## Materials and Methods
### Comparative Experiment in Terms of Threshing Performance  
To compare the threshing performance of both adjustment methods, the comparative experiment was implemented based on the feed rate and the threshing gap as the influence factors, and grain-entrainment loss rate, damage rate, threshing efficiency, and threshing power consumption as the performance specifications. In the field experiment, the forward speed of the combine harvester was used to control the feed rate based on the fixed cutting width and cutting table height [20]. The experiment, with its plan shown in Table 1, was implemented in two groups and five different forward speeds with the initial threshing gap set at 20 mm. In one group of the experiment, two adjustment methods were used to increase the threshing gap by 5 mm. The threshing gap with threshing drum adjustment type is 30 mm, while that with concave adjustment type is 20-30 mm. In the other group of the experiment, two adjustment methods were used to decrease the threshing gap. The threshing gap with threshing drum adjustment type is 10 mm, while that with concave adjustment type is 10-20 mm. Due to the fact that the threshing drum adjustment type and the concave adjustment type share the same threshing gap when the initial threshing gap is 20 mm. Only one group of experiment was implemented at the threshing gap of 20 mm. For all experiments, each group of experiment was repeated for three times and the average value was taken as the experiment result. \begin{table}
\begin{tabular}{c c c c} \hline
**Forward** & **Initial** & **Threshing Gap with Threshing** & **Threshing Gap with Concave** \\
**Speed/(m/s)** & **Gap/mm** & **Drum Adjustment Type/mm** & **Adjustment Type/mm** \\ \hline
0.6 & 20 & 30 & 20–30 \\  & & 10 & 10–20 \\
0.8 & 20 & 30 & 20–30 \\  & & 10 & 10–20 \\
1.0 & 20 & 10 & 10–20 \\  & & 30 & 20–30 \\
1.2 & 20 & 10 & 10–20 \\
1.4 & 20 & 30 & 20–30 \\  & & 10 & 10–20 \\ \hline \end{tabular}
\end{table} 
Table 1: Experiment plan. Figure 5: Electronic control self-locking device, 1. The first planetary gear set, 2. Constant speed spiral disc, 3. Claw, 4. Motor, 5. Motor gear, 6. Central gear, 7. Main shaft, 8. The second planetary gear set, 9. Connecting shaft, 10. Driver, 11. Displacement sensor: (**a**) Side view of electronic control self-locking device; (**b**) Front view of electronic control self-locking device. The experiment, as a field experiment, was implemented in Wujiang District, Suzhou City, Jiangsu Province with the combine harvester developed independently; the rice used in the experiment is \"Jiahua\" whose characteristics are partially shown in Table 2. As the basic model, YANMAR-AW82G (YANMAR, Osaka, Japan) was used as the combine harvester for the experiment with multiple devices and instruments installed, including in-line monitoring devices for grain impurity rate, damage rate and loss rate as well as the sensors for drum rotation speed and torque. The modified vehicle is also available for multiple control functions including the adjustment of cutting table height, position of the concave grid, the rotation speed of drum, the opening of lip sieve, forward speed, etc. Besides, real-time monitoring of operation parameters and performance parameters of the combine harvester is available as well [21; 22; 23; 24]. As shown in Figure 6, before the test, several fields with uniform rice growth were selected and tested. The harvesting length was 15 m in length for each test. The forward speed of the combine harvester was maintained within 0.6-1.6 m/s, to ensure the feeding rate. In the field test, the average cutting width is 2.58 m, the stubble height is 15 cm. After the material is separated by the threshing drum, the stalk is discharged from the grass discharge port and falls on the tarpaulin behind the combine harvester. After the test, the quality of stalks on the tarpaulin, the grain contained in the straw and the unpurified grain were collected by manual treatment to obtain the quantity of stalk, the rate of separation loss and the grain damage rate.