英文文献

The modern mechanical system concept is: Any mechanical product is a specific system which is composed with several components , the certain part equipment , with the definite quality, the rigidity and the damping certain objects which have relations with each other ,this system can complete the specific function the system , therefore calls it the mechanical system. The machine parts are compose the mechanical system the basic essential factor, the part are its subsystem。

The design work is a process which relapse carries on. In this process, we must experience several stages, in carries on the appraisal after the result, in returns to the front stage. Therefore , we may first in the system ensemble several components, carry on the analysis and the optimization to them, then carries on the synthesis again, looked they have any influence to the system other parts. The analysis and the optimization all requests us to establish or to make the system the abstract model, regarding this in order to carries on the mathematical analysis. We are called these models the mathematical model. When establishment mathematical model, we hoped can find to be allowed to simulate the actual physical system well the mathematical model.

Because of the highly competitive nature of most manufacturing businesses, the question of finding ways to reduce cost is ever present. A good staring point for cost reduction is in the design of the produce. The design engineer should always keep in mind the possible alternatives available to him in making his design .It is often impossible to determine the best alternatives without a careful analysis of the probable production cost. Designing for function, interchangeability, quality, and economy requires a careful study of tolerance, surface finishes, processes, materials, and equipment.

To assure sound and economical design from a standpoint, careful consideration of the following general design rules-both separately and together-is of paramount importance .the order of importance may vary according to design requirement, or factors, but the overall importance always remains the same.

Seek simplicity. Design for maxminum simplicity in functional and physical characteristics.

Determine the best production method. Seek the help of a production engineer to design for the most economical production methods.

Analyze materials. Select materials that will lend themselves to low-cost production as well as to design requirements.

Eliminate fixturing and handing problem. Design for ease of locating, setting up, and holding parts.

Employ maxinum acceptable tolerances and finishes. Specify surface roughness and accuracy no greater than which is commensurate with the type of part or mechanism being designed, and the production method or methods contemplated.

In addition, in the mechanical system design process, choosing the system components is also a very important link.

One of the primary considerations in designing any machine or structure is that the strength must be sufficiently greater than stress to assure both safety and reliability .To assure that mechanical parts do not fail in service ,it is necessary to learn why they sometimes do fail .Then we shall be able to relate the stresses with the strengths to achieve safety.

Ideally , in designing any machine element, the engineer should have at his disposal the results of a great many strength tests of the particular material chosen .These tests should have been made on specimens having the same heat treatment ,surface finish ,and size as the element he proposes to design; and the tests should be made under exactly the same loading conditions as the part will experience in service. This means that, if it is to be subjected to combined bending and torsion ,it should be tested under combined bending and torsion .Such tests will provide very useful and precise information. They tell the engineer what factor of safety to use and what the reliability is for a given service life. Whenever such data are available for design purposes, the engineering

Following several examples are some questions which the components should pay attentions to in the design and choice work :

A coupling is a device for connecting the ends of ends of adjacent shafts . In machine construction, couplings are used to affect a semi permanent connection between adjacent rotating shafts .The connection is permanent in the sense that it is not meant to be broken and restored in an emergency or when worn parts are replaced .

There are several types of shaft couplings their characteristics depend on the purpose for which they are used . If an exceptionally long shaft is required in a manufacturing plant or a propeller shaft on a ship ,it is made in sections that are coupled together with rigid couplings . A common type of rigid coupling consists of tow mating radial flanges (disk) that are attached by key-driven hubs to the ends of adjacent shaft sections and bolted together through the flanges to from a rigid connection .Alignment of the connected shafts is usually effected by means of a rabbet joint on the face of the flanges.

In connecting shafts belonging to separate devices (such as an electric motor and a gearbox ),precise aligning of the shafts is difficult and a flexible coupling is used .This coupling of the shafts is difficult and a flexible coupling is used .This coupling connects the shafts in such a way as to minimize the harmful effects of shaft misalignment . Flexible couplings also permit the shafts to deflect under their separate systems of loads and another .Flexible couplings can also serve to reduce the intensity of shock loads and vibrations transmitted form one shaft to another.

