This paper presents a new concept, the Admissible Gap, for collision avoidance. An admissible gap AG is defined as the gap that a robot may safely pass through, while obeying the shape and motion constraints. By employing this concept, a new obstacle avoidance approach was developed, improving the navigation performance in unknown cluttered environments. Unlike most state-of-the-art methods, our approach explicitly considers the robot shape and kinematic constraints rather than adapting a method originally designed for a holonomic pointlike robot. Experimental results demonstrated the power of the proposed AG approach. Moreover, a comparison with state-of-the-art methods showed that the AG approach generates more efficient, safer, and smoother trajectories.

A new reactive collision avoidance approach for mobile robots moving in cluttered and complex environments was developed and implemented. The novelty of this approach lies in the creation of a new method for analyzing openings in front of the robot that highly reduces their number when compared with the Nearness-Diagram Navigation (ND) technique, particularly in complex scenarios. Moreover, the angular width of the chosen (selected) gap with respect to the robot vision is taken into consideration. Consequently, oscillations are alleviated, the computational complexity is reduced and a smoother behavior will be achieved. Our technique adjusts the motion law proposed in the Smooth Nearness-Diagram Navigation (SND) method to generate safer paths for the robot by considering the ratio of threats on its sides and applying stricter deviation against an obstacle as it gets closer to the robot. Hence, the problem of deadlock occurring in narrow corridors, with high threats on one side and low threats on the other, is solved without affecting the smoothness behavior. Simulation and experimental results demonstrate the power of the proposed approach.