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2014年机电工程学院毕业设计(论文)进度计划表学生姓名:陈玉成 学号:1000110101序号起止日期计划完成内容实际完成内容检查日期检查人签名12013.12.1712.23教师填写,下同教师填写,下同22013.12.2412.3032013.12.31-2014.1.642014.1.7-1.1353.4-3.1063.11-3.1773.18-3.2483.25-3.31(本表同时作为指导教师对学生的16次考勤记录)2014年机电工程学院毕业设计进度计划表(续)学生姓名: 学号:序号起止日期计划完成内容实际完成内容检查日期检查人签名94.01-4.07教师填写,下同教师填写,下同104.08-4.14114.15-4.21124.22-4.28134.29-5.05145.06-5.12155.13-5.19165.20-5.26完成毕业设计,提交论文任务下达时间:2013年12月17日(本表同时作为指导教师对学生的16次考勤记录)第 1 页 共 2 页 桂林电子科技大学毕业设计(论文)外文翻译译文 第19页 共18页编号: 毕业设计(论文)外文翻译(译文)学 院: 国防生学院 专 业: 机械设计制造及其自动化 学生姓名: 李卓霖 学 号: 1000110106 指导教师单位: 桂林电子科技大学 姓 名: 曹泰山 职 称: 讲师 2014 年 3 月 09 日高架起重机桥架的建模与有限元分析C. Alkin, C. E. Imrak, H. Kocabas摘 要该论文以35吨级,13米跨度桥式起重机的两个箱式梁为研究对象进行设计研究。在该论文中,提出了常规设计计算f E.M规则和DIN标准进行了验证应力和挠度水平。起重机设计同时使用立方体和平面。有限元网格划分使用四个节点,用正四面体与四边形单元组成实体壳模型,再分别通过有限元分析进行比较,在正常计算下,结合已有的起重机性能,二次壳单元有限元分析是最接近实际结果的。研究结果表明,该高架起重机的设计是可行的。关键词:高架起重机,有限元分析法,建模,箱式梁。注释 两个侧板间的距离 下模版的宽度 导轨的静负载 装载后负载 主梁末端高度 侧板高度 滚轮间距 起重梁跨度 相邻支撑结构间距 平台重量 维护平台重量 均匀分布的桥架单元质量 上下夹板的厚度 侧板厚度 左侧板中心到起重机重心距离 导轨中心到起重机重心距离 导轨中心到中轴距离 上板到起重机重心距离 上板到中轴距离 X轴上的主要阻力 Y轴上的主要阻力 放大系数 动态系数1 引言起重机是让超重货物在建筑里轻松移动的最好方式之一。高架起重机是物料运输系统中运送重物最重要的部分。起重机的主要任务就是载重后从一个位置移动到另一个位置。因此经常被用与汽车工厂和船坞1,2。根据它们的主要用途有许多设计特征上的变化,例如:起重机的运动部件结构,工作载荷,起重机的位置,几何特征和环境条件。这些部分使起重机的设计规程高度标准化,大部分的时间花费在对现有的设计标准的执行和说明3。有很多关于结构和受力组成的研究,在静态和动态负载的起重机上安全进行5-16。Demirsoy已经进行了的关于桥的结构建模和有限元分析,研究其位移和应力测试值17。建模技术来源于公路桥结构,同时提供研究分析的有限元模型18。在该研究中,力和位移用F.E.M90软件分析。桥式起重机模型不同点的加载和有限元分析方法的应用由Celiktas完成19。她为高架起重机提供了有限元分析的结果。DIN标准和F.E.M(欧洲联合会)算法提供了被广泛接受的设计与验证方法和公式。DIN标准第44和185条收集了关于起重机设计的标准。DIN标准广泛规定了设计参数的标准值。F.E.M算法主要收集了起重机设计的规则指引。它包含了关于如何选择不同载荷方式下的起重机元件。在这项研究中,计算部分套用F.E.M算法和DIN标准,用于桥式起重机的箱梁。箱梁的计算使用CESAN有限公司的标准桥接器。桥式起重机的模型产生了同等规模的计算结果。使用有限元分析法执行静态分析。在开始解决方案之前,临界情况已经应用到实践。2 双箱式梁高架起重机双箱式梁高架起重机不仅仅只是提升重物,还要携带重物在其范围内移动。在双重梁高架起重机桥架上建造有可移动吊运车,桥架在导轨上运动,吊运车在桥架上升高或降低货物,桥架在导轨上运送货物。因此,执行了三个垂直正交的运动。如图一,货物用钢索固定在桥架上21,22。双箱梁同时受到水平和垂直方向的吊车重量,工作负载(吊钩)和动力载荷。关于双箱梁的制造,吊运车需要在梁之间或上面运行。图2说明了合适的建造要求和梁的结构标准。图1:高架起重机的总视图图2:箱形主梁的制造要求。3 高架起重机的有限元分析及应用在数字技术之中,有限元分析法被广泛使用得益与有很多实用和易于操作的商业软件。有限元分析法可以分析任何几何学,解决力学和位移问题23。有限元分析法几乎解决了研究中的全部或部分的有限元节点问题。该近似解明确表达了每个基础元素和之后整体装配获得的刚性矩阵,位移量和力矢量问题。在该论文中的有限元模型是用Cosmos Works和MSC商业版完成的。用Patran(有限元分析软件)和四面体单元与四边形壳单元为该高架起重机桥架建模。四面体单元是最简单的三维空间单元,应用于固体应力问题分析如支架的应力分析。该单元有四个节点,每个节点都有三个移动副和能在x,y,z轴上旋转的自由度。关于壳单元的定义,是指允许在平面和曲面上都能拥有长度的单元。它的宽度只能用于3D仿真。四面体壳单元因为装配弯曲元件而获得了一定的自由度。这充分表明壳单元的偏差必须在预先定义的壳厚度内,否则整个系统会在一个过大的偏差内运行。典型的四面体单元和四边形壳单元与它们的坐标系在图3中说明24。选择的四面体单元每个节点有六个自由度:x,y,z方向上的平移和绕x,y,z轴自由旋转。用正四面体壳单元为高架起重机梁建模,r 和s表示固有坐标系,是单元体的厚度。该体系没有任何水平力。轴向位移和总体的旋转整体来看都近似为零。此外节点的横向唯一整体来看也为零。对系统起作用的外力大部分来自于起重机的主梁质量(分布载荷)和作用在吊车滑轮沿起重机的力(有效载荷)。吊车滑轮上的力是因为吊车的质量,来自提升负载物和在起重机上移动。四节点四面体单元四节点二次壳单元图3:为高架起重机梁建模的单元体4 高架桥起重机立体有限元模型有限元分析法是一种可以用于为工程学内各种问题提供解决办法的计算方案。稳定的,瞬时的,线性的,非线性的应力分析问题,热传递,流量问题也可以用有限元方法解决。有限元分析法的基本步骤如下:预处理,解决方案,后处理。真实的起重机数据从CESAN有限公司收集来,一个土耳其公司引进了该高架起重机的大量生产。首先,起重机桥架是模拟成面。桥架几何体是适合于此方法的,长和薄的部分也同样被模拟成面。随后,一个网格建立成功。在研究中,使用二次单元模式。立体建模是为了计算起重机桥架,该立体模型展示在图4中20。 起重机桥架立体模型 起重机桥架的框架视图图4:起重机桥架模型5 高架起重机的数值算例研究对象为13T级高架起重机其总长13米总重22.5吨。该起重机结构见图1。该高架起重机组成部分包括两个大梁和两个连接它们的底座,一个可在轴向移动的起重机空中吊运车和滑轮驱动装置安装在其中一个大梁上。起重机支撑在两条轨道上,轨道梁安装在建筑中。为了计算结构的受力,使用有限元分析法1.001。桥架分析的设计理念来自F.E.M和DIN标准被列在表1中。表1:桥架属性值装卸量: =35 ton吊车重量: =3 ton桥长度: =13 m吊车两轮间距: =2m吊车速率: =20 m/min.起重机速率: =15 m/min.起吊速率: =2.7 m/min总使用寿命: U4工作级别: Q3设备组: A5装载型号: H (main load)动态系数:=1.15放大系数:= 1.11用有限元分析法先计算最大和最小应力然后计算剪切应力。使用有限元分析法考虑主梁,我们得到了压力值。我们由于固有重量而得到了静态负载,负载来自于工作载荷乘以动态系数,是水平方向上最不利的两个因素,不包括缓冲力。最大的应力来自于桥身固有重量的压力和吊车的固有重量,提升载荷的力,惯力和吊车收缩力。最小应力包括桥身固有重量和吊车固有重量的力。最大和最小应力的标准来自F.E.M规则20如下和动态系数的意义是来自于工作负载的载荷。放大系数的意义依赖应用级别组,其中维护台的重量为零。25。假设主负载(372780 N)作用于导轨的中点,而且每个主梁平均分担总负载。这个负载通过系统中两个吊车轮的接触点求得,因此每个点的作用力是93195 N。系统总负载的求解,最大应力值等于(1)143.90 N/mm2 精确到两位小数点,最小应力值等于(2)47.33 N/mm2 精确到两位小数点。根据图5,切变的许用应力包括剪应力和车轮力,定义如下:20最大剪应力值等于24.82 N/mm2 精确到两位小数点(5)。带入等式(1)-(3)可得到等效应力。等效应力值为150.18 N/mm2 精确到两位小数点。图5:箱形梁中的惯力和阻力6 四面体单元的梁模型结果为高架桥起重机梁用四面体单元建模,用Cosmoswork 软件进行有限元分析,用SolidWork 2003为梁生成立体模型。弹性模量(E)为2.1x105 N/mm2 ,泊松比()为0.3进行有限元分析。