WO1984001394A1

WO1984001394A1 - Yarn storing, feeding and measuring device

Info

Publication number: WO1984001394A1
Application number: PCT/EP1983/000254
Authority: WO
Inventors: Lars Helge Gottfrid Tholander
Original assignee: Iro Ab
Priority date: 1982-09-30
Filing date: 1983-09-30
Publication date: 1984-04-12
Also published as: EP0148356A2; EP0107110A1; JPH07102449A; EP0148356A3; EP0107110B1; JPS59501830A; JPH0555619B2; DE3371098D1; JPH07100900B2; DE3382053D1; JPS60500717A; EP0148356B1; JPH0359914B2

Abstract

A yarn storing, feeding and measuring device (1), particularly for jet looms, having a stationary drum (2) onto which an intermediate yarn store is wound by a winding-on device (3) and from which the yarn (F) is withdrawn, yarn sensing means (6) detecting the withdrawal of the yarn from the drum generating pulse signals indicating that the yarn passes a detection area of the yarn sensing means (6), a plurality of yarn stopping devices (10) being arranged at angular intervals around the storage drum (2) and a control device (8) adjustable to desired yarn lengths to be withdrawn, said control device being responsive to said pulse signals such that an actuating signal is transmitted to a selected yarn stopping device (10) whose angular position corresponds to the position rendered by the yarn when said desired yarn length has been withdrawn. Prior art devices of the above mentioned type required a great number of yarn sensors, said great number resulting in high costs of said device. The present invention improves this state of art by a device in accordance with the above mentioned type, wherein the yarn sensing means consists of yarn sensors (6), the number thereof being lower than and independent from the number of yarn stopping devices (10), and wherein said control device comprises storing means for storing information regarding the yarn stopping device (10) actuated at the end of the previous yarn withdrawal cycle and calculating means (20) for determining one yarn stopping device to be actuated next among the plurality of yarn stopping devices (10) on the basis of input information for the calculating means (20) representing said desired yarn length and on the basis of said stored information.

Description

YARN STORING, FEEDING AND MEASURING DEVICE

The present invention relates a yarn storing, feeding and measuring device, particularly for jet looms, in accordance with the generic clause of claim 1.

DE-A-3123760 receiving a yarn storing, feeding and measuring device for jet looms having a stationary storage drum onto which an intermediate yarn store is wound by a winding-on device and from which the yarn is withdrawn spiraling around the withdrawal end of the storage drum, yarn sensing means being arranged such that the yarn is passing its detection area during withdrawal from the drum, said yarn sensing means producing pulse signals, each pulse signal indicating that the yarn passes a detection area of the yarn sensing means, a plurality of yarn stopping devices being arranged at angular intervals around the storage drum, said yarn stopping devices consisting of yarn stopping elements and actuator means moving said stopping elements into and out of the path of the yarn being withdrawn, and an actuator control device adjustable to desired yarn length to be withdrawn, said control device being responsive to said pulse signals in such a way that an actuating signal is transmitted to a selected yarn stopping device whose angular position corresponds to the position rendered by the yarn when said desired yarn length has been withdrawn. The yarn sensing means of this prior art device consists in a plurality of yarn sensors, each of said sensors being associated with a yarn stopping device. Hence, the number of yarn sensors required for such a prior art device corresponds to the number of yarn stopping devices. Yarn storing, feeding and measuring devices of the above mentioned kind not only serve to intermediately storing the weft yarn on a storage drum, but also serve to supply the jet loom with a weft yarn having a desired length. For the latter purpose, this prior art device carries out the following steps in order to obtain the desired yarn length for each weft yarn insertion: After releasing or deactuating the yarn stopping device actuated at the end of a previous yarn withdrawal cycle the yarn is withdrawn spiraling around the withdrawal end of the storage drum. Thereby, the yarn subsequently passes the detection areas of the plurality of yarn sensors being arranged at the withdrawal end of the storage drum in a spaced, angular relationship with respect to each other.

Each yarn sensor generates a pulse signal indicating that the yarn passes its detection area, these pulse signals being fed to the control device. Hence, the control device receives a number of pulse signals, this number corresponding to the number of yarn sensors being passed by the yarn during the withdrawal. By counting the pulse signals received from the yarn sensor the control device generates a count value corresponding to the actual position of the withdrawal point of the yarn with respect to the yarn sensors. The count value corresponds to the length of yarn withdrawn from the storage drum. When the count value corresponds to the desired yarn length to be withdrawn, the control device actuates the stopping device being located with respect to the angular movement of the withdrawal point of the yarn behind the yarn sensor which generated the last pulse signal. Thereby, the withdrawal of the yarn is stopped so that the desired yarn length is obtained. This prior art device is costly and complicated due to the large number of yarn stopping sensors required to achieve a sufficiently large number of different yarn lengths. Furthermore, it is undesirable to have a large number of yarn sensors due to the fact that such yarn storing, feeding and measuring devices have to designed as compact as possible so as to meet with the technical requirements of the customers and users of such devices. A further drawback is caused by the fact that yarn sensors are also sensitive in operation, since they usually comprise optical elements which can be covered by lint. If one of the plurality of yarn sensors is covered by lint, it will no longer generate pulse signals when the yarn passes its detection area resulting in a wrong count value in the control device. Hence, the respective yarn length of the inserted weft yarn will become greater than the desired yarn length.

DE-A-3123760 also includes a yarn storing, feeding and measuring device using only one yarn sensor for detecting the withdrawal of one complete turn of yarn at the withdrawal end of the drum. In order to be able to adjust the yarn length to be withdrawn, this prior art device makes use of a drum whose diameter can be mechanically varied. The same concept is disclosed in FR-A-2166332 and PCT-A-WO 82/04446. A mechanical adjustment of the diameter of the drum calls for complicated mechanical means which makes the device costly and liable to malfunctions.

The present invention seeks to improve the device of the above mentioned type so as to give it a simpler, cost-saving structure and a more reliable function without giving up the advantage of adjustability of the yarn length to be withdrawn.

Tnis problem is solved in a device of the type referred to having the characterizing features of Claim 1.

