Method and Apparatus for Detecting the Faulty Working of Spinning Units of Open-End Spinning Machines

It is generally known in the spinning industry that, apart from the unevenness in the yarn, which may have the most varied amplitudes, periodic deviations occur which later become clearly visible in the yarn (yarn conversion table) and also in the woven fabric as a result of their position side by side. This phenomenon is generally known as the moire effect. The causes of such periodic faults in the yarn originate from the processing during which disturbances periodically occur. In a ring spinning frame, such disturbances may occur, for example, as a result of drawing rollers beating. During open end or rotor spinning, such disturbances appear particularly strikingly as a result of deposits in the rotor. Because it is known what generally causes the periodic disturbances, conclusions regarding the source of distrubance can be drawn from a yarn-unevenness diagram.

In open-end spinning, with regard to moire detection, it is known that the visible spacing of thick places appear on the yarn according to the circumference of the rotor. The difficulty in detection, however, lies in the fact that the delivery speed is variable and so the moire frequency is likewise variable.

It is true that it is possible to check a yarn production afterwards by random samples by means of a spectrograph (Uster) for whether such a moire effect has appeared or not. This often results in a major loss since the production has already taken place and, in any case, a relatively large amount of faulty yarn may have been produced depending on the frequency of the checking.

It is true that it is already known to detect the point of disturbance directly and immediately by monitoring individual spindles and so to avoid a large faulty production (DT-OS No. 2.409.882). According to the earlier proposal, this is effected so that, by measuring the yarn cross-section or yarn diameter, an electrical signal is produced which is subjected to an evaluation by means of at least one non-linear correction member.

In order to detect periodic faults in the spun yarn it is necessary, in this case, to convey the signal originating from a monitored yarn through electric filters which are adjusted to the expected repetition frequency of these faults, hereinafter termed moire frequency, and a detector has to be present at each spinning station. Since the delivery speed of the spun yarn is variable, either narrow-band filters have to be used, which are variable in their midband frequency, which leads to considerable costs, or very wide-band filters have to be used so that the moire frequency is transmitted by them even at different yarn delivery speeds. In the latter case, it is true that the costs for the circuit arrangement are reduced somewhat, nevertheless the wide-band nature of the filters has the effect that a considerable proportion of the frequencies of the normal unevenness of the spun yarn can pass through. When wide-band filters are used, therefore, a moire effect is only detected if it stands out very clearly from the normal unevenness of the yarn.

According to the invention, this problem is solved in that the yarn signal obtained is electrically multiplied by a signal of predetermined frequency, which is derived from the spinning machine and the differential-frequency signal thus obtained is filtered and subjected to a pulse shaping. The shaped pulse train is then integrated and compared with a preset threshold value. The signal of predetermined frequency is a rectangular signal which has the advantage that it is simple to produce and renders possible a simple multiplication by actuation of an on/off switch. The frequency of the rectangular signal may appropriately be derived from the speed of rotation of the yarn delivery roller. In order to better detect the frequency variations in the yarn signal, for example, as a result of slip of the yarn, the frequency of the rectangular signal is periodically altered. In one embodiment, the frequency of the rectangular signal is inexpensively altered mechanically. In another embodiment as a result of the fact that the frequency of the rectangular signal is altered electronically, external influences are eliminated.

In order to increase the certainty of detecting a moire effect, the filtered differential-frequency signal is compared with a second threshold value before the pulse shaping. The amplitude of the second threshold value is derived from the yarn signal, as a result of which the method can be used for a wider range of yarn counts. Its use for a wider range of speeds in the yarn delivery is rendered possible by the fact that the amplitude of the second threshold value is derived from the speed of rotation of the yarn delivery roller.

The advantage of a greater certainty of detection for a wider range of counts and a wider range of yarn delivery speeds also results from the fact that the amplitude of the threshold value with which the integrated differential-frequency signal is compared, is derived from the speed of rotation of the yarn delivery roller. The yarn signal is preferably obtained by measuring the yarn dimensions over the yarn tension.

The apparatus for carrying out the method, which is equipped with a measurement receiver, is characterized by a signal generator, a multiplier, a filter, a pulse shaper, an integrator and a comparator. The signal generator may appropriately consist of a perforated disc connected to the yarn delivery roller, with a light source and photoelectric cell associated therewith. In another embodiment the signal generator consists of a slotted disc with associated magnetic receiver. The periodic alteration of the frequency of the rectangular signal by mechanical means is achieved by connecting the perforated disc or slotted disc to the yarn delivery roller through a cone gear. The provision of a a frequency-voltage converter, a delta-voltage generator, an adding amplifier and a voltage-frequency converter renders possible the electronic alteration of the frequency of the rectangular signal. In order to increase the certainty of detecting a moire effect, a second comparator is connected between the filter and the pulse shaper.

