經(jīng)濟型數(shù)控車床進給伺服系統(tǒng)設(shè)計,經(jīng)濟型,數(shù)控車床,進給,伺服系統(tǒng),設(shè)計 畢 業(yè) 設(shè) 計 任 務(wù) 書（理工） 學院 工程技術(shù)學院 學生姓名 專業(yè) 機械設(shè)計制造及其自動化 班級 學號 指導老 師 職 稱 課題名稱 經(jīng)濟型數(shù)控車床進給伺服系統(tǒng)設(shè)計 起止日期 自 200 年 月 日起至200 年 月 日 一 、課題來源 畢業(yè)設(shè)計是學生在完成全部大學課程之后所進行的最后一個綜合性實踐性教學環(huán)節(jié)，是學習階段向工程技術(shù)階段的過渡，總目的是使學生受到基本的科研訓練，具體有以下幾點： 1、 通過運用有關(guān)手冊、常用標準及參考資料，培養(yǎng)學生查閱資料、使用資料的能力。 2、 通過總結(jié)、運用四年來所學的機械、電氣、液壓、計算機等有關(guān)知識，學會根據(jù)實際問題確定設(shè)計方案，構(gòu)思機械結(jié)構(gòu)，完成程序設(shè)計及調(diào)試的方法。 3、 培養(yǎng)學生獨立思考問題、解決問題的能力，為以后的工作打下堅實的基礎(chǔ)。 該課題來源與實驗課題。 設(shè)計要求： 將一臺CA6140普通車床改造成微機數(shù)控車床，對其進給伺服系統(tǒng)進行設(shè)計，采用單片機進行控制。 二 、主要涉及內(nèi)容： 4、 翻譯5000印刷符號的外文資料。 5、 機械部分改裝設(shè)計： （1） 進給部分裝配圖一套，0號圖紙 （2） 主要零件圖若干。 6、 硬件設(shè)計 畫出數(shù)控系統(tǒng)硬件電路圖，1號圖紙。 7、 軟件設(shè)計： （1） 數(shù)控程序框圖設(shè)計，1號圖紙。 （2） 8031單片機與步進電機接口圖，1號圖紙。 （3） 程序編制，調(diào)試及系統(tǒng)模擬調(diào)試。 三 、主要設(shè)計技術(shù)指標與參數(shù) 加工最大直徑：在床面上Φ400mm 在床鞍上Φ210mm 加工最大長度：1000mm 溜板及刀架重力：縱向800N 橫向600N 刀架快速速度： 縱向 2.4m/min 橫向 1.2m/min 最大進給速度： 縱向 0.6m/min 橫向 0.3m/min 主電機功率 7.5KW 起動加速時間 30ms 機床定位精度： 0.015mm 四、分階段指導性進度計劃： 第6周：布置任務(wù)，翻譯外文資料，查閱有關(guān)文獻，討論方案。 第7周：實習參觀，確定整體方案。 第8周：根據(jù)確定方案進行設(shè)計計算，繪制草圖。 第19~10周：機械部分設(shè)計，完成裝配圖及主要零件圖。 第11~12周：硬件電路設(shè)計、程序框圖及軟件編程。 第13周：程序調(diào)試與系統(tǒng)模擬調(diào)試。 第14周：編寫設(shè)計說明書。 第15~16周：整理全部文件，準備答辯。 五、 主要參考文獻資料： 《機械設(shè)計手冊 》 徐 灝 機械工業(yè)出版社 1993 《機械零件設(shè)計手冊》 楊黎明 國防工業(yè)出版社 1988 《金屬切削機床概論》 賈亞洲等 機械工業(yè)出版社 1994 《微型計算機原理及應(yīng)用》 鄭學堅等 清華大學出版社 1995 《微型計算機原理及接口技術(shù)》 張新義 機械工業(yè)出版社 1994 《經(jīng)濟型數(shù)控機床系統(tǒng)設(shè)計》 張新義等 機械工業(yè)出版社 1984 《金屬切削機床設(shè)計》 王啟義等 上?？茖W技術(shù)出版社 《機械設(shè)計圖冊》 華東紡織學院等 上?？茖W技術(shù)出版社 《畫法幾何及機械制圖》 山東工業(yè)大學制圖研究室等 山東科學技術(shù)出版社 1988 《機床電氣控制技術(shù)》 毛占慶等 機械工業(yè)出版社 1993 指導教師（簽字）： 20 年 月 日 系主任（簽字）： 20 年 月 日 參考文獻 參考文獻 [1] 徐 灝 機械設(shè)計手冊 機械工業(yè)出版社 1993 [2] 楊黎明 機械零件設(shè)計手冊 國防工業(yè)出版社 1988 [3] 賈亞洲等 金屬切削機床概論 機械工業(yè)出版社 1994 [4] 鄭學堅等 微型計算機原理及應(yīng)用 清華大學出版社 1995 [5] 張新義 微型計算機原理及接口技術(shù) 機械工業(yè)出版社 1994 [6] 張新義等 經(jīng)濟型數(shù)控機床系統(tǒng)設(shè)計 機械工業(yè)出版社 1984 [7] 王啟義等 金屬切削機床設(shè)計 上?？茖W技術(shù)出版社 [8] 機械設(shè)計圖冊 華東紡織學院等 上?？茖W技術(shù)出版社 [9]畫法幾何及機械制圖 山東工業(yè)大學制圖研究室等 山東科學技術(shù)出版社 1988 [10] 毛占慶等 機床電氣控制技術(shù) 機械工業(yè)出版社 1993 [11] 吳祖育 秦鵬飛 數(shù)控機床 上?？茖W技術(shù)出版社 1989 [12] American Machinist ， May 1990 [13]John Striger，Hydraulic System Analysis，Macmillan PressLTD.1976 - 44 - 畢業(yè)設(shè)計（論文） 題 目： 經(jīng)濟型數(shù)控車床進 給伺服系統(tǒng)設(shè)計 學 院： 機械工程學院 專 業(yè)：機械設(shè)計制造及其自動化 學生姓名： 指導教師： 畢業(yè)設(shè)計（論文）時間：二ОО 年 月 日～ 月 日 共 周 畢業(yè)設(shè)計開題報告（理工類） 設(shè)計題目 經(jīng)濟型數(shù)控車床進給伺服系統(tǒng)設(shè)計 學生姓名 學號 專業(yè) 機械設(shè)計制造及其自動化 一、課題的目的意義： 隨著社會生產(chǎn)和科學技術(shù)的發(fā)展，機械及加工產(chǎn)品的形狀和結(jié)構(gòu)不斷改進，對加工質(zhì)量的要求越來越高。產(chǎn)品更新?lián)Q代的速度加快，目前在一般機械加工中，單件、小批量生產(chǎn)的產(chǎn)品約占70%--80%。為了保證產(chǎn)品的質(zhì)量，提高生產(chǎn)率和降低成本，要求機床不僅有較好的通用性和靈活性，而且加工過程要盡可能實現(xiàn)自動化，基于這種情況，數(shù)控技術(shù)得以發(fā)展。 數(shù)控技術(shù)是以數(shù)字程序的形式實現(xiàn)控制的一門技術(shù)，它適用于加工多品種小批量零件、結(jié)構(gòu)復雜、精度要求較高的零件及要求頻繁改型的零件。 二、近年來國內(nèi)外研究現(xiàn)狀： 數(shù)控技術(shù)的應(yīng)用不但給傳統(tǒng)制造業(yè)帶來了革命性的變化，使制造業(yè)成為工業(yè)化的象征，而且隨著數(shù)控技術(shù)的不斷發(fā)展和應(yīng)用領(lǐng)域的擴大，它對國計民生的一些重要行業(yè)(IT、汽車、輕工、醫(yī)療等)的發(fā)展起著越來越重要的作用，因為這些行業(yè)所需裝備的數(shù)字化已是現(xiàn)代發(fā)展的大趨勢。從目前世界數(shù)控技術(shù)及裝備發(fā)展趨勢來看，其研究熱點有以下方面： 1 .高速、高精加工技術(shù)及裝備的新趨勢 效率、質(zhì)量是先進制造技術(shù)的主體。高速、高精加工技術(shù)能極大地提高效率，產(chǎn)品質(zhì)量和檔次，縮短生產(chǎn)周期和提高市場競爭能力。在加工精度方面，近10年來．普通級數(shù)控機床的加工精度由10um提高5um，精密級加工中心則從3~5um，提高到1~1.5um，且超精密加工精度已開始進入納米級(0.01um)。在可靠性方面，國外數(shù)控裝囂的MTBF值已達到6000h以上，伺服系統(tǒng)的MTBF值達到30000h以上，表現(xiàn)出非常高的可靠性。 