Motion Planning for Hybrid Dynamical Systems: Framework, Algorithm Template, and a Sampling-based Approach

TL;DR

This paper introduces a comprehensive framework and a sampling-based algorithm, HyRRT, for motion planning in hybrid dynamical systems, ensuring probabilistic completeness and applicability to systems with continuous and discrete behaviors.

Contribution

It formulates hybrid system motion planning using a general hybrid equation framework and develops HyRRT, a probabilistically complete RRT-based algorithm for hybrid systems.

Findings

HyRRT is probabilistically complete under mild conditions.

The algorithm successfully plans motions for bouncing ball and walking robot systems.

The approach relaxes traditional positive clearance assumptions.

Abstract

This paper focuses on the motion planning problem for the systems exhibiting both continuous and discrete behaviors, which we refer to as hybrid dynamical systems. Firstly, the motion planning problem for hybrid systems is formulated using the hybrid equation framework, which is general to capture most hybrid systems. Secondly, a propagation algorithm template is proposed that describes a general framework to solve the motion planning problem for hybrid systems. Thirdly, a rapidly-exploring random trees (RRT) implementation of the proposed algorithm template is designed to solve the motion planning problem for hybrid systems. At each iteration, the proposed algorithm, called HyRRT, randomly picks a state sample and extends the search tree by flow or jump, which is also chosen randomly when both regimes are possible. Through a definition of concatenation of functions defined on hybrid time domains, we show that HyRRT is probabilistically complete, namely, the probability of failing to find a motion plan approaches zero as the number of iterations of the algorithm increases. This property is guaranteed under mild conditions on the data defining the motion plan, which include a relaxation of the usual positive clearance assumption imposed in the literature of classical systems. The motion plan is computed through the solution of two optimization problems, one associated with the flow and the other with the jumps of the system. The proposed algorithm is applied to an actuated bouncing ball system and a walking robot system so as to highlight its generality and computational features.