Precision Ball Screw Research Articles

Development of lightweight precision ball screw shaft by swaging process

Development of lightweight precision ball screw shaft by swaging process

Design and Research of Test Bench for Loading and Performance Testing of Aerospace Precision Ball Screw

Aiming at the problem of insufficient research on the motion failure caused by the degradation of the grease of the precision ball screw pair under the typical working conditions of high frequency and high load in aerospace, a set of high frequency inertial loading test bench is designed. Loading and performance testing functions are integrated. The mechanical structure of the test bench, the inertia adjustment device and the connecting member of the pendulum rod are designed, which can simulate the loading under aerospace conditions. Installing multiple sensors can test the force response characteristics, vibration characteristics, temperature rise characteristics and transmission efficiency of the precision ball screw pair when it operates under different frequencies and different axial forces. The axial force of the nut with different rotational speeds under inertial load is tested by experiments.

Optimal operating condition of precision ball screws based on a transmission efficiency model

The operating condition of ball screws is generally applied to ensure the ball screws with a high transmission efficiency and a high positioning accuracy. Aiming at the optimal operating condition of double-nut ball screws, a transmission efficiency model considering the kinematic analysis and lubrication status was proposed. Firstly, the distributions of the film bearing pressure, asperity bearing pressure, film thickness, and ratio of the asperity bearing pressure were determined based on the Reynolds equation. Subsequently, the transmission efficiency model was established by calculating the friction coefficient and friction torque of ball screws under various lubrication statuses and operating conditions. The optimal operating condition of double-nut ball screws can be determined by estimating the transmission efficiency and lubrication status to improve the manufacturing quality. Finally, a friction torque test based on the simulated model was designed and implemented on a self-designed bed for validation of the proposed model. The comparisons showed that the experimental friction torque was consistent with the simulated friction torque, which verified the effectiveness and correctness of the transmission efficiency model. Results showed that the optimal operating conditions of the entrainment velocity and axial working load could ensure high transmission efficiency and a good lubrication status, which are of great reference to the green processing and manufacturing fields.

Reducing the Weight of Precision Ball Screw Shafts Using Drawing

In recent years, there has been a demand for lightweight shaft products to improve the tact time of equipment. Shaft products are stepped in order to use bearings at the shaft end. Therefore, drilling a hole in the center of a shaft product is not enough to reduce the weight of the product to ensure the wall thickness. Therefore, focusing on swaging technology, a type of drawing, we devised a weight reduction method in which both ends of a thin-walled steel pipe are plastically formed to form the shaft end and a structure with a large space inside is created. The thin-walled steel pipe is swaged to form the shaft ends, grooved with threads, heat-treated, and finished to produce a lightweight product. Calculation results show that the weight is 54% of that of the conventional product, a significant weight reduction. The allowable speed can be increased to 125% of the conventional product, which may contribute to an improvement in tact time. The prototypes manufactured by the drawing process showed no difference in appearance from the conventional product, and the measured weight was 55% of the conventional product, almost exactly as calculated. As a result of devising a weight reduction method using the drawing process and manufacturing a prototype, the possibility of significantly reducing the weight of a shaft product was seen. We will continue to evaluate the performance and life of the product in order to commercialize it.

Active coolant control onto thermal behaviors of precision ball screw unit

Being a critical factor affecting the motion accuracy of precision machine tools, structural thermal elongation of precision ball screw unit is generally caused by the comprehensive influence from heat generations of screw-nut pair/bearings and time-varying ambient temperature. To resist 2 thermal disturbances above to guarantee precisely the original length of screw shaft, an active coolant control strategy is proposed in this paper. This strategy is based on a premise hypothesis: For the slender and long tubular structure of screw shaft, the screw shaft temperature is approximately equal to its recirculating coolant temperature. The reason is that the intensive forced coolant convection is capable of eliminating screw shaft temperature rises caused by friction heat generations and ambient air convections. Based on this premise, screw coolant temperature can be consistently controlled by an active strategy, further to correct the thermal elongation of screw shaft. It can be experimentally verified that the thermal variations of machine positioning accuracy caused by the active coolant control strategy are not more than 10 μm, which are lower than traditional strategy. Besides, based on detected structural temperatures of precision ball screw unit, the theoretical model above is further proved to be reliable by FE simulation method.

