Note: Descriptions are shown in the official language in which they were submitted.
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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
~ade throu~h 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
insertio~ and when the wire is at rest in the terminal. The terminals
have poor elastic compliance and a high wire insertion force, with poor
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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. Basically, a
retaining member comprises two beams or legs having opposed, spaced apart,
substantially parallel inner edges, the lower portion of each leg tapered
upward and inward and the upper portion tapered upward and inward at the
outer edge, and an entrance portion defined by downwardly and inwardly
inclined upper edges of the beams, the upper edges merging into the
opposed inner edges by a radius. Particularly, 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 the 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 whlch:-
Figure 1 is a perspective view of a contact in accordance
with the invention;
Figures 2, 3 and 4 illustrate successive steps in insertlng
a conductor into a contact as in Figure 1;
Figures 5, 6 and 7 illustrate alternate forms of contact
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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 15. 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 11a and 12a and upper
portions 11b and 12b respectively, the neck 18 defining the junction of
the portions. It is preferred that the necks 18 are below the junction of
the inner edges 14 with the radii 20.
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 11b 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
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thin layer of insulation 27, seen at 27a9 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 11a and 12a.
The upper portions llb 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 11a 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
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 11b and 12b with the lower portions 11a
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 beams 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.
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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, 24 and 26 AWG telephone wire conductors. The various
dimensions indicated, and listed below, are for each conductor but are
approximate and can be varied. Thus the angle ~ can vary as can the radii
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r but the particular dimensions and values given are particularly suitable
for telephone conductors, having copper conductors, of the gauges given.
; All the generally used insulating materials can be stripped, e.g. paper
pulp, plastic, foam, foam skin, etc.
The part;cular dimensions and values for Figure 8 are as
follows:-
a ~ .1 inches
: b ~ .07"
c ~ .09"
d ~ .07"
e ~ .05"
f ~ .01"
r - .02"
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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 ~
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 sore and the
bending or spreading of the legs 11 and 12, which both also depend upon
; the conductor size. A typical material is phosphor bronze, of about .012"
thickness.
Cutting or other metal is minimized by the dual action beam
and there is m1nimal reduction in conductor strength after insulation into
the contact. This is true even when very thin material is used for the `
contact.
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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.
