Transmission accuracy–axial backlash–fatigue life-driven tolerance optimization of planetary roller screw mechanism

Liu Genshen,Wei Peitang,Liu Huaiju,Du Xuesong,Hu Rui,He Huilin,Zhou Pengliang,Tan Xiaoqing 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.6

The planetary roller screw mechanism (PRSM) is an advanced linear transmission device. The relationship between tolerance allocation and performance risk still remains elusive, which is a challenge for its future applications. This work proposes a novel transmission accuracy–axial backlash–fatigue life-driven tolerance optimization method for the screw, roller, and nut of PRSM. A computational framework for PRSM transmission accuracy, axial backlash, and fatigue life calculation is developed to work on the parametric variation of design parameters including the eccentric, pitch, nominal diameter, and flank angle. Combinations of parametric variation are obtained by the Latin hypercube sampling-based tolerance statistical model to rapidly evaluate PRSM performance risk under operation conditions and tolerance parameters. The optimal tolerance parameters with the expanded width of tolerance interval and the minimum PRSM performance risk probability are obtained using the non-dominated sorting genetic algorithm. Results reveal that PRSM performance risk probabilities change from 89.25 to 68.72% and 58.1 to 56.86%, with 29.94 and 17.38% tolerance interval width increase under the high-precision and heavy-loading operation cases studied, respectively.

Polymer gear contact fatigue reliability evaluation with small data set based on machine learning

Liu Genshen,Wei Peitang,Chen Kerui,Liu Huaiju,Lu Zehua 한국CDE학회 2022 Journal of computational design and engineering Vol.9 No.2

Polymer gears have shown potential in power transmission by their comprehensive mechanical properties. One of the significant concerns with expanding their applications is the deficiency of reliability evaluation methods considering small data set circumstances. This work conducts a fair number of polyoxymethylene (POM) gear durability tests with adjustable loading and lubrication conditions via a gear durability test rig. A novel machine learning-based reliability model is developed to evaluate contact fatigue reliability for the POM gears with such a data set. Results reveal that the model predicts reasonable POM gear contact fatigue curves of reliability–stress–number of cycles with 2.0% relative error and 18.8% reduction of test specimens compared with the large sample data case. In contrast to grease lubrication, the oil-lubricated POM gear contact fatigue strength improves by 10.4% from 52.1 to 57.6 MPa.

Conceptual design and optimization of polymer gear system for low-thrust turbofan aeroengine accessory transmission

Lu Zehua,Liu Chang,Liao Changjun,Zhu Jiazan,Liu Huaiju,CHENYIMING 한국CDE학회 2024 Journal of computational design and engineering Vol.11 No.1

The advancement in materials and lubrication has significantly improved the load-carrying capability of polymer gears, making them ideal for replacing metallic gears in power transmission. However, this conversion is not as simple as substituting steel with polymer; it requires a thorough redesign of the structural parameters specific to polymer gears. To enable the metallic-to-polymer conversion of gear in power transmission, a model for optimizing polymer gear systems was developed. An investigation of the accessory transmission system of a low-thrust turbofan aeroengine was conducted. A comprehensive performance index for the accessory transmission was developed using combined weighting coefficients to achieve the optimization goals including total mass, transmission efficiency, maximum transmission error, and so on. The polymer gear system developed using the proposed optimization model demonstrated a 70.4% reduction in total mass compared with the metallic gear system, as well as a transmission error decrease of over 29% when compared with polymer gear systems with standard tooth profiles. The contribution analysis results demonstrated that optimizing the tooth width, pressure angle, and addendum height of polymer gears can significantly enhance the load-carrying capacity of the polymer gear system while maximizing tooth profile flexibility.

Crystal elasticity analysis of contact fatigue behavior of a wind turbine gear

Hao Zhou,Peitang Wei,Huaiju Liu,Caichao Zhu,Wei Wang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.10

Rolling contact fatigue is the main factor limiting the service performance of wind turbine gears. The inherent microstructure of the gear material has a significant impact on its contact fatigue behavior and service life. In this research, a two-dimensional contact fatigue model considering the gear material microstructure and the elasticity anisotropy characteristics of the crystals is established. The predicted results reveal a pronounced scatter phenomena of the stress distribution in the subsurface and the localized stress concentration at the grain boundaries caused by crystal elasticity anisotropy. Changes of initial grain orientations can cause a certain fluctuation in the critical stress and its depth in the subsurface. Under the same load level, the gear contact fatigue life calculated by the crystal elasticity anisotropy model is lower compared to isotropic material. Considering the anisotropic properties of the crystal elasticity, an S-N curve based on the maximum contact pressure for the wind turbine gear is drawn.

