STUDY ON THE COMPENSATION TECHNIQUE OF POSITIONING ERRORS FOR NC MACHINE TOOLS

Through analysis of the basic transformation of a typical body,the error transformations of the position vector and the displacement vector are employed,a general model for positioning errors of NC machine tools by using kinematics of the multi body system is discussed.By means of 8031 single chip system,intelligent error compensation controller has been developed.The results of experiments on XH714 machining center show that the positioning accuracy is enhanced effectively by more than 50%.

Algorithm for Detecting Volumetric Geometric Accuracy of NC Machine Tool by Laser Tracker

Quick and accurate detecting the error of NC machine tool and performing the error compensation are important to improve the machining accuracy of NC machine tool. Currently, there are many methods for detecting the geometric accuracy of NC machine tool. However, these methods have deficiencies in detection efficiency and accuracy as well as in versatility. In the paper, a method with laser tracker based on the multi-station and time-sharing measurement principle is proposed, and this method can rapidly and accurately detect the geometric accuracy of NC machine tool. The machine tool is controlled to move in the preset path in a 3D space or 2D plane, and a laser tracker is used to measure the same motion trajectory of the machine tool successively at different base stations. The original algorithm for multi-station and time-sharing measurement is improved. The space coordinates of the measuring point obtained by the laser tracker are taken as parameter values, and the initial position of each base point can be determined. The redundant equation concerning the base point calibration can be established by the distance information of the laser tracker, and the position of each base point is further determined by solving the equation with least squares method, then the space coordinates of each measuring point can be calibrated. The singular matrix does not occur in calculation with the improved algorithm, which overcomes the limitations of the original algorithm, that the motion trajectory of machine tool is in a 3D space and there exits height difference between the base stations. Adopting the improved algorithm can expand the application of multi-station and time-sharing measurement, and can meet the quick and accurate detecting requirements for different types of NC machine tool.

Bayesian Reliability Modeling and Assessment Solution for NC Machine Tools under Small-sample Data

Although Markov chain Monte Carlo（MCMC） algorithms are accurate, many factors may cause instability when they are utilized in reliability analysis; such instability makes these algorithms unsuitable for widespread engineering applications. Thus, a reliability modeling and assessment solution aimed at small-sample data of numerical control（NC） machine tools is proposed on the basis of Bayes theories. An expert-judgment process of fusing multi-source prior information is developed to obtain the Weibull parameters＇ prior distributions and reduce the subjective bias of usual expert-judgment methods. The grid approximation method is applied to two-parameter Weibull distribution to derive the formulas for the parameters＇ posterior distributions and solve the calculation difficulty of high-dimensional integration. The method is then applied to the real data of a type of NC machine tool to implement a reliability assessment and obtain the mean time between failures（MTBF）. The relative error of the proposed method is 5.8020×10-4 compared with the MTBF obtained by the MCMC algorithm. This result indicates that the proposed method is as accurate as MCMC. The newly developed solution for reliability modeling and assessment of NC machine tools under small-sample data is easy, practical, and highly suitable for widespread application in the engineering field; in addition, the solution does not reduce accuracy.

Bayesian zero-failure reliability modeling and assessment method for multiple numerical control(NC) machine tools

A new problem that classical statistical methods are incapable of solving is reliability modeling and assessment when multiple numerical control machine tools(NCMTs) reveal zero failures after a reliability test. Thus, the zero-failure data form and corresponding Bayesian model are developed to solve the zero-failure problem of NCMTs, for which no previous suitable statistical model has been developed. An expert-judgment process that incorporates prior information is presented to solve the difficulty in obtaining reliable prior distributions of Weibull parameters. The equations for the posterior distribution of the parameter vector and the Markov chain Monte Carlo(MCMC) algorithm are derived to solve the difficulty of calculating high-dimensional integration and to obtain parameter estimators. The proposed method is applied to a real case; a corresponding programming code and trick are developed to implement an MCMC simulation in Win BUGS, and a mean time between failures(MTBF) of 1057.9 h is obtained. Given its ability to combine expert judgment, prior information, and data, the proposed reliability modeling and assessment method under the zero failure of NCMTs is validated.

