On-line error compensation of coordinate measuring machines

An on-line error compensation system for coordinate measuring machines (CMMs) is described, which is based on three laser optical Multi-Degree-of-Freedom Measurement Systems (MDFM systems), each for one axis of CMMs. Twelve of the twenty-one error components associated with a CMM are measured on-line by these MDFM systems. The remaining error components are measured by off-line methods which use commercially available measurement systems, such as a laser interferometer. Two mathematical error models have been developed to synthesize the error components and to predict the errors at the probe stylus tip. One model corresponds to the conventional off-line error compensation and the other to the on-line error compensation. The errors predicted by these models are then subtracted from the nominal coordinates of the CMM, thus improving its measurement accuracy. Diagonal tests using a laser interferometer system were designed to check the error compensation effect. Test results showed that the use of the on-line compensation system can further improve the compensation effect as compared with the conventional off-line compensation system.     

Evaluation of the measurement uncertainty of a positional error calibrator based on a laser interferometer

A positional error calibrator for evaluating the positioning accuracy of machine tools and coordinate measuring machines (CMM) under dynamic conditions has been developed. It is based on the Hewlett Packard 5529A laser interferometer, which is capable of performing dynamic calibration. This laser interferometer measures the position of the slide as it moves continuously along the machine axis under test. The data are collected on a position basis by triggering the laser interferometer from a position-based reference signal. A software package has been developed for data acquisition and presentation of the positional errors in accordance with ISO 230-2 standard. This paper deals with the evaluation of the measurement uncertainty of this positional error calibrator. In order to assess the total measurement uncertainty of this calibrator, an analysis of the individual errors that make up the accuracy and repeatability error budgets has been carried out. These error budgets consist of the following components: (1) uncertainties intrinsic to the laser system; (2) uncertainties due to environmental effects; (3) measuring uncertainties due to the installation. This uncertainty analysis was carried out when this calibrator was used to assess the positional errors of a moving bridge type CMM at UMIST.     

一种圆柱坐标测量仪控制系统的设计与实现

圆柱坐标测量仪具有结构简单、测量范围大、适合于测量圆弧类零件的特点,本文针对航空型材弯曲类钣金零件成形精度测量,设计开发了一种圆柱坐标测量仪,对其控制系统软硬件的体系结构和功能进行了研究.采用计算机扩展卡的方式开发了其控制系统硬件,采用多线程技术,利用VC开发了控制系统软件,并利用Matlab和VC混合编程技术开发了曲面重构模块.实验表明,其控制精度达到0.3mm,满足了钣金类零件测量的需求.     

基于激光的立铣刀圆角半径测量误差补偿方法

数控加工中心在使用激光对刀仪测量立铣刀圆角半径时，即使经过精度调整和标定依然存在系统误差。分析激光对刀仪测量立铣刀圆角半径的原理，提出激光遮蔽误差是产生该系统误差的主要因素；建立激光遮蔽误差补偿表达式，进行实验验证。结果表明：补偿后测量误差从0.08 mm降低到0.02 mm，证明了该补偿方法的实用性。     

基于灰度预测的三坐标测量机动态测量误差分析与研究

三坐标测量机在进行高速扫描测量时,由于机体的振动会产生较大的动态测量误差。对MC850三坐标测量机在高速测量中的动态特性进行分析,找出其动态误差产生的根源,并根据GM(1,1)灰度预测理论,将三坐标测量机看作线性动力系统,建立其灰度预测模型,运用该模型对坐标测量机进行动态误差预测。实验结果表明该模型可有效减少测量机的动态测量误差,表明灰色建模理论可用于动态误差预测。     

基于Solidworks Simulation的三坐标测量仪动态误差分析

采用三坐标测量仪进行高速测量时,由于受附加惯性力及自身重力的影响,机体会变形,从而导致动态误差。对三坐标测量机的动态误差进行理论分析;利用Solidworks Simulation有限元分析方法对移动桥进行受力变形分析;在z轴静止状态下,推导出滑架沿y轴方向加速(减速)和匀速的运动状态下动态误差补偿模型。仿真结果表明:各运动状态下的动态误差有效降低,为提高三坐标测量机的测量精度奠定基础。     

Development of computer integrated system for error diagnosis of a CMM using calibrated mechanical artefacts

