自動化專業(yè)英語句子

1、PART 2Unit 2A stability and the time responseThe stability of a continuous or discrete-time system is determined by its response to input or disturbance. Intuitively, a stable system is one that remains at rest (or in equilibrium) unless excited by an external source and returns to rest if all excit

2、ations are removed. The output will pass through a transient phase and settle down to a steady-state response that will be of the same form as, or bounded by, the input. If we apply the same input to an unstable system, the output will never settle down to a steady-state phase; it will increase in a

3、n unbounded manner, usually exponentially or with oscillation of increasing amplitude. 連續(xù)或離散系統(tǒng)的穩(wěn)定性由其對輸入或者干擾的響應(yīng)決定。直觀地說，如果一個系統(tǒng)是穩(wěn)定的，則其停留在穩(wěn)態(tài)（或者平衡點），除非是受到外部激勵，且當(dāng)外部激勵去除后，輸出又回到穩(wěn)態(tài)點。輸出經(jīng)過瞬態(tài)階段后將回到與輸入有相同形式的穩(wěn)態(tài)或者是在輸入的附近。如果我們將同樣的輸入作用于不穩(wěn)定的系統(tǒng)，其輸出將不會回到穩(wěn)態(tài)，而是以無界的方式增長，通常其幅值是指數(shù)增長或者振蕩增長。Stability can be precisely defined

4、in terms of the impulse response of a continuous system, Kronrcker delta response of a discrete-time system, as follows: A continuous (discrete-time) system is stable if its impulse response (Kronecker response ) approaches zero as time approaches infinity.系統(tǒng)的穩(wěn)定性可以用連續(xù)系統(tǒng)的脈沖響應(yīng)或者離散系統(tǒng)的Kronrcker 響應(yīng)來定義：一個

5、連續(xù)（離散）系統(tǒng)是穩(wěn)定的，如果其脈沖響應(yīng)（Kronrcker 響應(yīng)）當(dāng)時間趨于無窮大時趨于零。An acceptable system must at minimum satisfy the three basic criteria of stability, accuracy, and a satisfactory transient response. These three criteria are implied in the statement that an acceptable system must have a satisfactory time response to sp

6、ecified inputs and disturbances. So although we work in the Laplace and frequency domains for convenience, we must be able to relate these two domains, at least qualitatively, to the time domain.一個可接受的系統(tǒng)必須至少滿足：穩(wěn)定性、精度和滿意的瞬態(tài)響應(yīng)這三個指標。在陳述：“一個可接受的系統(tǒng)對指定輸入和擾動必須有滿意的時域響應(yīng)”已經(jīng)包含了這三個指標的含義。因此盡管我們?yōu)榱朔奖愎ぷ髟诶嫌蚧蛘哳l率域，我們

7、必須與時間域（至少是定性的）相聯(lián)系。With the transfer function in the form of Eq.(2-2A-1), the order of the system in defined as the order of the characteristic function D(s), the highest power of s appearing in D(s) establishes the order of the system.在傳遞函數(shù)所在的方程(2-2A-1)中，系統(tǒng)的階次定義為特征函數(shù)D(s)的階次，因此D(s)的最高次冪決定了系統(tǒng)的階次。The f

8、irst term is the forced solution, due to the input, and the second the transient solution, due to the system pole. Fig.2-2A-2 shows this transient as well as c(t). The transient is seen to be a decaying exponential, and the commonly used measured of the speed of decay is the time constant: The time

9、constant is the time in seconds for the decaying exponential transient to be reduced to e-1=0.368 of its initial value. Since when t=T, it is seen that the time constant for a simple lag is T seconds. This is, in fact, the reason a simple lag transfer function is often written in this form. The coef

10、ficient of s then immediately indicates the speed of decay, and it takes 4T seconds for the transient to decay to 1.8% of its initial value.第一項為強迫解，對應(yīng)于輸入；第二項為瞬態(tài)解，對應(yīng)于系統(tǒng)的極點。 在圖2-2A-2中，該瞬態(tài)解為c(t)。瞬態(tài)解看上去為指數(shù)衰減的，且通常用于衡量衰減速度的是時間常數(shù)：即指數(shù)衰減的瞬態(tài)解衰減至其初始值的36.8%所需的時間（秒數(shù)）。因為，當(dāng)t=T, ，對于一階慣性環(huán)節(jié)，時間常數(shù)是T秒。這也是為什么一階慣性環(huán)節(jié)要寫成這個形

