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外文資料
Introduction to Mechanical Design
Mechanical design is the application of science and technology to devise new or improved products for the purpose of satisfying human needs. It is a vast field of engineering technology which not only concerns itself with the original conception of the product in terms of its size, shape and construction details, but also considers the various factors involved in the manufacture, marketing and use of the product.
People who perform the various functions of mechanical design are typically called designers, or design engineers. Mechanical design is basically a creative activity. However, in addition to being innovative, a design engineer must also have a solid background in the areas of mechanical drawing, kinematics, dynamics, materials engineering, strength of materials and manufacturing processes.
As stated previously, the purpose of mechanical design is to produce a product which will serve a need for man. Inventions, discoveries and scientific knowledge by themselves do not necessarily benefit people; only if they are incorporated into a designed product will a benefit be derived. It should be recognized, therefore, that a human need must be identified before a particular product is designed.
Mechanical design should be considered to be an opportunity to use innovative talents to envision a design of a product, to analyze the system and then make sound judgments on how the product is to be manufactured. It is important to understand the fundamentals of engineering rather than memorize mere facts and equations. There are no facts or equations which alone can be used to provide all the correct decisions required to produce a good design. On the other hand, any calculation made must be done with the utmost care and precision. For example, if a decimal point is misplaced, a otherwise acceptable design may mot function.
Good designs require trying mew ideas and being willing to take a certain amount of risk, knowing that if the mew idea does not work the existing method can be reinstated. Thus a designer must have patience, since there is no assurance of success for the time and effort expended. Creating a completely new design generally requires that many old and well-established methods be thrust aside. This is not easy since many people cling to familiar ideas, techniques and attitudes. A design engineer should constantly search for ways to improve an existing product and must decide what old, proven concepts should be used and what new, untried ideas should be incorporated.
New designs generally have “bugs” or unforeseen which must be worked out before the superior characteristics of the new designs can be enjoyed. Thus there is a chance for a superior product, but only at higher risk. It should be emphasized that, if a design does not warrant radical new methods, such methods should not be applied merely for the sake of change.
During the beginning stages of design, creativity should be allowed to flourish without a great number of constraints. Even though many impractical ideas may arise, it is usually easy to eliminate then in the early stages of design before firm details are required by manufacturing. In this way, Innovative ideas are not inhibited. Quite often, more than one design is developed, up to the point where they can be compared against each other. It is entirely possible that the design which is ultimately accepted will use ideas existing in one of the rejected designs that did not show as much overall promise.
Psychologists frequently talk about trying to fit people to the machines they operate. It is essentially the responsibility of the engineer to strive to fit machines to people. This is not an easy task, since there is really no average person for which certain operating dimensions and procedures are optimum.
Another important point which should be recognized is that a design engineer must be able to communicate ideas to other people if they ate to be incorporated. Communicating the design to others is the final, vital step in the design process. Undoubtedly many great designs, inventions, and creative works have been lost to mankind simply because the originators were unable or unable or unwilling to explain their accomplishments to others. Presentation is a selling job. The engineer when presenting a new solution to administrative, management, or supervisory persons, is attempting to sell or to prove to them that this solution is a better one. Unless this can be done successfully, the time and effort spent on obtaining the solution have been largely wasted.
Basically, there ate only three means of communication available to us. These are the written, the oral, and the graphical forms. Therefore the successful engineer will be technically competent and versatile in all three forms of communication. A technically competent person who lacks ability in any one of these forms is severely handicapped. If ability in all three forms is lacking, no one will ever know how competent that person is!
The competent engineer should not be afraid of the possibility of not succeeding in a presentation. In fact, occasional failure should be expected because failure or criticism seems to accompany every really creative idea. There is a great deal to learn from a failure, and the greatest gains ate obtained by those wiling to risk defeat. In the final analysis, the real failure would lie in decoding not to make the presentation at all. To communicate effectively, the following questions must be answered:
1、Does the design really serve a human need?
2、Will it be competitive with existing products of rival companies?
3、It is economical to profit?
4、Can it be readily maintained?
5、Will it sell and make a profit?
