Computing wrench-feasible paths for cable-driven hexapods

Motion paths of cable-driven hexapods must carefully be planned to ensure that the lengths and tensions of all cables remain within acceptable limits, for a given wrench applied to the platform. The cables cannot go slack -to keep the control of the robot- nor excessively tight -to prevent cable breakage- even in the presence of bounded perturbations of the wrench. This paper proposes a path planning method that accommodates such constraints simultaneously. Given two configurations of the robot, the method attempts to connect them through a path that, at any point, allows the cables to counteract any wrench lying in a predefined uncertainty region. The feasible C-space is placed in correspondence with a smooth manifold, which facilitates the definition of a continuation strategy to search this space systematically from one configuration, until the second configuration is found, or path non-existence is proved at the resolution of the search. The force Jacobian is full rank everywhere on the C-space, which implies that the computed paths will naturally avoid crossing the forward singularity locus of the robot. The adjustment of tension limits, moreover, allows to maintain a meaningful clearance relative to such locus. The approach is applicable to compute paths subject to geometric constraints on the platform pose, or to synthesize free-flying motions in the full six-dimensional C-space. Experiments are included that illustrate the performance of the method in a real prototype.Postprint (published version

Diseño de una grúa torre

Este trabajo se centrará en el estudio de una de las grúas más empleadas en el mundo de la construcción, la grúa torre. El estudio de la grúa torre comprenderá desde conocer las estructuras que la conforman, así como conocer los elementos que forman parte de esta y que permitirán a la grúa realizar las tareas para las que ha sido diseñada. Se realizará una descripción de los elementos principales que permiten el funcionamiento de la grúa, y se harán los primeros pasos para el diseño y selección de varios de estos elementos entendiéndose que para un diseño más profundo requeriría de estudios mucho más complejos. No solo se tratarán los elementos mecánicos pertenecientes a la grúa, sino que también se realizará un estudio de los esfuerzos que se producen en las grúas torre para así poder tener una idea de qué partes de la grúa definirán más adelante su diseño estructural. Se realizará el dimensionamiento de dicha estructura mediante el programa CYPE, con el que elegiremos los perfiles que conformarán la estructura siempre con criterios económicos y normativos. En este trabajo también se mostrará cómo hacer uso de las normativas aplicables a la grúa objeto de este trabajo, de forma que las estructuras y elementos de la misma cumplan con las normativas que podemos encontrarnos actualmente

Universidad de Barcelona

150 páginasPeer reviewe

Planning wrench-feasible motions for cable-driven hexapods

Motion paths of cable-driven hexapods must carefully be planned to ensure that the lengths and tensions of all cables remain within acceptable limits, for a given wrench applied to the platform. The cables cannot go slack-to keep the control of the robot-nor excessively tightto prevent cable breakage-even in the presence of bounded perturbations of the wrench. This paper proposes a path-planning method that accommodates such constraints simultaneously. Given two configurations of the robot, the method attempts to connect them through a path that, at any point, allows the cables to counteract any wrench lying in a predefined uncertainty region. The configuration space, or C-space for short, is placed in correspondence with a smooth manifold, which facilitates the definition of a continuation strategy to search this space systematically from one configuration, until the second configuration is found, or path nonexistence is proved by exhaustion of the search. The force Jacobian is full rank everywhere on the C-space, which implies that the computed paths will naturally avoid crossing the forward singularity locus of the robot. The adjustment of tension limits, moreover, allows to maintain a meaningful clearance relative to such locus. The approach is applicable to compute paths subject to geometric constraints on the platform pose or to synthesize free-flying motions in the full 6-D C-space. Experiments illustrate the performance of the method in a real prototype.Postprint (author's final draft

Condiciones de accesibilidad y movilidad en el Polígono Industrial del Río Ripoll (Sabadell) : un análisis de metodología múltiple

