Grasping unknown objects in clutter by superquadric representation

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper, a quick and efficient method is presented for grasping unknown objects in clutter. The grasping method relies on real-time superquadric (SQ) representation of partial view objects and incomplete object modelling, well suited for unknown symmetric objects in cluttered scenarios which is followed by optimized antipodal grasping. The incomplete object models are processed through a mirroring algorithm that assumes symmetry to first create an approximate complete model and then fit for SQ representation. The grasping algorithm is designed for maximum force balance and stability, taking advantage of the quick retrieval of dimension and surface curvature information from the SQ parameters. The pose of the SQs with respect to the direction of gravity is calculated and used together with the parameters of the SQs and specification of the gripper, to select the best direction of approach and contact points. The SQ fitting method has been tested on custom datasets containing objects in isolation as well as in clutter. The grasping algorithm is evaluated on a PR2 robot and real time results are presented. Initial results indicate that though the method is based on simplistic shape information, it outperforms other learning based grasping algorithms that also work in clutter in terms of time-efficiency and accuracy.Peer ReviewedPostprint (author's final draft

Singularity-free computation of quaternions from rotation matrices in E4 and E3

A real orthogonal matrix representing a rotation in E4 can be decomposed into the commutative product of a left-isoclinic and a right-isoclinic rotation matrix. The double quaternion representation of rotations in E4 follows directly from this decomposition. In this paper, it is shown how this decomposition can be performed without divisions. This avoids the common numerical issues attributed to the computation of quaternions from rotation matrices. The map from the 4×4 rotation matrices to the set of double unit quaternions is a 2-to-1 covering map. Thus, this map cannot be smoothly inverted. As a consequence, it is erroneously assumed that all inversions should necessarily contain singularities that arise in the form of quotients where the divisor can be arbitrarily small. This misconception is herein clari¿ed. When particularized to three dimensions, it is shown how the resulting formulation outperforms, from the numerical point of view, the celebrated Shepperd’s method.Peer ReviewedPostprint (author's final draft

On Cayley's factorization with an application to the orthonormalization of noisy rotation matrices

The final publication is available at link.springer.comA real orthogonal matrix representing a rotation in four dimensions can be decomposed into the commutative product of a left- and a right-isoclinic rotation matrix. This operation, known as Cayley's factorization, directly provides the double quaternion representation of rotations in four dimensions. This factorization can be performed without divisions, thus avoiding the common numerical issues attributed to the computation of quaternions from rotation matrices. In this paper, it is shown how this result is particularly useful, when particularized to three dimensions, to re-orthonormalize a noisy rotation matrix by converting it to quaternion form and then obtaining back the corresponding proper rotation matrix. This re-orthonormalization method is commonly implemented using the Shepperd-Markley method, but the method derived here is shown to outperform it by returning results closer to those obtained using the Singular Value Decomposition which are known to be optimal in terms of the Frobenius norm.Peer ReviewedPostprint (author's final draft

Do oil price shocks matter? Evidence for some European countries

This paper analyzes the oil price-macroeconomy relationship by means of analyzing the impact of oil prices on inflation and industrial production indexes for many European countries using quarterly data for the period 1960-1999. First, we test for cointegration allowing for structural breaks among the variables. Second, and in order to account for the possible non-linear relationships, we use different transformation of oil price data. The main results suggest that oil prices have permanent effects on inflation and short run but asymmetric effects on production growth rates. Furthermore, significant differences are found among the responses of the countries to these shocks.oil price shocks, inflation, economic activity

Oil Prices, Economic Activity and Inflation: Evidence for Some Asian Countries

In this paper we study the oil prices-macroeconomy relationship by means of studying the impact of oil price shocks on both economic activity and consumer price indexes for six Asian countries over the period 1975Q1-2002Q2. The results suggest that oil prices have a significant effect on both economic activity and price indexes although the impact is limited to the short-run and more significant when oil price shocks are defined in local currencies. Moreover, we find evidence of asymmetries in the oil prices-macroeconomy relationship for some of the Asian countries.

