考虑质量时变的收获机械工作模态分析与试验

为研究复杂开放环境下收获机械田间作业过程由质量时变影响的工作模态及振动行为,该文搭建了一套收获机械工作模态测试系统,以4YZP-4HA型122 k W玉米联合收获机械为研究对象,建立收获机械车架工作模态测点模型,测定工作模态试验下的土壤-机器-植物等边界条件,并进行田间收获作业和运输工况的振动响应数据采集和时频域分析,利用时域随机子空间SSI(stochastic subspace identification)和频域的增强型频域分解EFDD(enhanced frequency domain decomposition)算法,辨识了在质量时变(田间收获作业)和质量非时变(运输工况)影响下的模态参数(模态频率、阻尼比及模态振型),并比较分析了2种算法的工作模态辨识结果。利用时频域分析方法获取了不同测点振动加速度幅值统计特征及频率分布规律,研究结果表明:田间收获作业工况振动强度高于运输工况,振动频率集中分布在20~150 Hz范围内,测点频率之间存在差异主要由不同位置刚度变化所致;通过比较SSI和EFDD方法辨识的模态频率,发现SSI和EFDD方法在相同频率范围内相差较小,且均落入傅里叶变换方法的频率分布区间,表明SSI和EFDD方法计算结果可信,能够较为准确地确定模态频率;质量时变下的收获机械车架模态振型特征主要表现为扭转、弯曲、弯扭和局部模态振型,其中1阶扭转振型频率接近29 Hz(SSI:29.578 Hz;EFDD:29.300 Hz)。研究结果可为复杂农田作业环境下收获机械的工作模态分析与试验提供参考。

Operating modal analysis and test of harvester induced by mass-varying process

Abstract: Harvesting machinery is a typical off-road vehicle, which is exposed to vibrations caused by soil, machine and plant under complex operating environment and conditions. Harvester vibration characteristics have an important influence not only on harvester structure''s lifetime and working precision, but also on driver''s comfort and grain loss. There is a common characteristic in agricultural harvesting machine that mass of the whole machine is increasing with time-varying, which reflects the crucial structural dynamics characteristics. Unfortunately, the mechanism and influence rule of vibration are not well known to people, especially in operating modal analysis and test method of harvester induced by mass-varying process were rarely studied. At the same time, operational modal analysis method and test technology are most important methods and techniques to realize optimization design of agricultural harvesting machinery equipment and improve reliability. In order to study operational modal characteristics and vibration behavior of harvester induced by mass-varying process, firstly, SSI (stochastic subspace identification) algorithm and EFDD (enhanced frequency domain decomposition) algorithm were derived, which are the bases of modal identification algorithm. Secondly, taking 4YZP-4HA corn combine harvester with 122 kW as a research object, according to the structure characteristics of corn combine frame, an operational mode test system was designed in field operating condition, which is convenient to install and has a high reliability. Thirdly, an operational modal measuring point model of harvester frame is established, and soil-machine-plant system boundary conditions were measured for operational modal test, the boundary condition including soil, machine and plant parameters, by means of time domain and frequency domain analysis method, time domain statistical characteristics and frequency domain distribution regulation of different measuring points were obtained. On this foundation, using 16 channels 24-bit 3062V dynamic test acquisition instrument, the response data of vibration was acquired. Finally, only through vibration response data (transportation condition and operating condition), using method of SSI and EFDD identify modal parameter (natural frequency, mode shape and damping ratio) induced by time-varying (field operation condition) and non-time varying (transportation condition) process, and comparison of frequency results of 2 algorithms to identify operating modes of harvester frame structure. The results showed that, the vibration intensity of field operating condition was higher than that of transportation condition, and the frequency distribution was concentrated between 20~150 Hz, and the frequency distribution of different measuring points was more consistent, and the main reason for difference is gradient change of stiffness of different measuring point after assembly. Vibration modal frequency parameters and rule of deformation of harvester frame in the field operation were identified by SSI and EFDD method, the result of fourier transform method are compared and analyzed, and it can be more accurate to determine the modal frequency, furthermore, identify modal shape of harvester frame, the modal shape are mainly characterized by bending, torsion and local modal shape, at the same time, the 1 order torsional vibration frequency is about 29 Hz (SSI method, 29.578 Hz; EFDD method, 29.300 Hz). The result of this paper provides reference for vibration characteristic and operational modal analysis approach which harvester machinery works in complex condition, and offers guidance and service for development, design and optimization of new harvest machinery, and improves working method and working reliability.