A combine harvester can be one of the most important links for the potatoes gathering and conveying. However, the current potato combine harvester cannot fully meet the large-scale production in recent years, such as the non-ideal performance of impurity removal, the high rate of potato damage, bruising and impure content in the soil cleaning. In this study, a potato combine harvester was designed with the elastic rubbing technology. The harvesting process was also selected by the "double vibration separation, elastic rubbing type, buffering and loss reducing potatoes gathering and conveying". The main components included the excavation, hydraulic control potato soil separation, elastic rubbing impurity removal, as well as the buffering and reducing losses potatoes gathering and conveying device. A systematic analysis was implemented to clarify the movement track and collision characteristics of potatoes, according the optimal structure of the whole machine, the characteristics of harvesting, and the working principle. A combination of structural parameters were then determined for the key components, in order to fully meet the requirements of efficient separation and impurity removal, as well as the loss reduction and prevention. The whole harvesting process was divided into the three sections of the double vibrating potato soil separation, the elastic rubbing type soil cleaning and impurity removal, as well as the buffer potatoes gathering and conveying. The frequency and amplitude of the vibration were adjusted under the harvest conditions in the double vibration adjustable separation device in time. The rates of the potato damage and bruising were then reduced during the process of the potato and soil separation. The longitudinal non-equidistant soil cleaning and impurity removal device was used to reduce the collision frequency of potato, and then slow down the drop impact response, indicating the higher harvest quality, and the lower impurity content. The buffering and reducing losses potatoes gathering and conveying device was optimized to accurately control the drop height and position of potato at the end of the conveyor belt, in order to effectively avoid the drop damage during potato harvesting. The experiment result showed that the loss rates of the prototype were 1.17% and 1.43%, the potato damage rates were 1.30% and 1.27%, the bruising rates were 1.98% and 1.84% and the productivity values were 0.41 and 0.54 hm²/h, respectively, when the operating velocity values were 3.17 and 4.16 km/h, respectively. All performance indicators were met the requirements of national standards. Once the harvester was operated at a high speed, there was the significant increase in the material flow entering the elastic rubbing impurity removal device in a unit time, indicating the increasing burden of soil cleaning and impurity removal. Among them, part of the soil, seedlings, and vines were remained to mix in the potato cluster, resulting in a high impurity content. By contrast, the low operation speed was greatly contributed to the reduced impurities entering the soil cleaning and impurity removal stage. A better performance was achieved in the removal from the surface soil layer of potatoes in the soil cleaning and impurity removal device. But there was the weak protective effect of the soil on the surface of potatoes, leading to an increase in the frequency of direct contact between potatoes and the soil cleaning and impurity removal wheel. As such, the impurity content was much lower, whereas, there was an increase in the damage and bruising rate of potatoes, compared with the high operation speed. This finding can provide a strong reference for the subsequent research, equipment development, and optimization improvement.

In view of the problems existing in the combined harvest of potatoes in China, such as short harvest period and the traditional mechanical cleaning methods that rely heavily on mechanical excitation for the separation of potato impurities, resulting in low efficiency, high skin breaking rate, and frequent mechanical failures caused by films and vines entanglement, this study proposes a non-contact pneumatic flexible potato cleaning technology. Traditional mechanical cleaning equipment mainly relies on physical contact sorting, which is difficult to handle the residual plastic films and vines during the mechanical harvesting process, intensifying the difficulty of manual cleaning and causing skin damage. Although the remaining films are usually processed by dedicated film recovery machines, long-term weathering can leave broken films in the soil, which are accidentally harvested along with the tubers, thereby intensifying the challenge of separation. Inspired by the wide application of pneumatic cleaning in crops such as rapeseed, corn and soybeans, this study designed a pneumatic vines and residual films removal device for potato machines, which is used after harvest and before storage. The main structure and working principle of the device were introduced in detail. The kinetic analysis of the materials entering the separation chamber and during the throwing process of the vibrating screen was carried out, and the lifting trajectory of the residual films was simulated to determine the key parameters affecting potato skin breakage rate and cleanliness rate. Under the condition of airflow velocity of 35 m/s, CFD simulation was carried out for the flow field at different height sections above the screen surface. CFD-DEM coupling simulation experiments were conducted under the conditions of feeding amount of 20 t/h, airflow velocity of 35 m/s, and vibration frequency of 5 Hz, and the simulation test results of 1.2, 3.8, and 6.0 s were analyzed. The coupling effects of vibration frequency and airflow at different velocity on the material lifting trajectory, stratification efficiency and demolding performance were studied. Taking the cleanliness rate and skin breaking rate as evaluation indicators, the parameter combination was optimized through single-factor and L9 (3⁴) orthogonal tests. Orthogonal experiments show that the primary and secondary factors affecting the cleanliness rate are airflow velocity, vibration frequency and feeding volume in sequence, while the order affecting the skin breaking rate is vibration frequency, feeding volume and airflow velocity in sequence. Under the conditions of a feeding rate of 20 t/h, a vibration frequency of 5 Hz, and an airflow velocity of 35 m/s, the cleanliness rate was 97.2% and the skin breakage rate was 0.98%. These results provide crucial technical support for the development of non-contact pneumatic flexible cleaning technology for potatoes, especially in optimizing the gas-solid two-phase flow dynamics of large irregular agricultural materials while minimizing mechanical damage. Meanwhile, the application of research methods such as CFD airflow and flow field simulation technology in production practice has promoted the application and development of computer measurement and control technology in agricultural mechanization and intelligence.

