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徐州工程學(xué)院
畢業(yè)設(shè)計(jì)（論文）開(kāi)題報(bào)告
課 題 名 稱(chēng)： 電動(dòng)螺旋起重機(jī)設(shè)計(jì)
學(xué) 生 姓 名： 徐新明 學(xué)號(hào)： 20040601411
指 導(dǎo) 教 師： 陳躍 職稱(chēng)： 講師
所 在 學(xué) 院： 機(jī)電工程學(xué)院
專(zhuān) 業(yè) 名 稱(chēng)： 機(jī)械設(shè)計(jì)制造及自動(dòng)化
徐州工程學(xué)院
2008 年 3月 4 日
說(shuō) 明
1．根據(jù)《徐州工程學(xué)院畢業(yè)設(shè)計(jì)(論文)管理規(guī)定》，學(xué)生必須撰寫(xiě)《畢業(yè)設(shè)計(jì)（論文）開(kāi)題報(bào)告》，由指導(dǎo)教師簽署意見(jiàn)、教研室審查，學(xué)院教學(xué)院長(zhǎng)批準(zhǔn)后實(shí)施。
2．開(kāi)題報(bào)告是畢業(yè)設(shè)計(jì)（論文）答辯委員會(huì)對(duì)學(xué)生答辯資格審查的依據(jù)材料之一。學(xué)生應(yīng)當(dāng)在畢業(yè)設(shè)計(jì)（論文）工作前期內(nèi)完成，開(kāi)題報(bào)告不合格者不得參加答辯。
3．畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告各項(xiàng)內(nèi)容要實(shí)事求是，逐條認(rèn)真填寫(xiě)。其中的文字表達(dá)要明確、嚴(yán)謹(jǐn)，語(yǔ)言通順，外來(lái)語(yǔ)要同時(shí)用原文和中文表達(dá)。第一次出現(xiàn)縮寫(xiě)詞，須注出全稱(chēng)。
4．本報(bào)告中，由學(xué)生本人撰寫(xiě)的對(duì)課題和研究工作的分析及描述，沒(méi)有經(jīng)過(guò)整理歸納，缺乏個(gè)人見(jiàn)解僅僅從網(wǎng)上下載材料拼湊而成的開(kāi)題報(bào)告按不合格論。
5. 課題類(lèi)型填：工程設(shè)計(jì)類(lèi)；理論研究類(lèi)；應(yīng)用（實(shí)驗(yàn)）研究類(lèi)；軟件設(shè)計(jì)類(lèi)；其它。
6、課題來(lái)源填：教師科研；社會(huì)生產(chǎn)實(shí)踐；教學(xué)；其它
課題
名稱(chēng)
小型電動(dòng)螺旋起重機(jī)設(shè)計(jì)
課題來(lái)源
模擬生產(chǎn)實(shí)際課題
課題類(lèi)型
工程應(yīng)用
選題的背景及意義
本課題來(lái)源于模擬生產(chǎn)實(shí)際,屬于工程應(yīng)用。起重機(jī)是當(dāng)代最為得力的起重設(shè)備之一。隨著國(guó)民經(jīng)濟(jì)的不斷發(fā)展,多種類(lèi)型的起重機(jī)廣泛的運(yùn)用于冶金、礦山、水泥、碼頭、化工、糧食等行業(yè)的各種場(chǎng)合。同時(shí)在各種場(chǎng)合對(duì)不同的工況所使用的起重機(jī)也不盡相同，近年來(lái)由于起重機(jī)的應(yīng)用范圍的擴(kuò)大，品種的增多以及質(zhì)量的不斷提高，對(duì)加工設(shè)計(jì)起重機(jī)提出了更高的要求。
本設(shè)計(jì)所研究的電動(dòng)螺旋起重機(jī)，又稱(chēng)作電動(dòng)螺旋升降機(jī)，它的原形也就是我們眾所周知的千斤頂。隨著社會(huì)的發(fā)展，解放勞動(dòng)力，采用電動(dòng)成了必然。因此本設(shè)計(jì)采用電機(jī)驅(qū)動(dòng)，開(kāi)發(fā)出新的產(chǎn)品。
研究?jī)?nèi)容擬解決的主要問(wèn)題
研究?jī)?nèi)容：
1． 電動(dòng)螺旋起重機(jī)機(jī)械機(jī)構(gòu)設(shè)計(jì)
2． 一級(jí)齒輪減速機(jī)構(gòu)設(shè)計(jì)
工作量：
1．A0圖紙三張，分別為系統(tǒng)裝配圖和各零件圖
2．畢業(yè)設(shè)計(jì)說(shuō)明書(shū)一本（2萬(wàn)字）；
3．相關(guān)外文資料翻譯（5000字）。
解決問(wèn)題：
根據(jù)起重重量的大小，設(shè)計(jì)出相應(yīng)的螺旋起重機(jī)構(gòu)，根據(jù)起重的速度設(shè)計(jì)出相應(yīng)的減速機(jī)構(gòu)，以及箱體、選擇電機(jī)等。
研究方法技術(shù)路線
