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The intelligent operation room

Laboratory: OR- Table with lights

Today's operating room (OR) is an environment for high tech equipment, used for therapeutic and diagnostic applications. The equipment is applied to treat the patient with new and better surgical techniques. This causes an increasing variety and complexity of surgical procedures which poses a further requirement on the staff. This is taken into account through intelligent functions, which should decrease the workload. Processes within the OR are new designed and optimized, to ensure the best patient treatment.

Within the shown laboratory, approaches in human machine interaction, patient positioning and collision control are evaluated. 3D sensors are used to observe the scene and algorithms of digital image processing are applied. Based on the results, the OR should achieve information about the OR state and situation in order to interact with the staff. Besides assisting functions, active manipulation of OR equipment through the interface is possible.

Our technical focus is in the development and implementations of sensor array systems. Because the OR- environment is very complex, due to many people and objects within a small room, the scene is observed from various viewpoints. Through this, the complete segmentation of objects becomes possible. This causes a lot of challenges in the fields of real time applicability, data fusion capability and consideration of complex picture failures, like reflection, shadowing and interfacial effects.

Contact person: M. Sc. Armin Dietz

Early recognition system for playing-related musculoskeletal disorders of professional musicians

Disorders, caused by unphysiological postures of the human body, are highly-relevant for our current and future society. Endangered are specialist working at a construction site or office, who lift heavy materials or sit on chairs respectively.

For professional musicians preventing disorders caused by unphysiological postures or movements are an extra-ordinary challenge. In the context of this study, it is focused on instrumentalists. For playing composition, like the 6th Paganini etudes with 1800 notes a minute – approximately 30 notes per second, musicians are expected to cross the limits of human capability. Such disorder can cause handicaps in musician‘s professional life or in worst case irreversible damage and the end of their musical career.

Therefore, the Institute of Measurement and Automatic Control is developing an early warning system for disorders induced by posture deficiencies with the help of optical and acoustical sensors. Based on Machine Learning, Object Detection, Pose Estimation and Motion Capturing, the instrumentalist, instrument and relative position and movements between them are recognized. If an unphysiological posture is detected, the musician will receive a direct feedback and is able to improve it instantly.

Contact person: M. Sc. Benjamin Fehlandt

3D geometry detection of rotating components by means of rotationally symmetrical fringe projection

System diagram

In industry, a common and important kind of dynamic object is rotating machinery part. It is of interest to know the 3D geometry information of rotating part under operational conditions. The fringe projection (FP) technique, with the advantages of full field, high accuracy and high point density, plays an important role in dynamic 3D shape measurement. The aim of this project is to develop a rotationally symmetric fringe projection (FP) system that can accurately measure the 3D shape of fast rotating objects. However, for objects with high rotational speed, the rotating movement in the duration of measurement will lead to dramatical image blur, which make the measurement become unreliable or invalid. In order to enable measure objects with high rotational speed, the optomechanical image derotator is introduced to compensate for the rotation movement. Three major issues will be addressed in this project, including system design considering optical image derotation, phase recovery with short sequence fringe patterns and error compensation, and system modeling and calibration based on the hybrid model.

This project is supported by the Humboldt Research Fellowship for Postdoctoral Researchers.

Contact: Dr.-Ing. Yongkai Yin

HyMon - Hand hygiene monitoring in hospitals

The system aims to support the user in real time at the hand disinfection process and informs about potential untreated areas.

Several studies since the mid-19th century indicate the impact of hand hygiene compliance on the decline of infections in the health sector. However, despite this knowledge and worldwide-accepted guidelines on hand hygiene, infection rates in today’s hospitals are still too high. E.g., the number of deaths related to infections with multi-resistant pathogens is 15,000 persons per year in Germany. Studies indicate an average compliance rate of hand hygiene guidelines of 41.2% – 55.2%. Required hand disinfection steps are either omitted or performed too shortly. E.g., the actual time spent during the hand disinfection process is often below 15 seconds, although the norm EN 1500 proposes 30 seconds.

