Ball Screw Nut Research Articles

Modeling of Ball Screw–Nut Interface Stiffness With Wear (Ball Screw Wear Dynamics)

Abstract The effects of wear, preload loss, and missing balls on the dynamics of ball screw drives in machine tools are modeled and incorporated into the finite element model of the drive assembly for condition monitoring. The contacts between the ball–nut and ball–screw are modeled using Hertzian springs, whose stiffnesses vary as a function of the worn contact area. These contact stiffnesses are then transformed to the finite element nodes on the nut and screw. The frequency response functions at the motor shaft and table, which can be measured by commercial computer numerical control (CNC), are predicted for various faults at different positions of the table. The experimentally validated model demonstrates that the faults primarily affect the first coupled torsional-axial mode of the ball screw drive and can be utilized for automated condition monitoring of ball screw drives.

Influence of Nonlinear Characteristics of Planetary Flywheel Inerter Actuator on Vehicle Active Suspension Performance

The planetary flywheel can significantly reduce the weight of the flywheel, allowing the inerter to be lightweight. When a planetary flywheel ball screw inerter-based active actuator is used in a vehicle suspension system, the nonlinear features of the actuator affect vehicle performance. The planetary flywheel inerter actuator’s nonlinear dynamic model is constructed in this study based on the dynamic features of the planetary flywheel ball screw inerter and the electromagnetic torque generating mechanism of the permanent magnet synchronous motor. The impact of ball screw–nut friction, transmission clearance, planetary gear friction, and gear backlash on the performance of an active tuned inerter damper suspension is then investigated. As a result, the impact and sensitivity of numerous nonlinear parameters on suspension performance are shown, providing a theoretical foundation for the design of planetary flywheel inerter actuator and active inerter suspension.

Design and Analysis of the Mechanical Structure of Land-Air Logistics UAV

In the post-epidemic era, drone distribution has attracted increasing public attention because of its excellent contact-free characteristics and capacity to greatly improve the efficiency and reliability of material distribution. Combining land-air drones with logistics distribution, this design breaks through the limitations of the single-movement ability of traditional drones and land robots to fly in the air or move on the ground. Based on the collection and statistics of technical indicators related to logistics distribution, this paper focuses on the design of land-air conversion mode, and proposes an innovative land-air conversion mechanism composed of ball screw nut pair and multiple sets of gears to complete the design of the related mechanical structure of land-air logistics UAV. In addition, the mechanical system simulation of drones is carried out by ADAMS software. Moreover, the static and aerodynamic simulation analysis of UAVs is conducted by ANSYS software to optimize the overall structure.

Calculation of the Heat Flux from a Ball Screw Nut to the Nut Raceway

In the field of precision machining, temperature fluctuation tends to cause the most significant machining errors. In particular, heat, which is generated in the nut of the ball screw feed system during movement, can deform the screw shaft significantly. In order to calculate and evaluate the thermal deformation of the ball screw shaft, the rate of the heat transfer from the nut to the screw shaft must be known. This rate can be calculated by subtracting the heat transfer rate to the nut raceway from the heat generation rate of the nut. Hence, it is necessary to calculate the heat flux from the nut to the nut raceway. This paper introduces a novel method to calculate the heat flux from the nut to the nut raceway. The new approach also enables calculations for different operating conditions. Furthermore, an experimental setup is established to measure the temperature increase, from 0 to 180 s after the nut starts moving, for various operating conditions. It is then theoretically shown that the 0–180 s temperature increase/heat flux curves for the nut are “universal”, i.e., the curve remains unchanged for the different operating conditions. Subsequently, a thermal model using the finite element method (FEM) is developed to simulate the nut temperature increase over time, which is then compared with the experimental data. As a result, it becomes possible to determine the heat flux from the nut to the nut raceway and calculate the 0–180 s temperature increase/heat flux curve (ΔT˜0~180s,Training Data) for the training group. Finally, the heat flux from the nut to the nut raceway is calculated for ten different operating conditions in the test group using the 0–180 s temperature increase/heat flux curve of the training group (ΔT˜0~180s,Training Data). The corresponding temperature curves are then calculated by inputting the values of the heat fluxes into the FEM model. The highest root mean square error (RMSE) between the calculated and experimentally measured temperature increase was 0.16 °C for Test 7 (the error was 10.7%). This result indicates that the new method is valid and feasible for calculating the heat flux from a ball screw nut to the nut raceway.

