Publication
Computing wrench-feasible paths for cable-driven hexapods
Technical Report (2015)
Abstract
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.
Categories
robot kinematics.
Author keywords
cable-driven robot, wrench-feasible c-space, parallel robots, higher-dimensional continuation, singularity-free path planning
Scientific reference
O. Bohigas, M. Manubens and L. Ros. Computing wrench-feasible paths for cable-driven hexapods. Technical Report IRI-TR-15-04, Institut de Robòtica i Informàtica Industrial, CSIC-UPC, 2015.
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