一种超精密大行程导轨直线度检测新方法

导轨直线度是超精密加工与检测机床最重要的基本几何误差之一,对机床性能影响很大。通过分析导轨直线度测量方法的研究现状,指出各测量方法在超精密大行程导轨直线度测量中的不足,提出一种导轨直线度检测的新方法,即采用加工和保存相对容易的短基准平尺进行拼接重构,采用最小二乘处理各段数据,获得大行程导轨全频段直线度数据。并通过实验验证:用此拼接方法所得导轨直线度与用基准长平尺测量的导轨直线度形状一致,数值基本相同。因此,采用此种方法可实现米级导轨直线度准确测量,并可实现导轨直线度误差补偿控制,将有效提升机床的精度水平。     

机床导轨误差的测量和补偿方法研究

以减小机床导轨的误差为研究对象,采用材料力学的方法分析导轨精度下降的基本原因,指出了温度变化和外力作用下对导轨精度的影响,分析了机床导轨在水平面和垂直面内产生的误差。通过比较导轨直线度误差的测量值和数控系统设定的误差值,所得到的数控代码经补偿模块处理,产生新的代码在数控系统中被执行,以达到提高机床导轨精度的目的。     

基于LabVIEW的数控车床导轨直线度分析系统

导轨在水平面内的直线度误差不仅影响工件的加工精度,还可能导致切削力发生变化。针对目前导轨直线度误差主要通过手动计算或者依靠测量仪器出现的测量精度低、计算复杂问题,以数控车床导轨为研究对象,利用图形化编程软件LabVIEW,设计了车床导轨直线度误差分析系统。该系统具有读取测量数据、分析直线度误差、保存计算结果等功能。经验证,该系统运行良好,数据分析速度快、计算结果直观、精度高,实现了导轨直线度误差分析的自动化和可视化。     

机床导轨直线度误差数据的微机处理

本文通过对机床导轨直线度误差测量及数据处理方法分析，进行数学建模及程序编制，对采用微机处理导轨直线度误差数据作了初步探讨。实验人员只需将检测数据键盘输入，屏幕上即可显示如下运算结果：误差曲线、最小包容线、导轨全长及任一米误差值，为进行修磨机床导轨提供依据。     

边界润滑条件下机床滑动导轨精度保持性研究

根据磨损理论推导出机床滑动导轨的精度保持性模型。选择100号导轨润滑油作为润滑媒介,在边界润滑条件下,使用自研制的导轨台架试验机,选择等距非等速滑动实验对精度保持性模型进行验证。利用所建立的精度保持性模型能够很好地预测机床滑动导轨的直线度衰减。利用该模型完成了精度保持时间与导轨工况参数的定量分析。     

基于拼接重构的长导轨直线度测量方法

为了有效解决超精密设备长导轨全行程直线度精确测量的难题,文章提出了一种基于拼接重构原理的测量方法。首先采用激光干涉仪对短基准平晶面形误差进行测量,并用于补偿到长导轨直线度测量结果;接着比较了不同倾斜误差消除方法的效果,并确定消倾斜误差的优选方法;然后分析了拼接重叠长度、拼接次数以及环境噪声对测量结果的影响规律;最后对金刚石飞切机床的超精密长导轨开展直线度测量,并将测量结果与采用长平晶测量结果进行对比。结果表明:两者的误差在15.8%以内,有效验证了文中提出的拼接重构方法的有效性,为解决超精密设备长导轨全行程直线度测量提供了一种新的思路。     

基于有限元分析的机床导轨热变形研究

高速高精度机床切削加工过程中,在多种热源的作用下导轨会产生热变形,影响工件与刀具间的相对位置,造成加工误差。找出导轨热位移较大的点,并分析其对加工精度的影响,对于减小加工误差提高加工精度至关重要。文章在对导轨热边界条件进行分析的基础上,应用有限元分析方法,建立了一类机床导轨的有限元热变形分析模型,并进行了热变形分析计算,为分析导轨的热变形对加工精度的影响提供了依据,并为机床综合热误差补偿提供参考。     

