The present invention relates to a multi-channel electrical connector such as is usable for, inter alia, data signal transmission between connected components.

Multi-channel or multi-track electrical connectors exist in a wide variety of forms, including plug-and-socket connectors making and breaking electrical connection by insertion of a plug into and removal of the plug from a socket. In general, the electrical connection within the plug and socket is produced by interengaging electrically conductive pins and sleeves or by frictionally interengaging surface areas. Problems commonly associated with conventional forms of such electrical connection are insecure interengagement, for example as a consequence of wear, and build-up of insulating oxide coatings at points of interengagement, leading to intermittent or permanent disruption of the electrical path produced by the interengagement. In addition, many such connectors are limited to specific relative rotational relationships of the plug and socket.

A further issue with conventional connectors is complexity of manufacture, such as precision production and positional fixing of pins and sleeves or other mating components which require specific alignments in the plug and socket.

It is therefore an object of the present invention to provide an electrical connector, particularly a connector suitable for, inter alia, low-voltage applications and providing multiple channels or paths, which while utilising the proven plug-and-socket concept enables creation of a secure electrical connection resistant to unintended interruption of the electrical path and offers an effective and simple means of realising electrically conductive regions of the connector.

A further object of the invention is to provide a connector of the kind mentioned which is of simple and compact construction and which, in particular, allows discrete make-and-break connection of multiple conductor tracks with a minimum of complexity and by an easy action.

A subsidiary object of the invention is provision of such a connector based on a plug-and- socket principle in which it may be possible to produce electrical connection in any desired relative angular relationship of plug-and-socket components. Other objects and advantages of the invention will be apparent from the following description.

According to the present invention there is provided a multi-channel electrical connector comprising: a socket, which comprises a socket body of electrically insulating material defining a bore which is circumferentially bounded by a wall and which has an open end forming an entrance of the socket, the socket body being provided in the wall of the bore with a plurality of annular grooves spaced apart axially of the bore and each having an electrically conductive surface and the socket body being further provided with a plurality of electrical conductors each electrically connected with the electrically conductive surface of a respective one of the annular grooves and each terminating in a respective electrical terminal in a region of the socket body remote from the socket entrance, each electrically conductive groove surface and respective electrical conductor being electrically isolated from the or each other electrically conductive groove surface and electrical conductor of the socket body, and a plurality of resilient electrically conductive annular contact elements each arranged in a respective one of the annular grooves to protrude into the bore, and a plug, which comprises a plug body of electrically insulating material defining a pin which is circumferentially bounded by a circumferential surface and has a free end and which is insertable by the free end into the bore of the socket body to be received within the annular contact elements of the socket, the plug body being provided on the circumferential surface of the pin with a plurality of electrically conductive annular contact zones spaced apart axially of the pin and the plug body being further provided with a plurality of electrical conductors each electrically connected with a respective one of the electrically conductive annular contact zones of the pin circumferential surface and each terminating in a respective electrical terminal in a region of the plug body remote from the free end of the pin, each electrically conductive annular contact zone of the pin circumferential surface and respective electrical conductor being electrically isolated from the or each other electrically conductive annular contact zone of the pin circumferential surface and electrical conductor of the plug body, wherein the annular grooves correspond in number and axial spacing with the annular contact zones so that each of the annular grooves and the respective annular contact element arranged therein are alignable with a respective one of the annular contact zones when the pin is inserted into the bore and received within the annular contact elements wherein the inner diameter of each annular contact element arranged in its annular groove is dimensioned to be smaller than the diameter of the electrically conductive annular contact zone with which it is alignable whereby when the pin is inserted in the bore and the annular contact elements are in alignment with the annular contact zones the annular contact elements will be disposed in resilient contact with the electrically conductive surfaces of the respectively aligned annular grooves and with the respectively aligned annular contact zones so as to produce a plurality of mutually discrete continuous electrical paths between the terminals of the electric conductors of the socket body and the terminals of the electrical conductors of the plug body via the electrical conductors of both the socket body and the plug body, the electrically conductive surfaces of the grooves of the socket body, the annular contact elements and the electrically conductive annular contact zones of the pin of the plug body, and wherein at least some of the totality of electrically conductive regions represented by the annular groove surfaces and the conductors of the socket body and the annular contact zones and conductors of the plug body are formed by discrete areas of electrically conductive material coated on the electrically insulating material of the relevant body.

