NC codes optimization for geometric error compensation of five-axis machine tools with one novel mathematical model

The International Journal of Advanced Manufacturing Technology - This paper presents the optimization compensation based on the mathematical expressions of geometric error model for the accuracy...     

基于球杆仪的五轴机床RTCP误差检测及补偿

引言RTCP(rotational tool center point)功能是五轴机床的一个重要功能,字面意思是“旋转刀具中心”,业内往往会稍加转义为“围绕刀具中心转”,也有一些人直译为“旋转刀具中心编程”。其实质为保持刀具中心点不变实现刀具的转动。RTCP功能的加入有效地提高了数控机床的加工效率,因此,RTCP精度是五轴联动数控机床的重要精度指标。     

Thermal error analysis,modeling and compensation of five-axis machine tools

The role of five-axis CNC machine tools (FAMT) in the manufacturing industry is becoming more and more important, but due to the large number of heat sources of FAMT, the thermal error caused by them will be more complicated. To simplify the complicated thermal error model, this paper presents a new modelling method for compensation of the thermal errors on a cradle-type FAMT. This method uses artificial neural network (ANN) and shark smell optimization (SSO) algorithm to evaluate the performance of FAMT, and developing the thermal error compensation system, the compensation model is verified by machining experiments. Generally, the thermal sensitive point screening is performed by a method in which a large number of temperature sensors are arranged randomly, it increases the workload and may cause omission of the heat sensitive point. In this paper, the thermal imager is used to screen out the temperature sensitive points of the machine tool (MT), then the temperature sensor is placed at the position of the heat sensitive point of the FAMT, and the collected thermal characteristic data is used for thermal error modeling. The C-axis heating test, spindle heating test, and the combined movement test are applied in this work, and the results show that the shark smell optimization artificial neural network (SSO-ANN) model was compared to the other two models and verified better performance than back propagation artificial neural network (BP-ANN) model and particle swarm optimization neural network (PSO) model with the same training samples. Finally, a compensation experiment is carried out. The compensation values, which was calculated by the SSO-ANN model are sent to the real-time error compensation controller. The compensation effect of the model is then tested by machining the ‘S’-shaped test piece. Test results show that the 32 % reduction in machining error is achieved after compensation, which means this method improves the accuracy and robustness of the thermal error compensation system.

     

五轴数控机床几何误差建模方法研究

五轴数控机床是实现工件复杂表面精密加工的重要设备,而机床本身精度是保证加工精度的重要前提。以一台大型五轴数控加工机床为研究对象,分析各项误差,应用多体系统运动学理论,建立移动轴与旋转轴的几何误差数学模型,推导出刀具相对工件坐标系的位置与姿态误差表达式,为误差补偿提供精确数学模型,提高机床加工精度。     

A new high-efficiency error compensation system for CNC multi-axis machine tools

To enhance the accuracy of CNC machines for the request of modern industry, an effective static/quasi-static error compensation system composed of an element-free interpolation algorithm based on the Galerkin method for error prediction, a recursive software compensation procedure, and an NC-code converting software, is developed. Through automatically analyzing the machining path, the new error prediction method takes into consideration the fact that the machine structure is non-rigid, and can efficiently determine the position errors of the cutter for compensation without computing a complex error model on-line. The predicted errors are then compensated based on a recursive compensation algorithm. Finally, a compensated NC program will be automatically generated by the NC-code converting software for the precision machining process. Because of the advantage of the element-free theory, the error prediction method can flexibly and irregularly distribute nodal points for accurate error prediction for a machine with complex error distribution characteristics throughout the workspace. To verify the algorithm and the developed system, cutting experiments were conducted in this study, and the results have shown the success of the proposed error compensation system.     

