【正文】 對(duì)于一件事物，它被不連續(xù)直流電壓脈沖驅(qū)使,是來(lái)自數(shù)傳計(jì)算機(jī)和其他的自動(dòng)化的非常方便的輸出控制系統(tǒng)。出現(xiàn)誤動(dòng)作時(shí)，控制單元繼續(xù)發(fā)出電脈沖。起初，因?yàn)樵葌鹘y(tǒng)的步進(jìn)電動(dòng)機(jī)的功率限制，開環(huán)系統(tǒng)幾乎全部用于輕加工場(chǎng)合，最近出現(xiàn)的電液步進(jìn)電動(dòng)機(jī)已越來(lái)越多地用于較重的加工領(lǐng)域。 那然后駕駛員能發(fā)行對(duì)步進(jìn)電機(jī)的電脈沖，直到錯(cuò)誤被減少對(duì)準(zhǔn)零位。在另一個(gè)稱為開環(huán)的系統(tǒng)中，機(jī)床僅由響應(yīng)控制器命令的步進(jìn)電動(dòng)機(jī)驅(qū)動(dòng)定位，工件的精度幾乎完全取決于絲杠的精度和機(jī)床結(jié)構(gòu)的剛度。為更好理解控制單元的作用，可將它與撥號(hào)電話進(jìn)行比較，即每撥一個(gè)數(shù)字，就儲(chǔ)存一個(gè)，當(dāng)整個(gè)數(shù)字撥好后，電話就被激活，也就完成了呼叫。帶有程序的長(zhǎng)帶子像電影膠片一樣繞在盤子上，相對(duì)較短的帶子上的程序可通過(guò)將紙帶兩端連接形成一個(gè)循環(huán)而連續(xù)不斷地重復(fù)使用。人工輸入裝置有鍵盤，撥號(hào)盤，按鈕，開關(guān)或撥輪選擇開關(guān)，這些都位于機(jī)床附近的一個(gè)控制臺(tái)上。當(dāng)工件改變時(shí)，指令程序就改變。數(shù)字、字母和符號(hào)用適當(dāng)?shù)母袷骄幋a為一個(gè)特定工件定義指令程序。人工方法作為輸人數(shù)據(jù)唯一方法時(shí)，只限于少量輸入。紙帶上的整個(gè)數(shù)控程序由這些連續(xù)數(shù)據(jù)單元連接而成?？刂茊卧邮芎蛢?chǔ)存編碼數(shù)據(jù)，直至形成一個(gè)完整的信息程序塊，然后解釋數(shù)控指令，并引導(dǎo)機(jī)床得到所需運(yùn)動(dòng)。接受到的信號(hào)與紙帶輸入的信號(hào)相比較，它們之間的任何偏差都可得到糾正。 環(huán)的一個(gè)分析者把真實(shí)的位置與需要的位置作比較，而且不同是考慮過(guò)的錯(cuò)誤。在開、閉環(huán)兩種系統(tǒng)中，閉環(huán)更精確，一般說(shuō)來(lái)更昂貴。比如，一臺(tái)數(shù)控銑床的工作臺(tái)突然過(guò)載，阻力矩超過(guò)電機(jī)轉(zhuǎn)矩時(shí)，將沒(méi)有響應(yīng)信號(hào)送回到控制器。當(dāng)多數(shù)是索引或其他的自動(dòng)化申請(qǐng)所必備者的時(shí)候，步進(jìn)電機(jī)對(duì)運(yùn)行一個(gè)精確的有角進(jìn)步也是理想的。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(lái)閱讀數(shù)據(jù)程序塊。穿孔紙帶是在帶有特制穿孔附件的打字機(jī)或直接連到計(jì)算機(jī)上的紙帶穿孔裝置上做成的。人工輸入需要操作者控制每個(gè)操作，這是一個(gè)既慢又單調(diào)的過(guò)程，除了簡(jiǎn)單加工場(chǎng)合或特殊情況，已很少使用。點(diǎn)位控制機(jī)床采用異步電動(dòng)機(jī)，因此，主軸的定位只能通過(guò)完成一個(gè)運(yùn)動(dòng)或一個(gè)電動(dòng)機(jī)的轉(zhuǎn)動(dòng)來(lái)實(shí)現(xiàn)。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 workpart 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 lowand mediumvolume production．It is much easier to write programs than to make major alterations of the processing equipment．There are two basic types of numerically 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 pletion 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． The N／C system consists of the following ponents：data input，the tape reader with the control unit，feedback devices，and the metal—cutting machine tool or other type of N／C equipment．Data input，also called“man—to—control 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 selectors．These are located on a console near the machine．Dials ale analog devices usually connected to a synchrotype resolver or potentiometer．In most cases，