Note: Descriptions are shown in the official language in which they were submitted.
CA 02553906 1997-10-15
_.
APPARATUS AND RELATED METHODS FOR
AUTOMATICALLY TESTING AND ANALYZING TIRES
This application is a Divisional of Application Ser. No. 2,218,352 filed
October 15, 1997.
TECHNICAL FIELD
The invention herein resides in the art of techniques and apparatus for
testing
pneumatic tires. More particularly, the invention relates to such methods and
apparatus
for performing both tire foot print tests and load-deflection tests, wherein
the data
collected from these tests is presented in several different formats.
Specifically, the
invention relates to such methods and apparatus for analyzing a tire by either
capturing
a digital image of the tire foot print or by extrapolating load-.deflection
.cuzves of .the
tire.
BACKGROUND ART
In the manufacture of pneumatic tires, it is well known that many
characteristics
or features of a tire may impact its performance, wear, noise generation and
the like.
Various types of tests and analyses have been performed on tires to evaluate
the
aforementioned characteristics and features of the tire. For example, some
tests monitor
the actual physical operation of the tire as upon a rotating drum or the like.
Analytical
testing of external and cross-sectional features of the tire have also been
undertaken.
It is also known to analyze the contact patch or foot print of the tire as it
makes contact
with the road or loading surface to determine therefrom various structural and
operational, characteristics thereof. It is also known that load-deflection
testing provides
an indication of tire structural performance. It will be appreciated that in
designing a
pneumatic tire, numerous tests are undertaken prior to production of the tire
to ensure
a high quality performance tire. As such, a significant portion of the tire
development
design phase is devoted to testing and analyzing the new design.
One example of foot print testing is disclosed in United States Patent No.
5,347,588, entitled "Method And Apparatus For Video Imaging Of Tire Ground
Contact
Patch." This patent discloses an apparatus which employs video imaging of a
tire foot
print. The video image is filtered in such a manner that all of the picture
elements or
pixels are assigned either a black pixel value or a white pixel value. The
pixel values
are then employed to derive the total foot print area, the foot print contact
area and the
foot print void area. Additionally, other features, such as a contour or
outline of the
CA 02553906 1997-10-15
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foot print image, can be derived.
Another example of tire testing is disclosed in United States Patent No.
5,357,799,
entitled "Method And Apparatus For Determining Abrasion Potential Of Tire
Treads."
This patent discloses an apparatus and technique for determining the abrasion
potential
of tire treads by capturing a video image of a tire as it is placed under a
radial load.
A plurality of markers are placed on the tire and a video image is generated
as the tire
is loaded and rotated between angular positions. The markers provide an
indication of
the frictional movement at the interface between the tire and support surface
which
corresponds to an indication of the propensity of the tire to wear. As in the
previous
disclosure, this disclosure employs a filtered video image to distinguish
contact pressure
and movement of the tire.
Tire testing machines are also known to generate load-deflection curves which
are
useful in predicting tire performance. As is well known, a load-deflection
curve
indicates how much a tire is deflected under a given load at a given inflation
pressure.
Prior art machines require that test data must be generated for five or more
inflation
pressures. Generating this load-deflection data is a time-consuming process
that extends
the time and cost of testing a tire.
Although the aforementioned inventions and tests are effective in
accomplishing
their desired objectives, it will be appreciated that these machines and other
similar
machines are usually only limited to performing one type of test on the tire.
Moreover,
these machines with video imaging capability do not fully utilize the video
image of the
foot print. Nor do any known machines additionally provide means for
extrapolating
load-deflection curves from at least two previously-generated load-deflection
curves.
Another consideration in testing tires is to determine what result imparting a
camber to
the tire has on the tire foot print and the load-deflective curves. By
imparting a camber
or tilt to the tire during loading, data regarding tire cornering capabilities
and wear can
be derived. Prior testing machines employed shims or other such rudimentary
devices
on or near the tire mounting fixture. These methods have been found to be
labor
intensive and difficult to control for the accurate testing of tires.
Based upon the foregoing, there is a need in the art to provide an apparatus
which
performs a plurality of tests on tires at different repeatable camber angles
at one station.
Moreover, there is a need in the art for a machine which assists in providing
quick and
accurate information in the tire design phase, thereby bringing new tires to
the market
CA 02553906 1997-10-15
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quicker and at much less cost.
