Design and Key Technologies for an Integrated Square Bale Straw Baling and Net-Wrapping Mechanism

Abstract

China boasts abundant straw resources but grapples with notable challenges in straw processing: returning straw to fields can lead to soil compaction and aggravated pests/diseases, while baled straw for off-field storage and transportation tends to scatter. Additionally, domestic netting technology for square bales remains underdeveloped, and imported equipment is ill-suited for small-scale farmers. To tackle these issues, this study developed an integrated straw baling and netting machine by modifying the 9YFSG-2.2 square straw baler. It integrates a conveying mechanism, an offset crank–connecting rod compression mechanism (300 mm crank, 885 mm connecting rod), a two-stage gear-driven net-wrapping mechanism (with hollowed-out large gears for weight reduction), and a sensor-controlled net-cutting device, forming a complete workflow of “straw pick-up–shredding–conveying–compaction–net wrapping–net cutting”. Via coupled simulation using RecurDyn 2019, EDEM 2020, and ANSYS Workbench 2018, straw particles were modeled as 28-mm-long segments (composed of three 7 mm spheres). Simulations showed straw compaction in 0.48 s, with the compression chamber and plate having equivalent stresses of 0.2767 MPa and 173.44 MPa and maximum deformations of 0.0012 mm and 0.66 mm—both well below structural steel’s yield strength. Field tests in Xinxiang, Henan (straw moisture 30.03%), yielded results exceeding standards: 99.4% bale formation rate, 96% regular bale rate, 93% drop resistance rate, 170 kg/m³ bale density, and 12 s per bale efficiency. Controlling netting time further boosted efficiency and reduced consumption, successfully realizing integrated straw baling and netting.

1. Introduction

As a major agricultural country, China boasts substantial straw resources. In 2021, the national recoverable straw volume reached 734 million tonnes, achieving a comprehensive utilization rate of 88.1% [1]. Nevertheless, straw management persists as a prominent challenge in grain production. Straw incorporation into fields often results in soil compaction and aggravated pest and disease issues. While off-field collection via balers facilitates shredding, compression, and collection, straw bales are susceptible to disintegration during storage and transportation. This not only causes environmental pollution but also impairs bale quality [2].

Baling technology has undergone sustained advancement in recent years, particularly in bale forming, key component design, wrapping, and system integration [3,4,5]. Studies and reports have shown that foreign manufacturers have continuously improved the reliability, automation level, and operational efficiency of square balers and baler–wrapper systems [6,7,8,9]. In addition, integrated baling and wrapping technology has gradually matured abroad, whereas baler research in China started relatively late and mainly developed through technology introduction, adaptation, and localized improvement [10,11,12]. In recent years, domestic enterprises have launched regionally adaptable baling equipment, but existing net-wrapping devices are still mainly used for round bales or small-scale applications, and some operating procedures still require manual assistance, resulting in relatively low efficiency and high labor intensity [13,14,15]. In contrast, foreign integrated equipment is predominantly large-scale and high-cost, making it less suitable for China’s smallholder farming model.

Although square bales are more convenient than round bales for storage and transportation, dedicated net-wrapping technology for square straw bales remains insufficiently developed, especially under the operating conditions of small- and medium-scale farming in China. Existing domestic equipment is mainly designed for round bales and often requires manual assistance, whereas imported integrated equipment is generally large-scale, expensive, and poorly adapted to local field conditions. Therefore, the aim of this study was to develop and evaluate an integrated square bale straw baling and net-wrapping machine based on a modified 9YFSG-2.2 baler (Xinxiang Huaxi Technology Co., Ltd., Xinxiang, China). The main innovations of this study include: (1) the integration of baling, bale discharge, net wrapping, net cutting, and counting into a continuous workflow; (2) the design of an offset crank–connecting rod compression mechanism and a gear-driven net-wrapping mechanism for square bales; and (3) the combined use of Recurdyn–EDEM–ANSYS coupled simulation and field experiments to verify the structural feasibility and operational performance of the proposed machine.

2. Overall Design of Square Straw Bale Baler with Integrated Net-Wrapping Mechanism

2.1. Design Basis and Overall Scheme Design

To address the issue that baled straw is susceptible to environmental factors during storage and transportation, which may lead to debris shedding or even complete scattering—thereby hampering storage and transportation operations while adversely affecting the surrounding environment and safety—this study designed and developed a combined straw baling and netting machine based on the existing straw baling machinery technology and the 9YFSG-2.2 square straw baler.

As illustrated in Figure 1, the integrated machine operated through a continuous workflow consisting of straw pick-up, straw shredding, straw conveying, straw compaction, bale discharge, net wrapping, and net cutting. The material flow direction and process transitions are indicated by arrows to clearly show the continuity of the integrated operation. In this study, the main focus was placed on the compression of chopped straw and the subsequent net-wrapping process during bale discharge.

Figure 2 presents the sensor-triggered sequence of the net-wrapping process during bale discharge. After bale formation, the discharged straw bale moved rearward and sequentially contacted Sensors 1–4. Sensor 1 started the motor and triggered timing; Sensor 2 stopped timing and enabled the calculation of bale discharge speed; Sensor 3 triggered the additional net wrapping and subsequent net cutting; and Sensor 4 completed bale counting and system reset. This sequence clarified both the functional relationship of the four sensors and the chronological order of the control process.

2.2. Overall Structural Design

The 9YFSG-2.2 straw square baler was primarily composed of a drawbar frame, cutting and shredding assembly, floating system, screw conveyor, feed mechanism, piston, compression chamber, knotting mechanism, density-adjusting device, and transmission system, as illustrated in Figure 3.

The primary operating parameters of the original 9YFSG-2.2 straw square baler are listed in

Table 1. Main operating parameters of 9YFSG-2.2 straw square baler.

Serial Number	Project	Design Value
1	Model Designation	/	9YFSG-2.2 Straw Square Bale Press
2	Hooking method	/	Towed
3	Operating dimensions (length × width × height)	mm	6520 × 2680 × 1730
4	Pick-up width	mm	2200
5	Spin-off roller rotational speed	min−1	2160
6	Number of knives thrown	group	22
7	Height of blade clearance from ground	mm	50
8	Number of feed forks	one	5
9	Reciprocating strokes of the baling piston	min−1	90–100
10	Piston stroke length	mm	550
11	Main shaft rotational speed of the baling mechanism	min−1	100
12	Screw conveyor diameter	mm	320
13	Screw conveyor rotational speed	min−1	313
14	Cable tie box capacity	volume	10

. These parameters were used as the basis of the prototype modification, whereas some structural parameters of the redesigned integrated baling and net-wrapping mechanism were further optimized in the present study.

