Determination of Yarn Defects

This invention relates to a method and apparatus for the determination of yarn defects.

Simple mechanical devices are known which seek to determine and eliminate thick places in yarn by pulling the yarn through a slot adjusted according to the normal yarn diameter. Such a device, called a yarn clearer, assesses the yarn cross section as the only criterion.

In addition, devices are also known, and in many cases in use, in which the yarn cross section is measured optically, capacitively or by means of another medium and transformed into an electrical signal which corresponds to the particular yarn cross section. If the cross section signal then exceeds a predetermined value, the duration of the excess values is also determined and goes into the measurement value. Such devices can therefore assess both cross section and also the lengths of any thick or thin places in the yarn, and these yarn clearers generally guarantee a satisfactory yarn quality. However, they fail in all cases in which a regular or irregular sequence of defects of small cross section and small length is present. Individual examples of such defects are not in themselves disruptive; and to cut out each small defect is not practical. A corresponding yarn clearer of known type is therefore adjusted so that it does not respond to thick places of this type. Only after detection of the multiple repetition of such defects at intervals of decimeters or meters does this lead to the corresponding yarn being considered unusable.

Still more disruptive is the case of periodic repetition, i.e., the occurrence of such thick places at strictly uniform intervals. A fabric produced from such yarn then has the so-called Morie effect, which is also visible when the individual thick places disappear in the general uneveness characteristic of the yarn. These thick places cannot therefore be determined by standard measurement technology merely by shifting the response limit of the yarn clearer near to the average yarn cross section. As the very disruptive Morie effect is only formed when sufficiently large yarn lengths are processed, it is necessary for the determination of such regular or irregular sequences of thick places to extend over correspondingly long yarn sections.

The present invention takes into account these requirements and provides a method for determining yarn defects, in which the yarn cross section is continuously scanned by means of suitable feeler elements of other type of converter device and is converted into a corresponding electrical signal. The invention is characterized in that, in addition to the cross section and length of the yarn defects, their frequency and periodicity is checked and used as a criterion for initiating a signal in the event of the occurrence of regular or irregular sequences of thick places and/or a display means is activated as an indication of this defective yarn.

The invention also provides an apparatus for the implementation of this method, the said apparatus having a transmission channel at the input of which the signal corresponding to the yarn cross section is introduced and sufficiently amplified, a frequency dependent element operable as an adjuster for only operating the defects having a predetermined minimum defect length, a first comparator for the adjustment of the defect amplitude to which the channel is responsive, a monostable multivibrator for shaping the comparator output, an integrator for determining fault frequency and magnitude, a further comparator for detecting the integrated value and a display or signal device for indicating an alarm condition.

The method and apparatus of the invention are advantageously used as an addition to known yarn clearers. Thus arranged, they form an additional evaluation facility for monitoring the yarn quality.

Depending on the character of the yarn defect thus determined it may be of further advantage if the yarn defects ascertained in this transmission channel activate their own display or signal device, which is independent of the actual function of the yarn clearer. It would be little help if in the event of the occurrence of yarn defects whose signals are able to pass the transmission channel according to the invention, there took place only a yarn cut and a piece of the defective yarn were removed. This would be unusable yarn, but the cause of this type of yarn defect should be sought as a fault in the spinning process, which should be eliminated at the source. For this purpose, an indication or signal display showing that such a fault has been detected is more suitable than merely cutting out a piece of yarn, which will shortly be followed by another such piece.

It is an object of the present invention to provide a method and apparatus for detection of yarn defects which not only responds to the detected cross section and length of yarn defects, but also to the frequency or periodicity thereof.

It is another object of this invention to provide a method and apparatus for detection of regularly or irregularly occurring sequences of thick places in a yarn.

It is a further object of the present invention to provide a method and apparatus for detection of yarn defects which may be used in combination with a standard yarn clearer or independently thereof.

These and other objects, features, and advantages of the present invention will become more apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a transmission channel in accordance with the present invention; and

FIG. 2 is a schematic diagram of another embodiment of the transmission channel in accordance with this invention.

Referring to FIG. 1, a yarn 1 to be monitored is taken off a bobbin 2 and wound in a known manner on a parallel bobbin 3. In so doing, the yarn 1 runs through a measurement device 4 in the form of a converter having an output which represents the cross section of the yarn as an electrical signal U1. Such converters are well known in the art and operate on different principles, such as variable capacitance, variable inductance, air pressure variations, resonant frequency variations, optical indications, etc.

This signal U1 is raised to a suitable voltage level in an amplifier 5. The amplifier 5 is followed by a low pass filter 6 with an adjustable band pass. The adjustment of the band pass by means of a control value Ut determines the length of the defect so that in this low pass filter, signals representing short defects which should not pass through the transmission channel are suppressed. In this regard, the low pass filter 6 has an adjustable time constant .tau.=RC in the range of the transition time of a yarn fault through the measuring device, which yarn fault should be suppressed.

The signals U2 passing the low pass filter 6 reach a first comparator 7. The amplitude of the signals U2 is compared with an adjustable ideal value Us in this comparator which may be adjustable for cross section increases from 20% to 300%. If the amplitude exceeds the ideal value Us, a signal U3 is transmitted to a monostable multivibrator 8. This monostable multivibrator generates a pulse U4 of constant amplitude and duration.

The pulses U4 received from the multivibrator 8 are added up in an integrator 9; however, during the pulse gaps, the pulse sum stored in the integrator is at least partially discharged. The output voltage U5 of the integrator 9 acts on a second comparator 10 which is controlled by a reference signal Ub.

If only single pulses U4 occur at the output of monostable multivibrator 8 at widely spaced intervals, the integration of these pulses cannot result in a voltage level having the value of the reference signal Ub. However, if the pulses U4 follow one another at relatively short intervals, which signifies an accumulation of yarn defects the integrator becomes increasingly charged until in the comparator 10 the reference signal Ub is reached or exceeded, as a result of which a defect signal U6 is initiated. This defect signal U6 can then be used to activate a suitable display or signal device, such as a method instrument 11, a lamp 12, an alarm 13, or a relay 14 for initiating further switching functions, or a combination thereof.

FIG. 2 shows a further embodiment of the transmission channel, which is advantageously used when preferably periodic defects are to be determined. In this case the low pass filter 6 according to FIG. 1 is replaced by a band pass filter 16, which is tuned to the corresponding repetition frequency. This repetition frequency is advantageously made adjustable by a control signal Up supplied from outside, so as to be able to pick up periodicities over a certain frequency range. The remaining component elements and their functions are unchanged from those in FIG. 1.

The band pass of filter 16 is to be adjusted at the repetition frequency of the yarn faults. However, it is more advantageous to use a band pass filter which will pass not only the repetition frequency but all harmonics of this frequency. In this way, the complete frequency spectrum of the repetition frequency contributes to the output signal U2, and therefore, a very strong standard is obtained for periodically occurring yarn faults.

The method and apparatus of the invention can in themselves form a monitoring installation, with which the yarn 1 running through the measurement element 4 is examined merely for yarn defects consisting of a regular or irregular sequence of thick points. Such an arrangement is used when yarn production is already so perfect that other yarn defects, such as sporadic thick places, of all kinds, or double threads no longer occur.

The method and apparatus of the invention can, however, also form an addition to existing yarn clearers or yarn clearing installations which shows up a type of defect which could not be picked up with the conventional clearing equipment.

While I have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.