In this paper, the influence of cable behavior, on Cable Driven Parallel Robots (CDPR) is studied. This study is conducted with the goal of designing a medium size CDPR for additive manufacturing. This robot needs to have a high level of rigidity to guarantee a given tracking tool path error. Firstly, the characterization of different thin cables (steel, Dyneema®, aramid) is presented. The mechanical properties of these cables, in terms of stiffness, damping, hysteresis and creep are compared with regard to additive manufacturing applications. A stiffness model, which takes into account the cable preload, and a dynamic model of CDPR is proposed. The simulations of these two models are compared with experimental results obtained for the range of cables studied using dynamic stiffness analysis on an 8-cable fully constrained CDPR. This paper concludes on the type of cable that should be chosen for our application.
In this paper, the static and dynamic performances of a cable-driven parallel robot (CDPR) are analyzed over all its entire workspace. The considered robot has 6 degrees of freedom and it is completely constrained with 8 cables. This paper aims at highlighting the effects of cable preloads on the robot's behavior. To this end, the stiffness matrix of the robot is computed from a second order approximation of the deformation energy of preloaded cables. Lagrange formulation is used to obtain dynamic equations of the robot for vibration mode calculation and trajectory tracking simulations. Static and modal analyses show that, for a given preload, the increase in the robot's stiffness and modal frequencies is relatively more significant using soft cables, made of nylon, rather than stiff cables made of steel. These results are confirmed by dynamic simulations illustrating the effects of preloaded cables on the accuracy of trajectory tracking performance.
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