On-Line Monitoring Shaft Misalignment of Feed Drive Systems Based on Time-Domain Shaft Rotating Holospectrum

Detection of early-stage misalignment of the ball screw in feed drive systems is the topic addressed in this study. The triaxial vibration amplitudes and phases of a rotating ball screw at the ball screw nut were extracted using the Vold–Kalman filtering order tracking (VKFOT). The rotating ball screw locus at the rotation speed and its multiplier in the time domain were then constructed to obtain corresponding holospectra. By using a self-organizing map, the features corresponding to various holospectra were extracted and quantified into metrices as a measure signifying the severity of ball screw misalignment. Experimental results indicated that the proposed method effectively detected the ball screw misalignment even though this misalignment was less than 30 μm in size. The experiments conducted in this study demonstrated the high sensitivity and effectiveness of the proposed method, which also has a clear advantage due to its simpler instrumentation compared with traditional accelerometry.

Virtual Sensor for Accuracy Monitoring in CNC Machines

Vibrations are limiting the productivity and the process quality of cutting machine tools. For the monitoring of these vibrations, often external sensors, such as acceleration sensors, are used. These external systems require additional cost and maintenance effort. This paper presents a virtual sensor, which is capable of detecting vibrations at the tool center point, based on internal machine data. External sensors are only necessary once for model identification. This reduces the overall cost of the system significantly. The virtual sensor uses the high-quality data of the linear position encoder near the ball screw nut and calculates the vibrations at the tool tip by using transmissibility functions. This paper explains the theory behind the used transmissibility functions and describes how they are measured, by comparing different experimental approaches to identify the modal parameters of cutting machine tools. After the identification of the sensor, a dynamical test cycle is used to prove the physical correctness.

Thermal Characteristics of a Vertical Hydrostatic Guideway System for Precision Milling Machine Applications

This paper investigates the thermal characteristics of a vertical guideway system for precision milling machine applications by considering three heat sources, namely motor heat, viscous shearing heat of hydrostatic bearings, and friction heat from a ballscrew nut. A finite element (FE) model using ANSYS/Fluent was used to simulate the thermal characteristics of the system by considering the oil film friction of the hydrostatic bearings in the operational feed speed and heat generation in the ballscrew nut. Eight K-type thermocouples were installed in the vertical hydrostatic guideway system to measure the temperature rise in the key components. Nine thermal experiments of the vertical hydrostatic guideway system under three operational feed rates, namely 1.25, 2.5 and 5 m/min were conducted to measure the temperature of seven thermocouples in practical running conditions. The experimental temperature data then was used to adjust the FE model setting to guarantee the accurate prediction of the thermal deformation in real operational conditions. The FE model of the vertical hydrostatic guideway system built in this study can be used to predict the thermal deformation of worktable at center point at any running conditions. At a sliding feed rate of 1 m/s, the thermal positioning error of worktable at center point was 0.1539 µm in the X direction, 0.0009 µm in the Y direction and 2.0246 µm in Z direction.

基于无人机的复杂地理环境植物采样系统研究

Aiming at the difficult problem of contact sampling of plant in complex geographical environment, a remote-controlled sampling method using an Unmanned Aerial Vehicles (UAV) is proposed. After configuration, mechanism parameter analysis & optimization, and dynamic analysis, a special lightweight sampling manipulator that integrates plant stem-and-leaf sample capture, cutting and storage is designed. The designed sampling manipulator is composed of a ball screw nut transmission pair and a symmetrical double-offset slider rocker. The minimum transmission angle of the rocker is 63.435°, the maximum opening displacement of the manipulator claw is 131 mm, and the cutting pressure is 226 N. Tests and experiments show that the sample manipulator has a mass of 2.35 kg, a cutting pressure of 214 N, and a maximum open displacement of the manipulator claws of 126 mm. It can be controlled locally or remotely using a UAV to grab, cut and storage plant samples with a diameter greater than 5 mm. The reliability of the sampling manipulator design and the feasibility of the sampling method are verified.

Influence of the ball screw stiffness on the positioning accuracy of the CNC machine tools

This work is researching the ball screw stiffness influence on the positioning accuracy of the feed kinematic linkage of a CNC machine tool fitted with an indirect type measuring system for positioning the moving element. Because the machine tool is equipped with an indirect measuring system, backlashes and elastic deformations in the kinematic linkage cannot be offset by the position loop, consequently these are directly affecting the positioning accuracy. In this context, methods are used for diminishing their influence as well as compensation methods with a view to improve the positioning accuracy. Ways to preloading the ball screws and bearings of the ball screw are presented as well, by focussing on the optimisation, through calculations, of the preloading force value. An important component, analysed in this work, consists of the research of the ball screw–nut stiffness that depends on the strategy being used on the axial bearing of the two ends of the ball screw. The experimental tests have been performed at idle running on the CNC milling machine (CPFH 500), fitted with three controlled axes (X, Y and Z). Based on the experimental results, it may be noticed that, once increased the ball screw stiffness, within the limits stated by the ball screw supplier, the positioning accuracy will increase as well.

