【作者】 王利；

【导师】 陈念年；

【作者基本信息】 西南科技大学 ， 计算机应用技术， 2016， 硕士

【摘要】 表面形貌测量是产品质量控制的关键任务,直接决定产品的外观特征及使用性能。目前测量朗伯表面形貌的技术已日趋成熟,但大多存在逐点测量速度慢、环境要求苛刻、测量范围小、计算量大、具有映射多义性、易出现测量盲区等缺点,难以用于反射表面的形貌测量。针对上述问题,对基于线光测量反射表面形貌的线激光三角法、横向剪切干涉法、同步偏振相移法进行了深入研究,主要研究成果如下:(1)将传统斜射式激光三角法扩展到反射表面形貌测量中,提出了一种高噪声背景下激光条纹亚像素中心提取的方法。线光投射至反射表面,被表面形貌调制并变形,变形光场被屏幕和CCD相机接收后形成激光条纹图像。采用高噪声背景下条纹亚像素中心提取的方法,计算出激光条纹与参考平面条纹的中心偏移量,根据光源、被测表面、设备的三角几何关系,解调出变形光场蕴含的表面形貌信息。实验表明,条纹中心提取的好坏直接影响表面形貌测量的精度,线激光三角法测量反射表面形貌的误差约为±0.25mm。(2)针对线激光三角法测量误差大的问题,对María Frade等的横向剪切干涉三维形貌仪进行改进,设计了不包含柱面镜和透镜、仅包含透镜的两种反射表面形貌测量方案,消除柱面镜和透镜联合使用引起的象散现象。利用Savart双折射晶体横向剪切展开线光,获得干涉条纹图像,采用傅里叶变换解析频率,计算被测表面与设备传感器之间的距离,仅需一帧图像就可测量表面上一条轮廓线的形貌。实验表明,剪切干涉的自比较和共路共线特性增强了反射表面形貌测量的抗环境振动和干扰能力,测量精度优于30μm。(3)利用同步偏振相移技术,解决了傅里叶变换解析图像时测量精度受干涉信号离散、参数选取等因素限制的问题。在横向剪切干涉反射表面形貌测量中,于Savart晶体后加入由1/4波片和偏振片组成的偏振移相装置,用空间位置不同的CCD相机同时采集剪切干涉条纹图像,经四步相移和相位解包裹获得相位斜率后,测量出反射表面的形貌。实验表明,由于剪切干涉抗环境干扰、相移抵消噪声及同步采集消除分时误差等优点,最终测量精度优于20μm,测量出的形貌结果及其变化趋势更接近真实值。更多还原

【Abstract】 Surface shape measurement is the crucial task for quality control, which directly determines the appearance characteristics and performance of products. Shape measurement techniques of Lambert surfaces are difficult to be used for measuring specular surfaces, because of their disadvantages such as slow speed, harsh environmental requirements, small measuring range, large computational quantity, mapping ambiguity and prone to blind areas, etc. To solve the abovementioned problems, the methods of specular surface shape measurement based on line light are studied, including laser triangulation, lateral shearing interferometry and synchronous polarization phase shift. The main research results are as follows:(1) Traditional inclined laser triangulation is introduced to specular surface shape measurement, and a method for sub-pixel center extraction of laser stripe in high noise background is proposed. Firstly, line light is projected to specular surface and modulated by the shape, then received by screen and CCD camera. Secondly, center offsets between laser stripe and reference plane stripe are calculated after obtaining the laser stripe image. Finally, the surface shape information contained by deformed light field is detected according to the triangular geometry relation among the light source, specular surface and devices. Experimental results show that extraction accuracy of the stripe center directly affects the precision of specular surface shape measurement, and the measurement error based on line laser triangulation is about ±0.25 mm.(2) To improve the measurement accuracy of line laser triangulation, two schemes for specular surface shape measurement are designed to eliminate the astigmatism. The schemes are based on the lateral shearing interferometry profilemeter proposed by María Frade, and one is without the cylindrical lens and the lens, the other is with the lens only. Firstly, shearing interferometry stripe image is obtained by using Savart birefringence crystal to later al shear the expanded line light. Secondly, the distance between surface and sensor is calculated after obtaining the frequency of stripe by Fourier transform. Finally, the shape of a whole surface profile can be measured with only one-frame image. Experimental results show that the anti-vibration and anti-disturbance ability of specular surface shape measurement can be enhanced by the self-comparison property and full common- path collinear setup of shearing interferometry, and the measurement accuracy is raised to better than 30 μm.(3) By using the synchronous polarization phase shift technique, the problems in Fourier transform, such as the dispersion of interference signal and selection of parameters, are solved. Firstly, the polarization phase shift device composed of quarter-wave plate and polarizer is added behind the Savart crystal. Secondly, the shearing interferometry stripe images are grabbed by CCD cameras with different spatial position at the same time. Finally, the phase slope is obtained by four step phase shift and phase unwrapping, and the shape of the specular surface is measured. Experimental results show that results and the variation trend of the measurement are closer to true values, and the measurement accuracy is improved to better than 20 μm, due to the advantages such as the anti-disturbance ability of shearing interferometry, noise canceling of phase shift, and time-sharing error eliminated by synchronous acquisition, etc.更多还原