摇篮式五轴机床空间误差的简化建模方法

针对摇篮式五轴机床进行空间误差建模研究。根据机床结构,综合考虑运动误差和主轴热误差的影响,提出了一种新的机床坐标系设置方法,从而降低了误差模型的复杂性,建立了简化的空间误差模型。该模型数学表达式简单,物理意义明确,为进一步进行误差辨识和误差补偿奠定了理论基础。     

五轴数控机床几何误差建模与分析

基于多体系统基本理论推导出相邻体理想坐标变换以及误差变换矩阵并通过拓扑方法拓展到任一体理想坐标及误差变化公式。进而应用到五轴机床对应的零部件进行机床几何误差建模。最后推导出刀具形成点与工件被加工点的空间位置误差模型。并结合实验探究五轴数控机床37项误差参数对实际运动中的刀具形成点的位置误差影响,为之后的误差补偿和机床精度预测奠定理论基础。     

转台-摆头式五轴机床几何误差测量及辨识

为降低转动轴几何误差对转台-摆头式五轴机床精度的影响,提出了基于球杆仪的位置无关几何误差测量和辨识方法。基于多体系统理论及齐次坐标变换方法建立了转台-摆头式五轴机床位置无关几何误差模型,依据旋转轴不同运动状态下的几何误差影响因素建立基于圆轨迹的四种测量模式,并实现10项位置无关几何误差的辨识。利用所建立的几何误差模型进行数值模拟,确定转动轴的10项位置无关几何误差对测量轨迹的影响。最后,采用误差补偿的形式实验验证所提出的测量及辨识方法的有效性,将位置无关几何误差补偿前后的测量轨迹进行比较。误差补偿后10项位置无关几何误差的平均补偿率为70.4%,最大补偿率达到88.4%,实验结果表明所提出的建模和辨识方法可用于转台-摆头式五轴机床转动轴精度检测,同时可为机床精度评价及几何精度提升提供依据。     

基于球杆仪的五轴数控机床误差快速检测方法

几何误差是五轴数控机床重要误差源,针对传统测量方法仪器昂贵、测量周期长问题,提出基于球杆仪的五轴数控机床几何误差快速检测方法。对于机床的平动轴误差,利用多体系统理论及齐次坐标变换法,建立平动轴空间误差模型,通过球杆仪在同一平面不同位置进行两次圆轨迹,辨识出4项平动轴关键线性误差;针对五轴机床的转台和摆动轴,设计基于球杆仪的多条空间测试轨迹,完整求解出旋转轴12项几何误差。实验结果显示,所提方法获得转角定位误差与激光干涉仪法最大误差为0.001 8°,利用检测结果进行机床空间误差补偿,测试轨迹偏差由16μm降至4μm,为补偿前的25%,验证了方法的有效性。提出的五轴机床几何误差检测方法方便、便捷,适用于工业现场。     

A general methodology for machine tool accuracy enhancement by error compensation

A general methodology for increasing the accuracy of machine tools by compensating for the inherent systematic errors is described. This methodology in     

数控机床误差检测技术新进展

介绍了现有的各种典型的检测方法和技术特点,重点介绍了国内外近二十年、特别是最近十年来数控机床误差检测领域的研究新进展,具体包括DBB法、激光干涉仪法应用研究的最新成果以及平面光栅和R-test等新型检测仪器和方法;分析了当前数控机床误差检测研究中存在的问题,并对今后的研究趋势做了进一步展望。     

大型数控龙门铣床几何误差补偿方法研究

针对大型数控龙门铣床几何误差的问题,建立了大型数控龙门铣床的几何误差模型,分析了大型数控龙门铣床的几何误差源;利用API(T3)激光跟踪仪高精度大尺寸的测量特点及数据处理能力,提出了X、Y、Z轴线位移误差、角位移误差及各轴间垂直度误差的辨识算法,通过激光测量与计算准确地辨识了大型数控龙门铣床的几何误差;建立了大型数控龙门铣床加工空间几何误差数学模型,采用基于对象的事件驱动机制的程序设计语言Visual Basic开发了几何误差补偿软件,实现了几何误差补偿;现场检测了大型数控龙门铣床空行程平面运动轨迹及工件的平面度。研究结果表明,该方法使平面加工精度提高了50.77%,并验证了几何误差模型的正确性及几何误差补偿方法的有效性。     

