# Autonomous Loading System for Load-Haul-Dump (LHD) Machines Used in Underground Mining
## 4 Experiments and Analysis
### Full-Scale Rock Excavation Experiments
Figure 24 shows a box plot of the excavation step duration for all loading attempts. The time taken for the excavation ranges from 6 to almost 20 s, depending on the conditions of the rock pile and the specific interaction between the bucket and the rock pile. Figure 25 shows a box plot of the fill factor that was obtained progressively through loading attempts. It can be seen that the biggest jump in performance happened in the second loading attempt. Some outliers with performance above 100% are also depicted for the second and third attempts and appear as a consequence of loading a large boulder. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**N-Attempts** & **N-Exp** & **Total-Attempts** & **\%-Experiments** & **Fill-Factor** \\ \hline
1 attempt & 9 & 9 & 30\% & 88\% \\ \hline
2 attempts & 4 & 8 & 13\% & 107\% \\ \hline
3 attempts & 11 & 33 & 37\% & 87\% \\ \hline
4 attempts & 6 & 24 & 20\% & 90\% \\ \hline TOTAL & 30 & 74 & 100\% & - \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Total average number of attempts and fill factors. Figure 23: Relevant variables in an autonomous loading attempt. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Total Average Number of Attempts** & **Total Average Fill Factor** \\ \hline
3.6 & 90\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Loading experiments and average fill factor per number of loading attempts. N-Attempts: number of attempts required to fill bucket. N-Exp: number of experiments. Total-Attempts: total number of performed attempts. %-Experiments: % of the experiments. Fill-Factor: average fill factor. Figure 24: Excavation step duration per loading attempt. Red “+” signs represent outliers. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**P-Attempts** & **N-Exp** & **Percentage** & **Duration** & **Fill-Factor** \\ \hline First attempt & 30 & 100\% & 12.7 s & 62\% \\ \hline Second attempt & 21 & 70\% & 10.2 s & 77\% \\ \hline Third attempt & 17 & 57\% & 10.8 s & 82\% \\ \hline Fourth attempt & 6 & 20\% & 10.7 s & 90\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Duration and fill factor in consecutive attempts. P-Attempts: progressive sequence of attempts. N-Exp: number of experiments. Duration: average duration. Fill-Factor: average fill factor. Figure 25: Progressive fill factor across loading attempts. Red “+” signs represent outliers. During experimentation, the value of accurately placing the bucket of the machine against the ground, prior to the charging against the rock pile, was recognized. A bucket tilted too far down would cause an early trigger of a collision detection, while a bucket tilted just slightly upwards has a relevant impact on how far the machine can penetrate into the rock pile. An even more relevant factor that affects the performance of the loading maneuver is the status of the rock pile. Newly blasted ore is far easier to load than draw points that have had more time to settle and compress due to the weight of the rock. Draw points with large amounts of ore are also easier to load than those that have little material left. Despite these relevant factors, the proposed method was able to extract full buckets each time, at the expense of the operator having to perform more than the usual number of reattempts required under manual operation. It is important to note that in a real mining operation, the efficiency of an LHD is measured in the amount of ore that it is able to haul from the extraction point to the dumping point (usually in tons/hour). Therefore, the percentage of bucket filling is not the only relevant factor when evaluating the system, but also the amount of time it uses to load the bucket. This is especially important when deciding if the system should make another attempt at the excavation procedure to achieve a fuller bucket. This criterion varies among different operations, as the dumping and haulage time is different.