数控技术发展趋势外文文献翻译、中英文翻译

1、 The development trend of the numerical control technology1. NUMERICAL CONTROLNumerical control(NC)is a form of programmable automation in which the processing equipment is controlled by means of numbers，letters，and other symbolsThe numbers，letters，and symbols are coded in an appropriate format to d

2、efine a program of instructions for a particular workpart or jobWhen the job changes，the program of instructions is changedThe capability to change the program is what makes NC suitable for low-and medium-volume productionIt is much easier to write programs than to make major alterations of the proc

3、essing equipmentThere are two basic types of numerically controlled machine tools：pointtopoint and continuouspath(also called contouring)Pointtopoint machines use unsynchronized motors，with the result that the position of the machining head Can be assured only upon completion of a movement，or while

4、only one motor is runningMachines of this type are principally used for straightline cuts or for drilling or boring The NC system consists of the following components：data input，the tape reader with the control unit，feedback devices，and the metalcutting machine tool or other type of NC equipmentData

5、 input，also called“mantocontrol link”，may be provided to the machine tool manually，or entirely by automatic meansManual methods when used as the sole source of input data are restricted to a relatively small number of inputsExamples of manually operated devices are keyboard dials，pushbuttons，switche

6、s，or thumbwheel selectorsThese are located on a console near the machineDials ale analog devices usually connected to a syn-chro-type resolver or potentiometerIn most cases，pushbuttons，switches，and other similar types of selectors aye digital input devicesManual input requires that the operator set

7、the controls for each operationIt is a slow and tedious process and is seldom justified except in elementary machining applications or in special casesIn practically all cases，information is automatically supplied to the control unit and the machine tool by cards，punched tapes，or by magnetic tapeEig

8、htchannel punched paper tape is the most commonly used form of data input for conventional NC systemsThe coded instructions on the tape consist of sections of punched holes called blocksEach block represents a machine function，a machining operation，or a combination of the twoThe entire NC program on

9、 a tape is made up of an accumulation of these successive data blocksPrograms resulting in long tapes all wound on reels like motion-picture filmPrograms on relatively short tapes may be continuously repeated by joining the two ends of the tape to form a loopOnce installed，the tape is used again and

10、 again without further handlingIn this case，the operator simply loads and unloads the partsPunched tapes ale prepared on type writers with special tapepunching attachments or in tape punching units connected directly to acomputer systemTape production is rarely error-freeErrors may be initially caus

11、ed by the part programmer，in card punching or compilation，or as a result of physical damage to the tape during handling，etcSeveral trial runs are often necessary to remove all errors and produce an acceptable working tape While the data on the tape is fed automatically，the actual programming steps a

12、le done manuallyBefore the coded tape may be prepared，the programmer，often working with a planner or a process engineer, must select the appropriate NC machine tool，determine the kind of material to be machined，calculate the speeds and feeds，and decide upon the type of tooling needed. The dimensions

13、 on the part print are closely examined to determine a suitable zero reference point from which to start the programA program manuscript is then written which gives coded numerical instructions describing the sequence of operations that the machine tool is required to follow to cut the part to the d

14、rawing specificationsThe control unit receives and stores all coded data until a complete block of information has been accumulatedIt then interprets the coded instruction and directs the machine tool through the required motionsThe function of the control unit may be better understood by comparing

15、it to the action of a dial telephone，where，as each digit is dialed，it is storedWhen the entire number has been dialed，the equipment becomes activated and the call is completedSilicon photo diodes，located in the tape reader head on the control unit，detect light as it passes through the holes in the m

16、oving tapeThe light beams are converted to electrical energy，which is amplified to further strengthen the signalThe signals are then sent to registers in the control unit, where actuation signals are relayed to the machine tool drivesSome photoelectric devices are capable of reading at rates up to 1

17、000 characters per secondHigh reading rates are necessary to maintain continuous machinetool motion；otherwise dwell marks may be generated by the cutter on the part during contouring operationsThe reading device must be capable of reading data blocks at a rate faster than the control system can proc

18、ess the dataA feedback device is a safeguard used on some NC installations to constantly compensate for errors between the commanded position and the actual location of the moving slides of the machine toolAn NC machine equipped with this kind of a direct feedback checking device has what is known a

19、s a closed-loop systemPositioning control is accomplished by a sensor which，during the actual operation，records the position of the slides and relays this information back to the control unitSignals thus received ale compared to input signals on the tape，and any discrepancy between them is automatic

