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I图书分类号：密 级：摘要螺旋起重机又称为螺旋升降机，它的原型就是我们所常见的千斤顶。它具有结构紧凑、体积小、重量轻、动力源广泛、无噪音、安装方便、使用灵活、功能多、配套形式多、可靠性高、使用寿命长等许多优点。可以单台或组合使用，能大致控制调整提升的高度，可以用电动机或其他动力直接带动，也可以手动。电动螺旋起重机基本原理是利用电机，通过减速器减速后，带动螺母旋转，转化为丝杆的轴向运动，从而推动物体上升。主要内容如下：对千斤顶的原理和螺旋起重的原理、方法进行了研究；设计螺旋起重机构；选择电动机；设计减速机构；控制电路的设计；简要阐述在流水线作业中，螺旋千斤顶的动作原理等。关键词关键词 千斤顶；电动；螺旋传动IIAbstractThe spiral crane is also known as the spiral screw lift crane .Its prototype is the jack as we common see. Its advantages as follows: small size, light weight, extensive power source, no noise, ease of installation, flexible, multi-function, supporting forms, high reliability and long service life, and so on. It can be used single or in combination, and can generally control the height. Motor can be used directly or other power driven, besides ,it can also be manually.And the basic principle is that the motor drives the rotary nut through the deceleration agencies, screw into the axial campaign, and then lift the objects .The main contents as follows: research the principle of spiral jack and the principles and methods of the spiral lifting, design the agencies of spiral lifting; motor choice; design deceleration agencies; select keys and bearings, design the control circuit; describe the principle of the screw jack on the assembly line operation.Keywords Spiral jack Electrical Spiral driveI目目 录录1 绪论.11.1 千斤顶的发展现状.11.2 千斤顶的分类.22 设计方案的确定.32.1 螺旋传动设计方案.32.1.1 螺旋传动概述.32.1.2 螺旋传动方案的确定.42.2 减速传动机构设计方案.53 传动系统的设计.63.1 螺旋传动部分计算.63.1.1 螺杆直径的计算.63.1.2 螺纹部分强度计算.63.2 电机的选择.83.2.1 电动机功率计算.93.2.2 传动效率.93.2.3 确定电机转速.103.3 减速机构的设计.113.3.1 材料的选择.113.3.2 蜗轮蜗杆传动基本尺寸.123.3.3 强度校核.153.3.4 蜗轮蜗杆传动中的作用力分析.153.3.5 实际传动动力参数.164 辅助装置的设计.184.1 轴承的选择.184.1.1 轴承的选择因素.184.1.2 轴承的型号确定.194.1.3 轴承校验.194.2 键的选择.224.3 联轴器的设计与计算.235 控制电路及过载保护系统的设计.255.1 过载及最大行程保护元件.255.1.1 热继电器.255.1.2 行程开关.26II5.2 电器控制基本电路设计.286 系统的改进与优化.306.1 力学传感器.306.1.1 电阻应变片力传感器.306.2 位置传感器.326.3 连续控制分析.34结论.35致谢.36参考文献.37附录.38附录 1.38附录 2.4911 绪论1.1 千斤顶的发展现状千斤顶起源于 20 世纪初的英、美、德等国家，在逐步发展中工艺逐渐成熟，因其具有抗腐蚀、耐高温，强度高、表面精美、百分之百可回收等无与伦比的良好性能，被广泛应用于建筑、交通、能源、石化、环保、城市景观、医疗、餐饮等各个领域，逐渐被人们所接受，也越来越多地走进寻常百姓的日常生活。我国千斤顶产业发展进步较晚，建国以来到改革开放前，我国千斤顶的需求主要是以工业和国防尖端使用为主。改革开放后，国民经济的快速发展，人民生活水平的显著提高，拉动了千斤顶的需求。进入上世纪九十年代后，我国千斤顶产业进入快速发展期，千斤顶需求的增速远高于全球水平。1990 年以来，全球千斤顶表观消费量以年均 6%的速度增长，而九十年代的十年间，我国千斤顶表观消费量年均增长率达到 17.73%，是世界年均增长率的 2.9 倍。进入二十一世纪，我国千斤顶产业高速增长。2000 年2004 年，我国千斤顶消费量从 188 万吨增长到 447 万吨，增加了 2.3 倍，年平均增长率在 27%以上。其中，2001 年，我国千斤顶表观消费量达到 225 万吨，超过美国成为世界第一千斤顶消费大国。同时，千斤顶进口也大幅度增加。1998 年，我国千斤顶进口 100 万吨，由此成为世界上最大的千斤顶进口国。2004 年与 1998 年比，千斤顶进口增长幅度年均达到 27.14%。预计 2005 年，中国千斤顶表观消费量将达到 500 万吨，进口仍将保持在 300 万吨左右。伴随着千斤顶市场的快速发展，我国千斤顶产量也结束了长期徘徊的局面，实现了高速增长。我国千斤顶产量从 2000 年的 46 万吨增长到 2004 年的 236 万吨，年平均增长率在 82.6%，占国内市场需求的比重也由 2000 年的 24.47%提高到 2004 年的 52.80%。而同期，世界千斤顶产量则仅以 6%左右的速度增长。从九十年代后期起，我国太钢、宝钢以及宝新、张浦等国有和合资企业通过引进和技术改造，先后建成了一系列千斤顶生产线，千斤顶工艺技术装备达到国际先进水平，千斤顶生产初具规模。千斤顶品种结构也发生了积极的变化，千斤顶产品质量迅速提高。特别是国内千斤顶冷轧板增长迅速，2003 年，国内冷轧板产量达到 170 万吨，首次超过进口量,自给率达到 66%；2004 年，国内冷轧板产量达到 200 万吨，自给率达到 70%以上。从 2004 年底到 2005 年底，国内冷轧千斤顶产能将增加约 150 万吨，基本满足国内市场需求。到 2007 年，我国将成为千斤顶的净出口国。从总体上看，我国千斤顶正在经历由规模小、水平低、品种单一、严重不能满足需2求到具有相当规模和水平、品种质量显著提高和初步满足国民经济发展要求的深刻转变，千斤顶需求将逐步实现自给。1.2 千斤顶的分类千斤顶有多种形式。如电动式，液压式，手动式（即一般意义上的千斤顶）等等。电动式千斤顶如图 1-1 所示。它的基本动力源是电机，由电机通过减速器带动螺母旋转，转化为丝杆的轴向运动，从而推动物体上升。它解放了人类的体力劳动，只需操纵按钮即可完成起重。可有效的避免了重物砸伤等事故。该形式的起重器也是本设计所讨论的。图 1-1液压千斤顶，又称为油压千斤顶。它的基本工作原理图如图 1-2 所示。其基本原理是利用封闭管路里液体的压强来工作的。当人以力 F 向下压手柄时，液体内部产生一定的压强，从而推动重物上升。图 1-21-小液压缸，2-排油单向阀，3-吸油单向阀，4-油路，5-截止阀，6-大液压缸手动式千斤顶也即一般普通的千斤顶，它是出现的最早的千斤顶，是所有千斤顶的鼻祖。手摇其手柄，带动螺母旋转，如图 1-3 所示3图 1-32 设计方案的确定2.1 螺旋传动设计方案2.1.1 螺旋传动概述螺旋传动是利用螺杆和螺母的啮合来传递动力和运动的机械传动。主要用于将旋转运动转换成直线运动，将转矩转换成推力。按工作特点，螺旋传动用的螺旋分为传力螺旋、传导螺旋和调整螺旋。（1）传力螺旋：以传递动力为主,它用较小的转矩产生较大的轴向推力,一般为间歇工作，工作速度不高，而且通常要求自锁，例如螺旋压力机和螺旋千斤顶上的螺旋。（2）传导螺旋：以传递运动为主，常要求具有高的运动精度，一般在较长时间内连续工作，工作速度也较高，如机床的进给螺旋（丝杠） 。（3）调整螺旋：用于调整并固定零件或部件之间的相对位置，一般不经常转动，要求自锁，有时也要求很高精度，如机器和精密仪表微调机构的螺旋。按螺纹间摩擦性质，螺旋传动可分为滑动螺旋传动和滚动螺旋传动。滑动螺旋传动又可分为普通滑动螺旋传动和静压螺旋传动。1）滑动螺旋传动通常所说的滑动螺旋传动就是普通滑动螺旋传动。滑动螺旋通常采用梯形螺纹和锯齿形螺纹，其中梯形螺纹应用最广，锯齿形螺纹用于单面受力。矩形螺纹由于工艺性较差强度较低等原因应用很少；对于受力不大和精密机构的调整螺旋，有时也采用三角螺纹。一般螺纹升程和摩擦系数都不大，因此虽然轴向力 F 相当大，而转矩 T 则相当小。传力螺旋就是利用这种工作原理获得机械增益的。升程越小则机械增益的效果越显著。滑动螺旋传动的效率低，一般为 3040%，能够自锁。而且磨损大、寿命短，还可能出现爬行等现象。2）静压螺旋传动 螺纹工作面间形成液体静压油膜润滑的螺旋传动。静压螺旋传动摩擦系数小，传动效率可达 99%，无磨损和爬行现象，无反向空程，轴向刚度很高，不自锁，具有传动的可逆性，但螺母结构复杂，而且需要有一套压力稳定、温度恒定和过滤要求高的供油系统。静压螺旋常被用作精密机床进给和分度机构的传导螺旋。这种螺旋采用牙较高的梯4形螺纹。在螺母每圈螺纹中径处开有 36 个间隔均匀的油腔。同一母线上同一侧的油腔连通，用一个节流阀控制。油泵将精滤后的高压油注入油腔，油经过摩擦面间缝隙后再由牙根处回油孔流回油箱。当螺杆未受载荷时，牙两侧的间隙和油压相同。当螺杆受向左的轴向力作用时，螺杆略向左移，当螺杆受径向力作用时，螺杆略向下移。当螺杆受弯矩作用时，螺杆略偏转。由于节流阀的作用，在微量移动后各油腔中油压发生变化，螺杆平衡于某一位置，保持某一油膜厚度。3）滚动螺旋传动用滚动体在螺纹工作面间实现滚动摩擦的螺旋传动，又称滚珠丝杠传动.滚动体通常为滚珠，也有用滚子的。滚动螺旋传动的摩擦系数、效率、磨损、寿命、抗爬行性能、传动精度和轴向刚度等虽比静压螺旋传动稍差，但远比滑动螺旋传动为好。滚动螺旋传动的效率一般在 90%以上。它不自锁，具有传动的可逆性；但结构复杂，制造精度要求高，抗冲击性能差。它已广泛地应用于机床、飞机、船舶和汽车等要求高精度或高效率的场合。滚动螺旋传动的结构型式，按滚珠循环方式分外循环和内循环。外循环的导路为一导管,将螺母中几圈滚珠联成一个封闭循环。内循环用反向器，一个螺母上通常有24 个反向器，将螺母中滚珠分别联成 24 个封闭循环，每圈滚珠只在本圈内运动。外循环的螺母加工方便，但径向尺寸较大。为提高传动精度和轴向刚度，除采用滚珠与螺纹选配外，常用各种调整方法以实现预紧。常用的载重螺旋有矩形，梯形和锯齿形等。矩形螺纹传动效率高，但螺纹强度较低，精确制造较困难，对中准确性较差，磨损后无补偿，因此应用受限制，矩形螺纹无标准。梯形螺纹加工容易，强度较大，但效率较低。锯齿形螺纹矩形螺纹效率高，梯形螺纹强度大的特点，一般用于承受单向压力，常用在压力机上。螺杆材料应具有足够的强度和耐磨性，以及良好的加工性能，不经热处理的螺杆一般选用 Q275，35，45 号钢，重要的经热处理的螺杆可以选用 65Mn，40Cr 或 20C rMnTi钢。精密传动螺杆可用 9MnV，CrMn，38CrMoAl 钢等。螺母材料除要有足够的强度外，还要求在与螺杆材料配合时摩擦系数小和耐磨。常选用铸造青铜 ZQSn6-6-3，ZQSn10-1，速度低，载荷较小时，也可选用高强度铸造铝青铜或铸造黄铜，重载时可用铸铁，耐磨铸铁。尺寸大的螺母可用钢或铸铁做外套，内部浇注青铜。高速螺母可浇注巴氏合金。螺旋传动用矩形，梯形或锯齿形螺纹，其失效形式多为螺纹磨损。而螺旋直径螺母的高度由耐磨性要求决定。传力较大时，应校验螺杆部分或其他危险部位强度，以及螺母，螺杆的螺纹牙的强度。要求自锁时，应检验螺纹副的自锁条件。对于长径比很大的受压螺杆，应检验其稳定性。因此，本设计中螺旋副材料选取钢青铜材料，螺杆选取 45 号钢。螺纹选用梯型螺5纹，右旋单线。2.1.2 螺旋传动方案的确定本设计的重点是如何将电机输出的回转运动转换为螺杆的直线运动。这也是整个传动系统设计的关键。根据机械设计等相关参考资料，可得到把回转运动转化为直线运动的四种方式：（1）螺杆转动，螺母移动（2）螺母转动，螺杆移动（3）螺母固定，螺杆转、移动（4）螺杆固定，螺母转、移动考虑到必须顶着重物上升，即与重物接触，而起重部件与重物间不可发生相对运动，而且必须与重物充分接触，因此排除方案（1） 、 （4） ，而方案（3）又不方便输入传动方案的设计，因此选择方案（2）作为起重部分的传动方案。