Abstract:
The deformation of corrugations in a corrugated conductive tape, utilized as a screened layer for screened cables or as an outer conductor for coaxial cables, due to pulling tension of the screened cable is prevented by an apparatus for manufacturing screened cables such that the corrugated conductive tape is transferred at the same rate as a cable core which is covered by the corrugated conductive tape by a forming device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an apparatus for manufacturing screened cables, and particularly to an apparatus for manufacturing screened or shielded cables wherein even if a thin conductive tape having a wavy pattern (including corrugation, embossment, and any other suitable wavy pattern, but hereinafter referred to simply as &#34;corrugated tape&#34;) is utilized for a layer as screening or shielding the cable or as an outer conductor for a coaxial cable, a cable core provided with an insulating layer can be longitidinally covered with such corrugated thin tape without deforming the corrugation thereof. 
     2. Description of the Prior Art 
     There has been proposed such screened cable, for example as shown in FIG. 1, wherein the circumference of a paper tape 2 wound around a cable core 1 is covered longitudinally with a corrugated aluminum tape 3, and then the resulting member has applied thereover a sheath 4. 
     In this type of screened cable, a corrugated aluminum tape 3 having a thickness of, for instance, 0.2 mm or more is used to withstand the pulling tension (e.g., the cable core 1 has a 15 mm outer diameter, and the aluminum tape 3 has a 1 mm wave crest and a 2.5 mm pitch) in order to avoid deformation of the member 3, even though the pulling tension of the cable is increased at the time of manufacturing the same. 
     FIG. 2 is an explanatory view showing an apparatus for manufacturing the above screened cable which comprises a delivery drum 5 around which the cable core 1 is wound, a taping machine 6 for winding the paper tape 2 around the cable core 1, a drum 7 for winding the corrugated aluminum tape 3 utilized for longitudinally covering the cable core 1 around which the paper tape 2 is wound, a forming die 8 for covering the cable core 1 provided with the paper tape 2 with the corrugated aluminum tape 3, a sheath extruder 9 for providing the sheath 4 around the outside of the longitudinally covered cable core, a cooler 10 for cooling the extruded sheath 4, and a wind-up drum 11 for pulling the resulting screened cable which has been cooled by means of the cooler 10 (a pulling capstan and like are omitted). 
     In the above apparatus, the paper tape 2 is wound around the cable core 1, transferred in the pulling direction thereof, by means of the taping machine 6. Then the resulting cable core is longitudinally covered with the corrugated aluminum tape 3, which has previously been wound around the aluminum tape drum 7, by means of the forming die 8 (for instance, the aluminum tape 3 has an overlapped dimension of 5 mm). Furthermore, the sheath 4 is provided around the longitudinally covered cable core to cover the same by means of the sheath extruder 9, and thereafter the resulting screened cable is cooled by the cooler 10. The screened cable thus manufactured is finally wound up by means of the wind-up drum 11. 
     However, in such conventional apparatus for manufacturing screened cables as mentioned above pulling tension applied to the corrugated aluminum tape 3 can not be relieved at the time of manufacturing the screened cables. Accordingly, there is such disadvantage that the corrugated aluminum tape 3 is deformed, thereby destroying the corrugation, if the pulling tension increases in response to speeding up of the manufacturing rate. 
     Particularly, since such a thin corrugated aluminum tape having a thickness of less than 0.2 mm is used in a small diameter screened cable, there is such disadvantage that it is difficult to manufacture such small diameter screened cables while maintaining a prescribed productivity. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide an apparatus for manufacturing screened cables whereby a corrugated conductive tape is applied longitudinally to cover the circumference of an insulating layer over a cable core, and is not deformed, even if pulling tension is applied to the cable core. 
     It is another object of the present invention to provide an apparatus for manufacturing screened cables by which such screened cables can be manufactured with a high productivity, even if the pulling speed of the cables is increased. 
     It is still another object of the present invention to provide an apparatus for manufacturing screened cables by which a high-quality screened cable with excellent electrical characteristics can be manufactured. 
     In order to attain the above stated objects, an apparatus for manufacturing screened cables according to the present invention includes means for disposing longitudinally a corrugated conductive tape around the circumference of an insulating layer of the cable, as a screened layer for shielding the cable or as an outer conductor for a coaxial cable, means for reducing pulling tension applied to the aforesaid corrugated conductive tape by making the corrugated tape advance at a rate in response to the pulling speed of the cable, and means for forming the corrugated conductive tape, the pulling tension of which has been reduced, around the insulating layer of the cable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cutaway view showing an example of a conventional screened cable; 
     FIG. 2 is a perspective view showing a conventional apparatus for manufacturing screened cables; 
     FIG. 3 is a perspective view showing a construction of an embodiment of the cable manufactured by the apparatus for manufacturing screened cables according to the present invention; 
     FIG. 4 is a perspective view showing an embodiment of the apparatus for manufacturing screened cables according to the present invention; 
     FIGS. 5(A), (B), (C) and (D) are sectional views illustrating the procedure of forming a screened cable by means of forming rolls in the apparatus of FIG. 4; and 
     FIG. 6 is a perspective view showing another embodiment of the apparatus for manufacturing screened cables according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 shows an example of a screened cable manufactured in accordance with the present invention and including a cable core 1 having wound therearound a paper tape 2, and the circumference of which is longitudinally covered with, for example, a corrugated aluminum tape 3 having a thickness t of less than 0.2 mm (a sheath is omitted from FIG. 3 for simplicity of illustration. 
