Planetary Roller Research Articles

Physics-informed and data-driven hybrid method for transmission accuracy design optimization of planetary roller screw mechanism

The planetary roller screw mechanism (PRSM) faces an ever-increasing precision transmission demand in current advanced equipment. The relationship between machining errors and transmission accuracy remains elusive due to the over-simplified physical models and small-sample experimental datasets. This work proposes a physics-informed and data-driven hybrid strategy for PRSM transmission accuracy evaluation and tolerance optimization. In the physical model, a PRSM transmission accuracy model is developed to calculate transmission error that considers 16 machining errors in eccentric, nominal diameter, pitch, flank angle, and roller consistency. In the dataset establishment, thread profile measurements and dynamic leadscrew inspections are conducted for the machining error and transmission accuracy data acquisition. A data augmentation approach combining the physical model with the generative adversarial network is utilized to predict travel deviation, variations, and axial backlash and estimate machining error contribution with the small-sample experimental dataset. It is firstly found that the roller consistency of nominal diameter significantly affects PRSM travel variation V2π with a 17.3 % importance value. With the developed framework, the key tolerances for screw, roller, nut, and roller consistency are optimized toward a typical precision transmission requirement using the non-dominated sorting genetic algorithm. It also provides a tolerance grade recommendation table with PRSM transmission accuracy level in engineering practice.

High-speed 50,000 rpm planetary roller reducer for electric vehicles: Design and transmission efficiency analysis

High-speed 50,000 rpm planetary roller reducer for electric vehicles: Design and transmission efficiency analysis

Fault diagnosis of planetary roller screw mechanism with a lightweight model based on federated learning

The fault data for Planetary Roller Screw Mechanisms (PRSM) is challenging to collect in real industrial settings due to the complex nature of practical operations and the lengthy accumulation period. Consequently, there has been little research on PRSM fault diagnosis. Additionally, the high processing cost of PRSM means that institutions are reluctant to make their fault data publicly available, creating a data barrier and further hindering research of the study on fault diagnosis of PRSM. To address these issues, Federated Learning (FL) is applied for PRSM fault diagnosis. In the FL framework, data remains in local storage, preserving data privacy. To reduce transmission costs, a lightweight model called SResNet18 is proposed. SResNet18 reduces parameters by 95.07 % and 61.93 % compared to ResNet18 and DSResNet18, respectively, which decreases the time needed for parameter uploading, model aggregation, and parameter returning. Additionally, SResNet18 has lower computational complexity, with 92.09 % and 36.66 % fewer FLOPs than ResNet18 and DSResNet18, respectively. Healthy and fault data of PRSM are collected on the PRSM testing rig, and the proposed method is evaluated. Results show that our method achieves the highest accuracy of 99.17 %, improving model performance while maintaining data privacy. The proposed SResNet18 also alleviates overfitting and reduces training time in the FL framework.

A comprehensive sliding wear prediction method for planetary roller screw mechanism

The thread-pairs wear has a significant role in the transmission accuracy, operational stability and service life of planetary roller screw mechanism (PRSM). Nevertheless, the previous literatures still lack the investigation on the wear evolution of roller, nut and screw. Hence, an accumulative wear depth (AWD) prediction model is proposed for PRSM with reciprocating motion. The presented model is validated by the measured wear phenomena of thread pairs and the experimental results in the literature. The equivalent sliding wear experiment of PRSM is designed and the sliding wear coefficient of PRSM material is obtained by the equivalent sliding wear experiment. Considering the thread profile error caused by AWD of roller, nut and screw, the load distribution (LD) and sliding velocities on screw-roller (SR) and nut-roller (NR) sides are calculated. More importantly, the interactions between the AWD, LD and sliding velocity are investigated. Furthermore, the effects of axial load on the AWD, sliding velocities in contact regions and load distribution coefficient are analyzed.