Error calibration and frequent reverification of coordinate measuring machines (CMMs) and machine tools are currently acknowledged as essential processes in order to maintain high performance of the machines and high quality of products. This paper shows a micro-computer integrated error calibration system, which is a fast and efficient error calibration system: a micro-computer stores calibration data of mechanical artefacts, such as ring and step gauges that have been calibrated with respect to more precise equipment, then the machine probes the gauges. The gauge probing data are compared with the gauge calibration data. The micro-computer plans measurement paths thus generating CNC codes for measurement of the mechanical artefacts located in a working volume of a commercial CMM. Then measurement operations are performed according to the planned paths for practical measurement of the gauges. For ring gauge measurement, the lobing error of the probe stylus has been efficiently measured then used for the probe compensation. The circular errors are successfully calculated from the comparison between the ring gauge geometry and the ring gauge probing data after the probe stylus compensation in terms of software. Then from the error pattern of circular error, machine errors such as scale errors and orthogonality error are successfully calculated, showing good approximation to the evaluated circular error. In the case of the step gauge measurement, the gauge probing data are compared with those of calibration data; thus complete linear displacement error analysis is successfully evaluated along any direction in a working volume. The error evaluations are then processes in real time, and presented in computer graphic environments. Practical application to a commercial CMM of CNC-type shows the validity and efficiency of the developed system. Thus a rigorous computer integrated error calibration system is proposed with the full potential of practical application to most commercial CMMs and machine tools of a CNC-type.     

CAD系统在CMM测量中的应用

对CAD系统在三坐标测量机测量中的应用进行了介绍。通过CAD系统可以完善和扩大测量机的功能,实现曲面测量时的测头半径补偿,并能对测量数据进行处理。文中对实现这些功能的方法和步骤进行了说明。     

Kinematic and geometric error compensation of a coordinate measuring machine

In this paper, kinematic modelling of a Coordinate Measuring Machine (CMM) is carried out and the methodology followed in modelling is explained in detail. The model is simplified by certain assumptions which may result in over-simplification of the model. Consequently, the model is investigated and enhanced by adding the relevant and suitable geometric error terms. Different approaches are employed to evaluate the model coefficients. In the first approach, a commercial ring gauge is measured in a structured lattice in the work volume of the CMM. Resulting errors in these measurements are used in conjunction with some statistical methods to arrive at sets of model coefficients values. The second approach is based on measurement of the individual 21 error terms in the CMM by means of laser interferometry. These measurements are used to evaluate another set of model coefficients. A compensation strategy is proposed and tested using the model and the sets of coefficients obtained. Volumetric Performance of the CMM is evaluated according to ASME standards, before and after compensation. Improvement in the CMM volumetric performance is demonstrated and compared.     

Integrated real time compensation system for errors introduced by measurement probe and machine geometry in commercial CMMs

In this paper, an integrated real time compensation system has been proposed for the errors introduced by the probe and machine geometry in commercial CMMS. For efficient probe error mapping, a compact notation (ε, θ) for probing direction and corresponding concentric diagram is proposed. A set of integrated volumetric error equations are also proposed for the volumetric error map integrating the probe error and the machine geometric error. For the real time error compensation scheme, an interface box and an appropriate software driver have been designed and implemented between the CMM and machine controller. The data flow is intercepted and corrected according to the integrated volumetric error map without the controller being noticed. Thus the real time error compensation system has been successfully implemented for the machine with minimum interference to the existing coordinate measurement system. The developed system has been applied to a commercial CMM on the shop floor, and the measurement accuracy has been improved remarkably.     

基于三坐标测量机的精密叶轮测量路径规划研究

研究了精密叶轮的三坐标测量机(CMM)测量路径规划,首先进行了精密叶轮的顶层测量规划:被测零件的定位、CMM测头的空间姿态优化和坐标系的匹配。然后实现了精密叶轮的底层测量路径规划:测量点的选择、分组、排序。采用参数线法生成了理论测量路径,分析了CMM各种扫描测量方式,构造了边界曲面,并对精密叶轮表面采用UV曲面划分测量,从而实现了对精密叶轮的CMM测量。     

A probing question: A customer''s investigation into the directional variability of a coordinate measuring machine touch trigger probe

The accuracy of measurements produced by coordinate measuring machines (CMMs) is constrained by a number of factors.Most machines use the Renishaw Touch Trigger probe to generate a signal and identify a point at which measurement coordinates are recorded. Under ideal conditions the measuring errors generated by this action are negligible when compared with typical drawing tolerances. This holds good as long as the measuring uncertainty of both the CMM and probe system are regularly checked and maintained. Furthermore the mode of operation can contribute to an accumulation of errors which can result in unnecessarily large variation.This paper presents the first part of an investigation which addresses these problems.The outcome provides useful guidelines for CMM users seeking to minimise measurement variation.     

