Wito Hartmann

Bio: Wito Hartmann is an academic researcher from University of Erlangen-Nuremberg. The author has contributed to research in topics: Functional ability & Surface finish. The author has an hindex of 6, co-authored 15 publications receiving 115 citations.

Function-oriented method for the definition and verification of microstructured surfaces

Abstract: Currently available measurement techniques enable high-resolution topography and structural measurements down to the subnanometer range Nevertheless, in many cases despite extensive geometric data of the manufactured, real workpiece it is not possible to make a clear statement about the functional ability, because conventional concepts of tolerancing are solely geometry-oriented and standardized surface parameters are not sufficient or even missing completely for characterizing the degree of ability to fulfil a function To define and determine appropriate parameters characterizing the functional behaviour, a method was developed based upon a parameterized mathematical–physical model of the function From this model function-related properties can be identified and geometric parameters can be derived, which can be different for the manufacturing and the verification process With this method it is possible to optimise the definition of the shape of the workpiece regarding the intended function by applying theoretical and experimental knowledge as well as modelling and simulation Especially for the verification process of functional microstructures a model-based testing has benefits: Using the model like a kind of “virtual functional gauge” imprecise standardized definitions and measurement evaluations can be omitted, while the functional ability is getting quantitatively predictable The exchange of information of the complex process chain from defining functional requirements, designing and dimensioning taking into regard the manufacturing process up to testing conformance and verification functional ability is increased Focussing attention on a function oriented conformity decision, development priorities can be separated better and processes are getting more objective and transparent Advantages of this approach for the design process, the manufacturing process and verification process will be discussed and demonstrated by the example of a microstructured inking roll

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

Abstract: 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.

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

Abstract: 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.

Anforderungen und Randbedingungen für den Einsatz optischer Messsysteme zur In-Line-Prüfung additiv gefertigter Bauteile

Abstract: RTejournal - Forum fur Rapid Technologie, Vol. 2012, Iss. 1 - Additive Fertigungsverfahren, wie das selektive Laserstrahlschmelzen (SLM), entwickeln sich durch Verkurzung von Fertigungs- und Nacharbeitszeiten zunehmend vom reinen Prototypenbau (Rapid Prototyping) hin zu stuckzahlflexibler Serienfertigung individueller Bauteile (Rapid Manufacturing). Trotz des hohen Potentials der werkzeuglosen Generierung von komplexen und individuellen Bauteilen bei nahezu uneingeschrankter Gestaltungsfreiheit herrscht dennoch Zuruckhaltung fur den Einsatz dieser Verfahren, aufgrund intolerabler Qualitatsmangeln hinsichtlich Gestalt und Festigkeit, welche hauptsachlich durch Schwankungen der Prozessparameter, wie Temperatur, Pulverqualitat, etc., wahrend der schichtweisen Fertigung verursacht werden. Um solche Fehler nicht erst – wie nach heutigem Vorgehen durch aufwandig und wirtschaftlichkeitsmindernd mit gebaute Ruckstellmuster und Probekorper – nach der Fertigung zu detektieren, wird eine in den Fertigungsprozess eingebettete Qualitatsprufung und eine daraus abgeleitete Prozessregelung immer wichtiger. Abhilfe soll eine inkrementelle In-Line-Messung schaffen, welche vor, wahrend und nach jedem Schichtauftrag durchgefuhrt wird. Zur Konzeptionierung eines geeigneten Messsystems, welches zukunftig eine dynamische und vollautomatisierte Prozessregelung ermoglichen soll, wird der SLM-Prozess hinsichtlich messtechnischer Anforderungen (vertikale und laterale Sensorauflosung, Reflexionseigenschaften, etc.) und Restriktionen durch die Fertigungsanlage (nutzbarer Bauraum, Temperatur, Staub, etc.) analysiert. Daruber hinaus werden geeignete Sensoren, welche in einem In-Line-Messsystem bei einem SLM-Prozess fur Polymere denkbar sind, auf ihre Eignung uberpruft und bewertet. Abschliesend wird ein mogliches Losungskonzept basierend auf Streifenprojektion vorgeschlagen.

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

Abstract: 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.

A reflectance model for computer graphics

Abstract: This paper presents a new reflectance model for rendering computer synthesized images. The model accounts for the relative brightness of different materials and light sources in the same scene. It describes the directional distribution of the reflected light and a color shift that occurs as the reflectance changes with incidence angle. The paper presents a method for obtaining the spectral energy distribution of the light reflected from an object made of a specific real material and discusses a procedure for accurately reproducing the color associated with the spectral energy distribution. The model is applied to the simulation of a metal and a plastic.

Quantitative characterization of surface topography using spectral analysis

Abstract: Roughness determines many functional properties of surfaces, such as adhesion, friction, and (thermal and electrical) contact conductance. Recent analytical models and simulations enable quantitative prediction of these properties from knowledge of the power spectral density (PSD) of the surface topography. The utility of the PSD is that it contains statistical information that is unbiased by the particular scan size and pixel resolution chosen by the researcher. In this article, we first review the mathematical definition of the PSD, including the one- and two-dimensional cases, and common variations of each. We then discuss strategies for reconstructing an accurate PSD of a surface using topography measurements at different size scales. Finally, we discuss detecting and mitigating artifacts at the smallest scales, and computing upper/lower bounds on functional properties obtained from models. We accompany our discussion with virtual measurements on computer-generated surfaces. This discussion summarizes how to analyze topography measurements to reconstruct a reliable PSD. Analytical models demonstrate the potential for tuning functional properties by rationally tailoring surface topography - however, this potential can only be achieved through the accurate, quantitative reconstruction of the power spectral density of real-world surfaces.