WO2005124928A1

WO2005124928A1 - A contact

Info

Publication number: WO2005124928A1
Application number: PCT/GB2005/002422
Authority: WO
Inventors: Rowland Spencer White
Original assignee: Rowland Spencer White
Priority date: 2004-06-21
Filing date: 2005-06-20
Publication date: 2005-12-29
Also published as: GB2415548A; GB0413864D0

Abstract

A contact for establishing an electrical connection with an electrically conductive wire, the contact having a base and a pair of elongate blades defining therebetween a channel within which a wire is to be received, each blade being linked to the base by a respective linking portion, a first blade of the pair being shaped and a second blade of the pair being substantially planar, the channel running towards the base from an entrance defined between an end of each blade remote from the base, wherein the linking portion of the shaped blade is narrower than the shaped blade at the point where the linking portion meets the shaped blade and the channel opens into an aperture between the shaped blade and the base.

Description

A CONTACT

The present invention relates to contacts for use in Insulation Displacement Connectors (I DCs) and in particular to contacts for use in I DCs which find application in the communications industry to connect wires serving as voice or data signal lines.

Typically, such wires are connected in pairs, and IDCs are employed because they make a swift and very reliable connection between sets of wire pairs, without the need for extensive wire preparation.

IDCs have been extensively fitted in the UK since the early 1980's, but since then dramatic developments in the electronics of transmission, together with the growth in data communication, have led to the need for improved electrical characteristics in the IDC.

IDCs consist of an array of metallic contacts used to cut through the insulation of an electrical wire, and make contact with the wire conductor within. They have been developed in two configurations, those with contacts arranged at substantially right angles to the wire axis, and those with contacts arranged at an angle (typically 45 degrees) to the wire axis.

When a contact is arranged at right angles to the wire, its two blades act as simple cantilevers, and are displaced outwards away from each other by a shearing force. The channel or slot into which the wire is inserted therefore opens in a "V" shape, being wider than the diameter of the wire at all points above the wire. This has the disadvantage that only one wire can be reliably terminated per contact. To connect another wire, either a second contact, or at the least a second channel is necessary, which makes the IDC relatively large.

An advantage of this arrangement is, however, that since the contacting blade is at right angles to the wire, the full thickness of the blade makes contact with the wire's conductor, giving the lowest possible resistance and most particularly the lowest inductance (inductance being an important consideration in high speed communications). IDCs using this configuration are disclosed in US 3,611 ,264 and comprise the Northern Telecom (Trade Mark) Bicx Connector.

When a contact is arranged at an angle to the wire to be terminated (for example 45°), its blades can be constrained to be displaced in torsion, rather than in shear. Thus the blades twist around the conductor, and tend to close the wire insertion channel above the position where a wire inserted near to the bottom of the channel rests.

This has the advantage that a second wire can be inserted into the channel above the first wire, so that two wires can be reliably connected without a second channel being required. This makes the connector relatively small.

However, in a typical IDC of this type, the angle of the contact blades means that two narrow points of contact are established with the wire, which yields a much smaller contact area than is the case with the previously discussed concept, and which results in greater connection resistance, but more critically it results in higher inductance at the point of contact. IDCs using this configuration are disclosed in US 4,171 ,857 and US 5,522,733. In both above-described IDC configurations, the channel or slot formed in the contact typically opens at the base of the contact into a circular or generally oval aperture.

It is an object of the present invention to overcome the problems associated with IDCs having contacts arranged at right angles and also with those arranged at 45 degrees.

GB 2,387,040 describes a contact which is arranged with one planar blade and one curved blade, and is positioned at 45 degrees or thereabouts to the wire axis. The planar blade is relatively rigid, and when a wire is inserted the curved blade is displaced away from the wire, maintaining pressure on the wire through spring action. The present invention is an improvement on that set forth in GB 2,387,040.

