GB2156603A - Flat cable - Google Patents

Abstract

A flat cable (10) which enables adjustment of the spacing of its leads (12) to accommodate the spacing of terminals to which the leads may be connected includes bond zones (22, 24, 26) where the leads are bonded together, and free zones (28, 30, 32) where the leads are unbonded and therefore free to move apart and together. The bond and free zones are arranged in a pattern (34, 36) that repeats itself along the length of the cable. The free zones of the pattern include at least one connect zone (28) having a length (B) along the length of the cable, which is less than the width (W) of the cable, to enable slight adjustment of the lead spacing to match the spacing of the terminals to which the leads can be connected, while ensuring that the leads are maintained at approximately the terminal spacing prior to connection to the terminals. <IMAGE>

Description

SPECIFICATION Flat cable This invention relates to flat cables. Such cables commonly include a group of leads lying in a common plane, with the insulative sheaths of the leads being held together as by melting them into one another. A cable containing a large number of such leads, for example, twenty-five of them, can be rapidly attached to a group of twenty-five insulationdisplacing terminals of a connector, by forcing the cable down against the group of terminals so that each conductive core of a lead enters the proper terminal to make contact with it.

An improper connection will result if the coreto-core spacing within the cable does not accurately match the terminal-to-terminal spacing of the connector. Accordingly, it has generally been necessary to manufacture the cable to close tolerances, to ensure that its core spacing will match the spacing of connector terminals along the entire length of the cable.

A typical flat cable includes a row of conductive cores embedded in an insulation which extends continuously along the entire length of the cable. One variation, shown in U.S. Patent 4,381,208, includes free zones spaced along the length of the cable, where the cable is divided into separate leads, each including a sheath of insulation around a conductive core. Each free zone has a length which is twice the width of the cable, to provide sufficient lengths of free leads to enable their connection to components at indeterminate spacings. However, both the typical continuously-bonded cable and the variation of the invention of the above patent wherein there are free zones along the length of the cable, require accurate spacing of the conductive cores along all the bonded regions which may be used to make a connection to the insulation-displacing terminals of a connector.

According to the invention in its broadest aspect there is provided a flat cable comprising a plurality of leads, each lead including an electrically conductive core and an insulative sheath surrounding the core, the sheaths being bonded together side by side in a common plane at a plurality of short bond zones spaced along the length of the cable, and the sheaths being separate and unbonded to each other at free zones lying between pairs of the bond zones, all in a pattern that repeats itself along the length of the cable, the free zone length being greater than the bond zone length in each pattern.

The pattern can include two of such terminal-connect free zones that are separated by a cutable bond zone which has a length less than twice the width of the cable. This permits cutting a cable along the cutable bond zone, to leave ends that each have a terminalconnect free zone, thereby to minimise wastage of the cable.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings.

Figure 1 is a plan view of a section of a flat cable constructed in accordance with the present invention.

Figure 2 is a view taken on the line 2-2 of Fig. 1.

Figure 3 is a plan view of a portion of the cable of Fig. 2, which is shown connected to terminals of a connector.

Fig. 1 illustrates a flat cable 10 which includes a group of leads 1 2 that lie substantially in a common plane. That is, as shown in Fig. 2, the centre 14 of the leads lie in a common plane 16. Each lead such as 12a, includes an electrically-conductive core 18 and an insulative sheath 20 which surrounds the core. The sheaths of the leads are bonded together at each of a number of bond zones 22, 24, 26 (Fig. 1) that are spaced along the length of the cable. The leads are separate and unbonded to each other at free zones 28, 30 and 32 that lie between the bond zones.

The bond and free zones are arranged in a pattern 34, the pattern being repeated along the length of the cable, with two of such patterns 34, 36 being shown. The particular cable shown in the figures is constructed by laying a group of separate leads against one another in a common plane. The insulative sheaths 20 (Fig. 2) of the leads are of thermoplastic material, and they are heated at the bond zones and flattened, so that the thermoplastic material of the sheaths merges into a flattened cable of a height H which is less than the diameter G of each of the leads in the free zones. While the top and bottom faces of the cable are flat along each bond zone, they have multiple bumps along their free zones.