Study on calculation method for dynamic load distribution of thread pair of planetary roller screw mechanism

To reveal the dynamic load distribution characteristics of planetary roller screw mechanism under the high-speed operating conditions, based on the spiral surface equation and deformation coordination relationship, a static contact force calculation method of the roller-screw and roller-nut thread at the contact point is proposed, and a formula for calculating the contact angle after bearing is derived. On this basis, further considering the inertial force generated by using high-speed operation, a dynamic load distribution model for planetary roller screw mechanism thread was established. By comparing with the finite element contact model of planetary roller screw mechansim, the error is below 5%, which verifies the correctness of the model established. Finally, the influence of the parameters such as screw speed, axial load, pitch, and tooth flank angle on the distribution of dynamic load was analyzed. The results show that the inertia force causes the roller to have a tendency to move closer to the nut and away from the screw resulting in a decrease in dynamic contact force on the roller screw side and an increase in dynamic contact force on the roller nut side. The degree of uneven distribution of dynamic load is positively correlated with the screw speed and pitch, and negatively correlated with the tooth side angle. The size of axial load has a significant impact on the distribution of dynamic load.

A comprehensive analysis method of the performance degradation of planetary roller screws under the time-varying load and errors

Time-varying loads, manufacturing errors, and assembly errors are the main factors leading to the performance degradation of the planetary roller screw mechanism. This paper proposes a comprehensive analysis method for the performance degradation of the planetary roller screw mechanism caused by time-varying loads and manufacturing and assembly errors. Firstly, a simulation analysis model of the planetary roller screw mechanism was established and its effectiveness was verified. A quantitative analysis was conducted on the influence of manufacturing and assembly errors on the load distribution, revealing the load-bearing mechanism under the influence of errors. Secondly, loading experiments were conducted on the planetary roller screw mechanism, and the degradation of its load-bearing performance was divided into the normal degradation stage, the accelerated degradation stage, and the failure stage. The experimental results prove that the initial transmission accuracy has a significant impact on the degradation of the load-bearing performance, determining the occurrence of the node where the accelerated degradation stage appears in the load-bearing performance. Thirdly, the wear status of the threads and gears was examined, and the results showed that material peeling was the main factor causing the degradation of load-bearing performance.

Multi-objective optimization and accelerated experimental research on load distribution of planetary roller screw mechanism

Load distribution is a critical characteristic that determines the load carrying capacity of planetary roller screw mechanism (PRSM). First, a load distribution calculation model is established. Subsequently, a multi-objective optimization model to achieve uniform load distribution is constructed based on NSGA-II. Then, considering the optimization effect, machining feasibility and machining efficiency, the optimal load uniform distribution design method for linear thinning of thread thickness is determined using the analytical hierarchy process. Finally, an accelerated test method of PRSM load-bearing characteristics based on abrasive technology is proposed for the first time. The experimental results show that after optimization, the maximum contact width decreases by 12.5% and the fluctuation amplitude decreases by 74.6%, which significantly improves the uniformity of PRSM load distribution.

Performance-Degradation Analysis of the Planetary Roller Screw Mechanism under Multi-Factor Coupling Effects.

The performance-degradation pattern of the planetary roller screw mechanism (PRSM) is difficult to predict and evaluate due to a variety of factors. Load-carrying capacity, transmission accuracy, and efficiency are the main indicators for evaluating the performance of the PRSM. In this paper, a testing device for the comprehensive performance of the PRSM is designed by taking into account the coupling relationships among temperature rise, vibration, speed, and load. First, the functional design and error calibration of the testing device were conducted. Secondly, the PRSM designed in the supported project was taken as the research object to conduct degradation tests on its load-bearing capacity and transmission accuracy and analyze the changes in transmission efficiency. Third, the thread profile and wear condition were scanned and inspected using a universal tool microscope and an optical microscope. Finally, based on the monitoring module of the testing device, the vibration status during the PRSM testing process was collected in real time, laying a foundation for the subsequent assessment of the changes in the performance state of the PRSM. The test results reveal the law of performance degradation of the PRSM under the coupled effects of temperature, vibration, speed, and load.

