# Autonomous Loading System for Load-Haul-Dump (LHD) Machines Used in Underground Mining
## 2 Background and Related Work
### Related Work  
[PERSON] analyzed the interaction forces in excavation processes and proposed that measurements of the resistive forces could be used for controlling them [21]. [PERSON] studied the LHD loading process and dealt with theoretical formulations on bucket trajectory and resistive forces during a scooping motion [7; 8; 10]. Other work has addressed the loading problem using laboratory-scale prototypes, under less realistic conditions [9; 11; 12; 22]. Research on autonomous loading showed scarce progress up until the past decade. In [13], full-scale experiments with a real LHD were performed using a proposed admittance-based controller for bucket commands. This work was further extended in [15; 16; 17] with support from the LHD original equipment manufacturer (OEM) Atlas Copco (now Epiroc), a study that led to a patented method [23]. It should be noted that this method addresses only the problem of ore excavating once the bucket is inside the rock pile. On the other hand, our approach comprehends the complete loading process, while also benefiting from human experience. Figure 4: Excavation method diagram. (**a**) LHD engages with the rock pile. (**b**) Bucket tilt used to excavate. (**c**) Boom lift used to control wheel traction. (**d**) End of the excavation phase. Caterpillar, another LHD OEM, is known to have been working on technical solutions for the autonomous loading problem, as demonstrated by patents [24; 25; 26]. While their patents show that they have tackled different issues of the autonomous loading problem, a general system has not been described, and their research has not been made available to the scientific community. However, it is uncertain if either of these solutions are able to handle the loading problem in block/panel caving draw points, which is significantly harder than loading from an ore pile or from draw points originated by other mining methods. As mentioned, loading from draw points is difficult due to many factors including: bucket-rock interaction forces that are difficult to model, humidity that increases cohesion forces, and the possible presence of boulders. According to the public information shared on the web sites of LHD OEMs, only Epiroc, Sandvik, and RCT Global have commercially available products that focus on the autonomous loading task. However, specific features, limitations, and applicability for block/panel caving or sublevel stoping underground mining are not publicly disclosed, and therefore no comments can be made on them. At least in Chile, where all major mining companies operate and where one third of the world's copper is produced, no autonomous loading system for LHD is in use. Figure 5: Relevant variables during the loading maneuver: Lift/Tilt command: manual bucket lifting/tilting command. Pedal command: manual machine acceleration command. Transmission Pressure: hydrostatic transmission pressure of the machine. Tilt Angle: tilt angle of the bucket. Lift Angle: lift angle of the boom. Skidding factor: estimated skidding factor. See the definitions of these variables in Sections 3.3 and 3.4. Work associated with standard front-end loaders was not considered in this analysis, because they operate on the surface, where the difficulties associated with underground draw points are not present. In addition, these types of vehicles usually deal with material that has already been processed by milling equipment. Our previous work on the topic of autonomous loading with LHDs was focused on laboratory-scale trials [27]. While useful for an initial approach to an experimental setup, laboratory experiments are limited due to the large deviation between real-world operating conditions and data from a small-scale and controlled environment. Other laboratory work is presented by [PERSON] [22], which has some similarities with the here-presented method, as excavation is modeled after the experience of human operators.