metrology and sensing - uni-jena.deand+sen… · metrology and sensing lecture 4: fringe...
TRANSCRIPT
![Page 1: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/1.jpg)
www.iap.uni-jena.de
Metrology and Sensing
Lecture 4: Fringe projection
2016-11-08
Herbert Gross
Winter term 2016
![Page 2: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/2.jpg)
2
Preliminary Schedule
No Date Subject Detailed Content
1 18.10. Introduction Introduction, optical measurements, shape measurements, errors,
definition of the meter, sampling theorem
2 19.10. Wave optics (ACP) Basics, polarization, wave aberrations, PSF, OTF
3 01.11. Sensors Introduction, basic properties, CCDs, filtering, noise
4 08.11. Fringe projection Moire principle, illumination coding, fringe projection, deflectometry
5 09.11. Interferometry I (ACP) Introduction, interference, types of interferometers, miscellaneous
6 22.11. Interferometry II Examples, interferogram interpretation, fringe evaluation methods
7 29.11. Wavefront sensors Hartmann-Shack WFS, Hartmann method, miscellaneous methods
8 06.12. Geometrical methods Tactile measurement, photogrammetry, triangulation, time of flight,
Scheimpflug setup
9 13.12. Speckle methods Spatial and temporal coherence, speckle, properties, speckle metrology
10 20.12. Holography Introduction, holographic interferometry, applications, miscellaneous
11 03.01. Measurement of basic
system properties Bssic properties, knife edge, slit scan, MTF measurement
12 10.01. Phase retrieval Introduction, algorithms, practical aspects, accuracy
13 17.01. Metrology of aspheres
and freeforms Aspheres, null lens tests, CGH method, freeforms, metrology of freeforms
14 24.01. OCT Principle of OCT, tissue optics, Fourier domain OCT, miscellaneous
15 31.01. Confocal sensors Principle, resolution and PSF, microscopy, chromatical confocal method
![Page 3: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/3.jpg)
3
Content
Moire effect
Illumination coding
Fringe projection
Deflectometry
![Page 4: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/4.jpg)
4
Moire Effect
Special pattern by using two identical but inclined gratings
Ref: R. Kowarschik
Sinusoidal grating Rotated grating Overlay: Moiré interference
![Page 5: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/5.jpg)
5
Moire Effect
Improved accuracy by
two inclined gratings
The new period is given by
0
sin( )
pp
elementary
period p1
increased
period p
elementary
period p2
Improved accuracy by two gratings with
slightly different periods p1 / p2
The new period is given by
1 2
2
p pp
p
rotation
angle
elementary
period po
increased
period
p = po/sin
![Page 6: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/6.jpg)
6
Moire
Point grating Moire
Moire effect for two
circular fringe systems
![Page 7: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/7.jpg)
7
Shadow Moire Setup
Ref: T. Yoshizawa
Shadow Moire
Illumination and observation propagated through the same
grating (multiplicative Moire)
Illumination:
transmission at position A
Observation:
transmission at position B
Total signal
with geometry
Finally gives
and allows to reconstruct the height h(x,y)
High frequencies are filtered out:
smoothed Moire signal
AA x
pyxt
2cos1),(
BB x
pyxt
2cos1),(
BA x
px
pyxI
2cos1
2cos1),(
P
PPB
P
PA
hl
xlhsx
hl
xlx
,
hl
hs
pyxKyxI
2cos1),(),(
![Page 8: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/8.jpg)
8
Shadow Moire
Typical formation of fringes
Moire period quite longer then
grating constant p
Ref: R. Kowarschik/Wyant
Moire period
grating period
illumination
observation
![Page 9: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/9.jpg)
9
Moire
Ref: R. Kowarschik
Shadow Moire for
different viewing
angles
Shadow Moire
filtering of the
elementary period
frequency
![Page 10: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/10.jpg)
10
Shadow Moire
Serat projection
Ref: R. Kowarschik
),(1 yxt ),(2 yxt
)),(2cos1(128 yx),(),( 21 yxtyxt
![Page 11: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/11.jpg)
11
Shape Measurement by Structured Illumination
Main idea:
- light pattern projected onto the scene under investigation
- deformation of the pattern due to 3D shape of the body
