Intermittent process hybrid measurement system on the machining centre

This study introduces the development of a hybrid measurement system integrated on a machining centre to carry out the possible intermittent measurement of a workpiece. The developed hybrid measurement system principally consists of a MP10 touch trigger probe system, a circular triangulation laser probe system, and the measurement software. The touch trigger probe system was primarily used to measure the regular geometric features, whereas the circular triangulation laser probe system was adopted to inspect the freeform surface part of a test carrier with the help of the developed measurement software. An adjustment device consisting mainly of an adjustment unit, a joint unit, and an assembly unit, was designed and manufactured to minimize the cosine error caused by the assembly inaccuracy for the laser probe. The measuring uncertainty analysis experiments for both the touch trigger probe system and the non-contact laser probe system were investigated by using a calibrated standard sphere and the HP5529A laser interferometer system, respectively. The information in the whole measuring system – which comprised a personal computer, a CNC machining centre controller, a Renishaw MP10 touch probe system, and the controller of a Wolf & Back OTM3A20 circular triangulation laser probe system – was integrated technically. The measurement software was also developed to simulate the measuring path, prevent collision, and generate the corresponding measuring NC codes. The developed system can also be used to digitize the data points of a 3D small complex workpiece, such as a tooth model and an IC part. A carrier, combined with free form surface and regular geometric feature referred to in the ISO 10791-7 cutting test standard, was designed, manufactured and inspected in order to evaluate the performance of the developed hybrid measuring system. The measurement results of this carrier were verified through a CNC coordinate measuring machine, with satisfactory consistency. According to the measuring results, the developed hybrid measuring system was successfully and effectively used to carry out the intermittent measurement.     

CNC机床在线测量系统校准方法研究

目前CNC机床在线测量系统的校准方法在国内有用激光干涉仪、标准量块等一些用于企业的针对性方法,缺少适用于计量校准机构的校准方法,本文根据该系统的工作原理,对CNC机床在线测量系统的校准方法进行研究,提出几项计量特性参数,并结合实际情况设计了校准方案,研制了校准用计量标准器,分析了数据的处理方法.经研究表明,本文的校准方...     

Computer-aided design,manufacturing and inspection system integration for optical lens production

The main objectives of this research are the development of an integrated manufacturing strategy and the construction of a database management system for the design, machining and inspection of sculptured surfaces. Specifically, the optical lens for colour display tube/colour picture tube is selected as an application example to show the effectiveness and efficiency of the developed manufacturing strategy and database construction methods. In the machining strategy, the total machining time reduction method is proposed for the rough cutting operation based on the optimum tool path planning. In the finish cutting operation, a modified cutter contact variable step method is employed, and optimal tool paths are generated by selecting the proper tool radius within the given tolerance of a designed model. In the inspection strategy, the shortest measuring path is calculated to reduce the inspection time in CMM. In addition, an efficient database management system, which conducts the process from the surface design stage to the inspection result analysis stage, is constructed for the optimization of the sculptured surface manufacturing process. Finally, the required simulation and experimental works are carried out to verify the proposed strategy.     

Design of Vibration Monitoring System of CNC Machine

CNC machine have a fast development and is widely used in China. Generally, CNC machine tool, includs CNC lathes and CNC milling machine. CNC machine tool is a necessary tool for machining. It plays an important role in the mechanical design and machining fields. CNC machine tool is mainly composed of two parts of the machine body and the computer control system. Mechanical equipment failures usually related information such as vibration, sound, pressure, temperature performance. CNC machine tool vibration monitoring system with piezoelectric accelerometer, the eddy current displacement sensor, signal amplifier, signal conditioning modules. We can take an advantage of the CNC machine tool vibration monitoring system for vibration monitoring and fault diagnosis of CNC machine tools.     