20、ally rectifiedIn an alternative system，called an openloop system，the machine is positioned solely by stepping motor drives in response to commands by a controllersThere are three basic types of NC motions, as follows: Point-to-point or Positional Control In point-to-point control the machine tool el

21、ements (tools, table, etc.) are moved to programmed locations and the machining operations performed after the motions are completed. The path or speed of movement between locations is unimportant; only the coordinates of the end points of the motions are accurately controlled. This type of control

22、is suitable for drill presses and some boring machines, where drilling, tapping, or boring operations must be performed at various locations on the work piece. Straight-Line or Linear Control Straight-Line control systems are able to move the cutting tool parallel to one of the major axes of the mac

23、hine tool at a controlled rate suitable for machining. It is normally only possible to move in one direction at a time, so angular cuts on the work piece are not possible, consequently, for milling machines, only rectangular configurations can be machined or for lathes only surfaces parallel or perp

24、endicular to the spindle axis can be machined. This type of controlled motion is often referred to as linear control or a half-axis of control. Machines with this form of control are also capable of point-to-point control.Continuous Path or Contouring Control In continuous path control the motions o

25、f two or more of the machine axes are controlled simultaneously, so that the position and velocity of the can be tool are changed continuously. In this way curves and surfaces can be machined at a controlled feed rate. It is the function of the interpolator in the controller to determine the increme

26、nts of the individual controlled axes of the machines necessary to produce the desired motion. This type of control is referred to as continuous control or a full axis of control.Some terminology concerning controlled motions for NC machines has been introduced. For example, some machines are referr

27、ed to as four-or five-or even six-axis machines. For a vertical milling machine three axes of control are fairly obvious, these being the usual X, Y, Z coordinate directions. A fourth or fifth axis of control would imply some form of rotary table to index the work piece or possibly to provide angula

28、r motion of the work head. Thus, in NC terminology an axis of control is any controlled motion of the machine elements (spindles, tables, etc). A further complication is use of the term half-axis of control; for example, many milling machines are referred to as 2.5-axis machine. This means that cont

29、inuous control is possible for two motions (axes) and only linear control is possible for the third axis. Applied to vertical milling machines, 2.5axis control means contouring in the X, Y plane and linear motion only in the Z direction. With these machines three-dimensional objects have to be machi

30、ned with water lines around the surface at different heights. With an alternative terminology the same machine could be called a 2CL machine (C for continuous, L for linear control). Thus, a milling machine with continuous control in the X, Y, Z directions could be termed be a three-axis machine or

31、a 3c machine, Similarly, lathes are usually two axis or 2C machines. The degree of work precision depends almost entirely upon the accuracy of the lead screw and the rigidity of the machine structureWith this systemthere is no self-correcting action or feedback of information to the control unitIn t

32、he event of an unexpected malfunction，the control unit continues to put out pulses of electrical currentIf，for example，the table on a NC milling machine were suddenly to become overloaded，no response would be sent back to the controllerBecause stepping motors are not sensitive to load variations，man

33、y NC systems are designed to permit the motors to stall when the resisting torque exceeds the motor torqueOther systems are in use，however，which in spite of the possibility of damage to the machine structure or to the mechanical system，ale designed with special hightorque stepping motorsIn this case

34、，the motors have sufficient capacity to“overpowerthe system in the event of almost any contingency The original NC used the closedloop systemOf the two systems，closed and open loop，closed loop is more accurate and，as a consequence，is generally more expensiveInitially，openloop systems were used almos

35、t entirely for light-duty applications because of inherent power limitations previously associated with conventional electric stepping motorsRecent advances in the development of electro hydraulic stepping motors have led to increasingly heavier machine load applications2.NC technology development t

36、rends2.1 NC system developments at home and abroad With the rapid development of computer technology, the traditional beginning of a fundamental change manufacturing, the industrial developed countries spent huge sums of money on the modern manufacturing technology research and development, to creat

37、e a new model. In modern manufacturing systems, CNC technology is the key to technology, which combines microelectronics, computers, information processing, automatic detection, automatic control, such as the integration of advanced, a high-precision, high-efficiency, flexible automation, and other

38、characteristics, the manufacturing industry Flexible automation, integrated, intelligent play the pivotal role. At present, NC technology is undergoing a fundamental change, from a special closed-loop control mode to general-purpose real-time dynamic open all closed-loop control mode. In the integra

39、ted on the basis of the CNC systems ultra-thin, ultra-light; on the basis of the intelligent, integrated computers, multimedia, fuzzy control, neural network and other technical disciplines, NC system to achieve high-speed, high-precision, Efficient control, automatic processing can be amended to re

