Method for braking a weft thread of a weaving machine

Abstract

In accordance with the invention a method (1) for braking a weft thread (2) of a weaving machine (3), in particular of a jet weaving machine (3) is provided, in said method a braking element (4) is brought into contact with the weft thread (2) and the braking element (4) is moved via a control device (5) by means of a drive (6). In this arrangement, during a weft thread insertion (7) a first measurement value (8) of a movement parameter (9) of the weft thread (2) is determined, a first estimate value (10) for the movement parameter (9) is estimated on the basis of the first measurement value (8) and a correction value (11) is determined from it. The movement parameter (9) of the weft thread (2) is then corrected on the basis of the correction value (11).

Description

The invention relates to a method for braking a weft thread of a weaving machine and to a weaving machine for carrying out the method.

It is known to use so-called ABS brakes in jet weaving machines, in particular in air jet weaving machines, for the controlled braking of the weft thread. In the context of this application, ABS stands for the automatic weft thread braking device. The goal in this case is, among other things, to avoid an over-stressing of the weft thread, which is caused in particular by the abrupt braking of the weft thread, e.g. by the stopper pin of the thread store. The ABS brake is realized e.g. in the form of a movable hoop with at least one deflection point for deflecting the thread. The braking force is influenced by a weft thread deflection which is caused by the braking hoop. The hoop is mainly rotatably journalled and is in active contact with a drive, e.g. with a magnetic coil, or with an electric motor, with the drive being connected in a signal transmitting manner to a suitable control system for control and/or regulation.

In the context of the present application the measurement of a physical movement parameter of the weft thread, such as for example the measurement of a thread tension or thread tension in the weft thread, can be understood to mean either a direct measurement, for example by means of a sensor such as a pressure sensor, or the indirect measurement of a movement parameter, which can be a derived parameter, such as for example the speed of the weft thread. By way of example, the speed of the weft thread can be measured only indirectly via the measurement of the path change of the weft thread within a time change. When a measurement is spoken of in the following, both the direct and the indirect measurement are meant.

In an air jet weaving machine in accordance with EP 0 548 185 a control device is disclosed which calculates the parameters for the control of the weft thread brake of the current weft thread insertion on the basis of the data of at least one or more previous weft thread insertions. This means that an average value of a movement parameter is determined over one or more weft insertions, from which a regulation parameter for a movement parameter of the weft thread, for example for braking the weft thread, is determined for a subsequent weft insertion.

The disadvantage of this method is evident: the reaction time of the system to changes in the boundary conditions of the weft thread insertion is relatively long, since one or more weft thread insertions must always have taken place before the control device can adapt the parameters for a subsequent weft insertion. In addition, brief disturbances, that is, disturbances which arise individually during a specific weft insertion can not be acted on immediately, since only average values over a plurality of weft insertions can ever be taken into consideration. If, for example, the control device calculates the parameters for the third weft thread insertion on the basis of two weft thread insertions, it then also consequently takes two weft thread insertions until the control device can react to a change. This dead time in the reaction of the control device is, as already stated, in particular very disadvantageous in the case of suddenly arising disturbances.

The object of the invention is thus to propose a jet weaving machine as well as an improved method for the weft thread insertion which avoids the features which are known from the prior art, so that the weft thread insertion is optimized.

The subjects of the invention which satisfy this object with regard to the method and apparatus are characterized by the features of the independent claims 1 and 10. The subordinate claims relate to particularly advantageous embodiments of the invention.

Thus in accordance with the invention a method for braking a weft thread of a weaving machine, in particular of a jet weaving machine, is provided, in said method a braking element is brought into contact with the weft thread and the braking element is moved via a control device by means of a drive. In this arrangement, during a weft thread insertion, a first measurement value of a movement parameter of the weft thread is determined, a first estimate value for the movement parameter is estimated on the basis of the first measurement value, and a correction value is determined from it. The movement parameter of the weft thread is then corrected on the basis of the correction value.

Thus, in accordance with the invention, the correction value for the correction of the movement parameter is determined as follows: at a first point in time a movement parameter, for example the speed of the weft thread, is measured. From this measurement the predicted value, for example the predicted value of the speed of the weft thread, can be extrapolated to a specific later point in time, at which the movement parameter is to be corrected with the thread brake, so that a value for the correction parameter can be estimated for the correction of the movement parameter at the later second point in time.

