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(11) | EP 0 463 824 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Cable tapping connector |
| (57) The connector (22) comprises a two part connector housing (24, 26) which receives
and holds a cable portion (10). A contact assembly (44) movably mounted within the
housing (24) comprises a hollow outer body (48) of non-conductive material and a conductive
contact (52) mounted within the hollow outer body (48) and movable lengthwise within
it. The hollow outer body (48) has a tapered penetrable end portion (60) which, when
the hollow outer body (48) is moved relative to the housing (24), penetrates at least
the outer covering of a received cable portion (10). Following penetration of the
cable by the penetrable end portion (60), the contact (52) is advanced to break through
the end portion (60) and establish electrical contact with the cable central conductor.
Where the cable portion is a coaxial cable, conductive knife blades (36) may be provided
to penetrate the outer casing of the cable and establish electrical contact with the
outer conductor thereof. |
[0001] The present invention relates to electrical connectors and in particular to connectors having a contact probe which penetrates the outer layers of a cable to make electrical contact with a central conductor.
[0002] The present invention has particular application when used with coaxial cables, to provide an electrical tap connection to the central conductor thereof, although it is not limited to such use.
[0003] A particular problem associated with tapping connectors is that of preventing the probe contact from becoming dirty as it is driven through the outer layers of a cable prior to making contact with the central conductor. Dirt collected on the probe contact surface can result in a poor electrical connection. between the probe and conductor. The problem is particularly acute in data communication networks using coaxial cable. In addition to the need to maintain good electrical contact to avoid degradation of signals entering or leaving the cable via the tap connection, the earthed outer shield of the cable must not be allowed to contact either the central conductor or the probe of the tapping connector. Many coaxial cables have an outer shield of braided copper wire and, as the probe is forced through the shield, strands of the copper wire may be carried along with the probe and into contact with the central conductor.
[0004] One coaxial tap connector which attempts to overcome these problems is described in U.S. patent no. 4437722 (Bianchi). Each of the two probes used (one probe entering from either side of a cable) has a tapered dielectric body with a metal tip. This is to ensure that, when in position with the metal tip of the probe in contact with the central conductor, the outer surface of the probe in contact with braided outer conductor is non-conductive such that the probe does not provide a short circuit path between the central and outer conductors. It is a particular feature of US 4437722 that the outer body of the probe is with with no ridges or projections at the junction of the metal tip and the dielectric body. By use of such a probe contact, the connector of US 4437722 seeks smooth penetration of the outer layers of a coaxial cable such that the outer braided conductor is not pushed inwards into contact with the central conductor.
[0005] Another coaxial tap connector which attempts to overcome such problems is described in European patent specification EP-A-0109229. In a first embodiment, a spring-biased probe contact is rotated as it is driven through the outer layers of a coaxial cable to "wipe" the probe contact surface in order to prevent the build up of debris thereupon. In a second embodiment, the outer surface of the probe contact is provided with a self-tapping screw thread such that the probe threads its way through the outer layers of the cable rather than being pushed through. The probe contact of the second embodiment is again spring-biased and, as it is rotated to screw it into the cable, the probe and thread surfaces are "wiped" to prevent the build up of debris. As with the probe contact of US 4437722, those of EP-A-0109229 are in the form of a dielectric body with a metal tip.
[0006] In order to prevent these probes picking up debris or dragging the outer layers of the cable with them as they are inserted, the probes should be manufactured with surfaces as smooth as possible. This however requires great precision and care in manufacture.
[0007] In accordance with the present invention there is provided an electrical connector comprising a connector housing, adapted to receive and constrain a cable portion, and a contact assembly, the contact assembly comprising a hollow outer casing of non-conductive material movable relative to the connector housing to penetrate at least the outer covering of a cable portion constrained by the housing, and a contact of conductive material mounted within the hollow outer casing and movable lengthwise within it, the hollow outer casing having a penetrable end portion at least substantially closing the end thereof, and the contact being movable within the hollow outer casing to break through the said end portion, when the hollow outer casing has penetrated at least the outer covering of a cable constrained by the housing, to make electrical contact with the central conductor of the cable portion.
