This PDF file contains the front matter associated with SPIE Proceedings Volume 10220, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Polarization is a unique property of light, providing a number of advantages in optical metrology. In this talk, I will discuss principles and experimental results of polarization techniques in fringe project metrology and interferometric measurement.

Image matching involves detecting the same points in two or multiple images that are captured from different viewpoints, at different time, and/or by different cameras. This paper presents using the image-matching-based techniques to carry out the static and dynamic 3D shape measurements. The process contains two crucial steps: (1) calibrate the cameras to get the intrinsic and extrinsic parameters; (2) perform matching of pixel points to detect the location disparities of the same physical points in the involved two or multiple images. A number of experiments are shown to demonstrate the applications to 3D shape, deformation, motion and vibration measurements.

This paper presents a method to overcome the light spectral range limitation of using digital-light-processing (DLP) projector for 3D shape measurement by developing a mechanical projector. The mechanical projector enables much broader spectral range of light than that the DLP projector allows. The rapidly spinning disk with binary structures can generate desired sinusoidal patterns at a frequency of 10 kHz or higher with a single DC motor. By precisely synchronizing the camera with the projector, phase-shifted fringe patterns can be accurately captured for high-accuracy 3D shape measurement. We further employed a computational framework that could enable absolute phase and thus absolute 3D shape measurement. We developed such prototype system that experimentally demonstrated the success of the proposed method.

This paper presents such a high-speed, high-accuracy structured light technique that could achieve large range 3D shape measurement. The enabling method is our recently proposed system calibration that splits the calibration process into two stages. Specifically, we calibrate the intrinsic parameters at a near position with a regular size yet precisely fabricated calibration target, and then calibrate the extrinsic parameters with the assistance of an additional large range yet low accuracy low cost 3D scanner (i.e., Kinect). We developed a system that achieved 500 Hz with a resolution 2304 × 1400. The field of view (FOV) of our structured light system is 0.9 m(W) × 1.4 m(H) × 0.8 m(D). Our experimental data demonstrated that such a large range structured light system can achieve an mean error of 0.13 mm with a standard deviation of 1.18 mm by measuring a 304.8 mm diameter sphere. We further experimentally demonstrated that proposed method can simultaneously measure multiple objects or large dynamically changing objects.

The design and implementation of an electronic system to real-time capture and processing speckle interference patterns is presented. Because of the random and instability speckle patterns nature, is very useful a system wich allows obtaining and visualizing interference speckle patterns in the shortest time possible. Proposed system captures the first speckle pattern as steady image while captures subsequent patterns from the same source. Images are electronically transformed separately into value arrays and subtracted to obtain real-time interference speckle patterns, these patterns are automatically archived for later analysis. System consist of a CCD camera, a computer interface that makes capturing, a transparent object and a 4f interferometric system whose source is a laser that passes through diffuser glass in order to obtain speckle effect. Experimental results and analytic explanation is showed bellow.

The requirement for a non-transparent Lambertian like surface in optical 3D measurements with fringe pattern projection cannot be satisfied at translucent objects. The translucency causes artifacts and systematic errors in the pattern decoding, which could lead to measurement errors and a decrease of measurement stability. In this work, the influence of light wavelength on 3D measurements was investigated at a stereoscopic system consisting of two filter wheel cameras with narrowband bandpass filters and a projector with a wide-band light source. The experimental results show a significant wavelength dependency of the systematic measurement deviation and the measurement stability.

In order to increase the measurement speed of pattern projection-based three-dimensional (3-D) sensors, in 2014, we introduced the so-called array projector which allows pattern projection at several 1,000 fps. As the patterns are switched by switching on and off the light sources of multiple slide projectors, each pattern originates from a different projection center. This may lead to a 3-D point deviation when measuring glossy objects. In this contribution, we theoretically and experimentally investigate the dependence of this deviation on the measurement object's reflective properties. Furthermore, we propose a procedure for compensating for this deviation.

This paper proposes an absolute phase unwrapping method for 3D measurement that uses two cameras and one projector. On the left camera image, each pixel has one wrapped phase value which corresponds to multiple projector candidates with different absolute phase values. We use geometric relationship of the system to map projector candidates into right camera candidates. By applying a series of candidate rejection criteria, a unique correspondence pair between two camera images can be determined. Then the absolute phase is obtained by tracing the correspondence point back to projector space. Experimental results demonstrate that the proposed absolute phase unwrapping algorithm can successfully work on both complex geometry and multiple isolated objects measurement.

The accurate measurement of optical phase has many applications in metrology. For biological samples, which appear transparent, the phase data provides information about the refractive index of the sample. In speckle metrology, the phase can be used to estimate stress and strains of a rough surface with high sensitivity. In this theoretical manuscript we compare and contrast the properties of two techniques for estimating the phase distribution of a wave field under the paraxial approximation: (I) A digital holographic system, and (II) An idealized phase retrieval system. Both systems use a CCD or CMOS array to measure the intensities of the wave fields that are reflected from or transmitted through the sample of interest. This introduces a numerical aspect to the problem. For the two systems above we examine how numerical calculations can limit the performance of these systems leading to a near-infinite number of possible solutions.

