This PDF file contains the front matter associated with SPIE Proceedings Volume 10667, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We propose to use deep convolutional neural networks (DCNNs) to perform 2D and 3D imaging through scattering media. The inverse scattering problem is solved based on learning a huge number of training target and speckle pairs. The proposed technique does not rely on a reference beam, thus employs a simpler optical setup than previous techniques without the need to know the imaging model and optical processes. This lack of the need to know a prior model of the forward operator is very important since many optimization techniques are very sensitive to errors caused by the inaccuracy of the forward model.

Structured light projection techniques in the visible spectrum of light (VIS) are widely used for fast, contactless, and nondestructive optical three-dimensional (3D) shape measurements. For instance, 3D reconstruction can be performed with a stereo camera system combined with corresponding pixel search and triangulation. Recently, we increased the measurement speed significantly by GOBO projection of aperiodic sinusoidal fringes. Due to their optical properties, such as being glossy, transparent, absorbent, or translucent, some materials cannot be measured in VIS. Changing the spectral range from VIS to infrared (IR) allows measuring the 3D shape of some of these materials. Instead of diffuse reflection of structured light in VIS, the absorption of structured light in IR (e.g., CO₂ laser at 10.6 μm) combined with energy conversion and re-emission of light according to Planck’s law is used. Detection can be carried out at 3–5 μm. Depending on optical and thermal material properties (e.g., complex spectral refractive index, thermal conductivity, specific heat capacity, emissivity), the parameters of the projection unit have to be adjusted, e.g., intensity or illumination time. In this paper, we investigate the influence of material, geometry, and irradiation parameters on the temperature contrast. We present a simulation tool based on the Beer-Lambert law and heat diffusion equation for irradiation-induced thermal pattern on the object’s surface. It allows to determine optimized irradiation settings for well-known material and geometry parameters. We compare the simulation outputs with experimental results.

With recent advances in high speed 3D measurement sensor technologies, focus changes from merely acquiring 3D sensor data fast. An advanced application area is to fusion multiple sensor streams into a complete object representation without occlusions. Even more challenging is how to process the high speed 3D streams online, instead of the current offline processing approaches. To this end we combine our cost-effective GOBO slide-based pattern projector (GOes Before Optics) with commodity GigE vision network sensors to a multi sensor system for complete online monitoring capabilities. The targeted use-case has to deal with partial occlusions and low latency requirements for machine control. Specifically, three active NIR stereo 3D sensors are aggregated through a 10Gb-Ethernet-switch and processed by a single GPU assisted workstation. Thus a combined continuous data-stream of up to 78 million 3D points is calculated online per second out of a raw 2D data-stream of up to approximately 1250 Mb/s. The systems latency for simpler 3D analysis task, like movement tracking, is ≤ 200 ms.

This paper proposes a motion compensation method to reduce the motion-induced error in phase shifting pro-filometry. We first estimate the motion of an object from the difference between two subsequent 3D frames. After that, by taking the advantage of projector's pinhole model, we can determine the motion-induced phase shifting error from the estimated motion. A generic three-step phase-shifting algorithm considering phase shift error is then utilized to compute the phase. We have conducted quantitative experiments to demonstrate that the proposed algorithm can effectively improve the measurement accuracy without additional information or further constraints.

For high-speed and high-accuracy 3D shape measurement, it has been demonstrated that using 1-bit binary patterns is advantageous over 8-bit sinusoidal phase-shifted fringe patterns especially on the digital-light-processing (DLP) projection platform. By properly defocusing the projector for specific square binary patterns, researchers have achieved the speed breakthroughs for high-accuracy 3D shape measurement, yet such a method requires carefully adjustment of the projector’s lens to within a small out-of-focus range, limiting its depth measurement capability. Optimizations based on pulse width modulation (PWM), optimal pulse width modulation (OPWM), and dithering/halftoning have substantially improved measurement quality, yet they only work well for a limited range of fringe period variations especially when a small number of phase-shifted fringe patterns are used. This paper proposes to generate high-quality phase using two sets of three phase-shifted binary patterns: the first set is generated by triangular pulse width modulation (TPWM) technique, and the second set being p shifted from the first set is also generated by TPWM technique. A three-step phase-shifting algorithm is then applied to compute the phase. Through optimizing the modulation frequency of the carrier signal, our simulation and experimental results demonstrate that high-quality phase can be generated for a wide range of fringe periods (e.g., from 18 to 1140 pixels) with only six binary patterns.

