an optical profilometer for spatial characterization of three … · summary a technique is...

NASA TP 1012 c . 1

NASA Technical Paper 1012 , '

An Optical Profilometer for Spatial Characterization of Three-Dimensional Surfaces

W. Lane Kelly IV, Ernest E. Burcher,

and Milton W. Skolaut, Jr.

SEPTEMBER 1977

i

https://ntrs.nasa.gov/search.jsp?R=19770025514 2020-03-25T07:27:50+00:00Z

NASA Technical Paper 1012

An Optical Profilometer for Spatial Characterization of Three-Dimensional Surfaces

W. Lane Kelly IV, Ernest E. Burcher,

and Milton W. Skolaut, Jr.

Langley Research Center

Harnpton, Virginia

National Aeronautics and Space Administration

Scientific and Technical Information Office

TECH LIBRARY KAFB, NM

0134300

1977

SUMMARY

A technique is described for obtaining spatial characterization of three- dimensional surfaces with uniform near-Lambertian reflectance using a noncontact optical profilometer. The design concept and system operation are discussed, and a preliminary evaluation of a breadboard system is presented to demonstrate the feasibility of the optical profilometer technique. Measurement results are presented for several test surfaces; and to illustrate a typical application, results are shown for a cleft palate cast used by dental surgeons. Finally, recommendations are made for future development of the optical profilometer technique for specific engineering or scientific applications.

INTRODUCTION

In manufacturing, engineering, and medical research, spatial characterization of a three-dimensional surface is often required. An electromechanical probe which rides on the surface of the sample is usually used. Occasionally, a noncontact method is required to prevent damage to the surface to be measured.

Optical techniques can be used to provide noncontact surface characterization. Drawing contour lines from a pair of stereo pictures with the aid of a drawing machine is most commonly used, but this method is not direct and requires expensive instruments. Another optical technique, called moire/ topography (ref. I ) , produces a contour line system on the sample surface. These optical techniques require additional processing to convert the contour lines to surface depths in digital form when the surface characterization is to be stored or manip- ulated in a computer.

The purpose of this paper is to describe a relatively simple and inexpensive electrooptical technique which provides digital information for the spatial characterization of three-dimensional surfaces. The optical profilometer concept consists of an optical system and photodetectors which observe the change in the energy distribution of an image spot of light as a function of the depth of the sample surface at the measurement point. The sample surface is scanned to provide measurement information over the complete surface. Changes in the output signal due to variations in surface slope, surface reflectance, and lamp intensity are greatly reduced by taking the ratio of the sample photodetector output to a reference photodetector output. Since the profilometer observes the reflected light from the test surface, its use is limited to sample surfaces which have a uniform near-Lambertian reflectance or which can be temporarily coated.

A breadboard optical profilometer has been developed and tested to demonstrate the feasibility of the optical profilometer concept. Measurement results are presented for several test surfaces to illustrate the operation and performance. To illustrate a typical application, measurement results are presented for a cleft palate cast used by dental surgeons to aid in the surgical reconstruction

of the palate. In addition, recommendations are made for further development of the instrument concept to meet specific engineering o r scientific requirements.

SYMBOLS

d depth, mm

VD output of voltage divider, V

Vr output of reference detector, V

VS output of sample detector, V

X axis along scan line

Y axis perpendicular to scan lines

Z vertical axis (depth)

e angle between surface normal and optical axis, deg

P surface reflectivity

Abbreviation:

A-D analog to digital

DESCRIPTION OF CONCEPT

As shown in figure 1, the basic configuration of the optical profilometer consists of an electrooptical system, a microprocessor, and a data recorder.

Electrooptical System

The electrooptical system provides an output voltage which is a function of the sample depth at the point of measurement. A light source is imaged by the lens into a spot on the sample surface. As the surface depth increases, the imaged spot becomes defocused and the spot size increases. The spot is reimaged by the lens and directed by a beam splitter to two photodetectors to provide sample and reference signals.

The sample detector, which acts as a field stop, is sufficiently small to view only the center portion of the spot and hence to observe a decrease in energy as the spot becomes defocused because of changes in sample depth. The energy reflected by the sample surface and observed by the sample detector is also dependent upon the illumination scattering function, which describes the angular dependence upon viewing and illumination geometry.

