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.
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.
凸凹接觸式行星滾柱絲杠的嚙合承載特性（Ｍｅｓｈｉｎｇ ａｎｄ ｂｅａｒｉｎｇ ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ ｏｆ ｃｏｎｖｅｘ-ｃｏｎｃａｖｅ ｃｏｎｔａｃｔ ｐｌａｎｅｔａｒｙ ｒｏｌｌｅｒ ｓｃｒｅｗ ｍｅｃｈａｎｉｓｍ）
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
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...
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.
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.
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.
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.
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.