System and method for straightening electrical cables

Abstract

The invention provides a straightening device (100), for straightening an electrical cable (200). The straightening device comprising a first roller (110) and a second roller (120) forming a roller pair (130). The roller pair is arranged to allow feeding the electrical cable between the first and second roller. In operation, the roller pair is arranged to induce a torsional load (207) on the electrical cable. Preferably, the straightening device is arranged to induce torsional loads both in a positive and a negative direction relative to the feeding direction (150) of the cable. Advantageously, inducing a torsional load allows straitening the electrical cable by reducing any residual twist present in the cable as it is unwound from a reel.

Description

[0001] System and method for straightening electrical cables

[0002] This invention relates to a straightening device for an electrical cable according to the pre-amble of claim 1. The invention furthermore relates to a method for straightening such a cable. Moreover, the invention relates to an electrical cable processing machine comprising a straightening device.

[0003] Processing machines for (flexible) electrical cables typically include multiple stations at which the cable is processed in a step-wise fashion, resulting in a final processed end product. Examples of the processing steps in one of the (dedicated) stations are: stripping, core separation, removing insulation, twisting, crimping, splicing, labelling or marking, plug assembly, cutting to appropriate length, etc.

[0004] The electrical cable to be processed may be a low voltage cable. Such (flexible) cables may comprise a single conductor. Alternatively, they may comprise multiple strands, optionally twisted or stranded around each other. Alternatively still, such cables may be of a co-axial type, comprising a single or multiple inner or core wire(s), an inner insulation coating, optionally a wrapped foil, a screening braid, and an external sheath providing insulation and mechanical protection to the cable.

[0005] The electrical cable to be processed typically is supplied to the processing machine from a cable drum, reel, or bobbin. When unwound from such a drum / reel / bobbin, the electrical cable, due to its flexibility, often is bent or twisted. Any of the subsequent processing steps consequently is detrimentally affected, as the bending and / or twisting of the electrical cable hampers proper alignment of a cable end to the processing stations. In order to alleviate this problem, the electrical cable usually is drawn through a straightening device prior to feeding the straightened cable to the (first) processing station of the cable processing machine.

[0006] A typical straightening device for electrical cables, as disclosed for examples in US2017173652A1, comprises of a first and a second row or rollers positioned adjacent to each other. The distance and overlap between the rollers of these two rows may be adapted in order to accommodate electrical cables with different (outer) diameters, and to induce bending of the cable into an undulation for straightening the cable. The rollers in both rows are rotatable about parallel rotation axes and these rotation axes are typically arranged in a line on a shared carrier for each row. The two rows of rollers (or roller lines) may be parallel to each other or may be angled to each other. Each roller may comprise a groove for centring the electrical cable. These groves may be V-shapes, U-shaped, or may have a semi-circular shaped cross section. The rotation axes of the first row usually are shifted in the cable feeding direction relative to the axes of the second row. This allows the rollers to be interlaced for forcing the cable into the undulation when pulled through the straightening device. Finally, it is not uncommon to use two of such straightening devices positioned sequentially along a feeding direction of the electrical cable. In the first straightening device, the two rows may be vertically displaced relative to each other, so as to form a usually fixed lower row and a positionable upper row. In the second straightening device, the rows may be horizontally displaced, so as to form a (optionally fixed) left row and a (optionally positionable) right row.

[0007] A drawback of these known straightening devices is that the electrical cables once drawn through them often are insufficiently straightened, even when two devices are applied in series as described above. Consequently, the cable processing stations positioned downstream of the straightening device(s) may still have difficulties with processing a cable end, for instance due to eccentric positioning of the cable end in a processing station as a result of residual twisting / bending of the cable. A further drawback of these known straightening devices is that they have a large number of adjustment parameters. As described above, an operator may adjust the diameter of the rollers; the overlap of the two roller lines; the angle between the roller lines for influencing the amount of overlap along the feeding direction; the overlap to increase or decrease along the feeding direction; the groove shape / form factors; etc. Proper adjustment of all these parameters requires a lot of know-how. Especially with untrained personnel, when changing over from one cable type to the next, this results in non-reproducible straightening results of the electrical cable. Another disadvantage of these known straightening devices is that they are prone to causing a loop in the cable when the pulling device drawing the electrical cable through the straightening device in a cable processing machine is intermittently operated. The effects of the sudden stopping of the pulling device, the (mass) inertia of the fast-spinning rollers of the straightening device, and the undulating path of the electrical cable through the straightening device cooperate to induce a cable loop forming between the straightening device and the pulling device, or between one roller and the next within the straightening device. This not only causes large forces on the cable to smooth / flatten the cable loop once the pulling device is reactivated during the next cycle, resulting in length deviations of the electrical cable, it also induces the risk of the cable loop getting snagged in / on components or parts of the cable processing machine.

