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1、 數(shù)控車床 在先進制造技術領域最根本的觀念之一是數(shù)控（NC）。數(shù)控來臨之前，所有機床是手工操作和控制。手動控制機床有許多限制，或許沒有比操作者的技能更突出。用手動控制，產品質量直接相關，并僅限于操作者的技能。 車床主要是為了進行車外圓、車端面和鏜孔等項工作而設計的機床。車削很少在其他種類的機床上進行，而且任何一種其他機床都不能像車床那樣方便地進行車削加工。由于車床還可以用來鉆孔和鉸孔，車床的多功能性可以使工件在一次安裝中完成幾種加工。因此，在生產中使用的各種車床比任何其他種類的機床都多。 車床的基本部件有：床身、主軸箱組件、尾座組件、溜板組件、絲杠和光杠 件在各種速度下回轉。主軸

2、箱基本上由一個安裝在精密軸承中的空心主軸和一系列變速齒輪(類似于卡車變速箱)所組成。通過變速齒輪，主軸可以在許多種轉速下旋轉。大多數(shù)車床有8~12種轉速，主軸箱安裝在內側導軌的固定位置上，一般在床身的左端。它提供動力，并可使工一般按等比級數(shù)排列。而且在現(xiàn)代機床上只需扳動2~4個手柄，就能得到全部轉速。一種正在不斷增長的趨勢是通過電氣的或者機械的裝置進行無級變速 由于機床的精度在很大程度上取決于主軸，因此，主軸的結構尺寸較大，通常安裝在預緊后的重型圓錐滾子軸承或球軸承中。主軸中有一個貫穿全長的通孔，長棒料可以通過該孔送料。主軸孔的大小是車床的一個重要尺寸，因此當工件必須通過主軸孔供料時，它確定

3、了能夠加工的棒料毛坯的最大尺寸。 這個問題導致了1959年自動編程工具（APT）語言的發(fā)展，使用類似數(shù)控英文語句來定義幾何零件，描述刀具配置，并制定所需的方案。新的APT語言的發(fā)展是重大的一步，推動數(shù)控技術的進一步發(fā)展。原來的數(shù)控系統(tǒng)廣泛使用穿孔紙，后來由磁性塑料帶代替。一個使用穿孔紙的人解釋了該機器的磁帶使用說明作為知名的數(shù)控概念發(fā)展（DNC）解決了紙張和塑料帶與數(shù)控相關作為執(zhí)行指令的編程語言磁帶的問題。在直接數(shù)字控制下，精密機床的束縛，通過數(shù)據(jù)傳輸鏈路，連接在主機和機器工具，通過數(shù)據(jù)傳輸連接需要。直接數(shù)字控制穿孔紙帶和塑料帶的應用上是一個重大的進步。但是，它受所有技術，在主機上卻有相同的

4、限制。當主機出現(xiàn)故障，機器工具也會出現(xiàn)故障。這個問題引導了計算機數(shù)控的發(fā)展。 關于可編程邏輯控制器（PLC）和微型計算機的發(fā)展使微處理器的發(fā)展。這兩項技術的發(fā)展，計算機數(shù)字控制（CNC）允許的數(shù)控系統(tǒng)。每臺機器工具，PLC或微型計算機，它為同樣的目的。這允許程序自動輸入和存儲在每個機床上。數(shù)控解決相關的主機停機的問題，但它推出了著名的數(shù)據(jù)管理的另一個問題。同樣的程序可能會被裝上10種不同的微型電腦，它們之間沒有溝通。此問題處理是在當?shù)貐^(qū)域網(wǎng)絡的過程中解決的connectDigital信號處理器的。 在形成了直接數(shù)字控制（DNC）這個概念之后，可以不再采用紙帶或塑料帶作為編程指令的載體，這樣

