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.     

Construction of an error map of rotary axes on a five-axis machining center by static R-test

This paper proposes an efficient and automated scheme to calibrate error motions of rotary axes on a five-axis machining center by using the R-test. During a five-axis measurement cycle, the R-test probing system measures the three-dimensional displacement of a sphere attached to the spindle in relative to the machine table. Location errors, defined in ISO 230-7, of rotary axes are the most fundamental error factors in the five-axis kinematics. A larger class of error motions can be modeled as geometric errors that vary depending on the angular position of a rotary axis. The objective of this paper is to present an algorithm to identify not only location errors, but also such position-dependent geometric errors, or “error map,” of rotary axes. Its experimental demonstration is presented.     

基于AFSA-ACO-BPN算法的五轴机床动态误差模型

为了提高五轴机床的加工精度,提出一种基于AFSA-ACO-BPN算法的五轴机床动态误差模型.通过建立灰色关联分析模型完成了建模变量的优化选择,并进行了AFSA与ACO-BPN的动态融合.通过实验验证该方法的预测结果与测量结果吻合较好.该方法综合反映了不同切削加工条件的影响,提高了误差模型的鲁棒性,为提高机床加工精度提供...     

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.     

基于空间样条曲线的数控五轴机床误差辨识研究

在划分球杆仪空间误差辨识区域的基础上,基于NUBRS空间样条曲线生成辨识轨迹。分析球杆仪空间辨识原理,并依据此原理建立适用于NUBRS空间曲线的误差辨识模型,该模型包含18个误差因素。依据五轴机床多体运动学的分析结果,提出了一种空间误差辨识方法。通过激光干涉仪的测量及误差补偿,在消除9项空间位移误差的基础上,使用生成的NURBS曲线对剩余9项角度误差因素进行辨识。经实验验证,在进行NUBRS曲线修正后,该方法可有效辨识出3个坐标系中的18项误差因素。     

五轴加工RTCP与非RTCP编程的比较

非RTCP编程需要预先根据五轴机床结构及特征参数对刀位点进行复杂的几何计算,从而得到控制各轴运动的坐标数据;RTCP编程是使用刀位点的三轴坐标再加上旋转轴角度矢量直接编程的方法,各轴实际控制坐标的复杂计算由机床系统自动进行。比较而言,RTCP程序与机床结构及特征参数无关,更具通用性,它可简化CAM编程和机床操作者之间的相互依赖关系。     

Measurement and verification of position-independent geometric errors of a five-axis machine tool using a double ball-bar

In this study, position-independent geometric errors, including offset errors and squareness errors of rotary axes of a five-axis machine tool are measured using a double ball-bar and are verified through compensation. In addition, standard uncertainties of measurement results are calculated to establish their confidence intervals. This requires two measurement paths for each rotary axis, which are involving control of single rotary axis during measurement. So, the measurement paths simplify the measurement process, and reduce measurement cost including less operator effort and measurement time. Set-up errors, which are inevitable during the installation of the balls, are modeled as constants. Their effects on the measurement results are investigated to improve the accuracy of the measurement result. A novel fixture consisting of flexure hinges and two pairs of bolts is used to minimize set-up error by adjusting the ball's position located at the tool nose. Simulation is performed to check the validation of measurement and to analyze the standard uncertainties of the measurement results. Finally, the position-independent geometric errors of the five-axis machine tool (involving a rotary axis and a trunnion axis) are measured using proposed method.     

基于PC104并口驱动的经济型五轴机床数控系统的研制

为构建一种精简的低成本经济型五轴机床数控系统,采用了基于实时嵌入式多任务操作系统RTLinux作为软件平台以及工业嵌入式计算机PC-104为硬件平台,采用并口作为步进电机驱动控制接口,并利用软件编程的方法完成步进电机位置控制。实验结果证明该数控系统可有效实现五轴机床联动控制。     

耳轴类铸件轴颈部位加工质量及效率提升

耳轴类产品作为矿山机械的一部分,在精加工时对尺寸及表面光洁度要求比较高,当前采用布砂轮磨削加工,加工质量和效率均不理想。在保证加工质量的同时确保加工效率是急需解决的难题,为此提出了两种对加工效率提升明显的改进方案。     

五轴加工中心RTCP误差检测及补偿方法

RTCP是五轴加工中心提供的空间五轴联动加工零件的一种先进功能,维护RTCP精度对提高机床加工精度有重要意义。针对机床不具备球杆仪等专用测量装置情况下,探索一种简单可行的RTCP误差检测与补偿的问题,改进了机床制造商提供的经验计算公式,对比了改进后与改进前机床的精度数据,说明了改进可行性。     

Five-axis milling machine tool kinematic chain design and analysis

Five-axis CNC machining centers have become quite common today. The kinematics of most of the machines are based on a rectangular Cartesian coordinate system. This paper classifies the possible conceptual designs and actual existing implementations based on the theoretically possible combinations of the degrees of freedom. Some useful quantitative parameters, such as the workspace utilization factor, machine tool space efficiency, orientation space index and orientation angle index are defined. The advantages and disadvantages of each concept are analyzed. Criteria for selection and design of a machine configuration are given. New concepts based on the Stewart platform have been introduced recently in industry and are also briefly discussed.     

五轴联动BC型木工雕刻机床结构与数控系统设计

针对现阶段木工雕刻机床结构单一的问题,设计一种经济型五轴联动BC型木工雕刻机床及其数控系统。通过建立机床的运动学模型,研究五轴BC型机床的正逆解;根据运动学求解的结果,采用NC系统嵌入PC机的开放式数控系统模式,设计了数控系统的硬件。采用Visual C++6.0对数控系统软件进行编制,运用线程对运动控制进行监管,并对刀轨文件进行仿真加工。通过对维纳斯石蜡模型的加工与测量,验证数控系统加工精度符合加工要求。