Nonlinear dynamics of planetary roller screw mechanism.

The synchronous meshing of the gear pair and the screw pair is a typical feature of the planetary roller screw mechanism. In order to fully derive and analyze the nonlinear dynamic characteristics of the system, this paper creatively incorporates the time-varying meshing stiffness of gear pair and the comprehensive transmission error into the research content. Combined with the thread contact force and friction force between the roller and the screw and between the roller and the nut, the nonlinear dynamic model of the planetary roller screw mechanism considering the meshing excitation of the gear pair is established. According to the time domain diagram, frequency domain diagram, phase plane diagram, Poincaré section diagram, three-dimensional spectrum diagram, and spatial phase diagram, the nonlinear behavior of the system is described in detail, and the bifurcation evolution process of the system under the excitation frequency parameters of the external load is revealed. In addition, based on the theory of multi-scale method and considering the variables such as meshing stiffness, meshing damping, and load fluctuation, the stability equation of the primary resonance of the system is derived. The analysis of the stability of the system under different working conditions shows that the parameters are selected within a reasonable range, which effectively reduces the primary common amplitude value and enhances the overall stability of the system. The research content improves the previous system dynamics modeling method and provides a theoretical basis for the nonlinear dynamics modeling method and parameter optimization design of the planetary roller screw mechanism.

Studies on meshing clearance of thread pairs of planetary roller screw mechanism in different directions

The helix surface model of planetary roller screw mechanism (PRSM) is established by utilizing the parametric equations of space surface according to the structural features of screw, roller and nut. The helix surface model of PRSM is improved in consideration of the PRSM assembly relationship. The normal vector equations of helix surfaces are obtained based on the helix surface model. The meshing clearance models of PRSM in axial, radial and circumferential directions are built considering the movement direction of parts utilizing surface meshing conditions. The influence of structural parameters on the meshing clearance of PRSM is also analyzed. The results show that the meshing points between the roller and the screw in three directions are not in the middle diameter. The meshing points in the three directions of the roller and the nut are in the middle diameter of the roller. The pitch, tooth angle and tooth thickness of the thread all have an influence on the meshing clearance of PRSM. Only by increasing the tooth thickness of the thread can the meshing clearance in the three directions be reduced at the same time. The pitch and tooth angle should be selected properly to meet the practical requirements.

Reliability analysis of aerospace planetary roller screw mechanism considering multiple failure modes

Abstract Faults in planetary roller screw mechanisms under typical aerospace operating conditions are usually caused by the combined effects of multiple coupled failure modes. Reliability analysis methods that ignore correlation often lead to significant errors. In this paper, the failure models of the planetary roller screw mechanism under fatigue elastic failure, wear failure, and fracture failure are analyzed based on the stress-strength interference model, and failure functional functions are provided. The improved O. Ditlevsen second-order reliability bound theory is used to characterize the relationships between multiple failure modes. Using this method, reliability analysis and calculation of planetary roller screw pairs considering multiple failure modes have been performed, verifying the rationality and effectiveness of this method.

Kinematics analysis of planetary roller screw mechanism with misalignment

The misalignment is unavoidable for planetary roller screw mechanism (PRSM) in practical application due to many uncertainties. The misalignment has a strong effect on the kinematic characteristics of PRSM. However, the relevant research has been rarely reported in the past. In order to clearly present the motion characteristics, a novel kinematics model of PRSM with misalignment is established in this article. The rotational tensor theory is introduced to obtain the coordinate transformation equations. The position vectors of PRSM with misalignment are acquired to calculate the position of the contact point. The motion model of PRSM with misalignment is derived by analyzing the velocity of the contact point. Compared with some published literature, the kinematic model of PRSM is verified. Moreover, a relationship between the misalignment variates, which are the misalignment angle, the misalignment azimuth angle, and the offset distance of the nut's ending point, respectively, and the kinematic characteristics of PRSM are investigated. The results indicate that those misalignment variates have a great influence on the kinematics of PRSM and lead to fluctuations in the PRSM's transmission velocity and angular velocity ratio. The fluctuation amplitude of transmission velocity is positively correlated with misalignment angle.