基本研究方法：利用電機(jī)，通過(guò)減速器減速后，帶動(dòng)螺母旋轉(zhuǎn)，轉(zhuǎn)化為絲桿的軸向運(yùn)動(dòng)，從而推動(dòng)物體上升。
基本研究技術(shù)路線：研究千斤頂原理，設(shè)計(jì)螺旋起重機(jī)構(gòu)；選擇電動(dòng)機(jī)；設(shè)計(jì)減速機(jī)構(gòu)；控制電路的設(shè)計(jì)；簡(jiǎn)要闡述在流水線作業(yè)中，螺旋千斤頂?shù)膭?dòng)作原理等。
研究的總體安排和進(jìn)度計(jì)劃
第1周：了解設(shè)計(jì)的基本要求，查閱相關(guān)資料
第2周：查閱相關(guān)資料，寫(xiě)開(kāi)題報(bào)告
第3周：外文資料翻譯
第4周：設(shè)計(jì)方案比較選擇
第5周：機(jī)械部分總體設(shè)計(jì)
第6周：機(jī)械部分設(shè)計(jì)計(jì)算
第7周：機(jī)械部分設(shè)計(jì)計(jì)算
第8周：傳動(dòng)系統(tǒng)設(shè)計(jì)計(jì)算
第9周：傳動(dòng)系統(tǒng)設(shè)計(jì)計(jì)算
第10周：電機(jī)選擇計(jì)算
第11周：繪制機(jī)械裝配圖
第12周：繪制機(jī)械零件圖
第13周：撰寫(xiě)畢業(yè)設(shè)計(jì)說(shuō)明書(shū)
第14周：撰寫(xiě)畢業(yè)設(shè)計(jì)說(shuō)明書(shū)
第15周：答辯準(zhǔn)備
第16周：答辯
主要參考
文獻(xiàn)
[1] 邱宣懷.機(jī)械設(shè)計(jì).第四版. 高等教育出版社, 2003.4
[2] 龔湘義. 機(jī)械設(shè)計(jì)課程設(shè)計(jì)指導(dǎo)書(shū).第二版.高等教育出版社.2004.2
[3] 張建中. 機(jī)械設(shè)計(jì)基礎(chǔ)課程設(shè)計(jì). 中國(guó)礦業(yè)大學(xué)出版社, 2005.2
[4] 哈爾濱工業(yè)大學(xué) 龔湘義. 機(jī)械設(shè)計(jì)課程設(shè)計(jì)圖冊(cè).第三版. 高等教育出版社, 2004.1
[5] 實(shí)用機(jī)械設(shè)計(jì)手冊(cè)編寫(xiě)組.實(shí)用機(jī)械設(shè)計(jì)手冊(cè).第二版.機(jī)械工業(yè)出版社
[6] 范思沖等編著《畫(huà)法幾何及機(jī)械制圖》. 機(jī)械工業(yè)出版社
[7] 李洪、曲中謙. 實(shí)用軸承手冊(cè). 遼寧科學(xué)技術(shù)出版社
[8] 楊黎明. 傳感器技術(shù). 國(guó)防工業(yè)出版社
[9] 徐寅主編，機(jī)械設(shè)計(jì)手冊(cè).北京，機(jī)械工業(yè)出版社，1991
指導(dǎo)教師
意 見(jiàn)
指導(dǎo)教師簽名：
年 月 日
教研室意見(jiàn)
學(xué)院意見(jiàn)
教研室主任簽名：
年 月 日
教學(xué)院長(zhǎng)簽名：
年 月 日
徐州工程學(xué)院畢業(yè)設(shè)計(jì)(論文)
摘要
螺旋起重機(jī)又稱(chēng)為螺旋升降機(jī)，它的原型就是我們所常見(jiàn)的千斤頂。它具有結(jié)構(gòu)緊湊、體積小、重量輕、動(dòng)力源廣泛、無(wú)噪音、安裝方便、使用靈活、功能多、配套形式多、可靠性高、使用壽命長(zhǎng)等許多優(yōu)點(diǎn)?？梢詥闻_(tái)或組合使用，能大致控制調(diào)整提升的高度，可以用電動(dòng)機(jī)或其他動(dòng)力直接帶動(dòng)，也可以手動(dòng)。
電動(dòng)螺旋起重機(jī)基本原理是利用電機(jī)，通過(guò)減速器減速后，帶動(dòng)螺母旋轉(zhuǎn)，轉(zhuǎn)化為絲桿的軸向運(yùn)動(dòng)，從而推動(dòng)物體上升。主要內(nèi)容如下：對(duì)千斤頂?shù)脑砗吐菪鹬氐脑?、方法進(jìn)行了研究；設(shè)計(jì)螺旋起重機(jī)構(gòu)；選擇電動(dòng)機(jī)；設(shè)計(jì)減速機(jī)構(gòu)；控制電路的設(shè)計(jì)；簡(jiǎn)要闡述在流水線作業(yè)中，螺旋千斤頂?shù)膭?dòng)作原理等。
關(guān)鍵詞 千斤頂；電動(dòng)；螺旋傳動(dòng)
Abstract