[0008] The invention intends to alleviate at least one of the above-mentioned drawbacks of the prior art. The invention proposes a straightening device providing superior and consistent straightening results advantageously having only a single adjustment parameter.

[0009] The objective of the invention is solved by the features of the independent claims. Advantageous further developments are shown in the figures and in the dependent claims.

[0010] According to an aspect of the invention, a straightening device is provided comprising a first roller and a second roller forming a roller pair; wherein the roller pair is arranged to allow feeding the electrical cable between the first and second roller; wherein, in operation, the roller pair is arranged to induce a torsional load on the electrical cable. Advantageously, inducing a torsional load allows straitening the electrical cable by reducing any residual twist present in the cable as it is unwound from a reel. The straightening device according to the invention contrast with the known straightening devices in that the later induce a (undulating) bending in the cable. Moreover, advantageously, the straightening device according to the invention obviate the need to adjust the overlap between subsequent the roller pairs. Furthermore, adaptation of the groove shape to the cable specification, as necessary in the known straightening devices can be omitted.

[0011] In an embodiment, the straightening device preferably comprises the roller pair forming an interlocked roller pair with a first rotation axis of the first roller and a second rotation axis of the second roller of the interlocked roller pair oriented at an angle (alpha) to each other. Advantageously, the non-parallel orientation of the two roller axes induces the torsional load on an electrical cable feed between the two rollers. It is to be understood that "interlocked" in the sense of the invention indicates a roller pair in which the axes of the rollers are non-parallel. Moreover, in a "noninterlocked" roller pair both axes of the rollers are positioned parallel.

[0012] In an embodiment, the angle alpha is in the range 0° < alpha < 70°, preferably in the range 20° < alpha < 60°, more preferably in the range 30° < alpha < 50°, preferred alpha = 45 deg. Advantageously, the torsional load is dependent on the angle alpha. Optionally, the straightening device maybe arranged such that the angle alpha is controllable. This allows the torsional load to be adjusted in line with the state in which the electrical cable is unwound from the reel.

[0013] In an embodiment of the straightening device, the first rotation axis is oriented at an angle 90° + alpha / 2, and the second rotation axis is oriented at an angle 90° - alpha / 2 relative to the feeding direction of the electrical cable. Advantageously, this allows equal torsional forces to act on both sides of the cable. Moreover, this arrangement avoids pulling the cable away at right angles to the conveying direction.

[0014] In another embodiment, the first and the second roller of the interlocked roller pair have a convex shape, preferably have the same convex shape. Advantageously, this allows supporting the electrical cable in a linear movement along the feeding or conveying direction and allows providing the torsional forces in a direction perpendicular to the feeding direction.

[0015] In yet another embodiment, the convex shape is dependent on the angle alpha between the first rotation axis and the second rotation axis. Advantageously, this allows creating a gap between the first roller and the second roller which is constant over the width of the rollers. The gap preferably is adjustable for allocating cable types having different diameters, and for adjusting the contact force of the rollers in a roller pair on the cable.

[0016] In an embodiment of the straightening device, a distance between the first roller and the second roller of the interlocked roller pair is controllable. Advantageously, controlling the distance between the rollers allows for adjusting the straightening device to different electrical cable types. Moreover, advantageously, the inter-roller distance is the single parameter needed to be adjusted for tuning the straightening device to different electrical cable types.

[0017] In an embodiment, the straightening device is arranged to apply a contact force on the electrical cable between 5N and 100N, preferably between ION and 50N, more preferably still between 15N and 30N. Advantageously, the contact force may be adjusted pneumatically.