2

Since the output voltage of the sample detector depends not only on the surface depth but also on the surface slope, a reference detector is used to observe the entire spot. A field lens is positioned to image the imaging lens onto the reference detector. The reference detector, therefore, collects all of the energy of the defocused spot which is reflected into the solid angle subtended by the imaging lens. This configuration almost entirely removes the reference detector's dependence on surface depth but does not affect its dependence on the average surface slope and reflectivity. By dividing the sample detector output by the reference detector output, the dependence on slope and surface reflectivity can be removed, since both detectors have the same viewing axis. The voltage divider output can be described as

where Vs is the sample voltage, Vr the reference voltage, 0 the angle between the surface normal and the optical axis, d the depth, and p the surface reflectivity. The output of the voltage divider is then amplified, digitized, and read by the microprocessor.

Microprocessor

The microprocessor serves as the control unit, provides data storage, per- forms minimal data processing, and formats the output for the data recorder. A simple 4-bit microprocessor with 4000 kbit word storage was used to provide an economical, yet flexible, control unit. Commands to the microprocessor are entered through a standard teletype, although several push-button switches would be sufficient. The microprocessor sends control signals to two stepper motors which drive gear assemblies to move the sample platform along the X- and Y-axis during data acquisition.

The microprocessor is used to command the analog-to-digital conversion (8 bits) and to read and store the digital data for each scan line along the X-axis. Data obtained from a scan line are compared with the data obtained during calibration to determine the appropriate output for representing surface depth at each measurement point. After each X-axis scan, digital data are output to the data recorder.

The microprocessor can also be used to automatically scan a calibration surface and store the data for comparison with subsequent sample data. This means of simple data processing is used since the variation of voltage with depth is not linear.

Data Recorder

The electrooptical system and the microprocessor provide data pertaining to the sample surface in several forms available for recording. Output data can be recorded in analog form by recording the motor step commands (for X and Y position) and the output voltage of the voltage divider ( Z information). Digi- tal data can be recorded from the microprocessor as 8-bit raw data or, after

3

comparison with calibration data, as depth information. The breadboard system described in this paper compares the raw data with calibration data and assigns an alphabetical character to be typed on the teletype. More sophisticated output display features, such as three-dimensional contour plots, surface areas, and surface slopes, could be obtained with additional storage and computational capability in the computer control unit.

DEVELOPMENTAL SYSTEM

A breadboard system was fabricated to evaluate the optical profilometer concept as a technique for generating three-dimensional data for surface characterization. The breadboard system is shown in figure 2, and pertinent design parameters are listed in table I.

Operation

Calibration of the optical profilometer is initiated by a command from the teletype to the microprocessor. The sample platform is then automatically moved to position the calibration surface in the optical path. The calibration surface consists of a wedge which provides a linear change in depth along the X-axis. As data are taken, the sample platform is automatically moved in equal increments along the X-axis. These digital data, which are a function of surface depth, are stored in tabular form by the microprocessor. With this calibration procedure, the slope of the calibration wedge determines the profilometer depth range and resolution within the operating limits.

Upon completion of calibration, the sample platform is automatically returned to the initial position. Manually, the operator vertically positions the sample platform so that the highest point on the sample is slightly below the maximum calibration height. Data acquisition is initiated by a teletype command, and the platform is moved in equal increments along the X-axis after each data point is taken and stored by the microprocessor. At the completion of each scan line the sample data are compared with the calibration data to select an output character to represent vertical height for each measurement point. Output data are displayed for the entire scan line, and the platform is returned along the X-axis and incremented along the Y-axis for the next line. The platform is returned to the initial position at the completion of all data acquisition.

The format selected for output data on the teletype consists of the 26 characters of the alphabet with A representing the highest depth interval and Z the lowest. The symbol @ is used to indicate surface depths above the highest calibration point and the period ( .> is used to indicate depths below the lowest calibration point. The surface depth interval represented by a character is determined by the slope of the surface used for calibration. Only 26 calibration points are needed to display the output data in this form. Additional display options include printing only a single line of output characters o r printing both the calibration and the sample data in hexadecimal format.

4

Evaluation

Data were obtained from several test surfaces to demonstrate the operation and evaluate the performance of the breadboard optical profilometer. Figure 3 shows a plot of digitized voltage divider output for a calibration wedge pro- viding a depth range of approximately 14 mm. The output voltage is a nonlinear function of depth, with diminishing depth resolution as the surface depth increases. This nonlinear function is essentially linearized by the microprocessor by storing calibration data for equal depth intervals in a look-up table.

