To simulate the interactions between a pneumatic cotton precision seed-metering device and coated delinted cotton seeds accurately, physical and simulation experiments based on a rotating drum apparatus were combined to calibrate the discrete element simulation parameters of E`kangmian-10 cotton seeds. Firstly, the contact parameters and the dynamic repose angle of the cotton seeds were measured through physical tests. Based on the particle size requirement of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) coupling simulation and the reverse engineering technology, the cotton seed discrete element bonded-particle model (BPM) was established. Secondly, taking the contact parameters as calibration objects and the simulated dynamic repose angle as the evaluation index, a Plackett–Burman (PB) test was designed for significance screening. The results of the screening test showed that the static friction coefficient of cotton seed–tough photosensitive resin, the impact recovery coefficient of cotton seed–cotton seed, and the static friction coefficient of cotton seed–cotton seed had a highly significant effect on the simulated dynamic repose angle. Next, a Box–Behnken Design (BBD) test was adopted to establish the quadratic regression model between significant parameters and the simulated dynamic repose angle, and then the multi-factor optimization solution was carried out to obtain the optimal combination of parameters: the static friction coefficient of cotton seed–tough photosensitive resin and the impact recovery coefficient and static friction coefficient of cotton seed–cotton seed were 0.33, 0.06 and 0.10, respectively. Lastly, verification tests on the rotating drum apparatus and the seed-metering device were performed, and their relative errors were less than 2%, which indicated that the discrete element models and the contact parameters of the coated delinted cotton seeds were reliable. This study provides a reference for the selection of the discrete element parameters of coated delinted cotton seeds for DEM-CFD coupling simulation and the optimal design of precision seed-metering device for cotton.

Rotary burying by tractor-hitched rotary tillers is a common practice in southern China for treating rice stubbles. Currently, it is difficult to maintain stable tillage depths due to surface unevenness and the residual stubbles in the field, which leads to unstable tillage quality and nonuniform crop growth in later stages. In this study, an RTK-GNSS was used to measure the real-time height and roll angle of the tractor, and a variable-gain single-neuron PID control algorithm was designed to adjust the coefficients (K_P, K_I, and K_D) and gain K in real-time according to the control effects. An on-board computer sent the angles of the upper swing arm u(t) to an STM32 microcontroller through a CAN bus. Compared with the current angle of the upper swing arm, the microcontroller controlled an electronic-control proportional hydraulic system, so that the height of the rotary tiller could be adjusted to follow the field undulations in real-time. Field experiments showed that when the operation speed of the tractor-rotary tiller system was about 0.61 m/s, the variable-gain single-neuron PID algorithm could effectively improve the stability of the working depth and the stubbles’ burying rate. Compared with a conventional PID controller, the stability coefficient and the stubbles’ burying rate were improved by 5.85% and 4.38%, respectively, and compared with a single-neuron PID controller, the stability coefficient and the stubbles’ burying rate were improved by 4.37% and 3.49%, respectively. This work controlled the working depth of the rotary tiller following the changes in the field surface in real-time and improved the stubbles’ burying rate, which is suitable for the unmanned operation of the rotary burying of stubbles in the future.