Accordingly, it is an object of the present invention to provide a method and apparatus for determining when components of a spinning machine are not functioning properly.

Another important object of the present invention is to provide an apparatus for monitoring the yarn being produced on open-end spinning machines for detecting the faulty working of spinning units and, in particular, the spinning compartment.

Still another important object of the present invention is to provide a method and apparatus which renders possible, in a simple manner, a reliable detection of periodically reoccuring faults in the spun yarn and, hence, faulty working of the spinning unit of an open end spinning machine.

These and other objects and advantages of the invention will become apparent upon reference to the following specification, attendant claims, and drawings.

FIG. 1 shows the block circuit diagram of the apparatus according to the invention;

FIG. 2 shows an apparatus for the mechanical alteration of the frequency of the rectangular signal;

FIG. 3 shows the block circuit diagram of a device for the electronic alteration of the frequency of the rectangular signal.

The monitoring apparatus illustrated as an example of an embodiment in FIG. 1 contains a measurement receiver 1 which converts a measured value obtained by sensing the yarn into an electric signal which is hereinafter called the yarn signal. The yarn signal is preferably produced by measuring the yarn mass via the yarn tension and converting it into an electric signal. For this purpose, the measurement receiver 1, which is not illustrated in detail, comprises two parallel coils, in the stray field of which there is movable a yarn sensor constructed in the form of a plate-spring, for example, gripped at one side, the natural frequency of which is lower than the lowest rotational frequency of the rotor of the open-end spinning apparatus and which exerts a pressure on the spun yarn in the region between the rotor and the yarn winding point. Such a device, by means of which the yarn mass if measured via the yarn tension using the centrifugal force acting on the yarn, and a measured value is produced therefrom, is known, so that a further explanation can be dispensed with.

Instead of the yarn mass, however, the yarn diameter or yarn cross-section may possibly be measured by well-known devices and the measured value obtained be converted into an electric signal.

The yarn signal originating from the measurement receiver 1 passes through an amplifier (not shown) and is then evaluated by a search-frequency process which utilizes a signal generator 2 that produces a signal of predetermined frequency derived from the moire frequency. The signal of predetermined frequency is preferably a rectangular signal which is simple to produce. When the rectangular signal from generator 2 and the yarn signal from sensor 1 are multiplied by one another, as will be explained later, frequencies result which correspond to the sum and the difference of the frequency proportions of the two signals. If a suitable frequency of the rectangular signal is selected, a filter adjusted to a fixed differential frequency can be used for the moire detection, even with a variable moire frequency, for example, at different yarn delivery speeds, which is an advantage for reasons of price.

The frequency of the rectangular signal is derived from the speed of rotation of the machine, only those rotating machine parts being considered which ensure that the frequency of the rectangular signal differs only slightly from the moire frequency. Preferably, therefore, the speed of rotation of the yarn-delivery roller, which--apart from the slip between roller and yarn--is in a fixed ratio to the moire frequency, is used to produce the rectangular signal. Furthermore, since it is a requirement that the method and the apparatus should be able to be used for a plurality of yarn-delivery speeds and yarn counts, while on the other hand, with this requirement, it is not possible, because of different yarn slip, to maintain the differential frequency between rectangular signal and moire frequency so constant that it comes with sufficient certainty within the pass range of the following filter, a device is provided which enables the frequency of the rectangular signal to be allowed to swing about a mean value. In this manner, at any yarn-delivery speed and with any yarn slip which usually occurs, the differential frequency passes periodically through the pass range of the following filter.

FIG. 2 shows a device for producing and periodically altering the frequency of the rectangular signal by mechanical means. A truncated cone 30 of a cone gear 3 which is connected to the yarn-delivery roller 4 for rotation therewith, is situated opposite a truncated cone 31 secured to a shaft 5 mounted for rotation in the machine frame. A drive belt 32 runs over the truncated cones 30 and 31. The position of the drive belt 32 and, hence, the transmission ratio, is continuously altered by an eccentric rod 33 with associated eccentric 34, which is continuously driven by a motor (not shown). Rigidly connected to the drive shaft 5 is a perforated disc 6, so that light pulses from a light source 60 can be transmitted to a photoelectric cell 61. The photoelectric cell 61 is electrically connected to a frequency divider 20 (FIG. 1). With suitable selection of the basic transmission ratio, the number of holes in the perforated disc 6 and the reduction ratio of the frequency divider 20 connected to the photoelectric cell 61 (FIG. 1), a pulse train results, the frequency of which corresponds approximately to the moire frequency. This frequency is periodically altered within narrow limits by the variable speed gearing. Instead of the perforated disc 6, other pulse producers, for example, a slotted disc with a magnetic receiver (not shown) associated therewith may also be used.

