Title of Invention	A METHOD AND A DEVICE FOR MONITORING A THREAD
Abstract	The invention relates to a method for monitoring a thread when melt spinning and winding up and to a device for carrying out the method. The thread is guided through an electric field of a capacitor. The change oin the capacitance of the capacitor which results from the charge and, according to the invention, wvaluated in orer to determine a thread breakage and to check a spin finish application.

Full Text

Method and device for monitoring a thread The invention relates to a method for monitoring a thread when melt spinning and winding up according to the preamble of Claim 1 and to a device for carrying out the method according to the preamble of Claim 9. When spinning a plurality of synthetic threads, the threads are formed in parallel side-by-side in each case by combining a plurality of freshly spun filaments. The filaments are for this purpose extruded through spinnerets, disposed side-by-side, of a spinning unit. After the filaments have been cooled, the filament bundle is consolidated by a spin finish unit. In this case the coherence between the filaments to form a thread is achieved by a spin finish. After the threads have left the spinning unit, they are guided for treatment through a treatment unit and then wound up to form a respective package. A spin finish must be applied to the threads in order to treat and wind up the threads in the desired manner and to achieve a thread state as desired for subsequent treatment. Should a thread have no spin finish application or one which is insufficient, individual filament breakages or even a thread breakage may occur. A method and a device for monitoring a thread when melt spinning and winding up are known from DE 198 39 816 Al in order to prevent phenomena of this kind. The method which is known from DE 198 39 816 Al is based on measuring the thread at two measuring points, once with and once without a spin finish application, in order to accurately determine the spin finish application. A conclusion can therefore be drawn as to the quantity of spin finish application from a comparison of the measuring signals. The known method focuses on obtaining a layer thickness on the thread which is as continuous as possible. However in practice threads of this kind are formed by a 5 plurality of individual filaments which in themselves must in each case have a spin finish application. It is in this respect not always possible to establish an outer spin finish layer. Therefore exact layer thickness measurements cannot be carried out. 0 The object of the invention is accordingly to further develop a method and a device of the type according to the preamble so as to avoid the above-mentioned disadvantages and at the same time achieve reliable process control which takes account of the practical concerns when melt spinning and winding up. This object is achieved according to the invention by a method having the features according to Claim 1 and by a device having the features according to Claim 9. Advantageous developments of the invention are defined by the features and feature combinations of the respective subclaims. The invention is characterised in that, in the event of an insufficient spin finish, the cause and the effect are combined. It is thus possible to easily identify the thread breakages originating from an insufficient spin finish application. On the other hand, all thread breakages not connected with the spin finish application can be identified. For this purpose, according to the invention, the change in capacitance caused by the charge of a thread is evaluated on the one hand to determine a thread breakage and on the other to check a spin finish application of the thread. In this respect the tendency is towards the possibility of establishing whether, for example, a minimum quantity of spin finish is contained in the thread. It is thus known that the electric charge of the thread is essentially influenced by the spin finish application. Thus a dry thread would result in a greater change in capacitance when compared with a spin-finished thread. It is therefore possible to draw a conclusion as to the spin-finished state of the thread from the intensity of a measuring signal. In contrast, a change in capacitance provides information as to whether a thread is sensed or whether, in the case of a thread breakage, no thread is sensed. The combination according to the invention enables a melt spinning process to be monitored as to thread breakage and thread spin finishing in a simple manner and with simple means. In order to determine a thread breakage, the measuring signal which is triggered by the change in capacitance is preferably compared with a threshold value which represents the state of the capacitor with a sensed thread. Should the measuring signal result in the threshold value not being reached, a control signal is generated. In order to check the spin finish application of the thread, it is proposed that the measuring signal be compared with a limit value range and that a control signal be generated if the limit value is exceeded. In