Volume 18 (2018): Edizione 3 (June 2018)

This paper introduces a robust, real-time loop closure correction technique for achieving global consistency in 3D reconstruction, whose underlying notion is to back-propagate the cumulative transformation error appearing while merging the pairs of consecutive frames in a sequence of shots taken by an RGB-D or depth camera. The proposed algorithm assumes that the starting frame and the last frame of the sequence roughly overlap. In order to verify the robustness and reliability of the proposed method, namely, Proportional Error Back- Propagation (PEB), it has been applied to numerous case-studies, which encompass a wide range of experimental conditions, including different scanning trajectories with reversely directed motions within them, and the results are presented. The main contribution of the proposed algorithm is its considerably low computational cost which has the possibility of usage in real-time 3D reconstruction applications. Also, neither manual input nor interference is required from the user, which renders the whole process automatic.

In this paper, the extremely low frequency magnetic field produced by the tablet computers is explored. The measurement of the tablet computers’ magnetic field is performed by using a measuring geometry previously proposed for the laptop computers. The experiment is conducted on five Android tablet computers. The measured values of the magnetic field are compared to the widely accepted TCO safety standard. Then, the results are classified by the Self-Organizing Map method in order to create different levels of safety or danger concerning the magnetic field to which tablet computer users are exposed. Furthermore, a brief comparison of the obtained magnetic field levels with the ones from typical laptops is performed. At the end, a practical suggestion on how to avoid the high exposure to the low frequency magnetic field emitted by the tablet computers is given.

A dust explosion is one of the key security issues for many industrial, pharmaceutical and agro-alimentary plants and for the safety of the workers. We have developed an optoelectronic sensor system to determine the mass of deposited dust and the resuspension rate. The authors also mount antennas on an optoelectronic sensor system to perform measurements remotely. The technique used is based on a non-invasive light absorption method. The paper reports a cost analysis in order to demonstrate the possibility to use, in our optoelectronic sensor system, several sensors to monitor large volume. In this paper the authors present the sensor system, the test and calibration of its components together with the results and the error analysis, demonstrating experimentally what is the maximum and the minimum readable range.

Magnetic resonance imaging (MRI) is a very popular tool for diagnostic applications and research studies. Low-field MR scanners, usually with an open design, are suitable for claustrophobic and obese patients, as well as for children, who may be fearful in closed MR scanners. However, these types of scanners provide lower spatial resolution and a lower signal-to-noise ratio (SNR) if compared with the same examination performed at the same time at high field scanners. It is dominantly caused by the low field strength and other factors, such as radiofrequency noise. Therefore, a long measurement time is usually necessary. This research paper is focused on the development of novel probes and preamplifiers for low-field MR scanners to improve SNR, and thus, shorten the measurement time. In this study, we describe the design of a high impedance preamplifier and a high temperature superconductor (HTS) coil. This novel instrumentation was compared with uncooled and cooled copper coils. Improvement in SNR in the case of an HTS coil is reported.

In the vacuum thermoforming process, the product deviations depend on several parameters of the system, which make the analysis, the computational modeling, and the optimization of errors a multi-variable process with conflicting objectives. In this sense, the aim of this work was to study the dimensional and geometrical errors as well as the optimization (minimization) of these errors in one typical vacuum thermoforming product made of polystyrene (PS). In particular, it was intended to predict and minimize errors in a range of ideal tolerances using Multiple Response Optimization (MRO) Models. Thus, through the fractional factorial design (2k-p), initial experimental tests were performed using proposed measurement procedures, and Analysis of Variance being the data analysis is discussed. Following that, the MRO models were implemented which were also validated to represent the sample data. Through this analysis of the results, it can be concluded that the regression models of errors are not linear functions, hence, the developed models are valid for the studied process, and finally that the validation results proved the efficiency of MOR models developed, but these models will not be able to generalize to new situations in a range far from the values studied.

In the paper the set of representative parameters for a comprehensive assessment of the surface texture status after slide burnishing has been proposed. The analysis of correlations between the parameters of the surface texture, obtained by slide diamond burnishing of 317Ti steel has been performed. Correlations have been determined and several groups of surface texture parameters with strong mutual correlations (also parameters uncorrelated with the other) have been selected. For both groups of parameters - representative and uncorrelated - experimental mathematical relations defining influences of the input parameters of slide diamond burnishing on the surface texture parameters have been developed. Also, interaction effects for individual parameters of this finishing process have been disclosed. It has been found that by appropriate selection of input conditions of the slide diamond burnishing process, it is possible to obtain a wide range of states of the surface texture.