AU667154B2 - Cable strain relief device - Google Patents

Description

imI 66715 4

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for Service: Invention Title: MOBILE ONE AUSTRALIA PTY LTD GREGORY OWEN ACKMAN H.R. HODGKINSON CO.

Patent Trade Mark Attorneys 26A Alfred Street MILSONS POINT NSW 2061 CABLE STRAIN RELIEF DEVICE Details of Associated Provisional Application.

No PL7313 filed 16 February 1993.

ft f f The following statement is a full description of this invention, including the best method of performing it known to us: L-~u IL L- I I CABLE STRAIN RELIEF DEVICE The present invention relates to strain relief clamps for cables but more particularly relates to a strain relief device including an integral clamp for resisting tension induced in cables.

In the telecommunications industry, signal cables are often used to link receivers and transmitters and these cables must be terminated at connection points in a way such that the cable and particularly its terminating end does not have to withstand tensile forces induced in the cable and 10 thus unwanted cold working of the cable by stretching or bending for instance, a fact which could eventually lead to e• cable breakage.

Cables used with telecommunication devices are very 0 often relatively weak and are often subjected to unwanted tensile and bending forces. Such loadings on the cable can cause breakage of the often very fine internal stands, thereby breaking communications and necessitating cable ooo• replacement or repair. There is a need to anchor these cables in a way such that there is no mechanical load on the 20 electrical connection and so the cable can absorb tensile and other forces at a location remote from the connection without upsetting the electrical connection.

*Numerous nmethods have previously been adopted to relieve the tensile and other loadings on cables at electrical connection points. One such method comprises winding the cable end the exposed internal conductor) around the shank of a screw or bolt then pressure clamping the cble between the head of the bolt and the item to which it is fixed to effect the anchorage. The aim behind clamping g r cables in this way is to ensure that the electrical termination point does not become a location of concentrated strain. Nevertheless tensile and bending forces will occur unless there is some additional means of isolating stresses from the termination. The cable termination point and in particular the electrical conductor should be not subjected to forces other than the clamping force which anchors and secures the cable at the termination point or at a short distance away from the termination point.

According to another of the prior art methods, the cable is typically anchored twice by screws or bolts. The first anchorage is for the electrical connection and the second which is usually at a short distance upstream from that connection provides the requisite clamping which prevents et..

15 tensile or bending load at the connection point. Clamping ooo: of cables in this way is often employed in radio aerial terminals.

One disadvantage of this prior art method is that the cable must be anchored twice. This is time consuming during assembly or installation and requires additional materials such as a screw and washer for the second clamping.

Other known methods of anchoring electrical cables Sinclude the use of a soldering iron. This requires additional time hence labor costs are increased.

•se 25 The present invention seeks to provide an alternative means of terminating a cable and isolating any strain on oe• oo# the electrical cable connection and without the need for an additional screw or other like mechanical clamp to withstand the forces generated in use.

More particularly, the invention provides an integral molded strain relief device having means to isolate induced cable tension from the electrical termination.

In its broadest form the present invention comprises an integral cable strain relief device, the device comprising; a first member having a primary through passage having first and second ends and adapted to receive a mounting bolt, a second member connected with the first member and including a second passage having first and second ends and which either communicates with or terminates near the primary through passage, wherein the first end of said first member receives the shank and head of said bolt and the second end of the first member penetrates a mounting device to which the strain relief device is fitted, said second through passage being either substantially parallel to or at an angle to the primary through passage and receiving 0000 •o therein in a cable to be anchored at an electrical 15 connection, 0*0*O nasaid second passage terminating at its first end in or near a set of jaws which grippingly engage the cable and *ooo meeting at its second end a saddle having a landing lying at an angle to the axis of the second passage and along which the cable travels before it enters the second through oe passage; wherein due to the at least one change in direction of travel of the cable between the landing and the electrical connection and the action of the jaws, tensile stresses 25 induced in the cable are thereby isolated from the electrical connection.

000* According to a preferred embodiment the strain relief device is formed from a plastics material manufactured in a mold. The device is manufactured in one piece with the first and second through passages and the set of jaws molded into the body of the device.

According to the preferred embodiment, the device is configured to allow at least two changes in direction of travel of the cable between the landing and the electrical connection. This virtually or completely eliminates tensile stresses at the electrical connection.

The device is particularly suitable for use with a radio aerial mounting base assembly and in particular those into which a fastening bolt is inserted to secure the assembly.

The electrical connection is formed by anchorage of the electrical conductor in the cable against a wall of a recess in the device by the head of the bolt.

In the preferred embodiment the second through passage is smaller than the primary through passage and parallel thereto. Preferably, the landing is disposed normally to the second passage although the landing may lie at an acute angle to this passage.

15 The present invention will now be described in more detail according to a preferred but non limiting embodiment and with reference to the accompanying illustrations 909 9@ .9 9*0* 9*r .9 9.

9 .9 wherein Figure Figure 9.* .9 999* a o oo 99 9 9 1: shows a perspective view of the cable strain relief device according to a preferred embodiment of the invention, 2: shows an exploded view of the device according to a preferred embodiment and including an anchorage bolt, 3: shows an underside view of the device of figure 1.

4: shows a side elevational of the device of figure 1 viewed along the landing, 5: shows a plan view of the device of figure 1, 6: shows a cross sectional elevation of the device fitted to an aerial mounting base.

25 Figure Figure Figure Figure Referring to figure 1 there is shown a perspective view of the cable strain relief device 1 according to a preferred embodiment of the invention. Device 1 which is preferably I IL~1 manufactured in a mold from a plastics material comprises a generally T shaped member which member comprises a first columnar member 2 which has a primary through passage 3 and is integral with and is supported by base 14.

