Rice is the second most important cereal in the world after wheat. Threshing is one of the most essential steps in the rice harvesting process. Previously, the drum rod toothed longitudinal axial-flow threshing device has been designed to reduce the blockage of the thresher and threshing power consumption. Specifically, the power consumption of the drum-shaped threshing cylinder can be reduced by 5% to 15% on average, compared with the traditional cylindrical one. Previous work has focused on the structural design of drum-shaped threshing cylinders. But it is still lacking in the uniformity of axial loads on the drum-shaped threshing cylinder. At the same time, the current rice combine harvester threshing and separating devices are focused mostly on the structural improvement and optimization of working parameters, with respect to the performance indicators, such as threshing power consumption, harvesting yield, entrainment loss, unthreshing rate, and crushing rate. The threshing power consumption is mostly measured directly by the power consumption detector during the bench test. Only a few studies have been reported to measure the threshing power consumption, where the axial load uniformity of the drum has been quantified to optimize the rod tooth and drum structure form. In this study, the rod teeth of a drum-shaped threshing cylinder were optimized to improve the axial load uniformity of the drum-shaped threshing cylinder for a higher reduction in power consumption. The impact mechanics model of rod tooth and rice grain was established to determine the structural parameters of the rod teeth that affected the axial load uniformity of the drum, including the diameter of the rod tooth and the threshing gap. Theoretical analysis was implemented to clarify the influence of rod tooth diameter and length on the threshing power consumption. The bending angle of the elbow rod tooth and closed bow tooth was calculated to be set at 45° for better consistency of the threshing gap. The structural parameters were determined for the axial load uniformity of drum rollers, including the rod tooth diameter (7-16 mm), and threshing gap (15-30 mm). The optimal structural parameters were determined with the smallest coefficient of variation in the axial load uniformity as an indicator. A series of simulation tests were conducted to investigate the influence of rod tooth diameter and threshing gap on the axial load uniformity of cylindrical rod tooth, elbow rod tooth, and closed bow tooth drum. The results showed that the axial load trend of the drum roller with the elbow rod tooth was more uniform than that of the cylindrical rod tooth and closed bow tooth. The optimal structural parameters of the rod teeth were 10 mm rod tooth diameter, and 25 mm threshing gap. A three-factor, three-level Box-Behnken response surface bench test was conducted with the feed rate, threshing cylinder speed, and rod tooth shape as the factors, while the threshing power as the indexes, in order to reduce the threshing power consumption. A regression model was established to optimize the working parameters for the threshing power consumption. The bench test showed that the optimal working parameters of the cylindrical rod teeth drum were achieved in the feeding rate of 1.1 kg/s, and the speed of cylinder 900 r/min under the optimal structure parameters, where the lowest power consumption was 4.61 kW. The optimal working parameters of the elbow rad tooth drum were the feeding rate of 0.95 kg/s, and the speed of cylinder 935 r/min, where the power consumption was 3.58 kW. The parameters of closed arch tooth drum were no longer optimized, due to the weak ability to transport stalks easily for the blockage. The rod tooth of the drum was optimized for the shape of the tooth of the elbow rod. The drum simulation and bench tests were carried out to verify the structure and working parameters before and after the optimization of the cylindrical and elbow rod tooth. The variation coefficient of axial load uniformity of the optimized elbow rod tooth drum was 10.34% lower than that of the cylindrical rod tooth drum. The power consumption was reduced by 7.15%, indicating that the optimized elbow rod tooth effectively reduced the threshing power consumption of the drum for the better performance of the drum. This finding can provide a strong reference to optimize the performance of small longitudinal axial flow harvesters in the hilly mountainous areas in China.