40、gulate compensation and the parameters for an online intelligent fault diagnosis and treatment of the network based on the CAD / CAM and CNC systems integration as one machine network, makes the central government centralized control of the group control processing. The application of the technology

41、 of numerical control has not only brought the revolutionary change to traditional manufacturing industry, make the manufacturing industry become the industrialized symbol , and with the constant development of the technology of numerical control and enlargement of application, the development of he

42、 some important trades (IT , car , light industry , medical treatment ,etc. ) to the national economy and the peoples livelihood plays a more and more important role, because these trade necessary digitization that equipped has already been the main trend of modern development.For a long time, China

43、s CNC system for traditional closed architecture, but only as a non-intelligent CNC machine controller. Process variables based on experience in the form of pre-fixed parameters, processing procedures before the actual processing by hand or through CAD / CAM and automatic programming system prepared

44、. CAD / CAM and CNC have no feedback control link, the entire manufacturing process CNC is a closed ring-opening implementing agencies. In a complex and changing environment under the conditions of processing tool in the process of composition, workpiece material, spindle speed, feed rate, tool path

45、, cutting depth, step, allowance and other processing parameters, not at the scene circumstances under external interference and real-time dynamic random factors, not by random amendment feedback control link CAD / CAM settings volume, in turn, affect the work of CNC machining efficiency and product

46、 quality. Clearly, the traditional fixed CNC system that controlled mode and closed architecture, limiting the CNC to the development of more intelligent control variables, can no longer meet the increasingly complex manufacturing process, therefore, the CNC technology in the potential for change in

47、evitable. The technology of numerical control of our country started in 1958, the development course in the past 50 years can roughly be divided into 3 stages: The first stage is from 1958 to 1979, i.e. closed developing stage. In this stages, technology of foreign countries blockade and basic restr

48、iction of terms of our country, the development of the technology of numerical control is comparatively slow. During Sixth Five-Year Plan Period , the Seventh Five-Year Plan Period of the country in second stage and earlier stage in the Eighth Five-Year Plan Period , introduce technology , digest an

49、d assimilate, the stage of establishing the system of production domesticization arisesing tentatively. At this stage , because of reform and opening-up and national attention , and study the improvement of the development environment and international environment, research , development and all mak

50、ing considerable progress in production domesticization of the products of the technology of numerical control of our country. The third stage is that on the later stage in the Eighth Five-Year Plan Period of the country and during the Ninth Five-Year Plan Period , implement the research of industri

51、alization , enter market competition stage. At this stage, made substantive progress in industrialization of the domestic numerical control equipment of our country. In the Ninth Five-Year Plan latter stage, domestic numerical control domestic market share of lathe reach 50% , mix domestic numerical

52、 control system (popular ) to up to 10%. Review the development course in the past 50 years of technology of numerical control of our country, especially pass the brainstorm of 4 Five-Year Plans, all in all has made following achievements.a. Have establish the foundation of the technical development

53、 of numerical control, has basically mastered the technology of modern numerical control. Our country know from numerical control system , servo urge , numerical control host computer , special plane and their basic of fittings basically already now, among them most technology have already possessed

54、 the foundation that is commercialized and developed , some technology has already, industrialization commercialized.a.Have formed the industrial base of numerical control tentatively. In tackling key problems the foundation that the achievement and some technology commercialize , set up the systema

55、tic factories of numerical control with production capacity of batch such as numerical control of Central China , spaceflight numerical control etc. Electrical machinery plant of Lanzhou, a batch of servo systems and first machine tool plant , first machine tool plant of Jinan of servo electrical ma

56、chinery factory and Beijing ,etc. several numerical control host computer factories such as the numerical control in Central China. These factories have basically formed the numerical control industrial base of our country.b.Have set up research of a numerical control, development , managerial talen

57、ts basic team . Though has made considerable progress in research and development and industrialization of the technology of numerical control, but we will realize soberly, the research and development of the technology of advanced numerical control of our country, there is greater disparity between

58、 current situation and current demand of our country of engineering level especially in industrialization. Though very fast from longitudinal development to watch our country, horizontal until (contrast with foreign countries ) , the engineering level has disparity, there is disparity too in develop

59、ment speed in some aspects, i.e. the disparity of engineering level between some high-grade , precision and advanced numerical control equipment has the tendency to expand . Watch from world , estimate roughly as follows about the numerical control engineering level of our country and industrialization level.2.2 Strategic consideration and Development tacticsOur country of strategic consideration makes the