Only time will provide the true answers to the preceding questions, but the product should be designed, manufactured and marketed only with initial affirmative answers. The design engineer also must communicate the finalized design to manufacturing through the use of detail and assembly drawings.
Quite often, a problem will occur during the manufacturing cycle. It may be that a exchange is required in the dimensioning or tolerancing of a part so that it can be more readily produced. This falls in the category of engineering changes which must be approved by the design engineer so that the product function will not be adversely affected. In other cases, a deficiency in the design may appear during assembly or testing just prior to shipping.
Engineering design is a systematic process by which solutions to the needs of humankind are obtained. The process is applied to problems (needs) of varying complexity. For example, mechanical engineers will use the design process to find an effective, efficient method to convert reciprocating motion to circular motion for the drive train in an internal combustion engine; electrical engineers will use the process to design electrical generating systems using falling water as the power source; and materials engineers use the process to design ablative materials which enable astronauts to safely the earth’s atmosphere.
The vast majority of complex problems in today’s high technology society depend for solution not on a single engineering discipline, but on teams of engineers, scientists, environmentalists, economists, sociologists, and legal personnel. Solutions are not only dependent upon the appropriate applications of technology but also upon public sentiment, government regulations and political influence. As engineers we are empowered with the technical expertise to develop new and improved products and systems, but at the same time we must be increasingly aware of the impact of our actions on society and the environment in general and work conscientiously toward the best solution in view of all relevant factors.
Design is the culmination of the engineering educational process; it is the salient feature that distinguishes engineering from other professions.
A formal definition of engineering design is found in the curriculum guidelines of the Accreditation Board for Engineering and Technology (AENT). ABEN accredits curricula in engineering schools and derives its membership from the various engineering professional societies. Each accredited curriculum has a well-deigned design component which falls within the ABEN guideline. The ABEN statement on design reads as follows:
Engineering design is the process of devising a system, component, or process to meet desired needs. It is a decision making process (often iterative ), in which the basic sciences, mathematic, and engineering sciences are applied to convert resources optimally to meet a stated objective. Among the fundamental elements of the design process are the establishment of objectives and criteria, synthesis, analysis, construction, testing, and evaluation. The engineering design component of a curriculum must include most of the following features: development of student creativity, use of open-ended problems, development and use of modern design theory mad methodology, formulation of design problem statements and specifications, consideration of alternative solutions, feasibility considerations, production processes, concurrent engineering design, and detailed system descriptions. Further, it is essential to include a variety of realistic constraints such as economic factors, safety, reliability, aesthetics, ethics, and social impact.
If anything can be said about the last half of the twentieth century, it is that we have had an explosion of information. The amount of data that can be uncovered on most subjects is overwhelming. People in the upper levels of most organizations have assistants who condense most of the things that they must read, hear, or watch. When you begin a search for information, be prepared to scan many of your sources and document their location so that you can find them easily if the date subsequently appear to be important.
Some of the sources that are available include the following:
1、 Exiting solutions. Much can be learned from the current status of solutions to a specific need if actual products can be located, studied and, in some cases, purchased for detailed analysis. An improved solution or an innovative new solution new solution cannot be found unless the existing solutions are thoroughly understood.
2、 Your library. Many universities have courses that teach you how to use your library. Such courses are easy when you compare them with those in chemistry and calculus, but their importance should not be underestimated. There are many sources in the library that can lead you to the information that you are seeking. You may find what you need in an index such as the Engineering Index. There are many other indexes that provide specialized information. The nature of your problem will direct which ones may be helpful to you. Don’t hesitate to ask for assistance from the librarian. You should use to advantage the computer databases found in libraries and often available through CD-ROM technology.
3、Professional organizations. The American Society of Mechanical Engineers is a technical society that will be of interest to students majoring in mechanical engineering. Each major in your college is associated with not one but often several such societies. The National Society of Professional Engineers is an organization that most engineering students well eventually join, as well as at least one technical society such as the society of manufacturing engineers, the American Society of civil engineers (ASCE), or any one of dozens that serve the technical interests of the host of specialties with which professional practices seem most closely associated. May engineers are members of several associations and societies.
