Patent Publication Number: US-10774854-B2

Title: Tube-fixing tool and actuator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2017-173672 filed on Sep. 11, 2017, the content of which is hereby incorporated by reference into this application. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a tube-fixing tool to be attached to an elastic tube composed of: a soft tube and a cover tube formed on an outside of the soft tube, and an actuator having this tube-fixing tool. 
     BACKGROUND OF THE INVENTION 
     A hollow elastic tube is expanded and contracted in a radial direction thereof by a fluid supplied to and discharged from an inside of the elastic tube, and also extended and contracted in a length direction thereof. Patent document 1 discloses an actuating apparatus provided with: an elastic tube and head pieces serving as fixing tools to be attached to two ends thereof. This elastic tube is constituted by a hose main body and strands knitted inside the hose main body, that is, twisted yarns. The head piece is composed of: an inside part that is fitted to the inside of the elastic tube and an outside part that is fitted to the outside of the elastic tube, and each end of the elastic tube is fixed between the inside part and the outside part. An annular protrusion is formed on an outer circumferential face of the inside part so as to enhance a fastening force of the elastic tube by the outside part. This actuating apparatus is applicable as an actuator that carries out an extension and contraction operation and a bending operation by expanding and contracting the elastic tube by using a fluid. 
     A bendable actuator is disclosed in Patent document 2. This actuator is provided with: a tube-shaped member made of rubber or a rubber-state elastic member; and an elastic extension member composed of a net-shaped reinforcing structure, that is, a knitted strand structure, which is arranged around the outside thereof. Each end of the elastic extension member is fixed between a sealing member fitted to the elastic expansion member and a caulking ring attached to the outside of the elastic extension member. This actuator carries out an extension and contraction operation and a bending operation by expanding and contracting the elastic extension member by using a fluid supplied to and discharged from the tube-shaped member. There are two types in the actuator, that is, one type constituted by one elastic extension member, and another type constituted by a plurality of elastic extension members bound together. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Translation of PCT International Application Publication No. 2002-541410 
     Patent Document 2: Japanese Unexamined Patent Application Publication No. H03-028507 
     As described in Patent documents 1 and 2, in a mode in which an inside part and a sealing member are fitted to the inside of a hose main body or an elastic extension member serving as an elastic tube, it is necessary to form a communication hole for use in supplying a fluid such as compressed air to the inside part or the like. Since the inside part is fitted to the elastic tube having a small diameter, the inside part to be fitted to the elastic tube cannot be made thicker, thereby causing an insufficient strength for fastening the outside part. For this reason, a conventional actuating apparatus and a actuator have a limited structure with a large inner diameter of an elastic tube, and none of the inside part and the sealing member are installed in an elastic tube having a small diameter. 
     The elastic extension member, that is, the elastic tube disclosed in Patent Document 2, is constituted by a tube-shaped member serving as an elastic tube made of an elastic member and a net-shaped reinforcing structure serving as a cover tube formed on the outside thereof, and has a two-layered structure or a stacked structure. In order to assemble an actuator by using the elastic extension member, a fixing tool made of a sealing member and a caulking ring is fixed to the end of the elastic extension member. Since both the tube-shaped member and the net-shaped reinforcing structure are elastically deformed, the thickness of the tube-shaped member corresponding to the portion of the fixing tool becomes thinner when the tube-shaped member is elastically deformed; therefore, the fixing strength of the tube-shaped member by the fixing tool is lowered. Therefore, when the elastic extension member having the stacked structure is fastened and fixed between the sealing member and the caulking ring, the elastic extension member might come off from the gap between the sealing member and the caulking ring by a fluid pressure supplied to the inside of the tube-shaped member, or the fluid might be externally leaked between the tube-shaped member and the sealing member. 
     For this reason, in order to improve the sealing property, an adhesive needs to be applied to the gap between the tube-shaped member and the sealing member. In order to further improve the sealing property between the tube-shaped member and the sealing member, the adhesive is applied to the gap between the entire outer circumferential face of the tube-shaped member and the sealing member, and the adhesive needs to be further applied to the gap between the net-shaped reinforcing structure and the caulking ring. Therefore, the conventional actuator encounters a problem that long time is required for applying process of the adhesive to cause a failure in improving the assembly workability of the actuator. Moreover, when the application of the adhesive is incomplete, a defective product tends to be produced, thereby causing a failure in enhancing a production yield of the actuator. 