This machine was configured to be towed by a tractor with a traction power of 58.8 kW or above and operated with a power take-off (PTO) shaft speed of 720 min⁻¹, a travel speed of 4–10 km/h, and a net working hourly productivity of 3000–10,000 kg/h [14]. During operation, power is transmitted to the working components through the drive shaft, gearbox, friction clutch, flywheel, and chain-belt transmission assembly.

In field operations, as the machine moves forward, the rotating blades mounted on the cutting and shredding roller interact with the stationary blades fixed to the housing. This interaction initiates the cutting and shredding of surface straw; the front roller then propels the material toward the rear roller, which further shreds and pulls the straw into strands. After undergoing cutting and node breaking, the straw is directly discharged from the cutting and shredding rollers onto the spiral conveyor auger—eliminating the need for additional shredding and fiber separation by the rear roller.

The processed straw is thus directly conveyed to the symmetrically arranged spiral augers, which push the material from both sides toward the baling chamber inlet. A feed fork then guides the accumulated material upward into the compression chamber [15]. Under the reciprocating motion of the piston, the material is gradually compacted inside the compression chamber. When the bale length reaches the preset dimension, the clutch of the baling mechanism engages. The baling mechanism then starts operating, triggering the knotter to fasten the two bale ties encircling the material into a secure knot. The tied bale is subsequently pushed gradually toward the baling chamber outlet by the continuous incoming material flow.

Based on this foundation, the present study focused on the design and research of the subsequent netting mechanism for the 9YFSG-2.2 straw square baler. After being pushed to the outlet of the compression chamber, the straw bale continued to move rearward along the direction guided by the push plate, and the subsequent netting operation was triggered and regulated by four contact sensors.

The overall structure of the baling and netting mechanism was mainly composed of the baling chamber, feeding and compaction mechanism, netting device, net-cutting device, netting counting mechanism, and transmission system. The complete configuration of this baling and netting mechanism is illustrated in Figure 4.

The feeding and compaction mechanism consisted of an auger, feeding fork, crank, connecting rod, and compaction piston. The net-wrapping assembly was composed of a large gear, small gear, net roller, bearings, drive shaft, wire mesh, and bolts/nuts. The sensor-counting device comprised four sensors and a connecting frame, while the net-cutting mechanism was made up of a cutter shaft, cutter holder, net hook, and connecting rod.

The feeding and compaction mechanism was located at the front end of the baling chamber: the auger and feeding fork conveyed the chopped straw into the chamber, and the crank–connecting rod mechanism drove the compaction piston to compress the chopped straw into bales through reciprocating motion. Meanwhile, the netting device was arranged at the rear end of the baling chamber; the motor drove the large netting gear disk to rotate via a geared transmission system, thereby realizing the net-wrapping operation. The sensors and connecting frames were integrated with the main frame through welding and mechanical fastening methods.

2.3. Structural Components

2.3.1. Conveying Mechanism

Before the chopped straw was compressed, it first needed to be fed into the baling chamber. This feeding process adopted a screw conveying mechanism and a roller conveying mechanism to convey the straw collected by the pick-up device from one side of the conveying system. The conveying auger conveyed the straw horizontally to the position where the feeding fork was located. The feeding inlet of the screw conveyor was fixedly connected to the baling chamber; the feeding fork lifted the straw upwards, and the lifted straw was subsequently compressed by the compaction piston. As illustrated in Figure 5, the screw conveyor was composed of a conveying auger, feeding inlet, feeding fork, feeding rod, and frame housing.

2.3.2. Design of the Compression Mechanism

The baling chamber was responsible for compacting and shaping the fed loose straw into bales. It comprised a rectangular cavity welded from steel plates, with an internal compaction piston connected to a crank–connecting rod mechanism. Seven rollers mounted on the piston engaged with five guide rails inside the chamber, ensuring that the piston performed directional reciprocating motion. The moving and stationary blades located at the front end of the piston and the bottom of the baling chamber were manufactured from 65Mn steel, with a hardness range of HRC 54–59. The moving blade had a thickness of 10 mm, while the stationary blade was 8 mm thick, and the two worked in tandem to cut the straw. Straw deflectors installed on the side plates and the knotter base plate prevented material rebound during the piston’s return stroke, while the protruding section of the baling chamber further compacted the straw bale. The baling chamber dimensions were set to 700 × 380 × 330 mm, with a wall thickness of 5 mm. The value of 700 mm referred to the chamber length in the bale movement direction rather than the nominal piston stroke. The reciprocating frequency of the compression piston was set to 100 min⁻¹, as illustrated in Figure 6.

Based on the design specifications, straw was chosen as the test material. When the moisture content is within the normal range, the bale density of straw and hay bales is measured. After conducting density tests on straw and hay bales using a square baler under standard operating conditions, the following trend was observed:

$$\mathrm{p}=0.98{\rho }^{2.32}$$

(1)

In the formula: p—compactor pressure per unit area (Pa);

$\rho$—weight per unit volume of hay (kg/m³);

To convert the weight per unit volume y after compaction into parameters for the crank–connecting rod mechanism, based on the operational changes of the plunger during the compaction process, the following expressions for the compactor compression force P, crank arm tangential torque T, and crank torque M can be derived:

$$\mathrm{P}=0.98\mathrm{F}{\left\{{\displaystyle \frac{\mathrm{G}}{1-\left(\cos \alpha -\frac{\mathrm{r}}{2\mathrm{l}}{\mathrm{s}\mathrm{i}\mathrm{n}}^2\alpha \right)}}\right\}}^{2.32}$$

(2)

$$\mathrm{T}=\mathrm{P}{\displaystyle \frac{\sin \left(\alpha +\beta \right)}{\cos \beta }}$$

$$\mathrm{M}=\mathrm{T}\mathrm{r}$$

In the formula: P—Compactor compression force (N);

T—Crank tangential force (N);

M—Crank torque (N·m);

G—The weight of hay compressed during a single compaction cycle;

F—Compaction unit working area (m²);

α—Crank angle during hay compression by the compactor;

r—crank radius (m);

l—Connecting rod length (m);

β—Corresponding connecting rod angle when the compactor compresses hay.

