4 research outputs found
Task oriented area partitioning and allocation for optimal operation of multiple industrial robots in unstructured environments
© 2014 IEEE. When multiple industrial robots are deployed in field applications such as grit blasting and spray painting of steel bridges, the environments are unstructured for robot operation and the robot positions may not be arranged accurately. Coordination of these multiple robots to maximize productivity through area partitioning and allocation is crucial. This paper presents a novel approach to area partitioning and allocation by utilizing multiobjective optimization and voronoi partitioning. Multiobjective optimization is used to minimize: (1) completion time, (2) proximity of the allocated area to the robot, and (3) the torque experienced by each joint of the robot during task execution. Seed points of the voronoi graph for voronoi partitioning are designed to be the design variables of the multiobjective optimization algorithm. Results of three different simulation scenarios are presented to demonstrate the effectiveness of the proposed approach and the advantage of incorporating robots' torque capacity
Numerical modelling of ellipsoidal inclusions
Within the framework of numerical algorithms for the threedimensional
random packing of granular materials this work presents an
innovative formulation for polydispersed ellipsoidal particles, including
an overlapping detection algorithm for an optimized simulation of the
mesostructure of geomaterials, particularly concrete.
Granular composite cement-based materials can be so reconstructed with
adequate precision in terms of grain size distribution. Specifically, the
algorithm performance towards the assumed inclusion shape (ellipsoidal or
spheric) and degree of regularity (round or irregular) is here discussed.
Examples on real grading curves prove that this approach is effective.
The advantages of the proposed method for computational mechanics
purposes are also disclosed when properly interfaced with visualization
CAD (Computer Aided Design) tools
Comparaison de méthodes de détection automatique d’intersections sur surfaces paramétriques
La question de déterminer si un modèle géométrique a des intersections non prévues
est commune à plusieurs domaines : simulations numériques, CAO/DAO, animation,
infographie, etc. C’est un problème dont la complexité varie avec la représentation
choisie pour créer le modèle. Pour les surfaces paramétriques c’est un problème difficile
à résoudre, mais pour lequel plusieurs solutions ont été proposées. Ces solutions diffèrent
les unes des autres dans leurs angles d’approche, leur complexité et la justesse de leurs
résultats. Dans ce mémoire, nous tenterons de comparer certaines de ces méthodes.
Nous nous concentrerons sur les méthodes dites failsafe, c’est-à -dire qui permettent
assurément de détecter la possibilité d’une intersection s’il y en a une. Ces méthodes sont
celles utilisées pour toutes les applications critiques, donc pour lesquelles un modèle mal
formé aurait des conséquences importantes.
Ce mémoire est à teneur principalement théorique. Nous comparerons les méthodes,
dans un premier temps, sur leur puissance de résolution. Nous discuterons, dans un
deuxième temps, de coût calculatoire. Nous avons finalement fait quelques implémenta-
tions pour appuyer nos observations théoriques, mais nous n’avons pas fait une analyse
empirique approfondie des coûts calculatoires. Ceci reste à faire.
Nous verrons entre autre qu’il existe un ordre partiel entre certaines des méthodes,
mais pas toutes. Par exemple, la méthode test-point est strictement plus puissante que
la séparation des enveloppes convexes, mais elle est ni plus ni moins puissante que la
méthode Volino-Thalmann.The question of determining if a given geometric model has extraneous intersections
is common to many domains: numerical simulation, CAD/CAM, animation, computer
graphics, etc. The complexity of this problem varies with the representation chosen
to generate the model. For parametric surfaces, it is a hard problem, but for which
many solutions have been proposed. Those solutions differ from one another by their
underlying ideas, their complexity and the exactitude of the result they give. In this
thesis, we will try to compare some of these methods. We will concentrate on the class
of methods we call failsafe, the methods that will surely detect the possibility of an
intersection if there is one. Those are the methods used in all critical applications, the
applications in which a malformed model would have important consequences.
The work of this thesis is mostly theoretical. First, we will compare the different
techniques on their power of resolution. Then, we will discuss the execution cost of
the different methods. We did some implementations while working on this thesis, but
only as a way to support our theoretical observations. A complete empirical study of the
execution times of the different methods would be left to do.
We will see that there is a partial order between some of the methods in their strength,
but not all of them. For example, the test-point method is strictly stronger than the
separation of the convex hulls method, but is neither stronger nor weaker than the Volino-
Thalmann method
Probabilistic Feature-Based Registration for Interventional Medicine
The need to compute accurate spatial alignment between multiple representations of patient anatomy is a problem that is fundamental to many applications in computer-integrated interventional medicine. One class of methods for computing such alignments is feature-based registration, which aligns geometric information of the shapes being registered, such as salient landmarks or models of shape surfaces. A popular algorithm for surface-based registration is the Iterative Closest Point (ICP) algorithm, which treats one shape as a cloud of points that is registered to a second shape by iterating between point-correspondence and point-registration phases until convergence.
In this dissertation, a class of "most likely point" variants on the ICP algorithm is developed that offers several advantages over ICP, such as high registration accuracy and the ability to confidently assess the quality of a registration outcome. The proposed algorithms are based on a probabilistic interpretation of the registration problem, wherein the point-correspondence and point-registration phases optimize the probability of shape alignment based on feature uncertainty models rather than minimizing the Euclidean distance between the shapes as in ICP. This probabilistic framework is used to model anisotropic errors in the shape measurements and to provide a natural context for incorporating oriented-point data into the registration problem, such as shape surface normals.
The proposed algorithms are evaluated through a range of simulation-, phantom-, and clinical-based studies, which demonstrate significant improvement in registration outcomes relative to ICP and state-of-the-art methods