Experiences with the master axis method for measuring spindle error motions

In this paper, the master axis method of machine tool spindle measurement is described. This method allows spindle measurements to be carried out at speed and under load. For example, a radial load representing the cutting force in a turning operation can be conveniently applied during characterization of a lathe spindle. The synchronous and asynchronous error motions have been observed to vary in both magnitude and shape with changes in load. Test results from both static and dynamic loads during testing are shown to demonstrate the utility of the method.     

精密数控机床主轴热伸长补偿技术研究

针对目前精密数控机床热误差补偿问题,在基于主轴热误差测量系统的基础上,提出一种基于FCM聚类、多元线性回归的热误差补偿模型。通过对某卧式加工中心主轴恒定转速和变速工况下进行温敏点测量,建立关键温敏点与机床主轴热伸长的几何关系,通过补偿结果和切削试验表明该方法可以有效地降低主轴热伸长误差,提升零件的加工精度。     

机床主轴径向误差运动在线检测与信号处理

在机床加工工件时,实时测量机床主轴的径向运动误差。测量对象是在该机床上加工的圆柱形工件,而不是通常所使用的标准棒。采用误差分离技术将工件的形状误差从所测信号中分离出来,实现在线测量主轴的径向误差运动。并采用基于自适应阈值的小波包算法去除加工时存在的噪声。同时,从谐波抑制特性和总体频域特性两个方面分析了测量系统频域特征。     

Frequency domain error analysis in turning

In spite of the large body of work on error analysis in turning, there are very few references that directly address the relationship between the original frequency content of the different dynamic errors of the machine tool and of the machining process and the resulting spatial frequency content of the machined surface. In this paper, the dynamic errors of a machine tool are classified into two categories: (a) kinematics-induced and (b) vibration-induced dynamic errors. Through a theoretical analysis, it will be shown that the spatial frequency content of the turned surface is not directly influenced by the original frequency factors of the machine dynamic error components, but by the aliased frequency factors which will be explained in this paper. On the basis of the establishment of the deterministic mathematical relationship between the frequency contents of the machine dynamic errors in the volumetric error model and the spatial frequency content of the turned surface in radial directions, a method for obtaining the frequency spectrum of the machined surface error in radial directions is given. In addition, a method to influence the number of spatial frequency components of the surface error in radial directions and to predict and control their magnitude is put forward. A case study of a flat surface turning is presented to highlight the effectiveness of the theoretical analysis and of the proposed methods. This study has potential applications in predicting and controlling the spatial content of machined surfaces, in selecting proper machining conditions, as well as in designing machine tools for applications in which strict spatial frequency requirements are placed on the workpiece surface.     

一种圆柱度测量基准的误差分离方法

通过对主轴回转误差运动的分析，结合三点法圆度误差分离技术，提出了一种完全分离圆柱度测量基准误差的分离方法，即利用主轴回转轴线平均线、测量传感器及直行导轨之间的空间位置关系，建立相应的坐标系，在分离出被测截面圆度误差、最小二乘圆心初始坐标的基础上，完整地分离出影响圆柱度精密测量的径向回转运动误差和导轨的直行运动误差。该技术不仅可以消除测量基准误差对圆柱度测量精度的影响，还可以实现主轴回转误差、导轨直线度以及导轨对主轴平行度误差的精密测量，对高精度误差补偿加工和机床的精度检验也具有重要意义。     

龙门数控机床主轴热误差及其改善措施

依据ISO和ASME标准建立龙门数控(Numerical control,NC)机床热误差测试条件,通过主轴恒转速和变转速热误差试验分析主轴箱温度场分布及其对主轴热误差的影响趋势。建立龙门机床误差元素模型,分析影响机床各坐标轴加工精度的主轴热误差分量。研究发现,主轴热误差和主轴箱温度存在单调对应关系,温度对主轴轴向的热伸长误差的影响要远大于主轴径向的热漂移误差,但温度变化相对各坐标变形存在热延迟和热惯性等特性。对主轴径向精度影响最大的热误差分量是由机床生热产生的同方向的偏移误差和与之垂直的偏转误差;对轴向精度影响最大的则是轴向的偏移误差。针对热误差特点和分布规律,提出结构优化、热平衡、误差补偿建模等3种减小热误差的措施,并对其各自优点进行了分析。     

