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BACKGROUND OF THE INVENTION
A variety of manufactured goods are available on the market which utilize
smooth sheet-like surfaces to enhance the appearance of the product.
Representative examples of such goods include sheets for use on trucks and
automobiles as body parts, large and small appliances such as washers,
dryers, ovens, refrigerators, automatic coffee-makers, and toasters; wall
coverings such as wood paneling and laminated sheets; glass or clear
plastic plates for use as windows, mirrors, room dividers and the like.
In the past, evaluation of the surfaces of smooth sheets was done by visual
observation. In actuality, the human eye is well-designed for use in
evaluating surface quality, at least for those surfaces used to enhance
product appearance. The reason is that ultimately it is the human eye
which will scrutinize the product containing the smooth surfaces in
determining whether to purchase that product.
The eye is a good qualitative judge of the acceptability of a particular
smooth surface, but reproducible quantitative evaluations of acceptability
cannot be rendered. Further, though the eye can distinguish good surfaces
from bad, it cannot accurately evaluate surfaces which lie in the range
between good and bad.
To address the problem of effectively analyzing smooth surfaces in a
quantitative manner, several companies have devised quantitative surface
analysis equipment. A representative of Daimler-Benz AG presented a paper
to the Society of Automotive Engineers in late February-early March of
1983, entitled "Method for Determining the `Long Term Waviness` of Large
SMC Panels". The article discloses the use of a digital length gauge which
contacts the surface to be evaluated. Data points corresponding to a
vertical deflection of the gauge tip as it passes over the surface to be
evaluated are collected and stored. The stored data are then processed to
determine an average deflection height, or amplitude, of the line on the
surface tracked by the length gauge. The average amplitude along the
single line provides a quantitative value which is said to correspond to
surface quality. A lower average amplitude corresponds to a better
surface.
A second method of quantitative analysis has been developed by ICI
Americas, Inc. and is presented in a paper by A. T. Hurst entitled
"Measurement Aspects And Improvement Of Surface Profile In Thin Gauge
Molded Sheet Molding Compounds", Polym.-Plast. Technol. Eng. 20(1), 65-77
(1983).
The method utilizes a surface wavemeter apparatus which consists of a
linear voltage displacement transducer attached to a gauge traversing
mechanism which permits the transducer to be drawn over the surface to be
evaluated. Both the horizontal and vertical position of the transducer can
be determined. The vertical displacement is exaggerated to more clearly
show variations on the evaluated surface. The voltage output from the
transducer is converted into a digital display and transmitted to a
microprocessor.
The transducer evaluates one line on the surface with each complete scan.
Generally, two scans are conducted over the object, the lines being at
60.degree. angles to each other in the center of the tested surface.
Analysis is performed only in the direction of the visual evaluation.
The digitized voltage output from the scans easily converts to a graphical
output which is then analyzed for wavelength, amplitude, wave area, and
slope of the ascending line. The analysis requires the presence of at
least two troughs which define the endpoints of a wave. Otherwise,
calculations and conclusions based on the data are not meaningful. In
addition to the need for scanning along the same lines of sight as a human
evaluator,it is also important that the scans begin nearest the observer
and travel away so that the slope measurement subsequently determined is
meaningful in correlating the mathematical values with human rankings.
A third quantitative surface analysis method has been developed by The Budd
Company and is described in an article by K. A. Iseler and R. E.
Wilkinson, entitled "A Surface Evaluation System For Class A
Applications", Society of the Plastics Industry, Inc., 39th Annual
Conference, Jan. 16-19, 1984. The Budd Analyzer was essentially the same
apparatus as that employed at Daimler-Benz AG, but evaluates the collected
data points based on different mathematical concepts. The theory is that
the evaluation should not be based on surface waviness, but rather on
random surface ripples along a grid line.
Weltlich U.S. Pat. No. 4,476,489 discloses a non-contact surface analysis
system which measures the microfinish of a workpiece and compares that
finish with known finishes. Weltlich transports the workpiece into a
position which permits illumination of the piece, illuminates the surface
of the workpiece, views the illuminated surface via a camera, digitizes
the signal generated by the camera on a pixel-by-pixel basis, stores the
digitized signal, classifies the pixels by varying intensity, and compares
the distribution curve of pixel intensity with other curves from
preselected finishes. Weltlich generates data points which are utilized
only to evaluate the overall reflectance of the analyzed piece and to
compare that piece's overall reflectance with those of preselected
finishes. The evaluation technique as practiced in Weltlich is also known
as the determination of the short-term waviness of the finish. The
short-term waviness of a surface correlates to the presence of peaks and
troughs of less than about one centimeter on the analyzed surface.
