Textiles: fiber preparation – Working – Drafting
Reexamination Certificate
2001-03-19
2002-12-31
Worrell, Danny (Department: 3765)
Textiles: fiber preparation
Working
Drafting
C019S240000
Reexamination Certificate
active
06499194
ABSTRACT:
BACKGROUND
The invention relates to a method or an apparatus for controlling the draft of a fiber mixture (e.g. of a sliver) of a textile machine, with means being provided to detect the fluctuations in mass of the fiber mixture which is supplied to the drafting arrangement. A changeable drafting zone compensates the fluctuations in mass and is provided with a delay time in order to take into account the running time of the fiber mixture from the measuring means to a control application point.
Prior literature (“Feedback control systems in modern sizing machines” by Prof. Burgholz—Textilpraxis 1963, July, p. 643) shows a drafting arrangement in which fluctuations in the mass of fiber material supplied to the drafting arrangement are detected by way of a measuring element. The movement of the measuring roller which is produced by the fluctuations in mass is stored via a mechanical storage element and is transmitted in a time-delayed manner to a mechanical device for influencing the draft quantity. A time delay for the control intervention is thus achieved in a mechanical manner, which intervention takes the distance between the measuring place and the actual control application point for the evening of the fiber mixture into account.
In newer devices, as have been described in DE-A1-36 19 248 for example, this intermediate storage of the signal of the measuring element is performed electronically. This cited publication states further that the time of delay is corrected according to the magnitude and type of the measured fluctuation in the mass, which means that as soon as the signal of the measured fluctuations in mass is located outside of the normal fluctuations of mass, the draft intervention will occur earlier. This reduces the distance between the control application point and the measuring location of the measuring element. This device allows in particular an improved compensation of sudden fluctuations in the mass of a sliver.
EPA-A2-803 596 further proposes an apparatus and method for the direct determination of set-points for the control application point of a draw frame. Several measured values of a quality-characterizing value such as the CV value are used in order to determine the optimized parameter, such as the control application point in a test run. This optimized control application point is to remain substantially unchanged during the operation. This method, which uses the CV value, leads to disadvantages particularly when the textile machine which is situated upstream of the drafting arrangement is supplied with only one untwisted sliver which shows relatively large fluctuations in mass.
An apparatus is further known from EP-A1 533 483, with influencing quantities which influence the measured signal of the measuring member being detected by a fuzzy logic control device and being linked to a knowledge base. A corrective value for the measured signal is produced therefrom. The delivery speed of the fiber material supplied by the drafting arrangement can be used as an influencing quantity for example. This means that the corrective value relates to the respective design of the determined measured value on the basis of influencing quantities and not to the determination of the control application point. For the purpose of correcting the control application point, it is proposed in this embodiment that a signal analysis is performed at the drafting arrangement output on the basis of the analysis of the response signal of the measuring element, thus enabling the performance of respective interventions. This means that a correction of the control application point will only be performed at a time when the flaw in the fiber material has already passed through the drafting arrangement and thus can no longer be corrected. Moreover, a further measuring element is required at the output of the drafting arrangement, as well as a complex fuzzy logic control device.
A device shown in DE-A1 42 15 682 in which a correction of the control application point is performed according to a specific method. The method for the correction of the control application point is only started when there is a transient signal in the measuring element before the drafting arrangement which exceeds a predetermined tolerance value. With the help of the response signal which is detected by a measuring element at the output of the drafting arrangement, a respective intervention is performed via the control unit comparison with the transient signal in order to correct the control application point. This system is not continuously in operation and additionally requires a measuring element at the output of the drafting arrangement. Moreover, a correction of the control application point is only performed when the sliver containing the flaw has already left the drafting arrangement.
Examinations have shown that the evenness of the formed sliver, or the CV value and the spectrogram image, changes once the fiber material is supplied to the draw frame at different delivery speeds. This means that one has noticed that the control application point between the two pairs of drafting rollers changes in its position depending on the delivery speed. This fact is usually not disadvantageous in “pure draw frames”, because these machines are usually operated with substantially constant speeds.
This fact is usually not disadvantageous in “pure draw frames”, because these machines are usually operated with substantially constant speeds.
If such a drafting arrangement unit is arranged downstream of a carding machine for further processing of the card sliver, major delivery fluctuations in the drafting arrangement must be expected as a result of the operating procedure in the carding machine. These delivery fluctuations in the carding machine are caused by changes in production, running down the machine during changes of the cans, running in new clothings, and other circumstances. As a result of this frequent change of the delivery speeds, there is also a displacement of the control application point with respect to the measuring place before the drafting arrangement. This leads to maintaining an adverse sliver quality in respect to sliver regularity (CV value) and the spectrogram image.
This fact is also not considered, or only partly with limitations, by the apparatuses mentioned in connection with the state of the art.
Various devices are further known from the state of the art, e.g. from EP-A1176 661, with the regulation of an autoleveller draw frame begin performed on the basis of inlet and outlet measuring element in conjunction with a predetermined setpoint value. In the exhibited example, the signal for influencing the control parameters which is measured at the output is used for overall amplification and the runtime of the controlling electronic system. This device is to be used in particular to correct abrupt changes in the supplied fiber mass. This device relates to the matching of the control parameters during the drafting process and not to any principal setting of the control intensity or calibration of the drafting arrangement.
Insofar as such drafting arrangement operates autonomously as a draw frame, it was common practice up until now to make respective settings of the control parameters on the draw frame by sliver tests which were performed in a stationary manner in the laboratory. The determined fluctuations in mass were determined in comparison with a predetermined setpoint value (sample sliver) and respective interventions in the control parameters on the drafting arrangement were made. The stopping and renewed start-up of the draw frame to perform such tests and for setting the draw frame did not have any major influence on the productivity or efficiency of the unit.
As soon as this drafting arrangement is operated in direct connection with an upstream textile machine (e.g. a carding machine), such sliver tests performed in the lab are not easily possible without reducing the overall efficiency of the entire system. This means that as soon as the sliver tests are performed in a stationary man
Gresser Götz Theodor
Griesshammer Christian
Müller Christian
Dority & Manning
Maschinenfabrik Rieter AG
Welch Gary L.
Worrell Danny
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