基于多体系统理论的矫直机几何误差的建模与补偿

针对矫直机的几何误差建模和补偿技术进行研究。将矫直机床视为一个多体系统结构,完成对矫直机的拓扑结构描述,并进行压头、夹头和跨距调整等关键运动部件的误差分析。通过其次变换矩阵体系统推导机床几何误差模型,基于建立的误差模型,采用激光干涉仪识别机床运动轴的几何位置误差。提出矫直机的几何误差补偿方法并设计与开发补偿软件,对矫直机定位精度进行补偿。通过实验进行了误差补偿效果评价,实验结果证明误差模型的正确性以及软件补偿的可行性。     

A new compensation method for geometry errors of five-axis machine tools

The present study aims to establish a new compensation method for geometry errors of five-axis machine tools. In the kinematic coordinate translation of five-axis machine tools, the tool orientation is determined by the motion position of machine rotation axes, whereas the tool tip position is determined by both machine linear axes and rotation axes together. Furthermore, as a nonlinear relationship exists between the workpiece coordinates and the machine axes coordinates, errors in the workpiece coordinate system are not directly related to those of the machine axes coordinate system. Consequently, the present study develops a new compensation method, the decouple method, for geometry errors of five-axis machine tools. The method proposed is based on a model that considers the tool orientation error only related to motion of machine rotation axes, and it further calculates the error compensations for rotation axes and linear axes separately, in contrast to the conventional method of calculating them simultaneously, i.e. determines the compensation of machine rotation axes first, and then calculates the compensation associated with the machine linear axes. Finally, the compensation mechanism is applied in the postprocessor of a CAM system and the effectiveness of error compensation is evaluated in real machine cutting using compensated NC code. In comparison with previous methods, the present compensation method has attributes of being simple, straightforward and without any singularity point in the model. The results indicate that the accuracy of positioning was improved by a factor of 8–10. Hence, the new compensation mechanism proposed in this study can effectively compensate geometry errors of five-axis machine tools.     

Accuracy enhancement of five-axis CNC machines through real-time error compensation

Although error modeling and compensation have given significant results for three-axis CNC machine tools, a few barriers have prevented this promising technique from being applied in five-axis CNC machine tools. One crucial barrier is the difficulty of measuring or identifying link errors in the rotary block of five-axis CNC machine tools. The error model is thus not fully known. To overcome this, the 3D probe-ball and spherical test method are successfully developed to measure and estimate these unknown link errors. Based on the identified error model, real-time error compensation methods for the five-axis CNC machine tool are investigated. The proposed model-based error compensation method is simple enough to implement in real time. Problems associated with the error compensation in singular position of the five-axis machine tool are also discussed. Experimental results show that the overall position accuracy of the five-axis CNC machine tool can be improved dramatically.     

五轴联动数控机床空间综合误差解耦技术研究

分析五轴联动机床的误差项和拓扑结构,给出伺服轴运动时理想情况和有误差情况下的坐标变换矩阵。以此为基础,给出五轴联动机床空间综合误差的计算方法。基于多体运动学的微分变换原理,给出五轴联动机床综合误差解耦算法。以某RTTTR型五轴联动机床为例,应用MATLAB进行实际综合误差解耦和补偿计算,结果验证了该解耦算法的正确性。     

五轴数控加工后处理关键技术分析与实现

从后处理的角度,分析了五轴数控加工的非线性误差,指出了其影响因素;提出了利用齐次变换矩阵和正向、逆向运动学相结合的误差计算方法以及相应的误差补偿策略;同时,引入了刀轴矢量"平滑化"的概念,提出了基于四元数向量插值的新算法;最后,以一个离心压气机叶轮为例,进行了计算机仿真加工和五轴机床试切加工实验.实验结果表明,所提出的方法改善了曲面加工精度和表面质量.     

基于多体系统理论的数控机床加工精度几何误差预测模型

针对多轴联动数控机床加工精度误差补偿问题,从分析数控机床误差产生机制和建立精度误差补偿模型的角度,提出基于多体系统理论的数控机床加工精度几何误差预测模型。分析B-A摆头五轴龙门数控机床的拓扑结构关系、低序体阵列、各典型体坐标变换,推导出B-A摆头五轴龙门数控机床的精度几何误差预测函数模型。采用平动轴十二线法误差参数辨识算法,计算出B-A摆头五轴数控机床21项空间几何误差,为精度几何误差预测函数提供有效的误差参数。该精度误差参数建模方法,对不同结构和运动关系的数控机床具有通用性,为后续数控机床误差动态实时补偿提高切削加工精度提供了理论基础。     

五轴联动立式磨床几何误差灵敏度研究

以一台五轴联动立式磨床为例,提出了一种分析几何误差灵敏度的方法。基于多体系统理论和齐次坐标变换建立了五轴联动立式磨床的33项几何误差模型,利用求导的方式给出了几何误差灵敏度分析的数学模型。并根据该模型找出了关键几何误差,研究了关键几何误差的灵敏度系数随平移轴运动的变化规律,研究结果为精密机床改进设计和误差的实时补偿提供了理论依据。     