Each pattern includes a loose wire free zone 32 (Fig. 1) having a considerable length A which is much greater than the width W of the cable, such as a length A of 2 1/2 times the cable width. This considerable length permits the cable to be cut along this zone, such as at the location 38, to provide access to individual leads, as to permit connection of each lead to a different discrete component or individual connector.

The two other free zones 28, 30 of each pattern are terminal-connect free zones which are provided to enable the connection of all of the leads 1 2 to the terminals of a connector, such as the insulation-displacing terminals 40 (Fig. 2) of a connector. A connector of this type is shown in U.S. Patent 4,068,912 the terminals each having a pair of arms 41 defining an insulation-displacing and conductor-engaging slot 43 between them. The terminals may be arranged in two staggered rows 42, 44 (Fig. 3) with the terminals staggered in the rows. In order to connect the leads to the terminals, it is necessary for alternate cores 14 to be spaced a distance 2X apart which is close to the spacing 2Y of the adjacent terminals of the same row.If the leads were bonded together at the location where they are joined to the terminals 40, then it would be necessary for the cable to be manufactured so that the spacing X between cores was held to close tolerances along the entire length of the cable. The need for close tolerances in the spacing of conductive cores along the entire length of the cable would result in increased cost for the cable.

In accordance with the present invention, a cable can be used which has relatively wide tolerances in the spacing between cores along the bonded areas or bond zones of a cable.

Yet, the cable can be reliably joined to terminals that may have a slightly different spacing from the core spacing in the bond zones of the cable. This is accomplished by providing the connect zones 28, 30, which each have a limited length B, C, along the cable but with each zone length being much greater than the width G of a single lead.

The length B, C of each connect zone is less than the width W of the cable so that the spacing of the leads 12, and therefore of their cores 14, is not too different from the lateral spacing Y between terminals even though their spacings do not closely match. The fact that the leads are free of bonding attachment to one another, permits the leads and therefore their cores 14 to move slightly together or apart in order to match the spacing between the terminals 40. In addition, the tips 45 of insulation-dispatchng terminals do not have to penetrate through insulation to separate the leads, which reduces the force required to press the leads into the slots 43 of the terminals.

The spacing B, C of the connect zones 28, 30 is preferably less than about the width W of the cable in order to provide a space within which the leads can bend slightly to one side or another. It may be noted that a typical distance Z between a pair of rows of terminals is small, such as about 1 /10to the width W of the cable so that most of the length such as B of a connect zone is utilised to permit slight sideward movement of a lead rather than to accommodate the distance between two rows of terminals. The zone length B is limited to the distance W, so the spacing X of a pair of leads is not more than about 25% different from the terminal spacing Y. A cap, which has recesses that receive the leads of the cable, can be used with the connector to make the connection.

The provision of two connect zones 38, 30 in a pattern permits a cable to be cut at a location 50 along a pattern, to leave two cable ends that each have a connect zone 28 or 30 near its end. This results in minimum wastage of cable and also results in a single cut leaving a connect zone near the end of the cable. The cut at 50 is through a cutable bond zone 24 having a length D equal to about one-half the width W of the cable.

When a cut at 50 is made through the centre of the cutable zone, this still leaves a sufficient length of bond zone on either side of the cut to ensure that the leads will not readily tear free from one another.

A pair of isolation bond zones 24, 26 lie between each connect zone 28 or 30 and an adjacent loose wire zone 32, to isolate each connect zone from a loose wire zone. The length E, F of each isolation zone is made slightly greater than the length of the cutable zone D, to avoid tearing through as a result of the wide spreading apart of leads of the loose wire zone 32. The lengths B, C of the connect zones are preferably equal, and the lengths E, F of the isolation zones are also preferably equal, to provide a cable that displays the same pattern when the cable is turned endfor-end.

