**6. Conclusions**

The proposed topological navigation and localization system for LHDs was developed and tested in simulation, field trials, and finally, in a production tunnel of a copper, underground, sublevel stoping mine. Using this system, the LHD was able to navigate safely inside the mine, maintaining a safe distance between the LHD and the tunnel's walls at all times.

Parameterization of the navigation conditions for each individual TM node was crucial for achieving the desired behavior on the underground industrial tests. The software modularization allowed the development of specific software components for tackling the different challenges of the autonomous navigation. The *Navigation Control* module manages the mission requests and the overall navigation behavior. *Deliberative Path Planning* generates local driving trajectories for the *Guidance* module to follow, while avoiding the tunnel walls and obstacles. *Command Executor* maintains a queue of consistent and smooth commands to guarantee short-term operation, while simultaneously maintaining system safety. Finally, global and local localization allows maintaining an estimation of the pose of the LHD inside the mine.

When comparing the automation system with a seasoned human operator, it shows a slightly slower performance (about 10% in terms of average instant speed), which is not that serious when taking into consideration all the safety and operational benefits of the system. Besides being faster, the human operator showed smoother driving and more control of the LHD, but this did not necessarily reflect on the performance of the system, or at least it was not noticeable when supervising the operation. It needs to be considered that the tunnel was very narrow and the system needed to be tuned to drive very near to the walls, at a distance of about 10 [cm], in order to be able to drive through some parts of the tunnel (the LHD manufacturer recommends a minimum distance of 50 [cm] to each side of the tunnel).

One of the major problems during testing on site was the lack of a wireless communication infrastructure with the capabilities of high speed roaming. This caused preemptive stops and/or speed reductions while going through the tunnel, hindering the optimizing process of the system and hurting the overall performance. A video showing the operator's graphic interface while the system is driving the LHD autonomously through the tunnel can be found at https://youtu.be/4Q34N25XjpA (accessed on 14 July 2021).

The system is now being installed and tested in a room and pillar mine in Germany, where a more robust, and better performing, network infrastructure will be used.

**Author Contributions:** Conceptualization, M.M., I.P.-T., C.T. and J.R.-d.-S.; methodology, M.M., I.P.-T., C.T. and J.R.-d.-S.; software, I.P.-T. and C.T.; validation, M.M., I.P-T. and C.T.; resources, J.R.-d.-S.; data curation, M.M.; writing—original draft preparation, M.M., C.T. and J.R.-d.-S.; writing—review and editing, M.M., I.P.-T., C.T. and J.R.-d.-S.; funding acquisition, J.R.-d.-S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Chilean National Research Agency ANID under project grant Basal AFB180004 and FONDECYT 1201170.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study is contained in the article itself.

**Acknowledgments:** We thank Paul Vallejos for the valuable discussions and support for on-site execution of the experiments, and Felipe Inostroza and Daniel Cárdenas for their valuable help in computing metrics for the results section. We acknowledge Compañía Minera San Gerónimo for providing the mine infrastructure for testing the system, and GHH Chile for supplying the LHD machine needed for this work.

**Conflicts of Interest:** The authors declare no conflict of interest.
