Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02891456 2015-05-12
DYNAMICALLY CALCULATED REFRACTIVE INDEX FOR DETERMINING
THE THICKNESS OF ROOFING MATERIALS
BACKGROUND
[0001] Asphalt shingles and asphalt roll roofing have been used extensively in
the roofing
industry. Asphalt shingles and asphalt roll roofing provide a durable and long
lasting roofing
material at an economical price. Numerous control processes exist for
manufacturing roofing
products that effectively control the manufacturing process.
SUMMARY
[0002] An embodiment of the present invention may therefore comprise a method
of controlling
the thickness of an asphalt roofing layer during manufacturing comprising:
measuring
temperature and density of the asphalt roofing layer; determining a refractive
index for the
asphalt roofing layer, that varies with density and temperature of the asphalt
roofing layer, using
empirical data; measuring time of flight of a light beam through the asphalt
roofing layer;
calculating the thickness of the asphalt roofing layer by multiplying the time
of flight by speed of
light divided by the refractive index to obtain a measured thickness;
comparing the measured
thickness of the asphalt roofing layer with a desired thickness to generate an
error signal; using
the error signal to generate a control signal in a controller; using the
control signal to control the
measured thickness of the asphalt roofing layer during manufacture of the
asphalt roofing layer.
[0003] An embodiment of the present invention may further comprise a method of
controlling
the thickness of an asphalt roofing layer during manufacturing comprising:
measuring
temperature and density of the asphalt roofing layer; determining a refractive
index for the
asphalt roofing layer, that varies with density and temperature of the asphalt
roofing layer, using
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empirical data; measuring time of flight of a light beam through the asphalt
roofing layer;
calculating the thickness of the asphalt roofing layer by multiplying the time
of flight by speed of
light divided by the refractive index to obtain a measured thickness;
calculating a target thickness
using a final desired thickness and a volumetric thermal expansion equation;
comparing the
measured thickness of the asphalt roofing layer with a target thickness to
generate an error
signal; using the error signal to generate a control signal in a controller;
using the control signal
to control the measured thickness of the asphalt roofing layer during
manufacture of the asphalt
roofing layer.
[0004] An embodiment of the present invention may further comprise a system
for controlling
the thickness of an asphalt layer comprising: a temperature gauge that
measures a temperature
value of the asphalt layer; a density gauge that measures a density value of
the asphalt layer; a
time domain spectrometer that measures time of flight of a light beam through
the asphalt layer
to obtain a time of flight value; a processor that calculates a refractive
index value for the asphalt
layer using the temperature value, the density value and the time of flight
value in a refractive
index equation derived from directly measured values of speed of light through
asphalt for
various filler percentages at various temperatures, and that calculates the
thickness of the asphalt
layer by multiplying the time of flight value by the speed of light divided by
the refractive index
value; a controller that compares the thickness of the asphalt layer with a
desired thickness to
generate an error signal, and generates a control signal, based upon the error
signal, that is used
to control the thickness of the asphalt layer during manufacturing of the
asphalt roofing layer.
100051 An embodiment of the present invention may further comprise a system
for controlling
the thickness of an asphalt layer comprising: a temperature gauge that
measures a temperature
value of the asphalt layer; a density gauge that measures a density value of
the asphalt layer; a
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time domain spectrometer that measures time of flight of a light beam through
the asphalt layer
to obtain a time of flight value; a processor that calculates a refractive
index value for the asphalt
layer using the temperature value, the density value and the time of flight
value in a refractive
index equation derived from directly measured values of speed of light through
asphalt for
various filler percentages at various temperatures, and that calculates the
thickness of the asphalt
layer by multiplying the time of flight value by the speed of light divided by
the refractive index
value to obtain a measured thickness of the asphalt layer, and that calculates
a target thickness
using a final desired thickness and a volumetric thermal expansion equation; a
controller that
compares the measured thickness of the asphalt layer with the target thickness
of the asphalt
layer to generate an error signal, and generates a control signal, based upon
the error signal, that
is used to control the thickness of the asphalt layer during manufacturing of
the asphalt roofing
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Figure 1 is a schematic block diagram of an asphalt roofing thickness
control system.
[0007] Figure 2 is a flow diagram illustrating the process for controlling
thickness of the asphalt
roofing during manufacturing.
[0008] Figure 3 is a graph illustrating the relationship between the final
product thickness and
the starting temperature of the asphalt.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0009] Figure 1 is a schematic block diagram of an asphalt roofing thickness
control system 100.
