Shape and deformation measurements by high-resolution fringe projection methods February 2018
Outline Motivation System setup Principles of operation Calibration Applications Conclusions & Future work
Motivation Advance current methods for quantitative data collection using a non-contact, robust technique, applicable to a wide range of applications. Art Conservation Range Mobility Resolution Accuracy Criterion Crack Propagation Versatility Ease-of-Use Time
System Setup 1. Single Frame Fringe Projection (High-speed Fringe Projection) - a near-ir light source, an optical imaging device, and a near infrared sensitive digital charged-couple device (CCD) camera. LED θ A O I PC
Digital Micromirror Device (DMD TM ) Ref. Texas Instruments Close-up of chip surface Ants Foot 20 mm
Digital Micromirror Device
Digital Micromirror Device
Digital Micromirror Device
Digital Micromirror Device
System Setup 2. Structured light projection with phase shifting - A spatial light modulator (SLM) and a digital charged-couple device (CCD) camera. The SLM, packaged by Vialux, contains a digital light processing (DLP ) unit from TI MEMS based Sinusoidal Fringe Projection SLM θ A O I 20 mm PC Actual Pattern Projection 16000 Sinusoidal Fringe Projection 14000 12000 Light Intensity 10000 8000 6000 4000 2000 0 100 200 300 400 500 600 Pixels
Principles of Operation Single Image Analysis DC Component Shape information Ii ( x, Recorded Intensity distribution bi ( x, Image Contrast ai ( x, Image Brightness FFT IMAG( x, ( x, arctan REAL( x, METHOD MATHEMATICS i( x, ( x,, Multiple Image Analysis Ii ( x, ai ( x, bi( x, cos i i( x, ( x, i Random phase Fringe Locus Function Induced phase shift ( x, arctan m m Ii sin[ 2 m k ( i 1) ] i 1 m I m k i cos[ 2 ( i 1)] i 1 Arctangent is a discontinuous function
Principles of Operation - Unwrapping Temporal phase unwrapping: u i1 ( x, i1 ( x, 2N i1
Principles of Operation - Unwrapping Spatial phase unwrapping: Difference between neighboring pixel FFT Base on regions orders Determine 2 Filter Phase information Mod ( x, inverse FFT Wrapped phase arctan Spatial unwrapping IMAG( x, REAL( x, Unwrapping Scale x, ( x, 2k i, j ( i, j
C ), ( 0 u 0 v α z y x M ), ( t R m M t R A m t r r r ~ 3 2 1 0 0 ~ 1 1 0 0 0 1 z y x v u v u s Homography matrices are estimated in MATLAB using nonlinear method of maximum likelihood estimation. 5 intrinsic parameters [A] and extrinsic parameters [R t] are computed. 1. Z. Zhang, A flexible new technique for camera calibration, IEEE Transactions on Pattern analysis and machine intelligence, 2000, pp. 1330-1334 Removing lens distortion by camera calibration Pinhole camera model: Pinhole method is used to obtain intrinsic and extrinsic parameters of camera A planar checkerboard is shown under 20 different orientations and the grid corners of the image are extracted. Extrinsic parameters Error [pixel]
Range Application Sculpture Digitization System Setup Ease-of-Use Resolution Accuracy Versatility Criterion Sculpture titled Funeral of a Young Maiden Casona, South Italy. Late 4 th Century BCE Optimization of setup for sculpture digitization.75 m Schematic of sculpture digitization setup Measurement System Rotational Stage
Representative Results Approximate x resolution =.015 in. Approximate y resolution =.015 in Approximate z resolution = 0.0027 in.. A 0 ⁰ 180 ⁰ A
Application Shape and Deformation Measurements on a Canvas The object under test is a 4150 cm 2 painting on canvas. The painting is subjected to an airflow of a fan at the distance of 0.5 m from the painting Original image Lens distortion removed image Perspective removed image 10 cm 3D Shape 3D Shape 2 mm The distance from projector to object is 1.75 m, and the field of view is 500X500 mm 2. -8
Application Shape and Deformation Measurements on a Canvas The object under test is a 4150 cm 2 painting on canvas. The painting is subjected to an airflow of a fan at the distance of 0.5 m from the painting Canvas under airflow phase (time 1) phase (time 2) 10 cm 3D deformation 1.5 mm phase (time 2) 0 The distance from projector to object is 1.75 m, and the field of view is 500X500 mm 2.
Application of Single Frame Projection- Surface Road Measurements * Courtesy of VOTERS website
SOPRA Surface Optical Profilometry Roadway Analysis Normalized sunlight spectrum under sunny day condition measured on March 10,16:44 EST Projector Cooler system Ronchi ruling grating Near-Infrared light source Camera Near-Infrared sensitive camera Bandpass Interference Filter, Near-IR Normalized Near-Infrared light source spectrum under lab condition measured on March 10,16:57 EST
Time Range Mobility Accuracy Application of Single Frame Projection- Surface Road Measurements Van Setup Primary Criterion Requirement Z resolution: mm Approximate x resolution at distance 1.75 from the system to the ground = 0.38 mm. Approximate z resolution = 0.4 mm.
Dynamic results of measurements of different RI surface The different RI under test at speed of 20 miles/hr, exposure time 253 um, gain value 33, the field of view 455455mm 2. (a), (b) and (c), Fringes projected on the different RI condition objects; (e), (f) and (g), 3D model respectively. (a) (b) (c) (e) (f) (g)
Dynamic results of measurements of road surface Measurement results of consecutive images analyzed using FFT methods. Measurements done at 20 miles/hr Y Z X the video of the dynamic results the image of road