In this arrangement the invention admittedly relates preferably to a method for braking a weft thread of a jet weaving machine, but is in principle not restricted to jet weaving machines. Rather, the invention relates to a method which can likewise advantageously be carried out in an analogous manner in other weaving machines, such as e.g. in a rapier weaving machine or in a projectile weaving machine.

The correction of the movement parameter, for example of the speed, which means the momentary speed of the weft thread, by means of the thread brake is accomplished in the methods which are known from the prior art in that a specific dynamic parameter of the weft thread, e.g. the thread tension or the speed of the weft thread, is measured over a plurality of weft insertions, and a correction parameter is then calculated from the thus won data by forming a suitable average value, with the aid of which a movement parameter, e.g. the speed of the weft thread, is then influenced during a successive weft insertion by means of the thread brake.

The reason why recourse is had in the prior art to an average value which is formed from a plurality of previous weft insertions for influencing a successive weft insertion is that it is in fact not even possible to measure a movement parameter at a given point in time and to influence the weft thread movement appropriately at the same point in time as a consequence of the result of the previously named measurement, e.g. via the thread brake. This is due, among other things, to the enormous speed at which the weft thread is inserted in the operating state. If the weaving machine for example is operated at a speed of rotation of 1000 rpm, then the momentary speed of the weft thread can easily reach several hundred m/s.

This means that if, for example, the thread speed is measured at a specific point in time, the measurement must be evaluated accordingly and a correction value determined from the measurement value of the measurement, with the aid of which a braking force can then, for example, be exerted on the thread through a suitable control of the thread brake. Thus, between the point in time at which a momentary value of the movement parameter, such as for example the momentary speed of the weft thread, is measured, up to the point in time at which a correction of the movement parameter would be possible at the earliest as a result of this measurement, as a result of the inertia of the entire arrangement, a not inconsiderable time always elapses in comparison with the high speed of the weft thread.

If, for example, at a first point in time the speed or the thread tension of the weft thread is measured then, as a result of this measurement, it can be determined whether the movement parameter at this point in time corresponds to a specific desired value or deviates from it. If a specific deviation is determined by the measurement, then, as a result of the magnitude of the deviation, it can in principle easily be determined how the thread brake should be controlled so that the movement parameter of the thread at the point in time of the measurement is regulated to the desired value. As a result of the enormous momentary speed of the weft thread in conjunction with the unavoidable inertia of the regulation system, the correction of the movement parameter can however not be carried out until a point in time which is later than the point in time of the measurement.

The result of this is that at a later point in time, at which the thread brake can at the earliest act in a corrective manner on the movement parameter of the weft thread, the movement parameter has actually had a different value for a long time than that at the point in time of the measurement, so that the correction value for the correction of the movement parameter of the weft thread which is obtained from the measurement is no longer of use. Accordingly, recourse was had in the prior art to an averaged correction value which was determined from a specific number of previous weft threads.

Through the invention the disadvantages which result from the use of an average value for the determination of the correction value are avoided, since through the invention it is now possible to estimate the correction value for a later point in time from an estimate of the movement parameter on the basis of a first measurement value and to determine from the estimate a correction value for the correction of the movement parameter at a point in time which lies after the measurement. The advantages of the method in accordance with the invention are evident. Because the correction parameter need no longer be averaged from an average value of a plurality of weft thread passages, brief fluctuations in the operating state of the weaving machine, or during the insertion of the weft thread into a shed, respectively are also taken into account for the correction of the movement parameter of the weft thread.

In a preferred exemplary embodiment of the method in accordance with the invention the determination of the first measurement value of the movement parameter of the weft thread, the estimation of the first estimate value for the movement parameter, as it is to act correctingly on the weft thread by means of the thread brake at a later point in time as a result of the estimation, the determination of the correction value, and the correction of the movement parameter of the weft thread at the later point in time, are carried out during one and the same weft thread insertion. Through this it is ensured that the correction of the movement parameter of each weft thread insertion is carried out as a result of data which were determined from the same, i.e. the momentary weft thread insertion.