11、式。S的系數(shù)立即給出了衰減的速度。而且，當(dāng)時間為4T時， 瞬態(tài)解衰減至初始值的1.8%。B：Steady StateA control system is designed to control the dynamic behavior( the time response) of a plant subject to commands or disturbances. The designer should be fully aware, however, of the role of the steady equations and errors in the overall proces

12、s, as well as their influence on the dynamic behavior of the plant.控制系統(tǒng)設(shè)計就是使裝置在有指令信號或者干擾時有滿意的行為（時域響應(yīng)）。設(shè)計者必須清楚地知道整個過程的穩(wěn)態(tài)方程和誤差，以及他們對裝置的動態(tài)性能的影響。An accuracy of a system is a measure of how well it follows commands. It is an important performance criterion; a guidance system that cannot place spacecraft

13、on a suitable trajectory is obviously useless no matter how well-behaved its transient response.衡量系統(tǒng)的精度之一，就是其如何跟蹤給定命令。這是一項重要的性能指標。一個導(dǎo)航系統(tǒng)如果不能將飛行器置于合適的軌跡，那么無論有多好的動態(tài)性能，都是沒有用。Actual system are also subjected to undesirable inputs, such as noise in command inputs and disturbances arising from changes in

14、the plant parameters or changes in the environment in which the plant is operating. Noise inputs that enter the system with the command input require filtering techniques to remove or suppress them without affecting the command input itself. We shall limit our discussion to disturbance inputs which

15、enter the system at the plant rather than at the controller.實際系統(tǒng)總是容易受到不希望的輸入干擾，例如， 命令輸入中的噪聲以及由于參數(shù)改變在被控對象中產(chǎn)生的干擾或者被控對象工作環(huán)境變化產(chǎn)生的干擾。隨著命令輸入進入系統(tǒng)的噪聲輸入需要濾波器進行驅(qū)除或者抑制并不對輸入信號產(chǎn)生影響。我們將限于討論通過被控對象進行系統(tǒng)的噪聲而不討論通過控制器進入系統(tǒng)的噪聲。It is often difficult to minimize both components of the error simultaneously. Obviously, it is

16、 necessary to have some knowledge as to the nature of probable disturbance inputs. Both error terms of Eq.(2-2B-7) can be set equal to zero by introducing an integrator into the controller. This additional integrator increases the type of the system ( from 1 to 2, for example) , thus eliminating the

17、 velocity error, and by being introduced ahead of the point of entry of the disturbance into the system, eliminates the steady-state error resulting from a step in the disturbance input. This additional integrator must be accompanied by at least one zero if the system is to remain stable.通常同時將誤差的兩個部

18、分最小化是困難的。很明顯，具有適當(dāng)?shù)母蓴_輸入特性的一些知識是很有必要的。方程2-2B-7的兩個誤差項都能通過在控制器中加入積分器而消除。這些附加的積分器增加了系統(tǒng)的型（例如，從1型系統(tǒng)變?yōu)?型系統(tǒng)），因此可以消除速度誤差，并通過在系統(tǒng)擾動進入點之前引入積分環(huán)節(jié)，可以消除由輸入信號中包含的階躍擾動引起的穩(wěn)態(tài)誤差。如果要保持系統(tǒng)穩(wěn)定該附加的積分器必須相應(yīng)增加至少一個零點。UNIT 3A：The Root LocusThe root locus technique is a graphical method of determining the location of the roots of th

19、e characteristic equation as any single parameter, such as a gain or time constant, is varied from zero to infinity. The root locus, therefore, provides information not only as to the absolute stability of a system but also as to its degree of stability , which is another way of describing the natur

20、e of the transient response. If the system is unstable or has an unacceptable transient response, the root locus indicates possible ways to improve the response and is a convenient method of depicting qualitatively the effects of any such changes. 根軌跡技術(shù)是當(dāng)一個單一的參數(shù)，例如增益或者時間常數(shù)從零到無窮大變化時，確定特征方程的各個根的位置的圖形技