[0008] The penetrable end portion of the hollow outer casing may smoothly taper to a point to provide improved penetration of the outer layer or layers of the cable portion being tapped, and the contact mounted within the hollow outer casing may be movable to break through the hollow outer casing at that tapered point. The pentrable end portion is preferably configured such that, when the contact breaks through it, the broken parts of the penetrable end portion move away from the contact.
[0009] Where the cable to be tapped is a coaxial cable, the connector may include means, such as conductive knife blades mounted within the connector housing, to penetrate the outer casing of the coaxial cable and make electrical contact with the outer conductor of the cable.
[0010] The connector housing may include resilient means positioned to urge a received cable against the contact assembly.
[0011] The electrical connector of the present invention overcomes the problems of debris collection described above with reference to the prior art devices by the use of the non-conductive hollow outer casing around the tap connector contact. Debris collected during penetration of the outer layers of a cable will accumulate on the outer surface of the penetrable end portion of the hollow outer casing. When the contact breaks through the hollow outer casing, preferably at a point adjacent the cable central conductor, the broken parts of the penetrable end portion and the collected debris will be pushed away from the contact thereby minimising the amount of dirt and debris which the contact may collect on its way to the cable central conductor.
[0012] Rotation of the hollow outer casing as it penetrates the outer layer or layers of the cable may assist in reducing the amount of debris collected in a similar manner to the rotated contact described in EP-A-0109229 referred to above.
[0013] One particular preferred embodiment will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a partially sectioned elevation of a portion of a coaxial cable tap connector embodying the present invention;
Figure 2 shows the position, relative to a tapped coaxial cable, of an earth shield contact used in the connector of figure 1;
Figure 3 is a sectional elevation of a part of the connector of figure 1 with the central conductor contact inserted in a coaxial cable; and
Figure 4 is a reduced scale perspective view of the connector of figure 1 attached to a coaxial cable.
[0014] Referring initially to figure 2, a coaxial cable 10 consists of a central conductor 12 in the form of a copper core around which is a layer of polytetrafluoroethane (PTFE) insulation material 14. Radially outward of the layer of insulation material 14 are layers of polar film 16, copper braiding 18, and an outer layer of insulation material 20 respectively.
[0016] The connector 22 has a two part housing comprising a body portion 24 and a concave cover 26. The body 24 has an upper surface 28 which the edges of the cover 26 abut. Resilient tongues 30 extending from the upper surface 28 engage a lip 32 on the inner surface of the cover 26 to hold the cover 26 against the upper surface 28. The end of the resilient tongues 30 and the lip 32 are chamfered (as shown in figure 1) such that the cover 26 has a snap-fit engagement with the body 24. A ridge 34 adjacent the edge of the upper surface 28 locates the edges of the cover 26 relative to the body 24.
[0017] The cover 26 and upper surface 28 define an aperture therebetween in which a coaxial cable 10 is received. On either side of the aperture, extending perpendicular to the upper surface 28, are conductive knife blades 36. The spacing of the knife blades 36 is less than the outer diameter of the coaxial cable layer of copper braiding 18 such that, when a cable 10 is pressed into the gap between the knife blades 36, they cut through the outer insulation 20 of the cable and make electrical connection with the layer of copper braiding 18.
[0018] The relative positions of a knife blade 36 and constrained cable 10 are shown in figure 2. As can also be seen from figure 2 the knife blade 36 has an elongated portion 38 extending therefrom to which electrical connection may be made.
[0019] Returning to figure 1, the inner surface of the cover 26 has three ridges 40,42 extending therefrom towards the cable 10. The ridges 40, 42 are substantially parallel to each other and to the axis of the cable. The two outer ridges 42 extend further from the cover 26 than does the central ridge 40 such that, in addition to pressing the cable 10 against the upper surface 28, the three ridges 40, 42 act to centre the cable with respect to the connector.
[0020] A contact assembly 44 is mounted below the upper surface 28 and is movable through an aperture 46 therein. The contact assembly 44 comprises a hollow outer casing 48, a contact mounting 50 and a conductive contact 52. A part of the outer surface 54 of the hollow outer casing is threaded and engages a corresponding threaded bore on the internal surface 56 of a cylindrical extension 58 below the upper surface 28 and about the aperture 46 therein.
[0021] At the end adjacent the cover 26, the hollow outer casing 48 tapers to a conical point 60. With the contact assembly 44 in a retracted position (not shown) the conical point 60 of the hollow outer body lies below the level of the upper surface.