As illustrated in Figure 1, a substrate material 102 is supplied to a
coater/metering roll/scraper
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104. The substrate 102 may be a fiberglass substrate. Various other types of
substrate materials
can be used, including felt, or a similar material. The coater includes a
metering roll, in which a
metered amount of asphalt is applied to the top surface of the substrate 102.
In a second step, a
back coating is applied to the substrate, which coats the lower side of the
substrate, which is then
scraped by a scraper to obtain the desired thickness. The output of the coater
104 is the asphalt
roofing layer 106, that has a thickness determined by the metering roll and
scraper of the coater
104. The coating asphalt is supplied from a heated coating and heated
limestone mixer 132. A
density/temperature gauge 134 provides a density signal and a temperature
signal 108 that is
applied to the A/D converter. The filled coating 136 is then provided to the
coater/metering
roll/scraper 104. The coater 104 provides a metered amount of asphalt to the
top layer of the
substrate 102. The bottom layer of the substrate 102 is then coated with an
asphalt layer that is
scraped by a scraper to obtain the desired thickness of the bottom layer of
asphalt. The metered
amount of asphalt that is applied to the substrate 102, as well as the
position of the scraper,
determine the thickness of the asphalt roofing layer 106.
[0010] It is desirable to have a uniform and consistent thickness of the
asphalt roofing layer 106,
so that variations in the product are minimized. The variations in thickness
of the asphalt roofing
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CA 02891456 2015-05-12
layer 106 become apparent in the differences in the weight of packets of
asphalt shingles and
rolls of asphalt rolled roofing. A uniform and consistent product is desirable
in order to ensure
quality of the asphalt roofing layer 106. In order to ensure a uniform
thickness, a thickness
control signal 130, generated by controller 128, is applied to the coater 104
to control the process
of metering the asphalt on the top layer of the substrate and controlling the
position of the
scraper to control the thickness of the bottom layer of asphalt on the
substrate 102.
100111 The density/temperature gauge 134, illustrated in Figure 1, provides
both a temperature
and a density signal that are digitized by the converter 112. The density
signal provides a value
for the density of the filled coating 136 prior to entering the coater 104.
The filled coating 136
has a density that varies with temperature, as a result of thermal expansion.
A temperature
detector, such as an infrared sensor that is part of the density/temperature
gauge 134, measures
the temperature of the asphalt roofing layer 106. An infrared sensor, or other
temperature
sensing device, is located proximate to the time domain spectrometer 124. In
this manner, the
temperature of the filled coating 136 can be detected at a location proximate
to the time domain
spectrometer 124, so that the density/temperature signal 108, generated by the
density/temperature gauge 134, measures the temperature of the asphalt roofing
layer 106,
proximate to the time domain spectrometer 124.
100121 In one embodiment of the device illustrated in Figure 1, the time
domain spectrometer
124 may comprise a terahertz time domain spectrometer that measures the time
of flight of light
beam 120 reflected from the top surface of the asphalt roofing layer 106, and
light beam 122 that
reflect from the bottom surface of the asphalt roofing layer 106. The
difference in the time of
flight of the light beam 120 and light beam 122 can provide a very accurate
measurement of the
thickness of the asphalt roofing layer 106. The time of flight signal 126 is
transmitted to the
CA 02891456 2015-05-12
processor 118, together with the digital density signal 114 and digital
temperature signal 116.
The processor 118 calculates the thickness of the asphalt roofing layer 106
and transmits the
thickness data signal 126 to the controller 128. The processor 118 calculates
the expected
contraction of the asphalt roofing layer due to the effects of thermal
expansion and determines
the target thickness of the asphalt roofing layer at the point of application
to achieve the desired
final thickness of the asphalt roofing layer of the final product. The
controller 128 may be a
simple proportional controller, a proportional-integral controller, a
proportional-integral-
derivative controller, a boundary controller, or a Model Predictive
Controller. In that regard, the
thickness data signal 136 may constitute the process variable (PV), which is
compared to the set
point (SP), which is the desired thickness of the asphalt roofing layer at the
point of application
106. The thickness control signal 130 constitutes the manipulated variable
(MV), that is used to
control the coater 104 to obtain the desired thickness of the asphalt roofing
layer 106.
[0013] The time domain spectrometer 124 may constitute a terahertz probe,
which is available
from Advanced Photonix/Picometrix, Inc. (API) 2925 Boardwalk, Ann Arbor, MI
48104 and
Thermo Fisher Scientific, Inc., 2650 Crescent Drive, #100, Lafayette, CO
80026. The time of
flight signal 126 may constitute the time of flight of the light beam 122
through the asphalt
roofing layer 106. The time of flight of the light beam 122 through the
asphalt roofing layer 106
can be calculated as the difference between the time of flight of the light
beam 120 and light
beam 122. The processor 118 performs various tasks that are outlined in more
detail in Figure 2.