Weltlich does not address the analysis of the long-term waviness of a
surface.
Other known methods of evaluating surface quality are based primarily on
visual inspection, and are qualitative determinations. The visual
evaluation of a surface with subsequent ranking has been discussed
earlier, and is essentially incapable of being quantified except by
statistical analysis of a large number of individual rankings. A variant
of the above-mentioned visual-based evaluation method employs a symmetric
grid shown onto a dark, polished surface, with subsequent evaluation of
the grid lines as they reflect back from the surface. The reflection may
be photographed for comparative study. Again, however, this method is
qualitative.
BRIEF DESCRIPTION OF THE INVENTION
It is an object of the present invention to quantitatively analyze smooth
surfaces via a method which more closely approximates the process employed
by a human evaluator when making a visual inspection.
It is a further object to quantitatively analyze smooth surfaces by a
method which is faster, more comprehensive, and more easily adapted to
rapid evaluations of large numbers of smooth surfaces.
It is still a further object to analyze smooth surfaces by a method which
does not require physical contact with the surface to be evaluated.
It is yet a further object to quantitatively determine both short-term and
long-term waviness of a surface to be evaluated using a non-contact
analysis method.
Briefly, smooth surfaces are evaluated by impinging light radiation onto an
object, the radiation being in the form of a straight line transverse to
the direction of propagation of the incident beam. The straight line
reflects from the surface of an object or deflects through an object and
is detected. The detected image is then transformed, into a digitized
signal from which data points are generated for subsequent mathematical
processing.
The light source may be any kind which results in reflection from a surface
or deflection through an object to be evaluated. Typically, the light
generated by an incandescent or fluorescent bulb may be used, but a
preferred light generator is the laser. By the use of appropriate optical
devices, the sharp point of light emitted from the laser can be widened to
form a light slit which impinges a wide section of the evaluated surface,
the slit being transverse to the direction of propagation of the incident
beam. The slit may be only a single laser point in height, but may be from
several inches to several feet in width. Visible and invisible light
sources may be used.
The light slit is a straight line at the point of generation. Upon shining
onto the surface of the object, the light slit is reflected from the
surface or deflected through the object to create an image which is
modified from that of a straight line based on the contour of the surface
or on the distortion in the object. This image is detected and then
quantified. The quantification process can be relatively simple, as where
the image is photographed and then laid onto a grid for conversion to a
series of X-Y coordinates, which serves as a basis for further
mathematical processing. A more elegant process detects the image by means
of a video camera. The signal proceeds to an image capture board which
digitizes the image and thereby permits storage in a computer for
subsequent mathematical processing.
A number of parallel, evenly-spaced light slits are trained over an entire
area of the surface to be evaluated. It has been found empirically that
analysis of an area approximately 10" by 10" is sufficient to effectively
determine the quality of a smooth surface having larger dimensions. After
quantification of the image, the coordinate points corresponding to the
image are processed via mathematic equations to produce a value which
correlates closely with visual evaluations and which therefore is
indicative of the quality of the surface.
The advantages of this invention will become more readily apparent from the
following detailed description of the invention and the drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of the evaluation apparatus utilizing laser generated
light radiation.
FIG. 2 is a depiction of a representative image generated by impinging
light radiation onto the smooth surface of an object.
FIG. 3 is a depiction of the image of FIG. 2 after digitization by a
computer.
FIG. 4 is a depiction of a reduced line corresponding to the digitized line
of FIG. 3.
FIG. 5 is a depiction of three adjacent reduced lines.
FIGS. 6a through 6f are representations of actual reduced and ideal lines
generated for various surfaces.
DETAILED DESCRIPTION OF THE INVENTION
Smooth surfaces 2 are evaluated for quality using light radiation to create
images which are transformed into numerical equivalents capable of being
displayed on a coordinate system of at least two dimensions. The numerical
equivalents are then processed mathematically to obtain a value indicative
of the quality of the smooth surface 2.
