Longitudinal Axial Flow Rice Thresher Performance Optimization Using the Taguchi Technique

: Combine harvesters are widely used worldwide in harvesting many crops, and they have many functions that cover the entire harvesting process, such as cutting, threshing, separating, and cleaning. The threshing drum is the core working device of the combine harvester and plays an inﬂuential role in rice threshing efﬁciency, threshing power requirement, and seed loss. In this study, two structures of rice threshers (conical-shaped and cylindrical-shaped) were tested and evaluated for performance under different thresher rotating speeds of 1100, 1300, and 1500 rpm and different feeding rates of 0.8, 1.1, and 1.4 kg/s. The experiment was designed using the Taguchi method, and the obtained results were evaluated using the same technique. The thresher structure and operating parameters were assessed and optimized with reference to threshing efﬁciency, required power, and productivity. The obtained results revealed that increasing thresher rotating speed and the feeding rate positively related to threshing efﬁciency, power, and productivity. The highest efﬁciency of 98% and the maximum productivity of 0.64 kg/s were obtained using the conical-shaped thresher under a 1500 rpm rotating speed and a feed rate of 1.4 kg/s, whereas the minimum required power of 5.45 kW was obtained using the conical thresher under a rotating speed of 1100 rpm and a feed rate of 0.8 kg/s.


Introduction
Rice is the second most important cereal after wheal, which together supply 95% of the world's population's whole staple food [1].
China is the biggest grain producer globally, with a planting area of 94,370.8 km 2 and accounting for 21.98% of the world's grain production [2].
The grain harvester is the most essential piece of agricultural machinery that improves harvesting efficiency and reduces labor costs [3][4][5][6].
Combine harvesters are widely used worldwide to harvest different crops under different environmental and operating conditions. They have many functions such as cutting, threshing, separating, cleaning, and sometimes storing crops.
Many small, medium, and giant threshers have existed for a long time, but because of their low performance compared to traditional threshing methods, they have never been adapted to a significant extent. Some of these threshers are hand-held, and others are pedal-operated [7].
Threshing is considered one of the most vital crop processing operations for separating grains from the ears and preparing them for the market [8].
Threshing is the process of separating the edible part of the cereal grain from the chaff that surrounds it, and it is done after harvesting the crop and before winnowing it [9]. The simplest threshing system is picking up rice stalks and trampling the panicles underfoot or beating them against a hard surface such as a rack, threshing board, or tub [10].

Testing Platform
To simulate the rice threshing process, a longitudinal axial flow threshing platform was constructed in a factory. The platform comprised a conveying belt, a longitudinal axial flow thresher, a concave thresher cover, receiving boxes, a diesel engine, a feeding device, Agriculture 2021, 11, 88 3 of 14 a frequency convertor, an electric motor, and a torque sensor. The platform is shown in Figure 1, and the characteristics of it are shown in Table 1.

Testing Platform
To simulate the rice threshing process, a longitudinal axial flow threshing platform was constructed in a factory. The platform comprised a conveying belt, a longitudinal axial flow thresher, a concave thresher cover, receiving boxes, a diesel engine, a feeding device, a frequency convertor, an electric motor, and a torque sensor. The platform is shown in Figure 1, and the characteristics of it are shown in Table 1.  The conveying mechanism composed of a rotating belt with dimensions of 6 × 0.5 m, and it was driven by an electric motor. Its speed was controlled using a frequency converter. It was used to transport rice to the feeding auger, which consisted of a rotating auger and a rotating chain with steel bars. The power was conveyed from the diesel en-  The conveying mechanism composed of a rotating belt with dimensions of 6 × 0.5 m, and it was driven by an electric motor. Its speed was controlled using a frequency converter. It was used to transport rice to the feeding auger, which consisted of a rotating auger and a rotating chain with steel bars. The power was conveyed from the diesel engine to the auger using a belt and pulley. Its function was to feed the rice from the conveying mechanism to the threshing unit. The threshing unit consisted of a longitudinal axial flow thresher with spike teeth, a thresher cover with helical blades, and a stationary concave. The thresher composed of 6 bars with spike teeth, and the rotational speed was conveyed from the engine to the thresher using a pulley and belt. Two kinds of thresher structures (cylindrical and conical), and three thresher rotating speeds of (1100, 1300, and 1500 rpm) were tested for the experiment. The threshers are shown in Figure 2.
Agriculture 2021, 11, x FOR PEER REVIEW 4 of 14 gine to the auger using a belt and pulley. Its function was to feed the rice from the conveying mechanism to the threshing unit. The threshing unit consisted of a longitudinal axial flow thresher with spike teeth, a thresher cover with helical blades, and a stationary concave. The thresher composed of 6 bars with spike teeth, and the rotational speed was conveyed from the engine to the thresher using a pulley and belt. Two kinds of thresher structures (cylindrical and conical), and three thresher rotating speeds of (1100, 1300, and 1500 rpm) were tested for the experiment. The threshers are shown in Figure 2.

