Improved machine tool linear axis calibration through continuous motion data capture

Machine tool calibration is becoming recognised as an important part of the manufacturing process. The current international standards for machine tool linear axes calibration support the use of quasi-static calibration techniques. These techniques can be time consuming but more importantly a compromise in quality due to the practical restriction on the spatial resolution of target positions on the axis under test. Continuous motion calibration techniques have the potential to dramatically increase calibration quality. Through taking several measurement values per second while the axis under test is in motion, it is possible to measure in far greater detail. Furthermore, since machine tools normally operate in dynamic mode, the calibration data can be more representative if it is captured while the machine is in motion. The drawback to measuring the axis while in motion is the potential increase in measurement uncertainty. In the following paper, different methods of continuous motion calibration are discussed. A time-based continuous motion solution is proposed as well as a novel optimisation and correlation algorithm to accurately fuse the data taken from quasi-static and continuous motion measurements. The measurement method allows for minimal quasi-static measurements to be taken while using a continuous motion measurement to enhance the calibration process with virtually no additional time constraints. The proposed method does not require any additional machine interfacing, making it a more readily accessible solution for widespread machine tool use than other techniques which require hardware links to the CNC. The result of which means a shorter calibration routine and enhanced results. The quasi-static and continuous motion measurements showed correlation to within 1 μm at the quasi-static measurement targets. An error of 13 μm was detailed on the continuous motion, but was missed using the standard test. On a larger, less accurate machine, the quasi-static and continuous motion measurements were on average within 3 μm of each other however, showed a standard deviation of 4 μm which is less than 1% of the overall error. Finally, a high frequency cyclic error was detected in the continuous motion measurement but was missed in the quasi-static measurement.     

基于6-TPS型并联机床的标定方法研究

以6-TPS型并联机床为对象,研究了并联机床运动学标定方法。首先假定了并联机床各结构参数单位误差,在与测量方式相一致的广义坐标上,通过并联机床正解的方式,利用所测的点数据,以数值法构造了机床末端位姿误差与结构误差的影响系数矩阵。通过这种方法,构造参数误差数学辨识模型,针对6-TPS型并联机床的特点,提出了测量并联机床平动和聚点性误差的方案,并在工程实际应用中验证了该标定方法的可行性。     

Uncertainty of calibration of 2D planar Coordinate Measuring Machine

When the kinematic parameters of 2D planar Coordinate Measuring Machine are calibrated in self-calibration method, it is shown how to estimate the uncertainty of calibration and how to estimate the uncertainty of measurement. In this paper, the uncertainty of probing and the uncertainty of sensors are considered as the contributors of uncertainty. Two different types of CMMs are applied to two different artefacts for calibration and those measures in some different orientations for estimation of uncertainty. The effectiveness of the difference of CMMs, the artefacts and the measurement orientations are compared. As a result, it is proved that the uncertainty distribution is different in the orientation of measurement and the uncertainty could be smaller by selecting measurement orientation.     

并联机床运动学自标定方法研究

以Stewart型并联机床为对象,研究一种能实现自标定的运动学标定方法,以提高标定效率.在建立两点之间距离误差的基础上,采用哑铃型球杆作为标准的检测量具,并以此建立机床结构参数误差与球杆标准长度之间的误差传递模型.提出了数据自动采集的方案,开发了专用标定软件,实现了数据采集、数据分析处理和机床结构参数补偿的集成.基于提出的方法,利用测头、球杆和为标定而开发的软件,作为加工叶片的Stewart型六自由度并联机床标定的工具.经两次标定,在机床工作空间内,并联机床的运动学定位误差控制在±0.02 mm以内.     

某机床的可维修性研究

以一牛头刨床为例,建立了其失效的概率模型,论述了机床可靠性维修的理论,探讨了机床的最佳维修周期的界定问题及计算方法。     

Kinematic calibration of gantry hybrid machine tool based on estimation error and local measurement information

This paper presents the kinematic calibration of a four degrees-of-freedom (DOF) hybrid machine tool based on a novel planar 3-DOFs parallel mechanism and a long movement of the worktable. Closed-form solutions are developed for both the inverse and direct kinematics about the parallel mechanism. The error model is built and the mechanism accuracy is investigated. Two types of kinematic calibration method are proposed by a simple measurement device. The first type of calibration method is based on estimation error, and can easy improve the machine tool accuracy quickly by estimating the error trends. The second type of kinematic calibration method is based on local measurement information, which includes the position errors and does not include the pose errors of the machine tool. The calibration tests showed the effectiveness of the calibration methods, which can be useful for the similar types of parallel machine tool.     

