**2. Materials and Methods**

#### *2.1. Experiment Influencing Factors and Evaluation Indexes*

During the cutting process, the cutter continues to be subjected to nonlinear force from the plant stalk until the stalk is cut off. The force for cutting plant stalks is the cutting force, which is closely related to cutting energy consumption. Large cutting resistance will inevitably cause greater power consumption in cutting. Therefore, the cutting stress on the cutter is selected as the evaluation index for cutting power consumption and cutting quality [24,25].

The reciprocating cutting system of the cutting machine includes a drive motor, an underdriving gear set, an eccentric wheel mechanism, a blade holder, and a cutting blade [14]. The reciprocating cutting blade is driven by an eccentric cam mechanism to create a reciprocating linear movement with fast cutting frequency and excellent dynamic balance ability while it is working. Its structure is shown in Figure 1.

**Figure 1.** The structure drawing of the reciprocating cutter system: 1—cutter holder; 2—cutter; 3—transmission mechanism; 4—motor.

In order to facilitate the theoretical analysis of the cutting process, it is assumed that the stalk is a homogeneous body, and the cutting blade is always in the same plane during the cutting process, regardless of the vibration during the cutting process. When the cutter first contacts the stalk, the stalk deforms elastically at the contact point. Since the absolute speed change is large at this time, the cutting resistance rises rapidly. There is a positive correlation between cutting feed and cutting resistance before reaching the allowable limit. When this limit is exceeded, the stalk undergoes plastic deformation. The length of the line contact between the blade and the stalk continues to change, and the cutting force presents a fluctuating process. At this time, the force of the stalk on the cutter is mainly horizontal cutting force *Fa*, vertical cutting force *Fp*, and inertial force *Fn*. In addition, *V1* and *V2* are the cutting speeds of the upper and lower blades, respectively, and β is the angle of the blade.

In the *XY* plane, the moving direction of the unit cutting force P is the same as the contact point of the cutting blade and the stalk. The movement path of the contact point is a composite of the lateral movement of the cutting blade and the forward movement of the harvesting machine. The cutting resistance on the cutting blade is the integral of the unit cutting force in the contact length between the cutter and the stalk (Figure 2b).

**Figure 2.** Reciprocating cutter-system cutting force diagram: 1—upper cutting blade; 2—bottom cutting blade; 3—stalk.

Therefore, the sliding friction force at the contact point can be decomposed into the component forces in the *X* and *Y* directions, and the direction is opposite to the relative movement direction [23]. For convenience in the analysis, the cutting resistance force *FR* at the contact point is decomposed into three mutually perpendicular component forces, which are the horizontal force *Fx* along the cutting direction, the horizontal force *Fy* along the feed direction, and the force *Fz* perpendicular to the *XOY* plane, as shown in Figure 2c. Then, the cutting force *FR* is expressed as follows:

$$F\_R = \sqrt{F\_x^2 + F\_y^2 + F\_z^2} \tag{1}$$

In this study, the smaller vertical component *Fz* was ignored, and only the horizontal direction forces *Fx* and *Fy* were considered. To avoid the effect of the cutting force that is changed with the stalk diameter of Chinese little greens, according to previous studies, the maximum cutting stress was taken as the evaluation index of the cutting property, and the cutting stress *σ* was calculated by Equation (2) [6]:

$$
\sigma = \frac{F\_{\text{max}}}{A} \tag{2}
$$

where the *Fmax* is the maximum cutting force in horizontal direction, N; and A is the cross-sectional area of the stalk at the cutting position, mm2.

The factors that affect the shear stress are the structural and movement parameters of the cutter [26–28]. In this study, the three factors, sliding–cutting angle, oblique angle, and average cutting speed, were taken as the factors that affect the cutting mechanical property was analyzed.
