Computing safe trajectories for an assistive cable-driven parallel robot by selecting the cables under tension and using interval analysis

Marionet-Assist is a CDPR designed for transfer operations. Our crane robot has a configuration that provides three translational d.o.f. Four wires are used to control the position of the end-effector, but as they have no elasticity, only three of them at most will be under tension. For a given position, different triplet of cables under tension are possible, and for a given trajectory, transition between two cable configurations may occur, which can lead to a loss of controllability. Therefore we propose a scheme that rank all the possible sequences for a given trajectory, using interval analysis to guaranty our computing. When a triplet of wires under tension is selected, the fourth one will be forced to be slack by adding purposely extra length. It allows to control changes of cable configurations and thus to have safer trajectories.