Procedure for Calibrating the Z-axis of a Confocal Microscope: Application for the Evaluation of Structured Surfaces

Abstract

This work describes a method for the metrological characterization of structured surfaces using a confocal microscope. The proposed method is based on the calculation of texture parameters established in ISO 25178-2:2012. To ensure the traceability of these parameters, a procedure for the calibration of the Z-axis of the confocal microscope is proposed. The calculation of uncertainty associated with each parameter employs the Monte Carlo method, as well as the concept of a virtual instrument. The validity of the algorithms has been verified through the use of synthetic data provided by the National Institute of Standards and Technology (NIST) and physical standards, with minimum differences being obtained between the certified values and calculated or measured values. Finally, using the proposed method, the topography of a structured surface manufactured by laser machining is evaluated, obtaining the most used roughness parameters, as well as their measurement uncertainties and possible correlations. In general, it can be affirmed that it is possible to obtain metrologically reliable results with the proposed method.

Industrial Calibration Procedure for Confocal Microscopes

“…To solve this problem, several authors [5,35] have proposed the use of step height standards ( Figure 8). Wang et al [35] used them with the nominal values 24, 7, 2, and 0.7 µm.…”

“…To solve this problem, several authors [5,35] have proposed the use of step height standards ( Figure 8). Wang et al [35] used them with the nominal values 24, 7, 2, and 0.7 µm. This kind of measurement standard has several grooves whose nominal depths cover the range of use of the confocal microscope on the Z-axis.…”

“…However, the short field of view of confocal microscopes makes it difficult to carry out the calibration with this type of measurement standard. To solve this problem, several authors [5,35] have proposed the use of step height standards ( Figure 8). Wang et al [35] used them with the nominal values 24, 7, 2, and 0.7 µm.…”

Simple Calibration Method for Confocal Microscopy Used in Micro-Additive Manufacturing Processes

“…However, the short field of view of a confocal microscope makes it difficult to carry out the calibration with this type of measurement standards. To solve this problem, several authors [16,43] propose to use step height standards. Wang et al [43] used them with nominal values 24, 7, 2 and 0,7 µ m. This kind of measurement standards have several grooves whose nominal depths cover the range of use of the confocal microscope on the Z-axis.…”

“…. [38,43,44,45] This kind of standard is typically used for roughness calibration. If the purpose is to make a calibration on Z-axis, these standards have the limitation of the groove's depth, which usually is small to cover the range of the Z-axis.…”