Dynamic analysis of a novel three-stage telescopic planetary roller screw mechanism with externally threaded nuts

A novel three-stage telescopic planetary roller screw mechanism (3TPRSM) with externally threaded nuts is proposed, in which the rollers at different stages are located nearly at the same axial position when it is fully retracted. Considering the forces acting on the external and internal threads of nuts and the power transmission paths among moving parts, a dynamic model of the 3TPRSM is developed. The model can be used to calculate the force and motion at the interfaces of the k ^th stage roller – external thread, the k ^th stage roller – internal thread and the hollow screw – stepped spline. The influence of screw rotational velocity, thread lead, flank angle, external force and friction coefficient on the transient and steady-state behaviors of the 3TPRSM is analyzed. The results show that the forces at the 1st stage roller – external thread interface are the largest among all thread contact interfaces. The maximum value of the driven torque acting on the stepped spline assembly exceeds two-thirds of that acting on the hollow screw. The initial efficiency is much lower than the steady-state efficiency and shows higher sensitivity to the thread lead. A smaller flank angle is more beneficial for reducing the thread contact stress and improving the efficiency of the 3TPRSM.