CA1051218A - Measurement of paper optical properties using reflectance and transmittance means - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
In an illustrated embodiment, brightness, color, opacity and fluorescent contribution to brightness are measured by an on-line sensing head providing for simultaneous measurement of transmitted and reflected light. By measuring two independent optical parameters, paper optical properties of a partially translucent web are accurately characterized substantially independently of paper grade and weight.
The instrument id designed so as to be capable of transverse scanning of a moving paper web on the paper machine, and so as to monitor desired paper optical characteristics with sufficient accuracy to enable on line control of the optical characteristics of the paper being manu-factured.

Description

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 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;

.. . .

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.

:

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 .

! ` -.

~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 ,. .

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-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.

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.

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.

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.

~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 . ..
' ,, , :

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 .. , .. _ . . __ _~. .. _ ,. _" .. __ .. _,,, . ._., ._ ._ _ .. ...... , .. _ . . _.. . , .~ .
' 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 ~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.

:

. .

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).

, _ ~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:

-~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 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 ,~

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.

~ .

.. , . . ... ~ .. ~ .

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.

- , 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~

-- . . ..
.

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.

.

.

. - :

.. ..

~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.

.

~ . ' ' ' `

: ' - -10~ ;19 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 .

. .

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.

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.

: ' .,, ~ ~ - , ., .
.

, ~, , ~', ' ,_, ..... __ ..... . .. . ... .. . .

. . - .

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 _ .. .. , ._,..................... .

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) 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

. . ~ . .

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

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

.

. ~ .

.
. , . . . ... .... _ .

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~

. . . .

.

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 .

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.

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.

.

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.

.. .. _ ~ , . .~ .

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.

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) )]

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.

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.

., .

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.

- -- 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.

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.

,~

~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, ~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.

-~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 ~- I

. . i ~ ' ~ . ' ' ' .

lO~Zi~3 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. , ' _ ~ _ , ~Y
I

. ` ' ' ~ ` ' ~ . ` ' 10~18 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.
1) .~4 i ,~ ' I
r ~ T~
.i ` .

. ~ f ~ .

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 ,~_ ~
."~gC

., ~.

j ' ', ~ ' I

10~i~218 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.

~K- ` ' `.
`~ ~: 5'7 - ~
. r ~
i ~ ' ' , ' ~ .
~! ` ` . .

Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. 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 sub-stantially homogeneous paper sheet material, said optical measuring device having an optical system with at least two substantially indepen-dent photometric sensors and at least two distinct light energy paths each including at least light source and spectral response filter means and a respective one of said photometric sensors, and each intersec-ting said receiving region prior to the respective associated photome-tric 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 reflec-tance or a transmittance measurement taken by itself.

2. Apparatus according to claim 1 with automatic digital computer means connected on line with said optical measuring device and coupled with the respective photometric sensors of said distinct light energy paths for receiving therefrom respective output signals in accordance with the reflectance and transmittance 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.

3. Apparatus according to claim 1 or 2 with said optical system having two distinct light energy paths each having a spectral response characteristic substantially corresponding to the standard brightness spectral distribution of light energy, and said quantitative indication representing the standard brightness of said paper sheet material.

4. Apparatus according to claim 1 or 2 with said optical system having two distinct light energy paths each having a spectral response characteristic with an effective wavelength of sub-stantially 457 nanometers and with a wavelength bandwidth and shape essentially in accordance with a standard brightness function.

5. Apparatus according to claim 1 or 2 with said optical system having two light energy paths each having a spectral response characteristic essentially simulating the C.I.E. tristimulus Y spectral response.

6. Apparatus according to claim 1 or 2 with said computer means being automatically operable to calculate TAPPI opacity.

7. Apparatus according to claim 1 or 2 with said computer means being automatically operable to compute printing opacity.

8. In the art of paper manufacture, apparatus for obtaining a quantitative 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 homoge-neous paper sheet material being produced by such machine, said on-machine optical monitoring device having an optical system with at least two substantially independent photometric sensors and at least two distinct light energy paths each including at least light source and spectral response filter means and a respective one of said photometric sensors, and each intersecting said web receiving region prior to the respective associated photo metric sensor, each of said at least two distinct light energy paths having substantially a common spectral response character-istic sufficient to characterize said paper optical property but being respectively arranged for collecting said light energy from the web receiving region after impingement on said web under respective substantially differentiated conditions such as to essen-tially characterize two essentially independent optical response parameters of the paper sheet material and such as to character-ize the paper optical property such as brightness, color or opacity with substantially greater accuracy than any characteriza-tion 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 output signals in accordance with the respective essen-tially independent optical response parameters and automatically operable on the basis of said output signals to calculate a quanti-tative indication of said paper optical property such as brightness, color or opacity.

9. Apparatus according to claim 8 with said two distinct light energy paths each having a spectral response charac-teristic substantially corresponding to the standard brightness spectral distribution of light energy, and said digital computer means supplying a quantitative indication of the standard bright-ness of said paper sheet material.

10. Apparatus according to claim 9 with said two distinct light energy paths each having a spectral response charac-teristic with an effective wavelength of substantially 457 nanometers and with a wavelength bandwidth and shape essentially in accordance with the standard brightness spectral response between 400 nano-meters and 510 nanometers.

11. Apparatus according to claim 8 with said two light energy paths each having a spectral response characteristic essentially simulating the C. I. E. tristimulus Y spectral response.

12. Apparatus according to claim 11 with said com-puter means being automatically operable to calculate TAPPI
opacity.

13. Apparatus according to claim 11 with said com-puter means being automatically operable to compute printing opacity.

14. Apparatus according to claim 8 with said optical system providing at least three spectral response characteristics for each of said two distinct light energy paths and said paths together providing two sets of three output signals for a given portion of said web such as to characterize the color of the por-tion of said web of paper sheet material with substantially greater accuracy than any characterization of said color of said paper sheet material by either one of the sets of three output signals taken alone.
15. Apparatus according to claim 14 where the two sets of three output signals represent the reflectance and trans-mittance values of the given portion of said web for respective transmittance and reflectance light energy paths having respective-ly in common ?, ? and ? spectral response characteristics.

accuracy than any characterization of said color of said paper sheet material by either one of the sets of three output signals taken alone.

15. Apparatus according to claim 14 where the two sets of three output signals represent the reflectance and trans-mittance values of the given portion of said web for respective transmittance and reflectance light energy paths having respective-ly in common x, y and z spectral response characteristics.

16 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 substantially homogeneous sheet material light 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 photomet-rically sensing the light energy such that each of the respective light energy paths has substantially a common spectral response characteristic sufficient to characterize said paper optical property, and such that the photometric sensors provide respective outputs which essentially characterize the reflectance and trans-mittance of the sheet material, whereby the optical property such as brightness, 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.

17. The method of claim 16 where the filtering and photometrically sensing provides respective associated light energy paths having substantially a common ? spectral response charac-teristic so as to provide reflectance and transmittance outputs which characterize the Y color value of the sheet material.

18. The method of claim 16 where the filtering and photometrically sensing is with respect to a source providing illumination in accordance with Illuminant C, and provides respective associated light energy paths with substantially a common spectral response characteristic so as to provide reflectance and transmittance outputs which characterize the opacity of the sheet material.