In order to regulate filament tension, bobbins are usually equipped with an electronic or electromechanical braking system. Such a solution is known from the patent DE 4321318.

A disadvantage of such a solution is the increasing complexity of the brake as the need for operation accuracy increases.

A particular problem occurs when, because of the breakage of one of the many threads, the next part of the process has to be stopped. This emergency brake should be able to stop the thread processing machine very quickly, often within one second. The stop must be realised before the broken end cannot be found anymore in the subsequent process, or can only be found with difficulty, as a result of the threads being wound up in that process. By means of a very fast stop it is possible to trace the breakage in the thread concerned, knot the two broken ends together, and then start the machine again.

Because of the high processing speed, bobbins will deliver the threads from the creel at high revolutions. Therefore the bobbins have a high kinetic energy. The current brakes are mostly not in a position to carry out such an emergency stop in a controlled way, which on the one hand leads to extra thread breakage and on the other hand to unwanted further unwinding of the threads. As a consequence of this second occurrence, the threads can end up hanging loose in the creel and can get tangled in the mechanics of the creel.

The invention described herein does not have these disadvantages and provides both a simple and effective solution for this problem by bringing the rapidly spinning bobbin to a stop, quickly and in a controlled manner, by means of a spring coil brake.

The invention is described on the basis of the drawings. These drawings only serve as an explanation of the invention described and should not be interpreted as being limiting.

Figure 1 shows a partial cross section of a release point with the braking part in the braking position.

Figure 2 shows a partial cross section of a release point with the braking part in a non- braking position.

Figure 1 shows a release point according to a possible embodiment of the invention with a fixed housing (1) in which a rotatable axle (2) is provided with bearings (3a and 3b). On the rotatable axle (2) a coil spring (4) is coaxially wound in such a way that, when there is no load on it, the inner surface of the coil spring (4), completely or nearly completely touches the surface of the rotatable axle (2). The one end (5) of the coil spring (4) is fixed to the housing and the other end is connected to an arm (6) that, at the end, is bent at a right angle. The arm (6) is connected to a fibre guide (7) that runs parallel to the rotating axis (2) which extends over at least a part but preferably the whole width of the bobbin. Between the conical part (8) of the rotatable axle (2) and the bus (11) with conical part (10), which can be moved lengthwise along the axle and locked up, the bobbin with the coils of thread (9), both partially shown as a cross-section, can be fixed on the rotatable axle in such a way that no slippage occurs.

To initiate the working of the coil spring brake, normally a relatively small force is needed.

By increasing the momentum by means of the arm (6), the necessary operating power is reduced to such an extent that even a thin thread can activate the coil spring brake.

Under normal operational circumstances, as a result of the tension of the thread, the fibres guide (7) and thereby the arm (6) will turn in the opposite direction of the rotating axle (2).

This will result in torsion of the coil spring (4) in the opposite direction of the windings, and consequently the inside of the coil spring windings will press slightly against the external surface of the rotating axle. The fixed end (5) of the coil spring stays in place. The

arm (6) can be turned to the extent that the windings are virtually free from the outer surface of the rotating axle, so that the remaining braking power is nil or minimal.

When thread tension is lost due to thread breakage for example, the fibre guide (7) and herewith the arm (6) turn in the direction of the rotating axle (2) and consequently the inner diameter of the windings of the coil spring (4) becomes smaller, which will set the braking operation in motion.

By synchronizing the winding direction of the coil spring and the rotation direction of the bobbin, the initial friction between the inside of the windings of the coil spring (4) and the outer surface of the rotatable axle (2), while rotating in one direction, will lead to a greater contact pressure by the windings on the surface of the rotating axle (2) and consequently to a greater friction which in its turn further increases the contact pressure. Likewise, the rotation of the rotatable axle (2) in the opposite direction will lead to a relaxation of the windings, whereby the frictional force is reduced. By providing the coil spring (4) with a sufficient number of windings the self-enforcing effect can be so strong that the system completely blocks.

In order to achieve a desired level of the actuating force of the brake a suitable choice can be made taking the diameter of the windings, the diameter of the thread, and the number of windings of the coil spring into consideration. In the no-load situation, the inside of the windings of the coil spring (4) should always almost completely touch the outer surface of the rotating axle (2).

Furthermore, the torque stiffness of a coil spring (4) decreases as the diameter of the windings increases. Also the number of windings is inversely proportional to the torque stiffness. A further advantage of the coil spring (4) is that the windings evenly increase or decrease in diameter as a result of torsion against the direction of the windings, or in the direction of the windings respectively.

Surprisingly enough it turns out that the actuating force of the movable arm (6) is not noticeably influenced by the force or the speed at which the braking takes place, so that the fibre guide (7) at the end of the movable arm (6) is pre-eminently suitable to be actuated by the threads that unroll from the bobbin. This also makes it possible to use the fibre guide (7) as a dance roller by pulling the fibre encircling the fibre guide (7) in a direction contrary to the roll-off direction of the bobbin (12).

In a preferred embodiment of the invention, the bobbin (12) is connected with the rotatable axle (2) by some means in such a way that mutual slip-free rotation can take place. However, for a smooth operation of the device it is necessary that the force required to make the bobbin (12) rotate is greater than half of the actuating force that must be exerted on the fibre guide (7) to release the brake.

To minimise the wear and tear between the coil spring (4) and the rotating axle (2) at the lifting of the self-enforcing effect of the brake it is furthermore advantageous to make the rotatable axle (2) from a hard and durable material, whereby at a more detailed level, the diameter of the rotatable axle (2) slightly decreases conically at the position of the fixed end (5) of the coil spring over the first few windings. These measures bring about that the first windings of the coil spring (4), at the place where the coil spring is connected to the fixed housing (1), during discontinuation of the braking operation, do not touch the surface of the rotatable axle (2), whereby friction and thereby wear and tear are lessened.

If the bobbin (12) turns clockwise during the unwinding process, a left winding coil spring can be applied whereby the movable arm (6) relative to the fixed part of the spring is closest to the bobbin. If the bobbin (12), during the unwinding process, turns anticlockwise, a right winding coil spring can be used whereby the moveable arm (6) relative to the fixed part of the spring is closest to the supply bobbin.

Finally, the rotatable axle (2) can be equipped with suitable sleeve bearings or rolling bearings, whereby a freewheel device can be applied to permit rotation in the unwinding direction and to prevent rotation in the winding direction. This is especially important if, in the case of a thread breakage, the braking spring will release its tension via the bobbin and, after reaching a standstill, driving the bobbin in the opposite direction. In order to avoid the braking process for stopping too abruptly it is advantageous to use a suitable damper which has a somewhat controlling effect on the impact of the brake.