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
2、年，称作 ENIAC (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 195
3、9 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 Parso
4、ns 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。 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。 19
5、49 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
6、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。 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
7、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 CONTROL Anyone working in the machine tool field cannot ignore t
8、he influence of the computer in manufacturing. The capabilities that these machine tools have given to the industry have forced 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 to
9、ols such as statistical process control gain a foothold in machine shops. EVOLUTION OF THE NC/CNC MACHINE Numerical control is nothing 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
10、 controlled by the presence or absence of a hole on the punched cards. The cards were the program for the machine. If the cards were 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 o
11、r absence of a hole determined if that note was played. Air was used to sense whether a hole was present. The invention of the computer 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 com
12、puter was very large. It occupied more than 1500 square feet and used approximately 18,000 vacuum tubes to do its calculations. The heat 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
13、tons and was very difficult to program. ENIAC was programmed through the use of thousands of switches. The $15 calculator available today 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 r
14、eplacement for the vacuum tube. It was very small, cheap, dependable, used very little power, and generated very little heat: the perfect replacement for the vacuum tube. The transistor did not see much industrial use until the 1960s. INTEGRATED CIRCUITRY In 1959 a new technology emerged: integrated
15、 circuits (ICs). Integrated circuits were actually control circuits on a chip. When manufacturers discovered how to miniaturize circuits, it helped reduce the size and improve the dependability of electronic control even more than the transistor had. Large-scale integrated circuits first were produc
16、ed in 1965. In 1974 the microprocessor was invented. This made the microcomputer, and thus small application, possible. Great strides in the manufacture of memory for computers helped make computers more powerful and affordable. The original conception of numerically controlled machine tools occurre
17、d in the 1950s as a method of producing airfoils of great accuracy for the government. These complex parts were made by manual machining methods and inspected by comparing them to templates. The templates also had to be manufactured by manual methods, which was very time consuming and inaccurate. Ho
18、wever, in a shop in Traverse City, Michigan, a man named John Parsons was working on a method to improve the production of inspection templates for helicopter rotor blades. Parsons started as a tool room apprentice and had no college degree. Parsons method involved calculating the coordinate points
19、along the airfoil surface. By calculating a large number of intermediate points and then manually moving the machine tool to each of these points, 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 t
20、o position the machine tool. Parsons submitted a proposal to the Air Force to develop a machine to produce these templates and received a development contract in 1948. His first attempts at automatic position control used punchcard tabulating machines to calculate the positions along the airfoil cur
21、ve and an ordinary manual milling machine to position the tool to the tabulated positions. He had two operators, one to move each axis of the 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 For
22、ce awarded Parsons a contract to produce a control system that could move the axis of a machine to calculated points automatically. The Massachusetts 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. P
23、arsons envisioned the following system. A computer would calculate the path that the tool should follow and store that information on punched 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
24、. In 1951 MIT was awarded the prime contract to develop the machine control. The first machine produced by Parsons and MIT was demonstrated in 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
25、 making programming easier for people was called APT (Automatically Programmed Tool) Symbolic Language. APT, invented in 1954, used English-like 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 that the machine could understand.