In such a connector the contact-making between socket and plug is achieved with a high level of maintained security by the resilient contact elements, which in the presence of the pin in the bore of the socket body are subjected to loading under compression in the annular grooves of the socket body and loading under expansion by the annular contact zones of the pin, thus are squeezed between the electrically conductive surfaces of the grooves and the electrically conductive contact zones of the pin. The outer diameter of the resilient annular contact element in the relaxed state of the element can be greater, preferably only slightly greater, for example 5 to 10%, than the outer diameter of the annular groove so that the contact element is constantly under light compression in the groove even in the absence of the pin. On the other hand, the inner diameter of the contact element as seated in the groove is dimensioned to be less, preferably only slightly less, for example 5 to 10%, than the diameter of the associated contact zone of the pin, so that the contact element is expanded when the pin is inserted into the bore and the annular contact zone is aligned with the element. These two sources of spring loading, provided by initial location of the contact element in the groove at the time of manufacture of the connector and by engagement of the pin in the bore during use of the connector, can be exploited to achieve contact of the contact elements under pressure with the relevant surfaces of the socket and pin bodies through the simple expedient of predetermination of appropriate diameters of the co-operating elements of groove, contact element and annular contact zone. Although the contact elements are preferably subject to compression in the grooves even in the absence of the pin, thus seated under permanent compression in the grooves, it is equally possible for tolerances to be selected so that the contact elements are retained in the grooves otherwise than under compression and are expanded to such an extent on insertion of the pin into the bore of the socket body that the contact elements are then and only then urged into contact under pressure with the electrically conductive surfaces of the grooves. In conjunction with the specific form of electrical contact-making embodied in the connector construction a particularly important feature is the formation of at least some of the electrically conductive regions of the socket body and/or plug body by discrete areas of electrically conductive material coated on the electrically insulating material of the relevant body. This means that the electrically conductive regions concerned can be provided in particularly simple and economic manner by, for example, areas or tracks of electrically conductive material bonded to - in particular plated on, such as by metallisation - a substrate of electrically insulating material constituting the relevant body. Instead of providing electrical conductivity by way of, for example, separately formed and individually attached components such as wires, the formation of some or all the electrically conductive regions from discrete areas of coated metal, carbon-based composites or other electrically conductive material may significantly reduce production cost and eliminates welded, soldered or other connections liable to fault or failure.

Preferably, all of the annular groove surfaces and the conductors of the socket body are formed by discrete areas of electrically conductive material coated on the electrically insulating material of the socket body. Thus, the entire socket body can be provided with a coating of electrically conductive material so that all of the electrically conductive regions on that body are provided in the same fashion with the same material and, advantageously, by one of the same coating process.

For preference, the areas of coated electrically conductive material forming the conductors of the socket body are provided on walls of passages in the socket body, so that conductor tracks can be conveniently led in and through the body from the terminals of the conductors to the electrically conductive surfaces. The passages can follow any desired route along and/or across the body in accordance with the geometric shape of the body. In one convenient embodiment, the passages in the socket body can comprise channels open at the outer circumference of the socket body and vias, i.e. tunnels, each extending between and communicating with a respective one of the channels and a respective one of the annular grooves. If the socket body is an injection-moulded plastics material component such channels can be easily formed at the time of moulding, whilst the tunnels, if not formed at that time, can be produced subsequently by drilling.

