Tool Condition Monitoring Based on Nonlinear Output Frequency Response Functions and Multivariate Control Chart

Tool condition monitoring(TCM)is a key technology for intelligent manufacturing.The objective is to monitor the tool operation status and detect tool breakage so that the tool can be changed in time to avoid significant damage to workpieces and reduce manufacturing costs.Recently,an innovative TCM approach based on sensor data modelling and model frequency analysis has been proposed.Different from traditional signal feature-based monitoring,the data from sensors are utilized to build a dynamic process model.Then,the nonlinear output frequency response functions,a concept which extends the linear system frequency response function to the nonlinear case,over the frequency range of the tooth passing frequency of the machining process are extracted to reveal tool health conditions.In order to extend the novel sensor data modelling and model frequency analysis to unsupervised condition monitoring of cutting tools,in the present study,a multivariate control chart is proposed for TCM based on the frequency domain properties of machining processes derived from the innovative sensor data modelling and model frequency analysis.The feature dimension is reduced by principal component analysis first.Then the moving average strategy is exploited to generate monitoring variables and overcome the effects of noises.The milling experiments of titanium alloys are conducted to verify the effectiveness of the proposed approach in detecting excessive flank wear of solid carbide end mills.The results demonstrate the advantages of the new approach over conventional TCM techniques and its potential in industrial applications.

AN INTELLIGENT TOOL CONDITION MONITORING SYSTEM USING FUZZY NEURAL NETWORKS

Reliable on line cutting tool conditioning monitoring is an essential feature of automatic machine tool and flexible manufacturing system (FMS) and computer integrated manufacturing system (CIMS). Recently artificial neural networks (ANNs) are used for this purpose in conjunction with suitable sensory systems. The present work in Norwegian University of Science and Technology (NTNU) uses back propagation neural networks (BP) and fuzzy neural networks (FNN) to process the cutting tool state data measured with force and acoustic emission (AE) sensors, and implements a valuable on line tool condition monitoring system using the ANNs. Different ANN structures are designed and investigated to estimate the tool wear state based on the fusion of acoustic emission and force signals. Finally, four case studies are introduced for the sensing and ANN processing of the tool wear states and the failures of the tool with practical experiment examples. The results indicate that a tool wear identification system can be achieved using the sensors integration with ANNs, and that ANNs provide a very effective method of implementing sensor integration for on line monitoring of tool wear states and abnormalities.

Method of Monitoring Wearing and Breakage States of Cutting Tools Based on Mahalanobis Distance Features

The Mahalanobis distance features proposed by P.C.Mahalanobis, an Indian statistician, can be used in an automatic on-line cutting tool condition monitoring process based on digital image processing. In this paper, a new method of obtaining Mahalanobis distance features from a tool image is proposed. The key of calculating Mahalanobis distance is appropriately dividing the object into several component sets. Firstly, a technique is proposed that can automatically divide the component groups for calculating Mahalanobis distance based on the gray level of wearing or breakage regions in a tool image. The wearing region can be divided into high gray level component group and the tool-blade into low one. Then, the relation between Mahalanobis distance features of component groups and tool conditions is investigated. The results indicate that the high brightness region on the flank surface of the turning tool will change with its abrasion change and if the tool is heavily abraded, the area of high brightness will increase apparently. The Mahalanobis distance features of high gray level component group are related with wearing state of tool and low gray level component group correlated with breakage of tool. The experimental results show that the abrasion of the tool’s flank surface affected the Mahalanobis distances of high brightness component of the tool and the pixels of high brightness component set. Compared with the changes of them, we found that the Mahalanobis distance of high brightness component of the tool was more sensitive to the abrasion of cutting tool than the area of high brightness component set of the tool. Here we found that the relative changing rate of the area of high brightness component set was not quite obvious and it was ranging from 2% to 15%, while the relative changing rate of the Mahalanobis distance in table 1 ranges from 13.9% to 47%. It is 3 times higher than the changing rate of the area.

