Browsing by Subject "Electrical/Computer Engineering"

Now showing 1 - 3 of 3
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    Linear quadratic regulator control of an under actuated five-degree-of-freedom planar biped walking robot
    (2010-07) Leines, Matthew Thomas
    Modern robotic systems are fully actuated with full information of themselves and their immediate surroundings. If faced with a failure or damage, robotic systems cannot function properly and can quickly damage themselves. A Linear Quadratic Regulator (LQR) control system is proposed to allow an under actuated (damaged) robotic system (five-degrees-of-freedom, planar, biped, walking robot) to continue to follow a human-like walking gait in a series of Matlab and Simulink simulations. The proposed LQR controller keeps joint position errors to below 4 degrees for the fully actuated system, performing the entire gait within the given step time and length. The under actuated control system can match the fully actuated system using a separate LQR controller. Use of time-varying control and Markovian jump methods can compile both controllers into a dynamically adaptive whole, capable of full to partial gait during both locked joint and free joint failures with brakes applied as needed.
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    Logic synthesis for networks of four-terminal switches.
    (2012-05) Altun, Mustafa
    We develop a synthesis method to implement Boolean functions with lattices of four-terminal switches. Each switch is controlled by a Boolean literal. We address the synthesis problem of how best to assign literals to switches in a lattice in order to implement a given target Boolean function, with the goal of minimizing the lattice size, measured in terms of the number of switches. We present an efficient algorithm for this task. The algorithm has polynomial time complexity. It produces lattices with a size that grows linearly with the number of products of the target Boolean function. We evaluate our synthesis method on standard benchmark circuits and compare the results to a lower-bound calculation on the lattice size. Although not tied to any particular technology, we comment that our synthesis results are applicable to emerging technologies such as nanowire crossbar arrays and magnetic switch-based structures. We address the problem of implementing Boolean functions with lattices of four-terminal switches in the presence of defects. We assume that such defects occur probabilistically. Our approach is predicated on the mathematical phenomenon of percolation. With random connectivity, percolation gives rise to a sharp non-linearity in the probability of global connectivity as a function of the probability of local connectivity. We exploit this phenomenon to compute Boolean functions robustly. A significant tangent for this work is its mathematical contribution: lattice-based implementations present a novel view of the properties of Boolean function duality. We study the applicability of these properties to the famous problem of testing whether two monotone Boolean functions in irredundant sum-of-products form are dual. This is one of the few problems in circuit complexity whose precise tractability status is unknown.
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    Micromagnetic analysis of co-based magnetic nanostructures.
    (2010-12) Hernandez, Stephanie
    Micromagnetic analysis was employed in order predict the dynamical behavior of a variety of magnetic structures utilized in information storage devices. First, the surprising behavior of homogeneous perpendicular recording media was micromagnetically investigated. It is common to model recording media as interacting coherently rotating magnetic moments, but real materials frequently exhibit perpendicular switching fields less than the anisotropy field and a different angular dependence than theoretically expected. Micromagnetic simulations were performed, which included multiple elements per grain and magnetostatic interactions between elements. Two likely explanations have emerged from this analysis: the existence of low anisotropy regions within the first few atomic layers of the sputtered film or anisotropy gradation throughout the grain thickness. Both explanations offer appropriate coercivity reductions; however, grains including anisotropy gradation display this effect at more realistic values of intragranular exchange. Secondly, the lack of inclusion of spin-dependent scattering effects in most micromagnetic studies was addressed in this work. An analytic expression that includes the effect of multiple reflections within the interface of a tri-layer spin-valve composed of materials with partial spin polarization was obtained. Inclusion of this term in a micromagnetic calculation demonstrates the effect of the spin polarization of the magnetic material on the current induced behavior of the structure. We show that neglecting to include interfacial scattering events results in an underestimation of the switching current compared to the method detailed in this thesis. Multiple reflections also produce a strong dependence of the switching current on the magnetocrystalline anisotropy of the fixed layer. This approach was then extended to structures consisting of more than two ferromagnetic layers. Micromagnetic calculations employing this method achieved good agreement with electrical measurements performed on Co/Cu multilayer nanowire arrays.