The spiral crane is also known as the spiral screw lift crane .Its prototype is the jack as we common see. Its advantages as follows: small size, light weight, extensive power source, no noise, ease of installation, flexible, multi-function, supporting forms, high reliability and long service life, and so on. It can be used single or in combination, and can generally control the height. Motor can be used directly or other power driven, besides ,it can also be manually.
And the basic principle is that the motor drives the rotary nut through the deceleration agencies, screw into the axial campaign, and then lift the objects .The main contents as follows: research the principle of spiral jack and the principles and methods of the spiral lifting, design the agencies of spiral lifting; motor choice; design deceleration agencies; select keys and bearings, design the control circuit; describe the principle of the screw jack on the assembly line operation.
Keywords Spiral jack Electrical Spiral drive
II
徐州工程學(xué)院畢業(yè)設(shè)計(jì)(論文)
目 錄
1 緒論 1
1.1千斤頂?shù)陌l(fā)展現(xiàn)狀 1
1.2千斤頂?shù)姆诸?lèi) 2
2 設(shè)計(jì)方案的確定 3
2.1螺旋傳動(dòng)設(shè)計(jì)方案 3
2.1.1螺旋傳動(dòng)概述 3
2.1.2螺旋傳動(dòng)方案的確定 4
2.2減速傳動(dòng)機(jī)構(gòu)設(shè)計(jì)方案 5
3 傳動(dòng)系統(tǒng)的設(shè)計(jì) 6
3.1螺旋傳動(dòng)部分計(jì)算 6
3.1.1螺桿直徑的計(jì)算 6
3.1.2螺紋部分強(qiáng)度計(jì)算 6
3.2電機(jī)的選擇 8
3.2.1電動(dòng)機(jī)功率計(jì)算 9
3.2.2傳動(dòng)效率 9
3.2.3確定電機(jī)轉(zhuǎn)速 10
3.3減速機(jī)構(gòu)的設(shè)計(jì) 11
3.3.1材料的選擇 11
3.3.2蝸輪蝸桿傳動(dòng)基本尺寸 12
3.3.3強(qiáng)度校核 15
3.3.4蝸輪蝸桿傳動(dòng)中的作用力分析 15
3.3.5實(shí)際傳動(dòng)動(dòng)力參數(shù) 16
4 輔助裝置的設(shè)計(jì) 18
4.1軸承的選擇 18
4.1.1軸承的選擇因素 18
4.1.2軸承的型號(hào)確定 19
4.1.3軸承校驗(yàn) 19
4.2鍵的選擇 22
4.3聯(lián)軸器的設(shè)計(jì)與計(jì)算 23
5 控制電路及過(guò)載保護(hù)系統(tǒng)的設(shè)計(jì) 25
5.1 過(guò)載及最大行程保護(hù)元件 25
5.1.1 熱繼電器 25
5.1.2 行程開(kāi)關(guān) 26
5.2電器控制基本電路設(shè)計(jì) 28
6 系統(tǒng)的改進(jìn)與優(yōu)化 30
6.1力學(xué)傳感器 30
6.1.1電阻應(yīng)變片力傳感器 30
6.2位置傳感器 32
6.3連續(xù)控制分析 34
結(jié)論 35
致謝 36
參考文獻(xiàn) 37
附錄 38
附錄1 38
附錄2 49
2
徐州工程學(xué)院畢業(yè)設(shè)計(jì)(論文)
附錄
附錄1
英文原文
CNC TECHNOLOGY
Numerical control (NC) 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 NC suitable for low-and medium-volume production. It is much easier to write new programs than to make major alterations of the processing equipment.