2.2 减速传动机构设计方案减速传动机构通常有蜗轮蜗杆传动，齿轮传动，带传动，链传动，摩擦轮传动等等。考虑到本设计要求的传动紧凑，传动比较大，因此选用蜗轮蜗杆传动作为本设计的减速传动机构。蜗杆传动用于传递交错轴之间的回转运动。在绝大多数情况下，两轴在空间上是互相垂直的，轴交角为 90 度。它广泛应用在机床、汽车、仪器、起重运输机械、冶金机械以及其他机械制造部门中，最大传动功率可达到 750 千瓦，通常用在 50 千瓦以下；最高滑动速度可达 35m/s，通常用在 15m/s 以下。蜗杆传动的主要优点是结构紧凑，工作平稳，无噪声，冲击振动小以及能得到很大的单级传动比。在传递动力时，传动比一般为 8100，常用的为 550。在机床工作台中，传动比可达几百，甚至达到一千。这时，需采用导程角很小的单头蜗杆，但传动效率很低，只能用在功率很小的场合。在现代机械制造业中正力求提高蜗杆传动的效率，多头蜗杆的传动效率已经可达到 98%。与多级齿轮传动相比，蜗杆传动零件数目少，结构尺寸小，重量轻。缺点是在制造精度和传动比相同的条件下，蜗杆传动的效率比齿轮传动低，同时蜗轮一般需用贵重的减磨材料制造。63 传动系统的设计3.1 螺旋传动部分计算3.1.1 螺杆直径的计算 式2 Fpdh p（3.1）表 3-1 滑动螺旋副许用比压P螺杆材料螺母材料许用比压速度范围钢青铜1825低速钢钢7.513低速钢铸铁13182.4m/min钢青铜11183.0m/min取钢青铜螺旋副p=20Mpa，f=0.080.1，最大负载 F=25000N，代入式（3.1）得: 225.9dmm根据梯形螺纹国家标准，取螺纹为 Tr30 6其基本参数为：螺杆外径：，30dmm中径：，2227dDmm螺杆小径：，323dmm螺母小径：，124Dmm螺母大径：，431Dmm螺距：6pmm73.1.2 螺纹部分强度计算梯形螺纹牙型角30当量摩擦角 arctanarctan/cos(/2)5vvff将螺纹部分展开，其受力图如图 3-1 所示， 图 3-126arctanarctan4.127pd作用在螺母上的扭矩12/2TQd2tan()/2vFd54059Nmm螺杆受力如图 3-2 所示，由图可知，螺杆上与螺母旋合处扭矩最大，且max154059TTNmm图 3-2根据第四强度理论，得：螺杆危险截面的当量应力822max33334()3()0.2vTFdd 2233334 2500054059()3()230.2 23 71.4Mpa表 3-2 螺杆与螺纹牙强度项目许用应力 Mpa螺杆强度 为屈服极限 3 5ss材料剪切弯曲min钢0.6（11.2）青铜30-404060铸铁404555螺纹牙强度耐磨铸铁405060蜗杆材料为 45 号钢，由表 3-2 可知，它的许用应力为=12072Mpa 3 5s3603 5，满足要求。 v自锁条件：=12m/s26m/s 和持续运转的工况，离心铸造的可得到致密的细晶粒组织，可取大值，沙型铸造的取小值。（2）铸铝青铜 适用于 Vs=10m/s 的工况，抗胶合能力差，蜗杆硬度应不低于45HRC。（3）铸铝黄铜 点蚀强度高，但磨损性能差，宜用于低滑动速度场合。（4）灰铸铁和球墨铸铁 适用于 Vs=2.25转速系数：，74. 0) 18(812nzn弹性系数：根据蜗轮副材料查表 3-7 得，MpazE147寿命系数：设机器使用寿命，则寿命系数hLh100006 . 116. 1250006hhLz接触系数：由参考文献1图 13.12I 线查得65. 2z接触疲劳极限：查参考文献表 3-7 得MpaH265lim14表 3-7 蜗轮材料 力学性能和设计数据力学性能设计数据bSHBS310EEZlimHlimFmaxfv蜗轮材料MpaMpa%MpaMpaMpaMpam/s22013080388.314726511512铸锡青铜33017090488.314742519026240120701298.115235016512铸锡青铜铸锡青铜27014080798.115243019026铸铝青铜49018010013122.616425040010续表 3-7 力学性能设计数据bSHBS310EEZlimHlimFmaxfv蜗轮材料MpaMpa%MpaMpaMpaMpam/s铸铝青铜54020011015122.61642655001063025015716122.616455027010铸铝青铜70030016013122.61646603771067031016718122.616425040210铸铝青铜7504001855122.616426550210注：表中每项第一行为砂型铸造，第二项为离心铸造接触疲劳最小安全系数： 取3 . 1minHS中心距：1532limmin2)(HHhnEaSzzzzTka代入数据得：， 取标准值mma1 .67mma80蜗杆头数：， 取71. 17 .16/ )804 . 27(/ )4 . 27(3iaz23z蜗轮齿数：， 取4 .3327 .1632ziz302z模数： ， 取5 . 47 . 3/)7 . 14 . 1 (2zam4m蜗杆分度圆直径：， 取标准值4 .3168. 0875. 03ad401d蜗轮分度圆直径：mmmzd12030422蜗杆导程角： 031.11tan蜗轮宽度： ， 取mmmdmb5 .30)15 . 0(212mmb322蜗杆圆周速度： 91. 2)100060/(333ndv蜗杆尺寸：齿顶圆直径 mmmdda48233齿根圆直径 mmhddff4 .302333蜗杆螺纹长度 ， 取mmzmb5 .441223mmb453蜗轮尺寸：齿顶圆直径mmmdhddaa128222222齿根圆直径mmmdhddff4 .1102 . 12222223.3.3 强度校核（1）齿面接触疲劳强度验算许用接触应力：MpaSzzHHhnH1733 . 126516. 074. 0minmin最大接触应力： 满足条13480551621 . 165. 2147332HAEHMpaaTkzz件16（2）轮齿弯曲疲劳强度验算齿根弯曲疲劳极限MpaF115lim弯曲疲劳最小安全系数4 . 1minFS许用弯曲疲劳应力MpaSFFF82minlim轮齿最大弯曲应力 满足条件。9 . 72222FAFMpadmbTk3.3.4 蜗轮蜗杆传动中的作用力分析在蜗杆传动中作用在齿面上的法向压力仍可分解为圆周力、径向力和轴向力。显然，作用于蜗杆上的轴向力等于蜗轮上的圆周力，蜗杆上的圆周力等于蜗轮上的轴向力；蜗杆上的径向力则等于蜗轮上的径向力。这些对应的力的数值相等，方向彼此相反。如图3-5 所示。图 3-5 蜗轮蜗杆受力图17蜗轮上作用力 NdTFt4 .9191205516222222NFFFtat17811tan4 .919tan221 NFFttr8 .53030tan4 .919tan223.3.5 实际传动动力参数由于蜗轮蜗杆各基本尺寸需圆整为标准值，传动比最终确定为且蜗轮蜗杆传动效率与估计值略有差别，因此，实际传动、动力参152/30/12ZZi数如下：（1）各轴实际转矩：螺母：Nmm540591T蜗轮：=54059/0.98=55162 Nmm22/54059T蜗杆： Nmm435215845. 055162)/(323iTT电机轴： Nmm7 .448599. 098. 04352)/(423TTd（2）各轴实际转速蜗杆：r/min13903n蜗轮： r/min7 .9215/139032inn螺母： r/min7 .92321innn螺杆：m/min556. 0006. 07 .9211pnv（3）电机实际功率KWF，满足条件，因此下20端轴承选用 51111 型。上端轴承受力比较小，因此只需考虑安装问题，结合自制螺母的直径，选用 51108型平面推力轴承。（2）蜗杆轴承的选择根据蜗杆的受力图可知，蜗杆牙部分除受径向力外还受轴向力的作用，因此选用轴承时考虑优先选用能同时承受径向力和轴向力的圆锥滚子轴承，型号：30205。4.1.3 轴承校验（1）计算圆锥滚子轴承寿命Fs2Fs1FR2Fa1Fr1FR1图 4-1 蜗杆及轴承受力分析已求得：蜗杆所受径向力,轴向力.NFr8 .5301NFa4 .9191查手册 30205 轴承主要性能参数：Cr=32.2KN，=37KN，=7000r/min，e=0.37，Y=1.6，=0.9，a=12.5rC00N0YNFFFrRR8 .530121NFFFrRR4 .26521121所以，附加轴向力；NYFFRs9 .826 . 124 .265211 NYFFRs9 .826 . 124 .265222因为，所以，右端轴承被压紧，则：21ssaFFF轴承轴向力,NFFsA9 .8211 NFFFasA3 .10029 .824 .919112，取=1，=0；eFFRA31. 04 .2659 .82111X1Y21，取=0.4，=0.4cot12.5=1.8eFFRA78. 34 .2653 .1002222X2Y考虑平稳运转，冲击载荷系数=1,df当量动载荷11111()265.4dRAPfX FY FN NFYFXfPARd5 .2016)(22222因为 P1T1（54059）mmN 49920012030165221mmN （2）螺杆与联轴器处键的选择参考轮毂及轴径，选择为的键，取键长 L=25mm；hb66许用转矩41pdhlT = T3(4352) 合格mmN 49875701925641mmN 4.3 联轴器的设计与计算联轴器是用于连接不同机构中两轴，使他们在传递运动和动力过程中一起回转而不脱开。联轴器主要有机械式，液力式和电磁式三种。机械式连轴器是应用最广泛的连轴器，它借助于机械构件相互间的机械作用力来传递转矩。液力式好电磁式是借助于液力和电磁力来传递转矩。联轴器广泛用于船舶，机车，汽车，冶金矿山，石油化工，其重运输，纺织，轻工，农业机械，印刷机械和泵，风机，机床等各类机械设备传动系统中。联轴器的种类很多，按其性能分为：（1） 刚性联轴器1）套筒联轴器2）凸缘联轴器243）夹壳联轴器4）紧箍咒夹壳联轴器（2）挠性联轴器1）无弹性元件挠性联轴器2）非金属弹性元件挠性联轴器3）金属弹性元件挠性联轴器联轴器选择应考虑的问题：在深知所设计产品的工况及技术要求的情况下，选择联轴器应考虑以下问题：（1）所需传递转矩大小、载荷性质及产品对缓冲和减振方面的要求；（2）轴的转速高低和引起的离心力大小；（3）两轴对位移大小（径向位移、轴向位移、角位移） ；（4）联轴器的制造、安装、维修、成本。在本设计中，选择联轴器的基本决定因素是联轴器所受扭矩的大小。 （也即电机轴的扭矩）求得，电机轴的扭矩mNmmNTd5 . 47 .4485由于联轴器已标准化，只需根据其所受最大扭矩及轴径大小选择联轴器，因此，综合考虑，选择 YL1 型凸缘联轴器，其基本参数见表 4-2。表 4-2YL1 型凸缘联轴器基本参数螺栓公称扭矩 TnmN 许用转速 n r/min轴孔直径mmLmmDmmD1mm数直径L0mm重量kg 108100193071533M6640.94 25图 4-2YL1 型凸缘联轴器5 控制电路及过载保护系统的设计5.1 过载及最大行程保护元件5.1.1 热继电器热继电器是一种电气保护元件。它是利用电流的热效应来推动动作机构使触头闭合或断开的保护电器，主要用于电动机的过载保护、断相保护、电流不平衡保护以及其他电气设备发热状态时的控制。 热继电器是用于电动机或其它电气设备、电气线路的过载保护的保护电器。电动机在实际运行中，如拖动生产机械进行工作过程中，若机械出现不正常的情况或电路异常使电动机遇到过载，则电动机转速下降、绕组中的电流将增大，使电动机的绕组温度升高。若过载电流不大且过载的时间较短，电动机绕组不超过允许温升，这种过载是允许的。但若过载时间长，过载电流大，电动机绕组的温升就会超过允许值，使电动机绕组老化，缩短电动机的使用寿命，严重时甚至会使电动机绕组烧毁。所以，这种过载是电动机不能承受的。热继电器就是利用电流的热效应原理，在出现电动机不能26承受的过载时切断电动机电路，为电动机提供过载保护的保护电器。 使用热继电器对电动机进行过载保护时，将热元件与电动机的定子绕组串联，将热继电器的常闭触头串联在交流接触器的电磁线圈的控制电路中，并调节整定电流调节旋钮，使人字形拨杆与推杆相距一适当距离。当电动机正常工作时，通过热元件的电流即为电动机的额定电流，热元件发热，双金属片受热后弯曲，使推杆刚好与人字形拨杆接触，而又不能推动人字形拨杆。常闭触头处于闭合状态，交流接触器保持吸合，电动机正常运行。 若电动机出现过载情况，绕组中电流增大，通过热继电器元件中的电流增大使双金属片温度升得更高，弯曲程度加大，推动人字形拨杆，人字形拨杆推动常闭触头，使触头断开而断开交流接触器线圈电路，使接触器释放、切断电动机的电源，电动机停车而得到保护。 可见，热继电器通常是直接断开接触器的控制回路来断开主回路的。热继电器的工作原理如图 5-1图 5-1 热继电器原理图由电阻丝做成的热元件，其电阻值较小，工作时将它串接在电动机的主电路中，电阻丝所围绕的双金属片是由两片线膨胀系数不同的金属片压合而成，左端与外壳固定。