Torque Sensor
The torque sensor ( Figure 3) was installed on the thresher shaft to measure thresher rotating speed, threshing torque, and required power. The torque sensor's measuring range was 0-10000 N.m and 0-12000 rpm.

Testing Instruments
An TD 1001 electronic digital balance with an accuracy of 0.01 g produced by the Chengdu Cheng Sheng tools group company, LTD; an Sdh-1202 rapid halogen moisture

Torque Sensor
The torque sensor ( Figure 3) was installed on the thresher shaft to measure thresher rotating speed, threshing torque, and required power. The torque sensor's measuring range was 0-10,000 N.m and 0-12,000 rpm. gine to the auger using a belt and pulley. Its function was to feed the rice from the conveying mechanism to the threshing unit. The threshing unit consisted of a longitudinal axial flow thresher with spike teeth, a thresher cover with helical blades, and a stationary concave. The thresher composed of 6 bars with spike teeth, and the rotational speed was conveyed from the engine to the thresher using a pulley and belt. Two kinds of thresher structures (cylindrical and conical), and three thresher rotating speeds of (1100, 1300, and 1500 rpm) were tested for the experiment. The threshers are shown in Figure 2.

Torque Sensor
The torque sensor ( Figure 3) was installed on the thresher shaft to measure thresher rotating speed, threshing torque, and required power. The torque sensor's measuring range was 0-10000 N.m and 0-12000 rpm.

Testing Instruments
An TD 1001 electronic digital balance with an accuracy of 0.01 g produced by the Chengdu Cheng Sheng tools group company, LTD; an Sdh-1202 rapid halogen moisture

Testing Instruments
An TD 1001 electronic digital balance with an accuracy of 0.01 g produced by the Chengdu Cheng Sheng tools group company, LTD; an Sdh-1202 rapid halogen moisture meter produced by the same instruments company, LTD; a TMS-PRO type texture analyzer produced by the FTC USA company; an MB45 moisture meter produced by the OHAUS USA company; an electronic digital display Vernier caliper; a tape; scissors; some sealing bags; a tachometer; and a frequency converter were used for the test.

Rice Cultivar
The Huanghuazhan rice variety was used for the experiment. It was planted in a field at Huazhong agricultural university, Wuhan, China. The planting method was artificial transplanting. Manual harvesting was used, with a stubble height of about 150 mm, and then the rice was transported to the university factory for testing.
Each rice stem was subjected to a three-point bending test and a shearing test using the TMS-PRO type texture analyzer at the engineering college's agricultural equipment laboratory, as shown in Figure 4. The properties of rice stalks and grains are shown in Table 2.
Agriculture 2021, 11, x FOR PEER REVIEW 5 of 14 meter produced by the same instruments company, LTD; a TMS-PRO type texture analyzer produced by the FTC USA company; an MB45 moisture meter produced by the OHAUS USA company; an electronic digital display Vernier caliper; a tape; scissors; some sealing bags; a tachometer; and a frequency converter were used for the test.

Rice Cultivar
The Huanghuazhan rice variety was used for the experiment. It was planted in a field at Huazhong agricultural university, Wuhan, China. The planting method was artificial transplanting. Manual harvesting was used, with a stubble height of about 150 mm, and then the rice was transported to the university factory for testing.
Each rice stem was subjected to a three-point bending test and a shearing test using the TMS-PRO type texture analyzer at the engineering college's agricultural equipment laboratory, as shown in Figure 4. The properties of rice stalks and grains are shown in Table 2.

