A biologically inspired computational vision front-end based on a self-organised pseudo-randomly tessellated artificial retina

This paper considers the construction of a biologically inspired front-end for computer vision based on an artificial retina pyramid with a self-organised pseudo-randomly tessellated receptive field tessellation. The organisation of photoreceptors and receptive fields in biological retinae locally resembles a hexagonal mosaic, whereas globally these are organised with a very densely tessellated central foveal region which seamlessly merges into an increasingly sparsely tessellated periphery. In contrast, conventional computer vision approaches use a rectilinear sampling tessellation which samples the whole field of view with uniform density. Scale-space interest points which are suitable for higher level attention and reasoning tasks are efficiently extracted by our vision front-end by performing hierarchical feature extraction on the pseudo-randomly spaced visual information. All operations were conducted on a geometrically irregular foveated representation (data structure for visual information) which is radically different to the uniform rectilinear arrays used in conventional computer vision

An orthogonal oriented quadrature hexagonal image pyramid

An image pyramid has been developed with basis functions that are orthogonal, self-similar, and localized in space, spatial frequency, orientation, and phase. The pyramid operates on a hexagonal sample lattice. The set of seven basis functions consist of three even high-pass kernels, three odd high-pass kernels, and one low-pass kernel. The three even kernels are identified when rotated by 60 or 120 deg, and likewise for the odd. The seven basis functions occupy a point and a hexagon of six nearest neighbors on a hexagonal sample lattice. At the lowest level of the pyramid, the input lattice is the image sample lattice. At each higher level, the input lattice is provided by the low-pass coefficients computed at the previous level. At each level, the output is subsampled in such a way as to yield a new hexagonal lattice with a spacing sq rt 7 larger than the previous level, so that the number of coefficients is reduced by a factor of 7 at each level. The relationship between this image code and the processing architecture of the primate visual cortex is discussed

Sensor integration for robotic laser welding processes

The use of robotic laser welding is increasing among industrial applications, because of its ability to weld objects in three dimensions. Robotic laser welding involves three sub-processes: seam detection and tracking, welding process control, and weld seam inspection. Usually, for each sub-process, a separate sensory system is required. The use of separate sensory systems leads to heavy and bulky tools, in contrast to compact and light sensory systems that are needed to reach sufficient accuracy and accessibility. In the solution presented in this paper all three subprocesses are integrated in one compact multipurpose welding head. This multi-purpose tool is under development and consists of a laser welding head, with integrated sensors for seam detection and inspection, while also carrying interfaces for process control. It can provide the relative position of the tool and the work piece in three-dimensional space. Additionally, it can cope with the occurrence of sharp corners along a three-dimensional weld path, which are difficult to detect and weld with conventional equipment due to measurement errors and robot dynamics. In this paper the process of seam detection will be mainly elaborated

Wear characterization of cemented carbides (WC-CoNi) processed by laser surface texturing under abrasive machining conditions

Cemented carbides are outstanding engineering materials widely used in quite demanding material removal applications. In this study, laser surface texturing is implemented for enhancing, at the surface level, the intrinsic bulk-like tribological performance of these materials. In this regard, hexagonal pyramids patterned on the cutting surface of a tungsten cemented carbide grade (WC-CoNi) have been successfully introduced by means of laser surface texturing. It simulates the surface topography of conventional honing stones for abrasive application. The laser-produced structure has been tested under abrasive machining conditions with full lubrication. Wear of the structure has been characterized and compared, before and after the abrasive machining test, in terms of changes in geometry aspect and surface integrity. It is found that surface roughness of the machined workpiece was improved by the laser-produced structure. Wear characterization shows that laser treatment did not induce any significant damage to the cemented carbide. During the abrasive machining test, the structure exhibited a high wear resistance. Damage features were only discerned at the contacting surface, whereas geometrical shape of pyramids remained unchanged.Peer ReviewedPostprint (author's final draft

Wear Characterization of Cemented Carbides (WC–CoNi) Processed by Laser Surface Texturing under Abrasive Machining Conditions

Cemented carbides are outstanding engineering materials widely used in quite demanding material removal applications. In this study, laser surface texturing is implemented for enhancing, at the surface level, the intrinsic bulk-like tribological performance of these materials. In this regard, hexagonal pyramids patterned on the cutting surface of a tungsten cemented carbide grade (WC–CoNi) have been successfully introduced by means of laser surface texturing. It simulates the surface topography of conventional honing stones for abrasive application. The laser-produced structure has been tested under abrasive machining conditions with full lubrication. Wear of the structure has been characterized and compared, before and after the abrasive machining test, in terms of changes in geometry aspect and surface integrity. It is found that surface roughness of the machined workpiece was improved by the laser-produced structure. Wear characterization shows that laser treatment did not induce any significant damage to the cemented carbide. During the abrasive machining test, the structure exhibited a high wear resistance. Damage features were only discerned at the contacting surface, whereas geometrical shape of pyramids remained unchanged

