Note: Descriptions are shown in the official language in which they were submitted.
1051218
SPECI~qCATION
In the prior art it is kn->wn to obtain an indication of color and
brigllaless characteristics of a paper web during manufacture by an
on-line measurement of re~lectance value (Rg), but this measurement
is decidedly different from that necessary for actual color and bright-
ness characterizations. Accordingly, such a measurement must be
accompanied by very frequent off-line testing, so as to enable an
adequate empirical calibration of the measuring instrument. Further,
a separate set of calibration parameters is required for each grade
and weight of paper. Off-line instruments which adequately measure
these characteristics require that a pad of several thicknesses of paper
be exposed to the light source aperture so that a different reflectance
vatue (Ro~,~ is obtained. Obviously this is impossible with an on-line
instrument unless the far more inaccessible reel itself is tested.
Only where the on-line measured reflectance value (Rg) approaches
the off-line value (Roo), as in instances of paper of extremely high
opacity such as heavily coated or heavily dyed paper, can the above
problems be minimized to the point where accuracy becomes sufficient
for control purposes.
- This invention relates to an optical device and method for sensing
optical properties of a paper sheet material, and particularly to an
on-the-paper-machine device and method for simultaneously sensing
both transmitted and reflected light so as to obtain measurements from
which the optical properties of interest can be calculated substantially
independently of grade and weight of paper involved.
Accordingly it is an object of the present invention to provide
an optical monitoring device and method for sensing optical properties
- 1 -
lOSlZ18
based on measurements made on a single thickness of partially translucent
paper sheet material and which measurements sufficiently characterize the
actual properties of interest that a minimum of empirical calibration is
required regardless of changes in grade and weight of paper.
Another object of the invention is to provide such an optical
monitoring device and method capable of accurately sensing optical properties
such as brightness, color, opacity and/or fluorescent contribution to bright-
ness.
While such an optical monitoring device is useful off-line for
sensing optical properties of a single thickness sample, it is a further
important object of the present invention to provide such an optical monitor-
ing device which is of sufficiently light weight and compact construction so
as to be adapted for on-line monitoring of the desired optical properties.
Another and further object of the invention is to provide an on-
the-paper-machine optical monitoring device of sufficient flexibility and
accuracy to enable control of desired optical properties during the paper
making process.
A unique feature of the on-line optical monitoring device is its
ability to simultaneously measure both reflected and transmitted light. By
measuring two independent optical parameters it is possible to thoroughly
characterize the paper optical properties of a partially translucent web
with a minimum of empirical correction for factors such as paper grade and
weight.
According to one broad aspect of the invention, there is provided
apparatus for obtaining a quantitative measure of a paper optical property
such as brightness, color or opacity, said apparatus comprising: an optical
measuring device having a receiving region for receiving in operative
relation thereto a single thickness of substantially homogeneous paper sheet
material, said optical measuring device having an optical system with at
least tw~ substantially independent photometric sensors and at least two
distinct light energy paths each including at least light source and spectral
~ -2-
~051218
response filter means and a respectiVe one o.f said photometric sensors,
and each intersecting said receiving region prior to the respective
assoc:iated photometric sensor, each of said at least two distinct light
energy paths having substantially a common spectral response characteristic
sufficient to characterize said paper optical property but being respectively
arranged for collecting reflected and transmitted light energy from the
receiving region after impingement of the light energy on a single thickness
of paper sheet material at said region so as to essentially characterize
the reflectance and transmittance of the paper sheet material, whereby the
paper optical property such as brightness, color or opacity is characterized
with substantially greater accuracy than any characterization of said paper
optical property by either a reflectance or a transmittance measurement
taken by itself.
According to another broad aspect of the invention, there is
provided apparatus with automatic digital computer means connected on line
with said optical measuring device and coupled with the respective photo-
metric sensors of said distinct light energy paths for receiving therefrom
respective output signals in accordance with the reflectance and transmit-
tance of the paper sheet material and automatically operable on the basis
of said output signals to calculate a quantitative indication of said paper
optical property.
Accordlng to a further broad aspect of the invention, there is
provided in the art of paper manufacture, apparatus for obtaining a quanti-
tative measure of a paper optical property such as brightness, color or
opacity, which comprises: an on-machine optical monitoring device for
mounting on a paper machine and having a web receiving region for receiving
in operative relation thereto a moving web of single thickness substantially
homogeneous paper sheet material being produced by such machine, said on-
machine optical monitoring device having an optical system with at least
tW~ substantially independent photometric sensors and at least two distinct
light energy paths each including at least light source and spectral response
~ -2a-
`- 10~ 218
filter means and a respective one of said photometric sensors, and each
intersecting said web receiving region prior to the respective associated
photometric sensor, each of said at least two distinct light energy paths
havirlg substantially a common spectral response characteristic sufficient
to characterize said paper optical property but being respectively arranged
for collecting said light energy from the web receiving region after impinge-
ment on said web under respective substantially differentiated conditions
such as to essentially characterize two essentially independent optical
response parameters of the paper sheet material and such as to characterize
the paper optical property such as brightness, color or opacity with sub-
stantially greater accuracy than any characterization of said paper optical
property by either one of such optical response parameters taken by itself,
and automatic digital computer means connected on line with said on-machine
optical monitoring device and coupled with the respective photometric sensors
of said distinct light energy paths for receiving therefrom respective out-
put signals in accordance with the respective essentially independent optical
response parameters and automatically operable on the basis of said output
signals to calculate a quantitative indication of said paper optical property
such as brightness, color or opacity.
According to yet another broad aspect of the invention, there is
provided the method for obtaining a quantitative measure of an optical
property of sheet material such as brightness, X, Y or Z color value, or
opacity, said method comprising: impinging on a single thickness of sub-
j stantially homogeneous sheet materiallight energy from a source providing
a broad band of visible light, collecting light energy from the source after
impingement on the sheet material by means of at least two substantially
independent photometric sensors and respective associated light energy
paths arranged for collecting reflected and transmitted light energy from
the sheet material~ and filtering and photometrically sensing the light
energy such that each of the respective light energy paths has substantially
` a common spectral response characteristic sufficient to characterize said
-2b-
10~ 218
paper optical property, and such that the photometric sensors provide
respective outputs which essentially characterize the reflectance and trans-
mittallce of the sheet material, whereby the optical property such as bright-
ness, X, Y or Z color value, or opacity is characterized with substantially
greater accuracy than any characterization of the optical property by either
a reflectance or a transmittance measurement taken by itself.
The invention will now be described in greater detail ~ith
reference to the accompanying drawings.
-2c-
-
105i1218
ON TIIE DRAWINGS
Fig. 1 is a fragmentary somewhat diagrammatic longitudinal
sectioIlal vicw of a paper machine showing in outline a side view of
an optical monitoring device in accordance with the present invention
operativcly mounted on line with the machine;
Fig. 2 is a fragmentary somewhat diagrammatic transverse
sectional view of the paper machine of Fig. 1 and taken generally as
indicated by the line I1-I1 of Fig. 1 and looking in the direction of the
arrows (toward the wet end of the paper machine), the view being taken
so as to show in outline a direct front view of the optical monitoring
device of Fig. 1;
Fig. 3 is a diagrammatic longitudinal sectional view of an on-
the-paper-machine optical monitoring device in accordance with the
present invention;
Fig. 4 is a partial diagrammatic plan view of the filter wheel
assembly utilized in the monitoring device of Fig. 3;
Fig. 5 is a somewhat diagrammatic view illustrating an optical
analyzer unit in electrical association with the optical monitorin~ device
of Figs. 1-4 and with a power supply unit;
Fig. 6 is an electric circuit diagram itlustrating the electrical
connections between the various components of Figs. 1-5;
--3--
.. . .
10~i1218
- Fig. 7 is a flow chart illustrating an existing direct digital
control analog point scan program which has been adapted to allow for
the collection and temporary storage of the reflectance and transmittance
data acquired from the system of Figs. 1-6;
- Figs. 8-16 when arranged in a vertical series represent
a program fourteen which is designed to read the reflectance and trans-
mittance values stored pursuant to Fig. 7 and generally to control the
operation of the system of Figs. 1-6 and to apply correction factorsto
the raw reflectance and transmittance data; and
Figs. 17-20 when arranged in a vertical sequence represent
a data reduction program forty-two whose purpose is to reduce the
correc~ed reflectance and transmittance data as produced by the program
of Pigs. 8-16 into terms with which papermakers are familiar and
upon which paper optical specifications are based, e.g. brightness,
opacity, color and fluorescence.
r
,
10~21~ -
Dctailed Description Of The Apparatus
Of Figs. 1 and 2
Figs. 1 and 2 will serve to illustrate the modifications of an
existing paper machine which are required for carrying out a preferred
emb~xlimen~ of the present invention. Referring to Figs. 1 and 2, an ;~
on-the-paper-machine optical monitoring device is diagrammatically
indicated at 10 and comprises an upper sensing head 11 and a lower
sensing head 12 which are maintained in precise relative alignment
and disposedfor operative association and transverse scanning move-
ment relative to a paper web located as indicated at 14 in Figs. 1 and
2. As will be described hereinafter with reference to Figs 3 and 4,
in a particular design of the optical monitoring device, upper head 11
includes a light source for projecting light onto the web such that a
portion of the light is reflected parallel to an optical axis indicated at
15, while a further portion of the light is transmitted through the paper
web for collection and measurement by means of the lower sensing
head 12.
Por purposes of illustration, Figs. 1 and 2 show portions of an
existing web scanner construction which is utilized to scan the web 14
for conventional purposes. The conventional scanner construction
includes fixed frame components such as 20, 21 and 22 forming what
is known as an "O" type scanner frame. The conventiQnal scanning
structure further includes upper and lower slides 25 and 26 for joint
horizontal movement aiong the horizontal beams 21 and 22. Associated
with the slides 25 and 26 are movable assemblies 27 and 28 carried -.
by the respective slides 25 and 26 and including vertically disposed
plates 31 and 32 and angularly disposed flange members such as
.
105i1218
indicated at 33 and 34 in Fig. 1. These flange portions 33 and 34
have broad surfaces lying in planes generally parallel to the plane of
the web 14 and are utilized for mounting of the monitoring device 10
of the present invention. In particular a top head mounting bracket is
indicated at 41 in Figs. 1 and 2 and is shown as being secured to the
existing flange part 33 so as to mount the upper head 11 for scanning
movement with the assembly 27. Similarly a lower head mounting
bracket is indicated at 42 and is shown as being secured to flange part
34 of the lower movable assembly 28 so as to mount the lower sensing
head 12 for scanning movement jointly with the upper sensing head 11.
For the purpose of electrical connection with the monitoring de-
vice 10 during its traverse of the web 14, electric cables are indicated
at 51 and 52 for electrical connection with the components of the upper
sensing head 11 and lower sensing head 12 of the monitoring device 10.
The cable 51 is shown as being fastened by means of straps 53 and 54
to a top carrier slide bracket 55. The bracket is shown as being se-
cured by means of fasteners 56 and 57 to the upper portion of vertical
- plate 31. As indicated in Fig. 2, successive loops of cable 51 aresecured to swivel type ball bearing carriers such as indicated at 61. A
trolley track 62 is supported from existing channels such as indicated
at 63 and mounts the carriers 61 for horizontal movement as required
to accommodate the scanning movement of the monitoring device 10
across the width of the web 14. Similarly, successive loops of the
cable 52 are fastened to the eyes such as indicated at 71 of a lower
series of carriers 72. As seen in Fig. 1 each of the carriers such
as 72 includes a pair of rollers such as 73 and 74 riding in the trolley
track 75 which is secured directly to the lower flange 22a of beam 22.
A lower carrier slide bracket 81 i~ secured to vertical plate 32 by
lO~Z18
means of fasteners 82 and 83 and is provided with a horizontally extend-
ing flange 84 ~or engaging with the first of the series of lower carriers
72. In particular, carrier 72 is provided with a shank 85 which extends
into a longitudinal slot 84a of flange 84. Thus, the first carrier 72 is
interengaged with the bracket 81 and is caused to move with the lower
assembly 28 and the lower sensing head 12. The remaining lower carriers
such as that indicat~lat 83 move along the trolley track 75 as necessary
to a~commodate movement of the monitoring device 10 transversely of the
web 14.
While Figures 1 and 2 have illustated the optical monitoring
device of the present invention as being mounted on linewiththe paper
machine and have further illustrated the case where the monitoring device
is to be scanned transversely of the web, it is considered that the opti-
cal monitoring device of the present invention would also be of great value
if redesigned for bench mounting. By placing a single sheet of paper in ~`
a sample mount of the device, a technician could simultaneously test the
sample for color, brightness, fluorescence, and opacity in a matter of
seconds.
In the illustrated embodiment~ however, lt is contempl~ted
that the monitoring device 10 will be mounted on line with the paper
machine and will be capable of movement to a position clear of the edge
of the web as indicated in Fig. 2 at the end of each hour of operation, for
example. Wten the end of a production run for a giv~n we b 14 has been
reached, or when a web break occurs for any other reason (such as
accidental severance of the given web), the monitoring device IO will be
moved clear of the edge of the web path as indicated in Fig. 2. Eàch dme
the monitoring device 10 is moved to the off-web position shown in Fig. 2
it is preferred that readings be taken of the reflectance and transmittance
-7 ^
- -
,
,
lO~Z18
values (without the web in theoptical path) for the purpose of obtaining
all updated calibration of the monitoring device. Thus, such updating
of calibration may take place automatically (for example under the
control of aprocess control computer controlling the paper manufac-
turing operation) at hourly intervals and also after web breaks. The
monitoring device can, of course, be retracted manually any time
desired by the operator for the purpose of checking calibration. By
way of example, the monitoring device 10 may be capable of a normal
scanning travel over a distance of 115 inches with provision for an
additional travel of 16 inches to the position shown in Fig. 2.
A flange is indicated at 87 which serves to insure proper re-engagement
of the sensing head with the web at the operator's side of the illustrated
paper machine (opposite the side indicated in Fig. 2).
The lower head 12 is designed to contact the web 14 during
scanning thereof. The design spacing between the` upper and lower
heads 11 and 12 is 3/16 inch. The optical opening in the upper head 11
is aligned with the optical axis 15 and is to be maintained in alignment `
with the center of the window in the lower head 12. Four adju~ting
screws such as those indicated at 91 and 92 a~eprovided for accurate
positionmg of the upper head 11. Similarly four position adjusting
screws such as 93 and 94 serve for the accurate positioning of the
lower head in conjunction with set screws such as indicated at 95 and
96. The adjlsting screws are located at each corner of mounting
brackets 41 and 42.
