A virtual machine concept for real-time simulation of machine tool dynamics

When designing CNC machine tools it is important to consider the dynamics of the control, the electrical components and the mechanical structure of the machine simultaneously. This paper describes the structure and implementation of a concept for real-time simulation of such machine tools using a water jet cutting machine as an application. The concept includes a real control system, simulation models of the dynamics of the machine and a virtual reality model for visualisation. The real-time capability of the concept, including the simulation of electrical and rather detailed mechanical component models is proofed. The validation process indicates good agreement between simulation and measurement, but suggests further studies on servo motor, connection and flexibility modelling. However, already from the initial simulation results presented in this paper it can be concluded that the influence of structural flexibility on manufacturing accuracy is of importance at desired feeding rates and accelerations. The fully automated implementation developed in this work is a promising base for dealing with this trade-off between productivity and accuracy of the manufacturing process through multidisciplinary optimisation.     

普通金属切削机床的数显改造

本文介绍了光栅位移传感器的原理和特点，以及在金属切削机床上的实际应用。     

数控机床对刀原则方法及其应用

阐述了数控机床中常用的对刀原则和方法，从实用的角度介绍各种不同类型的数控机床的常用对刀方法。     

基于SVPWM的数控机床控制系统仿真与分析

鉴于空间矢量脉宽调制法(SVPWM)诸多优点,如果能对其先进行一些仿真研究必定会给它在数控机床方面的应用实践带来不少裨益.由此,首先对SVPWM技术原理进行了介绍,特别对其线性组合SVPWM波形的实现方法进行了详细的讨论.其次,在MATLAB/SIMULINK环境下,把这种SVPWM实现方法放入了一个数控电机闭环转差控制系统中进行应用仿真.通过对定子磁链,转矩等进行仿真研究,结果表明与理论分析一致,从而为SVPWM在数控电机控制系统中应用提供了一定的参考价值.     

Vibration based preload estimation in machine tool spindles

Prevention of catastrophic bearing failures caused by excessive thermally induced preload is one of the key issues in the design and operation of high speed spindles. Temperature monitoring and shutting the spindle off in hazardous conditions is at present the most common method of avoiding bearing seizure. However, due to a rapid heat built-up and measurement delay, this solution in not reliable. An improved protection can be achieved either by custom systems with springs or hydraulic actuators that maintain a steady preload, or by monitoring the instantaneous preload and appropriate, predictive adjustment of machining conditions. While the former approach increases the cost of spindles and degrades their potential reliability, monitoring and proactive control of the actual preload eliminates these disadvantages. Its feasibility is predicated upon fast, reliable and accurate in-process preload estimation. A suitable estimation algorithm proposed in this paper employs vibrations of the spindle housing measured by means of accelerometer(s) and analyzed in the context of mechanical multi-degree-of-freedom model of the spindle assembly treated as a component of the entire machine tool. Representative experimental results are presented.     

数控慢走丝线切割机床锥度加工方法与技巧

分析了使用数控慢走丝线切割机床进行高精度锥度零件加工的要点,总结了锥度加工误差的修正步骤,提出利用EXCEL软件功能自动计算修正值的方法制作锥度修正器,简化了锥度修正计算的过程。通过实例分析,结合生产实践总结了一些锥度切割的技巧,对实际生产具有指导意义。     

机床主轴结构参数优化设计

以机床主轴为优化设计对象,将优化设计思想与Matlab相结合,利用外惩罚函数法对机床主轴进行建模优化,求解出参数并用分支定界法确定主轴参数。然后运用ANSYS对其进行模态分析,分析了主轴的前6阶固有频率、振型和临界转速,验证了机床主轴结构优化设计的合理性,为机床主轴的结构优化设计提供参考和依据。     

自动切管机切割路径的运动学分析

切管机是管材加工及应用行业的专用加工设备,管材的管-板相贯的几何特点给切割一次成形带来了很大的困难,基于一次成形的考虑,提出了管-板相贯求交的一个通用算法,根据这一算法设计的数控切管机成功地实现了这类坡口一次数控切割成形,并通过一个较为典型的例子作一详细的论述.     

