# Design and Experimental Study of Potato-Soil Separation Device for Sticky Soils Condition
## 1 Introduction  
To cultivate potatoes in winter-fallowed paddy fields of Southern China, the arable land required does not compete with other crops, thereby elevating land use rates and creating vast economic benefits [1]. The winter potato is harvested in the rainy season per year (March-May), and the soils are significantly sticky as compared with other areas, which are attributed to high moisture content in soils [2]. The moisture content in soils significantly impacts the potato harvester performance [3; 4; 5], thereby directly causing the difficulty of mechanically harvesting in Southern China. At this time, the coarse-textured (sand) soils in the North China Plain are currently targeted by most of all marketed potato harvesters, instead of for the wet soil in hilly and mountainous areas of Southern China. For this reason, a potato harvester suitable for operation under wet soil conditions should be developed. The prime targets for potato harvester working consist of soil excavation and potato-soil separation. To meet the mentioned objectives under wet soil conditions, a systemic study on the two critical devices (i.e., digging shovel and separation device) was conducted by predecessors. For digging devices, digging depth and overcoming resistance performance are determined by the shape size and structural form of the shovel. Vibratory [6; 7], bionic [8; 9], curved [10; 11], and other digging shovels are widely studied and applied to sticky soils to achieve resistance reduction, thus reducing the power consumption of thewhole machine. Digging depth is an important indicator, as the digging depth increases, the power consumption increases, the probability of potatoes not being harvested decreases. Due to the reduced soil-to-potato ratio, this makes subsequent soil separation more difficult, but also creates a buffer between the machine and the potato tubers, reducing the rate of potato damage [12; 13]. For the separation device, its design plays a decisive role in the soil separation effect. Numerous research have been done on the innovative design of the separation mechanism, such as swing sieve [14; 15; 16], lifting chain [13; 17; 18; 19], rotating disc [20; 21], and different types of separation mechanisms are suitable for different soil conditions. Under sticky clay soil conditions, the soil adheres to the surface of the mechanism, making it difficult to separate and break. To solve the problem, a rubber roller and auger blade grate cleaning mechanisms mounted below the lifting chain were used to assist in cleaning the soil, and the results showed that the thickness of soil adhering to the chain rods with the cleaning mechanism was much lower than that of the chain rods without the cleaning mechanism, and the separation efficiency was improved [22]. At the same time, clay tends to adhere to the potato surface, so that potatoes are not easily found after harvesting. To improve visible potato rate, a cross rotating agitator was installed at the lifting chain, so that the process of separating the potato-soil mixture is improved [23]; in addition, in order to effectively break the soil, a finger wheel type rubber roller was applied to the back of the digging shovel, which accelerated the breaking of the potato-soil mixture through the rotating strike of the finger [24]. A V-type distributor was also used to directly crush the potato/soil mixture to facilitate separation, and the optimal feeding speed was defined by theoretical calculations [18]. In addition to the structural innovation of the separation mechanism, the structure and operating parameters had been evaluated and optimized by a large number of studies to improve the separation efficiency and reduce damage rate of potato. Regarding the structural parameters, the length [14; 25], shape [17], inclination angle, spacing between chain rods [26; 27] and arrangement of lifting chain directions [28; 29] were considered to have an effect on the separation performance.