高速激光切割机床数控加工态势识别系统

当前方法设计的系统对机床数控加工态势进行识别时,没有对噪声进行回放,对切割平面度、切割定位精度、机床平稳性进行识别时,识别结果不准确,存在识别准确率低的问题。该文提出高速激光切割机床数控加工态势识别系统设计方法,首先,通过运动控制卡,伺服控制模块及加工态势识别模块构成高速激光切割机床数控加工态势识别系统的架构;其次,在加工态势识别模块中设计系统初始化、态势识别、自动诊断报警、运动控制、图形转码和G代码编译等子模块,在此基础上,通过噪音采集、噪音回放和信号分析等方法提高加工态势识别的准确率;最后,采用HMM算法构建高速激光切割机床数控加工态势识别模型,实现加工态势识别。实验结果表明,加工态势设计方法设计的系统可有效识别机床的切割平面度、切割定位精度和机床平稳性,识别准确率较高。     

Machining error compensation using radial basis function network based on CAD/CAM/CAI integration concept

This paper presents a machining error compensation methodology using an Artificial Neural Network (ANN) model trained by an inspection database of the On-Machine-Measurement (OMM) system. This is an application of the CAD/CAM/CAI integration concept. First, to improve machining and inspection accuracies, the geometric errors of a three-axis CNC machining centre and the probing errors are compensated using a closed-loop configuration. Then, a workpiece is machined using the machining centre, and the error distributions of the machined surface are inspected using OMM. In order to analyse efficiently the machining errors, two characteristic error parameters, W err and D err , are defined. Subsequently, these parameters are modelled using a Radial Basis Function (RBF) network approach as an ANN model. Based on the RBF network model, the tool path is corrected to effectively reduce the errors using an iterative algorithm. In the iterative algorithm, the changes of the cutting conditions can be identified according to the corrected tool path. In order to validate the approaches proposed in this paper, an experimental machining process is performed, and the results are evaluated. As a result, about 90% of machining error reduction can be achieved through the proposed approaches.     

Development of the Control System of V-groove Ultra-precision Machining Machine Tool

The control system of micro V-groove machining CNC machine was developed with Qt application tool.This paper described the micro V-groove processing technology,the control system hardware platform composed of " IPC+PMAC",and the CNC software for V-groove machining.The various functional modules in the software were developed on the platform of windows,and the part of motion control of the CNC software was programmed by calling PMAC’s motion control functions.To achieve a visual effect of the numerical control interface and obtain the real situation of the processing on ahead,an important simulation module was also completed by using QOpen GL.The system can effectively control the running of the machine and translate the NC code into 3-D image before processing,which is very helpful for actual production.     

CNC数控机床在线测量系统的校准装置研究

目前,国内尚无针对CNC数控机床在线测量系统的相关的标准和校准规范。为统一技术要求,本文研究了CNC数控机床在线测量系统的工况条件及其计量特性参数,提出了有别传统三坐标测量机校准方法的校准方案,研制了符合基于公差带位置判别废品原理的标准器组,以在线测量系统的测工件的方式,反向校准CNC在线测量系统的尺寸精度,解决其量值溯源问题。     

数控机床热误差的建模与预补偿

研究了数控机床热误差的预补偿方法。建立了基于主轴转速的热误差自回归模型,从而不需要测量机床的温度场就可以预测热误差。在加工前通过修改工作的数控加工程度即可进行补偿,大大简化了误差补偿过程。可应用于中等精度的数控机床。     

A radius compensation method of barrel tool based on macro variables in five-axis flank machining of sculptured surfaces

Barrel tool radius compensation is very important to improve the five-axis CNC machining precision and efficiency of sculptured surfaces. By combining macro variables and math function of CNC controller, a radius compensation method of barrel tool based on macro variables in five-axis flank machining of sculptured surfaces was presented. The basic principle of barrel tool radius compensation in five-axis flank machining was firstly investigated. For a specific five-axis CNC machine tool with dual rotary tables, a relationship equation between compensated cutter location (CL) data and machine control (MC) data could be derived. A post-processor with the function of five-axis barrel tool radius compensation was then developed by using the C++ language, which could generate the NC programme with macro variables of barrel tool radius compensation. Finally, the NC programme was obtained automatically by the developed post-processor for the aero-engine blade surface machining. The machining process was simulated on the software VERICUT, and machining experiments were also conducted on the five-axis machine tool. Both the simulation and experimental results showed that the proposed method could perform the function of barrel tool radius compensation in the NC programme for five-axis flank machining.     

