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Speed Gain in Elastic Joint robots: An Energy Conversion-Based Approach

IEEE robotICS AND AUTOMATION LETTERS 2021年第3期6卷 4600-4607页

作者： Mansfeld, Nico Keppler, Manuel Haddadin, Sami Tech Univ Munich TUM Munich Sch Robot & Machine Intelligence Chair Robot Sci & Syst Intelligence D-80797 Munich Germany German Aerosp Ctr DLR Inst Robot & Mechatron D-82234 Wessling Germany

Like humans or animals, robots with compliant joints are capable of performing explosive or cyclic motions by making systematic use of energy storage and release, and it has been shown that they can outperform their rigid counterparts in terms of peak velocity. For rigid joint robots, there exist well-established, computationally inexpensive tools to compute the maximum achievable Cartesian endpoint velocity, which is an important performance and safety characteristic for robot designs. For elastic joint robots, optimal control is usually employed to determine the maximum possible link velocity together with the associated trajectory, which is time consuming and computationally costly for most systems. In this letter, we propose methods to obtain estimates of the maximum achievable Cartesian endpoint velocities of gravity-free elastic joint robots that have computational requirements close to the rigid joint robot case. We formulate an optimal control problem to verify the methods and provide results for a planar 3R robot. Furthermore, we compare the results of our approach with those from real-world throwing experiments which were previously conducted on the elastic DLR David system. Finally, we apply the methods to derive and quantitatively compare the safety properties of DLR David and a hypothetically rigid version of this robot in terms of the Safety Map framework proposed in our previous work.

关键词： robots Safety robot sensing systems Springs Torque Trajectory Optimal control Compliant joints and mechanisms methods and tools for robot system design human-centered robotics physical human-robot interaction robot safety

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Joint Mechanical design and Flight Control Optimization of a Nature-Inspired Unmanned Aerial Vehicle via Collaborative Co-Evolution

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IEEE robotICS AND AUTOMATION LETTERS 2021年第2期6卷 2044-2051页

作者： Sufiyan, Danial Win, Luke Soe Thura Win, Shane Kyi Hla Soh, Gim Song Foong, Shaohui Singapore Univ Technol & Design SUTD Engn Prod Dev Pillar Singapore 487372 Singapore

In this work, a collaborative co-evolution approach is adopted to solve a joint physical design and feedback control optimization problem of a nature-inspired Unmanned Aerial Vehicle (UAV). Unlike traditional multirotors and fixed-wing aircraft, lift is achieved by spinning its entire body with attached aerofoils around a central axis and positional control is attained through regulation of 2 sets of independent aerodynamic surfaces and thrusters. The collaborative co-evolution process consists of 2 'species,' the first consisting of the mechanical design variables and the second consisting of Proportional-Integral-Derivative (PID) and central pattern generator (CPG) controller variables. Each species have their own respective individual Evolutionary Algorithm (EA) solvers, Covariance Matrix Adaptation-Evolutionary Strategy (CMA-ES) and Parameter Exploring Policy Gradients (PEPG). In each optimization iteration, the parameters of one species is combined with representatives with the highest fitness from the other species and fed into a shared model for fitness evaluation, with each species taking turns to send a representative. Detailed performance comparison in trajectory tracking and power consumption between the proposed jointly optimized system against a design-only optimized, control-only optimized and unoptimized baseline were conducted. It was found that configurations with optimized designs would draw on average 18% less power than the non-optimized designs, and configurations with optimized controllers reduce error by 56% on average. The best performing configuration is the one with jointly optimized mechanical design and controller which outperforms all other configurations individually and collectively.

关键词： Aerial systems mechanics and control evolutionary robotics methods and tools for robot system design

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ROS-NetSim: A Framework for the Integration of robotic and Network Simulators

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IEEE robotICS AND AUTOMATION LETTERS 2021年第2期6卷 1120-1127页

作者： Calvo-Fullana, Miguel Mox, Daniel Pyattaev, Alexander Fink, Jonathan Kumar, Vijay Ribeiro, Alejandro Univ Penn Dept Elect & Syst Engn Philadelphia PA 19104 USA MIT Dept Aeronaut & Astronaut Cambridge MA 02139 USA Univ Penn Dept Mech Engn & Appl Mech Philadelphia PA 19104 USA Tampere Univ Unit Elect Engn Tampere 33720 Finland US Army Res Lab Dept Computat & Informat Sci Adelphi MD 20783 USA

Multi-agent systems play an important role in modern robotics. Due to the nature of these systems, coordination among agents via communication is frequently necessary. Indeed, Perception-Action-Communication (PAC) loops, or Perception-Action loops closed over a communication channel, are a critical component of multi-robot systems. However, we lack appropriate tools for simulating PAC loops. To that end, in this letter, we introduce ROS-NetSim, a ROS package that acts as an interface between robotic and network simulators. With ROS-NetSim, we can attain high-fidelity representations of both robotic and network interactions by accurately simulating the PAC loop. Our proposed approach is lightweight, modular and adaptive. Furthermore, it can be used with many available network and physics simulators by making use of our proposed interface. In summary, ROS-NetSim is (i) Transparent to the ROS target application, (ii) Agnostic to the specific network and physics simulator being used, and (iii) Tunable in fidelity and complexity. As part of our contribution, we have made available an open-source implementation of ROS-NetSim to the community.

