Hierarchical Path Search with Partial Materialization of Costs for a Smart Wheelchair

In this paper, the off-line path planner module of a smart wheelchair aided navigation system is described. Environmental information is structured into a hierarchical graph (H-graph) and used either by the user interface or the path planner module. This information structure facilitates efficient path search and easier information access and retrieval. Special path planning issues like planning between floors of a building (vertical path planning) are also viewed. The H-graph proposed is modelled by a tree. The hierarchy of abstractions contained in the tree has several levels of detail. Each abstraction level is a graph whose nodes can represent other graphs in a deeper level of the hierarchy. Path planning is performed using a path skeleton which is built from the deepest abstraction levels of the hierarchy to the most upper levels and completed in the last step of the algorithm. In order not to lose accuracy in the path skeleton generation and speed up the search, a set of optimal subpaths are previously stored in some nodes of the H-graph (path costs are partially materialized). Finally, some experimental results are showed and compared to traditional heuristic search algorithms used in robot path planning.Comisión Interministerial de Ciencia y Tecnología TER96-2056-C02-0

A Hierarchical Extension of the D ∗ Algorithm

In this paper a contribution to the practice of path planning using a new hierarchical extension of the D ∗ algorithm is introduced. A hierarchical graph is stratified into several abstraction levels and used to model environments for path planning. The hierarchical D∗ algorithm uses a downtop strategy and a set of pre-calculated trajectories in order to improve performance. This allows optimality and specially lower computational time. It is experimentally proved how hierarchical search algorithms and on-line path planning algorithms based on topological abstractions can be combined successfully

U.S.-Mexico Joint Statement on Ministerial Consultations Under the North American Agreement on Labor Cooperation

U.S. Secretary of Labor Elaine Chao and Secretary of Labor and Social Welfare of Mexico, Carlos Carranza reaffirm their commitment to the effective enforcement of labor laws by their respective departments. The statement also discusses the responsibilities of both labor departments under the North American Agreement on Labor Cooperation

Analysis of the frictional slip between a layer and a half-space

The numerical analysis of a boundless elastic layer on an elastic halfspace with different material properties under the effects of an uniform surface pressure and a cyclic tangential surface force is presented. Frictional contact conditions are assumed. The study is focussed on the evaluation of the maximum amplitude of the tangential load which produces localized slip between the two regions during the first load cycle but not the subsequent ones. The more simple limit for which no slip exist even for the first cycle is also establishe

Respuesta dinámica de cimentaciones considerando condiciones de contacto con fricción

X Congreso Nacional de Ingeniería Mecánica, celebrado en Madrid en 1992En el presente trabajo se estudia la respuesta en el tiempo de una cimentación superficial situada sobre un semi-espacio, cuando un tren de ondas incide sobre ella. La interacción suelo-cimiento se considera no lineal con posibilidad de separación y deslizamiento, habiéndose supuesto fricción del tipo Coulomb. El algoritmo que se presenta se basa en el Método de los Elementos de Contorno en el dominio del tiempo, y resuelve, para cada intervalo lineal en el que las condiciones de contorno son constantes, el problema difractado.In the present work the time response of a sourface foundation on de half-space when a wave train acts on it, is studied . Non-linear soil-structure interaction. with uplifl .sliding and Colulomb type friction, is considered. The algoritm presented is based on the time domain Boundary Element Method fonnulation, solving the diffracted problem for the differents time steps where the boundary contition are constants

El uso de una solución fundamental compuesta para el cálculo de rigideces de cimentaciones mediante el método de los elementos de contorno

El problema de las rigideaes dinámicas de cimentaciones enterradas puede ser abordado por diversos métodos analíticos y numéricos más o me nos aproximados. Se presenta en primer lugar la formulación dinámica del Me todo de los Elementos de Contorno para este tipo de problemas. Se estudia cómo el empleo de una solución fundamental compuesta disminuye el número de términos despreciados al truncar la discretización de la superficie libre.- Se estudian algunos de los valores de las rigideces estáticas y dinámicas,- obtenidos con la solución fundamental compuesta, y se comparan con los - -- correspondientes a la simple. Se apr cia que en la mayor parte de los casos, con la solución compuesta, se produce una reducción del error debido al - - truncamiento en la discretización de la superficie libre del suelo

Mobile Interface for a Smart Wheelchair

Smart wheelchairs are designed for severely motor impaired people that have difficulties to drive standard -manual or electric poweredwheelchairs. Their goal is to automate driving tasks as much as possible in order to minimize user intervention. Nevertheless, human involvement is still necessary to maintain high level task control. Therefore in the interface design it is necessary to take into account the restrictions imposed by the system (mobile and small), by the type of users (people with severe motor restrictions) and by the task (to select a destination among a number of choices in a structured environment). This paper describes the structure of an adaptive mobile interface for smart wheelchairs that is driven by the context.Comisión Interministerial de Ciencia y Tecnología TER96-2056-C02-0