An Efficient and Generic 2D Inevitable Collision State-Checker

International audienceAn Inevitable Collision State (ICS) for a robotic system is a state for which, no matter what the future trajectory of the system is, a collision eventually occurs. ICS can be used for both motion planning (to reduce the search space) and reactive navigation (for obvious safety reasons, a robotic system should never ever move to an ICS). ICS are particularly suited for navigation in dynamic environments since they take into account the future behaviour of the moving objects. Using ICS in practice is difficult given the intrinsic complexity of their characterization. The main contribution of this paper is a generic and efficient ICS-Checker, ie an algorithm that determines whether a given state is an ICS or not, for planar robotic systems with arbitrary dynamics moving in dynamic environments. The efficiency is obtained by applying the following principles: (a) reasoning on 2D slices of the state space of the robotic system, (b) precomputing off-line as many things as possible, and (c) exploiting graphics hardware performances. The ICS-Checker has been applied to two different robotic systems: a car-like vehicle and a spaceship. It has also been integrated in a reactive navigation scheme to safely drive the car-like vehicle

Motion safety and constraints compatibility for multibody robots

International audienceIn this paper we propose a methodology to ensure safe behaviors of multibody robots in reactive control frameworks. The permanent satisfaction of constraints being insufficient to ensure safety, this approach focuses on the constraints expression: the compatibility between these constraints is studied, and safe alternatives are ensured when compatibility cannot be established. Case studies involving obstacles, joint position, velocity and acceleration limits illustrates the approach. A particular method is developed to take full advantage of a smooth state of the art avoidance techniques (Faverjon and Tournassoud in Proceedings of the 1987 IEEE international conference on robotics and automation, pp. 1152-1159, 1987) while maintaining safety. Experiments involving a 6-DOF manipulator operating in a cluttered environment illustrate the reliability of the approach and validate the expected performances

Collision Avoidance in Dynamic Environments: an ICS-Based Solution And Its Comparative Evaluation

International audienceThis paper presents ICS-Avoid, a collision avoidance scheme based upon the concept of Inevitable Collision State (ICS), i.e. a state for which, no matter what the future trajectory of the robotic system is, a collision eventually occurs. By design, ICS-Avoid can handle dynamic environments since ICS do take into account the future behaviour of moving objects. ICS-Avoid is designed to keep the system away from ICS. By doing so, motion safety is guaranteed (by definition a robotic system in a non-ICS state has at least one collision-free trajectory that it can use). To demonstrate the efficiency of ICS-Avoid, it has been extensively compared with two state-of-the-art collision avoidance schemes: the first one is built upon the Dynamic Window approach and the second one on the Velocity Obstacle concept. The results obtained show that, when provided with the same amount of information about the future evolution of the environment, ICS-Avoid outperforms the other two schemes. The first reason for this has to do with the extent to which each collision avoidance scheme reasons about the future. The second reason has to do with the ability of each collision avoidance scheme to find a safe control if one exists. ICS-Avoid is the only one which is complete in this respect thanks to the concept of Safe Control Kernel

Synthesizing Short-Circuiting Validation of Data Structure Invariants

This paper presents incremental verification-validation, a novel approach for checking rich data structure invariants expressed as separation logic assertions. Incremental verification-validation combines static verification of separation properties with efficient, short-circuiting dynamic validation of arbitrarily rich data constraints. A data structure invariant checker is an inductive predicate in separation logic with an executable interpretation; a short-circuiting checker is an invariant checker that stops checking whenever it detects at run time that an assertion for some sub-structure has been fully proven statically. At a high level, our approach does two things: it statically proves the separation properties of data structure invariants using a static shape analysis in a standard way but then leverages this proof in a novel manner to synthesize short-circuiting dynamic validation of the data properties. As a consequence, we enable dynamic validation to make up for imprecision in sound static analysis while simultaneously leveraging the static verification to make the remaining dynamic validation efficient. We show empirically that short-circuiting can yield asymptotic improvements in dynamic validation, with low overhead over no validation, even in cases where static verification is incomplete

Inevitable Collision States: a Probabilistic Perspective

International audienceFor its own safety, a robot system should never find itself in a state where there is no feasible trajectory to avoid collision with an obstacle. Such a state is an Inevitable Collision State (ICS). The ICS concept is particularly useful for navigation in dynamic environments because it takes into account the future behaviour of the moving objects. Accordingly it requires a model of the future evolution of the environment. In the real-world, the future trajectories of the obstacles are generally unknown and only estimates are available. This paper introduces a probabilistic formulation of the ICS concept which incorporates uncertainty in the model of the future trajectories of the obstacles. It also presents two novel probabilistic ICSchecking algorithms that are compared with their deterministic counterpart

Benchmarking Collision Avoidance Schemes for Dynamic Environments

International audienceThis paper evaluates and compare three state-of-the-art collision avoidance schemes designed to operate in dynamic environments. The first one is an extension of the popular Dynamic Window approach; it is henceforth called TVDW which stands for Time-Varying Dynamic Window. The second one called NLVO builds upon the concept of Non Linear Velocity Obstacle which is a generalization of the Velocity Obstacle concept. The last one is called ICS-Avoid, it draws upon the concept of Inevitable Collision States, i.e. states for which, no matter what the future trajectory of the robotic system is, a collision eventually occurs. The results obtained show that, when provided with the same amount of information about the future evolution of the environment, ICS-Avoid outperforms the other two schemes. The primary reason for this has to do with the extent to which each collision avoidance scheme reasons about the future. The second reason has to do with the ability of each collision avoidance scheme to find a safe control if one exists. ICS-Avoid is the only one which is complete in this respect thanks to the concept of Safe Control Kernel

An Anthropomorphic Navigation Scheme for Dynamic Scenarios

Session: Autonomous Navigation II (http://dblp.uni-trier.de/db/conf/icra/icra2011.html)International audienceThis paper is concerned with the navigation of personal robots in human-populated environments. The behavior of a person among its peers is governed by a number of unspoken social rules, e.g. maintaining an appropriate distance. The primary contribution of this paper is a navigation scheme that is anthropomorphic, i.e. that emulates human behaviors and seeks to adhere to these social rules. Unlike previous works in this area, the focus herein is on dynamic scenarios. The navigation scheme proposed explicitly reasons on the future behavior of the people involved so as to produce better socially acceptable trajectories (not to mention safer trajectories as well). The navigation scheme relies upon a novel cost function called the social costmap that captures in a unified way the different social rules imposed by the people populating the robot's workspace

Viability-Based Guaranteed Safe Robot Navigation

International audienceGuaranteeing 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