WEFT-FEELER WITH AUTOMATIC ADJUSTMENT OF THE DELAY TIME, FOR WEFT FEEDERS OF SHUTTLELESS LOOMS

Abstract: Device (2) for feeling and detecting weft yarn breakage (weft-feeler), of the type applied upstream of weft feeders (3) (between the weft yarn spools and the weft feeder) in the weft supply of shuttleless looms, in order to stop the loom (5) in due time in case of weft yarn breakage to prevent the insertion of broken or faulty wefts, the loom stopping signal (SP1) being sent from said device after a certain delay time T has elapsed from the moment in which the weft yarn breakage has been detected while the weft feeder is in operating conditions. In said weft-feeler, the delay time is automatically adjusted by an electronic circuit (23) of the weft-feeler, in relation to the momentary speed of the weft feeder motor.

Description: The present invention relates to a weft yarn feeling device for shuttleless looms - of the projectile, or gripper, or fluid jet type - wherein the weft yarn, unwound by being drawn from a fixed spool or bobbin, is intermittently fed to the weaving machine at a uniform and constant tension by a device storing a weft yarn reserve (weft feeder), which is usually controlled by an electric motor with speed variable according to the amount of yarn required by the loom. Weft yarn feeling devices (or, more simply, weft-feelers) are already normally provided on modern weaving machines, to indicate yarn breakages at the inlet of the loom. The weft yarn may break in the area between the weft feeder and the loom, while the fabric is being formed, or in the area between the yarn feeding spool and the weft feeder. In the first case, the weft-feeler stops the loom but cannot obviously prevent the insertion of the broken weft into the fabric: this calls for a subsequent search of the broken weft, with a waste of time and the possibility of permanent damage to the fabric. In the second case, it is instead possible to prevent the length of broken yarn from being inserted into the fabric, by arranging a weft-feeler at the inlet of the weft feeder (or, rather, between the yarn feeding spool and the weft feeder). On breaking of the yarn, the weft-feeler stops in fact the loom when a certain amount of yarn reserve is still present on the weft feeder drum; this prevents insertion of the broken weft into the fabric. By using a weft-feeler, it will thus simply be necessary to thread again the weft feeder after yarn breakage, thereby gaining time and improving the quality of the fabric. In the weaving practice it is already known to use, on each weft yarn, a device for feeling and detecting yarn breakage in either of the two aforementioned critical positions, that is: between the weft feeder and the loom, as described for example in the Italian Patent No. 1.010.273 of 30.04.1974; between the bobbin or spool and the weft feeder, as described for example in the Patent PCT/WO/81/02171 of 31.01.1980. The present invention concerns this second type of weft-feeler, essentially consisting of a sensor detecting the presence of yarn, and of an electronic circuit which processes the signal from said sensor. The sensor of the weft-feeler can detect the yarn motion if it is of the piezoelectric type, or the yarn tension if it is of the mechanical type with microswitch or with Hall effect, or simply the yarn presence if it is of the capacitive or optoelectric type. Also other types of sensors can be used. It should anyhow be noted that the sensor, whatever type it may be, is not apt to distinguish whether the yarn is broken or simply motionless or loose, as it happens when the weft feeder is not drawing yarn from the spool. Whereby, the signal from the sensor, indicating the presence of yarn, should be considered valid only when the weft feeder is moving. Furthermore, on starting the weft feeder, since the yarn does not instantly reach the right speed or tension or position on the weft-feeler, the sensor may detect a false lack of yarn and needlessly stop the loom. To prevent this from occurring, it is already known to accept the loom stopping signal only after a certain delay time, said delay having to be adjusted according to the weaving conditions, that is, according to the yarn drawing speed from the spool, which depends on many factors as, for example, the fabric width, the loom speed, the weft insertion program. It should also be borne in mind that too short delay times can cause stopping of the loom for false lack of yarn, and viceversa, that too long delay times cause stopping of the loom too long after the breakage, when all the reserve of the weft feeder is by then exhausted and the broken yarn end has thus been inserted into the fabric, destroying the advantages of the weft-feeler. From the above it appears evident that the adjustment of the delay time is a critical operation and that, since it also depends on the program of weft insertion into the loom, it involves the need to accept arrangements which may limit the functionality of the device. It may happen, for instance, that the first step of a program of weft insertion into the fabric, carried out on a loom fed with multicoloured weft yarns, may provide for the same weft yarn to be inserted for many consecutive beatings up, thus requiring the choice of a sufficiently short delay time in order to stop the loom before exhausting the yarn reserve. A second step of the weft insertion program may provide for a far shorter frequency, thereby requiring a longer delay time in order to avoid false stopping of the loom. Even in the