Apparatus for introducing a cable into a cable guide tube

Abstract: Apparatus for installing cables with a certain stiffness, more in particular glass fibre cables, into a duct (6, 24) of a channelization system, using the working of a compressed gas, which apparatus is adapted to exert pushing forces on a cable (26) being introduced in order to support the compressed gas working on the cable in the duct. The apparatus comprises cable advancing means and gas inserting means. The cable advancing means include a hollow, substantially rectilinear cable lead-through channel (3) with an entrance end (4) and an exit end (5), at least one pair of wheels (8, 10; 9, 11) mounted opposite to each other for moving on a cable (26) disposed between these wheels into the direction of the outlet end (21) of the duct (6), and a pneumatic motor (15) coupled to at least one of said wheels for providing a driving couple to it. At least one of the wheels is coupled to a pneumatic piston/cylinder combination (13, 14), in such a way that when compressed gas is supplied to the pneumatic cylinder (14), transverse forces will be exerted on the cable (26) disposed between the wheels (8, 10; 9, 11). The gas inserting means include a gas channel (7), which debouches into the cable lead-through channel (3) and which is adapted for inserting compressed gas into the lead-through channel (3) between the wheels and the exit end (5) of the lead-through channel (3). The motor (15) is capable of providing a driving couple, which is larger than the driving couple, which has to act on the cable (26) to compensate a pressure difference existing at the inlet end of the duct between the pressure inside and the pressure outside the cable lead-through channel (3) as a consequence of inserting the compressed gas via the gas channel (7) into the cable lead-­ through channel (3). The pushing forces are exerted by the wheels on the cable (26) as a consequence of the cooperative effect of the driving couple and the transverse forces. The gas channel (7), the pneumatic motor (15) and the piston/cylinder combination may be coupled to the same compressor. For use in a tandem arrangement the apparatus comprises further a coupling unit (18) to be coupled to an outlet end (21) of a preceding duct section (24), and which includes a mainly hollow housing (19), an outlet pipe (23) for diverting a flow of gas, which may leave the outlet end (21) of the duct section (24), and an outlet opening (22) through which a cable may be led into the direction of the entrance end (4) of the cable lead-through channel (3). Advantages: the exerted transverse forces are very acurately adjustable and substantially constant; the apparatus is non-destructive to the cable when cable introduction is slowing down or stagnates; in a tandem arrangement the apparatus needs hardly any human interference and is safe for the operating staff.

Description: A. Background of invention 1. Field of the invention The invention generally relates to an apparatus for introducing (instailing) cables, such as e.g. optical glass fibre cables, into a channelization system of guide tubes, in general designated as "ducts", which are disposed, as a rule in the ground, according to a predetermined arrangement. The present application is a division from the European patent application EP 0 292 037. 2. State of the art For introducing a cable into a cable duct two kinds of techniques are known, which make use of the working of a compressed gas. A technique of the first kind, wherein a compressed gas is used for pressurising a pulling shuttle coupled to the front end of a cable in the duct is known from the United Kingdom patent application GB 2151414. This citation discloses an apparatus for introducing a cable into a cable duct from an inlet end towards an outlet end of said duct, while inserting a compressed gas into the duct in the same direction. This known apparatus is provided with cable advancing means including a hollow, substantially rectilinear cable lead-through channel with an entrance end and an exit end for leading in and leading out a cable which has to be introduced into the relevant duct. Said cable advancing means further include a gas channel, which debouches into the cable lead-through channel and via which compressed gas can be supplied to the cable lead-through channel. For operation the exit end of the lead-through channel has a sealed coupling with the inlet end of the duct. Compressed gas is supplied for pressurizing a pulling shuttle coupled to the front end of the cable in the duct such that pulling forces are exerted on the front end of the cable for advancing the cable in the duct. Because of the fact that the pulling forces exerted on the cable are concentrated at one point, the front end of the cable, generally only cables with rather limited diameter and length may be installed using this