Patent Description:
Such connectors used in the laying of fibre optic cables. The cables are used, for example, to provide a fibre optic cable connection from a junction box to a building such as an office or residence in order to provide a connection for internet data.

The fibre optic cables are provided in bundles of individual fibres which can be up to several kilometres long. The fibre bundles/cables are fed through tubes (often referred to as ducts/microducts/conduits) which are typically <NUM> metres long, but can be as long as <NUM> metres. A number of tubes therefore may need to be connected together in order to support the full run of the fibre bundle.

Because of the manner of their use, there are unique set of demands on a fibre optic cable tube connector.

Its outer diameter must be as small as possible in order to minimise bulk as the connectors are often grouped together in large numbers.

The cable bundle running through the middle of the connector must be visible in use. This is because it is essential for an operator to be able to visually confirm whether a fibre bundle runs through a particular connector. The tubes will be laid and the fibres may not be passed through until much later. An operator therefore needs to be able to determine which tubing does not yet have a fibre in place. Further, in the event of a fibre failure the operator can determine from a visual inspection whether a fibre is in place at a particular connector. The connectors also need to be highly impact resistant. Cables are usually buried in the ground and, for maintenance, they need to be dug up. This is generally done by a labourer with a spade, and the first that the labourer will know if the presence of the cable is when it is struck by the spade. The connectors therefore need to be sufficiently robust to resist such an impact. In practice, they need to pass a '15J impact test'.

These latter two requirements, namely the need to be able to view the fibre and the need for high impact resistance represent conflicting requirements.

For most applications, connectors are made from an opaque plastic and these are readily available in the impact resistance forms. However, non-opaque materials are typically amorphous materials and are inherently more brittle than the opaque equivalents.

As a result of this, prior art fibre optic cable connectors use a number of circumferential ribs in order to reinforce the connector. However, this leads to further problems. The ribs create a discontinuous profile for the connector leading to highly radiused regions which affect transparency. Further, dirt and stones are trapped between the ribs. The presence of stones can lead to an impact being directly transmitted to the ribs thereby causing damage. Further, the dirt is likely to be compacted over time and is therefore difficult to clear when trying to make a visual inspection of the fibre.

US patent application publication <CIT> discloses a joint including a fitting for fluid conduits, a sleeve, and a pipe. The fitting exhibits a base body, an outer body and a supporting body, wherein the outer body and supporting body form a groove between them. The sleeve embraces a pipe end under a pre-stress, wherein the pipe end with the sleeve engages into the groove under a pre-stress.

The present invention addresses these problems.

According to the present invention, we have provided a fibre optic tube connector according to claim <NUM>.

The present invention therefore takes a completely different approach to impact protection from that of the prior art. Rather than providing a number of external ribs, the impact protection of the present invention is provided by an inner sleeve which is spaced from an outer sleeve to define a gap.

Now, any impact on the body which is likely to cause deformation of the body will tend to cause inward deformation of the outer sleeve. However, because of the presence of the gap, any impact which is not directly aligned with the web of material can cause an inward deformation of twice the width of the gap before the inner sleeve will be compressed.

The webs could be arranged to be diametrically opposed to one another as the chance of impact aligned with a web is relatively small. However, preferably the or each web is arranged such that upon radical impact directly aligned with the web, the outer sleeve can be deformed by the width of the gap before any deformation occurs on the inner sleeve.

Because of this effect, it is desirable to make the/each web as small as possible. In practice, this is limited by the requirements of the moulding process as the plastic which forms the inner sleeve is required to flow through the web region.

While the optimum performance is met by a single web, the limitations imposed by the moulding process may mean that more than one web is required in practice. If more than one web is used, each web is preferably angularly offset from the other webs such that no part of the inner sleeve is supported at diametrically opposed locations. If this were to occur, any impact in this direction would be directly transmitted to the inner sleeve.