El artículo analiza las condiciones de movilidad y de accesibilidad del PAE del río Ripoll de Sabadell. La metodología utilizada ha sido multiestratégica, puesto que se han combinado métodos cuantitativos, cualitativos y de observación directa. Además del contexto territorial y económico de la zona, la movilidad se determina por las características de los desplazamientos y por las percepciones de los trabajadores y las empresas. También se valoran los niveles de accesibilidad según el transporte público, el aparcamiento, la circulación de los vehículos pesados y el acceso en bicicleta y andando.L'article analitza les condicions de mobilitat i d'accessibilitat del PAE del riu Ripoll de Sabadell. La metodologia utilitzada ha estat multiestratègica, atès que s'hi han combinat mètodes quantitatius, qualitatius i d'observació directa. A més del context territorial i econòmic de la zona, la mobilitat s'hi determina per les característiques dels desplaçaments i per les percepcions dels treballadors i de les empreses. També s'hi valoren els nivells d'accessibilitat segons el transport públic, l'aparcament, la circulació dels vehicles pesants i l'accés amb bicicleta i caminant.L'article analyse les conditions de mobilité et d'accessibilité du PAE de la rivière Ripoll de Sabadell. Une méthodologie multi-stratégique a été utilisée, en combinant des méthodes quantitatives, qualitatives et d'observation directe. Outre le contexte territorial et économique de la zone, la mobilité est déterminée par les caractéristiques des déplacements et par les perceptions des travailleurs et des entreprises. Les niveaux d'accessibilité selon les transports publics, le parc de stationnement, la circulation des véhicules lourds, et l'accès en vélo et à pied sont aussi tenus en compte.This paper analyzes mobility conditions in the Ripoll River industrial park located in the municipality of Sabadell (Spain). A multi-strategic methodological approach combining qualitative and quantitative methods along with direct observation is used. In addition to the territorial and economic context of the area, mobility is also affected by the characteristics of the displacements and the perceptions of both the workers and the enterprises located in the park. Different levels of accessibility such as public transport, parking, heavy vehicles and bicycle or pedestrian access are also taken into account

Planning singularity-free force-feasible paths on the Stewart platform

This paper provides a method for computing force-feasible paths on the Stewart platform. Given two configurations of the platform, the method attempts to connect them through a path that, at any point, allows the platform to counteract any external wrench lying inside a predefined six-dimensional region. In particular, the Jacobian matrix of the manipulator will be full rank along such path, so that the path will not traverse the forward singularity locus at any point. The path is computed by first characterizing the force-feasible C-space of the manipulator as the solution set of a system of equations, and then using a higher-dimensional continuation technique to explore this set systematically from one configuration, until the second configuration is found. Examples are included that demonstrate the performance of the method on illustrative situations.Preprin

A general method for the numerical computation of manipulator singularity sets

The analysis of singularities is central to the development and control of a manipulator. However, existing methods for singularity set computation still concentrate on specific classes of manipulators. The absence of general methods able to perform such computation on a large class of manipulators is problematic because it hinders the analysis of unconventional manipulators and the development of new robot topologies. The purpose of this paper is to provide such a method for nonredundant mechanisms with algebraic lower pairs and designated input and output speeds. We formulate systems of equations that describe the whole singularity set and each one of the singularity types independently, and show how to compute the configurations in each type using a numerical technique based on linear relaxations. The method can be used to analyze manipulators with arbitrary geometry, and it isolates the singularities with the desired accuracy. We illustrate the formulation of the conditions and their numerical solution with examples, and use 3-D projections to visualize the complex partitions of the configuration space induced by the singularities.This work has been partially supported by the Spanish Ministry of Economy and Competitiveness under contract DPI2010-18449, and by a Juan de la Cierva contract supporting the fourth author.Peer Reviewe

On the numerical classification of the singularities of robot manipulators

This paper is concerned with the task to obtain a complete description of the singularity set of any given non-redundant manipulator, including the identification and the precise computation of each constituent singularity class. Configurations belonging to the same class are equivalent in terms of the various types of kinematic and static degeneracy that characterize mechanism singularity. The proposed approach is an extension of recent work on computing singularities using a numerical method based on linear relaxations. Classification is sought by means of a hierarchy of singularity tests, each formulated as a system of quadratic or linear equations, which yields sets of classes to which an identified singularity cannot belong. A planar manipulator exemplifies the process of classification, and illustrates how, while most singularities get completely classified, for some lower-dimensional subsets one can only identify a restricted list of possible singularity classes.Postprint (published version