Thermal Error Modeling Method with the Jamming of Temperature-Sensitive Points'Volatility on CNC Machine Tools

Aiming at the deficiency of the robustness of thermal error compensation models of CNC machine tools, the mechanism of improving the models＇ robustness is studied by regarding the Leaderway-V450 machining center as the object. Through the analysis of actual spindle air cutting experimental data on Leaderway-V450 machine, it is found that the temperature-sensitive points used for modeling is volatility, and this volatility directly leads to large changes on the collinear degree among modeling independent variables. Thus, the forecasting accuracy of multivariate regression model is severely affected, and the forecasting robustness becomes poor too. To overcome this effect, a modeling method of establishing thermal error models by using single temperature variable under the jamming of temperature-sensitive points＇ volatility is put forward. According to the actual data of thermal error measured in different seasons, it is proved that the single temperature variable model can reduce the loss of fore- casting accuracy resulted from the volatility of tempera- ture-sensitive points, especially for the prediction of cross quarter data, the improvement of forecasting accuracy is about 5 μm or more. The purpose that improving the robustness of the thermal error models is realized, which can provide a reference for selecting the modelingindependent variable in the application of thermal error compensation of CNC machine tools.

Identification of the key thermal points on machine tools by grouping and optimizing variables

The grouping and optimization approach to identify the key thermal points on machine tools is studied.To solve the difficulty in grouping because of the high correlated variables from distinct groups,the variables grouping technique is improved.Temperature variables are sorted according to their relativities with the thermal errors.The representative temperature variables are determined by analyzing the variable correlation in sort order and removing the other variables in the same group.Considering the diverse effect of importing the different variables on thermal error model,the method of variable combination optimization is improved.Regression models made up of different combination of representative temperature variables are evaluated by the index of both the determined coefficient and the average residual squares to select the combination of the temperature variables.For the machine tools with complicated structures which need more initial temperature measuring points the improvement is demanded.The improved approach is applied to a precision horizontal machining center to identify the key thermal points.Experimental results show that the proposed approach is capable of avoiding the high correlation among the different groups' variables,effectively reducing the number of the key thermal points without depressing the prediction accuracy of the thermal error model for machine tools.

GENERATE ROUGH TOOL-PATHS FROM UNORGANIZED POINT-CLOUD DIRECTLY

An approach is presented to generate rough interference-free tool-paths directly from massive unorganized data in rough machining that is performed by machining volumes of material in a slice-by-slice manner. Unorganized point-cloud is firstly converted to cross-section data. Then a robust data-structure named tool-path net is constructed to save tool-path data. Optimal algorithms for partitioning sub-cut-areas and computing interference-free cutter-locations are put forward. Finally the tool-paths are linked in a zigzag milling mode, which can be transformed into a traveling sales man problem. The experiment indicates optimal tool paths can be acquired, and high computation efficiency can be obtained and interference can be avoided successfully.

基于Pro/TOOLKIT的点坐标测量工具的开发

在工程实际中有时需要测量多个点的坐标。而Pro/E系统并未提供测量点坐标的工具,给设计过程带来诸多不便。论文以Pro/TOOLKIT为工具,开发了基于Pro/E系统的点坐标测量工具。在功能分析的基础上,进行了程序模块的划分。结合Pro/TOOLKIT函数的功能,介绍了功能模块的工作原理。最后通过一定方法验证程序的适应性和正确性。

X38CrMoV5 hot-work tool steel as tool material for thixoforging of steel:Numerical and experimental evaluation

Although thixoforming of low melting point alloys as aluminum or magnesium is now an industrial reality,thixoforming of high melting point alloys as steel is still at the research level.High working temperature,die wearing and production rate are problems that must be solved and are under investigation.The aim of this work is to evaluate the thermal and mechanical loadings applied to the tools during the steel thixoforging process in order to determine whether classical hot-work tool steel can be an appropriate tool material.This evaluation has been realized thanks to experimental trials and to simulations on the finite elements code Forge2008.The effect of the loadings on the tool's failure modes are highlighted and compared with the ones observed in classical hot forging.Beyond this,the failure modes of hot-work tool steel,the X38CrMoV5 or H11,were presented.