[0014] Figure 2 is a process 200 for controlling the thickness of an asphalt
roofing layer during
manufacturing. At step 202, the density of the asphalt roofing material is
measured, as well as
the temperature, by the density/temperature gauge 134. In other words, the
density is determined
at the temperature when the filled coating 136 is moved from the mixer 132 to
the
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coating/metering roll/scraper 104. At step 204, the temperature of the asphalt
roofing layer 106
is measured by the density/temperature detector 134 proximate to the location
of the time domain
spectrometer 124. This temperature signal is used to calculate the density of
the asphalt roofing
layer 106 at a location proximate to where the thickness of the asphalt
roofing layer 106 is
measured. The density/temperature signal 108 provides the density of the
filled coating 134 at a
first temperature. The density can then be recalculated in the processor 118
at the second
temperature 110 measured by the density/temperature detector 134 proximate to
the location
where the thickness of the asphalt roofing layer 106 is measured by the time
domain
spectrometer 124. In that manner, a more accurate measurement of thickness can
be provided
since a more accurate density value can be provided to the processor 118.
[0015] Referring again to Figure 2, at step 206, the AID converter 112
converts the
density/temperature signal 108 and the temperature signal 110 to a digital
density/temperature
signal 114 and a digital temperature signal 116. At step 208, the digital
density/temperature
signal 114 and the temperature signal 116 are sent to the processor 118. At
step 210, the time of
flight of the light beams 120, which reflects off the top surface of the
asphalt roofing layer 106,
and light beam 122, that reflects off the bottom surface of the asphalt
roofing layer, are detected.
Time domain spectrometer 124 then determines the difference in flight times,
which is indicative
of the flight time of the light beam 122 through the asphalt roofing layer
106. This time of flight
signal 126 is then transmitted to the processor 118. At step 212, the
processor 118 adjusts the
density of the asphalt roofing layer 106 based upon the temperature signal 108
and the
temperature signal 110 measured by density/temperature detector 134. Densities
of the filled
coating 136 can be measured empirically at various temperatures, so that the
density of the
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asphalt roofing layer 106 can be determined at the location of the
density/temperature detector
134 that is proximate to the time domain spectrometer 124.
[0016] As also illustrated in Figure 2, the refractive index of the asphalt
roofing layer 106 is
determined at step 214. The refractive index is determined by summing various
factors. The
first factor is the filler coating factor, which is the percent contribution
to the refractive index of
the filler, which is the ratio of limestone to coating in the filled coating.
As the ratio of limestone
to coating increases, the propagation speed of light decreases. In other
words, as the density
increases, the speed of light decreases. The second factor is the temperature
factor, which is the
contribution of the temperature of the filled coating to the refractive index.
As the temperature
of the filled coating decreases, the filled coating undergoes thermal
contraction, which increases
density and decreases the propagation speed of light through the filled
coating. The third factor
is the intercept value, which is a constant value applied to the refractive
index to account for an
increase in the propagation speed of light through the filled coating, by a
constant amount,
regardless of the ratio of limestone to coating and temperature. Propagation
data points for the
speed of light through an asphalt layer can be obtained for a variety of
different filler factors and
temperatures. These data points can be obtained using an External Reference
Structure (ERS) so
that the speed of light propagated through the asphalt layer can be directly
measured. These data
points are then used to generate a refractive index equation using regression
analysis or a least
squares analysis technique, or a combination of the two. The equation includes
an intercept
value, a variable filler factor and a variable temperature factor that is
multiplied by the
temperature of the asphalt layer. The filler factor varies the propagation
speed of light in the
asphalt layer as a function of the percentage of filler in the filled coating
136. The greater the
percentage of filler, the slower the propagation speed. The temperature factor
varies the
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propagation speed of light in the asphalt layer as a function of the
temperature. The higher the
temperature, the faster the propagation speed. The filler factor is multiplied
by the percentage of
filler and the temperature factor is multiplied by the temperature of the
asphalt roofing layer 106
to obtain refractive index values for these factors. These values, plus the
intercept value, are
added together to obtain a refractive index number. The refractive index
equation is given
below:
RI = (Filler factor) (% of Filler) + (Temp Factor) (Temperature) + Intercept
Value Eq. (1)
[0017] At step 216 of Figure 2, the measured thickness of the asphalt layer is
determined by
multiplying the time of flight signal 126, which is the difference between the
time of flight of
light beam 120 and light beam 122, by the speed of light. That product is then
divided by the
refractive index. In other words, the following equation is used to generate a
thickness number:
Thickness = (time of flight)*(speed of light/refractive index)
Equation (2)
[0018] At step 218 of Figure 2, the target thickness of the asphalt roofing
layer at the point of
application is determined in order to achieve a desired final product
thickness. The target
thickness of the asphalt roofing layer at the point of application is
calculated by taking the
temperature measurement from an infrared sensor in the density/temperature
detector 134, and
calculating the expected contraction of the material from the temperature of
the asphalt at the
point of the asphalt application to the asphalt roofing layer thickness in the
final product at room
temperature using equation (3).
