外文翻譯--現(xiàn)代的控制理論簡介

1：外文文獻翻譯原文及其譯文 Introduction to Modern Control Theory Several factors provided the stimulus for the development of modern control theory: a. The necessary of dealing with more realistic models of system. b. The shift in emphasis towards optimal control and optimal system design. c. The continuing developments in digital computer technology. d. The shortcoming of previous approaches. e. Recognition of the applicability of well-known methods in other fields of knowledge. The transition from simple approximate models, which are easy to work with, to more realistic models, produces two effects. First, a large number of variables must be included in the models. Second, a more realistic model is more likely to contain nonlinearities and time-varying parameters. Previously ignored aspects of the system, such as interactions with feedback through the environment, are more likely to be included. With an advancing technological society, there is a trend towards more ambitious goals. This also means dealing with complex system with a large number of interacting components. The need for greater accuracy and efficiency has changer the emphasis on control system performance. The classical specifications in terms of percent overshoot, setting time, bandwidth, etc. have in many cases given way to optimal criteria such as mini mum energy, minimum cost, and minimum time operation. Optimization of these criteria makes it even more difficult to avoid dealing with unpleasant nonlinearities. Optimal control theory often dictates that nonlinear time-varying control laws are used, even if the basic system is linear and time-invariant. The continuing advances in computer technology have had three principal effects on the controls field. One of these relates to the gigantic supercomputers. The size and the class of the problems that can now be modeled, analyzed, and controlled are considerably large than they were when the first edition of this book was written. The second impact of the computer technology has to so with the proliferation and wide availability of the microcomputers in homes and I the work place, classical control theory was dominated by graphical methods because at the time that was the only way to solve certain problems, Now every control designer has easy access to powerful computer packages for systems analysis and design. The old graphical methods have not yet disappeared, but have been automated. They survive because of the insight and intuition that they can provide, some different techniques are often better suited to a computer. Although a computer can be used to carry out the classical transform-inverse transform methods, it is used usually more efficient for a computer to integrate differential equations directly. The third major impact of the computers is that they are now so commonly used as just another component in the control systems. This means that the discrete-time and digital system control now deserves much more attention than Modern control theory is well suited to the above trends because its time-domain techniques and its mathematical language (matrices, linear vector spaces, etc.) are ideal when dealing with a computer. Computers are a major reason for the existence of state variable methods. Most classical control techniques were developed for linear constant coefficient systems with one input and one output (perhaps a few inputs and outputs). The language of classical techniques is the Laplace or Z-transform and transfer functions. When nonlinearities ad time variations are present, the very basis for these classical techniques is removed. Some successful techniques such as phase-plane methods, describing function s, and other ad hoc methods, have been developed to alleviant this shortcoming. However, the greatest success has been limited to low-order systems. The state variable approach of modern control theory provides a uniform and powerful method of representing systems of arbitrary order, linear or nonlinear, with time-varying or constant coefficient. It provides an ideal formulation for computer implementation and is responsible for much of the progress in optimization theory. Modern control theory is a recent development in the field of control. Therefore, the name is justified at least as a descriptive title. However, the foundations of modern control theory are to be found in other well-established fields. Representing a system in terms of