[0018] In an embodiment, the straightening device comprises a plurality of interlocked roller pairs. Advantageously, each of the interlocked roller pairs induces a torsional load on the electrical cable as it is routed through the straightening device.

[0019] In an embodiment, subsequent interlocked roller pairs in the straightening device are oriented such that the torsional load is inducible alternatingly in a positive (or clockwise) and in a negative (or anticlockwise) direction relative to the feeding direction of the cable. Advantageously, the subsequently positioned interlocked roller pairs are mirrored relative to a plane perpendicular to the cable feeding direction. Moreover, this arrangement allows reducing any residual twisting in the electrical cable, rather than adding a twist in case the subsequent roller pairs in the straitening device were non-mirrored, i.e. would all induce a torsional load in the same direction relative to the cable feeding direction. The latter, in a worst-case scenario, could lead to twist pile-up before the cable straightening device (in the direction of the reel / bobbin), and possibly also after the cable straightening device (in the direction of the processing stations of the cable processing machine).

[0020] In another embodiment, a centring element is positioned in front of at least one of the interlocked roller pairs for guiding the electrical cable to a centre point of the roller pair. Advantageously, the centring element contributes to preventing misalignment between the electrical cable and the roller pair. The centring element is not necessarily adaptable to the diameter of the cable to be straightened. Advantageously, it simply limits the movement of an electrical cable in a direction perpendicular to the cable feeding direction. Thus, the centring element contributes to roughly maintaining the cable positioned near the centre point of its associated interlocked roller pair. As a further advantage, a centring element having an opening between 1.3 and 5 times, preferably between 1.5 and 3 times, the diameter of the electrical cable avoids the need to change the centring element upon change-over to a cable type having a different diameter. Moreover, this avoids an error source, and thus reduces set-up costs of the cable processing machine.

[0021] In yet another embodiment, the straightening device further comprises a noninterlocked roller pair positioned relative to the cable feeding direction at least prior or post the interlocked roller pair, respectively pairs. Advantageously, the noninterlocked roller pair prevents any induced torsion to propagate into upstream or downstream assemblies or modules of a cable processing machine

[0022] According to another aspect, the invention provides a cable processing machine, for processing an electrical cable, comprising a straightening device as described above, and further comprising a cable conveying device for pulling the electrical cable through the straightening device.

[0023] According to a further aspect, the invention provides a method for straightening an electrical cable, the method comprising: feeding the electrical cable between a first roller and a second roller; and inducing a torsional load on the electrical cable.

[0024] In an embodiment, the method further comprises inducing the torsional load on the electrical cable alternatingly in a positive (clockwise) and in a negative (anticlockwise) direction relative to the feeding direction of the cable.

[0025] Further advantages, features and details of the invention will be apparent from the following description, in which embodiments of the invention are described with reference to the drawings.

[0026] The list of reference signs as well as the technical content of the patent claims and figures are part of the disclosure. The figures are described coherently and comprehensively. Identical reference signs indicate identical components, reference signs with different indices indicate functionally identical or similar components. The figures show: Fig. 1 a first embodiment of the straightening device according to the invention;

[0027] Fig. 2 a detail of a roller of the straightening device;

[0028] Fig. 3 a detail of an interlocked roller pair;

[0029] Fig. 4A force components induced on the electrical cable by a straightening device according to the invention;

[0030] Fig. 4B tortional force components induced on the electrical cable by a straightening device according to the invention;

[0031] Fig. 5 another embodiment of the straightening device according to the invention; Fig. 6 cable processing machine according to an aspect of the invention.

[0032] Fig. 1 schematically shows an example of a straightening device 100 according to the invention. Straightening device 100 comprises a first roller 110 and a second roller 120 forming a roller pair 130. The roller pair forms an interlocked roller pair 130 arranged to allow feeding an electrical cable 200 between the first 110 and second roller 120 in a feeding direction 150. The first and second rollers are rotationally mounted in a support bracket 140. The support bracket may be positioned on a support mount (not shown) functioning as an (mechanical) interface to a cable processing machine 1. Straightening device 100 may optionally comprise a centring element 141 contributing in preventing a misalignment between electrical cable 200 and roller pair 130. Advantageously, it limits the movement of electrical cable 200 between the first 110 and second 120 roller in a direction perpendicular to the cable feeding direction 150. Thus, centring element 141 contributes to maintaining cable 200 positioned near the centre point 131 of its associated interlocked roller pair 130.

