Obstacle Avoidance Based on the Null Space Control Approach for a Formation of an Aerial and a Ground Robot

This paper complements a previous study on obstacle avoidance using the null space-based behavioral approach to autonomously guide a formation composed of a differential-drive wheeled platform and an unmanned aerial vehicle, to overtake obstacles modeled as potential fields. The highest priority, regarding the null space behavioral control, is assigned to the task of overcoming an obstacle, with the lowest priority assigned to moving the formation to a destination point. The controller is designed considering the paradigm of virtual structure, which is the three-dimensional straight line linking the robots. This approach allows controlling the robots to move in a coordinate way, leading the formation to reach the desired point while keeping the proposed rigid structure. The obstacle avoidance proposal is adopted for the ground and the aerial robots. When the ground robot maneuver to avoid an obstacle in the ground the position of the point of interest for control also varies, since it is in the ground vehicle, so that the aerial vehicle does not need to break the formation, continuing "attached" to the ground vehicle during the maneuver. However, when the aerial robot faces an obstacle, the formation behaves differently. The formation shape is not guaranteed to be preserved during the maneuver of the aerial robot to avoid the obstacle. This is the behavior this paper proposes to discuss: the effect of the null space-based behavioral control over the navigation of the formation. The scenario for this case study is an automated warehouse, inside which several ground platforms and aerial vehicles are moving to suitably store goods, possibly with boxes in the ground, also obstacles for the ground vehicle.