A new method and device for motion accuracy measurement of NC machine tools. Part 1: principle and equipment

This paper describes in two parts a new method and device for measuring motion accuracy of numerical control (NC) machine tools. In the first part, the measurement principle and the characteristics of the prototype device are proposed. The device consists of a double-bar linkage with two rotary encoders. The working range of the device is disc-shaped with a radius of almost the double the link length, except a small area around the centre of the disc and an outer area both around the change points of the linkage at the centre and the circumference of the disc. Because the method has high resolution for any measuring point within the working range, it can be applied to measure most items of motion accuracy of NC machine tools. The method is particularly suitable to measure the trajectory accuracy of circular motions. The device has a compact structure and its installation on a machine tool to be measured is simple and quick. The experimental results show that the prototype device has very good response to small displacement and good repeatability with high precision to the measurement of circular motion trajectories. The influence of measurement noise is hardly observed in the experimental results.     

Development of a measuring method for motion accuracy of NC machine tools using links and rotary encoders

An instrument capable of measuring arbitrary NC tool paths in a three-dimensional space has been developed. This paper describes the structure of the newly developed device and an estimation method for determining the 11 error parameters associated with the link length errors and the inclination of the link axes. The estimated error parameters were applied to tool-path trajectories that were calculated from rotary encoder output angles.The apparatus was employed in several measuring experiments, including measurements of square and circular paths for a vertical machining center. The results from these experiments support the validity of this measurement apparatus and the error parameters estimation method.     

Prediction and identification of rotary axes error of non-orthogonal five-axis machine tool

This paper proposes an efficient and automated scheme to predict and identify the position and motion errors of rotary axes on a non-orthogonal five-axis machining centre using the double ball bar (DBB) system. Based on the Denavit-Hartenberg theory, a motion deviations model for the tilting rotary axis B and rotary C of a non-orthogonal five-axis NC machine tool is established, which considers tilting rotary axis B and rotary C static deviations and dynamic deviations that total 24. After analysing the mathematical expression of the motion deviations model, the QC20 double ball bar (DBB) from the Renishaw Company is used to measure and identify the motion errors of rotary axes B and C, and a measurement scheme is designed. With the measured results, the 24 geometric deviations of rotary axes B and C can be identified intuitively and efficiently. This method provides a reference for the error identification of the non-orthogonal five-axis NC machine tool.     

Analysis of circular trajectory equivalent to cone-frustum milling in five-axis machining centers using motion simulator

The present paper describes the effect of the half apex angle of the cone-frustum on the motion trajectory under simultaneous five-axis motion and the effect of the sensitive direction of the ball bar when the motion trajectory is measured along the three-dimensional circular conical path. In the present paper, simulation of the measurement by means of a ball bar instrument is mainly conducted using a motion simulator developed previously. In particular, a precise mathematical model was developed to express the pitch errors of the axes of rotation of the five-axis machining center having a tilting rotary table driven by worm gears. In the experiment and simulation, primarily the center position and half apex angle of the cone-frustum were varied. In addition, two sensitive directions of the ball bar were investigated. The motion simulator incorporating the pitch error model can express the detailed trajectories obtained by the ball bar, even if the half apex angle and center position of the cone-frustum and the sensitive direction of the ball bar were changed. Then, the influence of the frictional force of the linear axes of motion, and the backlash and pitch error of the axes of rotation on the circular trajectories were analyzed. In particular, for the case of a half apex angle of 45°, the trajectory due to the errors of the axis of rotation is strongly affected by the sensitive direction of the ball bar.     

Double ballbar test for the rotary axes of five-axis CNC machine tools

In this paper a new method that uses the double ballbar to inspect motion errors of the rotary axes of five-axis CNC machine tools is presented. The new method uses a particular circular test path that only causes the two rotary axes to move simultaneously and keeps the other three linear axes stationary. Therefore, only motion errors of the two rotary axes will be measured during the ballbar test. The theoretical trace patterns of various error origins, including servo mismatch and backlash, are established. Consequently, the error origins in the rotary block can be diagnosed by examining whether similar patterns appear in the motion error trace. The method developed was verified by practical tests, and the servo mismatch of the rotary axes was successfully detected.     

基于运动控制器的开放式激光焦点位置控制系统

激光切割焦点位置自动跟踪系统的控制精度直接影响着激光切割加工的质量。电感式LVDT传感器或电容传感器与单片机构成的控制系统存在着抗干扰能力较低、动态响应品质较差、开放程度差等缺点。本文介绍一种用数字式光码盘和运动控制器构成的控制系统 ,采用通用的运动控制器作为控制系统 ,提高系统的控制品质、开放性、稳定性、可靠性 ,可以有效地解决上述问题。     

Assessment of machine tool trunnion axis motion error, using magnetic double ball bar

A method is proposed in this paper to assess the axis motion errors of a trunnion-type A-axis using the magnetic double ball bar (DBB) as the measuring instrument. The proposed method consists of five DBB tests with a single setup for all of the tests and the exclusive motion of the trunnion axis during data acquisition. The single setup helps to reduce non-productive time by limiting the intervention of the operator within the machine workspace whereas the exclusive trunnion axis motion prevents the data from being contaminated by other axes motion errors within each test. Simulations show that setup errors cause eccentricities and radius changes of the ball bar data when viewed on a polar plot. Finally, the proposed method is applied to a VL30 Mitsui-Seiki vertical machine tool to identify its trunnion axis motion errors. The results show the effectiveness of the proposed method as well as its ease of use and the short time required.     

