An 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.
This paper presents ICS-AVOID, a collision avoidance scheme based upon the concept of Inevitable Collision State (ICS), ie 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 collisionfree trajectory that it can use). To demonstrate the efficiency of ICS-AVOID, it has been extensively compared with two state-ofthe-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.
For 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.
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