Design and experiment of the centrifugal rotary root-soil separation device for a multiple taro harvester

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.