附录科技译文：Numerical ControlNumerical Control(NC) is a method of controlling the movements of machineComponents by directly inserting coded instructions in the form of numerical data(numbers and data ) into the system.The system automatically interprets these data and converts to output signals. These signals ,in turn control various machine components ,such as turning spindles on and off ,changing tools,moving the work piece or the tools along specific paths,and turning cutting fluits on and off.In order to appreciate the importer of numerical control of machines ,let’s briefly review how a process such as machining has been carried out traditionally .After studying the working drawing of a part, the operator sets up the appropriate process parameters(such as cutting speed ,feed,depth of cut,cutting fluid ,and so on),determines the sequence of operations to be performed,clamps the work piece in a workholding device such as chuck or collet ,and proceeds to make the part .Depending on part shape and the dimensional accuracy specified ,this approach usually requires skilledoperators.Furthermore,the machining procedure followed may depend on the particular operators,and because of the possibilities of human error, the parts produced by the same operator may not all be identical .Part quality may thus depend on the particular operator or even the same operator on different days or different hours of the day. Because of our increased concern with product quality and reducing manufacturing costs,such variability and its effects on product quality are no longer acceptable this situation can be dliminated by numerical control of the mathining operation.We can illustrate the importance of numerical concrol by the following example. Asume that holes have to be drilled on a part in the positions shown in the picture.In the traditional manual method of machining thid part, the operator positions the drill with respect to the workpiece, using as erfererence points any of the three of the method shown. The operator then proceeds to drill these holes. Let,s assume that 100 parts, having exactly the same shape and dimensional accuracy, have to be dielled. Obviously, this operation is going to be tediious because the operator has to go throuth the same motions again and again. Moreover, the probabiluty is high that, faor warious reasons, some of the paths machined will be different fromorthers. Let`s further assume that during this production run, the order for these paths is changed, so that 10 of the paths now require holes in difficult positions. The machinisst now has to reset the mathine , wehich will be time consuming and subject to error. Such operations can be perfomedeasily by numerical conctrol machines that are capable of producing parts reeatedly and accurately and of handling differeent parts by simply londing differeent part programs.In numerical control ,data concerning all aspects of the machining operation,such as locations ,speeds,and cutting fluid,are stored on magnetic tape.,cassettes ,floppy or hard disks,or paper or plastic(Mylar,which is a thermoplastic polyester)tape,.Date are stored on punched 25 mm wide paper or plastic tape ,as originally developed and still used .The concept of NC control is that holes in the tape represent specific information in the form of alphanumeric codes ,The presence (on)or absence (off),of these holes is read by sensing devices in the contuol panel ,which then actuate relays and other devices (called hard-wired contuols),These devices control various mechanical and electrical system in the machine .This method eliminnated manual setting of machine positions and tool paths or the use of templates and othermechanical guides and devices. Conplex operations,such as turning a part having various contours and die sinking in milling machine ,can be carried out.Numerical control has had a major impact on all aspects of manufacturing operations.It is a widely applied technology ,particularly in the following areas:a)Machining centersb)Milling,turning,boring,drilling,and gringingc)Electrical-discharge,laser-beam,and electron-beam machiningd) Water-jet cuttinge) Punching and nibbling .f) Pipe bending and metal spinning.g) Sopt welding and metal spinning.h) Assembly operations.Numerical control machines are now used extensively in small-and-medium-quantity(typically 500 parts or less)of a wide variety of parts in small shops and large manufacture facilities. Older machines can be retrofitted with numerical control.Advantages and Limitations Numerical control has following advantages over conventional method of machine control:1.Flexibility of operation and ability to produce complex shape with good dimensional accuracy,repeatability,reduced scrap loss,and high production rates ,productivity,and product quality.2.Tooling costs are reduced,since templates and other fixtures are not required.3.Machine adjustments are easy to make with minicomputer and digital readout.4.More operations can be performed with each setup,and less lead time for setup and machining is required compared to conventional methods.Design changes are facilitated,and inventory is reduced.5.Programs can prepared rapidly and can be recalled at any time utilizing microprocessors,Less paperwork is involved.6.Faster prototype productiong is possible.7.Required operator skill is less,and the operator has more time to attend to other tasks in the work area.The major limitations of NC are the relatively high cost of the equipment and the need for programming and specialmaintenance,requiring trained personal.Because NC machines are complex systems,breakdowns can be very costly,so preventive maintenance is essential.However,these limitations are often easily outweighed by the overall economic advantages of NC.One of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control(NC) Controlling a machine tool using a punched tape or stored program is known as numerical control (NC).NC has been defined by the ElectronicIndustries.Association(EIA)as "a system in which actions are controlled by the direct insertion of numerical data at some point.The numerical data at some point.The numerical data required to produce a part is known as a part program.A numerical control machine toll system contains a machine control unit(MCU) and the machine tool itself(Fig2.16)The MCU is further divided into two elements:The data processing unit(DPU)and the control loops unit (CLU). The DPU processes the code data from the tape or other media and passes information on the position of each axis,required direction of motion,feed rate, and auxiliary function control signals to the CLU. The CLU operates the drive mechanisms ofeach of the axes and signals the completion of operation.The DPU sequentially reads the data.When each line has completed execution of operation.The DPU sequentially read thedata.When each line has completed execution as noted by the CLU,another line of data is read.A data processing unit consists of some or all of the following parts:1)Data input device such as a paper tapereader,RS232-C port,etc2)Data-reading circuits and parity-checking logic3)Decoding circuits for distributing data among the controlled axes4)An interpolator,which supplies machine-motion commands between data points for tool motionA control loops unit,on the other hand consists of the following:1)Position control loops for all the axes ofmotion,where ach axis has a separate control loop2)Velocity control loops,where feed control is required3)Deceleration and backlash take up circuits4)Auxiliary functions control,such as coolanton/off,gear changes,spindle on/off controlGeometric and kinematics data are typically fed from the DPU to the CLU.The CLU then governs the physical system based on the data form the DPU.Numerical control was developed to overcome the limitation of human operators,and it has done so.Numerical control machines are more accurate than manually operated machines,they can produce parts more uniformly,they are faster,and the long-run tooling costs are lower.The development of NC led to the development of several Other innovations in manufacturing technology ;Electic discharge machiningLaser—cutingElectron beam weldingNumerical control has also made maching tools more versatile their manually operated predecessors . An NC machine tool can automatically produce a wide variety of parts ,each involving an assortment of widely varied and complex machining processes . Numerical control has allowed manufacturers to undertaken the production of part ,each involving an assortment of widely varied and complex machining processes .Numerical control has allowed manufactures to undertaken the production of products thatwould not have been feasible from an economic perspective using manually controlled machine tools and processes.翻译：数字控制数控是一种用数字控制机床各部件运动的方法，通过直接向系统输入指令代码（数字和字母)完成的。