機械專業(yè)英語文章中英文對照5頁

1、英語原文NUMERICAL CONTROLNumerical control(N/C)is a form of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols, The numbers, letters, and symbols are coded in an appropriate format to define a program of instructions for a particular w

2、ork part or job. When the job changes, the program of instructions is changed. The capability to change the program is what makes N/C suitable for low-and medium-volume production. It is much easier to write programs than to make major alterations of the processing equipment.There are two basic type

3、s 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 only one motor is running. Machines o

4、f this type are principally used for straightline cuts or for drilling or boring. The N/C 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 N/C equipment.Data input, also called “mantoco

5、ntrol link”, may be provided to the machine tool manually, or entirely by automatic means. Manual methods when used as the sole source of input data are restricted to a relatively small number of inputs. Examples of manually operated devices are keyboard dials, pushbuttons, switches, or thumbwheel s

6、electors. These are located on a console near the machine. Dials ale analog devices usually connected to a syn-chro-type resolver or potentiometer. In most cases, pushbuttons, switches, and other similar types of selectors are digital input devices. Manual input requires that the operator set the co

7、ntrols for each operation. It is a slow and tedious process and is seldom justified except in elementary machining applications or in special cases.In practically all cases, information is automatically supplied to the control unit and the machine tool by cards, punched tapes, or by magnetic tape. E

8、ightchannel punched paper tape is the most commonly used form of data input for conventional N/C systems. The coded instructions on the tape consist of sections of punched holes called blocks. Each block represents a machine function, a machining operation, or a combination of the two. The entire N/

9、C program on a tape is made up of an accumulation of these successive data blocks. Programs resulting in long tapes all wound on reels like motion-picture film. Programs on relatively short tapes may be continuously repeated by joining the two ends of the tape to form a loop. Once installed, the tap

10、e is used again and again without further handling. In this case, the operator simply loads and unloads the parts. Punched tapes ale prepared on type writers with special tapepunching attachments or in tape punching units connected directly to a computer system. Tape production is rarely error-free.

11、 Errors 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, etc. Several trial runs are often necessary to remove all errors and produce an acceptable working tape. While the data on the tape is fed automatic

12、ally, the actual programming steps ale done manually. Before the coded tape may be prepared, the programmer, often working with a planner or a process engineer, must select the appropriate N/C machine tool, determine the kind of material to be machined, calculate the speeds and feeds, and decide upo

13、n 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 program. A program manuscript is then written which gives coded numerical instructions describing the sequence of operations that the machine tool

14、is required to follow to cut the part to the drawing specifications.The control unit receives and stores all coded data until a complete block of information has been accumulated. It then interprets the coded instruction and directs the machine tool through the required motions.The function of the c

15、ontrol unit may be better understood by comparing it to the action of a dial telephone, where, as each digit is dialed, it is stored. When the entire number has been dialed, the equipment becomes activated and the call is completed.Silicon photo diodes, located in the tape reader head on the control

16、 unit, detect light as it passes through the holes in the moving tape. The light beams are converted to electrical energy, which is amplified to further strengthen the signal. The signals are then sent to registers in the control unit, where actuation signals are relayed to the machine tool drives.S

17、ome photoelectric devices are capable of reading at rates up to 1000 characters per second. High reading rates are necessary to maintain continuous machinetool motion；otherwise dwell marks may be generated by the cutter on the part during contouring operations. The reading device must be capable of

18、reading data blocks at a rate faster than the control system can process the data.A feedback device is a safeguard used on some N/C installations to constantly compensate for errors between the commanded position and the actual location of the moving slides of the machine tool. An N/C machine equipp

19、ed with this kind of a direct feedback checking device has what is known as a closed-loop system. Positioning 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 unit. Signals thus received ale com

20、pared to input signals on the tape, and any discrepancy between them is automatically rectified.In an alternative system, called an openloop system, the machine is positioned solely by stepping motor drives in response to commands by a controllers. There is one basic type of NC motions. Point-to-poi

21、nt 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

22、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

23、 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 confi

24、gurations 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.The orig

25、inal N/C used the closedloop system. Of the two systems, closed and open loop, closed loop is more accurate and, as a consequence, is generally more expensive. Initially, openloop systems were used almost entirely for light-duty applications because of inherent power limitations previously associate