     FIG. 4 shows one embodiment of the apparatus according to the present invention wherein the same parts as those of FIG. 2 are designated by the same reference numerals as in FIG. 2, so that repeated explanations will be unnecessary. The apparatus comprises a supporting and advancing member 12, e.g. an endless web or belt, for transferring the corrugated aluminum tape 3 in the pulling direction of the screened cable, a motor 13 for moving the advancing member 12 in the direction indicated by arrows and at the same rate as the cable core 1, plural pairs of forming rolls 18a1, 18a2; 18b1, 18b2; 18c1, 18c2; 18d1, 18d2; . . . for forming the corrugated aluminum tape 3, a nozzle 14 for bonding overlapped portions at both sides of the corrugated aluminum tape 3 to each other (which may be omitted), a driving wheel 16a provided with a gear 15 which is driven by the motor 13, idle wheels 16b, 16c and 16d for stretching and carrying the advancing member 12, and a guide roll 17 for guiding the corrugated aluminum tape 3. Each of the aforesaid plural pairs of forming rolls 18a1, 18a2; 18b1, 18b2; 18c1, 18c2; 18d1, 18d2; . . . consists of a pair of upper and lower rolls disposed in such a manner that the cable core 1 is passed between concave surfaces of the upper and lower rolls, respectively. At least a part of the traveling plane of the advancing die 12 stretched between opposite wheels 16a and 16b and that between the opposite wheels 16c and 16d are constructed respectively to travel parallel to the under side of the cable core 1 and to travel together with the cable core 1 and the corrugated aluminum tape 3 between the respective pairs of the upper and lower rolls of the forming rolls 18a1, 18a2; 18b1, 18b2; 18c1, 18c2; 18d1, 18d2; . . . . 
     Furthermore, a squeezing die (designated by reference numeral 8 in FIG. 2) may be provided between the final pair of forming rolls (18d1, 18d2 in the embodiment of FIG. 4) and the nozzle 14. 
     In the above apparatus, the cable core 1 is delivered from a delivery drum 5 to a taping machine 6. The advancing member 12 is advanced by means of the driving wheel 16a driven by the motor 13 at the same rate as the cable core 1 in the directions indicated by the arrows. The corrugated aluminum tape 3 is drawn into a gap between the advancing member 12 and the cable core 1 at the position of the roll 16c, and then the tape is transferred on the advancing member 12 at the same rate as the cable core 1, thereby to smoothly pass through a gap between the forming rolls 18a1 and 18a2. As a result, the pulling tension of the cable core 1 applied to the aluminum tape 3 is relieved so that deformation thereof can be avoided. Concave surfaces are defined in the forming rolls, the profiles of which change gradually with progress of the operation as shown in FIGS. 5(A)-5(D), and a screened cable is formed by pressing the cable core 1 and the aluminum tape 3 together with the advancing member 12 between the respective concave surfaces 19 defined by the respective pairs of upper and lower forming rolls. The forming procedure will be described in more detail hereinbelow. Namely, FIGS. 5(A), 5(B) and 5(C) illustrate preliminary forming steps wherein the aluminum tape 3 is first pressed together with the advancing die member in between the rolls 18a1 and 18a2 as shown in FIG. 5(A). Then the aluminum tape 3 is pressed in a gap between the rolls 18b1 and 18b2, whereby both ends of the aluminum tape 3 rise upwardly as shown in FIG. 5(B). The two ends of the aluminum tape 3 thus raised are moved by means of the upper roll 18c2 to overlap with each other as shown in FIG. 5(C). The aforesaid upper roll 18c2 is defined to have a step like configuration in the concave surface 19, and one edge of the aluminum tape 3 is first shaped on the inner side with respect to the other edge of the aluminum tape by means of a projection 19a in the aforesaid configuration, while the latter edge of the aluminum tape 3 is formed to overlap the former edge of the aluminum tape by means of a recess 19b in the configuration. Then, the aluminum tape 3 is pressed between the rolls 18d1 and 18d2 to complete the forming thereof as shown in FIG. 5(D). It is to be noted that the rolls 18c1 and 18c2 may be omitted in the case where the edges of the aluminum tape 3 are shaped so as not to overlap each other, but to butt each other. 
     The overlapped portion (or the butted portion) of the aluminum tape 3 thus longitudinally formed is soldered by means of the nozzle 14, and then a sheath is applied thereon. 
     Speed control of the advancing member 12 is effected in such a manner that a sensor signal derived from a first sensor 100 outputting a signal in response to the speed of a pulling capstan (not shown) is compared with that of a second sensor 200 outputting signal in response to the speed of the advancing member 12 by means of a differential amplifier 300, whereby the speed of the motor 13 is controlled by a control circuit 400 in such a member that the difference between the signals compared becomes zero. Instead of such a control circuit as described above, an advancing die driving part may be connected with the pulling capstan through gears. 
     FIG. 6 illustrates another embodiment of the apparatus for manufacturing screened cables according to the present invention. In this embodiment the same parts as those of the embodiment of FIG. 4 are designated by the same reference numerals. Accordingly, the description relating to the overlapped constructions and operations of these embodiments will be omitted in the following explanation, but it is to be noted that the embodiment of FIG. 6 differs from that of FIG. 4 in that a forming die 8 is employed as the forming mechanism. The forming die 8 is constructed such that a cable core is covered with a corrugated aluminum tape introduced from the inlet side of the forming die while allowing the cable core to pass together with the tape through an inner bore surface of the forming die 8, the inner diameter of which decreases gradually, and the screened cable is produced when it is dicharged from the outlet side of die. 
     Furthermore, although the above embodiments have been described in connection with screened cables, it should be noted that the apparatus according to the present invention may also be applicable to the manufacture of coaxial cables in a manner similar to manufacture of the screened cables. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.