Note: Descriptions are shown in the official language in which they were submitted.
WO91/18281 PCT/CA90/00168
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ON-LINE DIRT COUNTER 2Q~58~
TECHNICAL FIELD
- The invention relates to a dirt counter for
measuring and recording dirt speck sizes and
intensities on paper. More specifically, the
invention relates to an on-line dirt counter which
measures the dirt speck sizes and intensities on a
surface of a web of moving paper.
BACKGROUND ART
Several off-line dirt counters have been
developed. A typical one, such as the BIOTRAN T
(of New Brunswick Scientific) extracts measurements
such as total area and total counts from two-
dimensional incoming images. Recently, an off-line
system PAPRICAN MICROSCANNER M (of Noram Quality
Control and Research Equipment Ltd.) image analyzer
applies the medium-pass filter as well as visual
impact principles to detect and measure dirt speck
size of two-dimensional images. The INTEC TM (Of
Intec Corp.) on-line dirt counter uses a laser light
source and fiber optic receivers. It can detect dirt
specks as small as 0.05 mm . However, this device is
not designed to measure dirt speck size using visual
impact principles similar to human judgment as
defined in TAPPI (Technical Association of the Pulp
and Paper Industry) count.
There are also issued patents of interest
which deal with the detection of flaws on surfaces.
U.S. Patent 4,172,666, Clarke, October 30, 1979 dis-
WO91/18281 PCT/CA90/00168
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tinguishes between different types of faults detected
on a moving web. A defect detector scans the surface
of the web with a laser and views the reflected light
with a view or several detectors at various angles.
Sums and differences between signals are used to
discern which defects scatter light and which absorb
it. The signal processing is not specifically
related to the emulation of visual inspection as is
the present invention.
U.S. Patents 4,794,264 and 4,794,265,
Quackenbos et al, December 27, 1988, relate to an
apparatus and method for uniquely detecting pits on a
smooth surface. The moving surface is illuminated
with a point source of laser light through a pair of
beam splitters. Flaws and pits reflect specularly
with different patterns. An annular mask shields one
detector to view the neighborhood of a focal point
and a window on the other detector constrains the
signal to the central focus.
The invention in the above patents uses a
beam splitter to view the same spot with a pair of
detectors and to difference a central spot signal
with a wider surround. However, Quackenbos et al
illuminate the sample with a laser through the same
beam splitter in order to observe glossy specular
reflectance but does not illuminate diffusely outside
the beam splitter to observe the fuse reflectance.
Further, Quackenbos et al use a single detector in
each beam rather than a linear array of detectors,
and Quackenbos et al mask the two detectors to see
only their intended domains of view rather than
WO91/18281 PCT/CA90/00}68
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having the two beams differ only in sharpness of
focus. Finally, Quackenbos et al use the difference
of detector signals to distinguish flaws from pits
but does not have a system wherein the signal
differences correspond to a sharpening operation.
U.S. Patent 4,740,079, Koizumi et al, April
26, 1988, teaches a method and apparatus for detect-
ing foreign substances, e.g. dirt specks or smudges,
on the glossy surface of a semi-conductor chip which
already contains delivered etches of the circuit. In
the Koizumi et al patent, a circuit component is
illuminated at near grazing incidence with a laser or
a pair of lasers as the chip is physically moved past
the detection configuration. A beam splitter divides
the view of the surface of the chip in two identical
beams with different polarization. Each beam is
viewed at the same focus by a linear array of
detectors. The difference signal corresponds to the
diffused scattering from dirt on the chip. However,
Koizumi et al does not calculate the integrated
optical density as a visual impact parameter.
U.S. Patent 4,724,481, Nishioka, February
9, 1988, teaches a flaw detector for detecting a flaw
in a sheet. The apparatus includes an array camera
or series of array cameras which view a moving sheet.
A circuit employs an electronic shading correction to
enhance the signal to noise ratio. A memory asso-
ciated with each photodetection element is used to
maintain a reference level for that element. The
novelty of this patent appears to reside in the
algorithm of shading correction and data reduction.
