Xuan-Loc Nguyen

High-speed 3D surface profilometry employing trapezoidal phase-shifting method with multi-band calibration for colour surface reconstruction

This paper presents a new optical measurement method employing a HSI (hue, saturation and intensity) colour model to form trapezoidal structured patterns for morphology reconstruction of a measured object at high speed. Profilometry on objects having non-monochromatic surfaces is considered as one of the remaining challenges most faced by the currently existing structured-light projection methods since the surface reflectivity to red, green and blue light may vary significantly. To address this, an innovative colour calibration method for a hue component is developed to determine the accurate reflectivity response of the measured surface. The trapezoidal colour pattern is calibrated to compensate the hue-shifted quantity induced by the reflective characteristics of the objects surface. The developed method can reconstruct precise 3D surface models from objects by acquiring a single-shot image, which can achieve high-speed profilometry and avoid in situ potential measurement disturbances such as environmental vibration. To verify the feasibility of the developed methodology, some experiments were conducted to confirm that the measurement accuracy can be controlled within 2.5% of the overall measurement range and the repeatability of 3.0% within ±3σ can be achieved.

High-speed 3-D machine vision employing Fourier Transform Profilometry with digital tilting-fringe projection

In this article, 3-D image acquisition for high-speed machine vision using Fourier transform profilometry (FTP) with digital tilting-fringe projection is presented. FTP employing tilting-fringe patterns is proposed to achieve real-time 3-D machine vision. To achieve this, the mathematical modeling of FTP with tilting-fringe projection is presented and the critical condition for measuring maximum surface gradients is analyzed. Based on the methodology established, a 3-D optical machine vision system was successfully developed and two experimental examples were conducted to verify the feasibility and accuracy of the method.

Dynamic 3D surface profilometry using a novel colour pattern encoded with a multiple triangular model

In this paper, a novel active structured fringe method for dynamic 3D surface profilometry is presented using a colour fringe pattern encoded with multiple phase-shifted triangular modulations. Rapid 3D surface profilometry is extremely important to automatic optical inspection (AOI), especially for in situ optical surface profilometry. In the proposed approach, three-step phase shifting can be simultaneously performed by encoding and analyzing components of red, green and blue colours in the projected colour fringe patterns. A significant advantage can be obtained in eliminating arctangent calculation and one-shot imaging for obtaining dynamic full-field 3D surface profile reconstruction. Experimental tests were conducted to verify the capability of the developed method in achieving high-speed 3D measurement with an average measurement error of less than 2.8% of the overall detection range.

Dynamic Surface Profilometry and Resonant-Mode Detection for Microstructure Characterization Using Nonconventional Stroboscopic Interferometry

In this paper, an innovative method of automatic resonant-mode detection employing nonconventional stroboscopic interferometry is developed for nanoscale dynamic characterization of microstructures. Considering that a tested microstructure having an individual vibrating excitation source cannot be analyzed directly by the traditional stroboscopic method, an optical microscopy based on new stroboscopic interferometry was established to achieve resonant-mode detection and full-field vibratory out-of-plane surface profilometry of microstructures. To verify the effectiveness of the developed methodology, a crossbridge microbeam was measured to analyze the resonant vibratory modes and full-field dynamic-mode characterization. The experimental results confirm that the dynamic behavior of the microstructures can be accurately characterized with satisfactory mode-detection accuracy and surface profilometry.

Novel 3-D Object Recognition Methodology Employing a Curvature-Based Histogram

In this paper, a new object recognition algorithm employing a curvature-based histogram is presented. Recognition of three-dimensional (3-D) objects using range images remains one of the most challenging problems in 3-D computer vision due to its noisy and cluttered scene characteristics. The key breakthroughs for this problem mainly lie in defining unique features that distinguish the similarity among various 3-D objects. In our approach, an object detection scheme is developed to identify targets underlining an automated search in the range images using an initial process of object segmentation to subdivide all possible objects in the scenes and then applying a process of object recognition based on geometric constraints and a curvature-based histogram for object recognition. The developed method has been verified through experimental tests for its feasibility confirmation.

Automatic object detection employing viewing angle histogram for range images

In this paper, a general scheme for automatic object detection is presented. Classification of three dimensional (3-D) objects using range images remains to be one of the most challenging problems in 3-D computer vision due to its noisy and cluttered scene characteristics. The key breakthroughs for this problem lie mainly in defining unique features that distinguish the similarity among various 3-D objects and developing robust segmentation algorithms that can effectively utilize these defined similarity features. In our approach, the object detection scheme can identify inspecting targets automatically in the range images using an initial process of object segmentation to subdivide all possible objects in the scenes and then applying a process of object classification based on geometric constrains (dimension, point density and surface types) and viewing angle histogram for object classification. The methodology computes the surface normal vector distribution of object model at each viewing angle and aggregates the features into histograms over mesh neighborhoods. These histograms are stored in the database for object searching. The classified objects are finally labeled with the consistent labels by finding the highest histogram matching coefficient according to the object list. The method was verified through some experimental tests for its feasibility confirmation.

Real-time 3-D robot vision employing novel color fringe projection

This article presents a novel 3-D image acquisition technique using color fringe projection with encoded triangular fringes for high-speed 3-D machine vision. In the developed method, three-step phase shifting operation can be performed simultaneously by encoding and analyzing RGB color components on single structured fringe patterns. The greatest advantage for using the proposed structured color fringe having triangular intensity is on its significant time reduction required in phase retrieving. A high-speed 3-D prototype robot vision system was successfully developed and some experiments were conducted to verify the feasibility and accuracy of the method. From the preliminary experimental result analysis, it was demonstrated that the speed of the 3D image acquisition can be achieved up to 60 frames per second (fps) or higher. The maximum measurement errors can be controlled within 2.8% of the overall depth detection range.

Portable Measurement System for Static and Dynamic Characterization of MEMS Component

MEMS performance can be determined from the static and dynamic characteristic. These two parameters can be measured by various measuring systems. In this chapter, a portable measurement system which is able to measure static and dynamic characteristic of MEMS in 2-D and 3-D aspects is presented. Nanoscale static microstructure profiles are measured by means of white-light interferometry with nanometer scale accuracy. Key for dynamic characteristic measurement is the employment of stroboscopic lighting which is synchronized with the excitation signal of the measured sample. The system is capable of measuring multimode resonant frequencies and also mode reconstruction for both in-plane and out-of-plane vibration. The main advantage of the system is its versatility and portability for testing different vibration modes with improved reliability and repeatability. Achievable repeatability of the resonant frequency measurement can reach 0.012 kHz for in-plane vibration, while the repeatability of the out-of-plane resonant frequency is 0.216 kHz for a controlled environment and 0.354 for an environment with disturbance from air conditioner.