One of the webs needs to be made sufficiently robust that it will maintain the support of the inner sleeve within the outer sleeve. However, additional webs may be provided for moulding purposes. When a number of webs are provided, these can be made thinner such that they are effectively sacrificial webs. In the event of an impact, any deformation which is transmitted through the wall of the outer sleeve may cause the closest web to fail leaving the other webs to maintain the optimal location of the inner sleeve. The loss of one such sacrificial web is not a problem in use as the remaining webs hold the inner sleeve in place. The loss of more than one web due to impact will not be problematic as the inner sleeve is supported by the previously assembled tube.

The webs preferably extend in a non-radial direction, for example tangentially to the inner sleeve so as to reduce the component of the force transmitted to the inner sleeve.

The webs are preferably in the same radial plane. They are preferably offset from the centre of the connector so as not to impair visibility in this region.

As will be understood from the above description, the web should occupy a relatively small area of the outer surface of the inner sleeve.

Preferably, the total circumferential extent of all of the webs is less than <NUM>%, preferably less than <NUM>%, more preferably less than <NUM>% and most preferably less than <NUM>% of the circumference of the outer wall of the inner sleeve. By occupying less than <NUM>% of the circumference of the outer wall of the inner sleeve, the web or webs can be arranged such that there is no diametric load path through two parts of the web at diametrically opposed locations on opposite sides of the inner sleeve.

Preferably, the web occupies less than <NUM>%, more preferably less than <NUM>% and most preferably less than <NUM>% of the axial length of the outer wall of the inner sleeve. Preferably, the web occupies less than <NUM>%, more preferably less than <NUM>% and most preferably less than <NUM>% of the area of the outer wall of the inner sleeve. All of these measurements represent the dimension of the web at its widest point.

Because of the different approach taken by the present invention to impact protection, the need for the ribs of the prior art can be significantly reduced. Preferably, the present invention eliminates the need for ribs all together so that preferably, the outer face of the connector bodies is devoid of ribs. This removes any stress concentrators at the outer surface of the connector as well as removing any potential dirt traps.

Preferably, at least the axially central third of the connector body has a continuous cylindrical outer surface of constant radius. This central portion corresponds to the region where the fibre will be exposed in the connector. More preferably, the requirement for a continuous cylindrical outer surface of a constant radius extends along substantially all of the length of the connector body. The ends of the connector body, however, may have a radius profile.

Not only does such an arrangement remove the stress concentrators and dirty traps, it also improves the clarity of the connector. The continuous cylindrical surface is much easier to see through than the ribs of the prior art in which, even after cleaning, a residual amount of dirt is likely to remain. Further, the use of ribs caused internal reflection of light which hampers direct visibility of the region at the centre of the connector. This does not happen with the cylindrical outer surface. Not only is this easy to wipe clean, but the mould can be polished in the central region providing further visibility improvements.

An example of a fibre optic cable tube connector in accordance with the present invention will now be described with reference to the accompanying drawings in which:.

The connector comprises a connector body <NUM> having a generally hollow cylindrical configuration centred on a main axis X. A connector <NUM> (described in greater detail below) is provided at either end to receive and grip a tube T at each end which is sealed by an O ring <NUM>.

The body <NUM> is moulded from a non-opaque plastic. The plastic must be such that it is clear enough that a visual inspection externally of the connector allows an operator to determine whether a fibre cable or fibre bundle F is present in the centre of the connector. Ideally, the body should be as close to transparent as possible. However, practical considerations mean that the body will not be truly transparent. Instead, the body is likely to translucent to a sufficient extent that the fibre is visible. Suitable materials are polycarbonate, polystyrene, polyester, acrylic and nylon. The body <NUM> is formed in a moulding process and can optionally be polished to improve the clarity of the body. As can be seen in the various figures, the outer profile of the body is a smooth configuration which is devoid of external ribs thereby eliminating any stress concentrations and orifices for the accumulation of dirt.

The body <NUM> is made up of an outer sleeve <NUM> and an inner sleeve <NUM> which are connected by at least one web <NUM> as described below.

The outer sleeve <NUM> has an axial bore <NUM> which is open at the distal end and which has a first step <NUM> and second step <NUM> which receive the connector <NUM> as described below.

The inner sleeve <NUM> is retained by the web <NUM> so as to form a gap <NUM> of generally uniform thickness as best seen in <FIG>.

