Design and Test of Rotary Envelope Combing-Type Tobacco Leaf Harvesting Mechanism

[Objective] China is a big tobacco producer in the world, where tobacco significantly contributes to the national economy. Among all production stages, the leaf harvesting process requires the most labor. Currently, tobacco leaf harvesting in China remains predominantly manual, characterized by low mechanization, high labor demand, a limited harvesting window, and high labor intensity. With the advancement of agricultural modernization, mechanized tobacco leaf harvesting has become increasingly essential. However, existing tobacco harvesters are oversized and cause substantial leaf damage, making them unsuitable for China's conditions. To address this, a rotary envelope combing-type harvesting mechanism is proposed to minimize leaf damage and loss during harvesting. [Methods] A tobacco plant model was developed based on morphological characteristics and assessed the mechanical properties of tobacco leaves using a digital push-pull force gauge to measure tensile and bending characteristics. Force measurements for leaf separation in various directions revealed minimal force requirements when separating leaves from top to bottom. Based on these findings, a rotary envelope comb-type harvesting mechanism was designed, featuring both a transmission mechanism and a picking wheel. During operation, the picking wheel rotates around the tobacco stem, employing inertial combing from top to bottom for efficient leaf separation. Analysis of interactions between the picking mechanism and tobacco leaves identified combing speed as the parameter with greatest impact on picking efficiency. The mechanism's structural parameters affecting the picking wheel's movement trajectory were examined, and an improved particle swarm optimization algorithm was applied using MATLAB to refine these parameters. Additionally, Abaqus finite element simulation software was utilized to optimize the wheel structure's mechanical combing process. Dynamic simulation tests using Adams software modeled the mechanism's process of enveloping the tobacco stem and separating leaves, validating suction efficiency and determining optimal envelope range and speed parameters at various traveling speeds. To evaluate the picking effect and effectiveness of the tobacco leaf picking mechanism designed in this study, a field experiment was conducted in Sanxiang town, Yiyang county, Henan province. The performance of the harvesting mechanism was analyzed based on two critical evaluation criteria: the rate of tobacco leaf damage and the leakage rate. [Results and Discussions] By optimizing the mechanism's structural parameters using MATLAB, horizontal movement was reduced by 50.66%, and the movement trajectory was aligned vertically with the tobacco leaves, significantly reducing the risk of collision during the picking process. Finite element analysis identified the diameter of the picking rod as the key structural parameter influencing picking performance. Following extensive simulations, the optimal picking rod diameter was determined to be 15 mm, offering an ideal balance between structural strength and functional performance. The optimal envelope circle diameter for the mechanism was established at 70 mm. Aluminum alloy was selected as the material for the picking rod due to its lightweight nature, high strength-to-weight ratio, and excellent corrosion resistance. Dynamics analysis further revealed that the combing speed should not exceed 2.5 m/s to minimize leaf damage. The ideal rotational speed range for the picking mechanism was determined to be between 120 and 210 r/min, balancing operational efficiency with leaf preservation. These findings provide crucial guidance for refining the design and enhancing the practical performance of the picking mechanism. Field tests confirmed that the mechanism significantly improved operational performance, achieving a leakage rate below 7% and a damage rate below 10%, meeting the requirements for efficient tobacco picking. It was observed that excessive leaf leakage primarily occurred when leaves were steeply inclined, which hindered effective stem envelopment by the harvesting mechanism. Consequently, the mechanism proved particularly effective for picking centrally positioned leaves, while drooping leaves resulted in higher leakage and damage rates. The primary cause of leaf damage was found to be mechanical contact between the harvesting mechanism and the leaves during operation. Notably, while increasing striking speed reduced leakage, it simultaneously led to a higher damage rate. Compared to the existing harvesting mechanism, this newly developed mechanism is more compact and supports layered leaf picking, making it especially well-suited for integration into small- and medium-sized harvesting machinery. [Conclusions] This study presents an effective and practical solution for tobacco leaf harvesting mechanization, specifically addressing the critical challenges of leaf damage and leakage. The proposed solution not only improves harvesting quality but also features a significantly simplified mechanical structure. By combining innovative technology with optimized design, this approach minimizes impact on delicate leaves, reduces leakage, and ensures higher yields with minimal human intervention. Analysis and testing demonstrate this mechanized solution's potential to significantly reduce production losses, offering both economic and operational benefits for the tobacco industry.