數(shù)控專業(yè)畢業(yè)設計外文翻譯--數(shù)控技術

1、<p><b>　　外文翻譯</b></p><p>　　NUMERICAL CONTROL</p><p>　　Numerical control(N／C)is a form of programmable automation in which the processing equipment is controlled by means of numb

2、ers，letters，and other symbols．The numbers，letters，and symbols are coded in an appropriate format to define a program of instructions for a particular work part or job．When the job changes，the program of instructions is c

3、hanged．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 </p><p>　　There are two basic types of numerically

4、 controlled machine tools：point—to—point and continuous—path(also called contouring)．Point—to—point machines use unsynchronized motors，with the result that the position of the machining head Can be assured only upon comp

5、letion of a movement，or while only one motor is running．Machines of this type are principally used for straight—line cuts or for drilling or boring．</p><p>　　The N／C system consists of the following componen

6、ts：data input，the tape reader with the control unit，feedback devices，and the metal—cutting machine tool or other type of N／C equipment．</p><p>　　Data input，also called “man—to—control link”，may be provided t

7、o 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 keyboar

8、d dials，pushbuttons，switches，or thumbwheel selectors．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，swi&l

9、t;/p><p>　　In practically all cases，information is automatically supplied to the control unit and the machine tool by cards，punched tapes，or by magnetic tape．Eight—channel punched paper tape is the most commonl

10、y 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

11、 of the two．The entire N／C program on a tape is made up of an accumulation of the</p><p>　　While the data on the tape is fed automatically，the actual programming steps ale done manually．Before the coded tape

12、 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 p</p><p>　　The control unit receives and sto

14、res 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．</p><p>　　The function of the

15、control 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 co

16、mpleted．</p><p>　　Silicon photo diodes，located in the tape reader head on the control unit，detect light as it passes through the holes in the moving tape．The light beams are converted to electrical energy，wh

17、ich 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．</p><p>　　Some photoelectric devic

18、es are capable of reading at rates up to 1000 characters per second．High reading rates are necessary to maintain continuous machine—tool motion；otherwise dwell marks may be generated by the cutter on the part during cont

19、ouring operations．The reading device must be capable of reading data blocks at a rate faster than the control system can process the data．</p><p>　　A feedback device is a safeguard used on some N／C installat

20、ions 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 equipped with this kind of a direct feedback checking device has wha

21、t 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 re

22、c</p><p>　　In an alternative system，called an open—loop system，the machine is positioned solely by stepping motor drives in response to commands by a controllers．There are three basic types of NC motions, as

23、 follows:</p><p>　　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

24、 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 pres

25、ses and some boring machines, where drilling, tapping, or boring operations must be performe</p><p>　　Continuous Path or Contouring Control In continuous path control the motions of two or more of the machin

26、e 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 in

27、terpolator 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 ref</p><p>　　Some terminology conce

28、rning 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,

29、 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 te

30、rminology an axis of control is any co</p><p>　　The original N／C used the closed—loop system．Of the two systems，closed and open loop，closed loop is more accurate and，as a consequence，is generally more expens

31、ive．Initially，open—loop systems were used almost entirely for light-duty applications because of inherent power limitations previously associated with conventional electric stepping motors．Recent advances in the developm

32、ent of electro hydraulic stepping motors have led to increasingly heavier machine load applications．</p><p><b>　　數(shù)控技術</b></p><p>　　數(shù)控是可編程自動化技術的一種形式，通過數(shù)字、字母和其他符號來控制加工設備。數(shù)字、字母和符號用適當?shù)母袷?/p>

33、編碼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，寫一段新程序遠比對加工設備做大的改動容易得多。</p><p>　　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。</p><p>　

34、　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)控設備。</p><p>　　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，開關或撥輪選擇開關，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，按鈕、開關和其他

35、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的過程，除了簡單加工場合或特殊情況，已很少使用。</p><p>　　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

36、。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、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。</p>

37、<p>　　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。</p><p>　　控制單元接受和儲存編碼數(shù)據(jù)，直至形

38、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。</p><p>　　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。</p><p>　　裝在控制單元里的紙帶閱讀機，通過其內的硅光二極管，檢測到穿過移動紙帶上的孔漏過的光線，將光束轉變成電能，并通過放大來進一步加強信號，然后將信號送到控制單元

39、里的寄存器，由它將動作信號傳到機床驅動裝置。</p><p>　　有些光電裝置能以高達每秒1000個字節(jié)的速度閱讀，這對保持機床連續(xù)動作是必須的，否則，在輪廓加工時，刀具可能在工件上產生劃痕。閱讀裝置必須要能以比控制系統(tǒng)處理數(shù)據(jù)更快的速度來閱讀數(shù)據(jù)程序塊。</p><p>　　反饋裝置是用在一些數(shù)控設備上的安全裝置，它可連續(xù)補償控制位置與機床運動滑臺的實際位置之間的誤差。裝有這種直接反饋檢

40、查裝置的數(shù)控機床有一個閉環(huán)系統(tǒng)裝置。位置控制通過傳感器實現(xiàn)，在實際工作時，記錄下滑臺的位置，并將這些信息送回控制單元。接受到的信號與紙帶輸入的信號相比較，它們之間的任何偏差都可得到糾正。</p><p>　　在另一個稱為開環(huán)的系統(tǒng)中，機床僅由響應控制器命令的步進電動機驅動定位，工件的精度幾乎完全取決于絲杠的精度和機床結構的剛度。有幾個理由可以說明步進電機是一個自動化申請的非常有用的驅動裝置。對于一件事物，它被不連

41、續(xù)直流電壓脈沖驅使,是來自數(shù)傳計算機和其他的自動化的非常方便的輸出控制系統(tǒng)。當多數(shù)是索引或其他的自動化申請所必備者的時候，步進電機對運行一個精確的有角進步也是理想的。因為控制系統(tǒng)不需要監(jiān)聽就提供特定的輸出指令而且期待系統(tǒng)適當?shù)胤磻墓_- 環(huán)操作造成一個回應環(huán)，步進電機是理想的。 一些工業(yè)的機械手使用高抬腿運步的馬乘汽車駕駛員，而且步進電機是有用的在數(shù)字受約束的工作母機中。 這些申請的大部分是公開- 環(huán) ,但是雇用回應環(huán)檢測受到驅策的成

42、份位置是可能的。 環(huán)的一個分析者把真實的位置與需要的位置作比較，而且不同是考慮過的錯誤。 那然后駕駛員能發(fā)行對步進電機的電脈沖，直到錯誤被減少對準零位。在這個系統(tǒng)中，沒有信息反饋到控制單元的自矯正過程。出現(xiàn)誤動作時，控制單元繼續(xù)發(fā)出電脈沖。比如，一臺數(shù)控銑床的工作臺突然過載，阻力矩超過電機轉矩時，將沒有響應信號送回到控制器。因為，步進電機對載荷變化不</p><p>　　最初的數(shù)控系統(tǒng)采用開環(huán)系統(tǒng)。在開、閉環(huán)兩種