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1、 黃石理工學院 畢業(yè)設計（論文）外文文獻翻譯 數(shù)控技術 數(shù)控技術是一種利用程序實現(xiàn)自動控制的技術，加工制造設備采用數(shù)控技術后能由數(shù)字、字符和符號等進行控制。這些數(shù)字、字符和符號等北邊麻城按一定格式定義的指令程序，用于特定的加工或工作。這種指令可采用兩種二進制編碼的數(shù)字系統(tǒng)中的任意一種進行定義，這兩種二進制編碼的數(shù)字系統(tǒng)分別為電工協(xié)會代碼和美國標準信息交換代碼。一般來說，ASCII編碼的機床控制系統(tǒng)不能接受EIA編碼的指令，反之亦然。當然，這樣的問題已經(jīng)逐漸得到解決。數(shù)控加工制造目前已經(jīng)廣泛地應用于幾乎所有的金屬加工

2、機床；車床，銑床，鉆床，鏜床，磨床，回轉沖床，電火花或線切割機床以及焊接機床，甚至彎管機也可采用數(shù)控加工技術。 數(shù)控技術的基本組成 一個數(shù)控系統(tǒng)主要由以下3個部分組成： (1)程序指令 (2)加工控制單元 (3)制造裝備 程序指令由一條一條的詳細指令組成，制造裝備按要求執(zhí)行這些指令。最常用的指令形式可以按要求使機床刀具主軸位于工作臺上的具體位置，工作臺是用于固定加工零件的。許多更高級的指令還包括主軸速度選擇，道具選擇及其他的一些功能。 加工控制單元包括一些用于閱讀和解釋程序指令并將其轉換為機床刀具或其他制造裝備的機械動作的電子和控制硬件。 制造裝備是一種

3、進行金屬加工的數(shù)控技術裝備，在常用的數(shù)控技術領域中，制造裝備用于進行機械制造。制造裝備包括工作臺、主軸、電機及控制驅動單元。 數(shù)控技術的類型 數(shù)控技術系統(tǒng)主要有兩種類型：點對點數(shù)控系統(tǒng)和輪廓線數(shù)控系統(tǒng)。 點對點數(shù)控系統(tǒng)也稱為位置數(shù)控系統(tǒng)，比輪廓線數(shù)控系統(tǒng)簡單，其主要的原理是移動刀具或工件從一個程序控制點到另一個程序控制點，通常像鉆床這樣的加工功能，每個點都可以通過NC程序中的指令進行控制。點對點數(shù)控系統(tǒng)適用于鉆孔，沉孔加工、沉孔鏜孔、鉸孔和攻螺紋等。其他沖孔機床、電焊機和裝配機床等也都采用點對點數(shù)控系統(tǒng)。 輪廓線數(shù)控系統(tǒng)也稱為輪廓線路徑數(shù)控系統(tǒng)，定位和切割操作都是以不同的速度沿著控制的

4、路徑進行的。由于刀具沿路徑進行切削，因此刀具的運動和速度的精確控制盒同步性能是非常重要的。輪廓線數(shù)控系統(tǒng)經(jīng)常應用于車床、銑床、磨床、焊接機床和加工中心中。刀具沿著路徑的運動可稱為插補，逐漸出現(xiàn)了幾個不同的方法。有多種插補方法用于處理在輪廓線數(shù)控系統(tǒng)中生產光滑的輪廓線時遇到的各種問題，幾種常用的方法有線性插補，圓形插補，螺旋形插補，拋物線插補和立方插補等。在所有的插補方法中，路徑控制是以刀具的旋轉中心為標準，在數(shù)控程序中對類型不同，直徑不同的刀具以及在加工過程中的不同刀具磨損量給于不同的補償。 數(shù)控系統(tǒng)的編程 一個數(shù)控系統(tǒng)（NC）的程序包括是數(shù)控機床進行操作和加工的一系列指令。數(shù)控程序可以由

