K-type modification of thread tooth for inverted planetary roller screw mechanism and its effect on load distribution

The transmission performance of the inverted planetary roller screw mechanism (IPRSM) is affected by nonuniform load distribution on the thread tooth. This phenomenon often leads to stress concentration at the load-bearing areas of the thread tooth, thereby causing fatigue failure. To address this issue, K-type modification of thread tooth is proposed to optimize the load distribution on the IPRSM. The effects of different modification coefficients and inclination angles on the relative optimal modification amount are analyzed. The contact stress distributions are determined through theoretical mechanical analysis and finite element modeling, before and after modification. Comparative results demonstrate that K-type modification suppresses maximum contact stress on the first meshing thread tooth at the load input end. For a positive K-type modification of 0.16 mm, the maximum stress is reduced by 18.1% relative to the unmodified condition. Similarly, a 21.3% reduction in maximum stress is achieved via a reverse K-type modification of 0.14 mm. In addition, the effects of different modification coefficients and inclination angles on the load distribution are small for the relatively optimal modification amount. This work provides an approach for load distribution design in IPRSM, offering a theoretical framework and practical guidance for enhancing transmission performance.