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(11) | EP 1 314 806 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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A control method and system for weft-braking devices for automatically adjusting the mechanical tension of the yarn in weaving maschines Verfahren und Vorrichtung zur Steuerung von Schussfadenbremsvorrichtungen zum automatischen Einstellen der Fadenspannung in Webmaschinen Méthode et dispositif de contrôle pour dispositifs de freinage de trame pour régler automatiquement la tension du fil dans les métiers à tisser |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to a control method and system for electrically-operated weft-braking devices, for automatically adjusting the mechanical tension of the yarn in weaving machines using mechanical picking.
[0002] More particularly, the invention relates to systems for automatically adjusting the mechanical tension of the yarn fed to weaving machines, in which the weft is gripped and inserted into the shed by mechanical means. Such machines include, among others, gripper looms and projectile looms, while fluid-jet weaving machines are outside the field of the invention.
[0003] As well known in weaving processes, the weft yarn is fed to the loom from the reel via a weft feeder provided with a manual-adjustment entry brake and then through at least an electrically operated weft-braking device; both braking devices being arranged between the reel and the loom.
[0004] Prior automatic-adjustment systems have been developed for controlling the electrically operated weft-braking devices, in order to achieve the following objects:
- keeping the mechanical tension of the yarn substantially constant during the weaving process independently of: a) changes of the reel geometry during its progression from the full configuration to the empty configuration, b) different configurations selected for said entry brake of the weft feeder, c) different angles of the weft yarn in the path between the reel and the loom, d) wear of the braking members;
- assuring that the mechanical tension of the weft yarn has an adequate strength during particular transient instants of the weft-picking process, typically during the gripping step, during the step in which the weft yarn is transferred from the holding grippers to the pulling grippers, and during the arrival step of the yarn,
- assuring that, during the entire process of weft insertion, the value of the mechanical tension of the yarn does not reach excessive levels, which, if exceeded, would cause the yarn to break at its weaker points.
[0005] To this purpose, the above mentioned automatic-adjustment systems act upon the electronic control of the weft-braking device by means of an adjustment loop which, as will be disclosed below, uses a signal measuring the actual tension of the yarn -- as generated by a measurement sensor -- as a feedback signal of the loop, whose reference is a predetermined signal corresponding to the tension that is desired for the yarn. The former signal is subtracted from the latter in order to obtain an error signal, and then the error signal is processed by logic means (PID-type logic block) in order to obtain a correction signal such that it will cancel the error. This correction signal will cause the weft brake to exert a braking action of a proportional intensity, via appropriate power circuits. Said correction signal will also be called "braking action" in the following disclosure.
[0006] EP 0 619 261 discloses a tension regulator device of the above kind. However, only one tension reference is allowed over the entire weft-picking cycle, and it is therefore impossible to establish different reference tension values for different stages in the cycle.
[0007] However, the curve of the signal corresponding to the actual tension of the weft yarn (which is drawn with thin lines in Fig. 3) as a function of the angular position (in degrees) of the main shaft of the weaving machine (which is fed by an assembly comprising the weft feeder and a weft-brake with overlapping laminae) clearly shows that said signal, which is obtained by controlling the weft brake by said known adjustment loop, is subjected to continuous fluctuations at high frequency.
[0008] Such fluctuations are generated by the variations of the above mentioned parameters of the weaving process (geometry of the reel, wear of the braking members, path of the yarn etc.) and destabilize the action of the adjustment loop. Therefore, an accurate control of the yarn tension and a proper performance of the weaving process are not attained, also because they undergo unforeseeable changes from one picking stroke to the next.
[0009] US 5 669 421 deals with a control method for regulating the tension of a yarn such as a weft in a weaving loom. In the method, the tension of the yarn is measured at closely spaced points in a weft-picking cycle, and homologous samples in successive cycles are averaged and compared with a control characteristic, which is progressively adapted or refined on the basis of the events. The method involves handling huge amounts of data in real time, and the feedback algorithm appears to be nonlinear.
[0010] The main object of the present invention is to improve the method for measuring the actual mechanical tension of the weft yarn and the weft-brake control system, in order to avoid said rapid fluctuations of the tension signal and prevent the ensuing operating instabilities of the adjustment loop controlling the excitation current of the weft braking device, whithout unduty increasing the cost and complexity of the control system.
[0011] This object is achieved, according to the present invention, by means of a method and system having the features recited in the attached claims.
[0012] Substantially, this invention is based on the concept of employing, in order to measure the direct tension of the yarn (which generates the feedback signal of the weft-brake adjusting loop), an average value rather than the instantaneous value of the tension, which average value is computed at predetermined intervals of the weft picking and for a predetermined number of picking strokes, so that it is substantially stable and not affected by said rapid fluctuations.
