Abstract:
A miniature rope formed of metal includes: a core wire; and a plurality of surrounding wires wound around the core wire so as to form a stranded wire as a whole, wherein the core wire is formed of a material whose characteristics differ from those of the surrounding wires. Specifically, the core wire may be a tungsten wire, a superelastic alloy wire, or a nickel-titanium alloy wire, while the surrounding wires may be stainless steel wires.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a miniature rope for use as an operating wire for an endoscope, and more particularly to a metallic miniature rope which is formed as a stranded wire as a whole by spirally winding aplurality of surrounding wires around a core wire.  
           [0002]    As a miniature rope for use in an endoscope, a miniature rope of a so-called 1×7 construction in which six surrounding wires are spirally wound around a core wire is widely used. In addition, miniature ropes of a 1×19 construction, 1×37 construction, and the like are also used. Stainless steel wires are generally used as the core wire and the surrounding wires.  
           [0003]    In some applications, however, there are cases where it is compelled to use a miniature rope having a high tensile strength without enlarging the outside diameter, or use a miniature rope in which a kink is difficult to occur.  
           [0004]    Accordingly, if the miniature rope is formed of tungsten wires having characteristics that the tensile strength is strong and a kink is difficult to occur, it is possible to obtain a miniature rope having excellent characteristics which cannot be obtained by stainless steel wires.  
           [0005]    However, since the tungsten wires are low in wear resistance, if they are rubbed against a hard object, the tungsten wires have the drawback of being cut off easily, so that it is impractical to fabricate a miniature rope using tungsten wires.  
         SUMMARY OF THE INVENTION  
         [0006]    Accordingly, it is an object of the invention to provide a miniature rope which exhibits excellent characteristics that cannot be obtained by a miniature rope of the conventional construction and which is capable of being put to practical use.  
           [0007]    In the present invention, a core wire is formed of a material whose characteristics differ from those of surrounding wires. This makes it possible to provide a miniature rope which exhibits excellent characteristics that cannot be obtained by a miniature rope of the conventional construction and which is capable of being put to practical use.  
           [0008]    In particular, if the core wire has characteristics which excel in the tensile strength and the difficulty of formation of a kink as compared with the surrounding wires, and the surrounding wires has a characteristic excelling in wear resistance as compared with the core wire, it is possible to obtain excellent durability in a case where the miniature rope is used as a wire for an endoscope.  
           [0009]    A miniature rope of a preferred embodiment of the present invention is formed of metal and includes: a core wire; and a plurality of surrounding wires spirally wound around the core wire so as to form a stranded wire as a whole, wherein the core wire is formed of a material whose characteristics differ from those of the surrounding wires.  
           [0010]    In the above arrangement, if the core wire has characteristics which excel in the tensile strength and the difficulty of formation of a kink as compared with the surrounding wires, and the surrounding wires has a characteristic excelling in wear resistance as compared with the core wire, it is possible to obtain a miniature rope exhibiting excellent durability.  
           [0011]    It should be noted that the surrounding wires may be stainless steel wires, and the core wire may be a tungsten wire, a superelastic alloy wire, or a nickel-titanium alloy wire.  
           [0012]    The present disclosure relates to the subject matter contained in Japanese patent application No. 2000-32959 (filed on Feb. 10, 2000), which is expressly incorporated herein by reference in its entirety. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a cross-sectional view of a miniature rope in accordance with an embodiment of the invention, and is taken along line I-I in a direction perpendicular to its axis in FIG. 2,;  
         [0014]    [0014]FIG. 2 is a side elevational view of the miniature rope in accordance with the embodiment of the invention;  
         [0015]    [0015]FIG. 3 is a side elevational view of an endoscope in which the miniature rope of the invention is used; and  
         [0016]    [0016]FIG. 4 is a plan view, partly in section, of a distal end portion of a snare for an endoscope in which the miniature rope of the invention is used. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Referring to the accompanying drawings, a description will be given of an embodiment of the invention.  
         [0018]    [0018]FIG. 2 is side elevational view of a miniature rope  10  in accordance with the embodiment of the invention, and FIG. 1 shows a section taken along line I-I perpendicular to an axis thereof.  
         [0019]    The miniature rope  10  is a slender metallic rope whose outside diameter is 1 mm or less or several millimeters or less. The miniature rope  10  in this embodiment is formed as a stranded wire as a whole by spirally winding six surrounding wires  12  around a core wire  11 . As the direction of spirally winding the surrounding wires  12  with respect to the core wire  11 , so-called Z twist or S twist in an opposite direction thereto may be used.  
         [0020]    Stainless steel wires (e.g., SUS  316 , SUS  304 , etc., in JIS) are used as all the six surrounding wires  12  surrounding the core wire  11 . Meanwhile, a tungsten wire is used as the core wire  11  which extends straightly in the center and is not exposed to the outer surface.  
