US20060108019A1

US20060108019A1 - Method for braking a weft thread of a weaving machine

Info

Publication number: US20060108019A1
Application number: US11/270,390
Authority: US
Inventors: Walter Siegl; Hans-Dieter Scorl
Original assignee: Sultex AG
Current assignee: Itema Switzerland Ltd
Priority date: 2004-11-22
Filing date: 2005-11-08
Publication date: 2006-05-25
Also published as: CN1782154A; DE502005007653D1; JP2006144218A

Abstract

The invention relates to a method (1) for braking a weft thread (3) of a jet weaving machine (10), in said method (1) a braking element (2) being brought into contact with the weft thread (3), with the braking element (2) being moved by means of a drive (21) in accordance with a predeterminable distance/time plot so that the weft thread (3) is deflected by the braking element (2) in accordance with a position function (23), so that the weft thread (3) is braked in accordance with a braking profile (31), characterized in that the position function (23) is matched to the braking profile (31) of the weft thread (3).

Description

The invention relates to a method for braking a weft thread of a jet weaving machine as well as to a jet weaving machine for carrying out the method of the invention in accordance with the preamble of the independent claim of the respective category.
It is known that so-called ABS brakes are used 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 automatic weft thread braking device. The aim of this is to avoid an overstressing of the weft thread, which is caused in particular by the abrupt braking of the weft thread, e.g. by the stopping pin of the thread store. The ABS brake is realized e.g. in the form of a movable hoop with two or three deflection points. The braking force is influenced by a weft thread deflection which is caused by the braking hoop. The hoop is usually rotatably journalled and is in active conection with a drive, e.g. with a magnetic coil, or with an electric motor, with the drive being connected to a suitable control system in a signal conducting manner for its control and/or regulation.
In the ABS brakes which are known from the prior art the hoop deflection takes place linearly in time e.g. up to a maximum predetermined deflection of the hoop, which is afterwards brought back linearly into the original position.
In the context of the present application the term “linear” (in time) relates to the distance traveled and is intended to characterize the fact that the speed of the object under consideration, e.g. of a brake element or of a weft thread, is at least constant section-wise and the distance/time plot at least linearly increases or decreases section-wise. The end of a section of this kind is as a rule characterized by an abrupt change of the velocity, that is, by a sharp “kink” in the distance/time plot. In corresponding manner, “non-linear” characterizes the fact that the acceleration of the object under consideration is not equal to zero and its distance/time plot is consequently also non-linear. In principle, abrupt changes of the velocity, that is, sharp kinks in the distance/time plot, can in principle arise naturally with non-linear movement sequences.
The disadvantage of a ramp-like predetermination of the position of this kind is that the hoop deflection is always changed linearly in time independently of a braking phase. This has the consequence that a greater weft thread stress can be caused precisely at the beginning of the braking phase, e.g. when the weft thread speed is still very high. The weft thread is thus abruptly stressed at the turning point, that is, when the direction of the hoop movement is reversed. Through this non-uniform weft thread stressing, weft thread breakages repeatedly occur in jet weaving machines in practice.
The object of the invention is therefore to propose an improved method for braking a weft thread so that stresses arising in the weft thread are kept to a minimum.
The subject matter of the invention which satisfies this object with regard to method and apparatus is characterized by the features of the independent claim of the respective category. The subordinate claims relate to particularly advantageous embodiments of the invention.
Thus in accordance with the invention a method for braking a thread in a weaving machine is proposed, in which a braking element is brought into contact with the weft thread, the braking element is moved by means of a drive in accordance with a distance/time plot which is to be predetermined, so that the weft thread is deflected by the braking element in accordance with a position function and is braked in accordance with a braking profile, and is characterized in that the position function is matched to the braking profile of the weft thread.
The braking profile is the speed/time plot of the weft thread. In order to achieve ideal braking results, the position function of the weft thread, that is, the time plot of the deflection of the weft thread during the braking, must be matched to the predetermined braking profile. The time plot of the deflection of the weft thread by the braking element during the braking is thus, in contrast to the methods known from the prior art, non-linear at least in certain braking phases. Rather, in order to achieve an ideal braking result and thus to achieve an ideal weft insertion, the deflection speed of the weft thread is continuously matched to its braking profile.