According to a first aspect of the present invention, there is provided a contact for establishing an electrical connection with an electrically conductive wire, the contact having a base and a pair of elongate blades defining therebetween a channel within which a wire is to be received, each blade being linked to the base by a respective linking portion, a first blade of the pair being shaped and a second blade of the pair being substantially planar, the channel running towards the base from an entrance defined between an end of each blade remote from the base, wherein the linking portion of the shaped blade is narrower than the shaped blade at the point where the linking portion meets the shaped blade and the channel opens into an aperture between the shaped blade and the base.

Preferably the linking portion of the shaped blade is wider in the region of the base than in the region of the shaped blade. Conveniently the width of the linking portion of the shape blade decreases linearly as a function of distance from the base from a maximum width where the linking portion meets the base to a minimum width where the linking portion meets the shaped blade such that the linking portion is of substantially trapezoidal shape.

Advantageously, the aperture is substantially triangular in shape having as its three sides an edge of the shaped blade linking portion, an edge of the planar blade linking portion and an edge of the shaped blade.

Preferably the shaped blade incorporates a curved portion and an edge of the shaped blade adjacent the linking portion comprises a free edge of the curved portion.

Conveniently, the free edge of the curved portion of the shaped blade extends along the entire length of the curved portion.

Advantageously, the shaped blade is wider than the planar blade.

Preferably, the shaped blade prescribes an arc about an axis substantially parallel to the direction of extension of the blades away from the base.

According to a second aspect of the present invention, there is provided a wire contact system incorporating a contact and a wire feeder having a slot for directing a wire to be inserted into the contact towards the contact, wherein the contact and the wire feeder are located relative to each other such that the channel of the contact is displaced from the slot of the wire feeder. Preferably, the magnitude of displacement of the channel of the contact from the slot of the wire feeder is between 25% and 30% of the diameter of an electrically conductive wire inserted, in use, in the channel.

According to a third aspect of the present invention there is provided an insulation displacement connector including a contact or a contact system.

In order that the present invention may be more readily understood, embodiments thereof may now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a side elevation view of a contact embodying the present invention;

FIGURE 2 is a cross sectional view taken along the line A - A of Figure 1 ;

FIGURE 3 is a perspective view of the contact of Figure 1 ;

FIGURE 4 shows a wire inserted into a contact embodying the present invention;

FIGURE 5 shows an Insulation Displacement Connector incorporating a plurality of contacts embodying the present invention; and

FIGURE 6 is a detailed cross-sectional view of a portion of Figure 5.

Turning firstly to Figure 1 , a contact 1 embodying the present invention is manufactured from a planar material and comprises a planar base 2 having an integrally formed terminal 3 depending therefrom. The base 2 and the terminal 3 are coplanar.

At the opposite end of the base 2 from the terminal 3, a first and a second elongate blade 4,5 are provided. The blades 4,5 extend away from the base 2 in the opposite direction to the terminal 3. The base 2, terminal 3 and blades 4,5 are formed by punching, stamping or pressing in a single action a single sheet of material, which is preferably copper alloy or any other material having suitable electrical and mechanical properties.

As shown in Figures 2 and 3, the first blade 4 is coplanar with the base 2 and the terminal 3, but the second blade 5 is shaped with respect to the base 2 such that it prescribes an arc radiussed about an axis substantially parallel to the longitudinal axes of the blades 4,5. The form of the radius is shown in Figure 2 but basically prescribes a curved portion of the blade 5. The contact 1 is an asymmetric contact - it has one planar and one curved blade.

A narrow slot or channel 6 is formed between the blades 4,5. An entrance 7 to the channel is defined between the ends 8,9 of each blade 4,5 which are remote from the base portion 2 of the contact 1. Where the channel 6 meets the base 2, the channel 6 opens out into a cut-out portion in the form of a triangular- shaped aperture 10, when the contact is viewed in side elevation, i.e. when viewed perpendicular to the plane of the planar blade 4, as in Figure 1. The aperture 10 is defined between: respective opposed edges 11 , 12 of two linking portions 13, 14 which each link a respective blade 4, 5 to the base 2; and an underside edge 15 of the shaped blade 5. This particular configuration is most preferred for the following three reasons: firstly, the aperture 10 in the contact 1 extends under the entire curved portion of the contact blade 5, so that the underside edge 15 of the shaped blade 5 presents a substantially horizontal portion at the top of the aperture 10;

secondly, the aperture 10 extends downwards away from the contact channel by a sufficient distance to enable the shaped blade 5 to be formed without stressing the contact material beyond its elastic limits; and

thirdly, the aperture 10 is as small as possible - i.e., the minimum amount of material must be removed to maintain the mechanical integrity of the contact 1.

