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5. 机床夹具的发展
回顾夹具6的历史，它是来源于以大量生产为基础的呼唤性零件的加工。 夹具最早出现于1798年，当时作为大量生产方式的创造者而名列前茅的“惠特尼”公司接受了美国政府订购的三年间制造一万支步枪的合同，把原来靠手工操作的步枪枪管锻件，由一个人从头到尾制造下来的方式改为雇用熟练工人进行简单操作、制造，使用了一系列夹具，使5步枪按时交货。
继而在1853年“科尔特”根据互换性方式建造了大型兵工厂，据说把涉及1400台机床的大部分作成了专用机床，并花费与机械设备的数量相同的费用，消耗在制造刀具和夹具上。这样通过使用刀具和夹具才使制造有互换性的零件成为可能。同时还简化了操作，为后来向大量生产的发展准备了条件。
第二次世界大战时期，世界机床技术的发展在很大程度上受军火生产多影响，战前用于生产汽车、无线电、民用产品的大量技术，在战时广泛移用于军需品的产品。为了提高生产率，应付熟练技术工人的不足，机床夹具得到了更大的发展。1920年，世界第一部几少夹具的书籍在德国出版。
夹具从产生到现在，大约可分为以下三个阶段：第一阶段主要表现在夹具与人的结合上，这时夹具只是作为人的单纯的辅助工具，使加工过程加速和趋于完善，生产率得到提高；第二阶段，夹具成为人与机床之间的桥梁，夹具的技机能发生变化，它主要用于工件的定位和夹紧。人们越来越认识到，夹具与操作人员改进工件及机床性能的提高有着密切的关系，所以对夹具引起了重视；第三阶段表现为夹具与机床的结合，夹具作为机床的一部分,成为机械加工中不可缺少的工艺装备.夹具在机械加工中的作用已如前面所述.
在近几十年中,夹具的基本组成部分并无明显变化,但随着机械工艺的迅速发展,对产品品种和生产率提出了愈来愈高的要求,使多品种、中小批生产成为机械工业生产的主流,为了适应机械工业这种发展的趋势,必然对机床夹具提出更高的要求.它主要表现在如下几方面:
i. 机床夹具的“三化”工作
为了加速新产品的投产,简化设计工作,加速工艺装备的准备工作,以获取良好的技术经济效果,必须重视机床夹具的标准化、系列化和通用化工作.标准化是多样化、自动化的前提,世界许多国家不但制定了组合夹具的标准.苏联、美国、英国、民主德国、日
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本等国还制定了专用和通用可调夹具的标准.大大达到了夹具设计和制造的劳动量,为组织专用夹具零部件的集中大量生产创造了有利条件.
目前各国都在尽量减少专用夹具的比重，积极采用各类标准的通用夹具，逐渐扩大标准件、通用件的使用范围。 ii. 大力研制推广使用新型机床夹具
1.单件、小批生产或新产品试制中，应推广使用组合夹具和半组合夹具。 2.在多品种、中小批生产中，应大力推广使用可调夹具，尤其是成组夹具。 iii. 高夹具的机械化、自动化水平
提高生产率是社会生产的一项经常的、一贯的要求，近几十年来，高小、自动化夹具得到了迅速地发转，主要原因是，一方面由于书空机床、组合机床及其它高小自动化机床的出现，要求夹具能适应机床的要求，才能更好地发挥机床的作用。另一方面，由于采用高速强力切削，机动时间得到了响应地缩短，但劳动生产率并未因此得到明显地提高，其原因就在于辅助时间没有减少不多。因此，只有采用高小机械化与自动化夹具，才能使生产力厂得以进一步大幅度提高。 a)
制高精度机床夹具
目前，机械制造工艺普遍朝精密化的方向发展。对精度要求较高的零件，除选用精密的机床外，尚需采用一些精密的夹具。 b)
展计算机辅助机床夹具设计的眼界工作
为了提高机床家具设计的质量与书牍，在机床夹具亿个度微的标准化、系列化和通用化的基础上，过外已可以用计算机进行机床夹具的设计工作。计算机辅助机床夹具设计乃是整个计算机辅助设计（CAD）的一个组成部分。计算机辅助机床夹具设计可以做到：哟功能标准化的夹具元件组成的专用夹具的设计；用标准化、规格化的夹具基体和调整件组成的成组夹具的设计；组合夹具的组装设计。
用计算机辅助机床夹具设计的最主要优点就在于：用计算机控制设计程序，哟功能自动绘图机来自动进行绘图，大大加快了设计速度，大大加速了工艺准备工作，缩短了生产准备周期；同时在设计过程中，根据需要可在光笔图象显示仪上随时显示所设计的方案图象，并且可用光笔进行实地修改，以达到夹具设计的最佳化。 c)
开展机床夹具设计中有关问题的研究
除上面 谈到的一些问题在机床夹具设计中需要加以研究之外，还有一些问题需要进一步加强眼界，以便更好地设计机床夹具。这些问题有：夹具设计中误差（定位误差、
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夹紧误差等）的综合分析；高精度零件检验夹具设计；夹具磨损极限的合理制定；夹具设计与制造工时定额的确定；夹具最佳标准件的确定；夹具设计中的尺寸与形位公差以及其它技术条件的合理制定；成组夹具的精度分析；机床夹具科学管理方法的研究；夹具定位系统、夹紧系统等的最佳设计程序；夹具刚度问题（尤其是可调夹具、组合夹具）的研究等等。
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6.附录：
6.1 英文原文
Cams
Various motions can be produced by the action of a cam against a follower.Mamy timing devices are operated by can action.The purpose of andy cam is to produce a displacement of its follower;a secondary follower is often .used to produce additional displacement in another location.The most popular type is the plate cam.The cylindrical type is used to transmit linear motion to a follower as the cam rotates.Three-dimensional cam are sometimes used;these provide some unusual follower motions,but also make follower design difficult.The camshaft in the automotive engine illustrates a simple but important application of a late cam.The cam assemblies in automatic record players illustrate a somewhat more complex application.
Cam profiles are accurately constructed by either praphical or mathematical methods.The transitiom from development drawings to working (shop) drawing can be made in several ways:
1.Make a full-scale template.This is desirable from the manufacturing standpoint,but it will not guarantee accurate cam profiles.
2.Use radial dimensions.This is fairly accurate,but sometimes produces layout problems in the shop.