BASIC COMPONENTS OF NC
A numerical control system consists of the following three basic components:
·Program of instructions
·Machine control unit
·Processing equipment
The general relationship among the three components is: the program is fed into the control unit, which directs the processing equipment accordingly.
The program of instructions is the detailed step-by-step commands that direct the processing equipment. In its most common form, the commands refer to positions of a machine tool spindle with respect to the worktable on which the part is fixtured. More advanced instructions include selection of spindle speeds, cutting tool, and other function. The most common medium in use over the last several decades has been 1-in. -wide punched tape. Because of the widespread use of the punched tape, NC is sometimes called “tape control”. However, this is a misnomer in modern usage of numerical control. Coming into use more recently have been magnetic tape cassettes and floppy diskettes.
The machine control unit (MCU) consists of the electronics and control hardware that read and interpret the program of instruction and convert it into mechanical actions of the machine tool or other processing equipment.
The processing equipment is the third basic component of an NC system. It is the component that performs useful work. In the most common example of numerical control, one that performs machining operations, the processing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them.
Types Of Control Systems
There are two basic types of control systems in numerical control: point-to-point and contouring. In the point-to-point system, also called positioning, each axis of the machine is driven separately by leadscrews and, depending on the type of operation, at different velocities. The machine moves initially at maximum velocity in order to reduce nonproductive time but decelerates as the tool reaches its numerically defined position. Thus in an potation such as drilling or punching, the positioning and cutting take place sequentially. After the hole is drilled or punched, the tool retracts, moves rapidly to another position, and repeats the operation. The path followed from one position to another is important in only one respect: The time required should be minimized for efficiency. Point-to-point systems are used mainly in drilling, punching, and straight milling operations.
In the contouring system, also known as the continuous path system, positioning and cutting operations are both along controlled paths but at different velocities. 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 interpolation, occurs incrementally, by one of several basic methods. In all interpolations, the path controlled is that of the center of rotation of the tool. Compensation for different tools, different diameter tools, or tool wear during machining, can be made in the NC program.
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 interpolation
·Helical interpolation
·Parabolic interpolation
·Cubic interpolation
Each of these interpolation procedures permits the programmer (or operator) to generate machine instructions for linear or curvilinear paths, using a relatively few input parameters. The interpolation module in the MCU performs the calculations and directs the tool along the path.
Linear interpolation is the most basic and is used when a straight-line path is to be generated in continuous-path NC. Two-axis and three-axis linear interpolation routines are sometimes distinguished in practice, but conceptually they are the same. The program is required to specify the beginning point and end point of the straight line, and the feed rate that is to be followed along the straight line. The interpolator computes the feed rates for each of the two (or three) axes in order to achieve the specified feed rate.
