Method and apparatus for evaluating yarn signals having an at least approximately periodic component

A method and apparatus for evaluating yarn signals having at least an approximately periodic component superimposed on an irregularity provides for determining the polarity values of successive signal components using a comparator and the evaluation of coincidence of such polarity values during a predetermined period using counting means.

The invention relates to a method of and an apparatus for evaluating yarn 
signals having an at least approximately periodic component superimposed 
on an irregularity. 
Modern methods of producing yarns make it necessary to monitor the yarn at 
the spinning positions continuously and directly. Irregularities at 
individual spinning positions may thus be detected immediately and 
necessary measures taken so that the production of faulty yarns is 
recognized at the moment of formation and is prevented as quickly as 
possible after detection. 
The plurality of spinning positions used in operation, however, also 
requires a plurality of monitoring devices. Accordingly, it is desirable 
to provide a method of monitoring which requires as low an outlay on 
devices for carrying out the method as possible. 
In order to do this, the number of requirements to be met by such 
monitoring methods has to be restricted to individual criteria. In order 
to detect the production of faulty yarns at an early stage, it is 
absolutely essential to determine periodic components superimposed upon 
the general irregularity caused by the production process. If such 
periodic components do not stand out particularly in the general 
irregularity, they may have a very disturbing effect during further 
processing of the yarn, for example, by producing a so-called Moire effect 
which makes the corresponding fabric unusable. 
Various methods and apparatus are already known for determining periodic 
components in the irregularity of yarn parameters. However, they are 
either too slow or require an additional expensive circuit. 
By restricting the evaluation of the irregularity, or of the yarn signal 
obtained from the detection of the irregularity, of the yarn by means of 
measuring instruments known per se merely to the periodic components 
thereof, it has been found that autocorrelation was initially suitable for 
this purpose, particularly since it affords a basis for evaluating the 
yarn signals by means of digital signa-processing methods. 
According to the present invention there is provided a method of evaluating 
yarn signals in which there is at least one approximately periodic portion 
superimposed on an irregularity, wherein yarn signals are obtained from 
the cross section or diameter of the yarn by means of detectors, the 
polarities of discrete values of the yarn signals are determined in 
comparators, and at least one counting device is used to determine how 
often a coinciding polarity of the yarn signals is found in constant 
intervals .tau., for all time intervals .tau. in a predetermined range 
.tau..sub.2 -.tau..sub.1. 
The invention also provides an apparatus for evaluating yarn signals having 
at least one approximately periodic portion superimposed on an 
irregularity, comprising comparators for determining the polarity of 
discrete values of the yarn signals, at least one counting device for 
determining the number of values in constant intervals with coinciding 
polarity for all intervals in a predetermined range .tau..sub.2 
-.tau..sub.1, and threshold value devices for determining if prescribed 
numerical values are exceeded in the counting devices.

