3.1. Analysis of Stem Cutter Blade Installation Angle
In
Figure 3a, the simulation shows the load generated when cutting the acrylic rod. High-speed camera shots showed the cutting process of the acrylic rod in the stem cutting test equipment (
Figure 3b). The torque values measured when cutting the acrylic rod using the stem cutting test equipment and simulation analysis are listed in
Table 2.
The results using the stem cutting test equipment were the average values of 20 replicate measurements at each installation angle. The torque values from the cutter blade in the simulation and stem cutting test equipment were shown at the installation angle of 0°; it was 930.92 N·mm in the simulation, whereas the highest value was 1026.49 N·mm using the stem cutting test equipment. As the angle increased, the torque decreased. The torque was 495.45 N·mm at the installation angle of 40° in the simulation, whereas the smallest torque was 485.97 N·mm using the stem cutting test equipment.
Consequently, we discovered that the optimal installation angle for creating the lowest load on the stem cutter blade was 40°. Compared with the torque at the installation angle of 0°, it was at a half-value level.
There were differences between the results obtained from the simulation and those from the stem cutting test equipment. However, the R
2 value between the two results was 0.99, indicating a significant correlation (
Figure 4). Using this regression for analysis, we could estimate the torque value exerted on the cutting blades at different angles. Therefore, despite the difficulty to obtain accurate results from actual experiments, the simulation analysis can be helpful in understanding the trends.
As the area where the rotating blade touches increases, more load is exerted on the motor. Therefore, with a larger installation angle, the area of the touched material increases, which can lead to damage due to the greater load exerted on the motor connected to the stem cutter blade. In addition, with a larger installation angle, the wind becomes stronger, consuming more power.
As shown in
Table 3, the results of the motor power consumption test at different installation angles indicate that the current consumption increased by approximately four times as the installation angle increased from 0° to 40°. This implies that a larger load is exerted on the motor as the installation angle increases.
Finally, the velocity of the wind raising the stem at different installation angles was measured using a portable anemometer; the results are listed in
Table 4. The wind velocity was measured as 0 m/s and 0.39 m/s at angles of 0 and 10 degrees, respectively, which was not suitable because there was no erection of the stem, as shown in
Table 5. At an angle of 20 degrees, the wind velocity slightly increased to 0.44 m/s. However, as shown in
Table 5, when the moisture content was 60%, it was possible to erect the stem, but the stem was only partially cut due to a slight lack of wind velocity. At 80%, it was not possible to cut because there was insufficient velocity to erect the stem. At angles of 30 and 40 degrees, the wind speed was measured as 0.75 m/s and 0.98 m/s, respectively, regardless of the water content, indicating that it was possible to cut the stem.
During the harvesting season in Korea, over 70% of the onion stems are lodged [
14] in onion farming fields.
However, the water content may differ depending on the weather conditions in the harvesting region or the onion variety. Considering these differences, it was found that the cutting blade should be installed at an angle greater than 30° to successfully cut the stem under any operational condition.
The stem cutter blade with an installation angle of 30° was deemed the most suitable for application in an actual stem cutting machine, considering the durability of the stem cutting machine and fuel consumption (
Figure 5).
3.2. Validation with the Tractor-Attachable Wind-Blast-Type Onion Stem Cutting Machine
The results of the test on the tractor-attachable wind-blast-type onion stem cutting machine conducted in Chang-nyeong, Gyeong-nam, in 2017 are presented in
Figure 6 and
Table 6. After stem cutting, the remaining stem length was aimed to be 10 cm. The test was repeated thrice at a traveling speed of 0.4 m/s. The average remaining stem length was 9.98 cm, with a standard deviation of 4.72 cm and a stem cutting rate of 96.8%. At traveling speeds of 0.6 and 0.8 m/s, the average remaining stem lengths after cutting were 9.75 and 13.03 cm, respectively, and the standard deviations were 4.56 and 11.00 cm, respectively. The stem cut rates were 96.1 and 87.3%, respectively. The best results were obtained when the tractor-attachable wind-blast-type onion stem cutting machine was operated at a traveling speed of 0.4 m/s. However, when stem cutting was performed at a traveling speed of 0.6 m/s, it was possible to cut the stem with an extremely high probability of approximately 96%, and the remaining stem length was similar to the target of 10 cm. If stem height control is improved in the future, work time and labor can be likely reduced. After the test, the cut onion stems were placed in furrows on both sides of the ridge, as shown in the right picture of
Figure 6. This was expected to reduce the load on the vinyl that covers the ridge during the removal process, minimize the possibility of tearing, and facilitate smoother work.
Using the stem cutter machine presented in this study, it was possible to cover an area of 10 hectare in just 1.5 h. This represents significant savings in time, labor, and cost compared to the 27.6 h [
5] it would take to cover the same area using manual labor.
However, if the field conditions are uneven or the rotating speed of the rotating blade is not constant, the remaining stems of the onion may be uneven or the top of the onion may be damaged. Research on precise control and posture is necessary so that workers can set the desired stem height and make accurate cuts to prevent the future occurrence of damaged onions.
As mentioned in the introduction, many researchers and companies are trying to develop new products to improve the mechanization rate of field farming. However, commercialization requires high production costs and demand, and practical problems, such as crop diversification and difficulty in purchasing due to high prices, limit improvements in the mechanization rate [
2]. Therefore, it is necessary to raise the level of the agricultural industry by preparing a system improvement and support plan at the governmental level.