In order to solve the problem of the poor seed-cleaning performance of the inside-filling pneumatic cotton precision seed-metering device, a double-sided seed-cleaning mechanism combining a seed-cleaning scraper and seed-disturbing air nozzle was designed which can realize alternate seed cleaning on both sides of the suction hole’s end surface. By constructing a mechanical model of the seed-cleaning process, the influence law of the seed-cleaning mechanism on the critical adsorption performance of cotton seed was clarified, and the key structure and parameters of the seed-cleaning mechanism were decided by combining a theoretical analysis with operational requirements. So as to explore the seed-cleaning performance, some relevant bench tests were carried out, with E’kangmian-10 coated de-linted cotton seeds with a moisture content of 8.92% (wet basis) serving as the test objects; and single seed rate, excessive cleaning rate, and missing cleaning rate were taken for test indicators. First of all, a single-factor comparison test was employed with the shape of the seed-cleaning scraper as the impact factor to choose the optimal one. The results of the comparison test showed that, no matter what shape of seed-cleaning scraper was adopted for the seed-metering device, the missing cleaning rates under the corresponding optimal seed-cleaning effect were greater than 5%, and the sharp scraper gave a better seed-cleaning performance than the flat scraper. Next, combining the sharp seed-cleaning scraper with the seed-disturbing air nozzle to form combined seed-cleaning mechanism of the seed-metering device, the Box–Behnken Design test was executed to explore the influence law about seed-cleaning distance, seed-disturbing distance, and seed-disturbing pressure on the seed-cleaning performance. Then the parameter optimization module was applied to achieve the best combination of operating parameters for the test factors. The test results indicated that the test factors influencing test indicators were in the following order: seed-cleaning distance, seed-disturbing pressure, and seed-disturbing distance. The optimal combination of parameters was a seed-cleaning distance of 3.1 mm, seed-disturbing distance of 6.2 mm, and seed-disturbing pressure of 2165 Pa. Lastly, based on the optimal combination, a verification test of seed-cleaning performance was performed, and the corresponding evaluation indexes were a single seed rate of 98.03%, missing cleaning rate of 1.42%, and excessive cleaning rate of 0.55%. In comparison with the optimal seed-cleaning effects under the single-sided seed-cleaning scrapers of flat and sharp shape, respectively, the combined double-sided seed-cleaning mechanism reduced 3.90 and 3.61 percentage points in missing cleaning rate, reduced 2.02 and 1.17 percentage points in excessive cleaning rate, and increased 5.92 and 4.78 percentage points in single seed rate, thus indicating that the combined double-sided seed-cleaning mechanism can effectively enhance the inside-filling pneumatic precision seed-metering device seed-cleaning performance. This study provides a reference for the design and parameter optimization of the seed-cleaning mechanism of a precision seed-metering device.

In order to solve the problems of poor seed filling performance and the low compensation accuracy of large- and medium-sized missed seeding compensation devices under medium- to high-speed conditions, a pneumatic missed seeding automatic compensation system based on speed synchronization was designed. The key structure and parameters in terms of the seed metering plate and seed feeding arm were determined by theoretical analysis. A universal compensation control system for single-seed missed seeding and continuous missed seeding was designed. With regards to exploring the working performance, some relevant bench tests were carried out, with Zhengdan-958 corn seeds and Zhonghuang-37 soybean seeds serving as the test objects. First of all, a single-factor test was conducted to determine the optimal level ranges of the factors that influence seed filling performance, such as suction hole diameter, seed stirring bar thickness, and negative pressure. The test indicators were qualified seed filling rate, multiple seed filling rate, and missed seed filling rate. Next, the Box–Behnken design test was executed to explore to the influence law of each test indicator on corn seed filling performance. Then, the parameter optimization module was applied to achieve the best combination of operating parameters for the test factors. The optimal combination of parameters was a suction hole diameter of 5.3 mm, seed stirring bar thickness of 2.9 mm, and negative pressure of 4.1 kPa. Based on the optimal combination, a verification test of corn seed filling performance was performed, and the corresponding evaluation indexes were a qualified seed filling rate of 95.46%, multiple seed filling rate of 2.47%, and missed seed filling rate of 2.07%. Lastly, a seed feeding performance verification test was employed with the seeding speed as the impact factor to verify the compensation accuracy of single-seed missed seeding and continuous missed seeding compensation. The results of the verification test indicate that, for corn seeds, when the seeding speed falls within the range of 8 to 12 km/h, the effective single-seed feeding rate exceeds 88%, the average single-seed feeding time is less than 0.18 s, the qualified seed feeding rate is higher than 90%, the multiple seed feeding rate is lower than 3%, and the missed seed feeding rate is below 7%. For soybean seeds, the effective single-seed feeding rate is higher than 85%, the average single-seed feeding time is less than 0.17 s, the qualified seed feeding rate exceeds 86%, the multiple seed feeding rate is less than 4%, and the missed seed feeding rate is below 10%. This system meets the agronomic requirements for the automatic compensation of missed seeding with respect to large- and medium-sized precision seeders, which could help to improve the operational performance of seeding machines.