Lesson 1
Machinery design may be simple or enormously complex, easy or difficult, mathematical or
nonmathematical, it may involve a trivial problem or one of great importance.
机械设计可能简单，可能复杂；可能容易，可能困难；可能要求精确，也可能不精确；有时要解决的可能是一些很平常琐碎的问题，也可能是非常重大的问题。
In the modern industrialized world, the wealth and living standards of a nation are closely linked with their capabilities to design and manufacture engineering products. It can be claimed that the advancement of machinery design and manufacturing can remarkably promote the overall level of a country’s industrialization.
在现代的工业化社会，一个国家的财富和生活水平与他们设计和制造工程产品的能力紧密相关，可以说机械设计和制造业的进步能显著地促进一个国家工业化整体水平的提高。
Definition of problem is necessary to fully define and understand the problem, after which it
is possible to restate the goal in a more reasonable and realistic way than the original problem
statement.
定义问题对全面认识、理解问题非常必要，之后可以更加合理可行的方式来重新阐述。
The synthesis is one in which as many alternative possible design approaches are sought,
usually without regard for their value or quality.
综合就是对各种可供选择的设计方法进行进一步研究，这时往往不考虑这些方法的设计特点和设计质量。
This is also sometimes called the ideation and invention step in which the largest possible  number of  creative solutions is generated.
这有时也称为构思和发明阶段，在这个阶段中要产生尽可能多的有创意的想法。
The competent engineer should not be afraid of the possibility of not succeeding  in  a  presentation
design翻译有能力的工程师不应该害怕在提高自己的方案时遭遇失败。
In fact, the greatest gains are obtained by those willing to risk defeat.
实际上，失败乃成功之母。
there is strong sense of satisfaction and pride inseeing the results of one's ceartive efforts emerge into actual products and processes that benefit people.
当看到自己创造性的努力成果转变成可以造福人们的实际产品和工作流程时，一种强烈的满足感和骄傲感油然而生。
the design engineer should not only have adequate technical training,but must also be a person of sound judgment and wide experence,qulities which are usually acquired only after considerable time has been spent in actual proessional work.
设计师不仅需要足够的技术训练，而且还必须是一个具备合理的判断和丰富经验的人，具备这些素质通常需要在实际工作中花费相当长的时间。
Lesson 2 mechanisms
1、a  mechanism is the  members  combination more than  two  or two  connections  with  the  members  to realize  the  regulation motion  made by  way of  the  activity. 机构是由两个或两个以上的构件通过活动联接以实现规定运动的构件组合，是机械的组成部分。
2、 Activity connections between two members that have the relative motion are called the motion pairs . 两个有相对运动的构件间的活动连接称为运动副。
3、All motion pairs contact with planes are called lower pairs and all motion pairs contact with points or lines are called high pairs .其中凡为面接触的运动副称为低副 凡为点或线接触的运动副成为高副。
4、The motion specific property  of mechanism chiefly  depends  on  the  relative  size be
tween the members, and the character of motion pairs, as well as the mutual disposition method etc.机构的运动特性主要取决于构件间的相对尺寸、运动副的性质以及相互配置方式等。
5、The member is used to support the members of motion in the mechanism to be called the machine frame and used as the reference coordinate to study the motion system.
机构中用以支持运动构件的构件称为机架，并被当做研究运动的参考坐标系。
6、The member that possesses the independence motion is called motivity member. The  member except machine frame and motivity member being compelled to move in the mechanism is called driven member.具有独立运动的构件称为原动件。机构中除机架和主动件之外的被迫做强制运动的构件称为从动件。
7、The independent parameter (coordinate  number) essential for description or  definite mechanism motion is called the free degree of mechanism.描述或确定机构的运动所必需的独立参变量（坐标数）称为机构自由度。
8、For gaining the definite relative motion between the members of mechanism, it  is necessary make the number of motivity members of mechanism equal the number of free degrees.为使机构的构件获得确定的相对运动，必需使机构的原动件数等于机构自由度数。
9、Mechanisms may be categorized in several different ways to emphasize their  similarities and differences.根据各个不同机构之间的异同点，常采用以下几种不同的分类方法。
10、A planar mechanism is one in which all particles describe plane curves in space and all these curves lie in parallel the loci of all points are plane curves parallel to a single common plane.在平面机构中，所有的点在空间绘出的是平面曲线，且所有的点的轨迹是与一个单一公共平面相平行的平面曲线。
11、The plane four-bar linkage, the plate cam and driven parts, and the slider-crank mechanism are familiar examples of planar mechanism.平面四连杆机构、平面盘形凸轮、从动件及曲柄滑块机构等都是平面机构的常见例子。
12、As such, cams are widely used in almost all machinery. They include internal combustion engines, a variety of machine tools, compressors and computers.这样便使凸轮广泛用于几乎所有的机械设备中，包括内燃机、各种机床、压缩机和计算机。

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