In order to increase the measurement speed of pattern projection-based 3D sensors, we have developed a GOBO slide-based pattern projector (GOes Before Optics) which allows for pattern projection at several 10,000 fps. After first experimental configurations have been mainly set up based on empirical study, in this contribution, we investigate the capabilities of a GOBO projection-based 3D sensor on a theoretical level. We discuss and optimize the parameters which influence the completeness and accuracy of the 3D result, and we experimentally verify the theoretical results by means of a GOBO projection-based 3D sensor operating in the near infrared.

Conference Presentation for "3D Optical metrology: An overview for 2018"

The advancements on 3D range imaging have been accelerating in the past few years promotes one fundamental issue in 3D imaging: how can one effectively store and deliver such enormously large 3D data? While 3D image data compression is still in its infancy, compression techniques for 2D images, however, are quite mature. As a result, researchers have developed a variety of methods to store 3D data as standard 2D images such that 2D image compression techniques can be leveraged. This paper will overview what has been done recently in my research team and provide our perspectives on each compression technique.

Structured light projection techniques are well established and an integral part of optical, accurate, and fast threedimensional (3D) measurements. Most problems occur when the projected patterns are not diffusely reflected at the objects’ surfaces. Therefore, we present a new optical 3D mid-wave infrared (MWIR) system based on a “shape from heating” approach with thermal pattern projection. Thus, the three-dimensional shape of materials that are transparent, translucent, or reflective in the visible wavelength range (e.g., glass, plastics, or carbon-fiber-reinforced material) can now be measured optically, contactless, and without a prior process of painting. The system operates with a stereo-vision setup of two cooled MWIR cameras (3-5 μm) and a CO₂ laser projection unit to heat up the objects’ surfaces with aperiodic patterns. A stack of thermal images can be used to find corresponding points in both MWIR cameras and to calculate the 3D information of the surface geometry. In this paper, we introduce the setup and measurement principle of the 3D MWIR system and show some relations between various system parameters (masks, temperature contrast, and material parameters) and the measurement accuracy. We demonstrate the capabilities of our sensor by presenting an impressive 3D result of a real object.

The use of laser line systems for cross sectional measurement on production parts is a method that has been in use for over 30 years with few changes in the equipment. A primary limitation of using a laser line triangulation methods has always been the inability to obtain good measurements on shiny or transparent surfaces. Not only is the return signal poor from such surfaces, but the presence of multiple reflections can cause problems. This paper will explore new methods to obtain better measurements on very shiny, mirror like surfaces as well as transparent materials such as plastic and glass. The paper will quantify what improvements may be expected with the improved methods possible today, as well as identify the remaining limitations of these methods. The results will be compared against the results obtained using methods other than line of light triangulation and discuss the comparisons in performance achieved.

Recently, a number of hyperspectral cameras with novel image sensors that are equipped with a monolithic pixel-by-pixel filter array have been introduced onto the market. In this contribution, we describe the design and implementation of a structured light 3D sensor consisting of two such snapshot mosaic sensors, each with 25 different spectral bands between 600 and 975 nm, and a broadband GOBO projector that images varying, aperiodic sinusoidal patterns into the measurement volume. We characterize the system with regard to accuracy, and we present measurements of different objects illustrating the benefits of hyperspectral 3D sensors.

In the flapping flight study, it is important to know the mechanics of the flapping wings to assist research in different fields such as biology and robotics. In this research, we propose a novel dynamic 3D strain measurement framework for robotic flapping wings. We set up a superfast 3D shape measurement platform with defocused binary stripe illumination to perform high-resolution dynamic 3D reconstruction. Then, we developed a novel point tracking algorithm based on geodesic computation. Finally, we performed dense 3D strain measurement by examining the curvature changes of tracked points. Experiments will demonstrate the success of our technology.