     An object of the present invention is to improve the assembly workability of a tube-fixing tool to an elastic tube, and also to improve the production yield of an actuator. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a tube-fixing tool to be attached to an end of an elastic tube provided with a soft tube and a cover tube that is formed on an outside of the soft tube, the tube-fixing tool comprising: a fixing-tool body having a fitting-cylinder part provided with: a fitting-inner face that is fitted to an outer face of the soft tube; and a fitting-outer face that is fitted to an inner face of the cover tube, the fitting-cylinder part being assembled between the soft tube and the cover tube; and a fixing sleeve having: an inner circumferential face that is opposed to the fitting-cylinder part via the cover tube; and a fastening part that is attached to the fixing-tool body, the cover tube being fixed between the fixing sleeve and the fixing-tool body. 
     According to another aspect of the present invention, there is provided an actuator comprising: an elastic tube has: a soft tube; and a cover tube that is formed on an outside of the soft tube; and a tube-fixing tool that is formed on an end of the elastic tube, wherein the actuator is extended and contracted by an elastic deformation in a radial direction of the elastic tube by a fluid supplied to or discharged from an inner space of the elastic tube. 
     Effects of Invention 
     The tube-fixing tool has: a fitting-cylinder part having a fitting-inner face; and a fitting outer surface, and is attached to an end of an elastic tube having a soft tube and a cover tube formed on the outside of the soft tube. An outer surface of the soft tube is fitted to the fitting-inner face and the inner face of the cover tube is fitted to the fitting outer surface. When fluid is supplied to the inner space of the elastic tube, the soft tube is tightly made in contact with the fitting-inner face of the soft tube by pressure of fluid so that fluid is prevented from externally leaking. A tube-fixing tool to be attached to the end of the elastic tube is not provided with a member to be inserted to the inside of the elastic tube, and the elastic tube having a small diameter is attachable to the tube-fixing tool. In this manner, an actuator having a small diameter can be easily assembled. 
     It is not necessary to apply an adhesive to the gap between the soft tube and the fitting-inner face so as to improve the sealing property between the elastic tube and the tube-fixing tool, so that the actuator can be improved in assembly workability. Moreover, no defective product is caused by an incomplete adhesive applying process, so that it becomes possible to improve the production yield of the actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an exploded perspective view showing a tube-fixing tool serving as one embodiment for assembling an actuator, and  FIG. 1B  is an exploded perspective view showing a cross section of  FIG. 1A ; 
         FIG. 2A  is a cross sectional view showing the tube-fixing tool that is being attached to an elastic tube, and  FIG. 2B  is a cross sectional view showing the tube-fixing tool attached to the elastic tube; 
         FIG. 3  is an enlarged cross sectional view showing a portion “A” in  FIG. 2B ; 
         FIG. 4A  is a cross sectional view showing a tube-fixing tool of a modified example, and  FIG. 4B  is an enlarged cross sectional view showing a Portion “B” of  FIG. 4A ; 
         FIG. 5A  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example, and  FIG. 5B  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example; 
         FIG. 6A  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example, and  FIG. 6B  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example; 
         FIG. 7A  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example, and  FIG. 7B  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example; 
         FIG. 8  is a cross sectional view showing a tube-fixing tool of another modified example; 
         FIG. 9A  is a perspective view showing a fixing ring shown in  FIG. 8 , and  FIG. 9B  is a perspective view showing a fixing ring serving as another modified example; 
         FIG. 10A  is an enlarged cross sectional view showing a portion “C” in  FIG. 8 , and  FIG. 10B  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example; and 
         FIGS. 11A to 11C  are cross sectional views each showing a tube-fixing tool of another modified example. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings, and common members the same as each other in the following embodiments and examples are denoted by the same reference number. 
     As shown in  FIGS. 1 and 2 , an actuator  15  is assembled from an elastic tube  10  and a tube-fixing tool  20  that is attached to an end of the elastic tube  10 . 
     The elastic tube  10  has: a soft tube  11  and a cover tube  12  that is installed on an outside of the soft tube, and the elastic tube  10  is freely elastically deformed in a radial direction as well as in a length direction. The soft tube  11  is formed by using fluorine resin or silicon resin that is freely elastically deformable. As material for the soft tube  11 , the soft tube  11  is not limited by these resins, and another synthetic resin, synthetic rubber or the like may be used as long as the material is freely elastically deformable. The soft tube  11  has a single-layered structure. On the other hand, it may have a stacked structure of layers made of the same material or different materials. 
