The wear problems are vital to the planetary roller screw mechanism (PRSM) as they have a great influence on transmission accuracy, working efficiency, and service life. However, the wear characteristics of the PRSM have been rarely investigated in the past. In this paper, a multiscale adhesive wear model is established by incorporating the effective wear coefficient and considering the thread surface roughness. The variation of surface roughness is characterized by the two-dimension Majumdar–Bhushan (MB) function. The multi-asperity contact regimes are used to estimate microcontact mechanics of the rough interface. Moreover, the influences of surface roughness, material properties, and working conditions on the wear depth and precision loss of the PRSM are studied in detail. The results reveal that as the surface roughness increases, the total actual contact area, wear depth, and precision loss rate rise. In addition, the adhesive wear increases with the growth of the axial load, and decreases with the increase in the material hardness and material elastic modulus ratio to a certain extent. The investigation opens up a theoretical methodology to predict the wear volume and precision loss with regard to thread surface roughness, which lays the foundation for the design, manufacturing, and application of the PRSM.

Misalignments are unavoidable in most applications of the planetary roller screw mechanism (PRSM) due to many potential causes. However, the effect of screw misalignments on the contact characteristics for the PRSM have not been thoroughly investigated. In this paper, a comprehensive analytical procedure for the PRSM performance considering screw misalignments is proposed. First, the contact positions and clearances of the PRSM with screw misalignments are calculated. Next, an improved model is presented for evaluation of the load distribution, in which the variation of axial clearances is taken into consideration. The numerical results are validated by finite element analysis. Then, the precision loss model caused by wear is derived considering the variation of contact forces. The results indicate that the contact positions slightly change due to the misalignment angle of the screw, while the axial clearances and load distribution at the screw-roller interface are significantly affected. At the same time, the contact forces over thread vary periodically. In addition, the screw misalignment aggravates the wear of the PRSM, resulting in accuracy degradation. The theoretical investigations lay the foundation for the engineering application of the PRSM.

Previous lubrication and wear analysis for the planetary roller screw mechanism (PRSM) has mainly concentrated on the isothermal conditions without considering temperature rise. However, the PRSMs applied in aviation and aerospace always operate in intensely varying thermal conditions with intricate thermal convection and thermal radiation environments. For this purpose, a modified Archard wear model is established by incorporating the entraining speed of threads and the load distribution, considering axial thermal errors. The variation of bulk temperature is characterized by the thermal network model (TNM). The modified Weierstrass–Mandelbrot (W-M) function is used to evaluate the lubrication conditions of the machined surfaces. Meanwhile, the contact flash temperature, wear depth, and precision loss rate are investigated in dry contact and lubricated phrase for mixed thermal elastohydrodynamic lubrication (TEHL) point contact. The results reveal that the temperature rise has a more pronounced influence on the precision maintenance capability compared to the uneven load sharing. The wear results are also compared to previous experimental simulation obtained using a rolling-sliding tribometer that utilize a rolling wheel on a rotating disk with similar patterns. It indicates that the wear life span of PRSMs can be improved by reasonable machining trajectory, thermal management, and lubrication parameters.

A systematic process of matrices-based wear profile modelling and a new optimization approach for planetary roller screw mechanism (PRSM) was proposed in this paper to improve the anti-wear performance with varied thread geometries. The wear evolution characteristics of thread surfaces for convex-concave contact and convex-straight contact were captured by incorporating updated axial clearances originated from accumulated thread wear, which provides a new perspective to predict the wear process of PRSM. The results show that the wear depth in convex-concave contact is 22% shallower than convex-straight contact with 10⁵ numbers of cycles, which suggests that thread wear can be limited with plausible geometrical parameters. Further analysis showed that as the surface roughness increases, the true equivalent pressure, the plastic strain and maximum wear depth becomes larger. In addition, the effect of the surface textures on the tribological properties of threads is also discussed to improve the applicability of the proposed methodology.

Obtaining the load distribution and radial deformations of planetary roller screw mechanism (PRSM) for the load carrying capacity design under complex loading conditions (multi-directional loads) is beneficial to decelerate fatigue and wear of threads. However, the combined effects of axial load, radial load and turning torque (overturning moment) were ignored in previous studies due to the complicated structure of PRSM. This paper presents a multi-roller beam-bar-spring (MR-BBS) model that incorporate radial load, turning torque and thread modification. The proposed model extended the theoretic method for calculating bending behavior of screw and rollers, which can more precisely describe the locus of the threads and roller axis. The load distribution of threads and load sharing among rollers of a PRSM under different external loads and cycling process are analyzed. The results show that the load distribution is more sensitive to turning torque of screw but relatively insensitive to the radial load. Moreover, the load distribution moderately changes with the variation of modification factor. Based on thread modification, the variable lead PRSM is proposed so that the uniformity of load sharing with complex load can be optimized.