21、術(shù)。因此，根軌跡不僅僅提供了系統(tǒng)絕對穩(wěn)定性的信息，還提供了穩(wěn)定程度的信息。穩(wěn)定程度實際上還是描述動態(tài)響應(yīng)特性的方式。如果系統(tǒng)是不穩(wěn)定的或者動態(tài)響應(yīng)不可接受，根軌跡還可以指出可能改進響應(yīng)的方法而且可以定性描述改進的效果。 A zero is a value of s that makes Z(s) equal to zero and is given the symbol . Do not automatically assume that this zero is also a closed-loop zero that makes N(s) equal to zero in the syst

22、em (closed-loop) transfer function; it may be, but is not necessarily so. A pole is a value of s that makes P(s)equal to zero and is given the symbol . The sn term represents n poles, all equal to zero and located at the origin of the s plane. A root of the characteristic equation has previously bee

23、n defined as value of s that makes D(s) equal to zero and is given the symbol . 零點是使Z(s)為零的s值，用符號表示。不能自動地假設(shè)這個零點就是使N(s)為零的閉環(huán)傳遞函數(shù)的零點。它可能是，但不一定。極點是使P(s)為零的s值，用符號表示。sn表示n 個極點，其值為零，位于s 平面的原點。特征方程的根前面已經(jīng)定義為使D(s)為零的s值，用符號表示。Since s is a complex variable and the poles and zeros may be complex, is a complex f

24、unction and may, therefore, be handled as a vector having a magnitude and an associated angle or argument. Each of the factors on the right side of Eq.(2-3A-2) can also be treated as a vector with an individual magnitude and associated angle, as shown in Fig. 2-3A-1. Note that the angle is measured

25、from the horizontal and is positive in the counterclockwise direction.由于s是一個復(fù)變量，極點和零點也可能是復(fù)數(shù)，也是一個復(fù)函數(shù)，因此有可能視為一個有幅值和相角的向量。方程(2-3A-2)右邊的每一個因子都可以視為有各自幅值和相角的向量，并如圖2-3A-1.所示。請注意相角是按從水平軸逆時針方向為正計算。If the part of the real axis between two o.l. poles ( o.l. zeros) belong to the loci, there must be a point of b

26、reakaway from , or arrival at, the real axis. If no other poles zeros are close by, the breakaway point will be halfway.如果實軸在兩個開環(huán)極點（開環(huán)零點）之間屬于根軌跡，則在其中必定有突破點（匯合點）。如果附近沒有極點或者零點，則突破點（匯合點）必定在（兩個開環(huán)極點/開環(huán)零點）的中間。 B：The Frequency Response Methods: Nyquist DiagramsThe nature of the input also influences the ch

27、oice of techniques to be used for system analysis and design. Many command input merely instruct a system to move from one steady-state condition to a second steady-state condition. This type of input can be described adequately by suitable steps in position, velocity, and acceleration, and the Lapl

28、ace domain is appropriate for this purpose. If, however, the interval between such step inputs is decreased so that the system never has time to reach the corresponding steady-state, the step representation and Laplace domain are no longer adequate. Such rapidly varying command inputs (or disturbanc

29、e) may be periodic, random, or a combination thereof. The wind loading of a tracking radar antenna, for example, results from a mean velocity component that varies with time plus superimposed random gusts. If the frequency distribution of these inputs can be calculated, measured, or even estimated,

30、the frequency response can be used to determine their effects upon the system output.輸入信號的特性可以影響到系統(tǒng)分析和設(shè)計的技術(shù)的選擇。許多的系統(tǒng)指令輸入僅僅是讓系統(tǒng)從一個穩(wěn)定狀態(tài)轉(zhuǎn)移到另一個穩(wěn)定狀態(tài)。這種類型的輸入可以用適當(dāng)?shù)奈恢谩⑺俣群图铀俣鹊碾A躍來描述。但是，如果減小這些階躍輸入的間隔，系統(tǒng)沒有足夠的時間來到達下一個相應(yīng)的穩(wěn)態(tài)，則階躍響應(yīng)以及拉普拉斯域就顯得不合適。這些快速變化的指令輸入可以是周期的、隨機的以及它們的組合。例如跟蹤雷達天線的風(fēng)力負載是由一個隨時間變化的平均速度成分與迭加的隨機陣風(fēng)組成的。