     The cover tube  12  is a knitted strand tube having a net-shaped structure that is formed into a tube shape by knitting fibers made of polyester fibers, aromatic polyamide fibers or the like. The cover tube  12  is made in contact with the outside of the soft tube  11 , and is not knitted into the soft tube  11 . Moreover, the cover tube  12  is not bonded to the soft tube  11 . One portion of the soft tube  11  is exposed onto the outside via gaps among the fibers forming the knitted strand tube. By forming the cover tube  12  on the outside of the soft tube  11 , the elastic tube  10  is improved in strength. In place of the knitted strand tube having a single layer, another structure formed by stacking knitted strand tubes may be used as the cover tube  12 . Moreover, materials formed by knitting wires made of metal and materials made of synthetic resin, synthetic rubber or the like and different from that of the soft tube  11  may be used as material for the cover tube  12 . Furthermore, without forming the cover tube  12  as the knitted strand tube, a tube having gaps or holes that covers the entire outer surface of the soft tube  11  may be used. 
     As shown in  FIG. 2B , the tube-fixing tool  20  is fixed to the end of the elastic tube  10  so that the actuator  15  is constituted by the elastic tube  10  and the tube-fixing tool  20 . When compressed air is supplied to an inner space  13  of the soft tube  11  via the tube-fixing tool  20 , the elastic tube  10  is expanded in a radial direction thereof and contracted in a length direction thereof. 
     For example, the actuator  15 , which is formed by attaching the tube-fixing tool  20  to each end of the elastic tube  10 , may be used for rocking an arm assembly body composed of two members that are coupled to each other by pins. In this use mode, the tube-fixing tool on one end side of the actuator  15  is attached to one of the members, and the tube-fixing tool on the other end side of the actuator  15  is attached to the other of the members. When a fluid such as compressed air or the like is supplied to or discharged from the inner space  13  from one or both of the tube-fixing tools, the elastic tube  10  is expanded and contracted so that the actuator  15  is expanded and contracted. In this manner, the actuator  15  can be used as an artificial muscle for use in rocking and driving the arm assembly body. In the actuator of a mode for supplying a fluid only from one of the tube fixing members, a closed structure is used as the other tube-fixing tool. 
     An actuator of a mode formed by binding the actuators  15  with one another may be used. In this case, tube-fixing tools formed on the ends of each actuator are bound with one another by fastening members as described in Patent Document 2. In this manner, in the actuator, there are a single type composed of a single actuator  15  and a bound type formed by binding a plurality of actuators  15  with one another. 
     The tube-fixing tool  20  has: a fixing-tool body  21 ; and a fixing sleeve  22  that is attached to the fixing-tool body  21 . As shown in  FIG. 2B , the fixing sleeve  22  is attached to the fixing-tool body  21 , and the center axis “O” of the fixing sleeve  22  is coaxial with the center axis of the fixing-tool body  21 . The fixing-tool body  21  and the fixing sleeve  22  are made of metal or hard resin. The fixing-tool body  21  has: an attaching part  23  disposed on the base end side; and a fitting-cylinder part  24  integrally formed with the attaching part  23  and disposed on the tip end side, and a communication hole  25  formed inside the fixing-tool body  21 . The fitting-cylinder part  24  is a cylinder part smaller in diameter than that of the attaching part  23 , and the tip face of the fitting-cylinder part  24  forms an opposing face  26  in a radial direction. A screw hole  27  is formed on the base end side of the communication hole  25 , and a joint for use in connecting a hose or the like is screw-coupled to the screw hole  27 . A fluid such as compressed air or the like supplied by the hose is supplied to the inner space  13  via the communication hole  25 . 
     An inner face of the fitting-cylinder part  24  corresponds to a fitting-inner face  28  that is fitted to an outer face of the soft tube  11 , and an outer face of the fitting-cylinder part  24  corresponds to a fitting-outer face  29  that is fitted to the inner face of the cover tube  12 . The elastic tube  10  has a stacked structure composed of at least two layers of the soft tube  11  and the cover tube  12 , the cover tube  12  is not bonded to the soft tube  11 , and when the end of the cover tube  12  is elastically deformed in a radially outward direction of the soft tube  11 , the end of the cover tube  12  is separated from the soft tube  11 . 
