GB2170282A - Flexible gaiters - Google Patents

Abstract

A flexible gaiter (e.g., for protecting a screw jack used in the adjustment of an antenna for a satellite communication system) is formed by a helical strip the edges of which are adapted to interlock with each other to form a tubular structure. The strip has a V-shaped or similar cross-section to provide one or more corrugations enabling the gaiter to expand and contract in an axial direction. <IMAGE>

Description

SPECIFICATION A flexible gaiter This invention relates to a flexible gaiter. It arose in connection with a particular problem in the maintenance of a satellite earth station antenna but is also applicable to many other fields.

The frequent use of screw jacks for the driving mechanisms of satellite earth station antennas has highlighted a problem with respect to the weather protection of the jack screw itself. Conventionally these jacks are usually grease lubricated and normally made of an alloy steel which requires total protection from the weather and from dust.

The normal method of providing such weather protection on a screw jack, which of necessity has to extend and contract, is to use a flexible gaiter having a corrugated wall so that it is shaped like a concertina or bellows. It is usually made of some coated fabric, often PVC or nylon which is stitched or, on occasions, moulded to form an extendible cover over the screw. The gaiter often consists of a series of annuli cut from a coated fabric, which are stitched alternately on their outer and inner edges to form the concertina shape.

Such a gaiter is fitted over one end of the jack screw before the jack screw is attached in position, usually by a clevis of yoke at one end and a jack nut and gear box at the other end. Once the screw jack is in position on the antenna it is impossible to replace the gaiter should it be damaged, wear out or deteriorate with the weather, without disconnecting at least one end of the screw jack.

On a satellite earth station antenna, disconnecting the screw jack invariably necessitates discontinuing the operation of the antenna.

Such a discontinuity in the operation of an earth station is not acceptable to most earth station operators and hence, there is at present a problem.

The invention provides a flexible gaiter comprising a helical strip or strips having faces which extend laterally with respect to the axis of the helix, and edges which are adapted to interconnect with each other to form a tubular structure.

The invention also provides a flexible gaiter having a corrugated wall so as to provide a concertina or bellows action allowing it to be expanded and contracted in length characterised in that the corrugated shape of the wall is formed by a helical recess and/or projection extending repeatedly around the gaiter and progressing from one end of it to the other and in that a helical joint extends parallel to the recess or projection also repeatedly around the gaiter and progressing from one end to the other.

It will be appreciated that by employing the invention it is possible to fit the gaiter to a jack without the need to detach either end of the jack from the components to which it is connected. Consequently the earth station, or other apparatus of which the jack forms a part, can remain operational whilst the gaiter is being fitted.

There are many different ways in which the aforementioned edges can be adapted to interconnect with each other. This is preferably done with an interlocking arrangement, e.g., by forming one edge with a longitudinal groove which receives and retains positively a longitudinal projection on the other edge. Such an interlocking connection can be made substantially weatherproof. Furthermore, if the strip is manufactured by extrustion, as is preferred, the longitudinal groove and projection can be produced by an extrusion die of suitable shape. The required helical shape can also be obtained during extrusion by suitable control over the extrusion process and/or suitable shaping of the die.

One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawings of a flexible gaiter constructed in accordance with invention. In the drawings: Figure 1 is a perspective view of part of a gaiter constructed in accordance with the invention; and Figure 2 is a cross-section through the axis of the gaiter shown in Fig. 1.

Referring to the drawings, the illustrated gaiter is formed from a helical extruded strip 1 of synthetic plastics material having a Vshaped cross-section. The two free longitudinal edges of the strip are formed, one with a longitudinal projection 2 and the other with a longitudinal socket 3. The projection can be pressed into the socket as illustrated so that the helix is formed into a tubular structure.

Walls 4 and 5 of the strip 1 extend laterally with respect to the axis 6 to produce a bellows or concertina shape having a continuous helical corrugation. This bellows or concertina shape allows the structure to expand or contract in the direction of the axis 6 either by flexing of the plastic of the plastic of the walls 4 and 5 or by bending or hinging at the ridge 7 or base 8 of the corrugation, or by a hinge action provided by the joint between the projection 2 and socket 3.

In use the helical strip is wound around the unit to be protected, such as a screw jack, and the projection 2 is then pressed, using the fingers, into the socket 3. The ends can be clamped in a similar way, not shown, to conventional bellows type gaiters or using a circlip fitting into the base of the corrugation.

In an alternative construction the single strip of V-shaped cross-section could be replaced by two flat helical strips, each providing the function of one of the walls 4 and 5. A further joint like that provided at 2 and 3 would then need to be provided at 6. Another possibility would be to use a W-shaped cross-section or indeed any other cross-section forming a part of the desired cross-section of the bellows shape.

The interlocking action between adjacent edges and provided by projection 2 and socket 3 is ideal because it can be formed during the extrusion of the plastic and because it provides a very simple method of assembly. However, other possibilities may be practicable and, for example, the use of adhesive to attach the co-operating edges might be satisfactory for some purposes.

Where the gaiter is used to protect a screw threaded mechanism such as a screw jack it is desirable that the handedness of the helix be opposite to that of the screw thread to avoid interengagement therebetween. Where the helix has been produced with a handedness which is the same as that of a screw thread to be protected it can be inverted to the appropriate handedness.

It is believed that the invention will provide a simple yet effective solution to the problem previously described in connection with earth stations for satellite communication purposes.

It is obviously equally useful for other machines which use jacks, and for other purposes which call for a flexible bellows type gaiter. An added advantage of using the invention is that the elimination of any need to disconnect the component protected by the gaiter avoids any need for re-adjustment after re-assembly as is often required after replacing conventional gaiters on rack and pinion steering systems for motor vehicles.

Claims (6)

1. A flexible gaiter comprising a helical strip or strips having faces which extend laterally with respect to the axis of the helix, and edges which are adapted to interconnect with each other to form a tubular structure.

2. A flexible gaiter according to Claim 1 in which one of the said edges has a longitudinal socket extending along it which receives a longitudinal projection extending aiong another of the said edges.

3. A flexible gaiter according to Claim 1 or 2 in which the or each strip is formed by extrusion.

4. A flexible gaiter having a corrugated wall so as to provide a concertina or bellows action allowing it to be expanded and contracted in length chracterised in that the corrugated shape of the wall is formed by a helical recess and/or projection extending repeatedly aroud the gaiter and progressing from one end of it to the other and in that a helical joint extends parallel to the recess or projection also repeatedly around the gaiter and progressing from one end to the other.

5. A flexible gaiter according to Claim 4 in which the said joint is formed by a groove on one edge into which fits a ridge in a co-operating edge.

6. A flexible gaiter substantially as described with reference to the accompanying drawings and substantially as illustrated therein.