Browsing by Author "Ghorbel, Fathi"

Now showing 1 - 5 of 5
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    Aluminum Nitride Memristors: The Fabrication and Analysis of a Next Generation Processor
    (2024-04-21) Attarwala, Ali; Spanos, Pol D; Ghorbel, Fathi; Tang, Ming
    This thesis details the experimental development of memristors with an Aluminum Nitride (AlN) insulative layer that can switch its resistance by adjusting its phase. Upon conducting an exhaustive literature review, the opportunity to study the ferroelectric properties of AlN in a resistive switching setting came about. The experimental study starts by detailing the fabrication of memristors utilizing atomic layer deposition (ALD) and electrode deposition. To study the characteristics of the device, relevant AlN memristor samples underwent a full electrical characterization. While there were some interesting results, the current-voltage (I-V) data did not match the expected behavior and results. To further investigate the data, transmission electron microscopy (TEM) analysis was conducted to look inside the device at the nanometer scale. The TEM data highlights the difficulties of memristor fabrication and processing. The experimental process provided insight into the behavior of the ferroelectric properties of AlN suggesting resistive switching applications. However, further exploration of the fabrication and processing of AlN in memristors is required, before any industrial applications are pursued.
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    AUV Control with Hard and Soft Actuators
    (2021-04-28) Zavislak, Colin; Ghorbel, Fathi
    Autonomous underwater vehicles (AUVs) find many applications in oceanography, environmental research, and inspection and maintenance of subsea energy assets. Subsea resident AUVs remain in subsea for extended periods of time that can last for several months. Maintaining depth or orientation using traditional hard actuators (HAs) is very energy expensive. Mimicking aquatic creatures by using propulsion and buoyancy control, it is shown in this thesis that HAs and proposed soft actuators (SAs) can collaborate in a novel way. This collaboration can stabilize AUVs at any desired depth and orientation with minimum energy consumption at steady state. Additionally, once in the desired position the SAs can be used to precisely adjust the orientation of the system while maintaining depth by changing the system's center of buoyancy. This allows for the system to utilize tools, pick up parts, or perform other functions that would result in system mass change. This is demonstrated using a laboratory AUV for which a nonlinear dynamic model was developed that uses experimentally validated system parameters. The AUV uses HAs to quickly reach any desired depth or orientation while SAs generate volume change to adjust the system’s buoyancy to maintain neutral buoyancy at the desired depth. In the neutral buoyancy state, the HAs shut off while the SAs stabilize and maintain the position with virtually zero energy consumption. A control algorithm architecture is developed to manage the HA and SA collaboration. The HAs use a proportional controller with a dead-band, while the SAs use a proportional-derivative-acceleration (PDA) feedback controller. The ability of both types of actuators to mitigate disturbance forces and mass error are explored and analyzed. Simulation results show that SAs alone can reject small disturbances and adjust buoyancy to mitigate shift in system CM, while using both SAs and HAs in collaboration can reject large disturbances and errors. Simulation results demonstrate that combining traditional HAs with SAs leads to dynamic performance and very low energy consumption capabilities that cannot be achieved by either one alone.
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    Femoral Venipuncture: Force Modeling and Experimentation of Multilayer Needle Insertion
    (2022-04-26) Ardic, Can; Ghorbel, Fathi
    Extra-corporeal membrane oxygenation (ECMO) is a procedure that allows the circulation and direct oxygenation of blood in the event of lung injury or dysfunction. ECMO requires a team of trained medical professionals which creates a burden to persons in need such as injured soldiers on the battlefield or those suffering from a pandemic in which medical staff is already stretched thin. This thesis explores the initial step of automating ECMO which is force modeling of needle insertion into jugular or femoral blood vessels. A comprehensive force model consisting of stiffness, cutting, and friction forces was created that accounts for each phase of needle insertion through multiple layers. This model is simulated and then adjusted to empirical results from porcine and bovine samples. This thesis presents a unique force model for a specific target location with multiple layers, as well as takes into account tissue deformation recovery which is an under-researched phenomenon. This reasonable lumped parameter model allows for the application of a control law.
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    Impedance Control Approaches for Series Elastic Actuators
    (2015-09-22) Mehling, Josh S; O'Malley, Marcia K.; Ghorbel, Fathi; Kavraki, Lydia
    For applications requiring interaction with humans or unstructured environments, robots are increasingly designed to leverage the intentional drivetrain compliance of series elastic actuators (SEAs). Impedance control, likewise, is of particular value in these applications, having long been considered an effective means of addressing dynamic interaction. Although impedance controlled SEAs appear often in the literature, a number of important questions remain unanswered. If, for example, robust contact stability is required, can an SEA render a virtual stiffness greater than its physical spring rate? Previous studies answer no, but this is largely a question of control architecture. It is proven here, as part of a larger study comparing the stability and passivity of five different control approaches, that this is in fact possible if disturbance observer based impedance control is adopted. The fidelity with which SEAs render desired impedances is important as well. In comparing the impedance rendering accuracy of multiple control approaches, experimental data in both the time and frequency domain point once more to disturbance observer based impedance control. This new SEA control architecture yields demonstrable improvement in actuator transparency, closed loop hysteresis, and the SEA's dynamic response to both reference commands and external torques. Two new performance metrics are formulated based on the H∞ and H2 system norms to further quantify SEA impedance rendering accuracy across the frequency spectrum. A novel model matching framework is then constructed that leverages these metrics for the optimal synthesis of SEA impedance control. Passive and accurate controllers result that, having been deployed on physical hardware, represent the first application of LMI-based, multi-objective, optimal control synthesis to series elastic actuation. These results are all confirmed experimentally on high performance SEAs. Three new actuator designs are presented that provide up to 350 Nm in peak torque and torque sensing resolutions as low as 0.006 Nm. This 58,333:1 dynamic range (an order of magnitude improvement over previous SEAs) is achieved in a torque dense, 94.3 Nm/kg package ideally suited for use in humanoid robots. Demonstrated SEA performance reinforces the practical utility of the recommended control approaches and speaks to the broader applicability of impedance controlled SEAs to human-centric robots.
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    Modeling and Control of AUVs using Buoyancy-Based Soft Actuation
    (2022-04-21) Hoppe, Christopher; Ghorbel, Fathi
    Nonlinear control of Autonomous Underwater Vehicles (AUVs) via the use of thrusters has been well established within the last 50 years. These AUVs can be used for various applications, including subsea inspection and maintenance, exploration, research, and observation. These thrusters are best suited for large thrust forces required by large movements, but are not optimal for fine control or in confined spaces. Research by our group into buoyancy control devices (BCDs) using reversible fuel cells (RFCs) has proven their viability and limitations. This thesis demonstrates nonlinear control of an AUV in the three dimensions directly controllable via BCDs while completing various mission profiles. An adaptive control law is derived that ensures stability throughout the completion of the desired mission. Simulation results demonstrate desired performance with low steady-state energy requirements.