2．5軸聯(lián)動加工和復合加工機床快速發(fā)展 采用5軸聯(lián)動對三維曲面零件加工，可用刀具最佳幾何形狀進行切削，不僅光潔度高。而且效率也大幅度提高。 3．智能化、開放式、網(wǎng)絡(luò)化是當代數(shù)控系統(tǒng)發(fā)展的趨勢 21世紀的數(shù)控裝備將具有一定智能化的系統(tǒng)，智能化的內(nèi)容包括在數(shù)控系統(tǒng)中的各個方面：智能化的自動編程、智能化的人機界面、智能診斷、智能監(jiān)控；開放式數(shù)控系統(tǒng)就是數(shù)控系統(tǒng)的開發(fā)可以在統(tǒng)一的運行平臺上，面向機床廠家和最終用戶；網(wǎng)絡(luò)化數(shù)控裝備是近2年國際著名機床博覽會的新亮點，數(shù)控裝備的網(wǎng)絡(luò)化將極大地滿足生產(chǎn)線、制造系統(tǒng)、制造企業(yè)對信息集成的需求，也是實現(xiàn)新的制造模式如敏捷制造、虛擬企業(yè)、全球制造的基礎(chǔ)單元。 4． 重視新技術(shù)標準、規(guī)范的建立 三、設(shè)計方案的可行性分析和預期目標： 設(shè)計方案的可行性分析： 經(jīng)濟型數(shù)控車床采用開環(huán)控制系統(tǒng)，在開環(huán)系統(tǒng)中，輸入裝置把輸入信號給數(shù)控裝置，經(jīng)數(shù)控裝置運算后分配出指令脈沖，通過步進電動機、減速裝置、滾珠絲杠帶動工作臺移動。 經(jīng)濟型數(shù)控車床在普通車床的基礎(chǔ)上改造的，由于普通車床的精度要求不是很高，所以改造后的車床用開環(huán)控制。數(shù)控機床傳動裝置的設(shè)計除了要求具有較高的精度之外，還應(yīng)具有良好的動態(tài)響應(yīng)特性，為確保數(shù)控機床進給系統(tǒng)的傳動精度和工作穩(wěn)定性，在設(shè)計機械傳動裝置時，采用了滾珠絲杠。滾珠絲杠傳動效率高，摩擦損失小，給予適當?shù)念A緊，可消除絲杠和螺母的螺紋間隙并且起動力矩小，運動平穩(wěn)。步進電動機輸出軸轉(zhuǎn)速高、轉(zhuǎn)矩低，因此用齒輪傳動裝置轉(zhuǎn)換成負載軸所要求的低轉(zhuǎn)速、高轉(zhuǎn)矩。 四、所需要的儀器設(shè)備、材料： 儀器設(shè)備：計算機、圖板、丁字尺 參考資料：機械設(shè)計手冊 徐 灝 機械工業(yè)出版社 1993 機械零件設(shè)計手冊 楊黎明 國防工業(yè)出版社 1988 金屬切削機床概論 賈亞洲等 機械工業(yè)出版社 1994 微型計算機原理及應(yīng)用 鄭學堅等 清華大學出版社 1995 微型計算機原理及接口技術(shù) 張新義 機械工業(yè)出版社 1994 經(jīng)濟型數(shù)控機床系統(tǒng)設(shè)計 張新義等 機械工業(yè)出版社 1984 金屬切削機床設(shè)計 王啟義等 上海科學技術(shù)出版社 機械設(shè)計圖冊 華東紡織學院等 上?？茖W技術(shù)出版社 畫法幾何及機械制圖 山東工業(yè)大學制圖研究室等 山東科學技術(shù)出版社 1988 機床電氣控制技術(shù) 毛占慶等 機械工業(yè)出版社 1993 五、課題分階段進度計劃： 序號 起止日期 工??作??內(nèi)??容 階段成果 1 翻譯外文資料，查閱有關(guān)文獻，討論方案。 完成開題報告 2 實習參觀，確定整體方案。 完成計算 3 根據(jù)確定方案進行設(shè)計計算，繪制草圖。 草圖繪制完成 4 機械部分設(shè)計，完成裝配圖及主要零件圖。 裝配圖繪制完成 5 硬件電路設(shè)計、程序框圖及軟件編程。 完成硬件系統(tǒng)設(shè)計 6 程序調(diào)試與系統(tǒng)模擬試調(diào)。 完成軟件設(shè)計 7 編寫設(shè)計說明書。 完成論文 8 整理全部文件，準備答辯。 準備答辯 指導教師意見： NC machine NC machine tool was developed as a new automation tool in the 50s of the 20th century, which use NC technique to solve mechanical cutting process. Following the advanced developing of the modern manufacture, NC machine tool was one of the most important basic equipments as FMC, FMS and CIMS. As the key technology of NC machine tool, NC technology is one of the professional technologies engineering college students should master. One The number of tool machine controls a technique to include tool machine and count to control system and outer circle technique，It constitutes to see form： Number's controlling tool machine is generally lain quality by control, the number control device, servo system and measure feedback device and tool machine host to constitute. Now to each constitute parts of brief introductions as follows:. 1st, control medium When the numerical control engine bed processes, needs each kind of control information must depend on some kind of middle carrier carry home and the transmission，This kind of carrier being called as control medium, The control medium is saves acts completely and the cutting tool which the numerical control processing needs is opposite in the work piece positional information intermedium, it is recording the components processing procedure. The control medium has many kinds of, like punched tape, punch card, magnetic tape and floppy disk and so on, also may need each kind of information through the correspondence connection direct input, uses what kind of control medium to be decided by the numerical control installment type. 2nd, numerical control installment The numerical control installment is the numerical control engine bed core, is the high-tech intensity product. It integrated the microelectronic technology, the