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1、The Development of numerical controlThe evolution of the machine tool industry could hardly be appreciated without a brief review of its birth and growth. John Wilkinson built his metal-cutting boring machine in the eighteenth century, but nearly two centuries of evolution were needed to produce the
2、 hydraulic tracer controlled copy mills and lathes. The next stare, automation, was brought about by mass production of automobiles, agricultural implements, household appliances, chemical products, as well as inventory and financial data handling. Three kinds of automation met the needs of society
3、for a major part of the twentieth century. There were:1)Automotive or fixed assembly line automation.2)Process control automation, primarily used in the manufacture of chemical and food products.3)Data processing first developed for processing payrolls, data collection, and inventory control.The Sec
4、ond World War marked the turning point in the ability of the metal-cutting industry to cope with the requirements facing it. The ambitious aircraft and missile projects of the U.S. air force, combined with the demands for commercial jets, made it quite clear that conventional manufacturing could not
5、 fulfill future needs. A study of the U.S. government showed that the combined resources of the entire U.S. metal-cutting industry in 1947 could not produce the parts needed by the air force along.Under contract to the U.S. air force，the Parsons Corporation under took the development of a flexible,
6、dynamic manufacturing system, designed to maximize productivity by emphasizing details required to achieve desired accuracies. This system would allow design changes without costly modifications to tooling and fix Turing, and it would fit in to modern, productive manufacturing management for small-t
7、o-medium-sized production runs. The Parsons Corporation subcontracted the development of the control system to the Massachusetts Institute of Technology in 1951. A control, which would be applicable to a wide variety of machine tools, would drive a slide lead screw through an interface, as instructe
8、d by the out put of a computer. MIT met the challenge successfully, and in 1952 demonstrated a Cincinnati Hydrotel milling machine equipped with the new technology, which was named Numerical Control (NC) and used a prepunched tape as the input media. Since 1952, practically every machine tool manufa
9、cturer in the Western world has converted part or all of its product to NC.The first NC machines used vacuum tubes, electrical relays, and complicated machine-control interfaces. The second generation of machines utilized improved miniature electronic tubes, and later solid-state circuits. As comput
10、er technology improved, NC underwent one of the most rapid changes known in history. The third generation used much improved integrated circuits. Computer hardware became progressively less expensive and more reliable and NC control builders introduced for the first time Read Only Memory (ROM) techn
11、ology. ROM was typically used for program storage in special-purpose application, leading to the appearance of the computer numerical control (CNC) system. CNC was successfully introduced to practically every manufacturing process. Drilling, milling, and turning to were performed on “machining centr
12、e” and “turning centre.” CNC took over glass cutting, pattern making, electrical discharge machining, steel-mill roll grinding, and coordinate measuring electron beam welding， Tube bending, drafting, printed circuit manufacturing, coil winding functional testing, robots, and many other processes. A
13、set of preprogrammed subroutines, named canned cycles, were developed for use in routine operations. They were recorded into the ROMs and remained there even after power was shut off. For the first time, this concept made it possible to read the machining program into memory and to operate the machi
14、ne from memory. In addition to the advantages of editing, the problems caused by erroneous tape reading disappeared. Along with the many canned cycle option, CNC builders introduced displays for visual editing of part programs in memory. Various in-cycle problems generated alarms and hundreds of dia
15、gnostic messages which could be displayed as applicable. Practically every function of the machine was tired into the system and monitored during operation. A constant surface speed control was incorporated and continuously anticipated the most efficient spindle speed for the next cut to minimize ti
16、me lost for spindle acceleration. The conventional linear and circular interpolation in cartesian (rectangular) coordinates were supplemented by polar coordinates and helical internal parameters, created an electronic crash barrier to prevent tool collision the latter group features marked the arrival of high technology to the manufacturing or metal-cutting industry.The improvement in drives was important for the system as the contribution of the microprocessor or the minico