One manufactured cable included twentyfive leads 12, each having a diameter G of about 0.6mm (millimeter) and a core width M of about 0.25 mm. The cable had a width W of about 16mm. The loose wire zones 32 had a length A of 40mm, the connect zones each had a width D of 8mm, and each isolation zone had a width E, F of 1 Omm. The sheaths of the leads were heat-bonded together in a process that flattened them to a height H of about 0.5mm.

Thus, the invention provides a flat cable which enables the conductive cores to be spaced apart with only relatively low precision, and yet which permits the cores to be reliably connected to terminals of a connector.

This is accomplished by providing terminalconnect free zones of relatively small length that are spaced along the length of the cable, with the leads and their cores and sheaths being free of attachment to one another along each of these free zones. The leads are spaced apart by distances approximately corresponding to the lateral spacing of the terminals, and yet the leads can move laterally by small amounts in order to match precisely the spacings of terminals to which they are to be connected. The cable can be formed with pairs of such connect zones that are spaced apart by a cutable zone, so that the cable can be cut at the cutable zone to leave two cable ends that each contain a connect zone near the end where the cable can be connected to the terminals of a connector.

Claims (8)

1. A flat cable comprising a plurality of leads, each lead including an electrically conductive core and an insulative sheath surrounding the core, the sheaths being bonded together side by side in a common plane at a plurality of short bond zones spaced along the length of the cable, and the sheaths being separate and unbonded to each other at free zones lying between pairs of the bond zones, all in a pattern that repeats itself along the length of the cable, the free zone length being greater than the bond zone length in each pattern.

2. A cable as claimed in claim 1 wherein the pattern includes at least one free zone having a length, as measured along the length of the cable, which is greater than the width of a single lead but which is less than the width of the cable, so as to enable slight adjustment of lead position to match the spacing of multiple terminals that can make a connection to the respective cores of the leads.

3. A cable as claimed in claim 1 wherein the pattern includes two of the free zones separated by a third bond zone, the third bond zone having a length less than twice the width of the cable, whereby the cable can be cut at the third bond zone to leave two ends, each with a free zone between two bond zones, that can each be connected to the multiple terminals of a connector.

4. A cable as claimed in claim 2, wherein the pattern includes two of the free zones separated by a third cutable bond zone, the cutable bond zone having a length less than twice the width of the cable, whereby the cable can be cut at the cutable bond zone to leave two ends that can each be connected to the multiple terminals of the connector.

5. A cable as claimed in claim 2, wherein each pattern includes two free zones that are spaced apart by a third cutable bond zone that has a length no greater than the width of the cable, first and second isolation bond zones each lying at the end of a terminalconnect free zone which is opposite the cutable bond zone of the pattern, and a loose wire free zone of a length at least twice the cable width and extending from an isolation bond zone of one pattern to an isolation bond zone of another pattern.

6. A cable as claimed in claim 2, wherein each of the sheaths is formed of thermoplastic material and the outside of each lead has a circular cross section along each free zone, and the width of the cable is the same at both the bond and free zones, but the height of the cable is less at the bond zones than the free zones, the cable having flat opposite faces along the bond zones where the sheaths have been flattened and merged in bonding, but the cable having opposing multiple-bump faces along the free zones where the sheaths are each of circular cross section.

7. A cable as claimed in claim 2 adapted to co-operate with a connector having two staggered rows of terminals, each terminal having a pair of arms defining an insulationdisplacing and conductor-engaging slot which has a width slightly less than the width of the cores of the leads, the terminals of each row being spaced along the row by twice the centre-to-centre spacing of the leads of the cable, the length along the cable of the connect free zone being greater than the distance between the terminal rows, and the leads of the cable along the connect free zone being engageable with the two rows of terminals, so that the cores of the leads lie in the terminal slots.

8. A flat cable substantially as described with reference to the accompanying drawings.