Method and apparatus for recognizing particle impurities in textile fiber

A method of recognizing particle impurities in textile material includes the following steps: forming a thin fiber web; detecting each particle impurity by an electron-optical sensor; applying signals from the sensor to an image processing system; determining a specific characteristic for each particle impurity by an evaluating device forming part of the image processing system; classifying the particle impurities based on the specific characteristic by comparison with reference data; and counting the particle impurities.

CROSS REFERENCE TO RELATED APPLICATION 
This application claims the priority of Federal Republic of Germany 
Application No. P 39 28 279.1 filed Aug. 26th, 1989, which is incorporated 
herein by reference. 
BACKGROUND OF THE INVENTION 
This invention relates to a method and an apparatus for recognizing 
particle impurities, such as trash fragments, neps, shell neps, burls and 
the like in textile fibers such as cotton, chemical fibers and the like. 
The determination of the degree of impurities (trash content) of the fiber 
is effected by electron-optical means: the fiber is scanned by a sensor 
and the measuring values are applied to an image processing device. 
Neps are fiber knots smaller than approximately 1 mm, while shell neps are 
grain shell fragments which have grown-on fibers. Burls, on the other 
hand, are fiber knots that are greater than approximately 1 mm and trash 
particles are, for example, leaf and shell fragments. Elongated trash 
particles (bark, grass or stem fragments) form a special class (subclass), 
whose length/width ratio is large. These particle impurities are 
summarized in FIG. 10. 
In a known process for cleaning and opening fiber to obtain fiber tufts, 
the fiber material passes through a feeding device and is thereafter 
submitted to a cleaning process. The degree of fiber impurity is 
determined during the supply of the fiber material to the cleaner. 
For performing the known impurity detecting process, between a feeding 
device and an opening/cleaning device a measuring line (measuring section) 
is provided for the fiber material. The measuring line comprises a 
channel-like guide having a transparent plate which is illuminated by a 
lamp and a conveyor belt which serves for pressing the fiber layer in the 
channel against the transparent plate, whose distance from the conveyor 
belt is approximately 2-4 cm. The measuring line further comprises a 
camera which applies signals to a grey scale value comparator, a counter 
and a computer. This apparatus serves for improving the cleaning process 
performed by the cleaner which receives the fiber material. The fiber 
material which is discharged by the cleaning device is introduced to a 
carding machine or a roller card unit. 
It is a disadvantage of the above-outlined process that the fiber tuft 
layer supplied to the cleaner is approximately 2-4 cm thick so that only 
impurities on the surface may be detected whereas those inside the 
material remain undetected. It is a further disadvantage of known 
processes that of the impurities determined on the surface in a reflecting 
light only a percent proportion in relation to the fibers can be summated. 
It is also a drawback that impurities such as neps, shell neps and burls 
which have a particularly adverse effect on the usual spinning processes 
cannot be detected. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved method and 
apparatus of the above-outlined type from which the discussed 
disadvantages are eliminated and which, in particular, are capable of 
detecting particle impurities inside the fiber layer and further, a 
determination and a differentiated evaluation of trash particles, neps, 
shell neps and burls are possible. 
This object and others to become apparent as the specification progresses, 
are accomplished by the invention, according to which, briefly stated, a 
thin fiber web is formed, then a sensor stepwise detects each individual 
particle impurity. An evaluating device determines specific characterizing 
magnitudes, for example, grey scale values for each individual particle. 
Based on the characteristic values the individual particles are 
classified, for example, according to type, shape and size and the 
individual particles are counted. 
By providing a thin, light-transmitting fiber web (which has a weight of, 
for example, 5 g/m.sup.2), particle impurities are detected both on the 
surface and inside the fiber web. According to the invention, the sensor 
stepwise detects each individual particle, for example, up to a magnitude 
of 0.1 mm. The sensor may be, for example, a camera which detects a 
certain zone of the fiber web and generates electric pulses which 
correspond to the detected image and which are applied to an electronic 
evaluating device. For each individual particle specific magnitudes are 
determined in the evaluating device, for example, based on a grey scale 
value analysis (identification as a particle impurity). Based on these 
magnitudes, the individual particle is classified by means of a 
comparison, for example, with predetermined stored data, particularly 
according to type, shape and size. Thereafter, the individual particles 
are counted so that, for example, a type classification (number of 
particles per type) or a size classification (number of particles for a 
certain size) is possible. 
