GB2088146A - Switch-controlled plug and socket assembly with an interlocking device - Google Patents

Abstract

A switch-controlled plug and socket assembly with an interlocking device particularly for explosive environments is disclosed. The plug and socket have telescoping skirts and a positioning lug (15) on the plug skirt. The switch is coupled to a rotatable disc (35) with a guide slot (38A) cooperable with a first reciprocable member (22) having a head (22B) for preventing rotation of the disc when the plug is removed. The disc has a cam (39) cooperable with a third reciprocable member (23) which urges a second reciprocable member (24) into a guideway section behind the positioning lug (15) to prevent removal of the plug when the switch is turned on. The positioning lug cooperates with a guideway in the socket skirt (20C) having longitudinal sections connected by a circumferential section and an abutment collar of the plug is set back farther from the opening end of the plug than on conventional plugs to prevent use of socket with the latter. <IMAGE>

Description

SPECIFICATION Switch-controlled plug and socket assembly with an interlocking device The present invention relates to switchcontrolled plug and socket assemblies for industrial use in explosive environments such as mines.

The invention relates more particularly to such plug and socket assemblies comprising a so-called explosion-proof socket provided with an interlocking device for disconnecting the socket contacts when no plug is in the socket.

Plug and socket assemblies are known comprising a plug and a socket with their contacts arranged in a recess and an insulating block inside their respective skirts, the skirts of the plug and socket being adapted to telescope inside each other.

The plugs have a lug engageable with a longitudinal groove in the sockets and a guard collar associated with a seal and a latch ring.

Numerous conventional plug and socket assemblies have been developed from this basic arrangement for use in explosive environments.

An object of the invention is to provide a switch-controlled plug and socket assembly with an interlocking device which is reliable and of relatively simple construction and operation.

According to the invention there is provided a switch-controiled plug and socket assembly with an interlocking device, the plug and socket assembly comprising a plug and socket having complementary contacts and telescoping skirts, the contacts being arranged in a recess and an insulating block inside the respective skirts, the skirts having means for limiting telescopic movement, the interlocking device comprising a first reciprocable member responsive to a positioning member on the plug skirt when the plug is in its fully inserted position for unlocking the switch for actuation, a second reciprocable member cooperable with the positioning member for retaining the plug in the socket when the switch is in its "on" position, and a coupling disc operatively interposed between the first and second reciprocable members coupled for movement with the switch operating member of the switch between its "on" and "off" positions comprising a guide slot cooperable with the first reciprocable member and a cam operatively associated with the second reciprocable member.

Preferably, the positioning member comprises a positioning lug on the outside of the skirt of the plug at the open end thereof cooperable with a guideway in the skirt of the socket, the first reciprocable member comprising a head, the head being engaged in the guide slot in the disc when the plug is removed to block rotation of the disc, the positioning lug being cooperable with the first reciprocable member for displacing the head of the first reciprocable member out of the guide slot to free the disc for rotation.

Preferably, the means for limiting telescopic movement of the skirt comprises a collar on the skirt of the plug cooperable with the skirt on the socket, the contacts of the plug extending into the recess defined by the inner wall of the skirt and the end wall of a central insulating block, the distance between the open end of the skirt of the plug and collar being substantially greater than the distance between the open end of the skirt of the plug and the end wall of the insulating block, the direction of insertion of the plug changing in the course of insertion from the end wall to the fully inserted position in which the collar cooperates with the skirt of the socket.

In conventional plugs the maximum insertion of the plug is approximately equal to the depth of the plug recess and there is no change of direction in the course of insertion of the plug in the socket. It is therefore particularly advantageous to select the depth of the recess substantially equal to that of conventional plugs to permit use with conventional sockets provided the positioning member is compatible with the groove in the socket therefor. On the other hand, a conventional plug of this type cannot be used with the present socket since the collar prevents full insertion of the plug and consequently the unlocking of the associated switch. Also, the provision of the change of direction in insertion precludes use of a conventional plug even when provided with unauthorised extended contact pins.Furthermore, it is not even possible to adapt such a conventional plug to the present socket by removing the positioning member or lug in order to permit the change of direction since the first reciprocable member is operated by the positioning member upon full insertion of the plug.