Since the frictional force on the weft thread at the point of action of the braking element, i.e. at the point where the braking element rubs against the weft thread, depends as a rule non-linearly on the speed of the weft thread, it has been established that the deflection of the weft thread can advantageously also be made non-linear in accordance with the position function. The braking elements which are known from the prior art are, on the one hand, moved out of the rest position with constant speed; and, on the other hand, the support surface of the braking element for the weft thread is designed in such a manner that the weft thread is also deflected linearly or nearly linearly. The weft thread, which has a very high speed at the beginning of the braking phase, is thereby subjected to an unnecessarily high stress. The term “rest position” will be understood to mean that position in which the braking element is not deflected, i.e. the position in which the braking element is not in contact with the weft thread. In contrast to the methods which are known from the prior art, the weft thread can, e.g., be moved through the method in accordance with the invention out of the rest position at low speed at the beginning of a braking phase, with the speed of the deflection of the weft thread then being continuously increased. In the context of this application the term braking phases will be understood to mean an operating state in which the braking element is in contact with the weft thread. The large frictional force and thus braking force acting on the weft thread, which is caused by the high speed of the weft thread at the beginning of the braking phase, can be matched with decreasing speed of the weft thread to the actual weft thread speed through a suitable control system and/or design of the braking element.
The stresses which act on the weft thread in the operating state can frequently be roughly classified into two groups: braking stresses on the one hand and dynamic stresses on the other hand. In the context of the invention, braking stresses are to be understood as those which change the sense of their direction at most when the direction of movement of the braking element also changes. Dynamic stresses are those which can continually change their direction, or the sense of their direction, during the braking process and which e.g. result from the properties of the entire oscillatory system. For example they can be stochastic or more or less periodic oscillations. The term oscillatory system will be understood in the following to mean the mechanical system with the jet weaving machine and the braking element.
The braking stresses which arise as a rule during the braking process include, among others, frictional forces which arise through the friction of the braking element at the, e.g., uneven weft thread surface and forces which originate at the deflection points which the weft thread passes. Among other things the braking element itself belongs to the deflection points. All these external forces lead to tensions in the weft thread, which in turn again produce reaction forces which act opposite to the forces which act from without. With decreasing speed of the weft thread these forces can become progressively smaller and substantially disappear at standstill of the weft thread.
The dynamic stresses, i.e. forces, result from the oscillations which arise at the weft thread, in particular during the braking process. They lead to dynamic tensions in the weft thread.
The tensions which arise through this collective stress in the weft thread can, in the worst case, lead to a destruction of the weft thread on exceeding specific threshold values.
In order to achieve a reduction of the stresses, correspondingly suitable measures are taken in accordance with the invention for braking stresses and dynamic stresses:
Through a slow increase of the speed of the deflection of the weft thread at the beginning of the braking phase a situation is achieved in which in particular the braking stresses which act on the weft thread at the beginning do not become too large. Through this the dynamic forces, i.e. stresses, are naturally also reduced.
By choosing the path changes in the distance/time plot of the braking element such that this plot is smooth, that is, substantially without kinks, the oscillatory properties of the oscillatory system are significantly improved. Thus stress peaks can be avoided through a movement of the braking element which is carried out in this manner, with stress peaks being understood to mean that they are more or less briefly arising mechanical tensions of large magnitude at the weft thread, which arise through general oscillatory effects, such as, say, resonance, and are caused e.g. by striking, jerking, jolting or frictional processes or oscillations.
It should be explicitly pointed out at this point that the distance/time plot can be realized in different manners. For example, the distance/time plot of the braking element can be directly predetermined in the control unit, with it being necessary as a rule to establish the correct distance/time plot through transformation from a predetermined position function of the weft thread deflection. In this transformation the geometric features of the braking element can in particular also be decisive. The position function as such, however, is ultimately important for the stresses arising at the weft thread, since it establishes a direct relationship to the forces in the weft thread.
The asymmetry of the distance/time plot is particularly advantageously arranged such that the braking element is moved slowly out of the rest position at the beginning and is rapidly moved into the rest position at the end. In the course of a time optimization of the braking process the distance/time plot is particularly advantageously arranged such that a predominant portion of the speed reduction takes place while the weft thread is moved out of the rest position into the maximum position. Once this is achieved, the weft thread can be moved rapidly back into the rest position. Attention should again be paid here that the moving in movement advantageously takes place continuously and without jerking while taking account of the dynamic stresses.
