Roller Screw Mechanism Research Articles

Load distribution over threads of planetary roller screw mechanism with pitch deviation

A model is proposed to calculate load distribution over threads of planetary roller screw mechanism (PRSM) with pitch deviation. Firstly, four kinds of machining errors of threads including pitch deviation, deviation of thread angle, division error of multiple threads and deviation of pitch diameter are analyzed, and the relationships among them are investigated. After analyzing the relationships among the errors, pitch deviation is chosen to be the main machining error to investigate because it can reflect the effects of other machining errors, and is the most influential machining error on the contact condition and deformation compatibility relationship, i.e. the load distribution of PRSM. Based on the proposed model, the effects of pitch deviation on the load distribution of PRSM are studied through numerical analyses, and load distributions under different machining precisions are analyzed. In order to experimentally verify the investigation, two PRSM samples are measured and tested under the same experimental conditions. The experimental results show that load distributions over threads will fluctuate because of the existence of pitch deviations. The pitch deviations, load distributions over threads and wear depths of threads in the samples show obvious accordance, which indirectly demonstrates the effects of pitch deviation on load distribution.

Transient thermal analysis of standard planetary roller screw mechanism based on finite element method

The thermal behavior of the standard planetary roller screw mechanism needs to be investigated since the large amount of heat generated by the friction torque on multiple contact points during the transmission process. In this article, a simplified transmission system model of standard planetary roller screw mechanism is first established for the finite element analysis. Second, the friction torque of standard planetary roller screw mechanism is calculated and the boundary conditions of thermal analysis are deduced. Then, the transient thermal analysis of the standard planetary roller screw mechanism based on finite element method is conducted by considering the moving heat source and thus temperature field distribution at any time and the temperature rise curve at different positions of the standard planetary roller screw mechanism can be obtained. Finally, the correlation between the experimental data and the calculated values confirms the validity of the proposed thermal model for the transient thermal analysis.

Электромеханический привод с планетарным роликовинтовым механизмом для электрохимического станка с вибрирующим электродом

Электромеханический привод с планетарным роликовинтовым механизмом для электрохимического станка с вибрирующим электродом

Thread Modification Method for Load Balance on Planetary Roller Screw Mechanism

Based on the relationship between the load distribution and the load deformation of the thread of the planetary roller screw mechanism (PRSM), a modification method of the roller thread is proposed. The nut side and the screw side of the roller thread are modified by different amount of modification, and the modified thread load distribution is calculated and analyzed. The results show that the effects of roller thread modification on the load distribution are significant, and the sensitivity of the load capacity of the nut and screw to the modification is different. Through the study of the influence of roller thread modification on thread load distribution, the optimal value of the roller thread modification on the nut side and the screw side is obtained under the PRSM parameters given in this paper, which provides a theoretical guidance for the future PRSM load balancing design.

Investigation on the uncertain factors of the elastic–plastic contact characteristics of the planetary roller screw mechanism

The scatter of uncertain factors of the planetary roller screw mechanism, which originated from the manufacturing process, has a significant influence on its serving performance. However, this influence remains insufficiently studied. Further, the elastic–plastic contact analysis of the planetary roller screw mechanism with considering the uncertainties needs large numbers of repetitive calculations by traditional finite element method, which is labor intensive and often impractical. In this paper, an uncertain model of the planetary roller screw mechanism, including parameterization and finite element calculation, is established to conduct the elastic–plastic contact analysis automatically. Besides, the finite element method results can be also obtained automatically with the self-compiled flow program and the secondary development platform using the design of experiment method. Then, a mathematic model is applied to value the influence of the uncertain factors on the contact characteristics. The Pareto graphs are plotted to clearly show this sequence of the percent effects of all the uncertain factors. The present work, for the first time, developed an automatic modeling method for analyzing efficiently the uncertain factors of planetary roller screw mechanism, which is worthy in industrial application.