26、d with conventional electric stepping motors. Recent advances in the development of electro hydraulic stepping motors have led to increasingly heavier machine load applications.中文譯文數(shù)控技術(shù)數(shù)控是可編程自動化技術(shù)的一種形式,通過數(shù)字、字母和其他符號來控制加工設(shè)備。數(shù)字、字母和符號用適當?shù)母袷骄幋a為一個特定工件定義指令程序。當工件改變時,指令程序就改變。這種改變程序的能力使數(shù)控適合于中、小批量生產(chǎn),寫一段新程序遠比對加

27、工設(shè)備做大的改動容易得多。數(shù)控機床有兩種基本形式：點位控制和連續(xù)控制(也稱為輪廓控制)。點位控制機床采用異步電動機,因此,主軸的定位只能通過完成一個運動或一個電動機的轉(zhuǎn)動來實現(xiàn)。這種機床主要用于直線切削或鉆孔、鏜孔等場合。數(shù)控系統(tǒng)由下列組件組成：數(shù)據(jù)輸入裝置,帶控制單元的磁帶閱讀機,反饋裝置和切削機床或其他形式的數(shù)控設(shè)備。數(shù)據(jù)輸人裝置,也稱“人機聯(lián)系裝置”,可用人工或全自動方法向機床提供數(shù)據(jù)。人工方法作為輸人數(shù)據(jù)唯一方法時,只限于少量輸入。人工輸入裝置有鍵盤,撥號盤,按鈕,開關(guān)或撥輪選擇開關(guān),這些都位于機床附近的一個控制臺上。撥號盤通常連到一個同步解析器或電位計的模擬裝置上。在大多數(shù)情況下,按

28、鈕、開關(guān)和其他類似的旋鈕是數(shù)據(jù)輸入元件。人工輸入需要操作者控制每個操作,這是一個既慢又單調(diào)的過程,除了簡單加工場合或特殊情況,已很少使用。幾乎所有情況下,信息都是通過卡片、穿孔紙帶或磁帶自動提供給控制單元。在傳統(tǒng)的數(shù)控系統(tǒng)中,八信道穿孔紙帶是最常用的數(shù)據(jù)輸入形式,紙帶上的編碼指令由一系列稱為程序塊的穿孔組成。每一個程序塊代表一種加工功能、一種操作或兩者的組合。紙帶上的整個數(shù)控程序由這些連續(xù)數(shù)據(jù)單元連接而成。帶有程序的長帶子像電影膠片一樣繞在盤子上,相對較短的帶子上的程序可通過將紙帶兩端連接形成一個循環(huán)而連續(xù)不斷地重復使用。帶子一旦安裝好,就可反復使用而無需進一步處理。此時,操作者只是簡單地上、

29、下工件。穿孔紙帶是在帶有特制穿孔附件的打字機或直接連到計算機上的紙帶穿孔裝置上做成的。紙帶制造很少不出錯,錯誤可能由編程、卡片穿孔或編碼、紙帶穿孔時的物理損害等形成。通常,必須要試走幾次來排除錯誤,才能得到一個可用的工作紙帶。雖然紙帶上的數(shù)據(jù)是自動進給的,但實際編程卻是手工完成的,在編碼紙帶做好前,編程者經(jīng)常要和一個計劃人員或工藝工程師一起工作,選擇合適的數(shù)控機床,決定加工材料,計算切削速度和進給速度,決定所需刀具類型,仔細閱讀零件圖上尺寸,定下合適的程序開始的零參考點,然后寫出程序清單,其上記載有描述加工順序的編碼數(shù)控指令,機床按順序加工工件到圖樣要求?？刂茊卧邮芎蛢Υ婢幋a數(shù)據(jù),直至形成一個完整的信息程序塊,然后解釋數(shù)控指令,并引導機床得到所需運動。為更好理解控制單元的作用,可將它與撥號電話進行比較,即每撥一個數(shù)字,就儲存一個,當整個數(shù)字撥好后,電話就被激活,也就完成了呼叫。 裝在控制單元里的紙帶閱讀機,通過其內(nèi)的硅光二極管,檢測到穿過移動紙帶上的孔漏過的光線,將光束轉(zhuǎn)變成電能,