5、就解決了與之有關的問題。在直接數(shù)字控制中，幾臺機床通過數(shù)據(jù)傳輸線路聯(lián)接到一臺主計算機上。操縱這些機床所需要的程序都存儲在這臺主計算機中。當需要時，通過數(shù)據(jù)傳輸線路提供給每臺機床。直接數(shù)字控制是在穿孔紙帶和塑料帶基礎上的一大進步。然而，它敢有著同其他信賴于主計算機技術一樣的局限性。當主計算機出現(xiàn)故障時，由其控制的所有機床都將停止工作。這個問題促使了計算機數(shù)字控制技術的產生。 微處理器的發(fā)展為可編程邏輯控制器和微型計算機的發(fā)展做好了準備。這兩種技術為計算機數(shù)控（CNC）的發(fā)打下了基礎。采用CNC技術后，每臺機床上都有一個可編程邏輯控制器或者微機對其進行數(shù)字控制。這可以使得程序被輸入和存儲在每臺機

6、床內部。它還可以在機床以外編制程序，并將其下載到每臺機床中。計算機數(shù)控解決了主計算機發(fā)生故障所帶來的問題，但是它產生了另一個被稱為數(shù)據(jù)管理的問題。同一個程序可能要分別裝入十個相互之間沒有通訊聯(lián)系的微機中。這個問題目前正在解決之中，它是通過采用局部區(qū)域網(wǎng)絡將各個微機聯(lián)接起來，以得于更好地進行數(shù)據(jù)管理。 在許多情況下的模擬信號會用各種方法處理問題，在很多方面像濾波和頻譜分析，設計模擬硬件來執(zhí)行這些職能是可能的，但已變得越來越少，由于更高的性能需求，靈活性的需求，以及需要削減減少開發(fā)/測試的時間的需求。正是在困難時，換句話說，是模擬信號的硬件設計分析改變了現(xiàn)狀。 抽樣一個信號是專門為嵌入式信號處

7、理的操作，這種處理器被稱為數(shù)字信號處理器，是數(shù)字信號處理器的代表。今天有數(shù)百個家庭的DSP從盡可能多的制造商，每一個特定的價格/性能/使用組來設計的。大的廠家很多，像德州儀器，摩托羅拉，都提供專門的DSP像馬達控制或調制解調器這些領域的，和一般的高性能DSP處理，可以執(zhí)行廣泛的任務范圍。軟件開發(fā)工具包也可以，也有公司做好DSP的，允許程序員可以實現(xiàn)復雜的處理算法，利用簡單的“拖放和下降”的方法的軟件開發(fā)工具。 DSP的或多或少取決于兩類下降的基礎架構的定點和浮點。定點設備操作一般在16位，而浮點器件上32-40位浮點操作。不用說，定點設備一般比較便宜。另一個重要的結構不同的地方是，定點處理器

8、往往只有一個“通用的蓄電池架構”，這使得他們的方案很棘手，更重要的是，制造的C-編譯器固有的低效率。浮點DSP的表現(xiàn)更像是共同的通用CPU的寄存器文件。 在市場上有成千上萬不同的數(shù)字信號處理器，找到項目最合適的數(shù)字信號處理器是一個艱巨的任務。最好的辦法可能是成立一個約束和心愿，并試圖針對它的最大制造商的處理器來進行比較。 MPEG音頻解碼，數(shù)字壓縮的數(shù)據(jù)反饋到執(zhí)行的DSP解碼，解碼后的樣本，將轉換成模擬域回來，與由此產生的信號放大器或類似的音頻設備。這個數(shù)字到模擬轉換（DCA）的工作由一個具有相同名稱和不同音頻媒體的電路提供不同的性能和質量，如THD（總諧波失真），對位，線性度，速度，

9、過濾特征和其他一些。 該TLS320family儀器由定點，浮點組成，數(shù)字信號處理器的多處理器（DSP）及foxed點DSP控制器。 TMS320系列數(shù)字信號處理器設計了實時信號處理具體的架構。F/C240是C2000DSP平臺，并控制應用而優(yōu)化。C24x的DSP控制器系列，結合這個控制器外設的實時處理能力，以創(chuàng)造一個控制系統(tǒng)應用的理想解決方案。以下特點使TMS320系列正確選擇應用廣泛的加工范圍： ---非常靈活的指令集 ---固有業(yè)務靈活性 ---高速性能 ---創(chuàng)新的并行結構 ---成本效益 一代的TMS320系列器件具有相同的CPU結構，但不同的片上存儲器和外設配置不同。

