EP0043437B1

EP0043437B1 - Retainer member with dual action cantilever beams

Info

Publication number: EP0043437B1
Application number: EP19810104120
Authority: EP
Inventors: Sharanjit Singh Aujla; John Davidson Lee
Original assignee: Northern Telecom Ltd
Current assignee: Nortel Networks Ltd
Priority date: 1980-07-03
Filing date: 1981-05-29
Publication date: 1985-03-06
Also published as: DE3169168D1; JPH0414855Y2; CA1115796A; JPH0355662U; EP0043437A3; JPS5730274A; EP0043437A2

Description

This invention relates to retaining members having dual action cantilever beams, that is with two spaced beams between which a further member is pushed to be retained therein. Particularly, though not exclusively, the invention is applicable to contacts for electrical conductors, and more particularly to insulation displacing contacts for insulated conductors.
Conductor contacts, and particularly insulation displacing contacts are well known, comprising generally, two spaced legs or beams, between which the conductor is pushed. Where the conductor is insulated, the insulation may be removed or displaced by crushing, cutting or slicing. In crushing the insulation is squeezed between conductor and terminal and pushed off the conductor. A typical example of such a terminal is described in U.S. patent 3,112,147. In cutting, the insulated conductor is pushed down between two cutting edges which extend in a direction normal to the axis of the conductor. In such terminals the cutting edges cut through the insulation, which may then be deformed sideways. U.S. patent 3,027,536 describes one form of such a terminal. In slicing, as described in U.S. patent 3,521,221, two parallel cuts are made through the insulation, in the direction parallel to the axis of the conductor, and a short length of insulation is removed from the conductor.
The previous forms of terminal generally have legs or beams which either have substantially parallel sides or taper in one direction, acting as cantilevers. As a conductor is pushed down between the beams or legs they are stressed, but the stress is not uniformly distributed, the stresses being concentrated at the roots of the beams, both during wire insertion and when the wire is at rest in the terminal. The terminals have poor elastic compliance and a high wire insertion force, with poor specific volume efficiency. Also, for insulated conductors, such terminals are often effective for only one type, or a limited number of types of insulation.
The present invention provides a retaining member which has improved qualities and a high degree of stress uniformity. The retaining member has, in general terms, a pair of cantilever beams extending from a base, the beams having opposed, spaced apart, substantially parallel inner edges, each beam having upper and lower portions and an entrance portion, each lower portion having an outer edge tapered upward and inward and each upper portion having an outer edge tapered upward and outward from the lower portion, the entrance portion defined by upwardly and outwardly inclined upper edges of the beams. A neck is formed in each beam at the conjunction of the upper and lower portions of the beams, the necks forming pivotting positions for the upper portions relative to the lower portions when a cylindrical member is forced through the entrance portion. The upper portions deflect outwards about the necks to a permanent deformation beyond the elastic limit of the material. Further forcing of the cylindrical member between the lower portions of the beam causes deflection of the lower portions, to a lesser extent than the upper portions and deforms the cylindrical member. A contact embodying the present invention provides a contact which will accept a range of conductor sizes and will accept conductors having many different types of insulation, with efficient stripping properties, improved connection quality and with a high degree of stress uniformity.
Initial deformation of the legs occurs at the top portions when a conductor is pushed in, the insulation being removed, the bare conductor then passing down between the lower portions of the beams, being deformed thereby.
The invention will be readily understood by the following description of certain embodiments of electrical contacts, by way of example, in conjunction with the accompanying drawings, in which:-

Figure 1 is a perspective view of a contact in accordance with the invention;
Figures 2, 3 and 4 illustrate successive steps in inserting a conductor into a contact as in Figure 1;
Figures 5, 6 and 7 illustrate alternate forms of contact using the basic design as in Figure 1;
Figure 8 illustrates a contact as in Figure 1, with the various important dimensions indicated.