These and other features of the invention will become more apparent from the description which follows with reference to an embodiment, given by way of nonlimiting example, with reference to the accompanying drawings, in which: Fig. 1 is a side elevational view, partly cutaway, of a plug of the switch-controlled plug and socket assembly; Fig. 2 is a fragmentary perspective view of a part of the socket skirt; Fig. 3 is a diagrammatic perspective view illustrating the coupling of the locking device with a switch operating member; Fig. 4 is a fragmentary longitudinal sectional view of the socket with the plug removed and therefore the interlocking device in the switch locking mode; and Fig. 5 is a sectional view similar to that of Fig. 4 with the plug fully inserted in the socket and the interlocking device freeing the switch operating member for actuation.

The plug of the plug and socket assembly illustrated in Fig. 1 is designated by general reference numeral 10 and comprises a cylindrical guide skirt 12, an insulating block 1 3 from which protrude the male contacts or pins 14 into a recess accommodating the same, defined by the inner wall of the skirt and the end wall of the insulating block 1 3. The contact pins 14 are recessed in the plug, with the free ends slightly set back with respect to the free edge of the skirt 12.

A generally parallelepipedic positioning member or lug 1 5 is provided on the outside of the skirt 12 at the open end thereof.

To this point the plug described is completely conventional. On the other hand, although it is conventional to provide a peripheral collar projecting outwardly from the skirt, collar 1 6 is disposed in the insulating block region of the plug substantially set back from the end wall of the block 1 3 and the recess into which the contact pins protrude.

Thus the distance L1 from the open end of the skirt 12 to the collar 16 (which corresponds to the maximum insertion of the plug in the socket) is substantially greaterthan the distance L2from the end wall of the insulating block 13 to the open end of the skirt 1 2, i.e., the depth of the recess accommodating the contact pins 14. The distance L2 of the plug is designed to be substantially equal to that of conventional plugs of the same type.

In actual practice the distance L, is preferably approximately between 1 .5L2 and 2L2. By contrast in conventional plugs of this type the distances L1 and L2 are substantially equal.

Accordingly, a plug 10 may be used either with a conventional socket or the so-called explosionproof socket disclosed herein, whereas a conventional plug cannot be used in the socket disclosed herein as will be brought out hereinafter.

The collar 1 6 limiting insertion of the plug in the socket may optionally be provided, as shown in broken lines with a gasket 1 7 cooperable with a free end of the skirt of the associated socket in which case the distance L1 is reduced correspondingly, and with a latch ring 1 8.

The socket of the plug and socket assembly illustrated only partially in the drawings is designated in by general reference numeral 20 and comprises an annular recess 20A for receiving the plug skirt 1 2 defined between a central insulating block 20B accommodating female contacts or sockets (not illustrated) adapted to engage contact pins 14 of plug 10, and an outer skirt 20.

A groove or guideway complementary in crosssection to the positioning lug or member 1 5 on the plug skirt 12 is formed in the inner wall of the socket skirt 20C and opens into the annular recess 20A. The guideway ensures in association with the positioning member 1 5 the guiding of the contact pins into their respective female contacts thereby preventing the contact pins from coming into engagement with the wrong female contacts.

The positioning member on the plug skirt acts as failsafe means in cooperation with the guideway.

Such failsafe means are known per se but in the present case the socket comprises a complementary guideway with a change of direction including two longitudinal sections 21 A, 21 B interconnected by a transverse or circumferential section 21 C requiring a change of angular orientation of the plug in the course of insertion of the plug skirt into the socket skirt.

The correct insertion of the plug 10 in the socket 11 thus requires, to begin with, a first axial displacement of the plug, then an angular displacement, clockwise as illustrated, and then a second axial displacement. The length L3 of the first longitudinal section 21 A reckoned from the open end of the plug is at least equal to the distance L2 defined above. Accordingly, if a conventional plug (in which L1 "" L2 as seen above) is inserted into the socket 10, its positioning member 1 5 stops short of the circumferential section 21 C of the guideway owing to the collar abutting against the end of the skirt to prevent rotation of the plug, full insertion of the plug and, ultimately, engagement of the complementary contacts of the plug and socket.Furthermore, the lengthening of the pins of the plug by unauthorised means does not permit the contacts of the plug to come into engagement with those of the socket.

The plug and socket assembly is controlled by an electrical switch designated by reference numeral 30 (Fig. 3), the switch housing 31 controlling the supply of power to the contacts of the socket and plug by an operating member or knob 32 mounted for rotation.

