This PDF file contains the front matter associated with SPIE Proceedings Volume 9489 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

This paper presents our recent research on 3D range data compression using the virtual fringe projection techniques. Specifically, the virtual fringe projection system converts arbitrary 3D object into one single red, green, and blue (RGB) color image that can be further compressed using standard image compression techniques. Since the virtual fringe projection system can be ideal (e.g., no ambient lighting, no surface reflectivity variations, perfect tele-centric lens), making it convenient to apply algorithms that is difficult to be realized in a practical fringe projection system. For example, only using three fringe patterns, pixel by pixel absolute phase can be calculated without adopting a global fringe analysis techniques (e.g., Fourier transform). We will demonstrate that extremely high compression ratios can be easily achieved with the proposed method.

Fringe projection is an established method for contactless measurement of 3D object structure. Adversely, the coding of fringe projection is ambiguous. To determine object points with absolute position in 3D space, this coding has to be unique.

We propose a novel approach of phase unwrapping without using additional pattern projection. Based on a stereo camera setup, an image segmentation of each view in areas without height jumps larger than a fringe period is necessary. Within these segments, phase unwrapping is potentially without error. Alignment of phase maps between the two views is realized by an identification process of one correspondence point.

Recently the transport–of–intensity equation (TIE) has extended from one wave to two waves and then applied to calculate the phase of the interference field. In this work we will present the experimental verification of the application of TIE in the reconstruction of two interfering wavefronts. A Fizeau interferometer with phase shift capability is used for testing a flat surface. An error analysis is performed on the difference between the reconstructed wavefronts using TIE and the one measured wavefronts using phase shifting method. The error analysis shows some systematic errors with RMS value less than 0.5rad or λ/10. The issues such as computation time and spatial resolution of the reconstructed waves are discussed and possible applications of the presented method are given.

Optical measurement techniques are often employed to digitally capture three dimensional shapes of components. The digital data density output from these probes range from a few discrete points to exceeding millions of points in the point cloud. The point cloud taken as a whole represents a discretized measurement of the actual 3D shape of the surface of the component inspected to the measurement resolution of the sensor. Embedded within the measurement are the various features of the part that make up its overall shape. Part designers are often interested in the feature information since those relate directly to part function and to the analytical models used to develop the part design. Furthermore, tolerances are added to these dimensional features, making their extraction a requirement for the manufacturing quality plan of the product. The task of “extracting” these design features from the point cloud is a post processing task. Due to measurement repeatability and cycle time requirements often automated feature extraction from measurement data is required. The presence of non-ideal features such as high frequency optical noise and surface roughness can significantly complicate this feature extraction process. This research describes a robust process for extracting linear and arc segments from general 2D point clouds, to a prescribed tolerance. The feature extraction process generates the topology, specifically the number of linear and arc segments, and the geometry equations of the linear and arc segments automatically from the input 2D point clouds. This general feature extraction methodology has been employed as an integral part of the automated post processing algorithms of 3D data of fine features.

In the real application environment of field engineering, a large variety of metrology tools are required by the technician to inspect part profile features. However, some of these tools are burdensome and only address a sole application or measurement. In other cases, standard tools lack the capability of accessing irregular profile features. Customers of field engineering want the next generation metrology devices to have the ability to replace the many current tools with one single device. This paper will describe a method based on the ring optical gage concept to the measurement of numerous kinds of profile features useful for the field technician. The ring optical system is composed of a collimated laser, a conical mirror and a CCD camera. To be useful for a wide range of applications, the ring optical system requires profile feature extraction algorithms and data manipulation directed toward real world applications in field operation. The paper will discuss such practical applications as measuring the non-ideal round hole with both off-centered and oblique axes. The algorithms needed to analyze other features such as measuring the width of gaps, radius of transition fillets, fall of step surfaces, and surface parallelism will also be discussed in this paper. With the assistance of image processing and geometric algorithms, these features can be extracted with a reasonable performance. Tailoring the feature extraction analysis to this specific gage offers the potential for a wider application base beyond simple inner diameter measurements. The paper will present experimental results that are compared with standard gages to prove the performance and feasibility of the analysis in real world field engineering. Potential accuracy improvement methods, a new dual ring design and future work will be discussed at the end of this paper.

