Lesson 16 Basic Concepts of Mechanisms

A combination of interrelated parts(相关零件的组合体) having definite（确定的）motions and capable of performing useful work may be called machine. 

具有确定的运动轨迹,并且能做有用的功联接在一起的零件的组合称为机器.

A mechanism is a component of a machine consisting of two or more bodies arranged so that the motion of one compels the motion of the others.

机构是机器的组成要素.机器由二个及以上的机构组合而成.因此其中一个构件的运动会带动其它的构件的连锁运动.

Kinematics is the study of motion in mechanisms without reference to the forces that act on the mechanism

运动学仅研究机构的运动而不考虑作用在机构上的力.

Dynamics is the study of motion individual bodies and mechanisms under the influence of forces and torques.

动力学研究独立构件的运动及力和扭矩作用下对机构的影响.

The study of forces and torques in stationary systems (and systems with negligible inertial effects) is called statics

研究平衡中的力和扭矩,该系统忽略惯性影响,称之为静力学.

Synthesis is the procedure by which a product (a mechanism, for example) is developed to satisfy a set of performance requirements

合成是一个程序,通过该程序能够不断改进一个产品(例如一个机构)直到满足一系列的性能要求.

If a product configuration is tentatively specified and then examined to determine whether the performance requirements are met, the process is called analysis.

如果需要探索性的详细阐述产品的构造结构,然后检验,判断该产品是否满足性能要求,这个过程称为分解.

The design of mechanisms involves both synthesis and analysis.

机构设计包括合成和分解.

The design process begins with the recognition of a need. A set of requirements is then listed

设计从对于需求的确认开始,罗列出一系列的要求.

Detailed analyses of displacements, velocities, and accelerations are usually required

通常需要对位移,速度,加速度进行具体分析.

This part of the design process is followed by an analysis of forces and torques.

设计过程中的这个部分是紧跟在对力和扭矩的分析之后.

The design process may continue long after（很久以后）the first models have been produced and may include redesigns of components that affect velocities, accelerations, forces, and torques

在制造完毕第一个模型之后,该设计过程仍有可能持续很长一段时间. 并且有可能会重新设计这些会影响速度,加速度及所知扭矩的零部件

In order to successfully compete from year to year, most manufactures must continuously modify their product and their methods of production

为了在年复一年的技术中取得优势,大多数制造商必须不断调整修改他们的产品及加工方式

.Increases in the production rate, upgrading of product performance, redesign for cost and weight reduction are frequently required

,为了增加出产率,提高产品的性能,经常需要重新设计来降低成本以及减轻重量.

Success may hinge on（决定于） the accuracy of the kinematic and dynamic analysis

对问题进行正确的运动学和动力学分析是成功的关键.

Many of the basic linkage configurations have been incorporated into（成为……的一部分）machines designed centuries ago, and the terms we use to describe them have changed over the years

很久以前,许多基本的连杆构造就已经运用在机器设计中去了,并且我们用来称呼它们的术语在不断的变化,.

Thus, definitions and terminology are not consistent throughout thetechnical literature.

因此技术供应文献中的定义和说明不是一成不变的

In most cases, however, meanings will be clear from the context of the descriptive matter.

在大多数的情况下,然而定义,义意可以在的解释性的描述内容中清晰的获得,

A few terms of particular interest to the study of kinematics and dynamics of machines are defined below

下面定义了在学习,研究机构运动学和动力学中一些特别重要的术语.

Link A link is one of the rigid bodies or members joined together to form a kinematic chain.

杆件 是一个刚体或者连接在一起形成运动链的零部件,因此被称为刚性构件或者是简单构件.

The term rigid link, or sometimes simply link, is an idealization used in the study of mechanisms that does not consider small deflections due to strains in machine members

刚性构件是在机械装置中的理想化模型.这样就不无需考虑由机器零部件所产生的应力造成的微小偏移量.

A perfectly rigid or inextensible link can exist only as a textbook type of model of a real machine member.

一个绝对刚性或不可延展的构件只能存在于教科书上的机械零部件的模型.

For typical machine parts, the maximum changes in dimension are on the order of only a one-thousandth of the part length.

对于典型的零部件,最大的尺寸变化量仅仅是沿着该部件长度方向的千分之一.

We are justified（合理的） in neglecting this small motion when considering the much greater motion characteristic of most mechanisms

当考虑到大多数的机构相对较为显着的运动特征,忽略这点微量的偏移是合情合理的.

The word link is used in a general sense to include cams, gears, and other machine members in addition to cranks, connecting rods and other pin-connected（铰接） components

通常意义所说的杆件包括凸轮,齿轮以及它的机器零件的曲柄,连杆机构和其它的销件连接部分.

