## 2 Materials and Methods
### Simulation Experiments for the Calibration of Contact Parameters
#### 2.4.1 Three-Dimensional Reconstruction of the Fresh Goji Berry Model  
In order to establish an accurate 3D model of the fresh goji berry and improve the realism of the simulation, we used the structure from motion coupled with clustering views for multi-view stereo (SFM-CMVS) technique to acquire the model of a fresh goji berry [31; 32]. The main steps include: image data acquisition, point cloud data pre-processing, point cloud data materialization, mesh partitioning, and mesh filling. As shown in Figure 10, we selected a fresh goji berry with near-average size and uniform shape as the object, took 128 2D images with an industrial camera, and imported the images into Visual SFM software to obtain the dense point cloud model of the goji berry. The point cloud filter tool of MeshLab software was used to remove noise and redundant points from the point cloud file and extract the contour area of the goji berry. The solid model of the goji berry was obtained by surface fitting the point cloud data, and the solid model was imported into HyperMesh software for meshing. The mesh was filled as a particle template in the EDEM software. The desired fresh goji berry model was obtained by using the modeling method of multiple spherical cells overlapping to form a particle cluster. Figure 10: The process of inverse acquisition of a 3D model of fresh goji berry. 4.2 Simulation Experiment for Collision Restitution Coefficient of Fresh Goji Berry-Silicone Rubber Material  
As with the physical experiment, the simulation experiment was carried out with H\({}_{0}\) = 300 mm as the initial condition. The particle displayed a free-fall motion to the silicone rubber plate with 0 initial velocity, as illustrated in Figure 11. The contact model between fresh goji berry and silicone rubber material was taken as Hertz-Mindlin (no slip) in the EDEM software. When setting the contact parameters between the fresh goji berry and contact material, the static friction coefficient and rolling friction coefficient had no effect on the rebound height of the particle; hence, these two parameters were set to 0. Table 2 presents the design scheme and results of the simulation experiment, where the collision restitution coefficient (Ex\({}_{1}\)) was considered as a factor and the highest rebound height (H\({}_{1}\)) was adopted as an index. 4.3 Simulation Experiment for Collision Restitution Coefficient of Fresh Goji Berry-Fresh Goji Berry  
As shown in Figure 12, a semicircular hollow pipe with a diameter of 320 mm was added to the EDEM software. In the pipe, two particles were generated at the bottom and 60 mm from the base point in the vertical direction. The intrinsic parameters of the pipe did not have a significant effect on the experimental process, so the pipe intrinsic parameters were set to be the same as the silicone rubber material. The collision restitution coefficient, static friction coefficient, and rolling friction coefficient were set to 0. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Group No.** & **Ex\({}_{1}\)** & **H\({}_{1}\)/mm** \\ \hline
1 & 0.1 & 2.214 \\
2 & 0.2 & 14.220 \\
3 & 0.3 & 30.659 \\
4 & 0.4 & 43.573 \\
5 & 0.5 & 74.025 \\
6 & 0.6 & 110.760 \\
7 & 0.7 & 151.756 \\
8 & 0.8 & 198.919 \\
9 & 0.9 & 256.737 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Design scheme and results of free-fall experiment. Figure 11: Simulation experiment for calibrating the collision restitution coefficient of fresh goji berry–silicone rubber material. Table 3 presents the design scheme and results of the simulation experiment, where the collision restitution coefficient (Ex\({}_{2}\)) was considered as a factor and the highest rising heights were adopted as indexes. 4.4 Simulation Experiment for Static Friction Coefficient of Fresh Goji Berry-Silicone Rubber Material  
A rectangular body (500 mm in length, 500 mm in width, and 10 mm in height) was added in the EDEM software, and its intrinsic parameters were set to be the same as those of the silicone rubber material.