The making of composite parts involves laying down multiple layers of tape in an organized manner. Misplaced ends, wrinkles or other factors can cause the part being built to have weaknesses or other imperfections. However, the actual edges of the tape do not stand out well with each layer reacting differently to lighting. The fiber nature of the tape will make the surface appear bright in some orientations and very dark in other. To complicate the problem, each layer of tape needs to be laid down at different angles, so can be dark, light or in-between, and at positions to fairly tight tolerances. This paper presents a study of several methods for determining the tape position and flaws, as well as details of a structured light method for determining the tape position. Considerations of tolerances, experimental results and how such a system might be implemented will be presented.

One form of additive manufacturing is to use a laser to generate a melt pool from powdered metal that is sprayed from a nozzle. The laser net-shape machining system builds the part a layer at a time by following a predetermined path. However, because the path may need to take many turns, maintaining a constant melt pool may not be easy. A straight section may require one speed and power while a sharp bend would over melt the metal at the same settings. This paper describes a process monitoring method that uses the intrinsic IR radiation from the melt pool along with a process model configured to establish target values for the parameters associated with the manufacture or repair. This model is based upon known properties of the metal being used as well as the properties of the laser beam. An adaptive control technique is then employed to control process parameters of the machining system based upon the real-time weld pool measurement. Since the system uses the heat radiant from the melt pool, other previously deposited metal does not confuse the system as only the melted material is seen by the camera.

Purpose – Powder bed fusion additive manufacturing (PBFAM) of metal components has attracted much attention, but the inability to quickly and easily ensure quality has limited its industrial use. Since the technology is currently being investigated for critical engineered components and is largely considered unsuitable for high volume production, traditional statistical quality control methods cannot be readily applied. An alternative strategy for quality control is to monitor the build in real time with a variety of sensing methods and, when possible, to correct any defects as they occur. This article reviews the cause of common defects in powder bed additive manufacturing, briefly surveys process monitoring strategies in the literature, and summarizes recently-developed strategies to monitor part quality during the build process.

Design/methodology/approach – Factors that affect part quality in powder bed additive manufacturing are categorized as those influenced by machine variables and those affected by other build attributes. Within each category, multiple process monitoring methods are presented.

Findings – A multitude of factors contribute to the overall quality of a part built using PBFAM. Rather than limiting processing to a pre-defined build recipe and assuming complete repeatability, part quality will be ensured by monitoring the process as it occurs and, when possible, altering the process conditions or build plan in real-time. Recent work shows promise in this area and brings us closer to the goal of wide-spread adoption of additive manufacturing technology.

Originality/value - This work serves to introduce and define the possible sources of defects and errors in metal-based PBFAM, and surveys sensing and control methods which have recently been investigated to increase overall part quality. Emphasis has been placed on novel developments in the field and their contribution to the understanding of the additive manufacturing process.

A growing number of applications like surveillance, thermography, or automotive demand for infrared imaging systems. Their imaging performance is significantly influenced by the alignment of the individual lens elements. Besides the lateral orientation of lenses, the air spacing between the lenses is a crucial parameter. Because of restricted mechanical accessibility within an assembled objective, a non-contact technique is required for the testing of these parameters. So far commercial measurement systems were not available for testing of IR objectives since many materials used for infrared imaging are non-transparent at wavelengths below 2 μm.

We herewith present a time-domain low coherent interferometer capable of measuring any kind of infrared material (e.g., Ge, Si, etc.) as well as VIS materials. The fiber-optic set-up is based on a Michelson-Interferometer in which the light from a broadband super-luminescent diode is split into a reference arm with a variable optical delay and a measurement arm where the sample is placed. On a photo detector, the reflected signals from both arms are superimposed and recorded as a function of the variable optical path. Whenever the group delay difference is zero, a coherence peak occurs and the relative lens’ surface distances are derived from the optical delay. In order to penetrate IR materials, the instrument operates at 2.2 μm.