The optimal straw-feeding rate for the compactor of the 9YFSG-2.2 square baler was 1.5 kg/s. Substituting this value into the formula for the mass of straw compacted in a single pass enables the calculation of the actual compression force. A comparative analysis of concentric and offset crank-slider mechanisms revealed that the offset design offered distinct advantages, including a longer slider stroke and a rapid return characteristic—this enhanced the return stroke speed, shortened the cycle time, and improved compression efficiency. Accordingly, an offset crank–connecting rod mechanism was adopted in this design.

Based on the design parameters of most domestic compression mechanisms, the vertical distance between the output shaft center of the reduction gearbox and the piston’s plane of movement was set to 60 mm. According to the original machine specifications, the nominal piston stroke of the 9YFSG-2.2 baler was 550 mm. In the present study, however, the compression mechanism was redesigned using an offset crank–connecting rod configuration. Considering that the feed inlet length was 450 mm, the effective design stroke of the piston was required to exceed this value by 25–35% to satisfy the compaction requirement. Therefore, an effective design stroke of 600 mm was adopted for the kinematic calculation of the redesigned mechanism. It should also be noted that the value of 700 mm referred to the chamber length in the bale movement direction rather than the nominal piston stroke. The piston’s extreme compression position was located inside the compression chamber, while its extreme retraction position was close to the filling port of the bottom pre-compression chamber. The extreme position angle θ was set to 3°, and the structure of the compression mechanism was illustrated in Figure 7.

In Figure 8, points A1 and A2 represent the two extreme positions of the piston, while point O denotes the center of the reducer’s output shaft. Let the radius r of the small circle stand for the crank length. The circumscribed circle passing through points A1, A₂, and O has its center at O1 and a radius of R. Draw line A1C through point A1, perpendicular to segment A1A₂; this perpendicular intersects the large circle at point C. The geometric relationships are as follows:

$$2\mathrm{R}\mathrm{s}\mathrm{i}\mathrm{n}\theta =\mathrm{s}$$

(3)

$$\mathrm{O}{\mathrm{A}}_2=\mathrm{L}+\mathrm{r}=2\mathrm{R}\mathrm{s}\mathrm{i}\mathrm{n}(\beta +\theta )$$

(4)

$$\mathrm{O}{\mathrm{A}}_1=\mathrm{L}-\mathrm{r}=2\mathrm{R}\mathrm{s}\mathrm{i}\mathrm{n}\beta$$

(5)

$$\mathrm{e}=\mathrm{O}{\mathrm{A}}_2\mathrm{s}\mathrm{i}\mathrm{n}\beta =(\mathrm{L}+\mathrm{r})\mathrm{s}\mathrm{i}\mathrm{n}\beta$$

(6)

From Equation (6) it follows that

$$\mathrm{L}+\mathrm{r}={\displaystyle \frac{\mathrm{e}}{\sin \beta }}$$

From Equations (3) and (4), it follows that

$$\mathrm{L}+\mathrm{r}=2\mathrm{R}\sin (\beta +\theta )={\displaystyle \frac{\mathrm{s}}{\sin \theta }}\sin (\beta +\theta )={\displaystyle \frac{\mathrm{e}}{\sin \beta }}$$

Thus obtained

$${\displaystyle \frac{\mathrm{e}\sin \theta }{\mathrm{s}}}=\sin \beta \sin (\beta +\theta )=-{\displaystyle \frac{1}{2}}\left[\cos (2\beta +\theta )-\cos \theta \right]\cos (2\beta +\theta )=\cos \theta -{\displaystyle \frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}$$

$$2\beta =\mathrm{a}\mathrm{r}\mathrm{c}\mathrm{c}\mathrm{o}\mathrm{s}\left[\cos \theta -{\displaystyle \frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}\right]-\theta$$

$$2\beta +\theta =\mathrm{a}\mathrm{r}\mathrm{c}\mathrm{c}\mathrm{o}\mathrm{s}\left[\cos \theta -{\displaystyle \frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}\right]=\alpha$$

$$\cos \alpha =\cos \theta -{\displaystyle \frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}$$

$$\sin {\displaystyle \frac{\alpha }{2}}=\sqrt{{\displaystyle \frac{1-\cos \alpha }{2}}}=\sqrt{{\displaystyle \frac{1-\cos \theta +\frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}{2}}}$$

$$\cos {\displaystyle \frac{\alpha }{2}}=\sqrt{{\displaystyle \frac{1+\cos \alpha }{2}}}=\sqrt{{\displaystyle \frac{1+\cos \theta -\frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}{2}}}$$

Since 2β + θ = α, it follows that

$$\sin \beta =\sin \left({\displaystyle \frac{\alpha }{2}}-{\displaystyle \frac{\theta }{2}}\right)=\sin {\displaystyle \frac{\alpha }{2}}\cos {\displaystyle \frac{\theta }{2}}-\cos {\displaystyle \frac{\alpha }{2}}\sin {\displaystyle \frac{\theta }{2}}$$

$$=\sqrt{{\displaystyle \frac{1-\cos \theta +\frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}{2}}}\cos {\displaystyle \frac{\theta }{2}}-\sqrt{{\displaystyle \frac{1+\cos \theta -\frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}{2}}}\sin {\displaystyle \frac{\theta }{2}}$$

$$\cos \beta =\sqrt{{\displaystyle \frac{1+\cos \theta -\frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}{2}}}\cos {\displaystyle \frac{\theta }{2}}-\sqrt{{\displaystyle \frac{1-\cos \theta +\frac{2\mathrm{e}\sin \theta }{\mathrm{s}}}{2}}}\sin {\displaystyle \frac{\theta }{2}}$$

From Equations (3) and (4), it follows that

$$\mathrm{r}=\mathrm{R}\left[\sin (\beta +\theta )-\sin \beta \right]={\displaystyle \frac{\mathrm{s}}{2\sin \theta }}\left[\sin (\beta +\theta )-\sin \beta \right]$$

$$\mathrm{L}=\mathrm{R}\left[\sin (\beta +\theta )+\sin \beta \right]={\displaystyle \frac{\mathrm{s}}{2\sin \theta }}\left[\sin (\beta +\theta )+\sin \beta \right]$$

