3,680 research outputs found
Bio-inspired visual information processing - The neuromorphic approach
No full textThis paper describes the bio-inspired visual inforamtion processing by neuromorphic system, mimicking the primitive behaviour of visual cortex. The neuromorphic components are investigated for implementation of the visual signal selectivity of cortex, based on the CMOS conductance-based synaptic connections and neurons of Hodgkin-Huxley formalism. The proposed neuromorphic system exhibits the biologically plausible function mimicking the cats visual cortex experimentation of Hubel and Wiesel. The detection of vehicle object or human head figure demonstrates the feasibilty of vision applications
Space Environment Characteristics of MWNT/Epoxy Composite
Get PDFMulti-walled carbon nanotube (MWNT)/epoxy composites were fabricated with different nanotube weight percent (wt.%) concentrations. Ultra-sonication and homogenization were simultaneously used to uniformly disperse MWNTs into the epoxy. The MWNT/epoxy composites were tested in simulated low earth orbit (LEO) environment. Effects of MWNTs content on space environment characteristics of the nanocomposites were studied herein. The LEO space environment simulation was characterized by high vacuum (~10-5 Torr), ultraviolet (UV) radiation (<200nm wavelength), temperature cycling (-70ºC~100ºC), and atomic oxygen atmosphere (AO flux of ~1016 atoms/cm2·s and kinetic energy of ~0.04 eV). The tensile properties as well as mass loss of the nanocomposites with various nanotube concentrations, exposed to the simulated LEO environment, were investigated. The surface morphology of MWNT/epoxy nanocomposites under space environmental effects was observed by scanning electron magnetoscope (SEM).항공우주공학전
Feed velocity feedback for high speed fused deposition modelling machines
No full textAdditive manufacturing (AM) is a manufacturing method with two distinct advantages over traditional subtractive methods. First, it allows for much higher form freedom, allowing for shapes that are unobtainable by conventional techniques. Second, this method is also referred to 'rapid prototyping' given the fact that objects, and mainly prototype iterations, may be produced in a matter of hours instead of days. Fused deposition modelling (FDM) is the most ubiquitous and accessible AM technology, relying on the layer-by-layer deposition of molten thermoplastics. While FDM is very accessible and shows great potential as a future manufacturing technique, it is still inferior to traditional techniques due to the very low production capacity and limited speed. Print speed is mainly limited by volumetric ow rate through the nozzle, of which the counter pressure at high velocity causes filament slip in the extrusion mechanism. Therefore, the goals of this thesis are (1) to design an accurate extruder model to describe input-output behaviour of feed velocity. This may yield better understanding of FDM extrusion and form a basis for model-based design. (2) The synthesis of an anti-slip controller allowing for high print speed while retaining object quality. When a higher print speed could be attained, one of the largest disadvantages of FDM would be mitigated and a new step is made towards industrial application of this technology. To make the model of the extruder, the only known velocity input-output model available was taken and verified. This black-box transfer function model accurately describes low-speed behaviour of the extruder. This model, however, did not incorporate slip phenomena, making it an inaccurate model at high volume flow. Hence, a model from the automotive industry, also known as the 'Magic Formula' was combined with this known transfer function, producing a new black-box model covering all feed velocities. This new model has opportunity to be used as a basis for model-based design of 3D printers, which are now generally designed based on past experience and trial-and-error. For the future, it would be highly interesting to find an analytical model rather than a transfer-based one in order to gain physical understanding in the influence of extruder parameters. Regarding the synthesis of an anti-slip controller, we implemented a type of extremum seeking hybrid control which essentially finds an feasible maximum velocity for a limited amount of slip. The logic of the controller was based on Schmitt trigger logic, defining three control parameters that together define the switching behaviour of the controller. After tuning, if was found that the controller improved extrusion errors as well as completion time compared to open-loop control, achieving the set goals. The successful application of such a controller could mitigate the low velocity disadvantages of FDM and facilitate the acceptance of this technology. In the future, it is recommended to further investigate the practical applications of the controller, find the limitations of the controller in real printing and explore different control architectures.Mechanical, Maritime and Materials EngineeringBiomechanical Engineerin
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