information technology, the automatic control technology, the actuation technology, the monitoring examination technology, the software engineering technology and the machine-finishing craft knowledge. The numerical control engine bed is precisely under its control, according to the procedure, which assigns automatically to the machine parts carries on the processing. From 50's in 20 centuries the number controlled tool machine to publish, number's controlling device is already developed CNC by NC. Especially microprocessor and microcomputer make the calculator number control function and credibility of device to raise continuously after counting to control to equip up the successful application, the cost descends continuously, and its high performance price ratio promoted number control the quick development of tool machine. The installment is composed by the hardware and the software. The CNC hardware is a special purpose computer, realizes partial or the complete numerical control function by the software, Through changes the software to be very easy to change or to expand its function. The installment basic skills work includes: Input, decoding, cutting tool compensation, feed rate processing, interpolation, position control, processing, demonstration and diagnosis and so on, It has the main function is as follows: (1) Multi-coordinates control (Multiple spindle linkage); (2)Realizes many kinds of function interpolation; (3) Many kinds of procedure input (Man-machine conversation, manual data feeds, by higher authority computer and other computer equipment excuse input), As well as edition and revision (4) Information transformation; (5)Compensation (Cutting tool radius compensation, cutting tool length compensation, transmission gap compensation, pitch error compensation and so on); (6) multi-processing Options; (7)The breakdown from examines the demonstration (8) Communications and networking. 3rd, The servo system The tool machine servo system is the conjunction link that the number controls device and tool machine, It is based on mobile components of the machine location and speed as the control of automatic control systems, NC device used to accept (or computing) interpolation generation of feed or feed pulse displacement, Driving Machine executive body movement. It includes spindle drive modules (mainly speed control), feed-driven modules, the spindle motor and feed motor, etc.. In general, CNC servo system requirements of a good rapid corresponding performance, feed rate scope, sensitive and accurate tracking and command functions and speed, in the larger context of a good job stability. What to use is the direct current servo system and communicates now servo system, and communicate the servo system is replacing the direct current servo system. 4th, the diagraph feedback equip. The device can be included in the servo system. It consists of measuring element and the corresponding circuit, whose main role is to detect the speed and displacement, Information and feedback control system to form closed loop control. No feedback device measurement systems become open-loop system. The common element is measured pulse encoder, resolve, lnductosyn, grating, and the magnetic-foot Laser Displacement Monitoring System. 