4、Trade journals. They are published by the hundreds, usually specializing in certain classes of products and services. Money and economics are part of engineering design and decision making. We live in a society that is based on economics and competition. It is no doubt true that many good ideas never get tried because they are deemed to be economically infeasible. Most of us have been aware of this condition in our daily lives. We started with our parents explaining why we could not have some item that we wanted because it cost too much. Likewise, we will not put some very desirable component into our designs because the value gained will not return enough profit in relation to its cost.
Industry is continually looking for new products of all types. Some are desired because the current product is not competing well in the marketplace. Others are tried simply because it appears that people will buy them. How do manufacturers know that a new product will be popular? They seldom know with certainty. Statistics is an important consideration in market analysis. Most of you will find that probability and statistics are an integral part of your chosen engineering curriculum. The techniques of this area of mathematics allow us to make inferences about how large groups of people react based on the reactions of a few
中文翻譯
機械設計簡介
機械設計是為了滿足人類需要而制定出的新產品或者改進舊產品時對科學與技術的應用。 它是工程技術的一個巨大領域,這個領域不僅關注原先這種產品的尺寸，形狀以及構造方式， 而且考慮涉及這種產品的制造，銷售和使用的其它各方面的因素。
進行機械設計的各種各功能的人們被通常叫為設計者或者設計工程師。 機械設計基本上是一次創(chuàng)造活動。 然而， 除富有創(chuàng)新精神之外， 一位設計工程師也必須在機械制圖，運動學，力學，材料工程，材料強度和制造工藝有一定的背景知識。
精確的說，機械設計的目的就是為了滿足人們的需求。 發(fā)明，創(chuàng)造和科學知識它們自己可能不能讓人獲益； 但是只要他們合并在一起并設計產品，其益處就會被得到。因此，在一種特別的產品被設計之前，人的需求必須被鑒定，這一點應該被認識到。
機械設計應被視為一個機會，利用創(chuàng)新人才的設想設計一個產品，分析系統(tǒng)，然后就如何制造產品作出正確的判斷。對工程基礎的理解而不是僅僅記住事實和方程式，這一點是很重要的。 沒有哪個事實或方程式能單獨提供要求生產一種好設計的全部的正確的決定。 另一方面，任何計算必須得最大限度小心和精密。 例如，一個小數(shù)點放錯，就有可能得不到所要設計得到的結果。
