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Structural design for planetary roller screw mechanism based on the developed contact modelling（22年基于接觸建模的行星滾滾柱絲杠結構設計）

The structural design of planetary roller screw mechanism (PRSM) with lower contact stress is beneficial to delay the fatigue failure and prolong the service life. However, few studies focused on this field and a reasonable contact model is therefore required due to its complexity structure. In this paper, a developed contact model is established for PRSM, and a process-based parameterization method is proposed to precisely calculate the contact characteristics along with the change of parameters. Based on the in-depth study of the parameter sensitivities of contact characteristics, the structure design to reduce contact stress for PRSM is realized through the multi-objective optimization under the proposed geometric constraints. The validity of this model is well verified by finite element method.

閱讀： 2022-04-10
Fatigue lifespan of a planetary roller-screw mechanism（22年行星滾柱絲杠機構的疲勞壽命）

Electro-mechanical actuators including planetary roller screw (PRS) support cyclic loads in aeronautical conditions. PRS multiple thread contacts between screw, rollers and nut allow the mechanism to support large loads. However, aeronautical accreditation requires fine prediction of fatigue lifespan. In this paper, a fatigue design strategy for PRS mechanisms is proposed combining Hertz contact model and a multi-axial fatigue criterion. The method is applied on two examples, one standard and one inverted PRS. The lifespan of PRS mechanism depends on maximal Dang Van stress. The Hertz sliding angle (Hertz contact main direction/sliding velocity) was introduced to analyze PRS performances. For both examples, the maximum stress at thread contact were located in bulk material but not at the surface. Dang Van stress mainly depended on curvature ratio, Hertz sliding angle and loads. Based on this analysis, Dang Van criterion was implemented to derive the loading domain of infinite lifespan of the mechanism. Critical contact was not always on the roller-screw side.

閱讀： 2022-01-16
凸凹接觸式行星滾柱絲杠的嚙合承載特性（Ｍｅｓｈｉｎｇａｎｄｂｅａｒｉｎｇｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｃｏｎｖｅｘ-ｃｏｎｃａｖｅｃｏｎｔａｃｔｐｌａｎｅｔａｒｙｒｏｌｌｅｒｓｃｒｅｗｍｅｃｈａｎｉｓｍ）

摘要：為提高行星滾柱絲杠的承載能力，分析優化行星滾柱絲杠的螺紋牙型，提出一種基于凸凹接觸的嚙合方式。設計凹圓弧的絲杠和螺母牙型輪廓，基于空間嚙合理論推導螺紋曲面方程、空間嚙合方程，并基于赫茲接觸理論和變形協調方程建立負載分布模型；采用數值計算的方法對嚙合點位置、軸向間隙和接觸應力進行求解，系統揭示了牙側角、螺距等參數對嚙合點位置、軸向間隙和負載分布的影響規律，并對比分析標準式和凸凹式行星滾柱絲杠的接觸應力。結果表明：牙側角對軸向間隙的影響最大，絲杠和螺母的凹圓弧半徑變化對接觸點位置和軸向間隙幾乎沒有影響，但對承載能力影響十分明顯；與標準式相比，凸凹接觸式行星滾柱絲杠的承載能力有較大的提高，絲杠和螺母凹圓弧半徑越小承載能力提高越明顯。本研究為研制高承載、高使用壽命的行星滾柱絲杠提供了優化設計和分析的依據。

閱讀： 2022-01-15
Investigation on the mechanical behavior of planetary roller screw with the effects of external loads and machining errors

Abstract: Planetary roller screws are the key mechanical components used in linear motion and could be subjected to radial and axial loads in application. However, the effect of radial force on load distribution and fatigue life has not been considered in previous studies...

閱讀： 2021-06-24
Analysis of transient mixed elastohydrodynamic lubrication in planetary roller screw mechanism（21年行星滾柱絲杠瞬態混合彈流潤滑分析）

Previous lubrication studies for planetary roller screw (PRSM) are mainly concentrated on steady-state condition without the consideration of entrainment angle. However, PRSM always operates in transient situations with frequent startup and shutdown process. In this paper, uneven friction distribution, the influence of helix angle on lubricating properties and transient behavior in the roller-screw interface are analyzed comprehensively based on transient mixed-EHL model, which considers real three-dimensional (3D) machined roughness and arbitrary entrainment velocity. The results show that smaller helix angle is beneficial to improve the lubrication performance. Increasing the rotating speed and declining axial load can moderate the uneven friction distribution. Besides, a relatively large angular acceleration may enlarge the film thickness and reduce the friction at the shut down status. The numerical simulation model can be utilized as a design optimization tool for the PRSM.