Rigidity Evaluation of Support Bearings and Ball-screw Nut under Practical Condition

Rigidity Evaluation of Support Bearings and Ball-screw Nut under Practical Condition

Examining the misalignment of a linear guideway pair on a feed drive system under different ball screw preload levels with a cost-effective MEMS vibration sensing system

This paper presents an innovative and cost-effective scheme for examining on line the degree of misalignment of a pair of linear guideway rails in a feed drive system. Prototype MEMS-based vibration detection modules were constructed and installed on the ball screw nut and linear guideway block. The ball screw preload was adjusted with four settings by changing ball sizes in this feed drive system. For each preload setting, a linear guideway rail was adjusted using feeler gauges to produce 11 misalignment statuses. The y-axis deviation caused by misalignment along the feed direction (x-axis) was measured with a dial gauge. For each preload and misalignment setting, the vibration signal was ascertained from the installed detection modules while the work table was driven by the controller. By analyzing the vibration signals from the detection module on the linear guideway block, we found that the characteristic frequency in a specific spectrum band could be used as a misalignment index. The characteristic frequencies exhibited a descending trend when the deviation was less than 40μm and an increasing trend when the deviation was 40–120μm. These findings demonstrate the feasibility of using cost-effective sensing units to examine the parallelism or distinguish the deviation between the linear guideway rails without disassembling the work table. This could be valuable for machine intelligence applications in the automation industry.

Stanowisko pomiarowe do wyznaczania charakterystyk zespołu śruba–nakrętka toczna podczas jego obciążania

Stanowisko pomiarowe do wyznaczania charakterystyk zespołu śruba–nakrętka toczna podczas jego obciążania

Issue of Rigidity of the Ball Screw Nut Exposed to Bending Stress during Bending Stress of the Ball Screw

Ball screws and nuts represent the inseparable part of machinetool building. The thread lead accuracy ranges in hundredths of millimetres per 1 m. In addition to the undesirable phenomena caused by heat (dilatability) and, e. g., torsional and transverse oscillations, the bending stress of the ball screw is considerably undesirable too. This stress and at the same time behaviour are transferred to the bending stress of the ball screw nut. This has a very harmful influence on setting of the ball screws, when the machine tool is assembled. Using the analysis by means of the FEM method, the paper conducts a survey of deformation issue of the arrangement "machine – ball screw – ball screw nut" during the assembly stage as well as a survey of compensation possibilities and other technical measures determined to limit the undesirable deformations and stress of the ball screw originating already in the manufacturing stage of the machine tool.

Ontology-based coupled optimisation design method using state-space analysis for the spindle box system of large ultra-precision optical grinding machine

With the increasing complexity of mechatronic products, traditional empirical or step-by-step design methods are facing great challenges with various factors and different stages having become inevitably coupled during the design process. Management of massive information or big data, as well as the efficient operation of information flow, is deeply involved in the process of coupled design. Designers have to address increased sophisticated situations when coupled optimisation is also engaged. Aiming at overcoming these difficulties involved in conducting the design of the spindle box system of ultra-precision optical grinding machine, this paper proposed a coupled optimisation design method based on state-space analysis, with the design knowledge represented by ontologies and their semantic networks. An electromechanical coupled model integrating mechanical structure, control system and driving system of the motor is established, mainly concerning the stiffness matrix of hydrostatic bearings, ball screw nut and rolling guide sliders. The effectiveness and precision of the method are validated by the simulation results of the natural frequency and deformation of the spindle box when applying an impact force to the grinding wheel.

A macro–micro compensation method for straightness motion error and positioning error of an improved linear stage

This research developed a linear stage with improved structures for reducing the error sources and proposed a macro–micro compensation method for both the straightness motion error and positioning error. One improved structure saw flexible steel sheet joints used instead of a rigid plate between the slide and nut to reduce radial error caused by the ball screw nut; the other saw a fine adjustment mechanism used for adjusting the installation angle of the adjustable guideway to reduce parallelism error. A high-precision two-axis (X and Y) micro-stage driven by piezoelectric (PZT) actuator was installed on the improved linear stage (macro-stage), and then compensations for straightness motion error and positioning error were achieved by utilizing the compensation motions of the XY-micro-stage after the coarse motion of the macro-stage. Experiments on the improved linear stage were conducted to verify the effectiveness of the proposed methods. The results have shown that the straightness motion error of the slide was compensated from 1.61 μm/100 mm to 0.55 μm/100 mm, and the forward mean and reverse mean of the positioning error were respectively compensated from 3.05 μm/100 mm and 3.23 μm/100 mm to 0.69 μm/100 mm and 0.79 μm/100 mm.

