## 5 Conclusions  
This paper addressed the haptic tele-operation of impact hammers. The proposed haptic tele-operation system is based on a 3D model of the environment, which is used to estimate repulsion forces that are transferred to the operator via a haptic device, so that the hammer does not collide with the structures of the mine. The system also allows for identifying the oversized boulders deposited on the grizzly, notifying the operator every time the orepass is blocked, as well as providing them with different 3D views of the environment.  
A proof of concept was presented using a scaled setup. The reported experiments show that the use of a 3D model of the environment and the use of haptic feedback improves the tele-operation experience. When using the proposed system, operators were able to increase the success rate of the tele-operation task, and at the same time to reduce the completion time and the length of the path that the end-effector must follow.  
As part of our future work, we will validate the tele-operation system using a real impact hammer operating in a real production environment of an underground mine. In that environment, it is expected that several aspects of the operation will emerge which are not reproducible or were not considered in our laboratory environment. The analysis of these new experiments allows for improving and adapting the haptic feedback algorithm to be applied in production systems. In addition, the system will be validated with expert rock breaker operators in order to be able to quantify the real operational impact of its use. Given that a professional operator has a higher level of expertise in controlling the hammer with the current limitations of traditional systems, the performance improvement could be different in relation to a non-expert operator.  
Further improvement will focus on the use of haptic feedback to develop assistive tele-operation to guide the operator to follow optimal trajectories. Assistive tele-operation requires defining hammer tip trajectories for successful positioning and providing haptic feedback when the operator uses commands that move the hammer tip away from these trajectories.  
Conceptualization, J.R.-d.-S. and M.C.; methodology, J.R.-d.-S., D.C. ([PERSON]), D.C. ([PERSON]) and M.C.; software, D.C. ([PERSON]) and D.C. ([PERSON]); validation, D.C. ([PERSON]) and D.C. ([PERSON]); formal analysis, J.R.-d.-S., D.C. ([PERSON]), D.C. ([PERSON]) and M.C.; investigation, J.R.-d.-S., D.C. ([PERSON]), D.C. ([PERSON]) and M.C.; resources, J.R.-d.-S. and M.C.; data curation, D.C. ([PERSON]) and D.C. ([PERSON]); writing--review and editing, J.R.-d.-S., D.C. ([PERSON]), D.C. ([PERSON]) and M.C.; supervision, J.R.-d.-S.; project administration, M.C.; funding [PERSON], J.R.-d.-S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Chilean National Research Agency ANID under project grant Basal AFB180004 and FONDECYT 1201170.  
Not applicable.  
The data presented in this study is contained in the article itself.  
We thank [PERSON], [PERSON], [PERSON], and [PERSON] for their valuable discussions and support.  
The authors declare no conflict of interest.