Potatoes have been widely used as food and vegetable, due to their drought resistance to low soil fertility, high water use efficiency and economic benefits. The potato industry is of great significance to ensuring national food security in poverty alleviation. Efficient and low-loss impurity removal can be one of the most important links in the mechanized harvesting of potatoes. The models and equipment of harvesting can be expected to promote the quality of potatoes. However, the planting and harvesting patterns of potatoes are varied greatly under different natural environments in each region. The various demand is required for the impurity removal, device structure and working principles for mechanized potato harvesting. It is very necessary for the device of seedling film impurity suitable for potato harvesting patterns in different regions. Furthermore, the potatoes often experience bruising or mechanical damage during movements, such as falling, impact, rolling, and friction, in mechanized harvesting. Therefore, the impact damage of potatoes can be expected to be explored during impurity removal. The innovative design and structural optimization of impurity removal devices are also important means to improve the performance of harvesting equipment. A tradeoff can be considered to balance the efficient impurity separation and low-loss harvesting. The research direction of potato impurity removal is how to separate the potato chunks from soil, seedlings, residual film, and debris, according to the harvesting of root and stem crops. This article aims to review the basic structure and technical status of the typical potato harvesters from the perspective of potato planting agronomy. A summary was also given on the membrane impurity treatment of mechanized potato harvesting seedlings, covering the device structure and working principle of potato soil separation, potato seedling separation, residual film recovery, and impurity cleaning. A comparison was then made to evaluate the technical indicators of different impurity removal devices. In response to the plastic film planting and soil viscosity in hilly areas in China, the influencing factors were proposed for potato impurity removal, including uneven development in different planting areas, large differences in mechanization level, difficulty in handling seedling film impurities, significant damage to potato harvest, and the need to improve mechanical technology and manufacturing level. A standardized and unified potato planting system should be established in the same planting area. The planting types were then recommended to reduce the cost of impurity removal in potato harvesting. Much attention can be pained on new technologies, such as sensors, electro-hydraulic control, image processing, machine vision, intelligent measurement and control. New structures and overload protection can be utilized to reduce the loss of the material in the key technologies of impurity removal. Advanced electromechanical, hydraulic and pneumatic technologies can be applied to improve the performance and reliability of products. The intelligent, precise, and information-based agricultural equipment can be focused on the key technical challenges, such as intelligent control, loss reduction, cost saving and high efficiency. New technologies, materials, equipment, and processes can greatly contribute to the mechanized impurity removal in potato harvesting.

High potato damage and peeling rates have been caused by the potato loading and unloading bag device. It is also unclear on the impact damage. In this study, a potato loading and unloading bag device test bench was constructed to reduce and prevent losses. Two aspects were mainly taken to optimize the structure: the potato collection device and the unloading device. A mechanical structure was adopted with the dual buffering of buffer rollers and limiting rollers, in order to reduce the impact damage of potatoes during bagging; Furthermore, two limiting rollers of "gather caching and separate bagging" mode were used to achieve uninterrupted harvesting for the high bagging efficiency; The lifting slide of the bag unloading device adopted the technology of "gradually decreasing with weight" to control the drop height of potatoes during bagging within a specific range, thus avoiding damage that caused by excessive drop height of potatoes. The position of the buffer roller was adjusted to determine the optimal movement trajectory of the potato, and then minimize the damage during potato bagging. The severity of the impact between potatoes and buffer rollers was evaluated to calculate the maximum contact stress. The main parameters of key components were then determined, according to the main structure and working principle of the device. The impact theory was analyzed during potato bagging. The key influencing factors were clarified on the potato skin damage. RecurDyn and EDEM were coupled to simulate the stress situation of potatoes under roller buffering and non-roller buffering states. The maximum collision contact force of potato blocks with roller buffering was reduced to 263.566 N, compared to those without roller buffering. Taking the conveying speed, buffer roller diameter, and feeding amount as the experimental factors, while the potato damage rate and skin breakage rate as evaluation indicators, a three-factor three-level orthogonal experiment was conducted using Box-Behnken neutral combination design function in Design-Expert. Variance analysis was also performed to analyze the impact of the interaction of various experimental factors on the evaluation indicators using the response surface method (RSM). The working parameters were optimized to determine the optimal values of each parameter, according to actual working conditions. A series of experiments were conducted to verify using an electronic potato impact detector. The results showed that the potato damage rate and skin breaking rate were 0.82% and 1.14%, respectively, when the conveying speed was 0.96 m/s, the diameter of the buffer roller was 83mm, and the feeding amount was 26 t/h. The peak impact acceleration was smaller than the critical damage threshold of potato impact acceleration. At the same time, the impact acceleration at the last point was much smaller than the initial one. The relative errors between the measured and the theoretical values after parameter optimization were 4.06% and 0.4%, respectively. The intensity of the potato impact decreased in a manner like wave, where the impact weakened gradually. Therefore, the potato bagging and unloading device achieved the expected goal of potato collecting and reducing loss. Field experiments showed that the potato damage rates were 0.97%, 1.32%, and 1.58%, respectively, and the skin breaking rates were 1.34%, 1.53%, and 1.87%, respectively, when the harvesting speeds were 0.6, 0.8, and 1.0 m/s, respectively. The high performance was all met the national standards.