Patent Description:
Fibre bundles for telecommunications use are often laid in tubes in shallow trenches. The bundles consist of multiple optical fibres and are gradually split at various locations as they are fed in reduced bundles to different locations. Reducing connectors are used at these junctions. The tubes that are connected to reducing connectors vary in size, but typically have an outer diameter of between <NUM> and <NUM>. However, the reducing connectors can be applied to other tube diameters if necessary.

Once a number of tubes have been connected together end to end, they are laid in place and then buried. Sometime later, possibly around a year, the fibre optic cables are blown through the tubes.

In co-owned <CIT>, we disclose a connector with tubes of the same diameter which has features to provide improved impact resistance. In co-owned <CIT>, we describe a similar connector which has various features to prevent the snagging of optical fibres which are blown through a connector from some distance away in order to reduce any snagging in the interface between the tube ends. <CIT> and <CIT> are incorporated by reference herein as if set forth in their entirety.

The present disclosure is aimed at addressing one or more of these issues. In particular, it provides a reducing connector having improved impact resistance features.

According to the present disclosure, there is provided a reducing fibre optic cable tube connector according to claim <NUM>.

The requirement that the first and second air gaps are spaced in an axial sense by less than <NUM> means that there must be an axial space of less than <NUM> between the gaps. There may be no axial gap at all, or the gaps may overlap in the axial sense (which is our current preference). If the gaps do overlap, this may be by more than <NUM>. For the avoidance of doubt, the <NUM> limitation refers to the minimum spacing between nonoverlapping gaps.

At each end of the body there is an annular inner sleeve which receives the tube and is spaced from the outer wall. This provides enhanced impact protection in that any impact on the side of the housing is not directly transmitted to the tube given the presence of the first and second air gaps. Because the narrow inner sleeve extends axially very close to or beyond the wide inner sleeve, there is a very limited or no direct radial load path from outside the housing to the tubes.

In the case of a small axial spacing between the air gaps, this may be small enough to effectively provide a constriction which reduces the transmission of any radial impact to the tube to an acceptable level. The air gaps are radially offset from one another so that with a small axial spacing, the material between the ends of the two end gaps is effectively angled with respect to a radial plane. The radial load transmission is therefore further limited as this angled material limits the potential direct radial load transmission path.

The material between the ends of the air gaps may be circumferentially intermittent material (effectively providing an array of spokes rather than a continuous annular connection) to further limit load transmission. The intermittent material may extend tangentially to further limit load transmission.

The material between the ends of the air gaps can be relatively thin. In particular, it does not matter to the performance of the connector whether the material shears between the air gaps once the tubes have been connected. This will not affect the sealing or gripping of the tubes. Indeed, the fact that this part is effectively sacrificial provides a further degree of impact protection.

If the ends of the first and second air gaps are coplanar or the first and second air gaps partially overlap in an axial sense any radial impact on the outer housing will encounter either the first or second air gap before it reaches either inner sleeve thereby enhancing the dissipation of the load through the body. This contrasts with <CIT> where the inner sleeves were supported on a discrete web of material which, provides enhanced impact protection but potentially still provides a direct load path to the inner sleeve. While the web can be made smaller to reduce this effect, the extent to which this can be done is limited as the web represents a flow restriction during the moulding process.

The present connector does not have this issue as it uses a narrow or non-existent axial gap between the air gaps to reduce load transmission and therefore provides enhanced impact protection for a reducing connector in a manner which is robust and easy to mould.

Optionally the connector further comprises an annular flange projecting into the through bore in the central region to provide an end stop for the first and second tubes. This annular flange allows a well-defined surface to be created to provide a well-controlled end stop for each of the tubes. The inner face of the flange is optionally tapered from the wide portion to the narrow portion. This effectively provides a guide surface to guide a fibre optic cable from the wide portion to the narrow portion.

The annular flange adjacent to the narrow portion is optionally configured to project radially inwardly to a greater extent than the inner diameter of the tube to be received in the narrow portion, and the innermost corner of the flange adjacent to the narrow portion is curved. This is a somewhat counter-intuitive step in that this means that the annular flange represents a constriction within the connector which is even narrower than the inner diameter of the tube received in the narrow portion. However, the fact that this provides a narrow constriction together with the curved inner most corner provides a well-defined surface which is devoid of any abrupt angles such that it will readily guide the cable over the end of the narrow tube. If the end of the tube has any burrs or other non-uniformities, these will generally be out of the way of the cable behind the flange so they will not cause a snagging hazard.

The faces of the flange which provide an end stop for the tubes are optionally undercut such that, in use, they will make contact with the radially innermost part of a tube with a planar end face ahead of the radially outermost part. This is done in order to minimise the gap between the inner diameter of the tube and the location at which it meets the flange. For example, if the end of the tube has not been cut square, the radially outermost diameter of the tube will be located within the radially outermost part of the undercut portion such that the innermost portion of the tube is still located on or close to the radially innermost part of the flange.

The connector may be a grab ring. This has a plurality of inwardly angles flexible teeth which grip an inserted tube. Any force tending to pull the tube out of the connector causes the teeth to deflect thereby increasing the gripping force on the tube.

However, optionally the connector further comprises a collet located in the open end of the body and having a ring and a plurality of flexible legs extending generally axially of the ring into the body, the body having a tapered surface convergent towards the open end and the collet legs having heads at their distal ends for engaging both of the tapered surface and a tube extending, in use, through the collet into the body to be compressed against the tube by the tapered surface with outward movement of the collet with respect of the body to secure the tube in the throughway.

The connector optionally further comprises a collet lock formed on the collet, the collet having a locked rotary position in which the lock holds the collet in an outward tube securing position and an unlocked rotary position in which the collet can move axially with respect to the throughway for release and engagement of a tube by the collet; wherein one of the body and the collet is provided with a cam surface and the other of the body and the collet is provided with a cam follower, the cam surface being provided to provide the locked and unlocked positions.

Instead of a separate locking clip that is used in prior art reducing connectors, this uses a locking mechanism which is integrated into the reducing connector. This is much simpler to operate as there is no additional component which is relatively difficult to manipulate and easy to lose in the dirty environment of the trench. The clip is also exposed to the dirt in the trench and can therefore be difficult to unlock should this be needed.

This type of is collet is used in a single diameter connector disclosed in our earlier <CIT> which is incorporated by reference herein as if set forth in its entirety.

Because the locking is done by the interaction between the body and the collet, the locking mechanism can effectively be internal to the housing. This can provide a low profile design and also protect the locking mechanism from impact damage and from the ingress of dirt.

The cam surface can be provided either on the body or the collet, but is optionally on the body. In this case, the cam surface can be moulded directly on to the body as part of the body moulding process. However, this requires relatively complex tooling. Optionally, therefore, the body includes a cap retained by a main body portion, the cap being provided with the cam surface.

Optionally the collet ring does not protrude axially beyond the body. This protects the collect ring from impact damage and from dirt.

Optionally, the collet ring is recessed into the body.

The connector body is optionally devoid of outer ribs. The above-described inner sleeve arrangement provides good impact protection. As such, the outer ribs which are present on a number of prior art connectors are not required. The absence of ribs eliminates the possibility for dirt to accumulate on the outside of the connector.

Optionally the body is a non-opaque body such that part of the through bore is visible, in use, from outside the connector body when the tubes are connected in place. This, together with the absence of outer ribs provides good visibility into the connector body to allow an operator to verify that the tubes are correctly located and to determine whether or not the fibre optic cable is running through the connector.

An example of a reducing fibre optic cable tube connector 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 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 be 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 connector body <NUM> has a wide portion <NUM> and a narrow portion <NUM>. The connectors <NUM> fitted in either end have the same construction as described below. The connector <NUM> in the narrow portion <NUM> is simply smaller than that of the wide portion <NUM>. The shape of the body in the central region <NUM> is, however, different in order to accommodate the transition from the wide portion <NUM> to the narrow portion <NUM>.

At the transition between the wide portion <NUM> and narrow portion <NUM> is an annular flange <NUM>. The annular flange <NUM> has a tapered inner surface <NUM> which tapers inwardly from the wide portion <NUM> to the narrow portion <NUM>. The annular flange <NUM> provides an end stop for the tubes T as shown in <FIG>. The corners <NUM>, <NUM> of the tapered inner face <NUM> have a smoothly curved profile so as to avoid any sharp corners which might provide a snagging hazard for a fibre F fed through the connector. The corner <NUM> adjacent to the wide portion <NUM> is configured to have a diameter which is approximately the same as the inner diameter of the tube T in the wide portion <NUM>. The corner <NUM> facing the narrow portion <NUM>, as shown in <FIG>, is designed to have an inner diameter which is smaller than the inner diameter of the tube T in the narrow end. As is apparent from <FIG>, this, together with the smoothly curved profile of the corner <NUM>, will guide the fibre F over the end of the narrow tube T as the inner diameter of the tube T is behind the annular flange <NUM> and the fibre F is helped over the end of the tube by the smoothly curved corner <NUM>.

As is apparent from <FIG> and <FIG>, each of the axial end faces <NUM>, <NUM> of the annular flange <NUM> is provided with an undercut. In practice, this means that each end face is inclined so that the part of the flange towards the innermost extremity extends axially towards the respective open end of the connector to a greater extent than the radially outermost part of the flange. The effect of this is shown in <FIG>. From this, it is clear that the inner diameter of a respective tube T will engage first with a radially innermost portion of the annular flange <NUM>. This is done in order to minimise the gap between the annular flange <NUM> and the tube T as such a gap might otherwise provide a snagging hazard. As shown in <FIG>, the end of each tube T is cut precisely in a radial plane. However, in practice, should the end of the tube be cut at a slightly oblique angle, or if there are any burrs formed on the tube, if these were towards the outermost portion of the tube T, they could hold the tube away from the flange <NUM> thereby enlarging the gap between the tube and the flange. With the current design, any such misalignment or burrs at the outermost portion of the tube can be accommodated, to some extent, in the undercut portion thereby minimising or eliminating any gap between the tube T and the flange <NUM>.

Projecting axially from the flange <NUM> towards the wide end <NUM> is an annular inner sleeve <NUM> creating an air gap <NUM> between the inner sleeve <NUM> and the body <NUM>. The inner sleeve <NUM> is designed to receive the tube T within the sleeve <NUM>. The inner sleeve <NUM> is also provided with a lead-in chamfer <NUM> and axial splines <NUM>. The lead-in chamfer <NUM> facilitates the location of the tube T within the inner sleeve <NUM>, while the spines <NUM> are configured to widen towards the annular flange <NUM>. If the tube T is supplied on a reel, it may have a slightly oval configuration when it is inserted into the connector. The spines <NUM> will help to deflect the oval configuration towards a circular configuration which, again will avoid any snagging hazards and also ensure that the seal with the O-ring <NUM> is adequately maintained.

As can be seen in <FIG> and <FIG>, the O-ring seal <NUM> in the wide portion <NUM> is held in place between the end of the inner sleeve <NUM> and a washer <NUM> which is retained within the body <NUM>. This is provided in the wide portion to meet burst pressure requirements by preventing the seal <NUM> deforming into the collet legs <NUM>. Depending on the relative dimensions of the connector, a similar washer may be provided in the narrow portion <NUM>. No such washer is illustrated in the present example as the dimensions in this example are too small to require this.

The narrow portion <NUM> of the connector is a scaled-down version of the structure described above in relation to the wide portion. In particular, an annular inner sleeve <NUM> extends axially from the annular flange <NUM> towards the narrow end <NUM> creating an air gap <NUM> between the inner sleeve <NUM> and the body <NUM>. The tube T in the narrow end <NUM> is received within this inner sleeve <NUM>.

As is apparent from <FIG> and <FIG>, the air gaps <NUM>, <NUM> overlap one another slightly in the axial sense in the vicinity of an annular flange <NUM>. As a result of this, there is no direct radial load path from outside the body <NUM> to the inner sleeves <NUM>, <NUM>. Thus, any radial impact cannot be directly transmitted via the body <NUM> to the tube T. Instead, any such impact will simply cause the outer wall of the body <NUM> to deflect inwardly into the respective air gap <NUM>, <NUM>. Only in an extreme case would an impact be sufficient to also deflect the inner sleeves <NUM>, <NUM>. In practice, therefore, this design provides the required levels of impact protection required for such a connector.

As well as providing enhanced impact protection, the air gaps <NUM>, <NUM> provide additional benefits. Without them, the wall of the housing surrounding the tube would be significantly thicker to preserve the constant external radius of the housing. A thick part will cool unevenly leading to clouding of the plastic material and loss of transparency. The thicker material is also stiffer and is therefore more prone to cracking and therefore creating leakage paths under impact, as opposed to the above described arrangement which can deflect more readily. The air gaps therefore contribute to enhanced transparency and better resiliency of the housing.

The inner sleeve <NUM> is provided with a similar lead-in chamfer <NUM> and splines <NUM> which serve the same purpose as the lead-in chamfer <NUM> and splines <NUM> described in relation to the wide end <NUM>. No washer equivalent to the washer <NUM> in the wide end is illustrated at the narrow end, although this could be present if required.

The connectors <NUM> (one at each end of the body <NUM>) will now be described in greater detail. The connectors have the same construction, but the connector in the wide end <NUM> is larger than the one in the narrow end <NUM>. The description below applies equally to both.

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>. The teeth <NUM> grip the wall of the body <NUM> to ensure that the cartridge <NUM> is permanently retained in the body <NUM>. At the end of the cartridge <NUM>, there is a tapered cam surface <NUM> which cooperates with the collet <NUM> as described below. At the opposite end, the end face of the cartridge <NUM> is provided with a pair of ramped surfaces <NUM> (see <FIG>). 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. Bumps <NUM> are provided at the interface between the high point <NUM> and the inclined face <NUM> and between the inclined 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 legs <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 T, this pulls the heads <NUM> towards the tapered cam surface <NUM> on the cartridge <NUM> deflecting the legs <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 collet further comprises cam followers <NUM> extending from the collet ring <NUM> towards the ramped surface <NUM> on the cartridge <NUM>. Although three followers <NUM> are used in the present example (see <FIG> and <FIG>), 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>.

The operation of the collet 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 <NUM> are at the low point <NUM> (see <FIG>). In this position, the collet <NUM> has a relatively large degree of axial freedom. If held in a depressed position by a user, the tube T can be withdrawn because the heads <NUM> are kept away from the tapered inclined cam surface <NUM> such that the collet cannot grip the tube T. The collet <NUM> then is rotated into the locked position shown in <FIG>. In doing so, the followers <NUM> move 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> (see <FIG>).

In the locked position, the collet <NUM> has nothing like the same degree of freedom as in the unlocked position so that it cannot be moved and held in an unlocked position where the teeth <NUM> disengage with the tube T.

The tube T can be inserted with the collet <NUM> in the unlocked position as this allows for more scope for the legs <NUM> to be deflected upon insertion of the tube. However, even in the locked position, there can be 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 <NUM> in the locked position. This can provide a simple assembly process. In this regard, the user needs only to insert the tube T into the collet <NUM>, and they do not need to concern themselves with the locking operation.

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> to the unlocked position, and manually hold the collet inwardly while pulling the tube out of the body <NUM>.

As can be best seen from <FIG> and <FIG>, the collet ring <NUM> is axially set back inside the body <NUM>. However, the tabs <NUM> extend beyond the end of the body <NUM>. In this position, the collet <NUM> is protected from external impacts by the body <NUM>. Further, because it is recessed within body <NUM>, it is, to some extent, shielded from the soil in which the cables are buried. With this connector, the only points where dirt or other particulates can potentially enter internal workings of the connector are between the collet ring <NUM> and the tube T, and between the collet ring <NUM> and the body <NUM>. However, these are interfaces where tight tolerances can be applied. Any dirt entering here cannot impair the visibility of the fibre F within the body <NUM>. Further, because of the rotary action required to unlock the collet, even if some dirt does enter into these gaps, this is unlikely to jam the collet <NUM> in place as a rotary motion can readily generate sufficient torque to overcome any such sticking.

Claim 1:
A reducing fibre optic cable tube connector, the connector comprising a connector body (<NUM>) made of a plastic, the body defining a through bore and having a connector (<NUM>) at either end for connection to a respective tube;
the body having a wide portion (<NUM>) terminating at a wide end and a narrow portion (<NUM>) terminating at a narrow end, the wide end being dimensioned to receive a first tube (T) of a first diameter and the narrow end being dimensioned to receive a second tube (T) of a second diameter smaller than the first diameter, the two portions meeting at a central region (<NUM>) of the body;
the wide portion (<NUM>) of the body comprising a wide outer body and an annular wide inner sleeve (<NUM>) extending from the central region towards the wide end, the outer wall of the wide inner sleeve being generally spaced from an inner wall of the wide outer body to define a first air gap (<NUM>), the distal end of the first tube (T) being receivable within the wide inner sleeve;
the narrow portion (<NUM>) of the body comprising a narrow outer body and an annular narrow inner sleeve (<NUM>) extending from the central region towards the narrow end, the outer wall of the narrow inner sleeve being generally spaced from an inner wall of the narrow outer body to define a second air gap (<NUM>), the distal end of the second tube (T) being receivable within the narrow inner sleeve;
characterized in that
at the central region (<NUM>) the annular narrow inner sleeve (<NUM>) extends towards the annular wide inner sleeve such that the first (<NUM>) and second (<NUM>) air gaps are spaced in an axial sense by less than <NUM>.