The thread stresses can be further reduced in that the surface of the braking element which is brought into frictional contact with the weft thread is designed such that the force is not transmitted at a single point, but rather is distributed over a surface. Through this the frictional heat which arises is also better distributed over the weft thread.
A further possibility of avoiding disturbing stresses is to ensure, by means of a control system, that a maximum force from the braking element which acts on the weft thread is not exceeded. In this case, ideally, no distance/time plot for the braking element need be predetermined, e.g. in the form of a mathematical function by means of an MC-control system. Instead the braking element can e.g. be controlled with a regulator only. The deflection of the braking element then takes place e.g. in dependence on the reaction force of the thread which is transmitted to the braking element. The regulation can then take place via the current of the drive for the braking element and/or via the measurement of the reaction force of the weft thread. Of course the entire process of the deflection of the braking element is also preferably carried out here without blows and jerk.
In an embodiment, which is particularly relevant in practice, the weft thread is deflected in an initial braking phase by the braking element in accordance with a position function with continually increasing speed from a rest position into a first position and is brought back into the rest position from a second position with continuously diminishing speed in a final braking phase.
In another exemplary embodiment, in an intermediate braking phase the weft thread is moved by the braking element in accordance with a position function out of the first position into a maximum position and out of the maximum position back into the second position. In this process the transitions at the beginning and end of the intermediate braking phase should preferably take place such that the rise or fall of the speed is not changed abruptly at the transitions.
In a further preferred exemplary embodiment the position of the weft thread is held substantially constant in the intermediate braking phase over a predetermined period of time. Substantially means here that the position change of the weft thread remains within a predeterminable tolerance over a predetermined period of time. The region within which a position change is tolerable depends essentially on the constitution of the thread and the thread speed.
In an exemplary embodiment which is particularly important in practice the position function of the weft thread is preset to be asymmetrical, e.g. in the form of a hyperbolic tangent function, in particular of a compound hyperbolic tangent function. With a suitable geometry of the braking element the distance/time plot of the braking element can, for example, then also be a hyperbolic tangent function. I.e., in this case, the distance/time plot of the braking element and the position function of the weft thread deflection are in proportional or nearly proportional dependence on one another.
The hyperbolic tangent function can be used particularly advantageously in order to realize the features of the position function in accordance with the invention in a simple manner. I.e. with its help the features in accordance with the invention can be particularly advantageously reproduced.
In a special exemplary embodiment a control unit is provided for controlling the drive of the braking element. Here control units mean all suitable control and regulation devices, e.g. MC-control systems as known from industrial control technology.
Of course the position function can also be realized through a suitable design of the shape of the braking element, as will be described further below.
The movement of the braking element can be realized through a motor, in particular an electric motor, or a magnet, in particular an electromagnet or a mechanical drive. In the context of this application the electric motors include e.g. all d.c. motors, a.c. motors, three phase motors, linear motors and stepping motors. The mechanical drive can e.g. be realized in such a manner that the braking element is driven via the main drive axle of the weaving machine. This relatively uncomplicated kind of drive is found quite frequently in the literature under the concept of master and slave drives. By way of example, the distance/time plot of the braking element and thus the position function can be matched in almost any desired manner to the respective requirements via transmissions with non-constant transmission ratios, such as, e.g., cam drives, in the narrower sense, eccentric devices.
As an alternative to this a simple distance/time plot can also be provided for the drive movement of the braking element and for this the geometry of the braking element can be chosen such that the desired position function for the weft thread deflection is achieved.
Furthermore, the invention includes a jet weaving machine, in particular an air jet weaving machine including a braking element for breaking a weft thread, with the braking element being designed and arranged in such a manner that it can be brought into contact with the weft thread and can be moved by means of a drive in accordance with a predeterminable distance/time plot. In this arrangement the weft thread can be deflected by the braking element in accordance with a position function and the weft thread can be braked in accordance with a braking profile. The jet weaving machine is designed here in such a manner that the position function can be matched to the braking profile of the weft thread.