The Institute of Measurement and Automatic Control is developing a system, which evaluates the quantity and quality of hand disinfection processes using an optical sensor and computer vision. The process of hand disinfection can be divided into sequences of gestures. The system is learning to distinguish those gestures during a training phase, which is commonly known as machine learning. Attributes such as gesture duration, kind, quantity and succession are recognized and evaluated. Finally, the system aims to support the user in real time at the hand disinfection process and informs about potential untreated areas.

Contact person: M. Sc. Armin Dietz

Development of a newly image derotator

The analysis of the dynamic behaviour of rotary objects under operating conditions is a great challenge due to the overlayed objects rotation.

At the Institute of Measurement and Automatic Control (IMR) a novel image derotator with a specially designed mirror arrangement is developed, that can simplify the analysis of fast rotating objects. By means of a laser doppler vibrometer or image processing the analysis of vibration or deformation can be accomplished.

Contact person: M. Sc. Bettina Altmann

Three-dimensional reconstruction from scanning electron microscope (SEM) micrographs

Schematic of the epipolar geometry
Disparity map of generated stereo images
projective reconstruction of the scenery

SEM micrographs allow the visualization of objects that can't be sufficiently magnified by conventional light microscopes. Nowadays modern devices achieve resolutions in the sub-nanometer range by using cold fieldemission cathodes and provide an excellent depth of focus and image quality. Nevertheless a crucial disadvantage is the fact that SEM micrographs don't contain information about the three-dimensional sample texture. Especially in investigations of particles and their morphology, depth maps are essential to generate a three-dimensional model of the specimen.

In the context of this project, the Institute of Measurement and Automatic Control is developing a method that allows the euclidean reconstruction of different-sized particles from SEM stereo micrographs. The method is based on the principles of epipolar geometry. Using a eucentrically tiltable specimen stage, a set of stereo images can be created. After the rectification of the image pairs, correspondences are determined using local and global matching algorithms. In the next step a disparity map can be computed that allows the triangulation of a point cloud and hence the computation of a projective reconstruction. Due to the uncalibrated scenery, the result isn't unambiguous and therefore it differs from an euclidean reconstruction by an unknow projective transformation. To determine this transformation, several approaches exist and thus a quantitative three-dimensional measurement of the examined specimen can be realized.

Contact person: Dipl.-Ing. Stefan Töberg

Inspection of microstructured surfaces in industrial conditions

Special microstructured surfaces can reduce the drag of components. The shape of this structure is motivated from skin of sharks and is called riblets. The field of application of this structure is found mainly on the outer skin of aircraft and compressor blades of aircraft engines. The structure consists of periodic elevations of the component surface. The period length of this structure corresponds to the prevailing flow conditions and is in the range of approx. 50-500 microns and the structure height is in the range of approx. 10-200 microns. The flow reducing effect of riblets has been known for some time, however, efficient production method of riblets are still in development.

In this project, new measurement systems are developed in order to make the manufacturing process of riblets efficiently. This includes in particular the development of measurement systems that allow microscopic inspections not only under laboratory conditions, but directly during the manufacturing process. These systems must firstly have a very high resolution, so that defects in the range of <10 microns can be found. On the other hand, the newly developed measurement system must be very robust against all manufacturing conditions. These include in particular impurities such as coolant during a grinding process or vibration.

The high resolution of the measuring systems for the inspection of riblets also leads to very low area ranges for a single measurement. In this project, possibilities are investigated to measure large, microstructured surfaces efficiently despite the small areas rates.

