*3.1. Experimental Scheme and Results*

Combined with Design-Expert software, the response surface BBD method experimental design [25,26] was carried out, and the spring-finger speed, forward speed and embedded depth were selected as the main influencing factors. The speed of the springfinger was set at 15–25 r/min, the forward speed at 0.4–0.8 m/s, and the embedded depth at 60–80 mm, and the table of test factor levels is shown in Table 5:


**Table 5.** Levels and codes of experimental variables.

The BBD test was chosen for this trial in order to reduce the number of trials. 17 groups of trials were conducted, each group was repeated three times and the final mean was selected in order to take into account the interaction of all factors, with loss rate and wounded potato rate as indicators. The results of the trials are shown in Table 6 below:


**Table 6.** Design and results of the orthogonal test in the numerical simulation.

#### *3.2. Analysis of Test Results*

Using Design Expert12 software multiple regression fitting analysis of the data in Table 6, a quadratic polynomial response surface regression model was established for the three independent variables, loss rate, wounded potato rate, for the spring spring-finger speed *A*, forward speed *B*, and embedded depth *C*. The mathematical model (13) was:

$$\begin{cases} \ Y\_1 = 1.05 - 0.22A - 0.42B + 0.75C + 0.63AB + 0.028AC - 0.070BC + 1.82A^2 + 1.03B^2 + 1.02C^2 \\\ Y\_2 = 99.77 - 2.02A + 0.74B + 2.28C + 2.71AB + 0.43AC + 0.31BC - 7.43A^2 - 6.16B^2 - 4.91C^2 \end{cases} \tag{13}$$

ANOVA was conducted on the model and the results are shown in Table 7. The *p*-values of the models for loss rate and wounded potato rate were less than 0.01 and the *p*-values of the misfit terms were greater than 0.05. The model coefficients of determination R2 were 0.9235 for loss rate and 0.9786 for wounded potato rate respectively, which shows that the optimised regression model was extremely significant and a good fit, and the model was reliable.


**Table 7.** Analysis variance table of test results.

Note: \* indicates general significance, 0.05 < *p* < 0.1; \*\* indicates highly significant, *p* < 0.01.