Evaluation of coordinate measurement uncertainty with use of virtual machine model based on Monte Carlo method

Advances in modern manufacturing techniques implies more efficient production but also new tasks for coordinate metrology. The main of them is evaluation of accuracy of the measurement, because according to technological requirements, results of measurements are useful only when they are given with their accuracy. Currently used methods for uncertainty assessment are difficult and require knowledge and measuring experience. It is therefore important to implement correct and validated methods that will also be easy to implement and will not require broad metrological knowledge from the personnel. Presented here simulation method, based on Monte Carlo method is one of them. The article presents the conception, implementation and validation of this method.     

Metrological characterization of a diagnostic test extending the Receiving Operating Curve analysis using Supplement 2 recommendations

Receiving Operating Curve (ROC) analysis is a powerful and statistical accepted method to assess the performance of a diagnostic test. ROC curve plots true positive rate against false positive rate, evaluated on a certain population. Instrumental and model uncertainty contributions can strongly affect the performance of the ROC analysis especially in the evaluation of performance metrics such as Area Under ROC (AUC) and Optimal Operating Points. Supplement 2 reports detailed instructions to handle and propagate uncertainty through a Multiple Input Multiple Output system, in case of correlate output variables, such as TPR and FPR. After a detailed revision of the existing literature, the present paper describes and applies a novel methodology, totally framed in the GUM and its supplements, to represent and propagate the uncertainty contributions estimated in a medical context, throughout the ROC analysis, providing new concepts such as ROC confidence region and Optimal Operating Region.     

基于参数化的机床产品快速变型设计

在产品的概念设计过程中,融入参数化技术,实现大规模定制化产品的快速设计.针对机床产品,以UG为软件平台,结合V C 和SQL Server数据库开发机床产品参数化变型系统,并讨论从功能需求到结构参数模型的映射过程、主要结构特征尺寸参数化等关键技术,通过参数化实现产品级的机床快速变型设计.     

基于SVM的可靠性评估方法研究

利用蒙特卡罗方法评估系统可靠性因需要大量的系统函数值，故存在所需运算量大、评估效率低等不足。首先尝试利用支持向量机建立一经验模型，以加速蒙特卡罗法，然后将其应用于对某一网络系统的可靠性评估，取得了良好的效果。     

Compensation of machine tool thermal deformation in spindle axis direction based on decomposition method

One of the fundamental areas in high precision cutting is represented by the machine's thermal state monitoring. Understanding of this state gives significant information about the overall machine condition such as proper performance of cooling system as well as software compensation of machine's thermal deformation during manufacturing. This paper presents a method focused on compensation of machine's thermal deformation in spindle axis direction based on decomposition analysis. The machine decomposition is performed with the help of specially developed measuring frame, which is able to measure deformation of machine column, headstock, spindle and tool simultaneously. Compensation is than calculated as a sum of multinomial regression equations using temperature measurement. New placements of temperature measurement like spindle cooling liquid or workspace are used to improve the accuracy of this calculation. Decomposition process allows describing each machine part's thermal dynamic more precisely than the usual deformation curve usually used one deformation curve for the complete machine. The residual thermal deformation of the machine is considerably reduced with this cheap and effective strategy. The advantage is also in the simplicity of presented method which is clear and can be used also on older machines with slower control systems without strong computing power.     

加工中心盘式刀库自动换刀控制系统设计

针对自主研发制作的微型盘式刀库加工中心,阐述了其具体的换刀过程,提出了一条基于单片机的自动换刀控制方案;重点介绍了通信和PWM脉冲输出等外围电路;IO电路中采用光隔,提高了系统的稳定性.该方案根据模块化的思想把自动换刀控制系统作为一个独立的单元进行设计,并通过RS232和数控系统进行通信,降低了对数控系统的依赖性,结构简单,成本低,通用性好,并通过多次重复试验验证了其稳定可靠性.     