Adapting the process conditions and performance in planetary roller melt granulation (PRMG) via the planetary spindle number

Continuous melt granulation with a planetary roller granulator is a new continuous method based on the orbital motion of planetary spindles driven by a rotating central spindle in a surrounding roller cylinder. Here the configuration of the processing section is a central design aspect, which defines the processing conditions and process performance. In this study, the number of applied planetary spindles as part of the module configuration was varied.As a result, a correlation between direct process parameters, processing conditions and process performance was identified. Hereby, the data normalization relativized successfully the effect of the module configuration. The results are also suitable to identify a module configuration and process settings in the context of a process optimization towards energy input efficiency or energy consumption. Finally, the accounting of the particle modification in terms of size was suitable to link the effect of the investigated parameters to the granulation regime.

Effects of Eccentric Errors on Sliding Velocity and Accumulative Wear Depth of Planetary Roller Screw Mechanism

Abstract The eccentric errors of planetary roller screw mechanism (PRSM) affect the contact kinematic characteristics and exacerbate the cumulative wear of thread pairs, which will reduce its transmission accuracy and reliability. Hence, it is significant to investigate the cumulative wear of PRSM with the eccentric errors. In this work, based on the conjugate surface contact condition and Archard wear theory, the sliding speed and cumulative wear depth of PRSM with eccentricity errors are modeled, respectively. The effects of eccentric errors on the sliding velocities and cumulative wear depth of PRSM are investigated. It has been determined that the eccentric errors of the screw and nut do not cause the sliding motion in the nut–roller contact region (NRCR). However, there are noticeable variations in sliding velocity and cumulative wear depth in the screw–roller contact region (SRCR). The eccentric errors of the screw and nut have a combined effect on the sliding velocity and wear between the screw and roller. This investigation and finding can provide a valuable reference for the processing and assembly of PRSM.

Kinematic analysis of inverted planetary roller screw considering skew error

To reveal the motion characteristics of inverted planetary roller screws under the influence of axial deviation error, the working principle of inverted planetary roller screws was elaborated, and a motion analysis model of inverted planetary roller screws based on deviation error was established. This paper analyzed the angle error, axial displacement error, and relative velocity error of the roller, and comprehensively analyzed the influence of errors and parameters on the motion state.

Impact of the spindle number on the material transport and mixing during planetary roller melt granulation

In comparison to the established twin-screw machines, the application of a planetary roller granulator for continuous operation of melt granulation is a promising alternative based on the unique process concept. An initial study focused on the material transport during processing as a key driver for the overall performance. Hereby, the impact of direct process parameters on the residence time distribution was the main objective.These investigations are complemented in this study by considering the free processing volume, which is defined by the number of planetary spindles applied within a module. The impact on the processing conditions is evaluated with respect to the process setting in terms of feed rate and rotation speed.The results highlight the potential of altering the underlying transport function in planetary roller melt granulation (PRMG) via the investigated direct process and equipment parameters. The impact of the feed rate is lower in comparison, while a higher rotation speed as well as a higher free processing volume promote material mixing. Moreover, a normalization of the determined residence time distribution (RTD) model data was feasible with respect to the process settings and the number of applied planetary spindles in the processing zone. This demonstrates the key role of the free processing volume in the fundamental mechanisms of material transport and mixing during PRMG.