The frequency of the rectangular signal can also be varied electronically, as is explained by way of example with reference to FIG. 3. In this case, the perforated disc 6 illustrated in FIG. 2 is secured directly to the yarn-delivery roller so that, while retaining the light source 60 and photoelectric cell 61, a pulse repetition frequency is produced which is proportional to the yarn-delivery speed. Connected to the photoelectric cell 61 is a frequency-voltage converter 7, the output of which is connected to the first input of an adding amplifier 71. Connected to the second input of the adding amplifier 71 is a delta-voltage generator 72. The adding amplifier 71 is followed by a voltage-frequency converter 73 which is electrically connected to the frequency divider 20 (FIG. 1).

According to this arrangement, the frequency of the rectangular signal produced is converted by the frequency-voltage converter into a voltage proportional thereto and then altered by a small amount by adding to this voltage a second voltage which is produced in the delta-voltage generator 72 and which is relatively low and alters slowly, for example within 2 minutes, in delta form. Accordingly, the frequency of the output signal of the voltage-frequency converter 73 also alters in comparison with the frequency of the input signal entering the frequency-voltage converter 7, by a small amount.

The signal processing is explained below with reference to FIG. 1. The rectangular signal of variable frequency, which is produced by the signal generator 2 consisting of the device shown in FIG. 2 or of the device shown in FIG. 3 with a perforated disc 6 mounted directly on the yarn-delivery roller 4, is supplied to the frequency divider 20 and a frequency-voltage converter 8. Different divider ratios can be set in the frequency divider 20 depending on the circumference of the spinning rotor, as indicated in FIG. 1. It should be pointed out here that only one of each of the components 2, 20 and 8 is present on each open-end spinning machine. Therefore, the production of the rectangular signal of variable frequency is only of minor importance as regards cost, in relation to the individual spinning stations. On the other hand, the components mentioned below are present at each spinning station.

The rectangular signal emerging from the frequency divider 20 reaches a multiplier 21 which electrically multiplies the rectangular signal by the amplified yarn signal originating from the sensor 1. The multiplication product passes to a demodulator 22, in which the rectangular signal is largely eliminated. Following the demodulator 22 is a selective filter 23 which is adjusted to the differential frequency between rectangular-signal frequency and moire frequency. The filter 23, however, does not only deliver a signal when there is a moire effect in the spun yarn but also responds to frequencies which are included in the normal irregularities in the yarn. The signal delivered in this case, however, is considerably lower.

An improvement in the signal-to-noise ratio and, hence, a greater certainty of detection of a moire effect is obtained if the differential-frequency signal formed is compared, before the further processing, with a threshold value which is designated as the second threshold value. This threshold value is referred to as the second threshold value so as to distinguish it from the threshold value fed in at the end of the system which is discussed below. The comparison takes place in a comparator 24. In order to adapt the method and the apparatus for use for a wider range of yarn counts, the amplitude of this second threshold value is derived from the yarn signal, in that the comparator 24 is connected to the sensor 1 through an amplifier 9. The amplitude of the second threshold value may, however, also be derived from the speed of rotation of the yarn-delivery roller 4, as a result of which it is possible to use the apparatus for a wide range of speeds in the thread delivery. In this case, the threshold voltage is supplied to the comparator 24 through the frequency-voltage converter 8 (broken line). Likewise, it is also possible, instead, to adjust the amplitude of the threshold value by hand.

The signal components leaving the comparator 24 reach a pulse shaper 25 in which the filtered differential-frequency signal is subjected to a pulse shaping. The shaped pulse train is subsequently integrated in an integrator 26, at the output of which a voltage builds up which depends on the extent of the moire effect. The integrated differential-frequency signal is supplied to a comparator 27 in which it is compared with a threshhold value, the height of which may appropriately be derived from the speed of rotation of the yarn-delivery roller 4, in order to obtain a greater certainty of detection of a wider range of yarn counts and wider range of yarn-delivery speeds. For this purpose, the comparator 27 is electrically connected to the frequency-voltage converter 8. The threshold value can, however, also be adjusted by hand if required. If this threshold value is exceeded by the integrated differential-frequency signal, and thus a specific extent of the moire effect is reached, the comparator 27 delivers a pulse to a component characterized, for example, by a switch or relay 28 which can be used to switch off the spinning station or to actuate an indicating device.

While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.