Note: Descriptions are shown in the official language in which they were submitted.
~07S034
The invention relates to the obtaining of a quantative measure of
an optical property, specifically colour or brightness of a sheet material,
particularly, but not exclusively, paper, either on or off a machine by which
the material is manufactured or treated.
The invention thus provides apparatu for measuring colour or
brightness of a sheet material, the apparatus comprising receiving means for
receiving the sheet material, and an optical system so arranged that light
characterizing the colour or brightness of sheet material at the receiving
means is directed from sheet material so received along first and second
paths to photometric sensor means, said optical system comprising means for
separately transmitting respective narrow bands together covering the spec-
trum required for characterizing colour or brightness.
The invention also provides a method of measuring colour or
brightness of a sheet material, the method having the step of receiving
light from the sheet material along first and second paths by photometric
sensor means, the light being modified so that the light received character-
izes the colour or brightness of the sheet material, in which the light is
transmitted in separate narrow bands together covering the spectrum required
for characterizing colour or brightness.
In a preferred embodiment, filter means are located in an
incident path between a light source and the receiving means.
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1075034
Instead of using a single filter, use for example of a series of
~ narrow-band filters, provides signals from the sensor n~ans which per-
mit a computer to simLlate brightness or colour spectral distribution,
by means of weighted ordinate integration.
m e invention will be more readily appreciated from the following
illustrative description and accompanying drawing, in which:
Fig. 1 is a schematic part-sectional side view of an apparatus
embodying the invention; and
Figs. 2 and 3 are schematic plan views of optical filter ~P~n.c
included in the apparatus of Fig. 1.
Figs. 1-3 illustrate an instrument intended primarily but not
exclusively for use independently of a paper machine. It is contem~
plated that in off-machine use this instrument will enable the develop-
ment of the relationships between off-machine specification and the on-
line instrument described in detail in the specification, and shown in
Figs. 1-20, of British Specification 1 498 417 (Serial No. 216125 -
Canada~. mese relationships would include the "grade-correction"
factors to be used in the on-line system of Figs. 1-2Q of British
Specification 1 498 417 relative to off-machine optical specifications.
m e instrument of the present Figs. 1-3 is shown as including a
specimen support 1000 having an aperture 1001 which may conform in
ter with the ape~ture 130 shown in Fig. 3 of said specification
1 498 417. The web support lOG0 is of extended area so as to be
capable of conveniently supporting a full-width web and for adjustment
of such web to expose successive portions thereof at the aperture 1001.
At the s æ ti~, the support 1000 will accommodate a small size paper
specimen such as indicated at 1002. Generally the hnusing for the
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-~ 107S034
optical components will conform with the housing 11 of the on-line
instrument of said specification 1 498 417 from the standpoint of
light proofing and interior finish.
The optical system as ~i~grammatically indicated includes a light
source means 1010 and the lenses 1011-lQ16 generally having the charac-
teristics of the lenses 202, 273 and 274 of the on-line instrument of
said specification 1 4~8 417 and such that the spectral response of
the system can duplicate that of that instrument. The illustrated
optical system further includes a fixed lamp socket lQ20 and an iris
diaphragm 1021 for attenuating the incident light beam.
Fig. 1 illustrates also a transmittance sensing head lQ25 which
may be hingedly secured to the support lQOQ at a single corner so as
to m;n;nn~e the obstruction provided to movement of a paper web over
the support surface 1000. The transmittance sensing head lQ25 may
include an optical window 1026 of the s æ diameter, thickness and
physical composition and characteristics as the window 135 of the on-
line instrument of said specification 1 4~8 417. As illustrated, the
lower surface of window 1026 may directly contact the paper specimen
`- 1002 which will be in smooth continuous contact therewith over the
optical viewing area of the system which may he of the same d~mensions
as that described with respect to the Prior on-line embod~ment. The
sensing head 1025 may comprise a light integrating cavity 1028 and
a transmittance sensing light photocell 103Q.
It will be understood that the reflectance and transmittance
light paths have the incident path in ccmmon, and that in the illustra-
ted embodiment the transmittance light path irto the integrating
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1075034~
cavity 1028 may confoDm with those described with respect to the
on-line instrument of said specification 1 498 417. Also, the
reflectance light path generally conforms with that of the on-line
instrument and includes a reflectance photocell 1032. The photocell
1032 may have a plate 1033 with a 3/8-inch aperture and may conform
with the pla_e of the on-line instrument. Thus, a piece of diffusing
glass corresponding to the glass oE the on-line instrument may be
located in the aperture so that the light distribution over the
surEace of the photocell 1032 will conform to the light distributi~
with respect to the surface of photocell 203 in the on-line ,'nstrument.
