1,721,009 research outputs found
Il Reverse Engineering per la diagnostica non invasiva in Ortognatodonzia: messa a punto di un sistema di misura dei volti automatico, basato sulla fotogrammetria
No full textLe analisi strumentali attualmente utilizzate in campo medico per valutare le proporzioni del volto si basano su radiogrammi bi o tridimensionali e fotografie cliniche. Un metodo non invasivo che soddisfi le esigenze cliniche, che utilizzi la sola fotografia clinica, non è stato ancora messo punto. Nella pratica Ortodontica le misurazioni del paziente devono essere ripetute ad intervalli regolari, per permettere di monitorare la crescita e gli effetti delle terapie. Nei pazienti malformati, inoltre, poter effettuare misurazioni periodiche permette di formulare diagnosi più accurate e valutare gli effetti della malformazione sulla crescita. Nel presente articolo si utilizza l’Ingegneria Inversa per nuove applicazioni specifiche in campo medico, per la misura delle variazioni delle caratteristiche di un volto, per monitorare e guidare la terapia ortognatodontica, e la misura delle dismorfie causate da particolari patologie genetiche o traumatiche. Il sistema è basato sull’uso di sensori foto-video digitali ad alta o altissima risoluzione, e sulla elaborazione delle immagini mediante software di fotogrammetria digitale in campo stretto per la estrazione dei punti tridimensionali e la ricostruzione CAD delle superfici dei volti
A stereo photogrammetry scanning methodology, for precise and accurate 3D digitization of small parts with sub-millimeter sized features
Full text linkThis paper presents a scanning methodology based on close-range stereo photogrammetry, suitable for precise and accurate 3D digitization of objects of few millimeters in length and features in sub-millimeter scale. The authors propose an efficient alternative to other scanning methodologies currently used for such applications, as the conoscopic holography, with the aim to reduce the scanning time and obtain a result which also contains information related to the real texture of the object. An experimental plan has been designed and implemented in order to investigate the accuracy and precision of the 3D scans
Multistack close range photogrammetry for low cost submillimeter metrology
No full textConsiderable research effort has been focused on evaluating the accuracy of meso-and macroscale digital close range photogrammetry. However, evaluations of accuracy and applications in the submillimeter scale are rare. In this paper the authors propose the development of a three-dimensional (3D) photogrammetric scanner, based on macrolens cameras, able to reconstruct the three-dimensional surface topography of objects with submillimeter features. The system exploits multifocal image composition and has been designed for installation on all types of Numerical Controlled or Robotic systems. The approach is exploitable for digitizing submillimeter features at mesoscale as well as macroscale objects
Study of compression properties of topologically optimized FDM made structured parts
No full textReverse Engineering software packages are not able to automatically and robustly detect the sub-regions of a tessellated model; it generally results in a first trial subdivision which subsequently has to be refined, requiring a large amount of human intervention and high computational effort.