5th, The host machine Host NC machine is the mainstay, including bed, box, rail, spindle, feed institutions mechanical parts. The numerical control engine bed structure has following several characteristics: As a result of the high-performance spindle feed servo drives, simplifying the CNC machine mechanical transmission structure, Drive a short chain. CNC machine tools with high mechanical structure of the dynamic characteristics of dynamic stiffness, damping precision, wear resistance and thermal deformation properties, continuous adaptation processing automation; More efficient use of transmission pieces, such as ball screws, linear motion guide, such as hydrostatic guideway. Three, NC Machine features 1st, the characteristics of CNC machine tools Modification of processing objects adaptability, As the NC processing machine parts change, only the need to re-establishment procedures, replacement of a new perforated paper tape or manually input we will be able to realize the processing of parts. It is different from traditional machines, not manufacture, replacement of a large number of tools, fixtures and equipment, no more re-adjustment machine. Therefore NC machine tools can quickly from a processing components into a processing components, which has single pieces, Trial Production small batch of new products and provide great convenience. It reduces the preparation cycle, and save a lot of equipment. For the use of point-to-point control system porous parts processing, when necessary design modifications, change some of the hole locations and size, only partial changes to delete the corresponding porosity zones, spent a very short time on the product can be modified to create new products, and Results for the products constantly attacking provide favorable conditions. 2nd, the high precision machining CNC machine tools are based on figures given in the form of instructions for processing. Since the NC device pulse equivalent up to 0.001mm， and feed chain drive space and reverse screw pitch error NC devices, etc. can be compensated, therefore, NC machine tools can achieve higher precision. For small and medium-sized CNC machine tools, positioning accuracy can be achieved 0.03mm general, repetitive positioning accuracy of 0.01mm. Because the transmission system with CNC machine tools and the structure has reached a very high stiffness and thermal stability, and improved its manufacturing precision, CNC machine tools, especially the automatic processing methods to avoid the producer human operational error, with a number of machined dimensional consistency, and the rate of qualified products, processing quality is quite stable. The introduction of point-to-point control of the drilling system, eliminating the need for the use of drilling template and the drilling package Drilling Template Error coordinates the impact would cease to exist。Also excluded due to the processing of cutting conditions can be improved and can be effective cooling, be processed with precision and surface quality has been enhanced. For complex parts of the contours of processing, the preparation process is taking into account the feed rate control，Can be done in curvature change, the tool cut along the contour to the feed rate is essentially the same, Surface processing can be obtained high precision and surface quality. 