Density Functions for Navigation-Function-Based Systems

In this paper, we present a scheme for constructing density functions for systems that are almost globally asymptotically stable (i.e., systems for which all trajectories converge to an equilibrium except for a set of measure zero) using navigation functions (NFs). Although recently proven converse theorems guarantee the existence of density functions for such systems, such results are only existential and the construction of a density function for almost globally asymptotically stable systems remains a challenging task. We show that for a specific class of dynamical systems that are defined based on an NF, a density function can be easily derived from the system’s underlying NF

Weak Input-to-State Stability Properties for Navigation Function Based Controllers

Due to topological constraints, Navigation Functions, are not, except from trivial cases, equivalent to quadratic Lyapunov functions, hence systems based on Navigation Functions cannot directly accept an Input-to-State stability (ISS) characterization. However a relaxed version of Input-to-State stability, namely almost global ISS (aISS), is shown to be applicable. The proposed framework provides compositional capability for navigation function based systems. Cascade as well as feedback interconnections of aISS navigation systems are shown to also possess the aISS property under certain assumptions on the interconnections. Several simulated examples of navigation systems are presented to demonstrate the effectiveness of the proposed scheme

Autonomous Task Planning for Heterogeneous Multi-Agent Systems

This paper presents a solution to the automatic task planning problem for multi-agent systems. A formal framework is developed based on the Nondeterministic Finite Automata with $\epsilon$-transitions, where given the capabilities, constraints and failure modes of the agents involved, an initial state of the system and a task specification, an optimal solution is generated that satisfies the system constraints and the task specification. The resulting solution is guaranteed to be complete and optimal; moreover a heuristic solution that offers significant reduction of the computational requirements while relaxing the completeness and optimality requirements is proposed. The constructed system model is independent from the initial condition and the task specification, alleviating the need to repeat the costly pre-processing cycle for solving other scenarios, while allowing the incorporation of failure modes on-the-fly. Two case studies are provided: a simple one to showcase the concepts of the proposed methodology and a more elaborate one to demonstrate the effectiveness and validity of the methodology.Comment: Long version of paper submitted to the IEEE ICRA 2023 Conferenc

Closed Loop Navigation for Mobile Agents in Dynamic Environments

We apply a novel motion planning and control methodology, which is based on a non-smooth navigation function, to a point mobile robot moving amongst moving obstacles. The chattering introduced by the discontinuous potential field is suppressed using nonsmooth backstepping. The combined controller guarantees global asymptotic convergence and collision avoidance. This controller is particularly suitable for real time implementation on systems with limited computational resources. The effectiveness of the proposed scheme is verified through computer simulations

Weak input-to-state stability properties for navigation function based controllers

Abstract — Due to topological constraints, Navigation Functions, are not, except from trivial cases, equivalent to quadratic Lyapunov functions, hence systems based on Navigation Functions cannot directly accept an Input-to-State stability (ISS) characterization. However a relaxed version of Input-to-State stability, namely almost global ISS (aISS), is shown to be applicable. The proposed framework provides compositional capability for navigation function based systems. Cascade as well as feedback interconnections of aISS navigation systems are shown to also possess the aISS property under certain assumptions on the interconnections. Several simulated examples of navigation systems are presented to demonstrate the effectiveness of the proposed scheme. I

Density functions for navigation function based systems

Abstract — In this paper, we present a scheme for constructing density functions for systems that are almost globally asymptotically stable (i.e., systems for which all trajectories converge to an equilibrium except for a set of measure zero) based on Navigation Functions. Although recently-proven converse theorems guarantee the existence of density functions for such systems, results are only existential and the construction of a density function for almost globally asymptotically stable systems remains a challenging task. We show that for a specific class of dynamical systems that are defined based on a navigation function, a density function can be easily derived from the system’s underlying navigation function. I

Translating temporal logic to controller specifications

Abstract — The problem of designing hybrid controllers in order to satisfy safety or liveness specifications has received much attention in the past decade. Much more recently, there is an increased interest in designing hybrid controllers in order to achieve more sophisticated discrete specifications, such as those expressible in temporal logics. A great challenge is how to compose safety and liveness controllers in order to achieve more complex specifications. Existing approaches are predominantly bottom-up, in the sense that the overall control and composition (or switching) logic requires verification of the integrated closed-loop hybrid system. In this paper, we advocate and develop a top-down approach for this problem by synthesizing controllers which satisfy the specification by construction. Given a flat linear temporal logic specification as an input, we develop an algorithm that translates the temporal logic specification into a hybrid automaton where in each discrete mode we impose controller specifications for the continuous dynamics. In addition to achieving the desired specification by construction, our methodology provides a very natural interface between high level logic design and low level control design. I