31、如果這些輸入的頻率的分布是可計算、測量、甚至可估計的，則頻率響應(yīng)可以用來決定系統(tǒng)輸出的效果。 From these equations we see that sinusoidal input to a linear stable system produces a steady-state response that is also sinusoidal, having the same frequency as the input but displaced through a phase angle and having an amplitude that may be differen

32、t. This steady-state sinusoidal response is called the frequency response of the system. Since the phase angle is the angle associated with the complex function G(j0) and the amplitude ratio （c0/r0） is the magnitude of G(j0), knowledge of G(j0) specifies the steady-state input-output relationship in

33、 the frequency domain. G(j0) is called the frequency transfer function and can be obtained from the transfer function G(s) by replacing the Laplace variable s by j0 . Consequently, if G(j0) can be determined from experimental data, G(s) can also be found by replacing j0 by s.根據(jù)以上方程，將正弦信號輸入于一個穩(wěn)定的線性系統(tǒng)

34、，產(chǎn)生的穩(wěn)態(tài)響應(yīng)也是一個與輸入信號具有相同頻率的正弦信號，但是其相角和幅值可能會不同。這個穩(wěn)態(tài)正弦響應(yīng)稱為系統(tǒng)的頻 響應(yīng)。由于頻率響應(yīng)的相角就是復(fù)函數(shù)G(j0)的角度。幅值比（c0/r0）就是的G(j0)幅值，所以G(j0)在頻率域定義了穩(wěn)態(tài)輸入-輸出關(guān)系。G(j0)成為頻率傳遞函數(shù)，并可以通過將傳遞函數(shù)G(s)的拉普拉斯變量s替換為j0而得到。，反之，G(j0)可以通過實驗得到，則傳遞函數(shù)也可以通過將j0替換為s得到。UNIT 4A：The Frequency Response Methods: Bode PlotsThe frequency transfer function of a s

35、ystem or of itsfunction can be presented either by the single Nyquist diagram( a polar plot) or by plots of the amplitude ratio and the phase angle against the input(forcing) frequency. It is customary to plot the amplitude ratio in decibels and the phase angle in degree against the common logarithm

36、 of the input frequency. In this form, the two plots are known as Bode plots(after H.W.Bode). There are exact Bode plots, which are best prepared with a computer, and straight-line asymptotic plots, which can be quickly and easily sketched or plotted by hand using the techniques to be developed and

37、discussed in this article.系統(tǒng)的頻率特性可以用Nyquist 圖（極坐標圖）或者用其幅值（比）和相角為因變量，輸入信號的頻率為自變量繪圖。在繪圖時通常幅值（比）用分貝表示，相角用度表示，輸入信號的頻率按常用對數(shù)取值。以上這兩個圖稱為伯德圖（以H. W. Bode命名）?？梢杂糜嬎銠C繪出精確的伯德圖。在本文中將討論用手工繪制的技巧簡單而快速地繪制直線漸進線圖。Bode plots of the system transfer function are used to determine the effects of various inputs (including a

38、 step) upon the steady-stat response of the system. Since the frequency response is a steady-state response, the system must be stable and its stability must be determined before the system Bode plots can be used.系統(tǒng)傳遞函數(shù)的伯德圖可以用于確定各種輸入（包括階躍輸入）下系統(tǒng)的穩(wěn)態(tài)響應(yīng)。因為頻率響應(yīng)為穩(wěn)態(tài)響應(yīng)，所以系統(tǒng)必須是穩(wěn)定且其穩(wěn)定性必須在繪制伯德圖之前確定。Bode plots

39、are most commonly used with the frequency function to examine the stability of a system. When the function has no pole or zero inside the right-half s plane, i.e. the function is minimum phase, the Bode plots can be sketched rather rapidly with a knowledge of the four elementary factors that appear

