靠模攻絲組合機床設(shè)計【臥式雙面攻絲組合機床】,臥式雙面攻絲組合機床,靠模攻絲組合機床設(shè)計【臥式雙面攻絲組合機床】,靠模攻絲,組合,機床,設(shè)計,臥式,雙面 The Basic Machines When a prehistoric man or woman used a stick to pry up a stone, the lever was invented. It is one of the six basic machines. A lever is a rigid piece or bar, like the early person’s stick, which turn on a point called the fulcrum. When force is applied at a second point, that force is transmitted to a third point where it can perform a work. A children’s seesaw is an excellent example of a lever. The point of balance on which the seesaw rests is the fulcrum; when downward force is applied to one end, the other end rises. The organized use of lever goes back beyond the beginning of recorded history. Levers were probably used to raise the huge blocks of stone from which Stone-henge was constructed. Perhaps the stones were raised by using tree trunks as levers until the stones toppled into place. The wheel and axle is the second basic type of machine. Like the lever, the wheel goes back to prehistoric times when someone probably discovered that it was easier to move heavy weights by sliding them on logs than by carrying them. The axle is a shaft on which a wheel can turn and the wheel and axle combination may have first used sometime around 3000B.C. for water-raising devices. It use for transportation evolved with the domestication of the horse. War chariots were the tanks of ancient times and wagons were the trucks. The third basic machine is the pulley. This simple device was used in ancient times for tasks such as raising water from wells or streams. A pulley contained in a housing is called a block. When a fixed block to which a weight is attached, downward pull on the rope will raise the weight. The device is called a block and tackle. The three remaining basic machines are so related to one another that they are sometimes grouped together. They are the wedge, the inclined plane, and the screw. The wedge is a triangle with two chief surfaces that meet in a sharp angle. Wedges are used for splitting open or pushing apart. They were used from very early times for cutting wood, as with an axe. A nail is a familiar form of the wedge. We have already mentioned the inclined plane as the probable method employed by the Egyptians for manipulating into place the huge blocks of stone in the pyramids. Early men and women knew that a weight could be pushed up to a hill or a ramp of earth with less effort than would be required to move the same weight vertically. The inclined plane is an important factor that concerns civil engineers when designing