High force contact

An electrical receptacle contact (10) having a contact termination section (20), a wire termination section (40), and an insulation gripping section (50). The contact termination section (20) includes a primary cantilever beam (26), a secondary cantilever beam (27), and an overstress stop (28) with a gap arranged therebetween for the purpose of assuring that the beams (26,27) are not preloaded. The alignment of the primary and secondary cantilever beams (26,27) with the overstress stop (28) advantageously protects the beams (26,27) from overstress.

The present invention relates to an electrical receptacle contact for 
receiving a pin or blade contact therein. More particularly, the present 
invention relates to an electrical receptacle contact having a pair of 
balanced cantilever beams therein for forcefully biasing against a blade 
or pin contact, and the receptacle contact includes an overstress member 
for preventing the overstress of the cantilever beams. 
BACKGROUND OF THE INVENTION 
An electrical receptacle contact is disclosed in U.S. Pat. No. 5,112,254. 
This known electrical receptacle contact includes a pair of cantilever 
beams for engaging a complementary pin contact for electrical connection 
therewith. This known connector includes a front cover portion for 
preventing the pin from being inserted behind one of the cantilever beams, 
and the cantilever beams are connected to each other with the lower of the 
two cantilever beams engaging a bottom of the receptacle contact. This 
known electrical connector advantageously provides a means for 
interconnection between a receptacle contact and a blade or pin contact; 
however, this known invention is likely to have high insertion forces 
because the cantilever beams are preloaded, i.e. they are in frictional 
engagement with each other prior to insertion of a beam or pin. Moreover, 
the lower cantilever beam is preloaded against a bottom surface of the 
receptacle thereby requiring additional force to deflect it during 
insertion of the pin, and the contact cover is an additional member which 
adds expense to the manufacture of the electrical contact. 
Another electrical receptacle contact is disclosed in U.S. Pat. No. 
3,836,947. This second known device provides a pair of deflectable 
cantilever beam arms in engagement with each other when a pin contact is 
inserted into the receptacle contact. Both cantilever beams are inclined 
at generally the same angle and in the same direction toward the pin to be 
inserted. The second cantilever beam member at the top is a stop means 
against which the other cantilever beam will engage in order to limit the 
deflection of the first, lower cantilever beam. The top cantilever beam 
acts as the functional equivalent of a spring assist relative to the lower 
cantilever beam. When a pin contact is inserted into the receptacle, both 
the lower cantilever beam and the top cantilever beam deflect, thereby 
increasing the gripping force of the lower cantilever beam on the pin. 
This known invention advantageously provides a means to interconnect 
receptacle and pin contacts; however, the fact that the top "assist" 
cantilever beam also acts as a stop member is likely to undesirably 
increase the variable rate of contact insertion force. Moreover, the top 
cantilever beam can cause the resistance to contact insertion to sharply 
increase at the moment that the top cantilever beam becomes fully 
operative against the lower cantilever beam. Additionally, when the pin 
has been fully inserted into the receptacle, the lower cantilever beam 
engages the assist cantilever beam and a portion of the receptacle contact 
wall that the assist cantilever beam extends from will undergo an 
"unfolding" force. 
A further known receptacle contact is disclosed in U.S. Pat. No. 5,281,175. 
This known receptacle contact provides two cantilever beams one of which 
primarily engages a pin contact when it is inserted into the receptacle, 
and the other cantilever beam is an assist cantilever beam relative to the 
primary beam. The assist cantilever beam is always in engagement with the 
primary cantilever beam. Neither of the cantilever beams comprise radius 
curves but, rather, include relatively small, acute angle bends. This 
known connector advantageously provides a means to electrically 
interconnect a pin contact with a receptacle contact; however, this 
arrangement is likely to require high insertion forces because of the 
additive effect of the flexure inertia associated with simultaneously 
deflecting the acute angle bends of both the assist and primary cantilever 
beams. 
SUMMARY OF THE INVENTION 
The present invention provides an electrical receptacle contact comprising 
a contact termination section for electrically receiving a further 
electrical contact having an insertion direction for inserting the further 
electrical contact into the receptacle contact, and the receptacle contact 
includes another section for connection to an electrical conductor. The 
contact termination section comprises resiliently deflectable primary and 
secondary cantilever beams, the primary beam is adapted to engage the 
further electrical contact, and the beams are in an unstressed state prior 
to insertion of the further contact. 