The control device of the yarn storing, feeding and measuring device in accordance with the present invention comprises a storing means for storing information regarding the yarn stopping device actuated at the end of a previous yarn withdrawal cycle. This enables the control device to have information regarding the withdrawal point of the yarn to be withdrawn at the beginning of each withdrawal cycle without requiring a yarn sensor associated to each yarn stopping device. The calculating means determines one yarn stopping device to be actuated next among the plurality of yarn stopping devices on the basis of input information for the calculating means representing the desired yarn length, which can be realized as a simple BCD-switch connected to the calculating means , and on the basis of said stored information regarding the stopping device actuated at the end of a previous yarn withdrawal cycle. This new design enables the device in accordance with the present invention to determine the yarn stopping device to be actuated next without requiring arry additional information regarding the withdrawal of the yarn after releasing the stopping device actuated at the end of a previous withdrawal cycle during the movement of the yarn between said released stopping device and the passing of the yarn through the detection area of the yarn sensor. This principle allows to essentially reduce the number of yarn sensors, as the number of yarn sensors becomes independent from the number of yarn stopping devices.

In accordance with claim 2, the yarn sensing means can be realized as a single yarn sensor resulting in a very simple structure of the device and further resulting in a simple circuit design of the control device as the control device uses one input-and-amplifier circuit for connecting the yarn sensor to the calculating means.

The device as described in claim 3 uses information regarding the stopping device actuated at the end of the previous withdrawal cycle which can be directly used as a basis for the determination of the yarn stopping device to be actuated next. Preferably, this stored information can be a number of the stopping device indicating its angular position with respect to said yarn sensor. Furthermore, it is possible to use the value of the angle between the stopping device and the yarn sensor as the stored information. Based on such stored information, the determination of the stopping device to be actuated next can be carried out by transfonming the desired yarn length into position numbers of the stopping devices, and to determine the stopping device to be actuated next by summing up the number of the stopping device actuated at the end of the previous withdrawal cycle and the number representing the desired yarn length, wherein this sum is reduced by a number corresponding to one complete turn of yarn, ie by the entire number of stopping devices if the sum exceeds said entire number of stopping devices.

Tne calculating means of the preferred device in accordance with claim 4 carries out a very fast and reliable determination of the point of time for actuating the determined stopping device. For thispurpose, the calculating means determines on the basis of the desired yarn length an actuation position of the withdrawal point of the yarn being withdrawn from the storage drum at which the determined stopping device is to be actuated. For having a time basis corresponding to the actual withdrawal speed of the yarn from the storage drum the calculating means measures the period of time between the occurrence of two subsequent pulse signals generated by the yarn sensor. Based on this information, the calculating means is enabled to carry out an estimation regarding the withdrawal point of the yarn being withdrawn from the storage drum with respect to the respective position of each yarn stopping device. The calculating means actuates the determined stopping device as soon as the calcu lated, i.e. estimated momentary position of the withdrawal point equals to said determined actuation position. A fough estimation of said actuation position resulting in the point of time for the actuation of the determined stopping device is sufficient as said determined stopping can be actuated as soon as the withdrawal point of the yarn has passed said stopping device one entire turn of withdrawal before it gets stopped by the stopping device.

An extremely reliable operation of the device can be achieved when designing the calculating means such that it carries out the calculation steps indicated in claim 5 for determining the estimated, momentary position of the withdrawal point of the yarn. At the beginning of each withdrawal cycle the calculated momentary position is set to a value corresponding to the position of the previously actuated stopping device. After releasing the previously actuated stopping device this value is incremented with a pre-determined rate. Preferably, the rate is chosen such that the calculated momentary position slips forward with respect to the actual position of the withdrawal point of the yarn. During incrementing said calculated, momentary position the calculating means repeatedly checks whether the momentary position equals to the position of a yarn sensor or whether the calculated momentary position equals to the actuation position. If the first condition is fulfilled, the calculating means holds the calculated, momentary position and checks whether the yarn sensor generates a pulse signal. By adaptedly choosing the pre-determined rate for the incrementation of the calculated, momentary position, the calculating means only holds the calculated, momentary position and checks whether the yarn störe sensor generates a pulse dignal during a very short period of time, which can be considerεd as a time-window for checking whether the yarn sensor generates a pulse signal. Tnis enables the calculating means to work with high reliability as. Noise peaks which might occur before and after opening and closing the time window are disregarded. As soon as the calculating means receives a pulse signal generated by the yarn sensor, it further prosecutes the calculation with the step of incrementing the calculated, momentary position, as the generation of said pulse signal indicated that the calculated momentary position equals to the real position of the withdrawal point of the yarn. As soon as the momentary position of the withdrawal point of the yarn equals to the actuation position, the calculating means actuates the determined stopping device by supplying it with an actuation current.

By choosing the advantages designed as claimed in claim 6 it is guaranteed that the movement of the stopping element of the determined stopping device has been completed even when making use of relatively slow stopping devices in high-speed yarn storing, feeding and measuring devices which usually withdraw the yarn from the storage drum with a rotational speed of about 10 milliseconds per revolution. More particularly, the actuation position of the withdrawal point of the yarn being withdrawn from the storage drum is determined such that the period of time lapsing during the movement of the withdrawal point of the yarn from said actuation position to the position of the stopping element of the determined stopping device is preferably 1-5 milliseconds greater than the response time of said stopping device, said response time being defined by the time delay between feeding an actuation current to the actuator means of the stopping device and the completing of the movement of the stopping element. In case the response time is in the order of 5 milliseconds, the stopping device will thus be actuated 6-10 milliseconds bεfore the withdrawal point of the yarn arrived at the Position of the stopping element of the determined stopping device.

Claims 4-6 teach how to use a calculated, momentary position of the withdrawal point of the yarn as a basis for timely actuating the determined. stopping device. While, particularly, these claims describe how the calculating means controls the actuation of the determined stopping device to be actuated next by estimating the position of the withdrawal point of the yarn and by periodically correcting said position each time when the yarn sensor generates the pulse signal .

Claims 7-9 include a modified teaching when compared with the teaching of Claims 4-6 in the respect that the calculation of a momentary position of the withdrawal point is replaced by a time- calculation ,. In each of these two cases the calculating means canbe a simple standard microprocessor being adapted to these purposes by a few interface-circuits and by a short program for carrying out the respective calculation.

In accordance with claim 7, the calculating means determines on the basis of the desired yarn length an actuation time defining the period time between releasing the stopping device actuated at the end of a previous withdrawal cycle and actuating the determined stopping device to be actuated next. There is a linear dependency between the desired yarn length and the actuation time, so that the information regarding the desired yarn length can be used as a basis for calculating said actuation time. The calculating means calculates the period of time lapsed. since the releasing or deactivation of said stopping device actuated at the end of the previous withdrawal cycle and periodically corrects this calculation of the period of time on the basis of the respective periods of time between two subsequent pulse signals received from the yarn sensor. By doing so, the calculation of the period of time can be adapted to a varying speed of withdrawing the yarn from the storage drum. In other words, the respective period of time between two subsequent pulse signals serves as a time basis for the calculation of the period of time lapsed since the releasing or deactivation of the stopping device actuated at the end of the previous withdrawal cycle. As soon as the calculated period of time corresponds to the determined actuation time, the calculating means generates an actuation signal for actuating the actuator means of the determined stopping device.