With respect to the required electrical isolation it can be advantageous if the electrically insulating material of the socket body has a general coating of the electrically conductive material and if the electrical isolation of the electrically conductive groove surfaces and the electrical conductors is provided by areas which separate those groove surfaces and conductors and are without the coating of electrically conductive material. In that case, the discrete areas of coated electrically conductive material can, if desired, be provided by selective application of electrically conductive coating material in just those areas or by selective masking of regions between those areas and applying electrically conductive material in the unmasked regions. However, in a particularly advantageous procedure for achieving the discrete areas of electrically conductive material, parts of the coating of electrically conductive material are simply removed, for example by grinding or laser ablation, in the separation areas. Thus, for example, in the case of the grooves in the wall of the bore in the socket body the coated bore can be machined, in particular reamed, to return the wall surface to the uncoated electrically insulating material, but to leave in place the electrically conductive material still lining the recessed grooves and thus forming the electrically conductive surfaces thereof, these groove surfaces being electrically isolated by the intervening sections of the now-uncoated bore wall of the socket body. Similarly, in the case of the passages defining the electrical conductors the channels can be electrically isolated by removing electrically conductive material either side of each channel so that the electrically conductive material on the walls of the channels is isolated. If vias, i.e. tunnels, are provided and, in particular, formed in the socket body before application of the overall coating, the tunnels will be lined or even filled with the electrically conductive coating material and this will be electrically isolated by the enclosure of each tunnel within the electrically insulating material of the socket body. If, for example, the terminals terminating the conductors are located at an end face of the socket body the coated electrically conductive material can be removed entirely from that face or at least to such an extent as to isolate the individual terminals. If the terminals are provided at the perimeter of such an end face the channels can run to the perimeter. However, if the terminals are provided inwardly of the perimeter, tunnels can be formed, prior to application of the coating, to run from each channel to an individual point on the end face and will be lined with the coating material in the same way as the tunnels connecting the channels with the groove surfaces. Creation of the required electrical isolation by removal of applied coating material as distinct from selective application of the material or masking represents a simple and economic way of achieving the desired electrically conductive and mutually insulated tracks and contact areas in the socket body. A combination of procedures is, however, possible if this should be advantageous.

In analogous manner, all of the annular contact zones and the conductors of the plug body can be formed by discrete areas of electrically conductive material coated on the electrically insulating material of the plug body. In similar manner to the socket body the entire plug body can thus be provided with a coating of electrically conductive material so that all of the electrically conductive regions on that body are provided in the same fashion with the same material and, advantageously, by one of the same coating process. Again, the areas of coated electrically conductive material forming the conductors of the plug body can be provided on walls of passages in the plug body. In this case, the passages in the plug body can comprise vias, i.e. tunnels, extending through the plug body and each communicating with a respective one of the annular contact zones. Provision of such tunnels can be conveniently achieved if the plug body is composed of a plurality of body members of the electrically insulating material permanently joined together at mating faces thereof, the tunnels in the plug body being formed by channels in at least one of the mating faces. These channels are formed before the body members are joined together and conjunctively form the tunnels when the bodies are so joined. The advantages and merits of a plug body furnished in such a way with the electrically conductive annular contact zones and the electrical conductors correspond with those recited above for the socket body.

Also analogously to the socket body, the electrically insulating material of the plug body can have a general coating of the electrically conductive material and the electrical isolation of the electrically conductive annular contact zones and the electrical conductors can then be provided by areas which separate those zones and conductors and are without the coating of electrically conductive material. The electrically isolating areas can be formed by the same described procedures, thus selective application of the electrically conductive coating material, masking of areas not to be coated and/or removal of material to create the electrically isolating areas by exposure of the electrically insulating material of the plug body. The advantages connected with provision of the electrically insulating areas by omission or removal of the electrically conductive coating material again correspond with those stated for the socket body.

For preference the contact elements are annular coil springs, in which case contact- making in each of the electrical paths by the respective spring is produced by multiple contact points, in particular each individual coil of the spring makes contact with the electrically conductive surface of the associated annular groove of the socket body at the outer circumference of the spring and with the electrically conductive contact zone of the pin of the plug body at the inner circumference of the spring. In the case of, for example, a spring with 50 coils, there can thus be up to 50 points or zones of electrical contact at each of the inner and outer circumferences of the spring. Even if contact-making is or becomes insufficient at isolated ones of these points or zones for any reason, overall contact is not and cannot be lost. The annular coil springs, in effect endless garter springs, are preferably canted coil springs, in which the coils are canted by comparison with the coils of a conventional coil spring. The canting of the coils assists radial compression and expansion of each spring, since compression and expansion is accommodated not only by change in stress in the spring, but also by change in the angle or lay of the individual coils. Canted coil springs are readily available as proprietary products, in which case choice of groove diameter and annular contact zone diameter can if desired be selected in accordance with a suitable commercially available size of spring.