Gaps are important in a wide range of measurements in manufacturing, from the fitting of critical assemblies too cosmetic features on cars. There are a variety of potential sensors that can measure a gap opening, each with aspects of gap measurements that they do well and other aspects where the technology may lack capability. This paper provides a review of a wide range of optical gages from structured light to passive systems and from line to area measurement. Each technology is considered relative to the ability to accurately measure a gap, including issues of edge effects, edge shape, surface finish, and transparency. Finally, an approach will be presented for creating an optimize measurement off gap openings for critical assembly applications.

It is possible to use of 3D lateral and longitudinal static speckle fields to determine the location of the optical axis in a system. In this manuscript we examine a variation of this idea where we use the 3D temporal correlation properties of multiple speckle fields to determine the axis. Previously it was shown how a spatial averaging approach could be used to estimate the 3D speckle orientation, here we compare the characteristics of this spatial averaging technique to a temporal averaging approach (where multiple speckle fields are used to produce an ensemble), experimental results are compared with the theoretical predictions and we present some conclusions.

Diamond turning is the powerful fabrication method for optics. Current process is very time consuming due to the lack of on-machine metrology. In this talk, we will first discuss the challenges and requirement of in-situ metrology, then we will present chromatic confocal on-machine metrology system developed in our lab and demonstrate its performance.

Novel materials and printing technologies can enable rapid and low cost prototyping and manufacturing of electronic devices with increased flexibility and complexity. However, robust and on-demand printing of circuits will require accurate metrology methods that can measure micron level patterns to verify proper production. This paper presents an evaluation of a range of optical gaging tools ranging from confocal to area 3D systems to determine metrological capability for a range of key parameters from trace thickness to solder paste volumes. Finally, this paper will present a select set of optimized measurement tools detailing both capabilities and gaps in the available technologies needed to fully realize the potential of printed electronics.

Many sheet products from plastic to structural composites are produce in tightly controlled thickness needed for functional applications. There are many methods that have been used to measure such sheeting from mechanical rollers to optical micrometers. However, many materials are produced with a thin protective film on either side that may not have critical dimensional controls. This paper addresses the challenge of measuring sheet products to critical thickness values in the presence of protective plastic films using high speed optical gaging methods. For this application, the protective films are assumed to be transparent though not necessarily scatter free, and have thickness variations that are comparable to the tolerances of the sheet product. We will examine the pros and cons of a number of different optical measurement methods in light of resolution, speed and robustness to the film thickness variation and present an approach able to address the desired sheet measurement tolerances.

A wide variety of characteristics of 3D printed objects have been linked to impaired structural integrity and use-efficacy. The printing material can also have a significant impact on the quality, utility and safety characteristics of a 3D printed object. Material issues can be created by vendor issues, physical security issues and human error. This paper presents and evaluates a system that can be used to detect incorrect material use in a 3D printer, using visible light imaging. Specifically, it assesses the ability to ascertain the difference between materials of different color and different types of material with similar coloration.

Previous work has discussed the impact of cybersecurity breaches on 3D printed objects. Multiple attack types that could weaken objects, make them unsuitable for certain applications and even create safety hazards have been presented. This paper considers a visible light sensing-based verification system’s efficacy as a means of thwarting cybersecurity threats to 3D printing. This system detects discrepancies between expected and actual printed objects (based on an independent pristine CAD model). Whether reliance on an independent CAD model is appropriate is also considered. The future of 3D printing is projected and the importance of cybersecurity in this future is discussed.

Prior work by Zeltmann, et al. has demonstrated the impact of small defects and other irregularities on the structural integrity of 3D printed objects. It posited that such defects could be introduced intentionally. The current work looks at the impact of changing the fill level on object structural integrity. It considers whether the existence of an appropriate level of fill can be determined through visible light imagery-based assessment of a 3D printed object. A technique for assessing the quality and sufficiency of quantity of 3D printed fill material is presented. It is assessed experimentally and results are presented and analyzed.

Structured-light projection is a well-established optical method for the non-destructive contactless three-dimensional (3D) measurement of object surfaces. In particular, there is a great demand for accurate and fast 3D scans of human faces or facial regions of interest in medicine, safety, face modeling, games, virtual life, or entertainment. New developments of facial expression detection and machine lip-reading can be used for communication tasks, future machine control, or human-machine interactions. In such cases, 3D information may offer more detailed information than 2D images which can help to increase the power of current facial analysis algorithms.

In this contribution, we present new 3D sensor technologies based on three different methods of near-infrared projection technologies in combination with a stereo vision setup of two cameras. We explain the optical principles of an NIR GOBO projector, an array projector and a modified multi-aperture projection method and compare their performance parameters to each other. Further, we show some experimental measurement results of applications where we realized fast, accurate, and irritation-free measurements of human faces.