In FIG. 1, smooth surface 2 is evaluated preferably by impinging an
incident beam of laser light 4 onto a portion of the surface 2. The
incident beam 4 is impinged onto the surface 2 at an angle, preferably in
the range of 60.degree. to 5.degree. relative to the plane of the surface
2. However, it is possible for the angle of incidence to fall outside the
preferred range depending on the relative positions of the components of
the evaluation system and the reflective characteristics of the evaluated
surface. Though less preferred, a beam of non-coherent light of sufficient
intensity may also be employed. The incident beam 4 is produced by
reflecting the coherent source 6 from laser 8 first onto oscillating
mirror 10 and then onto mirror 12. The incident beam 4 length is dependent
upon the extent of oscillation of mirror 10. Oscillation of the mirror 10
is produced by motor 14 which is connected to oscillating mirror 10 by
motor shaft 16. The incident beam 4 preferably has a length transverse to
the direction of propagation of the incident beam 4 of 2 to 20 inches, and
has a height of approximately 0.05-0.25 inches. The laser preferably
generates a continuous beam, and is a low-power type such as a 4 mW
Helium-Neon laser.
The light which reflects away from the smooth surface 2 in FIG. 1
constitutes the resultant beam 18. The smooth surface includes those
surfaces which are curved or bent. The term "smooth" is merely intended to
define a characteristic of the surface which will lend itself to analysis
using the described apparatus. Alternatively, where an object is
transparent or semi-transparent, the resultant beam may be deflected
through the object (not shown).
The resultant beam 18 impinges screen 20 to produce an image 22 which
corresponds to the modification imparted to the incident beam 4 by the
smooth surface 2. As the invention is presently practiced on reflective
surfaces, the screen 20 and laser 8 are located on a direct line above the
smooth surface 2 and are approximately 10 feet apart. The smooth surface 2
is located midway between the laser 8 and screen 20 and situated such that
the incident beam 4 strikes smooth surface 2 at an optimum angle in the
range of about 30.degree. to about 35.degree. relative to the plane of the
smooth surface. The image 22 is preferably detected by video camera 24
which is connected to central processing unit 26 connected to both a video
monitor 28, which is capable of monitoring the video camera 24 or a
digitized image produced by an image capture board in the central
processing unit 26, and a computer monitor 29 which generates a visual
output of the information stored in the central processing unit 26.
Other means may be employed in obtaining an image correlating to the
modification of a straight line incident beam by a smooth surface. For
example, a narrow height beam of noncoherent light, such as that generated
by an incandescent or fluorescent lamp radiating through a slit, may be
employed. However, the smooth surface must be relatively reflective to
produce a discernible image. Further, the image may be detected via some
means other than that of a video camera, such as by free-hand line tracing
or by film camera. The system utilizing a laser and video camera/CPU
elements is preferred, however, because of the speed and efficiency of
analysis.
The system as heretofore described has referred to an image 22 as being
reflected from the smooth surface 2. Light generated by the laser 8 has
sufficient intensity to reflect from smooth surfaces having a range of
reflectances. This ability to evaluate a wider variety of smooth surfaces
provides additional basis for preferring laser-generated light.
It should be further noted that the invention is not intended to be limited
strictly to the detection of images generated by reflection from a smooth
surface. Objects such as glass panes for use in window frames or for
display purposes, laminated glass/sheets for use in automobile
windshields, and transparent and semi-transparent plastic sheets, among
others, often need to be evaluated for the presence of optical distortion
when viewing through the transparent or semi-transparent medium. The
evaluation system described can be utilized in detecting a deflected image
of an incident beam to determine the presence and extent of optical
distortion in the object. The incident beam is projected through the
object at an angle, preferably in the range of about 90.degree. to about
30.degree. relative to the surface of the object.
After the image 22 has been generated, it is detected preferably by video
camera 24 or by other means. A depiction of a representative image
generated by impinging light radiation onto the smooth surface of an
object is shown in FIG. 2. In the preferred embodiment, the video camera
24 is connected to a central processing unit 26 capable of digitizing
images, such as an IBM AT Computer or an AT&T PC 6310 microcomputer
containing an AT&T Image Capture Board. The image 22 can then be
transformed to a digitized image 30 as depicted in FIG. 3. The central
processing unit 26 receives the electrical output from the video camera 24
corresponding to the image 22. The image 22 contains a range of
intensities of light, dependent on the instantaneous angles of reflection
of the smooth surface 2 along the beam width illuminated by incident beam
4. The angles of reflection ideally are equal, which would result in a
reflected image corresponding exactly with the incident beam 4.
