The Null-Space-based Behavioral Control for Mobile Robots with Velocity Actuator Saturations

In this paper we present the application of the Null-Space-based Be- havioral (NSB) approach to the motion control of mobile robots with velocity saturated actuators. The NSB is a behavior-based robot con- trol approach that uses a hierarchical organization of the tasks to guarantee that they are executed according to a desired priority: it uses a projection technique to avoid that, in the absence of actuator saturations, low-priority tasks could influence higher-priority tasks. The main contribution of this paper is the extension of the NSB ap- proach to the case where actuator velocity saturation bounds are ex- plicitly taken into account. The proposed solution dynamically scales task velocity commands so that the hierarchy of task priorities is pre- served in spite of actuator velocity saturations. The approach has been validated on two specific case studies. In the first case, the NSB elaborates the motion directives for a single mobile robot that has to reach a target while avoiding a point obstacle; in this case, the mission is composed of two tasks. In the second case, the NSB elab- orates the motion directives for a team of six mobile robots that has to entrap and escort a target; in this case the mission is composed of four tasks. The approach is validated by numerical simulations and by experiments with real mobile robots.