After transformation, the following expression is obtained:

$$\left\{\begin{array}{c}r={\displaystyle \frac{\mathrm{s}}{2}}\sqrt{1-{\displaystyle \frac{2\mathrm{e}}{\mathrm{s}}}\tan {\displaystyle \frac{\theta }{2}}}\\ L={\displaystyle \frac{\mathrm{s}}{2}}\sqrt{1+{\displaystyle \frac{2\mathrm{e}}{\mathrm{s}}}\cot {\displaystyle \frac{\theta }{2}}}\end{array}\right.$$

Substituting the known conditions e = 60, s = 600, and =3° into the above equation yields:

$$\mathrm{r}={\displaystyle \frac{600}{2}}\times \sqrt{1-{\displaystyle \frac{2\times 60}{600}}\times \tan 1.5°}\approx 299.25 \mathrm{mm}$$

$$\mathrm{L}={\displaystyle \frac{600}{2}}\times \sqrt{1+{\displaystyle \frac{2\times 60}{600}}\times \cot 1.5°}\approx 884.09 \mathrm{mm}$$

After rounding the lengths of the crank and connecting rod, r = 300 mm and L = 885 mm were adopted.

The compression piston came into direct contact with the straw and executed reciprocating compaction motion within the baling chamber. In accordance with the previously outlined structural design of the baling chamber, the piston dimensions adopted in this study are 370 mm × 290 mm. To ensure stable compaction performance, stiffening plates were attached to both sides of the piston. Three detachable cutting blades were mounted at the bottom to improve the fluidity of the straw during compaction, as illustrated in Figure 9.

The connecting rod connected the piston to the crankshaft. Given its susceptibility to fatigue wear and deformation under periodic rotational motion, a square steel I-beam configuration was adopted. To facilitate its connection to both the crankshaft and piston, bushings were installed at both ends, with a center-to-center distance of L = 885 mm. The crankshaft ends were constrained by the connecting rod and the reducer output shaft; under torque loading, they were susceptible to fatigue. Based on domestic and international application data and theoretical calculations, the crank length was designed as r = 300 mm. Following the 3D modeling of the piston, crankshaft, and connecting rod, the components were assembled. The schematic diagram of the entire compression mechanism and the crankshaft-connecting rod assembly was illustrated in Figure 10.

2.4. Key Component Structure

2.4.1. Net-Wrapping Device

The netting device served as the core component of the netting mechanism, with its primary function being to rotate the wire mesh on the netting roller at a preset speed to wrap the compacted material into bales. It was required to meet key requirements: continuous and jam-free operation of the netting gears, compatibility with high/low speeds and forward/reverse rotation, and low power consumption. The netting device comprised components including a drive gear, driven gear, and net roller (Figure 11). The motor drove the net-loaded roller to rotate synchronously via gear transmission, thereby completing the netting operation on the straw bales at the outlet of the baling chamber.

As a transmission component of the net-wrapping mechanism, the gear must take into consideration structural dimensions, bending strength, applied loads, and economic factors during transmission to ensure it satisfies strength and rigidity requirements during service. As the gear material, 45 steel was adopted, with a gear thickness of 16 mm. The pinion has a pitch circle diameter d₁= 180 mm, a tooth number z₁ = 18, and a central bore diameter d = 22 mm for drive shaft connection. According to the formula:

$${\mathrm{d}}_1={\mathrm{m}}_1{\mathrm{z}}_1$$

(7)

According to the relationship m = d/z, the gear module was recalculated as m = 180/18 = 10 mm. For meshing transmission between the large and small gears, the following conditions must be satisfied: equal modules and identical tooth profiles on the pitch circles. According to the transmission ratio formula:

$$\mathrm{i}={\displaystyle \frac{{\mathrm{z}}_2}{{\mathrm{z}}_1}}={\displaystyle \frac{{\mathrm{n}}_1}{{\mathrm{n}}_2}}$$

(8)

In the formula: n₁—rotational speed of the driving gear (min⁻¹);

n₂—rotational speed of the driven gear (min⁻¹);

z₁—number of teeth on the driving gear;

z₂—number of teeth on the driven gear.

Based on the transmission ratio i = z₂/z₁ = 98/18 ≈ 5.44, the number of teeth of the driven gear was determined as 98. Using the same module m = 10 mm, the pitch circle diameter of the driven gear was calculated as d₂ = mz₂ = 980 mm. To ensure normal rotation of the large gear and reduce motor power consumption, the large gear’s 800 mm inner diameter is hollowed out. Bearings mounted on the disc surface are secured by brackets, with the large gear installed upon these bearings to permit rotation about them. The parameters for the pinion and large gear are detailed in

Table 2. Pinion parameters.

Basic Parameters	Formula	Value
pitch	$\mathrm{p}=\pi ·\mathrm{m}$	$\mathrm{p}=$ 31.42 mm
tooth crown height	${\mathrm{h}}_{\mathrm{a}}$ = m	${\mathrm{h}}_{\mathrm{a}}$ = 10 mm
root height	${\mathrm{h}}_{\mathrm{f}}$ = 1.25 m	hf = 12.5 mm
tooth height	$\mathrm{h}=$ 2.25 m	h = 22.5 mm
Pitch circle diameter	$\mathrm{d} =$ m·z	$\mathrm{d}=$ 180 mm
Top diameter of tooth	${\mathrm{d}}_{\mathrm{a}}=$ m(z + 2)	${\mathrm{d}}_{\mathrm{a}}$= 200 mm
Root diameter	${\mathrm{d}}_{\mathrm{f}}=$ m(z − 2.5)	${\mathrm{d}}_{\mathrm{f}}=$ 155 mm

and

Table 3. Big gear parameters.

Basic Parameters	Formula	Value
pitch	$\mathrm{p}=\pi ·\mathrm{m}$	$\mathrm{p}=$ 31.42 mm
tooth crown height	${\mathrm{h}}_{\mathrm{a}}$ = m	${\mathrm{h}}_{\mathrm{a}}$ = 10 mm
root height	${\mathrm{h}}_{\mathrm{f}}$ = 1.25 m	hf = 12.5 mm
tooth height	$\mathrm{h}=$2.25 m	h = 22.5 mm
Pitch circle diameter	$\mathrm{d} =$ m·z	$\mathrm{d}=$ 980 mm
Top diameter of tooth	${\mathrm{d}}_{\mathrm{a}} =$ m(z + 2)	${\mathrm{d}}_{\mathrm{a}}$= 1000 mm
Root diameter	${\mathrm{d}}_{\mathrm{f}} =$ m(z − 2.5)	${\mathrm{d}}_{\mathrm{f}}=$ 955 mm

, respectively.

