蔬菜移栽机曲柄摆杆式夹苗机构的设计与试验

Design and experiment of crank rocker type clamp seedlings mechanism of vegetable transplanter

通过对穴盘苗进行抗压特性试验、试验平台的夹取试验,研究分析了适于夹取式自动取苗机构工作的相关参数组合以及最佳的钵苗含水率状况,为机构设计提供参考依据。该文基于辣椒穴盘苗抗压特性设计了全自动蔬菜移栽机曲柄摆杆式穴盘苗夹苗机构,该机构可与顶出机构配合完成全自动蔬菜移栽取苗和投苗工作。该文完成了曲柄摆杆式夹苗机构主要结构的设计,并对曲柄摆杆式夹苗机构的工作过程进行了力学、运动学分析和仿真,确定了结构和工作参数,即曲柄、连杆、摆杆长度分别为80、236.22、172.5 mm,夹苗爪具有较好的运动特性。曲柄摆杆式夹苗机构性能试验结果表明,夹取爪为金属材质,弹簧劲度系数为90 N/m,钵苗脱落率为0,钵苗破碎率为4.2%,综合取苗成功率可达95.8%,性能指标符合设计要求,夹苗爪"V"形结构设计有效防止穴盘苗在夹取过程中脱落,保证了取苗成功率。试验表明钵苗含水率为60.8%时,钵苗在不同的弹簧劲度系数及夹取爪材质下均有良好的适应性,在该含水率下钵苗的取苗平均成功率为94.4%。该机构从取苗到投苗采用圆弧形工作轨迹,夹苗爪采用八字形轨道与复位弹簧控制其开合,结构简单、性能可靠,无需调整即可适应多种不同尺寸穴盘苗的取苗工作,对不同含水率穴盘苗适应性强,对穴盘苗损伤小,机构成套使用可达到较高工作效率。

In designing a picking seedling mechanism, it is important to see the compressive characteristic of plug seedlings. So, in this research, the experiments were designed and conducted to get the compressive characteristic of plug seedlings. For more details, in the experiments, 20 pepper plug seedlings with growth period of 40 d were selected randomly. These seedlings were measured, their average height was 140 mm, the average height of the pot was 44 mm, the width of seedlings＇ leaves was 109.8 mm and the diameter of the seedlings＇ stem was 2.47 mm. Crank-rocker type seedling clamping mechanism was designed according to corresponding requirements. This mechanism was driven by an adjustable-speed motor and a crank and the movement of the rocker clamper was designed as reciprocating swing. In cooperation with the ejection mechanism, the rocker clamper could capture the seedlings at the right place and move them to the target position. Then, the rocker clamper could accomplish the processing of planting by loosening the 2 plates of the clamper. Also, in this research, an experimental platform of a crank-rocker type seedling clamping mechanism was fabricated and manufactured and with this platform a series of experiments were conducted. In these experiments, 3 experimental factors were set as claw clipping force, clipping claw material and moisture content of plug seedlings. Each experimental factor contained 3 levels and success rate of clamping, expulsion rate of seedlings and broken rate of seedlings were set as 3 test indices. Experiments were repeated by 8 times for each distinct condition, and totally 216 experiments were conducted under 27 different conditions. This research analyzed the mechanical parameters of the crank-rocker type seedling clamping mechanism and the corresponding moisture levels of the seedlings which could lead to the best planting performance. Furthermore, besides the design of the main components of the crank-rocker type seedling clamping mechanism, this research also conducted the mechanical and kinematics analysis on the working process of this seedling clamping mechanism. Also, the movement simulation was conducted with the aid of the simulation software i.e. Solid works COSMOS Motion. In this approach, the structures and the main parameters of the mechanism were properly designed. For more details, the length of the crank, the connecting rod and the swinging rod was respectively designed as 80, 236.22 and 172.5 mm. The test results indicated that when the rocker clamper was metal, the stiffness coefficient was 90 N/m respectively, the expulsion rate and the broken rate of seedlings and the success rate of clamping were 0, 4.2% and 95.8% respectively which meant that the Crank-rocker type seedling clamping mechanism could match the desired performance. The test results showed that when the moisture content of plug seedlings was 60.8%, the plug seedlings had excellent adaptation to different stiffness coefficient and material of clamper, and the average success rate of clamping was 94.4% in this condition. This mechanism could take seedlings from the initial position and put them to the target position by using circular trajectory. The condition of opening and closing of the claw could be controlled by trapezoid track and reset spring. The design was simple and reliable. This mechanism could work with plug seedlings with various shapes and sizes without additional adjustment, and it also contained high adaptability to the seedlings with different moisture levels. Also, it would minimize the damage of the plug seedlings and significantly improved the efficiency of the process of seedling capture and planting.