Improvement of the measurement uncertainty of a high accuracy single sinker densimeter via setup modifications based on a state point uncertainty analysis

The single sinker densimeter with magnetic suspension coupling is one of the state of the art methods for the accurate measurement of fluid densities. The uncertainties of experimental pressure, density and temperature data, measured with a single sinker densimeter, were thoroughly evaluated following the uncertainty propagation law. The main uncertainty sources of each magnitude were determined. Based on this statistical study, several modifications were performed to reduce the uncertainty associated to each magnitude. Firstly two new PTR-25 probes were added. Secondly a new pressure transducer for the low pressure range was added. Finally the sinker of the densimeter was replaced by a bigger one to improve the balance reading. After these modifications the uncertainty of each magnitude was evaluated and validated with a Monte Carlo simulation. Results yielded a significant reduction of 44% in temperature uncertainty, more than 92% on pressure below 2 MPa, and more than 22% on density.     

机器视觉非接触测量系统在线校准及不确定度分析

高精度、大面阵CCD和CMOS传感器件的出现,使得机器视觉非接触测量技术得到越来越广泛的应用。本研究以典型机器视觉非接触测量模型为研究对象,通过对其原理、测量数学模型和计量特性进行了阐述和分析,创新性提出了一种机器视觉非接触测量系统的在线校准方法,分析并确立了测量过程中的不确定度来源,并对校准结果进行了不确定度评定。实验表明,机器视觉非接触测量系统在线校准方法具备两个优点：一是易操作性,优化了测量标准的追溯关系;二是校准精度高,在95％的置信概率下。校准系统不确定度为0．008mm。     

Tool life prediction using Bayesian updating. Part 1: Milling tool life model using a discrete grid method

According to the Taylor tool life equation, tool life reduces with increasing cutting speed following a power law. Additional factors can also be added, such as the feed rate, in Taylor-type models. Although these models are posed as deterministic equations, there is inherent uncertainty in the empirical constants and tool life is generally considered a stochastic process. In this work, Bayesian inference is applied to estimate model constants for both milling and turning operations while considering uncertainty.     

Tool life prediction using Bayesian updating. Part 2: Turning tool life using a Markov Chain Monte Carlo approach

According to the Taylor tool life equation, tool life reduces with increasing cutting speed following a power law. Additional factors can also be added, such as the feed rate, in Taylor-type models. Although these models are posed as deterministic equations, there is inherent uncertainty in the empirical constants and tool life is generally considered a stochastic process. In this work, Bayesian inference is applied to estimate model constants for both milling and turning operations while considering uncertainty.     

机床大件结构复合优化方法研究

在分析机床广义模块设计和结构智能优化的基础上,论述基于人工神经网络和有限元优化的大件模块结构复合优化方法,给出大件模块结构的尺寸优化设计变量自动搜索寻优计算方法及整机部件间的协调优化方法,实现部件间关键尺寸的快速协调优化,提高产品的性能和设计效率.最后,给出某数控机床的大件结构复合优化案例,说明该方法的有效性.     

Use of coordinate measuring machine to measure angles by geometric characterization of perpendicular planes. Estimating uncertainty

The purpose of this paper is to estimate the uncertainty of angle measurements using a Coordinate Measuring Machine (CMM), through the geometrical characterization of two concurrent sides of a steel angle gauge block with four perpendicular sides.For the calculation of the uncertainty associated with the measurement and investigating the errors of the CMM associated with orientation and length in the work volume, two models: linear statistical model behavior of CMM and the Mitutoyo model behavior are used and compared. After having established two behavioral models for the CMM we have determined the values of the angles and their uncertainty by using Monte Carlo Method. The results show that the proposed methods are suitable to investigate CMM hardware performance and determine the contribution of machine variables to measurement uncertainty. We can affirm that the statistical model behavior is more immediate and less laborious in terms of calculation and implementation time than the Mitutoyo model.     

神经网络理论在数控机床热误差建模中的应用

使用神经网络理论对建立数控机床热误差数学模型进行研究分析,并将其与传统的最小二乘线性建模所得热误差数学模型进行综合对比。通过应用实例分析比较表明:神经网络模型与传统的最小二乘线性模型相比具有更好的拟合性和预测能力,并对温度传感器布点的鲁棒性优于传统的最小二乘法建模。     

基于面向对象和数据库技术的机床选择专家系统

机床选择是机械加工工艺设计中的一个重要环节。专家系统是人工智能的一个主要研究方向,非常适合处理需要大量经验知识的设计问题。提出将面向对象方法和数据库技术相结合,进行了机床选择专家系统总体结构设计,并介绍了各模块对应的功能,研究了基于产生式规则的知识表示方法、基于关系型数据库的知识库的管理和基于正向推理方式的推理机的设计和推理过程等关键技术,以Visual C++和Access为开发工具,实现了机床选择专家系统。