The effect of cable tensions on the stiffness of cable-driven parallel manipulators

A cable-driven parallel manipulator (CDPM) is driven by a set of cables instead of rigid links. Since cables have more flexibility than rigid links, stiffness of a CDPM has been a concern for applications requiring controllable system stiffness. This paper studies the effect of cable tensions on the stiffness of a CDPM that has six degrees of freedom and are driven by seven cables. Both upper and lower limits of the tension in a cable are taken into account in order to mimic real-world scenarios. The natural frequencies of the CDPM at all poses in the workspace are calculated based on interval analysis. Simulation results show that increasing antagonistic cable tensions does not necessarily increase the stiffness of the CDPM within a certain set of poses. The stiffness of a CDPM does not necessarily monotonically increase or decrease with the increase of antagonistic cable tensions. Moreover, a larger change of antagonistic cable tensions does not always lead to a larger change in the stiffness of the CDPM for a certain set of poses. Both cable tensions and the current pose contribute to the stiffness of the CDPM. The effect of cable tensions on the stiffness of a CDPM discussed in this paper provides a guideline to select the set of poses in order to control the stiffness of a CDPM via adjusting cable tensions.