基于改进遗传算法的机床主轴径向回转误差分离技术研究

以提高精密机床主轴回转误差的测量精度为研究目标,基于四点法矩阵算法,采用多圈重合式方法对主轴回转误差测量中的传感器输出数据进行处理。为提高传统遗传算法的收敛速度,降低优化结果对初始值的依赖性,对交叉和变异概率因子列式进行更新,并使用改进遗传算法对传感器安装角度和输出权值系数进行优化。使用改进遗传算法,收敛速率较传统遗传算法提高50%左右。利用多功能斜轨数控车床进行主轴径向回转误差测量及分离实验,分离后的标准芯棒形状误差值与标定值相比,误差在5%以内,且误差重复性低于5%。结果表明分离的结果精度较高,从而验证提出的算法的正确性和可行性。     

A comprehensive technique for measuring the three-dimensional positioning accuracy of a rotating object

A method for measuring the accuracy of rotating objects was studied. Rotating axis errors are significant; such as the spindle error of a machine tool which results in increased surface roughness of machined work pieces. Three capacitance-type displacement sensors were used to measure the position of a rotating master ball. The sensors were mounted at the three orthogonal points on the spindle axis. The measurement data were analysed for rotating spindle accuracy, not only for the average roundness error but also for the spindle volumetric positional error during rotation. This method is simple and economical for industrial field use for regular inspection of spindles using portable equipment. The time taken for measurement and analysis using this method is only about two hours. This method can also measure microscopic amplitudes in 3-D directions of vibrating objects.     

金刚石刀具刀尖圆弧波纹度的测量及评价

为实现金刚石刀具刀尖圆弧波纹度超精密测量,构建了基于原子力显微镜(AFM)和精密回转轴系的刀尖圆弧轮廓测量系统,研究了刀尖圆弧波纹度评价方法和控制测量系统引入误差的策略。提出了评价刀尖圆弧波纹度时截止波长的确定原则和方法,并介绍了刀尖圆弧波纹度测量原理及评价流程。讨论了精密回转轴系径向回转误差的测量和评定、刀具安装偏心和偏角误差的控制和原子力扫描系统Z向非线性误差的校准方法。最后,在构建的测量系统上测量了了金刚石刀具刀尖圆弧波纹度并对测量不确定度进行了分析。实验测量显示:所评价金刚石刀具的刀尖圆弧波纹度为0.106μm,测量不确定度为23.8nm,表明所构建的测量系统基本满足金刚石刀具刀尖圆弧波纹度纳米级测量及评价的需求,测量结果稳定可靠、精度高。     

An identification method for spindle rotation error of a diamond turning machine based on the wavelet transform

This paper presents an identification method for the spindle rotation error from the flatness error in the workpiece surface. The spindle rotation error is identified by the wavelet transform, Weierstrass function, and power spectral density (PSD). The flatness error comprises various errors of the machine tool, such as spindle rotation error, guideway error, motor error, and ball screw error, therefore, wavelet transform is used to process the measured result of the workpiece and the signal is decomposed into high-frequency and low-frequency signal. Weierstrass function is used to fit the spindle rotation error. According to the PSD analysis of the processed signal in the frequency domain, the spindle rotation error is identified from the measured flatness error, this method provides a basis for the identification of machine tool errors.     

