GB2303217A

GB2303217A - Measurement of tension in a fibre

Info

Publication number: GB2303217A
Application number: GB9513710A
Authority: GB
Inventors: Georgievich Shipilov
Original assignee: HES OPTICAL FIBRES
Current assignee: HES OPTICAL FIBRES
Priority date: 1995-07-10
Filing date: 1995-07-10
Publication date: 1997-02-12
Also published as: GB9513710D0

Abstract

Tension in a fibre 11 moving between first and second locations in a drawing process is determined by using a jet of gas from a nozzle 16 transverse to undeflected path of the fibre to cause the fibre to be displaced from this path and measuring the displacement. The nozzle is provided on a rotating annulus 17 so that jet of gas follows an orbit around the path of the fibre to cause a point on the fibre 11 passing between the first and second locations to follow, at least in part, a helical path. The speed of gas flow may be varied periodically. The fibre may be an optical glass fibre. The displacement is detected by an optical scanner 27.

Description

METHOD AND APPARATUS FOR MEASURING TENSION This invention relates to a method of and apparatus for measuring tension. It is particularly concerned with the measuring tension in a fibre which avoids any need for contacting the fibre.

In the manufacture of an optic fibre a drawing process is used in which a glass fibre is drawn from a molten tip of a glass pre-form and subsequently passed through at least one coating process. The tension in the fibre after leaving the molten tip and at least up to the or the first coating process, conveniently referred to as the initial path, is a critical matter. The tension affects to a greater or lesser extent the final diameter of the fibre along with its optical properties and the mechanical strength of the finished product. It is known that for a constant temperature for the furnace generating the molten tip the fibre tension in the initial path is related to the draw speed. An increase in furnace temperature results in a reduction in fibre tension in the initial path.

BACKGROUND ART GB Patent 2 127 544 (Rhone-Poulenc Fibres) discloses a method of operating a device for the continuous measurement of the tension of a moving 'filiform product' (whose definition includes any textile, plastic, metallic or optical yarn in the form, amongst others, of a multifilament, multi-ply or mono-filament), without contact of the product with the device used for the measurement, said device comprising a vibration exciting system for causing the product to vibrate, a system for remote detection and measurement of vibrations of the product, and electronic servo system connecting the vibration exciting system and the remote detection and measurement system, the system fro remote detection and measurement comprising an optical system including a laser which may shine a beam of light on the product, the reflection of which may be detected by said system for remote detection and measurement, the process including the steps of: vibrating the product with the vibration exciting system at a predetermined frequency; activating the laser and shining a beam of light on the product; detecting a reflection of the light of the product; and determining the tension from the reflection.

Among means of vibrating the product there is described the use of a loudspeaker whose audio output can be directed by means of an acoustic cone nozzle. Light is generated by means of a laser and the reflection is detected by means of a phot transistor. Effectively the proposal is concerned with the measurement of the resonant frequency (or a harmonic thereof) of the product from which the tension is then determined.

European Patent Application 0 226 396 (Corning Glass Works) discloses a non-contact method for measuring the tension in an optical waveguide fibre during a drawing process. The method use a system comprising means for sensing the motion of the fibre in a direction transverse to the direction in which the fibre is moving; means for analysing the sensed motion to determine at least one frequency component thereof; and means for monitoring the frequency component so determined so as to monitor the tension in the fibre. The specification refers (Page 18, line 1) to the need to 'blow on the fibre to increase the excitation level of the fundamental frequency'.

Displacement of the fibre from a datum path position is measured by directing a laser bean onto the fibre and sensing the position of the resultant shadow of the fibre on a linear diode array. Analysis of the diode array outputs provides frequency information enabling the fibre tension to be monitored.

This development is concerned with the measurement of a harmonic of the fundamental frequency of the drawn fibre. The frequency is either taken to occur naturally in the course of the production process or to be excited by blowing on the fibre.

European Patent Application 0 549 131 (AT & ) discloses a process of contactless monitoring the tension in a moving fibre, such as during the process of drawing optical fibres from preforms, and a non-contacting tension gauge which allows measurement of fibre tension at line speed.The process includes the steps of sensing an initial position of a moving optical fibre, applying a gas jet onto a section of the optical fibre in a direction transverse to the direction of movement of the fibre so as to cause deflection of the moving fibre axially of the gas jet, sensing the magnitude of deflection of the fibre relative to the initial position, and, depending on the magnitude of deflection, adjusting the tension in the fibre so as to cause the change in the magnitude of deflection to a preselected value. the monitoring is said to be especially suitable for monitoring the tension in an optical fibre being drawn from a heated preform, the tension being adjusted by adjusting the temperature of the fibre drawing furnace.