It is clear that the enumeration of the above described exemplary embodiments of the jet weaving machine in accordance with the invention and the described variants is not exhaustive and that the enumerated variants can be combined in any suitable form.
The invention will be explained in the following in more detail with reference to the drawings. Shown in schematic illustration, which is not to scale, are:
FIG. 1 an exemplary embodiment of a jet weaving machine which is known per se with a braking element in accordance with the invention
FIG. 2 a a distance/time plot of the braking element which is known from the prior art
FIG. 2 b a position function of the deflection of the weft thread which results from FIG. 2 a
FIG. 3 a a braking profile of the weft thread with the associated distance/time plot of the braking element
FIG. 3 b an exemplary embodiment of a position function in accordance with the invention
FIG. 4 an exemplary embodiment of a braking element in hoop shape
FIG. 5 an exemplary embodiment of a braking element in the shape of a fork
FIG. 6 an exemplary embodiment of a hoop braking element with an areal friction engagement surface
FIG. 7 a a braking element in accordance with FIG. 4 with expanded geometrical features
FIG. 7 b a further braking element in accordance with FIG. 7 a with expanded geometrical features
The method in accordance with the invention, which is designated in the following by the reference symbol 1, is used for braking a weft thread in jet weaving machines, in particular in air jet weaving machines.
FIG. 1 shows a section of an air jet weaving machine 10 of this kind, which is known per se, having a braking element 2 in accordance with the invention and a control unit 4 in accordance with the invention. It essentially includes a thread bobbin 6, from which a suitable length of weft thread 3 is wound up onto a storage drum 5, a braking element 2, an auxiliary nozzle 7 and a main nozzle 8. In the operating state, the weft thread 3, coming from the storage drum 5, is passed through the braking element 2, is accelerated in the two nozzles 7 and 8 and is then forwarded along a reed 9 through the shed. Furthermore, the drive 21 of the braking element 2 is shown. The details of the weft insertion of the jet weaving machine 10 are known per se and need therefore not be explained in more detail. The illustration of the shed and further components of the jet weaving machine, which are known per se, has been dispensed with for the sake of clarity.
FIG. 2 a shows distance/time plot 22′ which is designed in accordance with a method 1′ from the prior art and in accordance with which the braking element is moved. The time is plotted linearly on the abscissa and the distance is plotted linearly on the ordinate. Characteristic for a distance/time plot 22′ of this kind are the kinks in the movement. The movement of the braking element takes place linearly in time, i.e. its speed is constant over sections of the plot. For example the braking element is brought out of a rest position 111′ up to a maximum predetermined deflection 121′ and then back again into the rest position 111′. The disadvantage of a ramp-like specification of the position of this kind is that, as already explained, the hoop deflection always changes linearly in time independently of the braking phase. This has as the consequence that a greater weft thread stress is caused precisely at the start of the braking phase when, e.g., the weft thread speed is still very high. At the turning point as well, i.e. when the direction of the hoop movement is reversed, the weft thread is abruptly de-stressed. Through this non-uniform weft thread loading, weft thread breakages can continually arise in practice in jet weaving machines.
FIG. 2 b shows the position function 23′ of the weft thread deflection which results from the distance/time plot 22′ which is shown in FIG. 2 a. The time is plotted linearly on the abscissa and the position of the weft thread is plotted on the ordinate axis. The distance/time plot 22′, i.e. the distance/time plot of the deflection of the braking element, and the position function 23′, i.e. the weft thread deflection, are proportional to one another here. This proportionality can be assumed for braking elements the function of which results from the rotation of an element about an axis, providing the weft thread does not slide away significantly, e.g., in the direction towards the axis of rotation.
FIG. 3 a shows schematically a braking profile 31 for the weft thread 3. The time is plotted linearly on the abscissa and, on the ordinate, on the one hand, the position function 23 of the weft thread 3 and, on the other hand, the speed of the weft thread 3. The position function 23 is illustrated by a broken line. The illustrated plots are to be understood merely in an exemplary manner and can have other shapes in practice. As can be clearly seen, the position function 23 is matched to the braking profile 31 of the weft thread 3. I.e. the plot of the position function 23 of the weft thread 3 is not, as in the prior art, independent of the plot of the braking profile 31 of the weft thread 3.
FIG. 3 b shows a position function 23 of the weft thread deflection which is designed in accordance with the method 1 in accordance with the invention and a corresponding speed/time plot 24. The time is plotted linearly on the abscissa and the speed and distance are plotted linearly on the ordinate. The position function 23 is illustrated by a solid line and the speed/time plot 24 by a broken line. The characteristic positions into which the weft thread 3 is moved are characterized at the ordinate by their reference symbols.