As will be appreciated from <FIG>, the web <NUM> extends across only a very small part of the inner sleeve <NUM> so that the gap <NUM> is present for most of the length and circumference of the inner sleeve <NUM>.

Any impact on the outer sleeve <NUM> which occurs during the installation of the tubing, or when the tubing is dug up for maintenance can cause deformation of the outer sleeve <NUM>. By providing the gap <NUM>, the effect of any external impact on the outer sleeve <NUM> is isolated, to a significant extent, from the inner sleeve <NUM>, and hence is largely prevented from causing any change to the diameter of the inner bore <NUM> of the inner sleeve <NUM>. Initial tests show that this design is effective in resisting external impact. Further, this can be achieved in a manner which does not require the addition of ribs and does not require an increase in the outer diameter of the connector.

Use of the very small size of the web <NUM> means that the chance of an impact being directly transmitted from the outer sleeve <NUM> to the inner sleeve <NUM> via the web <NUM> is greatly reduced. Even if this were to occur (i.e. an impact were to be applied in the vertical downward direction in <FIG> at the centre point connector in <FIG>), the inner sleeve <NUM> can still deflect by an amount equivalent to the width of the gap <NUM> before any stresses occur on the inner sleeve which would have an adverse effect on the internal bore <NUM> of the inner sleeve <NUM>.

In order to mould the body <NUM> all of the plastic required for the inner sleeve <NUM> is required to pass through the webs <NUM>, <NUM>. This represents a reasonably significant amount of plastic which flows into a relatively complex and narrow flow path. In order to alleviate this, we are contemplating providing one or more additional webs <NUM> depicted schematically in <FIG> these are angularly offset with respect to the web <NUM> and may also be axially offset to ensure that there is no point at which the inner sleeve <NUM> is supported on diametrically opposed sides. The additional webs <NUM> provide further flow paths for the plastic into the inner sleeve during the moulding process. Multiple webs can be made weaker than a single web such that whichever web is closest to the impact will preferentially fracture under an applied load leaving the remaining ribs to support the inner sleeve <NUM>.

Instead of extending in a radial sense as shown in <FIG>, the or each web <NUM> may extend tangentially as shown in <FIG>, or in any other direction across the gap <NUM>. As shown in <FIG>, the webs <NUM> are axially offset from an annular flange <NUM> so that they do not impair the visibility into this region.

The manner in which the connector is configured in order to avoid snagging of the fibre F will now be described with reference to <FIG>, <FIG> with <FIG> being used to provide a comparison with the prior art.

<FIG> shows the connector body <NUM> with a tube T fixed and sealed in either end. Once connected in this way, the fibre F is blown from one end through the tube T, across the interface between the tubes and into the adjacent tube.

The tubes T abut against the annular flange <NUM> at a midpoint of the inner sleeve <NUM>. The connectors <NUM> and O-rings <NUM> broadly have the same inner diameter as the inner diameter of the inner sleeve <NUM> so that, when the tube T is pushed into the body <NUM>, it is guided into the inner sleeve <NUM>. The end of the tube T then abuts the annular flange <NUM>. As best seen in <FIG>, the annular flange <NUM> is provided undercut portion <NUM> such that the thickness of the annular flange <NUM> in the axial direction increases towards the axis X.

As a result of this, the innermost corner <NUM> of the tube T is the first part of the tube T to abut the annular flange <NUM>. This means that there is no gap between the inner face <NUM> of the tube T and the annual flange <NUM>.

The undercut portion <NUM> is radiused as shown in <FIG>. Similarly, the radially innermost corners <NUM> of the annular flange are radiused to present a smooth surface to the fibre.

In comparison with the prior art arrangement shown in <FIG>, the elimination of the gap G between the end of the tube T and the annular flange <NUM> means that there is no exposed abrupt edge of the tube T for the fibre F to snag on.

<FIG> depicts the situation where the left hand tube has been cut at an angle which is slightly oblique to a plane perpendicular to the axis X. As a result of this, the uppermost edge <NUM> of the tube T enters into the undercut region <NUM> and seats on the annular flange <NUM>.