As already mentioned, the movement parameter which is used for the monitoring and control and/or regulation of an optimal weft insertion can, e.g., be a position or a speed, preferably a momentary speed of the weft thread, an acceleration, a force, a mechanical tension, a thread tension, or another movement parameter of the weft thread.

In an example which is particularly important in practice the weft thread is braked in such a manner that the movement parameter of the weft thread, in particular the speed of the weft thread, reaches a value which is within a predetermined tolerance range at the end of the braking process. This is particularly important in order to avoid the “whip effect” or stopper strike at the end of a weft thread insertion, which is well known to the expert. This arises for example when the weft thread is too abruptly braked at too high a speed, for example by a thread stopper, shortly before it has been completely inserted into the shed, thus shortly before the weft thread reaches the stretching nozzle. Thus, it is of great importance for the speed of the weft thread to lie within a definite optimal tolerance range shortly before it reaches the stretching nozzle.

In cases in which particularly high requirements are placed on the weft thread insertion, for example in the case of very fine and/or high quality cloths, also in particular in the case of large weft thread lengths with high mass inertias of the thread, a second measurement value is measured during the weft thread insertion after the first measurement value and a second estimate value is estimated on the basis of at least the second measurement value and the movement parameter of the weft thread is influenced anew on the basis of the second estimate value. This means that in the course of one and the same weft thread insertion it is possible for the movement parameter to be measured, estimated and corrected more than once, so that e.g. the insertion of the weft thread into the shed can be matched to a predetermined ideal course of the movement parameter, which can be present or can be generated as a reference file for example in the form of a look-up table or in another suitable way.

This means that the correction value for influencing the movement parameter can be formed through a single comparison or successive multiple comparisons of the respective estimate values with a predetermined desired profile for the movement parameter, for example with a predetermined desired profile for the course of the momentary speed of the weft thread during insertion into the shed.

In another exemplary embodiment a second measurement value is measured during the weft thread insertion after the first measurement value, at least one first estimate value is estimated on the basis of the first measurement value and of the second measurement value, and the movement parameter of the weft thread is influenced on the basis of at least the first estimate value. Thus, e.g., the first measurement value can be the determination of a position of the weft thread at a specific first point in time and the second measurement value can relate to the determination of the position of the weft thread at a second point in time. Then the position of the weft thread at a later third point in time can be estimated from these two position measurements through linear interpolation and, as a result of this estimation, a movement parameter of the weft thread, e.g. the position and/or the speed can be corrected at the later third point in time.

Naturally it is possible to carry out more than two position measurements and/or speed measurements and/or more than two measurements of another movement parameter of the weft thread at more than two different points in time and to estimate from these measurements the movement parameter of the weft thread at a later point in time, for example through an interpolation with a polynomial of degree higher than the second or with another mathematical function or in another way. Thus, it is, for example, advantageous to interpolate the estimate of a speed of the thread at a later point in time from at least three measurements of a movement parameter at earlier points in time.

In this situation the movement parameter can also preferably be measured without contact by a sensor. For example, the speed of the weft thread can be measured by an optical sensor in particular.

However, other movement parameters of the weft thread can naturally also be measured for the determination of the correction value. Thus, in a special case, a sensor element can be provided which is brought into touching contact with the weft thread and thus the momentary thread force or the thread tension in the weft thread can, for example, be detected during the weft insertion.

The invention further relates to a jet weaving machine, comprising a braking element which can be brought into contact with a weft thread, with the braking element being movable by means of a drive and with a sensor and/or a sensor element being provided for the measurement of a movement parameter of the weft thread, and with a control device comprising a correction unit being provided. The control device is connected in a signal transmitting manner to the drive of the braking element, and is connected in a signal transmitting manner to the sensor and/or the sensor element for the determination of the movement parameter. Thus, during a weft thread insertion, a first measurement value of the movement parameter of the weft thread can be read into the correction unit and a first estimate value for the movement parameter can be estimated on the basis of the first measurement value. From this a correction value can be determined by the correction unit, and the movement parameter of the weft thread can be corrected by the braking element on the basis of the correction value.

