U.S. patent number 3,754,146 [Application Number 05/238,199] was granted by the patent office on 1973-08-21 for apparatus and method for detecting streaks in coated layers on a web.
This patent grant is currently assigned to E.I. du Pont de Nemours and Company. Invention is credited to Allan Tit-Shing Chow.
United States Patent |
3,754,146 |
Chow |
August 21, 1973 |
APPARATUS AND METHOD FOR DETECTING STREAKS IN COATED LAYERS ON A
WEB
Abstract
A detecting head and light source are synchronously traversed on
opposite sides of a continuous moving web. Photoelectric detector
elements are recessed in rectangular channels disposed
symmetrically about rectangular coordinate axes, the principal axis
of the rectangular channels is in the direction of web travel, and
centered on the detecting head opposite the center of the
synchronous traversing light source. A streak defect in a coated
layer on the web interferes with the transmitted light to the
detecting elements resulting in an electrical characteristic signal
across the detecting elements. The characteristic signal is
amplified, digitized and electronically processed for verification
of the presence of a streak defect. The verified signal can be used
to activate an alarm, halt the coating of the web or can be
recorded and used for the design of subsequent slitting operations
on the web.
Inventors: |
Chow; Allan Tit-Shing
(Piscataway, NJ) |
Assignee: |
E.I. du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
22896894 |
Appl.
No.: |
05/238,199 |
Filed: |
March 27, 1972 |
Current U.S.
Class: |
250/559.48;
356/239.1; 250/235; 250/208.6 |
Current CPC
Class: |
G01N
21/8921 (20130101) |
Current International
Class: |
G01N
21/892 (20060101); G01N 21/88 (20060101); G01n
021/32 () |
Field of
Search: |
;250/219DF,234,235,219WD,219WT,223B,209 ;356/237-239 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stolwein; Walter
Claims
I claim:
1. An apparatus for detecting irregularities in a web of material
comprising:
1. a light source disposed on one side of said web,
2. a detecting head having at least two symmetrically offset
channels and photoelectric detecting elements recessed therein,
said channels substantially collimating the light transmitted
through and normal to said web from said light source and
sequentially screening any variation in transmitted light incident
on one photodetecting element from another photodetecting
element,
3. a traversing mechanism for moving said detecting head across the
width of said web, and
4. means for sequentially sensing the amplitude and polarity of the
electrical signal produced by said photoelectric detecting
elements.
2. The apparatus of claim 1 wherein said light source is moved
synchronously with said detecting means across the width of said
web.
3. The apparatus of claim 1 wherein said symmetrically offset
channels are rectangular, the distance between centers of said
channels is substantially equal to the width of said channels, and
the depth to which said detecting elements are recessed in said
channels is at least 16 times the channel width.
4. The apparatus of claim 1 wherein said means for sensing
comprises means for converting the electrical signal produced by
said photoelectric detecting elements into recordable form, and
means for recording the converted signal.
5. The apparatus of claim 4 wherein said means for sensing
comprises a band pass amplifier including a differentiating network
for differentiating and amplifying the signal from said detecting
elements, and means for converting the amplified signal to a
digital logic level signal, and means for recording said digital
logic level signal.
6. An apparatus as recited in claim 1 wherein said detecting
elements are recessed in said channels to a depth of at least 1/2
inch.
7. A method of detecting irregularities in a web of material
comprising:
a. transmitting light from a light source through said web to a
detecting head having at least two symmetrically offset channels
with photoelectric detecting elements recessed therein, said
photoelectric detecting elements being adapted to produce
sequential electrical pulses of opposite polarity when traversed by
a web irregularity, and
b. sensing the time sequence and amplitude of said electrical
pulses to identify the existence of a web irregularity.
8. A method as recited in claim 7 wherein said electrical signal is
substantially sinusoidal and said sequential pulses are of
alternate polarity, and said signal is differentiated to enhance
the characteristics representative of said irregularity.
9. A method as recited in claim 7 wherein sensing includes
converting said electrical signal to digital logic level signal
pulses, generating logic level gating pulses from said signal
pulses, gating said signal pulses with said gating pulses to verify
the time sequence of said sequential pulses to produce a verified
defect signal.
