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1. Tunable Anisotropic Stiffness with Square Fiber Jamming

   https://doi.org/10.1109/RoboSoft48309.2020.9116030  

   Aktas, Buse ; Howe, Robert D. ( May 2020 , 2020 3rd IEEE International Conference on Soft Robotics (RoboSoft))

   null (Ed.)

   Jamming is a phenomenon in which a collectionof compliant elements is encased in an airtight envelope, anda vacuum-induced pressure enhances frictional and kinematiccoupling, resulting in dramatic changes in stiffness. This paperintroduces the jamming of square cross-sectioned fibers, whichallow for tunable and programmable anisotropic stiffness. Atheoretical model captures the effect of major geometric designparameters on the direction-variant bending stiffness of theselong and slender jamming elements. The model is experimen-tally validated, and a 13-fold stiffening in one direction anda 22-fold stiffening in the orthogonal direction is achievedwith a single jamming element. The performance of a square-fiber-jamming continuum robot structure is demonstrated in asteering task, with an average reduction of 74% in the measuredinsertion force when unjammed, and a direction-variant 53%or 100% increase in the measured tip stiffness when jammed. 

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2. Discrete Layer Jamming for Variable Stiffness Co-Robot Arms

   https://doi.org/10.1115/1.4044537  

   Zhou, Yitong ; Headings, Leon M. ; Dapino, Marcelo J. ( February 2020 , Journal of Mechanisms and Robotics)

   Abstract Continuous layer jamming is an effective tunable stiffness mechanism that utilizes vacuum to vary friction between laminates enclosed in a membrane. In this paper, we present a discrete layer jamming mechanism that is composed of a multilayered beam and multiple variable pressure clamps placed discretely along the beam; system stiffness can be varied by changing the pressure applied by the clamps. In comparison to continuous layer jamming, discrete layer jamming is simpler as it can be implemented with dynamic variable pressure actuators for faster control, better portability, and no sealing issues due to no need for an air supply. Design and experiments show that discrete layer jamming can be used for a variable stiffness co-robot arm. The concept is validated by quasi-static cantilever bending experiments. The measurements show that clamping 10% of the beam area with two clamps increases the bending stiffness by around 17 times when increasing the clamping pressure from 0 to 3 MPa. Computational case studies using finite element analysis for the five key parameters are presented, including clamp location, clamp width, number of laminates, friction coefficient, and number of clamps. Clamp location, number of clamps, and number of laminates are found to be most useful for optimizing a discrete layer jamming design. Actuation requirements for a variable pressure clamp are presented based on results from laminate beam compression tests. 

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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. Kinematics and Stiffness Modeling of Soft Robot With a Concentric Backbone

   https://doi.org/10.1115/1.4055860  

   Xiao, Qingyu ; Musa, Mishek ; Godage, Isuru S. ; Su, Hao ; Chen, Yue ( October 2023 , Journal of Mechanisms and Robotics)

   Abstract Soft robots can undergo large elastic deformations and adapt to complex shapes. However, they lack the structural strength to withstand external loads due to the intrinsic compliance of fabrication materials (silicone or rubber). In this paper, we present a novel stiffness modulation approach that controls the robot’s stiffness on-demand without permanently affecting the intrinsic compliance of the elastomeric body. Inspired by concentric tube robots, this approach uses a Nitinol tube as the backbone, which can be slid in and out of the soft robot body to achieve robot pose or stiffness modulation. To validate the proposed idea, we fabricated a tendon-driven concentric tube (TDCT) soft robot and developed the model based on Cosserat rod theory. The model is validated in different scenarios by varying the joint-space tendon input and task-space external contact force. Experimental results indicate that the model is capable of estimating the shape of the TDCT soft robot with an average root-mean-square error (RMSE) of 0.90 (0.56% of total length) mm and average tip error of 1.49 (0.93% of total length) mm. Simulation studies demonstrate that the Nitinol backbone insertion can enhance the kinematic workspace and reduce the compliance of the TDCT soft robot by 57.7%. Two case studies (object manipulation and soft laparoscopic photodynamic therapy) are presented to demonstrate the potential application of the proposed design. 

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5. 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)

   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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