WO1993017469A1

WO1993017469A1 - Improvements in cable grips

Info

Publication number: WO1993017469A1
Application number: PCT/GB1993/000359
Authority: WO
Inventors: Hugh Heathcote Gilbert; Bruce James Renfrew; Kenneth Paul Poberezny
Original assignee: Rotacon Limited
Priority date: 1992-02-21
Filing date: 1993-02-19
Publication date: 1993-09-02

Abstract

A device for gripping and locating an elongate member (10) in a housing (1) comprises a one-piece plate-like component of plastics material having a pair of opposed outer edges (7a), the housing being recessed to accommodate said opposed outer edges. The plate-like component has wall parts (4) defining therebetween a central blind opening leading to first and second recesses (12) which open on each side thereof towards said opposed outer edges. Respective third and fourth bounded openings (13) are also formed between said wall parts (4) and the adjacent opposed outer edges (7a), the first and second recesses (12) being designed to deform more readily in the face of outward pressure on the wall parts (4) caused by insertion of the elongate member (10) into the central opening than the deformation of the third and fourth bounded openings (13) caused by said insertion.

Description

IMPROVEMENTS IN CABLE GRIPS

Technical Field

This invention relates to a device for gripping and locating an elongate member. In particular, but not 5 exclusively, the invention relates to a device for gripping and locating an electrically insulated cable or conductor in a housing which may form part of an electrical coupling device.

Discussion of Prior Art 0 In an electrical coupling device such as an electrical plug or wire connector, there is often a requirement to grip the pluri-conductor insulated cable entering the coupling device so as to prevent the strain of any pull or torque applied to the cable being transferred to electrical terminals of the coupling device to which the conductors of the cable are separately connected. Furthermore there is often a requirement for a cable grip designed to meet the

■ first-mentioned requirement to be able to locate and grip a variety of sizes of cross-section of cable. Various ways in which these requirements have been met in the prior art are known. A common solution is to lay a flexible plate across the cable where it passes through a cable inlet passage in the housing of the coupling device which plate is then screwed down with screws located either side of the cable with enough force to prevent the cable slipping relative to the housing when the cable is pulled.. This known method has a number of disadvantages: it requires a number of separate components, at least three, which have to be disassembled prior to cable. insertion; the pressure applied to the cable 0 depends upon the skill of the assembler to make a secure fixing and it is possible that it will not be tightened enough to operate properly; and a screwdriver is required to effect assembly. Another known method, which does not require a screwdriver and comprises only one component, 5 operates by locating a hinged set of jaws around the cable such that the cable sits in a shaped receptor_. area defined by the jaws. The jaws with the contained cable is then wedged into a slot in the housing of the electrical coupling device such that the sides of the slot exert force on the jaws and maintain them in a closed position around the cable. In this known method, different cable sizes are accommodated by the cable receptor area deforming into cavities in the jaws. A disadvantage of this known method is that the jawed component has to be removed from the housing of the electrical coupling device to be assembled around the cable. Thus it is possible to misplace the jawed component, allowing electrical connection of the conductors of the cable to the electrical coupling device without the benefit of any strain-relieving cable grip being present. Another disadvantage of this known method is that the necessary provision of a cable receptor area in the otherwise parallel jaws reduces the range of cable diameters that can be accommodated within the jaws. For instance the range of cable sizes required to be accommodated in a UK domestic 13-amp electrical plug cannot be accommodated within this known cable grip. A further disadvantage of this known method is that an equal and opposite force to that applied to the cable is transmitted to the housing of the electrical coupling device. If the housing is made of a plastics material such as a thermoplastic and a large diameter cable is inserted into the cable grip, the housing may be bent, thus compromising its operation. Another known method, which does not require a screwdriver, consists of two stiff but slightly flexible flat sheet components of plastics material arranged in a "V" formation with a small gap at the point of the "V" . The two legs of the "V" are secured at the wide end only in a rigid location incorporated into .the housing of the electrical coupling device. A cable is inserted in a direction perpendicular to its major axis into the gap at the point of the "V", forcing the legs of the "V" apart and thus exerting pressure on the cable and gripping it. A disadvantage of this known method is that the action of inserting the cable tends to force the cable forward through the gap as it is pushed down. The electrical terminals are located beyond this gap and this action can bunch up the conductors between the grip and the terminals making it difficult to complete the wiring-up assembly of the electrical coupling device. A further disadvantage is that an equal and opposite force to that applied to the housing of the electrical coupling device is generated with the consequences of possible distortion of the housing as described above.

Summary of the Invention In its broadest aspect, the present invention relates to a device for gripping and locating an elongate member in a housing, comprising a one-piece plate-like component of plastics material having a pair of opposed outer edges, the housing being recessed to accommodate said opposed outer edges, said plate-like component having wall parts defining therebetween a central blind opening leading to first and second recesses which open on each side thereof towards said opposed outer edges, which is characterised in that respective third and fourth bounded openings are also formed between said wall parts and the adjacent opposed outer edges whereby the first and second recesses deform more readily in the face of outward pressure on the wall parts caused by insertion of the elongate member into the ^■ central opening than the deformation of the third and fourth bounded openings caused by said insertion.

