Browsing by Subject "small-scale"

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    Design and Modeling of Millimeter-Scale Soft Robots for Medical Applications
    (2021-04) McDonald, Gillian
    The advancement of soft robotics and the inherent ability of soft robots to interact safely with delicate environments has created a host of opportunities for innovation in a wide range of disciplines, from pipe inspection to muscle rehabilitation. The compliance of soft robots has potential to be particularly valuable in medicine where robots are becoming increasingly present in clinical settings. However, developing medically relevant soft robots at millimeter size scales and accurately predicting how they will interact with their environments is a challenge that has yet to be overcome. This work investigates how soft robot behavior is affected as the size of the robot is reduced using both novel experimental prototypes and efficient modeling methods. One core contribution of this work is a soft robot design that is capable of locomoting through tube-like environments, such as arteries or the intestinal tract. The overall robot is modeled using components of fluid power systems to enable the robot, comprised of multiple individual sections referred to as actuators, to move in sequence using just one control input. The experimental prototype was developed using custom fabrication methods to allow new designs and material combinations to be efficiently explored. A second key contribution is an interaction model that predicts the actuator shapes and forces that develop as a result of soft robots interacting with environmental constraints. The model utilizes a combination of Hencky bar-chain and linear complementarity methods to create a simple, efficient contact model that does not require computationally expensive finite element modeling and estimates shapes with errors of 1.06\% and forces on the order of grams-force. A third major contribution is the determination of the factors controlling the underlying dependence of soft actuator bending stiffness on actuation pressure, which ultimately plays a role in how robots behave. The presented work introduces the free-fold test to soft robotics to empirically estimate the bending stiffness of soft actuators, whether composite or homogeneous. This work concludes by tying together the proposed models and corresponding empirical studies to provide a design tool and overall understanding of how soft robot behavior is affected by size reduction. The work identifies fundamental challenges and performance limitations of producing increasingly smaller soft robots at the millimeter scale and provides a foundation on which to build in order to advance the viability of soft robots in medicine.
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    Modeling and Analysis of Small-Scale Hydraulic Systems
    (2015-05) Xia, Jicheng
    OBJECTIVE To determine the scaling law and design guidelines of small-scale hydraulic systems whose output power is in the range of 10 to 100 Watts. METHODS Fundamental fluid mechanics equations were employed to model the friction and leakage losses in the hydraulic components including cylinders, hoses, and pumps. Basic structural design equations were deployed to predict their weight. Customized test stands were built to validate the efficiency models, and catalog data of o-the-shelf components was compiled to validate the weight models. The electro-mechanical components including electric motors, gear heads and batteries were modeled using their catalog data. RESULTS The efficiency and the weight of both hydraulic and electro-mechanical components were modeled in analytical forms. These models were validated against either experimental data or existing catalog data. CONCLUSION The analytical models suggested the following design guidelines: first, high operating pressure is needed for hydraulic actuation systems to weigh lighter than equivalent electro-mechanical systems; second, critical dimension thresholds exist for hydraulic and electro-mechanical components, which should not be exceeded to achieve reasonable system efficiency; third, component efficiency plays a more important role than component weight to gain higher system power density; lastly, for applications where the actuator system weight matters the most, high pressure small scale hydraulic systems are preferred over electro-mechanical systems, but for applications where the overall system weight matters the most, electro-mechanical systems work better.