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1、数字控制的历史在机床领域工作的任何人都不能忽视计算机对制造业的影响。这些机床对工业的影响能力强迫公司经理和所有者更新他们的思想来保持竞争力。这些机床的固有准确性和反复性已经帮助了质量过程工具例如统计过程控制在金工车间获得立足处。NC/CNC机床的演变数字控制其实不是什么新东西。早在1808年织机装入带孔的金属卡片控制所生产布料的样式。机器的每根针由装入的卡上孔的有无来控制。卡片成为机器的程序。如果改变了卡片，样式也跟着改变。自动钢琴也是数字控制的例子。自动钢琴使用带孔的纸卷。孔的有无决定音符是否被演奏。空气被用于感应孔是否存在。计算机的发明是数字控制的一个转折点。1943年，称作ENIAC (
2、电子数字积分器和计算机)的第一台计算机被制成。ENIAC计算机非常大。它占地超过1500平方英尺并使用大约18,000根真空管运算。但真空管发热成为一个困扰的问题。计算机仅能运行几分钟管子就失效。另外，计算机重达数吨并非常难于编程。ENIAC通过使用数以万计的开关来编程。今天价值15美圆的计算器也远比这个早期的尝试更功能强大。计算机技术领域真正的转折点是1948年晶体管的发明。晶体管是真空管的替换品。它体积小，便宜，可靠，耗能少，并且发热低。真空管的完美取代品。直到20世纪60年代晶体管才在工业中大量使用。集成电路原件在1959年一种新技术涌现了：集成电路（ICs）。集成电路实际是芯片上的控制
3、电路。当制造商发现了如何小型化电路，它比晶体管更有助于减小尺寸和改进电子控制的可靠性。大规模集成电路大规模生产是在1965年。在1974年发明了微处理器。由此产生了微型计算机，使小规模运用成为可能。计算机记忆卡制造的巨大进步使它计算机更加功能强大而容易支付。作为政府生产高精度副翼的方法数控机床的原始构想源于20世纪50年代。这些复杂的零件用传统方法制造并且通过和模板作比较来检验它们。模板也必须用传统方法制造，是非常费时和不精确的。然而，在Michigan一个商店，一个叫做John Parsons的人正在研究一种新方法来改进直升机动叶片模板的制造方法。Parsons是工具室学徒而且没有大学学位。
4、Parson的方法是计算沿副翼表面的坐标点。通过计算大量的中间点然后移动机床到每个点，模板的精度就改进了。Parsons提出用穿孔的卡片来进行大量计算的主意。这些数据用来定位机床。1948年Parsons向空军递交发展生产这些模板的机器的提案并得到认同。他第一次试图在自动控制中使用穿孔卡制表机计算沿副翼曲线的方位并用普通铣床定位刀具到制表机位置。他有二名操作员，一个移动机器的每根轴。这种方法生产的副翼比先前方法高达十倍精度，但仍然是一个非常费时的过程。1949年，空军要求Parsons生产能移动机器的轴来自动计算点位置的一种控制系统。麻省理工学院(MIT)由Parsons转包来发展能控制机器轴
5、的马达。伺服电动机诞生了。Parsons构想了随后的系统。计算机能计算刀具应该遵循的轨迹并在穿孔卡上储存信息。机器的操作者能读出卡片。控制机器从操作者得到数据并控制附着在每根轴上的马达。1951年 MIT被授予开发控制机器的主要合同。第一台由Parsons和MIT生产的机器在1952年展出。叫做Cincinnati Hydrotel，它是一台三轴垂直心轴的铣床。这个控制机器使用真空管。在使人编程更容易的其中一个早期尝试叫做APT（自动编程工具）符号语言。APT，发明于1954年，使用机床能读懂的和英文相似的符号语言来编制程序。记住，机器需要零件的几何外型和例如速度、饲料和冷却液的机器指令来运行
6、。APT使人们写这些程序变得更容易，这些程序随后又被翻译成机器能读懂的另一种程序。1955年空军得到制造数控机器的35，000，000美圆的合同。第一台数控机床非常庞大。这个控制机器靠真空管运行并需要一个分开的计算机来生成它的二进制磁带代码。（二进制代码系统使用0和1）。复杂零件的编程需要非常专业的人员。随着继续的发展和提炼，60年代初期数字控制机器在工业中变得更加普通。数字控制机器广泛接受，它们变得更加功能强大和容易使用。直到大约1976年这些机器被称作NC（数字控制）机器。1976年CNC (计算机数字控制)机器出现了。这些控制机器使用微处理器给了他们额外的功能。他们也以外存储为特色。代表
7、性的NCs每次读取一步程序（块）并执行它；然而，CNC机床能够存储整个程序。20世纪70和80年代后期计算机技术的改善使数控机床的价格跌到一个很多制造公司不能再没有它们的水平。HISTORY OF NUMERICAL CONTROLAnyone working in the machine tool field cannot ignore the influence of the computer in manufacturing. The capabilities that these machine tools have given to the industry have forced
8、managers and owners of companies to update their thinking to stay competitive. The inherent accuracy and repeatability of these machine tools have helped quality process tools such as statistical process control gain a foothold in machine shops.EVOLUTION OF THE NC/CNC MACHINENumerical control is not
9、hing new. As early as 1808 weaving machines used metal cards with holes punched in them to control the pattern of the cloth being produced. Each needle on the machine was controlled by the presence or absence of a hole on the punched cards. The cards were the program for the machine. If the cards we
10、re changed, the pattern changed.The players piano is also an example of numerical control. The player piano uses a roll of paper with holes punched in it. The presence or absence of a hole determined if that note was played. Air was used to sense whether a hole was present.The invention of the compu
11、ter was one of the turning points in numerical control. In 1943 the first computer, called ENIAC (Electronic Numerical Integrator and Computer) was built.The ENIAC computer was very large. It occupied more than 1500 square feet and used approximately 18,000 vacuum tubes to do its calculations. The h
12、eat generated by the vacuum tubes was a constant problem. The computer could operate only a few minutes without a tube failing. In addition, the computer weighed many tons and was very difficult to program. ENIAC was programmed through the use of thousands of switches. The $15 calculator available t
13、oday is much more powerful than this early attempt.The real turning point in computer technology was the invention of the transistor in 1948. The transistor was the replacement for the vacuum tube. It was very small, cheap, dependable, used very little power, and generated very little heat: the perf
14、ect replacement for the vacuum tube. The transistor did not see much industrial use until the 1960s.INTEGRATED CIRCUITRYIn 1959 a new technology emerged: integrated circuits (ICs). Integrated circuits were actually control circuits on a chip. When manufacturers discovered how to miniaturize circuits
