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1. Dynamically Reconfigurable Discrete Distributed Stiffness for Inflated Beam Robots

   https://doi.org/10.1109/ICRA40945.2020.9197237  

   Do, Brian H.; Banashek, Valory; Okamura, Allison M. (May 2020, IEEE International Conference on Robotics and Automation (ICRA))

   null (Ed.)

   Inflated continuum robots are promising for a variety of navigation tasks, but controlling their motion with a small number of actuators is challenging. These inflated beam robots tend to buckle under compressive loads, producing extremely tight local curvature at difficult-to-control buckle point locations. In this paper, we present an inflated beam robot that uses distributed stiffness changing sections enabled by positive pressure layer jamming to control or prevent buckling. Passive valves are actuated by an electromagnet carried by an electromechanical device that travels inside the main inflated beam robot body. The valves themselves require no external connections or wiring, allowing the distributed stiffness control to be scaled to long beam lengths. Multiple layer jamming elements are stiffened simultaneously to achieve global stiffening, allowing the robot to support greater cantilevered loads and longer unsupported lengths. Local stiffening, achieved by leaving certain layer jamming elements unstiffened, allows the robot to produce "virtual joints" that dynamically change the robot kinematics. Implementing these stiffening strategies is compatible with growth through tip eversion and tendon steering, and enables a number of new capabilities for inflated beam robots and tip-everting robots. 

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2. Jamming Skins that Control System Rigidity from the Surface

   https://doi.org/10.1002/adfm.202006915  

   Shah, Dylan S.; Yang, Ellen J.; Yuen, Michelle C.; Huang, Evelyn C.; Kramer‐Bottiglio, Rebecca (September 2020, Advanced Functional Materials)

   Abstract Numerous animals adapt their stiffness during natural motions to increase efficiency or environmental adaptability. For example, octopuses stiffen their tentacles to increase efficiency during reaching, and several species adjust their leg stiffness to maintain stability when running across varied terrain. Inspired by nature, variable‐stiffness machines can switch between rigid and soft states. However, existing variable‐stiffness systems are usually purpose‐built for a particular application and lack universal adaptability. Here, reconfigurable stiffness‐changing skins that can stretch and fold to create 3D structures or attach to the surface of objects to influence their rigidity are presented. These “jamming skins” employ vacuum‐powered jamming of interleaved, discrete planar elements, enabling 2D stretchability of the skin in its soft state. Stretching allows jamming skins to be reversibly shaped into load‐bearing, functional tools on‐demand. Additionally, they can be attached to host structures with complex curvatures, such as robot arms and portions of the human body, to provide support or create a mold. We also show how multiple skins can work together to modify the workspace of a continuum robot by creating instantaneous joints. Jamming skins thus serve as a reconfigurable approach to creating tools and adapting structural rigidity on‐demand. 

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3. Flexure Mechanisms with Variable Stiffness and Damping Using Layer Jamming

   Aktas, Buse; Howe, Robert D. (October 2019, Proceedings of the IEEERSJ International Conference on Intelligent Robots and Systems)

   Flexures provide precise motion control without friction or wear. Variable impedance mechanisms enable adapt- able and robust interactions with the environment. This paper combines the advantages of both approaches through layer jamming. Thin sheets of complaint material are encased in an airtight envelope, and when connected to a vacuum, the bending stiffness and damping increase dramatically. Using layer jamming structures as flexure elements leads to mechan- ical systems that can actively vary stiffness and damping. This results in flexure mechanisms with the versatility to transition between degrees of freedom and degrees of constraint and to tune impact response. This approach is used to create a 2-DOF, jamming-based, tunable impedance robotic wrist that enables passive hybrid force/position control for contact tasks. 

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4. Compression stiffening of fibrous networks with stiff inclusions

   https://doi.org/10.1073/pnas.2003037117  

   Shivers, Jordan L.; Feng, Jingchen; van Oosten, Anne S. G.; Levine, Herbert; Janmey, Paul A.; MacKintosh, Fred C. (August 2020, Proceedings of the National Academy of Sciences)

   Tissues commonly consist of cells embedded within a fibrous biopolymer network. Whereas cell-free reconstituted biopolymer networks typically soften under applied uniaxial compression, various tissues, including liver, brain, and fat, have been observed to instead stiffen when compressed. The mechanism for this compression-stiffening effect is not yet clear. Here, we demonstrate that when a material composed of stiff inclusions embedded in a fibrous network is compressed, heterogeneous rearrangement of the inclusions can induce tension within the interstitial network, leading to a macroscopic crossover from an initial bending-dominated softening regime to a stretching-dominated stiffening regime, which occurs before and independently of jamming of the inclusions. Using a coarse-grained particle-network model, we first establish a phase diagram for compression-driven, stretching-dominated stress propagation and jamming in uniaxially compressed two- and three-dimensional systems. Then, we demonstrate that a more detailed computational model of stiff inclusions in a subisostatic semiflexible fiber network exhibits quantitative agreement with the predictions of our coarse-grained model as well as qualitative agreement with experiments. 

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5. Pump Up the Jam: Granular Media as a Quasi‐Hydraulic Fluid for Independent Control Over Isometric and Isotonic Actuation

   https://doi.org/10.1002/advs.202104402  

   Bakarich, Shannon_E; Miller, Rachel; Mrozek, Randy_A; O'Neill, Maura_R; Slipher, Geoffrey_A; Shepherd, Robert_F (March 2022, Advanced Science)

   Abstract Elastomer‐granule composites have been used to switch between soft and stiff states by applying negative pressure differentials that cause the membrane to squeeze the internal grains, inducing dilation and jamming. Applications of this phenomenon have ranged from universal gripping to adaptive mobility. Previously, the combination of this jamming phenomenon with the ability to transport grains across multiple soft actuators for shape morphing has not yet been demonstrated. In this paper, the authors demonstrate the use of hollow glass spheres as granular media that functions as a jammable “quasi‐hydraulic” fluid in a fluidic elastomeric actuator that better mimics a key featur of animal musculature: independent control over i) isotonic actuation for motion; and ii) isometric actuation for stiffening without shape change. To best implement the quasi‐hydraulic fluid, the authors design and build a fluidic device. Leveraging this combination of physical properties creates a new option for fluidic actuation that allows higher specific stiffness actuators using lower volumetric flow rates in addition to independent control over shape and stiffness. These features are showcased in a robotic catcher's mitt by stiffening the fluid in the glove's open configuration for catching, unjamming the media, then pumping additional fluid to the mitt to inflate and grasp. 

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