Ballbar dynamic tests for rotary axes of five-axis CNC machine tools

This paper proposes a new ball bar test method for the inspection of dynamic errors of rotary axes in five-axis CNC machine tools. The test circle is defined in a workpiece coordinate system and the ball bar test is performed by simultaneously driving of linear–rotary axis couple. The effects of the center position and the radius on the setting values, rotational range and measurement sensitivity of the rotary axis were investigated. The proposed ball bar test is performed in two steps: the circular positioning and the circular tracking with a continuous feed. Axial dynamic errors are obtained by subtracting the measured tracking errors from the positioning errors. A ball bar test system (BBTS) was developed to plan the tool path and the tool orientation, to communicate with the five-axis CNC controller and to process the measured data. Error patterns were simulated regarding the gain mismatch, backlash and tracking direction to help a fast diagnosis of the error sources. Simulations and experimental results prove the effectiveness of the new test method.     

Identification and compensation of systematic deviations particular to 5-axis machining centers

This paper presents an algorithm for identifying particular deviations such as angular deviations around linear axes relating to rotary axes in 5-axis machining centers. In this study, three kinds of simultaneous three-axis control motions are designed for each rotary axis to identify the deviations. In the measurement, two translational axes and one rotary axis are simultaneously controlled keeping the distance between a tool and a worktable constant. Telescoping ball bar is an effective instrument for measuring the relative displacement to the reference length in the work volume because its attitude is freely changed. In these three-axis control motions, the sensitive direction of the ball bar is kept constant. In order to determine the deviations, we derive eight equations from the relationship between the eccentricities obtained from the measured circular trajectories and the approximations derived from the mathematical model based on the simulation. In the simulation, a mathematical model considering the particular deviations is developed and then the characteristic diagrams are prepared for every deviation and every three-axis control motion. Based on the results, we propose a procedure for identifying the particular deviations in 5-axis machining centers and its procedure has been applied to identify the deviations actually. From both the simulation and the experiment, it has been confirmed that the proposed method gives precision results and is able to apply to the measurement of 5-axis machining center which is a tilting rotary table type.     

Enhancement of geometric accuracy of five-axis machining centers based on identification and compensation of geometric deviations

The present paper describes the enhancement of kinematic accuracy of five-axis machining centers with a tilting rotary table. Geometric deviations inherent to the five-axis machine are calibrated through the actual trajectories measured by two different settings of a ball bar in simultaneous three axis motion. Measurement using a cylindrical coordinate system is superior to measurement using a Cartesian coordinate system from the viewpoint of the number of measurements. In order to verify the effectiveness of the calibration method, the inherent geometric deviations measured on the cylindrical coordinate system were corrected through the post processing of NC data for cutting the cone-frustum.The relative displacement between the tool center point and the workpiece was detected by the ball bar. Based on the experimental results, it is confirmed that the radius, center position, and roundness of the three-dimensional circular trajectory are improved when the inherent geometric deviations are corrected.     

一种新型旋转锻打精密下料机的研制

针对传统金属棒料下料设备下料断面质量差、生产率低、能耗高和原材料浪费严重等不足,研制了一种新型环保下料机。该下料机是在传统旋锻机的基础上进行改进,采用PLC控制技术,对锻打频率和径向位移进行调节,实现了对棒料裂纹的发生、扩展的精确控制,最终实现棒料的精密下料。实验证明,研制的新型旋转锻打精密下料机能对不同直径的不同材料进行快速精密下料,下料所得坯料的几何精度可以满足精密塑性加工要求。     

基于球杆仪的空间误差测量分析方法研究

数控机床误差的检测对于提高机床加工精度具有重要的意义.在分析已有的空间测量方法之后,介绍了一种可用于测量机床空间圆运动轨迹误差的测量仪器—Renishaw QC20-W球杆仪,它可以创建典型的机床位置精度空间测量,获得总体圆度误差值等信息,为实施圆轨迹的误差补偿打下基础.     