highways or railroads. The mechanical engineer more frequently uses the screw, a spiral form of the inclined plane. The figure that results from wrapping the line of an incline plane around a cylinder is called a helix. Essentially all machines are variations or components that of the six basic types. There are a number of different kinds of mechanisms or components that transmit motion or change it in one way to another. Modern machines and their components have become so complex that a branch of the science of mechanics called kinematics evolved of most modern machines, it is their mechanisms that give them their great versatility and flexibility. Gears play such an important part in machines that they have become the they have become the symbol for machinery. They are wheel with teeth that engage or mesh with each other so that they work in pairs to transmit or change motion. They are frequently used to reduce or increase the speed of a motion and they can also change the direction of motion. The line around which a wheel rotates is its axis; gear can change axial motion. Another kind of mechanism is the cam. Like the gear, it consists of a pair of components; the cam itself is the input member and the follower is the output member. The cam is attached to a rotating shaft; it transmits motion to the follower. Cam comes in many different shapes-there are heart-shaped cams, clover-leafed cams and others. By means of these different shapes cams can change rotating into reciprocating motion or into oscillating or vibrating motion. The follower is usually a rod or shaft. Cams can also transmit exact motion at special times in a cycle. They are there useful where the timing of complex motions is important. They are in automobile engines to raise and lower ten valves and in sewing machines to control the movements of the needle. Another kind of mechanism is known as a linkage; it is a series of at least three rods or solid links that are connected by joints that permit the links to pivot. When one link is fixed the other links can move only in paths that are predetermined. Like cams, linkage are used to change the direction of motion, to transmit different kinds of motion, or to provide variations in timing in different parts of a cycle by varying the lengths of the links in relation to each other. The spring is a mechanism that is used in a wide variety of machines; it is frequently an elastic helical coil that returns to its original shape after being distorted. Springes are essential components in watches; in some cam mechanisms they hold