Hu Xie

Due to the lack of effective numerical simulation and the absence of an accurate and reliable bonded discrete element model for tobacco stalks during mechanised harvesting, the design and optimisation of tobacco stalk pulling and harvesting equipment have been largely hindered. In this study, post-harvest stalks of flue-cured tobacco transplanted in single-ridge cultivation were taken as the research object; Zhongchuan 208 stalk samples with an average outer diameter of 36.78 ± 1.05 mm and an average moisture content of 82.5% were selected, their intrinsic and contact parameters were measured, and a mechanical simulation model of the stalks was established based on the Bonding V2 contact model. With the maximum crushing force (F_C) as the response value, Plackett–Burman tests were first used to screen significant factors, the steepest ascent tests were then employed to determine the optimal region of the significant factors, and finally a second-order regression model between the maximum crushing force and the significant parameters was established using central composite design, yielding the optimal parameter combination: normal stiffness per unit area of 5.498 × 10⁹ N·m⁻³, tangential stiffness per unit area of 1.434 × 10⁹ N·m⁻³, critical tangential stress of 9.146 × 10⁶ Pa, and bonding radius of 1.304 mm. Under this parameter combination, compression and bending simulation tests were carried out; five independent repeated simulations gave an average maximum crushing force of 2410.22 N, a standard deviation of 225.39 N, and a coefficient of variation of 9.35%, with a relative error of 4.32% against the physical test mean; the relative errors of the peak displacement and the maximum bending force were 2.62% and 4.74%, respectively. In the physical control tests with and without epidermis, the relative error between the mean maximum bending forces of the two groups was 8.68%. The results indicate that the discrete element model established in this study can effectively characterise the macroscopic peak load-bearing response of tobacco stalks under the tested conditions and can provide data support for the design and parameter optimisation of stalk pulling equipment.

The V-shaped toothed roller cotton stalk puller has a low removal ratio and weak pulling effect. Hence, we constructed a simplified mathematical model of the V-shaped tooth roller stalk puller based on elastic collision theory and simple beam theory and conducted a mechanical analysis based on this model to explore the causes of pulling errors and fractures. Specifically, the V-shaped tooth plates of the machine were optimized in an orthogonal experiment with the rotational speed, cogging angle, and ground clearance as the influencing factors, and the removal ratio as the evaluation index. This experiment was designed to enable analysis of the physical characteristics of cotton stalks, and the forces applied during the pulling process. Additionally, a V-shaped toothed roller-type stalk-pulling test bench was constructed. The results revealed that, unlike the cogging angle, the ground clearance significantly affected the removal ratio. Furthermore, the highest removal ratio (i.e., 97%) was achieved when the ground clearance was −20 mm, the rotational speed was 300 rpm, and the cogging angle was 32.5°. An L₉ (3⁴) orthogonal field experiment was also conducted with the rotational speed, cogging angle, and ground clearance as the influencing factors to investigate their respective influences on the stalk removal ratio. The results revealed that the ground clearance most significantly influenced the ratio, followed by the rotational speed, and cogging angle. The ground clearance and rotational speed of the V-shaped toothed roller were each found to significantly influence the ratio. Furthermore, a ground clearance of −20 mm, rotational speed of 300 r/min, and cogging angle of 25° yielded an average removal ratio of 98.27%. Through this research, the mechanism of toothed roller stalk pulling is further deepened and the toothed series stalk pulling technology provides theoretical support.