WO91/18281 PCT/CA90/00168
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However, the Nishioka invention cannot be used on
paper sheets with realistic reflectance non-
uniformity associated with formation.
U.S. Patent 4,237,539, Piovoso et al,
December 2, 1980, teaches an on-line web inspection
system which includes a transverse web scanning
means. X-ray film is made at high speeds and must be
inspected for defects at speeds of up to 900 feet per
minute. In the '539 patent, a flying spot criss-
crosses the sheet with a scan repeat of l.5 mm. Thisrequires three scans per millisecond. A sophisti-
cated processing board in the host computer processes
the signal and sorts features with sharp edges by
size. In the '539 patent, a scanning laser is used
rather than a diode array. In addition, t-he '539
patent does not use a board level processing of the
signal to extract and sort the images of the defects.
Instead, sorting is accomplished by area and by the
sharpness of the edge of the feature, for example,
rather than by integration of the signal strength
within the bounds of a spot.
A system for detecting and classifying
flaws on metallic surfaces is taught in U.S. Patent
4,253,768, Yaroshuk et al, March 3, 1981. In the
'768 patent, a scanning laser illuminates a moving
surface of, for example, a pipe, which is viewed by
at least two detectors. The reflectance angles for
the detectors are chosen so that most of the light
reflects into the first detector when there are no
defects with a low but finite intensity reaching the
other detectors. The other detectors are positioned
WO91/18281 2~ 7 PCT/CA90/00168
to receive increased intensity when the laser beam
traverses a defect. The average signal serves as a
base line for comparisons. This system has, of
course, very little in common with systems for
detecting dirt specks on a sheet of paper, and
especially the system herein.
A particle detection method and system, for
scanning the surface of a semi-conducting wafer, is
taught in U.S. Patent 4,766,324, Saadat et al, August
23, 1988. The surfaces scanned by a laser beam, and
the scattered light indicates the presence of a dirt
speck. The central idea of this patent is a
procedure for identification of dirt that was already
present before the current processing step, and to
distinguish this from dirt added by the most recent
step. Once again, this has little in common with a
dirt counter for measuring dirt speck sizes on a web
of moving paper.
U.S. Patent 4,665,317, Ferriere et al, May
12, 1987, teaches a process and equipment for sensing
surface defects on a moving strip of rolled metal.
Successive video images of a moving sheet of the
metal are presented to a computer memory as a con-
tinuous representation of the surface. Two-
dimensional digital filters are used for contour
detection and the edge detection of defects. The
method makes successive demands upon the host
computer although the algorithms are quite general.
This system bears, again, no resemblance to the
system of the present application which does not use
two-dimensional filters.
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DISCLOSURE OF INVENTION
It is an object of the invention to provide an
on-line dirt counter for measuring and recording dirt
speck sizes and intensities on a first surface of a
web of moving paper.
It is a more specific object of the invention
to provide such a counter which includes a light
source disposed to reflect light off the first surface
of the web of moving paper.
It is a still more specific object of the
invention to provide such a counter wherein the
reflected light is split by a beam splitter, one of
the split beams being directed to an out-of-focus
detector, the other one of the split beams being
directed to an in-focus detector.
It is a still further object of the invention
to provide such a counter wherein the reading of the
sensor of the out-of-focus split beam is subtracted
from the reading of the sensor of the in-focus split
beam.
In accordance with the invention there is
provided an on-line dirt counter for measuring and
recording dirt speck sizes and intensities which
appear on a first surface of a web of moving paper,
comprising:
a light source spaced from said first surface
of said web of moving paper for directing a beam of
light at said first surface of said web of moving
paper, said beam of light being substantially
diffusely reflected from said first surface of said
web of moving paper;
an in-focus sensor means including first
focusing means and a first detector placed at an in-
focus position to receive a first part of said
reflected beam emitted at an angle with respect to
said surface, and to provide an in-focus magnitude
signal having an in-focus magnitude proportional to
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the magnitude of the light intensity of said first
part;
an out-of-focus sensor means including second
focusing means and a second detector having a same
aperture as said first detector placed at an out-of-
focus position to receive a second part of said
reflected beam emitted substantially at said angle
with respect to said surface, and to provide an out-
of-focus magnitude signal having an out-of-focus
magnitude proportional to the magnitude of the light
intensity of said second part;
means for subtracting said out-of-focus
magnitude from said in-focus magnitude to provide a
difference magnitude;
comparator means for comparing said difference
magnitude to a threshold magnitude; and
means for storing the occurrences and
magnitudes of said difference magnitude on all
occasions when said difference magnitude is greater
than said threshold magnitude.
