Method and apparatus for monitoring yarn tension

Abstract: A method and apparatus for monitoring the yarn tension at each of a plurality of yarn processing stations is disclosed and wherein the mean value of the monitored tension is continuously determined at each station, and the differential between the monitored value and the mean value is also continuously determined. In addition, an overall mean value is generated which is representative of an average of the mean valve signals from all of the individual stations, and the overall mean value is compared with the individual mean value of each station. In the event the mean value signal at a particular station differs from the overall mean value signal by more than a predetermined tolerance limit, an alarm signal is generated.

Description: The present invention relates to a method and apparatus for monitoring the yarn tension of a continuously advancing yarn, such as at each of the operating stations of a false twist crimping machine. U.S. Patent No. 4,720,702 to Martens discloses a method for continuously monitoring the yarn tension at each of a plurality of yarn processing stations (station mean value signal SM), and which involves continuously determining the mean value of the monitored tension at each station, and continuously determining the difference between the monitored value and the mean value. An alarm signal is generated whenever the mean value leaves a predetermined tolerance range, and also whenever the difference value leaves a second predetermined tolerance range. In the above described method, the upper limiting value of a mean value and the lower limiting value of a mean value are set so far apart from each other for the control of the entire false twist texturing machine, as to ensure that the mean values of all working stations are within these centrally set values. Consequently, the mean value of the individual stations is able to fluctuate within a relatively wide range, which adversely affects the accuracy of the method. It is accordingly the object of the present invention to provide a method and apparatus for monitoring the yarn tension at each of a plurality of yarn processing stations of a yarn processing machine, and wherein it is possible to respond to relatively small fluctuations of the mean value at each station. The above and other objects and advantages of the present invention are achieved in the embodiment illustrated herein by the provision of a method and apparatus for monitoring the tension of an advancing yarn and which includes the steps of continuously monitoring the value U of the tension of the advancing yarn at each of the yarn processing stations, while continuously determining the station mean value SM of the monitored tension of each of the yarns. A group mean value signal GM is generated which is representative of an average of the station mean value signals SM of all of the stations on the machine, and at each of the yarn processing stations on the machine, the group mean value signal GM is compared with the current station mean value signal SM of the station to generate a first difference signal D. An alarm signal is generated whenever the first difference signal D exceeds a predetermined tolerance limit . In one embodiment, the step of generating a group mean value signal GM comprises continuously summing the station mean value signals SM from all of said stations on said machine, and continuously dividing the sum by the number of the stations. In another embodiment, the step of generating the group mean value signal GM comprises determining a desired mean value signal, and generating such signal as a constant value. The method also preferably includes the step of continuously determining the second difference DU between the monitored value and the station mean value for each of the yarns, and generating a first alarm signal whenever the station mean value SM for one of the advancing yarns leaves a predetermined tolerance range, or whenever the difference value for one of the advancing yarns leaves a second predetermined tolerance range. The present method makes it possible with simple means to monitor not only the quality of the individual working stations, but also of the entire machine. This is of significance in the operation of a multi-station machine, such as a false twist crimping machine which has, for example, 216 working stations, inasmuch as the present method permits a uniform quality level to be achieved for a plurality of working stations. The mean value of the stations is determined for a plurality of working stations of the false twist crimping machine. To this end, it is possible to form the group mean value of the stations from station mean values which are simultaneously present, or from measured values which are simultaneously present on individual, selected stations. However, it is also possible to determine the mean value of the stations on a different machine, which serves as a pilot machine. It is further possible to determine the mean value of the stations one time based on a representative determination of a limited duration. Finally, it is possible to input the mean value of the stations by means of a continuous evaluation of the measured values or respectively mean values of individual, selected stations. Even when the mean value of the stations is not input constant