Workspace analysis of a 6-DOF cable-driven parallel robot considering pulley bearing friction under ultra-high acceleration

Cable robots can generate high velocities and accelerations due to the very small inertia of the end-effector. Therefore, CDPRs have been used widely in special industrial applications requiring high dynamics. However, the high acceleration generated affects the wrench-feasible workspace of a CDPR system significantly. In addition, as a pulley rotates, the frictional force at the pulley bearing disturbs the motion, changes the cable tensions. Thus, pulley bearing friction cannot be neglected in ultra-high acceleration systems where high tensions are imposed. A workspace analysis was carried out for a wrench-feasible condition in a 6-DOF CDPR system considering the pulley bearing friction connected in series. Then, the pulley bearing friction was modeled with the Coulomb friction model including the variation of wrapping angle of pulley and a loss factor. The simulated tension profiles considering pulley bearing friction were in good agreement with data measured with a load cell. And a wrench-feasible workspace analysis under various accelerations was carried out. In conclusion, as the external acceleration was increased, the whole tension was increased and workspaces to exceed available tension occurred in case of 100 m/s2. And the pulley bearing force increased or decreased the cable tension because of the direction of the signum function. As a result, the wrench-feasible workspace was changed in the presence of pulley bearing force effects.