Metrological characterization of interior circular features using digital optical machines: Calculation models and application scope

• Algorithms for evaluating the radius and roundness of circular feature are proposed.
• The degree of precision of each method and its application scope is determined.
• The input algorithms are images obtained using digital optical machines.
• Common methods for indirect characterization of circular features are analyzed.
• The model is interesting for measurements in sub-micromanufacturing environments.

The objective of this work is to analyze and compare common methods used for indirect metrological characterization of circular geometrical features: least square circle, minimum zone circle, maximum inscribed circle and minimum circumscribing circle, based on images obtained using digital optical machines. The self-developed calculation algorithms used were implemented with Matlab® software considering the following study variables: the amplitude of the angular sector of the circular feature, its nominal radius and the magnification used by the optical machine. Under different measuring conditions the radius and roundness error of an angular sector of a piece of LEGO and of a ring gauge were determined. That is, the proposed algorithms allow the characterization of both full circumferences as angular sectors. We were able to determine the degree of precision of each method and its scope of application by comparing the results obtained with different adjustments to values certified by an accredited laboratory.