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1. Controlling the Rotational DOF of Laminar Jamming Structures With End Clamping Mechanism

   https://doi.org/10.1115/SMASIS2020-2399  

   Allen, Emily A. ; Swensen, John P. ( September 2020 , ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems)

   null (Ed.)

   Variable stiffness structures lie at the nexus of soft robots and traditional robots as they enable the execution of both high-force tasks and delicate manipulations. Laminar jamming structures, which consist of thin flexible sheets encased in a sealed chamber, can alternate between a rigid state when a vacuum is applied and a flexible state when the layers are allowed to slide in the absence of a pressure gradient. In this work, an additional mode of controllability is added by clamping and unclamping the ends of a simple laminar jamming beam structure. Previous works have focused on the translational degree of freedom that may be controlled via vacuum pressure; here we introduce a rotational degree of freedom that may be independently controlled with a clamping mechanism. Preliminary results demonstrate the ability to switch between three states: high stiffness (under vacuum), translational freedom (with clamped ends, no vacuum), and rotational freedom (with ends free to slide, no vacuum).

    

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2. 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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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. The design space of strand displacement cascades with toehold-size clamps

   Wang, Boya ; Thachuk, Chris ; Ellington, Andrew ; Soloveichik, David ( August 2017 , DNA Computing and Molecular Programming 23)

   DNA strand displacement cascades have proven to be a uniquely flexible and programmable primitive for constructing molecular logic circuits, smart structures and devices, and for systems with complex autonomously generated dynamics. Limiting their utility, however, strand displacement systems are susceptible to the spurious release of output even in the absence of the proper combination of inputs—so-called leak. A common mechanism for reducing leak involves clamping the ends of helices to prevent fraying, and thereby kinetically blocking the initiation of undesired displacement. Since a clamp must act as the incumbent toehold for toehold exchange, clamps cannot be stronger than a toehold. In this paper we systematize the properties of the simplest of strand displacement cascades (a translator) with toehold-size clamps. Surprisingly, depending on a few basic parameters, we find a rich and diverse landscape for desired and undesired properties and trade-offs between them. Initial experiments demonstrate a significant reduction of leak. 

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5. A Modeling Framework for Jamming Structures

   https://doi.org/10.1002/adfm.202007554  

   Aktaş, Buse ; Narang, Yashraj S. ; Vasios, Nikolaos ; Bertoldi, Katia ; Howe, Robert D. ( February 2021 , Advanced Functional Materials)

   Jamming is a structural phenomenon that provides tunable mechanical behavior. A jamming structure typically consists of a collection of elements with low effective stiffness and damping. When a pressure gradient, such as vacuum, is applied, kinematic and frictional coupling increase, resulting in dramatically altered mechanical properties. Engineers have used jamming to build devices from tunable‐stiffness grippers to tunable‐damping landing gear. This study presents a rigorous framework that systematically guides the design of jamming structures for target applications. The force‐deflection behavior of major types of jamming structures (i.e., grain, fiber, and layer) in fundamental loading conditions (e.g., tension, shear, and bending) is compared. High‐performing pairs (e.g., grains in compression, layers in shear, and bending) are identified. Parameters that go into designing, fabricating, and actuating a jamming structure (e.g., scale, material, geometry, and actuator) are described, along with their effects on functional metrics. Two key methods to expand on the design space of jamming structures are introduced: using structural design to achieve effective tunable‐impedance behavior in specific loading directions, and creating hybrid jamming structures to utilize the advantages of different types of jamming. Collectively, this study elaborates and extends the jamming design space, providing a conceptual modeling framework for jamming‐based structures.

    

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