【正文】 的輸出指令而且期待系統(tǒng)適當(dāng)?shù)胤磻?yīng)的公開(kāi)環(huán)操作造成一個(gè)回應(yīng)環(huán),步進(jìn)電機(jī)是理想的。在另一個(gè)稱為開(kāi)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。反饋裝置是用在一些數(shù)控設(shè)備上的安全裝置,它可連續(xù)補(bǔ)償控制位置與機(jī)床運(yùn)動(dòng)滑臺(tái)的實(shí)際位置之間的誤差。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。紙帶制造很少不出錯(cuò),錯(cuò)誤可能由編程、卡片穿孔或編碼、紙帶穿孔時(shí)的物理?yè)p害等形成。帶有程序的長(zhǎng)帶子像電影膠片一樣繞在盤(pán)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。幾乎所有情況下,信息都是通過(guò)卡片、穿孔紙帶或磁帶自動(dòng)提供給控制單元。人工輸入裝置有鍵盤(pán),撥號(hào)盤(pán),按鈕,開(kāi)關(guān)或撥輪選擇開(kāi)關(guān),這些都位于機(jī)床附近的一個(gè)控制臺(tái)上。這種機(jī)床主要用于直線切削或鉆孔、鏜孔等場(chǎng)合。當(dāng)工件改變時(shí),指令程序就改變。第一篇：機(jī)械專業(yè)英語(yǔ)文章中英文對(duì)照英語(yǔ)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 work part or the job changes, the program of instructions is capability to change the program is what makes N/C suitable for lowand mediumvolume is much easier to write programs than to make major alterations of the processing 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 of this type are principally used for straight—line cuts or for drilling or 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 input, also called “man—to—control link”, may be provided to the machine tool manually, or entirely by automatic methods when used as the sole source of input data are restricted to a relatively small number of of manually operated devices are keyboard dials, pushbuttons, switches, or thumbwheel are located on a console near the ale analog devices usually connected to a synchrotype resolver or most cases, pushbuttons, switches, and other similar types of selectors are digital input input requires that the operator set the controls for each is a slow and tedious process and is seldom justified except in elementary machining applications or in special practically all cases, information is automatically supplied to the control unit and the machine tool by cards, punched tapes, or by magnetic —channel punched paper tape is the most monly used form of data input for conventional N/C coded instructions on the tape consist of sections of punched holes called block represents a machine function, a machining operation, or a bination of the entire N/C program on a tape is made up of an accumulation of these successive data resulting in long tapes all wound on reels like motionpicture on relatively short tapes may be continuously repeated by joining the two ends of the tape to form a installed, the tape is used again and again without further this case, the operator simply loads and1unloads the tapes ale prepared on type writers with special tape—punching attachments or in tape punching units connected directly to a puter production is rarely may be initially caused by the part programmer, in card punching or pilation, or as a result of physical damage to the tape during handling, trial runs are often necessary to remove all errors and produce an acceptable working the data on the tape is fed automatically, the actual programming steps ale done 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 upon the type of tooling dimensions on the part print are closely examined to determine a suitable zero reference point from which to start the 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 control unit receives and stores all coded data until a plete block of information has been then interprets the coded instruction and directs the machine tool through the required function of the control unit may be better understood by paring it to the action of a dial telephone, where, as each digit is dialed, it is the entire number has been dialed, the equipment bees activated and the call is photo diodes, located in the tape reader head on the control unit, detect light as it passes through the holes in the moving light beams are converted to electrical energy, which is amplified to further strengthen the signals are then sent to registers in the control unit, where actuation signals are relayed to the machine tool photoelectric devices are capable of reading at rates up to 1000 characters per reading rates are necessary to maintain continuous machine—tool motion；otherwise dwell marks may be generated by the cutter on the part during contouring reading device must be capable of reading data blocks at a rate faster than the control system can process the feedback device is a safeguard used on some N/C installations to constantly pensate for errors between the manded position and the actual location of the moving slides of the machine N/C machine equipped with this kind of a direct feedback checking device has what is known as a closedloop control is acplished by a sensor which, during the actual operation, records the position of the slides and relays this information back to the control thus received ale pared to input signals on the tape, and any discrepancy between them is automatically an alternative system, called an open—loop system, the machine is positioned solely by stepping motor drives in response to mands by a is one basic type of NC or Positional Control In pointtopoint control the machine tool elements(tools, table, etc.)are moved to programmed locations and the machining operations performedafter the motions are path or