Referring to the cross sectional view in figure 2 it can be seen that the through passage 3 receives shank 5 of a bolt 4. The bolt head 6 fits within recess 7. Device 1 also comprises a second member including a smaller through passage 8 which is preferably parallel to through passage 3 but may be at an acute angle to the passage 3.

Continuous with passage 8 is a landing 9 formed in a saddle 10. Landing 9 receives cable 11 and due to its attitude relative to passage 8 the landing allows a cable *e4.

fed into the device to first travel in one direction along :15 the landing and then to change direction and travel through o the passage 8. Passage 8 terminates in or near molded jaws 12 (see figure 3) which are able to grip the cable to prevent its withdrawal. After the cable 11 passes through jaws 12 the cable conductor 15 which is exposed is anchored 20 by bolt 4. The anchorage of the cable is effected by o o compression between the bolt head 6 and the bottom wall 13 of recess 7. When bolt 4 is at maximum penetration into passage 3 the bolt head 6 fits snugly within recess 7.

"Preferably, the exposed conductor 15 of the cable 11 is wound around the shank of the bolt underneath bolt head 6.

0. On positioning the bolt by applying an associated nut (see *of* figure 6) to shank 5 the exposed conductor 15 is clamped against the wall 13 of recess 7. Jaws 12 act to grip the cable 11 and if tension is induced in the cable in a direction tending to pull the electrical connection apart jaws 12 tighten on the cable thereby transferring the tensile forces directly to the jaws 12 thereby isolating the electrical connection from unwanted mechanical load.

r"g R I I In addition to the action of jaws 12 there are two changes of direction of travel in the cable 11 which are effected by shoulders 21 and 22 in the passage 8 and which provide additional resistance to cable tension particularly at bearing shoulder 21.

The result is that the jaws 12 along with the fact that the cable 11 travels along passage 8 before engaging the electrical connection prevent any tensile stress induced in the cable from being transferred to the cable connection point. Thus the device provides effective strain relief for the cable 11 and does not require any additional component to be affixed to the device to effect the strain relief.

Figure 4 shows a side elevational view of the device viewing along landing 9 along which cable 11 travels.

0" Figure 5 shows a plan view of the device of figure 1 0• showing the spatial relativity between passages 3 and 8.

too.. Referring to figure 6 there is shown a cross sectional 9 0 elevation of an aerial mounting base 19 with the strain relief device 1 according to a preferred embodiment of the invention fitted thereto.

It can be seen that cable 11 prior to fitting into the strain relief device 1 is stripped of the external insulator 16 to expose braid 17 which contacts a ground plate 18 of the aerial mounting base 19. Preferably, the braid is stripped to the extent that inner insulator 20 corners about shoulder 21 and enters passage 8. Preferably inner conductor 15 exits passage 8 via jaws 12.

The device 1 works in conjunction with the aerial mounting base 19 to clamp the cable 11 between it and ground plate 18. Ground plate 18 sandwiches mounting surface with the assistance of mounting block 26. Bolt 4 penetrates passage 3 and is secured by nut 27. Tightening of nut 27 urges bolt head 6 against the inner conductor to secure -s Irr I 1 L I ls18 f cable 11 effecting a mechanical and electrical connection.

It will be recognised by persons skilled in the art that numerous variations and modifications may be made to the invention as broadly described herein without departing from the overall spirit and scope of the invention.

0 6 0 0 0 a I--rrsr I-

Claims (9)

1. An integral cable strain relief device comprising; a first member having a primary through passage havit, first and second ends and adapted to receive a mounting bolt, a second member connected with the first member and including a second passage having first and second endo and which either communicates with or terminates near the primary through passage, wherein the first end c si.A first member receives the shank and head of said bolt ,tjd the second end of the first member penetrates a mounl *r,v device to which the strain relief device is fitted, said second through passage being either substantially parallel to or at an angle to the primary through passage and receiving ckc=- Ld (lia .JAOV therein a cable/ito be anchored at an electrical connection, said second passage terminating at its first end in or near a set of jaws which grippingly engage the cable and meeting at its second end a saddle having a landing lying at an angle to the axis of the second passage and along which the cable travels before it enters the second through passage; wherein due to the at least one change in direction of travel of the cable between the landing and the electrical connection and the action of the jaws, tensile stresses induced in the cable are isolated from the electrical connection. 5

2. A cable strain relief device according to claim 1 wherein, the internal conductor of the cable exits the second passage and passes through the jaws before engaging the head of the bolt which clamps the conductor against a wall of a recess at the first end of the first passage in which the bolt head sits.

3. A cable strain relief device according to claim 2 wherein the jaws are urged towards a closed condition under the action of tensile strain if placed on the cable thereby preventing withdrawal of the cable via the second passage.

4. A cable strain relief device according to claim 3 wherein the landing is substantially perpendicular to the second passage and is formed in a channel in the saddle.

A cable strain relief device according to claim 4 wherein the device is substantially T shaped with the first passage co-axial with the first member or upright member of the T and wherein the second passage has its axis perpendicular to the second member or cross member of the T.

6. A cable strain relief device according to claim wherein, when the device is fitted to an aerial assembly, the cable is sandwiched between the device and a ground :15 plate thereby effecting clamping of the cable.

7. A cable strain relief device according to claim 6 wherein the first passage is substantially parallel with and larger than the second passage.

8. A cable strain relief device according to claim 7 wherein the device is formed in a mold from a plastics material. O

9. A cable strain relief device as hereinbefore described and with reference to the accompanying illustrations. o DATED this 16th day of February, 1994. 0 MOBILE ONE AUSTRALIA PTY LTD By Its Patent Attorneys H.R. HODGKINSON CO.