       FIG. 2A  shows a state in which the end of the cover tube  12  is expanded in a radially outward direction thereof, and the fitting-cylinder part  24  is inserted between the soft tube  11  and the cover tube  12 . An abutment face  30  perpendicular to the center axis “O” is formed on the fixing-tool body  21 , and the abutment face  30  forms a border face between the inner circumferential face of the communication hole  25  and the fitting-inner face  28 . As shown in  FIG. 2B , by causing the end face of the soft tube  11  to about on the abutment face  30 , a position in axial direction of the fixing-tool body  21  relative to the soft tube  11  is determined. 
     A base end of the fixing sleeve  22  corresponds to a fastening part  31  that is attached to the attaching part  23  of the fixing-tool body  21 . An outer face of the attaching part  23  has a round shape in lateral cross section, and an inner face  32  of the fastening part  31  also has a round shape in cross section. The inner face  32  has an inner diameter slightly smaller than the outer diameter of the attaching part  23 , and the fastening part  31  of the fixing sleeve  22  is press-inserted into the attaching part  23  as shown in  FIG. 2B  so that the fixing sleeve  22  is fixed to the fixing-tool body  21  by the press-insertion. A first position-determining face  33  perpendicular to the center axis “O” forms a border face between the attaching part  23  of the fixing-tool body  21  and the fitting-cylinder part  24  smaller in diameter than the attaching part  23 , and a second position-determining face  34  is formed on the fixing sleeve  22  so as to abut on the first position-determining face  33 . By causing the second position-determining face  34  to abut on the first position-determining face  33 , a position in axial direction of the fixing sleeve  22  relative to the fixing-tool body  21  is determined. 
     A cylindrical inner circumferential face  35  is formed on the inner face of the fixing sleeve  22 . Therefore, with the fixing sleeve  22  attached to the fixing-tool body  21 , the inner circumferential face  35  is opposed to the fitting-cylinder part  24  via the cover tube  12 . Moreover, a gap  36  formed between the inner circumferential face  35  and the fitting-outer face  29  of the fixing sleeve  22  is substantially the same as the thickness of the cover tube  12  or slightly larger than the thickness of the cover tube  12 . A guide part  37  is provided to the tip end of the fixing sleeve  22 , and the guide part  37  has a cylindrical guide face  38  that is smaller in inner diameter than the inner circumferential face  35 , and the same as or slightly larger than an outer diameter of the elastic tube  10 . In  FIG. 3 , the cover tube  12  is separated from the fitting-outer face  29  and the inner circumferential face  35 , and the gap  36  is depicted in an exaggerated manner. 
     In this specification, the attaching part  23  of the fixing-tool body  21  is formed on the base end side of the fixing-tool body  21 , and the fitting-cylinder part  24  is formed on the tip end side of the fixing-tool body  21 . In the fixing sleeve  22 , the fastening part  31  is formed on the base end side, and the guide part  37  is formed on the tip end side. 
     As shown in  FIG. 3 , a stopper face  41  is formed on the fixing sleeve  22 , and the stopper face  41  is constituted by a border face between the inner circumferential face  35  and the guide face  38 . The stopper face  41  is opposed to the opposing face  26  of the fitting-cylinder part  24 . The stopper face  41  and the opposing face  26  are perpendicular to the center axis “O” of the tube-fixing tool  20 . As shown in  FIG. 3 , a gap  42  is formed between the stopper face  41  and the opposing face  26 , and the gap  42  has a width that is defined in a direction of the center axis of the gap  42  and smaller than the thickness of the cover tube  12 . Therefore, the cover tube  12  is sandwiched in the gap  42  between the stopper face  41  and the opposing face  26 , and the cover tube  12  is fixed to the fixing-tool body  21  by the gap  42 . In this manner, the gap  42  between the stopper face  41  and the opposing face  26  is smaller than the gap  36  between the inner circumferential face  35  and the fitting-outer face  29 . 
