外文翻译=数控=3000字文献翻译.doc

西北工业大学明德学院本科毕业设计论文 NUMERICAL CONTROLNumerical control 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 define a program of instructions for a particular work part 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 processing equipmentNumber control lather main use to carry on a car to pare towards revolving body spare parts, the Tang pare, drill to pare, the Jiao pare, offend silk etc. process of work preface. General ability auto inside completion outside cylinder noodles, conic surface, surface of sphere, cylinder thread, slot and carry noodles etc. the slice of work preface pare to process.The host is the topic that the number control lather and include a tool machine body, sign pillar, principal axis and enter etc. is to the organization machine parts. Number control equip, is number control tool machine of core, include hardware and correspond of software, used for an importation numeral turn of spare parts procedure, and completion importation information of saving, the transformation of data, put to repair operation and realization various control function. Drive to equip, he is number control the drive of organization of the tool machine performance parts, include a principal axis to drive unit and enter to the unit, principal axis electrical engineering and enter etc. to electrical engineering. He under the control that number control to equip pass electricity or electricity liquid servo system realization principal axis with enters give drive. When several enter to give allied move, can completion fixed position, straight line, process of flat surface curve and space curve. Assistance equips the index number control tool machine of some necessity of kit parts, in order to assurance number control tool machine of circulate, such as cool off, row scraps, lubricate, illuminate, monitor etc. It include a liquid to press friendly move equip, row scraps equip, exchange work set, number control to turn Taiwan and number control cent degree head. Plait distance and other subsidiary equipments, can use to carry on the procedure of spare parts to draw up outside machine, saving.Modern number control lather to all have X, Z two stalk of allied move function, knife position and point of a knife arc radius of compensate function, and process fix circulation function.The number control the structure of lather1. The number control a lather brief introductionThe number control constitute of lather: Number control system, bed body, principal axis and enter to the system, turn round a knife, operation front-panel and assistance system etc. (1) The economy number control lather: Adoption step enter electric motor and list slice machine to common the car of the lather pare into to the system carry on reformation behind formation of the simple number control lather. The cost is lower, automation degree and function be all more bad, the car pare to process accuracy also not high, be applicable to request not high of turn round type spare parts of the car pare to process.The economy number control lather(2) Common number control lather: Pare to process a request to carry on the structure according to the car specialized design, equipment in general use number control system but formation of number control lather. Number control system function strong, automation degree with process accuracy also more Ago, be applicable to general turn round type spare parts of the car pare to process. This kind of number control lather can control 2 sit a mark stalk in the meantime, namely x stalk and z stalk.Common number control lather(3)the car pare to process center: At common number control the foundation of lather up, increment C stalk and motive head, more high class of the tool machine still take a knife database, can control X, Z and C 3 sit mark stalk, allied move control stalk can BE(X, Z),(X, C) or(Z, C).Because increment C stalk and Xian pare a motive head, this kind of number control process of lather function consumedly strengthen, in addition to carry on general the car pare, also can carry on path to pare with stalk toward the Xian, the curved face Xian pare, the center line dont turn round in the spare parts center of bore and path pare toward the drill of bore etc. process.2. The liquid press card dish and liquid to press a tailThe liquid press card dish is number control a car to pare to process clip tight work piece of importance enclosure, rightness general turn round type spare parts can adoption common the liquid press card dish; To the spare parts be clip hold the part isnt the spare parts of cylinder form, demand adoption appropriation card dish; With the stick anticipate direct process spare parts demand adoption spring coil card dish.To stalk to the size and the path is to the specific value bigger spare parts of size, demand adoption install press a tail in the liquid up of live top carry on prop up to the spare parts end tip, then can assurance carry on to the spare parts exactitude of process. The tail has a common liquid to press tail and programmable liquid to press a tail.3. The number control the knife of latherNumber control lather can equipment two kinds of knife:(1) Appropriation knife from lather produce manufacturer oneself development, haft for use is also appropriation of. This kind of the advantage be that the manufacturing cost is low, but lack in general use.(2)in general use knife according to certain in general use standard(like VDI, Germany engineers association) but produce of knife, number control lather production manufacturer can according to number control the function of lather request to carry on a choice allocation.In general use knife4. The Xian pare a motive headNumber control lather knife top to install Xian after pare the motive head can consumedly expand number to control process of lather ability. Such as :Make use of the Xian pare a motive head to carry on stalk to drill a hole to pare stalk toward the slot with Xian.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 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，switches，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 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 tapeEightchannel 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 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 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 a computer systemTape production is rarely error-freeErrors may be initially caused 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 tapeWhile the data on the tape is fed automatically，the actual programming steps ale 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 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 drawing 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 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 moving 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 1000 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 process 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 as 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 automatically 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 elements (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 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 machine 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 perpendicular 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 of 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 increments 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 referred 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 angular 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 continuous 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 machined 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 a 3c machine, similarly, lathes is 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 the 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 mo