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1. 6N-DoF Pose Tracking for Tensegrity Robots

   Lu, S. ; Johnson, W. ; Wang, K. ; Huang, X. ; Booth, J. ; Kramer-Bottiglio, R. ; Bekris, K. E. ( January 2022 , International Symposium on Robotics Research (ISRR))

   Tensegrity robots, which are composed of compressive elements (rods) and flexible tensile elements (e.g., cables), have a variety of advantages, including flexibility, low weight, and resistance to mechanical impact. Nevertheless, the hybrid soft-rigid nature of these robots also complicates the ability to localize and track their state. This work aims to address what has been recognized as a grand challenge in this domain, i.e., the state estimation of tensegrity robots through a markerless, vision-based method, as well as novel, onboard sensors that can measure the length of the robot's cables. In particular, an iterative optimization process is proposed to track the 6-DoF pose of each rigid element of a tensegrity robot from an RGB-D video as well as endcap distance measurements from the cable sensors. To ensure that the pose estimates of rigid elements are physically feasible, i.e., they are not resulting in collisions between rods or with the environment, physical constraints are introduced during the optimization. Real-world experiments are performed with a 3-bar tensegrity robot, which performs locomotion gaits. Given ground truth data from a motion capture system, the proposed method achieves less than 1~cm translation error and 3 degrees rotation error, which significantly outperforms alternatives. At the samemore »time, the approach can provide accurate pose estimation throughout the robot's motion, while motion capture often fails due to occlusions.« less
2. A Recurrent Differentiable Engine for Modeling Tensegrity Robots Trainable with Low-Frequency Data

   https://doi.org/10.1109/ICRA46639.2022.9812135  

   Wang, Kun ; Aanjaneya, Mridul ; Bekris, Kostas ( May 2022 , 2022 International Conference on Robotics and Automation (ICRA))

   Tensegrity robots, composed of rigid rods and flexible cables, are difficult to accurately model and control given the presence of complex dynamics and high number of DoFs. Differentiable physics engines have been recently proposed as a data-driven approach for model identification of such complex robotic systems. These engines are often executed at a high-frequency to achieve accurate simulation. Ground truth trajectories for training differentiable engines, however, are not typically available at such high frequencies due to limitations of real-world sensors. The present work focuses on this frequency mismatch, which impacts the modeling accuracy. We proposed a recurrent structure for a differentiable physics engine of tensegrity robots, which can be trained effectively even with low-frequency trajectories. To train this new recurrent engine in a robust way, this work introduces relative to prior work: (i) a new implicit integration scheme, (ii) a progressive training pipeline, and (iii) a differentiable collision checker. A model of NASA's icosahedron SUPERballBot on MuJoCo is used as the ground truth system to collect training data. Simulated experiments show that once the recurrent differentiable engine has been trained given the low-frequency trajectories from MuJoCo, it is able to match the behavior of MuJoCo's system. The criterion for successmore »is whether a locomotion strategy learned using the differentiable engine can be transferred back to the ground-truth system and result in a similar motion. Notably, the amount of ground truth data needed to train the differentiable engine, such that the policy is transferable to the ground truth system, is 1% of the data needed to train the policy directly on the ground-truth system.« less
3. A Recurrent Differentiable Engine for Modeling Tensegrity Robots Trainable with Low-Frequency Data

   Wang, K. ; Aanjaneya, M. ; Bekris, K. E. ( January 2022 , IEEE International Conference on Robotics and Automation (ICRA))

