The present invention relates to a multiple stranding machine, and in particular to a stranding machine in which a bundle of wires, for instance made of copper, can undergo a quadruple twist before it is wound on the collecting bobbin.

The known stranding machines, for example from EP-A-123656, comprise a double twist device which is provided with a stationary support in which a bobbin can rotate for winding a finished cable, as well as with an arched structure which can rotate around this stationary support, so as the cable undergoes a double twist before it is wound on the bobbin. The wires forming the cable can come from a plurality of bobbins arranged upstream the double twist device or from a single bobbin on which a bundle of wires is wound.

These known machines cannot exceed a determined production speed limit depending upon the rotation speed of the arched structure, in turn depending upon the diameter and the number of wires to be twisted.

It is therefore an object of the present invention to provide a stranding machine which is free from said disadvantage, i.e. a stranding machine which can produce cables at a higher speed than the known machines. Said object is achieved with a stranding machine, the main features of which are disclosed in the first claim and other features are disclosed in the subsequent claims.

Thanks to the second double twist device which is arranged upstream the first device for releasing, not winding, the bundle of wires which will form the cable, simultaneously giving them a double twist, the stranding machine according to the present invention can produce cables with a quadruple twist, i.e. at a double speed with respect to the known stranders with the same number and diameter of the wires to be twisted.

Furthermore, since the second double twist device comprises many parts similar to the parts of the first device, the stranding machine according to the present invention is not much more complex and expensive to be built and maintained with respect to the known machines.

According to a particular advantageous aspect of the invention, the second double twist device can be provided with a mobile support which follows the arrangement of the bundle of wires wound on the bobbin, so as to improve the running of the same wires.

According to another particular advantageous aspect of the invention, the second double twist device can be provided with a pulley driven by preferably adjustable elastic means for stretching the bundle of wires, detecting its breaking, if any, and/or adjusting its tension.

According to a further particular advantageous aspect of the invention, the second double twist device can be provided with a mechanism which, according to the movement of said mobile support, orients the rotation axis of the pulleys which take the bundle of wires to its arched structure.

Further advantages and features of the stranding machine according to the present invention will be clear to those skilled in the art from the following detailed and nonlimiting description of an embodiment thereof with reference to the attached drawings, wherein:

• figure 1 shows a side view of the stranding machine according to said embodiment;
• figure 2 shows a cross-sectioned partial side view of the second double twist device of the strander of figure 1;
• figure 3 shows a first partial front view of the second double twist device of figure 2; and
• figure 4 shows a second partial front view of the second double twist device of figure 2.

Referring to figure 1, it is seen that the stranding machine according to the present invention comprises a double twist device 1 of the known kind, which can contain a bobbin 2 which is rotated in a stationary support 3 by an electric motor 4 for winding a finished cable 5. An arched structure 6 is in turn rotated around the stationary support 3, so that cable 5 undergoes a double twist before it is wound on bobbin 2. In particular, cable 5 to be twisted comes from the outside of the collecting unit 1 along a horizontal axis substantially coinciding with the rotation axis of the arched structure 6 and undergoes the two twists in two pulleys 7, 8 which are arranged upstream and downstream, respectively, the arched structure 6 and rotate with the latter, as well as around their axis. A mechanism provided with a plurality of pulleys 10 mounted on a support 11 suitable for moving with a periodic alternate motion moves cable 5 parallel to the axis of bobbin 2 for winding it around the latter in an ordinate manner.

According to the invention, the stranding machine according to the present invention comprises a second double twist device 12 arranged upstream the first device 1. Device 12 also comprises a bobbin 13 which is rotated in a stationary support 14, in particular by an electric motor 15. However, bobbin 13 is rotated for releasing a bundle of wires 16 which will form cable 5. An arched structure 17 is in turn rotated around the stationary support 14 for giving a double twist to the bundle of wires coming from bobbin 13. The bundle of wires 16 undergoes the two twists in two pulleys 18, 19 which are arranged upstream and downstream, respectively, the arched structure 17 and rotate with the latter, as well as around their axis. After these two twists, cable 5 formed by the bundle of wires 16 is forwarded to the first double twist device 1, which is preferably arranged with the rotation axis of the arched structure 6 aligned with the rotation axis of the arched structure 17. Further, the arched structures 6 and 17, thanks to electric and/or mechanical transmission devices of the known kind, can rotate substantially at the same speed or at similar speeds, but in opposite directions, so that cable 5 undergoes four twists, in particular in pulleys 18, 19, 7 and 8, before it is wound on bobbin 2.