To define an approximate depth resolution limit for the breadboard electrooptical system, the wideband root-mean-square noise voltage was measured at the output of the voitage divider and found to be 1.9 mV. A s evident from the voltage-depth curve shown in figure 3, the poorest depth resolution occurs near the maximum depth, where the slope can be approximated as 0.165 V/mm. For a minimum analog signal-to-noise ratio of 4, the minimum detectable depth interval would be on the order of 0.05 mm. Higher analog signal-to-noise ratios would occur for smaller surface depths, and better depth resolution could be obtained by reducing the total depth range. These results are, of course, dependent upon the particular lens and apertures used in the breadboard system and could be mod- ified by designing the optical system for a specific application.

To test the performance of the breadboard system, the calibration wedges described in table I1 were used as sample surfaces. Wedge C, which provides depth resolution of 0.53 mm over a 14-mm range, was used for calibration, and data were obtained for wedges A and B as sample surfaces. The sample platform was lowered 1.9 mm for wedge A and 3.8 mm for wedge B to place the sample surfaces in the’approximate center of the depth range. Output data, plotted in figures 4 and 5, accurately characterize the sample surfaces. For actual operation using sample surfaces with small depth variations, more precise results could be obtained by using the appropriate calibration wedges. On both wedges, the same line along the X-axis was scanned several times with identical output characters produced on the teletype, indicating excellent measurement repeatability.

Data were obtained from a section of a sphere with a known radius (33.1 mm) to verify that the profilometer output was not adversely affected by variations in surface slope. Initial results, which did not reconstruct the sphere radius to the accuracy expected, indicated that the slope dependence was not effectively being removed. Further investigation revealed that both photodetector outputs contained offset voltages. While the sample detector offset was considered negli- gible, the reference detector offset was significant. The reference detector offset voltage resulted from radiation reflected from the surfaces of the several elements in the imaging lens. Since this offset voltage was not a function of surface slope, proper operation of the division function (eq. (I)) was not possible.

To provide a temporary solution, the reference detector offset voltage, due to the surface reflections of the lens, was measured. A constant voltage equal to the offset was subtracted from the reference signal by an operational ampli- fier in a subtraction mode.

5

After completing t h i s mod i f i ca t ion , t he p ro f i lome te r was recalibrated and measurements were r e p e a t e d f o r t h e sphe r i ca l su r f ace . Ou tpu t data f o r t h e e n t i r e s u r f a c e are shown i n f i g u r e 6. I n f i g u r e 7 , t he c e n t e r l i n e o f o u t p u t data is p l o t t e d t o compare wi th a c i r c u l a r arc o f t he same r a d i u s as the sphere. Data are p l o t t e d as b locks wi th d imens ions equa l t o the sample i n t e rva l a long the X- and Z-axes to a l low d i r ec t compar i son be tween the o u t p u t r e s u l t s a n d the a c t u a l s u r f a c e characterist ics. The larger depth values approach the worst-case measurement cond i t ions fo r dep th r ange , s lope change , dep th r e so lu t ion , and small s i g n a l o u t p u t f o r the breadboard design. The close agreement between output data and the a c t u a l s u r f a c e i l l u s t r a t e s the f e a s i b i l i t y o f t h e o p t i c a l p r o f i l o m e t e r tech- n ique fo r cha rac t e r i z ing t h ree -d imens iona l su r f aces .

To i l l u s t r a t e a t y p i c a l a p p l i c a t i o n ( ref . 21, d a t a were o b t a i n e d f o r a c l e f t p a l a t e cast, which is used by d e n t a l r e s e a r c h e r s i n t h e s u r g i c a l r e p a i r o f c r a n i o - facial d i s o r d e r s . C a l i b r a t i o n was performed w i t h wedge C , and r e s u l t s are shown i n f i g u r e 8 a long wi th a photograph of t h e c l e f t p a l a t e cast i n f i g u r e 9.

It should be noted t h a t the performance of t he breadboard developmental system was limited by t h e 26-character format of t h e ou tpu t data; t h e r e f o r e , t h e r e s u l t s i l l u s t r a t e d here do n o t r e p r e s e n t t h e l imi t ing per formance of t he e l e c t r o - o p t i c a l d e s i g n .

POTENTIAL IMPROVEMENTS

A breadboard system was developed t o d e t e r m i n e t h e f e a s i b i l i t y o f t h e o p t i - cal prof i lometer concept . During the development , several design areas were recogn ized i n which performance could be improved or the sys tem adapted to meet spec i f i c r equ i r emen t s .

