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

Abstract

In this paper we present the application of the Null-Space-based Behavioral (NSB) approach to the motion control of mobile robots with velocity saturated actuators. The NSB is a behavior-based robot control 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 approach to the case where actuator velocity saturation bounds are explicitly taken into account. The proposed solution dynamically scales task velocity commands so that the hierarchy of task priorities is preserved 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 obstacle1 in this case, the mission is composed of two tasks. In the second case, the NSB elaborates the motion directives for a team of six mobile robots that has to entrap and escort a target1 in this case the mission is composed of four tasks. The approach is validated by numerical simulations and by experiments with real mobile robots.

Cooperative caging using autonomous aquatic surface vehicles

“…Since the vessels have a maximum velocity of 1.5 m/s, the saturation management technique presented in [7] has been used to manage the actuator saturation respecting the NSB task-priority.…”

Selective compliance control for an unmanned aerial vehicle with a robotic arm

“…It is worth noticing that (16) requires that dim{ζ} = n + 4 ≥ dim{v e } = 6, i.e., the number of DOFs characterizing the vehicle-manipulator system is, at least, equal to the dimension of the assigned task. In particular, if n+4 = 6, the vehicle-manipulator system is non-redundant, namely J ζ is square and the pseudo-inverse can be replaced by the inverse.…”

“…The Cartesian space approach requires to compute, via a suitable impedance filter, a reference value for the end-effector relative position and orientation with respect to the vehicle frame Σ b . Such a relative pose is adopted in the inverse kinematics algorithm (16) to compute new joint reference values for the low level controller. Since the kinematic inversion requires that the manipulator has a number of DOFs at least equal to the dimension of the assigned task (6 in case of position and orientation tracking) the Cartesian space impedance approach can be pursued for manipulators characterized by 6 or more DOFs.…”

“…Therefore, a multitasking priorized inverse kinematics algorithm, based on the Null Space Based (NSB) paradigm [16], could be used to compute the motion references, q r for the low level controller.…”

Cooperative caging and transport using autonomous aquatic surface vehicles

“…In the case considered here, the behavior are merged using the particular NSB technique presented in [11] that guarantees that the behavior are executed according to the desired priority, despite the presence of saturated actuators.…”