用激光干涉仪检测双丝杠驱动加工中心的方法与评定

介绍了使用激光干涉仪检测双丝杠驱动加工中心时,选择测量轴线的有效位置,能够真实地反映加工中心轴线的运动定位状态;提出检测双丝杠驱动加工中心定位精度和重复定位精度的方法,通过调整激光干涉仪和位移镜组件的安装位置,获得数控机床及加工中心的检测精度,并根据自动采集获得的测量数据进行有效地补偿,以提高和恢复数控机床及加工中心的最佳定位精度.     

Intelligent tool path correction for improving profile accuracy in CNC turning

This paper presents the development of an intelligent predictive tool for improving the accuracy of parts produced on CNC turning centers. Actual dimensions and shape (form) produced on components during machining differ from the nominal dimensions commanded in the CNC program. These dimensional and form errors on parts depend on a variety of factors such as tool/work deflections, machine tool accuracy, machining conditions etc. These errors, if predicted, can be used to correct the ideal CNC code and thus improve the part accuracy in CNC machining. In the present work artificial neural networks are used to capture the complex relationship between the errors on the component and the input process conditions. Significant improvement in part accuracy has been obtained using the corrected CNC code during machining.     

Heuristic optimization system for the determination of index positions on CNC magazines with the consideration of cutting tool duplications

This paper presents a meta-heuristic optimization system developed for the determination of optimal index positions of cutting tools on the tool magazines (automatic tool changer (ATC) or turret magazine, etc.) of CNC (computerized numerical control) machine tools. The selection of index positions is performed using a simulated annealing (SA) algorithm that takes the following as the input: (1) a list of cutting tools assigned to certain machining operations; (2) the number of copies of each cutting tool available in the workshop; (3) total number of index positions on the tool magazines; (4) the indexing time of a tool magazine of a CNC machine tool specified by manufacturer. Then, the SA algorithm determines index locations of cutting tools on the tool magazines. Dereli et al. and Dereli and Filiz previously studied the present problem by using genetic algorithms (GAs). However, the duplication of cutting tools was not taken into account in their works, although it can reduce the total tool-indexing time and therefore improve the productivity considerably. Nevertheless, the consideration of the ‘tool duplications’ makes the problem much harder to model and to solve. In this paper, a novel solution representation-scheme based on the SA, which enables easy manipulation during feasible neighbourhood solution generation, is proposed for the determination of the index positions of cutting tools on the CNC magazines with the consideration of ‘tool duplications’. Example problems are solved to present the implementation and merits of the proposed optimisation system. It is shown that it is possible to allocate the cutting tools in an efficient manner on the CNC magazines with the developed system.     

Enhancement of accuracy of multi-axis machine tools through error measurement and compensation of errors using laser interferometry technique

The present era is witnessing advancement in digital electronics and microprocessor which enables manufacturing sector capable to produce complex components within small tolerance zone in the tune of nanometre and at one machining center. All motion control systems have some form of position feed back system fitted with the machine. Such systems are not generally accurate due to the errors in the positioning performance of the machine tool which will change over time to time due to wear, damage and environmental effects. The complex structure of multi-axis CNC machine tools produce an inaccuracy at the tool tip caused by kinematic parameter deviations resulting in manufacturing errors, assembly errors or quasi-static errors. Analysis of these errors using a laser measurement system provides the manufacturers a way to achieve better accuracy and hence higher quality output from these processes. In this communication, techniques to measure the linear positional errors of axes of CNC machine tools by a laser interferometer calibration system and accuracy enhancement using the data obtained from the calibration cycle by feeding into the machine’s controller with the help of linear error compensation package are discussed.     

基于状态空间模型的机床加工精度分析

伺服进给系统的机电耦合特性直接影响数控机床的加工精度，单独针对伺服系统或机械系统建立的模型不足以准确分析系统参数对机床整机加工精度的影响。因此，综合考虑机床伺服系统与机械结构之间的耦合关系，建立伺服进给系统机电耦合动力学模型具有重要意义。首先，为保证伺服进给系统建模精度，利用状态空间法建立了机床机电耦合状态空间方程。其次，建立了伺服进给系统机电耦合Simulink模型，在此基础上采用复合控制提高系统的响应速度和加工精度。随后，利用多体动力学软件建立机床进给系统的刚柔耦合动力学模型，添加摩擦、阻尼等非线性因素，并导入Simulink与伺服系统建立耦合关系。最终，建立了卧式加工中心伺服进给系统的刚柔-机电耦合仿真加工平台，通过模拟机床加工轨迹以验证机电耦合状态空间模型的可靠性。结果表明：该状态空间模型能准确描述系统内部参数和系统输入输出的耦合关系；采用复合控制结构能有效提高系统的响应速度和加工精度。研究结果为数控机床的仿真建模和提高加工精度提供理论依据，为机床机电系统的设计提供有效指导。     