The electrically conductive annular surface of each of the grooves can be concave and substantially complementary to a convexity of the annular contact element, for example coils of a coil spring, arranged therein. This has the result, in the case of a coil spring, that each coil of each spring has substantially linear, rather than merely punctiform, contact with the contacted groove surface and thus an optimised contact area.

The contact elements can also be, for example, annular bodies of electrically conductive resilient material, for example elastomer with embedded conductive material such as carbon or graphite. However, in an advantageous embodiment each of the contact elements comprises an endless body composed of a series of interconnected alternatively inwardly and outwardly directed canted spring arms. In this spring construction the spring arms are preferably curved and have radiused ends so as to facilitate compression/expansion of the body and sliding contact with the co-operating surfaces of the socket body and plug body, thus the associated electrically conductive groove surface of the former and the associated electrically conductive contact zone of the latter. Such a body can be conveniently produced by, for example, three-dimensional printing to form a resilient structure of plastics material, which is then metallised.

Preferably, the socket body defines an axis and the bore is rotationally symmetrical with respect to the socket body axis. Similarly, for preference the plug body defines an axis and the pin is symmetrical with respect to the plug body axis. This significantly enhances handling, since the electrical paths may then be producible in any rotational setting of the pin in the bore and a requirement to produce interconnection of the socket and plug by observing a specific relative rotational relationship of the socket and plug bodies, such as is necessary with multi-pin connectors, is eliminated. The same quality of electrical connection is achieved by the co-operation of the annular contact elements with the electrically conductive annular surfaces of the grooves and with the electrically conductive annular contact zones of the pin circumferential surface regardless of the rotational settings of the socket and plug bodies. In addition, any torque exerted on either one of the bodies during use can be accommodated by relative rotation of the bodies without disrupting the electrical connection or damaging the socket. However, if so desired the bore and pin could also be, for example, polygonal so that interconnection is producible only in a defined number of relatively angular settings, depending on the number of sides of the polygon.

With advantage, the bore and the pin are substantially cylindrical. Formation of the bore and pin to be substantially cylindrical simplifies manufacture, since the grooves in the socket body can then all be of the same diameter with respect to one another, allowing use of contact elements of the same diameter as one another, and the annular contact zones of the pin of the plug body can also be of the same diameter with respect to one another. However, the bore and pin could, if desired, be of mutually complementary tapered form so as to ensure firm seating of the socket and plug bodies one in the other, in particular to resist tilting of the bodies relative to one another. For preference, however, this is achieved by providing the socket body and pin body with seating surfaces of mutually complementary tapering form interengageable to seat the bodies one on the other when the pin is inserted into the bore. In that way, the two bodies can be firmly seated while retaining the advantages of cylindrical shaping of the bore and pin.

The terminals of the conductors of the socket body can be disposed at an end face of the socket body and similarly the terminals of the conductors of the plug body can be disposed at an end face of the plug body. These terminal locations make it possible to provide external connections to the bodies generally in axial continuation of the bore and pin, which assists handling of the connector and overall compactness in the transverse dimension of the connector.

The invention also embraces a method of forming the discrete areas of coated electrically conductive material in a connector according to the invention, wherein firstly the relevant body is coated in its entirety with the electrically conductive material and then the discrete areas are defined by selective removal of the electrically conductive material around those areas, the selective removal preferably being is carried out by at least one of abrading and reaming. This represents a particularly simple and effective process for achieving electrical isolation of electrically conductive regions, especially if those regions possibly have complicated shapes, but the surrounding regions have shapes which are relatively straightforward to abrade, ream or otherwise mechanically process.