[0022] Due to the engagement of the threaded portions 54, 56, rotation of the hollow outer casing 48 in a first sense causes the conical point 60 to protrude above the level of the upper surface 28.
[0023] With a cable 10 held in position against the upper surface 28, rotation of the hollow outer body 48 causes the conical point 60 to penetrate the outer layers 20,18,16 of the coaxial cable. The conical point 60 penetrates the layer of PTFE insulation material 14 around the copper core 12 of the coaxial cable 10. As shown in figure 1, the depth of penetration is limited by the engagement of a shoulder 62 on the hollow outer body 48 with the rim 64 of the cylindrical extension 58. To assist with rotation of the hollow outer body 48, its outer surface 66 at the opposite end to the conical point 60 is hexagonal in form to allow use of sockets or box spanners to rotate it.
[0024] Within the hollow outer body 48 is the contact mounting 50 which holds the conductive contact 52. The outer surface 68 of the contact mounting 50 is threaded and engages a corresponding thread 70 on the inner surface of the hollow outer body 48. Movement of the contact mounting 50 and contact 52 relative to the hollow outer body 48 is achieved by rotation of the contact mounting 50. A profiled aperture 72 is provided in the lower end of the contact mounting 50 allowing the insertion of a suitably shaped tool to engage the contact mounting 50 and rotate it.
[0025] The conductive contact 52 is shrouded by the contact mounting 50 over its upper portion with the exception of a tapered point 74 at its upper end. When the conical point 60 of hollow outer body is being pushed through the outer layers of a cable, the tapered point 74 of the contact 52 is positioned in a correspondingly shaped aperture within the conical point 60.
[0026] When the conical point 60 has penetrated the cable to the required depth, the contact mounting 50 is rotated within the hollow outer body 48. This rotation causes the tapered point 74 of the contact 52 to break through the conical point 60 of the hollow outer body 48. Further rotation of the contact mounting 50 brings the tapered point 74 into contact with the copper core 12 of the cable as shown in figure 3.
[0027] Once the tapered point 74 of the contact has broken through, the broken pieces 60a, 60b of the conical point 60 are pushed away from the contact 50 such that any debris which has accumulated on the conical point 60 during its passage through the outer layers of the cable, and any strands of the copper braiding 18 of the cable shield, do not come into contact with either the tapered point 74 of the contact or the copper core of the cable.
1. An electrical connector comprising a connector housing (24, 26), adapted to receive
and constrain a cable portion (10), and a contact assembly (44), characterised in
that the contact assembly (44) comprises a hollow outer casing (48) of non-conductive
arterial movable relative to the connector housing (24, 26) to penetrate at least
the outer covering (20) of a cable portion (10) constrained by the housing (24, 26),
and a contact (52) of conductive arterial mounted within the hollow outer casing (48)
and movable lengthwise within it, the hollow outer casing (48) having a penetrable
end portion (60) at least substantially closing the end thereof, and the contact (52)
being movable within the hollow outer casing (48) to break through the said end portion
(60) when the hollow outer casing (48) has penetrated at least the outer covering
(20) of a cable (10) constrained by the housing, to make electrical contact with the
central conductor (12) of the cable portion (10) .
2. An electrical connector according to claim 1 in which the penetrable end portion (60)
is so shaped that, as the contact (52) breaks through it, the broken parts (60a,60b)of
the penetrable end portion are moved away from the contact (52).
3. An electrical connector according to claim 1 or claim 2, wherein the penetrable end
portion (60) is a conical shell and the contact (52) breaks through substantially
at the point thereof.
4. An electrical connector according to any of claims 1 to 3 wherein the connector housing
(24, 26) is adapted to receive and constrain a coaxial cable portion (10) and comprising
means (36) for penetrating the outer casing (20) of the coaxial cable portion (10)
to make electrical contact with the outer conductor (18) thereof.
5. An electrical connector according to claim 4, wherein the said means for penetrating
the outer casing (20) of the coaxial cable portion (10) comprise a pair of opposed,
conductive knife blades (36), the spacing of the knife blades (36) being less than
the outside diameter of the coaxial cable portion outer conductor (18).
6. An electrical connector according to any preceding claim, wherein the connector (24,
26) housing includes resilient means (40,42) positioned to urge a received cable (10)
against the contact assembly (44).