当热元件中通过的电流超过其额定值而过热时，由于双金属片的上面一层热膨胀系数小，而下面的大，使双金属片受热后向上弯曲，导致扣板脱扣，扣板在弹簧的拉力下将常闭触点断开。触点是串接在电动机的控制电路中的，使得控制电路中的接触器的动作线圈断电，从而切断电动机的主电路。 （1）热继电器的基本结构 包括加热元件、主双金属片、动作机构和触头系统以及温度补偿元件。 （2）热继电器的种类 热继电器的种类很多，常用的有 JR0、JR16、JR16B、JRS 和 T 系列。 （3）热继电器的型号及含义以 JR 系列热继电器为例，型号含义如图 5-2： 27图 5-2 热继电器型号含义5.1.2 行程开关行程行程开关又称限位开关，用于控制机械设备的行程及限位保护。在实际生产中，将行程开关安装在预先安排的位置，当装于生产机械运动部件上的模块撞击行程开关时，行程开关的触点动作，实现电路的切换。因此，行程开关是一种根据运动部件的行程位置而切换电路的电器，它的作用原理与按钮类似。行程开关广泛用于各类机床和起重机械，用以控制其行程、进行终端限位保护。在电梯的控制电路中，还利用行程开关来控制开关轿门的速度、自动开关门的限位，轿厢的上、下限位保护。行程开关按其结构可分为直动式、滚轮式、微动式和组合式。（1）直动式行程开关 其结构原理如图 5-3 所示，其动作原理与按钮开关相同，但其触点的分合速度取决于生产机械的运行速度，不宜用于速度低于 0.4mmin 的场所。图 5-3 直动式行程开关1-推杆 2-弹簧 3-动断触点 4-动合触点（2）滚轮式行程开关 其结构原理如图 5-4 所示，当被控机械上的撞块撞击带有滚轮的撞杆时，撞杆转向右边，带动凸轮转动，顶下推杆，使微动开关中的触点迅速动作。当运动机械返回时，在复位弹簧的作用下，各部分动作部件复位。28图 5-4 滚轮式行程开关1-滚轮 2-上转臂 3、5、11-弹簧 4-套架 6-滑轮 7-压板 8、9-触点 10-横板滚轮式行程开关又分为单滚轮自动复位和双滚轮(羊角式)非自动复位式，双滚轮行移开关具有两个稳态位置，有“记忆”作用，在某些情况下可以简化线路。（3）微动开关式行程开关 常用的有 LXW-11 系列产品本设计为方便控制螺杆做线性运动，采用上海人民电器开关厂有限公司生产的直动式行程开关，其基本尺寸如图 5-5 所示：图 5-5 直动式行程开关 295.2 电器控制基本电路设计结合螺旋起重机控制电路要求随时停车以及限制最大起重量以保护电机的特点，设计并绘制其电器控制基本电路图，如图 5-6 所示。其中，QS：三相电源开关；FU：熔断器；FR：热继电器；KM1、KM2：接触器；SB：按钮；SQ：行程开关；M：电动机。该电路基本工作原理如下：按下正向启动按钮 SB2（上升按钮）时，接触器 KM2 得电吸合，其常开主触点将电动机定子绕组接通电源，相序为 U、V、W，电动机正向启动运行。按下停止按钮 SB1 时，KM2 失电释放，电动机停转。按下反向启动按钮 SB3（下降按钮）时，KM3 线圈得电主触点吸合，其常开触点将相序为 W、V、U 的电源接至电动机，电动机反向启动运行。再按下停止按钮 SB1，电动机停转。SQ 为行程开关，控制重物的最大抬升高度。当重物上升至最大高度时，SQ 动作，其常闭触点断开，使接触器 KM2 失电，整个电路停电，此时只需长按反向启动按狃（下降按钮）SB3，即可下降。至合适位置时按下停止按钮 SB1。当螺杆下降至最小高度时，SQ动作，其常闭触点断开，使接触器 KM3 失电，整个电路停电，此时只需长按正向启动按狃（上升按钮）SB2，即可上升。至合适位置时按下停止按钮 SB1。30FRWVUQSFU1KM2KM3KM2KM3SQSQSB3SB2KM3KM2FU2KM3KM2MSB1FR图 5-6 电器控制图316 系统的改进与优化由本设计可以看出，它只适用于人工启动，手动控制。为适应生产自动流水线作业，使本产品的使用范围更加广泛，市场前景更加广阔，本设计的二次开发及优化中可增设电阻应变片式压力传感器，其基本动作原理是：托盘上有重物时，压力传感器变化信号，使电机启动，带动重物上升，上升到指定位置（该指定位置由位置传感器控制） ，重物被取走后，压力传感器信号复原，使电机反转，到指定位置停转。如此反复。在这个过程中，电阻应变片式压力传感器充当的作用是压力开关，光电式位置传感器充当的作用是光电开关，它们随着压力的有无和螺杆位置的变化指导着电机的正转，停止以及反转。因此，必须了解压力传感器及位置传感器的原理及种类。6.1 力学传感器力学传感器是将各种力学量转换为电信号的器件，力学量可分为几何学量、运动学量及力学量三部分，其中几何学量指的是位移、形变、尺寸等，运动学量是指几何学量的时间函数，如速度、加速度等。力学量包括质量、力、力矩、压力、应力等。压电式压力传感器 、压磁式转矩传感器 、压阻式压力传感器 、变面积式电容压力传感器 、差动变极距式电容压力传感器 、应变式压力传感器 、应变片式转矩传感器 、振筒式谐振压力传感器 、振膜式谐振压力传感器 、电阻应变式称重传感器。力学传感器的种类繁多，如电阻应变片压力传感器、半导体应变片压力传感器、压阻式压力传感器、电感式压力传感器、电容式压力传感器、谐振式压力传感器及电容式加速度传感器等。但应用最为广泛的是压阻式压力传感器，它具有极低的价格和较高的精度以及较好的线性特性。6.1.1 电阻应变片力传感器某些固体材料受到外力的作用后，除了产生变形，其电阻率也要发生变化，这种由于应力的作用而使材料电阻率发生变化的现象称为“压阻效应” 。利用压阻效应制成的传感器称为压阻式传感器。根据制作材料的不同，应变元件可以分为两大类。一种是利用半导体材料的体电阻做成粘贴式应变片，称为半导体应变片，用此应变片制成的传感器称为半导体应变式传感器，另一种是在半导体材料的基片上用集成电路工艺制成的扩散电阻，以此扩散电阻的传感器称为扩散型压阻传感器。（1）半导体应变片式传感器半导体应变片应变元件的工作原理基于导体和半导体的“应变效应” ，即当导体和半导体材料发生机械变形时，其电阻值将发生变化。电阻值的相对变化与应变的关系如式 6.1所示：32 式（6.1）KRR式中为材料的应变；K 为材料的电阻应变系数，即单位应变引起的电阻相对变化量。金属材料的 K 值约为 26，半导体材料的 K 值可达 60180。金属电阻应变片主要有丝式应变片和箔式应变片两种结构。如图 6-1 所示。图 6-1 电阻应变片结构丝式应变片由金属丝栅(亦称敏感栅)、基底、引线、保护膜等组成。敏感栅一般采用直径 0.0150.05mm 的金属丝，用粘合剂固定在厚 0.020.04mm 的纸或胶膜基底上。引线是由直径 0.10.2mm 低阻镀锡铜线制成，用于将敏感栅与测量电路相连。箔式应变片的敏感栅是用厚度为 0.0030.0lmm 的金属箔经光刻、腐蚀等工艺制成的。优点是表面积与截面积之比大，散热条件好，能承受较大电流和较高电压，因而输出灵敏度高，并可制成各种需要的形状，便于大批量生产。由于上述优点，它已逐渐取代丝式应变片。应变片与弹性元件的装配可以采用粘贴式或非粘贴式，在弹性元件受压变形的同时应变片亦发生应变，其电阻值将有相应的改变。粘贴式应变压力计可采用 1、2 或 4 个特性相同的应变元件，粘贴在弹性元件的适当位置上，并分别接入电桥的桥臂，则电桥输出信号可以反映被测压力的大小。为了提高测量灵敏度，通常采用两对应变片，并使相对桥臂的应变片分别处于接受拉应力和压应力的位置。应变式压力传感器所用弹性元件可根据被测介质和测量范围的不同而采用各种型式，常见有圆膜片、弹性梁、应变筒等。图 6-2 给出几种弹性元件和应变式压力传感器的结构及电桥式测量电路示意图。33图 6-2 几种弹性元件和应变式压力传感器的结构及电桥式测量电路示意图。电阻应变片的工作原理金属电阻应变片的工作原理是吸附在基体材料上应变电阻随机械形变而产生阻值变化的现象，俗称为电阻应变效应。金属导体的电阻值可用式 6.2 表示： 式SLR（6.2）式中：金属导体的电阻率（cm2/m）S导体的截面积（cm2）L导体的长度（m）我们以金属丝应变电阻为例，当金属丝受外力作用时，其长度和截面积都会发生变化，从上式中可很容易看出，其电阻值即会发生改变，假如金属丝受外力作用而伸长时，其长度增加，而截面积减少，电阻值便会增大。当金属丝受外力作用而压缩时，长度减小而截面增加，电阻值则会减小。只要测出加在电阻的变化（通常是测量电阻两端的电压） ，即可获得应变金属丝的应变情况。6.2 位置传感器位置传感器在自动化流水作业中有着举足轻重的作用，它的种类也比较多，这里只介绍用的比较多的光电位置传感器。光电传感器(光电开关)是光电接近开关的简称，它是利用被检测物体对光束的遮光或反射，由同步回路选通电路，从而检测物体的有无。其物体不限于金属，对所有能反射光线的物体均可被检测。光电开关是一种电量传感器。把电流或电压的变化以光电的方式传送出去。即进行电信号光信号电信号的转换，工作原理如图 6-3 所示。多数光电开关选用的是接近可见光的红外线。由于光电开关输出回路和输入回路是电隔离的（即电缘绝），所以它可以在许多场合得到应用。34采用集成电路技术和 SMT 表面安装工艺而制造的新一代光电开关器件，具有延时、展宽、外同步、抗相互干扰、可靠性高、工作区域稳定和自诊断等智能化功能。这种新颖的光电开关是一种采用脉冲调制的主动式光电探测系统型电子开关，它所使用的冷光源有红外光、红色光、绿色光和蓝色光等，可非接触，无损伤地迅速和控制各种固体、液体、透明体、黑体、柔软体和烟雾等物质的状态和动作。新型光电开关的优点是，体积小、功能多、寿命长、精度高、响应速度快、检测距离远以及抗光、电、磁干扰能力强等等。 目前，这种新型的光电开关已被用作物位检测、液位控制、产品计数、宽度判别、速度检测、定长剪切、孔洞识别、信号延时、自动门传感、色标检出、冲床和剪切机以及安全防护等诸多领域。此外，利用红外线的隐蔽性，还可在银行、仓库、商店、办公室以及其它需要的场合作为防盗警戒之用。光电开关工作原理图 6-3 所示是反射式光电开关的工作原理框图。图中，由振荡回路产生的调制脉冲经反射电路后，由发光管 GL 辐射出光脉冲。当被测物体进入受光器作用范围时，被反射回来的光脉冲进入光敏三极管 DU。并在接收电路中将光脉冲解调为电脉冲信号，再经放大器放大和同步选通整形，然后用数字积分或 RC 积分方式排除干扰，最后经延时（或不延时）触发驱动器输出光电开关控制信号。图 6-3 光电开关工作原理光电开关一般都具有良好的回差特性，因而即使被检测物在小范围内晃动也不会影响驱动器的输出状态，从而可使其保持在稳定工作区。同时，自诊断系统还可以显示受35光状态和稳定工作区，以随时监视光电开关的工作。6.3 连续控制分析这里只对螺旋起重机的连续动作进行简要的分析说明。在该连续螺旋起重系统中，我们考虑螺杆及与其连接的法兰盘的四个主要状态，即：（1）螺杆在原始点（低点） ，法兰盘上有重物（可视为重物刚放上去） ；（2）螺杆在控制点（高点） ，法兰盘上有重物；（3）螺杆在控制点（高点） ，法兰盘上无重物（可视为重物被取走） ；（4）螺杆在原始点（低点） ，法兰盘上无重物；我们把螺杆的位置和法兰盘上是否有重物看作两个事件，电机的正、反、停转则由这两个事件控制。假设螺杆在原始点时，向芯片输入低电平，在控制点时输入高电平；法兰盘上无重物时，向芯片输入低电平，有重物时输入高电平。因此可表示为：01 电机正转；11 电机停转；10 电机反转；00 电机停转。从而实现连续流水线作业。36结论本次毕业设计是大学所学知识的全面应用和检测，它使我对产品的先期调研、设计方案的提出、到最终设计的完成有了比较理性的认识，为以后的工作打下了基础，积累了经验。本次设计的电动螺旋起重机具有结构紧凑、体积小、重量轻、动力源广泛、无噪音、安装方便、使用灵活、功能多、配套形式多、可靠性高、使用寿命长等许多优点。可以单台或组合使用，能大致控制调整提升的高度，可以用电动机或其他动力直接带动，也可以手动。比如说如果用液压马达代替电动机，则可以实现液压的远程控制；也可以用柴油机代替电动机，在没有电的时候使用。在设计的时候，把起重的最大载荷和起重的速度作为设计的原始数据，因此，可以根据使用的场合不同、起重的最大载荷不同设计出相应的产品。通过这次比较完整的螺旋起重机设计，我摆脱了单纯的理论知识学习状态，和实际设计的结合锻炼了我的综合运用所学的专业基础知识，解决实际工程问题的能力，同时也提高我查阅文献资料、设计手册、设计规范以及电脑制图等其他专业能力水平，而且通过对整体的掌控，对局部的取舍，以及对细节的斟酌处理，都使我的能力得到了锻炼，经验得到了丰富，并且意志品质力，抗压能力及耐力也都得到了不同程度的提升。这是我们都希望看到的也正是我们进行毕业设计的目的所在。顺利如期的完成本次毕业设计给了我很大的信心，让我了解专业知识的同时也对本专业的发展前景充满信心，但也存在一定的不足，这新不足在一定程度上限制了我们的创造力。比如我的设计在蜗轮和螺母的材料选择上有一定的不足，我选择的材料是铸铝青铜，这种材料比较昂贵，以后必须研制出一种新型的低成本的减磨材料，这样产品才有推向市场，得到广泛推广的可能。在这个能源、原材料紧缺的社会中，这无疑是很让我自身感到遗憾的，可这些不足正是我们去更好的研究更好的创造的最大动力，只有发现问题面对问题才有可能解决问题，不足和遗憾不会给我打击只会更好的鞭策我前行，今后我更会关注新技术新设备新工艺的出现，并争取尽快的掌握这些先进的知识。