Reusing Test Cases Based on the Function Point

Reusing test cases from existing test case library is quite common in the software testing field. Testing practice tells us that there is a strong relationship between the granularity of a function unit under testing and that of the test case. A function unit with small granularity usually results in the test cases with the same small granularity. Therefore a test case defined as the function point,i. e.,the smallest size function unit,was provided for the first time.Though test cases with smaller granularity usually have better reusability,the cost of accurately reusing and integrating such test cases is also higher. In order to balance the test case reusability and the cost of test case reuse,a novel test case reuse model based on the function point was proposed in this paper. In this model,a reusable test case for specification-based testing was defined and some reuse strategies and three formal reuse methods were given. Finally,the complete automatic software process was realized by a reusing generation tool. The new method has improved reuse accuracy,while greatly enhances the software productivity.

Analysis of the Relationship between Landuse and Non-point Source Pollution in Ashi River Basin

Landuse is one of the most influential factors of non-point source pollution. Based on the three-year landuse data( 2000,2005 and 2008),Arc GIS and Fragstat were used to analyze the landuse type and the change of landscape pattern. The relationships between landuse and non-point source-total nitrogen( NPS-TN) and nonpoint source-total phosphorus( NPS-TP) were discussed with the methods of spatially statistical analysis,landscape pattern analysis and principal component analysis. The study results conveyed that agricultural land and forestland,which accounted for over 92% of the study area,were the major landuse type of Ashi River Basin.Meanwhile,the NPS pollution had close connections with landuse type and landscape pattern. When it comes to landuse type,the export risks of NPS-TN and NPS-TP were agricultural land > urban land > grassland > forestland. As for landscape pattern,NPS-TN and NPS-TP were positively related to SHDI and SHEI, while negatively connected with LPI,AI and COHESION. Therefore,the study could reach the conclusion that the more fragmented and complicated the landscape patterns were,the more serious the NPS pollution was.

基于Cutting Tool的FANUC激光切割系统研制

传统的激光切割多数采用五轴CO_2激光切割机,占地面积大,柔性差,设备采购及维护成本居高不下。为此,设计了基于Cutting Tool的FANUC激光切割系统,该系统包含Cutting Tool技术、离线编程技术、图形生成技术、工具中心点速度输出技术等多种关键技术,拓展了机器人激光切割系统的应用领域,为工业用户提供了一种新的技术解决方案。

A Fast Tool Servo System for Fabrication of Micro-structured Surfaces on A Diamond Turning Machine

A fast tool servo (FTS) system is developed for the fabrication of non-rotationally symmetric micro-structured surfaces using single-point diamond turning machines.The constructed FTS employs a piezoelectric tube actuator (PZT) to actuate the diamond tool and a capacitive probe as the feedback sensor.To compensate the inherent nonlinear hysteresis behavior of the piezoelectric actuator,Proportional Integral (PI) feedback control is implemented.Besides,a feed-forward control based on a simple feed-forward predictor has been added to achieve better tracking performance.Experimental results indicate that error motions in the performance of the system caused by hysteresis can be reduced greatly and the micro-structured surface is successfully fabricated by implementing the FTS.

基于传递矩阵法的指向式旋转导向工具主轴振动特性

指向式旋转导向工具应用于井眼轨迹控制时,其主轴的动力学特性将直接影响到井眼轨迹控制效果及作业安全,而在钻进工况下,工具钻压传递机构在主轴上的位置对主轴的动力学特性起着重要的作用。因此,为了分析钻压传递机构的位置对主轴动力学特性的影响,利用多体系统传递矩阵法建立了指向式旋转导向工具外壳-轴承-主轴系统的动力学模型。通过推导主轴上任意节点的几何和力学方程,该研究能够评估钻压传递机构的位置对主轴动态性能的影响规律。结合实例运算分析了钻压传递机构的安装位置对主轴固有频率和振型的影响,探讨了工具造斜时,钻压传递机构安装位置对主轴动态位移的影响。结果表明,随着钻压传递机构安装位置距离钻头越远,主轴固有频率和动态位移均增大,因此在满足工作要求下,推荐钻压传递机构安装位置尽可能靠近钻头端。为验证基于传递矩阵法建立的主轴动力学模型的正确性以及钻压传递装置安装位置对主轴动态位移影响规律,在指向式旋转导向工具试验台架上进行了钻进工况下主轴测点偏移量测试试验,结果表明,试验测得的数据与理论计算的数据基本吻合,误差最大仅为6.47%。

