Self-supporting cable and manufacturing method therefor

Abstract

A self-supporting cable includes a main cable constructed by covering a cable core with an inner cover layer and installing one or more strength members inside the inner cover layer such that they lie on a plane passing through the central axis thereof; a support member; and an outer cover layer formed so as to cover the main cable and the support member while they are arranged in parallel. A support member portion including the support member and a part of the outer cover layer and a main cable portion including the main cable and a part of the outer cover layer are connected by connecting portions, which are also a part of the outer cover layer, in the longitudinal direction thereof. The main cable portion is made longer than the support member portion so that there is an allowance in the length thereof.

What is claimed is:  
     
         1 . A self-supporting cable comprising: 
 a main cable constructed by covering a cable core with an inner cover layer, which is formed of a thermoplastic resin and which has a tubular shape, and installing one or more strength members inside the thermoplastic resin of the inner cover layer such that the strength members lie on a plane passing through the central axis of the inner cover layer;    a support member; and    an outer cover layer which is formed of a thermoplastic resin and which has a figure-8 shape in cross-section, and which is formed so as to cover the main cable and the support member while the main cable and the support member are arranged in parallel to each other,    wherein a support member portion, which includes the support member and a part of the outer cover layer around the support member, and a main cable portion, which includes the main cable and a part of the outer cover layer around the main cable, are connected to each other with connecting portions, which are also a part of the outer cover layer, with intervals in the longitudinal direction,    and wherein the main cable portion is made longer than the support member portion so that there is an allowance in the length thereof.    
     
     
         2 . A self-supporting cable according to  claim 1 , wherein the Young's modulus of the thermoplastic resin of the inner cover layer is higher than the Young's modulus of the thermoplastic resin of the outer cover layer.  
     
     
         3 . A self-supporting cable according to  claim 1 , wherein all of the strength members are disposed on a plane which passes through the central axis of the support member and the central axis of the main cable.  
     
     
         4 . A self-supporting cable according to  claim 3 , wherein the Young's modulus of the thermoplastic resin of the inner cover layer is higher than the Young's modulus of the thermoplastic resin of the outer cover layer.  
     
     
         5 . A method for manufacturing a self-supporting cable, comprising the steps of: 
 arranging a main cable, which includes a cable core and one or more strength members which are disposed at positions on a plane passing through the central axis of the main cable and which are apart from the central axis of the main cable, and a support member in parallel to each other; and    forming an outer cover layer so as to cover the main cable and the support member by extruding a thermoplastic resin in a crosshead of an extruder;    wherein the main cable is led to the crosshead of the extruder after being bent by a first roller which is disposed upstream of the crosshead, the first roller having a rotational axis which is parallel to a plane passing through the central axis of the support member and the central axis of the main cable in the crosshead of the extruder and is perpendicular to a moving direction of the main cable.    
     
     
         6 . A method for manufacturing a self-supporting cable according to  claim 5 , wherein a second roller having a rotational axis which is parallel to the rotational axis of the first roller is disposed between the crosshead and a winding device, and wherein the self-supporting cable, which exits from the crosshead after the extrusion process, is bent by being wound around the second roller, and is then wound around a drum by the winding device.  
     
     
         7 . A method for manufacturing a self-supporting cable according to  claim 5 , wherein a plurality of first rollers are provided and are arranged across the main cable in a zigzag manner with intervals along the moving direction of the main cable, and wherein the main cable is bent in alternately opposite directions by the first rollers.  
     
     
         8 . A method for manufacturing a self-supporting cable according to  claim 7 , wherein a second roller having a rotational axis which is parallel to the rotational axis of the first roller is disposed between the crosshead and a winding device, and wherein the self-supporting cable, which comes out from the crosshead after the extrusion process, is bent by being wound around the second roller, and is then wound around a drum by the winding device.  
     
     
         9 . A method for manufacturing a self-supporting cable according to one of  claims 5  to  8 , wherein a radius of the first roller is 100 times the distance between the central axis of the main cable and the strength members, or less.