the follower in place; they are found in scales and they help to cushion an automobile ride. There are many variations on the basic coiled of spring, including the leaf spring which is made of strips of elastic material and springs that depend on the compression and expansion of air. A ratchet is another paired mechanism consisting of a wheel with teeth and a pawl which drops into the spaces between the teeth. The ratchet mechanism is used to prevent a motion from being reversed or to change reciprocating into rotary motion. This is a brief introduction to the complex world of machine components. Open-Loop and Closed-Loop Control Open-Loop Control Systems The word automatic implies that there is a certain 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. Usually, the automatic feature is achieved by feeding the output variable back and comparing it with the command signal. When a system does not have the feedback structure, it is called an open-loop system, which is the simplest and most economical type of control system. Unfortunately, open-loop control system lack accuracy and versatility and can be used in none but the simplest types of applications. Consider, for example, control of the furnace for home heating. Let us assume that the furnace is equipped only with a timing device, which control the on and off periods of the furnace. To regulate the temperature to the proper lever, the human operator must estimate the amount of time required for the furnace to stay on and then set the timer accordingly. When the preset time is up, the furnace is turned off. However, it is quite likely that the house temperature is either above or below the desired value, owing to inaccuracy in the estimate. Without further deliberation, it is quite apparent that this type of control is inaccurate and unreliable. One reason for the inaccuracy lies in the fact that one may not know the exact characteristics of the furnace. The other factor is that one has no control over the outdoor temperature, which has a definite bearing on the indoor temperature. This also 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 conditions or to external disturbances. In the case of the furnace control, perhaps an experienced person can provide control for a certain desired temperature in the house; but if 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. An electric washing machine is another typical example of an open-loop system, because the amount of wash time is entirely determined by the judgment and estimation of the human operator. A true automatic electric