3th, processing productivity Time that spare parts need when processing includes mobile time and assistance time two parts. Number's controlling tool machine can reduce these two part of times effectively and therefore processing machine than the average productivity is much higher. CNC machine tool spindle speed and feed rate range than the scope of general machine tools, Every process can choose the most advantageous cutting capacity good structural rigidity to allow CNC Cutting Machine large amount of heavy cutting, effective mobile savings time. NC machine moving parts fast-moving and positioning adopted a deceleration and acceleration measures thus choice of a high velocity air journeys, consumed by the fast progress quick retreat and positioning of the machine than the average much less. CNC machine tools are processing the replacement parts is almost no need for re-adjustment machine, and the parts that were installed in simple positioning device to intensify, stands for parts for installation adjustments could save a lot of time. With a knife in the use of the devices and automatic tool change CNC Machining Center Machine, in a machine to achieve multiple processes of continuous processing reduced the turnaround time for semi finishes products, the enhancement of production efficiency even more apparent. 4th, Reduces operator's labor intensity CNC machine tool is according to the procedure which beforehand composes automatically completes to the components processing, the operator besides places the punched tape 'or’ operation keyboard, the loading and unloading components, the essential working procedure middle survey as well as observes the engine bed the movement, Does not need to carry on the arduous duplicated manual operation, the labor intensity and the tense degree may greatly for reduce, the work condition also has the corresponding improvement. For example in electronics industry printed wiring board drill hole，If drilling on the desktop manually processing, monotonous frequent manual workers is likely to result in extreme visual fatigue, so a lot of mistakes. It is often very difficult for one or more hours of continuous operation. When using high speed CNC drilling, will be able to fundamentally improve the operator's working conditions. 5th, Good economic returns When using the number controlled tool machine to process spare parts, the equipments expenses which share in each spare part was more expensive. But can save many other expenses under the situation that the single piece, small batch quantity produce, so can acquire a good economic performance. Using the number controls tool machine, saving lineation man-hour before processing, can reduce adjustment and process after the spare parts install to top in the tool machine with examination time, reduce direct factor cost. The other hand, as the CNC machine tool parts not hand model, Cam, drilling template and the other fixture. Saving technology equipment. The other hand, as the CNC machine tool parts not hand model, Cam, drilling template and the other fixture. Saving technology equipment. 6th、it is advantageous to a production control. Control tool machine to process spare parts with the number, the ability accurate calculation spare parts processes man-hour, and simplified an examination and work tongs, semi-processed goods effectively of management work. These characteristics are advantageous to make production control modern. CNC machine tools to use digital information with the standard code input, the most suitable place for contacts with the digital computer, the foundation had become the design, manufacturing and management of the calculator assistance integral whole to turn currently. Four, CNC machine’s applications The number controls many advantages that the tool machine really exists general tool machine not to have, but these advantages take certain condition as antecedent of. CNC machine tools on the application is continuing to expand, but it can not completely replace