Roller Screws Research Articles

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.

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.

Wear Prediction Method of Differential Planetary Roller Screws Considering the Ambient Temperature Variations

As a key component in fields such as high-precision machine tools, aerospace and weaponry, the thermal deformations in a differential planetary roller screw (DPRS) caused by the changes in ambient temperatures can lead to uneven load distribution and increased wear, which can seriously affect its transmission accuracy, efficiency, and service life. Therefore, the temperature rise of a DPRS at different ambient temperatures was studied using the block thermal network method, and the thermal deformations were calculated. A load distribution model of DPRS considering thermal deformation was developed, and a wear prediction method combined with surface roughness was proposed. The results show that the increase in ambient temperature has an obvious negative effect on the load distribution and wear depth of DPRS. Moreover, the DPRS temperature rise, load distribution and wear depth dramatically change with the variation of parameters such as load, speed and thread pitch. A DPRS durability test device that considers changes in ambient temperature was developed. Experiments with temperature rise and DPRS wear under different ambient temperatures were conducted to validate the theoretical analysis model.

Diagnostics of actuation system by Hadamard product of integrated motor current residuals applied to electro-mechanical actuators

The paper presents diagnostics methodology that can identify the event of occurrence of fault in the actuator or the linkage system of the flight control actuation system driven by Linear Electromechanical Actuators (LEMA). The standard data analysis like motor current signature analysis (MCSA) is good at identifying the incipient faults within the elements of the actuators in situations where-in the actuators are driving control surfaces. But in back driven cases, where-in LEMA is driven back by control surfaces, the faults outside the LEMAs are difficult to be detected due to higher mechanical advantages of transmission elements like roller screws, gear train and linkage arms scaling down their effects before reaching the motor. One such event occurred in a ground test, wherein the jet vanes were sheared when back driven by excessive gas dynamic forces. Neither the motor current nor the LEMA position feedback data has any clue of the instance of occurrence of such shearing. The case study is discussed in detail and diagnostics solution for such failures is proposed. A new methodology to pin point the event of occurrence is arrived at based on ground static test data of four independent channels. The same is reassured for its applicability using lab experiments on three samples mimicking the failure. The method's applicability is also extended for extracting events in actual flight, by comparing the flight telemetry data with the mimicked lab level (dry runs) data. The methodology uses the analysis of LEMA motor current data to arrive at the vital diagnostic information. The current data of LEMA directly cannot be interpreted due to non-stationary nature arising from variable speed and its pulsating form because of the pulse width modulation (PWM) switching, threshold voltages and closed loop dynamics of the servo. Hence the motor current is integrated using cumulative trapezoidal method. This integrated data is spline curve fitted to arrive at residuals vector. The Hadamard product is used on the residuals vector to amplify the information and suppress the noise. Further, normalizing is done to compare data across tests and samples. With this, necessary diagnostic information was extracted from static test data. The method is extended for extracting diagnostics information from actual flight using comparison analysis of, the test data in actual environment with mimicked lab level dry runs. It is also verified for applicability in faults directly driven by actuators in lab level experiments on three samples.

Development and studies of new rolling screw-type mechanisms

One of the tendencies in mechanical engineering is the transition from sliding friction to rolling friction in part joints moving under load, motor assemblies and machinery. For the present time, planetary roller screws (PRS), which are rolling mechanisms, possess the biggest potential as converters of rotational motion to linear motion. However production of high-precision parts for PRS requires special expensive equipment. The emerging world tendency for reduction of technological costs is to develop nutless roller screws (NRS), which is the most complex PRS part to manufacture. Its production requires an additional machine tool or a universal grinding machine for external and internal grinding. The new rolling NRS has been developed in line with this tendency. This paper focuses on the design and operation of the mechanism and on theoretical studies. A test model and a testing rig have been developed to confirm the results of the theoretical studies and to determine operation parameters of the new NRS. The experiments showed that the newly developed NRS loses to PRS in some parameters, while outperforming it in other. It is also simpler and cheaper to produce and after additional studies and tests rational applications for the newly developed NRS can be found.

Design and bearing characteristics of planetary roller screws based on aerospace high-load conditions

Under the background of the rapid development of today’s aerospace industry, the bearing characteristics of planetary roller screw drive under high overload conditions are studied. Designing a high-load, high-performance precision planetary roller screw drive is of practical and significant. An axially spaced RV type planetary roller screw with a single nut is designed under aerospace conditions. Under the conditions of the aerospace working load and efficiency, the parameters and structures of the planetary roller screw are completed. Based on this, the bearing characteristics of the planetary roller screw are studied and the equivalent finite element model of the planetary roller screw is analyzed. Those analyses include stress and strain, elastic–plastic properties, transmission efficiency, and dynamic load capacity. The results show that the design of planetary roller screw meets the design requirements for aerospace conditions. And the results can provide a basis for the design and manufacture of planetary roller screws under high loads.