in time, short-time fluctuations of the mean value are preferably filtered out, so as to limit the rate of change of the overall mean value. The present invention provides for two basic measures, namely: (a) An alarm signal is emitted at each station, whose continuous station mean value signal SM exceeds the upper limit of a group mean value UGM, which remains constant during the operation or the lower limit of a group mean value LGM, which remains constant during the operation. This measure allows to eliminate, i.e., discontinue the operation of stations, whose continuous mean value is considerably outside of the tolerance range provided for the group mean value, upon the occurrence of a certain number of errors. This ensures that only those stations are operated, which are within a certain, narrow tolerance range. As aforesaid, stations outside of this tolerance range are shut down, or the packages produced thereon are assigned an inferior class of quality. (b) An alarm signal is generated at all stations, for which a common group mean value is continuously produced from the continuously measured values or continuous mean values, when the group mean value leaves the tolerance range . In taking this measure, all stations are evaluated, for which a common group mean value is determined. When the group mean value of these stations leaves the tolerance range, an error signal is emitted, which leads to a lesser quality classification or even to a shutdown of the stations, when a certain number is exceeded. (c) The upper limit USM and the lower limit LSM for the station mean value of the individual stations are not input constant, but formed after the mean value of a group of stations. In so doing, the upper limit and the lower limit follow the continuous mean value of the group at a certain, predetermined interval, thus taking into account a possible scattering of the station mean values of the individual stations. It is made possible to establish a quite narrow tolerance range between the upper limit USM and the lower limit LSM. This measure is applicable in addition or as an alternative to the measures described under (a) and (b) above. The invention will be described below with reference to diagrams and the circuit diagram of a preferred embodiment. Some of the objects and advantages of the present invention having been stated, others will become apparent as the description proceeds, when taken in conjunction with the accompanying drawings, in which: Figure 1 is a diagram illustrating yarn tension versus time for three operating yarn processing stations; Figure 2 is a schematic diagram illustrating an apparatus and electrical control circuit in accordance with the present invention; Figure 3 is a diagram illustrating the yarn tension M1 of an individual station and the group mean value GM versus time, and further illustrating upper and lower group mean value limits; Figure 4 is a diagram illustrating the group mean value GM versus time, and further illustrating upper and lower limits thereof; and Figure 5 is a diagram illustrating the yarn tension M1 of an individual station and the group mean value GM versus time, and further illustrating established upper and lower limits for the mean value. Referring more particularly to the drawings, Figure 1 illustrates a recording of the values measured at three working stations of a multi-station yarn processing machine. The ordinate represents the magnitude of the measured value U, and the abscissa the time. As is shown, the recording of the measured values U1, U2, U3 is different over time. In the example, the group mean value GM of the stations is formed from the different measured values. This mean value of the stations may be constantly recorded for the entire machine. This means that the upper limit and the lower limit vary with the station mean value of the stations, however, with the width of the tolerance range remaining constant between the upper and the lower limiting value. It is possible to average the station mean value of the stations itself over a certain evaluation time, and to form a constant group mean value of the stations in this manner. In this event, the upper and the lower limiting value will also remain constant. Likewise, it is possible to determine the mean value of the stations only on one representative machine, for example, a well adjusted machine, and to input the mean value obtained therefrom on other machines, which process the same lot. Also in this instance, it is possible to continuously record this representative group mean value of the stations, or, however, to average same for a certain time and to finally input same as a constant value. Figure 2 is a schematic diagram illustrating a yarn processing station and associated control circuitry in accordance with the present invention. The left hand portion of the diagram illustrates one yarn processing station of a multi-station false twist machine, and wherein a yarn 10 is withdrawn from a supply roll or other source (not shown) by delivery roll 11. The yarn advances past a conventional yarn cutter 12, and then it is guided across and in contact with a heater 13, through a false twister 14, and past a yarn sensor 15. The yarn is withdrawn from the false twisting zone by delivery roll 16 and wound onto a package 17 by means of a conventional winder. The output signal U