Partially-flagged parallel manipulators: singularity charting and avoidance

Journal Article (2009)


IEEE Transactions on Robotics







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There are only three 6-SPS parallel manipulators with triangular base and platform: the octahedral, the flagged, and the partially-flagged studied in this paper. The forward kinematics of the octahedral manipulator is algebraically intricate, while those of the other two can be solved by three trilaterations. As an additional nice feature, the flagged manipulator is the only parallel platform for which a cell decomposition of its singularity locus has been derived. Here we prove that the partially-flagged manipulator admits also a well-behaved decomposition, technically called a stratification, some of whose strata are not topological cells, though. Remarkably, the adjacency diagram of the 5 and 6 dimensional strata (which shows what 5 dimensional strata are contained in the closure of a 6 dimensional one) is the same as for the flagged manipulator. The availability of such a decomposition permits devising a redundant 7-SPS manipulator, combining two partially-flagged ones, which admits a control strategy that completely avoids singularities. Simulation results support these claims.


manipulators, robot kinematics.

Author keywords

configuration space, kinematics singularities, parallel manipulators, redundant manipulators, robot design

Scientific reference

M. Alberich-Carramiñana, M. Garolera, F. Thomas and C. Torras. Partially-flagged parallel manipulators: singularity charting and avoidance. IEEE Transactions on Robotics, 25(4): 771-784, 2009.