Simulation Study of the Upper-limb Wrench Feasible Set with Glenohumeral Joint Constraints

The aim of this work is to improve musculoskeletal-based models of the upper-limb Wrench Feasible Set i.e. the set of achievable maximal wrenches at the hand for applications in collaborative robotics and computer aided ergonomics. In particular, a recent method performing wrench capacity evaluation called the Iterative Convex Hull Method is upgraded in order to integrate non dislocation and compression limitation constraints at the glenohumeral joint not taken into account in the available models. Their effects on the amplitude of the force capacities at the hand, glenohumeral joint reaction forces and upper-limb muscles coordination in comparison to the original iterative convex hull method are investigated in silico. The results highlight the glenohumeral potential dislocation for the majority of elements of the wrench feasible set with the original Iterative Convex Hull method and the fact that the modifications satisfy correctly stability constraints at the glenohumeral joint. Also, the induced muscles coordination pattern favors the action of stabilizing muscles, in particular the rotator-cuff muscles, and lowers that of known potential destabilizing ones according to the literature.Comment: 30 pages (double spacing), 10 figures, 2 table

A Recursive Watermark Method for Hard Real-Time Industrial Control System Cyber-Resilience Enhancement

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.International audienceCybersecurity is of vital importance to industrial control systems (ICSs), such as ship automation, manufacturing, building, and energy automation systems. Many control applications require hard real-time channels, where the delay and jitter are in the levels of milliseconds or less. To the best of our knowledge, no encryption algorithm is fast enough for hard real-time channels of existing industrial fieldbuses and, therefore, made mission-critical applications vulnerable to cyberattacks, e.g., delay and data injection attacks. In this article, we propose a novel recursive watermark (RWM) algorithm for hard real-time control system data integrity validation. Using a watermark key, a transmitter applies watermark noise to hard real-time signals and sends through the unencrypted hard real-time channel. The same key is transferred to the receiver by the encrypted nonreal-time channel. With the same key, the receiver can detect if the data have been modified by the attackers and take action to prevent catastrophic damages. We provide analysis and methods to design proper watermark keys to ensure reliable attack detection. We use a ship propulsion control system for the simulation-based case study, where our algorithm smoothly shuts down the system after attacks. We also evaluated the algorithm speed on a Siemens S7-1500 programmable logic controller (PLC). This hardware experiment demonstrated that the RWM algorithm takes about 2.8 μs to add or validate the watermark noise on one sample data point. As a comparison, common cryptic hashing algorithms can hardly process a small data set under 100 ms. The proposed RWM is about 32 to 1375 times faster than the standard approaches

On-line force capability evaluation based on efficient polytope vertex search

International audienceEllipsoid-based manipulability measures are often used to characterize the force/velocity task-space capabilities of robots. While computationally simple, this approach largely approximate and underestimate the true capabilities. Force/velocity polytopes appear to be a more appropriate representation to characterize the robot's task-space capabilities. However, due to the computational complexity of the associated vertex search problem, the polytope approach is mostly restricted to offline use, e.g. as a tool aiding robot mechanical design, robot placement in work-space and offline trajectory planning. In this paper, a novel on-line polytope vertex search algorithm is proposed. It exploits the parallelotope geometry of actuator constraints. The proposed algorithm significantly reduces the complexity and computation time of the vertex search problem in comparison to commonly used algorithms. In order to highlight the on-line capability of the proposed algorithm and its potential for robot control, a challenging experiment with two collaborating Franka Emika Panda robots, carrying a load of 12 kilograms, is proposed. In this experiment, the load distribution is adapted on-line, as a function of the configuration dependant task-space force capability of each robot, in order to avoid, as much as possible, the saturation of their capacit

Approximating robot reachable space using convex polytopes

International audienceThis paper presents an approach for approximating the reachable space of robotic manipulators based on convex polytopes. The proposed approach predicts the reachable space over a given time horizon based on the robot's actuation limits and kinematic constraints. The approach is furthermore extended to integrate the robot's environment, assuming it can be expressed in a form of linear constraints, and to account for the robot's link geometry.The accuracy of the proposed method is evaluated using simulations of robot's nonlinear dynamics and it is compared against the cartesian space limits, usually provided by manufacturers in standard datasheets.The accuracy analysis results show that the proposed method has good performance for the time horizons up to 250ms, encapsulating most of the simulated robot's reachable space while maintaining comparable volume. For a 7 dof robot, the method has an average execution time of 50ms, independent of the horizon time, potentially enabling real-time applications

Efficient calculation of human wrench capacity based on human musculoskeletal models Application in collaborative robot control

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Common wrench capability evaluation of a human-robot collaborative system

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On-line feasible wrench polytope evaluation based on human musculoskeletal models: an iterative convex hull method

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.International audienceMany recent human-robot collaboration strategies, such as Assist-As-Needed (AAN), are promoting humancentered robot control, where the robot continuously adapts its assistance level based on the real-time need of its human counterpart. One of the fundamental assumptions of these approaches is the ability to measure or estimate the physical capacity of humans in real-time. In this work, we propose an algorithm for the feasibility set analysis of a generic class of linear algebra problems. This novel iterative convex-hull method is applied to the determination of the feasible Cartesian wrench polytope associated to a musculoskeletal model of the human upper limb. The method is capable of running in real-time and allows the user to define the desired estimation accuracy. The algorithm performance analysis shows that the execution time has near-linear relationship to the considered number of muscles, as opposed to the exponential relationship of the conventional methods. Finally, real-time robot control application of the algorithm is demonstrated in a Collaborative carrying experiment, where a human operator and a Franka Emika Panda robot jointly carry a 7kg object. The robot is controlled in accordance to the AAN paradigm maintaining the load carried by the human operator at 30% of its carrying capacity

Rhoban Football Club: RoboCup Humanoid KidSize 2019 Champion Team Paper

International audienceIn 2019, Rhoban Football Club reached the first place of the KidSize soccer competition for the fourth time and performed the first in-game throw-in in the history of the Humanoid league. Building on our existing code-base, we improved some specific functionalities, introduced new behaviors and experimented with original methods for labeling videos. This paper presents and reviews our latest changes to both software and hardware, highlighting the lessons learned during RoboCup

Online task-space trajectory planning using real-time estimations of robot motion capabilities

Planning a robot's task-space movement according to its actual capacity is a difficult problem because this capacity depends on its state and thus can evolve significantly during the execution of the movement. This paper proposes a method for real-time trajectory planning based on time-optimal Trapezoidal acceleration profile (TAP) trajectories, that adapts to the real-time evolution of the robot's capacity. The method is based on an efficient approach for projecting the robot's kinematic limits in the trajectory direction, based on the convex polytope algebra. The method is experimentally validated on a Franka Emika Panda collaborative robot and compared with the classical approach considering fixed robot's Cartesian space motion capacity. The results show that the proposed method is able to better exploit true robot's motion capacity by generating faster trajectories for the same level of tracking accuracy