Optical System

The depth range could be increased or decreased f o r a p a r t i c u l a r a p p l i c a t i o n by s e l e c t i n g the l e n s f o c a l l e n g t h a n d l e n s diameter. To t a i l o r t h e o p t i c a l des ign t o ach ieve a spec i f i c dep th r ange , t r ade -o f f s shou ld be made regard ing the s i z e a n d t y p e s o f a p e r t u r e s f o r t h e l i g h t source and both detectors . Consid- erable f l e x i b i l i t y e x i s t s i n d e f i n i n g t h e s i z e a n d i n t e n s i t y d i s t r i b u t i o n o f t h e defocused spot , which affect the l i n e a r i t y o f t h e o u t p u t v o l t a g e as a func t ion of depth and the s p a t i a l r e s o l u t i o n on t h e sample surface.

A permanent and more a c c u r a t e s o l u t i o n t o t h e p rob lem o f vo l t age o f f se t s due t o f r o n t s u r f a c e r e f l e c t i o n s f r o m t h e l e n s is provided by a n a l t e r n a t e o p t i - ca l des ign . The l i g h t source should be moved t o the sample s ide of the imaging l e n s t o p r e v e n t the f r o n t s u r f a c e r e f l e c t i o n s f r o m r e a c h i n g t h e d e t e c t o r s . T h i s can be accomplished by us ing a s e c o n d l e n s t o image t h e l i g h t source on t h e sam- p le and by us ing a beam s p l i t t e r i n p l a c e o f t he f o l d i n g m i r r o r , as shown i n f i g u r e 10.

6

Microprocessor and Electronic System

The signal-to-noise performance may allow additional encoding levels to be used to improve system resolution and precision. System performance may improve by performing the division digitally with the microprocessor to avoid errors due to analog offsets in the analog voltage divider. Since the step interval along both the X- and the Y-axis is under microprocessor control, decreasing the step interval between data samples, which increases sampling frequency, can be investigated to improve the precision in measuring surface characteristics. Addi- tional microprocessor capability would allow surface areas and slopes to be cal- culated, and for industrial engineering applications, the microprocessor could format the digital output data to interface readily with digitally controlled machinery.

Output Data Display

The teletype used with the breadboard system represents the simplest form of output device which could be readily interfaced to a microprocessor. A simple microprocessor could also use a line printer, magnetic tape, paper tape, cathode- ray tube (CRT) display, or a digitally controlled plotter as an output display device. All of these options would display data with higher resolution in a man- ner particularly suited to the user.

CONCLUDING REMARKS

An optical profilometer concept for obtaining spatial information for characterization of three-dimensional surfaces has been investigated. The basic concept utilizes the change in the energy distribution of an imaged spot of light as the image moves out of focus to provide a photodetector output voltage which is a function of surface depth. Variations in the output signal due to changes in surface slope or reflectivity and light source intensity are greatly reduced by taking the ratio of the sample photodetector output to a reference photodetector output. Operation of a breadboard profilometer, which uses a microprocessor to control sample position, calibration, and simple data processing, was described.

A preliminary evaluation of the profilometer was performed by obtaining data for several test surfaces. Depth resolution of 0.53 mm over a 14-mm range was obtained with the breadboard developmental system which was limited by the 26 output characters. Measurements of noise voltage indicate that depth resolu- tions approaching 0.05 mm over a 14-mm depth range for a desired signal-to-noise ratio of 4 appear feasible with the breadboard optical system. Improved depth resolution could be achieved by operating over a smaller depth range. Data which accurately characterized a spherical surface were obtained to illustrate that variations in surface slope do not significantly affect system performance. Future developmental work on the optical profilometer should consider ( 1 ) trade- offs within the optical design to optimize the depth resolution and range, (2) separation of the optical path of the light source from that of the detector,

7

and (3) expansion of t h e m i c r o p r o c e s s o r c a p a b i l i t y t o i m p r o v e t h e p r o c e s s i n g a n d d i s p l a y of d a t a .

Langley Research Center Nat ional Aeronaut ics and Space Adminis t ra t ion Hampton, VA 23665 J u l y 21, 1977

REFERENCES

1 . Takasaki, H. : Moire Topography. Appl . Opt. , v o l . 9 , no. 6 , June 1970, pp. 1467-1472.