The instrument of Fig. 1 further includes an incident light
filter disk 1040 and a reflectance filter disk 1041. The disks may
be provi~ed with iOw torque motors 1042 and 1043 which may operate
essentially as described with respect to the motor 209 of the on-line
instrument. Both filter wheels 1040 and 1041 are under constant
torque from a motor and slip-clutch arrange~ent. Each is prevented
from turning by a stop pin seated in a small hole in the w~.eel. Each
of the twenty-one filters in a wheel has a corresponding hole. The
wheel rotates whenever a solenoid pulls the pin clear of the wheel.
It stops again after the pin is dropped and a new hole ccms under the
pin allowing it to seat. It will be apparent that the indexing of
the filter wheels 1040 and 1041 may be controlled fram an on-litte
camputer in the same manner as generally described with respect to
the on-line instrument.
Figs. 2 and 3 diagrammatically indicate the respective filters
1101-1121 and 1201-1221 of the filter disks 1040 and 1041. The
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1075034
filters 1101-1106 may conform identically to the incident
heam filters of the on-line instrument while filter
position 1107 may be open and free of a filter. In this
case, the complete number seven filter of the on-line
embodiment can be located at position 1207 in the
reflected beam. The filters 1108-1121 and 1208-1221
comprise interference type narrow-band filters which
; together transmit the complete visible spectrum.
By way of example each of the filter diameters
may be 3/4-inch. The reflectance and transmittance
photocells 1032 and lQ30 may be of the Schottky Silicon
Photodiode type. Amplifiers for each of the photodiodes
can be the Analog 234 ~ and AD 741 C. Two digital volt
` meters can be used, one for reflectance and the other
, 15 for transmittance and these may be 3 1/2 digit, 0.200
millivolt instruments with 8-4-2-1 ~CD positive logic
. outp~t.
As indicated at 1040a, a portion of each of the
filter wheels lQ4Q and 1041 is preferably exposed
- 20 outside of the case so that the number of the filter in
the optical train can be observed directly by the operator.
~ The filter wheel arrangement accommodates a manual place-
:~ ment of both wheels to any position desired. Thus manual
~; means is provided for unlocking the solenoid operated pin
for each of the wheels, whereupon the wheels may be
; manually manipulated at the exposed region such as 1040a.
:
1075034
The ability for any operator to test a machine wide
strip by moving it either left to right or right to left
is desirable and is accommodated by the illustrated
arrangement.
By providing at least one open position in the reflec- -
tance filter wheel, such as a position 1207, it will be
apparent that the filter wheels 1040 and 1041 may provide
the seven reflectance measurements and the six transmit-
tance measurements with respect to the paper specimen 1002
in precise conformity with the corresponaing measurements
of the on-machine instrument. Reflectance and transmit-
. tance values could be obtained by the on-line computer
from simultaneous readings of the photocells 1030 and 1032, -~
or the readings could be taken separately. Since the
sensing head 1025 is conveniently removable, the ir.strument
of Fig. 1 can also measure thickpad reflectivities, Roo.
The basic design consideration is that the reflectivity
value determined on a thickpad would be in agreement with
' the established scale and that the thickpad reflectivity
''f 20 calculated from a reflectance and transmittance measurement
made on a single sheet would be in agreement with the direct--
ly measured value. To accompiish this objective, the four-
teen narrow-band filters 1108-1121 and 1208-1221 are employed - -
to obtain data permitting calculation of the thickpad reflectivity
through the weighted-ordinate integration approach. nlters of
identical kind could be introduced in the incident and r~ected
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1075~34
beam. Transmittance and reflectance measurements would be
performed with the open hole position such as 1207 in the
reflected beam and the filter disk 1040 located through its
various positions in the incident beam. The open hole 1107 in
5 the incident beam could then be used with filter disk rotation
- in the reflected beam. In this way, fluorescence appearing in
any part of the spectrum could be handled properly.