washing machine should have the means of checking the cleanliness of the clothes continuously and turn itself off when the desired degree of cleanliness is reached. Although open-loop control system are of limited use, they form the basic elements of the closed-loop control system. In general, the elements of an open-loop control system are represented by the block diagram of Fig.15.1. An input signal or command r is applied to the controller, whose output acts as the actuating signal e; the actuating signal then actuates the controlled process and hopefully will drive the controlled variable c to the desired value. Controlled process Controller Reference input r Actuating signial e Controlled variable c Fig.15.1 Block diagram of an open-loop control system 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 control, the controlled signal c(t) must be fed back and compared with the reference input, and an actuating signal proportional to the difference of the output and the input must be sent through the system to correct the error. A system with one or more feedback paths like that just described is called a closed-loop system. Human beings are probably the most complex and sophisticated feedback control system in existence. A human being may be considered to be a control system with many inputs and outputs, capable of carrying out highly complex operations. To illustrate the human being as a feedback control system, let us consider that the objective is to reach for an object on a desk. As one is reaching for the object, the brain sends out a signal to the arm to perform the task. The eyes serve as a sensing device which feeds back continuously the position of the hand. The distance between the hand and the object is the error, which is eventually brought to zero as the hand reaches the object. This is a typical example of closed-loop control. However, if one is told to reach for the object and then is blindfolded, one can only reach toward the object by estimating its exact position. It is quite possible that the object may be missed by a wide margin. With the eyes blindfolded, the feedback path is broken, and the human is operating as an open-loop system. The example of the reaching of an object by a human being is described by the block diagram shown in Fig.15.2. Error detector Cotrolled Process Controller Input command Error Controlled variable Reach for object + _ Position of hand Fig.15.2 Block diagram of a human being as a closed-loop control system As another illustrative example of a closed-loop control system, Fig.15.3 shows the