Meshing Properties of Planetary Roller Screw Mechanism within Misalignments

The unavoidable misalignments of the screw, roller and nut have great influences on the performances of planetary roller screw mechanism (PRSM) such as load carrying capacity, efficiency and lifetime. A method is proposed to calculate the meshing positions and clearances of each pair of thread teeth in the PRSM under the consideration of misalignments. The tangency conditions of mating thread surfaces within misalignments are developed by employing the theory of gearing and the tooth contact analysis. The vector functions of thread surfaces on the screw, roller and nut are developed and the misalignments of each component are described by coordinate transformations. Then, the equations to calculate the meshing positions and clearance of each pair of mating thread surfaces at screw/roller and nut/roller interfaces in the misaligned PRSM are derived. By comparing the meshing positions of the aligned PRSM obtained by the existed method with those by the proposed method, the feasibility of the proposed method is validated. The meshing properties at screw/roller interface are analyzed when misalignment occurs. The results show that the meshing radius of multiple thread teeth of the screw or the roller are not identical and the meshing angles of those thread teeth are also different; the multiple pairs of mating thread teeth at screw/roller interface cannot mesh with each other simultaneously.