[0015] The features, objects and advantages of the method and system according to the present invention will appear from the following detailed description and with reference to the attached drawing, given by way of non limiting example, wherein:
- Fig. 1 is a block diagram of a system for feeding the weft yarn to a mechanical-picking loom with a weft-brake adjustment loop according to the prior art,
- Fig. 2 is a block diagram of a feeding system, similar to Fig. 1, which is improved according to the invention,
- Fig. 3 is a diagram comparing the yarn tensions obtained by the adjustment system of Fig. 1 with the tensions obtained by the improved system of Fig. 2, said tensions being given as a function of the angular position of the weaving machine.
[0016] With reference to Fig. 1, SAL is a known system for feeding a weft yarn F to a mechanical picking loom TE. The system comprises a reel RO on which weft yarn F is wound, a weft feeding device P, a weft brake LF, e.g. of a type having overlapping laminae as described in EP 622.485, which is interposed between feeder P and loom TE, and a sensor TM for directly measuring the value of the mechanical tension T of yarn F; said sensor being arranged downstream of brake LF. As known per se, feeder P comprises a cylinder TA on which a swivelling arm BR, operated by a motor MO, winds and restores a plurality of yarn loops, forming a weft reserve RT. On request of loom TE, at each weft insertion the yarn loops are unwound from cylinder TA an run through a yarn guide GA.
[0017] Similarly, as known per se, weft brake LF comprises a stationary lamina and a movable lamina, between which runs yarn F, and an electromechanical actuator MF. The latter is driven by an excitation current, modulated by the signal generated by sensor TM to push the movable lamina against the stationary lamina with more or less force, thereby adjusting the braking effect, i.e. the braking action AF exerted on yarn F.
[0018] To this purpose, sensor TM generates a signal tens-mis which substantially represents the feedback signal of loop A controlling weft brake LF. Such control loop comprises a subtracting logic block 1 in which signal tens-mis is subtracted from a reference signal tens-rif representing the desired value of the mechanical tension of weft yarn F. Accordingly, the output of subtractor 1 is an error signal error representing the difference between the reference tension and the tension measured at the instant under consideration.
[0019] Signal error is applied to the input of a known PID regulator 2, where an correction brake-reference signal fren-ref is computed, such as to cancel signal error. Signal fren-ref generates, by means of a logic block 3 and a power circuit DRV, an excitation current Ie causing brake LF to apply a braking action AF substantially proportional to said signal fren-ref. The loop is preferably closed by an additional feedback signal fren-info (e.g. consisting of a fraction of current Ie) which is sent to logic block 3.
[0020] With reference to Fig. 2, in which similar or corresponding items bear the same reference number, the improvement according to the invention will now be described. This improvement consists of subdividing the period of weft picking into predetermined and modifiable intervals x, e.g. given as rotation angles of the main shaft of loom TE (Fig. 3), as specified below:
- 1st interval in the range 70° to 100°, corresponding to the weft gripping step,
- 2nd interval, contiguous to the first, in the range 100° to 160°, corresponding to a step in which the weft is brought into the shed by the holding grippers,
- 3rd interval, contiguous to the second, in the range 160° to 200°, corresponding to a step in which the weft yarn is transferred from the holding grippers to the pulling grippers,
- 4th interval, contiguous to the third, in the range 200° to 280°, corresponding to a step in which the weft is brought into the shed by the pulling grippers,
- 5th and last interval, in the range 280° to 320°, corresponding to the end of weft-picking.
[0021] Obviously, the number of intervals x into which the insertion period is subdivided, as well as their angular amplitudes are not limitative and the values specified above are merely illustrative.
[0022] Moreover, according to the present invention and as shown in Fig. 2, braking reference values RFx are also defined for each of angular intervals x, where x is in the range 1 to n, n being the number of subdivision intervals (e.g. n = 5 in the illustrative example). Each of such references constitutes the desired value of the average braking acting on yarn F, in the corresponding x-th interval.
[0023] By the method according to the invention, the average tension corresponding to each interval x during picking is computed, so that a set of average values Tmxi is obtained, where "i" is the number of picking strokes considered. In addition to the average values of the current insertion (Tmxo), the machine controller, as further described below, also stores the average tension values corresponding to the last m picking strokes, where m is preferably in the range 0 (zero) to 7. In the example of Fig. 2, m is in the range 0 to 3, where the value 0 denotes a picking stroke under way.
