Chaoyang Li

Passivity-based control (PBC) is a powerful control strategy, excelling in stability through its energy-based framework. It is regarded as an effective method for enhancing the dependability of robotic rotary joints (RRJs). However, as a fundamentally model-based control method, PBC’s effectiveness heavily relies on accurate system modeling and parameter estimation. Consequently, its control performance is significantly degraded in RRJs, which exhibit complex nonlinear dynamics complicate parameter identification and frequently lead to parameter mismatches between theoretical models and physical systems. To address this limitation, this article presents a novel energy flow regulation-PBC (EFR-PBC) methodology. Leveraging the system’s polynomial characteristics, EFR-PBC incorporates a data-driven recursive polynomial response surface (RPRS) surrogate model to predict energy flow tensor (EFT) variations from input-output measurements, facilitating adaptive control law synthesis. By reducing dependence on precise mathematical models and system parameters, EFR-PBC maintains robust performance under uncertain conditions. Extensive comparative studies through both numerical simulations and experimental validations against conventional interconnection and damping assignment (IDA)-PBC and PID-PBC implementations demonstrate the effectiveness and superior performance of the proposed method.

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.

As a key component in fields such as high-precision machine tools, aerospace and weaponry, the thermal deformations in a differential planetary roller screw (DPRS) caused by the changes in ambient temperatures can lead to uneven load distribution and increased wear, which can seriously affect its transmission accuracy, efficiency, and service life. Therefore, the temperature rise of a DPRS at different ambient temperatures was studied using the block thermal network method, and the thermal deformations were calculated. A load distribution model of DPRS considering thermal deformation was developed, and a wear prediction method combined with surface roughness was proposed. The results show that the increase in ambient temperature has an obvious negative effect on the load distribution and wear depth of DPRS. Moreover, the DPRS temperature rise, load distribution and wear depth dramatically change with the variation of parameters such as load, speed and thread pitch. A DPRS durability test device that considers changes in ambient temperature was developed. Experiments with temperature rise and DPRS wear under different ambient temperatures were conducted to validate the theoretical analysis model.

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.

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.