农田地面不平度测试装置的设计与试验

Design and Experiment on Agricultural Field Profiling Apparatus

目前,农田地面不平度的测取并没有成熟的装置和方法,已有的不平度测试存在诸如测试效率不高、田间杂草或作物根茬对测试结果产生影响及测得的地面不平度数据难以与由其引起的农业机械振动数据实时对应等问题。为此,本研究设计开发了一种农田地面不平度测试装置,主要由测试机构和数据采集系统两部分组成,目的是实现农田地面不平度的随车动态测试,并有效解决测试中存在的上述问题。不平度测试装置的有效性由两个尺寸已知的梯形凸台在高粱茬地中进行试验验证,验证结果由凸台轮廓的实际高程与测试高程的均方根误差来衡量。同时,对高粱茬地、马铃薯收获地和田间草地这3种地面的不平度进行了测试,通过分析其时域和频域特征参数来揭示各农田地面的不平度特征。试验验证结果表明:左右凸台的均方根误差RMSE分别为3.4mm和4.5mm,多次试验的最大值都不超过6mm,相对于其自身轮廓的均方根值78.6mm和74.5mm都较小,表明所设计的不平度测试装置适合农田地面的不平度测试。农田不平度测试结果表明,3种农田地面不平度的频率指数W、不平度系数C和均方根值RMS值分别是1.37~1.95,3156~5646(10^(-8)m^(3-W))和20.7~34.2(10^(-3)m);同一类型农田地面在不同试验段的不平度功率谱密度W值、C值和时域RMS值的变化范围都较大;同一测试段左、右轮迹上的不平度参数W、C和RMS值的差别在多数情况下也都相对明显;农田地面不平度的频率指数W值均小于2,其平均值为1.75,说明相比ISO 8608所规定的W=2的路面特征,农田地面不平度功率谱密度的低频能量相对较少,高频能量相对增加。

At present, no suitable test device and method are used for measuring agricultural field roughness. The existing method of measuring agricultural field roughness has many problems, such as low testing efficiency, impact of weed or crop stubble on profiling results and difficulty of correspondence between field surface roughness data and vehicle dynamic response data. Therefore, a field profiling apparatus has been developed in this study, which was mainly composed of measuring mechanism of agricultural field roughness and data acquisition system. The purpose is to achieve dynamic measurement of field surface roughness, and effectively solve the problems in the profiling measurement mentioned above. The performance of profiling apparatus was validated by measuring two trapezoidal bumps with known dimensions. The validation results were assessed by the root mean square error（RMSE） of the actual elevation and the measured elevation of bump profile. At the meanwhile, profiling measurements were conducted in a sorghum stubble field, a harvested potato field and a grass field, and roughness features of the field profiles were characterized by analyzing parameters of profiles in time domain and frequency domain. The validation test results showed that the RMSEs of the left and right side bump profiles were 3.4 mm and 4.5 mm, respectively. And the maximum RMSE values of other tests were no more than 6 mm, which are quite small relative to the RMS values of 78.6 mm（0.7-meter bump profile） and 74.5 mm（0.9-meter bump profile）. Therefore, the developed profiling apparatus was suitable for measuring field surface roughness. The agricultural field profile measuring results showed that the frequency index W, the roughness coefficient C and the root mean square value RMS of three kinds of agricultural field roughness were 1.37-1.95,3156-5646（10-8 m3-W） and 20.7-34.2（10-3 m）, respectively. The ranges of W, C and RMS values of the same type of agricultural field profiles were relative large in different testing sections, the differences between the left and right track parameters of field surface roughness, such as W, C, RMS were relative great in most cases. At the meanwhile, the range of the W values of all measured field profiles from both tracks was less than 2 with the average of 1.75, which indicates that comparing to the road with the value W=2 specified in ISO 8608, the ratio of the short wave energy to the all wavelength energy of the field profile is relatively small, and the high-frequency energy is relatively increased.