The present invention relates to a method of winding a cable unit comprising two or more conductors on a rotary drum, with relative axial movement between on the one hand the drum and, on the other hand, the conductors which are freely arranged adjacent and substantially in parallel with each other.

More precisely, the invention relates to a method of simultaneously winding two or more separate conductors. By tradition, a cable unit is made of a number of conductors which are twisted together and provided with an enclosing sheath, the finished cable being substan¬ tially circular in cross-section. This coherent cable unit may be readily wound on a cable drum and unwound therefrom by means of prior-art techniques. However, it has recently been questioned whether the traditional design of the cable is optimal. Thus other types of cable unit have become increasingly widespread, consisting of bare conductors which are handled as a unit and arranged substantially in parallel with each other. Compared to a conventional cable, this unsheathed cable unit renders the manufacturing process less expensive. Further this new cable unit makes it possible to exchange a damaged conductor, in contrast to the traditional, sheathed cable unit which must be entirely replaced in case a conduc¬ tor is damaged. The cost of a damaged conductor in the unsheathed cable unit is thus less than one third as com¬ pared to a sheathed cable unit. A drawback of the unsheathed cable unit, however, is that a satisfactory method of winding this cable unit on a drum is not known. Difficulties also arise in the unwind¬ ing of the cable unit from the drum.

German Published Application 2,743,074 discloses a method of winding in which a plurality of conductors are simultaneously wound on a drum. The conductors are caused to engage the drum in parallel with each other and with

the axis of the drum. The points of engagement of the con¬ ductors thus are not offset in circumferential direction, which means that the beginning of a new cable layer is jeopardised. An even and controlled transition to the new cable layer is hardly obtainable, and there is a great risk that the conductors will climb onto each other.

US Patent Specification 4,130,248 discloses how a bundle of fibre-glass strands are wound into a package, the strands being advanced to the package in a plane per- pendicular to the axial direction of the package. Guide means which is movable in the axial direction guides the fibre-glass strands in the perpendicular plane towards the mandrel. A shoe is attached to the guide means and follows the reciprocating motion thereof along the axial direction of the mandrel. In this motion, the shoe presses the fibre-glass strands towards the underlying layers and in this manner facilitates the beginning of a new layer. Owing to the small dimensions and low friction coefficient of the fibre-glass strands, this method of changing the winding direction is feasible, but would not function for the conductors envisaged in the present invention owing to the high friction coefficient thereof and irregularities occurring in the sheath.

The object of the invention is thus to provide a method of winding the above-mentioned unsheathed cable unit on a drum.

A further object of the invention is to provide a winding method for said cable unit, which permits that satisfactory unwinding of the cable unit may be subse- quently effected.

One more object of the invention is to provide a method of winding relatively thick, rubber or lead sheath¬ ed conductors on a flanged drum in such a manner that each conductor is positioned closely adjacent the adjoining conductors in each cable layer, and that the cable layers become substantially even and have a uniform thickness corresponding to the diameter of a conductor.

The difficulty arising in the winding of such conduc¬ tors is that the high friction coefficients of the sheaths do not always permit a conductor to slide into position along an adjoining conductor. Therefore, instead of being axially wound, the conductor may begin to climb onto the adjoining conductor and be wound radially so as to form an uneven cable layer with beads consisting of a plurality of turns of conductors. On such occasions, the winding of all conductors is of course interfered with, and their poεi- tion relative to each other is upset, which means that their sequence may have been reversed as the winding pro¬ ceeds more normally in the axial direction of the drum. In order to try to overcome the above-mentioned difficulty it is customary either to manually supervise the winding ope- ration or to wind the conductors loosely, i.e. at a cer¬ tain distance from the adjoining conductor in the cable layer. Of course, such conventional solutions are not satisfactory, inter alia from the economic point of view. According to the invention, the objects above are achieved in that the individual conductors are caused to engage the drum at different points along the circumfe¬ rence thereof or the underlying cable layer, said points being spaced from each other in both axial and circumfe¬ rential direction, that the point of engagement of the axially leading conductor in the winding direction is positioned after the points of engagement of the other conductor(s) in the direction of rotation of the drum, that the sequence of the point of engagement of each con¬ ductor in the direction of rotation of said drum before the point of engagement of the axially leading conductor in the winding direction is reversed compared to the sequence of each conductor after the axially leading con¬ ductor of the cable layer in the winding direction, that the conductor of each new cable layer on the drum, which is axially leading in the winding direction, is caused by the flange of the drum, in cooperation with the succeeding conductor, to begin the new cable layer, and that the

