Accurate 3D object measurement and inspection using structured light systems

A new system for inspecting machine parts with three-dimensional characteristics is presented. The system consists of a binocular stereo mount, a three degrees of freedom positioning device and a structured light system. By means of an interactive interface the user may define the specific features to inspect, such as planes, holes, angles.., and other aspects such as tolerance zones or reference systems. Our interest mainly focuses on improving inspection planning and accuracy in measurement. In the first place, based on the CAD model and the features to inspect the system automatically designs an inspection strategy responsible for managing the different resources involved in the inspection process. This inspection plan is based on basic geometric features of the model (called entities), the feature extraction algorithm employed and the physical bounds the inspection system imposes. On the other hand, provided that the aim of the system is to obtain the greatest possible accuracy, uncertainty propagation is performed throughout the measurement process. Feature extraction algorithms, model part positioning and camera calibration are evaluated in depth in order to obtain the most reliable measurement that hardware resolution may provide.

This article deals with development and implementation of low-cost synthetic vision system primarily targeted for light sport aircrafts and general aviation. The system uses high resolution terrain database with 3D topographic objects and produces image comparable with flight simulators. The visualization includes emulation of head-up style display with 3D navigation data and instruments. The hardware part uses commercial off-the-shelf inertial units and the visualization part is based on gaming technology. This system is intended to work as a back-up system for non IFR experienced pilots in case of unintended flight into IMC.

System calibration is crucial for any 3-D shape measurement system. An accurate method is proposed to calibrate a 3-D shape measurement system based on a structured light technique. The projector is treated as a camera to unify the calibration procedures of a structured light system and a well-established stereo vision system. The key to realizing this method is to establish a highly accurate correspondence between camera pixels and projector pixels and generate digital micromirror device (DMD) image sets for projector calibration. A phase-shifting method is used to accomplish this task. A precalibrated lookup table and a linear interpolation algorithm are proposed to improve the accuracy of the generated DMD image, and accordingly improve the accuracy of the projector calibration and the 3-D measurement. Some experimental results are presented to demonstrate the performance of the system calibration.

System calibration, which usually involves complicated and time-consuming procedures, is crucial for any 3-D shape measurement system. In this work, a novel systematic method is proposed for accurate and quick calibration of a 3-D shape measurement system we developed based on a structured light technique. The key concept is to enable the projector to "capture" images like a camera, thus making the calibration of a projector the same as that of a camera. With this new concept, the calibration of structured light systems becomes essentially the same as the calibration of traditional stereovision systems, which is well established. The calibration method is fast, robust, and accurate. It significantly simplifies the calibration and recalibration procedures of structured light systems. This work describes the principle of the proposed method and presents some experimental results that demonstrate its performance.

To deal with the lack of accurate and efficient inspection methods in complex free-form surfaces, three-dimensional measurement method based on the optical measurement and computer image processing technology was proposed. It adopted laser scanning technology to get point clouds of free-form surface. Used rapid measurement software to inspect precision of point cloud& CAD model. What could be the cause of machining errors was analyzed. 3D deviation inspection of complex surfaces was applied by an artifact. Detected the machining error of an important section, and outputted test report. This research provides a convenient and swift method for the inspection of free-form surface and processing quality control.

Projector nonlinearity is a common problem for digital structured light-based three-dimensional (3-D) shape measurement techniques. A temporal-spatial binary encoding method is presented for the purpose of eluding it. We build a 3-D shape measurement scheme by combining our proposed method with phase measurement profiling. A standard sinusoidal fringe pattern is divided into more than two binary fringe patterns using specially designed temporal and spatial binary encoding rule based on intensity hierarchic quantification, and then are in-focus projected onto the measured object at a time sequence to reconstruct a frame phase-shifting fringe image. On account of the projected binary fringe pattern strictly consisting of zeros and ones, the influence of the projector nonlinearity on the measurement result can be effectively ruled out and simultaneously enables high-quality sinusoidality. In-depth investigations by theoretical analysis and experiments are conducted to demonstrate the performance of this method.

The main objective of this research project is to develop a low cost computerized system to automatically diagnose gait disorders and characterize their severity. The system uses 2 video cameras to provide a 3D position acquisition system connected to a personal computer. The patient gait and posture are analyzed from the data acquired by a vision-based gait acquisition system. The whole system will be an important novel tool in medical rehabilitation and diagnosis, resulting on a more effective functional rehabilitation of a patient's gait, assessing their clinical evolution and solving the limitations of the current subjective gait diagnosis tools. The system allows the calculation of 17 human gait joint trajectories. This system will provide a much more objective understanding of the patient's clinical evolution, and thus enables a more effective functional rehabilitation of a patient's gait. In this paper it is presented the selection of the relevant diagnosis parameters of the gait patterns, which is one of the steps to get to the main objective, the automatic diagnosis of human gaits.

