# Design and Experimental Study of Potato-Soil Separation Device for Sticky Soils Condition
## 4 Separation Device Performance Test
### Orthogonal Test
#### 4.4.2 Analysis of Orthogonal Test Results
The results of ANOVA indicated that the effect of potato-soil separation was largely impacted by moisture content, and the higher the moisture content, the lower the shattering degree would be; the more the soil adhered to the potato tuber, the lower the cleaning degree of the tuber would be. This was because moisture increased the soil stickiness and improved the difficulty degree of crushing and cleaning. The degree of potato damage was primarily impacted by the structure and run parameters of the potato harvester as impacted by the collision of the machined parts. The linear velocity of the second-stage lifting chain for mechanical parameters exerted the most prominent effect on the damage rate of potato tuber. This was because most of the soil was separated and sieved, and a buffer effect on potatoes decreased or even disappeared when the potatoes were transported to the second-stage lifting chain. Regression Model  
The 3 levels of the respective factor were expressed by \(-1\), 0, and 1, respectively, to study the significance of the effect of each factor on the assessment index and anticipate the outcome of test, and multiple linear regression models were built. For percentage of small soil \(\lambda\), the regression equations were yielded as:  
\[\lambda=79.4744-11.6317A-2.925B+1.175C+2.98D \tag{19}\]  
N = 9, R = 0.86333, F = 2.92677, S = 8.8873  
For the percentage of soil adhering to potato tuber \(\gamma\), the regression equations were obtained as follows:  
\[\gamma=0.2911+0.1917A-0.0833B+0.145C+0.0683D \tag{20}\]  
N = 9, R = 0.9, F = 4.26316, S = 0.15624  
For the damage rate of potato tuber \(K\), the regression equations were obtained as follows:  
\[K=6.9667-0.28A+0.58B+1.725C+1.235D \tag{21}\]  
N = 9, R = 0.7752, F = 1.50581, S = 2.21284  
Parameter Optimization and Field Verification  
To determine an optimal designing parameter of potato-soil separation device, the multi-objective programming of regression equation as described above was performed. By complying with the practical situation, the constraints \(K\leq 4\%\) for damage rate of potato tuber and \(\lambda\geq 90\%\) for a percentage of small soil were determined. The minimum was then obtained through programming by setting the percentage of soil adhering to potato tuber as the programming objective. The programming constraints are presented in Equation (22). \[\left\{ \begin{array}{c}-1\leq A\leq 1\\ -1\leq B\leq 1\\ -1\leq C\leq 1\\ -1\leq D\leq 1\\ 6.9667-0.28A+0.58B+1.725C+1.235D\leq 4\\ 79.4744-11.6317A-2.925B+1.175C+2.98D\geq 90\end{array} \right. \tag{22}\]  
The result of programming shows that the minimum value that meets all the constraints was obtained when A = \(-1\), B = \(-0.865\), C = \(-1\), D = \(-0.8259\). Accordingly, the best lever combination was moisture content of 18%; the rotational speed of the soil-crushing mechanism of 84.18 r/min; linear velocity of second-stage lifting chain of 0.75 m/s; and inclination angle of lifting chain of 15.87\({}^{\circ}\). To demonstrate the validity of the optimization parameters, the potato-soil separation device of the harvester was modified under the optimal lever combination as described above and a field harvesting test was performed in Changsha, Hunan. The moisture content of soil in the field was measured to be 20.06% during the test. The visible potato rate and damage rate of potatoes acted as the assessment indexes based on the method of the China National Standard NY/T 648-2015. An outcome trial was presented for visible potato rate of 94.31% and damage rate of potato of 0.89%. As the national standard requires that the damage rate of potato is less than 1.5%, the performance met the requirement, which illustrated the effectiveness of machine parameter optimization. The modified prototype and the harvesting effect are illustrated separately in Figure 13.