The use of Unmanned Aerial Vehicles (UAVs) is rapidly increasing in applications ranging from surveillance and first-aid missions to industrial automation involving cooperation with other machines or humans. To maximize area coverage and reduce mission latency, swarms of collaborating drones have become a significant research direction. However, this approach requires open challenges in positioning, mapping, and communications to be addressed. This work describes a distributed mapping system based on a swarm of nano-UAVs, characterized by a limited payload of 35 g and tightly constrained on-board sensing and computing capabilities. Each nano-UAV is equipped with four 64-pixel depth sensors that measure the relative distance to obstacles in four directions. The proposed system merges the information from the swarm and generates a coherent grid map without relying on any external infrastructure. The data fusion is performed using the iterative closest point algorithm and a graph-based simultaneous localization and mapping algorithm, running entirely on-board the UAV's low-power ARM Cortex-M microcontroller with just 192 kB of SRAM memory. Field results gathered in three different mazes from a swarm of up to 4 nano-UAVs prove a mapping accuracy of 12 cm and demonstrate that the mapping time is inversely proportional to the number of agents. The proposed framework scales linearly in terms of communication bandwidth and on-board computational complexity, supporting communication between up to 20 nano-UAVs and mapping of areas up to 180 m2 with the chosen configuration requiring only 50 kB of memory.

翻译：无人机在监控、急救任务到涉及与其他机器或人类协作的工业自动化等领域的应用正快速增长。为最大化覆盖面积并降低任务延迟，协作无人机集群已成为重要研究方向。然而，该方法需要解决定位、建图与通信方面的开放性挑战。本文描述了一种基于Nano无人机集群的分布式建图系统，其特点是有效载荷仅35克，且机载感知与计算能力受到严格限制。每架Nano无人机搭载四个64像素深度传感器，可测量四个方向与障碍物的相对距离。所提系统融合集群信息，在无需依赖任何外部基础设施的情况下生成连贯的栅格地图。数据融合采用迭代最近点算法与基于图的同步定位与建图算法，完全运行于无人机低功耗ARM Cortex-M微控制器上（仅192 kB SRAM内存）。在三种不同迷宫环境中对多达4架Nano无人机集群的野外测试结果表明，建图精度达12厘米，且建图时间与无人机数量成反比。所提框架在通信带宽与机载计算复杂度方面呈线性扩展，支持最多20架Nano无人机间的通信，在所选配置下可覆盖180 m²区域，仅需50 kB内存。