37致谢到今天我的毕业设计已经圆满的完成了。在此，我要特别感谢我的指导老师，在这段时间内他给了我莫大的帮助，对于我的每一个问题都耐心的讲解和指导。正由于他的热心地帮助和指导，我的毕业设计才能够顺利的完成。老师严谨治学的态度和精神也是我在这次设计过程中学到的宝贵的财富。指导老师不仅关心我的设计，还在找工作方面给了我无微不至的关怀和正确的建议，这些都是我不断前进的动力，必将对我今后的学习和生活受益匪浅，我将终生学习和铭记。在此，谨向指导老师的培育之恩表示最深的谢意！大学四年的学习和生活即将告别。感谢这四年各位任课老师对我的教诲，各位同学给我的帮助！感谢与我共同走过大学的朋友们、同学们！感谢所有帮助过我的老师、同学、朋友，同时祝愿你们在以后的日子里，开心、快乐！38参考文献参考文献1 邱宣怀.机械设计.第四版. 高等教育出版社, 2003.42 龚湘义. 机械设计课程设计指导书. 第二版.高等教育出版社, 2004.43 张建中. 机械设计基础课程设计. 中国矿业大学出版社, 2005.24 哈尔滨工业大学 龚湘义. 机械设计课程设计图册.第三版. 高等教育出版社, 2004.1 5 实用机械设计手册编写组编。实用机械设计手册 第二版 机械工业出版社6 范思冲等编著画法几何及机械制图. 机械工业出版社7 李洪、曲中谦. 实用轴承手册. 辽宁科学技术出版社8 杨黎明. 传感器技术. 国防工业出版社9 (德)尼曼，温特尔著.机械零件.第 2 版.第 1 卷，余梦生，倪文馨译，1985；第 2 卷，余梦生，王成焘，高建华译；1989；第 3 卷，张海明译，1991；北京，机械工业出版社10 徐寅主编，机械设计手册.北京，机械工业出版社，199139附录附录附录 1 1英文原文CNC TECHNOLOGYNumerical control (NC) is a form of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols. The numbers, letters, and symbols are coded in an appropriate format to define a program of instructions for a particular workpart or job. When the job changes, the program of instructions is changed. The capability to change the program is what makes NC suitable for low-and medium-volume production. It is much easier to write new programs than to make major alterations of the processing equipment.BASIC COMPONENTS OF NCA numerical control system consists of the following three basic components:Program of instructionsMachine control unitProcessing equipmentThe general relationship among the three components is: the program is fed into the control unit, which directs the processing equipment accordingly.The program of instructions is the detailed step-by-step commands that direct the processing equipment. In its most common form, the commands refer to positions of a machine tool spindle with respect to the worktable on which the part is fixtured. More advanced instructions include selection of spindle speeds, cutting tool, and other function. The most common medium in use over the last several decades has been 1-in. -wide punched tape. Because of the widespread use of the punched tape, NC is sometimes called “tape control”. However, this is a misnomer in modern usage of numerical control. Coming into use more recently have been magnetic tape cassettes and floppy diskettes.The machine control unit (MCU) consists of the electronics and control hardware that read and interpret the program of instruction and convert it into mechanical actions of the machine tool or other processing equipment.The processing equipment is the third basic component of an NC system. It is the component that performs useful work. In the most common example of numerical control, one that performs machining operations, the processing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them.40Types Of Control SystemsThere are two basic types of control systems in numerical control: point-to-point and contouring. In the point-to-point system, also called positioning, each axis of the machine is driven separately by leadscrews and, depending on the type of operation, at different velocities. The machine moves initially at maximum velocity in order to reduce nonproductive time but decelerates as the tool reaches its numerically defined position. Thus in an potation such as drilling or punching, the positioning and cutting take place sequentially. After the hole is drilled or punched, the tool retracts, moves rapidly to another position, and repeats the operation. The path followed from one position to another is important in only one respect: The time required should be minimized for efficiency. Point-to-point systems are used mainly in drilling, punching, and straight milling operations.In the contouring system, also known as the continuous path system, positioning and cutting operations are both along controlled paths but at different velocities. Because the tool cuts as it travels along a prescribed path, accurate control and synchronization of velocities and movements are important. The contouring system is used on lathes, milling machines, grinders, welding machinery, and machining centers.Movement along the path, or interpolation, occurs incrementally, by one of several basic methods. In all interpolations, the path controlled is that of the center of rotation of the tool. Compensation for different tools, different diameter tools, or tool wear during machining, can be made in the NC program.There are a number of interpolation schemes that have been developed to deal with the various problems that are encountered in generating a smooth continuous path with a contouring-type NC system. They include:Linear interpolationCircular interpolationHelical interpolationParabolic interpolationCubic interpolationEach of these interpolation procedures permits the programmer (or operator) to generate machine instructions for linear or curvilinear paths, using a relatively few input parameters. The interpolation module in the MCU performs the calculations and directs the tool along the path.Linear interpolation is the most basic and is used when a straight-line path is to be generated in continuous-path NC. Two-axis and three-axis linear interpolation routines are sometimes distinguished in practice, but conceptually they are the same. The program is required to specify the beginning point and end point of the straight line, and the feed rate that is to be 41followed along the straight line. The interpolator computes the feed rates for each of the two (or three) axes in order to achieve the specified feed rate.Linear interpolation for creating a circular path would be quite inappropriate because the programmer would be required to specify the line segments and their