By designing. The calculating means as claimed in claim 8 the calculated period of time lapsed since the releasing or deactivation of the stopping device actuated at the end of the previous withdrawal cycle can be considered as a representation of the momentary position or angular position of the withdrawal point of the yarn being withdrawn from the storage drum. By doing so, the generation of one pulse signal per revolution of the yarn withdrawn from the storage drum is sufficient to generate information regarding the course of the withdrawal point.

When designing the calculating means of the device as claimed in 9, a simple and reliable correction of the calculated time with respect to the period of time between two subsequent pulse signals generated by a yarn sensor is achieved. Preferably, the calculating means is a microprocessor having a memory. One storage cell thereof stores the calculated value representing the calculated period of time. At the beginning of each cycle said value is reset to zero by said calculating means when releasing or deactuating the stopping device actuated at the end of the previous withdrawal cycle. Hereinafter, the calculating means increments said value with a pre-determined rate and periodically checks whether said value equals to the actuation time, or whether said value equals to a pre-set time. This pre-set time is chosen to be a few percent, preferably 10% smaller than the period of time lapsing during the withdrawal of one turn of yarn from the storage drum. Furthermore, the calculating means checks whether said value equals to said pre-set time multi plied by n, n being a whole number greater than zero. By doing so, the calculating means detects whether said value equals to multiples of the period of time lapsing during the withdrawal of one turn of yarn from the storage drum. In case the value equals to the actuation time, the calculating means generates the actuation signal. In case said value equals to a pre-set time or a multiple thereof, the calculating means holds said value and checks whether the yarn sensor generates the next pulse signal. By doing so, the calculating means generates a time-window for checking whether the yarn sensor generates the next pulse signal. This feature reduces the sensitivity of the device with respect to noise peaks, as the signal received from the yarn sensor is only considered during a very small time window during which the pulse is expected to occur. As soon as the pulse is detected ,. the calculating means further prosecutes the calculation with the above mentioned incrementation of said value.

As the calculating means of the devices as claimed in claims 4-9 generate information regarding the momentary withdrawal point of the yarn on the storage drum, the calculating means has also continuous information regarding the momentary length of the withdrawn yarn. This information regarding the momentary length of the withdrawn yarn can be preferably used for controlling further operations of the jet lόom which have to be carried out in dependency from the momentary length of the yarn withdrawn from the storage drum. Preferred devices making use of said information are claimed in Claims 10-12.

Usually, devices for a jet loom have a jet nozzle for inserting the weft yarn during the process of weaving by means of compressed air, wherein the jet of compressed air generated by the jet nozzle can be controlled by means of an electromagnetic valve operable by a driving current for controlling the feeding of compressed air to said nozzle. Usually, the controlling of said electromagnetic valve has been carried out in synchronism with the rotation of the main shaft of the weaving -machine. 3h such a control, the opening of the valve for feeding compressed air to the jet nozzle has to be carried out a relatively long period of time before deactuating the stopping device actuated at the end of the previous withdrawal cycle for guaranteeing that the jet of compressed air has completely established before deactüating said stopping device. Tnis relatively long period of time was neeessary due to the fact that there did not exist a direct synchronism between the operation of the feeding device and the operation of the jet loom. For the same reason, the valve of the jet nozzle is clcsed a relatively long period of time after actuating the next stopping device at the end of the withdrawal cycle. The energy caused for generating compressed air has been essentially increased in recent years so that it has becorae desirable to reduce the consumption of compressed air as far as possible.

Claims 10-12 teach how to use the information regarding the withdrawn length of yam as contained in the calculating means of the devices in accordance wich claims 4-9 for effectively reducing the consumption of compressed air by controlling the electromagnetic valve by means of the calculating means in time-dependency from the actuation of the respective stopping devices.

In accordance with claim 11, the consumption of compressed air can be reduced by closing the valve of the jet nozzle a pre-determined period of time before activating the determined stopping device to be actuated next. By adaptedly choosing said pre-determined period of time the tension of the yarn being withdrawn from the storage drum is essentially reduced shortly before actuating the stopping device. By doing so, the actuation force of the stopping device can be also essentially reduced so that smaller, faster and cheaper stopping devices can be used. By reducing the tension of the yarn shortly before the withdrawal is stopped by an actuated stopping device, it is possible to take care of sensitive and weak yarns.

When carrying out the device in accordance with claim 12, an optimal time-dependency between the respective actuation and deactivation of the stopping devices and between the respective opening and closing of the valve of the jet nozzle is achieved, as the desired tension of the yarn is established by means of the jet of compressed air when deactuating the stopping device actuated at the end of the previous withdrawal cycle and as the tension of the yarn is rapidly reduced shortly before actuating the next stopping device.

When carrying out the device as claimed in claim 13, a very simple and cost-saving design can be achieved.

A further, acvantagesus development of the device is claimed in Claims 14 and 15. In prior art devices the respective yarn stopping element consists of a metal pin. It has tumed out that the sharp edge between the cylindrical wall and the piain, circular upper surface thereof often causes a damaging of the yarn when the yarn is pressed over this sharp edge during deactivation or releasing of said prior art stopping device. Furthermore, the relatively great upper surface of such a pin is liable to stick against a metal core of an electromagnetic. coil serving as an actuator means. The devices in accordance. with claims 14 and 15 overcome these drawbacks of the prior art devices by replacing said metal pin of the yarn stopping element of a metal ball being movably disposed in a radial bore provided in a guiding portion located dose to the withdrawal end of the storage drum. Preferably, the guiding portion is secured to the withdrawal end of the storage drum. Each actuator means comprises an electromagnetic coil being arranged in spaced relationship to said guiding portion so as to define a gap between the guiding portion and the coil. When supplying the coil with the actuation current, the metal ball is attracted by the coil so that the metal ball moves into the gap for stopping the withdrawal of the yarn. Also it is possible to move the metal ball back into the bore by mechanical means after switching off the actuation current, it has tumed out to be a more cost-saving and simple design to use a permanent magnet for this purpose, said magnet being located at one end of said bore.

A preferred embodiment of the present invention will be described hereinafter with reference to the attached drawings.

