# Design and Experimental Study of Potato-Soil Separation Device for Sticky Soils Condition
## 1 Introduction
There were some studies that showed that a new type of lifting chain under the condition of heavy soil had the best harvesting effect when the length of the lifting chain was 3.1 m, the linear speed of the lifting chain was 1.5 m/s, and the forward speed of the machine was 1.2 m/s [22]; a multi-stage separation buffer potato harvester achieved the visible potato rate of 99.1% by selecting a working speed of 1.05 m/s, a digging depth of 180 mm, and a screen inclination angle of 22\({}^{\circ}\)[27]. Other researchers found that the potato-soil mixture has different motion states on the vibration and wave segments [17]. In terms of operating parameters, numerous studies had revealed the relationship between machine forward speed [4; 13; 14; 16; 21], amplitude and vibration frequency of lifting chain [19], and separation screen operating speed [12; 17] and harvester separation performance. There are mathematical models showed that forward speed of 1.1 m/s, linear speed of transverse conveyor belt of 1.5 m/s, and circular track speed of 7 r/min were the best combination performances for efficient separation [21]. Likewise, the mathematical model based on each influencing factor on the evaluation index was established, and the result showed that the amplitude of 34.1 mm, the vibration frequency of 5.24 Hz, and the operating speed of the separation screen of 2.05 m/s was conducive to potato-soil separation [19]. For potato harvesters with alternating direction, the experiment found that a reasonable combination of machine operation parameters was a forward speed of 1.3 m/s, a separation screen operating speed of 1.2 m/s, and a separating screen inclination angle of 15\({}^{\circ}\)[28]. The material used to make the separation device was thought to be related to the potato-soil separation performance [30], such as the use of rubber sleeves to wrap the paddle fingers on finger-wheel potato harvesters, thus reducing the potato damage rate [24]. At the same time, research methods for potato-soil separation devices are being innovated. Technical means such as high-speed camera [12; 16; 19; 27], discrete element method (DEM) [26], and machine vision-assisted separation [3] had been used in the study of potato-soil separation. From the available studies, the reported potato harvesters are designed for specific conditions in the local area. Combined with research and production experience, there are currently a few models for mechanized harvesting of potatoes in winter idle paddy fields in South of China, so it is necessary to develop corresponding machine models in a targeted manner, and optimize the design of structural parameters. In this study, a new type of potato harvester, aiming at the problem of potato harvest in idle winter paddy field in South China, was developed. Potato-soil separation device (i.e., a soil-crushing mechanism and multi-stage lifting chain) based on the force analysis in the potato-soil separation and transportation and by complying with the characteristics of clay soil was designed to separate potato-soil mixture under combined shearing, bending, and collision. By the kinetic analyses for the potato-soil mixture of five function areas (i.e., shearing, bending, throwing, cleaning, and conveying), the vital factors of the separation effect are determined. Single-factor experiments and orthogonal tests considering both separation effect and potato injury were conducted, and the structure and operating parameters of the separation device were optimized.