Three-dimensional tool radius compensation for multi-axis peripheral milling

Few function about 3D tool radius compensation is applied to generating executable motion control commands in the existing computer numerical control (CNC) systems. Once the tool radius is changed, especially in the case of tool size changing with tool wear in machining, a new NC program has to be recreated. A generic 3D tool radius compensation method for multi-axis peripheral milling in CNC systems is presented. The offset path is calculated by offsetting the tool path along the direction of the offset vector with a given distance. The offset vector is perpendicular to both the tangent vector of the tool path and the orientation vector of the tool axis relative to the workpiece. The orientation vector equations of the tool axis relative to the workpiece are obtained through homogeneous coordinate transformation matrix and forward kinematics of generalized kinematics model of multi-axis machine tools. To avoid cutting into the corner formed by the two adjacent tool paths, the coordinates of offset path at the intersection point have been calculated according to the transition type that is determined by the angle between the two tool path tangent vectors at the corner. Through the verification by the solid cutting simulation software VERICUTwith different tool radiuses on a table-tilting type five-axis machine tool, and by the real machining experiment of machining a soup spoon on a five-axis machine tool with the developed CNC system, the effectiveness of the proposed 3D tool radius compensation method is confirmed. The proposed compensation method can be suitable for all kinds of threeto five-axis machine tools as a general form.     

符合阿贝原则的数控机床几何误差建模

为提高现有数控机床空间误差分析方法的准确度,本文基于阿贝原则对齐次转换矩阵(HTM)几何误差补偿模型进行优化。首先,推导出XYFZ型三轴机床适用的HTM几何误差补偿模型并给出模型正确使用的前提条件;然后,基于阿贝原则分析了三轴机床的空间误差传递机理,指出阿贝误差对机床定位精度的影响,给出理论计算公式并在机床运动轴上进行实验验证;最后,基于阿贝原则和布莱恩原则对现有的HTM几何误差补偿模型进行优化,采用该模型拟合体对角线空间误差,并与实测机床体对角线误差进行对比验证。现有HTM几何补偿模型可将机床空间误差由41.15μm补偿至16.37μm,补偿率为60.22%;优化后的补偿模型可将机床空间误差补偿至5.32μm,补偿率为87.07%,提高了26.85%。实验结果表明,优化后的补偿模型更加合理,进一步改善了空间误差的补偿精度。     

双转台五轴机床空间误差补偿技术研究

几何误差、热误差和切削力误差占到了机床总误差的75%,对这3项误差进行控制是提高机床加工精度的关键所在。以双转台五轴机床的空间误差作为研究对象,通过对加工位置、主要热源及电动机电流等相关因素进行分析,确定空间误差建模所需的位移变量、温度变量和切削力变量。以现有的多种误差建模方法为基础,通过对信息融合技术进行研究,提出一种机床空间误差的多模型融合预测方法,建立综合反映几何误差、热误差和切削力误差的最优空间误差模型。最后以DSP为核心,设计空间误差补偿器,实施空间误差补偿,验证补偿效果。结果显示,建立的模型预测精度较高,残差小于2μm,而实施空间误差补偿后,加工零件的轮廓误差也由15μm降到了5μm,补偿效果明显。     

A methodology for systematic geometric error compensation in five-axis machine tools

To enhance the accuracy, an efficient methodology was developed and described for systematic geometric error correction and their compensation in five-axis machine tools. The methodology is capable of compensating the overall effect of all position-dependent and position-independent errors which contribute to volumetric workspace. It was implemented on a five-axis grinding machine for error compensation and for the check of its effectiveness. Error compensation algorithm was designed, and a routine was written in Matlab software. The developed technique and software are based on an error table which interprets the function of axis through cubic spline technique and synthesis modeling of a machine tool. Recursive compensation methodology was used to remove the machine errors from the actual tool path and inverse technique was implemented to find the corrected positions of prismatic and rotary joints. Moreover, it can convert the corrected tool paths into practical compensated NC codes. The generated, corrected and modified NC codes directly fed to the controller of a five-axis machine tool. Validation of the technique was preceded by repeated experimentation of measurement and through machining of typical standard workpieces with some additional specific features. Experimental results exhibit effective compensation and remarkable improvement in the parametric and volumetric-workspace accuracy of the five-axis machine tool.     