absence of such difficulties, the operator still needs to adjust the delay time according to the working characteristics of the loom. This operation adds up to the many already required in order to obtain the highest efficiency of the machine, and it becomes particularly difficult when operating on looms using different colours, wherein a weft feeder and thus also a weft-feeler are provided for each colour of weft. The primary object of the present invention is therefore to supply a weft-feeler of the aforementioned type, which does not require the help of an operator to manually adjust the delay time. For this purpose, the weft-feeler according to the invention is characterized in that said delay time is automatically adjusted by an electronic circuit of the weft-feeler, in relation to the momentary speed of the weft feeder motor. Preferably, said delay time is adjusted by means of a frequency signal, directly obtained from the same circuit adjusting the motor speed of the weft feeder according to yarn requirements in the loom. Alternatively - when the motor is a fixed frequency AC motor or a DC motor, or if the motor speed is manually adjustable through a preselector the delay time is adjusted by means of a signal obtained from a sensor which detects the number of revolutions of the motor. Said delay time is suitably adjusted according to an inversely proportional law in respect of the motor speed of the weft feeder, with possible correction to reduce the delay time at lower speeds. The invention will now be described in further detail, with reference to the accompanying drawings, in which: Fig. 1 is the conventional assembly diagram of a weft yarn spool, of a first weft-feeler, of the weft feeder, of a second weft-feeler, and of a loom being fed with the weft yarn wound on the spool; Fig. 2 is a block diagram of the operating system of the first weft-feeler of figure 1; Fig. 3 shows in detail the operating system of the logic circuit forming part of the system of figure 2; Fig. 4 shows the time curves for the logic system of figure 3; Fig. 5 is a diagram illustrating, by way of example, the ratio between the speed of the weft feeder and the delay time; Fig. 6 is a block diagram of the weft-feeler (first weft-feeler in the diagram of figure 1) according to the invention; and Fig. 7 shows the time curves in relation to the diagram of figure 6. Fig. 1 shows schematically the conventional arrangement of the members provided on weaving looms in correspondence of the weft inlet side. To start with, there is the bobbin or spool 1 from which the weft yarn f is drawn, this latter passing through a weft-feeler 2 before being let into the weft feeder 3 to form a yarn reserve r. The weft f is drawn by the loom 5 after passing through a weft-feeler 4 arranged between the weft feeder and the loom. The weft-feeler 4 is meant to stop the loom if the weft yarn should break or be missing between the weft feeder 3 and the loom 5. The weft-feeler 2 is meant to stop the loom if the weft yarn should break or be missing between the spool 1 and the weft feeder 3. The block diagram of figure 2 illustrates the main components of the weft-feeler 2. The weft-feeler is always formed of a sensor 21 and of an electronic circuit 22 suited to the type of sensor used. These two components together generate a TP signal, active when the sensor detects the presence of weft yarn. As already said, the sensor 21 can be produced using different technologies as, for example, optoelectronic, electromagnetic, piezoelectric, Hall effect, triboelectric, and other solutions. As known, the weft feeder 3 winds, by means of a rotary arm operated by a motor, a weft yarn reserve r onto a cylindrical drum; said reserve r is controlled by a sensor 31 - in the example, a photoelectric sensor - which, through a suitable monitoring circuit 32, operates the motor of the weft feeder 3. The circuit 32 sends a signal MP, which is active only when the motor is caused to rotate. The signals TP and MP, from the sensor and from the monitoring circuit of the weft feeder, are processed by a logic circuit 23 which generates a signal SP1 if the yarn should break or be missing between the spool and the weft feeder. The signal SP1 is used to control a relay 25 by which the loom is stopped. If working on looms using different colours, similar systems will be provided for each weft yarn. The various signals SP1, SP2, ...., SPn, will end into an adder circuit 24, the output of which will energize the relay 25 to stop the loom. In known technique, the logic circuit 23 processes the signals TP and MP according to the operating system of figure 3 and the time curves of figure 4; the signal TP, active when the weft is detected by the sensor, is inverted by the circuit NOT 40 and multiplied in 41 by the signal MP, active when the motor is running, thereby generating a signal A, active only with non-detected weft yarn and running motor (interrupted yarn). To prevent false stopping of the loom, a monostable circuit 42 and an AND circuit 44 are introduced, so that the loom 5 may be stopped by the output signal SP1 from the circuit 23 only when a delay time T has passed, generated by the monostable circuit 42. The minimum delay time T should be at least equal to the time TA elapsing between the activation of the signal MP starting the weft feeder motor, and the moment in which the weft has sufficient tension and speed to be detected by the sensor 21. The maximum delay time T should instead be such as to prevent stopping of the loom when the weft yarn reserve