Design of loading test bench for precision ball screw based on LabVIEW+PXI

In order to discuss the dynamic characteristics of the aerospace ball screw pair, the paper designs a loading test bench based on Labview+PXI platform and magnetic powder brake. The test bench can simulate the loading condition up to 10Hz. In structural design, magnetic powder brake is used to apply the loading force. In hardware design, the system is built by using upper-lower computer system architecture based on PXI bus. In software design, the program is written in LabVIEW, which mainly includes the data processing and display program in the upper computer and the data acquisition program, the motor control program in the lower computer (PXI). Finally, the test bench was built and the inertia loading test and the rated speed loading test were carried out. The test results verify the effectiveness of the high-frequency loading measurement and control system, and provide a reliable test platform for the dynamic characteristics of the ball screw pair under high-frequency conditions.

Optimization and dynamic simulation of electric actuator transmission based on high precision ball screw

The actuator is an important component of missiles and other aircraft to maintain the flight attitude. A method to calculate the power of the electric servo motor was proposed according to the load characteristics’ of both the servo motor and actuator. An optimization method for the transmission reduction ratio was obtained by considering the load torque equation. Dynamics simulations of the actuator were conducted under a variety of conditions. The simulation results show that the clearance and the friction between the ball screw and the fork, which consist of the transmission mechanism, induce the torque fluctuations, as a source of noise in the motor load. According to the optimization design of the Electric, the Actuator prototype has passed the test, the performance meets the design requirements.

Stiffness Analysis of Inverted Tripod Parallel Manipulator

The concept of parallel manipulator is becoming more popular in modern manufacturing processes due to its various inherent advantages like rigidity, less inertia and accuracy. This project focuses on modeling, simulation and dynamic analysis of inverted tripod parallel manipulator which has three degree of freedom (1 transverse in z axis and rotation motion in x and y axis). The Stewart Gough parallel manipulator consists of moving platform connected to fixed platform with six links (6 Degree of Freedom).This inverted tripod parallel manipulator consists of movable platform connected to the fixed platform with only three links so it has better rigidity compared to Stewart Gough platform. The Stewart Gough parallel manipulator is considered to be highly stable because moving platform size is smaller than the fixed platform. Inverted type parallel manipulator consists of moving platform bigger than the fixed platform. So to improve the stiffness and precision ball screw is used for the support of links. The design of parallel manipulator is done considering rigidity, strength and efficiency of the system. The modeling of the tripod manipulator is done using PRO-E software. Kinematic analysis has been carried out and the stiffness analysis will be done by using ANSYS and ADAMS software.

Fabrication of Microstructured Surfaces by Five-Axis Ultra Precision Machine Tool

In this paper, a five-axis ultra precision machine tool for fabrication of microstructured surfaces is presented. This machine consists of two rotary axes (C&B) and three linear axes (X&Y&Z). High precision aerostatic bearing and torque motor are adopted in C axis (main spindle) and B axis. X axis and Z axis use the hydrostatic guideway and are driven by linear motors. Y axis is driven by torque motor and precision ball screw. This machine is able to realize multiple processing methods, including ultra precision diamond turning, ultra precision milling, fly-cutting, fast tool servo and slow tool servo diamond turning.Furthermore, a large number of experiment researches are carried out. Some typical microstructure surfaces are manufactured, for sinusoidal grid surface, the surface roughness Ra is 11.9nm, which is machined by slow tool servo diamond turning. Micro pyramid array surface is fabricated by using fly-cutting, which performs well both in the profile accuracy and the repeatability. These experiment researches prove that this ultra precision machine is superior in accuracy and system reliability.