In the following gear calculations and in Table 2 and Table 3, m denotes the gear module rather than a measurement unit.

Accordingly, the module, pitch circle diameter, and all derived geometric parameters of the pinion and the large gear were recalculated and unified in Table 2 and Table 3.

The wire mesh was installed on the net rollers. When the gears rotated, the net rollers rotated synchronously to execute the net-wrapping operation. The net rollers were cylindrical and rotatable around a central intermediate shaft. The dimensions of the intermediate shaft are specified as follows: length = 380 mm, cross-sectional diameter d = 40 mm. The net rollers have a length L = 270 mm and a cross-sectional diameter d = 100 mm. Each net roller was connected to the central shaft through bearings, and the roller material was plastic. A smooth-surfaced auxiliary roller with a diameter d = 40 mm was fixed to the net roller via a mounting bracket. This bracket was secured to the driven gear using bolts and double-ended studs.

2.4.2. Sensor-Counting Device

The sensing mechanism enabled motion control and real-time monitoring by sequentially triggering four sensors as the straw bale moved out of the discharge port, as illustrated in Figure 12. The sensors were installed on the connecting frame at the discharge port. Once the bale reached the preset length, it first triggered Sensor 1. The sensor rotated around its axis to activate and send a signal to the control system, which then activated the motor. The motor drove the large gear to rotate and initiate the net-wrapping operation, with the timer starting simultaneously. Subsequently, the bale triggered Sensor 2, and the net-wrapping process was maintained until the timer stopped. Using the formula:

$$\mathrm{V}={\displaystyle \frac{\mathrm{D}}{\mathrm{T}}}$$

(9)

In the formula: V—bale feed speed (cm/s);

D—bale length (cm);

T—time taken for one cycle (s).

The bale discharge speed was calculated, and the motor speed was adjusted accordingly to ensure the net-wrapping quality. After the bale triggered Sensor 3, the net-wrapping mechanism rotated for an additional two revolutions. The net-cutting and feeding mechanism was then activated, extending the cutting blade to cut the wire mesh. Subsequently, the net-wrapping gear rotated once, and the cutting blade reset. Finally, when Sensor 4 was triggered, the counting mechanism incremented the bale count by 1. The bale was automatically discharged, all sensors were reset, and the net-wrapping process was terminated.

The sensor-counting device’s mounting frame measured 800 mm in length, with installation clearance reserved at both ends. Four equidistant sensors were mounted on the frame at 210 mm intervals. The compatible bale dimensions were 700 × 380 × 330 mm, with the bale length being 700 mm.

2.4.3. Disconnected Network Structure

The net-cutting mechanism was mainly composed of a cutting shaft, blade holder, cutting blade, and connecting rod, all interfaced with the control circuit. The logic control circuit regulated the extension and retraction of the net-cutting blade according to the net-wrapping stage of the straw bale. The blade’s stroke displacement was controlled by the logic control circuit; powered by the baler’s power take-off (PTO) shaft, the blade’s movement was actuated by hydraulic components. The cutting shaft of the net-cutting device was installed in the slot of the base plate, facilitating the horizontal movement of the cutting blade mounted on the shaft. When the bale triggered Sensor 3, the cutting blade extended to sever the wire mesh before retracting. Subsequent net-wrapping operations initiated from the straw bale, obviating the requirement for manual net feeding. Thanks to the net-guiding roller, during the wrapping of subsequent bales, the rotating net-wrapping mechanism caused the wire mesh to catch onto the straw—this straw served as the starting point for wrapping, thereby completing the subsequent net-wrapping process without manual intervention. Based on the length of the sensor-mounting bracket, the position of Sensor 3, and practical design requirements, the length of the connecting shaft for the net-cutting device was set to L = 270 mm.

3. Coupled Simulation Analysis of the Compression Mechanism Based on Recurdyn-EDEM-ANSYS

3.1. Logical Framework for Coupled Simulation

After completing the design of key components for the compression mechanism, an advanced multi-software collaborative simulation approach was adopted to investigate its dynamic operational characteristics, the micromechanical behavior of straw particles, and the structural strength of critical components. Conventional single-software simulation methods face inherent limitations in accurately replicating the complex interactions among mechanical motion, particle flow, and structural deformation. To address this challenge, a systematic unidirectional coupling simulation framework was constructed. This framework aims to realize integrated analysis across multiple physical domains and scales through standardized data transmission, thereby providing comprehensive and reliable theoretical support for subsequent design optimization. The core workflow and data interaction relationships of this simulation framework are illustrated in Figure 13.

3.2. Multibody Dynamics Modeling of Compression Mechanisms

To streamline simulation computations, the relatively stationary components within the baler’s compression mechanism were merged into a single entity using Boolean operations. Given the challenges of mesh generation in ANSYS finite element analysis (FEA) for mechanisms with intricate surfaces or complex structures, all bolts, pins, and other similar fasteners were omitted. Furthermore, the remaining components mounted on the compression plate were simplified into a single planar structure, as illustrated in Figure 14.

SolidWorks 2022 was adopted for 3D modeling and assembly of the compression mechanism. The assembled model was exported in .stp format and imported into the multibody dynamics software Recurdyn 2019, as illustrated in Figure 15. All components were assigned a steel material property. Constraints and motion drivers were then configured for each component as follows:

In Figure 15, different colors are used only to distinguish the components of the Recurdyn model, and the arrows indicate the applied motion constraints and driving directions in the multibody dynamics setup.

Fixed joints were established between the base and the ground, as well as between the compression chamber and the ground;

Rotational joints were applied at the interfaces of base–crank, crank–connecting rod, and connecting rod–compression plate;

A translational joint was implemented between the compression plate and the ground.

Considering that EDEM software requires pre-generated straw particles prior to the compaction simulation, a rotational driver was added to the pivot joint between the base and the crank. The driver parameter was defined as IF(time−1:360−d,−360d,0), indicating that the crank starts rotating counterclockwise at 0 s with a rotational speed of 360°/s (60 min⁻¹) and stops after completing one compaction cycle at 1 s. Finally, all components were generated as boundary walls, the assembled model was exported, and the coupling function was activated to enable data interaction with subsequent simulation modules.