[0033] In operation, roller pair 130 is arranged to induce a torsional load 207 on electrical cable 200. Advantageously, inducing the torsional load 207 allows straightening the electrical cable 200 by reducing any residual twist present in the cable as it is unwound from a reel (not shown). Moreover, inducing the torsional load for reducing the intrinsic torsion present in the cable as it is pulled from a drum prevents the need for forcing the cable in an undulating path, and hence reduces the risk of loopformation. Fig. 2 schematically shows a detail of a roller 110 of the straightening device 200. Roller 110 has rotor part that is rotationally mounted by bearing 114 around a rotation shaft 111. The rotor part of roller 110 preferably comprises a concave part 112 as a middle section, and optionally a cylindrical part 113 on at least one of its ends. Advantageously, cylindrical part 113 facilitates the manufacturing of roller 110 by providing the possibility to clamp the roller on a lathe.

[0034] Fig. 3 shows a (top view) detail of an interlocked roller pair 130. First rotation axis 111 of first (or top) roller 110 is oriented at an angle alpha relative to the second rotation axis 121 of second (or bottom) roller 120 forming interlocked roller pair 130. Moreover, preferably interlocked roller pair is positioned symmetrically relative to cable feeding direction 150. In other words, when first rotation axis 111 makes an angle 90° - alpha / 2 with cable feeding direction 150, second rotation axis 121 makes an angle 90° + alpha / 2 (or visa versa). This arrangement avoids pulling the cable away at right angles to the conveying direction

[0035] The middle concave part 112 of roller 110 preferably has a radius r(x) as a function of the position x along rotation axis 111. This radius is provided by:

[0036] Here x ranges from -\_ / 2 to L / 2, with L the length of roller 110 in the direction of rotation axis 111; ro is the radius at x=0, i.e. the radius at the thinnest diameter of roller 110; and alpha is the angle between first rotation axis 111 of first roller 110 and second rotation axis 121 of second roller 120 of roller pair 130. Preferably, second roller 120 of interlocked roller pair 130 has the same concave form or shape as first roller 110. Advantageously, this allows supporting the electrical cable in a linear movement along the feeding direction and allows providing the torsional forces in a direction perpendicular to the feeding direction.

[0037] When two cylindrical rollers are positioned in a crossed fashion with an angle alpha between their two axes, and with a distance d = 0 between their cylindrical surfaces, these cylindrical rollers touch at a single point: centre point 131. In contrast, at a distance d = 0 in interlocked (concave) roller pair 130, first roller 110 and second roller 120 form a contact line running through centre point 131 and at right angle to feeding direction 150. In operation, however, the first and second rollers 110, 120 are positioned at a distance * 0, such that a gap is present between them for allocating electrical cable 200. Advantageously, at any point along the contact line in an interlocked roller pair 130 electrical cable 200 experiences in operation a symmetrical torsional load. In contrast, between two cylindrical rollers positioned in a crossed fashion, electrical cable 200 would only experience a symmetrical torsional load at centre point 131.

[0038] In an embodiment, the distance d between first roller 110 and second roller 120 for allocating different cable types may be controllable. This may be realized with an exchangeable spacer disc 142 of appropriate thickness allocatable in support bracket 140. Alternatively, the distance may be controllable by implementing a spring loaded or pneumatic adjustment mechanism in support bracket 140. Alternatively still, it may be controllable electronically implementing an (linear) actuator. Preferably, the straightening device has an interface through which a central processing unit of cable processing machine 1 can provide control signals for adjusting the distance d between the first and second roller 110, 120 of roller pair 130.

[0039] As evident form Figs. 4A and 4B, in operation first roller 110 causes an induced force 115 on (a top side of) cable 200. This first roller induced force 115 is oriented at an angel alpha / 2 relative to the cable feeding direction 150. Hence, induced force 115 has a linear force component 116 parallel to the feeding direction and a torsional force component 117 perpendicular to feeding direction 150. Similarly, second roller 120 causes an induced force on (a bottom side of) cable 200 at an angle -alpha / 2 (not shown), resulting in second roller torsional force component 127. These torsional force components are represented in Fig. 4B looking in feeding direction 150 at a cross section of cable 200. Since the torsional force components 117, 127 engage at two radially opposite points on the cable circumference, they induce torsional load 207.