Surface metrology based on Scanning Electron Microscopy

Sketch of the structure to reduce SE3 yield with possible electron trajectories

Surface metrology based on Scanning Electron Microscopy (SEM) makes it possible to study materials up to the atomic level. To do so, a sample is irradiated point by point and the resulting radiant intensities are recorded. Classic studies limit themselves to various intensities which are applied to image processing or visualization methods. For many years, the Institute of Measurement and Automatic Control (IMR) has been researching a method of high-precision 3-D electron microscopy which, in addition to intensity values, also reconstructs the surface profile of the sample. This 3-D SEM measurement technique does not only represent a unique new measurement method, but also provides new insights into the microstructure of material surfaces, based on which it is possible to develop new analysis techniques in various areas of application. For the time being, these research methods are still being developed, but in several years they could be market-ready.
The measurement technique developed at our institute uses several detectors for secondary electrons (SE), so that it is possible to work with lower radiation energies and to obtain high precision of the surface reconstruction. To do so, imaging procedures apply directional characteristic, from which it is possible to calculate the surface slope using sophisticated material models and, therefore, create a surface profile. At one of the first stages of development two detectors placed at a 180° angle were used. The results were promising, so that the next stage of development is currently being expanded by four Everhart-Thornley detectors and an elaborate electron "lens". Simulations and the first results obtained at this stage of development also allow to expect that the measurement results have a novel quality in comparison to the existing imaging procedures. The only obstacle in this approach is created by backscattered electrons (BSE) which can distort the measurement results, because these high-energy electrons release further SE on the surfaces of the sample chamber.
To significantly reduce this effect, the IMR plans to develop an electron-trap system based on nanostructures. This way, it could be possible to intercept the unwanted electrons. Therefore, the IMR expects to further improve the triggering of measurements. It makes most sense to place the electron-trap system on the bottom of the electron gun, because the majority of BSE occurs here. The structure should collect high-energy electrons and intercept the so-called SE3 emission that occurs in it. In order for the electron-trap system to perform this way, it is necessary, in addition to finding a suitable material, to find an optimal surface structure for the electron-trap system. It is most probably a square wave shape, however, the measurements of squares or the depth of holes must be first determined by means of several series of experiments.

Contact person: Renke Scheuer

Active Microoptics

This project works on the development of a novel concept for tunable micro-optic systems that are based on fluidic principles.

A magnetic liquid is moved by means of miniaturized coils in an adaptive opto-fluidic system. This mechanism can influence the shape of the fluidic lens indirectly. By moving the electro-magnetic liquid body (the ferro-fluid), the other optically active liquid is displaced within the fine canal structures. In order to guarantee the optimal adjustment to technical features like focal length and geometrical size, the project team works on the further development and improvement of the ferro-fluidic and optically active part of the system. To begin with, the researchers want to show that such a system permits the adaptive tuning of a fluidic lens. In a second step, they will inject a liquid into the especially molded cavities of the channels. The liquid’s refractive index is adjusted accordingly. Selected optical elements that are tailored to demand can be  placed in the light path. Due to the chosen micro-fluidic principle, it will be possible to realize different components of geometrical and diffractive optics. This modular concept is suitable for a variety of micro-optic applications. The actual optical component and the tuning mechanism are built in a compact way. This compactness reduces the size of these systems, which facilitates their integration into more complex devices. Such systems can be applied in adaptive lenses or tunable optical filters. The chosen approach, however, is most suitable for compact low energy systems.

Contact person: Dipl.-Ing. Thanin Schultheis

Stochastic Structures

multi sensor system to detect the stochastic structures
multi sensor system to detect the stochastic structures

The influence of stochastic shaft surface defects on the rotary shaft seal function is being investigated within the project “stochastic structures”. Two research centres are taking part in the project: Institute of Measurement and Automatic Control (IMR) and Institute of Machine Elements and Engineering Design (IMKT), Leibniz University in Hannover. The common purpose of the project is the investigation of stochastic surface defects with the view to the operation of rotary shaft seals. In this context, the influence of such defects on the leakage and wear is especially interesting. It is important to determine the limits for stochastic defects that are not critical and permissible for the further practical use. In other words, it is desirable to find the boundary between critical and non-critical shaft surface defects. An additional goal of IMR is the development of a production–related multi sensor system for the detecting critical surface defects.

To detect and to measure stochastic defects on the shaft contact surfaces the measuring methods, those are able to measure the lateral size of defects in the range of some millimeters (dents) as well as in the range of few tenths of millimeters (scratches), are needed. After the comparison of different methods, two measuring systems were chosen: light scattering sensor for the long-wave form deviations (dents) and chromatic sensor for the short-wave deviations (scratches). It was as well noted, that the light scattering sensor is able to detect the small scratches.