. . ,
WO91/18281 2 0 8 0 5 8 7 PCT/CA90/00168
BRIEF DESCRIPTION OF DRAWINGS
The invention will be better understood by
an examination of the following description, together
with the accompanying drawings, in which:
FIGURE l is a perspective view of a dirt
counter in accordance with the
invention;
FIGURE lA illustrates a possible arrange-
ment for driving the housing in a
cross-machine direction;
FIGURE 2 is a schematic view of the data
analysis board;
FIGURE 3 is a flow chart of the process in
accordance with the invention;
and
FIGURE 4 is a flow chart of an alternate
process.
DESCRIPTION OF PREFERRED EMBODIMENTS
It is the purpose of the present invention
to provide an on-line dirt counter device to handle
dirt speck detection and speck size estimation in the
same manner as human ~udgment described in TAPPI
count procedures. A discussion o' the principles
involved, without a description of specific apparatus
or method steps, is given in "Emulating the TAPPI
Dirt Count with a Microcomputer", Jordan et al,
Journal of Pulp and Paper Science, Vol. 14, No. l,
January 1988, pps Jl6 to Jl9.
WO91/18281 ~ PCT/CA90/00168
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g
For dirt speck detection, any potential
specks are detected whenever their contrast to
neighboring background is higher than a predetermined
threshold. A contrast image can be derived from an
original image by applying a two-dimensional medium-
pass filter. This is equivalent to extracting the
difference between an original image and its corres-
ponding out-of-focus one. Using two camera, for
example, charge coupled device linear arrays, one
viewing a paper portion in focus and the other
viewing the same portion, but partially out of focus,
a contrast image can be obtained from the difference
of the two linear array signals. Any clusters of
picture elements of the contrast image with their
lS digitized values higher than a predetermined
threshold are considered as dirt specks.
Integrated contrast values of the detected
dirt specks are measured and stored. After a pre-
determined time interval, or a predetermined paper
area coverage, all stored dirt speck integrated
values are retrieved, converted into corresponding
sizes by a precalculated look-up table, and
accumulated in a dirt speck histogram. The look-up
table can be constructed from graphs similar to that
shown at Figure 3 of Jordan et al referred to supra.
Accumulated statistical data and histograms
can be reported regularly in a specific time interval
until the paper roll is exhausted, or upon receipt of
an operator hault request. At this point, all data
are reset for preparing measurements of a new paper
roll.
WO91/18281 2 0 8 0 5 8 7 PCT/CA90/0016X
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Referring to Figure l, the counter, illus-
trated generally at l, comprises a housing 3.
Disposed within the housing is a light guide 5 whlch
guides light, as will be described below, to a
focussing lens 7. After passing through the lens,
the light is directed to a beam splitter 9 which
directs one beam of light at an out-of-focus camera,
for example, a CCD (charge couple device) sensor
linear array ll which is supported by a plate 13.
The other split beam of light is directed at an
in-focus camera, for example, a CCD sensor linear
array 15 which is supported on a plate 17.
The outputs of sensors ll and 15 are fed to
processor l9 via buses 21 and 23 respectively.
Spaced from the housing 3 (in the illus-
trated example, underlying the housing 3) are paper
guiding means comprising spaced stabilizer plates 25
and 27 having a space 29 between them. A web of
paper to be tested moves in the machine direction,
illustrated by the arrow A, in the space between the
stabilizer plates. The means for guiding the paper
is physically connected to the housing, to move with
the housing as will be described below, by beams 31.