侧板的最大应力值为12.07 N/mm2 精确到两位小数点,底板的最大应力值为15.08 N/mm2 精确到两位小数点,如图620。高架桥起重机模型的位移量来自于CosmosWorks,在图7中说明。梁的最大位移值大概为2.2 mm。图6:高架起重机梁的四面体单元受力情况图7:高架起重机梁的四面体单元位移量7 四节点二次壳单元的梁模型结果为高架桥起重机梁用四节点二次壳单元建模,用MSC Patran 软件进行有限元分析,早期系数(E)为2.1x10 N/mm2 ,泊松比()为0.3进行有限元分析。侧板的最大应力值为35.40 N/mm2 精确到两位小数点,底板的最大应力值为49.30 N/mm2 精确到两位小数点如图820。高架桥起重机梁模型的位移量获得自MSC Patran如图9。梁的最大位移量约为3.89mm。根据式(1)最大应力值计算得143.90 N/mm2 精确到两位小数点。起重机的安全系数设计为2到3。考虑到四面体单元的安全系数,侧板的最大应力在24.14到36.21 N/mm2之间精确到两位小数点。底板的最大应力值在30.16到45.24 N/mm2 之间精确到两位小数点。考虑到四节点二次壳单元的安全系数,其侧板的最大应力在70.8到106.2 N/mm2 之间精确到两位小数点。底板的最大应力值在98.60到147.90 N/mm2 之间精确到两位小数点。根据F.E.M规则梁的允许位移为13mm。通过四面体单元有限元模型获得的值在4.40到6.60之间,安全系数已考虑。通过四节点二次壳单元有限元模型获得的值在7.78到11.67mm之间,安全系数已考虑。图8:高架起重机梁二次壳单元的受力值图9:高架起重机四节点二次壳单元的位移量8 结论在该研究中,不像其他论文照搬原有理论,高架箱型梁的壳单元有限元模型已被验证。为了展示出壳单元的用处,给出了一个高架起重机桥架的实例。根据F.E.M算法和有限元分析法计算得,四面体单元的最大应力值是143.90 N/mm2 和45.24 N/mm2,四节点二次壳单元的最大应力值为147.9 N/mm2。等效应力为150.18 N/mm2 精确到两位小数点。通过MSC Patran考虑到安全系数,应力值应该在97-145.5N/mm2之间变化。高架起重机箱式梁的长厚比高于20.因此,为了展示高架起重机桥架分析的精确度,用四节点二次壳单元代替四面体单元进行有限元分析。数控机床的改造1 数控系统发展简史及趋势1946年诞生了世界上第一台电子计算机,这表明人类创造了可增强和部分代替脑力劳动的工具。它与人类在农业、工业社会中创造的那些只是增强体力劳动的工具相比,起了质的飞跃,为人类进入信息社会奠定了基础。6年后,即在1952年,计算机技术应用到了机床上,在美国诞生了第一台数控机床。从此,传统机床产生了质的变化。近半个世纪以来,数控系统经历了两个阶段和六代的发展。1.1 数控(NC)阶段(19521970年)早期计算机的运算速度低,对当时的科学计算和数据处理影响还不大,但不能适应机床实时控制的要求。人们不得不采用数字逻辑电路搭成一台机床专用计算机作为数控系统,被称为硬件连接数控(HARD-WIRED NC),简称为数控(NC)。随着元器件的发展,这个阶段历经了三代,即1952年的第一代-电子管;1959年的第二代-晶体管;1965年的第三代-小规模集成电路。1.2 计算机数控(CNC)阶段(1970年现在)到1970年,通用小型计算机业已出现并成批生产。于是将它移植过来作为数控系统的核心部件,从此进入了计算机数控(CNC)阶段(把计算机前面应有的通用两个字省略了)。到1971年,美国INTEL公司在世界上第一次将计算机的两个最核心的部件-运算器和控制器,采用大规模集成电路技术集成在一块芯片上,称之为微处理器(MICROPROCESSOR),又可称为中央处理单元(简称CPU)。到1974年微处理器被应用于数控系统。这是因为小型计算机功能太强,控制一台机床能力有富裕(故当时曾用于控制多台机床,称之为群控),不如采用微处理器经济合理。而且当时的小型机可靠性也不理想。早期的微处理器速度和功能虽还不够高,但可以通过多处理器结构来解决。由于微处理器是通用计算机的核心部件,故仍称为计算机数控。到了1990年,PC机(个人计算机,国内习惯称微机)的性能已发展到很高的阶段,可以满足作为数控系统核心部件的要求。数控系统从此进入了基于PC的阶段。总之,计算机数控阶段也经历了三代。即1970年的第四代-小型计算机;1974年的第五代-微处理器和1990年的第六代-基于PC(国外称为PC-BASED)。还要指出的是,虽然国外早已改称为计算机数控(即CNC)了,而我国仍习惯称数控(NC)。所以我们日常讲的数控,实质上已是指计算机数控了。1.3 数控未来发展的趋势1.3.1继续向开放式、基于PC的第六代方向发展基于PC所具有的开放性、低成本、高可靠性、软硬件资源丰富等特点,更多的数控系统生产厂家会走上这条道路。至少采用PC机作为它的前端机,来处理人机界面、编程、联网通信等问题,由原有的系统承担数控的任务。PC机所具有的友好的人机界面,将普及到所有的数控系统。远程通讯,远程诊断和维修将更加普遍。1.3.2向高速化和高精度化发展这是适应机床向高速和高精度方向发展的需要。1.3.3向智能化方向发展随着人工智能在计算机领域的不断渗透和发展,数控系统的智能化程度将不断提高。(1)应用自适应控制技术数控系统能检测过程中一些重要信息,并自动调整系统的有关参数,达到改进系统运行状态的目的。(2)引入专家系统指导加工将熟练工人和专家的经验,加工的一般规律和特殊规律存入系统中,以工艺参数数据库为支撑,建立具有人工智能的专家系统。(3)引入故障诊断专家系统(4)智能化数字伺服驱动装置可以通过自动识别负载,而自动调整参数,使驱动系统获得最佳的运行。2 机床数控化改造的必要性2.1 微观看改造的必要性从微观上看,数控机床比传统机床有以下突出的优越性,而且这些优越性均来自数控系统所包含的计算机的威力。2.1.1 可以加工出传统机床加工不出来的曲线、曲面等复杂的零件。由于计算机有高超的运算能力,可以瞬时准确地计算出每个坐标轴瞬时应该运动的运动量,因此可以复合成复杂的曲线或曲面。2.1.2可以实现加工的自动化,而且是柔性自动化,从而效率可比传统机床提高37倍。由于计算机有记忆和存储能力,可以将输入的程序记住和存储下来,然后按程序规定的顺序自动去执行,从而实现自动化。数控机床只要更换一个程序,就可实现另一工件加工的自动化,从而使单件和小批生产得以自动化,故被称为实现了柔性自动化。2.1.3加工零件的精度高,尺寸分散度小,使装配容易,不再需要修配。2.1.4可实现多工序的集中,减少零件 在机床间的频繁搬运。2.1.5拥有自动报警、自动监控、自动补偿等多种自律功能,因而可实现长时间无人看管加工。2.1.6由以上五条派生的好处。 如:降低了工人的劳动强度,节省了劳动力(一个人可以看管多台机床),减少了工装,缩短了新产品试制周期和生产周期,可对市场需求作出快速反应等等。以上这些优越性是前人想象不到的,是一个极为重大的突破。此外,机床数控化还是推行FMC(柔性制造单元)、FMS(柔性制造系统)以及CIMS(计算机集成制造系统)等企业信息化改造的基础。数控技术已经成为制造业自动化的核心技术和基础技术。2.2 宏观看改造的必要性从宏观上看,工业发达国家的军、民机械工业,在70年代末、80年代初已开始大规模应用数控机床。其本质是,采用信息技术对传统产业(包括军、民机械工业)进行技术改造。除在制造过程中采用数控机床、FMC、FMS外,还包括在产品开发中推行CAD、CAE、CAM、虚拟制造以及在生产管理中推行MIS(管理信息系统)、CIMS等等。以及在其生产的产品中增加信息技术,包括人工智能等的含量。由于采用信息技术对国外军、民机械工业进行深入改造(称之为信息化),最终使得他们的产品在国际军品和民品的市场上竞争力大为增强。而我们在信息技术改造传统产业方面比发达国家约落后20年。如我国机床拥有量中,数控机床的比重(数控化率)到1995年只有1.9,而日本在1994年已达20.8,因此每年都有大量机电产品进口。这也就从宏观上说明了机床数控化改造的必要性。3 机床与生产线数控化改造的市场3.1 机床数控化改造的市场我国目前机床总量380余万台,而其中数控机床总数只有11.34万台,即我国机床数控化率不到3。近10年来,我国数控机床年产量约为0.60.8万台,年产值约为18亿元。机床的年产量数控化率为6。我国机床役龄10年以上的占60以上;10年以下的机床中,自动/半自动机床不到20,FMC/FMS等自动化生产线更屈指可数(美国和日本自动和半自动机床占60以上)。可见我们的大多数制造行业和企业的生产、加工装备绝大数是传统的机床,而且半数以上是役龄在10年以上的旧机床。用这种装备加工出来的产品普遍存在质量差、品种少、档次低、成本高、供货期长,从而在国际、国内市场上缺乏竞争力,直接影响一个企业的产品、市场、效益,影响企业的生存和发展。所以必须大力提高机床的数控化率。3.2 进口设备和生产线的数控化改造市场我国自改革开放以来,很多企业从国外引进技术、设备和生产线进行技术改造。据不完全统计,从19791988年10年间,全国引进技术改造项目就有18446项,大约165.8亿美元。这些项目中,大部分项目为我国的经济建设发挥了应有的作用。