FORCE ANALYSIS OF A PLANETARY ROLLER DRIVE TAKING INTO ACCOUNT THE CONTACT COMPLIANCE OF THE MATING THREAD TURNS OF ITS PARTS

The objects of study are planetary roller drives (PRD), which have high performance characteristics and are the most promising mechanical converters of rotational motion into linear motion. They are widely used as part of high-tech machines. Their design requires reliable force analysis. To do this, we need to determine the forces acting on the roller, which is an intermediate part between the nut and the screw. Several works provide approximate methods for the force calculation of the PRD, but in them, as an assumption based on similar calculations of machine parts, the distribution of the load between the roller thread turns interacting with the screw turns and with the nut turns is accepted. In this work, based on the fundamental principles of mechanics, using the necessary assumptions, a numerical method for determining forces is developed. These forces act in the PRD between the mating thread turns of the roller and the screw and between the mating thread turns of the roller and the nut, taking into account only one influencing factor – the momentum that overturns the roller. To implement this method, due to the very large amount of calculations, a computer program was developed. Usually, for force calculations of roller drives, the coefficient of uneven loading (Кн) of roller thread turns is introduced. For the control calculation of a PRD of standard size 20×8 with a four-thread screw and a length of the threaded part of the nut of 56 mm, Кн = 1.509, which is a very large value and shows the large influence of the overturning momentum on the load distribution between the roller threads. To determine the real unevenness of load distribution in the PRD, it is necessary to conduct further research that takes into account other factors influencing the uneven distribution of load in the PRD. In this case, the next most important factor is the uneven distribution of the total axial force between the rollers. This force is applied to the PRD from the actuator.

Understanding the Dynamics of Polymer Extrusion: Simulation of Thermoplastics Processing with Planetary Roller Extruders

Resource efficient processing of polymers is of paramount importance to minimize energy consumption, processing time, and material losses in the polymer industry. This study is concerned with polymer processing in planetary roller extruders. A three-dimensional numerical flow simulation was tailored to understand the polymer flow through the extruder in detail. Using the simulation software ANSYS Polyflow, we quantified both directly measurable process parameters, such as pressure build-up, and more intangible parameters, such as material shear. By varying operational and material parameters in a sensitivity analysis, we showed that the dynamics, material stress and pressure build-up are controlled primarily by the number of spindles and their rotational speed. Notably, this work provides the first successful validation of a 3D simulation of a polymer flow in a planetary roller extruder against actual experimental data. The simulation showed robust agreement between the simulated and experimental values, provided that a critical backpressure length is reached. This computational approach minimizes labor-intensive experimental testing in polymer processing.

Elastohydrodynamic lubrication analysis with eccentric errors for planetary roller screw mechanism

The lubrication characteristics of planetary roller screw mechanism (PRSM) with eccentric errors are investigated in this work. And the formulas of entrainment velocities with eccentric errors are derived. The film thickness and pressure distributions of screw-roller (SR) and nut-roller (NR) thread pairs are analyzed. It finds that the film thickness of SR thread pair is larger than that of NR thread pair. Moreover, the effects of eccentric errors on comprehensive meshing radius, entrainment velocities and lubrication characteristics of SR and NR thread pairs are discussed. The results show that the eccentric errors have significant effects on lubrication characteristics of PRSM.

Review on errors and transmission characteristics of the planetary roller screw mechanism

The planetary roller screw mechanism, a novel high-performance electromechanical servo drive component, holds a central position in leading-edge equipment, attracting significant attention within the engineering community. This paper conducts a comprehensive review of current research and recent breakthroughs in the analysis of errors and transmission characteristics associated with the planetary roller screw mechanism. Drawing on the unique attributes of this mechanism, the analysis of errors is undertaken from two distinct angles: motion errors and machining errors. A foundational examination of the bearing characteristics of this mechanism serves as the cornerstone for assessing its transmission properties. The report delves into the impact on transmission performance from the perspectives of both accuracy and efficiency. In this study, each model and related literature are exhaustively described and examined in detail. Furthermore, we critically evaluate the key discoveries emanating from various models and numerical simulations, shedding light on potential future directions in the realm of errors and transmission characteristics of the planetary roller screw mechanism.