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A Real-Time Multi-Sensor 3D Shape Surface Measurement System Using Fringe Analysis

G eneral E ngineering R esearch I nstitute. A Real-Time Multi-Sensor 3D Shape Surface Measurement System Using Fringe Analysis. By Mohammad Al Sa’d. www.megurath.org. Introduction. General background Functional requirements of the system

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A Real-Time Multi-Sensor 3D Shape Surface Measurement System Using Fringe Analysis

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  1. General Engineering Research Institute A Real-Time Multi-Sensor 3D Shape Surface Measurement System Using Fringe Analysis By Mohammad Al Sa’d www.megurath.org

  2. Introduction • General background • Functional requirements of the system • Stages of the 3D surface reconstruction process • Specifications of the system • Hardware design of the system • Software design of the system • Results

  3. Fringe Pattern Profilometry Projector Background (1/2) Object • Optical non-contact 3D surface method • Fringes generation • Laser Interference • structured light projection • Measurement precision: from 1μm • Depends on the optical resolution of the fringes • Fringes width and their optical quality (depth of field, camera resolution and display resolution) • Light Wavelength • Applications • Inspection of components during the production process (turbine blades and circuit boards) • Reverse engineering (CAD data from existing objects) • Documenting objects of cultural heritage • Medical applications: live measuring of human body shape Camera Projected Pattern Image plane

  4. Metrology Guided Radiotherapy Background (2/2) • Radiation therapy is used since about more than 100 years for the treatment of cancer. • The goal is to destruct the cancer cells with minimal radiation damage to the surrounding healthy cells. • Pre-treatment stages: • 3D planning models are created (CT, MR or others) to accurately guide treatment. • Radiation treatment sessions are planned and radiation doses are calculated (dosimetry). • Treatment stages: • Radiation beam is shaped to precisely hit the target (site of tumour). • Radiation is delivered from multiple angles, using the controlled gantry and patient table. • Treatment is repeated over multiple sessions. • Any small movement (like breathing) or patient’s body changes during successive sessions affect the goal of the treatment. Rotating Gantry

  5. Field of View Functional Requirements 400mm • Spatial Resolution 400mm 400mm • At least 100 x,y points • At least 400mm × 400mm × 400mm • Measurement Error (Accuracy) • Not to exceed ±1 mm (according to the tolerance of the dosimteric models used in radiotherapy planning). • Dynamic Real-Time Measurement • At least FIVE measurements per second (to detect small movements, like breathing) Z X Y

  6. 3D Surface Reconstruction Stages(1/5)

  7. Fringe Profilometry Analyses 3D Surface Reconstruction Stages(2/5) • Spatial Fringe Analysis Techniques (modulation phase is generated from a single input image): • Fourier Profilometry: • Windowed Fourier Profilometry: Processing window passes through the image to find the phase at the centre pixel using forward and inverse FFT. • Wavelet Profilometry: Generating phase from the wavelets of the image line-by-line • Temporal Fringe Analysis Techniques (modulation phase is generated from multiple input images – at least three images): • Phase-Stepping Profilometry: Using least square method to extract the phase. 3 2 1 1 2 3

  8. Phase Unwrapping 3D Surface Reconstruction Stages(3/5) • To remove the phase ambiguity (2 modules). • Types: • Path-Dependent Unwrappers • Schafer Unwrapping Algorithm • Path-Independent Unwrappers • Path-Independent Unwrappers • Goldstein's Branch Cut Algorithm • Quality-Guided Path Following Algorithm • Flynn's Minimum Discontinuity Algorithm • Preconditioned Conjugate Gradient (PCG) Algorithm • Lp-Norm Algorithm • Reliability Ordering Algorithm • Synthesis Algorithm • Differ in speed and robustness.

  9. Absolute Height Calibration 3D Surface Reconstruction Stages(4/5) • Unwrapped phase map is converted to real world heights • Height calibration process: • Triangulation spot (embedded inside the fringe pattern) is detected. • Unwrapped phase value at the spot (x,y) location is subtracted from the unwrapped phase map (to generate a relative phase map). • Unwrapped phase map is linked to the real world heights via interpolation (using the height calibration volume). • To compensate the geometric distortions by optics and perspective. • X,Y world coordinates are generated for a number of height steps to generate the traversal calibration volumes • X,Y world coordinates are retrieved depending on the correspondent height value of each pixel and using interpolation. • Traversal (XY) Calibration

  10. Deliverables (so far!) Specifications of the System(1/3) • Speed: 8Hz (using Fourier Profilometryand Goldstein's unwrapper) 5Hz (using Fourier Profilometryand Reliability ordering unwrapper) • Field-of-view: (X,Y,Z) = 400mm × 500mm × 400mm • Spatial resolution: 262,144 x,y points • Multiple sensors: Coverage area around 270° • Measurement error: Accuracy around ±0.5 mm • Pre-processing Techniques: Noise Reduction and gamma Correction • Catalogue of measurement techniques: Ability to select different algorithms • User interaction and multi-user modes: GUI to interact with the user Normal and advanced modes (for both metrology experts and normal users) • Various operating modes: Online: for real-time measurements Offline: for pre-saved images and videos • 3D visualisation and 2D plotting. • Various image saving choices. Sensor1 Sensor3 Sensor2 Treatment coach

  11. Program snapshots Specifications of the System(2/3)

  12. Program snapshots Specifications of the System(3/3)

  13. Hardware Configuration Hardware Design of the System(1/3) Synchronisation Unit Main Control & Processing Unit Sensor1 Sensor2 Sensor3 Sensor Processing Unit Sensor Processing Unit Sensor Processing Unit

  14. Conventional LCD projector LCoSprojector • Sensor Components: Projector Hardware Design of the System(2/3) Canon XEED SX60

  15. Gige Camera Controller Fourier Triangulation Phase-Stepping • Sensor Components: Camera Hardware Design of the System(3/3) Gige Broadcasting Prosilica GE1380 • GigE technology: • Progressive scan CCD • 20 fps @ 1360 × 1024 • 35 fps @ 512 x 512 • Direct image registration to the system memory via a compatible Gigabit port • Upto 100 meter cable length

  16. Output Buffer Grabbed Images from the Camera Processing Thread Input Thread Output Thread Input Buffer Display and/or store according to the user preferences • Software Configuration: Processing Core Software Design of the System Multithreaded processing framework: • Input Thread: Project and grab frames • Processing thread: Apply measurement, unwrapping and calibration techniques • Output thread: Stream/save/display results

  17. Static Object Measurement – One Sensor Results(1/3)

  18. Static Object Measurement – Multi-Sensor Results(2/3) Sensor1 Sensor3 Sensor2 Treatment coach

  19. Moving Object Measurement – One Sensor Results(3/3)

  20. Thank You!

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