Title of Invention

A METHOD FOR MONITORING RUN/STOP CONDITIONS

Abstract

According to a method for monitoring run/stop conditions of a yam, particularly in knitting or warping machine by a yarn feeler comprising an electronic, yam actuated transducer operating with variable gain amplification of run input signals further processed into final output signals, during run of the yam and starting from a predeterminable maximum de- amplification gain for said run input signal permanently and automatically is controlled electronically with a constant reaction time delay towards a floating minimum just suffi- cient to derive stable, final output signals, and that by said reaction delay natural para- metric fluctuations of said run input signal are compensated for, while a sudden total drop of said run input signal due to a yam breakage is processed to a final output stop signal.

Full Text

Method for monitoring run/stop conditions of a yam The invention relates to an invention according to the preamble part of claim 1 and to a yarn feeler according to the preamble of claim 8. In order to detect a yam breakage in textile machines like knitting or warping machines a yarn feeler is known which is able to output a logical final output signal indicating the run/stop conditions of a yam actuating said transducer. A typical structure of a yarn feeler comprises said transducer, a variable gain amplifier, a detector/comparator operating with a threshold in order to gain a detected run signal and an output filter operating with a predetermined time delay to output final output signals. The electrical run input signal is generated on the basis of the yam speed but also on the basis of other parameters like yam tension, yam linear specific mass, yam count, yam flexibility, yam surface roughness, electrostatic charge of the yam directly contacting said transducer. A variable gain amplifier is used because the amplification gain needs to be adjusted towards a minimum just assuring a stable output signal irrespective of parametric natural influences. A too strong gain amplification results in a poor time definition of the output and an output sensitive to spurious yam motions simulated by external noise. A too low gain amplification results in an erratic output signal despite a correct run of the yam. In the known yam feeler the variable gain amplifier is adjusted manually, however, this is not well accepted by the users, because such empirical adjustment or trimming procedures are a waste of time and need particular skill, especially if a plurality of yarn feelers are installed at a machine. There also is a constant large risk that the adjustment is not carried out correctly. FR 2161471 B discloses a detector monitoring the presence of a running yam or the absence of said yam by means of two piezo-ceramic ultrasound pick-up heads defining a yam passage. Stop conditions of the yam present in the yam passage cannot be detected. A gain controller having a large time constant is provided to assure a stable oscillation of said ceramic pick-up heads. Within the signal evaluation circuit another gain corrector is provided serving to maintain the gain of an amplifier such that the output signals of said ceramic pick-up heads remain in a quasi-sinusoidal range. Said gain corrector is defined by resistors, a diode and a transistor. Without yam in the yam passage the output signal of said pick-up head is regulated to an average value, i.e. with regular amplitudes of the same magnitude. A yam present and running in said yarn passage is modulating the amplitudes of said output signal such that the magnitudes of the amplitudes vary with low frequency. A terminal transistor and a filtering device output a final logical signal zero or one depending on whether or not the amplitudes of the output signal remain unchanged or vary with low frequency. US 4,476,901 discloses a photoelectric contactless weft arrival feeler of an air jet loom. Said feeler is monitoring the presence or absence of the weft yam but does not monitor run/stop conditions of said weft yam. A gain changer circuit is associated to an amplifier in order to increase the gain factor, i.e. to change the operating point of the amplifier towards high in case that the optical sensitivity of the feeler head has deteriorated by dust or lint. A gain control is carried out by comparing two reference values, namely a reference voltage of a reference voltage power supply and the feeler output signal level when no weft yam is present. A correction signal is derived from said comparison and is supplied to the variable gain amplifier in order to increase its gain factor proportional to the decrease of the sensitivity of the feeler head and to keep the amplification gain constant all the time. It is a task of the invention to provide a method and a yam feeler allowing to operate on the basis of said method, both leading to high quality of yam monitoring, i.e. to avoid a poor time definition of the output signal, to achieve output signals being insensitive to external noise and to safely avoid an erroneously generated final output stop signal in case of a proper run of the yam. Said task is achieved with the features contained in claim 1 or with the features contained in claim 8. According to the method the gain amplification permanently and automatically is adjusted to an optimum, namely a minimum just sufficient to ensure stable final output signals. No manual adjustments are necessary. Since the yarn feeler is adapting itself to an optimum