--8--
:
1. ' ,
I
10~i~218
Modifications of Figs. 1 and 2
To Insure Accurate Scanning
Where the web is not perfectly horizontal, but instead is curved
ncross, its width, it is desirable to provide a web deflecting guide bar
as indicated at 97 in Fig. 3 for insuring stable contact between the web
14 and the web engaging surface 98 of the lower sensing head 12. By
way of example the guide bar may protrude from the lower surface of
the upper sensing head a distance of 5/16 inch so as toarerlap with ~ `
respet~t to the vertlcal direction a distance of 1/8 inch relative to the
lower sensing head web contacting surface 98. The guide bar 97 may
have a width to force down at least about four inches of the width of the
web at a section of web centered with respect to web engaging surface
98 of the lower sensing head relative to the machine direction. This
insures a minimum of a 1/8 inch bellying of the sheet as it travels
over the lower sensing head in all lateral positions of the sensing head.
In order to minimize changes in the 5/16 inch thickness dimension
of the guide bar 97 due to wear, the guide bar is provided with a flat
web engaglng surface 97a which has a dimension in the direction of
web movement of about one inch. By way of example, the guide bar
may be made of Teflon.
Since the guide bar 97 is not necessary when the web is fed from
the calender stack to the reel in a relatively planar configuration, it
has not been shown in Figs. 1 and 2,
Various modifications may of course be made to adapt the monitor^
ing device of the present invention to various types of paper machinery,
and to secure any desired degree of accuracy in the joint scanning
movement of the upper and lower sensing heads relative to the paper.
:
_g_
lO~i~Z18
Structure Of The Optical
Monitoring Device As Shown in Figs.
3 and 4
Referrring to Fig. 3, the upper~ensing head 11 is shown as
comprising a casing 110 having suitable connectors 111 and 112 for re-
ceiving suitable internally threaded fittings 114 and 115, Fig. 1, asso-
ciated with the electric cable 51. The casing 110 receives a top head
shoe 120 including an interior open rectangular fra~re 121 having a base
flange 121a spot welded to shoe plate 122. The upstanding portion
121b engages the adjacent wall of casing 110 along all four sides thereof
and is secured to the casing 110 by suitable fastening means such as
indicated at 124 and 125 in Fig. 3. An edge 122a of shoe plate 122 i8
bent up at an angle of 45 at the side of the sensing head 11 facing the ~ -
wet end of the paper machine, and a similar inclined edge 122b, Fig. 1,
is provided at each of the sides of the sensing head so as to prese~:
smooth faces to the paper web during scanning movement of the sensing
headO The shoe plate 122 is provided with a circular aperture of less -
than one mch diameter as indicated at 130 centered on the optical axis 15
of the device. In a present embodiment aperture 130 has a diameter of
about 7/8 inch. This aperture 130 is preferably of mlnimum diameter
necessary to accommodate the light paths of the instrument. In the
illustrated embodiment the light path for the incident light beam as indi-
cated at 133 is directed at an angle of approximately 45 and i9
focused to impinge on a window 135 at the optical axis 15. A reflected
light path as indicated at 137 is normal to the web engaging surface 98
~(which is the upper surface of window 135), and is coincident with the
optical axis 15, while light transmitted through the web 14 and through
~he window 135 is directed as indicated by rays 141-143, for example,
into an integrating cavity 145 of lower head 12.
-10- .
- ~ .
~0~ 2I~
The lower head 12 comprises a casing 150 having an annular
dished plate 151 secured thereto and providing a generally segmental
spherical web-contactigsurface 151a surrounding window 135. The
window 135 is preferably formed by a circular disk of translucent
diffusing material. In the illustrated embodiment the window 135 is
made of n polycrystalline ceramic material available under the trade- `;
mark "Lucalux" from the General Electric Company. This material
has physical properties similar to th t of sapphire. The opposite -
faces of window 135 are flat and parallel and the thickness dimension
is 1/16 inchO A lip is indicated at 153 for underlying an annular edge
portion of window 135. This lip provides a circular aperture 154
having a diameter of about ls/l6irch~that the effective viewing area
for the transmitted light is determined by the diameter of aperture
154. The casing 150 is shown as being provided with an electrical
connector terminal 155 for receiving a suitable internally threaded
fitting 156, Fig. 1, of cable 52.
.
10~i12~8
As diagrammatically indicated in Figs. 3 and 4, the upper
sensing head 11 includes a light source 201, incident optical path means
including lenses such as indicated at 202 and a photocell 203 for
measuring reflected light returning along the reflected light path 137.
A filter wheel 2I0 is shown diagrammatically as being mounted on a
shaft 20~ for rotation by means of a low torque motor indicated at 209.
As best seen in Fig. 4, the filter wheel mcIudeK an outer series of
apertures 211-217 for selective registry with the incident light beam
path 133, and include3 a series of inner apertures 221-227 for selec-
tive registry with the reflective light beam path 137. The various
apertures may receivesuitable filter elements as will hereinafter be
explained in detail such that a series of measurements may be tak~
by successively indexing the filter wheel 210 to successive operating
positions. In each operating position one aperture suchas 211 is in
alignment with the incident beam path 133 and a second aperture such
as indicated at 221 is in alignment with the reflected light beam path 137.
By ~ay of example, the motor 209 mal be continuously en~gized
.
-12-
! ` -
.
~O~Z18
during operation of the monitoring device, and the filter wheel may be
retained in a selccted angular position by engagement of a ratchet arm
230 with one of a serics of cooperating lugs 231-237 arranged generally
as indicated in Fig. 4 on the filter wheel 210. A solenoid is indicated
at 240 as being mechanically coupled with ratchet arm 230 for momen-
tarily lifting the ratchet arm 230 out of engagement with a co~perating
lug such as 231 so as to permit the filter wheel to index one position.
Immediately upon release of the energization of solenoid 240,the force ~t
gravityreturns the ratchet arm 230 to the position shown in Fig. 3 so
as to be disposed in the path of the lugs and thus to engage the next
lug in succession such as lug 232 as the motor 209 moves the filter wheel
210 into the next operating position.
As will hereafter be explained in greater detail, reed switches
are mounted in circles on respective switching boards 241 and 242,
Fig. 3, and the filter wheel shaft 208 carries a magnet 243 for
actuating a respective pair of the reed switches in each operating posi-
tion of the filter wheel 210. Thus the position of the filter wheel 210
determines which of the switches on the switching boards 241 and 242
are closed. As will be explained hereinafter, the reed switch on the
upper switching board 241 which is closed determines the gain setting
~.
of an upper head amplifier at a level appropriate for the set of filters
which are in the operating position. The reed switch on the lower
switching board 242 which is closed activates a relay on a circuit board
245 in the lower head 12, and such relay in turn sets the lower head
amplifier gain at the proper level. As wUl be explained in connection
with the electric circuit diagram for the monitoring device, certain
conductors of the cable 51 may be interconnected at a remote location
,. .
-13 -
f `- `
10~12~8
SO a3 tO cause an indexing movement of the filter wheel 210. This
external command serves to momentarily energize solenoid 240 and
lift the ratchet arm 230 about is pivot point 250, allowing the motor
209 to rotate the filter wheel 210. The ratchet arm 230 returns to the
position shown in Fig. 3 to catch the next lug on the filter wheel stalllng
the motor 209.
Four heatessuch as indicated at 251 are mounted around photo~
cell 204 so as to minimize the temperature variations of the photocell.
A circuit board for mounting an amplifier for photocell 203 and for
mounting the gain setting resistances associated withthe reed
switches is indicated at 255 in Fig. 3.
Referring to the lower head 12, Fig. 3 indicates a photocell .
260 for receiving light from the intergrating cavity 1~ and a series
of heaters such as 261 mounted around the photocell 260 to minimize
the temperature variations of the photocell. Circuit board 245 may
mount a suitable amplifier for photocell 260, the gain of which beiog
controlled by the relays previously mentioned.
The heaters 251 and 261 in the prototype unit were PennQyl-
vania Electronics Technology Type 12T55. (These are posltlve tem-
perature coefficient thermistors wlth 55~. switching temperatures.)
These heaters will t~nd to stabilize the te,~perature sin~e their
ability to provide heat decreases as the ambient temperature increases.
Above 55~., they provide essentiaUy no heat at all.
-
~ ~ -
.
-14 - - ~
, . ~ .. .. ...
~0~ 218
I)iscussion o~ Illustrative Operating
De~ails for the Monitoring Device
of ~igs. 3 and 4
A basic feature o~ the illustrated embodiment resides in its
ability to measure simultaneously both re~lected and transmitted light.
While in the illustrated embodiment, the reflected light path 137 and
the transmitted light path intersect the web 14 essentially at a common
point, reflected light could be obtained from a point on the sample or
web offset from the point where light is trànsmitted through the sample.
For example, a backing of some specified reflectance such as a black
body of zero or near zero re~lectance could be located on the lower
sensing head just ahead of or behind the transmitted light receptor
compartment (with respect to the machine direction of the sample or the
direction of movement of the web). In this case the upper sensing head
could contain the light source as well as a reflected light receptor
for receiving light reflected from the sample or moving web at a point
directly above the backing of specified reflectance. Both the reflected
Iight receptor in the upper sensing head and the transmitted light recep-
tor in the lower sensing head could then supply signals simultaneously
and continously during measurement operations. Many other variations
in the arrangement of the optics for measuring both reflected and trans-
mitted light will occur to those skitled in the art.
;~ ~ Referring to the detail~ of the illustrated embodiment, hawever, ` -
and to the case where it is desired to measure brightness, color, opa-
city and fluorescent contribution to brightness, light source 201, Fig, 3,
may consist of a Model 1962 Quartztine lamp operated at 5.8 volts as
measured at the lamp terminals. The 45~ incident beam path 133 and the
normal reaected beam path 137 correspond to those of a standard bright-
ness tester, and a casting (not shown) from a bench type standard bright-
-15-
lOS~ Zl~
ness tester was uæd in constructing a prototype of the illustrated em-
bodiment to glve rigid support for the optical components such as indi-
cated at 202 and 271-276 in Fig. 3. In the specific prototype unit, a
stock thickness polished Corning type 4-69 glass filter 271 and a
S second type 4-69 filter 272 ground and polished to an appropriate thick-
ness were used in the incident beam path to absorb most of the infrared
as well as to give proper spectral response.
The reflected light path 137 included a pair of lenses 273 and
274 which focus the light on a 3/8-inch aperture in the plate 275 of the
casting. A piece of diffusing glass 276 is located on the 3/8-inch aper-
ture so that the light distribution over the surface of photocell 203 will
be reasonably uniform. A Weston model 856 RR Phot~ronic cell was
employed.
The filter wheel 210 is designed and located in such a way
that either the incident or the reflected beam or both can be filtered as
desired. In the prototype, the wheel 210 was driven by a small motor
209 operated at reduced voltage so that it could operate continuously in
a stalled condition.
-16 -
lO~ilZ18
Commerically available color and brightness meters are
usually manufactured with the spectral response filters located in the
reflected beam. In the prototype device, and in the later on-machine
version here illustrated as well, however, the filters which determine
the spectral response of the first six filter positions are located in the
incident beam. There are two basic reasons for this choice of design.
(1) Both the reflected and transmitted light have the same
incident intensity and spectral response against which
each can be comparedO The alternate would necessitate
two sets of identical filters, one set located in the re-
flected beam and another in the transmitted beam--a dif-
ficult design to achieve in practice.
(2) Filters in the incident beam can be used to absorb all
ultraviolet light and prevent it from striking the specimen.
Thus, fluorescence, a phenomenon not accounted for by
Kubelka-Munk theory is avoided.
For reasonsexplained shortly, the seventh filter position is
an exception to the above in that substantial ultraviolet light i9 inten-
tionally permitted to exist within the incident beam. Outside of the
phenomenon of fluorescence the spectral response is independent of
whether such filters are located in the incident or the reflected beams.
- The spectral response provided by the respective positions
of the filter wheel 210 were as follows: (1) papermaker's brightness
(TAPPI brightness), (2) blue portion of the Ecx function, (3) red por-
tion of the Ecx function, (4) ECD function without fluorescence (5) ECY
function, (6) Eay function, and (7) ECD function, with fluorescence.
-17 -
10~1218
As is understood in the art, the symbols Ecx, Ecy, Eay,
and Ecz refer to tristimulus functions of wavelength as defined by the
Commission Internationale c l'Eclairage which is identified by the
abbreviation C. I. E. and is also known as the International Committee on
Illumination. The subscript a in the function designation ~y indicates
that the function is based on a standardized illumination designated as ~'
C. I. E. Illuminant A, while the subscript c in the other function designa-
tions refers to a somewhat different standardized illumination which is
designated as C. I. E. Illuminant C.
Filters for providing the above spectral response characteristics
in the respective operating positions of the filter wheel 210 have been
indicated in Fig. 4 by reference numeral 281-288. In the specific
example under discussion, apertures 221-226 are left open. Filter 281
is a standard filter for use in measuring TAPPI brightness, TAPPI re-
ferring to the Technical Association of the Pulp and Paper Industry.
This filter transmits a narrow band of wavelengths in the vicinity of
457 nanometers.
Filters 282-285 are standard filters for a four-filter colorimeter
and are conventionally designated X (blue), X (red), Z, and Yc~ These
filters provide the wavelength distributions required for the measurement
of the C. I. E. X, Y, and Z tristimulus values under Illuminant C.
Filter 28~ is conventionally designated as a YA filter and is
required by the TAPPI standard methodlfor opacity measurements. This
is a broad band filter producing the C. I. E. Y wavelength distribution
2~ for ~lluminant A, in conjunction with the source 201 previously described
in this section. A discussion bearing on the f~Hsibility of this type of
measurement is found in a paper by L. R. Dearth, et al entitled "Study
of Instruments for the Measurement of Opacity of Paper, V. Compari- .
10~i~218
son of Printing Opacity De~ermined with Several Selected Instruments,
Tappi, volume 53, No. 3 (March, 1970).
With respect to position No. 7 o~ the filter wheel 210, filters
287 and 288 are conventionally designated as Z (blue) and Z (yellow).
As previously indicated, the purpose of the filters is to p~vlde for a
determination of the C.I.E. Z tristimulus value with the fluorescenoe
component included. In filter position No. 4, filter 284 serves to re-
move the ultraviolet component fran~the incident beam so that a measure
of the Z tristimulus value without fluorescence is obtained. In position
No. 7 of the filter wheel, however, filter 287 in the incident beam is
designed to transmit the ultraviolet component, so that the fluoreseent
component if any will be transmitted to photocell 203. The ultraviolet
absorbing component of the Z type filter means is located in the re-
flected beam 137, whereas this component is in the incident beam for
the No. 4 position. The fluorescent component is lineally related to
the difference between the Z tristimulus values determined in the No. 4
and No. 7 positions of the filter wheel 210.
