EP0357138A1

EP0357138A1 - Method and device for monitoring the spun yarn path in a rotor spinner

Info

Publication number: EP0357138A1
Application number: EP89202172A
Authority: EP
Inventors: Francesco Ferro; Sergio Montali
Original assignee: Savio SpA; Savio Macchine Tessili SpA
Current assignee: Savio SpA; Savio Macchine Tessili SpA
Priority date: 1988-09-02
Filing date: 1989-08-28
Publication date: 1990-03-07
Also published as: IT1226604B; IT8821809A0

Abstract

A method is described for monitoring a moving yarn in an open-ended spinning station using a optoelectronic transducer (2) disposed between the extraction unit (3, 5) and the winding unit (1).

The device which effects this monitoring is also described.

Description

This invention relates to a method and device for continuously monitoring the path of yarn being wound in an open-end spinning station.
Open-end spinning machines are known in the spinning field, and in particular rotor spinners consisting essentially of a plurality of spinning units positioned in an adjacent progression. Each spinning unit comprises a feed device for the fibre sliver, a card for separating the fibres and a rotor spinning chamber, from which the yarn emerges extracted by a roller and cylinder, to be fed to the winding unit.
In such a known rotor spinning machine there is the problem of continuously monitoring the presence of the yarn travelling between the exit of the spinning unit and the cross-winding unit, so that if necessary, ie if the yarn breaks, suitable precautions can be taken such as halting the fibre feed to the spinning rotor. The devices for sensing the presence of the winding yarn which are currently used for this purpose largely comprise mechanical contact elements, ie contact feelers which continuously rest on the yarn, or contact feelers which rest thereon periodically.
Said mechanical contact elements, which monitor the yarn trajectory below the extraction rollers and are associated with the exit of each spinning unit, are generally in the form of rotatable arms acting as probes which bear on the yarn. If the yarn breaks, the arm rotates downwards to cause stoppage of the spinning unit by means of known contact elements.
This mechanical probe formed from an arm element bearing on the travelling yarn can influence said yarn in the sense of modifying its winding tension. In this respect, with such mechanical feelers not only is the path of the winding yarn disturbed but the winding yarn tension is increased.
This is a drawback particularly in the case of thin yarns under high spinning speeds, and it is also more difficult to form soft bobbins wound under low tension. This means that the mobile contacts, ie the arms which make contact with the mobile yarn being wound, must not be of substantial weight because such weight could negatively influence the yarn tension.
In contrast, contact arms of low weight would rise and fall with oscillatory motion due to machine vibration and oscillation. Such unstable contact can in the limit generate false command or information signals.
In rotor spinning units it is also a fact that the yarn emerges from the extraction rollers at constant speed but must be deposited for winding purposes at variable speed because of the variations in distance between the ends and the central part of the bobbin under formation. In such an operating process the periodical variation in the yarn length in the section between the extraction rollers and the point at which it is deposited on the bobbin circumference consequently generates variations in the tension of the yarn, which is periodically slackened and tightened.
Conditions of instability in the monitoring of the yarn presence therefore arise at the mechanical contact arm. Again, any slippage between the bobbin drive cylinder and the bobbin under formation, which frequently arises because of the type of friction drive used, often temporarily nullifies the tension in the yarn being collected. The arm resting on the yarn is no longer supported by the yarn tension and rotates downwards to consequently halt the spinning process. Because of the high yarn formation speed, such production holdups in the spinning unit assume considerable importance in terms of the reduction in bobbin-wound yarn production.
The operation of these and similar mechanical yarn monitoring devices is therefore unreliable and unsatisfactory. The object of the invention is therefore to provide a monitoring and control method which does not involve contact with the travelling yarn, and a device for implementing the monitoring procedure which is space-saving, of simple construction, and easy to mount on each rotor spinning unit.
This object is attained according to the invention by providing an optoelectronic yarn monitor which enables the path of the moving yarn to be monitored and the spinning unit to be stopped at each yarn breakage. The characteristics and principle of operation of the sensing light beam of said optoelectronic yarn monitor are already known in detail in the art. According to a preferred embodiment the optoelectronic yarn monitor is in the form of an optical monitor of either single-path, reflection or other known type. In the case of a single-path optical monitor the photoemitter and photoreceiver face each other, whereas in the case of reflection optical monitors the photoemitter and photoreceiver are placed side by side facing a reflector positioned a certain distance away. The purpose therefore of the present invention is to obviate the aforesaid drawbacks by using an optoelectronic monitor positioned above the extraction rollers in each spinning unit to monitor the path of the yarn without any mechanical contact therewith. This monitoring is done by a light beam with the result that even very thin and delicate yarns can be monitored without damage. The optoelectronic device which implements the method of the present invention also has the following advantages:
- it is insensitive to machine vibration because it uses a light emitting diode as the light source;
- it is insensitive to external light sources because of the use of modulated light for the monitoring light beam;
- it is of small dimensions and therefore easily installed on already existing spinning units;
- it is insensitive to any variation in the winding tension and to any change in the type of yarn being wound. The winding characteristics can therefore embrace any values;
- it is positioned above the extraction unit in a location close to the point of winding.
This latter operating advantage can be further clarified as follows. Accidental yarn breakages mainly occur around the yarn guide, which moves with reciprocating to-and-fro motion. As is well known to experts of the art, in such cases of interruption in yarn continuity the yarn winds around the extraction rollers, which continue to extract the yarn from the spinning unit. Thus a yarn monitor positioned between the spinning unit and the extraction rollers, as often proposed in the known art, does not detect this interruption with the result that it does not halt the fibre feed to the rotor, therefore resulting in considerable known damage. In contrast, a yarn monitor located in an intermediate position between the extraction rollers and the winding unit, as proposed in the present invention, detects such interruption in the yarn travel and halts the spinning unit. Although this intermediate section between the pair of extraction rollers and the winding unit is knowingly subject to tension variations because of the aforesaid causes, this has no influence on the yarn monitor of the present invention. In this respect the present invention proposes an optoelectronic device which is insensitive to any tension variation in the yarn being wound. These and further advantages are attained by the method and device of the present invention for continuously monitoring the path of the spun yarn in an open end spinning station, said monitoring being effected on the moving yarn under any state of tension, in a position intermediate between the extraction rollers and the winding unit, by an optoelectronic transducer not in contact with the yarn.
A preferred embodiment of the device of the present invention is described hereinafter by way of non-limiting example with reference to the single accompanying drawing. This is a schematic isometric perspective view of the optoelectronic yarn monitor shown positioned along the path of the winding yarn between the pair of extraction rollers and the cross-winding unit.
In the drawing:

1 is the drive cylinder which rotates the bobbin under formation;
2 is the opelectronic yarn monitor which monitors the presence of the travelling yarn 6 being wound;
3 and 5 are the pair of rollers for extracting the yarn 6 from the underlying spinning unit 4. Said rollers are kept pressed against each other to extract the yarn from said spinning unit 4 at constant speed and feed it by the way of the optoelectronic yarn monitor 2 to the overlying winding unit;
6 is the yarn travelling from the unit 4 to the winding unit in the direction indicated by the arrow 14;
7 is the blade for deflecting the path of the yarn 6;
8 is the cable connecting the optoelectronic transducer 2 to the control card 10 for the output signals from said transducer;
9 is the yarn guide element driven with reciprocating to-and-fro movement by the control shaft or rod 11, this latter extending along the entire operational winding face;
10 is the control card for the electrical output signals from the optoelectronic transducer 2.
In the case of a breakage in the yarn 6, said card 10 receives appropriate electrical signals which indicate the absence of the yarn being wound and immediately generates a signal which by way of the connection cable 12 causes the spinning unit 14 to stop;
15 is the support plate or strap for the optoelectronic yarn monitor 2.
Said plate is fixed to the machine frame, not shown;
16 is the bobbin formed with cross-wound yarn;
18 is the bobbin carrier arm.

The operation of the device for monitoring the path of the yarn 6 spun by the spinning unit 4 indicated on the accompanying drawing is apparent. In said drawing, those parts not essential for understanding the invention have been omitted for clarity. The yarn 6 is withdrawn at constant speed from the individual spinning unit 4 by the extraction rollers 3 and 5 and is deposited on the surface of the bobbin 16 under formation by the winding unit. The presence of the yarn 6 along its winding path is monitored by the optoelectronic transducer 2, which as a scanning device is constructed advantageously in the shape of a hollow yarn guide to correctly retain the yarn 6 in position.
Said optoelectronic transducer 2 is designed to provide at its output electrical signals which are advantageously amplified. Said electrical signals are fed through the cable 8 to the control card 10, they being either of oscillating and hence variable value or of constant value. An oscillating value indicates that the yarn is present whereas a constant value indicates that the yarn is absent (yarn breakage) or has come to rest by virtue of a winding blockage. In this respect, it should be noted that a yarn moving through an optoelectronic transducer produces an incident light of variable luminosity on the photoreceiver because the yarn diameter slightly oscillates about an average value (count) as is well known, and in addition the yarn vibrates during its travel. The light from the photoemitter encounters the moving yarn and strikes the photoreceiver with variable luminosity, to produce in the optoelectronic transducer associated with the photoreceiver a variation in electrical conditions, so resulting in oscillating electrical signals. These latter reach the control card 10 to confirm that the yarn is moving and being wound, with the result that the card produces no signal for stopping the spinning unit 4. In contrast, if the light from the photoemitter does not encounter yarn (yarn broken) or encounters yarn at rest because the winding is blocked, it strikes the photoreceiver with constant luminosity, to produce constant electrical conditions in the optoelectronic transducer associated with the photoreceiver, and resulting in the generation of electrical signals which are constant with time. These reach the control card 10 to indicate that the yarn 6 is absent (breakage) or is at rest. Said control card 10 immediately causes stoppage of the spinning unit 4, which then awaits the known rejoining operation to enable the rotor spinning process to be restarted.

Claims

1. A method for continuously monitoring the path of yarn spun in an open-end spinning station for the formation of cylindrical or frusto-conical bobbins, said station comprising a spinning rotor and a winding unit with a roller-cylinder extraction unit therebetween, characterised in that said monitoring is effected on the moving yarn under any state of tension, in a position intermediate between the extraction unit and the winding unit, by an optoelectronic transducer not in contact with the yarn.

2. A device for continuously monitoring the path of yarn spun in an open-end spinning station which comprises a spinning rotor and a winding unit with a roller-cylinder extraction unit therebetween, characterised by further comprising an optoelectronic transducer disposed between said winding unit and said extraction unit.