Finite Element Modelling of Ball Screw Feed Drive Systems

For full realization of the feasible drive performance on machine tools, the dynamic behaviour of the entire mechatronic system must be analysed and optimized integrally during design of the machine. To permit complete modelling of the machine tool frame structure with integral ball screw feed drive systems by means of the finite element method (FEM) a specific model approach for ball screw drives is presented, which is a prerequisite for the FEM modelling of a complete machine tool based on feed drives of this type. The feed axis of a feed drives test station serves here as an example for demonstration of the modelling of feed drives. The FEM model is integrated into a mechatronic model of the axis control system and the behaviour of the position and speed control loop is simulated.     

基于SERCOS-Ⅱ的机床数控系统实时通信与同步控制研究

现代数控机床和加工中心对实时接收数据和同步运动控制提出了更高的要求.论文对脉冲式数控系统进行简要述评的基础上,提出了基于SERCOSⅡ串行实时总线通信的机床数控系统架构:以运动控制器为主站,进给伺服驱动器为从站的主从式环形网络,并以通信周期为基准协调该多CPU结构.论文将提出的系统用于XKHL650型立式加工中心数字化控制,并提出了各进给轴伺服驱动电流环同步控制方法.该方法使各进给轴伺服驱动电流指令达到1μs的同步精度,从而保证了机床各进给轴动作的一致性.实验和加工运行表明基于SERCOSII总线通信的数控系统满足高实时性高精度的加工要求.     

Servo design of a vertical axis drive using dual linear motors for high speed electric discharge machining

This paper proposes a synchronous control scheme for a linear servo system applied to the vertical axis drive of a die-sinking electric discharge machine (EDM) tool. The investigated vertical axis drive is constructed with dual parallel linear motors, which are arranged to jointly drive the feed axis for improvement of the overall thrust and structural stiffness. A pneumatic cylinder is employed to compensate the gravitational effect of the feed axis with its electrode and holder. A mechanical coupling is designed to firmly bridge the two linear motors and carry the feed axis. Therefore, synchronous control for the motors is critical for not only position accuracy, but also machine safety. Moreover, by controlling the thrust outputs and positions of the motors to be as equal as possible, the potential “pull and drag” effect between the motors can be reduced and loads can also be equally shared. The proposed “position/thrust hybrid synchronous control” scheme is applied to the EDM to achieve high-speed, accurate machining, and the experimental results show that the synchronization error between the two parallel motors and the positioning accuracy are both satisfactory when operated under high-speed conditions.     

Control concept for piezo-based actuator-sensor-units for uniaxial vibration damping in machine tools

Additional piezo-based components in drive trains can significantly improve the dynamic behaviour of machine tools. In this article we present a piezo-based actuator-sensor-unit that is able to reduce uniaxial vibrations in ball screw driven feed axis of machine tools. A complex model of a feed axis including ASU was developed to design a controller. The control concept is based on the direct velocity feedback. A modular test bench was designed, assembled and investigated to verify the ASU’s suitability for different feed axis configurations. In conclusion, the results for the different configurations where evaluated regarding economical aspects.     

High speed servo control of multi-axis machine tools

Advances in high-speed machining technology, including those in spindle speeds and cutters, are out-pacing advances in the servo control performance of machine tools. To close this gap, new machine tools and improved controls must be developed. Improvements to machine tools under development include special-purpose machine tools, the use of advanced materials, the replacement of ball screws and ways with linear motors and roller guides, and the use of parallel link actuators. This paper focuses on the control issues that will become increasingly important as these high-speed machining and high-speed machine tool advances are realized.The main issues in high-speed servo control are feed rate planning, and servo loop control laws. A method is developed in this paper which takes advantage of the full performance envelope of each axis in an arbitrary path. This near-complete usage of the servo capabilities of a machine tool results in reduced cycle time or reduced path error. A servo loop control law is then developed that uses the axis performance envelope as well as instantaneous position, velocity, and acceleration information of the target path and machine axis to improve servo performance in the presence of disturbances.     