Identification and compensation of geometric errors of rotary axes on five-axis machine by on-machine measurement

The geometric errors of rotary axes are the fundamental errors of a five-axis machine tool. They directly affect the machining accuracy, and require periodical measurement, identification and compensation. In this paper, a precise calibration and compensation method for the geometric errors of rotary axes on a five-axis machine tool is proposed. The automated measurement is realized by using an on-the-machine touch-trigger technology and an artifact. A calibration algorithm is proposed to calibrate geometric errors of rotary axes based on the relative displacement of the measured reference point. The geometric errors are individually separated and the coupling effect of the geometric errors of two rotary axes can be avoided. The geometry error of the artifact as well as its setup error has little influence on geometric error calibration results. Then a geometric error compensation algorithm is developed by modifying the numeric control (NC) source file. All the geometric errors of the rotary errors are compensated to improve the machining accuracy. The algorithm can be conveniently integrated into the post process. At last, an experiment on a five-axis machine tool with table A-axis and head B-axis structure validates the feasibility of the proposed method.     

数控机床五轴变换系统设计与研究

为实现数控机床五轴联动加工,基于国内蓝天系列数控系统提出了控制系统结构的改进方法。数控系统分为任务层和运动层,五轴变换单元集成在运动层。在对五轴机床进行分类并分析其几何信息的基础上,设计了机床的五轴运动库。以CA摆头机床为例,推导了其正向和反向运动变换。基于改进系统及五轴运动库,设计并分析了机床旋转刀具中心控制和三维半径补偿端铣。改进系统具有较好的可移植性,可在数控加工中直接执行刀具位置和方向指令。     

五轴联动后处理中非线性误差控制的研究

文中分析了非线性误差的产生原因及有效估算方法.通过机床的运动学分析,建立了BV100五轴联动机床的运动变换数学模型;结合线性插补原理,提出了该类机床的非线性运动误差的估算及补偿模型;通过VB语言,开发了具有非线性误差补偿功能的专用后置处理器,并通过某叶轮的切削加工实验验证了该后置处理器的正确性和实用性.     

Analysis of geometric errors associated with five-axis machining centre in improving the quality of cam profile

A five-axis machine is presently one of the most versatile machine tools available and they are becoming increasingly common. To increase the accuracy capabilities of such machines, it is crucial to be able to study the geometric errors of the components and its effect on the quality of machined products. In five-axis machine tools, all linear axes are theoretically perpendicular (dot product, cos 90°=0) to each other and directed along or around the X, Y and Z of the cartesian coordinate system; but in working machines, the axes are nearly perpendicular (cos89.90°≠0) because of manufacturing error and assembly error or quasi-static error. The present paper discusses the development of a generalised error model for the effects of geometric errors of the components of the kinematic chain of a machine in the workspace and the results obtained by this model have been verified experimentally. The effect of geometric error has been studied further for cam profile generation using a five-axis machining centre and an improvement in the profile has been obtained.     

数控机床在线检测系统的定位误差补偿实验研究

为了提高数控机床在线检测精度,研究机床各个轴的定位误差对数控机床在线检测精度的影响。针对数控机床误差补偿进行实验研究,采用激光干涉仪在数控机床上测量出各个轴的定位误差,将各个轴的定位误差依次进行补偿;并以Visual C++6. 0为工具,编写了三次样条曲线的算法程序,将测量的数据点拟合成一条曲线,达到可以预测机床任意点误差的效果;进行标准块检测实验。结果表明:在数控机床在线检测系统中实施误差补偿,效果较为明显,利用补偿软件可以实现对数控机床任意点进行补偿。     

A general approach for error modeling of machine tools

This paper presents a general and systematic approach for geometric error modeling of machine tools due to the geometric errors arising from manufacturing and assembly. The approach can be implemented in three steps: (1) development of a linear map between the pose error twist and source errors within machine tool kinematic chains using homogeneous transformation matrix method; (2) formulation of a linear map between the pose error twist and the error intensities of a machine tool; (3) combination of these two models for error separation. The merit of this approach lies in that it enables the source errors affecting the compensatable and uncompensatable pose accuracy of the machine tool to be explicitly separated, thereby providing designers and/or field engineers with an informative guideline for the accuracy improvement by suitable measures, i.e. component tolerancing in design, manufacturing and assembly processes, and error compensation. Two typical multi-axis machine tools are taken as examples to illustrate the generality and effectiveness of this approach.     

Accuracy test of five-axis CNC machine tool with 3D probe–ball. Part I: design and modeling

The error model of CNC machine tool describes the relationship between the individual error source and its effects on the overall position errors. A practical problem in applying this technique to five-axis machine tool is that the predicted position errors cannot be justified. This paper, the first in a set of two, presents a new measurement device, the probe–ball, which can be used to measure the overall position errors of five-axis machine tools directly. To perform the accuracy test, a three-degree-of-freedom (3D) measuring probe is installed in the main spindle and a base plate is fixed on the turntable. The kinematic chain of the five-axis machine tool is then closed through connecting the central ball on the base plate with the extension bar of the probe. To generate simultaneous axes motion under the condition of closed kinematic chain, the central ball is defined as origin of the workpiece coordinate frame and the probe is driven along a path on a spherical test surface with the central ball as center. The overall position errors are measured with the 3D measuring probe. A theoretical model is derived to explain the nature of the probe–ball error measurements.     

