Surface Geometrical Features Research Articles

Feature-based machining of curved surfaces using the steepest directed tree approach

Abstract A novel and efficient approach for defining and machining curved-surface parts is presented. The intelligent cutter path planning method, called the steepest directed tree method, replicates the actions of an expert engraver by using cutter paths that are established from the surface form. The curved surface is defined by triangular facets, the density and structure of which are determined by the intricacy and shape of the surface. Appropriate decimation and subdivision algorithms are used with swap optimization of facet edges to develop a uniform chordal error surface model. Geometrical form definition and recognition of topological features of the surface triangulation mesh are used to generate cutter paths along successive and interconnected steepest pathways, or steepest directed trees. Thus, geometrical surface features and machining characteristics of the end-milling process are used to develop optimum cutter paths. Planetary cutter locations are adjusted to be moved along smoothly changing paths, and height values are adjusted to avoid surface interference. Two machined examples of intersecting and intricate surface parts are presented that illustrate the benefits of the new approach. It is shown that due to more consistent geometry matching between cutter and surface (in comparison with the current CC-Cartesian method), surface finish can be typically improved by a factor of 16.8:1 while reducing cutting time by a factor of 1.6:1

Molecular Surface Complementarity at Protein-Protein Interfaces: The Critical Role Played by Surface Normals at Well Placed, Sparse, Points in Docking

Rigid-body docking of two molecules involves matching of their surfaces. A successful docking methodology considers two key issues: molecular surface representation, and matching. While approaches to the problem differ, they all employ certain surface geometric features. While surface normals are routinely created with molecular surfaces, their employment has surprisingly been almost completely overlooked. Here we show how the normals to the surface, at specific, well placed points, can play a critical role in molecular docking. If the points for which the normals are calculated represent faithfully and accurately the molecular surfaces, the normals can substantially ameliorate the efficiency of the docking in a number of ways. The normals can drastically reduce the combinatorial complexity of the receptor-ligand docking. Furthermore, they can serve as a powerful filter in screening for quality docked conformations. Below we show how deploying such a straight forward device, which is easy to calculate, large protein-protein molecules are docked with unparalleled short times and with a manageable number of potential solutions. Considering the facts that here we dock (1) two large protein molecules, including several large immunoglobulin-lysozyme complexes; (2) that we use the entire molecular surfaces, without a predefinition of the active sites, or of the epitopes, of neither the ligand nor the receptor; that (3) the docking is completely automated, without any labelling, or pre-specification, of the input structural database, and (4) with a single set of parameters, without any further tuning whatsoever, such results are highly desirable. This approach is specifically geared towards matching of the surfaces of large protein molecules and is not applicable to small molecule drugs.

The effects of surface metallization on the thermal behavior of GaAs microwave power devices

The effects of surface metallization on the thermal behavior of GaAs microwave power devices have been studied numerically using the three-dimensional transmission-line matrix (3D TLM) method. Thermal results for a representative GaAs power device with no metallization, with an entire metal overlayer, and with realistic geometrical surface features are compared under both steady-state and transient conditions. The peak temperature within the device is found to be reduced by over 20 percent by the presence of surface metallization. The mechanism responsible for this improvement is identified and discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A fully autonomous active sensor-based exploration concept for shape-sensing robots

A technique is developed for the automatic, online generation of trajectories for robotic exploration of unknown objects. For manipulators and end effectors with an arbitrary assortment of sensing apparatus, especially tactile, the Kalman filtering approach is given for the estimation of unknown surface parameters. A cost function is found based on the inverse error covariance matrix for the parameter estimates. It is shown that this cost function can be written in terms of tangent vectors on the surface of the object. The cost can therefore be minimized over possible end effector velocities, resulting in optimally efficient exploration of the surface. Given an estimator and system model, the exploration path automatically generated in this way endows the robot with the ability to seek out geometric surface features that provide the most utility for the improved convergence of the parameter estimate. Computer simulations for a nine-dimensional surface parameter vector show that the algorithm is fast, accurate, and completely independent of the parametrization chosen for the analytic surface models. >

Effects of asperities on the van der Waals and electric double-layer interactions of two parallel flat plates

The role of geometric surface features on the van der Waals and electric double-layer interactions of two parallel flat plates is studied. Equations are developed using the Hamaker metod for van der Waals forces, and Derjaguin's method for electric double-layer forces. The surface features are limited to spherical and conical asperities which include truncated asperities as well. The importance of asperities in surface interactions is assessed by using the interaction ratio, defined as the ratio of the interaction energy of a sysem with an asperity to that of the system without one.

Current deflection at cracks—some insights from modelling : 39131 Holt, C.C.; Boness, K.D. Proceedings of the 4th European Conference on Non-Destructive Testing, London (United Kingdom), 13–17 Sep. 1987. Vol. 1, pp. 641–648. Pergamon Press, 3173 pp. (1988)

Eddy current testing by current deflection detects surface cracks and geometric features by sensing the re-routing of currents. Currents are diverted by cracks in two ways: down the walls, and along their length at the surface. Current deflection utilises the latter currents, detecting them via their tangential magnetic field. Results from 3-D finite element computer modelling, which show the two forms of deflection, are presented. Further results indicate that the current deflection technique is suitable for the detection of surface cracks in smooth materials with varying material properties.