Cross-lingual Linking on the Multilingual Web of Data (position statement)

Recently, the Semantic Web has experienced signi�cant advancements in standards and techniques, as well as in the amount of semantic information available online. Even so, mechanisms are still needed to automatically reconcile semantic information when it is expressed in di�erent natural languages, so that access to Web information across language barriers can be improved. That requires developing techniques for discovering and representing cross-lingual links on the Web of Data. In this paper we explore the different dimensions of such a problem and reflect on possible avenues of research on that topic

Financial Liberalization and Emerging Stock Market Volatility

In this paper we test whether volatility in six emerging markets has changed significantly over the period 1976:01-2002:03. This period corresponds to the years of more profound development of both the financial and the productive sides in emerging countries. We use alternative methodologies of of endogenous breakpoints detection that estimate the dates at which the behavior of the sotck market volatility changed. The analysis suggests that volatility has behaved in a di¤erent manner over the periodemerging markets, volatility, multiple structural breaks

Stock Market Cycles and Stock Market Development in Spain

In this paper we use Spanish stock market data to identify the bull and bear phases of the market and to analyze its characteristics during the period 1941-2002. We compare these characteristics with those of the US and of two other European countries (Germany and the UK). Our sample is divided in two subperiods in order to account for differences induced by the process of development undergone by Spanish capital markets in the late 1980's and early 1990's. We find that the Spanish stock market has become increasingly more similar to those of the more developed countries, although some differences still persist. Additionally, we show that concordance of the Spanish stock market with other developed markets has increased quite significantly.Stock market cycle; data generating process; financial development

Separador de agua y aceite

Este proyecto pretende responder a la demanda actual existente, en relación al reciclaje y la reutilización de los residuos generados por los seres humanos, concretamente para éste caso, el aceite usado (uso doméstico). Actualmente existen máquinas de separación de agua y aceite, pero únicamente de uso industrial. Igualmente existen contenedores de recogida de aceite de uso doméstico, pero éstos no realizan ningún tipo de discriminación entre la naturaleza de las mezclas que se vierten, pudiendo hacer ineficaz su función. Para ello se ha realizado el diseño de un prototipo de una máquina separadora de agua y aceite, con el objetivo de reducir los costes de tratamiento del aceite para su posterior reutilización y para dar una vida útil más larga al mismo, evitando así, la contaminación que este conlleva al medio ambiente. Para el proceso de diseño de la máquina separadora de agua y aceite, se partió de una máquina existente, que se ha ido mejorando a lo largo de varios diseños hasta concluir en un diseño funcional que cumplía las especificaciones requeridas. El diseño escogido finalmente, es simple de mantener y fácil de manejar, para poder realizar de la forma más sencilla y práctica posible su función, que en definitiva, es recuperar el aceite usado para después poder utilizarlo en la fabricación de jabones, detergentes, velas, ... y principalmente, para la producción de energías renovables como el biodiesel. Una vez definido el diseño definitivo, se han realizado un conjunto de planos correspondientes a cada una de las piezas que conforman el separador y se ha implementado un diseño en 3 dimensiones (3D en Solid Egde) que nos ofrece una visión real de cómo podría ser el prototipo. Todo ello está acompañado de un presupuesto real, en función del precio de las piezas y de los costes de ingeniería y mano de obra, y cumple las normativas especificadas en el pliego de condiciones (diseño, seguridad, medioambientales, etc.) Este proyecto ofrece una nueva vía explotable en materia de reciclaje, ofreciendo un producto viable, tanto funcional como económicamente, como bien reflejan los distintos estudios de viabilidad presentes en el proyecto

Anthropomorphism Index of Mobility for Artificial Hands

The increasing development of anthropomorphic artificial hands makes necessary quick metrics that analyze their anthropomorphism. In this study, a human grasp experiment on the most important grasp types was undertaken in order to obtain an Anthropomorphism Index of Mobility (AIM) for artificial hands. The AIM evaluates the topology of the whole hand, joints and degrees of freedom (DoFs), and the possibility to control these DoFs independently. It uses a set of weighting factors, obtained from analysis of human grasping, depending on the relevance of the different groups of DoFs of the hand. The computation of the index is straightforward, making it a useful tool for analyzing new artificial hands in early stages of the design process and for grading human-likeness of existing artificial hands. Thirteen artificial hands, both prosthetic and robotic, were evaluated and compared using the AIM, highlighting the reasons behind their differences. The AIM was also compared with other indexes in the literature with more cumbersome computation, ranking equally different artificial hands. As the index was primarily proposed for prosthetic hands, normally used as nondominant hands in unilateral amputees, the grasp types selected for the human grasp experiment were the most relevant for the human nondominant hand to reinforce bimanual grasping in activities of daily living. However, it was shown that the effect of using the grasping information from the dominant hand is small, indicating that the index is also valid for evaluating the artificial hand as dominant and so being valid for bilateral amputees or robotic hands