Quantitative 3d reconstruction from scanning electron microscope images based on affine camera models

Scanning electron microscopes (SEMs) are versatile imaging devices for the micro-and nanoscale that find application in various disciplines such as the characterization of biological, mineral or mechanical specimen. Even though the specimen’s two-dimensional (2D) properties are provided by the acquired images, detailed morphological characterizations require knowledge about the three-dimensional (3D) surface structure. To overcome this limitation, a reconstruction routine is presented that allows the quantitative depth reconstruction from SEM image sequences. Based on the SEM’s imaging properties that can be well described by an affine camera, the proposed algorithms rely on the use of affine epipolar geometry, self-calibration via factorization and triangulation from dense correspondences. To yield the highest robustness and accuracy, different sub-models of the affine camera are applied to the SEM images and the obtained results are directly compared to confocal laser scanning microscope (CLSM) measurements to identify the ideal parametrization and underlying algorithms. To solve the rectification problem for stereo-pair images of an affine camera so that dense matching algorithms can be applied, existing approaches are adapted and extended to further enhance the yielded results. The evaluations of this study allow to specify the applicability of the affine camera models to SEM images and what accuracies can be expected for reconstruction routines based on self-calibration and dense matching algorithms. © MDPI AG. All rights reserved

Investigation of harmful slip in a rolling bearing using a thermographic camera with a derotator

Due to their high availability and versatility, rolling bearings are a standard solution for mounting and support of rotating components. The service life of an entire rotating machine is often limited by the service life of rolling bearings. This can be shorter than expected if the rolling bearing is operated in harmful operating conditions, e.g. in the presence of slip. Slip means that there is a deviation between the theoretical angular velocity of the rolling element set and the actual angular velocity. In this context, slip is harmful if it leads to increased friction and thus heating of the bearing. The occurrence and properties of slip are not completely understood yet. Therefore, it is of interest to investigate a relationship between slip and heating of the rolling bearing in order to better understand damages of the rolling bearing. In this work, a method is presented in which, in addition to slip measurements with a high-speed camera, a thermal imaging camera is used to investigate the heating of the bearing during operation. Since the rotational movement and exposure time of the camera would cause motion blur, the thermal imaging camera is operated together with a derotator to optically eliminate the rotational movement. The investigations of the rolling bearing are carried out under different operating conditions (different loads and rotational speeds), which have an influence on the slip behavior of the bearing. Thus, the potential of this investigation method for deepening the understanding of heating and friction in rolling bearings is demonstrated

Topography Measurement for Monitoring Manufacturing Processes in Harsh Conditions

High precision manufacturing, e.g. milling and grinding, which have manufacturing tolerances in the range of <10 μm require microscopic measurement techniques for the inspection of the manufactured components. These measurement techniques are very sensitive to cooling liquids and lubricants which are essential for many manufacturing processes. Therefore, the measurement of the components is usually conducted in separate and clean laboratories and not directly in the manufacturing machine. This approach has some major drawbacks, e.g. high time consumption and no possibility for online process monitoring. In this article, a novel concept for the integration of high precision optical topography measurement systems into the manufacturing machine is introduced and compared to other concepts. The introduced concept uses a reservoir with cooling liquid in which the measurement object is immersed during the measurement. Thereby, measurement disturbance by splashing cooling liquids and lubricants can effectively be avoided.BMBF/03V047

22-GHz Modulation Bandwidth of Long Cavity DBR Laser by Using a Weakly Laterally Coupled Grating Fabricated by Focused Ion Beam Lithography

A 22-GHz directly modulated 3-dB bandwidth could be obtained by 1.3-mm-long weakly laterally coupled distributed Bragg reflector lasers fabricated by focused ion beam lithography. In addition to a high bandwidth, the lasers show a stable emission spectrum with side-mode suppression ratios of more than 40 dB and output powers exceeding 20 mW

Position Determination of a Robot End-Effector Using a 6D-Measurement System Based on the Two-View Vision

A mechatronic system based on the micro-macro-kinematic consists of an industrial robot and a piezoelectric stage mounted on the robot’s end-effector and has to carry out operations like micro-assembly or micro-milling. The piezoelectric stage has to compensate the positioning error of the robot. Therefore, the position of the robot’s end-effector has to be measured with high accuracy. This paper presents a high accuracy 6D-measurement system, which is used to determine the position and orientation of the robot’s end-effector. We start with the description of the operational concept and components of the measurement system. Then we look at image processing methods, camera calibration and reconstruction methods and choose the most accurate ones. We apply the well-known pin-hole camera model to calibrate single cameras. Then we apply the epipolar geometry to describe the relationship between two cameras and calibrate them as a stereo vision system. A distortion model is also applied to enhance the accuracy of the system. The measurement results are presented in the end of the paper

Fiber-optic fringe projection with crosstalk reduction by adaptive pattern masking