The development of embedded device to detect chatter vibration in machine tools and CNC-based autonomous compensation

The chatter vibration stands for a sudden relative vibration appeared between a material and a tool while processing with a machine. This vibration is a factor that seriously affects the quality of processed materials as well as being a factor which causes serious damages to the tool and the machine. This study is related to the detection and compensation of chatter vibration that can compensate chatter vibration faster and produce processed goods with more precision by autonomous compensation. The above-mentioned chatter vibration compensator includes the chatter vibration sensor and the chatter compensator that estimates the compensation value according to the sensor detecting the chatter vibration of machine tool and the chatter vibration detected from the sensor while having a feature of being organized by interlocking with the machine tool controller.     

数控机床螺距误差补偿技术研究

分析了数控机床螺距误差的产生原因和误差补偿原理,介绍了SINUMERIK802S/C系统数控机床螺距误差的等间距补偿方法和基于激光干涉仪的动态补偿方法,并给出了误差补偿实例。     

Mapping and compensation of geometric errors of a machine tool at different constant ambient temperatures

Thermo-mechanical effects due to changes in the ambient temperature on the shop floor and internal heat sources caused by the manufacturing process significantly contribute to the geometric deviations of a machine tool and therefore, the geometric deviations of the manufactured workpiece. Minimizing these thermally induced geometric deviations is worthwhile since the requested tolerances of machined workpieces become continually smaller nowadays. To investigate the overall deformations of a machine tool structure due to variations in ambient temperature the geometric errors of a five-axis machine tool at different ambient temperatures by means of a portable climate simulation chamber are systematically mapped. While positioning and squareness errors of the linear axes are significantly influenced by the ambient temperature, straightness as well as rotational errors were less sensitive to temperature effects. For the investigated machine tool errors of the two rotational axes are negligible due to an active cooling of these axes. Through numerical error compensation of the linear axes, the geometric errors of the investigated machine tool can be reduced up to 80%. Finally, an outlook how a temperature-dependent compensation could be derived from previously measured compensation fields at discrete temperatures and afterwards applied on-the-fly during manufacturing is given.     

基于激光干涉仪的数控机床几何误差检测与辨识

数控机床误差补偿技术通过设计和制造途径消除或减少数控机床可能的误差源,是提高数控机床加工精度的有效途径。其内容包括误差检测、误差建模和误差补偿。数控机床误差补偿效果好坏在很大程度上取决于误差综合数学模型建立的准确性。而误差元素模型是误差综合数学模型的基础。所以,误差补偿的首要任务是对数控机床误差元素进行准确检测。文中介绍了利用激光干涉仪检测和辨识数控机床几何误差的方法,建立了基于激光干涉仪的数控机床几何误差元素模型。     

基于线性回归理论的数控机床精度检测及误差补偿分析

为提高数控机床定位精度,需对精度的误差源进行分析及补偿。基于线性回归理论,采用激光干涉仪为检测工具,建立了BF-850B数控机床数据检测的精度检测与补偿模型,并根据各个测量点位误差特性进行分析,确定采用一次性线性补偿和多段式线性补偿方法;最后,结合具体的数控机床实例,根据得到的实验数据验证实现误差补偿,对定位精度的补偿效果进行了分析。结果表明:一次性线性补偿将X轴精度由4.853 1～35.025 0μm提高至-2.472 1～0.736 3μm;将Y轴精度由-14.425 0～-4.132 5μm提高至-2.481 2～0.752 9μm;将Z轴精度由-4.128 0～17.227 1μm提高至-0.501 5～1.324 5μm;多段式线性补偿将X轴精度提高至-1.364 1～0.484 0μm;将Y轴精度提高至-1.364 1～0.551 0μm;将Z轴精度提高至-0.412 0～0.495 2μm;补偿前根据数据分布的主要特点,采用呈线性或分段式对数控机床的系统误差进行相应的呈线性或分段式补偿有着很好的补偿效果。     

