填料箱蓋機(jī)械加工工藝過程卡及數(shù)控編程設(shè)計(jì)
填料箱蓋機(jī)械加工工藝過程卡及數(shù)控編程設(shè)計(jì),填料,機(jī)械,加工,工藝,過程,進(jìn)程,數(shù)控,編程,設(shè)計(jì)
Introductions to Control Systems
Automatic control has played a vital role in the advancement of engineering and science. In addition to its extreme importance in space-vehicle, missile-guidance, and aircraft-piloting systems, etc, automatic control has become an important and integral part of modern
manufacturing and industrial processes. For example, automatic control is essential in such industrial operations as controlling pressure, temperature, humidity, viscosity, and flow in the process industries; tooling, handling, and assembling mechanical parts in the manufacturing industries, among many others.
Since advances in the theory and practice of automatic control provide means for attaining optimal performance of dynamic systems, improve the quality and lower the cost of production, expand the production rate, relieve the drudgery of many routine, repetitive manual operations etc, most engineers and scientists must now have a good understanding of this field.
The first significant work in automatic control was James Watt’s centrifugal governor for the speed control of a steam engine in the eighteenth century. Other significant works in the early stages of development of control theory were due to Minorsky, Hazen, and Nyquist, among many others. In 1922 Minorsky worked on automatic controllers for steering ships and showed how stability could be determined by the differential equations describing the system. In 1934 Hazen, who introduced the term “ervomechanisms” for position control systems, discussed design of relay servomechanisms capable of closely following a changing input.
During the decade of the 1940’s, frequency-response methods made it possible for engineers to design linear feedback control systems that satisfied performance requirements. From the end of the 1940’s to early 1950’s, the root-locus method in control system design was fully developed.
The frequency-response and the root-locus methods, which are the core of classical theory, lead to systems that are stable and satisfy a set of more or less arbitrary performance requirements. Such systems are, in general, not optimal in any meaningful sense. Since the late 1950’s, the emphasis on control design problems has been shifted from the design of one of many systems that can work to the design of one optimal system in some meaningful sense.
As modern plants with many inputs and outputs become more and more complex, the description of a modern control system requires a large number of equations. Classical control theory, which deals only with single-input-single-output systems, becomes entirely powerless for multiple-input-multiple-output systems. Since about 1960, modern control theory has been developed to cope with the increased complexity of modern plants and the stringent requirements on accuracy, weight, and industrial applications.
Because of the readily available electronic analog, digital, and hybrid computers for use in complex computations, the use of computers in the design of control systems and the use of on-line computers in the operation of control systems are now becoming common practice.
The most recent developments in modern control theory may be said to be in the direction of the optimal control of both deterministic and stochastic systems as well as the adaptive and learning control of complex systems. Applications of modern control theory to such nonengineering fields as biology, economics, medicine, and sociology are now under way, and interesting and significant results can be expected in the near future.
Next we shall introduce the terminology necessary to describe control systems.
Plants. A plant is a piece of equipment, perhaps just a set of machine parts functioning together, the purpose of which is to perform a particular operation. Here we shall call any physical object to be controlled (such as a heating furnace, a chemical reactor, or a spacecraft) a plant.
Processes. The Merriam-Webster Dictionary defines a process to be a natural, progressively continuing operation or development marked by a series of gradual changes that succeed one another in a relatively fixed way and lead toward a particular result or end; or an artificial or voluntary, progressively continuing operation that consists of a series of controlled actions or movements systematically directed toward a particular result or end.Here we shall call any operation to be controlled a process. Examples are chemical, economic, and biological process.
Systems. A system is a combination of components that act together and perform a certain objective. A system is not limited to abstract, dynamic phenomena such as those encountered in economics. The word “system” should, therefore, be interpreted to imply physical, biological, economic, etc., system.
Disturbances. A disturbance is a signal which tends to adversely affect the value of the output of a system. If a disturbance is generated within the system, it is called internal, while an external disturbance is generated outside the system and is an input.