this case the control signal preferable initiates a process change. The development of the invention in which the measuring signal is converted into a multi-stage digital signal and into a further two-stage digital signal is particularly suitable for carrying out a separate evaluation. In this case the multi-stage digital signal is used to check the spin finish application and the two-stage digital signal to determine the thread breakage. The development of the invention according to Claims 7 and 13 is particularly suitable for monitoring a group of threads in a spinning process. Here the capacitors which are associated with the thread guide means are linked via an electronic measuring system such that the measuring signals are individually evaluated in order to determine the thread breakage and to check the spin finish application. The development of the invention according to Claim 8 can be carried out when using a roller spin finish unit. Faulty applications, in particular at the threads guided in the edge region of the group of threads, become apparent through installation errors and inclinations of the roller or of the spin finish container associated with the roller, i It is therefore sufficient to monitor the spin finish application at the outer threads of the group of threads. Further advantages of the invention are described in detail in the following on the basis of several embodiments with ) reference to the accompanying drawings, in which: Figure 1 represents in schematic form an embodiment of the device according to the invention for carrying out the method according to the invention Figure 2 represents in schematic form a further embodiment of the device according to the invention Figure 3 represents in schematic form the embodiment from Figure 2 when used in a spinning device A first embodiment of the device according to the invention for carrying out the method according to the invention is represented in schematic form in Figure 1. The device comprises a measuring sensor 26. The measuring sensor 26 is formed by a housing 29 and a guide means 27 which is formed at the housing 29. The guide means 27 is in this case formed by a guide groove 36 at one side of the housing 29. The guide groove 36 preferably comprises a wear protection, in particular a ceramic or a ceramic coating, at its groove walls. The guide groove 36 is encased by a capacitor 30 inside the housing 29. The capacitor 30 is linked to an electronic measuring system 31. The electronic measuring system 31 is linked via a signal line 28 to an electronic evaluation system 38. In this case the electronic evaluation system 38 is represented separately outside of the housing. However it may also form a common unit with the electronic measuring system 31 inside the housing. The signal line 28 is coupled on a signal input side in parallel with a comparator 40 and with an A/D circuit 41 inside the electronic evaluation system 38. The electronic evaluation system 38 is connected via a control line 32 to a control unit, which is not represented here, on the output side. A thread 1 is guided inside the guide groove 36 in order to monitor a melt spinning-winding-up process in the device which is represented in Figure 1. The thread 1 may in this respect be guided with contact or without contact inside the guide groove 30. An electric field is simultaneously generated by the previously charged capacitor 30. The electric charge which is carried in the thread 1 causes a change in capacitance of the capacitor 3 0 which results in a measuring signal inside the electronic measuring system 31. The measuring signal, which is formed, for example, by a noise signal of differing frequency and intensity, is fed via the signal line 28 to the electronic evaluation system 38. The measuring signal is routed to a comparator 40 inside the electronic evaluation system 38 in order to determine a thread breakage. A comparison with a predetermined threshold value takes place inside the comparator 40. The threshold value can be stored via an additional signal input 42 or in a memory unit. Here the threshold value characterises the state with a thread. The measuring signal is converted into a two-stage digital signal. A first stage of the digital signal is only generated if the threshold value is exceeded. This state corresponds to the presence of a thread, so that the first stage of the digital signal generates a "thread breakage" signal. The second stage of the digital signal is generated when the threshold value is not reached. The second stage of the digital signal signals a thread breakage, so that a control signal is derived directly from this and routed via the control line 32 from the electronic evaluation system 3 8 to a downstream control unit. The control signal will initiate a process change inside the control unit. The measuring signal is evaluated in the A/D circuit in parallel with the identification of the thread breakage. The analogue measuring signal could for this purpose initially be amplified and rectified, for example. Following conversion to a multi-stage digital signal, a mean value can be established