Plan-N-Scan: A Robotic System for Collision-Free Autonomous Exploration and Workspace Mapping

This paper presents a sensor-based robotic system, called Plan-N-Scan, for collision-free, autonomous exploration and workspace mapping, using a wrist-mounted laser range camera. This system involves gaze planning with collision-free sensor positioning in a static environment, resulting in a 3-D map suitable for real-time collision detection. This work was initially motivated by the great demand for autonomous exploration systems in the remediation of buried but leaking tanks containing hazardous nuclear waste. Plan-N-Scan uses two types of representations: a spherical model of the manipulator and a weighted voxel map of the workspace. In addition to providing efficient collision detection, the voxel map allows the incorporation of different types of spatial occupancy information. The mapping of unknown sections of the workspace is achieved by either target or volume scanning. Target scanning incorporates a powerful A*-based search, along with a viewing position selection strategy, to incrementally acquire scans of the scene and use them to capture targets, even if they are not immediately viewable by the range camera. Volume scanning is implemented as an iterative process which automatically selects scan targets, then employs the target scanning process to scan these targets and explore the selected workspace volume. The performance and reliability of the system was demonstrated through simulation and a number of experiments involving a real robot system. The ability of the Plan-N-Scan system to incrementally acquire range information and successfully scan both targets and workspace volumes was demonstrated.