To enable in-process inspection of industrial manufacturing processes, measuring devices need to fulfill time and space constraints, while also being robust to environmental conditions, such as high temperatures and electromagnetic fields. A new fringe projection profilometry system is being developed, which is capable of performing the inspection of filigree tool geometries, e.g. gearing elements with tip radii of 0.2 mm, inside forming machines of the sheet-bulk metal forming process. Compact gradient-index rod lenses with a diameter of 2 mm allow for a compact design of the sensor head, which is connected to a base unit via flexible high-resolution image fibers with a diameter of 1.7 mm. The base unit houses a flexible DMD based LED projector optimized for fiber coupling and a CMOS camera sensor. The system is capable of capturing up to 150 gray-scale patterns per second as well as high dynamic range images from multiple exposures. Owing to fiber crosstalk and light leakage in the image fiber, signal quality suffers especially when capturing 3-D data of technical surfaces with highly varying reflectance or surface angles. An algorithm is presented, which adaptively masks parts of the pattern to reduce these effects via multiple exposures. The masks for valid surface areas are automatically defined according to different parameters from an initial capture, such as intensity and surface gradient. In a second step, the masks are re-projected to projector coordinates using the mathematical model of the system. This approach is capable of reducing both inter-pixel crosstalk and inter-object reflections on concave objects while maintaining measurement durations of less than 5 s.DFG/CRC/TR 7

Texture direction analysis of micro-topographies using fractal geometry

In recent years fractal geometry has been repeatedly shown to help describe and characterize micro-topographies. Important properties of micro-topographies include roughness or texture direction. Consequently, in this work, fractal geometry is investigated to determine texture direction. For this purpose, synthetic data and real height maps of different micro-topographies are evaluated using the fractal power spectrum density method. The results are compared with a manual determination of the texture direction and determining the texture direction according to ISO 25 178 using the S td parameter. The results show that the fractal method is more accurate than the currently standardized method. Another advantage is that secondary texture directions can be detected. Thus, the fractal method is well suited for characterizing micro-topographies and can complement existing parameters from ISO 25 178

Digital image processing algorithms for automated inspection of dynamic effects in roller bearings

Unstable movement in roller bearings like cage or roller slip can lead to damages or eventually even to an early break of the bearing. To prevent slip, inadequate operating states should be avoided. Therefore, it is necessary to study the dynamic behavior of the bearing. Unfortunately, there is only a limited range of measurement methods for the dynamic of bearing components. Two possible approaches are using solely a high-speed camera or the combination of an optomechanical image derotator and a high-speed camera. This work focuses on a proposal which is suitable for both. Initially, the influence of the rotational velocity in the images is eliminated. In the next step the measurement data is reduced to a region of interest which displays a particular rolling-element. A rolling element is equipped with a linear marker which, in the next stage, is segmented by a thresholding method to multiple regions. The region representing the marker is extracted from the background and the position is calculated by a Principle Component Analysis. Depending on the shift of the angular position and the lag time between two images, the rotational velocity of the rolling element is calculated. Thus, it is possible to determine whether the rolling element is operating under ideal conditions. In conclusion, it can be said that this approach enables a simple and flexible non-invasive method to depict the occurrence of roller slip in roller bearings. © 2017 SPIE

Fast in-situ tool inspection based on inverse fringe projection and compact sensor heads

Inspection of machine elements is an important task in production processes in order to ensure the quality of produced parts and to gather feedback for the continuous improvement process. A new measuring system is presented, which is capable of performing the inspection of critical tool geometries, such as gearing elements, inside the forming machine. To meet the constraints on sensor head size and inspection time imposed by the limited space inside the machine and the cycle time of the process, the measuring device employs a combination of endoscopy techniques with the fringe projection principle. Compact gradient index lenses enable a compact design of the sensor head, which is connected to a CMOS camera and a flexible micro-mirror based projector via flexible fiber bundles. Using common fringe projection patterns, the system achieves measuring times of less than five seconds. To further reduce the time required for inspection, the generation of inverse fringe projection patterns has been implemented for the system. Inverse fringe projection speeds up the inspection process by employing object-adapted patterns, which enable the detection of geometry deviations in a single image. Two different approaches to generate object adapted patterns are presented. The first approach uses a reference measurement of a manufactured tool master to generate the inverse pattern. The second approach is based on a virtual master geometry in the form of a CAD file and a ray-tracing model of the measuring system. Virtual modeling of the measuring device and inspection setup allows for geometric tolerancing for free-form surfaces by the tool designer in the CAD-file. A new approach is presented, which uses virtual tolerance specifications and additional simulation steps to enable fast checking of metric tolerances. Following the description of the pattern generation process, the image processing steps required for inspection are demonstrated on captures of gearing geometries. © 2016 SPIE.DFG/CRC/TR 7

Development of a compact low coherence interferometer based on GPGPU for fast microscopic surface measurement on turbine blades

Vertical scanning interferometry (VSI) techniques are widely used to profile microscopic surface structures of industrial products. This paper introduces a high-precision fast optical measurement system with an optimized small sensor head for the measurement of precision surfaces on a turbine blade or blisks (blade integrated discs). The non-contact measurement system is based on a low coherence interferometer (LCI), which is capable of fast profiling of 3D sample surface with a nanometer resolution and has a larger measurement range compared to conventional microscopes. This results in a large amount of sampled data and a high computational time for the evaluation of the data. For this reason, the used evaluation algorithm in this paper is accelerated by the Compute Unified Device Architecture (CUDA) technology, which allows parallel evaluation of the data stack on independent cores of a General Purpose Graphics Processing Unit (GPGPU). As a result, the GPU-based optimized algorithm is compared with the original CPU-based single-threaded algorithm to show the approximate 60x speedup of computing the Hilbert Transformation, which is used to find the depth position in the correlogram of each pixel of the sampled data. The main advantage of the GPU computing for the evaluation algorithm of the LCI is that it can reduce the time-consuming data evaluation process and further accelerates the whole measurement. © 2015 SPIE.DFG/SFB/87