Transverse multi-cylinders device

Transverse multi-cylinders combination was the main body of threshing apparatus of combine harvester. In order to investigate the threshing and separating capability of transverse multi-cylinders, and to obtain the best operating parameters combination on different rice agronomic characteristics, a transverse multi-cylinders test bench was developed as shown in Fig. 1. The test bench was comprised of a conveying plat, feed auger, conveying chute, I threshing cylinder (I-TCy), II threshing cylinder (II-TCy), III threshing cylinder (III-TCy), and other parts shown in detail below. A group of reception boxes were fixed under the grid concave of the transverse multi-cylinder device to receive the grains and short stalks separated through the grid concave (Li et al., 2013). Operating parameters such as threshing cylinder speed and concave clearance are the most important factors that influence both the power consumption of the threshing apparatus and the grain loss ratio during the rice harvesting process. In this study, the cylinder speed and concave clearance combinations of three threshing cylinders were the primary operating parameters.

Diameters of the I-TCy, II-TCy, and III-TCy devices were 525, 515 and 450 mm, respectively; lengths were 548, 1280 and 1280 mm, respectively. The threshing teeth were spike teeth. A schematic diagram of the threshing cylinders is shown in Fig. 2. The three threshing cylinders were driven by the respective frequency conversion motors. During the threshing process, three HAD-CYB-803S torque sensors (Beijing Westzh M & E Technology Co., Ltd., China) measured the torque value and speed at measurement accuracy of 0.25% full scale and frequency response time of 100 μs. The rice straw was preliminarily threshed and separated by I-TCy, then moved to II-TCy, where any remaining un-threshed grain was re-threshed and re-separated. Finally, the un-separated grain was again separated by III-TCy.

In order to ensure the straw was fed smoothly into the threshing device, the distance between I-TCy and II-TCy (and between II-TCy and III-TCy) was very important. The most effective distance between the I-TCy axis and II-TCy axis was identified at 730 mm, the same as the distance between the II-TCy axis and III-TCy axis. The mutual positional relationship is shown in Fig. 3a. Once the rice was threshed and the grain was separated by I-TCy, II-TCy, and III-TCy, the straw was discharged through the discharge hole. To make sure the straw was discharged through the hole smoothly, the size of the discharge hole was optimized at 300 mm as shown in Fig. 3b.

Freshly-cut rice (72 kg) was placed on a 12 m × 1 m conveyer belt at a liner speed of 1 m/s (with constantly feeding rate of 6 kg/s). After the rice was threshed and the grain was separated through the grid concave (forming “collected grain”) a few grains remained that were not threshed from the rice panicle (un-threshed grain) some that had not separated from the straw (un-separated grain), and some that were crushed by the spike tooth (broken grain); all of these grains combined grains formed the “total grain”. The mass of the grains and the MOG were weighed on an electronic scale (JY60001, Shanghai Fangrui Instrument Co., Ltd.). The measurement accuracy of the electronic scale was ± 0.1 g, and its maximum range was 6 kg. The un-threshed grain ratio, un-separated grain ratio, and broken grain ratio were a mass percentage of the un-threshed grain, un-separated grain, and broken grain as they corresponded to the total grain. Three types of rice threshing test were conducted on the transverse multi-cylinders test bench. The first type was rice threshed only by I-TCy device, and the second was rice threshed by I-TCy and II-TCy devices (referred to as “I-TCy + II-TCy”) . The third type was rice threshed by I-TCy, II-TCy and III-TCy devices (referred to as “I-TCy + II-TCy + III-TCy”) .

Test rice material

The tested rice (Oryza sativa L. cv. Wujing15) was grown in Jiangsu Province, China. Its average characteristics are: moisture content of the stalks, 66.43%; grain moisture content, 25.02%; length of panicle, 100 mm; length of primary branch, 75 mm; number of primary branch, 12; number of grains in each primary branch, 12; and number of grains in each panicle, 150. Each branch, from the bottom of the panicle to the top, is marked as 1^st, 2^nd, ..., 12^th part.

