Hanno Dierke

Detection of Micro-Probe Displacement Using a Shack-Hartmann Wavefront Sensor

To decrease the effort to detect micromechanical features by touch probe measuring systems, multiple touch probes composed in an array are used to measure some of these structures at the same time, owing to the alignment of many similar structures on a wafer. While usually the touch probe signal is read out electronically, in this investigation a Shack-Hartmann sensor is used to observe the reflective back plane of the micro probe array. Shack-Hartmann wave-front sensors use microlens arrays in conjunction with a CCD array. A planar wave-front that is transmitted through a microlens array and imaged on a CCD sensor will form a regular pattern of bright spots. If, however, the wave-front is distorted, the light imaged on the CCD sensor will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wave-front that occurred on the microlens array.

Optisches Extensometer zur Verfolgung propagierender Verformungsbänder

Zusammenfassung Der Portevin-LeChatelier-Effekt (PLC-Effekt) bezeichnet Instabilitäten der plastischen Verformung von Legierungen. In bestimmten Bereichen von Verformungsrate und Temperatur erfolgt die ansonsten homogene Verformung des Materials lokalisiert in schmalen Zonen, die PLC-Bänder genannt werden. Da die PLC-Bänder sehr schnell auftreten, ist ein System mit hoher zeitlicher und räumlicher Auflösung erforderlich, um die Vorgänge bei der Entstehung gründlich zu untersuchen. In diesem Artikel wird ein neues Testsystem zur Beobachtung des PLC-Effekts präsentiert. Es besteht neben einer Zugmaschine aus einer Zeilenkamera zur globalen Beobachtung der Zugprobe sowie einer Hochgeschwindigkeitskamera mit hoher Vergrößerung zur lokalen Beobachtung mit hoher zeitlicher und räumlicher Auflösung. Durch Analyse der Daten der Zeilenkamera ist die Bestimmung der Position auftretender PLC-Bänder möglich. Diese Information wird dazu genutzt, die nur einen Teil der Zugprobe beobachtende Hochgeschwindigkeitskamera auszulösen bzw. einem über die Probe propagierenden Band nachzuführen. Abstract The Portevin-LeChatelier effect (PLC-effect) denominates instabilities during the plastic deformation of alloys. In certain regions of strain rate and temperature the — usually homogeneous — deformation of the material localizes in small areas of the specimen, called PLC bands. Because of these rapidly appearing PLC bands, a system with high resolution in time and space is required to observe and investigate the processes of the formation of these bands thoroughly. In this article, a novel testing method for the observation of the PLC-effect is presented. The test system consists of a tensile testing machine, a line-scan camera for the global observation of the specimen, and a high-speed camera with a large magnification, resulting in a local observation with a high spatio-temporal resolution. By processing the data of the line-scan camera it is possible to detect the positions of emerging PLC-bands. This information is used to trigger the high speed camera, observing only a part of the specimen or to move the high-speed camera in parallel to emerging bands propagating through the specimen, respectively.

TEM study of the dislocation structure at the transition from discontinuous to viscous glide in Cu–Al and Cu–Mn alloys at elevated temperatures

The dislocation structures developed during plastic deformation in the regimes of discontinuous glide (Portevin-Le-Chatelier effect, PLC) as well as viscous glide at elevated temperatures (600-800 K) have been studied by transmission electron microscopy in polycrystals of Cu-5Al, Cu-10Al, Cu-15Al and Cu-4.1Mn alloys (at.%). Discontinuous glide is characterized by correlated dislocation movement in few active slip planes due to breakaway of aged and rapid multiplication of fresh dislocations, while beyond the transition, when solute diffusion is fast enough to continuously reconstitute the solute cloud during dislocation motion, a homogeneous distribution of smoothly moving dislocations is observed in all alloys. Owing to the decrease of stacking-fault energy and increase of short-range order in the Cu-Al alloys a change from cell structure (Cu-5Al) to planar slip (Cu-10Al and Cu-15Al) occurs in the discontinuous glide regime; in the Cu-4.1Mn alloy with a stacking-fault energy like Cu and negligible short-range order, development of cells prevails also during discontinuous glide. The observations are discussed in terms of current views on deformation in the PLC regime.