Bending test
Shearing test

Taguchi Method and Experiment Design
The Taguchi method is used widely in engineering analysis. It is a dominant design that reduces the number of tests and minimizes the effects of factors that cannot be controlled [28,29]. It uses a loss function to calculate the deviation between the desired values and the experimental values. This loss function is converted into a signal-noise (S/N) ratio [29,30].
The S/N ratio can be divided into three categories given by Equations (1)

Taguchi Method and Experiment Design
The Taguchi method is used widely in engineering analysis. It is a dominant design that reduces the number of tests and minimizes the effects of factors that cannot be controlled [28,29]. It uses a loss function to calculate the deviation between the desired values and the experimental values. This loss function is converted into a signal-noise (S/N) ratio [29,30].
The S/N ratio can be divided into three categories given by Equations (1) The lower is better: The higher is better: where y is the average of observed data, s 2 y is the variation of y, n is the number of observations, and y is the observed data or each type of the characteristics.

Threshing Parameters and Their Levels
For the test, we used the cylindrical and conical types of threshers (A); three rotational speeds (B) of 1100, 1300, and 1500 rpm; and three feeding rates (C) of 0.8, 1.1, and 1.4 kg/s, as shown in Table 3. In this study, the Taguchi method was used to assess threshing performance and to compare two threshers' structures (cylindrical and conical). Taguchi's L 18 arrangement was used for experimenting. To determine the optimal threshing conditions and the best operating parameters, the S/N ratio was calculated. The lower is better was used to determine the S/N ratio for power requirement, and the higher is better was used for efficiency and productivity. The experiment results and S/N ratios are shown in Table 4.

Testing Procedure
The platform of the thresher was established in the factory. The conveyor belt's total length was 6 m, the first meter was left empty, and the rice straw was evenly spread on the last 5 m to ensure that it would be fed at a stable speed. The conveyor belt's speed was kept to 1 m/s, and different feeding rates of 0.8, 1.1, and 1.4 kg/s were tested. The drum speeds were 1100, 1300, and 1500 rpm. After the experiment, the rice grains were collected from the boxes under the concave and from the straw outlet, cleaned using a cleaning machine, and then weighed to measure the threshing efficiency and productivity. Additionally, the required power was measured using the torque sensor mounted on the thresher shaft.

Threshing Performance Indicators
Performance evaluation is a scientific method of ascertaining the working conditions of a system's main components to establish how the components contribute to the system's overall efficiency [32].
The criteria for evaluating threshing mechanisms' performance include threshing efficiency, grain loss, grain damage, output capacity, cleaning efficiency, and power requirement [33].
The crop's feed rate into the thresher and operating parameters such as drum speed significantly affected the threshing performance [34].

Threshing Efficiency
Threshing efficiency is the ratio between the mass of threshed grains received from thresher outlets and the total grain input per time unit expressed in percentage [25].
It was calculated regarding the following equation: TE = weight of threshed seed (g)/total weight of seed (g) × 100

Thresher Productivity
The throughput of a thresher is the mass of materials passing through the thresher per time unit [35]. Throughput = total weight of seed/threshing time

Power Requirement
The required power was calculated after analyzing the obtained data from the torque sensor. Threshing efficiency, power, and productivity were measured using Taguchi techniques, and the optimization of the control factors was provided by signal-to-noise ratios using the Minitab software. The lowest value of power was effective on threshing performance enhancing, so the lower is better equation was used to determine its S/N ratio. Additionally, the highest values of threshing efficiency and productivity were very effective on threshing performance, so the higher is better was used. The values of the S/N ratios are shown in Tables 5-7 and show the optimal levels of control factors for optimal threshing efficiency, power, and productivity. These levels are also shown in graph forms in Figures 5-7.