DISCLOSURE OF INVENTION
In light of the foregoing, it is a first aspect of the present invention to
provide an
apparatus and related methods for performing a plurality of tests on tires.
Another aspect of the present invention is to provide an apparatus which
includes
a frame that slidably receives a test pod that is coupled with the tire to
perform a
plurality of tests.
Still a further aspect of the present invention, as set forth above, is to
provide a
tire spindle with the necessary mechanical linkage to impart a' camber upon
the tire
during testing.
Still yet another aspect of the present invention, as set forth above, is to
provide
a motor connected to the tire spindle to selectively rotate the tire into
various testing
positions.
An additional aspect of the present invention, as set forth above, is to
provide a
load plate connected to the tire spindle to couple the tire to the test pod.
Still yet another aspect of the present invention, as set forth above, is to
provide
a load cell connected to the load plate to determine the amount of radial load
imparted
on the tire coupled to the test pod.
Yet a further aspect of the present invention, as set forth above, is to
provide a
deflection cell that monitors the amount of deflection of the tire as a load
is imparted
thereon.
Still yet another aspect of the present invention, as set forth above, is to
provide
an inflation pressure source connected to the tire so that a plurality of
inflation pressures
can be provided to the dre as it is coupled to the test pod.
Another aspect of the present invention, as set forth above, is to provide a
processor which controls the various aforementioned components of the
apparatus.
Still another aspect of the present invention, as set forth above, is to
provide the
test pod with a transparent plate and a cover plate slidable thereover,
wherein the
transparent plate is employed to obtain foot print test data and the slidable
cover pla!P
is employed to obtain load-deflection data.
Still yet another aspect of the present invention, as set forth above, is to
provide
a camera. within the test pod to capture a digital image of the tire coupled
to the
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transparent plate.
An even further aspect of the present invention, as set forth above, is
wherein the
processor performs various tests on the digital image obtained by the camera-
Yet a further aspect of the present invention, as set forth above, is wherein
the
processor converts the digital image into a gray-scale image and employs a
calibration
operation to correlate the gray values to contact pressure values.
Still a further aspect of the present invention, as set forth above, is
wherein the
processor extrapolates load-deflection curves from at least two load-
deflection curves
generated when the tire is coupled to the test pod.
The foregoing and other aspects of the invention which shall become apparent
as
the detailed description proceeds are achieved by an apparatus for testing
tires,
comprising: a frame; a loading plate mounted within the frame; a tire spindle
extending
from the loading plate, the tire spindle rotatably receiving a tire to be
tested; a test pod;
and a processor for controlling the operation of the loading plate to couple
the tire with
the test pod, the processor connected to the test pod, wherein the processor
and the test
pod perform a plurality of tests on the tire.
Another aspect of the invention which will become apparent herein is obtained
by
an apparatus for testing tires, comprising: a frame having a pair of opposed
slide tracks;
a loading plate mounted within the frame; a tire spindle pivotably extending
from the
loading plate, the tire spindle receiving a tire to be tested; and a test pod
slidably
received on the pair of opposed slide tracks, the loading plate coupling the
tire to the
test pod to generate tire test data.
Other aspects of the invention which will become apparent herein are obtained
by
a method for generating a tire foot print, comprising the steps of: providing
a frame
which receives a loading plate from which extends a tire spindle that receives
a tire;
coupling the tire to a transparent plate at a predetermined load level;
capturing a gray-
scale image of the tire with a camera positioned underneath the transparent
plate, the
gray-scale image including an array of pixels, wherein each pixel in the array
of pixels
is assigned a gray level value; assigning a trial calibration factor;
computing a trial load
value with the predetermined load level, the gray level values and the trial
calibration
factor; computing an actual calibration factor with the trial calibration
factor, the
predetermined load level and the trial load level; and computing a corrected
pixel
pressure value for each pixel with the actual calibration factor.
