Tunnel construction using the drill-and-blast method requires the 3D measurement of the excavation front to evaluate underbreak locations. Considering the inspection and measurement task's safety, cost, and efficiency, deploying lightweight autonomous robots, such as unmanned aerial vehicles (UAV), becomes more necessary and popular. Most of the previous works use a prior map for inspection viewpoint determination and do not consider dynamic obstacles. To maximally increase the level of autonomy, this paper proposes a vision-based UAV inspection framework for dynamic tunnel environments without using a prior map. Our approach utilizes a hierarchical planning scheme, decomposing the inspection problem into different levels. The high-level decision maker first determines the task for the robot and generates the target point. Then, the mid-level path planner finds the waypoint path and optimizes the collision-free static trajectory. Finally, the static trajectory will be fed into the low-level local planner to avoid dynamic obstacles and navigate to the target point. Besides, our framework contains a novel dynamic map module that can simultaneously track dynamic obstacles and represent static obstacles based on an RGB-D camera. After inspection, the Structure-from-Motion (SfM) pipeline is applied to generate the 3D shape of the target. To our best knowledge, this is the first time autonomous inspection has been realized in unknown and dynamic tunnel environments. Our flight experiments in a real tunnel prove that our method can autonomously inspect the tunnel excavation front surface. Our software is available on GitHub as an open-source ROS package.

翻译：钻爆法隧道施工需要对开挖掌子面进行三维测量以评估欠挖位置。考虑到巡检测量任务的安全性、成本及效率，部署轻型自主机器人（如无人机）变得愈发必要且普及。以往研究大多依赖先验地图确定巡检视角，且未考虑动态障碍物。为最大程度提升自主性，本文提出一种无需先验地图的、适用于动态隧道环境的视觉无人机巡检框架。该方法采用分层规划方案，将巡检问题分解为不同层级：高层决策器首先确定机器人任务并生成目标点；中层路径规划器寻找航点路径并优化无碰撞静态轨迹；最后，静态轨迹输入底层局部规划器以规避动态障碍物并导航至目标点。此外，本框架包含新型动态地图模块，可基于RGB-D相机同步跟踪动态障碍物并表征静态障碍物。巡检完成后，应用运动恢复结构（SfM）流程生成目标三维形态。据我们所知，这是首次在未知动态隧道环境中实现自主巡检。在真实隧道中的飞行实验证明，该方法能自主巡检隧道开挖掌子面。本软件已作为开源ROS程序包发布于GitHub。