[0040] Fig. 5 shows an example of an embodiment of the straightening device according to the invention comprising multiple interlocked roller pairs. In a first example of such a multiple interlocked roller pair straightening device, the straightening device 100 comprises only multiple interlocked roller pairs (not shown in Fig 5). Preferably, straightening device 100 comprises at least two interlocked roller pairs 331, 332, 333 according to any of the embodiments as described above. More preferably, the interlocked roller pairs 331, 332, 333 are arranged in a so-called mirrored configuration. Thus, the subsequently positioned interlocked roller pairs are mirrored relative to a plane perpendicular to the cable feeding direction 150. Advantageously, the two mirrored interlocked roller pairs 331, 332 are oriented such that the torsional load 207 is inducible alternatingly in a positive (clockwise) and in a negative (anti-clockwise) direction relative to the cable feeding direction 150 (or vice versa). Moreover, this arrangement allows reducing any residual twisting or intrinsic torsion in the electrical cable, rather than adding a twist in case the subsequent roller pairs in the straitening device were non-mirrored. Thus, while in some embodiments straightening device 100 may have any positive integer number of interlocked roller pairs 331, 332, 333 (such as 2, 3, 4, 5, 6, 7, 8, etc roller pairs), preferably straightening device 100, according to this first example, comprises an odd number of pairs (such as 3, 5, 7 ,9 etc roller pairs). In particular, the odd number of pairs are alternatingly arranged in a mirrored configuration.

[0041] In a second example (shown in Fig. 5) of such a multiple interlocked roller pair straightening device, straightening device 100 further comprises a single noninterlocked or non-crossed roller pair 335. Such a non-interlocked roller pair comprises two cylindrical rollers which each rotate about an axis of rotation oriented parallel to each other and at 90° relative to the cable feeding direction 150. Advantageously, a non-interlocked roller pair 335 prevents, depending on its upstream (see Fig. 5) or downstream position relative to the interlocked roller pairs, any induced torsion to propagate into upstream or downstream assemblies or modules of cable processing machine 1 comprising straightening device 100. Thus, preferably, the non-interlocked roller pair 335 is positioned relative to the cable feeding direction either prior or post to the interlocked roller pairs. Preferably prior, as the cable will have a free-end in the down-stream direction, while it is fixed by the bobbin (or other processing machine part) in the up-stream direction. In this case, to reduce an accumulation of the torsional load, in addition to a single non-crossed roller pair 335, straightening device 100 may comprise any positive integer number of interlocked roller pairs 331, 332, 333 (such as 2, 3, 4, 5, 6, 7, 8, etc roller pairs).

[0042] In a third example of such a multiple interlocked roller pair straightening device, straightening device 100 comprises two non-interlocked roller pairs: one upstream, the other downstream of the interlocked roller pairs (not shown in Fig. 5). In this case, to balance out the torsional load, in addition to the two non-crossed roller pairs 335, straightening device 100 preferably comprises an even number of interlocked roller pairs 331, 332, 333 (such as 2, 4, 6, 8, etc roller pairs).

[0043] Fig. 6 schematically shows a cable processing machine 1 according to an aspect of the invention. Cable processing machine 1 comprises a straightening device 100 according to the first aspect of the invention, and further comprises a cable conveying device 10 for pulling the electrical cable through the straightening device 100. In the feeding direction 150 subsequent to cable conveying device 10, cable processing machine may comprise one or more cable processing stations 20,30,40.

