*3.2. Results of Pressed Vines Experiment*

According to the experimental method, the experimental results of the peanut diggerinverter under the condition of pressed vines are shown in Table 6, and the range analysis and variance analysis are shown in Figure 6 and Table 7.


**Table 6.** Experimental design and results of pressed vines.

**Figure 6.** Range analysis of pressed vine experiment results, (**a**) Pm, (**b**) Ps, (**c**) Pf.


**Table 7.** Experimental variance analysis of pressed vines.

(Pf) R square = 0.99, (Pm) R square = 0.952, (Ps) R square = 0.981. Note: The critical value of significant judgment F0.01(2,2) = 99, F0.05(3,3) = 19, F0.1(2,2) = 9. \* indicates that the factors have some influence on the test index (0.05 < *p* ≤ 0.1), \*\* indicates that the factors have a significant influence on the test index (0.01 < *p* ≤ 0.05).

The variable R stands for range, and the range of a factor is the difference between the maximum and minimum values of the mean values of each level of the factor, t1 represents the average value of experimental results at the level of 1 for each experimental factor, t2 represents the average value of experimental results at the level of 2 for each experimental factor, and t3 represents the average value of experimental results at the level of 3 for each experimental factor.

According to the range analysis in Figure 6a, it can be seen that the order of influence of all factors on the rate of vines inverting is as follows: A > B > C. From comprehensive comparability, it can be seen that the higher the average value of each factor group, the better the level of that factor. Moreover, according to the variance results in Table 7, it can be seen that each factor has an extremely significant impact on the rate of vines inverting, so the maximum horizontal combination is A3B2C2. Similarly, according to the range analysis in Figure 6b, it can be seen that the order of influence of all factors on the rate of buried pods is as follows: A > B > C. From the comprehensive comparability, it can be seen that the lower the average value of each factor group for the rate of buried pods, the better the factor level. Moreover, from the variance results in Table 7, it can be seen that the traveling speed of the tractor has a significant impact on the rate of buried pods. The line speed of the conveyor chain and the line speed of the inverting roller had no significant effect on the rate of buried pods, so the minimum horizontal combination was chosen as A1B1C2. Similarly, according to the range analysis in Figure 6c, it can be seen that the order of influence of all factors on the rate of fallen pods is as follows: A > C > B. Based on comprehensive comparability, it can be seen that the smaller the average value of each factor group, the better the level of that factor. Moreover, according to variance results in Table 7, it can be seen that the influence of the traveling speed of the tractor on the rate of fallen pods is extremely significant, the influence of the line speed of the inverting roller on the rate of fallen pods is significant, and the influence of the line speed of the conveyor chain on the rate of fallen pods is insignificant, so the minimum horizontal combination is A1C2B1.

According to the comprehensive balance method of multi-index data analysis in an orthogonal experiment, the above analysis results are summarized, and the summary table is shown in Table 8.


**Table 8.** Summary of results of pressed vines.

As can be seen from Table 8, factor A is the most important at the level of A2, followed by factor C at the level of C2, and then factor B at the level of B2. In summary, the best horizontal combination can be A2C2B2, that is, the traveling speed of the tractor is 0.9~1.1 m/s, the line speed of the inverting roller is 1.88 m/s, and the line speed of the conveyor chain is 1.02 m/s. In order to further verify the operation effect, three repeated experiments were carried out under the above optimal working parameters: the average traveling speed of the tractor was 1.01 m/s, the rate of vines inverting was 74.29%, the rate of buried pods was 0.14%, and the rate of fallen pods was 0.33%. The rate of buried pods and the rate of fallen pods were far less than the identification standard of the peanut harvester.

#### *3.3. Results of Pairing Analysis between Unpressed Vines and Pressed Vines*

The paired *t*-test was conducted for the rate of vines inverting, the rate of buried pods and the rate of fallen pods, of unpressed and pressed vines, and the significance level was 0.05. The correlation of paired samples was shown in Table 9, the test results of paired samples were shown in Table 10, and the box diagram of paired sample comparison was shown in Figure 7.

**Table 9.** Correlation of paired samples.


Note: The critical value of significant judgment t0.01(8) = 2.896, t0.05(8) = 1.86, t0.1(8) = 1.397. \*\* indicates that the factors have a significant influence on the test index (0.01 < *p* ≤ 0.05), \*\*\* indicates that the factors have a very significant influence on the test index (*p* ≤ 0.01).

**Table 10.** Paired sample test.


Note: The critical value of significant judgment t0.01(8) = 2.896, t0.05(8) = 1.86, t0.1(8) = 1.397. \*\*\* indicates that the factors have a very significant influence on the test index (*p* ≤ 0.01).

