Note: Descriptions are shown in the official language in which they were submitted.
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TUBULAR ELECTRICAL SOCKET CONTACT
WITH SPLIT TINES
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates generally to socket and
pin electrical connectors and, more specifically, to
low-insertion force connectors of the type.
Description of the Prior Art
In the prior art, the tubular electrical
socket contact with split tines is familiar and has
been widely employed. Ordinarily, the process of
manufacturing the individual socket members, a
plurality of which may be included in a multiconnec~
tion electrical connector, have been manufactured by
processes including a step of bending or deforming
the tines in a radially inward fashion. This con-
stricts the aperture of the socket to an effective
diameter less than that of the pin such that when a
mating pin is inserted therein, a substantial frictional
gripping force is exerted against it. Usually, there
is some flaring of the tines outwardly at the aperture
or, in other cases, a small amount of countersink is -
put into the insulating body block holding the socket
connector members to provide some guidance, compensating -~
for slight pin misalignments as the connectors are mated.
Typical prior art sockets are extensively
described in the technical and patent literature, for
example, in U.S. Patent No. 3,286,222 and in the -
drawings of U.S. Patent No. 3,043,925. The socket -~
members in those patents are of the crimped or bent-tine
types. Those conventional socket contacts exhibit
several sensitive parameters that adversely effect the
achievability of repeatahle, low insertion force
while maintaining satisfactory contact pressure.
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Those areas of concern are: the modulus of elasticity
(or Young's modulus) of the material; length of the
beam (considering the tines as cantilevered beams);
the moment of inertia of the beam representing the
tines (governed by socket outside diameter, inside
diameter and slot width); beam deflection called for
by the design; and, finally, frictional characteristics
of the pins within the sockets.
Forces resisting the mating of the pin and
socket are essentially frictional forces arising from
the socket tines, producing a normal force; i.e., a
frictional force, on the pin. These forces, applied by
the socket tines, are more thoroughly analyzed herein-
after. Suffice it to say at this point in the descrip-
tion, that a particular minimum amount of normal force
is necessary to assure proper electric conduction.
Normal forces in excess of this minimum, however, con-
tribute little to electric conduction but still increase
the insertion forces.
In the manufacture of the individual socket
members according to prior art methods, the crimping
or bending of the tines radially inward produces plastic
(inelastic) deformation of the tines at their roots;
i.e., adjacent to the inward extremity of the slots which
are cut in to produce the tines themselves from the
tubular body of the material. Not only does this
operation result in work-hardening of the material in
the root area, it does so in a relatively unpredictable
fashion and nonuniformly with respect to the inside and -
outside fibers of the tine roots, these being subjected
to compressive and tensile deformation, respectively.
Since the pin-gripping force achievable,
according to the aforementioned prior art manufacturing ~
method, is highly variable; therefore, in order to insure ~--
the least minimum pin-gripping force for all connections,
overdesign in that respect is the usual approach. Thus,
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particularly in the connector assembly involvinq
the substantial number of socket members, the overall
insertion force can be quite large.
It may be said to have been the general ob-
jective of the invention to produce electrical connector
socket members which exhibit highly controllable and
repeatable pin-gripping force which may be minimized
without the risk of encountering unacceptably low values
in one or more socket members where a plurality of
these are assembled in a multicontact connector arrange-
ment. The connector assembly may thereby be designed for
low insertion force.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there
is provided a method of manufacture of a low insertion
force electrical connector socket, comprising the steps
of forming a length of generally tubular stock to have
a generally conical taper over a first predetermined
distance (E and F) from a first end thereof, and there-
after slotting the side walls of the tubing from said
first end to a second predetermined distance (D) axially.
The second distance does not exceed said first distance.
The slotting forms a pair of arcuate tines of length
equal to said second distance from said first end to a
tine root region whereby plastic deformation of the tines
at their root region is avoided.
According to another aspect of the invention, there
is provided an electrical connector socket member for -
receiving a conductive pin of generally circular cross-
section inserted longitudinally and extending into said
socket member from a forward end thereof comprising a
rear longitudinal portion of said socket member extending
from a rear end of the socket member to an intermediate
point thereof and a forward, hollow longitudinal portion
of the socket member embodying a plurality of integral -- -
arcuate tines extending from said intermediate point
to said forward end. The tines are arranged to elastically
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deflect radially outwardly when a pin is inserted,
for maintaining a radially inward contact pressure
against the pin. The rear and forward longitudinal
portions are formed from tubular stock having a
generally conical taper providing said forward portion,
and the tines being formed by slotting the conical
portion axially to a tine root region whereby plastic
deformation of said tines at said root region is
avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. l(a) is a cross-sectional view of a
typical prior art connector socket member prior to
tine crimping or bending.
Fig. l(b) is a pictorial of a socket member
such as in Fig. l(a) after the tine bending operation
has been accomplished.
Fig. l(c) depicts a typically shaped mating
pin insertable in the facing (aperture) end of the
socket of Fig. l(b).
Figs. 2(a) and 2(b) illustrate insertion force
and frictional pin-gripping forces, respectively.