Feedback control. Feedback control is an operation which, in the presence of disturbances, tends to reduce the difference between the output of a system and the reference input (or an arbitrarily varied, desired state) and which does so on the basis of this difference. Here, only unpredictable disturbance (i.e., those unknown beforehand) are designated for as such, since with predictable or known disturbances, it is always possible to include compensation with the system so that measurements are unnecessary.
Feedback control systems. A feedback control system is one which tends to maintain a prescribed relationship between the output and the reference input by comparing these and using the difference as a means of control.
Note that feedback control systems are not limited to the field of engineering but can be found in various nonengineering fields such as economics and biology. For example, the human organism, in one aspect, is analogous to an intricate chemical plant with an enormous variety of unit operations.The process control of this transport and chemical-reaction network involves a variety of control loops. In fact, human organism is an extremely complex feedback control system.
Servomechanisms. A servomechanism is a feedback control system in which the output is some mechanical position, velocity, or acceleration. Therefore, the terms servomechanism and position- (or velocity- or acceleration-) control system are synonymous. Servomechanisms are
extensively used in modern industry. For example, the completely automatic operation of machine tools, together with programmed instruction, may be accomplished by use of servomechanisms.
Automatic regulating systems. An automatic regulating system is a feedback control system in which the reference input or the desired output is either constant or slowly varying with time and in which the primary task is to maintain the actual output at the desired value in the presence of disturbances.
A home heating system in which a thermostat is the controller is an example of an automatic regulating system. In this system, the thermostat setting (the desired temperature) is compared with the actual room temperature. A change in the desired room temperature is a disturbance in
