Study of etched surface topography with the compensation of contactless vibrational measurement errors

Abstract

A comprehensive evaluation of surface topography can contribute to many appropriate responses on the properties of manufactured products. Precise measurement and data processing may allow for improvement in the control quality. Many advantages were achieved in the increasing accuracy of the surface topography measuring devices and whole control systems. Since contactless measuring equipment is much faster than tactile, analysis of surface topography for industrial applications was encouraged under the non-contact systems. However, those rapidly evolving measuring techniques are fraught with many external disturbances which can radically affect the final surface topography measurement results. One of the often considered errors is those strictly related to the vibrations. As the effect of this type of external disturbance, the surface topography measurement results are burdened with the occurrence of high-frequency noise. A standardised and often proposed method for the compensation of this type of measurement error is to repeat the measurement process and average the received results. It seems to be the most encouraging proposal, however, the time-reducing requirements from the industry performance do not pose this solution as optimal. Therefore, a well-known and often used in surface metrology is an S-filter, data processing algorithm based on the Gaussian weighting function. From many intensive studies, it was concluded that this filtering approach may increase errors in the calculation of ISO 25178 surface texture parameters. Some of the ISO 25178 surface texture parameters were distorted by more than 100%, especially those sensitive to the occurrence of high-frequency measurement noise. Therefore, alternatively, to the general Gaussian filter, many other filtering methods were applied in surface metrology. However, the process of selection of a vibrational noise reduction filter must be validated before any proposals. One of the main objectives of the present work is to guide the regular user on how to select an appropriate filtering method for many types of etched surface topographies measured with a contactless white light interference method considering the reduction of both high-frequency noise and its impact on the variations of surface texture parameters. From the studied filtering methods, the spline filter gave the most encouraging results. As the final, the proposed methodology was validated in terms of ISO 25178 surface texture parameters evaluation comparing them to the results obtained by an international procedure based on the measurement repetitions.