3.3.3. Layered Impurity-Controlled Cleaning Sieve

There were many stalks in threshed materials of Chinese milk vetch, and the residual materials were mainly glumes, broken stalks and weed seeds. A schematic diagram of the layered impurity-controlled cleaning sieve and the scale sieve's opening is shown in Figure 8, where *y* is the opening of the scale sieve.

**Figure 8.** Schematic diagram of the layered impurity-controlled cleaning sieve and the scale sieve's opening: (1) baffle plate; (2) upper shaking plate; (3) bearing; (4) air deflector; (5) lower shaking plate; (6) round-hole sieve; (7) connecting plate; (8) rubber plate; (9) front finger sieve; (10) back finger sieve; (11) scale sieve; (12) saw-teeth sieve.

It was mainly composed of the baffle plate, upper shaking plate, lower shaking plate, air deflector, front finger sieve, back finger sieve, scale sieve, saw-teeth sieve and roundhole sieve. The front and back finger sieves separated the long stalks and residual spikes from the threshed materials under the sieve, the scale sieve was designed as a parallel four-bar linkage structure and the opening of the scale sieve was ranged between 35 mm and 45 mm, which could guide the air flow to blow away glume shell, residual spikes and broken straws, so as to ensure the high-efficiency screening of Chinese milk vetch

seeds. The round-hole sieve could further separate the Chinese milk vetch seeds from the mixture of grains and thin stems that were dropped from the scale sieve surface, while the saw-teeth sieve, mounted on the rear of the cleaning sieve, could discharge remaining long straws, residual spikes and broken straws out of the machine backward step by step or multistage. Structural parameters of the layered impurity-controlled cleaning sieve are shown in Table 3.

**Table 3.** Structural parameters of the layered impurity-controlled cleaning sieve.


#### **4. Field Experiment and Result Analysis**

#### *4.1. Experiment Conditions*

The field harvest experiment of Chinese milk vetch was conducted in Yijiang Town, Nanling County, Wuhu City, as shown in Figure 9. The experiment time was from 11–13 May 2020. The Chinese milk vetch variety used for the experiment was Wanzi No. 4, and its yield was 608.95 kg·hm−2. The average height of Chinese milk vetch stems was 330.8 mm, the average height of the bottom pod was 118.5 mm, the average black pod rate was 80.68%, the natural seed loss was 3.31 g·m−<sup>2</sup> and one thousand seed weight was 3.3~3.5 g. The moisture content of harvested seeds was measured by a PM-8188-A moisture meter, and the moisture meter measurements ranged from 1% to 40%. The sample capacity was 240 mL, the temperature range was 0~40 ◦C, the measurement accuracy was 0.5% at the basis of the drying method and the water content of harvested seeds was measured three times, with an average value of 10.2%. The Chinese milk vetch plants grew well, and the average length and width of pods picked from 10 different Chinese milk vetch plants were 25.3 mm and 4.2 mm, respectively. The seeds in pods were kidney shaped, and about 3 mm in length.

**Figure 9.** Combined Chinese milk vetch seed harvester and field test process. (**a**) Three-dimensional diagram of the combined Chinese milk vetch seed harvester. (**b**) Chinese milk vetch field harvest test. (**c**) Materials in the seed bin.

#### *4.2. Experiment Indexes*

At present, there is no evaluation standard for the operation of the Chinese milk vetch seed combine harvester. In order to investigate the operation quality of the Chinese milk vetch seed combine harvester, according to leguminosae or cruciferae green manure seed harvest standards such as JB/T 11912-2014, GB/T 5262-2008 and so on, seed loss rate, breakage rate and impurity rate are used as the evaluation indexes for the operation performance of the Chinese milk vetch seed combine harvester. Among them, the machineharvested seed loss rate is determined by collecting all the seeds and pods, both those fallen in the sampling area and discharged out of the machine with Chinese milk vetch stems, and then removing the natural falling seeds. According to the quantity of harvested Chinese milk vetch seeds and the corresponding harvested area, the yield of Chinese milk vetch seeds per square meter is obtained. Impurities include long and short stalks, grass seeds, pebbles, etc. The broken seeds are incomplete cotyledons (including whole and half seeds), and transverse and broken grains. The specific calculation methods are shown in Equations (2)–(4):

$$Y\_1 = \frac{M\_{hl}}{M\_{h\text{hr}} + M\_{hl}} \times 100\% \tag{2}$$

$$Y\_2 = \frac{M\_{ci} - M\_{ps}}{M\_{ci}} \times 100\% \tag{3}$$

$$Y\_3 = \frac{M\_{ss} - M\_{ps}}{M\_{ss}} \times 100\% \tag{4}$$

where, *Y*<sup>1</sup> is the loss rate, %; *Y*<sup>2</sup> is the breakage rate, %; *Y*<sup>3</sup> is the impurity rate, %; *Mhl* is the seed loss quantity during harvest of Chinese milk vetch per square meter, g·m−2; *Mha* is the harvested seed quantity of Chinese milk vetch per square meter, g·m−2; *Mei* is the sample quality after removal of impurities, g; *Mps* is the sample quality after removal of impurities and broken seeds, g; *Mss* is the sample quality, g.