Figure 1 shows a side view of a device in accordance with the present invention, partially and cross-sectional representation;

Figure 2 shows a front view of the device as shown in Figure 1;

Figures 3 and 4 show details of the device shown in Figures 1 and 2;

Figure 5 shows a circuit diagram of a control device of the device shown in Figures 1-4, and

Figure 6 shows a flow diagram used in a microprocessor of the control device as shown in Figure 5.

Referring now to Figure 1, a feeding device (1) consists of a storage drum (2), a winding-on device (3) or orbiting feeder tube (3) and an electric motor (4). A yarn (F) being supplied to the orbiting feeder tube (3) driven by the electric motor (4) is wound onto the storage drum (2). This storage drum is a stationary storage drum being maintained in a stationary position with respect to its environment by a raagnetic means (not shown here). Devices of this type are known per se in the art. For purposes of the present disclosure, it should be noted that this art is exemplified by US-PS 3776480 and by US-PS 3843153. The feeding device (1) is provided with a storage sensor (5) being located close to the generally cylindrical surface of the storage drum (2). This storage sensor (5) can be a so-called maximum sensor preferably consisting of a light-emitting device and a light sensing device. This storage sensor (5) generates a signal indicating the amount of yarn stored on the drum, i.e. the number of turas of yarn wound onto the drum. Based on this signal, a storage control unit (7) controls the operation of the electric motor (4) in such a way that there is continuously a sufficient amount of yarn available on the yarn storage drum (2). Storage control units (7) are known per se in the art. For purposes of the present disclosure, it should be noted that this art is exemplified by DE-OS 2908743, FR-A-1562223 and PCT / EP83 / 00121 (applicant's own).

As shown in Figure 1, there is disposed a yarn sensing means (6) at the withdrawal end of the storage drum arranged such that the yarn is passing its detection area during withdrawal from the drum (2). This yarn sensing means preferably consists of a single yarn sensor (6) producing pulse signals, each pulse signal indicating that the yarn (F) passes a detection area of the yarn sensor (6). This sensor (6) could also be located in front of the withdrawal end of the storage drum, but has to be arranged such that the yarn is passing its detection area during withdrawal from the storage drum (2). A yarn stopping device (10) located at the withdrawal end of the storage drum (2) consists of an actuator means (11) comprising a plurality of electromagnetic coils (11), a plurality of coil cores (12), each of the electromagnetic coils (11) being wound around a coil core (12) supported of a balloon limiting ring (13) consisting of two U-shaped rings covering said plurality of electromagnetic coils (11). Said balloon limiting ring (13) is fixedly secured to the environment of the feeding device (1), for example, to a base plate thereof. A ring-shaped guiding portion (16) is connected to the withdrawal end of the storage drum (2). Said guiding portion (16) supports a plurality of yarn stopping elements (14), each of said yarn stopping elements (14) consisting of a metal ball (14) being movably disposed in a radial bore (15) provided in the guiding portion ( 16).

As shown in Figures 3 and 4, the respective electromagnetic coils (11) and associated cores (12) are arranged opposite to said bores (15). The balloon limiting ring (13) and the guiding portion (16) define a gap (18) being preferably in the order of 1-2 millimeters. The yarn (F) passes said gap when being withdrawn from the storage drum. A permanent magnet (17) is located at one end of each bore (15) for moving back said metal ball (14) into said bore (15) after switching off an actuation current fed to the respective electromagnetic coils (11). As shown in Figures 3 and 4, bore (15) is attracted by the magnetic force of coil (11) when switching on the actuation current fed to coil (11). The width of the gap (18) corresponds to the radius of the metal ball (15). When the coil (11) is not activated, the permanent magnet (17) will attract the metal ball (14), so that the ball will be completely positioned inside the bore (15), so that the yarn (F) can be freely withdrawn in the axial direction from the storage drum (2).

The magnetic force of each electromagnetic coil (11) is chosen such that this force will overcome the attraction force of the permanent magnet (17) when feeding the actuation current to the coil (11). The metal ball (14) will thereby move outwardly in the radial direction of the bore (15) and come into contact with the free end of the coil core (12). In this condition, approximately half of the metal ball locks the gap (18) for the passageof the yam (F) in such a way that the withdrawal of the yarn (F) from the storage drum (2) is terminated. When switching off the actuation current fed to the coil (11), the tension in the yam (F) being pulled at the beginning of the weft yam insertion co-acts with the magnetic force of the permanent magnet (17) such that the metal ball (14) will return to its starting position so as to come into contact with the permanent magnet (17). As the tension of the yarn co-acts with the magnetic force of the permanent magnet (17) due to the shape of the metal ball (14), the hoidϊng force of the permanent magnet (17) can be relatively low. Hence, only a small portion of the attracting force generated by the electromagnetic coil (11) is required for overcoraing the magnetic force of the permanent magnet (17). For this reason the yarn stopping device (10) in accordance with the present invention is working faster than prior art devices using stopping elements (14) which are needle-shaped or pin-shaped. For further enhancing the Operation of the yarn stopping device (10), a thin plate of non-magnetic material can be positioned at the outer end of the permanent magnet (17) and / or on the free end of the coil core (12) for eliminating a magnetic sticking or "adhesion" between the metal ball (14) and the permanent magnet (17) and / or the coil core (12).

The stopping element (14) can also have the form of a short-cylindrical pin with a piain inner end directed to the permanent magnet (17) and a rounded, preferably semi-spherical outer end.

Referring now to Figure 5, the control device (8) will be hereinafter descibed in detail. The control device (8) comprises a calculating means (20) which is a standard microprocessor. The microprocessor (20) is preferably a microprocessor of the type 8748 manufactured by the "INTEL" Corporation. The yarn sensor (6) is connected to an input (21) of a yarn sensor interface circuit (22). The yam sensor interface circuit (22) essentially consists in an operational amplifier (23) connected through a diode (24) and a resistor (25) in parallel connection to diode (24) to an inverter gate (26), the output thereof being. connected to input pins Nos 1 and 6 of the microprocessor (20). The input terminals of the inverter gate (26) are connected to ground via a capacitor (27). The gain of the operational amplifier (23) can be adjusted by a variable gain control resistor (28) connected to the operational amplifier (23). When a pulse is generated by the yarn sensor (6), it will current-amplified by the operational amplifier (23). The output current of the operational amplifier (23) passes the diode (24) and charges the capacitor (27). When the pulse signal goes back to zero potential, the capacitor (27) is discharged through resistors (25), (29) and (30) to ground. Düe to the switching threshold of the inverter gate (26), only pulses of a pre-determined voltage are detected, so that the yarn sensor inter face circuit (22) disregards small noise voltages. As the capacitor can be quickly charged through diode (24) and is only slowly discharged through resistors (25), (29) and (30), short input pulses are transformεd to longer output pulses as generated by gate (26). Such a broadening of the very short input pulses enables the microprocessor (20) to reliably detect the input pulses.