10. The process as recited in claim 9 including the additional step
of recording the verified defect signals and their lateral and
longitudinal location on the web.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus and method for detecting
streak defects in a wet or dry coated layer or layers on a web of
material, and more particularly to detecting, indicating,
monitoring and recording the location of streak defects in a coated
layer or layers of photographic emulsion on a web of photographic
support material.
2. Description of the Prior Art
Apparatus and methods for inspecting continuous moving webs for
defects are well known in the manufacturing arts and particularly
well known in the photographic materials manufacturing art.
However, most of the known apparatus and methods for inspecting
photographic materials for defects are not sensitive enough to
detect fine line streak defects that appear in multilayer slide
coatings of photographic emulsion layers on photographic support
materials. These streaks are also called pencil streaks and are
caused by oversize silver grains, gelatin slugs or entrapped air
bubbles in the feed slot or slide of a multilayer coating hopper as
taught in U.S. Pat. No. 3,005,440 and U.S. Pat. No. 3,474,758.
Wright, U.S. Pat. No. 3,286,567, Bunge, U.S. Pat. No. 3,564,265,
and Burgo, U.S. Pat. No. 3,206,606, recite apparatus for detecting
streaks in sheets of photographic material. The photodetection
systems employed by these three patents are based on the simple
observation or sensing of signal magnitudes as the photoelectric
cells traverse the moving sheet. Signals over a certain value are
interpreted as being caused by streaks, and signals below that
value are excluded as "noise." The apparatus of the present
invention, by contrast, employs at least two very closely adjacent,
symmetrically offset, recessed detecting elements which produce a
sinusoidal signal comprised of a plurality of electrical pulses of
opposite polarity characteristic of a streak. The signal is then
processed by characteristic signal verifying circuits. Since both
detecting elements look at the same general area of the web due to
their close proximity, gradual variations in coating weight, web
temperature, etc., produce no signal. Another advantage lies in the
ability to determine the type of streak from the characteristic
signal and to take proper corrective action to eliminate the streak
source.
SUMMARY OF THE INVENTION
It is an object of the invention to detect irregularities in a web
or length of sheet material and, more particularly, to detect the
formation of streaks in a coated layer or layers of photographic
emulsion and associated coated layers on a continuously moving web
of photographic support material just subsequent to the coating
process. Other objects of preferred embodiments of the invention
are to analyze and identify the particular type of streak that is
being formed so that timely corrective measures can be taken to
minimize the quantity of defective material coated, and to monitor
the presence and record the location of streak defects in the web
and use this information for the design of slitting patterns to
maximize the quantity of sheets obtainable from a web of
photographic material.
These and other objects of the invention are achieved by an
apparatus for detecting irregularities in a web comprising:
1. a detecting head having at least two symmetrically offset
channels with photoelectric detecting elements recessed therein,
preferably to a depth of at least 1/2 inch,
2. a light source disposed on the side of said web opposite said
detecting head,
3. a traversing mechanism for moving the detecting head across the
width of said web, and
4. means for sensing the electrical signal produced by said
photoelectric detecting elements.
Apparatus of the type just described is capable of producing an
electrical signal characteristic of streak defects in order to
accomplish the objects of the invention and is particularly suited
for detecting irregularities in a continuously moving web. The
means for sensing the signal of the detecting elements may include
electronic amplifying and waveshaping circuits for further
characterizing the signal for subsequent verification; electronic
digital circuits for verifying and categorizing the type of streak
defect; and recording instruments for monitoring the presence and
location of streak defects in the coated layers on the web.
The invention also includes a method of detecting irregularities in
a web of material, especially streak defects in a coated layer or
layers of photographic emulsion on a continuously moving web of
photographic support material, comprising:
a. transmitting light from a light source through said web to a
detecting head having at least two symmetrically offset channels
with photoelectric detecting elements recessed therein, said
photoelectric detecting elements being adapted to produce
sequential electrical pulses of opposite polarity when traversed by
a web irregularity,
b. sensing the time sequence and amplitude of said electrical
pulses to verify the existence of a web irregularity, and,
optionally,
c. recording the electrical pulses indicating the presence and
location of streak defects in said coated layer or layers.
The apparatus and method of this invention detect and verify the
formation of streaks in the coating process. The verified streak
signal may be used to activate an alarm and indicate remedial
action to eliminate the cause of the streak formation. The recorded
information, i.e., the presence and location of streak defects, may
be used in the design of slitting patterns for the coated material
and thus increase the yield of acceptable material from the coated
material.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective drawing of a traversing mechanism,
detecting head and light source of an embodiment of the
invention.