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Still other aspects of the invention which shall become apparent herein are
obtained by a method for generating a plurality of load deflection curves,
comprising
the steps of: providing a frame which receives a loading plate from which
extends a tire
spindle that receives a tire; inflating the tire to a first predetermined
inflation pressure
value; deflecting the tire onto a cover plate to a predetermined load level;
measuring a
first deflection vs. load curve of the tire; unloading the tire from the
plate; inflating the
tire to a second predetermined inflation pressure value; deflecting the tire
onto the cover
plate to another predetermined load level; measuring a second deflection vs.
load curve
of the tire; and extrapolating deflection amounts of the tire at other
inflation pressure
values from the first and second deflection vs. load values.
BRIEF DESCRIPTION OF THE DRAWINGS
For a complete understanding of the objects, techniques and structure of the
invention, reference should be made to the following detailed description and
the
accompanying drawings wherein:
Fig. 1 is a schematic front view of the apparatus of the invention;
Fig. 2 is a schematic side view of the apparatus of the invention;
Fig. 3 is a partial cross-sectional view of a load plate and a tire spindle
which
carries a tire and the mechanism for imparting a camber thereto;
Fig. 4 is a flow chart showing the calibration of the gray-scale image
generated
by a camera enclosed in a test pod carried by the apparatus;
Fig. S is a graphical representation of a trial calibration factor and an
actual
calibration factor;
Fig. 6 is a flow chart showing the extrapolation of load-deflection curves
from
load-deflection curves generated by the test pod; and
Fig. 7 is a graphical representation of a plurality of load-deflation curves.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to the drawings and more particularly to Figs. 1 and 2, it can
be
seen that an apparatus for automatically testing and analyzing tires is
designated
generally by the numeral 10. As shown schematically, a pneumatic tire 11 is
carried
by the apparatus 10 for providing at least a foot print image and load-
deflection curves
of the tire 11 which are employed to analyze the performance wear
characteristics
CA 02553906 1997-10-15
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thereof. The tire 11 is carried by a frame 12 which includes a plurality of
posts 14 that
are vertically oriented and supported by a ground surface. A plurality of
cross-pieces
16, which are horizontally oriented, interconnect the top of the posts 14. A
pair of side
bars 18 interconnect the posts 14 from front to back. Of course, other cross-
pieces and
S bars may be included to structurally stabilize the frame 12. It will be
appreciated that
various components carried by the frame 12 are actuated and moved by a
hydraulic
control system 24. Of course, other actuatable control mechanisms may be
employed
to move components carried by the frame. In a similar manner, a processor 28
is
connected to the hydraulic control system 24 and various data-gathering
instruments
carried by the frame 12. Those skilled in the art will appreciate that the
processor 28
contains the necessary hardware, software and memory to control the operation
of the
apparatus 10 and to perform at least the tests performed on the tire 11 which
will be
discussed hereinbelow. Where appropriate, letter designations indicate the
connection
of the processor 28 to the appropriate component carried by the frame 12. A
keyboard
30 is connected to the processor 28 and provides the necessary communication
between
an operator and the apparatus 10.
A hydraulic lift 32, which is connected to the hydraulic control system 24, is
disposed below the ground surface. A lift plate 34, which is connected to the
hydraulic
lift 32, is normally provided at the same level as the ground surface. The
lift plate 34
moves the tire 11 from a ground surface position to a position where it can be
loaded
onto the frame 12. Of course, other means may be employed to lift the tire 11
from the
ground surface into the frame 12.
A pair of opposed slide tracks 40 extend from the side bars 18 to carry a test
pod
42. It will be appreciated that the test pod 42 is moved upon the slide tracks
40 by the
hydraulic control system 24 and is also connected to the processor 28 for
sending test
data thereto. The test pod 42 includes a housing 44 from which extends a pair
of rails
46 that ride on the slide tracks 40. As best seen in Fig. 2, the' test pod 42
is movable
toward the rear of the apparatus 10 a sufficient distance to allow clearance
of the lift
plate 34 when the tire 11 is to be loaded onto the frame 12. I<Jpon completion
of the
loading of the tire 11 onto the frame 12, the test pod 42 is moved into a
position
underneath the tire 11. A pair of housing tracks 48 are disposed at the top
lateral edges
of the housing 44. A transparent plate SO is carried by the housing 44 and is
disposed
between the housing tracks 48. Although the transparent plate SO can be made
of any
CA 02553906 1997-10-15
_ 7 _
optically clear material, in the preferred embodiment the transparent plate 50
is made
of glass. A cover plate 52, which is connected to a pneumatic control system
(not
shown), is received upon the housing tracks 48 and is . movable to slide over
the
transparent plate 50 when desired. A pair of lights 54 are disposed near the
lateral
edges of the transparent plate 50 to provide a substantially constant
illumination thereof.