this system. The objective is to maintain the desired room temperature despite changes in outdoor temperature. There are many other examples of automatic regulating systems, some of which are the automatic control of pressure and of electric quantities such as voltage, current and frequency.
Process control systems. An automatic regulating system in which the output is a variable such as temperature, pressure, flow, liquid level, or pH is called a process control system.Process control is widely applied in industry. Programmed controls such as the temperature control of heating furnaces in which the furnace temperature is controlled according to a preset program are often used in such systems. For example, a preset program may be such that the furnace temperature is raised to a given temperature in a given time interval and then lowered to another given temperature in some other given time interval. In such program control the set point is varied according to the preset time schedule. The controller then functions to maintain the furnace temperature close to the varying set point. It should be noted that most process control systems include servomechanisms as an integral part.
控制系統(tǒng)介紹
自動控制在工程學(xué)和科學(xué)的推進(jìn)扮演一個重要角色。 除它的在空間領(lǐng)域應(yīng)用的極端重要性之外，在導(dǎo)彈制導(dǎo)和航空器的駕駛系統(tǒng)等等，自動控制成為了重要和整體的部分、現(xiàn)代制造和工業(yè)生產(chǎn)方法。 例如，自動控制在這樣工業(yè)操作中是必須的，如：在加工業(yè)中的控制壓力、溫度、濕氣、黏度和流程;加工、裝卸和在制造工業(yè)生產(chǎn)流水線部分和許多其他方面。
由于自動化控制的進(jìn)展，為動力系統(tǒng)實(shí)現(xiàn)最優(yōu)性能，在理論和實(shí)踐上的提供手段。提高質(zhì)量和降低生產(chǎn)成本，擴(kuò)大生產(chǎn)速度，減輕許多例行性，重復(fù)性的手工操作等，大部分工程師和科學(xué)家們現(xiàn)在在這一領(lǐng)域必須有一個良好的了解和合作。
在自動化控制一次具有重要意義的開拓性工作，是詹姆斯瓦特的離心調(diào)速器，在十八世紀(jì)為一臺蒸汽機(jī)進(jìn)行速度控制。在控制理論初期發(fā)展階段的其他重大工程，是出于米諾爾斯基、哈森和奈奎斯特等等。在1922年，米諾爾斯基對自動控制器制導(dǎo)船只并呈現(xiàn)出怎樣的穩(wěn)定性，確定由微分方程進(jìn)行系統(tǒng)描述。早在1934年，哈森將術(shù)語" 差補(bǔ) "引入了位置控制系統(tǒng)，討論了設(shè)計(jì)適應(yīng)變化的輸入的伺服繼電器。
在40年代這十年間，頻率響應(yīng)法，使工程師有可能為人們設(shè)計(jì)完全滿足設(shè)備性能要求的線性反饋控制系統(tǒng)。從1940年底至1950年初，根軌跡法在控制系統(tǒng)的設(shè)計(jì)得到充分的發(fā)展。
頻率響應(yīng)和根軌跡法，這是核心的經(jīng)典理論，引出的是一個穩(wěn)定系統(tǒng)，并滿足了或多或少一系列變化了的性能要求。這種系統(tǒng)，是在一般情況，而不是在任何意義上的最優(yōu)。自20世紀(jì)50年代末期開始，控制設(shè)計(jì)上的側(cè)重點(diǎn)問題已經(jīng)從有很多系統(tǒng)設(shè)計(jì)可以工作的系統(tǒng)，到設(shè)計(jì)一個一般意義上的最佳系統(tǒng)，使這些系統(tǒng)都可以工作。
一個現(xiàn)代裝置有許多輸入和輸出，變得越來越復(fù)雜，描述一個現(xiàn)代控制系統(tǒng)需要大量的方程。經(jīng)典控制理論，其中僅涉及到單輸入單輸出系統(tǒng)，完全無能為力，多輸入-多輸出系統(tǒng)變得更有效能。自約1960年，現(xiàn)代控制理論已經(jīng)成功發(fā)展，以應(yīng)付日益復(fù)雜的現(xiàn)代裝置，以及精度、重量和工業(yè)應(yīng)用方面的嚴(yán)格規(guī)定。
