*2.4. Experimental Factors, Indicators, and Methods*

#### 2.4.1. Experimental Factors

In the field experiment, there are many factors affecting the peanut digger-inverter, among which the traveling speed of the tractor is the most important factor. The traveling speed of the tractor will not only affect the working efficiency of the whole machine but also affect the working effect of the peanuts because the tractor is the most uncontrollable factor in the whole experiment process, which is also the biggest change. At the same time, driving the tractor too fast will lead to poor peanut planting and vine inversion. According to a literature review and calculation, the traveling speed range of tractors is 0.7~1.3 m/s [16,31,32]. The rotation speed of the loop conveyor chain is also a major factor; too fast rotation will lead to peanut straw dispersion, and too slow rotation will lead to peanut straw congestion, so take the line speed of the conveyor chain as an experimental factor. The known rotation radius is 0.08 m, the maximum rotation speed is determined to be 135 r/min, and the minimum rotation speed is 100 r/min. Through a literature

review and calculation, it can be known that the line speed of the conveyor chain range is 0.84~1.13 m/s [16,31,32]. In order to ensure the effect of peanut vines inverting, it is required that the absolute velocity of peanut vines landing be zero, so the rotation speed of the peanut inverting roll is a major experimental factor. Given that the radius of the inverting roll is 0.3 m, the maximum rotation speed is determined to be 70 r/min, and the minimum rotation speed is 50 r/min. Through literature review and calculation, it is known that the line speed of the inverting roller range is 1.57~2.12 m/s [16,31,32]. Therefore, the traveling speed of the tractor, the line speed of the conveyor chain, and the line speed of the inverting roller are determined as the main factors affecting the operation index.

The experimental scheme used in this paper is an orthogonal experiment with three factors and three levels. For the three test factors, the traveling speed of the tractor is A, the line speed of the conveyor chain is B, and the line speed of the inverting roller is C. The experimental research is carried out in the two states of pressed and unpressed vines. Experimental factors and levels are shown in Table 2. Orthogonal table L9 (34) is established [35].

**Table 2.** Test factors and levels.


Note: The travelling speed of the tractor is not the same value every time measured, so the values of the three levels are range values.

#### 2.4.2. Experimental Indexes

According to DB34/T534-2022 Anhui Provincial Standard "Technical Specification for Mechanized Peanut Harvesting" [36] and DG/T077-2019 agricultural machinery extension identification outline "Peanut Harvesting" [37], the travelling speed of the tractor and the rate of buried pods, the rate of fallen pods, and the rate of vines inverting of peanuts were measured in the field experiment of the peanut digger-inverter machine.

(1) Measurement of traveling speed of tractor

The length of the measuring area is 30 m, the rated speed of the tractor engine can be ensured (and the speed of the rear power output shaft can be ensured), the suitable working gear is selected for full operation, a stroke is measured, and the time through the measuring area is recorded. The operating speed is calculated according to Formula (1):

$$\mathbf{V} = \mathbf{L} / \mathbf{T} \tag{1}$$

where:

V—The traveling speed of the tractor, expressed in meters per second (m/s);

L—The length of the entire test area, expressed in meters (m);

T—Time to pass through the test area, expressed in seconds (s).

(2) Determination of the rate of buried pods, the rate of fallen pods, and the rate of vines inverting in the peanut digger-inverter

In the measuring area, three equal distances were taken, each of which was 3 m long and had one working width. All the pods falling on the ground and buried in the soil layer (after the removal of naturally falling pods) were collected in each plot and called quality. The rates of buried pods, fallen pods, and vines inverting were calculated according to Formulas (2)–(4), and the average value of the three plots was taken as the evaluation index.

$$P\_{\rm m} = \mathbf{M}\_{\rm m} / \mathbf{M}\_{\rm x} \times 100\% \tag{2}$$

$$\mathbf{P\_s = M\_s/M\_x \times 100\%} \tag{3}$$

$$P\_{\rm f} = 1/\text{L} \times 100\% \tag{4}$$

where:

Pm—The rate of buried pods, the weight of the pod buried in the soil layer in the plot divided by the total weight of the pod in the whole plot (%);

Mm—The pod mass (excluding naturally fallen pods) buried in the soil layer in the plot, expressed in grams (g);

Mx—The total pod weight of crops in the plot, expressed in grams (g);

Ps—The rate of fallen pods, the mass of pods dropped in the cell divided by the total mass of pods in the whole cell (%);

Ms—Mass of pods dropped in the plot, expressed in grams (g);

Pf—The rate of vines inverting; the number of peanut vines with no pod in the community divided by the total number of peanut vines in the community (%);

l—The number of peanut vines without pods on the ground after peanut harvest in the community; unit is the number of vines;

L—Total number of peanut vines in the community; unit is the number of vines.

#### 2.4.3. Experimental Methods

The self-developed peanut digger-inverter was driven by the tractor to carry out field experiments according to the working width of the machine; each experiment is 2 ridges and 4 rows. The theoretical traveling speed of the tractor was controlled by the gear position, and the actual operating speed was calculated at the end of each measuring area. The line speed of the conveyor chain and the line speed of the inverting roller are controlled by the rotating speed of the conveying shaft, and the orthogonal experiment between unpressed vines and pressed vines was carried out on the designed orthogonal experiment scheme. The range, variance, and comprehensive analysis methods were used to analyze the orthogonal experimental results, and the optimal working parameter combination was obtained [35,38–40]. The paired *t*-test method was used to test the correlation between the two states of pressed vines and unpressed vines, and the best working effect was obtained under the state of pressed vines and unpressed vines [35,38]. The field experiment process and effect are shown in Figure 4.

**Figure 4.** *Cont*.

(**a**) (**b**)

(**c**) (**e**)

**Figure 4.** Field experiment flow of peanut digger-inverter: (**a**) The process of field experiment of peanut digger-inverter. (**b**) The effect of peanut digger-inverter after field operation. (**c**) Random 3 m sampling of a stroke after peanut operation. (**d**) The sampled peanuts were picked manually. (**e**) The buried pod, fallen pod, and total pod weight of peanuts shall be weighed after operation.

There are two states in the experimental object of the peanut digger-inverter, namely unpressed vines and pressed vines. The unpressed vines refer to the upright peanut growing naturally, while the pressed vines refer to the two ridges of peanut vines falling to the middle of the ridges by artificial or mechanical means to reach the morphology of a trailing peanut. Through the comparison of these two ways of experimenting, it can be seen that the operation effect of the peanut digger-inverter harvester is better under the condition of pressed vines than unpressed vines.
