US3543227A - Contact spring for electrical socket contact - Google Patents

Description

Nov. 24, 1970 N. MOULIN 3,543,227

I CONTACT SPRING FOR ELECTRICAL SOCKET CONTACT Filed March 26, 1968 3 Sheets-Sheet 1- Fig. 10.

Norbert L. Moulin,-

INVENTOR,

ATTORNEY.

Nov. 24, 1970 N. L. MOULIN 3,543,227

CONTACT SPRING FOR ELECTRICAL SOCKET CONTACT.

Filed March 26, 1968 3 Sheets-Sheet 2 Fig. 2.

mfmmm Nov. 24, 1970 N. MOULIN 3,543,227

I CONTACT SPRING FOR ELECTRICAL SOCKET CONTACT Filed March 26, 1968 s Sheets-Sheet s Fig. 3G. :0

VIII

Fig. 3b. I3 28 24 25 .1 A I T ATTORNEY.

United States Patent Ofice 3,543,227 Patented Nov. 24, 1970 3,543,227 CONTACT SPRING FOR ELECTRICAL SOCKET CONTACT Norbert L. Moulin, Placentia, Calif., assignor to Hughes US. Cl. 339256 8 Claims ABSTRACT OF THE DISCLOSURE A contact spring and its manufacture. The contact spring is mounted on a socket body and the two elements together define a socket. When a pin is inserted 1n the socket a resilient contact finger on the contact spring provides contact pressure for a good connection between the socket and the pin. A locking dog on the contact spring secures it to the socket body. The contact spring is formed from a single piece of metal into a generally tubular configuration having an integral contact finger and an integral locking dog. The metal piece is held in the tubular configuration by an end-to-end dovetail seam. The contact spring is fabricated by feeding a strip of sheet metal to a specially designed progressive die which forms the strip into the desired configuration.

This invention relates to a contact spring and a method of making the same.

Connectors of the pin and socket type are well known. It is important that the pin and socket be able to withstand a large number of connect and disconnect cycles as Well as to afford a good electrical connection which retains its quality for the useful life of the connection. To ensure a good electrical connection the socket is commonly provided with a contact spring of some kind for applying pressure to the pin when it is inserted in the socket. One prior art socket employs a contact spring which wraps around the outside of a socket body and which has a formed portion that passes through a slot in the socket body to pressure engage the pin contact. Another prior art socket employs a leaf spring located in a slot in a socket body, captured therein by a sleeve overlying the socket body, and positioned to pressure engage the pin contact.

Such devices require time and effort to assemble the socket body and corresponding spring. Also, in the type of socket employing a wrap around spring a space is required for the spring to expand into when a pin is inserted into the socket. This is undesirable when one wishes to secure as many sockets as possible to a connector block of a given size.

It is desirable to provide a socket spring which can be quickly assembled on the socket body, employs a minimum number of parts, occupies a relative small space, and yet achieves a reliably good electrical connection when a pin is inserted into the socket. These desideratum are met in the contact spring of this invention.

The contact spring of the present invention is utilized in conjunction with a generally cylindrical socket body to define a socket connection of the type generally employed to receive a contact pin or plug. The contact spring which is of generally tubular configuration has a contact finger which has been lanced out of the contact spring and which is utilized for producing a contact pressure between the pin and the socket when the pin is inserted into the socket whereby a good electrical connection is achieved. The contact spring also has a locking member formed therein adapted for securing the contact spring to the socket body. According to another aspect of the invention the contact spring is fabricated in a single piece by passing a strip of sheet metal through a progressive die which contains a series of working stations.

According to the foregoing it is an object of the invention to provide a novel contact spring.

It is a further object to make such a contact spring by a relatively simple and expeditious process.

These and other objects of the invention will become more apparent from the following detailed description and the accompanying drawings which are illustrative and are not intended to limit the scope of the invention. In the drawings:

FIGS. 1A and 1C are plan and bottom views, respectively, of a form of contact spring embodying the invention;

FIG. 1B is a longitudinal sectional view taken along line BB of FIG. 1A;

FIG. 1D is a transverse sectional view taken along line DD of FIG. 1B;

FIG. 2 is a longitudinal sectional view of an exemplary socket body with which the contact spring may be used;

FIGS. 3A-3D are longitudinal sectional views which illustrate a manner in which the contact spring, socket body, and contact pin may be assembled into an electrical connection; and

FIG. 4 is a plan view of a strip of contact springs at various stages in the progressive die operation used to stamp and shape the contact spring.

