Photogrammetry%20for%20stress%20analysis%20of%20the%20hydrogen%20absorber%20window

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Photogrammetryfor stress analysis of the
hydrogen absorber window
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Purpose of Photogrammetric Measurememnts

• Measure the deflection of the window (delta Z) to
  compare with the delta Z computed by FEA

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FEA input applied pressure
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FEA output resultant deflection
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Window testing inputapply pressure
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Window testing outputresultant deflection
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Desired features

• Adequate resolution
• Typical deflection
• At operating pressure 250um
• Max deflection 2200um
• Non-contact targeting
• To avoid altering the windows properties

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Solution

• Adequate resolution
• Use a photogrammetric system
• 10um resolution
• Non-contact targeting
• Use a projection targeting system

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What is photogrammetry?

• Photogrammetry
• is 3-dimensional coordinate measuring technique
  that uses photographs as the fundamental medium
  for metrology
• (or measurement).

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Photogrammetic system

• V-STARS
• Video Stereo Triangulation And Resection Software
• Geodetic Services, Inc.

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V-STARS

• V-STARS uses high-resolution video cameras
  instead of film cameras. This is also referred
  to as videogrammetry or digital photogrammetry.

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3 pieces of equipment required

• 1) Camera
• 2) Targets
• 3) Software

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Camera

• INCA
• INtelligent CAmera
• Image size 18.2 x 27.6 mm
• Resolution (pixels) 2044 x 3072
• Lens focal length 17mm
• Field of view 56 deg x 76 deg

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INCA camera
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3 pieces of equipment required

• 1) Camera
• 2) Targets
• 3) Software

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Targets

• a) Reference targets
• (Autobar and coded targets)
• b) Object targets
• (we chose Pro-Spot projector)
• c) Scale bars

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Autobar
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Autobar
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Coded targets
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Targets

• a) Reference targets
• (Autobar and coded targets)
• b) Object targets
• (we chose Pro-Spot projector)
• c) Scale bars

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PRO-SPOT projector
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PRO-SPOT projector
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Projected targets
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PRO-SPOT projection targeting system
Projector strobe
Camera flash
24ms
14ms
10ms
0ms
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Targets

• a) Reference targets
• (Autobar and coded targets)
• b) Object targets
• (we chose Pro-Spot projector)
• c) Scale bars

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Scale bars
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3 pieces of equipment required

• 1) Camera
• 2) Targets
• 3) Software

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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

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V-STARS analysis - input
V-STARS analysis - input
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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

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V-STARS output
x,y,z position of each target
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V-STARS output
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V-STARS outputwith quadrant information
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V-STARS outputwith azimuthal information
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How does digital photogrammetry work?

• Step 1
• Determine camera locations from known
  (identifiable by the software) targets
• Step 2
• Determine unknown target locations from known
  camera positions

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Step 1 Determine camera location
Unknown CAMERA location
Known, fixed focal length
CCD image plane
Known TARGET location
Known TARGET location
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Step 2 Determine unknown target locations
Unknown TARGET location
Known CAMERA location
Known CAMERA location
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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

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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

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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

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Sources of error

• V-STARS analysis
• Determination of pressure
• FEA

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ErrorV-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
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ErrorV-STARS analysis

• V-STARS calculates the rms error in all 3
  dimensions

region of uncertainty
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ErrorV-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 ellipsoid

Unknown object TARGET location
Camera 1
Camera 3
Camera 2
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ErrorV-STARS analysis

• Xrms, Yrms, Zrms 5um

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Improvements made

• Increased information in central regions
• Increased stability of system
• Projector
• Camera (tripod, remote shutter)
• Pressurization system

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Old slide pattern
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Location of projected targets (old slide)
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New slide pattern
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Location of projected targets (New slide)
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Improvements made

• Increased information in central regions
• Increased stability of system
• Projector
• Camera (tripod, remote shutter)
• Pressurization system

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Initial projector mount
Learned that the projector support should be in
the focal plane of the projector
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Improved projector mount
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Improved projector mount
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Improvements made

• Increased information in central regions
• Increased stability of system
• Projector
• Camera (tripod, remote shutter)
• Pressurization system

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Tripod, remote shutter
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Improvements made

• Increased information in central regions
• Increased stability of system
• Projector
• Camera (tripod, remote shutter)
• Pressurization system

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Pressurization system
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Pressurization (0-50psi)
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Pressurization (50-100psi)
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Pressurization (100psi-burst)
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Equipment protection
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Equipment protection
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Equipment protection
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Equipment protection
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Future plans

• Use photogrammetry to measure the thickness of
  the window (currently use CMM)
• Procedure perform photogrammetric measurements
  on both surfaces of the window

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Newest discovery
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Newest discovery

• Periodic variation in deflection as f(azimuth)
  may be an indication of harmonic variations in
  the circumferential direction.