好的設計應該需要嘗試新的方法并且愿意承擔一定的風險，知道如果新想法不起作用，這種現(xiàn)有的方法可能被重新使用。由于為了成功所付出的時間以及努力是不能保證的，因此一個設計者必須要有耐心。創(chuàng)造一個完全新的設計一般要求很多舊的以及被建立起來的方法來推動。這并不容易因為很多人堅持舊的想法，技術和態(tài)度。設計工程師要不斷尋找方法，以改善現(xiàn)有的產品，并且決定哪些舊的、已被證明的概念須要采納，哪些新的、未曾嘗試的想法應該被包刮進來。
在那些新設計的優(yōu)勢特性可以被享有之前,新設計一般有"缺陷"或者一些未預見的缺點。因此，有機會，提供優(yōu)異的產品，但只有在較高的風險下。應該強調指出，如果一個設計并不需要激進的新方法，這種方法不應適用而僅僅是為了改變。
在設計的開始階段，創(chuàng)造性應該被提倡而沒有許多限制條件。 即使很多不實用的想法可能出現(xiàn)，在穩(wěn)定的細節(jié)生產被要求之前，這些在設計早期通常是容易消除的。以這種方法，富創(chuàng)新精神的想法不被抑制。 經(jīng)常，不止一種設計被提出，甚至到他們可能對彼此被進行比較的方面。 這是完全可能的：最終被接受的設計將可能使用被拒絕的設計之中的一個想法。
心理學家經(jīng)常談論努力使他們操作的那些機器適合人。努力使機器適應人基本上是工程師的責任。這不是一項容易的任務,因為真的沒有人能夠把某一個生產尺寸加工到最優(yōu)化的程度。
另一個要點是：一位設計工程師必須能把想法傳達給其他人，當他們的想法可以被采納時。 把設計思想傳達給其它人是最后環(huán)節(jié)，也是在設計過程里的至關重要的步驟。無疑很多重要的設計，發(fā)明和有創(chuàng)造性的作品被人們所不認同，僅僅是因為那些創(chuàng)始人不能或者不愿意對其它人解釋他們的成就。 贈送是一個出售的工作。 當提出一個新的解決方案，管理或者監(jiān)督的人的方法時，工程師， 正試圖出售或者向他們證明這個解決辦法是更好的。 除非這能被成功操作，否則關于獲得這個解決辦法所花費的時間和努力基本上是浪費的。
基本上，那里只有我們可用的3個通信手段。 它們是寫，口頭，以及圖表的形式。 因此成功的工程師將精通這3 種交際方式的能力。缺乏其中任何一個交際能力的一個技術人員就相當于嚴重殘疾。如果全部3個交際能力都缺乏的話，沒有人知道此人是多么有能力！
有能力的工程師不應該害怕推薦自己不成功的可能性。實際上，偶然的失敗應該被期望，因為失敗或者批評好像伴隨每個真的有創(chuàng)造性的想法。 有許多都是從失敗中獲悉，巨大收獲都是從那些冒險獲得的。歸根到底，真正的失敗將在于根本不會做推薦自己。 為了有效地交流，下列問題必須被回答：
(1)這設計真的能服務人需要嗎？
(2)它將與現(xiàn)有的競爭公司的產品競爭嗎？
(3)獲益是實惠的嗎？
(4)它能被比較容易的保持嗎？
(5)它將能被出售并且贏利嗎？
只有時間能提供上述問題的正確的答案，但是產品應該被設計，只用最初肯定的答案生產并且銷售。設計工程師也必須通過使用細節(jié)和裝配圖多溝通定稿設計到生產。
經(jīng)常，一個問題將在生產的循環(huán)期間產生。這可能是在一個部分的定尺寸或者加工過程中所要求一次交換，以便它能夠被更容易生產。這在被設計工程師批準的工程變化的種類方面下降，以便產品功能將不被相反影響。 在其他情況里，在設計過程中的一種缺陷可能在裝運之前的裝配或檢測測試期間出現(xiàn)。
工程設計是一個系統(tǒng)的過程，其中的解決方案是為了滿足人類需要而得到的。進程是不同的復雜性的問題（需求）的應用。例如，機械工程師，將利用設計過程中，以找到一個有效率的方式轉換成往復運動，在一個內部內燃機以圓周運動來驅動列車;電氣工程師在使用過程中，以設計電動發(fā)電機系統(tǒng)使用，水位下降為能源;材料工程師使用過程中，以設計燒蝕材料，使宇航員平安返回地球的大氣層。
在今天的高科技社會,絕大多數(shù)的復雜問題賴以解決的方案不僅僅取決于單一的工程學科，而且還取決于團隊的工程師，科學家，環(huán)境學家，經(jīng)濟學家，社會學家，法律人員。解決方案不僅取決于適當技術的應用而且還取決于公眾情緒，政府規(guī)章和政治影響力。作為工程師，我們有權與技術專家發(fā)展和改進新的產品和系統(tǒng)，但同時我們必須意識到我們行動的影響：對社會和環(huán)境的總體工作，認真對待最好的解決辦法，鑒于對所有的相關因素。