     The elastic tube  10  having the soft tube  11  and the cover tube  12  makes it possible to separate the cover tube  12  from the soft tube  11  at each end of the elastic tube  10 . The outer circumferential face of the soft tube  11  is made in contact with the fitting-inner face  28  of the fitting-cylinder part  24 , and in the cover tube  12 , a portion closer to its tip end than a portion between the fitting-cylinder part  24  and the inner circumferential face  35  is tightened by the opposing face  26  and the stopper face  41  and fixed to the tube-fixing tool  20 . 
     When compressed air is supplied to the inner space  13  from the outside, the soft tube  11  is tightly made in contact with the fitting-inner face  28  by pressure of compressed air supplied to the inner space  13 . That is, by pressure of compressed air supplied to the inner space  13 , the soft tube  11  is made tightly in contact with the fitting-inner face  28  by so-called “self-restraining action”. In this manner, compressed air supplied to the inner space  13  is prevented from being leaked from between the fitting-inner face  28  and the soft tube  11 , and prevented from being leaked to the outside from between the elastic tube  10  and the tube-fixing tool  20 . In this manner, since the tube-fixing tool  20  does not have a member to be fitted to an inner face of the soft tube  11 , the small-diameter soft tube  11  can be easily attached to the tube-fixing tool  20 . Moreover, by making the outer circumferential face of the soft tube  11  tightly in contact with the fitting-inner face  28 , it becomes possible to prevent leaking of compressed air. 
     Even if a force in an axial direction is applied to the elastic tube  10  so as to draw the elastic tube  10  from the tube-fixing tool  20 , as shown in  FIG. 3 , the cover tube  12  is sandwiched between the stopper face  41  of the fixing sleeve  22  and the opposing face  26  of the fitting-cylinder part  24 . In this manner, since the cover tube  12  is fixed to the fixing-tool body  21  by the fixing sleeve  22 , the elastic tube  10  is prevented from coming off from the tube-fixing tool  20 . 
     In this manner, the elastic tube  10  is fixed to the tube-fixing tool  20  by the cover tube  12 , and by adhesion between the soft tube  11  and the fitting-inner face  28 , a fluid inside the inner space  13  is prevented from leaking. 
     The actuator  15  is assembled from the above elastic tube  10  and the tube-fixing tool  20  to be attached to the end of the elastic tube  10 . The actuator  15  is fixed to a driven member (not shown) via the tube-fixing tool  20 . A fluid supply source for supplying a fluid such as compressed air or the like is connected to the fixing-tool body  21 , and the fluid is supplied to the inner space  13  via the communication hole  25 . By the fluid supplied to or discharged from the inner space  13 , the elastic tube  10  is expanded and contracted in a radial direction, and the actuator  15  is deformed by expanding and contracting the elastic tube  10 . The driven member can be driven by this expanding and contracting deformation. The elastic tube  10  has: a portion located so as to face the guide face  38 ; and a portion located outside the tube-fixing tool  20 . When the elastic tube  10  is expanded in a radial direction, the expansion in the radial direction of the elastic tube  10  inside the guide face  38  is regulated by the guide face  38 , while the expansion in the radial direction of the elastic tube  10  located outside the tube-fixing tool  20  is not regulated. Since the elastic tube  10  inside the guide face  38  is not tightened by the guide part  37 , the elastic tube  10  inside the guide face  38  is elastically deformed in accordance with the expansion of the elastic tube  10  located outside the tube-fixing tool  20 . 
     By attaching the tube-fixing tool  20  to both ends of the elastic tube  10 , a fluid can be supplied to the inner space from both ends of the elastic tube  10 . On the other hand, by attaching one tube-fixing tool  20  to one end of the elastic tube  10 , and by attaching another tube-fixing tool  20  having a blocked screw hole  27  to the other end of the elastic tube  10 , the actuator can be operated by the fluid supplied or discharged from one end of the actuator  15  so as to extend and contract the actuator. 
     Since the elastic tube  10  is designed to have a small diameter, a small-sized actuator  15  having a small diameter can be assembled. In the actuator in a mode in which the elastic tubes  10  are bound together as well, by using the elastic tube  10  having a small diameter, the small-sized actuator  15  having a small diameter can be produced. Moreover, since it becomes possible to prevent leaking of fluid without applying adhesive between the soft tube  11  and the fitting-inner face  28 , the actuator  15  can be improved in assembly workability. Furthermore, since it is not necessary to apply adhesive to the soft tube  11  and the fitting-inner face  28 , it becomes possible to prevent leaking of fluid from being caused by application failure of adhesive, thereby improving the production yield of the actuator. 
