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Yarn Monitoring

  • A precise analysis of the moiré effect { a fabric defect} has shown that the associated periodically occurring defects in the yarn lie in the area where measured thick  places , which usually occur in conjunction with thin place , are a disturbing factor only in their periodicity & not in their size .
  •  The size of a thick place is about 8-10% of the average yarn count, with lengths ranging from 5 to 10 mm. In order to prevent individual spinning units from producing such defective yarn on rotor bobbin, it is recommended that the yarn be continuously monitored .
  • When such a periodic disturbance occurs ,it can be detected & removed , either manually or with a programmed autocleaner or doffer.
  • There are to types of monitoring systems being marketed , namely:

An Individual Monitoring System

  • In this system every spinning unit has a detector, which is designed to measure continuously either the yarn diameter or the spinning tension.
  • In order to detect periodic faults in the yarn, it is necessary to convey the signal generated by the detector through electric filters , which are adjusted to the expected frequency of these faults, termed the moiré frequency, f0.
  •  The moiré frequency can be calculated according to the equation :  

             f0 = v0 / ( 3.14 * d ).

    •  Where, v0 is withdrawl speed & d is  rotor diameter.
  • One reported method subjects the yarn signal to pulse-shaping, after which the shaped pulse train is is integrated & compared with predetermined threshold value.
  • The range of yarn counts that can be monitored is extended as a result of the fact that the processing of the thread signal is kept independent of the thread delivery speed.
  • One well reported commercially available unit based on the continuous measurement of the yarn diameter is the peyer-turocon monitor.
  • The signal evolution system used in this method carries out a continuous frequency analysis of the yarn signal.
  • This is performed over a frequency band of from -5% to 5% of the moiré -defect frequency to achieve a good separation of the periodic moiré signal from simultaneously existing normal yarn irregularity.
  • Fmk mfg. Ltd. Manufactures an electronic multipoint tension monitoring system based on the principle of measuring the difference between the centrifugal force acting in the rotor on a defective length of yarn & that acting on a perfect length & comparing with a predetermined threshold value.
  • It has the trade name tenscan which contains a solid state transducer unit , which can be fitted to any yarn processing machine.
  • The tenscan system is entirely electronic & is now claimed to perform three primary functions :
    • It sequentially measures in groups of four positions the tension value of each yarn emerging from the spinning unit by an individual solid-state transducer, which reads the tension continuously over a pre-set measuring period;
    • It compares the tension measured on each position with the pre-set limit; &.
    •  It indicates on a data-logger display the location of each position found to be outside the permitted-deviation limits.
      •  If individual motor drives are fitted to the rotor machine, the current consumption of each motor can be used to monitor the yarn irregularity.
      •  To recognize the incidence of slubs & flaws or structured changes {or both } in the yarn, a sensor device located to respond to changes in the current flow to the motor is provided.
      • As with the previously mentioned system , if the changes in the value of the measured factor ( in this case , the current) exceeds a pre selected value , an electric signal is generated, which flashes a warning light or shuts off the rotor drive.

A Mobile Monitoring System

  • The proposed use of a mobile monitoring system is to offset the relatively high capital outlay associated with individual monitoring arrangements .
  • With the mobile - monitoring approach , a carriage is fitted to the spinning machine with a sensing device {or devices} of the type used for individual monitoring.
  • The carriage can be programmed to monitor each position consecutively for a given time interval or to monitor units giving a sample of the production selectively.
  • The carriage can be made to stop the rotor unit or mark individual rotor units where the running quality of yarn is below that required.

 



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