EST法测量机床导轨直线度误差分析

根据误差分离技术(EST)的基本原理,在超精密加工技术的发展对误差分离技术所提出的新要求基础上,采用时域双测头误差分离法测量导轨直线度误差,定量分析了传感器及安装引起的误差,测量方法引起的误差和测量环境对结果的影响,并进行实验分析。研究结果表明,采用双测头法测量直线度误差的方法实用可靠,计算简单,数据处理时间短,对于大型机床的测量能够满足测量精度的要求,为数控机床空间曲面加工的在线测量、误差补偿提供依据。     

数控机床导轨变形误差补偿技术研究

针对机床导轨变形特别是大型、重型机床的导轨变形降低加工精度的问题,提出了利用软件误差补偿技术来消除导轨变形对加工精度的影响.以数控车床为例,分析了导轨变形对加工零件的影响,提出了利用最小二乘法拟合导轨变形曲线,阐述了利用指令修正技术进行误差补偿的原理,为进行数控机床全局误差补偿提供了理论依据和技术参考.对CK6140型数控车床进行了补偿,有效地改善了加工精度.     

可抵消重力变形的横梁导轨面曲面设计

机床的横梁在前端运动部件的重力及倾覆力矩的影响下,很难保证横梁导轨所在轴轴线运动的直线度误差和角度偏差满足工艺规定的要求。在实际装配时通过多次刮研导轨面来保证横梁轴轴线运动的几何精度满足工艺规定的要求,装配效率低下,而横梁导轨所在轴最终的几何精度也不高。文中在考虑前端运动部件移动的情况下,利用有限元仿真方法得到了前端移动部件在横梁上各位置处横梁导轨面的变形,并采用反变形原理,对机床的横梁导轨安装面与靠面进行设计,将导轨安装面与靠面加工成微圆弧形式,可以抵消横梁以及前端运动部件引起的重力变形对横梁导轨所在轴的几何精度的影响,从而显著提高机床的装配效率,提高横梁导轨所在轴的几何精度。     

Development of straightness measurement technique using the profile matching method

The property of straightness is one of fundamental geometric tolerances to be strictly controlled for guideways of machine tools and measuring machines. Straightness measurement for long guideways is usually difficult to perform, and it requires additional equipment or special treatment with limited applications. In this paper, a new approach is proposed using the profile matching technique for the long guideways, which can be applied to most straightness measurements. An edge of relatively short length is located along a divided section of a long guideway, and the local straightness measurement is performed. The edge is then moved to the next section with several overlap points. After the local straightness profile is measured for every section along the long guideway with overlap, the global straightness profile is constructed using the profile matching technique based on the least-squares method. The proposed technique is numerically tested for two cases of known global straightness profile: arc profile and irregular profile, with and without random error intervention, respectively. The developed technique has been practically applied to a vertical milling machine of the knee type, and demonstrated a good performance. Thus the accuracy and efficiency of the proposed method are demonstrated, and show great potential for a variety of applications for most straightness measurement cases, including straight edges, laser optics and angular measurement equipments.     

Geometric adaptive straightness control system for the peripheral end milling process

A relationship between the tool deflection and the feed rate is modelled by a modified Taylor's tool-life equation. An off-line Geometric Adaptive Control (GAC) system to compensate for machining straightness error in the finished surface due to tool deflection and guideway error generated by the peripheral end milling process is proposed.

Without a priori knowledge of the variations of the cutting parameters, the time-varying parameters are estimated by an exponentially windowed recursive least squares method with only post-process measurements of the straightness error through a gap sensor. The location error is compensated by moving the milling bed through a numerical control command before cutting. The waviness error is regulated by using optimal feed rate manipulation as obtained from the proposed GAC method during machining although the parameters do not converge to fixed values.

Experimental results show that the location error is controlled within the range of fixturing error of the milling bed on the guideway, the waviness accuracy can be increased to more than three times that of the case with no control action. A single-pass milling operation can become feasible through practical application of the proposed GAC system for finish cutting conditions.     

