Review on thread profile modification methods for the planetary roller screw mechanism

The planetary roller screw mechanism (PRSM) is a high-precision actuator, widely used in aerospace, humanoid robots, and automotive systems. However, inherent structural and loading characteristics lead to uneven load distribution among thread teeth, causing contact stress concentration and accelerated wear, which limit transmission performance. Thread profile modification has emerged as an effective solution to optimize load distribution and reduce stress concentration. This study reviews the origin, classification, load-bearing characteristics, and kinematics of PRSM. It discusses local modification methods (half-thread thickness, pitch diameter, crest, and root) and global strategies (concave-convex arc reconstruction, multi-parameter optimization, etc.), highlighting their mechanisms, advantages, and limitations. Discrete modification can reduce average contact stress by approximately 35.55% and improve load uniformity. Additionally, the study addresses measurement techniques, potential negative effects of modification, and proposes a macro-meso-micro modification framework. Finally, current challenges and future research directions are summarized, providing a theoretical foundation for PRSM engineering applications.