Filters 281-288 have been shown in Fig. 4 with different types
of hatching wmch have been selected to represent generally the dif-
ferent lighttransmission properties of the filters. In particular, the
hatching for filters 281-288 are those for representing white, blue, red,
blue, green, orange, blue and yellow light transmission p~p~ties. The
selection of hatching is primarily for purposes of graphical illustration
and is not, of course, an exact representation of the light transmission
properties of the respective filters.
-19-
10~218
Detailed Description of Figs. 5 and 6
Fia. S illustrates diagrammatically the optical monitoring device
10 of Figs. 1-4, and illustrates by way of example an opticul analyzer
unit 300 which may be electrically associated with the monitorin~ device
and serve as an operator's console to be disposed at a convenient loca-
tion adjacent the paper machine. By way of example, the optical analy-
zer unit may be mounted near the dry end of the paper machine, andmay
receive conventional alternating current power from the paper machine
dry end panel. The optical analyzer unit 300 is illustrated as b~ing
coupled with the monitoring devlce 10 via a power supply unit 301
which is mounted adjacent the vertical column 20, Fig. 2, of the "O"
frame along which the monitoring device is to travel in scanning the
width of the web. For purposes of diagrammatic illustration,power supply
unit 30i is shown as being provided with a mounting plate 302 which is
secured by means of a bracket 303 to an end of horizontal beam 22 which
has been specifically designated by reference numeral 304 in Figs. 2
and 5. Referring to Fig. 2, it will be observed that the ends 305 and
306 of cables 51 and 52 are adjacent the end 304 of beam 22 so that
this is a convenient location for mounting of the power supply 301.
The electrical interconnections between the power supply unit 301 and the
optical analyzer unit 300 are indicated as extending via a signal conduit
311 and a control conduit 312. By way of example, the signal conduit
311 may con~ain shielded electric cables for transmitting miltivolt
signals from the analogue amplifiers of the upper and lower sensing
heads 11 and 12. The control conduit 312 may contain conductors which
are respectively-energized to represent the angular position of filter
wheel 210, and mav also contain a conductor for con~rolling the indexing
movement of the filter wheel as will be explained in detail in connection
with Fig. 6.
-20-
~0~i1218
Referring to the optical analyzer unit 300 of Fig. 5, the front
panel of the unit has been diagrammatically indicated at 320 as being
provided with a series of lamps 321-327 ~or indicating the angular posi- -
~ion of the filter wheel 210 within the upper sensing head 11. lbe
lamps 321-327 have been numbered 1 through 7 in correspondence with
the seven positions of the fllter wheel, and the color of the lampQ, for
example, may be selected so as to signify the characteristics of the
f~ters located in the openings of the filter wheel such as those indicated
at 211-21%
In order to provide a visual indication of the amplitude of the
millivolt signals supplied from the sensing heads 11 and 12, a suitable
meter is indicated at 330 and a selector switch is indicated at 331 for
selectively supplying to the meter the analogue signal from the upper
sensing head 11 or from the lower sensing head 12. A switch 332 i9
indicated for controlling thesupply of convenaonal alternating current
power to the meter, and a second switch 333 i9 indicated for controlling
- the supply of energizing power for the lamps 321-327. Another switch
334 may be momentarily aetuated so as to index the filter wheel 210 to a
desired station. The switcbes 331-334 may, of course, take any desir-
ed form, and have merely been indicated diagrammatically in Fig. 5.
~ ~ Referring to Fig. 6, various of the components previously refer-
; ~ red to have been indicated by electrical symbols, and for convenience of
correlation of Fig. 6 with Figs. 1 through 5, the same reference charac--
ters have been utilized. In particular, Fig. 6 shows symbolically a
; light source 2b1, associated photocells~ 203 and 260, filter wheel drive
motor 209, controi solendd 240, and permanent magnet 243 which rotates
with the filter wheel 210 so as to represeM the angular position of the
filter wheel. Also shown in Fig. 6, are the four hearcrs 251 associated
-2I--
. ..
' ,, , :
with photocell 203, and the ~our heaters 261 associated with the photocell
260. Further, lamps 321-327, millivoltmeter 330 and switches 331-
334 of the optical analyzer unit 300 have been symbolically indicated in
Fig. 6.
Referring first to the components associated wlth the upper sensing
head 11, there is illustrated in the upper left part of Fig. 6 a diode 340
connected across solenoid 240. For diagrammatic purposes, 2ermanent
magnet 243 is shown arra'nged between two series of reed switches 341- '~
347 and 351-357. A further reed switch 358 is indicated for actuation
in the number 1 position of the filter wheel 210 along with switches 341
-
and 351~ The conductors 359 and 360 associated with switch 3S8 may
.. . .
b~e connected with the optical analyzer unit 300, and may be connected
via the optical analyzer unit 300 with a remote cornputer, where the '
illustrated apparatus forms part of a computer control system for con-
trolling the associated paper machinery, ~ ~
The reed switches 341-347 are shown as being associated with ' "
an operational amplifier 361, so that switches 341-347 serve to select
the desired value of feed back resistance for the amplifier in each posi-
'tion'of the filter wheel 210. ~ Thus, switches 341-347 served to selectlve-
Iy connect in parallet with resistance 370, additional resistance values
371-377, respectively, for adjusting the total resistance between the
'input and output terminals of the amplifier 361. Thus, in the number
1 position of the filter wheel, permanent magnet 243 is in a position to
actuate switch 341, and connect resistance value 371 in parallel w*h
resistor 370. As will hereinafter be explained, resistance means 371-
377 may include variable resistors for adjustment so as to provide the ;
desired gain of ampUfier 361 in the respective filter positions, or fi~ed
resietance values may be inserted as indicated, once the desired values
-22-
.. , .. _ . . __ _~. .. _ ,. _" .. __ .. _,,, . ._., ._ ._ _ .. ...... , .. _ . . _.. . , .~ .
'
lO~ilZl~
have been determined for a given filter wheel. As indicated in Fig. 6,
the output of amplifier 361 may be transmitt~d by means of shielded
cables 381 and 382. These cables form part of the overall cable indi-
cated at 51 in Fig. 5 leading from the upper sensing head 11 to the power
supply unit 301.
Also forming part of the cable 51 would be the conductors such as
indicated at 383 from the respective reed switches 351-357. These con-
ductors such as 383 would connect with respective conductors 391-397 of
cable 52 leading from the power supply 301 to the lower sensing head 12.
Included as part of the power supply unit 301 would be components
such as relay actuating coil 401, associated normally open contact 402,
and resistors 403 and 404 shown at the upper left in Fig. 6. Further,
the power supply would include an adjustable direct current lamp power
supply component 410 for supplying a precisely adjusted or controlled
electrical energization for light source 201. Further, of course, the ~`
power supply would supply the required direct current operating poten-
tials for the upper sensing head as irldicated in Fig. 6.
The lower left section of Fig. 6 illustrates the electrical com-
ponents of the lower sensing head 12. In the lower sensing head, conduc-
tors 391-397 control energization of the operating coils of respective
relays K1 through K7. With the permanent magnet 243 in the number 1
position, reed switch 351 is closed, and operating coil 420 of relay K1
is energized closing the associated relay contact 421. The remaining
relays K2 through K7 are deenergized, so that the respective associated
contacts 422-427 remain open. The contacts 421-427 serve to control
the resistance in the feed back path of operational amplifier 429 in con-
junction with resistor 430 and resistance means 431-437. As explained
in reference to the upper sensing h~d, resistance means 431-437 may
lOSlZ18
include adjustable resis~ors, or fixed resistors as shown selected to
provide the desired gain of amplifier ~29 for the respective positions
of the filter wheel 210. The shielded cables ~1 and 442 from the out-
put of amplifier 429 connect with power supply unit 301 as part of cabte
52. The outputsfromthe amplifiers 361 and 429 are conducted from the
power supply unit 301 to the optical analyzer unit 300 via signal conduit
311, and within the optical analyzer unit connect with respective terminals
of the selector switch 331 as indicated at the lower part of Fig. 6.
Thus, in the upper position of the selector 331, the output of amplifier
361 is connected with the meter 330, while in the lower position of
selector 331, the output of amptifier 429 is supplied to the meter 330.
Of course, the optical analyzer 300 may further include analogue to
digital converters for converting the outputsof the amplifiers 361 and 429
to digital form for transmission to a remote computer, for example.
It will be apparent to ~hose skllled in the art that the remote computer
could be programmed to control the sequential actuation of relay 401
during each increment of scanning movement of the monitoring dev~ce
10 so as to obtain readings from each desired sampling region of the
web 14 for each of the seven positions of the fllter wheel 210. The replote
computer would then be in a posltion to correspondingly determine the av-
erage optical characteristics of a given length section of the paper web
1~, for example, and control suitable inputs to the paper machine so
as to maintain desired optical characteristics of the paper being manu-
factured. Alternatively, of course, the arrangement of Figs. 1-6 can
be utilized simply to take readings from the meter 330 for each filter
wheel position during scanning of the web, so as to obtain readings re-
!l~cting the optical characteristics of the length sections of the web
so scanned. Still further, of course, the circuitry o~ Figs. S and 6 can
- -24 -
~05121~
be utilized either with the monitoring device located in a fixed position
relative to the width of the web (by means of a C-t,vpe frame), or with
the device off-line from the paper machine, 80 as to obtain desire~
readings from the meter 330 for each position of the filter wheel 210
during optical excitation of fl single sheet sample of the web held in a
s~mple holder so as to be di~posed essentially as indicated for the web
1~ in Fig. 3.
`~
-25 ~
10~18
Exemplary Commcrcially Available Components
Commerically available componeMs which are included in
the present design of Figs. 1-6 are as follows.
Main power supply. Lambcla Electronics Corporation Model
LQS-DA-5124 providing a direct current (DC) output voltage of 24 volts
and a maximum current at 40C of 5 amperes.
Reed switches. For reflectance amplifier gain settings-
Model MMRR-2, and for transmittance amplifier gain settings-Model
MiNI-2; manufactured by Hamlin, Inc. The relays in the lower sensing
head of Type 821A of Grigsby-Barton, Inc.
Operational amplifiers, Moctel 233J chopper stabilized ampli-
fiers of Analog Devices,Inc. Model 904 power supply supplying plu8 or
minus 15 volts with a minimum full load output current of plus or minu3
50 milliampere~.
Digital panel meter (used for off-line studies and for on-line
operation before being interfaced with the computer). Weston Model
1290.
Filter wheel advance solenoiclr lype T 12x13-C-24 volt DC
flat plug~unger of (;uardian Electric Manufacturing Company~AMibottom-
ing washer made of polyurethane rubber. Operation of the solenoid-
until interfaced with the computer has been with the use of a time
adjusted relay, namely a Model CG 102A6 transistorized repeat cycle
timer of G. & W. l~agle Signal Co_
Filter wheel drive motor. Type lAD3001 Siemens brushless
DC motor. The drhe belt a~ld pulleys for coupling the m~tor 209 with the
- the shaft 208 are specified as positive drhe belt FS-80 and positive
drne pulleys ~C5-20 and FC5-40 o~ PIC Design Corporation, a Benrus
subsidiary. The belt has a stainless steel core and the p;llleys have a
1/4 inch diameter bore.
-26-
:
. .
105~218
Computer Interfacing
In preparing the monitoring device for on-line operation on
the paper machine, the zero to 140 millivolt DC signals from the
sensing heads will be supplied to respective emf-to-current cqnverters
of component 501, Fig. 6. As an example, Rochester Instrument
Systems Model SC-1304 emf-to-current converters may be used. Such
a com~erter will provide an output of 10 to 50 milliamperesDC suitable
for driving an analog to digital converter at the computer. The emf-
to-current converters will provide an isolated input and output so that
grounding will not be a problem.
The converters of component 501, will be housedwithoptical
analyzer 300, Fig. 5, and will connect with respective points thirty
one of G~oups five hundred and six hundred (not shown) at the control
computer analog signal input via conductors such as indicated at 502
and 503 in Fig. 6.
Conductors 505 and 506, Fig. 6, associated with filter
wheel indexing Rolenoid 240, Fig~. 3 and 6, may extend within cor~raJ
conduit 312, Fig. 5, and connect wlth the control computer output term-
inals at a location designated Groupforty two hundred and 9iX, point
nineteen (not shown). (Switch 334 should remain open (off) during
computer operation of Figs. 1-6. ~
Conductars 359 and 360, Fig. 6, may connect with an input
of the control computer at a location designated Group fourteen hundred,
point twenty-three (not shown).
,
_
--27--
~OS~Z18
DIS~USSION OF AN EARLIER PROTOTYPE
SYSTEM
Structure and Operation of a Prototype Optical Mon r~ Device
A prototype optical monitoring device was first constructed so as
to test the feasibility of the concepts of the present invention. As a re-
sult of the experimental work with the prototype system, a preferred
system has been designed and will hereinafter be described in greater
detail. Since the operation of the prototype system is somewhat differ-
ent from that of the later designed system, a description of the proto-
type system will serve to illustrate alternative features and an alterna-
tive method of operation in accordance with the present invention.
In the original setting up of the prototype system, the upper
and lower sensing heads should be brought into proper alignment and
spacing. The spacing should be just under 1/4-inch between the case
110 and the surface of the diffusing glass of window 135. (In the proto-
type unit, there were no additional parts between the case 110 and
window 135 such as the shoe plate 122 shown in Fig. 3, ) The lower
sensing head should be moved laterally in all directions to locate the
point where the maximum 1eading occurs from photocell 260 as well as
the point of least sensltivity to relative movement of the upper and
lower sensing heads. In an initial calibration of the prototype monitor-
ing device, potentiometers are included as part of the resistance means
371-377 and 431-437 and are adjusted for the respective positions of the
filter wheel 210 to give the correct readings ~or the reflectance and
transmittance of the diffusing glass 135 (in the absence any paper sample
between the upper and lower sensing heads). The values which were
used in this initial calibration are indicat ive of percentage absolute re-
flectance and transmittance on a scale of 100, and are as follows:
28 -
-
~OS12i8
Table 1
Table Showing Exemplary Calibration
for the l'rototype System-
Diffusing Glass Reflectanc~ and Transmittance
Values With No Paper Specimen Present
Filter WheelReflectanceTransmittance
Position Value, RSD Value, TSD
No. (Millivolts)(Millivolts)
35.4 54.0
2 3~.0 5~.1
3 34.4 56.9
4 34.6 56.6
34.7 56.4
6 34.5 56.6
7 34.8 0.6
The readings in millivolts can be converted to other desired unitsby comparing the readings in millivolts for a given paper specimen
with the readings obtained with a standard laboratory instrument, measur-
ing the reflectance of the specimen with the laboratory instrument while
backing the paper sheet with a piece of Lucalux and- a black-body. By
measuring the reflectance of the single sheet backed with a black body
(no fluorescence), the value of transmittance for the speclmen can be
calculated and this calculated value utilized for calibrating the lower
sensing head. If the fluorescent component is included in the labora-
tory inst~ument, and if fluorescence is involved, the fluorescence com-
ponent can be determined by means of a standard reflection meter, and
the fluorescent component can then be subtracted from the measured
data before making the calculation of transmittance.