other types of machine tools, not in the most economical solution to the machining of all the problems. CNC machine tools are usually the most appropriate processing is characterized by the following components: 1st, Multi- varieties small volume production Components Diagram 1 meant three types of spare parties of tool machines to process an amount relationship with comprehensive expenses. Figure seen parts of the batch processing for increased election CNC machine disadvantage. The reason lies in a number to control a tool machine oolsequipments expensive, measure appropriation tool complexity machine of producing the adoption with large quantity to compare, count to control a tool machine efficiency return not enough high. 2nd, The structure more complicated spare parts Diagram 2 meant three types of tool machines of are processed the spare parts complicated degree and spare parts the relation of batch quantity size. CNC machine tools are usually suitable for processing structure more complex than a few, CNC machine tools in the processing is the need for expensive processing equipment (tools, clamps and mold) parts. 3th、Frequent modifications to the parts In the national defense and the state-of-art industry sector, the components frequent modification necessity is well known. Introduced the competitive system in the consumer industry department, the product which in the market sold has also had unceasingly tore new, this has provided the user for the CNC machine tools. It saves a lot of technique and equipment costs, overall expenses declined. 4th, High value, and no scrap key parts 5th, The production cycle takes at least an urgent part CNC machine tools widely promoted are the biggest obstacle to the initial equipment investment, as the complexity of the system itself, increased maintenance costs. It will affect the machine utilization in some extent If satisfactory after-sales service, often fail to remove equipment failures. These factors can increase the synthesis production cost. The position-control system is number controls tool machine’s important partial, now introduces its control the concrete principle The position-control servo-mechanism which must reproduce at some remote point the motion applied to a handwheel located at a local command station .the output motion might be used to drive a heavy object (such as a missile launcher) into a required position; power amplification of the command and accurate reproduction are thus necessary. The signals can be transmitted by direct mechanical linkage or by hydraulic, pneumatic, or electric conduit. Apart from mechanical linkage the most rapid transmission may be achieved with electrical connection and this is often but not always used. Where it is used, the mechanical input and output signals are first converted into proportional electrical signals and then transmitted through wires to a subtracting device, which produces a signal proportional to the error. a typical arrangement is shown in fig.1. The low-power error signal is used to drive an amplifier, which also receives power from an external source and delivers controlled power to the motor. The combination of transducers and subtracting element from the error detector, the amplifier is the controller and the motor together with its gearbox from the output element. The amplifier may be purely electrical if the motor is electrical but must be either electro-hydraulic or electro-pneumatic if the motor is either hydraulic or pneumatic. It is emphasized that the object of the system