Figs. 3(a) and 3(b) illustrate the need for
and form of the typical tine partial flattening from
the aperture end of the socket according to the inven-
tion before flattening and after flattening, respectively.
Fig. 4(a) is a side view of a typical socket
member according to the invention.
Fig. 4(b) is an aperture end view of Fig. 4(a).
Fig. 4(c) is an enlarged end view of a tine of
the socket of Fig. 4(a) further illustrating the partial
flattening operation which produces the oblate tine
cross-section evident from Fig. 4(b).
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to Fig. 1, the cross-sectional
view is of a typical prior art socket member before
the bending of the tines is effected. The generally
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tubular walls of the socket are axially slotted to a
depth 12, producing tines 10 and 11. The OD (outside
diameter) of the aperture end is essentially that of
the stock, the same applying to the ID (inside diameter).
The beam length depicted in Fig. l(a) is of signifi-
cance throughout the description, this representing
the equivalent cantilevered beam represented by each ~ -
of the tines. The tine root area around 12 is obviously
the area of maximum stress as the tines are flexed in
operation or when they are inwardly bent as part of the
prior art manufacturing process, as illustrated in l(b).
Insertion of the pin 13 of Fig. l(c) flexes the tines 10
and 11 in Fig. l(b) radially outward so that they
effectively assume a "sprung-out" position gripping the
pin 13 along their internal surfaces. -
As hereinbefore indicated, a manufacturing step
involving the radially inward bending of the tines pro-
duces the configuration of l(b) and involves a plastic -
(inelastic) deformation in the tine root region. This
produces work-hardening of the copper base material in
the said root region, but not at all uniformly throughout
the tine roots. As previously indicated, the inside fibers
of each tine are compressed, whereas the outside fibers
are deformed plastically as a result of tensile over-
stressing. By overstressing, it is, of course, meant thatthe material exceeds its yield point and takes on a
"permanent set." As also previously indicated, this
prior art manufacturing technique results in large
variations in contact and, therefore, also in insertion
force, leading to the necessity for acceptance of a high
average force in a production lot of such sockets in
order to assure that all will have at least the minimum
necessary pin-gripping force. The only practical alternate
in using the prior art approach is individual inspection
and selection of those providing the minimum acceptable,
but not an excessive, amount of insertion resistance.
D.
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Figs. 2(a) and 2(b) are helpful in under-
standing the geometry of insertion forces and
pin-contact friction. Upon pin entry into the
socket aperture, the mating force is defined by
the relationship depicted in Fig. 2(a) and may be
expressed as:
Mating Force = R(N Cos ~ + Fr sin ~)
Once the pin is well within the socket, the
mating force may be defined as the product of R and Fr.
Where:
Fr = ~N -
R = number of tines
N = normal force
~ - coefficient of friction
The configuration of the socket, according to
the invention, beginning on the end opposite the pin
aperture end, comprises a first section of essentially
tubular (thin-walled, hollow, cylindrical) portion
followed by a second section of converging inside and
outside diameters (thin-walled conical section) and,
finally, into a third or aperture section, modified
from the conical convergence to make the cross-section
oblate at rest and circular to a larger radius at pin
insertion. The reasons for this partial flattening and
the method of achieving it will be more thoroughly
understood as this description proceeds. The slotting,
which forms the tines from the tubular socket walls,
comprises two opposite slots bisected by the major
diameter of the oblate cross-section formed as afore-
mentioned; in the two-tine preferred embodiment. It
may be noted at this point that the partial flatteninq
of each tine is accomplished over an axial length
sufficient to accommodate a full insertion of the
mating pin; but as a process step, bracing or blocking
of the slot outward from the tine roots is provided
during the flattening operation to prevent plastic
deformation in the vicinity of the tine roots.
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The so-called flattening operation produces
the oblate shape. It will be realized that the tubing
stock from which the part is manufactured, either by
machining operations entirely or by a combination of
drawing and machining, produces an aperture end of
reduced inside and outside diameter as a result of the
conical shaping operations hereinabove described.
Accordingly, the flattening operation restores the tine
aperture end (for a distance accommodating the pin in-
sertion) radius of curvature to that of the pin.
The structure and manufacturing processes of
the invention will be more fully understood as this des-
cription proceeds. It will be realized that the pin
insertion force in a socket member, according to the
invention, can be minimized, because the radially out-
ward deflection of the tines produces a resilient
gripping force based on more predictable parameters;
i.e., more satisfactorily controlled modulus of elasticity
and wall thickness of the socket tines at their roots,
these being the principal factors governing the frictional
pin-gripping force. The tines are tantamount to
cantilevered beams of spring-like material, as will be
seen from the description hereinafter.