Taro (Colocasia esculenta) is one of the perennial tuberous plants in the Araceae family. The global area of taro harvesting has reached 1.793 7 million hectares in 2022, with a total output of 12.394 5 million tons. The yield per unit area in China has been 2.75 times the world average in the world. The main production regions are situated in the Yangtze River Basin, the Pearl River Basin, and Taiwan Province. Taro can play a crucial role in the process of rural revitalization. However, manual harvesting has been predominant in recent years. It is still lacking in the specialized harvesting equipment for the mechanized production of taro. In a previous study, the bar-type screening device was employed to conduct taro harvesting experiments. The taro root system and the soil have also been adhered, wrapped, and entangled to form a "root-soil composite" structure during operation. This complex matrix can serve as the taro tubers to reinforce the fibers for the roots. Nevertheless, some challenges remain in actual production, including suboptimal soil crushing quality, ineffective root-soil separation, and elevated screening power consumption during mechanized harvesting. Furthermore, the existing bar-type screening device was unable to fulfill the requirement of taro root-soil separation requirements. In this study, the centrifugal rotary root-soil separation device was developed to fully meet the agronomic and harvesting requirements of multi-seed taro. A collision mechanics model of taro root-soil composite was developed for an impact crushing mechanics model of soil blocks. A systematic analysis revealed that the primary influencing factors on the efficacy of root-soil separation were ranked in the descending order of the spring tooth inclination angle, the rotational speed of the screen, and the aspect ratio of the flexible finger. The range of values was determined for the influencing factors after measurement. A discrete element model (DEM) of taro corm-root-soil composite was established using EDEM software, in order to analyze the process of soil fragmentation under impact collisions. The simulation experiment was conducted to couple the EDEM-Recur Dyn platform. A systematic analysis was made to determine the dynamic change of the taro root-soil composite during screening. There were the balance, instability, soil crushing, collision tumbling, and soil shedding. The single-factor test showed that the diameter and length of flexible fingers were 14, and 45 mm, respectively. A quadratic regression orthogonal test was conducted to identify the optimal combination of spring tooth inclination angle, rotary screen speed, and soil feed amount, with the root-soil separation rate and the maximum impact force of taro as the evaluation indices. The optimal combination of parameters was determined using the Design-Expert software. A high root-soil separation rate of 93.36% was achieved in the rotary screen speed of 110.00 r/min and a soil feed amount of 14.00 kg/s at an inclination angle of 16.00°. A series of field tests were conducted to validate the optimal parameters under identical operational conditions. The results indicated that the root-soil separation rate was 92.06%, which differed by 1.39% from the prediction of a regression model. At the same time, the taro damage rate was 4.86%. Five performance tests were conducted using the multiple taro harvester and the traditional bar-type rhizome harvester. The root-soil separation rate of the multiple taro harvester increased by 8.61 percentage points under identical operational conditions, while the damage rate increased by 0.99 percentage points. The centrifugal rotary device of root-soil separation fully met the requirements of root-soil separation of taro. The screening performance was better than the traditional grid-type screening device. The findings can serve as the sound foundation to design efficient and low-loss harvesting equipment in the crushing and separation of root-soil composite for root and tuber crops.

In order to address the issues of narrow seeding adjustment range and low accuracy of grain placement in the existing rice seeders, a mechanically and pneumatically adjustable precision hole-type seeder is designed. It is primarily composed of a seeding disk, air chamber, seed box, and seed discharge device. The design incorporates a symmetrical structure with dual disks and dual casings, enabling both single-sided and double-sided single-row and synchronized seeding. Based on theoretical analysis of seed charging, seed protection, and seed release, the following parameters were determined: seeding disk diameter of 192 mm, suction hole diameter of 1.48-1.52 mm, suction hole spacing of 3.04-9.41 mm, type hole distribution circle radius of about 62.1-77.0 mm, type hole diameter of 9 mm, stirrer plate length of 4.705-9.410 mm, and stirrer plate inclination angle of 0°-30°. Using a coupled simulation method of EDEM-Fluent, the impact of different type hole distributions, stirrer plate lengths, and inclination angles on seeding performance was analyzed. The results indicate that the main and secondary influencing factors on seed charging qualification rate are type hole diameter, stirrer plate inclination angle, and stirrer plate length. The optimal performance is achieved with a type hole diameter of 6 mm, stirrer plate length of 5 mm, and stirrer plate inclination angle of 10°, resulting in a seed charging qualification rate of 71.42%. Furthermore, Fluent software was utilized to analyze the influence of different suction hole spacings, diameters, and air chamber radii on seeding performance. The results revealed that the suction of rice seeds by the hole can be better realized with a suction hole spacing of 6 mm, a suction hole diameter of 1.5 mm, and an air chamber radius of 62 mm, at which the average negative pressure in the suction hole center was about 2824.56 Pa. A bench test and a field test were further performed on the device. The results showed that increasing the number of type holes and suction holes can contribute to more stable regulation of the seeding amount. The optimal single-sided seed metering could achieve a maximum qualified rate of 82.5%, a missing rate of 12.5%, and a repeating rate of 5%; while the optimal double-sided seed metering could obtain a maximum qualified rate, missing rate, and repeating rate of 72.5%, 15%, and 12.5%, respectively. This adjustable precision seeder can meet the requirements of precision sowing of Huanghuazhan rice varieties, and the research findings can provide reference for the structural optimization of precision rice seeders.