Suitably the wall parts of the central blind opening converge in the downstream, or insertion, direction of the elongate member therebetween.

Desirably the. third and fourth bounded openings also converge towards each other in the direction of insertion of the elongate member between the said wall parts.

Preferably, the downstream ends of the hird and fourth bounded openings are closer to the wall parts than the upstream ends of the first and second recesses. The central blind opening may include teeth or a roughened area on the wall parts thereof at least towards the upstream end thereof.

Desirably the distortion of the wall parts occasioned by insertion of the elongate member therebetween occurs substantially only in the central plane of the plate-like member.

Optionally the plate-like member is provided with a weakened area in a central region of a bottom bar forming a lower extremity of the blind opening between the first and second recesses which weakened area allows a bending of the bottom bar to increase the size of the blind opening at its upstream end, for the reception of elongate members of large cross-sectional area.

Brief Description of the Drawings

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is an end view of one form of grip according to the invention,

Figure 2 is a view from above of the grip of Figure 1,

Figure 3 is an end view of the grip of Figure 1 with a small diameter cable inserted,

Figure 4 is an end view of the grip of Figure 1 with a large diameter cable inserted,

Figures 5 and 6 are views of a second embodiment of grip according to the invention, Figure 5 showing the second embodiment of grip as seen from the outside of an electrical plug and Figure 6 the grip of Figure 5 seen from the inside of the plug, Figure 7 shows a grip corresponding to the second embodiment of Figures 5 and 6 opening up to accommodate a cable of large cross-section, and

Figure 8 shows the dimensions of a preferred form of plate-like moulding.

Figures 1 to 4 illustrate a first embodiment of cable grip formed as a single plate-like moulding 7 made from a resilient plastics material such as acetal or polyester.

Figures 1 and 2 show the grip plate 7 in its relaxed condition with its opposed outer edges 7a located in slots 5 in an at least semi-rigid housing 1. Two top support members 2 define a cable entry area 11 provided by wall parts 4 between which the cable is rested prior to insertion. On insertion, the wall parts 4 open and allow the cable to slide past the optional moulded teeth 6 on these wall parts and the intermediate support member 3 to rest on the inside face of a "U" shaped beam 8.

The cable entry area 11 defines a central blind opening leading to first and second recesses 12 which open on each side thereof towards the opposed outer edges 7a. Third and fourth bounded openings 13 are also formed between the wall parts 4 and the adjacent opposed outer edges 7a, the support member 3 bridging between the first recess and third opening on one side of the one wall part 4 and the second recess and fourth opening being separated by the support member 3 on the other side of the cable passage defined by the wall parts 4.

Figure 3 shows a cable 9 of relatively small cross- sectional diameter inserted into the cable grip 7. All the force exerted radially on the cable is contained within the grip plate 7, the first and second recesses 12 deforming more readily in the face of the cable-created outward pressure on the wall parts 4 than the deformation caused to the bounded openings 13.

Figure 4 shows a cable 10 of relatively large cross- sectional diameter inserted into the cable grip 7. In this Figure the "U" beam 8 has been distorted by the cable so that the tops of the "U" beam 8 are in contact with the walls of the slots 5 in the housing 1. Thus a proportion of the force being exerted radially on the cable derives from the stiffness of the housing 1. The proportion of the force transferred to the housing can be altered by changing the length of the slots 5. For a cable grip which is to accommodate a range of cables having a nominal conductor cross-sectional area of 0.5 mm² to 1.5 mm², the cable grip 7 may be 27 mm wide by 19 mm high with an average thickness of 3 mm.

In Figure 4 the teeth 6 are biting into the cable 10 with the force applied via the wall parts 4 providing resistance to a torque applied to the cable.

The gripping force is largely contained within the plate 7 by linking the two wall parts 4 by the relatively stiff "U" shaped beam 8 within which the cable gripping jaws reside. Connection between the jaws and this "U" shaped beam is effected by two sets of supports of varying thickness, one at the cable entry end of the jaws and one provided by member 3 located at approximately the mid-way point therealong. These supports each deflect outwardly to allow cables to enter the jaws of the grip and to accommodate a wide range of different cable sizes. The supports at the upstream cable entry end of the jaws are conveniently shaped to form the cable entry area 11 to aid cable entry. The mid-way support members 3 can be located such that a smaller cable passes beyond these when pushed down into the jaws of the grip and are thus prevented from working their way up between the jaws of the grip if a torque or an upward force is applied to the cable. The plate-like component of the grip can be housed loosely in the slots 5 in the housing 1 such that the grip is allowed to flex without coming into contact with the walls of the slot or alternatively is only allowed to flex a limited amount so that a proportion of the force generated by the insertion of the cable can be transmitted to the housing, the emainder being borne by the "U" shaped beam 8. Insertion of the cable is preferably achieved by laying the cable over the grip, resident in the housing slots, and forcing the cable between the jaws of the grip by pressing it towards the base of the "U" shaped beam. This action does not induce any significant movement in the cable in the direction parallel to the cable's major axis.