②Each kind of structure type bearing as a result of the different structure characteristic, may adapt in the different exploit action conditions, designs the personnel to be possible according to own to need to carry on the choice. Usually choosing the bearing type should synthesize the consideration of following  primary factors:

a. Loading condition: We should consider its size, the direction, as well as the nature.

b. High speed performance: The general friction moment small, the calorific capacity small bearing high speed performance is good. The ball bearing has the higher limit rotational speed compared to the roller bearings, therefore is high speed time should first consider selects the ball bearing

c. Axial hovers the performance: When common mechanical work, causes the axis because of the mechanical friction or the actuating medium relations to give off heat, thus has the thermal expansion to contract the production. When choice bearing structure type, should enable its axis to have the uranium to the possibility which hovers.

d. Permission space: In the machine design, generally all is first the true dead axle size, then determines the bearing according to the axis size the size. The small axis selects the ball bearing, the big axis generally all selects the roller bearings

e. installment and disassemble convenient: Generally all with difficulty equates the main engine service life regarding the bearing service life, uses the middle bearing in the reality to take the quick-wear part to have frequently the assembling and disassemble .Therefore, when selects the bearing structure type should request the assembling and dismantling to be convenient.

A designer only to considers comprehensively, rigorous, follow rules which we should have in the design process, can build the good foundation in order to design an outstanding product to. 

The mechanical system design is based on products with the characteristics, and design experts in the field of knowledge and experience to push volume and decision-making, the completion of several comprehensive. To achieve this stage of the computer-aided design, we must study the automatic acquisition of knowledge, expression, integration, coordination, management and use. To this end, the scholars at home and abroad designed for mechanical systems design knowledge of automated processing done a lot of research work, the method used can be summarized in the following few.

3.1 coding method

According to "campaign conversion" feature (the function million) institutions will be classified, described and use the code function yuan and institutional categories, which established a "body system design expert system" Knowledge Base. On this basis, will be the dual logic and fuzzy comprehensive evaluation of combining theory, the establishment of the "expert systems" reasoning mechanism, and for the four-position for the design of the machine.

Use of biological evolution theory, through natural selection and sexual reproduction to the principle of evolution of organisms to the body design, use of network theory methods to express the structure for topology, and then through the coding technology, the structure and institutions Performance of individual chromosomes into the binary string, and in accordance with design requirements of fitness, the use of biological evolution theory of reproduction control mechanism, through the selection, crossover, such as a sudden variation means to eliminate low value of the individual are not suited to the fast evolution Be the best adaptation of the individual, that is, most with the design requirements of the agency programme.

3.2 knowledge of the law mixed

The complex mechanical systems design, mixed use of the knowledge expression describes the design of various types of knowledge is particularly suited to this point has been the design of many scholars of the consensus.

In the development of complex product design intelligent decision support system dmdss, will be the rules, framework, processes and neural networks, and other knowledge that organic combination of methods to adapt to different types of knowledge in the design of the description. Knowledge will be a single expression of a variety of methods (rules, framework and process), according to object-oriented programming principles, the framework of the groove with that object's properties, with rules that target the dynamic characteristics, with the knowledge that the treatment process, group Into a hybrid form of knowledge, and successfully developed the "object-oriented NC gantry milling machine gearbox design intelligent system gbcdis" and "transmission structure design expert system gbsdes".

3.3 use of the knowledge-based development tool

Coupling in the cad system, the use of the knowledge-based development tools nexpert-object, through the use of object-oriented approach, to create an object-oriented database design method for coupling the designer to design and structural design Provided extensive and reliable method of the design spectrum.nexpert describe the use of linear guide the design of the need to design based on knowledge of the content, which seek to knowledge-based solutions, and developed a linear guide design expert system.

3.4 Design Law Directory

Construction of the "modules", "functional element solution" and "institutions" three progressive design directory, and this directory of three progressive design principles of the programme as a mechanical transmission system intelligent design and development of the knowledge base of design aids.

3.5 Based on the example of the way

In the development of expert systems design knowledge base, using the basic predicate described design requirements, design conditions and the selected programme, described by frame "Project" and various "concept entity," through case-based reasoning of the technologies used to produce candidate With the horsepower to product design requirements.

4, Intelligent Design

Intelligent design is the main characteristics: According to the theories of design, through the use of 3D graphics software, intelligent design software and virtual reality technology, and multimedia, hypermedia tools for product development design, the concept of products, description of the product frame.

In the use of mathematical systems theory at the same time, consider the theory of systems engineering, product design technology and systems development methodology VDI2221, developed for use in the early design of multimedia software development system MUSE.

