用于机械化栽植的西兰花钵苗力学特性试验

为了降低西兰花钵苗机械化栽植过程中的破损率,避免栽植嘴已经运行到栽植位置而钵苗还未滑到栽植嘴的底部而造成移栽失败,该文采用正交试验的方法,以土钵体积(表示穴盘规格)、苗龄和含水率为试验因素,针对栽植过程农艺要求,进行了不同方案下土钵的抗压强度试验和钵苗沿栽植嘴壁面下滑的运动阻力系数测试。通过建立西兰花土钵与栽植嘴壁面碰撞过程接触力学模型,分析得到为避免土钵破损钵苗和栽植嘴碰撞时不同组合允许的最大相对速度。以栽植作业中避免钵苗破损,同时运动阻力不能过大为目标,采用综合评分法,得到适宜机械化栽植的4个土钵体积、苗龄和含水率组合,进而对这4个组合进行模拟田间栽植试验,得到最优的组合:土钵体积为中(穴盘规格为128),苗龄为2~3片真叶,含水率约为63%。该研究为栽植机构的设计提供依据。

Mechanics property experiment of broccoli seedling oriented to mechanized planting

Abstract: In order to reduce the breakage rate of the broccoli seedling during mechanized planting and to avoid the transplanting failure caused by the discordance between planting nozzle and seedling while the planting nozzle has arrived at the planting location but the seedling has not slipped to the bottom of planting nozzle, the orthogonal experiments based on agronomic requirements has been carried out in this paper. The volume of soil block (represent plate size), seedling age, and moisture content of soil blocks are selected as the experimental factors. Every factor has three levels. One experiment has been carried out to test the compressive strength of soil blocks under different schemes. Through using the universal material testing machine, the relationships between compressive force and compressive amount have been obtained and expressed as curves. In order to analyze these curves, the compression elasticity of the soil block has been proposed, which was defined as the straight slope between point D (starting point of linear elastic) and point E (yield point). Then, several sets of compression elasticity and yield limit under different schemes have been obtained. Analysis results show that the compression elasticity increases at first, then decreases with the reduction of the volume of soil blocks, while the yield limit decreases with the reduction of the volume of soil blocks. Both of them have no significant relationship with seedling age, but decrease with the increase in moisture content. Another experiment was carried out to test the motion resistance coefficient between seedling and planting nozzle. The broccoli seedling was put on an incline, then the process of broccoli seedling sliding along the incline was recorded by the high-speed camera. The sliding acceleration along the incline of broccoli seedling was obtained by video processing technology. Afterwards, the motion resistance coefficient was derived by using Newtonian mechanics theory. Analysis results show that the motion resistance coefficient decreases with the reduction of soil block volume, and increases with the increase of both the seedling age and moisture content. The mechanics model of the colliding process between seedling and planting nozzle has been built, and the highest relative speed allowed was obtained from the model. In order to avoid the breakage of seedling, meanwhile the motion resistance coefficient shouldn't be too high, a comprehensive scoring method was applied to evaluate the combinations of soil block volume, seedling age, and moisture content. Four combinations were chosen by comparing the scores. In order to achieve the best combination, the field planting simulation experiment was conducted. This experiment was done indoors by using a rotating circular soil tank driven by the friction of tires. Breakage rate and rewind rate were obtained from this experiment. The best combination that is suitable for mechanized planting of broccoli seedling was obtained: medium soil block (128 holes plate), 2-3 leaves, and water content at 63%. This study provides reference for the design of planting mechanism.