By means of the process according to the invention, the particle impurities 
are detected even in the inside of the fiber layer and thus all the 
particle impurities in the entire fiber layer are accounted for. In 
addition to trash particles, other impurities such as neps, shell neps and 
burls are detected and eventually all particle impurities are classified 
in accordance with certain criteria, such as type, shape and size. 
According to further feature of the invention, the shell neps are detected 
in transmitted light and at least two different grey scale values are 
evaluated for the recognition of the shell neps. Preferably, the shell 
neps are determined by comparing the measuring results in transmitted 
light and reflected light. 
The novel apparatus for practicing the above-outlined method according to 
the invention has a measuring line which comprises a sensor assembly 
including a camera, for example, a diode-line camera or a two-dimensional 
camera, an electronic evaluating device (image processing unit), a 
classifying device, a counter and a computer. 
According to a further feature of the invention, a switching device is 
provided for activating either a light source from which light is passed 
through the textile material or a light source which generates light that 
is reflected from the fiber material. According to another feature of the 
invention, the electronic evaluating device includes a comparator for 
comparing electric pulses generated with transmitted light with those 
generated with reflected light. Further, the evaluating device preferably 
includes a grey scale value filter. According to a further feature of the 
invention the computer is connected with a quality detecting device 
involved in the carding process, such as a card information system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning to FIG. 1, there is illustrated therein a positioning device 
including a table I movable in the direction of the coordinates X and Y of 
a two-coordinate system. The table 1 has an upper cover face 1a, a glass 
plate 2a positioned thereon, a lower cover plate (not visible) and a 
second glass plate (also not visible) positioned on the lower cover plate. 
An illuminating device 24 is provided underneath the glass plate 2a. The 
fiber web (specimen) 25 is positioned on the upper glass plate 2a. The 
particle impurities in the fiber web 25 are designated at 26. Externally 
of the table 1 there is arranged a displaceable holding plate 3 on which a 
stepping motor 4 is mounted. The rotatable shaft of the motor 4 is a 
threaded spindle 5 which cooperates with a nut 6 fixed to a lateral face 
1d of the table 1. Upon rotation of the threaded spindle 5 the table 1 is 
displaced in the direction of arrows A, B. Externally of the table 1 and 
the holding plate 3 there is provided a stationary support plate 7 on 
which a stepping motor 8 is mounted. The shaft of the stepping motor 8 is 
a threaded spindle 9 which cooperates with a nut 10 which, in turn, is 
secured to the lateral face 3b of the holding plate 3. Upon rotation of 
the spindle 9 the holding plate 3 is moved in the direction of arrows C', 
D' and, at the same time, with the intermediary of a mechanical 
connection, the table 1 is displaced in the direction of the arrows C, D. 
The table 1 is straddled by an inverted U-shaped yoke 11 whose vertical 
legs 11a, 11b are secured on the support plate 7 and whose transverse head 
11c carries a camera 12 (for example, a diode-row camera) and an 
illuminating device 13. A digital image processing in which the image is 
divided into individual pixels is particularly adapted for practicing the 
invention. In addition to the stepping motors 4 and 8, limit switches (not 
shown) are provided which permit the assumption of a zero position. 
The apparatus further includes an image processing system 14 having a 
central processing unit 15 such as a microprocessor, an image processing 
device 16, an additional memory 17 and an interface unit 18. A 
two-coordinate control device 19 is connected to the interface unit 18 and 
to the stepping motors 4 and 8. Further, the image processing device 16 is 
connected with the camera 12 to receive signals therefrom. It is noted 
that a plurality of cameras 12 may be connected with the image processing 
device 16. The interface unit 18 is further connected with a printer 20, a 
screen terminal 21 and a keyboard 22. A data bus associated with the 
components 15-18 is designated at 23. 