Digital filtering for machine tool structural dynamic analysis by the dynamic data system (DDS)

The Dynamic Data System (DDS) methodology has been successfully used for machine tool structural analysis. In this paper, the digital filtering technique is proposed to reduce the adequate order of the Autoregressive Moving Average Vector (ARMAV) moel to overcome the difficulty in higher order modeling.Problems in digital filtering for the ARMAV model are analyzed, including: (1) the selection of an appropriate filter, (2) the elimination of phase distortion, (3) the methods of transformation from an analog filter to discrete filter, and (4) the choice of sampling interval. Two examples are illustrated using the digital filtering technique for identifying the modal and structural parameters of the system.     

Modeling of spindle-bearing and machine tool systems for virtual simulation of milling operations

This paper presents a general, integrated model of the spindle bearing and machine tool system, consisting of a rotating shaft, tool holder, angular contact ball bearings, housing, and the machine tool mounting. The model allows virtual cutting of a work material with the numerical model of the spindle during the design stage. The proposed model predicts bearing stiffness, mode shapes, frequency response function (FRF), static and dynamic deflections along the cutter and spindle shaft, as well as contact forces on the bearings with simulated cutting forces before physically building and testing the spindles. The proposed models are verified experimentally by conducting comprehensive tests on an instrumented-industrial spindle. The study shows that the accuracy of predicting the performance of the spindles require integrated modeling of all spindle elements and mounting on the machine tool. The operating conditions of the spindle, such as bearing preload, spindle speeds, cutting conditions and work material properties affect the frequency and amplitude of vibrations during machining.     

机床制造业的发展对焊接、切割及相关领域的需求分析

1 汽车工业领域的发展对机床装备业的需求分析 1.1 国内汽车工业的发展和需求概况 近几年来,中国的汽车工业不断持续发展.2006年,中国的汽车工业实现了调整性增长,汽车的产销量双双超过720万辆.     

基于二维激光切割机的型材多面切割装置方案设计

为满足在二维激光切割机上实现型材多面三维切割的需求,根据二维激光切割机结构、型材加工要求、机械加工夹具及自动控制等方面知识,对在二维激光切割机上加装型材夹紧、旋转装置提出三种设计方案并进行分析。与采用三维激光切割方案相比,大大节约投资。     

A study of back cutting surface finish from tool errors and machine tool deviations during face milling

The surface finish of mechanical components produced by face milling is given by factors such as cutting conditions, workpiece material, cutting geometry, tool errors and machine tool deviations. The contribution of the different tool teeth to imperfections in the machined surface is strongly influenced by tool errors such as radial and axial runouts. The surface profile of milled parts is not only affected by chip removal due to front cutting, but also by back cutting, which must be taken into account when predicting surface roughness. In the present work, the influence of back cutting on the surface finish obtained by face milling operations is studied. Final part surface roughness is modelled from tool runouts and height deviations that affect the surface marks provoked by back cutting. Round insert cutting tools and surface positions defined by cutter axis trajectory are considered, and milling experiments are developed for a spindle speed of 750 rpm, depth of cut of 0.5 mm and feeds from 0.4 to 1.0 mm/rev. Experimental observations are compared with the theoretical predictions provided by the surface roughness model, and good agreement is found between both results. Surface imperfections caused by front and back cutting are analysed, and discrepancies between experiments and numerical predictions are explained by undeformed chip thickness variations along the tool tooth cutting edge, the tearing of the workpiece material, and fluctuations in the feedrate and height deviation during machine tool axis displacement.     

Estimation of CNC machine–tool dynamic parameters based on random cutting excitation through operational modal analysis

