基于二阶欠阻尼阶跃响应的收获机割台液压缸选型分析

Selection Analysis of Hydraulic Cylinder of Harvester Header Based on Second-order Underdamped Step Response

割台是谷物收获机的重要组成部分,割台性能的好坏决定着收获机在收获作业时的作业质量。割台液压缸选型确定方面,传统方式大多采用对割台质量及液压系统工作负载进行分析,利用经典力学的方式进行割台油缸的选型。随着自动控制理论的发展,割台高度闭环控制技术也越来越多地开始出现在国外领先收获机机型上,仅考虑力学负载分析的方法已经无法满足割台高度自动控制系统的需要。针对控制系统稳态分析的要求,割台油缸在满足工作负载的前提下,还需考虑系统的超调量、反应时间及过调震荡时间等因素。为此,进行割台升降运动过程建模分析,论证出割台控制模型为二阶欠阻尼模型系统,发现固有频率ωn与阻尼比ζ决定着系统动态指标。通过对液压缸内部分析,求出了割台液压缸系统的传递函数,确定出当其他机械参数不变时,割台油缸的管径影响着割台液压缸系统的固有频率ωn与阻尼比ζ。综合采用上升时间tr、峰值时间tp、超调量σ%和调节时间ts等4种系统稳态指标确定了最佳割台油缸参数,并进行了Amesim仿真试验。研究结果为后续无人驾驶谷物联合收获机的研发设计提供了割台装置控制策略的理论依据。

Header is an important part of grain harvester.In the aspect of determining the type selection of header hydraulic cylinder,the traditional method mostly adopts the analysis of header weight and hydraulic system working load,and uses the method of classical mechanics to select the type of header hydraulic cylinder.With the development of automatic control theory,more and more header height closed-loop control technology began to appear on foreign leading har-vester models. At present, the method of only considering mechanical load analysis can not meet the needs of header height automatic control system. According to the requirements of steady-state analysis of the control system, on the premise of meeting the working load,the header oil cylinder also needs to consider the overshoot, reaction time,overshoot oscillation time and other factors of the system. In this paper, the header lifting movement process is modeled and ana-lyzed, and it is demonstrated that the header control model is a second-order underdamped model system. It is determined that the natural frequency and damping ratio determine the effect on the system dynamic index. Through the internal anal-ysis of the hydraulic cylinder,the transfer function of the header hydraulic cylinder system is obtained, and it is deter-mined that when other mechanical parameters remain unchanged, the diameter of the header cylinder affects the natural frequency and damping ratio of the header hydraulic cylinder system. The four system steady-state indexes of rise time, peak time, overshoot and regulation time are comprehensively used to determine the optimal header cylinder parameters. Finally,Amesim simulation test is carried out. This study provides a theoretical basis for the control strategy of header de-vice for the research and design of unmanned grain combine harvester.