FIG. 2 is a detail perspective drawing in partial section of a
detecting head and light source of an embodiment of the
invention.
FIG. 3 is a schematic drawing of the detecting elements and
amplifying and waveshaping circuits of an embodiment of the
invention.
FIG. 4 is a representative drawing of a streak defect and a
characteristic streak signal of an embodiment of the invention.
FIG. 5 is a block diagram of the electronic signal processing
circuits of an embodiment of the invention.
FIG. 6 is a timing diagram showing the signal processing operations
of an embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The apparatus of the invention employs a detecting head having at
least two channels. The channels are preferably rectangular and
symmetrically offset about the origin of coordinate axes as shown
in FIG. 4. For the detection of streaks the channels may also be
symmetrically offset about an axis, e.g., the Y axis of FIG. 4. If
such a configuration is used a thin opaque wall is required to
separate the channels. Alternatively any intermediate configuration
may be used with a thin opaque wall separating the channels where
they overlap. The preferred configuration, wherein the channels are
symmetrically offset about the origin of coordinate axes,
simplifies construction of the detecting head and enables the
apparatus to detect "chatter bars." Chatter bars are caused by
uneven application of the coating layer as the web passes the
coating station and appear as bars laterally across the web. The
preferred distance between centers of the channels is equal to the
width of the individual channels, and the width of said channels is
selected to correspond with the width of the streak to be detected.
The preferred depth of the channels, i.e., the distance the
photoelectric detecting elements are recessed in the channels, is
related to the width of said channels by a ratio of at least 16:1.
The length of the channels is not critical, but a ratio of length
to width of at least 10:1 is preferred. In the preferred embodiment
the width of the channels is 1/32 inch, the depth of recess of the
detecting element is 1/2 inch, and the length of the channels is
10/32 inch. The channels function to substantially collimate the
light incident on the detecting elements by admitting the
transmitted light normal to the web and screening out the diffused
light transmitted through the web.
The light source is preferably adapted to be moved synchronously
with the detecting means across the web but on the opposite side of
the web so that the detecting means and light source are always in
register. An infrared source is preferred.
The geometrical configuration and symmetrical characteristics of
the channels in the detecting head cause an electrical signal to be
produced across the differentially connected detecting elements,
recessed therein, when a streak defect is traversed. The electrical
signal is substantially sinusoidal with the polarity sequence
determined by the type of streak being traversed. The means for
sensing this signal is any element, alarm, indicator or circuit
which is responsive to the signal and which provides a readout of
the signal being sensed or records or uses the signal to govern
other circuitry or operations. For example, the detecting elements
may be connected to electronic amplifying and waveshaping circuits
for further characterizing the signals which are then processed by
electronic digital circuits for verifying and categorizing the type
of streak defect as further described below. These circuits may be
used to supply the input data to recording instruments for
monitoring the presence and location of streak defects and/or for
operating a web slitter or sorter such as described in U. S. Pat.
No. 3,286,567.
A preferred embodiment of such apparatus is described below with
reference to the attached drawings, in which the same numerals are
used throughout.
The detecting head 15 and light source 12 are disposed,
respectively, on upper and lower traversing guide tubes 13 and 14,
of a suitable traversing guide apparatus with stanchions 10 and 10'
as shown in FIG. 1. A suitable traversing guide apparatus is
available from the Du Pont Co., Instrument Products Division, Photo
Products Department, Wilmington, Delaware 19898, as a Model 110
Traversing Mechanism.
A continuous moving web W of photographic support material, e.g.,
polyethylene terephthalate, having a coated layer or layers of
photographic emulsion is conveyed by suitable web handling means,
e.g., drive rolls, between the detecting head 15 and light source
12, which are synchronously moved back and forth across the width
of the web.
Detecting head 15 has narrow rectangular channels 16 and 17
disposed about rectangular coordinate axes X and Y, centered on
said head, axis Y being parallel to the direction of web travel.
