气吸式玉米高速精量排种器投种性能分析与结构优化

为解决前期研制的气吸式玉米精量排种器在高速作业条件下存在投种位置不一致和横向飞种导致播种均匀性差的问题，该研究从力学角度对投种位置不一致和横向飞种现象进行分析，构建了不同吸附姿态和尖端直立深入吸附种子的力学模型以及相邻两粒种子间距的数学模型，明确了投种位置不一致和横向飞种的产生机理及速度和株距对投种均匀性的影响机制，提出一种末端拨离+直线投种方法，确定了末端拨离阻气件的关键参数。利用高速摄像技术和ProAnalyst运动分析软件对投种过程进行对比分析，结果表明，采用末端拨离+直线一致性投种方法，种子在竖直方向匀加速运动，在水平方向速度为0，到达投种位置后脱离种盘，沿竖直方向直线加速进入导种管，可实现均匀一致的直线投种。台架试验结果表明，采用末端拨离+直线投种的气吸式精量排种器在各个作业速度条件下排种性能较改进前均有所改善，在14 km/h时，合格指数提高了1.61个百分点，漏播指数降低了1.00个百分点，株距变异系数降低了1.79个百分点。田间试验结果表明，在作业速度小于等于12 km/h条件下，播种机的播种合格指数均大于94%，漏播指数小于5%，重播指数小于2%，株距变异系数小于20%，采用末端拨离+直线投种方式可大大改善播种效果，提高精量播种机作业速度。研究结果可为气吸式高速精量排种器的研究提供参考。

Performance analysis and structure optimization of the maize precision metering device with air suction at high-speed condition

Abstract: An air-suction maize precision metering device has been early developed in recent years. It is very necessary to balance the seeding position and transverse movement of seeds for better seeding uniformity at high speed. In this study, a systematic investigation was made to clarify the influence of speed and seed distance on the seed drop uniformity in the maize precision metering device with air suction under high-speed conditions, particularly from the mechanical point of view. At the same time, a mathematical model of adjacent seed spacing was established to determine the working parameters in the seed feeding process. The results showed that the spacing between two adjacent seeds decreased significantly, with the increase in operating speed, and the decrease in seeding spacing. The external interference during seeding was more likely to cause a sharp deterioration of seeding performance. According to the previous linear seeding theory, a specific mechanism was constructed from the seed top to avoid in-depth adsorption and push the seed to the end of the dial finger fixed-point seed. A terminal release and linear seeding mechanism was then developed to cooperate with the seed plate, linear seed pushing device, and gradual choke parts of the seed disk. The action range of the progressive seed-disk gas barrier was determined, together with the active surface parameters and the parameter equation. Finally, the key parameters were determined for the terminal dial-off gas barrier. The high-speed camera technology and ProAnalyst motion analysis software were also used to compare the motion characteristics of the seed dropping process. The results showed that the terminal dial-off and linear seed falling mechanism performed better, where the seeds were uniformly accelerated in the vertical direction, while, the seed speed was 0 in the horizontal direction, and at the working speed of 12 km/h, the time interval of the seeds from the plate was approximately 0.075 s, and the vertical velocity to the seed tube was approximately 1 325 mm/s. Specifically, the seeds were detached from the seed tray when reaching the seed dropping position, in order to accelerate into the seed tube in the vertical direction in a straight line, indicating the uniform and consistent linear seed dropping. At the same time, a bench comparison test was conducted to verify the performance of the improved maize precision metering device with the air suction, terminal dial-off, and linear seeding at all operating speeds. The qualified index of seeding spacing at the high speed increased by 1.61 percentage points at the working speed of 14 km/h, whereas, the missing seeding index and the coefficient of variation of seeding spacing were reduced by 1.00, and 1.79 percentage points, respectively, compared with the ordinary choke seeding. It indicated that the terminal dial-off and linear seeding mechanism effectively improved the seeding performance at a high working speed. Finally, the field tests were conducted under a working speed of 12 km/h or less. It was found that the qualified index of seeding spacing was greater than 94%, the missing and multiple seeding indexes of seeding spacing were less than 5%, and 2%, respectively, where the coefficient of variation of seeding spacing was less than 20%, indicating the better seeding performance to fully meet the requirements of precision seeding. The terminal dial-off and linear seed falling mechanism can be expected to balance the seeding position and transverse movement of seeds, in order to greatly improve the seeding performance at the increasing operation speed. The findings can also provide a strong reference for the feeding performance of the air-suction high-speed precision metering device.