Automatic teller machines in the design, the product of the entire development process summed up as "product planning" and "development" and "production planning" three stages, and made full use of existing cad cutting-edge technology - virtual reality technology. 1) product planning - idea products. Its task is to identify the external characteristics of products, such as color, shape, surface quality, ergonomics and so on, and the initial idea of using 3Dcad model show, to establish the appearance of the product simple model, the model can be virtual Environment in the establishment, through the use of data cap and three-dimensional mouse, users can to a certain extent, participate in this environment, and can rapidly generate different shapes and colors. Detection of three-dimensional model is the basis for the effect of external shape, but also variable geometry shows that the basis for the design, while still in the process of developing all types of foundation. 2) development - design products. The main stage according to the "synthesis" principle, the three-dimensional model on the configuration and integration of the elements of the design elements according to the different objectives have different meanings: It is the basic elements, such as bolts, or wheel shaft connected, and so it can also be a composite Elements, such as mechanical, electrical, electronic components, technology or software to control the transmission system; can also be requested, features, shape, and so on. Will achieve the critical functions of the elements targeted to three-dimensional model, to the configuration of products (design model of the relationship between elements) analysis, product configuration analysis is integrated "product planning" and "development" an important result. 3) production planning - processing and assembling products. At this stage, the main exposition of the assembly process in the application of cad technology, to use the computer image display of the elements in the appropriate location of the assembly process, that is revealed through virtual assembly model and shape the relationship between the assembly, which found that difficulties and problems And find a way to solve problems, and that will be integrated CAD technology applied to the three stages of product development, design can make the process of synthesis and analysis in the "product planning" and "development" and "production planning" to turn in a row Conduct. Therefore, it can be found earlier in various stages of the existing problems in product development in the process of continuous refinement and improvement.

中文翻译：

要研究机械系统设计，首先我们应明确它的概念，现代机械系统的概念是：任何机械产品都是由若干个零、部件及装置组成的一个特定系统，即是一个由确定的质量、刚度和阻尼的若干物体组成、彼此间有机联系并能完成特定功能的系统，故称之为机械系统。机械零件是组成机械系统的基本要素，部件是它的分系统。

设计工作是一个反复进行的过程。在这个过程中，我们要经历几个阶段，在对结果进行评价后，在返回到前面的阶段。因此，我们可以先综合系统中的几个零件，对它们进行分析和优化，然后再进行综合，看它们对系统其他部分有什么影响。分析和优化都要求我们建立或者作出系统的抽象模型，以便对此进行数学分析。我们将这些模型称为数学模型。在建立数学模型时，我们希望能够找到一个可以很好地模拟实际物理系统的数学模型。

由于大多数制造行业均具有高度的竞争性，因此寻找降低成本的途径这个问题一直是人们所关心的。降低成本的最好起点是在产品的设计阶段。设计工程师在进行设计时应该记住所有可供选择的方案。如果不对可能的生产成本进行认真的分析，通常不可能选定最好的方案。在对产品的功能、互换性、质量和经济性进行设计时，需要对其公差，表面粗糙度，加工方法，材料以及设备等问题进行认真的研究。

为了能够从制造上保证设计的合理性和经济性，认真考虑下列各项一般性规则—既要单独考虑没一项规则，又要对规则地进行整体考虑—是非常重要的。对于不同的设计要求或者因数，每一项规则的重要程度可能会发生变化，但是这些规则的总体重要性将不会发生变化。

（1）尽量简单啊。在功能特性和结构特性的设计方面应该为最简单。

（2）确定最好的加工方法。寻求生产工程师的帮助，设计最经济的加工方法。

（3）材料分析。选择既能满足设计要求，成本又低的材料。

（4）避免产生夹紧与装卸方面的问题。设计容易定位，夹持与装卸的工件。

（5）采用尽可能大的公差和表面粗糙度。在确定零件的表面粗糙度和尺寸精度时，不应该对零件或者机构的设计，以及将要采用的生产过程提出过高的要求。

此外，在机械系统设计过程中，对系统零件的选择也是一个很重要的环节。

在设计任何机器或结构时，所考虑的主要事项之一是其强度应该比它所承受的应力要大很多，以确保安全与可靠性。要保证机械零件在使用过程中不失效，就必须知道它们在某些时候为什么会失效的原因，然后，我们才能将应力与强度联系起来，以确保其安全。

