Measurement of degree of intermingling and measuring apparatus therefor

Method for measuring the degree of intermingling of yarns where an optical sensor is used to register intermingled and non-intermingled yarn sections, which comprises performing the measurement on a yarn which has been laid with no or low tension onto a moving support which transports the yarn past the optical sensor at a selectable, constant speed at a distance suitable for registering the yarn properties, and an apparatus for carrying out this method.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for the continuous measurement of 
the degree of intermingling of yarns and to a suitable measuring apparatus 
therefor. 
Their cohesion is of decisive importance for the further processing of 
yarns. In the production of yarns, yarn cohesion is obtained for example 
by twisting, or by intermingling the individual filaments in jet nozzles. 
Intermingling is a particularly economical measure. However, it does not 
produce completely uniform yarn cohesion over the entire length of the 
yarn, but leads to the formation of individual more or less regularly 
spaced-apart intermingled places where the filaments are closely bonded 
together, and looser, bulkier areas in between of low yarn cohesion. This 
structure on the one hand confers a particular textile overall appearance 
on the yarns, but on the other also affects their further processibility. 
The prerequisite for any non-damaging and problem-free further processing 
of intermingled yarns is that the intermingled areas are sufficiently 
close together. Missing intermingled areas have an adverse, in certain 
circumstances even catastrophic, effect on fabric quality and loom. It is 
therefore of particular importance to monitor the uniformity of the 
intermingling continuously. 
One problem with the monitoring of yarn intermingling and the detection of 
non-intermingled areas (yarn bulges) is that any tension applied to the 
yarn serves to thin out and hence to disguise the non-intermingled areas, 
which makes their detection very difficult. 
At present, four methods are used in industry for detecting 
non-intermingled areas in weaving counts: 
(1) Visual examination by an experienced yarn examiner ("water test") In 
this test method, described in DE Offenlegungsschrift No. 2,901,165, yarn 
sections are introduced without tension into a water-filled vessel having 
a dark floor and the intermingled areas are then detected visually. Even 
if this visual assessment were replaced by an automatic optical apparatus, 
this water test would remain unsuitable for continuous measurement. 
(2) Further merely batchwise test methods are the needle test and the 
falling hook test, based on the same principle described in U.S. Pat. No. 
2,985,995. 
(3) A continuous electrostatic test method is described in 
"Chemiefasern/Textilindustrie" (1978) page 788 et seq. In this method, the 
yarn is subjected to the impingement of a high electric charge and then 
guided through a grounded tube, and the filament spreads out considerably 
in the non-intermingled areas. The consequently more prominent yarn bulges 
can then be counted with a light barrier along which the yarn is passed. 
This method requires a relatively complicated measuring means and again 
only works satisfactorily if the yarn tension is not too high. 
(4) In mechanical sensing methods, which hitherto have permitted the 
highest yarn speed, the intermingled yarn is pulled through a gap between 
a stationary abutment and a force- or distance-recording sensing head 
supported by and liftable off the abutment. An instrument of this class is 
described for example in "Chemiefasern/Textilindustrie" volume 36 (1986), 
page 99 to 103. These instruments utilize the fact that the intermingled 
yarn sections cannot be pressed as flat as the non-intermingled yarn 
sections. The intermingled areas therefore exert a greater force on the 
sensing head than the non-intermingled areas. 
An unsatisfactory feature with all four methods is the very low test speed. 
The yarn cannot be analyzed at a transport speed of more than 10 meters 
per minute (in the case of mechanical sensing). The production speed, 
however, is in general several hundred meters per minute. For this reason, 
the measurement of the degree of intermingling is at present possible only 
batchwise. 
SUMMARY OF THE INVENTION 
The present invention overcomes this prior art defect by providing a method 
for measuring the degree of intermingling of yarns where an optical sensor 
registers intermingled and non-intermingled yarn sections, which is 
distinctive because the measurement is carried out on a yarn which has 
been deposited with low or no tension. The relative motion between the 
optical sensor and the yarn required for registering intermingled and 
non-intermingled yarn sections is advantageously obtained by effecting the 
low-tension or tension-free deposition onto a moving yarn transport 
support which transports the yarn at a selectable, constant speed past the 
sensor at a distance suitable for registering the yarn properties. To fix 
the yarn on the surface without subjecting it to any tension, use is made 
of an at least partly gas permeable yarn transport surface through which a 
gas stream is passed from the yarn deposition side. To avoid loop 
formation in the yarn to be measured, the measurement is advantageously 
carried out at the delivery speed predetermined by the yarn delivery 
system. This measuring speed can be within the range from 10 to 800 meters 
per minute.

