**3. Results and Discussions**

*3.1. Numerical Analysis of Movement during Jujube Branch Picking*

Figure 4 shows the dynamic analysis results obtained by the Rocky software. The simulation time is 20 s; the filling time of jujube branches varied from 0 s to 16 s with an average speed of one jujube branch per second. Jujube branches were conveyed, entangled, collided, escaped, and collected on the conveying device and picking mechanism. Figure 4a shows the state of jujube branches after the filling time of 4 s. Meanwhile, four jujube branches were piled up on the conveyor belt, and the first jujube branch was rolled sideways by the action of the gear shift. Figure 4b shows the state of jujube branches at 10 s, when the counter-roller gear starts to pick up the first jujube branch. Then, under the influence of gear and adjacent jujube branches, jujube branches close to the gear tooth begin to

collide and roll, which results in the escape of jujube branches. Figure 4c shows that jujube branches within the dotted line were leaving the test bed under the impact of collision when the time was 13.9 s. Under the working condition of this analysis, a total of three jujube branches fell off from the test bed, all of which slipped from the edge of the conveyor belt after collision and winding. Figure 4d shows that one jujube branch was successfully collected at 16.9 s. When jujube branches were regarded as supernormal particles, the meshless Galerkin method (MGM) could be used to describe the dynamic process of jujube branch movements, such as transportation, collision, and tumbling.

**Figure 4.** Dynamic picking process of jujube branches.

*3.2. Influence of Jujube Branch Size on Picking Rate*

In order to study the relationship between the size and picking rate of jujube branches, a numerical analysis was carried out on the movement law and picking rate changes for three sizes of jujube branches in the picking progress.

Figure 5a shows the movement of the simulation at the time point of 10.65 s when a total of 16 jujube branches with a size of 480 mm were fed. It can be found that the feeding was more uniform because the number of jujube branches was relatively small and there was little interference among each other. At the same time, due to the smaller size of the jujube branch, the weight was correspondingly lighter. Further study of the dynamic process showed that only winding and rolling occurred after the collision of jujube branches, not flinging. It is concluded that when the jujube branch was lighter, the force caused by collision can be reduced, the distance that the jujube branch was pushed away by the gear was shorter, and there was less rolling, which is beneficial to the final collection. Figure 5b shows the jujube branch's movement when jujube branch size was 640 mm and fed with a total of 23 jujube branches. As shown in the figure, due to the increase in the size of the jujube branches, the force between the jujube branch and the shifting teeth was more potent, resulting in throwing off the jujube branch. In addition, the jujube branch and the shifting teeth were also entangled due to the increase in twig size, leading to the decrease in the picking rate. Figure 5c shows the movement of jujube branches when the size of jujube branch was 800 mm and the total amount of jujube branch feeding was 30. As the size of jujube branches increased, the mass of a single particle also increased, but the amount of the dialing power of the dial tooth was limited; it was difficult for the dial tooth to dial the jujube branch, causing the jujube branches to pile up on each other. However, the jujube branches were transported by the conveyor belt and entered between the two gears, and then they were finally collected after throwing out the equipment under the agitation of

the gears. The simulation results showed that large-size jujube branches were helpful for collection due to the influence of weight and size. The impact of the collision caused by the shifting of the teeth only causes the jujube branch to roll, and the rolling jujube branch will have an entanglement and rolling influence on the subsequent jujube branch.

**Figure 5.** Movement behavior analysis of jujube branches in the picking mechanism. (**a**) State of jujube branches with a size of 480 mm when the time point is 10.65 s. (**b**) State of jujube branches with a size of 640 mm when the time point is 12.9 s. (**c**) Collection state of jujube branches with a size of 800 mm when the time point is 13.65 s.

In this research, the influence of the size of jujube branches on the picking up rate of jujube branches was obtained by single-factor analysis with experimental and numerical results (Figure 6). It can be found from Figure 6 that the picking rate of the test result was higher than that of the numerical simulation, the curve of the test result has relatively smaller fluctuation, and the numerical result has a deviation between the two values at the size of 640 mm. Further research on the number of jujube branches found that when the size is 640 mm, the number of jujube branches collected in the numerical result is 13 and the test result is 15, with the deviation between the two being 2.

**Figure 6.** Relationship between jujube branch size and picking rate.

The experimental and numerical results show that the influence of jujube branch size on the picking is parabolic distribution. When the size of jujube branches is 480 mm and 800 mm, the picking rate of jujube branches can reach 75%. Combined with the analysis of the field function equation, it can be found that the particle size of the jujube branch is one of the important factors affecting the particle movement. According to the field function equation, the particle size determines the mass mi of a single particle and affects the volume force Fbody of the particle. In addition, the particle size also influences the contact force Fcontact and tumbling force Frolling. At the same time, according to the weight function equation, it can be found that the particle size is related to the distance di from the node xi of the weight function to the field point x and the radius ri of the support domain. The change in the particle size will inevitably affect the value of the weight function.
