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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates generally to printing and package decoration
and, more particularly, to an apparatus for measuring the ink,
photographic emulsion, or other opaque medium coverage of a translucent
sheet of material which has been provided with opaque artwork identical to
that which is to be printed, in a particular color, on package material in
a mass-production package printing operation.
In the high-speed production of packaging material, each color which is
printed on a package is, in most cases, printed by a separate ink or dye
on a separate printing roll or press. In order to determine the amount of
ink that will be required for any particular packaging project, it is
customary for the manufacture of the product which is to be packaged to
furnish the package producer with separate transparencies having opaque
portions corresponding to the artwork for each color to be printed, i.e.
if three separate colors are to be printed on a package, the manufacturer
would furnish the package producer with three separate transparencies,
each showing the pring configuration for a particular color. The package
producer computes the total area coverage for each separate color from the
transparencies as a step in determining the total amount of ink of each
color which will be required for the particular project. The task of
determining the area coverage of a transparent sheet of material with
opaque medium may be relatively simple, as when the artwork for a
particular color consists of a few regular geometric shapes of constant
density or intensity. However, when artwork consists of irregular shapes,
such as alpha-numeric printing or the like, or of varying densities, the
task of accurate area coverage estimation may range from quite
time-consuming to nearly impossible. The conventional method for computing
area coverage for irregular opaque shapes is to break the shapes down into
a number of small, substantially regular figures, such as rectangles and
triangles, and to then take the sum of the areas of these small regular
figures. Due to the large number of computations and approximations that
must be made using this method, it is not uncommon for a draftsman to
spend the greater portion of a week estimating the area coverage of a
single average-sized, e.g. 20 inches by 30 inches, sheet having complex
artwork thereon. The large number of computations and approximations which
must be made in estimating the area of complex artwork tends to make such
an estimation process inaccurate because of the high risk of error in
making the many computations and because of the inherent inaccuracy in
approximating the area of certain irregular shapes using regular figures.
When the artwork grades from transparent to opaque, accurate estimates are
impossible. Estimation inaccuracies on the order of 20% to 25% are not
uncommon. In a large production run, e.g. 1,000,000 packages provided on
20 inch by 30 inch carton blanks, a 20% overestimate of the coverage of a
color which covers 80% of the package could result in the overpurchase of
approximately 500 gallons of ink at a cost of approximately 2 dollars per
gallon, resulting in a total unnecessary cost of approximately $1000 for
that color, in addition to the cost involved in preparing the coverage
estimate. Thus, it may be seen that a need exists in the packaging arts
for an apparatus capable of quickly and accurately measuring the medium
coverage of a transparency of the type provided to a package producer by a
manufacturer.
SUMMARY OF THE INVENTION
The present invention may comprise an apparatus for measuring the relative
coverage of a predetermined portion of a sheet of translucent material
with an opaque medium such as ink which may be arranged in varying
geometrical shapes and optical densities, comprising: (a) light source
means for providing a relatively constant intensity source of light over a
predetermined measuring area; (b) positioning means for positioning said
predetermined portion of said sheet of material to be measured over said
predetermined measuring area of said light source means; (c) light
measuring means for measuring the relative amount of light from said light
source means which is transmitted through said predetermined portion of
said sheet of material to be measured, whereby the relative amount of
opaque medium coverage of said portion of said sheet to be measured is
readily determinably by comparison of said measured amount of light
transmitted through said predetermined portion of said sheet to be
measured with predetermined calibration values.
The present invention may also comprise an apparatus for determining the
relative amount of opaque medium coverage of a translucent sheet of
material comprising: an apparatus for determining the relative amount of
opaque medium coverage of a translucent sheet of material comprising:
light box means havng a relatively planar light transmitting surface for
supporting the sheet of material thereon and for uniformly transmitting
light through the portions of said sheet of material which are not covered
by said opaque medium; light sealing enclosure means for light sealingly
enclosing the sheet of material and said light transmitting surface of
said light box means for preventing entry of light from light sources
other than said light box means into said sealing means; cropping means
operatively associated with said light box means and the sheet of material
for preventing light transmission from portions of said light box means
light transmitting surface other than the portion thereof covered by the
sheet of material from entering said light sealing enclosure means;
whereby substantially all light received in said light sealing enclosure
means enclosing said light box means is initially transmitted through the
sheet of material; light diffusion means positioned within said light
sealing enclosure means for uniformly diffusing said light transmitted
into said light sealing enclosure means and for preventing direct light
transmitted through any portion of the sheet of material from entering a
light intensity measuring means; light intensity measuring means
operatively associated with said light sealing enclosure means and said
light diffusion means for measuring the intensity of diffused light within
said light sealing enclosure means; said measured light intensity being
representative of the relative degree of coverage of the sheet of material
with opaque medium.