Thermo-mechanical coupling–based finite element analysis of the load distribution of planetary roller screw mechanism

In this article, 3D or three-dimensional finite element analysis is used to simulate and evaluate the load distribution characteristics of a planetary roller screw mechanism under thermo-mechanical coupling. The finite element model takes into account the installation modes of the planetary roller screw mechanism, which is verified by comparison with theoretical models for a certain load magnitude in four installation modes. In addition, the effects of the installation mode, load magnitude, and temperature condition on the load distribution are also systematically analyzed. The numerical results reveal a phenomenon of threads separating from the meshing, which indicates that the influence of thermo-mechanical coupling on the load distribution cannot be ignored. Furthermore, the influence of the installation mode on the screw–roller interface is larger than that on the nut–roller interface. Compared with the screw–roller interface, the temperature difference is one of the main conditions affecting the load distribution of the planetary roller screw mechanism and has a significant effect on the nut–roller interface. In addition, the influences of the screw rotational speed and the load magnitude on the load distribution on the screw–roller interface are larger than those on the nut–roller interface for the four installation modes.

Efficiency of Roller–Screw Mechanisms

The efficiency of roller–screw mechanisms in forward motion is analyzed as a function of significant parameters. A proposal is made for the synthesis of frictionally stable roller–screw mechanisms with the required kinematic transfer function and maximum efficiency in forward motion.

An improved thermal estimation model of the inverted planetary roller screw mechanism

The inverted planetary roller screw mechanism has recently become competitive in the electro-mechanical actuation system due to its high load-carrying capacity and small assembly size. However, a significant amount of heat at the frictional contact interfaces and power loss inside the electrical machine can be naturally generated in a compact and high-load inverted planetary roller screw mechanism system. The conductive heat leads to the temperature rise of inverted planetary roller screw mechanism components that subsequently results in thermal drift and error as well as the actuation accuracy degradation. An analytical approach is applied to calculate the friction torque of the contact pairs and support bearings in the inverted planetary roller screw mechanism system. As the thermal load, heat generation is derived from the friction in nut-roller-screw section and bearings. Then, the heat generation and convection boundary conditions are formulated to facilitate thermal behavior analysis. Finally, using the finite element method, steady-state and transient thermal-mechanical coupling analyses are performed to estimate the temperature distribution and thermal expansion of the inverted planetary roller screw mechanism components. Computational results reveal that operating conditions of rotation speed and external load have significant influence on the thermal characteristics of the inverted planetary roller screw mechanism. This study can serve as a foundation for modeling temperature field and analyzing coupled thermal-mechanical response of inverted planetary roller screw mechanism in electro-mechanical actuation system, which can be useful in determining thermal error compensation.

Development of Increased Load Capacity Structures of Planetary Roller Screw Mechanisms (Determination of Inter-axial Distance Increment)

One of the trends in development of mechanical engineering is that there is an inreasing load capacity of machines. For aerospace industry it is desirable to implement this increase without growing mass of an aircraft, which consists of aggregates, mechanisms, units and machine parts. Among the mechanisms, those that convert rotational motion into translational one account for a sizable proportion. The most promising of them are planetary roller screw mechanisms (PRSM). To increase the load capacity of the PRSM with the same mass is possible due to decreasing α angle of the turn profile of the threaded parts for these mechanisms (see the earlier published paper).The PRSMs have a number of features, one of which is the inequality of the helix angles of the screw and the roller in the contact area, because of which it is necessary to increase the inter-axial distance by increment value. In traditional PRSMs α=90º, and for them, as for a particular case with α=90º, the techniques to determine Δαw have been developed.For the general case, when α angle value is arbitrary (α<90° for increasing the load capacity), a technique to determine Δαw increment (see the second paper earlier published) and a technique for calculating dimensions of the PRSM main parts and their tolerance bands have been developed (see the third paper earlier published), in which Δαw increment is used. Hence, this increment is a key parameter. To determine Δαw a numerical method and a computer calculation program have been developed.This paper presents numerous results of Δαw increment computer calculation according to the developed technique. The Δαw increment value calculated by the developed technique has coincided with Δαw increment value, which was determined for traditional PRSM with the angle α=90º.The paper analyses an effect of various structural parameters on Δαw increment value. It has been found that the radius by which a profile of the roller turns is circumscribed essentially has no effect on Δαw value.The α angle of the profile of turns and the thread pitch of the PRSM parts significantly affect the Δαw value. The paper presents the graphs constructed to determine the coordinates of the point of initial contact of the mating thread turns of the screw and the rollers as well as the graphs to determine the distance from the point of initial contact to the edge of the turn of the screw and the roller. All the information presented can be used to design the PRSMs, including those with increased load capacity.