The housing 33 moves in a cross-machine
direction, illustrated by arrow B, along the rail 33
using means well known in the art. For example, as
illustrated in Figure lA, housing 3 can be attached
to a roller 3R which is guided for movement in the
cross-machine direction by slot 33S in rail 33. The
roller would be driven by a motor as is well known in
the art.
WO91/18281 PCT/CA90/00168
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A light source 35 is disposed to direct a
beam of light 37 to one surface of the web of moving
paper (in the illustrated embodiment, the top
surface). The beam 37 is reflected by the surface of
the web of moving paper to provide a reflected beam
39 which is received by the light guide 5. The light
guide 5 directs the beam 39 to the focussing lens 7
which in turn directs the focus beam to beam splitter
9.
Beam splitter 9 provides a first split beam
41, directed at the out-of-focus CCD sensor 11, and a
second split beam 43, directed at the in-focus CCD
sensor 15.
The output signals of the sensors 11 and 15
are transmitted to a data analysis board, which is
not illustrated in Figure 1, but which is installed
in the processor 19.
Referring to Figure 2, the data analysis
board comprises a subtractor 45 having its positive
input terminal fed with the in-focus signal and its
negative input terminal fed with the out-of-focus
signal. The sum of the focus signal less the out-
of-focus signal is fed to analog-to-digital converter
47 whose output is fed to one input of a comparator
49. The second input of the comparator 49 is fed a
predetermined threshold signal.
The output of the comparator 49 is fed to
an enable terminal of accumulator 51, and the output
of the analog-to-digital converter 47 is fed, in
WO91/18281 2 0 8 0 5 8 7 PCT/CA90/00168
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parallel, to the data input terminal of accumulator
51. The output of accumulator 51 is fed to the
processor.
In operation, and referring first to Figure
1, the dirt counter works as follows:
The reflected light 39 is guided, by guide
5, to the lens 7 where it is focussed and applied to
beam splitter 9. The beam splitter 9 directs a first
split beam 41 to the out-of-focus sensor 11, and a
second split beam, 43, to the in-focus sensor 15.
Turning now to Figure 3, it can be seen
that the two video signals are synchronized by using
the same data clock and exposure control signals.
The outputs of the in-focus array and out-of-focus
array are amplified, and the amplified signals are
then converted to digital signals. The out-of-focus
digital value is then subtracted from the in-focus
digital value, and the difference signal is then
compared with a program threshold signal. If the
difference signal exceeds the threshold signal, then
a logical signal is fed to an accumulator to activate
the accumulator. The signal is also fed to an
invigulator. The difference digital signal is sent
to the accumulator which, being enabled, computes the
sum of consecutive array elements of high difference
values, i.e., it performs the integration step.
When the difference signal falls to a value
lower than the threshold signal, the invigulator will
turn off the accumulator. The values in the
accumulator are stored in the processor memory array
and an integrated intensity histogram as well as
WO91/t8281 PCT/CA90/00168
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20805~7
other statistical data of each measured dirt speck is
formed. The histogram may be read at program timed
intervals or at program paper area coverages.
The integrated values are then converted
into their corresponding sizes using a predetermined
look-up table, and the size data is accumulated in a
second accumulator. It is now possible to receive
reports, for example, histograms, in terms of size
rather than in terms of integrated values.
As will be apparent, it is also possible to
use the data to stop the paper movement on detection
of speck sizes exceeding predetermined thresholds of,
for example, size and intensity.
As can be seen, the Figure 4 process is
very similar to the Figure 3 process except that the
subtraction is performed while the in-focus and out-
of-focus signals are still in their analog state.
The difference analog signal is then compared with a
program threshold analog signal. In all other
respects, the process as illustrated in Figure 4 is
the same as the process as illustrated in Figure 3.
Although specific embodiments have been
described, this was for the purpose of illustrating,
but not limiting, the invention. Various modifi-
cations, which will come readily to the mind of oneskilled in the art, are within the scope of the
invention as defined in the appended claims.