2. Berkowitz, Samuel: Stereophotogrammetric Analysis of Casts of Normal and Abnormal Palates. h e r . J. Orthod., vol. 60, no. 1 , Ju ly 1971, pp. 1-18.

8

TABLE I.- DESIGN PARAMETERS FOR BREADBOARD OPTICAL PROFILOMETER

[One-to-one imaging system used]

Foca l l ength o f imaging lens , cm . . . . . . . . . . . . . . . . . . . . . 16.5 Diameter of imaging lens , cm . . . . . . . . . . . . . . . . . . . . . . . 6.4 Aperture diameter of re ference photodetec tor , cm . . . . . . . . . . . . . 0.31 Aperture diameter of sample photodetector , cm . . . . . . . . . . . . . . 0.05 Reference photodetector . . . . . . . . . . . . . . . . . . . . . . UDT PIN-5 Sample photodetec tor . . . . . . . . . . . . . . . . . . . . . . . HP 5082-4205 Microprocessor . . . . . . . . . . . . . . . . . . . . . . . . . . . I n t e l l e c 4 Sample in t e rva l a long X-ax i s , cm . . . . . . . . . . . . . . . . . . . . 0.079 Sample in t e rva l a long Y-ax i s , cm . . . . . . . . . . . . . . . . . . . . 0.13 Sample in t e rva l a long Z -ax i s (wedge C ) , cm . . . . . . . . . . . . . . . 0.053 Range along X-axis, cm . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Range along Y-axis, cm . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Range a long Z-axis, cm . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4

Wedge

A

B

C

TABLE 11.- CALIBRATION WEDGES

Depth range, cm

0.45

.91

1.4

Depth i n t e r v a l p e r ou tpu t cha rac t e r , cm I I

I

0.018

.036

.053

0.091

. I 8

.27

9

Figure 2.- Breadboard optical profilometer.

HEXADECIMAL OUTPUT DATA

- 2

- Y

- x

- w - v

- u

- T

- s

- R

- Q -P 6 . cn

- 0 3 - N s

H

s V

PI

- M g w

- L 2 E

- K 2 - J

- I

- H

- G

- F

- E

- D

- C

- B

Figure 3.- Profilometer output data (digitized output voltage) as a function of depth.

12

14

12

10

8

B €- z PI w CI

E

' 1

i

I

-2

- Y

- x

- W

- v - u

- T

- s - R

- Q - P g - 0 2

3 - N s - M 2 "L

- K 2 "J

- I

PI

w

€- w

- H

- G

- F

- E

- D

- c

- B

A I I I I i I I I ! . ~ ! I I I I I , . "

1 1 2 3 4 5 6 7 8 9 A B C D E F HEXADECIMAL OUTPUT DATA

Figure 4.- Profilometer output data (digitized output voltage) for wedge A with wedge C used for calibration.

13

1 F

-2

- Y

- X

- W

- V

- U

- T

- S

- R

- Q

- p 2

s

cn

- 0 3 - N s " E

E4

u

ni

w ni

- L s - K ~4

E:

- J

- I

- H

- G

- F

- E

- D

- C

- B

"A

HEXADECIMAL OUTPUT DATA

Figure 5.- Profilometer output data (digitized output voltage) for wedge B with wedge C used for calibration.

14

I

Figure 6.- Profilometer output data for spherical surface.

15

X-AkIS [ )ISTAWCE, c m

0 1 2 3 4 5 r I I 1 I I I I I I I I A B C D - k I ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! I U L L l I ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! l

0

2

Figure 7. - Single scan

X - A X I S STEP INTERVALS

l i n e through cen te r of sphe r i ca l su r f ace .

R ......................... zyxw~vuuvwwY................................. ............................. ZYYYYYZ.................................~ .. . . . . . . . . . . . . . . . . . ~ . . . . . . Y T S S S S S S S R S R P Q R R S T W . . ~ ~ ~ . . . . ~ ~ . o o ~ ~ ~ . o . ~ ~ ~ . ~ * ....... ZVVXZ............QMLKKJJJJKKKLLLLMNOQSUZ....................... .......USSTTTV........YOLKJJJII,IJJJJKLKLLMNOPQSW.... ... . . . . T S S S S S T V . . . ~ . . . ~ M K J I I J J J K K L K K M L M M M N O O P R T ~ ~ ~ .. . . . . . R R R R R S S T U W . . . . . . . W S P N N N N O O N M M M M O ~ R R Q Q Q R S V . . .~.....SRSSSSSTW......YSOLKKKKKLMMLLLMNNOOOOPQRU...*...ZYYYXYY...~....