respective end points that are to be used to approximate the circle. Circular interpolation schemes have been developed that permit the programming of a path consisting of a circular arc by specifying the following parameters of the arc: the coordinates of its end points, the coordinates of its center, its radius, and the direction of the cutter along the arc. The tool path that is created consists of a series of straight-line segments, but the segments are calculated by the interpolation module rather than the programmer. The cutter is directed to move along each line segment one by one in order to generate the smooth circular path. A limitation of circular interpolation is that the plane in which the circular arc exists must be a plane defined by two axes of the NC system.Helical interpolation combines the circular interpolation scheme for two axes described above with linear movement of a third axis. This permits the definition of a helical path in three-dimensional space.Parabolic and cubic interpolation routines are used to provide approximations of free-form curves using higher-order equations. They generally require considerable computational power and are not as common as linear and circular interpolation. Their applications are concentrated in the automobile industry for fabricating dies for car body panels styled with free-form designs that cannot accurately and conveniently be approximated by combining linear and circular interpolations.Programming For NCA program for numerical control consists of a sequence of directions that causes an NC machine to carry out a certain operation, machining being the most commonly used process. Programming for NC may be done by an internal programming department, on the shop floor, or purchased from an outside source. Also, programming may be done manually or with computer assistance.The program contains instructions and commands. Geometric instructions pertain to relative movements between the tool and the work piece. Processing instructions pertain to spindle speeds, feeds, tools, and so on. Travel instructions pertain to the type of interpolation and slow or rapid movements of the tool or worktable. Switching commands pertain to on/off position for coolant supplies, spindle rotation, direction of spindle rotation, tool changes, work piece feeding, clamping, and so on.(1) Manual Programming 42Manual part programming consists of first calculating dimensional relationships of the tool, work piece, and work table, based on the engineering drawings of the part, and manufacturing operations to be performed and their sequence. A program sheet is then prepared, which consists of the necessary information to carry out the operation, such as cutting tools, spindle speeds, feeds, depth of cut, cutting fluids, power, and tool or work piece ally a paper tape is first prepared for trying out and debugging the program. Depending on how often it is to be used, the tape may be made of more durable Mylar.Manual programming can be done by someone knowledgeable about the particular process and able to understand, read, and change part programs. Because they are familiar with machine tools and process capabilities, skilled machinists can do manual programming with some training in programming. However, the work is tedious, time consuming, and uneconomical-and is used mostly in simple point-to-point applications.(2) Computer-Aided Programming Computer-aided part programming involves special symbolic programming languages that determine the coordinate points of corners, edges, and surfaces of the part. Programming language is the means of communicating with the computer and involves the use of symbolic characters. The programmer describes the component to be processed in this language, and the computer converts it to commands for the NC machine. Several languages having various features and applications are commercially available. The first language that used English-like statements was developed in the late 1950s and is called APT (for Automatically Programmed Tools). This language, in its various expanded forms, is still the most widely used for both point-to-point and continuous-path programming.Computer-aided part programming has the following significant advantages over manual methods: Use of relatively easy to use symbolic languageReduced programming time. Programming is capable of accommodating a large amount of data concerning machine characteristics and process variables, such as power, speeds, feed, tool shape, compensation for tool shape changes, tool wear, deflections, and coolant use. Reduced possibility of human error, which can occur in manual programming Capability of simple changeover of machining sequence or from machine to machine. Lower cost because less time is required for programming.Selection of a particular NC programming language depends on the following factors:a) Level of expertise of the personnel in the manufacturing facility.b) Complexity of the part.c) Type of equipment and computers available.43d) Time and costs involved in programming.Because numerical control involves the insertion of data concerning work piece materials and processing parameters, programming must be done by operators or programmers who are knowledgeable about the relevant aspects of the manufacturing processes being used. Before production begins, programs should be verified, either by viewing a simulation of the process on a CRT screen or by making the part from an inexpensive material, such as aluminum, wood, or plastic, rather than the material specified for the finished part.Cutting tool choice and cutting specifications