sequence of the conductors after the leading conductor is maintained, layer by layer, by reversing the mutual orien¬ tation of the conductors in horizontal direction, as each new cable layer is begun. By the expression "the axially leading conductor in the winding direction" is meant the conductor which in the winding operation begins a new winding layer before the other conductors and which always is the leading one of the group of conductors in the winding layer. Further developments of the invention are apparent from the characteristic features stated in the subclaims. A preferred application of the invention will now be described for the purpose of exemplification and with reference to the accompanying drawings in which: Fig. 1 is a schematic perspective view of the method of winding a cable unit comprising two or more freely arranged conductors on a rotary drum according to the invention;

Fig. 2 is a front view of the drum with a finished cable layer and the beginning of the next layer;

Fig. 3 is a side view of the drum in Fig. 2, in which the winding of the different conductors on the drum is illustrated in more detail; and

Figs 4-7 illustrate the relative order of the diffe- rent conductors when finishing a cable layer and when beginning the next.

Figs 1 and 3 show three conductors 1, 2 and 3 which are included in an unsheathed cable unit and which are each supplied from an uncoiler (not shown) via respective deflecting rollers 11, 12 and 13 to a drum 4 which rotates in the direction of arrow R. A control device (not shown) is suitably arranged before the deflecting rollers 11-13 for controlling the tension of the individual conductors 1-3 so that it is essentially the same in each conductor. The deflecting rollers are idler rollers, arranged above each other in a tiltable stand 10 which in the embodiment shown is mounted on the frame of the machine. The drum is

also rotatably supported on the frame and is axially dis- placeable.

The stand 10 is tiltable between two stable positions of equilibrium, in which the inclination of the stand is such that each deflecting roller, for example the deflect¬ ing roller 12, is laterally offset relative to the adjoin¬ ing deflecting roller, the deflecting roller 11 and 13, by a distance which substantially corresponds to the thick¬ ness of a conductor 1, 2 or 3. This means that each con- ductor is advanced to the drum 4 at a fixed angle to the axis of rotation of the drum, said angle being equally large for each conductor 1, 2 and 3. Expressed in a diffe¬ rent manner, this means that the conductors are advanced to the drum substantially in parallel with each other, but vertically offset.

As a result, the individual conductors 1, 2 and 3 engage the drum 4 at different points a, b and c along the circumference 5 of the drum or the underlying cable layer 6. The points of engagement of the conductors 1, 2 and 3 are designated a, b and c, respectively. These points are spaced from each other in both axial and circumferential direction in respect of the drum 4. The leading conductor 1 is the conductor which is the leading one in the winding direction of the group of conductors 1, 2 and 3, as they are being wound on the drum 4, see especially Figs 1 and 4. The conductors 1, 2 and 3 run over the deflecting rol¬ lers 11, 12 and 13 in the stand 10, and the deflecting roller 12 is arranged above the deflecting roller 13 and below the deflecting roller 11, whereby the point of engagement a of the leading conductor 1 is positioned after the point of engagement b of the succeeding conduc¬ tor 2 in the direction of rotation R of the drum 4. The point of engagement b of the last-mentioned conductor 2 is, in turn, positioned after the point of engagement c of the third conductor 3 in the direction of rotation of the drum. Generally, the sequence of the point of engagement c, b and a of each conductor 3, 2 and 1 in the direction

of rotation of the drum is reversed compared to the sequence of each conductor 1, 2 and 3 of the cable layer in the winding direction.