Design and Control of One Degree of Freedom Haptic Interface System with PID Controller

This paper presents a design of a one-degree-of-freedom haptic interface system with an aim to investigate control of the system. The system comprised master devices, a system interacting with a user, and slave devices, a system interacting with environments. Both sets of devices were coupled with a gripper, which was designed in a shape of a cantilever beam, to measure force, and a DC motor was employed to drive precision ball screws, which were attached to the gripper, so as to create linear motion. In addition, an encoder was installed so as to investigate motion of the gripper, and the analysis results were employed for a design of a controller, based on the P, PI, PD, and PID type. The aim of this is to provide an operator with tactile sensing through control of the master devices while the slave devices were in contact with an object. The simulation results showed that the stiffness of an object affects stability of the system with a designed controller, causing, limitation of operation, that is, the system was stable when stiffness of the object was less than 43.3 kN/m, and the operator obtained a good response of positions and resistance while contacting with an object as though the operator has direct interaction with such an object.

Model of Precision Loss for the Precision Ball Screw

Aiming at the precision retaining ability problems of the precision ball screw, the modeling on the motion precision loss process under load condition is studied. The mechanics and deformation of the interface of ball and groove under load condition is analyzed by using the classical mechanics and Hertz contact theory, also a precision loss model for precision ball screw is established based on the dynamic characteristics analysis of the ball screw. Regardless of the external interference, the impact of various factors on the precision loss is analyzed and calculated.

The Focusing Mechanism Design for Laser Anti-Counterfeit Platform in Production Manufacturing Engineering

Focusing mechanism is an important part of zoom lens in production manufacturing engineering, in order to meet the reading and detection of anti-counterfeiting label laser anti-counterfeit platform, this paper presents the principle and method of using linear driving mode focusing and introduces the focusing mechanism which consists of a stepping motor, linear guide rail, rail screw or gear rack, the DSP controller. By contrast test, it verifies the location precision ball screw type focusing mechanism for 0.061 ~ 0.067 mm which higher than the design requirements and it is suitable for use in laser anti-counterfeit authentication system in production manufacturing engineering.

A novel high speed/high precision ball screw

As a tried and tested technology, ball screw drive systems are still used in a majority of machine tools which can meet the demands of higher productivity and tight part tolerances due to their low cost and high degree of stiffness. High speed ball screw drive system generates more heat and it results in greater positioning error, adversely affecting the accuracy of high precision machined parts. In this paper, a novel/well designed high speed/high precision nut air cooling ball screw system was developed to avoid thermal errors which affect the positioning accuracy and the temperature rise of ball screw. In order to discuss the effectiveness of the developed high speed/high precision nut air cooling ball screw system, a series of tests was done. As the results, it shows that the positioning accuracy will significantly improve with the use of the nut air cooling ball screw drive system shown in this paper.

Tracking Control of Flexible Ball Screw Drives With Runout Effect and Mass Variation

Most machine tools rely on precision ball screw drives to accurately position the workpiece relative to the tool. The quality of the machining outcome depends significantly on the tracking performance of the workpiece position over a desired trajectory. This paper addresses the minimization of the tracking error in a ball screw drive system in the presence of dynamic variations. Three sources of dynamic variations are considered: mechanical flexibility, runout of the ball screw shaft, and workpiece mass change during operations. Dynamic variations due to flexibility and runout are related to the workpiece position which is continuously measurable, while the variation caused by the workpiece mass change is uncertain. The ball screw drive system affected by dynamic variations is expressed as an uncertain linear model with time-varying parameters. Based on this model, servo controllers are designed such that their parameters are adjusted in real time by the measurable workpiece position to improve the tracking performance and that their performance is maintained robustly over uncertain mass variation. The importance of taking into account flexibility and runout of the shaft, as well as mass variation, explicitly in controller design is demonstrated through a ball screw drive experimental setup.

Multiple Influencing Factors Analysis for Non-Conformal Contact Characteristics of Ball Screw

The contact between balls and screw races or nut races is a kind of typical non-conformal contact. The study of contact characteristics of ball screw will provide theoretical bases for improving transmission efficiency and working properties of ball screw. In this study, hertz contact theory was adopted to construct the solution formula of ball screw’s contact stiffness, ball screw’s contact characteristics in terms of axial load, design parameters and material properties was analyzed, and the contact deformation value of the contact between ball and screw races was got using finite element simulation method. The simulation result is close to the theoretic value, which proves the correctness of the theory analysis. The present study offers theoretical support for the design and application of high speed, heavy load and precision ball screws.