After the central processing unit 26 receives the signal output from the
video camera 24, the central processing unit 26 modifies the camera output
by imposing a threshold requirement. Portions of the signal corresponding
to low intensity scattered light which equate to a signal voltage lower
than the threshold value are ignored by the central processing unit 26.
The threshold limitation is set to ensure that the digitized image 30 has
an appearance similar to that of the image 22.
As can be seen in FIG. 3, digitized image 30 is comprised of a number of
vertical lines 32 having varying lengths. Arbitrarily, the unit of length
for each line is the pixel, each line being one or more pixels in length.
The pixel is a picture element on a video screen corresponding to an
individual point source of light. The AT&T Image Capture Board employed in
demonstrating the invention digitizes a 200.times.256 matrix of pixels.
The unit of length can be alternatively set at centimeters, inches, etc.
The distance between adjacent vertical lines 32 is one pixel.
The central processing unit 26 analyzes the individual height of each
vertical line 32 of the digitized image 30 and determines both a mean
height for all the vertical lines 32 and the standard, or root mean
square, deviation of the individual heights of all the vertical lines 32
along the digitized image 30. The determination of mean vertical line
height and standard deviation on the digitized image 30 does not take into
account the specific contour or slope of the image 30. It is possible,
however, that for other types of analysis, the contour or slope can be
used directly in conjunction with the mean line height and standard
deviation calculations.
The mean heights and standard deviation values for all of the digitized
images generated in the evaluation of the smooth surface 2 are averaged to
generate a number which serves as a measure of the appearance of the
smooth surface 2. This average mean image height value correlates to the
presence of peaks and troughs shorter than one centimeter on the surface
of the smooth surface 2. These peaks and troughs are also denoted as the
short-term waviness of the surface. The presence of such short wavelength
peaks and troughs results in a surface which looks similar to an orange
peel. A lower average mean image height value indicates that the smooth
surface 2 has fewer short wavelength peaks and troughs.
A second type of evaluation that is performed on smooth surfaces 2 involves
the determination of longer-wavelength peaks and troughs of from about one
to ten centimeters or greater. These longer-wavelength peaks and troughs
are evidenced visually by a wavy appearance in the smooth surface. The
wavy appearance is known as "long-term waviness" and is particularly
objectionable to a prospective buyer when found on the body panels of
automobiles.
The digitized image 30 as described above is used also in quantifying the
long-term waviness of the smooth surface 2. The individual vertical lines
32 comprising the digitized image 30 have a definite length, either as
calculated in pixels, inches, centimeters, or other unit. Each vertical
line 32 has a midpoint, or a mean. The central processing unit 26
determines the midpoint of each vertical line 32 along the digitized image
30. A plot of each midpoint of each vertical line 32 produces a reduced
line 34, which, as shown in FIG. 4, corresponds to the digitized image in
FIG. 3.
To evaluate smooth surface 2 for long-term waviness, the reduced lines
resulting from a number of images 22 must be generated. The images 22 are
obtained by impinging the incident beam 4 onto smooth surface 2 along a
number of parallel, equally-spaced intervals. Empirically the parallel
interval was set at 0.5 inch, thus resulting in the generation of
twenty-one images 22 in a 10 inch by 10 inch sampling area.
One method of evaluating the long-term waviness is evaluated by comparing
adjacent reduced lines 34. As shown in FIG. 5, reduced line 34 from FIG. 4
is flanked by adjacent reduced lines 36 and 38 generated in like manner.
The distance between corresponding reduced line points 40 on reduced lines
36 and 34 is determined for each set of corresponding points. When all the
distances between adjacent reduced lines 36 and 34 have been measured,
then the mean distance and the standard deviation of the distance are
calculated. The procedure is repeated for adjacent reduced lines 34 and
38, and so on, until all adjacent reduced line distances, mean distances,
and standard deviations have been calculated. Then, the average standard
deviation for all sets of adjacent reduced lines is calculated. This
average deviation is a measure of the parallelism of the smooth surface 2.
It can be seen, however, that adjacent lines may be parallel to each other
but still be nonlinear when compared to an idealized line. For example,
the adjacent reduced lines may be superimposable wavy curves. The average
standard deviation value may be very low, but yet the smooth surface 2 may
still be visually perceived as being flawed.