An interlocking device is provided so that the electrical switch is unlocked for actuation only upon full insertion of the plug into the socket and so that the plug is maintained in its fully inserted position or at least with the complementary contacts in engagement so long as the switch is in its "on" position.

The interlocking device comprises coupling means between the switch and the socket including a lug or pin 33 fixed for rotational movement with the rotatably mounted switch operating member 32 and received in a slot defined by a pair of pins 34 fixed for rotation with a disc 35 which in turn is rotatably mounted on the central block 20B of the socket about the longitudinal axis thereof at the end of the central block remote from the plug itself. Fasteners 36 extend through circumferential arcuate slots and notches 37 in the disc 35 to permit ielative angular displacement of the disc on the central block.To facilitate the transmission of motion between the switch operating member and the disc 35 the axis of rotation of the switch operating member and that of the socket are selected so that they lie in perpendicular planes; in other words the pin 33 is arranged generally at right angles to the pins 34 defining the slot therefor.

In order to lock and unlock the switch operating member the socket 20 is provided with first reciprocable members 22 only one of which is shown mounted for longitudinal translation in the central block 20B of the socket. Each of the first reciprocable members 22 comprises a pin 22A adapted to extend into the annular recess 20A which receives the plug skirt 12 and to retract inside the central block 20B of the socket, and a head 22B at the end of the reciprocable member remote from the free end of the pin 22A adapted to extend into an arcuate guide slot 38A in the disc 35 in the extended position and beyond the slot 38A in the disc in the retracted position of the pin 22A, in which position the smaller diameter pin is received in the guide slot.One of the first reciprocable members 22 is arranged so that its pin 22A extends into the groove 21 B in the skirt of the socket. A compression spring 22C is received on the pins 22A of the respective reciprocable members 22 bearing between a collar and an end wall closing off a cavity in which the spring 22C and the collar are housed. Each spring 22C urges its respective pin 22A towards the extended position.

The disc 35 has a switch "off" position in which the enlarged circular ends 38A of the arcuate slots 38B are in registry with the heads 22B of the pins 22A permitting the latter to be received in the enlarged ends 38A. In the "on" position the disc 35 is angularly displaced until the pins 22A are at the ends of the arcuate guide slots 38B remote from the enlarged ends 38A. The heads 22B on the pins 22A prevent the retraction of the pins 22A except in the switch "on" position since the width of the guide slots is narrower than the diameter of the heads.

In the extended positions of the pins 22A the heads 22B received in the enlarged ends 38A of the slots 38B prevent the turning of the disc.

Accordingly, if one attempts to close the switch without the plug of Fig. 1 in the fully inserted position in the socket, the heads 22B block the rotation of the disc 35 and therefore that of the switch operating member. On the other hand, when the contacts of plug are in engagement with the contacts of the socket the first reciprocable members are urged inwards, the heads 22B are disposed beyond the enlarged ends 38A of the slots 38B and it is then possible to actuate the switch 30 as the pins 22A do not prevent the rotation of the disc 35 in their position at the opposite ends of their respective slots 38B.

Without the positioning lug 1 5 a plug cannot release the interlocking device to unlock the switch.

In order to maintain the engagement of the complementary contacts of the plug and the socket so long as the switch 30 is in its "on" position, the interlocking device comprises a cam 39 defined by an inclined plane on the disc 35 cooperable with a third reciprocable member or plunger 23 which in turn cooperates with a second reciprocable member 24 perpendicular thereto housed in the socket skirt 20C. The plunger 23 has a frustoconical connecting zone 23B interconnecting reduced section part 23A and a large diameter part 23C.

The thinnest part of the cam 39 is in registry with the plunger 23 in the open position of the switch 30 (Fig. 4) and thickest part of the cam 39 is in registry with the plunger 23 in the closed position of the switch 30 (Fig. 5). A spring 25 urges the plunger 33 towards the cam 39.When the plunger 23 is in registry with the thinnest part of the cam 39 the plunger portion 23A of reduced section is in alignment with the second reciprocable member 24, the radially outer end 24A of the third reciprocable member 24 bearing against the plunger portion 23A of reduced section and the radially inner end 248 lying flush with the longitudinal section 21 B of the guideway for the positioning lug 1 5. The associated spring 26 urges the second reciprocable member away from the longitudinal section 21 B to its rest position.In the position of the plunger 23 in registry with the thickest part of the cam 39 (Fig. 5) the radially outer end 2;4Bof the third reciprocable member 24 bears against the large diameter part 23C of the plunger 23, the radially inner end of reciprocable member 24 prOjecting into section 21 B of the guideway behind the positioning lug 15.

