**1. Introduction**

Chinese little greens, whose scientific name is non-heading cabbage, are rich in nutrients and are one of the important vegetable varieties in China. With a large planting density and a short growth cycle, Chinese little greens can be harvested 18–25 days after sowing [1]. However, at present, the harvest of Chinese little greens is still completed manually with low harvesting efficiency and high work intensity. Mechanized harvesting operation is the key to solving this problem.

The stress–strain process for cutting failure of the plant stalk fiber layer can be divided into three stages: elastic deformation, plastic deformation, and shear failure. First, the cutter presses the stalk to bend and deform elastically. Then, the cutter continues to bend the stalk to produce plastic deformation and the fiber tensile stress continues to increase. Then, the fibers near the blade break off and eventually fail. Eventually, the entire fiber

**Citation:** Wang, W.; Lv, X.; Yi, Z. Parameter Optimization of Reciprocating Cutter for Chinese Little Greens Based on Finite Element Simulation and Experiment. *Agriculture* **2022**, *12*, 2131. https://doi.org/10.3390/ agriculture12122131

Academic Editor: Wen-Hao Su

Received: 18 October 2022 Accepted: 6 December 2022 Published: 12 December 2022

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layer slips and breaks, causing shear damage to the entire stalk [2]. Studies have found that the mechanical properties during cutting of crop stalks are closely related to the working parameters of the cutting device [3,4].

Relevant scholars studied cutting characteristics using the quasi-static experimental method [5]. Cui et al. [6] designed a shear fixture on a universal materials tester, and selected the blade distance, sliding–cutting angle, skew cutting angle, and shearing angle as test factors to study the shearing characteristics of lettuce stems, and obtained the best cutting combination parameters. Zhang et al. [7] also reported similar results in a shear stress test of a single rice stem, in which the peak cutting force decreased with the sliding–cutting angle. Esgici et al. [8] used a material testing machine to study the influence of grapevine diameter and age on the cutting force, and found that the cutting force was proportional to the vine diameter and age. Du et al. [9] established a mechanical model of the cabbage cutting process, and studied the influence of sliding–cutting angle and cutting speed on fracture, and verified and analyzed it through experimental data. In a study of cutting red bean stalks, the shear stress generated by the 28◦ bevel angle was smaller than that generated by the 0◦ bevel [10]. Clementson and Hansen [11] showed that the cutting force of the machete is smaller than that of the chopper in sugarcane harvesting. However, the quasi-static experimental method cannot fully reflect the cutting characteristics of crop stalks, and the influence factors such as the motion parameters of the cutting blade are ignored.

To simulate the actual operation mode of the cutting process, scholars have analyzed the effect of cutting and feeding speed on the cutting characteristics by developing a stalkcutting test bench [12–14]. Johnson et al. [15] conducted an in-depth study on the cutting energy of the cutting tool under different working parameters and found that the cutting energy of miscanthus stalk was proportional to the cutting speed. Mathanker et al. [16] used the same equipment to evaluate the effect of cutting speed and blade bevel on cutting energy, and found that the specific cutting energy increased with the increasing cutting speed. The research of Allameh and Alizadeh found that the cutting speed of the shear parts had a significant impact on cutting energy. When the cutting speed increased from 1.5 to 2.5 m/s, the cutting energy grew by 77%. At the same time, the interaction between the cutting angle and the bevel angle had a significant impact on the cutting energy [17]. Zhao et al. [18] selected the blade angle, blade shape, cutting speed, and cutting angle as the test factors and studied the effects of working parameters on power consumption by means of mathematical statistics on a self-designed testing system, and obtained the optimal parameter combination for cutting performance of maize stalks under no-support cutting status.

In general, the cutting process of plant stalks belongs to the category of typical highspeed collision and penetration. The contact process between the cutting blade and the stalk forms a randomly nonlinear interaction relationship; hence, it is difficult for traditional physical methods to analyze the cutting mechanism between them. At present, numerical simulation technology has become one of the important tools for solving engineering practice problems [19]. The dynamic simulation analysis can efficiently simulate the nonlinear dynamic contact conditions in stalk cutting, and visualize the force and deformation conditions during the cutting process. Meng et al. [20] established a simulation model and studied the influence of working conditions of the circular cutter to determine the best cutting parameters. Yang et al. [21] established an analytical three-dimensional model of the cutting system by using the ANSYS/LS-DYNA software f, and provided a reference for the optimization of the cutter's parameters and the cutting method. Huang et al. [22] studied the dynamic characteristics of the reciprocating cutting system, and evaluated the dynamic response of the cutting system by factors such as cutting speed and inclination angle by numerical simulation and cutting experiments. Qiu et al. [23] found that numerical simulation technology could accurately simulate the cutting process of sugarcane stalks, and analyzed the influence of external and internal factors in the cutting process on the cutting quality, and finally determined the best working parameters based on the simulation

results and orthogonal experiments. In summary, although most of the existing studies on numerical simulation of the cutting process of plant stems are focused on the cutting method of a circular saw blade, it shows that using computer technology can effectively solve stem-cutting problems.

Research on crop stalk-cutting devices has matured, but related research is mainly concentrated on sugarcane, hemp, miscanthus, and other crops. Therefore, it is necessary to study the structural and working parameters of the cutting devices that specially match with the mechanized harvesting of Chinese little greens.