Photoelectric detecting elements 18 and 19 are preferably recessed
in said channels away from the web surface, and are located in
end-to-end spaced relationship parallel to the direction of web
travel (Y) and are separated by a distance d, measured from center
to center in the direction of travel of the detecting head (X), as
shown in FIG. 2. The symmetrically offset relationship of the
channels is defined as either the lateral offset which functions to
detect longitudinal streaks in the coated layer on the web, or the
longitudinal offset which functions to detect defects in the coated
layer running laterally across the web. Although only one type of
defect, i.e., longitudinal streaks or lateral bars may be of
importance, either may be detected if the channels are
symmetrically offset about the origin of coordinate axes. The
channels may be symmetrically offset only about a longitudinal axis
if only longitudinal streak defects are to be detected. The
channels may be symmetrically offset only about a lateral axis if
only lateral bars are to be detected. In any of the three
configurations above, the symmetrical offset relates to either a
single axis or the origin of coordinate axes. Web edge sensors 11
and 11' are disposed on the lower surface of said head and spaced
respectively from each channel a minimum distance. The head and
particularly the inner surfaces of the channels are painted with
black nonreflective paint.
The light source 12 has a lamp 21 suitably mounted in holder 20 and
a condensing lens 23. A frosted glass 24 is disposed at the focal
point of said lens and a filter glass 25 is suitably mounted in the
light source.
Preferably the detecting head, particularly the inner surfaces of
said channels, is painted with black nonreflective paint. Lead
sulfide detectors have been found to be suitable detecting
elements. A suitable lamp has been found to be a Type MAZDA
manufactured by Westinghouse. It operates at 28 volts giving 21
candle power, and has a silvered envelope directing radiation only
through the front frosted window 22. The condensing lens is a
3-element f/0.62 lens with a diameter of 43.5 mm. Its transmission
should cover 2.5.mu.. The filter used is a Type RG1000 manufactured
by Schott and Jema, of Mainz, West Germany. Its transmittance is
from approximately 1.2.mu. to 2.7.mu.. The frosted glass disposed
at the focal point of the condensing lens improves the uniformity
of illumination from the light source.
The photoelectric detecting elements are differentially connected,
by which it is meant that their combined output signal is
proportional to the difference between the absolute values of the
signals produced by the elements. Although equivalent arrangements
may be employed, a convenient way to accomplish this is by means of
the circuit illustrated in FIG. 3. The photoelectric detecting
elements 18 and 19 are differentially connected between +15 volt
and -15 volt power supplies. Their common node is connected to the
plus input of operational amplifier 53 through a differentiating
network comprising capacitor 51 and resistor 52. Operational
amplifier 53 and the feedback network comprising capacitor 56,
resistor 55 and resistor 57 together with the differentiating
network constitute an active band pass filter.
The detection of a streak signal and formation of the
characteristic waveform can be readily understood by reference to
FIG. 4. The web W is traversed by the detecting head and light
source traveling synchronously from right to left. Assume the
streak S is lighter than the adjacent areas of the web W, when the
streak is between the light source and a particular rectangular
channel the transmitted light to the photoelectric detecting
element recessed in the channel is increased, the electrical
resistance of the detecting element is decreased, and the voltage
drop across the particular detecting element is decreased. A
differential electrical signal Vn is produced at the node between
the photoelectric detecting elements.
Rectangular channel 16 traverses the streak 15, the voltage across
detecting element 18 decreases; the voltage at the common node goes
positive, achieves a maximum value when the streak S is centered
under channel 16, and then decreases to zero. Rectangular channel
17 traverses the streak S, the voltage across detecting element 19
decreases, the voltage at the common node goes negative, and
achieves a maximum negative value when the streak is centered under
channel 17, and then decreases to zero. The voltage signal at the
common node Vn is differentiated to form the characteristic signal
Vo.
If the streak defect S were darker than the adjacent areas of web
W, the characteristic signal would be inverted.
Trim potentiometer 50 is provided to balance the response of
photoelectric detecting elements 18 and 19.
An operational amplifier that has been found particularly suitable
for use in the active band pass filter is the Model 3064/12C
manufactured by Burr-Brown. The frequency of the characteristic
signal is determined by the speed at which the detecting head and
light source traverse the web and the distance between centers of
the rectangular channels. The preferred width of the rectangular
channels is 1/32 inch on either side of the Y axis, and the
distance between centers (d) is also 1/32 inch. The preferred
traversing speed is 3 inches per second. The resulting frequency of
the characteristic signal is approximately 50 Hertz, and the pass
band of the filter is designed for this frequency. Spurious noise
signals and defect signals that are not within the frequency
response range of the active band pass filter are attenuated and
not processed by the characteristic signal verifying circuits.
