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.

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.

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.

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.

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.

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.

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.

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。

基于零件传输速度的CNC机床SCOP伺服法则

提出并建立了基于CNC数控机床组成FMS的第三种比机床伺服法则,该伺服法则SCOP,考虑了每一决策步传输装置的位置、移动速度及达到不同位置需移动的距离,还考虑了下一步加工零件的利用率及机床缓冲区的空间利用率,并给出了伺服法则的实例,以用于最佳、最大的机床利用率的批量生产工艺流程。

基于STEP-NC的切削加工机器人后置处理方法

为了解决当前切削加工机器人控制系统中存在的开放性、智能化和集成化程度低的问题,将STEP-NC标准引入机器人加工领域,构建了基于STEP-NC的切削加工机器人后置处理系统.基于STDeveloper软件开发了高效的信息提取类库STNCLib,提出了基于等照度线的复杂曲面分区刀具轨迹规划方法.在此基础上研究了机器人运动控制程序的自动生成方法,并最终生成机器人运动控制程序,实现机器人控制系统的信息集成.采用软件编程和仿真的方法对所提方法的正确性和有效性进行了验证,结果表明所提方法是合理和可行的.

基于华中数控系统HNC-818B/M的测头对刀技术研究

在磁流变抛光工艺装备中,自动对刀测量是完成确定性抛光工艺的必要前提,以实现建立工件坐标系、测量工件位姿及标定缎带。基于国产数控系统华中HNC-818B/M,采用雷尼绍MCP测头,设计了对刀测量方案和对刀功能模块,在国产数控机床上验证了对刀测量方案的可行性,实现重复对刀测量精度优于2μm,其高安全可靠性满足磁流变抛光的应用需求。

基于GNCP/PCNC一体化数控系统的研究与开发

提出了一种将图形编程和数控加工结合在一起的GNCP/PCNC(Graphic Numerical Control Program or Personnel Computer Numerical Control)一体化数控系统.该系统采用Windows平台下全软件数控系统的基本结构,通过简单直纹面将空间曲面有效离散化,进而解决了空间复杂曲面三维刀补和插补难以用统一数学模型描述,及刀具中心实时位置难以通过刀具半径补偿后计算得出的关键技术.形成了具有实际应用价值的GNCP/PCNC实验系统.采用该系统,能够实现数控加工常用工件的图形绘制、人机交互式工艺信息输入、数控加工程序代码自动生成,也可直接生成伺服信号,并通过系统外扩的I/O板卡将该信号传输到伺服控制系统中,最终实现数控系统的位置控制、速度控制直至控制数控加工等常规功能.

华中HNC-21MD数控系统的应用

本文介绍了华中HNC-21MD数控系统在XK713数控铣床上的应用,给出了电气系统配置及电气控制方案。

面向铣削加工的STEP-NC文件到G代码转换技术

为使STEP-NC能在传统的数控系统中得到应用,研究了面向铣削加工的STEP-NC数控文件到传统G代码程序的转换技术,提出了一种面向制造特征的刀具轨迹规划方法。首先对制造特征进行分类,然后为每类制造特征设计走刀轨迹模型,在进行G代码转换时,通过前置处理将制造特征的走刀轨迹模型转换成对应数控系统的宏程序,不但提高了G代码的转换效率,而且缩短了G代码程序的长度。论述了STEP-NC文件信息提取和信息处理技术,以及G代码程序自动转换过程。最后,以一个铣削类零件为例,对上述技术进行了测试和验证。

熔铸耐火陶瓷数控机床CNC系统研制

本文介绍了熔铸耐火陶瓷数控机床XMK—900A型CNC系统的硬件和软件设计,该系统硬件由与IBM—PC/XT完全兼容的“ALL—IN—ONE”STD总线工业控制计算机,输入/输出接口电路,步进电机和交流变频调速电机控制电路组成;控制软件采用前后台型的程序结构。

并联机床数控系统NC代码格式变换程序的开发

数控系统软件由数控处理软件和用户界面软件两部分组成。数控处理软件主要是如 何利用现成的NC代码在并联机床上实现加工,包括NC代码格式转换、插补、坐标变换、运动学变 换等,对NC代码格式转换进行了研究,给出了程序流程图。

HNC 21T系统数控车床的三种实用对刀方法

在零件加工生产实训的教学过程中,学生根据零件图能够手工编制出零件加工程序,却因为不会对刀而加工不出合格的零件。针对上述问题,文中采用HNC 21T系统的数控车床,结合复杂零件手工编程实例,依次使用刀具补偿T指令、G54~G59指令和G92指令三种方法进行了对刀操作,并详尽阐述了三种多刀的实际对刀方法的步骤、注意事项,为教学和中小企业的实际对刀提供一定的参考价值。