由于電子模擬的廣泛應(yīng)用，數(shù)字和混合計(jì)算機(jī)用于復(fù)雜的運(yùn)算，在控制系統(tǒng)的設(shè)計(jì)中電腦的使用和在運(yùn)行控制系統(tǒng)使用在線的電腦，正在成為普遍的做法。在現(xiàn)代控制理論最近期的發(fā)展，可以說是在既定方向上的最優(yōu)控制方面的確定性和隨機(jī)性系統(tǒng)，以及自適應(yīng)和學(xué)習(xí)控制的復(fù)雜系統(tǒng)。在生物學(xué)、經(jīng)濟(jì)學(xué)、醫(yī)學(xué)、社會學(xué)這些非工程學(xué)領(lǐng)域，現(xiàn)代控制理論的這種應(yīng)用，現(xiàn)在正在進(jìn)行之中，可以預(yù)期在不久的將來有著有趣和顯著的效果。
其次，我們應(yīng)引進(jìn)必要的術(shù)語來描述控制系統(tǒng)。
裝置.是設(shè)備，或者一套一起起作用機(jī)器的零件，目的是進(jìn)行特殊操作。 在這兒我們將被控制(例如熱化熔爐、一個化學(xué)反應(yīng)器或者航天器) 的所有物體叫做裝置。
過程.麥里亞.韋伯斯特字典將過程定義為一種自然的持續(xù)的操作或演變進(jìn)程。其特征是一系列漸進(jìn)的變化以相對固定的方式相繼發(fā)生在操作或演變進(jìn)程中，并產(chǎn)生特定的效果或結(jié)果；或者是人為或自發(fā)的、持續(xù)性的由一系列產(chǎn)生特定結(jié)果的被控操作或動作組成的工序。例子是化學(xué)、經(jīng)濟(jì)和生物學(xué)過程。
系統(tǒng).系統(tǒng)是一起行動并且執(zhí)行某一目的的組分的組合。 系統(tǒng)指不被限制的，例如在經(jīng)濟(jì)遇到的那些動態(tài)現(xiàn)象。，因此，詞“system” 應(yīng)該解釋為暗示物理、生物、經(jīng)濟(jì)等等系統(tǒng)。
干擾.干擾是傾向于對系統(tǒng)輸出產(chǎn)生不利的影響的信號。 如果干擾在系統(tǒng)之內(nèi)引起，它稱內(nèi)部干擾；而一個外在干擾在系統(tǒng)之外引起并且是輸入。
反饋控制.在干擾面前，傾向于減少和參考輸入的操作(或一個任意地變化的，期待狀態(tài))之間系統(tǒng)輸出的偏差，并且根據(jù)這個偏差進(jìn)行控制。 這里，變化莫測的干擾(即，那些預(yù)先未知的參數(shù))被同樣地選定，因?yàn)榕c可預(yù)測或已知的干擾，包括與系統(tǒng)的補(bǔ)償總是可能的，使得測量是多余的。
反饋控制系統(tǒng). 反饋控制系統(tǒng)是傾向于通過比較輸出和參考輸入之間偏差為既定的關(guān)系并作為控制的方法的一個系統(tǒng)。
注意反饋控制系統(tǒng)并沒有被限制在工程學(xué)的領(lǐng)域，而是能在各種各樣的非工程學(xué)領(lǐng)域例如經(jīng)濟(jì)和生物中找到。例如，人體組織，在一個方面，是類似于一個以龐大數(shù)量的操作單元組成的復(fù)雜化工廠。這個運(yùn)輸和化學(xué)制品反應(yīng)網(wǎng)絡(luò)中，過程控制介入各種各樣的控制回路。 實(shí)際上，人體組織是一個極端復(fù)雜反饋控制系統(tǒng)。
伺服系統(tǒng).伺服系統(tǒng)是輸出是一些位移、速度或者加速度的反饋控制系統(tǒng)。 所以，限位伺服系統(tǒng)和位置(或速度或者加速度)控制系統(tǒng)是同義的。 伺服系統(tǒng)廣泛應(yīng)用于現(xiàn)代產(chǎn)業(yè)。 例如，機(jī)床的完全地自動地工作，，也許是與程序指令一起成功的利用伺服系統(tǒng)。
自動調(diào)節(jié)系統(tǒng).一個自動調(diào)節(jié)的系統(tǒng)是參考輸入或期望輸出是常數(shù)或隨時間緩慢變化的反饋控制系統(tǒng)，并且在出現(xiàn)干擾之前保持實(shí)際輸出為期望值。
家庭供暖系統(tǒng)的溫度控制器的是一個自動調(diào)節(jié)系統(tǒng)的例子。在這個系統(tǒng)，溫度設(shè)置(期望溫度)與實(shí)際室溫比較。在期望室溫上的一個變化是這個系統(tǒng)的干擾。系統(tǒng)將盡量維持期望室溫在不斷變化的室外溫度之上。還有自動調(diào)節(jié)系統(tǒng)的許多其他例子，一些是壓力和電量自動控制例如電壓、電流和頻率。
過程控制.過程控制是輸出為溫度、壓力、流量、液位或pH值等變量的自動調(diào)節(jié)系統(tǒng)稱為過程控制系統(tǒng)。過程控制在工業(yè)中廣泛被應(yīng)用。過程控制例如的熱化熔爐溫度控制系統(tǒng)，根據(jù)預(yù)置程序進(jìn)行熔爐溫度控制，就是這樣系統(tǒng)。 例如，一個預(yù)置的程序可以是這樣的，爐溫在給定時間內(nèi)上升到給定值，然后在預(yù)定時間內(nèi)又下降到另一給定值。這樣的過和控制調(diào)整點(diǎn)根據(jù)預(yù)置程序變化?？刂破髟诮咏兓娜蹱t溫度調(diào)整點(diǎn)起作用維持爐溫。值得注意的是，多數(shù)過程控制系統(tǒng)包括伺服裝置作為整體的一部分。
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