A prototype optical encoder system with nanometer measurement capability

Optical gratings are becoming available with precision down to the 2 nm level, or below. Such gratings can be employed to make highly accurate measuring tools such as optical encoders and coordinate measuring tools which can find numerous applications in precision machining applications and integrated circuit industry such as image placement inspection. Such tools are significantly less expensive than interferometers because of the relaxed mechanical tolerances required on the associated stages. In this paper, a novel prototype optical encoder system is developed for grating-based measurement tools with nanometer accuracy. The location of the grating was determined with an error of 0.09 nm. This is comparable to the accuracy of state-of-the-art interferometers, but at much lower cost.     

复合进给电解加工机床控制系统设计与测试

为解决航空制造领域复杂零件的加工难题，针对研制的复合进给电解加工机床，开发了基于PC（ personal computer，个人计算机）和PMAC（programmable multi-axles controller，可编程多轴控制器）运动控制卡的开放式数控系统。基于虚拟仪器技术及其开发环境LabVIEW平台，遵循模块化设计思路，采用ActiveX自动化技术和CLF (call library function，调用库函数)节点设计了复合进给电解加工机床控制系统的人机交互界面，通过调用PMAC运动控制卡中的服务程序PmacServer，实现上位机与PMAC运动控制卡之间的功能交互。为了验证该控制系统的可靠性和运行稳定性，使用激光干涉仪进行了实验测试。实验结果显示，该控制系统响应迅速，运行稳定，人机交互界面易于操作；机床运动误差控制在-5~5 μm内，重复定位误差小于2.3 μm，能够满足航空发动机叶片的电解加工精度要求。研究结果在电解加工领域具有重要工程应用价值，可以为新一代高性能电解加工机床的设计提供参考。     

Virtual simulation of five-axis machine tool with consideration of CNC interpolation,servo dynamics,friction, and geometric errors

Abstract

A virtual machine tool (VMT) simulation system which considers tool center point (TCP) interpolation, geometric errors, servo dynamics, and friction effects for a five-axis machine tool is developed in this paper. A novel five-axis interpolation method is proposed to ensure that maximum velocity constraints for each axis can be satisfied. The geometric error model, including lead screw, straightness, angular and squareness errors is built to analyze the volumetric errors within the working space. The model which includes rigid body motion, friction model and servo control loops is utilized to evaluate servo dynamics and non-linear effects. The errors caused by the locations, servo dynamics, and friction effects are integrated into the VMT simulation program. Simulation results of TCP trajectory are represented by small line segments to generate NC codes. Then the NC codes are fed into VERICUT software to perform virtual cutting. To evaluate the interpolation design, cutting experiments are carried out on the five-axis engraving machine with a PC-based controller. The performances using the proposed interpolation method are comparable with the commercial CNC controller from Heidenhain. The effects of different error sources on the surface are demonstrated by cutting the sculpture of a human face. Path overcut caused by servo dynamics is found at sharp corners, and volumetric errors cause obvious tool marks and poor surface roughness. The proposed methodology can serve as a useful tool in evaluating the behaviors of error sources during the design stage.     

Tool path re-planning in free-form surface machining for compensation of process-related errors

Free-form surfaces are widely used in many applications in today’s industry. This paper presents a new approach to identify and compensate process-related errors in machining of free-form surfaces. The process-related errors are identified online by a newly developed in-process inspection technique. In this technique, the surface is first machined through an intermediate semi-finishing process that is specifically designed to machine different geometric shapes on the surface with different process parameters. An inspection method is developed to identify the process-related errors in the selected regions on the semi-finished surface. The relationship between the machining/surface parameters and process-related error is then achieved using a neural network. This relationship is used to predict the process-related errors in the finishing process. The process-related errors, together with the machine tool geometric errors identified using a method developed in our previous work, are compensated in the finishing tool paths through tool path re-planning. Experiment has been conducted to machine a part with a free-form surface to show the improvements in the machining accuracy.