Winding – tensioning – or guiding – Tension control or brake – Take-up coil drive control
Reexamination Certificate
2000-12-28
2003-07-22
Mansen, Michael R. (Department: 3654)
Winding, tensioning, or guiding
Tension control or brake
Take-up coil drive control
C226S118200, C242S154000, C242S413500, C242S419700
Reexamination Certificate
active
06595454
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fibre tensioning device and a method of controlling the tension applied to an optical fibre, particularly during the winding of the fibre.
2. Description of the Related Art
Typically, optical fibres are formed in draw towers from preforms of glass material. A draw tower is generally provided with a traction device (“capstan”), for example a motorized pulley, capable of drawing the optical fibre downwards and feeding it to a storage device; the latter usually comprises a motorized reel onto which the optical fibre is wound.
In many operating situations, the speed at which the optical fibre is drawn by the traction device (the drawing speed) may not coincide with the speed at which the optical fibre is fed into the storage device, for example owing to fluctuations of the speed of the motors which drive the traction device and the storage device. The difference between these speeds gives rise to variations of tension in the fibre with respect to a target tension; in particular, a fibre tension greater than the target tension may damage the fibre, while a tension lower than the target tension may make the storage process inefficient.
To solve this problem, there is a known practice of using tensioning devices which are to be interposed between the traction device and the storage device and are capable of controlling the tension of the optical fibre. In particular, there are known tensioning devices comprising at least one fixed pulley and one movable pulley which can guide the optical fibre. The movement of the movable pulley enables the tension of the optical fibre to be modified. Here and in the remainder of the description, the term “fixed pulley” denotes a pulley which is free to rotate about its axis and in which the position of the axis is fixed, while the term “movable pulley” denotes a pulley which is free to rotate about its axis and in which the position of the axis is variable.
U.S. Pat. No. 4,712,866 describes a tensioning device positioned between a traction device of a draw tower and a storage device comprising a take-up reel. This tensioning device comprises a pair of fixed pulleys and a movable pulley located on an oscillating arm, also called a “dancer arm”, which carries a weight. The dancer arm actuates a conventional speed control so that the fibre is wound onto the take-up reel at a tension determined by the aforesaid weight.
U.S. Pat. No. 5,790,292 relating to an optical fibre transmission line describes, among other things, a draw tower in which a tensioning device with two pulleys is interposed between a traction device and a take-up reel (FIG.
7
).
U.S. Pat. No. 4,138,069 describes a winding device for optical glass filaments in which a traction device draws the filament from a source of molten glass and feeds it through a tensioning device to a set of take-up reels. The tensioning device comprises two fixed pulleys and one movable pulley mounted on one end of a dancer arm. The dancer arm extends from an apparatus in which a spring or other means applies a constant force to move the movable pulley away from the fixed pulleys.
Tensioning devices can also be used in apparatus other than draw towers.
U.S. Pat. No. 5,076,104 describes an apparatus for measuring the load at failure of an optical fibre, in which tensioning devices comprising a pair of fixed pulleys and one movable pulley are provided. Also provided is a tensioning device comprising one fixed grooved wheel and one movable grooved wheel; the latter is positioned below the fixed grooved wheel, is movable in a vertical direction and is connected to a predetermined weight. The optical fibre, which in its path is wound around both the fixed grooved wheel and the movable grooved wheel, is thus kept at a constant tension.
U.S. Pat. No. 4,505,222 describes an extrusion coating device for optical fibres, in which a tensioning device is positioned immediately upstream of a take-up reel.
U.S. Pat. No. 4,127,370 describes an extrusion coating apparatus for an optical fibre, in which a first, a second and a third pulley are positioned at the entry to the apparatus, immediately downstream of the fibre take-off reel. The first and second pulley are spaced apart from each other and from the take-off reel. The third pulley has no support and is carried on the optical fibre between the first and second pulley, in such a way that the fibre passes, as a result of the weight of the third pulley, along a U-shaped path between the first and second pulley. A pair of photocells is used to detect the vertical position of the third pulley and to control the speed of rotation of the take-off reel in such a way that the vertical position of the third pulley, and therefore the tension of the fibre, remains essentially constant.
SUMMARY OF THE INVENTION
The applicant has observed that tensioning devices of known types, requiring the use of gravity and/or predetermined elastic action for controlling the position of the movable pulley, apply an uncontrollable predetermined force to the movable pulley. Therefore it is not possible to modulate in any way the force applied to the movable pulley in order to modify the response of the tensioning device. Consequently, the tension control obtained by means of the known devices, being of the non-modulatable type, might be inadequate in some operating conditions.
The applicant has found that the aforesaid problem can be at least partially overcome by using an optical fibre tensioning device in which there is a movable pulley on which the optical fibre runs, a device for measuring the tension applied to the optical fibre and a device for moving the movable pulley, capable of controlling the position of the movable pulley in accordance with the signal generated by the tension measuring device.
The tensioning device according to the present invention is capable of receiving at its input an optical fibre from a fibre guide or return element or from a device of another type, for example a traction device or a take-off device, and is capable of supplying the optical fibre from its output, after having automatically controlled its tension, to a further guide or return element, or to a further device, for example a storage device (particularly a reeling device) for the optical fibre.
In greater detail, the tensioning device according to the present invention comprises a fixed pulley carried by a supporting structure and a movable pulley carried by a slide which is slidable along a rectilinear guide carried by the supporting structure.
The optical fibre entering the tensioning device is wound around the fixed pulley for a certain length, and passes from here to the movable pulley around which it is wound for a further length. The distance between the axes of the fixed pulley and the movable pulley is variable to modify the length of the portion of fibre which extends between the two pulleys and consequently the tension applied to the fibre. To vary the distance between the axes of the fixed pulley and the movable pulley there are used, as mentioned above, a fibre tension measuring device, for example a load cell associated with the fixed pulley, and a device for moving the slide which can control the distance between the axes of the pulleys in accordance with the signal supplied by the tension measuring device, to automatically keep the tension in the fibre practically constant. The movement device can comprise an electric motor and a system for transmitting the motion from the motor to the slide, for example a screw and nut coupling in which the screw extends parallel to the rectilinear guide and is rotationally movable by the force of the motor and in which the nut is coupled to the slide, or a belt transmission, for example a toothed belt transmission.
Since it automatically controls the tension of the fibre without using the force of gravity or other predetermined forces, the aforesaid optical fibre tensioning device can be used to modulate in the desired way the tension applied to the optical
Pata Roberto
Roba Giacomo Stefano
Veronelli Franco
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Mansen Michael R.
Pirelli Cavi e Sistemi S.p.A.
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