In accordance with the process of the invention, the characteristic
signal is converted to digital logic level signal pulses from which
logic level gating pulses are produced. The signal pulses are then
gated with the gating pulses to verify the time sequence of the
sequential pulses produced by the detecting elements to produce a
verified defect signal. This process is described in greater detail
infra with reference to the drawings.
The characteristic signal Vo is applied to the sensor converter
circuits 103, 113 and 123. Sensor convertors 103 and 113 operate on
the positive and negative portions of a characteristic signal,
respectively, to convert the analog signal to digital logic level
signals with pulse width equal to the time duration that positive
and negative peaks of the analog signal are greater in magnitude
than threshold levels. The logic level signals are applied to
inverters 104 and 114. The output of inverter 104 is applied to a
delaying gate generator comprising delay timer circuits 105 and
106, AND gate 109, and also to the clock input of flip-flop 120.
The output of inverter 114 is applied to a delaying gate generator
comprising delay timers 115, 116 AND gate 119, and to the clock
input of flip-flop 110, all as shown in FIG. 5.
The output of AND gate 109 is applied to the data input of
flip-flop 110, and the output of AND gate 119 is applied to the
data input of flip-flop 120.
The one state output of flip-flop 110 is applied to AND gate 112
and the data input of flip-flop 125. The zero state output of
flip-flop 110 is applied to the reset input of flip-flop 110
through delay timer 111.
The one state output of flip-flop 120 is applied to AND gate 112
and the data input of flip-flop 126. The zero state output of
flip-flop 120 is applied to the reset input of flip-flop 120
through delay timer 121.
The one state output of flip-flops 125 and 126 are applied to
indicator lamps 136 and 137, respectively, through noninverting
amplifiers 127 and 128. The zero state outputs of flip-flops 125
and 126 are applied to isolated AC switch 133 through OR gate 122,
inverter 129 and switch 143. Isolated AC switch 133 applies 110
volts to the traversing drive motor (not shown). The direction of
the traversing motor is determined by isolated AC switches 131 and
132 and flip-flop 30. The one state output of flip-flop 30 is
applied to isolated AC switch 131, and the zero state output of
flip-flop 30 is applied to isolated AC switch 132.
The one state and zero state outputs of flip-flop 30 are also
applied to indicating lamps 138 and 139, respectively, through
noninverting amplifiers 134 and 135.
The output of edge sensors 10 and 11 is applied to sensor converter
124, and the output of sensor converter 124 is applied to the
inhibit input of inverters 104 and 114.
The characteristic signal is also applied to sensor converter 123.
The output of this sensor converter indicates the presence of a
defect, but is not processed for verification as a streak defect.
It may be used to drive an indicating lamp.
Potentiometer 143 is mechanically coupled to a gear or pulley (not
shown) on the traversing mechanism drive, and is calibrated to
provide transverse position data of the detecting head to a
recording apparatus.
All of the digital electronic circuits, i.e., sensor converters,
inverters, delay timers, AND gates, OR gates, flip-flops and
isolated AC switches, are available from the Digital Equipment
Corporation as K-Series Control Modules, and their operation is
more fully described in the Digital Control Handbook for 1971
published by that company.
The operation of the characteristic signal electronic processing
digital circuits can be readily understood with reference to the
timing diagram of FIG. 6.
The characteristic signal Vo is applied to sensor converter 103.
The positive going portion of Vo crosses the positive threshold
L.sup.+ at time T.sub.o causing the output of converter 103 to go
to the one state and remain in the one state until time T.sub.1
when the characteristic signal falls below threshold level L.sup.+.
The characteristic signal Vo is simultaneously applied to sensor
converter 113. The negative portion of Vo crosses the negative
threshold level L.sup.- at time T.sub.3 causing the output of
converter 113 to go to the one state and remain in the one state
until time T.sub.5 when the characteristic signal falls below the
threshold level L.sup.-. The characteristic signal Vo again exceeds
the threshold level L.sup.+ at time T.sub.7 causing the output of
converter 103 to again go to the one state until Vo falls below the
threshold level L.sup.- at time T.sub.9.
Logic level signal S103 is inverted producing signal S104 which is
applied to delay timers 105 and 106 of a delaying gate generator.