Thermal characteristics of a CNC feed system under varying operating conditions

In high-speed and high-precision feed systems, thermal positioning errors are mainly caused by the non-uniform temperature variations and resulting time-varying thermal deformations under different operating conditions. The research presented here ultimately aims to develop a generic method capable of evaluating the thermal characteristics (such as temperature rise of heat sources, thermal positioning error) of the feed system induced by varying operating conditions (feed speed, cutting load and preload of ball screw). The thermal contact resistance between the balls and the inner and outer rings of supporting bearing is calculated using the Hertzian theory and JHM method. Experiments were carried out on a high-speed feed system experimental bench, and the influences of operating conditions on temperature rises of supporting bearings and ball screw nut were analyzed. Based on a WNN-NARMAL2 model, the relationship between temperature rise of supporting bearings and operating conditions was established. Furthermore, with the temperature of the ball screw nut set to be a moving heat source load, the temperature and thermal deformation distributions of the ball screw were simulated. The work described lays a solid foundation for thermal error prediction and compensation of a feed system under varying operating conditions.

The Study of Thermal Raising and Transmission Torque of High Speed Ball-Screw Lubricated by Different Greases

Ball screw is a high-precision and high performance linear drive of mechanical elements. The frictional heat of internal components what is very significant impact for platform transmission in high speed and the high axial load and causes the thermal expansion of element. In this research , the influence of different greases on ball screw is investigated in thermal rising of nut and driving torque in high speed and high axial load. A vertical motion platform was used for driving performance test. Thermal rising of nut of ball screw and the variance of transmission torque whose lubricated by high viscosity base oil grease is significant larger than the lower one. High viscosity grease is not easy to carry out the friction heat generated at ball and raceway contact area due to the bad flowing properties. It also has more serious wear occurred at contact area and high friction force, whose causes the large variance of transmission torque.

Temperature distribution and thermal error prediction of a CNC feed system under varying operating conditions

In high-speed and high-precision feed systems, the thermal errors are mainly caused by the non-uniform temperature variations and time-varying thermal deformations under different operating conditions. The research work undertaken herein ultimately aims to develop a generic method which is capable of evaluating the temperature rises of heat sources (such as supporting bearings and ball screw nut) and thermal positioning error of the feed system induced by varying operating conditions (feed speed, cutting load, and preload of ball screw). Experiments were carried out on a high-speed feed system experimental bench, and the influences of operating conditions on temperature rises of supporting bearings and ball screw nut were analyzed. Based on wavelet neural network and NARMA-L2 model, the relationship between temperature rise of supporting bearings and operating conditions was established. Furthermore, with the temperature of ball screw nut set to be a moving heating source load, the temperature and thermal deformation distributions of ball screw under bearings and ball screw nut heat sources were simulated. The experiment and simulation results show that the recommended modeling method can be used to predict thermal positioning errors of feed system with good accuracy. The work described lays a solid foundation of thermal error prediction and compensation in a feed system under varying operating conditions.

A New Electric Drive System for a Disc Brake System Used in the Vehicle, Experimental Stand

Papers present a new solution for achieving downforce to a brake disc, using a drive gear and ball screw-nut, which the construction adopted, allows moving ball-screw and making the necessary downforce for breaking. The stand includes downforce creating system required by deceleration, and is equipped with a plurality of sensors to determine the following parameters. Measurement of downforce-ring load cell, displacement in the running drive-pressure transducer, mechanism decoupling travel-differential inductive transducer, electrical motor and gear drive mechanism speed-speed transducer, and electric drive motor torque-lamellar load cell. These transducers allow the control of screw ball to realize the forces that are acting on the brake linings in order to control the speed of the vehicle. Using this construction, brake actuation can get higher quality reactions in brake systems.

Resource-efficient Ball Screw by Adaptive Lubrication

In this paper, the development of a methodology for reducing the energy demand and increasing the life time of ball screws by minimizing the friction torque with adaptive lubrication of the ball screw nut is presented.Therefore, a simulation model of the feed axis has been developed and fitted metrologically at an especially designed test stand with an adaptive lubrication system for the ball screw nut. The model allows the calculation of the optimum friction torque of the feed axis and thus determines the need for lubricants in case a deviation to the measured friction torque of the feed axis should arise.The comparison of tests dealing with the life time of ball screws with standard lubrication and new adaptive lubrication aims at proving the increase of the life time. This endeavor will result in characteristic lubrication strategies for a resource-efficient operation of ball screws during constant operating conditions.