The microprocessor (20) is supplied with pulse signals generated by a crystal resonator (31) connected to input pins Nos. 2 and 3 of the microprocessor.

A trigg-input (32) receives a signal picked up at the main shaft of the loom. This signal is applied to the input of an opto-electro. nical coupling element (33). the output thereof being connected to pin No. 39 of the microprocessor (20). The trigg-signal serves to synchronize the operation of the loom with the operation of the microprocessor (20) Controlling the yarn storing, feeding and measuring device (1). Mbre particularly, the occurrence of the trigg-signal indicates that the next weft yarn is to be inserted.

A reset input (34) is connected through a reset input interface circuit (35) to input pin No. 5 of the microprocessor (20). Each time the main power of the device is switched on, a reset pulse is fed to the reset input (34) so as to reset the microprocessor (20) for ensuring that the calculation carried out by the microprocessor (20) begins with the first step of the prograrmme.

Input pins Nb. 7, 20 and 25 of the microprocessor (20) are connected to ground.

Pins Nos. 12-19 of the microprocessor (20) are connected through a SIL-resistor network (36) to a +5 volt potential. Said SIL-resistor network (36) consists of eight resistors, each of them connecting one these input pins with the +5 volt potential. Hence, each of the input pins Nos. 12-19 of the microprocessor (20) usually have a potential of +5 volt. Input pins nos. 16-19 are connectable to ground via a so-called DIP switch (37). Input pin No. 19 of the microprocessor (20) is connected to a test-switch (38), wherein the second input terminal of said test-switch (38) is connected to ground. By adaptively setting the DIP-switch (37) and by opening and closing of the test switch (38) a desirεd bit-combination can be fed to input pins Nos. 16-19 of the microprocessor (20) causing the actuation and deactivation of a respective group of stopping devices (10) by switching on or switching off an actuation current fed to their associated electromagnetic coils (11). By doing so, it is possible to check the correct operation of the respective yarn stopping devices. Such a checking can be considered as a test operation of the respective yarn stopping devices.

There is provided a yarn length setting switch (39), preferably consisting of three BCD switches (40-42), each BCD switch (40-42) having four input terminals and one output terminal. Each of the BCD switches can be set to a decimal number from zero-9. This decimal number is converted by the respective BCD switch (40-42) such that the corresponding one of its four input terminals is connected to its output terminal in accordance with the BCD code. When for example setting one of the BCD-switches (40-42) to the decimal number 5, then its first and third input terminal is connected to its output terminal, wherein its second and fourth input terminal is disconnected from the output terminal. The respective first input terms of the 1 BCD switches (40-42) are connected via diodes to input pin No. 12 of the microprocessor (20), the respective second input terminals of the BCD switches (40-42) are connected via diodes to input pin No. 13 of the microprocessor (20), the respective third input terminal of the BCD switches (40-42) are connected via diodes to input pin Nb. 14 of the microprocessor (20) and the respective fourth input terminals of the BCD switches (40-42) are connected via diodes to input pin No. 15 of the microprocessor (20). The respective output terminals of the BCD switches (40-42) are connected to input pins Nos. 36-38 of the microprocessor (20). Due to the proVision of the SIL-resistor network (36), each of the input pins Nos. 12-15 of the microprocessor (20) are-in their normally "high" state. Usually, although the input pins Nos. 36-38 of the microprocessor (20) are in the normally "high" state. For reading the BCD-value of one of the switches (40-42), the microprocessor (20) pulls down the voltage of one of its input pins Nos. 36-38. For example, for reading the BCD-value of BCD-switch (40), the. inicroprocessor sets its input pin No. 36 to zero potential, ie to the "low" logical state. 3h case the decimal number selected by switch (40) is "5" the voltage of input pins Nos. 12 and 14 of the microprocessor (20) will be pulled down to zero potential, ie to the "low" logical state, wherein the logical state of input pins Nos. 13 and 15 remains at "high" logical state.

Reference n-umerai 43 designates a reset line (43) connected through a reset interface circuit (44) to a reset input pin No. 4 of the microprocessor (20). Each time the main. power of the loom is switched on, a pulse signal is fed to the reset line (43) for resetting the microprocessor (20). In other words, this reset line guarantees that the microprocessor begins to carry out the control program with the first step after switching on the main power of the loom.

Output pins Nos. 27-34 of the microprocessor (20) are connected to input pins Nos. 1-8 of an amplifier circuit (45), this amplifier circuit (45) having eight output terminals number 11-18, each of these output terminals being associated to a respective input pin. When receiving an input signal of "high" logical state at its input pins Nos. 1-8, the amplifier circuit (45) connects the corresponding output terminal to a voltage source having a potential of -35 volts. Each of the output terminals Nos. 11-18 of the amplifier circuit (45) is connected to three electromagnetic coils (11). Twenty-four electromagnetic coils (11) associated to twenty-four yarn stopping devices (10) are arranged as a matrix having eight rows and three columns. The respective output terminals of the electromagnetic coils (11) arranged in one column are connected to a respective one of threε output lines (46-48).

Output pins Nos. 22-24 are connected to respective first input terminals of NAND-gates (49-51), the respective second input terminal of these NAND-gates (49-51) being connected to output pin No. 21 of the microprocessor (20). The output terminals of the NAND gates (49-51) are respectively connected through current amplifier circuits (52-54) to a respective pair of input pins Nos. 1-6 of an amplifier circuit (55). This amplifier circuit (55) includes three pairs of output teππ-inais Nos. 11-16, each pair being connectεd to a respective one of the lines (46-48). When receiving a "high" logical signal at one of its pairs of input terminals, the amplifier circuit (55) connects the corresponding pair of output terminals to a voltage source having a +5 volt potential. Due to the above described circuit arrangement, the microprocessor (20) is enabled to energize one of the twenty-four electromagnetic coils (11) by generating a high output signal at one of the output pins Nos. 27-34 determining the row of the coil (11) to be actuated, by generating an enable-signal at its output pin No. 21 and by generating a "high" output signal at one of its output pins Nos. 22-24 selecting the column of the electromagnetic coil (11) to be actuated. The above described matrix-arrangement allows to actuate one electromagnetic coil (11) among the twenty-four electromagnetic coils (11) with only eleven output pins Nos. 22-24, 27-34. The microprocessor (20) generates a strobe signal at its output pin No. 21 causing a periodical switching on and off of the actuation current flowing through the selected one of the electromagnetic coils (11). By strobing the actuation current it is possible to reduce the average power consumption although a high magietic actuation force generated by the selected electromagnetic coil (11) can be maintained due to the high peak-value of the actuation current. It has tumed out that a high magnetic force as generated by the determined electromagnetic coil (11) is only necessary for moving the stopping element (14) into the actuated position. Such a high magnetic force is generated during the first peak of the subsequent row of peaks of the actuation current fed to said coil (11). The average magnetic holding force corresponding to the average level of the subsequent peaks of the actuation current can be chosen to be essentially lower for maintaining the actuated stopping element (14) in the "yarn stop" position. By adaptively choosing the time relationship between "on" and "off" periods of time of the actuation current it is possible to adapt the time-dependency of the magnetic force as generated by the actuation current flowing through the determined electromagnetic coil (11) to the required time-dependency of the actuation force of the corresponding yarn stopping device (10).