The apparatus illustrated in FIG. 1 which may be used, for example, as a 
laboratory equipment, comprises the image processing system 14 
(encompassing the additional memory 17 and the interface unit 18), the 
terminal 21, the light source 24 for providing throughgoing light and a 
light source 13 for providing reflected light. The fiber web 25 may be 
positioned between the thin transparent plates. The camera 12 mounted on 
the transverse head 11c scans stepwise a programmable measuring range. The 
trash particles 26 and neps detected during this process are classified. 
The terminal 21 and the printer 20 may display the measuring results and 
size distributions (histograms). During examination in throughgoing light 
all opaque particles, for example, trash particles 26 or shell neps are 
detected and classified by size. During measurements taken in reflected 
light the neps and burls are highlighted by the illuminating and image 
receiving optics as locally limited, light zones. These zones are 
recognized as neps by the image processing system 14. The recognized neps 
and burls are also classified by size. The duration of the examination for 
detecting trash particles 26 and shell neps may last, for example, 3-20 
minutes. The particles visible in transmitted light are detected up to a 
minimum size of approximately 0.1 mm diameter, the maximum size may reach 
60 mm. The particles evaluated in reflected light are recognized as neps 
having a minimum diameter from approximately 0.1 mm. The maximum size of 
the burls is approximately 2 mm. 
Turning now to FIG. 2, there is illustrated therein a carding machine 30 
which has a feed roller 31, a feed table 32, a licker-in 33, a main 
carding cylinder 34, a doffer 35, a stripping roll 36, crushing rolls 37, 
38, transport rolls 39, 40, a web guiding element 4-, a sliver trumpet 42, 
calender rolls 43, 44, a sliver coiler 45 and travelling flats 46. The 
carding machine is supplied with a fiber batt (not shown) from a fiber 
tuft feeder 47. 
Between the crushing rolls 37, 38 which discharge a thin fiber web 58 and 
the transport rolls 39, 40 which receive and further advance the fiber web 
58 there are provided two transparent stationary plates 48, 49 in a 
channel-like arrangement which constitute a measuring section 50 and 
between which the fiber web 58 runs. The plates 48, 49 are spaced 
approximately 2-10 cm from one another. The transparent (or at least 
translucent) plates 48, 49 at the same time screen interfering air streams 
which could tear apart the thin fiber web 58, particularly at high-speed 
runs. The sliver discharged by the rolls 39, 40 is designated at 64. 
The apparatus for recognizing particle impurities in the fiber web 58 which 
passes through the measuring section 50 includes a camera 12 and an image 
processing system 14 (FIG. 1) which includes a grey scale value 
comparator, a counter and a computer. The image processing device 14 
applies signals to a control device 51, for example, a machine control of 
the card 30. The control device 51 is connected with a regulatable drive 
motor 52 which varies the distance of a mote knife 55 from the licker-in 
33 by means of a drive arrangement 53. It is also feasible to regulate in 
a similar manner an adjustable waste guide element or drives for various 
rotating rolls of the carding machine. In this manner, an on-line 
recognition and detection of particle impurities coupled with a regulation 
of the separation of the particles is effected. When predetermined limit 
values are exceeded, which are stored in the memory 17, the carding 
machine may be stopped by means of the control device 51 or a warning 
signal may be generated. The camera 12 may have an optical filter 57. 
Further, for generating reflected light, a light source 13 is arranged on 
the side of the camera, and for generating throughgoing light, a light 
source 24 is arranged on the transparent plate 48 on its side opposite the 
camera 12. 
The following zones in the carding machine 30 may be used as measuring 
locations for the fiber web: the fiber layer (arrow E) on the carding 
cylinder 34, the fiber layer (arrow F) on the doffer 35, the fiber layer 
(arrow G) on the stripping roll 36, the fiber web (arrow H) between the 
stripping roll 36 and the crushing rolls 37, 38, or the fiber web (arrow 
I) between the crushing rolls 37, 38 and the conveying rolls 39, 40. The 
particle impurities in the fiber web are recognizable only in reflected 
light on the carding cylinder 34, the doffer 35 and the stripping roll 36, 
for example, neps in case of chemical fibers, while the particle 
impurities between the stripping roll 36 and the crushing rolls 37, 38 or 
between the crushing rolls 37, 38 and the conveying rolls 39, 40 may be 
recognized in either transmitted light or reflected light. Expediently, 
the web is scanned along the extire axial length of the roll which 
supports the web. In this manner a determined impurity distribution may be 
indicative of a localized clothing defect in the carding machine. 