BP-Neural-Network-Based Tool Wear Monitoring by Using Wav elet Decomposition of the Power Spectrum

In a drilling process, the power spectrum of the drilling force is related tothe tool wear and is widely applied in the monitoring of tool wear. But the feature extraction andidentification of the power spectrum have always been an unresolved difficult problem. This papersolves it through decomposition of the power spectrum in multilayers using wavelet transform andextraction of the low frequency decomposition coefficient as the envelope information of the powerspectrum. Intelligent identification of the tool wear status is achieved in the drilling processthrough fusing the wavelet decomposition coefficient of the power spectrum by using a BP (BackPropagation) neural network. The experimental results show that the features of the power spectrumcan be extracted efficiently through this method, and the trained neural networks show highidentification precision and the ability of extension.

On-line Tool Condition Monitoring with Improved Fuzzy Neural Network

This paper presents an investigation of tool condition monitoring based on fuzzy neural network for drilling. In this study, five monitoring feature parameters, which will be used to monitor tool condition, are selected by means of vibration signal spectral analysis. In order to meet the need of the system real time, this paper presents a neural network with fuzzy inference. Fuzzy neural network requires less computation than backpropagation neural network, and can easily describe the relationship between the tool conditions and the monitoring indices. The experimental results indicate that the use of vibration signal for on--line drilling condition monitoring is feasible.

In-process tool wear monitoring using laser-CCD

A simple and reliabe monitoring method based on laser-CCD trigonometric measurement is Proposed for toolwear sensing in the automation of manufacturing processes, and experimental results show this method is good for in-dustrial use.

A Fuzzy Neural Network for Drilling Tool Condition Monitoring

This paper presents a fuzzy neural network used for monitoring breakage and wear of tools by vibration sig-nal. Which describes the relationship betwee too conditons and the monitoring indices and expermental results indi-cate it is feasible to vibration signal for on-line drilling condition monitoring.

A Modification of SOM Network(SLFM) and Its Applications in Tool Wear Monitoring and Quality Control

In this paper, a Supervised Linear Feature Mapping(SLFM) algorithm, as a modification of the Kohonen Self Organizing Mapping (SOM),is proposed. The applications in cutting tool wear estimation and quality control and the comparison with a back propagation (BP) algorithm are discussed. The results show that the SLFM algorithm requires less training time and has higher accuracy compared with the BP algorithm. It might be a great potential approach to integrate multi sensor information in process control.

Tool Wear Monitoring in Drilling Using Multiple Feature Fusion of the Cutting Force

This paper presents a tool wear monitoring method in drilling process using cutting force signal. The kurtosis coefficient and the energy of a special frequency band of cutting force signals were taken as the signal features of tool wear as well as the mean value and the standard deviation from the time and frequency domain. The relationships between the signal feature and tool wear were discussed; then the vectors constituted of the signal features were input to the artificial neural network for fusion in order to realize intelligent identification of tool wear. The experimental results show that the artificial neural network can realize fusion of multiple features effectively, but the identification precision and the extending ability are not ideal owing to the relationship between the features and the tool wear being fuzzy and not certain.

Real-Time Data and Visualization Monitoring of Computer Numerical Control Machine Tools Based on Hyper Text Markup Language 5

In order to ensure the safety,quality and efficiency of computer numerical control(CNC)machine tool processing,a real-time monitoring and visible solution for CNC machine tools based on hyper text markup language(HTML)5 is proposed.The characteristics of the real-time monitoring technology of CNC machine tools under the traditional Client/Server(C/S)structure are compared and analyzed,and the technical drawbacks are proposed.Web real-time communication technology and browser drawing technology are deeply studied.A real-time monitoring and visible system for CNC machine tool data is developed based on Metro platform,combining WebSocket real-time communication technology and Canvas drawing technology.The system architecture is given,and the functions and implementation methods of the system are described in detail.The practical application results show that the WebSocket real-time communication technology can effectively reduce the bandwidth and network delay and save server resources.The numerical control machine data monitoring system can intuitively reflect the machine data,and the visible effect is good.It realizes timely monitoring of equipment alarms and prompts maintenance and management personnel.

