1,721,060 research outputs found
Digital close range photogrammetry for 3D body scanning for custom-made garments
No full textAmong several biometric applications, one of those currently attracting great interest is the possibility of carrying out 3D digitisation of human individuals to analyse their physical characteristics. These characteristics can be used for several purposes, such as security, medicine and tailoring for custom-made clothing. In recent years, although the development of online 3D scanning systems has been accelerating fast, little work has been devoted to offline systems, which would be particularly suitable for the textile and clothing industries. In the present research the author presents a specially designed low-cost offline 3D body digitiser, based on digital close range photogrammetry. A specially designed photogrammetric 3D scanner of the human body is presented, featuring automatic image processing procedures. The scanning system consists of eight cameras with a resolution of 5 megapixels, equipped with 16 mm wide-angle lenses; there are four white-light illuminators, of 100 W each. Tests on a tailor's dummy and on whole human bodies are reported, demonstrating the usefulness of the technique for textile applications. The digitisations performed on human bodies generally yield worse results than the corresponding ones on the dummy, and full body digitisations are worse than corset digitisations owing to the lower point density and to target distortion. Nevertheless, the results are satisfactory for tailoring applications that do not require high accuracies
A generalized method aiming at predicting the polymer melt flow field in the metering zone of large-scale single-screw extruders
No full textSingle-screw extruders (SSE) are commonly used in a wide variety of applications, ranging from polymer-extrusion to pellet additive manufacturing (PAM). Existing mathematical models focus on Newtonian and power-law rheologies to model melt flow in the last screw vanes. However, molten polymers usually follow more complex rheological patterns, and a generalized extrusion model is still lacking. Therefore, a semi-analytical model aiming at describing the flow of molten polymers in SSE is presented, to encompass a wide range of non-Newtonian fluids, including generalized non-Newtonian fluids (GNF). The aim is to evaluate the molten polymer flow field under the minimum set of dimensionless parameters. The effect of dimensionless extrusion temperature, flow rate, channel width, and height on the flow field has been investigated. A full factorial plane has been chosen, and it was found that the impact of dimensionless flow rate is the most prominent. The results were initially compared to numerical computations, revealing a strong agreement between the simulations and the proposed GNF method. However, significant deviations emerged when employing the traditional power-law model. This is particularly true at high values of flow rate and extrusion temperature: the mean error on overall flow speed is reduced from 12.91% (traditional power-law method) to 1.04% (proposed GNF method), while keeping a reasonable computational time (time reduction: 96.70%, if compared to fully numerical solutions). Then, the predicted pressure drop in the metering section was benchmarked against established literature data for industrial-scale extruders, to show the model's accuracy and reliability. The relative errors of the traditional model range between 34.33 and 62%. The proposed method reduces this gap (errors ranging between 5.34% and 10.97%). The low computational time and high accuracy of the GNF method will pave the way for its integration in more complex mathematical models of large-scale additive manufacturing processes
Preliminary evaluation of artificial bee colony algorithm when applied to multi objective partial disassembly planning
No full textThe aim of this study is the first evaluation of the Artificial Bee Colony Algorithm when applied to multi objective partial disassembly planning. Several methodologies have been proposed by academic and industrial researchers for developing and implementing automated disassembly planning and the research literature is very extensive. In particular, nature-inspired heuristic techniques seem to be very promising and performing well to optimize the disassembly planning problem, among them, the Artificial Bee Colony (ABC) approach, which has not yet been tested. The authors propose the implementation of a discrete ABC algorithm to plan the disassembly sequence of products, following these steps: matrix system modelling, multi-objective function and solution search with an ABC algorithm. In particular the study provides details of the algorithm and heuristic rules, inspired by the behaviour of bees during food search, which is a very efficient natural process. Two case studies have been selected and reported to test the efficiency of the algorithm, while further research is required to compare ABC to other efficient heuristics
SENSORE DI FORZA, METODO PER EFFETTUARE UNA MISURA DI FORZA MEDIANTE DETTO SENSORE DI FORZA E METODO PER PRODURRE DETTO SENSORE DI FORZA
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