.~...~.RRRRRRSTTUW..~*..~..VTSRQPOOOPTUUTTTUVX....~~ZYXWWXXWWX....~~~. .. .....QQRRRRSSTTUVX~.*......WVTTSTWY....~.~...~..ZXWWVVWWWWWZ..o~~..

.......QQRRRRRSSfTTUW...~...~~XW~VVY..oooo........YXWWVVVVWVVVY.o.~... ~...o.YPPQRRRRSSSSTTUWY......YVVVVXZ....~o..o~.~.YWWWVVUUUVVVVWZo.~... ......WPPPPQQQRRRSRSTUWY.ZVRRWWVVWXY............YWWWVVVUUUUUUUWY....*. ......WOOOPPPQQQQRQRSSPMHJKNQSWWVWXY.~......~.ZXWVWVVVUUUUUUUUWY~..~~. ~ ~ ~ ~ ~ ~ T O N N O O O P P P P O O P O L G E F H J L Q S W X V W X Y Y ~ ~ V T U Y ~ ~ Z Y W ~ V V V V U U U U T T U U U V Y ~ ~ ~ ~ ~ ~ ......RNNNNOONNMKJLIEDEFGHKMPRVWVWXYX.YTQQOMLNRUXVUUVUUUTTTUUUVX ~~~o~~QMNMMLLMIHIIFBBBEGIJLMOPTWWWXYWZYUSQNLKIIJNTTTUVTTTTTTUTUV2~~~~~ ..... .PMLLLLLKIIHCAABCEHJKKLNRTWYWWXYZYSQ~MLJIHHHK~SSTTTTTTUUUVY..o.. ......OLLKKKJJKIDBABCDFIKJLLNSUZYWWYXXWSPONNNKKJIGGGJRTSSSSTUUTVZoo.*. 0 . . .MKKJJJJKJEBABBDEGJLKKMPTY.YXXYYZURPONMNLKJIHGFGHOTRSSSTUTUZ. .. ~...LKKJIJJKGCBABCEFHKKKLOSZ.ZYYZ...WTQONMMMLJIHGGGFHPTSRRSTTUY~.... ...... KJJJIIIIFCBBCDFHJLKLORV.ZYY...~..WSPNMMNLKIHHGGFGJSTSRSSSTY.... ...... JIIIHHIGDCCDDEG~LLLNQ.TZ.YYY.......UQONMMNLJIHGGGGIPSSQRRRTY..... ~ ~ ~ ~ ~ ~ I H H G G G H F D D E E E G I K L L O P S X ~ Z Y Y Y ~ ~ o ~ ~ ~ ~ W T P O M M N N K I I H G G H J O T P P Q Q R S X ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ I G H G G G G E E E E F F H J K L N P R U ~ ~ Z Z Z Z ~ ~ ~ ~ ~ ~ ~ Z U S P O N N ~ M J I H H I K K N ~ P P P P S V ~ ~ * ~ ~ ... . . . G F F F F G F E E E F F G I J L L O Q S V ~ ~ Z Z Z ~ ~ ~ ~ . . ~ ~ ~ W S R P O N N N L J I I J K L M Q O O N ~ O Q U e. eFFEEEEFDDDFGIIKLNOPSY .ZZY.. 0'. WUSRONMMMKJJJKKLPNONMPSV. . ~ ~ ~ ~ ~ V E F D D E E D E D D F H I I J L N N O Q Y ~ Z Z Z Y ~ ~ ~ ~ ~ ~ ~ ~ ~ X T T R O O N M M L K K K K M N O M M L N S V Z ~ ~ ~ ~ ~ .~...TEDDCCCEEEDFGHJKNMMOQX.ZYZYZY~.~...~..XUUPOONMMMKKMNLLMLLPSUW..~.~. . . . . . . K I D C B B B A A B D D I I J K M L N Q Y . Y Y Y Y Y Z ~ ~ . . . ~ ...... SMKJIGEDDDCEHHIJKLOPTZYYYYZ........YTRPONMLLLLLLMJJKORTWZ...~ .. . WONLKJICEEEDDGIHDGHI VYYXWY . .YUQONMLLLLKLLLJKORToY- .........SQOMLKJHFFFFFEEEFHM.YWWX.........XPONMLLKKKKKKKLNRTWY.....~... .... .......VTRPONMLKIHGGGGGHNZYWWX...o~~YRPONNMLKJJJKK~PQSUWY.....o..o. ....~......ZWUTRQPOONMLJIILS.YVUW.i...SONPPNLJJJKMOP~RSTVXZ~~~o~~~~~~~ ..oo....e...~ZXWVUTSSRQPOOY.ZVUUVY...TML~KKLLMNOPQRSTUVXY~.~~~~..~~~.~ .~ . .~ . . . . . . . . . . . .ZYXWWVUTWYYWUUUVX. .Y~MMLMNPQRSSTUUVWYZ. .o~oo. .o . . . .~~ ........................ZWWWVTUUUWZ.WRRRSTUUVVWWXYZ.o.~.~~.o~o~o...~~. ............................ zxwvuvY~~zzYxwwY...~.....................~ ...................................................................... ...................................................................... ...................................................................... ?

