*4.4. Design of Root Cutting Device*

The root-cutting device is one of the key components of the cabbage harvester. It works together with the clamping and conveying device. The main function is to cut off the root of the cabbage. The cutting effect has a great influence on the quality and efficiency of the subsequent harvesting operation. As the rhizomes of cabbage are relatively thick and some kinds of rhizomes are severely fibrotic, when a single disc cutter is used, a higher speed is required to reduce the imbalance of cutting force, which will cause considerable power consumption. Therefore, in order to ensure the stability of the force when cutting the root of the head cabbages and avoid incomplete cutting of the root of the head cabbages, this paper adopts the double disc cutting form. The two cutters keep a certain distance in the direction of the center line, and the two cutters should overlap a little to balance the horizontal force on the rhizome of the cabbage during the root-cutting process, so as to ensure the flatness and integrity of the root cutting. See Figure 14.

**Figure 14.** Root cutting device: (**a**) 1: tightening spring; 2: tensioning Wheel; 3: driving motor; 4: transmission shaft; 5: disc cutter; 6: conveyor belt. (**b**) Cutting device physical picture.

As shown in Figure 15, the power of the root-cutting device comes from two servo motors. In the process of root cutting, the roots of cabbage are subjected to cutting forces *F*1, *F*2, and *F*<sup>3</sup> in the *X*, *Y*, and *Z*-directions; *F*1*xy* and *F*3*xy* are the projection components of *F*<sup>1</sup> and *F*<sup>3</sup> in the *XY* plane, respectively; and *F*1*<sup>x</sup>* and *F*1*<sup>y</sup>* are the projection components of *F*1*xy* in the *X*-axis and *Y*-axis, respectively. *F*3*<sup>x</sup>* and *F*3*<sup>y</sup>* are the projection components of *F*3*xy* in the *X*-axis and *Y*-axis, respectively. *β* and *ϕ* are the angles between *F*1*xy* and *F*3*xy* and the *X*-direction, respectively. Because the cutting positions of the left and right cutters are asymmetric, and the two cutters overlap in the axial direction, there is still some cutting force in the *X*-axis and *Z*-axis directions (*F*2). Under the combined action of the forces *F*1*<sup>z</sup>* and *F*3*<sup>z</sup>* in the *Z*-axis direction and the feeding direction and the cutting friction force of the cabbage, the longitudinal component force above the cabbage is larger after receiving, which is helpful to clamp the rhizome of the cabbage [25]. Due to the actual root-cutting process, the vertical plane angle *γ*, which is the angle between the resultant force *F*3*xy* and the force *F*<sup>3</sup> in the *XY* plane, is small; therefore, *F*1*<sup>x</sup>* can be approximated as the root main

cutting force. In addition, considering the actual installation and use, *γ* is set to zero, and only the influence of pitch angle *θ* (the angle between the resultant force *F*1*xy* and the force *F*<sup>1</sup> in the *XY* plane) is considered in order to determine the best cutting parameters.

**Figure 15.** Root cutting force analysis.

As shown in Figure 16, it is assumed that the two disc cutters of the root cutting device are ideal discs, the cabbage is idealized as a round, and the diameter of the rhizome is *D*1.

**Figure 16.** Force on the rootstock of cabbage.

From the force analysis in the diagram, the following equations can be obtained:

$$R\_X = N\_X + F\_X \tag{32}$$

$$T\_Y = F\_Y + N\_Y \tag{33}$$

where *RX* is the root cutting force and *TY* is the clamping force of the cutter on the rhizome. *N* is the normal reaction force of the disc cutter on rhizomes; its horizontal component is *NX* and its vertical component is *NY*, N; *F* is the friction of the circular cutter disc on the friction force of the circular cutter on the root of cabbage; its horizontal component is *FX* and its vertical component is *FY*, N.

In order to make the rhizome be held by the disc cutter, the following conditions must be met [26]:

$$T\_Y > 0\tag{34}$$

It can be deduced that: *FY* > *NY*, where *F* = *N* · *f*, that is:

$$N \cdot f \cos \alpha \gg N \cdot \sin \alpha \tag{35}$$

Therefore, when *f* > *tanα*, the disc cutter has better clamping performance:

$$\alpha = \cos^{-1} \frac{L/2}{(D\_1 + D\_2)/2} = \cos^{-1} \frac{L}{D\_1 + D\_2} \tag{36}$$

where *f* is the friction coefficient between the disc cutter and the rhizome of cabbage; *α* is the angle between the reaction force of the disc cutter on the cabbage rhizome and the *x*-axis, (◦); *L* is the distance between two disc cutters, mm; *D*<sup>1</sup> is the root diameter of the cutting point, mm; and *D*<sup>2</sup> is the diameter of the disc cutter, mm.

The center distance of the designed double disc cutter is 190 mm, the diameter of the disc cutter is 200 mm, the angle *α =* 31.02◦, and the overlap thickness of the two cutters is 5 mm. At this time, *f* > *tanα*, which can meet the requirements of clamping performance.

### *4.5. Design of Data Acquisition System*

By installing torque and pressure sensors on the test platform to collect the speed and displacement of the cabbage in the harvesting system, the motion trajectory and speed–time curve of a single plant during the harvesting process are calibrated and tracked, and the damage to the cabbage after the harvesting operation is recorded and saved in order to find out the results of the movement of the cabbage in the pulling, conveying, and cutting of roots and determine the range of working parameters between different harvesting components.

The system uses the industrial tablet computer to install the INTOUCH HMI configuration software as the human–machine interface, which can ensure that the test bench starts operation according to the set test parameters. The monitoring acquisition system collects the operating data of each moving part, including torque, tension, speed, acceleration, and other data. The data acquisition cycle can be set, and the data chart curve can be automatically generated according to the recorded data.

The instrument panel graphics and text data list can display the following collected data: Left feeding inlet tension, right feeding inlet tension, conveying torque, left cutter torque, right cutter torque, left clamping conveying tension, right clamping conveying tension. Tension pressure data accuracy static: 1‰, tension pressure data dynamic static: 2‰, torque dynamic accuracy 2‰, each data can set the alarm value; if the data exceed the normal range, the system records and sends an alarm prompt. See Figure 17.

**Figure 17.** Data acquisition system: (**a**) test bench working parameters control interface; (**b**) data reports; (**c**) data curves.

According to the data obtained from the data acquisition system and the collection of cabbage in the aggregate box, the structural parameters and working parameters of each harvesting device in the harvesting system are adjusted in real time to reduce the damage rate of cabbage.

#### **5. Single-Factor Test of Low-Loss Harvesting Test Platform**

#### *5.1. Test Object and Equipment*

As shown in Figure 18, cabbage was selected as the test object, and the cabbage variety was "Chun xi". The expansion degree of cabbage is about 450–500 mm, the height of cabbage is about 140 mm, the width of cabbage is about 149 mm, the outer leaves are about 10–12, and the single cabbage quality range is 1.1–1.4 kg. By observing the working state of the pulling device, the reeling device, the clamping and conveying device, and the cutting device of the test platform. According to the characteristics of the cabbage harvested by the above device, the working frequency (0–50 Hz) of the servo motor driven by the above device is adjusted in real time.

**Figure 18.** Operation performance test: (**a**) conveying system of cabbage; (**b**) harvesting system of cabbage.
