Three-dimensional parametric contact analysis of planetary roller screw mechanism and its application in grouping for selective assembly

The planetary roller screw mechanism(PRSM)is a novel precision transmission mechanism that realizes the conversion between linear and rotary motions.The contact characteristics of helical surfaces directly determine PRSM’s performance in load-carrying capacity and transmission accuracy.Therefore,studying the contact characteristics of PRSM forms the fundamental basis for enhancing its transmission performance.In this study,a three-dimensional parametric analysis method of contact characteristics is proposed based on the PRSM meshing principle and PyVista(a high-level API to the Visualization Toolkit).The proposed method considers the influence of machining errors among various thread teeth.The effects of key machining errors on contact positions and axial clearance,as well as their sensitivities,are analyzed.With excellent solution accuracy,this method exhibits higher calculation efficiency and stronger robustness than the analytical and numerical meshing models.The influence of nominal diameter and pitch errors of the screw,roller,and nut on the axial clearance follows a linear relationship,whereas flank angle errors have negligible effects on the axial clearance.The corresponding influence coefficients for these three machining errors on the axial clearance are 0.623,0.341,and 0.036.The variations in contact positions caused by individual errors are axisymmetric.Flank angle errors and roller diameter errors result in linear displacements of the contact points,whereas pitch errors cause the contact points to move along the arc of the roller diameter.Based on the proposed threedimensional parametric contact characteristics analysis method,the Fuzzy C-Means clustering algorithm considering error sensitivity is utilized to establish a component grouping technique in the selective assembly of critical PRSM components,ensuring the rational and consistent clearances based on the given component’s machining errors.This study provides effective guidance for analyzing contact characteristics and grouping in selective assembly for PRSM components.It also presents the proposed method’s potential applicability to similar calculation problems for contact positions and clearances in other transmission systems.

Design optimization of a wind turbine gear transmission based on fatigue reliability sensitivity

Fatigue failure of gear transmission is one of the key factors that restrict the performance and service life of wind turbines.One of the major concerns in gear transmission under random loading conditions is the disregard of dynamic fatigue reliability in conventional design methods.Various issues,such as overweight structure or insufficient fatigue reliability,require continuous improvements in the reliability-based design optimization(RBDO)methodology.In this work,a novel gear transmission optimization model based on dynamic fatigue reliability sensitivity is developed to predict the optimal structural parameters of a wind turbine gear transmission.In the model,the dynamic fatigue reliability of the gear transmission is evaluated based on stress–strength interference theory.Design variables are determined based on the reliability sensitivity and correlation coefficient of the initial design parameters.The optimal structural parameters with the minimum volume are identified using the genetic algorithm in consideration of the dynamic fatigue reliability constraints.Comparison of the initial and optimized structures shows that the volume decreases by 3.58%while ensuring fatigue reliability.This work provides new insights into the RBDO of transmission systems from the perspective of reliability sensitivity.