Enrico Savio

Critical factors in SEM 3D stereo microscopy

This work addresses dimensional measurements performed with the scanning electron microscope (SEM) using 3D reconstruction of surface topography through stereo-photogrammetry. The paper presents both theoretical and experimental investigations, on the effects of instrumental variables and measurement parameters on reconstruction accuracy. Investigations were performed on a novel sample, specifically developed and implemented for the tests. The description is based on the model function introduced by Piazzesi and adapted for eucentrically tilted stereopairs. Two main classes of influencing factors are recognized: the first one is related to the measurement operation and the instrument set-up; the second concerns the quality of scanned images and represents the major criticality in the application of SEMs for 3D characterizations.

Testing of x-ray microtomography systems using a traceable geometrical standard

X-ray computed microtomography is an interesting imaging technique for many applications, and is also very promising in the field of coordinate metrology at the micro scale. The main advantage with respect to traditional tactile-probing or optical coordinate measurement systems is that x-ray tomography can acquire dimensional and geometrical data for both inner and outer surfaces, without accessibility restrictions. However, there are no accepted test procedures available so far and measurement uncertainty is unknown in many cases, due to complex and numerous error sources. The paper presents the first results of a test procedure implemented for determining the errors of indication for length measurements of x-ray microtomography systems, using a new reference standard featuring a regular array of inner and outer cylindrical shapes. The developed test method allows the determination of specific characteristics of x-ray microtomography systems and can be used for the correction of systematic errors.

New advances in traceability of CMMs for almost the entire range of industrial dimensional metrology needs

Abstract The paper reports on results of the European project EASYTRAC. The first main goal of this project was to significantly reduce the efforts associated with the traceability of industrial dimensional metrology laboratories by means of the almost exclusive use of coordinate measuring machines (CMMs) in combination with laser interferometers. The second main goal was to develop and validate CMM-specific methods for task-related measurement uncertainty analysis. In this paper, significant achievements from the EASYTRAC project are reported, with particular emphasis on: i) error compensation using reversal techniques; ii) use of laser interferometers on CMMs to reduce measuring uncertainty when calibrating standards of length; iii) development of other task-specific calibration techniques; and iv) use of multiple measurements strategies for uncertainty assessment. Uncertainty analyses of virtually any measurable feature were performed and validated, including freeform, gear and thread parameters. This work has provided an extensive experimental basis for the elaboration of the ISO/TS 15530 series of standards.

Fast technique for AFM vertical drift compensation

The paper presents implementation and validation of a method for accurate imaging of three-dimensional surface topographies, developed for AFM metrology but in principle applicable to the whole family of scanning probe microscopes. The method provides correction of the vertical drift, and can be applied to any AFM scanner system, without need for modification of the instrument hardware. Surface correction is performed based on two topographies taken with mutually orthogonal scanning directions. Reconstruction is rapidly achieved through the use of an automatic routine developed for the purpose. The proposed method has been tested by using an optical and a silicon flat and a high precision cylindrical artefact. Examples of successful reconstructions on different samples are also reported within the paper.

An artefact for traceable freeform measurements on coordinate measuring machines

Abstract The present paper describes an artefact based approach to obtain traceability of freeform measurements on coordinate measuring machines. First, the requirements for the traceability of freeform measurements and a strategy for the development of a feasible solution are presented. A new concept of artefact, called the “Modular Freeform Gauge” (MFG) has been developed. It is based on physical modeling of a given freeform surface by a combination of items with regular geometry, well calibrated on their dimensions and form. The relative position is accounted for during the procedure; this information is used to generate a “calibrated” CAD model as reference for freeform measurements. The architecture of the artefact, its collocation in the traceability chain, and the calibration procedure are described. Finally, a procedure for the uncertainty assessment of actual freeform measurements is presented. The work here described has been focused on implementation of the uncertainty assessment procedure for freeform measurements on turbine blades. A task-specific Modular Freeform Gauge was developed for this application.

Approaches to the Calibration of Freeform Artefacts on Coordinate Measuring Machines

Abstract The paper compares two different experimental methods to establish the traceability of freeform measurements on coordinate measuring machines: i) uncertainty assessment using Modular Freeform Gauges, and ii) uncertainty assessment using Uncalibrated Objects. The first approach is an application to freeform geometries of the method described in ISO TS 15530-3 based on comparisons. The second approach is inspired by the procedure currently being developed within ISO TC213, involving repeated measurements of a given object in different orientations with variation of measuring parameters etc. The feasibility of the two approaches for freeform geometries is demonstrated through the calibration of a turbine blade.

Coordinate metrology using scanning probe microscopes

New positioning, probing and measuring strategies in coordinate metrology are needed for the accomplishment of true three-dimensional characterization of microstructures, with uncertainties in the nanometre range. In the present work, the implementation of scanning probe microscopes (SPMs) as systems for coordinate metrology is discussed. A new non-raster measurement approach is proposed, where the probe is moved to sense points along free paths on the sample surface, with no loss of accuracy with respect to traditional raster scanning and scan time reduction. Furthermore, new probes featuring long tips with innovative geometries suitable for coordinate metrology through SPMs are examined and reported.

Acoustic scanning probe microscopy

From the contents: Overview of acoustic techniques.- Contact dynamics modelling.- Cantilever dynamics: theoretical modeling.- Finite elements modelling.- AFAM calibration.- Enhanced sensitivity.- UAFM.- Holography calibration.- UFM.- Friction/lateral techniques.- Harmonix.- Scanning microdeformation microscopy (SMM).- Tip wear.- Comparison with other techniques.- Applications polymer.- Thin films.

Uncertainty in testing the metrological performances of coordinate measuring machines

Performance verification of Coordinate Measuring Machines (CMMs) is a key task in quality assurance systems. Test results are influenced by various error sources that affect the test with their uncertainty contribution, therefore the correct identification and quantification of these error sources is a crucial task for a proper estimation of the test uncertainty. The paper discusses the identification of the uncertainty contributions to be taken into account for the estimation of the test uncertainty in connection to three tests for the verification of important CMM subsystems: i) rotary table test; ii) contact scanning probe test; iii) video probe test.

Error Sources in Atomic Force Microscopy for Dimensional Measurements: Taxonomy and Modeling

This paper aimed at identifying the error sources that occur in dimensional measurements performed using atomic force microscopy. In particular, a set of characterization techniques for errors quantification is presented. The discussion on error sources is organized in four main categories: scanning system, tip-surface interaction, environment, and data processing. The discussed errors include scaling effects, squareness errors, hysteresis, creep, tip convolution, and thermal drift. A mathematical model of the measurement system is eventually described, as a reference basis for errors characterization, with an applicative example on a reference silicon grating.