基于激光点云技术的机床夹具设计与改进

为了解决传统机床夹具通用性不高、多次对刀和装夹带来误差和效率较低的问题,提出了一种基于点云逆向建模技术的机床夹具改进方案。通过在夹具两侧加装激光扫描仪以获取工件和夹具的3维点云信息,分别采用曲率判别算法和基于粒子群搜索的迭代最近点算法对其进行去噪处理和坐标配准,建立工件与机床一体的3维空间坐标;最后根据参考点的点云坐标计算空间坐标系与机床坐标系的偏移量,将获得的偏移值录入数控系统进行加工。结果表明,改进后的夹具在加工工序较为复杂的零件时,可以有效减少对刀和装夹次数,总体工效提升约30%。该研究对于提升加工面较多、工序较为复杂零件的加工效率具有一定的参考价值。

基于视觉的并联机床位姿测量研究

为准确测量并联机床的位姿,提高并联机床的运动精度,提出一种基于视觉的位姿测量方法用于并联机构的末端位姿检测。采用Femto深度相机作为测量设备搭建测量平台,并用棋盘格标定板和MATLAB对相机进行标定;将标靶置于动平台进行位姿采集,利用点云库对采集后的数据进行过滤和提取;最后,将计算出的实际位姿与输入位姿进行实验比较。结果表明:X、Y、Z轴的最大误差分别为0.071、0.047、0.394 mm,绕X、Y、Z轴旋转的最大误差分别为0.09°、0.09°、0.14°,满足精度要求,证明了此方法的有效性。此方法操作高效便捷、成本低廉,在保证高检测精度的同时,可为位姿测量和后续标定实验提供新思路。

机床直线轴温度测点筛选与热误差预测方法

为揭示数控机床直线进给轴温度场信息与热误差之间的非线性映射关系,提高热误差预测模型效率和精度,提出了基于鹈鹕优化算法(POA)与随机森林(RF)的直线轴热误差预测方法。首先,采用Featts聚类算法将温度测点进行聚类分组,通过Spearman相关性分析计算温度与热误差之间的相关程度及热敏感点;其次,使用POA优化算法对RF模型参数进行寻优,确定RF网络的最佳决策树数量及叶子数等;最后,在三轴铣床加工中心上进行实验验证。结果表明,使用Featts聚类算法与Spearman相关分析方法提高了模型精度,有效避免温度测点间的多重共线性。与传统的BP神经网络及RF网络相比,POA-RF预测网络的均方根误差分别降低了46%和43%。

基于热图像的GWOA-BiLSTM机床主轴热误差预测

热误差是影响高精密数控机床加工精度的重要因素。为了提高机床加工精度和性能,减少机床运行中产生的热误差,文章提出一种基于热图像的灰狼优化算法(grey wolf optimization algorithm,GWOA)和双向长短期记忆神经网络(bidirectional long short-term memory,BiLSTM)混合的热误差预测模型。首先,采用热成像仪获取机床主轴区域的温度场信息;其次,利用DBSCAN聚类(density-based spatial clustering of applications with noise)算法和相关系数法筛选出温度敏感点;然后,通过模拟灰狼群体捕食行为,在参数空间中进行搜索以找到BiLSTM所需的最优参数;最后,使用获得的机床温度敏感点和热位移数据进行热误差预测,并在试验机床上进行验证。实验结果表明,使用GWOA优化BiLSTM神经网络的预测模型相比BiLSTM神经网络预测模型的均方根误差(root mean square error,RMSE)和平均绝对误差(mean absolute error,MAE)分别减小了约0.5180、0.3823μm,决定系数R^(2)提升了0.0578。与BiLSTM神经网络模型相比,利用GWOA优化后的模型具有更加优良的预测性能。

一种钻井指向式导向机构的力学分析

钻井导向机构的力学分析是导向工具设计和轨迹控制的基础。基于一种指向式导向机构的设计,通过纵横分析法和有限元法,建立不同的力学模型,分别对外壳、导向轴和向心关节轴承进行力学分析,研究导向机构不同安装位置对偏置力、钻头倾角和向心关节轴承所受应力大小的影响,同时分析外壳与导向轴刚度比对偏置力大小的影响,最后给出最佳的导向装置安装位置为距调心轴承0.3 m处,外壳和导向轴刚度比为5,可以增加造斜率和确保设计的合理性及可行性。