Output pin No. 34 of the microprocessor (20) is connected through a current amplifier (56) to a light-emitting element (57), which in turn is connected to ground via a resistor (58). The light-emitting element (57) actuates an opto-sensitive switching element (59) actuating a stop-motion-relay (not shown here) of the weaving machine.

Output pin No. 35 of the microprocessor (20) is connected through a current amplifier (60) to a light-emitting element (61), which in turn is connected via a resistor (62) to ground. The light-emitting element (61) actuates an opto-sensitive switching element (63), which in turn is connected to a relay controlling the operation of the valve of the main jet nozzle of the loom (not shown here).

The amplifier circuit (45) is a standard circuit element of the "UDN 2580A" type. The amplifier circuit (55) is also a standard circuit element of the type "UCN 2002A". Both amplifier circuits are available from "SPRAGUE" Corporation.

Referring now to Figure 6, there is shown a flow diagram of the control programs stored in the read-only memory of the microprocessor (20). When receiving a reset signal, the microprocessor (20) is reset so as to start the carrying out of the program with the first instruction thereof, being the "START" instruction.

At program step No. 1, the microprocessor (20) actuates a pre-determined yarn stopping device (10) for locking the yarn (F) in its start position. Preferably, said stopping device (10) is selected such that its angular position is 180 ° offset with respect to the angular position of the yarn sensor (6). The microprocessor (20) stores the number or the angular position of said stopping device in a pre-determined storage cell of its RAM.

At program step No.2, the microprocessor (20) consecutively reads the BCD-code of the switches representing the desired weft yarn length and stores the corresponding BCD-codes in pre-determined storage cells of its RAM.

At program step No. 3, the microprocessor (20) transfers the BCD-codes representing the desired weft yarn length to a digital value corresponding to the number of revolutions and 1/24 revolutions, wherein this digital value represents the revolutions of the withdrawal point of the yarn during the withdrawal of the desired weft yarn length. It is also possible to express said desired weft yarn length by a value corresponding to the time required for withdrawing said desired weft yarn length.

At program step No. 4, is a waiting routine, causing the microprocessor (20) to await the receipt of a trigg-signal from the weaving machine before going to program step Nb. 5. This waiting routine is realized by a program loop periodically checking whether the trigg-signal occurs. If said condition is fulfilled, the microprocessor continues with the program step No. 5th

At program step No. 5, the microprocessor generates a "high" signal at its output pin No. 35 for actuating the relay controlling the valve of the main jet nozzle in the weaving machine.

At program step No. 6, the stopping device (10) actuated during program step No. 1 is deactuated for releasing the yarn (F). At programs step No. 7, the microprocessor (20) checks whether the yarn passes the yarn sensor by repeatedly checking the logical states of its input pins Nos. 1 and 6. If this condition is fulfilled, the microprocessor (20) continues with program step No. 8th.

At program step No. 8, the microprocessor (20) bεgins with the measuring of the time lapsing since the generation of the pulse signal indicating the passing of the yam through the detection area of the yarn sensor (6).

At program step No. 9, the microprocessor (20) again carries out a waiting loop corresponding to the waiting loop of. programs step No. 7.As soon as the yam has past the yarn sensor (6), microprocessor (20) continues with the program step No. 10th

At program step No. 10, the microprocessor (20) stores the time between two subsequent pulse signal as reeeived from yarn sensor (6). The microprocessor (20) then starts again to measure the time.

At program step No. 11, the microprocessor (20) calculates at which yarn position the main jet nozzle is to be switched off.

At program step No. 12, the microprocessor (20) calculates at which yarn position the stopping device (10) determined during program step No. 3 is to be actuated.

At program step No. 13, the microprocessor (20) calculates the momentary position of the yarn based on the actual yarn withdrawal speed being measured during program step Nb. 10th

At program step No. 14, the microprocessor (20) checks whether the calculated, momentary position of the yarn as determined during program step No. 13 equals to the yarn position determined during program step No. 11. If this condition is fulfilled, the microprocessor (20) continues with program step No. 15. If not, it continues with program step Nb. 16. At program step No. 15, the microprocessor (20) switches off the main jet nozzle by pulling down its output pin No. 35 to zero potential.

At program step No. 16, the microprocessor (20) checks whether the calculated, momentary position of the yarn as determined during program step No. 13 corresponds to the yarn position as calculated during program step No. 12. If so, the microprocessor (20) goes to program step No. 23. Otherwise, it continues with carrying out program step Nb. 17th

At program step No. 17, the microprocessor (20) checks whether the calculated position as determined during program step No. 13 is close to the position of the yarn sensor (6). By doing so, a time window is realized. In case this condition is not fulfilled, the microprocessor (20) goes back to program step No. 13. If it is fulfilled, it continues with program step No. 18th

At program step No. 18, the microprocessor (20) again checks whether the yam past the yarn sensor (6). This program step corresponds to program step No. 7. If this condition is fulfilled, the microprocessor (20) continues with program step No. 19. Otherwise, it continues with program step No. 20th

At program step No. 19, the microprocessor (20) stores the measured time between two subsequent pulse signals as received from yarn sensor (6) and goes back to program step No. 13th

At program step No. 20 is a safety routine for checking whether a yarn breakage occurred. This safety routine is realized by comparing the calculated time with a time threshold which is only exceeded in case of a yarn breakage. In other words, the microprocessor (20) checks whether the measured time lapsed since the last passing of the yarn through the detection area of the yarn sensor (6) exceeds a time threshold. If this condition is not fulfilled, the microprocessor (20) continues with program step No. 18, wherein otherwise it goes to program step No. 21. At prograrrme step No. 21, the weaving machine is stopped since a yarn breakage has occurred. For this purpose, the microprocessor (20) generates a "high" logical potential signal at its output pin No. 34.