Results and Analysis
The optimum level for each control factor was found regarding the highest S/N ratio in the levels of that control factor. The levels of the factors giving the best efficiency and productivity were specified as A 2 B 3 C 3 . This means that the optimum efficiency and productivity were obtained using the conical shaped thresher (A 2 ), a rotating speed of 1500 (B 3 ), and a feed rate of 1.8 (C 3 ). On the other hand, the lowest power requirement was obtained with a thresher type (A 2 ), at rotating speed (B 1 ), and feeding rate (C 1 ).  Agriculture 2021, 11, x FOR PEER REVIEW and productivity were specified as A2B3C3. This means that the optimum efficie productivity were obtained using the conical shaped thresher (A2), a rotating 1500 (B3), and a feed rate of 1.8 (C3). On the other hand, the lowest power requ was obtained with a thresher type (A2), at rotating speed (B1), and feeding rate (C  Figure 5. Effect of operating parameters on S/N ratio for threshing efficiency.     Figure 7. Effect of operating parameters on S/N ratio for power.

Analysis of Variance
ANOVA was used to determine the individual interaction of all of the con tors in the test. In this study, ANOVA was used to analyze the effects of thresh rotating speeds, and feeding rates on threshing performance. The ANOVA re shown in Tables 7-9. This analysis was carried out at a 5% significance level an confidence level. The last column of the table shows the percentage value of

Analysis of Variance
ANOVA was used to determine the individual interaction of all of the con tors in the test. In this study, ANOVA was used to analyze the effects of thresh rotating speeds, and feeding rates on threshing performance. The ANOVA re shown in Tables 7-9. This analysis was carried out at a 5% significance level an confidence level. The last column of the table shows the percentage value of rameter contribution, which indicates the degree of influence on threshing perfo According to Table 8, the percent contributions of the A, B, and C factor threshing efficiency were found to be 4.87, 11.63, and 79%, respectively. Thus, important factor affecting the threshing efficiency was feeding rate.

Analysis of Variance
ANOVA was used to determine the individual interaction of all of the control factors in the test. In this study, ANOVA was used to analyze the effects of thresher type, rotating speeds, and feeding rates on threshing performance. The ANOVA results are shown in Tables 7-9. This analysis was carried out at a 5% significance level and a 95% confidence level. The last column of the table shows the percentage value of each parameter contribution, which indicates the degree of influence on threshing performance.
According to Table 8, the percent contributions of the A, B, and C factors on the threshing efficiency were found to be 4.87, 11.63, and 79%, respectively. Thus, the most important factor affecting the threshing efficiency was feeding rate. Referring to Table 9, the percent contributions of the A, B, and C factors in productivity were 16.16, 62.54, and 15.47%, respectively. Thus, the most effective factor on the productivity was thresher speed.
Regarding Table 10, the contributions percentage of the A, B, and C factors on the power were 2.11, 2.74, and 93.05%. Thus, the most effective factor was the feeding rate.

Results Evaluation and Discussion
After the test was carried out, and after the collected data were analyzed according to Taguchi techniques, some graphs were drawn using the Origin software in order to assure the former obtained results.

Effect of Feed Rate on Threshing Efficiency under Different Rotating Speeds for the Cylindrical and Conical Thresher
It was concluded that increasing the thresher's feeding rate and rotating speed increased the threshing efficiency from 96.98% to 98.41% for the cylindrical thresher and from 97.21 to 98.6% for the conical thresher, as shown in Figure 8. These results were in agreement with the results of Osueke, 2013 [36], and Ahuja et al., 2017 [37]. The increase in threshing efficiency with drum speed could be attributed to the high frequency of collisions and impacts between spikes and grain heads, resulting in more grain threshing and separating, and it could also be attributed to the increased friction between the concave and grain heads. The efficiency increased with the increase of feeding rate due to greater amount of mass of the crop fed to the thresher per the time unit.

Effect of Feed Rate on Power Requirement under Different Rotating Speeds for the Cylindrical and Conical Thresher
The required power increased with the increase in feeding rate and rotational speed. This may be attributed to a high load on the thresher because of the excessive stalks passing through the threshing gap. These results were the same as the obtained results by Ezzatollah et al., 2009 [8], who noticed that drum speed significantly affected the power requirements.
Using the conical-shaped thresher resulted in low power requirements when compared to the cylindrical thresher, as shown in Figure 9.