The scope of the program presently under way includes
construction of the instrument as shown in Figs. 1-3 and
testing of its operation to insure that it performs in
accordance with the basic objective predicting thickpad
reflectivity via the fourteen narrow-band filter and weighted
ordinate integration approach.
The results of a feasibility study conducted at The
Institute of Paper Chemistry in which an Automatic Colour-
Brightness Tester equipped with sixteen narrow-band filters was
` employed to obtain Ro and Roo values and the General Electric
Recording Spectrophotc1meter was employed to obtain transmittance data
indicate the success of this approach in calculating the thickpad
reflectivity compared to the directly measured values. This
work was conducted in connection with the related Application 55 170/74
(Canadian Serial No. 229,679~ and is set forth in the Appendix hereto.
Instead of transmitting light from the light source
through a series of narrow band filters such as the filters 1108-1121 and
1208-1221, it is possible to employ monochromatic or approxi-
mately monochromatic light, the frequency of which is varied
stepwise or is swept continuously between desired limits for
:1~';'5034
example those of the visible spectrum. Thus the light source
1010 can be replaced by a source of substantially monochromatic
light, the frequency of which can be varied over the desired
range in discrete steps or which can be swept over this range
without discontinuity, the variation being effected in either
case either manually or in a predetermined manner on initiation
of a preset programme. The cell output signal may be treated - - --
in the manner previously described.
Although the illustrated embodiment of the invention
employs two photocells, it is instead possible to employ only a
single cell to which both reflected and transmitted light from
the sheet materiaL is directed. The single cell can be arranged
to respond to light on the transmittance and reflectance light
paths, either or both of which can include light fibre optics,
in alternation. Instead of locating the cell receiving
reflected light on the same side of the sheet material as the
light source, both cells, or a single cell receiving both
transmitted and reflected light either alternately or in
combination, can be located on the other side from the light
20 source. Transmitted light is then made to impinge on a semi- -~
;reflecting window, so that the light reflected from the sheet
material is transmitted light reflected from the window and
re-reflected from the material.
It will thus be evident that the invention can be embodied
25 in a variety of ways other than as specifically described and illustrated -
within the scope, which is defined by the following claims.
~075034
APPENDIX
FEASIBILITY STUDY FOR THE DESIGN AND CONSTRUCTION OF
A LABORATORY INSTRU~ENT BASED OM TI~E PRINCIPLE OF OMOD
The ACBT equipped with the sixteen narrow-band filters
was used to obtain Ro and Roo values for six of Nekoosa
Edwards paper samples. Transmittance data for the same
specimens were obtained using the conventional GERS. Roo
values were calculated using the following formulas.
a = (1 + Ro2 - T2)/Ro
Roo = (a/2) -J(a/2)2 - 1
The values for R, Ro, Roo measured, Roo calculated values
are given in Table I. The data show reasonable agreement
between the measured and calculated Roo values. There are
several factors which contribute to the differences.
Fluorescence was not properly accounted for and some of the
samples do fluoresce, particularly Samples 18 and 29. The
samples were illuminated with a collimated beam whereas the
theoretical relationship is based on diffuse illumination and
diffuse viewing. The samples do change somewhat with handling
as a large number of readings must/be taken on each specimen.-
The same specimens were evaluated on filters No.- 6 and 21
after all the data were collected. The data given-in Table III
show that some changes occurred as a result of handling
during the many tests.
Tristimulus values were calculated from the Roo values
obtained from the T and Ro values using the weighting factors
given by the CIE system. These tristimulus values were then
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107S034
compared with the directly measured tristimulus values
obtained on the ACBT using the "tristimulus filters". The
data, given in Table II show good agreement for most of the
samples. Here again the same factors discussed earlier are
responsible for the differences. In addition, the broad-band
tristimulus functions of the ACBT no doubt differ slightly
from the theoretical functions. It appears that sample 29
(cherry bond) shows the largest discrepancy.
It appears feasible to design and construct an instrument
similar to OMOD but also equipped with narrow-band filters
which would give very nearly the correct tristimulus values
in either mode. Perhaps the reasons for the discrepancies
noted could be determined and further improvements made.