sensitivity assuring stable final output signals, poor time definitions of the output signals and influences of external noises are avoided as well as an erroneously final generated output stop signal in case of properly running yarn. Said minimum permanently is adapted to just cope with the instantaneous summary of all influencing parameters. The yarn feeler does not need any manual trimming or adjustments since it automatically is seeking an optimum gain amplification. In knitting or warping machines having a plurality of such yam feelers the quality of each yam feeler in view to its operation behaviour is enhanced significantly. The improved monitoring quality is achieved without necessary adjustment procedures carried out by operators. Of particular advantage is that a change of the yarn count or the yarn quality does not need any preparatory work at the yam feelers provided since each yam feeler has its own self-learning control adapting automatically to the instantaneous conditions and influencing parameters. The control strategy used is an automatic gain control technique interfering in a regulating fashion at the variable gain amplifier in order to maintain the final output signal within specified limits and independently of the amplitudes of the run input signal. A prerequisite is that the control band width is larger than the band width of the input run signal variation such that the control is able to follow these natural parametric variations. The control is operating with a constant reaction time. In order to avoid false output stop signals during normal run of the yarn the output signals are filtered with a time delay slightly longer than the reaction time of the control. Said additional delay is acceptable for applications where yarn speed variations are moderate and also where the top speed of the yarn during run is predeterminably moderate as on knitting or warping machines. Any type of electronic transducer can be integrated into the yarn feeler like piezo-electronic, electrostatic or other transducers. A final prerequisite of a correct function is that the band width of signals caused by yarn breakages is by far larger than the control band width. A yarn breakage will lead to an input run signal drop occurring much faster than the reaction 'time of the control so that a correct final output stop signal will result safely. Particularly in knitting or warping machines the natural parametric variations are slow enough, since the yarn starts its run with a mild acceleration, runs for a long time at essentially constant speed, until it then stops after a smooth deceleration. The slowness of the physical phenomenon provides enough time to adjust the gain amplification without the danger of generating false final stop signals, namely by filtering with an acceptable time delay prior to putting out the final output signal. It is advantageous to compare the amplified run input signal with a predetermined threshold in order to output a detected run signal, on the basis of which the final output signal can safely be generated, but which simultaneously can be used to control the gain amplification such that the amplified run input signal just is higher than said threshold. As already mentioned, the mutually related band widths of the control and the natural variations of the run input signal allow to follow said variations with the control in order to reliably achieve an essentially stable detected run signal, fluctuations of which are filtered by the output filter as long as such a fluctuation is not caused by a fast breakage drop. According to a further aspect of the method the variations of the gain amplification are controlled independently from the amplitudes of the run input signal in order to keep the final output signal within specified limits. Said AGC-control strategy can be carried out reliably and permanently by generating an amplification gain control signal on the basis of said detected run signal, to which amplification gain control signal the amplifier is responding by varying its amplification factor or sensitivity accordingly. As soon as said detected run signal shows the tendency to rise or to fall the gain amplification will be lowered or raised, accordingly. Since in the case of a piezo-electric transducer almost all parameters originating from the yarn and its run are essentially constant, except the yarn tension decisive for the run input signal, the amplification gain control signal generated on the basis of the detected run signal is reflecting relatively precisely the control effort necessary to compensate for tension variations. Said interrelationship can be used to measure the instantaneous yam tension. In order to generate a reliable, logical, detected run signal or run/stop signal it could also be necessary to vary the detection threshold. Since a final output stop signal also can occur within the correct operation cycle of the machine equipped with the yarn feeler, namely when the yam is stopped as intended but not due to a yam breakage, it is useful to evaluate the final output signals representing the run/stop conditions of the yarn in view to a sync-signal associated to normal or correct run/stop conditions. A final output stop signal representing a yam breakage leads to a stop of the machine when the associated to sync-signal is indicating that the yam should run. In the yam feeler it is advantageous to have a reaction time of the AGC-control strategy weak enough to compensate for natural parametrical fluctuation or spikes