A method for measuring the guideway straightness error based on polarized interference principle

This paper presents a new method for measuring guideway straightness error based on the polarized interference principle and affords a new way to measure straightness error in real-time with high precision. Firstly, the method is demonstrated and analyzed in theory, and then the layout of the optical modulator and the polarization angle detecting unit are discussed in details. Finally, a calibration process is introduced with linear function based on the least-square method. Calibration results show that the correlation coefficients R² of the fitting curves are above 0.9999 and the standard error of the estimated value is less than 0.2 μm. The theoretical analysis of the relationship between the straightness error and polarization angle is verified. The range of measuring straightness error is above 0.5 mm with 0.5 μm resolution. The system uncertainty (k=3) is less than 1 μm after the measurement system is calibrated. Experimental results demonstrate that this method possesses the advantages of minimizing the effects caused by the variation of light intensity and the shape and surface error of the guideway. The measurement accuracy is considerable with the autocollimator having the characteristic of high reliability and accuracy. It will have a prospective application in the industrial measurement field.     

Straightness error compensation for large CNC gantry type milling centers based on B-spline curves modeling

Fast and accurate modeling for the straightness errors of machine tools is significant important for the implementation of error compensation. To decrease the straightness errors which generally exist in gantry type milling centers, a novel approach for real-time compensation of straightness errors is presented, including an accurate spatial straightness error model which based on B-Spline curves method and a real-time errors compensation system which can compensate multiple errors at the same time in real-time. An experiment is carried out to measure the straightness errors of a gantry type milling center by using a laser interferometer. There are two straightness errors for one direction movement of an axis. As a result, there are six straightness errors for a three-axis milling center. The straightness error model is established by the B-Spline curves method. According to these six straightness error models, a spatial straightness error model is obtained by superposition of these straightness error models. In addition, an external real-time errors compensation system is developed based on the function of external mechanical origin offset in Fanuc CNC systems. The compensation experiments are conducted to verify the accuracy of the spatial straightness error model and the effectiveness of the error compensation system. The experimental results show that the straightness errors of the machined work-pieces are proved to have been decreased over 90% compared with that of non-compensations. The B-Spline curves modeling combining the errors compensation system can be utilized as an effective approach to improve the accuracy of the CNC gantry type milling centers.     

Geometric adaptive straightness control system for the peripheral end milling process with large error sources

An off-line Geometric Adaptive Control (GAC) scheme is proposed to compensate for machining straightness errors due to the machine tool's inaccuracy and those arising as a result of the metal cutting process during the finish peripheral end milling process. In the milling process, the workpiece travels along the guideway while the spindle system remains fixed. The scheme is based on the exponential smoothing of post-process measurements of relative machining errors due to the tool and bed deflections. Without a priori knowledge of the variations of the cutting parameters, the time-varying parameters are estimated by an Exponentially Weighted Recursive Least Squares (EWRLS) method. This method is able to incorporate a straightedge which is not necessarily accurate to identify the guideway errors. To reduce the drift of the cutting parameters, a single parameter adaptation method is introduced. Experimental results show that the location error is controlled within the range of the fixing error of the milling bed on the guideway. Further, the waviness error is reduced to less than 10 μm in the machining of a 508-mm long prismatic workpiece regardless of the machining conditions.     

Relationships between straightness and angular kinematic errors in machines

The software compensation approach for the improvement of machine tool and coordinate measuring machine accuracy depend to some extent on machine error modelling and measurement methodologies. The currently established methodology is based on the derivation of tool position error (for machine tools) or stylus tip position error (for coordinate measuring machines) by the combination of individual axis joint kinematic error parameters. The purpose of this paper is to propose a machine error analysis based on error classification. This taxonomic approach forms a conceptual basis for an analysis of machine errors with a deeper understanding of error mechanisms at more fundamental levels. The relevance of this approach is investigated through the case study of the coupling mechanism between joint kinematic angular and straightness errors of machine linear axes. The limitations of the joint kinematic straightness and angular error modelling based on purely abstract mathematical dependence principles are explored through simulations and experiments.     

Modeling and analysis of nonlinear guideway for double-ball bar (DBB) measurement and diagnosis

The purpose of this paper is to study nonlinear geometric errors in multi-axis machine tools. A general mathematical model for guideway systems that can be applied to high-precision machine tools such as CNC lathes is introduced. Using this model, most nonlinear error sources in the guideway systems can be diagnosed by measuring the contouring error using a double-ball bar (DBB). Diagnostic software has been developed to identify system parameters based on the least-squares estimation method. Inputting two or three contouring errors pattern data into this software enables parameters to be identified quickly, based on the nonlinear model.