3.Use coordinate dimensioning.This procedure will ensure accuracy.
In selecring one of these methods,one should consider the function of the cam in terms of desired preciseness.
Because the cam work outline already determined, therefore the cam structural design mainly was determines the curve outline axial thickness and the cam and the drive shaft connection way. When the work load compares the hour, curve outline axial thickness generally takes for the outline curve biggest radius of vector 1,/10 ～/5; Regarding a stress bigger important situation, must with carry on the design according to the cam contour surface from the contact intensity.
When determination cam and drive shaft joint way, should synthesize the consideration
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cam the assembling and dismantling, the adjustment and firmly grades the question. Regarding implementing agency more equipment, between its each execution component movement coordination usually determined by the cycle of motion chart, therefore in assembly cam gear time, the cam contour curve initial station (pushes regulation starts) the relative position to have according to the cycle of motion chart to carry on the adjustment, guarantees each execution component to be able according to the pre-set sequence synchronized action. Therefore, requests the cam in the structural design to be able to be opposite to the drive shaft carries on the rotation along the circumference direction, and reliably performs fixedly. The simplest method uses the clamping screw nail fixed cam, or with clamping screw nail pre- fixed, after treats adjusts uses the pin to be fixed again. From structural design: from structure: When design must consider from the guidance and prevented revolves. From movement rule design: Involves many aspects from the movement rule design the questions, besides consideration rigidity impact and flexible impact, but also should maximum speed vmax which has to each kind of movement rule, maximum acceleration amax and its the influence performs the comparison. 1) vmax bigger, then momentum mv is bigger. If from is suddenly prevented, the oversized momentum can cause the enormous impulse, endangers the equipment and the personal safety. Therefore, when is bigger from the quality, in order to reduce the momentum, should choose the vmax value smaller movement rule. 2) amax bigger, is bigger. Function in high vice- contact place stress bigger, the organization intensity and the wear resistant request is also higher. Regarding high speed cam, in order to reduce the harm, should choose the amax value smaller movement rule. First states several kind of movements rules vmax, amax, the impact characteristic and the suitable situation following table regarding swings from the cam gear, its movement graph x-coordinate expression cam corner, y-coordinate then separately expresses from, angular speed and angle acceleration. This kind of movement graph has the state of motion and above is same.
From structural design: from structure: When design must consider from the guidance and prevented revolves. From movement rule design: The cam gear design basic question 1. cam gears type choice, the definite cam shape, with from maintains the high vice- contact from the shape and the movement form and the cam the way 2. from the movement rule
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