Another method of evaluation is available which does not have this
potential problem and is thus preferred. The reduced lines 34 are
individually fit mathematically to a polynomial which determines an
idealized line fit for the specific reduced line 34. For flat, smooth
surfaces, a second order polynomial of the form
y=a+bx+cx.sup.2
produces a sufficiently close line fit. For more highly-curved sufaces,
third order and higher polynomials are needed. The higher order
polynomials, which correspond to the form of the second order polynomial
listed above, are used in evaluating the surface of a curved automobile
fender, the rounded edge of a home appliance, or the like.
The polynomial generates an ideal line corresponding to the actual reduced
line, of which line 34 is but one example. The ideal line is superimposed
on the reduced line 34 and the standard deviation of the measured line
from the ideal line is determined by comparing a plurality of
corresponding points on each line. Again, an average standard deviation
for all reduced lines is determined. The standard deviation is averaged
for all 21 lines to give a single value which relates to long term
waviness. A lower value indicates less long-term waviness and consequently
a more attractive smooth surface.
The resulting values indicating either short-term or long-term waviness can
be intercompared between analyzed surfaces because of the generation of a
calibration factor for each evaluation. The calibration factor for an
evaluation is determined by projecting from the laser 8 a calibration
reference line of light having a known length (about 42.5 cm) directly
onto the screen 20 which is approximately 10 feet from laser 8. This line
is viewed by the video camera 24, digitized and then stored in the central
processor unit 26. Typically, the calibration reference line will
encompass about 200 pixels from end to end when displayed on the video
monitor 28.
To calibrate the instrument, the laser incident beam 4 is first trained
onto the surface to be analyzed located approximately midway between laser
8 and screen 20 and the first and twenty-first images 22 in the 10 inch by
10 inch sampling area are reflected individually onto the screen 20,
viewed by video camera 24, and displayed as live images on video monitor
28. The images may be longer or higher, or both, than the field of view of
the video camera. The increased size is due to curvature in the analyzed
surface 2. To ensure that the reflected image 22 do not exceed the display
capability of the video monitor 28, the lens of the video camera 24 is
adjusted so that the reflected images 22 are entirely within and nearly
fill the video monitor 28. After this adjustment has been completed, the
calibration reference line is projected directly onto the screen 20,
viewed by the adjusted video camera 24, digitized, stored in the central
processor unit 26 and displayed on video monitor 28. The length of the
digitized calibration reference line as displayed on video monitor 28
after adjustment of the video camera is calculated from the digitized
image of that reference line. Two hundred (the number of pixels
encompassed by a "typical" digitized calibration reference line) divided
by the number of pixels encompassed by the digitized calibration reference
line after camera adjustment constitutes the calibration factor.
The sensitivity of the surface analyzer in measuring long-term waviness is
dependent on the angle of the incident beam as it strikes the surface in
relation to the plane of the surface 2. The angle typically falls in the
range of 5.degree. to 60.degree.. To obtain maximum sensitivity for a
variety of surface textures and component placements, however, it has been
found that the optimum angle of the incident bean varies with the specific
texture and placement chosen, and thus must be determined by case basis.
Using the above-described system for evaluation of a relatively flat,
shiny surface, the optimum incident angle is approximately 30.degree. to
35.degree. in relation to the plane of the surface 2.
OPERATING EXAMPLES
The following detailed operating examples illustrate the practice of the
invention it its most preferred form, thereby enabling a person of
ordinary skill in the art to practice the invention. The principles of
this invention, its operating parameters and other obvious modifications
thereof will be understood in view of the following detailed procedures.
OPERATING EXAMPLE I
After calibration of the surface has been completed, a beam of light from a
4 mW He--Ne laser is projected onto a General Scanning Model LK3002 mirror
assembly which spreads the point-source beam into a line of laser light
and directs the line at an angle in the range of 33.degree. to 35.degree.
