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Data fusion of areal measured microtopographies with plane of reference using optical sensors (DFG)

The Projekt „Data fusion of areal measured microtopographies with plane of reference using optical sensors” of Leibniz Universität Hannover (LUH) is funded by the German Research Founda-tion (DFG) and has the aim of impriving methods to increase the field of view of image processing microscopes by stitching.  Stitching is a technique that uses the fusion of partially overlapping meas-urements with high resolution to form a high resolution, large field of view measurement. Due to a number of deviations like distortion, missing measurement data, axial positioning errors and rotation between the axes of the CCD-chip and the translational axis the results of image registration (alignment) and fusion are often unsatisfactory.  Commercially available systems often lack sufficient correction of these deviations. In the project we researched the various deviations of 3D-microscopes with positioning stages on their influence to the creation of mosaics of measurements. We developed a software module that allows the characterization of radial distortion by measuring chessboard-like surface standards. Us-ing resolution, structure and flatness standards we measured the various rotational and translational positioning errors as well as the rotation of the CCD-chip against the positioning axes. The measured errors were used in a model based simulation of 3D-microscopes to characterize the influence of the positioning errors on the image registration.Measurements by 3D-microscopes, such as white light interferometers or confocal microscopes often exhibit false or missing data due to high surface gradients or bad lighting. These measurement data have to interpolate consistently in different measurements to allow an accurate image registration.  We researched the resulting similarity (measured by cross-correlation) of surfaces with varying degrees of statistical and deterministic bad measurement values and outliers after interpolation with a number of pixel and triangulation based interpolation methods. To allow for a robust method of image registration of overlapping measurements with unknown overlap we developed a method of image registration based on the calculation of one dimensional feature functions. These functions are calculated along the direction perpendicular to the direction of movement. By estimating the overlap using the simultaneous correlation of the feature functions and subsequently registering the measurements by correlation by Fourier transform we were able to decrease the necessary overlap from 35 to 20 % down to 10 % of the measurement area. This was tested using a model based simulation of a white light interferometer and simulated polished surfaces. A similar test was conducted for the characterization of registration by phase cor-relation which was also verified by a test conducted using a high precision piezo positioning stage.

Contact person: Dr.-Ing. Dipl.-Phys. Markus Kästner 

Geometry inspection of optically non-cooperative surfaces using fringe projection

Endbearbeitete Bauteile weisen meist glänzende Oberfächen auf
Endbearbeitete Bauteile weisen meist glänzende Oberfächen auf

Optical Measurement Systems deliver fast and flexible methods to measuring geometries aof technical parts, that can be used in different stadiums of the production process. They have the advantage, that they're non-invasive and thereby don't damage the surface of the part. They also deliver a fast analysis of dense data points, that can be measured arealy. The measurement precision of optical measurement methods are advancing towards that of tactile measurements.

That's why optical measurement techniques generally are industrially suitable. However optical methods make demands on the optical properties of the surfaces of measurement objects, that can be fullifilled under laboratory conditions quite easily, but that are hard to achieve in industrial manufacturing.

The transfer project T5 "Geometry inspection of optically non-cooperative surfaces" within the Collaborative Research Centre 489 deals with the treatment of technical surfaces to prepare them for the measurement using fringe projection triangulation technique.

Contact person: Dipl.-Ing. Omar Abo-Namous

Adaptronic Precision Positiong System in Chucks for Machine tools (CRC 489, subproject T4)

The industrial utilization of results of the Collaborative Research Center 489 "Process chain for the production of precision-forged high-performance components" is the objective of the transfer area. The initiated transfer-project T4 "Adaptronic precision positioning system in chucks for machine tools" deals with the precision positioning of gearwheels in automated industrial manufacturing processes. The fast and highly accurate laser measuring technique allows the optical geometry capturing of gearwheels inside of machine tools. The used conoscopic lasersensor ConoProbe Mark III takes a transverse plane of the clamped gearwheel. Through efficient algorithms, eccentric clamping positions of gearwheels, which may be a result of clamping errors, can be quickly and safely detected with standard deviations << 1μm. A calculated correction vector enables a precision positioning of the clamped gearwheel, which ensures the best possible position for the following machining of the functional surfaces.

Contact person: M.Sc. Dipl.-Ing. (BA) Achim Pahlke


Characterization of WEear MEchanisms and SURFace functionalities with regard to life time prediction and quality criteria - from micro to the nano range

The project WEMESURF is a Marie Curie Research Training Network, which is funded by the European Commission 6th Framework, with 13 partners from different european countries. The objective of the WEMESURF is to setup an effective and sustainable research platform for the study and development of innovative measuring methods and mathematical approaches for wear mechanisms on nano-metre scale. Within the project the IMR cooperates with the other partners to carry out investigations about the surface related wear analysis. Characterization of the Alusil cylinder liner surface in regard to its wear behaviour stand in the centre of the research works of IMR. In addition, the institute support the other project partners for the wear measurements by means of 3D optical sensors.