By comparison with <FIG> it can be seen that the gap between the tube T and the annular flange <NUM> is eliminated in the top half of the figure and the gap at the bottom is significantly reduced as compared to <FIG>.

As will to be apparent from <FIG>, the radially inward extent of the annular flange <NUM> is greater than the inner diameter of the tube T. As a result of this, the annular flange <NUM> protrudes slightly inwardly beyond the inner face <NUM> of the tube T. From a comparison of <FIG> and <FIG>, if it is assumed that the fibre F is fed from right to left, and in the vicinity of the connector <NUM> the tip of the fibre is travelling along the lower part of the inner face <NUM> in <FIG> and <FIG>, in the <FIG>, this will initially encounter the corner of the annular flange <NUM> which projects slightly beyond the inner surface <NUM> of the tube T. However, the fibre F can easily ride over this curved corner and, in doing so, this deflection should push the tip of the fibre above the exposed edge <NUM> of the tube T. By contrast, in <FIG>, annular projection S does not protrude beyond the inner surface <NUM> of the tube so there is nothing to begin to deflect the fibre F back towards the centre of the bore. Further, the gap G' in <FIG> is significantly larger than the corresponding gap in <FIG>. This, not only is fibre not deflected away from this gap, the presence of the large gap affords a significantly greater opportunity for fibre to enter the gap and become snagged on the edge <NUM> of the tube T.

A further feature which prevents snagging of the tube is the splined arrangement listed as best illustrated in <FIG> and <FIG>.

As can be seen from these figures, six axially extending splines <NUM> are equally spaced around the circumference of the inner sleeve <NUM>. These are shown having a constant cross-section in a plane perpendicular to the axis. However, they may have a thickness which increases towards the annular flange <NUM>.

As shown in <FIG> and <FIG>, a tube T has been fed from a coil and has taken on a flattened oval shape. As this enters the inner sleeve <NUM> the tube T engages with the enlarged portions of the tube T and tend to push this back to a more circular shape as shown in <FIG>.

Any number of splines may be used. However six has been found to be a reasonable number. This allows engagement with a flattened tube which is inserted in any orientation. A smaller number of flanges risks the possibility that the enlarged part of the tube enters between adjacent splines. On the other hand, adding more splines increases the insertion resistance for the tube T into the connector <NUM>.

The splines <NUM> are dimensioned such that where the splines are present is slightly smaller than the outer diameter of the tube. The splines <NUM> will therefore bite into the material of the tube T in these regions. This ensures a secure and robust fit of the tube T and also provides the maximum opportunity for the splines to reduce the eccentricity of the tube.

The connectors <NUM> (one at each end of the body <NUM>) will now be described in greater detail with reference to <FIG>.

The connectors <NUM> are formed of two components, namely a cartridge <NUM> and a collet <NUM>.

The cartridge <NUM> has a generally annular configuration. The outer surface is provided with a plurality of flexible metal teeth <NUM>. The cartridge <NUM> is inserted into an end of the body <NUM> until it seats against the second step <NUM>. The teeth <NUM> grip the wall of the body <NUM> to ensure that the cartridge <NUM> is permanent retained in the body <NUM>. At the end of the cartridge <NUM> adjacent to the second step <NUM>, there is a tapered cam surface <NUM> which cooperates with the collet as described below. At the opposite end, the end face of the cartridge <NUM> is provided with a pair of ramped surfaces <NUM>. Although two such surfaces are shown, there may be a single surface or there may be more than two. Each ramp surface has a low point <NUM> corresponding to an unlocked configuration and a high point <NUM> corresponding to a locked configuration within an inclined face <NUM> in between. A bump <NUM> is provided at the interface between the high point <NUM> and the inclined face <NUM>. A similar bump may be provided interface between the incline face <NUM> and the low point <NUM>. The low point <NUM> terminates at the first end stop <NUM> and the high point <NUM> terminates at a second end stop <NUM>.

Most of the features of the collet <NUM> are conventional. It has a collet ring <NUM> from which a plurality of flexible arms <NUM> extend. Each arm has a head <NUM> at its distal end as is provided with an inwardly projected metal tooth <NUM>.