五轴联动加工中进给速度的控制算法

目的研究刀具进给速度平稳性对五轴联动加工中复杂自由曲面表面粗糙度、轮廓精度的影响。方法首先对五轴联动机床运动过程中的空间线性插补原理进行了分析,推导出插补周期内各轴的分解速度数学模型。根据数控系统中不同的速度指令方式以及刀具在空间的实际运动距离,分端铣和侧铣两种情况,分别建立了刀具空间运动的实际速度计算模型,然后根据机床各轴的最高速度及加速度约束条件,对各轴分速度、分加速度进行校核处理,最终求得刀具实际的合成速度。最后,基于后置处理技术,用开发的专用后置处理软件进行刀位源代码后置处理,采用某叶轮试件进行了验证,并对实验结果进行了分析。结果在复杂曲面加工中,稳定的表面进给速度会获得较高的表面质量及轮廓精度,曲面曲率变化越大,速度变化对加工质量的影响越大。在同等条件下切削,刀具采用恒表面速度与采用恒进给速度相比,获得的叶片进出汽边轮廓误差值由0.1 mm减小为0.04 mm。结论在五轴联动加工中,越稳定的表面进给速度,越能获得较高的表面质量和轮廓精度,对于曲率变化较大的复杂曲面,需要严格控制刀具的进给速度,尽量获得稳定的表面速度以减少过切值,从而提高零件表面质量。     

High speed CNC system design. Part II: modeling and identification of feed drives

Accurate modeling and identification of the feed drives' dynamics is an important step in designing a high performance CNC. This paper presents a method for identifying the dynamic parameters, as well as the friction characteristics of machine tool drives. The inertia and viscous friction are estimated through an unbiased least squares scheme. The friction model is developed by observing the disturbance torque through a Kalman filter, while jogging the axes under closed loop control at various speeds. The overall axis model is used in designing a high speed feed drive control system, which has been presented in Part III of this paper. As verification of the identified friction model, contouring test results without and with friction compensation are also presented.     

Virtual prediction and constraint of contour errors induced by cutting force disturbances on multi-axis CNC machine tools

This paper presents a strategy to virtually predict and constrain the contouring errors contributed by cutting force disturbances on feed drives. The tracking errors on each feed drive are predicted as a linear function of tangential feed by evaluating the product of estimated power spectrum of cutting forces and disturbance frequency response function along the tool path in virtual CAM environment. The corresponding tool tip contouring and tool axis orientation errors are estimated and constrained by scaling the feed along the tool path. The algorithm is experimentally illustrated to improve the machining accuracy on a 5 Axis CNC machine tool.     

Adjustment of CNC machine tool controller setting values by an experimental method

This paper presents an adjustment technique on controller setting values in CNC machine tools by measurement of servo induced feed drive errors. At high feed rate operations of CNC machine tools, servo induced errors are usually dominant and large compared with geometric errors. For measurement of the servo induced errors, an experimental equipment which incorporates two linear displacement sensors and a steel cube was developed, and servo feed drive errors were evaluated along a square corner test path. Based on evaluations of servo feed drive errors with different combination of parameters in machine control system, optimum setting parameters were found. The measuring equipment and optimisation method are described.     

基于华中8型数控系统的蜗轮加工软件开发

为改变国内针对蜗轮滚削加工的研发大多基于国外数控系统的局面,在国产数控系统上建立相应的蜗轮滚切加工系统软件。在分析六轴四联动数控滚齿机齿轮滚切加工工艺的基础上,建立滚刀轴和各进给轴运动关系模型;基于华中HNC-848数控系统开放的上下位机体系结构,利用开放的APP接口函数进行蜗轮加工专用软件界面及功能二次开发;设计用户宏变量,编制蜗轮滚切加工宏程序,实现了蜗轮径向和切向滚切加工,蜗轮加工精度达到国标3级。结果表明：基于国产数控系统开发的蜗轮加工软件,操作简便、适用性强,满足数控蜗轮加工机床需求,为国产数控系统二次开发提供了一套实用的方法     

IA5F3200卧式镗铣加工中心的关键部件结构

文章对IA5F3200卧式镗铣加工中心的基本特点、性能指标作了概括性介绍;详尽阐述了该加工中心的关键部件结构设计,对主轴传动、45度万能铣头、刀具的松、拉刀、各坐标轴进给系统、电磁制动、Z轴双驱同步技术、润滑、冷却等部件作了充分描述.     

电火花成形机床双轴同步模型预测控制研究

为减少龙门式电火花成形机床双轴同步误差,以永磁交流同步伺服电机及滚珠丝杠为例建立了X轴的双轴进给系统模型;提出了动态矩阵控制算法,分别设计了与该算法相结合的并行同步控制策略、交叉耦合控制策略双轴同步控制器,通过与传统PID算法控制方案比较及Matlab仿真,最后选择同步误差更小的交叉耦合控制策略双轴同步控制器,并将该控...     

Adjustment of uncertain model parameters to improve the prediction of the thermal behavior of machine tools

Computer models, which simulate the thermo-elastic behavior of machine tools, are used for optimizing machine designs and more recently for controller-integrated online corrections. Sufficiently accurate corrections of errors caused by the thermal machine behavior require quick and precise identification of uncertain and irregularly distributed parameters based on measurements. The paper presents a systematic approach to conduct parameter identification during machine commissioning. In particular, the acquisition of required data for parameter adjustment and model optimization is addressed. Finally, the procedure is demonstrated on the example of a machine tool's feed axis.     

