CA1247713A - Strain relief device - Google Patents
Strain relief deviceInfo
- Publication number
- CA1247713A CA1247713A CA000475609A CA475609A CA1247713A CA 1247713 A CA1247713 A CA 1247713A CA 000475609 A CA000475609 A CA 000475609A CA 475609 A CA475609 A CA 475609A CA 1247713 A CA1247713 A CA 1247713A
- Authority
- CA
- Canada
- Prior art keywords
- strain relief
- gripping
- gripping member
- wire bundle
- sleeve
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Details Of Connecting Devices For Male And Female Coupling (AREA)
Abstract
ABSTRACT
STRAIN RELIEF DEVICE
The invention provides a strain relief device for a sleeved wire bundle.
The sleeve of a wire bundle is gripped between the telescoped portion of first and second annular gripping members , the gripping being effected indepen-dently of the wire bundle. The sleeve is gripped by the gripping members as a result of telescoping one member into the other. Preferably, the gripping members fit together with a snap-fit.
The device may be provided with a support for the wire bundle, to centre the bundle in the device and to provide further strain relief.
STRAIN RELIEF DEVICE
The invention provides a strain relief device for a sleeved wire bundle.
The sleeve of a wire bundle is gripped between the telescoped portion of first and second annular gripping members , the gripping being effected indepen-dently of the wire bundle. The sleeve is gripped by the gripping members as a result of telescoping one member into the other. Preferably, the gripping members fit together with a snap-fit.
The device may be provided with a support for the wire bundle, to centre the bundle in the device and to provide further strain relief.
Description
;iL~9L 7 7 ~la3 - l - FC211 CA
DESCRIPTION
STRAIN RELIEF_DEVICE
This invention relates to a strain relief device for a wire bundle.
Where a bundle of wires is joined, for example, to a connector the wires are susceptible to being torn away from the connector as a result of stresses on the wires, for example stresses caused by axial pulling stresses on the wires or by vibrating movements of the apparatus in which the connector is mounted. Vibrating movements are a particular problem in mobile equipment for example in land, sea and air vehicles. It is thus desirable to provide strain relief of the wire bundle at the point where it joins the connector in order to protect against tearing away of the wires.
one known type of strain relief device is described in US Patent Wo. 3732527. The device comprises a cylindri-cal metal collar, and a wire guide means having an arm extending generally parallel to the wire bundle. In use the collar is attached to the connector and a tie-wrap encircles the arm and the wire bundle to fasten the bundle to the device.
It is also known to use a sleeve, for example a braided sleeve to provide mechanical protection of the wires oE
a wire bundle, in particular to provide protectlon again0t abrasion, and al~o protection against molten metal r for example solder, which may be dropped onto the wires during soldering of another part of the con-nector assembly. However, where such a sleeve is used with a strain relief device as described, the sleeve does not protect the wire bundle right up to the collar, lt~
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DESCRIPTION
STRAIN RELIEF_DEVICE
This invention relates to a strain relief device for a wire bundle.
Where a bundle of wires is joined, for example, to a connector the wires are susceptible to being torn away from the connector as a result of stresses on the wires, for example stresses caused by axial pulling stresses on the wires or by vibrating movements of the apparatus in which the connector is mounted. Vibrating movements are a particular problem in mobile equipment for example in land, sea and air vehicles. It is thus desirable to provide strain relief of the wire bundle at the point where it joins the connector in order to protect against tearing away of the wires.
one known type of strain relief device is described in US Patent Wo. 3732527. The device comprises a cylindri-cal metal collar, and a wire guide means having an arm extending generally parallel to the wire bundle. In use the collar is attached to the connector and a tie-wrap encircles the arm and the wire bundle to fasten the bundle to the device.
It is also known to use a sleeve, for example a braided sleeve to provide mechanical protection of the wires oE
a wire bundle, in particular to provide protectlon again0t abrasion, and al~o protection against molten metal r for example solder, which may be dropped onto the wires during soldering of another part of the con-nector assembly. However, where such a sleeve is used with a strain relief device as described, the sleeve does not protect the wire bundle right up to the collar, lt~
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that is right up to the point of connection to a con-nector body. Furthermore, the clamping of the sleeve directly onto the wire bundle is advantageous since it can lead to harmful stresses on the individual wires particularly as a result of transverse stress and/or vibration. This can be a particular problem when the wire insulation comprises a fluoropolymer which, because of the generally low coefficient of friction of such materials, requires tight clamping.
