Note: Descriptions are shown in the official language in which they were submitted.
Q ~
I IELU O~ TIIE INVENIION:
The inventiorl relates to a system for the measurement of fiber
orientation in webs and t.o a method for the measurelnent of such
orientation. lhe system provides data on the statistical orient-
ati~n Or fiber~ irl a nlulti-lay~r struclure, which ~re of value in
proluction control arld (luality n~easurelllents in a variety of in-
dustries. The system of the invenlion can be used in the
n~easurelllerlt of Fil)er orientatiorl in webs of pal)er, collagen fibers
in tissues, etc.
BACKGROUND OF T_E INVENTION :_
The application describes an electro-optic method using a light
(e.g., laser) bean~ and specialized computational schemes to measure
fiber orientation in a web.
One already sugJested electro-optic method usiny a laser beam known
to the applicant, is colnprised of a laser diode source, focusing
optics, and a diodes photodetectors sensor, with images optics, which
Focuses the ellipse on the photodetectors plane (See illustration). --~
The ellipse s aspect ratio and orientation is derived from the re-
lative signals level Or these 6 diodes (which is linearly dependent
on the amount of light rallirly on each of thelll).
This system is very sensitive to lateral displacements between
source s and sensor s optical axes, which makes it unsuitable for on-
line FO measuren1ellt~ where mechanical displacement of about 1 mln
betweerl source and sensor, may occur.
Other known methods use ultrasonic waves, X-ray diffraction, micro-
wave attenuation and anisotropy o-f heat shrinkage.
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SUMMARY OF TliE INVENT~ON :
Tlle invention relates Lo a systenl for determinir~ fiber orientation
in we~s SUCll as uulp rilJers in paDer, collayen fibers in tissues and
the like. Ths system comprises a suitable source of light, which is
focused to a spot of l~redetermined size, on one surface of the web
to be measured, and a suit~ble sensor, such as a 2-dimensional CCD ~-
array with its focus al the other side of the web, means being pro~
, ~:
vided for evaluatiny the data gathered by such activity. The web
passes between the light source, generally a laser diode, and the CCD
array, resultlny in an elliptical light spot at the other slde of the
web, which is picke~ UD by the sensor. The systenl acquires the image
of the ellipse-shaped inlaye at a video rate and analyses a predetermined
part of the pictures at a desired rate. For example, every third pic-
ture can be evaluated at a rate of ten per second. The most prominent
parameters measured are the orientation of the ellipse and its aspect
ratio. These can be evaluated nlathelllatically or they can be displayed
graphically on two charts indicating aspect ratio and angular orientation
versus location of the measurelllellt in ti~e sample.
Fiber orientation in a multi-layer structure, such as a web of paper,
in the different.layers, is evaluated statistically. Such statistics
., :...: ... .
Ill~y l~e sll~ r rO~ y(?r~ Or ~ ? W~?l) Or l:~I(?y Illay di~f(?r.
:: : - : .,
A liyht spot is focused orl the surface oF the web and is scattered at .`~
the successive layers, resulting in a close to elliptical light spot
at the opposite surface of the web? whicll is the result of the light
. . .
passage through all the layers. Measurements have shown that such ellip~
tical images are statistically constant for given types of webs and that
the results are reproducible for every specific sample of web. The
phenomenon of fiber orientatiol- in such fiber webs is a macro phenanenon ; :
and its measurement is of value in quality control and for defining
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, ~ 3 - 2~
paper quality and tlle (lualitv of other pro~ucts.
It may be mentionecl that lhere exists a clear correlation between
mechanical strengt~i alld fiber orientation, and it has been found that
the greater the deyree of orientation of the fibers, the higher is the
mechanical strenyth of products such as paper.
A preferred embodilllerlt of the inventiorl coml)rises a suitable light
source of white or essentially monochrolllatic light, optical focusing
means, means for movirlg the system respective the measured web, and
sensor means focused at the other side of the web, adapted to deter-
mine the shape and size of the liyht spo~ a-t such resulting light
spot.
~ccording to the preferred embodinlent a laser, such as laser diode ;s
used as light source, the light beam o~ which is focused by a lens or
lens system on the surface of the product to be measured (such as
paper), there being provided a CCD camera on the other side of the
said web, focused onto the location of such resulting light spot,
the field of vision of such CCD camera being larger than that of the
resulting spot, allowing for a certain degree of misalignment of the
two main cpmponents of tlle system, located on different sides of the
product beiny measured. The resulting elliptical light spot is
evaluated, and yenerally the field of tlle CCD or other equivalent
sensor ought to be about 3 tlmes as larye as the dimensions of the
ellipse.
The focused circular liyht spot is collimated by a lens to a prede~
,
termined diameter, generally of the order of 50 to about 300ju, and
the light is scattered and guided by the fibers, whlch are part of a
mult;-layer structure, resulting in an elliptical light spot at the
other side of the web. It has been found that the main axis of the
ellipse coincides with the direction of most probable f;ber orient-
ation, the measurelllellt being essentially a statist;cal one.
2~123~ :
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..
The aspect rat;-io of the ellipse (ratio L)etweeIl lhe two axes) is higher
the more uniformly the fibers are direclionally orientated. These two
parameters ellipse s;ze aIld as~)ect ratio are determined by the highly
sensitive sensor an-l evaluated by computer means.