determination in CNC processingThe cutting tool choice and the cutting specifications determination is in the numerical control processing craft important content, it not only influence numerical control engine bed processing efficiency, moreover affects the processing quality directly. CAD/The CAM technology development, enables in the numerical control processing to become directly using the CAD design data possibly, specially the microcomputer and the numerical control engine bed joint, causes the design, the craft plan and the programming entire process completes completely on the computer, does not need to output the special technological document generally.Now, many CAD/The CAM software package all provides the automatic programming function, these software are generally prompt the craft plan in the programming contact surface the related question, for instance, cutting tool choice, processing way plan, cutting specifications hypothesis and so on, programmers so long as have established the related parameter, may automatically produce completes the processing the NC procedure and the transmission to the numerical control engine bed. Therefore, in the numerical control processing cutting tool choice and the cutting specifications determination is completes under the man-machine interactive condition, this forms the sharp contrast with the ordinary engine bed processing, at the same time also requests the programmers to have to grasp the cutting tool choice and the cutting specifications determination basic principle, when programming full consideration numerical control processing characteristic. This article the cutting tool choice and the cutting specifications which must face to the numerical control programming in determined the question has carried on the discussion, has produced certain principles and the suggestion, and to the question which should pay attention has carried on the discussion.First, numerical control processing commonly used cutting tool type and characteristicThe numerical control processing cutting tool must adapt the numerical control engine bed high speed, is highly effective and the automatic high characteristic, should include the general cuttingtool, the general connection hilt and the few special-purpose hilts generally. The hilt must join the cutting tool and install on the engine bed power head, therefore already gradual 44standardization and seriation. The numerical control cutting tool classification has the many kinds of methods. May divide into according to the cutting tool structure: (1) Integral type; (2) The mosaic, uses the welding or machine clamps the type connection, machine clamps the type to be possible to divide into does not index and may index two kinds; (3) Special pattern, like compound expression cutting tool, absorption of shock type cutting tool and so on. According to makes the materialwhich the cutting tool uses to be possible to divide into: (1) High-speed steel cutting tool; (2) Hard alloy tools; (3) Diamond cutting tool; (4) Other material cutting tools, like cubic boron nitride cutting tool, ceramic cutting tool and so on. May divide into from the cutting craft: (1) The turning cutting tool, divides the outer annulus, in the hole, the thread, cuts the cutting tool many kinds of and so on; (2) Drills truncates the cutting tool, including drill bit, reamer, screw tap and so on; (3) Boring cutting tool; (4) Milling cutting tool and so on. In order to adapt the numerical control engine bed durably to the cutting tool, is stable, easy change, may trade and so on the request, in recent years machine clamps the type to be possible to index the cutting tool to obtain the widespread application, reaches higher authorities in the quantity to the entire numerical control cutting tool 30% 40%, the metal excision quantity accounts for the total 80% 90%. Machining CentersMany of todays more sophisticated lathes are called machining centers since they are capable of performing, in addition to the normal turning operations, certain milling and drilling operations. Basically, a machining center can be thought of as being a combination turret lathe and milling machine. Additional features are sometimes included by manufacturers to increase the versatility of their machines.Numerical ControlOne of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control (NC). Prior to the advent of NC, all machine tools were manually operated and controlled .Among the many limitations associated with manual control machine tools, perhaps none is more prominent than the limitation of operator skills. With manual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control of machine tools.Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician writes a program that issues operational instructions to the machine tool. For a machine tool to be numerically controlled, it must be interfaced with a device for accepting and decoding the programmed instructions, known as a reader.45Numerical control was developed to overcome the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines, they can produce parts more uniformly, they are faster, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology:1.Electrical discharge machining.2.Laser cutting.3.Electron beam welding.Numerical control has also made machine tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide variety of parts, each involving an assortment of widely varied and complex machining processes. Numerical control has allowed manufacturers to undertake the production of products that would not have been feasible from an economic perspective using manually controlled