- detection of the changed pattern by camera
- analysis of the geometry to reconstruct the shape
Physics:
- incoherent illumination, light diffuse scattered into all directions
- incoherent illumination, light specular reflected by polished surface (deflectometry)
- coherent illumination, interferometry or holography
Special coding/decoding strategies gives fast and unique shape reconstruction:
coded structured light (CSL)
Single shot: phase unwrapping is critical
Classification of methods:
- single/multiple shots
- sparse/dense pattern (discretized, binary pattern/continuous grayscales)
- spatial/time multiplexing (binary encoding / phase shifting)
- black/white vs colored pattern
- number of cameras
- axis codification:
1D vs 2D pattern
![Page 12: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/12.jpg)
12
Measurement by Fringe Projection
Projection of a light sheet onto
a deformed surface
Corresponds to one fringe in
more complicated pattern
projection
![Page 13: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/13.jpg)
13
Linear Encoders
Main idea:
- linear scale as reference, linear pattern of fringes
- reading head with similar linear scale
- comparison of scales due to changes by movement or deformation
Optical encoding techniques by:
- Moire
- grating fringe projection
- interferometry
- holography
Quantitative evaluation of length by counting the periods/fringes
Unique demodulation by phase shifting techniques
Similar technique:
angle encoding
![Page 14: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/14.jpg)
14
Coded Illumination
Time multiplexing:
- binary codes
- n-ary codes
- gray code with phase shift
- hybrid methods
Spatial codification:
- non-formal codification
- M-arrays
- de Bruijn sequences
Direct codification:
- gray levels
- color coding
![Page 15: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/15.jpg)
15
Coded Illumination
Comparison:
binary graycode vs phase shift
Ref: R. Kowarschik
graycode
phase
shift
![Page 16: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/16.jpg)
16
Coded Illumination
Binary graycode
projection of different pattern in a time series
Ref: R. Kowarschik
![Page 17: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/17.jpg)
17
Absolute Encoders
Ref: R. Kowarschik
Absolute decoding:
simultaneously binary multi-track code
![Page 18: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/18.jpg)
18
Coded Illumination
Phase shift technique:
projection of the same periodic pattern for different phases
At least three phases are needed to guarantee a unique reconstruction
To relax noise influence:
4 or 5 phase values measured
(redundance)
Ref: R. Kowarschik
= = 0
2
= = 32
= = 0
2
= = 32
![Page 19: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/19.jpg)
19
Encoding with Moire
Linear encoders:
slightly different period in projection /
observation
![Page 20: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/20.jpg)
20
Wrapping
Full surface height h: z(x,y)
Wrapped onto a limited height h
Typical for recovery of angle/phase information onto the elementary interval 2
z(x,y) z(x,y) z(x,y) wrapped
h
h
![Page 21: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/21.jpg)
Shape measurement of a surface
Projection of a fringe pattern onto the surface
Observation of the fringe deformation by a camera, mostly by Scheimpflug geometry
A shift corresponds to a change in depth
Non-trivial image processing
Fringe Projection Setup
light
source
collector
amplitude
grating
condenser
surface
under test
sensor
objective for
detection
![Page 22: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/22.jpg)
22
Pattern Projection
Checkerboard projection pattern instead of simple linear fringes
![Page 23: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/23.jpg)
23
Pattern Projection Setups
General setup of a pattern projection
![Page 24: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/24.jpg)
24
Fringe Projection
Illumination:
1. telecentric / collimated
2. central / source point
surface z(x,y)
z
x
p
surface z(x,y)
z
x
p(x)
point
source
![Page 25: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/25.jpg)
25
Fringe Projection
Observation methods
1. structured detector