A preferred embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1A is a section, along the line I - I of Fig. 1 E, of a socket of a connector embodying the invention;

Fig. 1 B is a side view, in the direction of the arrow 1 B of Fig. 1 A, of the socket;

Fig. 1 C is a side view, in the direction of the arrow 1 C of Fig. 1 A, of the socket;

Fig. 1 D is a plan view of the socket;

Fig. 1 E is an inverted plan view of the socket;

Fig. 2A is a side view of a plug of the connector;

Fig. 2B is an axial section, along the line II - II of Fig. 2A, of the plug;

Fig. 2C is an axial section, along the line III - III of Fig. 2A, of the plug;

Fig. 2D is a plan view of the plug;

Fig. 2E is an inverted plan view of the plug; and

Fig. 3 is a composite sectional (socket) and side (plug) view, to enlarged scale, of the socket and plug similarly to the views of Figs. 1A and 2A, showing the socket and plug in states of partial (lefthand side) and full (righthand side) interengagement.

Referring now to the drawings there is shown a multi-channel electrical connector 10 which is suitable for, but not limited to, low-voltage applications in the field of data transmission. The connector of the preferred embodiment is capable of handling higher voltages up to about 50 Volts, but is scalable to conduct voltages even above that level.

The connector 10 comprises a socket 20 and a plug 30 which can be plugged together and unplugged, as described in the following, to make and break an electrical connection between multiple conductors (not shown), particularly multiple insulated wires, coupled to the plug and socket. Each wire coupled to the plug and respectively associated wire coupled to the socket represents an individual channel.

The socket 20 comprises a cylindrical socket body 21 of electrically insulating material able to bond with a metallic coating material, preferably a body integrally injection-moulded from a plastics material, such as polyurethane or nylon. The socket body 21 has an axial cylindrical bore 22 closed at one end and open at the other end to provide a socket entrance. The bore 22 is flared at the entrance to provide a conical centring surface 23. The circumferential wall of the bore 22 is formed with a plurality - here four - of identical equidistantly and axially spaced apart annular grooves 24 each having a concave profile in axial section of the body 21. The grooves 24 can be formed by a rotary milling tool acting on the wall of the bore 22 in a circular direction to undercut the wall at appropriately preselected spaced-apart axial locations.

The surfaces of the grooves 24 are electrically conductive and are electrically isolated from one another. This is achieved in this embodiment by metal-coating the entire socket body 21 and then abrading or reaming the bore wall to remove the coating from the segments of the wall between the grooves 24 and segments of the wall outwardly of the end grooves, thereby creating discrete areas of the electrically conductive coating material within the grooves; removal of coating material from the latter wall segments eliminates possible leakage paths to other areas of the socket body 21. The coating is optionally also removed, by abrading, from the centring surface 23. The coating process is preferably carried out by firstly copper-plating the body and then electroplating the copper layer with nickel.

In Figs. 1A to 1 E the areas retaining a coating of the electrically conductive material are dotted so as to facilitate recognition of electrically conductive areas. The socket body 21 also has a plurality of electrical conductors 25 each electrically connected with the electrically conductive surface of a respective one of the annular grooves and each terminating in a respective electrical terminal 26 at the end face, from which the coating of electrically conductive material has also been removed, of the socket body 21 remote from the socket entrance. Each such conductor 25 is provided by a coating of the electrically conductive material on the wall of a respective passage in the socket body 21 , in particular on the wall of a respective open channel 25a extending in the outer circumference of the socket body parallel to the axis of the bore 22 and on the wall of a tunnel 25b extending between that channel 25a and a respective one of the annular grooves 24. Each channel 25a extends from the vicinity of the mentioned end face of the socket body 21 to the vicinity of the associated annular groove 24 and consequently has a length dictated by the spacing of that groove from the end face. The channel 25a can extend to and open at that end face if the terminal 26 is located at the perimeter of the end face, but if it is located at a position disposed inwardly of the perimeter as shown in Fig. 1 E the channel can be linked with that position by a linking tunnel 25c, which also has a coating of the electrically conductive material on its wall. Such a configuration of the conductor 25 is evident in Figs. 1A to 1 E. The channels 25a and tunnels 25b, 25c are formed in the socket body 21 , such as by moulding or drilling, prior to coating the body with the electrically conductive material and this material in the coating process thus flows into and provides electrically conductive paths between the grooves 24, channels 25a and tunnels 25b, 25c.

