## Article
### 1 Introduction
Most of the reported work addressing tele-operation of impact hammers uses 2D cameras, and in some cases time-of-flight cameras (TOF) or stereo cameras. According to [3], TOF's low resolution is insufficient for this task, and stereo cameras obtain a single view of the scene. To the best of our knowledge, there are no previous works using 3D LIDAR (Laser Imaging Detection and Ranging) in this application, nor works reporting the use of haptic devices for the tele-operation of impact hammers. Regarding the autonomous operation of impact hammers, the reported results are very poor. In [3], an average success rate of 34% is obtained in the task of breaking rocks, which does not make it possible for the application of this technology in a real mining environment. For this reason, we believe that a good intermediate step to full-automation, which improves the current technology used for the tele-operation of impact hammers, is haptic tele-operation. In this context, this paper proposes the haptic tele-operation of impact hammers for improving the efficiency of the fragmentation process. 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 control device, so that the hammer does not collide with the structures of the mine. The repulsion forces are a function of the distances between the hammer's end-effector and the environment. The 3D model of the environment is built using point clouds acquired using range sensors, and updated continuously. The proposed system also allows identifying the oversized boulders deposited on the grizzly and notifying the operator every time the ore pass is blocked. Moreover, thanks to the use of 3D sensors and cameras placed on opposite sides of the hammer (see Figure 1), it is possible to show the operator the environment from different viewpoints and a 3D model of the rocks to be crushed. With this information, the operator can make better decisions. We do believe that the use of point clouds for improving tele-operation in mining applications will increase in the following years, thanks to the popularization of 3D scanning sensors, and the availability of libraries for processing this data (e.g., [6; 7]). Field applications, as the one described here, will use this haptic technology. In other industries, the use of point clouds (obtained using range sensors) for obtaining haptic feedback in tele-operation applications is not new, although most reported papers describe systems that operate in controlled or semi-controlled environments, which is not the case for underground mining. In ref. [8], a method of haptic feedback in real time, using streaming point clouds from RGB-D cameras, without using contact sensors and without preprocessing the data, is proposed. The concept of virtual world is used, in which the simulated robot can move freely. In this virtual world, the tip of the virtual effector or HIP (haptic interface point) is related to the movement desired by the user. This effector, in turn, is wrapped in a zone of influence called proxy, which is forbidden to interact with the point cloud. Therefore, if the effector tries to enter the point cloud (or be in a position very close to it), a difference between the position of the virtual effector or HIP with the center of the proxy will be produced. This difference in positions will result in a feedback force vector, which will cause the effector's motion to change direction. The work described in ref. [9] is based on the described feedback system, and introduces the concept of delay in tele-operation, where the motion is first performed in virtual space and then executed in the real world. This implementation and testing of the system were performed by teleoperation of a KUKA industrial robot, where the virtual world was created using point clouds obtained with an RGB-D camera.