Dynamic characteristics of planetary roller screw mechanism with time-varying load distribution and friction during discontinuous meshing

The multiple meshing pairs and multi-tooth structure of the planetary roller screw mechanism (PRSM) result in complex load-sharing and vibration characteristics. Few models capture the coupled effects of discontinuous meshing at the roller ends on load-dependent stiffness and friction. This study develops a dynamic model that incorporates time-varying load distribution and friction to describe radial and axial vibrations. The actual thread meshing positions are determined geometrically, and the load and stiffness of each tooth are calculated iteratively while accounting for periodic variations in the number of load-carrying teeth. The gear-mesh stiffness model further considers the effect of varying contact width on load distribution. Friction forces and torques at both meshing pairs are determined based on the instantaneous meshing geometry and contact forces. The model is validated through vibration experiments, and the simulated and measured responses exhibit consistent meshing frequency characteristics. The effects of external load on load distribution, stiffness, and acceleration responses are investigated, together with the vibration characteristics of the screw, rollers, and nut. Acceleration responses and phase portraits are also compared for different friction conditions.