is to make the relatable mass copy as nearly as possible the motion of the handwheel . Let us consider what will happen if the position of the handwheel is turned very rapidly through an angle , the mass being initially at rest. Initially the mass has no velocity and the output position θ0 is zero , thus a signal instantaneously appears at the terminals of the amplifier ;Power from the source is allowed to reach the motor, which then begins to drive the mass so as to reduce the error. As θ0 approaches the error gets smaller and thus less power is allowed to reach the motor, systems are usually designed so that the mass just overshoots the required position; Since is then greater than , the error becomes negative and the motor forces the mass to stop and reverse direction. Some undershoots and further overshoots will then probably take place before the mass finally settles at the required position ( equals to ). Only when exact coincidence occurs does the amplifier receive zero signal and thus the motor is forced to move either one way or the other until all motion dies away. The motor can therefore only come to rest when the signal entering the amplifier is zero. It becomes evident from the above discussion that unless very great care is taken in the design, it is quite possible that the oscillations about the desired position will build up instead of dying away quickly. a system in which oscillations build up is said to be unstable and much of the design work in control engineering is associated with producing a stable system . Adequate stability is, of course only one of several requirements, another requirement is faithful reproduction of a variety of input signals, and it has already been seen that the system of fig.1.is unlikely to reproduce a sudden change in input position with any degree of fidelity. Another type of input command might consist of handwheel motion of constant velocity .The system would then respond with an oscillatory transient and the mass would finally settle flown with a velocity equal to the command bur with a position lagging the command by a small angle .The slight difference between input and output positions would be of such magnitude as to produce an output torque from the motor sufficient to drive the mass at the required velocity against frictional torques .The error could not be zero otherwise the motor would stop and the error would the build up . It is thus apparent that whilst the output will automatically align itself with the command under static conditions, under dynamic conditions the output motion only approximates to that of the command. The closeness of the approximation can however usually be made as good as is necessary to overcome most physical; for example, in certain types of automatically controlled profile milling machines a tracking accuracy to 0.0001inch has been achieved. Another object of the position control system is that it must be capable of holding the output position equal to the presence of severe of severe load disturbances .for example, a launcher must remain pointing in the desired regardless of random guests of wind .the position control system of fig .1. If correctly designed, would be able to achieve quite good regulation against load disturbances of this kind but a steady load disturbances of this kind but a steady load disturbance would inevitably produce a small misalignment between output and command .In systems where such a misalignment would be intolerable, a more sophisticated type of controller must be used. - 9 -