US-4272148 discloses a shielded connector housing for use with a cable shielded by braided wire. The housing comprises a ferrule, and mating half shells which cooperate to encircle the ferrule. In use the braided wire shield of the cable is clamped between the ferrule and the mated half shells to provide good electrical contact between the braid and the connector housing, and to provide strain relief for the cable. Such a device comprises intricate components which generally are laborious to assemble.
The prior art devices comprise intricate components which generally are laborious to assemble. The present invention provides an alternative means for con-veniently reLieving the strain placed on a wire bundle which obviates the problems of the prior art devices.
A first aspect of the present invention provide9 a strain relief device for a sleeved wire bundle, which comprises ~irst and second annul~r gripplng member~
having respective portions which can be telescoped together, and which are arranged to grip the sleeve around its perimeter by the telescoping of the said portions, the gripping being effected independently of the wire bundle, characterised in that the telescopable ! ~
_ 3 - FC211 CA
portions of the gripping members provide respectively a flange and a cooperating collar which fit together with a snap fit.
The device of the present invention advantageously pro-vides a convenient means of attachment of a protection sleeve to a connector.
According to the invention, the first gripping member i9 a snap-fit with the second gripping member, i.e. the members becomes suddenly locked together as they are telescoped, for example by deformation of a part of one of the gripping members, especially by resilient deform ation. For example, one of the members may comprise an axially extending arm with a generally radially extending flange at an end thereof. ~lternatively, one of the members may comprise a radially expandable or compressible split ring. Thus, the snap-fit may be between, for example a collar in the form of a split ring and a flange which provides an appropriate recess.
It is an advantage of the present invention that assembly of the strain relief device so as to qrip the sleeve involves the simple operation of telescoping one of the gripping members within the other. By the word "telescope" is meant that one of the annular gripping members is slid axially into the other, in the manner of the sliding tubes of a hand-telescope. When the first grip~in~ member is a snap-fit with the second gripping member, particularly when at least part of one of the members is resiliently deformable, it is pre-ferable that the surface of one member which abuts the other member is profiled, for example inclined to the axis of sliding the members.
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It is envisaged that one or both of the gripping mem-bers may comprise two or more interlocking parts, such as generally arc-like parts which interlock to form an annulus. Such a construction will find particular application when access cannot be gained to the end of the cable, for example because the cable is terminated to a connector.
The gripping members are arranged to grip the sleeve around its perimeter when the members are telescoped together. The sleeve may be gripped for example bet-ween a collar on one member and resiliently deformable projections on the other; between a conical mandrel portion on one member and a collar on the other; bet-ween generally roughened but parallel surfaces on the two members; or between a series of circumferential flanges and recesses defined by the two members. Other arrangements for gripping the sleeve between the two annular gripping members will be apparent to those skilled in the art.
~dvantageously at least one of the gripping members may comprise a support for supporting the wire bundle within the annular gripping members. The support means may conveniently be provided by at least one inwardly directed, preferably resiliently deformable, finger on one of the gripping members. Generally, the support will be provided by a plurality of fingers. Preferably the support is arranged to centre the wire bundle.
Centering o~ the wire bundle i~ particularly advan-tageous since pulling ~tresses and transverse vibra-tions are transmitted symmetrically to the connector.
Where a plurality of inwardly directed fingers provide the support a large area is achieved over which the B
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strain-relief device and the wire bundle are in con-tact. Such a large contact area i5 advantageous since the wear inflicted on the contacted portions of the wire bundle is minimised.
Optionally, further strain relief for the wires of the bundle may be provided by the support, particularly relief from transverse strain and vibration. The strain relief provided by finger(s) may be maximised by the use of a tie-wrap to attach the fingers to the wire bundle.
Preferred embodiments of the first gripping member will now be described. In one embodiment, the first gripping member comprises an annular neck and one, or more projections extending axially from the neck in a direction, in the assembled device, towards the second gripping member. Preferably these projections are resiliently deformable, and in a particularly pre-ferred construction the or each projection is provided towards its free end with a transversely extending flange for engaging the second gripping member. If the projections lie outside the second gripping member in the assembled device, the flange will extend inwardly;
if the projections lie within the second gripping member, the flange will extend outwardly, and the external diameter of the outwardly extending flange is preferably qreater than the internal diameter of the second gripping member~ ~he arrangement compri 9 i ng flanged projections i9 particulary advantageous where the projections of the first gripping member are resi-liently deformable since the two members can be engaged simply by deforming the projections of the first gripping member to allow the gripping member to be telescoped, the resilience of the projections causing :
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them to spring back and causing the flanges to engage the second gripping member, in a snap-fit. The projec-tions of the first gripping member may instead be non-resiliently deformable, and be arranged to be deformed by the second gripping member when telescoped therewith, to engage the second gripping member in a friction-fit.