10、附帶了設備使用的片上存儲器和外設新組合，以滿足全球電子市場的需求范圍。通過整合到一個單一芯片內存和外設，TMS320系列設備降低了系統(tǒng)成本和節(jié)省電路板空間。 16位定點DSP的C24x核心器件模擬設計提供了數(shù)字解決方案，不犧牲精度和系統(tǒng)性能，可通過為技術先進的控制算法，如適應控制使用增強，卡爾曼濾波，和國家控制。C24x DSP控制器提供的可靠性和可編程性。模擬控制系統(tǒng)，一方面，是硬連線解決方案和經(jīng)驗，可能因老化性能降低，元件容差和漂移。 高速中央處理單元（CPU）可處理的數(shù)字化設計，事實上，并不是與查表結果近似的算法。這些指令集的DSP控制器，它集成了信號處理指令和通用控制功能，具有廣泛

11、的開發(fā)時間，并提供了結合傳統(tǒng)的8位和16位微控制器使用相同的環(huán)節(jié)。指令集還允許您保留您的軟件投資在其他普通C2x上，源代碼C2x代兼容，源代碼與德州儀器的數(shù)字信號處理器C5x代兼容。 在C24x架構也非常適用于控制信號的處理。它用于存儲中間結果的32位寄存器的16位字，并有兩個硬件可用號碼提供給獨立的CPU。這種組合減少量化誤差和截斷，以及附加功能增加進化的能力。這些職能可能包括取消陷波器，可以在一個系統(tǒng)或一個機械共振技術，可消除系統(tǒng)狀態(tài)的傳感器。 在C24xDSP控制器考慮讓德州儀器具備快速配置不同價格/性能點或各種系列的成員進行應用優(yōu)化的外設功能設置的優(yōu)勢。這兩個數(shù)字和混合信號外設庫包

12、括： ---定時器 ---串行通信接口（SCI的，SPI） ---模擬到數(shù)字轉換器（ADC） ---事件管理器 ---系統(tǒng)保護，如低電壓和看門狗定時器 該DSP控制器外設庫是不斷增長和變化的，以適應未來的嵌入式控制市場。 該TMS320F/C240于的介紹是第一個標準裝置中的DSP控制器24x系列。它決定一個單芯片的數(shù)字電機控制器的標準。該C240可以執(zhí)行20 MIPS。幾乎所有的指令執(zhí)行時間為50 ns。這一高性能允許實時非常完整的控制算法，如自適應控制，卡爾曼濾波的執(zhí)行。非常高的采樣率也可用于盡量減少循環(huán)延遲。 在240C具有高速信號處理和數(shù)字控制功能所必需的建筑特色，以及

13、它需要提供一個電機控制應用的單芯片解決方案的外設。該240C使用亞微米CMOS制造技術，實現(xiàn)了日志的功耗等級。還包括一些掉電模式，進一步節(jié)省功耗。 要作為一個系統(tǒng)管理員，必須有強大的DSP芯片上的I / O和其他外圍設備。該240事物管理器是不同于其他任何可以用一個數(shù)字信號處理器的處理器。此應用程序優(yōu)化的周邊裝置，與高性能的DSP核心，可提供了高精確度和高效率的全變速控制的所有汽車類型的先進控制技術。事物管理器包括特殊的脈沖寬度調制（PWM）生成功能，如可編程死區(qū)的功能和空間矢量PWM狀態(tài)機，3相馬達，提供了完善的設施，最先進的最高效率開關電源晶體管。 有獨立的定時器，每個與它自己比較的寄

