GB2353415A - Coaxial cable assembly involving wire stripping and termination - Google Patents

Abstract

The assembly has outer and inner insulating jackets 2, 4 and intermediate braid 3 and, within jacket 4, multiple coaxial cables 5 with drain wires 6. Both braid 10 and underlying insulation 11 of each cable 5 are stripped by applying a voltage using flat electrodes 30. This breaks the braid and melts the underlying dielectric 11. Drain wires 6 are individually insulated using an oversize heat shrink sleeve 40. Connectors 50 and (70, Figure 3 (b)) are then attached to the ends of the cables to provide the complete assembly (100).

Description

2353415 "A coaxial cable production process" The. invention relates to

production of cable assemblies having connectors at the ends. More particularly, the invention relates to production of such cable assemblies having multiple coaxial wires and different connectors at the ends. Such cable assemblies are typically used for intra-rack connections in telecommunications equipment.

Such cable assemblies are rather complex and therefore the prior approach has been to perform most of the operations manually. This has tended to lead to production 10 inefficiency and quality problems.

It is therefore an object of the invention to provide a production process which both involves a larger degree of automation and provides excellent quality.

According to the invention, there is provided a method of producing a cable assembly having a coaxial cable with an outer insulation jacket, a braid, and an inner insulation jacket surrounding a plurality of individual conductor wires each having a braid in contact with a drain wire, an insulating jacket, and an inner conductor, the method comprising the steps ofi cutting cable into pre-set lengths; preparing the cable ends by stripping the cable outer jacket, the braid and the inner jacket according to a product specification; 25 stripping braid from the exposed conductor wires by contacting each conductor wire at a pre-set location with a pair of opposed electrodes, applying a voltage across the electrodes sufficient to break the braid, and stripping away the excess braid to expose the insulator; 30 connecting terminations of the conductor wires and the drain wires to a connector at each end of the cable and covering the terminations with a housing to provide a cable assembly; and testing the cable assembly.

In one embodiment, the electrodes have flat wire-contacting surfaces.

Preferably, the applied electrode voltage is in the range of 2.0 V to 4. 5V.

In another embodiment, the wires comprise, in order from the outside, a braid, a dielectric, and the conductor core, and the electrodes are controlled to cause the dielectric to heat and break so that it is stripped off together with the braid.

Preferably, the drain wires are insulated after stripping the conductor wires.

In another embodiment, the drain wires are insulated by sliding an oversize sleeve over the exposed section of drain wire and heating to shrink the sleeve onto the drain wire.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: - Fig. I is a diagrammatic cross-sectional view of a cable for production of a cable assembly; Fig. 2 is a diagrammatic cross-sectional view of an individual wire of the cable; and Figs. 3 (a) and 3(b) are together a flow diagram illustrating a production process of the invention.

Referring to Figs. I and 2, there is shown a cable I for use in production of a cable assembly. The cable I comprises an outer insulation jacket 2, a braid 3, an inner insulation jacket 4, and eight coaxial wires 5. Each Aire 5 has an associated drain wire 6. An individual wire 5 is shown in Fig. 2. It comprises an outer braid 10, a foamed PP dielectric layer 11, an FEP insulation layer 12, and a solid copper conductor 13. The drain wire 6 is shorted to the braid 10 and is used at the terminations to make connections at the connectors.

The cable I is used to produce a cable assembly 100 shown at the end of the flow diagram of Figs. 3(a) and 3(b). In a step 15, a specified length of the cable I is cut by drawing it from a reel and automatically cutting at a fixed position beyond the reel. In step 16, there is a cable preparation. A plastics hosing 20 is used to hold three sections of a connector together. It is slid onto the cable 1, as is a ferTule 21 for the other end. Both ends are then prepared. One prepared end is shown in Fig. 3 (a), in which the outer jacket 2 is marked and cut at a particular location. The braid 3 and the inner jacket 4 are then likewise marked and stripped to expose the eight wires 5 and eight drain wires 6. A tape 22 is temporarily wound around the exposed end of the braid 3 to prevent fraying. The insulation jackets 2 and 4 are stripped using stripping tools having flat blades which cut only to the required depth and allow the excess to be pulled off The braid 3 is cut using steel blades which penetrate the braid. Both ends of the cable I are prepared, with the relative positions of stripping being set by the particular product specification.

The braid 10 and the dielectric layer I I of the individual wires 5 are then stripped at a location less than 10 mm beyond the cut end of the inner insulation jacket 4. This is performed at both ends, again according to the product specification. The wire stripping is performed in a simple and quick manner using a pair of flat electrodes or blades 30.