At program step No. 22, the microprocessor (20) goes back to the start-instruction of the programs when having received a reset signal.

At program step No. 23, the microprocessor (20) actuates the stopping device (10) for stopping the yarn withdrawal. Furthermore, the microprocessor (20) stores the number of the actuated stopping device in a pre-determined storage cell of its RAM.

At program step No. 24, the microprocessor (20) checks whether the trigg-signal as received at program step No. 4 has disappeared in the meantime. As soon as the trigg-signal disappears, the microprocessor goes to program step No. 25th

At program step No. 25, the microprocessor (20) carries out a program step corresponding to program step No. Second

At program step No ,. 26, the microprocessor (20) carries out a program step corresponding to program step no. 3rd

At program step No. 27 is a waiting routine for repeatedly checking whether a trigg signal is fed to the trigg input (32). Such a trigg-signal indicates that the loom is ready for the insertion of a further weft yarn. As soon as the trigg-signal is generated, the microprocessor (20) goes to program step No. 28th

At program step No. 28, the microprocessor (20) switches on the main jet nozzle of the weaving machine by generating a "high" logical potential signal at ouput pin No. 35.

At program step No. 29, the microprocessor (20) deactuates the stopping device actuated when carrying out the program step Nb. 23. The microprocessor (20) then goes back to program step No. 11. Appendix A enclosed herewith is a machine code or object code programs as stored in the read-only memory of the microprocessor (20). Based on this detailed program the microprocessor (20) is enabled to carry out the control of the feeding device as described with reference to Figure 6.

APPENDIX A

020000000409F1

0200030024C710

100007002496C515358023FF3923F03ABA07545390

10001700749323003480041F746935651625230300

1000270074599AF0BE00362D362D263123003480O0

100037003516863638363865B83342A018FEA01410

100047004A047442B924B11D342BB923A1BE00B9A7

1000570024A12364342BB824A018B000B92DF1AE25

10006700C9F114FBB926A119FEA1743183FB37032B

100077002237ABFC37032237ACBA15BE0004A61EE5

10008700FED28E168C043A24B3230034808A10746F

100097006923037459650065359AFOBE0016A605F5

1000A700EACABA18CCEBD5EAB2BA18ECAE54536523

1000B7007493B833F06218F0AE144A00009AEF4612

1000C700C204906487CCEBD104AE348604A61536FF

1000D700EC36EC6516F8B83342A0FE18A027625537

1000E700AE26E804A616F004D51EFED2F604D524E3

1000F700B31E04DDC8376037182E3770372E838A52

10010700E0809A7FB82E0837530FAF8AE09AFF0076

1001170008374753F04FA08AE09ADF180837530F84

10012700A08A20832EBF08376137F636A7244F6190

10013700972EF72EF7E643376137244B376137E6BB

100147004B61244C1EEF37972E83BE00BF08125F0A

100157002E97672E67EF55832E61672E67EF5583BE

10016700B828F007AOC6678318F007A0C67683B03B

1001770008C8BFFEA7FBA1883625525168583B889

1001870023F0AFBD0AED8C1693EF8A831E2490D51A

10019700AC76A5546C23E16255B5FC16A493FF37E2

1O01A70012B19AFE89FF23F9249E6461158AF09A99

1001B700F0BA0654532301B808B00018B000D7931B

1001C7000036E9D5ACC5FE96D94237033EE6D9D508

1001D70OFC9305B8O8CCEBF2BA18B0AE18B0002340

1001E70001D726E9B832E8ED26EF93EAD9BA18B075

0301F700DA24E324

10020000B830B000B82EF80302A8BC0327AE5437AC

10021000F630A9F047530F692E13002EF6305437ED

10022000F630A9F0530F692E13O02EF63OC8EC0EED

10023000B831A018FEA083A92EAF2E97F72EF72E67

10024000F652F72EF72EF652692E7F2EF652F72E23

10025000F72E8315FAAFE339FF0318E33A27625507

1002600035A5D5FF53FEAFC5166A2583C5FAE33918

09027000FA0318E33A8A10D58361

10030100FEFDFBF7EFDFBF7FFEFDFBF7EFDFBF7FFA

10031100FEFDFBF7EFDFBF7FE3E3E3E3E3E3E3E3CB

10032100E5E5E5E5E5E5E5E5E9E9E9E9E9E9E9E95C

10033100B826F0ABB82CF0AC83B832FOAEC8F0BF41

100341000918C860182E702EEF43B924B11419B1E1

1003510000C9342BB82CA083B8C8E85B0796598331 10036100FF4301AF2301249E566E566E8308F26946 1003710008F2698AFFB8FAE8780837F278C5EA83A3 10038100BA1854536469FB370312F68F04CC9AEF01 1003910004CC3406B82EF0B835A0B82FF0B836A08A 1003 A1003406B82EF0E835D09693B82FF0B836D0C1 0903B1009693B82E5400743A83 AF 00000001FF

Claims

1 CLAIMS:

1. Yarn storing, feeding and measuring device (1), particularly for jet looms, having a stationary storage drum (2) onto which an intermediate yarn store is wound by a winding-on device (3) and from which the yarn (F ) is withdrawn spiraling around the withdrawal end of the storage drum (2), yarn sensing means (6) being arranged such that the yam is passing its detection area during withdrawal from the drum (2), said yarn sensing means (6) producing pulse signals, each pulse signal indicating that the yarn (F) passes a detection area of the yarn sensing means (6), a plurality of yarn stopping devices (10) being arranged at angular intervals around the storage drum (2), said yarn stopping devices (10) consisting of yarn stopping elements (14) and of actuator means (11) moving said stopping elements (14) into and out of the path of the yarn being withdrawn, and an actuator control device (8) adjustable to desired yarn lengthsto be withdrawn, said control device (8) being responsive to sa id pulse signals in such a way that an actuating signal is transmitted to a selected yam stopping device (10) whose angular position corresponds to the position rendered by the yarn when said desired yarn length has been withdrawn, characterized in that said yarn sensing means ( 6) consists of yarn sensors (6), the number thereof being lower than and independent from the number of yarn stopping devices (10), and that said control device (8) comprises storing means (20) for storing an information regarding the yarn stopping device (10) actuated at the end of a previous yarn withdrawal cycle and calculating means (20) for determining one yarn stopping device (10) to be actuated next among the plurality of yarn stopping devices (10) on the basis of an input information for the calculating means (20) representing said desired yarn length and on the basis of said stored information in the order to obtain the desired yarn length.

