WO1991007344A1

WO1991007344A1 - An apparatus for unreeling a thread

Info

Publication number: WO1991007344A1
Application number: PCT/FI1990/000275
Authority: WO
Inventors: Teuvo Päivinen
Original assignee: Nokia Kaapeli Oy
Priority date: 1989-11-17
Filing date: 1990-11-15
Publication date: 1991-05-30
Also published as: AU6644990A; FI895496A; FI84049C; FI895496A0; FI84049B

Abstract

An apparatus for unreeling a thread, such as an optical fibre, comprising a supporting means (3) for rotatably supporting a reel (4), and a braking means (2) for braking the rotation of the reel. In order to achieve a high initial tension (F2) for the thread (8) to be unreeled with a low unreeling tension (F1), the apparatus comprises a brake wheel (6) which receives a thread (8) unwound from the reel, the brake wheel being connected to the reel by means of the braking means (2) in such a way that the reel and the brake wheel rotate in opposite directions.

Description

An apparatus for unreeling a thread

This invention relates to an apparatus for un¬ reeling a thread, such as an optical fibre, com- prising

- a body;

- a supporting means resting on the body for rotatably supporting a reel from which the thread is to be unreeled; and - a braking means for braking the rotation of the reel.

The invention will be described in the follow¬ ing mainly in connection with the production of optical cables as the invention can be particularly advantageously applied to the unreeling of optical fibres; however, the word "thread" is used in its wide meaning so that it refers not only to optical fibres but also to ordinary wires used in electric conductor elements and cables. The achievement and control of tension (load, tightness) in an optical fibre is essential in the production of the structural parts of a cable.

In the production of a tubular coating loosely surrounding a fibre bundle, the initial tension of the fibres should be relatively stable, so that all fibres in the multi-fibre tube will have approximate¬ ly the same tension. Fibre tensions applied in the production of a loose tubular coating are generally low, below 200 p. However, higher values of initial tension are required when the filling greases presently in use are replaced with stiffer filling greases used in the tubes. If the braking of the starting reel is increased to achieve a higher initial fibre tension, there exists a danger that the fibre cuts into the fibre layer on the reel during the unreeling of the fibre.

In the production of a fixed coating, a higher initial tension is usually applied than in the production of a tubular coating. Similarly, a stable and high initial tension is required when fibres are bundled e.g. by means of a binding thread in order to be able to control the tightness of the binding thread or the shrinkage of the binding sock by util¬ izing the recovery of stretch of the fibres. The control of the initial tension of fibres is often hampered by an asymmetric and loose reeling of the fibres on the reels.

On account of the tendency of the fibre to cut into the reeled layer at higher tensions, the fibre cannot be unwound directly from the fibre reel when initial tensions exceeding 200 p are to be obtained, but an auxiliary device has to be used after the un¬ reeling to achieve such a high tension.

It is known from prior art to brake the fibre reel by means of e.g. a magnetic powder brake which subjects the rotatory shaft of the fibre reel to an adjustable braking torque. This way of braking, how¬ ever, does not provide any higher initial tensions due to the above-mentioned cutting tendency of the fibres. A further drawback is that the initial tension varies substantially with the unreeling radius of the reel, which decreases continuously during the unreeling.

A more advanced way is to provide the brake with a feedback, such as a continuous measurement of tension and equivalent adjustment of the brake, or with a so-called dancer control. In this way, a constant initial tension is achieved irrespective of the unreeling radius of the reel; the measuring and control means are, however, relatively complicated. High initial tension values can be obtained by belt drive or multi-wheel drive means (capstans) but the unreeling apparatuses are thereby large as well as expensive. The object of the present invention is to provide an unreeling apparatus which avoids the above-mentioned drawbacks and enables the achievement and control of high initial tension values with relatively simple means. This object is achieved by means of an apparatus of the invention which is characterized in that it comprises a brake wheel receiving the thread unwound from the reel; and

- that the brake wheel is connected to the reel by means of the braking means in such a way that the reel and the brake wheel rotate in opposite direc¬ tions during the unreeling of the thread.

The invention is based on the idea that the movement of the thread unwound from the reel is utilized to increase the unreeling tension of the fibre to be unreeled to a desired initial tension without causing a corresponding increase in the un¬ reeling tension of the reel. Both low and high initial tensions can be obtained directly from the apparatus. Due to the operating principle of the apparatus the drawbacks caused by asymmetric and loose reeling are compensated for to some extent. The initial tension of the fibre emerging from the apparatus does not vary significantly with the un- reeling radius of the reel. Accordingly, long fibres can be unwound from the apparatus without any need to adjust the tension, which makes the apparatus simple in construction.

In the following the invention will be de- scribed in greater detail with reference to the attached drawing, in which

Figures 1 and 2 show one preferred embodiment of an unreeling apparatus according to the invention in two different directions; and Figure 3 illustrates schematically the oper¬ ating principle of the apparatus.