in the detected run signal, which fluctuations, as mentioned, occur slowly enough. Since to the contrary, a yam breakage leads to a sudden drop of the yam input signal, the then detected run signal cannot be maintained stable further on, and even the output filter cannot filter out said sudden drop, such that in the case of a yam breakage a reliable final output stop signal will be generated. The reaction time of the amplification gain control circuit ought to be adapted to the compensation of natural parametrical fluctuations. Any type of transducer can be used for the yarn feeler. Of particular advantage are piezo-electric or electrostatic transducers which operate reliably and safely. Embodiments of the invention will be explained with the help of the drawings. In the drawings is: Fig 1 a yam supply and intake position of a knitting machine, Fig 2 a block diagram of a yam feeler as used in Fig 1, and Fig 3 several superimposed diagrams representing the method of operation of the yarn feeler. As an example of a yarn consuming textile machine in Fig 1 a knitting machine K is shown, consuming a yarn Y intermediately stored at yarn feeder F. Yarn feeder F is equipped with rotatable storage body 1 carrying a braking ring 2, below which the yam is withdrawn through an outlet eyelet and via a yam feeler A into a knitting station 7 of knitting machine K. Yarn feeder F contains an electrical drive 3 controlled by a control unit 4 and sensors 5 monitoring the yam store on storage body 1. Yam feeler A is equipped with yam guide element 6 through which yam Y while being withdrawn is deflected such that it actuates by its speed and/or tension an electronic transducer T apt to generate signals processed in a control circuit C. Yam feeler A has the task to, e.g. stop knitting machine K and/or feeder F, in case that a yarn breakage has occurred. Furthermore, final output signals as provided by yam feeler A have to reliably represent run/stop conditions of the yam, e.g. in accordance with the operating cycle of the knitting machine or its sync-signal. Yam feeler A with its control circuit C is depicted in Fig 2 in the form of a block diagram. The output of transducer T (e.g. a piezo-electric or electrostatic transducer) providing run output signal S is connected to a variable gain amplifier VA generating an amplified run output signal, AS in the form of a so-called "coloured" noise signal for a detector/comparator D/C, which in turn outputs a detected run signal DS. For this purpose detector/comparator D/C is operating with a predetermined threshold, i.e. detected run signal DS will be present with running yam at the output of detector/comparator D/C as long as amplified output signal AS with its level will be higher than the threshold. Detected run signal DS is finally filtered by output filter OF and is outputted in the form of a final output signal OS, i.e. either a final output run signal or a final output stop signal. Said final output signals will be considered, e.g. in the control unit or stop motion relay of the knitting machine and/or the feeder, e.g. in correlation to a so-called sync-signal indicating that the yarn Y from yam feeder F should run or should not run. (A plurality of similar yarn feeders F may be arranged to feed several yarns to the knitting stations of knitting machine K, each having an own yarn feeler A.) In the control circuit of yarn feeler A of Fig 2 furthermore an amplification gain control circuit AGC is provided and connected to the adjustment inlet of variable gain amplifier VA and also to the output of detector/comparator D/C. Amplification gain control circuit AGC, e.g. in the form of a "blocked oscillator (oscillation frequency e.g. about 2.5 KHz) is able to generate an amplification gain control signal CS for varying the gain amplification of variable gain amplifier VA or the respective amplification factor or the amplified output signal AS, respectively. The momentary value or level of detected run signal DS is used as a decisive parameter for the generation of amplification gain control signal CS. Amplification gain control circuit AGC is operating with constant reaction time Tc of about 40 ms. Similarly output filter OF is operating with a predetermined constant time delay To e.g. about 50 ms. I.e., time delay To is at least slightly bigger than reaction time Tc. The operation of yarn feeler A will be described with the help of Figs 2 and 3. Prerequisites for a proper operation of yarn feeler A is the already mentioned difference between To and Tc. Furthermore, the control band width has to be broader than the band width of any natural parametric variations of the run input signal S so that the AGC control will be able to follow these natural parametric variations. A yarn breakage is no natural parametric variation of the run input signal but will cause a run input signal decrease much faster than the reaction time Tc of the AGC circuit. As shown in the first upper diagram of Fig 3 in a knitting machine the yarn is starting with weak acceleration, will then run for a long time at constant speed and will finally stop after a smooth deceleration, if no yarn breakage has occurred. In the second part of the curve in the first upper diagram the yarn again starts with moderate acceleration and then runs with essentially constant speed. However, in this case a yarn breakage B is occurring, meaning that the yarn speed is suddenly dropping to zero. The second curve in Fig 3 represents the amplification gain control signal CS as generated on