GB2140888A - Linkable rods - Google Patents

Abstract

Rapid action linkages are provided for a set of rods used to insert cables into ducts. The linkage between each pair of rods (3,5) comprises a primary coupling (10) on one rod which has a socket (19) with slots having longitudinally extending entrance portions (13A,B) and circumferentially extending retention portions (12A,B), and a secondary coupling (14) on the second rod which includes a nose (20) having retention studs (24A,B) adapted to engage with the slots. It also includes location means for restraining relative rotation of the linked rods taking the form of a spring loaded lever arm (26) on the first coupling having an inwardly extending boss (18). In the assembled linkage the boss engages with a location recess (25) on the nose of the second coupling. The outer surfaces of the couplings and location means lie substantially flush. <IMAGE>

Description

SPECIFICATION Linkable rods This invention relates to linkable rods which are suitable for insertion through conduits and, in particular, it relates to linkages for rods and to a set of rods, each pair having a linkage so that the set of rods can be joined end-to-end to create a long length.

Linkable rods have many applications. In telecommunications they are used when it is necessary to insert a new cable into a duct which already contains cables. In unfavourable circumstances the duct may be very nearly full and it is generally considered that the best way of introducing the new cable comprises: (1) introducing a flexible rod (2) using the rod to introduce a pulling cord, and (3) attaching the cable to the pulling cord so that the cable can be pulled into the duct.

In general, it is preferable to provide flexible rod in short lengths which can be connected to produce a length long enough to pass through the duct, eg up to 150 or 200m. The linkages are an important part of the system and the following are important properties of the linkages: (1) Rapidly connectable (2) Rapidly disconnectable (3) Security against unwanted disconnection (4) Ease of introduction and travel through a duct, even if the duct is almost full (5) An ability to withstand torque, compression and tensile forces.

Currently used linkable rods have certain disadvantages. For example, they may be difficult to connect and disconnect. The present invention provides a linkage for rods which overcomes problems encountered in prior art linkages.

According to the invention there is provided a linkage for rods comprising a primary coupling, a secondary coupling and location means, wherein the primary coupling comprises a socket provided with slots, each slot having a longitudinally extending entrance portion and a transversely extending retention portion; the secondary coupling comprises a nose with retention studs adapted, on linking, to pass via the entrance portions to the retention portions of the slots so that the nose is received in the socket, with the outer ends of the studs lying at, or inwardly of, the outer surface of the primary coupling; and the location means comprises a lever arm on the primary coupling with an inwardly biassed boss and a location recess in the nose so that, with the rods linked, the lever arm lies substantiallyflush with the outer surface of the primary coupling with the boss engaged in the recess.

The invention also provides a set of linkable rods, each pair of rods having a linkage comprising a primary coupling on one rod, a secondary coupling on the other rod and location means.

Preferably, the location means includes a spring, and a housing for the spring in the primary coupling, so that the spring biasses the end of the lever arm remote from the boss outwards.

Suitably, each rod has a primary coupling on one end and a secondary coupling on the other. However, the first and last of a set of linked rods may each have a coupling at one end only. Also, each rod could have two primary or two secondary couplings, rods of each kind being connected alternately.

As indicated above, rods according to the invention are suitable for inserting cables, including power cables, as well as telecommunications cables, into ducts and also into hollow poles. The rods also have other applications, eg tent poles and clearing blocked ducts such as drains.

A linkage according to the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing in which: Figure lisa side view of an embodiment of a primary coupling of a linkage for rods according to the invention; Figure 2 is a side view of an embodiment of a conformable secondary coupling; Figure 3 is a longitudinal cross section of the primary coupling shown in Figure land Figure 4 is an end view of the primary coupling shown in Figure 1.

Figure 1 shows a cylindrical rod 3 with a primary coupling (generally indicated by the numeral 10) having a socket 19 fitted onto one end. Figure 2 shows a cylindrical rod 5, of the same diameter as rod 3, with a secondary coupling (generally indicated by the numeral 14) on one end, formed with a nose (generally indicated by the numeral 20).. The nose 20 has a body 21 which tapers at an angle of 6" and a bevelled end 22. A pin 23 passes through the body 21 and projects to form retaining studs 24A and 24B.

The length of the pin is the same as the diameter of primary coupling 10. The body 21 is provided with location recesses 25 (only one of which is shown) which are off-set 90" from the studs 24A and 24B.

The primary coupling 10 includes a slot having a longitudinally extending entrance portion 13A parallel to the axis of the coupling 10. The inner end of the portion 13A connects to a transverse retention portion 12A which extends for 227/2" around the circumference. The coupling also comprises a second slot diametrically opposite the first, with entrance portion 13B and retention portion 12B.

The linkage also includes location means which comprises a lever arm 26, pivoted at 27 adjacent end wall 28 of the socket. One end of the arm 26 is formed with an inwardly extending locating boss 18.

The other end is formed as a finger pad 16.

Primary coupling 10 has a radially extending recess 29 which accommodates a biassing spring 17.

Spring 17 pushes pad 16 outwards (and boss 18 inwards), unless counter-acting pressure is applied to pad 16 to compress the spring, allowing the boss to move outwards.

Rods 3 and 5 are securely fitted to their respective couplings. The ends of the rods are received in cylindrical recesses on the couplings and are held by means such as a pin (not shown). It will be noted that the ends of the couplings are tapered slightly so that there is no edge liable to catch or cause damage on insertion into a duct. The rods are formed of any suitable material such as PVC and the linkage can be a metal, such as brass, or a plastics material.