[0024] To this purpose, operative logic block 1, comprising the above mentioned machine controller, computes the values Tmxi based on the instantaneous value of the tension tens-mis and the instantaneous value of the angular position tel-pos of the main shaft of loom TE, which is delivered by an angular sensor SA associated with the shaft. Moreover, at each picking stroke, a subsequent logic block 2 computes the average value TMx corresponding to the average of all previous values Tmxi corresponding to each interval x, as follows:
[0025] Furthermore, logic block 3 compares each braking reference value RFx with the average value TMx of the corresponding interval x and, based on the error resulting from such comparison, decides, as known per se, a braking action AFx (such as to cancel the error) that brake LF shall apply during the entire braking interval x for the next picking. Following this step, logic block 4 switches, as a function of the angular position tel-pos of the shaft of loom TE, the value AFx at output fren-ref. The latter signal, by means of logic block 5 and power circuit DRV, generates an excitation current Im which will energize brake actuator MF so that a corresponding braking action AFx is generated.
[0026] In the diagram of Fig. 3, the curve drawn with a fat line shows the values of the mechanical tension detected in the weft yarn and processed by the method using computed average values, according to the invention, over predetermined angular intervals x; such curve has no high-frequency fluctuations or variations.
- measuring instantaneous values of the yarn tension at successive points of each weft insertion;
- averaging, for each insertion period of the weaving machine, the yarn tension samples (tens_mis) over each of a plurality of predetermined intervals (x) of the insertion period to obtain a corresponding plurality of tension values (Tmxi) for each insertion;
- averaging each of said tension values (Tmxi) over a predetermined number of successive insertions as a running average to obtain a corresponding time-averaged tension value (TMx);
- comparing each of the time-averaged tension values (TMx) with a respective predetermined reference value (RFx) corresponding to the desired yarn tension in the respective interval, so that a respective error signal (AFx) is generated; and
- computing a correction signal (fren_ref) for a feedback loop controlling the weft-braking device (LF) so that the error is canceled.
a) first logic means (1)connected to said yarn tension sensor (TM) to receive instantaneous yarn tension samples (tens_mis) from it, connected to an angular sensor (SA) to receive instantaneous position signals (tel_pos) of a weft-insertion member of the weaving machine (TE), the first logic means being arranged to:
- average the samples over each of a plurality of predetermined intervals (x) of the insertion period, thereby generating a corresponding set of tension values (Tmxi) for each of a predetermined number of successive insertions (i); and
- repeat the averaging for each subsequent insertion (i) and substitute the resulting new set of tension values for the set corresponding to the earliest of said predetermined number of successive insertions (i);
b) second logic means (2) connected to receive said tension values (Tmxi) from said first logic means (1) and arranged to compute the averages of corresponding tension values from each of said sets to obtain one set of averaged tension values (TMx);
c) third logic means (3) for individually comparing each of said set of averaged tension values (TMx) with each of a corresponding set of braking reference values (RFx) to yield a set of error values (AFx);
d) fourth logic means (4) receiving said error values (AFx) from said third logic means (3) and said instantaneous position signals (tel_pos)from said angular sensor (SA) and switching each of said set of error values (AFx) to said brake-driving means (5, DRV) depending on the instantaneous position of said weft-insertion member of the weaving machine (TE).
- Messen von Momentanwerten der Fadenspannung an aufeinanderfolgenden Punkten eines jeden Schusseintrags;
- Mitteln der Fadenspannungswerte (tens-mis) für jede Eintragzeitspanne der Webmaschine über jedes einer Vielzahl von vorbestimmten Intervallen (x) der Eintragzeitspanne, um eine entsprechende Vielzahl von Spannungswerten (Tmxi) für jeden Eintrag zu erhalten;
- Mitteln jedes Spannungswerts (Tmxi) über eine vorbestimmte Anzahl von aufeinanderfolgenden Einträgen als einen laufenden Mittelwert, um einen entsprechenden zeitlich gemittelten Spannungswert (TMx) zu erhalten;
- Vergleichen jedes zeitlich gemittelten Spannungswerts (TMx) mit einem jeweiligen vorbestimmten Referenzwert (RFx), der der erwünschten Fadenspannung in dem jeweiligen Intervall entspricht, um ein jeweiliges Fehlersignal (AFx) zu erzeugem; und
- Berechnen eines Korrektursignals (fren_ref) für eine die Schussfadenbremsvorrichtung (LF) steuernde Rückkopplungsschleife, um den Fehler zu eliminieren.