of the sensor 15 is transmitted to a circuit 20, which is illustrated within the dash-dot line of Figure 2. Circuit 20 is associated with each station of the multi-station false twist machine, and with the yarn sensor 15 of such station. The circuit 20 receives predetermined tolerance values from a set limit value memory 22 which is described below in more detail. Memory 22 is associated with a group of stations of the multi-station texturing machine. Circuit 20 produces one output signal to the yarn cutter 12 and another output signal to a general alarm unit 23 which is also associated with a group of stations. Circuit 20, furthermore, produces output signals to alarm units 25, 26, 27, 28 which will be described below in more detail. These alarm units are correlated to the associated processing station. The output signal of yarn sensor 15 is fed to amplifier 30 and then to filter 32. The filter is a circuit containing an induction coil and a capacitor, the circuit having a delay time constant of for example one to three seconds. The output signal of the amplifier 30 is a voltage U which may be fed to a central microprocessor for further processing and calculation via line 34. The output of filter 32 is the station mean value SM which may also be fed to a general microprocessor via line 35 for further processing and calculation. On the other side, signal U and signal SM are fed to difference amplifier 38 producing an output signal DU which represents the difference of the input signals U and SM. The output signal DU of the difference amplifier 38 may be fed via line 36 to the central microprocessor for further processing and calculation. The output signal SM of the filter 32 is furthermore used to produce alarm signals A1 and A2, if the station mean value SM leaves the predetermined range of tolerance. The predetermined range of tolerance is defined by the upper limit of the station mean value USM and by the lower limit of the station mean value LSM, both of which are stored in the limit value memory 22 and fed to circuit 20 via respective lines. The circuit 20 for this purpose contains triggers 40 and 41. Trigger 40 is fed by the station mean value SM and the upper limit of the station mean value USM, and it is designed to produce an output signal A1, if the mean value exceeds the set upper limit of the station mean value. Trigger 41 is designed to receive the station mean value SM and set lower limit of the station mean value LSM as an input signal and to produce an output signal A2, if the station mean value SM is lower than the set lower limit of the station mean value. The circuit 20 also produces alarm signals A3, A4, if the second difference signal DU exceeds the predetermined range which is defined by a set upper limit of the second difference value UDU and the set lower value of the second difference value LDU. The predetermined upper and lower limits are stored in the limit value memory 22 and fed as input signals to triggers 42 and 43, respectively, of the circuit 20. The other input signal to the triggers 42 and 43 is the second difference signal DU which is the output of difference amplifier 38 as described above. If the second difference signal DU is greater than the set upper limit UDU, trigger 42 produces alarm signal A3. If second difference value DU is smaller than the set lower limit LDU, trigger 43 produces alarm signal A4. Each of the alarm signals A1, A2, A3, A4 is fed to either one of the alarm units 25-28 which are associated with this station and which are, e.g., designed as a light emitting diode integrated into the circuit 20. Furthermore, alarm signals A1 to A4 are fed to OR gate 44, delay time unit 45, memory 46 and amplifier 47. The OR gate 44 produces an output signal, if any one of the alarm signals A1 to A4 is present. The delay time unit has a delay constant of about 10 msec, and is designed to prevent an output signal from a transient and irrelevant disturbance of the yarn texturing process, and which could result in the yarn 10 being cut by yarn cutter 12. The memory 46 ensures that a general alarm unit 23, which is associated with a group of stations or with the entire machine, will be able to generate a permanent signal to show that the production is disturbed and/or terminated. The output signal of the memory 46 is also fed to an amplifier 47 and from there to OR gate 48, which receives another signal to be more fully described below. The output signal of the amplifier 47 produces an output signal of the OR gate 48, which in turn is fed to the yarn cutter 12 to cause cutting of the yarn and interruption of the texturizing or draw-texturizing process, as the case may be. The other input signal to OR gate 48 is produced by trigger 49 via delay time unit 50 and amplifier 51. Trigger 49 is fed by the value U representing the measured yarn tension and by a second set value LU stored in set limit value memory 22 and representing the lowest accepted value of the yarn tension. It should be noted that this value LU is preferably set at zero. Trigger 49 produces an output signal, if the measured value U is lower than or equal to the set value LU. The delay time constant of unit 50 may be about 10 msec. The output signal of trigger 49 is, as mentioned above, fed to OR gate 48 and causes yarn cutter 12 to cut the yarn upstream of delivery roll 11, if and when the yarn