technique of the first kind. A technique of the second kind wherein a compressed gas is used for applying dragging forces on the cable in the duct, is known from the European patent application EP 0,108,590. This second citation discloses a similar apparatus for introducing a cable in a cable duct, of which the cable advancing means moreover include a set of wheels mounted opposite to each other and partly reaching into the lead-through channel, and serving to advance a cable, disposed between these wheels and touching them, in the direction of the exit end. This known technique of the second kind is meant for installing lightweight, flexible optical fibre cables. To this end the exit end of the cable lead-through channel is coupled to the inlet end of a relevant duct portion. When supplying the compressed gas a flow of gas will be caused in the cable lead-through channel and the following duct portion, which flow exerts a drag force working on a cable as far as it has been already introduced into the cable lead-through channel and the duct next to it, due to which such a cable will be dragged through the duct to its outlet end. The two drive wheels forming part of the cable advancing means of the known device serve to compensate the opposing forces exerted on the cable at the entrance end of the cable lead-through channel, which opposing forces are caused by the difference in pressure between the interior of the cable lead-through channel and its outer environment. Because of the fact that the drive wheels can compensate said opposing forces and therefore would automatically take up a fibre member fed into the apparatus, the apparatus is mentioned as to be suitable for use in a tandem arrangement. These known techniques of both kinds are however not able to meet the need for the installation of much thicker, and consequently stiffer cables in ducts. The disclosed apparatus are not adapted for exerting extra pushing forces on the cable to be installed in its direction of advance for supporting the working of the compressed gas on the cable in the duct in order to install cables of greater length in one processing stroke. In addition the known apparatus of the first kind of techniques is totally unsuitable for tandem use. For example for such use no measures have been mentioned which prevent the strong flow of gas leaving the outlet end of a previous duct section for being harmful to the operating staff and for disturbing the feed of a cable into a next device in order to introduce the cable also in a next duct section. Also there is no teaching of measures to prevent for destruction of the cable being installed when temporarily or definitely the advancing of the cable in the previous or the next duct section slows down or even stagnates. Pneumatic motors and cylinders are known per se and have been used for cable tension and transport (see e.g. Fr-A-1 557 074 or EP-A-0 185 788) B. Summary of the invention The object of the present invention is to provide for an apparatus, which does not have the drawbacks indicated above. The invention to this effect provides an apparatus according to claim 1. The use of a pneumatic cylinder/piston combination for operating the wheels warants for substantially constant transverse forces, which are consequently very accurately adjustable not exceeding the maximum permissible squeezing pressure of a used cable; the use of a pneumatic motor provides for an apparatus which is non-destructive to the cable when the introduction of the cable in the duct temporarily or definitely is slowing down or even stagnates; whereas the combination of these features are particularly advantageous when more than one apparatus according to the invention are used in a tandem arrangement. Because in such an arrangement the apparatus need hardly any human interference, since speed control of the consecutive apparatus happens in fact through the very cable being introduced. Further prefered embodiments of the invention are summarized in the remaining subclaims and with their special advantages illucidated below. C. Brief description of the drawing The invention will be further explained hereinafter with reference to the drawing in which Fig. 1 shows a diagrammatic cross-sectional view of an embodiment which is illustrative of an apparatus according to the invention. D. Detailed description of the figure Figure 1 is illustrative of an embodiment of an apparatus according to the invention. More in particular figure 1 shows a diagrammatic cross-sectional view of a cable advancing unit in its generality designated by 1. This unit comprises a housing 2, in which a substantially rectilinear cable lead-through channel is formed, which channel has an inlet end 4 through which a cable can be led into the advancing unit, and an outlet end 5, which has been adapted to be coupled to a relevant duct 6, into which a cable has