This angle may be a similar knitting angle for a braided tube as used for a typical McKi artificial muscle. For example, the knitting angle can be between 15 and 30 degrees or it is preferably, for example, 20 degrees. In the restriction region 22, the braided tube 20 is circular knitted with a knitting angle suppressing radial strain adjacent to an end portion 11 of the elastic tube 10. The knitting angle in the restriction portion 22 may be larger than the knitting angle in the contraction portion 21, and the knitting angle of the restriction portion 22 is considered to be the most effective balance angle for suppressing radial strains, which is about 55 degrees. Incidentally, the balance angle is a knitting angle that allows the circular knitted braided tube 20 to achieve mechanical balance while not causing radial elongation or contraction in the longitudinal direction for the elastic tube 10. Accordingly, the knitting angle is larger in the restriction portion 22 than in the contraction portion, and is set suitably in a range up to the equilibrium angle depending on how much the radial strain adjacent to the end portions 11 is to be suppressed. In addition, an angle greater than the equilibrium angle has no effect on how much strain is suppressed. Therefore, the upper limit of the range may be the equilibrium angles.The braided tube 20 may be circular knitted to include the contraction portion 21 and the restriction portion 22 by appropriately controlling the rotation speed and winding speed of the bobbins of the circular knitting braiding machine.FIG. 2 illustrates an enlarged schematic partial lateral view of an end portion of the McKi artificial muscle of the present invention in a contracted state. In the figure, the same reference numerals as in FIG. 1 denote the same members as in FIG. 1, A region adjacent to the end portion 11 of the McKi artificial muscle of the present invention is formed as the restriction region 22 having the above-described configuration. Accordingly, as illustrated, even when the McKi artificial muscle is in the contracted state, the braided tube 20 and the elastic tube 10 do not expand radially in the restriction region 22. Therefore, the peripheral portion of the hood-shaped cap 12 disposed at the end portion 11 does not come into contact with the braided tube 20 or the elastic tube 10. This also effectively prevents steep deformation of the end portion 11 and prevents the end portion 11 from falling off the hood-shaped cap 12.The contraction portion 21 and the restriction portion 22 of the McKi artificial muscle of the present invention may be circular knitted so as to allow a sharp change in their knitting angle θ. Alternatively, the braided tube may be circular knitted in such a manner that the knitting angle continuously increases from the contraction portion 21 toward the restriction portion 22. For example, the knitting angle may be the smallest in the vicinity of the center in the longitudinal direction of the McKi artificial muscle, and the knitting angle may continuously increase toward the both end portions. With this configuration, it is possible to prevent excessive imbalance in pressure resulting from partial imbalance in a region where the knitting angle greatly changes.In addition, when the knitting angle of the braided tube is larger than the equilibrium angle, the McKiis artificial muscle radially contracts and stretches in the longitudinal direction. For example, the contraction portion 21 may be set at an angle larger than such a balance angle, and the restriction portion 22 may be set at an angle suppressing radial expansion. This configuration is also suitable for improving the durability of the end portion.In the above-described examples, the hood-shaped cap 12 is placed on the end portion 11, for example. However, the present invention is not limited thereto. The braided tube 20 of the McKi artificial muscle of the present invention has the restriction portion 22. the restriction portion 22 is circular knitted with a knitting angle suppressing radial strain adjacent to the end portion 11. Accordingly, the restriction portion 22 is configured to maintain the conditions of the elastic tube 10. The restriction portion 22 can therefore be used as an air supply pipe that supplies air into the elastic tube 10. FIG. 3 is a schematic side view for explaining a case where an end portion of the McKi artificial muscle of the present invention is formed as an air supply pipe. FIG. 3A shows a relaxed state and FIG. 3B shows a contracted state. In the figure, the same reference numerals as in Fig. 1 denote the same elements as in Fig. 1, and their explanations are omitted.As shown in the figure, in this example, one of the end portions 11 of the McKi artificial muscle is formed as an air supply pipe. A portion configured as the restriction portion 22 performs the function of the air supply pipe. That is, the