per unit of time. A limit value range is associated with the mean value. If the limit value range is exceeded, a control signal is triggered and routed via a control line 32 from the electronic evaluation system 38 to a control unit. If the mean value does not indicate that the limit value has been exceeded, no control signal is generated. The limit value range can be predetermined via the signal input 42 or can be separately determined directly before the start of each process. For this purpose the measuring signal is evaluated in a first measuring operation before the start of each process such that a tolerance band applying as limit values to subsequent measuring operations is set for an established mean value. Irrespective of the predetermination of the limit values, when these are exceeded the control signal which is generated is routed from the electronic control system 3 8 to a control unit. Inside the control unit the control signal can trigger a warning signal, for example through a visual or an acoustic signal, in order to cause an operator to intervene in the process. It is, however, also possible for the control signal to result directly in intervention in the process, in particular in the spin finish unit. A further embodiment of a device according to the invention for carrying out the method according to the invention is shown in Figure 2• The structure and the function of the embodiment according to Figure 2 are substantially identical to the embodiment according to Figure 1, so reference is made to the preceding description and only the differences are explained at this point. In the case of the measuring sensor 26 which is represented in Figure 2 a total of three threads 1 are guided in parallel side-by-side through three guide grooves 36 formed in parallel side-by-side. Charging and discharging operations are in this, case activated in the associated capacitors 30, these resulting in a respective change in capacitance of the capacitors 30. The capacitors 30 are linked to the electronic measuring system 31. Here the electronic measuring system 31 comprises means for feeding the measuring signals in series via the signal line 28 to the electronic evaluation system 38. The adjacent capacitors 30 are screened off from one another by a respective screening plate 35 in the housing 29. The screening plate 35 extends beyond the guide groove 36, so that the guide means 27 are separated. Inside the guide grooves 36 the groove walls are preferably provided with ceramic inserts, so that no unacceptable wear occurs in the guide grooves 36 even when the threads are guided with contact. The use of the embodiment from Figure 2 in a spinning device is indicated in the following for the purpose of further illustration. An embodiment of a spinning device is shown in Figure 3 in this connection. The spinning device consists of a spinning unit 2, a treatment unit 3, which is disposed below the spinning unit 2, and a wind-up unit 14, which is disposed downstream of the treatment unit 3. The spinning unit 2 is constructed by way of example with three spinning stations in order to spin three synthetic threads in parallel side-by side. For this purpose the spinning unit 2 comprises a spinning pump 4 which may be constructed as a gear pump, for example. The spinning pump 4 is driven by the pump drive 21. The pump drive 21 is coupled to a control unit 20. The spinning pump 4 is formed as a multiple pump and supplies a plurality of spinnerets 5 in parallel at the same time. Each of the spinnerets 5 has on the underside a spinneret plate 6 through which a plurality of filament strands 7 are extruded. Immediately after extrusion the filament strands 7 run through a cooling shaft 8 which is disposed below the spinnerets 5. A coolant, preferably injected cooling air, is directed at the filament strands 7 inside the cooling shaft 8, so that the filament strands 7 are cooled inside the cooling shaft 8. At the end of the cooling shaft 8 the filament strands 7 are brought together by a spin finish unit 9 and the thread guides 34 to form a respective thread 1. The spin finish unit 9 is formed as a roller spin finish, in which case the spin finish roller is driven by a roller drive 10, so that the spin finish roller, partly immersed in a liquid bath, rotates uniformly and the threads 1 guided on its surface are wetted with a spin finish which is contained in the bath. After the filament strands 7 have been brought together to form a respective thread 1, the threads are subsequently treated in the downstream treatment unit. The treatment unit 3 consists of a draw-off godet 11 and a stretching godet 22. A freely rotatable transfer roller 12 is associated with the draw-off godet 11 and the freely rotatable transfer roller 23 is associated with the stretching godet 22, so that the threads 1 are guided in parallel in a plurality of loops over the godets 11 and 22, The draw-off godet 11 is driven via the godet drive 13 and the stretching godet 22 by the godet drive 24. The control unit 20 controls the godet drives 13 and 24. A differential speed is set between the draw-off godet 11 and the