15、, it helped reduce the size and improve the dependability of electronic control even more than the transistor had. Large-scale integrated circuits first were produced in 1965.In 1974 the microprocessor was invented. This made the microcomputer, and thus small application, possible. Great strides in
16、the manufacture of memory for computers helped make computers more powerful and affordable.The original conception of numerically controlled machine tools occurred in the 1950s as a method of producing airfoils of great accuracy for the government.These complex parts were made by manual machining me
17、thods and inspected by comparing them to templates. The templates also had to be manufactured by manual methods, which was very time consuming and inaccurate.However, in a shop in Traverse City, Michigan, a man named John Parsons was working on a method to improve the production of inspection templa
18、tes for helicopter rotor blades. Parsons started as a tool room apprentice and had no college degree. Parsons method involved calculating the coordinate points along the airfoil surface. By calculating a large number of intermediate points and then manually moving the machine tool to each of these p
19、oints, the accuracy of the templates was improved. Parsons came up with the idea of using punched cards for the many calculations. The data could then be used to position the machine tool. Parsons submitted a proposal to the Air Force to develop a machine to produce these templates and received a de
20、velopment contract in 1948. His first attempts at automatic position control used punchcard tabulating machines to calculate the positions along the airfoil curve and an ordinary manual milling machine to position the tool to the tabulated positions. He had two operators, one to move each axis of th
21、e machine. This method produced airfoils tens of times more accurate than the preceding method, but was still a very time-consuming process.In 1949,the Air Force awarded Parsons a contract to produce a control system that could move the axis of a machine to calculated points automatically. The Massa
22、chusetts Institute of Technology (MIT) was subcontracted by Parsons to develop a motor that could control the axis of the machines. The servo motor was born.Parsons envisioned the following system. A computer would calculate the path that the tool should follow and store that information on punched
23、cards. A reader at the machine would then read the cards. The machine control would take the data from the reader and control the motors attached to each axis.In 1951 MIT was awarded the prime contract to develop the machine control. The first machine produced by Parsons and MIT was demonstrated in
24、1952. Called a Cincinnati Hydrotel, it was a three-axis vertical spindle milling machine. The machine control used vacuum tubes.One of the first attempts at making programming easier for people was called APT (Automatically Programmed Tool) Symbolic Language. APT, invented in 1954, used English-like
25、 symbolic language to produce a program that the machine tool could understand. Remember, a machine needs the geometry of the part and machining instructions such as speeds, feeds, and coolant to operate. APT made it easier for people to write these programs, which were then translated to a program
26、that the machine could understand.In 1955 the Air Force awarded $35million in contracts to manufacture numerical control machines. The first numerically controlled machine tools were very bulky. The machine control was vacuum-tube operated and needed a separate computer to generate its binary tape c
27、odes. (Binary coding systems use 1s and 0s). Programming complex parts took highly specialized people. Developments and refinements continued, and by the early 1960snumerical control machines became much more common in industry. As the acceptance of numerical control machines grew, they became easie
28、r to use and more powerful.Up until about 1976 these machines were called NC (numerical control) machines. In 1976 CNC (computer numerical control) machines were produced. These machine controls used microprocessors to give them additional capability. They also featured additional memory. The NCs ty
29、pically read one short program step (block) at a time and executed it; however, CNC machines could store whole programs.Improvements in computer technology in the late 1970s and 1980s brought the cost of numerical control machines down to a level where most manufacturing companies cannot afford to be without them.