但是有的引进项目由于种种原因,设备或生产线不能正常运转,甚至瘫痪,使企业的效益受到影响,严重的使企业陷入困境。一些设备、生产线从国外引进以后,有的消化吸收不好,备件不全,维护不当,结果运转不良;有的引进时只注意引进设备、仪器、生产线,忽视软件、工艺、管理等,造成项目不完整,设备潜力不能发挥;有的甚至不能启动运行,没有发挥应有的作用;有的生产线的产品销路很好,但是因为设备故障不能达产达标;有的因为能耗高、产品合格率低而造成亏损;有的已引进较长时间,需要进行技术更新。种种原因使有的设备不仅没有创造财富,反而消耗着财富。这些不能使用的设备、生产线是个包袱,也是一批很大的存量资产,修好了就是财富。只要找出主要的技术难点,解决关键技术问题,就可以最小的投资盘活最大的存量资产,争取到最大的经济效益和社会效益。这也是一个极大的改造市场。4 数控化改造的内容及优缺4.1 国外改造业的兴起在美国、日本和德国等发达国家,它们的机床改造作为新的经济增长行业,生意盎然,正处在黄金时代。由于机床以及技术的不断进步,机床改造是个永恒的课题。我国的机床改造业,也从老的行业进入到以数控技术为主的新的行业。在美国、日本、德国,用数控技术改造机床和生产线具有广阔的市场,已形成了机床和生产线数控改造的新的行业。在美国,机床改造业称为机床再生(Remanufacturing)业。从事再生业的著名公司有:Bertsche工程公司、ayton机床公司、Devlieg-Bullavd(得宝)服务集团、US设备公司等。美国得宝公司已在中国开办公司。在日本,机床改造业称为机床改装(Retrofitting)业。从事改装业的著名公司有:大隈工程集团、岗三机械公司、千代田工机公司、野崎工程公司、滨田工程公司、山本工程公司等。4.2 数控化改造的内容机床与生产线的数控化改造主要内容有以下几点:其一是恢复原功能,对机床、生产线存在的故障部分进行诊断并恢复;其二是NC化,在普通机床上加数显装置,或加数控系统,改造成NC机床、CNC机床;其三是翻新,为提高精度、效率和自动化程度,对机械、电气部分进行翻新,对机械部分重新装配加工,恢复原精度;对其不满足生产要求的CNC系统以最新CNC进行更新;其四是技术更新或技术创新,为提高性能或档次,或为了使用新工艺、新技术,在原有基础上进行较大规模的技术更新或技术创新,较大幅度地提高水平和档次的更新改造。4.3 数控化改造的优缺4.3.1 减少投资额、交货期短同购置新机床相比,一般可以节省6080的费用,改造费用低。特别是大型、特殊机床尤其明显。一般大型机床改造,只花新机床购置费用的1/3,交货期短。但有些特殊情况,如高速主轴、托盘自动交换装置的制作与安装过于费工、费钱,往往改造成本提高23倍,与购置新机床相比,只能节省投资50左右。4.3.2 机械性能稳定可靠,结构受限所利用的床身、立柱等基础件都是重而坚固的铸造构件,而不是那种焊接构件,改造后的机床性能高、质量好,可以作为新设备继续使用多年。但是受到原来机械结构的限制,不宜做突破性的改造。4.3.3 熟悉了解设备、便于操作维修购买新设备时,不了解新设备是否能满足其加工要求。改造则不然,可以精确地计算出机床的加工能力;另外,由于多年使用,操作者对机床的特性早已了解,在操作使用和维修方面培训时间短,见效快。改造的机床一安装好,就可以实现全负荷运转。4.3.4 可充分利用现有的条件可以充分利用现有地基,不必像购入新设备时那样需重新构筑地基。4.3.5 可以采用最新的控制技术可根据技术革新的发展速度,及时地提高生产设备的自动化水平和效率,提高设备质量和档次,将旧机床改成当今水平的机床。5 数控系统的选择数控系统主要有三种类型,改造时,应根据具体情况进行选择。5.1 步进电机拖动的开环系统该系统的伺服驱动装置主要是步进电机、功率步进电机、电液脉冲马达等。由数控系统送出的进给指令脉冲,经驱动电路控制和功率放大后,使步进电机转动,通过齿轮副与滚珠丝杠副驱动执行部件。只要控制指令脉冲的数量、频率以及通电顺序,便可控制执行部件运动的位移量、速度和运动方向。这种系统不需要将所测得的实际位置和速度反馈到输入端,故称之为开环系统,该系统的位移精度主要决定于步进电机的角位移精度,齿轮丝杠等传动元件的节距精度,所以系统的位移精度较低。该系统结构简单,调试维修方便,工作可靠,成本低,易改装成功。5.2 异步电动机或直流电机拖动,光栅测量反馈的闭环数控系统该系统与开环系统的区别是:由光栅、感应同步器等位置检测装置测得的实际位置反馈信号,随时与给定值进行比较,将两者的差值放大和变换,驱动执行机构,以给定的速度向着消除偏差的方向运动,直到给定位置与反馈的实际位置的差值等于零为止。闭环进给系统在结构上比开环进给系统复杂,成本也高,对环境室温要求严。设计和调试都比开环系统难。但是可以获得比开环进给系统更高的精度,更快的速度,驱动功率更大的特性指标。可根据产品技术要求,决定是否采用这种系统。5.3 交/直流伺服电机拖动,编码器反馈的半闭环数控系统半闭环系统检测元件安装在中间传动件上,间接测量执行部件的位置。它只能补偿系统环路内部部分元件的误差,因此,它的精度比闭环系统的精度低,但是它的结构与调试都较闭环系统简单。在将角位移检测元件与速度检测元件和伺服电机作成一个整体时则无需考虑位置检测装置的安装问题。当前生产数控系统的公司厂家比较多,国外著名公司的如德国SIEMENS公司、日本FANUC公司;国内公司如中国珠峰公司、北京航天机床数控系统集团公司、华中数控公司和沈阳高档数控国家工程研究中心。选择数控系统时主要是根据数控改造后机床要达到的各种精度、驱动电机的功率和用户的要求。6 数控改造中主要机械部件改装探讨一台新的数控机床,在设计上要达到:有高的静动态刚度;运动副之间的摩擦系数小,传动无间隙;功率大;便于操作和维修。机床数控改造时应尽量达到上述要求。不能认为将数控装置与普通机床连接在一起就达到了数控机床的要求,还应对主要部件进行相应的改造使其达到一定的设计要求,才能获得预期的改造目的。6.1 滑动导轨副对数控车床来说,导轨除应具有普通车床导向精度和工艺性外,还要有良好的耐摩擦、磨损特性,并减少因摩擦阻力而致死区。同时要有足够的刚度,以减少导轨变形对加工精度的影响,要有合理的导轨防护和润滑。6.2 齿轮副一般机床的齿轮主要集中在主轴箱和变速箱中。为了保证传动精度,数控机床上使用的齿轮精度等级都比普通机床高。在结构上要能达到无间隙传动,因而改造时,机床主要齿轮必须满足数控机床的要求,以保证机床加工精度。6.3 滑动丝杠与滚珠丝杠 丝杠传动直接关系到传动链精度。丝杠的选用主要取决于加工件的精度要求和拖动扭矩要求。被加工件精度要求不高时可采用滑动丝杠,但应检查原丝杠磨损情况,如螺距误差及螺距累计误差以及相配螺母间隙。一般情况滑动丝杠应不低于6级,螺母间隙过大则更换螺母。采用滑动丝杠相对滚珠丝杠价格较低,但难以满足精度较高的零件加工。滚珠丝杠摩擦损失小,效率高,其传动效率可在90%以上;精度高,寿命长;启动力矩和运动时力矩相接近,可以降低电机启动力矩。因此可满足较高精度零件加工要求。6.4 安全防护效率必须以安全为前提。在机床改造中要根据实际情况采取相应的措施,切不可忽视。滚珠丝杠副是精密元件,工作时要严防灰尘特别是切屑及硬砂粒进入滚道。在纵向丝杠上也可加整体铁板防护罩。大拖板与滑动导轨接触的两端面要密封好,绝对防止硬质颗粒状的异物进入滑动面损伤导轨。7 机床数控改造主要步骤7.1 改造方案的确定改造的可行性分析通过以后,就可以针对某台或某几台机床的现况确定改造方案,一般包括:7.1.1机械修理与电气改造相结合一般来说,需进行电气改造的机床,都需进行机械修理。要确定修理的要求、范围、内容;也要确定因电气改造而需进行机械结构改造的要求、内容;还要确定电气改造与机械修理、改造之间的交错时间要求。机械性能的完好是电气改造成功的基础。7.1.2先易后难、先局部后全局原系统的拆除必须对照原图纸,仔细进行,及时在图纸上作出标记,防止遗漏或过拆(局部改造情况下)。在拆的过程中也会发现一些新系统设计中的欠缺之处,应及时补充与修正,拆下的系统及零件应分门别类,妥善保管,以备万一改造不成功或局部失败时恢复使用。还有一定使用价值的,可作其他机床备件用。切忌大手大脚,乱扔乱放。7.2 合理安排新系统位置及布线根据新系统设计图纸,合理进行新系统配置,包括箱体固定、面板安放、线路走向和固定、调整元器件位置、密封及必要装饰等。连线工作必须分工明确,有人复查检验,以确保连线工艺规范、线径合适、正确无误、可靠美观。7.3 调试调试必须按事先确定的步骤和要求进行。调试人员应头脑冷静,随时记录,以便发现和解决问题。调试中首先试安全保护系统灵敏度,防止人身、设备事故发生。调试现场必须清理干净,无多余物品;各运动坐标拖板处于全行程中心位置;能空载试验的,先空载后加载;能模拟试验的,先模拟后实动;能手动的,先手动后自动。7.4 验收及后期工作验收工作应聘请有关的人员共同参加,并按已制定的验收标准进行。改造的后期工作也很重要,它有利于项目技术水平的提高和使设备尽早投产。验收及后期工作包括:7.4.1机床机械性能验收经过机械修理和改造以及全面保养,机床的各项机械性能应达到要求,几何精度应在规定的范围内。7.4.2电气控制功能和控制精度验收电气控制的各项功能必须达到动作正常,灵敏可靠。