基于傅里叶描述子和共振频率的不规则果形梨果硬度评估指标构建  

Establishment of firmness evaluation indexes for irregular shapes pears based on Fourier descriptor and resonance frequency

作　　者：王鹏[1] 吴杰[1,2] Wang Peng;Wu Jie(College of Mechanical and Electrical Engineering,Shihezi University,Shihezi 832000,China;Research Center of Agricultural Mechanization for Economic Crop in Oasis,Ministry of Education,Shihezi 832003,China)

机构地区：[1]石河子大学机械电气工程学院,石河子832000 [2]绿洲特色经济作物生产机械化教育部工程研究中心,石河子832003

出　　处：《农业工程学报》2021年第11期299-306,共8页Transactions of the Chinese Society of Agricultural Engineering

基　　金：国家自然科学基金地区科学基金项目(31560476)。

摘　　要：针对不规则果形梨果,为构建适用于评估果形不规则梨果硬度的硬度指标,该研究采用傅里叶描述子对梨果轮廓进行描述,并将试验模态分析和有限元模态分析相结合,研究果形变化对梨果振动频率的影响规律,基于振动频率和果形描述子构建硬度评估指标。结果表明,采用前15个傅里叶描述子可以准确描述啤梨果形轮廓特征,第1傅里叶描述子与啤梨低频弯曲、挤压、呼吸模态频率线性相关性较高,相关系数分别为-0.923、-0.922、0.700;挤压模态振动变形在赤道部较大,测试时易于提取共振频率,因此选取挤压模态频率构建含有第1傅里叶描述子的硬度指标,新指标评估硬度值与M-T穿刺硬度实测值决定系数为0.892。研究结果可为果形不规则梨果硬度评价提供参考。Firmness is one of the important indicators for the internal quality of fruits.Natural frequency has widely been expected to evaluate the fruit firmness in recent years.Several indices have successfully been applied for the firmness of sphere-shaped fruits using the natural frequency and fruit mass.However,the fruit with non-spherical or irregular shapes cannot be suitable for firmness evaluation,due mainly to the fact that the fruit shape can interfere with the resonance frequency.Thus,some dual-frequency indices were established to measure the firmness of fruit with ellipsoidal shapes.Nevertheless,these indices cannot accurately evaluate the firmness of complex and irregular pears.In this study,a Fourier descriptor was established as a reliable shape descriptor to evaluate the firmness,thereby representing complex,irregular,or a larger variation of pear shapes.Firstly,the shape images of pears were captured by a camera.Then,the boundary edges of pear images were extracted to calculate the normalized radiuses.After that,a Fourier transform was performed on the normalized radius to obtain the Fourier descriptor.Finally,the first 15 Fourier descriptors were screened to describe the complex shapes of pears.Meanwhile,an experimental modal combined with the Finite Element Method(FEM)was utilized to analyze the effect of fruit shape on the natural frequency.Three modes included bending,compression,and breathing during a test.The natural frequency was easy to measure the equatorial region of the pear fruit in the compression mode.The largest deformation appeared,when the pear was impacted on this region.As such,the pear was assumed to be linearly elastic,homogeneous and isotropic material in the FEM.A process of reverse engineering was utilized to form the geometric model of pears.The 3D 4-node tetrahedral structural solid element was selected,allowing three translational and three rotational degrees of freedom at each node.Consequently,three shapes and natural frequencies in FE modal analysis were highly related to th

关 键 词：无损检测 果实 傅里叶描述子 模态分析 果形 硬度评估指标 共振频率 

分 类 号：TP212[自动化与计算机技术—检测技术与自动化装置] S661.2[自动化与计算机技术—控制科学与工程]