Referring now to FIGS. lA-IC, a contact spring 10 according to the invention may be seen to comprise a tubular shell 11 which is of fixed diameter. This shell comprises a piece of sheet metal which has been rolled into a tubular shape. Certain of the piece edges comprise complementarily shaped parts which interlock at a multiple dovetail seam 12. A resilient contact prong or finger 13 is located in a generally U-shaped slot 14 provided near one end of the shell. Located at the other end of the shell is an open-ended slot 15 containing a locking member or dog 16. Both the contact finger 13 and the locking dog 15 can be struck out of the basic piece of sheet metal and are integral therewith. The material employed can be stainless steel, brass, beryllium-copper or other suitable resilient metals. It is preferred, however, to employ beryllium-copper about .006 inch thick. The overall longitudinal dimension of an exemplary shell 11 may be about .340 inch long. The slot 14 may be about .140 inch long and about .035 inch wide and the contact finger 13 of comparable dimensions so that the clearance between the contact finger and the edges of the slot is small. By so dimensioning the contact finger several advantages are derived as will be explained later. The dimensions and clearance of the locking member 16 and corresponding slot 15 are relatively non-critical. For example, the slot 15 may be about .070 inch long and the locking member 16 about .025 inch wide.

Referring now to the contact finger 13 in greater detail it can be seen in FIG. 1A that the finger may be notched, as at 17. The contact finger protrudes into the chamber defined by the shell with its free end 18 facing toward the adjacent or near end of the contact spring 10. In order to increase the structural rigidity of the contact finger 13 one may deform the contact finger by a coining operation to define a curved portion 19 as shown in FIG. 1B and in FIG. 1D. The portion 19 is curved in both the longitudinal and transverse directions so as to define an elongated dished outer surface wherein the degree of transverse curvature diminishes with increasing distance from the free end 18.

The above described contact finger structure is advantageous for several reasons. The notch 17 defines a portion of the contact finger 13 which is of reduced lateral width as opposed to the width of the contact finger portion near the fixed end thereof. The latter mentioned portion is relatively sturdy and helps to key or align the finger 13 in the slot 14. The portion of reduced width serves to prevent rubbing or jamming the sides of the contact finger 13 against the longitudinal edges of the slot 14 in the event that the contact finger 13 is somewhat misaligned. The above mentioned coining operation not only hardens the affected portion of the contact finger, but also serves to smoothen its contact pin engaging surface while at the same time accurately positioning the free end 18 of the contact finger 13 at a predetermined depth in the shell chamber. The shell is dimensioned so as to snugly fit over a slotted cylindrical socket body so that the degree of protrusion of the contact finger into the socket body slot is accurately controllable. Tests indicate that by use of this contact spring the force of connection between a contact pin and the contact finger 13 is relatively constant from connection to connection. In other words large numbers of contact fingers can be made wherein the ultimate force of connection falls within a relatively narrow range. This implies that the electrical resistance of the ultimate connection can be acurately predetermined. It is possible to use such connections in circuits wherein the electrical connection resistance can be accurately compensated if desired. It is preferred to dimension and locate the contact finger 13 so that the amount of contact finger deflection that takes place when a contact pin is inserted into the socket is well below the elastic limit of the contact finger material. This not only increases the useful life of the connector, in terms of the number of times the pin and socket can be joined and separated without materially affecting the connection resistance, but also renders it relatively easy to insert or remove the contact pin. The latter feature is significant where a large number of connectors are ganged together insofar as the facility of connection or disconnection would vary in proportion to the number of connectors involved.

Significantly, by having the free end 18 of the contact finger 13 face the pin-receiving end of the composite socket the length of the contact pin wiping path is increased. Should debris, corrosion, or oxidation be present, the relatively long wiping path would serve to enhance the characteristics of the connection. It is desirable to insure that the free end 18 of the contact finger 13 be tipped upward so that when a pin is inserted into the so ket the contact finger 13 can be cammed upward and outward without jamming of the contact pin and contact finger 13.

The locking member 16 desirably is tapered as can be seen in FIG. 18. It is provided with an inwardly directed locking tab 20. This member serves to lock the contact spring onto an underlying socket body. The tab 20 is rounded as shown at 21 so that when a socket body is inserted into the contact spring 10 the locking member 16 will ride up over the socket body and will not jam. As the insertion is completed the locking tab 20 falls or snaps into a corresponding groove, slot or other indentation on the socket body to secure or lock the contact spring 10 in place on the socket body. This means of locking the contact spring 10 in place and also its location is advantageous and relatively simple. The locking member 16, of course, need not share a common longitudinal axis with the contact finger 13 and may be located on any segment of the tube diameter. However, it is preferred to longitudinally align the locking member 16 with the contact finger 13 so that a socket body, such as that shown in FIG. 2, may be readily and quickly inserted into the contact spring. If these members did not share a common axis it would be more difficult to slide the contact spring 10 over the socket body and to avoid jamming during the insertion process. One might have to rotate the contact spring 1 0 relative to the socket body while pushing the contact spring 10 onto the socket body. Also one might need a tool to pry the locking member 16 away from the socket body when making the insertion. This would increase the time necessary to insert the socket body and would result in some loss of the ability of the tapered portion of the locking member 16 to grip the socket body when the contact spring 10 and socket body are assembled.