Frame The fixed or stationary link in a mechanism is called the frame

机架 机械装置中固定或静止不动的构件称为机架.

When there is no link that is actually fixed, we may consider one as being fixed and determine the motion of the other links relative to it

如果实际中确实没有构件是固定的,我们可以假设其中某个是固定的,这样可以判断出其它与之相连构件的运动.

In an automotive engine, for example, the engine block (see Fig.14.1) is considered the frame, even though the automobile may be moving

例如汽车发动机,我们通常是把发动机气缸视为机架,让它保持静止不动,实际上整部汽车者是运动的.

Degree of Freedom The number of degrees of freedom of a linkageis the number of independent parameters required to specify the position of every link relative to the frame or fixed link

自由度 连杆机构的自由度是给定独立参数的数目，需要自由度来确定某一个与机架或固定杆件相连接的构件的位置，

If the instantaneous configuration of a system may be completely defined be specifying one independent variable, that system has one degree of freedom

如果系统的瞬间结构完全可以由一个独立的变量来确定，这样系统就具有一个自由度，

An unconstrained rigid body has six degrees of freedom:

大多数实际上运用的机构装置只有一个自由度。

translation in three coordinate directions and rotation about three coordinate axes

一个不受约束的刚体它有六个自由度，沿着三个坐标平面的平移和绕着三个坐标轴的转动。

If the body is restricted to motion in a place, there are three degrees of freedom:

• 如果刚体受到约束在平面上移动，那么就有三个自由度，

• translation in two coordinate directions and rotation within the plane.

沿着两个坐标方向的移动以及在平面方向的转动。

Lower and Higher Pairs Connections between rigid bodies consist of lower and higher pairs of elements.

低副和高副 刚体连接的构件由低副和高副组成，

The two elements of a lower pair have theoretical surface contact with one another

低副的两个构件理论上是通过平面接触。

while the two elements of a higher pair have theoretical point or line contact (if we disregard deflections).

高副的两个构件理论上是点和线的接触（如果我们忽略变形）。

Kinematic Chain A kinematic chain is an assembly（集合） of links and pairs (joints). Each link in a closed-loop kinematic chain is connected to two or more other links

运动链 是若干个构件或运动链联接结合在一起，在闭式运动链中，每个构件都有相同两个及两个以上的其它构件相连接,

A linkage failing to meet the closed-loop criterion is an open-loop kinematic chain.

运动链没有满足闭式运动链的标准则称为开环运动链。

Linkage Since we may wish to examine kinematic chains without regard to their ultimate（最后） use, it is convenient to identify any assemblage of rigid bodies connected by kinematic joints as a linkage

连杆机构 由于我们希望检验运动链而不考虑它们的最终用途,可以非常方便的区分出任何做为连接机构的刚体的集合,这些连杆机构刚体是通过运动链连接在一起的，

Thus, both mechanisms and machines may be considered linkages

因此机构与机器都被视为连杆机构,

In some references, however, the term linkage is restricted to kinematic chains made up of lower pairs.

然而在某些参考文献中,linkage这个词仅仅限于由低副组成的运动链。

Planar Motion and Planar Linkages If all points in a linkage may be described as a planar linkage

平面移动和平面连杆机构 如果连杆机构上所有的点都同一平面内移动,则说明系统正在平移.

If we examine the linkage made up of the crank, connecting rod, and piston in a piston engine, we see that it is a planar linkage.

在活塞发动机中由曲柄,连杆和活塞组成的连杆机构,我们视为平面连杆机构.

Most of the mechanisms in common use may be treated as planar linkages.

大多数普遍使用的机械装置都被视平面连杆机构.

Spatial Motion and Spatial Linkages

空间运动和空间连杆机构

The more general case in which motion cannot be described as taking place in parallel planes is called spatial motion,

在更多一般情况下,不能在平面内进行运动的称为空间运动.

and the linkage may be described as a spatial or three-dimensional (3D) linkage.

该连杆机构被称为空间或三维连杆机构,

Inversion The absolute motion of a linkage depends on which of the links is fixed, that is, which link is selected as the frame

连杆机构的绝对移动取决于哪根连杆是构件是固定的,简而言之就是选择哪根杆件做为机架,

If two otherwise equivalent linkages(等效连杆机构) have different fixed link,

如果两根相当的连杆机构的固定机架是不同的,

then each is an inversion of the other. Relative motion will be the same in both linkages.那么一个就是另外一个的倒置.这在两个连杆机构中相当的运动都是相同的.