         [0021]    Thus since the surrounding wires  12  which are exposed on the surface of the miniature rope  10  are formed of stainless steel wires excelling in wear resistance, even if they are rubbed against a hard object, they are not easily worn. On the other hand, since the core wire  11  which is not exposed on the surface is formed of a tungsten wire having a high tensile strength, the core wire  11  increases the tensile strength without enlarging the outside diameter of the miniature rope  10 , and permits use in a portion where a lard load is applied.  
         [0022]    In addition, as a characteristic of the miniature rope  10  which is a stranded wire, if the miniature rope  10  is deflected, only a deflecting force is applied to the core wire  11  in the center, whereas a deflecting force and a twisting force are applied to the surrounding wires  12  wound therearound.  
         [0023]    In addition, a large deflecting stress is applied to the core wire  11  as compared to the surrounding wires  12  partly because the entire length of the core wire  11  is shorter than that of the surrounding wires  12 . For this reason, if the miniature rope  10  is repeatedly deflected, a kink is liable to occur in the core wire  11 .  
         [0024]    Accordingly, by using the tungsten wire which makes it difficult for the kink to occur in the core wire  11  as in this embodiment, even if the surrounding wires  12  are the stainless steel wires, it is possible to obtain the miniature rope  10  in which, as a whole, the kink is difficult to occur.  
         [0025]    It should be noted that, as a material in which the link is difficult to occur, a superelastic alloy formed of such as a nickel-titanium (Ni-Ti) alloy has a very excellent characteristic. Accordingly, if the superelastic alloy is used as the material of the core wire  11 , even if the surrounding wires  12  are the stainless steel wires or the like, it is possible to obtain the miniature rope  10  in which the kink is very difficult to occur.  
         [0026]    In addition, as for the nickel-titanium alloy wire, one having a composition excelling in its tensile characteristic and deflecting characteristic may be used as the core wire  11  even if it is not included among the superelastic alloys.  
         [0027]    Such a miniature rope  10  in accordance with the invention can be used for various applications.  
         [0028]    [0028]FIG. 3 shows an endoscope, in which a curved portion  2  connected to a distal end of an inserting portion  1  is arbitrarily deflected by a flexible operating wire  5  which is subjected to traction by a manipulating mechanism  4  which is disposed in a manipulating portion  3 .  
         [0029]    During traction, a large tensile force is applied to the flexible operating wire  5 , and the flexible operating wire  5  undergoes vehement rubbing against a curved tube made of stainless steel inside the curved portion  2 . In addition, the portion of the flexible operating wire  5  which is wound around a pulley  6  disposed in the manipulating mechanism  4  is bent with a small radius of curvature.  
         [0030]    Accordingly, if the miniature rope  10  in which the surrounding wires  12  formed of stainless steel wires are spirally wound around the core wire  11  formed of a tungsten wire is used as the flexible operating wire  5 , it is possible to obtain extremely excellent durability as compared with the miniature rope  10  in which both the core wire  11  and the surrounding wires  12  are formed of stainless steel wires.  
         [0031]    [0031]FIG. 4 shows a snare for an endoscope which is used for the purpose of constricting and incising a colonic polyp or the like, and a snare loop wire  23  formed of an elastic wire is connected through a stainless steel pipe-made connecting pipe  24  to a distal end of an operating wire  22  inserted and disposed in a flexible tube-made sheath  21  in such a manner as to be extendable and retractable in the axial direction.  
         [0032]    The snare loop wire  23  moves into and out of the sheath  21  by pulling or pushing the operating wire  22 , and bulges in loop form outside the sheath  21  by its own resiliency.  
         [0033]    As the snare loop wire  23  is pulled into the sheath  21 , the snare loop wire  23  undergoes elastic deformation and narrows, but when it is pushed out of the tip of the sheath  21 , the snare loop wire  23  must restore its original bulged form.  
         [0034]    Accordingly, the snare loop wire  23  must be provided with a characteristic that a kink is difficult to occur, so that it is sufficient to use the miniature rope  10  in accordance with the invention. In that case, if a superelastic alloy wire formed of a nickel-titanium Ni-Ti alloy or the like is used as the core wire  11 , since it can be safely the that practically no kink occurs in the core wire  11 , a kink hardly occurs in the snare loop wire  23 . Hence, even after the endoscope is repeatedly used, the snare loop wire  23  is able to maintain its bulged state outside the sheath  21 .  
         [0035]    In addition, although the nickel-titanium alloy is a material for which brazing, welding, and soldering are difficult to perform, if stainless steel wires, for example, are used as the surrounding wires  12 , brazing, welding, soldering, or the like can be used in connection to a member such as the connecting pipe  24 .  
         [0036]    It should be noted that the invention is not to be limited to the above-described embodiment, the invention may be applied to ropes of a 1×19 construction or 1×37 construction which, as a whole, are formed as stranded wires by spirally winding  18  or  36  surrounding wires  12  around the core wire  11 , or ropes having other types of strand construction.  
         [0037]    Furthermore, metal wires of material other than those described above may be used as the core wire  11  and the surrounding wires  12 , and an object to which the miniature rope  10  is applied is not to be limited to the one described above.