Definierte strukturierte Hartmetallwerkzeuge für abrasive Prozesse

The challenge of this dissertation concerns the surface structuration of the WC-CoNi hardmetal with defined geometry, despite the fact that the embedded WC grains have irregular geometrical properties and distribution. An advanced method should be found and applied to structure the WC-CoNi hardmetal tool surface. The structured surfaces should be favorable and beneficial to reduce friction or to remove material in abrasive machining processes. Based upon the surface topography characterization of existing abrasive tools, e.g., CBN honing stone, geometrical properties of abrasives can be measured and quantified. The obtained geometrical information can contribute to the reproduction of the abrasive tool surface on WC-CoNi hardmetal. Laser surface texturing is an advanced machining method with high precision and it can effectively avoid some common thermal damage. Therefore, this method is implemented to machine WC-CoNi hardmetal surfaces. It is found that the structured WC-CoNi hardmetal tool can effectively remove material and improve surface quality of the counterpart (workpiece). These surface patterned hardmetal tools emerge then as potential alternative to conventional abrasive tools. Meanwhile, other patterns have also been produced on the hardmetals, and they can be used in the tribological system to reduce friction and improve wear resistance. It is a methodological and technical innovation to fabricate abrasive machining tools using laser to produce defined structures on a hardmetal surface, because it not only expands the utilization of hardmetal as an abrasive tool material but also enables the control and design of abrasive tool surface topography with high precision.Die Herausforderung dieser Arbeit besteht in der geometrischen Strukturierung von WC-CoNi-Hartmetall-Oberflächen, wobei die eingebetteten WC-Körner geometrische unbestimmte Eigenschaften sowie zufällige Verteilungen aufweisen. Es sollen neue Methoden gefunden und angewendet werden, um WC-CoNi Hartmetallwerkzeugoberflächen zu strukturieren. Mit Hilfe dieser Strukturen soll die Reibung reduziert oder Material durch abrasive Bearbeitung gezielt abgetragen werden. Durch eine geeignete Charakterisierung der Oberflächentopographie vorhandener Abrasivwerkzeuge können die geometrischen Eigenschaften von abrasiven Körnern ermittelt und quantifiziert werden. Die erworbenen geometrischen Informationen können zur Reproduktion der Oberflächen von Abrasivwerkzeugen auf Hartmetalloberflächen genutzt werden. Die Laseroberflächenstrukturierung ist ein innovatives Bearbeitungsverfahren mit hoher Präzision und Effizienz. Diese Methode kann wirksam die üblichen thermischen Schäden vermeiden. Daher ist dieses Verfahren zur Bearbeitung von WC-CoNi Hartmetall vorteilhaft. Es konnte bestätigt werden, dass die neuartigen strukturierten WC-CoNi Hartmetallwerkzeuge die Materialien der Werkstücke abtragen und die Oberflächenqualität dieser verbessern. Diese oberflächenstrukturierten Hartmetallwerkzeuge können als potentielle Alternative zu konventionellen abrasiven Werkzeugen dienen. Parallel hierzu wurden weitere Strukturmuster auf Hartmetalloberflächen erzeugt. Die Strukturen können in einem tribologischen System angewendet werden, um Reibung zu reduzieren und Verschleißbeständigkeit zu verbessern. Die definiert erzeugten Strukturen können nicht nur bei Hartmetallen als Schleifwerkzeugmaterial eingesetzt werden, sondern ermöglichen auch eine gezielte Einstellung der Werkzeugoberflächentopographie

Single conjugate adaptive optics for the ELT instrument METIS

The ELT is a 39m large, ground-based optical and near- to mid-infrared telescope under construction in the Chilean Atacama desert. Operation is planned to start around the middle of the next decade. All first light instruments will come with wavefront sensing devices that allow control of the ELT's intrinsic M4 and M5 wavefront correction units, thus building an adaptive optics (AO) system. To take advantage of the ELT's optical performance, full diffraction-limited operation is required and only a high performance AO system can deliver this. Further technically challenging requirements for the AO come from the exoplanet research field, where the task to resolve the very small angular separations between host star and planet, has also to take into account the high-contrast ratio between the two objects. We present in detail the results of our simulations and their impact on high-contrast imaging in order to find the optimal wavefront sensing device for the METIS instrument. METIS is the mid-infrared imager and spectrograph for the ELT with specialised high-contrast, coronagraphic imaging capabilities, whose performance strongly depends on the AO residual wavefront errors. We examined the sky and target sample coverage of a generic wavefront sensor in two spectral regimes, visible and near-infrared, to pre-select the spectral range for the more detailed wavefront sensor type analysis. We find that the near-infrared regime is the most suitable for METIS. We then analysed the performance of Shack-Hartmann and pyramid wavefront sensors under realistic conditions at the ELT, did a balancing with our scientific requirements, and concluded that a pyramid wavefront sensor is the best choice for METIS. For this choice we additionally examined the impact of non-common path aberrations, of vibrations, and the long-term stability of the SCAO system including high-contrast imaging performance.Comment: 37 pages, 27 figures, accepted for publication in Experimental Astronom

On (2,2)-Domination in Hexagonal Mesh Pyramid

Network topology plays a key role in designing an interconnection network. Various topologies for interconnection networks have been proposed in the literature of which pyramid network is extensively used as a base for both software data structure and hardware design. The pyramid networks can efficiently handle the communication requirements of various problems in graph theory due to its inherent hierarchy at each level. Domination problems are one of the classical types of problems in graph theory with vast application in computer networks and distributed computing. In this paper, we obtain the bounds for a variant of the domination problem namely (2,2)-domination for a pyramid network called Hexagonal mesh pyramid