In the following the invention will be explained in more detail with reference to the drawings. Shown in schematic illustration are:

FIG. 1: an exemplary embodiment of a jet weaving machine in accordance with the invention;

FIG. 2: a movement parameter/time diagram of a weft thread;

FIG. 3: a diagram in accordance with FIG. 2 as the speed/time diagram of a weft thread.

FIG. 1 shows a section of an exemplary embodiment of a jet weaving machine 3 in accordance with the invention, in the present case an air jet weaving machine 3, including a braking element 4 with a drive 6 and a control unit 5. The air jet weaving machine 3 further comprises, in a manner which is known per se, a thread bobbin 15, from which a weft thread 2 of suitable length is wound up onto a drum store 16, a braking element 4, an auxiliary nozzle 17 and a main nozzle 18, with the weft thread 2 coming in the operating state from the drum store 16, being guided over the braking element 4, being accelerated in the two nozzles 17 and 18 and then being conveyed through the shed along a reed 19. The details of the weft thread insertion in a jet weaving machine 3 are known per se and thus need not be explained in further detail. The illustration of the shed as well as of further components of the jet weaving machine 3, which can for example be an air jet weaving machine 3 and which are known per se, has been dispensed with for reasons of clarity.

The exemplary embodiment which is shown in FIG. 1 of a jet weaving machine 3 in accordance with the invention has at least one optical sensor 14 at the drum store 16, with which e.g. a momentary position 9 of the weft thread 2 or a momentary speed 9 of the weft thread 2 is measured in a manner which is known per se during the drawing off of the weft thread 2 from the drum store 16 in the operating state. In this situation the momentary speed 9, which in the present example is the movement parameter 9, can be determined more precisely the more optical sensors 14 are provided at the drum store 16. Thus, for example, two, three, four or even more optical sensors 14 can be provided at the drum store 16, and can preferably be distributed uniformly over a circular periphery of the drum store 16, so that the momentary speed 9 of the weft thread 2 can be measured or calculated with the desired precision.

In FIG. 2 a movement parameter/time diagram of a weft thread 2 is schematically illustrated. In the present example the thread tension F as it acts in a weft thread 2 during the weft insertion is plotted on the ordinate as a function of the time t which elapses during the weft insertion of the weft thread 2 and which is plotted on the abscissa. In this plot the solid line shows the course of the thread tension F, which is here the movement parameter 9, in dependence on the time t for a weft insertion, such as is known in accordance with a procedure for weft insertion from the prior art. The broken line shows the corresponding time dependence of the thread force F for a weft insertion which was carried out in accordance with a method in accordance with the invention.

The weft insertion begins at a point in time t1, which means that at point in time t1 the weft thread 2 is released from the drum store 16 through withdrawal of a stopper pin. The thread force F then changes only slightly during a first phase of the weft insertion between the time t1 and a later point in time t2. During this first phase the weft thread 2 is at first not influenced by the braking element 4, which means that in this first phase of the weft insertion the weft thread 2 is at first not braked. At the point in time t2, when the weft thread 2 has already been inserted sufficiently far into the shed, the braking phase begins, which means that from the point in time t2 onwards the braking element 4 acts in a braking manner on the weft thread 2 until at a point in time t3 a stopper pin at the drum store 16 finally prohibits a further drawing off of the weft thread 2.

As already mentioned the solid curve in FIG. 2 shows the time dependence of the thread tension F in the weft thread 2 for a method for braking a weft thread 2 which is known from the prior art. Conspicuous is the so-called “whip effect”, which leads to the thread tension F in the weft thread 2 rising dramatically during the braking phase between the points in time t2 and t3, which is impressively expressed by the pronounced maximum in the solid curve between the points in time t2 and t3. It is evident that massive changes of the thread tension F of this kind act very negatively on the weft insertion as such and thus negatively influence the quality of the cloth. In the worst case the weft thread 2 can even break.