Turning now to consider preferred embodiments of the second gripping member. In one embodiment the second gripping support member comprises an annular neck and a plurality of extension portions extending therefrom, in a direction away from the first gripping member in the assembled device.
The second gripping means is preferably provided with a support in the form of inwardly directed fingers to support the wire bundle. Preferably, the ends of the finqers remote from the neck taper towards each other, the tapering portions acting to centre the wires of the bundle within the strain relief device. The fingers of the second gripping member are preferably arranged uni-formly around the neck, this uniform arrangement pro-viding uniform support for the wires in contrast to the known prior art device having a projecting arm that is encircled by a tie wrap, which device provides unde-sirable one-sided support of the wire bundle.
Preferably the fingers of the second ~ripping member are resiliently deformable inwardly or outwardly or both, It is advantageous Eor the Eingers to be defor-mable outwardly since this enables wire bundles to be accommodated which have an external diameter greater than the internal diameter defined by the fingers in their rest, unstressed position.
~477~3 _ 7 _ FC211 CA
In a preferred embodiment of the invention, one, pre-ferably the first, of the gripping members is provided with means for engagement to a connector such an electrical connector, or to another device of the invention. As examples the engagement means may comprise a separate collar adapted to interengage the said gripping member and the connector, or the means may be formed integrally with the said gripping member.
Preferably the gripping members and the engagement means are arranged such that the sleeve is gripped around its perimeter independently of the wire bundle, and such that a support extends from the end of the sleeve to the engagement means, the support being uni-form around the perimeter of the sleeve. The strain relief device is connected directly to the sleeve only, and not also to the wire bundle as in certain prior art devices. The strain relief device of the present invention therefore enables the strain placed on the wires of a sleeved wire bundle to be reduced signifi-cantly.
The gripping members may be made for example from metal for example aluminium, or from a polymeric material.
Preferred polymers that may be used are polycarbonates or poly-sulphones. Preferably a material is u9ed that has a large ela3tic reqion, that is one which can undergo a large strain beEore plastic deEormation occur s .
A second aspect of the present invention provides a strain relie~ assembly comprising a device according to the invention, a protection sleeve and a wire bundle that is protected by the sleeve, the sleeve being ~47'7~3 received between the telescoped portions of the gripping members, and gripped by the gripping members, the gripping being effected independently of the wire bundle. Preferably the sleeve is adapted to be folded back on itself so as to extend, in contact, along the outer surface of the outer gripping member, around an end thereof, and back along the inner surface thereof, between the telescoped portions of the gripping mem-bers. The opposite inside out arrangement is also possible, that is wherein the end of the sleeve is arranged to be folded back outside the body of the sleeve. The sleeve may, alternatively pass along the inner surface of the inner gripping member, around an end thereof, and back along the outer surface thereof.
Preferably a sleeve is used that contracts in cross section when subjected to axial tension. This may conveniently be achieved, for example by using a braided sleeve. The use of a sleeve that contracts in cross-section on axial tension is particularly advan-tageous when the projections of the gripping member are resiliently cleformable since any axial tension caused, for example, by vibration of the equipment causes the sleeve to contract in cross~section, which in turn causes the deformable projections to deform inwardly and therefore exert a tighter clamping force on the wires. Hence in this case the contracting sleeve hin-ders axial pull-out of the wires from the connector.
The advant~ge arise~ ~rom the gripping o~ th~ ~leeve being eE~ected independently of the wire bundle.
Furthermore, since the sleeve is connected to the con-nector directly via the strain relief device and is not clamped to the wire bundle the sleeve also provides strain relief protection against bending and transverse stresses. Thus the sleeve in combination with the ,~ .;, ,~
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strain relief device provides protection against axial pul~ing and transverse vibrational stresses in addition to providing simple mechanical protection of the wires, for example against abrasion and chemical attack.
The strain relief device may be used for a wire bundle to be connected to a round connector. In this case the annular gripping members are preferably substantially circular in cross-section. The strain relief device may also be used for a non-round wire bundle, including a flat cable, to be connected to a flat con-nector. In this case the annular gripping members are substantially rectangular in cross-section. Other sha-pes of gripping members such as oval or elliptical may be used according to the shape of the connector or of the wire bundle.
Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, wherein:
Figures 1 and 2, and Figure 3 are perspective views of the first and second gripping members, respectively of a strain relief device according to the present inven-tion;
Figure 4 is a side view of the second gripping member of Figure 3 in a deformed position;
Figures 5 and 6 are side elevation~ of an a~sembly according to the present invention before and after assembly respectively.
