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 ROBiri  IRI Robotics Group
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 Institute of Robotics and Industrial Informatics
 julia.borrasestudiant.upc.edu
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The octahedral manipulator revisited
Rojas Libreros, Nicolás Enrique; Borras Sol, Julia; Thomas Arroyo, Federico
IEEE International Conference on Robotics and Automation
Presentation's date: 2012
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On the primal and dual forms of the Stewart platform pure condition
Borras Sol, Julia; Thomas Arroyo, Federico
IEEE transactions on robotics
Date of publication: 2012
Journal article
Read the abstract Access to the full text Share Reference managersThe algebraic characterization of the singularities of a Stewart platform is usually presented as a 6 × 6 determinant, whose rows correspond to the line coordinates of its legs, equated to zero. This expression can be rewritten in a more amenable way, known as the pure condition, as sums and products of 4×4 determinants whose rows correspond to the point coordinates of the legs attachments. Researchers usually rely on one of these two expressions to find the geometric conditions associated with the singularities of a particular Stewart platform. Although both are equivalent, it is advantageous to use either line or point coordinates depending on the platform topology. In this context, an equivalent expression involving only plane coordinates, a dual expression to that using point coordinates, seems to be missing. This paper is devoted to its derivation and to show how its use is advantageous in many practical cases mainly because of its surprising simplicity: it only involves the addition of 4 × 4 determinants whose rows are plane coordinates defined by sets of three attachments. 
New geometric approaches to the singularity analysis of parallel platforms
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
Workshop Español de Robótica
Presentation's date: 2011
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Architectural singularities of a class of pentapods
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
Mechanism and machine theory
Date of publication: 2011
Journal article
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Singularityinvariant leg rearrangements in stewartgouch platforms
Borras Sol, Julia
Defense's date: 20110415
Institute of Industrial and Control Engineering (IOC), Universitat Politècnica de Catalunya
Theses
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Desplegament de l'exposició RSME imaginari a Catalunya. Fase 2011
Xambó Descamps, Sebastian; Plans Berenguer, Bernat; Borras Sol, Julia; Barja Yañez, Miguel Angel; Thomas Arroyo, Federico; Quer Bosor, Jordi; Torras, Carme; Alberich Carramiñana, Maria
Participation in a competitive project
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Singularityinvariant families of lineplane 5SPU platforms
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
IEEE transactions on robotics
Date of publication: 201110
Journal article
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Singularityinvariant leg rearrangements in StewartGough platforms
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
International Symposium on Advances in Robot Kinematics
Presentation's date: 2010
Presentation of work at congresses
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Singularityinvariant leg rearrangements in doublyplanar StewartGough platforms
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
Robotics: Science and Systems
Presentation's date: 2010
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersIn general, rearranging the legs of a StewartGough platform, i.e., changing the locations of its leg attachments, modifies the platform singularity locus in a rather unexpected way. Nevertheless, some leg rearrangements have been recently found to leave singularities invariant but, unfortunately, these rearrangements are only valid for StewartGough platforms containing rigid components. In this work, the authors go a step further presenting singularityinvariant leg rearrangements that can be applied to any StewartGough platform whose base and platform attachments are coplanar. The practical consequences of the presented theoretical results are illustrated with several examples including wellknown architectures.
Postprint (author’s final draft) 
Singularityinvariant leg substitutions in pentapods
Borras Sol, Julia; Thomas Arroyo, Federico
IEEE/RSJ International Conference on Intelligent Robots and Systems
Presentation's date: 2010
Presentation of work at congresses
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A distancebased formulation of the octahedral manipulator kinematics
Rojas Libreros, Nicolás Enrique; Borras Sol, Julia; Thomas Arroyo, Federico
IFToMM Symposium on Mechanism Design for Robotics
Presentation's date: 2010
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A family of quadraticallysolvable 5SPU parallel robots
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
IEEE International Conference on Robotics and Automation
Presentation's date: 2010
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersA 5SPU robot with collinear universal joints is well suited to handling an axisymmetric tool, since it has 5 controllable DoFs and the remaining one is a free rotation around the tool. The kinematics of such a robot having also coplanar spherical joints has previously been studied as a rigid subassembly of a StewartGough platform, it being denoted a lineplane component. It was shown that this component has 8 assembly modes corresponding to the roots of a biquartic polynomial. Here we identify a whole family of these 5SPU robots having only 4 assembly modes, which are obtained by solving two quadratic equations. This family is defined by a simple proportionality constraint relating the coordinates of the base and platform attachments. A geometric interpretation of the architectural singularities of this type of robots in terms of conics is provided, which facilitates their avoidance at the design stage. Parallel singularities obey also a neat geometric structure, which permits deriving a cell decomposition of configuration space. Two practical features of these quadraticallysolvable robots are the large maneuverability within each connected component and the fact that, for a fixed orientation of the tool, the singularity locus reduces to a plane. Index Terms—Parallel manipulators, StewartGough platforms, robot kinematics, kinematics singularities.