tension is below a set value or in case of a yarn break between delivery rolls 11 and 16. The above described circuit generally corresponds to that disclosed in U.S. Patent No. 4,720,702 to Martens. In accordance with the present invention, the station mean values SM of a certain number of stations which all correspond to the one as shown in Figure 2 and which all have the same circuit as shown in Figure 2, are fed to a device 80 for summing all of the station mean values, so that the sum of the station mean values of these stations is determined continuously. The output group signal GM of summing means 80 equals the current sum divided by the number of stations, in this case six stations. It should be mentioned that this summing means is common to the given number of stations. At each station, however, the output signal GM of the summing means 80 is fed to a trigger 81 together with the current station mean value SM of that station. Trigger 81 forms the first difference signal D-between the overall mean value of the set number of stations and the station mean value SM derived at the given station. This first difference signal D is fed to another trigger 82 together with a limit difference value which is taken from the set limit values memory 22. Trigger 82 gives an output signal, whenever the absolute value of the first difference signal D is greater than the absolute value of the difference limit value . The output signal is fed to the general alarm unit 23 or may also be used for marking the package or classifying the quality of the package as described in EP-A-0406736, entitled Method and Apparatus for Monitoring the Tension and Quality of an Advancing Yarn. The difference limit value LD represents the upper limit and the lower limit of the overall group mean value GM of the given number of stations in that it gives the tolerance by which the station mean value SM of each station has to correspond to the overall group mean value GM of all stations. The diagram of Figure 3 shows a recording of measured values with the station mean value SM1 of an individual station of a group and the group mean value GM, which is continuously formed from the measured values or mean values of all measuring points associated to the group. A positive interval from the group mean value GM and a negative interval are established. These intervals result in an upper limit line USM or a lower limit line LSM for the station mean values of all measuring points associated to the group. When now the mean value of one station, for example, SM1 of a measuring point under review, leaves the tolerance range between the upper limit USM and the lower limit LSM, a first alarm signal will be emitted with a time delay. This alarm signal is repeated at regular time intervals as long as the described faulty condition continues. Marked on the time axis are the faulty conditions with the individual alarm signals. Figure 4 represents as a diagram the portion of a recording with the group mean value GM of a group of measuring points. The group mean value GM is determined from the continuously measured values of the individual stations or from the continuous mean values of the individual stations. A tolerance range is established for the group mean value GM between an upper limit line UGM and a lower limit line LGM. An alarm signal is emitted at all stations associated to the group with a time delay, when the mean value of the group GM leaves its tolerance range. This alarm signal is repeated at regular time intervals as long as the described faulty condition continues. The respective faulty condition is again plotted on the time axis with the emitted alarm signals. As an alternative of Figure 3, the diagram of Figure 5 is a recording of the station mean value SM1 of a certain station as well as the group mean value GM of all measuring points associated to the group. Again, a tolerance range is established for the group mean value with an upper limit line UGM and blower limit line LGM. An alarm signal is emitted with a time delay at each measuring point, whose mean value, for example, SM1, leaves the tolerance range of the group mean value GM between the upper limit line UGM and the lower limit line LGM. Likewise, as was described already with reference to Figure 4, an alarm signal is emitted with a time delay at all stations associated to the group, when the mean value of the group GM leaves its tolerance range between the upper limit line UGM and the lower limit line LGM. The alarm signals are each repeated at regular time intervals as long as the described faulty conditions last. The emitted alarm signals can be only optical or acoustical signals. The alarm signals can be also used to shut down one station or a group of stations of the machine. Further, the alarm signals can be used to classify the quality of the produced yarns and packages. In this instance the number of the errors will determine the class of quality. In the drawings and specification, there has been set forth a preferred embodiment of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims: A method of monitoring the tension of an advancing yarn at each of a plurality of monitored yarn processing stations of a yarn processing machine, continuously monitoring the value (U) of the tension of the advancing yarn at each of the yarn processing stations, and continuously