to be installed, while at the same time forming a gastight closing. An inlet tube debouching into the lead-through channel and meant to be connected to a source of compressed gas (a compressor which is not shown in the figure) is designated by 7. In the case of a usual flow resistance of the relevant duct portion and a conventional compressor with a capacity of 75 Itr/sec and a maximum working pressure of 7.5 bar (overpressure), a flow of compressed gas (flow of air) in the order of magnitude of 75 ltr/sec will stream via said inlet tube. A set of wheels 8, 9, 10 and 11 is pivotally mounted in a housing and partly reaches into the lead-through channel. The set of wheels 8 and 9 is supported by a frame 12, which is pivotally coupled to a piston rod of a piston 13, which is movably mounted in a pneumatic cylinder 14. As diagrammatically shown in figure 1, the two wheels 8 and 9 can be set turning via a transmission mechanism by means of a pneumatic motor 15, which is mounted on the housing. Opposite to the embouchure of the gas inlet tube the cable lead-through channel is bounded by a streamlined small pipe 16, which ensures that the course of a cable disposed in the lead-through channel will remain substantially rectilinear, in spite of the strong flow of compressed gas. In other words, the cable will be prevented from being blown to a "buckling" in that portion, which would seriously hinder the introduction of the cable into the duct. A cable led into the lead-through channel via the inlet opening 4 forms via a diagrammatically drawn washer 17 a gastight closing. In consequence of the compressed air supplied there will be a difference in pressure between the interior and the exterior of the housing. Owing to this a force working will be exerted on the cable disposed in the lead-through channel, which takes the opposite direction with regard to the desired direction of movement of this cable. When compressed air is supplied to the cylinder 14 and to the motor 15, this "oppositely directed" force working will be compensated. A pneumatic motor has the advantage that the driving couple provided by it is proportional to the pressure caused in the housing; moreover, when compressed air is supplied, a pneumatic motor can be slowed down to a standstill without harmful consequences, and also be kept in such a state (if desired for a long time). The latter is a particular advantage when several cable advancing units are used in series (or in tandem connection). Within the scope of the present invention, however, the pneumatic motor is considerably more powerful than necessary for compensating the above-mentioned "oppositely directed" force working. Illustrative is e.g. a motor capable of providing a force working which is thrice as large as the force working necessary for the above-meant compensation. By means of a motor thus dimensioned it will be achieved that over a length area extending over a certain distance from the beginning of the relevant duct portion, a pushing force working is exerted on the cable disposed in the duct. In order to ensure that the pushing force working will not result in buckling in the duct it is essential that the relevant cable has a certain stiffness. The cables used in practice meet this requirement. In practical situations it has appeared that the length of the duct portion over which a cable can be installed by means of only one injection unit, can be extended by a factor of abt. two, when use is made of such a pushing force working. The speed at which the cable is introduced into a duct can be regulated by means of a pressure regulator (not shown in figure 1). To promote the engagement between the wheels and the cable to be moved on by them, each of these wheels has a hollow tread, which is provided with transversal knurls. The advantage of such a construction is that said wheels cannot get filled up with material from the cable sheath and pollutants, if any, taken along by the cable, and that slipping, even when the cable sheath is covered with a lubricant, will be effectively hindered. In the embodiment represented in figure 1 two driven wheels and two "counter pressure" wheels are used. However, if need be, also an embodiment with one respectively more than two driven wheels and one respectively more than two counter pressure wheels can be made use of. In the latter case it is advisable to use at least two pneumatic cylinders, each of the pneumatic cylinders operating two wheels at most, which are in this case mounted in a frame, which is pivotally coupled to the relevant piston rod. The pneumatic cylinder/piston combination serving to cause the pressing working has the advantage that in the case of a certain supply of compressed air the pressure force working exerted on the cable will be substantially constant. That means that notwithstanding variations in the thickness of the cable, this