A new method for directly measuring the position errors of a three-axis machine. Part 1: theory

This paper presents a measurement method and instrument to measure position changes in a three-axis machine workspace. The proposed instrument, named 3D step gauge, includes two parts. One is composed of three LVDTs and installed in the main spindle. The other is a plate that is fixed on the worktable. Many triangular pyramids are distributed on the plate. Each pyramid profile plane is the basic measurement plane for the LVDTs. When the spindle moves relative to the plate, the LVDTs’ tip ends slide on the pyramid profile planes. From the datum measured by the LVDTs, the differential position changes of the spindle can be obtained by the pyramid’s constructional parameters. In addition, the error effect analysis is used to investigate the accuracy of the method with respect to the factor of the device constructional parameters. Part 1 of this paper gives the basic theory of measuring the differential position changes in the multi-axis machine workspace. Part 2 gives the application of this theory and so the position error in the multi-axis machine workspace can be directly measured. This proposed method and the instrument have been tested using an actual machine tool. The measurement results show good repeatability and high accuracy.     

Mechanical model and contouring analysis of high-speed ball-screw drive systems with compliance effect

The compliance effect of a high-speed ball-screw feed-drive system is modelled in this work. A mechanical model of a ball-screw feed drive system including the motor, ball-screw, coupling, supporting bearing, linear guide and machine structure was developed. It was found that at high acceleration, the mechanical compliance caused a significant contouring error. Smoothing the acceleration and deceleration control input command did improve the transient deviation in the contouring error. However, the steady state error caused by the elastic elongation in the mechanical elements was not improved. It was also shown that the inertia force of the slide and saddle comprised the dominant loading on a high speed machine tool drive mechanism. A topology structure optimisation method is proposed to reduce the moving weight. This method can help the designer efficiently reduce the moving weight of a machine tool axis in a systematic way. More than a 30% weight reduction was demonstrated in a spindle carrier structural design.     

零传动滚齿机热特性的试验研究

在零传动滚齿机中,工件主轴的径向热变形严重影响工件的齿向加工精度,而滚刀主轴的轴向和径向热变形对工件的齿距偏差和齿向偏差都产生很大的影响。从试验的角度研究工件主轴和滚刀主轴的热变形,最后根据试验提出从结构优化和热误差补偿两方面来研究机床热变形的控制技术。     

Spindle Thermal Error Optimization Modeling of a Five-axis Machine Tool

Aiming at the problem of low machining accuracy and uncontrollable thermal errors of NC machine tools, spindle thermal error measurement, modeling and compensation of a two turntable five-axis machine tool are researched. Measurement experiment of heat sources and thermal errors are carried out, and GRA(grey relational analysis) method is introduced into the selection of temperature variables used for thermal error modeling. In order to analyze the influence of different heat sources on spindle thermal errors, an ANN(artificial neural network) model is presented, and ABC(artificial bee colony) algorithm is introduced to train the link weights of ANN, a new ABCNN(Artificial bee colony-based neural network) modeling method is proposed and used in the prediction of spindle thermal errors. In order to test the prediction performance of ABC-NN model, an experiment system is developed, the prediction results of LSR(least squares regression), ANN and ABC-NN are compared with the measurement results of spindle thermal errors. Experiment results show that the prediction accuracy of ABC-NN model is higher than LSR and ANN, and the residual error is smaller than 3 lm, the new modeling method is feasible. The proposed research provides instruction to compensate thermal errors and improve machining accuracy of NC machine tools.     

A new 2D error separation technique for performance tests of CNC machine tools

The error separation technique is widely adopted for many machine tool performance tests. The most common applications include roughness measurement, straightness measurement and spindle measurement. In this paper, two error-separation technologies, the straightness reversal technique and the semi-reversal technique, are developed. The straightness reversal technique can be adopted for the straightness measurement of a linear axis. The semi-reversal technique can be adopted for setting error separation in a contouring test and in the spindle error measurement. In this paper, mathematical models have been developed. In order to verify the possibility of the semi-reversal technique, related experimental work has been carried out.     