3.3. Multi-Software Coupled Simulation Method and Discrete Element Modeling Analysis

3.3.1. Discrete Element Modeling and Pre-Processing of Straw Pellets

In practical field operations, the baler collected post-harvest maize stalks scattered in the field, compacted them into structured bales, and wrapped them with netting for packaging. Mechanically harvested maize stalks were subjected to one to two stages of shredding, resulting in fragmented stalk segments. Consequently, the stalk particles were modeled as small segments with a cross-sectional diameter of 7 mm and length of 28 mm, constructed by the interlocking arrangement of three spheres (each with a radius of 7 mm), as illustrated in Figure 16. The material parameters of the maize stalk feedstock were presented in

Table 4. Material parameters of straw materials.

Designation	Numerical Value
Poisson ratio	0.35
Density	400 kg/m3
Shear modulus	7 × 108 Pa

.

The slight overlap in Figure 16 is part of the bonded-sphere construction of the discrete straw particle model and does not affect scientific understanding of the figure.

In line with the design requirements, the collected straw was compacted and shaped by the baler prior to undergoing fixed-length cutting, net wrapping, and final baling. Considering the dimensions of the compression chamber and the layout of sensors installed downstream, the resulting straw bales had approximate dimensions of 380 mm × 330 mm × 700 mm. To simulate the straw-feeding process, a virtual box was added at the feed inlet of the compression chamber’s geometric model to act as a particle generator, which produced stacked particles to replicate the fed straw material, as illustrated in Figure 17.

The baler was designed to complete the entire workflow of straw compression, net wrapping, baling, and net cutting within a single working cycle of 12 s. Correspondingly, the virtual particle generator (pellet factory) adopted a dynamic particle generation mode, with a total generated mass of 18 kg. The particle generation rate was set to 1.5 kg/s, ensuring the full material feeding process was completed within 12 s to match the actual operational rhythm of the baler.

The generated particles were exported from the straw particle pile at the compression chamber inlet to construct a new particle generator. Meanwhile, the equipment materials were defined as steel, with specific parameters detailed in

Table 5. Material parameters of compression mechanism of baler.

Designation	Numerical Value
Poisson ratio	0.29
Density	7801 kg/m3
Shear modulus	7 × 1010 Pa

. The inter-material and material–equipment interaction parameters were presented in

Table 6. Contact parameters of materials and equipment.

Project	Numerical
Straw-to-straw collision recovery coefficient	0.411
Straw—Static Friction Coefficient of Straw	0.566
Straw—Coefficient of sliding friction for straw	0.062
Straw–steel collision recovery coefficient	0.702
Straw–steel static friction coefficient	0.344
Straw–steel coefficient of sliding friction	0.059

.

The EDEM material parameters of maize straw and the straw–steel contact parameters were selected with reference to published studies on corn straw and crop-residue EDEM modeling and were further adjusted according to the physical characteristics of the chopped maize straw used in this study and preliminary simulation trials. Previous studies have shown that corn straw EDEM models are commonly established using Hertz–Mindlin with bonding or related contact models, and their parameters are typically calibrated through a combination of physical tests and simulation-based optimization, such as bending tests, shear-force tests, or repose-angle tests. Therefore, the density, Poisson ratio, shear modulus, restitution coefficient, and friction coefficients adopted in this study were used to reproduce the observed particle accumulation, feeding behavior, and compaction response of the prototype machine. More systematic parameter calibration will be carried out in future work to further improve parameter accuracy [16,17,18].

The wall models of the baler’s compression mechanism exported from Recurdyn (multibody dynamics software) were imported into EDEM. No component-driving settings were required within EDEM. The position and dimensions of the particle generator box were adjusted to match the spatial layout of the wall models. The Hertz–Mindlin (no-slip) contact model with bonding treatment was adopted for the DEM contact simulation.

The computational domain was defined as follows:

X-axis: −2200 mm to 450 mm;

Y-axis: −400 mm to 400 mm;

Z-axis: −250 mm to 150 mm.

Gravity was applied along the negative Y-axis with an acceleration of 9.81 m/s².

3.3.2. Recurdyn-EDEM Coupling Configuration and Analysis

The Euler time step of the EDEM solver was set to 19% of the Rayleigh time step, with a simulation duration of 1 s. To visualize the generation and compaction states of straw particles at each time step, the auto-save interval was configured to 0.01 s, and the cell size was set to 3 mm (consistent with the particle characteristic size for computational accuracy). To improve simulation efficiency, an 8-core parallel computing strategy combined with GPU acceleration was adopted.

After completing all EDEM parameter settings, the coupling switch was activated to enable the coupled simulation mode. Recurdyn was then launched for computation: the simulation duration was set to 1 s, and the iteration number was specified as 100. Finally, the coupled simulation calculation was executed.

Within Recurdyn, the motion curve of the baler’s compression mechanism during a single straw compression cycle was exported, as illustrated in Figure 18. In the EDEM post-processing interface, the wall models of the baler’s compression mechanism and the particle generator were hidden, retaining only the straw particles to observe their compression molding state. As shown in Figure 19, combined with the motion curve from Recurdyn, it was observed that the compression mechanism completed effective compaction of the straw at approximately 0.48 s, achieving a satisfactory compression molding effect.

In Figure 18, different colors are used only to distinguish the motion curves of different components/variables exported from Recurdyn.

Simultaneously, the average velocity data of the straw during the compression process was exported from EDEM. This velocity data was imported into Origin to generate the velocity–time curve depicted in Figure 20, which indicated that the average velocity of the straw during the compression stage was approximately 0.5 m/s.

The force and torque curves of all components in the compression mechanism were exported from Recurdyn, as illustrated in Figure 21. It was noted that in the EDEM simulation, only the forces acting on components in contact with straw particles can be analyzed.

In the EDEM post-processing interface, the pressure data of the compression plate and compression chamber in the baler’s compression mechanism was exported in both .axdt and .csv formats, as shown in Figure 22. The .axdt format data is used for subsequent ANSYS finite element simulation analysis, while the .csv format data is imported into Origin to plot the temporal variations of pressure acting on the compression plate and compression chamber.

