US3488625A - Electrical connector - Google Patents

Description

R. P. COLLIN ELECTRICAL CONNECTOR Filed March 27, 1967 an fr om alum ,.vN @N INVENTOR.

RoDERlCH P. COLUN ATTORNEY E7@ R. P. COLLIN l 3,488,625

ELECTRICAL CONNECTOR Filed March 27, 1967 2 Sheets-Sheet 2 FIG. 5o.,

INVENTOR. RODERICH F! COLLIN www ATTORNEY United States Patent O 3,488,625 ELECTRICAL CONNECTOR Roderich P. Collin, Southgate, Mich., assignor to Applied Dynamics, Inc., Ann Arbor, Mich., a corporation of Michigan Filed Mar. 27, 1967, Ser. No. 626,253 Int. Cl. Hlllr 13/24, 17/18 U.S. Cl. 339-177 7 Claims ABSTRACT F THE DISCLGSURE This invention relates to method and apparatus, and more particularly, to improved method, apparatus and devices for connecting coaxial cable to terminal posts or bars having a non-circular cross section, such as Wire- Wrap terminal bars. A wide variety of applications in the computer, communication, and instrumentation arts, and electronic arts generally require the connection of coaxial cables carrying high frequency signals to such terminal posts.

Because signal conductors may be connected or wired to automatically, under control of a computer program, for example, and because they require no soldering or complex connector, the automatic connection of complex electronic devices with so-called Wire-Wrap connections has become extremely common. Briefly, Wire- Wrap connections are those in which a conductor is tightly wrapped throughout a plurality of turns about a terminal post having corners or edges, so that the corners or edges of the post tend to bite into the conductive conductor which is wrapped around the post and make contact between the two. Because of the reliability and economy surrounding programmed provision of such connections, Wire-Wrap connections have achieved widespread use. Wire-Wrap connections have been particularly suitable for those applications (typified by digital computers) in which a very large number of connections of exactly the same type must be made in accordance with a predetermined machine program.

While Wire-Wrap connections have achieved widespread use in the digital computer arts, for example, their use has been much less common, if noticeable at all, in those arts in which high-frequency wide-band signals and similar signals must be connected. Such signals cornmonly are routed between various circuit elements by means of coaxial cables, which include a central signal conductor, a concentrically-disposed outer (ground) conductor, frequently in the form of a metal braid, ywhich is separated from the signal conductor by means of insulation, and a thin, outer insulation covering, such as polyvinyl chloride (or PVC).

A large majority of prior connectors for coaxial cables merely comprise reduced-scale fittings from the plumbing industry, and many prior art coaxial cable connectors occupy far too much space to allow their use in machines where most connections are made by Wire-Wrap connections or in other applications where adjacent terminal posts must be close together. The increasing bandwidth requirements in rnany devices, such as hybrid analog/ digital computers, dictates the use of coaxial cable connections in an increasing number of circuits. Most prior art Wire-Wrap terminations have involved either low frequency signals or digital computer signals of which limited bandwidth treatment was satisfactory, or have involved signal circuits in which shielding from noise and cross-talk was much less important than frequently is now the case. An increasing number of applications require the connection of coaxial cables to closely-spaced rectangular terminal posts, with the signal conductors of such cables appreciable shielded to minimize pickup of noise and cross-talk. A variety of electronic connection devices presently available on the market which have closely-spaced rectangular connection bars and which have been intended for and useful in the past solely for ordinary single-conductor wire-wrap terminations become useful in many additional applications if coaxial cables may be connected to their connection posts in a reliable and economical manner. Thus it is a primary object of the invention to provide an economical and reliable connection technique for connecting coaxial cables to closelyspaced non-circular bars or posts of the type to which Wire-Wrap connections usually are made.

It is another important object of the invention to provide connections of the type described Iwhich do not require machining, or soldering and little, if any, application of heat, and which may be made rapidly and reliably by unskilled personnel using simple hand tools, either in the factory or in the eld.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts, which will be exemplified in the constructions hereinafter set forth.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a cross-section view, not to scale, through a coaxial cable termination made in accordance with the invention, in which various of the parts are shown with expanded diameters for sake of clarity.

FIG. 2 is a cross-section view taken at 2-2 in FIG. 1.

FIG. 3 is a side view, also not to scale, of an alternate form of the invention.

FIG. 4 is an end view of the connector of FIG. 3.

FIG. 5a is a force diagram illustrating, in exaggerated form, the forces applied to a rectangular connector bar by the connectors of the invention, and FIG. 5B is a View taken at lines 5 5 in FIG. 2.

FIG. 6 is an elevation view illustrating several further modications of the invention.