A pair of light sensors 56 are disposed near corresponding light sources 54
and are
connected to a voltage regulator (not shown) to power the lights and maintain
a desired
illumination level. Those skilled in the art will appreciate that the light
sensors 56
provide a feedback to the voltage regulator so that whenever the illumination
level of
the light sources 54 changes, appropriate corrective action is taken. This
ensures that
the foot print testing, to be described hereinbelow, is properly performed.
The housing 44 includes a minor 58 which is disposed underneath the
transparent
plate 50 and is disposed at about a 45° angle. The minor 58 reflects an
image of the
tire 11, which is coupled to the transparent plate 50, to a camera 60 which is
connected
to the processor 28. In the preferred embodiment, the camera 60 is a charge
coupled
device which provides an array of picture elements or pixels in a 640 x 480
array. The
camera 60 generates a gray-scale image wherein each pixel represents a
corresponding
area of the dre foot print. The processor 28 receives for each pixel, an
intensity value
between gray levels of 0 (darkest) and 255 (brightest). This two-dimensional
array of
intensity values is stored in an image data file in the processor 28. Those
skilled in the
art will appreciate that a frame grabber board (not shown) is connected
between the
camera 60 and the processor 28 so that the proper image of the tire foot print
is stored.
The minor 58 is employed to maximize the field of view of the camera 60. In
other
words, the structure of the housing 48 can be made more compact by employing
the
minor 58 to transfer an image to the camera 60. It will also be appreciated
that the
camera 60 may include more than one camera to obtain the necessary field of
view. For
example, one camera, which has a 9" x 12" field of view, is typically used to
generate
an image of a regular passenger tire. Alternatively, a wide-view camera, which
can
capture a 16" x 20" field of view, may be employed tv capture images of race
tires.
A camera mount 62 may carry either or both of the cameras 60 mentioned above.
The
camera mount 62 is movable in at least two axes to allow adjustment in the
viewing
angle of the cameras. Movement of the camera 60 facilitates finding the center
of the
foot print image.
CA 02553906 1997-10-15
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To facilitate the generation of a gray-scale image of the tire foot print, a
reflective
paper 64, such as a photographic backing paper, or other medium is disposed on
the
transparent plate 50 prior to coupling the tire 11 thereto. Those skilled in
the art will
appreciate that the medium 64 functions as a reflective surface which provides
for the
generation of internal reflection light when a force is applied to the
transparent plate 50.
In particular, the foot print of the tire 11 is apparent through the internal
reflection light
generated when the tire 11 is forcefully loaded upon the reflective paper 64
against the
illuminated transparent plate 50. If desired, a video cassette recorder (not
shown) may
be connected to the camera 60 for storage of the foot print image for later
analysis.
Referring now to Figs. 1 through 3, a loading plate 70 is slidable on a pair
of
guide bars 71 that extend downwardly from the cross-piece 16. The loading
plate 70
can provide a load force of up to about 5000 pounds and has at least a 22-inch
range of
motion. The loading plate has a front side 72 which faces the tire 11 and a
rear side
74 which opposes the front side 72. A piston mount 76 extends from the front
side ?2
and interconnects the load plate 70 to a load piston 78. The load piston 78 is
actuated
by the hydraulic control system 24. A load cell 80, which is connected to the
processor
28, is positioned on the load piston 78 to accurately provide data which
indicates the
amount of load applied to the tire 11. The loading plate 70 includes a notch
84 near the
bottom thereof. A pair of opposed camber mounts 86 extend from the front side
72
with the notch 84 therebetween. A bushing 88 is provided in each of the camber
mounts
86. A spindle housing 90 is carried by the camber mounts 86 and is received
within the
notch 84. A pair of camber pins 92 extend outwardly from the spindle housing
90 and
are correspondingly received in each of the bushings 88 and pivot thereabout.