block diagram of the rudder control system of a ship. In this case the objective of control is the position of the rudder, and the reference input is applied through the steering wheel. The error between the relative positions of thee steering wheel and the rudder is the signal, which actuates the controller and the motor. When the rudder is finally aligned with the desired reference direction, the output of the error sensor is zero. Fig.15.3 Rudder control system The basic element and the block diagram of a closed-loop control system are shown in Fig.15.4. In general, the configuration of a feedback control system may not be constrained to that of Fig.15.4. In complex systems there may be a multitude of feedback loops and element blocks. Error sensor Controller Controlled Process Imput Error Feedback elements Fig.15.4 Basic element of a feedback control system 空氣驅(qū)動攻絲機 由線形傳送帶提供動力，在生產(chǎn)線上攻小孔。 在生產(chǎn)情況中，攻小孔是件棘手的事。容易產(chǎn)生破碎的螺紋。大部分現(xiàn)有的攻絲機都采用鉆模套來改進，它可以使絲錐在進入工件之前和進入工件之后所走的軌跡一致。如果你分析一下絲錐的運動，很明顯的，在進入工件之后絲錐需要一個確定的軸向?qū)?。一旦絲錐開始切削工件，工件本身對它有一種導(dǎo)向作用。 這個不同尋常的攻絲機只包括三個運動部分，但充分表明上面說到的這種情況。絲錐安裝在一個筒形紡錘體的末端，這個筒形紡錘體在一個固定的軸上浮動。在這個紡錘體的外部沿它的整個長度上，裝有標(biāo)準(zhǔn)齒條。另一個滑輪與紡錘體成90度安裝，它驅(qū)動一個傳送帶把動力傳到紡錘體上。 由于傳送帶的轉(zhuǎn)彎，它設(shè)法向靠近紡錘體的方向運動。但是，由于紡錘體在一個固定軸上浮動，傳送帶的運動就會推著紡錘體和絲錐向下運動。紡錘體和絲錐向工件的軸向移動是非常迅速的。一旦絲錐接觸到工件，剩下的任何運動都依賴于已經(jīng)加工的螺紋作導(dǎo)向。 當(dāng)螺紋加工完成時，動力裝置反向驅(qū)動，絲錐從工件中退出。一旦絲錐來離開工件，在傳送帶的帶動下。紡錘體迅速移動到頂部。只要傳送帶朝相反方向運動，便可以使絲錐退回，不需要再做其他調(diào)整。 在這種新型的動作器里，一條傳送帶被安放在一支被擠壓成方形的鋁管內(nèi)。管內(nèi)涂上厚厚的一層碳氟化合物，用來減小摩擦力和降低磨損?？諝獗蛔⑷雮魉蛶еg使傳送帶在整個管子的長度范圍內(nèi)滾動。 為了這種攻絲機的應(yīng)用，兩個24英寸的動作器被肩并肩的安置，共用一個傳送帶。當(dāng)傳送帶在兩個動作器之間傳送時，它使一個皮帶輪轉(zhuǎn)動，這個皮帶輪驅(qū)動動作器上的皮帶輪轉(zhuǎn)動。一個動作器驅(qū)動紡錘體向前移動，另一個驅(qū)動紡錘體向后移動。 一個四方位的閥門能控制這個基本的攻絲機。為了簡化設(shè)計采用了氣動方式，但卻伴隨產(chǎn)生了一些錯誤。例如，當(dāng)絲錐到達行程末端時，紡錘體上的一個放氣孔被開啟。這種結(jié)果信號使壓力作用到方向動作器上，使絲錐退回。 設(shè)置一個比正常攻絲周期長的時間，定時器給出一個阻止絲錐運動的信號。 由于紡錘體沒有遇到任何阻力的完成了整個行程，一個短周期探測器便發(fā)出信號表明絲錐或是工件不存在。一個來自向前動作器的信號重新設(shè)置這個探測器，表明傳送帶完成了它的一半行程。因而，如果紡錘體到達整個行程在向前動作器的半路點之前，這個缺失部分信號就會出現(xiàn)。 Beltac Corp發(fā)明了這個貝爾攻絲機并且給它申請了專利。它可作為執(zhí)照使用。標(biāo)準(zhǔn)形狀（大部分是擠壓成型的）組成了整個5-1b單元，因而它不需要特殊的加工。控制系統(tǒng)由標(biāo)準(zhǔn)的插入式閥門組成。Beltac在傳送帶動作器上也擁有專利。 自動鉆孔攻絲機床 更多說明 可選擇的離線會話程序員。策劃周詳和利用參考書的能力是有用的。 中心把工作地點和一個在36”×55” ×30” 的緊湊空間里的吸塵器結(jié)合起來為微型研磨粉碎技術(shù)提供了雙重好處。 從人體工程學(xué)的方面考慮設(shè)計，公司希望為工作人員提供一個舒適的工作環(huán)境，完成微型研磨粉碎機的苛刻的操作要求。一個前端裝載門，雙重日光燈，一個完整的消聲器和一個超大尺寸的磨削腔使工作人員在這個穩(wěn)定的生產(chǎn)環(huán)境中迅速，安靜，清潔的完成實際上的任意操作。 這家公司說：“這個吸塵器以一個大容量的儲塵腔和彈藥筒過濾技術(shù)為特色，用來清除細塵達到清潔，比一般傳統(tǒng)的吸塵器高效50%。一個自動化的振動器和一個帶有輕易滑動的門的便利儲存器使操作更加快速清潔。 自動鉆孔攻絲機床 這臺自動鉆孔并且可以同步完成攻絲的機床在各種孔的加工中被廣泛應(yīng)用。 