     Since it is not necessary to prevent leaking of fluid between the inner circumferential face  35  and the fitting-outer face  29 , and since the cover tube  12  is housed between the inner circumferential face  35  and the fitting-outer face  29 , the cover tube  12  may be bonded to the tube-fixing tool  20  by applying an adhesive between these faces. 
       FIG. 4A  is a cross sectional view showing a tube-fixing tool of a modified example, and  FIG. 4B  is an enlarged cross sectional view showing a Portion “B” of  FIG. 4A . 
     As shown in  FIG. 4 , a first fitting-outer face  29   a  and a second fitting-outer face  29   b  are formed on the fitting-cylinder part  24 . The first fitting-outer face  29   a  is disposed on the tip end side of the fixing-tool body  21 , and the second fitting-outer face  29   b  is disposed on the base end side of the fixing-tool body, and larger in diameter than the first fitting-outer face  29   a . In addition, a first inner circumferential face  35   a  and a second inner circumferential face  35   b  are formed on the fixing sleeve  22 . The first inner circumferential face  35   a  is opposed to the first fitting-outer face  29   a , and the second inner circumferential face  35   b  is opposed to the second fitting-outer face  29   b , and larger in diameter than the first inner circumferential face  35   a.    
     A first stopper face  41   a  forms a border face between the guide face  38  and the first inner circumferential face  35   a . A second stopper face  41   b  forms a border face between the first inner circumferential face  35   a  and the second inner circumferential face  35   b . The tip face of the fitting-cylinder part  24  corresponds to the first opposing face  26   a , and the second opposing face  26   b  forms a border face between the first fitting-outer face  29   a  and the second fitting-outer face  29   b . Therefore, in the tube-fixing tool  20  shown in  FIG. 4 , the cover tube  12  is sandwiched by a gap  42   a  between the first stopper face  41   a  and the first opposing face  26   a  and a gap  42   b  between the second stopper face  41   b  and the second opposing face  26   b . In this manner, when the cover tube  12  is fixed to the fixing-tool body  21  by sandwiching the cover tube  12  at two portions by using the fixing sleeve  22 , the fixing strength of the cover tube  12  can be improved. In this case, however, the cover tube  12  may be sandwiched by using only one of the gaps  42   a  and  42   b.    
     Each of  FIGS. 5A to 7A  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example, and each of  FIGS. 5B to 7A  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example. 
     In a tube-fixing tool  20  shown in  FIG. 5A , the opposing face  26  formed on the opening end of the fitting-cylinder part  24  has a face tapered toward the tip face, and the opposing face  26  is inclined relative to the center axis “O” of the fixing-tool body  21 . On the other hand, the stopper face  41  is inclined in a direction along the opposing face  26 , and is opposed to the opposing face  26 . The gap  42  formed between the opposing face  26  and the stopper face  41  has a width smaller than the thickness of the cover tube  12 . Therefore, the cover tube  12  is sandwiched between the opposing face  26  and the stopper face  41  that respectively form inclined faces, and fixed to the fixing-tool body  21  by the fixing sleeve  22 . In this manner, by inclining the gap  42 , the gap  42  is becomes longer in length than that of  FIG. 4 . 
     In a tube-fixing tool  20  shown in  FIG. 5B , the stopper face  41  is inclined in a reversed direction relative to the stopper face  41  shown in  FIG. 5A . That is, the stopper face  41  has a reversed taper face. The opposing face  26  opposed to the stopper face  41  of the reversed taper face has a portion inclined along the stopper face  41 , and the opposing face  26  also has a portion inclined in a reversed direction relative to the opposing face  26  shown in  FIG. 5A . In this manner, by reversely inclining the gap  42 , the cover tube  12  is fixed in a winding state, the fixing strength can be increased. 
     In a tube-fixing tool  20  shown in  FIG. 6A , a protruding part  43  is formed on the opposing face  26 , and a protruding part  44  is formed on the stopper face  41 . The protruding part  43  is opposed to the protruding part  44 , and the cover tube  12  is firmly sandwiched between two protruding parts  43  and  44  in comparison with other portions. The protruding parts may be formed on both the opposing face  26  and the stopper face  41 , or may be formed on at least one of them. The protruding part  43  is formed on the entire opposing face  26  in a radial direction so as to be connected annularly, and the protruding part  44  is formed so as to be connected annularly in the same manner. On the other hand, the protruding parts  43  and  44  may be formed so as to have intervals spaced in a circumferential direction. In this case, the protruding parts  44  may be formed in association with positions of the intervals of the protruding parts  43 . 