stretching godet 22 in order to stretch the threads. The wind-up unit 14, by means of which the threads 1 are wound up to form a respective package 15 after the treatment, is disposed below the treatment unit 3. For this purpose the wind-up unit 14 comprises a total of three winding stations 25 disposed side-by-side. For this purpose the packages 15 are retained in the winding stations 25 at a spindle 16 driven in overhanging fashion. The spindle 16 is driven by a winding drive 17 such that the threads 1 are wound up at a constant wind-up speed to form the package 15. The winding drive 17 is connected to the control unit 20. A pressure roller 19, around which the threads partly wrap, lies against the circumference of the package 15. A traversing unit 18 connected upstream of the pressure roller 19 serves to distribute the threads over the length of the respective packages 15, this unit comprising traversing thread guides for each winding station which guide the threads to-and-fro within a traversing stroke. A measuring sensor 26 with a plurality of integrated thread guide means 27 is disposed in the delivery region of the stretching godet 22 in order to monitor the process when producing the threads 1. The structure of the measuring sensor 26 is identical to the embodiment from Figure 2. The measuring sensor 26 is coupled to the control unit 20 via a control line 32. A thread collecting unit 33, which can be controlled via the control unit 20, is disposed in the thread path between the spinning unit 2 and the treatment unit 3. The thread collecting unit 33 comprises means for collecting, cutting and removing the group of threads. The thread collecting unit is known from EP 1 049 823, so that the cited publication can be referred to at this point. In the situation which is shown in Figure 3 the threads 1 are spread from the treatment spacing B to the winding station spacing A. The thread guidance which is required to spread the threads 1 here is performed directly by the measuring sensors 26. The winding station spacing A depends on the package width and lies in the range from 85 to 250 mm. For this purpose a top thread guide 39 is disposed upstream of each winding station 25, so that the threads 1 are spread from the treatment spacing B to the winding station spacing A by the measuring sensor 26 and the top thread guides 39. Should one of the threads 1 break or one of the threads have an insufficient spin finish application in the device which is represented in Figure 3, this is detected by the measuring sensor 26 and signalled via the control line to the control unit 20. The control signal of the measuring sensor 26 is converted into a control command for the thread collecting unit 33 inside the control unit 20 when a thread breakage occurs. The thread collecting unit 33 bundles and severs the threads and guides them via a suction system to a yarn container. The pump drive 21 is at the same time switched over by the control unit 20 to a creep speed. The creep speed of the spinning pump 4 is in this case selected so as to maintain a minimum throughput in the spinnerets 5. It is also to be noted, for the sake of completeness, that the melt-guiding parts are continuously heated by heating units. Should the measuring sensor 26 signal an insufficient spin finish application at one of the threads 1, a warning signal is triggered in the control unit 20. This indicates to an operator that the spin finish unit is not running satisfactorily. However it is also possible, for example if an insufficient quantity of spin finish is established at all the threads, for the control signal to serve directly for controlling the roller drive 10 inside the control unit 2 0 in order to increase the spin finish application at the threads 1 by increasing the circumferential speed of the spin finish roller 9. In the embodiment of the spinning device which is shown in Figure 3 the monitoring device is disposed directly at the exit of the treatment device 3. This installation location and the structure of the spinning device are exemplary. Generally speaking, it is possible to use a device according to the embodiment of Figure 1 which is preferably associated directly with a winding station of the wind-up unit. The formation of the treatment unit is equally exemplary. The treatment unit is substantially determined by the type of thread which is to be produced. Thus the device for monitoring a thread when melt spinning and winding up can be used in spinning devices for producing POY, FDY or HOY threads.

Documents:

1515-chenp-2006 abstract-duplicate.pdf

1515-chenp-2006 claims-duplicate.pdf

1515-CHENP-2006 CORRESPONDENCE OTHERS.pdf

1515-CHENP-2006 CORRESPONDENCE PO.pdf

1515-chenp-2006 description (complete)-duplicate.pdf

1515-chenp-2006 drawings-duplicate.pdf

1515-CHENP-2006 FORM 18.pdf

1515-chenp-2006-abstract.pdf

1515-chenp-2006-claims.pdf

1515-chenp-2006-correspondnece-others.pdf

1515-chenp-2006-description(complete).pdf

1515-chenp-2006-drawings.pdf

1515-chenp-2006-form 1.pdf

1515-chenp-2006-form 26.pdf

1515-chenp-2006-form 3.pdf

1515-chenp-2006-form 5.pdf

1515-chenp-2006-pct.pdf