DETAILED DESCRIPTION OF THE INVENTION 
As FIGS. 1 and 3 show, the yarn intermingled (3) is delivered by a delivery 
system (2) and deposited without tension onto a support (1) which is 
moving in the arrow direction (6) and which can be guided endlessly around 
deflection rolls (1a). A gas stream which is produced for example by a 
suction box (7a) and which penetrates the yarn and surface in the 
direction of the arrows (7) from the yarn side ensures that the yarn is 
pressed against the support without any tension being necessary in the 
yarn. The said airstream also has the effect that the non-intermingled 
yarn sections become spread out flat on the support and as a result are 
particularly readily distinguishable from the narrow intermingled yarn 
sections. The photosensor (8) therefore can satisfactorily identify 
intermingled and non-intermingled yarn sections. After the yarn has passed 
underneath the photosensor, it is lifted by rolls not shown in FIGS. 1 and 
3 off the support onto which it had been deposited without tension, and 
transported away. The gas stream passed through the yarn and the moving 
support is preferably limited to the region where the yarn is in contact 
with the support surface and the optical sensor. This has the advantage 
that, after the measurement, the yarn is easily removable again from the 
support. A particularly advantageous embodiment of the moving gas 
permeable support (1) on which the tension-free yarn is moved past the 
optical sensor during the measurement is essentially gas impermeable and 
has only a narrow zone (9) of gas permeability extending in the transport 
direction (arrow (6)). This embodiment has the substantial advantage that 
the yarn, which is delivered by the delivery system only to within the 
vicinity of the narrow gas permeable zone, becomes automatically centered 
on this zone and laid down flat. This ensures automatic centering in 
relation to the photosensor, which leads to particularly reliable 
measurements. 
To obtain a particularly strong useful signal from the photosensor, the 
yarn can be deposited for measurement onto a yarn transport support which 
has contrasting coloring to the color of the yarn. 
It has been found that the strength of the signal can be additionally 
improved to a considerable extent by depositing the yarn for measurement 
onto a yarn transport support having very different reflectance properties 
from the yarn. This is because if the deposited yarn and the yearn 
transport support have contrasting colorings, they have different 
reflectance spectra, but the total amount of reflected light preferably 
will be of similar magnitude. To obtain a sufficiently strong useful 
signal, it is therefore necessary to adapt the reflectance spectra and the 
spectral light sensitivity of the photosensor to one another in such a way 
that a very strong useful signal is obtained in one of the reflectance 
spectra, for example that of the yarn, while a very weak useful signal is 
obtained in the other reflectance spectrum, for example that of the 
support. This adaptation can present difficulties and, in certain 
circumstances, presuppose the interposition of color filters which cause 
additional light attenuation and hence a reduction in the useful signal. 
If, by contrast, the reflectance properties of the yarn and the yarn 
transport support are made different, this means that the quantities of 
light reflected by yarn and yarn transport support differ and that 
possibly, although not necessarily, there may in addition be spectral 
differences in the reflected light. In this way it is possible to obtain 
high useful levels for the signal emitted by the photosensor independently 
of the spectral sensitivity of the photosensor and without the 
interposition of filters and without adaptation of the spectral light 
sensitivity of the sensor material, i.e. without restriction in the choice 
of sensor. 
The reflectance properties of yarn and yarn transport support may differ 
because the yarn and the yarn transport support reflect the light 
diffusely, i.e. more or less uniformly in all directions, but to very 
different extents. FIG. 7 is a schematic illustration of this principle. 
It shows, in section, the yarn (3) deposited on a gas permeable region (9) 
of the yarn transport support (1). The incident light symbolized by the 
rays (28) is reflected approximately uniformly in all directions not only 
by the yarn transport support but also by the yarn, but the amount of 
light (29) reflected by the yarn and the amount of light (30) reflected by 
the yarn transport support differ, which is signified by the length of the 
arrows (29) and (30) symbolizing the reflected light. 