基于梯度提升树的回转体测量系统误差补偿

为提升回转体内径测量系统的测量精度,解决测量误差补偿问题,提出一种基于梯度提升树(GBDT)的回转体测量系统误差补偿方法。以自主研制的回转体内径测量机为研究对象,首先分析了其主要误差来源,然后测量标准件得到训练样本和测试样本,分别使用训练样本和测试样本对测量系统误差进行建模和补偿,最后与BP神经网络模型进行对比试验。结果表明,基于梯度提升树的测量误差补偿方法具有更好的补偿效果和稳定性,能有效提高测量的精度,使测量误差从4.7μm减小至1.2μm,误差减少了74.5%,具有工程应用价值。     

基于PMAC的折弯机送料测长系统设计

送料和折弯是铝隔条自动折弯机工作的两个主要动作,其送料精度直接影响最终折弯效果。为满足其精度要求,在折弯机送料部分采用同步输送的机械结构,并由工控机配合运动控制器PMAC及交流伺服系统等对其机械部分进行运动控制,使折弯机能够自动进行铝隔条直线进给及长度测量,保证最终铝框精度。     

A method of testing position independent geometric errors in rotary axes of a five-axis machine tool using a double ball bar

Ensuring that a five-axis machine tool is operating within tolerance is critical. However, there are few simple and fast methods to identify whether the machine is in a “usable” condition. This paper investigates the use of the double ball bar (DBB) to identify and characterise the position independent geometric errors (PIGEs) in rotary axes of a five-axis machine tool by establishing new testing paths. The proposed method consists of four tests for two rotary axes; the A-axis tests with and without an extension bar and the C-axis tests with and without an extension bar. For the tests without an extension bar, position errors embedded in the A- and C-axes are measured first. Then these position errors can be used in the tests with an extension bar, to obtain the orientation errors in the A- and C-axes based on the given geometric model. All tests are performed with only one axis moving, thus simplifying the error analysis. The proposed method is implemented on a Hermle C600U five-axis machine tool to validate the approach. The results of the DBB tests show that the new method is a good approach to obtaining the geometric errors in rotary axes, thus can be applied to practical use in assembling processes, maintenance and regular checking of multi-axis CNC machine tools.     

Total ballbar dynamic tests for five-axis CNC machine tools

The linear and rotary axes of a five-axis machine tool are driven simultaneously to generate a specified tool position and orientation in workpiece coordinates. It is crucial that these servo-controlled axes are of balanced dynamics to achieve high tracking accuracy. In this paper, ballbar circular tests for all possible combinations of linear and rotary axes of a five-axis machine tool are investigated and total ballbar dynamic tests are proposed. Through the relational arrangement of the test sequence, the total ballbar dynamic tests can be employed to identify dynamic differences between linear and rotary axes. More importantly, the velocity gains of the position control loops of all servo-controlled linear and rotary axes can be tuned synchronously to eliminate gain mismatch errors. Experimental results have proved the effectiveness of the new methods.     

Rotary ultrasonic machining for face milling of ceramics

Among the various material removal processes applicable to ceramic materials, rotary ultrasonic machining has the potential for high material removal rate while maintaining low machining pressure and resulting in less surface damage. The limitation of rotary ultrasonic machining is that only circular holes or cavities can be machined due to the rotary motion of the tool. Attempts have been made by other researchers to extend rotary ultrasonic machining process to machining flat surfaces or milling slots. However, these extensions either changed the material removal mechanisms or had some severe drawbacks. One of the reasons for this might be an insufficient understanding of the material removal mechanisms involved. In this paper, a new approach to extend rotary ultrasonic machining to face milling of ceramics is proposed, which keeps all the material removal mechanisms of rotary ultrasonic machining. The development of the experimental apparatus and the design of the cutting tool are described. Preliminary experimental results are presented and discussed.     

FINITE ELEMENT MODEL AND SIMULATION OF ROTARY FORGING OF A DISC

1.~onRotaryforginghasadVantagessuchassmallloading,highaccrryofworkpiece,lowernoiseandvibration,etc.Inmanycases,the~diedepressesspirallyandcontinuouSlyonapartofworkpiece,finallythewholempdefonnationisobtained.ItisespeciallysuitableforfoeingvariousaxisyITUnetricalParts['].SOfar,thetheoreticalanalysisisnotenoughbecausethemotionOfthedieandtheflowstateofmaterialsaresocomplex.Therefore,theprocessdesigndifficultyisincreasedandsomedefectssuchascenter--thewhngandcrackinginadiscworkpieceOftenoccurdu…     

A newly developed rotary-linear motion platform with a giant magnetostrictive actuator

Demands for machining and measuring three-dimensional geometries have recently increased in a variety of industries. In order to meet such demands, it is necessary to develop a compact versatile high performance spindle system. This paper presents a newly developed rotary motion platform combined with a linear motion mechanism driven by a giant magnetostrictive actuator. The developed platform can be characterized by a compact structure, a noncontact structure, and high accuracy. Performance evaluation results confirm that the developed platform provides precise linear motion during rotating.     

大弧度薄壁壳体内壁加工的优化方法

针对普通车床加工大弧度薄壁壳体内壁的难题,给出一种利用杠杆摆动式装夹装置实现大弧度薄壁壳体内壁加工的优化方法。该装置基于二力杆原理,通过螺纹副伸缩机构和刀体回转机构实现刀体在传动螺杆的拉动下绕刀杆回转轴做匀速圆周运动,达到了采用普通卧式车床就能实现薄壁壳体内壁加工的技术要求。采用计算机辅助设计软件Pro/E并结合图解法的实验结果表明:杠杆摆动式装夹装置的关键技术参数优化设计合理,能够达到预期的加工精度要求。杠杆摆动式装夹装置扩大了企业普通机床的使用范围,提高了车床的利用率,具有一定的应用价值。