the basis of or in order to stably maintain detected run signal DS (third diagram 'from the top). The second diagram from the top indicates that amplification gain control signal CS is controlled at a maximum when there is no yarn speed and varied indirectly proportional to the yarn speed behaviour. Actually, amplification gain control signal CS by the interference of AGC circuit and during the run of the yarn is adjusted to an optimum floating minimum M just sufficient to maintain a relatively stable detected run signal DS and also to assure a stable output signal OS (fourth diagram from the top). The most advantageous minimum of the sensitivity or the amplification gain in a certain point of time corresponds to a value with which a stable final output signal derived from the yarn speed and other parameters typical of the operating conditions will be generated, and for which minimum the final output signal remains insensitive to spurious yam motions only simulated by external noise and where there is no danger that an erroneously final output stop signal can be generated even though the yarn is running correctly. As already stated, signal CS is modulated essentially inversely proportional to the run input signal S or the speed profile of the yarn and so that the amplified run output signal AS always will remain just above the threshold as considered in detector/comparator D/C resulting in the signal chain DS, namely the detected run signal DS in the third diagram from the top. AGC circuit is operating with the above-mentioned reaction time Tc since parametric natural fluctuations cannot be avoided during the run of the yarn. Such fluctuations might cause spikes E in the signal chain of DS, resulting from the fact that the amplification gain control is compensating for such signal fluctuations upon their occurrence and with reaction time Tc. However, since such spikes E will be compensated for in a time shorter than time delay To of the output filter OF, the finally generated output run signals OS will be stable and without any spikes and will allow to reliably judge the run/stop conditions of the monitored yarn. The lowest diagram in Fig 3 is indicating the so-called sync-signal, namely a signal as e.g. emitted by the control unit of the knitting machine and indicating, e.g. for the respective yarn feeder or even the control circuit C of the yarn feeler A when the yarn should run and when not. If, as shown in the upper diagram, left-side, the yarn is decelerated to stand still as re-squired by the sync-signal, the end of detected run signal DS occurring in correspondence with the standstill of the yarn will result in final output stop signal (right-end flank of the left signal chain OS) which, however, will not be considered as being critical, e.g. in the control unit of the knitting machine, since this is only a confirmation of an expected stop condition of the yarn as required by the drop of the sync-signal. When, however, as shown in the right curve of the upper diagram in Fig 3 (V dropping due to yarn breakage B) the signal drop is occurring so fast that the amplification gain control signal CS is unable to follow and to compensate for this sudden signal drop, the amplified output signal AS will not reach the threshold so that the detected run signal DS will drop accordingly at SDS leading, due to time delay To of output filter OF, to a somewhat delayed final output stop signal SOS of signal chain OS. Since at this point in time sync-signal (lowest diagram in Fig 3) still is present indicating that the yarn actually still should run, the control unit of knitting machine K immediately recognises final output stop signal SOS as an indication of yarn breakage B and will switch off the knitting machine and/or the feeder. The applied AGC-control strategy must not allow false final stop signals during the normal operation. Unavoidable, natural signal fluctuations also must not generate a false stop. This is achieved by filtering the detected run signal DS for a time delay To slightly longer than the reaction time Tc of the AGC-circuit However, this added delay To is acceptable in case of knitting or warping machines operating with relatively slow natural parametric variations, because the slowness of the physical phenomena gives enough time to adjust the sensitivity or the gain amplification by the AGC-control strategy and to avoid the generation of false final stop signals by filtering the detected run output signal DS with said acceptable time delay To prior to output. Furthermore, (second diagram from the top in Fig 3) the amplification gain control signal CS in case of a piezo-electric transducer T, where all yarn parameters are essentially constant, except the yarn tension, also is actually a measurement of the control effort to compensate tension variations. As such CS can be taken to measure or monitor even the yarn tension. Amended Claims Method for monitoring run/stop conditions of a yam (Y), travelling with a yarn speed profile varying between minimum speed and maximum speed, particularly in knitting or warping machines, by means of an electronic yam feeler containing a yam actuated transducer (D) contacted by the yam and operating with variable gain amplification of run input signals (S) which are further processed to final output signals (OS, SOS) representing said run/stop conditions, characterised in that starting from a predetermined minimum yam speed related maximum the amplification gain for said run input signal (S) permanently and automatically