Tolerance design method for planetary roller screw mechanism based on transmission accuracy and considering thermo-mechanical coupling deformation

As a high-precision transmission device, the tolerance design of planetary roller screw mechanisms (PRSMs) is influenced by multiple factors. This study proposes a tolerance design method that incorporates transmission error sensitivity analysis, machining difficulty analysis, and thermo-mechanical coupling deformation. The proposed approach involves: establishing a PRSM transmission error computational model to quantify the sensitivity coefficients of critical geometric errors; developing a dual-objective error sensitivity-manufacturability optimization model by incorporating machining difficulty coefficients for screw, roller, and nut pitch errors, thereby determining their respective error contribution ratios to transmission error; computing the relative deformation of PRSM thread pairs under thermo-mechanical coupling through combined frictional thermal modeling and finite-element analysis; and ultimately performing tolerance optimization using the interior-point method with transmission accuracy as the objective function constrained by both critical thermal deformation and error distribution ratios, yielding optimal tolerance ranges for all error parameters at P3-grade precision levels. By comparing experimental results with numerical calculations under four operating conditions, the variations in PRSM stroke variation and mean stroke deviation were analyzed, thereby validating the accuracy of the proposed model.