Referring to the drawings Figure 1 shows an annular collar 2 the internal surface of which is screw threaded at 4 for rigid screw connection to a connector `~ill;`'~ ~
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(not shown). The collar thus provides means for enga-gement, of the strain relief device to a connector.
Other means of engagement, for example a bayonet fastening may also be used. The collar is provided on one end with an inwardly directed annular flange 6.
This flange 6 provides a stop to prevent withdrawal of the first gripping member from the collar 2 in the direction, in the assembled device, of the second gripping member.
Figure 2 shows the first gripping member 8. The gripping member 8 comprises an annular neck 10 and three projections 12 extending axially therefrom in a direction substantially axially of the annular neck 10. The projections 12 are uniformly spaced around the neck and are resiliently deformable inwardly. The neck 10 is provided with an outwardly extending annular flange 14 at its base. The diameter of the flange 14 is slightly smaller than diameter of collar 2 to enable the gripping member 8 to be fitted into the collar 2, but is slightly larger than the internal diameter of the flange 6 of the collar 2 such that the gripping member 8 abuts against the flange 6 of collar 2 thus providing the stop to prevent withdrawal of the gripping member 8 from the collar 2.
The free ends of the projections 12 are provided with outwardly extending flanges 16 for cooperation with the second gripping member. The flanges 16 extend out-wardly beyond the inner diameter of the Elange 6 of collar 2. The pro~eckion~ 12 are necked at 18 towards their base in order to enhance the resilient defor-mability of the projections 12. The neck 10 o~ the gripping member 8 i9 provided with notching (not shown) in order releasably to ].ock the gripping member 8 rela-tive to the collar 2 to prevent their relative rota-tion. Other forms of locking are also possible.
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Figure 3 shows the second gripping member 20 having an annular neck 22 and three uniformly spaced fingers 24 extending therefrom in a direction away from first gripping member in the assembled device. The free ends of the fingers 24 taper towards each other and thereby clamp and centre an inserted wire bundle. The fingers 24 neck significantly at their bases 26 thereby defining bearing surfaces 28, on the neck 22 of the second gripping member 20, for engagement with the flanges 16 of the projections 12 of the first gripping member 8. The inner diameter of the neck 22 of the second gripping member 20 is slightly larger than the outer diameter defined by the body of the projections 12 of the first gripping member 8, and larger than the than the outer diameter defined by the body of the pro-jections 12 of the first gripping member 8, and is slightly sma]ler than the outer diameter defined by the outwardly extending flanges 16 on the free ends of the projections 12 of the first gripping mernber 8. Thus the pro~ections 12 of the first gripping member 8 may be deformed inwardly to insert the first gripping member within the second gripping member. The resi-lient projections 20 then spring back such that the flanges 16 thereon engage the bearing surfaces 28 of the second gripping member in a snap fit.
The fingers 24 of the second gripping member are resi-liently deformable both inwardly and outwardly~
Figure 4 shows the finger~ 24 o~ the second gripping member resiliently deformed outwardly. This defor-mability enables the strain relief device to accom-modate wire bundles of different sizes. Preferably the inner diameter defined by the fingers 24 of the second gripping member 20 is from one quarter to one half of the diameter of the connector, this size allowing a ~47~7 i~3 large range of wlre combinations. The collar and the wire gripping members 8 and 20 are all made from poly-carbonate material.
Figure 5 shows the strain relief device collar 2 posi-tioned around the first gripping member 8, the second gripping member 20, and a braided mechanical protection sleeve 30. The strain relief device parts and the braided sleeve 30 together provide a strain relief assembly according to the present invention. In order to connect the braid 30 to the strain relief device, the braid is passed along the outer surface and around an end of of the second gripping member 20, and is then be folded back on itself to extend along the inner sur-face of the second gripping member 20. The first gripping member 8 with its prepositioned collar 2 is then telescoped within the second gripping member 20 to grip the braid 30 between the telescoped portions.
Figure 6 shows the parts of Figure 5 assembled together. The first gripping member 8 has been inserted into the collar 2 such that the flange 14 on the neck of the gripping member 8 abuts against the stop 6 of the collar 2. The braid 30 has been telescoped on itself to surround the gripping member 8, and the first and second wire gripping members 8 and 20 have been telescoped together and engaged in a snap-fit. The braid 30 is s~ueezed and gripped between the first and second wire qripping members and ther2by firmly fixed to the ~trAin relie,E device.
Pulling stresses on the braided wire bundle, for example during dismantling of the connector, cause the braid angle to change and hence the cross-sectional area of the braid to decrease. This in turn causes the braid to deform inwardly the finger 24 of the second '~
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gripping member 8. Thus the wires of the bundle are clamped more firmly against the pulling stress. Since the braid 30 is clamped directly to the strain relief device and not via the wire bundle transverse vibra-tions of the bundle are absorbed by the sleeve.