Design and development of a precision machine tool using counter motion mechanisms

In order to meet the increasing demand for high-quality miniature parts made of a wide variety of materials, the electronics, biomedical and optical industries are moving towards micro/nano-machining. Currently, mechanical micromachining can only be performed under very low feed rates and small depth of cut, which makes it very difficult to reach reasonable productivity. To cope with the low-productivity problem for micro/nano-machining of high-precision molds or miniature parts, a highly accurate and productive machining center has been designed and developed in this paper. The developed machine tool is equipped with counter balance axes, and each axis is driven at its center of gravity to achieve high acceleration/deceleration without causing any vibration. This paper describes the theoretical and practical background of the design of the machine tool and its control and measurement system. Then, experiments are carried out to evaluate the machining performance of this designed machine tool.     

镗床多功能刀架设计

针对没有平旋盘的镗床在加工过程中无法调整镗刀的径向进给量问题,通过对径向进刀系统传动链的运动分析和计算,设计一种镗床多功能刀架。使用该刀架能在主轴旋转的同时,手动或自动调节镗刀的径向进给量。并采用Pro/E软件建立了刀架的三维模型。使用该刀架能极大地方便加工操作,提高机床的加工效率。     

五轴数控机床转动轴与平动轴联动的轮廓误差仿真分析

以主轴头两摆的五轴联动数控机床为研究对象,对转动轴与平动轴联动加工不同空间位置圆弧时的轮廓误差进行了分析。采用D-H(Denavit-Hartenberg)法对按不同圆弧路径加工时各轴的进给指令计算公式进行了推导,并将指令输入到动态仿真工具Simulink构建的进给系统仿真模型中,比较刀具理想位置与实际位置的偏差,从而得到轮廓误差曲线。通过仿真曲线分析了轮廓误差的分布特性,得到了各参数对轮廓误差影响的对应关系,利用这种关系检测机床,达到提高机床性能的目的,同时为机床的调整与维修提供一种便捷手段。     

直线电机在机床工业中的最新应用及技术分析

直线电机在机床进给驱动上的应用日益广泛,比起传统的进给驱动方式,它能提供非常高的速度、加速度和位置精度,大大提高了生产率和加工件表面质量。文章介绍了直线电机在机床上的最新应用情况,并就应用中的关键技术问题进行了分析。     

Virtual High Performance Milling

The goal of future manufacturing is to design, test and manufacture parts in a virtual environment before they are manufactured on the shop floor. This paper presents a generalized process simulation and optimization strategy for 2 1/2 axis milling operations to increase Material Removal Rate (MRR) while avoiding machining errors. The process is optimized at two stages. Optimal spindle speed, radial and axial depth of cut are recommended to process planner by considering the chatter, and spindle's torque/power limits. The cutter-part engagement conditions are extracted from CAD system by geometrically processing the NC program and part geometry. Long tool path segments are broken into smaller segments whenever the geometry varies. The spindle speed and feed fields of the NC program are automatically optimized by constraining maximum torque, power, tool deflection and chip load set by the user. The acceleration and speed limits of the machine tool feed drives are considered to prevent frequent variations of the feed unnecessarily. The optimization is experimentally verified by milling a helicopter gear box cover on a high speed, horizontal machining centre.     

五轴铣床运动链构形方案分析

目前五轴CNC机床已经得到广泛的应用。大多数机床的运动学都是基于直角坐标系统。论文根据理论上自由度的可能性组合，将五轴铣床概念设计及其配置方案进行分类，并分析了各类设计的优缺点。在此理论分析的基础上，文中基于机床坐标系统的定义和机床构形码，进一步得出常用五轴铣床运动链设计限制条件及其可行构形数。该研究结果有益于工程师进行五轴铣床的方案设计以及评价。     

高速大推力直线电机直接驱动进给系统动态性能的分析

大推力直线电机直接驱动是一种新颖的高速数控机床直线进给系统驱动方式,它将直线电机的定子和动子分别安装在机床床身和工作台上,取消一切机械传动环节,大大提高进给系统的伺服性能,但这种驱动方式对外界干扰非常敏感,机床运行过程中切削力甚至进给系统运动部件质量的变化等均是系统的直接干扰.本文根据直接驱动进给系统的控制模型,分析了系统动态刚度的计算方法和主要影响因素,提出了提高动态性能的方法.根据系统的特点,设计动态质量估计器,实现直接驱动进给系统的动态质量在线估计和补偿.对实际系统的仿真分析表明,本文提出的基于系统动态质量在线估计与补偿方法,能大大提高系统的性能.