In Figure 22b, the non-English labels come from the original exported software interface and denote the total pressure curves of the compression plate and the compression chamber.

3.3.3. EDEM-ANSYS One-Way Coupled Simulation Analysis

The overall workflow of the EDEM–ANSYS one-way coupling procedure is shown in Figure 23. Within ANSYS Workbench, two projects were created: ANSYS DEM and Static Structural. Under the ANSYS DEM Solutions > Results branch, the .axdt file exported from EDEM was imported. Subsequently, the baler compression mechanism model was imported into ANSYS Workbench, and the EDEM simulation results were shared with the Static Structural > Setup branch, as illustrated in Figure 24.

In Figure 24, different colors are used only to distinguish the imported model components in ANSYS Workbench, and any non-English text shown in the figure comes from the software interface rather than from the analytical results.

To facilitate the visualization of stress distribution in the compression chamber and compression plate during straw compaction, all components except the compression chamber were suppressed in DesignModeler (DM). The loads transferred from EDEM were imported and applied to the model, with constraints added at the rotational axis of the compression plate. Automatic mesh generation was then performed, as illustrated in Figure 25. (The same pre-processing procedure was adopted for the compression plate analysis).

In Figure 25, the colors are used only to distinguish the meshed model components in ANSYS, and any non-English text shown in the figure comes from the software interface rather than from the simulation results.

The mesh of the compression chamber consisted of 4629 nodes and 2261 elements, while the compression plate—with its thickness adjusted to 10 mm—had a mesh comprising 19,769 nodes and 9689 elements.

In the ANSYS solution setup, separate simulations were performed to obtain the equivalent stress, equivalent strain, and total deformation of the compression chamber and compression plate. The simulation results were presented in Figure 26a–f.

In Figure 26, any non-English words shown in the panels come from the original ANSYS software interface and do not affect the interpretation of the finite element results.

Based on the simulation results presented in Figure 26a–c, the compression chamber exhibited an equivalent stress of 0.2767 MPa and a maximum total deformation of approximately 0.0012 mm during straw compaction. As shown in Figure 26d–f, the compression plate had an equivalent stress of 173.44 MPa and a maximum total deformation of approximately 0.66 mm.

Given that the yield strength of structural steel is 235 MPa—substantially higher than the equivalent stress borne by the components during straw compression molding—the compression chamber and compression plate fully met the structural strength requirements. Consequently, no structural failure would occur during practical operation.

4. Field Experiments

4.1. Experimental Conditions

A field experiment was conducted at the experimental base of Huaxi Yutian Technology Co., Ltd. in Xinxiang City, Henan Province, with a test plot area of 600 m × 300 m. The test material consisted of local post-harvest maize straw, with a measured straw yield of 3.26 kg/m² and a moisture content (wet basis) of 30.03%.

The power unit adopted was a Lovol M1404-x tractor (Weichai Lovol Intelligent Agricultural Technology Co., Ltd., Weifang, Shandong, China), with a rated power of 102.9 kW, a rated travel speed range of 2.38–33.16 km/h, and a power take-off (PTO) shaft speed of 540/750 min−1 (the 720 min−1 setting was selected for the experiment). The tested machine was an experimental prototype developed by modifying the 9YFSG-2.2 square straw baler (Xinxiang Huaxi Technology Co., Ltd., Xinxiang, Henan, China) for integrated baling and net wrapping. The key technical parameters of the tested prototype were as follows: matching power range of 58.8–117.6 kW, baling cycle time of 12 s per bale, pick-up width of 2200 mm, and operating travel speed of 2.38 km/h. This tractor was selected because its rated power falls within the matching power range required by the tested machine, while also providing sufficient power reserve for stable PTO-driven operation during baling and net wrapping. The overall configuration of the baler unit and its on-site operational status are illustrated in Figure 27.

4.2. Analysis of Net-Wrapping Device Performance and Standard Bale Formation Rate and Drop Resistance Rate

With net entanglement power consumption W and entanglement duration T as independent variables, and mesh consumption G as the evaluation metric, an intelligent digital torque meter CYT-30A was employed to collect instantaneous power data, according to

$$\mathrm{W}={\sum }_{\mathrm{i}=1}^{\mathrm{n}}{\mathrm{P}}_{\mathrm{i}}\mathrm{T}$$

(10)

In the formula: W—power consumption (kJ);

P_i—Instantaneous power (W);

T—Single acquisition time (6 s);

n—Number of times experimental data is collected.

Calculate power consumption by measuring the mass of the wire mesh (G₁) and the mass of the straw bale (G₂), according to

$$\mathrm{G}={\displaystyle \frac{{\mathrm{G}}_1}{{\mathrm{G}}_2}}$$

(11)

In the formula: G—Wire mesh consumption (kg/t);

G₁—Wire mesh quality (kg/tonne);

G₂—Mass of the test bale (kilograms per tonne).

Net consumption was calculated according to Equation (11), and the test was repeated to obtain the average value. The 14 observations obtained under practical operating conditions of the prototype machine are summarized in

Table 7. Experimental dataset for analyzing the effects of net-wrapping power consumption and wrapping duration on net consumption.

No.	Net-Wrapping Power Consumption (kJ)	Wrapping Duration (s bale−1)	Net Consumption (kg t−1)
1	2.24	27.5	3.32
2	1.88	25.2	3.26
3	3.02	31.6	3.64
4	1.86	25.8	3.38
5	2.85	30.8	3.64
6	3.03	32.4	3.76
7	2.13	26.8	3.22
8	3.48	34.6	3.92
9	2.73	29.8	3.58
10	2.36	27.5	3.44
11	2.17	26.6	3.37
12	3.52	36.8	4.12
13	2.44	28.6	3.51
14	2.93	30.5	3.56

, and the corresponding descriptive trend plots are presented in Figure 28. This dataset was used for descriptive analysis of the relationships among net-wrapping power consumption, wrapping duration, and net consumption.

Five straw bales were randomly selected, and the lengths of four sides of each bale were measured. If the difference between the maximum and minimum side lengths of a bale does not exceed 10% of its average side length, the bale is deemed regular. The regularity rate was calculated in accordance with Equation (12).

Two straw bales were selected and dropped freely from a height of 5 m twice consecutively. Bales remaining intact after both drops are considered compliant. The drop resistance rate was calculated as per Equation (13).

