Study Of Characteristics Evaluation Of Surface Topography Based On A Stylus System For Measuring Displacement

The surface morphology evaluation system of a stylus roughness profiler is an important part of the instrument function. At present, the evaluation system of precision instruments is closed in the world and it can’t be used in a new instrument. Meanwhile, study and application of the evaluation technique for surface morphology characterizes are limited at a certain extent. Besides, the surface morphology evaluation system is related to the hardware measurement system of the instrument. Therefore, it is very important to develop a set of surface morphology evaluation system for the stylus roughness profiler.In this paper, the study of the creeping of one-dimensional scanning system, the separation technique of surface profile, parameter evaluation technique, are carried out. Firstly, the micro-displacement signal acquisition principle and the working principle of one-dimensional scanning system are analyzed. Both the equivalent physical model and the dynamics model of the one-dimensional scanning system are established. The dynamic simulation is carried on through the Simulink module of MATLAB software, and the factors influencing the creeping of one dimensional scanning system are analyzed by theoretical deduction.Secondly, signal acquisition system is analyzed. Based on the separation principle of surface topography, the ISO filtering algorithm and advanced filtering methods are adopted to separate the surface profile. The DXF file is developed by analyzing the constitution of DXF file. Based on the principle of evaluating surface roughness parameters in Taylorsurf PGI 635 roughness profiler, the corresponding surface topography evaluation software was developed by using VC++6.0 for data processing and AutoCAD for image showing.Thirdly, the characteristics of primary profile are separated based on EMD. The average frequency of IMFs within unit length is defined by using the instantaneous weighed frequency of non-stationary signal and the frequency within an evaluation length is deduced. Then a Varied Amplitude Weighting Factor(VAWF) is designed and applied to the selected IMF with maximum frequency to constitute an EMD mixed mean line. Then the general calculating formula and the algorithm of EMD mixed mean line are formed.Finally, the experiments for on-the-fly calibration of the creeping of one dimensional scanning system, the separation technique and the parematers evaluation technique for the acquired surface profile using stylus displacement measuring system, are carried out. The experiments show that the creeping phenomenon disappeared and the running is stable after 0.275 second at the speed of 0.1 mm per second for one dimensional scanning system, and that both Gaussian mean line and EMD mixed mean line can be used to extract roughness profile. Also, EMD mixed mean line doesn’t suffer from edge distortion and five roughness parameters can be evaluated.