Change in Volume = (initial volume) * (Volumetric coefficient of thermal
expansion)
*(final temperature ¨ initial temperature)
Equation (3)
[0019] Utilizing the Volumetric Thermal Expansion Equation (Equation 3), the
required target
thickness of the asphalt roofing layer that is required to achieve the desired
final product
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thickness of the asphalt roofing layer is calculated based upon the volumetric
coefficient of
thermal expansion for the current filler percentage or density value as
measured by the density
gauge in the density/temperature detector 134 and the initial temperature at
the point of
application as measured by the infrared sensor in the density/temperature
detector 134. The
Volumetric coefficient of thermal expansion for filled coating can be obtained
for different filler
percentages by utilizing a time domain spectrometer 124, an infrared sensor,
and an external
reference structure (ERS) capable of holding liquid samples. The asphalt
samples at different
filler percentages are placed in an external reference structure and
convectively cooled to room
temperature while continuously measuring the volume and temperature of the
sample throughout
the entire temperature range of interest. These data points are used to
calculate the volumetric
coefficient of thermal expansion at different filler percentages. Setting the
target thickness of the
asphalt roofing layer at the point of asphalt application to account for the
expected changes in
thickness due to the thermal contraction of the material adjusts for the
impact of varying starting
temperature conditions of the filled coating as seen in Figure 3.
[0020] The target thickness data signal 136 determined by Equation (1), is
then sent to the
controller 128 as the process variable (PV) at step 218. The controller 128
compares the target
thickness data signal 136 with a desired target thickness 138 and generates an
error signal that is
processed by the controller 128, in a PID controller, PI controller, a simple
proportional
controller, or any desired type of controller known in the art. A manipulated
variable signal is
then generated by the controller 128 as the thickness control signal 130 at
step 220. The
thickness control signal 130 is then applied to the coater 104 to control the
thickness of the
asphalt roofing layer 106. These processes are performed by the controller
128, in accordance
with standard control methods.
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[0021] Figure 3 is a graph 300 that illustrates a final product thickness in
relationship to the
starting temperatures of the asphalt. As shown in Figure 3, the temperature
value is plotted on
the x axis of the graph 300, while the thickness value is plotted on the y
ordinate. As illustrated
in the graph 300, a final product thickness 304 of the asphalt layer at room
temperature
corresponds to thickness of the asphalt layer at a first starting temperature
306. In comparison, a
final product thickness 302 of the asphalt layer corresponds to a thickness at
a second starting
temperature 308 of the asphalt layer. As can be seen from Figure 3, the
starting temperature has
a proportional linear relationship to the final product thickness at room
temperature.
Accordingly, to obtain a desired final product thickness, a target thickness
at a particular starting
temperature must be used. Since there is a linear relationship between the
thickness and the
starting temperature and the thickness at room temperature, the measured
thickness for any
particular starting temperature can be adjusted to obtain the final product
thickness at room
temperature. Accordingly, the thickness control signal 130 can be adjusted to
adjust the coater
104 by using the desired final product thickness, the temperature and the
volumetric thermal
expansion equation that is illustrated in Figure 3.
[0022] Accordingly, embodiments are disclosed that can measure the thickness
of an asphalt
roofing layer 106 during the manufacturing process using time of flight data
and a refractive
index value that is representative of the speed of propagation of light
through the asphalt roofing
layer 106 using both temperature and density data. A thickness control signal
is generated by the
controller 128 to control the coating and scraping process for creating the
asphalt roofing layer
106 that has an accurate and consistent thickness.
[0023] The foregoing description of the invention has been presented for
purposes of illustration
and description. It is not intended to be exhaustive or to limit the invention
to the precise form
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disclosed, and other modifications and variations may be possible in light of
the above teachings.
The embodiment was chosen and described in order to best explain the
principles of the
invention and its practical application to thereby enable others skilled in
the art to best utilize the
invention in various embodiments and various modifications as are suited to
the particular use
contemplated. It is intended that the appended claims be construed to include
other alternative
embodiments of the invention except insofar as limited by the prior art.
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