Linear interpolation for creating a circular path would be quite inappropriate because the programmer would be required to specify the line segments and their respective end points that are to be used to approximate the circle. Circular interpolation schemes have been developed that permit the programming of a path consisting of a circular arc by specifying the following parameters of the arc: the coordinates of its end points, the coordinates of its center, its radius, and the direction of the cutter along the arc. The tool path that is created consists of a series of straight-line segments, but the segments are calculated by the interpolation module rather than the programmer. The cutter is directed to move along each line segment one by one in order to generate the smooth circular path. A limitation of circular interpolation is that the plane in which the circular arc exists must be a plane defined by two axes of the NC system.
Helical interpolation combines the circular interpolation scheme for two axes described above with linear movement of a third axis. This permits the definition of a helical path in three-dimensional space.
Parabolic and cubic interpolation routines are used to provide approximations of free-form curves using higher-order equations. They generally require considerable computational power and are not as common as linear and circular interpolation. Their applications are concentrated in the automobile industry for fabricating dies for car body panels styled with free-form designs that cannot accurately and conveniently be approximated by combining linear and circular interpolations.
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 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 work piece. Processing instructions pertain to spindle speeds, feeds, tools, and so on. Travel instructions pertain to the type of interpolation and slow or rapid movements of the tool or worktable. Switching commands pertain to on/off position for coolant supplies, spindle rotation, direction of spindle rotation, tool changes, work piece feeding, clamping, and so on.
(1) Manual Programming??
Manual part programming consists of first calculating dimensional relationships of the tool, work piece, and work table, based on the engineering drawings of the part, and manufacturing operations to be performed and their sequence. A program sheet is then prepared, which consists of the necessary information to carry out the operation, such as cutting tools, spindle speeds, feeds, depth of cut, cutting fluids, power, and tool or work piece ally a paper tape is first prepared for trying out and debugging the program. Depending on how often it is to be used, the tape may be made of more durable Mylar.
Manual programming can be done by someone knowledgeable about the particular process and able to understand, read, and change part programs. Because they are familiar with machine tools and process capabilities, skilled machinists can do manual programming with some training in programming. However, the work is tedious, time consuming, and uneconomical-and is used mostly in simple point-to-point applications.
(2) Computer-Aided Programming??
Computer-aided part programming involves special symbolic programming languages that determine the coordinate points of corners, edges, and surfaces of the part. Programming language is the means of communicating with the computer and involves the use of symbolic characters. The programmer describes the component to be processed in this language, and the computer converts it to commands for the NC machine. Several languages having various features and applications are commercially available. The first language that used English-like statements was developed in the late 1950s and is called APT (for Automatically Programmed Tools). This language, in its various expanded forms, is still the most widely used for both point-to-point and continuous-path programming.
Computer-aided part programming has the following significant advantages over manual methods:
· Use of relatively easy to use symbolic language
·Reduced programming time. Programming is capable of accommodating a large amount of data concerning machine characteristics and process variables, such as power, speeds, feed, tool shape, compensation for tool shape changes, tool wear, deflections, and coolant use.
· Reduced possibility of human error, which can occur in manual programming
· Capability of simple changeover of machining sequence or from machine to machine.
· Lower cost because less time is required for programming.
Selection of a particular NC programming language depends on the following factors:
a)???Level of expertise of the personnel in the manufacturing facility.
b)???Complexity of the part.
c)???Type of equipment and computers available.
d)???Time and costs involved in programming.
Because numerical control involves the insertion of data concerning work piece materials and processing parameters, programming must be done by operators or programmers who are knowledgeable about the relevant aspects of the manufacturing processes being used. Before production begins, programs should be verified, either by viewing a simulation of the process on a CRT screen or by making the part from an inexpensive material, such as aluminum, wood, or plastic, rather than the material specified for the finished part.
Cutting tool choice and cutting specifications determination in CNC processing
The cutting tool choice and the cutting specifications determination is in the numerical control processing craft important content, it not only influence numerical control engine bed processing efficiency, moreover affects the processing quality directly. CAD/The CAM technology development, enables in the numerical control processing to become directly using the CAD design data possibly, specially the microcomputer and the numerical control engine bed joint, causes the design, the craft plan and the programming entire process completes completely on the computer, does not need to output the special technological document generally.