GSS—A FAST, MODEL-BASED VISION SYSTEM FOR WORKPIECE RECOGNITION

This paper describes a new visual sensor system for the recognition of touching and overlapping workpieces, designed to meet the requirements of real applications in the factory. The system analyses the grey scale image and comprises two stages: a feature-extraction stage, which is designed mainly in special-purpose hardware, and a model-based analysis stage. The system works with edge-based geometrical primitives and surface features. The model comprises topographical and procedural information in order to control the image-analysis, which is based on the “heuristic-search” technique. The hardware and software design is modular. The system is working well in a wide range of environmental conditions and with different kinds of workpieces. A prototype version is completed and has proved its reliability and performance in several applications in the factory.

Surface region damage of machined inconel-718 nickel-base superalloy using natural and controlled contact length tools

The effect of cutting speed and chip-tool contact length on the surface integrity of Inconel-718 nickel-base superalloy machined under both dry and lubricated orthogonal conditions is investigated. The surface and surface region of machined workpieces are examined using a wide variety of diagnos tic techniques. The results of the investigation show that a wide variety of geometrical surface features (damage) are generated. The results also show that a plastically deformed surface region is generated that contains variations in microstructure and residual stress. The quality of the machined surface improved significantly at high cutting speeds with tools having controlled contact lengths. The results of the investigation are interpreted in terms of the interaction between the chip and tool interface and that between the tool cutting edge region and the freshly machined workpiece surface and in terms of the variation in the tool forces with cutting conditions.

A Model-Based Grey-Scale Sensor System for Robotics

Production devices for fabrication of medium and small aeries have to be flexible to meet the changing conditions of production. Scene- analysis systems for the recognition and inspection of workpieces are an important tool for flexible automation. Most vision systems currently available for robotics show severe limitations concerning recognition time, workpiece acquisition, illumination etc. This paper describes a Grey- Scale Sensor System for recognition of touching and overlapping workpieces, designed to meet the requirements of real applications in the factory. The system comprises 2 stages: a feature- extraction stage, which is designed mainly in special- purpose hardware and a model- based analysis stage realized in software. The system works with edge- based geometrical primitives and surface features. The model comprises topographical and procedural information in order to control the image- analysis, which is based on a Heuristic Search technique. A prototype version has been finished and interfaced to a robot. First experiences show that the system is working satisfactoryly in a wide range of environmental conditions and with different kinds of workpieces.

Surface Integrity in Machining Solution-Treated and Aged 2024-Aluminum Alloy, Using Natural and Controlled Contact Length Tools. Part I—Unlubricated Conditions

The effects of cutting speed, chip-tool contact length and tool surface finish on the surface integrity of a solution-treated and aged 2024-Aluminum alloy, that is machined under dry, orthogonal conditions are investigated. The surface region of machined workpieces is examined using a wide variety of diagnostic techniques. In addition, tool forces are measured and both the cutting geometry and cutting temperatures are calculated. The results of the investigation show that a wide variety of geometrical surface features are generated that contribute to the natural surface roughness. The results also show that a plastically deformed surface region is generated that contains variations in hardness, microstructure and residual strain. The results of the investigation are interpreted in terms of the type of chip produced, formation of the built-up edge, the mechanics and thermodynamics of the cutting process and the interaction between the tool nose region and freshly machined workpiece surface.

Surface Integrity in Machining Solution-Treated and Aged 2024-Aluminum Alloy, Using Natural and Controlled Contact Length Tools. Part II—Lubricated Conditions

The effects of cutting speed, chip-tool contact length, and tool surface finish on the surface integrity of solution-treated and aged 2024-aluminum alloy, that is machined under lubricated orthogonal conditions are investigated. The surface region of machined workpieces is examined using a variety of diagnostic techniques. In addition, tool forces are measured and the cutting geometry is determined. The results show that a variety of geometrical surface features are generated that contribute to the natural surface roughness, and that a plastically deformed surface region is generated that contains variations in hardness, microstructure, and residual plastic strain. The results are interpreted in terms of the type of chip produced, the mechanics and thermodynamics of the cutting process and the lubricating action of cutting fluids. When the results of the investigation are compared with similar results derived under nonlubricated conditions, it is found that at low cutting speeds application of a lubricant produces a reduction in tool forces, power consumption, surface roughness, surface defects, and subsurface deformation, whereas at high cutting speeds application of a lubricant has little influence on the cutting process.

Chemical effects of irregular interstellar oxide grains

The importance of chemically-active geometrical surface sites on the surfaces of interstellar oxide grains is discussed in terms of their catalytic behaviour in molecular formation. Surface features — such as steps and corners — are considered in detail, and the binding energies of the hydrogen atom and the proton at these sites are estimated. It appears likely that chemical effects of interstellar oxide grains are located not only at point defects discussed elsewhere, but also at these geometrical surface features. Adsorbed surface species, surface reaction schemes, and the possible effects of grain impurities are briefly considered.

Geometric features of chill-cast surfaces

Geometric features such as grooves, wrinkles, and laps are commonly observed on chill-cast surfaces. With lead used as a representative material, the occurrence of these features over a range of casting speeds from 0.025 to 17 cm/s (0.6 to 400 in./min) has been examined. On the basis of their assumed origin, three types of surface features have been recognized. The first two are associated with the mechanical behavior of the thermally stressed solidifying shell. Fine Type I grooves are the remnants of periodic shell corrugations formed near the meniscus during the earliest stages of solidification, and their spacing decreases with increasing casting speeds. More widely spaced Type II wrinkles are concavities that develop as solidification progresses, and are associated with the temperature perturbations that cause uneven thickening of the shell. Type III surface features occur at slow casting speeds when freezing of the meniscus gives rise to periodic surface lapping.