photogrammetry for stress analysis of the hydrogen absorber window
TRANSCRIPT
PhotogrammetryPhotogrammetryfor stress analysis of the hydrogen for stress analysis of the hydrogen
absorber windowabsorber window
Purpose of Photogrammetric Purpose of Photogrammetric MeasurememntsMeasurememnts
Measure the deflection of the window (delta Z) to compare with the delta Z computed by FEA
Delta Z
Pressure = 0 PSI
Pressure = X PSI
FEA input: FEA input: applied pressureapplied pressure
FEA output: resultant deflection
Window testing input:Window testing input:apply pressureapply pressure
Window testing output:resultant deflection
Desired features
Adequate resolutionTypical deflection:At operating pressure ~ 250umMax deflection ~2200um
Non-contact targetingTo avoid altering the window’s properties
Solution
Adequate resolutionUse a photogrammetric system
10um resolution
Non-contact targetingUse a projection targeting system
What is photogrammetry?
Photogrammetry is 3-dimensional coordinate measuring technique that uses photographs as the fundamental medium for metrology (or measurement).
Photogrammetic system
V-STARS
Video Stereo Triangulation And Resection Software
Geodetic Services, Inc.
V-STARS
V-STARS uses high-resolution video cameras instead of film cameras. This is also referred to as videogrammetry or digital photogrammetry.
3 pieces of equipment required
1) Camera
2) Targets
3) Software
Camera
INCA INtelligent CAmera
Image size: 18.2 x 27.6 mm
Resolution (pixels): 2044 x 3072Lens focal length: 17mm
Field of view: 56 deg x 76 deg
INCA camera
3 pieces of equipment required
1) Camera
2) Targets
3) Software
Targets
a) Reference targets (Autobar and coded targets)
b) Object targets (we chose Pro-Spot projector)
c) Scale bars
Autobar
Autobar
Coded targets
Targets
a) Reference targets (Autobar and coded targets)
b) Object targets (we chose Pro-Spot projector)
c) Scale bars
PRO-SPOT projector
PRO-SPOT projector
Projected targets
PRO-SPOT projection targeting system
Projector strobe
Camera flash
24ms14ms10ms0ms
Targets
a) Reference targets (Autobar and coded targets)
b) Object targets (we chose Pro-Spot projector)
c) Scale bars
Scale bars
3 pieces of equipment required
1) Camera
2) Targets
3) Software
V-STARS input
V-STARS measures the target positions on CCD
a) Reference targets (Autobar and coded targets)
b) Object targets (we chose Pro-Spot projector)
c) Scales
V-STARS analysis - inputV-STARS analysis - input
V-STARS analysis
Using the measured the target positions, V-STARS performs:
a) Resection (determines camera positions) and camera calibration
b) Triangulation to determine the x,y,z
position of each target
c) Dimensions the measurements
V-STARS output
rmsxx
rmsyy
rmszz
000 ,,
x,y,z position of each target
V-STARS output
V-STARS outputV-STARS outputwith quadrant informationwith quadrant information
V-STARS outputV-STARS outputwith azimuthal informationwith azimuthal information
How does digital photogrammetry work?
Step 1Determine camera locations from
known (identifiable by the software) targets
Step 2Determine unknown target locations
from known camera positions
Step 1 Determine camera location
Unknown CAMERA location
Known, fixed focal length
Known TARGETlocation
Known TARGET location
CCD image plane
Step 2 Determine unknown target locations
Unknown TARGET location
Known CAMERAlocation
Known CAMERA location
Resolution is a function of:
The resolution and quality of the camera
The size of the object being measured
The number of photographs taken
The geometric layout of the pictures
Correctness of the lens calibration
Resolution
VSTARS can measure to better than 1/50 of a pixel
How?
The software finds the centroid of an intensity weighted analysis of the target.
Optimally, 50 or more pixels/target are used for making that determination
Resolution
So, accepting this:
For INCA (2000 x 3000 pixel camera):
(2000 pixels/field width) * (1/50 parts/pixel) = 1part / 100,000
Assuming the field of view is 1 meter in diameter, this corresponds to a resolution of
1part/100,000 = 1m/100,000 = 10um
which is adequate for our purposes:
Sources of error
V-STARS analysis
Determination of pressure
FEA
Error:V-STARS analysis
V-STARS calculates the rms error for all 3 dimensions
Unknown object TARGET location
Camera 1 Camera 2
Note: V-STARS discards all 2-ray intersections as trivial
Error:V-STARS analysis
V-STARS calculates the rms error in all 3 dimensions
Unknown object TARGET location
Camera 1 Camera 3Camera 2
region of uncertainty
Error:V-STARS analysis
12-ray intersection is typical, resulting in an ellipsoid of uncertainty.
The rms errors reported by V-STARS are the semimajor axes of
the ellipsoidUnknown object TARGET location
Camera 1 Camera 3Camera 2
Error:V-STARS analysis
Xrms, Yrms, Zrms ~5um
Improvements made
Increased information in central regions
Increased stability of system Projector Camera (tripod, remote shutter) Pressurization system
Old slide pattern
Location of projected targets (old slide)
New slide pattern
Location of projected targets (New slide)
-150
-100
-50
0
50
100
150
-150 -100 -50 0 50 100 150
Improvements made
Increased information in central regions
Increased stability of system Projector Camera (tripod, remote shutter) Pressurization system
Initial projector mount
Should support here ONLYNot here
Learned that the projector support should be in the focal plane of the projector
Improved projector mount
Improved projector mount
Improvements made
Increased information in central regions
Increased stability of system Projector Camera (tripod, remote shutter) Pressurization system
Tripod, remote shutter
Improvements made
Increased information in central regions
Increased stability of system Projector Camera (tripod, remote shutter) Pressurization system
Pressurization system
Pressurization (0-50psi)pressure vs time
0.00
10.00
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40.00
50.00
60.00
0 200 400 600 800 1000 1200 1400 1600 1800 2000
time (seconds)
pre
ss
ure
(p
si)
Pressurization (50-100psi)
pressure vs time
40.00
50.00
60.00
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90.00
100.00
110.00
2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000
time (seconds)
pre
ss
ure
(p
si)
Pressurization (100psi-burst)
pressure vs time
80.00
85.00
90.00
95.00
100.00
105.00
110.00
115.00
120.00
125.00
4000 4200 4400 4600 4800 5000 5200
time (seconds)
pre
ss
ure
(p
si)
Equipment protection
Equipment protection
Equipment protection
Equipment protection
New plan
Plan to measure window thickness using photogrammetry (currently use CMM)
Procedure: perform photogrammetric measurements on both sides of the window.
Newest discovery50 PSI
deflection vs azimuth
0
50
100
150
200
250
300
350
400
450
500
0 50 100 150 200 250 300 350
azimuth (deg)
delt
a z
(u
m)
radius = 6mm
radius = 13mm
radius = 19mm
radius = 26mm
radius = 33mm
radius = 39mm
radius = 46mm
radius = 52mm
radius = 53mm
radius = 59mm
radius = 66mm
radius = 72mm
radius = 79mm
radius = 89mm
radius = 93mm
radius = 100mm
radiu s= 106mm
radius = 116mm
radius = 120mm
radius =127mm
radius = 134mm
Newest discovery
Periodic variation in deflection as f(azimuth) may be an indication of harmonic variations in the circumferential direction.