on the weft feeder is exhausted or insufficient. Figure 4 shows, in dashed lines, the time curves in case of yarn breakage. Figure 5 indicates how the delay time T should vary, on varying of the average weft yarn weaving speed, which is in turn equal to the average speed of yarn withdrawal from the spool, and thus to the speed of the weft feeder motor which winds the yarn onto the winding unit. The object of the present invention is to avoid having to provide for the manual adjustment of the delay time T, one for each weft yarn, on varying of the loom working conditions. The additional information, required to automatically obtain the delay time T, again comes from the weft feeder and supplies the logic circuit 23 with data concerning the rotation speed of the weft feeder motor. This information is already normally provided by the circuits 32, for adjusting the speed of the weft feeder motor, in the form of pulses the frequency of which is proportional to the motor speed. In the event it were not possible to derive this information directly from the circuit of the weft feeder, one could provide for a sensor apt to generate one or more pulses for each revolution of the motor shaft. In figure 2, this signal (from circuit 32 to circuit 23) is indicated by MC. Figure 6 is a block diagram showing an embodiment of the invention, while figure 7 shows the relative time curves. The signal MC (Motor Clock), sent by the circuit 32 of the weft feeder 3, is formed of pulses having a frequency proportional to the rotation speed of the weft feeder motor. The frequency range of the signal MC could for instance vary from 5 Hz to 70 Hz (equal to the frequency required to drive a motor with frequency change control in the speed range of from 300 to 4200 r.p.m.). Furthermore, as already known, the signal MP, also sent from the circuit 32 of the weft feeder 3, is active when the weft feeder motor is running, while the signal TP, sent from the electronic circuit 22 of the sensor 2, is active when the weft is detected by said sensor. This last signal is inverted in the block 50 and, placed in AND with the signal MP in the block 51, it keeps set to zero the counter-divider 52 having the modulus "m" ("m" means that it sends an output signal C after having counted on its input a number of pulses equal to 2 raised to "m"; in figure 7, by way of example, m=2). The diagram of figure 5 shows the ratio between the delay time T and the speed of the weft feeder. The ratio between the two magnitudes may not be simply inversely proportional and can be corrected by adding pulses to the signal MC by way of (figure 6) the adder 53 and of an oscillator 55 which generates a fixed frequency signal FC. In this case, the delay time T is considerably shortened, especially when working at low speed. In the event the signal TP should be missing, in the presence of an MP which is active, the signal R generated by the block 51 (figure 6) becomes inactive and the counter-divider 52 can start to count the pulses B sent from the adder circuit 53. Supposing, to start with, that the signal FC is null, the counter-divider 52 will send a signal C after a time inversely proportional to the frequency of the signal MC and, thus, to the speed of the weft feeder motor. The signal C will hence in turn generate, by way of the monostable circuit 54, the pulse SP for stopping the loom. The heretofore described and illustrated embodiment of the invention is evidently just one of the many possible embodiments which can be realized adopting different circuitry techniques. It is therefore understood that the present invention covers any other embodiments and variants differing from the one described, allowing to automatically adjust the delay time T according to weaving requirements, in relation to the speed of the weft feeder motor, by means of an algorithm which can simply be inversely proportional or the like, with correction, especially at the low working speeds.

Claims: Device for feeling and detecting weft yarn breakage (weft-feeler), of the type applied upstream of weft feeders (between the weft yarn bobbins or spools and the weft feeder) in the weft supply of shuttleless looms, in order to stop the loom in due time in case of weft yarn breakage to prevent the insertion of broken or faulty wefts, the loom stopping signal being sent from said device after a certain delay time T has elapsed from the moment in which the weft yarn breakage has been detected while the weft feeder is in operating conditions, characterized in that said delay time is automatically adjusted by an electronic circuit of the weft-feeler, in relation to the momentary speed of the weft feeder motor. Weft-feeler as in claim 1), wherein said delay time is adjusted by means of a frequency signal, directly obtained from the same circuit adjusting the motor speed of the weft feeder according to yarn requirements in the loom. Weft-feeler as in claim 1) wherein, when the motor is a fixed frequency AC motor or a DC motor, or if the motor speed is manually adjustable through a preselector, said delay time is adjusted by means of a signal obtained from a sensor which detects the number of revolutions of the motor. Weft-feeler as in claim 1), wherein said delay time is adjusted according to a law which is inversely proportional in respect of the motor speed of the weft feeder, with possible correction to reduce the delay time at lower speeds.

Inventors: GHIARDO, FIORENZO
Applicants: ROJ ELECTROTEX S.P.A.
Application year: 1988
Main classification: D03D51
IPC codes: D03D47, D03D51