Data Analytics for Noise Reduction in Optical Metrology of Reflective Planar Surfaces

On-line data collection from the manufactured parts is an essential element in Industry 4.0 to monitor the production’s health, which required strong data analytics. The optical metrology-based inspection of highly reflective parts in a production line, such as parts with metallic surfaces, is a difficult challenge. As many on-line inspection paradigms require the use of optical sensors, this reflectivity can lead to large amounts of noise, rendering the scan inaccurate. This paper discusses a method for noise reduction and removal in datapoints resulting from scanning the reflective planar surfaces. Utilizing a global statistic-based iterative approach, noise is gradually removed from the dataset at increasing percentages. The change in the standard deviation of point-plane distances is examined, and an optimal amount of noisy data is removed to reduce uncertainty in representing the workpiece. The developed algorithm provides a fast and efficient method for noise reduction in optical coordinate metrology and scanning.

QDC-2D: A Semi-Automatic Tool for 2D Analysis of Discontinuities for Rock Mass Characterization

Quantitative characterization of discontinuities is fundamental to define the mechanical behavior of discontinuous rock masses. Several techniques for the semi-automatic and automatic extraction of discontinuities and their properties from raw or processed point clouds have been introduced in the literature to overcome the limits of conventional field surveys and improve data accuracy. However, most of these techniques do not allow characterizing flat or subvertical outcrops because planar surfaces are difficult to detect within point clouds in these circumstances, with the drawback of undersampling the data and providing inappropriate results. In this case, 2D analysis on the fracture traces are more appropriate. Nevertheless, to our knowledge, few methods to perform quantitative analyses on discontinuities from orthorectified photos are publicly available and do not provide a complete characterization. We implemented scanline and window sampling methods in a digital environment to characterize rock masses affected by discontinuities perpendicular to the bedding from trace maps, thus exploiting the potentiality of remote sensing techniques for subvertical and low-relief outcrops. The routine, named QDC-2D (Quantitative Discontinuity Characterization, 2D) was compiled in MATLAB by testing a synthetic dataset and a real case study, from which a high-resolution orthophoto was obtained by means of Structure from Motion technique. Starting from a trace map, the routine semi-automatically classifies the discontinuity sets and calculates their mean spacing, frequency, trace length, and persistence. The fracture network is characterized by means of trace length, intensity, and density estimators. The block volume and shape are also estimated by adding information on the third dimension. The results of the 2D analysis agree with the input used to produce the synthetic dataset and with the data collected in the field by means of conventional geostructural and geomechanical techniques, ensuring the procedure’s reliability. The outcomes of the analysis were implemented in a Discrete Fracture Network model to evaluate their applicability for geomechanical modeling.

A Novel Measurement Standard for Surface Roughness on Involute Gears

Although manufacturers of coordinate measurement systems and gear measurement systems already provide instruments that enable an end-of-line-monitoring of the roughness properties of gears, the roughness measurement on gear flanks still lacks traceability with respect to the standardised SI-units. There is still a gap between well standardised roughness measurements on planar surfaces and gear measurements on involutes. This gap is bridged by a novel physical measurement standard (PMS), also referred to as material measure, for roughness measurements on involute gears that has been developed at the Physikalisch-Technische Bundesanstalt (PTB). The necessary transformations between the systems of roughness and gear measurements have been implemented. The measurement standard itself represents calibrated roughness values for the parameters Ra, Rz, Rq, Rk, Rpk and Rvk and Mr1 and Mr2. Furthermore, the PMS can be measured both with classic profilometers as well as gear measurement systems with integrated roughness probes.

Additively Printed Flexible Temperature Sensor for Wearable Applications

The flexible sensor has the capability to be mounted on any curved surfaces of applications and be used for portable devices. Additively printed sensors have received attention owing to their compact design and ability of application to non-planar surfaces. Wearable applications require capability of integration into a variety of surfaces with ability to flex, fold, twist and stretch under the stresses of daily motion. There is scarcity of data on the interaction of the process parameters with the realized performance. In addition, there is need for data focused on sensor accuracy, repeatability, and reliability. In this study, experimental analysis on function of the fabricated sensing board is conducted. The temperature sensors are made by direct write printing method with nScrypt printer. A calibration of the sensors has been conducted to confirm that resistance is well related to actual temperature and find TCR (temperature coefficient to resistance). The evolution of resistance has been correlated with the environmental temperature. The sensor hysteresis has been quantified using upswing and downswing of the environmental temperature. In addition, the effect of humidity on the temperature sensor accuracy and performance has been quantified. The effect of a polymide coat on the sensor to prevent humidity effects has also been quantified.