machine tools and processes.Like so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the U. S. Air force. In its earliest stages, NC machines were able to make straight cuts efficiently and effectively.However, curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter is the straight lines making up the steps, the smoother is the curve. Each line segment in the steps had to be calculated.This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major step forward in the further development of NC technology. The original NC systems were vastly different from those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development.A major problem was the fragility of the punched paper tape medium. It was common for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each successive time a part was produced on a machine tool, the paper tape carrying the programmed instructions had to be rerun through 46the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use.This led to the development of a special magnetic plastic tape. Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magnetic dots. The plastic tape was much stronger than the paper taps, which solved the problem of frequent tearing and breakage. However, it still left two other problems.The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instructions, it was necessary to interrupt machining operations and make a new tape .It was also still necessary to run the tape through the reader as many times as there were parts to be produced. Fortunately, computer technology became a reality and soon solved the problems of NC associated with punched paper and plastic tape.The development of a concept known as direct numerical control (DNC) solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control .machine tools are tied, via a data transmission link, to a host computer. Programs for operating the machine tools are stored in the host computer and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend on a host computer. When the lost computer goes down, the machine tools also experience downtime. This problem led to the development of computer numerical control.The development of the microprocessor allowed for the development of programmable logic controllers (PLCs) and microcomputers. These two technologies allowed for the development of computer numerical control (CNC).With CNC, each machine tool has a PLC or a microcomputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. It also allows programs to be developed off-line and downloaded at the individual machine tool. CNC solved the problems associated with downtime of the host computer, but it introduced another known as data management. The same program might be loaded on ten different microcomputers with no communication among them. This problem is in the process of being solved by local area networks that connect microcomputers for better data management.47Tool ChangerThe machining center is equipped whit a programmable automatic tool changer. Depending on the design, up to 200 cutting tools can be stored in a magazine, drum or chain(tool storage). Auxiliary tool storage is available on some special machining centers for many more cutting tools. The cutting tools are automatically selected with random access for the shortest route to the machine spindle. The tool-exchange arm shown Fig.4.5 is a common design. (See also Fig.4.2).It swings around to pick up a particular tool(each tool has its own tool holder)and places it in the spindle.Tools are indentified by coded tags, bar codes, or memory chips attached directly to the tool holders. A tool-changing time is typically between 5 and 10 seconds; they may be less than one second for small tools, or up to 30seconds for tools weighing 110kg(250lb). The trend in tool changers is to use simple mechanisms, resulting in faster tool-changing times.Machining centers may be equipped with a tool-and/or part-checking station that feeds information to the computer-numerical control to compensate for any variations in tool settings or tool wear. Touch probes(Fig.4.6)can be automatically installed into a tool holder to determine reference surfaces of the work piece, for the selection of tool setting, and for the on-line inspection of parts being machined.Note in Fig.4.6 that several surfaces can be contacted, and that their relative positions are determined and stored in the database of the computer software. The data are then used to program tool paths and to compensate for tool length and diameter, as well as for tool wear in more advanced machine tools.Types of Machining and Turning CentersAlthough there are various designs for machining centers, the two basic types are vertical spindle and horizontal spindle; many machines are capable of using both axes. The maximum dimensions that the cutting tools can reach around a work piece in a machining center is known as the work envelop; this term was first used in connection with industrial robots.Vertical-spindle machining centers, or vertical machining centers, are suitable for performing various machining operations on flat surfaces with deep cavities-for instance, mold and die making. A vertical-spindle machining center, which is similar to a vertical-spindle milling machining, is shown in Fig.4.7. The tool magazine is on the left of the figure and all operations and movements are directed and modified through the computer-control panel on the right.Because the thrust forces in vertical machining are directed downward, such machines have high stiffness and produce parts with good dimensional accuracy. These machines are generally less expensive than