Surface Measurement Method Based On Focus Variation Measurement Technology

Surface topography plays an important role in the functionality of a component.With the development of science and technology and the improvement of precision machining requirements,people increasingly pay more attention to surface topography measurement technology,especially optical measurement technology.Focus variation is a non-contact optical method that allows the measurement of three-dimensional surface topography using vertical scanning with limited depth of focus.This method can be used to measure steep flanks and has good robustness in relation to different materials.In this paper,we built a focus-variation measuring system and used several focus measurement functions and image processing technology to reconstruct the surface topography.In this paper,the main works are as follows.1.This paper introduced the development and application of surface topography measurement.The state-of the-art development and the research meaning of focus variation method was described in detail.The basic principle and working process of this method were studied in a deep-going way.2.Several focus measurement functions were used to process focus-variation images.Comparing with the anti-noise capability and computational efficiency of several focus measurement functions,and discussing the influence of window size of focus measurement function on measurement quality,we determined the parameter settings and range of application,and optimized the performance of focus measurement function.3.For the case that the precision of depth map which was calculated by focus measurement function is low,we proposed several interpolation and fitting methods which improved the calculation accuracy.Comparing with the computational efficiency and precision,we ensured the superiority of the Gaussian interpolation method.4.Consistency check was proposed to filter out singular point without change the original data.Using the consistency check,image pre-processing,and spatial filtering methods,we optimized calculation results.5.According to the sample measurement requirements,this paper selected the appropriate camera,lens and light source to design and built a focus-variation measuring system which contained a moving section,an imaging and acquisition section and a program section.Programs were written to control the system and realize image acquisition and processing.The proposed method were verified by measuring a MEMS micro resonator structure,a spherical probe,and a cutting edge.