Rainer Tutsch

Reflection grating photogrammetry : a technique for absolute shape measurement of specular free-form surfaces

While for non-reflecting surfaces a variety of optical techniques is available that allow the flexible geometric measurement of free-form surfaces, established approaches for the testing of specular surfaces are limited to basic geometries or slight deviations from an assumed reference geometry. As not only the intensified use of aspheric optics but also the increasing quality standards for technical surfaces call for an enhanced measurement range, the authors have developed two related techniques for the direct three-dimensional measurement of specular reflecting surfaces. These techniques are based on the observation of the mirror image of a grid-like reference structure and apply principles that are well-known from measurement systems for non-reflecting surfaces, such as photogrammetry and structured illumination, to the evaluation of specular surfaces. While the first of these approaches works with an active triangulation process based on one camera and a pseudo three-dimensional reference structure, the second one utilises a stereo-photogrammetric camera system in conjunction with a merely two-dimensional reference structure. Both systems allow the unambiguous measurement of reflecting free-form surfaces and may, by the use of multiple wavelength and photogrammetric stitching techniques, be extended to the measurement of rather complex geometries. Besides the fundamental mode of operation of this so-called reflection grating photogrammetry, the properties of a suitable reference structure will be presented in this contribution. Furthermore the photogrammetric calibration procedure and the used calibration models will be discussed. Finally the measurement uncertainty is evaluated based on both, experimental and theoretical considerations.

Propagation of deformation bands investigated by laser scanning extensometry

Abstract Luders band and Portevin–LeChatelier (PLC) band propagation in polycrystalline Cu–0.15at.%Al has been studied by multiple zone laser scanning extensometry during tensile deformation. The dependence of the propagation rate on the external deformation rate is investigated in a wide range ( e =6.67×10 −6 –1.3×10 −2 s−1) at selected temperatures (100–300 °C), in particular for the PLC bands of type B which propagate in a jerky manner. The local strain rates within the bands are determined and the results are compared with recent theoretical modelling of PLC band propagation.

Optical three-dimensional metrology with structured illumination

A variety of techniques have been developed to measure the three-dimensional shape of an object using structured illumination. The measurement of objects with diffusely reflecting surfaces by means of projected patterns can be considered a standard technique. Also more recently, methods for the measurement of specularly reflecting or transparent surfaces by evaluation of the images of regular patterns have been published. In this paper, we suggest a systematic treatment of all of these methods as generalized active or passive triangulation techniques.

Comparison of optical and tactile layer thickness measurements of polymers and metals on silicon or SiO2

The thickness measurement of transparent layers with optical techniques is very problematic. The observed deviations can easily reach 100% of the layer thickness to be measured. In order to analyse these deviations, tactile reference measurements have been developed. The proposed method is based on contact mode measurements with low contact pressure. With stylus instruments, this can be realized either by using the recommended tip radius of 2 µm and very small probing forces in the micronewton range (and low scanning speeds of 50 µm s−1) or by using the recommended probing force of 750 µN, but a large probing tip radius. Three metal layers on silicon or silicon dioxide and two polymer resist materials on a thin chromium adhesive layer on silicon are used as artefacts. The comparison of the optical measurements with the tactile reference values disclosed deviations of the optical measurements of up to 195% of the layer thickness. Layer thicknesses were between 200 nm and 4 µm. This paper analyses the deviations of two white light interference microscopes, one phase shift interference microscope, one confocal microscope, one autofocus sensor, a chromatic sensor, an interferometric film thickness sensor and one spectroscopic ellipsometer. Simple and well-known expressions for the description of the observed deviations are presented and discussed. The order of magnitude of the observed deviations can be described well by these correction formulas but further investigations are necessary in order to better understand the systematic deviations of optical surface measuring instruments on non-cooperating surfaces.