例如加工獨立的孔，依靠相似的孔加工，在一些制造單元或系統(tǒng)中與其他機械一起工作，它可以在金屬，塑料，堅硬的橡膠，木材，玻璃和實際上的任何金屬和非金屬材料上鉆孔和攻絲。 他有超過115個的電氣自動鉆子模型。他包括1/4-7 1/4的馬力可以產(chǎn)生超過1噸的推力。這個由美國制造的自動化生產(chǎn)線有4種鉆孔方式：一步反復(fù)鉆，在向前沖程的末端維持紡錘體自轉(zhuǎn)，用來加工管子和空心零件的跳躍僅給方式，步進鉆。 鉆頭有0.0006”的同軸度偏差和-0.0008 -- +0.0008的深度偏差。最大空載速度范圍從11，600轉(zhuǎn)/分到3，400轉(zhuǎn)/分電機的功率相應(yīng)的從1/4-7 1/4的馬力。鉆頭卡盤的容量范圍從1/8英寸/分到MT2和MT3為大單位。十三個氣動鉆頭模型有0.13馬力到0.60馬力的額定功率。在180 1bs的最大推力下鉆頭最大轉(zhuǎn)速為32，000。 公司采用了41個滾珠絲杠作為傳動裝置，把孔的加工帶入了一個可偏程序控制的世界。電機的功率在1/2馬力到1馬力之間，并且主軸轉(zhuǎn)速在240轉(zhuǎn)/分—7500轉(zhuǎn)/分。據(jù)說新型的MSX Mechatric是由一個會話型的數(shù)字計算機控制，可以輕易的存放100個獨立的程序，12個固定的孔加工程序，其中包括4個深孔加工的程序。在Mechatric里有40個程序可以被用戶選擇。這個自動進給系統(tǒng)擁有0.0004”的同軸度偏差和-0.0008 -- +0.0008的深度偏差。 公司稱無論孔的大小和材料如何，這個同步攻絲機有3種標(biāo)準(zhǔn)螺紋，在單精度和符合精度的應(yīng)用中。一個新型的數(shù)控單元提供了四個操作模式。 這種新型的進給技術(shù)可以把鉆孔和攻絲同步完成。公司稱使用這種鉆頭和絲錐組合的刀具，可以在同一通道上把兩個操作完成，縮減了50%甚至更多的進程。 這種自動進給系統(tǒng)有1/2hp和3/4hp兩種功率模式，平行度是0.0006”和3種螺紋標(biāo)準(zhǔn)。還策劃了其他的功率模式。 免費的軟件程序 現(xiàn)在公司向所有金屬工藝公司提供它的新的自定義軟件包。 這個軟件可以使用戶設(shè)計多任務(wù)處理工具，可以在一個操作中以完美的同軸度完成鉆孔，打平頭孔，擴孔等加工，它有以下特點：自定心，合二為一的設(shè)計削減了工具成本，提高了生產(chǎn)質(zhì)量，生產(chǎn)力和工具冷卻液使程序流程最優(yōu)化，工具壽命提高。 大直徑深孔的加工 這個超級鉆頭在加工4140鋼時的進給量是0.006”/rev，速度是180轉(zhuǎn)/分鐘，可以加工直徑1.93”—11.20”，深度是D×15的孔。它加工鋁的時候進給量是0.008”/rev，轉(zhuǎn)速是500轉(zhuǎn)/分。 切削刃由一個中心鉆頭，一個粗磨刀片和一個精整刀片組成。公司稱這個中心鉆頭是保證位置的。這種粗磨刀片和精整刀片的結(jié)合可以產(chǎn)生較小的切屑，方便排屑，還可以先少切屑對工件的磨損和切屑的滯留，甚至是在深孔加工時。 機械基礎(chǔ) 史前時期人們利用木杠撬起石頭時，就發(fā)明了杠桿。杠桿是6種基本機械之一。杠桿是一根剛性件或剛性棒，像早期人們用的木杠，它在稱為支點的一個點上轉(zhuǎn)動。當(dāng)外力作用在杠桿的第二點上時，該力就傳到可做功的第三點上。孩子們的蹺蹺板就是杠桿的一個極好的例子。使蹺蹺板保持平衡的點為支點，當(dāng)蹺蹺板一端受向下的作用力時，另一端就會上升。 有意識地使用杠桿可以追溯到文字記載的歷史以前。那時杠桿很可能用來撬起巨大的石塊，用這些巨大的石塊建造英格蘭史前時代的環(huán)形建筑。當(dāng)時也許是利用樹干作為杠桿把石塊撬起，直到預(yù)定的位置。 輪軸是機械的第二種形式，像杠桿一樣，輪軸也可以追溯到史前時代，或許那時人們發(fā)現(xiàn)將重物放在圓木上滾動要比扛運動容易。輪繞軸轉(zhuǎn)動稱為輪軸，大約在公元前3000年，輪軸的組合可能第一次被用作提水裝置。輪軸用于運輸是隨著馬的馴養(yǎng)而發(fā)展起來的。雙輪戰(zhàn)車就是古代的坦克，而四輪馬車則是那時的汽車。 第三種機械就是滑輪。這種簡單的裝置在古代用于從井中或河里提水。裝在殼內(nèi)的滑輪叫做滑車。將定滑輪與系有重物的動滑輪一起使用時，用力拉繩子就會使重物上升，這種裝置稱為滑輪組。 另外的三種基本機械相互關(guān)系十分密切，以致有時把它們歸為一類。這三種機械是楔，斜面和螺紋。楔是三角形，由兩個主要面相交成銳角。楔用于劈開或分開物體。很早以前人們用楔來砍柴，就像用斧子。釘子是楔的一種常見的形式。我們已經(jīng)提到過斜面，這可能是埃及人在修建金字塔是，把巨大的石塊安放就位所使用的方法。很久以前人們就知道要把重物推到小山或土坡上所付出的力要比垂直向上拉省力的多。斜面是土木工程師在設(shè)計公路或鐵路時要注意的一個重要因素。機械工程是經(jīng)常使用螺桿，即斜面的螺旋形式。把斜條纏在圓柱體上所形成的軌跡成為螺旋線。 所有機械基本上都是如前所述的6種基本機械的變形和結(jié)合。傳遞運動或改變運動方式的機構(gòu)或機件有多種多樣的類型?，F(xiàn)代機器與其零件已經(jīng)變得相當(dāng)復(fù)雜，為了研究這些機構(gòu)及其動作，稱為動力學(xué)的這一力學(xué)分支便形成了。不管現(xiàn)代機器的原始輸入和最后輸出是什么，正是機器的各種機構(gòu)是機器具有更大的適應(yīng)性和靈活性。 齒輪在機器中起著重要作用，并已稱為機械的象征。齒輪是帶有齒的輪子，相互嚙合，因此齒輪以成對形式工作，傳遞或改變運動方向。齒輪經(jīng)常用于降低或增加運動的速度，也可以用于改變運動的方向。齒輪圍繞一條直線旋轉(zhuǎn)，這條直線叫軸線。齒輪可以改變軸的運動。 另一種機構(gòu)是凸輪，像齒輪一樣，凸輪由一對機件組成。