The laboratory testing of the prototype system confirmed that a
monitoring device s~ch as illustrated in Figs. 1-4 should have a po~en-
tial accuracy equal to that of comparable off-line testers provided certain
web scanning requirements are met.
* ~he tranSmitt-lnCe value of the No. 7 filter posirion is not
needed, and cnnsequently a low amplification of this sign.ll was
arbitrarily selected.
-2~ -
:10~i~218
Laboratorv tests were run on color standard samples of the
grades ~nd colors usually run on the paper macMne shown in Figs. 1
and
and 2. In addition, a variety of opaques,/a variety of colored 50 pound
and 70 pound offsets were included in the tests. A four centimeter
diameter circle was scribed on each sample to insure that all tests
would be done witbin the same 12 square centimeter section of the
sample. Values of Ro~ Roo, and TAPPI opacity measurements were
made on the available standard laboratory instruments. All test were
made on the felt side of the sample with the grain in the standard
direction. For Roo measurements, the samples were backed by piles
of tabs cut from the edge of the same sheet of paper. In addition to
the TAPPI opacity measured on the s~andard opacime~er, TAPPI opacity
was calculated via Kubelka-Munk theory from data obtained with a stan-
dard automatic color-brightness ~ester.
The same ?aper s~mples were clamped into a holder which
held the simple under tension with the lower head of the monitoring
device bellying y8-inch to 1/4-inch into the sheet. The grain of the
s heet was oriented paratlel to the longitudinal axis of the upper sensin~
head (that iQ the machine direction of the sheet was in the same orienta-
tion as would occur on the paper machine as indicated in Fi~s. 1 and 2).
The felt side was always up. Care was taken to make sure that the
tested area was within the twelve square centimeter circle scribed on
the sample.
The transmittance and reflectance readin~s were taken from a
digital volt met~r attached to the output terminals of amplifiers 361 and
429. Calibration data was takenoff the Lucalux with no shee; presem.
Test values were taken on all filters with the sheet in place. The trans-
mittance and renectance values were keyed into a s~andard calculator
with the calibration data. Tbe calculator was programmed to calculate
-30-
105~218
the color (in C.l.E. X, Y, Z, for example), fluorescent component,
brightness, TAPPI opacity and printing opaci~y (based on Yc). By sup-
plying the basis weight, the computer could also be requested to calcu-
late s, the scattering coefficient (an index of the effect of pigment
- efficiency and fiber surface area), and k, the absorption coefficient (an
index of the effectiveness of dyes in the sheet), The coefficients s and
k are essentially independent of basis weight. Kubelka-Munk theory is
the basis of the calculations used.
All of thc samples were tested without changing the relative
position of the two sensing heads. One set of data was obtained with
the heads in a variety of positions to determine the effect of geometric
variations.
Since fluorescence is not compatible with Kubelka-Munk
theory, the prototype system was carefully designed so that all data usæ
for Kubelka-Munk analyses have excluded fluorescence. The prototype
system measures fluorescence separately. A fluorescent contribution
is determined from the prototype data by subtracting the Z distribution
reflectance without fluorescence (filter wheel position~No. 4) from the Z
distribution reflectance with fluorescence (filter wheel position No, 7),
and multiplying by the appropriate factor.
` An independent check on fluorescence measurements, a
modified brightness tester was utilized which had a filter wheel allowing
for s~andard brightness and Z distribution filters to be put in the reflect-
ed beam. In addition, the filter wheel containcd brightness and Z distri-
bution filters which had been modified by removing the ultraviolet absorb-
illg component of these filters. A special mount allows ~he operator to
put the appropriate ultraviolet absorbing filter in the incident beam.
Thus, measurements of brightnessatrl C.l.E. Z tristimulus, with and with~ut
fluorescence, could be made. Fluorescent contributions were calculated
.
~. . . _ _ , . .~ __ . . ._ . .
~05~218
by difference. Some measurements were made on single sheets with a
standard backing. Most of the samples were measured with an infinite
pack of tabs. The incident beam filter of the prototype's No. 7 positi~
was such that it permitted about twice the standard quandty of ultra-
violet light ~o strike the specimen. Consequently, measurements of the
fluorescent contribution measured on the modified brightness tester
and the prototype system correlated well (correlation coefficient of
.992) but the modofied brightness tester value is only 0.528 as large
as that measured by the prototype system. Calculations of prototype
data now involve calculation of the fluorescent component by multiply-
ing the difference of filter positions No. 7 and No. 4 by 0.528~ -
Because only one fluorescent dye (Tinopal, a trademark) in all of
the paper specimens was used, the fluorescent contribution needed to
be measured only once. The prototype data provides a basis for mea-
suring the fluorescent component Z. Measurements by an independent
laboratory showed that the paper specimens do not fluoresce signifi-
cantly in the ~ (red) or Y distributions; therefore, fluorescent contri-
butions need only be determined for the blue colored distributions.
linear regression was run on the independent laboratory data which
demonstrated that the fluorescent component for ~ (blue) can be pre-
dic~ed by multiplying the fluorescent component for Z by 1.204. A re-
gression run on fluorescent data from the modified brightness tester
shows that the fluorescent contribution for brightness can be calculated
by multiplying the fluorescent contribution for Z by 0. 864. In summ~,
fluorescent contributions are calculated by the following formulas:
Fz=0.528 (Z reflectance with fluorescerce minus Z reflectance without
fluorescence. )
Fx(blue) = 1.204 Fz FBrightness = - 864 Fz
-32 -
,~
1051218
These fluorescent contributions are added to the respective
calculated Roo values when calculating optical properties from prototype
data. The test results for fluorescent andrDn-fluorescent papers agree
with values measured on the standard automatic color-brightness tester.
~ .
- - -33 -
.. , . . ... ~ .. ~ .
lOS~Z18
~iscussion of the Results of Mechanical Life Testing of the Prototype
System and Design Features Selected for tte Preferred System ln Light
of Such Life Testin~
The following details concerning the results of life testing of
the prototype system are considered to reflect minor problems of con-
struction and operation which considered individually are readily correct-
ed for by those skilled in the art. In order to minimize the burden of
the total number of such minor problems, and thus to expedite practice
of the prototype system, solutions to the various problems which were
encountered are briefly referred to.
The filter wheel is advanced by a low torque stallable motor.
A timing bek links sprockets on the motor and the filter wheel shaft.
The original timing bek had a dacron core. The core of the original
b~lt broke--in- two-places resulting in stretching- and eventual loss of
teeth. Uneven rate of rotation of the filter wheel occurred due to bind-
ing of the belt. Eventually, the plastic drive sprocket broke. Both
sprockets were replaced with stainless steel sprockets and the timing
belt was replaced with a belt containing a steel core. Installation of
the steel sprockets and steel core bek revealed that excessive belt ten-
sion could stall the motor. The motor mount holes were slotted allowing
the motor to pivot slightly around one mounting screw. Belt tension was
adjusted by pivoting the motor. It is concluded that future models
should include an idier wheel or some other means of adjusting the
tension of the timing bek.
Some problems were experienced with respect to indexing of
the filter wheel with the ratchet arm stic~;ing on the tooth so that the rat-
chet arm does not clear the tooth when a command is given to inde~c the
filter wheel. The remedy has been to reduce the roughness of the mqting
. .
.
10~ 218
surfaces by filing on the too~h, or smoothing the tooth with a stone.
In future models, the shapes and/or smoothness of the ratchet arm and
the teeth should be altered to minimize sticking. One solution wt)uld
be to provide the ratchet arm and the teeth with highly polished mating `
surfaces.
The ratchet arm is lifted by a 24 volt direct current solenoid~ i
After some time, the plunger of the solenoid became magnetized and
would stick to the inside of the coil. This "hanging up" would prevent
the ratchet arm from catching the nexc tooth. A resistor was installed
in series with th~ solenoid coil to reduce the strength of the magnetic
field. The plunger of the solenoid was coated with a speciaI material.
The coated plunger worked well for about three months before it, too,
magnetized enough to hang up. The solution adopted was to provide
the solenoid with a flat topped plunger which is stopped at the end of
its stroke by a bumper of rubber-like material.
The response of a photocell ~s somewhat temperature sensitive.
For this reasons,it is necessary to keep the photocells at a consunt
temperature. Ambient temperatures on the O-frame of the No. 6 paper
(48C. )
machine indicated in Figs. 1 and 2 have ~een measured as high as 118F/
in the suml~r. The photocells in both heads ar;e mounted in massive
metal blocks. Each m~tal block has four thermistor heaters moumed in
close proximity to the photocell. These thermistors have switching
temperatures of 55C,(that is about 130~F). The intention of this de-
Sigll was to add enough heat to the instrument to hold the temperature
steady at about 55C. During bench studies, this temperature was
never reached due to the low capacity of the- heaters. At machine room
temperatures, however, the instrument temperature may reach 55C.
-35 -
- ,
10~i1.218 ~
During the bench studies, it was found that the heaters did
minimize temperature variations. The few degrees of temperature
variation that were observed during normal operation usually occurred
slowly. Changesin instrument temperature affected the output s1gnal
less thsn acticipated. Based on this èxperience in the ~oratory, the
maximum variation in head temperature should be less than 3~F per
hour. Temperature variations of this magnitude will not have a signi-
ficant effect on the output signal. Long term temperature changes
wouid be corrected for by the calibrations each time the head goes off
web.
In the laboratory, there was a minimum of dirt problems. On
the machine, howe~Ter, the hole could allow dirt to enter the upper head.
Up to a point, dirt on the lenses and filters will be corrected for by
the periodic calibration routine. ~xcessive dirt, however, will reduce
the sensitivity of the instrument and may even àffect its accuracy. Peri-
odic cl aning of the lexses and filters will be required. lf dirt accumu-
lates too rapidly, it may be necessary to attach an air purge to the
upper head.
The lower head of the prototype system is completely sealed so
that no dirt problem is anticipated inside the lowerhead. Because the
Lucolux window is in contact with the sheet, friction will keep it clean.
. '
'
.
r36~
-- . . ..
.
218
Mos~ of the filters consisted of two or three component parts. .
There have been some problems wi~h dirt ~etting between the components
of the filters.
The case on the lower head as well as the case on the upper
head should allow most general maintenance and trouble-shooting to
be done without dlsmounting the head. A completely removable
case would be desirable. AE a minimum access should be provided for
the following: (1) convenient; light bu'.b change, (available on the proto-
type), (2) cleaning of lenses, (available on the prototype), (3) cleaning
of the filters. (Access is presently available to one side of each filter.
The side which is most likely to collect dirt i8 not accessible in the
prototype.) (4) The amplifier. The ampUfier is a standard plug-in
module. In the event of a breakdown it could be replaced in seconds
if it is accessible. Furthermore, it is necessary to remove the
amplifier to do any trouble-shooting on the gain circuitry. ~5) The
circuit board holding all of the gain control resistors. The choice of
gain circuitry is controlled by reed switches which are not accessible
on the prototype without a- partial disas9embly of thè instrument.
Malfunctions of the reed switches, however, can easily be diagnosed
by removing the amplifier and taking resistance measurements on the
gain control circuits. There is also the possibility of mechanical or
electrical damage to a resistor or a potentiometer mounted on this
circuit board. With proper access a damaged part could be replaced
in five to twenty minutes. (6) The photocell. With proper access,
the photocell could be replaced quickly and easily. (7) The heater.
The heater are adJacent to the photocell and are generally just as
elsil~ serviced. (8) Indexing mechanism. The present acce-sibility
~37 -
. .
- .
10~218
to the ratchet teeth, rachet arm and solenoid is adequate but not very
convenient on the prototype. A certain amount of access to these parts
i9 needed to correct chronic indexing problems euch as sticking and
"hanging up".
The filters are presently mounted in the filter wheel of the
prototype by spring clips. Most of the filters are compound filters
containing as many as four component pieces of glass. During laboratG~ry
trials, increases intheoptical density of a filter were frequently observed
which could not be corrected by cleaning the surfaces of the filter. Upon
removing one of the filters, it was discovered that foreign material was
collecting between the components ofthe compound filter. The use of lens
cleaning solution on the filters may have accelerated the problem if
capillary action drew foreign material between the components. A set of
gaskets and some type of threaded mount should be used to mount the
filters in such a way as to minimize forelgn material (including cleaning
solutions) from getting between the components of compound filters.
ln mounting the prototype sensing heads on anO-frame, it is
necessary to bring the geometric alignment of the heads as close to their
optimum relationship as possible. The original intention was to set the
gap between the heads with the aid of a spacer; however, flexibility of the
sheet metal case of the prototype upper sensing head prevented the use of
a spacer for setting the gap. Accordingly, the shoe plate 122 of the new
upper sensing head shown in Fig~ 3 has been made of a thickness and
consequent rigidity so as to enable the use of a spacer gauge to set the
gap between the upper and lower heads. (Ihe gap is reduced by 1/16
inch to 3[16 inch because of the thickness of shoe plate 122.)
.
. . .. ..
~0~2~8
The g;lp between the he.lds is a most critic~l dimension as ~ar
as culibration and reproducability is concerned. In the prototype it
was intended to calibrate relative to an average gap, thus correcting
~he readings for variations in the gap from the average gap.
One of the criteria used in designing the prototype was minimum
head length in the machine direction. Un~ortunately, the upper head
was turned 90 in order to give the prototype unit the same geomerry as
the C`~neral Electric Brightness Me;er, Automatic Color-Brightness Tester,
and T~unterlab Color Meter. In this new position, the prototype head
is 12 1/4 inches long in the machine direction plus 2 1/2 inches for
cable connectors, Redesign should be possible to reduce the machine
direction dimension to about 8 inches and to relocate the position of the
cable connections,
The lining of the case for the upper head should be matte as
well as black to prevent reflection of ambient light within the case and a
pos5ible apuriou~ ~Ifect on ~he pho~ell reading.