控制精度应用系统本身的功能(如步进尺寸等)与标准计量器具(如激光干涉仪、坐标测量仪等)对照检查,达到精度范围之内。同时还应与改造前机床的各项功能和精度作出对比,获得量化的指标差。7.4.3试件切削验收可以参照国内外有关数控机床切削试件标准,在有资格的操作工、编程人员配合下进行试切削。试件切削可验收机床刚度、切削力、噪声、运动轨迹、关联动作等,一般不宜采用产品零件作试件使用。7.4.4图纸、资料验收机床改造完后,应及时将图纸(包括原理图、配置图、接线图、梯形图等)、资料(包括各类说明书)、改造档案(包括改造前、后的各种记录)汇总、整理、移交入档。保持资料的完整、有效、连续,这对该设备的今后稳定运行是十分重要的。7.4.5总结、提高每次改造结束后应及时总结,既有利于提高技术人员的业务水平,也有利于整个企业的技术进步。编号: 毕业设计(论文)外文翻译(原文)学 院: 国防生学院 专 业: 机械设计制造及其自动化 学生姓名: 李卓霖 学 号: 1000110106 指导教师单位: 桂林电子科技大学 姓 名: 曹泰山 职 称: 讲师 2014 年 3 月 09 日24Solid Modeling and Finite Element Analysis of an Overhead Crane Bridge C. Alkin, C. E. Imrak, H. KocabasAbstractThe design of an overhead crane bridge with a double box girder has been investigated and a case study of a crane with 35 ton capacity and 13 m span length has been conducted. In the initial phase of the case study, conventional design calculations proposed by F. E.M Rules and DIN standards were performed to verify the stress and deflection levels. The crane design was modeled using both solids and surfaces. Finite element meshes with 4-node tetrahedral and 4-node quadrilateral shell elements were generated from the solid and shell models, respectively. After a comparison of the finite element analyses, the conventional calculations and performance of the existing crane, the analysis with quadratic shell elements was found to give the most realistic results. As a result of this study, a design optimization method for an overhead crane is proposed.Keywords: overhead crane, finite element method, solid modeling, box girder.Notationb distance between two side platesbk width of lower plateFAA static load due to the trolleyFY load due to the working loadh0 height of the girder endh2 height of the side platesLA distance between trolley wheelsLK span of crane girderLP distance between two adjacent supportsq weight of one meter platformqK weight of one meter maintenance platformqP uniformly distributed mass units of bridget1 thickness of the upper and lower platest2 thickness of the side platesx2 distance between center of gravity and the midpoint of the left side platex4 distance between center of gravity and the midpoint of the raily1 distance between neutral axis and the midpoint of the raily3 distance between center of gravity and the midpoint of the top platey5 distance between neutral axis and the midpoint of the top plateWX1 moment of resistance on x-axisWY1 moment of resistance on y-axis amplifying coefficient dynamic coefficient1 IntroductionCranes are the best way of providing a heavy lifting facility covering virtually the whole area of a building. An overhead crane is the most important materials handling system for heavy goods. The primary task of the overhead crane is to handle and transfer heavy payloads from one position to another. Thus they are used in areas such as automobile plants and shipyards 1, 2. Their design features vary widely according to their major operational specifications, such as: type of motion of the crane structure, weight and type of the load, location of the crane, geometric features and environmental conditions. Since the crane design procedures are highly standardized with these components, most effort and time are spent on interpreting and implementing the available design standards 3. There are many published studies on structural and component stresses, safety under static loading and dynamic behavior of cranes 516. Solid modeling of bridge structures and finite element analysis to find the displacements and stress values has been investigated by Demirsoy 17.Solid modeling techniques applied for road bridge structures, and an analysis of these structures using the finite element method are provided in 18. In this study, stress and displacements were found using FEM90 software. Solid modeling of a crane bridge, the loading at different points on the bridge and then application of the finite element method have been studied by Celiktas 19. She presented the