The coated surfaces of the grooves 24 are electrically isolated by, as previously stated, removing the coating from the bore wall segments between and outside the grooves. The coated channels 25a are electrically isolated from one another by removing (abrading) coating material from areas of the outer Circumference of the socket body 21 surrounding the channels as evident in Figs. 1 B and 1 C; these areas can be formed by outermost faces of longitudinally extending and radially outwardly projecting steps at the outer circumference so as to facilitate the abrading process. The coated tunnels 25b connecting the channels 25a with the grooves 24 are electrically isolated from one another since they are entirely enclosed within the constituent electrically insulating material of the socket body 21. The coated linking tunnels 25c connecting the channels 25a with the terminals 26 at the end face of the socket body 21 are similarly enclosed by the electrically insulating material of the socket body and are isolated at its end face by removal of the coating material therefrom as mentioned beforehand. The terminals 26 can be, in the simplest form, the open ends of the linking tunnels 25c, into which bared ends of conductor wires can be inserted and electrically connected with the coating on the tunnel walls by, for example, soldering or any other suitable permanent or releasable form of connection, for example by mechanical clamping elements.

Although production of the socket body 21 by moulding in one piece is preferred, it is also possible to mould the body in two axial halves which are joined together by bonding at mating faces lying in a plane containing the bore axis. In that case the grooves 24 can be formed during the moulding rather than subsequently by milling or another material removal process. Each groove in each body half is semi-circular. If the body halves are coated with the electrically conductive material prior to joining, the mating faces then have to be cleaned of the coating to enable bonding. Other methods of producing the socket body 21 are conceivable, including machining from a blank and layer fabrication, thus 3D printing. The electrically conductive material can also be selectively applied just to the intended electrically conductive areas, for example by masking the intended electrically isolating areas.

The socket 20 comprises, additionally to the socket body 21 , a respective resilient electrically conductive annular contact element 27 arranged in each of the grooves 24 and protruding radially inwardly of the wall of the bore 22. In Fig. 1 A, for the sake of clarity with respect to the form of the socket body 21 , only one of the grooves 25 is shown with such an element 27, whereas in Fig. 3 the contact elements are shown in all of the grooves. In the embodiment, each contact element 27 is a circularly annular stainless-steel coil spring 27a, specifically a canted coil spring in which the individual coils have a slanted lay, such springs being known for applications such as seal expanders and as electrical conductors. By comparison with non-canted coils of a conventional annular coil spring, the cant of the coils imparts to the spring 27a a greater capability of deflection for a given coil-wire thickness, particularly in the sense of radial compression and radial expansion. Each annular coil spring 27a has an outer diameter slightly greater than that of the groove 24 in which it is arranged, so that the spring 27a is seated under compression in the groove. Fitting of each spring 27a in its groove 24 requires sufficient distortion of the spring to enable insertion into the bore 24 of the socket body 21 and easing into position in the groove 24, where the spring can seek to regain its annular form, but - due to the diametral difference of the spring and groove - cannot not fully relax and accordingly remains under compression in the groove. This ensures firm seating in the groove 24 and, in particular, contact of the radially outer extremities of the coils of the spring 27a with the electrically conductive surface of the groove 24, i.e. the nickel coating in the groove, under pressure and thus secures electrical contact-making with that surface. This contact-making is effective at multiple locations depending on the number of coils, for example 50 coils and consequently 50 contact locations. The convexity of the outer circumference of each coil spring 27a as conjunctively defined by its coils is substantially complementary to the convexity of the electrically conductive surface of the associated annular groove 24 so that the spring is a snug fit in the groove and the contact of each coil with the groove surface is linear, specifically curvilinear, rather than punctiform.

However, as already indicated, seating of the springs 27a under compression in the grooves 24 is preferred, but not essential. As long as the springs are not overly loose in the grooves, urging of the springs into firm contact with the groove surfaces can be produced during use of the connector, as described further below.