??? 設計是經(jīng)過工程教育的過程，這是區(qū)別其他工程專業(yè)的顯著的特點。
它的一個正式的定義是：工程設計是有工程與技術評審委員會（ AENT ）的指引下建立的 。 AENT委派的課程，在工程學校和源于其成員來自各工程專業(yè)社團。各派駐課程已有一套完善的設計部分，其中屬于ABEN的指引。該AENT聲明，對設計內容如下：
???工程設計是，制訂一個系統(tǒng)，組件的過程，以應付預期的需求。同時它也是一個決策過程（通常迭代） ，其中基礎科學，數(shù)學，科學和工程科學的應用轉換成資源，以最大限度地滿足目標。其中基本要素的設計過程中，是設立目標和標準，合成，分析，構造，測試和評價。工程設計組成的一個課程必須具有以下大部分特點：發(fā)展學生的創(chuàng)造力，利用不限名額問題，開發(fā)和利用現(xiàn)代設計理論的方法，配方設計問題，報表和規(guī)格，考慮其他的解決辦法，可行性的考慮，生產進程，并行工程設計，以及詳細的系統(tǒng)說明。此外，它必須包括各種現(xiàn)實的制約因素，如經(jīng)濟因素，安全性，可靠性，美學，倫理學和社會的影響。
關于最近二十世紀下半葉，其最大的特點，那就是：我們處在一個資訊爆炸時代?？砂l(fā)現(xiàn)的數(shù)據(jù)量大部分的科目是壓倒性的。在上級的大多數(shù)組織的人們已經(jīng)幫助凝聚在他們必須讀，聽，或看的大部分的事情。當你開始尋找資料，準備以瀏覽你的許多消息來源，并記錄其位置，如果有日期就能方便你能夠輕松的找到。
一些消息的來源也可以包括以下幾個方面：
1、飛離解決方案。在某些情況下，根據(jù)具體需要從目前的現(xiàn)狀解決辦法，如果實際的產品可以研究，購買詳細的分析，我們可以從中學到很多東西。一種改進的解決辦法或是一個嶄新的解決方案均不能被找到，除非現(xiàn)有的解決方案是徹底的了解。
2、你的圖書館。許多大學有課程，教你如何使用你的圖書館。此類課程的目的是很容易當你比較他們與那些在化學和微積分，但其重要性是不可低估的。在圖書館有許多來源，這些來源可以把你帶到你想要尋找的資料。你可以找到你所需要的一個指標，如工程索引。還有很多其他的指標，提供專門的信息。你的問題的性質，將直接哪些是可以幫助你。不要再猶豫向館員請求幫助。你應該使用，以圖書館建立的電腦數(shù)據(jù)庫，而且往往可以通過光盤技術。
3、專業(yè)組織。美國機械工程師學會是一個技術性的社會，這將是學生感興趣的主修機械工程。在你的大學里，每項重大的項目往往都是幾個社團一起協(xié)助的而不是一個。國家專業(yè)工程師協(xié)會，是一個大多數(shù)工程系學生都想加入的組織，以及技術協(xié)會如社會制造工程師，美國土木工程師協(xié)會（ASCE ） ，或任何一個幾十項服務技術東道國的利益的組織，專業(yè)與專業(yè)的做法似乎有最密切聯(lián)系在一起的。 5月工程師協(xié)會成員也是其它幾個社團和協(xié)會的成員。
4、貿易雜志。公布這些數(shù)據(jù)是由數(shù)百個團體，這些團體通常是專門從事某些類別的產品和服務。金錢和經(jīng)濟學是工程設計與決策的一部分。我們生活在一個基于經(jīng)濟及競爭的社會中。毫無疑問確實有很多好的想法從來沒有得到通過，是因為他們被認為在經(jīng)濟上不可行。我們大部分人已經(jīng)意識到我們日常生活的這種狀況。我們開始與我們的父母解釋為什么我們不能有我們所希望的一些項目，因為它的成本太高了。同樣，我們將不會把一些非常可取的成分融入我們的設計中，因為價值上漲將不會獲得足夠的利潤，相對于其成本。
工業(yè)正不斷尋求所有種類的新的產品。有些是可取的，因為在市場上目前的產品不能與之相互競爭。而其它的都試圖簡單，因為在它看來，人們會購買他們。制造商怎么知道一個新的產品將受歡迎呢？他們很少確定。在市場分析中統(tǒng)計是一項重要的考慮因素。你們中的大部分人會發(fā)覺：概率統(tǒng)計是一個不可分割的組成部分，在你所選擇的工程課程中。該技術在本領域的數(shù)學，使我們作出的推論：對如何大群體的人的反應的基礎上的反應數(shù)。