The set-up allows the contactless determination of thicknesses and air gaps inside of assembled infrared objective lenses with accuracy in the micron range. It therefore is a tool for the precise manufacturing or quality control.

This paper presents the experimental design and initial testing of a system to characterize the progress and performance of a 3D printer. The system is based on five Raspberry Pi single-board computers. It collects images of the 3D printed object, which are compared to an ideal model. The system, while suitable for printers of all sizes, can potentially be produced at a sufficiently low cost to allow its incorporation into consumer-grade printers. The efficacy and accuracy of this system is presented and discussed. The paper concludes with a discussion of the benefits of being able to characterize 3D printer performance.

The usage of lasers in ocean studies is widespread. Each step of laser beam propagation through the ocean is a major topic to be analyzed, often independently. The objective of this study is to focus on the interaction of laser beams with the air-ocean interface; specifically, the modeling and analysis of the effects of a gravity wave perturbed ocean surface on laser propagation. The directional energy spectrum of Neumann with the Fourier series expansion is used in a Monte Carlo simulation of the gravity wave perturbed ocean surface model. Beam tracing with the ABCD matrix approach is used for the laser beam propagation analysis rather than using ray tracing like found in similar studies. Specific parameters are used in the model to output not only a qualitative model but also numerical and realistic results. The main purposes of this study are implementing a numerical model to see the effects of the ocean surface on laser propagation and analyzing the feasibility of using the beam tracing approach in such a model.

A novel in-plane and out-of-plane deformation simultaneous measurement method using only two speckle patterns grabbed before and after deformation of an object with rough surfaces has been proposed. In the new optical system, a phenomenon of in-plane and out-of-plane deformation can be simultaneously recorded by only one camera by using the multi-recording method of speckle patterns. However, it is thought that there are some problems concerning measuring accuracy, because plural dimensional data has to be grabbed by single camera. The influence of factor of each error source to measuring accuracy of the method is investigated by using experimental results.

In industrial metrology, the system of fringe projection for the fast determination of 3D surface data has been established. The combination of areal and structured projection with two-dimensional optical sensors and triangulation measurement principle allows very high measurement point densities with reasonable accuracy. There are great difficulties with high gloss surfaces and with very dark surfaces for state of the art systems. Transparent materials cannot be measured using the visible spectrum of light. We have therefore developed a new structured light projection system that solves these problems. For the first time the physical principle of energy conversion is utilized in areal structured light projection. We are presenting first results to show the advantages and the capability of this new measurement principle.

Non-destructive terahertz reflection interferometry offers many advantages for sub-surface inspection such as interrogation of hidden defects and measurement of layers’ thicknesses. Here, we describe a terahertz reflection interferometry (TRI) technique for non-contact measurement of paint panels where the paint is comprised of different layers of primer, basecoat, topcoat and clearcoat. Terahertz interferograms were generated by reflection from different layers of paints on a metallic substrate. These interferograms’ peak spacing arising from the delay-time response of respective layers, allow one to model the thicknesses of the constituent layers. Interferograms generated at different incident angles show that the interferograms are more pronounced at certain angles than others. This “optimum” angle is also a function of different paint and substrate combinations. An automated angular scanning algorithm helps visualizing the evolution of the interferograms as a function of incident angle and also enables the identification of optimum reflection angle for a given paint-substrate combination. Additionally, scanning at different points on a substrate reveals that there are observable variations from one point to another of the same sample over its entire surface area. This ability may be used as a quality control tool for in-situ inspection in a production line. Keywords: Terahertz reflective interferometry, Paint and coating layers, Non-destructive

Packaging of electronic and photonic components requires high accuracy, which needs to be verified in the process of manufacturing and testing. Since very small misalignments and/or deformations can lead to unacceptable performance, a measurement approach is needed that would reveal displacements as small as a few tens of nanometers or less. In addition, misalignments and deformations occur both in the out-of-plane and in-plane directions, which may be very difficult to separate from each other. It was previously demonstrated that the two types of measurements can be implemented with different approaches: holographic interferometry for out-of-plane and Moiré interferometry for in-plane, but it is very desirable to have a single system with sufficient accuracy in both lateral and longitudinal directions. An optical technique developed by our group and presented in this paper is based on a holographic approach and combines the principles of holographic interferometry and phase modulating adaptive optics that could provide in-plane and out-of-plane measurements with high accuracy.