onto an untreated van hood compression molded from sheet molding compound
(SMC). A section of the hood approximately 10".times.10" is selected and
21 parallel lines spaced about 0.5 inch apart are sequentially projected
onto the selected area, reflected onto a white screen, viewed by a
Panasonic Model WV-1550 video camera, converted from an analog signal to a
digitized equivalent by an AT&T Image Capture Board, stored in digital
format in an AT&T PC 6310 minicomputer, and then displayed on a Sony video
monitor. FIG. 6a provides a representation of the 21 reduced lines
displayed as solid lines, and the polynomial line fit ideal lines as
superimposed interrupted lines. In Table 1, below, column two contains the
average line height in pixels of each reflected, digitized line corrected
for calibration. The closer the overall average line height value
approximates a minimum line height without being narrower than that
minimum height, the fewer short-term waviness deformations are present. As
a reference, the effective minimum line height after calibration
adjustment using a 4 mW laser having a 0.49 mm laser beam diameter
(measured at 1/e.sup.2) is approximately 1.90 pixels for a highly polished
chrome-plated flat surface. Column three contains the root mean square
(RMS) standard deviation values for each reflected, digitized line based
on a comparison of each reduced line with its corresponding fitted ideal
line. Multiplication of the average standard deviation with the
calibration factor provides a corrected RMS deviation result which, for
relatively flat surfaces, should fall in the range of 0.00 to 2.00. The
corrected RMS deviation result is directly proportional to the presence of
long-term waviness defects. A lower corrected RMS deviation result
indicates fewer long-term waviness defects.
TABLE 1
______________________________________
Corrected Average
Root Mean Square
Line Height (pixels)
Deviation
Line ("Short-Term")
("Long-Term")
______________________________________
1 3.4551 0.3948
2 3.2647 0.4873
3 2.8740 0.5181
4 3.7357 0.6740
5 3.7993 0.5983
6 3.5540 0.4689
7 3.7081 0.3338
8 3.9451 0.3549
9 3.9610 0.3980
10 3.6515 0.3940
11 3.9787 0.3512
12 4.7030 0.3929
13 4.4495 0.2795
14 4.1481 0.3691
15 4.8028 0.3371
16 5.2947 0.4762
17 4.8349 0.4319
18 4.6798 0.2800
19 5.0464 0.3813
20 5.3536 0.3001
21 5.5530 0.3381
Overall
Average: 4.2283 0.4076
______________________________________
Calibration Factor: 1.8868
Corrected RMS Deviation Result: 0.4076 .times. 1.8868 = 0.7690
OPERATING EXAMPLE II
The van hood from operating Example I is painted with primer and then
subjected to the same analysis procedure as described in Example I. Table
2 below sets out the pertinent derived numerical values. The
representation of reduced and ideal lines for the primed hood is provided
in FIG. 6b.
TABLE 2
______________________________________
Corrected Average
Root Mean Square
Line Height (pixels)
Deviation
Line ("Short-Term")
("Long-Term")
______________________________________
1 5.5362 0.6317
2 5.6111 0.7713
3 5.4947 0.7761
4 6.2302 0.7709
5 5.7125 0.8610
6 6.0117 0.6450
7 6.0898 0.6761
8 5.7132 0.5664
9 6.6513 0.6441
10 6.3030 0.6455
11 7.7830 0.6267
12 7.3934 0.5892
13 7.9415 0.5058
14 7.7330 0.7118
15 7.8519 0.7651
16 7.9568 0.7854
17 6.9827 0.5683
18 7.6830 0.4721
19 7.3951 0.5603
20 7.7374 0.3953
21 7.5795 0.3997
Overall
Average: 6.8281 0.6366
______________________________________
Calibration Factor: 1.8868
Corrected RMS Deviation Result: 0.6366 .times. 1.8868 = 1.2011
OPERATING EXAMPLE III
An automobile hood produced from Ashland Phase II sheet molding compound is
subjected to the same analysis procedure as described in Example I. Table
3 below sets out the pertinent derived numerical values. The
representation of reduced and ideal lines for the SMC automobile hood is
provided in FIG. 6c.
TABLE 3
______________________________________
Corrected Average
Root Mean Square
Line Height (pixels)
Deviation
Line ("Short-Term")
("Long-Term")
______________________________________
1 3.6208 1.4829
2 3.3929 1.2003
3 3.7168 0.9671
4 3.7056 0.7219
5 3.7102 0.5775
6 3.9800 0.5541
7 4.2141 0.5480
8 4.4248 0.5335
9 4.3815 0.6399
10 4.3891 0.4247
11 4.4954 0.4655
12 4.6393 0.4468
13 4.7424 0.4148
14 5.1388 0.4948
15 5.0942 0.5181
16 5.1788 0.6344
17 5.3481 0.6159
18 5.4849 1.0722
19 5.4873 0.8690
20 5.6463 0.6541
21 5.6317 0.6298
Overall
Average: 4.5915 0.6888
______________________________________
Calibration Factor: 1.4925
Corrected RMS Deviation Result: 0.6888 .times. 1.4925 = 1.0280
OPERATING EXAMPLE IV
The same shape automobile hood from Example III is formed from Ashland Fast
Cure Phase Alpha sheet molding compound. This hood is subjected to the
same analysis procedure as described in Example I. Table 4 below sets out
the pertinent derived numerical values. FIG. 6d provides the
representation of reduced and ideal lines for the fast cure SMC hood.