The present invention may also comprise a method of determining the
relative amount of opaque medium coverage of a predetermined portion of a
sheet of translucent material comprising: directing light from a uniform,
constant intensity light source area which is coextensive with the
predetermined portion of the sheet to be measured onto one side of the
sheet; measuring the amount of light from the light source that is
transmitted through the sheet; comparing the measured amount of light to
predetermined calibration values.
BRIEF DESCRIPTION OF THE DRAWING
An illustrative and presently preferred embodiment of the invention is
shown in the accompanying drawing in which:
FIG. 1 is a partially opened perspective view of an apparatus for measuring
the relative coverage of a sheet of translucent material with an opaque
medium.
FIG. 2 is a perspective view of the apparatus of FIG. 1 illustrating the
positioning of a sheet of translucent material with an opaque medium
thereon above a light source.
FIG. 3 is a perspective view of the apparatus of FIG. 1 illustrating the
cropping of the total light source area to an area conforming to the shape
of a sheet to be measured.
FIG. 4 is a perspective view of the apparatus of FIG. 1 illustrating the
positioning of the apparatus for measuring of light passage through a
sheet to be measured.
FIG. 5 is a cross-sectional view of the apparatus of FIG. 1 in the
operating state shown in FIG. 4.
FIG. 6 is a perspective view of another embodiment of an apparatus for
measuring the relative coverage of a sheet of translucent material with an
opaque medium.
FIG. 7 is yet another perspective view of an apparatus for measuring the
relative coverage of a sheet of translucent material with an opaque
medium.
FIG. 8 is a size-calibration graph.
FIG. 9 is an opaque coverage-calibration graph.
DETAILED DESCRIPTION OF THE INVENTION
The apparatus 10 of the present invention is used for measuring the
relative coverage of a predetermined portion of a sheet of translucent
material 11 with an opaque medium 13, such as ink. It will be understood
that the "predetermined portion" of the sheet of translucent material may
comprise the entire sheet of material or any smaller portion thereof which
an operator may select. It will also be understood that "opaque medium"
refers to anything contained in or on the sheet of otherwise translucent
material which would prevent or partially impede light from being
transmitted through the sheet of material. Thus, "portions of a sheet of
translucent material covered with opaque medium" may refer to portions of
a sheet of translucent material which are covered with opaque tape or the
like, or may refer to portions of a sheet of translucent material which
have been rendered optically dense or opaque by some machine process such
as surface abrasion, etc., or may refer to portions of the sheet of
translucent material covered by conventional ink and the like, etc.
In general, the apparatus 10 of the present invention comprises a light
source means 12 for providing a relatively constant intensity source of
light over a predetermined area which is at least as large as the area to
be measured of the sheet of material; a positioning means 14 for
positioning a predetermined portion (the entire sheet in FIGS. 1-5) of the
sheet of material 11 to be measured over the predetermined measuring area
of the light source means; a light measuring means 16 for measuring the
relative amount of light from the light source means 12 which is
transmitted through the predetermined portion of the sheet of material 11,
whereby the relative amount of opaque medium coverage of the portion of
sheet 11 to be measured may be determined by comparing the measured amount
of light transmitted through the predetermined portion of the sheet 11
with predetermined calibration values. Light blocking means 18 are
provided in operative association with the light measuring means 16 to
ensure that only light passing through the predetermined portion of the
sheet 11 to be measured is actually measured by the light measuring means.
The light blocking means 18 may comprise sealing enclosure means 20 which
prevents light other than light from the light source from entering the
light measuring means. The light blocking means may also comprise cropping
means 22 which are used for blocking off light from the light source means
12 other than light which passes through the portion of the sheet 11 to be
measured. Coverage-calibration means 26, which may comprise a plurality of
sheets of different known relative opacity, may be provided for
calibrating the apparatus 10. Data processing means 30 may be provided for
storing calibration values and for comparing measured light values
associated with the light transmitted through the predeterined portion of
the sheet 11 to be measured with the calibration values and/or for
performing other functions.