     In a tube-fixing tool  20  shown in  FIG. 6B , the opposing face  26  extends in a perpendicular direction relative to the center axis “O” of the fixing-tool body  21 , the stopper face  41  is not in parallel with the opposing face  26 , but is inclined relative to the center axis “O”. In this manner, by inclining the stopper face  41 , the cover tube  12  is tightened inside a gap  42  narrowed in a radially outward direction, the fixing strength can be increased. 
     In a tube-fixing tool  20  shown in  FIG. 7A  and different from that of  FIG. 6B , the stopper face  41  extends in a perpendicular direction relative to the center axis “O” of the fixing-tool body  21 , the opposing face  26  is not in parallel with the stopper face  41 , but is inclined relative to the center axis “O”. As shown in  FIGS. 6B and 7A , by setting one of the opposing face  26  and the stopper face  41  in a perpendicular direction, and by inclining the other of the opposing face  26  and the stopper face  41  relative to the center axis “O”, the fixing strength of the cover tube  12  relative to the fixing-tool body  21  can be increased. 
     In the above-mentioned respective embodiments, the protruding part shown in  FIG. 6A  may be formed on at least one of the opposing face  26  and the stopper face  41 . 
     In a tube-fixing tool  20  shown in  FIG. 7B , the guide face  38  extends toward the base end side of the fixing sleeve  22 , and the base end of the guide face  38  is opposed to the tip end of the fitting-cylinder part  24  in a radial direction thereof. A pressing part  45  is formed so as to press the cover tube  12  to the fitting-cylinder part  24  in a radially inward direction thereof by the guide face  38 . In this manner, in the tube-fixing tool  20  shown in  FIG. 7B , the fixing sleeve  22  presses the cover tube  12  to the fitting-cylinder part  24  in the radial inward direction, so that the cover tube  12  is tightened and fixed to the fixing-tool body  21 . 
       FIGS. 5 to 7  each show the tube-fixing tool  20  shown in  FIGS. 1 and 2 , and each show a portion “A” shown in  FIG. 2B , this structure can be applied to a mode provided with: a first fitting-outer face  29   a  and a second fitting-outer face  29   b , as in the case of the tube-fixing tool  20  shown in  FIG. 4 . In this case, the cover tube  12  is provided with two fixing portions shown in  FIGS. 5 to 7 . 
       FIG. 8  is a cross sectional view showing a tube-fixing tool of another modified example;  FIG. 9A  is a perspective view showing a fixing ring shown in  FIG. 8 , and  FIG. 9B  is a perspective view showing a fixing ring serving as another modified example; and  FIG. 10A  is an enlarged cross sectional view showing a portion “C” in  FIG. 8 , and  FIG. 10B  is an enlarged cross sectional view partially showing a tube-fixing tool of another modified example. 
     A tube-fixing tool  20  shown in  FIGS. 8 and 10A  has a fixing ring  46  that is fitted to the inner circumferential face  35  of the fixing sleeve  22 , and the fixing ring  46  is disposed on the outside of the fitting-cylinder part  24  via the cover tube  12 . A plurality of convex parts  47  protruding in the radially outward direction are formed on the outer circumferential face of the fitting-cylinder part  24 , and concave parts  48  are formed on the inner face of the fixing ring  46  so as to correspond to the convex parts  47 . The fixing ring  46  is formed of material that is elastically deformed in the radial direction, such as rubber, synthetic resin or the like, and fitted to the outside of the cover tube  12  while being expanded in the radial direction, with the end of the cover tube  12  fitted to the outside of the fitting-cylinder part  24 . 
     In a tube-fixing tool  20  shown in  FIG. 10B , the inner circumferential face  35  is a taper face whose inner diameter is gradually increased toward the end face of the cover tube  12 . On the other hand, the inner circumferential face  35  shown in  FIG. 10A  has a straight face in parallel with the center axis “O” of the fixing sleeve  22 . In this case, since the inner circumferential face  35  is formed as a taper face, the fixing sleeve  22  can be elastically deformed in a radial direction by moving the fixing sleeve  22  in the axial direction. In this manner, a fixing strength for the cover tube  12  exerted by the fixing sleeve  22  can be increased. 