Now, many CAD/The CAM software package all provides the automatic programming function, these software are generally prompt the craft plan in the programming contact surface the related question, for instance, cutting tool choice, processing way plan, cutting specifications hypothesis and so on, programmers so long as have established the related parameter, may automatically produce completes the processing the NC procedure and the transmission to the numerical control engine bed. Therefore, in the numerical control processing cutting tool choice and the cutting specifications determination is completes under the man-machine interactive condition, this forms the sharp contrast with the ordinary engine bed processing, at the same time also requests the programmers to have to grasp the cutting tool choice and the cutting specifications determination basic principle, when programming full consideration numerical control processing characteristic. This article the cutting tool choice and the cutting specifications which must face to the numerical control programming in determined the question has carried on the discussion, has produced certain principles and the suggestion, and to the question which should pay attention has carried on the discussion.
First, numerical control processing commonly used cutting tool type and characteristic
The numerical control processing cutting tool must adapt the numerical control engine bed high speed, is highly effective and the automatic high characteristic, should include the general cutting
tool, the general connection hilt and the few special-purpose hilts generally. The hilt must join the cutting tool and install on the engine bed power head, therefore already gradual
standardization and seriation. The numerical control cutting tool classification has the many kinds of methods. May divide into according to the cutting tool structure: (1) Integral type; (2) The mosaic, uses the welding or machine clamps the type connection, machine clamps the type to be possible to divide into does not index and may index two kinds; (3) Special pattern, like compound expression cutting tool, absorption of shock type cutting tool and so on. According to makes the material
which the cutting tool uses to be possible to divide into: (1) High-speed steel cutting tool; (2) Hard alloy tools; (3) Diamond cutting tool; (4) Other material cutting tools, like cubic boron nitride cutting tool, ceramic cutting tool and so on. May divide into from the cutting craft: (1) The turning cutting tool, divides the outer annulus, in the hole, the thread, cuts the cutting tool many kinds of and so on; (2) Drills truncates the cutting tool, including drill bit, reamer, screw tap and so on; (3) Boring cutting tool; (4) Milling cutting tool and so on. In order to adapt the numerical control engine bed durably to the cutting tool, is stable, easy change, may trade and so on the request, in recent years machine clamps the type to be possible to index the cutting tool to obtain the widespread application, reaches higher authorities in the quantity to the entire numerical control cutting tool 30% ~ 40%, the metal excision quantity accounts for the total 80% ~ 90%.
Machining Centers
Many of today’s more sophisticated lathes are called machining centers since they are capable of performing, in addition to the normal turning operations, certain milling and drilling operations. Basically, a machining center can be thought of as being a combination turret lathe and milling machine. Additional features are sometimes included by manufacturers to increase the versatility of their machines.
Numerical Control
One of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control (NC). Prior to the advent of NC, all machine tools were manually operated and controlled .Among the many limitations associated with manual control machine tools, perhaps none is more prominent than the limitation of operator skills. With manual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control of machine tools.
Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician writes a program that issues operational instructions to the machine tool. For a machine tool to be numerically controlled, it must be interfaced with a device for accepting and decoding the programmed instructions, known as a reader.
Numerical control was developed to overcome the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines, they can produce parts more uniformly, they are faster, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology:
1. Electrical discharge machining.
2. Laser cutting.
3. Electron beam welding.
Numerical control has also made machine tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide variety of parts, each involving an assortment of widely varied and complex machining processes. Numerical control has allowed manufacturers to undertake the production of products that would not have been feasible from an economic perspective using manually controlled machine tools and processes.
Like so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the U. S. Air force. In its earliest stages, NC machines were able to make straight cuts efficiently and effectively.
However, curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter is the straight lines making up the steps, the smoother is the curve. Each line segment in the steps had to be calculated.
This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major step forward in the further development of NC technology. The original NC systems were vastly different from those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development.
A major problem was the fragility of the punched paper tape medium. It was common for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each successive time a part was produced on a machine tool, the paper tape carrying the programmed instructions had to be rerun through the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use.
This led to the development of a special magnetic plastic tape. Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magnetic dots. The plastic tape was much stronger than the paper taps, which solved the problem of frequent tearing and breakage. However, it still left two other problems.
The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instructions, it was necessary to interrupt machining operations and make a new tape .It was also still necessary to run the tape th