Detachment force of rice panicle

Rice panicles consist of grains, pedicels, primary branches, secondary branches, rachides, and stems. The attachment force of the grain and pedicel on the panicle reflect the threshing difficulty level and the shattering habit where the grain was threshed. A computerized, electronic universal testing machine, WDW30005 (Changchun New Test Instrument Co., Ltd., China), measured the specific detachment force of the grain and pedicel by vertical stretching method. Lots of freshly-cut rice panicles were used to measure the specific detachment force of the grain and pedicel. After detachment force was measured, the moisture contents of grain and pedicel were determined by XY-105MW Electronic Moisture Analyzer (Shanghai Hong Ji Equipment Co., Ltd.; the test range of moisture range was 0-100%; the moisture readability was 0.01%; the test mass range was 0-110 g). Results of the same moisture content were classified as one group of test and were used to statistical analysis. At least five samples with the same moisture content were used to analysis the detachment force of the grain and pedicel. The entire parameter estimation procedure and the results of each test were repeated five times, in order to reduce the impact of the random influence on choice of validation set. The panicle attachment was connected to the holding clip of the force gauge in two bending positions: perpendicular to the front of the grain, and perpendicular to the side of the grain. The threshing force value, in tension, was significantly higher than the any other loadings (Kronbergs, 2000).

Optimal parameter comparison

Optimal parameters were designed around the threshing and separating performance of the transverse multi-cylinders test bench. Detection indexes of threshing and separating performance were defined by power consumption and lost grain ratio-when power consumption and lost grain ratio were lowest, threshing and separating performance was best. The lost grain ratio contained un-separated grain ratio, un-threshed grain ratio, and broken grain ratio. The separated grain ratio (valid grain, as opposed to un-separated grain, un-threshed grain, or broken grain,) was the total grain ratio minus the total lost grain ratio.

The performance index of the I-TCy device can be described as follows:

where α is the performance index of the I-TCy device; r₁is the un-separated grain ratio, t₁is the un-threshed grain ratio, s₁ is the breakage ratio, and P₁ is the power consumption of the device; Q is the total power of the transverse multi-cylinder test bench. The total power of all three frequency conversion motors Q=100 kW.

The performance index of I-TCy + II-TCy devices can be described as follows:

where β is the performance index of I-TCy+II-TCy devices; r₂is the un-separated grain ratio, t₂is the un-threshed grain ratio, and s₂ is the breakage ratio of the devices; P₂ is the power consumption of the II-TCy device.

The performance index of I-TCy + II-TCy + III-TCy devices can be described as follows:

where γ is the performance index of I-TCy + II-TCy + I-TCy devices, r₃is the un-separated grain ratio, t₃is the un-threshed grain ratio, and s₃ is the breakage ratio of the devices; P₃ is the power consumption of the III-TCy device.

According to Eqs. [1], [2] and [3], when detection indexes α, β, and γ were bigger, the threshing and separating performance was better.

Statistical analysis

The complete parameter estimation procedure and the results of all tests were repeated five times to reduce the impact of random influence on choice of validation set. Means ± standard errors (SE) were calculated using the same variables (n=5). The mean data were analyzed statistically using a factorial design in SPSS software (v. 13.0, SPSS Inc., CA, USA), then mean results were compared by least significant difference (LSD) post-hoc test at the 5% significance level (p<0.05). The grain distribution rules were drawn using MATLAB 7.6 software.

Detachment force of grain and pedicel

The grain moisture content of the rice panicles, shown in Table 1, was measured from one field. The attachment forces between grains and pedicels for each panicle at different moisture content were also measured. All results are shown in Table 1. According to the experiment results, detachment force decreased from the 1^st part to the 12^th part. This phenomenon was caused by differing moisture content, which was lower at 12^th part than other parts. Diameter was also lower at the 12^th part than other parts. These findings are in accordance with earlier reports by Ichikawa et al. (1990), Kawamura et al. (2002), Inoue et al. (2003) and Yang et al. (2012). As a general observation, the detachment force was different throughout any rice panicle. All grains threshed from a rice panicle must be threshed up to three times to deduce broken grain.

Table 1. Detachment force of each part of the grains and pedicels with different moisture contents. Data are shown as means ± standard errors (SE) (n=5).

Fig. 4 shows the relationship between average detachment force and moisture content deduced from the results shown in Table 1. Moisture content was different for each field. The difference between maximum and minimum moisture content was 22.79% (Fig. 4). The detachment force differed alongside moisture content. When the moisture content was 29.69%, the average detachment force was at its minimum. Optimal harvesting time, to this effect, is when moisture content is at 29.69%. This is in agreement with earlier reports by McCauley & Way(2002). But De Toro et al. (2012) indicated that in order to complete harvesting operations in most years, it was necessary to operate at a moisture ceiling of 17-24% (w.b.). This difference results could be due to the differing characteristics and variables of rice and different geographical and climatic conditions (Zhou et al., 2014).