portion configured as the air supply pipe has a larger knitting angle than the contraction portion 21, and may be circular knitted with, for example, the balance angle. The end portion 11 having such a structure may be used as the air supply pipe, and may be connected to a compressor or the like.According to the McKi artificial muscle of the present invention, a dome-shaped cap or any similar parts is not required. This makes the construction simple.Next, the description will consider a case where the McKi artificial muscles are made to be cut to a predetermined length after the elastic tube 10 and the braided tube 20 of the McKi artificial muscle of the present invention are continuously formed. FIG. 4 is a schematic side view for explaining a case where the elastic tube and the braided tube of the McKi artificial muscle of the present invention are continuously provided. In the figure, the same reference numerals as in Fig. 1 denote the same elements as in Fig. 1, and their explanations are omitted.Generally, the McKi artificial muscle is provided by knitting the braided tube on the elastic tube and rolling it up. Then, the chain is cut at predetermined lengths, and both end portions are processed to produce the McKi artificial muscles. The McKi artificial muscle of the present invention can be similarly continuously manufactured. However, a point for cutting may be located in the portion of the restriction region because the McKi artificial muscle of the present invention has the contraction region and the restriction region. Providing a mark at the cut-off point in the portion of the restriction area may be convenient.Accordingly, the braided tube 20 of the McKi artificial muscle of the present invention may have a mark 25 for marking a portion of the restriction portion 22 to be cut in the case where the contraction portion 21 and the restriction portion 22 are continuously provided alternately. The mark 25 may be provided in such a manner that the restriction portion 22 is colored by an inkjet printer or the like installed in the circular knitting machine when the restriction portion 22 is circular knitted. Otherwise, the dyeing can take place at the correct time in the section of the restriction area 22 when the tube is rolled up after circular knitting. Incidentally, the mark 25 is not limited to the coloring. An adhesive strip or the like or any other means may be used as long as it can make the point for cutting visible.In this way, according to the McKiben artificial muscle of the present invention, it is easy to see where to cut off even if the tube is continuously manufactured.The McKi artificial muscle according to the present invention is not limited to the illustrated examples described above, but various modifications may be made within the scope of the present invention. For example, several of the McKi artificial muscles of the present invention may be bundled together for use. Even in such a case, the durability can be improved because the movement of the end portions of each of the elastic tubes is restricted.Explanation of Reference Numerals1 McKi artificial muscle 10 elastic tube 11 end portion 12 dome-shaped cap 20 braided tube 21 contraction region 22 restriction region 25 marker 30 air supply pipe

Claims

An McKi artificial muscle that relaxes and contracts by fluid pressure, the McKi artificial muscle comprising: an elastic tube that is a hollow and cylindrical elastic housing part; and a braided tube formed by circular knitted threads having a predetermined knitting angle that are movably wound around a periphery of the elastic tube, wherein the braided tube has a contraction region and a restriction region that are continuously provided alternately, and wherein the braided tube is circular knitted in the contraction region with a knitting angle that allows the elastic tube to radially expand and contract in a longitudinal direction to thereby obtain a contracting force, and wherein the braided tube is circular knitted in the restriction region with a knitting angle, suppressing radial expansion in the vicinity of an end portion of the elastic tube, the braided tube having a mark to mark a portion of the restriction region intended to be cut off in a case where the contraction region and the restriction region are continuously provided alternately.The McKi artificial muscle according to claim 1, wherein the knitting angle suppressing the radial strain of the braided tube is an equilibrium angle.The McKi artificial muscle according to claim 1 or 2, wherein the braided tube is circular knitted in such a manner that the knitting angle continuously increases from the contraction portion toward the restriction portion.The McKi artificial muscle according to any one of claims 1 to 3, wherein the restriction portion is used as an air supply pipe that supplies air into the elastic tube.

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