results of finite element methods for an overhead crane. DIN-Taschenbuch and F. E. M. (Federation Europenne de la Manutention) Rules offer design methods and empirical approaches and equations that are based on previous design experience and widely accepted design procedures. DIN-Taschenbuch 44 and 185 are a collection of standards related to crane design. DIN norms generally state standard values of design parameters. F. E. M Rules are mainly an accepted collection of rules to guide crane designers. It includes criteria for deciding on the external loads to select crane components 3, 20.In this study, the calculations apply the F. E. M. rules and DIN standards, which are used for box girder crane bridges. The calculation of the box girder uses the CESAN Inc. standard bridge tables. Then a solid model of the crane bridge is generated with the same dimensions as in the calculation results. Then static analysis is performed, using the Finite Element Method. Before starting the solution, the boundary conditions are applied as in practice.2 Overhead cranes with a double box girderOverhead travelling cranes with a double box girder not only hoist loads but also carry them horizontally. A double beam overhead crane is built of a trolley travelling on bridges, and bridges travelling on rails. The trolley hoists or lowers the loads and carries them on the bridge structure. The bridges carry the loads on a rail. As a result, three perpendicular movements are performed. The system is depicted in Fig. 1, where the payload of the mass is attached to the bridge with wire ropes 21, 22. The double box girders are subjected to vertical and horizontal loads by the weight of the crane, the working (hook) load and the dynamic loads. With a double box girder construction, the trolley runs above or between the girders. The acceptable construction requirements and values for a box girder bridge structure are shown in Fig.2.Fig. 1: Overall view of an overhead craneFig. 2: Construction requirements for a box girder bridge3 Application of FEM to an overhead craneAmong numerical techniques, the finite element method is widely used due to the availability of many user-friendly commercial softwares. The finite element method can analyse any geometry, and solves both stresses and displacements 23. FEM approximates the solution of the entire domain under study as an assemblage of discrete finite elements interconnected at nodal points on the element boundaries. The approximate solution is formulated over each element matrix and thereafter assembled to obtain the stiffness matrix, and displacement and force vectors of the entire domain. In this study finite element modeling is carried out by means of the Cosmos Works and MSC commercial package. Patran and 4-node tetrahedral elements and 4-node quadrilateral shell elements have been used for modeling the overhead crane bridge.The four-node tetrahedral element is the simplest three-dimensional element used in the analysis of solid mechanics problems such as bracket stress analysis. This element has four nodes, with each node having three translational and three rotational degrees of freedom on the x, y, and z-axes. A shell element may be defined, which allows in the plane or curved surface of the element and posses both length. Itwidth and may only be used in 3-D simulations. The four-node shell element is obtained by assembling the bending element to the appropriate degrees of freedom. This is sufficient as long as the shell element deflection is within the predefined ratio of shell thickness, otherwise the system works as a large deflection.A typical four-node tetrahedral element and four-node quadratic shell element, and their coordinate systems are illustrated in Fig. 3 24. The four-node tetrahedral element chosen has six degrees of freedom at each node: translation in the nodal x, y, and z directions and rotations about the nodal x, y, and z directions. For