The present invention seeks to overcome the disadvantages of the prior 
contacts by providing a contact assembly which: has an overstress member 
for providing overstress protection to at least one of the beams 
independently of the at least one beam because the overstress member does 
not deflect therewith; advantageously includes preselected radii and 
flexure inertii (by preselecting cross sectional areas) for the respective 
cantilever beams for imparting a balanced degree of compliancy to the 
beams and thereby controlling the contact forces generated by insertion of 
the pin or blade; has a locking tab and tab aperture for preventing 
unfolding forces acting on the contact form; advantageously provides low 
initial contact insertion forces by virtue of the fact that the beams are 
not preloaded, but which forces increase at a desirably gradual rate 
without a sharp increase; and is easy to make and use, and is of a low 
manufacturing cost.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows an electrical receptacle contact 10 having a contact 
termination section 20, a wire termination section 40, and an insulation 
gripping section 50. Contact 10 is shown connected to a carrier strip 12 
as will be the case after the contact has been stamped and formed but 
prior to severance of contact 10 from the carrier strip 12. Contact 
termination section 20 includes a base portion 22 with a platform 22a, 
sidewalls 23, an outer top wall 24, an inner top wall 25, a primary 
cantilever beam 26 with a bend 26aand a tip 26b, a secondary cantilever 
beam 27 with a bend 27a and a tip 27b, an overstress stop 28, and an 
offset portion 29. Wire termination section 40 is a crimpable section for 
crimping to the conductive core of a wire not shown in the drawing. In 
like manner, insulation gripping section 50 is a crimpable section for 
crimping to the insulation surrounding the core of a wire not shown in the 
drawing. Plane "A" depicts a plane which intersects a portion of beams 26 
and 27, and overstress 28. 
Referring to FIG. 2, outer top wall 24 includes a tab aperture 24a which 
receives a locking tab 25a of inner top wall 25 for preventing unfolding 
forces acting on the contact form. 
Referring now to FIG. 3, a front, cross sectional view of the receptacle 
contact of FIG. 1 taken along line 3--3 is shown. FIG. 3 also shows how 
locking tab 25a fits into tab aperture 24a of top wall 24. 
Referring to FIG. 4, a side view of the receptacle contact 10 is shown with 
hole 23a of wall 23 exposing the end portions of primary cantilever beam 
26 and secondary cantilever beam 27. 
FIG. 5 shows the electrical contact according to the present invention 
while in the form of a blank of generally constant thickness. Blank 80 
shows two blank sections 82 and 84. Section 82 shows tab 25a, primary and 
secondary cantilever beams 26 and 27 in their preformed state as 26' and 
27', and shows inner top wall 25' with overstress stop 28'. Note the width 
of preformed primary beam 26' is relatively larger than the width of 
preformed secondary beam 27', thereby resulting in a differential as 
between the respective cross sectional areas of the beams for purposes of 
flexure, as further described below. Hole 23a is shown adjacent to tab 
aperture 24a. Blank section 84 shows primary cantilever beam 26 and 
secondary cantilever beam 27 after having been folded towards each other 
during a forming process. 
FIG. 6 shows a further embodiment of the present invention with 
substantially all of the features thereof the same as in FIG. 1. Contact 
receptacle 100 includes a contact termination section 120, a base portion 
122 with a platform 122a, side walls 123, outer top wall 124, an inner top 
wall 125, a primary cantilever beam 126, a bend 126a, a secondary 
cantilever beam 127 with a bend 127a, an overstress stop 128, an offset 
portion 129, and a wire termination section and insulation gripping 
section (not shown in the drawing). Additionally, a bend 126b has been 
added to the primary cantilever beam 126 with an angle .alpha. as shown. 
Moreover, a plane shown as "B" and a plane defined at "C" show that the 
overlapping feature as shown in plane "A" of FIG. 1 has been changed. 
Here, plane C shows an overlap between the cantilever beams 126 and 127, 
but which overlap does not align with plane B of the stop member 128 (as 
was the case in FIG. 1). 
