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1. Characterizing Continuous Manipulation Families for Dexterous Soft Robot Hands

   Sun, J. ; King, J. ; Pollard, N. ( April 2021 , Frontiers in robotics and AI)

   null (Ed.)

   There has been an explosion of ideas in soft robotics over the past decade, resulting in unprecedented opportunities for end effector design. Soft robot hands offer benefits of low-cost, compliance, and customized design, with the promise of dexterity and robustness. The space of opportunities is vast and exciting. However, new tools are needed to understand the capabilities of such manipulators and to facilitate manipulation planning with soft manipulators that exhibit free-form deformations. To address this challenge, we introduce a sampling based approach to discover and model continuous families of manipulations for soft robot hands. We give an overview of the soft foam robots in production in our lab and describe novel algorithms developed to characterize manipulation families for such robots. Our approach consists of sampling a space of manipulation actions, constructing Gaussian Mixture Model representations covering successful regions, and refining the results to create continuous successful regions representing the manipulation family. The space of manipulation actions is very high dimensional; we consider models with and without dimensionality reduction and provide a rigorous approach to compare models across different dimensions by comparing coverage of an unbiased test dataset in the full dimensional parameter space. Results show that some dimensionality reduction is typically useful in populating the models, but without our technique, the amount of dimensionality reduction to use is difficult to predict ahead of time and can depend on the hand and task. The models we produce can be used to plan and carry out successful, robust manipulation actions and to compare competing robot hand designs. 

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2. An untethered soft cellular robot with variable volume, friction, and unit-to-unit cohesion

   Matthew R. Devlin, Brad T. ( January 2020 , Proceedings of the IEEERSJ International Conference on Intelligent Robots and Systems)

   A fundamental challenge in the field of modular and collective robots is balancing the trade-off between unit- level simplicity, which allows scalability, and unit-level function- ality, which allows meaningful behaviors of the collective. At the same time, a challenge in the field of soft robotics is creating untethered systems, especially at a large scale with many controlled degrees of freedom (DOF). As a contribution toward addressing these challenges, here we present an untethered, soft cellular robot unit. A single unit is simple and one DOF, yet can increase its volume by 8x and apply substantial forces to the environment, can modulate its surface friction, and can switch its unit-to-unit cohesion while agnostic to unit-to- unit orientation. As a soft robot, it is robust and can achieve untethered operation of its DOF. We present the design of the unit, a volumetric actuator with a perforated strain-limiting fabric skin embedded with magnets surrounding an elastomeric membrane, which in turn encompasses a low-cost micro-pump, battery, and control electronics. We model and test this unit and show simple demonstrations of three-unit configurations that lift, crawl, and perform plate manipulation. Our untethered, soft cellular robot unit lays the foundation for new robust soft robotic collectives that have the potential to apply human-scale forces to the world. 

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3. Cable-Driven Jamming of a Boundary Constrained Soft Robot

   https://doi.org/10.1109/RoboSoft48309.2020.9116042  

   Tanaka, Koki ; Karimi, Mohammad Amin ; Busque, Bruno-Pier ; Mulroy, Declan ; Zhou, Qiyuan ; Batra, Richa ; Srivastava, Ankit ; Jaeger, Heinrich M. ; Spenko, Matthew ( May 2020 , 2020 3rd IEEE International Conference on Soft Robotics (RoboSoft))

   Soft robots employ flexible and compliant materials to perform adaptive tasks and navigate uncertain environments. However, soft robots are often unable to achieve forces and precision on the order of rigid-bodied robots. In this paper, we propose a new class of mobile soft robots that can reversibly transition between compliant and stiff states without reconfiguration. The robot can passively conform or actively control its shape, stiffen in its current configuration to function as a rigid-bodied robot, then return to its flexible form. The robotic structure consists of passive granular material surrounded by an active membrane. The membrane is composed of interconnected robotic sub-units that can control the packing density of the granular material and exploit jamming behaviors by varying the length of the interconnecting cables. Each robotic sub-unit uses a differential drive system to achieve locomotion and self-reconfigurability. We present the robot design and perform a set of locomotion and object manipulation experiments to characterize the robot's performance in soft and rigid states. We also introduce a simulation framework in which we model the jamming soft robot design and study the scalability of this class of robots. The proposed concept demonstrates the properties of both soft and rigid robots, and has the potential to bridge the gap between the two 

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4. Position Control and Variable-Height Trajectory Tracking of a Soft Pneumatic Legged Robot

   https://doi.org/10.1109/IROS51168.2021.9635966  

   Liu, Zhichao ; Karydis, Konstantinos ( September 2021 , 2021 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS))

   Soft pneumatic legged robots show promise in their ability to traverse a range of different types of terrain, including natural unstructured terrain met in applications like precision agriculture. They can adapt their body morphology to the intricacies of the terrain at hand, thus enabling robust and resilient locomotion. In this paper we capitalize upon recent developments on soft pneumatic legged robots to introduce a closed-loop trajectory tracking control scheme for operation over flat ground. Closed-loop pneumatic actuation feedback is achieved via a compact and portable pneumatic regulation board. Experimental results reveal that our soft legged robot can precisely control its body height and orientation while in quasi-static operation based on a geometric model. The robot can track both straight line and curved trajectories as well as variable-height trajectories. This work lays the basis to enable autonomous navigation for soft legged robots. 

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5. The Elliott and Connolly Benchmark: A Test for Evaluating the In-Hand Dexterity of Robot Hands

   Coulson, R. ; Li, C. ; Majidi, C. ; Pollard, N. ( April 2021 , IEEERAS International Conference on Humanoid Robots)

   null (Ed.)

   Achieving dexterous in-hand manipulation with robot hands is an extremely challenging problem, in part due to current limitations in hardware design. One notable bottleneck hampering the development of improved hardware for dexterous manipulation is the lack of a standardized benchmark for evaluating in-hand dexterity. In order to address this issue, we establish a new benchmark for evaluating in- hand dexterity, specifically for humanoid type robot hands: the Elliott and Connolly Benchmark. This benchmark is based on a classification of human manipulations established by Elliott and Connolly, and consists of 13 distinct in-hand manipulation patterns. We define qualitative and quantitative metrics for evaluation of the benchmark, and provide a detailed testing protocol. Additionally, we introduce a dexterous robot hand - the CMU Foam Hand III - which is evaluated using the benchmark, successfully completing 10 of the 13 manipulation patterns and outperforming human hand baseline results for several of the patterns. 

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