五轴数控机床综合误差补偿解耦研究

五轴数控机床具有3个移动副和2个转动副,能对复杂曲面实现高精度加工,然而其误差补偿运动却比较复杂,因为其各运动副的误差补偿运动量与刀具和工件间的误差值(位置及方向误差)间存在一定的耦合关系。通过分析五轴机床的运动特点,用齐次坐标变换的方法建立了各运动副坐标系间的变换矩阵。基于小误差补偿运动假设,分析了误差运动和补偿运动间的相互关系,对五轴机床各运动副的位置及方向误差补偿运动进行了解耦,建立了可以进行空间五个误差补偿量计算的数学模型,为五轴机床的误差实时补偿提供了理论基础。     

数控机床热误差的在线测量与补偿加工

对数控机床热误差的产生原因及特点进行了综合分析,简单介绍了应用激光干涉仪对其进行在线测量的基本原理,对数控机床热误差补偿的具体实施过程进行了详细阐述。利用PLC抗干扰能力强、可靠性高、运算速度快及良好的接口性能,给出了数控机床热误差补偿系统的硬件实现方法。应用PLC技术可以提高误差补偿精度,对误差补偿的硬件实施具有一定参考意义。     

恒定加工条件及定期补偿下的刀具渐变可靠性灵敏度分析方法

据统计,由刀具失效导致的停机时间超过机床被迫停机时间的1/3,故开展刀具渐变可靠性及其灵敏度分析的研究对提高机床的运行可靠性具有重要意义。采用连续时间、连续状态、具有非减独立增量的非平稳Gamma过程描述刀具磨损量的变化过程。根据加工偏差不大于机床给定加工精度的原则,构建刀具制造及磨损量检测有无误差两种情形下、恒定加工条件及定期补偿的刀具渐变状态函数,由此推导出相应的渐变可靠度模型。在此基础上给出渐变可靠度模型对各个参数的灵敏度计算方程。通过数值实例分析,阐述了通过提出的渐变可靠性模型及灵敏度分析方法提高刀具运行可靠性的应用过程。这一工作为提高恒定加工条件及定期补偿下刀具的运行可靠性提供切实可行的理论和方法基础。     

基于数控系统底层通信的实时误差补偿及应用

为提高数控机床加工精度,设计开发基于CNC底层通信的实时误差补偿功能模块,该模块通过GSK-Link网络通信协议与CNC底层进行数据交互。实时补偿过程为：通过温度采集模块和数据通信模块实时采集机床温度及各坐标轴坐标,误差补偿器计算误差补偿值并将计算结果直接送往CNC实时误差补偿功能模块,以实现机床误差实时补偿。该补偿过程的最大优点是实时补偿器与CNC底层直接通信,而不是目前国际上惯用的先通过PLC再与CNC底层通信的方式,因此实时补偿的速度和效率更高,补偿效果更好。GSK 25i数控系统的实时补偿结果表明,实时误差补偿可有效提高机床精度,最大可提高91.7%。     

数控机床加工中的刀具补偿

不同类型的数控机床与刀具，需要考虑不同的补偿形式。只有全面掌握刀具补偿的原理与方法，才能使编程员进行程序编制时，通过调用不同刀具号来满足刀补要求。     

刀具半径补偿在数控铣削加工中的作用

以FANUC0i系统为例,在铣削加工过程中,机床若不具备刀具半径补偿功能,那么编程需计算刀具中心轨迹,尤其当刀具因磨损、重磨、换新刀而引起刀具直径变化时,很难计算刀具中心轨迹,这样不仅给编程带来麻烦,而且也很难保证零件的加工精度。当机床具备刀具半径补偿功能时,只需按照零件轮廓编程,省去计算刀具中心坐标值,从而简化了编程。实际操作过程中,只要通过改变刀具半径补偿值即可控制零件的加工精度。     