the four-node quadratic shell element used to model the overhead crane girder, r and s denote the natural coordinates and is the thickness of the element.This system does not have any horizontal force. The axial displacements and rotations of the first and last faces are equal to zero. In addition, the transverse displacement is zero at the first and last face nodes.The external forces acting on the system are the mass of the main girder of the crane (distributed load) and the forces acting on the wheels of the trolley along the crane (active load). The forces acting on the trolley wheels are caused by the mass of the trolley, an the lifting load which will be moved on the crane.4-node tetrahedral element4-node quadratic shell elementFig. 3: Elements used to model an overhead crane girder4 Solid and finite element modeling of an overhead crane bridgeThe finite element method is a numerical procedure that can be applied to obtain solutions to a variety of problems in engineering. Steady, transient, linear or nonlinear problems in stress analysis, heat transfer, fluid flow and electrome chanism problems may be analysed with finite element methods. The basic steps in the finite element method are defined as follows: preprocessing phase, solution phase, and post processing phase. Real crane data was gathered from CESAN Inc., a Turkish company involved in mass production of overhead cranes. First, the crane bridge is modeled as a surface. Bridge geometry is suitable for this, and long and thin parts should also be modeled as a surface. Later, a mesh is created. In this study, a quadratic element type is used. Solid modeling is generated for the calculated crane bridge and the solid model is shown in Fig. 4 20.Solid model of a crane bridge Wireframe view of a crane bridgeFig. 4: Models of an overhead crane bridge5 Numerical example of an overhead craneA 35-ton-capacity overhead crane of overall length 13 m and total weight 22.5 tons was selected as a study object. The configuration of the overhead crane is shown in Fig. 1.The overhead crane consists of two girders, two saddles to connect them, and a trolley moving in the longitudinal direction of the overhead crane and wheels. The driving unit is installed in one of the two girders. The overhead crane is supported by two rails and the runway girders installed in building.In order to calculate the stress in the structure, the rules of F. E. M 1.001 are applied. The design values used in the bridge analysis from the F. E.M and DIN standards are given in Table 1.Table 1: Bridge property valuesHandling Capacity: =35 tonTrolley Weight: =3 tonBridge Length: =13 mDistance between wheels of trolley: =2mTrolley Velocity: =20 m/min.Crane Velocity: =15 m/min.Hoisting Velocit: =2.7 m/minTotal duration of use: U4Load spectrum class: Q3Appliance group: A5Loading type: H (main load)Dynamic coefficient:=1.15Amplifying coefficient:= 1.11First the maximum and minimum stresses and then the shear stress are calculated using the F. E. M. rules. Using the finite element method for the considered girder, we obtain the stress valnes. We obtain the static loads due to the dead weight, the loads due to the working load multiplied by the dynamic coefficient, and the two most unfavourable horizontal effects, excluding the buffer forces.The maximum stress consists of the stress on the bridge dead weights, the stress on the trolley dead weight, the stress from the hoisting load, stress from the inertia forces and the stress of the trolley contraction. The minimum stress includes the stress on the bridge dead weights and the stress on the trolley dead weight. The maximum and minimum stresses for the given values according to the F. E.M. rules 20 are written in standard form asand,The value of the dynamic coefficient is applied to the loading arising from the working load. The value of the amplifying coefficient depends the group classification of the