A triangular aperture 10 is thus most preferable as this shape enables the required horizontal aperture size and required vertical aperture size to be used, whilst retaining maximum rigidity owing to minimal removal of material, and is also a shape that is easy to pierce through the material. Furthermore a triangular shaped aperture encourages the curved blade 5 to twist and spring more effectively than is the case with any of the prior art. This triangular shaped aperture extends under the curved portion of the contact blade, whilst its flat portion is held more rigid. This allows the curved portion of the blade to twist when a wire is inserted, keeping its edge substantially parallel with the edge of the planar (substantially fixed) blade 4. It is this feature which ensures reliability of connection when a second wire is inserted above the first.

Other polygonal apertures, for example, a rectangular cut-out, could be used, although it would become more difficult to maximise the mechanical rigidity of the contact 1. The triangular aperture 10 thereby results in minimal, if any, modification of the linking portion 13 of the planar blade 4 but the linking portion 14 of the shaped blade is therefore trapezoidal in shape so that the benefits outlined above are achieved.

The triangular shape of the aperture 10 is a result of the width of the linking portion 14 of the curved blade 5 decreasing linearly as a function of distance from the base 2 from a maximum width W1 where the linking portion 14 meets the base 2 to a minimum width W2 where the linking portion 14 meets the shaped blade 5 such that the linking portion is of substantially trapezoidal shape - see Figure 1. The minimum width W2 of the linking portion 14, i.e. where it meets the shaped blade 5, is less than the width of the shaped blade at their meeting point.

The contact 1 is simple to manufacture, requiring a single stamping, punching or pressing step to cut out the contact outline, to form the blades 4,5, to cut out the aperture 10 and to radius the shaped blade 5 into the desired shape. Since the contact 1 is manufactured from a single sheet of material, there is no need to cut a slot of predetermined width from the sheet of material, rather, all that is required to form the two blades 4,5 and the channel 6 therebetween is to shear a portion of the sheet of material in the stamping step into the two blades so that one blade 5 is radiused.

Over the length of the channel 6, the blades 4,5 which define the channel 6 are parallel to one another. The mouth or entrance 7 to the channel 6 defined by the free ends 8,9 of the blades 4,5 provides a narrowing entrance between the blades 4,5 to guide a wire to be inserted between the blades 4,5 into the channel 6.

The planar blade 4 is intrinsically more rigid than the shaped blade 5 but, in use, and in order to more accurately balance the symmetry of the connection on the inserted wire (not to cut deeper on one side than the other), it is desirable that the two blades 4,5 each exert similar lateral forces on the wire insulation as it is slid down the channel 6.

This force symmetry is achieved by making the width W3 of the curved blade 5 substantially greater wider than the width W4 of the planar blade 4, as illustrated in Figure 2. In fact, about 35% additional width in the curved blade has been found to adequately compensate for the difference in geometry. The channel 6 in designs embodying the present invention is displaced from the contact centre line, i.e. is disposed more towards the planar blade 4 than the curved blade 5 owing to the curved blade 5 being wider than the planar blade 4. In the prior art, blades of the contact are typically made to be substantially the same width.

In the preferred embodiment of the present invention as illustrated in the accompanying Figures, a combination of the foregoing features controls the way in which the contact blades cut into the wire insulation such that close to equal penetration of the insulation and the wire is achieved on each side, but with sufficient force to ensure the entire thickness of the shaped blade is in contact with the wire conductor, ensuring superior electrical characteristics.

