【作者】 张南；

【导师】 叶贤基；

【作者基本信息】 华中科技大学 ， 理论物理， 2009， 硕士

【摘要】 激光测距是一种目前使用很广泛的精密测量方式,最新的电容位移传感,X射线衍射干涉仪,以及扫描隧道显微镜,虽然精度很高,但测量距离很短,不适用于空间长作用距离的测量,而激光测距可以实现长距离中的位移长度测量,这是其他精密测量方式所不具备的。激光测距中,对干涉信号的处理是此系统中非常重要的一环,直接关系到被测信息的精度和可靠性,传统的相位计由模拟器件构成,具有运算速度快,技术成熟的特点,但其精度一般不会太高,并且受环境的影响非常严重,随着高速芯片技术的飞速发展,对于信号的处理越来越趋向于采用数字的方式,解反三角函数的鉴相方法具有极高的精度,而且数字方法不容易受环境的影响。数字鉴相方法又分为两大类,一类是基于软件,一类是基于硬件。基于硬件,譬如FPGA的方法,相对于用计算机语言实现的方法运算速度更快,更有利于实现实时的控制和测量。然而,软件鉴相方法是其他方法的基础,基于硬件式的鉴相方法,用硬件取代CPU进行运算,其算法都是相同的。本文将详细讨论两种常见的软件鉴相方法,傅立叶变换法,数字相关法,为最终能实现数字鉴相奠定基础。另外,本文中所使用的软件鉴相方法都是基于C语言,相比于目前大部分基于MATLAB和LABVIEW的软件方法,使用中级语言编写,更有利于提高运算速度和后续改进。首先,本文先将介绍下激光测距系统的结构,以及位移与相位之间的转化关系,然后介绍两种鉴相方法的原理,可能出现的原理性误差和校正方法。然后,在第三章中,将分析各种方法的运算时间,以及各种噪声信号对其的影响。再在第四章中,将通过信号发生器模拟激光外差信号进行仿真测试。通过本论文能得到如下结论:首先,本文中所使用的软件鉴相方法,都能测量10KHz的信号,相位测量速率为100Hz,测量分辨率高于0.1°。采用更快速度的采集卡,可以提高外差信号的频率,和测量分辨率,采用更快的计算机系统可以提高运算速度。其次,傅立叶变换法实现的数字鉴相法,其适用范围,精度高于数字相关法,数字相关法只适用于同频信号的测量。数字相关法的优点在于运算速度要快于傅立叶变化法。更多还原

【Abstract】 Laser displacement-measuring system is widely used in many applications Although capacitance displacement sensor, x-ray interferometer, scanning tunneling microscope have comparable or even higher precision, they can’t be used in case of long dynamic range and/or long measurement baseline, which the laser displacement measurement can exactly be applied for.Signal processing for phase detection is very important in laser metrology system, it closely relates to the measurement precision and sampling performance. Conventional analog method of phase detection has a fast measuring speed but limited precision, and usually is affected obviously by environmental conditions. As the computer chip’s development is getting matured and the computing speed is getting faster, more and more systems use digital signal processing method instead of the analog’s method.There are two kinds of digital phase-measuring methods currently used, one by means of software and another by using hardware. The method by using hardware, just like FPGA, usually has a faster measuring speed than the software method does, so it is often used in real time systems. However, the method by using software is the basic of the method by using hardware. In this paper, I will discuss two familiar software phase-measuring methods: Fast Fourier Transform (FFT) and Correlation method. Besides, in order to make the method efficient and easily-readable, all programs will be written in C/C++ language.In this paper, I’ll introduce briefly the basic principle of laser displacement measurement system, the fundamental theory of the software phase-measuring methods, FFT and Correlation methods. The existed errors in these methods and their possible solving methods and corrections will be also mentioned. Finally, a simulation experiment for analyzing these errors will be demonstrated.According to the results we obtained from simulation experiments, I make a conclusion as follows.(1) Using the software method discussed in this paper, we can measure the signal’s frequency less than 10KHz, the phase resolution is better than 0.01, and the measuring speed must be controlled within 100Hz. If we could use a faster Analog-to-Digital Converter (ADC), a higher frequency and fast computing speed can be achieved.(2) The method by using FFT can be used more commonly and efficiently, because applications of the correlation method are limited by the condition that two signal frequencies must be equal exactly, that is very difficult to be met in general cases. However, the correlation method can measure more quickly due to a simple computing.更多还原