机械制造业数控机床几何误差自动控制

为了降低数控机床几何误差,提升加工精度,提出机械制造业数控机床几何误差自动控制方法。通过激光跟踪仪辨识机械制造业数控机床的几何误差,采用快速定位补偿算法与圆弧插补补偿算法相结合的方法补偿数控机床几何误差。利用计算机辅助制造软件生成刀位文件,依据刀位文件生成数控机床加工程序,通过补偿控制器生成数控机床各轴运动的控制指令,数控机床伺服系统接收控制指令后,自动控制数控机床各轴运动,以达到数控机床几何误差自动控制的目的。实验结果表明,采用该方法自动控制数控机床几何误差后,方向与角度的几何误差分别低于0.03 mm与0.1°,实际应用效果较好。     

五轴数控机床加工误差动态修正方法研究

为修正五轴数控机床加工误差,提高五轴数控机床加工质量,提出一种新的五轴数控机床加工误差动态修正方法.构建五轴数控机床加工误差计算模型,获取五轴数控机床加工的刀心方位、刀轴方位轮廓误差;锁定误差方位后,通过五轴数控机床误差的动态实时补偿方法,实现五轴数控机床加工误差动态修正.研究结果表明:所提方法可实现全方位、高效率的五...     

数控车床中刀补的建立及其应用

以广州数控系统980T为例,阐述了数控车床中刀补的建立及其应用.在数控机床上使用多把丰刀加工工件时,除了基准刀外,其他的几把刀具一般都要设置刀具补偿.刀补设置的正确与否,不但影响到工件的加工精度,还对其他方面诸如加工生产率等产生影响.正确并巧妙地设置刀具补偿,不但有效保证工件的加工精度,还可以简化加工编程,提高生产率.     

数控加工中刀具半径补偿功能的应用研究

编程人员编制零件加工程序时,以零件轮廓轨迹编写,与刀具尺寸无关,而数控机床加工时,控制的是刀具中心(刀位点)的轨迹,因此刀具补偿功能就显得尤为重要。对数控机床加工中刀具补偿功能进行了全面分析,并重点分析了刀具半径补偿功能。主要从刀具半径补偿的含义出发,研究分析其在数控加工中的应用及应该注意的问题,其在工程实践中的重大指导意义在于扩充系统的加工范围并提高整个数控系统的精度,使刀具补偿功能在数控机床加工中得到更好的发挥,使数控机床加工中的刀具补偿功能的综合性能得到更广泛的应用。     

Position error reduction of tool center point in multi-tasking machine tools through compensating influence of geometric deviations identified by ball bar measurements

A method to compensate the influence of geometric deviations on tool center point (TCP) for a multi-tasking machine tool is proposed in this paper. Some methods to compensate geometric deviations of a rotary axis in five-axis machining centers have been proposed. However, due to the special topological structure of multi-tasking machine tools, the identification and compensation methods for geometric deviations are different from those of the five-axis machining centers, which have been seldom researched until now. In this paper, the main attention is paid to analyze the eccentricities of the trajectories measured by a ball bar under simultaneous three-axis motions and to reduce the influence of the identified geometric deviations on the position error of TCP by the compensation method. It is divided into two sequential subtasks. At first, the geometric deviations are identified by using the eccentricities of measured trajectories. A simple and practical measuring procedure is proposed to identify geometric deviations of rotary axes existing in a multi-tasking machine tool. For the second step, a method is proposed by modifying the original NC code according to the kinematic chain model of the targeted machine tool to compensate the influence of the existing geometric deviations on TCP. An experiment is conducted on a multi-tasking machine tool with a swivel tool spindle head in the horizontal position. The repeatability of the measured eccentricities based on three experimental results is also investigated to reduce the influence of measuring error on the identified results. As a result, the corresponding values of geometric deviations after the compensation are less than 2.2 arcseconds or 2.4 μm. It is concluded that the influence of geometric deviations on TCP is compensated effectively, and the position error of TCP is reduced significantly.