determining the station mean value (SM) of the monitored tension of each of the yarns, characterized by the steps of generating a group mean value signal (GM) representative of an average of the station mean value signals (SM) of a group of said stations, and generating an alarm signal dependent on the current group mean value signal (GM) at each of said yarn processing stations, if a first difference signal (D) generated by comparing the group mean value signal (GM) with the current station mean value signal (SM) of the station exceeds a predetermined tolerance limit and/or if the group mean value signal (GM) exceeds a predetermined tolerance range. The method as defined in Claim 1, characterized by the fact that the step of generating a group mean value signal (GM) comprises continuously summing the station mean value signals (SM) from all of said stations of the group, and continuously dividing the sum by the number of said stations. The method as defined in Claim 1, characterized by the fact that the step of generating a group mean value signal (GM) comprises continuously summing the current tension value signals (U) from all of the stations of the group, forming the mean value of the sum, and continuously dividing the mean value of the sum by the number of said stations. The method as defined in Claim 1, characterized by the fact that the step of generating a group mean value signal (GM) comprises determining a desired mean value signal, and generating such signal as a constant value. The method as claimed in Claim 1, characterized in that a tolerance range is set as a constant positive and negative limit relative to said group mean value to thereby define an upper limiting line (USM) and a lower limiting line (LSM) for the station mean value of each station. A method as defined in anyone of the preceeding claims, characterized by the further steps of continuously determining a second difference value (DU) between the monitored value (U) of the yarn tension and the station mean value (SM) for each of the yarns, and generating a further alarm signal whenever the station mean value (SM) for one of the advancing yarns leaves a predetermined tolerance range(USM;LSM), or whenever the second difference value (DU) for one of the advancing yarns leaves a second predetermined tolerance range (UDU;LDU). The method as defined in anyone of the preceeding claims, characterized by the fact that the step of generating an alarm signal includes severing the yarn being processed at the associated yarn processing station upon the occurrence of either of the stated contingencies. The method as defined in Claim 7, characterized by the fact that the step of severing the yarn includes passing the alarm signal through a time delay circuit having a predetermined time constant so as to prevent the severing of the yarn in the event of the presence of a short and irrelevant alarm signal. The method as defined in Claim 7, characterized by the fact that the step of severing the yarn includes generating a general alarm signal which is associated with a group of yarn processing stations of the machine to indicate the yarn production at at least one of the associated stations has been terminated. A yarn processing machine having a plurality of stations for processing an advancing yarn, each station having sensor means at each of the yarn processing stations for continuously monitoring the value (U) of the tension of the advancing yarn, first circuit means at each of the yarn processing stations and operatively connected to said sensor means for continuously determining the station mean value (SM) of the monitored tension of each of the yarns, characterized by second circuit means for generating a group mean value signal (GM) representative of an average of the station mean value signals (SM) of a group of said stations on the machine, and third circuit means at each of said yarn processing stations for comparing the group mean value signal (GM) with the current station mean value signal (SM) of the station to generate a first difference signal (D), and for generating an alarm signal whenever the first difference signal (D) exceeds a predetermined tolerance limit . The yarn processing machine as defined in Claim 10, characterized by the fact that said first circuit means further comprises means for continuously determining the second difference value (DU) between the monitored value (U)of the yarn tension and the station mean value (SM) for each of the yarns, and means for generating an alarm signal whenever the station mean value (SM) for one of the advancing yarns leaves a predetermined tolerance range (USM; LSM), or whenever the difference value for one of the advancing yarns leaves a second predetermined tolerance range (UDU; LDU). The yarn processing machine as defined in Claim 10, characterized by the fact that each of said processing stations includes a false twist unit for imparting false twist to the advancing yarn, and yarn delivery means stationed downstream of said false twist unit, and that said sensor means is positioned between said false twist unit and said delivery means.

Inventors: DETERS LUDGER AUGUST DR, STUETTEM MANFRED, DETERS, LUDGER AUGUST, DR., STUETTEM, MANFRED, Stüttem, Manfred
Applicants: BARMAG BARMER MASCHF, BARMAG AG
Application year: 1991
Main classification: G01L5
IPC codes: D01H13, B65H59, B65H63