Implements or apparatus for applying pushing or pulling force – Method or apparatus for placement of conductive wire – By fluid pressure differential in conduit
Reexamination Certificate
1999-11-15
2001-07-24
Hail, III, Joseph J. (Department: 3723)
Implements or apparatus for applying pushing or pulling force
Method or apparatus for placement of conductive wire
By fluid pressure differential in conduit
C254S13430R, C254S13430R, C226S035000
Reexamination Certificate
active
06264171
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to apparatus and methods for installing cable, such as fiber optic communications cable, in duct or other conduit, such as underground duct.
BACKGROUND OF THE INVENTION
Various techniques are known for installing cable in duct or other conduit, which can be underground, above ground or in buildings. Sometimes the underground duct is known as “innerduct.” A first technique is to pull the cable through conduit with a previously positioned wire or string attached to a lead end of the cable.
The use of high speed moving air to drag a lightweight and flexible optical fiber member through the conduit is also known, such as described in U.S. Pat. No. 4,691,896, to Reeves et al. According to Reeves et al., the high speed air creates a fluid drag force distributed along the optical fiber member in order to pull the optical fiber member through the conduit.
U.S. Pat. Nos. 4,850,569 and 4,934,662 to Griffioen et al. describe combining high speed air flow with a pushing force applied at the entry end of the conduit to install the cable. U.S. Pat. Nos. 5,197,715 and 5,474,277 to Griffioen further describe the use of a leaky missile attached to the lead end of the cable which adds a tension force on the lead end of the cable, in addition to the motive forces applied to the cable via the high speed moving air.
The use of pressurized air in combination with a sealed missile, parachute or other device for creating a pressure difference at the lead end of the cable is also known. The pressure difference creates a pushing force on the missile or other device, which pulls the lead end of cable through the conduit.
Various concerns arise when cable is installed in conduit. One concern is the ease of installation. A further concern is avoidance of damage to the cable during installation. Damage can occur in a variety of ways including: 1) crushing the cable with the installation equipment in the diametral direction; 2) causing the cable to have bending damage or column damage (may be referred to as “accordion damage”) due to an excessive force applied in the longitudinal direction; and 3) damaging the protective cable jacket, such as by wearing, shredding or cutting the outer protective layer. Another concern is to minimize the amount of time needed to install the cable. Also, there is a concern to avoid splices in the cable as much as possible. Splices are time consuming to make, and may lead to a decrease in cable performance. Therefore, it is desirable to install the longest continuous length of cable possible to reduce the number of splices needed for the desired cable run.
There is a need in the prior art for further systems and methods which address the above-identified concerns, and other concerns.
SUMMARY OF THE INVENTION
The present invention concerns an apparatus for conveying a cable, such as through a conduit, in order to install the cable in the conduit. The apparatus is useful for installing fiber optic cable in underground duct, for example. A cable drive assembly frictionally engages an outside surface of the cable and applies a pushing force on the cable for insertion of the cable into the conduit. A drive assembly speed signal generator and a cable speed signal generator produce signals processed by a control system. Cable speed and drive assembly speed are monitored by the control system such that if the drive assembly exceeds a predetermined faster speed relative to the cable, the drive assembly will be stopped. Monitoring relative speeds is particularly useful in preventing cable jacket damage, such as might occur if the drive assembly is slipping and moving too fast relative to the cable, or when the cable has stopped due to an obstruction in the conduit, causing column or accordion damage.
Preferably, the cable drive assembly is used in combination with a cable blower assembly, and a sealed missile sealably and slideably engaged with an inner wall surface of the conduit. The cable blower and the missile create a pressure difference at the lead end of the cable, thereby creating a pull force on the cable. The combination of the cable drive assembly, and the missile and the cable blower assembly permits convenient installation of the cable in conduit, such as underground duct.
Preferably, the control system includes a high speed cable shut off system, and a low speed cable shut off system, both of which shut off the drive assembly when the speed of the cable either exceeds a certain predetermined maximum, or falls below a certain predetermined minimum.
In the preferred embodiment, the cable drive assembly includes two opposed tractor drive assemblies, each including a continuous chain and a plurality of cable engaging pads made from plastic and mounted to the chain. Preferably, the tractor drive assemblies are driven by hydraulic motors. In the preferred embodiment, the tractor drive assemblies are positioned at a predetermined spaced apart distance, and place a predetermined pressure on the cable, by the use of a hydraulic clamp cylinder. The clamp cylinder moves one tractor drive assembly toward and away from the other tractor drive assembly, as desired by the operator. The clamp cylinder allows a desired normal force to be placed on the cable by the tractor drive assemblies, so as to apply the proper frictional force to drive the cable forward, and yet not exceed the compressive limits of the cable. Hydraulics allow such normal force to be preset, and consistently repeated during operation.
The present invention also relates to a method of installing cable in a conduit including the steps of providing a drive assembly for moving the cable in a forward direction, generating a first signal indicative of movement of the drive assembly, and generating a second signal indicative of movement of the cable. The method further includes the steps of comparing the first and second signals over time, and generating a drive assembly shut off signal if relative speeds of the drive assembly and the cable exceed a predetermined difference. The method preferably includes providing the cable with a sealed missile sealably and slideably engaged with an inner wall of the conduit, and further applying air pressure to the missile so as to cause the missile to generate a pull force on the cable. The method also preferably includes monitoring cable high speed and low speed conditions, and generating a drive assembly shut off signal if the cable speed exceeds a predetermined maximum or falls below a predetermined minimum.
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Bruns Jason A.
Hoium Jonathan A.
Condux International, Inc.
Hail III Joseph J.
Merchant & Gould P.C.
Wilson Lee
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