As can be seen from Table 9, the correlation between unpressed vines and pressed vines to the rate of vines inverting was 0.913, which was significant (*p* = 0.001 < 0.01), the correlation between unpressed vines and pressed vines was 0.787, and the correlation was significant (*p* = 0.012 < 0.05), and the correlation between unpressed vines and pressed vines was 0.281, and the correlation was insignificant (*p* = 0.464 > 0.05). As can be seen from Table 10, at the significance level of 0.05, the paired *t*-test was conducted for the rate of vines inverting on unpressed vines and pressed vines, and the T-value was −5.479, and the significance *p* value was 0.001 < 0.01. It can be seen that unpressed vines and pressed vines not only have a significant correlation but also a significant difference in the rate of vines inverting. According to the comparison in Figure 7a, the mean and median values of the rate of vines inverting on pressed vines are higher than those on unpressed vines. At the significance level of 0.05, the paired *t*-test was conducted for the rate of buried pods of unpressed vines and pressed vines and the rate of fallen pods of unpressed vines and pressed vines. The *p* values of the rates of buried pods of unpressed vines and pressed vines and the rates of fallen pods of unpressed vines and pressed vines were all greater than 0.05. Therefore, there was no significant difference between the rate of buried pods of unpressed vines and pressed vines and the rate of fallen pods of unpressed vines and pressed vines. According to the comparison in Figure 7b,c, there was little difference between the average rate of buried pods and the average percentage of falling pods between the unpressed and pressed vines.

As summarized, under the condition of pressed and unpressed vines, the influence of various factors on the rate of fallen pods and the rate of buried pods is small, but there is a difference in the rate at which vines invert. The rate of vines inverting peanut under the state of pressed vines is higher than that under the state of unpressed vines.

**Figure 7.** Box diagram of paired samples. (**a**) the rate of vines inverting; (**b**) the rate of buried pods; (**c**) the rate of fallen pods.

#### **4. Discussion**

In the process of peanut digger-inverter operation, under the state of unpressed vines and pressed vines, the influencing sequence of each factor on each index is the same, that is, the traveling speed of the tractor has the greatest influence on the rate of vines inverting, the rate of buried pods, and the rate of fallen pods of the peanut digger-inverter. This is because when the tractor's travel speed is high, there will be many peanut vines and

pods on the peanut digger-inverter machine. First, it will cause blockage and serious vine accumulation, which is not conducive to the later vines flipping. Second, the peanut digging shovel will not maintain the digging depth at the beginning of the operation, which will break the peanut pod, resulting in buried pods and falling pods. Third, the pod's falling speed will also accelerate, which will cause the rigid acceleration of the peanut pod landing at that moment, resulting in a peanut falling pod. When the speed of the tractor is slow, the number of peanut vines will be small, and the peanut vines cannot stand on their hands independently, resulting in a very low rate of peanut vines inverting [16,41,42]. The line speed of the conveyor chain only has an effect on the rate of vines inverting; it has no effect on the rate of buried pods or the rate of fallen pods. This is because the line speed of the conveyor chain can only affect the number of peanut vines on the back of the inverting roller and has no effect on the peanut pod. However, the speed of the tractor, the line speed of the inverting roller is the most influential factor on the rate of vines inverting and the rate of fallen peanut pods, and it has no influence on the rate of buried pods. This is because the inverting roller is too large, which will lead to the peanut vines being thrown out, resulting in their inability to stand on their hands and the pod falling off. The inverting roller is too small, which will lead to the peanut vines not being able to turn over to the ground in time, resulting in congestion and the peanut vines not being able to turn over [28,43].

Under different states of unpressed vines and pressed vines, there are significant differences in the paired *t*-test of the rate of vines inverting for each factor of the peanut digger-inverter. This is because the lodging peanut vines are dependent, while the independent peanut vines have an extremely poor inverting effect, and the trailing and semi-trailing peanut varieties have a better inverting effect. Therefore, peanut planting row spacing should be matched with the harvester. The left and right rows of peanut vines support each other [32,44].

The relevant experimental results showed that the peanut vine inverting effect was better under the pressed vine state, and under the same conditions, the rate of vine inverting was 4.3% higher than that of unpressed vines and 3.1% higher than that of the turnover laying device of the peanut harvester. In addition, the peanut digger-inverter has a much smaller rate of fallen pods than the turnover-laying device of the peanut harvester. The data pairs for each experiment are shown in Table 11.


**Table 11.** Comparison of test results of performance indices.