In operation, as illustrated in FIG. 2, a sheet of material 11 for which
relative opaque medium 13 coverage is to be measured is initially
positioned on the positioning means 14 above the light source 12. Next, as
illustrated in FIG. 3, cropping means 22 are adjusted so as to block off
transmisson of light from all portions of the light source 12 other than
the portion positioned directly below the portion of the sheet of material
11 which is to be measured. Next, as illustrated in FIGS. 4 and 5, the
sealing enclosure means 20 is positioned in enclosing relationship over
the light source means, cropping means, and sheet 11 such that no light
other than light from the light source enters the light measuring means
16. In the embodiment illustrated in FIGS. 1-5, a light diffusion means
24, FIG. 5, is operatively associated with the sealing enclosure means 20
and the light measuring means 16 in a manner such that only light which
has passed through the portion of the sheet of material 11 to be measured
and which has been diffused by the diffusion means enters the light
measuring means. The measured intensity of the diffused light is
proportional to the total "apparent open area" of the portion of the sheet
of material 11 to be measured, i.e. the total area of the portion of the
sheet of material to be measured minus the area thereof covered with
opaque medium. Thus, the relative opaque mdium coverage is readily
determined by comparing the measured light intensity associated with the
portion of the sheet of material to be measured with calibration values
determined by measuring equal-sized portions of sheets having known
degrees of opacity, e.g. five sheets having opacities of 0%, 25%, 50%,
75%, and 100%, respectively. Having thus described the apparatus of the
present invention and method of operation thereof in general, the
invention will now be described in further detail.
As illustrated in FIG. 5, the light source means 12 may comprise a
conventional light talbe 40 having an opaque enclosure box 42 with
fluroescent lights 44 mounted therein. A translucent light-diffusing panel
46 is mounted in covering relationship with the open upper end of the box
42. In the embodiment of FIGS. 1-5, the positioning means 14 for
positioning the translucent sheet of material 11 over the light source
means 12 comprises the translucent panel 46.
The light measuring means 16 may comprise a conventional small-area light
intensity measuring device such as a device sold under the product name
PCT Digital Dot Area Meter, which is available from Tobias Associates,
Inc. of 50 Industrial Drive, P. O. Box 2699, Ivyland, Pa., 18974-0347. The
light intensity measuring device 50 is mounted on the sealing enclosure
means 20 directly above a small hole 51 at the top thereof, FIG. 5.
As best illustrated in FIG. 1, sealing enclosure means 20 may comprise a
hemisphere 52 fixedly mounted above the circular opening 53 in a
rectangular mounting plate 54 having the same configuration as the
translucent light panel 46 of the light table. The mounting plate 54 is in
turn pivotally mounted on the light table by a conventional hinge assembly
56, enabling the sealing enclosure means 20 to move between the open
position illustrated in FIG. 2 and the closed position illustrated in FIG.
4. Various peripheral sealing material such as felt, etc. (not shown) may
be provided at the periphery of the sealing enclosure means 20 to increase
the effectiveness of the light seal provided thereby. Thus, a light
enclosure cavity 58, FIG. 5, is provided above the light source means 12
into which substantially no light enters other than light from the light
source means.
As best illustrated in FIG. 1, cropping means 22 may comprise a
conventional photographic diaphram-type cropping device 60 having a
plurality of sliding plates 62, 64, 66, 68, 61, 63, 65, 67, which may be
moved relative one another to provide a rectangular opening 69 of any
desired rectangular configuration. The cropping device 60 is hingedly
mounted to the light table by hinging assembly (not shown) having
approximately the same pivot axis as the sealing enclosure means 20,
enabling the cropping means 22 to be pivoted between an open position, as
illustrated in FIG. 2, and a closed position, as illustrated in FIG. 3.
This cropping device may alternatively (not shown) be hinge mounted from
any of the remaining sides of 12.
As best illustrated in FIG. 5, light diffusing means 24 may comprise a
smooth, white, light-diffusing surface 72 provided on the interior of
hemisphere 52 such as by a flat or matte paint or the like. The light
diffusing means also comprises a white, light-diffusing ball 74 which may
be, e.g., a conventional white ping-pong ball or painted disc mounted on a
support wire 76 attached to the interior wall of the hemisphere. The
light-diffusing ball 74 is positioned directly below the opening 51 in the
hemisphere 52 and sufficiently close thereto to diffuse any direct light
from the light source 12 before it enters opening 51 whereby the light
intensity measured by the light measuring means 16 is representative of
the illumination of the entire enclosure 58 which is provided by all of
the light transmitted through the portion of the sheet 11 to be measured,
rather than being representative of direct light from a single portion of
the sheet which may be positioned directly opposite hole 51.
