## 2 Materials and Methods
### Parameter Design of Key Component  
#### 2.2.1 Determination of Ear Deformation Energy  
The drop test was important for testing the impact damage of the fruit. Previous studies have carried out the drop test to study the impact of the impact surface material type, drop height, drop direction and fruit maturity on the impact of fruit damage [27; 28; 29]. In order to determine the energy value required for ear deformation during ear snapping, a drop test was designed. The maize variety used in the drop test was Zhengdan 958, while the moisture content of the maize kernel was 30.41%. A high-speed camera was used to photograph the collision between the ears and ear snapping plate, as shown in Figure 2.  
Due to the differences in plant physical properties, the growth position and angle of the ears were random. In order to simulate the contact between the plant and ear snapping plate, the inclination angles of the ears when the ears fell were set to 90\({}^{\circ}\), 60\({}^{\circ}\), and 30\({}^{\circ}\), and 30 ears were taken from each angle for testing.  
The ear was placed at a certain height, and the critical points at which the kernels were cracked, dropped, and other damages were obtained after conducting the repeated tests. The height \(h_{1}\), speed \(v_{c}\), angular velocity \(\omega\) as well as other information pertaining to the ears after the collision with the steel plate were obtained by a high-speed camera, after which the mechanical energy before and after the collision was calculated. The mechanical energy \(E_{1}\) of the ear before the collision was the gravitational potential energy, and the mechanical energy \(E_{2}\) of the ear after the collision was the sum of the gravitational potential energy and kinetic energy of the ear after it bounced. Among them, the kinetic energy of the ear after collision was treated as the kinetic energy of a rigid body in plane motion. Then, the difference in the mechanical energy \(\Delta E\) of the ear before and after the collision when the ear was damaged was calculated.  
\[\left\{\begin{array}{l}E_{1}\ =\ mgH_{1}\\ E_{2}\ =\ mgh_{1}\ +\ \frac{1}{2}mv_{c}{}^{2}\ +\ \frac{1}{2}J_{C}\omega^{2}\\ \Delta E\ =\ E_{1}\ -\ E_{2}\end{array}\right. \tag{11}\]  
where, \(H_{1}\) was the height of the center of gravity of the ear before collision, mm; \(h_{1}\) was the height of the center of gravity of the ear after collision, mm; \(v_{c}\) was the speed of the center of gravity of the ear after collision, m\(\cdot\)s\({}^{-1}\); \(J_{C}\) was the moment of inertia of the ear, kg\(\cdot\)m\({}^{2}\); \(\omega\) was the angular velocity of the center of gravity of the ear after collision, rad\(\cdot\)s\({}^{-1}\).  
The trajectory of the center of gravity of the ear before and after collision was shown in Figure 3.  
Afterward, the energy loss such as heat energy during the collision was ignored, for which the difference was the ear deformation energy. The test result was shown in Table 1.  
Here, when the ears fell perpendicular to the ordinary steel plate, the energy for the damage and deformation of the ears was larger, with an average value of 0.842 J. When the ears were dropped at an inclination angle of 30\({}^{\circ}\), the energy for the damage and deformation of the ears was smaller, with an average value of 0.791 J. In light of the above data, when the ears fell at an oblique angle of 30\({}^{\circ}\), a minimum value \(E_{ft}\) for ear damage and deformation was present. In order to reduce ear damage during ear picking, the minimum ear deformation energy \(E_{ft}\) was taken as 0.424 J.  
Figure 2: Ear drop test. (1) High-speed camera; (2) light supplement lamp; (3) height marker; (4) steel plate.