Referring now to Fig. 4, a typical socket
according to the invention will be described. One
practical embodiment according to Fig. 4(a) has the
following dimensions: ~-
A = .353/.350
B = .083/.080
C = .153/.150
D = .182/.180
E+F ~ .200
G = .0495/.0485
H = .0060/.0055
J = .014/.013
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The socket member of Fig. 4(a) has a sleeve
portion 14 of axial length B. The inside diameter 18
of this portion 14 may be greater than indicated on
a relative visual scale, as might the corresponding
outside diameter also be larger than indicated. The
purpose of 14 is to provide a wire installing sleeve
or, alternatively, a sleeve for receiving an inter-
mediate stub or adaptor which is itself attached to a
wire. The purpose, in turn, of providing such an inter-
mediate stub is the avoidance of any crimping of thesleeve 14. The entire socket member according to
Fig. 4(a) is made of a material, preferably a copper
alloy, having significant spring properties, good
machinability, ductility and conductivity. However, such
an alloy may not be ideal for crimping at sleeve 14,
hence the intermediate stub alternative, the latter
being tightly inserted (press-fit, for example) into the
bore 18 of 14.
A shoulder which may be chamfered is shown at 15,
simply to facilitate mounting against a corresponding
internal shoulder in a connector assembly insulating block,
a typical expedient in electrical connectors.
A transition of mid-body section 16 having an
inside diameter 17 also has an outside dimension G. Its
length is equal to C - B and ID 17 is a mating pin
clearance dimension, although the pin would not always
be inserted to a depth even as great as the full length
of dimension D.
So far, the manufacturing process can be one of
straightforward machining operations.
Over the dimensions E and F, during manufacture,
the stock may be advantageously drawn into a die having the ~ -
conical shape which begins at the transition from 16 to E
and F. A drawing process is particularly advantageous
from the point of view that the tine root region around
l9 may be formed with closely held material thickness
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(tubular wall thickness), that being an important
factor in controlling the characteristics of the
tine considered as a cantilevered beam as afore-
mentioned. Typical dimension H will be seen to call
for holding this wall thickness within a .0005 range.
Of course, drawing does introduce work hardening,
but it is relatively uniform over the material cross-
section and is predictable and controllable. Thus,
the amount of work hardening introduced by drawing
can be predicted and, therefore, factored into the
design.
The next step in the process of manufacture
would normally be the slotting by cutting, or other
known process step, to the depth D and width J. At this
step, the slot of width J would continue to the aperture
of the socket 20. Tines 22 and 23 are thereby formed.
In lieu of drawing, however, full machining op-
erations can be used to complete the process, those
machine processes being largely adapted to automatic
sequential screw machines.
The process thus far described and the
structure which would result would produce the situation
depicted in Fig. 3(a). The tines which would be generated
obviously have the smaller circular cross-section pro-
duced by the conical shaping hereinbefore described. In
Fig. 3(a), 22' illustrates this fact, and it will be noted
the contact with the pin 13 is limited to two edges 27 and
28. Thus, not only would the spring tines tend to score
the pin, but the area of contact between socket end pin ~ -
is unduIy limited thereby. By partially flattening the ~ -
tines at their aperture ends and for a distance roughly -
equivalent to the depth of pin insertion into the socket
member, the contact area can be shifted more or less to
the circumferential inside center surfaces of the tines.
The illustrations in Figs. 3(a) and 3(b) are obviously
exaggerated for emphasis; however, this situation is
more realistically portrayed in the partial end view of
Fig. 4(c). Thus, the tines, 22 for example, in Fig. 4~a),
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have a longer radius, no longer centered on the axial
center line of the socket aperture. This is illus-
trated in Fig. 4(c) in that the radius R' of the un-
flattened tine 22' changes to R for the reshaped
tine 22.
Fig. 3(b) would indicate that the flattening
is such as to produce an effective tine radius greater
than the radius of pin 13. This is a possible con-
struction or design choice; however, the radius may be
as small as substantially that of the pin 13 itself.
The partial flattening, as it has been called,
referring to the process of modifying 22' to the form
of 22 for a predetermined distance inward from the
socket aperture, is actually a change of curvature and
not actually a flattening in the ordinary sense of that
adjective and, as such, does represent plastic deforma-
tion. In that connection, it is pointed out that bending
or flattening action which achieves this change of
curvature is accomplished by insertion of a mandrel
into the socket aperture or through the socket body
from the rear to prevent the application of sufficient
bending moment to the tine root region to cause the
plastic deformation which is particularly to be avoided.
The plastic deformation thus produced by tine
end curvature modification plays no part in the design
insofar as insertion and pin frictional forces are con-
cerned, since the new curvature R, once achieved, is a
fixed shape.
Fig. 4(b) illustrates that the outline of the
socket aperture after this so-called flattening operation
is an oblate circle; i.e., one in which the dimension 25
is less than the orthogonal dimension of the aperture at
the same axial point (same cross-sectional plane). When
the pin is inserted into this aperture, the radii of
the surfaces of 26 and 26' are at least equal to that
of the pin, if not greater.
Various modifications in the axial proportions
and dimensions of a socket member according to the
invention are obviously possible without departing
from the structural concepts and manufacturing methods -
which form the invention. Other dimensional and con-
figuration freedoms will obviously be possible. The
socket may obviously be scaled to be consistent with
an application.
In view of the possibility for modifications
and variations falling within the spirit and scope of
the invention, the drawings and this description are to be
regarded as typical and illustrative only.
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