# Design and Experimental Study of Potato-Soil Separation Device for Sticky Soils Condition
## 4 Separation Device Performance Test
### Orthogonal Test  
#### 4.4.1 Test Method  
Given the kinetic analysis of five functional areas of potato-soil separation device as presented above, the moisture content of potato-soil mixture, the rotational speed of the soil-crushing mechanism, the inclination angle of lifting chain, and the linear velocity of second-stage lifting chain were adopted as the test factors. Specific instructions are presented below:  
* The moisture content of potato-soil mixture. In this study, to harvest winter potatoes in idle paddy fields of Southern China, a potato-soil separation device was developed. The main reason for affecting harvesting quality was soil exhibiting a high water capacity in idle paddy fields. Thus, to examine the effect of the different moisture content on the separation effect of potato-soil separation device, the potato-soil mixture involving three different moisture contents (i.e., 18%, 23%, and 28%) was prepared as described in Section 4.1. for the separation test.
* The rotational speed of the soil-crushing mechanism. The rotational speed of the soil-crushing mechanism impacted the soil-crushing quality and the damage degree, as determined by the kinetic analysis of potato-soil mixture in the shearing area. The rotational speed of the soil-crushing mechanism was adopted as one of the orthogonal test factors to identify optimal running parameters of the soil-crushing mechanism. During the trial, three levels of the rotation speed of the soil-crushing mechanism were set to 70 r/min, 122 r/min, and 175 r/min, respectively. The linear velocity at  
Figure 11: The statistical comparison of the respective assessment index in different scenarios. (**a**) Percentage of small soil; (**b**) percentage of soil that adhered to potato tubers; (**c**) damage rate of potato tuber.  
the tip of the soil-crushing roller tooth was equated with that of the first-stage lifting chain at the rotation speed of the soil-crushing mechanism as 70 r/ min.
* The inclination angle of lifting chain. The inclination angle of the first-stage lifting chain set in this separation device was equated with that of the second-stage lifting chain. Given the kinetic analysis, as previously described, the inclination angle of the lifting chain had effects on the force and motion state of potato-soil mixture in the shearing area, the bending area, the throwing area, and the conveying area to identify the optimal inclination angle of lifting chain, that was employed as one of the orthogonal test factors. During the trial, three levels of the inclination angle of lifting chain were set to 15\({}^{\circ}\), 20\({}^{\circ}\), and 25\({}^{\circ}\), respectively.
* The linear velocity of second-stage lifting chain. The linear velocity of second-stage lifting chain impacted the force and motion state of potato-soil mixture, as determined by the kinetic analysis of potato-soil mixture in the conveying area. To identify optimal linear velocity of second-stage lifting chain, that acted as one of the orthogonal test factors. During the trial, three levels of the linear velocity of the second-stage lifting chain were set to 0.75 m/s, 0.99 m/s, and 1.23 m/s, respectively.  
As described in Section 4.2, the percentage of small soil \(\lambda\), percentage of soil adhered to potato tuber \(\gamma\), and damage rate of potato tuber \(K\) still were taken as evaluation indexes in this orthogonal test. The L\({}_{3}\)4 orthogonal table was used to arrange the experiment, and the orthogonal test scheme was given in Table 2 below.