A spindle
94 is rotatably received in the spindle housing 90. A tire mount 96 is located
at one end
of the spindle 94 and receives the tire 11. A chuck 98 secures the tire 11 to
the tire
mount 96 during testing. A deflection cell 99 is coupled to the loading plate
70 in a
manner well known in the art to measure the amount of deflection thereof
during
loading. An encoder 100, which is connected to the r.roces~or 28, is also
coupled to the
spindle 94 for monitoring the rotation thereof. A drive assembly i02, which is
connected to an electric motor 104, is mounted on the spindle housing 90 and
is
connected to the spindle 94 to control the rotation thereof. The motor 104 may
be
actuated by the hydraulic control system 24 or other electric power source.
A housing mount 106 extends from the spindle housing 90 and is connoted to a
CA 02553906 1997-10-15
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turnbuckle 108 which is connected at its opposite end to a plate mount 110
which
extends from the rear side 74 of the loading plate 70. The turnbuckle 108
includes a
threaded rod 112 which has a plurality of left-hand threads 114 at the end
near the platc
mount 110 and a plurality of right-hand threads 116 at the end of the threaded
rod 112
near the housing mount 106. A hex member 118 is disposed between the left-hand
threads 114 and the right-hand threads 116 and is connected to a ratchet 120.
A lock
nut 122 is disposed on the left-hand threads 114 while a lock nut 124 is
.disposed on the
right-hand threads 116. A reversing knob 126 is disposed at the end of the
ratchet 120
opposite the hex member 118. Those skilled in the art will appreciate that the
lock nuts
122 and 124 are loosened and the ratchet 120 is pivoted to expand or retract
the
turnbuckle 108 between the plate mount 110 and the housing mount 106.
Accordingly,
as the ratchet 120 is pivoted or stroked, a camber is imparted on the spindle
94. 'This
allows the tire 11 mounted to the spindle 94 to have a camber imparted
thereto. An
angle inclinometer 128 may be coupled to the motor 104, ~ spindle housing 90
or
connected attachments to determine the amount of camber imparted by the
ratchet 120.
These angle readings may be provided to the processor 28. Upon attaining the
desired
camber angle, the lock nuts 1Z2 and 124 are tightened to hold the spindle
housing 90
in place. In the preferred embodiment, the turnbuckle 108 and associated
linkage can
impart a range of dre camber angles of about +1-6°. It will be
appreciated that
different camber angles generate different tire foot prints when the tire 11
is coupled to
the transparent plate 50. Moreover, these different tire foot print test
patterns can
provide insight into how the tire may perform during use, such as in wear.
A pressurized air supply 130 is connected to the processor 28. A flexible hose
132 is connected between the pressurized air supply 130 and the tire 11 to
provide a
monitored air pressure to the tire. As will be described in further detail,
the tire 11 is
inflated by the pressurized air supply 130 to obtain the load-deflection
curves.
In use, the tire 11 is rolled onto the lift plate 34, whereupon the hydraulic
lift 32
positions the tire 11 so that it can be easily positioned onto the tire mount
96. The
operator then tightens the chuck 98 onto the tire mount 96 to secure the tire
i 1 to the
spindle 94. The lift plate 34 is retracted to the ground surface and the test
pod 42 is
positioned underneath the tire 11.
To perform the foot print testing on the tire 11, the cover plate 52 is
retracted on
the housing tracks 48 to expose the transparent plate 50 to the tire 11. The
light sources
CA 02553906 1997-10-15
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54 within the housing 44 are illuminated and the medium 64 is placed over the
transparent plate 50. The tire 11 is inflated to a predetermined pressure by
the air
supply 130, whereupon the loading plate 70 is lowered tv couple the tire 11 to
the test
pod 42. Upon loading, the camera 60 captures a gray-scale digital image of the
tire foot
print imparted on the medium 64. This tire foot print image is captured by the
processor 28, whereupon the testing analysis is performed. If desired, prior
to the
loading of the tire 11 onto the transparent plate 50, the spindle horsing 90
may be
imparted with a desired camber angle as described above. Once the foot print
image
of the tire 11 is obtained, the loading plate 70 lifts the spindle housing 90.
If desired,
the motor 104 engages the drive assembly 102 and rotates the spindle 94 a
predetermined amount. Typically, the tire 11 is rotated in about 120°
increments to
obtain three tire foot prints from a single tire. Upon completion of the
rotation of the
tire 11, the loading plate 70 is re-coupled with the test pod 42.
