机械类数控外文翻译外文文献英文文献数控.docx
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1、编号:时间:2021 年 x 月 x 日书山有路勤为径,学海无涯苦作舟书山有路勤为径,学海无涯苦作舟页码:第1页 共10页第 1 页 共 10 页Numerical ControlOne of the most fundamental concepts in the area of advanced manufacturingtechnologies is numerical control(NC).Prior to the advent of NC,all machine tools weremanual operated and controlled.Among the many limi
2、tations associated with manual controlmachine tools,perhaps none is more prominent than the limitation of operator skills.Withmanual control,the quality of the product is directly related to and limited to the skills of theoperator.Numerical control represents the first major step away from human co
3、ntrol ofmachine tools.Numerical control means the control of machine tools and other manufacturing systemsthough the use of prerecorded,written symbolic instructions.Rather than operating a machinetool,an NC technician writes a program that issues operational instructions to the machinetool,For a ma
4、chine tool to be numerically controlled,it must be interfaced with a device foraccepting and decoding the p2ogrammed instructions,known as a reader.Numerical control was developed to overcome the limitation of human operator,and ithas done so.Numerical control machines are more accurate than manuall
5、y operatedmachines,they can produce parts more uniformly,they are faster,and the long-run toolingcosts are lower.Thedevelopment of NC led to the development of several otherinnovations in manufacturing technology:1.Electrical discharge machining.2.Laser cutting.3.Electron beam welding.Numerical cont
6、rol has also made machine tools more versatile than their manuallyoperated predecessors.An NC machine tool can automatically produce a wide variety ofpar4s,each involving an assortment of undertake the production of products that would nothave been feasible from an economic perspective using manuall
7、y controlled machine toolsand processes.Like so many advanced technologies,NC was born in the laboratories of theMassachusetts Institute of Technology.The concept of NC was developed in the early 1950swith funding provided by the U.S Air Force.In its earliest stages,NC machines were able tomake stra
8、ight cuts efficiently and effectively.However,curved pathswere a problem because the machine tool had to beprogrammed to undertake a series of horizontal and vertical steps to produce a curve.Theshorter is the straight lines making up the step,the smoother is 4he curve.Each line segmentin the steps
9、had to be calculated.This problem led to the development in 1959 of the Automatically Programmed Tools(APT)language for NC that uses statements similar to English language to define the partgeometry,describe the cutting tool configuration,and specify the necessary motions.Thedevelopment of the APT l
10、anguage was a major step forward in the further development of NCtechnology.The original NC system were vastly different from those used punched paper,which was later to replaced by magnetic plastic tape.A tape reader was used to interpret theinstructions written on the tape for the machine.Together
11、,all/f this represented giant stepforward in the control of machine tools.However,there were a number of problems with NC编号:时间:2021 年 x 月 x 日书山有路勤为径,学海无涯苦作舟书山有路勤为径,学海无涯苦作舟页码:第2页 共10页第 2 页 共 10 页at this point in its development.A major problem was the fragility of the punched paper tape medium.It was
12、 commonfor the paper containing the programmed instructions to break or tear during a machiningprocess,This problem was exacerbated by the fact that each successive time a part wasproduced on a machine tool,the paper tape carrying the programmed instructions had to rerunthought the reader.If it was
13、necessary to produce 100 copies of a given part,it was alsonecessary to run the paper tape thought the reader 100 separate times.Fragile paper tapessimply could not withstand the rigors of shop floor environment and this kind of repeated use.This led to the development of a special magnetic tape.Whe
14、reas the paper tape carriedthe programmed instructions as a series of holes punched in the tape,theThis most importantof 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 instructions,it was necessary
15、tointerrupt machining operations and make a new tape.It was also still necessary to run the tapethought the reader as many times as there were parts to be produced.Fortunately,computertechnology become a reality and soon solved the problems of NC,associated with punchedpaper and plastic tape.The dev
16、elopment of a concept known as numerical control(DNC)solve the paper andplastic tape problems associated with numerical control by simply eliminating tape as themedium for carrying the programmed instructions.In direct numerical control,machine toolsare tied,via a data transmission link,to a host co
17、mputer and fed to the machine tool as neededvia the data transmission linkage.Direct numerical control represented a major step forwardover punched tape and plastic tape.However,it is subject to the same limitation as alltechnologies that depend on a host computer.When the host computer goes down,th
18、emachine tools also experience down time.This problem led to the development of computernumerical control.The development of the microprocessor allowed for the development of programmablelogic controllers(PLC)and microcomputers.These two technologies allowed for thedevelopment of computer numerical
19、control(CNC).With CNC,each machine tool has a PLCor a microcomputer that serves the same purpose.This allows programs to be input and storedat each individual machine tool.CNC solved the problems associated downtime of the hostcomputer,but it introduced another problem known as data management.The s
20、ame programmight be loaded on ten different microcomputers with no communication among them.Thisproblem is in the process of being solved by local area networks that connectDigital SignalProcessorsThere are numerous situations where analog signals to be processed in many ways,likefiltering and spect
21、ral analysis,Designing analog hardware to perform these functions ispossible but has become less and practical,due to increased performance requirements,flexibility needs,and the need to cut down on development/testing time.It is in other wordsdifficult pm design analog hardware analysis of signals.
22、The act of sampling an signal into thehat are specialised for embedded signal processingoperations,and such a processor is called a DSP,which stands for Digital Signal Processor.Today there are hundreds of DSP families from as many manufacturers,each one designed fora particular price/performance/us
23、age group.Many of the largest manufacturers,like Texas编号:时间:2021 年 x 月 x 日书山有路勤为径,学海无涯苦作舟书山有路勤为径,学海无涯苦作舟页码:第3页 共10页第 3 页 共 10 页Instruments and Motorola,offer both specialised DSPsfor certain fields like motor-controlor modems,and general high-performance DSPs that can perform broad ranges of process
24、ingtasks.Development kits an software are also available,and there are companies makingsoftware development tools for DSPs that allows the programmer to implement complexprocessing algorithms using simple“drag ndrop”methodologies.DSPsmoreorlessfallintotwocategoriesdependingontheunderlyingarchitectur
25、e-fixed-point and floating-point.The fixed-point devices generally operate on16-bit words,while the floating-point devices operate on 32-40 bits floating-point words.Needless to say,the fixed-point devices are generally cheaper.Another importantarchitectural difference is that fixed-point processors
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