Figure 8.- Profilometer output data for cleft palate cast.

17

L-'(o-'(oyy

Figure 9.- Photograph of cleft palate cast.

18

L i g h t s o u r c e

7 S a m p l e d e t e c t o r

R e f e r e n c e d e t e c t o r 1 r L i g h t b a f f l e L e n s

"""""

Beam s p l i t t e r

X-axis motor - V o l t a g e d i v i d e r e / I

e r , / Y-axis motor

A r 1

G a i n a n d o f f s e t c o n t r o l ""_ A-D c o n v e r t e r - * Microprocesso r

). P r i n t e r

4 ""-" T e l e t y p e

Figure 10.- Improved optical design for optical profilometer.

~- .

1. Report No. I 2. T m e n t Accession No.

4. Title and Subtitle

. .

NASA TP-1012

AN OPTICAL PROFLLOMETER FOR SPATIAL CHARACTERIZATION OF THREE-DIMENSIONAL SURFACES

7. Author(s1 ~.

W. Lane Kelly IV, Ernest E. Burcher, and Milton W. Skolaut, Jr.

NASA Langley Research Center Hampton, VA 23665

9. Performing Organization Name and Address .- - . .~

12. Sponsoring Agency Name and Address ~

National Aeronautics and Space Administration Washington, DC 20546

. - ~ . . -. . .

5. Supplementary Notes "

3. Recipient's Catalog No.

5. Repon Date September 1977

6. Performing Organization Code

8. Performing Organization Report No. -

L-11706 10. Work Unit No. 141-95-02-01

- 11. Contract or Grant No.

13. Type of Report and Period Covered Technical Paper

14. Sponsoring Agency Code

__ - . . . - . . . - .. -

6. Abstract

A technique is described for obtaining spatial characterization of three- dimensional surfaces with uniform near-Lambertian reflectance using a noncontact optical profilometer. The design concept and system operation are discussed, and a preliminary evaluation of a breadboard system is presented to demonstrate the feasibility of the optical profilometer technique. Measurement results are presented for several test surfaces; and to illustrate a typical application, results are shown for a cleft palate cast used by dental surgeons. Finally, recommendations are made for future development of the optical profilometer technique for specific engineering or scientific applications.

~~~~ .

7. Key Words (Suggested by Authoris)) .. .

Optical Spatial characterization Profilometer

" "

18. Distribution Statement -

Unclassified - Unlimited

Subject Category 35 " " . I

9. Security Classif. (of this report1 20. Security Classif. (of this page)

Unclassified Unclassified . .. " "~ . "" 19 $3.50 ~ ~ ."_ " - ~-

*For sa le by the National Technical information Service. Springfield, Vlrglnla 22161 NASA-Langley, 1977

National Aeronautics and Space Administration

Washington, D.C. 20546 Official Business

Penalty for Private Use, $300

SPECIAL FOURTH CLASS MA1 L BOOK

584 0 0 1 C l U D 770819 S00903DS DEPT OF TBE A I R FCRCE AF WEAPONS L AEOBATORY ATTN: T E C H N I C A L LIBRRRY {SUI.) R I R T L A N D AFB N M 87117

m

Postage and Fees Paid National Aeronautics and Space Administration NASA451 Fl USMAIL

POSTMASTER: If Undeliverable (Section 158 Postal Manual) Do Not Return

an optical profilometer for spatial characterization of three … · summary a technique is...

Documents