In the winding stage illustrated in Fig. 1, the wind- ing is thus effected on the drum from the right to the left in the Figure, the conductor 1 being the leading one in the winding direction of the group of conductors 1, 2 and 3 that is being wound. It is to be noted that the stand 10 inclines to the left. Reference is now made to Figs 4-7 in order to illu¬ strate the finishing of a cable layer 6 and the beginning of a new cable layer 8. Fig. 4 shows that the leading con¬ ductor 1 is caused to engage with the flange 7 of the drum 4. As the drum continues to rotate, the flange 7 of the drum causes the conductor 1, in cooperation with the suc¬ ceeding conductor 2, to climb onto the conductor 2 and be wound on the finished cable layer 6, see Figs 2 and 5. Subsequently, the conductor 2 is caused by the flange 7 and the succeeding conductor 3 to climb onto the conductor 3 and follow the conductor 1 in the new cable layer 8, see Fig. 6. In the same manner, the succeeding conductor(s) 3 are caused to climb onto the subsequent conductor and to follow the preceding conductor 2, see Fig. 7. This results in the sequence of the conductors 1, 2 and 3 being maintained, layer by layer, which is most important when the cable unit is to be unwound from the drum 4 in order to be laid.

As a new cable layer 8 is begun, the stand 10 and the deflecting rollers 11-13 will be tilted to the other posi- tion of equilibrium and incline in the winding direction, whereby the advancing angle of the conductors is reversed, i.e. the conductors 1, 2 and 3 are advanced to the drum 4 at a constant and equally large angle to the axis of rota¬ tion of the drum. The invention is based on the knowledge that by indi¬ vidual guiding of the conductors included in the cable unit it is possible to achieve optimal winding thereof on

a drum. The conductors are guided to the drum, offset relative to each other both in the vertical and in the horizontal plane. The axially leading conductor 1 in the winding direction is caused to be always arranged in hori zontal direction before the other conductors 2 and 3 of the unit. When for example the winding is effected from the right to the left, as shown in Fig. 1, the conductor is the horizontally leading one, i.e. to the left of the conductor 2 which is positioned to the left of the conduc tor 3. Moreover, in vertical direction, the conductor 1 i oriented above the conductor 2 which, in turn, is oriente above the conductor 3. As a result, the respective points of engagement a, b and c of the conductors on the drum ar spaced from each other both in axial and in circumferen- tial direction. The point of engagement a of the conducto 1 thus is positioned in the direction of rotation of the drum after the point of engagement b of the conductor 2 which, in turn, is positioned after the point of engage¬ ment c of the conductor 3, see Fig. 3. This displacement; in circumferential direction of the points of engagement is essential for the beginning of a new cable layer. Sinc the conductors are helically wound on the drum (owing to their thickness), a wedge-shaped gap will be formed for the conductor 1 when this is at the end of a cable layer. The wedge-shaped gap is defined by the end 7 of the drum and the succeeding conductor 2. Owing to the displacement of the points of engagement a and b in circumferential direction (a before b in the direction of rotation R), th conductor 1 is caused by the drum end 5 and the conductor 2 to evenly climb onto the latter and begin a new cable layer, see Fig. 5. Correspondingly, the conductor 2 and the conductor 3, respectively, are caused to follow the preceding conductor in the new cable layer 8, see Figs 6 and 7. As the new cable layer 8 is begun, the stand 10 is tilted so that the conductor 1 is positioned in the hori¬ zontal plane before the other conductors 2 and 3, respec¬ tively, of the unit, as described above. At the beginning

of the new cable layer 8, as illustrated in Figs 4-7, the stand will thus be caused to tilt from inclination to the right to inclination to the left in the Figure, as illu¬ strated in Fig. 1. The mutual displacement of the conduc¬ tors in horizontal direction corresponds approximately to the thickness of a conductor.

The invention is not restricted to what has been described above and shown in the drawings, but can be modified within the scope of the claims.