Postprint (author’s final draft) 
DESPLEGAMENT DE L'EXPOSICIÓ RSMEIMAGINARY A CATALUNYA  FASE 2010
Xambó Descamps, Sebastian; Torras, Carme; Thomas Arroyo, Federico; Barja Yañez, Miguel Angel; Plans Berenguer, Bernat; Quer Bosor, Jordi; Borras Sol, Julia; Alberich Carramiñana, Maria
Participation in a competitive project
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Straighteningfree algorithm for the singularity analysis of StewartGough platforms with collinear/coplanar attachments
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
Computational Kinematics
Presentation's date: 20090508
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersAn algorithm to derive the pure condition of any doubleplanar StewartGough platform in a standard form suitable for comparison is presented. By applying the multilinear properties of brackets directly to the superbracket encoding of the pure condition, no straightening is required. It is then shown that any 33 platform has a corresponding 66 platform having its same superbracket, meaning that they have identical singularity loci. In general, the superbracket of any doubleplanar platform can be written as a linear combination of the superbrackets of 33 platforms, leading to a direct singularity assessment by inspecting the resulting decomposition.
Postprint (author’s final draft) 
Kinematics of lineplane subassemblies in Stewart platforms
Borras Sol, Julia; Thomas Arroyo, Federico
IEEE International Conference on Robotics and Automation
Presentation's date: 2009
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersWhen the attachments of five legs in a Stewart platform are collinear on one side and coplanar on the other, the platform is said to contain a lineplane subassembly. This paper is devoted to the kinematics analysis of this subassembly paying particular attention to the problem of moving the aforementioned attachments without altering the singularity locus of the platform. It is shown how this is always possible provided that some crossratios between lines defined by points in the plane are kept equal to other crossratios between points in the line. This result leads to two simple motion rules upon which complex changes in the location of the attachments can be performed. These rules have interesting practical consequences as they permit a designer to optimize aspects of a parallel robot containing the analyzed subassembly, such as its manipulability in a given region, without altering its singularity locus. 
Polynomial solution to the position analysis of two Assur kinematic chains with four loops and the same topology
Borras Sol, Julia; Di Gregorio, Silvana
Journal of mechanisms and robotics
Date of publication: 2009
Journal article
Read the abstract View Share Reference managersThe direct position analysis (DPA) of a manipulator is the computation of the endeffector poses (positions and orientations) compatible with assigned values of the actuatedjoint variables. Assigning the actuatedjoint variables corresponds to considering the actuated joints locked, which makes the manipulator a structure. The solutions of the DPA of a manipulator one to one correspond to the assembly modes of the structure that is generated by locking the actuatedjoint variables of that manipulator. Determining the assembly modes of a structure means solving the DPA of a large family of manipulators since the same structure can be generated from different manipulators. This paper provides an algorithm that determines all the assembly modes of two structures with the same topology that are generated from two families of mechanisms: one planar and the other spherical. The topology of these structures is constituted of nine links (one quaternary link, four ternary links, and four binary links) connected through 12 revolute pairs to form four closed loops. 
On ¿transforms
Thomas Arroyo, Federico; Torras, Carme; Borras Sol, Julia
IEEE transactions on robotics
Date of publication: 2009
Journal article
Read the abstract Access to the full text Share Reference managersAnyset of two legs in a Gough–Stewart platform sharing an attachment is defined as a Δcomponent. This component links a point in the platform (base) to a line in the base (platform). Thus, if the two legs, which are involved in a Δ component, are rearranged without altering the location of the line and the point in their base and platform local reference frames, the singularity locus of the Gough–Stewart platform remains the same, provided that no architectural singularities are introduced. Such leg rearrangements are defined as Δtransforms, and they can be applied sequentially and simultaneously. Although it may seem counterintuitive at first glance, the rearrangement of legs using simultaneous Δtransforms does not necessarily lead to leg configurations containing a Δcomponent. As a consequence, the application of Δtransforms reveals itself as a simple, yet powerful, technique for the kinematic analysis of large families of Gough–Stewart platforms. It is also shown that these transforms shed new light on the characterization of architectural singularities and their associated selfmotions. 
On DeltaTransforms
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
IEEE transactions on robotics
Date of publication: 200912
Journal article
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A reconfigurable 5DoF 5SPU parallel platform
Borras Sol, Julia; Thomas Arroyo, Federico; Ottaviano, Erika; Ceccarelli, Marco
ASME/IFToMM International Conference on Reconfigurable Mechanisms and Robots
Presentation's date: 2009
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersThis paper presents a 5SPU platform whose base leg attachments can be easily reconfigured, statically or dynamically, without altering its singularity locus. This permits to adapt the platform’s geometry to particular tasks without increasing the complexity of its control. The allowed reconfigurations permit to reduce the risk of collisions between legs, or even improving the stiffness of the platform, in a given region of its configuration space. It is also shown that no architectural singularities are introduced by the proposed reconfigurations. 
Analysing the singularities of 6SPS parallel robots using virtual legs
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
International Workshop on Fundamental Issues and Future Research Directions for Parallel Mechanisms and Manipulators
Presentation's date: 2008
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersA virtual leg in a 6SPS parallel robot is defined as a leg whose length is determined by the lengths of a subset of the actual legs of the robot. This necessarily implies that this subset of legs defines a rigid subassembly. In this paper, we consider four different rigid subassemblies, and show how the singularities of a robot containing one or several of these subassemblies are modified when substituting its actual legs by virtual legs. 
Architecture singularities in flagged parallel manipulators
Borras Sol, Julia; Thomas Arroyo, Federico; Torras, Carme
IEEE International Conference on Robotics and Automation
Presentation's date: 2008
Presentation of work at congresses
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