【正文】
lling 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 halfaxis of control. Machines with this form of control are also capable of pointtopoint 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 fouror fiveor even sixaxis 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 plication is use of the term halfaxis of control。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。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(yuǎn)比對(duì)加工設(shè)備做大的改動(dòng)容易得多。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完成一個(gè)運(yùn)動(dòng)或一個(gè)電動(dòng)機(jī)的轉(zhuǎn)動(dòng)來實(shí)現(xiàn)。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(jī),反饋裝置和切削機(jī)床或其他形式的數(shù)控設(shè)備。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。撥號(hào)盤通常連到一個(gè)同步解析器或電位計(jì)的模擬裝置上。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)的過程,除了簡(jiǎn)單加工場(chǎng)合或特殊情況,已很少使用。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。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。帶子一旦安裝好,就可反復(fù)使用而無需進(jìn)一步處理。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。通常,必須要試走幾次來排除錯(cuò)誤,才能得到一個(gè)可用的工作紙帶??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)。 裝在控制單元里的紙帶閱讀機(jī),通過其內(nèi)的硅光二極管,檢測(cè)到穿過移動(dòng)紙帶上的孔漏過的光線,將光束轉(zhuǎn)變成電能,并通過放大來進(jìn)一步加強(qiáng)信號(hào),然后將信號(hào)送到控制單元里的寄存器,由它將動(dòng)作信號(hào)傳到機(jī)床驅(qū)動(dòng)裝置。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。裝有這種直接反饋檢查裝置的數(shù)控機(jī)床有一個(gè)閉環(huán)系統(tǒng)裝置。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。有幾個(gè)理由可以說明步進(jìn)電機(jī)是一個(gè)自動(dòng)化申請(qǐng)的非常有用的驅(qū)動(dòng)裝置。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。 一些工業(yè)的機(jī)械手使用高抬腿運(yùn)步的馬乘汽車駕駛員,而且步進(jìn)電機(jī)是有用的在數(shù)字受約束的工作母機(jī)中。 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,而且不同是考慮過的錯(cuò)誤。在這個(gè)系統(tǒng)中,沒有信息反饋到控制單元的自矯正過程。比如,一臺(tái)數(shù)控銑床的工作臺(tái)突然過載,阻力矩超過電機(jī)轉(zhuǎn)矩時(shí),將沒有響應(yīng)信號(hào)送回到控制器。然而,盡管有可能損壞機(jī)床結(jié)構(gòu)或機(jī)械傳動(dòng)系統(tǒng),也有使用帶有特高轉(zhuǎn)矩步進(jìn)電機(jī)的其他系統(tǒng),此時(shí),電動(dòng)機(jī)有足夠能力來應(yīng)付系統(tǒng)中任何偶然事故。在開、閉環(huán)兩種系統(tǒng)中,閉環(huán)更精確,一般說來更昂貴。