40、in the function. These terms are : Frequency-invariant terms K. Zeros and poles at the origin(j)n First order terms or real poles and zeros (j+1)n Second order poles and zeros . 伯德圖和頻率（特性）函數(shù)一起用來確定系統(tǒng)的穩(wěn)定性。當(dāng)該函數(shù)無零點和極點在S平面右半部時，即系統(tǒng)為最小相位系統(tǒng)，可以使用函數(shù)的四個快速地繪出伯德圖。這四個量分別是：與頻率無關(guān)的系數(shù)K。在原點的零點和極點個數(shù)。一階項，即實數(shù)零點和極點個數(shù)。二階項，

41、即零點和極點。For a product , and . The phase angle is expressed as a sum. The magnitude M will also be expressed as a sum, by using decibels(dB) as units: 對于乘積：，這里，而。相角表現(xiàn)為和的形式，幅值M如果使用分貝為單位也表現(xiàn)為和的形式：In Bode plots , the magnitude M in dB and the phase angle in degrees are plotted against on semilog paper. Th

42、e development has shown the following: Bode magnitude and phase-angle plots of are obtained by summing those of its elementary factors. These plot are much easier to make than polar plots or Nyquist diagrams, and can readily be interpreted in terms of different aspects of system performance.在伯德圖中幅值M

43、使用分貝，相角使用度，畫在為橫坐標的半對數(shù)紙上。以上推導(dǎo)表明：的幅值和相角伯德圖可以分別由各個基本因子的伯德圖相加而得到。這些伯德圖比極坐標圖要容易畫，且可以方便地解釋系統(tǒng)性能。In Bode plot, the phase margin m is the sum of 180and the phase angle at the frequency where (i.e., 0dB). Hence, as shown by the partial plots in Fig. 2-4A-2, the phase margin m is the distance of the phase-angl

44、e curve above -180 at the crossover frequency , where the magnitude plot crosses the 0 dB axis. Similarly, the gain margin equals 1 divided by the magnitude at the frequency where the phase angle is . , the gain margin in dB, is therefore the distance of the magnitude below 0dB at this frequency, as

45、 shown in Fig. 2-4A-2.在Bode圖中，相角穩(wěn)定裕量m為180加上時的頻率處對應(yīng)的相角值。因此，如圖2-4A-2所示，相角穩(wěn)定裕量m為相角曲線在穿越頻率（幅值曲線穿越0 dB線處）處與-180線的距離。同樣，增益裕量等于1除以相角為時對應(yīng)頻率的幅值。因此，,以dB來表示，為如圖Fig. 2-4A-2.所示的頻率處，幅值曲線與0分貝線的距離。教材中注釋1的翻譯：對于超前環(huán)節(jié)，其Bode圖同樣與相應(yīng)的滯后環(huán)節(jié)的Bode圖成鏡象。B: Nonlinear Control SystemIn practice, most systems are nonlinear for large

46、 enough variations about the operating point, and linearization is based on the assumption that these variations are sufficiently small. But this cannot be satisfied, for example, for systems that include relays, which can switch position for very small changes. Startup and shutdown also frequently

47、require the consideration of nonlinear effects, because of the size of the transients.實際上，大多數(shù)的系統(tǒng)當(dāng)在工作點周圍有較大的變化時，都是非線性的。線性化的是基于這樣的假設(shè)：變化足夠的小。但是這種條件通常得不到滿足，例如當(dāng)系統(tǒng)包含繼電器時，即使是很小的變化，也會引起較大的變化。起動和停止時通常也要考慮非線性的影響，因為相對系統(tǒng)的動態(tài)特性，系統(tǒng)的非線性是不能忽略的。The principle of superposition does not apply to nonlinear systems. This

48、has serious consequences. In fact, the analysis and design techniques so far, including the use of transfer function and Laplace transforms, are no longer valid. Worse, there is no general equivalent technique to replace them. Instead, a number of techniques exist, each of limited purpose and limite

49、d applicability. We only introduce the well-known phase plane and describing function methods. 迭加原理不適用于非線性系統(tǒng)。這一點的后果是嚴重的。事實上，至今為止所討論的分析和設(shè)計技術(shù)包括傳遞函數(shù)和拉氏變換已經(jīng)不適用了。更糟糕的是，并沒有一般的方法能夠取代它們。有那么幾種方法，但是各自存在限定的目的和范圍。我們將介紹比較熟知的相平面法和描述函數(shù)法。The nature of the response depends on input and initial conditions. For exampl