Referring now also to figures 2 and 3, it is seen that the second twist device 12, for collecting the bundle of wires 16 of bobbin 13 and forwarding it to the arched structure 17, comprises a mechanism provided with two or more pulleys 20, 21 mounted on a support 22 suitable for moving with a transversal motion, substantially parallel to the rotation axis of bobbin 13. Unlike the mobile support 11 of the first double twist device 1, the mobile support 22 does not move with a periodic alternate motion but follows the arrangement of the bundle of wires 16 on bobbin 13. For this purpose, the mobile support 22 is provided with means suitable for detecting and following the position of the bundle of wires 16 coming from bobbin 13 along the rotation axis of the latter. In the present embodiment of the invention said means comprise a seat, in particular a fork 23, arranged between bobbin 13 and the first pulley 20, so that the bundle of wires 16 can run through the same fork. Fork 23 is fixed to a horizontal lever 24 which is pivoted to a bar 25 fixed to the mobile support 22 for oscillating around an axis substantially perpendicular to the rotation axis of bobbin 13. A sensor 26, for instance of the magnetic kind, which detects the position of lever 24, is arranged on bar 25. Sensor 26 is connected directly or through electric and/or electronic devices to a motor 27 which is in turn connected mechanically, for example by means of a belt 28, to a threaded shaft 29. The threaded shaft 29 can rotate in a corresponding seat which transversely crosses the mobile support 22, so that the latter can run along a cylindrical guide 30 arranged parallel to shaft 29, according to the signals transmitted by sensor 26, i.e. to the position of fork 23.

With reference also to figure 4, it is seen that the bundle of wires coming from bobbin 13, when it is not aligned with the mobile support 22, moves fork 23, thus causing the oscillation of lever 24, the working of motor 27 and the consequent moving of the mobile support 22 until fork 23 is not aligned again with the bundle of wires 16. The latter, after it has passed pulley 20, crosses an opening in the mobile support 22 and reaches pulley 21, which is pivoted to a first arm 31 which can oscillate around an axis substantially parallel, preferably coinciding with the bundle of wires 16 stretched between pulleys 20 and 21. With this arrangement, pulley 21 can tilt toward the middle of the stationary support 14 when the mobile support 22 runs along guide 30, as in figure 4.

After pulley 21, the bundle of wires 16 runs in a third pulley 32 pivoted to a second arm 33 which can oscillate along an axis substantially parallel to the rotation axis of bobbin 13 and is pulled by preferably adjustable elastic means 34 which thus stretch the bundle of wires 16 for allowing a correct running thereof. The elastic means 34 can for instance comprise a helical spring having an end which can be moved by rotating a screw. The second arm 33 can also be connected to signaling means which are turned on when it is pulled in an extreme position of spring 34, so as to signal the breaking, if any, of the bundle of wires 16. The second arm 33 can further be connected, directly or through electric and/or electronic devices, to motor 15, so as to control its rotation speed according to the inclination of the same arm, i.e. to the tension of the bundle of wires 16. In particular, the rotation speed of motor 15 is increased or decreased, respectively, if the second arm 33 is more or less pulled by spring 34, i.e. if the bundle of wires 16 is less or more stretched. After the third pulley 32, the bundle of wires 16 passes in a fourth pulley 35 before reaching pulley 18, where it undergoes the first twist in the arched structure 17, as described above.

The fourth pulley 35 is preferably pivoted to a third arm 36 fixed to a tube 37 which can oscillate with respect to the stationary support 14 around its own longitudinal axis, which is parallel or coinciding with the rotation axis of the arched structure 17 and is crossed by the bundle of wires 16 stretched between pulleys 18 and 35. Also the second arm 33 is pivoted to tube 37, while support 36 is connected to the first arm 31 of pulley 21 through a telescopic bar 38. With this arrangement, during the movement of the mobile support 22, tube 37 oscillates together with the first arm 31, so that the rotation axis of pulleys 21, 32 and 35 are always parallel to each other.