閱讀： 2021-06-17
精密蝸桿傳動副磨損量補償及側隙調控方法

蝸桿傳動是機械傳動的一種主要形式，具有傳動比范圍寬、結構緊湊、體積小、運動平穩、噪聲低等優點，除被廣泛應用于動力傳動外，也是機床及精密儀器精密圓分度機構的首選部件...

閱讀： 2021-05-25
蝸桿傳動的發展及其分類

摘要：回顧了蝸桿傳動的發展歷程，并闡述了各種蝸桿傳動的優缺點。從蝸桿傳動中的首創體外形、齒部位置及嚙合區域、首創面齒廓三個方面出發對蝸桿傳動進行分類，以元素周期表為原型得出蝸桿傳動系統分類表，表中各類型、各系列及各形式之間在幾何結構和傳動性能上存在一定的普遍性和規律性...

閱讀： 2021-05-25
差動式行星滾柱絲杠承載特性分析

摘要：基于空間嚙合理論與赫茲接觸理論展開差動式行星滾柱絲杠承載特性分析，綜合考慮由滾柱與絲桿初始嚙合點偏置引起的接觸點位置變化對承載特性的影響，建立差動式行星滾柱絲杠空間嚙合...

閱讀： 2021-05-25
Multi-objective optimization of planetary roller screw mechanism based on improved mathematical modelling（21年行星滾柱絲杠基于改進的數學建模的多目標優化）

The optimization of obtaining the most uniform load distribution is important for the load carrying capacity design of the planetary roller screw mechanism (PRSM). However, the stiffness matrix of PRSM in traditional method based on the relationship between load and deformation of the thread may be destroyed when threads are no longer in contact due to machining errors, which would bring convergence problem in optimization process. In this paper, the mathematical model is firstly established to overcome the above drawbacks by proposing an improved iterative algorithm. Then, the multi-objective optimization is conducted to search the best designed pitches for the most uniform load distribution on both the screw-roller and nut-roller interfaces, and results are verified by the finite element method.

閱讀： 2021-04-15
A Multiscale Accuracy Degradation Prediction Method of Planetary Roller Screw Mechanism Based on Fractal Theory Considering Thread Surface Roughness（21年一種行星滾柱絲杠多維度精度下降預測方法）

Abstract: 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.

閱讀： 2021-05-23
Research on Fractal Model of Load Distribution and Axial Stiffness of Planetary Roller Screw Mechanism Considering Surface Roughness and Friction Factor（22年載荷分布和軸向剛度的分形模型研究）

The effects of surface roughness and material properties of the planetary roller screw mechanism (PRSM) on the axial stiffness and load distribution are rarely studied. In this paper, the load distribution model is presented by incorporating into friction factor and surface microtopography. The microcontact model is built by considering elastic and plastic regimes to calculate the total actual contact area. Moreover, the load distribution model is modified by introducing surface microcontact coefficient. Then, the influences of the nut position, fractal dimension, fractal roughness, friction factor, axial load, and material yield strength on the axial stiffness and load distribution are studied in detail. The numerical results show that the axial stiffness rises with the increment of the nut position, axial load, fractal dimension, and yield strength, and reduces with the fractal roughness and friction factor increasing. In addition, the uniformity of the load distribution increases with the increment of the fractal roughness, and drops with the increase of the fractal dimension and material yield strength. This investigation lays the foundation for the design, manufacturing, and use of the PRSM.

閱讀： 2021-03-09
Wear Behavior of Martensitic Stainless Steel in Rolling-Sliding Contact for Planetary Roller Screw Mechanism: Study of the WC/C Solution（16年馬氏體不銹鋼在行星滾柱絲杠滾動滑動接觸中的磨損行為）

The planetary roller screw mechanism is used in the aeronautics industry for electro-mechanical actuators application. It transforms a rotational movement into a translation movement, and it is designed for heavy loads. The main components are made of martensitic stainless steel, and lubricated with grease. Like most usual rolling mechanisms, smearing and jamming can occur before the theoretical fatigue lifetime, especially in poor lubrication conditions. The actuated load is carried by small contacts between the threads of the screw, the rollers and the nut. The static single contact can be described as an ellipsoid on flat contact with high contact pressure (3-4 GPa). The motion consists of rolling with spin associated with side slip up to 10%. The aim of our study is to investigate the wear behavior of the WC/C coated contact for different operating and design parameters such as load, speed and slip ratio. The contact is simulated by a free rolling roller loaded on a rotating disk. A specific apparatus is used to create a contact with a side slip component, i.e. perpendicular to the rolling direction. The wheel rolling speed and the tangential force generated by the slip ratio are measured. The wear behavior of a WC/C carbon-based composite coating is investigated. It reveals progressive wear and cracking in the rolling direction, i. e. perpendicular to the sliding direction. A wear map has been drawn to establish the damage mode depending on the contact conditions.

閱讀： 2016-11-02

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