Towards the Determination of Machining Allowances and Surface Roughness of 3D-Printed Parts Subjected to Abrasive Flow Machining

Abrasive flow machining (AFM) is considered as one of the best-suited techniques for surface finishing of laser powder bed fused (LPBF) parts. In order to determine the AFM-related allowances to be applied during the design of LPBF parts, a numerical tool allowing to predict the material removal and the surface roughness of these parts as a function of the AFM conditions is developed. This numerical tool is based on the use of a simplified viscoelastic non-Newtonian medium flow model and calibrated using specially designed artifacts containing four planar surfaces with different surface roughnesses to account for the build orientation dependence of the surface finish of LPBF parts. The model calibration allows the determination of the abrasive medium-polished part slip coefficient, the fluid relaxation time and the abrading (Preston) coefficient, as well as of the surface roughness evolution as a function of the material removal. For model validation, LPBF parts printed from the same material as the calibration artifacts, but having a relatively complex tubular geometry, were polished using the same abrasive medium. The average discrepancy between the calculated and experimental material removal and surface roughness values did not exceed 25%, which is deemed acceptable for real-case applications. A practical application of the numerical tool developed was demonstrated using the predicted AFM allowances for the generation of a compensated computer-aided design (CAD) model of the part to be printed.

Object-based illumination transferring and rendering for applications of mixed reality

In applications of augmented reality or mixed reality, rendering virtual objects in real scenes with consistent illumination is crucial for realistic visualization experiences. Prior learning-based methods reported in the literature usually attempt to reconstruct complicated high dynamic range environment maps from limited input, and rely on a separate rendering pipeline to light up the virtual object. In this paper, an object-based illumination transferring and rendering algorithm is proposed to tackle this problem within a unified framework. Given a single low dynamic range image, instead of recovering lighting environment of the entire scene, the proposed algorithm directly infers the relit virtual object. It is achieved by transferring implicit illumination features which are extracted from its nearby planar surfaces. A generative adversarial network is adopted in the proposed algorithm for implicit illumination features extraction and transferring. Compared to previous works in the literature, the proposed algorithm is more robust, as it is able to efficiently recover spatially varying illumination in both indoor and outdoor scene environments. Experiments have been conducted. It is observed that notable experiment results and comparison outcomes have been obtained quantitatively and qualitatively by the proposed algorithm in different environments. It shows the effectiveness and robustness for realistic virtual object insertion and improved realism.

Analysis of the Scattering from a Two Stacked Thin Resistive Disks Resonator by Means of the Helmholtz–Galerkin Regularizing Technique

In this paper, the scattering of a plane wave from a lossy Fabry–Perót resonator, realized with two equiaxial thin resistive disks with the same radius, is analyzed by means of the generalization of the Helmholtz–Galerkin regularizing technique recently developed by the author. The disks are modelled as 2-D planar surfaces described in terms of generalized boundary conditions. Taking advantage of the revolution symmetry, the problem is equivalently formulated as a set of independent systems of 1-D equations in the vector Hankel transform domain for the cylindrical harmonics of the effective surface current densities. The Helmholtz decomposition of the unknowns, combined with a suitable choice of the expansion functions in a Galerkin scheme, lead to a fast-converging Fredholm second-kind matrix operator equation. Moreover, an analytical technique specifically devised to efficiently evaluate the integrals of the coefficient matrix is adopted. As shown in the numerical results section, near-field and far-field parameters are accurately and efficiently reconstructed even at the resonance frequencies of the natural modes, which are searched for the peaks of the total scattering cross-section and the absorption cross-section. Moreover, the proposed method drastically outperforms the general-purpose commercial software CST Microwave Studio in terms of both CPU time and memory occupation.