In order to link rods 3 and 5 and the primary and secondary couplings 10 and 14, the nose 20 is offered up to the socket 19 and the studs 24A, 24B to the entrance slots 13A, 13B. The bevel 22 engages with and displaces the boss 18 outwards, thereby compressing spring 17. When the nose 20 is fully inserted, a relative rotation of 221/2 moves the studs 24A, 24B to the closed ends of retention slots 12A, 12B and aligns the boss 18 with one of the recesses 25.Lever arm 26 therefore moves under the action of spring 17 to engage the boss 18 with the recess thereby restricting relative angular displacement (until boss 18 is withdrawn by pressure on finger pad 16.) This procedure, involving only a short longitudinal motion and an eighth turn, is rapid and the resulting connection can transmit not only compressive and tensile forces but also torque (via the boss 18 and the recess 25). After use the linkage is easily separated. Finger pressure on finger pad 16 disengages boss 18 from recess 25 permitting relative rotation so that the nose 20 can be removed from the socket 19. The disconnection is also rapid.

Rods 3 and 5 are both cylindrical and they have the same diameter. Coupling 10 is also generally cylindrical and coupling 14 has a cylindrical portion 30.

After connection, the outer surfaces of coupling 10 and portion 30 lie flush with one another. The outer ends of studs 24A and 24B also lie flush with the outer surface of primary coupling 10 as the length of pin 23 is the same as the diameter of the coupling 10.

Furthermore, with boss 18 located in one of the recesses 25, arm 26 lies flush with the outer surface of primary coupling 10. Thus it can be seen that when rods 3 and 5 are connected, there are no protrusions. As a result, on insertion into a packed duct the progress of the rods is not unduly hindered and insertion of a set of rods can be carried out with relative ease. Also, since no part of the linkage between the rods protrudes, there is little danger of accidental disconnection. If finger pad 16, for example, were to project it might unintentionally be depressed during advance of the rods through the duct, which could allow the linkage to become disconnected. Recovery of the rods ahead of the disconnected linkage could present problems.

Only two rods are shown, but it will be appreciated that these may be two of a large number of linkable rods. Each rod is typically 2 to 3 metres long, 12 to 25mm in diameter, and it may be linked with other rods to form a linked set around 150 metres or more long. In each case, a secondary coupling on one rod is connected with a primary on another. Each rod may have one primary and one secondary. An operable arrangement can be achieved in other ways, eg, if half the rods have two primaries and half have two secondaries. In the preferred arrangement each rod has a primary on one end and a secondary on the other so that any free rod can be connected to a partly formed sequence. In a set of rods it may be convenient to include special terminal items to provide a means for connections to a pull-rope or other tool.

The couplings described above are particularly suitable for use as cabling rods. The linkages are strong enough to transmit the torque and compression forces needed to insert the rods into a crowded duct. They can also transmit the tensile forces needed to introduce a pulling-cord.

As stated above the body of the nose tapers at an angle of 6" and the socket is tapered to conform.

During disconnection there may be a bending moment at the linkage, eg, because it may be necessary to bend the rod if the entrance to the duct is obstructed or because of the weight of an unsupported rod out of the duct. In any case such a bending moment would tend to jam a cylindrical linkage. A small taper, eg 2'to 10 and preferably 6 , reduces the tendency to jam. The explanation may that a small longitudinal motion separates the surfaces so freeing the connection.

It will be appreciated that changes may be made to the embodiment described above. For example, the slots of the primary coupling need not extend through the full thickness of the wall of the socket; an outer section of the wall could extend across the slots. Instead of two slots, three or more could be provided. The couplings could be provided with shanks adapted to fit into recesses in the rods. In this case, the rods and couplings could have the same diameters.

Claims (11)

1. A linkage for rods comprising a primary coupling, a secondary coupling and location means; wherein the primary coupling comprises a socket provided with slots, each slot having a longitudinally extending entrance portion and a transversely ex- tending retention portion; the secondary coupling comprises a nose with retention studs adapted, on linking, to pass via the entrance portions to the retention portions of the slots so that the nose is received in the socket, with the outer ends of the studs lying at, or inwardly of, the outer surface of the primary coupling; and the location means comprises a lever arm on the primary coupling with an inwardly biassed boss and a location recess in the nose so that, with the rods linked, the lever arm lies substantiallyflush with the outer surface ofthe primary coupling with the boss engaged in the recess.

2. A linkage as claimed in claim 1, wherein the location means includes a spring, and a housing for the spring in the primary coupling, so that the spring biasses the end of the lever arm remote from the boss outwards.

3. A linkage as claimed in claim 1 or claim 2, wherein the nose has a bevelled end to engage with and displace the boss outwards during linking.

4. A linkage as claimed in any preceding claim, wherein the inner surface of the socket and the outer surface of the nose are tapered at an angle of 2" to 10 .

5. A linkage as claimed in claim 4, wherein the angle of taper is 6 .

6. A linkage as claimed in any preceding claim wherein, when linked, the outer surfaces of the primary and secondary couplings lie substantially flush with one another.

7. A linkage as claimed in any preceding claim wherein, when linked, the outer ends of the studs lie substantially flush with the outer surface of the primary coupling.

8. A set of linkable rods, each pair of rods having a linkage as claimed in any preceding claim, wherein the primary coupling is provided on one rod and the secondary coupling on the other rod.

9. A set of rods as claimed in claim 8, wherein each rod has a primary coupling on one end and a secondary coupling on the other end.

10. A linkage for rods, substantially as hereinbefore described, with reference to and as shown in the accompanying drawing.

11. A set of linkable rods, substantially as hereinbefore described, with reference to and as shown in the accompanying drawing.