Since the yarn in general is a diffuse reflector of a high proportion of 
the incident light, the reflectance of the yarn transport support is 
advantageously very low. 
This principle can be put into effect by reducing the reflectance of the 
yarn transport support as much as possible by application of black, matt 
colors, by burnishing, by eloxation and, if required, by additional 
roughening of the surface, for example by sand blasting. 
In practice it is found that none the less all the surfaces still give a 
certain weak but none the less disadvantageous reflectance. It is further 
found in practice that the reflectance of the yarn transport supports 
surface-treated in this manner can differ locally. 
It is then found that along the length of such a yarn transport surface the 
background reflectance fluctuates by an admittedly small but certainly 
disadvantageous amount--due to mechanical manufacturing tolerances, 
density differences on surface application, inhomogeneous surface 
roughnesses and the like. In relation to signal detection, this 
disadvantageously constrains the tolerances for setting threshold values 
and trigger levels. In certain circumstances, it is even necessary to 
employ "floating" limits - only possible with an expensive control system 
- to make a high sensitivity level meaningful again. 
A considerably farther reaching improvement is attainable, then, by making 
the reflectance of yarn and yarn transport support very different by 
(a) providing the support with a surface which gives off virtually no 
diffusely reflected light but which reflects bundled incident light very 
strongly in bundle form in a preferential direction and 
(b) using a light source which projects a bundled light beam at the 
measuring position at such an angle .alpha. that the light reflected by 
the support in substantially bundled form cannot impinge on the 
photosensor. The yarn itself of course retains its diffuse reflection 
characteristics. 
This principle can be realized in various ways. 
One possibility is to provide the yarn transport support with a surface 
which reflects incident light in accordance with the law of reflection; 
that is, the surface of the yarn transport support is mirror coated. The 
reflection of incident light by the law of reflection is such that a light 
beam incident upon the yarn transport support at an angle .alpha. relative 
to the normal is reflected by the surface at an angle -.alpha., measured 
from the normal. If therefore the yarn deposited on such a mirror coated 
yarn transport support is illuminated at an angle .alpha. and the 
photosensor is mounted above the yarn in the direction of the normal, the 
photosensor no longer receives any light reflected by the yarn transport 
support, but only receives light reflected by the diffusely reflecting 
yarn. This arrangement gives a dramatic increase in the strength of the 
useful signal. FIG. 8 illustrates this principle of measurement. It shows, 
in section, schematically the yarn (3) deposited on the gas permeable zone 
(9) of the yarn transport support (1), the light incident at an angle 
.alpha. relative to the normal (31) which is symbolized by the rays (28), 
the light reflected by the yarn transport support an angle -.alpha. 
relative to the normal (31) which is symbolized by the rays (30), and the 
light diffusely reflected by the yarn which is symbolized by the rays 
(29). It can be seen that the photosensor (8) is only impinged upon by the 
light diffusely reflected by the yarn. A certain technical difficulty with 
the realization of this principle of measurement is that the yarn 
transport support must consist of a material which is satisfactorily 
mirror coatable. Similarly, the production of a satisfactorily functioning 
mirror requires a substantially smooth surface structure on the yarn 
transport support. Although these requirements are technically manageable, 
they are inconvenient. 
A further substantial improvement in this measuring method results on 
providing the surface of the yarn transport support with a covering which 
always reflects incident light, irrespectively of its angle of incidence, 
back into the light source. FIG. 9 shows this embodiment of the measuring 
method according to the invention. It schematically shows in section the 
yarn (3) deposited on a permeable region (9) of the yarn transport support 
(1). The rays (28) symbolize the incident light and the rays (29) and (30) 
the reflected light. It can be seen that the light beam (28) incident upon 
the yarn transport support at an angle .alpha. relative to the normal (31) 
is reflected back at the same angle .alpha., whereas the light beam (28) 
which is incident upon the yarn is reflected diffusely in all directions. 
Here too the photosensor (8) is exclusively impinged upon by the light 
rays diffusely reflected by the yarn. 