state variables is equivalent to the approach of Hamiltonian mechanics, using generalized coordinates and generalized moment. The advantages of this approach have been well-known I classical physics for many years. The advantages of using matrices when dealing with simultaneous equations of various kinds have long been appreciated in applied mathematics. The field of linear algebra also contributes heavily to modern control theory. This is due to the concise notation, the generality of the results, and the economy of thought that linear algebra provides. Mechanism of Surface Finish Production There are basically five mechanisms which contribute to the production of a surface which have been machined. There are: (1) The basic geometry of the cutting process. In, for example, single point turning the tool will advance a constant distance axially per revolution of the work piece and the resultant surface will have on it, when viewed perpendicularly to the direction of tool feed motion, a series of cusps which will have a basic form which replicates the shape of the tool in cut. (2) The efficiency of the cutting operation. It has already been mentioned that cutting with unstable built-up-edges will produce a surface which contains hard built-up-edge fragments which will result in a degradation of the surface finish. It can also be demonstrated that cutting under adverse conditions such as apply when using large feeds small rake angles and low cutting speeds, besides producing conditions whi ch continuous shear occurring in the shear zone, tearing takes place, discontinuous chips of uneven thickness are produced, and the resultant surface is poor. This situation is particularly noticeable when machining very ductile materials such as copper and aluminum. (3) The stability of the machine tool. Under some combinations of cutting conditions: work piece size , method of clamping, and cutting tool rigidity relative to the machine tool structure, instability can be set up in the tool which causes it to vibrate. Under some conditions the vibration will built up and unless cutting is stopped considerable damage to both the cutting tool and work piece may occur. This phenomenon is known as chatter and in axial turning is characterized by long pitch helical bands on the work piece surface and short pitch undulations on the transient machined surface. (4) The effectiveness of removing sward. In discontinuous chip production machining, such as milling or turning of brittle materials, it is expected that the chip (sward) will leave the cutting zone either under gravity or with the assistance of a jet of cutting fluid and that they will not influence the cut surface in any way. However, when continuous chip production is evident, unless steps ate taken to control the swarf it is likely that it will impinge on the cut surface and mark it. Inevitably, this marking beside a looking unattractive, often results in a poorer surface finishing, (5) The effective clearance angle on the cutting tool. For certain geometries of minor cutting edge relief and clearance angles it is possible to cut on the major cutting edge and burnish on the minor cutting edge. This can produce a good surface finish but, of course, it is strictly a combination of metal cutting and metal forming and is not to be recommended as a practical cutting method. However, due to cutting tool wear, these conditions occasionally arise and lead to a marked change in the surface characteristics. Surface Finishing and Dimensional Control Products that have been completed to their proper shape and size frequently require some type of surface finishing to enable than to satisfactorily fulfill their function. In some cases, tit is necessary to improve the physical properties of the surface material for resistance to penetration or abrasion. In many manufacturing processes, the product surface is left with dirt, chips, grease, or other harmful material upon it. Assemblies that are made of different materials, or from the same materials processed in different manners, many require some special surface treatment to provide uniformity of appearance. Surface finishing many sometimes become an intermediate step processing. For instance, cleaning and polishing are usually essential before any kind of plating process. Some of the cleaning procedures are also used for improving surface smoothness on mating parts and for removing burrs and sharp corners, which might