Furthermore, since the braid 30 extends up to the collar 2 it provides mechanical protection right up to the point of contact with the connector.
The following are approximate dimensions of the parts of a typical strain relief device:
~4 7 7i3 Part Dimensions Size in mm Collar 2 neck inner diameter32 .0 thickness 1.5 flange 6 inner diameter29.0 First qripping member 8 flange 14 of neck 10 outer diameter31.5 projections 12 axial length 14.0 length of arc at free ends 18.0 length of arc at necked base 18 13.0 outer diameter defined by flanges 16 30.0 Second grippinq member 20 collar 22 outer diameter31.0 finqers 24 length 19.0 inner diameter of circle defined by free ends of fingers 24 in unstressed positionn 14 bearing surfaces 28 circumEerential 20.00 extent
that is right up to the point of connection to a con-nector body. Furthermore, the clamping of the sleeve directly onto the wire bundle is advantageous since it can lead to harmful stresses on the individual wires particularly as a result of transverse stress and/or vibration. This can be a particular problem when the wire insulation comprises a fluoropolymer which, because of the generally low coefficient of friction of such materials, requires tight clamping.
US-4272148 discloses a shielded connector housing for use with a cable shielded by braided wire. The housing comprises a ferrule, and mating half shells which cooperate to encircle the ferrule. In use the braided wire shield of the cable is clamped between the ferrule and the mated half shells to provide good electrical contact between the braid and the connector housing, and to provide strain relief for the cable. Such a device comprises intricate components which generally are laborious to assemble.
The prior art devices comprise intricate components which generally are laborious to assemble. The present invention provides an alternative means for con-veniently reLieving the strain placed on a wire bundle which obviates the problems of the prior art devices.
A first aspect of the present invention provide9 a strain relief device for a sleeved wire bundle, which comprises ~irst and second annul~r gripplng member~
having respective portions which can be telescoped together, and which are arranged to grip the sleeve around its perimeter by the telescoping of the said portions, the gripping being effected independently of the wire bundle, characterised in that the telescopable ! ~
_ 3 - FC211 CA
portions of the gripping members provide respectively a flange and a cooperating collar which fit together with a snap fit.
The device of the present invention advantageously pro-vides a convenient means of attachment of a protection sleeve to a connector.
According to the invention, the first gripping member i9 a snap-fit with the second gripping member, i.e. the members becomes suddenly locked together as they are telescoped, for example by deformation of a part of one of the gripping members, especially by resilient deform ation. For example, one of the members may comprise an axially extending arm with a generally radially extending flange at an end thereof. ~lternatively, one of the members may comprise a radially expandable or compressible split ring. Thus, the snap-fit may be between, for example a collar in the form of a split ring and a flange which provides an appropriate recess.
It is an advantage of the present invention that assembly of the strain relief device so as to qrip the sleeve involves the simple operation of telescoping one of the gripping members within the other. By the word "telescope" is meant that one of the annular gripping members is slid axially into the other, in the manner of the sliding tubes of a hand-telescope. When the first grip~in~ member is a snap-fit with the second gripping member, particularly when at least part of one of the members is resiliently deformable, it is pre-ferable that the surface of one member which abuts the other member is profiled, for example inclined to the axis of sliding the members.
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It is envisaged that one or both of the gripping mem-bers may comprise two or more interlocking parts, such as generally arc-like parts which interlock to form an annulus. Such a construction will find particular application when access cannot be gained to the end of the cable, for example because the cable is terminated to a connector.
The gripping members are arranged to grip the sleeve around its perimeter when the members are telescoped together. The sleeve may be gripped for example bet-ween a collar on one member and resiliently deformable projections on the other; between a conical mandrel portion on one member and a collar on the other; bet-ween generally roughened but parallel surfaces on the two members; or between a series of circumferential flanges and recesses defined by the two members. Other arrangements for gripping the sleeve between the two annular gripping members will be apparent to those skilled in the art.
~dvantageously at least one of the gripping members may comprise a support for supporting the wire bundle within the annular gripping members. The support means may conveniently be provided by at least one inwardly directed, preferably resiliently deformable, finger on one of the gripping members. Generally, the support will be provided by a plurality of fingers. Preferably the support is arranged to centre the wire bundle.
Centering o~ the wire bundle i~ particularly advan-tageous since pulling ~tresses and transverse vibra-tions are transmitted symmetrically to the connector.