As shown in FIG. 1, coverage-calibration means 26 may comprise a plurality
of relatively large sheets having different degrees of opacity. For
example, the coverage-calibration means may comprise a sheet 80 having 0%
opacity, a sheet 82 having 25% opacity, a sheet 84 having 50% opacity, a
sheet 86 havng 75% opacity, and a sheet 88 having 100% opacity. The
relative opacity of the sheets is preferably provided by light filter
material of different light densities. However, the different opacity
sheets may also be provided by covering portions of translucent sheets
with a uniform gridwork of lines of known width and spacing.
Data processing means 30 may comprise a conventional microcomputer or
minicomputer 92, a conventional CRT display 94, and a conventional input
terminal such as a standard keyboard 96. The output signal from 16 might
also be directly processed by 92 on operator command.
One specific method for determining the opaque medium 13 coverage of a
sheet 11 of transparent material of unknown area is as follows: Initially,
a large sheet, which may be sheet 80, which is constructed of a material
identical to the material from which sheet 11 and other sheets to be
measured are constructed and which has no opaque medium thereon, is
positioned in overlying relationship with the positioning means 14. Next,
a number of differently-sized areas, which are to be used as
area-calibration values, are selected. For example, for a light table
panel having a total area of 1000 square inches, areas in 100 inch
increments from 0 square inches to 1000 square inches may be selected.
Next, for each selected area, cropping means 22 is adjusted to provide an
opening 69 having that selected area and is positioned over the neutral
density sheet 80 in the position illustrated in FIG. 3. Next, the sealing
enclosure means 20 is positioned over the cropping means in the position
illustrated in FIG. 4. Next, the intensity of diffused light within the
enclosure 58 is measured with the light measuring means 16. Next, an
ordered recording is made of the area-calibration values and the light
measurement associated with each area-calibration value. In one
embodiment, this ordered recording is made in the form of a
size-calibration graph such as illustrated in FIG. 8, with the cropping
area (the area of opening 69) used as one coordinate axis and the measured
relative light intensity used as the other coordinate axis. Alternately,
this information could be stored in machine-readable form in the form of a
look-up table or least-squares fitted equation which is provided with an
appropriate sofeware program for interpolating between data points on the
look-up table or solving the equation. Next, the sheet of material for
which opaque medium coverage is to be measured is mounted on the light
box, as illustrated in FIG. 2. Next, as illustrated in FIG. 3, the
cropping means 20 is adjusted to block off portions of the light table
other than the portion thereof which is covered by the portion of the
sheet of material for which opaque medium coverage is to be measured. In
the embodiment illustrated, the portion of the sheet which is to be
measured is the entire sheet. Next, the sealing enclosure means 20 is
positioned over the sheet and cropping means, as illustrated in FIG. 4.
Next, the intensity of diffused light within the enclosure 58 is measured
by the light measuring means 16. Next, this measured light intensity is
recorded either in human-readable form or, alternately, in
machine-readable form. Next, the tested sheet is removed and a first one
of the coverage-calibration sheets is mounted on the light table. The
cropping means 22 is left in the same position, i.e. with the same-sized
opening 69 as was used in cropping the sheet 11 to be measured, and is
positioned over the coverage-calibration sheet in the manner as
illustrated in FIG. 3. Next, the sealing enclosure means 20 is positioned
over the cropping means and coverage-calibration sheet, as illustrated in
FIG. 4, and a light measurement is made. This process is repeated for each
of the coverage-calibration sheets, and the light measurement value
associated with each different degree of opacity of the different
coverage-calibration sheets is recorded in ordered form, e.g. by
constructing a coverage-calibration graph with percentage of opacity as
one coordinate and measured light intensity as the other coordinate as
illustrated in FIG. 9, or, alternately, in a machine-readable form such as
a look-up table or equation. Next, the light intensity measurement
recorded for the sheet 11 to be measured is compared with the recorded
light measurement values associated with the different opaque sheets, as
by comparison to constructed opaque coverage-calibration graph, FIG. 9, to
determine the relative coverage of the sheet of material with opaque
medium. For example, if the light measurement value associated with the
sheet 11 is equal to the light measurement value associated with the 25%
opaque sheet, then the coverage of the sheet 11 with opaque medium 13 is
25%. Next, the light intensity measurement associated with the sheet of
material 11 is compared to the area-calibration values, e.g. by comparison
of the measured light intensity value to the size-calibration graph to
determine the size of the uncovered area of the sheet 11. Alternately, a
light reading from neutral density sheet 80 may be taken using the
cropping means opening size used with sheet 11, and this light measurement
value may then be compared to the size-calibration graph to determine the
total area of sheet 11 directly. Next, the area of opaque medium coverage
of the sheet 11 is determined from the determined relative coverage value
and the determined uncovered sheet area or, alternately, the determined
total sheet area. It will, of course, be appreciated that, if the area of
the sheet 11 is known, then the necessity of measuring and recording
different light intensity values for a size-calibration sheet and
associated areas and determining the size of sheet 11 based on a
comparison to those calibration values is obviated.