With a tube T inserted for example as shown in <FIG>, any movement tending to pull the tube T out of the connector causes the teeth <NUM> to grip into the tube, this pulls the heads <NUM> towards the tapered cam surface <NUM> on the cartridge <NUM> deflecting the arms <NUM> inwardly to provide a progressively increasing gripping force on the tube T. This serves to hold the tube T securely in place. This is the conventional manner in which a collet operates.

The adaptation provided by the present invention is the presence of a pair of cam followers <NUM> extending from the collet ring <NUM> towards the ramped surface <NUM> on the cartridge <NUM>. Although two followers <NUM> are shown, in practice there are as many followers <NUM> as there are ramped surfaces <NUM>. Alternatively, the cam arrangement may be inverted such that the ramped surface(s) is/are on the collet and the follower(s) is/are on the cartridge.

The collet ring <NUM> is also provided with a pair of tabs <NUM> which extend from the collet ring <NUM> the opposite direction to the followers <NUM>. As shown in the drawings, the position of the tabs <NUM> corresponds to a number and position of the followers <NUM>. However, this may not be the case. The components can be offset from one another and there need not be same number of both.

The operation of the collet <NUM> will now be described with reference to <FIG>. The position shown in <FIG> is an unlocked position. In this position, the collet <NUM> has been rotated such that cam followers <NUM> abut the first end stops <NUM> such that the cam followers are at the low point <NUM>. As will be apparent from <FIG> (particularly when compared with <FIG>) in this position, the collet <NUM> has a relatively large degree of axial freedom as it can move from the position in which the heads <NUM> engage with the tapered cam surface <NUM> all the way to the left (with reference to <FIG>) in the position shown in that figure. If held in that position by a user, the tube T can be withdrawn because the heads <NUM> are kept away from the tapered inclined surface <NUM> such that the collet cannot grip the tube. The collet <NUM> is then rotated in the direction of arrow <NUM> into the locked position shown in <FIG>. In doing so, the followers <NUM> moves up the inclined faces <NUM>, over the bumps <NUM>, providing a tactile feel to the user that a position has been reached, and onto the high point <NUM>.

As will be appreciated from a comparison of <FIG> and <FIG>, in the locked position shown in <FIG>, the collet has nothing like the same degree of freedom as in <FIG> so that it cannot be moved and held into an unlocked position where the teeth <NUM> disengage with the tube T. This is more apparent from <FIG> which show the collet in the same locked position as in <FIG> but with the tube in place. Here it can be seen how the presence of the tube pushes the heads <NUM> back onto the tapered cam surface <NUM>.

The only way to remove the tube T in this locked configuration is for the user to grasp the tabs <NUM>, rotate the collet <NUM> in the direction of arrow <NUM> in <FIG> to the unlocked position, and manually hold the collet in the position shown in <FIG> while pulling the tube out of the body <NUM>.

The tube T will usually be inserted with the collet <NUM> in the unlocked position shown in <FIG> as this allows for more scope for the arms <NUM> to be deflected upon insertion of the tube. However, as can be seen in <FIG>, even in the locked position, there is a small clearance between the head <NUM> and the tapered cam surface <NUM>. Thus, it is possible to insert the tube T with the collet in the locked position. This provides a simple assembly process as the user needs only to be told to insert the tube into the collet. They do not need to concern themselves with the locking operation.

Claim 1:
A fibre optic cable tube connector, to connect tubes wherein fibre optic cables are fed, the fibre optic cable tube connector comprising a fibre optic cable tube connector body (<NUM>)
made of a plastic, the body defining a through bore and having an end connector at either end, each end connector (<NUM>) being configured to receive and grip a respective tube (T);
the body comprising an outer sleeve (<NUM>) and an inner sleeve (<NUM>), the inside of the inner sleeve being configured to receive the distal end of a respective tube;
the outer wall of the inner sleeve being generally spaced from an inner wall of the outer sleeve to define an air gap (<NUM>), the inner sleeve being supported on the outer sleeve by at least one circumferentially intermittent discrete web (<NUM>, <NUM>) of material which supports the inner sleeve and maintains the air gap between the inner and outer sleeve.