Where a plurality of inwardly directed fingers provide the support a large area is achieved over which the B
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- 5 - FC~ll CA
strain-relief device and the wire bundle are in con-tact. Such a large contact area i5 advantageous since the wear inflicted on the contacted portions of the wire bundle is minimised.
Optionally, further strain relief for the wires of the bundle may be provided by the support, particularly relief from transverse strain and vibration. The strain relief provided by finger(s) may be maximised by the use of a tie-wrap to attach the fingers to the wire bundle.
Preferred embodiments of the first gripping member will now be described. In one embodiment, the first gripping member comprises an annular neck and one, or more projections extending axially from the neck in a direction, in the assembled device, towards the second gripping member. Preferably these projections are resiliently deformable, and in a particularly pre-ferred construction the or each projection is provided towards its free end with a transversely extending flange for engaging the second gripping member. If the projections lie outside the second gripping member in the assembled device, the flange will extend inwardly;
if the projections lie within the second gripping member, the flange will extend outwardly, and the external diameter of the outwardly extending flange is preferably qreater than the internal diameter of the second gripping member~ ~he arrangement compri 9 i ng flanged projections i9 particulary advantageous where the projections of the first gripping member are resi-liently deformable since the two members can be engaged simply by deforming the projections of the first gripping member to allow the gripping member to be telescoped, the resilience of the projections causing :
~2~77~
them to spring back and causing the flanges to engage the second gripping member, in a snap-fit. The projec-tions of the first gripping member may instead be non-resiliently deformable, and be arranged to be deformed by the second gripping member when telescoped therewith, to engage the second gripping member in a friction-fit.
Turning now to consider preferred embodiments of the second gripping member. In one embodiment the second gripping support member comprises an annular neck and a plurality of extension portions extending therefrom, in a direction away from the first gripping member in the assembled device.
The second gripping means is preferably provided with a support in the form of inwardly directed fingers to support the wire bundle. Preferably, the ends of the finqers remote from the neck taper towards each other, the tapering portions acting to centre the wires of the bundle within the strain relief device. The fingers of the second gripping member are preferably arranged uni-formly around the neck, this uniform arrangement pro-viding uniform support for the wires in contrast to the known prior art device having a projecting arm that is encircled by a tie wrap, which device provides unde-sirable one-sided support of the wire bundle.
Preferably the fingers of the second ~ripping member are resiliently deformable inwardly or outwardly or both, It is advantageous Eor the Eingers to be defor-mable outwardly since this enables wire bundles to be accommodated which have an external diameter greater than the internal diameter defined by the fingers in their rest, unstressed position.
~477~3 _ 7 _ FC211 CA
In a preferred embodiment of the invention, one, pre-ferably the first, of the gripping members is provided with means for engagement to a connector such an electrical connector, or to another device of the invention. As examples the engagement means may comprise a separate collar adapted to interengage the said gripping member and the connector, or the means may be formed integrally with the said gripping member.
Preferably the gripping members and the engagement means are arranged such that the sleeve is gripped around its perimeter independently of the wire bundle, and such that a support extends from the end of the sleeve to the engagement means, the support being uni-form around the perimeter of the sleeve. The strain relief device is connected directly to the sleeve only, and not also to the wire bundle as in certain prior art devices. The strain relief device of the present invention therefore enables the strain placed on the wires of a sleeved wire bundle to be reduced signifi-cantly.
The gripping members may be made for example from metal for example aluminium, or from a polymeric material.
Preferred polymers that may be used are polycarbonates or poly-sulphones. Preferably a material is u9ed that has a large ela3tic reqion, that is one which can undergo a large strain beEore plastic deEormation occur s .
A second aspect of the present invention provides a strain relie~ assembly comprising a device according to the invention, a protection sleeve and a wire bundle that is protected by the sleeve, the sleeve being ~47'7~3 received between the telescoped portions of the gripping members, and gripped by the gripping members, the gripping being effected independently of the wire bundle. Preferably the sleeve is adapted to be folded back on itself so as to extend, in contact, along the outer surface of the outer gripping member, around an end thereof, and back along the inner surface thereof, between the telescoped portions of the gripping mem-bers. The opposite inside out arrangement is also possible, that is wherein the end of the sleeve is arranged to be folded back outside the body of the sleeve. The sleeve may, alternatively pass along the inner surface of the inner gripping member, around an end thereof, and back along the outer surface thereof.
Preferably a sleeve is used that contracts in cross section when subjected to axial tension. This may conveniently be achieved, for example by using a braided sleeve. The use of a sleeve that contracts in cross-section on axial tension is particularly advan-tageous when the projections of the gripping member are resiliently cleformable since any axial tension caused, for example, by vibration of the equipment causes the sleeve to contract in cross~section, which in turn causes the deformable projections to deform inwardly and therefore exert a tighter clamping force on the wires. Hence in this case the contracting sleeve hin-ders axial pull-out of the wires from the connector.
