Robotics and the World/Obstacle Avoidance

7. Obstacle Avoidance

Obstacle Avoidance is a robotic discipline with the objective of moving vehicles on the basis of the sensorial information. The use of these methods front to classic methods (path planning) is a natural alternative when the scenario is dynamic with an unpredictable behaviour. In these cases, the surroundings do not remain invariable, and thus the sensory information is used to detect the changes consequently adapting moving.

The research conducted faces two major problems in this discipline. The first is to move vehicles in troublesome scenarios, where current technology has proven limited applicability. The second one is to understand the role of the vehicle characteristics (shape, kinematics and dynamics) within the obstacle avoidance paradigm.

Most obstacle avoidance techniques do not take into account vehicle shape and kinematic constraints. They assume a punctual and omnidirectional vehicle and are doomed to rely on approximations. Our contribution is a framework to consider shape and kinematics together in a exact manner, in the obstacle avoidance process, by abstracting these constraints from the avoidance method usage. Our approach can be applied to many non holonomic vehicles with arbitrary shape.

For these vehicles, the configuration space is 3 dimensional, while the control space is 2-dimensional. The main idea is to construct (centered on the robot at any time) the two-dimensional manifold of the configuration space that is defined by elementary circular paths. This manifold contains all the configurations that can be attained at each step of the obstacle avoidance and is thus general for all methods. Another important contribution of the paper is the exact calculus of the obstacle representation in this manifold for any robot shape (i.e. the configuration regions in collision). Finally, we propose a change of coordinates of this manifold in such a way that the elementary paths become straight lines. Therefore, the 3-dimensional obstacle avoidance problem with kinematic constraints is transformed into a simple obstacle avoidance problem for a point moving in a 2-dimensional space without any kinematic restriction (the usual approximation in obstacle avoidance). Thus, existing avoidance techniques become applicable.