Electro mechanical linear actuator using roller screws

Electro Mechanical linear Actuators as the name suggests are linear actuators operated by electric motor. The linear motion is desirable to drive a high inertia weapon system in elevation axis. In this paper, design and development aspects of an Electromechanical linear actuator using Roller screw has been attempted. Initial Comparison with ball screw drive suggests that roller screws are favorable for high dynamic load application. Selection and functional parameters of roller screw had been evaluated to optimize the linear actuator based on roller screw. This paper studies in detail the design aspects of an electromechanical linear actuator. The variation of different parameters with respect to Lead of the roller screw has been studied.

An efficient method for analyzing the roller screw thread geometry

The thread geometry and location of the contact points are the first steps in any study involving forces in the roller screw, yet most of the current literature makes restrictive assumptions and proposes methods which cannot be applied in the general case. The influence of profile shapes was only studied for standard roller screws and no method exists for the inverted type. Moreover, published general methods lack detail and can appear tough to apply from an engineering, practical point of view. In this paper, we propose an original model for the mechanism’s geometry which satisfies a double purpose: first, it is applicable to both standard and inverted roller screws and second, it is fast to compute and easy to implement. The shapes of our profiles are different from existing models and they are defined in the normal plane, which is more representative of the machine tool's point of view. All solids are assumed to be infinitely rigid. The proposed solution takes axial backlash into account and was optimized using a Newton-Raphson algorithm to provide results instantly. Finally, the model is compared with literature and we show how it can be used in the roller screw design process.

Mathematical analysis of the meshing performance of planetary roller screws applying different roller thread shapes

This article investigates the meshing performance of planetary roller screws applying rollers with circular, elliptical, and parabolic threads. A mathematical model is established for the thread su...

Speeds, lead and characteristic defect frequencies of arbitrary roller screws

For many applications with high demands on axial forces and rigidity roller screws are being increasingly relied on. Lead and dynamic behavior are two of the key criteria concerning the design and use of roller screws. The lead results from the interaction of the threaded profile and the kinematics of each element of the roller screw. While their kinematics has been studied in recent literature, a compact equation for calculating the lead of arbitrary roller screws is still missing. Furthermore, their characteristic frequencies, as they offer a tool for the purpose of condition monitoring within the scope of a vibration analysis, are still unknown. In the following work the derivation of calculation methods for the lead of roller screws with arbitrary geometries is presented. Applying these methods, the lead of common roller screw types is calculated. In addition to the calculation of the lead, the methods allow an analysis of kinematic properties. For the purpose of condition monitoring, the characteristic frequencies of roller screws are analyzed. Exemplarily, a typical envelope spectrum of an acceleration signal that has been acquired in radial direction on a roller screw nut in good condition is presented.

Synthesis of roller screws

The synthesis of screw gears with specified transfer function is considered. The theory, classification, and design of screw gears are discussed.

Development of a fiber daylighting system based on the parallel mechanism and direct focus detection

In this paper, a fiber optic daylighting system based on the parallel mechanism is designed and fabricated. This system is composed of 49 concentrating cells, which are arranged in a 7×7 array. The array consists of 48 sunlight-collecting cells and a sun position sensor using direct focus detection. A linear actuator, which is composed of two stepper motors and two roller screws, is used to drive the concentrating array to track the sun with the movement in a plane parallel to the plane containing the array of fiber optic collecting aperture. The solid angle of the sun tracking angle range for the concentrating cells is 4π/3 sr (covering 2/3 of the sky), satisfying the demand for 8h of tracking. This system is suitable for building integration because it has a compact and flat shape. The sun position sensor consists of photodiodes and a fiber array in the shape of a cross. The sun position sensor can directly measure the high flux density of the focus (2500 suns). A series of tests were performed using a lux meter and spectrometer to investigate the photometric characteristics of the system for a lightless underpass of 8.6m×4.2m×2.3m. The experiments show that the transfer efficiency of this system can reach 25% (with a 10-m long fiber). The luminous efficacy can reach 250lum/W, which is two times than that of natural light because the fiber can filter out infrared light. The experiments also verified the feasibility of the daylighting system using the parallel mechanism and a direct detection device for highly concentrated light.

Stiffness of the Roller Screw Mechanism by the Direct Method

In this paper, the direct stiffness method is used to construct a stiffness model of the roller screw mechanism. This method models the entire roller screw mechanism as a large spring system composed of individual springs representing the various compliances. In addition to predicting the overall stiffness of the mechanism, the direct stiffness method can calculate the distribution of load across the threads of the individual bodies. With the load on the individual threads known, the contact stresses can be calculated. This allows for a better understanding of the sensitivities of stiffness and contact stresses in the mechanism with various design parameters and can ultimately be used to design roller screws that are stiffer and with lower contact stresses.