The advant~ge arise~ ~rom the gripping o~ th~ ~leeve being eE~ected independently of the wire bundle.
Furthermore, since the sleeve is connected to the con-nector directly via the strain relief device and is not clamped to the wire bundle the sleeve also provides strain relief protection against bending and transverse stresses. Thus the sleeve in combination with the ,~ .;, ,~
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_ g _ FC211 CA
strain relief device provides protection against axial pul~ing and transverse vibrational stresses in addition to providing simple mechanical protection of the wires, for example against abrasion and chemical attack.
The strain relief device may be used for a wire bundle to be connected to a round connector. In this case the annular gripping members are preferably substantially circular in cross-section. The strain relief device may also be used for a non-round wire bundle, including a flat cable, to be connected to a flat con-nector. In this case the annular gripping members are substantially rectangular in cross-section. Other sha-pes of gripping members such as oval or elliptical may be used according to the shape of the connector or of the wire bundle.
Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, wherein:
Figures 1 and 2, and Figure 3 are perspective views of the first and second gripping members, respectively of a strain relief device according to the present inven-tion;
Figure 4 is a side view of the second gripping member of Figure 3 in a deformed position;
Figures 5 and 6 are side elevation~ of an a~sembly according to the present invention before and after assembly respectively.
Referring to the drawings Figure 1 shows an annular collar 2 the internal surface of which is screw threaded at 4 for rigid screw connection to a connector `~ill;`'~ ~
tP. ~' ~4'~'7~
(not shown). The collar thus provides means for enga-gement, of the strain relief device to a connector.
Other means of engagement, for example a bayonet fastening may also be used. The collar is provided on one end with an inwardly directed annular flange 6.
This flange 6 provides a stop to prevent withdrawal of the first gripping member from the collar 2 in the direction, in the assembled device, of the second gripping member.
Figure 2 shows the first gripping member 8. The gripping member 8 comprises an annular neck 10 and three projections 12 extending axially therefrom in a direction substantially axially of the annular neck 10. The projections 12 are uniformly spaced around the neck and are resiliently deformable inwardly. The neck 10 is provided with an outwardly extending annular flange 14 at its base. The diameter of the flange 14 is slightly smaller than diameter of collar 2 to enable the gripping member 8 to be fitted into the collar 2, but is slightly larger than the internal diameter of the flange 6 of the collar 2 such that the gripping member 8 abuts against the flange 6 of collar 2 thus providing the stop to prevent withdrawal of the gripping member 8 from the collar 2.
The free ends of the projections 12 are provided with outwardly extending flanges 16 for cooperation with the second gripping member. The flanges 16 extend out-wardly beyond the inner diameter of the Elange 6 of collar 2. The pro~eckion~ 12 are necked at 18 towards their base in order to enhance the resilient defor-mability of the projections 12. The neck 10 o~ the gripping member 8 i9 provided with notching (not shown) in order releasably to ].ock the gripping member 8 rela-tive to the collar 2 to prevent their relative rota-tion. Other forms of locking are also possible.
'7'~
Figure 3 shows the second gripping member 20 having an annular neck 22 and three uniformly spaced fingers 24 extending therefrom in a direction away from first gripping member in the assembled device. The free ends of the fingers 24 taper towards each other and thereby clamp and centre an inserted wire bundle. The fingers 24 neck significantly at their bases 26 thereby defining bearing surfaces 28, on the neck 22 of the second gripping member 20, for engagement with the flanges 16 of the projections 12 of the first gripping member 8. The inner diameter of the neck 22 of the second gripping member 20 is slightly larger than the outer diameter defined by the body of the projections 12 of the first gripping member 8, and larger than the than the outer diameter defined by the body of the pro-jections 12 of the first gripping member 8, and is slightly sma]ler than the outer diameter defined by the outwardly extending flanges 16 on the free ends of the projections 12 of the first gripping mernber 8. Thus the pro~ections 12 of the first gripping member 8 may be deformed inwardly to insert the first gripping member within the second gripping member. The resi-lient projections 20 then spring back such that the flanges 16 thereon engage the bearing surfaces 28 of the second gripping member in a snap fit.
The fingers 24 of the second gripping member are resi-liently deformable both inwardly and outwardly~
Figure 4 shows the finger~ 24 o~ the second gripping member resiliently deformed outwardly. This defor-mability enables the strain relief device to accom-modate wire bundles of different sizes. Preferably the inner diameter defined by the fingers 24 of the second gripping member 20 is from one quarter to one half of the diameter of the connector, this size allowing a ~47~7 i~3 large range of wlre combinations. The collar and the wire gripping members 8 and 20 are all made from poly-carbonate material.
