摘要光学成像条码定位是一种基于条码识别技术和机器视觉测量的光电自动化测量方法，其中与定位相关的关键要素（物象比）可以在频域中通过分析计算得到，这就需要对标尺的特征谱线进行准确的提取。但是在实践中，由于信号序列的加窗截断和傅里叶变换谱采样的造成影响，使得到的条码频谱的幅值、相位和频率都会产生较大的误差。为了获取准确的频谱信息，需要提出一些能够获取较为精确的频谱的方法，对频谱中的各种误差进行修正，来使得定位的距离更加精确。67445

本文详细分析了获取特征谱线过程中产生的频谱泄漏和谱间干扰现象，也就是所谓的截断效应的原因，提出了窗函数法是解决截断效应的有效途径，并且探讨了几种不同窗函数对信号傅氏变换后频谱的影响,揭示各种窗的特点和作用,提出用窗函数进行频谱分析时的改进措施。其次，分析了离散傅立叶变换中所遇到的栅栏效应及其产生的原因，对由其产生的误差进行了分析，并介绍了补零过采样法和相位差矫正法这两种频谱修正的方法。之后，对实际工程中一定会遇到的噪声信号进行了分析，并提出了自相关这一修正噪声影响的方法。最后，本文对上述误差修正方法用Matlab软件进行了编程，利用计算机模拟，并通过和处理前的原始信号进行对比，验证了其合理性和可行性。

毕业论文关键词  条码定位，窗函数，频谱误差，频谱修正

毕业设计说明书（论文）外文摘要

Title      Spectral Modification In The Optical    Barcode Image Positioning                     

Abstract

Optical barcode image positioning(OBIP) is a kind of photoelectric automatic measuring method that is based on barcode recognition and machine vision technology.In OBIP the comparison between object and image that is a very important factor in positioning can be obtain by analysis and calculation,so the characteristic spectra of the barcode need to be extracted accurately.But in the practice the amplitude,the phase and the frequency of the barcode spectrum may have errors because of the window affect of the signal sequence and the spectrum sampling of the fourier transform.In order to obtain accurate spectrum information and positioning distance,we need some method of the spectral modification to revise all kinds of errors of the spectrum.

This article detailedly analyse the spectrum leakage and the spectrum interference phenomenon that is called truncation effect in the process of the obtaining characteristic spectra. We explain how it happened,propose that the window function method is a effective way to resolve the truncation effect.Then we analyse the influence of the signal spectrum by using different kinds of window functions and discuss the respective characteristic and effect of window functions.Further more the article illustrate the fence effect in the fourier transform and how it happened,analyse the errors that are caused by fence effect,and introduce two spectral modification method:zero-padding & oversampling method and phase difference modification method.In addition,the noise signal in the practical engineering is analysed and a method that is call autocorrelation is proposed to modify the noise affection.In the end,this article simulate the former spectral modification method by using Matlab on the computer platform,and prove the rationality and the feasibility of them by comparing with primary signal that was not manipulate.

Keywords  optical barcode image positioning(OBIP),window  function,spectrum errors,spectral modification

                           目   次