a) eine erste Logikeinrichtung (1), die mit dem Fadenspannungssensor (TM), um von diesem Momentanfadenspannungswerte (tens_mis) zu erhalten, und mit einem Winkelsensor (SA) verbunden ist, um Momentanpositionssignale (tel_pos) eines Schusseintragelements der Webmaschine (TE) zu erhalten, wobei die erste Logikeinrichtung dazu angeordnet ist, um:
- die Werte über jedes Intervall einer Vielzahl vorbestimmter Intervalle (x) der Eintragzeitspanne zu mitteln, um dadurch eine entsprechende Gruppe von Spannungswerten (Tmxi) für jeden Eintrag einer vorbestimmten Anzahl aufeinanderfolgender Schusseinträge (i) zu erzeugen; und
- die Mittelung für jeden nachfolgenden Eintrag (i) zu wiederholen und diejenige Gruppe, die der frühesten der vorbestimmten Anzahl aufeinanderfolgender Einträge (i) entspricht, durch die resultierende neue Gruppe von Spannungswerten zu ersetzen;
b) eine zweite Logikeinrichtung (2), die verbunden ist, um die Spannungswerte (Tmxi) von der ersten Logikeinrichtung (1) zu erhalten, und dazu angeordnet ist, Mittelwerte entsprechender Spannungswerte von jeder der Gruppen zu berechnen, um eine Gruppe gemittelter Spannungswerte (TMx) zu erhalten;
c) eine dritte Logikeinrichtung (3) zum individuellen Vergleichen jeder Gruppe gemittelter Spannungswerte (TMx) mit jedem Bremsreferenzwert einer entsprechenden Gruppe von Bremsreferenzwerten (RFx), um eine Gruppe von Fehlerwerten (Afx) zu gewinnen;
d) eine vierte Logikeinrichtung (4), die die Fehlerwerte (AFx) von der dritten Logikeinrichtung (3) und die Momentanpositionssignale (tel_pos) von dem Winkelsensor (SA) erhält und jeden Fehlerwert der Gruppe von Fehlerwerten (AFx) dem Bremsantriebsmittel (5, DRV) vermittelt in Abhängigkeit von der Momentanposition des Schusseintragelements der Webmaschine (TE).
- mesurer les valeurs instantanées de la tension du fil aux différents points d'insertion de la duite,
- pour chaque période d'insertion du métier à tisser, calculer la moyenne des échantillons de mesure de la tension de la duite (tens_mis) pour chacun des intervalles (x) prédéterminés de la période d'insertion afin d'obtenir les valeurs de tension (Tmxi) qui correspondent à chaque insertion,
- sur un nombre prédéterminé d'insertions successives, calculer la moyenne de chacune desdites valeurs de tension (Tmxi) qui servira de moyenne de fonctionnement afin d'obtenir une moyenne des valeurs de la tension en fonction du temps (TMx),
- comparer chacune des moyennes des valeurs de tension en fonction du temps (TMx) avec leurs valeurs de référence respectives prédéterminées (RFx) qui correspondent à la tension du fil souhaitée au sein de l'intervalle respectif, de manière à obtenir des signaux d'erreurs respectifs (AFx), et
- calculer un signal de correction (fren_ref) pour une boucle de rétroaction qui commande le dispositif de freinage de la duite (LF), pour ainsi éliminer l'erreur.
a) un premier moyen logique (1) relié audit capteur de tension du fil (TM) qui permet de recevoir instantanément l'échantillon de mesure de la tension de la duite (tens_mis), relié à un détecteur d'angle (SA) qui permet de recevoir les signaux de position instantanée (tel_pos) d'un élément d'insertion de duite du métier à tisser (TE), le premier moyen logique étant conçu pour :
- calculer la moyenne des échantillons pour chacun des intervalles prédéterminés (x) de la période d'insertion, pour ainsi générer un ensemble de valeurs de tension (Tmxi) pour chacune des insertions successives (i) dont le nombre est prédéterminé et
- recalculer la moyenne pour chacune des insertions (i) ultérieures et substituer le nouvel ensemble de valeurs des tensions obtenu par l'ensemble qui correspond à la première desdites insertions successives (i) dont le nombre est prédéterminé,
b) un deuxième moyen logique (2) raccordé pour recevoir lesdites valeurs de tension (Tmxi) dudit premier moyen logique (1) et agencé pour calculer les moyennes de valeurs de tension correspondantes pour chacun desdits ensembles afin d'obtenir un ensemble des valeurs de tensions moyennes (TMx),
c) un troisième moyen logique (3) qui permet de comparer individuellement chaque valeur desdits ensembles des valeurs de tensions moyennes (TMx) à chaque valeur de l'ensemble correspondant de valeurs de référence de freinage (RFx) afin d'obtenir un ensemble des valeurs d'erreur (AFx),
d) un quatrième moyen logique (4) qui reçoit lesdites valeurs d'erreur (AFx) dudit troisième moyen logique (3) et lesdits signaux de position instantanée (tel_pos) dudit détecteur d'angle (SA) et qui permet d'envoyer chacune desdites valeurs d'erreur (AFx) à ladite commande de frein (5, DRV) en fonction de la position instantanée dudit élément d'insertion de duite du métier à tisser (TE).