Reducing the influence of speckle structures on laser light sectioning sensors

Automated optical inspection is an important test procedure in electronic circuits assembly. Frequently 3d information is required and laser light sectioning sensors are often applied. However, some effects complicate the reliable automatic detection of the shape of such assemblies and their components. The packages of electronic components are often made of black plastics or ceramics so that the intensity available for the optical detection is quite low, especially in comparison to the surface of the PCBs where the components are mounted on. In addition due to the rough surfaces of the components and the coherence length of the laser light speckles arise. In the work presented here a piezo actuator is used to oscillate the illuminating laser lines along the direction of the lines. The aim is to reduce the visibility of the speckles by averaging while maintaining the geometrical shape of the lines. In addition, image processing methods like segmentation and skeletonization are used to allow the detection of the shape of components and assemblies also if materials with distinct differences in the reflectivity are involved. Investigations include the influence of the parameters amplitude and frequency of the piezo actuator.

Bestimmung der Auslenkung von Mikrotastern mit optischen Methoden

Zusammenfassung Zur Verringerung des Aufwands bei der Erfassung mikromechanischer Merkmale mit taktilen Messgeräten werden mehrere in einem Array angeordnete Taststifte benutzt, um mehrere gleichartige, auf einem Wafer angeordnete, Strukturen gleichzeitig zu messen. Normalerweise erfolgt das Auslesen des Sensorsignals elektrisch. In den hier beschriebenen Untersuchungen wurden verschiedene optische Methoden verwendet, um die spiegelnde Rückseite des Tasterarrays zu beobachten und die Auslenkung der Taststifte simultan zu detektieren. Dazu wurden ein Hartmann-Shack-Wellenfrontsensor sowie die Auswertung über Streifenprojektionsverfahren genutzt. In beiden Fällen führt eine Auslenkung der Taststifte zu einer Deformation der spiegelnden Rückseite des Tasterarrays und damit zu einer sichtbaren Veränderung im optischen Signal. Durch Vergleich mit einem Bild des unverformten Arrays als Referenz kann die Auslenkung der Taststifte bestimmt werden.

Detection of the displacement of micro touch probes using structured illumination

To decrease the effort to detect micromechanical features by touch probe measuring systems, multiple touch probes composed in an array are used to measure some of these structures at the same time, owing to the alignment of many similar structures on a wafer. While in previous works the touch probe signal is read out electrically, using optical techniques by observing the reflective back plane of the micro probe array is a promising approach to detect the displacement of several touch probes simultaneously. In this investigation a structured illumination measurement system is used to detect the deflection of the micro touch probes. By detecting several fringe patterns with different periods, orientations, and phase-shifts a correlation between the coordinate of a CCD camera pixel and the observed monitor pixel coordinate can be obtained. A deflection of the touch probe leads to a deformation of the reflective back plane of the micro probe array and, thus, a different monitor pixel coordinate is observed by the CCD pixel. Using an image obtained with an undeformed touch probe array as a reference, the displacement of the touch probe can be derived.

Experimental Investigations of the Dynamics of Plc Bands in Al3%Mg

The Portevin-Le Chatelier (PLC) effect is an undesired behaviour of ductile alloys consisting in a regime of unstable plastic deformation. A relevant feature of this phenomenon is the repetitive concentration of the strain in narrow regions, referred to as PLC bands, that resemble incipient neckings. Depending on the loading conditions and on material factors, three different kinds of band behaviour are traditionally distinguished in tensile tests: type A, a band moving with a constant velocity as a regular and continuous propagation along the specimen; type B, a series of stationary bands that emerge one beside the other at regular intervals in time and in space; type C, stationary bands that emerge with a regular frequency but disordered in space, [1]. Whereas this is a well established classification, the way in which a single band actually emerges is still an open question, but only in the last years a few investigations could start to deal with this aspect, [2] and [3].