     The fixing ring  46  shown in  FIG. 9A  is integrally formed in a circumferential direction. On the other hand, the fixing ring  46  may be formed into a C-shaped mode having a slit  49  extending in the axial direction as shown in  FIG. 9B . In this case, the attaching work of the fixing ring  46  on the outside of the cover tube  12  can be easily carried out. Moreover, the fixing ring  46  may be made of two semicircular members. In this case, the attaching work of the fixing ring  46  on the outside of the cover tube  12  can be more easily carried out, and the fixing ring  46  can be made of hard resin or metal material. In this manner, a mode for fixing the cover tube  12  to the fixing-tool body  21  via the fixing ring  46  may be applied to the tube-fixing tool  20  shown in  FIG. 4 . In this case, two fixing rings  46  are respectively fitted to the first and second inner circumferential faces  35   a  and  35   b  different in inner diameters from each other. 
       FIGS. 11A to 11C  are cross sectional views each showing a tube-fixing tool of another modified example. 
     In the above-mentioned tube-fixing tool  20 , the fixing sleeve  22  is fixed to the fixing-tool body  21  by press-inserting the fastening part  31  of the fixing sleeve  22  into the attaching part  23  of the fixing-tool body  21 . 
     On the other hand, in a tube-fixing tool  20  shown in  FIG. 11A , a male screw  51  is formed on the attaching part  23 , and a female screw  52  is formed on the fastening part  3  and screw-coupled to the male screw  51 . In this manner, the fixing sleeve  22  is screw-coupled to the attaching part  23 . 
     In a tube-fixing tool  20  shown in  FIG. 11B , attaching holes  53  are formed on the attaching part  23 , and attaching holes  54  are formed on the fastening part  31  so as to correspond to the respective attaching holes  53 . By coupling pins  55  that are press-inserted into the attaching holes  53  and  54 , the fixing sleeve  22  is fixed to the attaching part  23 . 
     In a tube-fixing tool  20  shown in  FIG. 11C , the attaching part  23  has: a small diameter part  23   a  disposed on the base end side; and a large diameter part  23   b  larger in diameter than the small diameter part  23   a . An engaging face  56  extending in the radial direction is formed between the small diameter part  23   a  and the large diameter part  23   b . An engaging claw  57  is formed on the base end face side of the fastening part  31 , and the engaging claw  57  is engaged with the engaging face  56 . An inclined face  58  gradually increased in inner diameter toward the base end face of the fixing sleeve  22  is formed on the base end face side of the engaging claw  57 . In  FIG. 11C , by press-inserting the fixing sleeve  22  into the fixing-tool body  21  from the right side in this figure, the inclined face  58  is guided by the large diameter part  23   b , and the engaging claw  57  is elastically deformed in a radially outward direction. Therefore, by press-inserting the fixing sleeve  22  into the fixing-tool body  21 , the engaging claw  57  is engaged with the engaging face  56 , and the fixing sleeve  22  is fixed to the attaching part  23 . 
     As shown in  FIG. 11 , as an attaching mode of the fixing sleeve  22  to the fixing-tool body  21 , a press-insertion mode, a screw coupling mode, a pin coupling mode, an engaging mode and the like may be employed. In each embodiment, the lateral cross sectional shape of the outer circumferential face of the attaching part  23  is formed into a round shape. On the other hand, this may be formed into a polygonal shape such as quadrangle, hexagon, or the like. Under the condition that the cross sectional shape of the outer circumferential face of the attaching part  23  is formed into a polygonal shape, the inner face  32  of the fastening part  31  to be fitted to the outside also has a polygonal shape. Moreover, a lateral cross sectional shape of the outer circumferential face of the fixing sleeve  22  is not limited by the round shape, a polygonal shape may be used. 
     The present invention is not limited by the above-mentioned embodiments, and it will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention. For example, as the elastic tube  10 , any mode may be used as long as a tube having at least two layers that are freely flexibly deformed is used, and the cover tube is not limited by the knitted strand tube as long as the tube allows the outside cover tube to be expanded outward from the soft tube.