Implements or apparatus for applying pushing or pulling force – Method or apparatus for placement of conductive wire – By fluid pressure differential in conduit
Patent
1988-03-14
1989-08-15
Watson, Robert C.
Implements or apparatus for applying pushing or pulling force
Method or apparatus for placement of conductive wire
By fluid pressure differential in conduit
B65H 5900
Patent
active
048567604
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a control method and apparatus.
Apparatus and a method for installing optical fibres in ducts, using the fluid drag of a gaseous medium such as air to propel the fibre, are described in European Patent Application No. 83306636.8.
In order to overcome the initial pressure gradient, some means such as the constant torque driving mechanism described in the above application is used.
The present applicants have now found that controlling the thrust on a member such as an optical fibre member, being inserted into a tubular pathway is advantageous, and surprisingly simple control means can be very effective in improving operation.
The control method and apparatus of the present invention are particularly (but not exclusively) suitable for use in fibre blowing. Only a brief description of fibre blowing is given here, and for a fuller treatment, the patent application mentioned above should be referred to. The invention may also be used in the installation of other members such as cables including wires and/or fibres.
Fibre blowing is a new and advantageous method for installing optical fibre transmission lines. A bundle of optical fibres is propelled along a duct by the fluid drag of compressed air which is fed into the duct. For the forces on the bundle of fibres to be adequate, the flow velocity of the air has to be much higher than the intended speed of the fibre bundle. Typically, the inner diameter of the duct is 6 mm, the outer diameter of the fibre bundle is 2 mm, its weight is 2 to 3 gm.sup.-1 and the pressure 150 psi (approx. 10.sup.6 Pa). Suitable material for both the duct and the fibre packaging is polyethylene, having a coefficient of friction of around 0.5.
There is a steep pressure gradient where the fibre bundle first enters a pressurised area. To assist the bundle at this point, drive wheels are incorporated in the drive unit, driven at a torque just sufficient to overcome the opposing force resisting entry of the bundle. Then pressurised air fed into the front end of the drive unit flows into the duct, its fluid drag force carrying the fibre bundle with it.
Depending on the precise dimensions, materials, pressures and so on used for fibre blowing, insertion of a fibre bundle into a considerable length of duct may be achieved. For example, with a single drive unit, fibres may easily be installed over 600 meters. For longer lengths, two or more drive units spaced, say, 600m apart, may be provided. Due to the fall in pressure along the length of a duct as distance from the previous drive unit increases, it is generally necessary to include drive wheels, or other means to provide forward thrust, in each drive unit to overcome the resistive forces due to the pressure gradient in the drive unit.
The present invention provides apparatus for controlling longitudinal forces on a flexible transmission line member moving through a passageway, the apparatus comprising a sensor for identifying lateral deviation of the transmission line member within the passageway and control means responsive to the sensor for adjusting propulsive forces on the line in response to data from the sensor.
In one embodiment, the passageway is curved. In this case undesirable compressive force on the transmission line member causes it to buckle towards a point on the outer side of the curve, and the sensor is located to detect the presence of the line at or near that point. It is very important to avoid buckling of a fibre member during fibre blowing, as this can cause expensive damage to the blowing unit. The invention can provide a very simple way of detecting when compressive forces are so high that buckling may occur, and taking preventative action to reduce the speed of the fibre member.
Within the context of this specification `curve` is to be construed to include angled or sharp bends as well as progressive bends.
Additionally or alternatively tensile force on the transmission line member causing it to move the inner side of the passageway may be detected, and a sensor is located to detect
REFERENCES:
patent: 4087748 (1978-05-01), Pigeon et al.
patent: 4508251 (1985-04-01), Harada et al.
"A Radically New Approach to the Installation of Optical Fibre Using the Viscous Flow of Air" by Cassidy et al, Britsh Telecom Technology Journal, vol. 2, No. 1, Jan. 1984.
Freeman Robert A.
Frost Peter L. J.
Keeble Peter J.
Warren John A.
British Telecommunications
Watson Robert C.
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