One reason for this behavior of the thread tension F in the methods for braking the weft thread 2 which are known from the prior art is that the thread tension F is used as the movement parameter 9 for the determination of the correction value 11, on the basis of which the braking element 4 is controlled for the braking of the weft thread 2. This means that the thread tension F which is measured with a force measurement apparatus, which can e.g. be integrated into the braking element 4 or which can determine the thread tension force F as a separate force measurement apparatus, which is e.g. measured from a contact pressing force of the weft thread 2 against the force measurement apparatus, is averaged over a plurality of previous weft thread insertions from which a correction value 11 is formed, on the basis of which the braking element 4 is then controlled and/or regulated for braking the weft thread 2.

In this situation it has proved that the thread tension F is, if anything, an unsuitable parameter in order to correctly determine the correction value 11 for the braking of the weft thread 2. One reason for this can be seen in the fact that, in the known methods, the use of a thread force sensor disturbs the passage of the thread by virtue of deflections. On the other hand the thread tension F is also an unsuitable parameter because the mass of the thread section to be braked naturally continually increases during the weft insertion, since the length of the inserted weft thread 2 continually increases during the insertion into the shed. Therefore it makes little sense to regulate the thread tension F alone to a predetermined level; but rather it has proved much more favorable for example to regulate the final speed of the weft thread in such a manner that a final speed of the weft thread 2 is achieved within a predetermined tolerance range, preferably under the boundary condition that the weft insertion time is maintained. For this, the braking of the weft thread must however be regulated as a result of data which stem from the very weft insertion which is to be regulated, and not from an average value of previous weft thread insertions, which can naturally not take into consideration current irregularities, a fact which leads among other things to the “whip effect” which is illustrated in FIG. 2 with the known negative consequence.

The broken line in FIG. 2 shows the time dependent plot of the thread tension F for a weft insertion which was carried out in accordance with a method 1 in accordance with the invention. In the first phase the thread tension F behaves exactly as in the known braking methods between the points in time t1 and t2, since the weft thread 2 is not yet braked in this phase. From point t2 onwards, the weft thread 2 is then braked in accordance with a method 1 in accordance with the invention, as will be explained below in detail with reference to FIG. 3.

The positive effects which the use of the method 1 in accordance with the invention has on the thread tension F in the braking phase between the points in time t2 and t3 can be clearly recognized with reference to the broken line. The fluctuations in the thread tension F are clearly damped; a “whip effect” such as occurs in the methods which are known from the prior art is practically completely suppressed. Through this the weft insertion of the weft thread is significantly improved, which in the end effect protects the weft thread 2 and improves the quality of the cloth, or enables an increase in performance respectively.

A further improvement consists in not using the thread tension F for the determination of the correction value which is used in the weft thread insertion in accordance with a method 1 in accordance with the invention such is shown in an exemplary manner in FIG. 2, but rather in using a jet weaving machine 3, as is illustrated in FIG. 1, which means that the momentary speed 9 of the weft thread 2 is calculated and determined without contact by an optical sensor 14, e.g. from the measured position 9 of the weft thread 2 for the determination of the correction value 11.

It should be noted at this point that it is in almost all cases more favorable to measure the movement parameter 9 of the weft thread 2 without contact, since a measurement with a sensor 14 which comes into touching contact with the weft thread 2 can already have a negative influence on the weft thread movement through this contact alone. In addition it has proved that the choice of the momentary speed 9 as the movement parameter 9 is the most favorable in almost all cases.

However, it must be clearly stated that the method 1 in accordance with the invention is not restricted to the measurement without contact. Rather, in special cases it can even be more favorable to operate with another sensor, which for example measures the thread tension F in a contacting manner.

In FIG. 3 a speed/time diagram for the plot of the momentary speed 9 of a weft thread 2 in the braking phase between the points in time t2 and t3 is illustrated, with the weft thread 2 being braked in accordance with a method 1 in accordance with the invention. The movement parameter 9 is plotted on the ordinate—in the present case this is the momentary speed 9 of the weft thread 2—whereas the time t is plotted on the abscissa. The braking of the weft thread 2 by means of the braking element 4 begins at the point in time t2. At a point in time Tm, which lies between the point in time t2 and the point in time t3, with t3 marking the end of the braking phase, the momentary speed 9 of the weft thread 2 is measured, e.g. by means of the optical sensor 14. On the basis of this measurement a first estimate value 10 for the movement parameter 9 is determined, which in the present case means that a momentary speed 9 is estimated which the weft thread 2 is predicted to have at a later point in time TR, and from this a correction value 11 is formed. On the basis of the correction value 11 the movement parameter 9, thus here the weft thread speed 9, is corrected at the later point in time TR. In this situation the correction value 11 is preferably determined such that the speed 9 of the weft thread 2 has a value within the tolerance range 12 at the end of the braking process, before the stopper pin stops a further insertion of the weft thread 2 at the point in time t3.