An alternate embodiment of an apparatus 110 for measuring the relative
coverage of a predetermined portion of a sheet 111 of translucent material
with an opaque medium 113 is illustrated in FIG. 6. Like the previous
embodiment, the apparatus 110 may comprise a light source means 112 for
providing a relatively constant intensity source of light over a
predetermined measuring area; positioning means 114 for positioning a
predetermined portion of a sheet of material 111 to be measured over a
predetermined measuring area of the light source means; light measuring
means 116 for measuring the relative amount of light from the light source
means which is transmitted through the predetermined portion of a sheet of
material to be measured; and light blocking means 118 for preventing light
other than light from the light source which is transmitted through the
predetermined portion of the sheet of material to be measured from
entering the light measuring means. The apparatus may also be provided
with data processing means 130 for storing measured data values and
comparing measured data values to calibration values for determining the
relative amount of coverage and/or the total area coverage of the sheet
material 111 with opaque medium 113. The light source means may comprise a
conventional light table 140, and the positioning means 114 may comprise a
conventional translucent light table cover 142 which may be provided with
a digitizing grid of the type used in many conventional
computer-aided-design (CAD) systems. Light measuring means 116 may
comprise a plurality of light measuring cells 144, 146, 148, etc., which
are relatively small, e.g. squares measuring 0.2 inches on a side, and
which are arranged in a rectangular gridwork 150 which is coextensive with
the translucent light table cover 142. Each light measuring cell
corresponds to a portion of the translucent light table cover and the
corespondence of the portions of the light table cover and the plurality
of light measuring cells is electronically stored in computer software in
data processing means 130. Light blocking means 118 comprises the light
cell gridwork 150 which is hinged to the light box and adapted to
sealingly cover the light box when it is pivoted into opposite
relationship therewith. A sealing peripheral edge 152 may be provided to
improve the ability of the light cell gridwork 150 to block off light from
light sources other than the light table. A cursor device 154 may be used
in association with the digitizing grid provided in translucent light
table cover 142 to cause only those cells in the light cell grid 150 which
are positioned directly opposite to a sheet of material 111 to be
operable. The cursor device 154 operates in combination with the
digitizing grid in the same manner as the cursors and digitizing grids of
conventional CAD systems, i.e. the cursor 154 is touched to the four
corners of the sheet 111 to define the area from which light is to
measured. Computer 130 processes this information and actuates only those
cells in gridwork 150 which are positioned directly opposite the portion
of translucent light table cover 142 which has been thus defined as a
measuring area with cursor 154. Thus, in this embodiment of the invention,
the cursor 154 and digitizing grid associated with the translucent light
table cover and the computerized selection of cells in gridwork 150 act as
an electronic cropping means for eliminating light from the light table
other than light passing through the selected portion of translucent sheet
111 from being measured. In an alternate embodiment of this invention, the
cursor device 154 may comprise a conventional "mouse-type" cursor device
which must be initially touched upon a fixed reference point on the
translucent light table cover 142 before being operable to define the four
corners of the portion of sheet 111 to be measured. Both types of cursors
are in common use and are well-known in the computer arts. The method of
operation of the apparatus 110 of FIG. 6 may be identical to that
described above with reference to FIGS. 1-4, except that the actual area
of sheet 111 is readily determined by the computer through electronic
computation based upon the reference points provided by cursor 154. It
will also be appreciated that the coverage value for each light cell must
be individually determined by comparison of the measured light intensity
from that cell to calibration values to determine the relative coverage
measured by that particular cell, and then the determined relative
coverage of each of the cells is averaged to determine the total average
coverage of the sheet 111.