STUDY ON NEW METHOD OF IDENTIFYING GEOMETRIC ERROR PARAMETERS FOR NC MACHINE TOOLS

The methods of identifying geometric error parameters for NC machine tools are introduced. According to analyzing and comparing the different methods, a new method-displacement method with 9 lines is developed based on the theories of the movement errors of multibody system (MBS). A lot of experiments are also made to obtain 21 terms geometric error parameters by using the error identification software based on the new method.

The Application of the GM(1,1) Metabolism Model to Error Data Processing of NC Machine Tools

This paper applied the gray system theory to error data processing of NCmachine tools according to the characteristic. It presented the gray metabolism model of error dataprocessing. The test method for the model needs less capacity. Practice proved that the method issimple, calculation is easy, and results are exact.

Research on virtual dynamic optimization design for NC machine tools

Virtual dynamic optimization design can avoid the repeated process from de-sign to trial-manufacture and test.The designer can analyze and optimize the productstructures in virtual visualization environment.The design cycle is shortened and the costis reduced.The paper analyzed the peculiarity of virtual optimization design,and put for-wards the thought and flow to implement virtual optimization design.The example to opti-mize the internal grinder was studied via establishing precise finite element model,modi-fying the layout of Stiffened Plates and designing parameters of the worktable,and usingthe technology of modal frequency revision and the technology of multiple tuned damper.The result of optimization design compared the new grinder with the original grinder showsthat the entire machine's first orders natural frequency is enhanced by 17%,and the re-sponse displacement of the grinding-head has dropped by 28% under the first order natu-ral frequency and by 41% under second order natural frequency.Finally,the dynamic per-formance of the internal grinder was optimized.

Research on Visual Virtual Design Platform for NC Machine Tools

The fundamental ideas on building the collaborative design platform of virtual visualization for NC machine tools are introduced. The platform is based on the globally shared product model conforming to the STEP Standard,and used PDM system to integrate and encapsulate CAD/CAE and other application software for the product development. The platform also integrated the expert system of NC machine tools design,analysis and estimation. This expert system utilized fuzzy estimation principle to evaluate the design and simulation analysis results and make decisions. The platform provides the collaborative intelligent environment for the design of virtual NC machine tools prototype aiming at integrated product design team. It also supports the customized development of NC machine tools.

Series Design of Large-Scale NC Machine Tool

Product system design is a mature concept in western developed countries. It has been applied in war industry during the last century. However,up until now,functional combination is still the main method for product system de-sign in China. Therefore,in terms of a concept of product generation and product interaction we are in a weak position compared with the requirements of global markets. Today,the idea of serial product design has attracted much attention in the design field and the definition of product generation as well as its parameters has already become the standard in serial product designs. Although the design of a large-scale NC machine tool is complicated,it can be further optimized by the precise exercise of object design by placing the concept of platform establishment firmly into serial product de-sign. The essence of a serial product design has been demonstrated by the design process of a large-scale NC machine tool.

METHOD OF ENHANCING THE POSITIONING ACCURACY FOR NC MACHINE TOOLS

Based on the kinematics of the multi-body system , a general model for the positioning errors of NC machine tools by means of the lower numbered body array and the geometric constraint is presented. The parameters identification of geometric errors by an improved 22-line method is discussed. Moreover , an intelligent error compensation controller has been developed. All these are verified by a series of experiments on XH714 machining center. The results show that the prosition- ing errors with compensation have been reduced to ±7 μm from 50 μm.

细分曲面的NC刀轨生成算法及实现

提出了一种基于LOOP细分规则的NC精加工刀轨生成算法 ,该算法将细分曲面应用于CAD/CAM系统 ,适用于任意拓扑的三角网格模型 ;通过控制曲面等距误差来生成满足给定精度要求的NC刀轨 .其核心思想是 :首先计算LOOP细分曲面控制顶点的极限点和法矢量 ,然后从极限点开始 ,沿其法矢方向以球头刀的半径长度按照给定精度向外等距 ,获得等距曲面 ,最后在等距曲面上生成精加工数控刀轨 .实例表明该算法稳定、高效。

数控机床误差补偿技术及应用──NC型误差补偿控制器的开发

如何实现数控机床空间误差值的控制是误差补偿技术关键之一。文章介绍以单片机为核心的ＮＣ型误差补偿控制器，并在ＸＨ７１４立式加工中心和ＸＨＦＡ２４２０仿形定梁龙门加工中心上得以实现。该方法对在其他机床及开放型数控系统上应用补偿技术有其重要的参考意义。