刀具磨损状态的多步向前智能预测

刀具状态的准确监测对于提高切削加工质量和加工效率至关重要。在当前广泛用于刀具磨损状态监测的间接法中,多以单步或短期预测为主,没有实现多步预测,且累积误差较大。高斯过程是间接法中应用较多的一种机器学习方法,然而传统的高斯过程回归由于模型结构和算法的限制,对刀具磨损预测的精度不高。针对上述不足,提出了改进的自回归递归高斯过程模型对刀具磨损进行多步预测。为了减小预测累积误差,在模型训练中应用了改进的模型更新方式、组合核函数,对样本设置了遗忘因子,在预测中加入了偏差校正方法。研究了各个改进因素对模型的影响并综合所有有利因素,实现了较准确的刀具磨损状态多步预测,在3个测试集上预测误差分别降低了85.68%,20.67%和63.32%。

实施国家义务教育英语学习质量监测,促进英语教育高质量发展

2021年,教育部印发《国家义务教育质量监测方案(2021年修订版)》,首次将英语学科纳入监测范围。2022年5月,教育部基础教育质量监测中心第一次在全国范围内实施了国家义务教育英语学习质量监测。通过本轮监测,监测中心客观掌握国家义务教育英语学习质量总体水平,全面了解影响英语教育质量的主要因素,进而推动英语教学改革,提高英语学习效率。未来,英语监测将在诊断教育问题、引领教育改革方面发挥重要作用,助力国家义务教育高质量发展。本文将从英语监测启动的意义、高质量英语监测的特征以及英语监测如何推动教育质量发展等方面,系统介绍国家义务教育英语学习质量监测。

多传感器信息融合的刀具磨损状态智能监测系统

为了提高数控机床刀具磨损状态智能监测的可靠性,提出一种基于多传感器信息融合的刀具磨损状态智能监测方法及系统。利用多种传感器分别采集刀具加工过程中的机床变频器输入电流信号、工件三向振动信号和声信号,然后对采集到的信号进行时域、频域和时频域处理分析。系统自动识别提取出其中与刀具磨损程度相关性较高的敏感特征变量,并利用马氏距离法对敏感特征向量进行分析计算,确定刀具不同状态下的阈值,并据此判断刀具的磨损状态。最后基于上述原理利用QT开发平台研发一套完整的数控机床刀具磨损状态智能监测系统。试验结果表明,该系统能够实时准确地监测出刀具的磨损状态。

基于累加式实时串并联变换算法的机械故障声学监测方法

针对基于物联网(IoT)的冲压机床故障监测问题,为了降低冲压机床故障监测的计算复杂度,并提高其低频识别的精度,提出了一种无需机器学习技术的实时性机械故障声学监测方法,即基于累加式实时串并联变换算法的机械故障声学监测方法。首先,研究了物联网场景中冲压机床声学低频分析的必要性,并给出了声学信号的表达式;然后,针对频率轴上多个周期信号重叠导致参数估计较为困难的问题,提出了一种累加式实时串并联变换算法,将输入的采样序列馈入多个具有不同输出端口的串并转换器,从累加的波形中检测出最大绝对值,并进行了比较;最后,通过样本时隙划分,将累加式实时串并联变换算法应用于机械故障监测;通过仿真和冲压机床实机测试,对累加式实时串并联变换算法和实时性机械故障声学监测方法的有效性进行了验证。研究结果表明:在无需大量信号样本的情况下,使用累加式实时串并联变换算法有利于提高低频带的识别精度;在直方图相关性方面,累加式实时串并联变换算法和Morlet小波变换具有相同的性能,且均明显优于短时傅立叶变换;同时,尽管累加式实时串并联变换算法需要的加法总数比Morlet小波变换多2.5倍,但是乘法总数减少了20447%,大幅减少了计算的复杂度。