As illustrated in Figure 1, a contact, indicated generally at 10, has two beams 11 and 12 extending upwardly from a base 13. The beams 11 and 12 have opposed inner edges 14 which are parallel and spaced apart a predetermined distance according to the wire size or sizes to be accepted, to define a slot 1 5. The outer edge of each beam is in two parts 16a and 16b and 17a and 17b respectively, the lower parts 16a and 16b inclined upwardly and inwardly and the upper parts 17a and 17b inclined upwardly and outwardly, the two parts of each surface conjoined at a neck position 18. Each beam has an upper or top edge 19 inclined upwardly and outwardly, from the slot 15, each top edge 19 is joined to the related inner edge 14 by a radius 20.
Thus each beam has a lower portion 11 a and 12a and upper portions 11 b and 12b respectively, the neck 18 defining the junction of the portions.
Figures 2, 3 and 4 illustrate certain steps in inserting a conductor into a terminal. In Figure 2 an insulated conductor 25, having a conducting core 26 and an insulating layer 27 is resting on the top edges 19. On initial pushing of the conductor into the terminal past the radii 20, two events occur. The top parts 11 b and 12b of the beams 11 and 12 deflect outwards, in effect pivotting at the necks 18.
At the same time the insulation is crushed and partially pushed off of the conductor core 26. This condition is illustrated in Figure 3, there having been some initial deformation of the core 26 and a thin layer of insulation 27, seen at 27a, still on the core. Further pushing in of the conductor, past the neck position 18, removes the insulation and finishes the deformation of the core, the conductor moving down into the slot 15 between parts 11 a and 12a.
The upper portions 11 b and 12b are extensively and plastically deflected or deformed past the elastic limit of the material, particularly at the neck 18, during the action of stripping the insulation, while the plastic deformation of the lower portions 11 a and 12a is minimized. The upper portions remain deformed, as illustrated in Figure 4, the angle between the top portion of the opposed sides 14 being ø and the angle between the bottom portions of the opposed sides being 0.
With the present invention, the relatively high stresses encountered during insulation stripping at the entry point are largely distributed in the upper portions 11 b and 12b with the lower portions 1 a and 12a being uniformly stressed, to a lower extent than the upper parts. With the tapering of the lower portions, the beams have improved specific volume efficiency and an increased elastic compliance. It is the lower stressed lower portions of the beam which provide the desired wire rest point properties. The contact provides lower insertion forces compared to conventional designs, while at the same time providing effective insulation removal and adequate contact forces to ensure a gas-tight connection and satisfactory conductor retention.
As compared with previous contacts, the present contact has independently deflecting cantilever type dual-taper beams, with dual action, as opposed to the more uniform or single taper beams previously used.
The dual action beams provide efficient insulation stripping at low wire insertion forces without sacrificing wire rest point compliance, whereas high insertion forces occur with previous designs during insulation stripping with similar or lower rest point compliance.
The present design permits the use of optimum tapered beams with more uniformly distributed stresses. This gives increased elastic compliance compared to previous terminals when the face end portion of each beam normally works at a lower stress than that at the base of a beam, resulting in a considerably greater permanent set in the beams.
The contacts are rugged and cheaply produced by stamping. With improved stress distribution, thinner material and a smaller overall size can be obtained.
Figures 5, 6 and 7, illustrate three variations or alternate arrangements of the contact as in Figure 1, and Figures 2 to 4. While in Figure 1, a single contact is illustrated, multiple forms can also be provided. Figure 5 illustrates a "back-to- back" arrangement with beams 11 and 12 extending from both sides of a common base 13. Figure 6 illustrates a strip arrangement, in which two or more contacts are formed from a long strip having a long base 13. Figure 7 illustrates a double contact in which the bases 13 are common with an interconnecting web 30.
As previously stated, a range of conductor sizes can be accommodated by one particular size of contact, if desired, although contacts can be designed specifically for each conductor size. In Figure 8 is illustrated a contact, as in Figure 1 and in Figures 2, 3 and 4, for acceptance of 22 AWG (.645 mm), 24 AWG (.511 mm) and 26 AWG (.409 mm) telephone wire conductors. The various dimensions indicated, and listed below, are for each conductor but are approximate and can be varied. Thus the angle A can vary as can the radii r but the particular dimensions and values given are particular dimensions and values given are particularly suitable for telephone conductors, having copper conductors, of the gauges give. All the generally used insulating materials can be stripped, e.g. paper pulp, plastic, foam, foam skin, etc.
The particular dimensions and values for Figure 8 are as follows:

a=.1 inches (25.4 mm)
b_-.07 inches (17.78 mm)
c-.09 inches (22.86 mm)
d=.07 inches (17.78 mm)
e-.05 inches (12.7 mm)
f-.01 inches (2.54 mm)
r-.02 inches (5.08 mm)
λ,=120°

As stated, it is preferred that the position of the neck 18 be below the junction of the radius 20 and the inner edges 14, and that the rest point of the conductor 26 is below the neck 18. The angle A and radius r affect the initial insertion force and the force applied to the insulation. The slot width f, radius r and dimension (a-b), determine both the amount of deformation of the conductor core and the bending or spreading or the legs 11 and 12, which both also depend upon the conductor size. A typical material is phosphor bronze, of about .012" (3.05 mm) thickness.
Cutting or other metal is minimized by the dual action beam and there is minimal reduction in conductor strength after insulation into the contact. This is true even when very thin material is used for the contact.
While specifically described for use with insulated conductors, the contact can be used with bare conductors. There may be reduced deformation of the beams, without the insulation, but the same basic situation occurs with deformation of the conductor occurring prior to entry into the slot 15. Similar structures can be used to retain small diameter rods or "wires" of other materials than metal, and it is possible to make the retaining member of non-metallic material, depending upon use.

Claims

1. A retaining member with dual action cantilever beams having a base (13) and a pair of cantilever beams extending from the base and having opposed, spaced apart, substantially parallel inner edges, each beam having upper and lower portions and an entrance portion; each lower portion being defined by an outer edge (16a, 16b) tapered upward and inward from the base and by a lower part of the inner edge (14); each upper portion being defined by an outer edge (17a, 17b) tapered upward and outward from the lower portion (11 a, 11 b) and by an upper part of the inner edge (14); the entrance portion being defined by upper edges inclined upwardly and outwardly from the inner edges (14): characterized by a neck (18) in each beam (11 and 12) the neck (18) being defined by the conjunction of the outer edges (16a, 16b, 17a, 17b) of the upper and lower portions (11a, 12a, 11b, 12b) and by the inner edge (14), the necks (18) providing pivotting positions for the upper portions (11b, 12b) relative to the lower portions (11a, 12a), the arrangement being such that on initial forcing of a cylindrical member (26, 27) through the entrance portion and between the upper portions (11b, 12b) the upper portions (11b, 12b) are adapted to deflect outwards about the necks (18) to a permanent deformation beyond the elastic limit of the material of the retaining member while initially deforming the cylindrical member (26), further forcing of the cylindrical member (26) between the lower portions (11 a, 12a), causing the lower portions to deflect to a lesser extent than the upper portions, while deforming the cylindrical member (26) into its final shape.

2. A retainer as claimed in claim 1, for use as a contact for reception of an electrical conductor characterized by the retainer (10) being of electrically conductive material.

3. A retainer as claimed in claim 2 characterized by the upper portions (11 b, 12b) being adapted to crush insulation (27) on the conductor (26) and initiate deformation of the conductor, the insulation (27) being removed from the conductor and the conductor (26) deformed at least to a major part on passage past the necks (18).

4. A retainer as claimed in claim 1, 2 or 3 characterized by the lower portions (11a, 12a) of the beams (11, 12) being tapered to provide substantially uniform stress distribution on insertion of a conductor (26).

5. A retainer as claimed in claim 1, 2, 3 or 4, characterized in that the upper portions (11b, 12b) are deformed such that the inner edges (14) at the upper portions are inclined to the inner edge (14) at the lower portions for each beam (11, 12) after insertion of a conductor (26).