   Tensegrity robots, composed of rigid rods and flexible cables, are difficult to accurately model and control given the presence of complex dynamics and high number of DoFs. Differentiable physics engines have been recently proposed as a data-driven approach for model identification of such complex robotic systems. These engines are often executed at a high-frequency to achieve accurate simulation. Ground truth trajectories for training differentiable engines, however, are not typically available at such high frequencies due to limitations of real-world sensors. The present work focuses on this frequency mismatch, which impacts the modeling accuracy. We proposed a recurrent structure for a differentiable physics engine of tensegrity robots, which can be trained effectively even with low-frequency trajectories. To train this new recurrent engine in a robust way, this work introduces relative to prior work: (i) a new implicit integration scheme, (ii) a progressive training pipeline, and (iii) a differentiable collision checker. A model of NASA's icosahedron SUPERballBot on MuJoCo is used as the ground truth system to collect training data. Simulated experiments show that once the recurrent differentiable engine has been trained given the low-frequency trajectories from MuJoCo, it is able to match the behavior of MuJoCo's system. The criterion for successmore »is whether a locomotion strategy learned using the differentiable engine can be transferred back to the ground-truth system and result in a similar motion. Notably, the amount of ground truth data needed to train the differentiable engine, such that the policy is transferable to the ground truth system, is 1% of the data needed to train the policy directly on the ground-truth system.« less
4. Dynamic Placement of Rapidly Deployable Mobile Sensor Robots Using Machine Learning and Expected Value of Information

   https://doi.org/10.1115/IMECE2021-70759  

   Agogino, A. ( October 2021 , ASME 2021 International Mechanical Congress Exposition (IMECE 2021)

   The Industrial Internet of Things has increased the number of sensors permanently installed in industrial plants. Yet there will be gaps in coverage due to broken sensors or sparce density in very large plants, such as in the petrochemical industry. Modern emergency response operations are beginning to use Small Unmanned Aerial Systems (sUAS) as remote sensors to provide rapid improved situational awareness. Ground-based sensors are an integral component of overall situational awareness platforms, as they can provide longer-term persistent monitoring that aerial drones are unable to provide. Squishy Robotics and the Berkeley Emergent Space Tensegrities Laboratory have developed hardware and a framework for rapidly deploying sensor robots for integrated ground-aerial disaster response. The semi-autonomous delivery of sensors using tensegrity (tension-integrity) robotics uses structures that are flexible, lightweight, and have high stiffness-to-weight ratios, making them ideal candidates for robust high-altitude deployments. Squishy Robotics has developed a tensegrity robot for commercial use in Hazardous Materials (HazMat) scenarios that is capable of being deployed from commercial drones or other aircraft. Squishy Robots have been successfully deployed with a delicate sensing and communication payload of up to 1,000 ft. This paper describes the framework for optimizing the deployment of emergency sensors spatially over time.more »AI techniques (e.g., Long Short-Term Memory neural networks) identify regions where sensors would be most valued without requiring humans to enter the potentially dangerous area. The cost function for optimization considers costs of false-positive and false-negative errors. Decisions on mitigation include shutting down the plant or evacuating the local community. The Expected Value of Information (EVI) is used to identify the most valuable type and location of physical sensors to be deployed to increase the decision-analytic value of a sensor network. A case study using data from the Tennessee Eastman process dataset of a chemical plant displayed in OSI Soft is provided.« less
5. Collaborative Robotics Toolkit (CRTK): Open Software Framework for Surgical Robotics Research

   https://doi.org/10.1109/IRC.2020.00014  

   Su, Yun-Hsuan ; Munawar, Adnan ; Deguet, Anton ; Lewis, Andrew ; Lindgren, Kyle ; Li, Yangming ; Taylor, Russell H. ; Fischer, Gregory S. ; Hannaford, Blake ; Kazanzides, Peter ( November 2020 , 2020 Fourth IEEE International Conference on Robotic Computing (IRC))

   Robot-assisted minimally invasive surgery has made a substantial impact in operating rooms over the past few decades with their high dexterity, small tool size, and impact on adoption of minimally invasive techniques. In recent years, intelligence and different levels of surgical robot autonomy have emerged thanks to the medical robotics endeavors at numerous academic institutions and leading surgical robot companies. To accelerate interaction within the research community and prevent repeated development, we propose the Collaborative Robotics Toolkit (CRTK), a common API for the RAVEN-II and da Vinci Research Kit (dVRK) - two open surgical robot platforms installed at more than 40 institutions worldwide. CRTK has broadened to include other robots and devices, including simulated robotic systems and industrial robots. This common API is a community software infrastructure for research and education in cutting edge human-robot collaborative areas such as semi-autonomous teleoperation and medical robotics. This paper presents the concepts, design details and the integration of CRTK with physical robot systems and simulation platforms.