【文章內(nèi)容簡介】 ies 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 magic plastic tape. Whereas the paper tape carried the progtammed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magic dots. The plastic tape was much stronger than the paper tape, 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 instuctions,it was necessary to interrupt machining operations and make a new tape. It was also still necessary to run the tape though the reader as many times as there were parts to be produced. Fortunately, puter technology became a reality and soon solved the problems of NC asociated with punched paper and plastic tape. 機械專業(yè)中英文文獻翻譯 The devslopment 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 puter. Programs for operating the machine tools are stored in the host puter 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 puter. When the hoet puter goes down, the machine tools also experience downtime. This problem led to the development of puter numerical control. The development of the microprocessor allowed for the development of programmable logic controllers (PLCs) and microputers. These two technologies allowed for the development of puter of puter numerical control (CNC). Whit CNC, each machine tool has a PLC or a microputer that serves the same purpose. This allows programs to be input and stord at each individual machine tool. It also allows programs to be devsloped offline and downloaded at the individual machine tool. CNC solved the probiems associated with downtime of the host puter, but it introduced another problem known as data management. The same program might be loaded on ten different microputers with no munication among them. This problem is in the process of being solved by local area works that connect microputers for better data management. 三 、 Programmers Skillful partprogrammers are a vital requirement for effective utilization of NC machine tools. Upon their efficiency of those machines and the financial payback of the significant investment in the machines themselves, the piant’s NCsupport facilities, and the overhead costs involved. Skillful NC partprogrammers are scarce. This reflects not only the general shortage of experienced people in the meyalworking industries but also the increasing demand for programmers as industry turns more to the use of numerically controlled machines to increase the capability, versaility, and productivity of manufacturing. On an industrywide basis,the obvious answer is to create new programmers by training themand there are a number of sources for such training. But first,what qualifications should programmers have, and what must programming trainees learn? According to the National Machine Tool Builder’s Assn booklet ―Selecting an Appropriate NC programming Method,‖the principal qualifications for manual programmers are as follows: Manufacuring Experience Programmers must have a thorough understading of the capabilities of the NC machines being programmed, as well as an understanding of the basic capabilities of the other machines in the shop. They must have an extensive knowledge of, and sensitivity to, metalcutting principles and practices and practices, cutting capabilities of the tools, and workholding fixtures and techniques. Programmers properly trained in these manufacturingengineering techniques can significantly reduce production costs. Spatial Visualization Programmers must be able to visualize parts in there dimensions, the cutting motions of the machine, and potential interferences bet