In an initial braking phase 11 the weft thread 3 is deflected with continuously increasing speed out of a rest position 111 up to and into a first position 112. Then the weft thread 3 is moved in an intermediate braking phase 13 out of the first position 112 into a maximum position 113 and is moved back out of the maximum position 113 into the second position 121. Finally, in the final braking phase 12, the weft thread 3 is brought back from the second position 121 into the rest position 111 with continuously diminishing speed. Decisive is that all distance changes in the position function 23 behave continuously and smoothly in contrast to the position function 23′ in FIG. 2 b which is known from the prior art, in particular in the initial braking phase 11 and in the final braking phase 12 and not, as has already been described in connection with FIG. 2, linear movement over section of the plot and/or with kinks. The position function 23 which is illustrated here is a hyperbolic tangent.
FIG. 4 shows a braking element 2 which is known per se from the prior art, which is designed as a hoop element and which can be controlled in accordance with the method 1 in accordance with the invention by a control unit 4 which is not shown here. The weft thread 3 is deflected once each at the two outer deflection points 16 and twice at the movable hoop 15. The greatest weft thread loading also frequently takes place at these deflection points. Naturally the hoop can also be designed as a simple bar with only one, or more than two, deflection points. The axle of rotation 17 of the hoop 15 can be journalled at one or both ends. The way the function of the braking element 2 is satisfied results essentially from the fact that frictional work and deformational work is done on the weft thread 3 at the deflection points. The kinetic energy of the weft thread 3 is converted into heat through the frictional and bending stresses acting and the weft thread 3 loses its energy through this. The drive 21 of the braking element 2 can take place through a magnet, in particular an electromagnet, a motor, in particular an electric motor, or a mechanical drive.
FIG. 5 shows another braking element 2, which is likewise connected in a signal-transmitting manner to a control unit 4 which is not shown here and can be controlled in accordance with the method 1 in accordance with the invention. It is designed here as a fork element and the axis of rotation 171 of the fork 151 lies in the normal direction with respect to the weft thread 3. The shape of the fork 151 can naturally be varied. Here as well the axis of rotation 171 can be journalled at one or both ends. The drive 21 of the fork element can take place through similar drives in a manner which is analogous to that of the exemplary embodiments which were discussed in FIG. 4.
FIG. 6 shows a further exemplary embodiment of a braking element 2 for carrying out the method 1 in accordance with the invention for further improving the braking properties of the braking elements 2 which are illustrated in FIG. 4 and FIG. 5. Because a shape is chosen for the braking element 152 which ensures a broad support surface of the weft thread 3, point-wise arising stresses of high magnitude are reduced and instead stresses of relatively low magnitude which act areally over a wide range of the weft thread are produced. Through this arrangement lower maximum stresses arise, whereby the tearing of the weft thread 3 is practically excluded. Naturally all deflection points of the braking element 2, such as, say, the deflection points 162, can be adapted in their shape in such a manner that point-wise arising stresses of high magnitude are reduced. The drive 21 of the braking element 2 can take place through the same or similar drives as in FIG. 4.
The following two figures show in highly simplified, schematic illustration braking elements 2 which realize an impressed, nonlinear position function 23 when the deflection of the braking element 2 e.g. takes place in a linear or else in a non-linear manner.
FIG. 7 a schematically shows a hoop 153 in the non-deflected state, it being possible for said hoop 153 to be moved with speed constant in sections about an axis of rotation 173 and for its geometrical construction to be designed in such a manner that the weft thread 3 is deflected in accordance with a position function 23 in accordance with the invention. The weft thread 3 can move over the hoop 153, through which a position function 23 in accordance with the invention with smooth transitions arises, as is illustrated in FIG. 3 b.
FIG. 7 b shows schematically another hoop 154 in accordance with FIG. 7 a. Through the complicated geometry of the hoop 154, shown here in an exemplary manner, a more complicated position function 23 for the weft thread 3 can be preset.
It is thus possible, using the method in accordance with the invention, to realize an improved control of an ABS brake, so that stresses which arise at the weft threads are reduced. In the distance/time plot in an initial braking phase the braking element is deflected out of a rest position into a first position with continuously increasing speed and is brought back into the rest position in a final braking phase with continuously diminishing speed. Through the method in accordance with the invention the braking element can, e.g., be moved out of the rest position at low speed at the beginning of the braking phase, with the speed then being increased continuously. The large frictional and thus braking force on the weft thread at the beginning of the braking phase which is caused by the high speed of the weft thread can be matched to the current weft thread speed with decreasing speed of the weft thread through a suitable control of the braking element.