The plug 30 can be constructed analogously to the socket 20 and accordingly comprises a plug body 31 again of electrically insulating material able to bond with a metallic coating material, preferably a body injection-moulded from a plastics material, such as polyurethane or nylon. The plug body 31 comprises a generally cylindrical grip member 32 of approximately the same diameter as the socket body 21 and a coaxial cylindrical pin 33 of smaller diameter extending from the grip member. The diameter of the pin 33 is smaller than the diameter of the axial bore 22 of the socket body 21 and the length of the pin slightly less than the length of the bore, so that the pin is insertable by its free end into the bore and can be entirely received in the bore. The end of the pin 33 adjoining the grip member 32 has a flared transition to the member so as to form a centring surface 34 substantially complementary to and co-operable with the conical centring surface 23 at the entrance of the bore 22 of the socket body 21.

The circumferential surface of the pin 33 is provided with a plurality - here four in correspondence with the number of grooves 24 in the socket body - of electrically conductive annular contact zones 35 equidistantly spaced apart axially of the pin 33, specifically at the same spacings as the grooves 24 in the socket body 21 and hence as the annular coil springs 27a seated in the grooves. The contact zones 35 are electrically isolated from one another. Similarly to the socket body 21 , the electrical conductivity of the contact zones 35 and mutual electrical isolation is achieved in this embodiment by metal-coating the entire plug body 31 and then selectively grinding the pin circumferential surface to remove the coating between the intended contact zones and also outwardly of the end zone closest to the grip member 32, thereby creating discrete areas of the electrically conductive coating material. To facilitate grinding, the circumference of the pin 33 can be slightly stepped in departure from a pure cylindrical form, specifically so that the contact zones 35 are very slightly recessed; coating material can then be ground off the proud regions of the pin between and outlying the contact zones by a tool which can operate with a clearance in relation to the recessed contact zones. The slight recessing of the contact zones 35, which may remain even after removal of the coating from the proud regions, may offer the advantage of a degree of protection of the edges of the coating in the contact zones from abrasion during movement of the pin 33 in the socket bore 22.

As with the socket body 21 , the coating process is preferably carried out by firstly copper- plating the plug body 31 and then electroplating the copper layer with nickel. Similarly to Figs. 1A to 1 E, in Figs. 2A to 2E the areas retaining the coating of electrically conductive material are dotted.

As a consequence of the described arrangement of the grooves 24 and contact zones 35, each contact zone is disposed in alignment with a respective one of the grooves - and thus with the coil spring 27a arranged in that groove - when the pin 33 is fully received in the bore 22 of the socket body 21 , as defined by the interengagement of the flared centring surfaces 23 and 34 respectively of the socket body and plug body.

Similarly to the socket body 21 , the plug body 31 has a plurality of electrical conductors 36 each electrically connected with a respective one of the electrically conductive annular contact zones 35 and each terminating in a respective electrical terminal 37 at the end face, from which the coating of electrically conductive material has also been removed, of the grip member 32 remote from the pin 33. Each of these conductors 36 is provided by a coating of the electrically conductive material on the wall of a respective passage in the plug body 31 , in particular on the wall of a respective tunnel 36a extending longitudinally in both the grip member 32 and the pin 33 parallel to the cylinder axis thereof and then radially to communicate with a respective one of the contact zones 35. The longitudinally extending part of each tunnel 36a thus runs from the mentioned end face of the grip member 32 to the vicinity of the associated contact zone 35 and consequently has a length dictated by the spacing of that contact zone from the end face. The configuration of the conductors 36 is evident in Figs. 2A to 2E. The tunnels 36a are formed in the plug body 31 , such as by drilling, prior to coating the body with the electrically conductive material and this material during the coating process thus flows into and provides electrically conductive paths between the contact zones 35 and the tunnels 36a.

The coated tunnels 36a connected with the contact zones 35 are electrically isolated from one another since they are entirely enclosed within the constituent electrically insulating material of the plug body 31. The tunnels 36a are similarly isolated at the free end face of the grip member 32 by removal of the coating material therefrom, as mentioned beforehand, so as to expose the insulating material of the plug body. Again analogously to the socket body 21 , the terminals 37 of the plug body 31 can be, in the simplest form, the open ends of the tunnels 36a, into which bared ends of conductor wires can be inserted and electrically connected with the coating on the tunnel walls by, for example, soldering or any other suitable non-detachable or detachable form of connection.