一种基于新灵敏度指标的五轴数控机床关键几何误差辨识方法

精度设计是提升机床加工精度的有效途径,而准确辨识关键几何误差并为其合理分配权重是实现精度设计的前提条件,因此,提出了一种识别关键几何误差的灵敏度分析方法。 首先基于多体系统理论建立了机床加工误差模型,并基于该模型构建了灵敏度分析模型,同时定义了一种新的灵敏度指标。 然后,通过仿真分析明确了第 10、17、22、24 和 37 项几何误差为关键几何误差,同时实现了对各项几何误差分配权重。 最后,通过补偿关键几何误差和全部几何误差的方式对“ S”形检测试件进行加工并对比其轮廓度误差,对比结果显示通过两种补偿方式获得的平均轮廓度误差在 3 条检测线上的差值很小,分别为0. 005、0. 004 和 0. 006 mm,因此证明了提出的灵敏度分析方法的正确性。     

一种新的数控机床热误差实时补偿方法

根据数控机床加工热误差,首先,利用粗集理论方法,分析各变量与热误差之间的相关性,选择出机床热误差补偿的重要特征参数。然后提出一种动态反馈网络建立数控机床加工热误差补偿模型,新的数控机床热误差实时补偿方法具有补偿误差精度高,网络学习收敛速度快,误差补偿实时性好等特点。仿真实验结果证明了该方法的可行性和有效性。     

A methodology for error characterization and quantification in rotary joints of multi-axis machine tools

A novel methodology was developed and implemented for error characterization, evaluation, and its quantification in a rotary joint of multi-axis machine tools by using a calibrated double ball bar (DBB) system as a working standard. This methodology greatly simplified the measurement setup and accelerated the error quantification. Moreover, the methodology is observed to be highly economical by reducing the tooling and instrumentation. However, considerable time and little more efforts are required in measuring and computing the errors. The developed methodology is capable of evaluating the five degrees of freedom (DOF) errors including two radial errors, one axial error, and two tilt errors out of six DOF error components of rotary joints. A DBB system with point accessory was used for direct measurement by change of length at multi-points and various locations, whereas mathematical modeling technique was implemented, and equation solvers were exercised for error evaluation and its quantification. Validation and authentication of the methodology and results obtained were carried out by simulation process prior to implementing the methodology on rotary joints of a five-axis turbine blade grinding machine. The results obtained from “A” and “B” rotary joints of the turbine blade grinding machine were presented by applying cubic spline technique for error modeling and its further utilization. The methodology was found extremely pragmatic, quite simple, efficient, and easy to use for error characterization and its quantification in rotary joints of multi-axis machine tools.     

Product of exponential model for geometric error integration of multi-axis machine tools

This paper proposes a product of exponential (POE) model to integrate the geometric errors of multi-axis machine tools. Firstly, three twists are established to represent the six basic error components of each axis in an original way according to the geometric definition of the errors and twists. The three twists represent the basic errors in x, y, and z directions, respectively. One error POE model is established to integrate the three twists. This error POE formula is homogeneous and can express the geometric meaning of the basic errors, which is precise enough to improve the accuracy of the geometric error model. Secondly, squareness errors are taken into account using POE method to make the POE model of geometric errors more systematic. Two methods are proposed to obtain the POE models of squareness errors according to their geometric properties: The first method bases on the geometric definition of errors to obtain the twists directly; the other method uses the adjoint matrix through coordinate system transformation. Moreover, the topological structure of the machine tools is introduced into the POE method to make the POE model more reasonable and accurate. It can organize the obtained 14 twists and eight POE models of the three-axis machine tools. According to the order of these POE models multiplications, the integrated POE model of geometric errors is established. Finally, the experiments have been conducted on an MV-5A three-axis vertical machining center to verify the model. The results show that the integrated POE model is effective and precise enough. The error field of machine tool is obtained according to the error model, which is significant for the error prediction and compensation.