When processing a yarn signal in an 8-bit microcomputer, the yarn signal is 
quantized into 256 quantization stages. However, the number of 
quantization stages may be reduced, if desired, to two quantization stages 
being obtained in the limiting case. Thus, for example, logic "1" is 
provided if the signal is positive or logic "" is provided if the signal 
is negative. In other words, the sign function of the yarn signal is 
formed which is defined as 
##EQU1## 
In this case, the autocorrelation function may be calculated very simply 
as: 
##EQU2## 
Since the EXOR function enters at the position of multiplication and may 
be effected in terms of circuitry by a gate or by a 2 .mu.sec command in 
the case of the microcomputer. This autocorrelation function at the sign 
function is also known as polarity coincidence detection. 
The analog-digital converter is reduced to a comparator. When processing 
with an n-bit microcomputer, n such quantized signals may be introduced in 
parallel. Such an arrangement is shown in FIG. 1. Yarn signals U.sub.11, 
U.sub.12, U.sub.13 received by the detectors 11, 12, 13 are quantized in 
comparators 21, 22, 23, i.e., are broken down into positive or negative 
signals q.sub.21, q.sub.22, q.sub.23 each of which is fed to an input of a 
microcomputer 30 for further evaluation. 
Since the signal amplitudes have no effect on the value of the sign 
function, control of amplification or sensitivity is unnecessary. In 
addition, the comparators 21, 22, 23 may be integrated into the detectors 
11, 12, 13. The detectors then emit only two possible initial states, thus 
increasing the protection from interference. 
However, this method of evaluation only allows periodic cross-sectional 
variations to be determined, but not those of increased irregularity. 
Another simplification is produced if the equation 
##EQU3## 
is calculated, instead of the autocorrelations function R (.tau.) 
according to equation 2 of the sign function. This function may be 
produced by means of a simple circuit without the need of a microcomputer. 
If the limits .tau..sub.1 and .tau..sub.2 are selected to be such that 
they include the range of the possible periods and evaluation continues 
over a sufficiently long period, this function is also capable of 
distinguishing yarn signals with a periodic portion from normal yarn. This 
can be confirmed experimentally. 
A circuit arrangement for producing the function P according to equation 3 
for a passage is shown in FIG. 2. 
The procedure begins with the clearing of an up/down counter 36. An 
amplitude value U' of the yarn signal U.sub.11 is then scanned by a 
"Sample-and-hold" stage 20. A comparator 21 produces the sign function. 
Depending on the polarity of the scanned value, "0" or "1" appears at the 
out output thereof. This value is read into a serial k-bit shift register 
31 and the entire content is shifted to the right by a bit. The value 
which is in the right-hand position usually overflows in this process. 
This shift register contains the k most recently scanned of the scanned 
values U' of the signal U.sub.11 reduced to the polarity symbol thereof. 
The switch 34 which is connected in parallel with a part 33 of the shift 
register 31 is now closed so that the contents of the part 33 of the shift 
register may be circulated once in shift register 33. In this process, 
each bit is compared with the new bit at the output of the comparator 21 
by means of an EXOR gate 35. 
If the two bits are equal, the EXOR gate 35 allows the counter 36 to count 
one unit upwards, and if not, to count one unit downwards. With a purely 
stochastic signal, the number of coinciding bits will be equal to the 
number of non-coinciding bits. The counter 36 thus counts upwards as 
frequently as downwards. Its final value after a monitoring interval of 
sufficient duration is thus approximately 0. However, if the yarn signal 
has a periodic portion, coincidences take place more frequently. The 
counter 36 then counts upwards more frequently than downwards and contains 
a value at the end of a cycle which exceeds a prescribed reference value 
so that a digital comparator 37 acting as a threshold device transmits a 
pulse to a switching means 38. The switching means 38 controls signaling 
or adjusting devices which indicate the appearance of yarn signals with 
periodic portions. 
The length of the first part 32 of the shift register 31 determines the 
avalue of .tau., and the length of the entire shift register 31 determines 
.tau..sub.2. This is illustrated in the following example. If the yarn is 
scanned at 1 cm intervals and if the entire shift register is 24 bits long 
with the reading after 10 bits, then .tau..sub.1 corresponds to a period 
length of 10 cm and .tau..sub.2 to a period length of 24 cm. However, the 
detectable range is not thus restricted to a period length of from 10 to 
24 cm but includes the range from 5 cm to 24 cm. A period of 5 cm does, in 
fact, have a first harmonic at 10 cm when the autocorrelation function 
(ACF) is formed and this first harmonic falls in the directly detectable 
range of from 10 cm to 24 cm. 
The line 40 in FIG. 3 shows the ACF R (.tau.) of the sign function of a 
yarn signal with a periodic portion wherein the period length has been 
determined with .tau..sub.x at a peak 41, for example, with 15 cm 
wavelength. The peak 41 means that a predominantly coinciding polarity is 
determined at intervals of 15 cm, for example, more frequently than in 
intervals of 20 cm. This peak is repeated at 42 (2 .tau..sub.x, at 3 
.tau..sub.x and so forth), which is a fundamental pproperty of the ACF. 
The value P according to equation 3 corresponds to the area above the 
abscissa minus the area below the abscissa. This value is larger if a peak 
41 is present as a result of a periodic portion in the yarn signal than 
when this is not the case. 
Since the length of a period which is present in all cases is not known in 
advance, it is not sufficient to calculate the ACF merely for a particular 
value of .tau.. Rather, it is determined for a range .tau..sub.2 
-.tau..sub.1, in which periods are possible or expected. 
FIG. 4 shows an ACF 44 with a period of 5 cm. The first peak 45 which 
represents the fundamental wave lies beneath the range .tau..sub.1 =10 cm 
to .tau..sub.2 =24 cm which may be measured in the example according to 
FIG. 3. The harmonics with peaks 46, 47, 48, however, lie within this 
range. Periods with shorter wavelengths may thus also be detected with a 
measurement range .tau..sub.2 to .tau..sub.1 from 10 to 24 cm. 
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 those 
of skill 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 those of ordinary skill in the art.