Kinematic Model of Planetary Roller Screw Mechanism With Run-Out and Position Errors

A kinematic model of the planetary roller screw mechanism (PRSM) is proposed, which accounts for the run-out errors of the screw, roller, nut, ring gear, and carrier, and the position errors of the nut and the pinhole in the carrier. The roller floating region, which contains all the possible positions of the roller inside the pinhole, is obtained by analyzing the axial clearances between mating thread surfaces and the radial clearance between the roller and carrier. The proposed model is based on the constraint that the set of roller floating region is not empty. Then, the additional rigid-body movement on the nut is derived and the path of motion transfer from the screw to the nut is obtained. According to the fundamental property of rigid-body kinematics, the axial velocity of the nut is derived and the transmission error of the PRSM is calculated. The proposed model is verified by comparing the calculated transmission error with experimental one. The results show that the transmission error of the PRSM with run-out and position errors is cyclic with a period corresponding to the rotation period of the screw and the magnitude of the transmission error can be much larger than the lead error of the screw. Besides, due to the run-out and position errors, the roller can move radially or transversally inside the pinhole of the carrier when the elements in the PRSM are regarded as rigid bodies.

A nonlinear six degrees of freedom dynamic model of planetary roller screw mechanism

A nonlinear six degrees of freedom (DOFs) dynamic model to determine the motion and internal forces acting on the moving parts of the planetary roller screw mechanism (PRSM) is proposed in this paper. A load distribution coefficient is assumed and introduced to describe the load distribution among threads of the screw, roller and nut. The friction forces at the screw-roller, nut-roller and ring gear-carrier interfaces are calculated by using the Coulomb friction, rolling contact and Couette flow principles, respectively. Because the friction and contact forces acting on the screw, roller, nut and carrier constitute a spatial force system, the equations of motion for the PRSM, which are derived by using Newton's second law, relate the forces to the six DOFs of those parts. The transient and steady-state behaviors of the PRSM under a heavy or light external load and the sinusoid motion of the mechanism are simulated and discussed. The results show that the load conditions have great influence on the motion and internal forces of the PRSM.

Bond graph-based dynamic model of planetary roller screw mechanism with consideration of axial clearance and friction

To reveal the dynamic characteristics of planetary roller screw mechanism, a dynamic model of planetary roller screw mechanism is developed in this study, which is based on the bond graph theory that accounts for friction, axial clearance, and screw stiffness. First, the bond graph models of friction, axial clearance, and load distribution are presented. Then, a bond graph model of the entire planetary roller screw mechanism for the dynamic analysis is established using the 20-sim software package, and the dynamic equations are solved using the Runge–Kutta–Fehlberg algorithm. Finally, the axial speed, axial acceleration, and contact force of the components are derived under different axial loads and with different axial clearances. Furthermore, the dynamic friction characteristics at different angular velocities of the screw and the dynamic stiffnesses for different axial clearances are also obtained. The results can provide a theoretical basis for planetary roller screw mechanism design with consideration of dynamic characteristics.

Планетарный роликовинтовой механизм преобразования вращательного движения в поступательное с фасонными роликами

Планетарный роликовинтовой механизм преобразования вращательного движения в поступательное с фасонными роликами

A General Case to Determine Dimensions and Their Tolerance Zones for the Thread Parts of Epicyclic Roller-Screw Mechanisms

A General Case to Determine Dimensions and Their Tolerance Zones for the Thread Parts of Epicyclic Roller-Screw Mechanisms

Vibration decrease of electromechanical actuators based on roller screw mechanisms

The reduction of the vibratory activity of the roller screw mechanism (RSM) for converting a rotational movement into a translational movement is discussed. A mathematical model of vibratory activity roller screw mechanisms on the basis of elastic compliances was developed. The resulting equation for calculating the natural frequencies of the basic RSM elements – screw, rollers and nut was obtained. It is proved that the RSM has a low vibroactivity that allows you to create mechatronic actuators, the maximum level of vibration does not exceed 60 to 62 dB, which is 11-16 dB below the level of vibratory activity gear mechanisms.