It should be noted that the present field test mainly served as a preliminary performance validation of the prototype machine under practical operating conditions. Owing to the limited number of sampled bales used for the regularity and drop resistance evaluation, the corresponding results should be interpreted as an initial verification of machine feasibility and functional effectiveness rather than a fully statistically representative assessment. Larger-sample and repeated field tests will be conducted in future work to further improve the statistical robustness of the evaluation.

$${\mathrm{S}}_{\mathrm{g}}={\displaystyle \frac{{\mathrm{I}}_{\mathrm{g}\mathrm{c}}-{\mathrm{I}}_{\mathrm{g}\mathrm{b}}}{{\mathrm{I}}_{\mathrm{g}\mathrm{c}}}}\times 100\%$$

(12)

$${\mathrm{S}}_{\mathrm{k}\mathrm{c}}={\displaystyle \frac{{\mathrm{I}}_{\mathrm{k}\mathrm{c}}-{\mathrm{I}}_{\mathrm{k}\mathrm{s}}}{{\mathrm{I}}_{\mathrm{k}\mathrm{c}}}}\times 100\%$$

(13)

In the formula: S_g—Standardised Grass Baling Rate (%);

I_gb—Irregular bales (bundles);

I_gc—Bales tested (bundles);

S_kc—Resistance to disintegration rate (%);

I_ks—Bales disintegrated during testing (bundles);

I_kc—Bales tested (bundles).

4.3. Analysis of Experimental Results

The data in Table 7 indicated that net consumption increased as net-wrapping power consumption and wrapping duration increased within the observed range. To facilitate descriptive interpretation, the relationships of net consumption with wrapping duration and net-wrapping power consumption were further illustrated in Figure 28. Based on the available exploratory dataset, both variables showed positive associations with net consumption. However, because the present dataset was obtained under practical operating conditions rather than a grouped factorial experimental design, and because net-wrapping power consumption and wrapping duration varied simultaneously across the tested runs, their independent effects could not be rigorously separated at this stage. Therefore, the current results supported only a descriptive observational conclusion that net consumption tended to be lower when both wrapping duration and net-wrapping power consumption were lower under the present test conditions. Further repeated experiments with grouped factor levels, larger sample size, and formal statistical analysis are still required to establish the relative contribution of each factor. The measured bale performance indices are summarized in

Table 8. Measured bale performance indices.

Project	Standard Indicators	Measured Value
Bundling rate %	≧98	99.4
Standard Bale Rate (%)	≧95	96
Bale Drop Resistance Rate (%)	≧90	93
Bale Density (kg/m3)	≧100	170

.

Under the present test conditions, all measured performance indicators met the corresponding design requirements, including a baling rate of 99.4%, a regular bale rate of 96%, a drop resistance rate of 93%, and a bale density of 170 kg/m³. These results indicated that the prototype machine was capable of completing integrated straw baling and net wrapping under field conditions. However, considering the limited sample size used for some evaluation indices, the present field test should be regarded as a preliminary validation, and further repeated experiments with a larger sample size are still required to strengthen the statistical representativeness of the results.

5. Conclusions

1. The integrated baling and net-wrapping structure, designed based on the modification of the 9YFSG-2.2 square straw baler, exhibited a reasonable and feasible structural design. By integrating the conveying mechanism, eccentric crank–connecting rod compression mechanism, dual-stage gear-driven net-wrapping device, and sensor-controlled net-cutting mechanism, the structure established a complete operational process covering “pick-up, shredding, conveying, compaction, net-wrapping, and net-cutting”. The optimized selection of key components and parameter configuration—including a crank length of 300 mm, a connecting rod length of 885 mm, and a hollowed-out large gear design for the net-wrapping device (aimed at weight reduction)—effectively satisfied the technical requirements of square straw bale forming and automated net wrapping. This integrated design obviated the need for separate baling and net-wrapping operations as well as manual intervention, thereby improving operational continuity and efficiency.

2. Recurdyn-EDEM-ANSYS Cross-Software Coupled Simulation Analysis. The Recurdyn-EDEM-ANSYS cross-software coupled simulation successfully realized multi-scale integrated analysis of the straw compression process. For the multibody dynamics model, reasonable simplifications were implemented—specifically, a discrete element method (DEM) straw particle model was constructed by assembling three 7-mm-radius spheres into a 28-mm-long segment, which closely approximates the actual physical properties and morphological characteristics of shredded maize straw. Simulation results indicated that the compression mechanism completed effective compaction of straw particles at 0.48 s. The equivalent stress of the compression chamber and compression plate was calculated as 0.2767 MPa and 173.44 MPa, respectively, with corresponding maximum total deformations of 0.0012 mm and 0.66 mm. Both stress values were lower than the yield strength of structural steel (235 MPa), verifying the safety and reliability of the structural design.

3. Field trials were conducted to systematically verify the comprehensive operational performance of the modified 9YFSG-2.2 integrated straw baling and net-wrapping machine. Under the test condition of 30.03% straw moisture content (wet basis), the machine achieved the following key performance indicators: a straw baling success rate of 99.4%, a straw bale regularity rate of 96%, a straw bale drop resistance rate of 93%, and a bale density of 170 kg/m³—all of which met or exceeded the preset design requirements. During the trials, the machine exhibited stable overall operation, with a baling cycle time of 12 s per bale, which fully satisfied the efficiency requirements of practical field production. Further analysis of the available exploratory dataset indicated that net consumption was positively associated with both wrapping duration and net-wrapping power consumption within the tested range. However, because the present dataset was not derived from a grouped factorial experiment, the relative contribution of the two factors could not be quantified rigorously at this stage. Additional repeated experiments, grouped factor-level tests, and formal statistical analysis are still needed to establish a stronger quantitative relationship. In addition, because the present field validation involved a limited sample size for some indices, larger-sample and repeated field experiments are still needed in future work to further verify the long-term stability and statistical robustness of the prototype performance. In addition, the present study mainly focused on structural design, coupled simulation, and field performance verification of the integrated baling and net-wrapping machine. The vibration characteristics of the machine during operation were not investigated in this work and will be considered in future studies to further evaluate dynamic stability, operator comfort, and long-term structural reliability. In addition, because the driving and driven gears of the net-wrapping device are exposed in the current prototype during operation, a protective cover should be developed in future work to improve operator safety and prevent accidental access to the transmission area.