Surfaces which always reflect incident light back into the light source are 
already known, and it is therefore easily possible to provide the yarn 
transport support with such a surface. The simplest thing in practice is 
to equip the yarn transport support with a foil which has the desired 
reflection characteristics. Such a foil, which is also used for example in 
the modern coating of traffic signs or even license plates, basically has 
the following structure: A base material which in the uncured state is 
plasticizable, hardenable or stabilizable, for example a base material 
made of silicone rubber, is vacuum vapor deposition coated or 
alternatively electroplated with a metal layer of high reflectance. A 
glass bead filled plastics material, for example a mixture of glass beads 
having an average diameter within the range from 65 to 130 .mu.m and a 
polycarbonate, is applied to this base material and pressed in under 
mechanical pressure. The pressing of the glass beads into the metallically 
vacuum vapor deposition coated or electroplated backing creates a large 
number of spherical cavities in the backing in accordance with the 
geometry of the beads. The base material is then stabilized by suitable 
measures. The metallically vacuum vapor deposition coated background is 
accordingly basically a mirror with a systematically embossed surface. A 
foil thus manufactured has the property of always largely reflecting 
incident light back into the light source irrespectively of the angle of 
incidence of the light. Foils of this type are commercially available. 
A further very convenient refinement of the measuring method according to 
the invention provides that the yarn is deposited on the at least partly 
gas permeable shell of a hollow roll which rotates about its longitudinal 
axis, a gas flowing through the shell from outside to inside. FIG. 4 
schematically shows an arrangement which is suitable for this embodiment 
of the method according to the invention. It can be seen that the yarn (3) 
is transported tensionlessly up to the hollow roll rotating in the arrow 
direction (6) and once there is forced by the gas stream flowing in the 
direction of arrows (7) through the porous shell (1) of the hollow roll 
flat against the shell of the roll. In this form, the yarn is transported 
by the rotating roll passed underneath the photosensor (8). Downstream of 
the photosensor the yarn is then again lifted loosely off the hollow 
transport roll. Here too it is possible to provide a special means for 
facilitating removal of the yarn off the hollow roll by providing on the 
inside of the hollow roll a separating wall (11) which partitions the 
interior of the hollow roll in the two compartments A and B, of which only 
compartment A is under reduced pressure. In this way, the gas stream 
forcing the yarn against the shell is limited to where the yarn has been 
deposited and to the region of the photosensor. The yarn removal, by 
contrast, is not impaired. 
A further, very advantageous refinement of the method according to the 
invention provides that the signals emitted by the photosensor are 
processed and registered by a connected arithmetic processing unit. It is 
particularly advantageous for the signals from the photosensor first to be 
sent to an electronic classifier which classifies the yarn irregularities 
by size and sends the classified signals separately by class to the 
arithmetic processing unit. The electronic classifier can work in a 
conventional manner, for example in that the signals from the photosensor 
which have been amplified by an analog amplifier are first sent to a gate 
of the Schmitt trigger type with faculatatively adjustable trigger 
voltages. A further advantageous embodiment of the method according to the 
invention and the apparatus according to the invention is obtained on 
using the above-described self centering of the yarn (for example over a 
row of holes) and a double light guide where one of the light guides 
projects a light spot and a second light guide measures the light 
reflected by said spot. 
In this case, the diameter of the projected light spot can be made smaller 
than the diameter of the non-intermingled yarn places and positioned 
outside the central axis of the yarn, so that it only impinges upon the 
bulges of the yarn and, if above an intermingled area, impinges 100% on 
the surface (and not the yarn). 
The effect of this arrangement is that from the start it emits only at the 
yarn bulges a positive signal which acts as a quasi trigger signal. The 
intervals between successive descending flanks of the trigger signal can 
be measured in multiples of a freely selectable unit time and the result 
can be used for classifying the yarn faults. It is of course also possible 
to use other known classifying options for the method according to the 
invention and realize them in the form of appropriate circuitry. 