The inverted output of delay timer 105 and the noninverted output
of delay timer 106 are applied to AND gate 109. The output of AND
gate 109, signal S109, is a gate pulse having a pulse width T.sub.4
-T.sub.2 and delayed T.sub.2 -T.sub.o seconds from the time T.sub.o
that Vo first crossed the threshold level L.sup.+. This delayed
gate pulse S109 is applied to the data input of flip-flop 110, and
it may be thought of as a window through which flip-flop 110 may
view the occurrence of a negative threshold crossing by the
characteristic signal Vo. At time T.sub.3 the characteristic signal
Vo crosses the negative threshold level L.sup.-, producing logic
level signal S113, and inverted signal S114. The negative
transition of S114 falls within the delayed gate pulse of S109 and
sets flip-flop 110 to the one state. Signal S114 is also applied to
delay timers 115 and 116 of a delaying gate generator. The inverted
output of delay timer 115 and the noninverted output of delay timer
106 are applied to AND gate 119. The output of AND gate 119, signal
S119, is a gate pulse having a pulse width T.sub.8 -T.sub.6 and
delayed T.sub.6 -T.sub.3 seconds from time T.sub.3 that Vo first
crossed the negative threshold L.sup.-. This delayed gate pulse
S119 is applied to the data output of flip-flop 120, and it also
may be thought of as a window through which flip-flop 120 may view
the occurrence of a positive threshold crossing by the
characteristic signal Vo. At time T.sub.7 the characteristic signal
Vo crosses the positive threshold level L.sup.+, producing logic
level signal S103. The negative second transition of S104 falls
within the delayed gate pulse of S119 and sets flip-flop 120 to the
one state.
The coincident one state outputs of flip-flops 110 and 120 applied
to AND gate 112 produce a logic level pulse signal S112 indicating
a verified streak defect. The verified logic level streak defect
signal is supplied to a suitable recording apparatus, along with
the lateral position signal from potentiometer 143. Longitudinal
position of the verified defect may be obtained by calibrating the
recording apparatus with the web speed.
The zero state output of flip-flop 120 is applied to delay timer
121 and to the clock input of flip-flop 125. The output of delay
timer 121 is a delayed pulse S121 which is applied to the reset
input of flip-flop 120. The one state output of flip-flop 110 is
applied to the data input of flip-flop 125, and flip-flop 125 is
set to the one state by the negative transition of the zero state
output of flip-flop 120.
The one state output of flip-flop 125 is applied to noninverting
amplifier 127 which drives indicating lamp 136. The zero state
output of flip-flop 125 is applied to OR gate 122 and through
inverter 129 and switch 143 controls isolated AC switch 133 and the
110 volt power to stop the traversing motor drive. This circuit may
be disabled by opening switch 143.
The one state output of flip-flop 30 is applied to indicator lamp
138 through noninverting amplifier 134, this lamp indicates the
detecting head and light source are traversing from right to
left.
The diagonal configuration of lamps 138 and 136 indicate the streak
signal is due to a light streak.
If the streak defect S were darker than the adjacent areas of web
W, the characteristic signal would be inverted, and the sequence of
threshold crossing would be L.sup.-, L.sup.+ and L.sup.-. This
opposite sequence is similarly processed by the characteristic
signal processing digital electronic circuits and lights lamps 138
and 137.
Flip-flop 125 must be manually reset by pushbutton 144 to clear the
apparatus after a streak signal has been verified.
The edge sensors 11 and 11' inhibit inverters 104 and 114 when the
detecting head and light source traverse beyond the edge of the web
and prevent confusing the edge of the web with a streak defect.
Although the preferred embodiment of the invention is described for
a transmitted light signal and a translucent web, it will also
operate with a reflected light signal on an opaque web. And
although the invention is preferably used immediately subsequent to
the coating process where the coated layers are still wet, other
uses are contemplated where the web may be a textile material or
the coated layer or layers may be others than a photographic
emulsion.
Although the invention is described with particular reference to a
continuous moving web and longitudinal streaks or lateral bars in
coated layers thereon, its application is not so limited. With
suitable modification to the means for traversing, the apparatus
may be used for inspection of stationary sheets. It also may be
used for inspecting textile webs or other web material for
longitudinal and lateral type defects.
* * * * *