Meshing Properties of Planetary Roller Screw Mechanism within Misalignments

Meshing Properties of Planetary Roller Screw Mechanism within Misalignments

A Methodology of Designing the Teeth Conjugation in a Planetary Roller Screw

Abstract The paper presents the methodology for designing the teeth conjunction of planetary gears in the planetary roller screw mechanism. A function of the planetary gears is to synchronize an operation of rollers in order to avoid axial displacements. A condition of the correct operation is no axial movement of rollers in relation to the nut. The planetary gears are integral parts of rollers and therefore an operation of the gear transmissions has a direct impact on cooperation of the screw, rollers and the nut. The proper design of gear engagements is essential for reducing slippage on surfaces of the cooperating threaded elements. For this purpose, in a designing method, both the limitations of operation and kinematic conditions of rollers’ operation have to be taken into account.

A Comprehensive Contact Analysis of Planetary Roller Screw Mechanism

A comprehensive contact analysis model to determine the contact positions and clearances of mating thread surfaces in the planetary roller screw mechanism (PRSM) is proposed in this paper. By introducing a three-dimensional clearance vector, the modified conditions of continuous tangency of mating surfaces are established, in which the clearances along all the directions and contact positions of an arbitrary pair of mating surfaces can be calculated. The deviations of the screw, roller, and nut from their nominal positions are considered in the transformation matrices, which describe the position relations of the screw, roller, and nut. Then, the equations of thread surfaces with deviations are derived. Using the modified conditions and the equations of surfaces, the meshing equations at the screw–roller and nut–roller interfaces are derived to compute the clearances along all the directions and contact positions of mating thread surfaces on each pair of thread teeth in the imperfect PRSM. The effectiveness of the proposed model is verified by comparing the contact positions at the screw–roller interface with those from the previously published model. Then, the effect of the direction of clearance vector on the clearances and contact positions is analyzed and discussed. Because of the roller deviation, the clearances between multiple pairs of thread teeth are no longer identical, and the contact positions of a pair of mating thread surfaces on different pairs of thread teeth are different. Also, the parameters of a PRSM without clearances can be obtained from the proposed model in the design process.

Load distribution of planetary roller screw mechanism and its improvement approach

A model of load distribution over threads of planetary roller screw mechanism (PRSM) is developed according to the relationships of deformation compatibility and force equilibrium. In order to make the applied load of PRSM uniformly distributed over threads, an improvement approach is proposed, in which the parameters of thread form of roller and nut are redesigned, and the contact conditions of roller with screw and nut are changed to compensate the axial accumulative deformation of shaft sections of screw and nut. A typical planetary roller screw mechanism is taken as example to analyze the load distribution, and the effects of installation configurations, load conditions and thread form parameters on load distribution are studied. Furthermore, the improvement approach is applied to the PRSM, and it is proved to be beneficial to reach uniform load distribution over threads.

On the Effect of Thread Turn Profile Angle of the Planetary Roller-Screw Mechanism Parts on Their Basic Parameters

One of the most important trends in mechanical engineering development is the constant improvement of load capacity of machines, mechanisms, units and parts without increasing their overall dimensions and weight. This is also true for today’s most prospective planetary rollerscrew mechanisms (PRSM) converting motion from rotary to linear type. The problem of PRSM load capacity improvement deserves more attention, because these mechanisms have very high performance characteristics, which leads to problems in the choice of support devices for these mechanisms. However, for many mechanical engineering industries it is important to decrease the PRSMs weight and dimensions, or to improve their reliability and durability. This has led to finding the reserves for improving the PRSM load capacity by decreasing the thread turn profile angle, α, of PRSM threaded parts, as compared to α = 90° in traditional mechanisms. When PRSM calculation methods were developed, it was decided to use α = 90° for transforming the mechanism parts into a physical model and a design pattern. It allowed us to reduce the PRSM designing to well-known roller bearing designing based on very extensive experimental data. Proposed PRSM designs do not contradict to accepted physical models and design patterns – they just have different basic characteristics of PRSM, i.e. static and dynamic load ratings. Proposed PRSM designs with a thread turn profile angle α=70° on their parts allow to increase the load capacity by 15%, as compared to traditional PRSMs, which have threaded parts with a thread turn profile angle α = 90°. There are two factors, which can improve the PRSM load capacity. The first one is the decrease of normal force between mating thread turns of a screw and a roller with the same operational axial force. The second one is the increase of the radius of the shaped profile of a roller thread turn resulting in the expansion of the contact area pattern between the mating thread turns of a screw and a roller. The first factor dominates here. For implementing the proposed PRSM designs into production, one has to explore additionally the effect of α-angle on linkage parameters, process requirements and specific features of the initial contact between the mating thread turns of a screw and a roller.