It is clear that for the correction of the speed 9 of the weft thread 2 during one and the same weft insertion the momentary speed 9 of the weft thread 2 can be measured or determined a plurality of times, so that an updated correction value 11 is in each case determined from a new estimate value 10, and thus the speed 9 of the weft thread 2 is adapted a plurality of times.

Claims

1. Method for braking a weft thread (2) of a weaving machine (3), in particular of a jet weaving machine (3), in said method a braking element (4) being brought into contact with the weft thread (2) and the braking element (4) being moved via a control device (5) by means of a drive (6), characterized in that during a weft thread insertion (7) a first measurement value (8) of a movement parameter (9) of the weft thread (2) is determined, a first estimate value (10) for the movement parameter (9) is estimated on the basis of the first measurement value (8) and a correction value (11) is determined from it; and in that the movement parameter (9) of the weft thread (2) is corrected on the basis of the correction value (11).

2. Method in accordance with claim 1, with the determination of the first measurement value (8) of the movement parameter (9) of the weft thread (2), the estimation of the first estimate value (10), the determination of the correction value (11), and the correction of the movement parameter (9) of the weft thread (2) being carried out during one and the same weft thread insertion (7).

3. Method in accordance with claim 1, with the movement parameter (9) of the weft thread (2) being a position (9) a speed (9), an acceleration (9), a force (9), a mechanical tension (9), a thread tension (9) or another movement parameter (9) of the weft thread (2).

4. Method in accordance with claim 1, with the weft thread (2) being braked in such a manner that the movement parameter (9) of the weft thread (2), in particular the speed (9) of the weft thread (2), achieves a value at the end of the braking process which is within a predetermined tolerance range (12).

5. Method in accordance with claim 1, with a second measurement value (8) being measured during the weft thread insertion (7) after the first measurement value (8), a second estimate value (10) being estimated on the basis of at least the second measurement value (8) and the movement parameter (9) of the weft thread (2) again being influenced on the basis of the second estimate value (10).

6. Method in accordance with claim 1, with a second measurement value (8) being measured during the weft thread insertion (7) after the first measurement value (8), at least one first estimate value (10) being estimated on the basis of the first measurement value (8) and of the second measurement value (8), and the movement parameter (9) of the weft thread (2) being influenced on the basis of at least the first estimate value (10).

7. Method in accordance with claim 1, with the correction value (11) for influencing the movement parameter (9) being formed through a comparison of the estimate value (10) with a predetermined desired profile for the movement parameter (9).

8. Method in accordance with claim 1, with the movement parameter (9) being measured without contact by a sensor (14).

9. Method in accordance with claim 1, with the position (9) and/or the speed (9) of the weft thread (2) being measured, in particular by an optical sensor (14).

10. Method in accordance with claim 1, with a sensor element being provided which is brought into touching contact with the weft thread (2).

11. Weaving machine, comprising a braking element (4) which can be brought into contact with a weft thread (2), with the braking element (4) being movable by means of a drive (6), and with a sensor (14) and/or a sensor element being provided for measuring a movement parameter (9) of the weft thread (2), characterized in that a control device (5) comprising a correction unit (51) is provided, with the control device (5) being connected in a signal transmitting manner to the drive (6) of the braking element (4) and being connected in a signal transmitting manner to the sensor (14) and/or the sensor element for the determination of the movement parameter (9), so that, during a weft thread insertion (7), a first measurement value (8) of the movement parameter (9) of the weft thread (2) can be read into the correction unit (51), a first estimate value (10) for the movement parameter (9) can be estimated on the basis of the first measurement value (8), a correction value (11) can be determined from it by the correction unit (51), and the movement parameter (9) of the weft thread (2) can be corrected by the braking element (4) on the basis of the correction value (11).