面向STEP-NC的铣削知识库建立及其刀轨规划方法

目的研究VC++环境下STEP-NC铣削知识库的建立及其刀具路径的生成方法.方法以Visual C++6.0为平台,建立基于知识工程(Knowledge-Baced Engineering,KBE)技术的STEP-NC知识库,在其基础上针对AP238程序中各加工特征进行刀具运动轨迹规划,驱动实验平台的刀具运动.结果STEP-NC知识库能够存储STEP-NC文件中与制造有关的刀具信息、铣削用量等制造信息及几何信息,为刀具路径生成模块提供数据源,生成各加工特征的刀具运动轨迹.结论STEP-NC知识库为面向AP238的刀具路径生成器提供了良好的数据支持,刀具路径生成器将AP238文件释译成机床可识别的刀具轨迹信息,使得STEP-NC程序能够被CNC系统所识别.

NC机床运动误差的矢量分析法

提出了数控机床圆弧插补运动误差的矢量分析方法。可用双球规测量装置测得数控机床圆弧插补运动的综合误差。在分析运动误差与误差矢量关系的基础上以几种典型误差为例，从理论上提出了单一误差源数学模型的建立方法，给出了与单一误差源所对应的误差特征曲线。用这些数学模型和特征曲线可以诊断出数控机床圆弧插补误差产生的原因。

自由曲面NC加工无干涉刀具轨迹生成

对自由曲面ＮＣ加工中的干涉情况和现有处理方法进行分析．以曲面模型→刀具接触点数据→无干涉刀位数据为基本求解策略，综合多种优化措施。

基于NC代码的工具配置方法研究

围绕着机械加工车间生产辅助工具的动态配送问题,研究了生产辅助工具的供应保障问题和离散制造车间的信息流动模式;研究并建立了基于NC代码的车间辅助工具的动态配送和现场调度相结合的生产辅助工具管理方法,开发了相应的信息系统,使得生产辅助工具能在生产现场动态调度,减少配送和回收次数及数量;从而降低生产工具的库存,提高了车间的生产能力和管理水平。系统已在企业成功实施,取得了很好的实际效果。

基于DNC的数字化设计与制造系统原理及应用

分析了数控机床通讯和管理的现状,阐述了CAXA的网络DNC的基本原理及数据管理方式。介绍了基于网络的数控机床联网方案,该方案已在实际应用中验证通过,效果良好,具有推广应用价值。

基于STEP-NC加工文件的换刀模块研究

以新型数控程序接口STEP-NO中有关刀具的定义为基础,对STEP-NO标准中的刀具结构、描述方式进行了分析,详述了由STEP-NO加工文件获取刀具相关信息的方法,最后提出了一种基于STEP-NO加工文件的自动换刀模块的设计方法,并概述了自动换刀流程以及检索方案。

基于图论和改进Dijkstra算法的STEP-NC复杂型腔最短刀具路径生成方法

针对STEP-NC(standard for the exchange of product data,STEP;STEP-compliant numerical control,STEP-NC)复杂型腔的刀具路径生成问题,本文提出了一种基于图论和改进Dijkstra算法的STEPNC复杂型腔最短刀具路径生成方法.在该方法中,首先根据走刀行距和基本元素的等距偏置,生成STEPNC复杂型腔封闭等距环.然后,基于图论得到封闭等距环的赋权有向图.最后,利用改进的Dijkstra算法生成STEP-NC复杂型腔最短刀具路径.通过实例验证了所提出方法的可行性和有效性.

基于STEP-NC车削解释器及刀具轨迹生成器的研究

提出了一种基于STEP-NC的数控车削加工系统,构建了系统的结构体系,研究了在VC++6.0环境下,应用STIX库及MFC类库等,通过检索和处理AP238文件信息来建立STEP-NC车削解释器的方法。并以此为基础应用解释器提供的数据源及参数和刀具数据库,来建立刀具轨迹生成器,实现STEP-NC车削系统刀具轨迹的自动生成。最后通过刀具轨迹的仿真来检验所生成的刀具轨迹是否符合加工要求。