# Autonomous Loading System for Load-Haul-Dump (LHD) Machines Used in Underground Mining
## 3 Proposed Autonomous Loading System
### Excavation Algorithm  
The excavation algorithm is based on the techniques used by experienced human operators from block caving, panel caving and sublevel stoping operations (which are the most common type of underground operations in Chile). From a control theory point of view, the proposed method acts as a traction controller during the excavation process. A diagram is shown in Figure 17. The pregenerated commands is simply a module in charge of generating precomputed commands for the pedal and tilt signals. These commands are  
Figure 15: Charging block diagram. The machine is driven forward while a collision detection routine analyzes the machine’s transmission pressure and an estimated skidding factor. similar to the commands observed during manual operation. Specifically, the acceleration pedal is maintained at a constant output value and the bucket tilt is intermittently activated in the form of a ramp function. A ramp function was only selected in order to have an extra parameter, although a parameter sensibility analysis could not be performed in the full-scale experiments due to time constrains. The traction controller acts on the lift command in order to suppress wheel skidding, a variable that is estimated from Equation (7), as explained in Section 3.3. In practice, a simple \"on/off\" controller was implemented, where the lift command was set at the maximum value if the estimated skidding factor raised over a predefined threshold. This choice was made to keep the methods simple in favor of achieving a validation of the complete system. Figure 16: Detection of the collision with the rock pile. Through analysis of the manual operation data, the transmission pressure signal and the estimated skidding factor were selected and used in a threshold detector. Figure 17: Control diagram of the excavation method. Tilt and pedal commands are predetermined from the human operator control method. The lift command is adjusted depending on the detected machine skidding, which is in turn estimated from the LIDAR odometry and machine tachometer data. The implementation of the excavation method was carried out using a two-state machine. In the first state, called \(S_{tilt}\), a fixed acceleration and a ramp-shaped bucket tilt command are selected. In the second state, called \(S_{push}\), the fixed acceleration command persists, and wheel skidding is analyzed. If the wheel-skidding factor rises above a predefined threshold, the boom lift command of the machine is activated in order to compensate for it. A machine-specific option, named \"full RPM\", is also activated during this state. This option forces the engine to maximize its power output, providing additional penetration force. Formally, the following equations apply for the machine commands:  
\[\begin{array}{ll}\mathit{pedal}&=P_{0}\\ \mathit{tilt}&=\left\{ \begin{array}{ll}R_{0}(t-t_{tilt})&\mathit{if}\ \mathit{state}=S_{tilt}\wedge b(t-t_{tilt})\leq 1\\ 1&\mathit{if}\ \mathit{state}=S_{tilt}\wedge b(t-t_{tilt})>1\\ 0&\mathit{if}\ \mathit{state}=S_{push}\\ lift&=\left\{\begin{array}{ll}0&\mathit{if}\ \mathit{state}=S_{tilt}\lor \mathit{skid}<\mathit{skid}_{max}\\ 1&\mathit{if}\ \mathit{state}=S_{push}\wedge\mathit{skid}\geq\mathit{skid}_{max} \end{array}\right.\\ \mathit{fullRpm}&=\left\{\begin{array}{ll}0&\mathit{if}\ \mathit{state}=S_{tilt}\\ 1&\mathit{if}\ \mathit{state}=S_{push}\end{array}\right.\end{array}  \tag{8}\]  
where \(P_{0}\), \(R_{0}\), and \(\mathit{skid}_{max}\) are predefined constant values; \(t_{tilt}\) is the start time of state \(S_{tilt}\), and \(\mathit{skid}\) is the skidding factor.