2. Device as claimed in claim 1, characterized in that the yarn sensing means (6) consists of a single yarn sensor (6).

3. Device as claimed in claim 2, characterized in that the stored information regarding the yarn stopping device (10) actuated at the end of the previous withdrawal cycle indicates the relative angular position of said stopping device (10) with respect to said yarn sensor (6).

4. Device as claimed in one of claims 1-3, characterized in that the calculating means (20) determines on the basis of the desirεd yarn lεngth an actuation position of the withdrawal point of the yarn (F) being withdrawn from the storage. drum (2) at which the determined stopping device (10) is to be actuated, that the calculating means (20) measures the period of time between the occurrence of two subsequent pulse Signals, generated by the yarn sensor (6), that the calculating means calculates the momentary position of the withdrawal point of the yarn (F) being withdrawn from the storage drum (2) with respect to the respective position of each yarn stopping device (10) on the basis of said measured period of time, and that the calculating means (20) actuates the determined stopping device (10) as soon as the calculated momentary position equals tσ said determined actuation position.

5. Device as claimed in claim 4, characterized in that the calculating means (20) carries out the following steps for determining the momentary position of the withdrawal point of the yarn (F):

a) Setting the calculated momentary position to a value corresponding to the position of the previously actuated stopping device (10),

b) Ihcrementing the calculated momentary position with a pre-determined rate and checking whether the calculated momentary position equals to the position of a yarn sensor (6) or whether the calculated momentary position equals to the actuation position,

c) In case the calculated momentary position equals to the position of the yarn sensor, holding the calculated momentary position and checking whether the yarn sensor generates a pulse signal; going back to step d) as soon as the yarn sensor generates said pulse signal, said generation of said pulse signal indicating that the calculated momentary position equals to the real position of the withdrawal point of the yam,

d) In case the momentary position equals to the actuation position, actuating said determinεd stopping device.

6. Device as claimed in claims 4 or 5, characterized in that the actuation position of the withdrawal point of the yarn (F) being withdrawn from the storage drum (2) is determined such that the period of time lapsing during the movement of the withdrawal point of the yarn (F) from said actuation position to the position of the stopping element (14) of the determined stopping device (10) is greatjer than the response time of said stopping device (10), said response time being defined by the time delay between feeding an actuation current to the actuator means (11) of the stopping device (10) and the completing of the movement of the stopping element (14).

7. Device as claimed in one of claims 1-3, characterized in that the calculating means (20) determines on the basis of the desired yarn length an actuation time defining the period of time between releasing the stopping device (10) actuated at the end of the previous withdrawal cycle and actuating the determined stopping device (10) to be actuated next, that the calculating means (20) calculates the period of time lapsed since the releasing or deactivation of said stopping device

(10) actuated at the end of thε previous withdrawal cycle, that the calculating means (20) corrects this calculation of the period of time on the basis of the respective period of time between two subsequent pulse signals received from the yarn sensor (6) , and that the calculating means (20) generates an actuation signal for actuating the actuator means (11) of the determined stopping device (10) as soon as the calculated period of time corresponds to the determined actuation time.

8. Device as claimed in claim 7, characterized in that the calculated period of time lapsed since the releasing or the deactivation of said stopping device (10) actuated at the end of the previous withdrawal. cycle represents an angular position of the withdrawal point of the yarn (F) being withdrawn from the storage drum (2).

9. Device as claimed in claims 7 or 8, characterized in that the calculating means (20) carries out the following steps for calculating the period of time lapsed sincε the releasing or deactivation of said stopping device (10) actuated at the end of the previous withdrawal cycle:

a) Resetting a value to zero when releasing or deactivating the stopping dev ice (10), said valuε representing said calculated period of time,

b) Incrementing said value with a pre-determined rate and checking,

bi) Whether said value equals to the actuation time or

bii) Whether said value equals to a pre-set time being chosen such that it is a few percent, preferably 10%, smaller than the period of time lapsing during the withdrawal of one turn of yarn (F) from the storage drum (2 ) or whether it equals to said pre-set time multiplied by n, n being a whole number greater than zero,

c) In case condition bi) is fulfilled generating the actuation signal, d) In case condition bii) is fulfilled holding said value being equal to the pre-set time or to a whole multiple thereof,

e) Then checking whether the yarn sensor (6) generates the next pulse signal, and

f) Going back to step b) as soon as condition e) is fulfilled.

10. Device for a jet loom having a jet nozzle for inserting the weft yam during the prccess of wεaving by means of compressεd air, wherein the jet of compressed air generated by the jet nozzle can be controlled by means of an electromagnetic valve operable by a driving current for controlling the feeding of compressed air to said nozzle, as claimed in one of claims 4-9, characterized in that the calculating means (20) is electrically connected to said valve for Controlling the opening and closing thereof in time-dependency from the actuation of the respective stopping devices (10).

11. Device as claimed in claim 10, characterized in that the calculating means (20) is arranged to open said valve a pre-determined period of time before deactivating the stopping device (10) actuated at the end of a previous yarn withdrawal cycle and to dose said valve a pre-determined period of time before activating the determined stopping device (10) to be actuated next.

12. Device as claimed in claim 11, characterized in that said pre-determined period of time corresponds to the response time of said valve and said jet nozzle, said response time being defined by the time delay between feeding the driving current to said electromagnetic valve and the point of time at which the jet of compressed air has completely established.

13. Device as claimed in one of Claims 1-12, characterized in that the calculating means (20) is a microprocessor (20).

14. Device as claimed in one of claims 1-13, characterized in that each yam stopping element (14) consists of a metal ball (14) being movably disposed in a radial bore (15) provided in a guiding portion (16) located close to the withdrawal end of the storage drum (2), that each actuator means (11) comprises an electromagnetic coil (11) being arranged in spaced relationship to said guiding portion (16) so as to define a gap (18) between the gαding portion (16) and the coil (11), and that the metal ball (14) is attracted by the coil when supplying the coil (11) with the actuation current so that the metal ball (14) moves into the gap (18 ) for stopping the withdrawal of the yarn (F).

15. Device as claimed in claim 14, characterized in that there is provided a permanent magnet (17) located at one end of said bore (15) for moving back said metal ball (14) into said bore (15) when the actuation current is switched off.