关键词： Physics robot kinematics Picture archiving and communication systems Synchronization robot sensing systems Communication channels Wireless sensor networks Multi-robot systems networked robots methods and tools for robot system design software architecture for robotic and automation

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A Motion Estimation Filter for Inertial Measurement Unit With On-Board Ferromagnetic Materials

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IEEE robotICS AND AUTOMATION LETTERS 2021年第3期6卷 4939-4946页

作者： Tafrishi, Seyed Amir Svinin, Mikhail Yamamoto, Motoji Kyushu Univ Dept Mech Engn Kyushu 8190167 Japan Ritsumeikan Univ Dept Informat Sci & Engn Kyoto 5258577 Japan

Magnetic distortions due to existing appliances and on-board objects with ferromagnetic materials cause serious bias and deviations in motion estimation by inertial measurement sensors with magnetometers. This problem requires a proper sensor fusion to do motion tracking with a minimal angular error. This letter presents a design of a complementary filter that compensates the strong magnetic effects of on-board ferromagnetic materials. Not only the attached permanent magnets may have serious biases on the magnetometer axes but also there is a magnetic distortion due to soft ferromagnetic materials, i.e., steel. After defining the signals of the inertial/magnetic sensors, the process and measurement models are described and a Kalman filter is constructed. The designed filter can be used for motion tracking in environments with magnetic distortions, and in robot actuators with magnetic parts. The performance of the proposed filter is verified under experiment and compared with conventional filters. Finally, we raise a question about whether the attachment of permanent magnets to inertial measurement sensors can serve as a magnetic shield improving the motion estimation.

关键词： Magnetic disturbance methods and tools for robot system design motion estimation robotics in hazardous fields sensor fusion

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design of Non-Circular Pulleys for Torque Generation: A Convex Optimisation Approach

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IEEE robotICS AND AUTOMATION LETTERS 2021年第2期6卷 958-965页

作者： Ludovico, Daniele Guardiani, Paolo Lasagni, Francesco Lee, Jinoh Cannella, Ferdinando Caldwell, Darwin G. Univ Genoa Dept Informat Bioengn Robot & Syst Engn I-16126 Genoa GE Italy Ist Italiano Tecnol IIT Adv Robot Dept I-16163 Genoa GE Italy Politecn Torino I-10129 Turin Italy German Aerosp Ctr DLR Inst Robot & Mechatron D-82234 Wessling Germany

Nowadays, robotic research focuses more and more on attaining energy-efficient and safe solutions. They are key-aspects of industrial robots, such as inspection and maintenance robots. The introduction of a mechanism that passively compensates the joint torque caused by the weight of the robot may offer a valid solution. Avoiding the need for actuators to balance gravity torques helps decrease the power consumption and the size of the actuators. Furthermore, a passive gravity compensation mechanism allows the robot to hold a static position without the need for an external power source, hence avoiding the risk of collapsing in case of failure of the actuators. This work focuses on designing a torque generator composed of a non-circular pulley and a spring, which, by solving a convex optimisation problem, offers a new methodology for creating any generic torque and thereby also succeeds in solving gravity compensation problems. This methodology guarantees the outcome of feasible non-circular pulleys which minimise the torque required to perform any specific task.

关键词： Mechanism design methods and tools for robot system design

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Granular Resistive Force Theory Implementation for Three-Dimensional Trajectories

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IEEE robotICS AND AUTOMATION LETTERS 2021年第2期6卷 1887-1894页

作者： Treers, Laura K. Cao, Cyndia Stuart, Hannah S. Univ Calif Berkeley Coll Engn Mech Engn Dept Berkeley CA 94709 USA

Modelling interaction forces as bodies intrude into granular media is a longstanding challenge in the design and control of machines that navigate and manipulate these highly complex materials. Granular Resistive Force Theory, or RFT, is a flexible, reduced-order model for predicting intrusion forces on bodies in granular media. 2D RFT describes the forces on a plate whose velocity and normal vectors lie in the same vertical plane. We introduce a 3D RFT method that projects the total velocity vector into two scenarios that can already be described by 2D RFT, which allows us to extend the model into 3D with minimal additional experimental characterization. We then superimpose these independently calculated forces, weighted by experimentally fit scaling factors, to determine the total force on the plate. When applied to discretized convex hulls, this method performs force estimates of arbitrary trajectories in 3D space. The proposed formulation predicts forces experienced by oscillating and circumnutating bodies, motions motivated by mole crab burrowing and plant root growth respectively. This method is well-suited to complement more complex computational tools, such as Discrete Element Method. By expanding the application of RFT to 3D scenarios, a broader set of real-world applications can now be analyzed.

