# Autonomous Loading System for Load-Haul-Dump (LHD) Machines Used in Underground Mining
## 4 Experiments and Analysis
### Full-Scale Rock Excavation Experiments  
Since the pile identification method was not fully optimized at the time of the onsite tests, and time for executing the experiments in the mine was limited, the development team divided the loading procedure in two stages in order to maximize the total number of full-scale rock excavation experiments and evaluate each stage separately. One stage included rock pile identification and positioning, and the other included the charging, excavation, pull back, and weighting processes. To perform this, loading experiments required a human operator to position the machine five to ten meters in front of the draw point, effectively bypassing the rock pile identification and positioning stages, and starting the system's state machine in \"positioning assistance\", as described in Section 3. A total of 30 complete loading experiments were carried out. Similar to in manual operation, multiple loading attempts were required in order to fill the bucket during each experiment. Manual operation of LHD in sublevel stopping mines usually needs two or three attempts to achieve a proper bucket fill factor, since the procedure is performed using line-of-sight radio control with limited visibility behind the LHD (safety regulations forbid operators to enter the stope area). In some attempts, the tip of the bucket was lowered too much, causing high resistive forces from the ground during charging, and thus triggering the collision detection too early. A total of 81 loading attempts were performed in order to fulfill the 30 complete loads. Of these, 7 failed (early collision trigger) and 74 were successful, resulting in the 91% success rate of the charging and collision detection method. For each experiment, a fixed value of 0.5 was used for the pedal command. An operator monitoring the system's behavior during the complete loading process from a remote-control station decided when the bucket was full enough, and hence if a new attempt was needed. The operator relied only on the visual input of the machine's forward camera to make this decision. Figure 23 shows an example of the relevant variables in an autonomous loading attempt, which has some resemblance to the operator-controlled loading shown in Figure 5.  
Table 3 shows the number of experiments carried out, classified by the number of attempts to achieve a full bucket, and the average fill factor for each category. It can be seen that most experiments required three loading attempts, and that the operator continued to reattempt loading until the fill factor was about 90%. This can be seen more easily on Table 4, where the average fill factor and average number of attempts for all experiments are shown. It must be noted that while the fill factor at the end of each experiment met the criteria for manual operation (since it was the same operator deciding when the bucket was full), the average number of attempts was found to be higher than that in manual operation, which, according to manual operators was between two and three attempts. Table 5 and Figures 24 and 25 show more detail about progressive filling of the bucket through loading attempts for the 30 loading experiments. Table 5 shows the average durations of the excavation step and the resulting fill factor, classified according to the progressive sequence of attempts, as well as the total number of experiments in each case. On average, the first attempt managed to fill 62% of the bucket capacity; then, the second attempt achieved 77%; the third attempt achieved 82%; and for the six experiments that needed a fourth attempt, the average that resulted was a 90% fill factor. The average excavation duration was about 10-12 s, which comprised the time between the collision of the LHD with the rock pile and the end of the excavation algorithm. The required time for positioning, charging, and weighing was not taken into account in this measurement. It can be seen that the average duration of the excavation in the first attempt is slightly longer than the others.