To avoid these limitations, the authors propose a multilevel local approach for the automatic identification of edge points in polygonized point clouds, exploiting the ability of a heuristic technique to solve the edge detection problem with low computational effort. The approach was applied to several complex-shaped models with sharp and smooth edges, confirming its robustness and efficiency
Compressive properties of FDM rapid prototypes treated with a low cost chemical finishing
No full textIn 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
Experimental study aiming to enhance the surface finish of fused deposition modeled parts
No full textFused deposition modeling (FDM) is an additive technology that suffers badly from low surface quality, requiring hand finishing for even the most basic levels of part quality. In this paper the authors study the influence of FDM machining parameters on acrylonitrile butadiene styrene (ABS) prototypes surface finish. The surface finish of products after the modification of extrusion parameters has been measured and processed through designed experiments. The chemical post-treatment does not require human intervention and has led to a significant improvement in surface finish at the expense of a negligible change in the prototype siz
Towards a Low-Cost Photogrammetric Face Scanner for Medical Purposes
No full textPhotogrammetry is very promising for the cost reduction of biometric systems but it still suffers of a high amount of human intervention. After having conducted several tests to verify the validity of the photogrammetric method, the present experimental study has been realized using a scanning system involving a dummy face in order to eliminate all the errors caused by un-intentional movements of the subject. The system is composed of three 10 megapixel CMOS sensors of commercial cameras and one coded flash projector synchronized by the software with the cameras. To increase the target visibility on the surface of interest, the acquisition has been realized using only the light of the projector. The preliminary automatic orientation of the images is performed exploiting a specifically designed retro-illuminated pattern. Experimental results point out that the system is able to 3D digitize the subject but enhancements are needed to increase the contrast of the targets on the human skin
Shrinkage evaluation and geometric accuracy assessment on 17–4 PH samples made by material extrusion additive manufacturing
Full text linkMaterial Extrusion Additive Manufacturing (MEX) is one of the most common Additive Manufacturing (AM) technology. The possibility to realize metal parts using this technology has several advantages and generates great costs reduction with respect to other metal Additive Manufacturing technologies. However, there are some disadvantages related to the design and production of these extrusion-based metal parts, especially when considering the fabrication of complex geometries. One of the main problems is related to the oversizing of the parts due to the shrinkage phenomenon occurring after the debinding and sintering steps.
In this work, a comprehensive study about the shrinkage phenomenon was conducted on 17–4 PH stainless steel parts realized via MEX, analyzing the influence of printing and sintering orientation, infill strategy and aspect ratio. With this aim, by using the Design of Experiment approach, samples were analyzed in both as-printed and as-sintered conditions. Shrinkage percentage values, geometric accuracy and density were the main investigated outputs. A commercial 3D structured-light scanner was used to collect the dimensional and geometric data.
Results showed a strong shrinkage anisotropy, more relevant for samples with different orientation during the printing and the sintering phase. Geometric accuracy, in terms of flatness, was also assessed comparing green and sintered parts
A 12-camera body scanning system based on close-range photogrammetry for precise applications
No full textA precise 3D body scanning system, designed for applications in the medical and biomedical field, is described. The system consists of 12 digital cameras, mounted on a rigid frame which maintains the B/H ratio constant. An LED lighting system, integrated with the rigid frame, ensures a homogenous illumination of the subject. A modified firmware installed on each device enables the synchronised remote release driven by remote control. Data transmission to the computer is carried out wirelessly. A process for the estimation of the extrinsic camera parameters has been implemented with the aim of obtaining a 3D model in 1:1 scale. Analyses have been performed in order to state the repeatability of the process used to estimate the external camera calibration parameters as well as the precision of the 3D digital models of a body obtained for a mannequin and for a live human subject
Additive manufacturing of copper parts using extrusion and sinter-based technology: evaluation of the influence of printing parameters and debinding method
No full textPurposeThis work is focused on the realization of copper parts using the material extrusion additive manufacturing debinding and sintering (MEX+D&S) technology.Design/methodology/approachA highly filled filament with 90 Wt.% of copper is used to realize nine different combinations varying the printing speed and the flow rate. The following thermal debinding and sintering are performed at 483 degrees C and 1057 degrees C, respectively, burying the samples in specific refractory powder and carbon. The green and sintered density are measured and an inspection at optical microscope is implemented for a detailed internal analysis of the defects.FindingsThe samples, that reported the highest values of the green density, become the worst in the sintered condition due to evident swelling defect generated by the entrapped polymer during the thermal debinding. On the other hand, the parts with the lower values of green density allowed to achieve a satisfying density value without significant external defects.Originality/valueThe realization of copper parts through laser-based additive manufacturing technologies shows several troubles related to the rapid heat transfer and the high reflectivity of copper, which is a hinder of the absorption of the laser power. The MEX+D&S becomes an easier and economical alternative for the realization of copper parts. The internal inspection of the samples revealed the need for the improvement on the process chain, adopting a different debinding process to open channels during the thermal debinding to avoid the entrapment of the polymer
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