.
.
-39 -
. - :
.. ..
~0~12~8
Concl-isions from Mechanical Tes~ing of the Prototype System
Following the correction of miscellaneous start up problems
the prototype system was found to function well mechanically. As a
test of its durability, the prototype system was placed in continuous
operation for a period of over ten months and no serious mechanical
problems resulted except the failure of the solenoid. The solenoid
failure was expected and the replacement solenoid is of a design which
is expected to give a long servioe life. The light application of sili-
cone lubricant spray to the indexing control ratchet arm and cooperating
teeth corrected a problem of malfunctioning of the filter wheel indexing ` ` -
mechanism (which occurred on two occasions during the ten months).
The prototype system was not intended to be a low maintenance instru-
ment; however, the expOEience during the durability test with the proto-
type in continuous operation indicates that the prototype system should
operate vn a paper machine with an acceptably small amount of down
time.
.
~ . ' ' ' `
: '
-40-
- -
10~ ;19
DISCUSSION OF LA13ORATORY TESTING
OF FIGS. 3-6
LaboratorvOPeration of the ~\~srem o~ Fi s ~-6
In the prototvpe svstem, potentiometers are included as
part of the resistance means 371-377 and 431-437 and are adjusted for
the respective positions of the filter wheel 210 togive desired values
such as given in the f~egoingTable 1. In the preferred system of Figs.
3-6, these potentiometers for adjusting amplifler gain are omitted
and are replaced with axed resistors 371-377 and 431-437 selected to
give scale readings from meter 330 in the respective fllter wheel
positions which are well above the values given in the preceding
TableL This is intended to improve the stability and increase the
sensitivity of measuremen~.
In calculating optical parameters from measurements relative
to various samples, values were first established for the reflectance
RD of the diffuser 135, Fig. 3, in the absence of a paper specimen,
for each fflter wheel position. Initially calculated values for RD were
used in a first computation of optical values, and then the values of
RD were adjusted slightly to give the best agreement with the correspond-
ing optical measurements by means of the standard automatic color-
brightness tester. The following table shows the reflectance values
which were established for certain laboratory testing of the system of
Figs. 3-6.
lO~Z18
Table 2
Table Showing Reflectance
of the Diffusing Glass With
No Paper Specimen Present . -
in a Laboratory Test of the
System of Figs. 1-6 :~
Filter Wheel Symbol Diffusing Glass Reflec- -
Position No. tance Value
.. . _ .. . .... . . .~ . .
RDl 0. 349
2 RD2 O. 347 `~
3 RD3 O. 355
- . 4 RD4 O. 349 .
RD5 O. 354 - `
6 RD6 0. 354
7 . RD7 . O. 349
The transmittance of the diffusing glass 135 need nOt be
known since the ratio of the.transmittance of the diffusing glass and
paper (in series) to the transmittance of the diffusing glass is employed ~ .
in calculating the desired optical parameters.
'
: ;, ~ . ' .
': ~
:'
;
~ _
10~2~8
A computer program was developed to process the data
collectcd during laboratory operation of the monitoring device 10 as well
as to compare the calculated reflectance value R and the calculated
fluorescent components with the data collected withthe standard auto-
matic color-brightness tester. A listing of the symbols employed in a
symbolic staten~nt of the computer program in the Fortran computer
language utilized in this laboratory study is set forth in Table 3 on the
following pages.
-` ~,
~i
.
. .
2S8
Table 3
I_isting of ~Svmbols (Including Input Data Symbols and
OUIPUt l)ata ~vmbols Wi~h a Brief Indicadon of Their
Si~niflcance).
Input Da~a Svmbols
RSD OMOD scale reading for reflectance with no
paper specimen in place. (Filters 1 through
6.)
RSP OMOD scale reading for reflectance with
paper specimeninp~siticn.(Filters 1 through
6.)
TSD OMOD scale reading eor transmittance with
no paper specimen in place. (Filters 1
through 6. )
TSP OMOD scale reading for transmittance with
paper specimen in posidon. (Filters 1
through 6. )
RSD7 OMOD scale reading for reflectance with no
specimen in place. (No. 7 fllter~
RSP7 OMOD scale reading for reflectance with
- paper specimen in position. (No. 7 filter.)
ARooFC ACBT reflectance including the fluorescent
component.
AFC ACBT fluorescent componem.
RSD4 OMOD scale reading for reflectance with no
paper specimen in place. (No. 4 filter.)
RSP4 OMOD scale reading for reflectance with
paper specimen in position. (No. 4 filter.
GC Grade Correction as determined by the
difference between R FC and AR FC
- ~ for each sample and each filter.
-44 - -
lO51Z~S `
Table 3 - Listin~ o~ Svmhols-continued
Output Data Symbols
R Reflectance of a single sheet backed with a
black bodv (no fluorescence) as calculated
from OMOD data.
T Transmittance of a single sheet backed with
a black bodv (no fluorescence) as calculated
from OMOD data.
R Reflectance of an opaque pad (no fluores-
cence) as calculated from OMOD data.
R FC Reflectance of an opaque pad (including
fluorescence) as calculated from OMOD data.
AR FC Reflectance of an opaque pad (including
fluorescence) ACBr.
DIFF Difference between R FC and AR FC.
oo oo,
FC Fluorescent component OMOD.
AFC Fluorescent component ACBT.
~C 5radeCorrection as determined by the
difference between R FC and AR FC for
each sample and eac\.filter.
: '
.,, ~ ~ - ,
., .
.
, ~, ,
~', '
-45-
,_, ..... __ ..... . .. . ... .. . .
. . - .
iO~i~2~
Table 3-Listing of Symbols-colltinued
~dditional Symbols (Used in the Computation
of the Output Data from
the Input Data)
RK Reflectance correction factor
(assigned a value of 1.000 for
laboratory operation).
TK Transmittance correction factor
(assigned a value of 1.000 for
laboratory operation).
RD - Value re~r~senting the absolute
reflectance of the diffuser (on a
scale of zero to 1.000) as adjusted
to give best agreement with opti-
cal measurements by means of
the standard automatic color-bright-
ness tesrer. (The values given
in Table 2 are used for laboratory
operation~
RPD Reflectance of paper specimen
when backed with the diffuser, as
calculated from current values of
RK, RD, RSD, and RSP.
TPD Transmittance of paper specimen
and diffuser in series, as calcu-
lated from current values of TK,
TSD, and TSP.
-~6-
. . . . . ~ .
~Q~ 8
In the foregoing listing of symbols, the letters of the symbol
OMOD are taken from the phrase on-machine optical device; however,
this particular section of the specification refers to a system essentially
- conforming to the system of Figs. 3-6 operated to measure optical proper-
ties of individual paper sheets under laboratory conditions. (The labo-
ratory work here reported was with an earlier version of the monitoring
device designed for on-machine operation, prior to adoption of a thicken-
ed shoe plate 122. The standard spacing between the upper and lower
sensing heads for the earlier version was 1/4 inch, rather than 3/16 inch
as with the final version of on-machine device as specifically shown in
Fig. 3. The OMOD scale readings are obtained from the meter 330, Figs.
5 and 6,with the filter wheel 210,Figs.3 and 4, in the respectivepositions
to activate the respective filters 281-286 (indicated as "Filters 1 through
, 6" in the preceding listing) and to activate filters 287 and 288 (indicated
as "No. 7 filter" in the listing), and with switch 331, Fig. 5, in its upper
position to measure reflectance, and in its lower position to measure
transmittance. As to reflectance measurements, the cavity 145 is con-
sidered to form essentially a~lack body backing for the diffusin~ glass 135.
The symbol "ACBT" in the foregoing listing of symbols is used
to designate a measurement made on the standard commercially avail-
able automatic color-brightness tester. The brightness measurement
obtained from the ACBT represents a value accepted as standard in the
U. S. Paper industry. A further appreciation of the importance of the
fact that the OMOD measurements can closely conform to this industry
~5 sta~lard is gained from a consideration of the article by L. R. Dearth et
al "A Study of Photoelectric Instruments for the Measurement of Color
Reflectance, and Transmittance, X~I. Automatic Color-Bri~htness
Tester", Tappi, The Journal of th~ Technical
10~21~
Association (-f the PLIIP and rnper Industry, Vol. 50, No. 2, February
1967, pages 51A througll 5~A. As explaincd in this article, the ACBT
is photometrically accurate, and the spectral response is correct for
the measurement of both color and standard brightness. The spectral
response of the ACBT very nearly matches the theoretical CE functions
as indicated by the special technique for determining spectral response.
This involves the determination of the tristimulus values for deeply
saturated colored glass filters a very rigorous check on the spectral
response, especially when it is noted that colored papers~re less
saturated.
The symbols in the foregoing Listing of Symbols which as
shown include lower case characters may also be written exclusively
with capital lettera. Th~ form of the sym~ols is convenient for com-
puter printoutO The alternate forms of these symbols are as follows:
AR FC or AROOFC; R or RO; R ROOar~ R FC or ROOFC.
00 0 00 Qo
-48 -
_ .. .. , ._,..................... .
10~21~
Table ~
Symbolic St;~t-~mcnt of th~ Computer Program
(Us~d for Pro~ossin~ the D~t;l Obt~ d l)uring the
L~bor~tory Operation of the ~iystem of Fi~s. 3-6)
6PS FORTRAN D COMPILER
C OMOD (220)
S~ 0001 WRITE (6~ 2001)
S~ 0002 2001 FORMAT (lH, 'SAMPLE', 6X, '
RD'~ 12X, 'T', 12X, 'ROO', 9X~
'ROOFC'~ 9X~ l'AROOFC'~ lOX,
'DIFF'~ 7X~ 'FC'~ 7X~ 'AFC'~ 7X~
'GC', /)
S. 0003 READ (5~ 1000~ RK~ TK~ RDl~ -
RD2~ RD3~ RD4~ RDS~ RD6
S~ 0004 102 M=O
S~0005 READ (5~ 1000) RSD4~ RSP4
S~ 0006 1000 FORMAT (lOF8~ 0)
S.0007 100 READ (5~ 1001) IA~ IN, ID~ RSD~
RSP~ TSD~ TSP, RSD7~ RSP7
AROOFC~ AFC~ R
S~ 0008 1001 FORMAT (12~ 12~ A4~ 9F8~ 0)
S~ 0009 GO TO (11~ 12~ 13~ 14~ 15~ 16)~ IN
S~ 0010 11 RD=RDl
S.0011 GO TO 17
S. 0012 12 RD=RD2
S~ 0013 GO TO 17
S~ 0014 13 RD=RD3
S.0015 GO TO 17
S~ 0016 14 RD=RD4
SoO017 GO TO 17
S~ 0018 15 RD=RD5
SoO019 GO TO 17
~49 ~
~ .
10~i1.218
S. 0020 lfi RD=RD6
S. 0021 17 RPD=((RD*RSP~RK)/RSD)
S. 00''') RPD4=RD4*RSP4~RKtRSD4
S. 00_~ TPDOTD=~TSP*TK)~TSD
S. 0024 RO=(RP;)-~RD~PDOTD**2)))/(1. -
(RD~ TPi)OTC)~2)
S. 002S T=~PDOTD*(l. -(RD*RPD)))/(l. -
(Rl ~TPi )OTD)**2)
S.0026 A=((l, t (RO**2))-(T*~2))/RO
S. 0027 ROO=(A/2. )-S~R~(((A/2. )**2)-1. )]
S. 0028 RP~7=RD4 *RSP7*RK/RSD7
S. 0029 IF (IN-2)1,2,3
S.0030 3 GO TO (7,7,7,4,7,7), IN
S. 0031 1 FC=(RPD7 -RPD4)*.450
S. 0032 GO TO 6
S. 0033 2 FC=(RPD7-RPD4)*.570
S.0034 GO TO 6
S. 0035 4 FC=(R Pi)7 -RPD4)*.510
S. 0036 6 ROOFC=ROO~FC
S.0037 GO TO 30
S. 0038 7 ROOFC=ROO
S. 0039 FC=0. 0
S. 0~0 30 IF (IA-2)18, 19, 19
S. 00~1 18 ROOFC=ROOFC+R `
5.0042 GO TO 20
S. 0043 19 ROOFC=ROOFC-l
S, 0044 20 DIFF--ROOFC-AROOFC
SoO{)4i GO TO (21,22), IA
-50-
. . ~ . .
105i1.21~
S. 00~6 21 WRITE (6, 200l))1D,RO,T,ROO,
ROOFC, AROOFC, DIFF, FC, AP C, R
S.00~7 2000 FOR~T (IH A4,7X,2(F8.6,4X),4
(F 10. 6,4X), 2(F5.4,4X), '+', F4. 3)
S.0048 TO TO 23
S.0049 22 WRITE (6,2002)1D,RO,T,ROO,
ROOFC, AROOFC, DIFF, FC, AFC, R
S. 0050 2002 FORMAT (IH, A47X, 2(F8. 6,4X),4
(F10. 6,4X), 2(F5.4,4X), '~',F4. 3
S. 0051 23 M=M+l
S. 0052 IF (M-6) 100, 102, 102
S. 0053 END
SIZE OF COMMON OOOOO
PROGRAM 01930
END OF COMPILATION MAIN
In the foregoing Table 4, rhe symbols repre-
senting basic mathematicl operations were as follows:
Operation Symbol Example
Addition + A~B
Subtraction - A-B
Multiplicstion ~ A*B
Division / A/B
Exponentiation ~* A**B(AB)
Equality = A--B
.
. ~ .
--51--
.
. , . . . ... .... _ .
10~i121~
To indicate more concre~ely the calculations which are
performed, the followin~ Table 5 will illustrate exemplary input and
output d~ta for a given sample. The meaning oi the various symbols
will be apparcnt from the listing of the symbols of Table 3: -
Table 5 - Table Showing Exemplary
Input and Output Data îor a
C.iven Sample
Sample No. 1, white Nekoosa Offset-60 pound paper,
sDecimen A RK=1.000, TK=1,000
_ _
Filter Wheel
Position No.