This describes the use of a single gas jet to laterally displace a drawn fibre from its drawn path and the use of a simple relationship between displacement and tension used to identify the fibre tension.

US Patent 5316562 (ATST Bell laboratories) discloses a tension monitoring technique for an optical fibre whilst it is being drawn. Air is directed at a portion of the fibre as a succession of air pulses, the pulses having a frequency near the natural frequency of the fibre portion. The frequency of the air pulses is then varied over a range of frequencies that included the natural frequency of the fibre portion. When the air pulse frequency equals the natural frequency a resonance occurs which greatly amplifies the amplitude of vibration of the fibre portion. The large deflection of the fibre that occurs at resonance is easy to detect and the air pulse frequency which causes such maximum deflection is taken as being equal to the resonant frequency and therefore to the natural frequency of the fibre portion.Changes in detected resonance can be interpreted in a straightforward manner as changes in optical fibre tension which, in turn, are used to make compensatory changes of temperature of the furnace.

This development is concerned with the generation of a resonant frequency, or of a harmonic thereof, in the drawn fibre to enable the tension to be determined.

DISCLOSURE OF INVENTION In what follows the term 'velocity' refers to a vector having both amplitude (speed) and direction relative to some datum. The term 'speed' refers to an entity characterised only by amplitude.

According to a first aspect of the present invention there is provided a method of of measuring tension in a fibre moving in a region along a first working path between first and second locations when the fibre is subject to no lateral forces, applying in the region a jet of gas transverse the first work path by means of a nozzle so as to cause the fibre to be displaced from the first work path to a second work path and measuring the displacement between the first and second work paths characterised in that the jet of gas is caused to follow an orbit around, while directed towards, the first work path so as to cause a point on the fibre passing between the first and second locations to follow, at least in part, a helical path relative to the first work path.

According to a first preferred version of the first aspect of the present invention the measurement of displacement involves a lateral dimension of an envelope defined by a locus of a point on the fibre passing through region while in the second work path.

According to a second preferred version of the first aspect of the present invention or the first preferred version thereof the jet of gas is provided at substantially constant speed.

According to a third preferred version of the first aspect of the present invention or the first preferred version thereof the jet of gas is periodically varied in speed.

According to a second aspect of the present invention there is provided apparatus for undertaking continuous measurement of tension of a fibre during a drawing process comprising wherein means defining a region through which the fibre is drawn along a first work path between first and second locations at least when the fibre is not subject to lateral displacement; and including means for directing a gas jet so as to laterally displace a fibre passing through the region towards a second work path from the first characterised by nozzle means providing for the gas jet to vary in velocity by following an orbit around, while directed towards, the first work path so as to cause a point on fibre passing between the first and second locations to follow, at least in part, a helical second work path relative to the first work path; a sensor for detecting the displacement of the fibre from the first work path to the second work path in the predetermined region; and means for determining from the transverse displacement of the strand the tension in the fibre in the second work path.

According to a first preferred version of the second aspect of the present invention there is provided gas flow control means whereby the speed of the gas flow is maintained substantially constant.

According to a second preferred version of the second aspect of the present invention there is provided gas flow control means whereby the speed of the gas flow is periodically varied.

According to a third aspect of the present invention there is provided a fibre manufactured by means of a production process including a method of measuring tension according to the first aspect.

According to a fourth aspect of the present invention there is provided a fibre manufactured by means of apparatus according to the second aspect.

EXEMPLARY EMBODIMENT An exemplary embodiment of the present invention will now be described with reference to the accompanying drawings of a station in an optical fibre production system of which: Figure 1 is a side view of components in the station; and Figure 2 is a perspective view of a component of Figure 1; and Figure 3 is a lateral section on section m-m of Figure 2.

The drawing shows a strand of glass fibre 11 being drawn down from a melting tip 12 of glass extending from a furnace 13 in the general direction of arrow A through a work station 14 before entering a first coating station 15. The undisplaced working path for the fibre is a straight line P1.

Work station 14 is now considered in more detail in relation to Figures 2 and 3.

A gas nozzle 16 is mounted on an annulus 17 which is rotatably mounted on a carrier 18 which has an internal passage 19 surrounding the path P1. Rotation of the annulus 17 in direction B about a centre located on path P1 results in the nozzle 16 rotating about a circular orbit in which the nozzle 16 is always directed towards the fibre 11.