Figure 5 shows the strain relief device collar 2 posi-tioned around the first gripping member 8, the second gripping member 20, and a braided mechanical protection sleeve 30. The strain relief device parts and the braided sleeve 30 together provide a strain relief assembly according to the present invention. In order to connect the braid 30 to the strain relief device, the braid is passed along the outer surface and around an end of of the second gripping member 20, and is then be folded back on itself to extend along the inner sur-face of the second gripping member 20. The first gripping member 8 with its prepositioned collar 2 is then telescoped within the second gripping member 20 to grip the braid 30 between the telescoped portions.
Figure 6 shows the parts of Figure 5 assembled together. The first gripping member 8 has been inserted into the collar 2 such that the flange 14 on the neck of the gripping member 8 abuts against the stop 6 of the collar 2. The braid 30 has been telescoped on itself to surround the gripping member 8, and the first and second wire gripping members 8 and 20 have been telescoped together and engaged in a snap-fit. The braid 30 is s~ueezed and gripped between the first and second wire qripping members and ther2by firmly fixed to the ~trAin relie,E device.
Pulling stresses on the braided wire bundle, for example during dismantling of the connector, cause the braid angle to change and hence the cross-sectional area of the braid to decrease. This in turn causes the braid to deform inwardly the finger 24 of the second '~
,~.: ,, ~ 7~
gripping member 8. Thus the wires of the bundle are clamped more firmly against the pulling stress. Since the braid 30 is clamped directly to the strain relief device and not via the wire bundle transverse vibra-tions of the bundle are absorbed by the sleeve.
Furthermore, since the braid 30 extends up to the collar 2 it provides mechanical protection right up to the point of contact with the connector.
The following are approximate dimensions of the parts of a typical strain relief device:
~4 7 7i3 Part Dimensions Size in mm Collar 2 neck inner diameter32 .0 thickness 1.5 flange 6 inner diameter29.0 First qripping member 8 flange 14 of neck 10 outer diameter31.5 projections 12 axial length 14.0 length of arc at free ends 18.0 length of arc at necked base 18 13.0 outer diameter defined by flanges 16 30.0 Second grippinq member 20 collar 22 outer diameter31.0 finqers 24 length 19.0 inner diameter of circle defined by free ends of fingers 24 in unstressed positionn 14 bearing surfaces 28 circumEerential 20.00 extent
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:
1. A strain relief device for a sleeved wire bundle, which comprises first and second annular gripping mem-bers having respective portions which can be telescoped together, and which are arranged to grip the sleeve around its perimeter by the telescoping of the said portions, the gripping being effected independently of the wire bundle, characterised in that the telescopable portions of the gripping members provide respectively a flange and a cooperating collar which fit together with a snap fit.
2. A strain relief device as claimed in claim 1, in which the first gripping member comprises an annular neck and a plurality of deformable projections, each projection providing a transversely extending flange, and in which the second gripping member comprises a collar which in use cooperates with the flanges on the projections to grip the sleeve.
3. A strain relief device as claimed in claim 1, in which the first gripping member provides a radially extending flange, and in which the second gripping member comprises a collar in the form of a deformable split ring which engages the flange on the first gripping member with a snap fit.
4. A strain relief device as claimed in claim 1, which includes a support for the wire bundle.
5. A strain relief device as claimed in claim 4, in which the support comprises a plurality of deformable fingers extending generally axially of the device.
6. A strain relief device as claimed in claim 5, in which one of the gripping members is integrally formed with the said deformable fingers.
7. A strain relief assembly for a sleeved wire bundle, which comprises a device as claimed in claim 1, and a protection sleeve, the sleeve being received between the telescoped portions of the gripping members and gripped between the gripping members independently of the wire bundle.
8. A strain relief assembly as claimed in claim 8, in which the sleeve extends along the outer surface of the outer one of the telescoped gripping members, around an end thereof, and back along an inner surface thereof.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000475609A CA1247713A (en) | 1985-03-01 | 1985-03-01 | Strain relief device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000475609A CA1247713A (en) | 1985-03-01 | 1985-03-01 | Strain relief device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1247713A true CA1247713A (en) | 1988-12-28 |
Family
ID=4129943
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000475609A Expired CA1247713A (en) | 1985-03-01 | 1985-03-01 | Strain relief device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1247713A (en) |
-
1985
- 1985-03-01 CA CA000475609A patent/CA1247713A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |