修正边界区域误差的共聚焦显微成像粗糙度测量

Surface Roughness Measurement Using Laser Confocal Microscope with Boundary Area Correction

为了对具有陡峭轮廓的物体进行非接触式表面粗糙度测量,常采用共聚焦成像对物体进行分层成像,进而重建出物体的表面三维轮廓,并采用高斯滤波的方法从表面三维轮廓中滤出粗糙度轮廓。在滤波过程中,会出现边界数据的缺失,常规的简单延伸原始轮廓两端数值的方法会导致滤波后的轮廓两端出现失真,该方法只适用于整体轮廓较为平缓的零件。引入了一种新的边界区域修正方法,该方法对表面弧度变化较大的零件也同样适用,能够准确提取物体的粗糙度轮廓。对整体轮廓较为平缓和陡峭的两组粗糙度样本分别进行共聚焦成像测量,对于整体轮廓较为平缓的样本,利用常规方法处理后,得到的均方根误差和粗糙度的平均值分别为0.080和2.86μm,与该样本粗糙度值2.94μm相比,相对误差为2.72%;利用边界区域修正方法处理后,得到的均方根误差和粗糙度的平均值分别为0.090和2.85μm,与该样本粗糙度值的相对误差为3.06%。整体轮廓较为陡峭的样本的粗糙度值为3.2μm,利用常规方法处理后,得到的均方根误差和粗糙度的平均值分别为0.120和3.31μm,与该样本粗糙度值的相对误差为3.48%;利用边界区域修正方法处理后,均方根误差和粗糙度的平均值分别为0.045和3.19μm,与该样本粗糙度值的相对误差为0.31%。研究结果表明,该方法能准确地测量整体轮廓较为陡峭的物体的表面粗糙度,为激光共聚焦粗糙度测量设备的研制提供了参考。

In order to achieve the non-contact surface roughness measurement of objects with steep contours,we usually use confocal imaging to layer the objects and thus to reconstruct the three-dimensional surface contours of objects.Meanwhile,a Gaussian filter is used to extract the roughness contours from the three-dimensional surface contours.However,the boundary data are missed during the process of filtering and simultaneously the usual simplified extension of two end data of original contours leads to contour distortion.This paper introduces a new type of method for boundary area correction.This correction method can be also useful for parts with large surface radian changes and can be used to accurately extract the roughness contours of objects.Confocal imaging measurements are performed on two sets of actual roughness samples with overall smooth and steep contours.For samples with overall smooth contours,the root mean square error(RMSE)and average roughness obtained by the conventional method are 0.080 and 2.86μm,respectively,and the error relative to the sample roughness value of 2.94μm is 2.72%.In contrast,after boundary area correction,the obtained RMSE and average roughness are 0.090 and 2.85μm,respectively,and the error relative to the sample roughness value is 3.06%.The roughness of the sample with an overall sharp contour is 3.2μm,and the RMSE and average roughness obtained by the conventional method are 0.120 and 3.31μm,respectively.The error relative to the sample roughness value is 3.48%,and after boundary area correction,the RMSE and average roughness are 0.045 and 3.19μm,respectively.The error relative to the sample roughness value is 0.31%.The research results confirm that this method can accurately measure the surface roughness of objects with overall steep contours and can provide a certain reference to the development of laser confocal roughness measurement equipment.