When the blades 30 contact the wire 5, the braid provides a current path. However this is only for a very short duration of less than I second is because the voltage level is set in relation to the braid thickness to cause it to separate like a fuse in this time period. The voltage is in the range of 2.0 to 4.5V and the braid draws current until sufficient power is provided to break the braid. Also, because the blades 30 are flat, there is sufficient applied pressure to cause the dielectric layer I I to melt at that location. The braid 10 and the dielectric layer I I are then both easily pulled off to reveal the insulation layer 12. The particular location for the blades 30 to contact the wire 5 is marked beforehand.

The drain wires 6 on one end of the cable are then insulated in step 35. This is performed by sliding an oversize plastics sleeve 40 of heat shrink material over each of the eight drain wires 6. There is a difference of 0.9mm between the inner diameter of the sleeve and the outer diameter of the wire 6. The sleeve 40 is then shrunk in situ by a warm air stream providing a temperature of approximately 190'C.

As indicated by the step 45, the wires 5 and the insulated drain wires 6 at one end are connected to a large IDC connector 50 at one end. This is performed using a commercially-available connectorising machine. The operator checks beforehand to ensure that the collar 21 had previously been slid onto the cable 1, and that it has the correct orientation.

In step 55, sub-sets of the wires 5 and the drain wires 6 at the other end are terminated in three small sections 60 which together form a connector. The operator ensures that the housing 20 is present and that it has the correct orientation.

The three sections 60 are then clipped together as a connector and the housing 20 is slid over them to complete a single connector 70 for that end of the cable 1. The housing 20 is secured in position by a tie wrap 71 tightened around a. groove at the inner end of the housing 20 and the cable 1. The required tension is chosen for the product specification and is set in the tie wrap gun.

In step 85, the collar 21 for the large connector 50 is crimped in position to securely surround the cable I and the inner end of a hood of the connector 50. The hood is in two halves which completely cover the wire terminations in the connector 50. Preparation for crimping involves peeling back the braid 3 by 4-7mm, gently pushing the cable with the 5 exposed inner jacket 4 into the hood, and pulling the braid 3 over the end of the hood. The collar 21 is then crimped to press against the braid 3 and the hood inner end.

The connectors at both ends are labelled in step 86, and the completed cable assembly 40 is tested in step 87. Testing involves connection of both connectors to a test fixture and transmitting various signals through the cable to perform continuity and high voltage breakdown at 50OV, 100%.

The invention provides a structured approach to production of cable assemblies from complex cable and connector arrangements, with excellent quality. It has been found that the manner of stripping the individual wires 5 for simultaneous stripping of both braid and an underlying dielectric layer provide excellent efficiency without damaging the inner insulation or conductor. Another important aspect is the manner of insulating the drain wires. This is very effective and efficient and also allows both the wires 5 and the drain wires 6 to be connectorised in a highly efficient manner with automated machines.

The invention is not limited to the embodiments described but may be varied in construction and detail within the scope of the claims.

Claims (8)

-6Claims

1. A method of producing a cable assembly having a coaxial cable with an outer insulation jacket, a braid, and an inner insulation jacket surrounding a plurality of 5 individual conductor wires each having a braid in contact with a drain wire, an insulating jacket, and an inner conductor, the method comprising the steps of:cutting cable into pre-set lengths; preparing the cable ends by stripping the cable outer jacket, the braid and the innerjacket according to a product specification; stripping braid from the exposed conductor wires by contacting each conductor wire at a pre-set location with a pair of opposed electrodes applying a voltage 15 across the electrodes sufficient to break the braid, and stripping away the excess braid to expose the insulator; connecting terminations of the conductor wires and the drain wires to a connector at each end of the cable and covering the terminations with a housing to provide a 20 cable assembly; and testing the cable assembly.

2. A method as claimed in claim 1, wherein the electrodes have flat wirecontacting 25 surfaces.

3. A method as claimed in claim 2, wherein the applied electrode voltage is in the range of 2.OV to 4.5V.

4. A method as claimed in any preceding claims, wherein the wires comprise, in order from the outside, a braid, a dielectric, and the conductor core, and the electrodes are controlled to cause the dielectric to heat and break so that it is stripped off together with the braid.

5 5. A method as claimed in any preceding claim, wherein the drain wires are insulated after stripping the conductor wires.

6. A method as claimed in claim 5, wherein the drain wires are insulated by sliding 10 an over-size sleeve over the exposed section of drain wire and heating to shrink the sleeve onto the drain wire.

7. A method substantially as described with reference to the drawings.

8. A cable assembly whenever produced by a method as claimed in any preceding claim.