Showing papers by "Thierry Fraichard published in 2019"

Viability-Based Guaranteed Safe Robot Navigation

Abstract: Guaranteeing safe, i.e. collision-free, motion for robotic systems is usually tackled in the Inevitable Collision State (ICS) framework. This paper explores the use of the more general Viability theory as an alternative when safe motion involves multiple motion constraints and not just collision avoidance. Central to Viability is the so-called viability kernel, i.e. the set of states of the robotic system for which there is at least one trajectory that satisfies the motion constraints forever. The paper presents an algorithm that computes off-line an approximation of the viability kernel that is both conservative and able to handle time-varying constraints such as moving obstacles. Then it demonstrates, for different robotic scenarios involving multiple motion constraints (collision avoidance, visibility, velocity), how to use the viability kernel computed off-line within an on-line reactive navigation scheme that can drive the robotic system without ever violating the motion constraints at hand.

Effect of Planning Period on MPC-based Navigation for a Biped Robot in a Crowd

Abstract: We control a biped robot moving in a crowd with a Model Predictive Control (MPC) scheme that generates stable walking motions, with automatic footstep placement. Most walking strategies propose to re-plan the walking motion to adapt to changing environments only once at every footstep. This is because a footstep is planted on the ground, it usually stays there at a constant position until the next footstep is initiated, what naturally constrains the capacity for the robot to react and adapt its motion in between footsteps. The objective of this paper is to measure if re-planning the walking motion more often than once at every footstep can lead to an improvement in collision avoidance when navigating in a crowd. Our result is that re-planning twice (or more) during each footstep leads to a significant reduction of the number of collisions when walking in a crowd, but depends on the density of the crowd.

Using Human Attention to Address Human–Robot Motion

Abstract: Let human–robot motion (HRM) denote the study of how robots should move among people, the work presented herein explores to what extent human attention can be useful to address the HRM. To that end, a computational model of the human visual attention is proposed to estimate how a person's attentional resources are distributed among the elements in their environment. Based on this model, the concept of attention field for a robot is used to define different attentional properties for the robot's motions such as distraction or surprise. The relevance of the attentional properties for HRM is demonstrated on a proof-of-concept acceptable motion planner on various case studies where a robot is assigned different tasks. It is shown how to compute motions that are non-distracting and non-surprising, but also motions that convey the robot's intention to interact with a person.

Effective Human-Robot Collaboration in near symmetry collision scenarios

Abstract: Recent works in the domain of Human-Robot Motion (HRM) attempted to plan collision avoidance behavior that accounts for cooperation between agents. Cooperative collision avoidance between humans and robots should be conducted under several factors such as speed, heading and also human attention and intention. Based on some of these factors, people decide their crossing order during collision avoidance. However, whenever situations arise in which the choice crossing order is not consistent for people, the robot is forced to account for the possibility that both agents will assume the same role i.e. a decision detrimental to collision avoidance. In our work we evaluate the boundary that separates the decision to avoid collision as first or last crosser. Approximating the uncertainty around this boundary allows our collision avoidance strategy to address this problem based on the insight that the robot should plan its collision avoidance motion in such a way that, even if agents, at first, incorrectly choose the same crossing order, they would be able to unambiguously perceive their crossing order on their following collision avoidance action.