When it is desired to perform load-deflection testing on the tire 11, the
processor
28 and the hydraulic control system 24 position the cover plate 52 over the
transparent
plate S0. The loading plate 70 is lowered and the tire 11 is coupled to the
test pod 42.
Once the tire 11 is coupled to the test pod at a minimal load value of about
250 pounds,
the deflection cell 99 measures the deflection of the tire 11 and transmits
this data to the
processor 28. Afterwards, the processor instructs the loading plate 70 to step
through
various increments of radial load forces and measures the corresponding
deflection
measurements provided by the deflection cell 99. Upon reaching a maximum load
level,
the processor 28 instructs the hydraulic control system 24 to release the
loading plate
70 and the tire is de-coupled from the test pod 42. At this time, the
processor 28
increases the tire inflation pressure and the above deflection data is
collected for that
particular inflation pressure.
From the foregoing description of the operation of the apparatus 10, it will
be
appreciated that the data collected from the foot print testing and the load-
deflection
testing can be used to provide various testing analyses. For example, a foot
print shape
analysis can be generated to automatically analyze several geometric
attributes of the tire
foot print. The gray-scale image generated by the camera 60 is analyzed to
determine
the foot print contact area, the void area (non-contacting area within the
foot print
perimeter), foot print width and foot print length at various locations across
the foot
print. These parameters are used in evaluating tire performance with respect
to wet and
~
CA 02553906 1997-10-15
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dry traction, tread wear and handling. The gray-scale image can also be
manipulated
to provide a foot print pressure mapping. The processor 28 converts the gray
level
intensity values over the foot print to contact pressure values. This yields a
high spatial
resolution of 640 x 480 pressure sensitive locations to map the foot print
pressure
distributions. This pressure data may be converted to a colorized display
"map"
showing contact pressure changes as color variations in a computer-generated
picture of
the foot print. The foot print pressure mapping can then be utilized to
identify locations
of non-uniformities or pressure disturbances that can impact tire wear, ride
or handling
properties. The foot print pressure map can be further analyzed for pressure
variations
(gradients) across lugs and ribs of the tire that specifically correlate to
irregular wear
performance. This analysis is beneficial because of the high spatial
resolution and
instantaneous data collection attributes provided by the apparatus 10. This
feature is
advantageous over the prior art in that traditional pressure measurement
methods utilized
a pressure probe imbedded in the ground and required multiple tire loadings to
sample
numerous locations of the foot print which were ill-suited to calculate
pressure gradient
values.
By employing the cover plate 52 in the testing of the tire 11, radial load-
deflection
curves can also be derived. By employing an automated process, only two
deflection-
curve readings are required to forecast other load-deflection curves at other
inflation
ZO pressures. This data can then be employed to determine a tire radial
stiffness which is
employed to evaluate tire dynamic and vibrational behavior.
It should now be readily apparent that the apparatus and methods just
described
are capable of obtaining foot print image data and load-deflection data to
improve the
accuracy and evaluation of a tire during its design phase.
