Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1999-06-18
2001-10-16
Williams, Hezron (Department: 2856)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559450, C250S559130, C250S559150, C250S559190, C356S430000, C356S238200, C340S677000, C057S264000, C057S265000, C073S570000
Reexamination Certificate
active
06303938
ABSTRACT:
The invention concerns a method for detecting untextured or defectively textured yarn segments in textured filament yarns during the texturing process and a device for carrying out this method.
The texturing of filament yarns, particularly multifilament yarns, is known. Texturing serves to a produce from a synthetic, flat and smooth multifilament yarn a crimped and structured yarn that has textile character because of its bulky and lofty structure. For this purpose, the multifilament yarn is generally unwound from a spool, guided through a first delivery device, then heated in a heater, cooled on a cooling rail, and guided through a twister and a second delivery device arranged thereafter, a so-called draw-off delivery device, ultimately to be wound onto a yarn spool. The twister serves to temporarily impart high torque to the multifilament yarn in one pass (temporary torque is also known as false twist) and makes it possible, by means of the residual torque that simultaneously develops, to heat-set the twisted state by heating and cooling in the region ahead of the twister. After the twister, the torque is removed again and the filament yarn is untwisted. Because of the heat-setting treatment effected in the twisted state, the yarn has the desired crimped structure.
The torque is imparted primarily with a three-shaft disk friction unit or by means of so-called crossed belts. The use of friction to impart the torque permits very high rotation speeds and thus also high production speeds. However, if the friction ratios between the twister and the yarn are not constant, this leads to disruptions of the process that are also known as instabilities, and thus to loss of quality in the yarn. Such defects can result from spinning problems, uneven application or distribution of the spinning preparation on the surface of the yarn, temperature fluctuations during texturing or contamination by the heating and/or cooling rails. Such disruptions can cause so-called ballooning of the yarn, which occurs in particular at high rotation speeds. Ballooning of the yarn causes uncontrolled travel of the yarn, fluctuations of the yarn tension, and losses of quality. In unstable processes, in particular, the yarn can skip across the surfaces of the disks in the friction unit. This so-called “closing up” of the twist
1
causes a torque deficit in the twist zone. Yarn that has been imparted high torque before the twister can therefore pass through the unit briefly or by segments without the torque being removed. This results in short untextured yarn segments (temporary twist slippage), so-called tight spots, and long untextured yarn segments (“surging,” prolonged twist slippage).
1
TRANSLATOR'S NOTE: German Drallschlu&bgr;. Schlu&bgr; can also be translated as “termination.”
The quality of the textured yarn is generally monitored by spot-check-type inspection of the finished textured yarn. Only a very small fraction of the total output can be inspected in this way. In recent years, so-called on-line production controls have been introduced in texturing, with the result that nearly the entire output can be monitored for quality. However, the yarns are not examined by the measuring equipment in an uninterrupted manner, since the measuring sensors and scanning rates used operate at low frequencies, and undesirable short tight spots thus often go undetected. On-line control in the texturing process is generally accomplished by measuring the yarn tension. Known are monitoring systems that are able to detect low-frequency fluctuations
2
and peaks of yarn tension, i.e., fluctuations of yarn tension that are due to relatively long defects in the yarn. These systems are unable to detect short malfunctions and defects.
2
TRANSLATOR'S NOTE: The German actually says “thread tension pivots” or perhaps “changes in the direction of thread tension” (Fadenzugkraftschwenkungen). We assume that this is a typographical error for “fluctuations of thread tension” (Fadenzugkraftschwenkungen), there being only a one-letter difference.
A yarn tension sensor for a textile machine has been disclosed (EP 0 531 753 A1) for the determination of short-period fluctuations of yarn tension. This device is intended to measure relatively high-frequency fluctuations of yarn tension—of up to 50 Hz, for example—at high yarn speeds. It can also, therefore, detect relatively high-frequency fluctuations of yarn tension caused by the displacement of the yarn. This is intended to give the yarn tension sensor a much broader field of application. Examples of such applications that are disclosed include the compensation of aperiodic fluctuations of yarn tension via yarn braking means, the generation of trouble signals in response to periodically occurring deviations from the specified yarn tension characteristic, and detection of the gradual increase in yarn tension that occurs when the last third of a cop is being wound at the spool location, with appropriate throttling of the winding speed to prevent breakage of the yarn.
German Patent Application (Unexamined) 41 19 780 proposes, for quality monitoring in a false-twist crimping machine, measuring the yarn tension continuously between the false-twister and the exit delivery device from the texturing zone. The mean of the measurement values is constantly taken and the position of this mean and/or the relative position of the current measurement value with respect to the mean is evaluated. To permit a statement regarding the nature of the defects that affect quality, it is further proposed to determine a plurality of means differing with respect to the length of the evaluation time and, in order to generate a quality signal, to determine the relative position of the measurement value with respect to one or more of the means and/or the relative positions of the means with respect to one another. However, this method comprising taking the mean is unable to specifically and independently detect and evaluate sudden, brief irregularities in the process, such as voltage peaks, which occur, for example, in the event of hindrances to the winding of the yarn onto the spool and which subsequently disappear completely.
EP 0 406 736 B1 also proposes monitoring the tension of a traveling yarn by the uninterrupted determination of the mean. A difference from the mean and the current yarn tension are also constantly determined. Whenever the mean and/or the difference pass out of prescribed tolerance ranges for set periods of time, corresponding alarm signals are generated. Quality data for the yarn are derived on the basis of the occurrence of such alarm signals during preset time intervals. However, time delay elements with time constants of about 10 milliseconds are used to filter out output signals caused by brief disturbances in the yarn texturing process that are classed as irrelevant.
The technical problem underlying the present invention is, therefore, to provide an improved method, performed during texturing, for detecting undesired, untextured or defectively textured yarn segments, in particular short lengths in filament yarns manufactured in particular by the friction false twist process.
The solution to the technical problem lies in the provision of a method according to the main claim, in particular a method for detecting untextured or defectively textured yarn segments in textured filament yarns during the texturing process, in which high-frequency yarn signals, in particular yarn tension signals, are measured and evaluated. The measured yarn signals permit statements as to the degree and evenness of crimping of the yarn. Tight spots in the yarn, particularly short, untextured tight spots, are determined, by the detection process effected during the texturing process, as correspondingly brief signals which according to the invention are measured and evaluated as evidence of such tight spots. In the context of the present invention, a short tight spot is understood to be a tight spot with a length of no more than approximately 50 mm, preferably 1 to 50 mm. In the context of the present in
Cui Beiheng
Weinsdorfer Helmut
Deutsche Institute fur Textil-und Faserforschung
Miller Rose M.
Pandiscio & Pandiscio
Williams Hezron
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