Service providers perform regular borescope inspection of field products to ensure system performance and prevent accidents. A full borescope inspection for large equipment usually takes several days to cover every region of interest in the turbine. One of the challenges that causes this long inspection time is the difficulty in navigating the borescope tip to some position of interest and aiming the view of the borescope in given direction. The image from the borescope tip is the only information available to the operator to judge the position of tip. In some cases, the operator can get lost due to the limited field-of-view and illumination provided by the borescope. It is very hard to tell the borescope tip position from one borescope image. This increases the difficulty of correlating the inspection results obtained at different times that might be used to predict potential machinery failure. This paper discusses various methods that have been investigated for 3D borescope tracking and presents a new approach using a shape sensor integrated in the borescope tube used with image based location determination to determine the position of the borescope tip during inspections. The shape sensor provides a real time estimate of the borescope tip position and orientation then the image based analysis uses the part CAD model to fine tune this position information. The tracking result can provide better information of the tip position for the operator. This enhanced position information can be used to better monitor defect changes over time by comparing the inspection result at different times in the parts lifetime.

It is very difficult to measure the inner profile geometry of small holes of less than a millimeter in size, yet that geometry may be important for some manufacturing operations. This paper will present a method to measure key dimensional parameters of small holes used in a variety of applications from cooling to lubrication. Precision shaped holes can consist of a hole at some angle to the surface of the part and an area around the entrance to the hole for the purpose of diffusing the air or lubricant across the surface of the part to achieve the most effective performance. The drive towards smaller and more complex hole geometries means that previous methods such as conventional touch probes do not provide a good mapping in a time that can be used as part of production. The advanced designs of the holes means simple pin gages do not provide enough information. This paper will discuss tests of various methods considered for mapping small hole inner diameters, and present some sample results of a possible solution.

An adaptive spatial filtering technique is described for enhancing image contrast of objects viewed against the background of an intense light source, both in the transmitting and reflecting imaging modes. The spatial distribution of the source captured in the back focal plane of the imaging lens corresponds to the angular distribution of the source. The measured distribution of energy is used to adaptively control the transmittance of a spatial light modulator positioned in the back focal plane of the imaging lens. The spatial light modulator blocks the transmission of the high energy hot spots through to the image plane. Subsequently the image formed by the objective lens is free of the bright background. Thus, the digital image capture system can use the full dynamic range of the detector and the analog to digital converter, giving rise to a captured image with the highest contrast possible. Contrast enhanced images of MEMS accelerometer are presented.

This paper presents a high resolution optical surveillance system which integrated an omni-directional imager as an event finder/ system trigger. The omni-directional optics, a fish-eye camera in this study, provides a wider field of view (FOV) which can monitor widely range continuously without scanning mechanism but offers sufficient information which includes sign of field event and direction and then drive high resolution surveillance camera for detail imaging. To archive an optical triggering surveillance system, the scale-invariant feature transform (SIFT) is implemented to detect features both from images taken by omni-directional imager and the high resolution surveillance camera. Considering the FOV of high resolution surveillance system is narrow, to ensure the pointing of high resolution surveillance system, feature matching is also implemented in this system to identify the images obtained by high resolution surveillance system are identical to the existing omni-directional image obtained from fish-eye camera. This provides a robust and accurate solution to the problem of optical radar surveillance system localization in unknown environments. An experiment is performed on outdoor image sequences with demonstrating the efficiency of our algorithm.