As shown in FIG. 3, the camera 12, the grey scale value comparator 61, the 
counter 62, the computer 15 and the control device 51 are connected in 
series. The classification and counting of the particle impurities are 
effected by corresponding computer softwares. 
For the classification of the particles, the following considerations 
apply: 
1) Type 
a) nep: 
recognition in reflected light after grey scale value filtering. 
b) trash particles: 
recognition in transmitted light after grey scale value filtering. 
c) elongated trash particles (bark, grass): 
this class forms a special class of trash particles. 
d) shell neps: 
either comparison in transmitted light (the core will become visible) and 
reflected light (the fibers of the neps will become visible), 
or only in reflected light: 
dark core (high grey scale stage), lighter fiber environment, as in case of 
a nep (low grey scale stage). 
In addition to the described methods of recognition a)-d), grey scale value 
operations, edge detections or the like may be used for a better 
differentiation of the particles. 
2) Size: 
the surface of the particles is determined in square millimeters (minimum 
diameter size is 0.1 mm). 
FIG. 4 shows a glass plate 49 which is situated between the crushing rolls 
37, 38 and the conveying rolls 39, 40 and over which the fiber web 58 
runs. Above the glass plate 49 there is situated the camera 12 and 
underneath the glass plate 49 there is arranged the light source 24 for 
emitting light for passing through the web 58. The direction of rotation 
of the crushing rolls 37, 38 and the conveying rolls 39, 40 is indicated 
by respective arrows drawn therein. 
Turning to FIG. 5, between the crushing rolls 37, 38 and the conveying 
rolls 39, 40 there is arranged a roll 59 oriented axially parallel to the 
rolls 37-40 and rotating in the direction of the arrow K. The roll 59 has 
a transparent (glass) wall, over which the fiber web 58 runs. The 
circumferential speed of the roll 59 is expediently the same as the 
running speed of the fiber web 58, so that no relative motion (and thus 
friction) between roll and web is generated. The light source 24 is 
arranged inside the roll 59. 
FIG. 6 shows an embodiment which is similar to that of FIG. 3, except that 
as a web support a convex glass plate 60 is provided over which the fiber 
web 58 slides and which ensures an improved web guidance when contacting 
the fiber web. The fiber web 58 is in contact with the glass plate 60 only 
with one part thereof. The upper crest point of the roll 59 and the glass 
plate 60 are expediently above the connecting line between the nip of the 
crushing rolls 37, 38 and the nip of the conveying rolls 39, 40. The 
arrows L and M indicate the direction in which the camera 12 may move. 
FIG. 7 illustrates an exemplary bar graph showing a type classification 
where the particle proportions are given in percent relative to the 
particle type. 
FIG. 8 shows in tabular form the grey scale value ranges of a web image 
wherein certain web elements (particle impurities and useful fibers) in 
each instance have been assigned particular grey scale values. 
FIG. 9 shows that the image portions a-e of the individual takes is smaller 
than the entire specimen so that the summarized result in obtained by 
means of overlapping juxtaposition of several specimens. 
FIG. 10 pictorially summarizes the four types of principal particle 
impurities (as described earlier in the Background of the Invention) 
intended to be detected by the method and apparatus according to the 
invention. 
As shown in FIG. 11, the camera 12 is connected to an analog/digital 
converter 63 and the computer 15. The counting of the particle impurities 
is effected with the aid of a software in the computer 15. The 
analog/digital converter 63 converts the sensor signal into a plurality of 
grey scale stages, for example, 200-300 in number. Expediently, the device 
illustrated in FIG. 2 has a CCD two-dimensional camera 12. Preferably, the 
two-dimensional camera 12 has a device for a short-time illumination 
(exposure) to avoid at the carding machine 30 a blurred image due to 
motion, and thus the image is quasi-"frozen". 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.