## 2 Materials and Methods
### Three-Dimensional and Finite Element Modelling  
#### 2.2.1 Three-Dimensional Model of the Picking System  
The picking system mainly includes two models: the picking mechanism model and the sugarcane leaf model. Whether the model is reasonable or not directly affects the accuracy and reliability of the simulation results. Because of the complex shape of the picking mechanism, the professional three-dimensional software SolidWorks is used to create its three-dimensional geometric model. The structural parameters of the picking mechanism are shown in Table 1. The schematic diagram of the picking system structure is shown in Figure 2.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Value** \\ \hline Radius of base circle (mm) & 41 \\ Radius of roller plate (mm) & 60 \\ Length of crank (mm) & 40 \\ Length of elastic tooth (mm) & 150 \\ Angle between elastic teeth and crank (\({}^{\circ}\)) & 52 \\ Three arc radius (mm) & 41/53/89 \\ Angle of upper & 24 \\ guard plate (\({}^{\circ}\)) & 4 \\ Number of elastic tooth rod & 4 \\ \hline \end{tabular}
\end{table}
Table 1: Structural parameters of the picking mechanism.  
Figure 1: The working mechanism of the returning machine (1: door frame; 2: guard plate; 3: elastic teeth roller picking mechanism; 4: conveying brush roller; 5: cutting knife roller).  
The picking mechanism is the key component of the sugarcane leaf cutting and returning machine, and is mainly composed of the guard plate, elastic teeth, cam plate, crank linkage, elastic teeth rod, roller wheel, roller plate, power shaft and so on. The geometric parameters of the elastic tooth are shown in Figure 3.  
The roller plate is fixed on both sides of the power shaft, and the tooth rod is hinged to the roller plate. The elastic tooth and the crank linkage are simultaneously fixed on the elastic tooth rod. The other end of the crank linkage is provided with a roller wheel which rolls in the cam slide of the cam plate. When the picking mechanism is in operation, the power shaft drives the roller plate to rotate at a constant speed, causing the circumferential tooth rod to move in a circular motion. Because of the restriction of the cam slide on the roller, the crank linkage drives the roller wheel to move according to its prescribed track. The tooth rod is hinged to the roller plate. The movement of the teeth is therefore controlled both by the circular rotational movement of the tooth rod and by the movement of the roller wheels in the cam slide, which rotate around the power shaft and swing around the elastic tooth rod.  
Mature sugarcane leaves are approximately 80-150 cm in length and 2-5.39 cm in width [20]. Take the sugarcane leaf model with a length of 100 cm and a width of 4 cm; the sugarcane leaf is made up of two parts, the vein and the blade. The crescent shape of the leaf  
Figure 3: Geometric parameters of the elastic tooth.  
Figure 2: Schematic diagram of the pick-up system structure (1: sugarcane leaf; 2: guard plate; 3: elastic teeth; 4: cam plate; 5: crank linkage; 6: elastic teeth rod; 7: roller wheel; 8: roller plate; 9: power shaft; 10: door frame; 11: ground).  
-vein cross-section is simplified to a semicircle with a radius taken as 0.24 cm, and the leaf blade cross-section is simplified to a rectangle with a thickness taken as 0.3 mm [21]. When establishing the geometric model of the pickup mechanism, in order to reduce the model scale and shorten the calculation time, it is necessary to simplify the model appropriately by ignoring the rounded corners and chamfers of the cam plate, roller plate and bolt holes of guard plate, and so on.