Referring now to FIGS. 7-8, operation of the contact 10 as an example of 
the invention will now be described with the understanding that the 
principles described below will be, in large part, equally applicable to 
contact 110. FIG. 7 shows a pin contact 60 inserted into contact 10 with 
the pin contact 60 engaging a radiused curve formed on tip 26b of primary 
cantilever beam 26 for sliding engagement with the primary cantilever 
beam. The radiused curve reduces the coefficient of sliding friction 
between tip 26b and pin contact 60. Prior to insertion of pin contact 60, 
however, the primary cantilever beam 26 and secondary cantilever beam 27 
comprise a gap between their respective tip ends 26b and 27b, therefore, 
the beams are not preloaded. This is an advantage over preloaded beams in 
that the lack of preload advantageously provides low initial contact 
insertion forces. 
Moreover, as the contact being inserted progresses and the beams 26 and 27 
come into contact with each other, the insertion force will increase 
gradually. As noted in FIG. 7, bend 26 has a complementary radius R1, and 
bend 27 has a complementary radius R2. In a preferred embodiment, R2 is 
greater than R1, and the cross sectional areas of the beams 26 and 27 in 
the area of the respective radii are such that the flexure inertia of beam 
27 is less than beam 26. During deflection of the primary and secondary 
cantilever beams 26 and 27, therefore, cantilever beam 27 will be 
relatively more compliant, i.e. will have a higher degree of flexibility 
or deflection because of its larger radius R2 and lower flexure inertia. 
Therefore, the flexibility of the beams, as the term is used here, is a 
force per unit deflection rather than a mere geometric measurement of 
deflection. Thus the beams 26 and 27 advantageously include a pair of 
respective preselected radius bends and flexure inertia for imparting a 
balanced degree of compliancy to the beams and thereby confining the 
contact forces generated by insertion of the pin or blade to a gradual 
increase. 
In view of the foregoing, prior to insertion of pin contact 60, there is a 
gap between tip 26b and 27b. However, it is preferred that there will be a 
gap between the tip of 27b of beam 27 and overstress 28. As shown in FIG. 
7, pin contact 60 when in the fully 20 inserted position, is biased 
against platform 29a by the additive biasing effects of the cantilever 
beam 26 and 27. The platform 29a defines the points of contact between the 
pin 60 and contact 10, and prevents stubbing. 
Now referring to FIG. 8, a use of the contact 10 with a test probe 70 is 
described. As shown in the drawing figure, test probe 70 is inserted at an 
angle which tends to deflect both beams 26 and 27 into engagement with 
each other, and beam 27 is deflected into engagement with overstress 
member 28. Plane A is shown in alignment with beams 26,27 and overstress 
28, which alignment is advantageous because both beams 26 and 27 have the 
benefit of the overstress member 28 in preventing the overstress thereof. 
This also helps to minimize deleterious tolerance factors. In a preferred 
embodiment, both cantilever beams 26 and 27 have the approximately same 
length, the beams will touch each other at the general vicinity of the 
centerline of overstress 28, and, as noted above, are arranged in an 
unloaded state before insertion of a pin contact 60 or test probe 70. 
However, when the pin contact 60 or probe 70 has been properly inserted, 
both beams 26 and 27 are always in engagement. 
It should be noted, however, that when a pin contact 60 or test probe 70 is 
inserted into contact 110 of FIG. 6 above, there will likewise be a gap 
between tip 126c and 127b of beams 126 and 127 prior to insertion of the 
pin contact. However, as the pin contact is inserted into contact 110, tip 
126c will slidingly engage the lower surface of cantilever beam 127, and 
bend 126b will slidingly engage the pin contact as the same is inserted. 
But only beam 126 will have the benefit of the overstress feature 128 when 
a test probe is, for example, inserted into contact 110 at an angle as 
shown in FIG. 8. 
It is preferred that contacts 10 and 110 are stamped and formed contacts 
made of a high strength, high conductivity, and low cost metal, for 
example: copper, brass, bronze, beryllium copper, copper alloys, steel, 
nickel, aluminum, or zinc. To assure both electrical and mechanical 
integrity of the contacts, the final manufacturing process preferably 
includes the application of a corrosive resistant finish known to those of 
ordinary skill as a coating or plating. Preferably, the plating material 
would comprise tin, tin low lead, tin lead, nickel, gold, silver, copper, 
zinc and/or palladium. The platings are preferably applied to the contacts 
by a process known to those of skill in the plating art as 
electro-deposition. 
Thus, while preferred embodiments of the invention have been disclosed, it 
is to be understood that the invention is not to be strictly limited to 
such embodiments but may be otherwise variously embodied and practiced 
within the scope of the appended claims.