The plug body 31 can be produced by moulding in one piece, in which case penetration of the electrically conductive coating material into the tunnels 36a to the extent necessary to achieve sufficient covering of the tunnel walls can be ensured by various methods including oversizing the tunnels and/or use of slave feed tunnels from which any coating can be subsequently removed at least in part. It also possible to produce the plug body 31 by moulding in two axial halves which are joined together by bonding at mating faces lying in a plane containing the common axis of the pin and grip member. In that case the tunnels can be easily formed, during the moulding, as channels open at the mating faces. If the plug body halves are coated with the electrically conductive material prior to joining, the mating faces then have to be cleaned of the coating to enable bonding. Other methods of producing the plug body are conceivable, including machining from a blank and layer fabrication, thus 3D printing. The electrically conductive material can also be selectively applied just to the intended electrically conductive areas, for example by masking the intended electrically isolating areas.

Each of the coil springs 27a forming one of the resilient electrically conductive annular contact elements 27 has an inner diameter slightly smaller than the respectively associated contact zone 35, i.e. the zone with which it is aligned when the pin 33 is fully received in the bore 22 of the socket body 21 as described further above. As a consequence of this diametral difference, each coil spring 27a is, on insertion of the pin 33 into the bore 22, expanded by the pin and, in the fully inserted state of the pin, disposed in contact with the respective contact zone 35 under pressure. The spring 27a is thereby resiliently urged into contact with both the electrically conductive surface of the groove 24 and the electrically conductive zone 35. As in the case of the groove 24, the coils of the coil spring 27a provide multiple points of electrical contact with the contact zone 35 and thus produce a highly positive and secure electrical connection between groove and zone. The connections produced by way of all pairings of groove 24 and contact zone 35 create a plurality of mutually discrete continuous electrical paths between the terminals 26 of the socket body 21 and the terminals 37 of the plug body 31 via the electrical conductors 25, 36, that is to say the channels 25a and tunnels 25b, 25c, 36a, of the socket and plug bodies 21 , 31 , the electrically conductive surfaces of the grooves 24 of the socket body 21 , the annular coil springs 27a and the electrically conductive contact zones 35 of the pin 33 of the plug body 31.

Use of the connector 10 is largely self-evident from the preceding description of its construction. When the connector is an operationally ready state, that is to say when external conductors such as sets of wires have been coupled to the terminals 26, 37 of both the socket body 21 and the plug body 31 , production of continuous electrical paths along the sets of wires is achieved by insertion of the pin 33 of the plug 30 into the bore 22 of the socket body 21 in the direction of the arrow in Fig. 3, and thus through the coil springs 27a seated in the grooves 24 in the wall of the bore 22, until the centring surfaces 23, 34 come into mutual contact, which denotes full receipt of the pin 33 in the bore 22. Partial insertion of the pin 33 is shown in the lefthand half of Fig. 3 and full insertion in the righthand half. Insertion of the pin 33 through the coil springs 27a is accompanied by light expansion of the springs, which are thereby resiliently urged into contact with the electrically conductive contact zones 35 of the pin and the electrically conductive surfaces of the grooves 24. If the springs were already seated under compression in the grooves, the degree of that compression is increased. If the springs were not already seated under compression in the grooves, compression is then achieved by the expansion of the springs, assuming a relatively snug fit of the springs in the grooves.

The resilient contact-making by the coil springs 27a provides a secure electrical coupling of the socket 20 and plug 30 and establishes individual and mutually electrically isolated electrical paths through the plug and socket by way of the participating conductive components described in the foregoing. In addition, the resilient contact of the springs with the contact zones of the plug provides frictional self-locking of the interengaged plug and socket and resists separation. The rotationally symmetrical construction of the socket body 21 and the pin 33 of the plug body 31 allows production of an electrical connection by the connector 10 in any relative rotational setting of the socket 20 and plug 30.