Graph‐based subterranean exploration path planning using aerial and legged robots

Abstract

Autonomous exploration of subterranean environments remains a major challenge for robotic systems. In response, this paper contributes a novel graph-based subterranean exploration path planning method that is attuned to key topological properties of subterranean settings, such as large-scale tunnel-like networks and complex multibranched topologies. Designed both for aerial and legged robots, the proposed method is structured around a bifurcated local-and global-planner architecture. The local planner utilizes a rapidly exploring random graph to reliably and efficiently identify paths that optimize an exploration gain within a local subspace, while simultaneously avoiding obstacles, respecting applicable traversability constraints and honoring dynamic limitations of the robots. Reflecting the fact that multibranched and tunnel-like networks of underground environments can often lead to dead-ends and accounting for the robot endurance, the global planning layer works in conjunction with the local planner to incrementally build a sparse global graph and is engaged when the system must be repositioned to a previously identified frontier of the exploration space, or commanded to return-to-home. The designed planner is detailed with respect to its computational complexity and compared against state-of-the-art approaches. Emphasizing field experimentation, the method is evaluated within multiple real-life deployments using aerial robots and the ANYmal legged system inside both long-wall and room-and-pillar underground mines in the United States and in Switzerland, as well as inside an underground bunker. The presented results further include missions conducted within the Defense Advanced Research Projects Agency (DARPA) Subterranean Challenge, a relevant competition on underground exploration.

TARE: A Hierarchical Framework for Efficiently Exploring Complex 3D Environments

“…• GBP [23]: An extension of NBVP, where the method constructs an RRG in the global space and searches the RRG for routes to relocate the vehicle. The method explicitly switches between exploration mode and relocation mode.…”

“…The framework does not involve heuristics, as GBP and MBP, for explicit mode switch. Experiment comparisons to NBVP [21], GBP [23] and MBP [24] show that our method explores much more completely and efficiently while consuming less computation.…”

“…Witting et al [22] extend NBVP by seeding the RRT with the vehicle's trajectory, which allows the vehicle to explore further in areas passed by previously. Dang et al improve the scheme further by proposing the Graph-Based exploration Planner (GBP) [23]. The method constructs a global RRG along the vehicle trajectory.…”

Motion Primitives-based Path Planning for Fast and Agile Exploration using Aerial Robots

“…The overall diagram of the proposed solution is shown in Figure 1. The local planning mode is detailed in [22], whereas the global planning functionality is analogous to the one presented in our previous contribution on subterranean exploration [23].…”

Indoor Path-Planning Algorithm for UAV-Based Contact Inspection

“…In recent years, several contributions to this topic have been introduced. Dang et al [ 31 ] introduced a two-level navigation system, the first one for local exploration (near to the vehicle) and the second one for the global planner. Li et al [ 32 ] presented a probabilistic navigation algorithm for exploration of indoor environment, focused on this case of underground mine exploration.…”