EP1314806A2

EP1314806A2 - A control method and system for weft-braking devices for automatically adjusting the mechanical tension of the yarn in weaving maschines

Info

Publication number: EP1314806A2
Application number: EP02013025A
Authority: EP
Inventors: Pietro Zenoni; Luca Gotti
Original assignee: LGL Electronics SpA
Current assignee: LGL Electronics SpA
Priority date: 2001-07-25
Filing date: 2002-06-13
Publication date: 2003-05-28
Anticipated expiration: 2022-06-13
Also published as: EP1314806A3; DE60216713D1; EP1314806B1; CN100439582C; CN1399022A; ITTO20010737A0; DE60216713T2; ITTO20010737A1

Abstract

An improved method for controlling electrically operated weft-braking devices, capable of automatically adjusting the mechanical tension of the weft yarn (F) in mechanical-picking weaving machines (TE), is disclosed herein. The excitation current (Ie) of the weft-braking device (LF) is controlled by an adjustment loop (A) using a signal (tens-mis), which is a measure of the actual tension of the yarn, as a feedback signal for the adjustment loop (A). The improvement comprises employing an average value (TMx), which is computed at predetermined intervals (x) of weft picking and for a predetermined number (i) of picking strokes, in order to measure the direct tension of the thread (F), so that said average value (TMx) is substantially stable and not affected by fluctuations due to variations of the parameters of the weaving process.

Description

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.
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.
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.
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.

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.
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.
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.
The present invention is directed to remove such drawback.
In particular, 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.
This object is achieved, according to the present invention, by means of a method and system having the features recited in the attached claims.
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.
Accordingly, the method of the invention consists of:

subdividing the overall time of weft picking in several intervals, e.g given as predetermined and modifiable rotation angles of the main shaft of the weaving machine,
setting, for each one of such intervals, predetermined reference values (which are modifiable) of the average yarn braking that is desired for said interval,
computing, during the insertion, the average tension corresponding to each interval by considering all the average values of the tension for each picking stroke,
computing, from the average values of each i-th picking stroke, the average value corresponding to the interval under consideration,
comparing each predetermined reference value with the corresponding measured average value so that an error signal and then a corresponding correction signal is obtained, which is used to produce a braking action that will cancel the error.

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.

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.
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.
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 tensrif 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.
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.
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.

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.
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.
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.
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:
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.
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.
Obviously, the implementation details can be changed extensively from what has been described and illustrated by way of non limitative example, without thereby leaving the scope of the invention.

Claims

A method for controlling electrically operated weft-braking devices, capable of automatically adjusting the mechanical tension of the weft yarn (F) in mechanical-picking weaving machines (TE), in which the excitation current (Ie) of the weft-braking device (LF) is controlled by an adjustment loop (A) using a signal (tens-mis) which is a measure of the actual tension of the yarn, as a feedback signal for the adjustment loop (A), characterized in that it consists in assuming an average value (TMx), computed at predetermined intervals (x) of weft picking and for a predetermined number (i) of picking strokes as a measure of the direct tension of the yarn (F), so that said average value (TMx) is substantially stable and unaffected by fluctuations due to variations of the parameters of the weaving process.
The method of claim 1, characterized in that it consists of:

subdividing the overall time of weft picking in predetermined and modifiable intervals (x),

setting, for each of such intervals (x), predetermined reference values (RFx) (which are modifiable at will) of the average yarn braking that is desired for said interval,

computing, during the insertion, the average tension (Tmxi) of the yarn (F) corresponding to each of the intervals (x) which are defined by considering a set (TMxi) of the average values of tension for each picking stroke,

computing, from the average values (TMxi) of each i-th picking stroke, the average value (TMx) corresponding to the considered interval (x),

comparing each predetermined reference value (RFx) with the corresponding measured average set of average values (TMx) to produce an error signal, and

computing an correction signal which is used to produce a braking action (AFx) that will cancel said error.
The method of claim 2, characterized in that said weft-picking period is subdivided into angular intervals (x) which are given as rotation angles of the main shaft of the weaving machine (TE).
The method of claim 3, characterized in that said weft-picking period is subdivided into five intervals (x1...x5) respectively corresponding to: a weft gripping step, a step in which the weft is brought into the shed by the holding grippers, a step in which the weft yarn is transferred from the holding grippers to the pulling grippers, a step in which the weft is brought into the shed by the pulling grippers, a final step of weft-picking.
A system for controlling electrically operated weft-braking devices (LF), capable of automatically adjusting the mechanical tension of the yarn in mechanical-picking weaving machines, characterized in that it comprises a sensor (TM) for measuring the mechanical tension of the yarn (F), and first functional logic means (1) capable of computing a series of average values (Tmxi) of the tension in corresponding intervals (x) in which the period of weft insertion is subdivided, in order to obtain a set (TMxi) of average tension values for each picking stroke (i), and second functional logic means (2 and 3) capable of comparing single braking reference values (RFx), which are predetermined and modifiable at will, with the corresponding measured average value (TMx), obtaining an error signal and a corresponding signal (AF) of braking action that further logic means (4, 55, DRV) turn into an excitation current (Ie) for the actuator (MF) of the electrically-controlled weft-brake causing the weft brake to exert said braking action.
The system of claim 5, characterized in that said first functional logic means (1) compute said average values (Tmxi) of the yarn tension (F) based on the instantaneous value of the tension (tens-mis) supplied by said sensor (TM) and on the instantaneous value (tel-pos) of the corresponding angular position of the main shaft of the loom (TE), which is supplied by a further angular sensor (SA) of said shaft.