Accordingly, when the plug is fully inserted into the socket and the switch turned on, the plug.

cannot be removed until the switch is first turned off. The switch operating member 32 cannot be operated until the plug is in its fully inserted position and once it is fully inserted the rotation of the disc 35 causes the plunger 23 to move outwards under the action of cam 39 which plunger in turn pushes the second reciprocable member 24 into the section 21 B of the guideway behind the positioning lug thereby preventing the withdrawal of the plug. Turning off the switch 30 by rotating the switch operation member 32 anticlockwise causes the rotation of the disc to bring the plunger 23 into registry with the thinnest part of cam 39, the inward displacement of the plunger 23 under the action of spring 25 and the retraction of the second reciprocable member out of groove 21 B, thereby freeing the plug for removal.

The invention is not intended to be limited to the illustrated and described embodiment but on the contrary encompasses other embodiments without departing from the scope of the appended

Claims (10)

claims. CLAIMS

1. A switch-controlled plug and socket assembly with an interlocking device, the plug and socket assembly comprising a plug and a socket having complementary contacts and telescoping skirts, the contacts being arranged in a recess and an insulating block inside the respective skirts, the skirts having means for limiting telescopic movement, the interlocking device comprising a first reciprocable member responsive to a positioning member on the skirt of the plug when the lug is in its fully inserted position for unlocking the switch for actuation, a second reciprocable member cooperable with the positioning member for retaining the plug in the socket when the switch is in its "on" position, and a coupling disc operatively interposed between the first and second reciprocable members coupled for rotation with the switch operating member of the switch between its "on" and "off" positions comprising a guide slot cooperable with the first reciprocable member and a cam operatively associated with the second reciprocable member.

2. A plug and socket assembly as claimed in Claim 1, wherein the positioning member comprises a positioning lug on the outside of the plug skirt at the open end thereof cooperable with a guideway in the skirt of socket, the first reciprocable member comprising a head, the head being engaged in the guide slot in the disc when the plug is removed to block rotation of the disc, the positioning lug being cooperable with the first reciprocable member for displacing the head of the first reciprocable member out of the guide slot to free the disc for rotation.

3. A plug and socket assembly as claimed in Claim 1 or 2, wherein the first reciprocable member is mounted for translatory movement between an extended position in which it extends into the guideway in the skirt of the socket and a retracted position under the action of the positioning lug.

4. A plug and socket assembly as claimed in Claim 1, 2 or 3, wherein a third reciprocable member arranged in the skirt of the socket is cooperable with the cam on the disc and with the second reciprocable member, the third reciprocable member being displaceable between an inward position freeing the second reciprocable member to retract and an outward position to displace the second reciprocable member to its position for retaining the plug in the socket.

5. A plug and socket assembly as claimed in Claim 4, wherein the second reciprocable member extends into the guideway in the skirt of the socket behind the positioning lug when the plug is fully inserted in the socket to retain the plug in the socket.

6. A plug and socket assembly as claimed in any of the preceding claims, in which the switch operating member is coupled to the disc by a pin and slot connection.

7. A plug and socket assembly as claimed in Claim 6, wherein the pin and slit are generally at right angles to each other.

8. A plug and socket according to any of the preceding claims, wherein the means for limiting telescopic movement of the skirts comprises a collar on the skirt of the plug cooperable with the socket skirt, the contacts of the plug extending into the recess defined by the inner wall of the skirt of the plug and the end wall of a central insulating block, the distance between the open end of the skirt of the plug and the collar being substantially greater than the distance between the open end of the skirt of the plug and the end wall of the central insulating block, the direction of insertion of the plug changing in the course of insertion beyond the end wall to the fully inserted position in which the collar cooperates with the skirt of the socket.

9. A plug and socket assembly as claimed in Claim 8, wherein the positioning member comprises a positioning lug on the outside of the skirt of the plug cooperating with a guideway in the socket, the guideway includes a transverse or circumferential section permitting the change of direction of the plug in the course of insertion in the socket.

10. A plug and socket assembly substantially as herein described and illustrated in the accompanying drawings.

1 A plug for a plug and socket assembly substantially as herein described and illustrated in the accompanying drawings.