Preliminary Study on the 3D Digitization of Millimeter Scale Products by Means of Photogrammetry

AbstractPhotogrammetry is a passive 3D digitization technique, mainly oriented to large sized objects, since its origins are in architectural and civil engineering. With the continuos development of digital imaging hardware and software, photogrammetric applications are involving smaller and smaller fields of view, with some critical aspects such as the depth of field getting narrower. In this conditions the lack of focus becomes important and affects heavily the possibility of accurately calibrate cameras. Bi-dimensional calibration patterns are affected by this problem when the camera principal axis has an angle with the pattern plane higher than a critical value. Moreover, the accuracy of the pattern, in terms of both shape and 3D positions of the targets, becomes critical decreasing the size of the pattern. In this paper the authors address these problems through a comparison of several calibration patterns included into the open source computer vision software library called OpenCV. 3D digitization of a small object is presented to test the best resulting calibration, using a consumer reflex camera equipped with macro lens and extension tube

Three-dimensional anthropometric database of attractive caucasian women: Standards and comparisons

The aim of this paper is to develop a database to determine a new biomorphometric standard of attractiveness. Sampling was carried out using noninvasive three-dimensional relief methods to measure the soft tissues of the face. These anthropometric measurements were analyzed to verify the existence of any canons with respect to shape, size, and measurement proportions which proved to be significant with regard to the aesthetics of the face. Finally, the anthropometric parameters obtained were compared with findings described in the international literature. The study sample was made up competitors in the Miss Italy 2010 and 2009 beauty contest. The three-dimensional (3D) scanning of soft tissue surfaces allowed 3D digital models of the faces and the spatial 3D coordinates of 25 anthropometric landmarks to be obtained and used to calculate linear and angular measurements. A paired Student t test for the analysis of the means allowed 3 key questions in the study of biomorphometric parameters of the face to be addressed through comparison with the data available in the literature. The question of statistical evidence for the samples analyzed being members of the populations samples reported in literature was also addressed. The critical analysis of the data helped to identify the anthropometric measurements of the upper, middle, and lower thirds of the face, variations in which have a major influence on the attractiveness of the face. These changes involve facial width, height, and depth. Changes in measurements of length, angles, and proportions found in the sample considered were also analyzed

Structural basis for PPAR partial or full activation revealed by a novel ligand binding mode

The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors involved in the regulation of the metabolic homeostasis and therefore represent valuable therapeutic targets for the treatment of metabolic diseases. The development of more balanced drugs interacting with PPARs, devoid of the side-effects showed by the currently marketed PPARλ 3 full agonists, is considered the major challenge for the pharmaceutical companies. Here we present a structure-based virtual screening approach that let us identify a novel PPAR pan-agonist with a very attractive activity profile and its crystal structure in the complex with PPARα and PPARλ 3, respectively. In PPARα this ligand occupies a new pocket whose filling is allowed by the ligand-induced switching of the F273 side chain from a closed to an open conformation. The comparison between this pocket and the corresponding cavity in PPARλ 3 provides a rationale for the different activation of the ligand towards PPARα and PPARλ 3, suggesting a novel basis for ligand design

Compressive Properties of FDM Rapid Prototypes Treated with a Low Cost Chemical Finishing

Abstract: In literature several studies have been performed to analyze the surface finish of rapid prototyped parts. These researches have been mainly aimed to the optimal build direction of prototypes to obtain the best possible surface finish on specific surfaces. Very diffuse technologies that suffers considerably of low surface quality are Fused Deposition Modeling (FDM) and extrusion based Rapid Prototyping machines in general. Hand finishing for even the most basic levels of part quality are often required by the customers, forcing the geometrical features of the prototypes to be controlled by the skill level of the operator. This study completes past researches performed by the authors on tensile and flexural properties of chemical dipped specimens after immersion in a dimethyl ketone-water solution. The authors aim to gain a more in-depth knowledge of this process, by analyzing and comparing the compressive properties of finished and non-finished FDM parts through the use of an experimental approach, totalizing about 100 tests

Analysis of Shape Geometry and Roughness of Ti6Al4V Parts Fabricated by Nanosecond Laser Ablation

