Wito Hartmann

Model and simulation of fringe projection measurements as part of an assistance system for multi-component fringe projection sensors

Multi-component fringe projection sensors allow the fast, holistic, exact, robust, contact free sampling of a workpiece surface. The success of an inspection relies on the skills, diligence and experience of the inspection planner. For setting up an inspection, there is no standardized method established yet. Therefore there is a need for assistance systems to support the operator. A prototype of an such assistance system for multi-component fringe projection sensors is introduced. The assistance system supports the inspection planner in determining the ideal sighting- and positioningstrategy. As key element, the result of a planned inspection is simulated. First, the optical performance of the designated fringe projection sensor is calculated by use of raytracing software. Then the measurement result and the measurement uncertainty for specific measurement tasks and a chosen measuring pose, is simulated. Fundament for this simulation is a complete mathematical-physical model of the measurement. Building on this and on the knowledge of influences, which were previously inscribed in entry masks, the measurement uncertainty can be estimated and displayed individually for each point of a workpiece surface. Thus the inspection planner can easily evaluate the quality of the planned inspection setup. Additional optimizing algorithms were implemented. The aim of the multi-criteria optimization is to determine the best configuration for the measurement device and the ideal sighting- and positioning-strategy. As measure of quality serves hereby the reduction of the measurement uncertainty.

Interpreting the probe-surface interaction of surface measuring instruments, or what is a surface?

When using dimensional measuring instruments it is assumed that there is a property of the object, which we call surface, that is present before during and after the measurement, i.e. the surface is a fundamental property of an object that can, by appropriate means, be used to measure geometry. This paper will attempt to show that the fundamental property ‘surface’ does not exist in any simple form and that all the information we can have about a surface is the measurement data, which will include measurement uncertainty. Measurement data, or what will be referred to as the measured surface, is all that really exists. In this paper the basic physical differences between mechanically, electromagnetically and electrically measured surfaces are highlighted and discussed and accompanied by measurement results on a roughness artefact.

Holistic Measurement in the Sheet-Bulk Metal Forming Process with Fringe Projection

Sheet bulk metal forming is a new forming technology, currently developed by several companies and research institutes. It creates high demands on the inspection of parts and tools, especially in the field of in-situ abrasion detection of the forming tool and its impacts on the work piece. This manuscript introduces two optical testing methods for fulfilling these inspection tasks: On the one hand the endoscopic fringe projection as a flexible small scale optical measurement principal with high depth of focus and accuracy for the acquisition of filigree form elements for a continuous abrasion determination and one the other hand the multi-scaled fringe projection for a holistic one shot measurement of the work piece for an adapted, multiscale deviation analysis. The development and advantages of both systems for the sheet bulk metal forming process are shown as well as potentials of the combination of the both systems close to the proposed application next to the production line.

Verifying the functional ability of microstructured surfaces by model-based testing

Micro- and nanotechnology enables the use of new product features such as improved light absorption, self-cleaning or protection, which are based, on the one hand, on the size of functional nanostructures and the other hand, on material-specific properties. With the need to reliably measure progressively smaller geometric features, coordinate and surface-measuring instruments have been refined and now allow high-resolution topography and structure measurements down to the sub-nanometre range. Nevertheless, in many cases it is not possible to make a clear statement about the functional ability of the workpiece or its topography because conventional concepts of dimensioning and tolerancing are solely geometry oriented and standardized surface parameters are not sufficient to consider interaction with non-geometric parameters, which are dominant for functions such as sliding, wetting, sealing and optical reflection.To verify the functional ability of microstructured surfaces, a method was developed based on a parameterized mathematical-physical model of the function. From this model, function-related properties can be identified and geometric parameters can be derived, which may be different for the manufacturing and verification processes. With this method it is possible to optimize the definition of the shape of the workpiece regarding the intended function by applying theoretical and experimental knowledge, as well as modelling and simulation. Advantages of this approach will be discussed and demonstrated by the example of a microstructured inking roll.

Automated extraction and assessment of functional features of areal measured microstructures using a segmentation-based evaluation method

In addition to currently available surface parameters, according to ISO 4287:2010 and ISO 25178-2:2012—which are defined particularly for stochastic surfaces—a universal evaluation procedure is provided for geometrical, well-defined, microstructured surfaces. Since several million of features (like diameters, depths, etc) are present on microstructured surfaces, segmentation techniques are used for the automation of the feature-based dimensional evaluation. By applying an additional extended 3D evaluation after the segmentation and classification procedure, the accuracy of the evaluation is improved compared to the direct evaluation of segments, and additional functional parameters can be derived. Advantages of the extended segmentation-based evaluation method include not only the ability to evaluate the manufacturing process statistically (e.g. by capability indices, according to ISO 21747:2007 and ISO 3534-2:2013) and to derive statistical reliable values for the correction of microstructuring processes but also the direct re-use of the evaluated parameter (including its statistical distribution) in simulations for the calculation of probabilities with respect to the functionality of the microstructured surface. The practical suitability of this method is demonstrated using examples of microstructures for the improvement of sliding and ink transfers for printing machines.

Modellbasiertes Prüfen zur Verifikation der Funktionsfähigkeit von mikrostrukturierten Oberflächen

Zusammenfassung Eine Methode zur Prüfung der Funktionsfähigkeit von Mikrostrukturen, welche verbesserte funktionale Eigenschaften wie Stoffübertragungs-, Dichtheits- oder Reibeigenschaften ermöglichen sollen, wurde entwickelt. Durch Modellieren und Simulieren der Funktion eines Werkstücks ist es möglich den Grad der Funktionserfüllung basierend auf dimensionellen Messungen zu berechnen. Vorteile dieses Ansatzes werden anhand einer mikrostrukturierten Druckwalze vorgestellt und erläutert.

QUALIFYING MEASURING SYSTEMS BY USING SIX SIGMA

The technology of sheet-bulk metal forming enables the production of complex workpieces with filigree surface structures in only a few forming steps. In order to provide a rapid and production-related workpiece inspection of not only large workpiece features, but also small features in an appropriate quality, a multi-sensor optical measurement system with different resolutions is required. Workpiece features of medium size can be measured by two types of fringe projection sensors. With a structured approach according to Six Sigma, which is based on the five phases design, measure, analyze, improve and control complex tasks are divided into smaller individual problems. In each phase the Six Sigma method recommends tools for solving the individual problems effectively. With the support of the Six Sigma guideline an exemplary sheet-bulk metal forming workpiece feature is used in order to qualify the two measuring systems for a production-related measurement. After defining the explicit goal for the investigations, a detailed analysis of the measurement process leads to a couple of relevant influences. These are input factors for the design of experiments. By a full factorial design, not only an influence of a factor itself, also the interactions between multiple factors can be detected. In the analyze-phase, these results are calculated by different statistical methods. To present the results in a comprehensible way several types of diagrams are used. The shown approach gives an example for a traceable and methodical way to qualify a measurement system for challenging measurement tasks.