Contact person: Dipl.-Ing. Qiang Hao

Material allowance based finepositioning (CRC 489, subproject A5)

The subproject A5 „Material allowance based finepositioning“ of the collaborative research centre 489 (CRC 489) ‘’Process chain for the production of precision-forged high-performance parts” researchs among other things a process-integrated measurement system. This determines the optimal position of the precision forged pinion shaft which features a certain allowance before the hard machining. Because of this, errors in position of the functional elements toothing and shaft due to the appearing deviations in form, size, and position can be detected and corrected. For this, conoscopic sensors are used which are properly positioned at the measurement component by a linear axis within the lathe. Through the analysis of the captured data the optimal position for the processing of the functional surfaces is determined.

Contact person: Dipl.-Wirtsch.-Ing. Rüdiger Gillhaus

Complete geometry inspection (CRC 489, subproject B5)

Measuring system

During the precision-forging of pinion shafts geometry deviations are created randomly on the component’s surface due to the molding of the die. In general, these cannot be detected by conventional tactile measurements. A solution is offered by fringe projection as an areal triangulation method. A complete areal capture of the functional surfaces after precision-forging with integrated heat-treatment builds the foundation for a production related analysis of the deviation of the gearing and the bearing seat of pinion shafts. By capturing the geometry before and after the hardening process distortions due to hardening can also be detected.

Contact person: Dipl.-Ing. Klaus Haskamp

Structure Oriented Surface Characterisation

signal processing software Strukturfinder displaying the detected structures in red
signal processing software Strukturfinder displaying the detected structures in red

The aim of this project is the characterisation and determination of the functionally relevant structures of the sample surfaces provided by the partner-institutes IFW und IW.
First, the samples are measured in area using optical profilers. The IMR has several of these, e.g. a white light inferometric optical profiler, a confocal microscope and a chromatic sensor. These devices illuminate the sample surface using white light, determine the topological information by analysis of the reflected light und thus provide a 3D visualisation of the surface. The so generated measurement data and the measurement parameters like profiler and profiler lens are saved as one dataset within a web based database.

Consecutively, this measurement data is analysed: First, the form of the sample included in the measurement data is eliminated using an adjustable reference surface filtering of first degree (in case of planes samples) and reference surface filtering of second degree (in case of round samples). For this purpose a software application is used, which is being developed by the institute. This application performs the characterisation of the surface by using appropriate morphological image processing and region finding algorithms. A detected region differs from its surrounding area significantly in certain properties: A dimple for example has a lower height with respect to its surroundings and has a round closed form.
There are other interesting properties like width, area, volume, form, projected form and primary direction of a region or arrangement and density of arrangement and distances of several regions. Since optical profilers can only scan a small area of a few sqaremillimeters, it has to be figured out if stable characteristics can be determined out of a single measurement, or if the measurement area must be expanded by stitching of several measurements.
These characteristics are saved into the database for later analyses as well. In a comparison of these with the tribological investigations of the other projects the operation-relevant characteristics are determined. In applying this knowledge new samples are produced by the other institutes in order to yield optimised surfaces; the characteristics of these optimised samples are determined again within this project in order to verify the improvements.

Contact person: Dipl.-Phys. Florian Engelke

Multiscale Methods for the Dimensional Characterisation of Surfaces and Interfaces (MARIO)

In automotive applications new approaches concerning innovative plasma spray surface coatings for liquid-lubricated high performance contact pairs, like cylinder liners in combustion engines, deal with porous material layers to optimise the tribological behaviour and lubrication in view of fuel efficiency.

The aim of this project is the research and development of methods for the dimensional characterisation of these porous surface coatings using multiscale methods for data acquisition and analysis. For a reliable measurement of the form, surface topography and volume information of the porous material layers, it is necessary to develop appropriate calibration and measurement strategies based on a combination of surface metrology and xray micro-tomography. Based on the generation of a volumetric data model, methods for a quantitative analysis of the dimensional parameters of the geometric features on or within the porous surface coatings should be developed. The correlation of these parameters with the tribological behaviour of the surface gives the key information for an optimisation of the plasma spraying process.

Contact person: M.Sc. Yibo Zou

Endoscopic geometry inspection by modular fibre-optic sensors (SFB/TR 73, TP B6)

A within quality inspection of assembly parts and tool surfaces becomes more and more important in times of advanced quality management. The trend leads for many parts to 100% checking methods within the running fabrication process. Suited measurement techniques therefore should be above all global and fast in order not to slow down the production process. Large area analysis of topographies nowadays can be realised with commercially available fringe projection systems with very high accuracy. However these systems reach their limits at assemblies of high complexities, because of formation of shades in the area of measurement.

In the frames of the Transregio 73 (SFB/TR73) research project, funded by the German research community (DFG), a new kind of micro fringe projection system is being developed. By using flexible imaging fibre bundles it shall become possible to collect complete data sets of filigree and hardly reachable assembly geometries.

These sets can be used to generate an own model or to complete data sets of large-scale systems. These models can immediately give feedback about the running manufacturing process and can be used for in situ optimization in the fabrication line to avoid high reject rates. Additionally measured data can be combined of functional surfaces with spot measurements of coordinate measurement systems.

Contact person: Dipl.-Ing. (FH) Christoph Ohrt