5、數(shù)控機床內部的程序庫開發(fā)生成，也可以從外面采購獲得。另外，程序可以通過手工編寫，也可以進行計算機輔助編程。 數(shù)控程序包括一系列的指令系統(tǒng)和命令系統(tǒng)。幾何類指令用于定義刀具和工件之間的相對位置和運動；加工類指令用于定義主軸轉速、進給、刀具轉速等；傳送類指令用于定義刀具或工作臺的運動速度和插補的類型等；開關類指令用于冷卻液供給、主軸旋轉、主軸旋轉方向選擇、換刀工件進給、夾具開關等。第一個用于數(shù)控編程的數(shù)控編程語言是20世紀50年代由麻省理工學院數(shù)控編程系統(tǒng)開發(fā)小組專家開發(fā)的，并被命名為自動編程工具（APT）。 直接數(shù)字控制和計算機數(shù)字控制 數(shù)控技術在批量生產和小批量生產中，不管是在技術上還是

6、在商業(yè)上都取得了顯著的成就。目前，已經(jīng)有兩種數(shù)控技術系統(tǒng)得到了發(fā)展，分別是： （1） 直接數(shù)字控制(DNC) （2） 計算機數(shù)字控制(CNC) 直接數(shù)字控制可以定義為這樣一個生產制造系統(tǒng)，該制造系統(tǒng)有許多臺加工機床，相互之間由一臺計算機采用直接連接，進行實時控制。這樣在傳統(tǒng)的數(shù)字控制技術中采用的磁帶閱讀器在直接數(shù)字控制中被取消，從而保證了系統(tǒng)的可靠性。不使用磁帶閱讀器，被加工的零件程序就從計算機的存儲器中直接傳送到進行加工的道具上。從原理上講，一臺計算機可以控制多達100臺加工機床，（在20世紀70年代一臺商業(yè)使用的DNC系統(tǒng)可以控制多達256個機床刀具）。直接數(shù)字控制計算機

7、按要求給每個進行加工的刀具提供加工指令，當機床需要控制指令時，計算機就可以馬上將指令傳送到機床上。 隨著直接數(shù)字控制技術和計算機技術的飛速發(fā)展，數(shù)字計算機尺寸和價格的大幅度降低，數(shù)字計算機計算能力的大大提高，大量傳統(tǒng)的以硬件線路為基礎的加工控制單元被以數(shù)字計算機為基礎的數(shù)字控制單元所替代。最初，在20世紀70年代使用了小型計算機。后來隨著計算機的進一步小型化，早期的小型計算機逐漸被現(xiàn)在的微型計算機所替代。 計算機數(shù)控使用專用的微型計算機作為加工控制單元。數(shù)字計算機都用于計算機數(shù)控和直接數(shù)控，應該注意兩者之間的區(qū)別，可以從3個方面來加以區(qū)分。 (1)DNC計算機是將指令數(shù)據(jù)發(fā)送到許多機床去

8、或從許多機床中收集數(shù)據(jù)，而CNC計算機每次只控制一臺或幾臺機床。 (2)DNC計算機一般位于距機床一定距離的位置，而CNC計算機一般都位于距機床較近的位置。 (3)DNC計算機開發(fā)的軟件不僅可以用于控制產品的單件生產，而且還可以用于企業(yè)制造部門的管理信息系統(tǒng)，而CNC計算機開發(fā)的軟件一般只用于某個特殊加工的工具。 Numerical Control Numerical control (NC) is a form of programmable automation in which the processing equipment is controlled by means

9、 of number, 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. The instructions are provided by either of the two binary coded decimal systems: the Electronic Industries Associations

10、(EIA) code, or the American Standard Code for Information Interchange (ASCII) ASCII-coded machine control units will not accept EIA coded instructions and vice versa. Increasingly, however, control units are being made to accept instructions in either code. Automation operation by NC is readily ad

11、aptable to the operation of all metalworking machines. Lathes, milling machines, drill presses, boring machines, grinding machines, turret punches, flame or wire-cutting and welding machines, and even pipe benders are available with numerical controls. Basic Components of NC A numerical control

12、system consists of the following three basic components: (1) Program instructions. (2) Machine control unit. (3) Processing equipment. The program instructions are the detailed step by step commands that direct the processing equipment. In its most common form, the commands refer to positions of

13、 a machine tool spindle with respect to the worktable on which the part is fixed. More advanced instructions include selection of spindle speeds, cutting tools, and other functions. The machine control unit (MCU) consists of the electronics and control hardware that reads and interprets the program