2. Moire
surface z(x,y)
z
x
CCD
sensor
surface z(x,y)
z
x
CCD
sensor
grating
projector
![Page 26: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/26.jpg)
26
Fringe Projection
Problems with shadowing
Ref: R. Kowarschik
![Page 27: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/27.jpg)
27
Measurement by Projection
Visibility and unvisible regions in projection
Here: measurement of a sphere
![Page 28: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/28.jpg)
Fringe period in projection
Lateral shift
Corresponding depth value z
1cos
ppx
21 coscos zu
2
21
1
21
cos
sin
cos
coscos)(
p
z
p
z
p
uxf
x
Signal Evaluation of Fringe Projection
test surface
P
P
1
2
z
u
x
z
2
1
projected fringes
p
px
observation
![Page 29: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/29.jpg)
29
Measurement by Central Projection
Evaluation in only 2 dimensions for central
projection
Mapping transform
'
)'(
xx
xxdtcZ
'
)'(
xx
xxdtcd
c
xX
![Page 30: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/30.jpg)
30
Fringe Projection
Systems
Ref: R. Kowarschik
Measuring of a seat with
kolibriROBOT
3D sensorhead
![Page 31: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/31.jpg)
31
Example Fringe projection
Monochromatic illuminated technical surface
![Page 32: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/32.jpg)
32
Fringe Projection
Examples
Ref: R. Kowarschik
Prepared stump, 4 different
perspectives
Complete jaw tooth
Measuring result;
Comparision with
CAD model
Sheetmetal
workpiece
![Page 33: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/33.jpg)
33
Shape Measurement
Reverse engineering:
from body to digital 3D data
Ref: W. Osten
![Page 34: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/34.jpg)
34
3D Shape Measurement for Biometry
Colored biometric fringe projection
Projection of a 2D triangular pattern
![Page 35: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/35.jpg)
35
3D Shape Measurement for Biometry
Biometric 3D mesh of a human face
Error-free identification of people
Ref: S. Zhang
![Page 36: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/36.jpg)
36
Deflectometry
Principle of deflectometry:
measurement of the deflection of light rays for reflective polished surfaces under the
specular direction
nature of the light source is known
measured object is a “part of the imaging system”
observation of the light source over the object
Ref: B. Fleck
![Page 37: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/37.jpg)
37
Deflectometry
General approach
Ref: B. Fleck
structured illumination of the object
quantitative 3D surface
topography
gradient field
object phase image
qualitative evidence of
macroscopic defects
Additional
information from
system calibration,
system geometry
![Page 38: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/38.jpg)
-38-
Deflectometry
Principle:
- an array of thin light pencils is incident on te surface under test
- the ray positions are measured by a camera after reflection from teh surface under test
- the nominal locations of the ray centroids must be calibrated
- to ensure a unique interpretation, several z-positions of the screen are measured
- only works for polished surfaces
- the pattern can be a 2D array or a line pattern
Accuracy:
- strongly depends on the size of the surface
- rough estimation: 1 mm
for small pieces, 0.2 mm can be
acchieved
Problems:
- ranges of large curvature:
lateral resolution is poor
- not usable before polishing
- calibration and reconstruction
algorithms complicated
moving camera position
camera
illumination
projector
mask with
pinhole array
screen
surface
under test
38
![Page 39: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/39.jpg)
39
Deflectometry
Setup for reflective sample
Setup for refractive/transmissive sample
![Page 40: Metrology and Sensing - uni-jena.deand+Sen… · Metrology and Sensing Lecture 4: Fringe projection 2016-11-08 Herbert Gross Winter term 2016](https://reader035.vdocuments.site/reader035/viewer/2022062317/5fbf2722a5ca7c10fd5a82ab/html5/thumbnails/40.jpg)
40
Deflectometry
Calculation and evaluation
p: stripe width
d:distance focusing screen - surface
Ref: B. Fleck
cameracamera
screen
bended surface
2tan(2 )d
p