Перспективные конструкции планетарных роликовинтовых механизмов

Перспективные конструкции планетарных роликовинтовых механизмов

Contact Kinematics in the Roller Screw Mechanism

This paper investigates the nature of the contact between the load transferring surfaces in the roller screw mechanism, i.e., between the screw and roller threads and between the nut and roller threads. The analysis is applied to both planetary roller screws and recirculating roller screws. Prior work has neglected to take a fundamental approach toward understanding the kinematics of the contact between these components and, as a consequence, detailed analyses of aspects such as contact mechanics, friction, lubrication, and wear are not correctly carried out. Accordingly, in this paper, the principle of conjugate surfaces is used to establish contact at the screw/roller and nut/roller interfaces. The in-plane angles to the contact points are derived and it is shown that for the screw/roller interface, the contact point cannot lie on the bodies' line of centers, as has been the assumption in previous papers. Then, based on the curved profile of the roller thread, the radii of contact on the roller, screw, and nut bodies are also derived. Knowledge of the contact point locations is necessary in order to understand the interaction forces between the key components of the roller screw mechanism. The principal radii of curvature at the contact points and the angle between the principal axes are also derived. Lastly, a brief example is developed showing how the developed theory may be used to design a roller screw for improved stiffness and decreased contact stresses.

A New Study on the Parameter Relationships of Planetary Roller Screws

As a more powerful transmission device, planetary roller screws (PRSs) recently have received more attention, compared to conventional ball screws. However, due to the complicated and unclear relationships among the PRS components’ parameters, it is difficult to design high‐quality PRSs. To facilitate the PRS design, a new study on the parameter relationships of PRS is conducted in this work. New models of the axial stiffness and the frictional moment of PRS are developed, and the relationships of the axial stiffness and the frictional moment in terms of contact angle, helical angle, and tooth number of the roller thread are investigated. This study could contribute to the research of PRS to improve its transmission performance, especially to increase its positioning accuracy.

Modelling approach for the simulation-based preliminary design of power transmissions

The promises of Model-Based Design have led to the development of numerous methodologies and software tools, especially for the specific or detailed design stages , from controller design to finite element analysis . However, the Model-Based Design of actuation systems lacks methodologies and expressive simulation models that are suited to preliminary design, where key technical decisions are taken considering various design alternatives and few available design details. In order to fill this gap, the present paper illustrates how scaling laws and acausal modelling can be used as a design tool, exploiting inverse simulation capabilities to evaluate technological alternatives quantitatively from limited design detail information. The application of the modelling approach is shown for two major components of mechanical transmission systems: roller bearings and ball and roller screws. The scaling laws presented are validated with manufacturers’ data. To conclude, the suitability of the proposed methodology is illustrated with the preliminary sizing of an electromechanical actuator for an aircraft primary flight control surface (aileron).

A comprehensive study on capabilities and limitations of roller–screw with emphasis on slip tendency

Abstract Transmission screw is a mechanism to convert the rotation into linear movement. Since sliding between screw and nut affects the motion accuracy, ball screws and roller–screws are used. Lead of a ball screw equals to screw pitch, which is usually in the order of millimeter while a roller–screw can present a wide range of leads. This paper comprehensively studies the capabilities and limitations of roller–screw and shows that large leads and extremely small leads are easily obtainable. The slip phenomenon has been studied regarding the forces acting on the roller during the rotation of screw. It is also shown for small leads between zero and pitch that the roller and the screw have inherent tendency to roll on each other with constant and stable lead. In addition, optimization of profile of threads has been studied. An investigation on the possible and permissible number of rollers around a screw has been carried out. The results of this study, confirmed by experiments, show that the roller–screw can be used for both fine and rough movement with flexible leads and desired accuracy.

Maintenance

The use of SKF roller screws is said to be helping Aviall Caledonian Engine Services Ltd, of Prestwick, one of the world's foremost aero engine overhaul companies, to reduce the turnaround time for engine rebuilds from 56 days down to just 35. The reliability, performance and predictability of the roller screws are proving to be a major factor in the company's development plans.

The U5.0 Undulator for the Advanced Light Source

The U5.0 Undulator, an 89 period, 5 cm period length, 4.6 m long insertion device has been designed, is being fabricated, and is scheduled for completion in early 1992. This undulator will be the first high brightness source, in the 50 to 1,500 eV range, for the Advanced Light Source at the Lawrence Berkeley Laboratory. A hybrid magnetic configuration using Nd–Fe–B permanent magnet material and vanadium permendur poles has been selected to achieve the field quality needed to meet performance requirements. The magnetic structure is modular with each half consisting of five assembly sections, which provide the periodic structure, and end structures, for entrance and exit correction, mounted on a steel backing beam. Each assembly section consists of 35 half-period pole assemblies bolted to a mount. The required 0.837 T effective peak field at a 1.4 cm gap has been verified with model measurements. Vertical field integral correction is accomplished with the end structures, each having an arrangement of permanent magnet rotors which will be adjusted to minimize electron beam missteering over the undulator operating field range. To reduce the effect of environmental fields, the steel backing beams are connected through parallel, low-reluctance, Ni–Fe hinges. The magnetic structure is connected through four rollernuts to the drive system that provides gap adjustment with an arrangement of roller screws, chain drives, a gear reduction unit, and a stepper motor driven by a closed loop control system. Magnetic structure and drive system support are from a 2.4 m high structure which includes a support base with four vertical supports. The vacuum chamber design is a two-piece machined and welded 5083-H321 aluminum construction of 5.1 m length. Pumping is with a combination of ion, titanium sublimation pump and nonevaporable getter pumps. Magnetic design, subsystem design, and fabrication progress are presented.