Referring now to FIGS. l and 2, numeral 10 indicates the wall of an electrical device through which a plurality of non-circular mutually-parallel bars or posts protrude, only two such posts 12 and 14 being shown in FIG. l. Wall 10 might comprise, for example, the rear wall of a computer patchbay, in which case many rows and columns of such bars equally spaced from each other may protrude through wall 10. Such matrices of connection bars are typically utilized when connections are intended to be made to them automatically by means of a Wire- Wrap machine. In some applications wall 10 is formed of an insulating material and no insulation is necessary to insulate the bars from each other. In other applications to which the present invention is principally directed, wall 10 either comprises a conductive metal plate or an insulating plate coated with conductive material to facilitate shielding of the individual conductors from each other to prevent cross-talk. In FIG. 1 Wall 10 is assumed to be such a conductive plate, and insulating bushings 16, 18 surround each post where it passes through `wall 10 in order to insulate it from wall 10.

A typical flexible coaxial cable 20 coming from an external circuit (not shown) is shown in cross-section as including a central signal conductor 22 surrounded by a cylindrical insulation layer 24, a braided metallic sheath outer or ground conductor 26 and an outer insulation covering 28. To install the connector of FIG. 1, the outer insulation layer 28 is stripped off a short length of cable 20 and a length of braid 26 folded back over the outer covering as shown in FIG. 1. One end of a piece of brass, copper or other conductive hollow tubing 30, preferably circular in cross section, is then crimped to surround the folded-back braid, using a conventional plier-like crimping tool which crimps to a controlled depth. Tube 30 extends forwardly from the folded back braid far enough to seat against and electrically contact conductive wall 10, thereby' providing shielding of the signal conductor along its entire length. The inner insulation 24 of the coaxial cable extends forwardly from where braid 26 is folded back to within a rubber, plastic or other insulating tube 34 and terminates adjacent the outer end of a rectangular tube 36, also preferably formed of brass or copper. Insulating tube 34 preferably is elastically expandable and surrounds tube 36 with a shrink tit, more tightly than is shown in FIG. 1. Alternatively, for ease of assembly, the inner diameter of a permanently-deformable tube 34 and the outer diameter of tube 36 may be chosen so that tube 34 is readily slidable over tube 36, and then the end of tube 34 may be necked down by crimping as shown at 34a in order to prevent tube 34 thereafter from sliding off tube 36. Also, rather than providing a shrink t or necked-down portion in tubing 34, the inner diameter of outer tube 30 may be selected so as to compress or conne insulating tubing 34 to maintain it in place. A portion of the signal conductor 22 is permanently attached to tube 36 by crimping the latter near its outer end as shown. Rectangular tube 36 slides on and attaches to rectangular post 12 with a friction lit provided by plural crimps in tube 36, as will be further mentioned in connection with FIGS. a and 5b. To prevent ground tube 30 of the connector assembly from contacting any adjacent equipment when the connectors are pressed on or pulled off of the connector posts, an outer insulating covering 29 also preferably having a shrink t, surrounds the entire connector.

By careful attention to mechanical tolerances it is possible to insure that the forward end of ground shield tube seats against conductive wall when rectangular tube 36 has been slid all the way onto post 12, but even then vibration and like influences may sometimes prevent good electrical contact between tube and wall 10, and the presence of a small space between tube 30 and wall 10 can allow a detectable amount of cross-talk. In extremely high-performance applications, such cross-talk may be eliminated substantially entirely by having the end of tube 30 protrude within the Wall 10 structure. For example, wall 10 may be provided with a conductive egg-crate structure on its rear side to surround each connector bar, as indicated by plates 40 and 42 in FIG. 1. Alternatively, recesses may be provided in wall 10, as indicated by dashed lines at 44', and tube 30 may be provided with a greater length, as indicated at 30' in dashed lines.

The manner in which rectangular tube 36 is made to engage post 12 reliably though removably, will be better understood by reference to FIGS. 5a and 5 b, wherein tube 36 is shown as having three inwardly-extending projections spaced along tube 36 to apply bending forces to the straight connection post 12 when the connector is pressed onto the post. The nature of the bending forces is illustrated in exaggerated form in FIG. 5a, where it will be seen that the inward-projections, which may comprise simple controlled-depth crimps in tube 36, attempt to bend connector post 12, and press tightly against the post at three points when the connector is installed. It also may be noted that the projections wipe the sides of the connector bar as the connector is pressed on the post, insuring good metal-tometal contact. It will be apparent that more than three such spaced crimps may be provided, though three are usually regarded to be ample. The use of only two crimps on opposite sides of tube 36 should be avoided. If spaced from each other along the tube they undesirably cause the connector to cant with respect to the connector post, and if spaced directly across the tube from each other the stiffness of the connector post does not contribute to maintaining good contact.

The connector devices of the invention may be made in a variety of sizes to fit different sizes of connector posts and to receive different sizes of coaxial cable. An exemplary embodiment which has found wide utility for connecting .125 inch O.D. coaxial cable utilizes 1.75 inch long pieces of circular brass tubing (having inside and outside diameters of .155 in. and .187 in., respectively) as ground tube 30, 1.0 inch long pieces of rectangular (square) brass tubing (having an inside dimension of .07 in. and an outside dimension of .10 in., respectively) as tube 36, with the three crimps spaced approximately one-eighth inch apart along the tube. Shrink tube polyolen insulation of Alpha Wire Type No. FIT-221 surrounds rectangular tube 36, and shrink tube insulation of the same type surrounds outer ground tube 30. Shrink-tube insulation of the type mentioned may be slid easily over the part to be insulated, and then be shrunk to tightly engage the part by the application of hot air. The outside diameter of a complete connector then is only .20 inch. It will be apparent that various other types of insulation may be substituted for shrink-lit insulation, to be wrapped on or painted on.