In this work, authors present a new application of electronic speckle pattern shearing interferometry (shearography) to a phenomenon known as creep compliance, which is an important mechanical property of viscoelastic materials. Two different sealing elastomers were tested in a short-term creep experiment, applying a constant tensile stress to a specimen. An experimental in-plane shearography setup was implemented to measure the in-plane creep strains produced in the tested object. In order to show the effectiveness of shearography for the assessment of this viscoelastic mechanical property, results were compared to that obtained with an equipment of Digital Image Correlation (DIC). It was demonstrated that shearography can be potentially and successfully applied to the creep analysis of these kind of materials. Finally, advantages and limitations of this measurement method are discussed.

The quantification of surface defects such as corrosion pitting, scratches and wear on high value aerospace parts offers many challenges. The parts may be highly curved airfoils, narrow slots in rotating parts, or widely scattered points on large structures that are not easily moved. The traditional precision tools for micron level measurements of this type are typically benchtop units in a microscope format that is not viable for mapping small areas on large, hard to handle parts. The large area 3D mappers have more flexibility but are hard pressed to provide the few micron measurement resolution needed while providing too much data on a volumetric area where only small local measures are needed. This paper will discuss the application of a hand portable, structured light system that offers both resolution and flexibility. The challenges of curved surfaces and hard to reach areas will be discussed in the context of the practical restraints imposed by system depth-of-field and good pattern contrast needed for high quality 3D measurements.

The use of multiple axis machines for direct write additive manufacturing offers the potential for the custom manufacture of a wide range of useful structures ranging from sensor on curved parts to electronics on unique shapes. The motion axis for such systems do not need the force and robustness of metal cutting applications, but the geometric requirements for electronic patterns means the machines need to compensate for a wide range of errors at micron levels. The types of errors of concern may include motion axis alignments in 5-axis and more specific printing tool or fixture variations. In order to correct for any such errors, there is a need for a mapping method that can be applied across machine platforms without the need for substantial modifications to the machines. This paper will describe the selection and application of well defined, readily available basic geometric artifacts that permit the separate mapping of key error sources in such a system. The ability to provide the error measurement using simple sensors commonly available will be contrasted to more expensive, traditional volumetric mapping methods.

Nanoparticles of various materials are known to possess excellent mechanical, chemical, electrical, and optical properties. However, it is difficult to deposit and transform nanoparticles into large two-dimensional and threedimensional structures in a controlled manner. A laser-based new additive manufacturing process is presented for depositing nanoparticles using an electrospray technology. This process is versatile and scalable, and uses less materials and energy. In this process, aqueous microdroplets of nanoparticle suspension are injected into a hollow laser beam that vaporizes the water, sinters the nanoparticles and deposits nanoparticles on rigid or flexible substrates. Nanoparticles of silver have been deposited on silicon wafer, card stock and polyimide film, and high precision deposition has been observed to occur under a particular microfluidic regime called microdripping mode. This process can promote roll-toroll manufacturing of a variety of energy and electronic devices such as conformal solar cells, sensors, and actuators.

Additive manufacturing offers new routes to lightweight optics inaccessible by conventional methods by providing a broader range of reconciled functionality, form factor, and cost. Predictive lattice design combined with the ability to 3D print complex structures allows for the creation of low-density metamaterials with high global and local stiffness and tunable response to static and dynamic loading. This capacity provides a path to fabrication of lightweight optical supports with tuned geometries and mechanical properties. Our approach involves the simulation and optimization of lightweight lattices for anticipated stresses due to polishing and mounting loads via adaptive mesh refinement. The designed lattices are 3D printed using large area projection microstereolithography (LAPuSL), coated with a metallic plating to improve mechanical properties, and bonded to a thin (1.25 mm) fused silica substrate. We demonstrate that this lightweight assembly can be polished to a desired flatness using convergent polishing, and subsequently treated with a reflective coating. *This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 within the LDRD program. LLNL-ABS-738806.

Structured light methods have seen wide use in obtaining 3D measurements of complex shapes from consumer good to aerospace parts. The use of phase shift analysis and improved high speed methods have made the method a viable tool for many time critical production applications. However, not every application requires full three dimensional measurement of the part, but rather just suffers from being difficult to do with simple 2D machine vision methods. For example, just locating bumps or holes on a part that has low contrast features as with many cast parts can be difficult and even unreliable. One of the first applications of structured light was for just such an application. Powder bed additive manufacturing creates a similar low contract challenge today. This paper will explore improved methods off using structured light to reliably determine location and orientation of low contrast features, and discuss several potential applications of the method.