Dynamic properties of the whole machine tool structure including tool, spindle, and machine tool frame contribute greatly to the reliability of the machine tool in service and machining quality. However, they will change during operation compared with the results from static frequency response function measurements of classic experimental modal analysis. Therefore, an accurate estimation of the dynamic modal parameters of the whole structure is of great value in real time monitoring, active maintenance, and precise prediction of a stability lobes diagram.Operational modal analysis (OMA) developed from civil engineering works quite efficiently in modal parameters estimation of structure in operation under an intrinsic assumption of white noise excitation. This paper proposes a new methodology for applying this technique in the case of computer numerically controlled (CNC) machine tools during machining operations. A novel random excitation technique based on cutting is presented to meet the white noise excitation requirement. This technique is realized by interrupted cutting of a narrow workpiece step while spindle rotating randomly. The spindle rotation speed is automatically controlled by G-code part program, which contains a series of random speed values produced by MATLAB software following uniform distribution. The resulting cutting produces random pulses and excites the structure in all three directions. The effect of cutting parameters on the excitation frequency and energy was analyzed and simulated. The proposed technique was experimentally validated with two different OMA methods: the Stochastic Subspace Identification (SSI) method and the poly-reference least square complex frequency domain (pLSCF or PolyMAX) method, both of which came up with similar results. It was shown that the proposed excitation technique combined successfully with OMA methods to extract dynamic modal parameters of the machine tool structure.     

一种基于并联机构的三维激光切割机的设计与仿真

设计了一种基于并联机构的三维激光切割机,为激光切割机产品设计提供了一种全新思路。运用ADAMS软件对Z轴、A轴及C轴在各自的行程范围内进行了逆运动学仿真,其结果和方法能够为进一步的研究和产品化提供参考依据。     

A study of thermally induced machine tool errors in real cutting conditions

A thermal error model for software error compensation is usually established from air cutting experiments. The accuracy of the air cutting model in real machining applications is often questioned. In this research the characteristics of thermal errors in real cutting conditions are studied. An analysis based on a regression error model and an artificial neural network-based error model are studied and compared for free air cutting and real cutting conditions. The result shows that the prediction accuracy of the air cutting model is unacceptable in real cutting applications. This is because the cutting load and the cutting coolant applications produce significant thermal effects not taken into account by the air cutting approach. In some cases the predicted result of an air cutting model may go in the opposite direction to the actual error in real cutting. On the other hand, the hybrid model derived from air cutting and real cutting data gives a satisfactory prediction for real cutting conditions.     

激光切割机机身有限元分析及实验研究

振动是激光切割机面临的问题之一,它能造成加工误差,影响零件加工精度。模态分析主要用于确定结构或机器部件的振动特性。运用有限元分析软件ANSYS对激光切割机整机进行模态分析,研究了整机的无阻尼自由振动,得到了整机机械系统的固有频率和振型。通过分析激光切割机的各阶振动模态的特点,得到后续的动态分析步长必须小于0.0072s这个周期,才可以保证模型计算准确性的结论。最后通过实验结果与理论结果对比,验证了建模的合理性,为动力学分析和优化设计提供理论依据和条件。     

A new perspective and analysis for regenerative machine tool chatter

The paper contains a practical perspective on regenerative machine tool chatter. Chatter is a well known phenomenon, occurrence of which is undesired in manufacturing. Aggressive machining conditions, in the sense of removing more metal rapidly, usually cause chatter. In most cases, these conditions can be determined a priori to the operation. A chatter stability study and its reasoning based on root locus plot analysis of time delayed systems is presented as a new and practical perspective in the field. At the junction of root locus and chatter concepts an area of particular interest to the authors arises: a new method for active vibration suppression, the Delayed Resonator. It is an active vibration absorber tuning of which is achieved utilizing a simple time delayed feedback. The cross linking between the Delayed Resonator study and the subject matter, machine tool chatter, is exciting to share. This is the primary motivation in pursuing this study. One of the highlights of the work appears at the phenomenon called Dual Frequency Delayed Resonator. This feature has been conjectured in the literature using the well known “stability lobes”, but never discussed with detail.     

一种新型并联机床的运动学分析及受力分析

提出了以四自由度空间并联机构作为主进给机构，辅以双向移动工作台实现多坐标数控加工的一种新型并联机床的布局设计方案。该并联机床具有工作空间大、可实现姿态角大、位置与姿态解耦等优点，建立了主进给机构的封闭形式的运动学方程，导出了一、二阶运动影响系数矩阵，通过建立机构的静力平衡方程，分析了切削加工载荷在各条驱动腿之间的分配情况，最后，给出了仿真研究的数值实例。