Resistance to movement in the direction of the cable's major axis is achieved by the stiffness of the plastics material from which the plate-like component is made and the thickness of the plate-like component. The plate-like component is prevented from moving in the direction of the cable's major axis by its being located in the slots 5 in the housing.

Figure 2 shows a preferred arrangement which provides enhanced stiffness through the provision of a second pair of jaws (shown as 4a) which project from the jaws 4 on the side facing into the interior of the housing 1. The auxiliary jaws 4a may or may not have teeth on the faces thereof that contact the cable but desirably they are somewhat sharper than the main jaws 4 and thus tend to bite more deeply into the cable sheath without cutting the same. Where these auxiliary jaws 4a are provided, any attempt to pull the cable out of the housing tends to draw the jaws 4a together due to their displaced position relative to the slot 5 thus resisting the pull.

Figures 5 and 6 show a second embodiment in which a groove 20 is provided centrally in the beam 8 to provide a weakened area in a central region of the blind opening between the first and second recesses 12. Auxiliary jaws 4a are also shown in this second embodiment (see Figure 6) .

Figure 7 shows how a grip such as shown in Figures 5 and 6 (or a grip such as shown in Figures 1 and 2 but provided with a groove 20 - shown dotted - to yield a partially cut-away beam 12) opens to receive a cable 22. The groove 20 in the beam thus acts as a hinge in the bottom bar which allows large cables to be inserted more easily. As the cable 22 in Figure 7 is pushed downwardly into the bottom part of the grip, the groove 20 closes up leaving the beam 8 in the form shown in Figure 4.

One significant difference between the designs of Figures 1 to 4 and Figures 5 to 7 is that the strength of the grip in the former, depends upon the strength of the bottom beam 8. In the latter design the beam has effectively been broken, and indeed will operate just as well as two separate components. In this case all the force- exerted by the cable on the grip is transmitted to the rigid housing containing the grip at the points marked X in Figure 7.

In both embodiments it will be noted that the downstream ends of the third and fourth bounded openings 13 are closer to the wall parts 4 than the upstream ends of the first and second blind openings 12.

Figure 8 shows a preferred form of plate-like moulding 7 formed from acetal or polyester. The dimensions shown by letters in Figure 8 in a moulding designed for a three-pin electrical plug are

The thickness of the moulding was 3.0 mm apart from over the thickened regions (shown with dashed lines) where a second pair of jaws 4a are provided (see Figure 6) and where the thickness rose to 4.4 ram

Figure 8 shows how the groove 20 virtually splits the beam 8 into two parts.

It will be noted that each wall part 4 has a cantilevered end at its downstream extremity where it partially closes off the respective first and second recess 12. The arcuate shapes of the third and fourth bounded openings 13 are broadly concentric with the upstream end of the blind opening which forms the cable entry area 11.

Although it is expected that an important application of this invention will be as a cable clamp for use in a rewirable 13-amp fused plug, and in particular in such a plug which can be wired and dewired by relative movement of two interengaged plug parts, it is anticipated that other useful applications will be found, some of which could be used to absorb axial tensions applied to flexible cords other than electrical cables. Thus, for example a stand¬ alone unit could be produced having the plate-like component disposed in a supporting housing which is not a plug housing.

Claims

1. A device for gripping and locating an elongate member in a housing, comprising a one-piece plate-like component of plastics material having a pair of opposed outer edges, the housing being recessed to accommodate said opposed outer edges, said plate-like component having wall parts defining therebetween a central blind opening leading to first and second recesses which open on each side thereof towards said opposed outer edges, characterised in that respective third and fourth bounded openings are also formed between said wall parts and the adjacent opposed outer edges whereby the first and second recesses deform more readily in the face of outward pressure on the wall parts caused by insertion of the elongate member into the central opening than the deformation of the third and fourth bounded openings caused by said insertion.

2. A device as claimed in claim 1, characterised in that the wall parts of the central blind opening converge in the downstream, or insertion, direction of the elongate member therebetween.

3. A device as claimed in claim 2, characterised in that the third and fourth bounded openings also converge towards each other in the direction of insertion of the elongate member between the said wall parts.

4. A device as claimed in claim 3, characterised in that the downstream ends of the third and fourth bounded openings are closer to the wall parts than the upstream ends of the first and second blind openings.

5. A device as claimed in any one preceding claim, characterised in that the central blind opening includes teeth or a roughened area, on the wall parts thereof at least towards the upstream end thereof.

6. A device as claimed in any one preceding claim, characterised in that the distortion of the wall parts occasioned by insertion of the elongate member therebetween occurs substantially only in the central plane of the plate- like member.

7. A device as claimed in any one preceding claim, characterised in that the plate-like member is provided with a weakened area in a central region of the blind opening between the first and second recesses.

8. A device as claimed in claim 7, characterised in that the weakened area is formed in a bottom bar of the plate-like member and allows bending of the bottom bar about the weakened area to increase the size of the blind opening at its upstream end.

9. A device as claimed in any one preceding claim, characterised in that the wall parts defining the central blind opening include auxiliary jaws on one side of the plate-like component.

10. An electrical plug comprising a device as claimed in any one preceding claim.