application, and the weight of one meter maintenance platform is zero in this work. 25.It is assumed that the total load (372780 N) is effected on the midpoint of the rail and each girder shares this total load equally. This load is applied via the contact points of the two trolley wheels in this system. Therefore the value of the acting force on each point is 93195 N. Applying the total load in the system, the value of the maximum stress according to Eq. (1) is 143.90 N/mm2 to two decimal places, and the value of the minimum stress according to Eq. (2) is 47.33 N/mm2 to two decimal places.According to Fig. 5, the permissible stress in shear consists of the shear stresses of the wheel forces, and is defined as 20The value of the maximum shear stress is 24.82 N/mm2 to two decimal places from Eq. (5). Substituting Eq. (1)(3) the equivalent stress is given by. The value of the equivalent stress is 150.18 N/mm2 to two decimal places.Fig. 5: Inertia and moment of resistance in a box girder6 Results from a girder model with a four-node tetrahedral elementTo model the overhead crane girder with a four-node tethrahedral element, Cosmosworks software was used for finite element analysis using the girder solid model generated by means of SolidWorks 2003. Youngs Modulus (E) is 2.1105 N/mm2 and the Poisson Ratio () is 0.3 for finite element analysis. The value of the maximum stress of the side plate is 12.07 N/mm2 to two decimal places and the value of the maximum stress of the bottom plate is 15.08N/mm2 to two decimal places from Fig. 6 20.The displacement of the modelled overhead crane girder was obtained from CosmosWorks, and is illustrated in Fig. 7. The value of maximum displacement of the girder is about 2.2 mm.Fig. 6: Stress values of an overhead crane girder with a four-node tetrahedral elementFig. 7: Displacements of an overhead crane girder with a four-node tetrahedral element7 Results from a girder model with a four-node quadratic shell elementTo model the overhead crane girder with a four-node quadratic shell element, MSC Patran software was used for the finite element analysis. Youngs Modulus (E) is 2.110 N/mm2 and the Poisson Ratio (_St) is 0.3 for finite element analysis. The value of the maximum stress of the side plate is 35.40 N/mm2 to two decimal places, and the value of the maximum stress of the bottom plate is 49.30 N/mm2 to two decimal places, from Fig. 8 20.The displacement of the modelled overhead crane girder was obtained from MSC Patran, and is illustrated in Fig. 9.The value of maximum displacement of the girder is about 3.89 mm. The value of the maximum stress according to Eq. (1) is calculated as 143.90 N/mm2 to two decimal places. The safety factor should be considered between 2 and 3 for overhead crane girder design. The maximum stress value of the side plate is between 24.14 and 36.21 N/mm2 to two decimal places, and the maximum stress value of the bottom plate is between 30.16 and 45.24 N/mm2 to two decimal places for a four-node tetrahedral element, taking into account the safety factor.The maximum stress value of the side plate is between 70.8 and 106.2 N/mm2 to two decimal places and the maximum stress value of the bottom plate is between 98.6 and 147.9 N/mm2 to two decimal places for a four-node quadratic shell element, taking into account the safety factor. The permissible displacement of the girder is 13 mm according to F. E.M. rules. The maximum displacement obtained from the finite element model with a four-node tetrahedral element is between 4.40 and 6.60 mm, taking into account the safety factor. The maximum displacement obtained from the finite element model with a four-node quadratic shell element is between 7.78 and 11.67 mm, taking into account the safety factor.Fig. 8: Stress values of an overhead crane girder with a quadratic shell elementFig. 