The ability to remove unbound biological material from a reaction site has applications in many biological protocols, such as those used to detect pathogens and biomarkers. One specific application where washing is critical is the Enzyme-Linked ImmunoSorbent Assay (ELISA). This protocol requires multiple washing steps to remove multiple reagents from a reaction site. Previous work has suggested that a passive mechanical comb filter can be used to wash particles in digital microfluidic devices. A method for the characterization of passive mechanical filtration of particles in Digital MicroFluidic (DMF) devices is presented in this work. In recent years there has been increased development of Lab-On-A-Chip (LOAC) devices for the automation and miniaturization of biological protocols. One platform for further research is in digital microfluidics. A digital microfluidic device can control the movement of pico-to nanoliter droplets of fluid using electrical signals without the use of pumps, valves, and channels. As such, fluidic pathways are not hardwired and the path of each droplet can be easily reconfigured. This is advantageous in biological protocols requiring the use of multiple reagents. Fabrication of these devices is relatively straight forward, since fluid manipulation is possible without the use of complex components. This work presents a method to characterize the performance of a digital microfluidic device using passive mechanical supernatant dilution via image analysis using a low cost vision system. The primary metric for performance of the device is particle retention after multiple passes through the filter. Repeatability of the process will be examined by characterizing performance of multiple devices using the same filter geometry. Qualitative data on repeatability and effectiveness of the dilution technique will also be attained by observing the ease with which the droplet disengages from the filter and by measuring the quantity of fluid trapped on the filter after each filtration step.

In this paper, we propose a high-speed 3-D shape measurement technique based on composite structured-light patterns and a multi-view system. Benefiting from the multi-view system, stereo phase unwrapping, as a novel method for the phase unwrapping algorithm, can eliminate the phase ambiguities and obtain absolute phase map without projecting any additional patterns. However, in order to ensure the stability of phase unwrapping, the period of fringe is generally around 20, which leads to the limited accuracy of 3D measurement. To solve the precision-limited problem reasonably, we mathematically developed an optimized design method of the composite pattern. By skillfully embedding speckles without compromising the phase measurement accuracy, we can realize phase unwrapping with high-frequency fringes. In addition, a computational framework will be provided to further achieve the robust and high-performance 3D acquisition. It is demonstrated by several experiments that our method can achieve a high-speed, dense, and accurate 3-D shape measurement with 64-period fringe patterns at 5000 frames per second.

Real-time computer vision systems that observe the actions of people have received increasing attention as they are important for a broad range of applications. Examples are intelligent man-machine interfaces or intelligent rooms that have the capability to understand the actions of their inhabitants. In this paper we present the design of a stereo vision system for the precise and robust real time tracking of human hands and heads that unlike previous systems uses low-cost industry standard components. The system uses color and motion information to find the human. Using previously calibrated cameras the 3D positions of hands and head are calculated. Because of its client-server architecture the system is scalable to an arbitrary number of cameras and application processes. Experimental results for the performance of the system are given.

The seemingly simple step of molding a cholesteric liquid crystal into spherical shape, yielding a Cholesteric Spherical Reflector (CSR), has profound optical consequences that open a range of opportunities for potentially transformative technologies. The chiral Bragg diffraction resulting from the helical self-assembly of cholesterics becomes omnidirectional in CSRs. This turns them into selective retroreflectors that are exceptionally easy to distinguish—regardless of background—by simple and low-cost machine vision, while at the same time they can be made largely imperceptible to human vision. This allows them to be distributed in human-populated environments, laid out in the form of QR-code-like markers that help robots and Augmented Reality (AR) devices to operate reliably, and to identify items in their surroundings. At the scale of individual CSRs, unpredictable features within each marker turn them into Physical Unclonable Functions (PUFs), of great value for secure authentication. Via the machines reading them, CSR markers can thus act as trustworthy yet unobtrusive links between the physical world (buildings, vehicles, packaging,…) and its digital twin computer representation. This opens opportunities to address pressing challenges in logistics and supply chain management, recycling and the circular economy, sustainable construction of the built environment, and many other fields of individual, societal and commercial importance.

3D surface measurements with isogeometric stereocorrelation—Application to complex shapes

Important trends and events are highlighted. The use of fuzzy logic expanded. The use of programmable logic controllers in distributed control made headway. Low-cost vision systems were introduced, as were faster X-ray laminography systems. Growing emphasis on keeping humans who work around robots safe was evident. More robust motion and speed controls for both robots and motors became available.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Vision recognition and RFID perception are used to develop a smart AGV travelling on fixed paths while retaining low-cost, simplicity and reliability. Visible landmarks can describe features of shapes and geometric dimensions of lines and intersections, and RFID tags can directly record global locations on pathways and the local topological relations of crossroads. A topological map is convenient for building and editing without the need for accurate poses when establishing a priori knowledge of a workplace. To obtain the flexibility of bidirectional movement along guide-paths, a camera placed in the centre of the AGV looks downward vertically at landmarks on the floor. A small visual field presents many difficulties for vision guidance, especially for real-time, correct and reliable recognition of multi-branch crossroads. First, the region projection and contour scanning methods are both used to extract the features of shapes. Then LDA is used to reduce the number of the features' dimensions. Third, a hierarchical SVM classifier is proposed to classify their multi-branch patterns once the features of the shapes are complete. Our experiments in landmark recognition and navigation show that low-cost vision systems are insusceptible to visual noises, image breakages and floor changes, and a vision-based AGV can locate itself precisely on its paths, recognize different crossroads intelligently by verifying the conformance of vision and RFID information, and select its next pathway efficiently in a bidirectional flow network.

During manufacturing of engineering components, it is a common practice to use the same tool for machining multiple parts. The wear on the tool affects the quality of the component produced. Using a worn-out tool leads to inferior quality components that do not conform to tolerances and have poor finish. However, prematurely replacing the tool leads to increased production costs. Hence, an optimum point of tool change which minimizes production costs and maximizes productivity must be determined. In this context, tool wear monitoring assumes special significance. This paper proposes a direct tool wear measurement method using a relatively low-cost vision system. The method uses CCD camera and image processing algorithms to record the flank wear to determine the health of the tool and whether or not the tool can be used for further machining of engineering components.