With reference now to Figs. 4 and S, it can be seen that the method of
obtaining
useful gray-scale images from a tire 11 is designated generally by the numeral
150. As
shown, a first step 152 requires that the tire 11 be loaded onto the apparatus
10 and in
particular the spindle 94. At step 154, the loading plate ?0 couples the tire
11 to the
transparent plate 50 with the medium 64 disposed therebetrveen, whereupon the
processor 28 records the actual load value imparted thereby for designation as
LOAD~~,.VAL~ At step 156, the camera 60 grabs the foot print image of the tire
11 and
transfers this gray-scale image to the processor 28. The processor 28, at step
158,
assigns gray level value corrections to each pixel within the foot print image
to
CA 02553906 1997-10-15
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compensate for uneven background lighting. In other words, light intensity
from the
lights 54 is not the same intensity at the center of the plate 50 as at the
edges of the
plate. A predetermined spatial correction factor adjusts each pixel gray level
value
based upon pixel location with respect to the light intensity to ensure the
accuracy of the
pressure mapping. The processor 28, at step 160, assigns an arbitrary trial
value for
the calibration factor (CF,.R,~~ to compute pressure values from the gray
level pixel
values. As seen in Fig. 5, there is a corresponding relationship between the
gray level
values and the pressure values. In other words, the CFTK,,,L value is
multiplied by the
gray value of each pixel to compute a pressure value at each pixel location,
as
designated in step 162. At step 164, these gray level pressure values are
summed over
the entire foot print area to derive a LOAD,.,~,r value. At step 166, the
processor 28
computes an actual calibration factor value (CFA~A~ by multiplying CR,.,~"L
times
(LOAD"~.uA~~(LOADT,~~. At step 168, the processor 28 re-computes the pressure
value at each pixel location by multiplying CFA~",r times the gray level value
of each
pixel in the foot print image. This corrected pressure data is then written to
the memory
within the processor 28 at step 170. The procedure eliminates the need for an
independent calibration test to determine CFp~,."AL each time the reflective
paper 64 is
replaced on the transparent plate 50, thereby saving substantial time and
costs. As seen
in Figs. 4 and 5, steps 160-168 generate a linear relation between pressure
and gray
level. Such a relation has been demonstrated for pressure ranges found in
passenger and
light truck tires, as well as race tires. As discussed previously, these
contact pressure
values associated with each pixel are employed in the foot print shape
analysis, the foot
print pressure mapping and the pressure gradient analysis. Upon collection of
the data
from a single foot print, the apparatus 10 then rotates the tire 11 to a
different position
on the tire to collect similar data. This data can then be stored and reviewed
at a later
time to assist in the design process.
With reference now to Figs. 6 and 7, it can be seen that a method of obtaining
load-deflection data from a tire is designated generally by the numeral 200.
As shown.
a first step 202 requires that the tire 11 be loaded onto the frame i2 in a
manner
described above. The tire 11 is then inflated by the pressurized air supply
130 to a first
inflation pressure at step 204. The loading plate 70, at step 206, couples the
tire 11 to
the cover plate 52 at predetermined load increments. At step 208, the
processor 28
records deflection values from the deflection cell 99 that are associated with
the
CA 02553906 1997-10-15
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predetermined load increments. At step 210, the processor 2$ releases the
loading plate
70. A1 step 212, the processor 28 instructs the pressurized air supply 130 to
increase
the pressure within the tire to a second inflation pressure. At step 214, the
loatiing plate
70 re-couples the tire 1 I to the cover plate 52 at predetermined increments
and, at step
216, the processor records the corresponding deflection values_ At step 218,
the load
is released and the tire is dismounted from the apparatus 10. AL step 220, the
processor
28 computes coefficient values which are employed to determine load-deflection
curves
at other inflation pressures. Those skilled in the art will appreciate Ihat
steps 206 and
208 and steps 212 and 214 collect between 100 to 200 equally spaced measures
of load
and deflection values over the test. When load-deflection curves at two or
more
inflation pressures are measured for a tire, a numerical regression analysis
of the
experimental data points is conducted to provide a "best bt" equation listed
below.
Load = C, (Def)ection)~i (Pressure)~3 (1)
It will be appreciated that the coefficients C~, CZ and C3 a~re~ coefficients
determined by a computer regression analysis implemented by the processor 2$.
Once
the coefrcients are determined, ,load-deflection curves at other in#lativn
pressures can
be extrapolated from the above equation, as shown at stepv'232. By employing
tire above
equation, time is saved and testing costs are reduced. In the preferred
embodiment, the
first inflation pressure is the minimal value desired from the load-deflection
curves and
the second inflation pressure is the highest value desired of the Load-
deflection curves.
This ensures the accuracy of the extrapolated load-deflection curves,
It should now be appreciated that an apparatus .and related methods have been
provided to a#low for obtaining a foot print analysis and load-doffection~
curves, wherein
such tests and data are employed to evaluate various tire wear ehaxacleristics
and
performance. ~ The apparatus and methods just described achieve the objects of
the
invention presented earlier herein and do so in a highly-accurate and
efficient manner.
Specif tally, the test data can be employed to quickly determine whether a
design change
is beneficial or detrimental to the performance of a tire. This reduces time
spent on the
tire design phase and allows bringing a tire to market much quicker than had
been
previously known. ~ .
While in accordance with the patent statutes only the best mode and preferred
embodiments of the invention have been presented and described in detail, it
is to be
understood that the invention is not limited thereto or thereby.