ボールねじの玉挙動とロストモーション（第２報）―ダブルナットあるいはオーバサイズ球予圧方式による荷重の影響―

It is well known that preloaded ball screws with double nut produced hysteretic motion between the rotary motion of the screw shaft and the linear motion of the nut, which is called “lost motion”, affects positioning accuracies of ball screws.Preloaded ball screws with a double nut have the characteristic that loaded balls wedge into a right angle direction to a ball rolling direction because the directions of screw shaft and nut raceways differ from the ball rolling direction. Loaded balls of preloaded ball screws with a double nut have two contact points geometrically. When the ball screw is operated under the condition of screw shaft turning and nut stationary, the balls have the velocity component perpendicular to the load line of action due to the helical raceway groove. Therefore the balls wedge into nut grooves. In the case of a ball screws with a circular-arc groove profile, “ball wedging” phenomenon is saturated when the force of resistance to ball wedging exceeds a frictional force between the ball and the raceway groove.In the present study, the authors experimentally investigated the lost motion of the X-table which is composed of a preloaded precision ball screw and a couple of linear air bearings, and the ball wedging behaviors under the condition of varied preload with double nut or over-sized balls have also measured.

S1101-1-3 ボールねじと歯車で構成される新たな差動回転直動変換機構の基礎的特性評価([S1101-1]機構の開発とシミュレーション)

Rotary to linear conversion is one of important mechanisms and has been widely used in various mechanical systems. We designed a new mechanism for rotary to linear conversion, which can provide linear output mechanically by using both screws and gears, and will be adequate for the both accurate positioning and high capacity. In this study, the compact mechanism designed for retrofit into mechanical devices was manufactured in order to investigate its fundamental performance. In the positioning accuracy test, the positioning accuracy of this mechanism was superior to that of a feed screw employed a precision ball screw. In the load output test, the load output of this mechanism was larger than that of a precision ball screw under some input torque condition.

Influence of Ball Behavior in Ball Screws on Lost Motion (1st Report)

Linear actuators driven by ball screw mechanism lead to non-linear relations between the linear motion of the nut and the rotary motion of the screw shaft when the ball screw drive is reversed even if the ball screw is preloaded with a double nut to remove backlash between the screw shaft and the nut. The behavior of the ball screw mechanism that is referred to as “lost motion”, can contribute positioning errors of linear actuators.This paper deals with a relationship between the lost motion and the ball behavior of the X-table which is composed of a preloaded precision ball screw and a couple of linear air bearings, and ball rolling behaviors. Ball rolling behavior is measured by the gap sensor which is inserted into a hole which is bored in the perpendicular to the outer surface of the cylindrical nut and is located on the opposite side of the ball circulation tube. The results are summarized as follows : (1) “Ball wedging” and ball wedging direction can be measured by developed experimental device. (2) The ball wedging direction is reversed when the ball screw drive is reversed in two-point contact ball screws. Therefore, the differences between forward stroke and backward stroke in ball rolling speed are occurred. (3) It is considered that the lost motion is produced in two-point contact ball screws when the ball wedging direction is reversed.

Technical Development of Precision Bearing and Ball Screw

Technical Development of Precision Bearing and Ball Screw

Sculptured Surface Machining of Die Steel by Applying Elliptical Vibration Cutting (1st Report)

New machining method and system are developed in the present research to realize sculptured surface machining of die steel by applying vibration cutting. The present report presents the new machining method, and a 4-axis controlled precision machine tool and special CAM software for the proposed method. It is expected that shape accuracy, tool life, machining efficiency and energy consumption are all improved by the proposed method as compared with the conventional ball end milling. The prototype machine tool is developed by employing an air spindle driven directly by a coreless servo mortar, precision ball screws and precision linear roller guides. The CAM software is developed by utilizing a commercial main processor and developing a new post processor to generate tool paths for the 4-axis controlled motion. A new 3-DOF elliptical vibration system, which is required to complete the present technology, and application to hard materials will be presented in the next reports. It is confirmed in the present report that mirror surface machining of aluminum alloy can be realized by applying the proposed machining method and the developed machine tool and CAM software.