Hybrid Discrete-Continuous Path Planning for Lattice Traversal

Lattice structures allow robotic systems to operate in complex and hazardous environments, e.g. construction, mining and nuclear plants, reliably and effectively. However, current navigation systems for these structures are neither realistic, as they assume simplistic motion primitives and obstacle-free workspaces, nor efficient as they rely solely on global discrete search in an attempt to leverage the modularity of lattices. This paper tackles this gap and studies how robots can navigate lattice structures efficiently. We present a realistic application environment where robots have to avoid obstacles and the structure itself to reach target locations. Our solution couples discrete optimal search, using a domain-dependent heuristic, and sampling-based motion planning to find feasible trajectories in the discrete search space and in the continuous joint space at the same time. We provide two search graph formulations and a path planning approach. Simulation experiments, based on structures and robots created for the Innovate UK Connect-R project, examine scalability to large grid spaces while maintaining performances close to optimal.