Input Data 1 2 3 4 5 6
RD 0.349 0,347 0,3550,349 0,354 0,354
RSD 0.515 0,529 0.5830,636 0,525 0,596
RSP 1.161 1.187 1.3391.422 1. 191 1.357
_ _
TSD 1.422 1,625 1.6271.702 1. 625 1.546
TSP 0.236 0.256 0.3540. 277 0.335 0.326
_
RSD7 0.568 0.568 0.5680.568 0.568 0.568
RSP7 1,381 1.381 1,3811,381 1,381 1,381
AROOFC 0.837 0.829 0.8470.830 0.839 0.844
AFC 0.034 0.034 0.0 0.036 0.0 0,0
RSD4 0,636 0.636 0.6360.636 0.63~ 0.636
. . _
RSP4 1.422 1.422 1.4221,422 1.42, 1.422
'3 006 0,0l4 -0,021 -0.007 -0.00S -0.012
~ .
.~ .
-5~-
. . ..
10~i~218
.
~ ll~
~ ~o a~ u~ ~ ~r ~r 0 ~
,~ _ X o~ X . o o o
_ o o o o o 1 ' ,. ~ ` :
. o~ _ o~ _ o ~ _
u~ ~ ~ o~ ~o 8 o o~
t- o _ o o o o o o o
.
~ _ _ _ _ o __
c~ ~D _ ~ ~ O ~
~ ~ t~ o~ O ~ .g O ~r ~o r~
~, 'Q'C- O O O X O 0 8 8 o.
l--- - -- :
~C) __ _
. ~ E o~ c~ cr~ ~ 80 ~
Q.~" ~ O ~ el
_I U) I~ U~ ~ O _~
S~ ~ O O O oX O O O O O
E _ _ _ _ _
~ _ _ ~ X ~ C~ _
,. , 5~ C~ ~`1 C~ O ~ c~ O I~ 0
~ o o o o o o 8. o, o.
.` ,
`' . .. ~ . _. _ _
.. . l . ~ o~ ~ C~ g o
U') 1` ~ I` C~
~ ._, a~ c~o~ ~ ~o ~ g o ~o ~
:,, ' ,,, ,. _ ~ O _ O O O O O ~ g
1~
53
. . . .
.
lO~lZ18
In the foregoing table showing e~emplary input and output data,
the input and output data symbols have been shown as they are actually
printed out by the co~uter with all letters capitalized. In the text,
certain of the input and output data symbols are shown in a more conven-
tional manner with subscripts since the symbols are more familiar in
such form.
The data such as exemplified in Table 5 are based on a single
determination for each specimen. The "grade correction" GC is based
on the average difference between RooFC and AR FC for two specimens,
specimens A and B.
The data as exemplified in Table S show thatthere is generally
good agreement between the calculated RooFC and ARooFC values. The
spread in values for the duplicate specimens (A and B) is good with the
excPption of several samples. Some difficulty was experienced in
positioning the specimen on the monitoring device 10 to give reproducible
resuksO The difficulty should be minimized when the unit is placed
"on-rnachine". The grade correction GC takes this discrepancy into
consideration so the correction should be established "on-machine".
The RD values shown in Table 5 were punched into the first
data card alon~ with the values for RK and TK for input to the computer
in advance of a desired computation. The factors RK and TK were
included as factors in the computations- so that the transmittance and
reflectance values could be adjusted independently, if desired. In this
evaluation, RK and TK were left at 1.000. (Calculated yalues for RD
were used in a first computer run and then the values were adjusted
slightly to give the best agreement with the standard automatic color-
brightness tester. The values for RD shown in Table 5 are the slightly
.
-54 -
10~218
ndjusted values utilized in obtainins t~e data discussed in this section of
the specification. )
A second set of data for the same fourteen samples wa~s
collected using the monitoring device in the same condition as for the
collection of the data previously given. All of the variables were left
the same to see how closely the dataccuId~ereproduced for the identical
specimens. The agreement was quite good except for samples 8 ard 14.
It appears that the~per may not have been lying flat in one or the other
tests. The grade correction GC on some of the grades was changed and
the second set d data was again calculated for samples 1, 2, 4, 5, 6, 8
and 14D This improved the agreement between the monitoring devioe and
the standard automatic0lor-brightness tester.
The reflectance head of the monitoring device was then lower-
ed 0.025 inch and another set of data was collected for the sam~ seven
samplesO The same ACBT data was used. The data show that lowering
the reflectance head reduces the reflectance while transmittance remains
essentially unchanged. The effects are not as large as was expected
and could be corrected through adjustment of RK; however, the variables
RK, TK and GC were again held constant.
The reflectance head was then raised to a spacing of 0.050
inch (0~,025 inch above the normal position for these tests), and another
set of data was collected for the same seven samples. The effects
were larger than when the reflectance head 11 was lowered. Again, an
adjustment of RK would improve the agreement.
-55 -
lO~lZl~
It was concluded from these test results that a change of
plus or minus 0.025 inch from "normal position" is larger than can
be tolerated. An estimate of a resonable tolerance, based on this and
earlier work, would be plus or minus 0.010 inch from "normal position".
All of the variables used in calculating the data for samples
1, 2, 4, 5, 6, 8 and 14, after the initial change in the grade correction
GC, wereheld the same to determine the effects of changing the reflec-
tance head position. The same input data for the case of the reflecta~ce
head being raised 0.025 inch were processed again but with RK e~ual to
0.975 instead of 1.00~. This reduces the reflectance value to the
proper levelD The data obtained in this way show good agreement
between the monitoring device and the standard automatic color-bright-
ness tester. Apparently the factor RK can be used quite effectively in
adjusting for some variation in the geometric relat~onship of the upper
and lower sensing heads. It would be preferred, of course, to maintain
proper alignment and spacing.
A second set of samples were evaluated after returning the
reflectance head to its normal spacing from the transmittance head.
Before calculating new output data, the computer program of Table 4 was
corrected in statements S. 0022 and S. 0028 by changing RD to RD4. The
corrected computer program has been shown herein since the error in
the previously referred to data was insignificant in most cases. Thus
with the corrected computer program, the input data for the second set
of samples were processed. The values RK and TK were set to 1.0~0
and the same grade correctionswOEeused as for samples 1, 2, 4, 5, 6,
8 and 14 previously referred to.
-56 -
.
10~.218
Conclusions drawn from all of the data are that the grade
correction GC will handle errors resulting from less than ideal
characteristics of the monitoring device 10 such as the relatively wide
bandwidth of light transmitted in the various filter positions in compari-
son to the requirements of Kubelka-Munk theory and the fact that this
theory applies strictly only to diffuse light rather than collimated light as
actually employed in the illustrated monitoring device 10. This correction
must be established "onn~chine". Use of the diffusing glass 135 to cali-
brate the monitoring device 10 will handle changes in light levelJ photo-
cell sensitivity and amplifier gain. The reflectances RD of the diffusing
glass 135 for the ~arious filters as established in the present work are
set forth in the previous Table 2 entitled "Table Showing Reflectance of
the Diffusing Glass With No Paper Specimen Present in a Laboratory Test
of the System of Figs. 1-6".
As previously mentioned, the transmittance of the diffusing
glass 135 need not be known as the ratio of the transmittance of the
diffusing glass and paper (in series), identified by the symbol TSP, to
the transmittance of the diffusing glass 135, identified by the symbol TSD,
is employed as will be apparent from the explanation of the calculations
employed set forth hereinafter.
The fluorescent component is handled through the difference
in reflectance as measured with the number 4 and the number7 filters
(RPD7 minus RPD4). The factors used in the subject computations, for
filters number 1, 2 and 4, are 0.500, 0.600 and 0.550 respectively.
This means of determining the fluorescent contribution FC appears to 'be
successful.
-57 -
.. .. _ ~ , . .~ .
10~1~218
The factor RK whereby the reflectance can be adjusted
to account for misalignment or incorrect spacing seems to function
better than was expected.
The following examples will serve to explain the calcula-
tions of the output data for the different filter positions in greater detail.
Table 6- Table Showing
Exemplary Calallation of Paper
Optical Pa ameters_
_
Calculation of R;~, T, Roo, FC and RooFC from OMOD
data with the No. 1 filter in position.
Input: RSDl, RSE'l, TSDl, TS~l, RSD7, RSP7, TK,
RK, RSD4, RSP4, RD1, RD4, and GC1
Calculation:
RPDl=(RDlxRSPlxRK)/RSDl
RPD4= (RD4xRSP4xRK)/RSD4
RPD7=(RD4xRSP7xRK)/RSD7
TPD/TD=(TSP1xTK )/TSD1
Ro=[RPDl -(RDl (TPD/TD)2)~/~1 -(RD1 (TPD/TD)2)]
T=[(TPD/TD)(1-(RDlxRPDl))]/[1-(RD1(TPD/TD) )]
A--(1+Ro - T )/Ro
RoO-(A/2) - I (A/2) - 1
FC=0. 500 (RPD7 - RPD4)
RoFC=~oo+FC+GCl
Calculation of R~, T, R~o, FC and R~3OFC from OMOD
data with the No. 2 filter in position
Input: RSD2, RSP2, TSD2, TSP2, RSD7, RSP7, TK,
RK, RSD4, RSP4, RD2 and GC2.
-58 -
lO~i~ Zl~
Calculation:
RPD2=(RD2xRSP2xRK)/RSD2
RPD4=(RD4xRSP4xRK)/RSD4
RPD7=(RD4xRSP7xRK)/RSO7
TPD/TD=(TSP2xTK)/TSD2
R~=[RPD2 - (RD2(TPD/TD) )]/[1-(RD2(TPD/TD) )]
T=[TPD/TD)(1-(RD2xRPD2))~/[1-(RD2(TPD/TD) )]
- 2 2
A=(1 + Ro -T )/Ro
Roo=(A/2) - ~I (A/2) - 1
FC=0. 600(RPD7 - RPD4)
RooFc=Roo+Fc~Gc2
Calculation of R;~, T, Roo FC and R;~C from OMOD
data with the No. 3 filter in position
Input: RSD3, RSP3, TSD3, TSP3, TK, RK, RD3 and GC3
Calculation:
RPD3=(RD3xRSP3xRK)/RSD3
TPD/TD=(TSP3xTK )/TSD3
Ro= [RPD3-(RD3(TPD/TD) )]/[1-(RD3(TPD/TD) )]
T=~(TPD/TD)(1-(RD3xRPD3))~1-(RD3(TPD/TD) )]
A=(1+Ro -T3/Ro
,
R~o=(A/2) ~ ~r (A/2) - 1
FC=û. 0
RooFC Roo+FC~GC3
Note: The calculations for Filters No. 5 and 6 are
carried out in the same manner as for filter No. 3
except that the appropriate filter data are employed.
FC is made equal to zero for filters No. 3, 5 and 6 for all samples.
-59 -
1()51218
O. . OO~ ooFC OMOD
data with the No. 4 filter in position.
Input: RSD4, RSP4, TSD~, TSP4, RSD7, TK, RK,
RD4 and GC4.
Calculation:
RPD4=(RD4xRSP4xRK)/RSD4
RPD7=(RD4xRSP7xRK)/RSD7
TPD~TD=~SP4xTK)ITSD4
R =[RPD4 - (RD4~PO/T~ )]/[l-(RD4(TPD~TD) )]
T=[(TPD/i'DXl-(RD4xRPD4))]/[l -Q~D4(TP~/TD)2)]
A=(l+R - T )/R
Roo=(A/2) - (A12) - 1
FC=0. 550a~PD7 - RPD4)
R FC=R +FC~GC4
oo oo
-fiO-
10~i~218
On the basis of further experiMental data, the factors relating
the fluorescent component, as measured on the monitoring device, to the
fluorescent component as m~asured with the standard automatic color-
brightness tester, have the following presently preferred value~ for
filter wheel position numbers 1, 2 and 4: 0.528, 0.636, and 0.456,
respectively.
-61 -
., .
lOS~Z18
DISCUSSION OF THE ON-MACHINE
SY~TEM OF FIGS. 1-6
Se~ Up Procedure For the System of Figs. 1-6
In the prototype system, potentiometers were included as par~
of the gain coMrol resistance means and were adjusted for the respective
positions of the filter wheel 210 ~o give values correlated directly with
absolute reflectance and transmittance of the diffusing glass, such as
given in the foregoing Table 1. In the preferred system of Figs. 1-6,
however, these potentiometers for adjusting amplifier gain are omitted
and are replaced.with fixed resistors 371-377 and 431-437 selected to
give ~cale readings from meter 330 in the respective filter wheel posi-
tions which are well above the values given in Table 1. The higher
gain values selected for the amplifiers 361 and 429 in the preferred
system are intended to provide improved stability and increased sensitivity
of measurement.
-6
lO~Z18
The upper and lower sensing heads are placed at a spacing of
3/16 inch by means of a gauging plate made of 3~16 inch Teflon. The
incident beam 133 forms a light spot of elliptical configuration on the
planar upper and surface 98 of the diffusing window 13S. The major
axis of the elliptical light spot has a length of about 5~8 inch and is
parallel to the direction of web movement, i.e. the machine direction,
while the minor axis has a length of about 3/8 inch and is at right
angles to the machine directionO The reflected beam 137 consists of
the total light reflected from a circularspot of approximately 3/8 inch
diameterO This viewed area lies substantially within the elliptical
illuminated area on surface 98; however, the two essentially c~incide
in the direction of the minor axis of the illuminated spot.
Since the effective optical aperture 154, Fig. 3, of the low~
sensing head is of a diameter of about 15/16 inch, the system will be s
insensitive to a certain amount of lateral offset between the optical
axis 15 of the upper sensing head and the optical axis 515 of the lower
sensing head.
-63 -
- -
- lOr'lZ18
ln setting up the system, the position of the lower sensing
head may be adjusted laterally so that the spot formed by the incideM
beam 133 is essentially~:ntered on the surface 98 of window 135.
The optimum relationship between the upper and lower sensing
heads can be precisely detected~yobserving the reflectance output from
the upper sensing head (in any position of the filter wheel 210) as the
heads are moved relative to one another while maintaining the spacing
. . .~ . . of 3/16 inch between the heads.: When the correct geometrical relation-
ship is attained between the incident beam 133, the reflected beam path
137 and the plane of the surface 98 of the window 135, the reflectance
signal will have a maximum value.
With the upper and lower sensing heads in the optimurn geome-
~ric relationship, and with the incident beam impinging on the central
part of surface 98, it is considered that relative shiîting between the
upper and lower heads in theplareofsurface 93 over a range of plus or
minus 1/8 inch in any lateral direction should have an insignificant
effect because of the flat planar conflguration of surface 98.
, .
.... . .
, ~ , .
.
_~,4 _ .
lQ~;~ Zl~
Discussion of the Claimed Subject ~latter
... . .