Lesson 30 Engineering Design 工程设计

Engineering design is a systematic process by which solutions to the needs of humankind are obtained. 工程设计是一个系统的方案，通过它人类可以获得需要的解决方案]The process is applied to problems (needs) of varying complexity这一过程被用于解决许多变化的复杂性的问题。

For example, mechanical engineers will use the design process to find an effective, efficient method to covert reciprocating motion to circular motion for the drive train in an internal combustion engine;例如，机械工程师应用设计过程去找到一种有效的高效的方法，把用于传动系统，这种运动的方法可以把内燃机中的往复运动转化为旋转运动；

electrical engineers will use the process to design electrical generating systems using falling water as the power source ; 电力工程师应用这一设计过程去设计用落水做动力源的发电系统通过采用下落水体做动力源的发电系统

and materials engineers use the process to design ablative materials which enable astronauts to safely reenter the earth’s atmosphere材料工程师采用将材料应用这一设计过程研制烧蚀材料，使宇航员能安全地重返地球（大气层）

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 political influencer, 现代高技术社会的大量复杂问题的解决，不是取决于单一的工程学科，而是取决于由工程师、科学家、环境保护专家、经济学家、社会学家和政治影响家组成的团队

Solutions are not only dependent upon the appropriate applications of technology, but also upon public sentiment(公众意见) as executed through government regulations and political influence.

解决问题不仅依靠技术的合理应用，而且要考虑通过政府法规和政治影响引起的大众情绪。

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(总体的) and work conscientiously toward the best solution in view of all relevant factors. 作为工程师被授权利用专门技术来研究和改进产品和系统，但同时我们必须知道我们的行为一般对社会和整个环境造成的影响，并考虑所有相关因素，尽责的工作，找出最好的解决办法

Design is the culmination of the engineering educational process; it is the salient feature that distinguishes engineering from other professions.

设计是工程教育过程的制高点（最终目标）；正是这一显著特征把(工程设计)和其他职业区分开来

A formal definition of engineering design is found in the curriculum guidelines(课程指导) of the Accreditation Board for Engineering and Technology (ABET). 工程设计的正式定义可以在工程技术鉴定合格委员会（ABET）的课程指导方针中找到。

ABET accredits(鉴定) curricula in engineering schools and derives its membership from the various engineering professional societies(行业协会).

ABET安排工程学校的课程，ABET的成员人数来自各种工程专业协会。

Each accredited curriculum has a well-defined design component which falls within the ABET guidelines. 每一门授权的课程有一个解释清楚的设计部分，该部分包含在ABET指导方针中。

The ABET statement on design reads as follows(内容如下): ABET对设计的解释如下：

Engineering deign is the process of devising a system, component, or process to meet desired needs. 工程设计是设计系统、元件的过程，或者是满足希望要求的过程。

. It is a decision making process (often iterative重复性的), in which the basic sciences, mathematics, and engineering sciences are applied to convert resources optimally to meet a stated objective(目标、目的). 它是一个决策指定的过程（经常需要反复），在此过程中为了达到规定的目标，最佳地应用基础科学、数学和工程科学，把它们转化成资源。

Among the fundamental elements of the design process are the establishment of objectives and criteria, synthesis（综合）, analysis, construction, testing, and evaluation.设计过程中的基本无素之间建立目标和标准，综合、分析、建造、测试和评价。

The engineering design component of a curriculum must include most include most of the following features: development of student creativity, use of open-ended problems, development and use of modern design theory and methodology, formulation of design problem statements and specifications, consideration of alternative solutions, feasibility considerations, production processes, and detailed system descriptions.

课程的工程设计部分必须包括以下大部分特性：学生创造性的培养、能适应未来发展的问题使用、现代设计理论和方法的发展和应用、设计问题的陈述和详细说明、其它解决问题方法的考虑、可行性研究、生产过程、并行工程设计以及详细的系统描述

Further, it is essential to include a variety of realistic constraints such as economic factors, safety, reliability, aesthetics, ethics, and social impact. 另外，还必须包括许多实际约束，如经济因素、安全、可靠性(reliability)、美学(aesthetis)、道德(ethics)和社会反响等

If anything can be said about the last half of the twentieth century, it is that we have had an explosion of information.

如果说二十世纪下半叶可以提到的大的事情，那就是信息的大爆炸。

The amount of data that can be uncovered on most subjects is overwhelming.

对大多数课题可以揭示的数据量是势不可挡的

People in the upper levels of most organizations have assistants who condense most of the things that they must read, hear, or watch. 在大部分组织的高层次人才都配有助手，这些助手把他们必须读到、听到和看到的大部分事情进行精简

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 data subsequently appear to be important. 当你查找一些信息资料时，如果这些资料很重要，做好准备浏览大量资料并记下它们的位置，这样做你能容易地获得

Some of the sources that are available include the following: 可得到的一些资源如下：

1.Exisiting 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(购买进行详细分析).