be harmful in later use. Another 馬棚網(wǎng) important need for surface finishing is for corrosion protection in a variety of environments. The type of protection procedure will depend largely upon the anticipated exposure, with due consideration to the material being protected and the economic factors involved. Satisfying the above objectives necessitates the use of main surface-finishing methods that involve chemical change of the surface mechanical work affecting surface properties, cleaning by a variety of methods, and the application of protective coatings, organic and metallic. In the early days of engineering, the mating of parts was achieved by machining one part as nearly as possible to the required size, machining the mating part nearly to size, and then completing its machining, continually offering the other part to it, until the desired relationship was obtained. If it was inconvenient to offer one par to the other part during machining, the final work was done at the bench by a fitter, who scraped the mating parts until the desired fit was obtained, the fitter therefore being a fitter in the literal sense. It is obvious that the two parts would have to remain together, and in the event of one having to be replaced, the fitting would have to be done all over again. I n these days, we expect to be able to purchase a replacement for a broken part, and for it to function correctly without the need for scraping and other fitting operations. When one part can be used off the shelf to replace another of the sa me dimension and material specification, the parts are said to be interchangeable. A system of interchangeability usually lowers the production costs as there is no need for an expensive, fiddling operation, and it benefits the customer in the event of the need to replace worn parts. Limits and Tolerances Machine parts are manufactured so they are interchangeable. In other words, each part of a machine or mechanism is made to a certain size and shape so it will fit into any other machine or mechanism of the same type. To make the part interchangeable, each individual part must be made to a size that will fit the mating part in the correct way. It is not only impossible, but also impractical to make many parts to an exact size. This is because machines are not perfect, and the tools become worn. A slight variation from the exact size is always allowed. The amount of this variation depends on the kind of part being manufactured. For example, a part might be made 6 in. long with a variation allowed of 0.003(three thousandths) in. above and below this size. Therefore, the part could be 5.997 to 6.003 in. and still be the correct size. These are known as the limits. The difference between upper and lower limits is called the tolerance. A tolerance is the total permissible variation in the size of a part. The basic size is that size from which limits of size are derived by the application of allowances and tolerances. Sometimes the limit is allowed in only one direction. This is known as unilateral tolerance. Unilateral tolerancing is a system of dimensioning where the tolerance (that is variation) is shown I only one direction from the nominal size. Unilateral tolerancing allow the changing of tolerance on a hole or shaft without seriously affecting the fit. When the tolerance is in both directions from the basic size, it is known as a bilateral tolerance (plus and minus). Bilateral tolerancing is a system of dimensioning where the tolerance (that is variation) is split and is shown on either side of the nominal size. Limit dimensioning is a system of dimensioning where only the maximum and minimum dimensions are shown. Thus, the tolerance is the difference between these two dimensions. Introduction of Machining of: Machining as a shape-producing method is the most universally used and the most important of all manufacturing processes. Machining is a shape-producing process in which a power-driven device causes material to be removed in chip form. Most machining is done with equipment that supports both the work piece and cutting tool although in some cases portable equipment is used with unsupported work piece. Low setup cost for small quantities. Machining has two applications in manufacturing. For casting, forging, and pressworking, each specific shape to be produced, even one part, nearly always has a high tooling cost. The shapes that may be produced by welding depend to a