A basic conception of the present disclosure is crucially
concerned with the art of paper manufacture wherein numerous grades
and weights of paper are to be manufactured, and wherein access to
the paper web for measurement of paper optical properties during the
manufacturing process is restricted to a section between the calender-
ing stack and the reel. The environment at this location has been
detailed in the preceding section. By measuring two essentially
independent optical parameters, for example measuring both the re-
flectance and transmittance with respect to incident light of the neces-
sary spectral distribution, it is possible to calculate paper optical
properties on the basis of existing theory with an essential indepen-
dence of basis weight. The feasibility and effectiveness of this
approach is confirmed in the preceding section.
Closely related to the foregoing is the conception of utilizing
as nearly as practicable the optical response characteristics and geo-
metry of existing instruments used in the paper industry, so as to
~chieve as close a correlation as possible with present off-line measure-
ments of color and brightness, for example. Also of substantial
significance is the conception of providing a rugged and compact tem-
perature-stabilized instrument capable of reliable and accurate on-
machine measurement of color, brightness and opacity.
The reduction to practice of these basic conceptions has
included several sponsored projects at the Institute of Paper Chemistry
as reflected by the preceding section and has included laboratory test-
ing of a prototype device ~or accuracy and reliability on a wide range
of paper samples, with careful comparison being made with corres-
^65 -
l()~lZ1~3
pondinK mc~surements usin~ standard laboratory instruments. Details
of tlle life testing of the prototypc unit o~er a ten-month period and
the adaption of the device to reliable and stable operation on the paper
machine have been included herein to document the practical imple-
mentation of the present invention. Because of the critical need for
rapid calculation of paper optical properties in an on-machine device,
the necessary computer programming has been developed alld is fully
disclosed hereinc In spite of the substantial hlvestments which have
been made to secure expert assistance in implementing the conceptions,
a period of time of over two years has been required to reach the
stage of reduction to practice disclosed herein.
lO~ ZlS
An important aspect of the disclosure relates to the measure-
ment of the basis weight of the moving paper web concurrently with the
simultaneous measurement of reflectan~e and transmittance values for
essentially a common region of the web. Using the calculated value of
S infinite reflectance R~(including the grade correction factor) and the
value of transmittance T, for example, for the same sample region,
along with a concurrently obtained, average value for basis weight,
essentially accurate values of scattering coefficient s and the absorp-
tion coefficient k are obtained. Such coefficients will exhibit essen-
tial independence of any variations in the basis weight of the paper
sheet material under these circumstances.
The measurement of both a reflectance and a transmittance
value for a common sample region has an advaltage over the measure-
ment of two reflectance parameters under conditions such as found in
the paper manufacturing process since the transmittance measurement
is relatively insensitive to misalignment or tilting of the optical axis 515
of the backing assembly or lower sensing head 12, FIG. 3, relative to
the optical axis 15 of the sensing head 11. This advantage is especially
important for sheet material of relatively high opacity where two re-
flectance parameters would tend to be relatively close in value.
Generally the results of laboratory tests discussed herein are
expected to be applicable to the on-line system. Thus the spread be-
tween values of Ro~C (See Table 3) obtained by the illustrated on-line
system and the corresponding values of ARo~C taken as standard should
not differ by more than about plus or minus two points on a scale of zero
to one hundred prior to any grade correction, for a wide range of paper
sheet materials of different color and basis weight.
-67 -
19~1Zl~
Tl-e salllplcs for wllich suull accura-:y W;IS obtained in the labora-
tory illCIuded .I rallgc of basis weigllts of from (0 ;,r.~ s pcr squ-lre met~r
to 17~ grams per square mcter for white paper. W ithout the use of a
corrcction factor, calculated R values which fell within tWO points of the
oo
measured value included samples of paper colored white (scveral tints~,
greell, blue, canary, russett, ivory, gray and buff. Colors including pink,
gold, salmon, and cherry required a significant correction factor for the
XR~ YC- and YA functions. All of the calculated R values involving the
XB and Z functions fell within 0.77 units of the measured value ona scale
of zero to 100, again without the use of any correction factor and regard-
less of color or basis weight.
.
~0~i121~3
DISCUSSION C)F THE CL~IMED SUB~ECT MATTER
The term quantitative measure of paper optical properties
as used in the claims refers to output quantities of a numerical
nature such as supplied by the on-line digital computer system
996, Fig. 6, programmed as explained herein with reference to Figs.
7-20. Examples of such quantities are those indicated in block 990,
Fig. 20; these quantities are identified with the corresponding con-
ventional paper optical properties in Table 21.
The term on-machine optical monitoring device is intended
generically and refers to the device 10, Figs. l and 2, and other
comparable devices for sensing two essentially independent optical
response parameters such that a paper optical property is characterized
, prior to use of any correction factors with substantially improved
accuracy in comparison to any characterization (prior to correction
fact~3 of such paper optical property from either of such optical
response parameters taken by itself. Such a monitoring device may be
used as an aid to manual control of the paper making process or m~y
be used as part of a closed loop automatic control system. Thus
"monitoring" does not exclude active control in response to the output
; 20 signals frorn the monitoring device.
: ~!
~ Within the scope of the present subject matter, one or more of
:!
the following paper optical properties may be sensed: brightness, color,
, fluorescence, and/or opacity. Control of brlghtness and fluorescenceoffers a very substantial potential for cost reduction in the production
of a significant range of paper types. Color control, on the other hand,
may have important consequences regarding flexibility of manufacturè,
product uniformity, and grade change flexibility.
-69
,~
~V~ Z1~3
The value of on-line opacity control has already been demon-
strated to a large degree in a prior closed loop analog opacity controller.
In this installation, the average opacity across the web is controlled almost
exactly at any given desired value. In previous manually controlled
operations, the PKT (Pigmentary Potassium Titamate, K20-6Ti02 by
du Pont) flow was set to some value chosen by the beater engineer and
usually held to such value for the duration of the run of a given grade and
weight. In the meantime, the paper opacity varied up and down, depend-
ing on process conditions at the time. Since the installation of the analog
opacity controller, the opacity set point is adjusted rather than the PKT
flow, thus holding opacity constant at the desired level. Instead of
opacity, the PKT flow now varies up and down to compensate for other
presently unavoidable process upsets resulting from variations in broke
richness, PKT solids, dye usage, save-all efficiency, and other machine
retention conditions. For a complete discussion of the installation of
the analog opacity controller, reference is mace to F. P. Lodzinski
article "Experience With a Transmittance~Type On-Line Opacimeter for
Monitoring and Controlling Opacity", Tappi, 'rhe Journal of The Technical
Association of The Pulp and Paper Industry, Vol. S6, No. 2, Feb. 1973.
Existing on-line color meters have two serious disadvantages
as follows:
1. Each measures a reflectance value (Rg) wmch is decidedly
different from that necessary for actual color and brightness charac-
terizations, Off-line instruments, which adequately measure these pro-
perties, require that a pad of several thicknesses (Roo) of the same
paper be expo~ed to the light source aperture. Obviously, this is im-
possible with an on~line instrument, unless the far more inaccessible
~'
10~121~
reel itself is tested. The use of ~ instead of Roo requires very
frequent off-line testing, and constant updating of an empirical
calibration procedure to maintain adequate accuracy. A separate set
of calibration parameters for each grade and weight is also required.
Only in instances of extremely high opacity such as heavily coated,
or heavily dyed colors where Rg approaches Roo, can the above
problems be minimized to the point where accuracy becomes sufficient
for control purposes.
2. Existing color instruments are not equipped to measure
transmitted light which is much more sensitive to differences and, so
far, the only commercially proven method for the continuous monitoring
of opacityO
To assist in indicating the scope of the present disclosure,
the substance of excerpts from an early conception record with respect
to the present subject matter are set forth in the following paragraphs,
headed "Proposal" and "Proposed Instrument Design" having reference
to the defects of existing on-line color meters just discussed:
Proposal:
An instrument built to the general specifications disclosed in the
2~ following section headed "Proposed Instrument Design" avoids the above
described defects and, at the same time, provides for a concise,
but extremely versatile, nearly total optical property monitor and
controller. Highly trained specialists in all fields required here,
including paper optlcs, color theory, photometry, computers and
others, if needed are available. As an example, exact specifications
for the filters, photocells, and light sources are essentially ready for
manufacture now. Such specialis!ts are also aware of factors important
lOS1218
to optical characterization frequently ignored by commercial producers
of optical instruments.
Proposed Instrument Design:
An instrument made up of two scanning sensing heads, one above
and one below the moving paper web, and a dedicated computer with
appropriate couplers for input and output, is envisioned. The bottom
head would receive light transmitted through the sheet and subsequently
analyzed for its X, Y, and Z tristimulus components. It would also con-
tain a backing of some specified effective reflectance (possibly a black
body of zero, or near zero, reflectance) located just ahead or behind
(machine direction) of the transmitted light receptor compartment(s).
The upper head could contain the light source, as well as a
reflected light receptor. The latter occurs after reflection from the
moving web at a point ~ust above the backing, on the bottom head and
would also be analyzed for its X, Y, and Z tristimulus components.
Both light receivers and, for that matter, the light source itself could
be integrating cavities of a type. This would be one way to insure the
uniform distribution of emitted, transmitted, and reflected light in the
X-direction in addition to providing identical samples of light going to
~0 each photoelectric cell installed with filters within the cavities them-
selves. Thermostatically controlled heaters o~r coolers would likely be
desirable for temperature control. The flux of the light source could be
~` monitored or controlled by a third partial, or full, set of filter-photocell
- combinations. The availability of both the transmitted (T) and reflected
(Rg) light signals described above allows for precise computation of the
reflectance with an infinite backing (Roo). It is the latter, Roo value,
which is required to character ze color, brightness,
-72 -
~o5~Z~
and an index of fluorescence. In addition, it would eliminate the need
for any grade corrections in measuring either printing or TAPPI opacity,
both of which could be made available if desired.
A small, rather low cost, dedicated computer with appropriate
S interface equipment, could be used to receive all signals, compute all
pertinent optical properties, and determine the signal for direct, closed
loop control of:
a. 2-5 separate conventional dye additions;
b. fluorescent dye feed to the size press; and
c. PKT, TiO2, or other slurry flow;
so that brightness, opacity, color (L, a, b) and fluorescence could be
maintained almost e2~actly as chosen by, perhaps even a master
computer, if desired.
Kubelka -Munk equations, quantitative color descriptions, and
their inter-relationships, recently acquired wet end mathematical
models, along with existing control theory, are all presently available
in some form or other to convert the input signals from the scanning
heads to optical measurements and flow feeds with which paper manu-
facturers are familiar. The combined mathematical technology above
is also sufficient for adequate decoupling of this otherwise complicated
information so that overlapped control is avoided.
-; Use of a dedicated computer would eliminate most of theelectronics now associated with optical measuring equipment. It could
also be used to integrate results across the web and simplify and/or
~5 maintain cali~ration. The package would lend itself to rather universal
application and minimize the time and effort on the part of thepurchaser.
The key feature of this proposed instrument, which distirguishes
it from e~isting on-line optical test7e3rs, is that it calls for the
lOS~Z~8
measurement of both transmitted and reflected light without undue
complications. This, in turn, can cause a great deal of improvements
regarding sensitivity, accuracy, flexibility, and thoroughness of a
continuous optical property measuring device.
The following Table will serve to identify the computer symbols
used in Figs. 17-20 with the corresponding conventional symbols
and terminology used in the text.
Table 21 - Identification of Computer Symbols Used in
F igs . 17 -20
Computer Conventional Conventional Term
Symbol Symbol for Symbol
SGCF GC(Table 3) specific grade
correction factor
RG RD(Table 3) Nominal reflectance
of the diffuser
window 135
TD Td Nominal transmit-
tance of the diffuser
window 135
RZERO R (Table 3) reflectance with
` (RZTABL) 0 black body backing
for each filter wheel
position I equals
zero through five.
T T(Table 3) Transmittance with
(TTABL) black body backing
for each filter wheel
position I equals
zero through five.
RINF ROOTable 3) infinite backing
(RITABL) reflectance for
filter wheel
positions 1 equals
~ero to five.
S S scatter coefficient
(STABL) for each filter
~74 -
lOSlZ~8
wheel position
1 equals zero
through five.
K K absorption
(KTABL) coefficient for
each filter wheel
position 1 equals
zero through
five.
~: 10 ZFLUOR - fluorescent
contribution to
tristimulus Z
reflectance
` ZRINF - tristimulus Z
infinite backing
reflectance with -:
fluorescence
. XBRINF - tristimulus X
infinite backinBg
reflectance with
fluorescence
BRRINF - TAPPI brightness
. (see Table I in
~j the first section
of this Topic for
' spectral distribu -
. tion of the first
. filter wheel
position~
.
POPAC Ro/Roo printing opacity
YAR89 Ro 89 tristimulus Y
. reflectance with
. . 89 backing
~, TOPAC Ro/Ro 89 TAPPI opacity
XTRI X C. I. E. t ristimulus
coordinate X
-. YTRI Y C. 1. E. tristimulus
coordinate Y
ZTRI Z C. I. E. tristimulus
coordinate Z
LH L Hunter coordinate
- L
AH, BH a.b Hunter coordinates a, b.
-75 -
-
~OS~z~8
Scope of the Early Conception of This Invention
Given the foregoing conception, it is considered that
many modifications and variations will be apparent to those skilled
in the art. The basic conception claimed herein is the sensing of
two essentially independent optical response parameters of a single
thickness relatively homogeneous sheet material such that any other
desired parameter or paper optical property can be accurately
calculated.
The present subject matter is limited on the determi-
nation of the specified optical properties of single thickness
relatively homogeneous sheet material with the use of filters of the
apparatus spectral response characteristics as explained in the
present specification. For the case of opacity measurement, for
example, the present invention, is particularly applicable to an
optical system wherein system spectral response essentially simulates
the C.I.E. tristimulus Y filter with either illuminant A or C and
to near-white papers as explained in the Lodzinski Article of
February, 1973 .
,~
.. ",,~ ~_
,~
10~1.21~ ~
P~OPOSED OFI`lCAL CONTROL STRATEGY
While the on~ine automatic control of paper optical properties
is an ultimate objective of the work reported herein, the claimed
subject matter relates to on~nachine monitoring of paper optical
properties whether used as an aid to conventional manual control or
for other purposes. Nevertheless, in order to provide a disclosure .
of the best mode presently contemplated for automatic control as a
separate but related area of endeavor, the following discussion is
presented.