Figure 4 shows a wire 16 inserted into a contact 1 according to the present invention, and is prepared from a cross-sectional "slice" of an actual terminated wire. As may be seen, the insulation 17 of the wire has been cut open by the blades 4,5 such that the blades 4,5 are in good electrical contact with the conducting wire core 18.

Referring now to Figure 5, an insulation displacement connector 19 is shown housing a plurality of contacts 1 embodying the present invention. The connector 19 has equally spaced troughs 20 separated by walls 21. The troughs 20 are intended to receive insulated wires 22 along their length and the walls 21 have cut-outs 23 at approximately 45 degrees to the troughs 20 and the wire axes W into which are housed the contacts 1. Thus, the contacts 1 are at approximately 45 degrees to the wire axes W.

It is important once a wire has been terminated in a contact that no relative movement is allowed to take place between the wire and the contact, as this will result in the generation of electrical noise, and will frequently lead to eventual failure of the joint. It has also been found advantageous to ensure, in the case of Teflon insulation, that the insulation cannot creep back into the contact area.

A small amount of tension in the terminated wire will help to keep the joint more mechanically stable, and this can be introduced by displacing the axis of the wire by about 25% to 30% of the conductor diameter "d" as it is inserted into the channel 6, as shown in Figure 6, which shows in cross-section an enlargement of one of the contacts of the connector of Figure 5 with the walls 21 not shown for clarity. This can be achieved by ensuring that the centre-line of the insertion channel 6 in the connector body is displaced off-centre of the contact channel 6 by the appropriate amount. Figure 6, which has been prepared from an actual cross- section of a wire terminated in a connector assembly, illustrates how this is achieved.

Additionally, the tension which is brought to bear on the outer side of this curve, together with the geometry of the shaped blade 5 of the contact 1 , physically lifts the insulation away from the wire at the point of contact, as may be seen from Figure 6 In present specification "comprises" means "includes or consists of and "comprising" means "including or consisting of.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A contact for establishing an electrical connection with an electrically conductive wire, the contact having a base and a pair of elongate blades defining therebetween a channel within which a wire is to be received, each blade being linked to the base by a respective linking portion, a first blade of the pair being shaped and a second blade of the pair being substantially planar, the channel running towards the base from an entrance defined between an end of each blade remote from the base, wherein the linking portion of the shaped blade is narrower than the shaped blade at the point where the linking portion meets the shaped blade and the channel opens into an aperture between the shaped blade and the base.

2. A contact according to Claim 1 , wherein the linking portion of the shaped blade is wider in the region of the base than in the region of the shaped blade.

3. A contact according to Claim 1 or 2, wherein the width of the linking portion of the shape blade decreases linearly as a function of distance from the base from a maximum width where the linking portion meets the base to a minimum width where the linking portion meets the shaped blade such that the linking portion is of substantially trapezoidal shape.

4. A contact according to any preceding claim, wherein the aperture is substantially triangular in shape having as its three sides an edge of the shaped blade linking portion, an edge of the planar blade linking portion and an edge of the shaped blade.

5. A contact according to any preceding claim, wherein the shaped blade incorporates a curved portion and an edge of the shaped blade adjacent the linking portion comprises a free edge of the curved portion.

6. A contact according to Claim 5, wherein the free edge of the curved portion of the shaped blade extends along the entire length of the curved portion.

7. A contact according to any preceding claim, wherein the shaped blade is wider than the planar blade.

8. A contact according to any preceding claim, wherein the shaped blade prescribes an arc about an axis substantially parallel to the direction of extension of the blades away from the base.

9. A wire contact system incorporating a contact according to any preceding claim and a wire feeder having a slot for directing a wire to be inserted into the contact towards the contact, wherein the contact and the wire feeder are located relative to each other such that the channel of the contact is displaced from the slot of the wire feeder.

10. A contact system according to Claim 9, wherein the magnitude of displacement of the channel of the contact from the slot of the wire feeder is between 25% and 30% of the diameter of an electrically conductive wire inserted, in use, in the channel.

11. An insulation displacement connector including a contact according to any of Claims 1 to 8 or a contact system according to Claim 9 or 10.