For milling tool life prediction and health management,accurate extraction and dimensionality reduction of its tool wear features are the key to reduce prediction errors.In this paper,we adopt multi-source information...For milling tool life prediction and health management,accurate extraction and dimensionality reduction of its tool wear features are the key to reduce prediction errors.In this paper,we adopt multi-source information fusion technology to extract and fuse the features of cutting vibration signal,cutting force signal and acoustic emission signal in time domain,frequency domain and time-frequency domain,and downscale the sample features by Pearson correlation coefficient to construct a sample data set;then we propose a tool life prediction model based on CNN-SVM optimized by genetic algorithm(GA),which uses CNN convolutional neural network as the feature learner and SVM support vector machine as the trainer for regression prediction.The results show that the improved model in this paper can effectively predict the tool life with better generalization ability,faster network fitting,and 99.85%prediction accuracy.And compared with the BP model,CNN model,SVM model and CNN-SVM model,the performance of the coefficient of determination R2 metric improved by 4.88%,2.96%,2.53%and 1.34%,respectively.展开更多
[目的]利用地理信息系统(Geographic information system,GIS)分析昆明市某城区1998～2003年脑卒中早死所致生命损失的地理分布变化。[方法]选择盘龙区作为城区的代表,以早死所致生命损失年(years of life lost,YLL)作为脑卒中疾病负担...[目的]利用地理信息系统(Geographic information system,GIS)分析昆明市某城区1998～2003年脑卒中早死所致生命损失的地理分布变化。[方法]选择盘龙区作为城区的代表,以早死所致生命损失年(years of life lost,YLL)作为脑卒中疾病负担的测量单位,采用3%的贴现率但不采用年龄权重按年计算标化每千人口YLL率;并分析其地理分布的变化趋势。[结果]昆明市盘龙区1998￣2003年脑卒中每千人口YLL率起伏波动。从地理分布来看,城区中心街道办事处的脑卒中每千人口YLL率明显高于偏远街道办事处,且连续6年处于较高水平。[结论]应加强盘龙区居民脑卒中的防治工作,尤其是城中心居民。展开更多
为了有效快速评估高可靠性长寿命产品在正常应力条件下的可靠性,提出了一种双应力恒加试验Weibull分布型产品置信可靠性评估模型。首先,采用加速寿命试验(accelerated life test,ALT)技术,建立广义Eyring-Weibull可靠性模型,假定试验各...为了有效快速评估高可靠性长寿命产品在正常应力条件下的可靠性,提出了一种双应力恒加试验Weibull分布型产品置信可靠性评估模型。首先,采用加速寿命试验(accelerated life test,ALT)技术,建立广义Eyring-Weibull可靠性模型,假定试验各应力水平组合下Weibull分布的形状参数相同,且尺度参数与各应力水平组合间呈对数线性关系。其次,给出了Weibull分布定时截尾双应力恒加试验的极大似然估计(maximum likelihood estimation,MLE)方法、与似然函数相关的Fisher信息矩阵以及模型参数的渐近协方差矩阵,构造了模型参数和一些可靠性指标的渐近置信区间。最后,通过仿真算例证明了所提方法的可行性。展开更多
基金financed with the means of Basic Scientific Research Youth Program of Education Department of Liaoning Province,No.LJKQZ2021185Yingkou Enterprise and Doctor Innovation Program (QB-2021-05).
文摘For milling tool life prediction and health management,accurate extraction and dimensionality reduction of its tool wear features are the key to reduce prediction errors.In this paper,we adopt multi-source information fusion technology to extract and fuse the features of cutting vibration signal,cutting force signal and acoustic emission signal in time domain,frequency domain and time-frequency domain,and downscale the sample features by Pearson correlation coefficient to construct a sample data set;then we propose a tool life prediction model based on CNN-SVM optimized by genetic algorithm(GA),which uses CNN convolutional neural network as the feature learner and SVM support vector machine as the trainer for regression prediction.The results show that the improved model in this paper can effectively predict the tool life with better generalization ability,faster network fitting,and 99.85%prediction accuracy.And compared with the BP model,CNN model,SVM model and CNN-SVM model,the performance of the coefficient of determination R2 metric improved by 4.88%,2.96%,2.53%and 1.34%,respectively.
文摘[目的]利用地理信息系统(Geographic information system,GIS)分析昆明市某城区1998～2003年脑卒中早死所致生命损失的地理分布变化。[方法]选择盘龙区作为城区的代表,以早死所致生命损失年(years of life lost,YLL)作为脑卒中疾病负担的测量单位,采用3%的贴现率但不采用年龄权重按年计算标化每千人口YLL率;并分析其地理分布的变化趋势。[结果]昆明市盘龙区1998￣2003年脑卒中每千人口YLL率起伏波动。从地理分布来看,城区中心街道办事处的脑卒中每千人口YLL率明显高于偏远街道办事处,且连续6年处于较高水平。[结论]应加强盘龙区居民脑卒中的防治工作,尤其是城中心居民。
文摘为了有效快速评估高可靠性长寿命产品在正常应力条件下的可靠性,提出了一种双应力恒加试验Weibull分布型产品置信可靠性评估模型。首先,采用加速寿命试验(accelerated life test,ALT)技术,建立广义Eyring-Weibull可靠性模型,假定试验各应力水平组合下Weibull分布的形状参数相同,且尺度参数与各应力水平组合间呈对数线性关系。其次,给出了Weibull分布定时截尾双应力恒加试验的极大似然估计(maximum likelihood estimation,MLE)方法、与似然函数相关的Fisher信息矩阵以及模型参数的渐近协方差矩阵,构造了模型参数和一些可靠性指标的渐近置信区间。最后,通过仿真算例证明了所提方法的可行性。