pressure force will remain constant. Moreover, an upper limit corresponding to the maximum working pressure of the supply compressor of 7.5 bar, has been set to the pressure force working exerted. This means that the permissible squeezing pressure of a cable used in practice will not be exceeded when using the pneumatic cylinder/piston combination. By means of the above-described construction the motor can be brought to a standstill by slowing down and bringing to a standstill the cable moved on by that motor. Figure 1 also shows a coupling or closing unit 18. Such a unit comprises a housing 19, which leaves space to a room 20, which is connected to the outer environments via an inlet opening 21, an outlet opening 22 and a compressed gas outlet pipe 23. The inlet end has been adapted to form a gastight coupling with the final part of a duct portion 24, at the beginning of which use is made of a cable advancing unit similar to the one shown in figure 1. The velocity at which the compressed air flows into the room 20 via the inlet end 21 is substantially determined by the magnitude of the flow of compressed air. In the case of values of abt. 7.5 bar and 75 ltr/sec this velocity will be in the order of magnitude of 150 m/sec for a duct with an inner diameter of 26 mm. For reasons of security and for the protection of an advancing unit located near the outlet opening 22 the compressed air outlet pipe has been designed in such a way that the compressed air supplied will be slowed down, via a widening initial part 25, without causing whirls, and led away, via this outlet pipe 23, to a place which is safe for the operating staff. As an alternative said outlet pipe can have been dimensioned in such a way that the velocity at which the compressed air streams out has been reduced to a safe value. The cable 26 installed in the duct portion 24 can be led to the next cable advancing unit, in this case the advancing unit 1, via the outlet opening 22, which is provided with a lining 27' capable of slowing down quick particles which may come along with the cable and/or the flow of compressed gas. As a rule the opening 22 is closed by means of a valve 27 pivotally mounted on the housing 19, which valve will attach itself firmly to the outside of the housing due to the acceleration of the flow of air there, when there is no cable at that place, in such a way that the valve will offer protection against the particles moving on at a high speed. By means of the cable supplied this valve can be opened, in which case the lining 27' will then fulfil the function of the valve 27. After that this cable can be installed via the advancing unit 1 into the duct portion 6, which follows after the duct portion 24. For that purpose the two advancing units have to work in series or in tandem. In connection with such a tandem working each cable advancing unit and coupling or closing unit which has to be used in that process, has been designed as two parts which are detachably fixed to each other. The special construction of the wheels described in what precedes makes it possible that a cable disposed between them will be moved on effectively without causing damage to the cable sheath, and no matter whether such a cable sheath is covered with a lubricant or not. The latter is an advantage when the tandem method is employed. For in that case a cable provided with a lubricant is supplied to an advancing unit. For a further improvement of the working of the wheels it may be advisable to provide the outer sheath of a cable to be installed with corresponding transversal knurls. These knurls may also result in an enhancement of the dragging working caused by the flow of compressed gas.

Claims: Apparatus for introducing a cable into a cable duct from an inlet end towards an exit end of said duct by inserting a compressed gas into the duct in the same direction, said apparatus comprising cable advancing means including a hollow, substantially rectilinear cable leadthrough channel (3) with an entrance end (4) and an exit end (5) for leading in and leading out a cable (26) which is to be introduced into the relevant duct (6), at least one pair of wheels (8, 10; 9, 11) mounted opposite to each other for advancing a cable (26) disposed between these wheels in the direction of the outlet end (21) of a relevant duct, the wheels being capable of being pressed against the cable for exerting transverse forces on the cable, and a motor (15) coupled to at least one of said wheels for providing a driving couple to it, cable advancing forces being exerted by the wheels on the cable (26) as a consequence of the cooperative effect of the driving couple and the transverse forces, and gas inserting means comprising a gas channel (7), which debouches into the cable lead-through channel (3) and which is adapted for inserting compressed gas into said lead-through channel (3) between said wheels and the exit end (5) of said lead-through channel (3), a piston (13) is provided, which wherein is movably mounted in a pneumatic cylinder (14) and which is also coupled to at least one of said wheels (8; 9), in such a way that when compressed gas is supplied to the pneumatic cylinder (14), said transverse forces will be exerted on a cable (26) disposed between the wheels (8, 10; 9, 11), and in that the motor (15) is a pneumatic motor capable of providing said driving couple, which is larger than the driving couple which has to act on the cable (26) to compensate for the pressure difference which exists at the inlet end of the duct between the pressure inside and the pressure outside the cable lead-through channel (3) as a consequence of said inserting of the compressed gas via said gas channel into said cable lead-through channel; the apparatus further including a coupling unit (18) comprising means for coupling said unit (18) to the outlet end (21) of a duct (24) in a gastight way; means (23) for diverting a flow of gas from the direction of a cable (26), which flow may leave said outlet end (21) when said unit is coupled to said outlet end of said duct in which a cable is being introduced; means (27') for slowing down particles, which may be carried along by said gas flow; means for leading a cable (26) which is being introduced in the direction of the entrance end (4) of said cable lead-through channel (3); the coupling unit further (18) comprising a mainly hollow housing (19), a duct inlet opening in said housing for receiving and coupling the outlet end of a cable duct (24); an outlet pipe (23), extending from the interior of said housing (19) through said housing, which pipe is suitable for leading away from said housing a high velocity flow of compressed gas, which flows from the outlet end of the cable duct section (24) into the housing as a consequence of the insertion of compressed gas at its inlet end, in a controlled manner; and a cable outlet opening (22) in said housing mainly directly across from the duct inlet opening, which cable outlet opening is provided with a cover valve (27) pivotally mounted on the outside of the housing (19), which cover valve (27) is capable of closing firmly said outlet opening (22), by attaching itself firmly to the outside of the housing due to the acceleration of the flow of air there, when there is no cable at that place, and which cable outlet opening is further provided with a lining (27') capable of slowing down quick particles dragged along with the high velocity flow of compressed gas and/or a cable (26) being introduced in said duct section (24), the interior of said housing having at least partly a profile such as to lead the front end of a cable (26) which is being introduced in the direction of said cable outlet opening (22). Apparatus according to claim 1, characterized in that the pneumatic motor (15) and the pneumatic cylinder (14) are adapted to be coupled to a common source of compressed gas. Apparatus according to claim 2, characterized in that said gas channel (7) is adapted to be coupled together with the pneumatic motor (15) and the pneumatic cylinder (14) to a common source of compressed gas, and in that between the connection for this source of compressed gas and the pneumatic motor a reducing valve has been placed for controlling the speed of the motor. Apparatus according to claim 1, 2, or 3, characterized in that two wheels (8, 9) are mounted in a frame (12), which is pivotally mounted to said piston (13), which wheels can turn and are adapted to co-operate with two wheels (10, 11) disposed opposite to the former wheels and which partly reach into the cable lead-through channel, and the pneumatic motor is coupled by a driving connection to one of the pairs of wheels. Apparatus according to one of the claims 1 to 4, characterized in that means (16) are disposed between the wheels and the exit end (5), and also at the place where the gas channel (7) debouches into the cable lead-through channel (3), which means are adapted to prevent the flow of gas supplied via the gas channel (7) from having a negative effect on the working of said pushing forces. Apparatus according to one of the claims 1 to 5, characterized in that the wheels have a hollow tread, the tread being provided with knurls substantially running parallel to the axis of rotation of the relevant wheel. Apparatus according to one of the claims 1 to 6, characterized in that cable advancing means (1) are composed of two parts which are detachably fixed to each other, in such a way that said means can be removed from a cable extending through the same.

Inventors: GRIFFIOEN WILLEM, JONG CORNELIS LEENDERT DE, DE JONG, CORNELIS LEENDERT, GRIFFIOEN, WILLEM
Applicants: NEDERLAND PTT, KONINKLIJKE PTT NEDERLAND N.V.
Application year: 1988
Main classification: G02B6
IPC codes: H02G1, G02B6