1、现有的解决方案。如果实际的产品可以被确定、研究，以及在某些情况下可以买到以用于详细的分析，则从现有的解决方案到特定的需要可以知道许多事情。

An improved solution or an innovative new solution cannot be found unless the existing solutions are thoroughly understood.

除非完全理解现有的解决方案，否则不能找到一个改进的或革新的解决方案。。

2.Your library. Many universities have courses that teach you how to use your library. 你的图书馆。许多大学设有教你如何使用你的图书馆的课程。

Such courses are easy when you compare them with those in chemistry and calculus(微积分), but their importance should not be underestimated(低估).

这些课程与化学和微积分学课程相比是容易的，但不能低估它们的重要性。

There are many sources in the library that can lead you to the information that you are seeking. 在图书馆里有很多资源能帮你找到你所要搜索的信息。

You may find what you need in an index such as the Engineering Index(工程索引).

在一个索引中可以找到你想要的东西，例如在工程索引中。

There are many other indexes that provide specialized information. 你的问题的性质将直接告诉你谁可以帮助你。

The nature of your problem will direct which ones may be helpful to you. Don't hesitate to ask for assistance from the librarian.

不要不好意思请求图书管理员的帮助。

You should use to advantage the computer databases found in libraries and often available through CD-ROM (Compact disc-read only memory)technology.

你应该充分利用图书馆的计算机数据库（database）和经常通过光盘只读存储器（CD-ROM）来获取信息。

3.Professional organizations. The American Society of Mechanical Engineers is a technical society that will be of interest to students majoring(主修) in mechanical engineering.

Each major in your college is associated with not one but often several such societies.

3、专业组织。美国机械工程师协会（The American Society of Mechanical Engineers）是一个技术协会，它对机械专业的学生非常有吸引力。

你学院的每一个专业不仅与一个而且经常与好几个这样的会有联系（be associated with）。

The National Society of Professional Engineers is an organization that most engineering students will eventually join, as well as at least one technical society such as the American Society of Civil Engineers (ASCE), the Institute of Electrical and Electronic Engineers (IEEE), or any one of dozens that serve the technical interests of the host of specialties with which professional practices seem most closely associated.

国家专业工程师协会是一个组织，大部分工程方面的学生最终要加入这一组织，以及至少一个技术协会如美国土木工程师协会（ASCE）、美国电气与电子工程师协会（IEEE）或十二个协会中的任何一个都对许多专业技术感兴趣，专业实践似乎与这些专业有非常紧密的联系。

Many engineers are members of several associations and societies.

许多工程师是几个协会和学会的会员。

4.Trade journals(行业杂志).

They are published by the hundreds, usually specializing in certain classes of products and services.

行业杂志有几百种，通常研究一定级别的产品和服务。

Money and economics are part of engineering design and decision-making.

We live in a society that is based on economics and competition.

钱和经济是工程设计和决策制定的一部分。

我们生活在一个以经济和竞争为基础(be based on)的社会。

It is no doubt true(勿容置疑) 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.

许多好的想法不能实施无疑(no doubt)是真的，因为这些想法被认为在经济上是不可行的。

我们中的大部分人都知道我们每天的生活条件。

We started with our parents explaining why we could not have some item that we wanted because it cost too much.

我们的父母给我们解释为什么我们不能得到某些我们想要的东西，是因为这些东西太贵。

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.

同样，我们也不能把某些非常渴望的东西加入到我们的设计中，因为我们获得的价值与它的成本相比(in relation to)不能获得足够的效益。

Industry is continually looking for new products of all types.

Some are desired because the current product is not competing well in the marketplace(市场).

Others are tried simply because it appears that people will buy them.

工业正在不断地寻找(look for)所有类型的新产品。

某些产品是渴望的，因为现有的产品在市场中不具有很好的竞争力。

其它的产品被简单的试做，因为似乎人们将买它们。

How do manufacturers know that a product will be popular(畅销的)?

生产厂商如何知道其生产的新产品是否受欢迎呢？

They seldom know with certainty.

他们很少能知道确切答案。

Statistics(统计学) is an important consideration in market analysis.

在市场分析时，统计数字是重要的考虑。

Most of you will find that probability(概率论) and statistics are an integral(组成的) part of your chosen engineering curriculum.

你们中的大部分人将会发现，概率和统计是你们所选课程的一个整体部分。

The techniques of this area of mathematics allow us to make inferences(推论) about how large groups of people will react based on the reactions of a few.

数学领域的技术可以使我们做出推论，即多大人群将根据少数人的反应而反应

专业英语课文翻译