## 2 Materials and Methods
### Three-Dimensional and Finite Element Modelling
#### 2.2.2 Finite Element Model of the Picking System  
The finite element model was built using the display dynamics software ANSYS/LS-DYNA, which does not have a fixed unit system and has to be defined by the user. In the numerical simulation and analysis of the pick-up system, the kg-m-s unit is used, and all other units can be derived on the basis of this unit system. The tetrahedral meshing method is simple, adaptable to the model and suitable for all kinds of complex geometric models. Hexahedral meshes have greater advantages in terms of computational accuracy, mesh quality and speed of computational convergence for simple models. For parts that are much thinner in one direction compared to the other, shell elements are generally used to divide the mesh. Therefore, tetrahedral grids are used to mesh the guard plate, cam plate, power shaft, crank linkage, elastic tooth rod, roller plate, roller wheel and door frame. Hexahedral grids are used to mesh sugarcane leaf. A shell element is used to mesh the elastic teeth. The total number of cells for the entire finite element model is 546,835, and the total number of nodes is 327,439. The elastic-plastic isotropic model (* MAT_Plastic_Kinetic) is selected as the sugarcane leaf model. This model is suitable for simulating isotropic and kinematic hardening plasticity, and the rate effect is considered. The hardening model used in this paper is the Prager model. The multi-segment linear elastic-plastic model (* Mat_Piecewise_Linear_Plasticity) is selected as the elastic model. This model can describe the constitutive relation of materials by defining the effective stress-strain curve considering the strain rate effect. To define the effective stress-strain curve, it is necessary to obtain the engineering stress-strain curve of the material. The engineering stress-strain curve for 65 Mn spring steel is referenced in this paper [22]. The engineering stresses and strains are converted into real stresses and strains by means of Equations (1) and (2). \[\varepsilon_{t} =ln(1+\varepsilon_{e}) \tag{1}\] \[\sigma_{t} =\sigma_{e}(1+\varepsilon_{e})\] (2) \[\varepsilon_{p} =\varepsilon_{t}-\sigma_{t}/E \tag{3}\]  
In Equations (1)-(3), \(\varepsilon_{t}\) represents real strain, and \(\varepsilon_{e}\) represents engineering strain.\(\sigma_{t}\) represents the true stress (Pa); \(\varepsilon_{e}\) represents the engineering stress (Pa); \(\varepsilon_{p}\) represents the effective strain; and \(E\) represents the modulus of elasticity (Pa). Equation (3) is then used to calculate the effective strain from the true stress and strain. Taking the part of the effective strain greater than 0, as the maximum effective plastic strain is considered, the part of the unloading drop is wiped out and the curve is kept as a rising state. Finally, an effective stress-strain curve is obtained. Based on the required material properties, the mechanical parameters of the cane leaves are referenced from experiments on the mechanical parameters of cane leaves carried out by [PERSON] et al. [23] at the Institute of Agricultural Machinery, Chinese Academy of Tropical Agricultural Sciences. The mechanical parameters of the elastic teeth are set according to the parameters of 65 Mn spring steel [24]. The material parameters for each component are shown in Table 2.  
The finite element model of the picking system consists of two main models, the picking mechanism and the sugarcane leaf. The sugarcane leaves are parallel to the power shaft and placed on the ground surface. In the finite element model, the shell element is used for the elastic teeth, while the solid element is used for the guard plate, the cam plate, the power shaft, the crank linkage, the elastic tooth rod, the roller plate, the roller wheel, the door frame, the ground and the sugarcane leaf. The finite element model of the picking system is shown in Figure 4.  
The speed of roller plate was set at 35 r/min, and the axis of rotation was in the positive direction of the z-axis, rotating counterclockwise.