苜蓿刈割压扁收获机械系统的优化和试验研究

发布时间：2018-05-26 10:47

本文选题：割草压扁机 + 仿形系统　；参考：《中国农业大学》2017年博士论文

【摘要】：为了实现苜蓿高效、低损和优质收获,论文从苜蓿刈割压扁收获机械工作过程出发,在研究苜蓿茎叶连接力学特性的基础上,通过虚拟样机技术与田间试验相结合,对苜蓿刈割压扁机的仿形系统和切割压扁系统的设计参数进行了优化,对机械系统在喂入区产生的气流场进行了模拟和实测研究。论文进行了苜蓿茎叶连接力学特性研究,为机械系统与苜蓿植株作用过程的研究提供理论参考。对于新鲜苜蓿植株,进行拉伸破坏时的最大载荷值根据破坏方式不同由大到小的排列顺序为:顺茬拉伸、垂直拉伸和逆茬拉伸;顺茬拉伸时茎叶连接点被拉扯破坏,逆茬拉伸时茎叶连接点被撕裂破坏,而垂直拉伸时则处于两者之间,从力学特性角度分析,收获时顺茬喂入为理想喂入方式。仿形系统是刈割压扁机实现高效收获的关键,论文建立了仿形系统的虚拟样机模型,并进行了四因素三水平虚拟正交实验,以平均割茬高度、割茬稳定性系数和割刀触土深度为优化指标,得出仿形系统最佳设计和工作参数为滑掌长度188 mm,割台倾角4.06°,拉力重力比0.85,前进速度2 m/s。在此条件下,利用仿形系统虚拟样机仿真的结果为平均割茬高度为69.77 mm,割茬稳定性系数为46.96%,割刀无触土现象。切割压扁系统是刈割压扁机实现低损收获的关键,论文通过建立切割压扁系统的虚拟样机模型,在不同切割压扁运行参数下进行了仿真试验,假设并定义了评判切割压扁系统对苜蓿植株的破碎作用程度的碎草系数ε的模型,得到切割压扁系统最佳运行参数为割刀转速ng=1875 r/min,压扁辊转速ny=749 r/min,此时切割压扁系统对苜蓿植株的破碎作用最小。样机田间试验表明:实测碎草率与碎草系数ε呈线性正相关,相关系数平方R2=0.9588,验证了碎草系数模型的正确性。刈割压扁机械系统形成的气流场能辅助完成苜蓿收获过程,论文利用CFX对喂入区气流场进行了模拟计算,发现了机器前方存在"气流交汇点",通过对气流速度分析得出,该交汇点上方、后方和前方的气流分别能起到避免重割、辅助喂入和利于切割的作用。利用响应面分析得到了关键气流场参数随切割压扁运行参数变化的关系模型。对机械系统进行优化后的9GYZ-1.2型自走式苜蓿刈割压扁机,田间作业的割茬高度为55.5 mm,超茬损失率为0.31%,碎草率为2.32%,压扁率为98.36%,均达到国家标准对刈割压扁机作业质量的要求。与人工收获的未压扁的苜蓿相比,利用样机进行压扁调制收获的苜蓿,田间晾晒时的干燥速率明显加快,样机压扁调制取得了理想的效果。
[Abstract]:In order to achieve high efficiency, low loss and high quality harvest of alfalfa, the paper studied the mechanical properties of alfalfa stem and leaf connection, and combined it with field experiment through virtual prototyping technology, based on the working process of cutting and flattening harvesting machine. The design parameters of the copying system and cutting flattening system of alfalfa cutting flattening machine were optimized. The airflow field produced by the mechanical system in the feeding area was simulated and measured. In this paper, the mechanical properties of alfalfa stem and leaf connection are studied, which provides a theoretical reference for the study of the interaction between the mechanical system and alfalfa plants. For fresh alfalfa plants, the order of maximum load during tensile damage was as follows: following stubble stretching, vertical stretching and reverse stubble stretching; The joint point of stem and leaf was torn and destroyed during the extension of the reverse stubble, but it was in the middle of the two in the vertical stretching. From the angle of mechanical properties, the ideal feeding mode was to feed along the stubble at harvest. The copying system is the key to the high efficiency harvest of the cutting and flattening machine. The virtual prototype model of the copying system is established, and the virtual orthogonal experiment of four factors and three levels is carried out to average the stubble height. The optimum design and working parameters of the copying system are as follows: the length of the slide palm is 188 mm, the slope angle of the cutting table is 4.06 掳, the pull gravity ratio is 0.85, and the forward speed is 2 m / s. Under this condition, the simulation results show that the average stubble height is 69.77 mm, the stubble stability coefficient is 46.96, and the cutting knife has no contact with soil. Cutting and flattening system is the key to realize low loss harvest of cutting flattening machine. This paper establishes a virtual prototype model of cutting flattening system and carries out simulation experiments under different cutting flattening operation parameters. Suppose and define the model of breaking coefficient 蔚 of cutting and flattening system to evaluate the degree of fragmentation of alfalfa plants. The optimum operating parameters of the cutting and flattening system were obtained as follows: cutting speed ng=1875 rmin and flattening roll speed ny=749 r / min. At this time, the cutting and flattening system had the least effect on the breaking of alfalfa plants. The field test of the prototype showed that there was a linear positive correlation between the measured sloppiness and the breaking coefficient 蔚, and the correlation coefficient square R _ (2) was 0.958 8, which verified the correctness of the model. The airflow field formed by the cutting and flattening mechanical system can assist in the alfalfa harvest process. In this paper, the air flow field in the feeding area is simulated by CFX, and the "air flow intersection point" in front of the machine is found, which is obtained by the analysis of the airflow velocity. The air flow above, behind and ahead of the intersection can avoid recutting, assist feeding and facilitate cutting. Based on the response surface analysis, the relation model of the key airflow field parameters with the cutting flattening operation parameters is obtained. After optimizing the mechanical system, the 9GYZ-1.2 self-walking cutting and flattening machine of alfalfa, the stubble height of field operation is 55.5mm, the loss rate of excess stubble is 0.31mm, the rate of sloppy crushing is 2.32cm, and the flattening rate is 98.36. All of them meet the requirements of the national standard for the operation quality of cutting flattening machine. Compared with the unflattened alfalfa harvested by artificial harvesting, the drying rate of the alfalfa, which was compressed and modulated by the prototype, was obviously accelerated when it was dried in the field, and the ideal effect was obtained by the flattening modulation of the prototype.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S817.11

【参考文献】