关键词： Contact modeling dynamics methods and tools for robot system design

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An Expressiveness Hierarchy of Behavior Trees and Related Architectures

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IEEE robotICS AND AUTOMATION LETTERS 2021年第3期6卷 5397-5404页

作者： Biggar, Oliver Zamani, Mohammad Shames, Iman Def Sci & Technol Grp Land Div Fishermans Bend 3207 Australia Australian Natl Univ Sch Engn Canberra ACT 2601 Australia

In this letter, we provide a formal framework for comparing the expressive power of Behavior Trees (BTs) to other action selection architectures. Taking inspiration from the analogous comparisons of structural programming methodologies, we formalise the concept of 'expressiveness'. This leads us to an expressiveness hierarchy of control architectures, which includes BTs, Decision Trees (DTs), Teleo-reactive Programs (TRs) and Finite State Machines (FSMs). By distinguishing between BTs with auxiliary variables and those without, we demonstrate the existence of a trade-off in BT design between readability and expressiveness. We discuss what this means for BTs in practice.

关键词： Control architectures and programming methods and tools for robot system design software architecture for robotic and automation

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A Versatile Inverse Kinematics Formulation for Retargeting Motions Onto robots With Kinematic Loops

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IEEE robotICS AND AUTOMATION LETTERS 2021年第2期6卷 943-950页

作者： Schumacher, Christian Knoop, Espen Bacher, Moritz Disney Res Stampfenbachstr 48 CH-8006 Zurich Switzerland

robots with kinematic loops are known to have superior mechanical performance. However, due to these loops, their modeling and control is challenging, and prevents a more widespread use. In this letter, we describe a versatile Inverse Kinematics (IK) formulation for the retargeting of expressive motions onto mechanical systems with loops. We support the precise control of the position and orientation of several end-effectors, and the Center of Mass (CoM) of slowly walking robots. Our formulation safeguards against a disassembly when IK targets are moved outside the workspace of the robot, and we introduce a regularizer that smoothly circumvents kinematic singularities where velocities go to infinity. With several validation examples and three physical robots, we demonstrate the versatility and efficacy of our IK on overactuated systems with loops, and for the retargeting of an expressive motion onto a bipedal robot.

关键词： robots Kinematics robot kinematics Actuators Legged locomotion Mechanical systems Parallel robots Kinematics methods and tools for robot system design parallel robots

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The robotarium: Automation of a Remotely Accessible, Multi-robot Testbed

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IEEE robotICS AND AUTOMATION LETTERS 2021年第2期6卷 2922-2929页

作者： Wilson, Sean Glotfelter, Paul Mayya, Siddharth Notomista, Gennaro Emam, Yousef Cai, Xiaoyi Egerstedt, Magnus Georgia Inst Technol Georgia Tech Res Inst Robot & Autonomous Syst Div Atlanta GA 30332 USA Optimus Ride Watertown MA USA Univ Penn GRASP Lab Philadelphia PA 19104 USA CNRS Inria IRISA F-35042 Rennes France Georgia Inst Technol Inst Robot & Intelligent Machines Atlanta GA 30308 USA MIT Dept Aeronaut & Astronaut Cambridge MA 02139 USA

The cost, in terms of both time and money, of instantiating a physical testbed can be prohibitive. To help resolve this issue, the robotarium offers a free, remotely accessible robotics lab to users around the world. Since allowing the general public to use it, hundreds of users have submitted thousands of experiments. The current and accelerating experiment submission rate poses an operational challenge that cannot be handled through manual or human supervised execution without devoting a full time operator to the platform. A solution to this problem is enable the robotarium to operate autonomously: improving the robustness and reliability of the system while reducing required human intervention to diagnose and recover from failures. In this pursuit, the hardware, software, and algorithms deployed on the robotarium have undergone numerous developments, including a new differential-drive robot, the use of modern virtualization techniques for the software infrastructure, and the inclusion of robust constraint-satisfaction methods for long-term safe operation. Over the past year of autonomous operation, these advances have resulted in 0.76% of the 3402 submitted remote experiments failing and requiring human intervention to recover from. This paper details these development efforts and best practices that have been learned automating a remote-access testbed to keep up with the experimental demand of a large, active, and growing userbase.

关键词： Collision avoidance methods and tools for robot system design multi-robot systems robot safety

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