Laser milling is a micro-machining process that uses a laser beam as a tool to remove material through the layer-by-layer ablation mechanism. Generally in laser ablation, the quality of parts is reduced by melt accretions and thermal damage; therefore, this problem is reduced with shorter pulse duration, although ablation efficiency decreases as well. Thus, laser ablation in the nanosecond range still offers a good compromise between process quality and efficiency. Therefore, laser milling with nanosecond laser ablation requires an accurate study to reduce geometric defects induced by the process. The aim of this paper was to study the shape geometry and roughness of Ti6Al4V parts fabricated by laser milling using a nanosecond Nd:YAG laser source. The impact of the laser processing parameters on machining outcomes was studied in order to determine the optimized processing conditions for reducing geometrical defects and improving surface quality. In particular, the influence of average laser power, frequency, and scanning speed was investigated. The geometry of micro-parts was revealed using a 3D digitizing system, the Optimet Mini Conoscan 4000, which combines a non-contact, single-point measuring sensor based on conoscopic holography technology. The use of this measurement technology yielded complete information of the shape geometry and dimensions of the built parts. In addition, the roughness of manufactured surfaces was assessed to complete the analysis

Use of Miniature Step Gauges to Assess the Performance of 3D Optical Scanners and to Evaluate the Accuracy of a Novel Additive Manufacture Process

In this work, we show how miniature step gauges featuring unidirectional and bidirectional lengths can be used to assess the performance of 3D optical scanners as well as the accuracy of novel Additive Manufacturing (AM) processes. A miniature step gauge made of black polyphenylene sulfide (PPS) was used for the performance verification of three different optical scanners: a structured light scanner (SLS), a laser line scanner (LLS), and a photogrammetry-based scanner (PSSRT), having comparable resolutions and working volumes. Results have shown a good agreement between the involved scanners, with errors below 5 μm and expanded uncertainties below 10 μm. The step gauge geometry due to the bidirectional lengths, highlights that there is a different interaction between the optical properties of the step gauge under measurement and each optical instrument involved and this aspect has to be considered in the uncertainty budget. The same geometry, due to its great significance in the detection of systematic errors, was used, as a novelty, to evaluate the accuracy of Lithography-based Ceramics Manufacturing (LCM), a proprietary additive manufacturing technology used for the fabrication of medical implants. In particular, two miniature step gauges made of Tricalcium Phosphate (TCP) were produced. Measurements conducted with the SLS scanner were characterized by a negligible error and by an uncertainty of about 5 μm. Deviations of the manufactured step gauges with respect to the Computer Aided Designed (CAD) model were comprised between ±50 μm, with positive deviations in the order of 100 μm on vertical sides. Differences in the order of 50 μm between the two step gauges were registered

Reconstruction of small components using photogrammetry:A quantitative analysis of the depth of field influence using a miniature step gauge

In this work, authors investigated the effect of the Depth of Field (DoF) reduction, arising when the acquisition of small objects is carried out with a photogrammetry-based system using a Digital Single Lens Reflex (DSLR) camera and the structure from motion (SfM) algorithm. This kind of measuring instrument is very promising for industrial metrology according to the paradigms of the fourth industrial revolution. However, when increasing the magnification level, necessary for the reconstruction of sub-millimetric features, there is a corresponding decrease of the DoF, leading to possible effects on the reconstruction accuracy. Thus, the effect of the DoF reduction was analysed through the reconstruction of a well-known artefact: the step gauge. The analysis was conducted considering the theory behind the DoF concept, the analysis of the 2D images, input of photogrammetric reconstruction and, finally, the results in terms of dimensional verification of the reconstructed step gauge

Photogrammetric 3D skull/photo superimposition: A pilot study

The identification of bodies through the examination of skeletal remains holds a prominent place in the field of forensic investigations. Technological advancements in 3D facial acquisition techniques have led to the proposal of a new body identification technique that involves a combination of craniofacial superimposition and photogrammetry. The aim of this study was to test the method by superimposing various computerized 3D images of skulls onto various photographs of missing people taken while they were still alive in cases when there was a suspicion that the skulls in question belonged to them. The technique is divided into four phases: preparatory phase, 3d acquisition phase, superimposition phase, and metric image analysis 3d. The actual superimposition of the images was carried out in the fourth step. and was done so by comparing the skull images with the selected photos. Using a specific software, the two images (i.e. the 3D avatar and the photo of the missing person) were superimposed. Cross-comparisons of 5 skulls discovered in a mass grave, and of 2 skulls retrieved in the crawlspace of a house were performed. The morphologyc phase reveals a full overlap between skulls and photos of disappeared persons. Metric phase reveals that correlation coefficients of this values, higher than 0.998â\u80\u930,997 allow to confirm identification hypothesis