14、存器，支持非對稱代（noncentered）以及對稱（中心）的PWM波形。 開環(huán)和閉環(huán)控制系統(tǒng) 開環(huán)控制系統(tǒng) 這個詞意味著有一個復雜的控制系統(tǒng)自動控制一定的數(shù)額。它通常意味著該系統(tǒng)通常是能夠適應不同的作業(yè)條件，并能有令人滿意的回應。然而，并非任何類型的控制系統(tǒng)都具有自動功能。通常情況下，自動控制功能是通過feed來完成的。 g的反饋結構，它被稱為開環(huán)系統(tǒng)，該系統(tǒng)是精確控制的一個事實，就是可能不知道確切的控制，特點在于最簡單，最經(jīng)濟，它有一個明確的軸承溫度。這也指出了一個開環(huán)控制系統(tǒng)的性能重要的缺餡，該系統(tǒng)不能夠適應變化的環(huán)境或外部干擾。在此控制情況下，或許是有經(jīng)驗的人提供了一個理想中的

15、外室溫控制，門或窗被打開或在營運期間，關閉間歇性，在房子里的最后溫度不會精確的受開環(huán)控制。 閉環(huán)控制系統(tǒng) 閉環(huán)控制缺少更準確和更適應由輸出反饋提高系統(tǒng)的輸入。為了獲得更準確的控制信號必須反饋，并參考輸入，以及一個驅動信號成比例的輸出和輸入的差異，必須通過系統(tǒng)發(fā)送而修正錯誤。與一個或更多反饋，就像是剛才所說的是被稱為閉環(huán)系統(tǒng)。人類系統(tǒng)是可能是最復雜和精密的反饋控制系統(tǒng)的存在。一個人可以被認為是一個控制系統(tǒng)有許多輸入和輸出，開展高度復雜的操作能力。 為了說明人類作為一個正反饋控制系統(tǒng)，讓我們考慮該計劃的目的是達成一個任務對象。眼睛作為傳感裝置，不斷地反饋手的位置。之間的距離和對象的錯誤，最終

16、到零。這是一個閉環(huán)控制的典型例子。然而，如果被告知要達到目標，然后是看不到的，只能達到對對象估計其確切位置。據(jù)國際檢索單位一個閉環(huán)控制系統(tǒng)的算例，表明了該控制系統(tǒng)基本的一個閉環(huán)控制系的圖框。如圖所示。一般來說，一個反饋控制系統(tǒng)配置不得限制該feedback。在復雜的系統(tǒng)有可能反饋回路和元素塊過多。 Numerical Control Lathes One of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control (NC).Pr

17、ior to the advent of NC, all machine tools were manual 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 l

18、imited to the skills of the operator . Numerical control represents the first major step away from human control of machine tools. Lathes are machine tools designed primarily to do turning, facing and boring, Very little turning is done on other types of machine tools, and none can do it with equal

19、 facility. Because lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the work piece. Consequently, more lathes of various types are used in manufacturing than any other machine tool. The essential components of a lathe are the be

20、d, headstock assembly, tailstock assembly, and the leads crew and feed rod. The headstock is mounted in a foxed position on the inner ways, usually at the left end of the bed. It provides a powered means of rotating the word at various speeds . Essentially, it consists of a hollow spindle, mounted

21、in accurate bearings, and a set of transmission gears-similar to a truck transmission—through which the spindle can be rotated at a number of speeds. Most lathes provide from 8 to 18 speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two t

22、o four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives. Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball type

23、s. The spindle has a hole extending through its length, through which long bar stock can be fed. The size of maximum size of bar stock that can be machined when the material must be fed through spindle. This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language

24、 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 system were vast

25、ly different from those used punched paper , which was later to replaced by magnetic plastic tape .A tape reader was used to interpret the instructions written on the tape for the machine .Together, all /f this represented giant step forward in the control of machine tools . However ,there were a nu

26、mber of problems with NC at this point in its development. The development of a concept known as numerical control (DNC) solve the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions . In direct numerica

27、l control, machine tools are tied, via a data transmission link, to a host computer and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However ,it is subject to the same limitation as

28、all technologies that depend on a host computer. When the host computer goes down , the machine tools also experience down time . This problem led to the development of computer numerical control. The development of the microprocessor allowed for the development of programmable logic controllers (P

29、LC) and microcomputers . These two technologies allowed for the development of computer numerical control (CNC).With CNC , each machine tool has a PLC or a microcomputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. CNC solved the problems

30、 associated downtime of the host computer , but it introduced another problem known as data management . The same program might be loaded on ten different microcomputers with no communication among them. This problem is in the process of being solved by local area networks that connectDigital Signal