设计任何机械零件的理想情况为，工程师可以利用大量的他所选用的这种材料的强度试验数据。这些试验应该采用与零件有着相同的热处理，表面光洁度和尺寸大小的试件进行，而且试验应该在与零件使用过程中承受的载荷完全相同的情况下进行。这表明，如果零件将要承受弯曲载荷，那么就应该进行弯曲载荷的试验。如果零件将要承受弯曲和扭转的复合载荷，那么就应该进行弯曲和扭转复合载荷的试验。这些种类的试验可以提供非常有用和精确的数据。它们可以告诉工程师应该使用的安全系数和对于给定使用寿命时的可靠性。在设计过程中，只要能够获得这种数据，工程师就可以尽可能好地进行工程设计工作。

以下几个例子是设计工作中对机械设计中零件选择应注意的一些问题

①联轴器是用来把两个相邻轴端连接起来的装置。在机械结构中，联轴器被用来实现相邻的两根传动轴之间的半永久性连接。在机器的正常使用期间内，这种连接一般不必拆开，在这种意义上，可以说联轴器的连接是永久性的。但是在紧急情况下，或者需要更换以磨损的零件时，可以先把联轴器拆开，然后再连接上。

联轴器有几种类型，它们的特性随其用途而定。如果制造工厂中或者船舶的螺旋桨需要一根特别长的轴，可以采用分段的方式将其制造出来，然后采用刚性联轴器将各段连接起来。一种常用的联轴器是由两个配对的法兰（盘）组成，这两个法兰盘借助靠键传动的轴套连接到相邻两节轴的两端，然后用螺栓穿过法兰连接起来形成刚性接头。相互连接的两根轴通常是靠法兰面上的槽口来对准的。

在把属于不同的设备（例如一个电动机和一个变速箱）的轴连接起来的时候，要把这些轴精确地对准是比较困难的，对此可以采用弹性联轴器。这种联轴器连接轴的方式可以把由于被连接轴之间的轴线的不重合所造成的有害影响减少到最低程度。弹性联轴器也允许被连接的轴在它们各自的载荷系统作用下产生偏斜或在轴线方向自由移动（浮动）而不致于相互干扰。弹性联轴器也可以用来减轻从一根轴传到另一根轴上的冲击载荷和振动的强度。

②各种结构类型轴承由于不同的结构特性，可适应于不同的使用条件，设计人员可根据自己的需要进行选择。通常选择轴承类型时应综合考虑下列各主要因素：

载荷情况：我们设计时应考虑它的大小、方向、以及性质。

高速性能：  一般摩擦力矩小、发热量小的轴承高速性能好。球轴承比滚子轴承有较高的极限转速，故高速时应优先考虑选用球轴承

轴向游动性能：一般机械工作时，因机械摩擦或工作介质的关系而使轴发热，从而有热胀冷缩产生。在选择轴承结构类型时，应使其轴有铀向游动的可能性。

允许的空间：在机械设计中，一般都是先确定轴的尺寸，然后根据轴的尺寸来确定轴承的尺寸。小轴选用球轴承，大轴一般都选用滚子轴承

安装与拆卸方便：对于轴承使用寿命一般都难以等同主机使用寿命，在实际使用中轴承作为易损件要经常装拆。因此，在选用轴承结构类型时应要求装拆方便。

一个设计人员只有在设计过程中考虑全面，严谨，遵循应有的规则，才有为设计出一个优秀的产品打下良好的基础。

机械系统的方案设计主要是依据产品所具有的特征，以及设计领域专家的知识和经验进行推量和决策，完成机构的型、数综合。欲实现这一阶段的计算机辅助设计，必须研究知识的自动获取、表达、集成、协调、管理和使用。为此，国内外设计学者针对机械系统方案设计知识的自动化处理做了大量的研究工作，采用的方法可归纳为下述几种。

3.1　编码法

根据“运动转换”功能(简称功能元)将机构进行分类，并利用代码描述功能元和机构类别，由此建立起“机构系统方案设计专家系统”知识库。在此基础上，将二元逻辑推理与模糊综合评判原理相结合，建立了该“专家系统”的推理机制，并用于四工位专用机床的方案设计中。