,
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Table I
Sample T Ro RINFM RINFC RINFM-RINFC
6-3 0.0940 0.61800.6250 0.6270 -0.0020
618 0.1070 0.47300.4740 0.4801' -0.0061
620 0.1150 0.55900.5700 0.5701 -0.0001
623 0.0420 0.44400.4450 0.4450 0.0000
629 0.0250 0.29400.2940 0.2942 -0.0002
:~ 630 0.0110 0.23300.2340 0.2330 0.0010
7-3 ' 0.1120 0.69200.7120 0.7095 0.0025
718 0.1270 0.76100.7880 0.7933 -0.0053
' 720 0.1350 0.59300.6100 0.6104 -0.0004
,. 723 0.0420 0.44400.4460 0.4450 0.0010
.~ 729 0.0280 0.31100.3110 0.3113 -0.0003
" 730 0.0090 0.219'00.2210 0.2190 0.0020
8-3 0.1350 0.72700.7580 0.7578 0.0002
' 818 0.1460 0.8200. 0.8740 0.8903 -0.0163
820 0.1500 0.6160 '0.6400 0.6398 0.0002
823 0.0490 0.46400.4660 0.4654 0.0006
' 829 0.0350 0.33000.3300 0.3305 -0.0005
, 20 830 0.'0120 0.23900.2400 0.2390 0.0010
9-3 0.1480 0.73700.7760 0.7768 -0.0008
918 0.1550 0.80500.8660 0.8765 -0.0105
920 0.1610 0.62400.6530 0.6525 0.0005
' 923 0.0630 0.49100.4940 0.4936 Ø0004
929 0.0240 0.2810 '0.2810 0.2812 -0.0002
: 930 0.0170 0.27000.2710 0.2701 0.00~9
, 10-3 0.1600 0.74600.7980 0.7962-0.0018
' 1018 0.1650 0.79800.8700 0.8778-0.0078
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~075~34
1020 0.1740 0.6380 0.6740 0.6738 0.0002
1023 0.1090 0.5820 0.5930 0.5928 0.0002
1029 0.0130 0.2090 0.2090 0.2090 -0.0000
1030 0.0430 0.3650 0.3690 0.3658 0.0032
511-3 0.1660 0.7520 0.8110 0.8089 0.0021
1118 0.1680 0.7950 0.8740 0.8766 -0.0026
` 1120 0.1750 0.6390 0.6750 0.6754 -0.0004
1123 0.1310 0.6260 0.6440 0.6445 -0.0005
1129 0.0090 0.1590 0.1590 0.1590 -0.0000
101130 0.0860 0.4700 0.4760 0.4745 0.0015
12-3 0.1680 0.7480 0.8090 0.8051 0.0039
1218 0.1730 0.7910 0.8760 0.8766 -Q.0006
1220 0.1670 0.6210 0.6510 0.6515 -0.0005
1223 0.1300 0.6170 0.6350 0.6346 0.0004
151229 0.0100 0.1400 0.1400 0.1400 -0.0000
1230 0.1220 0.5400 0.5530 0.5517 0.0013
` 13-3 0.1680 0.7420 0.8000 0.7971 0.0029
~ 1318 0.1740 0.7890 0.8760 0.8744 0.0016
-~ 1320 0.1520 0.5950 0.6170 0.6176 -Q.0006
~ 201323 0.1170 0.5920 0.6040 0.6049 -0.0009
j 1329 0.0110 0.1360 0.1360 0.1360 -0.0000
1330 0.1520 0.5960 0.6200 0.6186 0.0014
- 14-3 0.1700 0.7350 0.7900 0.7893 0.0007
.i 1418 0.1770 0.7880 0.8760 0.8769 -Q. OOQ0
251420 0.1280 0.5480 0.5600 0.5613 -0.0013
1423 0.0910- 0.5400 0.5470 0.5464 0.0006
1429 0.0160 0.1510 0.1510 0.1510 -0.0000
1430 0.1860 0.6450 0.6900 0.6878 0.0022
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1~75~34
Table I continued
Sample T Ro RINFM RINFC RINFM-RINFC
15-3 0.1680 0.7320 0.7870 0.78390.0031
1518 0.1800 0.7870 0.8780 0.8796--0.0016
1520 0.1000 0.5000 0.5060 0.5068-0.0008
1523 0.0690 0.4870 0.4900 0.4901-0.0001
1529 0.0470 0.3230 0.3250 0.32380.0012
1530 0.2290 0.7010 0.8000 0.79520.0048
16-3 0.1720 0.7330 0.7910 0.78820.0028
1618 0.1810 0.7880 0.8840 0.88320.0008