The apparatus shown in the drawing comprises a body 1 to which a magnetic powder clutch -2 is attached. A horizontal support shaft 3 for a fibre reel 4 from which the fibre is to be unwound is attached to one shaft of the clutch 2 while a brake wheel 6 is attached co-axially with the support shaft to its other shaft 5. Further, an idler wheel 7 is mounted rotatably to the body. The reel is attached unrotatably to the support shaft 3 and the brake wheel to the shaft 5.

The structure of the magnetic powder clutch is known per se. A clutch of this type is manufactured, e.g., by a French company S. A. EROBEL with the type marking EFAS 2. The clutch is connected electrically to a control device not shown for controlling the braking torque created by the clutch.

The unreeling apparatus operates in the following way: The braking torque of the clutch is adjusted electrically to a desired value. A fibre 8 is passed from the reel over the idler wheel and further onto the brake wheel and around it, in this particular case through 270°. When the fibre is drawn with a drawing means not shown, the reel and the brake wheel rotate in opposite directions, so that they brake the rotation of each other with the preset braking torque of the clutch. In the following a simple mathematical presen- tation of the behaviour of the tension of the fibre during the unreeling will be explained with reference to Figure 3. As the friction forces are very low, they are not taken into account. The following symbols will be used

FI = the unreeling tension of the fibre unwound from the reel, F2 = the initial tension of the fibre emerging from the apparatus Rk = the radius of the fibre reel, Rp - the radius of the brake wheel, Mj = the braking torque of the clutch, whereby the following equations will result:

Mj = FI x Rk (1)

Mj *^■** (F2 -FI) x Rp (2)

FI = F2 x Rp

Rk + Rp (3)

^{F2 "} ^ ^{+ F1 (4)}

Example 1

Assume that a high initial fibre tension F2 = 300 p is to be achieved, and the radius Rk of the reel is 9 cm and the radius Rp of the brake wheel is 8 cm, then the unreeling tension of the fibre will be

FI = 300 p x 8 cm ₌ 9 cm + 8 cm

A fibre exposed to this tension can be unreeled directly without any risk of the fibre cutting into the reeled layer.

Example 2

Assume that the initial tension F2 of the fibre is 150 p with a full reel, and the radius Rk of the full reel is 10 cm (fibre length about 20 km) and the radius Rp of the brake wheel is 8 cm, then the un¬ reeling tension of the fibre will be

FI = 150 p x 8 cm

10 cm + 8 cm 66.7 p.

The braking torque of the clutch will thus be

Mj = 66.7 p x 10 cm = 667 pcm.

If the radius Rk of the same reel is 8 cm when empty, the initial tension F2 of the fibre can be calculated as follows:

_m 667 pcm _m 8 cm *

_{F2 m} 83.3 p x 8 cm _{+ = fi}

8 cm

The change in the initial tension F2 of the fibre when reeling from a full reel to an empty reel is only 166.7 p - 150 p = 16,7 p, which is of no practical importance. The drawing and the description related to it are only intended to illustrate the idea of the in¬ vention. In its details, the apparatus may vary within the scope of the claims. The apparatus is pre¬ ferably used in providing a secondary sheathing on an optical fibre. In place of a magnetic powder clutch, it is possible to use a braking means of some other type for creating a braking torque between the reel and the brake wheel.

Claims

Claims:

1. An apparatus for unreeling a thread, such as an optical fibre, comprising - a body (1);

- a supporting means (3) resting on the body for rotatably supporting a reel (4) from which the thread is to be unreeled; and

- a braking means (2) for braking the rotation of the reel; c h a r a c t e r i z e d in that

- it comprises a brake wheel (6) receiving the thread (8) unwound from the reel (4); and

- that the brake wheel is connected to the reel by means of the braking means (2) in such a way that the reel and the brake wheel rotate •in opposite directions during the unreeling of the thread.

2. An apparatus according to claim 1, c h a r ¬ a c t e r i z e d in that the braking means (2) is a speed-adjustable magnetic powder clutch.

3. An apparatus according to claim 1 or 2, c h a r a c t e r i z e d in that . the supporting means (3) of the reel (4) is attached to one half of the braking means (2) and the brake wheel (6) is attached to another half of the braking means in such a way that the reel and the brake wheel are positioned co-axially with respect to each other.

4. An apparatus according to any. of the preceding claims, c h a r a c t e r i z e d in that the radius (Rp) of the brake wheel (6) is smaller than the radius (Rk) of a full reel (4).

5. An apparatus according to any of the preceding claims, c h a r a c t e r i z e d in that the body (1) is provided with an idler wheel (7) for passing the thread (8) from the reel (4) onto the brake wheel (6).