The Calculation Method for the Load Distribution in the Planetary Roller Screw Mechanism with the Roller Deviation
The unavoidable deviation of the roller will cause the seriously uneven load distribution among threads.It is one of the main reason for the collapse failure of thread teeth at the single-sided of the roller.Nevertheless,the axes of the screw,roller and nut are assumed to be parallel to each other in the previously published static models.A method is proposed to calculate the load distribution of the PRSM with the deviation of the roller and mesh-apart of thread teeth.A static model of the PRSM with the roller deviation is proposed.The stiffness matrix and equilibrium equation are derived with consideration of the change of the meshing states of thread teeth.The flowchart to solve the equation is given by dividing the external load of the nut into multiple load steps.By comparing the load distribution of the PRSM without/with the roller deviation obtained from the finite element model with those from the proposed method,the feasibility of the proposed method is validated.The meshing state and load distribution of the PRSM with the roller deviation is analyzed.The results show that the roller deviation angles φ and Ψq have great influences on the load distribution.A proper deviation angle φq could reduce the maximum contact force acting on threads.The maximum contact force on threads increases sharply with the increase of the deviation angle Ψq.When|Ψq|＞1.0',the mesh-apart of thread teeth can be observed and the maximum contact forces on the thread teeth is about 3 times larger than that on the thread teeth without deviation.
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