9: Displacements of an overhead crane girder with a four-node quadratic shell element8 ConclusionIn this study, unlike the other studies carried out previously, shell elements in finite element modeling of an overhead box girder have been examined. In order to show the use of shell elements, one illustrative overhead crane bridge example is given. The maximum stress value is 143.90 N/mm2 and 45.24 N/mm2 for a four-node tetrahedral element and 147.9 N/mm2 for a four-node quadratic shell element using both calculations according to the F. E. M. Rules and finite element analysis. The value of the equivalent stress is 150.18 N/mm2 to two decimal places. Taking into account the safety factor, the stress value varies between 97145.5N/mm2, which is obtained from MSC Patran.The ratio of length to thickness of the element used in modelling the overhead crane box girder is higher than 20. Therefore, in order to show the accuracy of the analysis of the overhead crane bridges, a four-node quadratic shell element is used instead of the four-node tetrahedral element for finite element analysis.AcknowledgmentIt is pleasure to acknowledge much stimulating correspondence with Dr. Haydar Livatyali and gratefully to acknowledge the support of CESAN Inc., which provided the design data.Machine tool numerical control reforms1 CNC systems and the development trend of history1946 birth of the worlds first electronic computer, which shows that human beings created to enhance and replace some of the mental work tools. It and human agriculture, industrial society in the creation of those who merely increase compared to manual tools, from a qualitative leap for mankinds entry into the information society laid the foundation. Six years later, in 1952, computer technology applied to the machine in the United States was born first CNC machine tools. Since then, the traditional machine produced a qualitative change. Nearly half a century since the CNC system has experienced two phases and six generations of development.1.1 Numerical Control (NC) phase (1952 to 1970)Early computers computational speed low and the prevailing scientific computing and data processing is not affected, but can not meet the requirements of real-time control machine. People have to use digital logic circuit tied into a single machine as a dedicated computer numerical control system, known as the hardware connection NC (HARD-WIRED NC), called the Numerical Control (NC). With the development of components of this phase after three generations, that is, in 1952 the first generation - tube; 1959 of the second generation - transistor; 1965 of the third generation - small-scale integrated circuits.1.2 Computer Numerical Control (CNC) phase (1970 to present)To 1970, GM has been a small computer and mass-produced. So it transplant system as the core component of NC, have entered a Computer Numerical Control (CNC) stage(in front of the computer should be universal word omitted). To 1971, the United States INTEL company in the world will be the first time the two most core computer components - computing and controller, a large-scale integrated circuit technology integration in a chip, called the microprocessor (MICROPROCESSOR) , also known as the central processing unit (CPU).1974 microprocessor to be used in CNC system. This is because the function of the computer is too small to control a machine tool capacity affluent (the time has been used to control more than one machine, called Group Control), as a reasonable economic use of the microprocessor. Minicomputer reliability and then not ideal. Early microprocessor speed and functionality while still not high enough, but can be adopted to solve the multi-processor architecture. As microprocessor core is a general computer components, it is still known as the CNC.By 1990, PC machines (personal computers, domestic habits that computer) performance has been developed to a high stage, as a CNC system to meet the requirements of the core
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