Development of a rapid profilometer with an application to roundness gauging

This paper presents the development of a real-time, contact-based, high frequency, response profilometer employed as a roundness gauge for measuring circular form error for 100% part inspection on the shop floor with an accuracy of better than 0.5 μm with measurement times of less than 1 s. The gauge head is a closed-loop controlled mechanism comprising a contact force probe that is rigidly attached to a high bandwidth linear translator. The gauge head assembly is, in turn, attached to a precision spindle. The objective of the complete tool is to contact the sidewall of the circular feature, translate the probe tip to produce a defined contact force with the workpiece and rotate the gauge head assembly. During rotation of the spindle, this contact force is maintained at a nominally constant value by dynamically translating the force probe along a radial direction to follow surface deviations. The gauge head assembly (including force probe and servo drive) has a fundamental mode natural frequency of 330 Hz while scanning the workpiece with a constant contact force typically less than 100 mN. Form error (deviation from a nominal circle) is measured using a capacitance-based displacement sensor measuring the relative radial displacement of the probe with the spindle rotating at a constant rotation speed. This paper discusses the design and characterization of this metrology tool.     

A new method for characterizing axis of rotation radial error motion: Part 1. Two-dimensional radial error motion theory

In the current standards of spindle metrology, the fundamental component of radial probe measurement is considered radial throw (eccentricity) of the installed test artifact and the fundamental radial error motion is treated as non-existent. The goals of this paper are: (1) to make evident the fact that fundamental radial error motion can actually exist; (2) to present a new two-dimensional (2D) method to analyze spindle radial error motion measurement; (3) to discuss the limitations of current spindle motion analysis methods. In the 2D framework, the radial error motion is an application-independent geometric property and thus separate from the consequence of radial error motion in spindle applications. The 2D method can not only determine the axis of rotation radial error motion, but also the consequence of error motion in all classes of spindle applications, including a new class of spindle applications with two radial sensitive directions. In comparison, the radial error motion values specified in current standards give the consequence of radial error motion in two classes of spindle applications, but do not represent radial error motion itself. The new method is presented in two parts. Part 1 focuses on the theory and illustration of the 2D method. Part 2 presents the experimental results of a ball bearing spindle and an aerostatic bearing spindle.     

A new method for characterizing axis of rotation radial error motion: Part 2. Experimental results

In the current standards of spindle metrology, the fundamental component of radial probe measurement is considered radial throw (eccentricity) of the installed test artifact and the fundamental radial error motion is treated. The goals of this paper are: (1) to make evident the fact that fundamental radial error motion can actually exist; (2) to present a new two-dimensional (2D) method to analyze spindle radial error motion measurement; (3) to discuss the limitations of current spindle motion analysis methods. In the 2D framework, the radial error motion is an application-independent geometric property and thus separate from the consequence of radial error motion in spindle applications. The 2D method can not only determine the axis of rotation radial error motion, but also the consequence of error motion in all classes of spindle applications, including a new class of spindle applications with two radial sensitive directions. In comparison, the radial error motion values specified in current standards give the consequence of radial error motion in two classes of spindle applications, but do not represent radial error motion itself. The new method is presented in two parts. Part 1 focuses on the theory and illustration of the 2D method. Part 2 presents the experimental results of a ball bearing spindle and an aerostatic bearing spindle.     

数控机床垂向滚珠丝杠制动装置

数控机床垂向滚珠丝杠制动装置采用带失电制动器的伺服电动机,再在数控机床的铅垂轴上,增加一个外置失电制动器。外置失电制动器装在滚珠丝杠的上部,带失电制动器的伺服电动机,通过传动结构与滚珠丝杠相连接。该装置可以取代数控机床铅垂轴的平衡锤和平衡油缸,避免了平衡锤和平衡油缸的缺点,结构简单。     

自动切槽机床及其设计

介绍一种自动切槽机床。机床采用移动式结构,工作时放置于工件上;主传动系统利用渐开线少齿差行星轮传动结构,仅用两对齿轮就使转速降至1/40;通过主轴与套筒的偏心异步旋转运动构成自动进给系统,使机床的主运动和进给运动巧妙地融为一体。