31、 Processors The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To made 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 t

32、o run the tape through the reader as many times as there were parts to be produced. Fortunately, computer technology became a reality and soon solved the problems of NC associated with punched paper and plastic tape. The development of a concept known as direct numerical control (DNC) solved the pa

33、per and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control, machine tools are tied, via a data transmission link, to a host computer. Programs for operating the machine tools are store

34、d in the host computer and fed to the machine tool an needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend on a host computer. When the ho

35、st computer goes down, the machine tools also experience downtime. This problem led to the development of computer numerical control. There are numerous situations where analog signals to be processed in many ways, like filtering and spectral analysis , Designing analog hardware to perform these fu

36、nctions is possible but has become less and practical, due to increased performance requirements, flexibility needs , and the need to cut down on development/testing time .It is in other words difficult pm design analog hardware analysis of signals. The act of sampling an signal into thehat are spe

37、cialised for embedded signal processing operations , and such a processor is called a DSP, which stands for Digital Signal Processor . Today there are hundreds of DSP families from as many manufacturers, each one designed for a particular price/performance/usage group. Many of the largest manufactur

38、ers, like Texas Instruments and Motorola, offer both specialised DSP’s for certain fields like motor-control or modems ,and general high-performance DSP’s that can perform broad ranges of processing tasks. Development kits an` software are also available , and there are companies making software de

39、velopment tools for DSP’s that allows the programmer to implement complex processing algorithms using simple “drag ‘n’ drop” methodologies. DSP’s more or less fall into two categories depending on the underlying architecture-fixed-point and floating-point. The fixed-point devices generally operate

40、on 16-bit words, while the floating-point devices operate on 32-40 bits floating-point words. Needless to say , the fixed-point devices are generally cheaper . Another important architectural difference is that fixed-point processors tend to have an accumulator architecture, with only one “general p

41、urpose” register , making them quite tricky to program and more importantly ,making C-compilers inherently inefficient. Floating-point DSP’s behave more like common general-purpose CPU’s ,with register-files. There are thousands of different DSP’s on the market, and it is difficult task finding the

42、 most suitable DSP for a project. The best way is probably to set up a constraint and wishlist, and try to compare the processors from the biggest manufacturers against it. Digital-to-analog conversion In the case of MPEG-Audio decoding , digital compressed data is fed into the DSP which performs

43、the decoding , then the decoded samples have to be converted back into the analog domain , and the resulting signal fed an amplifier or similar audio equipment . This digital to analog conversion (DCA) is performed by a circuit with the same name & Different DCA’s provide different performance and q

44、uality , as measured by THD (Total harmonic distortion ), number of bits, linearity , speed, filter characteristics and other things. The TLS320family consists of fixed-point, floating-point, multiprocessor digital signal processors (D[Ps) , and foxed-point DSP controllers. TMS320 DSP have an archi

45、tecture designed specifically for real-time signal processing . The’ F/C240 is a number of the’C2000DSP platform , and is optimized for control applications. The’C24x series of DSP controllers combines this real-time processing capability with controller peripherals to create an ideal solution for c

46、ontrol system applications. The following characteristics make the TMS320 family the right choice for a wide range of processing applications: --- Very flexible instruction set --- Inherent operational flexibility ---High-speed performance ---Innovative parallel architecture ---Cost effectiven

47、ess Devices within a generation of the TMS320 family have the same CPU structure but different on-chip memory and peripheral configurations. Spin-off devices use new combinations of On-chip memory and peripherals to satisfy a wide range of needs in the worldwide electronics market. By integrating

48、memory and peripherals onto a single chip , TMS320 devices reduce system costs and save circuit board space. The 16-bit ,fixed-point DSP core of the ‘C24x devices provides analog designers a digital solution that does not sacrifice the precision and performance of their system performance can be en

49、hanced through the use of advanced control algorithms for techniques such as adaptive control , Kalman filtering , and state control. The ‘C24x DSP controller offer reliability and programmability . Analog control systems, on the other hand ,are hardwired solutions and can experience performance deg