针对数控加工刀路特征刀尖点的横向光顺策略

针对刀尖点在工件拐角或边缘等特征区域的分布不一致问题,提出一种基于提高特征点横向一致性的刀路优化方法。建立约束条件用于识别刀路中的特征点;通过邻域搜索和区域生长算法进行特征点聚类,生成特征曲线,根据拟合方法得到曲线中超差点并进行修正。加工实验表明,优化刀路加工工件表面的粗糙度,相较于原始刀路降低了至少19%。

掺硼大单晶金刚石制备及其刀具切削温度在线检测研究

为了实时测量单晶金刚石刀具加工区域的温度和实时监测金刚石刀具超精密加工工件表面的质量,利用掺硼金刚石的半导体性质,建立掺硼金刚石电阻与温度的对应关系,得出其测量灵敏度为6.2Ω/℃;利用所研制的掺硼单点金刚石刀具在金刚石车床上分别对聚甲基丙烯酸甲酯(PMMA)和碳纤维增强塑料(CFRP)试件进行了单点金刚石刀具(SPDT)的切削温度测量,实验验证了所研制的掺硼金刚石刀具切削温度测量系统能够灵敏地测量精密切削过程中的切削温度;金刚石刀具切削CFRP试件时,切削温度和加工表面形貌出现周期性的变化,这一发现对于指导单点金刚石刀具超精密表面加工状态的在线监测也很有价值。

异型工装振动试验控制点位置选择与分析

试验室开展的航天器组件振动试验中,针对普通结构(如板型、L型)的产品工装,通常会在工装上的产品安装面布置控制传感器。然而,当面对结构复杂的异形工装时,缺乏明确的控制点布置要求和方法。若控制点位置选择不合理,可能严重影响试验结果,甚至导致产品失效或损坏。针对该问题,本文基于某型号航天器组件的异型工装,依次选择工装特征位置进行控制点位布置,开展振动试验,并分析试验数据,选出最佳的控制点位置。在满足试验要求的基础上,极大提高了试验效率和可靠性,保证产品安全。这一方法也将被应用于后续同类型产品的振动试验。

数控机床原点、参考点、工件零点的区别和联系

机床原点和参考点是定义数控机床运动的两个重要的概念,二者既有区别又有联系。机床原点也就是机床坐标系的零点是数控机床进行位置测量、控制、显示的统一基准。本文从新的视角定义了数控机床参考点的概念,概述了参考点在数控机床中的作用以及在什么条件下需要重新设定参考点。结合实际工作中设定数控机床X、Y、Z轴参考点的操作方法,通过总结其内在原理进一步阐明了参考点的特性。通过设定或建立参考点之后机床的原点才有实际意义,而机床的原点是在机床设计之初就确定的,只有有了机床的原点才能设定参考点的位置,这就是二者之间的区别和联系。工件零点是工件坐标系的原点,它是在机床坐标系的基础上为方便数控编程而根据工件的特点设定的。

虚拟TCP设置及其在机器人数字化编程与加工中的应用

数字化制造中,机器人加工装备在数字化空间中实现轨迹生成、优化和加工仿真,需要利用TCP坐标系对轨迹进行转换并实现与实际加工一致的轨迹运动仿真,提高加工精度。当机器人采用工件在手的作业方式时,其TCP坐标系和轨迹点同时处于机器人末端,无法驱动机器人运动。通过设置虚拟TCP坐标系并利用虚拟TCP坐标系与轨迹点重合的约束条件,统一工件在手和工具在手的轨迹转换方法。在运行轨迹点时,机器人的TCP坐标系依次与转换后的轨迹点重合,保证仿真过程与机器人实际加工过程的一致。通过设置多个虚拟TCP坐标系,可以对相同轨迹点进行复用,提高编程效率。为验证虚拟TCP坐标系设置的正确性,分别在机器人铣削和磨削加工的数字化空间中设置虚拟TCP坐标系,通过对实际产品的加工,验证了两个空间中轨迹运行的一致性。通过调整数字化空间中的虚拟TCP位置,其磨削精度可以达到0.15 mm。