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Volume 27 Issue 7 - Publication Date: 1 July 2008
 
Self-Motions of General 3-RPR Planar Parallel Robots
 
Sébastien Briot, Vigen Arakelian Département de Génie Mécanique et Automatique, Institut National des Sciences Appliquées (INSA), Rennes, France, Ilian A. Bonev Department of Automated Production Engineering, École de Technologie Supérieure (ÉTS), Montréal, Canada, Damien Chablat and Philippe Wenger Institut de Recherche en Communications et Cybernétique de Nantes 1, rue la Noë – BP 92101 44321, Nantes Cedex 3, France
 
We study the kinematic geometry of general 3-RPR planar parallel robots with actuated base joints. These robots, while largely overlooked, have simple direct kinematics and large singularity-free workspace. Furthermore, their kinematic geometry is the same as that of a newly developed parallel robot with SCARA-type motions. Starting from the direct and inverse kinematic model, the expressions for the singularity loci of 3-RPR planar parallel robots are determined. Then, the global behavior at all singularities is geometrically described by studying the degeneracy of the direct kinematic model. Special cases of selfmotions are then examined and the degree of freedom gained in such special configurations is kinematically interpreted. Finally, a practical example is discussed and experimental validations performed on an actual robot prototype are presented.
 
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