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Robotic Granular Jamming

Student thesis: Doctoral ThesisDoctor of Philosophy

Granular jamming is a phenomenon where discrete granules can transition their macro behavior between a fluid-like and a solid-like state. In the context of soft robotics, this thesis examines granular jamming in three key aspects. The first aspect investigates the modeling of the granule behavior as it is jammed and unjammed. A simplified model was developed where the macro stiffness of the granules in different states is encompassed in one variable, E. In an engineering context, the usage of this one variable enables structures of different types to be quantitatively compared. The second aspect investigates the structure of mechanisms using granule jamming. For the granules, experiments were
performed on different shapes, sizes, and materials. The results show that there can be a significant change in the stiffness range and profile when a parameter of the granule is changed. The properties of the membrane holding the granules and properties of the interparticle fluid were also studied for their affect on the behavior of the stiffnesses. For the membrane, the boundary layer applying the external stress, different materials and designs were found to have as much as a significant impact as changing granule type.
For the interparticle fluid, the effects of air and water as the inter-granule fluid were compared, which showed that there is no significant difference between the stiffness range. However, the use of water can shrink the transition region between the fluid-like and solid-like states of granular behavior. While this smaller transition region limits the tunability of compliance for a granular jamming mechanism, it gives the added benefit of requiring less volume of fluid to create vacuum, due to the incompressibility to water. This effectively
untethers granular jamming mechanisms from cumbersome vacuum pumps, a key step in mobilizing the technology in the context of robotics. Lastly, this thesis focuses on the aspect of control for granular jamming. This encompasses the development of granular jamming-based actuators and the control of those actuators though impedance control.
Original languageEnglish
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Award date2014

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