利用生物进化理论，通过自然选择和有性繁殖使生物体得以演化的原理，在机构方案设计中，运用网络图论方法将机构的结构表达为拓扑图，再通过编码技术，把机构的结构和性能转化为个体染色体的二进制数串，并根据设计要求编制适应值，运用生物进化理论控制繁殖机制，通过选择、交叉、突然变异等手段，淘汰适应值低的不适应个体，以极快的进化过程得到适应性最优的个体，即最符合设计要求的机构方案。

3.2　知识的混合型表达法

针对复杂机械系统的方案设计，采用混合型的知识表达方式描述设计中的各类知识尤为适合，这一点已得到我国许多设计学者的共识。

在研制复杂产品方案设计智能决策支持系统DMDSS中，将规则、框架、过程和神经网络等知识表示方法有机地结合在一起，以适应设计中不同类型知识的描述。将多种单一的知识表达方法(规则、框架和过程)，按面向对象的编程原则，用框架的槽表示对象的属性，用规则表示对象的动态特征，用过程表示知识的处理，组成一种混合型的知识表达型式，并成功地研制出“面向对象的数控龙门铣床变速箱方案设计智能系统GBCDIS”和“变速箱结构设计专家系统GBSDES”。

3.3　利用基于知识的开发工具

在联轴器的CAD系统中，利用基于知识的开发工具NEXPERT-OBJECT，借助于面向对象的方法，创建了面向对象的设计方法数据库，为设计者进行联轴器的方案设计和结构设计提供了广泛且可靠的设计方法谱。则利用NEXPERT描述直线导轨设计中需要基于知识进行设计的内容，由此寻求出基于知识的解，并开发出直线导轨设计专家系统。

3.4　设计目录法

构造了“功能模块”、“功能元解”和“机构组”三级递进式设计目录，并将这三级递进式设计目录作为机械传动原理方案智能设计系统的知识库和开发设计的辅助工具。

 3.5　基于实例的方法

在研制设计型专家系统的知识库中，采用基本谓词描述设计要求、设计条件和选取的方案，用框架结构描述“工程实例”和各种“概念实体”，通过基于实例的推理技术产生候选解来配匹产品的设计要求。

4、智能化设计方法

智能化设计方法的主要特点是：根据设计方法学理论，借助于三维图形软件、智能化设计软件和虚拟现实技术，以及多媒体、超媒体工具进行产品的开发设计、表达产品的构思、描述 产品的结构。

在利用数学系统理论的同时，考虑了系统工程理论、产品设计技术和系统开发方法学VDI2221，研制出适合于产品设计初期使用的多媒体开发系统软件MUSE。

在进行自动取款机设计时，把产品的整个开发过程概括为“产品规划”、“开发”和“生产规划”三个阶段，并且充分利用了现有的CAD尖端技术——虚拟现实技术。1) 产品规划—构思产品。其任务是确定产品的外部特性，如色彩、形状、表面质量、人机工程等等，并将最初的设想用CAD立体模型表示出，建立能够体现整个产品外形的简单模型，该模型可以在虚拟环境中建立，借助于数据帽和三维鼠标，用户还可在一定程度上参与到这一环境中，并且能够迅速地生成不同的造型和色彩。立体模型是检测外部形状效果的依据，也是几何图形显示设计变量的依据，同时还是开发过程中各类分析的基础。 2) 开发—设计产品。该阶段主要根据“系统合成”原理，在立体模型上配置和集成解元素，解元素根据设计目标的不同有不同的含义：可以是基本元素，如螺栓、轴或轮毂联接等；也可以是复合元素，如机、电、电子部件、控制技术或软件组成的传动系统；还可以是要求、特性、形状等等。将实现功能的关键性解元素配置到立体模型上之后，即可对产品的配置(设计模型中解元素间的关系)进行分析，产品配置分析是综合“产品规划”和“开发”结果的重要手段。3) 生产规划—加工和装配产品。在这一阶段中，主要论述了装配过程中CAD技术的应用，提出用计算机图像显示解元素在相应位置的装配过程，即通过虚拟装配模型揭示造形和装配间的关系，由此发现难点和问题，并找出解决问题的方法，并认为将CAD技术综合应用于产品开发的三个阶段，可以使设计过程的综合与分析在“产品规划”、“开发”和“生产规划”中连续地交替进行。因此，可以较早地发现各个阶段中存在的问题，使产品在开发进程中不断地细化和完善。