An investigation on the influence of modification parameters on transmission characteristics of planetary gear system

Xiangyang Xu,Xupeng Fan,Peng Diao,Huaiju Liu 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7

A new gear tooth modification model of planetary gear system was established by considering the characteristics of tooth longitudinal crowning modification and tooth profile modification. Using this model, the influences of modification parameters on the time-varying mesh stiffness, transmission error, contact spots and dynamic response of the planetary gear system were analyzed through numerical analysis. The results show that tooth profile modification can effectively restrain the mesh stiffness sudden variation in the single and double tooth alternation of both the internal and external mesh pairs, and significantly decrease the transmission error fluctuation. However, longitudinal crowning modification has no marked influence on mesh stiffness sudden variation or transmission error fluctuation. The tooth profile modification can significantly reduce the sudden variation of tooth surface load during gear mesh course. Longitudinal crowning modification can make the tooth surface load evenly distributed in tooth width direction. When the external meshing pairs are modified at the tooth profile individually, the magnitude values of main response resonance peaks of internal meshing pairs have a great reduction, but those values of external meshing pairs change slightly. In the case of tooth profile modification of the internal meshing pairs, the phenomenon is reversed. By contrast with tooth profile modification, longitudinal crowning modification has little influence on the resonance peaks of internal and external meshing pairs.

Study on the relationship between machining errors and transmission accuracy of planetary roller screw mechanism using analytical calculations and machine-learning model

Wu Hanlin,Wei Peitang,Hu Rui,Liu Huaiju,Du Xuesong,Zhou Pengliang,Zhu Caichao 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.1

Correlation between machining errors and transmission accuracy of planetary roller screw mechanism (PRSM) plays an important role in tolerance design. In this study, analytical calculations, machine learning, and experimental verification are utilized for exploring the internal correlation between the machining errors and the transmission accuracy of the PRSM. A multi-roller meshing transmission error model is established, which comprehensively considers the eccentric error, nominal diameter error, flank angle error, and cumulative pitch error of the screw, roller, and nut. The importance coefficients of various machining errors on the transmission error are determined using the random forest algorithm. A genetic algorithm-back propagation neural network algorithm-based method is utilized for training the dataset generated via analytical calculations. The results show that the proposed analytical calculation model reflects the alternate meshing characteristics of rollers during the PRSM motion, providing a more accurate prediction of the transmission error than the existing prediction methods. For an actual mean travel deviation, the most significant machining error is the cumulative pitch error of the screw, whereas for the actual bandwidth of useful travel, the most significant machining errors are the eccentric errors of the screw and nut. The proposed prediction formulae for transmission error considering the essential machining errors illustrate reasonable prediction accuracy, with an average error of 10.63% for the actual mean travel deviation and 14.27% for the actual bandwidth of useful travel compared with the experiments, which can effectively support the direct design of PRSM tolerance in engineering practice.

A comparative study of fatigue behavior between S-shaped and involute POM gears

Wu Ruo,Wei Peitang,Lu Zehua,Liu Huaiju,Zorko Damijan,Xie Huaijie 한국CDE학회 2022 Journal of computational design and engineering Vol.9 No.6

Applications of polymer gears have been gradually expanding from motion transmission to power transmission fields. Design of new gear teeth profiles plays a crucial role in meeting the requirement of replacing metallic gears with polymer ones. This work develops a computational framework consisting of tooth profile generation and fatigue life prediction of S-shaped and involute POM gears. The contact and bending fatigue performances of S-shaped and involute POM gears under oil lubrication are comparatively studied. It is found that the S-shaped profile reduces the tooth root stress by 25% and significantly improves the bending fatigue life by 10 times compared with the involute profile, especially under medium or high loading levels. Furthermore, the S-shaped gear with a single circular-filleted root curve benefits a 20% reduction of tooth root stress and a 30% increase in bending fatigue life compared to a double circular-filleted root curve S-shaped gear.

Experimental investigation of crack growth behaviors and mechanical properties degradation during gear bending fatigue

Huan Yan,Peitang Wei,Pengliang Zhou,Ling Chen,Huaiju Liu,Caichao Zhu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.3

Tooth bending fatigue remains as a fundamental bottleneck restricting the safety and reliability of modern high-performance gear. In this study, a serial of bending fatigue tests on case carburized and shot peening treated gears is conducted. The fatigue crack propagation behaviors during bending fatigue test were analyzed. The alternations of macroscopic mechanical properties and microstructure features of gear samples subjected to bending fatigue are experimentally examined and analyzed in detail. It is found that the measured tooth root crack trajectories basically conform to the dangerous section of the tooth root determined by the 30° tangent method with a slight variation of about 1°. The phenomena of residual stress relaxation in gear bending fatigue is observed with the maximum residual compressive stress decreasing from -698 MPa of intact state to -572 MPa of failure state. Furthermore, the content of retained austenite of tooth root surface decreases by about 3.8 % after the gear bending fatigue failure, and the grain size of the tooth root core region illustrates a certain tendency of coarsening.