TABLE 4
______________________________________
Corrected Average
Root Mean Square
Line Height (pixels)
Deviation
Line ("Short-Term")
("Long-Term")
______________________________________
1 2.2243 0.3526
2 2.3664 0.4858
3 2.2970 0.5251
4 2.5250 0.3908
5 2.5832 0.3071
6 2.5599 0.3915
7 2.5532 0.4377
8 2.5574 0.3729
9 2.7928 0.3702
10 2.8777 0.3127
11 2.9156 0.3506
12 3.0468 0.4287
13 3.2174 0.4645
14 3.4644 0.6885
15 3.4916 0.6416
16 3.6650 0.6310
17 3.7313 0.5649
18 3.7402 0.5819
19 3.8471 0.5300
20 3.9957 0.5525
21 3.8669 0.6653
Overall
Average: 3.0628 0.4784
______________________________________
Calibration Factor: 1.4925
Corrected RMS Deviation Result: 0.4784 .times. 1.4925 = 0.7140
The surface of this hood can be seen visually to have less long term
waviness than the hood in Example III, as corroborated quantitatively by
the lower Corrected RMS Deviation Result for Example IV.
OPERATING EXAMPLES V AND VI
To demonstrate the sensitivity of the non-contact analysis system in
differentiating similar parts by long-term waviness defects, two flat
plaques produced from sheet molding compound are compared. Example V is a
flat SMC plaque with no induced defects. Example VI is a similar flat SMC
plaque having a defect induced by removing the plaque from its mold while
hot using a suction cup. The line representations of Examples V and VI can
be seen in FIGS. 6e and 6f, respectively. Table 5 sets out the RMS
deviation and corrected RMS deviation results for each plaque.
TABLE 5
______________________________________
Root Mean Square
Deviation
("Long-Term")
Line Example V Example VI
______________________________________
1 0.6293 1.8545
2 0.7222 1.7003
3 0.7455 1.3927
4 0.4465 1.0953
5 0.5972 0.8181
6 0.9872 0.9319
7 0.8201 0.8480
8 0.6546 1.1623
9 0.3505 1.3102
10 0.6472 1.0299
11 0.6869 1.1309
12 0.8518 0.9229
13 0.7449 0.7930
14 0.6079 0.8635
15 0.6245 0.7206
16 0.4102 0.7675
17 0.4136 0.6701
18 0.7409 0.4957
19 0.5394 0.6233
20 0.4520 0.5339
21 0.6919 0.6215
Overall
Average: 0.6364 0.9660
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Calibration Factor: 1.1364
Corrected RMS Deviation Result: 0.7232 1.0978
Note the large dissimilarity in RMS Deviation values between Examples V and
VI for lines 1 through 4 and lines 8 through 11. FIG. 6f roughly outlines
the suction cup mark in the upper left-hand portion of the line
representation.
The above mathematical treatment of data points obtained using a reflected
image surface evaluation apparatus is intended to demonstrate one means of
utilizing the apparatus, not to limit its applicability. The apparatus is
useful in quickly and quantitatively evaluating smooth surfaces having a
variety of textures. The apparatus is capable of determining both
short-term and long-term waviness from a single set of data points. In
contrast to surface analysis machines which utilize mechanical sensors to
determine changes in contour, the instant invention analyzes a larger area
of the surface more quickly and without coming into direct contact with
the surface. Further, an apparatus utilizing light radiation employs fewer
moving parts than mechanical apparatuses, and is less likely to require
repair and recalibration. A light radiation surface evaluation apparatus
can be devised to analyze individual surfaces moving along an assembly
line. The light radiation apparatus is also inherently portable, and as
such can be positioned at any angle relative to the ground plane to
evaluate the individual surface. The apparatus therefore can also operate
independent of the angle of the individual surface in relation to the
ground plane.
The apparatus is able to evaluate a variety of materials and surface
textures. For example, | | |