14、 of instructions and convert it into mechanical actions of the machine tool or other processing equipment. The processing equipment is the component that performs metal process. In the most common example of numerical control, it is used to perform machining operations. The processing equipment con

15、sists of the workable and spindle as well as the motors and controls needed to drive them. Types of NC There are two basic types of numerical control systems: point to point and contouring. Point to point control system, also called positioning, are simpler than contouring control system. Its pr

16、imary purpose is to move a tool or workpiece from one programmed point to another. Usually the machine function, such as a drilling operation, is also activated at each point by command from the NC program. Point to point system are suitable for hole machining operations such as drilling, countersin

17、king, counterboring, reaming, boring and tapping. Hole punching machines, spotwelding machines, and assembly machines also use point to point systems. Contouring system, also known as the continuous path system, positioning and cutting operations are both along controlled paths but at different vel

18、ocities. Because the tool cuts as it travels along a prescribed path, accurate control and synchronization of velocities and movements are important. The contouring system is used on lathes, milling machines, grinders, welding machinery, and machining centers. Movement along the path, or interpolati

19、on, occurs incrementally, by one of several basic methods. There are a number of interpolation schemes that have been developed to deal with the various problems that are encountered in generating a smooth continuous path with a contouring type NC system. They include linear interpolation, circular

20、interpolation, helical interpolation, parabolic interpolation and cubic interpolation. In all interpolations, the path controlled is that of the center of rotation of the tool. Compensation for different tools, different diameter tools, or tools wear during machining, can be made in the NC program.

21、 Programming for NC A program for numerical control consists of a sequence of directions that causes an NC machine to carry out a certain operation, machining being the most commonly used process. Programming for NC may be done by an internal programming department, on the shop floor, or

22、 purchased from an outside source. Also, programming may be done manually or with computer assistance. The program contains instructions and commands. Geometric instructions pertain to relative movements between the tool and the workpiece. Processing instructions pertain to spindle speeds, feeds, t

23、olls and so on. Travel instructions pertain to the type of instruction and slow or rapid movements of the toll or worktable. Switching commands pertain to on/off position for coolant supplies, spindle rotation, direction of spindle rotation, tool changes, workpiece feeding, clamping and so on. Th

24、e first NC programming language was developed by MIT developmental work on NC programming systems in the late 1950s and called APT (Automatically Programmed Tools). DNC and CNC The development of numerical control was significant achievement in batch and job shop manufacturing, from both a technol

25、ogical and commercial viewpoint. There have been two enhancements and extensions of NC technology, include: (1) Direct numerical control. (2) Computer numerical control. Direct numerical control can be defined as a manufacturing system in which a number of machines are controlled by a computer th

26、rough direct connection and in real time. The tape reader is omitted in DNC, thus relieving the system of its least reliable component. Instead of using the tape reader, the part program is transmitted to the machine tool directly from the computer memory. In principle, one computer can be used to c

27、ontrol more than 100 separate machines. The DNC computer is designed to provide instructions to each machine tool on demand. When the machine needs control commands, they are communicated to it immediately. Since the introduction of DNC there have been dramatic advances in computer technology. The

28、physical size and cost of a digital computer has been significantly reduced at the same time that its computational capabilities have been substantially increased. In numerical control, the result of these advances has been that the large hard-wired MCUs of conventional NC have been replaced by cont

29、rol units based on the digital computer. Initially, minicomputers were utilized in the early 1970s. As further miniaturization occurred in computers, minicomputers were replaced by today’s microcomputers. Computer numerical control is an NC system using dedicated microcomputer as the mach

30、ine control unit. Because a digital computer is used in both CNC and DNC, it is appropriate to distinguish between the two types of system. There are three principal differences: (1) DNC computers distribute instructional data to, and collect data form, a large number of machines. CNC computers con

31、trol only one machine, or a small number of machines. (2) DNC computers occupy a location that is typically remote from the machines under their control. CNC computer are located very near their machine tools. (3) DNC software is developed not only to control individual pieces of production equipm

32、ent, but also to serve as part of a management information system in the manufacturing sector of the firm. CNC software is developed to augment the capabilities of a particular machine tool. 8