Contact person: Dipl.-Phys. Alexander Leis

Cutting Line Deviations in Stone Cutting

Schwingungsmode einer Trennschleifscheibe, mit dem IMR-Derotator gemessen
Deflection shape of a cut-off wheel

In cooperation with the Institut für Fertigungstechnik und Werkzeugmaschinen  (IFW) of the Leibniz Universität Hannover and the Forschungsgemeinschaft Werkzeuge und Werkstoffe e.V. Remscheid, the influence of various parameters on the cutting line in stone cutting was investigated. A major goal was to obtain a correlation between cutting parameters like cut-off wheel and flange diameter or cutting speed on the vibration of the cut-off wheel. The vibration conditions were measured under different rotational speeds of the wheel by using a Scanning Laser Doppler Vibrometer. To track a fix measuring point on the wheel - even under rotation - an optomechnical derotator was used to compensate for the rotation. Different series of measurements were carried out under lab condition with a free spinning wheel as well as under cutting condition using a stone cutting machine. The measurement data indicate a strong dependency of the eigenfrequencies and decay time on cutting wheel diameter, flange diameter and cutting speed. Under cutting conditions the frequencies of vibration were dominated by multiples of the rotational frequencies due to the teeth of the blade hitting the stone. Eigenfrequencies were suppressed but it is expected that Eigenfrequencies can be measured when the rotaional frequency matches a Eigenfrequency which was not the case in the experiments. The Project was supported by the Arbeitsgemeinschaft industrieller Forschungsvereinigungen
"Otto von Guericke" e.V. (AiF)

Contact person: Dipl.-Phys. Maik Rahlves

Cleansky - Quantification of the Degradation of Microstructured Coatings

Experimental set-up consisting of linear stages, a high-speed camera and a projection lens with the sample.

Even modern passenger airplanes require several tons of kerosene for every operation hour. Therefore, it is a matter of top priority to introduce some savings, due to both the environment and economy. As it is clearly seen from the project „Riblets on Compressor Blades“, riblet-structured surfaces can drastically minimise friction losses on parts circulated by air. One of the possible approaches towards the reduction of friction losses on airplanes is the structuring of airplane surfaces with riblets. By means of laboratory tests developed by imr, it is possible to determine the riblet quality locally. To be able to apply it in the series production, however, it is necessary to guarantee a large-scale quality control close to the production premises. For this purpose the imr is engaged in the EU-funded project Cleansky, in order to develop a control unit based on a high-speed camera to be able to determine the quality of riblet-structured surfaces.

Contact Person: Dipl.-Ing. Renke Scheuer

Riblets on compressor blades

This project deals with the measurement of riblet structures on surfaces of compressor blades.

Riblets are trapezoid, triangular or parabolic structures which are aligned in the direction of flow to significantly reduce surface friction, and consequently the overall flow resistance of coated objects. The typical dimensions of these structures depend on the Reynolds number, thus on the density, velocity of the surrounding medium, etc.,  and vary from a few millimeters for watery media to 20-50µm for gaseous media. Due to the typical width of riblets on compressor blades, the tip radii of the structures are in the range of 200 – 800nm.

The accurate production of structures with such measurements is a nontrivial problem, because slight changes in the geometry have a huge effect on efficiency. Therefore, the quality control plays an important role in the production of riblets structures. Because of the high possible scanning speed, an areal scanning method should be used to detect local fluctuations of the structure. Since a scanning electron microscope (SEM) fits the requirements, it may principally be used to evaluate the produced surfaces. However, there is a huge drawback to a SEM – it is only capable of producing two dimensional images. A logical consequence is a SEM which can be utilized as a three dimensional measurement device. Hence, the IMR is working on a design for a 3D-measurement device based on a conventional SEM.

Contact Person: Dipl.-Ing. Renke Scheuer