horizontal-spindle machines.48Horizontal-spindle machining centers, or horizontal machining centers, are suitable for larger as well as tall work piece that require machining on a number of their surfaces. The pallet can be swiveled on different axes(Fig.4.3)to various angular positions.Another category of horizontal-spindle machines is processing centers, which are computer-controlled lathes with several features. A three-turret computer numerical-controlled turning center is shown in Fig.4.8. This machine is designed with tow horizontal spindles and three turrets equipped with a variety of cutting tools used to perform several operations on a rotating work piece.Universal machining centers are equipped with both vertical and horizontal spindles. They have a variety of features and are capable of machining all surfaces of a work piece(vertical, horizontal, and diagonal).Characteristics and Capabilities of Machining CentersThe following are the major characteristics of machining centers:They are capable of handling a variety of part size and shapes efficiently, economically, and with repetitively high dimensional accuracy ;dimensional tolerances are on the order of 0.0025mm(0.0001in).The machines are versatile, having as many as six axes of linear and angular movements, and are capable of quick changeover from one type of product to another, so the need for a variety of machine tools and floor space is significantly reduced.The time required for loading and unloading work piece, changing tools, gaging, and troubleshooting is reduced, so productivity is improved, reducing labor requirements(particularly for skilled labor)and minimizing production costs.They are highly automated and relatively compact, so that one operator can attend two or more machines at the same time.The machines are equipped with tool-condition monitoring devices for the detection of tool breakage and wear, as well as probes for tool-wear compensation and for tool positioning.In-process and post-procwss gaging and inspection of machined work pieces are now features of machining center.Machining centers are available in a wide variety of size and features, and their costs range uo 75KW(100hp) and maximum spindle speeds are usually in the range of 4000-8000rpm; some are as high as 75000rpm for special applications using small-diameter cutters. Some pallets are capable of supporting work piece weighing as much as 7000kg(15000lb), although higher capacities are available for special applications.Many machines are now being constructed on a modular basis, as that various peripheral equipment and accessories can be installed and modified as the demand for different types of 49products changes.Because of the high productivity of machining centers, large amounts of chips are produced and must be controlled and disposed of properly several designs are available for chip collection, one example of which is shown in Fig.4.9. Note the two chip conveyors at the bottom of the cross-sectional view of a portion of a horizontal-spindle machining center. These particular converyors are of the spiral(screw) type; they collec chips along the two toughs and deliver them to a collection pint. Other systems may use chain-type conveyors.Machine-tool SelectionMachining centers can require significant capital expenditures, so to be cost effective, they generally have to be used for at least two shifts per day. Consequently, there must be sufficient and continued demang for products made in machining centers to justify this purchase. Because of their inherent versatility, however, machining centers can be used to produced a wide range of products, particularly with just-in-time manufacturing.The selection of the type and size of machining centers depends on several factors, among which are the following:The type of products, their size, and their shape complexityThe type of machining operations to be performed and the type and number of cutting tools requiredThe dimensional accuracy requiredThe production rate requiredAlthough versatility is the key factor in the selection of machining centers, these considerations must be weighed against the high captal investment requires and compared to the cost of manufacturing the same products using a number of more traditional machine tools.50附录 2中文译文CNCCNC 技术技术数控（NC）是可编程的自动化的一种形式。其加工设备由一系列的数字、字母和其他符号控制。这些数字、字母和符号被编成一定的格式，以便为一个特定的工步或者工作定义一个指令程序。当工作改变时，指令程序也随之改变。这种改变程序的能力使 NC适应小、中批量生产。编写新的程序要比大批量调换生产设备容易的多。NC 的基本组成部分的基本组成部分一个数控系统包括以三个组成部分： 指令编程 机械控制单元 加工设备三者之间的关系是：程序导入控制单元，控制单元直接指导加工设备的动作。指令程序是细化的一步步的命令，它控制加工设备。在它的一般形式中，命令涉及到机床主轴和放置工件的工作台的相对位置。许多先进的指令包含有选择主轴速度，切削工具等功能。程序编在一个适当的媒介中，再导入到控制单元中。在几十年前最常用的媒介是一英尺宽的穿孔纸带。由于穿孔纸带的广泛应用，NC 也叫做“纸带控制” 。现在磁带和软盘得到了广泛的应用。加工设备的 NC 系统的第三个基本组成部分。它是有效工作的执行部分。在许多数控的例子中，加工设备包括工作台、主轴和驱动和控制它们的设备。控制系统的种类控制系统的种类在 NC 中有两种基本控制类型：点到点和仿型定位。在点到点系统中（也叫做点定位），机床的每一个轴都单独驱动。为了减少不加工时间，机床一最大的速度运动。但刀具达到定位点时开始减速。因此在一个加工过程中，比如钻削或冲压，加工过程和回程独立完成。在孔被钻出或冲出后，刀具撤回，移动到另一个地方，继续下一次加工。从一点到另一点的路径在一个放面十分重要：为提高效率，所需时间必须最小。点定位主要用于钻削、虫牙和立式洗削加工。在仿型定位系统中（也被称为沿路径加工系统） ，定位和加工都沿着指定的路径，但速度不一样。因此刀具沿着指定的路径运动，速度和运动的同步精确控制十分重要。仿型定位系统用于车床、磨床、焊接机械和加工中心中。在几种基本方法之一的控制之下，刀具沿着路径发生微量的移动。在 NC 程序中，不同的刀具有不同的刀具补偿。为使仿型数控加工中有光滑的路径，开发了许多补偿方式用以处理这些问题。他们包括：51 直线插补 圆弧插补 螺旋插补 抛物线插补 三次曲线插补直线插补是最基本的。当仿型加工路线是直线时用到它。两轴和三轴直线插补在实际运用中有一定的区别，但概念上是一致的。程序需要指定直线的起点和终点，并指定沿直线的进给速度。为了得到指定的沿直线的进给速度，插补要计算出两轴（三轴）的每一轴的进给速度。如果要创建一个圆弧路径，直线插补是不合适的。因为程序需要指定圆弧和它们各自的终点。圆弧插补已经发展了。它允许路径的程序包含圆弧，这个圆弧由以下参数定义：终点坐标、圆弧中心坐标、半径和沿圆弧加工的方向。创造出的刀具路径包含一系列的直线线段，但这些线段由插补模型计算，而不是程序本身。刀具沿着每一条线段一条接一条的移动，加工出光滑的圆弧路径。圆弧插补的限制是圆弧存在的平面必须在一个由CNC 系统的二轴定义的平面内。螺旋插补使两轴描述的圆弧插补和第三轴的直线运动结合了起来。它允许在在三维空间里定义一个三维的路径。抛物线和三次曲线插补利用一个高阶方程提供一个复杂的自由曲线。它们通常需要很大的计算量，因此不如直线和圆弧插补常用。它们