50、e, a nonlinear system can change from sable to unstable, or vice versa, if the size of step input is doubled.（非線性系統(tǒng)）響應(yīng)的特性取決于輸入或者初始條件。例如，當(dāng)階躍輸入的的幅度增大一倍時，非線性系統(tǒng)可能會從穩(wěn)定變得不穩(wěn)定；反之亦然。Instability shows itself frequently in the form of limit cycles. These are oscillations of fixed amplitude and frequency which

51、can be sustained in the feedback loop even if the system input is zero. In linear systems an unstable transient grows theoretically to infinite amplitude, but nonlinear effects limit this growth.（非線性系統(tǒng)）的不穩(wěn)定性通常表現(xiàn)為極限環(huán)的形式。其振蕩以固定的幅值和頻率在反饋環(huán)中維持即使系統(tǒng)的輸入為零。對于不穩(wěn)定的線性系統(tǒng)其瞬態(tài)過程的幅值在理論上會趨于無窮大，但是非線性特性會限制其增長。The jump

52、phenomenon is illustrated by the frequency response plot in Fig.2-4B-1. If the frequency of the input is reduced from high value, the amplitude of the response drops suddenly at the vertical tangent point C to the value at D.跳躍現(xiàn)象如圖Fig.2-4B-1所示，該圖解釋了輸出幅值與輸入頻率之間的關(guān)系。如果輸入的頻率從一個比較高的數(shù)值減小，響應(yīng)的幅值會突然垂直的相切點C下降

53、到點D。Unit 5A: Introduction to Modern Control TheoryWhen differential equations are encountered, they are linearized and subjected to whatever constraints are necessary to establish useful input-output relationships.當(dāng)使用微分方程時，要對其進行線性化并受限于一定的約束條件才能建立有用的輸入-輸出關(guān)系。A recognition of the applicability of well-

54、known methods in other fields of knowledge. 認識到其他領(lǐng)域的一些有名的方法的適用性。Optimal control theory often dictates that nonlinear time varying control law be used, even if the basic system is linear and time-invariant. 即使系統(tǒng)是線性定常的，最優(yōu)控制理論通常給出非線性時變控制律。When nonlinearities and time variation are present, the very bas

55、is for classical techniques is removed. Some successful techniques such as phase-plane, describing function, and ad hoc methods, have been developed to alleviate this shortcoming . 當(dāng)系統(tǒng)存在非線性和時變特性時，經(jīng)典方法賴以存在的基礎(chǔ)就不存在了。一些成功的方法，如相平面法、描述函數(shù)法以及一些特定的方法可以改進經(jīng)典控制理論。翻譯示例：With an advancing technological society, th

56、ere is a trend towards more ambitious goals. This also means dealing with complex system with a larger number of interesting components. The need for greater accuracy and efficiency has changed the emphasis on control system performance. The classical specifications in terms of percent overshoot, se

57、ttling time, bandwidth, etc., have in many cases given way to optimal criteria such as minimum 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 non

58、linear time varying control law be used, even if the basic system is linear and time-invariant. 隨著社會技術(shù)的進步，人們總是選擇更高的目標。這就意味著要處理復(fù)雜的具有更多相互作用的部件的系統(tǒng)。由于需要更高的精度和效率控制系統(tǒng)的性能指標已經(jīng)發(fā)生變化。經(jīng)典的指標如超調(diào)量、調(diào)節(jié)時間、帶寬等已經(jīng)讓位于最優(yōu)化指標如最小能量、最小成本已經(jīng)最小時間等。即使系統(tǒng)是線性定常的，最優(yōu)控制理論通常給出非線性時變控制律。The concept of state occupies a central position in

59、modern control theory. However, it appear in many other technical and non-technical context as well. In thermodynamics the equations of state are prominently used. Binary sequential networks are normally analyzed in term of their state. In everyday life, monthly financial statements are commonplace. The President state of the Union meesage is an