Claims

1. Method for braking a weft thread (3) of a jet weaving machine, in which a braking element (2) is brought into contact with the weft thread (3), the braking element (2) is moved by means of a drive (21) in accordance with a predeterminable distance/time plot so that the weft thread (3) is deflected by the braking element (2) in accordance with a position function (23) and the weft thread (3) is braked in accordance with a braking profile (31), characterized in that the position function (23) is matched to the braking profile (31) of the weft thread (3).

2. Method in accordance with claim 1, with the weft thread (3) being deflected in accordance with the position function (23) in an initial braking phase (11) by the braking element (2) with a continuously increasing speed from a rest position (111) into a first position (112) and, in a final braking phase, (12) being brought back from a second position (121) into the rest position (111) with continuously diminishing speed.

3. Method in accordance with claim 1, with the weft thread (3) being moved in an intermediate braking phase (13) out of the first position (112) into a maximum position (113) and being moved back out of the maximum position (113) into the second position (121).

4. Method in accordance with claim 1, with the position of the weft thread (3) remaining substantially constant in the intermediate braking phase (13) over a predetermined period of time.

5. Method in accordance with claim 1, with the distance/time plot of the braking element being linearly predetermined at least section-wise.

6. Method in accordance with claim 1, with the position function (23) of the weft thread (3) being an asymmetrical position function.

7. Method in accordance with claim 1, with the position function (23) of the weft thread (3) being predetermined in at least one of the braking phases by a real or complex trigonometric position function.

8. Method in accordance with claim 1, with the position function (23) being a hyperbolic tangent function.

9. Method in accordance with claim 1, with the braking element (2) being moved by a motor, in particular by an electric motor, or by a magnet, in particular by an electromagnet, or by a mechanical drive.

10. Jet weaving machine, in particular an air jet weaving machine (10), including a braking element (2) for braking a weft thread (3), with the braking element (2) being designed and arranged in such a manner that it can be brought into contact with the weft thread (3) and can be moved by means of a drive (21) in accordance with a predeterminable distance/time plot, with the weft thread (3) being deflectable by the braking element (2) in accordance with a position function (23) and with it being possible to brake the weft thread (3) in accordance with a braking profile (31), characterized in that the position function (23) can be matched to the braking profile (31) of the weft thread (3).

11. Jet weaving machine in accordance with claim 10, with a control unit (4) being provided for controlling and/or regulating the drive (21), by means of which the drive (21) can be controlled in such a manner that in an initial braking phase (11) the weft thread (3) can be deflected with continuously increasing speed from a rest position (111) into a first position (112) and can be brought in a final braking phase (12) from a second predeterminable position (121) back into the rest position (111) with continuously diminishing speed.

12. Jet weaving machine in accordance with claim 10, with a magnet, in particular an electromagnet, a motor, in particular an electric motor, or a mechanical drive being provided as the drive (21) of the braking element (2), and with the braking element (2) being provided as a hoop element or as a twistable fork element.