The present invention further provides a measuring apparatus for carrying 
out the measuring method according to the invention. Such a measuring 
apparatus has a moving, at least partly gas permeable support on which the 
yarn to be measured is deposited and transported with low or no tension, a 
gas pressure gradient between the two sides of the support, which 
generates a gas stream through the support directed from the yarn 
deposition side to the back of the support, deposition and removal means 
which effect a low-tension or tensionless deposition of the yarn and its 
removal and its continued transport, and a stationary optical sensor which 
in relation to the moving yarn transport support is positioned in such a 
way that it can detect the yarn geometry and that intermingled and 
non-intermingled yarn sections lead to different signals. A schematic 
representation of the essential developments of such a measuring means 
according to the invention is shown in the above-described FIG. 1. 
In a particularly advantageous embodiment, the measuring apparatus 
according to the invention includes a yarn transport support possessing 
only a narrow gas permeable zone extending in the transport direction of 
the support. The gas permeability of the yarn transport support can be the 
result of the support or the gas permeable zone of the support having 
small bores through which the gas can flow in accordance with the pressure 
gradient. Other possibilities are to form the gas permeable support or 
zone from a porous material, for example a sintered glass or ceramic 
material or an open-pored foam. An open-pored organic foam can if 
necessary be provided by combination with a mechanically stable grade of 
metal or plastics wires or an equivalent stabilization. The gas permeable 
support or zone can of course also be realized in the form of a finely 
meshed sieve. 
Advantageously, the apparatus according to the invention is provided with a 
device which adapts the speeds of the yarn transport support and the 
delivery speed of the yarn to one another to such an extent that the yarn 
comes to be laid virtually tension-free on the support. Such a control 
system can be for example realized by making the yarn form a small freely 
suspended loop between the delivery system and the deposition point onto 
the yarn transport support, the size of the loop controlling the speed of 
the transport support and/or of the yarn delivery system. Basically, any 
control means which controls the transport speed and/or the delivery speed 
as a function of the length of the yarn delivered per unit time is 
suitable for this purpose. 
A further preferred embodiment of the measuring apparatus according to the 
invention provides that the yarn transport support is the at least partly 
gas permeable shell of a hollow roll which on the inside and preferably 
locally has a lower gas pressure than on the outside. It is particularly 
preferable for the shell of said hollow roll not to be gas permeable as a 
whole but to have a gas permeable zone which encircles the roll on a 
perpendicular section line. Such an embodiment has the advantage that the 
yarn deposited thereon becomes automatically centered on the gas permeable 
zone and hence always remains in the same favorable position relative to 
the photosensor even in the course of prolonged high-speed yarn transport. 
A preferred measuring apparatus improved within the meaning of the 
observations about the measuring method provides that the support for the 
yarn to be measured has reflection characteristics different from the 
yarn. 
One way of realizing this feature is to equip the support by one of the 
above-indicated measures, for example blacking or burnishing with or 
without additional roughening, with a surface which is a diffuse and very 
weak reflector. A further dramatic improvement of the useful signal from 
the photosensor is obtainable by using a measuring apparatus 
(a) whose yarn transport support has a surface which reflects bundled 
incident light very strongly in a preferential direction in bundled form 
and 
(b) which has a light source which projects a bundled light beam at the 
measuring position at such an angle .alpha. that the light reflected by 
the support does not impinge on the photosensor. 
A possible way of realizing this preferred principle is for the yarn 
transport support of the measuring apparatus to have a planarized and 
mirror coated surface, so that it reflects incident light in accordance 
with the law of reflection. 
A particularly preferred embodiment of the measuring apparatus according to 
the invention provides that the surface of the yarn transport support 
reflects incident light back into the light source. 
This is advantageously achieved by providing the surface foil described 
above and as marketed for example by the company Scotch. 
A further, preferred embodiment of the method according to the invention, 
where the measurements are processed with a connected arithmetic 
processing unit, gives rise to further appreciable advantages: for example 
a freely adjustable zero point for the reproducible setting of 
count-related pressure lines, the choice of the yarn test length, the 
classification of faults and counting of classified faults per unit yarn 
length, and production of a fault histogram. The evaluation of the number 
of intermingling points thus determined and, if of interest, their size 
and distribution as well is effected by means of conventional arithmetic 
algorithms; the further processing of the measurements is then adapted to 
the particular problem situation. 