Effect of Feed Rate on Power Requirement under Different Rotating Speeds for the Cylindrical and Conical Thresher
The required power increased with the increase in feeding rate and rotational speed. This may be attributed to a high load on the thresher because of the excessive stalks passing through the threshing gap. These results were the same as the obtained results by Ezzatollah et al., 2009 [8], who noticed that drum speed significantly affected the power requirements.
Using the conical-shaped thresher resulted in low power requirements when compared to the cylindrical thresher, as shown in Figure 9.

Effect of Feed Rate on Power Requirement under Different Rotating Speeds for the Cylindrical and Conical Thresher
The required power increased with the increase in feeding rate and rotational speed. This may be attributed to a high load on the thresher because of the excessive stalks passing through the threshing gap. These results were the same as the obtained results by Ezzatollah et al., 2009 [8], who noticed that drum speed significantly affected the power requirements.
Using the conical-shaped thresher resulted in low power requirements when compared to the cylindrical thresher, as shown in Figure 9.

Effect of Feed Rate on Productivity under Different Rotating Speeds for the Cylindrical and Conical Thresher
Increasing the feed rate increased the productivity of the thresher from 0.27 to 0.51 kg/s for the cylindrical thresher and from 0.33 to 0.64 kg/s for the conical thresher, as illustrated in Figure 10. These results were in agreement with the work of Osueke, 2013 [36]. This may be attributed to the higher mass of rice passing through the thresher per time unit. Additionally, the increase of the rotational speed increased productivity because the higher speed resulted in a low threshing time, which increased the threshed Increasing the feed rate increased the productivity of the thresher from 0.27 to 0.51 kg/s for the cylindrical thresher and from 0.33 to 0.64 kg/s for the conical thresher, as illustrated in Figure 10. These results were in agreement with the work of Osueke, 2013 [36]. This may be attributed to the higher mass of rice passing through the thresher per time unit.
Additionally, the increase of the rotational speed increased productivity because the higher speed resulted in a low threshing time, which increased the threshed crop per the time unit. The conical thresher gave a higher productivity than the cylindrical thresher.
Agriculture 2021, 11, x FOR PEER REVIEW 12 of 14 crop per the time unit. The conical thresher gave a higher productivity than the cylindrical thresher. Figure 10. Effect of operating parameters on threshing productivity.

Conclusions
1. In this paper, two thresher structures were tested and evaluated for performance under different operating parameters such as thresher speed and feeding rate. The Taguchi technique was used to reduce the testing time and number and to analyze the data for experimental variable optimization The obtained results revealed that increasing the feed rate and rotating speed positively correlated with threshing efficiency, productivity, and power requirements. 2. The highest threshing efficiency and highest productivity of 98.6% and 0.64 kg/s, respectively, were achieved using the conical thresher under a rotating speed of 1500 rpm and a feeding rate of 1.4 kg/s. 3. The lowest required power of 5.45 kW was obtained using the conical thresher under a rotational speed of 1100 rpm and a feeding rate of 0.8 kg/s. 4. It was concluded that the conical thresher was more effective than the cylindrical thresher because it achieved a higher efficiency, a higher productivity, and a lower power requirement. 5. This research provides a new method for assessing rice thresher performance and presents a new threshing drum structure that will be more efficient for rice threshing with a combine harvester.

Feeding Rate (Kg/s)
Cylindrical thresher Conical thresher Figure 10. Effect of operating parameters on threshing productivity.

1.
In this paper, two thresher structures were tested and evaluated for performance under different operating parameters such as thresher speed and feeding rate. The Taguchi technique was used to reduce the testing time and number and to analyze the data for experimental variable optimization. The obtained results revealed that increasing the feed rate and rotating speed positively correlated with threshing efficiency, productivity, and power requirements.

2.
The highest threshing efficiency and highest productivity of 98.6% and 0.64 kg/s, respectively, were achieved using the conical thresher under a rotating speed of 1500 rpm and a feeding rate of 1.4 kg/s. 3.
The lowest required power of 5.45 kW was obtained using the conical thresher under a rotational speed of 1100 rpm and a feeding rate of 0.8 kg/s.

4.
It was concluded that the conical thresher was more effective than the cylindrical thresher because it achieved a higher efficiency, a higher productivity, and a lower power requirement.

5.
This research provides a new method for assessing rice thresher performance and presents a new threshing drum structure that will be more efficient for rice threshing with a combine harvester.