1620 0.0820 0.4560 0.4600 0.45990.0001
1623 0.0530 0.4370 0.4380 0.4385-0.0005
1629 0.1680 0.6070 0.6400 0.63630.0037
1630 0.2430 0.7220 0.8610 0.85320.0078
17-3 0.1770 0.7400 0.8080 0.80180.0062
1718 0.1840 0.7880 0.8920 0.88820.0038
1720 0.0680 0.4220 0.4240 0.4244-0.0004
1723 0.0410 0.3960 0.3960 0.3968-0.0008
1729 0.2400 0.7140 0.8240 0.8321-0.0081
1730 0.2470 0.7240 0.8790 0.86540.0136
18-3 0.1870 0.7480 0.8290 0.82280.0062
1818 0.1880 0.7900 0.9020 0.90010.0019
1820 0.0660 0.4170 0.4190 0.4192-0.0002
1823 0.0380 0.3880 0.3880 0.3887-0.0007
1829 0.2520 0.7300 0.8780 0.8928-0.0148
1830 0.2510 0.7240 0.8850 0.87390.0111
19-3 0.1950 0.7560 0.8530 0.84500.0080
;
~ -12-
lV75034
1918 0.1930 0.79000.9140 0.9111 0.0029
1920 0.0710 0.42300.4250 0.4256 -0.0006
1923 0.0410 0.3930-0.3940 0.3938 0.0002
1929 0.2580 0.73000.8980 0.9111 -0.0131
~; 5 1930 0.2550 0.72300.8900 0.8806 0.0094
20-3 0.2030 0.76400.8790 0.8715 0.0075
`` 2018 0.19~30 0.7930O.g270 0.9345 -0.0075
2020 0.0660 0.41100.4130 0.4132 -0.0002
2023 0.0400 0.38400.3840 0.3847 -0.0007
2029 0.2610 0.72800.9080 0.9142 -0.0062
2030 0.259~ 0.72400.8960 0.8940 0.0020
`~ 21-3 0.2110 0.76300.8960 0.8838 0.0122
, ,
` 2118 0.2020 0.78900.9340 0.9337 0.0003
`~ 2120 0.0900 0.46500.4770 0.4699 0.0071
2123 0.0560 0.44100.4480 0.4427 0.0053
`~.i 2129 0.2610 0.72400.9110 0.8999 0.0111
...~
,~ 2130 0.2600 0.71800.8980 0.8792 0.0188
~'`y T Transmittance measured with GERS
'r~ Ro Reflectance with black backing measured on the ACBT
~ 20 RINFM Reflectance of opaque pad measured on the ACBT
~;
RINFC Reflectance of opaque pad as calculated from Ro and T
RINFM-RINFC Difference between the measured and calculated
,,
Roo values
;:~ Sample The first number (6 through 21) designates the filter
~':-?
number. The last two characters designate the
' sample number.
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1~75034
Table II
X Y Z
Sample C M C M C M
3 17.7 77.9 79.6 79.3 90.4 90.6
18 86.5 86.3 88.0 87.6 102.4 102.5
49.3 50.0 55.1 52.2 76.4 76.3
23 45.0 45.3 52.8 52.9 59.7 59.9
29 52.2 50.9 34.2 31.5 33.0 31.8
71.1 69.9 68.5 68.2 34.0 33.9
C Values calculated from narrow-band filter data.
M Values determined using the "tristimulus filters".
Sample Description
3 Advantage offset wave 50 lb.
18 S-20 Nekoosa Bond
20S-20 Nekoosa Bond Blue
23 S-20 Nekoosa Bond Green
29 S-20 Nekoosa Bond Cherry
30S-20 Nekoosa Bond Buff -
:
Table III
Change in the Measured Roo Values with Handling for No. 6 and
21 Filters on the ACBT
No. 6 Filter (401 nm)
3 18 20 23 29_ 30
Start of test 0.625 0.474 0.570 0.445 0.294 0.234
End of test0.623 0.465 0.570 0.445 0.293 0.234
; No. 21 Filter (697 nm)
3 18 20 23 29 30
Start of test 0.896 0.934 0.477 0.448 0.911 0.898
End of test0.889 0.927 0.474 0.446 0.895 0.898
... . - . - , -, - .