Particular preference is given to those embodiments of the measuring method 
according to the invention and the measuring apparatus according to the 
invention where a plurality of preferred features are present. 
The method according to the invention and the robust measuring apparatus 
according to the invention are highly suitable for the continuous 
monitoring of the degree of intermingling of production material in the 
laboratory. 
Since the method according to the invention can be operated at yarn 
transport speeds which correspond to the high transport speeds of 
texturing machines, it is even possible to carry out on-line control of 
the degree of intermingling, so that even immediate, preferably automatic, 
management of yarn production process parameters can be effected. 
The example which follows shows an embodiment of the apparatus according to 
the invention, its function and the implementation of the measuring method 
according to the invention using this apparatus. The advantageous 
embodiment of the method according to the invention described here by way 
of example utilizes an apparatus according to FIGS. 6a and 6b which 
includes a yarn deposition and transport means in the form of a hollow 
roll. The apparatus consists of two mutually inserted halves, of which one 
half, the rotor (13), can be set in rotation by means of a drive motor 
(18) while the other half, the stator (15), remains stationary. Ball 
bearings (17) ensure the positive connection between these two halves. 
The rotor, which has the form of a hollow roll, has been provided on its 
shell with a row of holes (14) approximately 1 mm in diameter exactly in a 
plane perpendicular to the axis of rotation. The opening (16) of the 
stator has been put under reduced pressure via an appropriate connection 
pipe. 
A separating wall (11) likewise attached to the stator and facing the 
inside of the hollow roll confines the reduced pressure on the inside of 
the hollow roll to the upper compartment A. This separating wall has on 
the rotor side a drag lip which provides a substantially airtight seal. 
The shell surface of the rotor has a dark or matt black color to avoid 
light reflection or, in a preferred embodiment, is covered with a light 
reflection foil which reflects incident light back into the light source. 
The apparatus described here is coupled as per FIG. 5 via the analog 
amplifier (32) and the electronic evaluator (33) to the arithmetic 
processing unit (34). 
If the functioning, i.e. rotating and depressurized, perforated hollow roll 
is supplied with a yarn from a delivery system, the yarn becomes fixed and 
centered on the row of holes in the rotating hollow roll owing to the air 
sucked from the outside through the holes onto the inside of the hollow 
roll. In the apparatus described, it is sufficient if the yarn is brought 
to a distance of about 100 mm from the hollow roll; it is then extracted 
and as it were automatically fixed and accurately centered. 
This system offers a further advantage. Owing to the suction effect, the 
otherwise rather rotation-symmetrical non-intermingled areas flatten out 
against the rotor surface, temporarily assuming a plainer and spread-out 
state. The diameter of the non-intermingled areas even become somewhat 
larger as a result, in the same way as if the yarn was laid onto a flat 
metal surface and then pressed firmly against this metal surface by means 
of a glass plate. The yarn becomes fixed on the rotating hollow roll in 
the region of the reduced pressure chamber A and, on leaving this region 
owing to its continued transport by the hollow roll, is released again. 
Downstream of this point the yarn can be taken up again and guided to its 
further use. 
As the yarn is transported on the yarn deposition and transport means past 
the photosensor (19), the latter emits an electrical signal (current or 
voltage) whose strength corresponds to the spreading out of the yarn. This 
signal is supplied to an analog amplifier and an electronic evaluator, for 
example a time digital converter (TDC). In a possible embodiment of this 
electronic evaluator, the analog signal switches a Schmitt trigger whose 
hysteresis is determined by the switching voltages (trigger levels) 
supplied via the lines (24a) and (24b). Through suitable choice of the 
hysteresis, the sensitivity of the apparatus becomes infinitely adaptable 
to the nature of the yarn to be tested. The switching-on times of the 
Schmitt trigger are measured by means of a supplied digital time signal in 
multiples of a choosable unit. In this way, the digital converter 
classifies the intermingling faults by summed time signals into single, 
double, triple or larger intermingling areas. A time cycle starts each 
time trigger level 1 is passed through and is stopped when trigger level 2 
is passed through. The ultimately desired intermingling fault histogram is 
produced by the arithmetic processing unit (22) and printed out by the 
printer (23).