Accuracy improvement of miniaturized machine tool: Geometric error modeling and compensation

A novel capacitance–sensor based multi-degree-of-freedom (DOF) measurement system has been developed for measuring geometric errors of a miniaturized machine tool (mMT) overcoming the size limitations. In the present work five geometric error components of a three-axis mMT are measured simultaneously along each axis and the squareness errors are determined by the slopes of straightness error profiles. Least-squares fitting method is used to represent the analytical models of geometric errors. A kinematic chain consisting of various structural members of mMT is introduced to establish the positional relationships among its coordinate frames. Based on this kinematic chain a general volumetric error model has been developed to synthesize all geometric error components of a miniaturized machine tool. Then, a recursive compensation method is proposed to achieve error compensation efficiently. Test results show that the positioning accuracy of miniaturized machine tool has been improved with compensation.     

五轴联动刀具空间半径补偿研究

五轴联动数控机床主要应用于自由曲面的加工，得到广泛的应用。但五轴联动所涉及的刀具补偿就目前所见资料而言，未能得到很好解决。本文重点分析了刀轴有两个旋转自由度(如B，C)的五轴联动的刀具补偿问题。结果表明经研制的刀具补偿模块在南京四开电子企业的五轴联动数控机床上得到较好应用。     

Accuracy test of five-axis CNC machine tool with 3D probe-ball. Part II: errors estimation

To improve the accuracy of CNC machine tools, error sources and its effects on the overall position and orientation errors must be known. Most motional errors in the error model of five-axis machine tool can be measured with modern laser interferometer devices, but there are still some not measurable geometric errors. These not measurable errors include constant, inaccurate link errors of components such as rotary axes block, main spindle block and tool holder. After setting all measured errors in the error model, a reduced error model is defined, which describes the influence of each unknown and not measurable link error on the overall position errors of the five-axis machine tool. On the other hand, the newly developed probe-ball device can measure the overall position errors of five-axis machine tools directly. Based on the reduced model and the overall position errors, the link errors can be estimated very accurately with the least square estimation method. The error model is then fully known and can be used for advanced purposes such as error prediction and compensation.     

Validation of volumetric error compensation for a five-axis machine using surface mismatch producing tests and on-machine touch probing

In order to validate volumetric error compensation methods for five-axis machine tools, the machining of test parts has been proposed. For such tests, a coordinate measuring machine (CMM) or other external measurement, outside of the machine tool, is required to measure the accuracy of the machined part. In this paper, a series of machining tests are proposed to validate a compensation strategy and compare the machining accuracy before and after the compensation using only on-machine measurements. The basis of the tests is to machine slots, each completed using two different rotary axes indexations of the CNC machine tool. Using directional derivatives of the volumetric errors, it is possible to verify that a surface mismatch is produced between the two halves of the same slot in the presence of specific machine geometric errors. The mismatch at the both sides of the slot, which materializes the machine volumetric errors is measured using touch probing by the erroneous machine itself and with high accuracy since the measurement of both slot halves can be conducted using a single set of rotary axes indexation and in a volumetric region of a few millimetres. The effect of a compensation strategy is then validated by comparing the surface mismatch value for compensated and uncompensated slots.     

双摆台五坐标铣削后置处理软件Star-Fpost研究

针对MIRON UCP800双摆台立式五坐标加工中心,研究其五坐标加工的数学模型.推导出刀心和刀轴矢量六坐标转换成AC双摆台式五坐标的算法公式.利用坐标矩阵转换的方法实现直线圆弧插补刀轨源文件到机床代码的后置处理过程.使用面向对象程序,采取逐行读取刀轨文件关键字触发的方式,开发了专用的五坐标铣削后置处理软件Star-Fpost,在VERICUT仿真环境中完成五坐标机床的建模,在UGNX通过三元整体轴径流式叶轮的仿真加工,仿真结果验证了后置处理软件的功能,可以为MIKRON UCP800五坐标机床实际加工提供参考.     

数控机床平动轴误差辨识及补偿研究

为了大幅提升数控机床平动轴的运动精度,从而满足当代数控系统对其高精度的要求,针对机床平动轴的空间几何误差开展了深入研究,提出了可以有效辨识平动轴空间几何误差的便捷方法,并基于齐次坐标变换原理建立了平动轴空间几何误差的辨识模型;针对机床平动轴定位误差的特性,提出了可以实现有效补偿的增量式误差补偿原理,并建立了相应的误差补偿模型。经验证,所提出的平动轴误差辨识法和增量式误差补偿原理不仅理论正确,而且可以大幅地提高机床平动轴的定位精度。