As a consequence the nozzle 16 directs a flow of gas F, Figure 3, which displaces the fibre 11 away from the nozzle 16 and causes the fibre to follow a path P2. While path P2 is circular as viewed along path P1 it represents the locus of a point on the fibre 11 as it moves through the work station 14 and when acted on by the gas flow F, is caused to follows helical path P2 about path P1.

In the region of the nozzle 16 displacement D for an optical fibre with a diameter of 0.125 mm is envisaged as being about 02 to 0.3 mm that is to say the displacement D amounts to about 160 to 24070 of the fibre diameter.

The annulus 17 rotates freely on carrier 18 which has an internal chamber 21 into which a compressed inert gas, typically nitrogen, is fed by way of inlet pipe 22.

Annulus 17 is caused to rotate by means of cogged wheel 23 driven by electric motor 24. The motor 24 is powered by lead 25. Pressurised gas from internal chamber 21 flows (arrow F') into nozzle 16 by way of passage 26 in the annulus 17 and from thence out of nozzle 16 as gas flow F. Other powering means can be used such as pneumatic or hydraulic power sources.

An optical scanner 27 is located to measure the displacement D of the fibre path P2 from the undisplaced path P1. In a steady state condition with constant drawing speed and unvarying tension the displacement D will remain constant. In the event that the displacement D is detected by the scanner as changing from a steady state value then appropriate corrective action can be taken either by means of control loop of which scanner 26 is a part or by control inputs applied to the system directly by an operator.

Such corrective action could be to means applying tension to the fibre. In an alternative embodiment the scanner can be housed in the carrier 18.

The present invention provides for substantial benefits over existing known systems.

Firstly the amount of displacement of the fibre can be measured continuously by means of the scanner rather than at periods during a repeated cycling displacement.

Secondly the amplitude of displacement of the fibre 11 from the path P1 to path P2 can be smaller than would be necessary to get a practicable output from earlier systems with fixed gas velocity. Thirdly apart from the non-contact nature of the monitoring system the energy input applied to the fibre by the displacement of the present invention is relatively small by comparison with earlier system obliging a drawn fibre to be driven into a resonant condition (or to a harmonic thereof).

Claims

1A method of measuring tension in a fibre moving in a region along a first working path between first and second locations when the fibre is subject to no lateral forces, applying in the region a jet of gas transverse the first work path by means of a nozzle so as to cause the fibre to be displaced from the first work path to a second work path and measuring the displacement between the first and second work paths characterised in that the jet of gas is caused to follow an orbit around, while directed towards, the first work path so as to cause a point on the fibre passing between the first and second locations to follow, at least in part, a helical path relative to the first work path.

2 A method of measuring tension as claimed in Claim 1 characterised in that the measurement of displacement involves a lateral dimension of an envelope defined by a locus of a point on the fibre passing through the region while in the second work path.

3 A method of measuring tension as claimed in Claim 1 or Claim 2 characterised in that the jet of gas is a substantially constant speed.

4 A method of measuring tension as claimed in Claim 1 or Claim 2 characterised in that the jet of gas is periodically varied in speed.

5 Apparatus for undertaking continuous measurement of tension of a fibre during a drawing process comprising wherein means defining a region through which the fibre is drawn along a first work path between first and second locations at least when the fibre is not subject to lateral displacement; and including means for directing a gas jet so as to laterally displace a fibre passing through the region towards a second work path from the first characterised by nozzle means providing for the gas jet to vary in velocity by following an orbit around, while directed towards, the first work path so as to cause a point on fibre passing between the first and second locations to follow, at least in part, a helical second work path relative to the first work path; a sensor for detecting the displacement of the fibre from the first work path to the second work path in the predetermined region; and means for determining from the transverse displacement of the strand the tension in the fibre in the second work path.

6 Apparatus as claimed in Claim 5 characterised by gas flow control means whereby the speed of the gas flow is maintained substantially constant.

7 Apparatus as claimed in Claim 5 characterised by gas flow control means whereby the speed of the gas flow is periodically varied.

8 A fibre manufactured by means of a production process characterised by a method of measuring tension as claimed in Claim 1, 2, 3 or 4.

9 A fibre manufacturing process characterised by the use of apparatus as claimed in Claim 5, Claim 6, and Claim 7.

10 A method of measuring tension in a fibre as hereinbefore described with reference to the accompanying drawings.

11 Apparatus for undertaking continuous measurement of tension of a fibre as hereinbefore described with reference to the accompanying drawings.