Optimum part deposition orientation for multiple objectives in SL and SLS prototyping

In the present work an attempt has been made to achieve minimum average part surface roughness (best overall surface quality), minimum build time and support structure for stereolithography (SL) and selective laser sintering (SLS) processed parts by determining optimum part deposition orientation. A conventional optimisation algorithm based on a trust region method (available with MATLAB-7 optimisation tool box) has been used to solve the multi-objective optimisation problem. It is observed that the problem is highly multi-modal in nature and a suitable initial guess, which is used as an input to execute the optimisation module, is important to achieve a global optimum. A simple methodology has been proposed to find out the initial guess so that global minimum is obtained. Finally the surface roughness simulation is carried out with optimum part deposition orientation to have an idea of surface roughness variation over the entire part's surface before depositing the part. Case studies are presented to demonstrate the capabilities of the developed system. The major achievements of this work are consideration of multiple objectives for the two rapid prototyping processes, successful use of conventional optimisation algorithm available with MATLAB to handle multiple objectives and development of graphical user interface-based system.     

The optical properties of CuGa0.5In0.5Se2 thin films

CuGa_0.5In_0.5Se₂ thin films with thickness in the range 50 to 280 nm were deposited by thermal evaporation of prereacted material on glass substrates. The films were found to be polycrystalline with single phase having chalcopyrite structure as that of bulk material. The optical constants of these films were determined by transmittance and reflectance measurements at normal incidence for light in the wavelength range 400 to 1200 nm. Three characteristic energy gaps of 1.30, 1.55 and 2.46 eV were obtained from an analysis of the optical absorption spectrum. The optical constants of the films appear to be independent of the substrate temperature.     

Room-temperature deformation of PdIn

Room temperature tensile testing of the B2-structured compound Pd-52 at% In produced, a yield strength of 50 MPa, a fracture strength of 130 MPa, and limited tensile ductility (3%). Examination, in the transmission electron microscope, of the deformed microstructure indicated that it deforms by 001 {100} slip. Extra reflections and streaking were observed in selected area electron diffraction patterns, which appear to be a thin foil effect.     

Extended stigmergy in collective construction

We've described a scheme by which a swarm of robots can automatically assemble solid structures of square building blocks in two dimensions according to a high-level user-specified design. We discuss the use of extended stigmergy: augmenting the basic notion of stigmergy by increasing the capabilities of environmental elements. In this construction setting, the elements are the building blocks, the basic information they carry is the simple fact of their presence at a location, and extensions include cases where they can store additional information, perform computations, and/or communicate with physically attached neighbors. Benefits can include increased robustness and faster completion of a desired structure. We review three variants of that construction scheme that use extended stigmergy to different degrees. We focus on analysis of the algorithms and their comparative performance, mainly theoretical but also through simulation experiments.     

Robust regulation with 2 performance

We consider the problem of minimizing the ₂ norm of a feedback system subject to the constraint that the controller robustly regulate against constants and sinusoids. We show that, for any ε > 0, there exists a controller that both achieves robust regulation and renders the closed-loop ₂ norm within ε of the optimal norm (the norm achievable without the robust regulation constraint). We also provide conditions that are both necessary and sufficient for there to exist a robustly regulating controller that achieves the optimal ₂ norm. All proofs are constructive.