In yet another embodiment of the invention, as illustrated in FIG. 7, the
apparatus 210 comprises a light source means 212, a positioning means 214,
a light measuring means 216, a light blocking means 218, and a data
processing means 230 which perform the same general functions as described
above with reference to FIGS. 1-5 and FIG. 6. In this embodiment, sheet
sizing assembly 232 is also provided which enables the size of a sheet to
be quickly measured and electronically stored in computer 230. In this
embodiment of the invention, the light source means 212 comprises a
conventional light table 240 having a narrow transversely extending slit
242 at the center thereof which provides only a narrow band of light
extending across the light table. The positioning means 214 comprises
means for moving a sheet of material to be measured in a direction
indicated at 250 which is perpendicular to the direction of extension of
light slit 242. The positioning means comprises an opaque sheet support
260 over which a sheet of material 211, as indicated in phantom, passes.
The positioning means also comprises a first belt drive 262 positioning in
covering box 252 which is adpated to be located opposite a portion of
sheet support 260 positioned upstream of light slit 242, and a second belt
drive 264 mounted in covering box 252 and adapted to be positioned a
portion of support sheet 260 locations downstream of light slit 242. The
two belt drives operate in a manner similar to that of conventional
copying machines to move a sheet of material 211 across the surface of
support sheet 260 at a constant rate. Light measuring means 216 comprises
a plurality of light cells 244, 246 arranged in a single cell width,
narrow transverse band 248 which is positioned immediately above light
slit 242 when bos 252 is pivoted into position above light table 240.
Light blocking means 218 comprises covering box 252 in which the belt
drives and light measuring means are mounted, which is hingedly attached
to the light table by a conventional hinging assembly (not shown). A
peripheral sealing strip 254 may also be provided to block out light other
than light from the light table from entering the light measuring means.
Sheet sizing assembly 232 comprises a horizontal support surface 261 which
is provided with transversely adjustable members 272, 274, which may be
spread apart or moved together into touching relationship with the edges
of a sheet 211 positioned therebetween for determining the transverse
dimension of the sheet. The sizing assembly 232 also comprises a
longitudinally adjustable member 266 which may be moved forwardly and
rearwardly to a position in touching engagement with the rear edge of a
sheet 211 whose forward edge is engaged by transverse stop member 268.
Sheet sizing assemblies are well-known in the copying machine arts. Infeed
means (not shown) associated with a lower edge of stop member 268 enables
a sheet of material 211 to be fed into moving engagement with first drive
belt 262 through actuation of an infeed switch (not shown). The point in
time at which the sheet of material is fed into the first drive belt 262,
as well as the dimensions of the sheet, are electronically stored in the
data processing means 230. Based upon these stored values, light
measurement data from light cells 244, 246, etc., are stored by the
central processing unit 230 only from measurements beginning at a point in
time at which the leading edge of the sheet of material 211 to be measured
is positioned in overlying relationship with light slit 242. Thereafter,
the data signals from the light measuring cells 244, 246 are continuously
monitored and stored until the trailing edge of the sheet passes over
light slit 242. The data processing means may determine the occurrence of
this trailing edge passage from the dimensions of the sheet 211 and the
feed rate provided by belt drives 262 and 264. Based upon the
electronically stored transverse dimension of the sheet, input signals
from only those light measuring cells below which the sheet will pass are
used; i.e. light measuring cells positioned transversely outwardly of the
edges of the sheet 211 are electronically blocked off. In this embodiment
of the invention, the light intensity of light passing through any portion
of the sheet which is momentarily positioned above light slit 242 is
measured directly by light measuring cells 244, 246, etc. The light
intensity signal provided by each cell 244, 246, etc. is translated into a
relative coverage signal by comparison of the measured light intensity
value from each cell of predetermined calibration values. The coverage
signal for each cell is then integrated in time between the first point in
time when the sheet of material 211 began passage over the light slit and
a second point in time when it ended passage over the light slit. This
integrated value is then divided by the total amount of time between said
first and second points in time to provide an average coverage value for
each light cell. The average coverage value for all of the measuring light
cells are then averaged to determine the average coverage value for the
entire sheet 211. After passage across the support sheet 260, the sheet of
material may be collected on a collection tray 270.
While an illustrative and presently preferred embodiment of the invention
has been described in detail herein, it is to be understood that the
inventive concepts may be otherwise variously embodied and employed and
that the appended claims are intended to be construed to include such
variations except insofar as limited by the prior art.
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