50、radation due to aging , component tolerance, and drift. The high-speed central processing unit (CPU) allows the digital designer to process algorithms in real time rather than approximate results with look-up tables. The instruction set of these DSP controllers, which incorporates both signal proce

51、ssing instructions and general-purpose control functions, coupled with the extensive development time and provides the same ease of use as traditional 8-and 16-bit microcontrollers. The instruction set also allows you to retain your software investment when moving from other general-purpose‘C2xx gen

52、eration ,source code compatible with the’C2x generation , and upwardly source code compatible with the ‘C5x generation of DSPs from Texas Instruments. The ‘C24x architecture is also well-suited for processing control signals. It uses a 16-bit word length along with 32-bit registers for storing inte

53、rmediate results, and has two hardware shifters available to scale numbers independently of the CPU . This combination minimizes quantization and truncation errors, and increases p2ocessing power for additional functions. Such functions might include a notch filter that could cancel mechanical reson

54、ances in a system or an estimation technique that could eliminate state sensors in a system. The ‘C24xDSP controllers take advantage of an set of peripheral functions that allow Texas Instruments to quickly configure various series members for different price/ performance points or for application

55、optimization. The DSP controller peripheral library is continually growing and changing to suit the of tomorrow’s embedded control marketplace. The TMS320F/C240 is the first standard device introduced in the ‘24x series of DSP controllers. It sets the standard for a single-chip digital motor contr

56、oller. The ‘240 can execute 20 MIPS. Almost all instructions are executed in a simple cycle of 50 ns . This high performance allows real-time execution of very comple8 control algorithms, such as adaptive control and Kalman filters. Very high sampling rates can also be used to minimize loop delays.

57、 The ‘ 240 has the architectural features necessary for high-speed signal processing and digital control functions, and it has the peripherals needed to provide a single-chip solution for motor control applications. The ‘240 is manufactured using submicron CMOS technology, achieving a log power dis

58、sipation rating . Also included are several power-down modes for further power savings. Some applications that benefit from the advanced processing power of the ‘240 include: ---Industrial motor drives ---Power inverters and controllers ---Automotive systems, such as electronic power steering ,

59、antilock brakes, and climate control ---Appliance and HVAC blower/ compressor motor controls ---Printers, copiers, and other office products ---Tape drives, magnetic optical drives, and other mass storage products ---Robotic and CNC milling machines To function as a system manager, a DSP must h

60、ave robust on-chip I/O and other peripherals. The event manager of the ‘240 is unlike any other available on a DSP . This application-optimized peripheral unit , coupled with the high performance DSP core, enables the use of advanced control techniques for high-precision and high-efficiency full var

61、iable-speed control of all motor types. Include in the event manager are special pulse-width modulation (PWM) generation functions, such as a programmable dead-band function and a space vector PWM state machine for 3-phase motors that provides state-of-the-art maximum efficiency in the switching of

62、power transistors. There independent up down timers, each with it’s own compare register, support the generation of asymmetric (noncentered) as well as symmetric (centered) PWM waveforms. Open-Loop and Closed-Loop Control Open-loop Control Systems The word automatic implies that there is a certa

63、in amount of sophistication in the control system. By automatic, it generally means That the system is usually capable of adapting to a variety of operating conditions and is able to respond to a class of inputs satisfactorily . However , not any type of control system has the automatic feature. Usu

64、ally , the automatic feature is achieved by feed. g the feedback structure, it is called an open-loop system , which is the simplest and most economical type of control system.inaccuracy lies in the fact that one may not know the exact characteristics of the further ,which has a definite bearing on

65、 the indoor temperature. This alco points to an important disadvantage of the performance of an open -loop control system, in that the system is not capable of adapting to variations in environmental conitions or to external disturbances. In the case of the furnace control, perhaps an experienced pe

66、rson can provide control for a certain desired temperature in the house; but id the doors or windows are opened or closed intermittently during the operating period, the final temperature inside the house will not be accurately regulated by the open-loop control. Closed-Loop Control Systems What is missing in the open-loop control system for more accurate and more adaptable control is a link or feedback from the output to the input of the system . In order to obtain more accurate bontrol, th