[0044] As will be clear to the person skilled in the art, the embodiments and methods shown in the figures or described herein may also be combined and interchanged within the concept of the invention. As an example, the multiple and preferably pair-wise mirrored interlocked roller pairs may be positioned on a support mount functioning as an (mechanical) interface to a cable processing machine. Also, the non-interlocked roller pair may be positioned on such a support mount. As another example, the straightening device may have an interface through which a central processing unit of the cable processing machine can provide control signals for adjusting the distance d between the first and second roller 110, 120 of each of the roller pairs 331, 332, 333, 335 individually. List of reference signs

[0045] 1 Cable processing machine

[0046] 10 Cable conveying device

[0047] 20 Cable processing station 1

[0048] 30 Cable processing station 2

[0049] 40 Cable processing station 3

[0050] 100 Straightening device

[0051] 110 First roller

[0052] 111 First roller axis

[0053] 112 (First) roller convex part

[0054] 113 (First) roller cylindrical part

[0055] 114 (First) roller bearing

[0056] 115 Induced force first roller

[0057] 116 Linear force component first roller

[0058] 117 Torsional force component first roller

[0059] 120 Second roller

[0060] 121 Second roller axis

[0061] 127 Torsional force component second roller

[0062] 130 Interlocked roller pair

[0063] 131 Roller pair centre point

[0064] 140 Support bracket

[0065] 141 Centring element

[0066] 142 Spacer disk

[0067] 150 Cable feeding direction

[0068] 200 Electrical cable Torsional load on the cable First interlocked roller pair Second interlocked roller pair Third interlocked roller air Non-interlocked roller pair

Claims

Claims1. A straightening device (100), for straightening an electrical cable (200), comprising: a first roller (110) and a second roller (120) forming a roller pair (130); wherein the roller pair is arranged to allow feeding the electrical cable between the first and second roller in a feeding direction (150); wherein, in operation, the roller pair is arranged to induce a torsional load (207) on the electrical cable.

2. The straightening device (100) according to claim 1, wherein the roller pair (130) forms an interlocked roller pair (130) with a first rotation axis (111) of the first roller (110) and a second rotation axis (121) of the second roller (120) of the interlocked roller pair oriented at an angle alpha to each other.

3. The straightening device (100) according to claim 2, wherein the angle alpha is in the range 0° < alpha < 70°, preferably in the range 20° < alpha < 60°, more preferably in the range 30° < alpha < 50°, preferred alpha = 45°.

4. The straightening device according to claims 2 to 3, wherein the first rotation axis (111) is oriented at an angle 90° + alpha / 2, and the second rotation axis (121) is oriented at an angle 90° deg - alpha / 2 relative to the feeding direction (150) of the electrical cable5. The straightening device (100) according to any of claims 2 to 4, wherein the first (110) and the second (120) roller of the interlocked roller pair (130) have a convex shape, preferably have the same convex shape.

6. The straightening device (100) according to claim 5, wherein the convex shape is dependent on the angle alpha between the first rotation axis (111) and the second rotation axis (121).

7. The straightening device (100) according to any of claims 1 to 6, wherein a distance between the first roller and the second roller of the interlocked roller pair is controllable.

8. The straightening device (100) according to any of claims 1 to 7, wherein the straightening device is arranged to apply a contact force on the electrical cable (200) between 5N and 100N, preferably between 10N and 50N, more preferably still between 15N and 30N.

9. The straightening device (100) according to any of claims 1 to 8, wherein the straightening device comprises a plurality of interlocked roller pairs (130).

10. The straightening device (100) of claim 9, wherein subsequent interlocked roller pairs (130, 331, 332, 333) are oriented such that the torsional load (207) is inducible alternatingly in a positive and in a negative direction relative to the feeding direction (150) of the cable (200).

11. The straightening device (100) of claim 9, wherein a centring element (141) is positioned in front of at least one of the interlocked roller pairs (130, 331, 332, 333) for guiding the electrical cable (200) to a centre point (131) of the roller pair.

12. The straightening device (100) according to any of claims 1 to 11, further comprising a non-interlocked roller pair (335) positioned relative to the cable feeding direction (150) at least prior or post the interlocked roller pair, respectively pairs.

13. A cable processing machine (1), for processing an electrical cable, comprising a straightening device (100) according to any of the claims 1 to 12, and further comprising a cable conveying device (10) for pulling the electrical cable through the straightening device (100).

14. A method for straightening an electrical cable (200), the method comprising:Feeding the electrical cable between a first roller (110) and a second roller (120); andInducing a torsional load (207) on the electrical cable.

15. The method according to claim 14, further comprising inducing the torsional load (207) on the electrical cable (200) alternatingly in a positive and in a negative direction relative to the feeding direction (150) of the cable.

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