Vibration induced phase-shift interferometer

This paper presents the concept and the experimental setup of an interferometric system that is designed to work without vibration isolation and uses the random mechanical vibrations as phase shifter. An additional high temporal resolution detector system consisting of three photodiodes is used for the determination of the phase shifts that occur at the recording of the interference images. Two orthogonally polarized laser beams of different wavelengths, a continuous He-Ne laser and a pulsed laser diode, are coupled and expanded to the test and reference plates. To resolve the ambiguity problem of the profile orientation, additional information is obtained from the signals of two adjacent optical fibers placed in the He-Ne interference field. The laser beams are also split and expanded to a plate with tilted surfaces. The fringes that occur at the reflection on the surfaces are used to analyze the wavelength stability of the laser diode, taking the He-Ne wavelength as reference. An adequate PSI algorithm for random phase shifts is proposed.

MCSEM- a modular Monte Carlo simulation program for various applications in SEM metrology and SEM photogrammetry

MCSEM is a Monte Carlo simulation program for the modeling of image formation in scanning electron microscopy. The program is written entirely in C++ and uses object-orientated programming techniques. Different aspects of the image formation process, as the probe forming, the geometric specimen model, the electron-specimeninteraction, and the electron detection are modeled in separate program modules. Due to this modular structure, the program can easily be enhanced and adapted to new simulation tasks by integration of new modules.

Measurement of optically effective surfaces by imaging of gratings

Due to the increasing use of aspherical optics, there is a demand for innovative measuring methods that allow the flexible testing of a wide variety of optical components. With the measuring method presented in this paper the imaging properties of the optical component under test may be determined by making it part of an imaging system consisting of an electronic camera with lens, a special grid pattern and the object itself. The grid pattern is taken as a reference object whose resulting image recorded by the camera is evaluated in order to obtain the properties of the tested optical component. In favor of a high measurement accuracy phase shifting techniques and photogrammetric methods are used in the course of the evaluation of the reference structure and the characterization of the tested optical surface. Unlike other techniques the presented measuring method does not require particular previous knowledge of the tested component and may be applied to both reflective and refractive optical surfaces. Measuring examples for reflective and refractive components are given, demonstrating the potential of the method.

Force transducer based on a geometric-optical displacement sensor

The vast majority of current force measurement methods determine the deformation of an elastic body to measure the effective force. The leading sensor technology in this market segment is the resistance strain gauge. Because of the measurement principle the stain gauge has some drawbacks. For instance, the measurement suffers from the so-called creeping and a local weakening of the elastic element is necessary to create sufficient local strains. This is also a reason for this technique being limited with respect to the measurement of dynamic loads. In order to overcome these limitations, in this paper a new contactless working geometric-optical displacement transducer is proposed. An optical lever principle is used to reach the required high position resolution to measure the force-induced deformation of an elastic body.

Vorhersage des Phasenrauschens in optischen Messsystemen mit strukturierter Beleuchtung

Zusammenfassung In dieser Arbeit wird eine Methode vorgestellt, mit der sich ein Schätzwert für das Phasenrauschen in optischen Messsystemen mit strukturierter Beleuchtung direkt aus den aufgezeichneten Grauwerten berechnen lässt. Das verwendete Rauschmodell basiert auf einer Richtlinie zur Charakterisierung von Bildsensoren (EMVA 1288), so dass die benötigten Parameter direkt einem konformen Datenblatt entnommen werden können. Alternativ wird in dieser Arbeit auch eine Methode beschrieben, mit der die Parameter ohne zusätzlichen Geräteaufwand experimentell ermittelt werden können. Abstract

Assembly of hybrid microsystems using an assembly system with 3D optical sensor

For the assembly of hybrid microsystems a high accuracy in the range of a few micrometers is required. The combination of a parallel robot with an integrated 3D vision sensor uses positioning marks on the objects for object recognition. Within the assembly process, relative positioning accuracies in the submicrometer range have been obtained. Therefore, it is necessary to use a calibration strategy for matching the coordinate system of the 3D vision sensor with the coordinate system of the robot. The construction of the system, the calibration applied and the positioning accuracy achieved by the robot will be discussed.