Fig. 5 shows the distribution proportion of detachment force (according to results shown in Table 1), where detachment force distributions were observed within three different ranges. The first range, 1.0-1.7 N, was 39.81%, and the second, 1.7-2.0 N, was 40.74%. Due to differences in detachment force distribution, these grains should be threshed by different threshing devices. The third detachment force distribution, 2.0-2.3 N, showed the lowest threshing value at 19.44%. Different device operating parameters must be applied to the rice in accordance with different attachment force values.

Threshing capability of transverse multi-cylinders

Operating parameter combinations

In order to test the threshing performance under different cylinder speed combinations, rice threshing performance experiments were conducted at a feeding rate of 6 kg/s and concave clearance of 40 mm for each cylinder. Detailed programs and test results are shown in Table 2. The preliminary threshing capability of I-TCy was 45.32-47.83% and the preliminary separating capability of I-TCy was 12.26-14.08%. This demonstrates the strong threshing and separating ability of the I-TCy device. The average moisture content of grains threshed and separated by I-TCy was 28.34%. Separated grain ratio, breakage, and power consumption all increased with increasing cylinder speed. As shown in Table 2, when the rotation speed of I-TCy was 600 rpm, its threshed grain ratio was 47.83%. The separated grain ratio and power consumption of I-TCy was 14.08% and 3.82 kW, respectively.

Table 2. Threshing and separation results of the transverse multi-cylinder device. The data are shown as means ± standard errors (SE) (n=5).

At different cylinder speeds, the threshing and separating performance detection indexes α, β, and γ of the transverse multi-cylinder device were calculated using Eqs. [1], [2], and [3], respectively. The calculated results are shown in Table 3. The biggest threshing and separating performance index α was 3.69, which were said that the optimal rotation speed of I-TCy was 600 rpm. According to Table 2, the separated grain ratio and threshed grain ratio of I-TCy was 14.08% and 47.83% (un-threshed grain ratio was 52.17%). The power consumption of I-TCy was 3.82 kW. The biggest threshing and separating performance index β was 2.98 in Table 3. That indicated the optimal rotation speed of II-TCy was 650, with the rotation speed 600 rpm of I-TCy. According to Table 2, when the rotation speed of I-TCy was 600 rpm and the rotation speed of II-TCy was 650 rpm, the threshed grain ratio of II-TCy was 42.16% (because the un-threshed grain ratio of I-TCy+II-TCy was 10.01%). The separated grain rate of II-TCy was 57.49% (because the total separated grain rate of I-TCy+II-TCy was 71.57%), and its power consumption was 20.35 kW. According to Table 3, the biggest threshing and separating performance index γ was 2.66, which mean the optimal rotation speed combinations of I-TCy, II-TCy, and III-TCy was 600, 650, 700 rpm. According to Table 2, the transverse multi-cylinder test bench un-separated grain ratio was 1.31%, un-threshed grain was 0.24%, and breakage was 0.43%. The total power consumption of the transverse multi-cylinder test bench was 36.63 kW.

Table 3. Threshing and separating performance index of the transverse multi-cylinder device. The detection index α was calculated using Eq. [1], β by Eq. [2], and γ by Eq. [3].

Rice threshing and separating tests on the transverse multi-cylinders were performed at cylinder speeds of 600 rpm (I-TCy), 650 rpm (II-TCy), and 700 rpm (III-TCy) and concave clearances of 35 mm (I-TCy), 40 mm (II-TCy), and 45 mm (III-TCy), at a feeding rate of 6 kg/s. The programs and test results are shown in Table 4.

Table 4. Threshing test of transverse multi-cylinders with different concave clearances. Data are shown as means ± standard errors (SE) (n=5).