APPLICATION OF ACOUSTIC EMISSION SENSOR IN DETECTING TOOL BREAKAGE IN MICRO-MILLING

Acoustic emission （AE） sensors are used to monitor tool conditions in micro-milling operations. Together with the microphone, the AE sensor can detect the tool breakage more accurately and more effectively by applying the wavelet analysis. The processed tool breakage technique by AE sensor is used to perform the wavelet analysis on the experimental data. Results indicate the feasibility of using the AE signals for monitoring the tool condition in micro-milling.

智能刀具设计及关键技术研究进展

随着“工业4.0”及“中国制造2025”战略计划的兴起,制造业中的智能制造及自动化水平不断提升,刀具作为生产过程中的重要一环,也变得更加精密化和智能化。智能刀具是实现智能制造和自动化生产的重要环节和必要保障,本文围绕智能刀具的最新研究进展进行了详细论述,包括智能刀具设计、智能刀具关键技术、数字孪生技术及智能刀具系统等方面内容。归纳了国内外学者们在智能刀具集成优化与结构设计、智能刀具监测和调控技术、基于刀具管控和推荐的智能刀具系统的研究成果,简述了数字孪生技术在智能刀具领域中的应用,并指出了智能刀具目前存在的不足及未来发展方向。

基于改进信息熵的直接刀具状态监测设备部署

在不拆刀情况下,基于机器视觉的在线刀具状态监测系统可完成刀具磨损测量和状态评估,但与在线捕获刀具图像质量息息相关的系统部署参数选择却鲜有研究.为解决上述问题,本文构建基于改进信息熵的多项式回归模型以实现刀具状态监测系统的最优部署.首先,使用自适应阈值方法去除捕获刀具图像中背景要素干扰,并通过信息熵指标评估图像中刀具磨损区域的成像质量;然后,构建相机工作距离、曝光时间与所提出评价指标之间的多项式回归模型以描述部署参数与提出评价指标的映射关系;最后,应用最小二乘法求取多项式模型系数获得最优部署参数.在确保自变量的因子水平涵盖最优部署参数情况下设计正交实验,实验结果表明:提出的评价指标与工作距离、曝光时间等部署参数之间均存在主效应关系,符合光学成像系统的变化规律;与支持向量机、决策树和K近邻(K-nearest neighbor,KNN)算法等非线性回归预测模型相比,三次多项式回归模型预测误差最小,其平均绝对误差、均方误差、均方根误差分别为0.022631,0.00068,0.026069;在多项式回归模型求解的最优部署参数下,所捕获的刀具图像的测量精度达到96.76%,提高0.74%,满足刀具状态监测的精度要求.

基于特征融合与域自适应的刀具磨损在线监测

机床状态监测对于机床健康管理以及保证工件加工质量具有重要意义。针对现有刀具磨损预测模型存在训练时间长、收敛速度慢以及泛化能力弱等问题,提出了一种分布式一维卷积神经网络对刀具磨损进行预测。采用残差连接与通道注意力模块顺序堆叠的方式作为特征提取模块,并通过交叉验证以选择合适的网络层数。由于不同传感器所提取到的特征信息可能存在冗余,使用权重差异策略以提高特征提取的有效性以及全面性。此外,考虑到训练集与测试集分布可能存在差异从而影响模型的泛化性能,引入了域自适应方法提高模型在未知数据集中的表现。为验证模型效果,使用PHM 2010铣刀磨损数据集进行实验。实验结果表明,该模型在C1、C4、C6三把刀具上的平均RMSE和平均MAE分别为6.97和6.29,与TCN、TDConvLSTM等模型相比有12%以上的提升。