Research On Laser-interference Profilometer With Large Range For Surface Measurement

Contact measurement is most widely used in engineering surface measurement at present. But the old stylus apparatus has some shortcomings such as small measurement range, low precision, few parameters and inconvenient operation and so on. Application in engineering, so many important worked surfaces have curved shape. The characteristics of these curved surfaces will influence use performance. The measurement for curved surface involves not only roughness, but also waviness and shape error. This requires the profilometer owns high precision and large range. So a laser-interference profilometer has been developed to own characteristics of large range, high precision and complete parameters. The main research contents are as follow:Based on the theory of laser interference, the factors that influence the interferential stripe's are analyzed, and the optical sensor of the instrument is designed. At the same time, the pyramidal prism brings the nonlinear relation in large range between light travel distance and measured displacement is deduced by vector coordinate transforms, compensatory method is also given in this paper.As the conclusion of the reasoning and experimentation with real situation, simple and convenient way for getting better signal of interferential stripes is presented. Besides that, the mathematic model for amending the signal is founded. A circuit is developed to finish subdividing and backward-forward counting of the interferential stripes and the A/D conversion that is used to ensure the fine division of the stripes.Virtual instrumentation technology is applied in this apparatus. Based on LabWindows/CVI, the instrument driver is developed and a complete-function user program with soft virtual panel is programmed. By the soft virtual panel, the user can conveniently set parameters for measuring, and choose the ways for fitting and filtering. The parameters for characterizing 2-D surface are completely given, and ones for 3-D surface are partly given. There are also some necessary graphs in the panel. All of those can be printed out.For verifying its precision and feasibility, the case study is conducted with this system through measuring the reticle templet and the outer and inner roll trails of the roller bearing. The experimental results show that its measurement range is ±3mm, the resolution can reach 0.01μm.