large degree on the shapes of raw material that are available. By making use of generally high cost equipment but without special tooling, it is possible, by machining, to start with nearly any form of raw material, so long as the exterior dimensions are great enough, and produce any desired shape from any material. Therefore, machining is usually the preferred method for producing one or a few parts, even when the design of the part would logically lead to casting, forging or pressworking if a high quantity were to be produced. Close accuracies, good finishes. The second application for machining is based on the high accuracies and surface finishes possible. Many of the parts machined in low quantities would be produced with lower but acceptable tolerances if produced I high quantities by some other process. On the other hand, many parts are given their general shapes by some high quantity deformation process and machined only on selected surfaces where high accuracies are needed. Internal threads, for example, are seldom produced by any means other than machining and small holes in pressworked parts may be machined following the pressworking operations. 現(xiàn)代的控制理論簡介 下列幾方面為現(xiàn)代控制理論發(fā)展的促進因素 : 1.處理更多的現(xiàn)實模型系統(tǒng)的必要性 2.強調(diào)向最佳的控制和最佳的系統(tǒng)設(shè)計的升級 3.數(shù)字化計算機技術(shù)的持續(xù)發(fā)展 . 4.當(dāng)前技術(shù)的不成熟 . 眾所周知的方法在其它知識領(lǐng)域的適用性得到承認 . 從容易解決的簡單近似的模型到更多的現(xiàn)實模型的轉(zhuǎn)變產(chǎn)生了兩種效果：首先，模型必須包括很多的變量。其次，一個十分逼真的模型是盡可能 的包括非線性和隨時間變化的參數(shù)。早先的忽略了系統(tǒng)的一些方面，例如很有可能的一方面就是在環(huán)境中有著反饋的交互作用。 在現(xiàn)代科技高度發(fā) 達的社會，存在一種非常雄心的目標(biāo)的趨勢，這也意味著要處理有著很多相互關(guān)聯(lián)成分的復(fù)雜系統(tǒng)，高精確度與高效率的需要改變了控制系統(tǒng)的執(zhí)行重點。在超頻百分比，時間設(shè)置，頻寬等等方面的經(jīng)典規(guī)范，在很多情況下解決了優(yōu)化標(biāo)準如最小能量，最小花費，最小時間控制，優(yōu)化這些標(biāo)準時很難避免和不開心的非線性打交道。即使基礎(chǔ)系統(tǒng)是線性的和不隨時間變化的，優(yōu)化控制理論顯示非線性時間變化控制也被應(yīng)用到了。 不停發(fā)展的計算機技術(shù)在控制領(lǐng)域創(chuàng)造了三條最重要的影響。其中一項是有關(guān)數(shù)字化的超級計算機，較之這本書首印時期，現(xiàn)在能模擬，分析，控制的 問題的大小和種類都要大得驚人。 計算機技術(shù)的第二個問題就是必須處理微型計算機在家庭和工作地的擴散與廣泛的可靠性。古典的控制理論是以圖畫似的方法為主導(dǎo)的 . 因為在時間那是唯一的解決確定的問題的途徑。為了系統(tǒng)分析和設(shè)計 ,現(xiàn)在每一個控制設(shè)計者很容易有機會接近強大的計算機內(nèi)部。老的圖畫似的方法不但沒有消失 , 并且還使其自動化了 .它們之所以能生存是因為提供了洞察力與直覺，許多不同的技術(shù)經(jīng)常能更適合于計算機。雖然計算機能被用于執(zhí)行經(jīng)典的改變 -到轉(zhuǎn)的改變方法，但它通常更多的有效用于直接整合微分方程。 計算機的第三個，也是 最重要的方面，就是它們現(xiàn)在已經(jīng)如此普遍地應(yīng)用于控制系統(tǒng)，儼然其中的一員。其價格，型號和穩(wěn)定性使得能夠在許多系統(tǒng)中常規(guī)的使用。這也意味著離散的 -時間和數(shù)字的系統(tǒng)控制現(xiàn)在比在它過去更受人關(guān)注。 現(xiàn)代的控制理論更適合上面的趨勢 . 因為它的時間 -領(lǐng)域技術(shù)和它的數(shù)學(xué)的語言(公式 , 線性向量空間 , 等等 .) 是處理計算機時的方法。 . 計算機是狀態(tài)變量方法存在的主要原因。 最多的古典的控制技術(shù)是為了發(fā)展只有一個輸入和一個輸出 (或許少許輸入和輸出 )線性常數(shù)系數(shù)系統(tǒng) . 古典的技術(shù)的語言是拉普內(nèi)斯或 Z-改變和傳送功能 . 就在那 個時候非線性和時間變量出現(xiàn)了 , 這些古典的技術(shù)的基礎(chǔ)遠離了 . 一些成功的技術(shù)例如階段 -平面方法 , 描述函數(shù) , 和其他的特別方法 ,發(fā)展并緩和了這些缺點。然而 , 最大的成功被這些低級命令系統(tǒng)限制了 . 現(xiàn)代的控制理論的狀態(tài)變量接近供應(yīng)統(tǒng)一和強大的方法表現(xiàn)任意的訂購的系統(tǒng) , 線的或非線性的 , 有時間 -改變或常數(shù)系數(shù) .它為形成計算機的執(zhí)行提供了理論，同時也對大多數(shù)優(yōu)化理論的進程負有責(zé)任。 現(xiàn)代的控制理論是在控制領(lǐng)域的最近發(fā)展 . 因此 , 這個名字至少替換了一個描述性的標(biāo)題 . 然而 , 現(xiàn)代的控制理論的基礎(chǔ)在其它已知領(lǐng)域也 被發(fā)現(xiàn)了 . 用一般化坐標(biāo)和一般化瞬間表現(xiàn)一個系統(tǒng)時，在相關(guān)狀態(tài)變量上，其等同到接近哈密爾敦函數(shù)機械學(xué) ,. 這接近的優(yōu)勢在古典的物理學(xué)已經(jīng)聞名了許多年 . 應(yīng)用數(shù)學(xué)領(lǐng)域中，在處理各種形式相類似的方程時，利用母式的優(yōu)越性早已表現(xiàn)出來了，線性代數(shù)學(xué)也很大程度上歸功于現(xiàn)代的控制理論。 這是由于線性代數(shù)學(xué)所提供的簡明的符號 , 結(jié)果的普遍性 , 和思考的效率。 表面粗糙度的技術(shù) 在已經(jīng)進行機械加工過的表面，有五種基本的影響其表面粗糙度的技術(shù)。 1、切斷過程的基本幾何學(xué) . 例如，在單點車削時，工件每轉(zhuǎn)一周，刀具就沿軸線方向進 給一個固定的距離。從垂直刀具進給的方向觀察，所得到的表面上有很多尖角，這些尖角的形狀與切削刀具的形狀相同。 2、切斷操作的效率 . 已經(jīng)提過的用不穩(wěn)定的切削瘤切削將會加工出包含有堅硬的切削瘤碎片在上面的表面，而這些將會導(dǎo)致表明粗糙度的等級降低。已經(jīng)證明，在采用進給量大，前角小，切削速度低的不利情況下，除了產(chǎn)生不穩(wěn)定的切削瘤外，切削過程也會不穩(wěn)定。同時，在切削區(qū)里進行的也不再是切削，而是撕裂，導(dǎo)致厚度不均勻，不連續(xù)的切削，加工出的表面質(zhì)量差。在切削加工延展性良好的金屬材料，如銅和鋁時，這種情況就尤為突出。 3、機械工具的穩(wěn)定性。在許多聯(lián)合切削的情況下：工件的大小，夾緊的方法，和切斷工具相對于機床結(jié)構(gòu)的堅硬度，不穩(wěn)定性是建立在使其變化的工具上的。在某些情況下，這種變化將達到并保持很長一段時間，在另外一些情況下，這種變化將會產(chǎn)生，除非切斷停止，否則，將肯定會同時對切斷刀具和工具產(chǎn)生破壞。這種現(xiàn)象就是知名的刀振，在軸向轉(zhuǎn)動被描述為在工件表面的長間距螺旋狀帶和段間距波動在機械加工的過渡表面。 4、刀刃的移動效率。在不連續(xù)的產(chǎn)品加工過程中例如易碎材料的磨或旋轉(zhuǎn)，我們期望碎片在重力作用或在冷卻液的噴射作用下將離開切削面域 。而且怎么也不會影響切削表面。然而，在連續(xù)切削時，產(chǎn)品是明顯的，除非逐步控制刀刃，否則他很有可能中級切削表面并在其上留下記號。不可避免，這記號在旁邊樣子不美的 , 時常導(dǎo)致差的表面粗糙度。 5、切斷工具的有效清除角。由于副切削刃的某種幾何特征減輕和清除了角，使得在主切削面上主切削刃切削和副切削刃打磨變得可能。這樣能加工出良好的表面粗糙度，但是，當(dāng)然，它嚴格來講，是一種金屬切削和金屬成型的綜合，而不失被認為的一種實際的切削方法。然而，歸功于切削工具的表面處理，這些情況偶爾才會出現(xiàn)，并導(dǎo)致了表面特性的標(biāo)志性改變。 表面精整加工與尺寸控制 產(chǎn)品在被加工成它們的適