Preferably the multiple dovetail seam 12 is located diametrically opposite or 180 from the contact finger 13 and locking member 16 to facilitate the progressive die operations. However, one could easily locate this seam elsewhere on the tube diameter. Also the number of dovetail joints in the seam may be varied. Two dovetail projections and two corresponding dovetail slots are shown and as a practical matter this is sufficient to ensure good alignment of the tube ends when the complimentary edges of the metal work piece are spanked together to form the closed tube. Surfaces 22 and 23 have been work hardened by a coining operation. The bevelled surface 23 functions to guide a socket body into the contact spring.

The exemplary socket body 24 shown in FIG. 2 can be made of hard brass plated with silver and/or gold. The dimension between the pin receiving end 30 of the socket body 24 and annular groove 25 is comparable to the dimension of the contact spring 10. The outer diameter of this portion of the socket body 24 is dimensioned for a snug fit with the internal diameter of contact spring 10. The other end of the socket body 24 has a bore 26 for receiving a conductor. The bore 27 is adapted to receive a contact pin. An open ended elongated longitudinal slot 28 is bevelled at 29 so that when the contact spring 10 and socket body 24 are being assembled the locking tab 20 of the contact spring may be cammed up onto the outer surface of the socket body 24 thereat. Surface 30 is bevelled for guiding an incoming pin and is coined so as to be work hardened.

Turning now to the sequence of assembling the contact spring 10, socket body 24, and the contact pin it can be seen that FIG. 3A shows the contact spring 10 ready for assembly. FIG. 3B shows the socket body 24 being inserted into the contact spring 10, the contact finger 13 being in registration with socket body slot 28 and the locking dog 16 riding over the outer surface of the socket body 24. FIG. 3C shows the contact spring 10 and socket body 24 assembled with the locking dog 16 in position in annular groove 25 on the socket body. FIG. 3D shows the contact finger 13 firmly engaging an incoming contact pin. The contact finger 13, being resilient, is flexed radially outward and its springback force produces a good electrical connection.

FIG. 4 shows a manner in which a strip of sheet metal may be processed into a plurality of contact springs in accordance with the invention. The metal strip is fed by conventional means into a specially designed progressive die (not shown). The progressive die is provided with suitable punch and die tools at various work stations or locations which operate simultaneously, continuously, and at high speeds to economically produce a large quantity of contact springs in a short time. The strip is piloted step by step to each work station where it is held stationary while a tool operation is performed.

As can be seen, the strip 40 is fed along a directed path of travel 41. In order to ensure accurate piloting of the strip from station to station the strip is advanced to a first station S where it is perforated to provide an indexing aperture 42. Subsequently as the strip is advanced from station to station the indexing apertures 42 are brought into registration with indexing pins thereby accurately positioning the strip relative to the stations. It is not necessary that an indexing pin be provided for each indexing aperture.

After indexing aperture 42 has been provided the strip is advanced to a second station S where a U-shaped piece of metal is removed to define an elongated projection 43 in a U-shaped slot 44. The strip is then indexed to a third station S where a piece of metal is removed to leave a second elongated projection 45 in a second slot 46.

At a fourth station 5.; a rectangular slot 47 is formed laterally adjacent slot 46. The material between slot 46 and slot 47 forms a bridge 48. The strip is then advanced part way towards a fifth station S The fifth station is located away from the fourth station 8.; by a distance equal to a multiple of the distance between the centers of indexing apertures 42, but not less than twice the distance between the centers of the indexing apertures. With the strip in this intermediate position, the fourth station 8.; forms a rectangular slot 47 in the segment of the strip then underlying the fourth station S As a result a second bridge 48 is formed.

The strip is then progressed to the fifth station S where a piece of metal is removed thereby defining a first profile having at least one projection or tenon 49 and a second profile having a complementary space or mortise 50. The strip is then piloted away from the fifth station S whereby a different segment of the strip is brought into alignment with the fifth station S Station S now operates on this segment in the same manner as previously described. This latter operation is sufficient to completely define the profile or contour of the contact spring development blank which is held attached to the strip only by bridges or connecting members 48. The strip is then piloted to a sixth station S where the second projection 45 is bent slightly near its fixed end so as to protrude upward from the plane of the strip at a slight angle relative thereto while the tip or free end is bent straight upward. As a result of this operation the projection 45 now corresponds to the locking member 16 shown in FIG. 1B.