At different concave clearances, the threshing and separating performance detection indexes α, β, and γ of the transverse multi-cylinder device were calculated by Eqs. [1], [2], and [3], respectively. Calculation results are shown in Table 5. By comparing the threshing and separating performance detection indexes (Table 3) of the transverse multi-cylinder device, it becomes clear that the most favorable cylinder rotation combination was 600 rpm (I-TCy), 650 rpm (II-TCy), 700 rpm (III-TCy). Results showed that grains with lower moisture content were threshed and separated first by I-TCy. Grains with higher moisture content were threshed and separated secondly by II-TCy. Grains with power detachment force were threshed and separated by III-TCy. According to Table 4, the separated grain ratios of I-TCy, II-TCy, and III-TCy all decreased with increase of concave clearance. Table 5 shows that when the concave clearance of I-TCy was 40 mm, its highest threshing and separating performance index α was at 3.69. The most effective concave clearance combination of multi-cylinders devices was 40 mm (I-TCy), 35 mm (II-TCy), 40 mm (III-TCy), determined by comparing the threshing and separating performance detection indexes. The observed operating parameter combination for transverse multi-cylinders in this study is similar to a previous study by Sun (2014).

Table 5. Threshing and separating performance index of the transverse multi-cylinder device. The detection index α was calculated by Eq. [1], β using Eq. [2], and γ by Eq. [3].

Distribution of separated material

In order to obtain the distribution rule of the transverse multi-cylinder test bench, a combination of operating parameters of cylinder speed (600, 650 and 700 rpm) and concave clearance (40, 35 and 40 mm) were tested at a feeding rate of 6 kg/s. After the rice was threshed and separated, the mixed material (grains and material other than grain) separated from the grid concave were collected in boxes. The separated grain and MOG are shown in Fig. 7. Grains were threshed and separated through transverse multi-cylinder griddle concaves, then dropped into the boxes. The percentages of grains in each material box are shown in Table 6.

Figure 7. Mixed material and rice straw threshed by transverse multi-cylinders.

Table 6. Grain distribution percentages for each transverse multi-cylinder’s box. The entire parameter estimation procedure and the results of each test were repeated five times to reduce the impact of random influence on choice of validation set.

Fig. 8 shows three-dimensional distribution of percentages of grain in boxes drawn by Matlab software, based on information found in Table 6. I-TCy separated relatively little grain, instead, most of the grain was threshed and separated by II-TCy. Rice was threshed mainly in the I-TCy device, and grain was separated mainly in the II-TCy device. Grains which were particularly difficult to thresh were mainly threshed and separated in the III-TCy device.

Figure 8. Distribution rules of grain in each transverse multi-cylinder box.

Application of structures and parameters

Structure and operating parameters for transverse multi-cylinders were applied to a rice combine harvester (Zhejiang Liulin Agricultural Machinery Co., Ltd., China). A structural diagram of the transverse multi-cylinder combine harvester is shown in Fig. 9. When rotation speed and operating parameters were applied to the combine harvester at cylinder speeds of 600 rpm (I-TCy), 650 rpm (II-TCy) and 700 rpm (III-TCy) and concave clearances of 40 mm (I-TCy), 35 mm (II-TCy), 40 mm (III-TCy), at a feeding rate of 6 kg/s, results showed an un-threshed grain ratio of 0.64%, un-separated grain ratio of 0.35%, and broken grain ratio of 0.22%. So, the structure of transverse multi-cylinders, plus specific operating parameter combinations, was proved to be effective for rice harvesting.

In summary, moisture content differed in each field, which results in different attachment force between the grain and pedicel on the panicle. Detachment force decreased from the 1^st part to the 12^th part of each branch. The first range, 1.0-1.7 N, showed 39.81% moisture content. The second range, 1.7-2.0N, showed 40.74%. The third range, 2.0-2.3 N, showed 19.44%. The most effective harvesting time was identified at moisture content of 29.69%. Different moisture content requires specialized threshing devices and operating parameters. Grains with lower moisture content were threshed and separated first by the I-TCy device, grains with higher moisture content were threshed and separated second by the II-TCy device, and grains with power detachment force were threshed and separated by the III-TCy device. The optimal operating parameter combination was cylinder speeds of 600 rpm (I-TCy), 650 rpm (II-TCy), 700 rpm (III-TCy), and concave clearance of 40 mm (I-TCy), 35 mm (II-TCy), 40 mm (III-TCy), which showed an un-threshed grain ratio of 0.64%, un-separated grain ratio of 0.35%, and broken grain ratio of 0.22% at a feeding rate of 6 kg/s. The results of this research can be used to design successful, efficient transverse multi-cylinder rice combine harvesters.