Annex A of this specification I)resents some al(lorithllls used in measure-
ments according to the nreseIlt invention. Ap!)licants do not want to be
bound by any specific theory aIld these are presented by way of illus-
tration only.
The invention is illustrated with reference to the enclosed schematical
drawiny not aocordiIl(J to s~ale irl whicII l~iyure 1 is a schematical slde- ;~
view oF a system oF I:he inveIltiol~ wilh wel) in position in said system.
As shown in Figure 1 the system comprises a laser light source 11 which
provides a parallel beam of light 12 which is focused by lens 13 to a
focus at 14 (on the front side of the web 15) said spot resulting in an
elliptical image at 1~ on ~he other side of the web 15 CCD camera
sensor 17 being focused on said imaye 1~ said sensor being connected
with FraIne Grabber and ConIputer 18.
The coherent light beam of the laser is focused to a spot of the order
of 50 to 300 /um depending on the type of web and its thickness. ~`
The picture of the spot at the oprlosite side of the web is ac(luired by
the sensor 17 and frame yral)l)er 1~3 at video rate picture analysis
beiny effected by a nlicrocoillputer wllich o~erates at a fast algorithm
to calculate the parameters of the ellipse at a desired rate say 10
per second. `~
An experimental device comPrises a laser diode in the near IR (about
800 nm) which ls collimated to a scot of about 150 mll and focused to ~ --
a distance of 250 mm with depth of focus of a few millimeters. - -
: :: .. ',,-
~2~ ~
Laser diodes of the order of 10 to 100 mW gave satisfactory
results.
As sensor there is used a CC~ camera sensor of h;yh resolution, wh;ch
;s low ligilt level sensitive and whicll can be operated in an industrial
environment. The optics used is a lens or lens system of about 4x
maynification. Advantageously there is used an interference filter
to elilninate backyround illumillation disturbances.
Experiments with on-line paper fiber measurenlents indicate that fiber
orientation can be determined with paper sheets having a width of the
order of 10 meters and which is runniny in the machine at a speed of
theord~r of 120 km/hour (about 30 m/sec), with the system of the inven-
tion used to scan in the cross-direction, along paper pane width, at a
speed of the order of 3 m/sec. The sensor and the light-source system
are driven on both sides of the paper pane in a simultaneous manner,
preferably by the same motor, on separate rails, as these cannot be
mechanically linked.
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~l~orithm
_________
The al~orithm, in general, uses calculations of moments of some
orders. The moments may be calculated ~or a grey level picture or
for a thresholded picture, as well. (The thresholded picture is a
result of a transformation of pixel value, where a threshold value
i5 set in grey level units. Then, ever-y pixel with a grey level
value below this thr-eshold value gets a zero value, and pixels
with grey level values above it, get a "one" value. The resultant
picture consists of two levels only). `
In general, the grey levels' moments calculations are more
accurate but more time consumming.
' ~ .
Two possibilities exist : ~ ~
1~ Grey level moments' calculations for accurate results but 510w : ~;
measurement rate.
~ ; :
2. 1 bit ( 2 levels) moments' calculations for less accurate
results, but fast measurements' rate.
The picture is composed out of 51Z x 512 pixel elements (or
~80 x 480 elements in another version). -
,, .: , . . . .
moment of i ! j order is defined by
, ~ ' ' '"
lZ 51Z
(x ~ y - y~)~ f~x,y)
K= 1 y' 1 .`, ` -~
~I~ ~ _____________________________________________________ .
512 5~2 -
~ ~ f (x,y)
y = l y = l . , ~ , .. , . .:;
;' ,`'''' ;';"'';:.' ':, ;''' ` ; ;'i'': '~''``: '
Where f ~x,y) i5 the grey level value o-F the ~x,y) pixel and s
512 512 512 512
x~ x F ~x,y~ f (x,y)
x=l y=l x=l y=l
.
51Z 51Z 51Z 512
yc.= ~ ~ y f ~x,y) ~ f ~x,,v)
x=l y=l ~-1 y=l
The point ~x~, y,.~) is the center oF gravity oF the image.
We will define M by :
M~ = Me<:~ 5in20 + 2 M.. cos~ sinO ~ Mc~eu co520
The angular orientation of the ellipse is calculated by :
Z M1.
O~= 1/2 arctg
~ e~
., ,
and the aspect ratio is calculated by :
~R = ~~~~~~~~~~~~~~~~~~~~
Mn~ (O = 0~. - 90)
~ ,
When using the I bit moments, the moment of order i,i is
calculated only for pixels ~x,y) with f(x~y) = 1 ~ .
~ .
N = O
FOR y = 1 to 512 DO BEGIN ~ ~
- '
M = 1~ ~1 + ( Y Y ~ ) ~ * i ) *
A = O
For x = 1 to 512 DO
Begin
I f f ( x, y ) = 1 THEN 13EG I N
A = A + ( x -- x.. ) * * i ::
N = N + 1 ; :
END
END :
END
M, ~ = M,~ / N
: -., ' ' . ',-:
.':,' ,. :,
' ~ ', ~ " ,,
. :': ,.: ':
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