is controlled electronically substantially inversely proportional to the yam speed profile and with a constant reaction time delay (Tc) towards a floating minimum (M) just sufficient to derive a stable, output run signal (OS), that by said reaction time delay (Tc) natural parametric fluctuations (E) of said run input signal (S) are compensated for, while a sudden total drop of said run input signal due to a yam breakage (B) is processed to a final output stop signal (SOS), and that the momentary final output signal (OS, SOS) constantly is evaluated in view to a simultaneously present signal indicating when the yam should run and when not, e.g. a so-called sync-signal associated to expected yam run/stop conditions. Method as in claim 1, characterised in that said run input signal (S) is amplified into an amplified run output signal (AS) which permanently is compared to a predetermined threshold in order to achieve a detected run signal (DS), and that said amplification gain is controlled towards said floating minimum (M) on the basis • of said detected run signal (DS) such that said amplified run output signal (AS) is maintained just above said threshold in order to ensure a stable final output signal-Method as in claim 1, characterised in that controlling said amplification gain towards said floating minimum is carried out with a band width larger than the band width of natural parametric variations of said run input signal (S) but with a band width being significantly narrower than the band widths of run input signal variations caused by a yarn breakage (B), such that said control follows natural, parametric run input signal variations but is unable to follow rapid variations caused by a yam breakage. 4. Method as in claim 2, characterised in that for controlling said amplification gain towards said floating minimum (M) an amplification gain control signal (CS) is generated on the basis of said detected run signal (DS).. 5. Method as in claim 2, characterised in that for achieving said final run output signal (OS) said detected run signal (DS) is filtered with a time delay (To) slightly larger than said control reaction time delay (Tc) used for controlling said amplification gain. 6. Method as in claim 1, characterised in that said run input signal (S) is generated by a piezo-electric or electrostatic transducer (T) at least responding to speed and/or the tension of the yam (Y) contacting said transducer (T). 7.. Method as in claim 4, characterised in that the momentary yam tension is derived from said amplification gain control signal (CS) by piezo-electric transducer (T) of said yam feeler (A) responding to yam tension variations. 8. Yarn feeler (A) for monitoring run/stop conditions of a yam (Y) running with a yam speed profile between minimum speed and maximum speed, particularly in a knitting or warping machine, comprising an electronic transducer (T) generating a run input signal (S) upon contact actuation by the running yam (Y), an amplifier (VA) with variable amplification gain connected to said transducer for amplifying said run input signal (S) into an amplified run output signal (AS), a detector/comparator. (D/C) for comparing said amplified run output signal (AS) to a detection threshold for generating a detected run signal (DS) and an output filter (OF) connected to said detector/comparator for filtering said detected run signal (DS) with a time delay (To) in order to output final output signals (OS, SOS) representing said yarn/stop conditions, characterised In that an amplification gain control circuit (AGC) is provided and connected to the exit of the detector/comparator (DC) and the amplifier (VA) for generating an amplification gain control signal (CS) for varying the amplification gain towards a momentary floating minimum (M) and on the basis of said detected run signal (DS), such that with said minimum said output filter (OF) is apt to generate final run output signals (OS) remaining within specified limits, that said amplification gain is variable by said amplification gain control circuit (AGC) with a constant reaction time delay (Tc) which is shorter than the larger time delay (To) of said output filter (OF), and that said yam feeler (A) comprises a piezo-electric or electrostatic transducer (T) apt to create said run input signal (S) depending on the speed and/or the tension of the yam (Y) actuating said transducer (T) by direct deflection contact. 9. Yam feeler as in claim 8, characterised in that said time delay (Tc) of said amplification gain control circuit (AGC) is adapted to the compensation of natural parametric fluctuations of said run input signal (S) or of said detected run signal (DS), respectively. 10. Method for monitoring run/stop conditions of a yarn substantially as herein described with reference to the accompanying drawings. 11. Yarn feeler for monitoring run/stop conditions of a yarn substantially as herein described with reference to the accompanying drawings.

Documents:

in-pct-2001-1205-che-abstract.pdf

in-pct-2001-1205-che-claims filed.pdf

in-pct-2001-1205-che-claims granted.pdf

in-pct-2001-1205-che-correspondnece-others.pdf

in-pct-2001-1205-che-correspondnece-po.pdf

in-pct-2001-1205-che-description(complete)filed.pdf

in-pct-2001-1205-che-description(complete)granted.pdf

in-pct-2001-1205-che-drawings.pdf

in-pct-2001-1205-che-form 1.pdf

in-pct-2001-1205-che-form 26.pdf

in-pct-2001-1205-che-form 3.pdf

in-pct-2001-1205-che-form 5.pdf

in-pct-2001-1205-che-other document.pdf

in-pct-2001-1205-che-pct.pdf