Virtual machining considering dimensional,geometrical and tool deflection errors in three-axis CNC milling machines

Virtual manufacturing systems can provide useful means for products to be manufactured without the need of physical testing on the shop floor. As a result, the time and cost of part production can be decreased. There are different error sources in machine tools such as tool deflection, geometrical deviations of moving axis and thermal distortions of machine tool structures. Some of these errors can be decreased by controlling the machining process and environmental parameters. However other errors like tool deflection and geometrical errors which have a big portion of the total error, need more attention. This paper presents a virtual machining system in order to enforce dimensional, geometrical and tool deflection errors in three-axis milling operations. The system receives 21 dimensional and geometrical errors of a machine tool and machining codes of a specific part as input. The output of the system is the modified codes which will produce actual machined part in the virtual environment.     

安全相关控制系统中的安全总线分析和研究

较全面地阐述目前安全相关控制系统中6种主流安全总线的结构和特点,分析信息传输可能发生的错误,研究各总线在信息级应对传输错误所采取的具体防范措施以及为提高通讯安全在结构上所采取的安全机制,从而为深入理解各安全总线不同的安全工作机制、分析和设计安全总线以及安全监控系统总线的选择提供了借鉴和指导.     

Nonparametric kernel density estimation near the boundary

Standard fixed symmetric kernel-type density estimators are known to encounter problems for positive random variables with a large probability mass close to zero. It is shown that, in such settings, alternatives of asymmetric gamma kernel estimators are superior, but also differ in asymptotic and finite sample performance conditionally on the shape of the density near zero and the exact form of the chosen kernel. Therefore, a refined version of the gamma kernel with an additional tuning parameter adjusted according to the shape of the density close to the boundary is suggested. A data-driven method for the appropriate choice of the modified gamma kernel estimator is also provided. An extensive simulation study compares the performance of this refined estimator to those of standard gamma kernel estimates and standard boundary corrected and adjusted fixed kernels. It is found that the finite sample performance of the proposed new estimator is superior in all settings. Two empirical applications based on high-frequency stock trading volumes and realized volatility forecasts demonstrate the usefulness of the proposed methodology in practice.     

主从式测量系统中传感器标定方案的研究及实现

针对主从式测量系统中传感器的标定问题,提出从上位机软件进行标定的方案,着重分析软件标定的数据采集及处理过程,并根据标定直线及标定常数的数值判定是否需要进行原点补偿。实验证明,从上位机软件角度对传感器进行标定更加简单方便,并且降低了对生产线标定人员的专业知识要求,该方法适合应用于工业现场对传感器进行标定,有较高的实际应用价值。     

Implicit Bayesian Inference Using Option Prices

Abstract. A Bayesian approach to option pricing is presented in which posterior inference about the underlying returns process is conducted implicitly via observed option prices. A range of models allowing for conditional leptokurtosis, skewness and time‐varying volatility in returns are considered, with posterior parameter distributions and model probabilities backed out from the option prices. Models are ranked according to several criteria, including out‐of‐sample predictive and hedging performance. The methodology accommodates heteroscedasticity and autocorrelation in the option pricing errors, as well as regime shifts across contract groups. The method is applied to intraday option price data on the S&P500 stock index for 1995. While the results provide support for models that accommodate leptokurtosis and skewness, no one model dominates when all criteria are considered.     

含温度补偿的便携式土壤水分测定仪研制

针对现有土壤水分测定仪的不足,研制了一种新型的便携式土壤水分测定仪。传感器快速测量出土壤温、湿度数据,GPS自动获取时间、经纬度信息,数据既可临时保存在仪器的存储芯片中,又可通过GPRS/GSM将数据及时发送到后台数据库和手机用户。通过温度补偿和野外验证实验得出,温度补偿项为Δy=0.0002 t3-0.011 t2+0.444 1 t-6.423 2,仪器所有功能运行正常,测量绝对误差为-3.64%~3.82%,平均绝对误差为2.24%,精度较高,适合在地方农技和水利部门推广应用,有助于农业水利信息化水平的提高。     

关于提高热电阻温度测量精度的设计方法研究

为了提高热电阻温度测量的精度,从温度传感器的选型、测量方案的设计、实际测量电路、硬件自校正、微处理器的选择、模拟信号预处理、滤波算法和软件非线性校正等方面给出了具体的设计方案。详细分析了自校正补偿及微信号采集转换电路的设计方案,设计了与DSP F2812的接口电路。实际应用表明,通过上述改进方案,热电阻温度测量准确度可以达到10 ppm的设计要求。     

用于光刻系统仿真的多边形处理算法

为提高光刻仿真效率,通过对光刻原理进行研究,提出了2种多边形处理算法,将掩模上的多边形图案进行切分优化,将其划分成若干矩形或三角形。在Linux环境下应用C语言设计出一个完整的光刻仿真系统,设计的具体光学参数为:光源波长为193nm,数值孔径为0.3~0.8,部分相干系数可调范围为0.2~0.8,可一次性仿真1μm×1μm到10μm×10μm范围内的45 nm~0.18μm工艺的复杂版图,并通过多次实验进行验证。实验结果表明:原版图图像的边缘细节得到保留,且该算法有效地减少了光刻模拟的计算复杂度与计算时间,整体效率提升20%以上,为当前智能传感器系统芯片的制造节省了宝贵时间。     

固定多摄像头的视觉拼接技术

视频拼接技术是计算机图形学和计算机视觉的重要分支,它的发展基于静态图像的拼接技术,但由于视频信息的复杂性,视频拼接也有区别于图像拼接,针对实际运用中的实时拼接的需要,本文提出了一种基于控制帧的固定摄像头视频拼接方法。首先采集控制帧图像,对摄像头进行参数标定获得相机内参和光心坐标,再使用一种改进的畸变矫正方法去除摄像头畸变带来的成像失真。然后对控制帧图像进行SIFT特征提取并进行粗匹配,再用RANSAC的方法剔除误匹配点并拟合出图像变换单应阵。最后使用查表法将各摄像头的图像同步投影到大场景图片上,对重合区域进行光亮补偿和多带融合。最终实现速度可达25帧/秒的实时视频拼接。     

一种在扩散加权图像降噪中的算法

扩散加权图像中的噪声为莱斯噪声并且图像本身含有丰富的边界信息,因而要求对DWI图像有效降噪的同时,能够较好地保留图像的边界信息。由于BEMD算法可将图像分解为细节图像及余项图像,其所分解的细节图像包括DWI图像的边界信息以及主噪声,而余项图像则描述图像的趋势信息。因此,提出一种将二维经验模态分解算法与改进的维纳滤波器相结合的降噪算法,并将该算法应用于DWI图像的降噪中。通过实验,将所提出的算法与其他算法应用于DWI图像的降噪处理,并通过对结果的分析比较证明所提出的算法能够更有效地对DWI图像进行降噪处理。