The optical properties of a sheet of paper are dependent upon
all of the materials of which it is made but primarily upon the furnished
pulp, fillers, pigments, dyes, and some additives. It is often very
difficult to maintain the optical attributes of the pulp, fillers and
additives constant within a given production run. Such variation is
even greater between runs. The optical properties of the finished paper
may, however, be reasonably controlled to specified standards by
varying the additions of dyes and fillers and pigments until the desircd ~
compensations are achieved. The problem is that each furnished ¦'
ingredient affects each of the resulting paper optical properties in a
rather complicated' manner. Indeed the incuition of experienced
papermakers has essentially been the sole method of optical property
cGntrol. Unfortunately, this approach is inefficient, resulting in
considerable off-standard paper and/or waste of costly materials.
Accordingly, a dire need exists within'the paper industry for a highly
reliable and continuous optical property monitor'coupled with a closed F
loop computer control system.
The value of such closed loop control, based on a feedback
~'` ' ~ '
D 77 '`
` .
1 ' ' . ` . ~
10~ 18
color detector, has already been demonstrated for the ~D ntinuous
addition of two and sometimes three dyes. (1) (2)Target dye conccntra-
tions changes of up to three dyes can be determined by solving three
simultaneous equations containing three unknowns. ~1) One disadvantage
of such control i9 that accurate color monitoring is not presently
available unless large and frequent empirically determined correction
factors are applied to the original output results. A second dis- j
advantage arises whep bpacity and the fluorescence must also be ¦
simultaneously controlled. ~n this case the number of independently
controlled continuous additions increases from three to five. An
optical brightener and an opacifying pigment constitute the two
additional factors.
An object of this invention i8 to demonstrate a method by
whicb fluorescence can be continuously monitored. A means by which
the optical brightener addition can be separately and independently
-controlled is inherently implied. The paper color is also analyzed
without the fluorescent contribution. It is, of course, this latter
characterization (without fluorescence) which should be, but which
has not in the past been, used to determine the required addition of
the conventional dyes. In other words, the effect of the optical
brightener is decoupled from th¢ three conventional dyes making
possible the simultaneous control of all four dyes.
Another portion of this invention demonstrates a means of
continuously determining the scattering coefficient of the moving web
for each of the six available light spectrums. It'is possible to determine
the scattering coefficient required to achievc a given opacity specification
whenever ~he basis weight and absorption coefficient are known. When
.~ ~_ .
.~ ' - -'' ' '" ` , ,,, ' ` ~ .
lO~ilZ18
the latter are set equal to a given set of product specifications, then
the calculated scattering coefficient becomes the target scattering
coefficient. ¢Ihc absorption coefficient can be acquired by off~ine
testing of a sample of the standard color to be matched. In reality, .
this becomes a target absorption coefficient as well.) The dyes have t
little, if any, effect on the scattering coefficient but the effect of the
slurry pigment is very large. Thus the target scattering coefficient
is used as the sole feedback variable to control the slurry pigment feed.
This will insure that the opacity is at or near the specification as , .
long, as the absorption coefficient and basis weight are also on target.
The absorption coefficient should, of course, be on target by virtue
of the independent color control. A completely independent system
controls the basis weight.
A method by which the decoupling of three conventional dyes,
one cptical brightener and one opa~ifying pigment has hereby been
explained. -Heretofore, such decoupli~g as revealcd in the prior
art has been limited to three absorptive dyes and thereby neglecting
the need to also achieve a specified degree of fluorescence and opacity.
References
1. The development of dynamic color control on a paper
machinc by H. Chao and W. Wickstrom;`Automatica, Vol.
~ PP 5-18, Pergamon Press, 1970. ¦-
2~ Another consideration for color and formation by Henry
H. Chao and Warren A. Wickstrom, color engineering, Sept/
Oct. 197 1.
~~ ~
' ' . '
`! `
.. . ..................... .. - I'
105;~ 2~8 ,
Dl~Cl~SSION OF TI~E CLAIM TERMINOLOGY AND SCOPE
The present invention is for the purpose of obtaining a
quantitative measure of an optical property such as brightness, color,
opacity or fluorescence of single thickness sheet material.
The sheet material is substantially homogeneous in its thickness
dimension such that the optical property of interest can be reliably cal-
culated from reflectance and transmittance measurements on the basis of
existing theory. Thus the present invention is not applicable to the
sensing of localized surface effects (such as due to surface migration
of light absorbing powder particles, for example). To the contrary the
present invention is concerned with the average or bulk optical charac^
teristics of the sheet material considered as a whole, and especially
is concerned with the characteristics of paper sheet material as it is ~ `
delivered from a paper machine after completion of the paper manufac- t
turing process.
The present invention in its broader aspect does not require
strictly homogeneous material since empirical correction factors can
be applied for cases where theory is less effective. For example,
the paper optical properties of calendered and coated papers may be
effectively measured by the system of the present invention using grade
correction factors to correlate on-machine results with the measurements
obtained by standard off-line instruments.
The optical system of the monitoring device includes compo-
nents such as those shown in Fig. 3 which define or optically affect the
incident, reflected andtransmitted light paths suçh as inàicated at 133,
137 and 141-143 in Fig. 3. For the case of a filter wheel as indicated
in Fig. 4, each filter wheel position may be considered to define a
separate light ener~y path with its own predetermined spect~alresponse
characteristics .
~- ~
r~ ~ ~
V
2~3 ir
In each filter wheel position, there are two distinct light
energy paths for measuring a reflectance value and a transmittance value,
respectively. In the illustrated embodiment each such light energy path
includes a common incident light path 133, but the paths diverge, one
coinciding with the reflectance sensing light path 137 and the other
including the transmittance sensing light path. The photometric sensors c
203 and 260 thus provide simultaneous reflectance and transmittance
output slgnals with respect to essentially a common region of the web.
The reflectance sensing light path collects light from a circular region
with a diameter of about 3/16 inch, and the transmittance sensing light
path collects light from a total elliptical region which includes substan- i
tially the same circular region as mentioned above. Because of sheet
- formation effects and other localized variations in web characteristics 1 -
it is considered valuable that the reflectance and transmittance output
signals are based on readings from essentially a common region of the
web.
Y~ By taking at least one reading in each traverse of the web, and
taking such readings at different points along the width in successive
traverses, it is considered that accuracies equal to or superior to those
of an off-line sampling of a finished reel can be achieved, while at the
same tirne the readings are available immediately instead of after comple-
tionof a manufacturing run. ,
By way of example, in the illustrated system a traversal of
the web by the sensing head takes about forty-five seconds, so that the
sensing head operates at a rate of a~ least one traversal of the width .
of the web per minute in the time intervals between the hourly off-sheet
standardizing operations.
L
',~ ~_ ,,
~t
. ...................... 10~121t3 , `
a~l Im~7~ovem~.~
In accordance with the teachings oflthe present invention, the
optlcal window 135 is itself selected as to its optical characteristics so as
to provide the basis for off-sheet standardization, To this end it is advan-
tageous that the optical window exhibit an absolute reflectance vàlue as
measured by the standard automatic color-brightness tester of at least about
thirty-five per cent (3~%). The corresponding absolute transmittance value
as measured on the G.E. Recording Spectrophotometer with conventional
optics is about fifty-six per cent (56%). With the illustrated embodiment,
once the system is properly ad]usted with respect to the zero reflectance
readings (as by the use of a black sheet of known minimal reflectance) the
system maintains such zero adjustment quite stably; accordingly the higher
the reflectance value of the optical window, the more effective is the re-
flectance standardization by means of the optical window. On the other hand
a transmittance value which is of a reasonable magnitude is also desirable,
so that the provision of an optical window with substantial values of absolute
reflectance and cransmittance is advantageous.
With the illustrated embodiment, the transmittance readings for the
moving web are relatively more nearly independent of misalignment of the
upper and lower sensing heads than the reflectance readings. Further it is
considered that tilting of the lower sensing head relative to the optical axis
of the upper sensing head has less effect on transmittance readings than on
reflectance readings. Thus it is considerèd that it would be advantageous
. .
to have an optical window such as 135 with an absolute reflectance value of
seventy per cent (70~70) or mare. A value of reflectance as high as ninety
per cent (40~YO) wauld not be unreasonable and would generally still permit
a transmietance value of a substantial magnitude to give reasonably com-
par.lble accuracy of reflectance and transmittancc readings for on-line opera-
tion as hcrein described.
~_
.~ , , ' .
:~ . ' , ' ' ~ .
~0~:121~3 1
While separate photometric sensing means for the reflectance and
transmittance readings have been shown, it is possible with the use of
fiber optics, for example, to use a common photometric sensor and alter- ¦
nately supply light energy from the reflectance and transmittance light
paths thereto, providing the response rime of the sensor enables reflectance
and transmittance readings to be obtained for essentially the same region
of the moving web. Generally the possibility of such time multiplexing of
reflectance and transmittance readings will depend on the speed of move- ,
ment of the web and the degree of uniformity of sheet formation and the
like.
It is very desirable that the system of the present invention be ¦`
applicable to sheet materials having a wide range of characteristics such
as basis weight and sheet formation, and operable at high speeds of move-
rnent sucb as 100 to 30C~feet per minute. Further, for maximum accuracy,
it is necessary that a region of the sheet material being sampled have sub-
stantially uniform opacity. Accordingly, especially for sheet material of
relatively low basis weight and relatively poor sheet formation, greater I .
accuracy can be expected when the responce of the photometric sensor is
relatively fast, and when reflectance and transmittance readings are taken
simultaneously and are a measure of the characteristics of a common sam-
pling region of minimum area (consistent with adequate signal to noise ratios). I
Thus multiplexing of re'flectance and transmittance readings is not prefer- !
red for the case of high speed paper machinery and comparable environ-
ments, nor is it desirable to use reflectance and transmittance light paths
which intersect the web at spacially offset regions.'
With respect to speed of response of the photometric sensing means,
substantial improvements over the previously described components
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are deemed presently available. If the spectral response and other
necessary characteristics are suitable, a sensor with such a higher ¦
speed of response is preferred for the illustrated embodiment. Good
experience has been had with a silicon photocell presently considered
as having an appropriate spectral response characteristics for color
and other measurements in accordance with the present invention. The
specific silicon cell referred to is identified as a Schottky Planar Diffuse
Silicon Pin 10 DP photodiode of a standard series supplied by United
Detector Technology Incorporated, Santa Monica, California. , '
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In place of a rotatable filter wheel arrangement as shown in FIGS.
3 and 4, a set of twelve fiber optic light paths may define six simultaneous~
ly operative reflectance light paths in upper sensing head 11 and six sim- !
ultaneously operative transmittance light paths in lower sensing head 12.
The six reflectance fiber optic paths would include respective fllters cor-
responding to filters 281-286 and respective individual photocells and would
be located to receive respective portions of the reflected light which i8 1 .
reflected generally along path 137 in FIG. 3. The six transmittance fiber
optic paths would also include respective filters corresponding to filters
281-286 and respective indiuidual photocells, and ~uld be located to re-
ceive respective portions of the transmitted light which is transmitted gen- ',
erally along paths such as 141-143 in FIG. 3. The filter means in the l `
incident light path such as indicated at 133 in FM. 3 might include a filter
in series with filters 271 and 272 for filtering out the ultraviolet component
from the incident beam, so that the twelve simultaneous photocell readings
corresponding to those designated RSD1 through RSD6, and TSDl th~ugh
TSD6 (when the device is off-sheet), and corresponding to those designated
RSPl through RSP6, and TSP1 through TSP6 (when the device is on-sheet) I,`
will exclude a fluorescent contribution. (See Table 3 where th`is notation
is introduced. ~ i
.If a reflectance reading corresponding to RSD7 (when the device is
off-sheet ) and correspondingtoR~P.7(when the device is on-sheet) is desired
,
so as to enable computation of fluorescent contribution to brightness, it
would be necessary to mechanically remove the ultraviolet filter from the
incident light path, or otherwise introduce an ultraviolet component of .
proper magnitude, and obtain another brightress (Z) reading; for example.
from the number four reflectance photocell.
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As an alternative to the above fiber optic system with a common
incident light path, seven fiber optical tubes incorporating filters corres- ¦
~nndirg to 281-287 of FIGS. 3 and 4, respectively, at say the light exit
points of the tubes, could be used to supply the incident light to seven
different points on the paper web. The reflected light from each of these
seven points could be monitored by seven different systems, each involving
lenses and a photocell, and the number seven reflected light path including
also a filter corresponding to fiker 288, FIG. 4. The transmitted light
from the first six points would also need to be kept separately, and this
could be accomplished by six integrating cavities and six photocells.
As a further alternative the seven fiber optical tubes defining the f
seven incident light paths could have a second set of seven fiber optical
tubes and photocells respectively disposed to receive reflected light from
the respective illuminated points. Another set of six fiber optical tubes
and photocells could be associated with the first six illuminated points
for receiving transmitted light. This could eliminate the need for the
light collecting lenses in the upper sensing head and the integrating cavi-
ties in the lower sensing head.
The last two mentioned alternatives with seven fiber optical tube
defining the incident light paths appear to he rather complicated systems,
but they do offer means of eliminating both the mechanical filter wheel
; as well as any mechanical device to control the presence of ultraviolet
light in the incident beam.
Still another alternative is to use "screens" in addition to the
filters in the embod~nent of PIGS. 1~. The new photodiodes are consider-
ed sensitive enoughtomeasure reduced light intensites so that screenswith
differerlttransmittance values could be used with six of the incident beam
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filters so that the net photocell output for each reflectance light path,
and for each transmittance light path, would be similar enough so that
separate and invidual pre-amplification for the respective reflectance
outputs would not be necessary, and so that separate and individual pre-
amplification for each transmittance output would not be necessary.
This means that reed switches 341-347 and 351-357, and relays K1
through K7 in FIG. 6 could be eliminated, and that the feeback paths
for amplifiers 361 and 429 could have the same resistance value in each
filter wheel position. A means of sensing filter wheel position would still
be necessary, butthis could be done in a number of simple ways, one of
which would be a single reed switch such as reed switch 358 shown in
PIG. 6. The number of necessary conductors in the cables 51 and 52,
FIG. 5, would, of course, be reduced in this modification.
The term "screen is understood in the art as referrirgto a net- I`
work of completely opaque regions and intervening openings or completely
translucent regions, such that light energy is uniformly attenuated over the
entire spectrum by an amount dependent on the proportion of opaque to
transmitting srea.
The device of Figs. 1 and 2 has been tested on a m~chine
operating at about 1000 feet per minute, and no problems have appeared
in maintaining the necessary uniform and stable contact geometry be-
tween the head and the moving web.
It will be apparent that many further modifications and variations
may be effected wi~hout departing from the scope of the novel concepts
of the present invention.
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