CMM测量曲面测头半径补偿与路径规划研究

根据测量曲面的目的把三坐标测量机测量曲面的模式分为两种,即检测模式和重构模式。按照两种不同的测量模式对三坐标测量机测头半径补偿与曲面测量路径规划进行研究。通过实例证明本文所述方法是正确的、实用的。     

数控机床定位误差的激光干涉法检测与补偿

用激光干涉法测量误差的原理,通过计算机控制的误差补偿系统对数控机床不的定位误差进行补偿,实验结果表明这种方法可以大幅度提高数控机床的定位精度。     

Compensating technique of field-distorting error for the CO2 laser galvanometric scanning drilling machines

Laser galvanometric scanning system has been widely used in the laser drilling machines to form the microvias of high-density interconnected printed circuit boards (HDI PCBs). Although the galvanometric scanning system can increase the speed and efficiency of laser drilling process, it is usually associated with a field distortion error. The investigation discusses the field distortion error of a laser scanning system based on a CO₂ laser drilling machine and provides a method for correcting this distortion error. The field distortion error is a random error in the laser galvanometric scanning system. This irregular error is usually corrected using pre-compensation methods that apply an error function. The paper gives a pre-compensation technique to correct the distortion error of scanning image, which using the two-dimensional (2D) Lagrangian polynomials modified the control commands of the galvanometric scanning system. The results in this study indicate that the compensation method effectively amended the field distortion and increased the accuracy of the positioning of the holes that were drilled using a laser galvanometric scanning drilling machine. The positioning errors of drilling holes have reduced from ±0.3 to ±0.05 mm after error compensation. This pre-compensation method could be widely adopted in all galvanometric scanning system, such as pre-objective and post-objective scanning system.     

基于ARM_Linux的数控机床热误差补偿控制器的设计

以减小机床热误差,提高加工精度为主要目标,设计以S3C2440A处理器与嵌入式Linux操作系统为控制平台,运用BP神经网络建立误差模型的热误差补偿控制器。首先,控制器通过布置在机床关键温度点上的温度传感器采集加工中心的温度信号,该信号经温度采集模块处理后送到CPU处理器计算出温度值。同时,用激光干涉仪检测出机床对应时刻的误差值。BP神经网络模型根据温度值与误差值计算出综合误差补偿值。然后,将计算出的补偿值通过接口传送给CNC控制中心,CNC控制中心做出误差控制指令,修正机床热变形造成的被加工工件的尺寸误差。仿真实验结果表明了补偿效果的可行性。     

Adaptive compensation of quasi-static errors for an intrinsic machine

An adaptive compensation strategy for quasi-static error correction in intrinsic machines is proposed and tested. The proposed methodology consists of systematic modelling of the machine forward kinematics, including quasi-static errors, as well as direct modelling of the inverse kinematics using nonlinear regression analysis. The result is a model which is a hybrid of physical modelling and regression analysis modelling. In addition, the methodology includes a compensation strategy of the machine contouring errors using the state observer technique for on-line adaptive compensation. A CMM is chosen as a test bed for validation of the proposed methodology. Systematic modelling is carried out in two stages for the forward and inverse kinematics. Regression based models are verified using two different tests. The statistical analysis of variance technique (ANOVA) is used to select the best model in addition to model testing using an independent set equal to approximately 10% of the fitting data. The obtained models are then employed in two compensation strategies; one for the measurement error correction, and another one for the contouring error correction by motion command modification in the forward control path. For contouring tests, the CMM behavior at different thermal states is estimated using experimentally obtained Effective Coefficient of Thermal Expansion (ECTE). Simulations of the machine in contouring selected trajectories are carried out over a range of thermal states. Results obtained show an improvement in the CMM performance to a level close to the machine resolution. The CMM performance is tested using the standard ASME B.89.1.12M-1990 evaluation test, as well as a novel modified version of the test accounting for a thermally varying environment. Machine errors are significantly reduced using the proposed methodology.     

基于激光跟踪仪的数控机床空间误差测量及补偿

为了改变机床空间误差综合性的测量手段和补偿技术在国内机床制造和生产中应用较少的现状和研究数控机床空间精度提升方法，介绍数控机床平动轴的21项误差和激光跟踪仪的空间误差测试原理，阐述测量与辨识机床空间误差的步骤和方法。在桥式五轴加工中心上进行空间误差测试，给出数控机床空间误差结果，并生成误差补偿文件，通过西门子的VCS功能进行了误差补偿。并对比分析了补偿前后的21项误差，对补偿前后数据的差异进行原因分析，并通过对机床空间体对角线的测量验证了空间误差测量与补偿的实际效果，补偿后误差缩小为原来的11.2%,应用该技术能够大大提高机床的空间精度。     

An application of real-time error compensation on a turning center

A real-time error compensation (RTEC) system is developed to correct thermally-induced and geometric errors on a four-axis dual-spindle turning center. These errors vary with different cutting tool positions as well as different thermal conditions, thus real-time correction is required. Two problems in the current RTEC approach are addressed: (1) the difficulty in the actual measurement of error components according to the defined coordinates and (2) the selection of a small set of appropriate temperature variables from numerous candidate thermal sensors on a machine structure. A flexible error measurement method and an optimal temperature variable selection process are proposed to overcome these difficulties. After machine errors were characterized and modeled, the effectiveness of the developed RTEC system was evaluated by using laser inspection and an actual cutting test. The maximal diagonal displacement error is corrected from 75.0 to 7.5 μm. In the cutting test, the part diameter error of a car steering joint is reduced from 60 to 10 μm.     

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.