凸輪本身是輸入構(gòu)件，而從動件是輸出構(gòu)件。凸輪固定在旋轉(zhuǎn)軸上，并把運動傳給從動件。凸輪有許多不同的形狀:有心形凸輪，三星凸輪，橢圓形凸輪等等。借助于這些不同的形狀，凸輪可把旋轉(zhuǎn)運動變成往復(fù)式運動，還可以變成擺動或振動。從動件一般是桿或軸。凸輪可以特定的時間周期的傳遞準(zhǔn)確的運動。因此，在復(fù)雜運動中定時非常重要的地方，凸輪是非常有用的。在汽車發(fā)動機中凸輪用來升降閥門，在縫紉機中用來控制針的運動。 另一種機械裝置稱為連桿裝置，連桿裝置至少有三個桿件串聯(lián)起來，各連桿間靠能使其轉(zhuǎn)動的接頭連接。當(dāng)一個連桿固定，其余連桿只能在預(yù)定的路線中移動。像凸輪一樣連桿裝置用于改變運動的方向，傳遞各種不同運動，或通過改變連桿相互間的長度以改變一周期內(nèi)的各個不同部位的定時。 彈簧是用于各種機器的一種機構(gòu)。它通常是一個彈性螺旋圈，使其變形后可復(fù)原。在手表中彈簧是基本構(gòu)件。在一些凸輪機構(gòu)中，彈簧使從動件固定在一定的位置上，彈簧也用于彈簧秤，彈簧還有助于汽車減震。在螺旋彈簧的基礎(chǔ)上有許多變種，其中有用彈簧剛才制成的片簧，還有的彈簧靠空氣壓縮和膨脹。 棘輪是另一種成對的機構(gòu)。它由一個帶齒的輪和一個落于兩齒空間的止動爪組成。棘輪機構(gòu)用于機構(gòu)防止逆轉(zhuǎn)，或用于將往復(fù)運動變?yōu)樾D(zhuǎn)運動。 本文只是對于龐雜的機器零件領(lǐng)域的一個簡要介紹。 開環(huán)和閉環(huán)控制 開環(huán)控制系統(tǒng) “自動的”這個詞匯意味著控制系統(tǒng)具有一定的復(fù)雜性。通常，自動的意味這個系統(tǒng)可以適應(yīng)多種不同的工作條件，能夠滿意地響應(yīng)一類輸入信號。但是， 并不是所有形式的控制系統(tǒng)都具有自動的特性。通常，自動特性是通過將變化的輸出信號反饋回來并與指令信號進行比較而產(chǎn)生的。當(dāng)一個系統(tǒng)不具備反饋結(jié)構(gòu)，就叫做開環(huán)系統(tǒng)，它是最簡單，最經(jīng)濟的控制系統(tǒng)。遺憾的是，開環(huán)控制系統(tǒng)缺乏精度和多用途性，只有用于最簡單的應(yīng)用場合。 例如，來考慮家庭采暖鍋爐的控制系統(tǒng)。讓我們假設(shè)鍋爐只裝備了定時裝置，它只控制鍋爐開關(guān)和關(guān)閉的周期。要想將溫度調(diào)節(jié)到適當(dāng)?shù)乃剑芾砣藛T必須估計鍋爐需要保持打開的時間長短，從而設(shè)定定時器。當(dāng)設(shè)定時間到了，鍋爐關(guān)閉。然而，房間的溫度很可能是在要求溫度之上或者之下，這是因為估計存在誤差。不容置疑，很顯然這種形式的控制是不夠精確和不可靠的。這種不精確的原因之一在于人不可能準(zhǔn)確地了解鍋爐的特性；原因之二是人不適應(yīng)環(huán)境條件的變化，不能適應(yīng)外界的干擾。在鍋爐控制的例子中，即使是一個很有經(jīng)驗的人將房間溫度控制在某一要求的水平，但是，如果在鍋爐工作期間，門和窗戶間歇地開閉，開環(huán)控制也不能精確地控制屋內(nèi)的最終溫度。 電動洗衣機是開環(huán)控制系統(tǒng)的另一個典型例子，因為洗滌時間的長短完全是根據(jù)操作人員的判斷和估計確定的。一個真正的自動洗衣機應(yīng)該連續(xù)檢查衣服洗凈度的方法和當(dāng)洗凈度達到要求時自動關(guān)機。 盡管開環(huán)控制系統(tǒng)的應(yīng)用有限的，但它構(gòu)成了閉環(huán)控制系統(tǒng)的基本問題。通常，一個開環(huán)控制系統(tǒng)的原理可由圖15.1表示。輸入信號和指令r都施加在控制器上，其輸出作為驅(qū)動信號e；該驅(qū)動信號再驅(qū)動控制過程，并希望使控制變量c達到理想值。 閉環(huán)控制系統(tǒng) 開環(huán)控制系統(tǒng)中所缺少的，能使控制更加精確和更具適應(yīng)性的東西是從輸出到輸入的連接即反饋。為了獲得更精確的控制，必須將被控信號c（t）反饋回去與參考輸入量相比較，且須將與輸出和輸入之差成比例的促動信號送給系統(tǒng)以校正偏差。以上提到的這樣一個具有一個或多個反饋通道的系統(tǒng)叫做閉環(huán)系統(tǒng)。人類可能是現(xiàn)今存在的最復(fù)雜，最成熟的反饋控制系統(tǒng)。人可以被認為是具有多個輸入和輸出的控制系統(tǒng)，可以完成高度復(fù)雜的操作。 為了說明人作為反饋控制系統(tǒng)，我們來考慮拿到放在桌面上的物體這樣一個目的。當(dāng)人伸手去拿這個物體時，大腦對胳膊發(fā)出一個信號去完成這個任務(wù)。眼睛作為傳感設(shè)備，將不斷反饋手的位置。手和物體之間的距離就是偏差，當(dāng)手接觸到物體時，這個偏差為零。這是一個閉環(huán)控制系統(tǒng)的典型例子。但是，如果如果人拿到這個物體，然后蒙起他的眼睛，這個人只能估計物體的準(zhǔn)確位置，向它伸手，反饋通道被打斷，這個人就像一個開環(huán)系統(tǒng)。人去拿東西的例子由圖15.2表示。 另一個閉環(huán)控制系統(tǒng)得說明舉例是船的舵控制系統(tǒng)，如方塊圖15.3所示。在這種境況下，控制的目的是舵的位置，參考輸入信號施加在方向盤上。方向盤與舵之間的相對位置的偏差就是信號，它驅(qū)動控制器和電動機。當(dāng)舵終于與要求的參考方向一致時，偏差傳感器的輸出為零。 圖15.4為一個閉環(huán)控制系統(tǒng)的基本原理和方框圖?？傊?，反饋控制系統(tǒng)的結(jié)構(gòu)不一定局限于圖15.4的結(jié)構(gòu)。在一個復(fù)雜系統(tǒng)中，可以有更多的反饋回路和組成元素。