## 3 Key Components Design
### Collection Mechanism  
The winter jujube is easily damaged by collision because it contains more water, and the fruit meat is more brittle. When the jujube falls, if it falls on the ground directly, it will cause surface injury. The quality and storage time of the winter jujubes will decrease. Currently, the traditional solution for farmers is that they put plastic cloth around the jujube trees to prevent the jujubes from landing on the ground directly. Although this method has a certain buffering effect, there are still some flaws. First, the plastic cloth is directly in contact with the ground. When the ground is dry and hard, the buffering effect will be greatly reduced. Second, when the jujubes fall onto the plastic cloth, they cannot be collected in time, and the later fallen jujubes may hit the first dropped jujubes, causing double damage [19]. In response to such problems, a variable area umbrella-like collecting mechanism as shown in Figure 8 was designed. Figure 8: Folding umbrella collection mechanism: (1) Skeleton; (2) nonwoven fabric; (3) falling entrance. Figure 6: The vibration displacement cloud map of jujube tree at different vibration points: (**a**) \(l=500\) mm, the fourth order, 16.107 Hz; (**b**) \(l=750\) mm, the fourth order, 16.107 Hz; (**c**) \(l=1000\) mm, the fourth order, 16.107 Hz; (**d**) \(l=1250\) mm, the fourth order, 16.107 Hz; (**e**) \(l=1500\) mm, the fourth order, 16.107 Hz. Figure 7: The maximum displacement of each node of jujube tree at the same time. Ignoring the influence of air resistance, the jujubes are free falling in the process of falling. According to the law of conservation of energy, the speed of the jujubes when they contact the ground is:  
\[\
u=\sqrt{2 gH} \tag{18}\]  
where, \(\
u\) is the speed when the jujube hits the ground, m/s; g is the acceleration of gravity, m/s\({}^{2}\); \(H\) is the distance between the jujube and the ground, m.  
Then, combining the theorem of momentum \(m_{p}v=Ft_{c}\), the average impact force when the jujube hits the ground can be obtained by Equation (19). \[F=\frac{m_{p}\sqrt{2 gH}}{t_{c}} \tag{19}\]  
where, \(F\) is the average impact force, N; \(m_{p}\) is the mass of winter jujube, kg; \(t_{c}\) is contact time, s.  
It can be seen that the average impact force is inversely proportional to the contact time. Compared with the falling on the ground directly, the contact time of falling on the nonwoven fabrics with a certain elasticity is increased greatly, and the impact force on the jujube can be reduced effectively [20]. Due to the different canopy sizes of jujube trees, the umbrella with fixed area cannot meet the demands for use. Therefore, this paper designed a composite folding umbrella bone, as shown in Figure 9. When the tree canopy is large, it can be connected with the second rod on the first rod. One end of the connecting rod is connected with the second rod by rotation, and the other end is connected with the sliding block by rotation. The sliding block can be moved along the first rod and the limit block is used to define the limit position of the movement. Each rod is connected by a rotation spindle and pin, which can be disassembled easily, and the fruit farmers can carry out multistage combination in accordance with the actual situation. In the design process, the length of each rod is \(L\), then the collection area of the first rod can be obtained by Equation (20). \[S_{1}=\pi r_{g}^{2}=\pi L^{2}\cos\theta^{2} \tag{20}\]  
where, \(S_{1}\) is the collection area of the first rod, m\({}^{2}\); \(L\) is the length of the rod, m; \(\theta\) is the angle of the first rod and horizontal plane, (\({}^{\circ}\)). When another rod group is increased, the corresponding collection area is as follows:  
\[S_{2}=\pi(L\cos\theta+L\cos\theta^{\prime})^{2}=\pi L^{2}(\cos\theta+\cos \theta^{\prime})^{2} \tag{21}\]  
where, \(S_{2}\) is the collection area of the second rod, \(\theta^{\prime}\) is the angle of the second rod and horizontal plane, (\({}^{\circ}\)).