At a seventh station S the projection 43 is deformed in a coining die and caused to protrude upwardly from the plane of the strip. Projection 43 now corresponds to the contact finger 13 shown in FIG. 1B.

At stations S S and S the profiles are progressively bent toward each other to define a cradle 51 having its longitudinal axis perpendicular to the length of the strip. At the eleventh station S the profiles are spanked together in interdigitating fashion thereby defining the tubular shell 11 shown in FIGS. lA-lC having an end-to-end dovetail joint 12 as shown in FIG. 1C. This operation aligns the tube ends and fixes the tube diameter. The contact springs 10, having been formed, may now be severed from the strip at a subsequent station and then collected.

However, it is preferred to exit the contact springs from the progressive die while still attached to the strip. The strip and contact springs may then be coiled and placed in a furnace and heated to about 600 Fahrenheit for about two hours to work harden the material. Subsequently one may rig up a machine for indexing the contact springs to a work station where a socket bod is automatically inserted into each contact spring. The socket bodies may be supplied to the work station from a vibratory feeder bowl via a chute or magazine having an escapement mechanism which is synchronized with the indexing machine. The assembled socket body and contact spring may then be separated from the strip by merely twisting the assembly relative to the strip.

While a particular sequence of process steps has been disclosed, it should be apparent that these steps can be permutated, combined and/or modified, and that other steps or refinements, such as might be suggested to a skilled workman could be added without departing from the invention aspects hereof. For example the cradle 51 need not be formed by using three work stations. The contact finger 13 and locking dog 16 may be formed simultaneously. The surfaces 21, 22, and 23 of the contact spring may be bevelled and/ or coined at intermediate stations or simultaneously with the operations at the work stations mentioned. The notch 17 can be formed either when the contact finger 13 is being formed or thereafter.

The invention as described is by way of illustration and not limitation.

What is claimed is: 1. A contact spring, adapted for use with a socket body to form a socket in conjunction therewith, comprising:

an elongated tube of sheet metal of closed cross section having a front end and a back end and being lanced at a first location between the ends of the tube to afford a first portion integral therewith and being lanced at a second location to afford a second portion integral therewith; said tube having a first slot formed by the lancing of said first portion therefrom and a second slot formed by the lancing of said second portion therefrom;

said first and second portions respectively being aligned with said first and second slots;

said first portion being a resilient contact prong bent toward the center of said tube and having a distal end located interiorly of said tube closer to said front end than the balance of said first portion;

said second portion being a resilient locking dog having a distal end located interiorly of said tube closer to said back end than the balance of said locking dog; and

said distal end of said locking dog being a locking tab bent toward the center of the tube.

2. The contact spring set forth in claim 1 wherein said contact prong and said locking dog are longitudinally aligned.

3. The contact spring set forth in claim 1 wherein said tube includes a longitudinal dovetail seam.

4. The contact spring set forth in claim 1 wherein said locking dog extends longitudinally rearward substantially within said second slot.

5. A contact spring, adapted for use in conjunction with a socket body, comprising:

a tube of sheet metal that has a longitudinal dove-tail seam and that includes a first portion and a second portion each integral with said tube with the first portion being intermediate the tube ends and each in registry with a slot in the tube;

said first portion being an elongated resilient contact prong extending obliquely into the tubes interior with its distal end being closer to the front end of the tube than the balance of the contact prong; and

said second portion being a resilient locking dog extending longitudinally with its distal end being a locking tab directed inwardly toward the center of the tube.

6. The contact spring set forth in claim 5 wherein said locking dog extends toward the back end of the tube whereby its locking tab is closer to the back end of the tube than the balance of the locking dog.

7. The contact spring set forth in claim 5 wherein said locking tab is bevelled at its tip.

8. The contact spring set forth in claim 5 wherein said contact prong includes a first and a second section meeting at a transverse juncture between the contact springs distal end and the tube and wherein said second section includes said distal end and wherein said sections are each of 7 uniform width therealong with said second section being FOREIGN PATENTS narrower than said first section. 486,220 9/1952 Canada Reference Cited 246,700 2/1926 Great Britain. 5 961,815 6/1964 Great Britain. UNITED STATES PATENTS 5 2 128 132 193 Frederick 3 5 MARVIN CHAMPION: Pnmary Examlner 2,699,535 1/1955 Flora 339-263 J. H. MCGLYNN, Assistant Examiner 3,023,396 2/1962 Swanson et a1 339-258

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