FIGS. 3 and 4 show a slightly modified female connector having a foreshortened outer insulating covering 29 to allow a known form of box contact 55 (Amp, Inc. Catalog No. 85487-2LP) to be fixedly attached to the forward end of ground tube 30, with one linger of box contact 55 extending a short distance inside ground tube 30 and another nger lying against the outer surface of tube 30, to which it is preferably soldered. Contact 55 may be soldered to tube 30 before the tube is crimped to the coaxial cable braid, so that no heat need be applied to the coaxial cable. When assembled, the device of FIGS. 3 and 4 contacts two adjacent posts 12 and 14, connecting the ground tube 30 of the connector to adjacent post 14, as is shown in FIG. 6. As is apparent from FIG. 4, box contact 55 is circumferentially located on tube 30 so that the sides of its postreceiving recess are substantially parallel to a pair of sides of rectangular tube 36.

FIG. 6 illustrates the use of connections made in accordance with the invention with several different modications. A plug-type connector (Amp, Inc. Catalog No. 582766-2) of a type frequently used to engage the edges of an etched circuit card is shown having a plurality of upwardly-extending rectangular connection bars 52, 52 usually intended to be connected to by Wire-wrap processes. Female connector 54 shown attached at the left end of connector 50 comprises the connector shown in FIG. 3. The box contact 55 is shown mounted on and engaging the adjacent post of connector device 50.

Connector 56 in FIG. 6 corresponds to the connector of FIG. 1 except that an insulated dangle wire 58 has been connected to the upper end of the connector, the bare end (not shown) of dangle wire 58 being crimped together with the folded-back metal braid at the upper end of tube 30. The remote end 59 of dangle wire 58 carries a rectangular tube 36 identical to tube 36 of FIG. 1 and a surrounding shrink-lit insulating covering like covering 36 of FIG. 1. The insulated rectangular tube 36' is pressed on another connector bar. Because dangle wire 58 is connected to ground at connector 56, no surrounding ground tube is necessary.

While the rectangular connector post 12 shown in FIG. 2 is shown with a square cross-section, it will be apparent at this point how the dimensions may be altered to connect to posts having other rectangular cross-sectioned shapes, and indeed to posts having other non-circular and even circular cross-sectional shapes.

The steps involved in connecting a cable terminator of the type shown are preferably as follows (with the dimensions herein stated merely being exemplary). The braid and insulation coverings at the end of the coaxial cable are stripped to allow approximately 1A inch of bare central conductor to protrude. Approximately 1A inch of the outer conductor is then folded back over the outer insulation, the end of rectangular tube 36 is crimped on the protruding portion of central conductor, and then the shrink tubing is fitted over tube 36. Next, the outer tubing 30 is slid over the free end of tube 36 until the ends of the two pieces of tubing register, and then outer tube 30 is crimped about the folded-back portion of metal braid. Lastly, the outer shrink tubing is fitted over tube 30. It will be seen that all of the above operations are extremely simple and may be performed by unskilled personnel using simple tools.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are ef'liciently attained, and since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A cable terminator for connecting to an elongated bar a coaxial cable having a central conductor, insulation concentrically surrounding said central conductor and a concentric outer conductor, said terminator comprising, in combination: a first metallic tube surrounding a portion of said concentric outer conductor at one end thereof and being crimped to grip and electrically contact said outer conductor; a second metallic tube substantially concentrically disposed within said first tube, said second tube being crimped at one end to grip said central conductor and having a plurality of inwardly-extending projections spaced along its length to provide bending forces to said elongated bar; and an insulation covering surrounding said second metallic tube.

2. A cable terminator according to claim 1 in which said second metallic tube has a non-circular cross-section.

3. A cable terminator according to claim 1 having a metallic spring box contact aixed to the open end of said first tube and adapted to engage a second elongated bar which extends parallel to the previously-mentioned elongated bar.

4. A cable terminator according to claim 1 havin-g a further wire having an end extending within said rst metallic tube, said end of said furtherI wire being crimped together with said outer conductor within said first metallic tube.

5. A cable terminator according to claim 2 in which the bore of said second metallic tube is rectangular in cross-section.

6. A cable terminator according to claim 4 having a. third metallic tube crimped at one end to grip said further w1re.

7. A cable terminator according to claim 1 in which both ends of said second metallic tube are situated within said first tube.

References Cited UNITED STATES PATENTS 2,941,028 6/1960 Edlen et al. 339-177 X 3,295,094 12/1966 De Lyon et al 339-l77 3,297,978 1/1967 Stark 339-177 3,302,159 l/1967 Schumacher 339-276 X OTHER REFERENCES Horwath; Coaxial Wire Termination; April, 1965; I.B.M. Technical Disclosure Bulletin.

RICHARD E. MOORE, Primary Examiner U.S. Cl. X.R. 339--256

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